acetonitrile synthesis

Acetonitrile from NH4-acetate

Acetonitrile prep

PATENT SPECIFICATION

Application Date: Oct 10, 1935 No 28007/35.

464,106 Complete Specification Left: Sept 23, 1936.

Complete Specification Accepted: April 12,1937.

PROVISIONAL SPECIFICATION

Improvements in or relating to the Manufacture of Aliphatic Acid Nitriles We, BRITISH CFLANES:S LIMITED, a Company incorporated in accordance with the laws of Great Britain, of Celanese House, 22 & 23, Hanover Square, London, S W 1, HORACE FINNINGLEY OXLEY and EDWARD BOADEN THOMAS, both subjects of the King of Great Britain, of the Works of British Celanese Limited, Spondon, near Derby, do hereby declare the nature of this invention to be as follows:This invention relates to the manufacture of aliphatie acid nitriles and especially acetonitrile and the nitriles of other lower fatty acids.

According to the invention an aliphatic acid nitrile is produced by decomposing by the action of heat the ammonium salt of the corresponding aliphatic acid in presence in the free state of a quantity of the same acid The production of acetonitrile, which is an important embodiment of the invention, is thus effected by decomposing amllonium acetate by the action of heat in presence of a quantity of free acetic acid.

In carrying out the process of the invention the ammonium salt to be decomposed may be heated under a fractionating column, together with a quantity of the corresponding acid in the free state, under conditions such that the nitrile will distil off as it is produced.

In such a process the presence of a quantity of free acid equal to about 40% of that combined in the ammonium salt gives excellent results and avoids the presence of substantial quantities of unchanged ammonium salt in the distillate.

Larger quantities of acid may be employed, if desired, although it is found that no advantage is secured by using a quantity of free acid greater than that combined in the salt.

4,5 In practice it has been found that the quantity of free acid thus employed may be reduced very substantially by carrying out the production of the nitrile as a continuous operation This object may be achieved by heating the mixture of ammonium salt and free acid to the decomposition temperature under a fractionating column, operated so as to permit distillation into a suitable receiver of the nitrile as it is formed, and provid 55 ing a continuous supply of fresh ammonium salt-acid mixture to the distillation vessel Operating in this manner it has been found possible to obtain excellent results by supplying to 60 the distillation vessel a mixture containing free acid equal to 15-20 % of that combined in the ammonium salt Such a mixture may be maintained in a liquid form suitable for continuous feeding by 65 warming e g to a temperature of 60-7 00 C.

In such a process the distillation vessel may, if desired, be charged initially with a mixture containing a rather larger 70 proportion of free acid than is present in the mixture continuously supplied; for instance the vessel may be charged with a mixture containing free acid in quantity equal to 20-50 % of the weight of 75 the acid combined in the ammonium salt employed.

The decomposition temperature employod may be varied according to the particular nitrile to be produced, and 80 according to other operating conditions.

In general, temperatures of 200-220 C.

are very suitable for the production of acetonitrile, temperatures of 200-210 C.

being very satisfactory Where, as will 85 usually be the case in practice, the distillation is effected under a fractionating column, the head of the column should be maintained at a temperature such that the nitrile distills over while the free 90 acid is as far as' possible returned to the distillation vessel In the production of acetonitrile a still-head temperature of about 92 C has been found very satisfactory in practice 95 It has been found that the production of the nitriles can be accelerated very considerablv by the use of an iron catalyst.

The iron mav he introduced into the distillation vessel in the form of a compound 100 and phosphates of iron, e g Fe{( 12 POG) have been found very suitable for use in this manner Alternatively, a distillation vessel made of a corrosive-resistant ferrous alloy such a Stavbrite may be 105 employed, in which case it is found that % 00 %A, a ITT-246,O the small amount of corrosion which does take place is sufficient to provide the iron catalyst.

Separation of the nitrile produced from the distillate obtained may be effected in any desired manner, for instance by fractional distillation, if desired, after the addition of sufficient acetic acid to convert all the acetate present into acid acetate and thus prevent distillation of ammonia.

The aqueous nitriles contaminated with the ammonium salt of the corresponding acid obtained in the process of the present invention may be purified very efficiently by a process comprising salting out the nitrile with the ammonium salt This may be effected by neutralising with ammonia free acid contained in the crude nitrile, and if necessary, adding a further quantity of the ammonium salt.

Such a salting out process produces in the case of acetonitrile an upper layer of aqueous nitrile of 95 % concentration, which, o-n fractionation, yields first a constant boiling nitrile-water mixture containing 84 % nitrile and subsequently the anhydrous nitrile It is possible by this means to obtain the bulk of the nitrile contained in the crude product in an anhydrous condition.

Fractionation of the ammonium acetate layer irom the salting out operation yields a distillate consisting of aqueous 35 nitrile containing free ammonia which can be used in neutralising a further batch of crude nitrile, and so likewise can ammonia obtained from the 84 % nitrile obtained by fractionating the 40 salted out product The residue from the fractionation of the ammonium acetate layer consists of ammonium acetate and the acid acetate and is available for use as starting material in the pro 45 duction of a further quantity of nitrile.

While the invention has been described above more particularly with regard to the manufacture of acetonitrile it is not limited in this respect and may be applied 50 to the manufacture of other aliphatic acid nitriles For example, by employing ammonium propionate as starting material propionitrile may be produced and likewise from ammonium butyrate 55 there may be obtained butyronitrile.

Dated this 9th day of October, 1935.

STEPHENS & ALLEN, Chartered Patent Agents, Celanese House, 22 & 23, Hanover Square, London, W l.

