# Study of Soot Deposits during Continuous Methane Pyrolysis in a Corundum Tube
## 4 Conclusions  
In this work, soot deposits formed during continuous methane pyrolysis in a corundum tube were studied.  
It was shown that with an increase in the temperature of the pyrolysis process from 1000 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C, the yield of hydrogen increases from 28.64% to 92.74% at a flow rate of 1 L/min and from 1.10% to 72.09% at a flow rate of 5 L/min. It was revealed that to increase the yield of hydrogen, the highest possible temperatures are required.  
Experiments were carried out with an increase in temperature and methane flow rate for soot production, which showed that at a process temperature of 1400 \({}^{\circ}\)C, the largest amount of soot (43.9 g) is formed, and at 1000 \({}^{\circ}\)C, the smallest (1.28 g). In the temperature range of 1050-1100 \({}^{\circ}\)C, a sharp increase in the formation of soot was observed (from 2.76 to 18.77 g). It was shown that with an increase in the flow rate, the proportion of soot that remains in the tube decreases. It has been established that the linear velocity of methane affects the presence of soot inside the tube. It has also been observed that in the region of the reactor where maximum heating occurs, the accumulated soot sinters and forms dense growths. It has been established that blockages occur during the pyrolysis process, which lead to an increase in pressure in the system. It was found that these blockages were due to clogging of the pipeline (with an internal diameter of 14 mm) between the reactor (corundum tube) and the filter. The maximum observed pressure was about 100 mm Hg. When a certain pressure was reached, the blockages broke through, and the pressure returned to near atmospheric pressure. It has been revealed that the greatest number of blockages occurs in cases where the soot is still oily, but its production rate is greater than at low temperatures.  
The microstructure of soot was studied. Results showed that the particles of soot obtained at 1100 \({}^{\circ}\)C are stickier. At 1050 \({}^{\circ}\)C, the particle size of soot varies from 155 to 650 nm, at 1200 \({}^{\circ}\)C--from 157 to 896 nm, and at 1400 \({}^{\circ}\)C--from 77 to 532 nm.  
The specific surface and impurity compositions of the obtained carbon black were studied. The specific surface was 3.5 m\({}^{2}\)/g for the sample taken after the experiment at 1000 \({}^{\circ}\)C and 8.0 m\({}^{2}\)/g for the soot obtained at 1400 \({}^{\circ}\)C. The purity of the produced carbon black was about 99.95%.  
It can be assumed that the process of pyrolysis in tubes of other materials can also occur, but the dynamics of soot deposition in these tubes may differ from what we observe in a corundum tube.  
This study may be useful in selecting materials and technical solutions for a pilot methane pyrolysis plant to produce hydrogen and pure carbon black with reduced CO\({}_{2}\) emissions.  
Formulation of the research problem: M.S.V., A.O.D. and M.S.G.-T. Analysis of the samples and preparation of micrographs of the samples obtained after the experiment: A.V.G. and A.O.D. Writing--the main manuscript text: M.S.G.-T. Writing--review and editing: M.S.V. and A.O.D. Funding and administration: M.S.V. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Ministry of Science and Higher Education of the Russian Federation (State Assignment No. 075-01129-23-00).  
**Institutional Review Board Statement:** Not applicable.