Mixing and settling

In principle, at least, any mixer may be coupled with any settler to provide the complete stage. There are several combinations which are especially popufar. Continuously operated devices usually, but not always, place the mixing and settling functions in separate vessels. Batch-operated devices may use the same vessel alternately for the separate functions. 

When two immiscible liquids are stirred together, one phase becomes dispersed as tiny droplets in the second liquid which forms a continuous phase. Liquid-liquid extraction, a process using successive mixing and settling stages (Volume 2, Chapter 13) is one important example of this type of mixing. The liquids are brought into contact with... 

The Chlorex process utilizes simple countercurrent mixing and settling tanks (four to seven stages) or modern vertical packed towers. Solvent recovery involves conventional flash columns and strippers operated under vacuum (26 to 28 inches of mercury) at about 300° to 325° F. Low temperatures are desirable to minimize decomposition and formation of hydrochloric acid. 

Fig. 6 Mixing and settling zones in the spiral column undergoing type-J planetary motion. (From Ref. [12].)...

The main parameters affecting scale-up have been analyzed in detail by Sutherland et al. [10]. For scale-up of CCC to be successful, they recommended that two measures or responses had to be maintained as the process was scaled up retention of the stationary phase and resolution of the sample components. It was emphasized that even if it was possible to retain phases as the tubing bore increased, it was possible that the hydrodynamics of the mixing and settling zones may not work as well, as the bulk volume to surface area ratio increased. 

The effect of flow on resolution is shown in Fig. 2 for the process CCC [10] running at 1200 rpm. The resolution is between benzyl alcohol and phenyl ethanol resolved using the heptane-ethyl acetate-methanol-water (1.4 0.1 0.5 1.0) phase system. Resolution drops off with increasing flow as would be expected, as the sample will have experienced fewer mixing and settling steps before it elutes and... 

However, before this can be realized, the engineering of the coil planet centrifuge will have to be made more reliable. The cyclical forces that produce the unique mixing and settling zones within the coiled tubes can cause them to shake apart and loosen. Janaway et al. [12] have solved this problem by developing new techniques for winding coils. As the scale in-... 

The success of this process depends on the low solubility of calcium carbonate, which is also what allows this process to be used for small-scale production of sodium hydroxide by a batch process. For batch operation, the functions such as slaking, mixing, and settling may be carried out in the same wooden (or steel) vessel. Separate units are required for these steps in the continuous process. A further chemical feature important to the recycle of the spent lime of this process is the relatively easier thermal loss of carbon dioxide from calcium carbonate than from sodium carbonate. Since sodium bicarbonate (NaFICOs) may be calcined at 175°C to obtain carbon dioxide loss, it might be expected that sodium hydroxide could be made by heating sodium carbonate at a higher temperature followed by hydration of the resulting oxide (Eqs. 7.21 and 7.22). 

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