Thermocatalytic CO2 hydrogenation for methanol and ethanol production: Process improvements

Abstract

This study investigates various design aspects for the valorization of industrially captured CO2 towards methanol and/or ethanol. In the framework of the CO2 conversion unit, two novel concepts are examined aiming to the improvement of the process performance, one for methanol and another for ethanol production. For the methanol case (CO2 + 3H2 → CH3OH + H2O), a new scheme of employing a membrane reactor with high selectivity either in methanol permeation (organophilic) or in water permeation (hydrophilic) is explored via process simulation. The methanol extraction has a beneficial effect on the methanol yield and requires a more compact sized reactor. In ethanol case (2CO2 + 6H2 → C2H5OH + 3H2O), a new process configuration through the intermediate DME (di-methyl ether) synthesis is presented and compared to the conventional method based on CO2 conversion to CO in a reverse water gas shift (rWGS) reactor followed by the mixed alcohol synthesis reactor. The novel synthesis route via DME has a higher efficiency (total energy efficiency: 70.3% on LHV basis whereas the corresponding efficiency of the conventional scheme is 63.2%) because of lower heat and power demands for its effective operation. From the economic analysis, it is shown that the novel ethanol plant results to lower ethanol production cost than the conventional one through the rWGS by 18% but the high cost for H2 production through water electrolysis keeps it far for competitive levels.