Process and apparatus for continuously recovering carbon dioxide from a carbon-dioxide-containing gas atmosphere

Abstract

The present invention relates to a process for continuously recovering carbon dioxide from a carbon-dioxide-containing gas atmosphere, which process is easily scalable and can be carried out particularly energy efficiently and cost effectively, and to an apparatus for carrying out this process. The process comprises: (a) an absorption step, which includes continuously bringing a carbon-dioxide-containing gas flow into contact with a liquid sorbent in a counter-flow or cross-flow principle at ambient temperature and under normal pressure, wherein the liquid sorbent absorbs carbon dioxide and a carbon-dioxide-laden liquid sorbent and a carbon-dioxide-enriched gas flow are formed; and (b) a desorption step, which includes continuously heating the carbon-dioxide-laden liquid sorbent to a temperature which is higher than the ambient temperature and / or continuously passing the carbon-dioxide-laden liquid sorbent through an atmosphere having a carbon-dioxide partial pressure lower than normal pressure, wherein the carbon-dioxide-laden liquid sorbent desorbs carbon dioxide and the liquid sorbent is regenerated. The process is further characterised in that the liquid sorbent comprises polyethyleneimine.

Description

[0001] Method and device for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere

[0002] Field of the invention

[0003] The invention generally relates to a method and a device for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere. In particular, the invention relates to a method for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere, which is easily scalable and can be carried out in a particularly energy-efficient and cost-effective manner, as well as to a device for carrying out this method.

[0004] Technical background

[0005] Fossil fuels, which have so far formed the basis of the global energy and economic system, are responsible for a constantly increasing concentration of carbon dioxide in the atmosphere - and thus also for climate change. Against this backdrop, future emissions must be avoided and a net-zero emissions strategy initiated. For this purpose, the direct air capture (DAC) process, among others, was developed. This is a process for the direct extraction of carbon dioxide from ambient air using a suitable sorbent and usually comprises an absorption step and a desorption step. The carbon dioxide extracted in this way can be further recycled either chemically (solvents, urea, plastics, etc.), physically (carbonization, preservation, refrigerants, etc.) or as eFuel, or removed from the cycle through sequestration.The high international relevance and increasing interest in DAC technology is also reflected in the literature, as shown, for example, in a 2022 report by the International Energy Agency (IEA) (“Direct Air Capture: A key technology for net zero”).

[0006] The major challenge in the direct extraction of carbon dioxide from ambient air lies, on the one hand, in the low carbon dioxide concentration of approximately 415 ppm, which leads to high air volume flows and the associated high energy input during the absorption step. In particular, efficient extraction of carbon dioxide from ambient air requires gas volume flows that are significantly higher than those achieved in flue gas scrubbing. When selecting suitable separation processes, it is therefore important to ensure that the air volume flow is as unaffected as possible by any changes in state, such as temperature or pressure changes.Furthermore, the low carbon dioxide concentration requires a sorbent that exhibits the highest possible selectivity for carbon dioxide and, despite the high air flow rates, is not released into the environment from a system configured for the DAC process. On the other hand, the energy consumption during the desorption step must also be considered, as the desorption of carbon dioxide is comparatively energy-intensive and requires electricity or heat at different temperature levels.

[0007] The currently known DAC processes can be primarily differentiated into low- and high-temperature processes. In the low-temperature processes, which are usually carried out at a desorption temperature of around 100°C, the use of short-chain, solid-bound amines such as monoethanolamine (MEA), diethanolamine (DEA) or methyldiethanolamine (MDEA) as sorbents predominates. The low desorption temperature of around 100°C is usually achieved by setting a negative pressure in the desorption unit (hereinafter referred to as desorber), which severely limits its installation space. Since adsorption and desorption are only separated from each other in time and not in space, this also applies to the absorption unit (hereinafter referred to as absorber). As a result, the known low-temperature processes can only be carried out discontinuously (i.e.In batch mode, the process is carried out in a controlled manner, resulting in increased material stress, fluctuating product gas quality, and increased control engineering effort. Scaling can only be achieved by interconnecting many individual modules, which in turn leads to increased material costs.

[0008] The high-temperature processes are based on the use of aqueous alkali or alkaline earth metal hydroxide solutions as sorbents and can therefore be designed as continuous processes. However, the use of aqueous alkali or alkaline earth metal hydroxide solutions requires desorption temperatures of up to 900°C. To achieve such high desorption temperatures, natural gas is usually burned, which leads to the release of new carbon dioxide. A further problem is that the desorption cycle, which involves several chemical conversion processes, is technically complex and cost-intensive and, in contrast to the low-temperature processes, no waste heat from low-temperature processes such as electrolysis or methanation can be incorporated. An overview of currently used low- and high-temperature processes for extracting carbon dioxide from ambient air can be found in Viehbahn et al. (Energiewirtsch.Tagesfragen 69(12), 30-33), Fasihi et al. (J. Clean. Prod. 224, 957-980) and Heß et al. (“Use of CO2 from air as a raw material for synthetic fuels and chemicals”, study commissioned by the Ministry of Transport Baden-Württemberg, Karlsruhe Institute of Technology, December 2020).

[0009] Summary of the invention

[0010] Problems to be solved

[0011] As explained above, the currently known low-temperature processes have the disadvantage that they cannot be carried out continuously, which leads to increased material stress, fluctuating quality of the recovered carbon dioxide, and increased control engineering effort. In contrast, the common high-temperature processes have the problem that high desorption temperatures are required and no waste heat from low-temperature processes can be utilized, which leads to high energy consumption and thus to further release of carbon dioxide and increased energy costs. Taking this fact into account, the object underlying the present invention was to provide a process and a device for the continuous recovery of carbon dioxide from a carbon dioxide-containing gas atmosphere, which at least partially overcomes the disadvantages of the prior art.In particular, the process should be particularly energy-efficient and cost-effective by combining the advantages of known low-temperature processes with those of known high-temperature processes. The invention is defined in the claims.

