Laminated mordenite/ZSM-5 hybrid membranes by one-step synthesis: Preparation, membrane microstructure and pervaporation performance

Laminated mordenite/ZSM-5 hybrid zeolite membranes were fabricated on seeded porous α-alumina tubes with ZSM-5 crystals by one-step hydrothermal treatment for dehydration of industrial solutions. The microstructure was clarified with observations by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD) analysis on the membranes synthesized as a function of crystallization time. The synthesized hybrid membranes were composed by two layers. The upper mordenite layer overgrew with 2 μm thick above the ZSM-5 lower layer with 3 μm thick. The formation sequence was estimated to be that (1) the ZSM-5 layer crystallized in the early stage of 4 h; (2) then the mordenite crystals nucleated and grew on the lower ZSM-5 layer; (3) elongated mordenite grains crystallized for 4–8 h to form the tightly packed layer.The potential pervaporation (PV) performance of dehydration was investigated for industrial solvents of 2-propanol (IPA) and acetic acid (AAc). In the results of PV at 75 °C for a mixture of water (50 wt.%)/IPA (50 wt.%), the membrane exhibited higher permeation flux up to 6.4 kg m−2 h−1 and separation factors (α) with 1800. In the results of PV at 80 °C for a mixture of water (50 wt.%)/AAc (50 wt.%), a higher permeation flux with 5.6 kg m−2 h−1 and a small amount of leakage of AAc with 0.68 wt.% into the permeates or the separation factor α = 150 were observed. These higher separating features in the laminated mordenite/ZSM-5 hybrid membrane could be caused by tightly assemblage of mordenite crystals that were formed uppermost layer of the membrane.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two-layer of mordenite and ZSM-5 zeolite membranes. ► One-step hydrothermal treatment was sufficient. ► Higher permeance 3.2 × 10−6 [mol m−2 s−1 Pa−1] and separation factors (α) with 1800. ► High reproducibility was confirmed in the synthesis. ► Different crystallizing mechanisms for lower ZSM-5 layer and upper mordenite layer.