WO2014000113A1

WO2014000113A1 - Techniques for biocatalytic treatment of co2-containing gas and for separation of biocatalyst from ion loaded streams

Info

Publication number: WO2014000113A1
Application number: PCT/CA2013/050510
Authority: WO
Inventors: Sylvie Fradette; Jingui HUANG; Geert Frederik Versteeg
Original assignee: Co2 Solutions Inc.
Priority date: 2012-06-29
Filing date: 2013-07-02
Publication date: 2014-01-03

Abstract

Various enzyme-enhanced CO₂ capture techniques are described. In some implementations, a process for CO₂ capture includes absorption and desorption stages, and a separation stage for removing at least a portion of the enzymes from the ion loaded solution. The enzyme-depleted solution is supplied to desorption, while the enzyme-enriched solution is recycled back into the absorption stage. A filtration membrane may be used for the separation stage. In some scenarios, the separation may provide the enzyme enriched solution with sufficient fluidity for liquid transport through a conduit back into the absorption stage. The separation may be conducted in accordance with a selected absorption compound, such as an amino or carbonate compound, such that the recycle flow of the enzyme-enriched solution is sufficiently low so that the enzyme-enhanced CO₂ capture system maintains energy efficiency. Other techniques related to enzyme separation are described and can further improve CO₂ capture.

Description

TECHNIQUES FOR BIOCATALYTIC TREATMENT OF C0₂-CONTAINING GAS AND FOR SEPARATION OF BIOCATALYST FROM ION LOADED STREAMS

FIELD OF THE INVENTION

The present invention generally relates to the treatment of a C0₂ containing gas using biocatalysts. The invention also relates to a process for producing a C0₂ capture product and a process for separating biocatalyst from an ion-loaded fluid.

BACKGROUND

The treatment of C0₂-containing gas has been conducted by leveraging biocatalysts to enhance the absorption of C0₂ into an aqueous absorption solution. Biocatalysts have been provided immobilized within a reactor or flowing with the solution in the reactor either as dissolved biocatalyst or on particles. There are various technical and economic difficulties associated with these techniques.

When biocatalysts, such as enzymes, are dissolved or suspended in the absorption solution or the enzymes are immobilized with respect to particles suspended in the absorption solution, the biocatalysts may be present in the ion loaded solution withdrawn from the absorption reactor. This ion loaded solution is often treated to remove the bicarbonate ions and thus regenerate a solution that may be recycled as the absorption solution. The regeneration may include desorption where C0₂ gas is desorbed or carbonation where the bicarbonate ions are transformed into solids. The regeneration stage may have conditions that tend to denature the biocatalysts present in the ion loaded solution. For instance, a desorption unit can be operated at high temperatures that various biocatalysts cannot withstand. The denaturing of biocatalyst incurs various disadvantages, such as costly addition of fresh biocatalysts into the absorption solution or more complex methods for delivering the biocatalysts to decrease denaturing. For example, there may be a significant temperature swing going from approximately 25-65'C, or 35-45^*0, under absorbing conditions, up to 80-130Ό, or 105-120Ό, under regeneration conditions in a desorption stage.

The biocatalysts may be enzymes. Enzymes accelerating the reaction of C0₂ with water are found naturally in living organisms. A non-limiting example of biocatalyst for the transformation of C0₂ into bicarbonate and hydrogen ions, is carbonic anhydrase, which catalyses the following hydration reaction: carbonic anhydrase

C0₂+ H₂0 - - HCO3- + H⁺

Some carbonic anhydrases can denature and/or lose activity at temperatures above 40'C, while other carbonic anhydrases can withstand higher temperatures for a certain amount of time. However, high temperature resistant carbonic anhydrases may be difficult to design and produce, and can be relatively expensive.

Although enzyme stability and durability may be improved under absorbing conditions, there is still a challenge associated with enzymes in desorption conditions that can result in severe or complete degradation of the enzymes.

There is a need for a technology that overcomes at least some of the problems encountered in this field, in order to improve techniques for the treatment of C0₂- containing gas.

SUMMARY OF THE INVENTION

Various techniques are provided for biocatalytically-enhanced C0₂ capture operations. The techniques may involve generating a biocatalyst-containing ion loaded solution that is withdrawn from a C0₂ absorption reactor and is subjected to a separation step to produce a biocatalyst-enriched stream and a biocatalyst-depleted stream. The separation step may be performed using filtration, for example using a filtration membrane, and may be controlled to provide various advantages. In some implementations, there is provided a process for treating a C0₂-containing gas, the process comprising the steps of: a) contacting within a reaction chamber, the C0₂-containing gas with a hybrid reactive solvent which is water based and comprises a biocatalyst selected from the group consisting of free enzymes, free enzymes analogues, enzymes released from a porous matrix located within the reaction chamber, immobilized enzymes and immobilized enzymes analogues, the biocatalyst accelerating an enzymatic conversion of C0₂ into bicarbonate ions, comprising: i) dissolving the C0₂-containing gas in the hybrid reactive solvent; and ii) promoting the enzymatic conversion of the dissolved C0₂ into bicarbonate and hydrogen ions; b) obtaining a C0₂-depleted C0₂-containing gas, optionally defining a treated gas, the C0₂-depleted gas being then released from the reaction chamber; c) obtaining a hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst, optionally defined as an ion loaded solution; and d) removing from the reaction chamber at least a portion of the hybrid reactive solvent of step c) and filtering the same on a filtration membrane, optionally a filtration membrane that is inert to the hybrid reactive solvent, said filtration membrane being provided with pores optionally having smaller diameter than a diameter of the biocatalyst and having an upstream side and a downstream side; to thereby obtain: i) at the upstream side of the filtration membrane, a retentate fluid rich in the biocatalyst and which is bicarbonate loaded, and ii) at the downstream side of the filtration membrane, a permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst.

In some implementations, the retentate fluid has a flow rate FR1 which may vary from 1 % FF to 10% FF, or from 5% FF to 10% FF, and wherein the permeate fluid has a flow rate FR2 which may vary from 90% FF to 99% FF, or from 90% FF to 95% FF, with FF corresponding to a feed flow rate to the membrane. In some implementations, the feed flow rate may vary from 100 m³/h to 20,000 m³/h, or from 500 m³/h to 10,000 m³/h. The retentate fluid flow rate may be adjusted in order to minimize its impact on the total energy penalty of the process, which may be due to the rich C0₂ loading of the retentate flow and to the C0₂ desorption requirements in a downstream desorption unit.

In some implementations, the retentate fluid includes a sufficient amount of liquid to provide fluidity for liquid transport via a conduit, such as a pipeline.

In some implementations, a ratio FR1 / FR2 is provided so as to keep the retentate fluid pumpable with the biocatalyst solubilised or suspended therein. The biocatalyst may be completely dissolved or partially dissolved with some precipitated biocatalyst in suspension.

In some implementations, a portion of the permeate fluid obtained from step d)-ii) is recycled to the retentate fluid to dilute the same and adjust the ratio FR1 / FR2 within a range keeping the retentate fluid pumpable with the biocatalyst solubilised or suspended therein. It should also be noted that the retentate fluid may include biocatalyst precipitates and once the retentate fluid is combined with a regenerated solution produce from desorption, the resulting solution is effectively diluted and ensures dissolution of the biocatalysts. In some implementations, the ratio FR1/FR2 defines the ratio of flow rate of the permeate to flow rate of the retentate and may be controlled. In some scenarios, FR1 may be between 1 % and 50% of FF, between 5% and 50% of FF, between 10% and 40% of FF, or between 20% and 30% of FF. The ratio FR1/FR2 may also be between 0.01 to 1 (which corresponds to about 1 -50% of the FF as the retentate and about 50-99% of the FF as the permeate), or between 0.05 to 0.1 (which corresponds to 5-10% of the FF as the retentate and 90-95% of the FF as the permeate).

In some implementations, the retentate fluid flows tangentially with respect to the upstream side of the membrane.

In some implementations, at least a portion of the retentate fluid obtained from step d)-i) is further recycled to the reaction chamber.

In some implementations, at least a portion of the permeate fluid obtained from step d)-ii) is further fed to a regeneration unit to produce a C0₂ capture product and a regenerated hybrid solvent.

In some implementations, the process produces a C0₂ capture product, such may include C0₂, a precipitated bicarbonate and/or a precipitated carbonate. In such a case, a two-stage filtration can be performed. In a case where free enzyme is used and that precipitated bicarbonate/carbonate are larger particles than the enzyme, a first step would be to remove the precipitated compound first and then remove the free enzyme. The sequence for the removal of the precipitated bicarbonate/carbonate and the free enzyme and /or immobilized enzymes depends on their relative size.

In some implementations, the regenerated hybrid solvent is recycled back into the reaction chamber to form at least part of the hybrid reactive solvent. In some implementations, the regenerated hybrid solvent is combined with the retentate fluid to form at least part of the hybrid reactive solvent prior to being introduced into the reaction chamber.

In some implementations, the process is a continuous process.

In some implementations, the biocatalyst is selected from the group consisting of free enzymes and free enzymes analogues.

In some implementations, the biocatalyst is selected from the group consisting of free enzymes, free enzymes analogues, and free enzymes released from a porous matrix located within the reaction chamber, preferably carbonic anhydrase free enzymes or analogues thereof, having a molecular mass ranging from 5 kDa to 120 kDa.

In some implementations, the free enzymes or free enzymes analogues comprise carbonic anhydrase or analogues thereof. Also, carbonic anhydrase may be selected from the group consisting of monomeric and multimeric carbonic anhydrases from different classes.

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes or immobilized enzymes analogues in which said enzymes or enzymes analogues are attached to an insoluble support consisting of particles composed of nylon, cellulose, silica, alumina, silica gel, chitosan, polystyrene, polymethylmethacrylate, magnetic material, titanium oxide, zirconium oxide or any combination thereof. The biocatalysts may be supported on any other particle material suitable for enzyme immobilization. In the case of providing the biocatalyst on particles, particle size may be below 10 microns, for example, to enhance the biocatalytic impact in the absorption solution. In some scenarios, the particles may be sized to provide an enhanced impact where the enzyme is present in the liquid film at the gas-liquid interface. In some implementations, the particles are nylon or alumina or titanium oxide or zirconium oxide particles

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues, and wherein enzymes or enzymes analogues have a molecular mass ranging from 5 kDa to 120 kDa.

In some implementations, the enzymes or analogues thereof comprise carbonic anhydrase or analogues thereof. Also, carbonic anhydrase may be selected from the group consisting of monomeric and multimeric carbonic anhydrases from different classes.

In some implementations, the filtration membrane is inert to the hybrid reactive solvent.

In some implementations, the filtration membrane is a nano-filtration membrane. The filtration membrane in some other scenarios, may be an ultrafiltration membrane or may include other "super" filtration means.

In some implementations, the nano-filtration membrane is provided with pores having a diameter that is smaller than 15 nm.

In some implementations, the nano-filtration membrane is provided with pores having a diameter between 1 and 5 nm.

In some implementations, the filtration membrane is a hollow fiber membrane or comprises elements of a hollow fiber membrane.

In some implementations, the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone, polyethylene (PE), polypropylene (PP), polysulfone (PS), polyamide (PA), polyamide-imide (PAI), polyvinylidene difluoride (PVDF), polyetheretherketone (PEEK), polyetherimide (PEI), polyvinylpyrrolydone and/or polyimide (PI) hollow fiber (HF) membranes. In some implementations, the hybrid reactive solvent is a mixture of water and of a compound comprising at least one of piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1 ,3-propanediol (Tris also known as AHPD), N- methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), diethanolamine (DEA), diisopropylamine (DIPA), methyl monoethanolamine (MMEA), TIA, TBEE, HEP, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)- ethane (BTEE), ethoxyethoxyethanoltertiarybutylamine (EEETB), bis- (tertiarybutylaminoethyl)ether, 1 ,2-bis-(tertiarybutylaminoethoxy)ethane or bis-(2- isopropylaminopropyl)ether, and the like, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, and derivatives such as taurine, N.cyclohexyl 1 ,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine, sarcosine, methyl taurine, methyl-a-aminopropionic acid, N-^-ethoxy)taurine, N-^-aminoethyl)taurine, N-methyl alanine, 6- aminohexanoic acid and potassium or sodium salts of the amino acids, or mixtures thereof, sodium carbonate, potassium carbonate and ammonium carbonate. The concentration of the compound in the hybrid reactive solvent may vary from 0.2 to 8 M.

In some implementations, the compound of the hybrid reactive solvent is selected from the group consisting of primary amines, secondary amines, tertiary amines, primary alkanolamines, secondary alkanolamines, tertiary alkanolamines, primary amino acids, secondary amino acids, tertiary amino acids, and carbonates.

In some implementations, the component of the hybrid reactive solvent comprises a carbonate selected from the group consisting of potassium carbonate, sodium carbonate, ammonium carbonate and mixtures thereof. In some implementations, there is provided an installation for the treatment of a C0₂- containing gas, the installation comprising: a) a reactor provided with a reaction chamber receiving a hybrid reactive solvent which is water based and comprises a biocatalyst selected from the group consisting of enzymes, enzymes analogues, enzymes released from a porous matrix located within the reaction chamber, immobilized enzymes and immobilized enzymes analogues, preferably enzymes or enzymes analogues supported on particles, the biocatalyst accelerating the conversion of C0₂ into bicarbonate ions; the reactor further comprising: a-1) a gas inlet in fluid communication with a source of C0₂-containing gas to be treated, for contacting the C0₂-containing gas with the hybrid reactive solvent, dissolving the gas in the hybrid reactive solvent, and promoting the biocatalytic conversion of the dissolved C0₂ into bicarbonate ions, for i) producing a C0₂-depleted gas, optionally defining a treated gas, and ii) providing hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst; a-2) a gas outlet in fluid communication with the reaction chamber for the release the C0₂-depleted gas; and a-3) a hybrid reactive solvent outlet in fluid communication with the reaction chamber for collecting at least a portion of the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst; b) a filtration unit comprising: b-1) a filtration membrane, optionally a filtration membrane that is inert to the hybrid reactive solvent, the reaction membrane being provided with pores optionally having smaller diameter than a diameter of the biocatalyst, the membrane having an upstream side and a downstream side; b-2) a hybrid reactive solvent inlet which is in fluid communication with the hybrid reactive solvent outlet of the reactor and in fluid communication with the upstream side of the filtration membrane; b-3) an outlet in fluid communication with the upstream side of the filtration membrane for recovery of a retentate fluid collected on the upstream side of the filtration membrane and rich in the biocatalyst; and b-4) an outlet in fluid communication with the downstream side of the filtration membrane for the recovery of a permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst.