[0012] EP 2700440 A2 and DE 102004053 167 A1 each disclose a method and a system for the continuous recovery of carbon dioxide from a flue gas stream generated by the combustion of fuel. The methods comprise an absorption step, which comprises continuously contacting the flue gas stream with a liquid sorbent in a countercurrent flow, wherein the liquid sorbent absorbs carbon dioxide and forms a carbon dioxide-laden liquid sorbent and a carbon dioxide-depleted flue gas stream, and a desorption step, which comprises continuously heating the carbon dioxide-laden liquid sorbent, wherein the carbon dioxide-laden liquid sorbent desorbes carbon dioxide and regenerates the liquid sorbent.The liquid sorbent used in EP 2 700 440 A2 comprises a water-soluble, amino group-containing polymer, while DE 102004 053 167 A1 requires the use of a polymer with a degree of branching of < 35% and a molecular weight of 500 to 100,000 g / mol.

[0013] Means to solve the problems

[0014] In a first aspect to achieve the above-described object, the present invention thus relates to a process for the continuous recovery of carbon dioxide from a carbon dioxide-containing gas atmosphere, as defined in claim 1. The process according to the invention comprises:

[0015] (a) an absorption step comprising continuously contacting a carbon dioxide-containing gas stream with a liquid sorbent in countercurrent or cross-current flow at ambient temperature and under atmospheric pressure, whereby the liquid sorbent absorbs carbon dioxide and forms a carbon dioxide-laden liquid sorbent and a carbon dioxide-depleted gas stream; and

[0016] (b) a desorption step which comprises continuously heating the carbon dioxide-laden liquid sorbent to a temperature higher than ambient temperature and / or continuously passing the carbon dioxide-laden liquid sorbent through an atmosphere with a carbon dioxide partial pressure lower than normal pressure, wherein the carbon dioxide-laden liquid sorbent desorbes carbon dioxide and regenerates the liquid sorbent, wherein the liquid sorbent comprises polyethyleneimine.

[0017] In a second aspect to achieve the above-described object, the invention relates to a device for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere, as defined in claim 14. The device according to the invention comprises:

[0018] (a) a supply line for a gas stream containing carbon dioxide;

[0019] (b) a supply line for a liquid solvent;

[0020] (c) a supply line for a liquid sorbent;

[0021] (d) a discharge line for a gas stream depleted in carbon dioxide;

[0022] (e) a discharge line for a liquid sorbent loaded with carbon dioxide;

[0023] (f) a carbon dioxide discharge line;

[0024] (g) an absorber comprising at least one first inlet opening connected to the supply line for a carbon dioxide-containing gas stream, a second inlet opening connected to the supply line for a liquid solvent, a third inlet opening connected to the supply line for a liquid sorbent, means for continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a countercurrent or crosscurrent manner at ambient temperature and under atmospheric pressure to form the carbon dioxide-laden liquid sorbent and the carbon dioxide-depleted gas stream, a first outlet opening connected to the discharge line for a carbon dioxide-depleted gas stream, and a second outlet opening connected to the discharge line for a carbon dioxide-laden liquid sorbent; and

[0025] (h) a desorber comprising at least one first inlet opening connected to the discharge line for a liquid sorbent loaded with carbon dioxide, means for continuously heating the liquid sorbent loaded with carbon dioxide to a temperature elevated relative to ambient temperature and / or means for continuously passing the liquid sorbent loaded with carbon dioxide through an atmosphere with a carbon dioxide partial pressure reduced relative to normal pressure for desorption of carbon dioxide and regeneration of liquid sorbent, a first outlet opening connected to the supply line for a liquid sorbent, and a second outlet opening connected to the discharge line for carbon dioxide; wherein the liquid sorbent comprises polyethyleneimine.

[0026] In a third aspect, the invention relates to the use of a liquid solution of polyethyleneimine for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere. Advantageous embodiments of the method and apparatus of the present invention are defined in the subclaims.

[0027] Short description of the drawings

[0028] Fig. 1 shows a schematic representation of an apparatus for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a first embodiment of the present invention.

[0029] Fig. 2 shows a schematic representation of an apparatus for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a second embodiment of the present invention.

[0030] Fig. 3 shows a schematic representation of an apparatus for continuously recovering carbon dioxide from a carbon dioxide-containing atmosphere according to a third embodiment of the present invention.

[0031] Fig. 4 shows a schematic representation of an apparatus for continuously recovering carbon dioxide from a carbon dioxide-containing atmosphere according to a fourth embodiment of the present invention.

[0032] Fig. 5 shows a schematic representation of an apparatus for continuously recovering carbon dioxide from a carbon dioxide-containing atmosphere according to a fifth embodiment of the present invention.

[0033] Fig. 6 shows a schematic partial representation of an apparatus for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a sixth embodiment of the present invention.

[0034] Fig. 7 shows a schematic partial representation of an apparatus for continuously recovering carbon dioxide from a carbon dioxide-containing atmosphere according to a seventh embodiment of the present invention.

[0035] Fig. 8 shows a schematic representation of a cylindrical counterflow absorber (left) and a rectangular crossflow absorber (right). Fig. 9 shows a cross-section through a crossflow absorber as an embodiment of an absorber that can be used in a device according to the invention for the continuous extraction of carbon dioxide from a carbon dioxide-containing atmosphere.

[0036] Fig. 10 shows a plan view and a section through a cross-flow absorber according to Fig. 9 with a circular base. Fig. 11 shows a plan view and a section through a cross-flow absorber according to Fig. 9 with an octagonal base.

[0037] Fig. 12 shows a plan view and a section through a cross-flow absorber according to Fig. 9 with a rectangular base area.

[0038] Fig. 13 shows a cross section through a thin-film evaporator as an embodiment of a desorber which can be used in a device according to the invention for the continuous extraction of carbon dioxide from a carbon dioxide-containing atmosphere.

