Membrane-solvent selection for CO2 removal using membrane gas-liquid contactors

Membrane gas–liquid contactors can provide very high interfacial area per unit volume, independent regulation of gas and liquid flows and are insensitive to module orientation, which make them very attractive in comparison with conventional equipments for offshore application. However, the membrane adds an additional resistance in the process of mass transfer. The mass transfer resistance of the membrane is affected by the presence of the liquid inside the membrane pores. This wetting of the membrane is determined by the properties of the membrane and the liquid mutually. Hence, a proper choice of the membrane–solvent combination is a critical and determining step in developing membrane gas absorption processes. Important criteria for the selection of the membrane–solvent combination for membrane gas–liquid contactors, such as the critical entry pressure, contact angle and critical solvent surface tension are evaluated in this paper. These characterizing properties of membranes and solvents are experimentally measured for various membrane and solvent combinations for the case of bulk CO2 removal. For selected combinations the actual gas–liquid mass transfer process for CO2 absorption is explored experimentally in the flat sheet as well as in the hollow fiber membrane configuration. The experimental results were compared to the theoretical calculations to determine possible mass transfer limitations due to wetting effects. The polypropylene membrane in combination with propylene carbonate as an absorption liquid was found to be a suitable combination for bulk CO2 removal using membrane gas–liquid contactors.