Separation of volatile organic compounds (BTEX) from aqueous solutions by a composite organophilic hollow fiber membrane-based pervaporation process

A new composite hollow fiber membrane module, employing hydrophobic microporous polypropylene hollow fibers, having a thin layer of cross-linkable vinyl-terminated silicone rubber, polydimethylsiloxane (PDMS) coated on the inside diameter has been developed. A perfect-coated pin-hole or leak free module has been achieved in this process. The separation of mixture of benzene, toluene, ethyl benzene and xylene (BTEX) (representative of an industrially significant family of aromatic hydrocarbon chemicals produced from industrial wastes) from water using the newly developed composite membrane was investigated. In this study, the permeation process employed bore-side feed flow. The influence of feed-solution velocity, permeate pressure, temperature, feed concentration and membrane thickness (based on wt% of PDMS in coating solution) on the membrane separation efficiency, permeation behaviour and performance were systematically investigated. The BTEX flux was found to increase with increase in feed-solution velocity, and the performance of this membrane has been found to improve as the driving force across the membrane decreases. That is, the optimum permeate pressure is in the range 80–100 mm Hg, when the BTEX flux is still at its maximum plateau value and the water flux is small. Increasing the permeate pressure reduces the operating cost while the separation is enhanced. As expected, the permeation fluxes of both BTEX and water were found to increase with increase in temperature and feed concentration, and a plateau value was obtained for water flux with further increase in concentration and temperature. Arrhenius plot of BTEX, water and total fluxes against reciprocal of absolute temperature shows good linearity and thus indicates the results agree with the Arrhenius effect of temperature on fluxes. The overall activation energies of pervaporation were found to be 54 and 33 kJ/mol for BTEX and water permeation fluxes, respectively. The observed enrichment in BTEX increases with increasing membrane thickness.