Integrated processs and systems for production of fuels from carbon dioxide

Abstract

A system or process for the production of a sustainable paraffinic fuel is provided. A gaseous feed comprised of a carbon dioxide rich feedstock, and a liquid feed comprised of an aqueous feedstock, are used as an input for a carbon dioxide electrolysis unit. The carbon dioxide electrolysis unit comprises an anionic exchange membrane (AEM), a cationic exchange membrane (CEM, or a bipolar membrane, and further comprises at least cathodic and anodic output streams. The cathodic output stream comprises an ethylene product and is coupled to one or more units for the production of a sustainable paraffinic fuel. The sustainable paraffinic fuel may comprise synthetic kerosene and / or naphtha for use in sustainable aviation fuel.

Description

Field of the Invention

[0001] This invention relates to systems and methods for producing sustainable paraffinic fuels from waste gaseous carbon dioxide.Background of the invention

[0002] The aviation industry currently accounts for almost 3% of worldwide greenhouse gas (GHG) emissions.Given its inherent operational features, the aviation sector requires fuels with high specific energy and energy density. This technical requirement limits electrical propulsion technology to niche aviation segments such as low capacity and short-range aircraft.

[0003] Sustainable Aviation Fuel (SAF) is a type of jet fuel derived from sustainable sources that can significantly reduce the carbon footprint of a major part of the aviation industry compared to conventional petroleum-based fossil fuels. SAF is designed to be a drop-in replacement for traditional jet fuel, meaning it can be used in existing aircraft engines and infrastructure without modifications. This compatibility is crucial as it allows airlines to transition to more sustainable practices without extensive overhauls to their current operations. Additionally, SAF can meet the same specifications as kerosene or naphtha-type conventional jet fuels including Jet A, Jet A-1, JP-5 and JP-8 (kerosene type), or Jet B and JP-4 (naphtha-type). SAF can also be blended with traditional jet fuel, ensuring seamless integration into current systems.

[0004] Currently there are several pathways to produce SAF, each utilizing different feedstocks and processes. One common method is Hydroprocessed Esters and Fatty Acids (HEFA), which uses used biomass derived oils, animal fats, algal oils and other non-fossil derived lipids. These lipids are hydroprocessed to remove oxygen and create hydrocarbons, similar to those found in jet fuel, resulting in hydroprocessed renewable jet (HRJ) fuel.

[0005] Another method is Fischer-Tropsch (FT) Synthesis, which can use biomass, municipal solid waste, or waste gases as feedstock. The feedstock is gasified to produce a synthesis gas, or syngas, (a mixture of hydrogen and carbon monoxide), which is then converted into liquid hydrocarbons through the Fischer-Tropsch process, producing FT synthetic paraffinic kerosene (FT-SPK).

[0006] Power-to-Liquid (PtL) utilizes renewable electricity, water, and carbon dioxide (CO 2 ) to produce hydrogen and carbon monoxide (CO) combined into a syngas, or other intermediates such as methanol. Carbon dioxide may be captured from various sources, including exhaust from industrial processes and direct air capture (DAC). Capturing carbon dioxide is essential not only for producing hydrocarbons but also for mitigating greenhouse gas emissions by repurposing carbon dioxide that would otherwise be released into the atmosphere. The Reverse Water-Gas Shift (RWGS) reaction powered by renewable electricity can be used, where carbon dioxide reacts with hydrogen (H 2 ) to produce carbon monoxide (CO) and water (H 2 O). The carbon monoxide may be combined with the hydrogen to form a syngas that can be processed via Fischer-Tropsch (FT) synthesis to produce PtL synthetic paraffinic products. This synthesis takes place under high temperature and pressure, using a catalyst to facilitate the conversion. The outcome is a mixture of hydrocarbons that can be refined into various fuels, including synthetic paraffinic kerosene (SPK) suitable for aviation.

[0007] Whilst PtL can contribute to a circular carbon economy it also faces challenges. The process is highly energy-intensive, requiring substantial amounts and a stable supply of renewable electricity. Currently, PtL is more expensive than traditional fossil fuel-based processes due to the high costs and intermittent nature of renewable electricity.

[0008] Berkelaar et al. (Chemical Engineering Research and Design 182(2022)194-206) assesses a variety of approaches for the design of an electrochemical production facility to convert carbon dioxide into ethylene at scale. The authors selected the most promising routes based on Faradaic efficiency, current density, overpotential, and material availability. Berkelaar et al. favoured an electrochemical device, in which carbon dioxide and water are reacted to syngas. In a sequential reactor, the syngas-to-methanol reaction is carried out and a methanol-to-olefins reaction, followed by a separation train, resulting in ethylene, propylene, and, in lower quantities, higher olefins. Direct electrochemical production of ethylene from carbon dioxide and water was rejected as commercially non-viable due to apparent low Faradaic conversion efficiency.

