Engineering Zeolitic Imidazolate Framework Materials for Acid Gas Separations

Josh A Thompson (School of Chemical & Biomolecular Engineering, Georgia Institute of Technology)

The demand for natural gas is predicted to increase significantly over the next 25 years. Classical separation techniques to purify raw natural gas (e.g., liquid absorption of acid gases such as CO2 and H2S) require large amounts of water, are energy-intensive, and are not easily adaptable for different gas streams. Microporous materials offer a unique solution for low-energy separations. These materials can often be used as adsorbents and membranes for molecular separations. Among candidate materials, metal-organic frameworks (MOFs) . materials formed using metal centers connected by organic linker molecules . show substantial promise. My work has examined several ways to engineer microporous materials for possible use as either adsorbents or membranes. Specifically, a synthetic technique has been developed to create Zeolitic Imidazolate Frameworks (ZIFs, a subclass of MOFs) with controlled compositions of different organic linker molecules in the framework. By controlling the linker composition, the structural and adsorptive properties of these materials can be tuned for different gas separations. Using nitrogen physisorption at cryogenic temperatures, control over .gating phenomena. related to structural deformation is demonstrated by tuning the linker composition. In addition, CO2 and methane adsorption measurements show interesting improvements in the adsorption performance by controlling the framework composition. Composite membranes fabricated with mixed-linker ZIF materials show enhancement in diffusion and permeation selectivity for CO2/CH4 over composite membranes containing the commercially-available ZIF-8.

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