Adsorption break time

As can be understood from Figure 11.5, the amount of adsorbate lost in the effluent and the extent of the adsorption capacity of the fixed bed utilized at the break point depend on the shape of the breakthrough curve and on the selected break point. In most cases, the time required from the start of feeding to the break point is a sufficient index of the performance of a fixed-bed adsorber. A simplified method to predict the break time is discussed in the following section. 

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. 

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. 

Conventional elution chromatography has the serious disadvantage of dilution, and usually a concentration step must follow. The technique of displacement chromatography circumvents dilution and may even result in an eluant more concentrated than the feed. A displacer compound breaks the desired product from the chromatographic material sharply, and a column heavily loaded with several biochemicals will release them one at a time depending on their adsorption equilibria. However, the displacers tena to be expensive and can be troublesome to remove from the product. 

Another way to examine the effeet of earbon partiele size on kineties is to look at the bleed emissions from a earbon eanister [20,35]. Bleed emissions are those emissions that oecur prior to break through. They are the result of the diffusion of gasoline vapor components that ean develop during extended soak times between purge and adsorption events. 

The reinforcing properties measured as M300/M100 are similar for the two vulcanized samples. However, the cured A1 compounds show lower ultimate elongation at break, higher curing rate (T90), and shorter breakdown time (T2), which are the signs of lower adsorption of accelerators on the A1 particles surface. 

The process of contact adsorption can be viewed in the following way (Fig. 6.90) First, a hole of area of at least 1U —where r, is the radius of the bare ion—is swept free of water molecules in order to make room for the ion. At the same time, the ion strips itself of part of its solvent sheath and then jumps into the hole. During this process, the involved particles—electrode, ion, water molecules—break old attachments and make new ones (change of enthalpy, AH) and also exchange freedoms and restrictions for new freedoms (change of entropy, AS). 

The time required from the start of feeding to the break point can be estimated with the assumption of the constant pattern stated above. Thus, substitution of Equation 11.10 into Equation 11.6 gives the following equation for the rate of adsorption ... 

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... 

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