Process and installation to perform a gas product separation on a gas stream comprising ethylene, carbon dioxide, hydrogen and water

Abstract

A process to perform a gas separation comprising a) providing a gas stream (5)being devoid of carbon monoxide and methane, being the cathode product gas phase of an CO2 to ethylene conversion electrolyser (3) and comprising ethylene, carbon dioxide, hydrogen, and water; c) performing a carbon dioxide removal on the gas stream (5) or on the compressed gas stream (11) to produce a CO2-lean gas stream (21); d) drying said CO2-lean gas stream (21) to produce a dehydrated gas stream (29); e) performing a hydrogen separation to produce an H2-lean gas stream (35) f) performing a cryogenic separation on the H2-lean gas stream (35), by cooling said H2-lean gas stream (35) to reach a temperature ranging from -29°C to -60°C. to obtain an ethylene-containing stream (41).

Description

[0001]PROCESS AND INSTALLATION TO PERFORM A GAS PRODUCT SEPARATION ON A GAS STREAM COMPRISING ETHYLENE, CARBON DIOXIDE, HYDROGEN ANDWATER Technological fieldThe present disclosure relates to a process and installation to perform a gas productseparation of a gas stream comprising ethylene, carbon dioxide, hydrogen, and water such asa product gas phase downstream of a CO2 to C2H4 electrolyser..Technological backgroundElectrochemical carbon dioxide reduction (CO2R) offers an attractive route to upgradegreenhouse gases such as CO2 to valuable fuels and feedstocks. However, today it is curtailed at least in part by the limits of having a high selectivity into specific products. Achieving a narrow product distribution with cheap CO2R catalysts is challenging and conventional material modifications offer limited control. Ethylene is the most important organic precursor of the chemical industry used mainly for the production of polyethylene. It is synthesized, with a worldwide production of about 180 million tons per year, typically by steam cracking of a wide range of fossil hydrocarbon feedstocks, a process emitting CO2 and increasing its concentration in the atmosphere. Thus, it is desirableto develop alternatives for the production of non-fossil ethylene. While challenging, selectiveCO2 or CO electroreduction to ethylene using renewable energy sources is one of the most attractive possibilities.Once CO and / or CO2 are converted into ethylene, another challenge is to separate it from theproduct gas stream in a process that allows the highest selectivity possible such as obtainingan ethylene polymer commercial grade, with reduced energy consumption.It is known to remove CO2 from a gas stream with an amine solution. As an alternative to theamine-based solvents, K2CO3 solution can be used to remove CO2, with the overall reaction written as: CO2 + K2CO3 + H2O ↔ 2KHCO3K2CO3 system offers greater process flexibility due to the lack of solvent degradation, lower heat of reaction with CO2, and the ability to operate the absorber and regenerator at hightemperature (> 100 °C) as shown by Kothandaraman et al. in “Carbon dioxide capture bychemical absorption: a solvent comparison study”; Vol. 72, N° 01 (2010). The last point isdesirable if the flue gas is hot, i.e., cooling before entering the absorber column is notnecessary (see Milidovich, S., & Zbacnik, E. “Increasing efficiency of hot potassium carbonateCO2 removal systems”; UOP LLC: Des Plaines, IL, USA, 11-14 (2013)).Penteado et al. in “Biogas as a renewable feedstock for green ethylene production viaoxidative coupling of methane: Preliminary feasibility study”; Chemical EngineeringTransactions, 61, 589-594 (2017), describes the process of producing ethylene from biogasvia oxidative coupling of methane. They recommend using a cascade of polyimide membranes to remove the bulk of the CO2before proceeding to the chemical absorption unit by amine solution. Employing cryogenic distillation to remove CO2is an option discussed by Xu, G., et al. in “An improved CO2separation and purification system based on cryogenic separation anddistillation theory”; Energies, 7(5), 3484-3502 (2014). Namely, after removing water from theflue gas, the rest of the gases, including CO2, enter the cryogenic distillation column that operates at a specific temperature and pressure, at which liquid CO2 and C2H4 are obtained at the bottom of the cryogenic column, and the rest of the gases at the top of the column. However, further downstream treatment is required for CO2and C2H4separation, which poses additional difficulties. One way to separate CO2from C2H4is via flash to form an ethylene vapour stream and solid CO2, similar to the solution proposed by US9,964,352 for the mixture of CO2 and ethane.Embedding the CO2 to C2H4 electrolyser within the plant for ethylene oxide production hasbeen proposed by Barecka et al. in “Economically viable CO2 electroreduction embeddedwithin ethylene oxide manufacturing”; Energy & Environmental Science, 14(3), 1530-1543(2021).The conversion of ethylene-to-ethylene oxide is a selective process (90 %), with the rest ofthe ethylene completely oxidizing to CO2. This waste CO2 could be recycled back to the electrolyser. CO2 is also used for dilution purposes during ethylene oxide production, thereforethe flue gases coming from the electrolyser can be directly used.Apart from chemical absorption solvents, there also exist physical absorption solvents for acidgas treatment, such as dimethyl ether of polyethylene glycol or DEPG (Selexol™ or CoastalAGR®), NMP or N-methyl-2-pyrrolidone (Purisol®), methanol (Rectisol®), and propylenecarbonate (Fluor Solvent™) see Burr & Lyddon in “A comparison of physical solvents for acidgas removal”; Gas Processors’ Association Convention, Grapevine, TX. (2008, March). Physical solvents are used only if the flue gas is at high pressure since it is a pressure-driven process. Although physical solvents are a good choice if the percentage of CO2 is high in the flue gas stream, it is not advised to use them in the presence of hydrocarbons, since the co- absorption of hydrocarbons in a solvent can happen. However, physical solvents are a very good choice for purifying synthesis gas from CO2.US6141988 describes a process for recovering olefins from a gas stream containing olefinsand hydrogen. The process comprises compressing the gas stream in at least one compression stage to form a compressed gas stream, contacting the compressed gas stream with a membrane at conditions effective to obtain a permeate stream rich in hydrogen and a retentate stream depleted in hydrogen, and introducing the permeate stream into a pressure swing adsorption system at conditions effective to obtain a nonadsorbed stream rich in hydrogen and a desorbed stream comprising olefins.US2015368167 discloses processes for producing and separating ethane and ethylene. Insome embodiments, an oxidative coupling of methane (OCM) product gas comprising ethane and ethylene is introduced to a separation unit comprising two separators. Within the separation unit, the OCM product gas is separated to provide a C2-rich effluent, a methane-rich effluent, and a nitrogen-rich effluent. The separation can be achieved with little or noexternal refrigeration requirement.US2023175146 discloses systems and methods for increasing the concentration of desiredCOx reduction reaction products. The systems and methods include ethylene purification.There is still a need for a process and installation for gas separation to separate ethylene fromthe product gas stream downstream of a CO2 to C2H4 electrolyser (such as to obtain ethylenepolymer grade purity) that is efficient and which requires reduced energy intensity. Summary of the disclosureOne or more of the above needs can be fulfilled by a process and an installation