Introduction
The increasing problem of the CO2 emissions besides some energy security concerns has strengthened the interest in alternative,
nonpetroleum-based sources of energy. Biomass is the only suitable and renewable primary energy resource than can provide
alternative transportation fuels such as bioethanol or biodiesel in
the short-term (Hamelinck et al., 2005; Sun and Cheng, 2002) .
Current production of bioethanol relies on ethanol from starch
and sugars but there has been considerable debate about its sustainability. In this context, bioethanol produced from lignocellulosic biomass is an interesting alternative since lignocellulosic
raw materials do not compete with food crops and they are also
less expensive than conventional agricultural feedstocks.
Lignocellulose is the most abundant renewable biomass; its annual production has been estimated in 1 1010 MT worldwide
(Sánchez and Cardona, 2008). The biological conversion of different
lignocellulosic feedstocks such as forest and agricultural residues,
or lignocellulosic crops dedicated to ethanol offers numerous benefits but its development is still hampered by economic and technical obstacles (Sánchez and Cardona, 2008). In this context, some
of the most important factors to reduce ethanol production cost
are: an efficient utilization of the raw material to obtain high ethanol yields, high productivity, high ethanol concentration in the
distillation feed, and also process integration in order to reduce