Abstract
Biogas offers a promising biogenic carbon source for renewable methanol, but differences in CH4/CO2 ratio across feedstocks and possible upstream CO2 handling can shift syngas stoichiometry away from the methanol synthesis target range. This work quantifies how biogas composition and reformer operation influence the stoichiometric number (SN) and the associated conditioning requirement needed to meet methanol synthesis targets. A steady-state Aspen Plus® model of an integrated biogas-to-methanol process is used as the analysis framework. A base-case operating point is defined, followed by parametric evaluation of biogas CH4/CO2 ratio, reformer temperature, reformer pressure and steam-to-methane (S/C) ratio. The studied CH4/CO2 ratio range covers CO2-rich to CH4-rich cases that may occur across sites and upgrading levels. The resulting SN shifts are tracked and converted into a quantitative correction requirement to maintain the methanol design target (SN = 2.01). Temperature determines the upper limits of conversion and SN, while pressure and S/C ratio have secondary effects once high-temperature operation is reached. By comparison, the CH4/CO2 ratio has the strongest influence on syngas composition, defining H2-deficiency and H2-excess regimes. Methanol production increases as SN approaches the required target range but shows diminishing gains beyond it, indicating limited benefit from excess hydrogen under fixed synthesis conditions.