to perform agas separation downstream of an electrolyser that includes a hydrogen separation beforeethylene separation. Indeed, it was found that using membranes for H2 separation upstreamof the cryogenic separation allows for the energy intensity of the cryogenic separation sectionto be lowered significantly.According to a first aspect, the disclosure provides a process to perform a gas separationcomprising the following steps: a) providing a gas stream being the cathode product gas phase of a CO2 to ethyleneconversion electrolyser and comprising ethylene, carbon dioxide, hydrogen, and water;b) optionally, subjecting said gas stream to compression to obtain a compressed gasstream; c) performing a carbon dioxide removal on the gas stream or on the compressed gasstream to produce a CO2-lean gas stream; d) drying said CO2-lean gas stream to produce a dehydrated gas stream; f) performing a cryogenic separation to obtain an ethylene-containing stream;wherein the process is remarkable in that the gas stream is devoid of carbon monoxide andmethane; in that the process further comprises a step e) of performing a hydrogen separationbefore step f) of cryogenic separation to produce an H2-lean gas stream and in that the stepf) of cryogenic separation is performed on the H2-lean gas stream by cooling said H2-lean gasstream to reach a temperature ranging from -29°C to -60°C.With preference, step f) of cryogenic separation is performed in a single refrigeration stage ona cryogenic distillation column.Indeed, it has been found that performing a hydrogen separation before the cryogenicseparation allows performing it at a higher temperature than the one used to separate bothhydrogen and ethylene so that only one refrigeration cycle is needed. As shown by the examples, by using membranes for H2 separation upstream of the cryogenic separation, theenergy intensity of the cryogenic separation section can be lowered by some 65%, so that theenergy intensity of the whole process is reduced. In an embodiment, the gas stream provided in step a) is the cathode product gas phase of an electrolyser, and the process further comprises a preliminary step of producing the gas streamby performing a CO2 to ethylene conversion with an electrolyser.According to the disclosure, the gas stream provided in step a) is devoid of carbon monoxideand methane.Carbon monoxide and / or methane may be present in the gas phase product of an electrolyserperforming a two-step CO2 electroconversion process; whereas in a one-step CO2electroconversion process, the gas phase product downstream of an electrolyser will bedevoid of carbon monoxide and methane. Thus according to the disclosure, the gas streamprovided in step a) is the gas phase product downstream of an electrolyser performing a aone-step CO2 electroconversion process.Thus, preferably, the electrolyser is a membrane electrode assembly with a bipolar membraneand / or the CO2 to ethylene conversion is a one-step CO2 electroconversion process.For example, the CO2 to ethylene conversion is conducted in neutral or acidic conditions.For example, in the preliminary step of producing the gas stream by performing a CO2 toethylene conversion with an electrolyser, the cathode catalyst comprises one or more selected from copper, gold, silver, zinc, nickel, bismuth, copper oxide, tin oxide, titanium dioxide, or any mixture thereof; preferably the cathode catalyst is or comprises copper and / or copper oxide.One or more of the following can be used to further define the steps a) and b) of the processaccording to the disclosure: -step b) of compression is conducted and the compressed gas stream has a pressureranging from 1.0 to 4.0 MPa; and / or -the gas stream provided in step a) comprises, based on the total molar content of thegas stream, at least 20 mol.% of ethylene; at least 15 mol.% of carbon dioxide; at least 15 mol.% of hydrogen, and at least 10 mol.% of water.One or more of the following can be used to further define step c) of the process according tothe disclosure. For example, the step c) of carbon dioxide removal is a step or comprises a sub-step of carbondioxide removal by amine solution; with preference:- the amine solution comprises one or more amines selected from monoethanolamine,diethanolamine, diglycolamine, methyldiethanolamine, triethanolamine, piperazine and (piperazinyl-1)-2-ethylamine; and / or -the amine solution comprises from 10 to 40 wt.% of amine based on the total weightof the amine solution. For example, the step c) of carbon dioxide removal is a step or comprises a sub-step of carbondioxide removal by an alkaline solution; with preference:- the alkaline solution is selected from a sodium hydroxide solution, a calcium hydroxidesolution, a potassium hydroxide solution, and any mixture thereof; and / or- the alkaline solution comprises from 10 to 35 wt.% of a base based on the total weightof the alkaline solution, wherein the base is selected from sodium hydroxide, calciumhydroxide, potassium hydroxide, and any mixture thereof.For example, step c) of carbon dioxide removal comprises a sub-step of carbon dioxideremoval by an amine solution followed by a sub-step of carbon dioxide removal by an alkaline solution; with preference, the amine solution comprises from 10 to 40 wt.% of monoethanolamine based on the total weight of the amine solution, and / or the alkaline solution comprises from 10 to 35 wt.% of sodium hydroxide based on the total weight of the alkaline solution. With preference, the CO2-lean gas stream contains less than 1 molar ppm of CO2 based on the total molar content of the stream. One or more of the following can be used to further define the step d) of the process according to the disclosure: -the step d) of drying comprises a first sub-step of vapor-liquid separation or adsorption,followed by a second sub-step of drying using molecular sieves; and / or -the dehydrated gas stream contains less than 1 weight ppm of water based on the totalweight content of the stream.One or more of the following can be used to further define the steps e) :- the hydrogen separation is performed using membranes and / or- the hydrogen separation is performed at a pressure ranging from 15 to 80 barg withthe feed / product pressure ratio of 2.5 to 3. With preference, the H2-removal unit comprises one or more H2separation membranesproducing H2-lean gas stream (non-permeate) at high pressure (35 to 40 barg) and H2-richstream (permeate) at low pressure (11-15 barg) with up to 98 mol% purity.With preference, the ethylene-containing stream obtained in step f) comprises at least 99.9mol.% of ethylene as determined by ASTM D2505-88 (2015).According to a second aspect, the disclosure provides an installation to perform a gasseparation downstream of an electrolyser to perform the process according to the first aspect;wherein the installation is remarkable in that it comprises, in the following order:- a CO2-removal unit;- a drying unit;- a H2-removal unit; and- a cryogenic separation unit comprising a cryogenic distillation column.With preference, the installation further comprises a gas compressor unit placed upstream ofthe CO2-removal unit.In an embodiment, the installation further comprises an electrolyser comprising a cathode andan anode, and a membrane. With preference, the electrolyser is a membrane electrodeassembly with a bipolar membrane and / or the electrolyser is a membrane electrode assemblybeing a one-gap electrolyser wherein the membrane is in contact with the cathode.With preference, the cathode comprises a catalyst wherein the cathode catalyst comprisesone or more selected from copper, gold, silver, zinc, nickel, bismuth, copper oxide, tin oxide,titanium dioxide, or any mixture thereof; preferably the cathode catalyst is or comprises copperand / or copper oxide. In an embodiment, the CO2-removal unit comprises an amine absorption column and a caustic tower. For example, the drying unit comprises a vapor-liquid separator followed by a molecular sieves dryer system. With preference, the H2-removal unit comprises one or more H2separation membranes.With preference, the cryogenic separation unit comprises propene as the refrigerant.With preference, the installation comprises a recycle line recycling the stream from the top ofthe column to the stream entering the H2-removal unit. Description of the Figures -Figure 1 is a schematic view of an installation according to the disclosure.