High purity hydrogen generation using palladium-based membrane reactors

Increased concerns of greenhouse gas emissions, pollution & the future of energy supply have made the generation and purification of hydrogen an extremely important research area especially for portable power and on-board vehicular applications. Pd and some Pd-alloys (Pd-Ag, Pd-Cu. Pd-Au etc.) selectively permeate hydrogen while blocking the trans-membrane transport of all other species. This property is exploited in a membrane reactor to generate high purity hydrogen which can be directly fed to a fuel cell. A membrane reactor is essentially the combination of a reactor for hydrogen generation (e.g., reformer) and a hydrogen separation unit.;Membrane reactor studies have been carried out using two reaction systems: ammonia decomposition and methanol steam reforming. The studies can be broken down into three major areas. In the first area the effects of the non-hydrogen reaction species on the trans-membrane hydrogen flux have been experimentally studied. A first principle model has been developed to predict the drop in this trans-membrane flux under reaction conditions. In the second part of the study the reaction systems have been studied both in packed bed reactors (PBRs) and in single-fiber packed bed membrane reactors (PBMRs) in order gain an understanding of the productivity limiting step(s) and to determine the effects of various design and operating parameters. A 2-dimensional model has been developed to predict and further clarify the performance. In the third part of the study the 2-dimensional model has been scaled up to a 3-dimensional model in order to simulate large-scale multi-fiber membrane reactors. Optimum designs have been proposed for commercial scale membrane reactors that can generate high purity hydrogen on-board a 50 kW fuel-cell vehicle.