The present invention generally relates to the field of enzyme enhanced CO2 capture, sequestration and separation from mixed gases, and more particularly to carbonic anhydrase enhanced CO2 removal and desorption processes.
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 CO2 emissions will require reductions from the electricity production sector, the single largest source of CO2 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 CO2, representing nearly 40% of total global anthropogenic CO2 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 CO2 emissions generated by this sector be mitigated, with carbon capture and storage (CCS) providing one of the best known solutions.
The CCS process removes CO2 from a CO2-containing flue gas, and enables production of a highly concentrated CO2 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 CO2 can also be used for enhanced oil recovery, injection into greenhouses, chemical reactions and production, and other useful applications.
Current technologies for CO2 capture are based primarily on the use of 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 CO2 capture with available technology, based primarily on the use of monethanolamine (MEA), is an energy intensive process that involves heating the solvent to high temperature to strip the CO2 (and regenerate the solvent) for underground sequestration. The use of MEA involves an associated capture cost of approximately US $60 per ton of CO2 (IPCC), which represents approximately 80% of the total cost of carbon capture and sequestration (CCS), the remaining 20% being attributable to CO2 compression, pipelining, storage and monitoring. This large cost for the capture portion has, to present, made large scale CCS unviable; based on data from the IPCC, for instance, for a 700 megawatt (MW) pulverized coal power plant that produces 4 million metric tons of CO2 per year, the capital cost of MEA based CO2 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.
In order to help address the high costs associated with traditional CCS systems, biocatalysts have been used for CO2 absorption applications. For example, CO2 transformation may be catalyzed by the enzyme carbonic anhydrase as follows:
While biocatalysts are known and have been used for absorption of CO2 into a solution, catalyzed desorption methods, which can provide the potential for additional efficiency and cost improvements, have not been greatly studied.
There is a need for a technology that overcomes some of these problems and challenges of known CO2 capture technologies.
The present invention responds to the above need by providing a carbonic anhydrase enhanced CO2 desorption process.
Accordingly, in one aspect, there is provided an enzyme catalyzed desorption process for releasing CO2 gas from an ion-rich solution containing bicarbonate ions, the process comprising: providing carbonic anhydrase in the ion-rich solution such that in a desorption unit the carbonic anhydrase is allowed to flow with the ion-rich solution while promoting conversion of the bicarbonate ions into CO2 gas and generating an ion-depleted solution; and releasing the CO2 gas and the ion-depleted solution from the desorption unit.
In one optional aspect of the process, a concentration of carbonic anhydrase in the ion-rich solution is controlled by adding an amount of the carbonic anhydrase prior to feeding the ion-rich solution into the desorption unit.
In another optional aspect of the process, the conversion of the bicarbonate ions into CO2 gas is performed in order to promote CO2 bubble formation within the ion-rich solution.
In another optional aspect of the process, the desorption unit comprises a plurality of desorption units arranged in series or in parallel.
In another optional aspect of the process, the process also includes controlling an initial concentration of the bicarbonate ions in the ion-rich solution below a predetermined denaturation threshold to avoid denaturing the carbonic anhydrase in the desorption unit.
In another optional aspect of the process, the process also includes controlling the temperature of the ion-rich solution below a predetermined enzymatic denaturing temperature threshold to avoid denaturing the carbonic anhydrase in the desorption unit.
In another optional aspect of the process, the process also includes managing an initial concentration of the bicarbonate ions in the ion-rich solution and temperature of the ion-rich solution, in the desorption unit, to provide rheology that promotes CO2 bubble formation and release from the ion-rich solution.
In another optional aspect of the process, the process also includes the ion-rich solution in the form of a slurry and comprises dispersed precipitates.
In another optional aspect of the process, the process also includes promoting the dissolution of the dispersed precipitates during enzymatic conversion of the bicarbonate ions into CO2 gas, thereby forming additional bicarbonate ions for enzymatic conversion into CO2 gas.
