Nano-structure of Carbons Deposited from CH₄ Blowing to and Injecting into Molten Slag

Abstract

How to produce the green hydrogen is important problem for reducing the CO₂ emission. Among many processes on the production of hydrogen, a thermal decomposition reaction of CH₄ can produce the pure hydrogen without CO and CO₂ gases. When the reaction proceeds by using a waste heat, the obtained hydrogen will be approached to the green hydrogen.
The thermal decomposition reaction of CH₄ is mainly studied kinetically from several decades ago.
CH₄(g) = C(s)+ 2H₂(g)
However, the decomposition reaction on the surface of molten slag was not studied. Authors have studied the kinetics of decomposition reaction of CH₄ on the surface of the molten slag in the previous study. The rate constant at 1700 K for the surface of the molten slag was about four times larger than that of graphite surface. In addition to the kinetics of the reaction, the carbon properties precipitated are quite interesting, because the structures of carbon are changed by the conditions such as the temperature and kind of solid/liquid surface which provided the reaction sites. In this study, it was found that two kinds of carbon were precipitated during the decomposition of CH₄, when a molten slag existed in the system. The micro- and nano-structures of carbons precipitated were examined using SEM and TEM. The onion type carbon sphere were clarified, which were formed in the gas phase, furthermore, the high oriented graphite film was formed on the surface of molten slag.