[0039] Detailed description of the invention

[0040] The process according to the invention for the continuous recovery of carbon dioxide from a carbon dioxide-containing gas atmosphere necessarily comprises an absorption step and a desorption step. The term "carbon dioxide-containing gas atmosphere," as used in the present application, refers to any gas atmosphere that comprises at least carbon dioxide as a constituent. This means that the term essentially encompasses both a gas atmosphere consisting purely of carbon dioxide and a gas atmosphere that comprises one or more other constituents in addition to carbon dioxide. Other constituents that come into consideration are, in particular, nitrogen, oxygen, and noble gases, which can be mixed with carbon dioxide in any desired ratio. With regard to a configuration as a DAC process, however, the carbon dioxide-containing gas atmosphere preferably does not contain any flue gas.More preferably, the carbon dioxide-containing gas atmosphere is air, whereby the term "air" includes both ambient air and exhaust air (e.g., from industrial processes). Ambient air is particularly preferred, although its water content may vary depending on the respective local conditions (temperature, pressure, etc.).

[0041] The absorption step comprises continuously contacting a carbon dioxide-containing gas stream with a liquid sorbent using a countercurrent or crosscurrent principle at ambient temperature and under atmospheric pressure, whereby the liquid sorbent absorbs carbon dioxide and forms a carbon dioxide-laden liquid sorbent and a carbon dioxide-depleted gas stream. The term "carbon dioxide-containing gas stream," as used in the present application, refers to a gas stream obtained from the carbon dioxide-containing gas atmosphere defined above using suitable technical means and comprising at least carbon dioxide as an essential component.Accordingly, the carbon dioxide-containing gas stream is preferably an air stream, and particularly preferably an ambient air stream, which is typically introduced into an absorber via a correspondingly configured line (hereinafter also referred to as the supply line for a carbon dioxide-containing gas stream) and there, under suitable conditions, brought into contact with a liquid sorbent capable of absorbing carbon dioxide. The liquid sorbent is generally introduced into the absorber via a separate supply line (hereinafter also referred to as the supply line for a liquid sorbent).

[0042] The liquid sorbent used in the present invention is a sorbent comprising polyethyleneimine (PEI) as an essential component. Polyethylenimines are polymers formally obtained by polymerizing ethyleneimine (aziridine) and containing a large number of amino groups. Due to their strongly basic properties, polyethyleneimines are usually present as polycations, which makes them highly soluble in water and other protic solvents. At the same time, polyethyleneimines generally have a number-average molecular weight of at least several thousand g / mol, resulting in a relatively low vapor pressure. The latter represents a significant advantage over the short-chain amines known, for example, from flue gas scrubbing, since high air volume flows are required for the direct extraction of carbon dioxide from ambient air.Due to these high air flow rates, the use of short-chain amines with a relatively high vapor pressure in the DAC process would lead to high amine losses in the scrubbing liquid. The low vapor pressure of (long-chain) polyethyleneimines counteracts this problem by minimizing the risk of amine leaching from the liquid sorbent.

[0043] The liquid sorbent used in the process according to the invention comprises polyethyleneimine dissolved in a liquid solvent. Examples of liquid solvents within the meaning of the present application include both aprotic solvents and protic solvents, with protic solvents such as water, methanol, ethanol, or mixtures thereof being preferred. The liquid solvent is particularly preferably water, which means that an aqueous sorbent containing polyethyleneimine can be used in particular. The polyethyleneimine itself can be linear or branched, with branched polyethyleneimines being preferred. The number-average molecular weight of the polyethyleneimine is not particularly limited, but is preferably in a range from 1,000 to 200,000 g / mol, more preferably 2,500 to 150,000 g / mol, and most preferably 5,000 to 100.000 g / mol, as determined by gel permeation chromatography. Suitable polyethyleneimines are known in the art and are commercially available from Alfa Aesar, Sigma-Aldrich, and TCI Chemical, among others. The concentration of polyethyleneimine in the liquid sorbent is typically in the range of 5 to 35 wt.%, and preferably in the range of 10 to 25 wt.%, based on the total weight of the liquid sorbent.

[0044] By using a liquid sorbent instead of a solid-bound sorbent, the process according to the invention can be operated continuously without any problems and without any special technical effort. At the same time, due to the use of polyethyleneimine as an absorbent, the process according to the invention achieves a significant advantage of known low-temperature processes, namely a low desorption temperature of carbon dioxide. Thus, the absorption and desorption steps can be spatially separated and individually adapted to the respective conditions. This is important because an absorber used in the absorption step must be as large as possible due to the high gas volume flow, while a desorber used in the desorption step should be as small as possible to reduce energy consumption.Such an adaptation is not possible in batch operation, since the absorption and desorption steps are not spatially separated but take place in one and the same apparatus. Consequently, the invention combines the advantages of known high-temperature and low-temperature processes, which is why a liquid solution of polyethyleneimine can be advantageously used for the continuous recovery of carbon dioxide from a carbon dioxide-containing gas atmosphere.

[0045] According to the invention, the carbon dioxide-containing gas stream is brought into contact with the liquid sorbent using a countercurrent or crosscurrent principle at ambient temperature and under atmospheric pressure, whereby the liquid sorbent absorbs carbon dioxide and forms a carbon dioxide-laden liquid sorbent and a carbon dioxide-depleted gas stream. The term "ambient temperature," as used in the present application, essentially refers to the temperature prevailing at the respective location during the process. Depending on the location of a device configured for carrying out the process, the ambient temperature is thus typically in a range from -20 to 50°C, preferably 0 to 40°C, and particularly preferably 5 to 35°C.In contrast, the term "standard pressure," as used in this application, refers to the atmospheric pressure prevailing at the respective location during the process. For example, if the process is carried out at sea level, the standard pressure is 1013.25 hPa or approximately 1 bar. If the process is carried out at 1000 m above sea level, the standard pressure decreases to 891 hPa.

[0046] Adequate absorption of carbon dioxide during the absorption step is achieved by contacting the carbon dioxide-containing gas stream with the liquid sorbent using a countercurrent or crosscurrent principle (see Fig. 8). A countercurrent absorber theoretically offers numerous advantages over a crosscurrent absorber. These advantages include, among others, higher absorption efficiency, since the carbon dioxide-containing gas stream to be purified and the liquid sorbent flow in opposite directions, thus creating a maximum concentration difference within the absorber, and the concentration difference represents the driving force for the absorption reaction.Further advantages include improved mass transfer (since the continuous collision of the carbon dioxide-containing gas stream and the liquid sorbent over the entire length of the absorber continually creates new phase interfaces between gas and liquid), a reduced risk of channeling, and easier aerosol separation. To prevent aerosols from being discharged from the absorber, a demister can be used in the process according to the invention, for example. Such a demister can easily drip downwards when the countercurrent principle is applied.

