Studies on the solvent exchange technique for making dry cellulose acetate membranes for the separation of gaseous mixtures

The effect of the pore size on the surface of the water‐wet reverse osmosis membrane and the solvents used in the solvent exchange process on the pore size of the resulting dry cellulose acetate membrane was studied with respect to the separation of a CO2/CH4 mixture. It has been found that there is a critical pore size on the surface of wet membrane that results in the smallest pore size on the dry membrane and, consequently, in the highest separation factor. Such critical pore sizes become greater when the boiling point of the second solvent is increased.