Effect of swelling on mass transfer performance in membrane extraction

The membrane extraction experiments were performed with tributyl phosphate/ acetic acid (HAc)/water, n-butanol/HAc/water and 20% Alamine (in kerosene); HAc; and water as working systems. HAc was transferred from the aqueous ph ase to the organic phase. The effect of flat membranes swelling on mass tra nsfer was studied. The membranes were microporous polysulfone and microporo us polytetrafluoroethylene. The overall mass transfer coefficients based on the water phase were calculated and compared between nonswollen and swolle n membranes. The experimental results show that the physical structure of t he flat membranes used in our experiments was changed if soaked by organic solvents; however, change in thickness was not found. The overall mass tran sfer coefficients clearly were decreased after the flat membranes were swol len. The most likely reason is that the mass transfer resistance was increa sed because of the change of the membrane structure. The results also show that it is better to choose a hydrophilic membrane to reach high mass trans fer performance when the equilibrium constant is very low. (C) 1999 John Wi ley & Sons, Inc.