- Figure 2 is a block diagram of a method for ethylene from CO2 and H2O with an MEAelectrolyser. -Figure 3 is a scheme illustrating the CO2 to ethylene conversion in an electrolyser.- Figure 4 is a graph related to the temperature and concentration profile within CO2absorption column with amines. -Figure 5 is the energy intensity embedded with a design margin of gas cathodeseparation process for: a) the case with no H2 membranes envisaged, b) with the membranes envisaged.Detailed descriptionFor the disclosure, the following definitions are given: The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do notexclude additional, non-recited members, elements or method steps. The terms "comprising”,"comprises" and "comprised of" also include the term “consisting of”. The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g.1 to 5 can include 1, 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.The installation and the process are described jointly with reference to Figure 1 in referenceof a gas phase product of an electrolyser.A CO2-containing feedstream is provided to an electrolyser 3 and a conversion process fromCO2 to ethylene is performed wherein different streams are produced comprising a cathodeproduct gas phase 5, a cathode product liquid phase (not shown) and anode product liquid and gas phase (not shown) The disclosure provides for a process to perform a gas separation comprising the following steps: a) providing a gas stream 5 being the cathode product gas phase of an CO2 to ethyleneconversion electrolyser 3 and comprising ethylene, carbon dioxide, hydrogen, andwater; b) optionally, subjecting said gas stream 5 to compression to obtain a compressed gasstream 11; c) performing a carbon dioxide removal on the gas stream 5 or on the compressed gasstream 11 to produce a CO2-lean gas stream 21;d) drying said CO2-lean gas stream 21 to produce a dehydrated gas stream 29;f) performing a cryogenic separation to obtain an ethylene-containing stream 41;wherein the process is remarkable in that the gas stream 5 is devoid of carbon monoxide andmethane; in that the process further comprises step e) of performing a hydrogen separationbefore step f) of cryogenic separation to produce an H2-lean gas stream 35 and in that thestep f) of cryogenic separation is performed on the H2-lean gas stream 35, by cooling said H2-lean gas stream 35 to reach a temperature ranging from -29°C to -60°C.The disclosure further provides for an installation to perform a gas separation; remarkable inthat the installation comprises, in the following order: -an optional gas compressor unit 7;- a CO2-removal unit 13;- a drying unit 23;- a H2-removal unit 31; and- a cryogenic separation unit 37 comprising a cryogenic distillation column.When the gas separation is made downstream of an electrolyser 3, the installation may furthercomprises an electrolyser 3 comprising a cathode and an anode, and a membrane; withpreference, the electrolyser 3 is an electrode assembly with a bipolar membrane and / or theelectrolyser 3 is a membrane electrode assembly being a one-gap electrolyser wherein themembrane is in contact with the cathode.For example, the cathode comprises a catalyst wherein the cathode catalyst comprises oneor more selected from copper, gold, silver, zinc, nickel, bismuth, copper oxide, tin oxide,titanium dioxide, or any mixture thereof; preferably the cathode catalyst is or comprises copperand / or copper oxide. As regards the step a)In a prefered embodiment, the gas stream 5 provided in step a) is from the cathode productgas phase of an electrolyser 3.In a prefered embodiment, the disclosure provides for a process to perform a gas separationdownstream an electrolyser and the step a) is providing a gas stream 5 being the cathodeproduct gas phase of an electrolyser 3 wherein the gas stream 5 is comprising ethylene,carbon dioxide, hydrogen, and water.In a preferred embodiment, the gas stream 5 to be used in the gas separation process is thecathode product gas phase of an electrolyser 3. It has been found that, in a conversion processfrom CO2 to ethylene, the cathode product gas phase comprises a mixture of ethylene, carbondioxide, hydrogen, and water, each with different molar content depending on the conversionperformances. In the present disclosure, the cathode product gas phase is devoid of methaneand carbon monoxide.In an embodiment the process further comprises a preliminary step of producing the gasstream 5 by performing a CO2 to ethylene conversion with an electrolyser 3; with preference,the CO2 to ethylene conversion is conducted in neutral or acidic conditions. For example, the preliminary step of producing the gas stream 5 is performed in presence of a cathode catalyst comprising one or more selected from copper, gold, silver, zinc, nickel,bismuth, copper oxide, tin oxide, titanium dioxide, or any mixture thereof; preferably thecathode catalyst is or comprises copper and / or copper oxide.For example, the electrolyser 3 is a membrane electrode assembly with a bipolar membraneand / or the CO2 to ethylene conversion is a one-step CO2 electroconversion process.CO2 to ethylene conversion is well known to the person skilled in the art and is described for example in WO2022148837, WO2019185622 and WO2019206882 which are incorporated herein by reference.In the context of the disclosure, an electrolyser is a system (vessel) that uses electricity tobreak molecules. It comprises an electrolyte, a cathode and an anode, and a membrane.The electrolyser 3 can be selected from a membrane electrode assembly (MEA) or a solid-oxide electrolyser cell (SOEC) in a two step process. In a preferred embodiment, theelectrolyser 3 is a membrane electrode assembly (MEA).A solid-oxide electrolysis cell (SOEC), is an electrolyser with a solid-oxide as electrolyte,operating at high temperatures (ca. 750 °C). SOEC are known to the person skilled in the artand for example as described in Rainer Küngas; J. Electrochem. Soc. 167044508 (2020).A membrane electrode assembly (MEA) is an electrolyser with liquid electrolyte operating atlow temperature (30–60 °C, 1 bar). Several types of MEA can be considered in the context ofthe disclosure. For example, a suitable membrane electrode assembly (MEA) is anelectrolyser architecture where the membrane is tightly pressed onto the cathode meaningthat it is in contact with the cathode (i.e., there is no liquid catholyte compartment), or with theanode (i.e., there is no liquid anolyte compartment). Both architectures are also named one-gap electrolysers. In some cases, the membrane is in contact with both the cathode and theanode (i.e., no liquid catholyte compartment and liquid anolyte compartment). Such anelectrolyser is also named a zero-gap electrolyser. In other cases, the MEA comprises both aliquid catholyte compartment and a liquid anolyte compartment. Such an electrolyser is alsonamed a two-gap electrolyser.In a preferred embodiment, the MEA is selected to be a one-gap electrolyser, wherein themembrane is in contact with the cathode (i.e., there is no liquid catholyte