BACKGROUND OF THE INVENTION Aminonitriles are a class of important chemicals that have a variety of industrial applications. For example, aminonitriles can be used as monomers for producing high mo- lecular weight polyamides. Specifically, 6- aminocapronitrile can be used to produce nylon 6.

Aminonitriles can be produced by catalytic partial hy- drogenation of dinitriles. See, for example, US2208598, US2257814, US2762835, US3322815, US3350439, US3591618, US4389348, US4601859, US5151543, US5296628, US5512697, US5527946, US5986127, US6080884, DE836938, DE848654, DE-A- 19636768, JP-A-9040630 and WO00/64862, all of which are in- corporated by reference herein for all purposes as if fully set forth. However, the yield of and selectivity to a de- sired aminonitrile using some of the known processes may not be as high as desired, and the amount of the complete hydro- genation product (diamine) is also generally higher than de- sired.

US5986127 and WO00/64862 mentioned above describe the use of certain additives in the partial hydrogenation proc- ess to improve the yield of and/or selectivity to the de- sired aminonitrile product, and/or reduce the amount of fully hydrogenated product (diamine) produced.

We have now found new classes of compounds that also effectively function as improved yield and/or selectivity additives in the partial hydrogenation processes such as,

for example, those mentioned in previously incorporated ref- erences.

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a process for preparing an aminonitrile from a corresponding dinitrile by contacting the dinitrile with a hydrogen-containing fluid in the presence of a sol- vent, a hydrogenation catalyst and an additive to improve the yield of and/or selectivity to the desired aminonitrile product, characterized in that the additive comprises an am- ide compound of the formula R-N (R') (R2), wherein R is an in- organic moiety, or an organic moiety attached to the nitro- gen by other than a carbonyl group; and R'and R 2 are each independently hydrogen, an inorganic moiety, or an organic moiety attached to the nitrogen by other than a carbonyl group.

Another aspect of the present invention relates to a method for improving the yield of and/or selectivity to an aminonitrile obtained by partially hydrogenating a corre- sponding dinitrile with a hydrogen-containing fluid in the presence of a solvent and a hydrogenation catalyst, compris- ing the step of partially hydrogenating the dinitrile in the further presence of an effective amount of an additive com- prising an amide compound of the formula R-N (R1) (R2), wherein R is an inorganic moiety, or an organic moiety attached to the nitrogen by other than a carbonyl group; and R1 and R2 are each independently hydrogen, an inorganic moiety, or an organic moiety attached to the nitrogen by other than a car- bonyl group.

In yet another aspect of the present invention, there is provided a catalyst composition comprising a combination of (1) a hydrogenation catalyst suitable for hydrogenating a dinitrile to an aminonitrile; and (2) an additive comprising

an amide compound of the formula R-N (R1) (R2), wherein R is an inorganic moiety, or an organic moiety attached to the ni- trogen by other than a carbonyl group; and R1 and R2 are each independently hydrogen, an inorganic moiety, or an organic moiety attached to the nitrogen by other than a carbonyl group.

An advantage of this invention is that an aminonitrile can be produced in higher yield and/or having a higher se- lectivity to the aminonitrile with the additive than with- out.

These and other features and advantages of the present invention will be more readily understood by those of ordi- nary skill in the art from a reading of the following de- tailed description. It is to be appreciated that certain features of the invention which are, for clarity, described below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to this invention, a dinitrile is contacted with a hydrogen-containing fluid in the presence of a sol- vent, a catalyst and an amide compound.

Suitable dinitriles for use herein have the general formula R (CN) 2, wherein R is a hydrocarbylene group selected from the group consisting of an alkylene, arylene, alkenyl- ene, alkarylene and aralkylene group. One dinitrile or com- binations of different dinitriles may be used. Preferred hydrocarbylene groups contain from 2 to 25, more preferably 2 to 15, and most preferably 2 to 10 carbon atoms per group.

In other words, preferred dinitriles contain from 4 to 27, more preferably 4 to about 17, and most preferably 4 to 12,

carbon atoms per dinitrile molecule. The preferred type of hydrocarbylene group is an alkylene group.

