CO₂ Self-Sufficiency in Renewable Methanol Production from Biomethane and Biohydrogen: Techno-Economic Assessment for Spain

Renewable methanol is commonly proposed either as biomethanol from biomass or biomethane reforming, or as e-methanol from CO₂ hydrogenation using electrolytic hydrogen. This work proposes a third concept: CO₂-self-sufficient biomethanol from biomethane, where biohydrogen and biogenic CO₂ are internally produced through biomethane reforming with carbon capture and utilisation. Four process routes are assessed for Spain, combining conventional CO/H₂ methanol synthesis and CO₂/H₂ hydrogenation. The proposed routes use biohydrogen rather than electrolytic hydrogen. In route 1 (baseline case), fossil methane and CO₂ in conventional methanol production are replaced by renewable alternatives. Route 2 produces hydrogen and CO₂ through steam biomethane reforming with carbon capture and utilisation, generating a CO₂ surplus. Route 3 uses a fraction of biomethane to produce CO₂ and biohydrogen, supplying the CO₂ required by route 1 and yielding excess hydrogen. Finally, route 4 integrates routes 1 and 2, using the CO₂ surplus from route 2 as feedstock for route 1. Routes 1 and 4 produce exclusively methanol and achieve the highest yields (108.6 t and 102.7 t per GWh-HHV of biomethane, respectively). All routes except route 1 are CO₂ self-sufficient. A detailed techno-economic assessment of routes 1 and 4 gives methanol costs of 403–817 €/t and 496–933 €/t, respectively.