Assessing the environmental potential of carbon dioxide utilization: A graphical targeting approach

Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO2 is intrinsically difficult due to its low energetic state. Thus, a positive environmental effect of a CO2-consuming reaction cannot be taken for granted. In this work, we therefore present a graphical method to identify promising reaction schemes using CO2 as a feedstock. Reactant mixtures leading to minimal life-cycle greenhouse gas (GHG) emissions are determined. The optimal reaction schemes strongly depend on the reactants’ global warming potential (GWP); in the case of CCU, the future GWP values of CO2 and H2 are particularly critical and subject to major uncertainty today. The graphical method therefore provides GWP targets for CO2 capture and H2 production technologies. The method is demonstrated for the production of methanol. Five optimal reaction schemes are identified depending on the GWP values of CO2 and H2. Thus, four threshold relations for the GWP of CO2 and H2 are derived showing directly under which conditions the utilization of CO2 as a feedstock is environmentally preferential.