A process for the enzymatic co2 capture using a stabilized carbonic anhydrase

Abstract

The present invention relates to a process for the capture of CO2 using a stabilized enzyme.

Description

[0001] "A process for the enzymatic CO2 capture using a stabilized carbonic anhydrase"

[0002] DESCRIPTION

[0003] The present invention finds application in the field of CO2 capture .

[0004] Background

[0005] Some of the CO2 capture processes already known are based on the use of the enzyme carbonic anhydrase in order to increase the CO2 capture performance of the absorption solutions.

[0006] These processes are composed of two main units: an absorption unit to absorb the CO2 from a CCy-containing gas and a stripping unit, where the absorbed CO2 is released from the CO2 rich-absorption solution and consequently the absorption solution is regenerated.

[0007] A simplified CCy-capture process configuration is shown in Figure 1.

[0008] The process comprises two areas: the absorption zone operating at low temperature and the stripping zone operating at a higher temperature .

[0009] In such a process, a CCy-containing gas (1) is fed to the absorption unit (2) , where it flows upward while contacting an aqueous absorption solution (4) ; as the gas contacts the absorption solution, the CO2 is absorbed by the solution.

[0010] The treated gas (3) then leaves the absorption unit and is released to the atmosphere or sent to other units for further treatments or use. The absorption solution containing the absorbed CO2 (5) is then pumped (pump 6) through two heat exchangers (7,8) , where its temperature is increased and then it is fed to a stripping unit (9) wherein the conditions are adjusted such that the CO2 is released from the solution and the solution is regenerated.

[0011] A heat exchanger (8) is often optional.

[0012] The gas (19) leaving the stripping unit (9) is fed to a condenser (14) , wherein the steam is condensed.

[0013] The gas-liquid stream (20d) is then sent to a separator (14a) , wherein the high CO2 concentration gas (20b) exits the separator (14a) and is sent ( compressor / vacuum pump 36) for its use or for further treatments (stream 20) .

[0014] The condensed steam (20a) is returned to the process.

[0015] Part of the CCq-lean absorption solution leaving the stripping unit (10) is sent back to the absorption unit using a pump (16) , while the other part of the CCt-lean absorption solution (11) is pumped via pump (17) to a reboiler (12) .

[0016] Alternatively, the CCy-lean absorption solution leaving the stripping unit (10) is entirely sent back to the absorption unit using the pump (16) or is pumped via pump (17) to a reboiler (12) .

[0017] The solution is then boiled to produce steam and the produced steam / liquid mixture (13) is sent to the stripping unit (9) .

[0018] The steam moves upward and acts as a stripping gas to favor the

[0019] CO2 desorption from the solution. Prior to being fed to the absorber, a portion of the solution (15) may be cooled through one or more heat exchangers (7, 18) .

[0020] When it is used in combination with the above-mentioned techniques, the absorption solution is usually an alkaline solution characterized by a pH higher than 8.5, the absorption unit operates at temperatures ranging from 10-50°C, the CCy-rich absorption solution is heated up to temperature ranging from 50 °C to 90 °C prior to being fed to the stripping unit, which may be operated under vacuum conditions or pressure conditions close to the atmospheric pressure.

[0021] Therefore, the enzyme used in such CO2 capture processes is exposed to alkaline pHs higher than 8.5, temperatures up to 90°C, and large gas / liquid interfacial areas.

[0022] Alkaline pHs, high temperatures and large gas-liquid interfacial areas are all detrimental conditions, which expose an enzyme to inactivation conditions.

[0023] As a consequence of the denaturation, an enzyme progressively loses quaternary, tertiary and then its secondary structure by unfolding and forming a molten globule and will eventually form aggregates with other denatured enzymes.

[0024] Eventually, the enzyme loses its catalytic activity.

[0025] Most references reporting enzyme-based (carbonic anhydrase-based) CO2 capture processes emphasize the catalytic role of the enzyme leading to the increased performance of the CO2 capture process.

[0026] Enzyme lifetime in such processes is a key issue, as it dictates the enzyme consumption and cost. This aspect has been addressed by stabilizing the enzyme to increase the enzyme thermostability in several ways.