[0009] Environmentally, SAF offers the potential for a significant reduction in greenhouse gas emissions, contributing to climate change mitigation. From an energy security perspective, SAF reduces dependence on fossil fuels and promotes the use of locally available resources. For the aviation industry, SAF supports the commitment to reducing its carbon footprint and achieving sustainability goals, ensuring the viability of the industry in an increasingly eco-conscious market. Hence, it would be desirable to provide alternative routes for production of SAF.

[0010] These and other objectives of the invention will become apparent to the skilled reader, providing a solution to these hitherto unmet needs.Summary of the Invention

[0011] The present invention provides in a first aspect a system for the production of a sustainable paraffinic fuel, the system comprising: a gaseous feed comprised of a carbon dioxide rich feedstock, and a liquid feed comprised of an aqueous feedstock, the gaseous and liquid feeds being in providing an input for a carbon dioxide electrolysis unit, wherein the carbon dioxide electrolysis unit comprises at least one of an anionic exchange membrane (AEM), a cationic exchange membrane (CEM), or a bipolar membrane, and further comprises at least cathodic and anodic output streams, wherein the cathodic output stream comprises an ethylene product; and wherein the cathodic output stream is coupled to one or more synthetic units for the production of a sustainable paraffinic fuel.

[0012] In a second aspect the invention provides a process for the production of a sustainable paraffinic fuel, the process comprising undertaking an electrochemical conversion of a gaseous carbon dioxide feedstock in an electrolysis unit, in order to produce a gaseous product that comprises ethylene as a major component, and using the ethylene as a feedstock in a paraffin synthetic process, wherein the electrolysis unit is powered by a source of renewable electricity and wherein the gaseous carbon dioxide feedstock comprises carbon dioxide obtained from industrial exhaust gas, biogenic source or from direct air capture (DAC).

[0013] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible.Brief Description of the Drawings

[0014] Figure 1 is a diagram showing a system line up for the production of sustainable paraffinic fuels through the electrochemical conversion of carbon dioxide to ethylene according to a first embodiment of the invention that utilises an acidic electrolysis system that utilises an electrolysis unit having a cationic exchange membrane; Figure 2 shows an embodiment of a system incorporating that of Figure 1 that includes additional components for the isolation and recycling of various by-product streams; Figure 3 is a diagram showing a system line up for the production of sustainable paraffinic fuels through the electrochemical conversion of carbon dioxide to ethylene according to a further embodiment of the invention that uses an alkaline system that utilises an electrolysis unit having an anionic exchange membrane; Figure 4 shows an embodiment of a system incorporating that of Figure 3 that includes additional components for the isolation and recycling of various by-product streams; Figure 5 shows an alternative embodiment of a system that includes additional components for the isolation and recycling of various by-product streams and utilises an electrolysis unit having a bipolar membrane carbon dioxide electrolyser system. Detailed Description of the Invention

[0015] All references cited herein are incorporated by reference in their entirety. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0016] Prior to setting forth the invention, a number of definitions are provided that will assist in the understanding of the invention.

[0017] As used herein, the term 'comprising' means any of the recited elements are necessarily included and other elements may optionally be included as well. 'Consisting essentially of' means any recited elements are necessarily included, elements that would materially affect the basic and novel characteristics of the listed elements are excluded, and other elements may optionally be included. 'Consisting of' means that all elements other than those listed are excluded. Embodiments defined by each of these terms are within the scope of this invention.

[0018] The terms 'feed', 'feedstock' or 'feedstream' should be considered as synonymous. These terms relate to at least one input material or substance that is introduced into an electrolytic cell or a reactor and which is destined for chemical conversion into at least one output stream either in the form of a reaction product that contributes to the yield, or as a byproduct such as a waste stream.

[0019] As used herein, the term 'renewable energy source' generally refers to one or more technologies that utilize replenishable energy sources such as energy from water, wind, the sun, geothermal sources, and biomass sources such as energy crops. Such renewable energy sources may include without limitation, a wind generator, a solar panel array, solar panel strings, wind turbines, hydroelectric power stations that utilize hydroelectricity and hydropower, solar panels (including solar photovoltaic technology, solar thermal collectors, solar assisted heat pumps and / or solar concentrator technologies), solar arrays (e.g. arrays of solar panels), cogeneration plants that utilize biomass materials, biofuels, biodiesels, geothermal energy, and a combination thereof. Renewable electrons (e -< ) are, thus, components of an electricity power supply that is derived from a renewable energy source.

