DIRECT NON-OXIDATIVE METHANE CONVERSION VIA H2-PERMEABLE TUBULAR CERAMIC MEMBRANE REACTOR
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Conversion of methane to higher hydrocarbons has the potential as the substitute for liquid petroleum in petrochemical and other chemical industries. Direct non-oxidative methane conversion (DNMC) reaction has attracted much attention given its unique capability to convert methane into C2 (acetylene, ethylene, and ethane), aromatics, and hydrogen, while circumventing the intermediate energy intensive steps found in the conventional indirect “syngas” routes. In addition, DNMC has better atom efficiency compared to the indirect routes since COx products can be avoided. However, the main drawbacks of the DNMC reaction are due to the low methane equilibrium conversion, high endothermicity, and high rate of carbon formation.
This dissertation aims to development a novel catalyst/membrane system to circumvent the limitations of the DNMC reaction for the efficient and effective hydrocarbons production. The single iron sites confined in the lattice of silica matrix (Fe/SiO2) is an emerging methane activation catalyst for the DNMC reaction. By coupling the Fe/SiO2 catalyst with the H2-permeable tubular ceramic membrane reactor, part of the hydrogen produced from the DNMC reaction can be removed from the effluent gas, which shifts the equilibrium of the reaction to the product side, and in turn, increases the methane conversion. In addition, different sweep gases (H2, air, O2) can be used to promote different additional capabilities of the membrane reactors. The product distribution of the DMNC reaction can be tuned by either removing or adding H2 to the DNMC reaction. Dual production of higher hydrocarbons and CO (or syngas) from two major global greenhouse gases can be achieved when CO2 is used as the sweep gas. On one side of the membrane tube, CH4 upgrading to C2+ hydrocarbons was realized via DNMC reaction over the Fe/SiO2 catalyst, with co-production of H2 gas. On the opposite side, the hydrogen permeate reacted with CO2 sweep to form CO and H2O via the RWGS reaction. Autothermal operation of the membrane reactor is potentially feasible by providing the heat required for the endothermic DNMC reaction from the heat released from the combustion of permeated H2 when O2 is used as sweep gas. In addition, a dual DNMC reactor and H2-permeable membrane system was proposed in order to enhance the production of aromatics from CH4, with pure H2 as a beneficial byproduct. By recycling the effluent gas to the DMNC reactor after partial H2 removal, in certain conditions, the aromatics yield reached >50%, which is significantly higher than single-pass results.