Carbonation and deactivation kinetics of a mixed calcium oxide-copper oxide sorbent/oxygen carrier for post-combustion carbon dioxide capture

Removing carbon dioxide from industrial effluents via solid carbonate sorbents is a potential greenhouse gas mitigation strategy that can also produce hydrogen from the effluent in water gas shift reactors downstream. However, to regenerate the calcium oxide (from the carbonate) requires high temperature that is provided via an oxidation step. To avoid costly oxycombustion to regenerate the CaCO3, it is possible to use the heat generated during the reduction of copper oxide and manganese oxides as chemical looping agents. Unfortunately, sorbents sinter thereby and consequently the surface area drops in the regeneration step. A mixed CuO-CaO sorbent with 10% calcium aluminate binder lost 84% of its initial BET surface area during the first 100 min on stream. Homogeneous calcium-copper-cement oxide sorbent deactivate to the 0.5 order with respect to the remaining surface area and a decay constant equal to 2.86 min−1. An empirical equilibrium power law model characterizes the carbonation rate from 425 °C to 665 °C with 10% to 20% CO2 in a 45 mm fixed bed. The apparent activation energies of the forward and reverse reaction are 220 and 120 kJ mol−1, respectively. In addition to sintering, the reaction rate of the regeneration step decreases with time on stream following a zero order process. We attributed this gradual irreversibility to increased crystallinity, reducing the diffusion rate of CO2 to the active carbonate phase. By integrating this resistance to the kinetic model, we are able to explain 99% of the variance in the gas profiles measured by a mass spectrometer.