# Biomass and Cellulose Dissolution--The Important Issue in Renewable Materials Treatment
## 3 Dissolution of Biomass and Its Components
### Ionic Liquids
#### 3.6.4 The Impact of Ionic Liquid Cation on Cellulose Dissolution Effectiveness  
The general order of cations in ionic liquids, which are most effective for cellulose dissolution, is imidazolium ILs \(>\) pyridinium ILs \(>\) ammonium ILs, which makes imidazolium-based solvents the most frequently studied in biomass dissolution processes [113]. In the imida \begin{table}
\begin{tabular}{c c c c c} \hline
**Cellulose Type** & **Ionic liquid** & **Temperature [\({}^{\circ}\)C]** & **Solubility [wt. \%]** & **References** \\ \hline MCC & [bmim][HCOO] & & 12.5 & \\ \begin{tabular}{c} [bmim][CH3 COO] \\ [bmim][CH3 CH2 COO] \\ [bmim][CH3 CH2 COO] \\ [bmim][CH3 CH2 COO] \\ \end{tabular} & 70 & 15.5 & [99] \\ \begin{tabular}{c} [bmim][CH3 CH2 COO] \\ [bmim][CH3 CH2 COO] \\ \end{tabular} & 14.0 & \\ \hline MCC & [emim][CH3 COO] & & 27.0 & [100] \\ \begin{tabular}{c} [emim][DEP] \\ \end{tabular} & 90 & 15.0 & [100] \\ \hline MCC & [DBUH][HCOO] & & 18.9 & \\ \begin{tabular}{c} [DBUH][CH3 COO] \\ [DBUH][CH3 CH2 COO] \\ \end{tabular} & 90 & 14.8 & [101] \\ \begin{tabular}{c} [DBUH][CH3 CH2 COO] \\ \end{tabular} & 12.6 & \\ \hline MCC & [N2226][CH3 COO] & 80 & 15.0 & [102] \\ \hline Commercial Cellulose & [emim][CH3 COO] & & 35.2 & \\ \begin{tabular}{c} [emim][DEP] \\ [DBUH][CH3 COO] \\ [DBUH][[Prop] \\ [DBNH][CH3 COO] \\ [DBNH][Hex] \\ \end{tabular} & 80 & 23.0 & \\ \begin{tabular}{c} [DBUH][CH3 COO] \\ [DBNH][Hex] \\ \end{tabular} & 80 & 22.5 & [103] \\ \
\begin{tabular}{c} [DBUH][Prop] \\ [DBNH][CH3 COO] \\ [DBNH][CH2 OOO] \\ [DSHH][Hex] \\ \end{tabular} & 80 & 4.3 & \\
\begin{tabular}{c} [DBNH][CH3 COO] \\ [DBNH][CH3 COO] \\ [Hex] \\ \end{tabular} & 22.0 & \\ \hline MCC & [amim][MP] & 80 & 22.0 & [107] \\ \hline Commercial cellulose & [him][CH3 CHCH(OH)COO] & 80 & 5.0 & [108] \\ \hline MCC & [ammorp][CH3 COO] & 80 & 17.0 & [109] \\ \hline \end{tabular}
\end{table} 
Table 3: Cellulose solubility in ionic liquids. zolium cation structure, alkyl substituents are common, e.g., 1-ethyl-3-methylimidazolium [emim]\({}^{+}\), 1-butyl-3-methylimidazolium [bmim]\({}^{+}\), 1-hexyl-3-methylimidazolium [hnim]\({}^{+}\), 1-octyl-3-methylimidazolium [omim]\({}^{+}\), and 1-allyl-3-methylimidazolium [amim]\({}^{+}\). With the increase in the alkyl chain length, the effectiveness of cellulose dissolution decreases. For instance, the solubility of cellulose at 100 \({}^{\circ}\)C in ionic liquids [_alkyl_/mim]Cl decreased from 14 wt.% for [emim]Cl and 10 wt.% for [bmim]Cl to 5 wt.% for [hnim]Cl and nearly 0% for [omim]Cl [114,115]. It was also revealed that smaller cations in ILs enhance the solubility of cellulose. For example, 14.5 wt.% cellulose can be dissolved in 1-allyl-3-methylimidazolium chloride [amim]Cl at 80 \({}^{\circ}\)C [116]. This process is additionally supported by the entropic effect, which is a result of possible hydrogen bonds, due to the presence of a double bond in the cation structure [97]. The double bond is also responsible for the lower viscosity of the solvent, which has a beneficial impact on the process efficiency [117]. It could be concluded that cellulose-dissolving effectiveness increases if the imidazolium cation contains electron-donating substituents. 6.5 The Impact of the Addition of Other Chemicals and Process Conditions on Cellulose Dissolution Effectiveness in Ionic Liquids  
Ionic liquids, despite the many advantages mentioned in this paper, have some drawbacks as solvents. Many ILs are viscous liquids, and their production costs are also quite high. In order to solve the viscosity problem, many researchers have added other solvents to the process. Organic polar aprotic solvents, e.g., DMSO or DMF, can significantly reduce the viscosity of ionic liquids, which results in better mass transport and increased polymer dissolution efficiency, without cellulose modifications [95,118,119]. Other solvents, such as acetonitrile or ethylene glycol, have a similar effect--they can reduce the viscosity of IL, e.g., [emim][CH\({}_{3}\)COO] and [bmim][CH\({}_{3}\)COO], by up to 50% [120].