Esterification of jatropha oil by sequential ultrasonic irradiation with auto-induced temperature rise and dosing of methanol and sulfuric acid catalyst

• Ultrasonic irradiation (UR) can auto-induce temperature rise.
• Esterification at higher temperature (T) by UR offers greater reduction of acid value.
• Sequential UR followed by dose of mixture (M/C) of methanol (M) and sulfuric acid catalyst (C) can enhance the esterification conversion efficiency (η).
• UR of jatropha oil (JO) at higher T results in less water content in JO-ester as product.
• A 99.35% of η is achievable via sequential UR and dosing of 5 mL per dose for 20 doses of M/C with 200 mL of JO.

The esterification of jatropha oil applying sequential ultrasonic irradiation (UR) with auto-induced temperature rise followed by adding a mixture of methanol/sulfuric acid catalyst (M/C) dose in a high temperature interval was studied. Comparisons with various doses of 5, 10, 16.6 and 25 mL in different temperature intervals of 93.32 to 100 °C, 108.9 to 120 °C and 128.5 to 140 °C were made. System parameters examined include: esterification times (tE) for UR, 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 jatropha oil and ester product were measured. The esterification conversion efficiencies (η) were determined and assessed. An η of 99.35% was obtained in temperature interval of 108.9 to 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% in temperature interval of 75 to 120 °C with 25 mL per dose for 4 doses and tE of 108.79 min (noted as Process U120-25). The jatropha ester produced via sequential UR and dose 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 UR and dose at higher temperature interval can give higher reduction of AV compared with 36.56 mg KOH 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 UR, temperature higher than boiling point of methanol used and micro-mixing and emulsification caused by UR/cavitation improve the esterification extent.