In some implementations, the installation also has a hybrid reactive solvent inlet in fluid communication with the reaction chamber for the addition of fresh hybrid reactive solvent to the reaction chamber.

In some implementations, the membrane may be of the type used for nano-filtration, ultra-filtration or micro-filtration systems. More particularly, membranes for nano- filtration or ultra-filtration systems are preferred for free enzymes, free enzymes analogues and immobilized nano-particles filtration; while membranes for micro- filtration system are preferred for the immobilized system with an average particle size of 1 μηι or larger , for example 5-7 μηι or larger. Also, other larger particles (e.g., > 10 μηι) may be separated by sedimentation, hydrocyclones, or centrifugal separation, decantation, etc.

In some implementations, a first conduit is provided between the hybrid reactive solvent outlet of the reactor, and the hybrid reactive solvent inlet of the filtration unit, to allow fluid communication therebetween of the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst, to the filtration unit, the first conduit being optionally further provided with a pumping device for pumping the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst therethrough.

In some implementations, the installation also has a first conduit assembly comprising conduits for the recycling of at least a part of the retentate fluid rich in biocatalyst to the reaction chamber, said first conduit assembly being optionally provided with a pumping device for pumping the retentate fluid therethrough.

In some implementations, the installation also has a second conduit assembly comprising conduits for the recovery of the permeate fluid collected downstream of the filtration membrane and for optionally recycling at least a portion thereof to the upstream side of the filtration membrane to dilute the retentate fluid; a device for the measurement of physical properties (such as viscosity, temperature, etc.) of the retentate fluid collected on the upstream side of the filtration membrane; said device controlling a valve provided across the conduits of the second assembly for controlling the recycling of the permeate fluid to the upstream side of the filtration membrane; and optionally said second conduit assembly is provided with a pumping device for pumping the permeate fluid therethrough.

In some implementations, the device is configured to actuate the valve for recycling at least a part of the permeate fluid with the retentate fluid flowing at the upstream side of the filtration membrane, to set a flow rate FR1 at the upstream side of the filtration membrane, which with respect to a flow rate of the permeate fluid flowing at the downstream side of the filtration membrane, with a ratio FR1 / FR2 allowing to keep the retentate fluid pumpable with the biocatalyst solubilised or suspended therein.

In some implementations, the retentate fluid has a flow rate FR1 which may vary from 1 % FF to 10% FF, and wherein the permeate fluid has a flow rate FR2 which may vary from 90% FF to 99%FF, with FF corresponding to a feed flow rate to the membrane. Preferably, the feed flow rate may vary from 100 m³/h to 20,000 m³/h, more preferably from 500 m³/h to 10,000 m³/h. In some implementations, the ratio FR1/FR2 defines the ratio of the flow rate of the permeate to the flow rate of the retentate and may vary from 0.01 to 1 (which corresponds to 1-50% of the FF as the retentate and 50-99% of the FF as the permeate).

In some implementations, the installation also includes a third conduit assembly comprising conduits for feeding a regeneration unit, optionally a desorption unit, with the permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst, said regeneration unit being further provided with an outlet for a C0₂ capture product and an outlet for a regenerated hybrid solvent comprising the permeate fluid depleted in bicarbonate ions, said third conduit assembly being optionally provided with a pumping device for pumping the permeate fluid therethrough.

In some implementations, the C0₂ capture product includes C0₂ for sequestration or enhanced oil recovery, or includes precipitated bicarbonate and/or precipitated carbonate as pure chemicals or as mineralized industrial residues. Also, it is possible to use the bicarbonate or carbonate containing solution as a nutrient product to grow algae. The bicarbonate solution could also be used as cleaning agent, biopesticide and some other applications such as neutralization of acids and bases, as well as pH level adjustment for swimming pools, spas and garden ponds, etc.

In some implementations, the installation also includes a third conduit assembly comprising conduits for feeding a regeneration unit, optionally a desorption unit, with the permeate fluid defining a bicarbonate loaded fluid depleted in biocatalyst, said regeneration unit being further provided with an outlet for a C0₂ capture product and an outlet for a regenerated hybrid solvent comprising the permeate fluid depleted in bicarbonate ions, said third conduit assembly being optionally provided with a pumping device for pumping the permeate fluid therethrough; a fourth conduit assembly comprising conduits for recycling the regenerated reactive solvent to the reaction chamber and optionally at least a portion thereof with the retentate fluid flowing at the upstream side of the filtration membrane to dilute it, said fourth conduit assembly being optionally provided with a pumping device for pumping the regenerated hybrid solvent therethrough; a device for the measurement of physical parameters (such as viscosity, temperature, etc.) of the retentate fluid collected on the upstream side of the filtration membrane; said device controlling a valve provided across the conduits of the fourth assembly for controlling the recycling of the regenerated hybrid solvent to the upstream side of the filtration membrane; and optionally said fourth conduit assembly is provided with a pumping device for pumping the regenerated hybrid solvent therethrough.

In some implementations, the device when measuring preset physical parameters actuates the valve for recycling at least a part of the regenerated hybrid solvent with the retentate fluid flowing at the upstream side of the membrane to set a flow rate FR1 , which with respect to a flow rate of the permeate fluid flowing at the downstream side of the filtration membrane, at a ratio FR1 / FR2 within such a range to keep the retentate fluid pumpable with the biocatalyst solubilised or suspended therein.

In some implementations, the ratio FR1/FR2 defines the ratio of flow rate of the permeate to flow rate of the retentate and may be controlled. In some scenarios, FR1 may be between 1 % and 50% of FF, between 5% and 50% of FF, between 10% and 40% of FF, or between 20% and 30% of FF. The ratio FR1/FR2 may also be between 0.01 to 1 (which corresponds to 1 -50% of the FF as the retentate and 50-99% of the FF as the permeate). FF corresponds to a feed flow rate to the membrane and can be correlated to a flux. As an example, the flux may range from 1 - 50 LMH/bar (in the case of a reverse osmosis), from 40 - 150 LMH/bar (in the case of nanofiltration), from 50 - 1000 LMH/bar (in the case of ultrafiltration, and from 300 - 2000 LMH/bar (in the case of microfiltration).

In some implementations, a continuous process is carried out in the installation.

In some implementations, the retentate fluid includes sufficient amount of liquid to provide fluidity for liquid transport via a conduit. In some implementations, the retentate fluid flows tangentially with respect to the upstream side of the membrane.

In some implementations, the process is a continuous process.

In some implementations, the biocatalyst is selected from the group consisting of free enzymes, free enzymes analogues and free enzymes released from a porous matrix located within the reaction chamber.

In some implementations, the biocatalyst is selected from the group consisting of free enzymes and free enzymes analogues having a molecular mass ranging from 5 kDa to 120 kDa.

In some implementations, the free enzymes or analogues thereof comprise carbonic anhydrase or analogues thereof. Also, carbonic anhydrase may be selected from the group consisting of monomeric and multimeric carbonic anhydrases from different classes.

In some implementations, the biocatalyst is selected from the group- consisting of immobilized enzymes and immobilized enzymes analogues, in which said enzymes or enzymes analogues are attached to an insoluble support consisting of particles composed of nylon, cellulose, silica, alumina, silica gel, chitosan, polystyrene, polymethylmethacrylate, magnetic material, titanium oxide, zirconium oxide or any combination thereof.

In some implementations, the particles are nylon or alumina, or titanium oxide or zirconium oxide particles.

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues, wherein enzymes or enzymes analogues have a molecular mass ranging from 5 kDa to 120 kDa.

In some implementations, the filtration membrane is a nano-filtration membrane.

In some implementations, the filtration membrane is a hollow fiber membrane or comprises a hollow fiber membrane portion.

In some implementations, the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone or on a mixture of polyether sulfone and polyvinylpyrrolydone.

In some implementations, the hybrid reactive solvent is a mixture of water and of a compound comprising at least one of piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1 ,3-propanediol (Tris also known as AHPD), N- methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), diethanolamine (DEA), diisopropylamine (DIPA), methyl monoethanolamine (MMEA), TIA, TBEE, HEP, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)- ethane (BTEE), ethoxyethoxyethanoltertiarybutylamine (EEETB), bis- (tertiarybutylaminoethyl)ether, 1 ,2-bis-(tertiarybutylaminoethoxy)ethane or bis-(2- isopropylaminopropyl)ether, and the like, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, and derivatives such as taurine, N.cyclohexyl 1 ,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine, sarcosine, methyl taurine, methyl-a-aminopropionic acid, N-^-ethoxy)taurine, N-^-aminoethyl)taurine, N-methyl alanine, 6- aminohexanoic acid and potassium or sodium salts of the amino acids, or mixtures thereof, sodium carbonate, potassium carbonate and ammonium carbonate..

In some implementations, the component of the hybrid reactive solvent comprises a carbonate selected from the group consisting of potassium carbonate, sodium carbonate, ammonium carbonate and mixtures thereof.

In some implementations, there is provided a process for treating a C0₂-containing gas, comprising: contacting the C0₂-containing gas with a hybrid reactive solvent comprising a biocatalyst catalyzing hydration of dissolved C0₂ into bicarbonate ions, thereby producing a bicarbonate loaded solution comprising the biocatalyst; separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst; recirculating the biocatalyst stream for reuse in the hybrid reactive solvent; treating the bicarbonate loaded stream by regeneration to remove at least a portion of the bicarbonate ions therefrom and produce a regenerated hybrid solvent; and recirculating the regenerated hybrid solvent to form at least part of the hybrid reactive solvent.

In some implementations, the process also includes one or more features as defined in the above-mentioned implementations.

In some implementations, there is provided a process of producing a C0₂ capture product, comprising: contacting a C0₂-containing gas with hybrid reactive solvent comprising a biocatalyst catalyzing hydration of dissolved C0₂ into bicarbonate ions, thereby producing a bicarbonate loaded solution comprising the biocatalyst; separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst; recirculating the biocatalyst stream for reuse in hybrid reactive solvent; treating the bicarbonate loaded stream by regeneration to remove at least a portion of the bicarbonate ions therefrom, to produce the C0₂ capture product and a regenerated hybrid solvent; and recirculating the regenerated solution to form at least part of the hybrid reactive solvent.

In some implementations, the C0₂ capture product comprises C0₂, a precipitated bicarbonate and/or a precipitated carbonate.

In some implementations, the process is a continuous process. In some implementations, the biocatalyst is selected from the group consisting of free enzymes, free enzymes analogues and free enzymes released from a porous matrix located within the reaction chamber.

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues in which said enzymes or enzymes analogues are attached to an insoluble support consisting of particles composed of nylon, cellulose, silica, alumina, silica gel, chitosan, polystyrene, polymethylmethacrylate, magnetic material, titanium oxide or zirconium oxide or any combination thereof.

In some implementations, the particles are nylon, alumina, titanium oxide or zirconium oxide particles.

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues wherein enzymes or enzymes analogues have a molecular mass ranging from 5 kDa to 120 kDa.

In some implementations, the step of separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst is carried out on a filtration membrane provided with pores having smaller diameter than a diameter of the biocatalyst.

In some implementations, the filtration membrane is a nano-filtration membrane.

In some implementations, the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone, or based on a mixture of polyether sulfone and polyvinylpyrrolydone.

In some implementations, the hybrid reactive solvent is a mixture of water and of a compound comprising at least one of piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1 ,3-propanediol (Tris also known as AHPD), N- methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), diethanolamine (DEA), diisopropylamine (DIPA), methyl monoethanolamine (MMEA), TIA, TBEE, HEP, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)- ethane (BTEE), ethoxyethoxyethanoltertiarybutylamine (EEETB), bis- (tertiarybutylaminoethyl)ether, 1 ,2-bis-(tertiarybutylaminoethoxy)ethane or bis-(2- isopropylaminopropyl)ether, and the like, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, and derivatives such as taurine, N.cyclohexyl 1 ,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine, sarcosine, methyl taurine, methyl-a-aminopropionic acid, N-^-ethoxy)taurine, N-^-aminoethyl)taurine, N-methyl alanine, 6- aminohexanoic acid and potassium or sodium salts of the amino acids, or mixtures thereof, sodium carbonate, potassium carbonate and ammonium carbonate.

In some implementations, there is provided a process for separating a biocatalyst from a bicarbonate loaded fluid, comprising: managing temperature and concentration of the bicarbonate loaded fluid to avoid precipitation and substantial denaturing of the biocatalyst, and removing a biocatalyst rich stream from the bicarbonate loaded fluid such that the biocatalyst rich stream retains sufficient fluidity for liquid transport.

In some implementations, the process may also include one or more of the following features: absorption temperature: from - δΟ , optionally from 20^ - 40'C; [NaHC0₃] : 0.6 M or less (optionally or 1-5 wt% of NaHC0₃), or 0.6 M (or 5 wt% of NaHC0₃); or

[Na₂C0₃] : 0.3 M or less (or optionally 1 - 3.2 wt%), or 0.3 M (or 3.2 wt% of Na₂C0₃).

In some implementations, the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues, wherein enzymes or enzymes analogues have a molecular mass ranging from 5 kDa to 120 kDa. In some implementations, the enzymes or analogues thereof comprise carbonic anhydrase or analogues thereof. Also, carbonic anhydrase may be selected from the group consisting of monomeric and multimeric carbonic anhydrases from different classes.

