Height equivalent of a theoretical plate HETP

Many operating variables, such as sample volume, flow rate, column length, and temperature, must be considered when performing any separation. The relative importance of these variables for Toyopearl HW-55F resin columns has been specifically evaluated. For example. Fig. 4.47 shows the relationship between column efficiency, or height equivalent of a theoretical plate (HETP),... 

As with distillation, the correlation for overall tray efficiency for absorbers, given in Equation 10.7, should only be used to derive a first estimate of the actual number of trays. More elaborate and reliable methods are available, but these require much more information on tray type and geometry and physical properties. If the column is to be packed, then the height of the packing is determined from Equation 9.64. As with distillation, the height equivalent of a theoretical plate (HETP) can vary... 

From the number of plates in the column, the height equivalent of a theoretical plate (HETP), usually abbreviated to plate height (H), can easily be calculated ... 

The empirical expressions derived are generally applicable to all types of column chromatography and are used universally, first as a measure of column performance and efficiency, expressed in terms of the number of theoretical plates N) and the height equivalent of a theoretical plate (HETP) denoted by H, and secondly, to measure the resolution R ) attained in the chromatogram. For a fuller discussion the reader is directed to Chapter 2, though a brief resume of the expressions for these parameters is presented below. 

While A is a useful concept to compare the efficiency of separation among columns, or between laboratories, it is difficult to use to assess the factors that affect that efficiency. This is due to the fact that it refers to the behavior of a single component during the separation process, and is unsuited to describing the separation of two components or the resolving power of a capillary. A more useful parameter is the height equivalent of a theoretical plate (HETP). ... 

When we want to compare columns of different lengths, we use the height equivalent of a theoretical plate HETP (the plate number is generally expressed by/r) ... 

Except for the short introductory Section 1.3. to this point the entire analysis of separation processes has been equilibrium based. Effects of nonequilibrium operation have been lunped into either a stage efficiency f Sections 4.11.10.2.12.5. and 13.51 or to the height equivalent of a theoretical plate (HETP Sections 10.9 and 10.111. We must move beyond an equilibrium analysis if we want to be able to predict values of the stage efficiency and the HETP fChapter 161. to study membrane separators fChapter 171. or to study sorption separations fChapter 181. For all of these situations, we must look at the mass transfer occurring in the separator. This chapter presents the fundamentals of diffusion and mass transfer in sufficient detail so that the analysis in the remaining chapters is understandable. Additional information on mass transfer is presented as needed in Chapters 16 to 18. If you have already studied mass transfer and diffusion, most, but probably not all, of this chapter will be a review, and you will not have to spend much time studying the material. 

As already mentioned in Section 4.1., information with respect to transport properties can be obtained from the profile of an SFC peak. Binary diffusion coefficients Di2 at- infinite dilution can be determined from SFC experiments according to the so-called peak-broadening method using a long void column and the following relation for the height equivalent of a theoretical plate HETP... 

Furthermore, a distillation operation can also be described differentially in terms of a continuum as presented, for instance, by Hoffman. This representation is more suitable for, say, packed columns vis-a-vis plate columns, although the information is sometimes interchangeable for example, in terms of the height equivalent of a theoretical plate (HETP). Other concepts used include what is referred to as the height of a transfer unit (HTU) and the number of transfer units (NTUs). 

An alternative measure of efficiency, which is independent of the length of a chromatographic column, is the plate height, H (or Height Equivalent of a Theoretical Plate, HETP), and given by... 

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