ABSTRACT
Abstract
A formulation and process for capturing CO2 use an absorption mixture containing water, biocatalysts and a carbonate compound. The process includes contacting a CO2-containing gas with the absorption mixture to enable dissolution and transformation of CO2 into bicarbonate and hydrogen ions, thereby producing a CO2-depleted gas and an ion-rich solution, followed by subjecting the ion-rich solution to desorption. The biocatalyst improves absorption of the mixture comprising carbonate compounds and the carbonate compound promotes release of the bicarbonate ions from the ion-rich solution during desorption, producing a CO2 gas stream and an ion-depleted solution.
Description
PRIORITY CLAIM
This application is a continuation of and claims priority to U.S. patent Ser. No. 14/698,159 filed on Apr. 28, 2015, which is a continuation of U.S. patent application Ser. No. 14/106,102 (issued as U.S. Pat. No. 9,044,709) filed on Dec. 13, 2013, which is a continuation of U.S. patent application Ser. No. 13/388,871 filed on Feb. 3, 2012 (issued as U.S. Pat. No. 8,722,391), which is the national stage entry of PCT/CA2010/001214, filed on Aug. 4, 2010, which claims priority to U.S. Provisional Application No. 61/231,037, filed on Aug. 4, 2009, which is incorporated herein by reference for all purposes.
FIELD OF INVENTION
The present invention relates generally to CO 2 capture and more particularly to a formulation and process for CO 2 capture using carbonates and biocatalysts.
BACKGROUND OF THE INVENTION
Increasingly dire warnings of the dangers of climate change by the world's scientific community combined with greater public awareness and concern over the issue has prompted increased momentum towards global regulation aimed at reducing man-made greenhouse gas (GHGs) emissions, most notably carbon dioxide. Ultimately, a significant cut in North American and global CO 2 emissions will require reductions from the electricity production sector, the single largest source of CO 2 worldwide. According to the International Energy Agency's (IEA) GHG Program, as of 2006 there were nearly 5,000 fossil fuel power plants worldwide generating nearly 11 billion tons of CO 2 , representing nearly 40% of total global anthropogenic CO 2 emissions. Of these emissions from the power generation sector, 61% were from coal fired plants. Although the long-term agenda advocated by governments is replacement of fossil fuel generation by renewables, growing energy demand, combined with the enormous dependence on fossil generation in the near to medium term dictates that this fossil base remain operational. Thus, to implement an effective GHG reduction system will require that the CO 2 emissions generated by this sector be mitigated, with carbon capture and storage (CCS) providing one of the best known solutions.
The CCS process removes CO 2 from a CO 2 containing flue gas, enables production of a highly concentrated CO 2 gas stream which is compressed and transported to a sequestration site. This site may be a depleted oil field or a saline aquifer. Sequestration in ocean and mineral carbonation are two alternate ways to sequester that are in the research phase. Captured CO 2 can also be used for enhanced oil recovery.
Current technologies for CO 2 capture are based primarily on the use of amines solutions which are circulated through two main distinct units: an absorption tower coupled to a desorption (or stripping) tower.
A very significant barrier to adoption of carbon capture technology on large scale is cost of capture. Conventional CO 2 capture with available technology, based primarily on the use of amine solvents, is an energy intensive process that involves heating the solvent to high temperature to strip the CO 2 (and regenerate the solvent) for underground sequestration. The conventional use of amines involves an associated capture cost of approximately US $60 per ton of CO 2 (IPCC), which represents approximately 80% of the total cost of carbon capture and sequestration (CCS), the remaining 20% being attributable to CO 2 compression, pipelining, storage and monitoring. This large cost for the capture portion has, to present, made large scale CCS unvariable; based on data from the IPCC, for instance, for a 700 megawatt (MW) pulverized coal power plant that produces 4 million metric tons of CO 2 per year, the capital cost of conventional CO 2 capture equipment on a retrofit basis would be nearly $800 million and the annual operating cost and plant energy penalty would be nearly $240 million. As such, there is a need to reduce the costs of the process and develop new and innovative approaches to the problem.
Due to the high costs associated with amine systems, some work has been done based on carbonate solutions. In such carbonate systems, at pH higher than 10, the predominant mechanism for CO 2 absorption is:
CO 2 +OH â
HCO 2 â
HCO 2 â +OH â
CO 2 2â +H 2 O
At pH lower than 8 the principal mechanism is:
CO 2 +H 2 O
H 2 CO 2
H 2 CO 2 +OH â
HCO 2 â +H 2 O
The main advantages of carbonate solutions over amine based solutions are higher capacity, higher stability to oxygen and high temperatures and lower energy requirements for desorption. However, such known carbonate solutions are characterized by a low rate of absorption of CO 2 which results in large capture equipment and corresponding capital costs.
Another feature of carbonate based solutions is that, as CO 2 reacts with the compound, the product may form precipitates. The presence of solids in the absorption solution enables the shift of the chemical reaction equilibria resulting in a constant CO 2 pressure when the loading of the solution increases.
Biocatalysts have also been used for CO 2 absorption purposes. More specifically, CO 2 transformation may be catalyzed by the enzyme carbonic anhydrase as follows:
CO
2
+
H
2
â¢
O
â¢
â·
â¢
carbonic
â¢
â¢
anhydrase
â¢
â¢
H
+
+
HCO
3
-
Under optimum conditions, the catalyzed turnover rate of this reaction may reach 1Ã10 6 molecules/second.
Carbonic anhydrase has been used as an absorption promoter in amine based solutions to increase the rate of CO 2 absorption. Indeed, particular focus has been made on amine solutions for use in conjunction with carbonic anhydrase in CO 2 capture processes. One reason why amine solutions have been favoured is that they have relatively low ionic strength, which is a property viewed as significant for carbonic anhydrase hydration activity, since high ionic strength could be detrimental to the stability and function of the protein.
There is a need for a technology that overcomes at least some of the disadvantages of the processes and techniques that are already known, and offers an improvement in the field of CO 2 capture.
SUMMARY OF THE INVENTION
The present invention responds to the above mentioned need by providing a formulation, a process and a system for CO 2 capture using carbonates and biocatalysts.