In some implementations, the step of separating the bicarbonate loaded fluid into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst is carried out on a filtration membrane provided with pores having smaller diameter than a diameter of the biocatalyst.

In some implementations, the filtration membrane is a nano-filtration membrane.

In some implementations, the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone or based on a mixture of polyether sulfone and polyvinylpyrrolydone.

In some implementations, the process includes a step for minimizing liquid in the biocatalyst stream.

In some implementations, the biocatalyst stream has sufficient fluidity to facilitate mixing into an aqueous absorption solution. In some implementations, the temperature, biocatalyst concentration, bicarbonate concentration and/or viscosity of the biocatalyst stream are controlled to enable the sufficient fluidity for liquid transport.

In some implementations, there is provided a process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separating step comprises managing the enzyme enriched solution so as to comprise sufficient water to be a pumpable and pipelinable solution; and pumping at least a portion of the enzyme loaded solution through a recycle pipeline back into the absorption reactor.

In some implementations, the step of managing the enzyme enriched solution comprises controlling relative flow rates of the enzyme depleted solution and the enzyme enriched solution.

In some implementations, the step of managing the enzyme enriched solution comprises controlling solids content of the enzyme enriched solution.

In some implementations, the separating step comprise subjecting the ion loaded solution to filtration, such that the enzyme enriched solution is a retentate fluid and the enzyme depleted fluid is a permeate fluid.

In some implementations, the filtration is performed with a membrane filter. In some implementations, the step of managing the enzyme enriched solution comprises controlling a pressure of the ion loaded solution and providing a membrane pore size of the membrane filter.

In some implementations, the enzyme depleted fluid comprises no carbonic anhydrase.

In some implementations, the process includes supplying the enzyme depleted fluid to a desorption reactor; operating the desorption reactor under conditions to promote release of C0₂ gas from the ion loaded solution, thereby producing a regenerated solution; releasing the regenerated solution from the desorption reactor; and supplying the regenerated solution back to the absorption reactor.

In some implementations, the process includes combining at least a portion of the regenerated solution and at least a portion of the enzyme enriched solution to produce a combined solution; and feeding the combined solution back into the absorption reactor as the absorption solution.

In some implementations, the enzyme enriched solution includes precipitated and/or suspended solid carbonic anhydrase, and the step of combining the regenerated solution with the enzyme enriched solution is performed so as to substantially dissolve the carbonic anhydrase prior to feeding the combined solution back into the absorption reactor.

In some implementations, there is provided a process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separating step comprises managing the enzyme enriched solution so as to retain sufficient fluidity for liquid transport; and transporting at least a portion of the enzyme loaded solution through a recycle pipeline back into the absorption reactor.

In some implementations, there is provided a process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme loaded solution, wherein the enzyme depleted solution comprises residual carbonic anhydrase; and supplying the enzyme depleted solution to a desorption reactor, wherein the residual carbonic anhydrase provides catalysis of the desorption of C0₂, to form a regenerated solution.

In some implementations, the separating step is controlled such that the residual carbonic anhydrase in the enzyme depleted solution comprises at most about 25 wt% of the carbonic anhydrase in the ion loaded solution.

In some implementations, the separating step is controlled such that the residual carbonic anhydrase in the enzyme depleted solution comprises at most about 15 wt%, about 10 wt%, about 5 wt% or about 2 wt% of the carbonic anhydrase in the ion loaded solution. In some implementations, the separating step comprise subjecting the ion loaded solution to filtration, such that the enzyme enriched solution is a retentate fluid and the enzyme depleted fluid is a permeate fluid.

In some implementations, the process includes operating the desorption reactor under conditions such that a portion of the residual carbonic anhydrase undergoes denaturation and a portion of the residual carbonic anhydrase retains activity upon release from the desorption reactor; and supplying the regenerated solution including an amount of active carbonic anhydrase back into the absorption reactor.

In some implementations, there is provided a process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase immobilized with respect to a porous matrix, to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein a portion of the carbonic anhydrase leaches out of the porous matrix as released carbonic anhydrase such that the ion loaded solution includes at least a portion of the released carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution; and recycling at least a portion of the enzyme enriched solution back into the absorption reactor.

In some implementations, the porous matrix comprises a polymeric immobilization material.

In some implementations, the polymeric immobilization material is coated onto a substrate. In some implementations, the substrate comprises fixed packing material within the absorption reactor.

In some implementations, the porous matrix is fixed within the absorption reactor.

In some implementations, the porous matrix is configured in the form of particles within the absorption solution.

In some implementations, the particles flow with the absorption solution and the ion loaded solution released from the absorption reactor, and the process further comprises a particle separation step for separating the particles from the ion loaded solution prior to the step of separating the released carbonic anhydrase from the ion loaded solution.

In some implementations, the C0₂ capture product comprises C0₂ gas, a precipitated bicarbonate and/or a precipitated carbonate.

In some implementations, the step of separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst is carried out on a filtration membrane provided with pores having smaller diameter than a diameter of the biocatalyst. In some implementations, the filtration membrane is inert to the hybrid reactive solvent.

In some implementations, the filtration membrane is a nano-filtration membrane.

In some implementations, the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone.

In some implementations, there is provided a process for separating a biocatalyst from a bicarbonate loaded fluid, comprising managing temperature and concentration of the bicarbonate loaded fluid to avoid precipitation and substantial denaturing of the biocatalyst, and removing a biocatalyst rich stream from the bicarbonate loaded fluid such that the biocatalyst rich stream retains sufficient fluidity for liquid transport.

In some implementations, the process also includes minimizing liquid in the biocatalyst rich stream while retaining the sufficient fluidity for liquid transport.

In some implementations, the biocatalyst rich stream has sufficient fluidity to facilitate mixing into an aqueous absorption solution.

In some implementations, the process also includes controlling temperature, biocatalyst concentration, bicarbonate concentration and/or viscosity of the biocatalyst rich stream, to enable the sufficient fluidity for liquid transport.

In some implementations, there is provided a system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution and C0₂-depleted gas, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separation apparatus is configured such that the enzyme enriched solution comprises sufficient water to be a pumpable and pipelinable solution; and a recycle pipeline for receiving at least a portion of the enzyme enriched solution and being fluidly connected to the absorption reactor for supplying the at least a portion of the enzyme enriched solution back into the absorption reactor. implementations, there is provided a system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution and C0₂-depleted gas, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separation apparatus is configured such that the enzyme depleted solution comprises residual carbonic anhydrase; and a desorption feed pipeline for receiving the enzyme depleted solution from the separation apparatus; a desorption reactor in fluid communication with the desorption feed pipeline for receiving the enzyme depleted solution, wherein the residual carbonic anhydrase provides catalysis of the desorption of C0₂, to form a regenerated solution and C0₂ gas. implementations, there is provided a system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase immobilized with respect to a porous matrix, to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein a portion of the carbonic anhydrase leaches out of the porous matrix as released carbonic anhydrase such that the ion loaded solution includes at least a portion of the released carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched fraction; and a transport system for receiving at least a portion of the enzyme enriched solution and being connected to the absorption reactor for supplying the at least a portion of the enzyme enriched fraction back into the absorption reactor.

In some implementations, the enzyme enriched fraction has sufficient fluidity for liquid transport and the transport system comprises a recycle pipeline.

In some implementations, the separation apparatus comprises a filtration membrane.

It should be noted that the systems described above may have one or more additional features as described above or herein.

In some implementations, there is provided a method for improving energy efficiency of a enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage produced by the absorption stage at a recycle flow of at most 30% of the bicarbonate loaded solution, the method comprising providing a carbonate-based absorption solution for circulating through the enzymatic C0₂ capture system.

In some implementations, the separation stage comprising membrane filtration.

In some implementations, the separation stage is regulated such that the recycle flow of the enzyme enriched bicarbonate loaded stream is a sufficiently low proportion of a flow of the bicarbonate loaded solution to have a minimal impact on the energy efficiency compared to no recycling of the enzyme enriched bicarbonate loaded stream back into the absorption stage.

In some implementations, the enzyme enriched bicarbonate loaded stream is at most about 20% of the bicarbonate loaded solution produced by the absorption stage.

In some implementations, the enzyme enriched bicarbonate loaded stream is at most about 10% of the bicarbonate loaded solution produced by the absorption stage.

In some implementations, the carbonate-based absorption solution comprises potassium carbonate and/or sodium carbonate.

In some implementations, there is provided a method for capturing C0₂ with an enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage, the method comprising regulating the separation stage such that a recycle flow of the enzyme enriched bicarbonate loaded stream is a sufficiently low proportion of a flow of the bicarbonate loaded solution to have a minimal impact on energy efficiency of the enzymatic C0₂ capture system compared to no recycling of the enzyme enriched bicarbonate loaded stream back into the absorption stage.

In some implementations, the separation stage comprising membrane filtration.

In some implementations, the absorption solution that for circulating through the enzymatic C0₂ capture system is a carbonate-based absorption solution and the step of regulating the separation stage comprises providing the recycle flow to be at most 30% of the flow of the bicarbonate loaded solution.

In some implementations, the recycle flow is at most 20% of the flow of the bicarbonate loaded solution.

In some implementations, the recycle flow is at most 10% of the flow of the bicarbonate loaded solution.

In some implementations, the absorption solution that for circulating through the enzymatic C0₂ capture system is an amino-based absorption solution and the step of regulating the separation stage comprises providing the recycle flow to be at most 5% of the flow of the bicarbonate loaded solution.

In some implementations, there is provided a method for capturing C0₂ with an enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage, the method comprising minimizing energy consumption by selecting an absorption compound for use in an absorption solution for circulating through the enzymatic C0₂ capture system and selecting a recycle flow of the enzyme enriched bicarbonate loaded stream. In some implementations, the separation stage comprising membrane filtration.

In some implementations, the absorption compound is selected to be a carbonate and the recycle flow is selected to be at most 30% of a flow of the bicarbonate loaded solution.

In some implementations, the carbonate is selected to be potassium carbonate and/or sodium carbonate.

In some implementations, the carbonate is selected to be sodium carbonate.

In some implementations, the absorption compound is selected to be an amino- based absorption solution and the recycle flow is selected to be at most 5% of a flow of the bicarbonate loaded solution. In some implementations, the absorption compound is selected to be an alkanolamine. In some implementations, the alkanolamine is selected to be a tertiary amino compound. In some implementations, the absorption compound is selected to be MDEA.

It should be noted that the methods described above may have one or more additional features as described above or herein.

Other features and embodiments of the present invention will become more apparent from the following description, and in reference to the appended drawings and given as examples only as to show how the invention may be put into practice.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a process flow diagram. Figure 2 is another process flow diagram.

Figure 3 is yet another process flow diagram including a desorption unit. Figure 4 is still another process flow diagram.

Figure 5 is yet another process flow diagram where the reaction chamber of the absorption reactor is packed with material supporting a biocatalyst.

Figure 6 is a schematic of a tangential membrane filter.

Figure 7 is a process flow diagram of a laboratory scale system.

Figure 8 is a graph of flow rate versus pressure variation for various flows of pure water.

Figure 9 is a graph of flow rate versus pressure variation.

Figure 10 is a graph of flow rate versus pressure variation for various flows of aqueous solution of enzyme (100 mg/litre).

Figure 11 is a graph of flow rate versus pressure variation for various flows of aqueous solution of enzyme (400 mg/litre).

Figure 12 is a graph of flow rate versus pressure variation, including various permeate flow (Φ_{ίΜ( t} ) curves for a 28 ml/min flow rate of water, an aqueous solution of lower concentration of enzyme (100 mg/litre) and an aqueous solution of higher concentration of enzyme (400 mg/litre).

Figure 13 is a graph of absorbance (A) versus concentration of enzyme for Experimental 5.

Figures 14 and 15 are graphs of flow curves for an HFc membrane and an HFs membrane using plain water in Experimental 5.1 . Figure 16 is a graph of time development of the flow curves of the 400 mg/l carbonic anhydrase solution for an open microfiltration HFc membrane for Experimental 5.2. The solid line represents the water flow from Figure 14.

Figure 17 is a process diagram of an experimental setup.

DETAILED DESCRIPTION

Various techniques are described for removing biocatalyst from an ion loaded solution withdrawn from a biocatalytically-enhanced C0₂ absorption reactor and handling the biocatalyst-enriched and biocatalyst-depleted streams. The removal step may include managing the flow rates, biocatalyst concentrations, ion concentrations, precipitation levels and/or fluidities of the biocatalyst-enriched and biocatalyst-depleted streams, as will be further described below. The absorption solution for absorbing C0₂ may be a hybrid solution including an absorption compound and the biocatalysts may be removed from the ion loaded solution by means of a filtration membrane adapted for the hybrid solution.

Description of various implementations

Figure 1 shows an example installation 1 for the treatment of a C0₂-containing gas. More particularly, this installation is intended for a continuous treatment of a C0₂- containing gas.

