Alkaline used for this process include sodium hydroxides,
potassium hydroxides, ammonia and lime. Treatment using
hydroxides incurs more cost and has less recovery due to the
formation of salts. Utilization of lime seems more promising
as it has low cost, assures safety and easy recovery. The
commonest used alkaline is sodium hydroxide even though
ammonia is considered most effective because it seems
possible to recover up to 90% from the process and the
leftover ammonia also serves as a source of nitrogen for the
fermentation process. Crude xylan extracted with sodium
hydroxide showed a compositional analysis of 79% xylose,
5.3% arabinose, 1.7% glucose, 5.6% lignin and ash (Wei
et al. 2018). This technique can be an effective process for
hemicellulose removal and it has been employed in many
studies for extracting hemicellulose from different biomass
(Lawther et al. 1996; Vena et al. 2013).
3.3 Hydrothermal Pretreatment
This involves the removal of hemicellulose and some part of
lignin from lignocellulosic biomass using water under high
temperature and pressure. This process does not require
chemicals, hence no need for corrosion-resistant reactors. It
includes liquid hot water pretreatment, steam pretreatment
and steam explosion pretreatment. Steam explosion yields
high solubility of the hemicellulose (generating mainly
oligosaccharide) with low lignin solubility (Seidl and Goulart 2016). Combining steam explosion process with enzymatic saccharification is a promising route to enhance the
quantity of fermentable sugars (Canilha et al. 2012). Autohydrolysis is a form of hydrothermal treatment that involves
breaking down of hemicellulose links permitting the solubilization of reducing sugar and uronic acids. This process
also releases the acetyl groups, which results in ethanoic acid
formation which amounts to decrease in the pH of the
reaction medium, thereby increasing depolymerization rate
(Baêta et al. 2016).
3.4 Wet Oxidation
This involves oxidizing suspended or dissolved material in
water with dissolved oxygen using high temperature (Tungler
Fig. 4 Inhibitors formed during
acid hydrolysis and their source
320
V. C. Akubude et al.
potassium hydroxides, ammonia and lime. Treatment using
hydroxides incurs more cost and has less recovery due to the
formation of salts. Utilization of lime seems more promising
as it has low cost, assures safety and easy recovery. The
commonest used alkaline is sodium hydroxide even though
ammonia is considered most effective because it seems
possible to recover up to 90% from the process and the
leftover ammonia also serves as a source of nitrogen for the
fermentation process. Crude xylan extracted with sodium
hydroxide showed a compositional analysis of 79% xylose,
5.3% arabinose, 1.7% glucose, 5.6% lignin and ash (Wei
et al. 2018). This technique can be an effective process for
hemicellulose removal and it has been employed in many
studies for extracting hemicellulose from different biomass
(Lawther et al. 1996; Vena et al. 2013).
3.3 Hydrothermal Pretreatment
This involves the removal of hemicellulose and some part of
lignin from lignocellulosic biomass using water under high
temperature and pressure. This process does not require
chemicals, hence no need for corrosion-resistant reactors. It
includes liquid hot water pretreatment, steam pretreatment
and steam explosion pretreatment. Steam explosion yields
high solubility of the hemicellulose (generating mainly
oligosaccharide) with low lignin solubility (Seidl and Goulart 2016). Combining steam explosion process with enzymatic saccharification is a promising route to enhance the
quantity of fermentable sugars (Canilha et al. 2012). Autohydrolysis is a form of hydrothermal treatment that involves
breaking down of hemicellulose links permitting the solubilization of reducing sugar and uronic acids. This process
also releases the acetyl groups, which results in ethanoic acid
formation which amounts to decrease in the pH of the
reaction medium, thereby increasing depolymerization rate
(Baêta et al. 2016).
3.4 Wet Oxidation
This involves oxidizing suspended or dissolved material in
water with dissolved oxygen using high temperature (Tungler
Fig. 4 Inhibitors formed during
acid hydrolysis and their source
320
V. C. Akubude et al.