Abstract
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.
