Height equivalent to theoretical plates HETP

The width of the band eluting from the chromatographic system depends on the distance it has traveled. The proportionality factor between the two, termed height equivalent to theoretical plate (HETP), or plate height in short, is defined in the following way ... 

For a phenomenological description of chromatographic separation, the concept of theoretical plate is often used. Chromatographic column is considered to consist of a large number of theoretical plates, in each of which equilibrium relations between fluid and particle phases hold (Fig. 10.1). Height equivalent to theoretical plate (HETP) and number of theoretical plate (NTP) are then related to column length z as... 

HETP height equivalent to theoretical plate, m HTU height equivalent to a transfer unit, m... 

A column in which the ascending vapour is in contact with the refluxing liquid is used for this purpose. The reflux is generated by an overhead condenser. Due to the phase transfer in the column, a height equivalent of theoretical plate HETP can be defined where the two phases, liquid and vapour, are in thermodynamic equilibrium. The theoretical plate number is defined as... 

If the comparison between the two techniques were to be based on the criterion of HETP (height equivalent to theoretical plate) values, HPLC can easily be shown to be a more efficient technique than HPTLC. The conventionally packed HPLC columns used in most analytical laboratories are capable of providing approximately 10,000 theoretical plates. Special HPLC columns, such as capillary columns, are capable of even greater efficiency. However, HPTLC gains certain advantages, which are outlined below, because it is an open-bed system while HPLC is a closed-bed system. 

The main reason to preserve the structure of the monolith on different scales is to make the transfer of chromatographic methods very simple and straightforward. Keeping a constant structure, the resin efficiency, normally measured in terms of height equivalent of theoretical plate (HETP), is also kept constant. Therefore, method transfer time can be significantly shortened since fewer experiments are required. 

The separation efficiency of packed column is usually expressed in terms of height equivalent of theoretical plate (HETP). According to the Fenske equation, the slop of ln(ir ) versus Z plot is equal to where is the relative volatility of the... 

The properties of a fractionating column which are important for isotope separation are (1) the throughput or boil-up rate which determines production (2) HETP (height equivalent per theoretical plate) which determines column length (3) the hold-up per plate which determines plant inventory and time to production (4) the pressure drop per plate which should be as small as possible. The choice of a particular column is invariably a compromise between these factors. The separation in a production column is of course less than it would be at total reflux (no product withdrawal). The concentration at any point in the enriching section can be calculated from the transport equation (see, e.g., London 1961)... 

Height of a theoretical plate (HETP) Height of packing in a distillation column that gives a separation equivalent to one theoretical stage. 

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) ... 

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). 

Packing material can be plastic, metal, or ceramic. Packing efficiencies can be expressed as HETP (height equivalent to a theoretical plate). 

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 ... 

HETP = height equivalent to a theoretical plate, ft HTU = height of a transfer unit, ft L = liquid mass velocity, Ib/hr-ft m = exponent a 1.0 n = exponent 0.44 Pr = Prandtl number, dimensionless Sc = Schmidt number dimensionless U, = linear velocity of gas based on total column cross-sectional area, ft/sec... 

HETP = Height equivalent to a theoretical plate/tray/stage, in. or ft, or possibly mm... 

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