Patent Application Titled "Compositions and Methods for Analysis of C02 Absorption" Published Online (USPTO 20160010142)
By a News Reporter-Staff News Editor at Biotech Business Week -- According to news reporting originating from
, by NewsRx journalists, a patent application by the inventors Salmon, Sonja (
); House, Alan (
); Whitener, Margaret (
), filed on March 14, 2014, was made available online on January 21, 2016 (see also Biotechnology Companies
The assignee for this patent application is Novozymes North America, Inc.
Reporters obtained the following quote from the background information supplied by the inventors: "Carbon dioxide (CO.sub.2) emissions are a major contributor to the phenomenon of global warming. CO.sub.2 is a by-product of combustion and it creates operational, economic, and environmental problems. CO.sub.2 emissions may be controlled by capturing CO.sub.2 gas before emitted into the atmosphere. There are several chemical approaches to control CO.sub.2 emissions. One approach is to pass the CO.sub.2 through an aqueous liquid containing calcium ions, allowing the CO.sub.2 to precipitate as CaCO.sub.3. Preferred techniques for capturing CO.sub.2 gas from combustion processes are ones in which the product of the capture process is CO.sub.2 in the form of a gas that can be compressed and transported to storage sites, or for useful purposes.
"The most well-established technique for extracting CO.sub.2 from a gaseous feed and capturing the extracted CO.sub.2 gas for use or storage is absorption of CO.sub.2 into aqueous solutions, such as aqueous solutions of amines, for example, monoethanolamine (MEA) or methyldiethanolamine (MDEA), or aqueous solutions of inorganic salts, such as potassium carbonate, sodium carbonate, ammonium carbonate, potassium phosphate, or sodium phosphate. In the case of primary amines, such as MEA, CO.sub.2 is mainly described as being absorbed as a result of chemical reaction between CO.sub.2 and the amine to form a carbamate compound. Additional absorption can occur as a result of ionic complexation between protonated amines and CO.sub.2 molecules which have been hydrated to bicarbonate. In the case of tertiary amines, such as MDEA, absorption occurs as a result of ionic complexation between protonated amines and CO.sub.2 molecules which have been hydrated to bicarbonate. In the case of inorganic salts, absorption occurs as a result of ionic complexation between the cation of the salt, such as potassium or sodium, and CO.sub.2 molecules which have been hydrated to bicarbonate. CO.sub.2 hydration preferentially occurs at alkaline pH and results in a decrease in pH as the conversion of CO.sub.2 to bicarbonate increases. Depending on the pH, an equilibrium of carbonic acid, bicarbonate and carbonate ions will be present in the solution. To complete the CO.sub.2 capture process and recycle the solvent, after absorption, a driving force, such as heat and/or a change in pressure, is typically used in one or more desorption process stages to release CO.sub.2 from the 'CO.sub.2--Rich' absorption solution and recycle the 'CO.sub.2-Lean' absorption solution back to the absorption stage. Alternatively, CO.sub.2-containing anions in the absorption solution may be precipitated as insoluble salts, such as calcium carbonate, and removed from the liquid in the solid form.
"Catalysts are able to increase the rate of the reversible CO.sub.2 hydration (forward reaction) and dehydration (reverse reaction) reactions shown in the following reaction.
"Certain biological catalysts, such as the enzyme carbonic anhydrase, can catalyze the conversion of CO.sub.2 to bicarbonate at a very high rate (turnover numbers up to 10.sup.6 molecules of CO.sub.2 per second are reported).
"Selection of a high performing carbonic anhydrase to catalyze the CO.sub.2 hydration reaction under application relevant conditions depends on several factors including: (i) enzyme robustness to temperature stress or impurities or enzyme poisons that may be present, (ii) enzyme longevity and (iii) enzyme activity. The degree to which an enzyme resists temperature stress or impurities or enzyme poisons, the length of time an enzyme retains activity when exposed to certain conditions, and the magnitude of a particular enzyme sample's activity can all be assessed using an enzyme activity assay, such as provided by embodiments of the present invention. Selection of a high-performing non-enzyme catalyst, or a combination of enzyme and non-enzyme catalysts, also depends on the factors described above. Examples of non-enzyme catalysts that can be evaluated according to the methods of the present invention are zinc-centered organo-metallic compounds, such as zinc-centered tris(triazolyl)pentaerythritol and analogous compounds, which are reported to catalyze the hydration of carbon dioxide (
Pat. No. 8,394,351).
