Exergy analysis of the demonstration plant for co-production of hydrogen and benzene from biogas

The dehydro-aromatization reaction of methane is one of the methods to utilize biogas and co-produces hydrogen and benzene. To demonstrate the industrial co-production of hydrogen and benzene from biogas, we constructed a demonstration plant. The purpose of this study is to evaluate the feasibility of the demonstration plant, which can co-produce 134 N m³/day of hydrogen and 8.6 L/day of benzene from 200 N m³/day of biogas, by means of clearing energy requirement, exergy loss and CO₂ emission. Energy requirement was 3783 MJ/day. Only 21% of the input exergy was converted to hydrogen and benzene, and 79% was consumed. The sub-system of the dehydro-aromatization reformer showed the largest exergy loss among the eight sub-systems. Assuming electricity was supplied by thermal power generation, CO₂ emission was 634 kg/day. On the other hand, assuming electricity was supplied by biogas engine, fuel biogas requirement was 555 N m³/day. However, CO₂ emission was not counted in this case because of the carbon-neutral principle.