MXPA01000634A - Improved method for simultaneous production of 6-aminocapronitrile and hexamethylenediamine - Google Patents

Abstract

The invention relates to a method for simultaneous production of 6-aminocapronitrile and hexamethylenediamine from adipodinitrile, comprising the following steps:a) hydrogenating adipodinitrile in the presence of a catalyst containing an element of the VIII subgroup thereby obtaining a mixture containing 6-aminocapronitrile, hexamethylenediamine, adipodinitrile and high boilers;b) distillative separation of hexamethylenediamine from the mixture containing 6-aminocapronitrile, hexamethylenediamine, adipodinitrile and high boilers or c1) distillative separating 6-aminocapronitrile and subsequently d1) distillative separation of adipodinitrile or c2) simultaneous distillative separation of 6-aminocapronitrile and adipodinitrile into separate fractions. The invention is characterized in that temperatures in the bottoms of the column in steps d1) or c2) are under185°C. The adipodinitrile thus obtained contains less impurities than for instance 1-amino-2-cyanocyclopentenes.

Description

IMPROVED PROCEDURE FOR THE SIMULTANEOUS OBTAINING OF 6-AMINOCAPRONITRIL AND HEXAMETILENDIAMINE Description The present invention relates to a process for simultaneously obtaining 6-aminocapronitrile and hexamethylenediamine, starting from adiponitrile, comprising the following steps a) hydrogenation of adiponitrile in the presence of a catalyst, which contains as a catalytically active component an element of the eighth secondary group, obtaining a mixture containing 6-aminocapronitrile, hexamethylenediamine, adiponitrile and high-boiling components, b) distillative separation of hexamethylenediamine from the mixture containing 6-aminocaproni ryl, hexamethylenediamine, adiponitrile and high-boiling components, and, alternatively, cl) Distillative separation of 6-aminocapronitrile followed by di) the distillative separation of adiponitrile, or c2) Simultaneous distillative separation of 6-aminocapronitrile and adiponitrile in separate fractions, which process is characterized in that the background temperatures in steps d) or c2) are below 185 ° C.

It is known to hydrogenate adiponitrile in the presence of elements of the eighth secondary group, especially in the presence of catalysts predominantly containing iron, cobalt, nickel, ruthenium or rhodium, solvents, such as, for example, ammonia, amines or alcohols, and optionally additives, such as, for example, inorganic bases, giving mixtures starting from 6-aminocaprony-trile, hexamethylenediamine and unreacted adiponitrile. Here, catalysts dissolved homogeneously in the liquid phase and fixed-bed catalysts used as a fixed or suspended bed are used.

The iron catalysts which are often used as high-pressure fixed bed catalysts in the liquid phase are described, for example in DE 4,235,466, WO 96/20166, WO96 / 20,043 and DE 19,636,767. Co catalysts are known, for example, from DE 954,416, WO 96/20166 and DE 19,636,768. Nickel catalysts are used in DE 848,654, eg as support catalysts (nickel on A10), but above all, for example, according to US 2,762,835, WO 96/18603 and WO 97 / 10,052 in the form of nickel Raney endowed or not endowed. Fixed bed catalysts are known from US 3,322,815, homogeneously dissolved ruthenium catalysts are known from WO 96/23802 and WO 96/23804. Rhodium catalysts, such as, for example, rhodium on magnesium oxide, are mentioned, for example, in US 4,601,859.

The partial hydrogenation of adiponitrile in mixtures from 6-aminocapronitrile, hexamethylenediamine and unreacted adiponitrile is carried out to obtain 6-aminocapronitrile and hexamethylenediamine in a desired ratio, regulated by appropriate selection of the reaction conditions. The 6-amino-capronitrile can be cyclized, eg according to US 5,646,277, in the liquid phase, in the presence of oxidic catalysts, giving caprolactam. Caprolactam is an important starting product for obtaining nylon 6, hexamethylenediamine is one of the starting materials for obtaining nylon 6. 6 DE-A 19,548,289 discloses a process for the simultaneous preparation of 6-aminocapronitrile and hexamethylenediamine by hydrogenation of adiponitrile in the presence of a catalyst, reaching a partial concentration, the separation of hexamethylenediamine and 6-aminocaproniyl from the mixture and the reaction of 6-aminocapronitrile in caprolactam, as well as the recycling of a portion substantially consisting of adiponitrile to the process.