In some implementations, the installation 1 comprises: a) a bioreactor 3 provided with a reaction chamber 5 containing a hybrid reactive solvent 7 that may include water, an absorption compound and a biocatalyst which may be carbonic anhydrase, the biocatalyst accelerating the conversion of C0₂ into bicarbonate and hydrogen ions; the reactor 3 further comprising: a-1) a gas inlet 9 in fluid communication with a source of C0₂-containing gas 11 to be treated, for contacting the C0₂-containing gas with the hybrid reactive solvent 7, dissolving it in the hybrid reactive solvent 7, and promoting the enzymatic conversion of the dissolved C0₂ into bicarbonate and hydrogen ions, for i) providing a depleted C0₂-containing gas defining a treated gas, and ii) providing hybrid reactive solvent enriched in bicarbonate and hydrogen ions and comprising the biocatalyst; a-2) a gas outlet 15 in fluid communication with the reaction chamber for the release of the treated gas; and a-3) a hybrid solvent outlet 17 in fluid communication with the reaction chamber 5 for collecting at least a portion of the hybrid reactive solvent enriched in bicarbonate and hydrogen ions and comprising the biocatalyst; ation unit 23 comprising b-1) a filtration membrane 25 that is inert to the hybrid reactive solvent and provided with pores having smaller diameter than a diameter of the biocatalyst, the filtration membrane 25 having an upstream side 27 and a downstream side 29; b-2) a hybrid reactive solvent inlet 31 which is in fluid communication with the hybrid reactive solvent outlet 17 of the reactor and in fluid communication with the upstream side 27 of the filtration membrane 25; b-3) a retentate outlet 33 in fluid communication with the upstream side 27 of the membrane 25 for recovery of a retentate fluid including the biocatalyst collected on the upstream side 27 of the filtration membrane 25; and b-4) a permeate outlet in fluid 37 communication with the downstream side 29 of the filtration membrane 25 for recovery of a permeate fluid loaded with the bicarbonate and hydrogen ions.

Optionally, as illustrated on Figure 1 , the reactor 3 may be further provided with a hybrid reactive solvent inlet 13 in fluid communication with the reaction chamber 5 for the addition of fresh hybrid reactive solvents to the reaction chamber 5.

The reactor may be a packed tower, a spray reactor, a bubble column or another type of reactor.

As illustrated on Figure 1 , the reactor 3 may be a bubble column type reactor that is filled with the hybrid reactive solvent containing the biocatalyst up to the level L and a first conduit 41 is provided between the hybrid solvent outlet 17 and the hybrid reactive solvent inlet 31 , to allow a fluid communication therebetween, the first conduit 41 being optionally further provided with a pumping device 43. Of course, any type of pumping device well known to a person ordinary skilled in the art can be used. As an example, it may consist of a centrifugal pump.

The installation 1 illustrated in Figure 1 allows treatment of a C0₂-containing gas, preferably continuously, according to a process comprising the steps of: a) contacting within the reaction chamber 5, the C0₂-containing gas with the hybrid reactive solvent 7 further comprising the biocatalyst, the biocatalyst accelerating an enzymatic conversion of C0₂ into bicarbonate and hydrogen ions, by i) dissolving the C0₂-containing gas in the hybrid reactive solvent; and ii) promoting the enzymatic conversion of the dissolved C0₂ into bicarbonate and hydrogen ions; b) obtaining a depleted C0₂-containing gas defining a treated gas, the treated gas being then released from the reaction chamber at the gas outlet 15; c) obtaining a hybrid reactive solvent enriched in bicarbonate and hydrogen ions and comprising the biocatalyst; and d) removing from the reaction chamber 5 at the hybrid reactive solvent outlet 17, through the pipe 41 , and the inlet 31 , optionally including a pumping device 43, at least a portion of the hybrid reactive solvent of step c) and filtering it via the filtration membrane 25 that is inert to the hybrid reactive solvent 7 and provided with pores having smaller diameter than a diameter of the biocatalyst, the filtration membrane 25 having an upstream side 27 and a downstream side 29; to thereby obtain: i) at the upstream side 27 of the filtration membrane

25, the retentate fluid comprising bicarbonate and hydrogen ions and being rich in the biocatalyst, and ii) at the downstream side 29 of the filtration membrane

25, the permeate fluid comprising bicarbonate and hydrogen ions and being depleted in the biocatalyst.

The retentate fluid is recovered through the outlet 33 of the filtration unit 23 and optionally recycled back into the reaction chamber 5 via a conduit 24, optionally including a pump 26, in fluid communication with the outlet 33 and a recirculation inlet 19, to thereby return the biocatalyst in the hybrid reactive solvent 7. Alternatively, fresh hybrid reactive solvent comprising the biocatalyst may be added to the bioreactor via the inlet 13.

The hybrid reactive solvent includes an absorption compound, which may be provided at relatively high concentration and may provide high pH to enhance the absorption. The high concentration combined with the properties of certain basic absorption compounds may lead to damage or reduced functionality of filtration membranes made of certain materials. Selection of the filtration material is preferably made so as to be inert with the absorption compound. For example, PS, PES, PVDF and PI membranes all are good, but less expensive for the polysulfone (PS) and polyethersulfone-based (PES) HF membranes.

As illustrated on Figure 2, there is illustrated and installation 101 which is similar to the installation 1 of Figure 1 , except it is further provided with a device 151 for the determination of physical parameters (such as for example the viscosity, concentration and/or temperature) of the retentate fluid. The device 151 is provided with an inlet 153 and an outlet 155. In Figure 2, elements identical to those of in Figure 1 , are identified with the same reference numbers and of course have the same meanings.

The second conduit 171 allows a fluid communication of the retentate fluid between outlet 33 and the inlet 153 of the device 151 for the determination of aforesaid physical parameters of the retentate. The third conduit 191 allows a fluid communication between the outlet 155 and the recirculation inlet 19 of the bioreactor 3. The third conduit 191 is optionally further provided with a pumping device 181 to pump the retentate fluid and enzymes contained therein in the hybrid reactive solvent of the bioreactor 3. Of course, any type of pumping device well known to a person ordinary skilled in the art can be used. As an example, it may consist of a centrifugal pump.

Between the outlet 37 and the recirculation inlet 32, there may be provided an assembly comprising with a three-way valve 253 having one inlet 255 and two outlets 257 and 259, a fifth conduit 21 1 between the outlet 37 and the inlet 255; a sixth conduit 221 in fluid communication with the outlet 257; a seventh conduit 231 between the outlet 259 and the recirculation inlet 32 of the filtration unit 23. The sixth conduit may be optionally provided with a pumping device 241. Of course, any type of pumping device well known to a person ordinary skilled in the art can be used. As an example, it may consist of a centrifugal pump. The permeate fluid obtained through the sixth conduit 221 may be stored and/or directed to a processing unit such as a desorption unit (not illustrated here).

The installation illustrated in Figure 2 allows treatment of a C0₂-containing gas, preferably continuously, according to a process having steps similar to those of the process associated with the installation of Figure 1 , except the retentate fluid recovered through the outlet 33 of the filtration unit 23 is recycled to the recirculation inlet 19 of the bioreactor 3, via an assembly comprising the device 151 which is for the determination of the viscosity concentration and/or temperature of the retentate fluid. The device 151 controls the three-way valve 253 having one inlet 255 and two outlets 257 and 259 eventually dilute the retentate fluid circulating at the upstream side 27 of the membrane 25 at a flow rate FR1 , and have with respect to the permeate fluid circulating at the downstream side 29 of the membrane 25 at a flow rate FR2, a ratio FR1 / FR2, keeping the retentate fluid pumpable with the biocatalyst solubilised or suspended therein.

According to another embodiment, the invention relates to an installation as defined hereinabove, wherein it is possible to use from 0.5 to 1.0 % of the permeate fluid for backwash purposes, at an equivalent FF flow rate and a frequency of about 10-15 s per 20-30 min.

According to another embodiment, the invention relates to an installation for implementation of immobilized biocatalysts as defined hereinabove, for pumping purpose, if a solid volume of 20% v/v is considered, around 5% of the permeate may be needed, assuming a loading of the immobilized biocatalyst solids of 20 g/L is used , and 95% of the solvent is permeated.

According to another embodiment, the invention relates to an installation as defined hereinabove, operational parameters may comprise a 2 - 5 bar pressure, preferably for nanofiltration a 10 bar or higher pressure, with a temperature ranging from 5 to 80 . As illustrated on Figure 3, there is illustrated and installation 301 which is similar to the installation 1 of Figure 1 , except a conduit 351 is further provided between the outlet 37 and inlet 305 of the desorption unit 302. This conduit 351 may be optionally provided with a pumping device 381. The desorption unit 302 is provided with an outlet 315 for the C0₂ gas and an outlet 307 for the permeate depleted in bicarbonate/carbonate ions. In Figure 3, elements identical to those of in Figure 1 , are identified with the same reference numbers and of course have the same meanings.

The installation illustrated in Figure 3 allows treatment of a C0₂-containing gas, preferably continuously, according to a process having steps similar to those of the process associated with the installation of Figure 1 , except the permeate fluid recovered from the outlet 37 is directed to the inlet 305 of the desorption unit 302. A C0₂ gas is released at the outlet 315 and a permeate fluid depleted in carbonate ions is obtained at the outlet 307.

Also, this permeate fluid depleted in carbonate ions obtained at outlet 307 is pumped by the pumping device 26 along with the retentate fluid obtained from the outlet 33, toward the inlet 13 to be recycled within the reaction chamber 5. Optionally, the permeate fluid depleted in carbonate ions and the retentate fluid can be mixed together, in an appropriate mixer, before being pumped toward the reaction chamber via the inlet 13.

In Figure 3, any type of pumping device well known to a person ordinary skilled in the art can be used. As an example, it may consist of a centrifugal pump.

As illustrated on Figure 4, there is illustrated and installation 401 which is similar to the installation 101 of Figure 2, except the retentate fluid recovered through the outlet 33 of the filtration unit 23 and is recycled to the recirculation inlet 19 of the bioreactor 3, via an assembly comprising the device 151 which is for the determination of physical parameters (such as for example the viscosity, concentration and/or temperature) of the retentate fluid. The device 151 is similar to the one described in the installation 101 of Figure 2. Also, the permeate fluid obtained from the outlet 37 is directed to the inlet 405 of the desorption unit 402 by a conduit 411 optionally provided with a pumping device 381 , and the device 151 controls the two-way valve 461.

The two-way valve 461 has one inlet 463 and one outlet 465, and is part of an assembly provided with conduit 471 and conduit 481. The conduit 471 is between the outlet 407 and the inlet 463, while the conduit 481 is between the outlet 465 and the inlet 32. Optionally, a pumping device 491 may be provided across conduit 471 or 481.

The device 151 is configured to control the two-way valve 461 to eventually dilute the retentate fluid circulating at the upstream side 27 of the membrane 25 at a flow rate FR1 , in order that it has with respect to the permeate fluid circulating at the downstream side 29 of the membrane 25 at a flow rate FR2, a ratio FR1 / FR2 allowing to keep the retentate fluid pumpable with the biocatalyst solubilised or suspended therein. Preferably, the ratio FR1 / FR2 corresponds to the ratio of the flow rate of the permeate to the flow rate of the retentate and may vary from 0.01 to 1 (which corresponds to 1-50% of the FF as the retentate and 50-99% of the FF as the permeate). FF corresponds to a feed flow rate to the membrane and can be correlated to a flux.

Of course, any type of pumping device well known to a person ordinary skilled in the art can be used. As an example, it may consist of a centrifugal pump.

The installation illustrated in Figure 4 allows treatment of a C0₂-containing gas, preferably continuously, according to a process having steps similar to those of the process associated with the installation of Figure 2, except the permeate fluid recovered through the outlet 37 of the filtration unit 23 is directed via a conduit 411 to the inlet 405 of the desorption unit 402 for producing C0₂ gas released at the outlet 415 and permeate fluid depleted in carbonate ions at the outlet 407.

A portion of the permeate fluid obtained from the outlet 407 may be added if necessary to the retentate fluid on the upstream side of the filtration membrane 25, to dilute the retention fluid in order to have the retentate fluid flow at the upstream side 27 of the membrane 25 at a flow rate FR1 , the permeate fluid flowing at the downstream side 29 of the membrane 25 at a flow rate FR2, and a ratio FR1 / FR2 within such range to keep the retentate fluid pumpable and the biocatalyst solubilised or suspended therein. Preferably, the ratio FR1 / FR2 corresponds to the ratio of the flow rate of the permeate to the flow rate of the retentate and may vary from 0.01 to 1 (which corresponds to 1-50% of the FF as the retentate and 50-99% of the FF as the permeate). FF corresponds to a feed flow rate to the membrane and can be correlated to a flux.

As illustrated on Figure 5, there is illustrated and installation 501 which is similar to the installation 401 of Figure 4, except the retentate fluid recovered through the outlet 33 of the filtration unit 23 and is recycled to the inlet 13 of the bioreactor 3, via an assembly comprising the device 151 which is for the determination of physical parameters (such as for example the viscosity, concentration and/or temperature) of the retentate fluid. The device 151 is similar to the one described in the installation 101 of Figure 2. Also, the permeate fluid obtained from the outlet 37 is directed to the inlet 405 of the desorption unit 402 by a conduit 411 optionally provided with a pumping device 381 , and the device 151 controls the three-way valve 561.

The three-way valve 561 has one inlet 563 and outlets 565 and 657,, and is part of an assembly provided with conduit 471 , conduit 481 and conduit 482. The conduit 471 is between the outlet 407 and the inlet 563, the conduit 481 is between the outlet 565 and the inlet 32, and conduit 482 is between the outlet 657 and an inlet 510 of a mixer 509. Optionally, a pumping device 491 may be provided across conduit 471 , 481 or 482.

The mixer 509 may consist of any kind of mixers well known to a person ordinary skilled in the art for the mixing of fluids. This mixer has the inlet 510, 512, 513 and 515 and an outlet 517. The inlet 513 is in fluid communication with a source of fresh hybrid reactive solvent 507, the inlet 515 is in fluid communication with a source of enzymes 505, and the outlet 517 is in fluid communication with the inlet 13. The inlet 512 is in fluid communication with the outlet 155 via conduit 24.

The device 151 is configured to control the three-way valve 561 to eventually dilute the retentate fluid circulating at the upstream side 27 of the membrane 25 at a flow rate FR1 , in order that it has with respect to the permeate fluid circulating at the downstream side 29 of the membrane 25 at a flow rate FR2, a ratio FR1 / FR2 allowing to keep the retentate fluid pumpable with the biocatalyst solubilised or suspended therein. Preferably, the ratio FR1 / FR2 corresponds to the ratio of the flow rate of the permeate to the flow rate of the retentate and may vary from 0.01 to 1 (which corresponds to 1-50% of the FF as the retentate and 50-99% of the FF as the permeate). FF corresponds to a feed flow rate to the membrane and can be correlated to a flux.