compartment).The membrane is the electrolyser part used to separate an anolyte from a catholyte, to avoidunwanted secondary reactions and to isolate the products formed on the anode and cathode.Different membranes exist such as cation membranes, anion membranes, and bipolarmembranes. A cation-exchange membrane (CEM) is a semipermeable membrane designedto conduct cations. An anion-exchange membrane (AEM) is a semipermeable membranedesigned to conduct anions. A bipolar membrane (BPM) is an ion exchange membraneconstituted by a cation and anion exchange layer, allowing the generation of protons and hydroxide ions via a water dissociation mechanism.In a preferred embodiment, the electrolyser 3 is a membrane electrode assembly (MEA)selected from a membrane electrode assembly with a bipolar membrane (MEA-BPM) or amembrane electrode assembly with an anion membrane (MEA-AEM); more preferably, theelectrolyser 3 is a membrane electrode assembly with a bipolar membrane (MEA-BPM).Indeed, it was found that for MEA–BPM, the crossover of CO2 from the inlet on the cathode side to the anode side is reduced compared to membrane electrode assembly with an anion membrane (MEA-AEM).The electrolyser 3 comprises electrolytes. An electrolyte is a substance that conducts electriccurrent as a result of a dissociation into ions, which migrate toward (or are discharged) at thecathode and anode. An electrolyte can be an acid, base, or salt, which ionizes when dissolvedin solvents, such as water. In the absence of solvent, many salts behave as electrolytes whenmelted. Some electrolytes are even in a solid state. The anolyte is the electrolyte that is locatedaround the anode, and the catholyte is the electrolyte that is located around the cathode.The electrolyte that circulates inside the cell and the reactions proceeding both on the catalystand in the bulk phase determine the pH of the cell. For example, for an alkaline cell, thecirculating electrolyte was 3 M KOH, while it was 0.1 M KHCO3for a neutral cell (or MEA, anolyte side).The catholyte can be acidic, neutral, or alkaline.When the catholyte is alkaline, it has a pH of more than 7.5; preferably more than 8.0; andmore preferably more than 8.5. For example, the acidic catholyte has a pH of from 8.0 to 15.0; preferably, from 10.0 to 14.5; even more preferably from 12.0 to 14.0 or from 12.5 to 13.8. When the catholyte is neutral, the CO2to ethylene conversion is performed in neutralconditions. In a preferred embodiment, the catholyte is neutral or acidic; more preferably thecatholyte is neutral. A neutral catholyte has a pH ranging from 6.0 to 8.0; preferably ranging from 6.5 to 7.5. When the catholyte is acidic, it has a pH of less than 6.5; preferably at most 6.0; and morepreferably at most 5.5. For example, the acidic catholyte has a pH of from 0 to less than 6.5;preferably, from 1.0 to at most 5.0; even more preferably from 1.5 to 5.5 or from 2.0 to 5.0. Indeed, it was found that the alkaline cell for CO2 to C2H4 results in a very low CO2 utilization since the majority of CO2, instead of converting into the product, is lost in the electrolyte.For example, the gas stream 5 comprises at least 20 mol.% of ethylene based on the totalmolar content of the gas stream 5; preferably at least 25 mol.%; more preferably at least 28mol.%. The molar content of the gas stream is determined according to Gas Chromatography(GC).For example, the gas stream 5 comprises at least 15 mol.% of carbon dioxide based on thetotal molar content of the gas stream 5; preferably at least 18 mol.%; more preferably at least20 mol.%. For example, the gas stream 5 comprises at least 15 mol.% of hydrogen based on the total molar content of the gas stream 5; preferably at least 18 mol.%; more preferably at least 20 mol.%.For example, the gas stream 5 comprises at least 10 mol.% of water based on the total molarcontent of the gas stream 5; preferably at least 15 mol.%; more preferably at least 18 mol.%.The molar content of H2O present in the cathode product gas phase for the low-temperatureelectrolyser corresponds to the assumed 100% humidification of the gas stream at ca.60 °C.It was found that the use of an electrolyser 3 being an MEA–BPM, was an option with highCO2utilization and a lower number of different molecules in the product stream on the cathode side (no CO and CH4). For example, the gas stream 5 comprises, based on the total molar content of the gas stream 5, at least 20 mol.% of ethylene; at least 15 mol.% of carbon dioxide; at least 15 mol.% ofhydrogen and at least 10 mol.% of water. In the present disclosure, the gas stream 5 is devoidof carbon monoxide and / or methane. On the anode side, oxygen is produced from water. However, one can also observe some amount of CO2 in the product stream. It happens due to the crossover of CO2 from the cathode to the anode side through the membrane in form of ions, such as CO32–, HCO3–or HCOO–.This was described in Larrazábal et al. in “Analysis of mass flows and membrane cross-overin CO2 reduction at high current densities in an MEA-type electrolyser.”; ACS applied materials& interfaces, 11(44), 41281-41288 (2019).It has been found that this crossover could be minimized by using a BPM. The simplified blockdiagram for ethylene production starting from CO2 and H2O is shown for the case of MEA–BPM in Figure 2. Liquid product separation and recycling of the electrolyte, as well as the gasproduct separation on the anode side, are not shown in this block diagram.As regards the optional step b) of subjecting the gas stream to compressionThe process of a gas separation can be conducted at atmospheric pressure or not. In casethe process is conducted at atmospheric pressure, step b) is not conducted.However, in a preferred embodiment, the process is conducted on compressed gas, so stepb) is conducted and a compressed gas stream 11 is obtained. For example, the compressedgas stream 11 has a pressure ranging from 0.5 to 5.0 MPa; preferably from 1.0 to 4.0 MPa;more preferably from 1.2 to 3.8 MPa, and even more preferably from 1.5 to 3.6 MPa.When step b) is conducted, the installation comprises a gas compressor unit 7 placedupstream of the CO2-removal unit 13; wherein the gas compressor unit 7 comprises one ormore gas compressors 9.When step b) is conducted, the CO2-lean gas stream 21 is understood to be a compressedCO2-lean gas stream; the dehydrated gas stream 29 is understood to be a compresseddehydrated gas stream; and the H2-lean gas stream 35 is understood to be a compressed H2-lean gas stream. As regards the step c) of performing a carbon dioxide removalThe carbon dioxide removal can be made by any means; for example, step c) of carbon dioxideremoval can be done in a single step or in two or more sub-steps. In a preferred embodiment,step c) of carbon dioxide removal is a two-sub-step procedure. In that respect, the installationto perform the gas product separation process comprises a CO2-removal unit 13.In any case, it is preferred that step c) of carbon dioxide removal (CO2-removal) is a step orcomprises a sub-step of CO2-removal by amine solution. The same is preferably performed ina CO2-removal unit 13 comprising an amine absorption column 15. CO2-removal by aminesolution is well-known to the person skilled in the art and is described for example in Dubois et al. in “Carbon dioxide absorption into aqueous amine-based solvents: modeling andabsorption tests”; Energy Procedia 4, 1353–1360 (2011), which is incorporated herein byreference.In an embodiment, the amine solution comprises one or more amines selected frommonoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA),methyldiethanolamine (MDEA), triethanolamine (TEA), piperazine (PZ) and (piperazinyl-1)-2- ethylamine (PZEA); preferably selected from monoethanolamine (MEA), diethanolamine (DEA), piperazine (PZ) and (piperazinyl-1)-2-ethylamine (PZEA); more preferably, the aminesolution comprises one or more amines selected from monoethanolamine (MEA),diethanolamine (DEA), and piperazine (PZ); even more preferably, the amine solutioncomprises monoethanolamine (MEA) and / or diethanolamine (DEA); and most preferably, theamine solution comprises monoethanolamine. Indeed, monoethanolamine was found to showhigh reactivity with CO2.For example, the amine solution comprises piperazine (PZ) at a concentration ranging from 5to 35 wt.