[0047] To minimize the total energy consumption of the absorption step, which is determined primarily by the active supply of the carbon dioxide-containing gas stream to the absorber and the circulation of the liquid sorbent in the absorber, a slow flow of the carbon dioxide-containing gas stream through the absorber is desired. The latter implies a reduction in flow velocity at a constant gas volume flow, which ultimately requires an increase in the absorber's inflow area, resulting in a larger area requirement when using the counterflow principle. A cross-flow absorber offers the advantage of better floor space utilization compared to a counterflow absorber, since the inflow area can be extended vertically.In this way, a generally cylindrical counterflow absorber develops into a rather flat and rectangular crossflow absorber, which, due to its orientation in the prevailing wind direction, can better utilize natural air movement than a counterflow absorber. Taking this into account and with regard to scaling, it is therefore preferred according to the invention for the absorption step to comprise the continuous contacting of the carbon dioxide-containing gas stream with the liquid sorbent using the crossflow principle, although at first glance the use of a crossflow absorber entails disadvantages compared to the use of a counterflow absorber.

[0048] The carbon dioxide-laden liquid sorbent formed during the absorption step is then fed to a desorption step. The desorption step comprises continuously heating the carbon dioxide-laden liquid sorbent to a temperature elevated above ambient temperature and / or continuously passing the carbon dioxide-laden liquid sorbent through an atmosphere with a carbon dioxide partial pressure reduced compared to normal pressure, whereby the carbon dioxide-laden liquid sorbent desorbes carbon dioxide and regenerates the liquid sorbent.For this purpose, the carbon dioxide-laden liquid sorbent is typically removed from the absorber via an appropriately configured line (hereinafter also referred to as the carbon dioxide-laden liquid sorbent discharge line) and introduced into a desorber, where the carbon dioxide-laden liquid sorbent is treated using suitable technical means to release previously bound carbon dioxide. This carbon dioxide can then be removed from the desorber via an appropriately configured line (hereinafter also referred to as the carbon dioxide discharge line) and, if necessary, further processed.

[0049] A device designed to carry out the process according to the invention therefore comprises at least one absorber, one desorber, a feed line for a carbon dioxide-containing gas stream, a feed line for a liquid solvent, a feed line for a liquid sorbent, a discharge line for a carbon dioxide-depleted gas stream, a discharge line for a carbon dioxide-laden liquid sorbent, and a carbon dioxide discharge line.The absorber comprises at least one first inlet opening connected to the feed line for a carbon dioxide-containing gas stream, a second inlet opening connected to the feed line for a liquid solvent, a third inlet opening connected to the feed line for a liquid sorbent, means for continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in countercurrent or crosscurrent flow at ambient temperature and under atmospheric pressure to form the carbon dioxide-laden liquid sorbent and the carbon dioxide-depleted gas stream, a first outlet opening connected to the discharge line for a carbon dioxide-depleted gas stream, and a second outlet opening connected to the discharge line for a carbon dioxide-laden liquid sorbent.The desorber comprises at least one first inlet opening connected to the discharge line for a carbon dioxide-laden liquid sorbent, means for continuously heating the carbon dioxide-laden liquid sorbent to a temperature elevated relative to ambient temperature and / or means for continuously passing the carbon dioxide-laden liquid sorbent through an atmosphere with a carbon dioxide partial pressure reduced relative to normal pressure for the desorption of carbon dioxide and regeneration of liquid sorbent, a first outlet opening connected to the supply line for a liquid sorbent, and a second outlet opening connected to the carbon dioxide discharge line. Specific embodiments of such a device are illustrated in Figs. 1 to 5.

[0050] Regarding the absorption step, as described above, it is preferred that this involves continuously bringing the carbon dioxide-containing gas stream into contact with the liquid sorbent using the cross-flow principle. While a cross-flow absorber designed as a wall module solves the problem of the high floor space requirement of a counter-flow absorber, new challenges arise in connection with gas conveyance and particle separation. For example, conveying the carbon dioxide-containing gas stream upstream of the packing and separating unwanted particles downstream of it requires the entire inflow area of ​​a cross-flow absorber to be covered, which requires a high level of material and component input.In order to take this problem into account, the absorption step of the process according to the invention particularly preferably additionally comprises the removal of the carbon dioxide-depleted gas stream in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream during absorption and in a direction opposite to the flow direction of the liquid sorbent during absorption.In such a constellation, a device configured to carry out the method according to the invention consequently comprises an absorber which, in addition to the above-mentioned components, further comprises means for continuously bringing the carbon dioxide-containing gas stream into contact with the liquid sorbent using the cross-flow principle and optionally means for discharging the carbon dioxide-depleted gas stream from the absorber in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream in the absorber and a direction opposite to the flow direction of the liquid sorbent in the absorber, wherein the expression "in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream during absorption" as used herein includes both a right angle of 90° and a deviation of ± 20° from the right angle.Preferably, the deviation from the right angle is in the range of ± 10°.

[0051] In a case in which the carbon dioxide-depleted gas stream is discharged in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream during absorption and opposite to the flow direction of the liquid sorbent during absorption, it is further preferred that the carbon dioxide-depleted gas stream be sucked out of the absorber in a suitable manner. For this purpose, the absorber can be configured such that it is uniformly supplied with carbon dioxide-containing gas over its entire surface area (i.e., the carbon dioxide-containing gas is sucked in over the entire surface area) and simultaneously enables efficient removal of the carbon dioxide-depleted gas.In practice, this is preferably achieved by the means for discharging the carbon dioxide-depleted gas stream from the absorber comprising a gas duct and a fan connected to the gas duct, the gas duct being spatially arranged around the longitudinal axis of the absorber, and the gas duct being enclosed by the means for continuously bringing the carbon dioxide-containing gas stream into contact with the liquid aqueous sorbent in a cross-flow manner. By spatially arranging the gas duct around the longitudinal axis of the absorber, a narrowing of the cross-section is also achieved, which results in a low flow velocity at the inlet and a high flow velocity at the outlet of the absorber and, due to a longer residence time of the carbon dioxide-containing gas stream in the absorber, reduces pressure losses, among other things, and improves the absorption capacity of the liquid sorbent.