[0027] Enzyme stabilization will result in increasing the period for which the enzyme will remain active during the process operation; it will also increase the possibility to reuse the enzyme and its operational stability.

[0028] Enzyme stabilization can be obtained by different methods such as: immobilization, encapsulation, pegylation, chemical modification, protein engineering and medium engineering.

[0029] Immobilization consists in immobilizing the enzyme to a solid support and the success, that is the effect of the immobilization on the enzyme performance, depends on the chemical method, the support material, and the enzyme itself .

[0030] Even though the enzyme may be stabilized it can lose some of its original activity because of an improper 3D configuration; moreover, the support may cause a mass transfer limitation of the substrate to the enzyme or of the product release to the medium, thus reducing the effect of the enzyme in the process.

[0031] The enzyme encapsulation consists in confining a solution droplet containing the enzyme molecules inside a porous capsule; the capsule introduces a mass-transfer limitation similarly to immobilization, thus reducing the catalytic impact of the enzyme in the process where it is used. Pegylation is a method mainly used in pharmaceutical industry where PEG molecules are covalently linked to drugs or to therapeutic proteins .

[0032] Chemical modifications consist in adding via covalent bond small molecules to the surface of an enzyme to increase its stability; the success of the method depends on the chemical method, number of modifications on the enzyme surface and the enzyme itself.

[0033] Protein engineering consists in modifying the enzyme primary sequence to change its structure via replacement of some amino acids at specific sites; the results in terms of increased stability depends on the specific mutations and their number.

[0034] Medium engineering consists in the addition of molecules, such as inorganic salts, polyols and sugars, to the medium containing the enzyme with the purpose of retaining its activity during storage and use .

[0035] In the context of the enzymatic carbon capture, there are different strategies on how the enzyme can be used.

[0036] In a first strategy, the enzyme is used in the absorption zone of the process wherein the process temperature to which the enzyme is exposed is the lowest.

[0037] This strategy is applied in different ways: the enzyme may be immobilized to the packing material and thus stabilized, when the gasliquid contactor is a packed column; in such a configuration the enzyme is always in the absorber and thus exposed to low temperature conditions . The enzyme may also be stabilized by immobilization to microparticles in suspension in the absorption solution.

[0038] In such a configuration, once the absorption solution exits the absorber, the micro-particles are separated out of the CCy-rich absorption solution and reinjected in the absorption solution prior to its feeding to the absorption unit.

[0039] The enzyme may be used free or solubilized in the absorption solution and the enzyme is filtered out of the solution similarly to micro-particles. In this first strategy, the enzyme is only exposed to pH and temperature conditions present in the absorption zone of the process .

[0040] In a second strategy, the objective is to develop an enzyme active and robust to operation conditions in both the absorption and stripping zones of the process.

[0041] The increase in the enzyme stability is achieved by using carbonic anhydrase enzymes robust to the process conditions selected from natural microorganisms or by genetically modifying carbonic anhydrase enzymes .

[0042] A third strategy consists in combining new robust enzymes with immobilization techniques to further stabilize the enzyme and use this robust immobilized enzyme in the absorption zone only or in both the absorption and stripping zones.

[0043] Prior-art document US 2011 / 223650 discloses the capture of CO2 from a CO2 containing gas with a membrane reactor using a conventional aqueous solution comprising carbonic anhydrase. Prior-art document CA 2.848.447 discloses a process to capture CO2 from a SAGD installation using an absorption / desorption process, wherein the aqueous absorption solution comprises a carbonic anhydrase free, dissolved or immobilized.

[0044] The prior-art document US 2008 / 148939 discloses the absorption of CO2 from a CO2 containing gas, wherein a carbonic anhydrase is used in combination with a PEG solution with the purpose of increasing the CO2 absorption rate and wherein the enzyme stability is not an issue.

[0045] The prior-art document CN 114768519 discloses a long-lasting and environmentally friendly f ormaldehyde-removing agent comprising an enzyme within a gel composition at a slightly acidic pH (5.5-6.5) .

[0046] Summary of the invention

[0047] The inventors of the present patent application have surprisingly found how to stabilize a carbonic anhydrase enzyme for application in a process for capturing CO2, wherein the enzymatic activity is not impaired .

