Effect of coexistence of H2S on production of hydrogen and solid carbon by methane decomposition using Fe catalyst

Biogas derived from livestock manure and food residue contains CO2 and H2S as well as methane. The effect of CO2 and H2S coexistence on the production of hydrogen and solid carbon by methane decomposition over iron oxide catalysts was investigated. The catalytic activity for methane decomposition was decreased by the coexistence of H2S. Moreover, the activity decrease was aggravated by the coexistence of CO2 as well as H2S, and higher temperature was required to mitigate the activity decrease by the coexistence of CO2. By increasing the amount of catalyst, the upstream catalyst was preferentially poisoned, but the downstream catalyst developed catalytic activity thanks to its sacrifice. With 2 g of catalyst, the maximum conversion of pure methane was about 85% at 840 degrees C, but it was slightly less than 80% in the presence of H2S or H2S + CO2. When the catalyst amount was increased to 4 g, the conversion of pure methane was about 90% at 800 degrees C, but 84% in the presence of H2S and 80% in the presence of H2S + CO2. The poisoning by H2S was irre-versible at low temperatures but became reversible at higher temperatures. Since H2S is adsorbed by the deposited carbon, the procedure for further removal of H2S may be omitted. The coexistence of H2S also affected the shape of the deposited carbon. Although carbon-based catalysts are known to be effective for methane decomposition in the presence of H2S, iron oxide catalysts have the advantage of superior methane conversion at low temperatures. By flowing methane with CO2 and H2S from the downstream side after the reaction flowing from the upstream side for a certain period of time, the catalytic lifetime was drastically extended and the amount of hydrogen and solid carbon produced was dramatically increased, compared to the case of flowing from upstream all the way.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The effect of CO2 and H2S coexistence on the production of hydrogen and solid carbon by methane decomposition over iron oxide catalysts was investigated. The catalytic activity for methane decomposition was decreased by the coexistence of H2S. Moreover, the activity decrease was aggravated by the coexistence of CO2 as well as H2S.