Examples of suitable dinitriles include, but are not limited to, adiponitrile; methylglutaronitrile; alpha, omega- pentanedinitrile; alpha, omega-heptanedinitrile; alpha, omega- nonanedinitrile; alpha, omega-dodecanedinitrile; alpha, omega- pentadecanedinitrile; alpha, omega-icosanedinitrile ; al- pha, omega-tetracosane-dinitrile; 3-methylhexanedinitrile; 2- methyl-4-methylene-octanedinitrile; and combinations of two or more thereof.

Preferably the carbon atoms of the starting dinitrile are arranged in a branched or linear chain. Preferred exam- ples are adiponitrile (hydrogenated to 6-aminocapronitrile), methylglutaronitrile (hydrogenated to two isomeric aminoni- triles: 5-amino-2-methylvaleronitrile and 5-amino-4-methyl- valeronitrile) and alpha, omega-dodecanedinitrile (hydrogen- ated to the corresponding aminonitrile). The preferred dinitrile is adiponitrile because its selective hydrogena- tion product, 6-aminocapronitrile, is a well-known monomer for polymerization applications.

Any hydrogen-containing fluid can be used in the inven- tion as long as there is sufficient hydrogen in the fluid to selectively hydrogenate a dinitrile to an aminonitrile. The term"fluid"refers to liquid, gas or both. The hydrogen content in the fluid can range from 1 to 100%, preferably about 50 to about 100%, and most preferably 90 to 100% by volume. The presently preferred hydrogen-containing fluid is substantially pure hydrogen gas.

The molar ratio of hydrogen (in the hydrogen-containing fluid) to dinitrile is not critical as long as sufficient hydrogen is present to produce the desired aminonitrile.

Hydrogen is generally used in excess. Hydrogen pressures are generally in the range of about 50 to about 2000 psig

(about 0.45 to about 13.89 MPa), with from about 200 to about 1000 psig (about 1.48 to about 7.00 MPa) preferred.

Any solvent that comprises either liquid ammonia or an alcohol can be used in the invention. The concentration of liquid ammonia in the solvent can range from about 20 to about 100%, preferably about 50 to about 100%, and most preferably about 80% to about 100%, by weight of total sol- vent. A substantially pure liquid ammonia is preferred.

However, if an alcohol is also present in the solvent, the concentration of ammonia can be adjusted based on the quan- tity of alcohol used, which is discussed in further detail below. The molar ratio of ammonia to dinitrile is prefera- bly about 1: 1 or greater, and is generally in the range of from about 1: 1 to about 30: 1, more preferably from about 2: 1 to about 20: 1.

Any alcohol that can facilitate the selected hydrogena- tion of a dinitrile to an aminonitrile can be used in this invention. Preferred are alcohols with 1 to 10, more pref- erably 1 to 4, carbon atoms per molecule. Examples of suit- able alcohols include, but are not limited to, methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl al- cohol, pentanol, hexanol, heptanol, octanol, nonanol, de- canol, and combinations of two or more thereof. The most preferred alcohol (when used) is methanol. The alcohol can generally be present in the solvent in the concentration of from about 20 to about 100%, preferably about 30 to about 99%, by weight based on the total solvent weight.

Typically when an alcohol is use, the solvent further comprises a base that is substantially soluble in the sol- vent. The term"substantially"refers to"more than triv- ial". Preferred bases are ammonia, an ammonium base or an inorganic base such as, for example, alkali metal oxides, alkaline earth metal oxides, alkali metal hydroxides, alka-

line earth metal hydroxides, partially neutralized acids in which one or more protons of the acids are replaced with am- monium ion, alkali metal ions, alkaline earth metal ions, or combinations of two or more thereof. Specific examples of suitable bases include, but are not limited to ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium bicarbonate, or combinations of two or more thereof. The most preferred bases are ammonia, lithium hydroxide and sodium hydroxide for they are readily available and inexpensive.

