bases can be used in a much more diluted concentration than acids, but much
longer residence times are required. Normally this kind of treatment results in the
complete removal of lignin, improving the reactivity of cellulose and hemicellulose in further degradation processes (McIntosh and Vancov 2010; Bhatia et al.
2012). Acid treatment uses diluted or concentrated acids to break lignocellulosic
material; the most commonly used acid is sulfuric acid that has demonstrated to be
effective in the treatment of many different materials. Acids can be used in a
concentrated or diluted form, and though both treatments are effective, they have
different drawbacks. Concentrated acids require large quantities of acid and may
cause the production inhibitors of further degradation, while the use of diluted
acids requires a much longer residence time and higher temperatures to be
effective, and can also result in the formation of inhibitory by-products. The main
advantage of acid treatments is that it can render fermentable sugars that require no
further treatment to be used (Martínez et al. 2005; Zhu et al. 2009).
7.4.3 Solvents
Ionic liquids are salts composed of a large organic cationic part along a small
anion that remain liquid at room temperature and have a very low vapor pressure.
These liquids can be adjusted to dissolve cellulose directly from different plant
biomass sources (Swatloski et al. 2002). Binder and Raines (2009) reported the
direct production of 5-hydroxymethylfurfural (HMF) from untreated corn stover
using N,N-dimethylacetamide (DMA) containing lithium chloride (LiCl) as solvent, this allows the synthesis of HMF in a single step with a yield between 32 and
47 % against 50 % obtained from pure cellulose; conversion of cellulose into
HMF was not affected by lignin or protein content. HMF is a six-carbon molecule
that can be used as an analog of terephthalic acid and hexamethylenediamine and
therefore can be converted into an assortment of acids, aldehydes, alcohols, and
amines, as well as 2,5-dimethylfuran (DMF), a chemical with potential as gasoline
substitute. The process reported is fast and simple and, more important, it allows
the use of raw material to produce fuel and chemicals in simple steps. A common
limitation to ionic liquid treatment is cellulose inactivation; the necessary use of
high-pressure equipment and the high cost of ionic liquids even when near to 99 %
of it can be recovered by evaporation due to low vapor pressure (Perepelkin 2007).
7.4.4 Biological Delignification
Fungi degrade lignin through a family of extracellular enzymes collectively called
lignases. These can be divided into two main families, laccases (phenol oxidases)
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S. de J. Romero-Gómez
longer residence times are required. Normally this kind of treatment results in the
complete removal of lignin, improving the reactivity of cellulose and hemicellulose in further degradation processes (McIntosh and Vancov 2010; Bhatia et al.
2012). Acid treatment uses diluted or concentrated acids to break lignocellulosic
material; the most commonly used acid is sulfuric acid that has demonstrated to be
effective in the treatment of many different materials. Acids can be used in a
concentrated or diluted form, and though both treatments are effective, they have
different drawbacks. Concentrated acids require large quantities of acid and may
cause the production inhibitors of further degradation, while the use of diluted
acids requires a much longer residence time and higher temperatures to be
effective, and can also result in the formation of inhibitory by-products. The main
advantage of acid treatments is that it can render fermentable sugars that require no
further treatment to be used (Martínez et al. 2005; Zhu et al. 2009).
7.4.3 Solvents
Ionic liquids are salts composed of a large organic cationic part along a small
anion that remain liquid at room temperature and have a very low vapor pressure.
These liquids can be adjusted to dissolve cellulose directly from different plant
biomass sources (Swatloski et al. 2002). Binder and Raines (2009) reported the
direct production of 5-hydroxymethylfurfural (HMF) from untreated corn stover
using N,N-dimethylacetamide (DMA) containing lithium chloride (LiCl) as solvent, this allows the synthesis of HMF in a single step with a yield between 32 and
47 % against 50 % obtained from pure cellulose; conversion of cellulose into
HMF was not affected by lignin or protein content. HMF is a six-carbon molecule
that can be used as an analog of terephthalic acid and hexamethylenediamine and
therefore can be converted into an assortment of acids, aldehydes, alcohols, and
amines, as well as 2,5-dimethylfuran (DMF), a chemical with potential as gasoline
substitute. The process reported is fast and simple and, more important, it allows
the use of raw material to produce fuel and chemicals in simple steps. A common
limitation to ionic liquid treatment is cellulose inactivation; the necessary use of
high-pressure equipment and the high cost of ionic liquids even when near to 99 %
of it can be recovered by evaporation due to low vapor pressure (Perepelkin 2007).
7.4.4 Biological Delignification
Fungi degrade lignin through a family of extracellular enzymes collectively called
lignases. These can be divided into two main families, laccases (phenol oxidases)
240
S. de J. Romero-Gómez