In another optional aspect of the process, the process also includes managing the concentration of the carbonic anhydrase in the desorption unit in accordance with the concentration of bicarbonate ions and the temperature of the ion-rich solution, in order to maximize the desorption rate.
In another optional aspect of the process, the carbonic anhydrase is provided free in solution, immobilized on the surface of solid or porous particles, immobilized within porous particles, entrapped by particles, in the form of cross-linked enzyme aggregates (CLEAs), or in the form of cross-linked enzyme crystals (CLECs), magnetic particles or a combination thereof.
In another optional aspect of the process, the carbonic anhydrase is provided associated with particles, the particles having a size and a density suitable to be mixable within the ion-rich solution by the CO2 bubble formation.
In another optional aspect of the process, the ion-rich solution further comprises at least one compound selected from the following: primary, secondary and/or tertiary amines; primary, secondary and/or tertiary alkanolamines; primary, secondary and/or tertiary amino acids; and/or carbonates;
In another optional aspect of the process, the ion-rich solution further comprises at least one compound selected from the following: piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, 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 and potassium or sodium salts of the amino acids, or a mixture thereof.
In another optional aspect of the process, the absorption solution comprises a carbonate, such as potassium carbonate, sodium carbonate, ammonium carbonate, or mixtures thereof.
In another optional aspect of the process, the absorption solution consists in a mixture of two or more compounds selected from carbonates, amines, alkanolamines and/or amino acids. For instance, the absorption solution may be a combined MDEA-piperazine solution, MDEA-MEA solution, or piperazine-potassium carbonate solution. In one optional aspect, the absorption solution comprises at least one slow absorption compound such as MDEA and at least one fast absorption compound such as MEA. In one optional aspect, the slow-fast compound combination solution is prepared such that the total and relative amounts of the compounds are sufficient so as to improve both the absorption and desorption stages compared to the stage when only one of the compounds is employed. For instance, the use of the slow absorption compound in the mixture improves the desorption efficiency compared to a solution with only fast absorption compound, while the use of the fast absorption compound in the mixture improves the absorption rate in the absorption stage.
The present invention also provides a CO2 capture process comprising: contacting a CO2-containing effluent gas with an absorption solution in an absorption unit, to convert CO2 into bicarbonate and hydrogen ions in the absorption solution, thereby producing a CO2-depleted gas and an ion-rich solution; feeding the ion-rich solution to a desorption unit wherein carbonic anhydrase is present within the ion-rich solution, thereby allowing the carbonic anhydrase to flow with the ion-rich solution while promoting the conversion of the bicarbonate ions into CO2 gas and generating an ion-depleted solution; and releasing the CO2 gas and the ion-depleted solution from the desorption unit; and preferably, recycling the ion-depleted solution to make up at least part of the absorption solution.
In one optional aspect of the process, the absorption solution comprises a chemical compound for increasing the CO2 absorption capacity and/or transfer rate.
In another optional aspect of the process, the chemical compound is a fast absorption accelerator. The chemical compound may be at least one of a primary alkanolamine and a secondary alkanolamine. The chemical compounds may also be amino acids.
In another optional aspect of the process, the chemical compound is a tertiary alkanolamine.
The present invention also provides a method of decreasing the CO2 desorption temperature in a desorption unit, the desorption unit receiving an ion-rich solution containing bicarbonate ions and the ion-rich solution being heated to favor desorption of CO2 therefrom, the method comprising providing carbonic anhydrase within the ion-rich solution and allowing the carbonic anhydrase to flow with the ion-rich solution while catalyzing the conversion of the bicarbonate ions into CO2 gas and generating an ion-depleted solution. Without enzyme, lowering desorption temperatures would result in lower CO2 desorption rates and decreased efficiency. However, a same CO2 desorption rate could be maintained at a lower temperature since the enzyme catalyst increases the bicarbonate dehydration rate in such a way that it compensates for the decrease in the solution reaction rate at this lower temperature.
