Life cycle of methanol from coal and rice residual biomass in Brazil: Carbon footprint analysis

ABSTRACT This article presents the first environmental assessment study of methanol production by co-gasification of coal and residual rice biomass from the perspective of life cycle sustainability in Brazil. This study provides a comprehensive comparative analysis of the processes and activities contributing to greenhouse gas emissions (GHG) throughout the production chain, spanning from the initial generation of waste biomass to the stages of coal mining preceding methanol production. The evaluation was performed using the life cycle assessment (LCA) methodology, using data collected in situ, secondary data and obtained through simulation in Aspen Plus. Three major scenarios for methanol production were considered: scenario A with 100% coal, scenario B with 70% coal and 30% rice straw, and scenario C with 70% coal and 30% rice husk. The results showed that in scenario A, the impact on global warming is 3.14 kg CO 2eq /kg methanol, with the methanol production stage accounting for the largest environmental burden in all scenarios, mainly due to coal gasification and conditioning processes. In contrast, systems B and C demonstrate a significant mitigation potential, showing approximately a 10% reduction in global warming impact, resulting in 2.84 kg CO 2eq /kg methanol for scenario B and 2.82 kg CO 2eq /kg methanol for scenario C. This advantage is a consequence of the use of biomass, which is inherently carbon-neutral due to its capacity to absorb and release carbon dioxide in a closed cycle, thereby contributing to the reduction of net greenhouse gas emissions. Additionally, the results of a sensitivity analysis showed that carbon neutral and straw route are the most influential parameters on the carbon footprint.