COMPLETE SPECIFICATION

Improvements in or relating to the Manufacture of Aliphatic Acid Nitriles We, BRITISH CELANE Sn, L Im I Tn D, a Company incorporated in accordance with the laws of Great Britain, of Celanese go House, 22 & 23, Hanover Square, London, W.1, HORACE FINNINGLEY OX:LY and E Dw ARD BOADEN T Hom As, both subjects of the King of Great Britain, of the Works of British Celanese Limited, d B Spondon, near Derby, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

This invention relates to the manufacture of aliphatic acid nitriles and especially acetonitrile and the nitriles of other lower fatty acids.

According to the invention an aliphatic acid nitrile is produced by decomposing by the action of heat the ammonium salt of the corresponding aliphatic acid in presence in the free state of a quantity of the same acid The production of aceionitrile, which is an important embodiment of the invention, is thus effected by decomposing ammonium acetate by the action of heat in presence of a quantity of free acetic acid.

In carrying out the, process of the 85 invention the ammonium salt to be decomposed may be heated under a fractionating column, together with a quantity of the corresponding acid in the free state, under conditions such that the 90 nitrile will distil off as it is produced.

In such a process the presence of a quantity of free acid equal to about 40% of that combined in the ammonium salt gives excelent results and avoids the 95 presence of substantial quantities of unchanged ammonium salt in the distillate.

Larger quantities of acid may be employed, if desired, although it is found that no advantage is secured by 100 using a quantity of free acid greater than that combined in the salt.

In practice it has been found that the quantity of free acid thus employed may be reduced very substantially by carry 105 ing out the production of the nitrile as a continuous operation This object may be achieved by heating the mixture of ammonium salt and free acid to the decompqsition temperature under a frac 110 464,1 OU a 464,106 tion ating column, operated so as to permit distillation into a suitable receiver of the nitrile as it is formed, and providing a continuous supply of fresh ammonium salt-acid mixture to the distillation vessel Operating in this manner it has been found possible to obtain excellent results by supplying to the distillation vessel a mixture containing free acid equal to 15-90 % of that combined in the ammonium salt Such a mixture may be maintained in a liquid form suitable for continuous feeding by warming e g to a temperature of 60-700 C.

In such a process the distillation vessel may, if desired, be charged initially with a mixture containing a rather larger proportion of free acid than is present in the mixture continuously supplied; for instance the vessel may be charged with a mixture' containing free acid in quantity equal to 20-50 % of the weight of the acid combined in tbh ammonium salt employed.

The decomposition temperature employed may be varied according to the particular nitrile to be produced, and according to other operating conditions.

In general, temperatures of 200-2290 C.

are very suitable for the production of acetonitrile, temperatures of 200-210 C.

being very satisfactory Where, as will usually be the case in practice, the distillation is effected under a fractionating column, the head of the column should be maintained at a temperature such that the nitrile distills over while the free acid is as far as possible returned to the distillation vessel In the production of acetonitrile a still-head temperature of about, 920 C has been found very satisfactory in practice.

It has been found that the production of the nitriles can be accelerated very considerably by the use of an iron catalyst.

The iron may be introduced into the distillation vessel in the form of a compound and phosphates of iron, e g Fe(l 12 P 4), have been found very suitable for use in this manner Alternatively, a, distillation vessel made of a corrosive-resistant ferrous alloy such a Staybrite may be employed, in which case it is found that the small amount of corrosion which does take place is sufficient to provide, the iron catalyst.

Separation of the nitrile produced from the distillate obtained may be effected in ( any desired manner, for instance by fractional distillation, if desired, after the addition of sufficient acetic acid to convert all the acetate present into acid acetate and thus prevent distillation of ammonia.

The aqueous nitriles conlandnated with the ammonium salt of the corresponding acid obtained in the process of the present invention may be purified very efficiently by a process comprising Malt 70 ing out the nitrile with the ammonium salt This may be efiected by neutralising with ammonia free acid contained in the crude nitrile, and if necessary adding a further quantity of the ammllo 75 nium salt.

Such a salting out process produces in the case of acetonitrile an upper layer of aqueous nitrile of 95 % concentration, which, on fractionation, yields first a con 80 stant boiling nitrile-water mixture containing 84 % nitrile and subsequently the anhydrous nitrile It is possible by this means to obtain the bulk of the nitrile contained in the crude product in an 85 anhydrous condition.

Fractionation of the ammonium acetate layer from the salting out operation yields a distillate consisting of aqueous nitrile containing free ammonia which 90 can be used in neutralising a further batch of crude nitrile, and so likewise can ammonia obtained from the 84 % nitrile obtained by fractionating the salted out product The residue from 95 the fractionation of the ammonium acetate layer consists of ammonium acetate and the acid acetate and is available for use as starting material in the production of a further quantity of nitrile 100 While the invention has been described above more particularly with regard to the manufacture of acetonitrile it is not limited in this respect and may be applied to the manufacture of other aliphatic acid 105 nitriles For example, by employing ammonium propionate as starting material propionitrile may be produced and likewise from ammonium butvrate there may be obtained butyronitrile 110 The following Example illustrates the invention as applied to the production of acetonitrile:EXAMPLE.

A mixture of about 88 % amnionium 115 acetate and 12 % acetic acid, prepared by adding acetic acid to ammonium carbonate, is continuously fed to a still provided with a Viigreux column and containing either a quantity of the feed mixture 120 or a residue from a previous operation.


[Edited on 18-11-2005 by BASF]