More particularly, the present invention provides a process for capturing CO 2 from a CO 2 -containing gas comprising: contacting the CO 2 -containing gas with an absorption mixture comprising water, biocatalysts and a carbonate compound to enable dissolution and transformation of CO 2 into bicarbonate and hydrogen ions, thereby producing a CO 2 -depleted gas and an ion-rich solution; and subjecting the ion-rich solution to desorption wherein the carbonate compound promotes release of the bicarbonate ions from the ion-rich solution producing a CO 2 gas stream and an ion-depleted solution.
In an optional aspect, the process includes removing the biocatalyst from the ion-rich solution prior to subjecting the ion-rich solution to the desorption.
In another optional aspect, the process includes removing the biocatalyst from the ion-rich solution after subjecting the ion-rich solution to the desorption.
In another optional aspect, the process includes recycling the ion-lean solution to form at least a part of the absorption mixture for re-contacting the CO 2 -containing gas.
In another optional aspect, the process includes adding an amount of biocatalyst into the ion-lean solution to convert the same into at least part of the absorption mixture for recycling to contact the CO 2 -containing gas.
In another optional aspect, the carbonate compound is selected and used in a sufficient amount in the absorption mixture such that the ion-rich solution contains bicarbonate precipitates.
In another optional aspect, the process includes removing the bicarbonate precipitates from the absorption mixture prior to subjecting the ion-rich solution to the desorption.
In another optional aspect, the bicarbonate precipitates remain in the ion-rich solution upon subjecting the ion-rich solution to the desorption, thereby converting into part of the CO 2 gas stream. The bicarbonate precipitates may be composed of bicarbonate species comprising potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate, or a mixture thereof.
In another optional aspect, the carbonate compound comprises potassium carbonate, sodium carbonate or ammonium carbonate, or a combination thereof.
In another optional aspect, the absorption mixture comprises an additional absorption compound. The additional absorption compound may be piperidine, piperazine and derivatives thereof which are substituted by at least one alkanol group, alkanolamines, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), amino acids, potassium or sodium salts of amino acids, glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, valine, 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-α-aminopropionic acid, N-(β-ethoxy)taurine, N-(β-aminoethyl)taurine, N-methyl alanine, 6-aminohexanoic acid, or a combination thereof.
In another optional aspect, the process includes contacting the absorption mixture with the CO 2 -containing gas is performed in an absorption stage comprising at least one reactor selected from a packed tower, a vertical or horizontal spray scrubber, a fluidized bed reactor or a series of reactors comprising the same.
In another optional aspect, a sufficient level of CO 2 loading is provided in the absorption stage to promote the precipitation of bicarbonate precipitates.
In another optional aspect, the carbonate compound and biocatalysts are provided in concentrations to achieve a maximum range of relative CO 2 transfer rate, with respect to a CO 2 transfer rate without biocatalyst. The carbonate compound is preferably provided in the absorption mixture in a concentration of at least about 0.1 M. The carbonate compound may also be provided in the absorption mixture in a concentration at or below saturation thereof.
In another optional aspect, the carbonate compound may comprise potassium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise ammonium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 10° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise sodium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the biocatalyst is carbonic anhydrase.
In another optional aspect, the biocatalyst is provided free in the water; dissolved in the water; immobilized on the surface of supports that are mixed in the water and are flowable therewith; entrapped or immobilized by or in porous supports that are mixed in the water and are flowable therewith; as cross-linked aggregates or crystals; or a combination thereof. The biocatalysts may preferably be supporte
PRIORITY CLAIM
This application is a continuation of and claims priority to U.S. patent Ser. No. 14/698,159 filed on Apr. 28, 2015, which is a continuation of U.S. patent application Ser. No. 14/106,102 (issued as U.S. Pat. No. 9,044,709) filed on Dec. 13, 2013, which is a continuation of U.S. patent application Ser. No. 13/388,871 filed on Feb. 3, 2012 (issued as U.S. Pat. No. 8,722,391), which is the national stage entry of PCT/CA2010/001214, filed on Aug. 4, 2010, which claims priority to U.S. Provisional Application No. 61/231,037, filed on Aug. 4, 2009, which is incorporated herein by reference for all purposes.
FIELD OF INVENTION
The present invention relates generally to CO 2 capture and more particularly to a formulation and process for CO 2 capture using carbonates and biocatalysts.
BACKGROUND OF THE INVENTION
Increasingly dire warnings of the dangers of climate change by the world's scientific community combined with greater public awareness and concern over the issue has prompted increased momentum towards global regulation aimed at reducing man-made greenhouse gas (GHGs) emissions, most notably carbon dioxide. Ultimately, a significant cut in North American and global CO 2 emissions will require reductions from the electricity production sector, the single largest source of CO 2 worldwide. According to the International Energy Agency's (IEA) GHG Program, as of 2006 there were nearly 5,000 fossil fuel power plants worldwide generating nearly 11 billion tons of CO 2 , representing nearly 40% of total global anthropogenic CO 2 emissions. Of these emissions from the power generation sector, 61% were from coal fired plants. Although the long-term agenda advocated by governments is replacement of fossil fuel generation by renewables, growing energy demand, combined with the enormous dependence on fossil generation in the near to medium term dictates that this fossil base remain operational. Thus, to implement an effective GHG reduction system will require that the CO 2 emissions generated by this sector be mitigated, with carbon capture and storage (CCS) providing one of the best known solutions.
The CCS process removes CO 2 from a CO 2 containing flue gas, enables production of a highly concentrated CO 2 gas stream which is compressed and transported to a sequestration site. This site may be a depleted oil field or a saline aquifer. Sequestration in ocean and mineral carbonation are two alternate ways to sequester that are in the research phase. Captured CO 2 can also be used for enhanced oil recovery.
Current technologies for CO 2 capture are based primarily on the use of amines solutions which are circulated through two main distinct units: an absorption tower coupled to a desorption (or stripping) tower.
