A viable membrane reactor option for sustainable hydrogen production from ammonia

Abstract

Conventional hydrogen production from ammonia is both energy and process intensive, requiring high temperature and independent purification units. Here, we present a compact process of energy conversion from NH3 to electricity using a novel membrane reactor, comprised of a dense metallic Pd/Ta composite membrane and Ru/La-Al2O3 pellet catalysts, and a fuel cell unit. The fabricated Pd/Ta composite membrane, having ca. 5 times higher H2 permeability than conventional Pd-Ag membranes, can both lower NH3 dehydrogenation temperature and completely remove an additional hydrogen purification unit. Compared to a packed-bed reactor without membrane, ammonia conversion improves by 75 and 45%, respectively at 425 and 400&#8239

°C, and >99.5% of conversion is achieved at 450&#8239

°C under pressurized ammonia feed of 6.5&#8239

bar. Main barriers of practical application of Pd/Group V metals as a composite hydrogen permeable membrane, embrittlement and durability issues, are overcome owing to pertinent operating temperatures (400&#8211

450&#8239

°C) of ammonia dehydrogenation coupled with membrane separation. Finally, as-separated hydrogen with <1&#8239

ppm of NH3 is provided directly to a polymer electrolyte membrane fuel cell, showing no performance degradation for an extended time of operation. The combined results suggest a feasible and less energy/process intensive option for producing hydrogen or electricity from ammonia.