Production of hydrogen and carbon nanotubes from methane using a multi-pass floating catalyst chemical vapour deposition reactor with process gas recycling

Converting natural gas into hydrogen and solid carbon materials using methane pyrolysis presents a promising opportunity to produce sustainable fuels and materials. The production of hydrogen and bulk carbon nanotubes (CNTs) via methane pyrolysis has been demonstrated independently, but concurrent production from the same reactor has remained elusive. Here we present a multi-pass floating catalyst chemical vapour deposition (FCCVD) reactor that converts methane into hydrogen and CNT aerogel. Whereas previous FCCVD CNT production consumed hydrogen, the multi-pass reactor recycles the carrier gas to eliminate the need for a hydrogen input. This results in a net output of 85 vol% hydrogen alongside CNT aerogel and a 446-fold increase in molar process efficiency. Furthermore, the demonstrated use of biogas to produce CNT aerogel enables a potential net sequestration of CO₂ from the atmosphere. The results of this study have been extrapolated to a pilot-scale reactor, using data gathered at a commercial facility, to consider the challenges and opportunities associated with scale-up.