A very significant barrier to adoption of carbon capture technology on large scale is cost of capture. Conventional CO 2 capture with available technology, based primarily on the use of amine solvents, is an energy intensive process that involves heating the solvent to high temperature to strip the CO 2 (and regenerate the solvent) for underground sequestration. The conventional use of amines involves an associated capture cost of approximately US $60 per ton of CO 2 (IPCC), which represents approximately 80% of the total cost of carbon capture and sequestration (CCS), the remaining 20% being attributable to CO 2 compression, pipelining, storage and monitoring. This large cost for the capture portion has, to present, made large scale CCS unvariable; based on data from the IPCC, for instance, for a 700 megawatt (MW) pulverized coal power plant that produces 4 million metric tons of CO 2 per year, the capital cost of conventional CO 2 capture equipment on a retrofit basis would be nearly $800 million and the annual operating cost and plant energy penalty would be nearly $240 million. As such, there is a need to reduce the costs of the process and develop new and innovative approaches to the problem.
Due to the high costs associated with amine systems, some work has been done based on carbonate solutions. In such carbonate systems, at pH higher than 10, the predominant mechanism for CO 2 absorption is:
CO 2 +OH â
HCO 2 â
HCO 2 â +OH â
CO 2 2â +H 2 O
At pH lower than 8 the principal mechanism is:
CO 2 +H 2 O
H 2 CO 2
H 2 CO 2 +OH â
HCO 2 â +H 2 O
The main advantages of carbonate solutions over amine based solutions are higher capacity, higher stability to oxygen and high temperatures and lower energy requirements for desorption. However, such known carbonate solutions are characterized by a low rate of absorption of CO 2 which results in large capture equipment and corresponding capital costs.
Another feature of carbonate based solutions is that, as CO 2 reacts with the compound, the product may form precipitates. The presence of solids in the absorption solution enables the shift of the chemical reaction equilibria resulting in a constant CO 2 pressure when the loading of the solution increases.
Biocatalysts have also been used for CO 2 absorption purposes. More specifically, CO 2 transformation may be catalyzed by the enzyme carbonic anhydrase as follows:
CO
2
+
H
2
â¢
O
â¢
â·
â¢
carbonic
â¢
â¢
anhydrase
â¢
â¢
H
+
+
HCO
3
-
Under optimum conditions, the catalyzed turnover rate of this reaction may reach 1Ã10 6 molecules/second.
Carbonic anhydrase has been used as an absorption promoter in amine based solutions to increase the rate of CO 2 absorption. Indeed, particular focus has been made on amine solutions for use in conjunction with carbonic anhydrase in CO 2 capture processes. One reason why amine solutions have been favoured is that they have relatively low ionic strength, which is a property viewed as significant for carbonic anhydrase hydration activity, since high ionic strength could be detrimental to the stability and function of the protein.
There is a need for a technology that overcomes at least some of the disadvantages of the processes and techniques that are already known, and offers an improvement in the field of CO 2 capture.
SUMMARY OF THE INVENTION
The present invention responds to the above mentioned need by providing a formulation, a process and a system for CO 2 capture using carbonates and biocatalysts.
More particularly, the present invention provides a process for capturing CO 2 from a CO 2 -containing gas comprising: contacting the CO 2 -containing gas with an absorption mixture comprising water, biocatalysts and a carbonate compound to enable dissolution and transformation of CO 2 into bicarbonate and hydrogen ions, thereby producing a CO 2 -depleted gas and an ion-rich solution; and subjecting the ion-rich solution to desorption wherein the carbonate compound promotes release of the bicarbonate ions from the ion-rich solution producing a CO 2 gas stream and an ion-depleted solution.
In an optional aspect, the process includes removing the biocatalyst from the ion-rich solution prior to subjecting the ion-rich solution to the desorption.
In another optional aspect, the process includes removing the biocatalyst from the ion-rich solution after subjecting the ion-rich solution to the desorption.
In another optional aspect, the process includes recycling the ion-lean solution to form at least a part of the absorption mixture for re-contacting the CO 2 -containing gas.
In another optional aspect, the process includes adding an amount of biocatalyst into the ion-lean solution to convert the same into at least part of the absorption mixture for recycling to contact the CO 2 -containing gas.
In another optional aspect, the carbonate compound is selected and used in a sufficient amount in the absorption mixture such that the ion-rich solution contains bicarbonate precipitates.
In another optional aspect, the process includes removing the bicarbonate precipitates from the absorption mixture prior to subjecting the ion-rich solution to the desorption.
In another optional aspect, the bicarbonate precipitates remain in the ion-rich solution upon subjecting the ion-rich solution to the desorption, thereby converting into part of the CO 2 gas stream. The bicarbonate precipitates may be composed of bicarbonate species comprising potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate, or a mixture thereof.
In another optional aspect, the carbonate compound comprises potassium carbonate, sodium carbonate or ammonium carbonate, or a combination thereof.
In another optional aspect, the absorption mixture comprises an additional absorption compound. The additional absorption compound may be piperidine, piperazine and derivatives thereof which are substituted by at least one alkanol group, alkanolamines, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), amino acids, potassium or sodium salts of amino acids, glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, valine, 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-α-aminopropionic acid, N-(β-ethoxy)taurine, N-(β-aminoethyl)taurine, N-methyl alanine, 6-aminohexanoic acid, or a combination thereof.
In another optional aspect, the process includes contacting the absorption mixture with the CO 2 -containing gas is performed in an absorption stage comprising at least one reactor selected from a packed tower, a vertical or horizontal spray scrubber, a fluidized bed reactor or a series of reactors comprising the same.
In another optional aspect, a sufficient level of CO 2 loading is provided in the absorption stage to promote the precipitation of bicarbonate precipitates.
In another optional aspect, the carbonate compound and biocatalysts are provided in concentrations to achieve a maximum range of relative CO 2 transfer rate, with respect to a CO 2 transfer rate without biocatalyst. The carbonate compound is preferably provided in the absorption mixture in a concentration of at least about 0.1 M. The carbonate compound may also be provided in the absorption mixture in a concentration at or below saturation thereof.
In another optional aspect, the carbonate compound may comprise potassium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise ammonium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 10° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise sodium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the biocatalyst is carbonic anhydrase.
