Study of Soot Deposits during Continuous Methane Pyrolysis in a Corundum Tube

Methane pyrolysis is one of the promising methods for producing low-carbon hydrogen, while one of the main problems of methane pyrolysis technology is soot clogging of the reactor space. In this work, soot deposits were studied during continuous methane pyrolysis in a corundum tube with an inner diameter of 50 mm. Experiments were carried out at temperatures of 1000 °C, 1050 °C, 1100 °C, 1200 °C and 1400 °C with methane flow rates of 1 L/min and 5 L/min. Each experiment lasted 1 h. The formed soot accumulated inside the reactor (corundum tube) and the connected filter, where the gaseous product of methane pyrolysis was separated from the soot. The gaseous product was studied by gas chromatography. The soot was studied by SEM, BET and ICP-MS. With an increase in the temperature of the pyrolysis process from 1000 to 1200 °C, the hydrogen yield increased from 28.64 to 92.74% and from 1.10% to 72.09% at a methane flow rate of 1 and 5 L/min, respectively. The yield of soot increased from 1.28 g at 1000 °C to 43.9 g at 1400 °C (at a methane flow rate of 1 L/min). With an increase in the flow rate of methane from 1 to 5 l/min, the yield of soot at 1200 °C increased by almost two times to 75.65 g. It was established that in the region of the reactor where maximum heating occurs, the accumulated soot sinters and forms dense growths. At 1050 °C, the particle size of soot varies from 155 to 650 nm, at 1200 °C—from 157 to 896 nm, and at 1400 °C—from 77 to 532 nm. The specific surface of soot was 3.5 m2/g at 1000 °C and 8.0 m2/g at 1400 °C. The purity of the produced carbon black was about 99.95%. This study is useful in the selection of materials and technical solutions for a pilot plant for methane pyrolysis.