Improvements in and relating to methods and apparatus for capturing carbon dioxide from a fluid, in particular a gas

Abstract

The present invention concerns the use of the combination of an electrochemical cell and of at least one heat pump, in the implementation of a process or apparatus for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a liquid sorbent and a liquid desorbent, the liquid sorbent transfers the CO2-containing anions or cations to obtain the loaded liquid desorbent with CO2-containing anions, in which the heat pump is configured to deliver heat prior to desorption of the carbon dioxide, said combination enabling, to shift the equilibrium of the desorption reaction of carbon dioxide and to lower the voltage and the energy consumption of the electrochemical cell (no figure)

Description

[0001]Improvements in and relating to methods and apparatus for capturing carbon dioxide from a fluid, in particular a gas Field of the Disclosure The present disclosure relates to methods and apparatus for capturing carbon dioxide from a fluid, in particular a gas and has particular reference to carbon capture from the air. Background of the Disclosure Direct air capture of carbon dioxide (“DAC”) is a potential route to reducing carbon dioxide concentration in the atmosphere. Carbon dioxide captured from the air can be bottled for transport, compressed into a tanker for transport, fed into a pipeline for transport, or fed directly into a carbon dioxide utilisation process such as a CO2-to-fuels process, a CO2-to-chemicals or plastics process, or a refrigeration process. Carbon dioxide captured from the air can also be fed directly into a carbon dioxide sequestration process; for example carbon dioxide mineralisation or underground sequestration in an aquifer or disused oil or gas well. Processes for direct air capture of carbon dioxide from ambient air typically utilise solid sorbents or liquid sorbents (also called liquid solvents) to contact and capture carbon dioxide (by adsorption onto a solid sorbent or absorption by a liquid solvent). The sorbent is then regenerated. The present disclosure concerns improvements and developments in liquid solvent direct air capture technology. The improvements may be applicable to the capture of carbon dioxide or other target species from other gases, such as industrial exhaust gases. A number of techniques have been proposed for regeneration of a liquid solvent in a direct air capture process, including electrochemical regeneration, crystallisation and techniques that rely on the Kraft process. Existing techniques have drawbacks in the high energy requirements for regeneration. There is a need for a direct air capture process which improves the carbon dioxide capture efficiency of the sorbent, provides a high purity carbon dioxide output, and minimises energy consumption for regeneration of the sorbent and / or desorbent. WO 2022 / 195299 A1 describes direct air capture using a liquid sorbent with electrochemicalsorbent regeneration. A gas containing a target species is contacted with a first absorbent solution containing a large capture species such as an amine-functionalised polymer. The target species is dissolved in the first absorbent solution to form a target anion, which is electrochemically separated from the first absorbent solution by contacting the first absorbent solution with one or more ion- exchange membranes. The target anion is transferred through the ion-exchange membrane into a second absorbent solution from which the target species is released. The one or more ion-exchange membranes are not permeable to the large capture species, so the capture species does not pass through the one or more ion-exchange membranes. In such a process, to maintain a given reaction rate and current in the cell, the cell must reach a relatively high voltage and therefore consume a relatively high electrical power. Optionally, the second absorbent solution may comprise an electrically-conductive organic carbonate, such as dimethyl carbonate, but this would decompose to carbon dioxide and methanol in the presence of water and, owing to its miscibility with water, would be susceptible to leach through the membranes to the sorbent. DMC is also relatively volatile and would evaporate from the sorbent, requiring it to be constantly topped up. Alternatively, an acid may be used as the electrolyte for the desorbent, to increase its conductivity, thereby allowing the ionic strength and therefore conductivity to be increased. Polystyrene functionalised with sulfonic acid groups is disclosed for use as the anion of the dissociated acid to prevent diffusion across the anion exchange membranes into the sorbent. It is undesirable to use an acid as the electrolyte for the desorbent because the larger the pH gradient between the sorbent and desorbent, the larger the reversible voltage that is required acrosseach membrane. If the acid concentration is too high, this will increase the voltage across eachmembrane unduly. US 2022 / 0097004 A1 describes direct air capture using a liquid sorbent with electrochemicalsorbent regeneration. Ambient air is brought into contact with an aqueous solution of an alkali metalor alkaline earth metal to form a bicarbonate or carbonate of the metal. Electrodialysis of the solutionprovides a solution enriched in (bi-)carbonate anions. Thermal desorption of the carbon dioxide from the solution by steam stripping (i.e. at temperatures of at least 100 degrees Celsius) is performed in order to obtain a carbon dioxide-steam mixture and a solution depleted in carbon dioxide which is recycled. Water is removed from the carbon dioxide-steam mixture by cooling to condense the steam, and possibly further drying of the carbon dioxide. Such a process aims to reduce the required voltage on the electrochemical cell by steam stripping the carbon-rich desorbent solution, but is not energy efficient, owing to the high temperatures required and energy lost as sensible heat and to the latent heat of water vaporisation. The present disclosure seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present disclosure seeks to provide improved carbon capture methods and apparatus. Summary of the Disclosure In a first aspect of the present disclosure, there is provided a use of the combination of an electrochemical cell and of at least one heat pump, in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a liquid sorbent and a liquid desorbent, the liquid sorbent containing carbon dioxide in the form of carbon dioxide-containing anions (CO2- containing anions), and being able to transfer CO2-containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, or the liquid sorbent containing cations and carbon dioxide in the form of CO2-containing anions, and being able to transfer said cations by the electrochemical cell across one or more of its ion exchange membranes, to become the liquid desorbent loaded with CO2-containing anions, in which the heat pump is configured to deliver heat below 100 degrees Celsius and to transfer heat to said loaded liquid desorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction, to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. It was surprisingly found out by the Inventors that the combination of an electrochemical cell and of at least one heat pump in the implementation of a process for capturing carbon dioxide has a synergic effect as it enables, at the same time, to decrease the cell voltage (see Figures 9 and 20), to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber at a lower solubility of the carbon dioxide in the liquid desorbent and also unexpectedly to increase the Faradaic efficiency (Figure 13). Without to be bound by the theory, it seems that the increase in Faradaic efficiency is related to an increase in the water dissociation efficiency of the bipolar membranes and to a decreased total CO2 concentration in the desorbent, which lowers the rate of back-diffusion from desorbent to sorbent. The decrease of the voltage of the electrochemical cell seems to be related to the following reasons: lower reversible voltages across the ion exchange membranes, a lower overpotential for water dissociation in bipolar membranes, a lower resistance of anion / cation exchange membranes and a lower resistance of sorbent and desorbent. This combination advantageously allows to achieve an average decrease in the total energy consumption (Figure 12), and to obtain an overall energy benefit by using a heat pump, in particular a heat pump having a coefficient of performance (COP) higher than unity. According to the present description, “carbon dioxide-containing anions” refer to anions species which contain carbon dioxide, namely CO2-containing anions, wherein said species contain at least one molecule of carbon dioxide which is bound reversibly and therefore can be released. Such anions are for example, but not limited, carbonate anions (CO32-), bicarbonate anions (HCO3-) and carbamate. According to the present description, the term “normally” refers to normal conditions of the implementation of the process for capturing carbon dioxide, in particular in terms of concentration of the species, of temperature and of pressure. Therefore, the expression “can normally desorb in the desorber without heating said loaded desorbent” refers to a comparison in the same conditions of the implementation of the process, with the exception of heating the loaded desorbent. According to the present description, the term sorbent refers to a liquid stream that contains carbon dioxide in the form of CO2-containing anions. The carbon dioxide content may come from the absorption of CO2from a gas stream, either atmospheric air or flue gases, or alternatively from a liquid stream already rich in carbon dioxide According to the present description, the term desorbent refers to a liquid stream that can sequentially increase its carbon dioxide concentration through an electrochemical cell and release the CO2in a CO2releasing step. According to the present description, a cation-exchange membrane (CEM) refers to a selective ion-conducting membrane composed of materials that facilitate the passage of cations while restricting the movement of anions and other particles. Advantageously constructed from polymers functionalized with sulfonic acid, carboxylic acid, or other cation-exchange groups, the membrane is used in applications such as electrodialysis, fuel cells, and ion separation processes. As a non-limitingexample, it may be composed of a polymer backbone as the main chain, and a side chain of cationexchange functional groups. As non-limiting examples, advantageously the polymeric backbone typically uses polysulfone (PSF) or polystyrene (PS) to connect divinylbenzene (DVB), and advantageously ion exchange groups are those containing single bond SO3−, single bond PO32-or single bond HPO3-, single bond PO3–, single bond COO–, and single bond C6H4O–). According to the present description, a “anion exchange membrane (AEM)” refers to a selective ion-conducting membrane composed of materials that facilitate the passage of anions while restricting the movement of cations and other particles. Advantageously composed of polymers functionalized with quaternary ammonium groups or other anion-exchange functionalities, the membrane is utilized in applications such as electrodialysis, fuel cells, and ion separation processes. As a non-limiting example, it may be composed of a polymer backbone as the main chain, and a side chain of anion exchange functional groups. As non-limiting examples, advantageously the polymeric backbone typically uses polysulfone (PSF) or polystyrene (PS) to connect divinylbenzene (DVB), and advantageously ion exchange groups are those containing ammonium (–NH3+, -RNH2+, -RN+, =R2N+) or phosphonium (-R3P+) groups. According to the present description, “monovalent selective anion exchange membrane” refers to a specific type of anion exchange membrane (AEM) which is engineered to selectively permit the passage of monovalent anions, such as chloride (Cl⁻) or bicarbonate (HCO₃⁻), while rejecting divalent or multivalent anions, such as carbonate (CO₃²⁻), sulfate (SO₄²⁻) or phosphate (PO₄³⁻). Advantageously constructed from polymers functionalized with quaternary ammonium or other anion- exchange groups, the membrane is further tailored with structural or chemical modifications to achievehigh selectivity for transport of monovalent anions over divalent or multivalent anions. As non-limiting examples, advantageously the bulk ammonium moieties can be modified by usingtrimethylamine N(CH3)3 (TMA), triethylamine N(CH2CH3)3 (TEA), trim-propylamine N(CH2CH2CH3)3 (TPrA), tri-n-butylamine N(CH2CH2CH2CH3)3 (TBA) and tri-n-pentylamine N(CH2CH2CH2CH2CH3)3 (TPA) groups. As non-limiting example, polystyrene cross-linked withdivinylbenzene and functionalized by a quaternary ammonium functional group is used as themembrane of a hydrogencarbonate (i.e., bicarbonate HCO3-) ion-selective electrode. According to the present description, “bipolar ion-exchange membrane (BPM)” refers to a composite ion-exchange membrane consisting of a cation exchange layer and an anion exchange layer joined together. Advantageously, at their interface, the membrane facilitates the dissociation of water molecules (water-splitting) into hydrogen (H⁺) and hydroxide (OH⁻) ions under the influence of anelectric field. H+ are transferred from the interface through the cation exchange layer, while OH- aretransferred from the interface through the anion exchange layer. As non-limiting examples, advantageously the main components of BPMs are the polymer matrix and the functional groups. The polymer matrix grants the BPM mechanical properties, and acts as the carrier for the functional groups. Cation-exchange layer used for commercial bipolar membranes usually contains sulfonic acid groups, or in rare cases, phosphonic acid groups. Anion-exchange layer used for commercial bipolar membranes usually contains quaternary ammonium groups on a polystyrene matrix. Other anionic groups include tertiary and secondary amines, and different di- amines, polysulphone, or PVDF. In preferred embodiments, the use is according to the present disclosure, wherein the liquid sorbent contains carbon dioxide in the form of CO2-containing anions, and is able to transfer the CO2- containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent. In preferred embodiments, the use is according to the present disclosure, wherein the liquid sorbent contains cations and carbon dioxide is in the form of CO2-containing anions, and is able to transfer said cations by the electrochemical cell across one or more of its ion exchange membranes, to become the liquid desorbent loaded with CO2-containing anions. In preferred embodiments, the sorbent or the desorbent is able to flow into the electrochemicalcell again following desorption and to get basified in the basifying chamber of said cell before flowing back to the contactor. In preferred embodiments, the use is according to the present disclosure, wherein said heat pump is a low temperature heat pump configured to deliver heat at temperatures below 100 degrees Celsius, in particular at temperatures of 40-90 degrees Celsius, preferably at temperatures of at least 45-75 degrees Celsius and has a coefficient of performance (COP) of higher than unity, in particular said heat pump is a gas source heat pump. The range of “temperatures below 100 degrees” comprises the ranges: of 40-45, of 45-50, of 50-55, of 55-60, of 60-65, of 65-70, of 70-75, of 75-80, of 80-85, of 85-90, of 90-95 degrees Celsius. In preferred embodiments, the use is according to the present disclosure, wherein the electrochemical cell comprises an electrolysis cell or an electrodialysis cell, preferably an electrodialysis cell. In preferred embodiments, the use is according to the present disclosure, wherein the liquid sorbent and / or the liquid desorbent are aqueous liquids. In preferred embodiments, the use is according to the present disclosure, wherein the liquid sorbent comprises a base as a solvent which can react with carbon dioxide to form CO2-containing anions. In preferred embodiments, the liquid sorbent and / or the liquid desorbent comprise reactive species which can react with carbon dioxide to form the CO2-containing anions, said anions enabling to cross said one or more ion exchange membranes of said electrochemical cell. In preferred embodiments, said reactive species are ions. In particular preferred embodiments, said reactive species are neutral species, preferably a neutral base. Preferably, said reactive species have a low molecular weight, in particular equal or lower than 500 or 400 or 250 g / mol. In another embodiments, said reactive species are polymeric species, in particular ionic polymer, preferably with a molecular weight greater than 600 g / mol. In some embodiments, the liquid sorbent and / or the liquid desorbent comprise polymeric species which can react with carbon dioxide to form the CO2-containing anions, said polymeric species being not able to cross said one or more ions exchange membranes of said electrochemical cell. In preferred embodiments, the liquid sorbent and / or the liquid desorbent do not contain polymeric species, in particular ionic polymer, which can react with carbon dioxide to form the CO2- containing anions. According to the present description, “reactive species” can also be named “capture species” when said species may reversibly bind and release target species, such as carbon dioxide. In preferred embodiments, the use is according to the present disclosure, further comprising the use of one or more heaters for heating the loaded liquid desorbent prior to desorption of carbon dioxide in the desorber. Advantageously, more than one heat pump may be used in one apparatus in order to adapt to the sizes of the electrochemical cell and heat pump. In some embodiments, said heat pump or said one or more heaters are configured to heat the liquid sorbent and / or desorbent. In some embodiments, said one or more heaters are configured to heat liquid desorbent after desorption of carbon dioxide in the desorber and prior to crossing the electrochemical cell. In some embodiments, said one or more heaters are a heat pump or link to a heat pump. Preferably the use of one or more heaters is such as described below. Preferably said one or more heaters are configured to deliver waste heat from an industrial process or power plant. In preferred embodiments, the use is according to the present disclosure, wherein the liquid sorbent is continuously recirculating between the electrochemical cell and a gas contactor, and wherein the liquid desorbent is continuously recirculating between the electrochemical cell and the desorber. In preferred embodiments, the use is according to the present disclosure, further comprising the use of a contactor for absorbing carbon dioxide from a fluid, preferably from a gas. Preferably said contactor and its means are such as described below. In preferred embodiments, the use is according to the present disclosure, further comprising the use of a compressor for compressing the desorbed carbon dioxide gas. Preferably said compressor and its means are such as described below. In another aspect of the present disclosure, there is provided a use of the combination of an electrochemical cell and of at least one heater, in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a liquid sorbent and a liquid desorbent, the liquid sorbent containing carbon dioxide in the form of CO2-containing anions, and being able to transfer the CO2-containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, or the liquid sorbent containing cations and carbon dioxide in the form of CO2-containing anions, and being able to transfer said cations by the electrochemical cell across one or more of its ion exchange membranes, thereby acidifying the liquid sorbent, to become the liquid desorbent loaded with CO2- containing anions, in which the heater is configured to deliver heat below 100 degrees Celsius and to transfer heat to said loaded liquid desorbent prior to desorption of carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. In particular preferred embodiments, said at least one heater is configured to deliver waste heat from an industrial process or power plant. In one aspect of the present disclosure, there is provided a use of the combination of an electrochemical cell and of at least one heater, in the implementation of a process for capturing target species from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a liquid sorbent and a liquid desorbent, the liquid sorbent containing target species in the form of target ions, and being able to transfer target ions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with target ions and to obtain the loaded liquid desorbent, or the liquid sorbent containing cations and target species in form of target ions, and being able to transfer said cations by the electrochemical cell across one or more of its ion exchange membranes, to become the liquid desorbent loaded with target ions, in which the heater is configured to deliver heat, preferably below 100 degrees Celsius, and to transfer heat to said loaded liquid desorbent prior to desorption of the target species, said desorption taking place in a desorber, preferably at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of target species in the desorber and increase the rate of the desorption reaction toallow desorption of target species at a solubility of target ions lower than the value at which targetspecies can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption respectively required to reach the solubility of target ions in the loaded liquid desorbent at which the target species can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. In particular preferred embodiments, said at least one heater is a heat pump, preferably configured to deliver heat at temperatures below 100 degrees Celsius, in particular at temperatures of 40-90 degrees Celsius, preferably at temperatures of at least 40-75 degrees Celsius and preferably has a coefficient of performance (COP) of higher than unity, in particular said heat pump is a gas source heat pump. In particular preferred embodiments, said at least one heater is configured to deliver waste heat from an industrial process or power plant. In a second aspect of the present disclosure, there is provided an apparatus for capturing carbon dioxide from a fluid, in particular from a gas stream, preferably from atmospheric air, comprising:- means for absorbing carbon dioxide from the fluid,- an electrochemical cell configuredto transfer carbon dioxide in the form of CO2-containing anions contained in a liquid sorbent across one or more ion exchange membranes to a liquid desorbent to load the liquid desorbent with CO2- containing anions and to obtain the loaded liquid desorbent, or to transfer cations contained in a liquid sorbent containing carbon dioxide in the form of CO2- containing anions across one or more ion exchange membranes, thereby acidifying the liquid, to transform said liquid sorbent to a liquid desorbent loaded with CO2-containing anions,- at least one heat pump configured to deliver heat below 100 degrees Celsius and to transfer heat tosaid loaded liquid desorbent prior to desorption of carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, wherein the combination of the electrochemical cell and at least one heat pump is configured to enable, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and to enable the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. In preferred embodiments, the apparatus is according to the present disclosure, wherein the one or more ion exchange membranes of the electrochemical cell are permeable to reactive species contained in the liquid sorbent and / or the liquid desorbent, said reactive species being able to react with carbon dioxide to form CO2-containing anions. In preferred embodiments, the apparatus is according to the present disclosure, wherein the one or more ion exchange membranes of the electrochemical cell are permeable to carbon dioxide- containing anions. In preferred embodiments, the apparatus is according to the present disclosure, wherein the one or more ion exchange membranes of the electrochemical cell are monovalent selective anion exchange membrane permeable to carbon dioxide-containing anions, in particular bicarbonate ions (HCO3-). In some embodiments, the apparatus of the present disclosure is as described above, wherein the one or more ion exchange membranes of the electrochemical cell are impermeable to polymeric ions contained in said liquid sorbent which are able to react with carbon dioxide to form CO2- containing anions. In some embodiments, the apparatus of the present disclosure is as described above, wherein the one or more ion exchange membranes of the electrochemical cell are impermeable to polymeric ions contained in said liquid sorbent which are able to react with carbon dioxide to form CO2- containing anions. In preferred embodiments, the apparatus is according to the present disclosure, wherein the electrochemical cell comprises one or more anion exchange membranes and possibly bipolar membranes and is configured for electrochemically transporting the CO2-containing anions contained in the liquid sorbent across said one or more anion exchange membranes into the liquid desorbent, thereby enabling to move CO2-containing anions from the liquid sorbent loaded with CO2-containing anions into the liquid desorbent to obtain the liquid desorbent loaded with CO2-containing anions which is a solution more acidic and / or concentrated in carbon dioxide than said loaded liquid sorbent. In preferred embodiments, the apparatus is according to the present disclosure, wherein the electrochemical cell comprises one or more cation exchange membranes and possibly bipolar membranes and is configured for electrochemically transporting cations contained in the liquid sorbent loaded with carbon dioxide in the form of CO2-containing anions across said one or more cation exchange membranes to move said cations from said liquid sorbent, which are replaced by protons formed at an anode or at bipolar membranes of the electrochemical cell, thereby lowering thepH of said loaded liquid sorbent to transform it to said loaded liquid desorbent.In preferred embodiments, the apparatus is according to the present disclosure, wherein said heat pump is a low temperature heat pump configured to deliver heat at temperatures below 100 degrees Celsius, in particular at temperatures of 40-90 degrees Celsius, preferably at temperature of at least 45-75 degrees Celsius, and has a coefficient of performance (COP) of higher than unity, In preferred embodiments, the apparatus is according to the present disclosure, wherein the electrochemical cell comprises an electrolysis cell or an electrodialysis cell, preferably an electrodialysis cell. In preferred embodiments, the apparatus is according to the present disclosure, wherein one or both of the liquid sorbent and liquid desorbent comprise an alkali metal cation, an amine or aminoacid salt, or a mixture of an alkali metal cation and an amine or amino acid salt, as a base.In particular said alkali metal cation is selected from potassium ion (K+) or sodium ion (Na+). In particular the amine or amino acid salt is an amino acid selected from glycine, threonine, histidine, aspargine, glutamine, proline, lysine, phenylalanine, methionine, alanine, taurine, amino- butyrate, serine and sarcosine, or an amine selected from monoethanolamine (MEA), diethalolamine (DEA), triethanol amine (TEA), methyldiethanolamine (MDEA), aminomethylpropanol (AMP), diglycolamine (DGA) and diisopropanolamine (DIPA). In some embodiments, the base in one or both of the liquid sorbent and liquid desorbent, is an amine or amino acid salt at a concentration higher than 0,5 mol / L. In another embodiment, said base is selected from an alkali metal cation, an amine or amino acid salt, and may further comprise another amine or amino acid salt acting as sorption or desorption catalyst, at a concentration lower than 0,5 mol / L. In preferred embodiments, the apparatus is according to the present disclosure, further comprising one or more heaters for heating the loaded liquid desorbent prior to desorption of carbon dioxide in the desorber, In preferred embodiments, the apparatus is according to the present disclosure, said heater is configured to deliver waste heat from an industrial process plant or power plant, preferably said industrial process is an industrial carbon dioxide utilization process. In preferred embodiments, the apparatus is according to the present disclosure, further comprising a gas compressor for compressing the desorbed carbon dioxide gas, which comprises at least one compressor module and at least one post-compressor cooler module; the cooler module comprising a cooler heat exchanger which is configured and arranged to transfer heat from the output gas stream to the liquid desorbent prior to desorption of the carbon dioxide therefrom. In preferred embodiments, the apparatus is according to the present disclosure, wherein said fluid is a gas stream and said means for absorbing carbon dioxide is a gas contactor, wherein said heat pump is a gas source heat pump, in particular configured and arranged to transfer heat from a gas to the liquid desorbent preferably to transfer heat from the gas stream exiting the gas contactor to the liquid desorbent. In preferred embodiments, the apparatus is according to the present disclosure, wherein the gas source heat pump comprises a gas-refrigerant heat exchanger and a refrigerant circuit; wherein the gas-refrigerant heat exchanger is integrated with the gas contactor such that the gas-refrigerant heat exchanger is positioned in the gas stream in use, to transfer heat from the gas stream to a refrigerant in the refrigerant circuit. In preferred embodiments, the apparatus is according to the present disclosure, wherein the gas contactor comprises at least one fan which is configured and arranged to drive the gas stream through or over the gas contactor and over the gas-refrigerant heat exchanger. In preferred embodiments, the apparatus is according to the present disclosure, wherein the gas contactor which includes a housing having an inlet for admitting the gas stream into the housing and an outlet for exhausting the gas stream therefrom, the gas-refrigerant heat exchanger being disposed proximate the outlet; the gas contactor further comprising a first gas contactor fan proximate the inlet for impelling the gas stream into the housing and a second heat pump fan proximate the outlet for assisting passage of the gas stream over the gas-refrigerant heat exchanger. In some embodiments, the apparatus of the present disclosure is as described above, wherein the gas contactor comprises a housing defining a plenum and having an inlet and an outlet, a plurality of spaced parallel tubes that extend through the plenum and at least one fan for driving a gas stream through the plenum from the inlet to the outlet; each tube comprising a wall that is formed at least partially of an anion exchange polymer, and the tubes being configured and arranged to pass a flow of a liquid sorbent therethrough, such that in use the carbon dioxide is absorbed through the walls of the tubes from the gas stream into the liquid sorbent as the CO2-containing anions. In a third aspect of the present disclosure, there is provided a method of capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air comprising: i) transferring carbon dioxide in the form of CO2-containing anions contained in a liquid sorbent, from said liquid sorbent to a liquid desorbent in an electrochemical cell across one or more of its ion exchange membranes to load the liquid desorbent with CO2-containing anions and obtain the loaded liquid desorbent, or transferring cations contained in a liquid sorbent containing carbon dioxide in the form of CO2- containing anions, in an electrochemical cell across one or more of its ion exchange membranes to transform said liquid sorbent to a liquid desorbent loaded with CO2-containing anions, ii) heating said loaded liquid desorbent by using at least one heat pump configured to deliver heat below 100 degrees Celsius, prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, and obtaining desorbed carbon dioxide wherein, by heating said loaded desorbent liquid, the equilibrium of the desorption reaction of carbon dioxide in the desorber is shifted and the rate of the desorption is increased to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and wherein the voltage and the energy consumption of the electrochemical cell is lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent In preferred embodiments, the method is according to the present disclosure, wherein the liquid desorbent is heated prior to desorption of carbon dioxide in the range of less than 100 degrees Celsius; in particular about 40-95 degrees Celsius; preferably about 40-90 degrees Celsius; more preferably about 45-75 degrees Celsius. In preferred embodiments, the method is according to the present disclosure, wherein the liquid sorbent and the liquid desorbent are circulated in separate loops and the liquid desorbent has a minimum temperature which is higher than a maximum temperature of the liquid sorbent, In some embodiments, the liquid sorbent temperature is in the range of 10-40 °C, and the liquid desorbent temperature is in the range of 40-70 °C. In preferred embodiments, the method is according to the present disclosure, further comprising compressing the desorbed carbon dioxide, cooling the compressed carbon dioxide bytransferring heat therefrom to the liquid desorbent prior to desorption of the carbon dioxide therefrom.In preferred embodiments, the method is according to the present disclosure, wherein one or both of the liquid sorbent and liquid desorbent comprise an alkali metal cation, an amine or amino acid salt, or a mixture of an alkali metal cation and an amine or amino acid salt, as a base. In some embodiments, the method of the present disclosure is as described above, wherein said alkali metal cation is selected from potassium ion (K+) or sodium ion (Na+) and the amine or amino acid salt is an amino acid selected from glycine, threonine, histidine, aspargine, glutamine, proline, lysine, phenylalanine, methionine, alanine, taurine, amino-butyrate, serine and sarcosine, or an amine selected from monoethanolamine (MEA), diethalolamine (DEA), triethanol amine (TEA), methyldiethanolamine (MDEA), aminomethylpropanol (AMP), diglycolamine (DGA) and diisopropanolamine (DIPA). In some embodiments, the method of the present disclosure is as described above, wherein said base is an amine or amino acid salt, at a concentration higher than 0,5 mol / L. In some embodiments, the method of the present disclosure is as described above, wherein said base is selected from an alkali metal cation, an amine or amino acid salt, and may further comprise another amine or amino acid salt acting as sorption or desorption catalyst, at a concentration lower than 0,5 mol / L. In some embodiments, the method of the present disclosure is as described above, further comprising prior to step i), a step of absorbing carbon dioxide from a fluid, preferably from a gas, into the liquid sorbent in the form of one or more CO2-containing anions. In one aspect of the present disclosure, there is provided a method of capturing carbon dioxidefrom a gas comprising: absorbing carbon dioxide from a gas stream comprising carbon dioxide into a liquid sorbent in the form of one or more CO2-containing anions to form a loaded sorbent, the liquid sorbent comprising a base as a solvent for the CO2-containing anions therein; receiving the loaded sorbent in an electrochemical cell comprising an ion exchange membrane; applying a voltage to the electrochemical cell to cause the CO2-containing anions or cations of the base to be transported across the ion exchange membrane to form a loaded desorbent in which the CO2-containing anions have a lower solubility; heating the loaded desorbent with one or more heaters, including at least one heat pump, to provide a heated loaded desorbent; receiving the heated loaded desorbent in a desorber; and desorbing carbon dioxide as a gas from the heated loaded desorbent in a desorber to release carbon dioxide leaving a depleted desorbent stream. The one or more heaters may preferably be configured to heat the liquid desorbent to a temperature in the range of less than 100 degrees Celsius immediately before the desorption step; suchfor example as about 45-95 degrees Celsius, preferably about 50-80 degrees Celsius, more preferablyabout 55-75 degrees Celsius. In some implementations as disclosed herein, the method may advantageously comprise using at least one heat pump to transfer heat to the liquid desorbent. Preferably, the at least one heat pumpmay comprise a low temperature heat pump, as further described hereinbelow.The at least one heat pump may preferably have a coefficient of performance of greater than unity. In some implementations, the at least one heat pump may preferably have a coefficient of performance greater than about 2, more preferably greater than about 3 and even more preferably greater than about 4. In some implementations, the at least one heat pump may be configured and arranged to transfer heat to the liquid desorbent from the surroundings. Thus, in some implementations, the at least one heat pump may comprise a gas or ground source heat pump. Preferably, the at least one heat pump may comprise a gas source heat pump, which is configured and arranged to transfer heat from the air or another gas to the liquid desorbent, e.g. from the gas stream containing carbon dioxide. In some implementations, the at least one heat pump may be configured and arranged to transfer waste heat from an industrial process or power plant to the liquid desorbent. Typically, the method may further comprise recirculating the liquid sorbent from the electrochemical cell to the gas contactor. In some implementations, the one or more heaters maycomprise at least one heat pump that is configured and arranged to transfer heat from the liquid sorbentintermediate the electrochemical cell and the gas contactor to the liquid desorbent. Advantageously, the at least one heat pump may comprise a combination gas and liquid source heat pump that is configured and arranged to transfer heat from the gas stream to the liquid desorbent before the desorption step and to transfer heat from the liquid sorbent intermediate the electrochemical cell and the gas contactor to the liquid desorbent. The method of the present disclosure may further comprise recirculating the liquid desorbent from the desorber to the electrochemical cell. In one aspect of the present disclosure, therefore, there is provided an apparatus for capturing carbon dioxide from a gas comprising a gas contactor for absorbing carbon dioxide from a stream of the gas into a liquid sorbent in the form of one or more CO2-containing anions, the liquid sorbent comprising a base as a solvent for the CO2-containing anions therein; an electrochemical cell for moving the CO2-containing anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the CO2-containing anions have a lower solubility; a desorber for desorbing carbon dioxide from the liquid desorbent as a gas; and one or more heaters including at least one heat pump for heating the liquid desorbent prior to desorption of the carbon dioxide therefrom. Typically, the gas contactor may be configured to receive the gas in the form of a gas stream, for example an air stream, (for example to receive and enable the flow through or past of the gas). The electrochemical cell may typically comprise an electrolysis or electrodialysis cell for transporting the CO2-containing anions across the ion exchange membrane when a voltage is applied across the cell. The use of an electrochemical cell allows a liquid desorbent to be formed in which the solubility of the CO2-containing anions is decreased so that desorption can occur at temperatures below the boiling point of the liquid desorbent. In some implementations, the electrochemical cell may be configured for electrochemically transporting the base cations across a cation exchange membrane to move the base cations from the liquid sorbent, which are replaced by protons formed at an anode or bipolar membrane of the electrochemical cell, thereby lowering the pH of the liquid sorbent to form the liquid desorbent. The one or more CO2-containing anions may have a lower solubility at lower pH. In such implementations, the CO2-containing anions remain within the liquid sorbent, which is transformed into the liquid desorbent in the electrochemical cell by increasing its acidity. However, in preferred implementations, the electrochemical cell may be configured for electrochemically transporting the one or more CO2-containing anions across an anion exchange membrane into the liquid desorbent, thereby to move the CO2-containing anions into a solution which is more acidic and more concentrated in carbon dioxide than the liquid sorbent. In this way, not only is the solubility of the one or more CO2-containing anions decreased, but also the loading of the CO2- containing anions is increased in the liquid desorbent relative to the liquid sorbent. In preferred implementations, the electrochemical cell may comprise an electrodialysis cell. Heating the liquid desorbent prior to desorption of carbon dioxide allows desorption to occur at a lower concentration of the CO2-containing anions in the liquid desorbent. This allows the electrochemical cell to be operated at a lower voltage. Meanwhile the use of at least one heat pumpallows the energy required for heating to be significantly decreased as compared with heating by othermethods, since the energy required to operate the heat pump is the heat it delivers divided by its coefficient of performance. The at least one heat pump suitably comprises refrigerant and may be configured to enable the flow of the refrigerant within the heat pump in a refrigerant loop. The gas contactor may be connected to the electrochemical cell by a first outward channel and a first return channel, thereby to enable passage of a liquid sorbent from the gas contactor to the electrochemical cell in the first outward channel in use, and passage of the liquid sorbent from the electrochemical cell to the gas contactor in the first return channel, thus providing a first circulation loop through which the liquid sorbent flows. In some implementations, the liquid sorbent may be circulated through the gas contactor two or more times in each circuit of the complete first loop, such that the flow rate of the liquid sorbent through the gas contactor is greater than it is through the electrochemical cell, to ensure a sufficient flow rate of the liquid sorbent through the gas contactor. In some implementations, the liquid sorbent may be circulated through the electrochemical cell two or more times in each circuit of the complete first loop, such that the flow rate of the liquid sorbent through the electrochemical cell is greater than it is through the gas contactor, to ensure a sufficient flow rate of the liquid sorbent through the electrochemical cell. Furthermore, it may be desirable to recirculate the sorbent and desorbent at different flow rates to optimise the heat transfer and temperatures of the two liquids within the electrochemical cell. The electrochemical cell may be connected to the desorber by a second outward channel and a second return channel, to thereby enable during use the passage of a liquid desorbent from the electrochemical cell to the desorber in the second outward channel, and the passage of the liquid desorbent from the desorber to the electrochemical cell in the second return channel, thus providing a second circulation loop through which the liquid desorbent flows. In some implementations, the liquid desorbent may be circulated through the desorber two or more times in each circuit of the complete second loop, such that the flow rate of the liquid desorbent through the desorber is greater than it is through the electrochemical cell, to ensure a sufficient flow rate of the liquid desorbent through the desorber. In some implementations, the liquid desorbent may be circulated through the electrochemical cell two or more times in each circuit of the complete first loop, such that the flow rate of the liquid desorbent through the electrochemical cell is greater than it is through the desorber, to ensure a sufficient flow rate of the liquid sorbent through the electrochemical cell. Suitably, the at least one heat pump may be configured and arranged to heat the liquid desorbent as it flows in the second outward channel. The gas contactor may be configured so that during flow of the liquid sorbent through the gas contactor, the liquid sorbent absorbs carbon dioxide from the gas stream in the form of the CO2- containing anions. The electrochemical cell may typically comprise a membrane assembly including at least one cation exchange membrane. The electrochemical cell may be configured so that during flow of the loaded liquid sorbent through the electrochemical cell, cations of the base are transported out of the liquid sorbent across the cation exchange membrane. The base cations may be replaced by protons which are formed at an anode of the electrochemical cell and / or at at least one bipolar membrane of the electrochemical cell, thereby lowering the pH of the liquid sorbent to form the loaded liquid desorbent, which may then be passed through the desorber. The depleted liquid desorbent may then be returned to the electrochemical cell on the other side of the at least one cation exchange membrane to receive the base cations, thereby to regenerate the liquid sorbent, which is then passed to the gas contactor. In this way, the first and second loops may be configured to circulate liquid sorbent from the gas contactor, through the electrochemical cell to the desorber and from the desorber, through the electrochemical cell to the gas contactor. In preferred implementations, however, the electrochemical cell may comprise a membrane assembly including at least one anion exchange membrane, the electrochemical cell being configured so that during flow of the liquid sorbent and the liquid desorbent through the electrochemical cell, the CO2-containing anions are transported from the liquid sorbent to the liquid desorbent across the anion exchange membrane. In this way, the CO2-containing anions may be transported into the liquid desorbent which is more acidic and has a higher carbon loading that the liquid sorbent. In such an arrangement, the first and second loops may be configured as separate closed loops. The desorber is suitably configured so that during flow of the liquid desorbent through the desorber, carbon dioxide is desorbed from the liquid desorbent. Suitably the first and second loops comprise fluid pumps for causing the liquid sorbent and desorbent to flow therein as described. The gas contactor may be adapted to cause or allow the liquid sorbent to flow therethrough or therepast for interaction with the gas stream. The electrochemical cell may be adapted to cause or allow the liquid sorbent and liquid desorbent to flow therethrough or therepast in juxtaposition with one another, for interaction therebetween. The desorber may be adapted to cause or allow the liquid desorbent to flow therethrough or therepast for desorbing carbon dioxide from the liquid desorbent. In some embodiments of the disclosure, the first loop may be a closed loop. The second loop may be a closed loop. Preferably, the first and second loops may be “closed”, such that the liquid sorbent and liquid desorbent do not mix with one another, i.e. so there is no direct contact between the liquid sorbent and the liquid desorbent. Advantageously, this helps to reduce the loss of sensible heat in the apparatus in use. Such an arrangement is particularly preferred when the one or more CO2-containing anions are transported across an anion exchange membrane in the electrochemical cell. In preferred implementations, the one or more heaters are configured to heat the liquid desorbent to a temperature in the range of less than 100 degrees Celsius; for example such as about 45-95 degrees Celsius; preferably about 50-80 degrees Celsius; more preferably about 55-75 degrees Celsius. In preferred implementations, the one or more heaters may include at least one gas (e.g. air) source heat pump. In some implementations, the one or more heaters may include at least one gas (e.g. air) source heat pump and at least one heat pump using the liquid sorbent as its heat source. In some implementations, the one or more heaters may include at least one gas (e.g. air) source heat pump and at least one heat pump using the liquid desorbent as its heat source. In some implementations, the one or more heaters may include at least one gas (e.g. air) source heat pump, at least one heat pump using the liquid desorbent as its heat source, and at least one heat pump using the liquid sorbent as its heat source. In some implementations, the one or more heaters include at least one heat pump using the liquid desorbent as its heat source and at least one heat pump using the liquid sorbent as its heat source. In particular, the one or more heaters may include one or more gas source heat pumps which are configured and arranged to transfer heat from a gas, e.g. air, to the liquid desorbent. Preferably, at least one gas source heat pump may be configured and arranged to transfer heat from the gas stream in the gas contactor to the liquid desorbent. In preferred implementations, the gas source heat pump comprises a first gas-refrigerant heat exchanger and a first refrigerant circuit; wherein the first gas-refrigerant heat exchanger is integrated with the gas contactor such that the first heat gas-refrigerant exchanger is positioned in the gas stream in use, to transfer heat from the gas stream to a refrigerant in the first refrigerant circuit. In preferred implementations, the gas contactor comprises at least one fan which is configured and arranged to drive the gas stream through or over the gas contactor and over the first gas-refrigerant heat exchanger. In preferred implementations, the gas contactor includes a housing having an inlet for admitting the gas stream into the housing and an outlet for exhausting the gas stream therefrom, the first gas-refrigerant heat exchanger being disposed proximate the outlet; the gas contactor further comprising a first gas contactor fan proximate the inlet for impelling the gas stream into the housing and a second heat pump fan proximate the outlet for assisting passage of the gas stream over the first gas-refrigerant heat exchanger. Preferably, said gas-contacting surface of the first heat exchanger is coated with heat conducting fibres. In preferred implementations, the apparatus is according to the present disclosure, further comprising a moisture receptacle which is configured and arranged to receive moisture that condenses on the gas-contacting surface of the first heat exchanger in use and a moisture infeed for feeding the received moisture into the liquid sorbent or liquid desorbent. In preferred implementations, the apparatus is according to the present disclosure, further comprising a first liquid sorbent circulation loop for continuously circulating the liquid sorbent between the gas contactor and the electrochemical cell. In some implementations, the one or more heaters may comprise at least one heat pump that is configured and arranged to transfer heat from the liquid sorbent intermediate the electrochemical cell and the gas contactor to the liquid desorbent intermediate the electrochemical cell and the desorber. Such an arrangement may be especially useful when the liquid sorbent exits the electrochemical cell at an elevated temperature, and it is desirable to reduce its temperature prior to entry into the gas contactor. In some implementations, the gas source heat pump further comprises a second sorbent- refrigerant heat exchanger, which is configured and arranged to transfer heat to the refrigerant from the liquid sorbent intermediate the electrochemical cell and the gas contactor. In some implementations, the gas source heat pump further comprises a refrigerant-desorbent heat exchanger that is configured and arranged to transfer heat from the refrigerant to the liquid desorbent intermediate the electrochemical cell and the desorber. In some implementations, the apparatus is according to the present disclosure, further comprising a second liquid desorbent circulation loop for continuously circulating the liquid desorbent between the electrochemical cell and the desorber. In some implementations, the one or more heaters may include at least one heat pump that is configured and arranged to transfer heat to the liquid desorbent at a location in the second loop upstream of the desorber from the liquid desorbent at a different location in the second loop, e.g. intermediate the desorber and the electrochemical cell. In some implementations, the at least one heat pump may comprise a plurality of components which are distributed in the apparatus. Typically, the at least one heat pump may thus comprise at least one evaporator for extracting heat from the surroundings, such for example as a first gas- refrigerant heat exchanger for extracting heat from the gas (e.g. air) that passes through or past the contactor, and at least one output heat exchanger such, for example, as a refrigerant-desorbent heat exchanger for delivering heat to one or more heat sinks such, for example, as the liquid desorbent in the second outward channel. The heat pump may further comprise at least one heat pump compressor for increasing the temperature of the refrigerant before it reaches the heat exchanger and at least one heat pumpexpansion valve for reducing the temperature of the refrigerant before it reaches the evaporator(s).In some embodiments, as described hereinbelow in more detail, at least one heat pump may comprise at least one additional input heat exchanger. For example, in some embodiments, at least one heat pump may comprise a second sorbent-refrigerant heat exchanger for extracting heat from the liquid sorbent in the first return channel and warming the refrigerant before it enters the heat pump compressor. The additional input heat exchanger may advantageously be situated after the at least one evaporator for extracting heat from the surroundings for cooling the liquid sorbent before it enters the contactor. As described herein, components of the at least one heat pump may contact both of the first and second loops. In some embodiments, one or more components of the at least one heat pump, especially the evaporator, may be integrated with the gas contactor. For the purposes of the present disclosure, “liquid sorbent” (or “liquid solvent”) shall be taken to mean a liquid into which carbon dioxide is absorbed in the form of one or more CO2-containing anions. For the purposes of the present disclosure, “liquid desorbent” shall be taken to mean a liquid from which carbon dioxide is desorbed. Suitably, one or both of the liquid sorbent and liquid desorbent may contain a suitable solvent, as described herein. The solvent may preferably comprise a base as described herein in more detail. Depending on the context, the term “solvent” is used herein to describe the liquid sorbent or liquid desorbent or to the chemical species that is used as the base to increase the solubility of the one or more CO2-containing anions. The liquid sorbent flowing in the first loop is hereafter be referred to as a “sorbent stream”. The liquid desorbent flowing in the second loop is hereafter be referred to as a “desorbent stream”. In some implementations, heat delivered by the at least one heat pump may advantageously be supplemented by heat from other sources such for example as at least one heat exchanger that is adapted to deliver heat from an industrial process or power plant, as described below. In some implementations, the one or more heaters may comprise only one or more heat pumps; preferably low temperature heat pumps. Advantageously, the first and second loops may preferably be completely separate from one another. Alternatively, the first return channel may fully or at least partly overlap (i.e. intersect) with the second outward channel and / or second return channel. For example, in some implementations, at least part of the first return channel may be shared with at least part of the second outward channel or second return channel. The sorbent and desorbent streams may thus be caused or allowed to mix in at least a portion of the first return channel. In some implementations as described above, particularly where base cations are transported across a cation exchange membrane in the electrochemical cell to reduce the solubility of the one or more CO2-containing anions in the liquid sorbent, the first and second loops may be arranged to form a single loop, such that the liquid sorbent flows from the gas contactor, through the electrochemical cell on one side of the cation exchange membrane(s), to the desorber, and from the desorber, through the electrochemical cell on the other side of the cation exchange membrane(s), to the gas contactor. In such an arrangement, the liquid sorbent first transforms to the liquid desorbent on its first pass through the cell and then reverts to the liquid sorbent on its second pass through the cell. The at least one heat pump, in particular the output heat exchanger, more particularly the refrigerant-desorbent heat exchanger, being configured and arranged to heat the liquid desorbent as it flows in the second outward channel may therefore include the heat pump also being configured and arranged to heat the liquid sorbent as it flows in the first return channel in an arrangement wherein there is at least some mixing of the liquid sorbent and liquid desorbent. The output heat exchanger, particularly the refrigerant-desorbent heat exchanger, of the at least one heat pump may preferably be situated upstream of the desorber in the second loop. The membrane assembly may comprise one or more ion exchange membranes, which may be anion exchange membranes or cation exchange membranes, as described above. In preferred implementations, the electrochemical cell may comprise an electrolysis cell comprising at least one anion exchange membrane. Generally, in an electrolysis cell, protons (H+) are consumed or hydroxide ions (OH-) are produced at a cathode. Meanwhile, protons are produced or hydroxide ions are consumed at an anode. The one or more CO2-containing anions may be transferred across the at least one anion exchange membrane into the liquid desorbent, which is heated with the heat pump to desorb carbon dioxide and fed back to the electrolysis cell. In this cell, protons and hydroxide are only produced by the oxidation of water and the reduction of water respectively. In some implementations, hydrogen gas may be produced at the cathode and fed to a gas- diffusion anode, such that oxidation of hydrogen occurs at the anode. Preferably, however, the electrochemical cell may comprise an electrodialysis cell. The membrane assembly may therefore comprise one or more anion exchange membranes and one or more bipolar or cation exchange membranes. The apparatus of the present disclosure may advantageously allow a lower overall energy consumption by the apparatus for sorbent / desorbent regeneration owing to the use of a combination of the electrochemical cell and at least one heat pump for thermal regeneration of the sorbent / desorbent. The use of an electrochemical cell advantageously allows desorption of carbon dioxide to occur in the desorber at temperatures below about 100 degrees Celsius, preferably below about 75 degrees Celsius, as described below in more detail. Advantageously, this allows a low temperature heat pump of the kind described herein to heat the desorbent sufficiently to cause or allow desorption of carbon dioxide at 1 atmosphere. Meanwhile, raising the temperature of the desorbent to temperatures of at least about 50 degrees Celsius prior to desorption reduces the energy requirements of the electrodialysis cell. Advantageously, a heat pump has a coefficient of performance of more than 1, making it an economical and environmentally friendly source of heat for heating the desorbent stream. Ordinary,low temperature heat pumps are typically capable of delivering temperatures of at least 55-75 degreesCelsius. Thus, use of at least one heat pump in combination with an electrochemical cell for regenerating the liquid sorbent and liquid desorbent is particularly advantageous. In implementations in which the gas is air, for example, carbon dioxide may be absorbed intothe liquid sorbent (i.e. through the gas contactor) from the air at a concentration of around 400 ppm,providing a sweetened exit air stream at a lower carbon dioxide concentration of for example around 100 ppm. Work is done by the electrochemical cell through the application of a voltage across the cell, for example, to drive the transfer of the carbon dioxide (in the form of the one or more CO2- containing anions anions) from the liquid sorbent to the liquid desorbent. Desorption occurs in the desorber, where the carbon dioxide is desorbed (at for example atmospheric pressure), driven by the ion concentration gradients created in the electrochemical cell and the heat supplied to the desorbent. Desorption could occur without heating the desorbent or applying a vacuum, but this would require excessive work by the electrochemical cell (i.e. an uneconomically high voltage) to drive the CO2- containing anions to a high enough concentration in the desorber to allow desorption at ambient temperature and pressure, without the need to apply a vacuum. According to the present disclosure, the one or more heaters heat the desorbent stream prior to it reaching the desorber and thus desorption occurs in the desorber at a lower CO2-containing anion concentration. Thus, the desorbent may be heated to a temperature to enable desorption of carbon dioxide in the desorber without requiring excessive work by the electrochemical cell. In other words,use of heat shifts the equilibrium in the second loop to a lower CO2-containing anion concentrationfor desorption. The use of at least one heat pump allows this heat to be supplied with a coefficient of performance of higher than unity. In a further advantage, it is noted that the pH difference between the sorbent and desorbent may be smaller in the apparatus of the present disclosure when in operation than for example in a prior apparatus in which no heat is supplied. This is because the equilibrium carbon loading for heated desorbent is less than for unheated desorbent at a given partial pressure of the carbon dioxide, meaning that the desorbent pH is higher, and the pH differential is reduced (reducing the required voltage onthe cell). By way of example, for a carbon dioxide partial pressure of say 1 atm, the equilibrium carbondioxide loading of the desorbent stream is lower at say 70 degrees Celsius than it is at say 25 degrees Celsius. Use of one or more heaters such for example as at least one heat pump which are configured to operate below 100 degrees Celsius, for example in the range of 45-95 degrees Celsius, preferably 50-80 degrees Celsius, more preferably 55-75 degrees Celsius, to aid desorption provides a further particular advantage over, for example, steam stripping methods which require temperatures in excess of 100 degrees Celsius. The apparatus of the present disclosure reduces energy losses and conserves water. Use of at least one heat pump may be particularly economic for heating the desorbent to a suitable temperature for desorption by dint of its advantageous coefficient of performance. Further, the overpotential required in an electrochemical cell to drive water oxidation and reduction at a particular rate by electrolysis may be decreased by increasing the temperature. Advantageously, heated desorbent enters the electrochemical cell hot and may transfer heat to the ion exchange membranes and to the sorbent. This means that the electrical conductivities of the sorbent, desorbent and membranes may be increased as compared to an unheated system, and this may further reduce the voltage of the cell. In implementations which comprise one or more bipolar membranes, the overpotential required to drive water dissociation may be decreased at higher temperature, which is another effect which decreases the overall cell voltage. Advantageously, the electrochemical cell, especially the electrolysis or electrodialysis cell, may be thermally insulated to reduce heat loss from the apparatus in use. Suitably, the pipes used to convey the liquid sorbent and liquid desorbent round the first and second loops respectively may also be thermally insulated. When the first and second loops are closed loops in which there is no direct contact between the liquid sorbent and the liquid desorbent, the loops can be more readily maintained at different temperatures, providing further energy efficiencies over systems which utilise a single loop or inwhich the sorbent and desorbent streams are mixed. It may be advantageous in accordance with thepresent disclosure to maintain the first closed loop at a lower average temperature than the average temperature of the second loop, since carbon dioxide may be captured at a relatively low temperature; for example at ambient temperature. It may be advantageous to maintain the second closed loop at a higher average temperature than the average temperature of the first loop, which is more favourable for carbon dioxide desorption, (thereby reducing the energy input required of the heat pump since the temperature variation in the second loop is kept to a minimum). In some implementations, in use, the liquid desorbent in the second loop has a minimum temperature which is higher than a maximum temperature of the liquid sorbent in the first loop. In some implementations, the electrochemical cell and first and second loops are configured to circulate liquid sorbent from the gas contactor, through the electrochemical cell to the desorber and from the desorber, through the electrochemical cell to the gas contactor. According to one aspect of the present disclosure therefore there is provided apparatus for capturing carbon dioxide from a gas comprising a gas contactor for absorbing carbon dioxide from a stream of the gas into a liquid sorbent stream in the form of one or more CO2-containing anions; an electrochemical cell for electrochemically transporting the one or more CO2-containing anions across an anion exchange membrane into a liquid desorbent stream; a desorber for desorbing carbon dioxide from the liquid desorbent stream as a gas; a first liquid sorbent circulation loop for continuously circulating the liquid sorbent stream between the gas contactor and the electrochemical cell; a second liquid desorbent circulation loop for continuously circulating the liquid desorbent stream between the electrochemical cell and the desorber; and one or more heaters, which preferably include at least one heat pump, for heating the liquid desorbent stream prior to desorption of the carbon dioxide therefrom; wherein the first and second loops are closed loops which are separate from one another and, in operation, the liquid desorbent stream in the second loop has a minimum temperature which is higher than a maximum temperature of the liquid sorbent stream in the first loop. In preferred implementations, the apparatus is according to the present disclosure, wherein the electrochemical cell comprises an electrolysis cell or an electrodialysis cell; preferably an electrodialysis cell. In preferred implementations, the apparatus is according to the present disclosure, wherein one or both of the liquid sorbent and liquid desorbent comprise an alkali metal cation, an amine or amino acid salt, or a mixture of an alkali metal cation and an amine or amino acid salt as the base. Preferably, the one or more heaters include at least one heat pump, as disclosed herein. Preferably, the second loop may be slightly pressurised; for example, to around 1-10 atmospheres; preferably about 4-8 atmospheres. Suitably, the first loop may be slightly pressurised; for example, to around 1-10 atmospheres; preferably about 4-8 atmospheres. Pressurising the sorbent and / or desorbent stream may help to reduce bubbling i.e. desorption of carbon dioxide in locations other than in the desorber, such for example as inside the electrochemical cell, where bubbles would undesirably increase Ohmic resistance and thereby cell voltage. Most suitably, the first and second are both pressurised; preferably to about the same pressure. Suitably, the apparatus may comprise a plurality of fluid pumps configured and arranged to direct