Dry Methane Reforming in a Directly Irradiated Solar Particle Reactor Without a Metal Catalyst

Methane reforming with carbon dioxide in a directly irradiated particle receiver seeded with carbon black is presented in this study. Carbon particles were entrained in the reacting gases and acted as heat transfer and reaction surface. The reactions were not catalyzed by a metal catalyst. The molar ratio between the entrained carbon particles and the working gases (Ar, CO₂ and CH₄) was 4–7 mmol carbon/mol gas. The temperature of the reforming experiments varied from 900°C to 1450°C with CO₂/CH₄ ratios of 2–6. Experimental results show that methane reacts at lower temperatures than expected for its thermal decomposition; this indicates that the decomposing reaction is enhanced by the presence of the carbon black particles. At 1170°C 90% of the methane reacted in the receiver during a residence time of 0.3 s. The reaction between carbon dioxide and carbon black is faster than is documented in the literature, but the reaction rate does not seem to change if only carbon dioxide and carbon black are present in the receiver, compared to experiments where methane is also part of the gas mixture. The experimental results indicate that a high solar flux, i.e., about 2500 kW/m² or higher, significantly accelerates the reaction rate of methane decomposition. Total or partial blockage of the solar radiation reduced the yield by about 50%, compared to tests when the receiver was exposed to the full solar radiation flux, at the same operating temperature.