Packed columns physical

Determination of pressure drop through the column (for packed columns, correlations dependent of packing type, column-operating data, and physical properties of the constituents involved are available to estimate the pressure drop through the packing for plate columns, the pressure drop per plate is obtained and multiplied by the number of plates)... 

Due to the varying physical nature of the different packings, it appears that no one has developed a specific function for (com) for a packed column, but it was suggested... 

Unfortunately, any equation that does provide a good fit to a series of experimentally determined data sets, and meets the requirement that all constants were positive and real, would still not uniquely identify the correct expression for peak dispersion. After a satisfactory fit of the experimental data to a particular equation is obtained, the constants, (A), (B), (C) etc. must then be replaced by the explicit expressions derived from the respective theory. These expressions will contain constants that define certain physical properties of the solute, solvent and stationary phase. Consequently, if the pertinent physical properties of solute, solvent and stationary phase are varied in a systematic manner to change the magnitude of the constants (A), (B), (C) etc., the changes as predicted by the equation under examination must then be compared with those obtained experimentally. The equation that satisfies both requirements can then be considered to be the true equation that describes band dispersion in a packed column. 

In a similar manner to the design process for packed columns, the physical characteristics and the performance specifications can be calculated theoretically for open tubular columns. The same protocol will be observed and again, the procedure involves the use of a number of equations that have been previously derived and/or discussed. However, it will be seen that as a result of the geometric simplicity of the open tubular column, there are no packing factors and no multi-path term and so the equations that result are far less complex and easier to manipulate and to understand. 

The design process for open tubular columns is similar to that for packed columns, and the physical characteristics and performance specifications can be calculated... 

With soft gels, column packing has often been plagued with such problems as inferior reproducibility and excessive time requirements. These problems are alleviated with physically stable Toyopearl HW media. However, an improperly packed column can have significantly reduced efficiency. The two key variables for the successful packing of Toyopearl HW media, packing velocity and column size, have been evaluated to determine the optimal packing conditions. 

All packing materials produced at PSS are tested for all relevant properties. This includes physical tests (e.g., pressure stability, temperature stability, permeability, particle size distribution, porosity) as well as chromatographic tests using packed columns (plate count, resolution, peak symmetry, calibration curves). PSS uses inverse SEC methodology (26,27) to determine chromatographic-active sorbent properties such as surface area, pore volume, average pore size, and pore size distribution. Table 9.10 shows details on inverse SEC tests on PSS SDV sorbent as an example. Pig. 9.10 shows the dependence... 

The nomographs can be used to make a quick, rough, estimate of the column height, but are an oversimplification, as they do not take into account all the physical properties and other factors that affect mass transfer in packed columns. 

Supercritical fluids possess favorable physical properties that result in good behavior for mass transfer of solutes in a column. Some important physical properties of liquids, gases, and supercritical fluids are compared in Table 4.1 [49]. It can be seen that solute diffusion coefficients are greater in a supercritical fluid than in a liquid phase. When compared to HPLC, higher analyte diffusivity leads to lower mass transfer resistance, which results in sharper peaks. Higher diffusivity also results in higher optimum linear velocities, since the optimum linear velocity for a packed column is proportional to the diffusion coefficient of the mobile phase for liquid-like fluids [50, 51]. 

This chapter deals with the properties of high-pressure liquid chromatography columns. It is divided into two sections column physics and column chemistry. In the section on column physics, we discuss the properties that influence column performance, such as particle size, column length and column diameter, together with the effect of instrumentation on the quality of a separation. In the section on column chemistry, we examine in depth the surfaces of modern packings, as well as the newer developments such as zirconia-hased packings, hybrid packings or monoliths. We have also included a short section on... 

The physical properties of silica are determined by its specific surface area, pore volume, average pore diameter, porosity, and the particle diameter and shape [8]. The latter two are responsible for the efficiency, the physical stability and the pressure drop of the packed columns and do not contribute to retention and selectivity. 

With decreasing packing size in SEC columns, the probability of physical entrapment of macromolecules increases. To estimate the molecular weight limit above which ultrafiltration will occur, we must first calculate an average radius of the interstices formed in a packed bed. This is done by assuming that the packed column consists of a bundle of capillaries in which the capillary radius can be estimated from the bed hydraulic radius ... 

The optimized operating conditions for each analytical method including the detector system of choice are reported in Table II. The reported columns and operating conditions yield satisfactory peak shapes and resolution of all the potential interferents evaluated for HCCP and HCBD. Two potential interferents—tetrachloro-l,2-difluoroethane and 1,2-dichloroethane— could not be separated from 1,2-DCP with conventional packed columns. Tetrachloro-l,2-difluoroethane, a compound with physical properties similar to 1,2-DCP, is not likely to be found with... 

The mass transfer coefficients considered so far - namely, kQ,kj, KQ,andKj - are defined with respect to known interfacial areas. However, the interfacial areas in equipment such as the packed column and bubble column are indefinite, and vary with operating conditions such as fluid velocities. It is for this reason that the volumetric coefficients defined with respect to the unit volume of the equipment are used, or more strictly, the unit packed volume in the packed column or the unit volume of liquid containing bubbles in the bubble column. Corresponding to /cg, Kq, and we define k a, k, a, K, /i, and K a, all of which have units of (kmol h m )/(kmol m ) - that is, (h ). Although the volumetric coefficients are often regarded as single coefficients, it is more reasonable to consider a separately from the Ar-terms, because the effective interfacial area per unit packed volume or unit volume of liquid-gas mixture a (m m ) varies not only with operating conditions such as fluid velocities but also with the types of operation, such as physical absorption, chemical absorption, and vaporization. 

The effective interfacial areas for absorption with a chemical reaction [6] in packed columns are the same as those for physical absorption, except that absorption is accompanied by rapid, second-order reactions. For absorption with a moderately fast first-order or pseudo first-order reaction, almost the entire interfacial area is effective, because the absorption rates are independent of as can be seen... 

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). 

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. 

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