Sabina K. Gade

Dense Carbide/Metal Composite Membranes for Hydrogen Separations Without Platinum Group Metals

This creates the need for cost-effective separation processes to purify hydrogen from these components as well as other contaminants. Hydrogen-selective membranes are of particular interest for this purpose, as they are energy–effi cient and allow for co-production of hydrogen while maintaining a CO 2 -rich retentate at high pressure for capture or use. Additionally, if a hydrogen-selective membrane is incorporated into a reforming or shift reactor, the removal of products can drive reactions (1–3) toward complete conversion. A number of materials are available that selectively transport hydrogen. [ 2–4 ] Among the options, polymers are eliminated by temperature constraints, while microporous ceramic systems are limited with regard to selectivity. An appealing option is dense metal fi lms from groups III–V of the periodic table, which transport hydrogen via a solution-diffusion mechanism. In this mechanism, hydrogen is dissociatively adsorbed onto the membrane feed surface and dissolved into the bulk. The dissociated hydrogen is then transported by site-hopping diffusion and recombined on the low-pressure membrane permeate surface. [ 5 ] As only hydrogen can be transported in this fashion, pinhole-free fi lms of these metals will therefore have theoretically infi nite selectivity. At present, palladium and its alloys dominate research and industrial practice in this class of materials due to their ability to both dissociate hydrogen and display high permeability

Palladium-Copper and Palladium-Gold Alloy Composite Membranes for Hydrogen Separations

Electroless plating was used to fabricate PdCu and PdAu alloy composite membranes using tubular Al2O3 and stainless steel microfilters to produce high temperature H2 separation membranes. The composite membranes were annealed and tested at temperatures ranging from 350 to 400°C, at high feed pressures (≤250 psig) using pure gases and gas mixtures containing H2, carbon monoxide (CO), carbon dioxide (CO2), H2O and H2S, to determine the effects these parameters had on the H2 permeation rate, selectivity and recovery.