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1. * GB780080 (A)
Description: GB780080 (A) ? 1957-07-31
Manufacture of hydrogen cyanide
Description of GB780080 (A)
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The EPO does not accept any responsibility for the accuracy of data
and information originating from other authorities than the EPO; in
particular, the EPO does not guarantee that they are complete,
up-to-date or fit for specific purposes.
PATENT SPECIFICATION
Date of Application and filing Complete Specification: Oct. 18, 1954.
Application made in Germany on Oct. 19, 1953.
Complete Specification Published: July 31, 1957.
780,080 No. 29984/54.
Index at acceptance:-Classes 1(2), F1U(3A:12); 39(3), H(1A:2A:3E1);
and 90, K(4:5).
International Classification:-CO1b, c, H05b.
COMPLETE SPECIFICATION
Manufacture of Hydrogen Cyanide We, KNAPSACK-GRIESHEiM
AicTIENGESELLSCHAFT, a Body Corporate organised under the Laws of
Germany, of Knapsack bei K8ln, Germany, do hereby declare the
invention, for which we pray that a patent may be granted to us, and
the method by which it is to be performed to be particularly described
in and by the following statement:-
The present invention relates to' a process for preparing hydrogen

2. cyanide.
It is already known to convert hydrocarbons with ammonia, in the
presence of noble metal catalysts and in the absence of oxygen, into
hydrogen cyanide, while simultaneously obtaining hydrogen. The process
involves, however, technical difficulties as regards the supply of the
heat required for the reaction. Furthermore, the noble metal catalyst
is not easy to handle and rather 20expensive, especially since in the
long run losses in the noble metal occur.
It is further known that hydrogen cyanide can be obtained from
hydrocarbons and ammonia at temperatures of above 1150C.
in the absence of catalysts in a smooth-walled reaction tube with the
application of a rapid current of gas, using more than 1 mol of
ammonia per gram-atom of carbon present in the hydrocarbon. This
process, however, requires the application of large quantities of heat
which must be transferred very rapidly to the starting mixture by
means of very large heat exchanging surfaces, that is to say, very
narrow tubes, in practice. The time of stay of the gas in the reaction
zone, i.e., in the tubes, must be very short, otherwise the hydrogen
cyanide obtained decomposes. The short time of stay assumes that the
starting materials are conducted rapidly through the reaction tubes,
whereby the rapid heating up of the starting mixture is impaired.
According to another known process the heat required for the reaction
is partially or completely obtained by combustion of a part of the
hydrocarbon. This process also [Price 3/ 61 involves great
difficulties as to apparatus.
Great losses in material occur and there is a danger that the hydrogen
cyanide obtained may be partially saponified by the reaction water
accumulating. 50 Furthermore, some processes are known which describe
the preparation of hydrogen cyanide from hydrocarbons, nitrogen and
hydrogen in an electric arc. These processes provide, however, only
very small yields with 55 respect to energy and in many cases very
small yields of material.
The present invention is based on the observation that these
disadvantages in the preparation of hydrogen cyanide can be 60 avoided
by passing low molecular weight aliphatic hydrocarbons containing 1-4
carbon atoms and at most 1 olefinic bond, together with ammonia
through an electric arc, while using 0.5 to 1.2 and preferably about 1
mol 65 of ammonia per gram-atom of carbon present in the hydrocarbon.
There are preferably used, for example, about 2 mols of ammonia per
mol of ethane and about 4 mols of ammonia per mol of butane. The
reaction 70 time i.e., the time that the gas actually is in the
electric arc ranges from 0.001 to 0.00002 second, a reaction time of
about 0.0001 second being most suitable. It is, however, necessary
that the resultant reaction mixture 75 containing larger quantities of

