Page 92 - Lignocellulosic Biomass to Liquid Biofuels

68 Lignocellulosic Biomass to Liquid Biofuels

potential to replace petroleum-derived transportation fuels, because
bioethanol has broader flammability limits, higher octane number, higher
heat of vaporization, and higher flame speeds [2]. The cost involved in
the production of ethanol from different biomasses including sugarcane
and the food-versus-fuel debate over corn ethanol forced us to search for
new feedstocks. Not only that, lignocellulose-rich agriculture waste has
also been considered as potential alternative new generation feedstocks.
Fast-growing short-rotation forest trees having large amounts of cellulose-
rich biomass have emerged as a promising source for bioenergy and at the
same time biopolymer production.
The biofuel can be produced from a variety of feedstock, such as plant
oils, sugar beets, cereals, organic waste, and the processing of biomass. Out
of them, the most promising is lignocellulosic biomass (e.g., wood, straw,
and grasses). Bioconversion of straw to bioethanol represents an attractive
alternative in comparison with conventional fuel ethanol production from
grain [3]. Wheat straw is a promising substrate because it is the largest bio-
mass feedstock in Europe and the second largest in the world after rice
straw. Wheat straw has a great potential as feedstock in the future [4].
However, lignocellulose usually carries the structure of the plant biomass
and is difficult substrate to degrade. Therefore thermochemical and enzy-
matic pretreatments are necessary for lignocellulose degradation to make
the monomers available for further processing. The hydrolysis step is neces-
sary for the conversion of biomass into monomer sugars for subsequent fer-
mentation into bioethanol [5]. Hydrolysis can be acid or enzymatic. This
latter has several advantages over the use of acid, because acid hydrolysis
has relatively low yield, no selectivity, and it needs a high process tempera-
ture (ranging between 140°C and 160°C) and neutralization after hydroly-
sis. Enzymatic hydrolysis of cellulose is catalyzed by a class of enzymes
called cellulases. There are several factors influencing the efficiency of
hydrolysis. The aim of this chapter is to identify the optimum conditions
of enzymatic hydrolysis of wheat straw lignocelluloses that remain after
furfural production. However, it is very hard to depolymerize lignocellu-
losic materials because of the presence of complex lignin and hemicellu-
loses over cellulose. Different chemical pretreatment methods are
employed to increase cellulose accessibility [6]. Therefore the production
of fermentable sugars from lignocellulosic biomass tends to be complex
and capital intensive, with, also, inherent environmental concerns.
Recently, marine macroalgal species have gained considerable global
attention as source of third-generation biofuels [7]. The major advantages