Design, implementation and piloting of an integrated hydrogen- and oxygen-added process for conversion of biogas to methanol

Abstract

An integrated biogas-to-methanol (B2M) conversion system combining autothermal reforming (ATR) with regenerative methanol (MeOH) synthesis, integrating both oxygen (O₂) and hydrogen (H₂) from water electrolysis, is designed, commissioned and investigated operationally. The pilot plant is operated under real world conditions at a wastewater treatment plant in western Germany to demonstrate the process using sewage-derived biogas and to investigate its applicability and suitability for decentralized, efficient value-added bio-chemical production from renewable feedstock. The studies conducted at the test plant evaluate system effectiveness by optimizing operational parameters for both ATR (steam-to-carbon ratio [S/C], oxygen-to-fuel ratio [λ]) and the methanol (MeOH) synthesis process (stoichiometric number [SN], reaction temperature and gas space velocity [GHSV]). Additionally, stable start-up procedures are developed for reliable operation under dynamic conditions, as is expectable in industrial process application. To compare different MeOH synthesis pathways, regenerative synthesis gas-based MeOH-production is set against direct CO₂-to-MeOH conversion. Results demonstrate that ATR of biogas produces CO₂-rich synthesis gas (SynGas) with excellent methane (CH₄) conversion and extremely low soot formation at relatively low reforming temperatures below 750 °C. Although the high CO₂-content reformate requires substantial H₂ injection for stoichiometric MeOH synthesis SynGas conditions, the H₂-enhanced SynGas route proves superior to CO₂-only operation of the pilot plant, highlighting possible synergies in oxygen-injected ATR and MeOH-synthesis applications. The combined ATR-H₂-injection approach yields higher MeOH yields with reduced water formation and improved conversion. The findings from this study support the technical feasibility of the integrated B2M-system and provide operational foundations for economically viable decentralized MeOH-production at biogas facilities and future system scale-up.