CaCO3 hydrogenation to CH4 using natural limestone and a Ni-based catalyst for CCU applications

Carbon capture and utilization (CCU) has emerged as a promising strategy for mitigating CO2 emissions while producing valuable chemicals. However, conventional CCU relies on separate capture, purification, and conversion steps. Integrated carbon capture and utilization (ICCU) processes enables the direct conversion of CO2 from diluted streams in a single unit. In this context, most ICCU approaches have focused on the development of synthetic dual functional materials (DFM), which often involve laborious synthesis routes, high costs and limited long-term stability. In this work, commercially available materials, such as natural limestone and Ni-based catalyst, have been evaluated as an alternative for CCU applications. The hydrogenation of CaCO3 was investigated to determine the operating conditions that maximize CH4 production. The influence of temperature, pressure, gas residence time and mass ratio CaCO3/catalyst were evaluated to elucidate the governing reaction pathways and thermodynamic limitations. An optimal temperature window between 500–550 ºC was identified, and near-equilibrium CH4 concentrations were achieved under adequate residence times. Notably, this work represents the first demonstration of CaCO3 hydrogenation to CH4 at early-stage TRL-3 reactor, achieving a CH4 concentration of 9.46 vol% at 8 bar and 550 ºC, in line with equilibrium predictions. The practical application of the proposed CCU route was demonstrated through its integration into a sorption-enhanced methanation (SEM) process over 20 cycles, achieving an overall carbon-to-methane yield of 100% with a remarkable cyclic stability. These findings highlight the potential of commercially available materials for efficient and scalable CH4 production in CCU applications.