## 4 Results and Discussions
### Species Distribution
#### 4.1.2 The Behavior of Components H\({}_{2}\)O, CO\({}_{2}\)  
As Figure 2 illustrates, water vapor, which is one of the products of FT synthesis, increases over the reactor height and over the time. Since the FT reaction occurs under a co-supported catalyst,  
Figure 1: Results of Fischer–Tropsch (FT) Simulation; The behavior of CO, H\({}_{2}\) in gas phase (**a**,**c**) and liquid phase (**b**,**d**) from start-up to steady state conditions (D\({}_{\text{t}}\) = 0.1 m, H = 2.5 m, \(\varepsilon_{\text{cat}}\) = 0.34, U\({}_{\text{g,in}}\) = 0.17 m/s).  
no water gas shift reaction is promoted and the inlet CO\({}_{2}\) acts as an inert through the process. The CO\({}_{2}\) concentration increases due to the volume reduction of off-gas and syngas consumption. It is worth noting that the presence of diluents such as CO\({}_{2}\), CH\({}_{4}\) or N\({}_{2}\) has a beneficial influence in slurry bubble column reactors. The inert (here as carbon dioxide) enables supplementary mixing energy to the slurry system to maintain catalyst suspension. On the other hand, in FBRs we need to avoid diluents since they elevate the pressure drop across the reactor bed [32].  
1.3. The Behavior of Components CH\({}_{4}\), C\({}_{2}\)H\({}_{6}\), C\({}_{4}\)H\({}_{10}\)  
Methane, ethane and butane increase over time and achieve their highest concentration at the final time in the reactor outlet. These highest values in the gas phase reach around 85, 35 and 50 mol/m\({}^{3}\) for CH\({}_{4}\), C\({}_{2}\)H\({}_{6}\) and C\({}_{4}\)H\({}_{10}\), respectively as shown in Figure 3.  
Figure 2: Results of FT Simulation; The behavior of H\({}_{2}\)O and CO\({}_{2}\) in gas phase (**a**,**c**) and liquid phase (**b**,**d**) from start-up to steady state conditions (D\({}_{\text{t}}\) = 0.1 m, H = 2.5 m, \(\varepsilon_{\text{cat}}\) = 0.34, U\({}_{\text{g,in}}\) = 0.17 m/s).  
1.4 The Behavior of Liquid Products C\({}_{10}\)H\({}_{22}\), C\({}_{18}\)H\({}_{38}\), C\({}_{30}\)H\({}_{62}\)  
In this mathematical modeling, three components are considered as representatives of each specific carbon cut. C\({}_{10}\)H\({}_{22}\), C\({}_{18}\)H\({}_{38}\) and C\({}_{30}\)H\({}_{62}\) were introduced as naphtha, diesel and wax respectively, which are derived from three condensers with reaction water in each condenser and collected in each related drum [12]. The results of modeling show that all three sets of products have a similar profile through the slurry reactor. As illustrated in Figure 4, the liquid products have an upward trend over time through the reactor height and the highest magnitude belongs to the middle distillate whereas diesel and wax stand at lower values respectively.  
Figure 3: Results of FT Simulation; The behavior of CH\({}_{4}\), C\({}_{2}\)H\({}_{6}\) and C\({}_{4}\)H\({}_{10}\) in gas phase (**a**,**c**,**e**) and liquid phase (**b**,**d**,**f**) from start-up to steady state conditions (D\({}_{1}\) = 0.1 m, H = 2.5 m, \(\epsilon_{\text{cat}}\) = 0.34, U\({}_{\text{gin}}\) = 0.17 m/s).  
These simulations results relate to base load conditions (volumetric gas flow rate 5 m\({}^{3}\)/h). The computer model is also able to work quite well under variable loads of synthesis gas. Therefore, the flow rate in the model was changed in the range of 3.5-7.5 m\({}^{3}\)/h to find maximum CO conversion and FT product selectivity.