[0048] The approach of the present invention does not comprise the immobilization of the enzyme.

[0049] Brief description of the figures

[0050] Figure 1 shows a simplified process for the capture of CO2.

[0051] Figures 2 and 3 show the results of the stability assays performed according to the present invention with two exemplary carbonic anhydrase enzymes.

[0052] Object of the invention In a first object, the present invention discloses a process for the absorption of CO2 from a CCy-containing gas.

[0053] In a particular aspect, it is also disclosed an absorption solution comprising a stabilized enzyme.

[0054] In a second object, the present invention discloses a method for the stabilization of carbonic anhydrase with the use of polyethylene glycol .

[0055] Detailed description of the invention

[0056] According to a first object, the present invention discloses a process for the absorption of CO2 from a CCy-containing gas.

[0057] For the purposes of the present invention, the disclosed process comprises an absorption step, wherein CO2 is absorbed from a CO2- containing gas and a stripping step for the release of CO2.

[0058] In particular, in the absorption step, a CCy-containing gas is contacted with a CCy-lean absorption solution so that the CO2 is absorbed and a CCy-rich absorption solution is formed.

[0059] In particular, in the stripping step, CO2 is stripped from the CCy-rich absorption solution thereby forming a CCy-lean absorption solution and a CCy-rich gas.

[0060] For the purposes of the present invention, a CCy-containing gas may be selected from the group comprising: post-combustion flue gas, a process gas, a biogas, a natural gas or air obtained from different sources . For the purposes of the present invention, the absorption step is carried out in an absorber or in an absorption unit, which is a gasliquid contactor.

[0061] In particular, the absorber may be represented by a packed column, a tray column or a rotating packed bed.

[0062] In a preferred embodiment, the absorber is represented by a rotating packed bed.

[0063] For the purposes of the present invention, the stripping step is carried out in a stripper or in a stripping unit, which is a gas-liquid contactor .

[0064] In particular, the stripper may be represented by a packed column, a tray column, a rotating packed bed or a falling-film evaporator.

[0065] In a preferred embodiment, the stripper is represented by a rotating packed bed.

[0066] The stripping gas required to enable the CO2 stripping in the stripper or stripping unit is generated by circulating a fraction of the absorption solution leaving the stripper through a reboiler (as depicted in figure 1) .

[0067] Heat is provided to the reboiler to heat up the absorption solution until its boiling point and then generate steam from the solution.

[0068] For the purposes of the present invention, the absorption solution is an alkaline aqueous solution.

[0069] In particular, the alkaline aqueous absorption solution comprises an alkali metal salt in a concentration of from about 1 M to about 6

[0070] M and preferably of about 1 M to about 2 M. In particular, the absorption solution has a pH of from about 8.5 to about 11.

[0071] Preferably, the absorption solution has a pH of about 8.5-10.

[0072] In particular, the absorption solution comprises an alkali metal salt selected from carbonate, bicarbonate; or mixture thereof .

[0073] In particular, the metal ion may be represented by potassium and / or sodium.

[0074] Preferably, the absorption solution comprises one or more of: potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate; and / or mixture thereof.

[0075] According to a preferred embodiment, the absorption solution comprises potassium carbonate.

[0076] In addition to an alkali metal salt, the absorption solution may also comprise tertiary amines, tertiary alkanolamines, tertiary amino acids .

[0077] In particular, tertiary amines may be selected from the group comprising: N, N-dethylmethylamine , N, N-Diisopropylethylamine, triethylenediamine, triethylamine .

[0078] In particular, tertiary alkanolamines may be selected from the group comprising: N-methyldiethanolamine (MDEA) , dimethylmonoethanolamine (DMMEA) , diethylmonoethanolamine (DEMEA) , triisopropanolamine (TIPA) .

[0079] In particular, tertiary amino acids may be selected from the group comprising: N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine . According to an embodiment of the present invention, the absorption solution may comprise an antifoam compound.

[0080] For the purposes of the present invention, the absorption solution has a temperature of from about 10-90°C.

[0081] Preferably, the absorption solution has a temperature of from about 15-80°C.

