Column resistance parameter

Another term of practical importance is the column resistance parameter, (f), where... 

Column Type Minimum Reduced Plate Height Minimum Reduced Velocity flow Resistance Parameter Separation Impedance... 

A liquid chromatographic column packed with 5.00 fim diameter solid support particles and having a porosity e = 0.400 is found to have a flow resistance parameter 750. Calculate the specific permeability K0. Assume that the flowrate/pressure drop relationship is identical to that of a bundle of identical parallel capillaries whose axes are spaced (in a square cross-sectional array) a distance of 5.00 /im from one another. What is the single capillary diameter of the hypothetical bundle ... 

MECC separations are conducted in open capillaries, hence eddy diffusion is not problematic. However, the columns behave in many ways like packed columns, with the micelles functioning as uniformly sized and evenly dispersed packing particles. In packed columns, resistance to mass transfer in the mobile phase is reduced (i.e., efficiency improved) when smaller particles are used because the "diffusion distance" between particles is decreased. Average inter-micellar" distance is the analogous parameter in MECC. This distance can be decreased by increasing surfactant concentration. 

The velocity we can obtain at a given pressure will also be limited by the resistance to flow presented by the column, known as the specific column permeability. In equation (17-16) the permeability is broken up into its two main components the flow resistance parameter, ( ), and the particle diameter squared, dl, and can be expressed as... 

Column type Minimum reduced plate height Minimum reduced velocity Flow resistance parameter Separation impedance... 

Another measure of column permeability is the fiow resistance parameter It is a dimensionless quantity ... 

On a practical level, a parameter that is useful for evaluating columns is the flow resistance parameter ) defmed as ... 

The terms (1/1 SOS Xef /(1 — Sff)

column resistance factor (d>). This parameter is known as the Knox quality of a column. Rearranging Eqs. (6) and (7) shows the relationship between pressure drop and particle... 

For particles with a bidispersed pore structure, the mass-transfer parameter in the LDF approximation (column 2 in Table 16-12) can be approximated by the series-combination of resistances... 

Other parameters that have been used to characterize column performance include the column pressure drop and the column flow resistance.1617 The column pressure drop is simply the difference in pressure observed when the column is or is not in-line. The column flow resistance normalizes for particle diameter, solvent viscosity, and column length. One may also wish to compare issues of cost per analysis and column lifetime in evaluating a column.18... 

At Merck KGaA in Darmstadt (Germany), in-line UV spectroscopy has been used for monitoring a distillation setup for solvent purification." A transmission probe was implemented at the top of the column. Solarization-resistant UV fibers guided the light to a diode array spectrometer. From the spectra, a quality parameter was extracted and fed to the process control system (PCS). As an example, the quality parameter would exhibit a transient behavior upon column startup. Below a defined threshold value of the parameter, the PCS would assume sufficient product quality and switch the exit stream from waste to product collection. The operation of the spectrometer does not take place in a direct manner, but rather via the PCS. 

In pHPLC, there are numerous types of columns used. The comparison and characterization of these columns are often discussed in terms of thermodynamic properties and kinetic characteristics. The retention factor, k, selectivity, a, and the peak asymmetry are believed to be representative parameters for the thermodynamic properties, while the kinetic characteristics are often expressed in dimensionless magnitudes of reduced plate height, h, separation impedance, E, and flow resistance factor, ( ). 3... 

The resistance of the electrolyte, Ra, represents the ohmic resistance of the complete column of electrolyte between both electrodes. Note that in this way of presentation, the Faradaic impedance cannot necessarily be correlated with an occurring process, therefore it is represented by a general symbol ZF. It can be seen in this case that the total impedance consists of contributions from the working and the counter/reference electrodes, and knowledge of the behaviour of only the working electrode needs manipulation. A simple possibility is to use a CE/RE electrode with much larger surface than the WE. However, in the work presented in this book, this manipulation is not done, because the system used here will be used in applications as a set of two identical electrodes. In addition, one of the parameters that we are interested in is the electrolyte resistance, a parameter that is suppressed when using electrodes of different surface areas. 

It is important to have the correct set of variables specified as independent and dependent to meet the modeling objectives. For monitoring objectives observed conditions, including the aforementioned independent variables (FICs, TICs, etc.) and many of the "normally" (for simulation and optimization cases) dependent variables (FIs, TIs, etc.) are specified as independent, while numerous equipment performance parameters are specified as dependent. These equipment performance parameters include heat exchanger heat transfer coefficients, heterogeneous catalyst "activities" (representing the relative number of active sites), distillation column efficiencies, and similar parameters for compressors, gas and steam turbines, resistance-to-flow parameters (indicated by pressure drops), as well as many others. These equipment performance parameters are independent in simulation and optimization model executions. 

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