“Designer” Biodiesel: Optimizing Fatty Ester Composition to Improve Fuel Properties†

Biodiesel is a domestic and renewable alternative with the potential to replace some of the petrodiesel market. It is obtained from vegetable oils, animal fats, or other sources with a significant content of triacylglycerols by means of a transesterification reaction. The fatty acid profile of biodiesel thus corresponds to that of the parent oil or fat and is a major factor influencing fuel properties. Besides being renewable and of domestic origin, advantages of biodiesel compared to petrodiesel include biodegradability, higher flash point, reduction of most regulated exhaust emissions, miscibility in all ratios with petrodiesel, compatibility with the existing fuel distribution infrastructure, and inherent lubricity. Technical problems with biodiesel include oxidative stability, cold flow, and increased NOx exhaust emissions. Solutions to one of these problems often entail increasing the problematic behavior of another property and have included the use of additives or modifying the fatty acid composition, either through physical processes, such as winterization, or through genetic modification. Methyl oleate has been proposed as a suitable major component of biodiesel in this connection. In this work, the properties of various potential major components of biodiesel are examined and compared. For example, while methyl oleate has been suggested as such a major component, methyl palmitoleate has advantages compared to methyl oleate, especially with regards to low-temperature properties. Other materials that are examined in this connection are short-chain (C8-C10) saturated esters, with only C10 esters appearing suitable. It is also suggested that to obtain biodiesel fuel with favorable properties, it is advantageous for the fuel to consist of only one major component in as high a concentration as possible; however, mixtures of components with advantageous properties as described here may also be acceptable.