Some time ago, Mr. Laurent Naudin, it will be remembered,[1] devised a
method of converting the aldehydes that give a bad taste and odor to
impure spirits, into alcohol, through electrolytic hydrogen, the
apparatus first employed being a zinc-copper couple, and afterward
electrolyzers with platinum plates.
[Footnote 1: See SCIENTIFIC AMERICAN SUPPLEMENT of July 29, 1882, p.
5472.]
His apparatus had been in operation for several months, in the
distillery of Mr. Boulet, at Bapeaume-les-Rouen, when a fire in
December, 1881, completely destroyed that establishment. In
reconstructing his apparatus, Mr. Naudin has availed himself of the
experience already acquired, and has necessarily had to introduce
important modifications and simplifications into the process. In the
zinc-copper couple, he had in the very first place proposed to employ
zinc in the form of clippings; but the metal in this state presents
grave inconveniences, since the subsidence of the lower part, under the
influence of the zinc's weight, soon proves an obstacle to the free
circulation of the liquids, and, besides this, the cleaning presents
insurmountable difficulties. This is why he substituted for the
clippings zinc in straight and corrugated plates such as may be easily
found in commerce. The management and cleaning of the pile thus became
very simple.
[Illustration: FIG. 1.--APPARATUS FOR HYDROGENIZING IMPURE SPIRITS.]
The apparatus that contains the zinc-copper couple now has the form
shown in Fig. 1. It may be cylindrical, as here represented, or, what is
better, rectangular, because of the square form under which the sheets
of zinc are found in commerce.
In this vessel of wood or iron plate, P, the corrugated zinc plates, b,
b', b", are placed one above the other, each alternating with a flat
one, a, a', a". These plates have previously been scoured, first with a
weak solution of caustic soda in order to remove every trace of fatty
matter derived from rolling, and then with very dilute hydrochloric
acid, and finally are washed with common water. In order to facilitate
the disengagement of hydrogen during the reaction, care must be taken to
form apertures in the zinc plates, and to incline the first lower row
with respect to the bottom of the vessel. A cubical pile of 150
hectoliters contains 105 rows of No. 16 flat and corrugated zinc plates,
whose total weight is 6,200 kilogrammes. We obtain thus a hydrogenizing
surface of 1,800 square meters, or 12 square meters per hectoliter of
impure spirits of 50° to 60° Gay-Lussac. The raw impure spirits enter
the apparatus through the upper pipe, E, and, after a sufficient stay
therein, are drawn off through the lower pipe, H, into a reservoir, R,
from whence, by means of a pump, they are forced to the rectifier.
The hydrogen engendered during the electrolysis is disengaged through an
aperture in the cover of the pile.
As a measure of precaution, the hydrogen saturated with alcoholic vapors
may be forced to traverse a small, cooled room. The liquefied alcohol
returns to the pile. At a mean temperature of 15°, the quantity of
alcohol carried along mechanically is insignificant. In order to secure
a uniformity of action in all parts of the spirits, during the period
devoted to the operation, the liquid is made to circulate from top to
bottom by means of a pump, O. The tube, N, indicates the level of the
liquid in the vessel. The zinc having been arranged, the first operation
consists in forming the couple. This is done by introducing into the
pile, by means of the pump, O, a solution of sulphate of copper so as to
completely fill it.
The adherence of the copper to the zinc is essential to a proper working
of the couple, and may be obtained by observing the following
conditions:
1. Impure spirits of 40° Gay-Lussac, and not water, should be used as a
menstruum for the salt of copper.
2. The sulphatization should be operated by five successive solutions of
½ per cent., representing 20 kilogrammes of sulphate of copper per 100
square meters of zinc exposed, or a total of 360 kilogrammes of sulphate
for a pile of 150 hectoliters capacity.
3. A temperature of 25° should not be exceeded during the
sulphatization.
