Packings plugging

This is done in a snout-ended tube (see Fig. 67) with an asbestos plug packed in the snout and timed to allow a rate of flow of air of about 15 c.cs. per minute. A filling of about 24 cms. of wire-form CuO is used, and this is held in place by a small asbestos plug. Behind the boat is placed a short CuO gauze spiral. 

Bubble columns, in which the liquid is the continuous phase, are used for slow reactions. Drawbacks with respect to packed columns are the higher pressure drop and the important degree of axial and radial mixing of both the gas and the liquid, which may be detrimental for the selectivity in complex reactions. On the other hand they may be used when the fluids carry solid impurities that would plug packed columns. In fact, many bubble column processes involve a finely divided solid catalyst that is kept in suspension, like the Rheinpreussen Fischer-Tropsch synthesis, described by Kolbel [1], or the former I. G. Farben coal hydrogen process, or vegetable oil hardening processes. Several oxidations are carried out in bubble columns the production of acetaldehyde from ethylene, of acetic acid from C4 fractions, of vinylchloride from ethylene by oxychlorina-tion, and of cyclohexanone from cyclohexanol. 

Pack the catalyst into a Pyrex combustion tube about 90 cm. long and 15 mm. bore, and place plugs of glass wool at 25 cm. intervals inseit into a tube furnace and adjust to a temperature of 330° full details of the complete apparatus are given in Section 111,72 and Fig. Ill, 72, 1. 

Discussion of the concepts and procedures involved in designing packed gas absorption systems shall first be confined to simple gas absorption processes without compHcations isothermal absorption of a solute from a mixture containing an inert gas into a nonvolatile solvent without chemical reaction. Gas and Hquid are assumed to move through the packing in a plug-flow fashion. Deviations such as nonisotherma1 operation, multicomponent mass transfer effects, and departure from plug flow are treated in later sections. 

Often, complete mixing cannot be approached for economic reasons. Inactive or dead zones, bypassing, and limitations of energy input are common causes. Packed beds are usually predominantly used in plug flow reactors, but they may also have small mixing zones... 

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