Techno-economic ionic liquid-based capturing, electrochemical reduction, and hydrogenation of carbon dioxide in the simultaneous production of formic acid and biomethane

CO2 utilization is vital for mitigating climate change by converting CO2 into valuable products, promoting environmental protection and resource efficiency. Novel pathways for CO2 utilization to produce formic acid are proposed namely solute phase electroreduction, gas phase electroreduction, and hydrogenation, are investigated. Employing multi-objective optimization with a deep neural network surrogate model, this study identifies optimal process conditions balancing capital and operational expenditures. The result shows that CO2 hydrogenation ($868 ton -1) exhibits the lowest production cost followed by gas-phase electroreduction ($986 ton -1) and solute-phase electroreduction ($2103 ton -1). The result also shows that without any intervention at all only hydrogenation can generate profit. Furthermore, an in-depth analysis of CO2 emissions indicates that gas phase electroreduction results in the lowest CO2 emissions (0.7 kg CO2 kgHCOOH- 1) among the examined pathways. Insights from our research suggest a minimum current density of 417.3 mA cm -2 is recommended to achieve at least parity with hydrogenation in terms of production cost. To push the commercialization of gas-phase electroreduction, besides current density improvement, electricity cost reduction, and carbon trading mechanism is proposed to reduce the production cost.