A masking technique for high quality MFI membranes

A procedure for the preparation of high quality zeolite membranes was developed. This procedure relies on a masking approach that fills all support pores with wax while leaving the top surface free for deposition of the zeolite film, thus, protecting the support from the synthesis mixture. Zeolite films of different thickness were grown on masked and non-masked supports using a seeded growth method. The zeolite-coated supports were calcined in order to remove the wax from the support and the template molecules from the zeolite. The membranes were characterized by SEM, XRD, single gas and multi-component permeation measurements. Support masking reduces the zeolite membrane thickness and the width of the cracks in the zeolite film. Thicker films, especially those prepared without masking, are defective. Masked membranes with a film thickness of 500 nm show no cracks or pinholes. These membranes have a H-2 permeance of 220 x 10(-7) mol/(s m(2) Pa), an n-butane permeance of 9.8 x 10(-7) mol/(s m(2) Pa) and an n-butane/iso-butane separation factor of 9.0 at 25 degreesC. The separation factor for a mixture of n-hex ane/2,2 -dimethyl-butane was 227 at 400 degreesC and the n-hexane permeance was 5.6 x 10(-7) mol/(s m(2) Pa). The p-xylene permeance was 2.7 x 10(-7) mol/(s m(2) Pa) and the para/ortho separation factor was 17 at 400 degreesC for a mixture of xylenes. (C) 2003 Elsevier B.V. All rights reserved.