United States Patent Office 2,770,641

Patented Nov. 13, 1956

2
is continued, the reflux becomes more and more a mixture
of benzonitrile and water. Solvent is, of course, taken
2,770,641. off together with an increasing proportion of benzonitrile.
PREPARATION OF BENZONTRLE The first runnings can be fractionated to give the de
5 sired product free of solvent. This start-up method is
Charles H. McKeever, Meadowbrook, and Joseph W. of convenience in the lack of benzonitrile, but is essen
Nemec, Philadelphia, Pa., assignors to Rohm & Haas tially equivalent to the procedure above described.
Company, Philadelphia, Pa., a corporation of Delaware When it is desired to shut down the operation, addi
No Drawing. Application August 13, 1954, 0.
tion of benzoic acid is discontinued but flow of ammonia
Serial No. 449,784 is continued at gradually decreasing rates. Product is
2 Claims. (C. 260-465) taken off until the volume in the reactor is small, for
example, 10%. The head temperature tends to increase
to about 185° C. and the temperature in the reactor to
about 300° C.
This invention deals with a process for preparing ben 5 Residue from the reactor is mostly recoverable. It is
Zonitrile. According to this invention this compound conveniently drawn off, allowed to cool, and crushed to
is prepared from benzoic acid and ammonia in liquid a finely divided state. The powdered material is heated
phase with removal of both benzonitrile and water formed with excess of aqueous 10% sodium hydroxide solution.
during reaction under conditions which will be fully set A period of six to ten hours can be allowed for this oper
forth below. 20 ation. The mixture is cooled and filtered. The basic
BenZonitrile has been prepared by reacting toluene filtrate is acidified, as with hydrochloric or sulfuric acid,
and ammonia in gaseous phase at high temperatures. and filtered to remove benzoic acid. The filtered solid
It is desirable, however, to avoid such temperatures and is treated to recover the catalyst. Usually the solid
it would be simpler to work in liquid phase. Attempts
have been made to prepare benzamide and convert this 25 can be treated with nitric acid and washed with water
to the nitrile, as in the presence of acid anhydride or to give a reusable catalyst. It may be noted that since
the process can be operated over considerable periods of
aluminum chloride. Yields are not always favorable time, recovery of materials from the residue is not es
in Such methods and the product often lacks the qualities sential to the economies of the process. Hence, if de
essential for its successful use as in the conversion to sired, the residue may be discarded.
benzoguanamine and formation of resins therefrom. Im 30
The condensate which is taken off consists of benzo
purities which act as inhibitors and which are otherwise nitrile and water. Addition of about 2% of salt to the
objectionable are very difficult to remove. There is thus condensate may help in the separation of nitrile and
a real need of an efficient method for preparing benzoni water. The aqueous layer may be discarded. The organic
trile of high purity. layer still contains about one percent of water, which
We have discovered a method for producing benzoni 35
trile in a high yield and of high quality. Our prime is removable by heating, conveniently under reduced
reactants are benzoic acid and ammonia. These are
pressure. This layer may also be treated with a drying
agent and filtered. The product is quite pure benzo
Supplied to a reactor wherein benzonitrile, which may nitrile.
have been previously formed by any desired method, Adidtion of salt as above noted is not essential, as
together with a catalyst, is being heated under reflux. the water contains ammonia from the excess used and
As benzoic acid is added, the temperature of the mixture this by itself is often sufficient by itself to give a good,
in the reactor is advanced until the temperature thereof clean separation of phases. If desired, the excess am
is in the range of 200 to 250° C., preferably 225° to monia can be recovered and recycled. This is not, how
245 C. At the same time vapors from the reaction ever, essential since this process without recovery of ex
Zone of the apparatus are passed through a fractionating 45 cess is already highly economical.
