Greenhouse gas emissions of rice straw-to-methanol chain in Southern Brazil

Brazil is the largest producer of paddy rice in the American Continent, straw discarded in the field after the rice harvest can be used for methanol production and help mitigate the impact of global warming. This paper presents the first environmental impact study of the life cycle of rice straw methanol in Brazil, whose objective was to produce an inventory and determine impacts on global warming based on collected data from actual logistic process of rice straw grown in a region in southern Brazil, since there is no such information in the Brazilian literature. Methanol production from rice straw involves different activities associated with rice cultivation, straw collection, straw transportation, and methanol production. The study focuses on the detailed evaluation of the processes responsible for direct and indirect emissions, including emissions from decomposition processes in the flooded rice fields and carbon neutral emissions from the methane production stage. The results show that the removal of rice straw from the field after harvest promoted the reduction of biogenic emissions of methane, on the other hand increased nitrous oxide and carbon dioxide emissions due to the higher use of fertilizers to maintain the yield of harvested rice. The rice straw required for the methanol plant with an annual production of 148.70 thousand tons level is 4.52 kg per of kg methanol and the life cycle carbon footprint is 8.09 x 10(-01) kg CO2eq per kg methanol, of which straw collection stage is the largest contributor with a share of 43.15%, followed by transport of straw bales with 15.32%. Comparing to fossil methanol, biomethanol has the potential to reduce GHG emissions by 67-74%. This advantage is a consequence of the carbon dioxide emissions from the gasification, gas conditioning, and rice straw burning processes being considered as neutral carbon.

Automated summary

This study presents the first environmental impact assessment of rice straw methanol life cycle in Brazil, with focus on emissions from different stages of production process. Results show that removing rice straw from the field can reduce methane emissions but increase nitrous oxide and carbon dioxide emissions. The carbon footprint of rice straw methanol production is 8.09 x 10(-01) kg CO2eq per kg methanol, with biomethanol having the potential to reduce GHG emissions by 67-74% compared to fossil methanol.