Water Gas Shift Reaction And Gaseous Mixture Separation Process In Pd Composite Membrane Reactor

The production of hydrogen from foil fuel is regard as the desired fueling way for proton exchange membrane fuel cells (PEMFC). And how to remove the by-product of CO, being the poison for the Pt-anode catalyst of PEMFC, has received much attention. In this work, Pd/ceramic hollow fiber (HF) composite membrane, with high separation area to volume ratio, was firstly attempted in reaction in the world. The reactor combined the conventional fixed-bed water gas shift reaction (WGSR) with the hydrogen permeable membrane in one unit. Thus, it is possible to reduce the cost for separation and simultaneously, to simplify the technique and to save the space for the FC equipment. The WGSR in a Pd/ceramic HF composite membrane was investigated primarily. From the investigation, it was found that the CO conversion of the membrane reactor can be not only higher than that of fixed-bed reactor, but than the corresponding equilibrium conversion value as well.On the other hand, the decomposition of ammonia in Pd membrane reactor is receiving much attention because it can directly by one step afford highly pure hydrogen for PEMFC. The separation of the products of ammonia decomposition, H₂/N₂ mixture, by Pd membrane is the key step for the decomposition of ammonia to supply hydrogen, which is sure to be complex and interesting for investigation. Firstly in the work, thin fresh Pd/ceramic HF membranes were analyzed regardinghydrogen permeation behavior under gaseous mixture conditions with H₂/N₂ for different operating conditions referring to both experimental data and simulation studies. The good agreement between simulated data and experimental results showed definitively the applicability of the model to describe the transport process in a broad parameter range. And these results proved that the co-existence of nitrogen within certain time with hydrogen has no effect on hydrogen permeation through Pd composite membranes. Then, from the point of practical application, studies on the effect of long-term co-existing nitrogen on hydrogen permeation through thin Pd composite membranes were carried out for a broad temperature range. It was found that the long-term coexistence of nitrogen with hydrogen on Pd membrane surface caused the membranes poisoned or even deactivated during certain temperature range. The possible mechanism was probed and detailed discussions were made based on the suggested mechanisms. Based on the mechanism, the proper conditions for the regeneration of the deactivated membranes were found out. These results on the other hand also showed that the Pd/ceramic HF composite membranes, prepared by the improve electroless plating technique developed in our group, have good long thermal and chemical stability as well as the high performance of hydrogen permeance and perm-selectivity, which suggests their good application potential and further investigation is under way.