GAS SEPARATION USING AN ELECTROCHEMICAL MEMBRANE MODULE

Abstract

Conventional gas separation with membranes is achieved using a pressure gradient to drive one gas component from a gas mixture through a thin film barrier into a collection compartment. A typical example of the separation process is the Prism membrane module where hydrogen is enriched from a gas mixture based on the pressure difference applied to the membrane. In order to overcome the concentration effect, the pressure differences of over 50 bars across the membrane are usually required for uncharged gas species. The situation would be significantly different for charged gas species in the presence of an electric potential, especially for the low level contaminant removal. This study focuses on the development of an electrochemical membrane module for removal of carbon dioxide from a breathing gas mixture. The effects of operating variables such as CO2 input rates and current densities on the extent of CO2 separation have been carried out. A mathematical model has also been formulated to simulate the process for the CO2 removal. The theoretical predictions show good agreement with the experimental results obtained under various operation conditions. Comparison between the theoretical and experimental results indicated that the effectiveness of the electrochemical membrane area used in this study for CO2 removal is 50%. The simulation results reveal that the gas phase mass transfer resistances in both cathode, 1 / kcAg and anode, 1 / kaAg compartments are negligible. Transfer of CO2 in the electrochemical membrane module is mainly controlled by the resistances in the electrolyte solution. These resistances include CO2 absorption in the cathode, diffusion and ionic migration, and CO2 evolution in the anode. The mathematical model derived in this study has shown the possibility of using fundamental transport equations to simulate the complex electrochemical membrane process.