Quality and composition of lipids used in biodiesel production and methods of transesterification: A review

This study presents a brief overview of the composition and properties of various oils used in biodiesel production and the alkali, acidic and enzymatic transesterification reactions used in production. Nowadays, vegetable and microalgae oils are mostly used in biodiesel production. Recently, however, animal fats, processed oils, industrial oils and yeast and bacterial oils have also gained importance. Although all fats and oils are roughly similar, their saturated fatty acids (SFA), polyunsaturated fatty acids (PUFA), monounsaturated fatty acids (MUFA), free fatty acids (FFA), cholesterol or glycerol contents may be different and affect the production and efficiency of the biodiesel. Triglycerides are the most significant lipids in biodiesel production. Triglycerides in vegetable oils dominantly contain C18:1ω9 and C18:2ω6 fatty acids. Whereas, triglycerides in animal fats mostly include C16:0 and C18:1ω9 fatty acids. Microalgae are rich in long-chain fatty acids such as C20 and C22. Also, fatty acids such as C14:0, C16:1ω7, C18:0, C20:0, C22:0, C24:0, C22:1ω9, C18:3ω6, C20:4ω6 and C20:5ω6 are present in oils and fats. However, their proportions change from feedstock to feedstock. Rendered animal-originated fats include larger quantities of FFA than waste vegetable oils and, as known, excessive amounts of FFA generate soap in reactions with the alkaline catalyst, reducing biodiesel efficiency. For this reason, generally vegetable and microalgal oils containing a large number of triglycerides and less FFA are preferred for biodiesel production. Bacteria can synthesize branched fatty acids. It has been reported that biodiesel produced from branched fatty acids has advantages according to biodiesel produced from other lipids. Consequently, the use of correct and reliable lipids in biodiesel production is very important for the quality of fuel.