Large pore zeolitic imidazolate frameworks for energy-efficient separation of hydrocarbons

Abstract

Metal organic frameworks (MOFs) are ultra-microporous crystalline materials with pore tunability and structural versatility. Due to their partial organic nature, metal organic frameworks are preferred fillers in fabricating the mixed matrix membranes (MMMs) without interfacial voids. Among various MOF families, zeolitic imidazolate frameworks (ZIFs) have gained recent interest due to its stability under humid conditions and superior molecular sieving properties. Up to date, ZIF structures with small pore aperture (typically, < 0.45nm) have been largely reported and promising separation performances in natural gas processing and light hydrocarbon processing are investigated. Recently, ZIFs with extra-large pore dimensions (with aperture size > 0.45nm) with 8, 12 and 14-membered ring structure have been reported ㅡ these large pore apertures are extremely useful in the separation of hydrocarbon molecules with a kinetic diameter larger than 0.45nm. In this study, energy-efficient separation of light-to-heavy hydrocarbons (C4+) will be demonstrated using ZIFs with extra-large pores. Vapor sorption isotherm and kinetic uptakes of the hydrocarbon molecules for large pore ZIFs are thoroughly analyzed. Entropic contribution for the diffusion selectivity in ZIFs are exclusively investigated and the corresponding membrane separation performance are tested in the form of mixed matrix membrane.