Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention is directed to an improved process Eor the
preparation of nitriles by catalytic conversion of alcohols or aldehydes
with ammonia. More specifically, it has been foulld that the addition of
hydrogen to the ammonia substantially prolongs the catalyst life and
increases the product yield~
Various methods are presently known for producing carboxylic
acid nitriles. For example, ammonium salts of carboxylic acids can be
dehydrated to form the corresponding nitriles. Also, mixtures of
carboxylic acids with ammonia can be converted to the nitriles by splitting
off water. These reactions are carried out in the presence oE a dehydration
catalyst such as silica gel or A1203 at a temperature of 360 to 500 C.
~A.C. Cope, R.J. Cotter, and L.L. Esters, Org. Syntheses 34, 4 ~1954) ).
These methods have the disadvantage of requiring relativcly
high reaction temperaturcs, with attendant high and uneconomic energy
requirelnents. This is also true for the corresponding catalytic
dehydration of amides, which is carried out, for exampleJ in conjunction
with A1203 (D. Boehmer and F. Andrews, J. Amer. Soc. 38, 2504 ~1916) ).
It is also possible to convert acid amides to their corresponding nitriles
by non-catalytic means. This is usually done using dehydration agents
such as aluminum chloride, phosphorus pentoxide, phosphorus chloride or
thionyl chloride. This method can be used for most nitriles, but is
economical only in a few cases.
It has been found advantageous to use aldehydes or alcohols as
starting material for the preparation oE nitriles. These substances are
often available as a result of large scale industrial processes, such as
the oxo syntheses.
For example, it is well known that i-butyronitrile can be
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prepared by reacting i-butyraldehyde wlth ammonia over a ThO2 catalyst
(F. Mailhe, Compt. Rend. 166, 216, (1918)) or a silver catalyst (United
States Patent 2,337,421) or a copper catalyst (United States Patent
2,337,~22) on dehydrating carrier material.
In addition, other alcohols, such as propanol and n-butanol,
are also converted in an analogous manner to their nitriles by reaction
with ammonia over molybdenum (VI) oxide/A1203 (United States Patent
2,~187,299) or over nickel/A120~ (C.A. 52, 19~25 (1958)).
The foregoing conversions suffer from a decrease in catalyst
activity coupled with the formation of undesirable by-products after a
relatively short operating time. Some short-~erm improvement in catalyst
behavior can be obtained by such conventional measures as raising the
temperature, altering the residence tlme, and changing the catnlyst load.
In most cases, however, the catalyst is rapidly deactivated.
It is, therefore, among the objects of the presen~ invention
to provide a process which will enable the conversion of alcohols or
aldehydes to nitriles in ~he presence oE such of catalysts, without the
aforementioned disadvantages.
It is also among the objects of this invention to provide a
process for the catalytic preparation of nitriles which will permit
extended catalyst life and improved selectivity.
The present invention is an improvement on the process for
preparation of a nitrile from an alcohol or aldehyde with ammonia in the
presence of a supported copper catalyst. The improvement comprises
carrying out the reaction in the presence of from 20 to 50% by volume of
hydrogen, based upon the ammonia/hydrogen mixture. This modification
dramatically improves the long term behavior of the copper catalysts
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belng used. This is particularly suprising and unexpected since hydrogen is
liberated in the conversion of both alcohols and aldehydes with ammonia at
tlle reaction temperatures ~270 to 320C). 'I`hus, a decrease in the conversion
or selectivity would be expected when hydrogen was added. In fact, however,
the presence o-E hydrogen as aforesaid not only improves the selectivity of the
catalyst in favor of nitrile formation, but also substantially prolongs the
life thereof, while maintaining a high conversion rate.
More specifically, in the prior art processes, it is necessary to
regenerate the catalyst within three to four weeks at most; whereas when using
the present procedure, no decrease in catalyst performance is noticeable, even
after three months' continuous operation.
Moreover, the addition of hyclrogen improves the alcohol or aldehyde
conversion to nitrile, 'I`he prior art metllocls are capable of producing at most
90 to 95% yield "~llile the process oE tile present invention is capable oE a
conversion rate of 99.0 to 99.5%. In addition to the foregoing, the present
invention permits raising of the specific velocity ~or throughput) from the
prior art value of 0.2 V/Vh to 0.28 V/Vh. This constitutes a 40% increase in
throughput.
Thus~ the present invention permits the preparation of nitriles from
their corresponding alcohols or aldehydes while achieving dramatic improve-
ments in economy and long term catalyst behavior.
In carrying out the present process, the hydrogen is passed over the
catalyst together with the ammonia and the alcohol or aldehyde. As previously
stated, the hydrogen constitutes from 20 to 50% by volume of the ammonia and
hydrogen together. In a preferred form of the invention, the hydrogen is from
25 to 35% by volwne.
~seful starting materials are preferably aliphatic alcohols or alde-
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hydes, especially -those having 3 -to 8 carbon atoms. Of particular value are
normal and isopropanol, 2-ethylbutanol, 2-ethyl-3-methylpen-tanol, 2-ethyl-
hexanol and, in particular, normal and/or isobutanol. Of course, the
corresponding aldehydes may also be used with equally satisfactory results.
It has bsen found advantageous to react the alcohol or aldehyde
with ammonia in a molar ratio of from 0.1:1 to 0.5:1. Copper on a suitable
carrier material serves as the catalyst. The preferred catalysts contain from
10 to 80% by weight of copper based upon the total reduced catalyst. Useful
carrier materials include silicon dioxide (as silica gel or kieselguhr),
aluminum oxide, magnesium oxide, aluminum silicates, and mixtures of aluminum
oxide and silicon dioxide. Of these, the silicon dioxide based carriers are
most preferable.
