Gas permeation properties of MFI zeolite membranes prepared by the secondary growth of colloidal silicalite and application to the methylation of toluene

MFI zeolite membranes were prepared by secondary growth on alpha-alumina microfiltration membranes. Colloidal silicalite, the size of which was approximate to100 nm, was used as seed crystals. An MFI membrane, in which the zeolite layer was oriented to the (10 1) plane, showed a n-C4H10, permeance of 1.5 x 10(-5) m(3)(STP)m(-2)s(-1)kPa(-1) and a n-li-C4H10 selectivity of 15 at 150 degreesC. N-2 permeated faster than He at temperatures lower than 150 degreesC, probably because of surface diffusion of the adsorbed N-2 in the Henry regime. After ion-exchanging the MFI zeolite membranes from the Na-type to the H-type, the alkylation of toluene with methanol was carried out. A maximal p-xylene selectivity of 80% was achieved using the H-MFI zeolite membranes at 450-500 degreesC. (C) 2002 Elsevier Science Inc. All rights reserved.