The present invention also provides a method of decreasing the CO2 desorption reactor size, the desorption reactor being configured to receive an ion-rich solution containing bicarbonate ions, the method comprising providing carbonic anhydrase within the ion-rich solution and allowing the carbonic anhydrase to flow with the ion-rich solution while catalyzing conversion of the bicarbonate ions into CO2 gas and generating an ion-depleted solution.
The present invention also provides a method of decreasing the CO2 desorption energy input in a desorption unit, the desorption unit receiving an ion-rich solution containing bicarbonate ions and the ion-rich solution being heated to favor desorption of CO2 therefrom, the method comprising providing carbonic anhydrase within the ion-rich solution and allowing the carbonic anhydrase to flow with the ion-rich solution while catalyzing the conversion of the bicarbonate ions into CO2 gas and generating an ion-depleted solution.
It should be understood that the methods and processes defined hereinabove and herein may be combined with any of the additional features described, illustrated or exemplified in herein. For instance, the features of system design and operating conditions referred to herein in the drawings and/or details description may be combined with the concepts and/or embodiments of the present invention and with any one of the concepts and/or embodiments defined in the claims.
In one aspect, in the processes or methods there is a chemical compound which may be a slow absorption compound such as tertiary amines, tertiary alkanolamines, sodium carbonate, potassium carbonate, or at least one amino acid. The slow absorption compound may include a non carbamate-forming solution.
In another aspect, in the processes or methods the carbonic anhydrase or variants or analogues thereof is selected as a single type thereof. The single type of carbonic anhydrase may have similar reaction constants for hydration and dehydration.
In another aspect, in the processes or methods the carbonic anhydrase or variants or analogues thereof is selected to comprise at least two different types thereof. The two different types of carbonic anhydrase may have respectively different reaction rate constants, wherein a first carbonic anhydrase type has a higher hydration reaction rate constant and a second carbonic anhydrase has a higher dehydration reaction rate constant. The second carbonic anhydrase type may also have a higher temperature stability than the first carbonic anhydrase type. The carbonic anhydrase or variants or analogues thereof may be chosen or made pursuant to knowledge that is incorporated herein by reference in several documents; they may be naturally occurring, recombinants, variants, and combinations thereof; many carbonic anhydrase types are known in the art and may be used in connection with the processes, systems and methods of the present invention in accordance with the present disclosure.
In another aspect of the processes or methods, the carbonic anhydrase is provided in an amount sufficient to enable a reduction in energy input compared to use of a carbamate-forming solution. The carbonic anhydrase may be provided in an amount sufficient to enable a reduction in energy input from 10% to 60% compared to use of a carbamate-forming solution. The carbonic anhydrase is provided in an amount sufficient to enable a reduction in energy input from 10% to 60% compared to use of a piperazine.
Referring to
The ion-rich solution 24 is then fed to the desorption unit 14, in which it can be regenerated and a CO2 gas can be separated for sequestration, storage or various uses. The ion-rich solution 24 is preferably heated, which may be done by a heat exchanger 32, to favor the desorption process. Referring to
Referring to
In order to provide the carbonic anhydrase to the ion-rich solution 34 entering the desorption reactor 36, there may be an enzyme feed stream 48 prior to the inlet into the desorption reactor 36. It should be noted that the carbonic anhydrase may be provided in a number of other ways. For instance, carbonic anhydrase may be provided to the absorption solution 20 which flows through the absorber reactor 16 and is not removed from the ion-rich solution 34 which is fed to the desorption reactor 36. In this scenario, the carbonic anhydrase is introduced into the overall CO2 capture process 10 via an absorption solution make-up stream 50, which is preferably mixed with the recycled ion-depleted solution 42. Referring to
In one optional aspect, a mixture of different enzymes is used: a first enzyme with activity that is optimal for CO2 hydration reactions taking place in the absorption unit and a second enzyme with activity that is optimal for CO2 dehydration taking place in the desorption unit, each enzyme being robust to operating conditions encountered in the absorption and desorption units.