The space velocity, based on liquid alcohol or aldehyde, is advantag-
eously 0.1 to 0.3 V/Vcath-
[t is believed that the beneEicial inEluence of hydrogen in the
present conversion can be attributed to prevention or delaying of the form-
ation of activity-reducing deposits on the catalyst surface. Thus, the
activity and selectivity of the catalyst are maintained over a dramatically
longer period at an average higher level than in the case of the prior art
methods. When the present process is being used, regeneration of the catalyst
need be carried out only after comparatively long periods of operation and, in
particularly favorable cases, such regeneration can be omitted entirely.
In carrying out the present method, it is merely necessary, when
starting up the plant, to add the required amount of hydrogen to the system.
The hydrogen formed in the synthesis can be recycled by the gas circulation.
Thus, continuous operation requires only that the hydrogen concentration in the
circulating gas be maintained at 20 to 50% by volume, based on the total of
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hydrogen and ammonia present in the circulating gas.
Should a reduction in catalyst activity occur, as in -the case of
especially long operating times, -the catalyst can be regenerated in situ in the
known manner by a step-wise treatment with air/nitrogen mixtures at a temper-
ature of 160 to 320C, while gradually raising the oxygen content from 1% to
20%~ The subsequent reduction step is preferably carried out with a hydrogen/
nitrogen mixture ~3% by volume hydrogen) in the same temperature range of 160
to 320C. The space velocity is 1,000 V /V t h
The following Examples are illustrative of the invention:
xample 1
Approximately 40 ml/h of i-butanol (0.27 V/Vh), together with
40 Nllh o:f NH3 and 18 Nl/h of H2 are passed over 150 ml of a reduced copper
catalyst. The temperature is maintained at 290C and the catalyst contains
approximately 50% copper supported on silicon dioxide. The reaction takes
place in a quartz tube having an internal diameter of 20 to 22 mm and located
in an electrically heated aluminum block furnace. The reaction product is
separated into an org~m ic phase and an aqueous phase. The former contains
88 to 90% i-butyronitrile, 5 to 6~ i-butylamine, 1.5 to 2% di-i-butylamine,
1 to 2% of Schiff base, and 0.5 to 0.7% of unreacted i-butanol. The aqueous
phase, which amounts to about 25% of the total reaction product, contains
about 5 to 6% of i-butyronitrile, about 22% by weight of ammonia, and 2 to 3%
of unidentified components. The long term behavior of the catalyst is
summarized in Table 1.
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1~313E~
Comparison Exa ple l
30 to 40 ml/h of i-butanol, together wi*h 25 to 30 Nl/h of Nl13 are
passed over a reduced copper catalyst. The temperature is initially 280C, and
no hydrogen is added. Dur:ing -the first ten days of operation, the conversion
to i-butyronitrile is 90 -to 96%. However, thereafter the degree of conversion
decreases. It can be maintained at 85 to 90~ up to the 26th day oE operation
by raising the reaction temperature in stages; first to 290C and then to 300C.
After 30 days of operation, the catalyst had deteriorated so substantially
that the experiment had to be terminated. In all other respects, Comparison
Example 1 followed the procedure of Example 1. As can readily be seen, a
considerably shorter active life of the catalyst is obtained in the event that
hydrogen is omitted.
[t is known that catalysts of this character, whose activity has
deteriorated, can be regenerated with oxygen/nitrogen mixtures under controlled
conditions, followed by activation by reduction. This regeneration process
will permit the catalyst to regain almost all of the original activity. How-
ever, when the catalyst is re-used, the drop in degree of conversion to the
nitrile usually takes place more rapidly than in the first operating period.
Thus, even with regeneration of the catalyst, the prior art processes cannot
achieve the results of the present process.
Example 2
In order to prepare 2-ethylbutyronitrile, 40 ml of 2-ethylbutanal in
the vapor state, together with 45 Nl/h of ammonia plus 15 Nl/h of hydrogen are
passed over 150 ml of a pelletized copper catalyst according to Example 1 at a
temperature of 280C. The reaction product is separated into aqueous and
organic phases. Even after approximately 80 days of continuous operation, the
organic phase continues to contain 95 to 98% of 2-ethyl-butyronitrile. The
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89~
conversion of the starting material (2-ethylbutanal) is virtually complete,
leaving a residue of merely approximately 0.2% by weight. After 80 days
operating time, a gradual decrease in the formation of the nitrile occurs,
but this can be reversed by increasing the reaction temperature to 290 to
320C.
Comparison Example 2
The process of Example 2 is carried out except that the hydrogen is
omitted. It is then found that there is a definite decrease in catalyst
activity after only approximtely 26 days. Moreover, although the desired
reaction product comprises 95 to 98% of the organic layer at the outset of the
reaction, this proportion falls increasingly after the 26 day period of
operation. The conversion can be mainta:ined at 85 to 90% for up to about
~5 operating days by raising the temperature to 300 to 320C. Thereafter,
the decrease in act:ivity is so substantial that the reaction productl because
of its ]ack of purity, can no longer be purifiecl to an economically acceptable
level.
Example 3
A mixture of 30 ml/h of 2-ethyl-3-methylpentanol, together with
25 Nl/h ammonia and 7 Nl/h hydrogen are passed over a similar catalyst to that
used in Example 1 at 280 to 300C. The organic phase of the product obtained
comprises up to 99% of 2-ethyl-3-methylvaleronitrile. No reduction in
catalyst activity whatsoever is observed during the 60 day period of operation.
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