## 3 Results
### Optimal of Biocrude Production
for the same microalga at slightly higher temperatures, 375 \({}^{\circ}\)C, (9.9 wt%, 74.7 wt%, 5.2 wt%, 0.4 wt% and 8.5 wt% for H, C, N, S and O, respectively) [2]. Biocrude properties are highly dependent on H/C, N/C and O/C atomic ratios. The Van Krevelen diagram shown in Figure 5 shows the values of these atomic ratios in the biocrude obtained at the optimal operating conditions and the starting biomass. The O/C and N/C ratios of the biocrude (0.998 and 0.120, respectively) were remarkably lower than the value of these ratios in the starting microalga (0.9993 and 0.11968, respectively) since N and O compounds are mainly recovered in the aqueous phase. The H/C ratio of the biocrude was also lower than in the initial biomass (1.753) because of the production of water-soluble compounds. These results were similar to those obtained by [PERSON] et al. at 300 \({}^{\circ}\)C and 60 min [31]. These authors proposed a consecutive treatment of the product to remove the nitrogen and oxygen entirely. The organic compounds of the biocrude obtained at the selected optimum operating conditions were determined by GC-MS analysis and grouped into families (Figure 6). The hydrocarbon content in the biocrude was remarkable high (30%), mainly consisting of linear and branched hydrocarbons, with some unsaturations. In comparison, aromatics only accounted for 3% of the total compounds in the biocrude. The hydrocarbon content was higher than that obtained by [PERSON] et al. at 260 \({}^{\circ}\)C and 60 min of reaction with _N. gaditana_ (28% linear and branched and 0% aromatic hydrocarbons) [19] and those obtained by [PERSON] et al. (<5%) a 300 \({}^{\circ}\)C and 60 min for the same biomass [31]. However, the results showed a high content of nitrogen compounds, mainly nitriles (23%), amides (4%) and amines (2%). These compounds were formed after protein hydrolysis [5; 31; 35]. A ketone content of 25% was measured, explaining the relatively high amount of oxygen in the biocrude. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\mathbf{Y_{B}}\) **(wt%)** & \(\mathbf{Y_{WSP}}\) **(wt%)** & \(\mathbf{Y_{GP}}\) **(wt%)** & \(\mathbf{Y_{SR}}\) **(wt%)** & \(\mathbf{Y_{LP}}\) **(wt%)** \\ \hline
42.3 \(\pm\) 0.8 & 32 \(\pm\) 1 & 18 \(\pm\) 2 & 7.42 \(\pm\) 0.08 & 92.58 \(\pm\) 0.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental yields at the optimum conditions (320 \({}^{\circ}\)C, 10 min and 10 wt% biomass concentration) for _N. gaditana_. The volatility of the biocrude was measured by the simulated distillation analysis (Figure 7). The biocrude showed temperatures of 450, 497 and 530 \({}^{\circ}\)C for the evaporation of 65, 85 and 95%, respectively. These temperatures were higher than those of a reference type C diesel fulfilling the European regulations (EN-590 standard), i.e., 250, 350 and 370 \({}^{\circ}\)C, respectively. Therefore, a post-treatment is necessary to lower the boiling point to make it suitable for heating fuel. Figure 5: Van Krevelen diagram: (**a**) O/C-H/C and (**b**) N/C-H/C from _N. gaditana_ (\(\blacktriangle\)) and biocrude obtained under optimal conditions: 320 \({}^{\circ}\)C, 10 min and 10% of biomass (\(\blacksquare\)). Figure 6: Chemical composition of biocrude obtained at 320 \({}^{\circ}\)C, 10 min and 10 wt% of microalgae. Figure 7: Simulated distillation of biocrude obtained at 320 \({}^{\circ}\)C, 10 min and 10 wt% of biomass (\(\blacktriangle\)). In the water-soluble phase, the recovery of water after the separation of the different fractions was 90 wt%. The pH of this fraction was 8.4 due to the presence of basic compounds formed during the reaction [36]. The carbon content was 1283 \(\pm\) 4 mg/L, due to soluble organic compounds. It is noteworthy that this phase contained most (>85%) of the metals (Na, K, Mg, Fe) and P from the starting biomass, except for Ca, the content of which in the WSP corresponded to 1 wt% of the initial content in the microalgae. The organic compounds present in the water phase were determined by GC-MS analysis.