Turquoise hydrogen and carbon materials production from thermal methane cracking: An experimental and kinetic modelling study with focus on carbon product morphology

Abstract

Methane (CH4) cracking is emerging as a bridge technology for hydrogen (H2) production fostering the transition from current carbon-intensive production processes (e.g. steam reforming) to the fixation of the carbon content of the feedstock in the form of valuable carbon materials. With the valorization of the carbon product being a key factor to lower H2 prices by improving the overall process economics, the understanding and the description of the complex network of homogeneous and heterogeneous reactions involved in CH4 thermal cracking and, in particular, in the formation of valuable carbon and of undesired byproducts (carbon nanoparticles) is key to technology design and operations. In this work we present a systematic experimental study of pure methane cracking in a tubular quartz reactor in the temperature range T = 875–975 °C at initial flow rates QCH4,0 = 30, 45 and 60 ml/min. CH4 conversion and H2 yields have been measured quantitatively and complemented with the identification of key aromatic precursors supporting the interpretation of the mechanistic phenomena aided by an existing chemical kinetic model and chemical kinetic analyses. A careful analysis of the carbon products allowed to explore the different morphologies of deposited carbon and carbon nanoparticles in the gas phase, as well as their strong dependence from homogeneous gas-phase reactivity, motivating further model developments aimed to describe currently missing complex heterogeneous reaction pathways towards a quantitative description of the observed features.