Potential valorization of waste cooking oils into sustainable bio-lubricants

This work explores the feasibility of using waste cooking oils (WCO) as eco-lubricants. Five WCO from different food facilities were studied. Three of them were fractionated into both lighter and heavier fractions by molecular distillation. A comprehensive chemical characterization (fatty acids distribution, polar compounds and acidity) was carried out on all WCOs and their fractions, which led to set relationships with the oils' properties (such as viscosity index, low temperature viscous flow behavior, oxidation resistance, etc.). It is worth mentioning the high viscosity index values found in waste cooking oils with both low total polar compounds and acidity level, as well as the benefit which acidity had on their fluidity at low temperature and their lubricity. Moreover, it was also noteworthy that the lighter fractions, merely constituted by free fatty acids (FFA), presented an improved oxidative resistance. The largest OOT enhancement, 12.4%, was found for the light fraction of a non-segregated oil. Moreover, a better thermal stability was shown by the heavier fractions. Finally, both fractions exhibited enhanced friction-reducing capability as compared to their parent WCO. The light fractions from a nonsegregated oil, a fast food restaurant oil and a deep-fried food establishment oil yielded wear reductions of 11.7%, 44.3% and 36.8%, respectively. Therefore, molecular distillation has been proved to be a key strategy to obtain more efficient liquid eco-lubricants.

Automated summary

This study investigates the feasibility of using waste cooking oils as eco-lubricants and separates them into lighter and heavier fractions through molecular distillation. A comprehensive chemical characterization is conducted, revealing high viscosity index values in waste cooking oils with low polar compounds and acidity levels. It is also found that the lighter fractions composed of free fatty acids demonstrate improved oxidative resistance, while the heavier fractions exhibit better thermal stability. Furthermore, both fractions show enhanced friction-reducing capability compared to their parent waste cooking oils.