Preparation of heteroatom isomorphously substituted MEL zeolite membranes for pervaporation separation of dimethylformamide/water mixtures

摘要

The recovery of dimethylformamide (DMF) by pervaporation is less energy intensive and more economical than the traditional distillation method. High/pure silica zeolite is a typical organics perm-selective material for pervaporation membrane due to its hydrophobic nature, demonstrating great potential for recovering organic components from aqueous solutions. In this study, as an attempt to further enhance the membrane hydrophobicity, titanium and zirconium-substituted MEL type zeolite membranes (Ti-silicalite-2 and Zr-silicalite-2) were synthesized on the alpha-Al2O3 discs by a secondary growth method. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results confirmed the isomorphous substitution of the MEL framework by Ti and Zr atoms. The effects of isomorphous substitution, feed temperature and concentration on the DMF recovery performance were investigated via systematically designed pervaporation experiments. The fluxes and separation factors both increased with the isomorphous substitution of heteroatom, as well as increasing feed temperature and decreasing feed concentration. The Ti-silicalite-2 membrane exhibited a high separation factor of 6.4 with a total flux of 0.98 kg center dot m(-2)center dot h(-1) for a 5 wt% DMF/water feed at 343 K.