Life Cycle Assessment of CO2-to-Methanol: Comparative Evaluation of Direct and Alcohol-Assisted Hydrogenation Routes

Abstract

The increasing severity of global warming, primarily driven by greenhouse gas emissions, underscores the urgent need for CO₂ reduction and utilization strategies. Converting CO₂ into methanol presents a promising approach, as methanol serves both as a fuel and a feedstock in various industries. This study evaluates the life cycle environmental impacts of three methanol production routes: (1) direct CO₂ hydrogenation, (2) ethanol-assisted CO₂ hydrogenation, and (3) propanol-assisted CO₂ hydrogenation. Two energy scenarios are considered: conventional energy and wind power. Process simulations were performed using Aspen Plus V.14, and inventories were analyzed through Life Cycle Assessment (LCA) using the ReCiPe 2016 (H) method under a cradle-to-gate approach for 1,000 kg of methanol. The alcohol-assisted processes operated at a lower reaction temperature (150 °C) and consumed less CO₂, H₂, and compression energy than the conventional process (250 °C), thereby reducing environmental impacts. However, methanol purification remained energy-intensive. Under conventional energy, the propanol-assisted process exhibited the highest global warming potential (GWP), followed by the ethanol-assisted process, while the conventional route showed the lowest. The elevated impact of the propanol route was primarily attributed to higher alcohol feedstock and energy consumption. The use of wind power significantly reduced GWP in the separation stage of alcohol-assisted routes, resulting in the lowest GWP for the ethanol-assisted process.