No abstract

The CO 2 carbonation was studied by synchrotron radiation in-situ x-ray diffraction. Measured reaction rates are 5 times higher than the values available in literature. Intrinsic chemical kinetics data were obtained, minimizing the external diffusion. CaO conversion-time curves are dependent on the CaO crystallite size (CS CaO ). A linear relationship between the final conversion and the CS CaO was identified. a b s t r a c tIn this work, in-situ synchrotron radiation x-ray powder diffraction (SR-XRPD), performed at the Advanced Photon Source (APS) facilities of the Argonne National Laboratory, was applied to investigate the CaO-CO 2 reaction. A set of CO 2 absorption experiments were conducted in a high temperature reaction capillary with a controlled atmosphere (CO 2 partial pressure of 1 bar), in the temperature range between 450 1C and 750 1C using CaO based sorbents obtained by calcination of commercial calcium carbonate. The evolution of the crystalline phases during CO 2 uptake by the CaO solid sorbents was monitored for a carbonation time of 20 min as a function of the carbonation temperature and of the calcination conditions. The Rietveld refinement method was applied to estimate the calcium oxide conversion during the reaction progress and the average size of the initial (at the beginning of carbonation) calcium oxide crystallites. The measured average initial carbonation rate (in terms of conversion time derivative) of 0.280 s À 1 (7 13.2% standard deviation) is significantly higher than the values obtained by thermo-gravimetric analysis and reported thus far in the literature. Additionally, a dependence of the conversion versus time curves on the initial calcium oxide crystallite size was observed and a linear relationship between the initial CaO crystallite size and the calcium oxide final conversion was identified.

In this work, the evolution of the CaCO3 crystalline phase during the CaO–CO2 reaction was investigated by means of in situ synchrotron radiation X-ray powder diffraction performed at the Advanced Photon Source (APS) facilities of the Argonne National Laboratory. CO2 absorption experiments were carried out in a high temperature reaction capillary with a controlled atmosphere of pure carbon dioxide (CO2 partial pressure of 1 bar) and in the temperature range between 450 and 750 °C, using CaO-based sorbents obtained by calcination of commercial calcium carbonate. The Rietveld refinement method was applied to estimate the average size of the CaCO3 crystallites formed during a carbonation time of 20 min, as a function of the carbonation temperature and of the initial calcination conditions. Local maxima were observed in the CaCO3 crystallite size versus time curves and were identified as the critical CaCO3 crystallite sizes, marking the transition between the first fast carbonation stage and the second reaction stage controlled by product-layer diffusion. A relationship between this parameter and the reaction temperature, as well as with the initial (at the beginning of carbonation) CaO crystallite size, were found. The CaCO3 critical crystallite sizes were used to estimate the active surface areas of the CaO sorbent particles where CaCO3 crystals form and grow. The computed active surface areas were utilized to calculate the kinetic parameters of the surface carbonation reaction: a reaction rate constant of 4.41 × 10–4 mol/m2 s, with zero-activation energy, was obtained.