Entrainer Effect of Water and Ethanol on Solubility of Caffeine in Supercritical Carbon Dioxide

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Entrainer effects of water and ethanol on solubility of caffeine in supercritical carbon dioxide (CO₂) were measured at 313.2 K and 15.0 MPa. Experiments were carried out by a circulation-type apparatus combined with an on-line Fourier transform infrared (FT-IR) spectroscopy. The solubilities of caffeine in supercritical CO₂ and supercritical CO² with entrainers were determined with the peak absorbance at 1190 cm^-1 of IR spectra of caffeine. At the lower concentration range of caffeine, the absorbances obeyed the Lambert-Beer law. At higher concentration range of caffeine, the absorbances became a constant. The intersection of these two lines at the lower and the higher concentration ranges denotes the solubility of caffeine. The solubilities of caffeine in supercritical CO₂ increase with increasing the concentration of either water or ethanol. The increasing rate of solubility of caffeine with saturated water is about 24 %, and that with 1mol% ethanol is about 45%. Then, ethanol was added to the system of supercritical CO₂ + caffeine + saturated water, and the solubility of caffeine increased by addition of ethanol.