1998 Volume 31 Issue 1 Pages 153-156
The pervaporation (PV) of an aqueous solution by a porous hydrophobic membrane is considered as simple distillation in a membrane pore. It’s separation factor (α) is generally smaller than the equilibrium one (αeq) by simple distillation, but we obtained larger separation factors than the equilibrium one under limited experimental conditions in the previous work. In order to investigate this phenomena, we carried out adhesion experiments using two types of membranes, hydrophobic and hydrophilic membranes. Hydrophobic membranes exhibited ethanol-selective adsorption properties. With the results of the adhesion experiments, we rearranged the previous data and obtained the following results. In the case that the downstream (permeate side) pressure P2 was small enough and close to vacuum, PV was controlled by simple distillation. Permeate flux (JT) was proportional to (P* – P2) and α was smaller than αeq. In the case that P2 became large and was close to the saturated pressure P*, PV performance was significantly affected by the hydrophobicity of the membrane. JT was small and α became large and exceeded αeq because the contact time of solution with hydrophobic membrane became long and the concentration near the surface on the membrane increased by the selective ethanol adsorption properties on the hydrophobic membrane.
