Breakthrough/adsorption columns

The design of an activated carbon adsorption column can be accomplished using kinetic equations that require data obtained from the development of breakthrough... 

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. 

Aluminum oxides As(V) and As(lll) adsorption on activated alumina pH dependence, kinetics, and column breakthrough. Regeneration by desorbing with NaOH. Modeling with pH-dependent Langmuir isotherm (for As) and surface complexation model (for protons) Ghosh and Yuan (1987)... 

Other phenomena besides conformational processes can also lead to multizoning effects with polypeptides and proteins when they interact with adsorptive HPLC sorbents. The so-called split peak effect is probably the easiest of these phenomena to be identified and steps taken to remedy. The split peak effect is very often seen in HP-BAC, RP-HPLC, and HP-HIC and to a lesser extent in the HP-IEX of proteins.325-327 This effect is manifested by the presence of a weakly retained (or occasionally as a nonretained peak) and a more strongly retained peak with the bound-to-free ratio between the weakly retained to strongly retained species dependent on the diffusion and adsorption kinetics. An extreme case of the split peak effect involves the weakly interacting component elution in or near to the column breakthrough volume. In this case, the amount of protein in the breakthrough zone is influenced by the nominal pore diameter and ligand density of the sorbent, the flow rate, and the injection volume. This effect can be circumvented by... 

As mentioned before, the unit operation of bed adsorption may be carried out in a moving-bed mode, either co-currently or countercurrently. When the breakthrough experiment is carried out, the superficial velocity should also be recorded. The reason is that adsorption is a function of the time of contact between the liquid phase containing the solute to be adsorbed and solid-phase carbon bed. Thus, for the breakthrough data to be applicable to an actual prototype adsorption column, the relative velocities that transpired during the test must be maintained in the actual column. When the relative velocities between the flowing water and the carbon bed are maintained, it is immaterial whether or not the bed is moving. 

Figure 9.38. Schematic representation of the response of the chromatographic column for different adsorption isotherms (top). The column breakthrough of a step concentration change without disperson effects is shown (below) for different isotherms (a) linear and (b) convex. The abscissa tItQ is equivalent to the number of pore volumes eluted. (Adapted from Biirgisser et al., 1993.)...

Carbon Adsorption. The water removed from the oil-water separator is directed through two carbon adsorption columns that operate in series for removal of soluble organics. The liquid stream between the two carbon columns is routinely sampled to detect breakthrough in the first carbon column. 

A fixed-bed adsorption has several advantages over batch and continuous stirred tank reactor (CSTR) because the rates of adsorption depend on the concentration of viruses in solution. This point is especially important for virus removal because of the low concentration of viral contaminants. The design of a fixed-bed adsorption column involves estimation of the shape of the breakthrough curve and the appearance of the breakpoint. Computer simulation studies were done here to demonstrate the performance of a virus adsorber using the surface-bonded QAC beads which have a higher binding affinity for viruses over other proteins. 

Figures 5(a) and 5(b) show the simulated breakthrough curves of both total protein and HSV-1 respectively. It should be noticed that the dimensionless time scales in these two figures differ by four orders of magnitude. The breakpoint of HSV-1 is the operating endpoint at which the effluent from the adsorption column can no longer meet the desired sterilization criterion. Since the HSV-1 has a much higher affinity to the bead surface, the breakpoint of HSV-1 appears much later than that of the total protein. To optimize the protein recovery, one should improve the design of the bead surface (better selectivity, higher loading capacity), size, and operating parameters of the filter to further delay the breakpoint of the virus elution. A stochastic approach to model the removal process may be more appropriate in low concentrations of viruses.

Two macroscopic methods to design adsorption columns are the scale-up and kinetic approaches. Both methods rely on breakthrough data obtained from pilot columns. The scale-up method is very simple, but the kinetic method takes into account the rate of adsorption (determined by the kinetics of surface diffusion to the inside of the adsorbent pore). The scale-up approach is useful for determining the breakthrough time and volume (time elapsed and volume treated before the maximum allowable effluent concentration is achieved) of an existing column, while the kinetic approach will determine the size requirements of a column based on a known breakthrough volume. 

