Packed pulse column

Bender et al (1979) have discussed the operating characteristics of pulsed packed columns, wherein the efficiency can be improved by a factor of two through the introduction of pulsations. Raschig rings are not recommended, since the droplets of the dispersed phase are likely to adhere to the packings. Pulsed columns work well in situations where the liquid properties do not change substantially in the column. On the whole, a pulsed packed column is not a very efficient column, and it requires that the density difference between the two phases be more than 0.08 g/cm3. 

Pulsed Columns. The efficiency of sieve-plate or packed columns is increased by the appHcation of sinusoidal pulsation to the contents of the column. The weU-distributed turbulence promotes dispersion and mass transfer while tending to reduce axial dispersion in comparison with the unpulsed column. This leads to a substantial reduction in HETS or HTU values. 

FIG. IS-S Pulsed columns a) Perforated-plate column with pump pulse generator, (h) Packed column with air pulser. 

U.Tallarek, E. Bayer, G. Guiochon 1998, (Study of dispersion in packed chromatographic columns by pulsed field gradient nuclear magnetic resonance), J. Am. Chem. Soc. 120, 1494. 

A recent and extremely important development lies in the application of the technique of liquid extraction to metallurgical processes. The successful development of methods for the purification of uranium fuel and for the recovery of spent fuel elements in the nuclear power industry by extraction methods, mainly based on packed, including pulsed, columns as discussed in Section 13.5 has led to their application to other metallurgical processes. Of these, the recovery of copper from acid leach liquors and subsequent electro-winning from these liquors is the most extensive, although further applications to nickel and other metals are being developed. In many of these processes, some form of chemical complex is formed between the solute and the solvent so that the kinetics of the process become important. The extraction operation may be either a physical operation, as discussed previously, or a chemical operation. Chemical operations have been classified by Hanson(1) as follows ... 

A pulse test procedure [6] begins with an injection of a small pulse of the feed mixture to be separated into a desorbent stream flowing through a packed adsorbent column at a fixed flow rate and temperature. The on-line column effluent composition is then determined as a function of time or volume of desorbent passed by gas or liquid chromatography. Particularly important is the sequence and time when each of the feed components exit the packed adsorbent column because these characteristics describe the specific adsorbate and adsorbent interactions. By determining the interactions using the pulse test, the separation process can be optimized. 

Fig. 12. Pulse columns (a) liquid-pulsed, perforated-plate column (6) air-pulsed, packed column (T2).

Continuous chromatography in the packed annular space between the walls of two concentric cylinders can be done by rotating the assembly about its longitudinal axis (1, 2, 3). Rotation transforms the temporal separation that would be obtained under fixed, pulsed operation into a spatial separation that permits continuous operation. It has recently been shown that continuous reaction chromatography can be done in similar apparatus (4, Jj). This not only provides a means of carrying out chemical reaction and separation simultaneously in one unit, but for A B + C the product separation suppresses the rate of the back reaction and provides a means of enhancing the reaction yield. Yield enhancement in pulsed column chromatography has been demonstrated (6, 8). Yields of... 

Centrifugal contraction or pulsed columns are used for these solvent extraction operations in preference to longer packed columns because the latter would complicate the... 

In the chromatographic method a pulse or step change in sor-bate concentration is introduced into the carrier stream at the inlet of a packed adsorption column and the diffusional time constant is determined from the dispersion of the response signal at the column outlet. Since heat transfer in a packed bed is much faster than in a closed system the chromatographic method may, in principle, be used to follow somewhat faster sorption processes. 

Recommendations For a cylindrical packed bubble-column, the use of Eq. (7-23) for the calculation of axial dispersion coefficient in the liquid phase is recommended. The axial dispersion in the gas phase of large columns needs to be investigated. Future study on this subject should concentrate on the pulsed-flow regime and the hydrocarbon systems. 

The initial pulse of polymer solution which was injected into the column entry becomes diluted and attenuated as the different species are separated on the gel packing. The column effluent is monitored by detectors which respond to the weight concentration of polymer in the flowing eluant. The most common detector is a differential refractometer. Spectrophotometers, which operate at fixed frequencies, are also used as alternative or auxiliary detectors. Some special detectors which are needed particularly for branched polymers or copolymers are mentioned in Section 3.4.4. 

Extraction columns can be further sub-divided according to the method used to promote contact between the phases packed, plate, mechanically agitated, or pulsed columns. Various types of proprietary centrifugal extractors are also used. 

Pulsed columns Packed column Sieve tray column No internal moving parts, can deliver moderate to high efficiency, can handle moderate production rates, well suited to highly corrosive or toxic feeds requiring a hermetically sealed system Nuclear Petrochemical Metallurgical... 

Tallarek et al. applied Pulsed Field Gradient (PFGNMR) to study mass transfer, flow, and dispersion in packed chromatographic columns, using NMR [76]. The measurements allow the determination of the probability distribution of all... 

Although packed columns are simple and have no moving parts, their large space requirements have resulted in the replacement of packed columns by pulsed columns, or by other more compact contactors, in more recent installations for reprocessing irradiated reactor fuel. 

Pulsed-reactant procedures [192—196] allowed pulsing of the alcohol and/or the photon flux in systems involving alcohol vapour flowing over a powdered sample of the metal oxide (cf. Fig. 10). Surfaces of the metal oxide were preconditioned by heating to 623 K either in the N2 stream (referred to as mildly reduced surfaces) or in a stream of oxygen (referred to as pre-oxidised surfaces) and cooled prior to contact with a pulse of reactant(s). Such reactant pulses then passed through the packed GLC column for separation and subsequent quantitative analysis by the flame ionisation detector. Adsorption of reactant alcohol on the preconditioned... 

Packed columns were used in the first Windscale plant (Sellafield, UK). Pulsed columns were used at Hanford (USA), in the old Eurochemic plant at Mol (Belgium), and are currently in use in the newer La Hague and THORP plants. Mixer-settlers have be used at Savannah River (USA), in the Magnox plant at Sellafield (UK), and at La Hague (France). Centrifugal extractors have bear installed at Savannah River and at La Hague. 

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