Life Cycle Greenhouse Gas Emissions of Biodiesel and Renewable Diesel Production in the United States

This study presents a life-cycle analysis of greenhouse gas (GHG) emissions of biodiesel (fatty acid methyl ester) and renewable diesel (RD, or hydroprocessed easters and fatty acids) production from oilseed crops, distillers corn oil, used cooking oil, and tallow. Updated data for biofuel production and waste fat rendering were collected through industry surveys. Life-cycle GHG emissions reductions for producing biodiesel and RD from soybean, canola, and carinata oils range from 40% to 69% after considering land-use change estimations, compared with petroleum diesel. Converting tallow, used cooking oil, and distillers corn oil to biodiesel and RD could achieve higher GHG reductions of 79% to 86% lower than petroleum diesel. The biodiesel route has lower GHG emissions for oilseed-based pathways than the RD route because transesterification is less energy-intensive than hydro-processing. In contrast, processing feedstocks with high free fatty acid such as tallow via the biodiesel route results in slightly higher GHG emissions than the RD route, mainly due to higher energy use for pretreatment. Besides land-use change and allocation methods, key factors driving biodiesel and RD life-cycle GHG emissions include fertilizer use and nitrous oxide emissions for crop farming, energy use for grease rendering, and energy and chemicals input for biofuel conversion.

Automated summary

This study analyzes the greenhouse gas emissions of biodiesel and renewable diesel production from different oilseed crops and waste fats. The results show that biodiesel and renewable diesel can achieve significant reductions in greenhouse gas emissions, with waste cooking oil and distillers corn oil showing the highest reduction potential. The lower emissions of biodiesel compared to renewable diesel in oilseed-based pathways is attributed to the less energy-intensive process of transesterification. However, using feedstocks with high free fatty acid content for biodiesel production may result in slightly higher emissions due to higher energy use for pretreatment.