Optionally, water obtained from a water source 503 can be added to the retentate fluid, to dilute it. Optionally, as illustrated, a heat exchanger 51 1 may be provided upstream the filtration unit 23, preferably across conduit 41. Of course any kind of heat exchanger well known to a person ordinary skilled in the art can be used.

The installation illustrated in Figure 5 allows treatment of a C0₂-containing gas, preferably continuously, according to a process having steps similar to those of the process associated with the installation of Figure 4, except the reaction chamber is provided with a packing 8 of particles, the hybrid reactive solvent and enzymes flowing across said packing, and the permeate fluid recovered through the outlet 37 of the filtration unit 23 is directed via a conduit 41 1 to the inlet 405 of the desorption unit 402 for producing C0₂ gas released at the outlet 415 and permeate fluid depleted in carbonate ions at the outlet 407.

In Figure 6, there is illustrated a schematic view of a tangential filtration unit 23. More particularly, it is to be noted that said filtration unit 23 comprises: a filtration membrane 25 that is inert to the hybrid reactive solvent and provided with pores having smaller diameter than a diameter of the biocatalyst, the filtration membrane 25 having an upstream side 27 and a downstream side 29; a hybrid reactive solvent inlet 31 which is in fluid communication with the hybrid reactive solvent outlet 17 of the reactor and in fluid communication with the upstream side 27 of the filtration membrane 25; a retentate outlet 33 in fluid communication with the upstream side 27 of the membrane 25 for recovery of a retentate fluid including the biocatalyst collected on the upstream side 27 of the filtration membrane 25; and a permeate outlet in fluid 37 communication with the downstream side 29 of the filtration membrane 25 for recovery of a permeate fluid loaded with the bicarbonate and hydrogen ions.

Of course, the filtration unit has physical characteristics concerning the membrane such as its surface, thickness, porosity, etc., that are selected to optimize the efficiency of the filtration, with respect to the characteristics of the fluids involved.

Description of implementations with porous matrix and leached biocatalyst

In some implementations, the carbonic anhydrase may be immobilized in a porous matrix within the absorption chamber and an amount of the carbonic anhydrase leaches out of the porous matrix and is carried out of the absorption reactor in the ion loaded solution. The porous matrix may be a polymeric immobilization material that is sprayed or otherwise coated onto packing material that is fixed within the absorption reactor. The carbonic anhydrase may be entrapped within the pores of the porous matrix, and some of the carbonic anhydrase leaches out of the pores, which may occur gradually over time such that free leached enzyme is gradually brought into the surrounding solution. The leached enzyme may continue to catalyse the hydration reaction of C0₂. The leached enzyme is released from the absorption reactor as a component of the ion loaded solution, and may be subsequently removed by various techniques such as those described above in relation to a filtration membrane. The carbonic anhydrase that is removed may be recycled back into the absorption reactor.

In some implementations, the porous matrix is in the form of particles or a coating on the surface of particles, and the particles may flow with the liquid through the absorption chamber. In this scenario, the particles may be removed from the ion loaded solution and then the leached free enzyme may be subsequently removed, to form the enzyme depleted solution that is supplied to the regeneration unit.

In some implementations, the porous matrix is composed of a material such that the leaching of the enzymes is relatively slow, providing a slow-release type of mechanism.

In some implementations, the enzyme enriched solution or fraction that is separated from the ion loaded solution may be re-immobilized within a porous matrix before reintegrating the enzyme into the process.

In some implementations, the porous matrix is composed of a polymeric immobilization material that is spray-coated onto packing material that is mounted within the absorption chamber of the absorption reactor.

Description of implementations with other separation steps In some implementations, the process of system may be similar to one of the examples illustrated or described above, yet the separation of the ion loaded solution is performed by a separation device other than a filtration membrane. For example, the separation may be performed using a hydrocyclone or a centrifuge.

In some implementations, the separation device may be configured and operated so as to produce a biocatalyst enriched stream having certain pre-determined characteristics. For example, the biocatalyst enriched stream may have sufficient fluidity to enable liquid transport, may contain biocatalysts in soluble state only (no solids), and/or may have a pre-determined flow rate for minimizing the amount of bicarbonate ions that are recycled back into the absorption reactor.

It is also noted that various alternate implementations are possible, some of which are described and/or illustrated in the present application. It should also be understood that different terms may be used herein to describe the same or similar elements (e.g., hybrid solvent and absorption solution containing an absorption compound) and thus the present description should be read in this context.

Examples, simulations and experimentation

A goal of some of the following examples is to illustrate, on a laboratory scale, that a flow of an aqueous solution of a biocatalyst, can be separated by a separation membrane into a flow of a retentate fluid rich in the biocatalyst, and a flow of a permeate fluid (also called filtrate) depleted in the biocatalyst.

More particularly, the following experiments were carried out with the following enzyme solutions and installation.

Enzyme solutions

Aqueous solutions of an enzyme (i.e. the biocatalyst) were prepared. The enzyme used was a variant of human carbonic anhydrase type II. Solutions were prepared using an enzyme stock solution by mere dissolution of an appropriate amount of the enzyme in water to prepare a 100 mg/litre enzyme solution or a 400 mg/litre enzyme solution.

Laboratory scale installation

With reference to Figure 7, a laboratory scale installation 701 was provided. It was comprising a storage vessel 703, a filtration unit 723, a tubing 741 , a tubing 724, a tubing 711 , and a tubing 738.

The storage vessel 703 contains an amount of the aqueous solution of enzyme. This vessel 703 was provided with an outlet 705 and an inlet 707. It is also provided with a magnetic stir bar 709 which is moved into a rotational movement to stir the solution by a conventional laboratory magnetic stirrer 710.

The filtration unit 723 is provided with a housing 722 within which a filtration membrane 725 is positioned. This housing 722 has an inlet 731 , an outlet 733 and an outlet 737. The filtration membrane consists of a bundle of parallel hollow fiber (HF) membranes each having opposite ends. One end of each HF membrane is in fluid communication with the inlet 731 , while the opposite end of each HF membrane is in fluid communication with the outlet 733. The interior of each hollow fiber membrane defines the upstream side of the filtration unit 723. The exterior of each hollow fiber membrane defines the downstream side of the filtration unit 723. The permeate fluid accumulates into the housing 722 which is in fluid communication with the outlet 737 and allow said permeate fluid to flow therethrough.

The membrane module consists of a bundle of 100 hollow fibers, each fiber having a length of 30 cm, an interior diameter of 0.9 mm, said bundle having a surface of 0.084 m². The HF membrane is made of polyethersulfone (PES) combined with a separating layer of sulfonated polyethersulfone (SPES). This membrane was supplied by Pentair X-Flow (www.x-flow.com).

The tubing 741 has opposite ends. One end of said tubing is in fluid communication with the vessel outlet 705, while the opposite end of said tubing 741 is in fluid communication with the inlet 731 of the housing 722. The tubing 741 is further provided with a pump 743 and a flowmeter 744. The pump 743 is a centrifugal pump (Grundfos Alldos (DMI 18-3, 5A -PV/T/T-T-G144F). This pump generates within the tubing 741 a flow of the solution of enzyme and transport it from the outlet 705 to the inlet 731 of the housing 722 at a given flow rate and pressure. The flow rate is measured by the flowmeter 744.

The tubing 724 has opposite ends. One end of said tubing 724 is in fluid communication with the outlet 733 of the housing 722 and the inlet 707 of the storage vessel 703. This tubing 724 is further provided with a backpressure valve 726, a manometer 728, a flowmeter 151 , a three-way valve 730 and a three-way valve 732. In this laboratory installation 701 , it is the flow of the solution of enzyme that generates the flow of the same within the hollow filtration membrane, and therefore the flow of the retentate fluid circulating within the tubing 724 and the flow of the permeate fluid circulating within the housing 722.

The backpressure valve 726 is designed to prevent undesired backflow of the flow of the retentate fluid within the tubing 724. Also, the manometer 728 and the flowmeter 151 allow measuring the pressure and the flow rate of the retentate fluid within the tubing 724. Also, the three-way valve 730 has two of its branches mounted in fluid communication across the tubing 724 to allow said retentate fluid to flow therethrough, and a third of its branches that is open-ended to allow the collection of samples of the retentate fluid (for analysis of its content in enzyme). The three-way valve 732 has two of its branches mounted in fluid communication with the tubing 724 to allow a flow of said retentate fluid therethrough, and a third of its branches in fluid communication with the tubing 738 for an optional redirection of at least a portion of the retentate fluid toward a three-way valve 736 to thereby allow the control the flow of the retentate fluid back to the inlet 707 of the vessel 703.

The tubing 71 1 has opposite ends. One end of this tubing 71 1 is in fluid communication with the outlet 737 of the housing 722 and two branches of a three- way valve 736 are mounted in fluid communication across the tubing 711. This three- way 736 has a third of its branches that is open-ended to allow the collection of samples of the permeate fluid (for analysis of its content in enzyme).

The tubing 738 has opposite ends. One end of said tubing 738 is in fluid communication with one branch of the three-way valve 732 while the opposite end of said tubing 738 is in fluid communication with one branch of the three-way valve 738, for optionally returning the permeate fluid to the vessel 703.

In operation (bore feed, standard filtration), this laboratory scale installation 701 works as follows:

A portion of the solution of enzyme contained in the vessel 703 is transported by the pump 743 through the tubing 741 , enters the housing 722 and is transported through the bundle of hollow fiber membranes. While being transported in the HF membrane, a permeate fluid permeates through the hollow fibers, accumulates within the housing 722 and flows toward the outlet 737, while a retentate fluid which becomes more concentrated in enzyme, is transported toward the tubing 724. The pump determines the flow rate and the operating pressure of the retentate fluid and the permeate fluid within the installation.

A sample of the retentate fluid circulating in the tubing 741 may be collected by setting open-ended branch of the three-way valve 730 in fluid communication with the retentate fluid circulating in the tubing 741 , and allowing at least a portion thereof to flow therethrough collection into any appropriate sampling container for further analysis by UV spectrophotometry (Varian CARY^® 50) at 280 nm and measurement of the enzyme content. Enzyme content is determined by measuring the absorbance of the solution at a wavelength of 280 nm and using a correlation curve relating enzyme concentration to absorbance. Once the sampling container has received a determined amount of the retentate fluid, the three-way valve 730 is returned to its initial setting for preventing the retentate fluid to flow through the open-ended branch of said three-way valve 730 and allowing the retention fluid to flow through the two other branches which are in fluid communication with the tubing 741. A sample of the permeate fluid circulating in the tubing 711 is collected by setting open-ended branch of the three-way valve 736 in fluid communication with the permeate fluid circulating in the tubing 741 , and allowing at least a portion thereof to flow therethrough and being collected into any appropriate sampling container for further analysis by UV spectrophotometry (Varian CARY^® 50) at 280 nm and measurement of the enzyme content. Once the sampling container has received a determined amount of the permeate fluid, the three-way valve 736 is returned to its initial setting preventing the permeate fluid to flow through the open-ended branch of said three-way valve 736 and allowing the permeate fluid to flow through the two other branches in fluid communication with the tubing 711. Enzyme content is determined by measuring the absorbance of the solution at a wavelength of 280 nm and using a correlation curve relating enzyme concentration to absorbance.

In a reverse filtration (shell feed) operation, this laboratory scale installation 701 works as for the standard filtration except tubing 741 is connected to the outlet 737 (which becomes an inlet to the housing 722) to have the enzyme solution flowing through the hollow fiber membrane from the outside of the membrane toward the inside. Tubing 71 1 is then connected to the inlet 731 (which becomes an outlet of the housing). The permeate fluid can be transported via tubing 711 and/or 723 and then returned to the vessel 703 and optionally samples can be collected via the three-way valve 736 for analysis purposes.

Various experiments were carried out with the above-mentioned laboratory scale installation 701 , at different flow rates, pressures and enzyme concentrations to validate the efficiency of the enzyme separation with filtration membrane, using for the experiment a bundle of the HF membranes. Results of those experiments are gathered in the following tables and Figures.

Experimental 1

Experiments with pure water

Standard filtration (Bore feed) In this case the vessel 703 was filled with pure water and this water was pumped with the pump 743 via the tubing 741 to the inlet 731 of the housing 722 and is passed across the bundle of hollow filtration membrane. The flow rate was measured by the flowmeter 744 and the pressure was measured across the tubing 724 with the manometer 728.

Reverse filtration (Shell feed)

In this case the vessel 703 was filled with pure water and this water was pumped with the pump 743 via the tubing 741 to the inlet 737 of the housing 722 and is passed across the bundle of hollow filtration membrane. The flow rate was measured by the flowmeter 744 and the pressure was measured across the tubing 724 with the manometer 728.

Figure 8 represents various back pressure - filtration flow curves for various flows of pure water. More particularly, Figure 8 illustrates that the flow rate of the permeate fluid (i.e. Φ _fii_trate) in litre per hour was a direct function of the pressure difference (ΔΡ, in bars) across the membrane. It is to be noted that this figure includes data related to the total flow (for standard filtration) and the reverse total flow through the membrane of the installation 701. More particularly, reverse (shell feed) filtration was when the liquid (i.e. water in the present case) is flowing across the membrane from the outside of said membrane. Data of Figure 8 are reported into the following Table 1.

TABLE 1

Table 1 represents water - mass balance (pure water) data. More particularly, this table illustrates from the data of Figure 8, the total flow (Φ _totai) , the permeate flow (Φ filtrate) and the retentate flow (Φ _retentate) a different feed pressures with a pressure drop (ΔΡ, in bars) across the membrane for filtration in the standard filtration (i.e. bore feed) and reverse filtration (shell feed). This table indicates that the amount of water passing through the hollow filtration membrane was a direct function of the pressure difference (ΔΡ) across the membrane.

