Process for manufacturing an aliphatic diamine

Abstract

A process for manufacturing and purifying an aliphatic primary diamine and a chemical reaction unit for manufacturing the same is provided, wherein the process comprises the following steps: a) reacting an aliphatic dinitrile and a hydrogen-containing gas in the presence of a catalyst in a reaction unit R1 to form a medium M1 containing the aliphatic primary diamine, and b) subjecting a stream F1 resulting from the medium M1 to a distillation sequence comprising a distillation step to recover a first fraction containing the aliphatic primary diamine in purified form and a second fraction, wherein the second fraction is subjected to a catalytic hydrogenation step, or the second fraction is subjected to a further distillation step to recover a third fraction, which is subjected to a catalytic hydrogenation step.

Description

[0001] Process for manufacturing an aliphatic diamine

[0002] Description

[0003] The present invention relates to a process for manufacturing and purifying an aliphatic primary diamine, especially hexamethylenediamine, comprising a catalytic hydrogenation step of an aliphatic dinitrile and a purifying step of the resulting diamine, and to a chemical production unit for carrying out said process.

[0004] Background of the invention

[0005] Aliphatic diamines, especially hexamethylene diamine, are commonly used as monomers in the manufacture of polymers, such as polyamides, as intermediates in the manufacture of isocyanates or as a cross-linking agent in epoxy resins.

[0006] Virtually all hexamethylenediamine, also referred to HMD herein-below and further known as 1 ,6-diaminohexane or 1 ,6-hexanediamine, is industrially produced by the catalytic hydrogenation of adiponitrile. Two main processes using different catalysts in liquid phase and reaction conditions are known. The high-pressure process, operating generally at a pressure of 20 to 35 MPa and a temperature of 100 to 150°C, is usually carried out in the presence of a catalyst based on a metal oxide, such as iron oxide or cobalt oxide, and often in the presence of ammonia. The low-pressure process is usually caried out at a moderate pressure, e.g., 2 to 5 MPa, and temperature, e.g., 60 to 100°C, using, for example, water or an alcohol as liquid medium and a metal catalyst, for example, of Raney type, such as Raney nickel or Raney cobalt.

[0007] Various by-products, both light by-products and heavy by-products, may be formed during the catalytic hydrogenation and / or during work-up of the hydrogenated product. These by-products may cause, for example, yellow coloring or branching in polyamides manufactured as well as adverse product properties of, for example yarns or fibers or engineering plastics, produced therefrom. Additionally, the water, added and / or generated, should be removed.

[0008] If hexamethylenediamine is the desired product, by-products may be, for example, hexamethyleneimine (HMI), 1 ,2-diaminocyclohexane (DCH) or isomers thereof, 2-aminomethyl- cyclopentylamine (AMCPA), 6-aminocapronitrile (ACN), bis(hexamethylene) triamine (BHT), other imines, such as tetrahydroazepine (THA), 1 ,2-aminocyclohexanol (ACHOL), 6- aminocaproamide (ACA) or oligomers, especially dimers, composed of imines and hexamethylenediamine.

[0009] Accordingly, the hydrogenated products, especially hexamethylenediamine, are usually recovered by a sequence of distillation steps intended to remove water and by-products. Several processes have been proposed for purifying hexamethylenediamine in order to obtain the desired diamine with a high degree of purity. WO 2009 / 0472919 A1 discloses a process for purifying hexamethylenediamine, wherein contaminating amounts of imines, especially tetrahydroazepine, are separated by distilling said mixture with a short residence time of less than 15 minutes.

[0010] US 5,961 ,788 A discloses a sequential distillation process for removing tetrahydroazepine from aminocapronitrile in the presence of sodium hydroxide, wherein the bottom fraction of the second distillation is recycled to the incoming feed of the first distillation. The mass flow ratio of distillate to feed was 0.7. An overall aminocapronitrile recovery of 97% is described.

[0011] WO 2005 / 000785 A1 discloses a process for purifying hexamethylenediamine, wherein the diamine is subjected to a hydrogenation treatment in the presence of a catalyst based on palladium-on-charcoal.

[0012] WO 98 / 11052 A1 discloses a process for separating 2-aminomethylcyclopentylamine from a hexamethylenediamine-containing mixture by distilling at a pressure from 1 to 300 mbar and recovering hexamethylenediamine as bottom product.

[0013] WO 98 / 34901 A1 discloses a process for separating 2-aminomethylcyclopentylamine from a hexamethylenediamine-containing mixture by distilling in the presence of added water.

[0014] US 6,139,693 A discloses a process for recovering hexamethylenediamine from an adiponitrile partial hydrogenation mixture by distilling in 3 stages, wherein adiponitrile, obtained as a mixture with 6-aminocapronitrile in the first stage and separated therefrom, may be recycled to partial hydrogenation.

[0015] WO 2003 / 099768 A1 discloses a process for reducing the level of tetrahydroazepine from a reaction effluent from a partial hydrogenation of adiponitrile by a) reacting said effluent with an anionic nucleophile, like potassium phthalimide, b) distilling the resultant mixture to obtain the desired product as head product and c) further distilling the bottom product at a temperature lower than in step b) to obtain further desired product, which may be recycled to step a).

[0016] WO 97 / 023454 A1 discloses a process for simultaneous manufacturing caprolactam and hexamethylenediamine from adiponitrile, wherein the intermediate 6-aminocapronitrile is purified in five distillation steps and at least a part of the by-products, obtained in a step, is recycled to an earlier step.

[0017] WO 2019 / 166482 A discloses a process for purifying hexamethylenediamine by subjecting a mixture comprising hexamethylenediamine and by-products to a distillation step in a dividing wall column and recovering purified hexamethylenediamine from a side stream. WO 2019 / 166483 A discloses a process for purifying hexamethylenediamine by subjecting a mixture comprising hexamethylenediamine and by-products to a distillation step, wherein the bottom pressure of the distillation apparatus is below about 35 kPa.

[0018] WO 2007 / 147960 A2 discloses a process for manufacturing hexamethylenediamine by hydrogenating adiponitrile and purifying the product via four distillation steps, wherein heavy by- product-containing streams of the second and fourth distillation column are further distilled to recover hexamethylenediamine to be recycled to the second or fourth distillation step. The process is described to require less energy in the third and fourth distillation step and exhibit hexamethylenediamine of high purity.

