**11. Biodiesel production from algal oil**

Biodiesel is a mixture of fatty acid alkyl esters obtained by transesterification (ester exchange reaction) of vegetable oils or animal fats. These lipid feedstocks are composed by 90–98% weight) of triglycerides and small amounts of mono and diglycerides, free fatty acids (1–5%), and residual amounts of phospholipids, phosphatides, carotenes, to copherols, sulphur compounds, and traces of water [17].

Transesterification is a multiple step reaction, including three reversible steps in series, where triglycerides are converted to diglycerides, then diglycerides are converted to monoglycerides, and monoglycerides are then converted to esters (biodiesel) and glycerol (by-product). The overall transesterification reaction is described in Fig. 3 where the radicals R1, R2, R3 represent long chain hydrocarbons, known as fatty acids.

For the transesterification reaction oil or fat and a short chain alcohol (usually methanol) are used as reagents in the presence of a catalyst (usually NaOH). Although the alcohol: oil theoretical molar ratio is 3:1, the molar ratio of 6:1 is generally used to complete the reaction accurately. The relationship between the feedstock mass input and biodiesel mass output is about 1:1, which means that theoretically, 1 kg of oil results in about 1 kg of biodiesel.

A homogeneous or heterogeneous, acid or basic catalyst can be used to enhance the transes‐ terification reaction rate; although for some processes using supercritical fluids (methanol or ethanol) it may not be necessary to use a catalyst [295]. Most common industrial processes use homogeneous alkali catalysts (e.g. NaOH or KOH) in a stirred reactor operating in batch mode.

Recently some improvements were proposed for this process, in particular to be able to operate in continuous mode with reduced reaction time, such as reactors with improved mixing, microwave assisted reaction [44,65], cavitations reactors [43, 44] and ultrasonic reactors [130, 68].

Transesterification is process algae oil must go through to become desired product biodiesel which is required two chemicals (Methanol and Sodium hydroxide) and following steps to be done as mix Methanol and Sodium hydroxide which make sodium methoxide now this sodium methoxide mix with algae oil and allow it to settle for about 8 hours. Now filter biodiesel to 5 microns and drain glycerin. This glycerin is used to make products such as soap and others.
