CO2 desorption using high-pressure bipolar membrane electrodialysis

Abstract

The electrodialysis of gas evolving solutions may prove to be an important technology for many gasseparation applications, including CO 2 and SO 2 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 CO 2 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 À2 ), the CO 2 desorption energy from aqueous bicarbonate solutions under highpressure operation can be 29% lower than under ambient-pressure operation.

CO2 extraction from seawater using bipolar membrane electrodialysis

“…The acidic solution converted the HCO 3 À and CO 3 2À into dissolved CO 2 which then bubbled out of solution. 3,4 In contrast, the extraction of CO 2 from seawater described in this article does not involve the transport of HCO 3 À or CO 3 2À across the AEMs (see Fig. 2b).…”

“…3,4 The previous work on the extraction of CO 2 from KHCO 3 /K 2 CO 3 solutions was performed for solutions with concentrations in the range of 0.125M-2M, for which HCO 3 À and CO 3 2À were the primary anions present in solution. In these experiments, CO 2 was extracted by transporting HCO 3 À ions and CO 3 2À ions across AEMs into adjacent solutions that were acidified via the operation of BPMs, with the HCO 3 À and CO 3 2À ions effectively acting View Online as ''carrier molecules'' for CO 2 .…”

“…1,2 In previous experiments, our lab investigated the use of bipolar membrane electrodialysis (BPMED) for CO 2 desorption from potassium carbonate and bicarbonate solutions at ambient pressure 3 and elevated pressures as high as 10 atm. 4 The electrodialytic desorption of CO 2 gas from aqueous solutions has the potential to improve the efficiency of CO 2 separation from a wide array of mixed gas sources, including power-plant flue-gas 5,6,7 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 CO 2 in the mixed-gas source, adding significant challenges to the separation of CO 2 from dilute sources such as the atmosphere.…”

“…4 The electrodialytic desorption of CO 2 gas from aqueous solutions has the potential to improve the efficiency of CO 2 separation from a wide array of mixed gas sources, including power-plant flue-gas 5,6,7 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 CO 2 in the mixed-gas source, adding significant challenges to the separation of CO 2 from dilute sources such as the atmosphere. 12,13 One way around this problem is to notice that the CO 2 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 (HCO 3 À ) at the ocean pH of 8.…”

Ion-exchange membranes in chemical synthesis – a review

“…This recovery process is attractive due to very low energy consumption -as low as 0.55 kWh kg -1 CO 2 for alkaline carbonates [203][204][205] and around 2−4 kWh kg -1 CO 2 for ammonia [206]. The main obstacle in BMED-based CO 2 desorption is CO 2 gas evolution inside the membrane module compartments, resulting in an increased stack resistance and high energy consumption at high current densities [207]. This was avoided by operating a BMED stack at elevated pressures, up to 6 atm and the controlled release of CO 2 dissolved outside of the module.…”