Synthesis of Dimer Acid 2-Ethylhexyl Esters and their Physicochemical Properties as Biolubricant Base Stock and their Potential as Additive in Commercial Base Oils

Previously synthesized C36-dimer acids (DA) have been esterified (97 ± 0.2% conversion at 120 °C for 72 hours) with 2-ethylhexanol (2-EH) to produce a new class of C52-DA 2-EH esters that have potential application in biolubricant formulations such as base oils and additives. Investigation of physicochemical and lubricant properties showed the bio-based esters have good solubility in commercial base stocks such as polyalpha olefin (PAO-6) (>20 w/w) and high-oleic sunflower oil (HOSuO) (>20 w/w). The neat C52-DA 2-EH esters displayed a three- to eightfold higher kinematic viscosity and comparable viscosity index (VI = 134) as a commercial base stock, PAO-6 (VI =137). Both C52-DA 2-EH esters, whose parent C36-DA were synthesized with two different zeolite catalysts, were oxidatively stable above 176 °C. Blending C52-DA 2-EH esters in HOSuO improved the pour point (PP) of HOSuO from ?18.8 to ?21.0 °C at 1% w/w and the cloud point (CP) from ?6.3 to ?10.6 °C at 8% w/w of C52-DA 2-EH ester 1. A similar trend was observed for C52-DA 2-EH ester 2, indicating that the esters possess PP depressant (PPD) characteristics in HOSuO blends. Blending C52-DA 2-EH esters in PAO-6 increased the VI of PAO-6, which is an indication that the bio-based esters were acting as VI improvers (VII). It was concluded that C52-DA 2-EH esters can be employed commercially as bio-based base oils and as PPD and VII additives in lubricant formulations.