Energy and economic analysis of the hydrothermal reduction of CO2 into formate

Abstract

In this work, the mass and energy balances and the economic analysis of a continuous process for the reduction of CO2 (captured as NaHCO3) into sodium formate using Zn as the reductant are studied. The reaction in hydrothermal media has the advantage of easily integrating the conversion system with the CO2 capture process by absorption in basic solutions. The process conditions (pressure, Zn/NaHCO3 molar ratio, and residence time) were theoretically optimized. A reaction temperature of 275 °C was selected, obtaining formate yields greater than 70%. A continuous process design was proposed based on available information and on our experimental experience in the process. Mass and energy balances were solved and the potential for an energy integration was studied. Additionally, both capital and operating costs for a plant treating 1000 kg/h of CO2 were estimated. The cost calculated for transforming CO2 was EUR 1.28/kg CO2.