Zone to a condensing Zone, where benzonitrile and water As catalyst for promoting and accelerating the reaction
are condensed with reflux. When equilibrium conditions to form benzonitrile there is preferably used molyb
are reached, the temperature at the head of the frac denum oxide. Molybdic acid or ammonium molybdate,
tionating Zone is between 125° and 175 C., preferably technical or reagent quality, may likewise be used. Other
150-170° C. Benzonitrile and water are then with 50
catalysts which improve the rate of reaction are tungstic
drawn at partial take-off, reflux being maintained at a acid, molybdenum-alumina catalysts, cobalt oxide, cobalt
ratio sufficient to maintain temperatures within the above
Stated ranges. acetate, chromia on titania, chromia on zirconia, cobalt
on zirconia, vanadium pentoxide, and the like. An active
The process thus becomes continuous, if so desired. 55 catalyst, metal or metal oxide, may be extended or sup
Benzoic acid and ammonia are continuously fed to the ported on a carrier Such as zirconia, titania, or alumina,
reactor, while benzonitrile and water are taken off. Oc or it may be promoted with a second metal, its salt or its
casionally small additions of catalyst may be necessary oxide, such as cerium, thorium, zinc, magnesium, beryl
to keep the rate of production at a desired high level. lium, or zinc.
At the optimum conditions of operation the temperature 60 Yields by our process are excellent, being in excess
in the reactor is held at 240-5° C. while the overhead of 95% based on benzoic acid. No noticeable by
temperature is maintained at 155-5° C. Rates of products are present in the benzonitrile obtained. The
addition of benzoic acid and removal of product and benzonitrile as obtained is so pure that no distillation is
heating and cooling are adjusted to maintain these tem needed.
peratures. We have found that an excess of ammonia over the
As an alternative means for starting the process, the 65
benzoic acid is necessary for efficient operation. Am
reaction zone may be partially charged with an inert monia may be used directly from commercial cylinders.
organic solvent, boiling from about 125 to about 180° Ratios from 1.2/1 to 1.8/1 of moles of ammonia to
C., such as xylene or a high boiling naphtha. The solvent moles of benzoic acid appear to be optimum, since the
is heated to reflux, whereupon benzoic acid and excess 70 best production rates ensue, but the process is success
ammonia are introduced. These react in the presence of fully carried out with more or less ammonia. While we
a catalyst with formation of benzonitrile. As the process have operated with close to the theoretical ratio, produc
 2,770,641
3 4.
tion rates have been then found to be relatively slow. time of 130 hours. At this time there had been fed
While it is desirable to use fairly pure benzoic acid 5824 parts of ammonia and 26,572 parts of benzoic acid.
as a matter of principle, this is not essential for the suc The mixture of benzonitrile and water was resolved
cessful operation of our process. Any good grade of by adding thereto sodium chloride in an amount of 2%
this acid can be used. Even material containing traces 5 of the mixture, which contained about 26% of water.
of inorganic material can be used, these accumulating Layers formed and were separated. The benzonitrile
in the residue. The benzoic acid may be introduced layer was treated with calcium chloride and filtered. The
readily in liquid form from a preheater, this acid melting yield was 21,328 parts of pure benzonitrile. About 300
at 122 C. It may also be fed as a solid. parts of benzonitrile were recoverable from treating ap
The exact nature and the size of the reactor are not O paratus and drying agent.
critical factors. More important considerations are the The residue was taken from the reaction pot and treated
heat transfer arrangements for supplying heat to the with aqueous 10% sodium hydroxide solution for eight
reaction zone and for condensing the vapors. These are hours under reflux. This mixture was filtered. The
important factors in determining rate of production. They filtrate was cooled and acidified with hydrochloric acid.
must, however, be related to the efficiency of fractiona 15 Benzoic acid separated out, was filtered off, was washed,
tion. The balance of these factors is accurately defined and dried. It amounted to 476 parts.
by reference to the temperature of the materials in the The adjusted yield of benzonitrile was 96.4%.