[0020] Typically, an electricity supply may be derived from an electrical grid. As used herein the term 'electrical grid' or 'grid supply' relates to a system for distributing electrical power. As an integrated network, the electricity grid power system comprises a plurality of interconnected components, including but not limited to generators, transformers, transmission lines, and distribution networks. The primary objective of the electricity grid power system is to facilitate the efficient and reliable transmission of electric energy, especially that produced from renewable sources, to end-use applications of the type described herein. Suitably, power grid management may include the capacity for bidirectional power flow, real-time monitoring and various other control mechanisms.

[0021] An 'electrolysis unit' is used synonymously with the terms 'electrolyser' or 'electrolytic cell'. In the context of the present invention electrolysers may be used to achieve electrochemical reduction of feedstocks such as carbon dioxide and / or water. In general, an electrolyser uses electricity to drive an otherwise non-spontaneous chemical reaction. The electricity may comprise renewable electrons and be connected to a grid supply.

[0022] An electrolysis unit for the electrolysis of carbon dioxide (carbon dioxide) is designed to convert carbon dioxide into useful chemical products, typically ethylene, using electrical energy, usually electrical energy from renewable sources. This process involves the following reaction, expressed below in acidic form:         2CO 2 + 12H +< + 12e → C 2 H 4 + 4H 2 O However, if the reaction is performed in alkaline media, so as to be consistent with the prevailing pH conditions the reaction may be expressed as:         2CO 2 + 8H 2 O + 12e → C 2 H 4 + 12OH Low-temperature (i.e. <100 degrees Celsius) electrolysis allows for reduced operating costs compared to competing high-temperature (700-900 degrees Celsius) solid-oxide-based carbon dioxide electrolysis.

[0023] The unit comprises two electrodes - an anode (positive) and a cathode (negative) - immersed in an electrolyte solution or solid electrolyte medium. When current is applied, carbon dioxide molecules are reduced at the cathode, forming carbon monoxide and / or other carbon-based products such as ethylene (C 2 H 4 ), while oxygen is released at the anode. This technology is significant for carbon capture and utilization (CCU) efforts, transforming carbon dioxide, for example, from industrial emissions or direct air capture (DAC) into valuable chemicals and green fuels.

[0024] As described, carbon dioxide can be converted into ethylene directly via electrochemical processes. Ethylene represents a core synthetic building block for downstream products that include fuels, and particularly the components of SAF. A variety of reduction reactions of carbon dioxide exist that form intermediate compounds for the production of ethylene. Besides direct electrochemical conversion of carbon dioxide into ethylene, electrochemical conversion into ethanol or reduction of carbon dioxide to carbon monoxide or to methanol are alternatives for the electrochemical step of directly upgrading carbon dioxide to ethylene. Approaches that utilise methanol or ethanol as intermediates in the production of SAF are referred to as alcohol-to-jet processes.

[0025] In the direct electrochemical conversion of carbon dioxide to ethylene, carbon dioxide is fed along with water to an electrochemical cell (also referred to as an 'electrolyser unit') where carbon dioxide is converted into C 2 + products including predominantly ethylene and ethanol at the cathode surface. An oxygen evolution reaction (OER) takes place at the anode surface. One advantage of this approach is the production of ethylene in a single electrochemical device, thereby reducing the equipment count in the process line-up for SAF production and, hence, minimizing the capital costs.

[0026] The direct conversion of carbon dioxide to ethylene can take place in three main different electrochemical cell configurations: 1. Acidic 2. Alkaline 3. Bipolar Membrane Cell

[0027] A number of reactions can occur during the process of electrochemical reduction of carbon dioxide. These reactions are summarised below in Table 1. Table 1 - main reactions occurring within an electrochemical cellProducts Reaction Nernst Potential [V] Ethylene2CO2+2H2O → C2H4+3O21.15Ethanol2CO2+3H2O → C2H5OH+3O21.14Carbon MonoxideCO2 → CO+0.5O21.33HydrogenH2O → H2+0.5O21.23Formic acidCO2+H2O → HCOOH+0.5O21.34MethaneCO2+2H2O → CH4+2O21.06

[0028] In an acidic system using acidic media, iridium (IV) oxide (IrO 2 ) is typically used as a catalyst for the anode reaction. Due to its scarcity IrO 2 can add to the expense of the system and the process. However, cross-over of carbon dioxide from cathode to anode side can be controlled due to presence of a Cation Exchange Membrane (CEM) within the cell. Avoiding the cross-over of carbon dioxide allows acidic systems to achieve higher single pass conversion of carbon dioxide to Ca +< , such as ethylene, of up to 60-80%.

