(568a) A Simple Method for the Fabrication of b-Oriented MFI Silicalite-1 Membranes with Controlled Grain Boundary Structure

Zeolite membranes have attracted a great deal of research interest due to their ability for high resolution gas separation.1 Control of microstructure such as preferential orientation of pores, size and shape of grain boundary and membrane thickness are often desirable to improve gas separation performance of zeolite membranes.2 For instance, Lai et al.3 has demonstrated that b-oriented MFI zeolite membranes show dramatically increased membrane performance as compared to randomly-oriented or other oriented ones. Despite this promising result, the current methods still pose technological challenges to the commercial applications of zeolite membranes.4,5 These challenges include control of membrane microstructure, low reproducibility, and time-consuming and complicated synthesis steps.

In this talk, we will demonstrate a simple method, termed as microtiles and mortar method, that is commercially viable to make continuous b-oriented MFI membranes with controlled grain boundary structure. The method is a modified secondary growth method. The key feature of our method is to preserve the orientation of b-oriented seed crystals by passivating the flat crystal faces with a thin layer of sputtered gold/palladium. This thin metal layer suppresses the nucleation and growth of crystals along the out-of-plane direction while allowing the growth of crystals along the in-plane direction. In addition, the method allows us to systematically manipulate the membrane thickness by using plate-like seed crystals with different thickness along the b-axis ranging from 0.5 μm to 2.0 μm. We will also present, for the first time, the effect of the grain boundary structure on membrane performance by comparing the performance of b-oriented MFI membranes with and without removing TPA from the grain boundary. The b-oriented MFI membranes with controlled grain boundary structure are characterized by various methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence-mode laser scanning confocal microscopy (LSCM), and transmission electron microscopy (TEM). We will discuss the performance of the b-oriented MFI membranes based on the binary separation of xylene and butane isomers. Our method has great potentials to address some of the current engineering challenges for practical applications of zeolite membranes by enabling the fabrication of highly oriented zeolite membranes in a simple manner.

(1) Caro, J.; Noack, M. Microporous and Mesoporous Materials 2008, 115, 215-233.

(2) Lai, Z. P.; Tsapatsis, M.; Nicolich, J. R. Advanced Functional Materials 2004, 14, 716-729.

(3) Lai, Z. P.; Tsapatsis, M. Industrial & Engineering Chemistry Research 2004, 43, 3000-3007.

(4) Lai, Z. P.; Bonilla, G.; Diaz, I.; Nery, J. G.; Sujaoti, K.; Amat, M. A.; Kokkoli, E.; Terasaki, O.; Thompson, R. W.; Tsapatsis, M.; Vlachos, D. G. Science 2003, 300, 456-460.

(5) Wang, Z. B.; Yan, Y. S. Microporous and Mesoporous Materials 2001, 48, 229-238.