Optimization of High Free Fatty Acid Reduction in Mixed Crude Palm Oil Using Ultrasound: A Response Surface Methodology Approach

Abstract

Reduction of the acid value in mixed crude palm oil (MCPO) with methanol and acid-catalyst H2SO4 was carried out in an ultrasonic homogenizer at a low-frequency of 18 kHz with 1,000 W. This work was undertaken with fixed values of 1.62 W.mm-2 for the high surface power density at the horn tip and 20 W.mL-2 for the volumetric acoustic energy. The objective was to determine the relationship between various important parameters and the response variable of acid-catalyzed esterification to obtain the lowest acid value. Response surface methodology was used to optimize the operating parameters of the ultrasonic esterification process. A 5-level, 3-factor, central composite design was applied to optimize the three key reaction variables (methanol concentration, sulfuric acid concentration and ultrasonic irradiation time) to reduce the acid value of the MCPO from 28 mg.g-1 KOH to less than 2 mg.g-1 KOH. The results indicated that the factors have significant effects on the reduction of the acid value. Furthermore, optimization of the reduction of the acid value could be achieved with 24.8% (by volume) methanol, 3.7% (by volume) sulfuric acid and an ultrasonic irradiation time of 96 s.