The use of spirits is justified by the fact that the presence of the
alcohol notably retards the precipitation of copper. As each charging
with copper takes twenty-four hours, it requires five days to form the
pile. At the end of this time the deposit should be of a chocolate-brown
and sufficiently adherent; but the adherence becomes much greater after
a fortnight's operation.
Temperature has a marked influence upon the rapidity and continuity of
the reaction. Below +5° the couple no longer works, and above +35° the
reaction becomes vigorous and destroys the adherence of the copper to
such a degree that it becomes necessary to sulphatize the pile anew. The
battery is kept up by adding every eight days a few thousandths of
hydrochloric acid to a vatful of the spirits under treatment, say 5
kilos. of acid to 150 hectoliters of spirits. The object of adding this
acid is to dissolve the hydrate of oxide of zinc formed during the
electrolysis and deposited in a whitish stratum upon the surface of the
copper. The pile required no attention, and it is capable of operating
from 18 months to two years without being renewed or cleaned.
[Illustration: FIG. 2.--ELECTROLYZING APPARATUS.]
Passing them over, the zinc-copper couple does not suffice to deodorize
the impure spirits, so they must be sent directly to a rectifier. But,
in certain cases, it is necessary to follow up the treatment by the pile
with another one by electrolysis. The voltameters in which this second
operation is performed have likewise been modified. They consist now
(Fig. 2) of cylindrical glass vessels, AH, 125 mm. in diameter by 600 in
height, with polished edges. These are hermetically closed by an ebonite
cover through which pass the tubes, B' C' and B C, that allow the
liquid, E+E-E'+E', to circulate.
The current of spirits is regulated at the entrance by the cock, R,
which, through its division plate, gives the exact discharge per hour.
In addition, in order to secure great regularity in the flow, there is
placed between the voltameters and the reservoir that supplies them a
second and constant level reservoir regulated by an automatic cock.
In practice, Mr. Naudin employs 12 voltameters that discharge 12
hectoliters per hour, for a distillery that handles 300 hectoliters of
impure spirits every 24 hours. The electric current is furnished to the
voltameters by a Siemens machine (Fig. 3) having inductors in
derivation, the intensity being regulated by the aid of resistance wires
interposed in the circuit of the inductors.
The current is made to pass into the series of voltameters by means of a
commutator, and its intensity is shown by a Deprez galvanometer. The
voltameters, as shown in the diagram, are mounted in derivation in
groups of two in tension. The spirits traverse them in two parallel
currents. The Siemens machine is of the type SD2, and revolves at the
rate of 1,200 times per minute, absorbing a motive power of four horses.
[Illustration: FIG. 3.--ARRANGEMENT OF THE SIEMENS MACHINE.]
The disacidification, before entering the rectifier, is effected by the
metallic zinc. Let us now examine what economic advantages this process
presents over the old method of rectifying by pure and simple
distillation. The following are the data given by Mr. Naudin:
In ordinary processes (1) a given quantity of impure alcohol must
undergo five rectifications in order that the products composing the
mixture (pure alcohol, oils, etc.) may be separated and sold according
to their respective quality; (2) the mean yield in the first
distillation does not exceed 60 cent.; (3) the loss experienced in
distillation amounts, for each rectification, to 4 per cent.; (4) the
quantity of essential oils (mixture of the homologues of ethylic
alcohol) collected at the end of the first distillation equals, on an
average, 3.5 per cent.; (5) the cost of a rectification may be estimated
at, on an average, 4 francs per hectoliter.
All things being equal, the yield in the first operation by the electric
method is 80 per cent., and the treatment costs, on an average, 0.40
franc per hectoliter. The economy that is realized is therefore
considerable. For an establishment in which 150 hectoliters of 100°
alcohol are treated per day this saving becomes evident, amounting, as
it does, to 373 francs.
We may add that the electric process permits of rectifying spirits
which, up to the present, could not be rectified by the ordinary
processes. Mr. Naudin's experiments have shown, for example, that
artichoke spirits, which could not be utilized by the old processes,
give through hydrogenation an alcohol equal to that derived from Indian
corn.--_La Nature_.
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