Design and Optimization of Highly Productive Zeolitic Imidazolate Framework, ZIF-8, Membranes For Industrial Propylene/Propane Separations
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The goal of the proposed work is to design and optimize zeolitic-imidazolate framework ZIF-8 membranes with high productivity for industrial olefin/paraffin separations (in particular propylene/propane separations). Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs), offer unique opportunities in gas separations due to their ultra-micropores (pores smaller than 5 Ã ), unique thermal/chemical stabilities, and unparalleled framework flexibilities. Of particular interest is ZIF-8, composed of Zn and 2-methylimidazole ligands, forming the sodalite (SOD) zeolite structure with effective pore size in the range of 4.0 - 4.2 Ã . This suggests that high-quality ZIF-8 membranes could effectively distinguish propylene from propane based on size. However, many of the fundamental challenges hindering zeolite membranes from being more widely used in commercial applications still remain for ZIF membranes. These challenges include slow batch crystallization, grain boundary defects, and expensive porous supports. A fundamentally different strategy needs to be developed in order to fully harvest the potential of this emerging class of nanoporous framework materials for membrane-based gas separations. One such technology that the LPI's group has been developing is a one-step in situ synthesis technique based on the concept of counter diffusion. This simple yet highly versatile method enabled the rapid preparation of well-intergrown high-quality ZIF-8 membranes showing outstanding separation performance of a propylene/propane mixture (propylene permeance ~ 80 GPU (1 GPU = 3.348Ã 10-16 molï m/m2/s/Pa) and selectivity ~ 55).........