Synthesis of biolubricants by the esterification of free fatty acids from castor oil with branched alcohols using cationic exchange resins as catalysts

Three cationic exchange resins (PD206, CT269DR and CT275DR), supplied by Purolite®, with different physicochemical properties have been evaluated in the esterification reaction of the free fatty acid from the castor oil with 2-ethylhexanol in order to obtain products with interesting properties to be used as biolubricant basestock. These resins have been characterized by SEM, elemental analysis (CNHS), TG/DTA and XPS. Likewise, these catalysts have been analyzed after the catalytic reaction to evaluate changes in the active phase during the esterification reaction. The catalytic data reveal that the macroreticular-type resins (CT269DR and CT275DR) show higher conversion values, about 95% after 4 h, than a gel-type resin (PD206) due to several factors, such as the higher amount of available acid sites or the denser divinylbenze matrix, which provides higher thermal and mechanical resistance and minimizes sulfur leaching. The deactivation of the active phase has been ascribed to the strong adsorption of reagents and products on the sulfonic groups located at the surface, as indicated in the XPS spectra of the spent catalysts. The products characterization showed that 2-ethylhexyl ricinoleate exhibited excellent properties at low temperature (pour point −39 °C), viscosity index value compatible with commercial synthetic basestock oils, higher biodegradability than mineral oil and better oxidation stability than the original feedstock.