Pervaporation of acetic acid aqueous solutions by organosilica membranes

Organosilica membranes were prepared from bis(triethoxysilyl)ethane (BTESE) by sol–gel processing and applied to the dehydration of aqueous acetic acid (AcOH) solutions in pervaporation. BTESE-derived membranes were found to show high permselectivity with excellent stability. The permeate flux for aqueous AcOH solutions (AcOH: 90 wt%, 75 °C) was 2.0–4.0 kg/(m2 h) with water selectivity of 200–500, corresponding to water permeance of (2.5–5)×10−6 mol/(m2 s Pa). Long-term stability tests in aqueous AcOH solutions revealed that BTESE membranes showed approximately unchanged flux and separation factors, confirming the excellent stability of organosilica membranes. Comparison with gas permeation properties suggests the separation mechanism is dominated by the molecular sieving effect. Concentration dependency was examined for AcOH concentrations ranging from 30 to 90 mol%. An increase in AcOH concentration decreased both water and AcOH permeance, suggesting that adsorbed AcOH on BTESE membranes reduced the effective pore sizes for permeation of the 2 molecules.