Title of Invention

A PROCESS FOR CATALYTIC HYDROGENATION OF ADIPONITRILE TO HEXAMETHYLENEDIAMINE

Abstract

Improved process for preparing hexamethylenediamine Abstract A process for catalytic hydrogenation of adiponitrile to hexamethylenediamine at elevated temperature and elevated pressure in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent comprises a) hydrogenating adiponitrile at from 70 to 220oc and from 100 to 400 bar in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent to obtain a mixture comprising adiponitrile, 6-aminocapronitrile, hexamethylenediamine and high boilers until the sum total of the 6-aminocapronitrile concentration and the adiponitrile concentration is within the range from 1 to 50% by weight, based on the ammonia-free hydrogenation mixture, b) removing ammonia from the hydrogenation effluent, c) removing hexamethylenediamine from the remaining mixture, d) separating 6-aminocapronitrile and adiponitrile from high boilers individually or together, and e) returning 6-aminocapronitrile, adiponitrile or mixtures thereof into step a).

Full Text

Improved process for preparing hexamethylenediamine Specification This invention relates to a process for catalytic hydrogenation of adiponitrile to hexamethylenediamine at elevated temperature and elevated pressure in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent, which comprises a) hydrogenating adiponitrile at from 70 to 220°C and from 100 to 4 00 bar in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent to obtain a mixture comprising adiponitrile, 6-aminocapronitrile, hexamethylenediamine and high boilers until the sum total of the 6-aminocapronitrile concentration and the adiponitrile concentration is within the range from 1 to 50% by weight, based on the eunmonia-free hydrogenation mixture, b) removing ammonia from the hydrogenation effluent, c) removing hexamethylenediamine from the remaining mixture, d) separating 6-aminocapronitrile and adiponitrile from high boilers individually or together, and e) returning 6-aminocapronitrile, adiponitrile or mixtures thereof into step a). US 3696153 discloses hydrogenating adiponitrile to hexamethylenediamine at temperatures of 100 to 200oc and pressures of about 340 atm in the presence of granulated catalysts comprising very predominantly iron and small amounts of aluminum oxide and in the presence of ammonia as solvent. Hexamethylenediamine yields of 98.8%, 98.8%, 97.7% and 97.7% are reached in the examples of Table 1 (run 2) and Table 2 (runs 1 to 3) at pressures of 340 atm. Complete conversion is reported for the first three examples and 99.9% conversion for the fourth example. With regard to the life of the iron catalysts. Tables 1 and 2 merely reveal that catalyst activity is high at the end of the runs (after around 80 to 120 hours). J.S. 4064172 discloses hydrogenating adiponitrile to hexamethylenediamine at pressures of 20 to 500 bar and temperatures of 80 to 200oc in the presence of iron catalysts synthesized from magnetite and in the presence of ammonia. A hexamethylenediamine yield of 98.2% is reported in Example 1. U.S. 4282381 describes the hydrogenation of adiponitrile to hexamethylenediamine with hydrogen at temperatures of 110 to 220°C and a pressure of about 340 atm in the presence of ammonia and iron catalysts. The hydrogenation effluent contains 0.04 to 0.09% by weight of adiponitrile and 0.2 to 0.5% by weight of 5-aminocapronitrile. McKetta, Encyclopedia of Chemical Processing and Design, Marcel bekker Inc. 1987, volume 26, page 230, Table 3, confirms that a typical hydrogenation product contains 0.01 to 0.11% by weight of adiponitrile and 0.10 to 0.21% by weight of aminocapronitrile. illustrations 2 and 4 reveal that these small aminocapronitrile [uantities can be separated off and returned into the lydrogenation. 