Production of hydrogen and carbon black by methane decomposition using DC-RF hybrid thermal plasmas

A continuous production of carbon black and hydrogen has been investigated by thermal decomposition of methane using a prototype processing system of direct current (dc)-radio frequency (RF) hybrid thermal plasma, which has great advantage over other thermal sources like combustion or dc plasma torches in synthesizing new nanostructured materials by providing high-temperature environment and longer residence time for reactant gases due to its larger hot core region, and lower flow velocity. Appropriate operation conditions and reactor geometries for the effective synthesis process are predicted first from the relevant theoretical bases, such as thermodynamic equilibrium calculations, two-dimensional thermal flow analysis, and chemical kinetic simulation. Based on these derived operation and design parameters, a reaction chamber and a dc-RF hybrid torch are fabricated for the processing system, which is followed by methane decomposition experiments with it. The methane injected into the processing system is converted mostly into hydrogen with a small volume fraction of acetylene, and fine carbon particles of 20-50 nm are identified from their transmission electron microscope images. Material analyses of Brunauer-Emmett-Teller , dibutyl phthalate adsorption, and X-ray diffraction indicate that the synthesized carbon black has excellent properties, such as large surface area, high electrical conductivity, and highly graphitized structures with good crystallization.