High-Temperature Solar Methane Dissociation in a Multitubular Cavity-Type Reactor in the Temperature Range 1823-2073 K

Methane cracking is a possible route for the coproduction of hydrogen and carbon black avoiding CO2 emission. An indirect heating solar reactor prototype, allowing thermal dissociation of methane without catalyst, is tested at high temperatures. It is composed of a cubic graphite cavity receiver (20 cm side.) equipped with four independent vertical tubular reaction zones. The concentrated solar radiation (2-4 MW/m(2)) is absorbed through an hemispherical quartz window by a 9 cm-diameter aperture. A set of experimental results on solar methane dissociation is presented for the temperature range 1823-2073 K. The effects of temperature, residence time from 10 ms and beyond 100 ms, gas flow-rates up to 12 NL/min (2 x 10(-4) Nm(3)s(-1)) Of methane, and methane concentration up to 100% are investigated. Moreover, an experimental run was also carried out with natural gas instead of pure methane. Typical hydrogen and carbon mass balances show that methane is efficiently converted into hydrogen, whereas it is not as well converted into solid carbon due to the production of acetylene. A two-step mechanism for methane dissociation is presented in order to accurately define the reactor efficiencies (thermal efficiency and solar-to-hydrogen thermo-chemical conversion).