(462b) Methanol Steam Reforming in Pd-Ag Membrane Reactor

Pd membrane based reactors have the potential to generate high purity H2 in a single unit for stationary and mobile applications spanning power stations, soldier-power, and vehicles. Previous studies from our group have analyzed in some detail the use of methanol reforming in membrane reactors as a way of intensifying the reaction and separation/purification into a single unit [1,2]. In the current study methanol steam reforming was carried out in both a conventional packed bed reactor (PBR) and several packed bed membrane reactor (PBMR) configurations. Pd-Ag membranes (ca. 3 micron thickness nanopore membrane [5]) were used in the PBMR to separate the hydrogen from the reaction mixture. The catalyst used in this study was Cu/ZnO/Al2O3. Since our previous studies [3, 4] have highlighted that radial transport of hydrogen can limit the space-time yield and hydrogen utilization in the membrane reactor, the reactor diameters of the PBMRs were varied to further study this effect. The methanol conversion, volume productivity, hydrogen utilization and outlet CO/CO2 ratio for the PBR and the PBMRs were compared at different pressures and temperatures. Separate studies were carried out to investigate the effect of the reactants and products (methanol, water, CO, CO2) on the H2 flux through the Pd-Ag membrane. A 2-dimensional model was also developed to simulate the results and to elucidate the rate limiting processes. The results of these experiments and simulations were then used to develop a 3-dimensional model for multi-fiber PBMR in which various aspects of the design were explored, including spacing between the membranes.

References

1. Harold, M.P., B. Nair, and G. Kolios, ?Hydrogen Generation in a Pd Membrane Fuel Processor: Assessment of Methanol-Based Reaction Systems,? Chemical Engineering Science, 58, 2551-2571 (2003).

2. Lattner, J.R., and M.P. Harold, ?Comparison of Methanol Based Fuel Processors for PEM Fuel Cell Systems,? Appl. Catalysis B. Environmental, 56, 149-169 (2005).

3. Nair, B., and M.P. Harold, ?Experiments and Modeling of Transport in Composite Pd and Pd/Ag Coated Alumina Hollow Fibers,? J. Membrane Sci , 311, 53-67 (2008).

4. Israni, S.H., B. Nair and M. P. Harold, ?Hydrogen Generation and Purification in a Composite Pd Hollow Fiber Membrane Reactor: Experiments and Modeling,? Catalysis Today,139, 299-311 (2008).

5. Nair, B., and M.P. Harold, ?Pd Encapsulated and Nanopore Hollow Fiber Membranes: Synthesis and Permeation Studies,? J. Membrane Sci., 290, 182-195 (2007).