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

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 degrees C, 108.9 to 120 degrees C and 128.5 to 140 degrees C were made. System parameters examined include: esterification times (t(E)) for UR, settling time (t(S)) after esterification and temperature (T). Properties of acid value (AV), iodine value (IV), kinematic viscosity (KV), density (rho(LO)) and water content (m(w)) of jatropha oil and ester product were measured. The esterification conversion efficiencies (eta) were determined and assessed. An eta of 99.35% was obtained in temperature interval of 108.9 to 120 degrees C with 5 mL per dose for 20 doses and t(E) of 167.39 min (denoted as Process U120-5), which is slightly higher than eta of 98.87% in temperature interval of 75 to 120 degrees C with 25 mL per dose for 4 doses and t(E) 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 gI(2)/100 g, KV of 9.89 mm(2)/s, rho(LO) of 901.73 kg/m(3) 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 t(S) and t(E) 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. (C) 2014 Published by Elsevier B.V. on behalf of Taiwan Institute of Chemical Engineers.