Energy life-cycle assessment and CO2 emissions analysis of soybean-based biodiesel: a case study

In this study the energy consumption and CO2 emissions of biodiesel production from soybean in Golestan province of Iran were studied. For this purpose, the life-cycle process of biodiesel was considered as five stages of agricultural soybean production, soybean transportation, soybean crushing, biodiesel conversion, and its transportation. The results indicated that the total fossil energy consumption with coproduct allocation was 8617.7 MJ ha−1 and the renewable energy output content (biodiesel as the final outcome) was estimated as 16,991.4 MJ ha−1. The net energy gain (NEG) and the fossil energy ratio (FER) were calculated as 8373.7 MJ ha−1 and 1.97, respectively, which show soybean is a suitable energy crop for biodiesel production. Agricultural soybean production stage ranked the first in energy consumption among the five main stages where it consumed 50.56% of total fossil energy consumption in the biodiesel life-cycle process. The greenhouse gas (GHG) emissions data analysis revealed that the total GHG emission was 1710.3 kg CO2eq ha−1 which biodiesel production life-cycle was only account for 311.96 kg CO2eq ha−1 if the mass allocation is considered. Overall, biodiesel production from soybean in Iran can be considered as a way to increase energy security in the near future. Also, soybean cultivation must be considered along with other common oilseeds cultivation in order to prevent food competition between biodiesel feedstocks and food production in Iran.