[0082] Typically, the absorption solution has a lower temperature in the absorption unit and a higher temperature in the stripping unit.

[0083] For instance, the temperature of the absorption solution may be of about 15-35°C in the absorption unit and of about 60-80°C in the stripping unit.

[0084] For the purposes of the present invention, the absorption solution comprises a biocatalyst.

[0085] In particular, the biocatalyst used in the process of the present invention is an enzyme represented by a carbonic anhydrase.

[0086] For the purposes of the present invention, any carbonic anhydrase can be used.

[0087] In an embodiment of the invention, the enzyme can be present in a concentration of about 0-2 g / 1, preferably of about 0.05-1 g / 1 and more preferably of about 0.05-0.3 g / 1.

[0088] According to the present invention, the absorption solution comprises an enzyme stabilizing agent.

[0089] More in particular, such stabilizing agent is represented by a synthetic polymer. More in particular, such stabilizing agent is represented by polyethylene glycol (PEG) .

[0090] As PEG with molecular weight of more than 20.000 g / 1 are also referred to as polyethylene oxides (PEG) , in the following, when PEG is referred then PEO can be also intended.

[0091] In an embodiment of the present invention, PEG has a molecular weight higher than 2.000 g / mol .

[0092] In a preferred embodiment, PEG has a molecular weight higher than 4.000 g / mol .

[0093] In an embodiment of the present invention, PEG has a molecular weight up to 1.000.000 g / mol.

[0094] In a preferred embodiment, PEG has a higher molecular weight up to 20.000 g / mol .

[0095] According to a preferred embodiment of the invention, PEG is comprised within the absorption solution in a specific mole ratio with respect to the enzyme.

[0096] In a preferred embodiment, PEG and the carbonic anhydrase enzyme are in a mole ratio of from 1 to 16.

[0097] In a more preferred embodiment, PEG and the carbonic anhydrase are in a mole ratio of 1:1, 2: 1, 4: 1, 8:1, 12:1 or 16:1.

[0098] A PEG: carbonic anhydrase mole ratio of 4 :1 or 8 :1 is even more preferred .

[0099] More preferably, the PEG: carbonic anhydrase mole ratio is about 4:1. As per the preparation of the absorption solution, there can be followed three methods:

[0100] - method A of direct contacting PEG molecules with the enzyme before preparing the aqueous absorption solution, or

[0101] - method B of adding PEG molecules to the aqueous absorption solution containing the enzyme, or method C of adding enzyme to the aqueous absorption solution containing PEG molecules.

[0102] In particular, as per Method A, PEG is added with the appropriate quantity so as to achieve the specific PEG / enzyme mole ratio, to the enzyme stock solution as a powder or dissolved in a PEG aqueous solution; the mixture is then agitated to dissolve PEG and obtaining a homogenous solution, which is then injected into the CO2 capture process (see figure 1, 5' or close to 5' ) .

[0103] In particular, as per Method B, PEG is dissolved in an aqueous solution and is injected into the absorption solution stream of the CO2 capture process.

[0104] The PEG quantity injected is adjusted to maintain the optimal PEG / enzyme ratio in the process.

[0105] The PEG solution may injected at a location nearby the enzyme injection point (see for instance figure 1, 5' ) .

[0106] In particular, as per Method C, the enzyme is dissolved or added in liquid form into the PEG containing absorption solution stream of the CO2 capture process. The PEG and enzyme quantities injected are adjusted to maintain the optimal PEG / enzyme ratio in the process.

[0107] Preferably, the PEG solution is injected at a location nearby the enzyme injection point (see for instance figure 1, 5' ) .

[0108] For the purpose of the present invention, the enzyme is not immobilized onto the PEG.

[0109] The absorption solution above disclosed represents a further object of the present invention.

[0110] According to a second object of the invention, it is disclosed a method for the stabilization of an enzyme represented by a carbonic anhydrase .

[0111] In particular, said stabilization is obtained under one or more of the following conditions:

[0112] Alkaline pH of from 8 to 11,

[0113] Salt concentration higher than 1 M

[0114] Temperature of 40-100°C,

[0115] Large gas-liquid interface.