[0029] In alkaline systems, the oxygen evolution reaction is typically carried out using a nickel iron (NiFe) anode. This provides a significant cost advantage over acidic systems eliminating the need for rare or precious metals at the anode side. However, alkaline systems which use an anion exchange membrane (AEM) can be susceptible to carbon dioxide cross-over, where carbon dioxide reacts with hydroxide ions to form bicarbonate ions that cross over to the anode side where they are oxidised back to carbon dioxide and oxygen. The cross-over can lower the carbon dioxide conversion efficiency into useful products (the so-called Faradaic conversion efficiency) in alkaline setups as typically only 10-25% percent of the carbon dioxide is converted into products at the cathode whilst up to 90% may cross over crosses over to the anode. To mitigate this issue, Faradaic conversion efficiency can be enhanced by recycling produced carbon dioxide in the effluent back to the electrolyser. This can increase the overall costs of ethylene production slightly as it requires a step of separation of carbon dioxide from oxygen.

[0030] As shown in Table 1 (above), in addition to main synthetic reactions occurring during electrochemical reduction of carbon dioxide in alkaline media, there are also a range of side reactions that may contribute to formation of undesirable by-products mainly carbon monoxide, hydrogen and ethanol.

[0031] Bipolar membranes provide an alternative solution to AEM and CEM. The problem of cross-over is solved by using bipolar membrane which has CEM side facing the cathode side thus preventing the anions (carbonates and bicarbonates) crossing the membrane to the anode side. Instead, carbonates and bicarbonates remain at the CEM interface and are converted into carbon dioxide on the cathode side. The bipolar membrane also has an AEM on the anode-facing side, which permits the use of NiFe anode catalysts which avoid the need for rare metal catalysts such as iridium (IV) oxide (IrO 2 ) . The compromise with the use of bipolar membranes is that overpotential increases as a result of the thicker membrane configuration. In some circumstances BPM systems may operate at a higher electrical resistance when compared to acidic or alkaline systems.

[0032] In specific embodiments of the invention the electrolyser unit comprises an anion exchange membrane (AEM). The AEM provides an alkaline environment by transferring hydroxide (OH), carbonate (CO 3 2-< ) , and bicarbonate (HCO 3 -< ) to a lesser extent. A typical AEM should be permselective to anions and impermeable to cations (such as K +< or Na +< ). AEMs are generally comprised of a hydrophobic core polymer (e.g., polysulfone, polyphenylene or polystyrene) with added hydrophilic cationic functionalities (e.g., quaternary ammonium, alkylphosponium, pyridinium, or imidazolium), that are either comprised within the core polymer main chain (Fumasep ™< FAA-3, PiperIon ™< , Sustainion ™< , Aemion ™< ) or anchored as side chains. The availability of both a hydrophobic backbone and hydrophilic cations in the AEM usually contributes to a hydrophobic / hydrophilic phase segregated structure, where hydrophilic cationic species form ion and water-containing channels that assist in transporting the anions across the AEM. AEMs that have a high concentration of cationic species in the polymeric backbone can inhibit the migration of cations via electrostatic repulsion thereby increasing the impermeability of the membrane. An AEM based electrolyser unit according to the process line ups described herein can demonstrate conversion efficiency of carbon dioxide into ethylene of over 50% and up to as much as 75%.

[0033] The electrolytes commonly used in alkaline AEM systems may include but are not limited to potassium hydroxide (KOH), sodium hydroxide (NaOH) and caesium hydroxide (CsOH).

[0034] In an embodiment of the invention, the electrolyser unit receives inputs of gaseous carbon dioxide,liquid water, and where appropriate an electrolyte. Additional inputs may include recycled water and / or carbon monoxide that is produced in the electrolyser unit and recycled following downstream separation. The electrolyser unit is powered by renewable electricity and operates at a temperature of up to around 40 degrees Celsius, producing a mixture of products: including mainly ethylene, ethanol, propanol, oxygen, hydrogen and carbon monoxide along with other trace components. These products are output in separate product streams: (i) an anode stream, comprised mainly of gaseous components of oxygen, unreacted carbon dioxide, and liquid components of ethanol, water, trace side products (e.g. propanol, formates etc.); and (ii) a cathode stream, comprised mainly of gaseous ethylene, hydrogen, carbon monoxide, and minor amounts of liquid water and ethanol.

