Tungsten incorporated mobil-type eleven zeolite membranes: Facile synthesis and tuneable wettability for highly efficient separation of oil/water mixtures

Abstract

Tungsten (W) incorporated mobil-type eleven (MEL) zeolite membrane (referred to as W-MEL membrane) with high separation performance was firstly explored for the separation of oil/water mixtures under the influence of gravity. W-MEL membranes were grown on stainless steel (SS) meshes through in-situ hydrothermal growth method facilitated with (3-aminopropyl)triethoxysilane (APTES) modification of stainless steel meshes, which promote the heterogeneous nucleation and crystal growth of W-MEL zeolites onto the mesh surface. W-MEL membranes were grown on different mesh size supports to investigate the effect of mesh size on the separation performance of the membrane. The as-synthesized W-MEL membrane supported on 500 mesh (25 μm) (W-MEL-500) exhibit the hydrophilic nature with a water contact angle of 11.8˚ and delivers the best hexane/water mixture separation with a water flux and separation efficiency of 46247 L·m−2·h−1 and 99.5%, respectively. The wettability of W-MEL membranes was manipulated from hydrophilic to hydrophobic nature by chemically modifying with the fluorine-free compounds (hexadecyltrimethoxysilane (HDTMS) and dodecyltrimethoxysilane (DDTMS)) to achieve efficient oil-permselective separation of heavy oils from water. Among the hydrophobically modified W-MEL membranes, W-MEL-500-HDTMS having a water contact angle of 146.4˚ delivers the best separation performance for dichloromethane/water mixtures with a constant oil flux and separation efficiency of 61490 L·m−2·h−1 and 99.2%, respectively along with the stability tested up to 20 cycles. Both W-MEL-500-HDTMS and W-MEL-500-DDTMS membranes also exhibit similar separation performances for the separation of heavy oil from sea water along with a 20-fold lower corrosion rate in comparison with the bare stainless-steel mesh, indicating their excellent stability in seawater. Compared to the reported zeolite membranes for oil/water separation, the as-synthesized and hydrophobically modified W-MEL membranes shows competitive separation performances in terms of flux and separation efficiency, demonstrating the good potentiality for oil/water separation.