Propylene-Permeable Catalytic Carbon Molecular Sieve (CMS) Membrane Reactors for Low Temperature Propane Dehydrogenation

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Propylene is a starting material for many commercial products and is often derived from petroleum cracking biproducts. However, the current supply of biproducts is not expected to keep pace with growing demand. An alternative route to intentional propylene synthesis starts with propane, now available from low-cost natural gas. However, transforming propane to propylene, using a process called dehydrogenation, requires high temperatures to obtain even low yields of 30-50%. In this project, the investigators aim to develop improved catalysts and separation membranes to produce propylene at lower temperatures and higher yields. These lower temperatures have the additional advantage of reducing unwanted side-products, such as coke, during the reaction. The investigators plan to accomplish these aims by optimizing the catalysts structure for low-temperature operation and optimizing the pore size in the separation material to remove the product, propylene, from the starting material, propane. This separation strategy has the added benefit of driving the reaction to continue to produce propylene. The fundamental concepts and technologies obtained from this project will open new avenues of material discovery and technique development that can transform natural gas into value-added chemicals.This proposal aims to improve propylene yield from propane dehydrogenation (PDH) reactions by reducing membrane deactivation due to coke formation at high reaction temperature. The PIs hypothesize that controlling the structure and activity of Pt-Cu/zeolite dehydrogenation catalysts will result in low temperature propane activation and thermodynamically suppress side reactions and coke formation. To test this hypothesis the investigators will synthesize Pt-Cu/zeolite catalysts with varying synthesis parameters in order to control catalyst composition and properties. The catalysts will be tested using a fixed-bed microreactor system and reactor effluents will be characterized using concurrent gas chromatographic and mass spectrometric analysis. In a second aim, novel polyamide-derived carbon molecular sieve (CMS) membranes with highly-rigid pore structure will be created to provide attractive propane/propylene separation performance at 350-450 degrees C. The permeability and selectivity of these membranes will be evaluated by studying the high-temperature C3H6/C3H8 adsorption kinetics and isotherms using thermogravimetric analysis. The Pt-Cu/zeolite catalysts and (CMS) membranes will be evaluated together to demonstrate cooperative catalysis-transport in a membrane reactor. The outcome of the proposed activities will be fundamental understanding of (i) the structure-property relationships between carbon molecular sieve and entropic diffusion selectivity under PDH conditions, (ii) effects of single-atom metal alloy catalysts on low temperature C3H8 activation, (iii) kinetic effects of propylene and/or H2 concentration on propane activation and coking, and (iv) cooperative catalysis-transport in PDH reactors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.