Hydrothermal reduction of CO2 captured by aqueous amine solutions into formate: Comparison between in situ generated H2 and gaseous H2 as reductant and evaluation of amine stability

Abstract

By CO₂ Capture and Utilization technologies (CCU), organic compounds can be produced industrially in a sustainable manner, generating an economic benefit that offsets the cost of CO₂ capture. In this context, the use of CO₂ chemisorbed by amines to generate chemicals is an attractive alternative, given that large-scale facilities using absorption to capture CO₂ are already operational. The aim of this work is to convert CO₂ captured in aqueous amines, specifically 3-amino-1-propanol (AP) and 2-amino-2-methyl-1-propanol (AMP), to produce formate, using either Zn, Al or gaseous H₂ as reductants and Pd/C as catalyst. The highest yield of formate (68 %) was achieved with AP (125 °C, 75 bar, 120 min) using gaseous hydrogen as reductant. Using metals as reductants, reaction yields were lower, with a 12 % yield at 200 °C as the best result. After reduction, NMR analyses show that the amines did not suffer degradation, raising the possibility of reusing them for CO₂ capture in a continuous process. These results indicate that CO₂-loaded amines reduction is a promising CCU technology that can be integrated with the current technologies for gas treatment.