Equilibria in the Copper Hexafluoroacetylacetonate–CO₂–Al₂O₃ System¹

The solubility of copper(II) hexafluoroacetylacetonate monohydrate Cu(hfa)₂⋅H₂O in carbon dioxide was studied. The solubility increases with increasing temperature in the range of 303–353 K and was observed to increase nonlinearly with increasing CO₂ density in the supercritical (SC) region. The dependence of the solubility on the parameters of state (temperature, CO₂ density) was described by the Chrastil equation. The adsorption of Cu(hfa)₂⋅H₂O from a solution in SC-CO₂ on three γ-Al₂O₃ samples differing in the presence of acidic and basic additives was investigated. The adsorption isotherms have a shape with a sharp increase in the adsorption value in the initial part, which indicates a high affinity of the complex for the surface of the substrate and/or its heterogeneity, as well as the presence of sites with high adsorption energy. An increase in the CO₂ density from 355 to 780 kg/m³ at a constant temperature (313 K) leads to a decrease in the adsorption of Cu(hfa)₂⋅H₂O on all three Al₂O₃ samples. At a constant medium density of 355 kg/m³ and an increase in temperature from 313 to 343 K, a more complex behavior of the adsorption isotherms is observed depending on the characteristics of the support and the concentration range of the adsorbed substance.