Esterification of jatropha oil via ultrasonic irradiation with auto-induced temperature-rise effect

•Esterification of jatropha oil is pronounced under ultrasonic irradiation (UI).•UI can auto-induce temperature rise.•The induced temperature rise assists the mixing of UI in enhancing esterification.•UI offers better esterification than mechanical mixing with external heating.•An 83.23% reduction of FFA in jatropha-ester is achievable via UI in 30 min.

Auto-induced temperature-rise effects of ultrasonic irradiation (UI) on the esterification performance of jatropha oil (JO) were studied. Comparisons with other methods of mechanical mixing (MM) and hand shaking mixing were made. Major system parameters examined include: esterification time (tE), settling time (tS) after esterification and temperature. Properties of acid value (AV), iodine value (IV), kinematic viscosity (KV) and density of JO and ester product were measured. The esterification conversion efficiencies (η) were determined and assessed. Sulfuric acid was used to catalyze the esterification using methyl alcohol. For esterification without temperature control, η at tE = 10 and 30 min for UI of 56.73 and 83.23% are much higher than those for MM of 36.76 and 42.48%, respectively. At tE = 10 min, the jatropha oil esters produced via UI and MM respectively possess AV of 15.82 and 23.12 mg KOH/g, IV of 111.49 and 113.22 g I2/100 g, KV of 22.41 and 22.51 mm2/s and density of 913.8 and 913.58 kg/m3, showing that UI is much better than MM in enhancing the reduction of AV. The tE exhibits more vigorous effect on AV for UI than MM. The UI offers auto-induced temperature-rise, improving the mixing and esterification extents.