Waste fish oil (WFO) esterification catalyzed by sulfonated activated carbon under ultrasound irradiation

• Esterification of free fatty acids of waste fish oil (WFO) was studied.
• Sulfonated activated carbon as an esterification catalyst was applied.
• The influences of the different operating parameters were investigated.
• Response surface methodology (RSM) was used to find the best operating parameters.
• An accurate correlation was developed for the esterification conversion.

In the present research work, esterification reaction of waste fish oil (WFO) catalyzed by sulfonated activated carbon under ultrasound irradiation was studied. The application of this catalyst, in addition to the elimination of purification process, leads to the green biodiesel production. The influences of various operating variables such as catalyst loading (1–12 wt%), methanol to oil molar ratio (6–15), and ultrasonic power (100–400 W) on the esterification conversion have been investigated. Response surface methodology (RSM) based on Box–Behnken design (BBD) has been employed. 88% conversion for the esterification reaction has been obtained under the best conditions (i.e., catalyst loading of 11.4 wt%, ultrasonic power of 296.09 W, and methanol to oil molar ratio of 14.85). An accurate mathematical correlation has been developed for the prediction of the esterification conversion. 56% conversion for the esterification reaction has been obtained in the same operating conditions in the absence of ultrasound irradiation.