Page 68 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel feedstocks and their prospects 45

over ethanol and biodiesel. This estimate considers future potential savings from that
could come from an optimized production processes. Production costs have already
fallen 70% over the last 25 years, and additional reductions could come from reduced
costs of water and wastewater cleanup, as well as from reduced energy use, in further
enhanced ABE processes.
For more than 20 years, research has been directed toward the development of
improved microorganisms for the fermentation of pentose sugars. For cost-effective
processing, such organisms must be able to coferment feed streams containing glucose
and xylose together. Although C5 pentoses are generally more difficult to ferment,
new yeast strains are being developed that may effectively use these sugars. Currently,
there are no known natural organisms that have the ability to convert both C6 and C5
sugars at high yields, although there have been some claims toward this goal using
genetically modified microorganisms. Significant progress has been made in engi-
neering microorganisms for cofermentation of glucose and pentose sugars; however,
they still have problems with sensitivity to inhibitors and production of unwanted
byproducts that have not yet been overcome.
The Bioenergy Technologies Office (BETO) of NREL (National Renewable
Energy Laboratory) of the US Department of Energy (DOE) set a target price of
0.79$/L for biofuels’ gate price projection, based on current process and plant design
assumptions consistent with applicable best practices. The economic viability of
renewable fuel production could be improved by using noncommercial biomass, such
as forest residues as feedstock, and by generating revenue from selling coproducts
[50]. In the previous sections, it was mentioned that several intermediate products
of food crop processing into biofuels are already sold as animal feed (e.g., DDGS,
CGM, CGF). However, some production chains generate coproducts, such as indus-
trial chemicals, with high added value in significant quantities. One such product is
furfural, identified by the DOE as a promising chemical platform, as it can be
converted into more than 80 chemicals of common use or could be a substitute for
others. The major industrial uses of furfural are in the steel/foundry, pharmaceutical,
agriculture chemicals, plastics, and wood treatment industries, and a few bioplastic
companies make use of furfural as a building block in their chemistry or have
expressed an interest in using it.
Also, high-value c-products have been produced by extraction of coproducts from
algae to improve the economics of microalgae biorefineries. Examples of these high-
value products are pigments, proteins, lipids, carbohydrates, vitamins, and antioxi-
dants, with applications in cosmetics, as well as the nutritional and pharmaceutical
industries.
To promote the sustainability of such processes, innovative microalgae biorefinery
schemes are being implemented for extraction of multiple products in the form of
high-value products and biofuel. Modern technologies can apply supercritical fluid
extraction, which gives higher yield, ease of operation, and economic processing.
The feasibility of multiproduct generation has already led to more efficient production
pathways and enhanced recovery of materials and energy [51]. Significant improve-
ment must be done on the current economics of algae biofuel production to make them
competitive in the market with fossil fuel. Some conversion methods used are