The disadvantage of this process is that the adiponitrile recovered in the further processing of the reaction discharge contains undesired by-products, especially amines, such as p. ex. l-amino-2-cyanocyclopentene (ACCPE), 2- (5-cyanopentyl-amino) -tetrahydroazepine (CPATHA) and bishexa-methylenetriamine (BHMTA).

The by-products can not be separated by distillation of the adiponitrile by the described process due to the formation of azeotropes or quasi-azeotropes. This results, especially when the adiponitrile is recycled, to an accumulation in the total process.

In recycle, the 2-aminomethylcyclopentylamine derivative (AMCPA), which contaminates the valuable product, hexamethylenediamine, can be formed from the ACCPE in the hydrogenation step. From US-A 3,696,153 it is known that AMCPA is very difficult to separate from hexamethylenediamine.

From DE 19,636,766 it is known to add adiponitrile to recycle 0.01 to 10% by weight of an acid, with respect to adipodinitrile, or an acid ion exchanger, to separate the adiponitrile from this mixture and to recycle it in the hydrogenation reactor . Here the basic by-products containing nitrogen are neutralized by the addition of the acids. The disadvantage of this method is that salts are formed, which must be removed from the process and eliminated. For which an additional procedural stage is needed.

The object of the present invention is therefore to provide a process for separating, in a technically simple and economical manner, adiponitrile from a mixture containing adiponitrile, hexamethylenediamine, 6-amincaproni -tryl and components with a boiling point above that of the adipoditrile ("high-boiling components), obtained by partial hydrogenation of adiponitrile, avoiding the aforementioned disadvantages, as well as recycling the adiponitrile in a pure form as possible.

This object is achieved by the procedure defined above.

The partial hydrogenation of adiponitrile can be carried out according to one of the known processes, for example, according to one of the known processes described in US Pat. No. 4,601,859.1, US Pat. No. 2,762,835, US Pat. No. 2,208,598, DE-A 848,654, DE-A 95.44. .161, WO 96/18603, WO 97 / 10,052, DE-A 42.35.466 or WO 92/21505, carrying out the hydrogenation, in general, in the presence of an element of the eighth secondary group or their mixtures, for example, catalysts containing nickel, cobalt, iron, ruthenium or rhodium. The catalysts can be used as homogeneously dissolved or suspended catalysts or as support catalysts or solidly arranged catalysts. Suitable support catalysts are, for example, aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, active carbons and spinels. Suitable catalysts are, for example, Raney nickel and Raney cobalt, which can be additionally provided with other elements.

Generally, the catalyst loading in the region of 0.05 to 10 kg, preferably 0.1 to 5 kg of adiponitrile / 1 cat is selected. x h.

The hydrogenation is generally carried out at temperatures of 20 to 220 ° C, preferably 50 to 150 ° C, and at hydrogen partial pressures of 0.1 to 40 MPa, preferably 0.5 to 30 MPa.

Preferably, hydrogenation is carried out in the presence of a solvent, such as, for example, ammonia, amines or alcohols, especially ammonia. The amount of ammonia is generally selected from such a mill, ranging from 0.1 to 10 kg, preferably 0.5 'to 3 kg of ammonia / kg of adiponitrile.

The molar ratio between 6-aminocapronitrile and hexamethylenediamine and thus the ratio between caprolactam and hexamethylenediamine can be regulated by the selected conversion of adiponitrile. Preferably, adiponitrile conversions are worked from 10 to 90%, preferably from 30 to 80%, in order to obtain high selectivities of 6-aminocapronitrile.

As a general rule, the sum of 6-aminocapronitrile and hexamethylenediamine is increased according to the catalyst and the reaction conditions to 95 to 99%, the most important by-product being hexamethylene-mine.

As catalysts, preferably compounds containing nickel, ruthenium, rhodium, iron and cobalt are used, especially those of the Raney type, especially Raney nickel and Raney cobalt. The catalysts can also be used as support catalysts, using as support, for example, aluminum oxide, silicon dioxide, zinc oxide, activated carbon or titanium dioxide (S. Appl. Cat.Het., 1987, pp. 106). 122; Catalysis, Vol. 4 (1981) pp. 1 to 30). Above all, Raney nickel is preferred.

The catalysts of nickel, ruthenium, rhodium, iron and cobalt-may be advantageously modified with metals of groups VIB (Cr, Mo, W) and VIII (Fe, Ru, Os, Co (only in case of nickel), Rh, Go, Pd, Pt) of the periodic system. According to the observations made to date, for example, according to DE-A 22.60.978; Bull. Soc. Chem. 13 (1946) p. 208), the use of, in particular, modified Raney nickel catalysts, for example with chromium and / or iron, provides higher selectivities of 6-aminocapronitrile.