In another optional aspect, the biocatalyst is provided free in the water; dissolved in the water; immobilized on the surface of supports that are mixed in the water and are flowable therewith; entrapped or immobilized by or in porous supports that are mixed in the water and are flowable therewith; as cross-linked aggregates or crystals; or a combination thereof. The biocatalysts may preferably be supported by micro-particles that are carried with the water.
The present invention also provides a formulation for capturing CO 2 from a CO 2 -containing gas comprising: a water solvent for allowing dissolution of CO 2 therein; biocatalyst for enhancing dissolution and transformation of CO 2 into bicarbonate and hydrogen ions into the water solvent; and a carbonate compound in the water solvent in a sufficient amount for promoting the release of the bicarbonate ions dissolved into the water solvent as gaseous CO 2 when subjected to desorption.
In one optional aspect, the carbonate compound comprises potassium carbonate, sodium carbonate or ammonium carbonate, or a combination thereof.
In another optional aspect, the carbonate compound is selected and used in a sufficient amount in the absorption mixture to promote precipitation of bicarbonate precipitates.
In another optional aspect, the bicarbonate precipitates are composed of bicarbonate species comprising potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate, or a mixture thereof.
In another optional aspect, the absorption mixture comprises an additional absorption compound. The additional absorption compound may comprise piperidine, piperazine and derivatives thereof which are substituted by at least one alkanol group, alkanolamines, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), amino acids, potassium or sodium salts of amino acids, glycine, taurine, N, cyclohexyl 1,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, alanine, diethylglycine, or dimethylglycine, or a combination thereof.
In another optional aspect, the carbonate compound is provided in the absorption mixture in a concentration of at least about 0.1 M. In another optional aspect, the carbonate compound is provided in the absorption mixture in a concentration at or below saturation thereof.
In another optional aspect, the carbonate compound may comprise potassium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise ammonium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 10° C. and about 70° C.
In another optional aspect, the carbonate compound may comprise sodium carbonate and be provided in the absorption mixture in a concentration up to the solubility limit at a temperature range between about 40° C. and about 70° C.
In another optional aspect, the biocatalyst is carbonic anhydrase or an analogue thereof.
In another optional aspect, the biocatalyst is provided free in the water; dissolved in the water; immobilized on the surface of supports that are mixed in the water and are flowable therewith; entrapped or immobilized by or in porous supports that are mixed in the water and are flowable therewith; as cross-linked aggregates or crystals; or a combination thereof. The biocatalysts may preferably be supported by micro-particles that are carried with the water.
The present invention also provides a system for capturing CO 2 from a CO 2 -containing gas. The system comprises an absorption unit comprising a gas inlet for the CO 2 -containing gas, a liquid inlet for providing an absorption mixture comprising a water solvent for allowing dissolution of CO 2 therein, biocatalysts for enhancing dissolution and transformation of CO 2 into bicarbonate and hydrogen ions into the water solvent, and a carbonate compound in the water solvent in a sufficient amount for promoting the release of the bicarbonate ions dissolved into the water solvent as gaseous CO 2 when subjected to desorption. The system comprises a reaction chamber for receiving the absorption mixture and the CO 2 -containing gas, in which the dissolution and transformation of CO 2 into bicarbonate and hydrogen ions occurs. The system comprises a gas outlet for expelling the CO 2 -depleted gas and a liquid outlet for expelling the ion-rich mixture. The system comprises a regeneration unit for receiving the ion-rich solution and allowing desorption by releasing the bicarbonate ions from the ion-rich solution to produce an ion-depleted solution. The ion-depleted solution may be recycled back into the absorption unit. The system may also have optional features or aspects as described above and hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a process diagram of an embodiment of the present invention, wherein biocatalytic particles or enzymes flow in the absorption solution.
FIG. 2 is a process diagram of another embodiment of the present invention, wherein an absorption unit is coupled to a desorption unit and biocatalytic particles flow in the absorption solution.
FIG. 3 is a graph of relative CO 2 transfer rate for carbonic anhydrase concentration ranging from 0 to 1000 mg/L in a 1.45 M K 2 CO 3 solution with CO 2 loading ranging from 0 to 0.2 mol/mol.
FIG. 4 is a graph of relative CO 2 transfer rate for 500 mg/L Human Carbonic Anhydrase Type-II (HCAII) in K 2 CO 3 solutions at concentrations of 0.5, 1 and 1.45 M.
FIG. 5 is a graph of relative CO 2 transfer rate for 500 mg/L HCAII in Na 2 CO 3 solutions at concentrations of 0.1, 0.25 and 0.5 M.
FIG. 6 is a graph of relative CO 2 transfer rate in a 0.5 M Na 2 CO 3 solution at loadings of 0, 0.2 and 0.5 mol CO 2 /mol Na 2 CO 3 with enzyme concentrations of 0.1 and 1 g/L.
FIG. 7 is a graph of CO 2 transfer rate in K 2 CO 3 solutions in the presence of 0.5 g/L of carbonic anhydrase at a temperature of 20° C.
FIG. 8 is a graph showing evolution of residual activity of enzyme micro-particles exposed to MDEA 2M at 40° C., illustrating stability effect.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
FIGS. 1 and 2 respectively show two different embodiments of the process and system of the present invention. It should also be understood that embodiments of the formulation of the present invention may be used in conjunction with the process and system.
In one aspect of the present invention, the formulation comprises water for allowing dissolution of CO 2 , biocatalyst such as carbonic anhydrase for catalyzing the transformation of CO 2 into bicarbonate and hydrogen ions into the water, and carbonate compounds. These components may be provided as a pre-mixed solution or for mixing on site during the CO 2 capture operation. Carbonate compounds promote the release of the bicarbonate ions from the water solvent during desorption. Thus, the absorption step of the CO 2 capture process is improved due to the activation ability of the biocatalysts and the desorption step is rendered more efficient by virtue of the predominance of carbonate compounds. This improvement aids in enhancing the overall CO 2 capture process.
