## 4 Results and Discussions
### Model Comparison with Experimental Data  
The comparison of the model results with experimental data was conducted based on the composition (volume %) of syngas and off-gas which were measured by a GC device under base load and change load conditions. Figures 5-7 show a comparison of the predicted values by the computer  
Figure 4: Results of FT simulation; The behavior of C\({}_{10}\)H\({}_{22}\), C\({}_{18}\)H\({}_{38}\) and C\({}_{30}\)H\({}_{62}\) in liquid phase (**a**,**c**,**e**) and gas phase (**b**,**d**,**f**) from start-up to steady state conditions (D\({}_{\rm t}\) = 0.1 m, H = 2.5 m, \(\varepsilon_{\rm cat}\) = 0.34, U\({}_{\rm g,in}\) = 0.17 m/s).  
model with the measured data from the conducted experiments. In general, the results show that the predicted model is in good agreement with the experimental data. When compared with FT products only in the case of naphtha (C\({}_{8}\)-C\({}_{10}\)) is there a noticeable difference between model and laboratory data in all three operating conditions. This is due to the volatility of this carbon cut and difficulty in collecting them together. In product distribution (Figures 5c, 6c and 7c) only, two groups (C\({}_{8}\)-C\({}_{15}\)) and (C\({}_{30}\)-C\({}_{40}\)) show a deviation as well as discontinuities in the model prediction. The deviation is probably due to the neglect of olefin formation in the reactor modeling and the discontinuities can be attributed to the model equations which were solved for specific classes of FT species (C\({}_{1}\), C\({}_{2}\), C\({}_{4}\), C\({}_{10}\), C\({}_{18}\) and C\({}_{30}\)). As mentioned earlier, the \(\alpha\)-value can be derived from the slope of the drawn line in all three load conditions. In the model, the \(\alpha\)-value for volumetric flow rate of 3.5, 5 and 7.5 m\({}^{3}\)/h is calculated to be 0.89, 0.9 and 0.88 respectively. It shows that change load conditions have almost no influence on the \(\alpha\)-value or catalyst selectivity as predicted from the experiment.  
Figure 5: The comparison of the predicted model with experimental data at base load conditions (volumetric gas flow rate 5 m\({}^{3}\)/h, T = 503 K, \(\epsilon_{\text{cat}}\) = 0.34, P = 20 bar): (a) off-gas molar fractions; (b) FT products (naphta, diesel, wax); (c) ASF distribution.  
Figure 6: _Cont._  
The results show that the CO conversion both in the model and experiments has lower values at a higher superficial velocity of syngas. This is due to the decreasing residence time of reactants at higher values of velocity. Thus, the maximum CO conversion occurs at 3.5 m\({}^{3}\)/h which is equal to 60%. As Figure 8 shows, the CO conversion also is in good agreement with the experimental data; however, the model values are slightly overestimated. This is due to larger area for gas-liquid mass transfer in the result of the assumption of the single bubble class diameter.  
Figure 6: The comparison of the predicted model with experimental data at change load conditions (volumetric gas flow rate 3.5 m\({}^{3}\)/h, T = 503 K, \(\epsilon_{\rm cat}\) = 0.34, P = 20 bar): (**a**) off-gas molar fractions; (**b**) FT products (naphta, diesel, wax); (**c**) ASF distribution.  
Figure 7: The comparison of the predicted model with experimental data at change load conditions (volumetric gas flow rate 7.5 m\({}^{3}\)/h, T = 503 K, \(\epsilon_{\rm cat}\) = 0.34, P = 20 bar): (**a**) off-gas molar fractions; (**b**) FT products (naphtha, diesel, wax); (**c**) ASF distribution.