The amount of the catalyst is generally selected in such a way that the amount of cobalt, ruthenium, rhodium, iron or nickel varies from 1 to 50% by weight, preferably from 5 to 20% by weight, based on the amount of dinitrile used.

The catalysts can be used as fixed bed catalysts in the depletion or runoff method, or as suspended catalysts.

In a preferred embodiment, the adipodinitrile is partially hydrogenated in 6-aminocapronitrile at high temperature and high pressure, in the presence of a solvent and a catalyst, using a catalyst containing i) a compound based on a metal selected from the group comprising nickel, cobalt, iron, ruthenium and rhodium, ii) from 0.01 to 25% by weight, preferably from 0.1 to 5% by weight, with respect to i), of a promoter based on a metal selected from the group comprising palladium, platinum, iridium, osmium, copper , silver, gold, chromium, molybdenum, tungsten, manganese, rhenium, zinc, cadmium, lead, alumunium, tin, phosphorus, arsenic, antimony, bismuth and rare earths, as well as iii) from 0 to 5% by weight, preferably from 0.1 to 3% by weight, based on i), of a compound based on an alkali metal or alkaline earth metal.

Preferred catalysts are those, in which component i) contains, at least, a compound based on a metal, selected from the group of nickel, cobalt and iron, in an amount of 10 to 95% by weight, as well as ruthenium and or rhodium in an amount of 0.1 to 5% by weight, each time with respect to the sum of the components i) to iii), component ii) contains, as a minimum, a promoter based on a metal selected from group comprising silver, copper, manganese, rhenium, lead and phosphorus, in an amount of 0.1 to 5% by weight, with respect to i), and component iii) contains, as a minimum, a compound based on metals alkaline and alkaline earth metals, selected from the group comprising lithium, sodium, potassium, cesium, magnesium and calcium, in an amount of 0.1 to 5% by weight Especially preferred catalysts are those, which contain i) an iron-based compound, eg iron oxide and ii) from 0 to 5% by weight, with respect to i) of a promoter based on one element or 2, 3, 4, 5 or 6 elements selected from the group comprising aluminum, silicon, zirconium, vanadium, manganese and titanium, as well as iii) from 0 to 5% by weight, preferably from 0.1 to 3% by weight, in particular from 0.1 to 0.5% by weight, with respect to i), of a compound based on an alkali metal or alkaline earth metal, selected, preferably, from the group comprising lithium, sodium, potassium, rubidium, cesium, magnesium and calcium.

The catalysts used can preferably be mastic catalysts or support catalysts. Suitable support materials are porous oxides, for example, aluminum oxide, silicon oxide, aluminum silicates, lanthanide oxide, titanium dioxide, zirconium dioxide, magnesium oxide, five oxide and the zeolites, as active carbon or mixtures thereof.

Generally, the catalysts are obtained in such a way that precursors of component (i) are precipitated, if desired, together with precursors of the promoter components (ii) and, if desired, with precursors of the components (iii) , in the presence or absence of support materials (depending on the type of catalyst to be obtained), forming the catalyst precursor thus obtained, if desired, in macaroni or tablets, dried and then calcined. The support catalysts can also be prepared, generally, by impregnating the support with a solution of the components (i), (ii), and, optionally (iii), the individual components can be added simultaneously or successively, or by spraying the components (i), (ii), if desired, (iii), on the support according to methods known per se.

As precursors of components i), generally well-soluble salts are suitable in water of the aforementioned metals, such as mitrates, chloride, acetates, formates and sulfates, preferably nitrates.

As precursors of component ii), generally well-soluble salts are suitable in water or complex salts of the aforementioned metals, such as nitrates, chlorides, acetates, formates and sultans, as well as hexachloroplatinate, preferably nitrates and hexachloroplatinate.

Suitable precursors of components iii) are generally water-soluble salts of the aforementioned alkali and alkaline earth metals, such as hydroxides, carbonates, nitrates, chlorides, acetates, formates and sulphates, preferably hydroxides and carbonates.

The precipitation is carried out, generally, from the aqueous solutions, adding, if necessary, precipitation reagents, varying the pH value or varying the temperature.

Normally, the intermediate catalyst mass thus obtained is dried at temperatures of, generally, 80 to 150 ° C, preferably 80 to 120 ° C. Calcination is usually carried out at temperatures of 150 to 500 ° C, preferably 200 to 450 ° C in a gas stream from air or nitrogen.