[0035] In certain instances, such as in alkaline systems where an AEM based electrolyser unit is used, there can be incomplete conversion of the carbon dioxide reactants by the electrolyser unit, hence, it is beneficial to separate the unreacted carbon dioxide from other gaseous products (e.g. O 2 ) and recycle it back to the upstream electrolytic process. Thus, the overall conversion of carbon dioxide can be increased. In embodiments of the invention a carbon dioxide separation / capture unit is provided downstream of an electrolyser unit that receives gaseous effluent from the anode side of the electrolytic cell (anode stream).

[0036] A carbon dioxide separation / capture unit may comprise a Pressure Swing Adsorption (PSA) unit, amine-based carbon dioxide capture or utilise cryogenic separation processes. In one embodiment the carbon dioxide capture unit comprise Amine-based Deep Absorption Process - eXtended (ADIP-X). An ADIP-X unit employs an advanced amine-based solvent that provides superior carbon dioxide absorption performance of greater than 90% capture compared to conventional amines (see Meerman et al. (2012) Int. J. Green. Gas. Cont. 9:160-171). The process involves the absorption of carbon dioxide in a contactor where the gaseous output stream from the electrolyser unit is treated with the ADIP-X solvent (a mixture of methyldiethanolamine and piperazine in water). The carbon dioxide-rich solvent is then regenerated in a stripper column, where the absorbed carbon dioxide is released and the lean solvent is recycled back to the contactor. This cyclic process ensures high carbon dioxide capture efficiency and solvent recovery. The carbon dioxide isolated from the cathode output stream and is recycled to an input of the electrolyser unit.

[0037] Liquid products from the anode and cathode streams may combined and comprise mainly ethanol and water, with some trace amounts of other products. This liquid stream may be subjected to distillation to separate volatile components, such as ethanol, from the water. Water may be recycled as an input to the electrolyser unit at any point in the system. Ethanol may be subjected to dehydration to form ethylene using conventional techniques within an ethanol dehydration unit. By way of non-limiting example, a catalytic dehydration of ethanol to form ethylene may be employed using an acid catalyst selected from: alumina, a transition metal oxide, silicoaluminophosphate (SAPO), HZSM-5 zeolite catalyst, and heteropolyacid catalysts (e.g. silicotungstic acid or tungstophosphoric acid).

[0038] Gaseous products from the cathode stream of the electrolyser unit comprise mainly ethylene, carbon monoxode and hydrogen. The cathode stream output mixture is directed to an ethylene separation unit in which ethylene is separated from the carbon monoxide and hydrogen. Ethylene can separated from the other gaseous components using various separation methods such as membranes, Cryogenic separation or Pressure Swing Adsorption (PSA). The separated pure ethylene output stream is directed for further synthetic processing. The remaining carbon monoxide / hydrogen containing stream may be utilised in a variety of different ways. Firstly, the carbon monoxide / hydrogen containing stream may be used as a syngas. Alternatively, the carbon monoxide / hydrogen containing stream can be recycled back to the electrolyser unit or can be further separated to obtain pure hydrogen as a product or reagent (i.e. for further use downstream) or can be oxidized within a gas turbine to obtain power or can be combined with oxygen / carbon dioxide anode stream to consume oxygen and obtain power. Power generated within the system can be used to supplement the renewable electricity supply. Exhaust carbon dioxide generated via oxidation / combustion may be recycled to the input of the electrolyser unit. In this way a circular carbon utilisation loop can be created.

[0039] Ethylene produced directly from the electrolyser unit and separated from other gaseous products may be combined with ethylene obtained from the dehydration of ethanol to provide a combined ethylene product stream. The ethylene product stream is available for a range of synthetic processes that may be employed to produce sustainable fuels, such as sustainable aviation fuel (SAF).

[0040] In an embodiment of the invention, the ethylene stream is used as a feedstock in an ethylene oligomerisation unit. The ethylene oligomerisation unit comprises a reactor vessel that is designed to convert ethylene into longer-chain hydrocarbons through a catalytic process. Nickel-based catalysts are widely used in the process of ethylene oligomerization. These catalysts are favoured due to their high activity and selectivity towards producing LAOs. The catalytic process typically involves the coordination of ethylene to the nickel centre, followed by a series of insertion steps that elongate the carbon chain. Nickel-based catalysts are efficient at operating under relatively mild conditions, which helps to lower energy costs and reduce the formation of undesirable by-products. By way of example, highly active α-diimine-nickel complexes, first disclosed by Brookhart in the late 1990s, have been used successfully for the formation of high molecular weight polyethylene. In addition, iron- and cobalt-based catalyst systems are also widely known in the art.

[0041] Suitably oligomerization may occur in two stages. Firstly, oligomerization (i.e., ethylene dimerization) may occur in the presence of a nickel catalyst is nickel deposited on a silico-aluminate support material with nickel loading of around 0.2 to 3 wt%. In a second stage of oligomerization, acidic catalysts such as silico-aluminates or solid acid catalysts such as Amerlyst-70 can be used to extend the chain length.

