ABSTRACT
At present, the alkaline catalyst method is applied commercially to produce biodiesel. However, the process is not simple and not applicable to wastes of oils and fats. Therefore, a one-step supercritical methanol method, the Saka process, was developed as a noncatalytic process. In this process, even wastes of oils and fats that are high in water and free fatty acids can be converted to biodiesel. However, the reaction conditions are drastic (350°C, >20 MPa), thus a special alloy such as hastelloy is required for the reaction vessel. Additionally, the biodiesel produced is thermally deteriorated. Therefore, to realize milder reaction conditions, a two-step supercritical methanol method, the Saka-Dadan process, was developed, which consisted of the hydrolysis of oils and fats in subcritical water and subsequent methyl esterication of the fatty acids produced in supercritical methanol. In this process, milder reaction conditions (270°C, <10 MPa) can be realized using ordinary stainless steel instead of a special alloy. Moreover, due to the removal of the glycerol after the hydrolysis process, the biodiesel satises most of the requirements of the EU and U.S. standards.
