Microalgal Species Selection for Biodiesel Production Based on Fuel Properties Derived from Fatty Acid Profiles

Muhammad Islam,Godwin Ayoko,Marie Magnusson,Kirsten Heimann,Md Nabi,Richard Brown

doi:10.3390/en6115676

Abstract

Physical and chemical properties of biodiesel are influenced by structural features of the fatty acids, such as chain length, degree of unsaturation and branching of the carbon chain. This study investigated if microalgal fatty acid profiles are suitable for biodiesel characterization and species selection through Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA) analysis. Fatty acid methyl ester (FAME) profiles were used to calculate the likely key chemical and physical properties of the biodiesel [cetane number (CN), iodine value (IV), cold filter plugging point, density, kinematic viscosity, higher heating value] of nine microalgal species (this study) and twelve species from the literature, selected for their suitability for cultivation in subtropical climates. An equal-parameter weighted (PROMETHEE-GAIA) ranked Nannochloropsis oculata, Extubocellulus sp. and Biddulphia sp. highest; the only species meeting the EN14214 and ASTM D6751-02 biodiesel standards, except for the double bond limit in the EN14214. Chlorella vulgaris outranked N. oculata when the twelve microalgae were included. Culture growth phase (stationary) and, to a lesser extent, nutrient provision affected CN and IV values of N. oculata due to lower eicosapentaenoic acid (EPA) contents. Application of a polyunsaturated fatty acid (PUFA) weighting to saturation led to a lower ranking of species exceeding the double bond EN14214 thresholds. In summary, CN, IV, C18:3 and double bond limits were the strongest drivers in equal biodiesel parameter-weighted PROMETHEE analysis.

Highlights

Algae have recently received a lot of attention as a new biomass source for the production of renewable energy in the form of biodiesel and as a feedstock for other types of fuel [1,2]
The current study focused on using theoretical maximal yields of fatty acids to calculate fuel properties of biodiesel derived from a range of microalgae in order to rank the suitability of these species for further development
An equal parameter weighted PROMETHEE analyses established that the marine microalgae Nannochloropsis oculata, Extubocellulus sp. and Biddulphia sp. outranked the other six microalgal specieswhile the three freshwater chlorophytes (Scenedesmus dimorphus, Franceia sp., and Mesotaenium sp.) did not meet the ASTM D6751-02 and EN14214 standards

Summary

Introduction

Algae have recently received a lot of attention as a new biomass source for the production of renewable energy in the form of biodiesel and as a feedstock for other types of fuel [1,2]. Several biomass conversion processes have been explored for the production of renewable diesel from microalgae, such as hydrothermal conversion and gasification followed by Fisher-Tropsch synthesis [3]. While both process technologies can yield designer fuels thereby meeting the required specifications of different renewable fuels more (e.g., devoid of oxygen, nitrogen, sulphur, aromatics and degree of unsaturation is controlled through hydrogenation of double bonds), initial set up costs are high, the processes are typically more energy intensive, as they require heating to high temperatures and pressure, and the latter process has the added disadvantage of requiring dried biomass input (an additional energy cost) [3]. Limitations can, be minimised by selecting a suitable algal species and manipulating the initial fatty acid profile by varying the growth conditions and extraction process

Methods

Results

Conclusion