Recycling of used lubricating oil: Evaluation of environmental and energy performance by LCA

Abstract

Used lubricating oils (ULOs) represent a serious problem for environment and human health due to the presence of highly harmful contaminants, being mandatory an adequate management based on efficient collection systems and treatment processes. Within this work, the environmental and energy performance of a re-refining process for ULOs upgrading is evaluated. The proposed regeneration process is based on the extraction of organic contaminants with liquid propane followed by a cascade of three consecutive distillation stages (two under atmospheric conditions and an additional one under vacuum). This process operates at plan scale in Spain recovering base oil for reuse. All the operations were simulated using Aspen Plus 8.6 and environmental issues and performance was determined by LCA, considering global warming potential, cumulative energy demand, acidification and toxicity as impacts categories. Results show that the whole upgrading process generates up to 363kg-eq CO2/tonne base oil (mainly associated with distillations heating requirements) and it consumes 6144MJ/tonne base oil. Vacuum distillation is the most important contributor to acidification and toxicity, due to heating and electricity requirements of the column. These parameters were compared for upgraded base oil and refinery lubricant oil, and results suggested that great environmental impacts can be reduced by recycling oil. Finally, different LCA scenarios were considered by partitioning impacts among base oil and plant by-products, using mass flow and economic criteria. Regardless the impacts allocation method, results clearly indicate that manufacturing base oil by ULOs recycling is a more environmental friendly option than the conventional refinery process.