# Analysis of Sequential Pretreatments to Enhance the Early-Stage Biorefinery Designs
## 3 Results
### Techno-Economic Analysis  
After analyzing operating indicators and raw materials, the mass yield and the water and energy requirements of the pretreatment sequences, were discussed as shown in Table 4. The \(\rm I_{Y}\) indicates the potential of all the valorizable streams in terms of cellulose content in the WIS, hydrolyzed pentoses, and soluble lignin in the liquors since they will be used as future platform products. High \(\rm I_{Y}\) values are desired in biorefinery schemes to improve the overall economic performance. It was observed that, for the cellulose-based schemes, all sequences had an \(\rm I_{Y}\) in the 50-55% range, except for the sequential pretreatment of DA and alkali, due to the low lignin removal compared to other schemes, which would gradually decrease the valorization yields of this heteropolymer. However, as expected, these values were higher than all hemicellulose-based schemes due to the small and medium hexose removals, as in the pretreatments involving organosolv and LHW with cellulose removals of 19.6% and 29.8%, respectively. Meanwhile, for lignin sequences, the SE and WAO scheme showed the highest yields since cellulose isolations were higher than 90%, and fractionations of 95% for hemicellulose and 97% for lignin were achieved. Indeed, those schemes where WAO was implemented showed the best \(\rm I_{Y}\) for both cellulose and lignin schemes. The mass and energy yields depend on the operating conditions (i.e., temperature, pressure, and feed ratio) of each pretreatment, as well as the removal yield. Therefore, energy demand must be minimized and not reflected in operating costs. A high energy demand leads to a higher requirement for either steam or electricity. Regarding water consumption, its volume will depend on feed ratios, dilutions performed, and WIS washings after each pretreatment. Biotechnological processes demand high water ratios. Some studies have shown that, in large-scale wood-based biorefineries, processing water represents more than 95% of the raw materials [8], given its extensive use in pretreatments for dilution rates and reaction and separation schemes. In general, there was not much difference for all sequences, with an average demand of 27.9 m\({}^{3}\) ton\({}^{-1}\) of feedstock. \begin{table}
\begin{tabular}{c l c c c c c} \hline \hline \multirow{2}{*}{**Fraction**} & \multirow{2}{*}{**Sequential Scheme**} & \multirow{2}{*}{\(\rm I_{Y}\) *} & \multirow{2}{*}{\(\rm I_{WD}\) **} & \multicolumn{3}{c}{**Utility Yields (\(\rm I_{E}\))**} \\  & & & & **(\(\rm\bf kg\) 100 \(\rm\bf kg^{-1}\))** & & **(\(\rm\bf m^{3}\) ton\({}^{-1}\))** & **Steam *** (\(\rm\bf m^{3}\) kg\({}^{-1}\))** & **Cooking Water** (\(\rm\bf kW\) ton\({}^{-1}\))** \\ \hline \multirow{6}{*}{Cellulose} & DA + alkali & 46.01 & 18.57 & 4.54 & 0.65 & 74.76 \\  & DA + WAO & 53.35 & 24.84 & 16.39 & 3.01 & 82.28 \\  & Kraft + DA & 50.55 & 29.68 & 60.31 & 12.29 & 88.92 \\  & Kraft + SE & 50.14 & 27.35 & 60.31 & 12.29 & 78.57 \\  & Kraft + WAO & 52.12 & 35.27 & 62.60 & 12.15 & 90.60 \\  & SE + WAO & 54.56 & 39.85 & 3.61 & 6.79 & 63.52 \\ \hline \multirow{6}{*}{Hemicellulose} & LHW + DA & 37.06 & 18.57 & 5.96 & 0.92 & 75.24 \\  & LHW + organosolv & 42.22 & 17.02 & 37.50 & 4.93 & 83.16 \\  & Organosolv + DA & 43.98 & 15.65 & 309.85 & 99.39 & 354.47 \\  & SE + DA & 38.67 & 33.69 & 1.30 & 6.74 & 52.67 \\  & SE + LHW & 37.39 & 33.65 & 1.16 & 6.65 & 52.67 \\  & SE + organosolv & 45.40 & 31.45 & 17.12 & 12.05 & 87.96 \\ \hline \multirow{6}{*}{Lignin} & DA + alkali & 47.25 & 27.15 & 6.92 & 1.01 & 104.53 \\  & DA + kraft & 50.32 & 18.53 & 5.43 & 0.80 & 65.63 \\ \cline{1-1}  & DA + WAO & 53.47 & 24.84 & 16.39 & 0.73 & 82.28 \\ \cline{1-1}  & SE + kraft & 50.38 & 33.20 & 0.62 & 6.35 & 52.19 \\ \cline{1-1}  & SE + alkali & 46.30 & 33.64 & 0.39 & 6.37 & 55.79 \\ \cline{1-1}  & SE + WAO & 54.55 & 39.85 & 3.61 & 6.79 & 63.52 \\ \hline \hline \end{tabular}  
* See Equation (10). ** Process water demand per ton of feedstock. *** Total steam requirement as the sum of low-, medium-, and high-pressure steam.  
\end{table}