the flow of the liquid sorbent in the first loop and to direct the flow of the liquid desorbent in the second loop. The liquid sorbent and / or desorbent may comprise a solvent for increasing the concentration of carbon dioxide therein as one or more CO2-containing anions. Suitably, the solvent should exhibit fast sorption kinetics, fast desorption kinetics, a high maximum carbon dioxide loading, high electrical conductivity, low or zero toxicity, low heat capacity and low vapour pressure. In some implementations, the solvent may comprise an alkali metal cation. Suitable alkali metal cations include potassium and sodium cations; potassium being especially preferred. In some implementations, the solvent(s) may comprise a small organic molecule. Preferably the small molecule may be monomeric. Small molecules are preferred because they have greater mobility in solution than large molecules such as polymers. Preferably, the liquid sorbent and / or desorbent may comprise an amine or amino acid salt. Suitably, the amine or amino acid salt may be monomeric. Preferably therefore the amine or amino acid salt solvent is not a polymer. The amine solvent may comprise at least one alkanolamine as a capture species for the carbon dioxide. In principle, any amino acid salt known to those skilled in the art may be used in accordance with the present disclosure, but preferred salts include those of glycine, threonine, histidine, asparagine, glutamine, proline, lysine, phenylalanine, methionine, alanine, taurine, amino-butyrate, serine and sarcosine; especially the alkali metal, e.g. potassium, salts. In some implementations, the solvent may comprise only an amine, amino acid salt. However, in some preferred implementations, the liquid sorbent and / or liquid desorbent may comprise an alkali metal cation solvent in which the alkali metal cation primarily serves to balance the charge of hydroxide, bicarbonate and carbonate ions in solution. The liquid sorbent and / or liquid desorbent may preferably further contain a relatively small quantity of at least one amino acid salt and / or amine solvent to act as a sorption or desorption catalyst. Suitable solvents such for example as alkali metal cations and amine and amino acid salt solvents are known to those skilled in the art. Suitably, the solvent may be non-acidic. In some embodiments, the solvent may be alkaline, optionally mildly alkaline. The solvent may preferably comprise a base. The liquid sorbent may comprise an aqueous liquid sorbent. The liquid desorbent may comprise an aqueous liquid desorbent. Preferably the liquid sorbent may comprise a solvent having a pKa > 7.Preferably, the liquid desorbent may comprise a solvent having a pKa > 7. Advantageously, in some embodiments, the liquid sorbent and the liquid desorbent may comprise the same solvent. In practice, there may be some leakage of the solvent from the liquid sorbent, e.g. the “sorbent stream” to the liquid desorbent, e.g. the “desorbent stream”, and vice versa in the electrochemical cell. While the choice of sorbent / desorbent in accordance with the present disclosure is not limited by the need to avoid such leakage, by using the same solvent on both sides of the electrochemical cell, this leakage can be tolerated without significantly impairing the performance of the cell. It is therefore not required to design the electrochemical cell to provide absolute barriers to prevent such leakage or to select the solvent(s) on the basis of preventing leakage. In accordance with another aspect of the present disclosure therefore there is provided apparatus for capturing carbon dioxide from a gas comprising: a gas contactor for absorbing carbondioxide from a stream of the gas into a liquid sorbent in the form of one or more CO2-containinganions, the liquid sorbent comprising an amine or amino acid salt, optionally in combination with an alkali metal cation, as a solvent for the CO2-containing anions therein; an electrochemical cell for moving the CO2-containing anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the CO2-containing anions have a lower solubility; a desorber for desorbing carbon dioxide from the liquid desorbent as a gas; and one or more heaters, which preferably include at least one heat pump, for heating the liquid desorbent prior to desorption of the carbon dioxide therefrom; wherein the liquid sorbent and liquid desorbent comprise the same amine or amino acid solvent. In preferred implementations, the apparatus is according to the present disclosure, wherein the amine or amino acid salt solvent is an amino acid selected from glycine, threonine, histidine,aspargine, glutamine, proline, lysine, phenylalanine, methionine, alanine, taurine, amino-butyrate,serine and sarcosine, especially the alkali metal, e.g. potassium, salts; or an amine selected from monoethanolamine (MEA), diethalolamine (DEA), triethanol amine (TEA), methyldiethanolamine (MDEA), aminomethylpropanol (AMP), diglycolamine (DGA) and diisopropanolamine (DIPA). As mentioned above, in some implementations, the solvent may comprise an amount of an amine or amino acid salt which is sufficient to balance the charge of hydroxide, bicarbonate and carbonate ions in solution. However, in some implementations, a potentially good choice of solvent may be an alkali metal cation as the base cation with an addition of a relatively small amount of an amino acid salt or amine as a catalyst. Such a combination solvent may provide the fast kinetics of the amine or amino acid salt, but the main CO2-containing anion would be bicarbonate rather than carbamate, which may be preferable since bicarbonate may behave more predictably in its transfer across an anion exchange membrane. An amine or amino acid salt solvent, or an alkali metal cation solvent combined with a relatively small amount of an amino acid salt or amine as a catalyst, may thus provide relatively fastabsorption and desorption reaction kinetics as compared with other solvents, thereby improving theuptake of carbon dioxide, and reducing the temperature required for desorption in the desorber; thereby reducing the energy demand on the heat pump. In accordance with one aspect of the present disclosure therefore there is provided apparatus for capturing carbon dioxide from a gas comprising: a gas contactor for absorbing carbon dioxide froma stream of the gas into a liquid sorbent in the form of one or more CO2-containing anions, the liquidsorbent comprising a base as a solvent for the CO2-containing anions therein; an electrochemical cell for moving the CO2-containing anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the CO2-containing anions have a lower solubility; a desorber for desorbing carbon dioxide from the liquid desorbent as a gas; and one or more heaters, which preferably include at least one heat pump, for heating the liquid desorbent prior to desorption of the carbon dioxide therefrom; wherein the liquid sorbent comprises an amine or amino acid salt, optionally in combination with an alkali metal cation, as the base, and the one or more heaters are configured to heat the liquid desorbent to a temperature of less than 100 degrees Celsius. As mentioned above, the one or more heaters may be configured to heat the liquid desorbentto a temperature such for example as about 45-95 degrees Celsius, preferably about 50-80 degreesCelsius, more preferably about 55-75 degrees Celsius. In preferred implementations, the apparatus is according to the present disclosure, wherein the liquid sorbent and liquid desorbent comprise the same amine or amino acid salt solvent. In preferred implementations, the apparatus is according to the present disclosure, wherein the one or more heaters include at least one heater that is configured to deliver waste heat from an industrial process or power plant. Since the second loop may be operated at a lower temperature than apparatus utilising steam stripping or other high temperature (i.e. in excess of 100 degrees Celsius) desorption, when the first and second loops are closed loops, the temperature differential between the first and second loops may be further reduced, thereby further reducing the loss of heat from the desorbent stream to the sorbent stream in the electrolysis or electrodialysis cell. Preferably, the one or more heaters include at least one heat pump, as disclosed herein. Advantageously the at least one heat pump may comprise an air source heat pump, as disclosed herein. Preferably, the at least one heat pump may comprise a low temperature heat pump which is capable of heating the liquid desorbent to a temperature of more than about 45 degrees Celsius, preferably more than about 55 degrees Celsius, and less than about 100 degrees Celsius. More preferably the low temperature heat pump may be operable to heat the liquid desorbent to a temperature in the range of about 55-75 degrees Celsius. In some implementations, the one or more heaters may comprise two or more heat pumps where additional heat input is required. Thus, for example, a series of two or more heat pumps maybe configured and arranged to deliver heat sequentially to the desorbent before it enters the desorber.The heat pumps may thus be configured and arranged to increase the temperature of the desorbent stepwise. In some implementations, the one or more heaters may include at least one heater that is adapted to deliver heat such, for example, as waste heat from an industrial process, power plant or the like to the liquid desorbent. The one or more heaters may for example comprise at least one heat pump that utilises such a source of heat. The heat pump may be configured and arranged to harness the heat and redirect it to heat the desorbent stream. Such an industrial process may comprise carbon dioxide mineralisation. The industrial process may comprise Fischer-Tropsch synthesis of hydrocarbons. The industrial process may comprise waste heat from carbon dioxide methanation. The industrial process may comprise a chemical reaction, for example an exothermic reaction. The industrial process may comprise the synthesis of polymers using carbon dioxide, such for example as polyurethanes or polyolefins. The power plant may comprise a solar power plant, a geothermal power plant, a nuclear power plant, bioenergy carbon capture and storage (BECCS), or other power plant. When a solar power plant is used as the source of waste heat for the heater to heat the liquid desorbent, there is obtained the additional benefit of cooling of the solar modules to improve their power output and lifetime. In some implementations, the one or more heaters may include at least one heat pump such for example as an air-source heat pump and at least one heat exchanger that is adapted to deliver waste heat from an industrial process or power plant. In some implementations, the gas may be air. Thus in some preferred embodiments, the apparatus may be adapted for capturing carbon dioxide from air. The air may be atmospheric air or may comprise exhaust gas from an industrial process. The exhaust gas may comprise carbon dioxide. Suitably, the gas contactor may comprise an air contactor. The gas stream may comprise an air stream. The gas stream may alternatively or additionally comprise a stream of biogas, flue gas or another gas stream comprising carbon dioxide. The apparatus may preferably comprise a direct air capture apparatus. Alternatively, the apparatus may comprise a point source carbon capture apparatus for capturing carbon dioxide from an industrial source. The one or more CO2-containing anions may comprise one or more of bicarbonate, carbonate, and carbamate. Preferably, the at least one heat pump may comprise an air-source heat pump. In some embodiments, the at least one heat pump may comprise another kind of heat pump such, for example,as a geothermal heat pump or an absorption heat pump. As mentioned above, in some implementationsthe at least one heat pump may utilise a source of waste heat. In some implementations, the one or more heaters may include a combination of different kinds of heater, including at least one heat pump such for example as an air source heat pump and at least one other kind of heat pump. Advantageously, use of an air-source heat pump enables one or more components of the air- source heat pump to be integrated with one or more components of the gas contactor as disclosed herein, thereby to provide further improvements to the apparatus of the present disclosure. As mentioned above, the at least one heat pump may comprise one or more heat exchangers. One or more of the heat exchangers may comprise a gas-liquid heat exchanger. One or more of the heat exchangers may comprise a liquid-liquid heat exchanger. The above-mentioned additional heat exchanger may comprise a liquid-refrigerant heat exchanger. The output heat exchanger may comprise a refrigerant-liquid heat exchanger. Suitable liquid-liquid heat exchangers include plate or shell and tube heat exchangers. The at least one evaporator may comprise a gas-refrigerant heat exchanger. The at least one heat pump may be integrated with the gas contactor so that the evaporator is positioned and arranged with respect to the gas stream to transfer heat from the gas stream to the refrigerant. The least one heat pump being integrated with the gas contactor may mean, for the purposes of the present disclosure, the evaporator of the heat pump being spatially arranged so as to be proximate the gas contactor. The evaporator (or gas-refrigerant heat exchanger) may be co-located with the gas contactor. In addition, a further advantage is that moisture in the gas stream and / or moisture lost from the sorbent as a result of evaporation in the gas contactor can be condensed on the surface of the evaporator, and can thereafter be collected and fed into the sorbent to reduce the water demand on the apparatus in use. The gas-refrigerant heat exchanger may suitably comprise a gas-contacting surface that is coated with heat conducting fibres. Use of heat conducting fibres which may for example, comprise metal wires, promotes condensation through increasing surface area. Typically, the at least one heat pump, for example an air source heat pump, may be a lowtemperature heat pump, having an operational temperature during use of 40-90 degrees Celsius. Inother words, as mentioned above, the at least one heat pump may be configured to heat the desorbent stream to a temperature in the range of 55-85 degrees Celsius in use. The at least one heat pump, for example an air source heat pump, may have an operational temperature in use in the range 50-75 degrees Celsius. In other words, the heat pump may be configured to heat the desorbent stream to a temperature in the range of 65-75 degrees Celsius in use. The apparatus may further comprise a moisture receptacle, which is configured and arranged to receive moisture that condenses on the evaporator during passage of the gas stream over the evaporator. Thus, as described above, moisture in the gas stream and / or moisture lost from the sorbent stream as a result of evaporation in the gas contactor can be condensed on the surface of the evaporator,and can thereafter be collected in the moisture receptacle, and fed into the sorbent to reduce the netwater demand on the apparatus in use. The collected moisture may be mixed with sorbent, prior to being fed into the sorbent. The moisture receptacle may suitably comprise a drip tray. The evaporator may be positioned above the drip tray in use so that condensation falls from the evaporator into the drip tray in use. The above-mentioned additional input heat exchanger of the at least one heat pump may conveniently be integrated with the first loop. In some implementations, the at least one heat pump may therefore be integrated with the gas contactor and the first loop in the sense that the evaporator is spatially arranged proximate the gas contactor and the additional input heat exchanger is arranged proximate the first loop. An advantage of such an arrangement is that heat may be transferred from the sorbent stream after passage through the electrochemical cell to the refrigerant, to warm the refrigerant. Warming the refrigerant in this manner may reduce the demand on the heat pump compressor (i.e. helping to recover heat for desorption), providing further energy efficiencies. By extracting some of its heat input from the sorbent, the at least one heat pump may achieve an even greater coefficient of performance, because the liquid sorbent flowing into the gas contactor will tend to be hotter than the gas from which heat is extracted using the heat pump. At the same time, cooling of the sorbent stream may mean that a shorter transportation distance may be required for the first return channel since it is not necessary to rely on passive cooling alone to reduce the temperature of the sorbent stream to a suitable temperature for absorption of carbon dioxide. The sorbent stream may be pre-cooled before it reaches the gas contactor, so that carbon dioxide can be captured more effectively. In a further advantage, when the temperature of the sorbent stream is controlled in this manner, the rate of evaporation in the gas contactor may be reduced. As noted above, the additional input heat exchanger may suitably be situated downstream of the evaporator in the refrigerant loop. In some implementations, the at least one heater may comprise a first heat pump that is configured and arranged to extract heat from the surroundings, e.g., the air, as described above and supply it to the desorbent upstream of the desorber, and a second heat pump that is configured to extract heat from the sorbent downstream of the electrochemical cell, upstream of the gas contactor, and / or from the desorbent downstream of the desorber, and to supply heat to the desorbent upstream of the desorber, optionally downstream of the first heat pump. These configurations may be beneficial in case that sorbent would otherwise enter the gas contactor too warm and should be cooled to avoid excessive water or sorbent evaporation or the desorbent would otherwise enter the electrochemical cell too warm and should be cooled to avoid damaging components of the cell. The at least one output heat exchanger of the at least one heat pump may comprise a refrigerant-desorbent heat exchanger. The at least one heat pump may be integrated with the second loop so that the at least one output heat exchanger is positioned and arranged with respect to the second outward channel to transfer heat from the refrigerant to the liquid desorbent as the liquid desorbent flows from the electrochemical cell to the desorber. The at least one output heat exchanger may be situated downstream of the heat pump compressor in the refrigerant loop. Thus, the at least one output heat exchanger may be situated upstream of the desorber, so that the desorbent stream can be heated to a temperature suitable for desorption of carbon dioxide. In some implementations, the at least one heat pump may comprise a 2-stage output heat exchanger, in which heat from the refrigerant is first transferred, via an intermediate refrigerant-liquid heat exchanger, to an intermediate liquid, e.g. an aqueous or non-aqueous solution such for example as water, and then to the desorbent via a liquid-desorbent heat exchanger. Such configuration may be useful in implementations where the heat pump cannot efficiently increase the temperature of the desorbent directly to a desired temperature for desorption of the carbon dioxide in the desorber. In such a case, the heat pump may instead heat the intermediate medium by a first temperature difference via the intermediate refrigerant-liquid heat exchanger; the liquid-desorbent heat exchanger between the intermediate medium and the desorbent may then increase the temperature of the desorbent by a second temperature difference. For example, the heat pump may be configured to increases the temperature of the intermediate medium between 70 and 75 °C. The intermediate medium may then heats the desorbent between 45 and 65 °C. Such a heat transfer is possible by carefully selecting the relative flow rates of the intermediate medium and the desorbent. The desorber may be configured to provide an output gas stream comprising carbon dioxide. Suitably, the output gas stream may consist substantially wholly of substances desorbed from the desorbent. In some preferred implementations of the present disclosure, the output gas stream may comprise a carbon dioxide gas stream. Typically, the output gas stream may further comprise a small proportion of water vapour. In some embodiments, the apparatus of the present disclosure may comprise a carbon dioxide compressor configured and arranged to compress the output carbon dioxide stream, the carbon dioxidecompressor comprising at least one compressor module and at least one post-compressor coolermodule. The cooler module may advantageously comprise a cooler heat exchanger positioned and arranged with respect to the output carbon dioxide stream to transfer heat from the output carbon dioxide stream to the liquid desorbent as the liquid desorbent flows from the electrochemical cell to the desorber. Thus at least some of the heat input required to heat the desorbent stream to a temperature suitable for desorption can be provided by the waste heat of the carbon dioxide compressor. Thus in one aspect of the present disclosure, there is provided apparatus for capturing carbon dioxide from a gas comprising a gas contactor configured to receive and enable the flow through or past of the gas in a gas stream, an electrochemical cell, a desorber, one or more heaters, and a carbon dioxide compressor. The gas contactor, electrochemical cell and desorber may be substantially as described above. The one or more heaters may be configured and arranged to heat the liquid desorbent as it flows in the second outward channel. Preferably, the one or more heaters may include at least one heat pump, as disclosed herein. The electrochemical cell may comprise an electrolysis cell or, preferably, an electrodialysis cell. The carbon dioxide compressor may advantageously be configured and arranged to compress the output carbon dioxide and may comprise at least one compressor module, and at least one post-compressor cooler module comprising a cooler heat exchanger which is configured and arranged to transfer heat from the output gas to the liquid desorbent as the liquid desorbent flows from the electrochemical cell to the desorber. Suitably, the carbon dioxide compressor may be configured and arranged so that the compressor heat exchanger is situated upstream of the heat pump in the second loop in use. In accordance with one aspect of the present disclosure therefore there is provided apparatus for capturing carbon dioxide from a gas comprising: a gas comprising a gas contactor for absorbing carbon dioxide from a stream of the gas into a liquid sorbent in the form of one or more CO2-containing anions, the liquid sorbent comprising a base as a solvent for the CO2-containing anions therein; an electrochemical cell for moving the CO2-containing anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the CO2-containing anions have a lower solubility; a desorber for desorbing carbon dioxide from the liquid desorbent as a gas; and one or more heaters for heating the liquid desorbent prior to desorption of the carbon dioxide therefrom; wherein the one or more heaters include at least one heater that is configured to deliver waste heat from an industrial process or power plant. In preferred implementations, the at least one heater that is configured to deliver waste heat from an industrial process or power plant comprises a heat pump. In preferred implementations, the apparatus is according to the present disclosure, wherein the industrial process is an industrial carbon dioxide utilisation process, e.g. carbon dioxide mineralisation, Fischer-Tropsch synthesis, carbon dioxide methanation, or synthesis of polymers using carbon dioxide. In preferred implementations, the apparatus is according to the present disclosure, wherein the desorber is configured to provide an output gas stream which consists predominantly of carbon dioxide, the apparatus further comprising a gas compressor for compressing the output gas stream, which comprises at least one compressor module and at least one post-compressor cooler module; the cooler module comprising a cooler heat exchanger which is configured and arranged to transfer heat from the output gas stream to the liquid desorbent prior to desorption of the carbon dioxide therefrom. In preferred implementations, the apparatus is according to the present disclosure, wherein the cooler heat exchanger is situated upstream of the refrigerant-desorbent heat exchanger. In accordance with one aspect of the present disclosure therefore there is provided apparatus for capturing carbon dioxide from a gas comprising: a gas comprising a gas contactor for absorbing carbon dioxide from a stream of the gas into a liquid sorbent in the form of one or more CO2-containing anions, the liquid sorbent comprising a base as a solvent for the CO2-containing anions therein; an electrochemical cell for moving the CO2-containing anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the CO2-containing anions have a lower solubility; a desorber for desorbing carbon dioxide from the liquid desorbent as a gas, and a gas compressor for compressing the desorbed gas; wherein the gas compressor comprises at least one compressor module and at least one post-compressor cooler module; the cooler module comprising a cooler heat exchanger which is configured and arranged to transfer heat from the desorbed gas to theliquid desorbent prior to desorption of the carbon dioxide therefrom. In preferred implementations, the apparatus is according to the present disclosure, further comprising at least one solar PV module; wherein the liquid sorbent is passed through a conduit which contacts the solar PV module upstream of the electrochemical desorption module for transferring heat from the solar PV module to the liquid sorbent. In preferred implementations, the solar PV module comprises a rainwater receptacle, the solar PV module being configured to direct rainwater into the rainwater receptacle; the apparatus further comprising a water infeed for feeding the received rainwater into the liquid sorbent or liquid desorbent. In preferred implementations, the gas contactor comprises a housing defining a plenum, and a plurality of spaced parallel tubes extending through the plenum; each tube having a semi-permeable wall that is formed at least partially of an anion exchange polymer; wherein in use the liquid sorbent flows through the tubes, and the gas stream flows through the plenum between the tubes. In accordance with another aspect of the present disclosure there is provided a method of capturing carbon dioxide from a gas comprising: absorbing carbon dioxide from a gas stream into a liquid sorbent in the form of one or more CO2-containing anions to provide a loaded sorbent, the liquid sorbent comprising a base as a solvent for the CO2-containing anions; receiving the loaded sorbent in an electrochemical cell comprising an ion exchange membrane; removing the CO2-containing anions or cations of the base across the ion exchange membrane in the electrochemical cell to form a loaded desorbent in which the CO2-containing anions have a lower solubility; heating the loaded desorbent using one or more heaters including at least one heat pump to provide a heated loaded desorbent; receiving the heated loaded desorbent in a desorber; and desorbing carbon dioxide from the heated loaded desorbent stream in the desorber to release the carbon dioxide as a gas leaving a depleted desorbent stream. In preferred implementations, the method is according to the present disclosure, further comprising using the heat pump to transfer heat from the gas stream to the liquid desorbent before the desorption step. In preferred implementations, the method is according to the present disclosure, further comprising recirculating the liquid sorbent from the electrochemical cell to the gas contactor. In preferred implementations, the method is according to the present disclosure, further comprising using the heat pump to transfer heat from the liquid sorbent intermediate the electrochemical cell and the gas contactor to the liquid desorbent. In preferred implementations, the method is according to the present disclosure, further comprising recirculating the liquid desorbent from the desorber to the electrochemical cell. In preferred implementations, the method is according to the present disclosure, wherein the liquid desorbent is heated by the one or more heaters to a temperature in the range of less than 100 degrees Celsius; such for example as about 45-95 degrees Celsius; preferably about 50-80 degrees Celsius; more preferably about 55-75 degrees Celsius. In preferred implementations, the method is according to the present disclosure, wherein the liquid sorbent and liquid desorbent are circulated in separate loops and the liquid desorbent has a minimum temperature which is higher than a maximum temperature of the liquid sorbent. In preferred implementations, the method is according to the present disclosure, further comprising compressing the desorbed carbon dioxide, cooling the compressed carbon dioxide bytransferring heat therefrom to the liquid desorbent prior to desorption of the carbon dioxide therefrom.In accordance with another aspect of the present disclosure there is provided a method of capturing carbon dioxide from a gas comprising: absorbing carbon dioxide from a gas stream into a liquid sorbent in the form of one or more CO2-containing anions to provide a loaded sorbent, the liquid sorbent comprising a base as a solvent for the CO2-containing anions; receiving the loaded sorbent in an electrochemical cell comprising an ion exchange membrane; moving the CO2-containing anions or cations of the base across the ion exchange membrane in the electrochemical cell to form a loaded desorbent in which the CO2-containing anions have a lower solubility; heating the loaded desorbent to provide a heated loaded desorbent; receiving the heated loaded desorbent in a desorber; desorbing carbon dioxide from the heated loaded desorbent stream in the desorber to release the carbon dioxide as a gas leaving a depleted desorbent stream; compressing the desorbed carbon dioxide; and cooling the compressed carbon dioxide by transferring heat therefrom to the liquid desorbent prior to desorption of the carbon dioxide therefrom. Thus the desorbent stream may advantageously be pre-warmed before reaching the at least one output heat exchanger of the heat pump, thereby reducing the energy demand on the heat pump. In preferred implementations, the method is according to the present disclosure, further comprising using at least one heat pump to heat the loaded desorbent. In preferred implementations, the method is according to the present disclosure, wherein the electrochemical cell comprises an electrolysis cell or an electrodialysis cell. In preferred implementations, the method is according to the present disclosure, wherein the liquid sorbent and / or liquid desorbent comprise an alkali metal cation, an amine or amino acid salt or a mixture of an alkali metal cation and an amine or amino acid salt as the base. In some implementations, the gas compressor may comprise a series of compressor modules which are interspersed with a plurality of cooler modules. Each cooler module may be situated after a respective compressor module. Advantageously, each cooler module may comprise a cooler heatexchanger which is positioned and arranged with respect to the output gas stream to transfer heat fromthe output gas stream to the liquid desorbent as the liquid desorbent flows from the electrodialysis cell to the desorber. The precise number of compression modules and cooler modules may vary depending on the scale of the apparatus and compression ratios required. In some arrangements, there may be no gas compressor at all. The apparatus of the present disclosure may further comprise at least one solar photovoltaic (PV) module. The solar PV module may be positioned and arranged with respect to the first loop to transfer heat to the liquid sorbent in the first outward channel. In some implementations, the first loop may comprise at least one length of pipe for the liquid sorbent, intermediate the electrochemical cell, which contacts a surface of the solar PV module, e.g. a rear surface (backsheet) of the solar PV module. In use, the solar PV module gets warm and heat is transferred therefrom to the liquid sorbent within the length of pipe. Thus, advantageously, the temperature gradient between the liquid sorbent and liquid desorbent in the electrochemical cell may be reduced, so as to reduce heat losses from the desorbent stream to the sorbent stream during use. The portion or portions of the first loop that contact the solar PV module may be situated downstream of the gas contactor. Alternatively, or additionally, warming liquid sorbent with heat from the at least one solar PV module and using the liquid sorbent as a source of heat for the at least one heat pump may reduce the demand on the heat pump compressor. Cooling the solar PV module may improve its electricity output and prolong its lifetime. Current generated by the solar PV module may advantageously be used to power one or more components of the apparatus of the present disclosure such, for example, as the at least one heat pump, fluid pumps in the first and second loops, the gas compressor etc. to help reduce the energy demand of the apparatus. The solar PV module may include a rainwater receptacle. Parts of the solar PV module may be configured to direct rainwater into the rainwater receptacle. Rainwater collected in this way may be used to top up the liquid sorbent and / or liquid desorbent, to help reduce the amount of water that must be supplied to the apparatus in use. The gas contactor may typically comprise at least one gas contactor fan arranged to drive the gas stream through or over the gas contactor in use. The at least one heat pump may typically comprise at least one heat pump fan arranged to drive the gas stream through the gas contactor in use. In some implementations, the at least one heat pump may be integrated or otherwise physically associated with the gas contactor so that the at least one gas contactor fan and at least one heat pump fan operate in concert to direct the gas stream through the gas