Effects of Silica-Particle Coating on a Silica Support for the Fabrication of High-Performance Silicalite-1 Membranes by Gel-Free Steam-Assisted Conversion

Abstract

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste.

Hydrophobic *BEA-Type Zeolite Membranes on Tubular Silica Supports for Alcohol/Water Separation by Pervaporation

“…The hydrophobic *BEA membrane proved to be selective to ethanol and butanol in the separation in each case of the aqueous solution by PV and to have a high flux. However, for ethanol/water separation, the separation factor of ethanol was lower than that previously reported for silicalite-1 membranes [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. In general, in the case of ethanol/water separation using silicalite-1 membranes, ethanol molecules (0.43 nm) are preferentially adsorbed on the MFI-type zeolite pores (approximately 0.55 nm), thus blocking the zeolite channels.…”

“…Zeolite is a crystalline aluminosilicate, which has unique molecular-sized pores, and its adsorption characteristics (hydrophilic/hydrophobic) can be controlled by the ratio of Si and Al constituting its framework. In particular, membranes made from silicalite-1, which is a pure-silica MFI-type zeolite, exhibit high hydrophobicity, and thus are widely studied as hydrophobic separation membranes for organic matter recovery from dilute solutions, especially ethanol/water mixtures [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. However, for industrial applications, it is necessary to prepare a membrane with sufficient selectivity and high permeability.…”

“…For preparation of pure-silica *BEA membranes, a novel tubular silica support composed of pure silica was used to prevent the incorporation of Al from the support. The use of a silica support can be expected to produce a high-quality pure silica *BEA membrane because there is no influence of thermal strain between the support and the zeolite membrane layer, and there is no change in the membrane characteristics due to Al component elution from the support [15,16,17]. In this study, pure-silica *BEA membranes were prepared using the hydrothermal synthesis method, and the effects of the synthesis conditions, such as the H 2 O/SiO 2 and NH 4 F/SiO 2 ratios in the synthetic gel, on the membrane formation process were investigated.…”

Formation Process of Columnar Grown (101)-Oriented Silicalite-1 Membrane and Its Separation Property for Xylene Isomer

“…As these pore sizes are close to sizes of middle hydrocarbons, an MFI-type zeolite membrane is anticipated to separate these mixtures by the molecular sieving effect. Therefore, much research on the separation of ethanol/water [14], butane isomer [6], hexane isomer [6,7], and xylene isomer [6,[8][9][10][11] with MFI-type zeolite membranes have been reported. Xylene isomer separation is particularly important, however a difficult target of the MFI-type zeolite.…”

Contribution of Pore-Connectivity to Permeation Performance of Silicalite-1 Membrane; Part I, Pore Volume and Effective Pore Size

“…MFI-type zeolite membranes were studied previously for the separation of C 4 -C 8 hydrocarbons, such as butane isomers, hexane isomers and xylene isomers [4][5][6][7][8][9][10][11][12][13]. In addition, alcohol recovery from an aqueous solution was also carried out by using an MFI-type zeolite membrane [14,15]. Although some membranes have exhibited excellent separation performance, the flux is still too low to make them practical.…”