Measurement and Modeling of the Solubility of Copper(II) Acetylacetonate in CO2 and CO2/Acetonitrile Mixtures

Abstract

The solubility of copper(II) acetylacetonate [Cu(acac)2] in carbon dioxide (CO2) and CO2/acetonitrile mixtures was measured at 313.15, 333.15, and 353.15 K and pressures up to 200 bar using a static gravimetric method. Since Cu(acac)2 decomposes before melting, its critical properties cannot be measured experimentally. To model this system alongside literature data, four thermodynamic models were evaluated: the Peng–Robinson (PR), Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), modified Chrastil, and Méndez–Santiago–Teja equations. Regressing the critical properties within the PR framework yielded physically implausible behavior, highlighting the limitations of cubic equations of state for thermally unstable precursors. For PC-SAFT, we implemented a COSMO-constrained parametrization strategy to determine the segment parameters (m and σ), successfully circumventing parameter degeneracy. The resulting model outperformed the PR equation of state and achieved accuracy comparable to the semiempirical density-scaling correlations. For the ternary system, both the density-scaling models and PC-SAFT─utilizing a cross-association scheme─satisfactorily reproduced the cosolvent-induced solubility enhancement. This improvement is attributed to localized Lewis acid–base coordination between the nitrile lone pair and the electron-deficient copper center.