contactor and over the heat pump evaporator (gas-refrigerant heat exchanger) in use. The use of both fans together may increase the gas flow through the gas contactor. This spatial configuration may reduce the necessary fan power required of the contactor fan to achieve a given gas speed. In some implementations, there may be no dedicated heat pump fan, and at least one gas contactor fan may advantageously be configured and arranged both to move the gas stream through or over the gas contactor in use and to function as a heat pump fan (for example, to draw the gas stream through the at least one heat pump). In some implementations, the gas contactor may comprise a plurality of spray nozzles which are configured and arranged to spray liquid sorbent into the gas stream in use such that liquid sorbent presents a large surface area for absorbing carbon dioxide. The liquid sorbent in the first loop may thus be caused or allowed to flow through the spray nozzles, thereby creating droplets which fall under gravity. Suitably, the spray nozzles may be directed downwards in use. The gas stream may be caused or allowed to flow (by at least one fan, as described above) counter to or across the droplets; for example, upwards. The droplets of loaded sorbent may impinge on structured or random packing within the gas contactor as they fall and then flow downwards thereon to be collected by a suitable receptacle beneath the nozzles and / or packing for continued flow in the first loop. The receptable may suitably comprise a tray beneath the packing. The gas contactor may thus comprise a modified cooling tower-type arrangement. In some implementations, the gas contactor may include a housing having an inlet for admitting the gas stream into the housing and an outlet for exhausting the gas stream therefrom. In some implementations, the at least one input heat exchanger (evaporator) may be disposed proximate the outlet. The gas contactor may further comprise a gas contactor fan proximate the inlet for impelling the gas stream into the housing and a heat pump fan proximate the outlet for assisting passage of the gas stream over the first heat exchanger In some implementations, the gas contactor may further comprise a gas manifold in communication with the outlet of the housing. The gas manifold may be positioned to receive the gas stream exiting the housing in use. A gas contactor fan may be situated at a first end of the gas manifold intermediate the housing. A heat pump fan may be situated at a second end of the gas manifold remote from the housing. The gas contactor fan and heat pump fan may operate together, as described above, to draw the gas stream successively through the gas contactor. Suitably, the housing may accommodate the above-mentioned spray nozzles and receptacle. The gas manifold may be positioned above the nozzles. At least one fan may be arranged to draw the gas stream upwards within the housing, past the spray nozzles, into the gas manifold. In a particular aspect of the present disclosure, the gas contactor may comprise a housing, which defines a plenum, and a plurality of spaced parallel tubes which extend through the plenum,each tube comprising a semi-permeable wall that is formed at least partially of an anion exchangepolymer. In use the liquid sorbent may be caused or allowed to flow through the tubes, and the gas stream may be caused or allowed to flow through the plenum between the tubes. Previous gas contactor designs typically work by spraying droplets of the liquid sorbent into an air flow, or by flowing the liquid sorbent in the form of a thin film. Such designs suffer from a considerable drawback in respect of the amount of water that is lost through evaporation (of the order of several tonnes of water per tonne of carbon dioxide captured). It has now been discovered that use of an anion exchange membrane which contacts the liquid sorbent on one side of the membrane and the gas stream on the other side may provide an arrangement in which carbon dioxide may be drawn into the polymer and diffuse by ion exchange into the liquid sorbent without requiring droplet formation or any other form of direct gas-liquid contact. Such an arrangement, by providing a barrier that helps to contain the liquid sorbent and by utilising a flow- through of liquid sorbent without spraying, may provide a considerable reduction in evaporation and greatly reduce the water lost from the gas contactor. According to one aspect of the present disclosure therefore there is provided an apparatus for capturing a target species, preferably carbon dioxide, from a gas comprising a gas contactor for absorbing the target species from a stream of the gas into a liquid sorbent stream in the form of one or more target anions, the liquid sorbent comprising a base as a solvent for the target anions therein; an electrochemical cell for moving the target anions or cations of the base across an ion exchange membrane, thereby to form a liquid desorbent in which the target anions have a lower solubility; a desorber for desorbing the target species from the liquid desorbent as a gas; and a heater for heating the liquid desorbent prior to desorption of the target species therefrom; wherein the gas contactor comprises a housing defining a plenum, and a plurality of spaced parallel tubes extending through the plenum; each tube having a semi-permeable wall that is formed at least partially of an anion exchange polymer; wherein in use the liquid sorbent flows through the tubes, and the gas stream flows through the plenum between the tubes. According to one aspect of the present disclosure there is provided a gas contactor for use in an apparatus for capturing a target species from a gas in the form of one or more target anions, the gas contactor comprising a housing defining a plenum and having an inlet and an outlet, a plurality of spaced parallel tubes that extend through the plenum and at least one fan for driving a gas stream through the plenum from the inlet to the outlet; each tube comprising a wall that is formed at least partially of an anion exchange polymer, and the tubes being configured and arranged to pass a flow of a liquid sorbent therethrough, such that in use the target species is absorbed through the walls of the tubes from the gas stream into the liquid sorbent as the one or more target anions. In some implementations, the gas contactor may comprise a second fan to drive the gas stream through the plenum from the inlet to the outlet. In some implementations, the gas contactor may further comprise at least one gas-refrigerant heat exchanger which is positioned within the gas stream in use; for example within the plenum or proximate the inlet or outlet of the housing, preferably proximate the outlet. The at least one gas- refrigerant heat exchanger may be configured to form part of a heat pump as disclosed herein. Suitably, the gas contactor may comprise a gas manifold arranged to direct the gas stream away from the outlet wherein the first fan and optionally the second fan are arranged with respect tothe manifold to drive the gas stream through the plenum from the inlet to the outlet and subsequentlythrough the gas manifold.As disclosed herein, the target species is preferably carbon dioxide, which may be absorbed from the gas stream in the form of one or more CO2-containing anions including carbonate, bicarbonate and carbamate. The CO2-containing anions may be transported across one or more anion exchange membranes within the electrochemical cell, or base cations may be transported across one or more cation exchange membranes to lower the pH of the sorbent through the substitution of protons formed at the anode or in one or more bipolar membranes that are interleaved with the one or more cation exchange membranes. The ion exchange polymer of the semi-permeable wall of each tube of the gas contactor may suitably comprise an anion exchange polymer. In operation, carbon dioxide may thus migrate from the gas stream to the liquid sorbent by reacting with water in the anion exchange polymer to form carbonic acid, which dissociates into bicarbonate and a proton, or by reacting directly with hydroxide ions in the anion exchange polymer to form bicarbonate, and then diffusing into the liquid sorbent. The anion exchange membrane reduces the direct liquid sorbent to air contact and thus evaporation of sorbent.as compared with previously known gas contactor designs. The gas stream may flow through the gas contactor in a direction counter to the direction of flow of the liquid sorbent. A counterflow may advantageously increase the driving force for absorption of carbon dioxide. Preferably, the electrochemical cell comprises an electrodialysis cell comprising a plurality of alternating sorbent and desorbent channels, which are spaced apart between electrodes of the cell; the desorbent channels being defined by the membrane assembly. The membrane assembly may comprise a first series of spaced anion exchange membranes and a second series of bipolar or cation exchange membranes which are interleaved with the anion exchange membranes. In use, the one or more CO2- containing anions may be caused or allowed to be transported across the anion exchange membranes from the sorbent stream into the desorbent stream. Alternatively, the membrane assembly may comprise a first series of spaced cation exchange membranes and a second series of bipolar membranes which are interleaved with the cation exchangemembranes. In use, the base cations may be caused or allowed to be transported across the cationexchange membranes and are replaced by protons formed at the anode or in the bipolar membranes, which serve to lower the pH of the sorbent stream, thereby forming a desorbent stream, as disclosed above. Thus, the CO2-containing anions may be transported from the sorbent stream to the desorbent stream under a potential difference across the electrodialysis cell. Protons flow in the counter direction through the cell when cation exchange membranes are used. In the case of bipolar membranes, protons may be generated in the bipolar membranes themselves. The CO2-containing anions may be driven against a concentration gradient, i.e. from relatively low carbon dioxide loading in the sorbent stream, towards relatively high carbon dioxide loading in the desorbent stream. Use of cation exchange membranes in conjunction with anion exchange membranes may provide certain advantages over use of bipolar membranes; for example they are more durable and less expensive. They tend to be thinner and therefore have a smaller Ohmic voltage drop over them, reducing the energy consumption of the electrodialysis cell. In addition, since they allow protons to travel from the sorbent to desorbent, they do not require as high a voltage as bipolar membranes, which require an overpotential to drive water dissociation. Use of bipolar membranes may provide different advantages, since positively charged ions are blocked, and migration of base from sorbent to desorbent can thus be minimised. It will be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure. For example, the method of the disclosure may incorporate any of the features described with reference to the apparatus of the disclosure and vice versa. In another aspect of the disclosure, there is provided the use of an acidification step of CO2- rich liquid sorbent containing carbon dioxide in the form of carbon dioxide-containing anion to lowerpH conditions prior to desorption of said liquid sorbent in a desorber, in the implementation of aprocess for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air. According to the present disclosure, a CO2-rich solvent is a solvent, the total CO2concentrations in the liquid of which are above the total CO2 concentration of the same liquid at thermodynamic gas-liquid equilibrium with a partial pressure of CO2 > 100ppm. According to the present disclosures, a CO2-lean solvent is a CO2-rich solvent with a total CO2 concentration in the liquid lower by at least 0.05 mol / L compared to the concentration before the acidification step. For the purposes of the present disclosure, “CO2-rich solvent” shall be taken to mean “CO2- rich liquid sorbent”, and “CO2-lean solvent” shall be taken to mean “CO2-lean liquid sorbent”. In the implementation of the process, to lower pH conditions allows to create conditions that favour the release of carbon dioxide in a gas stream. Advantageously, to lower pH conditions corresponds to obtain pH <10. Advantageously, the acidification and the desorption steps can be carried out at the same time during the process, in particular in the same reactor or vessel. As non-limiting examples of CO2-rich solvent,- Example 1: solvent can be 2M KOH. In the CO2-rich state, the solvent is in thermodynamic gas-liquid equilibrium with a partial pressure of CO2of 420ppm which would result in a total concentration of CO2in the liquid of 1.18 molCO2 / L. In the CO2-lean state, the total concentration of CO2in the liquid is at least lower than 1.13 molCO2 / L, for instance 0.8 molCO2 / L.- Example 2: solvent can be 2M K-glycine. In the CO2-rich state, the solvent is in thermodynamicgas-liquid equilibrium with a partial pressure of CO2of 420ppm which would result in a total concentration of CO2in the liquid of 0.8 molCO2 / L. In the CO2-lean state, the total concentration of CO2in the liquid is at least lower than 0.75 molCO2 / L, for instance 0.5 molCO2 / L.- Example 3: solvent can be 2.8M AMP. In the CO2-rich state, the solvent is in thermodynamicgas-liquid equilibrium with a partial pressure of CO2of 420ppm which would result in a total concentration of CO2in the liquid of 0.59 molCO2 / L. In the CO2-lean state, the total concentration of CO2in the liquid is at least lower than 0.54 molCO2 / L, for instance 0.45 molCO2 / L. The sorbent / desorbent concepts are described in previous embodiments with the possibility to eithertransfer CO2-anions from the sorbent to the desorbent or to transfer cations from the sorbent and toacidify it to become the desorbent, both of these occurring in an electrochemical cell.In the present implementation of the process having an acidification step, the solvent which is rich in CO2 (CO2-rich solvent) is regenerated by different means from an electrochemical cell and thereforethere is no need to define a desorbent stream which would be rich in CO2-anions. In that case, it ismore relevant to define a CO2-rich and a CO2-lean solvent as the regeneration of the CO2 capture capacity of the solvent is performed through the reduction of its CO2 liquid concentration due to an acidification step (CO2 release in the form of a gas). In a preferred embodiment, the use is according to the present disclosure, wherein said acidification of the liquid sorbent containing carbon dioxide in the form of carbon dioxide-containing anions is carried out by mixing an acid flow generated by an electrochemical cell. Advantageously, the CO2-lean liquid sorbent after desorption in the desorber is introduced inthe electrochemical cell to generate an acid flow and a basic flow, the basic flow being sent back as a CO2-lean liquid sorbent to absorb CO2in the contactor to produce the CO2-rich liquid sorbent containing carbon dioxide in the form of carbon dioxide- containing anions, the acid flow being sent to be mixed with said CO2-rich sorbent containing carbon dioxide in the form of carbon dioxide-containing anions from the contactor to obtain the CO2-rich sorbent containing carbon dioxide in the form of carbon dioxide-containing anions with lower pH conditions prior to desorption in a desorber and therefore create conditions that favour the release of the carbon dioxide in a gas stream. In a preferred embodiment, the CO2-rich and CO2-lean solvents contain a salt, such as potassium sulfate. The integration of a salt makes it possible to generate an acid flow and a basic flow, the basic flow favouring the absorption of CO2 in the process and the acidic flow favouring the desorption process. Advantageously, the electrochemical cell is used to split the salt and to produce a basic flow and an acid flow. In another aspect of the disclosure, there is provided the use of the combination of an electrochemical cell and of at least one heat pump, in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a CO2-rich and CO2-lean liquid sorbents, wherein the CO2-rich liquid sorbent containing carbon dioxide in the form of carbon dioxide-containing anions is mixed with the acid flow generated by the electrochemical cell to obtain the loaded CO2-rich liquidsorbent with CO2-containing anions with lower pH conditions and therefore create conditions thatfavour the release of the carbon dioxide in a gas stream, in which the heat pump is configured to deliver heat below 100 degrees Celsius and to transfer heat to said CO2-rich liquid sorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said CO2-rich liquid sorbent, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction, to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded sorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded CO2-rich sorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid sorbent, without heating said loaded liquid sorbent. The advantage of these embodiments lies in the fact of running the electrochemical cell that splits the CO2-lean solvent into an acid and a basic streams and to provide the heat by means of a heat pump to overall lower the energy consumption of the process. According to one aspect of the present disclosure therefore there is provided an apparatus forcapturing carbon dioxide from a gas comprising an electrochemical cell, wherein the membraneassembly of said electrochemical cell comprises -a first series of spaced anion exchange membranes and a second series of bipolar membranes which are interleaved with the anion exchange membranes (see Figure 8E), or- -a first series of spaced cation exchange membranes and a second series of bipolar membranes which are interleaved with the cation exchange membranes (see Figure 8F). In a preferred embodiment, the apparatus described in Figure 8E or 8F may be equipped with a heat pump to heat up a liquid stream. In preferred embodiments, the apparatus is according to the present disclosure, wherein the one or more ion exchange membranes of the electrochemical cell are monovalent selective anionexchange membrane permeable to carbon dioxide-containing anions, in particular bicarbonate ions(HCO3−). In accordance with another aspect of the present disclosure there is provided a method of capturing carbon dioxide from a gas comprising: i) mixing a CO2-rich liquid sorbent containing carbon dioxide in the form of CO2-containing anions with an acid flow generated by an electrochemical cell to obtain a loaded CO2-rich liquid sorbent loaded with CO2-containing anions with lower pH conditions and therefore create conditions that favour the release of the carbon dioxide in a gas stream ii) heating said loaded CO2-rich liquid sorbent by using at least one heat pump configured to deliver heat below 100 degrees Celsius, prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, and obtaining desorbed carbon dioxide wherein, by heating said loaded CO2-rich liquid sorbent, the equilibrium of the desorption reaction of carbon dioxide in the desorber is shifted and the rate of the desorption is increased to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded CO2-rich liquid sorbent. In another aspect of the disclosure, there is provided the use of two different liquid sorbents, namely liquid sorbent 1 and liquid sorbent 2, and a liquid desorbent in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, the liquid sorbent 1 containing carbon dioxide in the form of CO2-containing anions, and being able to transfer CO2-containing anions to the liquid sorbent 2 to load the liquid sorbent 2 with CO2- containing anions, the liquid sorbent 2 containing carbon dioxide in the form of CO2-containing anions, and being able to transfer CO2-containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, the loaded liquid desorbent containing carbon dioxide in the form of CO2-containing anions being desorbed in a desorber to release carbon dioxide. Advantageously, the use of two different liquid sorbents allows:- to carry out the absorption of CO2 with a solvent of type 1 as liquid sorbent 1 and- to transfer CO2-containing anions of the sorbent liquid in the desorbent liquid by theelectrochemical cell with a solvent of type 2 as liquid sorbent 2. Thus, this allows to adapt to the absorption of CO2in a contactor with a fast-reacting solvent to capture CO2as the liquid sorbent 1 and to reduce the specific energy consumption per mol of transferred CO2, improve the faradaic efficiency and / or conductivity in the electrochemical cell with an adapted solvent for the electrochemical cell as liquid sorbent 2. In another aspect of the disclosure, there is provided a use of the combination of an electrochemical cell and of at least one heat pump and a use of two different liquid sorbents, liquid sorbent 1 and liquid sorbent 2, and a liquid desorbent in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, the liquid sorbent 1 containing carbon dioxide in the form of CO2-containing anions, and being able to transfer CO2-containing anions to the liquid sorbent 2 to load the liquid sorbent 2 with CO2- containing anions, the liquid sorbent 2 containing carbon dioxide in the form of CO2-containing anions, and being able to transfer CO2-containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, in which the heat pump is configured to deliver heat below 100 degrees Celsius and to transfer heat to said loaded liquid desorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction, to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. According to one aspect of the present disclosure therefore there is provided an apparatus for capturing carbon dioxide from a gas comprising two different liquid sorbents, liquid sorbent 1 and liquid sorbent 2, and a liquid desorbent, wherein -the liquid sorbent 1 carries out the absorption of CO2 and is linked to a gas-liquid contactorallowing to absorb CO2 from a fluid, in particular air, to obtain the liquid sorbent 1 containing carbon dioxide in the form of CO2-containing anions, and -the liquid sorbent 1 is linked to liquid sorbent 2 by means allowing to transfer CO2-containing anions of the liquid sorbent 1 into the liquid sorbent 2 to load the liquid sorbent 2 with CO2-containing anions, -the liquid sorbent 2 enables to transfer CO2-containing anions of the sorbent liquid 2 withCO2-containing anions in the desorbent liquid by an electrochemical cell to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, -the loaded liquid desorbent containing carbon dioxide in the form of CO2-containinganions after passing through the electrochemical cell, is desorbed in a desorber to release carbon dioxide. In preferred embodiments, the apparatus is according to the present disclosure, comprises: -a liquid tank or a liquid-liquid mixer configurated to mix the liquid sorbent 1 containingCO2-containing anions and the liquid sorbent 2 and allowing the transfer of CO2- containing anions from liquid sorbent 1 to liquid sorbent 2, due to thermodynamic equilibrium -a solvent separation unit configurated to separated liquid sorbent 1 low of CO2-containinganions and liquid sorbent 2 enriched of containing CO2-containing anions, as means allowing to transfer CO2-containing anions of the liquid sorbent 1 to the liquid sorbent 2 to load the liquid sorbent 2 with CO2-containing anions. Advantageously, liquid sorbent 1 of solvent type 1 and liquid sorbent 2 of solvent type 2 are separated into a solvent separation unit as follows- if solvent type 2 captures CO2-containing anions onto solid particles, in particular withcharged polymeric particles or functionalized solid particles such as amine functionalized silica, the separation can be a membrane filtration -if solvent type 1 and 2 are bi-phasic, the separation step can be a phase separator or decanter,- if solvent type 2 forms a solid precipitate upon reacting with CO2-containing anions, theseparation can be a membrane filtration. In preferred embodiments, the liquid sorbent 1 of solvent type 1 is chosen among the solvents of the following list: natural and non-natural amino acids, such as but not limited to asparagine, threonine, glutamine, serine, glycine, aspartic acid, sarcosine, hydroxy-proline, amino-proline, hydroxy-lysine. In preferred embodiments, the liquid sorbent 2 of solvent type 2 is chosen among the solvents of the following list: alkyl amines such as but not limited to ethyl-, propyl-, butyl-amines covalently attached to the surface of solid particles including polyethylene or polypropylene imines chosen in pair to solvent type 1 such that pKa of amino group in solvent type 2 is larger (hence, the compound is more basic) than that of the amine in the solvent type 1. Advantageously the liquid sorbent 1 and the liquid sorbent 2 are selected to allow the transfer of CO2- containing anions from liquid sorbent 1 to liquid sorbent 2, due to thermodynamic equilibrium. In preferred embodiments, the apparatus is according to the present disclosure, wherein liquid sorbent 1 is in a loop in which the liquid sorbent 1 is sent back to the contactor after passing through the means allowing to transfer CO2-containing anions of the liquid sorbent 1 into the liquid sorbent 2 to load the liquid sorbent 2 with CO2-containing anions. In preferred embodiments, the apparatus is according to the present disclosure, wherein liquid sorbent 2 is in a loop in which the liquid sorbent 2 is sent back to be mixed with liquid sorbent 1 after passing through the electrochemical cell in which CO2-containing anions of liquid sorbent 2 are transferred to the desorbent liquid. A preferred embodiment is illustrated in Figure 22 A. In preferred embodiments, the apparatus is according to the present disclosure, comprising a combination of the electrochemical cell and a heat pump, wherein said heat pump is configured to deliver heat below 100 degrees Celsius and to transfer heat to said loaded liquid desorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reaction, to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent. In accordance with another aspect of the present disclosure there is provided a method of capturing carbon dioxide from a gas comprising: i) mixing a liquid sorbent 1 containing carbon dioxide in the form of CO2-containing anions, and a liquid sorbent 2, in which said liquid sorbent 1 and said liquid sorbent 2 are selected to allow the transfer CO2-containing anions from liquid sorbent 1 to liquid sorbent 2 by thermodynamic equilibrium and to obtain a mixture of the liquid sorbent 1 having low CO2-containing anions and of the liquid sorbent 2 enriched with containing CO2-containing anions, ii) separating said mixture to obtain a flow of the liquid sorbent 1 having low CO2-containing anions and a flow of the liquid sorbent 2 enriched with containing CO2-containing anions, iii) transferring CO2-containing anions from said flow of liquid sorbent 2 enriched with containing CO2-containing anions to a liquid desorbent by an electrochemical cell, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent. In preferred embodiments, the method of the disclosure further comprises: iv) heating said loaded liquid desorbent by using at least one heat pump configured to deliver heat below 100 degrees Celsius, prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, and obtaining desorbed carbon dioxide wherein, by heating said loaded desorbent liquid, the equilibrium of the desorption reaction of carbon dioxide in the desorber is shifted and the rate of the desorption is increased to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent. In another aspect of the disclosure, there is provided a use of a solid fixed bed reactor in the implementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, said solid fixed bed reactor is configured to sequentially enable: -to adsorb CO2-containing anions from a liquid sorbent containing CO2-containing anions,- to release CO2 gas from the solid fixed bed reactor containing CO2-containing anions byleaching said solid fixed bed reactor containing CO2-containing anions by an acid flow of pH<8, and -to regenerate its capture capacity of CO2-containing anions of the solid fixed reactor byleaching said solid fixed bed reactor by a basic flow of pH>9, According to one aspect of the present disclosure therefore there is provided an apparatus for capturing carbon dioxide from a gas which comprises: -an air contactor configured to absorb CO2 from the air into a liquid sorbent,- a solid fix bed reactor configurated to be able sequentially:- to absorb CO2-containing anions onto the solid fixed bed reactor by contacting theliquid sorbent containing CO2-containing anions, -to release CO2 gas from the solid fixed bed reactor containing CO2-containing anionsby leaching said solid fixed bed reactor containing CO2-containing anions by an acid flow of pH<8,- to regenerate the capture capacity of the solid fixed reactor by leaching said solidfixed bed reactor by a basic flow of pH>8, -an electrochemical cell being able to split a salt contained in a liquid flow mix circulatingfrom the fixed bed reactor (mixing the liquid streams from the CO2release step and the capture capacity regeneration steps) to the electrochemical cell into an acid flow and a basic flow. A preferred embodiment is illustrated in Figure 22 B. In accordance with another aspect of the present disclosure there is provided a method of capturing carbon dioxide from a gas, in particular air comprising the following three sequentially steps of: i) absorbing CO2-containing anions onto a solid fixed bed reactor by contacting a liquidsorbent containing CO2-containing anions to obtain the solid fixed bed reactor containing CO2-containing anions as solid sorbent bed and a liquid sorbent containing a lowerconcentration of CO2-containing anions, in particular less than 0.05 mol / L, ii) releasing CO2 gas from said solid fixed bed reactor containing CO2-containing anions byleaching said solid fixed bed reactor containing CO2-containing anions by an acid flow of pH<8, to obtain the solid fixed bed reactor free from the CO2 released in the gas form and an acid stream after having leached the solid sorbent bed, iii) regenerating the capture capacity of said solid fixed reactor obtained after step ii) byleaching said solid fixed bed reactor by a basic flow of pH>8, to obtain a basic stream having regenerated the solid sorbent bed and the fixed bed reactor regenerated and enabled to carry out another step i). In preferred embodiments of the method of the disclosure, the acid flow of step ii) and the basic flow of step iii) are provided by an electrochemical cell. This "salt" is a liquid stream resulting of the mixing of the acid stream after having leached the solid sorbent bed, and of the basic stream having regenerated the solid sorbent bed. Advantageously, said electrochemical cell is able to split a salt contained in a liquid flow circulatingfrom the fixed bed reactor to the electrochemical cell into an acid flow and a basic flow. According tothe present description, "salt" is a liquid stream resulting of the mixing of the acid stream after havingleached the solid sorbent bed, and of the basic stream having regenerated the solid sorbent bed. The"acid stream after having leached the solid sorbent bed" is produced at step ii and the "basic streamhaving regenerated the solid sorbent bed" is produced at step iii. Advantageously, said salt is a potassium sulfate (K2SO4), said acid flow provided by the electrochemical cell contains sulfuric acid (H2SO4) and said basic flow provided by the electrochemical cell contains potassium hydroxide (KOH). In preferred embodiments of the method of the disclosure, the liquid sorbent containing CO2- containing anions is obtained by contacting the liquid sorbent with air through an air contactor and reaches a total CO2concentrations in the liquid after the air contactor which is above the CO2concentration of the same liquid at thermodynamic gas-liquid equilibrium with a partial pressure of CO2> 100ppm. And wherein the liquid sorbent containing CO2-containing anions after circulating through the solid fixed bed reactor has a total CO2concentration in the liquid lower by at least 0.05 mol / L compared to the concentration before circulating through the solid fixed bed reactor. Advantageously, the liquid sorbent is a basic water solution of amino acid (AA-NH2+ OH-) which enables by entering in the contact with air, to capture CO2formed in the form of carbamate (AA-NH- COO-). Advantageously, said solid fixed bed reactor contains surface (R) functionalized by covalent bonds with amine (R-NH2). Importantly, pKa of solid-based amines is higher than that of the amino group of the amino acid. Under these conditions, CO2 in the form of carbamate can be transferred onto the amine functionalized surface. The liquid sorbent containing amino acid solution becomes CO2-lean and returns to the air contactor. Chemical reaction of liquid sorbent when capturing CO2 to form carbamate as CO2-containing anions:AA-NH2 + OH- + CO2 → AA-NH-COO- + H2OChemical reaction of liquid sorbent containing carbamate as CO2-containing anions with the solid bed reactor to obtain absorbed CO2-containing anions and the regeneration of amino acid of the liquid sorbant:AA-NH-COO- + R-NH2 → R-NH-COO- + AA-NH2 In preferred embodiments of the method of the disclosure, the acid flow in step ii) of CO2 release contains sulfuric acid. Upon contact of the solid fixed bed containing carbamate with sulfuric acid, CO2gas is released CO2.R-NH-COO- + H2SO4 → CO2 + R-NH3+ + SO4-. In preferred embodiments of the method of the disclosure, the basic flow in step iii) contains potassium hydroxide. Advantageously, KOH allows to remove sulphate salts and to regenerate the solid-based amines for the next CO2 capture and transfer cycle. 