An Innovative, Unorthodox, and General Strategy for the Synthesis of Zeolitic-Imidazolate Framework (ZIF) Membranes for Olefin/Paraffin Separations

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1132157JeongThe goal of the proposed work is to develop an innovative, unorthodox, and general strategy to synthesize metal-organic framework (specifically zeolitic-imidazolate framework) membranes in a commercially viable manner for high resolution separations of olefin/paraffin mixtures such as propene/propane and ethene/ethane. 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 Å), their unique thermal/chemical stabilities, and their unparalleled framework flexibilities. For example, in ZIFs, the fundamental separation mechanism based on the differences in the solubilities and the diffusivities of gases can be controlled due to a so called gate-opening effect (more broadly known as a breathing effect) in which the adsorption and diffusion of specific molecules can be regulated by threshold pressures (i.e., flexible frameworks). Since these threshold pressures vary for different gas molecules, ZIFs possess tremendous flexibility for separation applications. 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. Additionally, zeolite membranes of different topology are often synthesized by trial-and-error approaches and reproducibility is still a major problem. 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. Many researchers working on MOF membranes come from a zeolite membrane background and thus try to apply the same techniques and experiences that they have used in the past. In contrast, the PI proposes to take a unique perspective on the synthesis of ZIF membranes that breaks away from conventional thought. The key hypothesis is that a radically different transformative approach to synthesizing MOF membranes can be developed due to the fact that the chemistry of these materials are fundamentally different from zeolite chemistry. The proposed work will be built upon the rapid thermal deposition (RTD) technique developed in the PI's group. The proposed plan has three main objectives: 1) development of an innovative, unorthodox, and general synthesis strategy based on the RTD technique, 2) characterization and control of ZIF membrane microstructure, and 3) testing of membrane performance. The innovative strategy proposed here will be applicable for the large-scale synthesis of any MOF membrane in an unprecedented manner, thereby potentially rendering their practical applications a reality. This work will enable the PI to determine if a transformative synthesis strategy based on rapid thermal deposition can be successfully developed for ZIF membranes. The proposed fundamental research will lead to a set of design rules for the rapid synthesis of any ZIF membrane with a unique microstructure. ZIF membrane microstructures (in particular, grain boundary defects) will be characterized for the first time and then controlled to maximize separation performance. The effects of the ZIFs' framework flexibility on the pore and grain boundary structures will be determined which will in turn determine the performance of the ZIF membranes. The development of membranes capable of performing olefin/paraffin separations will lead to a technology that consumes less energy than the current practice of distillation, thereby leaving a much smaller carbon footprint. While the focus of this work is olefin/paraffin separations, the materials and their membranes investigated here will be relevant to other difficult separations facing the chemical and petrochemical industries. The interdisciplinary nature of the work, spanning material design and synthesis, characterization, and membrane fabrication and testing, will lead to a truly multidisciplinary research experience for the students (one graduate and one REU undergraduate) involved. The educational outreach activity development of science videos based on the proposed research will positively impact K-12 education by increasing public interest in science and engineering.