Low-Temperature H2S Removal from Steam-Containing Gas Mixtures with ZnO for Fuel Cell Application. 2. Wash-Coated Monolith

Abstract

This work is part of our efforts to explore more-effective ways to remove hydrogen sulfide (H2S) for fuel cell applications. Various absorbents (ZnO, SnO2, coprecipitated NiO−MoO3, supported CuO−ZnO, V2O5−ZnO, and ZnO supported on γ-alumina) were tested for H2S removal. The absorbents that were wash-coated onto the monolith were compared with particulate traps in the inlet H2S concentration range of 0.5−8 parts per million by volume (ppmv). The monolith provides much-higher dynamic capacity (the amount of H2S trapped before breakthrough) under the same conditions. The ZnO-based monolith demonstrated the best performance. An extremely low H2S outlet concentration (as low as 20 parts per billion, by volume (20 ppbv)) was observed over ZnO-based monolith samples for extended periods of time, under various conditions relevant for the desulfurization of gas products from the autothermal reforming of hydrocarbon fuels for a proton-exchange membrane fuel cell. The capacity of the H2S trap is dependent on the monolith characteristics (active component loading per cubic inch, and the number of cells per square inch) and operating conditions (including inlet H2S concentration, space velocity, and temperature). Wash−coating of ZnO that was chemically modified by an ammonium carbonate treatment onto a monolith with 400 cells per square inch gave the best H2S absorbence with higher dynamic capacity.