Preparation of high selectivity silicalite-1 membranes by two-step in situ hydrothermal synthesis

Abstract

High selectivity silicalite-1 membranes were synthesized on silica tubes by in situ hydrothermal synthesis. Using a two-step synthesis, a membrane with a separation factor of 99 was prepared for separating an ethanol/water mixture at 60°C. The average (n = 4) flux and separation factor of the membranes were 0.47 kg m 2 h 1 and 89, respectively. The membranes exhibited high reproducibility, and the relative standard deviation of the average (n = 4) flux and separation factor were only 5.3% and 9.2%, respectively. These results suggest that silica is a suitable support for synthesis of high-performance silicalite-1 membranes.high-selectivity, silicalite-1 membrane, hydrothermal synthesis, pervaporation, silica tube In recent years, much progress has been made in the preparation, characterization, and industrial application of zeolite membranes [1][2][3]. Zeolite membranes with excellent separation performance in a wide range of industrial processes, including gas separation, catalysis, pervaporation, and membrane reactors, have been produced [4][5][6]. Zeolite membranes can be used to separate different mixtures, and have low energy consumption and are environmentally friendly. Consequently, zeolite membranes have attracted attention in the field of separation technology [7][8][9]. In 2001, Morigami group [10] reported the first largescale pervaporation plant made of 16 NaA membrane modules, which produced 530 L/h of solvents at less than 0.2 wt% of water from 90 wt% solvent at 120°C. Compared with NaA or FAU membrane, FMI (including ZSM-5 and silicalite-1) membranes are still prepared and used within different laboratories up to now, and this may be caused by the following reasons: one is the higher preparation cost compared with NaA or FAU membranes, and another reason is that MFI membranes should be calcined in order to remove the templates, and this often results in the formation of cracks, which decreases the separation performance of the as-synthesized membranes [11]. Furthermore, the low separation performance and low reproducibility may be the main reason to limit the preparation of MFI membranes in largescale [12].An important potential application of hydrophobic silicalite-1 membranes is the separation of organic compounds, such as ethanol, 1-butanol, and other fermentation products, from fermentation broth [13,14]. In this application, silicalite-1 membranes show higher separation performance than polymer membranes [15]. Hydrophobic silicalite-1 membranes may also be used to extract small organic molecules from wastewater for recycling and to reduce environmental pollution. In order to prepare silicalite-1 membranes, in situ hydrothermal synthesis is often used to prepare silicalite-1 membranes because the conditions are simple to control. However, it is not easy to obtain high-performance membranes with this method. High-performance silicalite-1 membranes can be obtained by using the secondary growth

Surface-gel-conversion synthesis of submicron-thick MFI zeolite membranes to expedite shape-selective separation of hexane isomers

“…Among different zeolites, MFI-type (ZSM-5 and silicalite-1) zeolite is a representative in membrane application because it has 5.5 Å multidimensional pores for sieving molecules of industrial interest (i.e., H 2 /N 2 ) and tunable adsorption properties favorable in separating important petrochemical compounds (i.e., alkanes) [2,3]. Although some progress has been made to enhance membrane performances by chemical synthesis (i.e., microwave irradiation) [4] and membrane engineering (i.e., crystal orientation) [5], MFI zeolite membranes still can hardly substitute existing technologies (i.e., distillation) due to their high fabrication cost [6][7][8][9]. One feasible way to compensate the high capital investment is to increase the flux in the separation process while maintaining the selectivity [10].…”