Background: Microalgae are a promising feedstock to produce biofuels such as biodiesel, since their
culture does not compete with food crops. In order to make a microalgae biodiesel process cost
effective, a biodiesel production process, which consists in separating the microalgae unsaponified
lipids (such as carotenoids) from the biodiesel produced, has been tested.
Methods: In this process, the 1st step is an alkali reaction (saponification) between microalgae lipids
and potassium hydroxide (KOH) (1.26 mmol OH-/g methanol), followed by a 2nd acid reaction step
(esterification) using sulphuric acid (H2SO4) (1.65 mmol H+/g methanol) with a total methanol to lipid
ratio of 13 mL/g. Between these 2 steps, a solvent extraction (hexane) separates the unsaponified lipids
from the reaction mixture.
Results: This 2-step process resulted in a FAME yield of 91 g FAME/kg dry biomass, a biodiesel purity of 260 mmol
FAME/100 g biodiesel and an unsaponified lipid yield of 170 g lipid/kg dry biomass. The 2-step process (with a hexane
separation between both steps) tested in this study achieved a higher FAME yield and a higher biodiesel purity compared
to a lipid crystallization separation. When crystallization with hexane at 0°C was tested at the same biodiesel production
conditions as the 2-step process, a maximum FAME yield of 35 g FAME/kg dry biomass with a biodiesel purity of 52
mmol FAME/100 g biodiesel were obtained.
Conclusion: Despite the fact that this 2-step process produces an important amount of salt (4.8 kg K2SO4/kg FAME), for
the best operating conditions tested, in comparison to a conventional vegetable oil-based biodiesel obtained by 1-step
alkali homogeneous catalytic processes (0.03 kg K2SO4/kg FAME), it is effective and simple, and could help biodiesel
from microalgae be cost effective.