A base can be present in the solvent in any quantity so long as the quantity can facilitate the selective hydrogena- tion of a dinitrile to an aminonitrile. Generally, a base can be present in the solvent in the range of from about 0.1 to about 10 weight%, based on the total weight of the start- ing dinitrile.' The catalyst in the process is a hydrogenation catalyst suitable for hydrogenating a dinitrile to an aminonitrile.

Preferred are catalysts based on transition metals selected from the group consisting of iron, cobalt, nickel, rhodium and combinations thereof. The catalyst may also contain one or more promoters in addition to the transition metals men- tioned above, for example, one or more of Group VIB and Group VII metals such as chromium, molybdenum and tungsten.

The catalyst can also be in the form of an alloy, including a solid solution of two or more metals, or an individual metal.

The catalytic metal can also be supported on an inor- ganic support such as alumina, magnesium oxide and combina- tions thereof. The metal can be supported on an inorganic support by any means known to one skilled in the art such as, for example, impregnation, coprecipitation, ion ex- change, and combinations of two or more thereof. The pre-

ferred inorganic support is magnesium oxide, and the pre- ferred supported catalyst is a magnesium oxide supported nickel-iron catalyst.

The catalyst can be present in any appropriate physical shape or form. It can be in fluidizable forms, extrudates, tablets, spheres or combinations of two or more thereof. The catalyst may be in sponge metal form, for example, the Ra- ney3 nickels and Raneys cobalts. The molar ratio of cata- lyst to dinitrile can be any ratio as long as the ratio can catalyze the selective hydrogenation of a dinitrile. The weight ratio of catalyst to dinitrile is generally in the range of from about 0.0001 : 1 to about 1: 1, preferably about 0.001 : 1 to about 0.5 : 1. If the catalytic metal is supported on an inorganic support or is a portion of alloy or solid solution, the catalytic metal is generally present in the range of from about 0.1 to about 60, preferably about 1 to about 50, and most preferably about 2 to about 50 weight %, based on the total catalyst weight.

The preferred catalyst is a sponge metal type catalyst.

The metallic component is iron, cobalt, nickel or combina- tions thereof. Commercially available catalysts of this type are promoted or unpromoted Raneys Ni or Raneys Co cata- lysts that can be obtained from the Grace Chemical Co. (Co- lumbia, Maryland), or alternative sponge metal catalysts available, for example, from Activated Metals Corporation (Sevierville, Tenn. ) or Degussa (Ridgefield Park, N. J.).

In the case of the preferred supported nickel/iron catalyst, the rate of adiponitrile conversion increases with the amount of Ni deposited on the support. The preferred concentration of Ni is between about 5 and about 50 weight%, and especially between about 25 and about 35 weight%, based on the catalyst weight (metals + support). The preferred concentration of Fe is between about 0.2 and about 20

weight%, and especially between about 0.5 and about 10 weight%, based on the catalyst weight (metals + support).

Further details on the above components can be found from various of the previously incorporated references.

Specific reference may be had, for example, to US2208598, US2257814, US2762835, US3322815, US5151543, US5296628, US5512697, US5527946, US5986127, US6080884 and WO00/64862.

A wide variety of the amides have been found that can effect the selectivity/yield improvement in the invention.

The term"improvement"is referred to as enhanced se- lectivity to aminonitrile product at conversions greater than about 70%, preferably conversions greater than about 80%, and especially conversions greater than about 90%, as compared to the selectivity without the use of the additive of this invention. An"effective amount"of the additive is amount required to achieve the aforementioned enhanced se- lectivity and/or an improved overall yield of aminonitrile, as compared to without the use of the additive.

As used herein, the"amide"means nitrogenous compounds related to or derived from ammonia, but in this case not having a carbonyl group attached to the amide nitrogen.

Such compounds can be characterized by the formula R-N (Rl) (R2), wherein R is an inorganic moiety, or an organic moiety attached to the nitrogen by other than a carbonyl group; and Rl and R2 are each independently hydrogen, an in- organic moiety, or an organic moiety attached to the nitro- gen by other than a carbonyl group. Of course, when R, and R2 are an organic moiety, that organic moiety must be such that the compound must still be considered an amide within the understanding of a person of ordinary skill in the art (as opposed, for example, to an amine or substituted amine).

