## 3 Results
### Optimization and Catalysts
#### 3.4.2 Optimization  
Figure 14 shows the optimal conditions for the production of sugars from pea pod waste. It shows that even though the concentration of sugars obtained is the highest using H\({}_{2}\)SO\({}_{4}\) as a catalyst, the amount of liquid phase obtained at 180 \({}^{\circ}\)C for 1 h without catalyst is greater, making the yield bigger as well. At higher temperatures and longer reaction times, the sugars react to produce the other PC or undergo degradation, which makes the yield decrease. The best conditions would then be at 180 \({}^{\circ}\)C for one hour with H\({}_{2}\)SO\({}_{4}\) as a catalyst or without it. If the process is meant to be cleaner, then it is suggested to not implement the catalyst, as a good yield is obtained without its use.  
The yield of formic acid production (Figure 15) is highly influenced by high temperatures and the use of catalysts, obtaining the best results under the conditions of 180 \({}^{\circ}\)C, 2 h, and NaHCO\({}_{3}\) as a catalyst. Good yields are also achieved using CH\({}_{3}\)COOH as a catalyst at 180 \({}^{\circ}\)C or at 260 \({}^{\circ}\)C without a catalyst. It is suggested then, in order to achieve a good yield of formic acid, to use weak acids or bases as catalysts for the process for longer times, or, in the case of the use of only water, higher conditions of HTC favor the degradation of other PC to formic acid.  
Figure 14: Optimization of conditions (temperature (\({}^{\circ}\)C), time (h), and catalysts) for the obtention of sugars. W/O = Without.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Time**} & \multirow{2}{*}{**Catalyst**} & \multicolumn{5}{c}{**Concentration PC (g/L)**} & \multirow{2}{*}{**Yield (\%w)**} \\ \cline{3-3} \cline{5-6}  & & **Sugars** & & **Levulinic Acid** & & **Formic Acid** & **HMF** & **Furfural** \\ \hline
1 & NO & 34.818 & 0.577 & & & 70.001 \\
1 & H\({}_{2}\)SO\({}_{4}\) & 36.363 & 0.785 & & 0.619 & 59.668 \\
1 & CH\({}_{3}\)COOH & 20.660 & & 18.394 & & 73.003 \\
1 & KOH & 16.498 & & & & 21.938 \\
1 & NaHCO\({}_{3}\) & 13.876 & & 9.976 & & 43.144 \\
2 & NO & 26.341 & 1.063 & 2.392 & 0.299 & 62.284 \\
2 & H\({}_{2}\)SO\({}_{4}\) & 23.182 & 0.769 & & 1.059 & 39.755 \\
2 & CH\({}_{3}\)COOH & 14.518 & 5.152 & & 1.097 & 53.488 \\
2 & KOH & 1.791 & 1.896 & 9.351 & 0.761 & 1.146 & 50.178 \\
2 & NaHCO\({}_{3}\) & 20.753 & & 23.953 & & 81.427 \\ \hline \hline \end{tabular}
\end{table}
Table 12: Concentration and yields of platform chemicals obtained with catalysts.  
Levulinic acid's optimal conditions for production are reported in Figure 16. The use of weak acid catalysts and longer reaction times (2 h) favor the formation of levulinic acid remarkably. Temperatures over 200 \({}^{\circ}\)C but under 260 \({}^{\circ}\)C also produce high yields of levulinic acid without the need for catalysts, with 200 \({}^{\circ}\)C being the best condition. At temperatures above 260 \({}^{\circ}\)C, the acid starts to degrade into smaller molecules, decreasing the yield.  
Finally, Figure 17 shows the optimal conditions for HMF and furfural production. On this platform, chemicals can be highly unstable, and precise conditions are needed for them to be produced. The use of catalysts helps produce HMF and furfural in shorter times, but the yield is not the best possible. On the other hand, the use of higher reaction times at 180 \({}^{\circ}\)C allows for the obtention of higher yields due to the softer conditions for the reactions to take place. At higher temperatures (220-260 \({}^{\circ}\)C), the conditions are too strong for this PC to be stable, and they degrade into other products that are not of interest.  
Figure 16: Optimization of conditions (temperature (\({}^{\circ}\)C), time (h), and catalysts) for the obtention of levulinic acid.  
Figure 15: Optimization of conditions (temperature (\({}^{\circ}\)C), time (h), and catalysts) for the obtention of formic acid.