'hese processes suggest that the reaction conditions in the ndustrial production of hexamethylenediamine have to be directed o achieving complete conversion of the adiponitrile and of the -aminocapronitrile intermediate of the hydrogenation. he disadvantage with this is that this requires a relatively igh temperature and a very high reaction pressure. If the diponitrile and 6-aminocapronitrile conversion decreases arkedly in the course of the hydrogenation, it has to be pushed ack up again by raising the temperature and optionally the eaction pressure and/or lowering the catalyst loading, or a not nconsiderable loss of product of value will be incurred. f, to obtain complete conversion, the temperature cannot be arther increased because of decreasing hexeunethylenediamine slectivity and/or the pressure cannot be further increased for thechnical reasons, then the catalyst loading has to be reduced, pwever, this means that catalyst productivity, i.e., the amount of hexamethylenedieunine produced per unit time, will decrease. If be productivity drops below a certain level, the hydrogenation Lant has to be shut down and the iron catalyst moved and splaced with an unused or regenerated catalyst. The greater the requency of such shutdowns required per year, the lower the examethylenediamine quantity which a given production plant can reduce per year. ; is an object of the present invention to provide a process for be catalytic hydrogenation of adiponitrile to ixamethylenedicunine in the presence of catalysts comprising very predominantly elemental iron and ammonia as solvent in an economical and technically simple manner while avoiding the disadvantages mentioned. We have found that this object is achieved by the process defined at the beginning. The process of the invention does not require complete adiponitrile and 6-aminocapronitrile conversion. This provides distinctly higher catalysts onstream times at lower pressures, fewer shutdowns for the hydrogenation plant and hence distinctly higher hexamethylenediamine productivities compared with the prior art. It was unforeseeable and hence it is surprising that recycling 6-aminocapronitrile, adiponitrile or mixtures thereof into the hydrogenation stage does not cause any shortening of the catalyst onstream time. It is also surprising that the entire recycle does not cause any troublesome buildup of by-products in the system. The adiponitrile used in the process of the invention can generally be prepared by conventional processes, preferably by reaction of butadiene with hydrocyanic acid in the presence of catalysts, especially nickel(0) complexes and phosphorus-containing cocatalysts, via pentenenitrile as intermediate. The catalysts used can be conventional iron catalysts known for the production of hexamethylenediamine by hydrogenation of adiponitrile. Preferred catalyst precursors are those which comprise from 90 to 100% by weight, preferably from 92 to 99% by weight, based on the total mass of the catalyst precursor, of iron oxides, iron(II, III) oxide, iron(II) oxide, iron(II) hydroxide, iron(III) hydroxide or iron oxyhydroxide such as FeOOH. It is possible to use synthetic or naturally occurring iron oxides, iron hydroxides or iron oxyhydroxides, magnetite, which has the idealized formula of Fe3O4, brown ironstone, which has the idealized formula of Fe203 x H2O, or hematite, which has the idealized formula of Fe203. Preferred catalysts are those which comprise a) iron or a compound based on iron or mixtures thereof, b) from 0.001 to 5% by weight based on a) of a promoter based on 2, 3, 4, 5 or 6 elements selected from the group consisting of aluminum, silicon, zirconium, titanium, vanadium and manganese, and c) from 0 to 5% by weight based on a) of a compound based on an alkali metal or on an alkaline earth metal. Further preferred catalyst precursors are those in which component b) comprises from 0.001 to 5% by weight, preferably from 0.01 to 4% by weight, especially from 0.1 to 3% by weight, of a promoter based on 2, 3, 4, 5 or 6 elements selected from the group consisting of aluminum, zirconium, silicon, titanium, nanganese and vanadium. further preferred catalyst precursors are those in which component c) comprises from 0 to 5% by weight, preferably from 0.l to 3% by weight, of a compound based on an alkali or alkaline earth metal preferably selected from the group consisting of ithium, sodium, potassium, rubidium, cesium, magnesium and calcium. the catalysts can be supported or unsupported catalysts. Examples of suitable support materials are porous oxides such as aluminum axide, silicon oxide, alumosilicates, lanthanum oxide, titanium lioxide, zirconium dioxide, magnesium oxide, zink oxide and eolites and also activated carbon or mixtures thereof. reparation is generally effected by precipitating precursors of omponent a) if desired together with precursors of the promoter omponents b) and if desired