In one embodiment of the invention, the carbonate compound is of the type and is added in sufficient quantities to promote precipitation of a bicarbonate species during absorption. The process parameters may be controlled to further promote such precipitation. The carbonates may be chosen such that the corresponding precipitates have characteristics making them easy to handle with the overall process, by allowing them to be suspended in the reaction solution, pumped, sedimented, etc., as the case may be. The precipitates may be part of the ion-rich solution that is sent for desorption or treated separately for conversion into CO 2 gas. More particularly, the precipitates may be bicarbonate species, such as KHCO 3 , NaHCO 3 or NH 4 HCO 3 , and the carbonate compounds may be chosen to allow precipitation of such species.
In another embodiment of the invention, the carbonate compounds also enable lower energy process parameters for desorption. In one embodiment, when the enzymes are provided on or in particles flowing with the solution, the particles may be removed from the ion-rich solution before the ion-rich solution is fed into the desorption unit. Due to their nature and method of immobilisation on the particles, the biocatalysts may be more or less vulnerable to high temperatures. Thus, when desorption is operated at temperatures that could denature the given biocatalysts, the particles are preferably removed before desorption and recycled back into the absorption unit. The carbonates remain in the solution and enhance desorption. It may be preferred that the particles are provided such that they may be easily separated from the bicarbonate precipitate, if need be. In another embodiment, when the biocatalysts are allowed to be present during desorption, the desorption is preferably operated at pressures and temperatures that are tolerable for the given biocatalyst so that the biocatalysts retain their activity, increase desorption rate by catalyzing bicarbonate ion dehydration and can be recycled back into the absorption unit. Desorption may be managed in such cases by reducing the pressure rather than raising the temperature.
In one optional aspect, the biocatalysts in the absorption mixture may be enzymes and more particularly carbonic anhydrase.
In one other embodiment of the invention, the biocatalysts include carbonic anhydrase to enhance performance of absorption solutions for CO 2 capture. The enzyme may be provided directly as part of a formulation or may be provided in a reactor to react with incoming solutions and gases. For instance, the enzyme may be fixed to a solid non-porous packing material, on or in a porous packing material, on or in particles flowing with the absorption solution within a packed tower or another type of reactor. The carbonic anhydrase may be in a free or soluble state in the formulation or immobilised on particles within the formulation. It should be noted that enzyme used in a free state may be in a pure form or may be in a mixture including impurities or additives such as other proteins, salts and other molecules coming from the enzyme production process. Immobilized enzyme free flowing in the absorption solution could be entrapped inside or fixed to a porous coating material that is provided around a support that is porous or non-porous. The enzymes may be immobilised directly onto the surface of a support (porous or non porous) or may be present as âcross linked enzymes aggregatesâ (CLEA) or âcross linked enzymes crystalsâ (CLEC). CLEA comprise precipitated enzyme molecules forming aggregates that are then crosslinked using chemical agents. The CLEA may or may not have a âsupportâ or âcoreâ made of another material which may or may not be magnetic. CLEC comprise enzyme crystals and cross linking agent and may also be associated with a âsupportâ or âcoreâ made of another material. When a support is used, it may be made of polymer, ceramic, metal(s), silica, solgel, chitosan, cellulose, magnetic particles and/or other materials known in the art to be suitable for immobilization or enzyme support. When the enzymes are immobilised or provided on particles, such as micro-particles, the particles are preferably sized and provided in a particle concentration such that they are pumpable with the absorption solution. Biocatalysts may also be provided both fixed within the reactor (on a packing material, for example) and flowing with the formulation (as free enzymes, on particles and/or as CLEA or CLEC), and may be the same or different biocatalysts. One of the ways carbonic anhydrase enhances performance of carbonate solutions is by reacting with dissolved CO 2 and maintaining a maximum CO 2 concentration gradient between gas and liquid phases and then maximizing CO 2 transfer rate from the gas phase to the solution. The carbonate compounds may also enable the precipitation of precipitates to further improve the CO 2 concentration gradient between gas and liquid phases and thus further increasing CO 2 transfer rate.
The biocatalysts may be provided using means depending on the concentration and type of carbonate compound, the process operating parameters, and other factors. For instance, when a high concentration of carbonate compounds is provided, the enzymes may be immobilised on a support to reduce the possibility of deactivation by the carbonates. In some embodiments, the biocatalysts may be advantageously immobilised in a micro-porous structure (which may be a support or a material coating a support) allowing access of CO 2 while protecting it against high concentrations of carbonate compounds.
In one optional aspect of the present invention, the carbonate compounds used in the formulation may include potassium carbonate, sodium carbonate, ammonium carbonate, promoted potassium carbonate solutions and promoted sodium carbonate solutions or promoted ammonium carbonate or mixtures thereof.
The following are some advantages, improvements and/or features of some embodiments of the present invention:
The absorption solution is given an increased CO 2 absorption rate. Introducing biocatalysts into carbonate solutions increases the absorption rate of carbonates, coupled with the regeneration efficiencies, to levels which will be advantageous over existing amine based processes. The enhanced increase of CO 2 absorption and relative transfer rates and decrease of energy required for desorption provide an advantageous overall CO 2 capture process. This is a major step to bringing such technologies to their industrial application in post combustion CO 2 capture. Without the biocatalysts, carbonate absorption solutions would have very limited viability as alternative CO 2 capture processes, losing benefits of stability, cost, low volatility, etc.
Biocatalyst-enhanced carbonate-based CO 2 capture systems offer significant advantages over conventional processes including lower energy consumption, higher operating stability, lower consumables costs and reduced environmental footprint. As a predominance of bicarbonates rather than carbamates is formed upon CO 2 absorption into the carbonate solution, the subsequent production of pure CO 2 during the desorption phase requires less energy due to the weak affiliation of CO 2 with the solution. As such, lower temperature desorption may be achieved, resulting in the potential for using less expensive, lower grade steam from the power plant operation rather than costly high-grade steam typical of amine-based processes. The potential lower temperature in the desorption stage may also give rise to another advantage in that biocatalysts may also be used in the desorption stage with lower risk of denaturing. In a carbonate system without biocatalysts, slow absorption kinetics which would demand large absorption vessels and correspondingly high capital costs, negating the low energy of desorption. Hence, the biocatalyst provides an important enabling feature by accelerating the absorption rate to allow for the use of the low-energy carbonate solution while reducing the size of the absorption equipment. In addition, conventional amine-based CO 2 capture systems can suffer from a lack of stability of the amine solution which can be susceptible to oxygen and contaminants in the power plant flue gas, such as sulphur dioxide (SO 2 ). This results in the situation where either inhibitors need to be added or additional pre-treatment of the flue gas is required, increasing the cost and complexity of the system. As a result of higher stability of carbonates, solution makeup may be required on a less frequent basis, further improving the economics of the process in this case. Additionally, carbonate solutions, namely potassium and sodium carbonate, are less costly to procure than amine solvents. Carbonate solutions possess relatively favourable environmental properties. Potassium and sodium carbonate solutions are relatively benign when compared to amine solutions, significantly reducing the potential for toxic events and limiting any water and waste treatment related issues. Overall, the above advantages of carbonate solvents can provide for an attractive operating scenario, providing that absorption can be enhanced to meet the requirements for an economic rate of capture, which the biocatalysts enable.
