Preparation of a supported acidic ionic liquid on silica-gel and its application to the synthesis of biodiesel from waste cooking oil

An environmental acidic ionic liquid was prepared with 1-allyl-1H-imidazole, 1,3-propyl sulfonic acid lactone and H2SO4 and was immobilized on silica-gel to synthesize the catalyst used to prepare biodiesel from waste cooking oil by a one-step method. The structure of the catalyst was characterized by BET, FTIR, DSC/TGA and SEM. The effect of methanol oil mole ratio, catalyst dosage, reaction temperature, and reaction time on the conversion of waste cooking oil to biodiesel was investigated, and the optimum reaction conditions were determined by an orthogonal test. The optimum reaction conditions were shown as follows: methanol oil mole ratio of 25:1, catalyst dosage of 5 wt% of oil, reaction temperature of 60 °C, reaction time of 20 h, and the yield of 87.58%. The yield could reach 70.02% after reusing the catalyst 5 times.