with precursors of the trace omponents c) in the presence or absence of support materials depending on which type of catalyst is desired), if desired recessing the resulting catalyst precursor into extrudates or ablets, drying and subsequently calcining. Supported catalysts re generally also obtainable by saturating the support with a Dlution of said components a), b) and if desired c), the tidividual components being added simultaneously or in accession, or by spraying said components a), if desired b) and ) onto the support in a conventional manner. aitable precursors for components a) are generally readily ater-soluble salts of iron such as nitrates, chlorides, betates, formates and sulfates, preferably nitrates. Suitable precursors for components b) are generally readily water-soluble salts or complexes of the aforementioned metals and metalloids such as nitrates, chlorides, acetates, formates and sulfates, preferably nitrates. Suitable precursors for components c) are generally readily water-soluble salts of the aforementioned alkali metals and alkaline earth metals such as hydroxides, carbonates, nitrates, chlorides, acetates, formates and sulfates, preferably hydroxides and carbonates. precipitation is generally effected from aqueous solutions, selectively by addition of precipitants, by changing the pH or by changing the temperature. The catalyst prematerial thus obtained is usually dried, generally at from 80 to 150oC, preferably at from 80 to 120oc. Calcination is customarily effected at temperatures within the range from 150 to 500oc, preferably from 200 to 450°C, in a gas stream comprising air or nitrogen. After calcination, the catalyst material obtained is generally activated by exposing to a reducing atmosphere, for example by exposing it for from 2 to 100 hours to a hydrogen atmosphere or to a gas mixture comprising hydrogen and an inert gas such as nitrogen at from 200 to 500oc, preferably at from 250 to 400oc. The catalyst loading during this activating step is preferably 200 1 per liter of catalyst. The activation of iron catalysts by reduction of iron oxides with lydrogen can be carried out in a conventional manner, for example iS described in U.S. 3758584, with mixtures of hydrogen and ammonia at from 300 to 600oc or, as described in U.S. 4480051, in three steps, a first step of reducing the iron oxide with lydrogen or mixtures of hydrogen and ammonia, a second step of preating the resulting elemental iron with an oxygen-comprising pas, and then a third step of repeating the reduction of the first step. i.S. 3986985 describes a deeper stabilization of reduced syrophoric iron catalysts, for example in order that they may be ransported. The original catalytic activity can be restored by a rief treatment of the stabilized catalyst with hydrogen. The activation of the catalyst is advantageously carried out directly in the synthesis reactor, since this customarily dispenses with the otherwise necessary intermediary step, i.e., the passivation of the surface, customarily at from 20 to 80°C, preferably at from 25 to 35oC, by means of nitrogen-oxygen mixtures such as air. The activation of passivated catalysts is then preferably carried out in the synthesis reactor at from 180 to 500oC, preferably at from 200 to 400oc, in an atmosphere comprising hydrogen. The catalysts may preferably be used as fixed bed catalysts in upflow or downflow mode or else as suspension catalysts. the hydrogenation can be carried out batchwise, but is preferably carried out continuously using suspended, but preferably fixed ped, catalysts in the presence of ammonia. [f fixed bed catalysts are used, the fixed bed reactor R 1 (see figures 1 and 2) can be operated in downflow or upflow mode. It Ls possible in this connection to employ the operating mode of a straight pass through one reactor or through a plurality of consecutive reactors with or without intermediary cooling or an sperating mode involving one or more reactors with product •ecycling in the liquid circulation system around the reactor(s). the reaction temperature is generally within the range from 70 to 20oC, especially within the range from 80 to 170oc, and the ressure is generally within the range from 100 to 400 bar, specially within the range from 150 to 350 bar, particularly referably within the range from 200 to 250 bar. he catalyst loading is customarily within