Height equivalent theoretical plate HETP

Before releasing a process column for chromatography, it is advisable to perform some test to measure efficiency, such as calculating height equivalent theoretical plates (HETP), both to forestall any problems in the column bed and to provide a benchmark by which to measure column reproducibility and predict degradation of the bed or material. Examples of compounds that are relatively innocuous for use in pharmaceutical applications are 1% NaCl (for gel filtration), concentrated buffer solutions (for ion exchange), and benzyl alcohol and parabens for reverse phase LC.10... 

FIGURE 22 Dependence of height equivalent theoretical plate (HETP) on flow velocity at different temperatures on a Chiralcel OJ CSP. (From Ref. 9.)... 

The separation between two successive equilibria is called a theoretical plate. If this is a height H along some physical column, it is called the height-equivalent theoretical plate (HETP). 

Packing height can be evaluated with either the transfer-unit or the height equivalent theoretical plate (HETP) approach. Traditionally, the transfer-unit approach has been used with absorption and stripping systems and the HETP approach for fractionation services. The method used here is the HETP approach. The method is applicable to distillation and... 

The column internals are either trays or packing. In a CS with trays, the vapor and liquid only come into contact at discreet points (i.e., on the trays). In a packed CS, there is continuous contact between vapor and liquid streams. The principle of height equivalent theoretical plate (HETP) is therefore used, which allows to model both packed and trayed CSs using the same position variable, n. Thus, the position variable, w, is often referred to as the number of trays or stage number. However, since it may represent a continuous packing rather than discreet points, neR. 

The efficiency of a system may be expressed as the height-equivalent theoretical plate (HETP) in centimeters (or inches) per plate. The HETP is related to the number of theoretical plates n by... 

Heidolph micro-rotary evaporator, 103 height-equivalent theoretical plates (HETPs), 60 heliotropine, 494 heptanal... 

The methods for estimating the heights of transfer units, HTU, given in Section 11.14.3 can be used for distillation. The relationship between transfer units and the height of an equivalent theoretical plate, HETP is given by ... 

The plate number as well as the corresponding height of an equivalent theoretical plate (HETP) is well known in chemical engineering as a common measure for ideal mass transfer within packed beds (Eq. 2.19). 

The height of an equivalent theoretical plate (HETP) in each section should be about the same. 

Figure 42-1. The dependence of the height of equivalent theoretical plate (HETP) on the flow velocity of the mobile phase for LiChrospher RP phases with different particle diameters. The test solute u.sed was benzo(a)anthracene and the mobile phase was acetonitrile/water 75/25 (v/v) (Source Merck).

When discnssing column efficiency in the context of the Plate Theory, the concept of the height of the equivalent theoretical plate (HETP) was introduced as H = (Z/N), where I is the length of the bed of stationary phase in the column and N is the number of theoretical plates (Section 3.3.5). H can conveniently be expressed as ... 

K is a thermodynamic member and corresponds to the median distribution coefficient of two neighbouring coefficients). Assuming almost equal selectivities in the gas and liquid phases and a uniform R value of 0.5 with GC and LC which is common in practice, LC approaches the efficiency of GC, as far as comparable N values or heights of equivalent theoretical plates (HETP) which are closely related to this. 

Thus a very sharp peak, that is, a small amount of dispersion, implies a large number of theoretical plates. Values of several million plates are not uncommon in analytical systems. This plate number is used to define the height of an equivalent theoretical plate (HETP), a parallel to the height of a transfer unit ... 

In the case of a plate column the performance of a real plate is related to the performance of a theoretical one by the plate efficiency. In the case of a packed column the height equivalent to a theoretical plate HETP) gives a measure of the contacting efficiency of the packing. 

Sometimes the height equivalent to a theoretical plate (HETP) is employed rather than and to characterize the performance of packed towers. The number of heights equivalent to one theoretical plate required for a specified absorption job is equal to the number of theoretical plates,... 

An alternative to determining packed height is through the use of an empirical term, height equivalent to a theoretical plate (HETP). This term can be measured in a fashion similar to that used for the overall plate efficiency of a column (eq. 44) ... 

Height equivalent to a theoretical plate (HETP) plate tower data ... 

Use of HETP Data for Absorber Design Distillation design methods (see Sec. 13) normally involve determination of the number of theoretical equihbrium stages or plates N. Thus, when packed towers are employed in distillation appRcations, it is common practice to rate the efficiency of tower packings in terms of the height of packing equivalent to one 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),... 

Column efficiency (number of theoretical plates) As in batch chromatography, one needs to determine the efficiency of the column in order to evaluate the dispersion of the fronts due to hydrodynamics dispersion or kinetics limitations. The relationship of N proportional to L can be expressed in terms of the equation for height equivalent to a theoretical plate (HETP) as ... 

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