[0052] In order to absorb large amounts of carbon dioxide, a large phase interface is also advantageous, for which random packings or packings are generally used in combination with spray nozzles or distribution channels. While spray nozzles consume a great deal of energy due to the upstream pressure, distribution channels tend to result in an inhomogeneous distribution of the scrubbing liquid. By passing the liquid sorbent through a perforated plate with suitable perforations arranged above the reaction chamber before contacting it with the carbon dioxide-containing gas stream, an extremely homogeneous distribution of the scrubbing liquid can be achieved with minimal energy consumption. Accordingly, the absorption step of the process according to the invention preferably further comprises passing the liquid sorbent through a perforated plate to control the spray density of the liquid sorbent before contacting it with the carbon dioxide-containing gas stream.In such a constellation, a device configured to carry out the method according to the invention consequently comprises an absorber which, in addition to the above-mentioned components, further comprises a perforated plate for controlling the sprinkling density of the liquid sorbent in the absorber.

[0053] As mentioned above, the desorption step may comprise continuously heating the carbon dioxide-loaded liquid sorbent to a temperature elevated relative to ambient temperature. In a case where the desorption step involves continuously heating the carbon dioxide-loaded liquid sorbent to a temperature elevated relative to ambient temperature, providing the temperature elevated relative to ambient temperature preferably comprises transferring heat energy from the liquid sorbent of the desorption step to the carbon dioxide-loaded liquid sorbent of the absorption step.In such a configuration, a device configured to carry out the method according to the invention therefore further comprises, in addition to the aforementioned components, a means connected to the absorber and the desorber for transferring thermal energy from the absorber to the desorber, wherein the means is preferably a high-temperature heat pump. The transfer of thermal energy using a high-temperature heat pump enables both active cooling of the liquid sorbent in the sump of the absorber and energy-efficient heating of the carbon dioxide-laden liquid sorbent in the desorber. By actively removing the heat introduced into the absorber, the liquid sorbent's capacity to absorb carbon dioxide increases, while simultaneously reducing the evaporation rate of the liquid solvent.On the other hand, by exploiting the Joule-Thompson effect, the heat for the desorption step can be provided much more efficiently than if the heating were done purely electrically.

[0054] In a case in which the desorption step comprises continuously passing the carbon dioxide-laden liquid sorbent through an atmosphere having a carbon dioxide partial pressure reduced compared to normal pressure, providing the carbon dioxide partial pressure reduced compared to normal pressure preferably comprises reducing the absolute pressure and / or mixing the carbon dioxide-laden liquid sorbent with at least one stripping gas, wherein the simultaneous reduction of the absolute pressure and mixing of the carbon dioxide-laden liquid sorbent with at least one stripping gas is considered particularly preferred.In such a configuration, a device configured to carry out the method according to the invention consequently comprises a desorber, which, in addition to the aforementioned components, further comprises means for reducing the absolute pressure and / or means for mixing the carbon dioxide-laden liquid sorbent with at least one stripping gas. By reducing the absolute pressure or setting a negative pressure specific to the respective location, the temperature required for evaporation of the liquid sorbent can be lowered, thus reducing the energy required for the desorption step. This allows, among other things, high-temperature heat pumps to be used as a heat source.Since the generation of negative pressure also consumes energy, the absolute pressure is preferably chosen such that an energetic optimum is achieved between the energy required for a pressure reduction and the energy saved by a temperature reduction.

[0055] Mixing the carbon dioxide-laden liquid sorbent with at least one stripping gas also reduces the carbon dioxide partial pressure at the phase interface. Stripping gases suitable for use in the process according to the invention, which can be introduced into the desorber in a device configured to carry out the process according to the invention via a stripping gas supply line connected to a second inlet opening of the desorber, are known in the art and include, among others, air, steam, hydrogen, and nitrogen. The stripping gas is preferably steam, hydrogen, nitrogen, or a mixture thereof, the advantage of using steam being that the water contained in the product gas stream can be condensed out without major difficulties.A disadvantage is the high evaporation enthalpy required for heating the liquid sorbent and for generating water vapor from liquid water. To address this problem, the process according to the invention particularly preferably further enables the transfer of thermal energy from the product gas stream of the desorption step to the liquid sorbent of the absorption step and / or to liquid water, which is to be supplied to the carbon dioxide-laden liquid sorbent in the form of water vapor as a stripping gas during the desorption step.In such a constellation, a device configured to carry out the method according to the invention comprises, in addition to the above-mentioned components, a means connected to the discharge line for carbon dioxide and the feed line for a liquid sorbent for transferring thermal energy from the product gas stream to the liquid sorbent (to be fed to the absorber), and / or a means connected to the discharge line for carbon dioxide and the feed line for stripping gas for transferring thermal energy from the product gas stream to liquid water, wherein the means is preferably a high-temperature heat pump. If hydrogen or nitrogen is used as stripping gas, the thermal energy required to generate steam is reduced. Furthermore, especially when coupling the method according to the invention with a downstream process such asIn a chemical reaction using synthesis gas, the appropriate ratio of carbon dioxide and stripping gas (especially hydrogen) can be set in advance depending on the type of downstream process, which significantly reduces the technical effort required for purification of the product gas stream.

[0056] In a case in which the provision of the carbon dioxide partial pressure reduced compared to normal pressure comprises mixing the carbon dioxide-laden liquid sorbent with at least one stripping gas, it is preferred that the at least one stripping gas is at least partially separated from the desorbed carbon dioxide after the desorption step and returned to the desorption step. In such a configuration, a device configured to carry out the method according to the invention consequently further comprises, in addition to the aforementioned components, a means connected to the carbon dioxide discharge line and the stripping gas supply line for at least partially separating stripping gas from the desorbed carbon dioxide, wherein the means is preferably a membrane.For example, the product gas stream obtained in the desorption step can be fed to a downstream condensate separator and / or a downstream membrane (if hydrogen or nitrogen is used as the stripping gas), where the stripping gas is separated from desorbed carbon dioxide and pumped back to the desorber via appropriately configured lines. In this way, stripping gas consumption can be effectively reduced, thus significantly reducing the costs of operating the continuously operated process for extracting carbon dioxide from a carbon dioxide-containing gas atmosphere.

