Column diameter selection

Packed Tower Design and Applications COLUMN DIAMETER SELECTION ... 

Design Theory, Simplified Design Procedures, Column Diameter Selection, Water Deaeration, Water Decarbonation, Ammonia Stripping, Amine Regeneration, Hot Carbonate Regeneration, Side Strippers, Example Problem, Notation, References... 

Once packing heights are determined in other sections from HETP (distillation) or Koa (absorption), the height allowances for the internals (from Figure 1) can be added to determine the overall column height. Column diameter is determined in sections on capacity and pressure drop for the selected packing (random dumped or structured). 

The column diameter is normally determined by selecting a superficial velocity for one (or both) of the phases. This velocity is intended to ensure proper mixing while avoiding hydrodynamic problems such as flooding, weeping, or entrainment. Once a superficial velocity is determined, the cross-sectional area of the column is obtained by dividing the volumetric flowrate by the velocity. 

The diameter of the column is selected from the volume of sample that is to be processed. As a rule of thumb the maximum productivity is obtained at a sample volume of 2-6% of the bed volume in preparative gel filtration on a 50-/rm chromatographic medium (Hagel et al., 1989). Thus, the required column diameter is calculated from the bed volume needed to cope with the sample volume and the column length needed to give the resolution desired. 

The flow rate in SEC significantly affects the resolution. Depending on the selectivity wanted, linear flow rates have to be adapted to the column dimensions. In general, running the column at a low flow rate results in higher resolution, but diffusion may produce diminishing resolution when the flow rate is too low. The flow rates recommended for a particular column diameter should not be increased. In the case of Superformance columns, the best results can be obtained by applying linear flow rates of about 30-80 cm/hr. Of course, linear flow rates below 30 cm/hr can contribute to further increased resolution. 

Once a minimum reflux has been established (which is not an operating condition), then a realistic reflux ratio of from 1.5 to as much as 10 times the minimum can be selected. Of course, the larger the reflux value down the column the more vapor has to be boiled up, and the greater will be the required column diameter. So, some economic balance must be determined. 

To determine the column (with trays) diameter, an approach [130] is to (1) assume 0 hours (2) solve for V, Ib/hr vapor up the column at selected, calculated, or assumed temperature and pressure (3) calculate column diameter using an assumed reasonable vapor velocity for the type of column internals (see section in this volume on Mechanical Designs for Tray Performance ). 

The choice of plate type (reverse, single pass or multiple pass) will depend on the liquid flow-rate and column diameter. An initial selection can be made using Figure 11.28, which has been adapted from a similar figure given by Huang and Hodson (1958). 

First Dimension Optimization After the second-dimension separation has been developed, the first-dimension flow rate is determined. This includes selecting a first-dimension column diameter to work at the flow rate selected. We illustrate the selection process with an application that addresses a column method for proteins that functions as a replacement for planar 2D gel electrophoresis (2DGE) within a narrow molecular weight and p/range. In the planar experiment, isoelectric focusing is performed in the first dimension and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS/PAGE) in the second dimension. 

Many precolumns and trap cartridges for sample clean-up are commercially available. In our experience, a 2 to 3 cm short column with twice the analytical column inner diameter and packed with the same particles performs satisfactorily. An antibody affinity column for selective removal of highly abundant proteins from human serum samples provides better sensitivity for the discovery of low abundance protein markers that may represent revolutionary therapeutic diagnosis and monitoring. 

Hydraulic analysis Using Figure 3.27, the appropriate gas superficial velocity and the column diameter for the heterogeneous flow regime can be selected. An appropriate choice for the reactor diameter and the superficial gas velocity is 0.5 m and 0.1 m/s, respectively. The height to diameter ratio in columns is greater than unity and a value of 5 is reasonable. Therefore, the value of 2.5 m has been selected for the column height. As a result, the reactor volume is equal to 0.49 m3. This volume is occupied by the reaction mixture, which is the gas, the liquid, and the solid phase. 

An understanding of this macroporosity and the hydrophobicity of many polymers is useful for the selection of the solvent sequence used in wetting. This sequence must promote complete permeation of the water into all of the pores of the polymer, and the adsorbent column must be operated so that the test water passes through these pores. To accomplish this nonchannelized flow of water, the right combination of wetting, particle size, and column diameter and length is needed. 

Because HPLC methods were originally elaborated to replace TLC separations, the stationary-and mobile-phase selection was largely inspired by previous experience with TLC. Hence, normal silica was used mostly as the stationary phase, although both aminopropyl- (43 - 46) and diol-modified silica (47,48) have become increasingly popular. Besides, smaller column diameters are... 

For this application, we select Multipack packing, fully characterized by hydraulic correlations [9]. Table 8.8 gives the geometric characteristics. For smaller column diameters Multipack-I seems appropriate. Note that the catalyst... 

At the same flow rate, columns of varying IDs operate at different linear velocities therefore, to compare the performance of several different columns, you need to operate each column at the same linear velocity. Figure 6-6 gives the relationship between linear velocity and flow rate for selected column diameters. This figure assumes the same packing density in each column. The linear velocity is marked on the top line. The corresponding flow rate for various diameter columns would be found on the lower line. For instance, a linear velocity of 0.5 cm/sec would occur at 4.0 mL/min on a 4.6-mm ID column, at 3.0 mL/min on a 4.0-mm ID column, and at 0.75 mL/ min on a 2.0-mm ID column. Linear velocity can be calculated for each column by the equation... 

Calculate a preliminary column diameter from Equations 6.23.1 and 6.23.2 by assuming a superficial velocity of 2 ft/s. If D < 2.5 ft, select a packed column. Otherwise, select a tray column. 

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