Referring to figure 9, it is illustrated for pure water, from data extracted from Figure 8 and table 1 , showing that for a given bundle of hollow filtration membranes as defined for the installation 701 , the Φ filtrate W3S!

(Φ filtrate) = ΔΡ * A * K with K . A = 0.2198, since A is 0.085 m², as defined hereinabove, and K is a constant equal to 2.6 litre/h«m²«bar.

Experimental 2

Experiments with aqueous solution of enzyme (100 mg/litre) Standard filtration (Bore feed)

In this case the vessel 703 was filled with the 100 mg/litre aqueous enzyme solution (prepared in accordance with the protocol defined above). This solution was pumped with the pump 743 via the tubing 741 to the inlet 731 of the housing 722 and passed across the bundle of hollow filtration membrane. The flow rate was measured by the flowmeter 744 tubing 741 and the pressure and the flow rate in the tubing 724 were measured with the manometer 728 and the flowmeter 151.

Reverse filtration (Shell feed)

In this case the vessel 703 was filled with the 100 mg/litre aqueous enzyme solution (prepared in accordance with the protocol defined above). This solution was pumped with the pump 743 via the tubing 741 to the inlet 737 of the housing 722 and passed across the bundle of the hollow fiber membrane. The flow rate was measured by the flowmeter 744 in the tubing 741 and the pressure and the flow rate in the tubing 724 were measured with the manometer 728 and the flowmeter 151.

Figure 10 represents various filtration flow curves for various flows of aqueous solution of enzyme (100 mg/litre). More particularly, this figure (Figure 10) illustrates that the flow of the permeate fluid (i.e. Φ _fii_trate) in litre per hour was also a direct function of the variation of pressure in bars (ΔΡ) across the membrane. It is to be noted that this figure includes data related to the total flow and the reverse total flow through the hollow fiber membrane of the installation 701. Also, data of Figure 10 are reported into the following tables 2 to 4.

TABLE 2

This table 2 represents data concerning the aqueous enzyme solution (100 mg/liter) - mass balance. More particularly, this table illustrates, the total flow (Φ _totai), the permeate flow (Φ _mrate) and the retentate flow (Φ _retentate) for various variation in pressure in bars (ΔΡ) and concerning the filtration in the standard direction (bore feed) and reverse filtration (shell feed) for the aqueous enzyme solution. This table indicates that the flow of the permeate fluid (Φ_{ίΜ( t} ) passing through the HF membrane was a direct function of the variation of pressure.

TABLE 3

Also, this table 3 represents from data extracted from table 2, the variation of enzyme concentration in sample collected from the open-ended branch of the three- way valve 736, in the sample collected from the open-ended branch of the three-way valve 730, and in a sample of the initial aqueous enzyme solution and in a sample of pure water. In this regard, it is to be noted that in samples 3, 5, 7, 9 and 11 the permeate fluids did not contain enzyme, and in samples 2, 6, 8, 10 and 12 the retentate fluids had a concentration in enzyme that was increased with respect to the original enzyme solution.

TABLE 4

This table 4 illustrates variations of mass balance of enzyme concerning selected flow of the aqueous enzyme solution listed in table 3. More particularly, concerning this table 4, the samples numbers of table 3 are indicated between brackets.

Experimental 3

Experiments with aqueous solution of enzyme (400 mg/litre) Standard filtration (Bore feed)

In this case the vessel 703 was filled with the 400 mg/litre aqueous enzyme solution (prepared in accordance with the protocol defined above). This solution was pumped with the pump 743 via the tubing 741 to the inlet 731 of the housing 722 and passed across the bundle of hollow filtration membrane. The flow rate was measured by the flowmeter 744 in the tubing 741 and the pressure and the flow rate were measured in the tubing 724 with the manometer 728 and the flowmeter 151.

Reverse filtration (Shell feed)

In this case the vessel 703 was filled with the 400 mg/litre aqueous enzyme solution (prepared in accordance with the protocol defined above). This solution was pumped with the pump 743 via the tubing 741 to the inlet 737 of the housing 722 and passed across the bundle of HF membrane. The flow rate was measured by the flowmeter 744 in the tubing 741 and the pressure and the flow rate were measured in the tubing 724 with the manometer 728 and the flowmeter 151.

Figure 11 represents filtration flow rate curves for various feeds of the aqueous solution of enzyme (400 mg/litre). More particularly, this figure (Figure 11) illustrates that the flow of the permeate fluid (i.e. Φ _fii_trate) in litre per hour was also a direct function of the variation of pressure across the membrane (ΔΡ, in bars). It is to be noted that this figure includes data related to the total flow (bore feed) and the reverse (shell feed) total flow through the hollow fiber membrane of the installation 701. TABLE 5

This table 5 represents data concerning the aqueous enzyme solution (400 mg/liter) - mass balance. More particularly, this table illustrates, the total flow (Φ _totai), the permeate flow (Φ _mate) and the retentate flow (Φ _retentate) for various pressure drops across the membrane (ΔΡ, in bars) related to filtration in the standard (bore feed) direction and reverse (shell feed) filtration of the aqueous enzyme solution. This table also indicates that the flow rate of the permeate fluid (Φ^ _t ) passing through the HF membrane was a direct function of the variation of pressure. Experimental 4

Comparaison water, enzyme solution (100 mg/liter) and enzyme solution (400 mg/liter) concerning the permeate flow (Φ_{ΠΙί t} )

Figure 12 represents various permeate flow (Φ_{ίΜ( t} ) curves for a 28 ml/min flow rate of water, an aqueous solution of enzyme (100mg/litre) and an aqueous solution of enzyme (400mg/litre), versus variations of pressure in bars (ΔΡ). More particularly, this Figure 12 illustrates that the flow of the permeate fluid (i.e. Φ _mrate) in litre per hour was a direct function of the variation of pressure in bars (ΔΡ).

It is understood that above preferred embodiments are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the present invention.

Experimental 5

Further experiments were carried out using the laboratory scale installation of Figure 7, except the membrane 725 and the enzyme were the following:

The enzyme was a monomeric carbonic anhydrase enzyme (M6x) obtained from a concentrate (9.22 mg/ml). This enzyme had a molecular weight of 29kDa and an effective size of around 4.5 nm. Enzyme solutions for the following filtration experiments were prepared by dilution of the concentrated enzyme sample in water to 0.4 mg/ml.

The membrane 725 was selected from three types of fiber membranes, all provided by Pentair. One comprised a standard ultra-filtration membrane (UFC-LE) that has a molecular weight cut-off (mwco) of 200kDa. The two others had a slightly different chemistry and included a tight ultra-filtration membrane (HFs) with an mwco of 10kDa and an open micro-filtration membrane (HFc) with an mwco of 1 .5 kDa.

The membrane 725 defines a module consisting of 100 fibers with a 0.8 mm diameter and an effective filtration area of 0.06 m². Also, the end pieces of the 30 cm long fibers were poured in a resin. Each module can withstand transmembrane pressures (TMP) up to 4 bar.

In the following tests, either pure water or the diluted enzyme solution was placed in the storage vessel 703. The membrane liquid pump 743 was used to pump pure water or the enzyme solution through the membrane filtration unit 723. The back-pressure valve 726 was installed to regulate the flow through the membrane filtration unit 723. The set-up was equipped with two flow meters 151 and 744 to indicate the flow of the filtrate (or permeate circulating through the housing 722 and the tubing 71 1 ) and the flow of the retentate through the membrane filtration unit 723 (and circulating through the tubing 724).

In order to change these flows, the back pressure valve 726 is set. From each stream coming out from the membrane filtration unit a sample is taken. The streams' flow rates are measured by opening the valves for filtrate and retentate and catching the stream into a graduated cylinder during one minute. The total flow can be measured using the same technique, by catching the flow of liquid from the tube 724 ending in the reactor vessel 703. Samples taken were analyzed by a Varian Cary 50 UV-Vis spectrophotometer at wavelength of 280 nm. A calibration of the Varian Cary 50 UV-Vis spectrophotometer at a wavelength of 280 nm was performed in the concentration range from 0 to 1000 mg/l. Results were reported in the following table 6 and in Figure 13.

Using different back-pressures in the range 0 to 4 bar, the flows in the system were measured and sampled after 2, 4, and 24 hours of operation to check time effects of the membrane. This was performed for both pure water and the 0,4 mg/ml enzyme solution. Accuracy of the experiment was governed by the overall mass balance equation (1 ):

Φ X C = Φ . X C + Φ . X C

total enzyme,total filtrate enzyme, filtrate retentate enzyme, retentate ^ I ) where O's are the flows and c_enzyme's the concentrations of the respective streams measured.

Experimental 5.1 The water fluxes that were going through the open microfiltration membrane(HFC, mwco = 1 .5 kDa) are given Figure 14 and in Table 7. For the open microfiltration membrane (HFC, mwco = 1 .5 kDa) a hydraulic permeability of K = (6.42 ± 0.1 1 ) ml^»s^{"1 »}bar^{"1 »}m^"2 was determined.

In the case of the tight ultrafiltration membrane (HFs, mwco = 10 kDa) only for two total flow rates were possible to create a back pressures to balance the filtrate flow. The results are given in Figure 15 and in Table 8. Although the data seem to be concave, it has been determined a hydraulic permeability of K = (48.8 ± 1 .0) ml'S^"1'bar^"1'm^"2 Table 8

HFc membrane (mwco = 10 kDa) using water

P Φ Φ Φ

total filtrate retentate

(bar)

(ml/min) (ml/min) (ml/min)

0 75.5 0 75.5

0.5 75.5 75.5 0

0.2 75.5 44 31 .5

0.3 75.5 58 17.5

For the regular ultrafiltration membrane (UFC-LE, mwco = 200 kDa) it was not possible to build up a back pressure. This means that the water needs no (or negligible) pressure drop to flow through the pores of the membrane irrespective of the flow rate. Hence, no permeability can be given.

Experimental 5.2

Measured data of the 400 mg/l enzyme solution through the HFc membrane after 2, 4, and 24 hours are given in table 9 and displayed in Figure 16. Only for back pressures greater than 2 bar the solution was pushed through the membrane.

From the results it can be clearly seen that no enzyme was found in the filtrate; the slight negative values were experimental inaccuracies.

Apparently the HFc membrane effectively filtered the enzyme as one may expect for a 29 kDa molecule for a membrane with a 1 .5 kDa cut-off. Using the mass balance equation (1 ), it can be seen that most experiments have deviation less than 5%. Table 9

HFc membrane (mwco = 1 .5 kDa) using 0.4 mg/ml enzyme solution

Time effect within one day seems negligible for the flow. However, there is a considerable effect in the total presence of the enzyme.

Comparison of these results with those in Figure 12 for an enzyme concentration of 400 mg/L, shows that to provide a same filtrate flow rate, a higher back pressure was required for the polyethersulfone membrane. Further analysis of the results showed that this may be due to the membrane material, polyethersulfone might cause some enzyme fouling at the surface of the membrane and then increase back pressure.

It may thus be advantageous in some implementations to consider the interaction between the membrane and the enzyme in selecting the membrane.

Experimental 6

Potential impact of enzyme filtration on a commercial application

In order to evaluate the impact of enzyme filtration on a commercial application, C0₂ capture process simulations were carried out using PPS, a proprietary process simulation by Procede Group BV. Simulations were carried out by implementing a bypass stream of the rich solvent from the absorber back to the inlet of the absorber.

For the tested MDEA-based C0₂ capture system the energy efficiency appeared to increase from 3.3 MJ/kg C0₂ to 3.5 and 4.0 MJ/kg C0₂ when 0%,10% and 30% of the rich solvent, respectively, was used as bypass. The membrane unit can thus have a negative impact on the performance depending on the quantity of the bypass flow.

For a sodium carbonate-based C0₂ capture process, similar simulations and showed that up to a bypass stream of 30% of the total flow rate, the impact on the energy efficiency of the process was minimal.

Experimental 7

Examples : Filtration experiments - enzyme in absorption solutions

To demonstrate the potential of filtering the enzyme carbonic anhydrase from a hybrid solvent, a filtration setup as shown in Figure 17 was used. First, the feed tank was filled with a solution consisting of a hybrid solvent and enzyme. The enzyme was an alpha class carbonic anhydrase with a molecular weight of 29 kDa. The tested enzyme concentrations were 0.5, 1 and 1.5 g/L. These concentrations correspond to values expected to be used in a given hybrid solvent in a C0₂ capture process. However, in some implementations, the enzyme concentration can be different and may be increased up to 10 g/L for example. For these filtrations experiments, hybrid solvents were selected from conventional C0₂ absorption solution classes such as carbonates, primary alkanolamines and tertiary alkanolamines. However, other solution classes or mixtures of different compounds from different classes can also be used.

Tests were first focused on enzyme filtration for a carbonic anhydrase in K₂C0₃ solution. Three hollow fiber membranes with different molecular weight cut-offs were selected: 1.5 and 200 kDa. The 1.5 membranes are made of a mixture of Polyethersulfone and the 200 kDa membrane is made of a mixture of Polyethersulfone and polyvinylpyrrolydone. Membranes were provided by Pentair. Tests were conducted in duplicates. It should be noted that the flow rates, concentrations and enzyme retention values that were obtained for these tests should not be seen as limiting or optimized for enzymatic C0₂ capture operations, and may be modified in accordance with operating parameters that are implemented in various C0₂ capture systems.

Detailed operating conditions and results are shown in Table below.