% based on the total weight of the solution; preferably from 10 to 20 wt.%.In a preferred embodiment, the amine solution comprises monoethanolamine (MEA) at aconcentration ranging from 10 to 40 wt.% based on the total weight of the amine solution;preferably from 10 to 20 wt.%.Advantageously, the CO2 removal unit 13 comprises an amine absorption column 15, whereCO2 is removed, and a regeneration (stripper) column (not shown), where the chemicallybonded CO2is released in a separate gas stream on top of the column. The regeneratedamine solution is sent back to the absorption column 13 through a recycle loop.Having in mind that the CO2absorption with amines involves chemical reactions, higher pressure favours kinetics of the CO2absorption, and results consequently in a lower amountof the amine that circulates in the CO2 removal unit 13. However, higher pressure translatesinto a higher cost of the gas compression section upstream of the CO2absorber and a highercost of the construction material . Thus, the CO2 removal by amine is preferably conducted ata pressure ranging from 0.5 to 5.0 MPa; preferably from 1.0 to 4.0 MPa; more preferably from1.2 to 3.8 MPa, and even more preferably from 1.5 to 3.6 MPa. For example, an operatingpressure of the CO2absorption column 15 ranging from 1.2 to 2.0 MPa results in acceptableflow rates of the amine solution with acceptable gas compression cost upstream the column15.Since amines in water solution are weak bases, there may be some remaining portion of CO2present in the gas phase 17 after CO2 removal with the amine solution, typically in the rangeof 50-500 ppm CO2. Therefore, the CO2 removal step by amine is preferably followed by aCO2 removal step with an alkaline solution (also named caustic washing), such as with asolution of KOH and / or NaOH (also named caustic soda) in a caustic tower 19. The caustictower 19 consists of two packed beds. The top bed operates with circulating wash water to remove any residual caustic entrained with the vapors in the gas stream from being carried over to downstream equipment while the bottom bed operates with circulating caustic.Advantageously, the base used is strong.The CO2-removal step aims to obtain a CO2-lean gas stream 21 that contains less than 1molar ppm of CO2 based on the total molar content of the CO2-lean gas stream 21, which isdesirable to have upstream the cryogenic separation column 39.Thus, in an embodiment, step c) of carbon dioxide removal (CO2-removal) is a step orcomprises a sub-step of CO2-removal by an alkaline solution; with preference, the alkalinesolution is selected from a sodium hydroxide (NaOH) solution, a calcium hydroxide solution(Ca(OH)2), a potassium hydroxide (KOH) solution, and any mixture thereof.For example, the alkaline solution comprises from 10 to 35 wt.% of a base based on the totalweight of the alkaline solution, wherein the base is selected from sodium hydroxide, calciumhydroxide, potassium hydroxide, and any mixture thereof; preferably the base is sodiumhydroxide and / or potassium hydroxide.In a preferred embodiment, step c) of carbon dioxide removal comprises a sub-step of carbondioxide removal by an amine solution followed by a sub-step of carbon dioxide removal by analkaline solution.For example, the CO2 removal is performed in two steps:1) chemical absorption by an amine solution wherein the amine solution comprises from10 to 40 wt.% of monoethanolamine based on the total weight of the amine solution, and 2) removal of the remaining CO2 with chemical absorption by an alkaline wherein thealkaline solution comprises from 10 to 35 wt.% of sodium hydroxide based on thetotal weight of the alkaline solution. As regards the step d) of drying The purpose of driers in the H2O removal step is to remove the water from the vapor productby adsorption on the adsorbent bed to ensure that the stream has less than 1 weight ppmwater before the cryogenic distillation such as a column 39. Water can freeze in the coldsections affecting column performance and causing maintenance issues.This drying step may be accomplished by using one of several methods. Examples aretriethylene glycol contacting, membrane permeation, or adsorption with a regenerableadsorbent such as a small pore molecular sieve. A suitably designed drying unit 23 will drythe stream to a few parts per million water.Regenerant is heated in the regenerant heater to about 230 °C using temperature control andcontacts the adsorbent in up flow direction. A shell & tube steam heater or an electric heater or a combination of both may serve as the heater. If a steam heater is used, the temperature is controlled by regulating the condensate flow. In the case of an electric heater, the temperature is controlled by regulating the power to the electric heater bundle elements. The regenerant effluent from the drier is cooled in the regenerant cooler and flows to the regenerant knockout drum. Any liquids collected in the regenerant knockout drum are removed using the level control. Regenerant effluent from the regenerant knockout drum is then routed to the downstream system. The regeneration system pressure will be floating on the back pressure of the downstream system depending on where the regenerant effluent is routed. Regenerant effluent may be routed to the fuel gas system or hydrogen purification system (PSA). After the heating step, the drier is cooled and readied to be placed online. The drier that has been regenerated is placed online while the other drier is taken offline for regeneration. In a preferred embodiment, the step d) of drying consist of or comprises using a vapor-liquidseparator 25.In an embodiment, step d) of drying consist of or comprises using small pores molecular sieves 27. Molecular sieves are crystalline metal aluminosilicates having a three-dimensionalinterconnecting network of silica and alumina tetrahedra. The critical pore diameter value is3.2 Å. Small pores molecular sieves with a pore diameter of 3 Å are commercially availablefrom Merck, UOP or BASF.In a preferred embodiment, step d) of drying comprises a first sub-step of vapor-liquidseparation or adsorption, followed by a second sub-step of drying using small pores molecularsieves. For example, the drying unit 23 comprises a vapor-liquid separator 25 followed by a molecularsieves dryer system 27. In another example, the drying unit comprises an adsorption systemfollowed by a molecular sieves dryer system; with preference, the adsorption system comprises a plurality of hollow fibers.A dehydrated gas stream 29 exits the drying unit 23 and is directed to an H2-removal unit 31for hydrogen separation. As regards the step e) of hydrogen separationAccording to the disclosure, a step of hydrogen separation is performed before step f) ofcryogenic separation to produce an H2-lean gas stream 35 and the cryogenic separation isperformed on the H2-lean gas stream 35.The hydrogen separation is preferably performed in an H2-removal unit 31 comprising one ormore H2 separation membranes 33. Suitable H2 separation membranes are known to theperson skilled in the art. For example, suitable H2 separation membranes comprise palladiumor palladium alloys and are described in US8747766B2 which is incorporated herein byreference. For example, the H2 separation membrane may comprise an alloy comprising aGroup 5 element selected from V, Nb, Ta, or a combination thereof and Ir. Such an H2separation membrane is disclosed in EP2596851B1 which is incorporated herein byreference.An H2-lean gas stream 35 is exiting the H2-removal unit 31 and is directed to a cryogenicseparation unit 37 for ethylene separation and purification.As regards the step f) of cryogenic separationThe cryogenic separation unit 37 comprises one or more columns 39, ethylene is separatedfrom the rest of the gases. At the bottom of the column 39, ethylene with required purity iscollected. Indeed, the H2-lean gas stream 35 is purified by cryogenic separation and a polymergrade ethylene is obtained.For example, a polymer grade ethylene comprises:- at least 99.9 mol.