After calcination, the mass of the catalyst obtained is generally subjected to a reducing atmosphere ("activation"), for example by subjecting it for 2 to 24 hours at a temperature of 80 to 250 ° C, preferably 80 to 180 ° C. to catalysts based on ruthenium or rhodium as components i), or from 200 to 500 ° C, preferably from 250 to 400 ° C to catalysts based on one of the metals selected from the group nickel, cobalt and iron as component i), to an atmosphere of hydrogen or a mixture of gas containing hydrogen and an inert gas, such as, for example, nitrogen. The catalyst charge here preferably is 200 1 per liter of catalyst.

Advantageously, activation of the catalyst is carried out directly in the synthesis reactor, since in this way, the intermediate step normally required, namely the passivation of the surface at temperatures of, generally, 20 to 80 ° C, is generally suppressed. , preferably from 25 to 35 ° C by nitrogen-oxygen mixtures, such as, for example, air. Activation of passivated catalysts is then preferably carried out in the synthesis reactor at a temperature of 180 to 500 ° C, preferably 200 to 400 ° C, under an atmosphere containing hydrogen.

The catalysts can be used in a Rl reactor as fixed bed catalysts in the depletion or runoff method or as suspension catalysts (see Figure 1).

When the reaction is carried out in a suspension, then temperatures are generally chosen in the region of 40 to 150 ° C, preferably 50 to 100 ° C, most preferably 60 to 90 ° C; the pressure is generally chosen in the region of 2 to 30 MPa, preferably 3 to 30 MPa, most preferably 4 to 9 MPa. The residence times depend substantially on the performance, the desired selectivity and the desired conversion; normally, the residence time is chosen in such a way that a maximum yield is reached, for example, in the region of 50 to 275 minutes, preferably 70 to 200 minutes.

In the suspension method, liquid diluents, advantageously primary, secondary or tertiary amines, such as monoamines, diamines and triamines having 1 to 6 carbon atoms, for example, trimethylamine, triethylamine, tripropylamine and tributylamine, or alcohols, can advantageously be added. , especially methanol and ethanol, preferably, ammonia or mixtures thereof. Suitably, a concentration in adipodinitrile is chosen in the region of 10 to 90% by weight, preferably 30 to 80% by weight, most preferably 40 to 70% by weight, based on the sum of adiponitrile and diluent.

The amount of catalyst is generally chosen to vary in the region from 1 to 50% by weight, preferably from 5 to 20% by weight, based on the amount of adiponitrile used.

It is also possible to carry out the partial hydrogenation in batch or continuous form in a fixed bed catalyst, applying the method by exhaustion or run-off, generally selecting a temperature in the region of 20 to 150 ° C, preferably 30 to 90 ° C. , and, generally, a pressure in the region of 2 to 40 MPa, preferably of 3 to 30 MPa.

Advantageously, liquid diluents, advantageously primary, secondary or tertiary amines, such as monoamines, diamines and triamines having 1 to 6 carbon atoms, for example trimethylamine, triethylamine, tripropylamine and tributylamine, or alcohols, especially, can be added. methanol and ethanol, preferably ammonia, or mixtures thereof.

In a preferred embodiment, an ammonia content is chosen in the region of 1 to 10 g, preferably 2 to 6 g per g of adiponitrile. Preferably, a catalyst loading is chosen in the region of 0.1 to 2.0 kg, preferably 0.3 to 1.0 kg of adiponitrile / 1 x h. Here, too, the conversion can be specifically regulated and with it the selectivity, varying the residence time.

It has proven advantageous to add basic additives, especially hydroxides, carbonates or alcoholates of the alkali metals or calcalinotérreos or mixtures of such compounds, in the hydrogenation according to step a).

When a diluent is used in step a), it can be removed advantageously between step a) and step b) in a manner known per se, preferably by distillation, and, for example, be used again in stage a) .

The discharge of the hydrogenation can be further carried out according to the invention in two stages by distillation (see FIGS. 1 and 2).

Hexamethylenediamine, together with the secondary product, hexamethyleneimine, can be separated from the reaction mixture (step b)). This can be done in two or more columns, preferably in a column (K 1).

In a preferred embodiment the background temperature in step b) should be below 185 ° C, preferably below 180 ° C, it being advisable, due to the low vapor pressure of the compounds to be separated, to work at a temperature of at least 100 ° C, preferably at least 130 ° C. The pressures at the bottom of the column should advantageously be from 0.1 to 100, in particular from 5 to 40 mbar. Preferably, the residence times of the bottom product in the distillation according to step b) must be from 1 to 60, in particular from 5 to 15 minutes.

