Strong interests in developing the global hydrogen economy for the 21^st Century have generated considerable R&D effort in hydrogen production. Although from an environmental point of view, electrolysis of water by solar energy will probably be one of the more desirable ways for hydrogen production, steam reforming of natural gas at high temperatures and pressures will remain as a major hydrogen source in the foreseeable future. In addition, hydrogen production from coal gas will play an important role due to the large US coal reserves. Therefore, developing technologies which can economically produce hydrogen with CO₂ at high pressures suitable for sequestration, is of great importance to the hydrogen economy. Pd-based membrane reactors can satisfy these requirements. Furthermore,  high temperature Pd-based membrane reactors are especially suited for process intensification by combining reaction, product concentration and separation in a single unit operation, eliminating the need for high and low temperature shift reactors, PreOx and hydrogen separator required in a conventional steam reforming process. In the case of coal gas, process intensification can also be accomplished using membrane shift reactors to carry out the requisite water gas shift reaction.
We have developed unique patented technologies for producing composite ultra thin Pd membranes with high hydrogen flux and long-term durability at high temperatures (~500^ºC) and pressures. This presentation will describe the fundamental concept we developed for improving the long-term thermal stability of composite Pd and Pd/alloy porous stainless steel (PSS) membranes by the controlled in-situ oxidation of the PSS substrate and bi-metal multi-layer (BMML) deposition to generate an intermetallic diffusion barrier layer. The permeance of membranes prepared by the electroless plating technique with this intermetallic barrier layer was as high as 91 m³/m²-h-atm^1/2, which exceeded the US DOE 2015 target. Furthermore, membranes with areas ranging from 20-30 cm² to 0.2 m² have been produced to demonstrate the scalability of the WPI technologies. The developed technologies have been successfully transferred to industry for possible commercialization.
Sulfur tolerant membranes are also required for upgrading syngas from coal gas. In this direction, sulfur tolerant composite Pd/Cu and Pd/Au membranes were prepared and characterized. Although long term testing is still required, initial results showed partial regeneration of sulfur poisoned Pd/Cu membranes was possible. Moreover,  Pd/Au membranes showed hydrogen permeance 50% higher than that of pure Pd membranes and preliminary data showed some sulfur resistant.
Finally, another major objective of this study is the development of a systematic framework for process analysis and intensification.  In particular, the behavior of the membrane reactor is analyzed and characterized through a suitably structured model that arises from mass and energy balance equations capturing the detailed kinetics of the methane-steam reforming, water-gas-shift and methanation reaction pathway.  Detailed simulation studies were performed with the aid of Matlab® software, and reactor performance characteristics were evaluated under a broad range of operating conditions by varying temperature, pressure, steam-to-methane ratio and sweep gas flow rate. In all simulation studies conducted, superior performance of the membrane reactor over the conventional packed-bed one is amply demonstrated.