[0019] The presence of by-products, preferably imines, especially THA, may be detected and measured by polarographic analysis, expressed by the polarographic index (PI or POLI), or by UV analysis, expressed by the UV index.

[0020] The known processes for manufacturing diamines do not yet fully meet the requirements, especially with respect to the amount of contained components detectible by polarographic analysis or UV analysis. There is still a need for a process of manufacturing diamines of high purity and in an economical matter.

[0021] It is therefore an object of the invention to provide a process for manufacturing and purifying a diamine having a high purity, especially with respect to the amount of contained components detectible by polarographic analysis, in a higher yield and I or allowing a facilitated work-up procedure.

[0022] Summary of the invention

[0023] It has now been found that recycling of a bottom fraction with minor amounts of the desired diamine, optionally after a further distillation step, may significantly reduce the content of byproducts, which are detectible by polarographic analysis and / or by UV analysis, and facilitate the work-up.

[0024] Therefore, in a first aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, the process comprising a) reacting an aliphatic dinitrile and a hydrogen-containing gas in the presence of a catalyst in a reaction unit Ri to form a medium Mi containing the aliphatic primary diamine, and b) subjecting a stream Fi resulting from the medium Mi to a distillation sequence comprising a distillation step to recover a first fraction containing the aliphatic primary diamine in purified form and a second fraction, wherein the second fraction is subjected to a catalytic hydrogenation step, or the second fraction is subjected to a further distillation step to recover a third fraction, which is subjected to a catalytic hydrogenation step. In a further aspect, the invention relates to a chemical production unit for carrying out a process, as defined in any aspect herein, the chemical production unit comprising: a first hydrogenating reaction unit Ri for forming a medium Mi; a distillation unit for recovering a first fraction containing the aliphatic primary diamine in purified form and a second fraction; and a means for passing the second fraction to a hydrogenating reaction unit, or a further distillation unit UFfor recovering a third fraction and a means for passing the third fraction to a hydrogenating reaction unit.

[0025] Detailed description of the invention

[0026] The term “light by-products”, as used herein, means, in the field of distillation of organic compounds, the compounds exhibiting a lower boiling point than that or those of the hydrogenated compounds, which have to be recovered.

[0027] The term “heavy by-products”, as used herein, means, in the field of distillation of organic compounds, the compounds exhibiting a higher boiling point than that orthose of the hydrogenated compounds, which have to be recovered.

[0028] The pressure in bar or mbar, as used herein, means the pressure in bar or mbar absolute.

[0029] As used herein, the indefinite article “a” comprises the singular but also the plural, i.e., an indefinite article in respect to a component of a composition means that the component is a single compound or a plurality of compounds. If not stated otherwise, the indefinite article “a” and the expression “at least one” are used synonymously.

[0030] Figure 1 shows a schematic overview of a system for performing a preferred embodiment containing one hydrogenation reaction unit without a further distillation step.

[0031] Figure 2 shows a schematic overview of a system for performing a preferred embodiment containing one hydrogenation reaction unit and a further distillation step.

[0032] Figure 3 shows a schematic overview of a system for performing a preferred embodiment containing one hydrogenation reaction unit and a further distillation step.

[0033] Figure 4 shows a schematic overview of a system for performing a preferred embodiment containing one hydrogenation reaction unit without a further distillation step.

[0034] Figure 5 shows a schematic overview of a system for performing a preferred embodiment containing one hydrogenation reaction unit and a further distillation step.

[0035] Figure 6 shows a schematic overview of a system for performing a preferred embodiment containing two hydrogenation reaction units and a further distillation step. Figure 7 shows a schematic overview of a system for performing a preferred embodiment containing two hydrogenation reaction units and a further distillation step.

[0036] The process of manufacturing and purifying an aliphatic primary diamine usually comprises a step of hydrogenating an aliphatic dinitrile in the presence of a suitable catalyst in a hydrogenation reactor and a step of purifying said diamine.

[0037] The process of step a) includes reacting an aliphatic dinitrile with a hydrogen-containing gas in the presence of a catalyst in a hydrogenating reaction unit Ri to form a medium Mi containing the aliphatic primary diamine. The medium Mi usually contains the aliphatic primary diamine as a main product, the catalyst, one or more by-products and optionally a diluent, preferably water.

[0038] The process of step a) is generally a complete hydrogenation of an aliphatic dinitrile, i.e. a process using conditions, wherein the aliphatic primary amine is the desired product as monomer. The process of step a) does generally not comprise a partial hydrogenation of an aliphatic dinitrile with coproduction and isolation of an aliphatic primary diamine and an aliphatic primary monoamine having a residual nitrile function (an aliphatic a,w-aminonitrile) as desired products, for example to be used as monomers. Preferably, the instant process does not comprise a partial hydrogenation of adiponitrile with coproduction of hexamethylenediamine and 6-aminocapronitrile.

[0039] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein step a) does not comprise a partial hydrogenation of an aliphatic dinitrile with coproduction of an aliphatic primary diamine and an aliphatic a,w-aminonitrile, preferably the process does not comprise comprise a partial hydrogenation of adiponitrile with coproduction and isolation of hexamethylenediamine and 6- aminocapronitrile.

[0040] The process may be applied to manufacture an aliphatic primary C2-Ci2-diamine, preferably C4- Ci2-diamine, which may be linear or branched. The aliphatic primary C2-Ci2-diamine is preferably selected from the group consisting of 1 ,4-diaminobutane, 1 ,5-diaminopentane, 2- methyl-1 ,5-diaminopentane, 1 ,6-diaminohexane and 1 ,12-diaminododecane.

[0041] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the diamine is a C2-Ci2-diamine, preferably a C4- Ci2-diamine.

[0042] The aliphatic primary diamines may be prepared from the corresponding dinitriles.

[0043] Hexamethylenediamine and 2-methylpentanediamine, which are obtained by hydrogenation of adiponitrile or of methylglutaronitrile, are preferred. More preferred is a process for manufacturing hexamethylenediamine from adiponitrile.

