Optimization of ethyl ester production assisted by ultrasonic irradiation

Continuous Ultrasound-Assisted Esterification and Transesterification of Palm Fatty Acid Distillate for Ethyl Ester Production

Ethyl ester production from palm fatty acid distillate (PFAD) with ethanol in the presence of sulfuric acid and potassium hydroxide was performed in a continuous three-step process using the ultrasound clamps and an ultrasonic probe. The ultimate goal was to produce biodiesel from the PFAD. In the first and second esterification steps, 16 units of a 400 W ultrasound clamp (20 kHz) were attached 100-m apart along each tubular reactor. In the third transesterification step, a 1000-W ultrasonic homogenizer (18 kHz) was used in a 100-mL continuous reactor. A composite central design of experiments and the response surface methodology (RSM) were used to develop predictive models and identify the optimal conditions of each step based on the purities of ethyl ester. The optimal conditions in the first step were 46.1 vol.% ethanol, 1.4 vol.% sulfuric acid, and purity 66.68 wt.% ethyl ester. In the second step, the optimized conditions were 57 vol.% ethanol, and 2.1 vol.% sulfuric acid, purity 95.32 wt.% ethyl ester. The final transesterification step was carried out with 14.6 vol.% ethanol and 3.9 gKOH L−1. As a result, a final ethyl ester purity of 98.15 wt.% was achieved in the biodiesel using the three-step process.

Enzyme-catalyzed synthesis and kinetics of ultrasonic-assisted biodiesel production from waste tallow

The use of ultrasonic processing was evaluated for its ability to achieve adequate mixing while providing sufficient activation energy for the enzymatic transesterification of waste tallow. The effects of ultrasonic parameters (amplitude, cycle and pulse) and major reaction factors (molar ratio and enzyme concentration) on the reaction kinetics of biodiesel generation from waste tallow bio-catalyzed by immobilized lipase [Candida antarctica lipase B (CALB)] were investigated. Three sets of experiments namely A, B, and C were conducted. In experiment set A, two factors (ultrasonic amplitude and cycle) were investigated at three levels; in experiment set B, two factors (molar ratio and enzyme concentration) were examined at three levels; and in experiment set C, two factors (ultrasonic amplitude and reaction time) were investigated at five levels. A Ping Pong Bi Bi kinetic model approach was employed to study the effect of ultrasonic amplitude on the enzymatic transesterification. Kinetic constants of transesterification reaction were determined at different ultrasonic amplitudes (30%, 35%, 40%, 45%, and 50%) and enzyme concentrations (4, 6, and 8 wt.% of fat) at constant molar ratio (fat:methanol); 1:6, and ultrasonic cycle; 5 Hz. Optimal conditions for ultrasound-assisted biodiesel production from waste tallow were fat:methanol molar ratio, 1:4; catalyst level 6% (w/w of fat); reaction time, 20 min (30 times less than conventional batch processes); ultrasonic amplitude 40% at 5 Hz. The kinetic model results revealed interesting features of ultrasound assisted enzyme-catalyzed transesterification (as compared to conventional system): at ultrasonic amplitude 40%, the reaction activities within the system seemed to be steady after 20 min which means the reaction could proceed with or without ultrasonic mixing. Reversed phase high performance liquid chromatography indicated the biodiesel yield to be 85.6±0.08%.