Continuous pulsed packed column

It is shown, that the performance of a pulsing packed column can be split up into its two component parts, the pulses and the zones in between pulses. The pulses can be described as parts of the bed already in the dispersed bubble flow regime the zones-in between the pulses as parts of the bed still in the gas-continuous regime. The pulse frequency is linearly dependent upon the real liquid velocity. The properties of the pulse, like holdup, velocity and height are quite independent upon all the parameters except gas flow rate. 

Pulsed packed column HETS increases exponentially with diameter. 0.7 m at 1 m diameter max. diameter 2.5 m superficial velocity of the combined flow of continuous and discontinuous phases 5 to 6.4 with usual value of 5.5 L/s m. ... 

Extraction apparatus with continuous phase contact Spray column Packed column Pulsed packed column Rotating disc contactor, Oldshue-Rushton column, Graesser-Contactor, Kuhni column Podbiehiiak- Extractor, Luigi-Westfalia- Extractor, De Laval-Extractor... 

In pulsed packed columns [6.19, 6.43], the loadability decreases with increasing pulsation frequency, but generally increases with larger dimension of the filling material and an increasing void fraction. The type of mass transfer, continuous -> disperse or disperse - continuous, generally influences the droplet motion and separation efficiency ... 

Pulsed-packed column Continuous seeded copolsmierization of styrene and methyl methacrylate 181... 

There are three wo well known types of column that can be used for continuous countercurrent liquid/liquid contacting rotating disc contactors (RDC) and pulsed packed columns (PPC) (these are not to be confused with three-phase packed coplumn reactors, operated under pulsed flow conditions, see section 4.7.2.3). 

When a narrow residence time distribution is desired, good heat transfer will usually require high flow rates, which in combination with a given residence time would result in long or tall reactors. Occasionally very long coaxial tubes are used for single liquid phase processes. For processes wiUi a liquid as the continuous phase, a cascade of stirred tanks (sections 3.3.3 and 7,2,1,3) or a pulsed pack column (section 45,15) may then be interesting alternatives. 

HoedemsJcers, G.F. and Thoenes, D. (1990), Continuous Emulsion Polymerisation in a Pulsed Packed Column, in PJ.Lemstra and L.A.Kleintjes, Eds. 

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. 

FIG. 15 53 Effect of pulsing on extraction in a packed column methyl isobutyl ketone-acetic acid-water (continuous). Tower diameter = 1.58 in, 27-in depth of V4-in Raschig rings. = Vc = 7.5 to 10. To convert inches to centimeters, multiply by 2.54. [Data of Chanhy, von Berg, and Wiegandt, Ind. Eng. Chem., 47, 1153 (1.9.55), with permission. ... 

The best values of the parameter Cj are 1.51, 1.36, and 2.01 for no mass transfer, d and c direetion of transfer respectively. The product af is considered as the agitation variable in the equation, since the fit could not be improved if a and / were treated separately. The average absolute value of the relative deviation in the predicted values of d 2 from the experimental points is 16.3%. Even in packed columns, the separation can be substantially improved by pulsing of the continuous phase resulting from greater shear forces that reduce the drop size and increase the interfacial area [1, Chapter 8]. 

One of the popular methods for evaluating effective diffusivities in heterogeneous catalysts is based on gas chromatography. A carrier gas, usually helium, which is not adsorbed, is passed continuously through a column packed with catalyst. A pulse of a diffusing component is injected into the inlet stream and the effluent pulse recorded. The main advantages of this transient method are its applicability to particles of arbitrary shapes, and that experiments can be carried out at elevated temperatures and pressures. Haynes [1] has given a comprehensive review of this method. 

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... 

Liquid-liquid extraction can take place in a column with various internals to foster contact between the dispersed and continuous liquid phases. Internals can include sieve trays, baffle trays and packing, as well as mechanical agitation and pulsing of the liquid. 

Addition of a strongly competing ion can enhance desorption of As (Darland and Inskeep, 1997b). In a column experiment at pH 4.5, a one pore volume pulse of 143 fiM As(V) was added to a column packed with sand, followed by elution with 20 pore volumes of As(V)-free water. About 20% of the As(V) was recovered. The column was then continuously eluted with 1420 iM P(V), which resulted in an additional 40% recovery of As(V). 

For readable discussions of plug flow and the concept of dispersion the reader is referred to the literature [1, 2, 17]. Here we shall confine ourselves to a brief illustration of axial and radial dispersion. Let us consider the behavior of a tracer introduced into a stream flowing through a packed bed reactor, as sketched in Fig. 7.12. Here (a) shows the axial dispersion or spread by the time it reaches the exit of a tracer pulse introduced uniformly over the cross-sectional area of the column at a given axial position. Figure 7.12b depicts the radial dispersion of a tracer introduced continuously at a point source. 

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