[0044] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the diamine is hexamethylenediamine or 2- methylpentanediamine, preferably hexamethylenediamine.

[0045] The aliphatic dinitriles may be derived from any suitable source. Adiponitrile may be, for example, derived from the reaction of adipic acid with ammonia, the reaction of dichlorobutane with HCN, the hydrogenation of dicyanobutane, etc.. Methylglutaronitrile, for example, may be obtained in conjunction with adiponitrile in the process for the hydrocyanation of butadiene, followed by distilling to recover methylglutaronitrile as a distillation fraction containing a few percent of ethylsuccinonitrile and by further distilling said fraction to obtain purified methylglutaronitrile. The processes are known in the art.

[0046] The hydrogenation step of the dinitrile may be carried out according to any process known in the art, for example, as described in US 3398195, GB 1164354 A, US 3821305, US 3056837, WO 00 / 37424 A1 or WO 00 / 03972 A1.

[0047] Usually, step a) comprises feeding a hydrogen-containing gas and the aliphatic dinitrile to a reaction unit Ri containing a reaction medium Mo.

[0048] The reaction medium Mousually contains the catalyst and optionally a diluent and an inorganic basic compound.

[0049] The catalyst used in step a) of the instant process is a hydrogenation catalyst suitable for hydrogenating a dinitrile to a diamine. The catalyst may comprise a Group VIII element including iron, cobalt, nickel, rhodium, or ruthenium. The metal can be used in combination with one or more promoter elements. Suitable examples of a promoter element include molybdenum, tungsten, titanium, chromium, iron, nickel, cobalt, copper, silver, gold, zinc, cadmium, lead, tin, palladium, platinum, osmium, rhenium, iridium, antimony, bismuth and rare earth metals.

[0050] The catalyst may be supported or unsupported. Suitable examples of a support include alumina, silica, titanium dioxide, zirconium dioxide, magnesium oxide, active carbons and spinels.

[0051] Among non-supported catalysts, a preferred catalyst is a catalyst of Raney-type, more preferably Raney nickel or Raney cobalt, optionally comprising one or more promoter elements. Examples of a promoter element, particularly suited to Raney nickel or to Raney cobalt, include titanium, molybdenum, tungsten, chromium, iron, zinc, copper, silver and gold.

[0052] A suitable example of a catalyst is a metal catalyst based on Raney nickel or Raney cobalt. Such catalysts are commercially available or may be produced, as described, for example in WO 2000 / 67903 A1 or US 1 ,628, 190. The amount of the catalyst, especially the quantity of catalytically active metal, may vary dependent on the desired reaction rate. Preferably, the amount of catalyst is in the range of from 1 to 50 wt%, based on the total weight of the medium Mi, more preferably from 10 to 35 wt%, especially 10 to 30 wt%.

[0053] The catalyst may have any shape such as powder, grains or pellets.

[0054] The catalyst may be used in the form of a suspension or as a fixed bed. The catalyst may be regenerated to be used, for example, after being subjected to an activation treatment with hydrogen before the reaction.

[0055] The instant process applies, in particular, when the reaction step a) is carried out in the presence of a catalyst based on a Raney metal, such as Raney nickel, Raney cobalt or a combination thereof.

[0056] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the catalyst in the reaction unit Ri is based on a metal catalyst of Raney-type, preferably Raney nickel, Raney cobalt or a combination thereof.

[0057] More preferably, the catalyst in the reaction unit Ri is used in form of a catalyst suspension, wherein the catalyst is a catalyst based on Raney nickel, Raney cobalt or a combination thereof, especially a catalyst based on Raney nickel.

[0058] The hydrogen-containing gas may be hydrogen or a mixture containing hydrogen and an inert gas like argon or nitrogen.

[0059] The reaction step a) is usually carried out at an absolute hydrogen pressure < 50 bar, preferably < 40 bar, more preferably of from 10 to 35 bar.

[0060] The reaction step a) may be carried out at a temperature of from 50 to 140°C. The choice of temperature is usually dependent on the catalyst. Preferably, the reaction step a) is carried out at a temperature of from 60 to 100°C with a metal catalyst of Raney-type, preferably a catalyst based on Raney nickel, Raney cobalt or a combination thereof, especially a catalyst based on Raney nickel.

[0061] The reaction step a) may be carried out with or without a diluent, preferably in the presence of a diluent. The diluent may be water, an alcohol, the aliphatic primary diamine or a mixture thereof. A mixture may include a mixture containing one or more alcohols and water, a mixture of two or more alcohols or a mixture of the aliphatic primary diamine and water. An alcohol may be methanol, ethanol, n-propanol, 2-propanol, n-butanol, glycols, like ethylene glycol, or a mixture thereof. Preferably, the reaction step a) is carried out in the presence of a diluent, more preferably water.

[0062] The reaction step a) is usually carried out in the presence of a basic inorganic compound. Suitable examples include an alkali metal hydroxide and ammonium hydroxide. The basic inorganic compound is preferably sodium hydroxide or potassium hydroxide. The basic inorganic compound is usually used in an amount of from 0.1 to 2 mol per kg of catalyst, i.e., kg of catalytically active metal, preferably from 0.3 to 1.5 mol.

[0063] The reaction step a) may be carried out in a conventional reaction unit and at standard conditions. Any suitable reactor for a hydrogenation reaction may be employed. Examples of a reaction unit include a stirred tank reactor, a piston reactor, a trickle bed reactor, a bubble column reactor, or a plug-flow reactor.

[0064] The hydrogen-containing gas may either be added to make up for the consumption during the reaction or continuously circulated through the reaction unit. The hydrogen-containing gas is usually added to the reaction unit at a rate that will maintain hydrogen in molar excess relative to the aliphatic dinitrile, in order to form an essentially complete hydrogenation.

[0065] The reaction step a) may be carried out batchwise or continuously, preferably continuously.

[0066] Typically, the aliphatic dinitrile is added to the reaction unit such that the space velocity of the aliphatic dinitrile is of from 0.1 to 50 h-1, preferably 0.1 to 10 h-1, more preferably 0.5 to 5 IT1. The term “space velocity”, as used herein, means the unit weight of aliphatic dinitrile fed into the reaction unit per hour, per unit weight of the catalyst.

