Improving biodiesel fuel properties by modifying fatty ester composition

TLDR

Biodiesel, an alternative diesel fuel made from alkyl esters of vegetable oils, animal fats, or other feedstocks, mirrors the fatty acid profile of its source—typically dominated by C16/C18 fatty acids—and suffers from poor low‑temperature properties and oxidative stability, prompting research into five main improvement approaches. The article aims to briefly review the five existing biodiesel improvement strategies, emphasizing those that modify fatty ester composition. The review discusses how altering fatty ester composition—by varying the alcohol, adjusting the fatty acid profile through physical methods, genetic engineering, or selecting alternative feedstocks—constitutes a key approach among the five strategies.

Abstract

Biodiesel is an alternative to petroleum-derived diesel fuel composed of alkyl esters of vegetable oils, animal fats or other feedstocks such as used cooking oils. The fatty acid profile of biodiesel corresponds to that of its feedstock. Most common feedstocks possess fatty acid profiles consisting mainly of five C16 and C18 fatty acids, namely, palmitic (hexadecanoic), stearic (octadecanoic), oleic (9(Z)-octadecenoic), linoleic (9(Z),12(Z)-octadecadienoic) and linolenic (9(Z),12(Z),15(Z)-octadecatrienoic) acids, with the exception of a few oils such as coconut oil, which contains high amounts of saturated acids in the C12–C16 range or others. While in many respects biodiesel possesses advantages or is competitive with petroleum-derived diesel fuel, virtually all biodiesel fuels, typically the methyl esters, produced from these oils have performance problems such as poor low-temperature properties or insufficient oxidative stability. Considerable research has focused on solving or alleviating these problems and five approaches have been developed. Besides the approach of using additives, changing the fatty ester composition by either varying the alcohol or the fatty acid profile of the oil have been studied. Changing the fatty acid profile can be achieved by physical means, genetic modification of the feedstock or use of alternative feedstocks with different fatty acid profiles. In some cases approaches may overlap. This article briefly summarizes the five approaches currently used with an emphasis on those dealing with changing the fatty ester composition of a biodiesel fuel.