Breakthrough curves adsorption columns

Breakthrough curves from column experiments have been used to provide evidence for diffusion of As to adsorption sites as a rate-controlling mechanism. Darland and Inskeep (1997b) found that adsorption rate constants for As(V) determined under batch conditions were smaller than those necessary to model breakthrough curves for As(V) from columns packed with iron oxide coated sand the rate constants needed to model the breakthrough curves increased with pore water velocity. For example, at the slowest velocity of 1 cm/h, the batch condition rate constant was 4 times smaller than the rate constant needed to model As adsorption in the column experiment. For a velocity of 90 cm/h, the batch rate constant was 35 times smaller. These results are consistent with adsorption limited by diffusion of As(V) from the flowing phase to sites within mineral aggregates. Puls and Powell (1992) also measured more retardation and smaller rate constants for As(V) at slower flow velocities where there was sufficient time for diffusion to adsorption sites. 

The shape of breakthrough curves from column experiments provided evidence that Mo(VI) transport was not equilibrium controlled. The decrease in slope as the adsorption limb of the... 

A single-column system for liquid-phase carhon adsorption is used in situations where the following conditions prevail laboratory testing has indieated that the breakthrough curve will be steep the extended lifetime of the earbon at normal operating conditions results in minor replacement or regeneration eosts the eapital... 

Fig. 7 presents partial results of dynamic regime experiments for chromate adsorption and desorption by ODA-clinoptilolite. As shown by breakthrough curves, ODA-clinoptilolite column quantitatively removes chromate species from simulated waste water , apparently more efficiently by lower flow rate. Consequently to similar configuration of chromate and sulfate molecules, such loaded column was more efficient to regenerate with Na2S04 than NaCl solution, as elution curves at the Fig. 7 illustrate. 

Figure /. Breakthrough curves of arsenate and pH profiles of column effluents during adsorption from feeds in t he absence and presence of foreign anions.

Figure 4. Breakthrough curves of Pb(II) in the adsorption of Pb(II) by FPS-f and FP-f packed columns. Column 1.5 ml of wet fiber (0.4 g in dry state), feeding solution 0.01 M lead nitrate. Flow rates in space velocity (h-1) are denoted on the figure.

In the downstream processing of bioprocesses, fixed-bed adsorbers are used extensively both for the recovery of a target and for the removal of contaminants. Moreover, their performance can be estimated from the breakthrough curve, as stated in Chapter 11. The break time tg is given by Equation 11.13, and the extent of the adsorption capacity of the fixed bed utilized at the break point and loss of adsorbate can be calculated from the break time and the adsorption equilibrium. Affinity chromatography, as weii as some ion-exchange chromatography, are operated as specific adsorption and desorption steps, and the overall performance is affected by the column capacity available at the break point and the total operation time. 

Theoretical Prediction of Breakthrough Curves for Molecular Sieve Adsorption Columns... 

Prediction of the breakthrough performance of molecular sieve adsorption columns requires solution of the appropriate mass-transfer rate equation with boundary conditions imposed by the differential fluid phase mass balance. For systems which obey a Langmuir isotherm and for which the controlling resistance to mass transfer is macropore or zeolitic diffusion, the set of nonlinear equations must be solved numerically. Solutions have been obtained for saturation and regeneration of molecular sieve adsorption columns. Predicted breakthrough curves are compared with experimental data for sorption of ethane and ethylene on type A zeolite, and the model satisfactorily describes column performance. Under comparable conditions, column regeneration is slower than saturation. This is a consequence of non-linearities of the system and does not imply any difference in intrinsic rate constants. 

Tphe breakthrough curve for a fixed-bed adsorption column may be pre-dieted theoretically from the solution of the appropriate mass-transfer rate equation subject to the boundary conditions imposed by the differential fluid phase mass balance for an element of the column. For molecular sieve adsorbents this problem is complicated by the nonlinearity of the equilibrium isotherm which leads to nonlinearities both in the differential equations and in the boundary conditions. This paper summarizes the principal conclusions reached from a recent numerical solution of this problem (1). The approximations involved in the analysis are realistic for many practical systems, and the validity of the theory is confirmed by comparison with experiment. 

The PSA operation was carried out at 30-1000 and atmospheric pressure by using a N2 carrier gas (60 ml/min). Adsorbates was butanone. Before PSA operation the adsorbents was pretreated at 400-90010 for 2 h in flowing N2. In the adsorption operation, N2 with butanone vapor (27.2 or 5.44 Torr) was passed through a column of the adsorbent (0.3 g for 27.2 Torr and 0.6 g for 5.44 Torr of butanone pressure) until there was almost no further adsorption (2 h). In the desorption operation, pure N2 was passed through the column in a countercurrent way for 2 h instead of evacuation. The concentration of the organic solvent vapor in the effluent gas was always monitored with a TCD detector to obtain breakthrough curves. Amounts of adsorption and desorption were calculated from the breakthrough curves. 

One simple way to analyze the performance of a fixed-bed adsorber is to prepare a breakthrough curve (Figure 10.12) by measuring the solute concentration of the effluent as a function of time. As the solution enters the column, most of the solute will be adsorbed in the uppermost layer of solid. The adsorption front will move downward as the adsorption progresses. The solute concentration of the effluent will be virtually free of solute until the adsorption front reaches the bottom of the bed, and then the concentration will start to rise sharply. At this point (tb in Figure 10.12), known as the break point, the whole adsorbent is saturated... 

There is a fundamental relationship described in chromatographic theory between the retention volume of a elution peak and the mid-point of a breakthrough curve achieved by operating the column under frontal analysis conditions (41 ). In the Henry s Law region of the adsorption isotherm, the net retention volume and its measurement can be used to describe the variation of sorbate breakthrough volume as illustrated in Figure 8. Utilizing the experimental apparatus described in the last section, retention volumes were measured as a function of pressure at 40°C (T =... 

FIGURE 34 Effect of the flow rate, feed concentration, and temperature on the experimental breakthrough curve for the adsorption of human serum albumin to Cibracron Blue F3G-A immobilized onto Fractosil 1000 against the amount of protein applied to the column. 

FIGURE 43 Comparison of the shape and position of the breakthrough curves in terms of time or the amount of protein applied and generated for the corresponding packed and fluidized columns for the adsorption of HEWL (a) and (b), respectively, and HSA (c) and (d), respectively, to Cibacron Blue F3G-A immobilized onto Fractosil 1000. The superficial velocities applied were 0.64 cm/min in (a) and (b) and 3.84 cm / min in (c) and (d), respectively. 

Several theoretical models were constructed to describe the chromatographic process in the frontal 116.191 and the zonal elution mode 20. The conventional method of obtaining the kinetic parameters consists in fitting the model to the experimental breakthrough curves. Another method based on the split-peak effect is a direct measurement of the apparent association rate constant (7,211. Because of the slow adsorption process, a fraction of the solute injected as a pulse into the immunochromatographic column is eluted as a nonretained peak. This behavior is observed at high flow rates, with very short or low-capacity columns 121—251. 

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