# Fractionation of Lignocellulosic Biomass by Selective Precipitation from Ionic Liquid Dissolution
## 3 Results and Discussion  
### Effect of the Water:Acetone Ratio  
The barley straw dissolved in [EMIMAcO] was reconstructed by the addition of an antisolvent. The antisolvents employed were mixtures of water:acetone (W:A) with different mass ratios: 1:0, 2:1, 1.5:1, 1:1, 1:1.5, 1:2 and 0:1. The solid precipitated after the addition of the solvent was labeled \"Solid 1\", and a second solid was obtained after the evaporation of acetone, labeled \"Solid II\". To evaluate the fractionation ability of the antisolvent employed, the mass of each solid was measured and compared with the theoretical amount that corresponds in Solid I to the sum of cellulose and hemicellulose and in Solid II to lignin. In addition, the recovered in each solid and total biomass was calculated by comparing the sum of the masses recovered in the two filtrations and the sum of cellulose, lignin and hemicellulose present in the biomass added at the beginning of the experiment. The results obtained from precipitation with the different antisolvents are shown in Table 2.  
The total recovered biomass was high, approximately 90%, in all cases, respect the sum of hemicellulose + cellulose + lignin present in the starting barley straw. In Solid II the recovery is between 70 and 80% while in Solid II is 10-17%, depending on the mixture of antisolvent employed. This effect was also observed in the % expected which depends also on the mixture employed. When \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample a**} & \multirow{2}{*}{**Antisolvent**} & \multicolumn{3}{c}{**\% Solid I**} & \multicolumn{3}{c}{**\% Solid II**} & \multirow{2}{*}{**\% Recovered**} \\ \cline{3-3} \cline{5-6}  & & **\% Initial** & & & **Siomass b** & \\ \hline
**WA-10** & Water & & & No separation found & & 89\% \\
**WA-2:1** & Water:Acetone 2:1 & 77.6\% & 113.4\% & 10.4\% & 53.1\% & 88\% \\
**WA-1:5.1** & Water:Acetone 1:5.1 & 79.9\% & 112.9\% & 11.1\% & 55.0\% & 91\% \\
**WA-1:1** & Water:Acetone 1:1 & 71.2\% & 102.9\% & 17.8\% & 90.0\% & 89\% \\
**WA-1:1.5** & Water:Acetone 1:1.5 & 78.6\% & 113.6\% & 10.4\% & 52.5\% & 89\% \\
**WA-1:2** & Water:Acetone 1:2 & 78.1\% & 114.2\% & 9.9\% & 50.4\% & 88\% \\
**WA-0:1** & Acetone & & & No separation found & & 87\% \\ \hline \hline \end{tabular}  
* The samples are called WA-X:Y, where WA refers to “Water:Acetone” and the numbers X and Y indicate the water:acetone ratio used. b % of biomass recovered based on the initial mass of cellulose + hemicellulose + lignin present in raw barley straw. c % of mass recovered if Solid I is only the sum (cellulose + hemicellulose) and Solid II is the mass of lignin (Table 1).  
\end{table} 
Table 2: Mass balance of matter based on dry barley straw after precipitating the biomass with different water:acetone antisolvent mixtures. The barley straw samples were dissolved in [EMIMAcO]) at 105 \({}^{\circ}\)C for 3.5 h.  
pure solvent (water or acetone) was employed, only Solid I was obtained, which implies no separation of components by selective precipitation. However, the properties of the obtained solid were quite different depending on the pure solvent employed. When water was used as an antisolvent, Solid I was easy to manipulate, wash and filter, but in the case of acetone, the solid obtained was very difficult to handle, wash and filter. However, when the antisolvent was a mixture of water:acetone, the presence of two solids (Solid I and Solid II) was observed (Table 2). In all cases, the amount of Solid I was higher than the theoretical sum of cellulose and hemicellulose (>100%), and the amount of Solid II was lower than the theoretical amount of lignin (<100%). The values of mass recovered indicate that in Solid I, some lignin was incorporated with the cellulose and hemicellulose. However, these amounts changed with the W:A ratio The most interesting results were obtained for the ratio 1:1, where both Solid I and Solid II were close to 100%. Based on these results, the optimal antisolvent used was the W:A = 1:1 mixture.