Membrane K₂C0₃ Enzyme Permeate Retentate TMP Enzyme size cone. (M) cone. flow rate flow rate retention

(bar)

(g/s) (g/s) (%)

(g/L)

1.5 kDa 0.3 0.5 0.28 83 1.12 100

1.5 kDa 0.45 1.0 0.25 41.7 1.76 100

200 kDa 0.6 1.5 2.36 25 1.25 75 Various techniques are described above pertaining to biocatalyst-based hybrid C0₂ capture systems, processes and installations including a separation step for removing at least part of the biocatalysts from the ion loaded solution. In some implementations, there is a filtration membrane to filter out the biocatalysts before the solvent enters the regeneration stage (e.g., the desorption stage) of a C0₂ capture operation. In the present description, the term «enzyme» includes analogues thereof. The enzymes may be recycled as a concentrate of enzyme in a retentate fluid resulting from the filtration, to the absorption reactor of the C0₂ capture process. In this way, enzymes avoid being subjected to the thermal shock inherent to the operating temperatures of many desorption reactors, to have the enzyme degradation significantly limited or even prevented in the overall process. Although enzymes also show benefits in desorbing C0₂ from water, in some implementations substantially all of the enzymes is removed prior to desorption. Since the enzyme's impact on desorption may be of lower significance compared to its impact on absorption, particularly when using hybrid reactive solvents as the bond of C0₂ in the solvent is too strong to be easily broken or released by the enzyme, and mass transfer may be a substantially limiting feature of the process for the release of C0₂. Therefore, performance of the C0₂ desorption in the desorption reactor can be maintained even when removing enzymes from the hybrid reactive solvent before solvent regenerations. Recycling filtered enzymes back into the hybrid reactive solvent to a concentration of several grams up to several hundred grams per liter of hybrid solvent can also enhance C0₂ absorption significantly as absorption often is mass transfer limited. Enzyme concentration in the hybrid reactive solvent may range from about 0.1 g/L up to 500 g/L, for example. In summary, appropriate enzyme removal strategies and recycling back into the absorption solution (e.g., hybrid reactive solvent) can enhance the performance and overall economic implementation of various C0₂ capture operations.

Claims

1. A process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separating step comprises managing the enzyme enriched solution so as to comprise sufficient water to be a pumpable and pipelinable solution; and pumping at least a portion of the enzyme loaded solution through a recycle pipeline back into the absorption reactor.

2. The process of claim 1 , wherein the step of managing the enzyme enriched solution comprises controlling relative flow rates of the enzyme depleted solution and the enzyme enriched solution.

3. The process of claim 1 or 2, wherein the step of managing the enzyme enriched solution comprises controlling solids content of the enzyme enriched solution.

4. The process of any one of claims 1 to 3, wherein the separating step comprise subjecting the ion loaded solution to filtration, such that the enzyme enriched solution is a retentate fluid and the enzyme depleted fluid is a permeate fluid.

5. The process of claim 4, wherein the filtration is performed with a membrane filter.

6. The process of claim 5, wherein the step of managing the enzyme enriched solution comprises controlling a pressure of the ion loaded solution and providing a membrane pore size of the membrane filter.

7. The process of any one of claims 1 to 6, wherein the enzyme depleted fluid comprises no carbonic anhydrase.

8. The process of any one of claims 1 to 7, further comprising: supplying the enzyme depleted fluid to a desorption reactor; operating the desorption reactor under conditions to promote release of C0₂ gas from the ion loaded solution, thereby producing a regenerated solution; releasing the regenerated solution from the desorption reactor; supplying the regenerated solution back to the absorption reactor.

9. The process of claim 8, further comprising: combining at least a portion of the regenerated solution and at least a portion of the enzyme enriched solution to produce a combined solution; and feeding the combined solution back into the absorption reactor as the absorption solution.

10. The process of claim 9, wherein the enzyme enriched solution includes precipitated and/or suspended solid carbonic anhydrase, and the step of combining the regenerated solution with the enzyme enriched solution is performed so as to substantially dissolve the carbonic anhydrase prior to feeding the combined solution back into the absorption reactor.

1 1. A process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separating step comprises managing the enzyme enriched solution so as to retain sufficient fluidity for liquid transport; and transporting at least a portion of the enzyme loaded solution through a recycle pipeline back into the absorption reactor.

12. A process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme loaded solution, wherein the enzyme depleted solution comprises residual carbonic anhydrase; and supplying the enzyme depleted solution to a desorption reactor, wherein the residual carbonic anhydrase provides catalysis of the desorption of C0₂, to form a regenerated solution.

13. The process of claim 12, wherein the separating step is controlled such that the residual carbonic anhydrase in the enzyme depleted solution comprises at most about 25 wt% of the carbonic anhydrase in the ion loaded solution.

14. The process of claim 12, wherein the separating step is controlled such that the residual carbonic anhydrase in the enzyme depleted solution comprises at most about 15 wt%, about 10 wt%, about 5 wt% or about 2 wt% of the carbonic anhydrase in the ion loaded solution.

15. The process of any one of claims 12 to 14, wherein the separating step comprise subjecting the ion loaded solution to filtration, such that the enzyme enriched solution is a retentate fluid and the enzyme depleted fluid is a permeate fluid.

16. The process of any one of claims 12 to 15, further comprising: operating the desorption reactor under conditions such that a portion of the residual carbonic anhydrase undergoes denaturation and a portion of the residual carbonic anhydrase retains activity upon release from the desorption reactor; supplying the regenerated solution including an amount of active carbonic anhydrase back into the absorption reactor.

17. A process for capturing C0₂, comprising: contacting a C0₂-containing gas with an absorption solution in an absorption reactor in the presence of carbonic anhydrase immobilized with respect to a porous matrix, to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein a portion of the carbonic anhydrase leaches out of the porous matrix as released carbonic anhydrase such that the ion loaded solution includes at least a portion of the released carbonic anhydrase; releasing the ion loaded solution from the absorption reactor; separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution; and recycling at least a portion of the enzyme enriched solution back into the absorption reactor.

18. The process of claim 17, wherein the porous matrix comprises a polymeric immobilization material.

19. The process of claim 18, wherein the polymeric immobilization material is coated onto a substrate.

20. The process of claim 19, wherein the substrate comprises fixed packing material within the absorption reactor.

21. The process of any one of claims 17 to 19, wherein the porous matrix is fixed within the absorption reactor.

22. The process of any one of claims 17 to 19, wherein the porous matrix is configured in the form of particles within the absorption solution.

23. The process of claim 22, wherein the particles flow with the absorption solution and the ion loaded solution released from the absorption reactor, and the process further comprises a particle separation step for separating the particles from the ion loaded solution prior to the step of separating the released carbonic anhydrase from the ion loaded solution.

24. A process for treating a C0₂-containing gas, comprising: contacting the C0₂-containing gas with a hybrid reactive solvent comprising a biocatalyst catalyzing hydration of dissolved C0₂ into bicarbonate ions, thereby producing a bicarbonate loaded solution comprising the biocatalyst; separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst; recirculating the biocatalyst stream for reuse in the hybrid reactive solvent; treating the bicarbonate loaded stream by regeneration to remove at least a portion of the bicarbonate ions therefrom and produce a regenerated hybrid solvent; and recirculating the regenerated hybrid solvent to form at least part of the hybrid reactive solvent.

25. A process of producing a C0₂ capture product, comprising: contacting a C0₂-containing gas with hybrid reactive solvent comprising a biocatalyst catalyzing hydration of dissolved C0₂ into bicarbonate ions, thereby producing a bicarbonate loaded solution comprising the biocatalyst; separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst; recirculating the biocatalyst stream for reuse in hybrid reactive solvent; treating the bicarbonate loaded stream by regeneration to remove at least a portion of the bicarbonate ions therefrom, to produce the C0₂ capture product and a regenerated hybrid solvent; and recirculating the regenerated solution to form at least part of the hybrid reactive solvent.

26. The process of claim 25, wherein the C0₂ capture product comprises C0₂ gas, a precipitated bicarbonate and/or a precipitated carbonate.

27. The process of claim 25 or 26, wherein the biocatalyst is selected from the group consisting of free enzymes and free enzymes analogues.

28. The process of any one of claims 25 to 27, wherein the step of separating the bicarbonate loaded solution into a biocatalyst stream having sufficient fluidity for liquid transport and a bicarbonate stream depleted of the biocatalyst is carried out on a filtration membrane provided with pores having smaller diameter than a diameter of the biocatalyst.

29. The process of claim 28, wherein the filtration membrane is inert to the hybrid reactive solvent.

30. The process of claim 28 or 29, wherein the filtration membrane is a nano-filtration membrane.

31. The process of claim 30, wherein the nano-filtration membrane is provided with pores having a diameter that is smaller than 15 nm.

32. The process of any one of claims 28 to 31 , wherein the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone.

33. A process for separating a biocatalyst from a bicarbonate loaded fluid, comprising: managing temperature and concentration of the bicarbonate loaded fluid to avoid precipitation and substantial denaturing of the biocatalyst, and removing a biocatalyst rich stream from the bicarbonate loaded fluid such that the biocatalyst rich stream retains sufficient fluidity for liquid transport.

34. The process of claim 33, further comprising minimizing liquid in the biocatalyst rich stream while retaining the sufficient fluidity for liquid transport.

35. The process of claim 33 or 34, wherein the biocatalyst rich stream has sufficient fluidity to facilitate mixing into an aqueous absorption solution.

36. The process of any one of claims 33 to 35, further comprising controlling temperature, biocatalyst concentration, bicarbonate concentration and/or viscosity of the biocatalyst rich stream, to enable the sufficient fluidity for liquid transport.

37. A process for treating a C0₂-containing gas, the process comprising the steps of: a) contacting within a reaction chamber, the C0₂-containing gas with a hybrid reactive solvent which is water based and comprises a biocatalyst, optionally a biocatalyst selected from the group consisting of free enzymes, free enzymes analogues, enzymes released from a porous matrix located within the reaction chamber, immobilized enzymes and immobilized enzymes analogues, the biocatalyst accelerating an enzymatic conversion of C0₂ into bicarbonate ions, by i) dissolving the C0₂-containing gas in the hybrid reactive solvent; and ii) promoting the enzymatic conversion of the dissolved C0₂ into bicarbonate and hydrogen ions; b) obtaining a depleted C0₂-containing gas, optionally defining a treated gas, the depleted C0₂-containing gas being then released from the reaction chamber; c) obtaining a hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst; and d) removing from the reaction chamber at least a portion of the hybrid reactive solvent of step c) and filtering it on a filtration membrane, optionally a filtration membrane that is inert to the hybrid reactive solvent, said filtration membrane being provided with pores having smaller diameter than a diameter of the biocatalyst and having an upstream side and a downstream side; to thereby obtain: i) at the upstream side of the filtration membrane, a retentate fluid rich in the biocatalyst, and ii) at the downstream side of the filtration membrane, a permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst.

38. The process of claim 37, wherein the retentate fluid has a flow rate FR1 from about 1 % FF to about 10% FF, or 5% FF to about 10% FF, wherein FF corresponds to a feed flow rate to the filtration membrane.

39. The process of claim 38, wherein the permeate fluid has a flow rate FR2 from 90% FF to 99% FF, or from 90% FF to 95% FF.

40. The process of any one of claims 37 to 39, wherein the retentate fluid includes sufficient amount of liquid to provide fluidity for liquid transport via a conduit.

41. The process of any one of claims 37 to 40, comprising providing a ratio FR1 / FR2 so as to keep the retentate fluid pumpable with the biocatalyst dissolved and/or suspended therein.

42. The process of any one of claims 37 to 41 , wherein a portion of the permeate fluid obtained from step d)-ii) is recycled to the retentate fluid to dilute the same and adjust the ratio FR1 / FR2 within a range keeping the retentate fluid pumpable with the biocatalyst dissolved and/or suspended therein.

43. The process of any one of claims 37 to 42, wherein the retentate fluid flows tangentially with respect to the upstream side of the membrane.

44. The process of any one of claims 37 to 43, wherein at least a portion of the retentate fluid obtained from step d)-i) is further recycled to the reaction chamber.

45. The process of any one of claims 37 to 44, wherein at least a portion of the permeate fluid obtained from step d)-ii) is further fed to a regeneration unit to produce a C0₂ capture product and a regenerated hybrid solvent.

46. The process of claim 45, wherein the C0₂ capture product is C0₂ gas, a precipitated bicarbonate and/or a precipitated carbonate.

47. The process of claim 45 or 46, wherein the regenerated hybrid solvent is recycled back into the reaction chamber to form at least part of the hybrid reactive solvent.

48. The process of any one of claims 45 to 47, wherein the regenerated hybrid solvent is combined with the retentate fluid to form at least part of the hybrid reactive solvent prior to being introduced into the reaction chamber.

49. The process of any one of claims 37 to 48, wherein the biocatalyst is selected from the group consisting of free enzymes, free enzymes analogues and free enzymes released from a porous matrix located within the reaction chamber.

50. The process of any one of claims 37 to 49, wherein the biocatalyst is selected from the group consisting of free enzymes and free enzymes analogues having a molecular mass ranging from 5 kDa to 120 kDa.

51. The process of claim 49 or 50, wherein the free enzymes or analogues thereof comprise carbonic anhydrase or analogues thereof.

52. The process of any one of claims 37 to 48, wherein the biocatalyst is selected from the group consisting of immobilized enzymes and immobilized enzymes analogues that are attached to an insoluble support consisting of particles composed of nylon, cellulose, silica, alumina, silica gel, chitosan, polystyrene, polymethylmethacrylate, or magnetic material or titanium oxide or zirconium oxide, or any combination thereof.

53. The process of claim 52, wherein the particles are composed of nylon, or alumina or titanium oxide or zirconium oxide.

54. The process of any one of claims 37 to 53, wherein the filtration membrane is inert to the hybrid reactive solvent.

55. The process of any one of claims 37 to 54, wherein the filtration membrane is a nano-filtration membrane.

56. The process of claim 55, wherein the nano-filtration membrane is provided with pores having a diameter that is smaller than 15 nm.

57. The process of claim 55, wherein the nano-filtration membrane is provided with pores having a diameter between 1 and 5 nm.

58. The process of any one of claims 37 to 57, wherein the filtration membrane is a hollow fiber membrane or comprises a hollow fiber membrane portion.

59. The process of any one of claims 37 to 58, wherein the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone or based on a mixture of polyether sulfone and polyvinylpyrrolydone.

