United States Patent Office Patented Dec
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3,360,541 United States Patent Office Patented Dec. 26, 1967 2 ferred to hereinafter as “adiponitrile precursors.” The rela 3,360,54. MANUFACTURE OF ADEPONTRILE tive proportions of these products within the contaminated Walter John Korchinsky, Lafayette, Ind., and Joseph reaction product may vary with any particular catalyst Sikora, St. Hilaire, Quebec, and John Murray Earls used and with actual reaction conditions employed. In Hill, St. Lambert, Quebec, Canada, assignors, by mesne 5 general, the cyanovaleramide and ammonium cyanoval assignments, to E. I. du Pont de Nemours and Con erate are found in higher proportions than the adipamide, pany, Wilmington, Del, a corporation of Delaware ammonium adipamate and diammonium adipate. Adipo No Drawing. Filed Apr. 13, 1965, Ser. No. 447,874 nitrile precursors containing carboxylic acid groups or Caims priority, application Canada, May 5, 1964, being salts thereof will be referred to hereinafter as "acid 902,100 ic precursors'; adipamide and cyanovaleramide will be 9 Claims. (C. 260-465.2) O referred to hereinafter as "neutral precursors.' Adiponitrile and water are only partially miscible at room temperature; for example, adiponitrile saturated ABSTRACT OF THE DISCLCSURE with Water contains about 7 to 8% of water. Because of A process for the production of adiponitrile from adipic 5 this partial solubility the catalytic dehydration reaction acid and ammonia which results in an easier separation of product of adipic acid and ammonia forms two layers the condensed product into an adiponitrile containing oil upon cooling. In one layer adiponitrile is the main com phase and an adiponitrile precursor containing aqueous ponent and this gives the layer an oily appearance. This phase by adjusting the pH of the condensate of the de layer will hereinafter be sometimes referred appearance. hydration reaction to from 7.0 to 10.00 and in an increase 20 This layer will hereinafter be sometimes referred to as in yield due to a method of converting the adiponitrile the “oil layer.' The other layer, containing water as the precursors from the aqueous phase into adiponitrile by main component, will hereinafter be sometimes referred removing water from the adiponitrile precursor in the to as the “aqueous layer.' aqueous phase prior to a second dehydration reaction. It has now been found that adiponitrile acidic precursors partition predominantly into the aqueous layer and that the partition of the neutral precursors between the oil and The present invention relates to an improved process for aqueous layers is relatively independent of the pH of the the manufacture of adiponitrile from adipic acid and am aqueous layer. It has also now been found that, because monia. of the high solubility in the aqueous layer of the am One of the more important uses of adiponitrile lies in 3) monium salts of the acidic precursors, the partition of the preparation of hexamethylene diamine which is a all the acidic precursors into the aqueous layer may be useful intermediate in the preparation of nylon. improved considerably by making the medium alkaline, It is known that adiponitrile may be prepared by the preferably with a volatile base such as ammonia. This catalytic dehydration of adipic acid/ammonia mixtures. method of separating adiponitrile precursors from the One such process is disclosed in U.S. Patent 2,200,734 in 35 bulk of adiponitrile obtained by the catalytic dehydration which a mixture of ammonia, in molecular excess, and of diammonium adipate is an improvement over the con adipic acid is passed over a compound of boron and phos ventional technique involving distillation since the pre phorus, acting as a dehydration catalyst, at a temperature cursors and particularly the acidic ones, tend to decom between 300 and 550 C. pose under the conditions of prolonged heating at high The catalytic dehydration of mixtures of adipic acid 40 temperatures prevailing in such distillation processes. and ammonia to yield adiponitrile may be regarded as It is an object of the present invention to separate an one involving the successive elimination of four molecules enriched stream of adiponitrile precursors from the con of water from ammonium adipate according to the fol taminated reaction product obtained by the catalytic de lowing scheme: hydration of diammonium adipate. HOOC(CH2)CO OH -- NEOH - NIHO OC(CEI), COONH adipic acid annonia diammonium adipate -1H2O NHO C (CH2)4CO ONH annonium adipamate -E:O / NN-1HO Z Y NC (CH2)CO ONE NHOC(CH2)CONH ammonium cyamovalerate adipamide - HON Y -1H2O NC (CH2)CN e - NC (CH2)4CONH adiponitrile cyanowaleramide Thus, adiponitrile may be considered as the final product A further object of the present invention is to provide of the catalytic dehydration of diammonium adipate. a method for the conversion of neutral and acidic pre The involved nature of the catalytic dehydration reac 65 cursors obtained in said catalytic dehydration reaction to tion of mixtures of adipic acid and ammonia to yield adiponitrile results in a contaminated reaction product. adiponitrile in yields economically attractive. Amongst the contaminants are diammonium adipate, am Yet a further object of the present invention is to pro monium adipamate, adipamide, ammonium delta-cyano vide a process for the manufacture of adiponitrile which valerate and delta-cyanovaleramide. These products are 70 increases the economic efficiency of the conversion of adi noteworthy since each may itself be used as a starting ma pic acid to adiponitrile in the catalytic dehydration of a terial in the manufacture of adiponitrile and will be re mixture of adipic acid and ammonia. 