Valorization of Waste Cooking Oil into Biodiesel over Heterogeneous Catalysts

Abstract

Biodiesel can be prepared by the transesterification of triglycerides or the esterification of free fatty acids (FFAs) with short-chained alcohols. Generally, biodiesel is produced via transesterification of vegetable oils or animal fats with short-chain alcohols (e.g., methanol), which is carried out by acid or base catalysis. To improve the economic feasibility of biodiesel, cheap low-quality feed stocks such as waste cooking oil (WCO), animal fat and tall oil instead of refined vegetable oil have been used. The amount of WCO generated in each country is huge and varies depending on the use of vegetable oil. Currently, the inexpensive and large quantity of WCO from households and restaurants are collected and used either as animal feed or disposed of, causing environmental pollution. Thus, WCO offers significant potential as an alternative low–cost biodiesel feedstock which could partly decrease the dependency on petroleum-based fuel. Traditionally, homogeneous catalysts have been used in the esterification and transesterification reactions. However, solid catalysts have many advantages over liquid ones. They do less harm to the environment and do not have the same corrosion or disposal problems. They are reusable and easy to be separated from liquid products. In this work, the use of heterogenous catalysts for biodiesel production from waste cooking oil will be reviewed.