Adsorption equilibrium of citric acid from supercritical carbon dioxide/ethanol on cyano column

Supercritical adsorption equilibrium has a significant role in defining supercritical adsorption behavior. In this paper, the adsorption equilibrium of citric acid from supercritical CO₂/ethanol on a cyano column was systematically investigatedwith the elution by characteristic pointmethod. Equilibriumloadingwas obtained at 313.15 K and 321.15 K with supercritical CO₂/ethanol densities varying from0.7068 g·cm^-3 to 0.8019 g·cm^-3. The experimental results showed that the adsorption capacity of citric acid decreasedwith increasing temperature and increasing density of the supercritical CO₂/ethanol mobile phase. The adsorption equilibrium data were fitted well by the Quadratic Hill isotherm model and the isotherms showed anti-Langmuir behavior. Themonolayer saturation adsorption capacity of citric acid is in the range of 44.54mg·cm^-3 to 64.66mg·cm^-3 with an average value of 56.86 mg·cm^-3.