Study of CO2 diffusion and adsorption on calcined layered double hydroxides:: The effect of particle size

This paper describes a study of CO(2) diffusion and adsorption in layered double-hydroxide (LDH) adsorbents using a gravimetric method. Four different particle size fractions, namely, 53-75, 75-90, 90-180, and 180-300 mu m, were used in the study. The LDH materials were calcined in situ prior to the experiments, which resulted in significantly higher CO(2) adsorption capacities than previously reported. The CO(2) adsorption was shown to follow a Sips-type isotherm, while the adsorption capacity at saturation was found to be independent of the particle size. Two models, the homogeneous surface diffusion model (HSDM) and the bidisperse pore model (BPM), were used to fit the experimental data and to estimate the diffusivities. The main assumption made in the BPM is that the adsorbent particle is an agglomerate of a number of equal-sized, single-crystal microparticles, and before a CO(2) molecule is adsorbed in the microparticles, it has to diffuse through the intercrystalline porous region. Both models perform well in fitting the experimental data. However, the HSDM yields diffusivities that are a strong function of the particle size, whereas the diffusivities estimated using the BPM are almost independent of the particle size.