3. hydrogen in addition to hydrogen cyanide is cooled rapidly after it
has left the electric arc.
When larger amounts of hydrocarbon in relation to the ammonia are used
the formation of acteylene increases, whereas larger amounts of
ammonia give rise to an increased formation of nitrogen by
decomposition.
As starting hydrocarbons may be used low molecular weight
straight-chained or 85 branched aliphatic hydrocarbons, either
saturated or containing at most 1 olefinic bond and containing 1-4
carbon atoms; mixtures of these hydrocarbons, for example methane,
ethane, ethylene, propane, propyX 780,080 lene, butane, butylene,
isobutane or isobutylene; furthermore, natural mixtures of
hydrocarbons, such as natural gas, or mixtures of hydrocarbons
obtained in industry, such as 5gases obtained by hydrogenation
processes.
The reaction according to the invention can be carried out in a common
electric arc, for example between carbon electrodes or cooled metal
electrodes. It is of advantage but not necessary to use direct
current. The reaction is carried out at a low potential down to about
20 volts and a ratio of volt: ampere of about 1:10.
The process of the invention offers the advantage that the
difficulties in supplying the heat indispensable for the endothermic
formation of hydrogen cyanide can be avoided and that no expensive
noble metal catalyst which can be handled only with difficulty is
required. The value of the process is further enhanced by the large
quantities of valuable hydrogen obtained.
An apparatus suitable for use in carrying out the process of this
invention is shown diagrammatically by way of Example in the
accompanying drawing.
A mixture of about equimolecular quantities of ammonia and low
molecular weight hydrocarbons is passed through an electric arc
produced by two electrodes 1 and 2 at such a rate that the mixture is
exposed to the action of the arc for a period within the range from
0.001 to 0.00002 second. The electrode 1, which serves as cathode when
direct current is applied, has a borehole 4 through which the gas
mixture enters a walled-up iron case 3 cooled with water. The cooling
water is supplied through pipe 9 and led off through delivery pipe 10.
The two carbon electrodes are installed in the iron case 3 in such a
manner that no gas can escape. The reaction gases consisting of
hydrogen cyanide vapour, hydrogen and nonreacted gases are cooled down
to atmospheric temperature as quickly as possible in tube 5
constructed as a water cooler, tube 12 serving as supply pipe and tube
11 serving as delivery pipe for the cooling water. The gases are then
freed from any fine soot formed in a filter 6 provided with fillers or

4. glass wool, and the hydrogen cyanide is separated from the hydrogen in
washing tower 7 by dissolving out with water. The hydrogen cyanide may
also be separated in the form of sodium cyanide by washing it with
sodium hydroxide solution. The washing liquid is advantageously
circulated by means of pump 8. It enters the washing tower 7, which is
charged with fillers, at 13 and leaves it at 14, and 60flows through
siphon 15 towards pump 8.
From supply vessel 16, a small amount of washing liquid continually
flows by way of siphon 17 into the washing tower 7. The amount of
washing liquid to be used is 65measured by a measuring device not
shown in the drawing and the regulating cock 18.
Par Fpassut with the introduction of the washing liquid from supply
vessel 16 into the washing tower 7, the cyanide or hydrogen cyanide
solution flows off at 19 and passes 70 through siphon 20. The hydrogen
formed in the course of the reaction leaves the washing tower by way
of conduit 22 fitted with a valve 21.
The following Exampnles are given for the 75 purpose of illustrating
the invention:
EXAMPLE 1.
A mixture of 200 normal litres of ammonia and 202 normal litres of
methane (normal litre meaning a litre at 0OC. under a pressure 80 of
760 millimetres of mercury), is passed, per hour, between the two
carbon electrodes 1 and 2 connected with a direct current source.
The mixture is passed at such a rate that it is exposed to the action
of the arc for not 85 more than about 0.0001 second. The potential
between the carbon electrodes is 32 volts.
The current strength amounts to 254 amperes.
Electrode 1 serving as cathode has a borehole 4, of a diameter of 8
millimetres, and 90 a diameter of 11 millimetres through which
reaction gases are introduced.
With an electrical output of 8-9 kWh an arc of about 4 millimetres is
produced. The reaction mixture bounds against the whitehot anode and
reacts there. The reaction gases are worked up as illustrated in the
accompanying drawing. In addition to large quantities of hydrogen,
about 245 grams of hydrogen cyanide are obtained per hour, 100 which
corresponds to an extent of conversion of more than 99 per cent,
calculated upon the ammonia.
EXAMPLE 2.
An apparatus is used which differs from 105 that described in Example
1 only in that the iron case 3 is fitted with three electrodes
arranged with respect to one another at an angle of 120 and supplied
with three-phase current. The potential amounts to 62 volts 110 and
the current strength to 250 amperes.
Through one of the electrodes which has a borehole of a diameter of

5. about 8 mm and a diameter of 25 mm similar to that of electrode 1
shown in the drawing a mixture of 115 1100 normal litres of ammonia
and 365 normal litres of propylene is introduced per hour into the
electric arc at such a rate that the reaction mixture is exposed to
the action of the electric arc for not more than 0.0001 120 second.
Since propylene contains 3 carbon atoms, the molecular proportions of
ammonia and propylene in the reaction mixture are 3:1. After having
passed the electric arc, the reaction mixture consisting of hydrogen
cyanide vapour, hydrogen, ammonia, nitrogen, small amounts of
acetylene, and soot, is worked up as described above. 742 Grams of
hydrogen cyanide and 18.8 grams of soot are obtained, the latter
having been 130 780,080 formed by partial decomposition of the
propylene. The yield of hydrogen cyanide amounts to about 55 per cent,
calculated upon the ammonia used. From the hydrogen cyanide solution
about 365 grams of ammonia are recovered, which corresponds to 43 per
cent of the ammonia used, and returned into the reaction apparatus so
that the total yield of material amounts to about 98 per cent.
calculated upon the ammonia.
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