Experimental Study Toward Integrated Capture and Conversion of CO ₂ to Methanol: Mechanistic Insights into the Competition Between Amine Reactivity and Methanol Production

Carbon capture and utilization represents a promising strategy to mitigate anthropogenic CO2 emissions; however, the energy-intensive stripping and compression steps render the process economically challenging. To decrease the overall energy consumption, the concept of integrated capture and conversion of CO2 to methanol (IC3 M) was introduced, in which the carbamate arising from carbon capture is directly hydrogenated toward methanol. In this work, the hydrogenation of the equilibrium-loaded amine is investigated using dipropylamine (DPA) as the carbon capture amine and several noble-metal catalysts supported on γ-Al2O3, at a total pressure of 40 bar, temperatures between 125 and 175 °C and varying residence times. Besides trace amounts of methanol, 1-propanol, propylamine, tripropylamine, and N,N-dipropylformamide are identified as major reaction products, revealing complex amine reactivity under hydrogenation conditions. N,N-dipropylformamide is established as the key intermediate, undergoing either C–N bond cleavage to methanol or C–O bond cleavage to N-methyldipropylamine, with selectivity strongly dependent on reaction temperature, hydrogen partial pressure, and residence time. Additional amine-derived products originate from a Schiff-base-type transformation of carbamate species. The results demonstrate that methanol formation from captured CO2 is mechanistically viable within integrated systems while highlighting intrinsic competition with amine reactivity, providing a foundation for a two-step process with enhanced methanol productivity.