Thermodynamic study of methanol and DME production via syngas obtained from biogas reforming

A thermodynamic equilibrium study was performed using the Gibbs free energy minimisation method in Aspen Plus to optimise operating conditions for producing alternative fuels and value-added chemicals from biogas. The system consisted of at least two reactors: a reformer that converts biogas into syngas, followed by synthesis reactor(s) for methanol and/or dimethyl ether (DME). The study evaluated methane and CO 2 conversions, H 2 and CO yields, and carbon formation in the reformer under varying temperature, pressure, and steam-to-carbon (S/C) ratios; the resulting H 2 /CO ratio—key for methanol and DME synthesis—was also analysed. Thermodynamic analysis of the synthesis reactors for methanol and DME production identified optimal conditions adjusting the outlet H 2 /CO ratio. For a typical biogas composition of 60 % CH 4 and 40 % CO 2 , the optimal conditions identified were: for methanol production, the reformer should operate at 900 °C and 1 bar with a S/C ratio of 0.65 and a H 2 /CO molar ratio of 1.56, while the methanol reactor should operate at 200 °C and 100 bar, achieving a 77.5 % yield. For single-stage DME synthesis, the reformer should maintain the same temperature and pressure, but with a lower S/C ratio of 0.35 and a H 2 /CO molar ratio of 1.4. The synthesis reactor should operate at 200 °C and 30 bar, resulting in a 64.5 % yield. For two-stage DME production, which includes an intermediate methanol synthesis stage following the biogas reformer, the methanol synthesis conditions remain unchanged, and the subsequent DME reactor should operate at 220 °C and 30 bar, with a DME yield of 56.7 %. Additional analyses showed that biogas with higher CH 4 content increases methanol and DME yields.