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

Authors: ISAH, SHEHU - Delaware State University; ZHANG, JAINWEI - South China University Of Technology; Biresaw, Girma; Strahan, Gary; Nunez, Alberto; Wyatt, Victor; Ngo, Helen; OZBAY, GULNIHAL - Delaware State University

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2020
Publication Date: 3/6/2021
Citation: Isah, S., Zhang, J., Biresaw, G., Strahan, G.D., Nunez, A., Wyatt, V.T., Ngo, H, Ozbay, G. 2021. Synthesis of Dimer Acid 2-Ethylhexyl Esters and their Physicochemical Properties as Biolubricant Base Stock and their Potential as Additive in Commercial Base Oils. Journal of the American Oil Chemists' Society. 98(6):683–695. https://doi.org/10.1002/aocs.12455.
DOI: https://doi.org/10.1002/aocs.12455

Interpretive Summary: Base oils and additives used in the lubricant industry are predominantly derived from petroleum. This work describes the chemical modification of plant-based molecules that can be used as lubricant base oils or as additives that can provide improved physical properties of lubricants. Bioproducts made from fats and oils have cold temperature properties that can cause them to gel or form precipitates at low temperatures. Additives are the most cost-effective means to improve poor cold temperature properties. This study examined new compounds synthesized from plant oils that can be blended with commercial base oils or used as additives to improve the physical properties of lubricants. These compounds have specialized chemical structures that can reduce the temperature where the oil begins to lose its ability to flow (the pour point) and can also reduce the negative effect of temperature on viscosity. The results of this study show that the new plant-based molecules are comparable or superior to common commercial base oils and can, therefore, be used in lubricant base oils formulations and as additives to improve physical properties. This research will directly benefit the lubricant and US farming industries.

Technical Abstract: Previously synthesized C36 dimer acids have been esterified (97 +/- 0.2 percent conversion at 120 degrees C for 72h) with 2-ethylhexanol (2-EH) to produce a new class of C52 dimer acid esters that have potential application in bio-lubricant formulations as base oils and additives. Investigation of physico-chemical and lubricant properties showed the bio-based esters have good solubility in commercial base stocks such as poly alpha olefin (PAO-6) (greater than 20 w/w) and high oleic sunflower oil (HOSuO) (greater than 20 w/w). The neat dimer acid 2-EH esters displayed a 3 to 8-fold higher kinematic viscosity and comparable viscosity index (VI = 134) as a commercial base stock, PAO-6 (VI =137). Both dimer acid 2-EH esters, whose parent dimer acids were synthesized with two different zeolite catalysts, were oxidatively stable above 176 degrees C. Blending dimer acid 2-EH esters in HOSuO improved its cold flow properties. Thus, the pour point (PP) of HOSuO was lowered from -18.8 degrees C to -21 degrees C at 1 percent w/w, while the cloud point (CP) was lowered from -6.3 degrees C to -10.6 degrees C at 8 percent w/w of dimer acid 2-EH ester 1. Similar trend was observed for dimer acid 2-EH ester 2. This indicates that the esters possess pour point depressant (PPD) characteristics in HOSuO blends. Blending dimer acid 2-EH esters in PAO-6 increased the VI of PAO-6, which is an indication that the bio-based esters were acting as viscosity index improvers (VIIs). It is concluded that dimer acid 2-EH esters can be employed commercially as bio-based base oils and as PPD and VII additives in lubricant formulations.