Column packings physical parameters

Having chosen the test mixture and mobile diase composition, the chromatogram is run, usually at a fairly fast chart speed to reduce errors associated with the measurement of peak widths, etc.. Figure 4.10. The parameters calculated from the chromatogram are the retention volume and capacity factor of each component, the plate count for the unretained peak and at least one of the retained peaks, the peak asymmetry factor for each component, and the separation factor for at least one pair of solutes. The pressure drop for the column at the optimum test flow rate should also be noted. This data is then used to determine two types of performance criteria. These are kinetic parameters, which indicate how well the column is physically packed, and thermodynamic parameters, which indicate whether the column packing material meets the manufacturer s specifications. Examples of such thermodynamic parameters are whether the percentage oi bonded... 

Once the number of transfer units has been found, the height of the tower is determined from the product of the number and the height of each transfer unit (HTU). The HTU is determined by physical parameters such as the droplet size, the flow patterns in the tower, and the effect of any packing. These all affect the rate of mass transfer, which is addressed in Chapter 9. Very often the rate of mass transfer cannot be estimated from first principles, and it is necessary to estimate the height by determining the number of transfer units achieved and then dividing the actual height of the column employed by the number of transfer units, i.e. ... 

A variety of physical parameters have been shown to correlate with chromatographic retention. Several physical properties, measured SFC capacity factors, as well as GLC derived retention indices for the PAHs studied are listed in Table II. The capacity factors, k, were calculated from an isoconfertic-isothermal SFC separation of a mixture of the PAHs on an octadecyl bonded packed column using CC>2 as the mobile phase (4500 psi, 100°C). 

Physical parameters (P) column length, flowrate, particle size, column diameter (packed columns). 

Vo is the exclusion limit of the column and equal to the interstitial volume of the packed SEC column (volume of eluent between the particles of stationary phase). Fi is the pore volume of the packing (the internal solvent volume in the pores). Ft is the total permeation volume. The volume of solvent at which a solute elutes from the column or the volume of liquid corresponding to the retention of a solute on a column is known as the retention volume (Fr). Fr can be related to the physical parameters of the column as follows ... 

Even within the best supports available there wiU be some irregularities in the particle shapes which will lead to non-uniform channels through which the molecules will permeate. Optimisation of the physical parameters of the column, the type of stationary phase and the method of packing are normally directed at overcoming these effects. 

It became clear that two parameters must be understood before such a tool could be usable the correct description of the solute (protein) exposed to the SEC process and the physical description of the internal pore spaces seen by the eluting species, usually as some function of The correct physical or hydrodynamic description of the protein solute and the column packing material exists as a challenge today. 

Table 2 lists some characteristic features of GC, SFC, and LC. In most cases GC is used as open-tubular GLC, and LC is performed in packed columns. As can be seen from the physical parameters of density, viscosity, and diffusion coefficient, SFC lies between GC and LC and it is no surprise that it can be used equally well with open capillaries and packed columns. The values in the table are to some extent arbitrary but are typical. The values of the three basic physical parameters are not only of theoretical interest but are linked directly to some of the main... 

Resolution can be improved by increasing the column plate number, N, and/or the separation factor (selectivity of packing materials), a [a = the ratio of the capacity ratios (retention factors) of the two compounds]. N is the physical parameter and a is the chemical parameter for the separation. 

The objective of this study was to demonstrate the physical transport of TCE by EO through cores of undisturbed soil. While research approaches have been performed on packed columns of pure clay (e.g. kaolinite), few have used native soils, and only in the form of slurries. At this time, no information is available for transport of TCE by EO through intact cores of natural soil. Therefore, the results of EO experiments using undisturbed soil are more applicable to actual site conditions than using single mineral soil. Parameters governing TCE transport in the soil are used in a one dimension advective model to describe TCE transport during the experiment. 

Thermodynamic non-idealities are taken into account while calculating necessary physical properties such as densities, viscosities, and diffusion coefficients. In addition, non-ideal phase equilibrium behavior is accounted for. In this respect, the Elec-trolyte-NRTL model (see Section 9.4.1) is used and supplied with the relevant parameters from Ref. [50]. The mass transport properties of the packing are described via the correlations from Refs. [59, 61]. This allows the mass transfer coefficients, specific contact area, hold-up and pressure drop as functions of physical properties and hydrodynamic conditions inside the column to be determined. 

In addition, the separating behaviour of a packed column cannot be completely described from a physical point of view by only one parameter, such as the HETP or the HTU value. Sizniann [159] has shown that material transfer in a packed column is the more intense the easier it is for the components to get from inside one phase to the liquid-vapour interface and from there to the interior of the other phase. Hence, two resistances to transfer, Wp and IFp, for material transport in the vapour and liquid phases, respectively, have always to be considered. The magnitudes of these resistances depend on the mean path travelled in the respective phase, the frequency of mixing at certain points along the flow path, the formation of turbulence and other factors which have been discussed in chap. 4.2. The distribution of the resistances to mass transfer for 7 different packings as determined by Sizmann is given in Table 18. It is seen that the proportion of the resistance in the vapour phase may vary from 9 to 96% of the total resistance. 

If we cannot use the Ergun equation to scale a packed column unit operation, then we must devise a different method for scaling such a unit operation. Since scaling is based on dimensionless parameters, we should base our new scaling procedure for packed columns on dimensional analysis. We can perform a dimensional analysis of fluid flow through packed columns because the variables of the process are well known and have been studied for many decades [13,14]. The variables are fluid velocity v [LT ], column diameter D [L], characteristic length of the material mass Tchar that is dependent upon the size and shape of the material particles [L], pressure difference per physical height of the material column AP/Z [ML T ], fluid density p [ML ], and fluid viscosity p, [ML T ]. The Dimension Table for these variables is... 

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