60. The process of any one of claims 37 to 59, wherein the hybrid reactive solvent is a mixture of water and of a compound comprising at least one of piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1- propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl- 1 ,3-propanediol (Tris or AHPD), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DM MEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), diethanolamine (DEA), diisopropylamine (DIPA), methyl monoethanolamine (MMEA), TIA, TBEE, HEP, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)-ethane (BTEE), ethoxyethoxyethanoltertiarybutylamine (EEETB), bis-

(tertiarybutylaminoethyl)ether, 1 ,2-bis-(tertiarybutylaminoethoxy)ethane or bis-(2- isopropylaminopropyl)ether, and the like, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, and derivatives such as taurine, N.cyclohexyl 1 ,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine, sarcosine, methyl taurine, methyl-a-aminopropionic acid, N-^-ethoxy)taurine, Ν-(β- aminoethyl)taurine, N-methyl alanine, 6-aminohexanoic acid and potassium or sodium salts of the amino acids, or mixtures thereof, sodium carbonate, potassium carbonate and ammonium carbonate.

61. The process of any one of claims 37 to 59, wherein the hybrid reactive solvent is a mixture of water and of a compound comprising primary amines, secondary amines, tertiary amines, primary alkanolamines, secondary alkanolamines, tertiary alkanolamines, primary amino acids, secondary amino acids, tertiary amino acids, and/or carbonates.

62. The process of any one of claims 37 to 59, wherein the hybrid reactive solvent is a mixture of water and of a compound comprising a carbonate selected from the group consisting of potassium carbonate, sodium carbonate, ammonium carbonate and mixtures thereof.

63. An installation for the treatment of a C0₂-containing gas, the installation comprising: a) a reactor provided with a reaction chamber containing a hybrid reactive solvent which is water based and comprises a biocatalyst, optionally a biocatalyst selected from the group consisting of enzymes, enzymes analogues, enzymes supported on particles and enzymes analogues supported on particles and free enzymes released from a porous matrix located within the reaction chamber, the biocatalyst accelerating the conversion of C0₂ into bicarbonate ions; the reactor further comprising: a-1) a gas inlet in fluid communication with a source of C0₂-containing gas to be treated, for contacting the C0₂-containing gas with the hybrid reactive solvent, dissolving it in the hybrid reactive solvent, and promoting the enzymatic conversion of the dissolved C0₂ into bicarbonate ions, for: iii) providing a depleted C0₂-containing gas, optionally defining a treated gas, and iv) providing hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst; a-2) a gas outlet in fluid communication with the reaction chamber for the release the depleted C0₂-containing gas; and a-3) a hybrid reactive solvent outlet in fluid communication with the reaction chamber for collecting at least a portion of the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst; b) a filtration unit comprising: b-1) a filtration membrane, optionally a filtration membrane that is inert to the hybrid reactive solvent, the reaction membrane being provided with pores having smaller diameter than a diameter of the biocatalyst and having an upstream side and a downstream side; b-2) a hybrid reactive solvent inlet which is in fluid communication with the hybrid reactive solvent outlet of the reactor and in fluid communication with the upstream side of the filtration membrane; b-3) an outlet in fluid communication with the upstream side of the filtration membrane for recovery of a retentate fluid collected on the upstream side of the filtration membrane and rich in the biocatalyst; and b-4) an outlet in fluid communication with the downstream side of the filtration membrane for the recovery of a permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst.

64. The installation of claim 63, further comprising a hybrid reactive solvent inlet in fluid communication with the reaction chamber for addition of fresh hybrid reactive solvent into the reaction chamber.

65. The installation of claim 63 or 64, further comprising a first conduit provided between the hybrid reactive solvent outlet of the reactor, and the hybrid reactive solvent inlet of the filtration unit, to allow fluid communication therebetween of the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst, to the filtration unit, the first conduit being optionally further provided with a pumping device for pumping the hybrid reactive solvent enriched in bicarbonate ions and comprising the biocatalyst therethrough.

66. The installation of claim 65, further comprising a first conduit assembly comprising conduits for the recycling of at least a part of the retentate fluid rich in biocatalyst to the reaction chamber.

67. The installation of claim 66, wherein the first conduit assembly is provided with a pumping device for pumping the retentate fluid therethrough.

68. The installation of claim 66 or 67, further comprising: a second conduit assembly comprising conduits for the recovery of the permeate fluid collected downstream of the filtration membrane and for optionally recycling at least a portion thereof to the upstream side of the filtration membrane to dilute the retentate fluid; and a device for the measurement of physical properties of the retentate fluid collected on the upstream side of the filtration membrane; said device controlling a valve provided across the conduits of the second assembly for controlling the recycling of the permeate fluid to the upstream side of the filtration membrane.

69. The installation of claim 68, wherein the second conduit assembly is provided with a pumping device for pumping the permeate fluid therethrough.

70. The installation of claim 68 or 69, wherein the device is configured to actuate the valve for recycling at least a part of the permeate fluid with the retentate fluid flowing at the upstream side of the filtration membrane, to set a flow rate FR1 at the upstream side of the filtration membrane, which with respect to a flow rate of the permeate fluid flowing at the downstream side of the filtration membrane, within a ratio FR1 / FR2 allowing to keep the retentate fluid pumpable with the biocatalyst dissolved and/or suspended therein.

71. The process of any one of claims 68 to 70, further comprising a third conduit assembly comprising conduits for feeding a regeneration unit, optionally a desorption unit, with the permeate fluid defining a bicarbonate loaded fluid depleted in the biocatalyst, said regeneration unit being further provided with an outlet a C0₂ capture product and an outlet for a regenerated hybrid solvent comprising the permeate fluid depleted in bicarbonate ions, said third conduit assembly being optionally provided with a pumping device for pumping the permeate fluid therethrough.

72. The installation of claim 71 , wherein the C0₂ capture product is C0₂ gas, a precipitated bicarbonate and/or a precipitated carbonate.

73. The installation of claim 70 or 71 , further comprising: a third conduit assembly comprising conduits for feeding a regeneration unit, optionally a desorption unit, with the permeate fluid defining a bicarbonate loaded fluid depleted in biocatalyst, said regeneration unit being further provided with an outlet a C0₂ capture product and an outlet for the a regenerated hybrid solvent comprising the permeate fluid depleted in bicarbonate ions, said third conduit assembly being optionally provided with a pumping device for pumping the permeate fluid therethrough; a fourth conduit assembly comprising conduits for recycling the regenerated reactive solvent to the reaction chamber and optionally at least a portion thereof with the retentate fluid flowing at the upstream side of the filtration membrane to dilute it, said fourth conduit assembly being optionally provided with a pumping device for pumping the regenerated hybrid solvent therethrough; and a device for the measurement of physical parameters of the retentate fluid collected on the upstream side of the filtration membrane; said device being configured for controlling a valve provided across the conduits of the fourth assembly for controlling the recycling of the regenerated hybrid solvent to the upstream side of the filtration membrane.

74. The process of claim 73, wherein the fourth conduit assembly is provided with a pumping device for pumping the regenerated hybrid solvent therethrough.

75. The installation of claim 73 or 74, wherein the device for measuring physical parameters is configured to actuate the valve for recycling at least a part of the regenerated hybrid solvent with the retentate fluid flowing at the upstream side of the membrane to set a flow rate FR1 , which with respect to a flow rate of the permeate fluid flowing at the downstream side of the filtration membrane, at a at a ratio FR1 / FR2 within a range to keep the retentate fluid pumpable with the biocatalyst dissolved and/or suspended therein.

76. The installation of any one of claims 63 to 75, wherein the filtration membrane comprises a hollow fiber membrane.

77. The installation of any one of claims 63 to 76, wherein the filtration membrane is based on polyethersulfone combined with a separating layer of sulfonated polyethersulfone, or based on a mixture of polyether sulfone and sulfonated polyether sulfone.

78. A system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution and C0₂-depleted gas, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separation apparatus is configured such that the enzyme enriched solution comprises sufficient water to be a pumpable and pipelinable solution; and a recycle pipeline for receiving at least a portion of the enzyme enriched solution and being fluidly connected to the absorption reactor for supplying the at least a portion of the enzyme enriched solution back into the absorption reactor.

79. A system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution and C0₂-depleted gas, wherein the ion loaded solution includes at least a portion of the carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched solution, wherein the separation apparatus is configured such that the enzyme depleted solution comprises residual carbonic anhydrase; and a desorption feed pipeline for receiving the enzyme depleted solution from the separation apparatus; a desorption reactor in fluid communication with the desorption feed pipeline for receiving the enzyme depleted solution, wherein the residual carbonic anhydrase provides catalysis of the desorption of C0₂, to form a regenerated solution and C0₂ gas.

80. A system for capturing C0₂, comprising: an absorption reactor comprising: a gas inlet for supplying a C0₂-containing gas; a liquid inlet for supplying an absorption solution; a reaction chamber in communication with the gas inlet and the liquid inlet, the reaction chamber being configured to allow contact of the C0₂-containing gas with the absorption solution in the presence of carbonic anhydrase immobilized with respect to a porous matrix, to catalyse the hydration reaction of C0₂ into bicarbonate and hydrogen ions, thereby producing an ion loaded solution, wherein a portion of the carbonic anhydrase leaches out of the porous matrix as released carbonic anhydrase such that the ion loaded solution includes at least a portion of the released carbonic anhydrase; a gas outlet for releasing the C0₂-depleted gas from the reaction chamber; and a liquid outlet for releasing the ion loaded solution from the reaction chamber; a separation apparatus for separating the ion loaded solution into at least an enzyme depleted solution and an enzyme enriched fraction; and a transport system for receiving at least a portion of the enzyme enriched solution and being connected to the absorption reactor for supplying the at least a portion of the enzyme enriched fraction back into the absorption reactor.

81. The system of claim 80, wherein the enzyme enriched fraction has sufficient fluidity for liquid transport and the transport system comprises a recycle pipeline.

82. The system of any one of claims 78 to 81 , wherein the separation apparatus comprises a filtration membrane.

83. A method for improving energy efficiency of a enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage produced by the absorption stage at a recycle flow of at most 30% of the bicarbonate loaded solution, the method comprising providing a carbonate-based absorption solution for circulating through the enzymatic C0₂ capture system.

84. The method of claim 83, wherein the separation stage comprising membrane filtration.

85. The method of claim 83 or 84, wherein the separation stage is regulated such that the recycle flow of the enzyme enriched bicarbonate loaded stream is a sufficiently low proportion of a flow of the bicarbonate loaded solution to have a minimal impact on the energy efficiency compared to no recycling of the enzyme enriched bicarbonate loaded stream back into the absorption stage.

86. The method of any one of claims 83 to 85, wherein the enzyme enriched bicarbonate loaded stream is at most about 20% of the bicarbonate loaded solution produced by the absorption stage.

87. The method of any one of claims 83 to 85, wherein the enzyme enriched bicarbonate loaded stream is at most about 10% of the bicarbonate loaded solution produced by the absorption stage.

88. The method of any one of claims 83 to 87, wherein the carbonate-based absorption solution comprises potassium carbonate and/or sodium carbonate.

89. A method for capturing C0₂ with an enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage, the method comprising regulating the separation stage such that a recycle flow of the enzyme enriched bicarbonate loaded stream is a sufficiently low proportion of a flow of the bicarbonate loaded solution to have a minimal impact on energy efficiency of the enzymatic C0₂ capture system compared to no recycling of the enzyme enriched bicarbonate loaded stream back into the absorption stage.

90. The method of claim 89, wherein the separation stage comprising membrane filtration.

91. The method of claim 89 or 90, wherein the absorption solution that for circulating through the enzymatic C0₂ capture system is a carbonate-based absorption solution and the step of regulating the separation stage comprises providing the recycle flow to be at most 30% of the flow of the bicarbonate loaded solution.

92. The method of claim 91 , wherein the recycle flow is at most 20% of the flow of the bicarbonate loaded solution.

93. The method of claim 91 , wherein the recycle flow is at most 10% of the flow of the bicarbonate loaded solution.

94. The method of any one of claims 91 to 93, wherein the carbonate-based absorption solution comprises potassium carbonate and/or sodium carbonate.

95. The method of claim 89 or 90, wherein the absorption solution that for circulating through the enzymatic C0₂ capture system is an amino-based absorption solution and the step of regulating the separation stage comprises providing the recycle flow to be at most 5% of the flow of the bicarbonate loaded solution.

96. A method for capturing C0₂ with an enzymatic C0₂ capture system including absorption and desorption stages and a separation stage for removing an enzyme enriched bicarbonate loaded stream from a bicarbonate loaded solution produced by the absorption stage for recycling back into the absorption stage, the method comprising minimizing energy consumption by selecting an absorption compound for use in an absorption solution for circulating through the enzymatic C0₂ capture system and selecting a recycle flow of the enzyme enriched bicarbonate loaded stream.

97. The method of claim 96, wherein the separation stage comprising membrane filtration.

98. The method of claim 96 or 97, wherein the absorption compound is selected to be a carbonate and the recycle flow is selected to be at most 30% of a flow of the bicarbonate loaded solution.

99. The method of claim 98, wherein the carbonate is selected to be potassium carbonate and/or sodium carbonate.

100. The method of claim 98, wherein the carbonate is selected to be sodium carbonate.

101. The method of any one of claims 98 to 100, wherein the recycle flow is at most 20% of the flow of the bicarbonate loaded solution.

102. The method of any one of claims 98 to 100, wherein the recycle flow is at most 10% of the flow of the bicarbonate loaded solution.

103. The method of claim 96 or 97, wherein the absorption compound is selected to be an amino-based absorption solution and the recycle flow is selected to be at most 5% of a flow of the bicarbonate loaded solution.

104. The method of claim 103, wherein the absorption compound is selected to be an alkanolamine.

105. The method of claim 103, wherein the alkanolamine is selected to be a tertiary amino compound.

106. The method of claim 104 or 105 wherein the absorption compound is selected to be MDEA.