# Analysis of Sequential Pretreatments to Enhance the Early-Stage Biorefinery Designs
## 3 Results
### Heuristic Analysis
\begin{table}
\begin{tabular}{l l c c c c c c} \hline \hline \multirow{2}{*}{**Fraction**} & \multirow{2}{*}{**Sequential Scheme**} & \multicolumn{6}{c}{**\(\mathbf{I_{CapEx}}\)**} & \multicolumn{6}{c}{**\(\mathbf{I_{OpEx}(M-USD Year^{-1})}\)**} \\ \cline{3-8}  & & **(M-USD)** & **Raw Materials** & **Utilities** & **Others \({}^{*}\)** & **Total** \\ \hline \multirow{6}{*}{Cellulose} & DA + alkali & 1.60 & 5.20 & 2.06 & 0.37 & 7.62 \\  & DA + WAO & 2.98 & 1.63 & 6.28 & 0.63 & 8.54 \\  & Kraft + DA & 2.82 & 2.72 & 2.23 & 0.60 & 5.55 \\  & Kraft + SE & 2.64 & 2.70 & 2.23 & 0.57 & 5.50 \\  & Kraft + WAO & 2.87 & 2.69 & 2.25 & 0.61 & 5.55 \\  & SE + WAO & 2.84 & 1.31 & 8.26 & 0.61 & 10.18 \\ \hline \multirow{6}{*}{Hemicellulose} & LHW + DA & 1.51 & 1.8 & 2.55 & 0.35 & 4.7 \\  & LHW + organoslov & 2.35 & 17.29 & 11.15 & 0.51 & 28.96 \\ \cline{1-1}  & Organoslov + DA & 10.3 & 50.43 & 148.43 & 2.04 & 200.90 \\ \cline{1-1}  & SE + DA & 1.44 & 1.75 & 7.85 & 0.34 & 9.93 \\ \cline{1-1}  & SE + LHW & 1.36 & 1.18 & 7.73 & 0.32 & 9.23 \\ \cline{1-1}  & SE + organoslov & 2.97 & 20.57 & 15.65 & 0.63 & 36.85 \\ \hline \multirow{6}{*}{Lignin} & DA + alkali & 1.96 & 6.18 & 2.81 & 0.44 & 9.42 \\ \cline{1-1}  & DA + kraft & 1.53 & 2.84 & 2.33 & 0.35 & 5.53 \\ \cline{1-1}  & DA + WAO & 2.98 & 1.56 & 3.92 & 0.63 & 6.1 \\ \cline{1-1}  & SE + kraft & 1.45 & 10.37 & 7.34 & 0.34 & 18.06 \\ \cline{1-1}  & SE + alkali & 1.47 & 6.25 & 7.34 & 0.34 & 13.92 \\ \cline{1-1}  & SE + WAO & 2.84 & 1.31 & 8.26 & 0.61 & 10.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Capital and operating cost of the sequential schemes. Based on the sequential pretreatments for hemicellulose fractionation, the final scores were lower than the cellulose sequences. Despite the high I\({}_{\text{R}}\), these pretreatments usually removed hexes fractions from cellulose or hemicellulose (i.e., \(\beta\)-d-glucose, \(\beta\)-d-mannnose, \(\alpha\)-l-rhamnose, \(\alpha\)-d-galactose, and \(\alpha\)-l-tucose) and lignin [35], decreasing I\({}_{\text{A}}\), I\({}_{\text{CR}}\), I\({}_{\text{Y}}\), and I\({}_{\text{V}}\). However, the best sequential schemes for hemicellulose were SE with DA and LHW with DA. DA was identified as the second pretreatment stage, leading to better fractionation of the remaining hemicellulose due to the incomplete breakdown of the lignin-carbohydrate matrix or hydrolysis of pentose oligomers formed in LHW [36] or SE [37]. Similar results were reported in the literature, where hemicellulose removals greater than 93% were achieved following the LHW and DA sequence, explained by the partial removal of lignin as a physical barrier to further pentose hydrolysis [13]. The results in Table 6 indicate that the proposed sequences are driven toward maximizing pentose removal from hemicellulose, largely achieved during the first pretreatment stage. A second stage should be proposed to isolate lignin instead of removing the remaining hemicellulose, as it decreases the possibility of valorization of the second liquor, which may be contaminated with an excess reagent or unwanted fractions that prevent good processing. For example, following the SE and LHW sequential pretreatment, the second liquor would have a theoretical composition of 43.5% cellulose, 12.5% hemicellulose, and 44.0% lignin, demonstrating the lower composition of pentoses. Therefore, the cellulose-based sequences demonstrate a higher I\({}_{\text{V}}\), as the first liquor is rich in pentoses, and the second liquor is rich in soluble lignin, along with high I\({}_{\text{CR}}\). This analysis was also demonstrated in the sequences for lignin isolation, where pretreatments were proposed for pentose fractionation first, and a subsequent process was emphasized for deligifications. Different results were observed when comparing sequential pretreatments for hemicellulose and lignin valorization. (i) Hemicellulose-based schemes did not show high lignin removals; in contrast, liquours would be abundant in either hydrolyzed sugars or inhibitor formation.