Enhancing Pervaporation Performance for Alcohol Recovery from Aqueous Solutions with Silicalite-1/Polydimethyldiethoxysilane (PDMDES) Nanocomposite Membranes

This study presented a newly prepared silicalite-1/polydimethyldiethoxysilane (PDMDES) nanocomposite membrane through the incorporation of nanosized silicalite-1 particles to enhance the pervaporation performance for alcohol recovery from aqueous solutions. Preheating was strategically employed to facilitate the formation of chemical bonds between silicalite-1 and the cross-linking agent vinyltriethoxysilane (VTES), thereby improving the compatibility between silicalite-1 and the PDMDES polymer. Comprehensive characterizations including FT-IR, XRD, TGA, and CA demonstrated a notable increase in hydrophobicity and thermal stability, attributable to the well-incorporated silicalite-1 nanoparticles. FE-SEM observation revealed two distinct cross-sectional morphologies of the nanocomposite membrane: a dense packed structure with uniformly dispersed silicalite-1 nanoparticles within the PDMDES polymer matrix and a loosely accumulated structure where silicalite-1 was adhered by the PDMDES polymer. This phenomenon was linked to the low viscosity of PDMDES during the membrane preparation, which also resulted in the actual loading of silicalite-1 in the prepared nanocomposite membranes being higher than the intended one. The separation performance, influenced by silicalite-1 loading, operating temperature, and feed concentration, was thoroughly evaluated. Accordingly, the separation factor was enhanced by 90% compared to pure PDMDES membrane, and the optimal pervaporation performance was achieved with a 10 wt % silicalite-1 loading in the nanocomposite membrane, manifesting a high total flux of 5.72 kg m^-2 h^-1, a PSI of 31.36 kg m^-2 h^-1, and an ethanol permeability of 184.3 × 10^-6 mol m^-1 h^-1 kPa^-1, when separating ethanol from 5 wt % ethanol/water solution at 40 °C. Based on the experimental findings, lower feed concentration and operating temperature were suggested in the applications of the silicalite-1/PDMDES nanocomposite membranes for efficient alcohol recovery from aqueous solution.