Page 311 - Advances in Eco-Fuels for a Sustainable Environment

268 Advances in Eco-Fuels for a Sustainable Environment

Spent coffee Antioxidant
ground extraction Lipid extraction Sugar extraction Pyrolysis

Biodiesel
production Fermentation Gas
Bio oil

Bioethanol
Antioxidants Biodiesel and other Bio char
biochemicals

Fig. 9.4 Biorefinery approach on the utilization of spent coffee ground.

through this biorefinery scheme. After several stages of biochemical processing, the res-
idues then can be introduced into a pyrolysis reactor to obtain renewable gas, bio-oil,
and biochar [130]. Instead of using the remaining solid char as a biosorbent or soil
amendment material, the resulting biochar can be utilized as an active electrode material
to build a high-performance supercapacitor after ZnCl 2 activation, as demonstrated by
Rufford et al. [131]. The mentioned biorefinery scheme of spent coffee ground utiliza-
tion is illustrated in Fig. 9.4.

9.5 Conclusions

Although biodiesel is a promising renewable fuel currently produced on an industrial
scale, the current production of biodiesel may be unsustainable due to the use of edible
oils as feedstock. The potential uses of inedible raw materials (rice bran, microalgae,
and spent coffee grounds) as biodiesel feedstock have been reviewed in this chapter.
However, these inedible feedstocks have different compositions than those of com-
monly used edible oils, so that the conventional process to produce biodiesel is
unsuitable for them. Therefore, several novel technologies have also been reviewed,
including catalytic and noncatalytic processes.
The noncatalytic in situ trans(esterification) of rice bran using a subcritical water–
methanol mixture can produce not only biodiesel but also dimethyl ether, methyl
levulinate, methyl formate, and a sugar solution that can be fermented subsequently
to produce ethanol. Under optimum operating conditions (T ¼200°C, P ¼4MPa
under CO 2 atmosphere, 3h reaction time, and 43.8wt% methanol), 100% oil in the
bran can be recovered and 66.1% FAME content can be achieved. Besides that, the
subcritical water-methanol mixture can also extract bioactive compounds in rice bran,
such as γ-oryzanol. The purification of crude biodiesel by using DES, a new type of
green solvent, was also promising. The DES (prepared by mixing choline chloride and
ethylene glycol at a molar ratio of 1:2) can increase the purity of biodiesel up to 96.6%
to meet that specified by international standards and extract more than 90% of