Optimization of continuous acid-catalyzed esterification for free fatty acids reduction in mixed crude palm oil using static mixer coupled with high-intensity ultrasonic irradiation

The major problem of biodiesel production from mixed crude palm oils (MCPOs) is the high free fatty acid (FFA) content. To achieve good conversion from MCPO to esters, the FFA should not exceed 1 wt.% or 2 mgKOH g−1 of acid value when using base-catalyzed transesterification to produce biodiesel. In this study, reduction of the acid value in MCPO with methanol in the presence of sulfuric acid as an acid-catalyst was performed in continuous esterification using static mixer coupled with ultrasonic reactor. A 1000 W ultrasonic homogenizer was operated at 18 kHz frequency in a 100 mL continuous-reactor. Response surface methodology (RSM); a 5-level, 2-factor, central composite design (CCD), was employed to optimize the two important reaction variables (methanol and sulfuric acid concentrations). To minimize chemical costs in order to reduce the acid value from 28 mgKOH g−1 to less than 2 mgKOH g−1, 18 vol.% of methanol, 2.7 vol.% of sulfuric acid, and 20 L h−1 of MCPO flow rate are recommended.

► Continuous esterification using static mixer coupled with ultrasonic irradiation.
► Response surface methodology was employed to optimize the two reaction variables.
► Acid value can be reduced from 28 mgKOH g−1 to less than 2 mgKOH g−1.
► Ultrasound can shorten settling time of the esterified oil and the waste.