Industry knows only one means of obtaining an excellent product, and
that is to diminish the quantity of fine alcohol which comes from a same
lot of spirits, and to make a large number of successive distillations.
Hence the large expenses attending rectification, which produce fine
alcohols necessarily at an elevated price. We may remark, in passing,
that the toxic action of commercial alcohols is in great part caused by
the presence of essential oils, amylic alcohol, and ethers, absolutely
pure alcohol, as compared with these, being relatively innocent.
Why is it that our present apparatus cannot produce good results in
rectifying alcohol? Because they are limited by the temperature at which
they must operate. Between 78° and 100° the tension of the vapors of all
the liquids mixed in the spirits is considerable for each of them; they
all pass over, then, in certain proportions during the operation of
rectification.
We have been led, by examining the theoretical question, to ascertain
that the proportion of alcohol which evaporates from a mixture is
maximum at low temperatures; consequently, we should seek to establish
some arrangement which can realize the following conditions: (1) Render
variable, at will, the temperature of the boiling liquid; and (2),
render variable the pressure of the vapors which act on the liquid.
Thus, to effect the rectification of alcohol it suffices to cause its
ebullition at very low temperatures, and to keep up the ebullition
without changing such temperatures when once obtained.
It is exactly these two conditions that we have fulfilled in the
apparatus that we have just installed in our factory in Rue Immeubles
Industriels, at Paris.
By their arrangement, which is shown in the opposite figure, they form
a mechanical system permitting of the rectification of alcohols at
temperatures as low as -40° or even -50°. They verify experimentally, by
their operation, the theoretical deductions which precede. The boilers,
A, which, in an industrial application, may be more numerous, receive
their supply of spirits from the country distilleries in the vicinity of
the factory. There may even be introduced directly into them _vinasses_,
or washes, that is to say, liquids, such as are obtained by alcoholic
fermentation.
Above the boiler rises a rectifying column composed of superposed plates
inclined one over the other, and surmounted by a tubular condenser,
which serves to effect the retrogression of the first condensation by
means of a current of water supplied by the reservoir placed above.
On leaving this condenser, the vapors which have escaped condensation
pass into the refrigerator, C, where they are totally condensed by a
current of water which goes to the reservoir above.
The first products obtained contain ethers and impure alcohols, which
are collected in the reservoir, E.
When the first products have been thus introduced into the reservoir,
and it is ascertained by tasting that good alcohol is passing over,
the liquid produced is directed into the second boiler, F. The sliding
valve, operated by a screw having a very fine pitch, establishes a
communication between the refrigerator, C, and the second boiler, F. The
office of this valve we shall learn further on. This first rectification
is performed in a vacuum, for a system of metallic pipes connects the
entire apparatus with an air-pump, O. The temperature at which the
liquids shall enter into ebullition in the boilers, A A, may, then, be
regulated in advance.
The operations will be carried on with a more or less complete vacuum,
according to the nature of the products to be rectified. The distiller
will have to be guided in this by practice alone.
The good tasted products are received in boiler No. 2, F, and there the
liquids are submitted to the action of an almost absolute vacuum. As we
have before said, their temperature falls immediately and spontaneously.
The vapors which issue from this liquid contain almost solely pure
alcohol. The other substances, which passed over in the first
distillation, no longer emit vapors at temperatures ranging between -10°
and +5°. Their temperature is shown by a thermometer running into the
boiler, F.
These vapors, purified by ebullition at a low temperature, rise into a
second rectifying column, G, which terminates in the refrigerator, H,
filled with liquid sulphurous anhydride. This refrigerator is like those
which we employ in our sulphurous anhydride frigorific apparatus. Under
the action of a special pump, M, this liquid produces and maintains a
constant temperature of -25° to -30° in the refrigerator. The vapors of
alcohol condense therein at this low temperature, and the cold liquid
alcohol flows into the lower part of the refrigerator.
By the action of a return cock, a portion of this liquid falls upon
the plates of the column, G, and descends, while the vapors are rising
therein. The other portion of the liquid obtained flows into the
reservoir, K, at the beginning of the operation, and into the reservoir,
L, during all the remainder of the rectification. The ice-making machine
keeps up of itself alone the two operations.
In fact, the exhaust of the steam engine which actuates the sulphurous
anhydride pump is directed into a worm which circulates through the
first boiler, A, and the refrigerator, H, of the frigorific machine
keeps up the second rectification, which was brought about below the
surrounding temperature, and which for this reason takes place without
necessitating any combustion of coal. It suffices to cause the current
of water which issues from the condenser of the frigorific machine to
pass into the worm of the boiler.
We have, then, two results, two like operations, both produced by
the working of a single machine. Moreover, these two operations are
performed _in vacuo_, and we know that under these conditions they are
effected at lower temperatures. Owing to this fact, likewise, the weight
of the water that must be evaporated diminishes just so much. Now, one
kilogramme of water requires 636 heat units to cause it to pass from the
liquid to the gaseous state, while one kilogramme of alcohol requires
only 230 heat units to vaporize it. Thus every decrease of temperature
in rectification has for an immediate corollary an important economy of
fuel, which is proved by the diminution of radiation, and by the less
quantity of water to be distilled.
Between the boilers, A, in which is maintained a temperature bordering
on +50° to +60°, and the refrigerator, H, in which is easily obtained
a temperature of -30° to -40°, there is at our disposal a range of
temperature of nearly 100°, an immense difference compared with that
which can be made use of in ordinary apparatus. Thanks to this powerful
factor, which is manageable at will, we can take directly from the
apparatus alcohols marking 98 and 99 degrees by the centigrade
alcoholmeter. Such results are unobtainable by the usual methods.
We have likewise ascertained that at low temperatures the ebullition of
alcohol is as active as at near 100°.
For a same range of temperature between the boiler and the refrigerator,
the weight of alcohol which distills in an hour is constant. By the
operation of the valve, D, it becomes easy to allow all the liquid
condensed in the first refrigerator to pass into the second boiler;
and thus the second rectification, which is effected in a more perfect
vacuum, is supplied with exactness. The object of this valve, then, is
to allow the liquid to pass, and yet to cut off the pressure in such
a way as to have a double fall of temperature throughout the whole
apparatus; from 60° to 20° in the first operation, and from 0° to -40°
in the second. We may add that the regulation of the valve is extremely
easy, because of the screw which actuates it.
To sum up the commercial advantages that our process procures, we may
say that it realizes the following _desiderata_: 1. With the cost of a
single distillation we have, at once, distillation and rectification,
or a single expense for two results. 2. With one operation at a low
temperature we obtain products which are almost impossible to get even
by an indefinite number of rectifications at a high temperature, the
temperature having an intrinsic value in the operation. 3. The alcohols
obtained are wholesome, and can be put on the market without danger. 4.
Their superior quality gives these alcohols an extra value difficult
to calculate, but which is very notable. 5. The whole operation being
performed in closed vessels, there is absolutely no waste. 6. For the
same reason there is scarcely any danger of fire. 7. The management of
the works and the service are performed by the pressure of the gases
entirely; there are only a few cocks to be turned to perform all the
interior maneuvers, empty and fill the vessels, etc. Hence economy in
_personnel_.
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