## 2 Materials and Methods
### Modeling Methodology
#### 2.2.1. Gasification Process  
Several thermochemical reactions occur during gasification at different temperature zones: drying zone (>150 \({}^{\circ}\)C), decomposition zone (250-700 \({}^{\circ}\)C), combustion zone (700 \({}^{\circ}\)C to 1500 \({}^{\circ}\)C), and gasification zone (800 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C) [31]. At drying stage, the moisture content is removed from pyrolysis oil. The decomposition stage is initiated at about 250 \({}^{\circ}\)C when the labile bonds between the aromatic clusters are cracked, generating light molecular weight fragments. This stage generates gaseous molecules such as H\({}_{2}\), CO, CH\({}_{4}\), as well as light char and tar. After decomposition, pyrolysis oil undergoes combustion, which practically provides the thermal energy required to sustain the endothermic reactions. This stage generates gaseous molecules such as CO\({}_{2}\) and H\({}_{2}\)O [32]. A series of endothermic reactions, such as water gas, Boudouard, water gas shift, and steam methane reforming reactions occur at this stage [14]. Useful combustible gases such as H\({}_{2}\) and CO are produced at gasification stage. At the end, the whole gasification process generates a syngas composed mainly of CO, CO\({}_{2}\), H\({}_{2}\), and CH\({}_{4}\). The production of CO, CO\({}_{2}\), CH\({}_{4}\), H\({}_{2}\), and steam in the whole process can be explained by the reactions given in (Equations (R-1)-(R-8)), which occur at various stages [15]. \begin{tabular}{l l l} C + \(\frac{1}{2}\)O\({}_{2}\)\(\rightarrow\) CO & \(-\)111 MJ/kmol & Combustion reaction (R-1) \\ C + O\({}_{2}\)\(\rightarrow\) CO\({}_{2}\) & \(-\)283 MJ/kmol & Combustion reaction (R-2) \\ H\({}_{2}\) + \(\frac{1}{2}\)O\({}_{2}\)\(\rightarrow\) H\({}_{2}\)O & \(-\)286 MJ/kmol & Combustion reaction (R-3) \\ C + CO\({}_{2}\)\(\leftrightarrow\) 2 CO & \(+\)172 MJ/kmol & Boudouard reaction (R-4) \\ C + 2H\({}_{2}\)\(\leftrightarrow\) CH\({}_{4}\) & \(-\)75 MJ/kmol & Methanation reaction (R-5) \\ C + H\({}_{2}\)O \(\leftrightarrow\) CO + H\({}_{2}\) & \(+\)131 MJ/kmol & Water gas reaction (R-6) \\ CO + H\({}_{2}\)O \(\leftrightarrow\) CO\({}_{2}\) + H\({}_{2}\) & \(-\)41 MJ/kmol & Water gas shift reaction (R-7) \\ CH\({}_{4}\) + H\({}_{2}\)O \(\leftrightarrow\) CO + 3H\({}_{2}\) & \(+\)206 MJ/kmol & Steam methane reforming reaction (R-8) \\ \end{tabular}   
The gasification model is based on the following assumptions, i.e.,  
1. Pyrolysis oil feed rate is 1000 kg/h. 2. Gasification is assumed to be steady state, isothermal, and simulated using a kinetic-free model [32]. 3. Pyrolysis oil devolatilization occurs instantaneously and the volatile products mainly include H\({}_{2}\), CO, CO\({}_{2}\), CH\({}_{4}\), H\({}_{2}\)S, NH\({}_{3}\), and H\({}_{2}\)O. 4. All gases are ideal gases and uniformly distributed in the gas phase. 5. All reactions take place at a chemical equilibrium state and the pressure loss was not considered. A kinetic-free equilibrium model was designed for the gasification process by using Aspen plus. Gasification process is usually divided into four stages, as presented in Figure 1: drying (R1), decomposition (R2), combustion (R3), and gasification (R4). Table 2 lists a brief explanation of the units used in the gasification process. Firstly, the wet pyrolysis oil (stream 1) was fed into R1 block to  
Figure 1: Process flow diagram of the Aspen Plus model for methanol synthesis via pyrolysis oil gasification. model the drying process. Dry pyrolysis oil and moisture were separated by the SEP-1 block. Secondly, dry pyrolysis oil (stream 3) was fed into reactor R2 where pyrolysis oil is decomposed into its elemental components (C, H, O, N, S, etc.). The elemental distribution of pyrolysis oil was specified according to its ultimate analysis (see Table 1). R2 block was used to convert nonconventional pyrolysis oil into conventional components. The nonconventional definition of pyrolysis oil is shown in Appendix A. Thirdly, combustion of pyrolysis oil is modeled by a Gibbs reactor.