Modification of epoxidized soybean oil for lubricant formulations with improved oxidative stability and low pour point

To produce soybean oil-based lubricants with good oxidative stability and low pour point, epoxidized soybean oil (SBO) was chemically modified. Epoxidized SBO was reacted with various alcohols in the presence of sulfuric acid as a catalyst to give a ring-opened intermediate product. In this step, the epoxy group was transformed to the functional group of-CH(OR1)CH(OH)-(where the R1=methyl, 1-butyl, 2-butyl, 1-hexyl, cyclohexyl, 2,2-dimethyl-1-propyl, or 1-decyl). The 1H nuclear magnetic resonance spectra of the products indicated that transesterification was accompanied by the ringopening reaction except when the bulky 2,2-dimethyl-1-propanol was used. Acid anhydride was used to esterify the hydroxy groups in the ring-opened product. This resulted in a fluid that is a lubricant candidate with the functional group of −CH(OR1)CH(OCOR2)−. Pour point studies of the resulting products showed that the pour points varied with the substituents, R1 and R2. Products with R1=CH3(CH2)5− and R2=CH3(CH2)2−, (CH3)2CH−, or CH3(CH2)4-showed the lowest pour points (−39, −39, and −45°C, respectively) when 1% of pour point depressant was added. For the oxidative stability test, two products, in which R1, R2=CH3(CH2)5−, (CH3)2CH− and R1, R2=CH3(CH2)5−, CH3(CH2)4−, were chosen for a modified Penn State micro-oxidation test. In the oxidative stability test, the products gave 69–71% of oxidative evaporation and 10–17% of tetrahydrofuran-insoluble deposits in 3 h at 175°C. The amounts of deposits were much lower than those of soybean oil (96%) and epoxidized SBO (83%) and even less than those of most petroleum-based lubricant basestocks (3–93%).