Production of biodiesel from waste cooking oil using heterogeneous catalysts KI/γ-Al₂O₃

Biodiesel is a promising alternative fuel that can be produced from vegetable oil through the esterification process. Conventional homogeneous acid or base catalysts result in a lower biodiesel yield and a longer reaction time and require separation from the product, which lead to inefficient production. This research was aimed at utilising the heterogeneous catalyst potassium iodide (KI)/γ-aluminium oxide (γ-Al₂O₃) for esterification of waste cooking oil into biodiesel. The catalyst was prepared using the impregnation method in which calcination was conducted at 500°C for 3 h. The esterification operation condition was set to a temperature of 65°C for 3 h and a molar ratio of oil to methanol of 1:14. Moreover, the heterogeneous catalyst was compared with a homogeneous catalyst with respect to the yield of biodiesel. The results showed that at a 2% (g catalyst/g oil) catalyst concentration, the esterification using the catalyst KI/γ-Al₂O₃ produced a higher yield of biodiesel (88·03%) compared with using γ-aluminium oxide (58·86%) and a conventional catalyst (82·23%). The reusability study of the catalyst KI/γ-Al₂O₃ showed that after the first reuse, the catalyst could still produce biodiesel with a yield of 61·30%. After the second reuse, the yield of biodiesel was 52·61%, and the third reuse produced a yield of 21·50%.