Preparation And Pervaperation Performance Evaluation Of The Fumed-silica-filled PDMS-PA Composite Membrane

As a novel separation technology for liquid mixtures, pervaperation greatly depends upon the corresponding membrane. Silicon rubber (Polydimethysilicone PDMS) membrane is a promising pervaporation membrane on removing lesser volatile organic compounds from Organic/Water mixture, and thus has a prominent applicable prospect. Howerver, pervaporation properties of PDMS membrane, such as permeate flux and selectivity can not still satisfy requirements of practical applications. In order to enhance its pervaporation performances, researchers has been developing several methods to modify PDMS membrane, such as filling, grafting, copolymerization, blend, organofunctionalising and so on. Filling inorganic nano-particles into a polymer membrane has been a simple and effective physical method to elevate performances of the membrane.In this study, PDMS-PA composite membrane was prepared by polycondensation of a PDMS base polymer, using a microporous PA membrane as the supporting layer. Fumed-Silica-filled PDMS-PA composite membranes with fumed silica content of 5%, 10%, 15% and 20% were prepared by introducing the hydrophobic fumed nano-silica into PDMS skin layer. Meanwhile, the PDMS-PA composite membrane filled with modified fumed silica by silane coupling agent was prepared. The cross-section morphology of these composite membranes was observed by scanning electron microscope (SEM). Their pervaporation performances were tested with aqueous ethanol solution at 30℃, 35℃and 40℃.It could be seen from the SEM pictures that, PDMS intruded lightly into the pores and got a good adhesion with the porous support layer. In filled mutilayer composite membranes, the fumed silica particles were deposited on near interface of PDMS skin layer and porous support layer, and the aggregate size was around 100nm, the cohesion of PDMS skin layer and PA support layer was not so good. For the modified-fumed-silica-filled composite membrane with silane coupling agent, the skin had a firm cohesion with the support layer, which was much better than that of filled membranes without silane coupling agent. It was found from pervaporation tests that increasing amount of the fumed silica resulted in significant elevating fluxes and slightly droping selectivity for the membrane. When the content of the fumed silica in PDMS skin layer was 20%, for 5% ethanol-water mixture at 40℃, the flux reached 2400 g·m-2·h-1 and was twice of that of the unfilled PDMS-PA composite membrane, while the selectivity was 7, contrasting to 8.5 of the unfilled PDMS-PA composite membrane. At the same time, the filled membrane behaved as the unfilled membrane, when the feed temperature and concentration were changing. With the increase of feed temperature, the fluxes of filled membranes increased, while the separation factors decreased slightly. The decreasing of the ethanol concentration of feed resulted decreasing fluxes and slightly enhanced selectivities of filled membranes. Both of the flux and selectivity of the filled membrane with modification of silane coupling agent decreased.