Laminar jet absorber

Both phases in a continuous form packed columns thin-film contactors wetted-wall columns contactors with flat surface laminar jet absorber disc (sphere) columns... 

There are several other types of apparata used for reactive absorption, though these are less widespread. In mechanically agitated bubble columns it can be assumed that both phases are ideally mixed, whereas in the jet absorber, the gas stream breaks on a liquid surface and is dispersed in the liquid. In spray towers and venturi scrubbers, liquid is sprayed as fine droplets. Thin-jilm contactors, in which liquid film is scrapped from the walls by impellers, are applied for reactive absorption in viscous liquids. Some units, such as wetted-wall columns, contactor, laminar jet absorber and disc (sphere) column are used mainly in laboratory. 

Measurements of kinetic parameters of liquid-phase reactions can be performed in apparata without phase transition (rapid-mixing method [66], stopped-flow method [67], etc.) or in apparata with phase transition of the gaseous components (laminar jet absorber [68], stirred cell reactor [69], etc.). In experiments without phase transition, the studied gas is dissolved physically in a liquid and subsequently mixed with the liquid absorbent to be examined, in a way that ensures a perfect mixing. Afterwards, the reaction conversion is determined via the temperature evolution in the reactor (rapid mixing) or with an indicator (stopped flow). The reaction kinetics can then be deduced from the conversion. In experiments with phase transition, additionally, the phase equilibrium and mass transport must be taken into account as the gaseous component must penetrate into the liquid phase before it reacts. In the laminar jet absorber, a liquid jet of a very small diameter passes continuously through a chamber filled with the gas to be examined. In order to determine the reaction rate constant at a certain temperature, the jet length and diameter as well as the amount of gas absorbed per time unit must be known. 

The major difference between this reactor and other gas-liquid reactors such as the wetted-wall column, the laminar-jet absorber, the disk contactor, and the stirred cell is that the experimenter has independent control of the physical factors, such as individual film resistances and interfacial area. 

Various absorbers used for the measurements of absorption rates in gas-liquid reaction processes can also be used to make similar measurements for the gas-liquid-solid reaction processes. Commonly-used absorbers are the laminar-jet absorber (Fig. 5-19). the wetted-wall column absorber (Fig. 5-20), the rotary-drum absorber, the disk column absorber (Fig. 5-21), the single-pellet absorber (Fig. 5-22). and the gradientless contactor (Fig. 5-23). The key features of these absorbers... 

The possible existence of an interface resistance in mass transfer has been examined by Raimondi and Toor(12) who absorbed carbon dioxide into a laminar jet of water with a flat velocity profile, using contact times down to 1 ms. They found that the rate of absorption was not more than 4 per cent less than that predicted on the assumption of instantaneous saturation of the surface layers of liquid. Thus, the effects of interfacial resistance could not have been significant. When the jet was formed at the outlet of a long capillary tube so that a parabolic velocity profile was established, absorption rates were lower than predicted because of the reduced surface velocity. The presence of surface-active agents appeared to cause an interfacial resistance, although this effect is probably attributable to a modification of the hydrodynamic pattern. 

Under these conditions, the interfacial area in a given reactor can be found by measuring the rate of absorption of O2 with the same partial pressure of O2, the same absorbent, and the same temperature and pH in laboratory equipment such as a wetted falling film, laminar jet, or stirred vessel in which the interfacial area A is known. It is emphasized that... 

This general analysis of the chlorine-toluene system based upon first order reacticxi was developed in parallel with a series of experimental measurements (9), in which chlorine was absorbed in toluene in a laminar jet. This absorption device provides remarkable control of surface area and with a flat velocity profile the penetration time is reasonably well defined so that the penetration theory can be directly applied without any uncertainty concerning the complications of convective transport. Experimental mixing cup temperatures for Cl -toluene ranged from i C to 6°C. These can be interpreted as the amount of heat accumulated per unit of Jet surface as the jet plunges into the receiver via the equation... 

A number of experiments have been performed absorbing sulphur trioxide into a laminar Jet of liquid toluene (16). In these experiments, an estimate of the temperature achieved on the surface of the jet on entry into the Jet receiver can be obtained by interpreting the mixing cup temperature of the Jet as it becomes fully mixed in the receiver take-off line. The form of the heat transfer profile is as shown in Fig. 16. The depth of heat penetration into the Jet is assumed to be given by... 

In certain cases, when the chemical system is more complicated a "point" model may not be applicable (67,69). Under these conditions the theoretical predictions would also have been either too complicated -if indeed possible- or would lead to large errors in several instances. On the other hand, it appears that if one builds a "complete" (or integral) model of the gas absorber, the behaviour of the industrial equipment (for instance, total absorption rate or the composition of gas or liquid leaving the column etc.) can be obtained with sufficient accuracy from the results of an appropriate sphere column. The rules to be obeyed by the "complete" model are as given in Table 13 if both phases are essentially in plug flow. Recently Charpentier and his coworkers (71,72) tried to simulate a venturi scrubber by a laminar jet. They have assumed the validity of Eqns. (21) -(24), in other words the rules given in Table 13. Strictly... 

On using a laminar liquid jet absorber, the second-order rate constant for this reaction at 20°C was found to be 1.4 X 10 M s with hydroxide and 2.8 x 10 M s with bicarbonate, which agree well with the rates calculated earlier. Injecting chlorine diluted in helium at low pressure into unbuffered hydroxide at pH 8-11 to avoid depletion of hydroxide at the interface yields a similar second-order rate constant of 6 x 10 M s at 20°C. ... 

Pure sulphur dioxide is absorbed at 295 K and atmospheric pressure into a laminar water jet. The solubility of SO2, assumed constant over a small temperature range, is 1.54 kmol/m-1 under these conditions and the heat of solution is 28 kJ/kmol. 

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