[0116] In a particular aspect of the present invention, the process of the invention is carried out under large gas / liquid interface.

[0117] Such conditions are for instance represented by bubbling conditions .

[0118] Such conditions, for instance, occur when, in the CO2 capture process, the absorption solution flows through the reboiler and the stripper . In an embodiment of the present invention, the stabilization of carbonic anhydrase is obtained with the preparation of an absorption solution comprising the carbonic anhydrase enzyme and PEG according to one of the above Methods A, B or C.

[0119] In a preferred embodiment, PEG has a molecular weight higher than 2.000 g / mol .

[0120] In a preferred embodiment, the PEG has a molecular weight higher than 4.000 g / mol.

[0121] In an embodiment of the present invention, the PEG has a molecular weight up to 1.000.000 g / mol.

[0122] In a preferred embodiment, the PEG has a molecular weight higher up to 20.000 g / mol.

[0123] According to a preferred embodiment of the invention, PEG is comprised within the absorption solution in a specific mole ratio with respect to the enzyme.

[0124] In a preferred embodiment, PEG and the carbonic anhydrase enzyme are in a mole ratio of from 1 to 16.

[0125] In a more preferred embodiment, PEG and the carbonic anhydrase are in a mole ratio of 1, 2, 4, 8, 12 or 16.

[0126] A PEG: carbonic anhydrase mole ratio of 4 or 8 is even more preferred and a PEG: carbonic anhydrase mole ratio is 4.

[0127] The invention will be further disclosed in more detail with reference to the following non-limi tative examples.

[0128] EXAMPLE 1 Determination of optimal PEG molecular weight and PEG / enzyme molar ratio

[0129] The experiment was carried out using the thermal shift assay and SYPRO orange using the following conditions: Temperature range: 40-100°C Temperature ramp: 0.5°C / cycle

[0130] Cycle times: 20, 40 and 80 seconds.

[0131] Enzymes: Carbonic anhydrases A and B (CA-A & CA-B) PEG MW: 4.600 and 20.000 Da

[0132] PEG / Enzyme mole ratio: 1, 2, 4, 8, 12* and 16* (* tests only with PEG 20 000 Da)

[0133] Enzyme concentration: 0.25 g / L

[0134] Solution composition: 1.45 M K2CO3 / KHCO3 pH 9.75

[0135] Figures 2 and 3 shows the results obtained for two exemplary carbonic anhydrase enzymes using PEG 4600 and 20000 at ratio 0, 4 and 8 mol PEG / mol enzyme.

[0136] Carbonic anhydrase A (CA-A) has the sequence corresponding to SEQ. ID. No. 1.

[0137] The following results are obtained:

[0138] PEG addition results in decreased relative fluorescence unit (RFU) for a given temperature. As less hydrophobic residues are exposed the enzyme structure is less degraded. It shows that PEG effectively stabilizes the enzyme.

[0139] PEG 20.000 has a higher stabilization effect on the enzyme as shown by the decrease in the RFU.

[0140] An analogous effect has been demonstrated for a second carbonic anhydrase enzyme as shown in Figure 3.

[0141] EXAMPLE 2

[0142] Determination of the impact of presence of PEG on carbonic anhydrase enzyme stability under bubbling conditions

[0143] A test was carried out to evaluate the stabilization impact of PEG in the presence of the enzyme carbonic anhydrase under conditions of large gas / liquid interface. This is obtained by bubbling a gas containing CO2 into the absorbing solution. The experimental setup consists in a 500 mL graduated cylinder containing a solution containing the enzyme and PEG according to the test's conditions. The gas containing CO2 is bubbled at the bottom of the cylinder at a rate of 6 g Io1min-1. The CO2 concentration in the gas is adjusted at a value enabling the pH of the solution to remain stable over the duration of the test.

[0144] The test conditions are the following:

[0145] Enzyme concentration: 0.5 g / L

[0146] Enzyme : CA-A

[0147] Solution composition: 1.45 M K2CO3 / KHCO3 at pH 9.75 containing 5 mM KNO2, 50 mM KNO3 and 100 mM K2SO4.