3,360,541. 3 4. In its broadest aspect, the present invention provides the residue may be converted directly to adiponitrile, in a process for the manufacture of adiponirtile which con the presence of ammonia, with the aid of a dehydration prises the steps of adjusting the pH of the aqueous com catalyst or it may first be blended with adipic acid or cya ponent of crude adiponitrile product obtainable by the de novaleramide and other neutral precursors recovered from hydration of adipic acid in the presence of ammonia to 5 the oil layer, prior to its conversion to adiponitrile. from 7.0 to 10.0 at 25 C.; separating the aqueous con It is generally preferred to use adipic acid and ammonia ponent and removing water therefrom; contacting the resi as starting materials in the preparation of adiponitrile. due so obtained with a dehydration catalyst in the pres Hence, the present invention has been described with ref. ence of ammonia and recovering adiponitrile from the erence only to these two starting materials. However, it product. will be understood that certain derivatives of adipic acid, In particular, the present invention provides a process O Such as adipamide, adipimide, esters of adipic acid, for the manufacture of adiponitrile which comprises the adipanic acid and cyanovaleric acid or amide, obtain steps of contacting a mixture of ammonia, in molecular able as contaminants in the catalytic dehydration of mix excess, and adipic acid with a dehydration catalyst at a tures of adipic acid and ammonia may also be used as temperature between 300 and 500 C.; condensing the 5 starting materials in place of adipic acid and, for the product so obtained; expelling ammonia from the con purposes of the present invention, will be considered densate; adjusting the pH of the condensate to from 7.0 equivalent to adipic acid. Depending upon the physical to 10.0 at 25 C.; allowing the alkaline condensate to Set properties of these derivatives of adipic acid they may tle into an aqueous layer and an oil layer; separating the be reacted with ammonia as powdered solids, liquids, aqueous layer from the oil layer at a temperature between 20 gases or in solution or suspension in suitable solvents. 10° and 75 C.; removing water from the aqueous layer; The process of the present invention is preferably prac contacting the residue from the aqueous layer with a de tised at atmospheric pressure although there is no disad hydration catalyst in the presence of ammonia and re vantage in operating at higher or lower pressures than at covering adiponitrile from the product so obtained and mospheric in order to increase the capacity of a given from the oil layer. 25 reaction vessel or to facilitate vaporization of high boiling When the dehydration is carried out by a vapour phase Feactants. process, the preferred dehydration catalyst in both in The following examples serve to illustrate, but do not stances is boron phosphate. Phosphoric acid is recom limit the scope of the present invention as set forth in mended as the dehydration catalyst when the dehydration the claims hereto. All parts are parts by weight. of the reisdue from the aqueous layer is carried out in 30 the liquid phase. Boron phosphate, unlike other well Example 1 known dehydration catalysts such as the oxides of alu A stream of ammonia was passed over boron phosphate minum or silicon, appears to promote better the reaction catalyst having a particle size of from 8 to 14 mesh and leading to the formation of adiponitrile, thus reducing being maintained at a temperature of 330 to 380, the losses to contaminants, and maintains a high degree of 35 main part of the catalyst being at 360° to 375 C. Adipic activity for a longer time partly owing to the slower rate acid vapour was passed with the ammonia at a uniform at which its surface becomes covered with carbon de rate, the molecular ratio of ammonia to adipic acid being posits. 8 to 1, and the time of contact being approximately 5 The amount of alkali added to the condensate prior to seconds. In traversing the catalyst, the vapor mixture was its separation into an aqueous layer and an oil layer is 40 dehydrated to yield a vaporous product rich in adipo preferably that required to give a pH in the aqueous layer nitrile and water.