# Pretreatments Applied to Wheat Straw to Obtain Bioethanol
## 3 Pretreatments Applied to Wheat Straw
### Chemical Pretreatments Applied to Wheat Straw
#### 3.2.1 Alkaline Pretreatment  
Through alkaline pretreatment with solutions, such as lime, ammonium hydroxide, sulphite, sodium hydroxide, and hydrogen peroxide, lignin is selectively removed without losing sugar and carbohydrate reduction, while biomass porosity and surface area are increased and enzymatic hydrolysis is improved [51]. Alkaline pretreatment methods are, in general, more effective, as a large part of the lignin is solubilized.  
The major advantages of this type of pretreatment are that the reactivity of the cellulose increases, a small amount of sugar is degraded, and the costs for raw materials are much lower compared to acid hydrolysis.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Methods** & **Chemical Reagent** & **Pretreatment Effect** & **R** \\ \hline Ionic liquid & [BMI] MeV\({}_{4}\)-H\({}_{2}\)SO\({}_{4}\) & Cellulose digestibility 77\%, & [31] \\ pretreatment & [emim] [CH\({}_{3}\)COO] & Glucose yield 76\% & [31] \\  & Oxalic acid dihydrate, & Total reducing sugar 42\%, glucose & [31] \\ Acid pretreatment & dilute sulfuric acid 2\% & yield 90\% & [31] \\  & H\({}_{2}\)SO\({}_{4}\) & Glucose yield 93.1\%, Lignin & \\ Alkaline & Cold alkaline (aqueous & removals 59.1\%, Xylan digestibility & [33] \\ pretreatment & ammonia 10\% NaOH & 88\%, Glucose yield 73.8\% & \\ Organic solvent & 5-10\% Formic acid & Glucose yield 40\% & \\ pretreatment & acid-free organosolv & Theoretical ethanol production & [34] \\  & glycerol organosolv & yield of 96\% Lignin removals 65\% & \\ \hline \hline \end{tabular} R-references.  
\end{table}
Table 1: Chemical pretreatment methods applied to wheat straw (data from [31; 33; 34]).  
By alkaline pre-extraction, the enzymatic hydrolysis of wheat straw was improved [51; 52; 53]. The removal of silica at different times and concentrations was carried out using the alkaline reagents Na\({}_{2}\)CO\({}_{3}\) and NaOH.  
The highest biomass yield was obtained for the treatment with Na\({}_{2}\)CO\({}_{3}\) compared to the alkaline pretreatment with NaOH. By treating the straw for 6 h at an alkaline concentration of 0.25 mol/L, the biomass yields were 91.1% and 86.3% for the pretreatments with Na\({}_{2}\)CO\({}_{3}\) and NaOH, respectively, because Na\({}_{2}\)CO\({}_{3}\) can dissociate less hydroxide ions than NaOH. The extraction of hemicellulose increased with the increase in the pH value and the pretreatment time of the wheat straw with NaOH.  
By alkaline pretreatment of wheat straw, silica was removed, leading to the reduction in its negative effect during enzymatic hydrolysis [54; 42].  
Table 2 shows the production of bioethanol obtained by alkaline pretreatment [39; 51]. It can be observed that the best results were obtained by pre-treating the wheat straw with the alkaline Na\({}_{2}\)CO\({}_{3}\) pretreatment (11%), while a glucose reduction yield of 85.7% was obtained, lignin was removed in 70.4%, and the yield production of ethanol at 65 (g/L).  
By pretreating wheat straw with hydrogen peroxide, 98% of silicon was removed, and hemicellulose was removed with increased pretreatment time [54].