Microstructural Control to Achieve High Performance MFI Type Zeolite Inorganic Membranes

Dr. Jungkyu Choi
University of California, Berkeley
Department of Chemical Engineering

ABSTRACT
It has been addressed that a robust, reliable fabrication of defect-free zeolite membranes are critical to contribute considerably to energy-saving in separation processes as alternative to conventional cost-intensive counterparts (distillation, crystallization, etc.). Therefore, much research has been focused on the field of zeolite membranes with respect to control of pore orientation and film thickness on diverse supports. We developed a reliable methodology, i.e., so called secondary growth, which leads to achieving preferentially out-of-plane oriented zeolite films reproducibly, in contrast with other approaches that often fail. In the first part of this presentation, I will demonstrate the robust protocol to synthesize uniformly a-oriented MFI films: an a-oriented seed layer was achieved and the subsequent hydrothermal growth of the seed layer led to the uniformly a-out-of-plane oriented MFI film.

The performance of a-oriented MFI films, however, was very poor unlike our expectation. This could be attributed to the presence of non-zeolitic parts that are known to be detrimental to membrane performance. In spite of many researchers’ substantial efforts to avoid them, the inevitable defect formation and accordingly poor separation performance led us to explore a totally different approach deviating from a general belief that the slow heating rate would avoid defect formation. In the second part, I will introduce a simple but surprisingly effective way to eliminate or at least reduce the non-zeolitic parts, especially grain boundary defects, by a using rapid thermal processing (RTP) on as-synthesized c-oriented MFI films. The separation performance of such membranes were significantly improved for both aromatics (~ 120 p-/o-xylene separation factor) and linear/branched alkanes (~ 34 n-/i-butane separation factor), as compared to that of conventionally calcined ones. This was attributed to the lessened density of grain boundary defects between MFI polycrystalline grains as evidenced in Fluorescence Confocal Optical Microscopy (FCOM) images, though other microstructural characteristics were virtually identical to conventionally calcined films. The RTP strategy was further successfully applied to c-oriented MFI membranes made on industrially desirable stainless steel tubes leading to unprecedented separation performance (~ 28 p-/o-xylene separation factor).

BIO
Dr. Jungkyu Choi received a B.S. degree in Chemical Engineering from Seoul National Universityin 2003 and a Ph.D. from the University of Minnesota in 2008. His dissertation addressed the synthesis, characterization, and application of zeolite membranes in the group of Professor Michael Tsapatsis. Dr. Choi has been a postdoctoral fellow in the Iglesia group at the University of California, Berkeley since 2008, where he is developing frequency modulation flow protocols to measure the dynamics of diffusion, adsorption, and chemical reactions within microporous solids.