[0067] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary amine, wherein the reaction step a) is carried out a-i) at an absolute hydrogen pressure of from 10 to 35 bar, a-ii) at a temperature of from 60 to 100°C, a-iii) in the presence of a catalyst based on Raney nickel, a-iv) in the presence of a diluent containing water, a-v) in the presence of a basic inorganic compound, and a-vi) preferably, the aliphatic dinitrile is fed to the reaction unit with a space velocity of from 0.1 to 50 h1.

[0068] The medium Mi formed during step a) usually contains the aliphatic primary diamine as a main product, the catalyst, one or more by-products and optionally a diluent.

[0069] Prior to step b) the medium Mi is usually separated from the catalyst resulting in a stream Fi, preferably by filtration or separation by settling of catalyst used in suspension. A stream Fi resulting from a medium Mi formed in step a) contains usually the aliphatic primary diamine in crude form. The stream Fi is then subjected to a distillation sequence of step b).

[0070] The by-products are mainly formed during step a).

[0071] If hexamethylenediamine is the desired product, by-products may be, for example, hexamethyleneimine (HMI), 1 ,2-diaminocyclohexane (DCH) or isomers thereof, 2-aminomethyl- cyclopentylamine (AMCPA), bis(hexamethylene) triamine (BHT), 6-aminocapronitrile (ACN), other imines, such as tetrahydroazepine (THA), 1 ,2-aminocyclohexanol (ACHOL), 6- aminocaproamide (ACA) or oligomers, especially dimers, composed of imines, such as THA, and hexamethylenediamine.

[0072] If 2-methylpentanediamine is the desired product, the by-products may include bis(2-methyl- pentamethylene) triamine or one or more isomers of methylcyclopentanediamine.

[0073] The amount of any by-product, for example 6-aminocapronitrile (ACN), preferably a by-product detectible by polarographic analysis, in the stream Fi may vary and may be up to 10000 ppm, preferably up to 5000 ppm, based on the total weight of the aliphatic primary diamine, more preferably up to 3000 ppm. The amount of any by-product may be determined by gas chromatography (GC).

[0074] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary amine, wherein the amount of any by-product, preferably 6-aminocapronitrile, in the stream Fi is up to 5000 ppm, based on the total weight of the aliphatic primary diamine.

[0075] A stream Fi resulting from a medium Mi formed in step a) contains usually the aliphatic primary diamine in crude form. The stream Fi is then subjected to a distillation sequence of step b).

[0076] The distillation sequence of step b) comprises a distillation step in a distillation unit, wherein at least 2 fractions are recovered. The fraction containing the aliphatic primary diamine in purified form is referred to as “first fraction”. The first fraction may be recovered as a head fraction or as a side stream fraction. The second fraction is usually recovered as a fraction at a lower level of the distillation unit, preferably as a bottom fraction. Said fraction generally contains heavy byproducts, for example 6-aminocapronitrile.

[0077] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the first fraction is a head fraction or a side stream fraction, and the second fraction is a bottom fraction.

[0078] The third fraction is usually obtained from the second fraction which is treated in a further distillation step. The third fraction is preferably recovered as a head fraction HF, containing, for example 6-aminocapronitrile. Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the third fraction is a head fraction HF.

[0079] More preferably, the second fraction is a bottom fraction containing, for example 6- aminocapronitrile, and the third fraction is a head fraction HF, containing, for example 6- aminocapronitrile.

[0080] The mixture to be distilled (stream Fi) is usually subjected to a first distillation step in a distillation unit Ui to recover a head fraction Hi, generally containing mainly water and imines, for example, hexamethyleneimine, present, and a bottom fraction Bi containing the aliphatic primary diamine.

[0081] The bottom fraction Bi may then be subjected to a second distillation step in a distillation unit U2to recover a bottom fraction B2, generally containing by-products with a boiling point greater than that of the diamine (heavy by-products), and a head fraction H2containing the aliphatic primary diamine.

[0082] The head fraction H2may then be subjected to a third distillation step in a distillation unit, which may be a distillation unit U3to recover a head fraction and bottom fraction or a distillation unit of a dividing wall column design to usually recover a head fraction, a bottom fraction and a side stream fraction.

[0083] In one preferred alternative, the head fraction H2may be subjected to a third distillation step in a distillation unit H3to recover a head fraction, generally containing by-products with a boiling point lower than that of the diamine (light by-products), and a bottom fraction B3containing the aliphatic primary diamine.

[0084] The bottom fraction B3may then be subjected to a fourth distillation step in a distillation unit U4to recover a head fraction H4, containing the aliphatic primary diamine, and a bottom fraction B4, generally containing heavy by-products. The head fraction H4has usually the desired purity.

[0085] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein step b) comprises b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the diamine, and a bottom fraction B2; b-iii) subjecting the head fraction H2to a third distillation step to recover a bottom fraction B3, containing the diamine, and a head fraction H3; and b-iv) subjecting the bottom fraction B3to a fourth distillation step to recover a head fraction H4, containing the diamine in purified form, and a bottom fraction B4. In a second preferred alternative, the distillation sequence comprises a dividing wall column (Petlyuk column). Preferably, the distillation sequence of step b) comprises a step b-i) and a step b-ii), as described herein-before.

[0086] The head fraction H2from step b-ii) may then be subjected to a third distillation step in a distillation unit U3D, especially in a divided wall column, to recover a head fraction H3D, generally containing by-products with a boiling point lower than that of the diamine (light by-products), a bottom fraction B3D, generally containing by-products with a boiling point higher than that of the diamine (heavy by-products) and side stream fraction containing the aliphatic primary diamine. The side stream fraction SDhas usually the desired purity.

[0087] Accordingly, in a further preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein step b) comprises b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the diamine, and a bottom fraction B2; and b-iii’) subjecting the head fraction H2to a third distillation step, especially comprising a dividing wall column, to recover a side stream fraction SD, containing the aliphatic primary diamine, a head fraction H3Dand a bottom fraction B3D.

