## 3 Results and Discussion
In this figure the uppermost cluster is associated with sulfite charge of 5% or higher, suggesting the role of lignin sulfonation, reported by several authors [28; 29]. In addition, the enzymatic yield in the range 86.6-88.7%, obtained for 5s_1 ac and 5s_2.5 ac, is higher than that obtained for the 15s_0 ac solid residue (82.9%), despite the low lignin content of the 15s_0 ac solid residue (6.4% of lignin vs. 19.5-21.1%; Table 1, SRY column). It should be mentioned, however, that the enzyme charges regarding the carbohydrates in the solid residue 15s_0 ac are slightly lower than the charges for the 5s_2.5 ac sample, due to the higher lignin content of the last one. These results suggest that the presence of sulfonated lignin in the solid residue, even in very high amounts, does not impair the enzymatic rate and extent, probably because sulfonation decreases the non-productive adsorption of enzymes on lignin [28; 29]. Lignin extraction from the solid residue significantly enhances the process, but it seems that lignin extraction is not a prerequisite for extensive enzymatic hydrolysis, even for relatively low enzymatic charges, as is the case in the present work. Figure 1: Effect of the enzymatic hydrolysis time on the total carbohydrates yield for biomasses pretreated with different liquor compositions at 170 \({}^{\circ}\)C for 30 min. To study the influence of temperature, some pretreatments were carried out at 190 \({}^{\circ}\)C. Figure 3 shows the effect of pretreatment temperature on enzymatic hydrolysis yield, for wood pin chips treated with 2% and 15% sulfite and 0 and 5% sulfuric acid. As it can be seen in Figure 3, increasing the pretreatment temperature from 170 to 190 \({}^{\circ}\)C increased the initial rate of carbohydrates release during the enzymatic hydrolysis for all tested solid residues, even when the enzymatic hydrolysis extent remained unaffected (15s_0 ac and 15s_5 ac). Both effects are particularly notorious in the solid residue pretreated with 2s_1 ac, where the extent of the reaction was also positively affected (from 51.7 to 65.9% for 170 and 190 \({}^{\circ}\)C, respectively), in addition to the initial reaction rate. These results are in good agreement with the increase of the WRV of the solid residues from 1.31 g/g to 1.35 g/g. The corresponding increase in WRV for the 15s_0 ac was from 1.39 g/g to 1.51 g/g. Figure 3: Effect of pretreatment temperature on total carbohydrates yield throughout the enzymatic hydrolysis. Figure 2: Effect of global porosity (\(\varepsilon\)) on the enzymatic yield. Regarding the effect of the wood chip size on the acid sulfite pretreatment there is a very notorious decrease of mass removal with the increase of chip size, from the wood pin chips to the conventional chips size (Table 11), which evidence the effect of the mass transfer rate on the acid sulfite pretreatment. The effect on the enzymatic hydrolysis yield is much smaller, around 2%, which indicates that reducing the size of the chips in the pretreatment is not worth it. Table 2 presents the experimental data respecting WRV, global porosity estimated from the WRV (\(\epsilon\) (WRV)) and the increment in porosity due to material removal (\(\Delta\epsilon\)(SRY)), porosity concerning pores with hydrodynamic radii higher than 2.65 nm (\(\epsilon\) (>2.65 nm)), the external SSA and the maximum extent of polysaccharides enzymatic hydrolysis for some selected solid residues. The enzymatic yield correlates positively with the WRV, which includes the water in the fiber wall but also the water between fibers. Because of this, WRV is not directly correlated with the internal porosity of the fiber wall. In addition, the increase in WRV can also be due to the lignin sulfonation, which increases its hydrophilicity. The porosity concerning pores with hydrodynamic radii higher than 2.65 nm (\(\epsilon\) (>2.65)) increased from 28% (0s_0 ac, autohydrolysis) to 35% (2s_1 ac), for moderate acid sulfite treatment conditions, but just a little more to 38% even for the harshest conditions (15s_5 ac).