The bottom product obtained from the distillation according to step b) may be further elaborated by two alternative methods, according to steps cl) and di), or step c2).

According to step c2 (FIG. 1), the bottom product is introduced into a K 2 column, in which 6-aminocapronitrile is separated as heads, adiponitrile in a side discharge and high-boiling components in the bottom.

The bottom temperature in step c2) is, according to the invention, below 185 ° C, preferably below 180 ° C, being recommended, due to the low vapor pressure of the compounds to be separated, a temperature of of at least 100 ° C, preferably at least 130 ° C. The pressures at the bottom of the column should advantageously be from 0.1 to 100, in particular from 5 to 40 mbar. Preferably, the residence times of the bottom product in the distillation according to step c2) are from 1 to 60, in particular from 5 to 15 minutes.

According to steps cl) / dl) (FIG. 2), the bottom product is introduced into a K 2a column, in which the 6-amino-capronitrile is detylated as heads (step cl)), the product is introduced Fonso in a K 2b column where the adiponitrile is distilled as heads (stage di)) and high boiling components through the bottom.

In a preferred embodiment, the background temperature in step cl) must be below 185 ° C, preferably below 180 ° C, it being advisable, due to the low vapor pressure of the compounds to be separated, to work at a bottom temperature of at least 100 ° C, preferably at least 130 ° C. The pressures at the bottom of the column should advantageously be from 0.1 to 100, in particular from 5 to 40 mbar. Preferably, the residence times of the bottom product in the distillation according to step cl) must amount to 1 to 60, especially 5 to 15 minutes.

The bottom temperature in step di) is, according to the invention, below 185 ° C, preferably below 180 ° C, it being advisable, due to the reduced vapor pressure of the compounds to be separated, to work at a background temperature of at least 100 ° C, preferably at least 130 ° C. The pressures at the bottom of the column should advantageously be from 0.1 to 100, in particular from 5 to 40 mbar. Preferably, the residence times of the bottom product in the distillation according to step di) must amount to 1 to 60, especially 5 to 15 minutes.

In order to reduce the content of by-products in the recovered adiponitrile, it is advantageous to add, in the process of the invention, advantageously, at the bottom of the column K 2b in batch form or, preferably, continuously, an organic or inorganic acid, or purifying the adiponitrile obtained after the K 2 or K 2b columns in batch form or, preferably, continuously with an organic or inorganic acid.

The adipodinitrile obtained after the two alternatives can be used, advantageously, in the partial hydrogenation giving 6-aminocapronitrile and hexamethylenediamine, for example, by recycling it to step a) of the process of the invention, or in a complete hydrogenation process giving hexamethylenediamine.

Surprisingly, it has been found in the recycling of the adiponitrile recovered according to the process of the invention in partial hydrogenation, that the reduction according to the invention of the amount of l-amino-2-cyanocyclopentene in the recycled adiponitrile is very advantageous for hydrogenation, the distillative purification of hexamethylenediamine and the permanence of the hydrogenation catalyst Example 1: a) Obtaining the iron hydrogenation catalyst For the partial hydrogenation of adiponitrile in 6-aminoca-pronitrile and hexamethylenediamine, an iron catalyst based on a magnetite obtained according to DE 19,636,767, example 2 a) is used. The granulometric fraction of the particle size of 3 to 5 mm is used. b) Adipodinitrile partial hydrogenation A tubular reactor (length 180 cm, d = 30 mm) is filled with 720 ml (1630 g) of the mass of catalyst prepared according to a) and without pressure it is reduced in the hydrogen stream (500 Nl / h).

In this process the temperature rises within 24 hours from 30 ° C to 340 ° C and then it is maintained for 72 hours at 340 ° C.

After lowering the temperature, 330 g / h of DNA, 1200 g / h of ammonia and 140 Nl / h of hydrogen are introduced into the reactor at 250 bar and 90 ° C of feed temperature.

Hydrogenation is carried out for 1500 hours under the indicated conditions. During the entire course of the hydrogenation and given a conversion of 60% DNA is a constant total selectivity (sum of the selectivities of 6-amino-capronitrile and hexamethylenediamine) of 99%. The selectivity of 6-aminocaproni rile decreases during the process from 50% to 48.5%. c) Further elaboration of the hydrogenation discharge For the subsequent batch processing, the hydrogenation discharges are collected during the test.