[0042] The product of the ethylene oligomerisation unit comprises a range of olefins in jet range which are transferred to a hydrogenation unit located downstream of the ethylene oligomerization unit. The hydrogenation unit performs catalytic hydrogenation of the olefins to produce a range of paraffinic products. The hydrogenation unit may comprise a plug-flow reactor comprising a supported hydrogenation catalyst. Typical catalysts may include platinum, palladium, rhodium, and ruthenium form highly active catalysts, which can operate at lower temperatures and lower pressures of hydrogen. Non-precious metal catalysts may include Raney nickel and Urushibara nickel, although these may require operating conditions with higher temperature (250 to 400 degrees Celsius) and pressures of hydrogen (around 20 to 40 bar).

[0043] The paraffin products of the hydrogenation unit may be subjected to fractionation via conventional methods to isolate desirable end products, including naphtha, diesel and kerosene. Hence, an advantage of the systems and processes described herein is a more direct and energy efficient route to the production of SAF components, such as synthetic paraffinic kerosene (SPK), from waste and atmospheric carbon dioxide.Detailed Description of the Drawings

[0044] Figure 1 shows a process line up for a system 100 according to a first embodiment of the invention. A source of carbon dioxide 101 is provided as a feedstock to an input for a CEM electrolyser unit 110. Water 102 is provided as additional input feedstock for the electrolyser unit 110. Gaseous product in the form of carbon monoxide, hydrogen and ethylene 111 exit the cathode side of the electrolyser unit 110 as a mixed product stream and are conveyed to an ethylene separation unit 120. Separately a liquid product stream comprising ethanol 112 is directed to an ethanol separation unit 130. Oxygen 184 is generated from the anode side of the electrolyser unit 110 and may be used as a product or vented to atmosphere. The liquid product stream is distilled within the ethanol separation unit 130, allowing for separated ethanol to be directed to a dehydration step within an ethylene conversion unit 140, whereas wastewater 131,141 is recycled to the electrolyser unit 110, or may be released as a bleed.

[0045] Ethylene separation occurs within the ethylene separation unit 120 allowing for carbon monoxide and hydrogen 122 to be diverted to a carbon monoxide purification unit 150 which is in gaseous communication with the ethylene separation unit 120. Separated carbon monoxide 152 is recycled to the electrolyser unit 110.

[0046] Ethylene 121 is conveyed to an ethylene oligomerisation unit 160. The product stream from the ethylene conversion unit 140 maybe combined with the ethylene product stream 121 prior to entry into the ethylene oligomerisation unit 160. Polymerisation reactions occur within the ethylene oligomerisation unit 160, as described previously herein, and products in form of olefins are conveyed to a hydrogenation unit 170. Hydrogen 151 obtained from the carbon monoxide purification unit 150 may be used as a full or partial feed for the hydrogenation unit 170. Hydrogenated products, typically in the form of a mixture of paraffins, are conveyed to the fractionation unit 180 where they are separated into product streams that may include naphtha 181, kerosene 182 and diesel 183. Naphtha 181 and kerosene 182 fractions may be used as blend components in the production of sustainable jet fuels.

[0047] In Figure 2 a process system line up 200 is provided that presents an alternative approach to the embodiments shown in Figure 1. A source of carbon dioxide 201 is provided as a feedstock to an input for an CEM electrolyser unit 210. Water 202 is provided as additional input feedstock for the electrolyser unit 210. Gaseous product in the form of carbon monoxide, hydrogen and ethylene 211 exit the cathode side of the electrolyser unit 210 as a mixed product stream and are conveyed directly to an ethylene oligomerisation unit 260. Oxygen 284 is generated from the anode side of the electrolyser unit 210 and may be used as a product or vented to atmosphere. Separately a liquid product stream comprising ethanol 212 is directed to an ethanol separation unit 230. The liquid product stream is distilled within the ethanol separation unit 230, allowing for separated ethanol to be directed to a dehydration step within an ethylene conversion unit 240, whereas wastewater 231,241 is recycled to the electrolyser unit 210, or may be released as a bleed. Downstream synthetic processing of the ethylene into paraffinic fuels is carried out substantially as described previously. Carbon monoxide and hydrogen within the mixed product stream 211 can passed through oligomerization 250 unreacted and are treated as inerts in the oligomerization reactor. Depending on the choice of oligomerization catalyst, small amounts of carbon monoxide may even exert a positive impact on oligomerization reactor yield.

