Methanol production by CO2 hydrogenation: Analysis and simulation of reactor performance

Methanol is a very valuable chemical with a variety of uses, either as a fuel or as building block for the synthesis of other chemicals. In the last years, interest was growing in the production of methanol from CO2, based on the so called "Power-to-Fuel" concept. In this research, an equilibrium analysis of a methanol reactor with pure CO2 and H-2 in the feeding stream was developed. Three novel reactor configurations at equilibrium conditions were considered: once-through reactor, reactor with recycle of unconverted gases after separation of methanol and water by condensation; reactor equipped with membrane permeable to water. An additional important feature of this work was the development of a methodology that assists in comparison of different process schemes by simulation of two different methanol plants configurations in ChemCad (R). An adiabatic kinetic reactor with recycle of unconverted gases was considered and simulated in Aspen Plus (R), while the performance of a methanol reactor with heat exchange at the pipe wall was simulated in MATLAB. Results show that at equilibrium conditions a reactor with the recycle of unconverted gases ensures the highest CO2 conversion: 69% at 473 K and 55 bar. In addition, the use of pure CO2 and H-2 in the feeding stream allows an overall reaction enthalpy change lower than that obtained by the use of syngas in the feed. The kinetic simulation of the methanol reactor in MATLAB showed that axial dispersion phenomena are negligible and the effect of the global heat exchange coefficient on reactor performance is less important than the effect of isothermal heat exchange fluid temperature. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.