the range from 0.1 to kg of adiponitrile/1 of cat. x h, especially within the range rom 0.5 to 2 kg of adiponitrile/1 of cat. x h. the parameters, such as temperature, pressure and catalyst pading, for adjusting the sum total of the 6-aminocapronitrile ancentration and the adiponitrile concentration, based on the nmonia-free hydrogenation mixture, in the reactor effluent to be range from 1 to 50% by weight, preferably 2 - 40% by weight, articularly preferably 3 - 40% by weight, especially 5 - 30% by eight, required by the invention can be easily determined by means of a few simple preliminary experiments. The hydrogenation effluent of step a) has the ammonia removed from it in step b) in a conventional manner, preferably by distillation, for example as described in DE 19548289. The ammonia can then with advantage be reused in step a). The mixture then has removed from it in a conventional manner, preferably by distillation, hexamethylenediamine and the by-produced hexamethyleneimine. In the case of a distillative removal, this can be accomplished in a plurality, such as two or three, columns or preferably one column Kl. The hexamethylenediamine obtained in step c) can then be purified in a conventional manner, preferably by distillation. The product stream remaining after step c) comprises adiponitrile, 6-aminocapronitrile, by-products and compounds having a boiling point above that of adiponitrile ("high boilers"). These include nitrogen bases, such as 2-(5-cyanopentylamino)tetrahydroazepine and 2-(6-aminohexyleunino)tetrahydroazepine. In step d), 6-aminocapronitrile and adiponitrile are removed from this product stream in a conventional manner, preferably by distillation, individually or together with high boilers. In the rase of distillative removal, this can be accomplished in plural, such as two {K2a and K2b in Figure 2) or three, columns or one column (K2 in Figure 1). In the case of one column (K2), it is advantageous to obtain adiponitrile by sidestream takeoff, 3-aminocapronitrile overhead and high boilers as bottom product, adiponitrile can be converted in the presence of the nitrogenous pases present in the bottom products, such as 2-{5-cyanopentylamino)tetrahydroazepine and -{6-aminohexylcunino)tetrahydroazepine, into substantial amounts of l-amino-2-cyanocyclopentene. Pure adiponitrile, in contrast, fives rise only to small amounts of l-amino-2-cyclopentene at pase of column temperatures of 200°C. the l-amino-2-cyanocyclopentene content, based on adiponitrile, n the adiponitrile used in step a), which comprises fresh diponitrile and 6-aminocapronitrile, adiponitrile or mixtures hereof recycled from step e), should be below 5000 weight ppm, dvantageously within the range from 10 to 5000 weight ppm, referably within the range from 10 to 3000 weight ppm, articularly preferably within the range from 10 to 1500 weight pm, especially within the range from 10 to 100 weight ppm. Lowering the level of l-amino-2-cyanocyclopentene content in the, adiponitrile used in step a), which comprises fresh adiponitrile and 6-aminocapronitrile, adiponitrile or mixtures thereof recycled from step e), increases the yield of 6-cuninocapronitrile and hexamethylenediamine and facilitates the purification of pexamethylenediamine. [n the case of a distillative removal, the base of column temperature should be advantageously below 220oc, preferably below 90oC, especially below 185oC, and because of the low vapor pressure of the compounds to be separated a base of column temperature of at least l00oc, preferably at least 140oc, especially at least 160oC, is advisable. The pressures at the base of the column should be advantageously within the range from 0.1 o 100, especially from 5 to 40, mbar. The residence times of the ottom products in the distillation should advantageously be ithin the range from 1 to 60, especially within the range from 5 0 15, minutes. n a preferred embodiment, these distillation conditions are pplied to the removal of adiponitrile from high boilers. in a preferred embodiment, the bottom product contains 1 to 80% weight of adiponitrile, based on high boilers. Further diponitrile may subsequently be obtained from this product tream, advantageously in an evaporator at a pressure of from 1 50 mbar, preferably from 2 to 25 mbar. step e), 6-aminocapronitrile, adiponitrile or mixtures thereof be returned into step