Adsorption and desorption of n-hexane, methyl ethyl ketone, and toluene on an activated carbon fiber from supercritical carbon dioxide

The adsorption equilibrium and regeneration efficiency of n-hexane, methyl ethyl ketone (MEK), and toluene under supercritical CO2 on an activated carbon fiber were experimentally determined. When the densities of the supercritical fluids were fixed at 0.32, 0.45, and 0.62 g/cm(3), the Langmuir model agreed with the experimental isotherms at the temperatures 308, 318, and 328 K. As the concentration of adsorptive in supercritical CO2 was kept constant, the crossover of the equilibrium loading at different temperatures was observed at relatively high pressure and the crossover pressure of MEK was lower than that of n-hexane. In both cases, the crossover pressure increased with an increase in concentration. Also, the activated carbon fiber loaded with toluene and MEK was regenerated by supercritical CO2 in the range of 0.69-0.90 g/cm(3). Desorption became favorable with an increase in pressure, and there was an optimal temperature at every pressure condition. However, the regeneration efficiency increased with temperature at the same density of supercritical CO2. In the case of the MEK/toluene mixture, the difference in the desorption rate and desorption amount between two adsorbates was decreased as the pressure was increased. A one-parameter mathematical model assuming linear desorption kinetics matched the experimental data using an activated carbon fiber.