Abstract During biodiesel preparation via alkaline catalyst, water washing method was used to remove the impurities in the ester layer and the introduction of water leading to a stable emulsion formation. How to destroy the emulsion quickly and effectively becomes the difficulty of water washing process. Different demulsification methods,such as heating, high speed centrifugation, addition of saturated salt solution and addition of hydrochloric acid solution were evaluated. The experimental class of "the formation, types and damage of emulsion" takes the water washing process of crude biodiesel as an example not only can help students fully understand the formation reasons and types of emulsion, demulsification methods and the corresponding mechanism but also can enhance the activity of students and improve the theory teaching quality because of the great interests shown by students for biodiesel.