% of ethylene as determined by ASTM D2505-88 (2015),- less than 1 ppm volume of CO2 as determined by ASTM D2505-88 (2015),- less than 10 ppm volume of H2 as determined by ASTM D2504-88 (2015), andless than 1 ppm volume of water as determined by ASTM D1142-95 (2021).For example, ethylene-containing stream 41 obtained in step f) comprises at least 99.85 mol.%of ethylene as determined by ASTM D2505-88 (2015); preferably at least 99.90 mol.%; more preferably at least 99.95 mol.% and more preferably at least 99.99 mol.%.The H2-lean gas stream 35 is introduced into the cryogenic column that separates and drawsonly ethylene at the bottom of the column, with only one refrigeration stage. Propene isrequired to cool down the process stream on top of the distillation column, resulting intemperatures on top of the distillation column of about -29°C.As the gas stream 5 is devoid of CO and CH4, the installation preferably comprises a recycleline 43 recycling the stream from the top of the column 39 to the stream entering the H2-removal unit 31. Thus, in a prefered embodiment, the process comprise a sub-step of recyclingat least a part of the stream from the top of the column 39 to the stream entering the H2- removal unit 31; with preference the whole stream is recycled.Since hydrogen is separated before cryogenic separation, the recycle stream with a low flowrate from the top of the cryogenic column can contain a high percentage of ethylene (such as65 mol% as shown in the examples). Methods of characterizationEthylene content in a stream (in mol%) is determined using ASTM D2505-88 (2015) ASTM D2504: Standard Test Method for Noncondensable Gases in C2 and Lighter Hydrocarbon Products by Gas Chromatography (H2, N2, O2, CO). ExamplesThe below examples have been produced using Aspen Hysys and Aspen Plus software bothversion 9.0.The product gas stream composition was estimated from laboratory scale cells (5 cm2), seeTable 1. Some details on the liquid product composition are given later in the text, in Table 4.Table 1: Product gas stream data corresponding to different types of electrolysers.Cathode product, gas-phase, mol %MEA–AEM MEA–BPMC2H4 20-30 25-35CO2 25-35 20-30H2 20-30 20-30CH4 / / CO / / H2O 15-25 15-25Utilization (CO2), % 35 65Utilization (CO), % / / Anode product, gas-phase, mol % CO2 35-45 5-15O2 35-45 65-75H2O 15-25 15-25In Eq.1, the flowrate Fin, cath(CO2) for MEA can be calculated as: ^^^,^^^^(^^^) = ^^^^^,^^^^(^^^) + ^^^^,^^^^(^^^) + ^^^^^(^^^)where Fout, cath(CO2) is the molar flowrate of CO2at the outlet of the cathode, and Flost(CO2) is the molar flowrate of CO2that reacted with the electrolyte to form (bi-)carbonate and subsequently crossed the membrane in form of ions and bubbled out at the anode side as CO2. Therefore, for MEA: ^^^^^(^^^) = ^^^^,^^(^^^)The flowrate Fout, an(CO2) can be calculated with the information in Table 1 (product composition on the anode side) and by calculating the flowrate of oxygen on the anode side. Table 2 lists the global reactions that occur in parallel in an MEA cell. These global reactions are obtained by summing up the half-reactions on the cathode and anode side, respecting theelectroneutrality. For example, the global reaction 2H2O ↔ 1O2 + 2H2 in a basic environment(the same conclusion can be reached in an acidic environment) is the result of the so-calledhydrogen evolution reaction 2H2O + 2e– ↔ H2 + 2OH– occurring on the cathode, and theoxygen evolution reaction 4OH– ↔ O2 + 4e– + 2H2O occurring on the anode.Table 2: Global reactions in electrolysers of interest: one-step CO2 to C2H4 MEACO2 to C2H4 MEA 2CO2 + 2H2O ↔ 1C2H4 + 3O22CO2 + 3H2O ↔ 1C2H5OH (liq) + 3O22CO2 + 2H2O ↔ 2HCOOH (liq) + 1O26CO2 + 8H2O ↔ 2CH3CH2CH2OH (liq) + 9O22CO2 + 2H2O 1CH3COOH (liq) + 3O22H2O ↔ 1O2 + 2H2See also figure 3.The molar flow rate of oxygen produced on the anode side, as well as the molar flow rate ofconverted CO2 and H2O, see Table 3, can be calculated by observing the coefficients in Table 2.Table 3: Calculation of O2 production and CO2 and H2O consumption in one-step CO2 to C2H4MEA CO2 to C2H4 MEA ^^^^^^(^^) = ^3 ∗ ^^^^^ + 3 ∗ ^^^^^^^ + 0.5 ∗ ^^^^^^ + 4.5 ∗ ^^^^^^^ + 3 ∗ ^^^^^^^^ + 0.5 ∗ ^^^^^^^^^^^^^^^^ (^^^) = ^2 ∗ ^^^^^ + 2 ∗ ^^^^^^^ + ^^^^^^ + 3 ∗ ^^^^^^^ + 2 ∗ ^^^^^^^^^^^^^^^^^^^^^ (^^^) = ^2 ∗ ^^^^^ + 3 ∗ ^^^^^^^ + ^^^^^^ + 4 ∗ ^^^^^^^ + 2 ∗ ^^^^^^^^+^^^^^^^^^^^Table 4 lists the mass and molar product flowrates, as well as the consumption of CO2and H2O for the case of MEA–BPM and tandem configuration. The base for these values is 50 kt / y of produced ethylene as target, and information in Table 1 and 3. Basis = 8000 operating hours per year. Table 4. Product stream flowrates and consumption data for MEA–BPM based on 50 kt / y of C2H4 at the outlet of the reactor. MEA–BPM, CO2 to C2H4 Component in the product stream, cathode m, kt / y m, kg / h F, kmol / hCO2 67 8405 614C2H4 50 6250 223C2H5OH (liquid) 25 3110 68HCOOH (liquid) 0.25 31 1C3H7OH (liquid) 5 622 10CH3COOH (liquid) 0.5 62 1H2 3 384 191Component in the product stream, anode m, kt / y m, kg / h F, kmol / hO2 260 32528 1017CO2 44 5516 125Summary CO2 consumed 216 27043 614H2O consumed 127 15917 883CO2 in 328 40964 931Gas Compression and CO2Removal Step CO2removal was simulated in two steps: 1) chemical absorption with 30 wt%monoethanolamine (MEA) solution followed by the 2) removal of the remaining CO2 withchemical absorption by 25 wt% sodium hydroxide solution. The system consists of an amine (30 wt% MEA) absorption column, where CO2 is removed, and a regeneration (stripper) column, where the chemically bonded CO2is released in a separate gas stream on top of the column. The regenerated amine solution is sent back to the absorption column through a recycle loop.Table 5: Aspen Hysys simulation specifications CO2 removal section.Unit Operation Input ParametersCooler Aspen Hysys block: CoolerInlet stream (effluent stream from electrolyser): F= 820 kmol / h, T = 60 °C, P = 0.09 barg, comp. see Table1Outlet temperature: 40 °C Flash Aspen Hysys block: SeparatorTemperature: 40 °C Compressor Aspen Hysys block: CompressorOperating mode: Centrifugal Outlet pressure: 5 or 16 barg CO2 absorber Aspen Hysys block: AbsorberProperty package: Acid Gas Chemical Solvents* Calculation type: Efficiency Number of stages: 20 Gas feed stage: 20 Amine solution feed stage: 1, m = 56 kg / s (F = 8255 kmol / h), T = 35.29 °C Pressure top stage: 16 barg Pressure bottom stage: 16.1 barg Cross-heat exchanger Aspen Hysys block: Heat ExchangerOutlet temperature (cold side): 102 °C Preducing valve Aspen Hysys block: ValveOutlet pressure: 1.5 barg CO2 stripper Aspen Hysys block: DistillationProperty method: Acid Gas Chemical Solvents* Calculation type: Efficiency Number of stages: 20 Feed stream: stage 2 Condenser: Partial-Vapour-Liquid Reboiler: Kettle Pressure top stage: 0.9 barg Pressure bottom stage: 