2 R-NH3+ + SO4- + 2 KOH → K2SO4+ 2 R-NH2+ 2 H2O Moreover K2SO4 salt solution is flushed into the electrochemical cell and splits the salt into H2SO4 and KOH that are then used in the steps ii) and iii) respectively. In preferred embodiments, amino acid salts such as potassium lysinate or potassium glycinate are used. They can offer low volatility, low toxicity, and fast absorption kinetics in the contactor. This process allows CO2 to be transferred from a doubly charged carbamate to a singly charged carbamate, to reduce the number of protons necessary for desorption. Description of the Drawings Following is a description by way of example only with reference to the accompanying drawings of implementations of the present disclosure. In the drawings: Figure 1 is a high level system diagram of a carbon capture apparatus according to the embodiment of the present disclosure; Figure 2 is a general arrangement of the carbon capture apparatus of Figure 1; Figures 3A-3B are schematic views of the sorbent and desorbent loops in interaction with the electrochemical cell according to the present disclosure. Figures 3C-3D are schematic representations of the electrochemical cell membranes according to the present disclosure. Figure 3E is a schematic view of the sorbent and desorbent loops in interaction with the electrochemical cell comprising monovalent selective anionic membranes. Figure 4 is a schematic side view of an air contactor which forms part of the carbon capture apparatus of Figure 1; Figure 5A is a schematic end view of the air contactor of Figure 3; Figure 5B is a schematic side view of a tube forming part of the air contactor of Figures 3and 4;Figure 6A-6B are respectively first and second parts of a process flow diagram for the carboncapture apparatus of Figure 1;Figure 7 is a flow chart illustrating a method of capturing carbon dioxide from a gas; Figures 8A-8D illustrate schematically different implementations of the carbon capture apparatus of the present disclosure, which have different respective heat pump configurations. Figures 8E-8F illustrate schematically different implementations of pre-acidification with the electrochemical cell comprising anionic or cationic membranes. Figure 9 is a chart that shows how voltage applied to an electrodialysis cell varies in use. Figure 10 is a schematic diagram of apparatus including a heater and an electrolyser, which was used to generate the graph of Figure 9. Figure 11 is a labelled photograph of actual experimental apparatus corresponding to that of Figure 9, which was used to generate the results of Figure 9. Figure 12 is a bar chart that compares energy consumption between heated and unheated experiments using the apparatus of Figure 11, where total energy consumption is calculated by translating energy consumption of the heater to that of a representative heat pump. Figure 13 is a graph which shows an increase in Faradaic efficiency of the apparatus of Figure 11 when heat is applied. Figure 14 is a graph of sorbent temperature over time for heated and unheated experiments using the apparatus of Figure 11. Figure 15 is a graph of heat input from the heater over time. Figure 16 is a graph of temperature of steel end plates of the electrolyser over time in a heated experiment. Figure 17 is a graph of average cell pair voltage vs temperature with a current densityof 600 Am-2 , 8 mm electrolyte gaps and four anion exchange membranes and three bipolar membranes. Figure 18 is a graph of cell voltage vs time data for the same experiments that make up the graph of Figure 17. Figure 19 is a graph that illustrates electrical conductivity of 2 mol L-1KHCO3 vstemperature. Figure 20 is a bar chart that illustrates a difference in average cell voltage between heated (55 °C) and unheated stacks of the same configuration as Figure 10 at two current densities. Figure 21 is a general arrangement of a different carbon capture apparatus in accordance with the present disclosure, in which a liquid sorbent passes twice through an electrochemical cell in a single circuit around the apparatus, serving alternately as sorbent and desorbent with each passage. Figures 22 A-B are schematic representations of the apparatus in accordance with the present disclosure, comprising 2 types of solvents for FIG 22A and a solid sorbent bed for FIG 22B. Detailed Description A carbon capture apparatus 100 according to an example embodiment of the presentdisclosure (Fig. 1) comprises, at a high schematic level, an air contactor 101, an electrodialysis (“ED”) cell 103, a heat pump 105, and a carbon dioxide desorber 107. In some variants of the present example embodiment, more than one heat pump may be employed as described in more detail below. An aqueous liquid sorbent is pumped from the air contactor 101, to the electrodialysis cell andback to the air contactor round a first closed loop 109. Meanwhile, an aqueous liquid desorbent ispumped from the electrodialysis cell 103 to the desorber 107 via an output heat exchanger 135 of theheat pump 105, and back to the electrodialysis cell round a second closed loop 111. An air stream 113 flowing through the air contactor contacts the aqueous liquid sorbent in the air contactor 101, and carbon dioxide in the air stream is absorbed into the sorbent solution in anionic form, e.g. as carbonate, bicarbonate and / or carbamate, as described in more detail below. The rich sorbent solution loaded with carbon dioxide flows to the electrodialysis cell 103. In the electrodialysis cell 103, anions pass from the rich sorbent solution into the desorbent solution. The CO2-depleted sorbent solution then flows back to the air contactor 101 for further loading with carbon dioxide. In this manner, the sorbent solution is continuously recycled. The carbon dioxide rich desorbent solution flows from the electrodialysis cell 103 to the output heat exchanger 135 of the heat pump 105 where it is heated. The output heat exchanger 135 is arranged intermediate the electrodialysis cell 103 and the desorber 107. The output heat exchanger 135 comprises a refrigerant-desorbent heat exchanger, such that the heat pump is thereby arranged toheat the desorbent stream prior to desorption of carbon dioxide from the desorbent stream, by thedesorber 107. In the present example embodiment, the output heat exchanger 135 is arranged proximate the desorber 107, so that it is disposed immediately upstream of the desorber 107. In this arrangement, heat loss from the desorbent stream between the heat pump and desorber prior to desorption may be minimised. The heated desorbent flows from the output heat exchanger 135 to the desorber 107, where carbon dioxide is removed from the desorbent solution. The CO2-depleted desorbent solution then flows back to the electrodialysis cell 103 for further loading with carbon dioxide. In this manner, the desorbent solution is continuously recycled. In an alternative implementation, two or more heat pumps 305A, 305B may be employed, with their output heat exchangers 335A, 335B arranged in series to heat the desorbent solution prior to the desorber 107, as shown in Figure 8A, in which parts that are common to the arrangement shown in Figure 2 have the same reference numerals as in that figure. Such a configuration may be used if asingle heat pump could not transfer sufficient heat to the desorbent.In another alternative implementation, as shown in Figure 8B, an air source heat pump 405 may be configured to transfer heat from the air to the desorbent immediately upstream of the desorber 107 via an intermediate water-refrigerant heat exchanger 420. Heat is first transferred to water as an intermediate medium and then the water heats the desorbent via a water-desorbent heat exchanger 435. This configuration may be used if the heat pump 405 cannot efficiently increase the temperature of the water directly by the temperature difference required. In this case the heat pump 405 first heats water by a smaller temperature difference and then the water-desorbent heat exchanger 435 between the water and the desorbent increases the temperature of the desorbent by the required amount. For example, the heat pump 405 may increase the water temperature between 70 and 75 °C, and the water may heat the desorbent between 45 and 65 °C. Such a heat transfer is possible by carefully selecting the relative flow rates of the water and the desorbent. In use, a method 200 of capturing carbon dioxide from a gas according to the example embodiment comprises a series of steps (Fig. 7). In a first step 201, carbon dioxide is absorbed inanionic form as disclosed herein, from the air stream into the sorbent stream in the first closed loop 109to provide a carbon dioxide-rich sorbent stream and a sweetened air stream. In a second step 203, the rich sorbent stream is received in the electrodialysis cell 103. In a third step 205, CO2-containing anions are transported in the electrodialysis cell from the loaded sorbent stream across an anion exchange membrane into the desorbent stream to provide a loaded desorbent stream. Meanwhile, protons are transported into the desorbent stream, thereby acidifying the desorbent stream. In a fourth step 207, the rich desorbent stream is received at the output heat exchanger 135 of the heat pump 105. In a fifth step 209, the rich desorbent stream is heated using the heat pump 105 to provide a heated rich desorbent stream. In a sixth step 211, the heated rich desorbent stream is received in the desorber. In a seventh step 213, carbon dioxide is desorbed from the heated rich desorbent stream to provide a heated lean desorbent stream. In an eighth step 215, the heated lean desorbent stream is returned in the electrodialysis cell to provide the aqueous liquid desorbent stream. The sorbent and desorbent streams flow through pipes disposed between the main components of the apparatus. The pipes connect the components of the apparatus, for example connecting the electrodialysis cell 103 with the air contactor 101, and connecting the heat pump 105 with the desorber 107 to provide the first and second closed loops. Suitable pipes will be well known to those skilled in the art and widely available. A plurality of pumps situated in the first and second closed loops 109, 111 cause the flow of the sorbent and desorbent streams though the connecting pipes, as best shown in Figs.6A-6B. In the example embodiment, first and second sorbent fluid pumps 104a, 104b are arranged to direct the sorbent stream around the first closed loop 109, the pumps 104a, 104b being situated at an inlet side and outlet side of the electrodialysis cell 103 respectively. First and second desorbent fluid pumps 106a, 106b are arranged to direct the desorbent stream around the second closed loop 111, thepumps 106a, 106b being situated at the inlet side and outlet side of the electrodialysis cell 103respectively. As with the pipework, suitable pumps are widely available and well known to those skilled in the art and in practice more or fewer pumps may be used as required. Advantageously, the number of heat pump can be adapted by those skilled in the art when it comes to building the plant to fulfil the feature of the use or the apparatus according to present description. In the present example embodiment of the disclosure, the sorbent solution comprises at least one alkali metal, amine or amino acid salt solvent for increasing the solubility in the solution of carbon dioxide in the form of CO2-containing anions and the rate of the sorption and desorption reactions. The desorbent solution suitably comprises the same at least one solvent, although in some implementations different solvents may be used in the sorbent and desorbent solutions. In preferred embodiments the sorbent solution consists of an amino acid salt such as potassium or sodium glycinate or lysinate, alternatively potassium or sodium hydroxide, or an alkanolamine such as ethanolamine. The concentration should be at least 1 mol / L, preferably at least 2 mol / L and less than 5 mol / L. Suitably, the amine solvent is an alkanolamine, especially a primary, secondary or tertiary alkanolamine. More particularly, in the present example embodiment, the amine solvent comprises water and monoethanolamine (MEA), but other suitable alkanolamine solvents may be used such, for example, as diethalolamine (DEA), triethanol amine (TEA), methyldiethanolamine (MDEA), aminomethylpropanol (AMP), diglycolamine (DGA) and diisopropanolamine (DIPA). Suitably, the amine solvent may comprise about 20-35 %wt. MEA. Where a different amineor amines are used, the relative amount of amine may be suitably adjusted. Thus, for example, the amine solvent may contain about 20-25 %wt. DEA, about 30-55 %wt. MDEA, or about 50 %wt. DGA. Carbon dioxide absorption by an amine solvent such for example as MEA may comprise formation of a carbamate zwitterion, which is neutralised by the amine solvent to form carbamate, CO2 + R1NH2 ⇌ R1NH2+COO- R1NH2+COO- + R1NH2 ⇌ R1NHCOO- + R1NH3+ , and hydration of carbon dioxide to form carbonate and bicarbonate ions accompanied by hydrolysis of the carbamate, CO2 + OH-⇌ HCO3- , . The amine solvent may enable protonation of the amine electron pair to form a positively charged ammonium group (R1NH+3): HC1 + − 2O3 ⇌ RNH3+ HCO3, where R1 is the residue of the amine. The resulting dissociated and ionised CO2-containing anions are more soluble in solution and are thus trapped, or “scrubbed”, by the amine solvent and can be removed from the gas phase. At the outlet of the air contactor 101, the sweetened gas is thus depleted in carbon dioxide. In the present example embodiment of the disclosure, the desorbent solution comprises at least one amine solvent. Advantageously, in the present example embodiment, the desorbent solution comprises the same amine solvent as the sorbent solution, e.g. monoethanolamine (MEA). In the present example embodiment, there is no direct contact between the sorbent and desorbent solutions, meaning that the streams can be maintained at different average temperatures. In other words, the first loop 109 is distinct from the second loop 111. Whilst there is no direct contact between the sorbent and desorbent streams, there may be some transfer of the amine solvent (i.e. the capture agent) from the sorbent stream to the desorbent stream or vice versa, in the electrodialysis cell 103 which does not hinder desorption. As an alternative to an amine solvent, the sorbent and desorbent solution may comprise an amino acid salt solvent. A range of suitable amino acid salt solvents are known to those skilled in the art. In principle, any amino acid salt may be used. Particularly preferred amine acid salt solvents include salts of glycine, threonine, histidine, aspargine, glutamine, proline, lysine, phenylalanine,methionine, alanine, taurine, amino-butyrate, serine and sarcosine. The potassium salts areparticularly preferred. As an alternative to an amine or amino acid solvent, the sorbent and / or desorbent solution may comprise an alkali metal cation-based solvent in which an alkali metal cation primarily balances the charge of hydroxide, bicarbonate and / or carbonate ions in solution and a minor amount of an amine or amino acid salt serves as a sorption or desorption catalyst. A range of suitable alkali metal cation- based solvents are known to those skilled in the art. Potassium based solvents are particularly preferred. In the electrodialysis cell 103 (Fig. 2), the sorbent solution and desorbent solution are separated by a membrane assembly 108. The membrane assembly 108 comprises a plurality of membranes arranged between opposing cell electrodes 102a, 102b. In the simplest configurations of the electrodialysis cell, one anionic exchange membrane is between two bipolar membrane (Fig.3B) or one bipolar membrane is between two anionic exchange membranes (Fig.3A). In the example embodiment, the plurality of membranes comprises three (Fig. 10, 3A and 3B) or five membranes (Fig.2) for ease of illustration, but in practice, the plurality of membranes may comprise 10 or more, for example 20, 50, 100 or more membranes (Fig. 3C and 3D). In some implementations, the membrane assembly may comprise up to 200 or even 400 membranes. The membranes 110a, 110b are arranged between and define the parallel channels 112 to separate the sorbent and desorbent solutions. The sorbent stream flows in sorbent channels 112a. The desorbent stream flows in desorbent channels 112b. The sorbent and desorbent channels alternate across the assembly 108 between the electrodes 102a, 102b. The membrane assembly 108 comprises alternating bipolar membranes 110a and anion exchange membranes 110b such that each sorbent channel 112a is separated from an adjacent desorbent channel 112b by a bipolar membrane 110a intermediate the cathode and an anion exchange membrane 110b intermediate the anode. Suitable anion exchange membranes may comprise Fumasep FAB-PK-130 or NEOSEPTA AID membranes. Suitable bipolar membranes may comprise Fumasep FBM and NEOSEPTA bipolar membranes. The bipolar membranes generate hydroxide ions (OH-) and protons (H+) by dissociating water. The membrane assembly in Figure 3E comprises monovalent selective anionic membrane 110c. Meanwhile, the anion exchange membranes permit only the passage of small anions. Thus, in operation, carbon in the form of carbonate (CO32-), bicarbonate anions (HCO3-) and / or carbamate are allowed to pass from the sorbent channels 112a into the desorbent channels towards the anode, through the interposed anion exchange membranes to form a desorbent stream of increased carbon loading. Meanwhile, protons produced in the bipolar membrane pass into the desorbent channels towards the cathode, thereby acidifying the latter. In operation, the sorbent and desorbent solutions flow in the sorbent and desorbent channels 112a, 112b in the same direction through the electrodialysis cell i.e. from an inlet side 129a to an outlet side 129b of the electrodialysis cell. Carbonate, bicarbonate and / or carbamate anions pass from the rich sorbent solution to the lean desorbent solution under the electric potential of the cell. The cell thus does work to drive the carbon from the sorbent solution into the desorbent solution. After transfer of carbonate, bicarbonate and / or carbamate ions from the sorbent solution to the desorbent solution, lean sorbent solution in the sorbent channels 112a exits the electrodialysis cell 103 at the outlet side 129a is recycled back to the air contactor 101 for further loading with carbon dioxide. In the sorbent stream, as described above, the captured carbon dioxide reacts with the amine solvent to form a carbamate salt, as described above, which transforms into a bicarbonate salt. Secondary and tertiary amines may immediately form bicarbonate salts. The chemical equilibrium in the sorbent channels 112a may be represented as follows: R1NH3+ + OH-⇌ R1NH2(aq) + H2O It will be understood therefore that reducing the acidity of the sorbent stream in the electrodialysis cell 103 serves to increase the solubility of carbon dioxide by increasing the availability of the amine solvent. It should be noted that some carbamate anions may be transferred directly from the sorbent to the desorbent, which may lead to a progressive increase in the solvent concentration in the desorbent relative to the solvent concentration in the sorbent until the rate of back-diffusion of charged and neutral solvent species from desorbent to sorbent is equal to the rate of current driven forwards transport from sorbent to desorbent. In the desorbent channels 112b, once carbon has been transferred from the sorbent stream tothe desorbent stream, the rich desorbent solution flows onwards towards the output heat exchanger 135of the heat pump 105 and desorber 107, where carbon dioxide is extracted in gaseous form, asdescribed above. Lean aqueous liquid desorbent then flows back to the electrodialysis cell 103 forfurther loading with carbon dioxide. The chemical equilibria in the desorbent channels 112b may be represented as follows: HCO3- + H+⇌ H2CO3 ⇌ CO2(aq) + H2OHCO3-⇌ CO2 + OH- RNHCOO- + H+⇌ RNH2 + CO2(g)Considering the first closed loop 109, in the example embodiment, an optional solar PV module 114 is positioned between the air contactor 101 and the inlet side 129a of the electrodialysiscell 103, as shown in Fig. 2. The solar PV module 114 becomes warm in use and is arranged to heatthe sorbent stream prior to entry to the electrodialysis cell 103. Heat generated by the solar PV module is thus utilised to heat the sorbent stream. The solar PV module is configured so that sorbent flows in the first loop 109 over a metal plate with a serpentine flow channel affixed to a rear surface (or backsheet) of the solar PV module. Pre-heating of the sorbent stream before it enters the electrodialysis cell 103 advantageously reduces the temperature difference between the sorbent and desorbent streams in the electrodialysis cell 103, which may improve the thermal efficiency of the apparatus overall (by reducing the quantity of heat transferred from the desorbent to the sorbent in the cell). In the example embodiment, the solar PV module 114 is additionally arranged to powerpartially the apparatus 100. In an alternative embodiment the solar PV module may be arranged topower fully the apparatus; or an alternative power source may be utilised instead of solar power.Considering the second closed loop 111, in the example embodiment, in the desorber 107, the heated desorbent flows through a packed column of the kind known and available in the art in whichthe carbon dioxide desorbs and flows out of the top of the column as the desorbent flows down intothe bottom of the column. In an alternative embodiment, the heated desorbent may flow into a continuously stirred reactor vessel and bubble out of it to escape through an opening in a top of the reactor vessel. In other arrangements, the desorbent may flow through the reactor vessel from one side to another rather than from top to bottom. There may be a small loss of pressure after carbon dioxide desorption in the desorber 107. The pressure may be restored as the aqueous liquid desorbent is pumped by the first desorbent fluid pump 106a in the second loop 111. The desorbent flowing in the second loop 111 is suitably pressurised to a pressure of up to about 10 atmospheres, preferably in the range about 4-8 atmospheres, which helps to prevent bubble formation in the cell and heat exchangers of the second loop. The liquid sorbent in the first loop 109 may similarly be pressurised to a pressure which is about equal to the pressure in the second loop 111. The lean desorbent stream is then returned to the electrodialysis cell 103 to be reloaded with carbon dioxide. In the present example embodiment, a compressor 115 is configured and arranged to receive carbon dioxide that is released as a gas from the aqueous desorbent stream as it is stripped by the desorber 107, as best shown in Fig. 2. The compressor 115 is configured to receive and compress a carbon dioxide stream exiting the desorber 107 and to provide a stream of pressurised carbon dioxide for bottling or otherwise transporting onwards, or directly mineralising, providing to a reaction, or storing underground. In the present example embodiment, the compressor 115 comprises four successive compressor units 117a-117d (only two units depicted in Fig.2, with all four units depictedin Fig. 6B) connected in series to provide staged compression, and four cooler units 119a-119d (onlytwo units depicted in Fig. 2, with all four units depicted in Fig. 6B), interspersed between the compressor units. After each stage of compression, the carbon dioxide stream is cooled by a respective cooler unit 119a-119d. In alternative embodiments of the disclosure, an alternative type of compressor may be used, having a different number, i.e. more or fewer, compressor units and cooler units. A first cooler unit 119a comprises a first cooler heat exchanger 132a. A second cooler unit 119b comprises a second cooler heat exchanger 132b. A third cooler unit 119c comprises a third cooler heat exchanger 132c. A fourth cooler unit 119d comprises a fourth cooler heat exchanger 132d. In the present example embodiment, the cooler units 119a -119d are suitably configured and arranged so that heat emitted from the respective cooler units during cooling of the carbon dioxide stream is used to heat the aqueous liquid desorbent as it flows from the electrodialysis cell 103 towards the output heat exchanger 105 of the heat pump and desorber 107. The desorbent and carbon dioxide stream flow counter-current to one another through the heat exchangers. Thus, the rich aqueous liquid desorbent is pre-warmed before it reaches the output heat exchanger 135 of the heat pump 105, thereby reducing the energy requirement on the heat pump for heating the desorbent stream for carbon dioxide desorption. Considering the second closed loop 111, after the desorbent stream absorbs heat from thecooler units 119a – 119d, the rich aqueous liquid desorbent flows to the output heat exchanger 105.The heat pump 105 in the present example embodiment is advantageously an air source heat pump, which is configured to heat the rich aqueous liquid desorbent prior to it reaching thedesorber 107 to promote desorption of carbon dioxide as gas in the desorber 107. In an alternativeembodiment the heat pump may be a ground source heat pump or another type of heat pump. The heat pump is configured to pre-heat the aqueous liquid desorbent before it reaches the desorber 107, thus reducing the energy requirements on the electrodialysis cell 103. In the example embodiment, several components of the heat pump 105 are co-located with the air contactor 101 and the first and second closed loops 109, 111 so as to provide certain additional advantages as disclosed herein. The heat pump 105 thus comprises a heat pump fan 118, as shown in Fig.6A. The heat pump 105 is advantageously configured and arranged so that the heat pump fan 118 directs (or helps todirect) air through the air contactor 101 for carbon dioxide scrubbing. Thus, the heat pump fan 118and the air contactor 101 may be mutually arranged such that the heat pump fan 118 lies in the path of the air stream flowing through the air contactor 101, thereby to aid flow of air through the air contactor. In the present example embodiment, the heat pump fan 118 is positioned to the rear of the air contactor 101 relative to the direction of the airflow through the air contactor in operation, as bestshown in Fig. 6A. Advantageously, such an arrangement allows moisture from evaporation in the aircontactor to be recovered by an evaporator 130 of the heat pump, which is discussed in more detail below. In another embodiment, the heat pump fan 118 may be positioned at or towards the front of the air contactor 101 or otherwise placed substantially within the air stream 113. In some embodiments, the heat pump fan 118 and air contactor 101 may be integrated, so that the heat pump fan 118 is integral with the air contactor 101. In some implementations, the air contactor may include the heat pump fan 118 and an additional air contactor fan 148 (Fig.3), as described below. However, in some arrangements a single fan which serves as both air contactor fan and heat pump fan may suffice. The heat pump includes a refrigerant flowing in a third closed loop 122. In the example embodiment, the heat pump comprises three heat pump heat exchangers (120, 130, 135), a refrigerantfluid pump 137, a heat pump compressor 124 and a heat pump expansion valve 128, with refrigerantflowing therebetween. A first input heat pump heat exchanger 130 of the heat pump comprising a gas-refrigerant heat exchanger is positioned within the air stream 113 of the air contactor 101 to serve as an evaporator to remove heat from the air stream 113. The evaporator 130 of the heat pump may thus be at least partly integrated with the air contactor 101. A second input heat pump heat exchanger 120 of the heat pump comprising a liquid- refrigerant heat exchanger is positioned and arranged with respect to the first loop 109 to remove heat from the sorbent stream. In some implementations of the present disclosure, the second input heat pump heat exchanger 120 may be omitted. A third output heat pump heat exchanger 135 of the heat pump, which is the above-mentioned output heat pump heat exchanger, is a refrigerant-liquid heat exchanger, positioned and arranged with respect to the second loop 111 to supply heat to the desorbent stream. In an alternative embodiment there may be no refrigerant fluid pump. A number of different heat exchanger designs will be known to those skilled in the art, but in the present implementation, the second input (refrigerant-sorbent) heat exchanger 120 and the third output (refrigerant-desorbent) heat exchanger 135 may suitably comprise plate or shell and tube heat exchangers. In use, the refrigerant is heated by the first input heat exchanger (evaporator) 130 of the heatpump 105. Heat is extracted from the surrounding air with first input heat exchanger 130 being locatedin the air stream 113 flowing through the air contactor 101 as described above. The refrigerant isheated by the first input heat exchanger 130, absorbing heat from the air stream 113. The refrigerant then flows, driven by the refrigerant fluid pump 137, to the second input heat exchanger 120 where it is heated further, absorbing heat from the aqueous liquid sorbent exiting the electrodialysis cell 103. The refrigerant then flows, to the heat pump compressor 124 where the refrigerant temperature is caused to increase considerably before flowing to the third output heat exchanger 135, where heat is transferred to the desorbent stream as a heat sink, to heat the same prior to desorption as described above. The cooled refrigerant then flows to the heat pump expansion valve 128 which causes a decrease in the pressure of the refrigerant and consequently lowers the temperature further. The cooledrefrigerant is then returned to the first heat exchanger 130 where it is heated again by absorption ofheat from the air stream 113. Water lost from the sorbent stream through evaporation in the air contactor 101 is, in the present example embodiment, at least partially recaptured by condensation on the surface(s) of the first input heat pump heat exchanger (evaporator) 130. In the present example embodiment, the air- contacting surface(s) of the first input heat pump heat exchanger 130 may be coated with heat conducting fibres such for example as metal fibres. The heat conducting fibres suitably have a high surface area to volume ratio to promote condensation. The condensed moisture is pumped via a first water pump 131a (Fig.6A) and collected in a collection vessel 134 (Fig.6B). There it is mixed with the solvent (e.g. MEA) and fed back to the sorbent solution via a second water pump 131b (Fig.6A- 6B). Advantageously the water demand on the air contactor may be thus reduced. In a further example embodiment, the solar PV module 114 (Fig. 2) may be configured to collect rainwater and to feed collected rainwater into the sorbent solution in the first loop 109. The first loop 109 (Fig.3A and 3B) comprises a sorbent collector 109a, a circuit allowing the circulation of the CO2-unloaded sorbent 109b prior to the entry in a CO2absorption unit, a circuit allowing the circulation of the CO2-loaded sorbent 109c and a sorbent distributor 109d. The second loop 111 (Fig.3A and 3B) comprises a desorbent collector 111a, a circuit allowing the circulation of the CO2-loaded desorbent 111b prior to the entry in a CO2desorption unit, a circuit allowing the circulation of the CO2-unloaded desorbent 111c and a desorbent distributor 111d. Considering the first closed loop 109, the aqueous liquid sorbent flows from the electrodialysiscell 103 through the second input heat pump heat exchanger 120 to the air contactor 101. As it passesthrough the second input heat pump heat exchanger 120, the warm, lean sorbent stream exiting theelectrodialysis cell 103 is cooled by the cool refrigerant to about ambient air temperature. An advantage of this particular configuration is that a portion of the heat extracted by the heat pump is extracted at a higher temperature than the ambient air temperature, which may increase its coefficient of performance. A further advantage is that by cooling the sorbent stream before it enters the aircontactor 101, water loss owing to evaporation can be decreased. Yet another advantage is that thereis a reduction in the standard Gibbs free energy of carbon dioxide absorption if the temperature at which the airflow contacts the sorbent stream is decreased. This means the energy input of the electrodialysis cell, which regenerates the sorbent, can be decreased. In an alternative implementation as illustrated schematically in Figure 8C, a second heat pump 505 is provided to transfer heat from the sorbent leaving the electrodialysis cell 103, via an input heat exchanger 520 in the first loop 109, to the desorbent entering the desorber 107, downstream of the output heat pump heat exchanger 135 of the heat pump 105, via an output heat exchanger 535. The use of such a separate second heat pump 505 may be used instead of the above-mentioned additional input heat exchanger 120 in the first mentioned heat pump 105 and may serve to cool the sorbentbefore it enters the air contactor 101. This may be beneficial where the sorbent would otherwise enterthe gas contactor 101 too warm and should be cooled to avoid excessive water or sorbent evaporation. In the present example embodiment, the air contactor 101 (Fig. 4) comprises a housing 140 defining an interior recess 125. The housing 140 has an air inlet near its base 144, and an air outlet near its top 145 when positioned ready for use. The incoming air flows upwards through the interior recess 125 from the air inlet to the air outlet. The air stream exiting the air contactor through the air outlet flows into a manifold 150, through which it passes before exiting the manifold as an outgoing air stream. In some implementations, the interior recess 125 may contain structured or random packing. In the present example embodiment, the interior recess 125 contains a plurality of hollow tubes 116 (Fig.5A and 5B), as described in more detail below. In the present example embodiment, the air contactor 101 comprises an air contactor fan 148 (Fig. 4) which is situated directly above the housing 140 at the air outlet (i.e. at the entrance to themanifold 150). The incoming air stream is pulled through the air contactor by the contactor fan 148.In the present implementation, the contactor fan is aided by the heat pump fan 118, situated at the exit of the manifold 150, but in some implementations the air contactor fan 148 may be arranged also toserve as the heat pump fan, as described above. In the present implementation, the heat pump fan 118and air contactor fan 148 thus operate together to direct air through the air contactor 101, thereby reducing the energy consumption of the contactor fan for moving a given volume of air per minute. In an alternative embodiment, one