[0057] Another possibility for reducing energy consumption in the desorption step is film evaporation of the liquid sorbent. Since the desorption of carbon dioxide occurs via a phase interface and requires an increase in temperature and / or a reduction in the carbon dioxide partial pressure, forming a thin film in the desorber can limit both the volume of gas and the volume of polyethyleneimine per phase interface, thereby reducing the energy required for desorption. Therefore, the desorption step of the process according to the invention preferably further comprises providing the carbon dioxide-laden liquid sorbent as a film with a film thickness of less than 3 mm, and particularly preferably less than 1 mm.In such a constellation, a device configured to carry out the method according to the invention consequently comprises a desorber which, in addition to the above-mentioned components, further comprises a means for providing the liquid sorbent loaded with carbon dioxide as a film with a film thickness of less than 1 mm, wherein the means is preferably a thin-film evaporator.

[0058] In addition to the absorption step and the desorption step, the process according to the invention can comprise one or more additional steps, such as a filtration step, a pre-wash step, a gas conditioning step, and a control step. To protect the liquid sorbent used in the absorption step from coarse contamination and thus from an undesirable reduction in absorption capacity, the process according to the invention preferably further comprises a filtration step, which involves filtering the carbon dioxide-containing gas stream prior to the absorption step.In such a constellation, a device configured to carry out the method according to the invention therefore further comprises, in addition to the above-mentioned components, a means for filtering the carbon dioxide-containing gas stream, which means is connected to the feed line for a carbon dioxide-containing gas stream and the first inlet opening of the absorber, wherein the means is preferably a dust or pollen filter which prevents the entry of coarse impurities into the washing liquid.

[0059] In a process for the continuous recovery of carbon dioxide, which is based on the use of an aqueous sorbent and generally uses demineralized water (DE water) as the liquid solvent to protect against deposits, the carbon dioxide-containing gas stream becomes almost 100% saturated with water. This results in the discharge of water from the scrubbing liquid, which must be replenished accordingly. To counteract this problem, the process according to the invention preferably further comprises a pre-washing step, which involves pre-washing the carbon dioxide-containing gas stream with water before the absorption step, wherein the water is preferably decalcified water.In such a configuration, a device configured to carry out the method according to the invention comprises, in addition to the aforementioned components, a means for pre-washing the carbon dioxide-containing gas stream with water, which means is connected to the supply line for a carbon dioxide-containing gas stream and the first inlet opening of the absorber or is integrated into the absorber. The means is preferably a gas pre-washer. The gas pre-wash achieves both a reduction in the amount of deionized water required and an additional filter function, and can be maintained by cyclical replacement of the washing liquid.

[0060] To compensate for water losses due to saturation of the carbon dioxide-containing gas stream with water during the absorption step, the process according to the invention may alternatively comprise a gas conditioning step which comprises recovering liquid solvent from the carbon dioxide-depleted gas stream after the desorption step and humidifying the carbon dioxide-containing gas stream with the recovered liquid solvent before the absorption step.In such a configuration, a device configured to carry out the method according to the invention comprises, in addition to the aforementioned components, a means connected to the supply line for a carbon dioxide-containing gas stream and the discharge line for a carbon dioxide-depleted gas stream for recovering liquid solvent from the carbon dioxide-depleted gas stream and for humidifying the carbon dioxide-containing gas stream with the recovered liquid solvent, wherein the means is preferably a sorption wheel. If the supply air and the exhaust air of the absorber are connected to one another via a sorption wheel or a rotary dehumidifier, not only heat but also moisture can be transferred, since the sorption wheel is coated with a hygroscopic material such as silica gel or zeolite.Compared to the use of a gas pre-scrubber described above, a sorption wheel also offers the advantage that not only the amount of demineralized water used but also the overall water consumption of the device can be reduced.

[0061] The invention is described in more detail below using some concrete embodiments.

[0062] Examples

[0063] Example 1

[0064] Fig. 1 shows a schematic representation of an apparatus for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a first embodiment of the present invention. Based on known DAC processes, an aqueous sorbent comprising polyethyleneimine is brought into contact with ambient air in an absorber designed as a gas scrubber using the countercurrent principle. The air flow through the absorber is achieved by means of a blower. A dust or pollen filter installed upstream of the blower prevents the ingress of coarse contaminants into the aqueous sorbent. In the absorber, the phase interface between the aqueous sorbent and the air is increased by the use of packing or bed material.The carbon dioxide-laden aqueous sorbent is conveyed to the desorber by means of a feed pump, where it is heated and the carbon dioxide is desorbed. The still-moist carbon dioxide is treated in a downstream process step (not shown) by dehumidification using a condensate separator. The regenerated aqueous sorbent is returned from the desorber to the absorber, where it is once again available to absorb carbon dioxide. The carbon dioxide-depleted air is removed from the absorber and removed from the system.

[0065] Example 2

[0066] Fig. 2 shows a schematic representation of a device for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a second embodiment of the present invention. In addition to the components mentioned in Example 1, the device further includes a high-temperature heat pump connected to the absorber and the desorber, which transfers heat energy from the absorber to the desorber, thus enabling both active cooling of the aqueous sorbent in the absorber sump and energy-efficient heating of the carbon dioxide-laden aqueous sorbent in the desorber.

[0067] Example 3

[0068] Fig. 3 shows a schematic representation of a device for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a third embodiment of the present invention. In addition to the components mentioned in Example 2, the device further comprises a second high-temperature heat pump connected only to the desorber, which transfers thermal energy from the carbon dioxide removed from the desorber to liquid water, thus enabling both active cooling of the desorbed carbon dioxide and energy-efficient generation of the water vapor supplied to the desorber as stripping gas. Since the second high-temperature heat pump operates at a comparatively high temperature level, the high-temperature heat pump can be operated with greater efficiency than the high-temperature heat pump described in Example 2.