[0088] Accordingly, in a further preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein step b) comprises in a first alternative b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the aliphatic primary diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the aliphatic primary diamine, and a bottom fraction B2; b-iii) subjecting the head fraction H2to a third distillation step to recover a bottom fraction B3, containing the aliphatic primary diamine, and a head fraction H3; and b-iv) subjecting the bottom fraction B3to a fourth distillation step to recover a head fraction H4, containing the aliphatic primary diamine in purified form, and a bottom fraction B4as second fraction; or in a second alternative b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the aliphatic primary diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the aliphatic primary diamine, and a bottom fraction B2; and b-iii’) subjecting the head fraction H2to a third distillation step, especially comprising a dividing wall column, to recover a side stream fraction SD, containing the aliphatic primary diamine, as a first fraction, a head fraction H3Dand a bottom fraction B3Das a second fraction.

[0089] The first alternative comprising the steps b-i) to b-iv) is more preferred. The bottom fraction B4or B3D as the second fraction generally containing heavy by-products, for example, BHT, ACN, ACHOL or ACA, or oligomers composed of imines, such as THA, and the aliphatic primary diamines, especially hexamethylenediamine, may be fed to a hydrogenating reaction unit R. The hydrogenating reaction unit R may be the reaction unit Ri of step a) or an additional hydrogenating reaction unit R2or to both after dividing the bottom fraction B4or B3D. The reaction unit R2is a unit for catalytic hydrogenation.

[0090] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the catalytic hydrogenation step of the second fraction is carried out in the reaction unit Ri and / or a reaction unit R2.

[0091] Preferably, the hydrogenation unit R is the reaction unit Ri or the reaction unit R2, especially the reaction unit Ri.

[0092] The reaction unit R2for a further catalytic hydrogenation step, hereinafter referred to step c) is generally of the same type as the reaction unit Ri.

[0093] The conditions of the further hydrogenation step c) in the reaction unit R2are usually similar to the conditions, as mentioned for the reaction step a), preferably the same.

[0094] Preferably, the catalyst in the reaction unit R2is based on a metal catalyst of Raney-type, preferably Raney nickel, Raney cobalt or a combination thereof. More preferably, the catalyst in the reaction unit R2is used in form of a catalyst suspension, wherein the catalyst is a catalyst based on Raney nickel, Raney cobalt or a combination thereof.

[0095] The capacity of the reaction unit R2may be similar or may be reduced with respect to the reaction unit Ri.

[0096] Accordingly, the further catalytic hydrogenation step c) is carried out c-i) at an absolute hydrogen pressure of from 10 to 35 bar, c-ii) at a temperature of from 60 to 100°C, c-iii) in the presence of a catalyst based on Raney nickel, c-iv) in the presence of a diluent containing water, and c-v) in the presence of a basic inorganic compound.

[0097] The bottom fraction B2, generally containing heavy by-products, may be discharged or may be fed to a further distillation step in a distillation unit UF. The further distillation step is preferably the final distillation step.

[0098] Preferably, the bottom fraction B2is subjected to a further distillation step (b-v) within the first alternative of step b) or (b-iv’), resp., within the second alternative of step b). More preferably, the bottom fraction B2and the bottom fraction B4or B3Dare subjected to a further distillation step (b-v) or (b-iv’). The bottom fraction B2and the bottom fraction B4or B3D may be fed to the distillation unit UFas separate streams or as a combined stream, especially as a combined stream. In case of separate streams of bottom fraction B2and bottom fraction B4or B3D, said streams are usually introduced into the distillation unit at a similar or same level.

[0099] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the bottom fraction B2is subjected to a further distillation step (b-v) or (b-iv’).

[0100] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing and purifying an aliphatic primary diamine, wherein the bottom fraction B4or B3Das a second fraction and the bottom fraction B2are subjected to the further distillation step to recover the head fraction HF.

[0101] The further distillation step provides a head fraction HFas a third fraction. The head fraction HFmay be recovered by distillation of the second fraction (bottom fraction B4or B3D), the bottom fraction B2or both, i.e., the bottom fractions B4or B3Dand B2.

[0102] The further distillation step provides a head fraction HFas a third fraction, generally containing mainly additional aliphatic primary diamine, for example, in an amount > 95 wt%, based on the total weight of the head fraction HF, preferably > 97 wt%, and especially > 98 wt% or even higher, and by-products, like THA, detectible by POLI.

[0103] The head fraction HFas a third fraction recovered from the further distillation unit is preferably recovered as a top-side stream at a level of the distillation unit UFabove the internals, preferably the plates.

[0104] The head fraction HFmay be fed to the reaction step a) or to a further catalytic hydrogenation step c) in the reaction unit R2.

[0105] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary diamine, wherein the head fraction HFas a third fraction is subjected to a catalytic hydrogenation step in the reaction unit R2.

[0106] Further preferred is a process for manufacturing an aliphatic primary diamine, wherein the catalytic hydrogenation step of the second fraction and / or the third fraction is carried out in the reaction unit Ri and / or a reaction unit R2.

[0107] The further catalytic hydrogenation step c) may be carried out in the reaction unit R2with the bottom fraction B4or B3Dand / or with the head fraction HF. The head fraction HF may be formed by a distillation step of bottom fraction(s) B2and / or B4or B2and / or B3D. The further catalytic hydrogenation step c) usually provides a medium M2, wherein a stream F2is withdrawn, for example, by separating the catalyst. The stream F2may be subjected to the distillation sequence of step b). The stream F2may be fed separately to the first distillation step or combined with the stream Fi. Preferably, the stream F2is subjected to the distillation sequence of step b) as a combined stream with stream Fi.

[0108] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary diamine, wherein a stream F2resulting from a medium M2formed in the reaction unit R2is subjected to the distillation sequence of step b).

[0109] The various distillation steps are carried out in conventional and standard distillation units. The distillation units are usually distillation columns. The distillation units may have one or multiple number of so-called theoretical steps.

[0110] Examples of suitable distillation units are distillation columns with internals, such as

[0111] - a plate column, like a perforated plate column, a valve tray column or a bubble cap tray column,

[0112] - a packed column, like a column with a structured packing or a column with a random packing,

[0113] - a column of thin film evaporation type, or

[0114] - a dividing wall column.

