Ultrasound-assisted dispersion of bifunctional CaO-ZrO2 nanocatalyst over acidified kaolin for production of biodiesel from waste cooking oil

The work aimed to produce biodiesel from waste-cooking-oil (WCO) using a novel catalyst from acid-modified kaolin with ZrO2 and CaO. The catalyst was created by acid-treatment of kaolin and then impregnating kaolin with ZrO2 as an acid-active-component and CaO as a base-enhancer. Ultrasound was applied to disperse promoters on kaolin(T) and improve specific-surface-area and pore-volume. XRD, FESEM, FTIR, 3D-surface, EDX-dot mapping, TEM, BET-BJH, TPD-NH3, and TPD-CO2 analyses were used for characterization. A one-pot experiment has been performed to generate biodiesel from WCO by esterification and transesterification under the reaction-conditions of 10 wt% catalyst-loading, 110 °C, 3 h, and m.r = 20. The selected-nanocatalyst, Zr-Ca/Kaolin(T)-U(300), was found to have a high-activity for producing biodiesel from WCO with total-conversion, FFA-conversion, and TG-conversion rates of 93.4%, 99.0%, and 73.4%, respectively. This outstanding performance is attributed to the high acid and base strength of the catalyst (total-acid-density = 0.453 mmol NH3/g and total-base-density = 0.324 mmol CO2/g), its well-dispersed enhancer, and its high specific-surface-area (22.49 m2/g) and pore-volume (0.09 cm3/g). The selected-nanocatalyst also demonstrated great stability against five-successive-cycles (activity-reduction = 2.1%) and NaCl as an impurity of WCO (activity-reduction = 1.6%). Overall, this work presents a promising-approach for producing biodiesel from WCO using a highly efficient and stable bi-functional nanocatalyst.