Suitable amides can include a wide variety of organic and inorganic compounds, but preferred are alkali and alka- line earth metal amides, wherein R is an alkali or an alka- line earth metal; and cyanamides, wherein R is a cyano group. In these preferred types of amides, Rl and R2 may each independently be hydrogen or any other type of moiety described above, but it is further preferred that R'and R 2 are each independently hydrogen or an inorganic moiety (in the sense that neither R1 nor R2 is bound to the nitrogen di- rectly through a carbon atom). Specifically preferred R1 and R2 groups include hydrogen, metals (such as alkali metals, alkaline earth metals and zinc), and silyl groups (particu- larly trisubstituted silyl groups such as tri (alkyl/aryl) silanes.

Examples of suitable amide compounds include, but are not limited to, lithium amide, sodium amide, potassium am- ide, cesium amide, magnesium amide, lithium bis (trimethylsilyl) amide, sodium bis (trimethylsilyl) amide, potassium bis (trimethylsilyl) amide, cyanamide, sodium cyana- mide, zinc cyanamide, calcium cyanamide and disodium cyana- mide. As indicated above, combinations of two or more amide compounds are also suitable.

The additive is present during the contacting in any quantity that can improve the selective hydrogenation of a dinitrile to its corresponding aminonitrile (e. g. , an effec- tive amount). Generally, the weight ratio of the additive to the catalyst is in the range of from about 0.01 : 1 to about 5: 1, preferably about 0.05 : 1 to about 3: 1, more pref- erably about 0.1 : 1 to 2: 1, and especially about 0.1 : 1 to about 1: 1.

The catalyst and additive can be separately introduced into contact with a dinitrile; however, it is preferred that the catalyst, whether it is in its metal form or in an alloy

or solid solution or on an inorganic support, is precon- tacted with the additive. This may be done in a solvent such as, for example, an alcohol, ether, ester, ammonia or combinations of two or more thereof. Further preferably the precontacting is also carried out in a hydrogen-containing fluid such as described above. Contacting of the catalyst and additive produces a pretreated catalyst. The pretreated catalyst can be washed with a solvent disclosed above, pref- erably under anaerobic condition to produce an additive- treated catalyst.

The contacting of the catalyst and additive can be car- ried out under any conditions effective to produce an addi- tive-treated catalyst that can improve selective hydrogena- tion of a dinitrile or the selectivity to an aminonitrile.

Generally, the entire process for producing the additive- treated catalyst can be carried out by contacting a catalyst with an additive disclosed above at a temperature in the range of from about 20°C to about 150°C, preferably about 30°C to about 100°C, under the same general pressures as de- scribed above, for about 5 seconds to about 25 hours.

The partial hydrogenation process of the present inven- tion can be carried out at a temperature in the range of from about 25 to about 150°C, preferably about 40 to about 100°C, most preferably about 60 to about 80°C, at a total pressure generally in the range of about 50 to about 2000 psig (about 0.45 to about 13.89 MPa), with from about 200 to about 1000 psig (about 1.48 to about 7.00 MPa) preferred, for a time period generally in the range of from about 15 minutes to about 25 hours, preferably about 1 hour to about 10 hours.

The process of the invention can be operated batch wise or continuously in an appropriate reactor. Stirring or agi- tation of the reaction mixture can be accomplished in a va-

riety of ways known to those skilled in the'art. The par- tial hydrogenation of the starting dinitrile to its corre- sponding aminonitrile with high selectivity at high conver- sions of the dinitrile makes this process efficient and use- ful.

Further general and specific process details can be found from various of the previously incorporated refer- ences. Specific reference may be had, for example, to US2208598, US2257814, US2762835, US3322815, US5151543, US5296628, US5512697, US5527946, US5986127, US6080884 and WO00/64862.

The following examples further illustrate the process of the invention and are not to be construed to unduly limit the scope of the invention.

The meaning of terms used in the Examples is defined as follows: Yield of aminonitrile is the measured concentration of aminonitrile divided by the starting concentration of dini- trile.

