An Extrinsic-Pore-Containing Molecular Sieve Film: A Robust, High-Throughput Membrane Filter

Abstract

MFI type zeolites with 10-membered-ring pores (ca. 0.55 nm) have the ability to separate p-xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non-zeolitic micropores (ca. 0.6-1.5 nm) and mesopores (ca. 2-7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non-zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p-xylene perm-selectivity and molar flux. Specifically, compared to a conventional, crack network-containing MFI membranes of similar thickness (ca. 1 mu m), the mesoporous MFI membranes showed almost double p-xylene permeance (ca. 1.6 +/- 0.4x10(-7) mol m(-2) s(-1) Pa-1) and a high p-/o-xylene separation factor (ca. 53.8 +/- 7.3 vs. 3.5 +/- 0.5 in the conventional MFI membrane) at 225 degrees C. The embedded non-zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation.