Molecular Composition of Impurities in Used Cooking Oil and Their Effect on Hydrotreated Biofuel Quality

Biodiesel and biojet fuel production from hydrogenation of used cooking oil (UCO) is one of the essential measures to achieve global energy transition and sustainable development. A systematic molecular composition characterization method of UCO feedstocks and their hydrotreated products has been established to trace the undesirable components during the industrial hydrogenation process. The influences of soluble hydrocarbons and oxygen-containing impurities in UCOs on the hydroconversion of UCO into green diesel were researched by analyzing specific low-quality UCO feedstocks and products obtained from industrial production process. The results revealed that some common bioactive constituents abundant in low-quality UCOs may be responsible for the unqualified properties of the hydrotreated oils. Steradienes and sterols can convert to high boiling point substances and decrease the yield of green diesel. Tocopherols are a potential source of abnormal monocyclic aromatic hydrocarbons in hydrotreated oils and affect the properties of fuel. This study proposed that some soluble hydrocarbons and oxygen-containing impurities in the industrial UCO feedstocks can also significantly affect the quality of biofuels, which has not been mentioned in previous works. The detailed characterization of UCO feedstocks and their hydrotreated products offers valuable insights for quality control of feedstock and process optimization in biofuel production, contributing to conversion of low-quality UCO feedstocks to highly valuable biofuels.