Impact of natural gas composition on steam thermal plasma assisted pyrolysis for hydrogen and solid carbon production

Pyrolysis of simulated natural gas (NG) was studied experimentally in the reactor equipped with a steam thermal plasma torch. Simulated NG consisted of 75 % of methane, 15 % of ethane, 5 % of propane and 5 % of butane. Experimental composition of the output gas was compared with the equilibrium calculations corresponding to the gaseous mixture entering the reactor. NG input flow rate 100 slm was considered the best in terms of agreement between the experimental and calculated compositions. Consequently, for this flow rate, the majority of natural gas was reformed into the mixture of hydrogen and solid carbon. For the NG input flow rates of respectively, 200 slm and 500 slm, a non-negligible amount of unconverted methane (from 37 slm to 155 slm) was found to remain in the output gas. On the other hand, the specific energy requirement with respect to the produced hydrogen was better for 500 slm of NG (1.1–1.6 kWh/m³.H₂) than for 200 slm (1.8–2.7 kWh/m³.H₂) or 100 slm (3.2–3.6 kWh/m³.H₂). In all the studied experimental conditions, practically no CO₂ was formed, only a small amount of CO corresponding to oxygen from the steam plasma was detected. A comparison with the previously published works, where methane and natural gas were not distinguished, showed that NG composition can play an important role in the pyrolysis process. In particular, the presence of higher hydrocarbons decreased the effectivity of methane conversion and also reduced the specific energy requirement, with respect to the pure methane pyrolysis.