Permselective palladium membranes for hydrogen separation

The primary obstacles for deployment of Pd membrane devices are inadequate hydrogen flux, permselectivity, and long-term stability. This work focuses on overcoming these obstacles. Pd and Pd/Ag membranes are synthesized on the surface and within the pores of gamma-Al2O3 coated alpha-Al2O3 hollow fibers.; A comprehensive study was carried out involving electroless plating (ELP) synthesis and permeation characterization of a series of Pd and Pd/Ag membranes on alpha-Al2O3 hollow fibers. A multi-fiber ELP apparatus with film thickness monitoring enabled Pd and Ag deposition rates to be measured in real time. The membrane synthesized and tested includes Pd (13 mum)/alpha-Al 2O3, Pd/(12 wt.%) Ag (11 mum)/alpha-Al2O 3, and Pd (5 mum)/gamma-Al2O3/alpha-Al 2O3. The H2 fluxes vary from 0.05 to 0.65 mol/m 2s and separation factors ranging from 10,000 to 200.; Novel supported Pd membranes are developed for high temperature H 2 separation. Sequential combinations of boehmite sol slip casting and film coating, and electroless plating (ELP) steps are designed to synthesize "Pd encapsulated" and "Pd nanopore" membranes supported on alpha-Al 2O3 hollow fibers. The fresh encapsulated membrane exhibited very good performance with ideal H2/N2 separation factors of 3000-8000 and H2 flux ∼0.4 mol/m2s at 370°C. The fresh Pd nanopore membranes (2.6 and 0.6mum) had a lower initial flux (0.1-0.25 mol/m2s) and permselectivity (500-50), but exhibited superior performance with extended use (200 hours). Nanopore membranes stabilized after 40 hours of operation, in contrast to a continued deterioration of the permselectivity for the other membranes.; Concentration polarization inherent to a membrane separator system is shown to limit the hydrogen flux in binary mixture separations and is analyzed in detail. Permeation models accounting for transverse gas phase transport resistance are developed and used to elucidate the mixture permeation behavior. The model predictions predict key experimental trends.; A single fiber packed bed membrane reactor was fabricated to evaluate the Pd membrane during coupled hydrogen generation and purification using the catalytic ammonia decomposition. The in-situ removal of H2 helps in obtaining higher ammonia conversions when compared the conventional packed bed reactor operated at similar conditions especially at lower temperatures and membrane reactor operation revealed modest volumetric permeate hydrogen productivities.