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Published January 8, 1997 | public
Journal Article

Preparation of highly selective zeolite ZSM-5 membranes by a post-synthetic coking treatment

Abstract

Zeolite ZSM-5 membranes with high n-butane:isobutane selectivities, e.g., 322 at 185°C, are obtained by a selective deposition of coke into non-zeolitic pores. The zeolite membranes are prepared by in situ crystallization on either bare porous α-Al_2O_3 support disks or disks that are pretreated to include a diffusion barrier. The post-synthetic coking treatment is accomplished by impregnating these membranes with liquid 1,3,5-triisopropylbenzene (TIPB) for 24 h at room temperature and then calcining them in air at 500°C for 2 h. Calcination at 500°C for up to 30 h does not destroy the high n-butane:isobutane selectivity. Thermogravimetric analysis (TGA) experiments on two model pore systems ZSM-5 (5.5 Å) and Vycor glass (40–50 Å) suggest that micro-defects are selectively eliminated by the TIPB coking treatment while the intracrystalline pore space of the ZSM-5 is not affected. The elimination of non-zeolitic pores results in a large increase of n-butane:isobutane pure gas flux ratio (45 vs. 320 at 185°C) accompanied by a fourfold reduction of the n-butane flux. The permeation experiments reveal that the n-butane flux increases nonlinearly with the partial pressure in the feed while the n-butane:isobutane pure gas flux ratio remains relatively unchanged.

Additional Information

© 1997 Elsevier. Received 8 April 1996; revised 5 July 1996; accepted 5 July 1996. The authors would like to thank Christopher B. Dartt for his help with the UV diffuse reflectance measurements and Neil E Fernandes, John E. Lewis and Dr. Masahito Yoshikawa for their assistance with the TGA experiments. This research was funded by National Science Foundation Grant No. CTS-9504901.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023