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Co2 Extration from Seawater

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Co2 Extration from Seawater ( co2-extration-from-seawater )

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View Online / Journal Homepage Energy & Dynamic Article LinksC< Environmental Science Cite this: DOI: 10.1039/c2ee03393c www.rsc.org/ees PAPER CO2 extraction from seawater using bipolar membrane electrodialysis† Matthew D. Eisaman,‡* Keshav Parajuly, Alexander Tuganov, Craig Eldershaw, Norine Chang and Karl A. Littau Received 6th December 2011, Accepted 23rd January 2012 DOI: 10.1039/c2ee03393c An efficient method for extracting the dissolved CO2 in the oceans would effectively enable the separation of CO2 from the atmosphere without the need to process large volumes of air, and could provide a key step in the synthesis of renewable, carbon-neutral liquid fuels. While the extraction of CO2 from seawater has been previously demonstrated, many challenges remain, including slow extraction rates and poor CO2 selectivity, among others. Here we describe a novel solution to these challenges – efficient CO2 extraction from seawater using bipolar membrane electrodialysis (BPMED). We characterize the performance of a custom designed and built CO2-from-seawater prototype, demonstrating the ability to extract 59% of the total dissolved inorganic carbon from seawater as CO2 gas with an electrochemical energy consumption of 242 kJ mol1(CO2). Introduction The separation of CO2 from any mixed-gas source typically involves two steps: (1) the selective capture of CO2, usually accomplished by contacting the CO2-containing mixed-gas source with a solid or liquid adsorber/absorber; and (2) the desorption of pure CO2 gas from the adsorber/absorber.1,2 In previous experiments, our lab investigated the use of bipolar membrane electrodialysis (BPMED) for CO2 desorption from potassium carbonate and bicarbonate solutions at ambient Palo Alto Research Center (PARC), 3333 Coyote Hill Rd., Palo Alto, CA, 94304, USA † Electronic supplementary information (ESI) available: details of the membrane contactor efficiency measurement, numerical values for the data plotted in Fig. 3, and details of the calculation of CO2 extraction efficiency. See DOI: 10.1039/c2ee03393c ‡ Present address: Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton, NY 11973, USA. E-mail: meisaman@bnl.gov; Tel: +631-344-8315. pressure3 and elevated pressures as high as 10 atm.4 The elec- trodialytic desorption of CO2 gas from aqueous solutions has the potential to improve the efficiency of CO2 separation from a wide array of mixed gas sources, including power-plant flue-gas5,6,7 and the atmosphere.3,4,8,9,10,11 For such capture/desorption systems, the volume of gas that must be processed scales inversely with the concentration of CO2 in the mixed-gas source, adding significant challenges to the separation of CO2 from dilute sources such as the atmosphere.12,13 One way around this problem is to notice that the CO2 in the atmosphere establishes equilibrium with the total dissolved inorganic carbon (DIC) in the oceans,x which is largely in the form of bicarbonate ions (HCO3) at the ocean pH of 8.1–8.3.14,15 This means that an efficient method for extracting CO2 from the DIC of the oceans would effectively enable the separation of CO2 from atmosphere without the need to process large volumes of air. x The total dissolved inorganic carbon (DIC) is given by DIC 1⁄4 [CO2] + [HCO3] + [CO32], where [CO2] 1⁄4 [CO2(aq)] + [H2CO3].14,15 Broader context The efficient separation of CO2 from the atmosphere would be a transformational technology, enabling direct reduction of the atmospheric CO2 concentration, the mitigation of CO2 emissions from ‘‘mobile emitters’’ such as the transportation sector, and the synthesis of carbon-neutral liquid fuels. One of the primary challenges, however, is the large volume of air that must be processed. The equilibrium between atmospheric CO2 and the dissolved inorganic carbon (DIC) of the oceans implies that an efficient method for extracting CO2 from the DIC of the oceans would effectively enable the separation of CO2 from atmosphere without the need to process large volumes of air. We describe a novel technique for extracting CO2 gas from the DIC of seawater and reverse osmosis brine solutions using bipolar membrane electrodialysis (BPMED). Seawater is pumped through a BPMED system and results in two output streams: acidified and basified seawater. In the acidified stream, the HCO3 and CO32 ions in the input seawater area converted into dissolved CO2, which is subsequently vacuum stripped, producing a stream of pure CO2 gas. The CO2-depleted acidified solution can then be combined with the basified solution, creating a neutral-pH solution that can be returned to the ocean. This journal is a The Royal Society of Chemistry 2012 Energy Environ. Sci. Downloaded by University of Oxford on 26 March 2012 Published on 06 February 2012 on http://pubs.rsc.org | doi:10.1039/C2EE03393C

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