[0048] Figure 3 provides a process system line up 300 that utilises an AEM based carbon dioxide electrolyser unit. This embodiment includes additional functionality for handling gaseous by-products of the AEM electrolyser unit 310 in the form of unreacted carbon dioxide as well as oxygen produced by the electrolysis of water. A mixed stream obtained from the anode side of the electrolyser unit comprises carbon dioxide and oxygen 313. This is conveyed to a carbon dioxide capture unit 390 where carbon dioxide is isolated as described elsewhere herein. A carbon dioxide recycle stream 391 is redirected to the input of the electrolyser unit 310 and may be combined with the carbon dioxide feedstream 301. Oxygen 392 separated within the carbon dioxide capture unit 390 may be used as a product or vented to atmosphere. Processing of the liquid and downstream products is substantially as described in relation to Figure 1.

[0049] Figure 4 provides a system line out that expands upon the embodiment shown in Figure 3 including equivalent processing capability. This embodiment of the invention includes additional functionality for handling gaseous by-products of the electrolyser unit 410 in the form of unreacted carbon dioxide and oxygen produced by the electrolysis reaction. A mixed stream obtained from the anode side of the electrolyser unit comprises carbon dioxide and oxygen 413. This is conveyed to a carbon dioxide capture unit 490 where carbon dioxide is isolated as described elsewhere herein. A carbon dioxide recycle stream 491 is redirected to the input of the electrolyser unit 410 and may be combined with the carbon dioxide feedstream 401. Oxygen 492 separated within the carbon dioxide capture unit 490 may be used as a product or vented to atmosphere.

[0050] Figure 5 shows an alternative system line up 500 to that shown in the other embodiments so far described. In this set up a source of carbon dioxide 501 is provided as a feedstock to an input for a bipolar membrane electrolyser unit 510. Water 502 is provided as additional input feedstock for the electrolyser unit 510. Gaseous product in the form of carbon monoxide, hydrogen and ethylene, as well as any unreacted carbon dioxide 514 exit the cathode side of the electrolyser unit 510 as a mixed product stream and are conveyed to a carbon dioxide capture unit 590 where carbon dioxide is isolated as described elsewhere herein. A carbon dioxide recycle stream 591 is redirected to the input of the electrolyser unit 510 and may be combined with the carbon dioxide feedstream 501. A gaseous stream obtained from the anode side of the electrolyser unit 510 comprises mainly comprises oxygen 592 which may be separated as a product or vented to atmosphere.

[0051] Gaseous product in the form of carbon monoxide, hydrogen and ethylene 511 exit the carbon dioxide capture unit 590 as a mixed product stream 511 and are conveyed directly to an ethylene oligomerisation unit 560.

[0052] Separately a liquid product stream comprising ethanol 512 is directed to an ethanol separation unit 530. The liquid product stream is distilled within the ethanol separation unit 530, allowing for separated ethanol to be directed to a dehydration step within an ethylene conversion unit 540, whereas wastewater 531,541 is recycled to the electrolyser unit 510, or may be released as a bleed. Downstream synthetic processing of the ethylene into paraffinic fuels is carried out substantially as described previously.

[0053] The invention will now be further illustrated by reference to the following non-limiting examples.Examples

[0054] A simulation was performed relating to performance of an AEM based carbon dioxide electrolyser system, of the type shown in the process line up in Figure 3 and described above. The AEM electrolyser unit receives carbon dioxide (Stream 1) and water (Stream 2) as feedstock along with green electrons (renewable source of electrical power). The anode side of the electrolyser unit generates a mixture of oxygen and carbon dioxide. As mentioned previously, carbon dioxide (Stream 6) is separated downstream of the electrolyser unit and recycled back to cathode side while the oxygen stream can be vented or provided as product. The product stream (Stream 4) generated on cathode side primarily contains ethylene, carbon monoxide and hydrogen. This product stream is subjected to ethylene separation. The carbon monoxide and hydrogen streams (Stream 3) are further separated into pure carbon monoxide, which is recycled back to electrolyser unit, and hydrogen. The hydrogen stream (stream 7) can be exported as a side product and / or utilized in downstream processes (e.g. hydrogenation reactions). The separated ethylene (Stream 5) is sent to an oligomerization reactor to produce oligomers in the range of jet fuel. The oligomers are further sent to a hydrogenation reactor to obtain paraffinic fuel. The paraffinic fuel is separated by fractionation to obtain kerosene, naphtha and diesel fractions (streams 8 to 10). Table 1 (below) shows the rection conditions associated with each of the Streams 1 to 10 described above. Table 1Stream No. 1 2 3 4 5 6 7 8 9 10 Stream name CO 2 Water Cathode gas C 2 H 4 from EtOH Ethylene CO 2 recycle Hydrogen Naphtha Kerosene Diesel Component Mole frac [%] CO 2 100 99.1 CO 2.2 0.03 0.3 H 2 33.1 99.7 H 2 O 100 6.9 Oxygen 0.9 Ethylene 53.5 100 99.97 Ethanol 4.3 Methane Ethane 0.4 Propane 0.1 Naphtha (C 5 -C 9 ) 99.5 Kerosene (C 9 -C 16 ) 100 Diesel (C 16 -C 22 ) 100 Total 100 100 100 100 100 100 100 100 100 100 Temperature [°C] 20 20 40 43 7.5 17 102 30 40 25 Pressure [bar] 1.4 2.0 1.1 21.3 20.5 2 40 1.03 1.01 1.01 Mass flow [t / h] 380.2 256 137.6 11.0 116.1 3323 3.3 1.4 104.8 0.8 Density [kg / m 3< ] 2.5 998 0.8 25.4 28.8 .7 2.7 665 734 779

