Upgrading and purification of biolubricants by extraction of fatty acid methyl esters with dense CO2

Abstract

In the last years, there has been an increasing use of eco-friendly lubricant options produced from renewable raw materials, which are less toxic to humans and ecosystems. As the demand for sustainable products rises, lubricants derived from vegetable oils and animal fats are gaining attraction. In this study, we evaluate the purification of a biolubricant synthesized via classical alkali-catalyst esterification of fatty acid methyl esters (FAME) with trimethylolpropane (TMP) using CO2 as solvent media. Unlike conventional purification solvents, using CO2 minimizes environmental impact and aligns with green chemistry principles. We investigate the purification and upgrading of the filtrated biolubricant (28 wt% FAME) using CO2 -both in its liquid and supercritical states- as a green solvent for designing a more sustainable separation process. The study examines phase equilibria of the multicomponent mixture (liquid-liquid-vapor to liquid-vapor phase transition), solubility of biolubricant in CO2 (8.0–22.4 mg/g biolubricant/CO2 according to operating conditions) and the purification process. The final bio-based base oils are analyzed to determine their FAME content, viscosity, and viscosity index. Results show that purified bio-based base oils contain as little as 2.9 wt% FAME, with a viscosity of 0.051 Pa.s at 313.2 K and a viscosity index of 196, comparable to those of the trimethylolpropane triolein standard. These findings suggest that the bio-based base oils produced and purified are suitable for lubrication applications, matching or exceeding the quality of conventional lubricants.