Plates

The plates in both analyser and rectifier are perforated as already described. The arrangement of the wash pipes over the plates in the rectifier is shown in Fig. 123.

Fig. 123.-The inlet is connected by a bend to the corresponding pipe on the plate above. The outlet to the corresponding pipe on the plate below.

Starting And Control Of Coffey's Still

To start the still, steam is turned on so as gradually to heat up first the analyser and then the rectifier. When the latter is warm enough, as shown by the temperature at the level of the spirit plate, the wash pump is started. After a time the rectifying column becomes charged with enough alcohol to begin running off. When running smoothly the steam pressure at the base of the analyser and at the upper part of the vapour pipe are kept as steady as possible. The actual pressures vary with the size and proportions of the still. Samples are continuously taken from 1. Vapour at the base of the analyser to test the exhaustion of wash.

2. The vapour pipe from analyser to rectifier.

3. The spirit plate. The running of the still is controlled by keeping the temperature correct at the spirit plate, and by the indications of the pressure already referred to, and by the strength of the samples.

French Stills

In France the rectification of alcohol has been brought to a very high pitch of perfection. Innumerable modifications in design of the stills have been introduced with the object of purifying the final product.

Two types of distilling plant will be described. A large number of the stills in use are based on the same principles as those to be described, though the differences in detail are very numerous. For further details see Mariller,1 and Messrs. Egrot and Grange's trade-catalogue.

Continuous Distillation Direct Rectification Plant

Fig. 124 is a diagram of a still of this type. The wash to be distilled flows from a to the preheater b, where its temperature is raised by heat exchange with the spent wash. The preheated wash enters the wash column c at h. From the rectifying column d, the pasteurised alcohol (see p. 311) is drawn off near the top, passing to F, and the head products pass to m. The amyl alcohol is removed at G.

Sometimes the wash column is placed by the side of the rectifying column. The procedure followed, and the results obtained, are very similar to those of the Coffey still.

1 La Distillation fractionnee, 1917.

Fig. 124.

In some cases small subsidiary columns are provided to free the amyl alcohol and head products from ethyl alcohol. The latter is in this case returned to the main column.

As already stated, the removal of the head products is more difficult to effect from concentrated than from dilute aqueous alcohol. If a more complete removal of these impurities is required, a purification of the alcohol before concentration in the rectifying column must be effected. The distilling plant now to be described is designed for this purpose.

Continuous Distillation and Indirect Rectifying Plant The wash is first distilled in the still shown in Fig. 125.

The wash to be distilled flows from the reservoir a through the pre-heater b, in which its temperature is raised by a heat exchange with the spent wash. It enters the column at g and flows down, meeting steam which is admitted at h. The plates above g exercise a small rectifying effect.

The vapour from the top of the column passes to the condensers d and e, which supply the necessary condensate to the column. The distillate flows down to f.

Fig. 125.

Fig. 126.

By this means spirit containing about 40 per cent of alcohol is obtained, which is then continuously rectified in a second still, Fig. 126.

The spirit prepared in the previous operation flows from a to the preheater b, in which its temperature is raised by heat exchange with the exhausted liquid leaving the base of g. It then passes by the pipe c to a point t in the upper part of column d. At this point it is discharged on to a plate of the column, down which it flows, being subjected to a gentle ebullition. By this means it is gradually freed from head products which, together with some alcohol, tend to accumulate at the top of the column. The plates above t exercise a certain fractionating action by means of which the head products are freed to a considerable extent from alcohol and pass after partial condensation in n and q to the test glass e.

The spirit, partially freed from head products but still containing most of the impurities of the amyl alcohol class, leaves the base of the column with a slightly reduced alcoholic content, owing to the unavoidable loss of alcohol mixed with the head products at e. It passes by pipe m to the distilling column g. The vapour evolved in g is rectified in h in the manner already described The finished alcohol is run off at K, and the oils from some point s near the base of the column. A further quantity of head products are run off by x to the test glass p. In some cases this part of the distillate is returned to the appropriate point in the column d, so as to avoid collecting two separate lots of head products.

Fig. 127.

German Still

Fig. 127 represents the Ilges continuous distilling and rectifying plant.

The wash to be distilled flows from the reservoir A and regulator b through the tubular dephlegmator c to the wash column d. The wash flows down d, meeting steam which is introduced at x, and its rate of outflow is regulated by e, and its freedom from alcohol tested at f. The vapour from d enters the base of the column g, which is provided with an additional water-cooled dephlegmator h. The column g is filled with porcelain balls. The liquid condensed at the base of g flows through the oil separator k to a small column l down which it flows, and leaves the base of this column free from alcohol. The vapour evolved in the column l is returned to g.

Samples of the liquid leaving the base of l are tested at m to see that they are free from alcohol.

The vapour leaving the top of G consists of very strong alcohol freed from oils but still containing aldehyde and other head products. The removal of these is effected in the column n, which is packed with porcelain balls. The vapour on entering the column n is heated by the steam coil o. The head products tend to accumulate at the top of the column (near which a water-cooled dephlegmator is placed to supply the condensate necessary for the proper working of the column) and pass over to the condenser v and test glass z, having been freed as far as possible from alcohol. The condensate in the column flows downwards and is again submitted to a partial evaporation by the steam coil p. The liquid leaving the base of the column consists of purified alcohol. It is cooled in the condenser t. The rate of flow is regulated by the test glass w.

Fractionation of Fusel Oil Distillate

A technical distillate from fusel oil, on fractionation on a laboratory scale with a Young 12 pear-bulb still-head, gave indications that it is capable of being resolved into fairly pure fractions of the individual compounds. One litre of it was therefore distilled from a glass flask fitted with a plain glass tube as still-head, 4 cm. in diameter by 140 cm. high, which was completely filled with Lessing contact rings made of copper ; approximately 4000 1/4-inch rings were employed.