Matthew D. Eisaman

CO2 separation using bipolar membrane electrodialysis

Caustic solvents such as sodium or potassium hydroxides, converted viaCO2 capture to aqueous carbonates or bicarbonates, are a likely candidate for atmospheric CO2 separation. We have performed a comprehensive experimental investigation of CO2 gas regeneration from aqueous potassium carbonate and bicarbonate solutions using bipolar membrane electrodialysis (BPMED). This system allows the regeneration of pure CO2 gas, suitable for subsequent sequestration or reaction to synthetic hydrocarbons and their products, from aqueous carbonate/bicarbonate solutions. Our results indicate that the energy consumption required to regenerate CO2 gas from aqueous bicarbonate (carbonate) solutions using this method can be as low as 100 kJ (200 kJ) per mol of CO2 in the small-current-density limit.

CO2 extraction from seawater using bipolar membrane electrodialysis

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 mol−1(CO2).

CO2 desorption using high-pressure bipolar membrane electrodialysis

The electrodialysis of gas evolving solutions may prove to be an important technology for many gas-separation applications, including CO2 and SO2 separation from mixed-gas streams. Progress on the use of electrodialysis for gas separation has been hampered by the increased resistance caused by gas bubbles on the surface of the electrodialysis membranes. This effect reduces the effective membrane surface area, causing increased voltages and reduced membrane lifetimes due to localized “hot spots” of high current density. To overcome this problem, we designed, constructed, and tested a bipolar membrane electrodialysis (BPMED) system designed to operate up to pressures as high as 20 atm. For given process conditions, operation at a sufficiently high pressure keeps all gas dissolved in solution, eliminating the problems caused by gas bubbles on the membrane surfaces. We performed CO2 desorption from aqueous bicarbonate solutions, demonstrating that high pressures decrease the resistance, voltage, and energy of the desorption process. Our results demonstrate that at high current densities (139 mA cm−2), the CO2 desorption energy from aqueous bicarbonate solutions under high-pressure operation can be 29% lower than under ambient-pressure operation.