Increasing the circularity of methane pyrolysis by using the solid carbon co-product in cements: a plant-scale study

Abstract Methane pyrolysis (MP) is a promising method to produce hydrogen with no reaction-based carbon dioxide emissions. It has been speculated that the solid carbon co-produced from MP may be sequestered in cementitious systems to lower the environmental impact of both the hydrogen and cement industries. In this paper, for the first time, we report on the feasibility of incorporating solid carbon co-product, in the form of carbon nanotube pulp (CNTP), from a commercial-scale MP plant in cementitious composites. Mechanical strength tests alongside rheological tests are conducted on composites in which Portland cement has been replaced by various amounts of this CNTP from 0 to 1% by weight. The addition of this material mildly increases the early-age compressive strength of the CNTP-cement composites. The fresh properties of CNTP-cement composites are significantly impacted with a large increase in yield stress, resulting in 74.2% increase for a paste replacing cement with 1% (wt.) CNTP relative to a plain cement paste. The results indicate that cementitious composites may be used to sequester MP-coproduced carbon, although the complex form and poor dispersion of the material at high replacements limits large-scale implementation as-is.