WO2015038679A1

WO2015038679A1 - Catalyst preparation and hydrogenation process

Info

Publication number: WO2015038679A1
Application number: PCT/US2014/055038
Authority: WO
Inventors: Tseng H. Chao; Stewart Forsyth; Thomas A. Micka; Michael C. QUINN III; John J. Ostermaier; Douglas J. RIESTERER; Ferdie J. TOZER
Original assignee: Invista Technologies S.A R.L.
Priority date: 2013-09-13
Filing date: 2014-09-10
Publication date: 2015-03-19
Also published as: TW201514132A; CN105658618A

Abstract

Disclosed is a method for hydrogenating a dinitrile, such as adiponitrile, in the presence of ammonia to form a diamine, such as hexamethylenediamine. Also disclosed is a method for preparing a catalyst for this hydrogenation reaction by reducing iron oxide with hydrogen. Anhydrous ammonia is separated from a liquid mixture of ammonia and diamine in three distillation steps. The pressure of the liquid is reduced from, for example, 500 psig (3,549 kPa) to, for example, 2 psig (115 kPa), over the course of these three distillation steps. The anhydrous ammonia, which is separated from liquid mixture of ammonia and diamine is recovered and may be recycled to the hydrogenation reaction.

Description

CATALYST PREPARATION AND HYDROGENATION PROCESS

FIELD OF THE INVENTION

[0001] The disclosures herein relate to a method for preparing a catalyst and to a hydrogenation process for which the same catalyst is effective. More particularly, the invention relates to the catalytic hydrogenation of an organonitrile in the presence of a heterogeneous iron catalyst. Examples of such reactions include the hydrogenation of adiponitrile to

hexamethylenediamine and the hydrogenation of methylglutaronitrile (especially 2- methylglutaronitrile) to 2-methylpentamethylenediamine.

BACKGROUND OF THE INVENTION

[0002] Processes for the hydrogenation of compounds comprising nitrile groups to amines are known. Hydrogenation of dinitriles to the corresponding diamines is a process which has been used for a long time, in particular the hydrogenation of adiponitrile to hexamethylenediamine, a basic material in the preparation of nylon-6,6.

[0003] There has been an increasing interest in recent years in the hydrogenation (also sometimes known as semihydrogenation) of aliphatic dinitriles to aminonitriles, in particular the hydrogenation of adiponitrile to 6-aminocapronitrile, resulting either directly, or via caprolactam, in nylon-6.

[0004] U.S. Patent No. 5,151 ,543 to Ziemecki et al. discloses a process for the selective hydrogenation of aliphatic dinitriles to the corresponding aminonitriles, at 25-150°C and under a pressure of greater than atmospheric pressure, in the presence of a solvent in a molar excess of at least 2/1 with respect to the dinitrile, the solvent comprising liquid ammonia or an alcohol with 1 to 4 carbon atoms and an inorganic base which is soluble in the said alcohol, in the presence of a Raney catalyst, the aminonitrile obtained being recovered as main product.

[0005] U.S. Patent No. 3,696,153 to Kershaw et al. discloses a process for the catalytic hydrogenation of adiponitrile in the presence of a catalyst derived from an iron compound, such as iron oxide, in granular form, which has been activated with hydrogen at a temperature not exceeding 600°C.

[0006] U.S. Patent No. 3,758,584 to Bivens et al. discloses a process for the catalytic hydrogenation of adiponitrile to hexamethylenediamine in the presence of a catalyst derived from a cobalt or iron compound, such as iron oxide, which has been activated in a mixture of hydrogen and ammonia at a temperature in the range of about 300°C to about 600°C.

[0007] In a process for making a diamine by reacting a dinitrile with hydrogen in the presence of liquid or supercritical ammonia, there is a need to recover and recycle ammonia. After unreacted hydrogen has been recovered from the reaction product, a portion of the ammonia may be recovered in a distillation or flash evaporation step taking place at a pressure within the general range of 400 to 600 psig. However, the liquid bottoms stream for this ammonia recovery step still contains a substantial amount of ammonia.

[0008] Another portion of the ammonia may be recovered in a second distillation step taking place at essentially atmospheric pressure, for example, from about 2 psig to 50 psig. However, the overhead vapor stream produced in the second step includes a small amount of diamine in addition to ammonia.

[0009] It is desirable to recycle the ammonia from the second recovery step to the first recovery step. However, in order to recycle this ammonia, the vapor stream from the second step must be compressed to increase the pressure of the stream to the level of the pressure used in the first distillation step.

SUMMARY OF THE INVENTION

[0010] In accordance with embodiments disclosed herein, it has been discovered that diamine in the vapor from the second distillation step is condensed and may be solidified in the compressor. The solidification of diamine is especially problematic when the compressor is a reciprocating compressor. The accumulation of solids can, at best, cause reliability problems by clogging the interstage coolers, and at worst, cause catastrophic compressor failure.

[001 1] A diamine is separated from ammonia. The process comprises steps (a) - (g).

[0012] Step (a) comprises introducing a liquid comprising diamine and ammonia into a first distillation zone. Step (b) comprises distilling the liquid in the first distillation zone of step (a) to obtain a first overhead vapor stream enriched in ammonia and a first liquid bottoms stream enriched in diamine. Step (c) comprises introducing liquid from the first liquid bottoms stream from step (b) into a second distillation zone. Step (d) comprises distilling the liquid in the second distillation zone of step (c) to obtain a second overhead vapor stream enriched in ammonia and a second liquid bottoms stream enriched in diamine. Step (e) comprises passing vapor from the second overhead vapor stream of step (d) through a multi-stage compressor and then into the first distillation zone. Step (f) comprises introducing the second bottoms stream from step (d) into a third distillation zone. Step (g) comprises distilling the liquid in the third distillation zone of step (f) to obtain a third overhead vapor stream enriched in ammonia and a third liquid bottoms stream enriched in diamine.

