Influence of hydrogen addition on carbon growth & morphology in microwave plasma driven pyrolysis of methane

Plasma pyrolysis of methane can be used for the production of valuable hydrocarbons, such as acetylene and ethylene, where solid carbon precipitates form as a byproduct. To better understand the different formation mechanisms of solid carbon, we investigate the morphology and growth rates of carbon as well as gas composition under different conditions. It is well known that the H radical plays an important role in production of carbon deposits, both in the dehydrogenation process of hydrocarbons during pyrolysis as well as in the formation of carbon skeleton. In this study we explored the influence of hydrogen addition on carbon morphology in microwave plasma methane pyrolysis by adding different hydrogen content (in volume %) to the main methane flow. We measured the H₂ rotational temperature in the plasma with Raman Spectroscopy. Carbon samples were then collected from multiple locations in the reactor under these varying reaction conditions. The characteristics of the materials including microstructure, hydrogen content and crystallinity were analyzed using TEM, SEM, and surface Raman. The amount of deposited carbon and the growth rate of carbon was measured using GC and Stylus Profilers. The results indicate that hydrogen addition promotes the dehydrogenation of carbon materials, facilitating their transformation from amorphous to crystalline. This finding enhances understanding of the carbon formation mechanism in pyrolysis of methane.