Thermally self-sufficient process for cleaner production of e-methanol by CO₂ hydrogenation

Abstract

The hydrogenation of CO₂ to methanol is a technology that converts a greenhouse gas into a valuable chemical compound that efficiently stores energy. Several alternatives to perform this process have been proposed, but they are either not thermally self-sufficient and depend on using external fuel, or the power usage per ton of methanol is insufficiently optimized, or part of the raw materials must be purged and therefore there is a loss of methanol yield. This original study aims to develop a novel thermally self-sufficient process for e-methanol production (at practically 100% yield along with water by-product of 0.37 kg_water/kg_product) that only uses green electricity. The main innovation of the process is an effective thermally self-sufficient heat-integration scheme that only needs 0.0059 m³_water/kg_methanol combined with using a dividing wall column to recover the unreacted CO₂ and obtain high purity methanol. In addition, the pressure reduction in the reaction-separation loop is limited to the pressure drop of the circuit to minimize the overall green electricity use to only 656 kWh per ton methanol, resulting in net CO₂ emissions of −1.13 kg_CO2/kg_MeOH or 0.78 kg_CO2/kg_MeOH when the plant operates with green or grey hydrogen and electricity, respectively. Finally, the operating pressure in the reactor is optimized at 65 bar to minimize the total annualized cost.