Regarding delivery of the enzyme to the process, the enzyme is preferably provided directly as part of a formulation or solution. There may also be enzyme 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 solutions 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 CLEAs or CLECs. CLEA comprise precipitated enzyme molecules forming aggregates that are then crosslinked using chemical agents. The CLEA may or may not have a ‘support’ or ‘core’ 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 ‘support’ or ‘core’ made of another material. When a support is used, it may be made of polymer, ceramic, metal(s), silica, solgel, chitosan, cellulose, alginate, polyacrylamide, 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 solution throughout the process.
When the enzymes are provided on particles, the particles may be sized in a number of ways.
In some embodiments, the particles may be micro-particles, which may be sized to facilitate separation of the micro-particles from the ion-rich mixture. For instance, the micro-particles may be sized to have a diameter above about 1 μm or above about 5 μm. The micro-particles may also be sized to have a catalytic surface area comprising the biocatalysts having an activity density so as to provide an activity level equivalent to a corresponding activity level of soluble biocatalysts above about 0.05 g biocatalyst/L, optionally between about 0.05 g biocatalyst/L and about 2 g biocatalyst/L, and preferably between about 0.05 g biocatalyst/L and about 0.5 g biocatalyst/L, or up to 5 g biocatalyst/L, for the case of biocatalysts having a minimum activity of about 260 WA units/mg. Furthermore, the absorption solution and the CO2 form a reactive liquid film having a thickness and the micro-particles may be sized so as to be within an order of magnitude of the thickness of the reactive liquid film. The micro-particles may also be sized so as to be smaller than the thickness of the reactive liquid film. The thickness of the reactive liquid film may be about 10 μm. In another optional aspect, the micro-particles are sized between about 1 μm and about 100 μm. It should also be noted that precipitates may be formed in the ion-rich solution and the micro-particles may be sized to be larger or heavier than the precipitates or to be easily separable therefrom. In some optional aspects of the process, the particles may be sized so as to be nano-particles. In some optional aspect of the process, the micro-particles may have an activity density of at least about 0.06 WA/mm2, optionally of about 0.5 WA/mm2 or more. The micro-particles may also be provided in the absorption solution at a maximum particle concentration of about 40% w/w. In some optional aspects, the maximum micro-particle concentration may be 35% w/w, 30% w/w, 25% w/w, 20% w/w, 15% w/w, 10% w/w, or 5% w/w, 2% w/w, or 1% w/w. The micro-particles may be composed of support material(s) that is at least partially composed of nylon, cellulose, silica, silica gel, chitosan, polystyrene, polymethylmetacrylate, alginate, polyacrylamide, magnetic material, or a combination thereof. The support may preferably be composed of nylon. The density of the support material may be between about 0.6 g/ml and about 6 g/ml.
In other embodiments, the particles are sized and provided in a concentration such that the particles are smaller, preferably substantially smaller, than the thickness of the reactive film. The reactive film may be defined in the absorption stage or the desorption stage of the overall CO2 capture process or may be an average or approximation between the two stages.
The particles may be sized to facilitate separation of the particles from the ion-rich mixture. The enzymatic particles may be sized to have a diameter at or below about 15 μm. Optionally, the particles are sized to have a diameter at or below about 10 μm. Optionally, the particles are sized to have a diameter at or below about 5 μm. Optionally, the particles are sized to have a diameter at or below about 1 μm. Optionally, the particles are sized to have a diameter at or below about 0.5 μm. Optionally, the particles are sized to have a diameter at or below about 0.2 μm. Optionally, the particles are sized to have a diameter at or below about 0.1 μm. In some preferred embodiments, depending on the thickness of the reactive film of given process operating parameters and conditions, the particles are sized to have a diameter of about 0.001 μm, 0.005 μm, 0.01 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.05 μm, 1.1 μm, 1.15 μm, 1.2 μm, 1.25 μm, 1.3 μm, 1.35 μm, 1.4 μm, 1.45 μm, 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm, 1.85 μm, 1.9 μm, 1.95 μm or 2 μm or a diameter in between any two of the aforementioned values. In some optional embodiments, the particles are sized to have a diameter about one to about four orders of magnitude below the reactive film thickness. The particles are preferably sized so as to be at least about two orders of magnitude smaller than the thickness of the reactive film.