A wastewater flowrate of 180 m /day has a TOC (total organic carbon level) of 200 mg/L. A flxed-bed GAC adsorption column wiU be used to reduce the maximum effluent concentration to 8 mg/L. A breakthrough curve. Figure 7.12, has been obtained from an experimental pilot column operated at 2(BV)/hr. Other data concerning the pilot column are mass of carbon = 4.13 kg, water flowrate = 15 L/hr, and packed carbon density = 400 kg/m. Using the scale-up approach, determine the values of the following parameters for the design column ... 

How would a lower amount of dispersion in an adsorption column affect the breakthrough curve ... 

Many of the design principles that apply to adsorption columns may also be applied to ion-exchange columns. For example, breakthrough curves from a pilot column along... 

Most of the industrial processes of adsorption with activated carbon operate in adsorption columns where a continuous fluid stream crosses the column and an adsorbate is removed by the stationaiy fixed carbon bed. As the adsorption process proceeds, the adsorption capacity of the activated carbon diminishes due to the fact that the adsorbate molecules are filling the pores. Finally, when the adsorption capacity of the activated carbon is exhausted, the adsorbate concentration level at the outlet begins to rise until it reaches the inlet level (breakthrough plot), the carbon adsorbent becoming unsuitable for further use so that it must be replaced by fresh activated carbon. 

Belmabkhout Y, Pirngruber G, Jolimaitre E, Methivier A (2007) A complete experimental approach for synthesis gas separation studies using static gravimetric and column breakthrough experiments. Adsorption 13 341-349... 

Consider an adsorption column that initially contains no solute. At t = tf e a feed with a concentration Cp is introduced. The breakthrough solution, which is the behavior of Cqu, is... 

If the equilibrium isotherm is linear, analytic expressions for the concentration front and the breakthrough curve may, in principle, be derived, however complex the kinetic model, but except when the boundary conditions are simple, the solutions may not be obtainable in closed form. With the widespread availability of fast digital computers the advantages of an analytic solution are less marked than they once were. Nevertheless, analytic solutions generally provide greater insight into the behavior of the system and have played a key role in the development of our understanding of the dynamics of adsorption columns. 

In the simplest type of adsorption processes in which an adsorption column is used to remove a trace impurity from a process stream, the main requirement for rational design is an estimate of the dynamic or breakthrough capacity of the bed. In such systems the adsorbable impurity is invariably strongly adsorbed with a favorable isotherm and the concentration profile therefore rapidly approaches constant-pattern form. The constant-pattern assumption provides the basis of a very simple design method which permits reliable scale-up from small-scale laboratory experiments. 

Except for the limiting case of the irreversible isotherm discussed above the prediction of the temperature and concentration profiles requires the simultaneous solution of the coupled differential heat and mass balance equations which describe the system. The earliest general numerical solutions for a nonisothermal adsorption column appear to have been given almost simultaneously by Carter and by Meyer and Weber. These studies all deal with binary adiabatic or near adiabatic systems with a small concentration of an adsorbable species in an inert carrier. Except for a difference in the form of the equilibrium relationship and the inclusion of intraparticle heat conduction and finite heat loss from the column wall in the work of Meyer and Weber, the mathematical models are similar. In both studies the predictive value of the mathematical model was confirmed by comparing experimental nonisothermal temperature and concentration breakthrough curves with the theoretical curves calculated from the model using the experimental equilibrium... 

EXAMPLE 12.3-1. Scale-Up of Laboratory Adsorption Column A waste stream of alcohol vapor in air from a process was adsorbed by activated carbon particles in a packed bed having a diameter of 4 cm and length of 14 cm containing 79.2 g of carbon. The inlet gas stream having a concentration of 600 ppm and a density of 0.00115 g/cm entered the bed at a flow rate of 754 cm /s. Data in Table 12.3-1 give the concentrations of the breakthrough curve. The break-point concentration is set at dCg = 0.01. Do as follows. 

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