Page 110 - Advances in Eco-Fuels for a Sustainable Environment

Prospects of biodiesel feedstock as an effective ecofuel source and their challenges 83

across the globe. It has been found that oils from feedstocks can also be extracted by
the enzymatic approach. Unfortunately, the major challenge of this technique is the
cost of production for large-scale set-up and the need to improve the yield [22, 73].
It has been found that most edible and nonedible oil feedstocks give a high yield of
biodiesel. They have their biodiesel properties following the specified standard ASTM
D6751. However, in order to improve their properties such as viscosity, cloud, flash,
pour, and cold filter plugging points, blending of biodiesels from various feedstocks
can help to achieve this. A typical example is the blending of Sterculia foetida methyl
ester and coconut methyl ester, which improved the viscosity of SFME significantly
[71]. In addition, microwave-assisted biodiesel production significantly helps in
reducing reaction time and lessens the cost of production [76]. In order to lower sep-
aration costs for fatty acid esterification, to reduce the maintenance cost (such as cor-
rosion control), and the cost of neutralization associated with use of homogeneous
catalysts for fatty acid esterification, the use of heterogeneous catalysts is advisable
[19, 77]. These problems are best solved using a continuous set-up of reactive distil-
lation. Reactive distillation is a process intensification method that incorporates mass
transfer of species and simplifies the process flowsheet. It accommodates the biodiesel
formation as well as the separation of reaction products [77, 78]. Extensive study on
the various catalysts and their methods of preparation has been done and more work is
ongoing [19]. Nevertheless, it is worthy to note that a highly active heterogeneous cat-
alyst enhances the achievement of low residence time (20–60min), which in turn
increases the rate of production. Similarly, membrane reactors can equally achieve
this aim by also increasing conversion for the case of equilibrium-limited reactions
by simply removing some product from the reactant stream via the membrane
[79, 80]. This feature is an advantage of membrane reactor systems for biodiesel pro-
duction over the reactive distillation. Dub e et al. has a comprehensive study of the
possibility of biodiesel production from canola oil with methanol using a two-phase
tubular membrane reactor. A well-regulated flow rate of reacting species will help in
achieving improved conversion without blockages of the pores of the membrane
medium.

3.5 Conclusion

Biodiesel is gaining more attention as a result of its advantages over petroleum diesel,
though its production is still faced with many challenges. These in relation to the
choice of feedstocks include the feedstock cultivation process, postharvest technolo-
gies, the presence of high free fatty acids in most oils used, and the nonavailability of
the majority of oils in the open market. Among the various sources of feedstocks
reviewed, nonedible oils seem to have more prospects than edible oils and animal fats
in the biodiesel industry. This is because most of the nonedible oil plants are highly
pest- and disease-resistant and noncompetitive with food, in additional to the fact that
most of them can grow on wastelands. Furthermore, the advantages of nonedible oils
are their liquid nature portability, ready availability, renewability, higher heat content,