Green route for biomethane and hydrogen production via integration of biogas upgrading using pressure swing adsorption and steam-methane reforming process

Abstract

Biogas is a cornerstone within a clean and sustainable energy portfolio, while hydrogen production from biogas is a key enabler for methane conversion and carbon dioxide valorization for greenhouse gases emissions mitigation. In this work, pressure swing adsorption (PSA) configuration of two vessels-four adsorption beds connected in series was tested for upgrading low-grade biogas (50% CH4 and 50% CO2). To resolve CH4 spillage issue, steam-methane reforming (SMR) plant was proposed as a green route for converting CH4 and portion of CO2 in the waste stream of PSA system into hydrogen. The integrated system (PSA-SMR) was performed on two stages i.e., PSA runs were conducted experimentally in lab while SMR system was simulated using Aspen Hysys software under operating conditions from a real plant. Response surface methodology was applied into Design Expert software to optimize the effects of system pressure, CH4 concentration, and biogas/steam flowrate ratio on H2, CO2, H2O, and CO molar fractions in the product. The results revealed that four adsorption beds in serial configuration successfully recorded ultrapure CH4 of 99.9% and recovery of 84.9% along with average CO2 content of 60% in the waste stream. For SMR system, produced syngas comprised of 42.2% H2, 28.46% CO2, 13.84% N2, 8.88% H2O, and 6.66% CO with 100% conversion of the CH4 and about 52.56% conversion of the CO2. The optimum conditions that achieved the highest H2 content of 51% from SMR were system pressure below 32 bar, methane content in feed stream ≥61%, and biogas/steam ratio in the range of 0.41–0.66 to record H2.