The particles may be made, sized and used as described in U.S. provisional patent application No. 61/439,100 which is incorporated herein by reference.
Enzymes 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 enzymes, including carbonic anhydrase. One of the ways carbonic anhydrase enhances performance of CO2 capture solutions in the desorption unit is by reacting with dissolved bicarbonate ions and maintaining a maximum CO2 concentration gradient between gas and liquid phases to improve CO2 transfer rate from the liquid solution phase to the gas phase. When the incoming ion-rich solution 34 also comprises carbonate/bicarbonate precipitates, which are solids that make the ion-rich solution 34 a slurry-like consistency, the carbonic anhydrase flowing with the ion-rich solution 34 is able to enhance performance in the desorption unit by reacting with dissolved bicarbonate ions and maintaining a maximum bicarbonate ion concentration gradient between solid and liquid phases to improve carbonate/bicarbonate transfer rate from the solid phase into the liquid solution phase thus promoting the dissolution of the precipitates. In some cases, the ion-rich solution 24 exiting the absorption unit may be treated by removing excess liquid and thus pre-concentrating the solids prior to the desorption unit, and the removed liquid stream (not illustrated) can be recycled back into the process, e.g. back into stream 42. The carbonic anhydrase includes any analogue, fraction and variant thereof and may be alpha, gamma or beta type from human, bacterial, fungal or other organism origins, having thermostable or other stability properties, as long as the carbonic anhydrase can be provided to function in the CO2 capture or desorption processes to enzymatically catalyse the reaction:
In some aspects of the process, different types of absorption solutions may be used: amine solutions, carbonate solutions, amino acid solutions, and so on.
The absorption solution may comprise a chemical compound for enhancing the CO2 capture process. For instance, the ion-rich solution may further contain at least one compound selected from the following: piperidine, piperazine, derivatives of piperidine or piperazine which are substituted by at least one alkanol group, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, 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 and potassium or sodium salts of the amino acids, or mixtures thereof.
The solution may be a carbonate-based solution, such as potassium carbonate solution, sodium carbonate solution, ammonium carbonate solution, promoted potassium carbonate solutions, promoted sodium carbonate solutions or promoted ammonium carbonates; or mixtures thereof. These carbonate-based solution may be promoted with one or more of the above-mentioned chemical compounds.
Regarding the selection of chemical compounds for use in the CO2 capture solution, it may be preferred to have compounds facilitating desorption efficiency. For instance, it should be noted that the reaction mechanisms between primary/secondary amines and tertiary amines with CO2 in absorption/desorption are different. The reaction between CO2 and primary/secondary amines is significantly faster than the reaction between CO2 and tertiary amines. As a result of the faster reaction the absorption column may be shorter when primary/secondary amines are used. However, the advantage of tertiary amines is that the regeneration energy is significantly lower than the regeneration energy of primary/secondary amines. As a result of the lower regeneration energy of tertiary amines, the costs for desorption/stripping is less. It would be advantageous to have a combination of both fast absorption and low regeneration energy. In one aspect, one may use carbonic anhydrase enhanced absorption with a low desorption energy compound, such as tertiary amines, which facilitate lower energy requirements for desorption and lower temperatures, which can also reduce or avoid denaturing of the carbonic anhydrase and enable use of a smaller desorption tower. In another aspect, one may use a fast absorption compound, such as primary and/or secondary amines for enhanced absorption, with carbonic anhydrase enhanced desorption to lower the energy requirements for the primary/secondary amine solution regeneration.
In another aspect, the enzyme carbonic anhydrase is provided to flow with the solution throughout the process, to not only accelerate the transformation of CO2 to HCO3−, but also the reverse reaction, which is of major importance during the regeneration of the CO2 loaded solution (also referred to as “carbonate loaded solution” or “ion-rich solution” herein).
