Preferential sorption with reference to preferential permeation for membrane pervaporation was investigated. It was clarified that both sorption selectivity and diffusion selectivity are important to the overall permeation selectivity. Preferential sorption affects, but does not necessarily lead to preferential permeation.

Integral asymmetric aromatic polyetherimide membranes consisting of a dense skin layer and a porous substrate were developed for isopropanol dehydration. The membranes were prepared by the phase inversion technique. At ambient temperature, a permeation flux of 2.5 mol/m².h and a separation factor of 173 were achieved for breaking the water-isopropanol azeotrope, and a larger separation factor (384) with a lower flux (0.8 mol/m².h) were obtained for dehydrating isopropanol at 0.96 mole fraction. Membranes with better performance are expected by optimizing the membrane preparation conditions. The variables involved in the procedure for the membrane preparation were studied. In particular, the three major aspects, namely, membrane casting composition, solvent evaporation and polymer precipitation with reference to membrane formation were elucidated.

A resistance model approach to the asymmetric membranes was developed to rationalize the relationship between membrane selectivity and the resistance to mass transport offered by the different component pLrts of the membrane. It was shown that the permeation selectivity achievable in an asymmetric membrane was affected not only by the relative resistance of the dense skin layer and the porous substrate, as normally considered, but also by the relative resistance of the polymer matrix and the pores in the substrate. On the basis of the resistance model, the asymmetric structures of the membranes can be differentiated quantitatively in terms of relative resistance components in the membrane.

Silicone-based membranes were studied for the removal of isopropanol from aqueous solutions. It was shown that the homogeneous polydimethylsiloxane membrane and the symmetric silicone-polycarbonate membranes were preferentially permeable to isopropanol, but the ultrathin silicone-polycarbonate membrane was slightly selective to water permeation. The latter membrane was modified by coating a thin layer of silicone material on the membrane surface, resulting in an isopropanol selective membrane. Mathematical modelling of the batch pervaporation process was pursued. Starting from material balance, the model equations were developed and the applicability of the equations was examined with experimental data. For a given separation task, the product concentration and product recovery as well as membrane area and batch time required to achieve the separation can be predicted. This model provides a theoretical basis for the design of batch pervaporation systems.

The build-up of permeate pressure in hollow fiber membranes during pervaporation was studied. Silicone rubber hollow fiber membranes were used. It was found that the local permeation flux through the membrane decreased with an in crease in the permeate pressure, and the pressure dependence of permeation flux could be described by a parabolic and a linear equation. The differential form of Hagen-Poisseuille equation was shown to be adequate to describe the flow of permeate vapour in the fiber. It was shown that the permeate pressure build-up in a fiber reduced the permeate productivity of the fiber, and the fiber dimensions needed to be optimized in order for a hollow fiber membrane module to achieve maximum permeate productivity.

A novel approach to concentration polarization in pervaporation separation processes was established on the basis of the "film theory", and the validity of the approach was testified with experimental data. By using this approach, the concentration polarization index can be related quantitatively to membrane permeability, hydrodynamic conditions of feed flow as well as membrane selectivity. It was elaborated that concentration polarization was not necessarily more severe in the pervaporation of dilute solutions, while at considerably high feed concentrations concentration polarization was unlikely to pose a severe problem.