Chemical compositions, properties, and standards for different generation biodiesels: A review

Continuously growing world's energy demand and global climate change due to green house gas emissions have created need to find out renewable and sustainable energy solution. Biodiesel is one of the most promising substitute of diesel fuel that can be produced from vegetable oils, animal fats, waste oils etc. It is broadly classified in four generations i.e. edible oils (first generation), non-edible oils (second generation), waste oils (third generation) and advance solar biodiesel (fourth generation). There are some limitations associated with biodiesel as a fuel in diesel engines like cold flow, oxidation stability etc. Selection of biodiesel due to the above reasons is region specific and depends on the specific properties which are mainly governed by fatty acid composition of that oil. This review discusses the physicochemical properties of different generation biodiesel using 52 types of feedstocks. The chemical composition and physicochemical properties of 31 raw oils have also been discussed. As different fatty acid methyl esters (FAME) structures behave differently, it is not possible to develop a unique approach for obtaining optimum composition of FAME. The low concentration of polyunsaturated FAME and long-chain saturated FAME is more favorable for oxidation stability, low-temperature operability, and satisfactory performance. American Society for Testing and Materials (ASTM), European committee for standardization (CEN), Bureau of Indian Standards (BIS), etc. provided the specifications for the biodiesel and their blends.