Height equivalent to a theoretical plate HETP

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 ... 

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 ... 

Height equivalent to a theoretical plate (HETP) A measure of the efficiency of a column usually expressed in millimeters. HETP — LIN, where L is the length of a column and N is the number of theoretical plates. The reciprocal of HETP is also used to describe efficiency and is often expressed by the terms plates per meter. 

Time-dominated processes inherently govern chromatography. The horizontal axis of a chromatogram is time (and not energy as in spectroscopy). To describe the quality of a chromatographic system the concepts of the height equivalent to a theoretical plate, HETP or H, and the number of theoretical plates N are used (Equation 4.1) ... 

Now you have a column with one-point-six theoretical plates. Is that good you ask. Relative to what, I say. If that column is six feet high, that s terrible. The Height Equivalent to a Theoretical Plate (HETP) is 3.7feet/ plate. Suppose another column also had 1.6 theoretical plates, but was only 6 inches (0.5 ft) high. The HETP for this column is 3.7in/plate, and if it were 6 feet high, it would have 19 plates. The smaller the HETP, the more efficient the column is. There are more plates for the same length. 

The magniiude of relative band spreading in the column is often measured by the height equivalent to a theoretical plate (HETP) which is ilriuilcil l>) H rtiul calculated rioiii (he o plcssiun tU)J... 

These successive equilibria are the basis for the static model for which the column length L is partitioned into N theoretical plates numbered from 1 to N, all with the same height. For each of these plates, the concentration of analyte in the mobile phase is in equilibrium with the main concentration of analyte in the stationary phase. The height equivalent to a theoretical plate (HETP or II) is thus given by equation (1.5) ... 

If the liquid holdup is too low, fractionation efficiency will be bad. We say that the height equivalent to a theoretical plate (HETP) will be high. If the liquid holdup is too high, fractionation efficiency will also be poor. We again say that the HETP will be high. This idea is expressed in Fig. 7.6. When the holdup rises above the point that corresponds to the minimum HETP, we can say that the packing is beginning to flood. The minimum HETP point on Fig. 7.6 corresponds to the point of incipient flood, discussed in Chap. 1. 

The concept of plate theory was originally proposed for the performance of distillation columns (12). However, Martin and Synge (13) first applied the plate theory to partition chromatography. The theory assumes that the column is divided into a number of zones called theoretical plates. One determines the zone thickness or height equivalent to a theoretical plate (HETP) by assuming that there is perfect equilibrium between the gas and liquid phases within each plate. The resulting behavior of the plate column is calculated on the assumption that the distribution coefficient remains unaffected by the presence of other... 

Height equivalent to a theoretical plate (HETP) for vapor-liquid contacting is 1.3-1.8 ft for 1 in. pall rings, 2.5-3.0 ft for 2 in. pall rings. 

H = LIN is the height equivalent to a theoretical plate (HETP). It can be considered as the thickness of a transverse slice of column. Since it is often difficult to measure accurately the peak width a), one can use the peak width at half height, and N = 5.54(fr/3)2. 3 is the thickness of the peak at half height, it is different from 2a. 

Dingenen [9], who studied the effect of the mobile phase velocity on the height equivalent to a theoretical plate (HETP) at different temperatures for benzotriazole derivatives, obtained the results shown in Figure 22, which represents the HETP values found for methanol and the hexane-ethanol mixture. Both curves of Figure 22 clearly demonstrate that the kinetic circumstances are less favorable at low temperatures. A slow mass transfer between the two phases clearly determines the band-broadening process at temperatures below 20°C. This... 

The amount of resin to pack in a column, column geometry, flow rates, pressure, column hardware, and wetted materials of construction should all be evaluated in development. Chromatography columns must be properly packed prior to validating the purification process. From a business perspective there should be some criteria other than purification of the product by which the quality of the packed column can be assessed prior to applying the feedstream, which by this time in the process is quite expensive. Height equivalent to a theoretical plate (HETP) and asymmetry determinations can be used to evaluate the quality of column packing, but may have limited value for some types of packed columns... 

In an experiment to determine the effects of sample size and amount ofliquid phase on the height equivalent to a theoretical plate (HETP) in gas chromatography, it was necessary to utilize solid support material from different batches. It was therefore imperative that the resulting data be checked for homogeneity prior to attempting to develop any quantitative expressions regarding the effects of these variables on HETP. Several sets of data points were selected at random and examined using Bartlett s test. 

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