Effect of Column Height

With increasing column height (more packing), the peak shifts to a greater elution angle (Fig. 1.5). An increase in the column height also results in a slight increase in peak width. 

Clearly, size-exclusion chromatography is a valuable technique for the separation of protein from non-protein components as well as in the separation of various proteins components present in a mixture. The model has to be improved to take into account angular dispersion, interaction of components and also adsorption on the porous media. 

This chapter examines in some detail the different techniques available to an investigator in the field of hpase purification. Lipases tend to follow very specific patterns of purification. The techniques used to purify the lipase need to be optimized to obtain maximum efficiency. Purification strategies need to be arranged in the proper order to maximize the level of lipase purification. Clearly, more detailed work is needed to estabhsh what factors enable the selection of one strategy over the other. Last, but not the least, theoretical models of continuous purifica- 

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Foster, G. D., 1998, Effects of Column Height on DNAPL Behavior In Nonaqueous-Phase Liquids, Remediation of Chlorinated and Recalcitrant Compounds (edited by G. B. Wickramanayake and E. Hinchee), Battelle Press, Columbus, OH, pp. 25-30. 

Table II. Effect of Column Height on Survival of B. Subtilis Var. Niger Spores after Ozone Treatment ...

No appreciable effect of column height (5 ft 4 in. to 8 ft 8 in.) on the transfer coefficient was noticed. Sea water and fresh water gave similar results. Contrary to Garwin s experience, the heat-transfer coefficients were found to be larger when the top of the column was hot than when the top was cold. With GJGc = 2.58 and F=0.6, values of 8180 and 7030 Btu/ft /hr/°F for hot and cold top, respectively, were obtained with spray base as the dispersed phase. The maximum values of the volumetric heat-transfer coefficient were 11,500 and 8500 Btu/ft /hr/°F for the hot and cold top, respectively. These results probably reflect the natural convection currents in the column as well as with the very pronounced effect of fluidity of the oil on the volumetric heat-transfer coefficient (W12, Fig. 12). Since Garwin worked with benzene, it is likely that this fluidity effect would have been relatively less pronounced in his experiments. 

Equations 12.21 and 12.22 contain terms corresponding to column efficiency, column selectivity, and capacity factor. These terms can be varied, more or less independently, to obtain the desired resolution and analysis time for a pair of solutes. The first term, which is a function of the number of theoretical plates or the height of a theoretical plate, accounts for the effect of column efficiency. The second term is a function of a and accounts for the influence of column selectivity. Finally, the third term in both equations is a function of b, and accounts for the effect of solute B s capacity factor. Manipulating these parameters to improve resolution is the subject of the remainder of this section. 

The terms (DJ0305) and (Z/3.05) are included in the equations to allow for the effects of column diameter and packed-bed height. The standard values used by Cornell were 1 ft (0.305 m) for diameter, and 10 ft (3.05 m) for height. These correction terms will clearly give silly results if applied over too wide a range of values. For design purposes the diameter correction term should be taken as a fixed value of 2.3 for columns above 0.6 m... 

Figure 13.45. Number of stages per meter (reciprocal of HETP), pressure loss per meter and pressure loss per theoretical stage in a 500 mm dia column filled with metal pall rings. Other charts in the original show the effects of packing height and column diameter, as well as similar data for Raschig rings (Billet, 1979). (a) Methanol/ethanol at 760Torr and total reflux in a column 500 mm dia. (b) Ethylbenzene/styrene at 100 Torr and total reflux in a column 500 mm dia.

Closely examine the considerations in Sec. 9.3.3. Use these to scale up the HETP from the above steps to your column. Pay attention to effects of diameter, height, and wetting. Judgment is required. It may pay to look at the original reference from which the data were derived in order to check whether distribution, data scatter, or test procedure have influenced the data. 

HETP (Height equivalent to a theoretical plate). A measure of band spreading which compensates for the effect of column length. 

A clearcnt example of the effect of column diameter on plate height (Karlsson 1988) is shown in Figure 3.17. The data were interpreted not in terms of the van Deemter equation but rather the Knox Equation (Equation [3.49]) (Kennedy 1972). This equation is very similar to the original van Deemter form, but is expressed in terms of reduced (dimensionless) variables in an attempt to provide a basis for comparison of different columns packed with... 

Also measured were the reactivity effects of columns of pyrex spheres from 3/8 to 7/8-in. diam and circular pyrex rods from 5/16 to 1-in, diam. It was found that, for the same height, a column of spheres has the same reactivity effect as the rod of the same volume. The lateral projected area of the rod is thus 4% greater than that of the equivalent column of spheres. 

In the adsorption column, the adsorption is taken place only in certain part of column height as represented by the red bracket shown in Fig. 6.1. The parabolic form of concentration distribution is obvious due to the wall effect. 

We will return to these expressions, and those that follow, for a more detailed examination in Chapter 8, Illustration 8.1. It will be shown there that Equation 2.11c and Equation 2.lid represent the so-called operating lines used in the graphical representation of scrubber performance. For our present purposes, we limit ourselves to the observation that these balances resulted in AEs, as predicted and stipulated in Table 2.1. We note further that neither Equation 2.11c nor Equation 2.lid contains the distance variable z. They can therefore tell us nothing about the concentration variations as a function of column height and cannot help us establish the size of column required to effect a reduction of solute content from Yj to Y2. 

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