## 3 Results and Discussion
### Mass Balance
#### 3.1.2 Effect of Dilute Acid Impregnation on Fractionation  
Acid impregnation has been considered to play a vital role for steam explosion treatment [4; 19]. Keeping this in view, the effects of dilute acid on the fractionation process was studied with the feedstock impregnation in dilute sulfuric acid (0.5, 1, 2 wt%) for 4 h. Steam explosion process was further operated at residence time of 20 min and temperature of 220 \({}^{\circ}\)C, which showed the highest severity score so that the effect of dilute acid concentration can be compared clearly. Figure 3 shows the mass distribution of solid fractions obtained from EFB at various acid concentrations.  
Mass composition of EA-S did not affect by the acid concentration clearly until the concentration reaches 2.0%. Moreover, at 0.5 and 1.0% dilute acid concentrations, EA-S from ACSE also showed no remarkable changes in the mass distribution. In the range of 0%-1.0% dilute acid concentration, yields of EA-S decreased from 73.0 to 70.8 wt%. However, EA-S-CS from ACO decreased with an increase in the acid concentration. In the same range of 0%-1.0% dilute acid concentration, EA-S-CS decreased from 59.0 to 45.9 wt%. At 2.0% dilute acid concentration, EA-S and EA-S-CS decreased with an increase in the acidity.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Holocellulose (wt%)**} & ** Lignin (wt%)** \\ \hline \multicolumn{2}{c}{Raw EFB} & 70.6 \(\pm\) 0.2 & 18.0 \(\pm\) 0.2 \\ \hline \multirow{8}{*}{E-S} & 180-5 & 70.2 \(\pm\) 0.1 & 23.3 \(\pm\) 0.0 \\  & 180-10 & 69.3 \(\pm\) 0.2 & 22.9 \(\pm\) 0.1 \\  & 180-15 & 70.8 \(\pm\) 0.2 & 25.1 \(\pm\) 0.2 \\  & 200-5 & 71.2 \(\pm\) 0.1 & 24.2 \(\pm\) 1.0 \\  & 200-10 & 69.9 \(\pm\) 0.1 & 27.9 \(\pm\) 0.8 \\  & 200-15 & 71.6 \(\pm\) 0.4 & 29.3 \(\pm\) 0.8 \\  & 220-5 & 68.3 \(\pm\) 0.1 & 29.4 \(\pm\) 0.8 \\  & 220-10 & 67.5 \(\pm\) 0.0 & 33.7 \(\pm\) 0.1 \\  & 220-15 & 67.9 \(\pm\) 0.3 & 34.6 \(\pm\) 0.2 \\ \hline \multirow{8}{*}{E-S-CS} & 180-5 & 80.8 \(\pm\) 0.3 & 20.1 \(\pm\) 0.1 \\  & 180-10 & 80.3 \(\pm\) 0.2 & 20.2 \(\pm\) 0.1 \\ \cline{1-1}  & 180-15 & 81.1 \(\pm\) 0.2 & 21.6 \(\pm\) 0.3 \\ \cline{1-1}  & 200-5 & 83.6 \(\pm\) 0.1 & 20.6 \(\pm\) 0.1 \\ \cline{1-1}  & 200-10 & 80.2 \(\pm\) 0.2 & 22.8 \(\pm\) 0.5 \\ \cline{1-1}  & 200-15 & 81.5 \(\pm\) 0.1 & 22.9 \(\pm\) 0.9 \\ \cline{1-1}  & 220-5 & 83.8 \(\pm\) 0.2 & 21.5 \(\pm\) 0.6 \\ \cline{1-1}  & 220-10 & 74.9 \(\pm\) 0.8 & 24.6 \(\pm\) 0.5 \\ \cline{1-1}  & 220-15 & 76.2 \(\pm\) 0.1 & 22.8 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Component analysis of pretreated EFB solid fractions under different temperatures and residence times.  
Table 3 shows the holocellulose and lignin contents of EA-S and EA-S-CS calculated for each experimental run. The total amount of holocellulose harshly decreased with increasing dilute acid concentration. At 0.5% dilute acid concentration, 41.3 and 26.8 wt% of holocellulose still remained in EA-S and EA-S-CS, respectively. When the concentration increased to 2.0%, however, only 28.1 and 16.0 wt% of holocellulose remained in EA-S and EA-S-CS, respectively. Lignin exhibited somewhat different behavior in mass decrease. The amount of lignin did change slightly by the steam treatment. Hwoever, after ACO, 4.3%-6.7% of lignin was removed from the solid fractions. The removal efficiency of lignin between 0.5% and 2.0% acid concentration respectively. Similar studies were reported for the dilute acid treatment of rice straw [20] and corn stover [21]. However, the proper acid concentration or removal efficiencies of hemicellulose and lignin were different by feedstock properties. Since the purpose of this experiments is to lower only hemicellulose and lignin contents in EFB, so a high acid concentration was not adapted to avoid the loss of holocellulose contents.