Ultrasound assisted transesterification of high free fatty acids karanja oil using heterogeneous base catalysts

Abstract

In present study, production of fuel-quality biodiesel from high free fatty acid (FFA) feed stock, such as karanja oil, was investigated by ultrasonic assisted technique using dual step process. The initial acid value of oil was found to be 33 mg KOH/g corresponding to FFA level of 18 %, which was far above 1 % limit for satisfactory transesterification reaction using alkali catalyst. Hence, the dual-step process, H2SO4 catalyzed esterification followed by transesterification in the presence of heterogeneous base Ba(OH)2·8H2O catalyst was performed with ultrasonic technique at 30 kHz and amplitude 80 %. In the esterification step, effect of different operating parameters such as alcohol to oil molar ratio (6:1–12:1); catalyst loading, H2SO4 (0.5–1.5 %); reaction time (30–120 min); and temperature (30–60 °C) to reduce the FFA content was investigated. In the second step, heterogeneous Ba(OH)2·8H2O catalyzed transesterification of acid esterified oil was carried out by studying the effects of following variable on maximum conversion level: the concentrations of Ba(OH)2·8H2O catalyst, reaction time, temperature, and alcohol to oil molar ratio. The product conformation was done using 1H-NMR (proton nuclear magnetic resonance). The physicochemical properties were determined and compared with the biodiesel standards. In addition, thermo-oxidative stability and cold flow properties of karanja oil and its methyl ester were also investigated.