"Several assays for carbonic anhydrase activity have been described in the literature. These assays involve diluting the enzyme in aqueous buffers to either assess enzyme esterase activity by measuring p-nitrophenyl acetate conversion to p-nitrophenol (for example, Bond, G. M. et al. 2001. Energy and Fuels. 15: 309); or assess enzyme CO.sub.2 hydration/HCO.sub.3.sup.- dehydration activity by measuring the change in pH that accompanies each reaction, either by using a pH meter or a pH sensitive colorimetric indicator (for example, Wilbur, K. M. and N. G. Anderson. 1948. J.
"Biol. Chem. 176: 147), or by measuring the change in gas pressure in the headspace over the reaction by using manometry (for example, Roughton, F. J. W. and V. H. Booth. 1946. Biochem. J. 40: 309).
"Assays for CO.sub.2 hydration typically use CO.sub.2 saturated water as substrate, converting CO.sub.2(g) (carbon dioxide molecules in the gas phase) to CO.sub.2(aq) (carbon dioxide molecules dissolved in aqueous solution). Using CO.sub.2 saturated water divorces the rate of gas-liquid mass transfer from the enzyme catalyzed rate of CO.sub.2(aq) hydration, and allows the assay to only measure the hydration activity. Alternatively, assays for CO.sub.2 hydration can involve exposure of the assay liquid to a headspace containing CO.sub.2 gas. In this case, the reaction rate of the assay will be influenced by both the rate at which CO.sub.2 gas encounters and enters the liquid phase, and the rate at which dissolved CO.sub.2 is converted to bicarbonate. The partial pressure of CO.sub.2 in the headspace will influence the reaction rate. A high partial pressure of CO.sub.2 in the headspace will typically accelerate the absorption reaction. A low partial pressure of CO.sub.2 in the headspace will typically result in a slower absorption reaction. A very low partial pressure of CO.sub.2 in the headspace, such as could be achieved by sweeping the headspace with a non-CO.sub.2 gas, such as nitrogen gas, or applying a vacuum to the headspace will typically result in the rate of the desorption reaction occurring faster than the rate of absorption. An example of a method that utilizes the presence and absence of CO.sub.2 in the headspace to carry out the dehydration reaction for monitoring carbonic anhydrase activity has been reported (WO 2010/081007). Aliquots of assay reaction mixture containing aqueous potassium carbonate and phenolphthalein pH indicator dye and different levels of carbonic anhydrase were first exposed to a 20% CO.sub.2 atmosphere, which caused the solution pH to decrease and the pH indicator to turn colorless. The colorless aliquots were removed from the 20% CO.sub.2 atmosphere and the bicarbonate dehydration rate was determined by monitoring the change in absorbance at 550 nm using a plate reader. Carbonic anhydrase activity was calculated from the onset time at which the absorbance of the reaction mixture reached a set optical density value.
"Although published methods can be used, there is no uniform standard, indicating the established methods have drawbacks and there is a continued need for improved methods for analysis of enhanced CO.sub.2 absorption. There is also a need for improved carbonic anhydrase compositions for use in CO.sub.2 absorption."
In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventors' summary information for this patent application: "Facilitation of CO.sub.2 absorption and desorption using catalysts, such as carbonic anhydrase, is important for applications requiring separation of CO.sub.2 from mixed gases, such as, CO.sub.2-containing gases such as flue gas from power plants burning fossil fuel (e.g. coal or natural gas) or biomass (e.g. wood) or combustible waste materials (e.g. municipal waste) or mixtures of these, biogas, landfill gas, ambient air, recycled air (such as in a confined environment), synthetic gas or natural gas or any industrial or process off-gas containing carbon dioxide, and/or transformation, mineralization and/or utilization of CO.sub.2 in the hydrated bicarbonate form, such as for enhanced algae growth and pH control or adjustment. Improved CO.sub.2 absorption and desorption analytical methods are needed to reduce variability in the analyses, simplify the analyses, make the analyses more application relevant, such as by conducting the analyses at or above ambient temperature, increase sample throughput, and decrease the use of reagents. Improved analytical methods can be used to efficiently identify new catalysts and monitor the performance of catalysts.
"The present invention relates to improved methods for analysis of carbon dioxide (CO.sub.2) absorption and desorption into a liquid enhanced by the presence of a compound that accelerates the absorption reaction resulting in a more rapid pH change in the liquid than in the absence of the compound. The compound may react chemically with CO.sub.2 to form a new compound while concurrently causing a pH change, or, in some embodiments, the compound is a catalyst, such as an enzyme catalyst, that accelerates CO.sub.2 absorption without forming a sustained chemical bond with CO.sub.2. In some embodiments, the enzyme catalyst is carbonic anhydrase.
