Packed columns behaviour

The specialities of chromatographic behaviour of cypermethrin, permethrin, X-cyhalothrin, deltamethrin and fenvalerate were investigated in this work. Gas chromatographic determination was cai ry out with use of packed column with stationai y phase of different polarity (OV-101, OV-210 OV-17) and capillary and polycapillary columns with non-polai ic stationary phase. Chromatographic peak identification was realized with attraction GC-MS method. 

Gayler, R. and Pratt, H. R. C. Trans. Inst. Chem. Eng. 31 (1953) 69. Liquid-liquid extraction. Part V — Further studies of droplet behaviour in packed columns. 

Fernandez, M. A., Laughinghouse, W. S., and Carta, G. J. Chromatogr. A, 746 (1996) 184-198. Characterisation of protein adsorption by composite silicapolyacrylamide gel anion exchanges II mass transfer in packed columns and predictability of breakthrough behaviour. 

B. Benadda, K. Kafoufi and M. Otterbein, Hydrodynamic behaviour of packed column under high pressure, High Pressure Chemical Engineering, Process Technology Proceedings 12, 679-685, by Ph. Rudolf von Rohr and Ch. Trepp, Elsevier, Amsterdam (1996). 

Hydrodynamic Behaviour of Packed Column under High Pressure... 

This study, which contributes towards the understanding of hydrodynamic behaviour of gas-liquid reactors at elevated pressure, has shown the influence of pressure on the gas flow in a packed column through the axial dispersion coefficient. The gas flow diverges from plug flow when the pressure increases. As for the gas hold-up, an important parameter for the calculation of the reactional volume of a reactor, the pressure has no effect on this parameter in the studied range. This result allows to extrapolate gas hold-up values obtained... 

Hanson, M. Aspects of retention behaviour of steroids in packed column supercritical fluid chromatography. Chromatographia, 1995, 40, 58-68... 

Ponter et al. [8c] investigated the effect of adding an interface-active substance on the efficiency of a packed column. They observed an increase in packing efficiency corresponding to a change of the wetting behaviour as determined by contact angle... 

In addition, the separating behaviour of a packed column cannot be completely described from a physical point of view by only one parameter, such as the HETP or the HTU value. Sizniann [159] has shown that material transfer in a packed column is the more intense the easier it is for the components to get from inside one phase to the liquid-vapour interface and from there to the interior of the other phase. Hence, two resistances to transfer, Wp and IFp, for material transport in the vapour and liquid phases, respectively, have always to be considered. The magnitudes of these resistances depend on the mean path travelled in the respective phase, the frequency of mixing at certain points along the flow path, the formation of turbulence and other factors which have been discussed in chap. 4.2. The distribution of the resistances to mass transfer for 7 different packings as determined by Sizmann is given in Table 18. It is seen that the proportion of the resistance in the vapour phase may vary from 9 to 96% of the total resistance. 

Another point of interest is the dynamic behaviour of packed columns. Heise, Hiller and Wagner [162] investigated the response of a packed column to marked disturbances of the liquid-vapour ratio in the countercurrent distillation of the ternary, almost ideal mixture ethyl acetate-benzene-trichloroethylene (see chap. 4.2, 4.15). 

Roes, A.W.M., The Behaviour of a Gas-Solid Packed Column at Trickle Flow, Ph.D. thesis, Twente University of Technology, The Netherlands, 1978. 

A number of tests were made by Alper and Danckwerts (68,69) to see whether the model could be successfully used to predict gas absorption behaviour in a packed column. For economical reasons they were unable to work with a packing larger than 1/2 in., and the scaling factor was about 3. It was possible to make the value of kj the same in the sphere column and the... 

Hirata (22) also studied the behaviour of an Oldershaw column, a packed column and a sieve-tray column as distillation reactors for the esterification of ethanol and acetic acid. He found reflux ratio to be an important factor affecting not only separation but also conversion. 

The above remarks apply solely to columns which are correctly packed to an even density with spherical beads which retain their shape, and where the voidage between particles is constant. Under practical conditions, it is not unusual both in laboratory and plant scale units, to find channels passing down long sections of column, resulting from unsatisfactory initial packing, or the movement, attrition or adhesion of resin grains as a result of repeated expansion and contraction. These occurrences clearly result in severe abnormalities of column behaviour. 

On the base of various heterogeneous azeotropic mixtures, as acetone/toluene/water or 1-propanol/l-butanol/water, the distillation behaviour and its modelling in a packed column is discussed. A detailed description of the experimental equipment and the results is presented in (Repke and Wozny, 2002) and in (Repke, 2002), but a brief overview is listed in (Table 1). 

The observed behaviour of the packed column can only be described and explained by regarding of the nonequilibrium model. The equilibrium model fails in this case. The physical reason for the unusual behaviour is based on the volumetric ratio of the both liquid phases in the area of the miscibility gap. As well as the fact, that the liquid phase can flow separately on the packed surface and not in an ideal mixture like in a tray column. A very detailed description is given in (Repke, 2002) furthermore additional heterogeneous mixtures are considered there. 

In the presentation the nonequilibrium model for the calculation of the three-phase distillation in a packed column is presented. The model considers the mass transfer between all three existing phases. A remarkable point is that by using normal two-phase methods mass transfer coefficients and interfacial areas can be calculate in a first step. The study is strongly influenced by the interaction between the development of the model and the experiments. The validation was carried out in a packed column of the institute on experiments at total and finite reflux. Two different heterogeneous azeotropic mixtures have been separated by distillation. The distillation run at finite reflux showed an unusual behaviour, which is based in the heterogeneity of the liquid phase. In this case a nonequilibrium model is needed. A comparison of the simulation results and the experimental specifications shows the performance of the developed... 

From today s point of view, the work published by Mersmann [4, 5] is an exemplary demonstration of how to derive general considerations on the hydraulic behaviour of random packings using the model of film flow in packed columns. It has maintained its scientific relevance until today [10, 11, 14,19],... 

This book also takes into account Billet s [15] experimental data on the hydraulic behaviour of packed columns for the development of a new method for the standard presentation of the fluid dynamics of columns with any type of packing design. The basic principles of the method for determining the separation efficiencies of packed columns have already been publicised in joint presentations and individual publications by the author and Billet [16-18]. 

Figures 7-2,7-3,7-4,7-5 and 7-6 illustrate the behaviour of the dispersed phase throughout the entire operating range of packed columns up to the flooding point.

This behaviour of packed columns was already discussed in previous chapters in relation to gas/liquid systems. 

According to fluid dynamic behaviour of packed column, a maximum mass transfer area in non-pulsed packed columns is expected during droplet flow, mostly for the mass transfer direction C —> D from the continuous to the dispersed phase. 

In contrast to other studies, this book uses a different approach for logging processes within packed columns, which is based on the specific flow behaviour of droplet systems. 

For many years now, there has been a constant demand for low pressure drop column internals in rectification, absorption, stripping and liquid/hquid extraction. The prevailing trend in the chemical industry is to replace tray columns with those containing modem structured and random packings. When planning the design of packed columns, it therefore particularly important to use reliable methods for predicting the mass transfer and hydrodynamic behaviour of the two-phase flow. 

The progress in terms of the accuracy in designing packed columns for gas/hquid and Kquid/liquid system is considerable. The results of this work have led to accurate predictions of the fluid dynamic behaviour of random packing elements, simply based on their geometric form without requiring any chemical engineering tests. 

II Given these conditions, what would be the minimum diameter of a 25 cm column, packed with 5 /an particles, if the column is to show infinite diameter behaviour ... 

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