Thin Hydrogen-Selective SAPO-34 Zeolite Membranes for Enhanced Conversion and Selectivity in Propane Dehydrogenation Membrane Reactors

We demonstrate significantly enhanced conversion and selectivity in high-temperature propane dehydrogenation (PDH) membrane reactors via the synthesis and use of small-pore SAPO-34 zeolite membranes. The reduction of SAPO-34 membrane thickness to similar to 1 mu m levels while maintaining good H-2 selectivity is challenging. Initial reductions in membrane thickness were achieved using a single structure-directing agent (SDA) and concentrated precursor solution, leading to a large permeance increase and good H-2/hydrocarbon selectivity. We further show that thinner (similar to 1 mu m) SAPO-34 membranes can be fabricated on a large area (similar to 18 cm(2)) tubular ceramic supports by the use of both base and salt forms of the SDA to independently control the SDA concentration and pH. EDX analysis and elemental mapping confirmed the formation of micrometer-thin (similar to 1 mu m) SAPO-34 zeolite membrane layers on alpha-alumina tubular supports. Micrometer-thin SAPO-34 membranes reach propylene selectivities greater than 80% as well as high propane conversions (65-75% at weight hourly space velocities of 0.1-0.5 h(-1)), because of their efficient removal of hydrogen generated in the PDH reaction.