"The improved methods additionally relate to novel combinations of aqueous solutions and indicators that improve CO.sub.2 absorption assay reliability due to having similar acid dissociation constants (pKa). Preferably, the improved methods comprise aqueous solutions of a buffer compound comprising a tertiary amine together with an indicator, wherein the buffer compound and the indicator have similar acid dissociation constants (pKa), wherein the aqueous solution is used in an assay measuring CO.sub.2 absorption and desorption. Preferably, the improved methods comprise aqueous solutions of bicine together with cresol red, a pH indicator. The methods utilize carbon dioxide (CO.sub.2) as the assay substrate and measure the ability of a compound, such as carbonic anhydrase, to accelerate CO.sub.2 absorption by aqueous solutions for useful applications. Results of performing the methods can be presented as a numerical quantification of the enzyme activity, useful, for example, for allowing numerical comparison of the catalytic activities among different samples.
"The improved methods also relate to analysis of CO.sub.2 desorption out of aqueous liquids containing bicarbonate and/or carbonic acid, enhanced by the presence of a compound that accelerates the desorption reaction resulting in a more rapid pH change in the liquid than in the absence of the compound. In some embodiments, the compound is a catalyst, such as an enzyme catalyst, that accelerates CO.sub.2 desorption without forming a sustained chemical bond with bicarbonate, carbonic acid or CO.sub.2. In some embodiments, heat or vacuum or a combination of these is applied during the method to exaggerate the desorption effect.
"Measurement of the performance of non-catalyst compounds that influence CO.sub.2-hydration and/or dehydration reactions can also be made using the methods of the present invention, which is useful for the selection or identification of such compounds, for example, surfactants or salts. In one embodiment of the invention, the effect of compounds that inhibit the catalytic performance of a CO.sub.2-hydration and/or dehydration enhancing compound can be measured by methods of the present invention.
"The present invention relates to improved compositions for CO.sub.2 absorption comprising an aqueous solution comprising carbonic anhydrase and a buffer compound comprising a tertiary amine, wherein the buffer compound is added in an amount effective to enhance CO.sub.2 absorption as a result of the carbonic anhydrase activity. The present invention relates to improved compositions for CO.sub.2 absorption comprising an aqueous solution comprising bicine, wherein bicine is added in an amount effective to enhance CO.sub.2 absorption as a result of the carbonic anhydrase activity.
"The present invention also provides methods for improving the activity of a carbonic anhydrase comprising adding zinc to a composition comprising one or more carbonic anhydrases. Such methods may be applied in the context of a method for carbon dioxide (CO.sub.2) absorption. The invention also relates to compositions comprising one or more carbonic anhydrases and zinc ions, wherein the zinc ions were added to the composition independent of the natural zinc content of the one or more carbonic anhydrases. The zinc ions are added in an amount effective to increase the catalytic activity of a carbonic anhydrase.
"FIG. 1 shows a graph of enzyme activity (change in absorbance with change in time) as a function of enzyme solution volume measured using an embodiment of the assay methods of the present invention.
"FIG. 2 shows a graph comparing the assay measurement using different embodiments of the assay methods of the present invention.
"FIG. 3 shows data collected using the assay methods of the present invention to determine the effect of salt concentration on the determination of carbonic anhydrase activity for a form of the enzyme that precipitates in the absence of salt.
"FIG. 4 shows data collected using a bubble tank reactor and used to graph the percent of CO.sub.2 absorbed over time in solutions comprising mixtures of bicine, carbonate and carbonic anhydrase."
For more information, see this patent application: Salmon, Sonja; House, Alan; Whitener, Margaret. Compositions and Methods for Analysis of C02 Absorption. Filed March 14, 2014 and posted January 21, 2016. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4807&p=97&f=G&l=50&d=PG01&S1=20160114.PD.&OS=PD/20160114&RS=PD/20160114
Keywords for this news article include: Amines, Anions, Energy, Alkalies, Chemistry, Oil & Gas, Natural Gas, Bicarbonates, Electrolytes, Carbonic Acid, Carbon Dioxide, Inorganic Chemicals, Potassium Carbonate, Enzymes and Coenzymes, Biotechnology Companies, Inorganic Carbon Compounds, Novozymes North America Inc..
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