Rice bran oil as a potential resource for biodiesel : A review

Biodiesel (BD) is receiving increased attention as an alternative, non-toxic, biodegradable, and renewable diesel fuel. Exploring new energy resources, such as BD fuel, is of growing importance in recent years. The main concern with BD fuel is its high price. One of the future aims in BD research is on the selection of inexpensive feedstock with high value–added byproducts. Rice bran is a by-product of rice milling that contains 15-23% lipids and a significant amount of nutraceutical compounds. Due to the presence of active lipase in the bran and the lack of economical stabilization methods, most bran is used as livestock feed or boiler fuel and most rice bran oil (RBO) produced is not of edible grade. Thus RBO is relatively an inexpensive raw material for the production of BD. The utilization of by-product such as defatted rice bran for the production of proteins, carbohydrates, phytochemical, and the isolation and purification of value added nutraceutical generated during BD production from RBO are attractive options to lower the cost of BD. Production of BD from RBO can be carried out either via in situ esterification, lipase-catalyzed esterification, acid-catalyzed or base-catalyzed reactions. A single step reaction for the conversion of RBO with high free fatty acid content into BD, via acid-catalyzed, base-catalyzed or lipase-catalyzed, fails to attain high conversion in reasonably short time. Pretreatment of crude RBO such as dewaxing/degumming is a crucial step because of its efficient methanolysis. The fatty acid composition of dewaxed/degummed RBO is similar to that of other vegetable oils, which are used as BD feedstock. Various byproducts generated from the rice bran during the production of BD and their applications are also addressed.