Pyrolysis of biogas for carbon capture and carbon dioxide-free production of hydrogen

Abstract

Methane pyrolysis is considered an auspicious approach for large-scale hydrogen production and simultaneous carbon capture, hereby contributing to a decarbonization of the chemical industry. While commonly pure methane or natural gas serve as a feedstock, the usage of biogas may allow exploitation of the pyrolysis process as a carbon sink. In this context, the present study reports on biogas pyrolysis in a high-temperature reactor at temperatures between 1000 °C and 1600 °C, residence times between 1 s and 7 s, and molar CH₄ : CO₂ ratios in the biogas between 1 : 1 and 4 : 1. Among these conditions, high residence times, a high CH₄ content, and the introduction of a carbonaceous fixed bed in the reactor benefit high educt conversion, H₂ selectivity, and solid carbon yield. A carbon fixation of up to 95% was achieved during reference measurements with pure CH₄ feeds, whereas a carbon yield of 75% was found for biogas feeds. The analysis of the reaction product distribution uncovered a consumption of CO₂via dry reforming, water gas shift, and Boudouard reactions, resulting in a maximum H₂ : CO ratio of 3 : 1 in the effluent gas stream. Herewith, the study underscores that optimized reactor operation parameters allow for maximizing CH₄ and CO₂ conversion as well as for achieving H₂ : CO ratios that are viable for further industrial applications, along with an efficient deposition of solid carbon.