Analysis of methanol synthesis using CO2 hydrogenation and syngas produced from biogas-based reforming processes

Utilizing the greenhouse gas CO2 as a feedstock in chemical processing can offer alternative solutions to long-term storage. In this study, a systematic analysis of methanol synthesis performance was analyzed based on both thermodynamic equilibrium and kinetic models using captured CO2 and syngas produced from biogas as feedstock. Using reactor inlet temperature as a parameter, it was found that methanol yield can be enhanced by increasing residential time from increased reactor diameter. The longer reactor can increase the residential time but a large pressure drop caused a decrease in methanol yield. Due to the exothermic reaction nature, methanol yield from an adiabatic reactor is lower than that from the isothermal reactor due to temperature rise. From the results obtained for CO2 hydrogenation, methanol yield can be enhanced by water removal. The CO2 conversion was found to increase with increased reaction temperature due to methanol and carbon monoxide productions. Using CO and CO2 as limiting species, high combined CO and CO2 conversion can be obtained from syngas with low CO2/H-2 and high CO/H-2 ratios. However, methanol production per mole of H-2 depends on the H-2 utility instead of combined CO and CO2 conversion. Finally, syngas produced from biogas by using combined dry and steam reforming reactions was used as the feedstock for the methanol synthesis. To obtained the syngas composition suggested from industrial applications, CH4 and H2O were added in the combined reforming process. With higher CH4 content in the biogas, higher methanol production and lower water production can be obtained. With an increased recycle ratio for unreacted syngas, methanol production can be enhanced.

Automated summary

This study analyzed the methanol synthesis performance using CO2 and syngas as feedstock, finding that increasing reactor diameter can enhance methanol yield but large pressure drops may reduce the yield. Removing water and increasing reaction temperature were found to increase methanol yield and CO2 conversion. Additionally, higher CH4 content in the biogas can lead to higher methanol production and using a higher recycle ratio for unreacted syngas can enhance methanol production.