Total Column

Vapor rising from the top of the column is partially condensed the vapor and liquid are separated the vapor is taken out as a distillate or overhead product at its 

Liquid from the column bottom tray is sent to the reboiler, stage N, where it is partially vaporized. The vapor is sent back to the column bottom tray, stage N-1, and the liquid is taken out as a bottoms product at its bubble point. In this configuration, the reboiler is a partial reboiler, acting as an additional equilibrium stage. 

The feed to the column could be at any thermal condition superheated or saturated vapor, mixed phase, or saturated or subcooled liquid. The feed tray could be any tray between (and sometimes including) the condenser and reboiler. Regardless of its thermal condition, the feed is assumed to mix and equilibrate with the liquid and vapor on the feed tray. 

The top section of the column, or the rectifying section, is that part of the column above the feed and including the condenser. In the rectifying section, liquid flowing down selectively absorbs the heavier component, thereby raising the purity of the lighter component in the distillate and the recovery of the heavier component at the bottoms. 

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A B Percent of total A B Percent of total A B Percent of total Total, column B... 

The term in equation 42 is called a Souders-Brown capacity parameter and is based on the tendency of the upflowing vapor to entrain Hquid with it to the plate above. The term E in equation 43 is called an E-factor. and E to be meaningful the cross-sectional area to which they apply must be specified. The capacity parameter is usually based on the total column cross section minus the area blocked for vapor flow by the downcomer(s). Eor the E-factor, typical operating ranges for sieve plate columns are... 

When only a few solutes are separated, they may occupy only a small portion of the total column volume at any given instant. In such cases, the productivity is improved by cyclic feed injections, timed so that the most strongly retained component from an injection elutes just before the least strongly retained component from the following injection (see Fig. 16-57). For a mixture of two components with k > 1, when the same resolution is maintained between bands of the same injections and bands of successive injections, the cycle time tc and the plate number requirement are ... 

The maximum allowable mass velocity for the total column cross section is calculated as follows ... 

The F factor is used in the expression U = F/(pv)° to obtain the allowable superficial vapor velocity based on free column cross-sectional area (total column area minus the downcomer area). For foaming systems, the F factor should be multiplied by 0.75. 

Clear liquid velocity (ft/sec) through the downcomer is then found by multiplying DL by 0.00223. The correlation is not valid if Pl - pv is less than 301b/ft (very high pressure systems). For foaming systems, DL should be multiplied by 0.7. Frank recommends segmental downcomers of at least 5% of total column cross-sectional area, regardless of the area obtained by this correlation. 

Equivalent Decane Content (Dimethyl Octane) Total Column Volume... 

The XK column system is a medium-pressure jacketed glass column system designed for operating pressures up to 5 bar (0.5 MPa). Column dead volumes are less than 0.1% of the total column volume. Wetted materials include EPDM, TEFZEL, superpolyoxymethylene, and flurorubber. Columns use nylon nets of 10-)Lim mesh size and may be used with most SEC media with particle diameters >20 /xm. Columns are intended for use with aqueous solutions and... 

The injection volume should be kept as small as possible to attain maximum resolution in analyses. This is particularly important in analyses on columns packed with small particle size resins such as SuperH. Injection volumes of 0.1 % or less of the total column volume are recommended on SuperH columns. A few times larger injection volumes may be applied to other series of H type columns. 

Larger injection volumes, e.g., 2% of the total column volume, are sometimes advantageous in the preparative fractionation of polymers (33). More samples can be injected using larger injection volumes with a slight decrease in resolution. When the same amount of sample is injected with a smaller injection volume and a higher sample concentration, the resolution decreases more significantly. 

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... 

To solve the total column length for the SMB system, one eliminates the fluid velocity ... 

HETP = height equivalent to a theoretical plate, ft HTU = height of a transfer unit, ft L = liquid mass velocity, Ib/hr-ft m = exponent a 1.0 n = exponent 0.44 Pr = Prandtl number, dimensionless Sc = Schmidt number dimensionless U, = linear velocity of gas based on total column cross-sectional area, ft/sec... 

Now the total volume (Vc) of a column radius (r) and length (1) will be nr l. Furthermore, the volume occupied by the mobile phase will be approximately 0.6Vc (60% of the total column volume is occupied by mobile phase).Thus as a general rule the maximum sample volume that can be employed without degrading the resolution of the column is... 

As noted before, the whole spectrum of particle sizes between 38 and 357 nm is encompassed with a AV of U.O ml or about 6% of the total column void volume. This low capacity of the HDC system is counterbalanced by its excellent resolution both of itself and in comparison to porous packing systems. The latter point is addressed in the next section. 

The A term represents the contribution from eddy diffusion, the B term the contribution from longitudinal diffusion, and the C terms the contributions from mass transfer in the mobile and stationary phases to the total column plate height. By differentiating equation (1.31) with respect to the mobile phase velocity and setting the result equal to zero, the optimum values of mobile phase velocity (u ) and plate height (HETP ) can be obtained. 

As first trial take downcomer area as 12 per cent of total. Column cross-sectioned area... 

The total column dispersion is due to the combined effects of flow dispersion, longitudinal diffusion and mass transfer. 

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