Ultraviolet Activation of Small-Pore Zeolite Disk and Hollow Fiber Membranes for Gas Separation

Zeolite membranes synthesized using organic structure-directing agents (SDAs) require an activation step to remove SDA and obtain the desired permeation properties. Activation is typically done by high-temperature calcination. In many cases this process creates thermally-induced mechanical strains leading to crack or defect formation and results poor selectivity. UV irradiation has been previously shown to oxidize and remove organic SDAs from mesoporous and medium/large-pore microporous materials at near-ambient conditions. However, the applicability of UV-irradiation for activating small-pore (< 0.4 nm) zeolite materials and membranes has remained unknown and has not been studied systematically. In this talk, we discuss in detail the effectiveness of UV irradiation for the activation of chabazite (specifically SSZ-13) zeolite membranes with a pore size of 0.38 nm. Using a UV lamp of fixed intensity, we study the evolution of gas permeation properties as a function of exposure duration, and also comparatively characterize the microstructure of membranes activated by UV and calcination methods. We shows that UV-activated disk membranes show distinctly favorable performance over calcined membranes. We then synthesized SSZ-13 ceramic hollow fiber membranes, which have the advantage of high packing density and reduced module cost. Upon UV activation using protocols developed for the disk membranes, high-quality gas separation characteristics are obtained. These properties are described in detail for a series of small-molecule gases. A more detailed study of CO₂/CH₄ mixture separation is also described to demonstrate practical separation capability.