Esterification of high FFA content waste cooking oil through different techniques including the utilization of cement kiln dust as a heterogeneous catalyst: A comparative study

Abstract The aim of this work was to compare two different techniques for the esterification of waste cooking oil having high free fatty acids (FFA) content. The first method was esterification using sulfuric acid as the catalyst, wherein the effect of methanol to oil molar ratio and catalyst loading were studied and optimized via response surface methodology (RSM). The optimum conditions were molar ratio 52:1 and catalyst loading 3.5%, and the observed conversion of FFA to methyl esters was 96.2%, after 1 h, at 65 °C. The second method was heterogeneously catalyzed esterification using cement kiln dust (CKD). In this case, the optimum conditions were: esterification time 6 h, methanol to oil molar ratio 18:1, catalyst loading 2%, and 65 °C leading to 98.8% conversion. A comparison between the two methods revealed that using CKD can be a potentially economical catalyst more than using a homogeneous catalyst.