Purification technologies for crude biodiesel obtained by alkali-catalyzed transesterification

For commercial application, the ester product of alkali-catalyzed transesterification of vegetable oil or animal fats should be refined after glycerol separation by settling to fulfill the biodiesel standard specifications. This crude biodiesel, after neutralization and methanol removal, should be further cleaned by either one of the following methods: wet washing, dry washing, membrane extraction or using ion liquids. This paper presents a review on the traditional (wet and dry washing) and novel (membrane separation technology and usage of ion liquids) methods of crude biodiesel purification. It also provides a comparison of crude biodiesel purification methods. Each method has its advantages and disadvantages, which should be carefully analyzed when choosing the proper one for refining crude biodiesel.