In addition, the combination of the concentration of carbonate solution with the concentration of biocatalysts relative to a specific CO 2 loading is a further feature of some optional aspects of the process, which can enable reaching an optimum range of relative CO 2 transfer rate during absorption. The optimum range can be defined in a number of ways and should not be limited to a specific point. The optimum range may be defined as a range containing the maximum value for CO 2 relative transfer rate with a certain standard deviation, as a range of values around the actual maximum at which the process is economically viable, or defined in other ways. Illustrations of maximum or optimum ranges are illustrated in various examples hereinbelow.
One embodiment of the process and system is shown in FIG. 1 and will be described in further detail hereafter. First, the biocatalysts, which may be provided on or in particles, are added to the lean absorption solution in a mixing chamber (E-4). The lean absorption solution refers to the absorption solution characterized by a low concentration of the species to be absorbed. This solution is either fresh solution or comes from the mineral carbonation process or the CO 2 desorption process (10). The absorption solution with biocatalysts (11) is then fed to the top of a packed column (E-1) with a pump (E-7). The packing material (9) may be made of conventional material like polymers, metal and ceramic. The geometry of the packing may be chosen from what is commercially available. It is also possible to chose or arrange the packing to promote certain deflections and collisions with the micro-particles, or to avoid accumulation of the micro-particles within the reactor. For instance, the packing preferably has limited upward facing concavities to avoid the accumulation of micro-particles therein. Also preferably, the micro-particles and packing are chosen so that the micro-particles can flow through the reactor without clogging. In some alternative embodiments, the biocatalysts can be provided on the packing rather than in the absorption mixture. Counter-currently, a CO 2 containing gas phase (12) is fed to the packed column (E-1) and flows on, through, and/or around the packing (9) from the bottom to the top of the column. The absorption mixture with biocatalysts that may be supported by particles and carbonate solution flows on, through, and/or around the packing material (9) from the top of the column to the bottom. As the absorption mixture and biocatalytic micro-particles progress on, through, and/or around the packing, the absorption solution becomes richer in the compound that is being absorbed, which is CO 2 . Biocatalysts, present near the gas-liquid interface, enhance CO 2 absorption by immediately reacting with CO 2 to produce bicarbonate ions and protons and thus maximizing the CO 2 concentration gradient across the interface. At the exit of the column, the rich absorption mixture containing the biocatalysts and bicarbonates ions (13) are pumped (E-5) to a particle separation unit (E-3). Rich absorption solution refers to the absorption mixture characterized by a concentration of absorbed compound which is higher than that of the lean solution. The separation unit may comprise a filtration unit (such as a tangential filtration unit), a centrifuge, a cyclone, a sedimentation tank or a magnetic separator and any other units or equipments known for particle or solid separation. The separation unit also enables a certain quantity of solution to be retained with the biocatalytic micro-particles so they do not dry out which can denature the biocatalysts. In one optional aspect, the quantity of retained solution enables the biocatalytic micro-particles to be pumped to a storage unit or directly back to a mixing chamber (E-4) for addition into the absorption unit. In another optional aspect, the biocatalysts with retained solution may be gravity fed into the mixing chamber (E-4), which may be enabled by performing separation above the mixing unit, for example. The separation may be conducted in continuous or in batch mode, and may be managed to ensure the proper amount of solution is retained to ensure enzyme activity. It may also be preferred that the biocatalytic micro-particles are provided such that they may be easily separated from any solid precipitates (e.g. bicarbonate precipitates) that may be entrained in the ion-rich solution, if need be. The absorption mixture without biocatalytic micro-particles (15) is then pumped (E-9) to another process stage such as a regeneration stage, which may include CO 2 desorption or mineral carbonation (10). Biocatalytic micro-particles (16) are mixed with the CO 2 lean absorption solution. This suspension is then fed once again to the absorption column (E-1).
In another embodiment, the absorption unit is coupled to a desorption unit as shown in further detail in FIG. 2 . In this embodiment, the absorption solution rich in CO 2 without biocatalytic micro-particles (15) is pumped (E-9) through a heat exchanger (E-10) where it is heated and then sent on to the desorption column (E-11). In the desorption unit, the solution is further heated in order that the CO 2 is released from the solution in a gaseous state. Because of relatively high temperature used during desorption, water also vaporizes. Part of the absorption solution (18) is directed toward a reboiler (E-12) where it is heated to a temperature enabling CO 2 desorption. Gaseous CO 2 together with water vapour are cooled down, water condenses and is fed back to the desorption unit (19). Dry gaseous CO 2 (20) is then directed toward a compression and transportation process for further processing. The liquid phase, containing less CO 2 , and referred to as the lean absorption solution (17) is then pumped (E-14) to the heat exchanger (E-10) to be cooled down and fed to the mixing chamber (E-4). The temperature of the lean absorption solution (17) should be low enough not to denature the enzyme if present.
