Dehydration of acetic acid and esterification product by acid-stable ZSM-5 membrane

ZSM-5 membranes were prepared on mullite supports by a static secondary hydrothermal synthesis without applying organic structure directing agents. The ZSM-5 membrane had Si/Al ratio of 13.1 and selectively permeated water from the binary acetic acid/water mixtures and the quaternary acetic acid/ethanol/water/ethyl acetate (HAc/EtOH/H2O/AcOOEt) mixtures by pervaporation. The deviation of the dehydration performance of the membranes prepared in different batch was small, suggesting the high reproducibility of the synthesis. Part of the Na+ in the ZSM-5 membrane was replaced to H+ during the dehydration of acetic acid solution. Cation type was changed back to Na+ by immersing the membranes in 0.1 M sodium hydroxide (NaOH) or sodium chloride (NaCl) solutions. The perm-selectivity of the membranes was maintained even after applying pure HAc liquid for 77 h and applying esterification product of ethanol and acetic acid for 98 days. No change in the membrane structure was observed before and after the dehydration of acidic solutions by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis characterizations. These results confirm the high acidic stability of the membrane.

PV performance of ZSM-5 membrane for dehydration of esterification product of ethanol and acetic acid at 75 °C as a function of immersion period.Figure optionsDownload as PowerPoint slideHighlights
► Well acid-stable and reproducible ZSM-5 membranes were successfully prepared.
► Flux and αH2O/HAcαH2O/HAc were 2.21 kg m−2 h−1 and 250 at 75 °C for 50 wt.% HAc/H2O mixture.
► ZSM-5 membrane had excellent H2O perm-selectivity for HAc/EtOH/H2O/AcOOEt mixtures.
► Hydrophilicity of ZSM-5 membrane was recovered by the 0.1 M NaOH or NaCl solution.