Upgrading of biolubricants by CO2 technology

PIZZANO, ALDANA; RODRIGUEZ REARTES, SABRINA BELÉN; HEGEL, PABLO EZEQUIEL

Los Cocos, Córdoba, Argentina

Conferencia; VI Iberoamerican Conference on Supercritical Fluids - PROSCIBA 2023; 2023

Universidad Nacional de Córdoba and Universidad Nacional del Sur

Lubricants play a vital role in modern society for the functioning of vehicles and the operation of industrial units. However, mineral oils have a significant environmental impact, and there is an increasing use of more eco-friendly options produced from renewable raw materials, which are less toxic to humans and ecosystems. In this context, the demand for lubricants made from oils and fats of vegetable and animal origin increases as the trend towards more sustainable products advances. Biolubricants can be obtained from biodiesel through a reaction with special tertiary alcohols like trimethylolpropane (TMP). Biolubricants obtained through this pathway have interesting applications in the steel industry as special hydraulic oils. In the reaction, fatty acid esters are usually in excess to ensure complete conversion of TMP and the production of trimethylolpropane trimethyl esters (the desired product). As a result, fatty acid esters remain after the reaction in the final biolubricant product, affecting its viscosity index and oxidation stability.In this study, we evaluate the use of liquid and supercritical CO2 for the purification of a biolubricant obtained through classical esterification of fatty acid methyl esters (FAME) with TMP at 120 ºC for a 4-hour reaction under vacuum. The product obtained is filtered at 5 ºC to isolate solids and other undesired products, and the final biolubricant is analyzed to determine its FAME content. Subsequently, we investigate the purification and upgrading of this biolubricant using liquid and supercritical CO2 as solvents.For this study, we utilize a high-pressure view cell to examine the phase equilibria of the biolubricant and CO2, as well as the purification of the biolubricant through a single-stage contact. We introduce a specific mass of biolubricant (approximately 7 g) and CO2 (approximately 35 g) at room temperature. The temperature of the cell is then set under stirring, and once the system reaches a stable desired temperature and pressure, we sample the system to determine the composition of the liquid and solvent phases. Next, we perform a complete extraction of the heavy liquid phase to assess the characteristics of the final product. The results demonstrate that both, liquid and supercritical CO2, can be used to extract the remaining FAME in the biolubricant. Using liquid CO2, up to 3% of FAME can be obtained in the solvent phase, allowing for the removal of up to 80% of the initial FAME content present in the biolubricant. Conversely, supercritical CO2 (40 ºC and 150 bar) exhibits a solubility of 8 wt.%, making it possible to remove 99% of the FAME.