[0055] Although particular embodiments of the invention have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims, which follow. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A system for the production of a sustainable paraffinic fuel, the system comprising: a gaseous feed comprised of a carbon dioxide rich feedstock, and a liquid feed comprised of an aqueous feedstock, the gaseous and liquid feeds being in providing an input for a carbon dioxide electrolysis unit, wherein the carbon dioxide electrolysis unit comprises at least one of an anionic exchange membrane (AEM), a cationic exchange membrane (CEM), or a bipolar membrane, and further comprises at least cathodic and anodic output streams, wherein the cathodic output stream comprises an ethylene product; and wherein the cathodic output stream is coupled to one or more synthetic units for the production of a sustainable paraffinic fuel.

2. The system of claim 1, wherein the one or more synthetic units for the production of a sustainable paraffinic fuel comprise at least one or more of: an ethylene oligomerisation unit; a hydrogenation unit; and a fractionation unit.

3. The system of claim 1, wherein the one or more units for the production of a sustainable paraffinic fuel comprise in sequential arrangement: an ethylene oligomerisation unit; a hydrogenation unit; and a fractionation unit.

4. The system of any of claims 1 to 3, wherein the aqueous feedstock comprises an electrolyte.

5. The system of claim 4, wherein the electrolyte comprises potassium hydroxide, sodium hydroxide and / or caesium hydroxide.

6. The system of any one of claims 1 to 5, wherein carbon dioxide electrolysis unit comprises an AEM.

7. The system of any one of claims 1 to 6, wherein the carbon dioxide electrolysis unit exhibits a carbon dioxide to ethylene Faradaic conversion efficiency to ethylene of at least 25%, suitably at least 60% and optionally at least 80%.

8. The system of any of claims 1 to 7, wherein the carbon dioxide is obtained from industrial exhaust gas or from direct air capture (DAC).

9. The system of any one of claims 1 to 8, wherein the carbon dioxide electrolysis unit is powered using renewable electricity.

10. The system of any one of claims 6 to 9, wherein the anodic output comprises unreacted carbon dioxide which is directed to a carbon dioxide separation unit, optionally wherein the carbon dioxide separation unit comprises: a Pressure Swing Adsorption (PSA) unit; an amine-based carbon dioxide capture unit; or a cryogenic separation unit.

11. The system of claim 10, wherein the carbon dioxide obtained from the carbon dioxide separation unit is recycled as a gaseous feed to the carbon dioxide electrolysis unit.

12. The system of any one of claims 1 to 11, wherein the sustainable paraffinic fuel comprises a synthetic kerosene that conforms to Jet A, Jet A-1, JP-5 and JP-8 standards, and / or a synthetic naphtha that conforms to Jet B and JP-4 standards; or a blend component suitable for use therewith.

13. A process for the production of sustainable paraffinic fuel, the process comprising undertaking an electrochemical conversion of a gaseous carbon dioxide feedstock in an electrolysis unit, in order to produce a gaseous product that comprises ethylene as a major component, and using the ethylene as a feedstock in a paraffin synthetic process, wherein the electrolysis unit is powered by a source of renewable electricity and wherein the gaseous carbon dioxide feedstock comprises carbon dioxide obtained from industrial exhaust gas or from direct air capture (DAC).

14. A process as claimed in Claim 1, wherein the sustainable paraffinic fuel comprises a synthetic kerosene that conforms to Jet A, Jet A-1, JP-5 and JP-8 standards, and / or a synthetic naphtha that conforms to Jet B and JP-4 standards; or a blend component suitable for use therewith

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