# Analysis of Sequential Pretreatments to Enhance the Early-Stage Biorefinery Designs
## 3 Results
### Pretreatment Screening
Regarding the possibility of valorization of sub-streams (I\({}_{\text{V}}\) indicator), those sequences involving WAO showed the best results due to their high lignin removal capacity, which was proposed after a selective pretreatment mainly for hemicellulose-based schemes. For schemes based on hemicellulose fractionation, large overall removals were obtained. However, it is crucial to control operational conditions to avoid the degradation of both monomers and oligomers toward furans and aliphatic compounds. Even with low acidic characteristics, such as LHW or SE sequential pretreatment, there is a decrease in the pH of the medium given to the formation of aliphatic compounds such as acetic acid, favoring catalyzed hydrolysis for the dehydration of pentoses toward furural and hydroxymethylfurural [28]. Similar overall removals were also observed for lignin sequences contemplating WAO pretreatment; however, there was no complete removal for the other schemes, such as in DA with alkali or SE with alkali. Therefore, there is a remaining lignin fraction between 14% and 32% in the final WIS. Given the structural character of hemicellulose and lignin, both biopolymers are usually removed together, decreasing the accessibility in the WIS compared to cellulose sequences (see the I\({}_{\text{CR}}\) indicator). However, the average accessibility for schemes based on both lignocellulosic fractions was 74.4%. Finally, the possibilities of sub-stream valorization were lower for pentose isolation due to the accessibility of lignin in the liquors and low cellulose recovery. For the lignin sequences, it was observed that the first hydrolysate contains a large part of the initial five-carbon sugars of the biomass, so the valorization of the second liquor may be negligible. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fraction** & **Sequential Scheme** & **I\({}_{\text{R}}\) (\%)** & **I\({}_{\text{A}}\) (\%)** & **I\({}_{\text{CR}}\) (\%)** & **I\({}_{\text{S}}\)** & **I\({}_{\text{V}}\) (\%)** \\ \hline \multirow{8}{*}{Cellulose} & DA + alkali & 15.90 & 86.69 & 84.11 & 7.08 & 69.60 \\  & DA + WAO & 16.27 & 98.62 & 83.73 & 7.63 & 71.51 \\  & Kraft + DA & 18.89 & 93.04 & 81.11 & 6.93 & 63.39 \\  & Kraft + SE & 12.10 & 91.07 & 87.90 & 6.19 & 72.26 \\  & Kraft + WAO & 16.38 & 95.64 & 83.62 & 6.89 & 51.90 \\  & SE + WAO & 9.25 & 97.57 & 90.75 & 7.52 & 72.34 \\ \hline \multirow{8}{*}{Hemiccellulose} & LHW + DA & 99.87 & 66.48 & 63.25 & 7.67 & 34.07 \\  & LHW + organosolv & 99.26 & 62.67 & 56.42 & 7.21 & 48.69 \\ \cline{1-1}  & Organosolv + DA & 99.90 & 64.01 & 72.46 & 7.20 & 44.59 \\ \cline{1-1}  & SE + DA & 99.80 & 75.55 & 88.02 & 6.82 & 32.18 \\ \cline{1-1}  & SE + LHW & 97.90 & 71.70 & 68.54 & 7.56 & 31.86 \\ \cline{1-1}  & SE + organosolv & 98.80 & 71.27 & 78.53 & 7.09 & 46.85 \\ \hline \multirow{8}{*}{Lignin} & DA + alkali & 69.70 & 77.72 & 84.11 & 7.08 & 59.04 \\ \cline{1-1}  & DA + kraft & 87.20 & 77.44 & 81.11 & 6.93 & 67.28 \\ \cline{1-1}  & DA + WAO & 97.80 & 78.40 & 83.73 & 7.63 & 75.19 \\ \cline{1-1}  & SE + alkali & 68.00 & 76.66 & 91.16 & 6.97 & 62.56 \\ \cline{1-1}  & SE + kraft & 86.50 & 76.50 & 87.90 & 6.82 & 69.86 \\ \cline{1-1}  & SE + WAO & 97.60 & 76.81 & 87.9 & 7.52 & 78.87 \\ \hline \hline \end{tabular}  
DA, dilute acid; WAO, wet air oxidation; SE, steam explosion; LHW, liquid hot water.  
\end{table} 
Table 2: Proposed sequential schemes and their operational indicators.