The characterization of three commercial activated carbons (Filtrasorb-400, Norit ROW 0.8, and Norit ROX 0.8) was carried out using the adsorption of various compounds in the aqueous phase. For this purpose the generalized adsorption isotherm was employed, and modification of the Dubinin-Radushkevich pore filling model, incorporating repulsive contributions to the pore potential as well as bulk liquid phase nonideality, was used as local isotherm. Eight different flavour compounds (ethyl propionate, ethyl butyrate, ethyl isovalerate, benzaldehyde, methyl salicylate, isobutyl acetate, hexyl acetate, 2-ethylhexyl acetate) were used as adsorbates, and the isotherms were jointly fitted to yield a common pore size distribution for each carbon. The bulk liquid phase nonideality was incorporated through the UNIFAC activity coefficient model, and the repulsive contribution to the pore potential was incorporated through the Steele 10-4-3 potential model. The mean micropore network coordination number for each carbon was determined from the fitted saturation capacity based on percolation theory. Good agreement between the model and the experimental data was observed. In addition, excellent agreement between the bimodal gamma pore size distribution and density functional theory-cum-regularization- based pore size distribution obtained by argon adsorption was also observed, supporting the validity of the model. The results show that the liquid phase adsorption, using adsorptive molecules of different sizes, can be an effective means of characterizing the pore size distribution as well as connectivity. Alternatively, if the carbon pore size distribution is independently known, the method can be used to "measure" critical molecular sizes.
The effect of pore network connectivity on the prediction of binary liquid phase adsorption equilibria using the ideal adsorbed solution theory (IAST) has also been studied. The liquid phase binary adsorption experiments have been performed using ethyl propionate, ethyl butyrate, and ethyl isovalerate as the adsorbates and commercial activated carbons Filtrasorb-400 and Norit ROW 0.8 as the adsorbents. As the single component isotherm, a modified Dubinin-Radushkevich equation was used. The results of comparison with the experimental data show that incorporation of the pore network connectivity, consideration of the percolation processes which associated with different molecular sizes of the adsorptives in the mixture, and their different corresponding accessibility, can improve the prediction of binary adsorption equilibria using the LAST. It is also seen that the selectivity of adsorption for larger molecule in binary systems increases with the increasing of pore network coordination number, as well with the increasing of mean pore width and the spreading of the pore size distribution.
The solubility of ethyl propionate, ethyl butyrate, and ethyl isovalerate on supercritical carbon dioxide was measured at the temperature range from 308.15 K to 333.15 K and the pressure range from 85 to 195 bar. At the same pressure, the solubility of these compounds increase with temperature. The cross over pressure region was also observed in this study. The experimental data were correlated by semi empirical Chrastil equation and Peng-Robinson equation of state using several mixing rules. The Peng-Robinson equation of state gives better solubility prediction than the semi empirical Chrastil equation.
The supercritical desorption of ethyl propionate, ethyl butyrate, and ethyl isovalerate from Filtrasorb-400 activated carbon was also studied at the pressures of 85 and 145 bar, and the temperatures of 313.15 K, 323.15 K, and 333.15 K. The Langmuir, Freundlich and the Dubinin-Radushkevich adsorption equations were used to correlate the experimental data. These equations can describe the experimental data well. Among those equations, the Dubinin-Radushkevich model gave more consistent and meaningful parameter values than the Langmuir and Freundlich equations.