[0115] The distillation step of step b) to recover a first fraction containing the aliphatic primary diamine in purified form and second fraction is carried out in a distillation units selected from a plate column, a packed column and a dividing wall column. In case the first fraction is recovered as a head fraction (H4), the distillation unit is preferably a plate column or a packed column, preferably a packed column with a structured packing.

[0116] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary diamine, wherein the distillation steps of step b) to recover a first fraction containing the aliphatic primary diamine in purified form and second fraction is carried out in a distillation unit selected from a plate column, a packed column and a dividing wall column.

[0117] Especially, the further distillation step (b-v) or (b-iv’) is carried out with a plate column.

[0118] Accordingly, in a preferred aspect, the invention relates to a process for manufacturing an aliphatic primary diamine, wherein the further distillation step is carried out in a plate column.

[0119] The operating conditions for the various distillation are usually as follows:

[0120] The first distillation step generally provides a head fraction Hi, containing mainly water from the stream Fi and imines, like HMI, and a bottom fraction Bi, containing the desired diamine and water in minor amount of less than about 500 ppm. The first distillation unit Ui usually operates under a top pressure of 5 to 500 mbar, having preferably a number of theoretical steps of from 5 to 20. The first distillation unit Ui is preferably a packed column with structured packing.

[0121] The bottom fraction Bi is fed to a second distillation unit U2usually operating under a top pressure of 5 to 500 mbar, having preferably a number of theoretical steps of from 1 to 5. The second distillation unit U2is preferably a plate column. The bottom fraction B2recovered from the second distillation step contains heavy by-products, preferably in an amount of from 1 to 10 wt%, based on the total weight of heavy by-products present in Fi.

[0122] In the first alternative of the distillation sequence of step b), the head fraction H2recovered from the second distillation step is fed to a third distillation unit U3usually operating under a top pressure of 5 to 500 mbar, having preferably a number of theoretical steps of from 10 to 80. The third distillation unit U3is preferably a packed column with structured packing. The head fraction H3contains mainly light by-products.

[0123] The bottom fraction B3recovered from the third distillation step is fed to a fourth distillation unit U4operating under a top pressure of 5 to 500 mbar, having preferably a number of theoretical steps of from 10 to 70. The fourth distillation unit U4is preferably a plate column or a packed column, especially a packed column with structured packing.

[0124] The head fraction H4recovered from the fourth distillation unit contains the aliphatic primary diamine in purified form. The head fraction H4is preferably recovered as a top-side stream fraction at a level of the distillation unit U4above the internals, preferably the plates. A top-side stream fraction recovered above the internals is understood as a head fraction, which is different from a side stream fraction SD.

[0125] In the second alternative of the distillation sequence of step b), the head fraction H2recovered from the second distillation step is fed to a third distillation unit U3D, which is preferably a dividing wall column. The dividing wall column is usually operating under a top pressure of 1 to 250 mbar and a bottom pressure of 1 to 400 mbar. The bottom pressure is selected such that it is higher than the top pressure. The dividing wall column has preferably a number of theoretical steps, especially plates, of at least 50, more preferably of from 50 to 200. The dividing wall is usually in the region, preferably in the middle third of the column, between the inlet of the head fraction H2and the side stream fraction SD. The side stream fraction is usually recovered above the inlet of the head fraction H2.

[0126] The bottom fraction B2and / or the bottom fraction B4or B3Dmay be fed to a further distillation step, typically distillation unit UF, usually operating under a top pressure of 5 to 500 mbar, having preferably a number of theoretical steps of from 10 to 50. The further / fifth distillation step is preferably a plate column.

[0127] The stream Fi, F2for example combined with stream Fi or as separate stream, and the fractions B3and H2are usually fed at an intermediate level of the column of the respective distillation step. The fraction Bi is usually fed at a lower level of the second distillation step, preferably at a level lower the internals.

[0128] The purified aliphatic primary diamine has a significantly reduced content of by-products, preferably by-products detectible by polarographic analysis, to meet the target for downstream processes, like the manufacturing of polyamides.

[0129] The process may be carried out with a chemical production unit comprising a sequence of various distillation units and at least one hydrogenation reactor.

[0130] Accordingly, in a further aspect, the invention relates to a chemical production unit, the chemical production unit comprising: a first hydrogenating reaction unit Ri for forming a medium Mi; a distillation sequence containing a distillation unit for recovering a first fraction containing the aliphatic primary diamine in purified form and a second fraction; and a means for passing the second fraction to a hydrogenating reaction unit, or a further distillation unit UFfor recovering a third fraction and a means for passing the third fraction to a hydrogenating reaction unit R.

[0131] Preferably, the distillation sequence of step b) comprises at least 2 distillation units, equipped prior to the distillation unit for recovering a first fraction containing the aliphatic primary diamine in purified form and a second fraction, more preferably in a first alternative

[0132] - a first distillation unit Ui for recovering a bottom fraction Bi and a head fraction Hi;

[0133] - a second distillation unit U2for recovering a bottom fraction B2and a head fraction H2; and

[0134] - a third distillation unit U3for recovering a bottom fraction B3and a head fraction H3; or in a second alternative

[0135] - a first distillation unit Ui for recovering a bottom fraction Bi and a head fraction Hi; and

[0136] - a second distillation unit U2for recovering a bottom fraction B2and a head fraction H2

[0137] Further preferred is a chemical production unit which additionally comprises a means for passing the bottom fraction B2to the further distillation unit UF.

[0138] Also preferred is a chemical production unit which additionally comprises:

[0139] - a means for passing the bottom fraction B2to the further distillation unit UF;

[0140] - a second hydrogenating reaction unit R2for forming a medium M2; and

[0141] - a means for passing a stream F2resulting from the medium M2to the first distillation unit Ui.

[0142] The general flow of reactants and products through a system to convert an aliphatic dinitrile to an aliphatic primary diamine may be described with reference to the figures 1 to 7.

[0143] Referring to figure 1 , a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to a first distillation unit Ui, also referred to as dehydration column, to recover a head fraction Hi, which is discharged, and a bottom fraction Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2, which is discharged. The head fraction H2containing the desired diamine is fed to a third distillation unit U3to recover a head fraction H3, which is discharged, and a bottom fraction B3containing the desired diamine. The bottom fraction B3is fed to a fourth distillation unit U4to recover the desired diamine in purified form and a bottom fraction B4. The bottom fraction B4is recycled to the catalytic reaction unit Ri (hydrogenation unit Ri).

