Multilayer composite SBS membranes for pervaporation and gas separation

[Display omitted] ► Multilayer composite SBS-based membranes prepared as hollow fiber and flat sheet. ► Thick defect-free SBS layers via high polymer concentration in one step. ► Thin defect-free SBS layers via cyclo-hexane and supports with smaller pore size. ► SBS thickness of some tens of microns suited for pervaporation applications. ► Composite membranes with an intermediate layer scaled-up in spiral-wound modules. Composite membranes based on poly(styrene- b-butadiene- b-styrene), triblock copolymer (SBS) with 28 wt.% of styrene, were prepared by coating porous hollow fibers and flat sheet supports. The membrane preparation was optimized by modulating different experimental parameters, such as support type, SBS concentration, solvent type, coating thickness, support pre-treatment. On a laboratory scale both normal and vacuum assisted dip-coating methods were used for the hollow fiber geometry, while dope casting was adopted for flat sheet membranes. Single gas permeation measurements were carried out to determine the effective thickness of the coating layer and its integrity. This characterization, coupled with morphological analysis, allowed the optimization of the coating procedure. Appropriate coating conditions yield dense films with a good contact of the coating layer to the support. At sufficiently elevated SBS concentration, the high solution viscosity avoided the polymer infiltration into the support pores. The thickness of the SBS films, ranging from few microns to some tens of microns, meets the requirement for application in pervaporation. Therefore, pilot scale spiral-wound modules of SBS on poly(vinylidenefluoride- co-tetrafluoroethylene) (Fluoroplast-42 or F-42) supports for potential use in gas separation and pervaporation ( e.g. for ethanol/water separation) were manufactured. An intermediate silicone or poly(ether urethane urea) (PU) layer reduced the infiltration of the polymer solution, improving the adhesion between the selective and support layers and modulating the transport properties. Permeation tests evidenced a clear role of the intermediate layer in the gas transport, with highly enhanced gas selectivity in case of the PU intermediate layer.