## 3 Results and Discussion  
### Analysis on Bio-Oil Conversion under Different Reaction Conditions  
In running the process model, the operating temperatures for the mild hydrogenation reactor was set at 250 \({}^{\circ}\)C, 280 \({}^{\circ}\)C, and 300 \({}^{\circ}\)C, respectively, and the corresponding pressures were 5.6 MPa, 8 MPa, and 10 MPa. The deep hydrogenation stage used a Ni/Al2O3 catalyst under the operating conditions of 400 \({}^{\circ}\)C and 15 MPa. As per the simulation results shown in Figure 3, among the various products from the bio-oil upgrading, the yield of the bio-fuel is the highest (45%) and the total amount of coke is the lowest with the mild hydrogenation reactor temperature of 300 \({}^{\circ}\)C. However, the yields of bio-fuel and the total coke deposits at 280 \({}^{\circ}\)C and 300 \({}^{\circ}\)C are very similar. Moreover, the lower operating temperature is beneficial for the sake of process safety as the corresponding pressure is lower. The selection of optimal reaction temperature for the mild stage will be further discussed in the energy analysis section. The amount of insoluble coke deposit increases with the elevated reaction temperature, which is consistent with the reported trend of insoluble coke deposit with reaction temperature in the literature [17]. According to the Arrhenius reaction formula, the higher temperature promotes endothermic reactions. However, the production of insoluble coke deposits is the main reason for catalyst deactivation. The yield of the oil phase (ODF) in the first stage does not increase linearly with increasing temperature.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Kinetic Reactions** & **A** & **E (kJ/mol)** \\ \hline BIO-OIL + 0.22H2\(\rightarrow\)0.742 ODF + 0.192 AQO + 0.121H2O + 0.076 CO2 & 4.31 \(\times\) 10\({}^{6}\) (m\({}^{3}\) MPa\({}^{-1}\) kg\({}^{-1}\) h\({}^{-1}\)) & 80 \\ BIO-OIL\(\rightarrow\)1.869C\({}_{\mathrm{s}}\) & 1.67 \(\times\) 10\({}^{4}\) (m\({}^{3}\) h\({}^{-1}\) kg\({}^{-1}\)) & 9.4 \\ BIO-OIL\(\rightarrow\)1.869C\({}_{\mathrm{s}}\) & 5.09 \(\times\) 10\({}^{8}\) (m\({}^{3}\) h\({}^{-1}\) kg\({}^{-1}\)) & 169.5 \\ C\({}_{\mathrm{s}}\)\(\rightarrow\)0.535 BIO-OIL & 0.5003 (h\({}^{-1}\)) & 44.3 \\ ODF\(\rightarrow\)1.269C\({}_{\mathrm{s}}\) & 6.58 \(\times\) 10\({}^{4}\) (m\({}^{3}\) h\({}^{-1}\) kg\({}^{-1}\)) & 16 \\ C\({}_{\mathrm{s}}\)\(\rightarrow\)0.787 ODF & 2 (h\({}^{-1}\)) & 45.3 \\ AQO\(\rightarrow\)2.705C\({}_{\mathrm{s}}\) & 1.2 \(\times\) 10\({}^{3}\) (m\({}^{3}\) h\({}^{-1}\) kg\({}^{-1}\)) & 14.6 \\ C\({}_{\mathrm{s}}\)\(\rightarrow\)0.396 AQO & 5 (h\({}^{-1}\)) & 46.7 \\ C\({}_{\mathrm{s}}\)\(\rightarrow\)C\({}_{\mathrm{is}}\) & 1.54 \(\times\) 10\({}^{3}\) (h\({}^{-1}\)) & 52.6 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Kinetic parameters of bio-oil hydrogenation in the mild hydrogenation stage.  
A more detailed material balance of the whole industrial process under different reaction conditions is shown in Tables A1-A3. Since the amount of catalyst is unchanged during the reaction, the flow of catalyst is not shown in the stream summary tables. The slight mass imbalances (0.1-0.6%) in the stream tables were caused by the inherent convergence issues of the Aspen Plus v7.2 software (AspenTech, Boston, Massachusetts, US).