Conversion of the dinitrile is the difference between the starting and the instant concentration of dinitrile, di- vided by the starting concentration of dinitrile.

Selectivity to aminonitrile is the measured yield of aminonitrile divided by conversion of the dinitrile at that instance.

COMPARATIVE EXAMPLE 1 A sponge Ni catalyst (1.2 g) promoted with Fe and Cr (Activated Metals, A4000, without any further additives) was added to a 50 cc autoclave together with 3.2 g adiponitrile (ADN) and 35cc of liquid ammonia to form a mixture. Hydro- gen was introduced to the autoclave and the ADN was hydro- genated at 60°C under the total pressure of 1045 psig (7.31 MPa) at ca. 1500 rpm. Total conversion of ADN was reached

within 30 minutes on stream. The maximum yield of aminoca- pronitrile was 57% at 90% ADN conversion for a selectivitiy of 63%.

COMPARATIVE EXAMPLE 2 To a 300 cc autoclave, was charged 7.7g Raney Co (ob- <BR> <BR> tained from W. R. Grace Co. , catalog number 2724), 0.77 g wa- ter, 26 g ADN, and 139 g liquid ammonia. The content was hydrogenated at 70°C, under the total pressure of 1000 psig (7.00 MPa) at 1000 rpm. Total conversion of ADN was reached within 40 minutes on stream. The maximum yield of aminoca- pronitrile was 58% at 90% ADN conversion for a selectivity of 64%.

COMPARATIVE EXAMPLE 3 To a 50 cc autoclave, was charged 1.2g of a 5% rhodium on alumina catalyst (obtained from Engelhard), 3.2 g ADN, and 35 ml liquid ammonia. The content was hydrogenated at 80°C, under the total pressure of 1060 psig (7.41 MPa), at 1500 rpm. Total conversion of AND was reached within 30 minutes on stream. The maximum yield of aminocapronitrile was 41% at 96% ADN conversion, with the major product being hexamethylene diamine.

EXAMPLE 1 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.2 g of lith- ium bis (trimethylsilyl) amide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added. The mixture was heated to 80°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 120 minutes, the yield of 6-aminocapronitrile reached ca. 73% at 95% ADN conversion for a selectivity of 77%.

EXAMPLE 2 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.2 g of lith-

ium bis (trimethylsilyl) amide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added. The mixture was heated to 70°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 135 minutes, the yield of 6-aminocapronitrile reached ca. 72% at 94% ADN conversion for a selectivity of 77%.

EXAMPLE 3 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.1 g of po- tassium bis (trimethylsilyl) amide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added.

The mixture was heated to 70°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 6 hours, the yield of 6-aminocapronitrile reached ca. 71% at 89% ADN conversion for a selectivity of 80%.

EXAMPLE 4 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.05 g of po- tassium bis (trimethylsilyl) amide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added.

The mixture was heated to 70°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 180 min- utes, the yield of 6-aminocapronitrile reached ca. 71% at 87% ADN conversion for a selectivity of 82%.

EXAMPLE 5 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.1 g of cy- anamide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added. The mixture was heated to 90°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 4.5 hours, the yield of 6- aminocapronitrile reached ca. 71% at 90% ADN conversion for a selectivity of 79%.

EXAMPLE 6 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.25 g of cy- anamide, 12 g of ADN was injected into the autoclave and 65 ml of liquid ammonia was added. The mixture was heated to 90°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 9.5 hours, the yield of 6- aminocapronitrile reached ca. 71% at 89% ADN conversion for a selectivity of 80%.

EXAMPLE 7 1.2 g of sponge Ni catalyst (Degussa BLM 112W) was charged into a 100cc autoclave, together with 0.05 g of so- dium dicyanoamide, 12 g of ADN was injected into the auto- clave and 65 ml of liquid ammonia was added. The mixture was heated to 90°C, and reacted with hydrogen at a total pressure of 1030 psig (7.00 MPa). After 9.5 hours, the yield of 6-aminocapronitrile reached ca. 73% at 92% ADN con- version for a selectivity of 79%.