Ethanol separation from ethanol aqueous solution by pervaporation using hydrophobic mesoporous silica membranes

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Pervaporation of ethanol from ethanol/water mixture solution using surface-modified mesoporous silica membranes has been carried out. The mesoporous silica layers were prepared on commercially available porous alumina tubes by dip-coating in a series of silica sols. Subsequently, organosilane compounds with different alkyl chain lengths [CnH2n+1(CH3)2SiCl; n = 1, 3, 8, 12, and 18] were covalently reacted to the surface of these mesoporous layers with high coverage. Surface-modified mesoporous silica membranes showed ethanol permselectivity and the total flux increased with increasing ethanol concentration in feed composition and feed temperature. Ethanol separation factors in the range from 7.90 to 8.24 and total flux of 2.76–2.89 kg·m−2·h−1 were obtained by pervaporation at 323 K and at 5 wt % ethanol feed composition using surface modified membranes. In the presence of 1 wt % acetic acid in a ternary model fermentation (5 wt % ethanol–94 wt % water–1 wt % acetic acid), separation factor and total flux were decreased, and this tendency was minimized by increasing pH above pKa⊖ (pKa⊖ = 4.74 at 298 K) and changing HOAc to OAc− ions in the feed solution.