From these discharges, ammonia is first distilled in a column with 20 theoretical plates by the head. As a background product, a mixture is obtained, which according to gas chromatographic analysis consists of approx. 30 mol% 6-aminocaproni rile, 39 mol% adiponitrile and 30 mol% hexamethylenediamine. Hexamethyleneimine is the most important byproduct.

From 1000 g of bottom product obtained, 296 g of hexamethylenediamine are removed in the same column at a bottom temperature of 180 ° C, containing apros. 0.5% by weight of hexamethyleneimine. 695 g of the obtained bottom product are distilled in a continuous-running column in such a way that about 305 g of 6-aminocapronitrile are removed from the head, 380 g of adiponitrile are discharged laterally and 10 g of components are removed from the bottom. of high boiling putno containing adiponitrile. It is distilled at a head pressure of 20 to 40 mbar.

The bottom temperature of the column is varied, changing the head pressure. The reflux ratio is 2: 1. Table 1 shows how the amount of l-amino-2-cyano-cyclopentene in the adiponitrile of the lateral discharge varies as a function of the background temperature of the column.

Table 1 1) ppm of l-amino-2-cyanocyclopentene, with respect to the adiponitrile contained in the side discharge

Claims (14)

Claims

1. Procedure for the simultaneous obtaining of 6-aminoca-pronitrilo and hexamethylenediamine, starting from adiponitrile, which comprises the following steps a) hydrogenation of adiponitrile in the presence of a catalyst, which contains as a catalytically active component an element of the eighth secondary group, obtaining a mixture containing 6-aminocapronitrile, hexamethylenediamine, adiponitrile and high-boiling components, b) distillative separation of hexamethylenediamine from the mixture containing 6-aminocapronitrile, hexamethylenediamine, adiponitrile and high-boiling components, and, alternatively, cl) Distillative separation of 6-aminocapronitrile followed by di) the distillative separation of adiponitrile, or c2) Simultaneous distillative separation of 6-aminocapronitrile and adiponitrile in separate fractions, process which is characterized in that the background temperatures in steps d) or c2) are below 185 ° C.

2. The method according to claim 1, wherein the background temperatures in steps di) or c2) are below 180 ° C. Process according to claim 1 or 2, wherein the

The catalyst in step a) contains as a catalytically active element iron, cobalt, nickel, ruthenium or rubidium or their mixtures.

4. Process according to claims 1 to 3, wherein The catalyst in step a) contains iron, cobalt or nickel or their mixtures as the catalytically active element.

5. Process according to claims 1 to 4, wherein

The catalyst in step a) is based on Raney nickel or Raney cobalt or mixtures thereof. Process according to claims 1 to 4, wherein in step a) a catalyst is used, which contains 25 i) a compound based on a metal selected from the group comprising nickel, cobalt, iron, ruthenium and rhodium, Iv) from 0.01 to 25% by weight, preferably from 0.1 to 5% by weight, with respect to i), of a promoter based on a metal selected from the group comprising 35 dioxide, platinum, iridium, osmium, copper, silver, gold, chromium, molybdenum, tungsten, manganese, rhenium, zinc, cadmium, lead, alu unio, tin, phosphorus, arsenic, antimony, bismuth and rare earths, as well as v) from 0 to 5% by weight, preferably from 0.1 to 3% by weight, based on i), of a compound based on an alkali metal or alkaline earth metal.

7. Process according to claims 1 to 4, wherein in step a) a catalyst is used, which contains i) an iron-based compound, iv) from 0 to 5% by weight, with respect to i) of a promoter based on one element or 2, 3, 4, 5 or 6 elements selected from the group comprising aluminum, silicon, zirconium, vanadium, manganese and titanium, as well as v) from 0 to 5% by weight, with respect to i), of a compound based on an alkali metal or alkaline earth metal.

8. Process according to claims 1 to 7, wherein in step a) a diluent is additionally used.

9. Process according to claim 8, wherein primary, secondary or tertiary amines, ammonia or alcohols or their mixtures are used as the diluent.

10. Process according to claim 8 or 9, wherein the diluent is separated between steps a) and b).

11. Process according to claims 1 to 10, wherein in step a) additional basic substances are added.

12. Process according to claim 11, wherein hydroxides, carbonate or alcoholates of the alkali or alkaline earth metals or mixtures thereof are used as basic substances.

13. Process according to claims 1 to 12, wherein after step di) or c2) the adiponitrile is recycled to step a).

14. Process according to claims 1 to 12, wherein after step di) or c2) the adiponitrile is hydrogenated in hexamethylenediamine.