Total bed volume

The bed level is not weU defined in a circulating fluidized bed, and bed density usually declines with height. Axial density profiles for different CFB operating regimes show that the vessel does not necessarily contain clearly defined bed and freeboard regimes. The sohds may occupy only between 5 and 20% of the total bed volume. 

Volume of voids + volume of solids, i.e. total bed volume)... 

FIGURE 2.9 Industrial fractionation by SEC using Sephacryl S-lOO in three BPSS columns (L = 30 cm, i.d. = 140 cm) to give a total bed volume of 1500 liters. Courtesy of R. Hersberg. (Reproduced by permission of Amersham Pharmacia Biotech.)... 

The intraporous volumes and solid matrix volumes can be expressed as a percentage of the total bed volumes and should be equivalent to 50-55 and 15-18%, respectively. The solid matrix volume depends on the packing density and can be taken as a qualitative number for the control of the reproducibility of repeated packing procedures. 

The actual loading capacity always depends on the sample composition and the separation problem. As a rule the volume of the loaded sample should not exceed 5% of the column volume. However, this recommendation is valid only for preparative runs. For analytical applications when a high resolution is needed, the volume of the injected sample should be about 1% of the total column volume or even less. For a preparative run on a 1000 X 200-mm column (bed height 60 cm), two different sample volumes were injected. If the sample volume is 0.3% of the total bed volume, the separation is more efficient... 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

Ve = elution volume Vo = interstitial volume Vt = total bed volume X = model parameter, Eq. (67) z = charge on solute... 

The functional dependence of jD on Reynolds number has been the subject of study by many investigators [e.g., Thodos and his co-workers (77, 78), and Wilson and Geankoplis (79)]. A variety of equations have been proposed as convenient representations of the experimental data. Many of these correlations also employ the bed porosity (eB) as an additional correlating parameter. This porosity is the ratio of the void volume between pellets to the total bed volume. 

Finally the solvent is evaporated, the residue redissolved in butanol and applied to a column of LH-20 in the same solvent. The first third of the fractions between dead volume and total bed volume is pooled, the solvent is evaporated, and the silicone is heated to 180°C for one hour in vacuo. A clear silicone of a viscosity of about 50 000 centi-stokes at room temperature is obtained. 

Carefully layer the reaction mixture on the top of the column. Open the valve to the column, and allow the antibody solution to flow into the column until it just enters the bed resin. Carefully add phosphate buffer to the top of the column. The conjugated antibody elutes in the excluded volume (about one-third of the total bed volume). 

Chemistry. The indium metal was melted (mp 156°C) into a flask where it was dissolved in hot 6 M HC1. Since the target material was known to contain Sb impurity, filtration was required at this point in the procedure. After filtration the solution was adjusted to 3 M HC1 by the addition of a suitable volume of distilled water. Table I is a list of the elements that must be separated to obtain pure Cd-109. This solution was applied to an AG-1X8 anion column, 200 to 400 mesh (8). The column was 1.2 cm in diameter with a total bed volume dependent on the quantity of target used. Bed volumes of 20 ml and 40 ml were successfully used. 

The capacity or retention factor (k) is a measure of retention of a sample component. It should not be confused with the loading capacity of a column, which is expressed as milligrams of sample bound per milliliter of gel and represented by the area under a peak. The capacity factor may be calculated for any individual peak in a chromatogram. For example, the capacity factor for peak 2 in Figure B4.2.4 is derived from Equation B4.2.3, where Vjq is the elution volume of peak 2 and Vm is the volume of the mobile phase (i.e., the total bed volume). 

Adsorption techniques such as ion exchange, HIC, chromatofocusing, reversed-phase chromatography, and affinity chromatography can have high capacity factors because experimental conditions can be manipulated so that the elution volume for a peak can exceed the total bed volume (VM as is the case with peaks 2 and 3 in Fig. B4.2.4.) However, in gel filtration, which is a nonad-sorptive technique, all peaks must elute within the volume Vy- V(h as is the case with peak 1 in Fig. B4.2.4. 

In molecular exclusion chromatography, resolution is directly related to the sample loading volume, since the higher the sample volume, the higher the volume in which the protein is eluted. Usually, sample volume should be 0.5-5% of the total bed volume. For volumes below 0.5% the sample becomes too diluted, while volumes above 5% work well only for molecules with large differences in size. For desalting, due to the pronounced difference in the molecular size of the components, sample volumes can reach up to 30% of the column capacity without a significant decrease in resolution. 

In eq 1 the porosity e of the fluidized bed is the void volume of the fluidized bed (volume of interstices between grains, not including any pore volume in the interior of the particles) divided by the total bed volume, ps is the apparent density of the solid, and H is the height of the fluidized bed. 

To check the quality of the columns of the SMB pilot plant, a pulse test is performed on all the columns connected in series, the eluent flow rate being fixed to 4 liters/h. The total bed volume of the pilot plant being 2.016 liters, assuming an external porosity of 0.4, the zero retention time associated to... 

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