In further aspects of the process, the ion-rich solution may contain from about 0.1 M to 8 M of bicarbonate ions. The carbonate loading of the solution will depend on the operating conditions, reactor design and the chemical compounds that are added. For instance, when potassium or sodium bicarbonate compounds are used in the absorption solution, the ion-rich solution may contain from about 0.5 M to 1.5 M of bicarbonate ions and when other compounds such as tertiary amines are used the ion-rich solution may contain from about 1 M to 8 M of bicarbonate ions. When the ion-rich solution is highly loaded with carbonate/bicarbonate ions, it may become much more viscous which can have a detrimental effect of mass transport within the solution. The presence of carbonic anhydrase flowing with the solution further enhances the mass transport along with the enzymatic reaction, thus improving the desorption unit and overall CO2 capture process, for instance by supersaturating the solution with bubbles of gaseous CO2. In addition, temperatures in the desorption unit may range between about 0° C. and about 150° C., for example.
The invention also provides a method of decreasing the CO2 desorption temperature in a desorption unit, decreasing the CO2 desorption reactor size and decreasing the CO2 desorption energy input in a desorption unit. By using carbonic anhydrase in the solution, these system design parameters can be modified to give a more efficient process. Decreasing the temperature and energy input may be realized in a retrofitting of an existing desorption reactor, while new desorption reactors may be built so as to have a smaller size than would have been required.
Referring now to
The ion-rich solution 24 can be released from the absorption reactor 16 through one or more streams, for instance streams 24a and 24b. One of the streams may be fed into a first desorption reactor 36a, such as stream 24a in
The desorption reactor 36 may be in the form of a column and may be provided with a plurality of units and liquid inlets.
The CO2 streams 38, 38′ are preferably captured, stored and/or used for any number of uses such as industrial, agricultural, enhanced oil recovery, and so on.
The processes of the present invention are applicable to a variety of industries and purposes. For instance, the process can be used to remove CO2 gas from mixed gases such as power plant flue gases, industrial effluent gases in order to bring such gases within specifications or certain limits, biogas for improving it to natural gas quality, air, and so on. The isolated CO2 gas can be used for industrial, petrochemical and/or agricultural uses, such as enhanced oil recovery and supplying to greenhouses.
The desorption reactions H++HCO3−→H2O+CO2 and HCO3−→CO2+OH− may occur and the desorption reaction H++HCO3−→H2O+CO2 is catalyzed by the enzyme carbonic anhydrase. Under optimum conditions, the catalyzed turnover rate of this reaction may reach 2×105 to 6×105 s−1. In some embodiments of the present invention, this provides for the ability to efficiently utilize alternative solvents, which would normally be too kinetically limited for efficient CO2 capture, but which have lower energies of regeneration, such as tertiary alkanolamines, carbonates and amino acids. Due to this, carbonic anhydrase can provide for potentially significant energy and cost savings.
Several experiments were conducted on CO2 desorption with carbonic anhydrase. A schematic presentation of the setup that was used is given in
Both the gas and liquid phase were operated batch-wise. At the start of each run, a known amount of a solution with known composition (see Table 1) was introduced into the reactor and the liquid phase stirrer was turned on at approx 155 rpm. The solution was degassed for a period of time in order to remove any dissolved gases. Next the solution was allowed to equilibrate at the set temperature (10° C.) and its vapor pressure. This temperature was used in order to ensure that the particular carbonic anhydrase that was used was not denatured. After equilibration, the valve between the vacuum pump and the reactor was carefully opened for a very short time, and some of the gaseous component was transferred from the reactor by means of the pressure difference. At the same time, some of the solvent vapor present in the gas phase was transferred along with the gaseous component. The removed solvent vapor was however replaced within a few seconds by the liquid solvent, and any very small change in the concentration of the solvent can be neglected. The sudden pressure decrease in the reactor was followed by a slow pressure increase of the gaseous compound (mostly CO2) from the liquid phase into the gas phase until phase equilibrium was reached.
Possible reactions responsible for the liberation of CO2 from the bicarbonate solution are:
HCO3−+H3O+→CO2+2H2O
HCO3−→CO2+OH−
Next,
During runs 1 and 2, the pressure was decreased with 60-65 mbar, while during run 3 the pressure was decreased with 100 mbar. This larger decrease in combination with the higher amount of enzyme present in the solution resulted in the formation of a bubble layer at the gas-liquid interface.
