A MEMBRANE REACTOR FOR METHANOL SYNTHESIS

Methanol synthesis from CO2 and H-2 is a promising chemical energy sto rage reaction for hydrogen. The methanol yield of the synthesis is lim ited by the thermodynamic equilibrium at the temperatures required by state-of-the-art catalysts. Substantial conversion improvements would be achieved by selective product separation from the catalyst bed of a synthesis reactor. A perfluorinated cation exchange material (Nafion( R), DuPont) is evaluated for use as a vapour permeation membrane at te mperatures up to 200 degrees C. The permselectivities for methanol and water with respect to hydrogen depend on the counter ion in the polym er, and drop as a function of temperature. With respect to long term s tability and performance, lithium is best suited as a counter ion, wit h permselectivities of 32 for water, and 5.6 for methanol, respectivel y. Permeability and permselectivity are found to increase with increas ing partial pressures of both methanol and water vapours. The capabili ty of the Li-Nafion membrane to separate products from a commercially available catalyst bed operating on CO2 and H-2 at 200 degrees C is de monstrated using a simple tubular membrane reactor module.