or more fans may be located at the air inlet of the air contactor. In an alternative embodiment there may be no manifold. Positioned on the outer side of the heat pump fan 118 with respect to the manifold 150 is the first input heat pump heat exchanger (evaporator) 130 of the heat pump 105. Beneath the first input heat pump heat exchanger 130 is a receptacle 142 which is arranged to collect water drips from moisture condensed on the evaporator130. The air contactor 101 of the present example embodiment of the present disclosure advantageously uses an anion exchange polymer across which carbon dioxide is transferred from airinto the liquid sorbent stream. The air contactor 101 comprises a plurality of spaced hollow tubes 116which are arranged in parallel within interior recess 125 of the housing 140, as illustrated schematically in Figs.4 and 5. For purposes of illustration, the air contactor 101 is shown to comprise nine tubes, eight of which are positioned circumferentially around a centrally positioned tube. In an alternative embodiment, there may be a different number of tubes. Each tube comprises a cylindrical outer wall 121 which is formed at least in part of an anion exchange membrane which defines an inner space 123 through which the liquid sorbent flows. Intermediate the tubes 116 within the housing 140 the interior recess125 serves as a plenum through which air is directed to flow through the air contactor 101. In the present example embodiment the anion exchange membrane is suitably a polymer membrane such for example as a quaternary ammonium functionalised hydrocarbon membrane. Those skilled in the art will appreciate that alternative anion exchange membranes may be used as desired. In the present example embodiment, each cylindrical outer wall 121 comprises a single material, i.e. of an anion exchange polymer. In an alternative embodiment, the outer wall may comprise an anion exchange polymer and one or more other structural or functional materials. For example, each outer wall 121 may comprise at least one additional material to provide mechanical strength, e.g. PEK, PEEK and / or Kevlar. In use, the liquid sorbent flows through the tubes 116 in a counter direction to the direction of air flow through the air contactor 101. A counterflow of the sorbent stream to the air flow provides an increased driving force for absorption. During carbon dioxide absorption, ion exchange occurs between the air and the aqueous liquid sorbent, through the anion exchange membrane 121. Carbon dioxide diffuses into the wet membrane and reacts with hydroxide to form (bi)carbonate ions, which pass into the sorbent by ion exchange. The (bi)carbonate anions (CO32- , HCO3-) flow in accordance with a concentration gradient from the membrane into the aqueous liquid sorbent (i.e. transporting carbon dioxide captured from the air into the sorbent solution) making the sorbent solution slightly more acidic. At the same time, hydroxide (OH-) anions flow in the opposite direction from the aqueous liquid sorbent into the anion exchange membrane 121. The chemical equilibrium in the anion exchange membrane 121 may be represented as follows: R2 4N+ (aq) + OH- (aq) + CO2(g) ⇌ R2 4N+ (aq)+ HCO3- (aq) where R2 are the residues of the quaternary ammonium ion, which may be the same or different from one another. Typically, in a temperate climate, the aqueous liquid sorbent passing through the air contactor 101 has a temperature of approximately 15-25 degrees Celsius (Figs.6A and 6B), i.e. at approximately ambient air temperature. As the aqueous liquid sorbent passes across the solar module 114, it is typically heated by approximately 3-10 degrees Celsius, although depending on the intensity of the sun, it may be heated by up to 30 degrees Celsius. The aqueous liquid sorbent thus enters the electrodialysis cell 103 at a temperature warmer than the ambient air temperature. In the electrodialysis cell 103, the sorbent solution absorbs heat from the desorbent solution (since the desorbent solution has a higher temperature than the sorbent solution), and is heated by approximately 10-25 degrees Celsius before exiting the electrodialysis cell 103. The sorbent solution then cools toapproximately ambient temperature as it flows back to the air contactor 101.The carbon dioxide rich aqueous liquid desorbent exiting the electrodialysis cell 103 has a temperature of about 45-55 degrees Celsius (Figs.6A and 6B). The aqueous liquid desorbent is heated by approximately 1-5 degrees Celsius by the first cooler heat exchanger 132a of the first cooler unit 119a adjacent the first compressor unit 117a. The aqueous liquid desorbent is then heated by approximately 1-5 degrees Celsius by the second cooler heat exchanger 132b of the second cooler unit 119b adjacent the second compressor unit 117b. The aqueous liquid desorbent is then heated by approximately 1-5 degrees Celsius by a third cooler heat exchanger 132c of the third cooler unit 119c adjacent the third compressor unit 117c. The aqueous liquid desorbent is then heated by approximately 1-5 degrees Celsius by a fourth cooler heat exchanger 132d of the fourth cooler unit 119d adjacent the fourth compressor unit 117d. The aqueous liquid desorbent thus flows to the third output heat exchanger 135 of the heat pump 105 (i.e. the heat exchanger in the heat pump 105 which provides heat to the desorbent stream which constitutes a heat sink) having been pre-heated. The aqueous liquid desorbent is heated to a maximum temperature in the range of about 40- 90, preferably about 45-80 degrees Celsius wherein carbon dioxide is expelled from the desorbentstream. By virtue of the electrodialysis cell 103, the carbon-loading of the desorbent solution issufficiently high to allow this to occur below 100 degrees Celsius. A temperature in the range of about 65-80 degrees Celsius is within the normal capability of an air source heat pump, whilst being below the boiling point of water (thereby avoiding heat loss through boiling) yet is cold enough that thermal degradation of the amine or amino acid solvent, as a sorbent or as a catalyst should be significantly slower compared to standalone thermal desorption at in excess of 100 degrees Celsius. The carbon dioxide stream exits the desorber 107 and is stepped through the above-described series of compressor units and cooler units (117a-d; 119a-d) to provide a compressed carbon dioxide stream 152. The compressed carbon dioxide may be stored in a suitable storage tank 160 before being permanently sequestered via mineralisation or underground injection, for example. Alternatively, the desorbed carbon dioxide may be bottled, e.g. for transport or storage. Water may be recovered fromthe water-carbon dioxide mixture and pumped to the collection vessel 134 using a suitable pump 131c,as shown in Figure 6B. In the present example embodiment, the aqueous liquid desorbent flowing in the second loop 111 has a minimum temperature that is higher than the maximum temperature of the aqueous liquid sorbent flowing in the first loop 109: the desorbent stream has a minimum temperature in the range of about 45-55 degrees Celsius (when exiting the electrodialysis cell 103); the sorbent stream has a maximum temperature in the range of about 30-40 degrees Celsius (when exiting the electrodialysis cell 103). The first and second closed loops 109, 111 may be maintained at substantially different temperatures, since there is no direct contact between the sorbent and desorbent streams. The sorbent stream may therefore be kept relatively cool, aiding efficient capture of carbon dioxide from the ambient air, while the desorbent stream may be kept relatively warm, aiding efficient expulsion ofcarbon dioxide in the desorber 107. There is a significant advantage in the reduction in required heatinput. The temperature difference between the aqueous liquid sorbent and the aqueous liquid desorbent is at a minimum when the two streams flow through the electrodialysis cell 103. Heat is lost from the desorbent stream to the sorbent stream in the electrodialysis cell 103 because the two streams are separated only by membranes, which are generally poor thermal insulators. The apparatus of the present disclosure is thus optimised in order to reduce the heat loss. For example, the sorbent stream is pre-heated prior to entry to the electrodialysis cell 103, helping to minimise the temperature difference between the streams. The electrodialysis cell 103 may be thermally insulated (not shown) to reduce further heat loss from the apparatus. Likewise, the pipes used to convey the liquid sorbent and liquid desorbent roundthe first and second closed loops 109, 111 respectively may also be thermally insulated (not shown).Despite the loss of heat from the desorbent stream to the sorbent stream across the membranes in the electrodialysis cell 103, there is still an advantage in providing a warmer desorbentstream than sorbent stream in the electrodialysis cell 103. The average temperature within theelectrodialysis cell 103 should advantageously be high enough to provide good electrolytic conductivity to facilitate the ion exchange process and to keep the cell voltage as low as possible while still achieving the desired carbon loading in the desorbent stream. Furthermore, the voltage required for water dissociation in the bipolar membranes will be lower at higher temperatures. That said, in some implementations, it may be desirable to cool the desorbent stream somewhat after it leaves the desorber 107, prior to entry into the electrodialysis cell 103. Thus, as shown in Figure 8D of the drawings, a second heat exchanger 605 may be provided to transfer heat from the desorbent stream downstream of the desorber 107 prior to the electrodialysis cell 103, via an input heat exchanger 620, to the desorbent stream upstream of the desorber 107 downstream of theoutput heat exchanger 135 of the first mentioned heat pump 105, via an output heat exchanger 635.Such an arrangement may be especially advantageous where the desorbent would otherwise enter the electrodialysis cell 103 too warm and should be cooled to avoid damaging components of the electrodialysis cell 103. The method and apparatus according to the present example embodiment seek to provide an optimal solution given the constraints of a warm desorbent temperature required for efficient carbon dioxide expulsion and a cool sorbent temperature required for carbon dioxide capture, while balancing the voltage of the cell 103 to attain the required carbon loading for desorption at temperatures beneath 100 degrees Celsius. In an advantage over methods and apparatus of the prior art, use of thermal desorption in the desorber 107 means that the same carbon dioxide transfer rate (and current) can be achieved, but since the pH gradient is smaller (owing to the increased desorption temperature) the required voltage is smaller. Experiments Figure 9 is a graph of cell voltage vs time comparing a heated (line 301) vs unheated (line 303)carbon dioxide desorption apparatus, which shows a significant drop in cell voltage is achieved byheating the desorbent, e.g. to 55 °C.The graph in Figure 9 was generated via the following procedure: 500 mL of starting solution simulating loaded sorbent: 2 mol L-1 KHCO3, and 1250 mL of the same solution simulating loaded desorbent were circulated through an electrodialysis stack using a peristaltic pump while a current of4 A was applied. A schematic diagram of the apparatus used is shown in Figure 10, while a photographof the actual apparatus is shown in Figure 11. The electrodialysis stack used was the ElectroCell® Electro MP Cell which has an active electrode area of 0.01 m2 , meaning the current density was 400 A m-2. The electrolyte gap between the anode and first membrane and the cathode and last membrane was 8 mm, while the intermembrane electrolyte gaps in the main stack were 2 mm. A total of six anion exchange membranes (Fumasep FAB-PK-130) and five bipolar membranes (Fumasep FBM) were stacked in alternating order between a platinised titanium cathode and an iridium oxide coated titanium anode. Sorbent and desorbent were pumped through alternating gaps between pairs of anion exchange and bipolar membranes. Over time, the applied current causes the transfer of carbon dioxide in the form of (bi)carbonate ions from the sorbent to desorbent, from which it then evolves as gas and escapes to the air in the lab from the desorbent tank. The temperature of the sorbent and desorbent were measured using thermocouples and the pH of aliquots of each solution was measured at the beginning and end of the 1-hour experiment. By recording the initial and final pH of the sorbent it was possible to calculate the change in carbon dioxide loading and thereby the number of moles of carbon dioxide which were desorbed in each experiment. In heated experiments a Julabo® circulating immersion heater was used to stir and heat the desorbent, and in unheated experiments it was used only for stirring. Its energy consumption was measured using a power meter. The purpose of the experiments was to compare the energy consumption of a standalone electrochemical carbon dioxide desorption system, to a system of the kind disclosed herein, in which a heat pump such for example as an air source heat pump is used to heat the desorbent. The energy consumption of a representative heat pump was calculated by first subtracting the energy consumption of the immersion heater when only stirring from its consumption when heating and then dividing this number by the coefficient of performance of a representative heat pump. The coefficient of performance was calculated by applying an efficiency of 60 % to the Carnot coefficient of performance of the heat pump, assuming an air temperature of 15 °C. The energy consumption for the unheated system was calculated by integrating under the graph of cell power vs time and the energy consumption for the heated system was calculated by adding the calculated energy consumption of a representative heat pump to the integral. The difference in voltage between the heated and unheated experiments can be explained by several factors. The simplest is that higher temperatures increase the electrical conductivity of thesorbent and desorbent, as is shown in Figure 19. Likewise, the conductivity of the anion exchangemembranes and bipolar membranes increase with temperature. Furthermore, the overpotential required to drive water dissociation to hydroxide and hydronium in bipolar membranes decreases with temperature. Finally, the higher temperature of the desorbent pushes its equilibrium towards desorption of carbon dioxide, which decreases its carbon loading and thereby increases its pH. Furthermore, the rate of desorption in the desorbent tank is increased by the higher temperature of the desorbent which means it returns to the cell with a lower carbon dioxide loading and higher pH. In other words, the higher temperature shifts the desorbent equilibrium further towards desorption and increases the desorption kinetics such that the desorbent circulates at a concentration closer to equilibrium. The result is a smaller difference in pH and carbon dioxide loading across the membranes which reduces their thermodynamic membrane potentials. Figure 12 shows a comparison of energy consumption between two repeats of heated and unheated experiments under the same conditions as described above, where the total energy consumption is calculated by translating the energy consumption of the heater to that of a representative heat pump. An average decrease in total energy consumption of 8 % was achieved by heating the desorbent, which is due to a combination of two factors. The first is the decrease in cell voltage shown in Figure 9 and the second is an increase in Faradaic efficiency, which is shown in Figure 13. The increase in Faradaic efficiency can be explained by the reduced carbon dioxide concentration gradient across the anion exchange membrane, which results in a lower rate of back diffusion of CO2-containing anions between desorbent and sorbent. Without wishing to be bound by theory, another likely contributing factor is an increase in water dissociation efficiency in the bipolar membranes. The energy overall energy consumption for using the immersion heater with electrodialysis is higher than for electrodialysis alone. Only once the heat input is divided by the coefficient of performance of a representative heat pump in accordance with the present disclosure is there an energy advantage. This illustrates that other forms of heating in which energy is must be input to generate heat, such as resistive or photothermal heating which have coefficients of performance less than unity, will not give an overall energy benefit, whereas heat pumps do. Figure 14 shows the change in sorbent temperature over time for a heated and unheated experiment. Since the same insulation is used in both experiments, the resistive heating of the unheated cell causes the temperature of the sorbent and desorbent to increase over time. This explainsthe gradual decrease in cell voltage 303 over time for the unheated system shown in Figure 9. It isnotable in Figure 14 that the sorbent temperature does not reach a steady level until approximately ten minutes into the experiment, but that the cell voltage is nonetheless almost constant over this period. Figure 15 shows the heat input from the immersion heater over time. It can be seen that a large input of heat is initially required to bring the system to a steady temperature, after which it significantly decreases. This highlights a difference between these experiments which are carried out in batch mode so that the carbon dioxide desorption rate can be easily calculated from changes in solution pH compared to a real-world continuous system in which the sensible heat required to heat the sorbent and desorbent would be constant. Figure 16 shows the change in the temperature of steel end plates of the electrolyser over time in a heated experiment. In a real-world system the sorbent and desorbent would reach a thermal steady state with the materials of the electrolyser. However, in the laboratory experiments the cell increases in temperature over the course of the experiment. This results in the experiments overestimating the required heat input for the reaction compared to a real-world system. Figure 17 shows the average cell pair voltage vs temperature for one-hour experiments conducted via the same experimental protocol as listed above, but with a current densityof 600 A m-2 , 8 mm electrolyte gaps throughout the cell, and only four anion exchange membranes and three bipolar membranes. Between 35 and 75 °C desorbent temperature, the cell voltage decreases linearly. Figure 18 shows the cell voltage vs time data for the same experiments which make up the graph in Figure 17. Two unheated experiments were run: the first before the heated runs and the second after them. The voltage vs time graphs of the first and second unheated experiments overlap, showing that running with the desorbent as hot as 75 °C for at an hour does not cause any measurable change in membrane performance. Figure 19 shows the electrical conductivity of 2 mol L-1KHCO3 vs temperature.Figure 20 shows the difference in average cell voltage between heated (55 °C) and unheated stacks of the same configuration as for Figure 9 at two current densities. At the higher and more industrially relevant current density, the drop in cell voltage achieved by heating is greater. In accordance with the present disclosure, use of a solvent such for example as an amine or amino acid salt, alone or in combination with an alkali metal cation, advantageously provides greater carbon solubility and faster reaction kinetics for desorption, making it possible to achieve the same rate of desorption with a lower carbon loading (relative to equilibrium) in the desorbent. An amine or amino acid salt base improves the kinetics of absorption and desorption as compared to an alkali metal cation base alone. The acidic pH in the desorbent stream favours desorption of carbon dioxide. Acidification of the desorbent stream favours association to form carbonic acid and then decomposition to carbon dioxide and water: H+ (aq)+ HCO3- (aq) <---> CO2 + H2OIon exchange in the electrochemical cell is driven by the potential difference across the electrodes of the cell. No polymeric catalyst is needed for the desorption reaction because the high desorption temperature leads to a sufficiently fast desorption rate without requiring a catalyst. While energy is expended in the electrodialysis cell to achieve satisfactory loading of the desorbent stream, the use of a heat pump as well as other high performance efficiency or waste energy sources allows the desorbent stream to be heated at low cost to a temperature sufficient to achieve desorption. The above-described example embodiment makes preferred use of an electrodialysis cell 103 for transporting carbon dioxide in the form of (bi)carbonate or carbamate anions from a sorbent stream to a desorbent stream across an anion exchange membrane. However, it will be appreciated that in other implementations, an alternative form of electrochemical cell such for example as an electrolysis cell (which includes at least one anion exchange membrane but no cation exchange membrane or bipolar membrane) may be substituted for the electrodialysis cell 103. An arrangement of this kind is not shown schematically in the drawings. For example, in some implementations, instead of transporting the CO2-containing anions across an anion exchange membrane, an electrochemical cell may be configured to transport base cations across a cation exchange membrane, thereby reducing the solubility of the CO2-containing anions in the sorbent as the base cations are replaced by protons produced at the anode or in a bipolar membrane. An arrangement of this kind is shown schematically in Figure 21 of the drawings, in whichparts that are the same as corresponding parts in Figure 2 have the same reference numerals.The apparatus 700, like the above-described example embodiment, comprises an air contactor 101, an electrochemical cell 703, at least one heat pump 105, a gas desorber 107, and first and second loops 709, 711 for circulating a liquid solvent from the air contactor 101, where it absorbs carbon dioxide as one or more CO2-containing anions, through the electrochemical cell, where electrochemical work is done to reduce the solubility of the CO2-containing anions in the solvent, through an output heat exchanger of the heat pump 105, where the solvent is heated to decrease further the solubility of the CO2-containing anions therein, to the desorber 107. The principal differences reside in the configuration of the electrochemical cell 703 and the connections of the first and second loops 109, 111 to the electrochemical cell.703. Thus instead of comprising a stack of alternating anion exchange membranes and cation exchange membranes or bipolar membranes, the electrochemical cell 703 comprises a stack 708 of alternating bipolar membranes 710a and cation exchange membranes 710b, which define alternating first and second channels 712a, 712b respectively through the cell 703, from an inlet side 729b to an outlet side 729a, between an cathode 102a and an anode102b. While the first and second loops 109, 111 of the above-described example embodiment form closed, separate loops, the first and second loops 709, 711 of the presently described apparatus 700 are connected serially to form a single path for the liquid solvent which passes through the electrochemical cell 703 twice, once through the first channels 712a and then through the secondchannels 712b for each complete loop through the apparatus 700. As it passes through the apparatus,the solubility of the CO2-containing anions is adjusted electrochemically such that the liquid solvent serves alternately as the sorbent and the desorbent. As described above, the solvent may preferably comprise a base, which increases the solubility of carbon dioxide therein in the form of one or more CO2-containing anions. The base may comprise an amine or amino acid salt as described herein or an alkali metal in combination with a small catalytic amount of such an amine or amino acid salt. In the electrochemical cell 703, the liquid solvent returned from the desorber 107 flows through the second channels 712b, with bipolar membranes 710a intermediate the cathode 102a and cation exchange membranes 710b intermediate the anode 102b. Base cations are driven towards the cathode 102a through the cation exchange membranes 710b into the liquid solvent in the second channels 712b as described below, and hydroxide anions formed in the bipolar membranes 710a also migrate into the liquid solvent, thereby increasing its solubility for CO2-containing anions forming a sorbent. The sorbent is then circulated to the air contactor 101 through the first loop 709 where it absorbs carbon dioxide from the air or other gas stream in the manner described above. The loadedsorbent is then returned to the electrochemical cell 703, where it flows this time through the firstchannels 712a, with bipolar membranes 710a intermediate the anode 102b and cation exchange membranes 710b intermediate the cathode 102a. As mentioned in the preceding paragraph, base cations are driven towards the cathode 102a through the cation exchange membranes 710b into the liquid solvent in the second channels 712b and are replaced by protons formed at the anode 102b or at the bipolar membranes 710a. The increased acidity of the liquid solvent and loss of base cations makes it less soluble for the CO2-containing anions forming a desorbent. The liquid solvent then flows in the second loop 711 from the electrochemical cell 703 to the desorber 107 via the output heat exchanger of the heat pump 105, which serves to increase the temperature of the desorbent as described herein, further reducing the solubility of the CO2-containing anions therein which are then desorbed as carbon dioxide in the desorber 107. The depleted liquid solvent is then returned to the electrochemical cell 703 where it enters the second channels 712b and the process is repeated. In this arrangement therefore, loaded sorbent leaving the contactor 101 is fed into the first channels 712a of the electrochemical cell 703 on an acidic side of the bipolar membranes 710a. Base cations such as RNH3+ or K+ are transferred across the cation exchange membranes 710b into the second channels 712b on a basic side of the bipolar membranes 710a, while protons generated in the bipolar membranes 710a take their place. This means that the incoming sorbent moves from being mainly composed of the base salt (i.e. KHCO3) towards being composed more of carbonic acid (H2CO3) as the base cations are replaced with protons. This drives the equilibrium of the solutiontowards desorption of carbon dioxide. The liquid solvent is then pumped to the desorber 107. Theliquid solvent, upon returning from desorption has had its carbon dioxide removed and so this time it flows through basifying channels 712b of the electrochemical cell 703 where hydroxide anions generated in the bipolar membranes 710a are balanced by the charge of the base cations leaving the incoming sorbent. A key difference between this configuration and the above-described example embodiment is that there is only one liquid stream, and the liquid solvent serves alternately as sorbent and desorbent on successive passes through the electrochemical cell. An advantage of this particular arrangement is that cation exchange membranes tend to be more conductive than anion exchange membranes, which could contribute to decreasing the cell voltage. Further advantages are that carbamate forming solvents which may have faster absorptionkinetics can be used in this configuration because there is only one liquid stream. In the originalembodiment, carbamate anions would be transferred across the anion exchange membrane, causing the amine to become diluted in the sorbent and concentrated in the desorbent over time. Furthermore electro-osmotic drag of water across the ion exchange membranes does not need to be rebalanced because there is only a single liquid stream. Implementation of monovalent selective AEM in a method of capturing carbon dioxide from a gas. Schematic diagram of the electrodialysis regeneration with monovalent selective AEMs is represented in Fig.3E. To circumvent the problems of amine carbamate crossover from sorbent to desorbent in the process embodiment using a separate sorbent and desorbent liquid flows and transferring CO2 containing anions using standard anion exchange membranes, the following configuration is described in which monovalent selective anion exchange membranes are used in place of standard anion exchangemembranes, and a capture solvent is used for which the carbamate formed has a charge of 2- or greater.For example an amino acid salt in which the amino acid has negative charge of 2 - or greater at the pHat which the sorbent stream enters the electrodialysis cell, and forms a carbamate with a negativecharge of 2 - or greater, or an amine which predominantly forms carbamates with a negative chargeof 2 - or greater at the pH at which the sorbent stream enters the electrodialysis cell. Non-limiting examples include: tetraethylenepentamine, tris(2-aminoethyl)amine, iminodiacetic acid, aspartic acid, isophoronediamine, spermine, and oligopeptides such as: H-Lys-Asp-OH, H-Lys-Glu-OH, H-Gly- Asp-OH, H-Glu-Glu-OH. As in the configuration using standard AEMs, a sorbent stream recirculates between the electrodialysis stack and the air contactor and transfers CO2containing anions across anion exchange membranes and is basified by hydroxide ions generated by bipolar membranes. However, the multiply charged carbamate species formed are electrostatically blocked from crossing the monovalent selective AEMs so that they substantially remain in the sorbent stream and do not enter the desorbent stream, which recirculates between the electrodialysis stack via first a heat pump and then a desorption reactor vessel in which CO2 desorbs from the desorbent, before it enters the electrodialysis stack once more. Advantageously, since multivalent carbamate ions and carbonate ions are unable to cross the AEMs the only species capable of crossing are monovalent ions such as bicarbonate and hydroxide, resulting in an increased Faradaic efficiency and therefore lower energy consumption per tonne of CO2 desorbed. The use of monovalent selective AEMs allows carbamate forming capture solvents to be used without them becoming diluted from the sorbent and concentrated in the desorbent over time. This is advantageous because carbamate forming capture solvents typically have faster CO2absorption kinetics than those which do not form carbamates, and furthermore, non-toxic, non-volatile, andelectrically conductive amino acid salts which meet the criteria of having anions of at least 2 - chargeand carbamates of at least 2- charge at the pH and CO2 loadings they experience in the air contactorand electrodialysis stack, can be used. The following protocol can be carried out to evaluate the electrodialysis regeneration with monovalent selective AEMs: A volume, preferably at least 500 mL of initial sorbent solution is made up. The initial sorbent is preferably an amino acid salt or amine salt in which the amino acid or amine anion has a negative charge of 2 or greater and forms a carbamate with a negative charge of 2 or greater. As non-limiting examples include: tetraethylenepentamine, tris(2-aminoethyl)amine, iminodiacetic acid, aspartic acid, isophoronediamine, spermine, and oligopeptides such as: H-Lys-Asp-OH, H-Lys-Glu-OH, H-Gly- Asp-OH, H-Glu-Glu-OH. Advantageously, the concentration is at least 1 mol / L, preferably at least 2 mol / L and less than 5 mol / L. Then, an aliquot of the initial sorbent is taken, preferably at least 5 mL. One carbonates the initial sorbent, for example by sparging compressed air through the solution or circulating the solution through an air contacting device such as an air humidifier, until the pH and or electrical conductivity approach a constant value. Then, an aliquot of carbonated sorbent is taken, preferably at least 5 mL and one measures the weight and volume of the solution to account for any losses due to evaporation. One makes up a solution of initial desorbent preferably equal to the initial volume of the sorbent, which preferably will be the same as the initial desorbent solution, but could also be another conductive or acidic solution such as potassium sulfate or sulfuric acid. One carbonates the initial desorbent by sparging pure CO2through it so it becomes saturated and the pH and or electrical conductivity approach a constant value. One takes an aliquot of at least 5 mL of the carbonated desorbent and measures the weight and volume of the solution to account for any losses due to evaporation. One measures the CO2concentration in the initial and carbonated sorbent and desorbent solutions preferably by means of total inorganic and total organic carbon content analysis, alternatively by NMR or titration. One measures the amine concentration in both solutions via total nitrogen content analysis or NMR. One assembles an electrodialysis stack with at least one repeating unit: AEM-BPM using monovalent selective AEMs, with the cationic layers of the BPMs facing the cathode. One pumps the sorbent through the flow channels contacting the anionic layers of the BPMs and the desorbent through the flow channels contacting the cationic layers of the BPMs. Both solutions should be recirculated from the electrodialysis stack into their individual containers. The container for the desorbent should be gas tight and contain an outlet for CO2 to flow through a gas flow meter to measure the CO2 flow rate. One applies a current to the electrodialysis stack so that the current density is at least 100 A / m², preferably below 1000 A / m² and measures the voltage across the stack at the current supplyingelectrodes and separately across at least one repeating unit. One continuously measures the pH andconductivity of each solution. One applies the current for a time estimated to decrease the sorbent CO2concentration by preferably at least 50 %. The time can be estimated by considering the current density, solution volume, number of repeating units and an estimate of the Faradaic efficiency (for example between 50 and 75 %). One drains the electrodialysis stack and measures the weights and volumes of each