1.2 barg Reflux ratio (molar basis): 0.3908 Boilup ratio (molar basis): 0.03447 Pump Aspen Hysys block: PumpDischarge pressure: 16 barg *Peng-Robinson for vapor phase and the electrolyte non-random two-liquid (eNRTL) activity coefficient model for electrolyte thermodynamics Having in mind that the CO2absorption with amines involves chemical reactions, higher pressure favours kinetics of the CO2absorption and results consequently in a lower amount of the amine that circulates in the system. However, higher pressure translates into a higher cost of the gas compression section upstream of the CO2absorber and a higher cost of the construction material . The operating pressure of the CO2absorption column of 16 barg results in acceptable flowrates of the amine solution with acceptable gas compression cost upstream of the column. The results of the gas compression section with intercooling and liquid separation are given in Table 6.Table 6: Gas compression section results.Cooler 1, duty (kW) 1362 Outlet temperature (°C) 40 Separator 1 Liquid outlet (kmol / h) 116.5 Composition xi(mol / mol) CO2 0.0001 H2O 0.9999 Gas outlet (kmol / h) 703.5 Composition xi (mol / mol) CO2 0.2944 H2O 0.0676 C2H4 0.3435 H20.2945 Compressor 1, duty (kW) 1384 Outlet temperature (°C) 212.5 Outlet pressure (barg) 5.0 Cooler 2, duty (kW) 1873Separator 2 Liquid outlet (kmol / h) 39.13 Composition xi(mol / mol) CO2 0.0008 H2O 0.9992 Gas outlet (kmol / h) 664.4 Composition xi(mol / mol) CO2 0.3117 H2O 0.0127 C2H4 0.3638 H20.3118 Compressor 2, duty (kW) 742 Outlet temperature (°C) 142.6 Outlet pressure (barg) 16.1 Cooler 3, duty (kW) 847.2Separator 2 Liquid outlet (kmol / h) 5.319 Composition xi (mol / mol) CO20.0021 H2O 0.9978 Gas outlet (kmol / h) 659.1 Composition xi(mol / mol) CO2 0.3142 H2O 0.0048 C2H4 0.3667 H2 0.3143 After the gas is compressed to 16.1 barg pressure, it enters at the bottom of the column for CO2 removal with MEA (amine) solution. The simulation results for the absorber–strippersection are given in Fig.4 and Table 7.Table 7: Simulation results – CO2 absorption / desorption with 30 wt.% MEA solution, and 15wt. % solution. Absorber 30 wt. % MEA 15 wt.% MEA case case Gas stream entering the bottom the same as for of absorber 30 wt.% case Ftotal (kmol / h) 659.1 xi(mol / mol) CO2 0.3142 H2O 0.0048 C2H4 0.3667 H20.3143 Lean amine loading0.398 0.098(mol CO2 / mol MEA) Rich amine loading0.607 0.307(mol CO2 / mol MEA) Column temperature range,35–56 35–47absorber (°C) Purified gas stream on top of the absorber Ftotal (kmol / h) 438.8 447.8 xi (mol / mol) CO26.3E-5 1.24E-06 H2O 0.0033 0.0034 C2H40.5259 0.5378 H20.4708 0.4588 Stripper Stripper, condenser temperature63.3 100.9(°C)Stripper, condenser duty (kW) 1238 1877Stripper, reboiler temperature112.8 124.4(°C)Stripper, reboiler duty (kW) 7493 20470CO2rich stream on top Ftotal (kmol / h) 248.9 466.7 xi(mol / mol) CO2 0.8306 0.4448 H2O 0.1232 0.5498 C2H40.0439 0.0018 H2 0.0023 0.0036 MEA 8E-14 4E-08 Liquid stream on bottom with MEA Ftotal (kmol / h) 8225 19618 xi (mol / mol) CO20.0480 0.005 H2O 0.8316 0.945 MEA 0.1204 0.0505 MEA makeup (kmol / h) 3.6E-4 5.2E-4 H2O makeup (kmol / h) 28.0 (can be 256.1 (can be recycled) recycled) It should be mentioned that the lean and rich amine loading of 0.398 and 0.607 mol CO2 / mol MEA, respectively, are somewhat high for the 30 wt.% MEA case, see Table 13, and the operation could result in material corrosion. One recommendation for non-corrosive operation is to use 10-15 wt.% MEA solution and aim for lean and rich loading of 0.1 and 0.3 mol CO2 / mol MEA, respectively. However, in that case, the energy consumption of the reboiler for the 15 wt.% MEA case is some 2.7 higher in value compared to the 30 wt.% MEA case. At the top of the stripper column, some amount of ethylene can be found in the gas stream, which got physically absorbed in the absorption column along with CO2that got chemically absorbed. Since the gas stream from the stripper column is rich in CO2, it is envisaged thatthis stream with some amount of C2H4 is recycled back to the electrolyser inlet (notdemonstrated here). The pump duties associated to the caustic tower, or the ‘polishing CO2’ section downstream the amine absorption column, are given in Table 8.Table 8. CO2 absorption with 25 wt.% NaOH solution, pump dutiesCaustic circulation pump, duty (kW) 4 Flowrate (m3 / h) 11.7 Water circulation pump, duty (kW) 2.2 Flowrate (m3 / h) 9.2The caustic and water circulation pumps are appropriate sizing from the reference design.H2O Removal Step Table 9. H2O removal with adsorbent bed, duties of the heater and cooler for drier regeneration Outlet moisture level (wt. ppm) <1Regeneration cycle time (hrs) 24Regen heater, duty (kW) 293.3 Outlet temperature (°C) 230 Regen cooler, duty (kW) 512.1 Outlet temperature (°C) 40 H2 removal step and cryogenic separation At the bottom of the cryogenic distillation column, ethylene is collected with high purity, see Table 10. All the other specifications for polymer grade ethylene are met as well.The case where upstream H2 separation by membranes is envisaged, as already explained,results in higher temperatures throughout the distillation column due to less stringent specifications at the top of the column, see Table 10.Table 10. Simulation results – cryogenic distillation columnNo upstream H2 separation with Upstream H2 membranes separation with membranes Condenser temperature-115.0 -29.61(°C) Condenser duty (kW) 1106 680.9Reboiler temperature (°C) -34.44 -5.616Reboiler duty (kW) 112.8 202.4Stream on bottom Ftotal (kmol / h) 222.8 222.8 xi (mol / mol) C2H4 0.999995 0.999990 H2O 8.95E-7 4.36E-07 H2 4.00E-6 8.60E-06 Stream on top Ftotal (kmol / h) 214.5 11.7 xi (mol / mol) H2 0.962 0.3465 C2H4 0.037 0.6535 H2O 1.05E-6 1.05E-6 Reflux ratio (mol / mol) 1.13 24.77To obtain the required condenser duty at a certain temperature on top of the distillation column, a refrigeration loop exists. The simulation results for this part of the process scheme are given in Table 11.Table 11: Simulation results – refrigeration loop at the top of the cryogenic distillation columnNo upstream H2 Upstream H2 separation with separation with membranes membranes Propene refrigeration loop Compressor duty (kW) 1741.6 528.5Cooler duty (kW) 3558.9 1205.7Cooler temperature (°C) 50 50 Binary refrigeration loop Compressor duty (kW) 2089.2 N.A.Cooler duty (kW) 1366.0 N.A.Cooler temperature (°C) 50 N.A.Cross-heat exchanger (kW)1817.3 N.A.heat exchange between propene and binary mixtureIt can be seen from Table 11 that conception of membranes for H2 separation upstream of thecryogenic distillation column results in a less complex refrigeration section, as expected from the temperature value at the top of the distillation column. Energy Intensity Breakdown If the duties of coolers / heaters and work duties of pumps and compressors are considered for all the sections, the energy intensity of the downstream gas cathode separation process can be broken down as shown in Fig.5. It should be stressed once again that the total energy intensity does not account for the anode gas product separation and the liquid product separation, which will be discussed in separate documents. The substantial contribution to the total energy intensity of the process comes from the CO2removal section, more precisely, from the heat duty of the reboiler in the stripper section. This duty can be lower in the case less CO2is present in the flue gas coming from the electrolyser,i.e., CO2 conversion per pass is higher in the electrolyser upstream of the separation section.By envisaging membranes for H2separation upstream of the cryogenic distillation column, theenergy intensity of the cryogenic separation section can be lowered by some 65%.

