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248 Advances in Eco-Fuels for a Sustainable Environment

3h reaction time, and 43.8wt% methanol), 100% oil in the bran can be recovered and
67.4% FAME yield can be achieved. Complex carbohydrates in the bran were also
hydrolyzed into soluble sugars. Sugar concentration in the aqueous phase was higher
under a CO 2 atmosphere than that under an N 2 atmosphere due to the higher hydrolysis
rate of starch at lower pH. The highest sugar concentration of about 1g/L was achieved
at 180°C. Higher temperature and longer reaction time caused sugar degradation while
higher methanol concentration decreased the hydrolysis rate.
For oils with high saturated to unsaturated fatty acid ratio (S/U), such as palm oil,
winterization is needed before use as a biodiesel feedstock. For biodiesel feedstock
with low S/U and a high content of polyunsaturated fatty acid such as soybean oil,
oxidation and polymerization may occur. From Table 9.5, the S/U value of RBO is
intermediate and therefore suitable as a feedstock for biodiesel production without
any further refining.

9.3.2 Catalytic and noncatalytic biodiesel conversion from
microalgae
Extraction of lipids from the microalgae cell followed by transesterification is usually
employed for biodiesel production from microalgae. Extraction assisted by rupturing
the cell helps release more lipids because such pretreatment is able to break down the
thick and rigid cell wall, which makes lipid extraction easier and more lipids can be
extracted. Either a mechanical or a nonmechanical (chemical and biological) method
can be applied to disrupt the cell wall. Mechanical methods such as microwave,
ultrasonication, or high-pressure homogenization (HPH) result in a higher lipid yield
with a shorter extraction time and can be scaled up easily. However, those processes
are energy intensive. In comparison, chemical methods using acids, salts, surfactants,
or ionic liquid/DES as the solvent are efficient, selective, and scalable. Huang and
Kim [73] used a mixture of trimethylamine and methanol as the solvent for the simul-
taneously disrupted cell wall and extracted lipids in wet Chlorella vulgaris. Their pro-
cess resulted in a 95% lipid yield. However, the method depends on microalgae
composition, environmental condition, and the later separation process used. Biolog-
ical methods use enzymes such as cellulase, lipase, and protease, or a combination of
multiple enzymes to disrupt the cell wall. The advantages of this method are low
energy consumption and milder operating conditions. Wu et al. [74] extracted lipid

Table 9.5 Typical fatty acid composition (%) of RBO and other refined vegetable oils
a b b b
Fatty acids RBO RBO RBO Soybean Palm
Palmitic 17.7 18.7 14.7 10.4 40.2
Oleic 47.3 43.4 42.2 24.8 43.3
Linoleic 31.3 37.9 37.8 52.5 9.0
S/U 0.25 0.28 0.21 0.19 0.86
a
[63].
b
[5].