Enhancing CO2 Hydrogenation to Methanol by Super-Hydrophobic Zeolite Membrane Reactor

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Methanol is both an important feedstock for the synthesis of commodity chemical products and is a promising energy carrier for long-term energy storage. Production of methanol by reacting carbon dioxide with hydrogen makes possible conversion of a greenhouse gas to a useful chemical product or fuel. However, this reaction has a low methanol yield limited by thermodynamic equilibrium constraints and side reactions. Progress has been made in developing hydrophilic (water attracting) membranes selective for water permeation over methanol. Their use in membrane reactors for CO2 hydrogenation to methanol has improved methanol yield through increasing CO2 conversion. However, these hydrophilic zeolite membrane reactors show a maximum methanol yield of 50% due to the limit in the improvement of either reaction selectivity or conversion. This project is focused on studying a new hydrophobic (water repellent) membrane reactor for conversion of CO2 to methanol, with simultaneous removal of methanol instead of water from the chemical reactor. This new membrane reactor is designed to produce high purity methanol directly from the reactor with significantly improved CO2 conversion and methanol selectivity. The project will lead to an improved understanding of vapor/gas separation properties for hydrophobic zeolite membranes and how to operate the new membrane reactor for maximized CO2 conversion. The membrane reactor will enable efficient synthesis of methanol, an important chemical feedstock and promising energy carrier critical to chemical production and energy storage. The project will provide valuable training experiences for a diverse group of graduate students, produce important scientific findings to be disseminated through publications and conference presentations, and narrow the public’s knowledge gaps about chemical engineering, membrane science and sustainability through a new internet-based outreach activity.Production of methanol by CO2 hydrogenation would make possible the conversion of a greenhouse gas to a useful chemical or storable fuel. However, this reaction, with current reactor and catalyst designs, has a low methanol yield and selectivity that are limited by a combination of thermodynamic equilibrium constraints and undesired side reactions. This project is focused on studying a hydrophobic zeolite membrane reactor for CO2 hydrogenation to methanol with in-situ removal of methanol from the reaction zone. Such a new membrane reactor is expected to produce high purity methanol directly from the reactor with significantly improved CO2 conversion and methanol selectivity. The objectives of this project are to understand methanol-containing vapor/gas separation properties of the super-hydrophobic zeolite membranes and to optimize design of the new zeolite membrane reactor and its operation conditions that maximize methanol selectivity and yield of CO2 hydrogenation reactions. This project is directed towards (1) synthesis and characterization of super-hydrophobic, high crystallinity, aluminum-free MFI-type zeolite membranes on zirconia supports, (2) an experimental and modeling study of permeation and separation properties of vapor/gas mixtures of methanol, water vapor, CO2, CO and H2 for the super-hydrophobic membranes at conditions relevant to membrane reactor applications, (3) modeling analysis of a hydrophobic zeolite membrane reactor for CO2 hydrogenation to methanol, and (4) experimental verification and optimization of the methanol-selective zeolite membrane reactor for high-yield and high selectivity synthesis of methanol from CO2 and H2. These proposed research activities will improve the understanding of design, synthesis, and operation of the new super-hydrophobic, alcohol-selective zeolite membranes and membrane reactor to enhance both the conversion and selectivity for chemical reactions of low product yield limited by the equilibrium conversion and side reactions. The project will advance new technologies that impact chemical processing energy and environmental sustainability, will provide a valuable training experience for graduate students, and improve public’s knowledge about chemical engineering, membrane science and sustainability.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.