Claims

CLAIMS 1. A process to perform a gas separation comprising the following steps:a) providing a gas stream (5) being the cathode product gas phase of an CO2 toethylene conversion electrolyser (3) and comprising ethylene, carbon dioxide,hydrogen, and water;b) optionally, subjecting said gas stream (5) to compression to obtain acompressed gas stream (11);c) performing a carbon dioxide removal on the gas stream (5) or on thecompressed gas stream (11) to produce a CO2-lean gas stream (21);d) drying said CO2-lean gas stream (21) to produce a dehydrated gas stream (29);f) performing a cryogenic separation to obtain an ethylene-containing stream (41);wherein the process is characterized in that the gas stream (5) is devoid of carbon monoxide and methane; in that the process further comprises a step e) of performinga hydrogen separation before step f) of cryogenic separation to produce an H2-leangas stream (35) and in that the step f) of cryogenic separation is performed on the H2-lean gas stream (35), by cooling said H2-lean gas stream (35) to reach a temperatureranging from -29°C to -60°C.

2. The process according to claim 1 is characterized in that step f) of cryogenic separationis performed in a single refrigeration stage on a cryogenic distillation column; and / or inthat hydrogen separation is performed using membranes.

3. The process according to claim 1 or 2 is characterized in that the process furthercomprises a preliminary step of producing the gas stream (5) by performing a CO2 toethylene conversion with an electrolyser (3).

4. The process according to claim 3 is characterized in that the electrolyser (3) is amembrane electrode assembly with a bipolar membrane and / or in that the CO2 toethylene conversion is a one-step CO2 electroconversion process.

5. The process according to claim 3 or 4 is characterized in that the preliminary step ofproducing the gas stream (5) is performed in presence of a cathode catalyst comprising one or more selected from copper, gold, silver, zinc, nickel, bismuth, copper oxide, tin oxide, titanium dioxide, or any mixture thereof; preferably the cathode catalyst is orcomprises copper and / or copper oxide.

6. The process according to any one of claims 1 to 5 is characterized in that step c) ofcarbon dioxide removal is a step or comprises a sub-step of carbon dioxide removal by amine solution.

7. The process according to claim 6 is characterized in that the amine solution comprisesone or more amines selected from monoethanolamine, diethanolamine, diglycolamine,methyldiethanolamine, triethanolamine, piperazine and (piperazinyl-1)-2-ethylamine.

8. The process according to any one of claims 1 to 7 is characterized in that step c) ofcarbon dioxide removal comprises a sub-step of carbon dioxide removal by an amine solution followed by a sub-step of a carbon dioxide removal by an alkaline solution.

9. The process according to claim 8 is characterized in that the amine solution comprisesfrom 10 to 40 wt.% of monoethanolamine based on the total weight of the amine solution.

10. The process according to claim 8 or 9 is characterized in that the alkaline solutioncomprises from 10 to 35 wt.% of sodium hydroxide based on the total weight of the alkaline solution.

11. The process according to any one of claims 1 to 10 is characterized in that step d) ofdrying comprises a first sub-step of vapor-liquid separation or adsorption, followed bya second sub-step of drying using molecular sieves.

12. The process according to any one of claims 1 to 11 is characterized in that theethylene-containing stream (41) obtained in step f) comprises at least 99.9 mol.% ofethylene as determined by ASTM D2505-88 (2015).

13. The process according to any one of claims 1 to 12 is characterized in that the gasstream (5) provided in step a) comprises, based on the total molar content of the gasstream (5), at least 20 mol.% of ethylene; at least 15 mol.% of carbon dioxide; at least 15 mol.% of hydrogen and at least 10 mol.% of water.

14. An installation to perform a gas separation on a gas stream comprising ethylene,carbon dioxide, hydrogen, and water characterized in that the installation comprises,in the following order: -a CO2-removal unit (13);- a drying unit (23);- an H2-removal unit (31); and- a cryogenic separation unit (37) comprising a cryogenic distillation column.

15. The installation according to claim 14 is characterized in that it further comprises agas compressor unit (7) placed upstream of the CO2-removal unit (13).

16. The installation according to claim 14 or 15 is characterised in that it further comprisesan electrolyser (3) comprising a cathode and an anode, and a membrane.

17. The installation according to claim 16 is characterized in that the electrolyser (3) is amembrane electrode assembly with a bipolar membrane.

18. The installation according to claim 16 or 17 is characterized in that the electrolyser (3)is a membrane electrode assembly being a one-gap electrolyser wherein themembrane is in contact with the cathode.

19. The installation according to any one of claims 16 to 18 is characterized in that thecathode comprises a catalyst wherein the cathode catalyst comprises one or moreselected from copper, gold, silver, zinc, nickel, bismuth, copper oxide, tin oxide, titanium dioxide, or any mixture thereof; preferably the cathode catalyst is or comprisescopper and / or copper oxide.

20. The installation according to any one of claims 14 to 19 is characterised in that theCO2-removal unit (13) comprises an amine absorption column (15) and a caustic tower(19).

21. The installation according to any one of claims 14 to 20 is characterized in that thedrying unit (23) comprises a vapor-liquid separator (25) followed by a molecular sievesdryer system (27).

22. The installation according to any one of claims 14 to 21 is characterised in that the H2-removal unit (31) comprises one or more H2 separation membranes (33).

23. The installation according to any one of claims 14 to 22 is characterised in that thecryogenic separation unit comprises propene as the refrigerant.

24. The installation according to any one of claims 14 to 23 is characterized in that itcomprises a recycle line (43) recycling the stream from the top of the column (39) tothe stream entering the H2-removal unit (31).

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