In Situ Growth of Continuous b-Oriented MFI Zeolite Membranes on Porous α-Alumina Substrates Precoated with a Mesoporous Silica Sublayer

Abstract

Continuous b-oriented MFI membranes were prepared on a mesoporous silica sublayer-coated porous R-alumina substrate by in situ crystallization. Single gas permeation of butane isomers through the MFI membrane was carried out as a function of temperature from 298 to 473 K. A decreased permeance of butane isomers on the b-oriented MFI membrane with increasing temperature is observed in this temperature range, which is attributed to a weak adsorption effect. Meanwhile, it was revealed that the b-oriented membrane can maintain a high ideal selectivity of n-butane/i-butane at elevated temperatures. On the contrary, a discrete membrane with a randomly oriented top layer was obtained on the uncoated R-alumina substrate. Further investigation on the evolution of the MFI membranes on the two kind substrates was performed with the focus on the understanding of the oriented growth of zeolite crystals. The surface properties of the substrates used played an important role in the formation of MFI membranes with different morphologies. IntroductionIn the past decade, considerable research effort has been applied to the synthesis of high-performance zeolite membranes due to their great potential for application as selective membranes, catalytic membrane reactors, and chemical sensors. 1-5 Because many zeolites consist of microcrystals with an anisotropic structure, the orientation of the zeolite microcrystals can influence the membrane performance in most of these applications. 3,6-8 For the MFI (Silicalite-1 and ZSM-5) membranes, a particularly active research field mainly because of the crystal channel systems with pore diameter (about 0.55 nm) near the sizes of many industrially important organic molecules, the zeolite channel system is 2D: straight channels (b-direction) of elliptical cross section are interconnected with sinusoidal channels (a-direction) of circular cross section; the c-direction represents the tortuous path. There are mainly two approaches for the preparation of continuous, oriented, MFI zeolite membranes. One is the secondary growth technique, 7-11 and the other is the in situ

Fabrication of AC@ZSM‐5 core‐shell particles and their performance in Fischer–Tropsch synthesis

“…(B)). Unlike previously reported results, these crystallites were not embedded in a hydrogel layer which was formed with the help of leached aluminum. The crystallites on the support surface did not form at the same time because new crystallites appeared even after 2.5 h hydrothermal treatment.…”

Manufacture of b-Oriented ZSM-5/Silicalite-1 Core/Shell Structured Zeolite Catalyst

“…[23] Gora et al [20] found that the stability of the precoating silica was essential for b-oriented films formation, which supposed that the structure of silica surface might induce strong potential energy to force the silicalite-1 crystals densely packed as an oriented layer along the external surface of the core crystal.…”

Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

“…[8] Generally, b-oriented MFI zeolite films/membranes are prepared under alkaline synthesis conditions by the secondary growth method. [7,8,[17][18][19][20][21] To prevent Al leaching from the porous alumina supports,a ni ntermediate silica layer should be precoated on the support surface. [7,[19][20][21] This process is tedious and requires additional treatment steps prior to membrane synthesis.T he silica layer may also dissolve in the alkaline synthesis solution.…”