a). be present invention likewise proposes that hexamethylenediamine removed, together with 6-aminocapronitrile, from the mixture ptained in step b) and then the mixture of hexamethylenediamine d 6-aminocapronitrile be separated into the two components. a further preferred embodiment, the adiponitrile stream to be turned into step a) has by-products, especially amino-2-cyanocyclopentene, removed from it in a conventional nner, for example by distillation or extraction. a further preferred embodiment, the adiponitrile stream to be turned into step a) is purified in a conventional manner, for ample by treatment with an inorganic acid, such as mineral id, organic acid, such as carboxylic acid, or an acidic ion exchanger or by treatment with an oxidizing agent, such as air, ozone, hydrogen peroxide or an inorganic or organic peroxide. The process of the present invention surprisingly provides distinct advantages with regard to the hydrogenation, the distillative purification of hexamethylenediamine and the onstream time of the hydrogenation catalyst. WE CLAIM; 1. A process for catalytic hydrogenation of adiponitrile to hexamethylenediamine at elevated temperature and elevated pressure in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent, which comprises a) hydrogenating adiponitrile at from 70 to 220°C and from 100 to 400 bar in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent to obtain a mixture comprising adiponitrile, 6-aminocapronitrile, hexamethylenediamine and high boilers until the sum total of the 6-aminocapronitrile concentration and the adiponitrile concentration is within the range from 1 to 50% by weight, based on the ammonia-free hydrogenation mixture, b) removing ammonia from the hydrogenation effluent, c) removing hexamethylenediamine from the remaining mixture, d) separating 6-aminocapronitrile and adiponitrile from high boilers individually or together, and e) returning 6-aminocapronitrile, adiponitrile or mixtures thereof into step a). 2. The process as claimed in claim 1, wherein the separating of the adiponitrile from high boilers is effected distillatively at base of column temperatures of below 220°C. 3. The process as claimed in claim 2, wherein the separating of the adiponitrile from high boilers is effected distillatively at base of column temperatures of below 185°C. 4. The process as claimed in any of claims 1 to 3, wherein the separating of the adiponitrile from high boilers is effected distillatively and the high boilers stream obtained as bottom product is set to an adiponitrile content of from 1 to 80% by weight, based on the high boiler content. 3.The process as claimed in claim 4, wherein the main fraction of the adiponitrile in the stream of high boilers and adiponitrile is removed from the stream in a downstream evaporator at from 1 to 50 mbar. 6. The process as claimed in any of claims 1 to 5, further comprising reducing the level of l-amino-2-cyanocyclopentene by-product in the adiponitrile stream between steps d) and e). 7. The process as claimed in any of claims 1 to 6, further comprising treating the adiponitrile stream with an acid between steps d) and e). 8. The process as claimed in claim 7, wherein the acid used is a mineral acid, a carboxylic acid or an acidic ion exchanger. 9. The process as claimed in any of claims 1 to 8, further comprising treating the adiponitrile stream with an oxidizing agent between steps d) and e). 10. The process as claimed in claim 9, wherein the oxidizing agent used is air, ozone, hydrogen peroxide or an inorganic or organic peroxide. 11. The process as claimed in any of claims 1 to 10, wherein the l-amino-2-cyanocyclopentene content of the adiponitrile used in step a), which comprises fresh adiponitrile and 6-aminocapronitrile, adiponitrile or mixtures thereof returned from step e), is below 5000 weight ppm based on adiponitrile. 12. A process for catalytic hydrogenation of adiponitrile to hexam ethylenediamine substantially as herein described with reference to the accompanying drawings.

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in-pct-2001-0427-che abstract.pdf

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in-pct-2001-0427-che claims.pdf

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in-pct-2001-0427-che form-19.pdf

in-pct-2001-0427-che form-26.pdf

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