Simulated adsorption breakthrough curves

Figure 5. Simulated adsorption breakthrough curves of total protein and HSV-1...

Horstmann and Chase [35] have used the mass transfer parameters determined in stirred tank experiments to simulate the breakthrough curves of affinity chromatography experiments. Numerical methods using different computer packages were carried out to solve the differential equations of the stirred tank adsorption and to predict the performances of a packed bed chromatographic column. 

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. 

The thermodynamics of adsorption of a given species are thus characterised by bifl and Ai/ads,i. By fitting the breakthrough curves, expressions for the kinetics of adsorption/desorption can be developed Fig. 27 shows simulated, as well as measured, breakthrough curves. 

McCoy and Liapis [36] used two different kinetic models to represent the column affinity process. In both models the transport of the adsorbate in the adsorbent particle is considered to be governed by the diffusion into the pores. In model I the adsorption is assumed to be completely reversible with no interaction between the adsorbed molecules, In model 2, it is assumed that the biomolecule may change conformation after adsorption. Although these two models represent different overall adsorption mechanisms, the differences between the simulated breakthrough curves is very small. 

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.

Simulation of Mo(VI) breakthrough by the equilibrium sorption model is compared with the experimental data from the 0.043 mmol/1 column in Figure 3. Results for the 0.096-, 0.01- and 0.0016-mmol/l columns were similar and are not shown. The model simulates a very steep slope for the adsorption limb of the breakthrough curve and complete site saturation by the second pore volume. Experimental data from the column show that complete breakthrough did not occur until the sixth pore volume, which indicates the effects of a rate process. The equilibrium model also simulated complete rinse-out of Mo(VI) by the 9th pore volume whereas Mo(VI) in the column effluent did not reach zero until the 15th pore volume, which indicates that desorption also was affected by a rate process. 

Adsorption of some organic solvent vapours onto HSZ were studied. Binary adsorption equilibriums except azeotropic mixture-HSZ systems could be correlated by Markham-Benton equation for the whole concentration range, and the break times could be estimated well by using the Extended-MTZ-Method. For azeotropic mixture-HSZ systems, the equilibriums and the break times could be correlated and estimated only for a part of the all concentration range. Then, two azeotropic points appeared in the adsorption equilibriums for IPA-TCE -Y-type system. For this binary systems adsorption equilibrium data could be expressed by proposed equation, similar to liquid-vapour azeotropic equilibrium equation. Breakthrough curve could be simulated using the Stop Go method in the whole range for azeotropic mixture systems as well as for zeotropic systems. 

The general guidelines for developing a gas separation process based on adsorption are reviewed. Two important industrial cases based on adsorption processes are selected the separation of propane/propylene mixtures and n/iso-paraffins mixtures. The 13X zeolite and Ag -Amberlyst were used as adsorbent for propane/propylene mixture taking into account information from the open literature. The 5A zeolite was selected for n/iso-paraffins system the adsorption equilibrium and diffusivity data were obtained from gravimetric and ZLC techniques respectively. A mathematical model for the bulk separation in fixed bed upon non-isothermal non-adiabatic conditions is formulated and solved numerically. The simulated results are compared with the available experimental breakthrough curves. Finally, a cyclic process based in the PSA-VSA and TSA concepts is proposed for these systems. 

Breakthrough curves can be considered as the last of the essential characterizations of an activated carbon. Equilibrium isotherm data provide information of the capacity of a carbon. Next, the kinetics of the adsorption processes must be known, giving information of the rates at which adsorptives are adsorbed by the adsorbent. Finally, the performance of a carbon (so characterized) in an industrial situation can be simulated by making use of the breakthrough curves. 

A stochastic model could be applied satisfactorily in the simulation of the behavior of the fixed-bed adsorber and the prediction of the breakthrough curves for single-solute adsorption. The parameters such as the number of compartment and backflow ratio were estimated from a least-squares fit of the compartmental model to the observed data obtained from the pulse response test. The intensity mi2, which is expected to be a function of the flow pattern at the interphase between liquid and solid, was determined by fitting the initial portion of the breakthrough curve. An equation was introduced for improving the estimation of the parameter miv... 

Abstract In this chapter, adsorption process is simulated by using computational mass transfer (CMT) models as presented in Chap. 3. As the adsorption process is unsteady and accompanied with heat effect, the time parameter and the energy equation as presented in Chap. 2 are involved in the model equations. The simulated concentration profile of the column at different times enables to show the progress of adsorption along the column as an indication of the process dynamics. The simulated breakthrough curve and regeneration curve for adsorption and desorption by the two CMT models, i.e., the - Sc- model and the Reynolds mass flux model, are well checked with the experimental data. Some issues that may cause discrepancies are discussed. 

---