Adsorption and Desorption of n-Hexane, Methyl Ethyl Ketone, and Toluene on an Activated Carbon Fiber from Supercritical Carbon Dioxide

Abstract

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/cm3, 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/cm3. 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.

Improvement of soluble coffee aroma using an integrated process of supercritical CO2 extraction with selective removal of the pungent volatiles by adsorption on activates carbon

“…From the results shown in Table 1 for both solutes it can be deduced that at a low pressure (13 MPa) the adsorption cycle is faster (shorter breakthrough time), the capacity of the adsorbent (amount of solute adsorbed per kg of adsorbent) is higher and utilization of the bed improves. This result suggests that at a low pressure the interaction forces between solute and activated carbon surface are higher than the corresponding solute-solvent binding forces (Ryu et al, 2000). Moreover at a low pressure all mass transfer resistances decrease and it is possible to get a higher degree of fractional bed utilization (Lucas et al, 2004b).…”

Supercritical Regeneration of an Activated Carbon Fiber Exhausted with Phenol

“…Some authors affirm that density is the controlling parameter at pressures just above the critical pressure, and regeneration gets worse with increasing temperatures [7,14,15]. It is also stated that as the fluid is compressed, viscosity becomes progressively more influential and the negative effect of temperature is then mitigated [7,9,14,15].…”

“…Furthermore, the extracted adsorbate can be easily recovered to be reused or destroyed once the SCCO 2 is cooled and depressurized to atmospheric pressure. SCCO 2 is usually employed to regenerate ACs saturated with volatile organic compounds like benzene [7], toluene [8][9][10][11], m-xylene [12], cyclohexane [13], or ethyl acetate [14,15]. The regeneration of ACs saturated with inorganic compounds is less usual and co-solvents must be used to efficiently extract these adsorbates [16].…”

Thermodynamic modeling of solute adsorption equilibrium from near-critical carbon dioxide

“…By examining the form of Eq. (19), the adsorption distribution coefficient is determined by two terms: ln ϕ ∞ 1 /(ϕ ∞ 2 ρ) and −C 1 − C 2 /T . The two terms reflect the effects of fluid phase property, the so-called solvating power, and the system temperature respectively.…”