[0069] Example 4

[0070] Fig. 4 shows a schematic representation of a device for the continuous extraction of carbon dioxide from a carbon dioxide-containing atmosphere according to a fourth embodiment of the present invention. In addition to the components mentioned in Example 1, the device further includes an upstream gas pre-scrubber integrated into the absorber, in which the air pre-cleaned by the dust or pollen filter is saturated with decalcified water and simultaneously freed from further contaminants. An additionally integrated droplet separator or demister prevents entrainment losses of the scrubbing water from the gas pre-scrubber into the actual absorber.

[0071] Example 5

[0072] Fig. 5 shows a schematic representation of a device for the continuous extraction of carbon dioxide from a carbon dioxide-containing atmosphere according to a fifth embodiment of the present invention. In addition to the components mentioned in Example 1 (and instead of the gas pre-scrubber described in Example 4), the device includes a sorption wheel, which uses energy to transfer heat and moisture from the carbon dioxide-depleted air discharged from the absorber to the carbon dioxide-containing air supplied to the absorber, thus reducing the overall water consumption of the device.

[0073] Example 6

[0074] Fig. 6 shows a schematic partial representation of a device for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a sixth embodiment of the present invention. In addition to the components mentioned in one of Examples 1 to 5, the device includes a condensate separator for dehumidifying the carbon dioxide discharged from the desorber, as well as a membrane module downstream of the condensate separator for at least partially separating hydrogen from the dehumidified carbon dioxide. A mixture of carbon dioxide and hydrogen obtained in this way can be fed to a downstream process as synthesis gas, while the hydrogen separated by means of the membrane module circulates and is reintroduced into the desorber as stripping gas.

[0075] Example 7

[0076] Fig. 7 shows a schematic partial representation of a device for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere according to a seventh embodiment of the present invention. In addition to the components mentioned in one of Examples 1 to 5, the device includes a condensate separator for dehumidifying the carbon dioxide discharged from the desorber, as well as a membrane module downstream of the condensate separator for at least partially separating nitrogen from the dehumidified carbon dioxide. A mixture of carbon dioxide and nitrogen obtained in this way can be fed to a downstream process, while the nitrogen separated by means of the membrane module circulates and is reintroduced into the desorber as stripping gas.

[0077] Example 8

[0078] Fig. 9 shows a cross-section through a cross-flow absorber as an embodiment of an absorber which can be used in a device according to the invention for the continuous extraction of carbon dioxide from a carbon dioxide-containing atmosphere. The cross-flow absorber draws in air via the side surfaces with the aid of a fan (2) arranged centrally above an extraction duct (1), which air then passes through the packing (3) in cross-flow to the aqueous sorbent. To prevent the ingress of contaminants into the absorber and the discharge of water from the absorber, both fins (4, 5) and a pollen filter (6) are arranged upstream of the packing (3). A demister (7) at the absorber outlet prevents particles from being discharged into the environment.The aqueous sorbent, which is circulated by a circulation pump (8), is fed via a sorbent distributor (9) at the upper end of the packing and is collected centrally at the lower end by a sorbent sump (10).

[0079] The cross-flow absorber shown in Fig. 9 can, for example, be provided with a circular base area (see Fig. 10), with an octagonal or polygonal base area (see Fig. 11), or with a rectangular base area (see Fig. 12). It offers, among other advantages, that it is evenly supplied with air over its entire surface area and, thanks to the central extraction duct, simultaneously enables efficient removal of the carbon dioxide-depleted air using at least one fan. Due to the design described above, the number of fans can be kept small in relation to the inflow area, meaning that the desired extraction effect can be achieved either with a single large, powerful fan or with a few medium-sized fans.By keeping the number of fans small, both the production costs and the maintenance costs of the cross-flow absorber are reduced.

[0080] By providing a central suction channel arranged spatially around the longitudinal axis of the absorber, a narrowing of the cross-section is also achieved, resulting in a low flow velocity at the inlet and a high flow velocity at the outlet of the absorber. This reduces pressure losses due to the longer residence time of the carbon dioxide-containing air in the absorber and improves the absorption capacity of the aqueous sorbent as well as the separation efficiency of the demister. With regard to the demister, it is important to note that higher flow velocities generally correlate with better separation efficiency, but excessive flow velocity should be avoided for energy reasons. By widening the cross-section of the suction channel at the outlet, the flow velocity of the air in the demister can be designed to an energetically reasonable level while simultaneously achieving good separation efficiency.Further advantages of the cross-flow absorber described above include: energetically efficient use of the available floor space, as the shell surface provides a very large inflow area for air; use of natural air movements independent of the prevailing wind direction, as the shell can be exposed to airflow from all sides; modularization by "planking" a basic structure with a standardized element with a rectangular or polygonal base area; relatively simple and cost-effective production, as a gap- or annular gap-shaped design of the absorber is less material-intensive; and easy and cost-effective scalability.

[0081] Example 9

[0082] Fig. 13 shows a cross-section through a thin-film evaporator as an embodiment of a desorber that can be used in a device according to the invention for the continuous recovery of carbon dioxide from a carbon dioxide-containing atmosphere. The thin-film evaporator is configured such that the carbon dioxide-laden aqueous sorbent obtained from the absorber is provided as a film with a film thickness of less than 1 mm and brought into contact with stripping gas. In this way, both the volume of gas and the volume of polyethyleneimine per phase interface can be limited, thereby reducing the energy required for desorption in the desorber.

Claims

Patent claims 1. A process for the continuous recovery of carbon dioxide from a carbon dioxide-containing gas atmosphere, comprising the following steps: (a) an absorption step comprising continuously contacting a carbon dioxide-containing gas stream with a liquid sorbent in countercurrent or cross-current flow at ambient temperature and under atmospheric pressure, whereby the liquid sorbent absorbs carbon dioxide and forms a carbon dioxide-laden liquid sorbent and a carbon dioxide-depleted gas stream; and (b) a desorption step which comprises continuously heating the carbon dioxide-laden liquid sorbent to a temperature higher than ambient temperature and / or continuously passing the carbon dioxide-laden liquid sorbent through an atmosphere with a carbon dioxide partial pressure lower than normal pressure, wherein the carbon dioxide-laden liquid sorbent desorbes carbon dioxide and regenerates the liquid sorbent, wherein the liquid sorbent comprises polyethyleneimine.