In another optional aspect of the present invention, if a robust enzyme (biocatalysts robust to desorption conditions) is available, the biocatalysts might also help in improving the rate of CO 2 dehydration and thus increasing CO 2 desorption rate resulting in smaller desorption equipment. In such a process configuration the biocatalysts may have an impact in the absorption unit by increasing the CO 2 absorption rate but also in the desorption unit since an enzyme such as carbonic anhydrase can increase the rate of bicarbonate ion transformation into CO 2 (which is one of the reactions that would take place in the desorption unit). In this configuration, the removal unit (E-3) would be required to remove deactivated biocatalysts and unit E-4 to add fresh biocatalysts. However. it may be advantageous to have a separation unit such as a filter between (E-11) and (E-12) to avoid flow of biocatalysts through the reboiler and their contact with very high temperatures (depending on the thermoresistance of the enzymes).
The mixing chamber (E-4) preferably comprises an inlet for receiving recycled biocatalysts from the separation unit (E-3) and also an inlet/outlet for both removing a fraction of deactivated biocatalysts and replacing them with new fresh biocatalyst, thereby refurbishing the overall batch of biocatalysts in the system. In some embodiments, biocatalysts are filtered, centrifuged, cycloned, sedimented or separated magnetically in a first separation unit (according to their above-mentioned support system) and other small particles such as bicarbonate precipitates can be separated in a preceding or subsequent separation unit.
In one embodiment, biocatalysts are used in conjunction with additional absorption compounds in the absorption mixture. The absorption compounds may be primary, secondary and/or tertiary amines (including alkanolamines); and/or primary, secondary and/or tertiary amino acids. The absorption compound may more particularly include amines (e.g. piperidine, piperazine and derivatives thereof which are substituted by at least one alkanol group), alkanolamines (e.g. monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA) and triethanolamine), dialkylether of polyalkylene glycols (e.g. dialkylether or dimethylether of polyethylene glycol); amino acids which may include potassium or sodium salts of amino acids, glycine, taurine, N- cyclohexyl 1,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, alanine, diethylglycine, dimethylglycine, methionine, alanine, proline, and/or sarcosine; and/or mixtures thereof. Absorption compounds are added to the solution to aid in the CO 2 absorption and to combine with the catalytic effects of the carbonic anhydrase. Due to the structure or high concentration of some absorption compounds, the activity or longevity of the carbonic anhydrase can be threatened. For instance, free enzymes may be more vulnerable to denaturing caused by an absorption compound with high ionic strength. Immobilising the carbonic anhydrase can mitigate the negative effects of such absorption compounds. By providing enzymes immobilised on a support material, such as for example on micro-particles, the process can yield high CO 2 transfer rates in the presence of absorption compounds while mitigating the negative effects such compounds could otherwise have on free enzymes.
EXAMPLES
The following examples present different ways to activate absorption solutions with carbonic anhydrase and generally elaborate on the embodiments of the present invention.
Example 1
An experiment was conducted in an absorption packed column. The absorption solution is an aqueous solution of potassium carbonate (K 2 CO 3 ) 20% (w/w) (equivalent to 1.45 M). This absorption solution is contacted counter-currently with a gas phase with a CO 2 concentration of 130,000 ppm. Liquid flow rate was 0.6 g/min and gas flow rate was 60 g/min corresponding to L/G of 10 (g/g). Gas and absorption solution were at room temperature. Operating pressure of the absorber was set at 1.4 psig. The column has a 7.5 cm diameter and a 50 cm height. Packing material is polymeric Raschig rings 0.25 inch. Three tests were performed: the first with no biocatalyst, the second with carbonic anhydrase biocatalyst immobilized to packing support and the third using carbonic anhydrase free in solution at a concentration of 0.5 g per liter of solution.
The results obtained showed that CO 2 transfer rate or CO 2 removal rate increased from 3 to 14 mmol CO 2 /min with carbonic anhydrase immobilized onto the surface of Raschig rings. Using free enzymes i.e carbonic anhydrase free flowing in the absorption solution, CO 2 transfer rate increased up to 37 mmol/min. These results indicate that under tested conditions, CO 2 transfer rate can be increased by more than 5 fold using free or immobilized enzymes in the same equipment.
Example 2
An experiment was conducted in an absorption packed column. The absorption solution is an aqueous solution of sodium carbonate (Na 2 CO 3 ) 0.5M. This absorption solution is contacted counter-currently with a gas phase with a CO 2 concentration of 130,000 ppm. Liquid flow rate was 0.65 g/min and gas flow rate was 65 g/min corresponding to L/G of 10 (g/g). Gas and absorption solution were at room temperature. Operating pressure of the absorber was set at 1.4 psig. The column has a 7.5 cm diameter and a 50 cm height. Packing material is polymeric Raschig rings 0.25 inch. Three tests were performed: the first with no biocatalyst, the second with carbonic anhydrase immobilized to packing support and the third using carbonic anhydrase free in solution at a concentration of 0.5 g per liter of solution.
The results obtained showed that CO 2 transfer rate or CO 2 removal rate increased from 5 to 18 mmol CO 2 /min with carbonic anhydrase immobilized onto the surface of Raschig rings. In the presence of free enzyme i.e. carbonic anhydrase free flowing in the solution, the transfer rate increased to 38 mmol/min. These results clearly demonstrate the positive impact of adding the enzyme in a packed column.
Example 3
An experiment was conducted in an absorption packed column. The absorption solution is an aqueous solution of ammonium carbonate (NH 4 ) 2 CO 3 /(NH 4 )OH 8M (ammonium). This absorption solution is contacted counter-currently with a gas phase with a CO 2 concentration of 130 000 ppm. Liquid flow rate was 0.25 g/min and gas flow rate was 63 g/min corresponding to L/G of 4 (g/g). Gas and absorption solution were at room temperature. Operating pressure of the absorber was set at 1.4 psig. The column has a 7.5 cm diameter and a 50 cm height. Packing material is polymeric Raschig rings 0.25 inch. Two tests were performed: the first with no biocatalyst, and the second using carbonic anhydrase immobilized to packing.
The results obtained showed that CO 2 transfer rate or CO 2 removal rate increased from 190 to 216 mmol CO 2 /min with carbonic anhydrase immobilized onto the surface of Raschig rings. In this case, the absorption performance is increased by 14% under tested operating conditions.
