| Soybean oil is an excellent candidate to replace petroleum-based lubricants in aluminum rolling applications, with improved technical performance and favorable economic incentives. Intuitively, it would seem that soybean oil is preferable from an environmental perspective due to its renewable nature; however, a life cycle assessment (LCA) indicates some fundamental tradeoffs between soybean oil and petroleum lubricants. Using baseline data obtained from the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model, this study compiles inventory results for the unit processes of soybean agriculture, soybean oil processing, crude oil extraction, petroleum refining, and transportation. Using Monte Carlo Analysis (MCA), a separate nitrogen fractionation model is constructed to quantify nitrogen fluxes in agriculture to supplement the existing model data. Simulated model distributions are compared to independent data sets to validate the approach. With the functional unit defined as a mass of emission per unit of metal surface area, use phase scenarios are constructed to determine a comparative life cycle inventory. The inventory data are translated into environmental impacts using the Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI), using location specific impact factors. The results of the assessment indicate that the comparative environmental impacts are largely dependent on the performance of soybean oil in the use phase. Fundamental tradeoffs between the carbon and nitrogen cycles are discussed, and the relevant contributions to environmental impacts are identified. This research raises larger questions about increased bio-based product substitution, focusing on the tradeoff between global climate change and regional issues such as hypoxic zones, acidification, and ground-level ozone formation. |
