Solubility of caffeine in the supercritical CO2-methanol binary solvent

The caffeine-methanol association constant at 313 K has been determined by H-1 NMR spectroscopy. The caffeine solubility in the supercritical carbon dioxide (SC-CO2)-methanol mixed solvent has been calculated using the association constant experimentally measured by NMR in the framework of the associated solution + lattice (ASL) model, which is based on the theory of molecular association and a simple lattice model. Individual contributions to the solubility have been determined, and the relative role of various factors determining the solubility of caffeine in the mixed solvent has been analyzed. The caffeine solubility as a function of the methanol content of the SC-CO2-methanol system is predicted to pass through a maximum.