## 3 Results and Discussion  
### Mass Balance  
#### 3.1.1 Effect of Residence Time and Temperature on Fractionation  
The effects of residence time and temperature on the fractionation process were studied at various intervals (residence time 5, 10, 15 min and temperature 180, 200, 220 \({}^{\circ}\)C). Figure 2 shows the mass distribution of solid fractions obtained from EFB at various temperatures and residence time conditions.  
Mass composition of the fraction was affected by residence time. At all temperature conditions, E-S from the steam explosion, and its subsequent, E-S-CS from organosolv treatment decreased with increasing residence time. For example, at 200 \({}^{\circ}\)C and in the range of 5-15 min, yields of E-S and E-S-CS decreased from 79.0 wt% and 73.8 wt% to 68.3 wt% and 61.2 wt%, respectively. The lowest yield was obtained when the residence time was kept for 15 min, regardless of reaction temperatures. The effect of temperature was not much clear as that of residence time. Under the same residence time condition, the yield of E-S and E-S-CS decreased only 3-8 wt%. The combined effect of temperature (T) and residence time (t) can be expressed as severity factor (\(\log_{10}\left(R_{0}\right)\)) [\(R_{0}=\) t \(\times\) exp((T\(-\)100)/14.75)) [17]. The severity factor obtained ranged from 3.1 to 4.7. There was a scant negative correlation between the severity factor and the solid fraction yield, showing that increasing temperature and residence time results in the removal of compounds from solid fractions.  
In general, both mechanical and chemical effects take place when an acetyl group derived from hemicellulose acts as an acid at high temperature during the steam explosion [18]. These effects play important roles in the hydrothermal degradation of holocellulose. Hemicellulose and lignin are isolated by the high temperature in the steam condition. Organosolv treatment, however, on the other hand, solubilize lignin and provide holocellulose by using organic solvent mixture and inorganic catalysts [7]. Therefore, holocellulose and lignin compositions of solid fractions were also analyzed to examine the fractionation efficiency of the process.  
Holocellulose and lignin contents of E-S and E-S-CS were calculated for each experiment (Table 2). Percentage of holocellulose composition decreased with increasing severity of steam explosion. A maximum of 24.1 wt% of holocellulose (220-15) was dissolved in E-L. On the contrary, the percentage of lignin composition increased with increasing severity factor. It can be anticipated that lignin melts under a high temperature and pressure, then condensed with other compounds like extractives or ash while cooling. Solid fractions which have undergone organosolvation showed an unremarkable change  
Figure 2: Yields of the solid fractions from steam explosion and organosolv treatment of EFB under different temperatures and residence times.  
of holocellulose contents. In addition, a considerable amount of lignin content still remained in the solids. Maximum 7.5% of lignin (220-15) was solubilized in 50% ethanol mixture. Lignin fractionation efficiency of organosolv treatment from EFB was falling short of our expectation because of its low lignin removal. These results showed EFB presents a high level of recalcitrance to the fractionation process. Thus, dilute acid pretreatment to level down the EFB recalcitrance had considerable effects and the results are discussed in Section 3.1.2.