# Study of Soot Deposits during Continuous Methane Pyrolysis in a Corundum Tube
## 3 Results and Discussion
### Yield of Soot  
Table 2 shows the mass of soot produced in the methane pyrolysis process at different temperatures and flow rates in different parts of the experimental plant (in reactor tube and in filter). As can be seen from the results, the amount of soot produced increases with increasing temperature and methane flow rate. With increasing temperature, the yield of soot increases significantly, as shown in the table: from 1000 \({}^{\circ}\)C to 1400 \({}^{\circ}\)C the mass of soot produced increased from 1.28 g to 43.9 g. The main part of the soot is acc \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{3}{c}{**Volumetric Content of the Component in the Gas Sample Depending on Methane Flow Rate and Process Temperature, vol.\%**} \\ \cline{2-7}  & \multicolumn{3}{c}{**1000 \({}^{\circ}\)C**} & \multicolumn{3}{c}{**1100 \({}^{\circ}\)C**} & \multicolumn{3}{c}{**1200 \({}^{\circ}\)C**} \\ \cline{2-7}  & **1 L/min** & **5 L/min** & **1 L/min** & **5 L/min** & **1 L/min** & **5 L/min** \\ \hline H\({}_{2}\) & 28.64 & 1.10 & 81.41 & 52.06 & 92.74 & 72.09 \\ \hline CH\({}_{4}\) & 68.25 & 98.63 & 16.59 & 44.82 & 6.00 & 23.86 \\ \hline O\({}_{2}\) & 0.05 & 0.03 & 0.3 & 0.001 & 0.03 & 0.46 \\ \hline N\({}_{2}\) & 0.10 & 0.05 & 0.17 & 0.02 & 0.15 & 1.40 \\ \hline C\({}_{2}\)H\({}_{6}\) & 0.15 & 0.04 & 0.12 & 0.13 & 0.09 & 0.09 \\ \hline C\({}_{2}\)H\({}_{4}\) & 0.45 & 0.14 & 1.15 & 1.97 & 0.66 & 1.17 \\ \hline C\({}_{2}\)H\({}_{2}\) & 0.02 & 0.01 & 0 & 0.01 & 0 & \textless{}10^{-4}\) \\ \hline C\({}_{3}\)H\({}_{8}\) & 0.53 & 0.01 & 0.08 & 0.001 & \textless{}10^{-4}\) & \textless{}10^{-4}\) \\ \hline C\({}_{3}\)H\({}_{6}\) & 0.56 & \textless{}10^{-4}\) & 0.44 & 1.06 & 0.33 & 0.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Volumetric content of the component in the gas sample of gaseous product of methane pyrolysis depending on methane flow rate (1 and 5 L/min) and process temperature (1000, 1100 and 1200 \({}^{\circ}\)C). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**T, \({}^{\circ}\)C**} & \multirow{2}{*}{**Methane Flow Rate,**} & \multicolumn{3}{c}{**Operation Time, min**} & \multicolumn{3}{c}{**Mass of Soot, g**} & \multicolumn{3}{c}{**Soot Generation Rate, g/min**} \\ \cline{3-10}  & & **Through** & **Through** & **In the** & **In the** & **Tube** & **In the** & **In the** & **Filter** & **Total** \\ \hline
1000 & 1 & 74 & 60 & 1.28 & 0 & 1.28 & 0.017 & 0 & 0.017 \\ \hline
1050 & 1 & 69 & 60 & 2.4 & 0.36 & 2.76 & 0.035 & 0.006 & 0.041 \\ \hline
1100 & 1 & 90 & 78 & 12.12 & 6.65 &  
Separate experiments were carried out at 1200 \({}^{\circ}\)C for 5 L/min to assess soot formation as a function of methane flow rate. As a result, the amount of soot produced increased by two times, with the bulk of the carbon observed in the tube, as shown in Figure 5. Due to the sintering of soot particles and the formation of build-ups in the reaction zone, the main part of the carbon is not blown out by the gas flow into the filter and accumulates in the tube. Figure 4: Dense carbon build-up after the experiment at 1400 \({}^{\circ}\)C and a methane flow rate of 1 L/min. Figure 5: Mass of soot produced in different parts of experimental plant during methane pyrolysis depending on flow rate. A—experiment at 1200 \({}^{\circ}\)C and 1 L/min, B, C—experiments at 1200 \({}^{\circ}\)C and 5 L/min. The soot produced is not evenly distributed across the tube, but rather starts in the middle, i.e., the reaction zone, and ends at the tube outlet, as the incoming gas flow blows the produced soot further into the filter. Such carbon blockages are one of the key problems of methane pyrolysis technology. The solution to this problem is an important technical challenge. Figure 6 shows the change in pressure in the tube during the experiments. Pressure surges are caused by blockages in the pipeline between the corundum tube and the filter, the inner diameter of which is 14 mm. Soot builds up in the constriction and pressure surges are observed.