Biodiesel Production by Microalgal Biomass and Strategies to Improve Its Quality

Microalgal oil has been described as the raw material with the greatest potential for third-generation biodiesel production, without competing with arable land suitable for food production. The fuel quality of biodiesel depends on the raw materials, the reagents used, and the values of the operational variables in the transesterification. ASTM D6751 and EN 14214 standards describe the limits of biodiesel properties values such as Cetane Number (CN), Oxidation Stability (OS), Kinematic Viscosity (KV), Acid Value (AV), Iodine Value (IV), and Cold Flow Properties. These properties are highly influenced by the chain length and degree of unsaturation of the Fatty Acid Methyl Esters (FAMEs) that constitute biodiesel. The CN represents the ignition quality of biodiesel in the engine, high cetane value is the indicator of better combustion and low emission of nitrous oxide. In general, the presence of long-chain FAMEs with a high proportion of saturated fatty acids (SFA) increases CN and improves oxidative stability. In contrast, biodiesel with a relatively high content of monounsaturated fatty acids (MUFA) or polyunsaturated fatty acids (PUFA) tends to perform better in cold climates. Microalgae have a significantly higher yield of lipids, compared to conventional crops for biodiesel production; however, the fatty acid composition varies with the species of microalgae and may differ in the size of the carbon chain and/or in the presence and amount of unsaturation. Thus, to choose the most suitable microalgae for biodiesel production, other factors such as the fatty acid composition must be evaluated. This chapter gives detailed information about parameters to consider for improving microalgae biodiesel properties. In addition, updated research, challenges, and strategies to improve its quality are also presented.