[0148] Temperature gas and solution: 70°C

[0149] Test duration: 48 h PEG MW: 20.000 Da

[0150] PEG / Enzyme mol ratios: 0, 4 and 8.

[0151] The CO2 hydration activity of the carbonic anhydrase enzyme is measured at the beginning of the test (TO) and at the end of the test (TF) . In order to determine the stabilization effect of PEG on the enzyme, the activity loss under the three PEG / Enzyme ratios conditions are compared .

[0152] The results are provided in the Table below:

[0153] *Relative enzyme half-life: (Enzyme half-life at PEG / Enzyme ratio (4 or 8) / Enzyme half-life at PEG / Enzyme ratio 0)

[0154] **Relative enzyme consumption: (Enzyme consumption at PEG / Enzyme ration 4 or 8) / (Enzyme consumption at PEG / ratio 0)

[0155] EXAMPLE 3

[0156] Determination of the impact of presence of PEG on carbonic anhydrase enzyme stability under bubbling conditions

[0157] A test was carried out to evaluate the stabilization effect of PEG in the presence of the enzyme carbonic anhydrase under conditions of large gas / liquid interface. This is obtained by bubbling a gas containing CO2 into the absorbing solution. The experimental setup consists in a 500 mL graduated cylinder containing a solution containing the enzyme and PEG according to the test' s conditions. The gas containing CO2 is bubbled at the bottom of the cylinder at a rate of 6 g In1min-1using a nozzle with an opening of 760 microns. The CO2 concentration in the gas is adjusted at a value enabling the pH of the solution to remain stable over the duration of the test.

[0158] The test conditions are the following:

[0159] Enzyme concentration: 0.5 g / L

[0160] Enzyme: CA-A

[0161] Temperature gas and solution: 70°C

[0162] Test duration: 24 h

[0163] PEG MW: 20.000 Da

[0164] PEG / Enzyme mol ratios: 0, 4.

[0165] The CO2 hydration activity of the carbonic anhydrase enzyme is measured at the beginning of the test (TO) and at the end of the test (TF) . In order to determine the stabilization effect of PEG on the enzyme, the activity loss under the two PEG / Enzyme ratios conditions are compared.

[0166] The results are provided in the Table below:

[0167] *Relative enzyme half-life: (Enzyme half-life at PEG / Enzyme ratio

[0168] (4) / Enzyme half-life at PEG / Enzyme ratio 0) for a same pH. **Relative enzyme consumption: (Enzyme consumption at PEG / Enzyme ration 4) / (Enzyme consumption at PEG / ratio 0) at a same pH.

[0169] The results demonstrate that the presence of PEG stabilized the enzyme when present in a potassium carbonate solution at 70°C under bubbling conditions .

[0170] From the above disclosure, the advantages of the present invention will be immediately evident.

[0171] The cost of the overall process for the CO2 capture using the stabilized enzyme of the invention are not increased, because the longer lifecycle of the enzyme overcome the additional cost for the use of polyethylene glycol.

[0172] In addition, the stabilization does not require any chemical reaction, so that the procedure is not rendered more complex.

[0173] In fact, contrarily to other methods such as the pegylation or the chemical modification, there is no need for a chemical modification of the enzyme at specific reactive sites or for introducing new residues; accordingly, there is avoided the need of additional steps like purification, which otherwise would impact substantially the complexity and cost of the CO2 absorption process.

Claims

CLAIMS1. A process for the capture of CO2 from a CCy-containing gas comprising an absorption step for the absorption of CO2 from the CO2- containing gas, wherein said CCy-containing gas is contacted with an absorption solution so that a CCy-rich absorption solution is obtained, and a stripping step for the release of CO2 from said CCt-rich absorption solution, wherein CO2 is stripped from the CCt-rich absorption solution, obtaining a CCt-lean absorption solution and a C02-rich gas, wherein said absorption solution comprises an enzyme represented by carbonic anhydrase and an enzyme stabilizing agent represented by a synthetic polymer.

2. The process for the capture of CO2 from a CCy-containing gas according to the preceding claim, wherein said synthetic polymer is polyethylene glycol (PEG) .

