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The objective of this study was the use of vacuum distillation to increase fatty acid methyl ester (FAME) content and quality of microalgae biodiesel produced through direct transesterification. Microalgae biodiesel obtained from direct transesterification of microalgae (crude biodiesel) has a FAME content of 64.98 ± 2.88%, viscosity of 17.7 ± 0.17 (mm 2 /s), and a humidity level of 3.72%. As biodiesel's properties are related to FAME content, to increase FAME content and produce higher quality biodiesel two vacuum distillation experiments were conducted using different vacuum conditions. The best results were obtained in experiment 2 with two consecutive distillations, where FAME content increased from 64.98 ± 2.88% in crude biodiesel to 85.50 ± 2.60% in the D2.2 fraction, while viscosity decreased from 17.70 ± 0.17 (mm 2 /s) in crude biodiesel to 3.76 ± 0.01 (mm 2 /s) in the D2.2 fraction. Vacuum distillation, therefore, may represent an excellent alternative for the purification of microalgae-based biodiesel.

The knowledge of density and viscosity is important both for the optimization of diesel engines operation and the fuel quality specification. To this end, the present work focuses on the study of these thermophysical properties for three algal biodiesels. The samples were produced by transesterification of dry biomass supplied from different microorganisms, the marine strain Nannochloropsis gaditana, the freshwater strain Scenedesmus almeriensis and the freshwater cyanobacteria Spirulina platensis. The protocol of production is detailed. The purity of biodiesels is low, ranging from 63,7% to 68,1% because the produced biodiesel was not purified in order to evaluate the characteristics of the crude biodiesel produced from microalgae. The relative new technique based on a simple process is attractive for an industrial point of view. The (FAMEs) profile of the biodiesels were characterized using a GC-MS technique. The density measurements were performed over expanded ranges of pressure [0,1-140 (MPa)] and temperatures [293,15 (K)-353,15 (K)] compatibles with their engines applications. The isothermal compressibility and the isobaric thermal expansion were estimated within the same experimental range by density differentiation. The cinematic viscosity was also measured for the three biodiesels at atmospheric pressure for temperatures ranging from 293.15 (K) to 353.15 (K). The storage stability of the biodiesels was assessed in terms of reproducibility of the measured properties. Spirulina biodiesel was not affected by oxidation process. Additionally, its density and viscosity values meet the standards specifications that support the use of this production process.

Microalgae biotechnology has grown very rapidly in the last few decades due to the multiple applications that these microorganisms have from pharmaceuticals and cosmetics to foods/feeds and biofuels. One of the main challenges in expanding this industry is to enlarge the single use of the biomass produced in addition to reducing the high biomass production cost of the current technologies. To overcome this bottleneck, the development of microalgae-based biorefineries has been proposed. The issue is to obtain as many bioproducts as possible from the cultivated biomass, including biofuels. Consequently, biodiesel production (from the lipid fraction), bioethanol (from carbohydrate fraction), and biogas or bio-oil (from the whole biomass) have been posited. In this book chapter, we review the current state of the art in the production of sustainable biofuels from microalgae and analyze the potential of microalgae to contribute to the biofuel sector.