Microalgal fatty acid composition: implications for biodiesel quality

Abstract

The fuel properties of microalgal biodiesel are predicted using published microalgal fatty acid (FA) compositions and predictive fuel models. Biodiesels produced from the microalgae investigated are predicted to have extremely poor oxidative stabilities and the majority also have poor coldflow properties. The cetane number in most cases is out of specification, but less so than the oxidative stability and cold flow. These findings support the idea that feedstocks rich in monounsaturated fatty acids (MUFAs) are desirable for biodiesel but the composition of the saturated fatty acids (SFAs) is also shown to be of great importance. There is an apparent relationship between algal class and the percentage of FAs represented by MUFA. This potentially allows for the identification of high-MUFA algal classes, or at least provides some basis for researchers to make initial selections of target classes for bioprospecting. Comparisons of FA groups between algal classes also show that the SFAs of Mediophyceae contain significantly higher proportions of C14:0, which is in contrast to the normally abundant C16:0 and the Mediophyceae therefore have better cold-flow characteristics than other classes with similar total SFA contents. Certain particularly promising cases for biodiesel production are presented as species level examples of feedstocks that are close to satisfying the biodiesel standards and to further illustrate the challenges that remain. Variation in FA composition as a response to changes in certain environmental variables forms another important facet to feedstock selection and is briefly considered, with suggestions for further research.

Effect of Salinity and pH on Fatty Acid Profile of The Green Algae Tetraselmis suecica

“…The mixture of saturated, unsaturated and polyunsaturated fatty acids looks very promising as a base for biodiesel production and should meet the requirements for cold-flow, ignition properties, viscosity and oxidative stability [10]. The same behaviour of Nannochloropsis saline was be obtained by Fakhry and El Maghraby [5].…”

“…The fatty acid profiles were also determined using GC-MS and increasing salinity induced the synthesis of fatty acids with one double bond (monounsaturated), which are ideal for biodiesel production [10,11]. It appears likely that growing T. suecica at high salinity will result in a favourable mix of fatty acids for biodiesel.…”

“…The number of characteristics of the fatty acids can change including length (number of carbons) and presence/absence and number of double bonds (i.e., degree of unsaturation). The properties of the fatty acids affect the properties of the biodiesel produced [10].…”

“…EN 14214 is the fuel standard used in Europe). This standard ensures that the ignition properties of the fuel, its viscosity and oxidative stability all fall within acceptable limits [10]. Fully saturated fatty acids tend to add stability to the fuel, but can cause problems in cold weather [11].…”

“…Fatty acids rich in monounsaturated fatty acids are likely to be suitable and should make up a high proportion of the biodiesel. Polyunsaturated fatty acids are detrimental to fuel due to their susceptibility to oxidation [10]. The chain length is also important with C16 and C18 fatty acids being most suitable.…”