Near-equilibrium analysis of CO2 partial pressure on carbonate hydrogenation in an integrated carbon capture and utilization scheme

Abstract

The integrated carbon capture and utilization (ICCU) technology, combined with the reverse water-gas shift reaction (RWGS), is considered a promising strategy for mitigating carbon emissions. This study investigates the limestone calcination and hydrogenation processes under relatively high partial pressures of CO₂ in near-equilibrium conditions, at partial pressures (P) close to the equilibrium pressure (P_eq), relevant to the ICCU-RWGS process, particularly during the in-situ CO₂ conversion stage. The decomposition of CaCO₃ during conventional calcination and hydrogenation under near-equilibrium conditions was initially examined using micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) and a particle-injecting method. The results indicated that limestone decomposition during conventional calcination was inhibited under near-equilibrium conditions, with conversion near 0%. However, during the hydrogenation process, the interaction between H₂ and CaCO₃ further activated the decomposition of limestone. At 750 °C and P/P_eq=0.9, limestone particles took ∼100 s to achieve complete conversion (100%). Given the known self-catalytic activity of CaO in converting carbonate to CO during hydrogenation, a dual-layer limestone hydrogenation process was further conducted using a fixed bed reactor. At 850 °C and a 30 vol.% H₂ atmosphere, the limestone decomposition rate increased significantly and subsequently reacted with H₂ to form CO, resulting in an H₂/CO ratio of approximately 2.5. These findings support the viability of ICCU-RWGS approaches for future commercialization, with the product gas serving as the feedstock for the Fischer–Tropsch Synthesis (FTS) process.