A Compact Membrane Reactor for Producing Pure Hydrogen From Anhydrous Ammonia

A significant barrier to the use of fuel cells for portable and small stationary applications is the lack of a supply of pure hydrogen with high specific energy. Anhydrous ammonia is an attractive fuel because it has very high intrinsic specific energy, requires no water for decomposition, and has established distribution channels throughout the world. A compact membrane reactor hydrogen generation system using anhydrous ammonia as a fuel has been developed which produces greater than 99.95% purity hydrogen at a rate sufficient to power a 100 W_e PEM fuel cell. Ammonia concentrations in the resultant hydrogen product are non-detectable. Hydrogen recovery through the membrane is as high as 80% and the membrane reactor thermal efficiency (LHV) is 70%. The primary features of this system are a catalytic reactor, a hydrogen separation membrane integrated into the reaction chamber, and a catalytic combustion module to provide heat for the ammonia decomposition reaction and subsequent conversion of trace ammonia reject. The membrane reactor is planar in configuration and allows for a simple, single unit design to provide pure hydrogen for fuel cell applications. The total system can provide specific energies of greater than 500 Wh/kg for a 72 hour run making it an attractive solution of portable and long unattended run time applications.