A KCr/calcium oxide (CaO) bifunctional catalyst was synthesized from CaO from eggshells and impregnated with K2Cr2O7 (KCr). The catalysts were assessed in a transesterification reaction between waste cooking oil and ethanol (EtOH) for the biodiesel production. The properties of the KCr/CaO catalyst were investigated by using scanning electron microscopy, X-ray diffraction, ATR/FTIR, TGA, and FESEM-EDS. The results show that Cr2O72– can be reduced by trace elements (Mg, Si, and C) in CaO and converted to Cr2O3, which facilitates catalytic activity. The reactions were optimized using a Box-Behnken design and response surface methodology (RSM), and the results were analyzed by analysis of variance. According to the RSM, the consequences showed that an EtOH-to-WCO molar ratio of 12, KCr/CaO of 4.0% w/w, and 180 min produced an 89.32% biodiesel yield. Reaction catalysts and time were key factors influencing the biodiesel synthesis. The biodiesel under these conditions was found to be substantially consistent with the parameters given in ASTM D6751 and EN 14214.
Chuepeng et al. (2026) studied this question.