## 3 Results and Discussion
we focused on similarities in the experimental conditions, such as the material used as a catalyst, reactor design, and temperature. Table 4 shows that stainless steel tube with Fe powder has better results on CH\({}_{4}\) conversion--from 28.5%, the methane conversion increased to 92% at a process temperature of 1100 \({}^{\circ}\)C. The methane conversion result of the nickel tube was 73.21%, which is better than that of the titanium tube, where the CH\({}_{4}\) conversion was 42.2%, but worse than that of the corundum tube. At the same time, reduced nickel oxide showed a methane conversion of 20% at a process temperature of 500 \({}^{\circ}\)C. The tube made of corundum (\(\alpha\)-Al\({}_{2}\)O\({}_{3}\) tube) shows a 75.7% CH\({}_{4}\) conversion, a result which is the best for other tubes made in different materials. The porous alumina tube showed slightly similar results (71%) at a flow rate of 1000 cm/min. One of the main points in the process of thermal decomposition of methane is the residence time of methane in the heating region (t). To determine this indicator, you need to know the speed of gas movement along the reactor channel (v). And to determine it, you need to know two quantities: the volumetric amount of gas (Q) and the cross-sectional area of the flow (S). Then, the speed of gas movement can be expressed through the following equation:  
\[v=Q/S\]  
The volume of gas passing through a given cross section per unit time (Q) is known under normal conditions. However, in the heating zone, this volume increases, since when heated, the gas expands according to the law V/T = const. Due to the lack of experimental data on the gas temperature distribution inside the reactor along its length, we continue to estimate the volume of gas without taking into account its heating. The following equation is used to calculate gas velocity:  
\[v=Q/S_{0}=4Q/\left(\pi d^{2}\right),\]  
where S\({}_{0}\) is the area of the flow section of the reactor tube, and (d) is the inner diameter of the tube. The residence time of methane in the heating zone (t) is calculated by the following equation:  
\[t=l/v,\]  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**No** & **Material** & **T\({}_{\text{c}}\)\({}^{\circ}\)C** & **Flow Rate, cm/min** & **CH\({}_{4}\) Conversion, \%** & **Source** \\ \hline \multirow{2}{*}{1} & Stainless steel tube & \multirow{2}{*}{1100} & \multirow{2}{*}{30} & \multirow{2}{*}{28.5} & \multirow{2}{*}{this work} \\  & & tube & & & \\ \hline \multirow{2}{*}{2} & Stainless steel tube with Fe powder & \multirow{2}{*}{1100} & \multirow{2}{*}{50} & \multirow{2}{*}{92.0} & \multirow{2}{*}{[34]} \\ \cline{1-1} \cline{5-5} \cline{  
where 1 is the length of the heating zone. The length of the T-tube is 8 cm. The length of the T-tube can be considered as the length of the heating zone of the reactor (l). Therefore, in our case, 1 = 8 cm. The residence time of methane in the heating zone is presented in Table 5. The calculation of the residence time was carried out for a methane flow rate of 2 L/h. In the tube with the smallest flow area (in our case, it is a corundum tube with an inner diameter of 4 mm), the methane flow rate was 4.42 cm/s. In the tubes with the largest flow area (in our case, these are stainless steel and titanium tubes with an inner diameter of 6 mm), the methane flow rate was 1.97 cm/s. Thus, the residence time in the heating zone of the reactor was the shortest for the corundum tube (1.8 s), and the longest for the stainless steel and titanium tubes (about 4 s). There are two main parameters influencing the degree of methane decomposition--temperature and residence time. The increase in both the temperature and the residence time leads to an increase in the degree of methane decomposition. In [34], it was shown that the increase in residence time at one temperature always leads to an increase in the yield of hydrogen. In this study, the highest yield of hydrogen (73.35 vol.%) was achieved at the lowest residence time in the heating zone (1.8 s) in the corundum capillary tube.