CO2 desorption using high-pressure bipolar membrane electrodialysis

Abstract

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.