Examples of enzyme enhanced CO2 capture and desorption are presented below.
From the results shown in
Furthermore, increasing the enzyme concentration resulted in a higher CO2 pressure in the gas phase, indicating that more bicarbonate ions were converted into CO2 in the solution and diffused back in the gas phase and as a result the bicarbonate concentration in the solution with the higher enzyme concentration is lower than for the 100 mg/L and 0 mg/L concentrations.
Applying this for a desorption unit means that if a bicarbonate containing solution is fed to a given desorber, with specific dimensions and operating conditions, bicarbonate removal rate is higher when enzyme is used and a higher enzyme concentration will result in a higher bicarbonate removal rate, given of course that the desorber efficiency is not 100%.
In another way, given that the overall bicarbonate reaction rate is faster in presence of the enzyme, if a desorber with a height of H1 is required without enzyme to reach a given CO2 desorption rate, having the enzyme present in a concentration E2 will result in a smaller desorber having a height of H2 where H1>H2. If an enzyme concentration E3 (higher than E2) is used, then the required desorber with have a height H3 such that H3<H2<H1, similarly to what has been found on the absorber side of the process. The solution would preferably contain compounds that are known to absorb and stock CO2 in the form of bicarbonate ions such as sodium carbonate, potassium carbonate, tertiary amine like MDEA and tertiary amino acid such as diethylglycine, dimethylglycine and sarcosine.
Simulations were run to demonstrate the impact of carbonic anhydrase on absorber height and energy requirement in a CO2 capture desorption process.
Simulation parameters were the following:
For the case where MDEA is used with enzyme; MDEA concentration was 2M. For the MDEA and piperazine solution, the total concentration of MDEA and piperazine was 2M.
Simulations were first conducted to compare absorber height for different scenarios with enzyme and with piperazine. Results are shown in
If no enzyme is present, the turnover factor (or factor) is equal to 1 and the reaction rate constant k1 is the same as the physico-chemical reaction. In the graph of
The results obtained for piperazine also indicate that increasing piperazine concentration leads to a reduction of the absorber height. For a piperazine concentration of 10% (0.2 M), absorber height is 18.7 m, which is similar to the height of the absorber obtained with a turnover factor of 25,000. This turnover factor was corresponding to an enzyme concentration of 0.4 g/L of human carbonic anhydrase type II or to 1 g/L of an enzyme variant. So, it is seen that different enzymes used at different concentrations can result in a same turnover factor.
In a second step, simulations were run to model the CO2 capture desorption process shown in
The following references are incorporated herein by reference and it should be understood that the aspects described therein may be combined with those described herein: PCT/CA2010/001212, PCT/CA2010/001213, PCT/CA2010/001214, U.S. Pat. No. 6,908,507, U.S. Pat. No. 7,176,017, U.S. Pat. No. 6,524,843, U.S. Pat. No. 6,475,382, U.S. Pat. No. 6,946,288, U.S. Pat. No. 7,596,952, U.S. Pat. No. 7,740,689, U.S. Pat. No. 7,514,056, U.S. Pat. No. 7,521,217, U.S. 61/272,792, U.S. 61/439,100 which are all currently held by the Applicant. The reactors and processes described in the preceding references may be used in connection with the processes described herein.
It should also be understood that various alterations, modifications and changes may be made to the embodiments described herein and elements and aspects described and illustrated in different embodiments and examples herein may be combined with any other embodiments and examples herein including those incorporated by reference. For instance, the methods for decreasing CO2 desorption temperature, reactor size and/or energy input may be combined with any of the elements of the process described herein such as the particle delivery of the enzymes, process streams, chemical compounds, etc., and any combination thereof described herein.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CA11/01210 | 10/28/2011 | WO | 00 | 4/24/2012 |
Number | Date | Country | |
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61344869 | Oct 2010 | US |