Membrane Filtration as an Environmentally Friendly Method for Crude Biodiesel Purification

Biodiesel is the first alternative fuel the physicochemical properties of which are regulated by appropriate standards: American ASTM D 6751 and European standard EN 14214. The process of biodiesel production consists of three main phases: 1) preparation of feedstock, 2) transesterification, and 3) processing of the reaction product – purification of crude biodiesel to meet the specification provided by the previously mentioned standards. The purification process of crude biodiesel is usually carried out by two notable techniques: wet and dry washing. The most commonly used process is wet washing. A major drawback in the use of water in purification process is the generation of a large amount of wastewater that greatly increases biodiesel production costs, followed by drying of the product, which requires an additional amount of energy and is time consuming. The greatest disadvantage of dry washing using different ion-exchange resins is the inability to remove glycerol and methanol from crude biodiesel to those limits prescribed by EN 14214, followed by the disposal problem of spent ion-exchange resins. Because of the aforementioned, the use of membrane technology in the process of biodiesel purification has appeared as an alternative for the existing purification techniques. The membrane filtration is environmentally friendly and requires less energy. By membrane filtration, the glycerol, methanol, and water contents in biodiesel can be decreased to the amounts prescribed by the standards. In the frame of this review article, the short overview of the possibility of using ultra- and/or micro-filtration in the purification process of biodiesel is presented.