MODELING OF MULTICOMPONENT PERVAPORATION FOR REMOVAL OF VOLATILE ORGANIC-COMPOUNDS FROM WATER

A resistance-in-series model was used to study the pervaporation of multiple volatile organic compounds (VOCs)-water mixtures. Permeation experiments were carried out for four membranes: poly (dimethylsiloxane) (PDMS) polyether-block-polyamides (PEBA), polyurethane (PUR) and silicone-polycarbonate copolymer (SPC) membranes. Three VOCs, i.e., toluene, 1,1,1-trichloroethane and methylene chloride were studied. Both organic and water permeabilities of the PEBA membrane for 1 VOC-water, 2 VOCs-water and 3 VOCs-water mixtures were found to be comparable with each other. Coupling effects for trace organic transfer through the membrane were not observed when the downstream pressure was close to zero. However, at high downstream pressure, if the downstream side mass transfer resistance dominated the overall mass transport, coupling effects might occur within the vapor phase. The downstream pressure effect for the PDMS membrane was determined. The experimental results were correlated very well by a simple mass transfer equation. The downstream pressure may have positive or negative effects on the separation factor, depending on the ratio of overall organic permeability over water permeability, beta(perm). The value of beta(perm) is a function of the intrinsic organic and water permeabilities, liquid boundary layer mass transfer coefficient as well as membrane thickness. The vapor phase mass transfer resistance was found to be negligible at low downstream pressure ( < 15 mmHg). It was clearly shown in this work that the resistance-in-series model could be used effectively to describe the pervaporation of dilute multiple VOCs-water mixtures through polymeric membranes.