## 3 Results
### Optimal of Biocrude Production  
Table 3 shows the theoretical value based on the adjustments obtained in the statistical equations of the three responses (Equations (4)-(6)). The results showed that the operating conditions maximising biocrude yield and those minimising nitrogen and oxygen contents were not coincident. Therefore, it was decided to continue with the conditions that maximise biocrude yield since it is possible to reduce the heteroatoms with subsequent treatments. According to Table 3, the values that maximised the biocrude yield were: 320 \({}^{\circ}\)C, 10 min and a biomass concentration of 10 wt%. Table 4 shows the yields of the different phases obtained under optimal conditions. The biocrude yield, obtained at the optimal conditions, was 42.3 \(\pm\) 0.8 wt%, similar to the theoretical result predicted by the model, and comparable to the results found in the literature at similar operating conditions without the use of catalysts (34.4 wt% at 250 \({}^{\circ}\)C and 54.2 wt% at 375 \({}^{\circ}\)C) [2]. The yield of the gas phase obtained at 320 \({}^{\circ}\)C was 18 \(\pm\) 2 wt%, lower than the 30 wt% measured by [PERSON] et al. at the same temperature [32]. On the other hand, the value of the yield of WSP was 32 \(\pm\) 1 wt%. This value was lower than that obtained by Valdez at the same time and similar temperatures (43 wt%) [33]. Regarding \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Real Value**} & \multicolumn{3}{c}{**Codified Value**} & \multicolumn{3}{c}{**Theoretical Response**} \\ \cline{2-10}  & **T** & **t** & **CS** & **T** & **t** & **CS** & \(Y_{BC}\) & \(C_{O}\) & \(C_{N}\) \\  & (\({}^{\circ}\)**C**) & **(min)** & **(wt\%)** & **(\({}^{\circ}\)C)** & **(min)** & **(wt\%)** & **(wt\%)** & **(wt\%)** & **(wt\%)** \\ \hline Max \(Y_{BC}\) & 320 & 10 & 10 & 320 & 10 & 10 & 43.15 & 14.71 & 3.1 \\ Min \(C_{N}\) & 200 & 180 & 10 & 200 & 180 & 10 & 14.89 & 21.30 & 3.33 \\ Min \(C_{O}\) & 200 & 93.5 & 50 & 200 & 93.5 & 50 & 15.60 & 7.93 & 5.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Theoretical values to maximise the biocrude yield and minimise de N and O content. the solid residue, the yield obtained was 7.42 \(\pm\) 0.08 wt%, which is within the usual ranges for this fraction in other microalgae systems [32; 33]. This solid residue value was slightly higher than the ash value of the starting biomass (5 wt%), indicating no biomass was left to convert. The calorific value of the biocrude obtained at the optimum conditions was 35.74 \(\pm\) 0.02 MJ/Kg. This value was within the range of microalgal biocrudes reported in the literature (30-43 MJ/Kg) [9], and supposed an increase of the calorific power with respect to the microalgae biomass (21.75 MJ/Kg). The energy recovered (63 wt%) was comparable to the values reported in the literature (50-75 wt%) [4; 34]. The biocrude analysis showed a carbon content of 73.71 \(\pm\) 0.08 wt% (Table S4, Supplementary Materials), and 40% of the carbon contained in the starting raw biomass was recovered in that phase. The hydrogen content was 9.18 \(\pm\) 0.01 wt%, which represented a recovery of 43 wt% in the biocrude. Consistently, the recovery of both carbon and hydrogen was similar since they are generally found in the same compounds. Part of the new molecules formed after the HTL process are soluble in water and, therefore, go to WSP [31]. Regarding heteroatoms, the composition of N and O were 6.12 \(\pm\) 0.02 wt% and 10.77 \(\pm\) 0.16 wt%, respectively. These values meant that elimination in biocrude, with respect to the starting biomass, reached 59.5 wt% for nitrogen and 61.92 wt% for oxygen. A low sulfur content (0.32 \(\pm\) 0.02 wt%) was also measured. The high elimination of nitrogen, oxygen and sulfur in the biocrude produces an improvement in its quality and simplifies their subsequent downstream processing [3]. These values for HCNSO obtained are comparable to those collected by [PERSON] et al.