Page 312 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 269

γ-oryzanol in crude biodiesel. However, the method to isolate γ-oryzanol from DES so
that it can be commercialized still needs further investigation.
For microalgae, in situ trans(esterification) using a subcritical water-methanol with
an acid catalyst (HCl) and cosolvent (choloroform) seems to be the most promising
method because it requires no oil extraction and drying processes. Under optimum
operating conditions, the biodiesel yield can be as high as 99.7%. This method also
converts cellulose in microalgae into ethyl levulinate, ethyl formate, and diethyl ether.
Besides that, microalgae contain pigments such as carotenoids, chlorophylls, and
phycobiliproteins, which can be extracted using solvent or supercritical fluid.
In situ trans(esterification) using the supercritical methanol seems to be the most
promising method to produce biodiesel from spent coffee grounds. Under optimum
operating conditions, a biodiesel yield around 97.5wt% can be achieved, even in
the presence of water. In addition to lipids and carbohydrates, spent coffee grounds
contain chlorogenic acid, an antioxidant compound that can be extracted easily using
pure water or aqueous ethanol.
This review shows that wet in situ trans(esterification) is the preferred method to
produce biodiesel directly from alternative inedible feedstocks (rice bran, microalgae,
and spent coffee grounds), as it can be carried out without drying and oil extraction
steps to reduce production cost and energy. Because those raw materials are also rich
in carbohydrates and bioactive/antioxidant compounds, commercialization of those
byproducts can further decrease the total production costs of biodiesel. Therefore,
by using a biorefinery approach where biodiesel is produced alongside several
byproducts, it is expected that economically feasible biofuel can be produced from
alternative inedible feedstocks.

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