solution. One takes note of the total volume of CO2desorbed from the flow meter readout. One takes aliquots of at least 5 mL of each solution and measures the CO2and amine concentrations via the same methods as detailed above. Hence, by accounting for the mass of CO2desorbed as measured from the solution aliquots and flow meter the Faradaic efficiency of desorption can be calculated. Also considering the voltage across the stack of the electrodialysis regeneration the energy consumption to desorb a given mass of CO can be calculated. Using the initial and final volumes of each solution and the amine concentrations any unwanted crossover of amines can be quantified. Implementation of a pre-acidification in a method of capturing carbon dioxide from a gas. Schematic diagrams of the acidification of the sorbent and the basification of the sorbent by an electrochemical cell with AEM-BPM or CEM-BPM are represented in Fig.3C and 3D. Schematic diagrams of the acidification of the CO2-rich-stream are represented in Fig.8E and 8F. The CO2 loaded in the contactor is released in a pre-acidification step by mixing the CO2-rich stream with an acid stream, for example sulfuric acid. A salt in solution (ie potassium sulfate) is resulting from the pre-acidification stream. To circumvent the problems of amine carbamate crossover from sorbent to desorbent in the process embodiment using a separate sorbent and desorbent liquid flows and transferring CO2 containing anions using anion exchange membranes, and also to eliminate the requirement to operate the electrochemical stack at pressures greater than 1.5 bar to suppress the formation of CO2 bubbles within the desorbent in that configuration, the following configuration is described in which the sorbent is acidified and CO2 is desorbed prior to the liquid flows entering the electrochemical stack. Ideally, a non-volatile, non-toxic, electrically conductive, low cost, solvent with fast reaction kinetics for the absorption of CO2 such as for example potassium lysinate, is used as the sorbent. It absorbs CO2from the air in the air contactor before being mixed in a desorber reaction vessel with an acidifying solution such as sulfuric acid, which decreases the pH environment of CO2containing species such as carbamates and (bi)carbonate to promote desorption of CO2gas. The resulting neutralised solution, which is a salt of the basic capture solvent and the acid of the acidifying solution is then pumped into the electrochemical cell which is preferably a bipolar membrane electrodialysis stack comprised of repeating units of alternating cation exchange membranes and bipolar membranes. The liquid flow contacting the cation exchange layers of the BPM will be acidified by protons produced at in the BPM and will lose cations, for example K+, which cross the CEMs into the other liquid flow. The other liquid flow is the regenerated sorbent, which is basified by hydroxide ions produced in the BPMs and receives cations, such as K+, from the regenerated acidifying solution across the CEMs. It is advantageous to heat the neutralised solution using a heat pump before it enters the electrodialysis cell, to reduce its voltage and energy consumption. It is also advantageous to recover heat from the regenerated sorbent exiting the electrodialysis stack first using a heat exchanger pre-heating the neutralised solution prior to its heating with the heat pump, and then a second heat exchanger pre- heating the sorbent exiting the contactor prior to desorption. The following protocol by external acidification can be carried out to evaluate the efficiency of the electrodialysis regeneration in the CEM-BPM configuration of these embodiments: One makes up a volume of preferably at least 500 mL of initial sorbent solution. As non-limiting example, said initial sorbent solution is a solution of potassium glycinate at a concentration of 2 mol / L. One takes an aliquot of the initial sorbent, preferably at least 5 mL. One carbonate the initial sorbent, in particular by sparging compressed air through the solution, until the pH and or electrical conductivity approach a constant value as measured by a pH electrode and solution conductivity meter. One takes an aliquot of preferably at least 5 mL of the carbonated sorbent and measures the weight and volume of the solution to account for any losses due to evaporation. One measures the CO2 concentration in the initial and carbonated sorbent solutions, preferably by means of total inorganic and total organic carbon content analysis. One takes aliquots, in particular 2 mL of the 5 mL, of the initial and carbonated sorbents and dilutes them, in particular 10 times by adding for example 2 mL to a 20 mL volumetric flask and making the solution up to the mark with deionized water. One titrates them against in particular 0.1 mol / L hydrochloric acid, while monitoring the pH with a pH meter to determine the number of moles of protons required to desorb approximately 100 % of the CO2, which is be marked by an equivalence point in the titration curve and the appearance of gas bubbles. One makes up a solution of initial desorbent equal to the remaining volume of the carbonated sorbent.As non-limiting example, sulfuric acid, at a concentration such that the solution contains a number ofmoles of protons sufficient to desorb 100 % of the CO2in the carbonated desorbent. One takes an aliquot of the initial desorbent, a preferably said aliquot is of at least 5 mL of One mixes the full volumes of carbonated sorbent and initial desorbent so as to desorb CO2from the carbonated sorbent. One measures the weight and volume of the resulting neutralized solution and measures and take an aliquot of preferably at least 5 mL One measures the remaining CO2concentration by the means detailed above. One makes up preferably 500 mL of 1 mol / L KOH solution to be used as the common electrolyte rinse for the anode and cathode chambers. One assembles an electrodialysis stack. Preferably the electrodialysis stack is REDSTACK LABSTACK using 0.8 mm spacers of five repeating units: CEM-BPM, with the cationic layers of the BPMs facing the cathode. Advantageously, the overall stack configuration is: cathode, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM. In particular the CEM used should be Fumasep FKB-PK-130 and the BPM used should be Fumasep FBM. One splits the volume of the neutralized solution into two equal parts within two containers. One uses a centrifugal pump, one begins pumping the electrolyte rinse through the anode and cathode chambers at a flow rate of preferably 1.5 L / min so that the flows exiting the anode and cathode chambers return to the container from which they were pumped. One pumps one solution, named the “regenerated sorbent” at a flow rate of preferably 1.7 L / min through the flow channels contacting the anionic layers of the BPMs and the other solution can be called the “regenerated desorbent” at preferably 1.7 L / min through the flow channels contacting the cationic layers of the BPMs. Both solutions should be recirculated from the electrodialysis stack into their individual containers. One applies a current, preferably of 4 A, to the electrodialysis stack so that the current density is preferably 400 A / m², and one measures the voltage across the stack at the current supplying electrodes and separately across four repeating units, advantageously by using 0.2 mm diameter Pt wires as the electrodes. One continuously measures the pH and conductivity of the regenerated sorbent and desorbent solutions. One applies the current, preferably for at least 140 minutes. One drains said electrodialysis stack and measures the weights and volumes of each solution. One takes aliquots of preferably at least 5 mL of each solution One dilutes the regenerated sorbent aliquot, in particular 2 mL of aliquot is diluted 10 times as described above and one titrates against hydrochloric acid (preferably 0.1 mol / L) to measure itsalkalinity. One dilutes the regenerated desorbent, preferably 2 mL by 10 times as described above andone titrates the regenerated desorbent aliquot against NaOH (preferably 0.1 mol / L) to measure its acidity. Advantageously using these measurements and the final masses and volumes, the molar quantity of K+ transferred across the CEM can be calculated and the Faradaic efficiency of the electrodialysis regeneration can therefore be calculated. One re-carbonates the regenerated sorbent using one of the same methods as above and complete the same CO2measurements on its aliquots. Once again, one mixes the carbonated sorbent, this time with the regenerated sorbent, and completes the same measurements as above. From these measurements, the total CO2absorbed and desorbed in a single cycle can be calculated. One repeats the electrodialysis regeneration once again under the same conditions, until the pH and conductivity of the regenerated sorbent and desorbent reach the same values as at the end of the previous experiment. One repeats the acid and base titrations also as previously to calculate the Faradaic efficiency of the repeat. Hence, by accounting for the mass of CO2 absorbed and desorbed in the second absorption and desorption and the Faradic efficiency and voltage across the stack of the second electrodialysis regeneration the energy consumption to absorb and desorb a given mass of CO2 can be calculated. It is important that the values from the second cycle of the experiment are used, as these better represent steady state operation of the absorption, desorption, and regeneration steps together. Implementation of a solid fixed bed in a method of capturing carbon dioxide from a gas. Schematic diagram of the implementation of a solid fixed bed as solid desorbent is represented in Fig. 22B. Amino acid salts are ideal candidates for liquid CO2 absorption because of their low toxicity, volatility, cost, and fast absorption kinetics. However, salts with fast kinetics, such as potassium glycinate and lysinate form carbamates with double negative charges which require two protons for the reaction of CO2release, which limits the Faradaic efficiency of electrochemical desorption reactions. Furthermore, these salts contain an excess of amino acid anions which can further reduce Faradaic efficiency when they are transferred across anion exchange membranes or protonated in place of CO2containing ions such as carbamate or (bi)carbonate. The process described below transfers CO2from an amino acid salt solutions to a solid functionalised with amine groups which predominantly form singly negatively charged carbamates upon reaction with CO2and therefore require fewer protons for desorption, and enable a higher Faradaic efficiency to be achieved. The new process comprises three different steps that are done sequentially. 1. CO2capture and transfer, and liquid sorbent regeneration. Basic water solution of amino acid (AA-NH2 + OH-) enters in the contact with air and captures CO2from it. Main product of amino acid reaction with CO2 is carbamate (AA-NH-COO-). Loaded amino acid then enters the compartment / column that contains a bed / surface covalently functionalized with amines (R-NH2). Importantly, pKa of solid-based amines is higher than that of the amino group of the amino acid. Under these conditions, CO2 in the form of carbamate is transferred onto the amine functionalized surface. Amino acid solution becomes CO2-lean and returns to the air contactor.AA-NH2 + OH- + CO2 → AA-NH-COO- + H2OAA-NH-COO- + R-NH2 → R-NH-COO- + AA-NH22. CO2 release and collection. Compartment is emptied and filled with the next solution, sulphuric acid. Upon contact with the carbamate it releases CO2 which is carried to the collection point outside of the compartment. Solid-based amines remain in the sulphate salt form.R-NH-COO- + H2SO4 → CO2 + R-NH3+ + SO4- 3. Solid sorbent regeneration. The compartment is emptied and filled with the third solution, KOH to remove sulphate salts and regenerate the solid-based amines for the next CO2 capture and transfer cycle. 2 R-NH3+ + SO4- + 2 KOH → K2SO4 + 2 R-NH2 + 2 H2O K2SO4 salt solution is flushed into the ED cell and split into H2SO4 and KOH that are then used in the steps 2 and 3 respectively. The following protocol can be carried out to test carbamate transfer in solution: One selects amino acid and amine such that pKa of amino acid is lower than that of the amine. As non-limiting examples, asparagine (Asn) and ethylaminoethanol (EAE) are chosen in particular. Then one prepares air-equilibrated K-amino acid by mixing the corresponding ratio of said amino acid, KOH and KHCO3, in particular air-equilibrated K-Asn by mixing right ratio of Asn, KOH, KHCO3. One prepares same volume and concentration of the amine, in particular EAE. One mixes equimolar amounts of said amino-acid and said amine solutions in a separate vial, in particular of Asn and EAE solutions. One performs13C NMR measurement and compares carbamate / bicarbonate peaks between air-equilibrated said amino acid solution and said amine- said amino acid mixture, in particular Asnsolution and EAE-Asn mixture. The following protocol can be carried out to test the full cycle: I. Using amine-functionalized particles and without ED cell. One prepares air-equilibrated K-amino acid solution, in particular K-Asparagine or K-Glycine solutions using the right ratios of the amino acid, KOH, and KHCO3. Collect a sample for NMR and TIC / TOC analysis → ‘0’ or reference sample. One prepares a suspension of the amine-functionalized silica gel in equimolar KOH solution. In a vial or a test tube, an aliquot of amino-acid-CO2solution with an equimolar amount of Si-R-NH2solution is introduced. One stirs properly and lets the silica gel precipitate at the bottom of the vial. One collects a sample of the solution above the Si suspension using syringe. One exchanges the syringe needle to a fresh one and, using syringe filter, collects the solution for NMR and TIC / TOC analysis into a separate vial → sample to estimate how much carbamate was transferred from the amino acid to solid-based amine.One filters out the solution from the Si-R-NH-COO- particles. One keeps it and equilibrate with theair amount of CO2 through sparging with compressed air or by adding a portion of KHCO3 (that is determined based on how much carbamate was transferred). One prepares a solution of H2SO4 (~0.1 M). Add a volume of this solution that corresponds to the 5% molar excess of acid vs amount of CO2 on the Si-RNH2. One stirs the suspension, leave it to let the particles settle. One carefully removes the solution into a separate vial. One titrates the decanted solution with KOH to determine how much of acid was consumed. One prepares ~0.1 M KOH. One adds preferably a volume of this solution that corresponds to the 5% molar excess of base vs amount of protonated amines Si-R-NH3. One stirs the suspension, leaves it to let the particles settle. One carefully removes the solution into a separate vial. One titrates the decanted solution with acid to determine how much of KOH was consumed to regenerate solid-based amines:2 R-NH3+ + SO4- + 2 KOH → K2SO4 + 2 R-NH2 + 2 H2O. One repeats the cycle several times noting how much CO2 is transferred and released and amine regenerated after each stage. II. Using amine-functionalized column, air humidifier, and ED cell. Main steps are the same as in the part I. Amino acid solution is equilibrated with air using the air humidifier, is pumped from there into an amine-functionalized column, and returned back into it after passing it. Then, the pump is stopped, and staged 2 is initiated, along with the stage 3. After passing through the column in the stages 2 and 3, acid and base streams are mixed and then split up again via flowing through the ED stack. One continues this process in a loop until the base stream is ~0.5 pH units higher than the pKa of the solid-based amine. While the present example embodiments have been described with reference to the direct capture of carbon dioxide from the air, the methods and apparatus of the present disclosure may be adapted for capturing carbon dioxide from other gases such for example as exhaust gases from industrial processes, biogases, flue gases or other gas streams comprising carbon dioxide. While the use, the apparatus and methods of the present disclosure have been described and illustrated with reference to particular embodiments, it will be appreciated by those skilled in the art that the disclosure lends itself to many different variations not specifically illustrated herein. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually setforth. Reference should be made to the claims for determining the true scope of protection affordedby the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the disclosure, may not be desirable, and may therefore be absent, in other embodiments. Examples Example 1 : protocol to evaluate the electrodialysis regeneration with monovalent selective AEMs : Make up a volume of 500 mL of initial sorbent solution of 2 mol / L potassium salt of DL-Aspartic acid by adding potassium hydroxide in a 2:1 molar ratio to the amino acid, dissolving in deionized water and making the solution up to the mark in a volumetric flask and once all solids are dissolved take an aliquot of 5 mL of the initial sorbent. Then carbonate the initial sorbent by sparging compressed air through the solution until the pH and electrical conductivity approach a constant value as measured using a pH electrode and conductivity meter. Once constant values have are reached for pH and conductivity, take an aliquot of 5 mL of the carbonated sorbent and measure the weight of the solution using an electronic balance and volume of the solution using a measuring cylinder to account for any losses due to evaporation. Make up a solution of initial desorbent solution of 2 mol / L potassium salt of DL-Aspartic acid by adding potassium hydroxide in a 2:1 molar ratio to the amino acid, dissolving in deionized water and making the solution up to the mark in a volumetric flask. Then carbonate the initial desorbent by sparging pure CO2through the solution until the pH and electrical conductivity approach a constant value as measured using a pH electrode and conductivity meter such that the solution is saturated with CO2. Take an aliquot of 5 mL of the carbonated desorbent and measure the weight and volume of the solution to account for any losses due to evaporation. Measure the CO2 concentration in the initial and carbonated sorbent and carbonated desorbent solutions by means of total inorganic and total organic carbon content analysis. Measure the amine concentration in both solutions via total nitrogen content analysis. Make up 500 mL of 1 mol / L KOH solution to be used as the common electrolyte rinse for the anode and cathode chambers. Assemble an electrodialysis stack (REDSTACK LABSTACK using 0.8 mm spacers) of five repeating units: CEMBPM, with the cation exchange layers of the BPMs facing the cathode. The overall stack configuration is: cathode, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM. The BPMs are Fumasep FBM and the AEMs are ASTOM NEOSEPTA AXP-D. Assemble the apparatus such that the fluid connections from the stack to the container for the carbonated desorbent are gas tight and such that the container itself is gas tight and contains an outlet tube through which CO2 can flow via a Bronkhorts MV-104 Mass flow meter. Using a centrifugal pump, begin pumping the electrolyte rinse through the anode and cathode chambers at a flow rate of 1.5 L / min so that the flows exiting the anode and cathode chambers return to the container from which they were pumped. Pump the carbonated sorbent at a flow rate of 1.7 L / min through the flow channels contacting the anion exchange layers of the BPMs and the other solution which can be called the “regenerated acidifying solution” at 1.7 L / min through the flow channels contacting the cation exchange layers of the BPMs. Both solutions should be recirculated from the electrodialysis stack into their individual containers. Apply a current of 4 A to the electrodialysis stack so that the current density is 400 A / m², and measure the voltage across the stack at the current supplying electrodes and separately across four repeating units using 0.2 mm diameter Pt wires as the electrodes. Continuously measure the pH and conductivity of the regenerated sorbent and acidifying solution. Apply the current for 60 minutes. Drain the electrodialysis stack and measure the weights and volumes of each solution. Take note of the total volume of CO2 desorbed from the flow meter readout. Take aliquots of 5 mL of each solution and measure the CO2 and amine concentrations via the same methods as detailed above. By accounting for the mass of CO2 desorbed as measured from the solution aliquots and flow meter the Faradaic efficiency of desorption can be calculated. Also considering the voltage across the stack of the electrodialysis regeneration the energy consumption to desorb a given mass of CO can be calculated. Using the initial and final volumes of each solution and the amine concentrations any unwanted crossover of amines can be quantified. Example 2 : protocol to evaluate the electrodialysis regeneration in the CEM-BPM configuration Firstly, make up a volume of 500 mL of initial sorbent solution: potassium glycinate at a concentration of 2 mol / L by dissolving the salt in deionised water and making the volume up to the mark in a volumetric flask. Then take an aliquot of 5 mL of the initial sorbent. Next, carbonate the initial sorbent by sparging compressed air through the solution until the pH and or electrical conductivity approach a constant value as measured by a pH electrode and solution conductivity meter. Take an aliquot of 5 mL of the carbonated sorbent and measure the weight of the solution using an electronic balance and volume using a graduated measuring cylinder to account for any losses due to evaporation. Measure the CO2 concentration in the initial and carbonated sorbent solution aliquots using total inorganic and total organic carbon content analysis. Take 2 mL of the 5 mL aliquots of the initial and carbonated sorbents and dilute them 10 times by adding 2 mL to a 20 mL volumetric flask and making the solution up to the mark with deionised water. Titrate them against 0.1 mol / L hydrochloric acid, while monitoring the pH with a pH meter to determine the number of moles of protons required to desorb approximately 100 % of the CO2, which is be marked by an equivalence point in the titration curve and the appearance of gas bubbles. Make up a solution of initial acidifying solution equal to the remaining volume of the carbonated sorbent: sulfuric acid, at a concentration such that the solution contains a number of moles of protons sufficient to desorb 100 % of the CO2in the carbonated sorbent. Take an aliquot of 5 mL of the initial acidifying solution and then mix the full volumes of carbonated sorbent and initial acidifying solution so as to desorb CO2from the carbonated sorbent. Measure the weight and volume of the resulting neutralised solution and measure and take an aliquot of at least 5 mL and then measure the remaining CO2concentration by the means detailed above. Make up 500 mL of 1 mol / L KOH solution to be used as the common electrolyte rinse for the anode and cathode chambers. Assemble an electrodialysis stack -REDSTACK LABSTACK using 0.8 mm spacers) of five repeating units: CEM-BPM, with the cation exchange layers of the BPMs facing the cathode. The overall stack configuration is: cathode, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM, CEM, BPM. The CEM used should be Fumasep FKB-PK-130 and the BPM used should be Fumasep FBM. Next, split the volume of the neutralised solution into two equal parts within two containers.Using a centrifugal pump, begin pumping the electrolyte rinse through the anode and cathodechambers at a flow rate of 1.5 L / min so that the flows exiting the anode and cathode chambers return to the container from which they were pumped. Pump one solution, we name the “regenerated sorbent^ at a flow rate of 1.7 L / min through the flow channels contacting the anionic layers of the BPMs and the other solution we can call the “regenerated acidifying solution^ at 1.7 L / min through the flow channels contacting the cation exchange layers of the BPMs. Both solutions should be recirculated from the electrodialysis stack into their individual containers. Apply a current of 4 A to the electrodialysis stack so that the current density is 400 A / m², and measure the voltage across the stack at the current supplying electrodes and separately across four repeating units using 0.2 mm diameter Pt wires as the electrodes. Continuously measure the pH and conductivity of the regenerated sorbent and acidifying solution. Apply the current for 140 minutes. Drain the electrodialysis stack and measure the weights and volumes of each solution. Take aliquots of 5 mL of each solution. Dilute the 2 mL of the regenerated sorbent aliquot 10 x as described above and titrate against 0.1 mol / L hydrochloric acid to measure its alkalinity. Dilute 2 mL of the regenerated acidifying solution by 10 x as described above and titrate the regenerated acidifying solution aliquot against 0.1 mol / L NaOH to measure its acidity. Using these measurements and the final masses and volumes, the molar quantity of K+transferred across the CEM can be calculated and the Faradaic efficiency of the electrodialysis regeneration can therefore be calculated. Re-carbonate the regenerated sorbent using one of the same methods as above and complete the same CO2measurements on its aliquots. Once again mix the carbonated sorbent, this time with the regenerated sorbent, and complete the same measurements as above. From these measurements, the total CO2absorbed and desorbed in a single cycle can be calculated. Repeat the electrodialysis regeneration once again under the same conditions, until the pH and conductivity of the regenerated sorbent and acidifying solution reach the same values as at the end of the previous experiment. Repeat the acid and base titrations also as previously to calculate the Faradaic efficiency of the repeat. By accounting for the mass of CO2absorbed and desorbed in the second absorption and desorption and the Faradaic efficiency and voltage across the stack of the second electrodialysis regeneration the energy consumption to absorb and desorb a given mass of CO2can be calculated. It is important that the values from the second cycle of the experiment are used, as these better represent steady state operation of the absorption, desorption, and regeneration steps together.Example 3: Process with fixed solid bed - Protocol to test a critical part of the full process: carbamatetransfer in solution 5 mL of 2 M solution of a mixture of DL-Asparagine monohydrate (Asn, >99% purity, purchased from TC Europe, pKa 8.76), KOH (85%, purchased from Merck), and KHCO3 (99%, purchased from Merck) in molar ratio 1:0.5:0.5 was prepared in a glass vial using DI water. In another glass vial, 5 mL of 2 M solution of 2-(Ethylamino)ethanol (EAE, >98% purity, purchased from TCI Europe, pKa 10.12) is prepared. In a separate glass vial, 1 mL of each solution is mixed, the vial is closed tightlyand shaken. Additionally a reference 5 mL of 2 M solution of EAE-CO2 species is made by premixingEAE and KHCO3 in molar ratio 1:0.5. Then, 500 uL aliquote of each of the solutions is transferred to separate NMR tubes and 100 uL of D2O is added to the each of them.13C NMR spectra are obtained and compared. Formation of EAECO2 species is confirmed by appearance of a new peak in the range of 160-170 ppm of C chemical shift and corresponded to approximately 25% CO2 transfer. This demonstrates that the crucial step of the new process idea is chemically feasible: carbamate of Asparagine can be transferred to an amine with higher pKa value which corresponds to the higher basicity. The next step is to demonstrate the functioning of all the components of the new process together in one system.Example 4 : Process with fixed solid bed - Protocol to test the full processA. Using amine-functionalized particles and without ED cell. Prepare 25 mL 2 M solution DL-Asparagine monohydrate (Asn), KOH, KHCO3 in molar ration 1:0.5:0.5. Collect a sample for NMR by mixing 500 uL of this solution and 100 uL D2O in an NMR tube. Prepare a sample for TIC / TOC analysis by taking 500 uL of this solution and dilution it to 50 mL with DI water. These will be further used as reference samples to be compared to the final samples after the full cycle of the process is finished. Next, prepare a suspension of the primary or secondary amine-functionalized silica gel in equimolar KOH solution. Specifically, take 10 g of 3-Aminopropyl-functionalized silica gel (40-63 uM, 1 mmol / g NH2 labeling, purchased from Merck), add 20 mL of DI water, and equimolar amount of KOH, 0.3 g and wait till it dissolves, and solution cools down to the room temperature after heating up from the KOH dissoution. In a separate vial or a test tube, mix a 10 mL aliquot of Asn solution with an equimolar amount of Si-R-NH2 solution. Stir properly and let the silica gel particles precipitate at the bottom of the vial. Collect 500 uL sample of the solution above the particle suspension using syringe. Exchange the syringe needle to a fresh one and, using syringe filter, collect the solution for NMR and TIC / TOC analysis into a separate vial. NMR and TIC / TOC sample are further prepared in the same way as the reference sample of Asn solution. These samples are used to estimate how much CO2 species (carbamate, carbonate, bicarbonate) were transferred from Asn to particle-based amine. Notably, amino acids and priary amines mostly form one type of species, carbamates. Through the acid-base equilibria the carbamate of asparagine gets transferred onto primary and / or secondary amines of the covalently functionalized particles, preserving the selectivity in CO2speciation in the solution. Next, filter out the solution from the Si-R-NH-COO- particles. Keep it andequilibrate with the air amount of CO2 through sparging with compressed air for 6 hours or by adding a portion of KHCO3, 0.25 eq. relative to Asn. Prepare 100 mL solution of sulfuric acid H2SO4, 0.1 M. Add a volume of this solution to the previously obtained remaining Si particles, that corresponds to the 5-10% molar excess of acid against amount of CO2 on the Si-R-NH2 which is confirmed from NMR measurements of the previous step. Stir the suspension, leave it to let the particles settle. Carefully remove the solution into a separate vial. Titrate the decanted solution with 0.1 M KOH to determine how much of acid was consumed. Prepare 100 mL of 0.1 M KOH. Add a volume of this solution to the particles remained after the last filtration, that corresponds to the 5-10% molar excess of base vs amount of protonated amines Si-R-NH3. Stir the suspension, leave it to let the particles settle. Carefully remove the solution into a separate vial. Titrate the decanted solution with the 0.1 M sulfuric acid to determine how much of KOH was consumed to regenerate solid-based amines (2 R- NH3+ + SO4- + 2 KOH → K2SO4 + 2 R-NH2 + 2 H2O). Repeat the cycle several times noting how much CO2 is transferred and released and quantity of amine regenerated after each stage based on change in CO2 concentration from TIC / TOC and NMR data. B. Using amine-functionalized column, air contacting unit, and ED cell. Main steps are the same as in the part I, however all quantities are scaled up by factor of 100 to 1000. Asn solution is pumped through the air contacting unit until the CO2 loading is reached approximately 0.5 mol CO2 / mol solvent. Once the solution is equilibrated with air, it is directed through a column or compartment with amine-functionalized wall surface using a peristaltic pump. After passing this compartment, solution is returned back into the air contacting unit. Then, the pump is stopped, and staged 2 is initiated, along with the stage 3 according to the general description. It is advantageous to raise the internal temperature of the compartment up to 40-45 ℃ to accelerate the rate of CO2species transfer onto the solid-based amines. After passing through the column in the stages 2 and 3, acid and base solution streams are mixed and then split up again via flowing through the ED stack. Continue this process in a loop until the base stream is ~0.5 pH units higher than the pKa of the solid-based amine (>9 in the case of asparagine). After each stage 0.5 mL aliquots of solutions exiting the compartment are taken for NMR and TIC / TOC analysis which allows to quantify CO2 transfer and amine regeneration at each stage. It is advantageous to keep the compartment under 2-5 bars pressure during the stage 2 (CO2 release from the solid-based amine) to drive CO2bubble formation outside of the compartment. Here, we have demonstrated a different process setup compared to those previously covered in this patent for the direct air capture. It still uses liquid amine-containing water-based solvents and electrochemically fueled pH-swing regeneration but includes multiple sequential stages (i.e., the process is run semi-continuously) and moves the regeneration process outside of the ED cell (permitting the use of simpler setup for salt splitting). The process takes advantage of fast CO2absorption kinetics of less basic amine, e.g., amino acid, selectivity of formed CO2species upon contact with air especially in terms of charge which then determines energy required for the solid- based amine regeneration, overall simplicity and cost-efficiency of the implemented parts. Depending on the running mode, liquid flowrates, and exact chemical nature of the chosen amine couple, the CO2transfer efficiency in each cycle ranges from 20 to 60%, meaning that after passing once the compartment with solid based amine the liquid amine solution gets depleted in CO2 by 20- 60% compared to before entering the compartment. Further, the efficiency of CO2 release from the solid-based amine and the subsequent recovery of the latter are quantitative processes since both use 5-10% excess of CO2-releasing agent (sulfuric acid) and solid-based amine-regenerating agent (potassium or sodium hydroxide). Overall the system uses readily available low-cost stable chemicals and has no issues of material compatibility. Consequently, it demonstrates high cyclic capacity and can be run up to 100 cycles without significant degradation of the functional parts which offers a promising basis for the industrial scale-up.