Example 4
To demonstrate the impact of free carbonic anhydrase, tests were conducted in a stirred cell at enzyme concentrations of 250, 500 and 1000 mg/L in a 1.45 M K 2 CO 3 solution at a temperature of 25° C. Initial CO 2 loading of the solution was adjusted to 0, 0.1 and 0.2 mol CO 2 /K 2 CO 3 . Enzyme used is a variant of human carbonic anhydrase type-II, designated as 5à (this enzyme contains five genetic mutations as compared to the original enzyme). CO 2 absorption tests are performed in a stirred cell, a simple device that can be used to evaluate CO 2 absorption rates under different conditions. The stirred cell contains the absorption solution (and the enzyme when required). A known pressure of pure CO 2 is applied to the solution, the pressure corresponds to the CO 2 partial pressure that can be found in an industrial post-combustion flue gas. In these tests, initial CO 2 pressure is 200 mbar. Then the pressure decrease is monitored and used to calculate CO 2 transfer rate in the absorption. Tests were conducted with and without enzyme to enable determination of the enzyme impact. Results are expressed as a ratio of the CO 2 transfer rate with enzyme to the CO 2 transfer rate in the absence of the enzyme (see FIG. 3 ). Results clearly indicate that adding enzyme to the 1.45 M K 2 CO solution brings an important benefit for all tested conditions. Impact is more important when the enzyme concentration is higher. Results also indicate that the CO 2 loading of the solution has an impact on the improvement brought by the enzyme. The impact obtained in stirred cells is similar to that obtained in a packed column (see Example 2). It is assumed, as for other system reported in literature, that we could predict from stirred cell results the impact of the enzyme in a packed column.
Example 5
Tests were conducted in a hydration cell at an enzyme concentration of 500 mg/L in K 2 CO 3 solutions with concentrations of 0.5, 1 and 1.45 M at a temperature of 20° C. Enzyme used is human carbonic anhydrase type II. Initial CO 2 loading is 0 mol CO 2 /mol K 2 CO 3 . The hydration cell and testing methods are different from the one described in Example 4 in that a continuous flow of pure CO 2 is flushed in this cell at a pressure of 1 atma, at the surface of the liquid phase (with or without enzyme) and pH change of the solution is monitored. Changes in pH are correlated to changes in inorganic carbon concentration which are used to calculate CO 2 transfer rates. Results are expressed as a ratio of CO 2 transfer rate with enzyme to CO 2 transfer rate in the absence of the enzyme (see FIG. 4 ). It is important to note, that as such, as the hydration cell is used for more rapid, Indicative testing of enzyme catalytic activity, the corresponding results are not viewed to be as precise as those obtained in Example 4. This fact generally explains any variation in observed results between the two testing systems under similar conditions. Results clearly indicate that enzyme brings an important benefit for all tested K 2 CO 3 solutions.
Example 6
Tests were conducted in a hydration cell at an enzyme concentration of 500 mg/L in K 2 CO 3 solutions at concentrations of 0.5 and 1.45 M at a temperature of 40° C. (method is as described in Example 5). Enzyme used is the variant 5Ã. Initial CO 2 loading is 0 mol CO 2 /mol K 2 CO 3 . Results indicate that under these experimental conditions enzyme brings a benefit for the 1.45 K 2 CO 3 solution only (Table 1), indicating that temperature may have an influence on the impact of the enzyme on CO 2 absorption rate.
TABLE 1
Relative CO 2 transfer rates in K 2 CO 3 solutions at a temperature
of 40° C. with an enzyme concentration of 500 mg/L.
K 2 CO 3 concentration (M)
Relative Transfer rate
<tr class="des
CLAIMS
Claims ( 12 )
The invention claimed is:
1. An enzymatic process for CO2 capture, comprising:
supplying a CO2 containing gas into a lower portion of an absorption unit;
supplying an absorption solution comprising sodium or potassium carbonate into an upper portion of the absorption unit;
counter-currently and directly contacting the CO2 containing gas and the absorption solution in the absorption unit in the presence of carbonic anhydrase while operating at an absorption pressure to enable dissolution and biocatalytic transformation of CO2 into bicarbonate and hydrogen ions, thereby producing a CO2 depleted gas and an ion-loaded solution;
removing the ion-loaded solution from the lower portion of the absorption unit;
supplying the ion-loaded solution to an upper portion of a desorption unit;
desorbing CO2 from the ion-loaded solution in the desorption unit operated at a desorption pressure that is lower than the absorption pressure, to produce desorbed CO2 gas, water vapor, and a regenerated absorption solution;
removing the regenerated absorption solution from a lower portion of the desorption unit;
removing a gas stream comprising the desorbed CO2 gas and the water vapor from the desorption unit; and
recycling at least part of the regenerated absorption solution back as at least part of the absorption solution fed into the absorption unit; and
wherein the carbonic anhydrase is provided to be flowable with the absorption solution and circulates with the ion-loaded solution and the regenerated solution through the absorption unit and the desorption unit.
2. The process of claim 1 , further comprising:
cooling the gas stream to produce condensed water and dry gaseous CO2; and
feeding the condensed water back into the desorption unit.
3. The process of claim 2 , further comprising supplying the dry gaseous CO2 to a compression process.
4. The process of claim 1 , wherein the regenerated absorption solution is pumped back as part of the absorption solution.
5. The process of claim 1 , wherein the absorption solution comprises potassium carbonate.
6. The process of claim 1 , wherein the carbonic anhydrase is dissolved in the absorption solution.
7. The process of claim 1 , wherein the carbonic anhydrase is supported by micro-particles that are carried with the absorption solution.
8. The process of claim 1 , further comprising:
cooling the gas stream to produce condensed water and dry gaseous CO2.
9. The process of claim 1 , wherein the desorption unit comprises a reboiler and a portion of the regenerated absorption solution is directed toward the reboiler for heating to a temperature enabling CO2 desorption.
10. The process of claim 9 , further comprising separating the carbonic anhydrase from the portion of the regenerated absorption solution fed into the reboiler.
11. The process of claim 10 , wherein the separating is performed using a filter.
12. The process of claim 1 , wherein the absorption solution comprises potassium carbonate that is provided in the absorption solution in a concentration of at least about 0.1M.
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