[0144] Referring to figure 2, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to a first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom fraction Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2. The head fraction H2containing the desired diamine is fed to a third distillation unit U3to recover a head fraction H3, which is discharged, and a bottom fraction B3containing the desired diamine. The bottom fraction B3is fed to a fourth distillation unit U4to recover the desired diamine in purified form and a bottom fraction B4. The bottom fractions B2and B4are fed as combined streams to a further distillation unit UFto recover a bottom fraction BF, which is discharged, and a head fraction HF, which is recycled to the catalytic reaction unit Ri.

[0145] Referring to figure 3, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to the first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom fraction Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2. The head fraction H2containing the desired diamine is fed to a third distillation unit U3to recover a head fraction H3, which is discharged, and a bottom fraction B3containing the desired diamine. The bottom fraction B3is fed to a fourth distillation unit U4to recover the desired diamine in purified form and a bottom fraction B4. The bottom fraction B2is fed to a further distillation unit UFto recover a bottom fraction BF, which is discharged, and a head fraction HFwhich is recycled to the catalytic reaction unit Ri. The bottom fraction B4is recycled to the catalytic reaction unit Ri.

[0146] Referring to figure 4, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to the first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom stream Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2, which is discharged. The head fraction H2containing the desired diamine is fed to a third distillation unit U3D, which is a dividing wall column, to recover a head fraction H3D, which is discharged, a side stream fraction SDcontaining the desired diamine and a bottom fraction B3D, which is recycled to the catalytic reaction unit Ri.

[0147] Referring to figure 5, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to the first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom stream Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2. The head fraction H2containing the desired diamine is fed to a third distillation unit U3D, which is a dividing wall column, to recover a head fraction H3D, which is discharged, a side stream fraction SDcontaining the desired diamine and a bottom fraction B3D. The bottom fractions B2and B3Dare fed as combined streams to a further distillation unit UFto recover a bottom fraction BF, which is discharged, and a head fraction HF, which is recycled to the catalytic reaction unit Ri.

[0148] Referring to figure 6, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to a first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom fraction Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2. The head fraction H2containing the desired diamine is fed to a third distillation unit U3to recover a head fraction H3, which is discharged, and a bottom fraction B3containing the desired diamine. The bottom fraction B3is fed to a fourth distillation unit U4to recover the desired diamine in purified form as a head fraction H4and a bottom fraction B4. The bottom fractions B2and B4are fed as combined streams to a further distillation unit UFto recover a bottom fraction BF, which is discharged, and a head fraction HF, which is fed as stream F2to a second hydrogenation reaction unit R2. The product stream withdrawn from the reaction unit R2is recycled to the stream Fi.

[0149] Referring to figure 7, a reactor feed Fois fed to a catalytic reaction unit Ri. The stream Fi to be distilled is derived from a medium Mi formed in the catalytic reaction unit Ri. The stream Fi generally includes the desired hydrogenated product, i.e., the aliphatic primary amine, water and by-products. The stream Fi passes through a line to a first distillation unit Ui to recover a head fraction Hi, which is discharged, and a bottom stream Bi containing the desired diamine. The bottom fraction Bi is fed to a second distillation unit U2to recover a head fraction H2and a bottom fraction B2. The head fraction H2containing the desired diamine is fed to a third distillation unit U3to recover a head fraction H3, which is discharged, and a bottom fraction B3 containing the desired diamine. The bottom fraction B3is fed to a fourth distillation unit U4to recover the desired diamine in purified form as head fraction H4and a bottom fraction B4. The bottom fraction B2is fed to a further distillation unit UFto recover a bottom fraction BF, which is discharged, and a head fraction HF, which is fed to a second hydrogenation reaction unit R2. The bottom fraction B4is fed to a second hydrogenation reaction unit R2, either combined with the head fraction HFor as separate stream (as shown). The product stream withdrawn from the reaction unit R2is recycled as stream F2to the stream Fi.

[0150] The preferences for the process for manufacturing an aliphatic primary diamine also applies to the chemical production unit.

[0151] The instant process allows for the preparation of an aliphatic primary diamine having a high purity, which may be improved compared to a process, for example, as described in WO 2007 / 147960 A2. The step of re-hydrogenating a fraction containing by-products and optionally additional desired diamine, usually detectible by polarographic analysis or UV analysis, improves the quality and yield of the desired product, compared to a step of recycling said fraction to the front-end of the work-up, i.e., the distillation sequence.

[0152] The further catalytic hydrogenation step allows for converting by-products to the desired diamine and / or to by-products which are easier to separate in the distillation steps. The specification of the desired diamine may be met without sacrificing loss of the desired diamine caused by a purge stream, usually performed in prior art processes, to limit the level of byproducts, especially THA.

[0153] Thus, the instant process allows for the reduction of polarographically reducible by-products and or by-products detectable by UV analysis to an improved quality of the aliphatic primary diamine, for example, to manufacture polymers.

[0154] Moreover, the overall energy consumption is lower, for example in less steam consumption at the distillation steps.

[0155] All percent, ppm or comparable values refer to the weight with respect to the total weight of the respective composition except where otherwise indicated. The terms “% by weight” and “wt%” are used herein synonymously. All cited documents are incorporated herein by reference.

[0156] The following examples shall further illustrate the present invention without restricting the scope of this invention.

[0157] Examples

[0158] Determination of the UV index The UV index was obtained by measuring the UV absorbance at a wavelength of 275 nm of a 32.4 wt% solution of a mixture containing hexamethylenediamine and by-products in water in a cell with a length of 5 cm.

[0159] Determination of the polaroqraphic index (POLI)

[0160] The polarographic index was determined by differential pulse polarography using a mercury electrode. The by-products exhibit a polarographic wave of reduction at a voltage of -1 .55 V / Ag- AgCI ±0.05 V. The content thereof is expressed in mmol of isobutanal per tonne of hexamethylenediamine (mmol iB / t).