Claims

Claims1. Use of the combination of an electrochemical cell and of at least one heat pump, in theimplementation of a process for capturing carbon dioxide from a fluid, in particular a gas, preferably atmospheric air, comprising the use of a liquid sorbent and a liquid desorbent, the liquid sorbent containing carbon dioxide in the form of carbon dioxide-containing anions (CO2- containing anions), and being able to transfer the CO2-containing anions to the liquid desorbent by the electrochemical cell across one or more of its ion exchange membranes, to load the liquid desorbent with CO2-containing anions and to obtain the loaded liquid desorbent, or the liquid sorbent containing cations and carbon dioxide in the form of CO2-containing anions, and being able to transfer said cations by the electrochemical cell across one or more of its ion exchange membranes, thereby acidifying the liquid sorbent to become the liquid desorbent loaded with CO2- containing anions, in which the heat pump is configured to deliver heat below 100 degrees Celsius and to transfer heat to said loaded liquid desorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, said combination enabling, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of the desorption reactionto allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value atwhich carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and enabling the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent.

2. The use according to claim 1, wherein said heat pump is a low temperature heat pumpconfigured to deliver heat at temperatures below 100 degrees Celsius, in particular at temperatures of 40-90 degrees Celsius, preferably at temperatures of at least 45-75 degrees Celsius and has a coefficient of performance (COP) of higher than unity, in particular said heat pump is a gas source heat pump.

3. The use according to any of claims 1-2, wherein the said at least one heat pump is integratedor otherwise physically associated with the gas contactor.

4. The use according to any of claims 1-3, wherein at least one gas contactor fan is configuredand arranged both to move the gas stream through or over the gas contactor in use and to function asa heat pump fan.

5. The use according to any of claim 1-4, wherein the gas contactor comprises a housing defininga plenum, and a plurality of spaced parallel tubes extending through the plenum; each tube having asemi-permeable wall that is formed at least partially of an anion exchange polymer.

6. The use according to any of claims 1-5, wherein the liquid sorbent and / or the liquid desorbentare aqueous liquids.

7. The use according to any of claims 1-6, wherein the liquid sorbent comprises a base as asolvent which can react with carbon dioxide to form CO2-containing anions.

8. The use according to any of claim 1-7, further comprising the use of one or more heaters forheating the loaded liquid desorbent prior to desorption of carbon dioxide in the desorber and wherein said one or more heaters are configured to deliver waste heat from an industrial process or power plant.

9. The use according to any of claim 1-8, wherein the liquid sorbent is continuously recirculatingbetween the electrochemical cell and a gas contactor, and wherein the liquid desorbent is continuouslyrecirculating between the electrochemical cell and the desorber.

10. Apparatus for capturing carbon dioxide from a fluid, in particular from a gas stream,preferably from atmospheric air, comprising:- means for absorbing carbon dioxide from the fluid,- an electrochemical cell configuredto transfer carbon dioxide in the form of CO2-containing anions contained in a liquid sorbent across one or more ion exchange membranes to a liquid desorbent to load the liquid desorbent with CO2- containing anions and to obtain the loaded liquid desorbent,or to transfer cations contained in a liquid sorbent containing carbon dioxide in the form of CO2- containing anions across one or more ion exchange membranes, thereby acidifying the liquid sorbent, to transform said liquid sorbent to a liquid desorbent loaded with CO2-containing anions,- at least one heat pump configured to deliver heat below 100 degrees Celsius and to transfer heat tosaid loaded liquid desorbent prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, wherein the combination of the electrochemical cell and said at least one heat pump is configured to enable, by heating said loaded desorbent liquid, to shift the equilibrium of the desorption reaction of carbon dioxide in the desorber and increase the rate of desorption reaction to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and to enable the voltage and the energy consumption of the electrochemical cell to be lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent.

11. Apparatus according to claim 10, wherein, wherein the said at least one heat pump isintegrated or otherwise physically associated with the gas contactor.

12. Apparatus according to claim 10 or 11, wherein at least one gas contactor fan is configuredand arranged both to move the gas stream through or over the gas contactor in use.

13. Apparatus according to any of claims 10-12, wherein the gas contactor comprises a housingdefining a plenum, and a plurality of spaced parallel tubes extending through the plenum; each tubehaving a semi-permeable wall that is formed at least partially of an anion exchange polymer.

14. Apparatus according to claim 10, wherein the one or more ion exchange membranes of theelectrochemical cell are permeable to reactive species contained in the liquid sorbent and / or the liquid desorbent, said reactive species being able to react with carbon dioxide to form CO2-containing anions.15 Apparatus according to claim 14, wherein the one or more ion exchange membranes of the electrochemical cell are monovalent selective anion exchange membrane permeable to carbon dioxide-containing anions, in particular bicarbonate ions (HCO3−).

16. Apparatus according to claims 7-15, wherein the electrochemical cell comprises one or moreanion exchange membranes and possibly bipolar membranes and is configured for electrochemically transporting the CO2-containing anions contained in the liquid sorbent across said one or more anion exchange membranes into the liquid desorbent, thereby enabling to move the CO2-containing anions from the liquid sorbent loaded with carbon- containing anions into the liquid desorbent to obtain the liquid desorbent loaded with CO2-containing anion which is a solution more acidic and / or concentrated in carbon dioxide than said loaded liquid sorbent.

17. Apparatus according to claims 7-15, wherein the electrochemical cell comprises one or morecation exchange membranes and possibly bipolar membranes and is configured for electrochemically transporting cations contained in the liquid sorbent loaded with carbon dioxide in the form of CO2- containing anions across said one or more cation exchange membranes to move said cations from said liquid sorbent, which are replaced by protons formed at an anode or at bipolar membranes of the electrochemical cell, thereby lowering the pH of said loaded liquid sorbent to transform it to said loaded liquid desorbent.

18. Apparatus according to claims 7-17, wherein said heat pump is a low temperature heat pumpconfigured to deliver heat at temperatures below 100 degrees Celsius, in particular at temperatures of 40-90 degrees Celsius, preferably at temperature of at least 45-75 degrees Celsius, and has a coefficient of performance (COP) of higher than unity.

19. Apparatus according to claims 7-18, wherein the electrochemical cell comprises anelectrolysis cell or an electrodialysis cell, preferably an electrodialysis cell.

20. Apparatus according to claims 7-19, wherein one or both of the liquid sorbent and liquiddesorbent comprise an alkali metal cation, an amine or amino acid salt, or a mixture of an alkali metal cation and an amine or amino acid salt, as a base.

21. Apparatus according to claims 7-20, further comprising one or more heaters for heating theloaded liquid desorbent prior to desorption of carbon dioxide in the desorber,22. Apparatus according to claim 21, said one or more heaters are configured to deliver wasteheat from an industrial process plant or power plant, preferably said industrial process is an industrial carbon dioxide utilization process.

23. Apparatus according to claims 7-22, further comprising a gas compressor for compressing thedesorbed carbon dioxide gas, which comprises at least one compressor module and at least one post- compressor cooler module; the cooler module comprising a cooler heat exchanger which is configured and arranged to transfer heat from the output gas stream to the liquid desorbent prior to desorption of the carbon dioxide therefrom.

24. Apparatus according to claims 7-23, wherein said fluid is a gas stream and said means forabsorbing carbon dioxide is a gas contactor, wherein said heat pump is a gas source heat pump, in particular configured and arranged to transfer heat from a gas to the liquid desorbent preferably to transfer heat from the gas stream exiting the gas contactor to the liquid desorbent.

25. Apparatus according to claim 24, wherein the gas source heat pump comprises a gas-refrigerant heat exchanger and a refrigerant circuit; wherein the gas-refrigerant heat exchanger isintegrated with the gas contactor such that the gas-refrigerant heat exchanger is positioned in the gasstream in use, to transfer heat from the gas stream to a refrigerant in the refrigerant circuit.

26. Apparatus according to claim 25, wherein the gas contactor comprises at least one fan whichis configured and arranged to drive the gas stream through or over the gas contactor and over the gas- refrigerant heat exchanger.

27. Apparatus according to claim 26 wherein the gas contactor which includes a housing havingan inlet for admitting the gas stream into the housing and an outlet for exhausting the gas stream therefrom, the gas-refrigerant heat exchanger being disposed proximate the outlet; the gas contactor further comprising a first gas contactor fan proximate the inlet for impelling the gas stream into the housing and a second heat pump fan proximate the outlet for assisting passage of the gas stream over the gas-refrigerant heat exchanger.

28. A method of capturing carbon dioxide from a fluid, in particular a gas, preferably atmosphericair comprising:i) transferring carbon dioxide in the form of CO2-containing anions contained in a liquid sorbent, from said liquid sorbent to a liquid desorbent in an electrochemical cell across one or more of its ion exchange membranes to load the liquid desorbent with CO2-containing anions and obtain the loaded liquid desorbent, or transferring cations contained in a liquid sorbent containing carbon dioxide in form of CO2- containing anions, in an electrochemical cell across one or more of its ion exchange membranes, thereby acidifying the liquid sorbent, to transform said liquid sorbent to a liquid desorbent loaded with CO2-containing anions, ii) heating said loaded liquid desorbent by using at least one heat pump configured to deliver heat below 100 degrees Celsius, prior to desorption of the carbon dioxide, said desorption taking place in a desorber at a temperature lower than 100°C, and obtaining desorbed carbon dioxide wherein, by heating said loaded desorbent liquid, the equilibrium of the desorption reaction of carbon dioxide in the desorber is shifted and the rate of the desorption reaction is increased to allow desorption of carbon dioxide at a solubility of CO2-containing anions lower than the value at which carbon dioxide can normally desorb in the desorber without heating said loaded desorbent, and wherein the voltage and the energy consumption of the electrochemical cell is lower than the voltage and the energy consumption required to reach the solubility of CO2-containing anions in the loaded liquid desorbent at which carbon dioxide can normally desorb in the desorber from said loaded liquid desorbent, without heating said loaded liquid desorbent.

29. Method according to claim 28, wherein the liquid desorbent is heated prior to desorption ofcarbon dioxide in the range of less than 100 degrees Celsius; in particular about 40-90 degrees Celsius; preferably about 45-75 degrees Celsius.

30. Method according to any of claims 28-29, wherein the liquid sorbent and the liquid desorbentare circulated in separate loops and the liquid desorbent has a minimum temperature which is higher than a maximum temperature of the liquid sorbent,31. Method according to any of claims 28-30, further comprising compressing the desorbedcarbon dioxide, cooling the compressed carbon dioxide by transferring heat therefrom to the liquid desorbent prior to desorption of the carbon dioxide therefrom.

32. Method according to any of claims 28-31, wherein one or both of the liquid sorbent and liquiddesorbent comprise an alkali metal cation, an amine or amino acid salt, or a mixture of an alkali metal cation and an amine or amino acid salt, as a base.

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