In-situ synergistic effect of ultrasonic irradiation and solvent addition for enhancing CaO catalyzed transesterification.

• High-efficiency biodiesel production using mixed solvent in ultrasonic reactor. • In-situ synergistic effect from mixed solvent addition for CaO catalyzed transesterification. • In-situ generation of calcium glyceroxide occurred during combination of ultrasonic and acetone. • Ultrasonic combined with mixed solvent achieves high biodiesel yield (97.3%) and yield efficiency. This work focuses on the improvement of biodiesel production with the addition of solvents (acetone, THF, and methyl myristate) in CaO catalyzed transesterification of palm oil and methanol in an ultrasonic reactor using a methanol to oil molar ratio of 9:1, reaction temperature of 60 °C, and CaO loading of 5 and 10 wt%. The addition of acetone and THF in the presence of ultrasonic irradiation expressed the synergistic effect which can accelerate the initial transesterification rate by increasing the solubility and in-situ generations of microbubble droplets and calcium glyceroxide as a new active species. The addition of methyl myristate enhanced the biodiesel yield by acting as an emulsifier of the reaction mixture and producing microemulsion droplets with the help of ultrasonic irradiation. Moreover, the mixed acetone and methyl myristate with existing ultrasonic irradiation can promote CaO catalyzed transesterification by accelerating the initial rate and achieving a high biodiesel yield (97.3%). The quality of the synthesized biodiesel in terms of physical properties is proven to meet the biodiesel standard. [ABSTRACT FROM AUTHOR]