A thermodynamic analysis of biogas-to-methanol conversion with CH4 recycling and CO2 utilization using Aspen HYSYS

Abstract

Hydrocarbon reforming routes are renowned for producing a multitude of energy-effective renewable fuels and/or chemicals. In this study, Aspen HYSYS simulation software was employed to assess the feasibility of a biogas-to-methanol conversion process via coupling CH₄ recycling and CO₂ sequestration with the dry reforming of biogas. The results revealed that CH₄ conversion dramatically enhanced via the recycling of unreacted CH₄, followed by CO₂ mitigation to a more considerable extent. Simulation runs were performed while varying the reactor pressure and temperature in the ranges of 1.0 to 2.5 bar and 700 to 900 °C, respectively. It was observed that the CO₂ conversion decreased continuously as the pressure increased, while there were negligible differences in terms of CH₄ conversion using the recycling loop, especially at temperatures of ≥800 °C. At 900 °C and 1 bar, the stoichiometric product (H₂/CO) ratio, with CH₄ conversion of 83.7% and CO₂ conversion of 99.9%, was achieved. An increase in temperature did not significantly affect the WGSR, and 96.6% reactor conversion, with a H₂/CO ratio of 1.98, was obtained at a temperature of 150 °C and a pressure of 1.0 bar. The reported study inferred that methanol can be produced at a rate of 24.7 kg h⁻¹ using a biogas molar flow of 1.0 kg mol h⁻¹ under the optimal conditions of 200 °C (temperature) and 100 bar (pressure), with a net thermal efficiency of 67.3%. Overall, it is concluded that biogas dry reforming could allow a sustainable methanol synthesis process with CO₂ mitigation at a potentially lower cost, especially in rural areas.