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Biocatalyzed accelerated post combustion CO2 capture and stripping in monoethanolamine Prakash C. Sahoo, Manoj Kumar, Amardeep Singh, Mahendra P. Singh, and Suresh K. Puri Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01322 • Publication Date (Web): 12 Sep 2017 Downloaded from http://pubs.acs.org on September 13, 2017
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Biomatrix based CO2 capture and low temperature desorption in MEA was explored 204x144mm (119 x 127 DPI)
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Biocatalyzed accelerated post combustion CO2 capture and stripping in monoethanolamine Prakash C. Sahoo, Manoj Kumar*, Amardeep Singh, Mahendara. P. Singh, Suresh. K. Puri Indian Oil Corporation Limited Research and Development center, Sector-13, Faridabad, Haryana-121007, India Keywords: Enzyme; Monoethanolamine; Carbon dioxide capture; Immobilization; Desorption
*Corresponding Address Dr. Manoj Kumar Email:
[email protected] Industrial Biotechnology Department, Research and Development Centre, Indian Oil Corporation Limited, Sector-13, Faridabad. Haryana-121007, India
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Abstract: The existing solvent mediated CO2 capture process is energy intensive due to high temperature requirement for solvent regeneration. Therefore, improvement of solvent systems for optimized and low energy intensive CO2 capture and desorption is of enormous interest. In this regard, we report a novel matrix composed of ZnO/Fe2O3 encapsulated mesoporous silica tethered thermostable carbonic anhydrase (CA) (designated as CA@fn-Zn/Fe/MS). The enzyme coupled matrix was used for efficient post combustion CO2 capture and low energy intensive desorption. It was observed that the use of CA@fn-Zn/Fe/MS (0.5 wt%) in 30% Monoethanolamine (MEA) enhances the CO2 uptake to 0.82 mol/mol of solvent and the regeneration efficiency by 2.6 times as compared to the neat MEA at 30 wt% . The enzyme coupled matrix is stable over a broad range of pH and can be used for several cycles. The development adds values to improve conventional amine based CO2 scrubbing technology.
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1. Introduction The increasing amount of CO2 into the atmosphere is a major societal and environmental concern because this leads to global warming; hence, to ameliorate the concern various technological intervention in CO2 captures and its sequestration are being explored. In the process of electricity and heat generation industries releases more than 13 giga tonnes of the CO2 each year into the atmosphere1. Among various options, CO2 capture has benefit of separating CO2 and can be retrofitted to existing power plants. The most commonly used technology for CO2 capture relies on amine scrubbing, in which solvent monoethanolamine (MEA) is widely used2. In a typical amine scrubbing system, CO2 capture occurs primarily via carbamate formation and bicarbonate formation. Regeneration of the solvent is done by heating the solution, which drives the equilibrium toward the reactants 2. Although, MEA has a fast CO2 absorption rate with high carrying capacity but requires considerable energy (>120 °C) to regenerate the solvent. Hence, overall process is much expensive3. In order to reduce parasitic energy in regeneration of solvent used in conventional CO2 capture process, use of alternate solvents and adding certain additive is well reported in the literature.4-10 A number of additives, such as AMP/morpholine, piperazine/ N-methyl-2,2-iminodiethanol, piperazine/ 2-amino-2-methyl- 1-propanol (AMP), and AMP/ methylmonoethanol amine have been known to accelerate CO2 sorption rate when mixed with amines 10,11. However, these solvent systems has limitation of high cost due to high desorption energy and some of these additives are extremely corrosive and toxic to environment 10,12. Therefore, an alternative strategy to blend amine solvents with benign additives with a high CO2 absorption and desorption rate are required.
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Recently, enzymatic processes for CO2 capture in chemical industries have acquired a great deal of interest due to their outstanding CO2 hydration rate compared to other CO2 sequestration processes 10, 13, 14. One of the representative biocatalyst carbonic anhydrase (CA) can hydrate CO2 at unprecedented rate (kcat = 106 s-1) and thus has excellent prospects 10. However, to withstand the flue gas condition the enzyme itself has to be thermo tolerant. Additionally, for a convenient application, the native enzyme (CA) should be immobilized on suitable support to facilitate storage stability, thermal stability and its reusability. Here, we have developed an enzyme coupled matrix by tethering a thermostable CA onto a mesoporous support co-functionalized with nano-ZnO and Fe2O3. This is blended with 30% MEA and provides superior CO2 absorption and desorption. This matrix coupled enzyme has advantageous features as bio-catalytic performance of the enzyme and the inherent CO2 absorption ability of the solid matrix has been integrated simultaneously in one platform. The cofunctionalized ZnO/ Fe2O3 in the matrix assists in two important activities (1) the active ZnO sites in the silica behaving as a strong site for CO2 due to its Lewis-catalytic nature 15, 16 and (2) Fe2O3 induces magnetism for easy separation of the matrix. Moreover, porous silica matrix allows for high enzyme loadings, facilitates easy mass transfer with increased pH and temperature tolerance.17 CO2 absorption/desorption was studied in MEA solvent using enzyme coupled matrix as an additive. This approach offers a sustainable opportunity to develop benign additives that could take amine-based solvents to the next stage of development in terms of CO2 capture.
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2. Experimental section
2.1. Materials The solvents and chemicals such as tetraethyle orthisilicate, cetyltrimethylammonium bromide (CTAB), glutaraldehyde (50 wt% in water), ethanol, hexadecanol, hydrochloric acid, acetonitrile, para-nitrophenyl acetate (p-NPA), para-nitrophenol (p-NP), Zinc nitrate, ferrous chloride, ferric chloride, 3-aminopropyltriethoxysilane (APTES) and trizma-base, were supplied by M/s Sigma– Aldrich. Nutrient broth, sodium bicarbonate, potassium hydroxide, ammonia, 2-proponal and ammonium sulfate were obtained from Blulux, India. Bushnell Haas and sodium hydroxide was brought from SRL Pvt.Ltd., India. Glycerol and yeast extract were obtained from Himedia, India. Millipore grade de-ionized (DI) water was used throughout the experiments. Cylindered CO2 (99.9%) were employed for CO2 absorption and desorption study. 2.2. Synthesis and functionalization of matrix ZnO and Fe2O3 nano particles were synthesized by precipitation methods as reported previously 18,19. The materials were dried at 60 oC and stored in desiccators. The neat mesoporous silica (MS) was synthesized by a standard procedure reported elsewhere20. ZnO and Fe2O3 impregnated MS was synthesized using a procedure as follows. Typically, 2.0 g of CTAB was dissolved in 400 ml DI at 80 oC; subsequently 10 ml of 2N NaOH was added. In a separate beaker 0.1 g of ZnO and 0.05 g of Fe2O3 was sonicated in 100 ml of DI for 15 min to make a homogeneous solution. 25 ml of this solution was transferred into the beaker containing CTAB and then 10 ml of TEOS was added drop wise. After stirring for 2 h, it was filtered and washed with DI water. The solid was dried over night at 60 oC in an oven. The solid was calcined at 450
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o
C for 5 h to get rid of surfactant and it was designated as Zn/Fe/MS. For functionalization, 0.5
grams of calcined Zn/Fe/MS was suspended in a round bottom flask with 10 ml ethanol and drop wise addition of 0.5 ml APTES was done21. The contents were refluxed for 2 h. The solid recovered by centrifugation was washed with ethanol and DI and dried at room temperature for 12 h. The product leveled as fn-Zn/Fe/MS was highly stable in pH ranging from 8 to 11. However, at low pH (
