Reduction of FFA in jatropha curcas oil via sequential direct-ultrasonic irradiation and dosage of methanol/sulfuric acid catalyst mixture on esterification process

• Ultrasonic irradiation (UI) can auto-induce temperature rise.
• Esterification at higher temperature (T) by UI offers greater reduction of acid value.
• Sequential UI and catalyst dosing enhance esterification conversion efficiency (η).
• UR of jatropha oil at higher T results in less water content on ester as product.
• A 99.35% of η is achievable via sequential UI and dosing of 5 mL per dose.

Production of jatropha-ester (JO-ester) from jatropha oil (JO) under sequential direct-ultrasonic irradiation (UI) with auto-induced temperature rise followed by adding a mixture of methanol/sulfuric-acid catalyst (M/C) dose between high temperature intervals was studied. Comparisons with various doses of 5, 10, 16.6 and 25 mL at different temperature intervals of 108.9–120 °C, 100–120 °C, 85–120 °C and 75–120 °C respectively were performed. System parameters examined include: esterification times (tE) for UI, settling time (tS) after esterification and temperature (T). Properties of acid value (AV), iodine value (IV), kinematic viscosity (kV), density (ρLO) and water content (mw) of JO and JO-ester product were measured. The esterification conversion efficiencies (η) were determined and assessed. An η of 99.35% was obtained at temperature interval of 108.9–120 °C with 5 mL per dose for 20 doses and tE of 167.39 min (denoted as Process U120-5), which is slightly higher than η of 98.87% at temperature interval of 75–120 °C with 25 mL per dose for 4 doses and tE of 108.79 min (noted as Process U120-25). The JO-ester obtained via sequential UI with adding doses of 5 mL possess AV of 0.24 mg KOH/g, IV of 124.77 g I2/100 g, kV of 9.89 mm2/s, ρLO of 901.73 kg/m3 and mw of 0.3 wt.% showing that sequential UI and dose at higher temperature interval can give higher reduction of AV compared with 36.56 mg KOH/g of original oil. The effects of tS and tE on AV are of minor and moderate importance, respectively. The combined effects of auto-induced temperature-rise of UI and temperature higher than boiling point of methanol used improve the mixing and esterification extent.