Investigation of the physical and tribological properties of Iso-oleic acid

Authors: Biresaw, Girma; Ngo, Helen; Dunn, Robert

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2018
Publication Date: 12/18/2018
Citation: Biresaw, G., Ngo, H., Dunn, R.O. 2018. Investigation of the physical and tribological properties of Iso-oleic acid. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.12177.
DOI: https://doi.org/10.1002/aocs.12177

Interpretive Summary: Fatty acids and their derivatives obtained from vegetable oils and animal fats are important components of lubricants for a wide range of applications. Fatty acids and their esters are used as boundary additives in many commercial lubricant formulations. Fatty acid-based derivatives are also being developed for use as biobased base oils. Currently, farm-based products, including fatty acids, make up a miniscule share of the lubricant market. Increased utilization of agricultural products in lubrication requires development of new and competitive biobased additives and base oils via thermal, chemical and/or enzymatic processing of vegetable oils and animal fats. In the work described here, oleic acid was converted into iso-oleic acid using a solid zeolite catalyst. The process produced a mixture of iso-oleic acid structures, with a methyl branching and unsaturation randomly distributed along the fatty acid chain. The physical and tribological properties of the neat iso-oleic acid product mixture and its blends in biobased and petroleum-based base oils were investigated. The study showed that, relative to oleic acid, neat iso-oleic acid displayed several improvements including: lower pour point, lower cloud point, and better oxidation stability. In blend studies, increasing the concentration (0–10% w/w) of iso-oleic and oleic acid in polyalphaolefin base oil resulted in increasing viscosity index and lower coefficient of friction. The improved oxidation stability and cold flow property of neat iso-oleic acid relative to neat oleic acid could lead to increased application of fatty acids in biobased lubricants and other biobased products, thereby increasing the demand for seed oil crops and other farm products. The findings of this study will be useful additions to the database available to scientists and engineers engaged in the development of biobased lubricants from fatty acids.

Technical Abstract: Oleic acid was isomerized into iso-oleic acid using a modified ferrite zeolite catalyst. The isomerization produced a mixture of iso-oleic acid isomers, with a methyl branching at the double bond, whose position has been randomly distributed along the fatty acid chain. The effect of isomerization on the physical and tribological properties of iso-oleic acid relative to oleic acid was investigated. The neat fatty acids and their blends in polyalphaolefin (PAO-6) and high-oleic sunflower oil (HOSuO) base oils were used in the investigations. Relative to neat oleic acid, neat iso-oleic acid displayed: higher kinematic viscosity but lower viscosity index (VI) and acid number; lower pour point (PP) and cloud point (CP); better oxidation stability; similar four-ball (4-ball) antiwear friction and wear; and similar 4-ball extreme pressure weld point. Blends (0–10%, w/w) of iso-oleic and oleic acid in PAO-6 displayed the following similar trends with increasing concentration: mildly decreasing kinematic viscosity at 40 and 100 °C; increasing VI; lower coefficient of friction; and no change in wear. Blends (0–10%, w/w) of iso-oleic and oleic acid in HOSuO displayed the following similar trends: decreasing oxidation stability with increasing concentration; constant PP and CP with increasing concentration.