The effect UV-B mutation on biodiesel from microalgae Botryococcus braunii using esterification, transesterification and combination of esterification-transesterification

Biodiesel from microalgae as a third-generation fuel is promising due to its sustainability and eco-friendly energy source. The objective of this study was comparing conversion of lipid from microalgae Botryococcus braunii mutated with UV-B using esterification, transesterification and combination of esterification-transesterification processes. In this study, Ultraviolet (UV-B) light was used to perform mutation of microalgae. It was used to damage the cell walls of microorganism. The conversion of lipid to biodiesel from UV-mutated and native microalgae using esterification method were 2.05% and 1.11%, respectively, under 1: 10 molar ratio of algae lipid and methanol at 60°C, 1.5% w/w H₂SO₄, 200 rpm stirring speed for 2 h. Transesterification method did not produce biodiesel under 1: 7 molar ratio of algae lipid and methanol with 0.5% w/w NaOH catalyst at 60°C, 200 rpm stirring speed for 1 h. Furthermore, the combination esterification-transesterification method resulted in 24.82% and 3.87% yield for mutated and native algae, respectively. In the first stage, esterification of the mutated and native algae decreased acid value from 24.13 to 0.567 mg KOH/g and from 23.21 to 0.486 mg KOH/g, respectively, under 1: 8 molar ratio of algae lipid and methanol, 1.5% w/w H₂SO₄ catalyst, 60°C, 400 rpm stirring speed for 2 h. The next stage of transesterification was conducted at a molar ratio of 9: 1, 0.75% wt KOH catalyst concentration, 65°C at 600 rpm for 1 h. The results showed that combination esterification-transesterification was the best method to convert lipid to biodiesel.