Enhanced Methanol Synthesis Process via an Integrated Process Involving CO2 Hydrogenation under Plasma Conditions

An integrated process combining CO2 reduction with hydrogen under plasma conditions and catalytic methanol synthesis offers an encouraging option for the conversion of CO2 from exhaust gas marine emissions. The process interconnects a microwave-induced plasma reactor and a methanol synthesis fixed-bed reactor. The paper explores the CO2 hydrogenation process in the microwave-induced plasma reactor via an unsteady-state, two-dimensional (2-D) axisymmetric, nonisothermal model and the catalytic methanol synthesis in the fixed-bed reactor via an unsteady-state, two-scale, isothermal model, highlighting the impact of key parameters on the integrated process performance. In the microwave-induced plasma reactor, CO2 conversion reaches 82% when the reactor is supplied with only H2 and CO2 and 74% when H2 is supplied in the diesel engine exhaust (H2/CO2 ratio = 3). However, this enhanced CO2 conversion at large H2/CO2 ratios is achieved by increasing the power of microwave plasma to compensate for the temperature drop induced by the amplified radial heat transport and radiative wall heat transfer. The specific energy input required to achieve a reasonable CO2 conversion is close to the specific energy input of the conventional thermal catalytic process for H2/CO2 = 1 and when H2 is supplied in the diesel engine exhaust. A large specific energy input into plasma reactor allows for high CO2 conversion and low energy efficiency. Methanol synthesis process in the fixed-bed reactor is improved by the amplification of H2/COx ratio and when CO2 is progressively substituted by CO, which is easily achieved via the reverse water-gas shift reaction in a microwave-induced plasma reactor located upstream from the methanol synthesis reactor.