2. A process according to claim 1, wherein the carbon dioxide-containing gas atmosphere does not comprise flue gas.

3. A process according to claim 1 or 2, wherein the carbon dioxide-containing gas atmosphere is ambient air.

4. A process according to any one of claims 1 to 3, wherein the polyethyleneimine is branched polyethyleneimine.

5. The process according to any one of claims 1 to 4, wherein the polyethyleneimine has a number-average molecular weight of 1,000 to 200,000 g / mol.

6. A process according to any one of claims 1 to 5, wherein the absorption step comprises continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a cross-flow manner.

7. A process according to any one of claims 1 to 6, wherein the absorption step comprises continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a cross-flow manner and discharging the carbon dioxide-depleted gas stream in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream during absorption and opposite to the flow direction of the liquid sorbent during absorption.

8. The method according to any one of claims 1 to 7, wherein providing the elevated temperature relative to ambient temperature comprises transferring heat energy from the liquid sorbent of the desorption step to the carbon dioxide-laden liquid sorbent of the absorption step.

9. The method according to any one of claims 1 to 8, wherein providing the carbon dioxide partial pressure reduced compared to normal pressure comprises reducing the absolute pressure and / or mixing the carbon dioxide-laden liquid sorbent with at least one stripping gas.

10. The method according to claim 9, wherein the at least one stripping gas is steam, hydrogen, nitrogen or a mixture thereof.

11. The method according to claim 9 or 10, wherein the at least one stripping gas is at least partially separated from the desorbed carbon dioxide after the desorption step and recycled to the desorption step.

12. The process according to any one of claims 1 to 11, further comprising a filtration step which comprises filtering the carbon dioxide-containing gas stream prior to the absorption step.

13. The method according to any one of claims 1 to 12, further comprising a pre-washing step which comprises pre-washing the carbon dioxide-containing gas stream with water before the absorption step, wherein the water is preferably decalcified water.

14. A process according to any one of claims 1 to 12, further comprising a gas conditioning step which comprises recovering liquid solvent from the carbon dioxide-depleted gas stream after the desorption step and humidifying the carbon dioxide-containing gas stream with the recovered liquid solvent before the absorption step.

15. The method according to any one of claims 1 to 14, wherein the absorption step further comprises passing the liquid sorbent through a perforated plate to control the sprinkling density of the liquid sorbent prior to contacting it with the carbon dioxide-containing gas stream.

16. The method according to any one of claims 1 to 15, wherein the desorption step further comprises providing the carbon dioxide-loaded liquid sorbent as a film having a film thickness of less than 3 mm.

17. Apparatus for the continuous extraction of carbon dioxide from a carbon dioxide-containing gas atmosphere, comprising the following components: (a) a supply line for a gas stream containing carbon dioxide; (b) a supply line for a liquid solvent; (c) a supply line for a liquid sorbent; (d) a discharge line for a gas stream depleted in carbon dioxide; (e) a discharge line for a liquid sorbent loaded with carbon dioxide; (f) a carbon dioxide discharge line; (g) an absorber having at least one first inlet opening connected to the feed line for a carbon dioxide-containing gas stream, a second inlet opening connected to the feed line for a liquid solvent, a third inlet opening connected to the feed line for a liquid sorbent, means for continuously bringing the carbon dioxide-containing gas stream into contact with the liquid sorbent in countercurrent or crosscurrent mode at ambient temperature and under atmospheric pressure to form the carbon dioxide-laden liquid sorbent and the carbon dioxide-depleted gas stream, a first outlet opening connected to the discharge line for a carbon dioxide-depleted gas stream, and a a second outlet opening connected to a discharge line for a liquid sorbent loaded with carbon dioxide; and (h) a desorber comprising at least one first inlet opening connected to the discharge line for a liquid sorbent loaded with carbon dioxide, means for continuously heating the liquid sorbent loaded with carbon dioxide to a temperature elevated relative to ambient temperature and / or means for continuously passing the liquid sorbent loaded with carbon dioxide through an atmosphere with a carbon dioxide partial pressure reduced relative to normal pressure for desorption of carbon dioxide and regeneration of liquid sorbent, a first outlet opening connected to the supply line for a liquid sorbent, and a second outlet opening connected to the discharge line for carbon dioxide; wherein the liquid sorbent comprises polyethyleneimine.

18. Apparatus according to claim 17, wherein the absorber comprises means for continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a cross-flow manner.

19. Apparatus according to claim 17 or 18, wherein the absorber comprises means for continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a cross-flow manner and further comprises means for discharging the carbon dioxide-depleted gas stream from the absorber in a direction substantially perpendicular to the flow direction of the carbon dioxide-containing gas stream in the absorber and opposite to the flow direction of the liquid sorbent in the absorber.

20. Apparatus according to claim 19, wherein the means for discharging the carbon dioxide-depleted gas stream from the absorber comprise a gas duct and a fan connected to the gas duct, the gas duct is spatially arranged around the longitudinal axis of the absorber, and the gas duct is enclosed by the means for continuously contacting the carbon dioxide-containing gas stream with the liquid sorbent in a cross-flow manner.

21. Apparatus according to any one of claims 17 to 20, further comprising a means connected to the carbon dioxide discharge line and a stripping gas supply line for at least partially separating stripping gas from the desorbed carbon dioxide, wherein the means is preferably a membrane.

22. Apparatus according to any one of claims 17 to 21, further comprising a means connected to the supply line for a carbon dioxide-containing gas stream and the discharge line for a carbon dioxide-depleted gas stream for recovering liquid solvent from the carbon dioxide-depleted gas stream and for humidifying the carbon dioxide-containing gas stream with the recovered liquid solvent, wherein the means is preferably a sorption wheel.

23. Use of a liquid solution of polyethyleneimine for the continuous recovery of carbon dioxide from a gas atmosphere containing carbon dioxide.

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