Main > GASES > Gas Separation Membranes > Org.: USA. V. (Ceramics: H2 Sepn.) > Work Description
Authors, have been working on highly permeable and selective silica-alumina ceramic membranes for hydrogen separation. "Our permselective membranes are inorganic and therefore robust and can be used at high temperatures and pressures". "They have higher permeability than palladium, yet are composed of inexpensive materials: alumina and silica."
The membranes are prepared by chemical vapor deposition of a thin SiO2 layer on a porous alumina substrate. The support is prepared by dip-coating a commercial macroporous alumina tube with a series of boehmite (AlOOH) sols of decreasing particle sizes.
"The membranes have multilayer structures, with size-graded layers of alumina deposited on a porous support". "The topmost layer is a 2030-nm-thick layer of permselective silica. The size gradation allows the structure to be thin--less than 1 µm and defect free. The resulting silica-on-alumina composite membrane has excellent permeability for hydrogen over CO2, N2, CO, and CH4.
"The membrane does not have continuous pores, but rather consists of a network of solubility sites," he adds. "The permeation mechanism is different from all other membranes. The permeating molecules jump between adjacent solubility sites."
Author and colleagues have also studied the antagonistic effects of pressure on reaction equilibrium and permeability in membrane reactors. In these reactors, a reaction and separation are carried out simultaneously. The system they studied was the catalytic dry-reforming of methane with carbon dioxide (CH4 + CO2 s 2CO + 2H2) using an alumina-support rhodium catalyst and a silica-on-alumina composite membrane.
The group showed that as pressure increased, the enhancement of H2 and CO yields in the reactor went through a maximum and then declined. "This occurred because, although the rate of hydrogen separation increased with increasing pressure, the conversions of the reactants decreased with increasing pressure," the authors note. "Thus, the maximum was due to a trade-off between a transport property (hydrogen separation) and a thermodynamic quantity (hydrogen production), which had opposing pressure dependencies."
Work Description's products
This section has no products