Diffusion of Liquid and Supercritical Carbon Dioxide into a Chitosan Sphere

The diffusion and loading of liquid and supercritical carbon dioxide into chitosan spheres with a diameter of 0.5 cm and a mass of 0.055 g was experimentally explored at temperatures of 25, 35, and 45 °C and at fixed carbon dioxide densities of 0.65, 0.75, and 0.85 g/cm3. Loading as high as 1.25 g of carbon dioxide/g of chitosan was achieved. Carbon dioxide loading increased as the carbon dioxide density and temperature each increased. By modeling the loading as unsteady-state radial Fickian diffusion, a diffusion coefficient of carbon dioxide into the chitosan sphere could be obtained at a given exposure temperature and pressure. These diffusion coefficients were on the order of 10-7 m2/s and increased with temperature. Carbon dioxide density did not seem to have a significant effect on the diffusion coefficients, but it did influence the maximum achievable loading.