3. The process for the capture of CO2 from a CCy-containing gas according to the preceding claim, wherein PEG has a molecular weight higher than 2.000 g / mol .

4. The process for the capture of CO2 from a CCy-containing gas according to the preceding claim, wherein PEG has a molecular weight higher than 4.000 g / mol.

5. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein PEG has a higher molecular weight up to 20.000 g / mol.

6. The process for the capture of CO2 from a CCq-containing gas according to any one of the preceding claims 1 to 4 , wherein PEG has a molecular weight up to 1.000.000 g / mol .

7. The process for the capture of CO2 from a CCq-containing gas according to any one of the preceding claims, wherein said CO2- containing gas is selected from the group comprising: post-combustion flue gas, a process gas, a biogas, a natural gas or air.

8. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorption step is carried out in an absorber or in an absorption unit, which is a gas-liquid contactor.

9. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorber is represented by a packed column, a tray column or a rotating packed bed.

10. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorption solution is an alkaline aqueous absorption solution.

11. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the alkaline aqueous absorption solution comprises an alkali metal salt in a concentration of from about 1 M to about 6 M and preferably of about 1 M to about 2 M.

12. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorption solution has a pH of from about 8.5 to about 11.

13. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorption solution comprises a carbonate or a bicarbonate salt; or mixture thereof .

14. The process for the capture of CO2 from a CCy-containing gas according to the preceding claim, wherein the salt is an alkali metal salt represented by potassium and / or sodium.

15. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein said salt is potassium carbonate.

16. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorption solution comprises tertiary amines, tertiary alkanolamines, tertiary amino acids .

17. The process for the capture of CO2 from a CCy-containing gas according to the preceding claim, wherein tertiary amines are selected from the group comprising: N, N-dethylmethylamine , N,N- Diisopropylethylamine, triethylenediamine, triethylamine; tertiary alkanolamines are selected from the group comprising: N- methyldiethanolamine (MDEA) , dimethylmonoethanolamine (DMMEA) , diethylmonoethanolamine (DEMEA) , triisopropanolamine (TIPA) ; tertiary amino acids are selected from the group comprising: N-methyl N- secondary butyl glycine, diethylglycine, dimethylglycine.

18. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the absorptionsolution has a temperature of from about 10-90°C and preferably of from about 15-80°C.

19. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the enzyme is present in a concentration of about 0-2 g / 1, preferably of about 0.05- 1 g / 1 and more preferably of about 0.05-0.3 g / 1.

20. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein PEG and the carbonic anhydrase enzyme are in a mole ratio of from 1 to 16.

21. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein PEG and the carbonic anhydrase are in a mole ratio of 1:1, 2:1, 4 :1, 8:1, 12 : 1 or 16:1.

22. The process for the capture of CO2 from a CCy-containing gas according to the preceding claims, wherein PEG: carbonic anhydrase mole ratio is of 4:1 or 8:1 and preferably is of 4:1.

23. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein PEG is contacted directly with the enzyme before preparing the aqueous absorption solution .

24. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims 1 to 21, wherein PEG is added to an absorption solution containing the enzyme.

25. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims 1 to 21, wherein the enzyme is added to the aqueous absorption solution containing PEG.

26. The process for the capture of CO2 from a CCy-containing gas according to any one of the preceding claims, wherein the process is carried out under bubbling conditions .

27. A method for the stabilization of an enzyme within an absorption solution, wherein said absorption solution comprises a synthetic polymer represented by polyethylene glycol (PEG) .

28. The method according to the preceding claim, wherein said enzyme is a carbonic anhydrase and said absorption solution is a potassium carbonate containing solution.

29. The method according to the preceding claims 27 or 28 wherein said polyethylene glycol has a molecular weight higher than 2.000 g / mol .

30. The method according to any one of the preceding claims 27 to29, wherein said polyethylene glycol has a molecular weight higher than 4.000 g / mol .

31. The method according to any one of the preceding claims 27 to30, wherein said polyethylene glycol has a higher molecular weight up to 20.000 g / mol .

32. The method according to any one of the preceding claims 27 to31, wherein said polyethylene glycol has a molecular weight up to1.000.000 g / mol .

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