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

Abstract

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 1wt.% or 2mgKOHg−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 1000W ultrasonic homogenizer was operated at 18kHz frequency in a 100mL 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 28mgKOHg−1 to less than 2mgKOHg−1, 18vol.% of methanol, 2.7vol.% of sulfuric acid, and 20Lh−1 of MCPO flow rate are recommended.