Rate-Controlled Separations

Analysis and parametric sensitivity of the behavior of overshoots in the concentration of a charged adsorbate in the adsorbed phase of charged adsorbent particles: practical implications for separations of charged solutes

“…However, the PCC operational configuration may not be an economically viable or easy-toimplement mode of operation because (i) the length of the column segments would have to be cut to a very specific tolerance requiring the construction of each PCC column system to be unique, (ii) the length of the column segments would have to change as the flow-rate of the liquid phase changes, which implies that a PCC column system to exploit the overshoot phenomenon would only be able to accommodate one flow-rate, (iii) the dynamics of the system would change as the particle diameter changes and, therefore, the lengths of the column segments would have to change as the particle diameter changes, which implies that a PCC column system to exploit the overshoot phenomenon would only be able to accommodate one particle diameter, and (iv) the dynamics of the system would be very difficult to control. As an alternative to the PCC mode of operation, one could exploit the overshoot in the concentration of the adsorbate in the adsorbed phase by employing a radial flow [26] column (RFC) where the feed stream passes through the outer surface of the column and flows along the radius of the column toward the center, while the effluent stream exits the column through a thin annulus at the center of the column. The flow could also pass from the inner annulus to the outer surface of the column as well; of course, a series of simulations should be performed in order to determine the best direction for the flow in the RFC but, as an initial estimate, due to the fact that a significant portion of the particles are located near the outer surface of the RFC, the overshoot in the concentration of the adsorbate in the adsorbed phase could be better developed in the particles located near the outer surface of the column when the feed stream passes from the outer surface of the column to the inner annulus.…”

“…In preparative chromatographic column systems, the development of the overshoot in the concentration of the adsorbate in the adsorbed phase could be exploited by employing systems that have very low residence times. Therefore, one could possibly use a periodic countercurrent (PCC) operational configuration [24,25] employing a series of packed columns very short in length, or one could alternately use a radial flow [26] column (RFC). While the PCC operational configuration may not be an economically viable or easy-to-implement mode of operation, a radial flow column could offer the potential to exploit the concentration overshoot phenomenon over a wide range of operational policies and system configurations.…”

Effect of channel geometry, degree of activation, relative humidity and temperature on the performance of binderless activated carbon monoliths in the removal of dichloromethane from air

“…The relative small variation of FBU can be explained because the increase of temperature has two opposite effects on the length of the mass transfer zone which compensate to each other. On the one hand, the curvature of the adsorption isotherm decreases with temperature, which reduces the spread of the mass transfer zone according to the solute movement theory [22], and on the other hand, diffusion is enhanced, which reduces it. The higher variation of FBU for HX-HA monolith may suggest that the activation energy of diffusion in this monolith is lower than in the others, due to its larger pores, so that the positive effect of temperature on diffusion is smaller.…”

Granular activated carbon for the recovery of the main pear aroma compound: Viability and kinetic modelling of ethyl-2,4-decadienoate adsorption

“…The model is aimed at the prediction of the evolution with time of the concentration of the adsorbate in the fluid leaving the GAC column, as a function of the operation conditions (Rivero, Ibañ ez, & Ortiz, 2002. The main assumptions of the model are (i) fast intrinsic adsorption kinetics, so instantaneous local equilibrium is considered and (ii) both the external resistance of solute mass transfer from the bulk liquid phase to the particle surface and the internal resistance associated to solute diffusion within the particle pores are considered (Ruthven, 1984;Wankat, 1996).…”