Modeling of the carbonation kinetics of a synthetic CaO-based sorbent

• A synthetic CaO-based sorbent showed excellent CO2 capture capacity and stability.
• The carbonation kinetics of the sorbent was investigated by two different models.
• The random pore model (RPM) was compared to the overlapping grain model (OGM).
• The kinetic and diffusion parameters obtained by OGM were higher than those by RPM.
• The carbonation behavior of the sorbent over multiple cycles was well predicted.

A synthetic CaO-based sorbent composed of 20 wt% Ca9Al6O18 and 80 wt% CaO showed excellent activity and stability over multiple carbonation–calcination cycles. The improved CO2 capture performance was mainly ascribed to the even distribution of the inert Ca9Al6O18 within the sorbent. The random pore model (RPM) and the overlapping grain model (OGM) were used to predict the carbonation behaviors of CaO–Ca9Al6O18 that experienced one cycle or many cycles over a temperature range of 500–700 °C and the CO2 partial pressure of 0.005−0.015 MPa. Both models described the carbonation of the sorbent very well, and the estimated activation energies by the RPM model for the surface reaction and for the effective product layer diffusion were 28.4 and 88.7 kJ/mol, respectively, which were comparable to those obtained by the OGM model, 32.3 and 113.1 kJ/mol, respectively. As far as the intrinsic rate constant and the effective product layer diffusion coefficient were concerned, the values obtained by the OGM model (average values of 1.67×10−5 m/s and 2.74×10–13 m2/s at 500−700 °C) were somewhat higher than those by the RPM model (5.44×10−6 m/s and 1.03×10–14 m2/s), which was related with the different approaches of the two models in dealing with the carbonation of the sorbent. This study is expected to contribute to a better understanding of the carbonation kinetics between CO2 and the CaO-based sorbents.

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