reaction Zone and at the head of the fractionating Zone. We claim:
We have observed that in order to maintain these
20
1. A process for preparing benzonitrile which com
two temperatures within the stated ranges at a good rate of prises charging to a reaction Zone in a reaction system
production of benzonitrile, the fractionating zone should benzonitrile in an amount to fill a fraction of said zone,
have the equivalent of at least four theoretical plates. Supplying to said Zone a dehydration catalyst, heating
More seems desirable as rate is increased. With eight the charged benzonitrile until vapors thereof pass through
or more theoretical plates rate of production can be 25 a fractionating Zone to a condensing zone where the
relatively high. The fractionating zone may be packed vapors are condensed with reflux of benzonitrile, passing
or it may utilize plates in a column. The important into the reaction Zone benzoic acid and ammonia in
factor is that only benzonitrile and water and the ex molecular excess of the said acid while maintaining re
cess NH3 be obtained at the head of this zone. flux of the benzonitrile, heating the reaction zone until
The temperatures stated are for a system operating 30 the contents thereof are between 200 and 250° C. and
with the condensing zone at normal atmospheric pressure. the vapor temperatures at the head of the fractionating
Adjustments in temperatures can be made if pressures zone are maintained between 125° and 175° C. while
are reduced or increased. Increased pressures are evi addition of benzoic acid and ammonia is continued, tak
dently advantageous because they increase the solubility ing off benzonitrile and water while maintaining reflux
of ammonia in the system and, therefore, promote higher 35 of benzonitrile and water. -
utilization of ammonia. 2. A process for preparing benzonitrile which com
Further details of the process of this invention will prises charging to a reaction zone in a reaction system
be found in the following illustrative example. Parts benzonitrile in an amount to fill 5% to 20% of said
therein are by weight. Zone, Supplying to said Zone molybdenum oxide as a
. Example I 40 dehydration catalyst, heating the charged benzonitrile
A reaction system was constructed having a reaction until vapors thereof pass through a fractionating zone
pot directly connected to a short column filled with pack to a condensing Zone where the vapors are condensed
ing which in turn was connected to a condenser equipped with reflux, passing into the reaction zone benzoic acid
with a partial take-off device. The reaction pot con and ammonia in molecular excess of the said acid while
tained an efficient stirrer and tubes for bringing a stream 45 maintaining reflux of the benzonitrile, heating the reac
of ammonia gas and liquid benzoic acid from a pre tion zone containing the mixture of benzonitrile, benzoic
heater where it could be melted. There was placed in acid and ammonia and maintaining the mixture therein
the pot 400 parts of benzonitrile and 50 parts of molyb at 225 to 245 C. and the vapor temperatures at the
denum oxide powder. This mixture was stirred and head of the fractionating zone at 150 to 170° C., con
heated until reflux was occurring freely. Addition was then 50 densing benzonitrile and water in the condensing zone,
begun of molten benzoic acid. Flow of ammonia was taking off benzonitrile and water and at the same time
started at the rate of 0.5 part per minute, the rate being returning benzonitrile and water to help maintain tem
increased later to about 45 parts per hour. The rate of peratures of 150 to 170° C. at the head, and continuing
flow of benzoic acid was brought to 207 parts per hour. addition of benzoic acid and ammonia and withdrawal
By this time the reaction temperature had been raised of benzonitrile and water.
to 240° C. and was there maintained and the head tem
perature reached about 160° C. When a steady state References Cited in the file of this patent
was reached benzonitrile and water were removed at UNITED STATES PATENTS
partial take-off. After 40 hours and again after 95 hours 60 2,100,401 Linstead et al. ---------- Nov.30, 1947
of operation, 35 part portions of catalyst were added. 2,591,493 Arnold et al. ----------- Apr. 1, 1952
When it was decided to discontinue operation, the supply
of benzoic acid was shut off. The reactor temperature OTHER REFERENCES
was raised to 290 C.; the head temperature was carried Mitchell et al.: J. Am. Chem. Soc. vol. 53, p. 329
to 180° C. The operation was discontinued after a total 65 (1931).