[0161] Gas chromatography

[0162] The analyses of a mixture containing hexamethylenediamine and by-products on gas chromatography were performed on a GC-FID using hydrogen as carrier gas. The column is a polyethylene glycol column that is designed for primary amines’ analyses. The whole analysis can be done within 30 minutes by separating all the main impurities with a very low level of limit of detection (ppm).

[0163] Example 1

[0164] A head fraction of the further distillation step (distillation unit UF, fed from two bottom fractions) was taken to be hydrogenated in a 0.1 I batch reactor with a catalyst (Raney nickel) at 80°C and 25 bar of hydrogen for one hour.

[0165] Example 2

[0166] The procedure of Example 1 was repeated with the exception that a head fraction of a different batch was hydrogenated.

[0167] The UV index and the polarographic index as well as the amounts of impurities were measured before and after the hydrogenation treatment. The results are shown in Table 1.

[0168] Table 1

[0169] Example 3

[0170] A bottom fraction of a distillation step (distillation unit U4) was taken to be hydrogenated in a 0.1 I batch reactor with a catalyst (Raney nickel) at 80°C and 25 bar of hydrogen for one hour. The UV index and the polarographic index as well as the amounts of impurities were measured before and after the hydrogenation treatment. The results are shown in Table 2.

[0171] Table 2

Claims

Claims1. A process for manufacturing and purifying an aliphatic primary diamine, the process comprising a) reacting an aliphatic dinitrile and a hydrogen-containing gas in the presence of a catalyst in a reaction unit Ri to form a medium Mi containing the aliphatic primary diamine, and b) subjecting a stream Fi resulting from the medium Mi to a distillation sequence comprising a distillation step to recover a first fraction containing the aliphatic primary diamine in purified form and a second fraction, wherein the second fraction is subjected to a catalytic hydrogenation step, or the second fraction is subjected to a further distillation step to recover a third fraction, which is subjected to a catalytic hydrogenation step.

2. A process according to claim 1 , wherein the first fraction is a head fraction or a side stream fraction, and the second fraction is a bottom fraction.

3. A process according to claim 1 or 2, wherein the third fraction is a head fraction HF.

4. The process according to claim 1 , 2 or 3, wherein the catalytic hydrogenation step of the second fraction and / or the third fraction is carried out in the reaction unit Ri and / or a reaction unit R2.

5. The process according to any one of the preceding claims, wherein step b) comprises in a first alternative b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the aliphatic primary diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the aliphatic primary diamine, and a bottom fraction B2; b-iii) subjecting the head fraction H2to a third distillation step to recover a bottom fraction B3, containing the aliphatic primary diamine, and a head fraction H3; and b-iv) subjecting the bottom fraction B3to a fourth distillation step to recover a head fraction H4, containing the aliphatic primary diamine in purified form, and a bottom fraction B4as second fraction; or in a second alternative b-i) subjecting the stream Fi to a first distillation step to recover a head fraction Hi, containing water, and a bottom fraction Bi, containing the aliphatic primary diamine; b-ii) subjecting the bottom fraction Bi to a second distillation step to recover a head fraction H2, containing the aliphatic primary diamine, and a bottom fraction B2; and b-iii’) subjecting the head fraction H2to a third distillation step, especially comprising a dividing wall column, to recover a side stream fraction SD, containing the aliphatic primary diamine, as a first fraction, a head fraction H3D and a bottom fraction B3D as a second fraction.

6. The process according to any one of the preceding claims, wherein the bottom fraction B2is subjected to the further distillation step to recover the head fraction HFto be subjected to a catalytic hydrogenation step.

7. The process according to any one of the preceding claims, wherein the bottom fraction B4or B3D as a second fraction and the bottom fraction B2are subjected to the further distillation step to recover a head fraction.

8. The process according to any one of the preceding claims, wherein the head fraction HFas a third fraction is subjected to a catalytic hydrogenation step in the reaction unit R2.

9. The process according to any one of the preceding claims, wherein a stream F2resulting from a medium M2formed in the reaction unit R2is subjected to the distillation sequence of step b).

10. The process according to any one of the preceding claims, wherein the distillation step of step b) to recover a first fraction containing the aliphatic primary diamine in purified form and second fraction is carried out in a distillation unit selected from a plate column, a packed column and a dividing wall column.

11. The process according to any one of the preceding claims, wherein the further distillation step is carried out in a plate column.

12. The process according to any one of the preceding claims, wherein the diamine is a C2-Ci2- diamine, preferably a C4-Ci2-diamine.

13. The process according to any one of the preceding claims, wherein the diamine is hexamethylenediamine or 2-methylpentanediamine, preferably hexamethylenediamine.

14. The process according to any one of the preceding claims, wherein the catalyst in the reaction unit Ri and the reaction unit R2is based on a metal catalyst of Raney-type, preferably a catalyst of Raney nickel.

15. The process according to any one of the preceding claims, wherein the amount of a byproduct, preferably 6-aminocapronitrile, in the stream Fi is up to 5000 ppm, based on the total weight of the aliphatic primary diamine.

16. The process according to any one of the preceding claims, wherein step a) does not comprise a partial hydrogenation of an aliphatic dinitrile with coproduction of an aliphatic primary diamine and an aliphatic-a,w-aminonitrile.

17. The process according to any one of the preceding claims, wherein the reaction step a) is carried outa-i) at an absolute hydrogen pressure of from 10 to 35 bar, a-ii) at a temperature of from 60 to 100°C, a-iii) in the presence of a catalyst based on Raney nickel, a-iv) in the presence of a diluent containing water, a-v) in the presence of a basic inorganic compound, and a-vi) preferably, the aliphatic dinitrile is fed to the reaction unit with a space velocity of from 0.1 to 50 h1.

18. A chemical production unit for carrying out a process, as defined in any one of the claims 1 to 17, the chemical production unit comprising: a first hydrogenating reaction unit Ri for forming a medium Mi; a distillation unit for recovering a first fraction containing the aliphatic primary diamine in purified form and a second fraction; and a means for passing the second fraction to a hydrogenating reaction unit, or a further distillation unit UFfor recovering a third fraction and a means for passing the third fraction to a hydrogenating reaction unit.

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