[0013] The pressure in the second distillation zone of step (d) is less than the pressure in the first distillation zone of step (b). The pressure in the third distillation zone of step (g) is less than the pressure in the second distillation zone of step (d). [0014] In one embodiment, the first distillation zone comprises a distillation column, and both the second distillation zone and the third distillation zone comprise at least one flash tank. In another embodiment, the first distillation zone comprises a collection of distillation vessels, such as flash tanks.

[0015] The liquid introduced into the first distillation zone of step (a) may comprise less than

80 wt% diamine and more than 20 wt% ammonia, based on the total weight of diamine and ammonia in the liquid. The liquid introduced into the second distillation zone of step (c) may comprise from 70 to 95 wt% diamine and from 5 to 30 wt% ammonia, based on the total weight of diamine and ammonia in the liquid. The liquid introduced into the third distillation zone of step (c) may comprise more than 85 wt% diamine and less than 15 wt% ammonia, based on the total weight of diamine and ammonia in the liquid.

[0016] Fluid which is passed through the compressor of step (e) may be heated to maintain the temperature of the fluid passing through this compressor above the freezing point of diamine passing through the compressor. For example, the compressor of step (e) may comprise at least one intercooler cooler, which is cooled by charging cooling water into the intercooler. The cooling water may be maintained at a temperature at least 1°C above the freezing point of the diamine.

[0017] According to one embodiment, the diamine is hexamethylenediamine (HMD).

According to another embodiment, the diamine is 2-methylpentamethylenediamine (MPMD).

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0018] Figure 1 is a diagram showing a four stage conversion process for hydrogenating dinitriles to produce diamines.

[0019] Figure 2 is a diagram showing a catalyst activation system for preparing a catalyst by reducing iron oxide with hydrogen.

[0020] Figure 3 is a diagram showing details of an ammonia recovery system shown in

Figure 1.

[0021] Figure 4 shows a first portion of a reaction section for reacting adiponitrile with hydrogen in the presence of liquid ammonia to form hexamethylenediamine.

[0022] Figure 5 shows a second portion of a reaction section for reacting adiponitrile with hydrogen in the presence of liquid ammonia to form hexamethylenediamine.

[0023] Figure 6 shows a first portion of a recovery section for recovering components of the product stream produced in the reaction section of Figures 4 and 5.

[0024] Figure 7 shows a second portion of a recovery section for recovering components of the product stream produced in the reaction section of Figures 4 and 5. [0025] Figure 8A shows a first example of a refining section for obtaining a refined dinitrile product.

[0026] Figures 8B and 8C show examples of distillation sections shown in Figure 8A.

[0027] Figure 9 shows a second example of a refining section for obtaining a refined dinitrile product.

[0028] Figure 10 is a plan view of a catalyst cartridge.

[0029] Figure 11 is a side view of a catalyst cartridge.

[0030] Figure 12 is a cutaway view of the catalyst cartridge of Fig. 2 along line 3-3.

[0031] Figure 13A is a plan view of a converter.

[0032] Figure 13B is an exploded view of a converter.

[0033] Figure 14A is a side view of a converter.

[0034] Figure 14B is a cutaway view of the converter of Figure 14A along line 2B-2B.

[0035] Figure 15 is a plan view of a locking mechanism for a converter.

[0036] Figure 16 is a cross-sectional view of a containment vessel with a locking

mechanism

DETAILED DESCRIPTION OF THE INVENTION

[0037] Each of the following terms written in singular grammatical form: "a," "an," and "the," as used herein, may also refer to, and encompass, a plurality of the stated entity or object, unless otherwise specifically defined or stated herein, or, unless the context clearly dictates otherwise. For example, the phrases "a device," "an assembly," "a mechanism," "a component," and "an element," as used herein, may also refer to, and encompass, a plurality of devices, a plurality of assemblies, a plurality of mechanisms, a plurality of components, and a plurality of elements, respectively,

[0038] Each of the following terms: "includes," "including," "has," '"having," "comprises," and

"comprising," and, their linguistic or grammatical variants, derivatives, and/or conjugates, as used herein, means "including, but not limited to."

[0039] Throughout the illustrative description, the examples, and the appended claims, a numerical value of a parameter, feature, object, or dimension, may be stated or described in terms of a numerical range format. It is to be fully understood that the stated numerical range format is provided for illustrating implementation of the forms disclosed herein, and is not to be understood or construed as inflexibly limiting the scope of the forms disclosed herein.

[0040] Moreover, for stating or describing a numerical range, the phrase "in a range of between about a first numerical value and about a second numerical value," is considered equivalent to, and means the same as, the phrase "in a range of from about a first numerical value to about a second numerical value," and, thus, the two equivalently meaning phrases may be used interchangeably.

[0041] It is to be understood that the various forms disclosed herein are not limited in their application to the details of the order or sequence, and number, of steps or procedures, and sub- steps or sub-procedures, of operation or implementation of forms of the method or to the details of type, composition, construction, arrangement, order and number of the system, system sub-units, devices, assemblies, sub-assemblies, mechanisms, structures, components, elements, and configurations, and, peripheral equipment, utilities, accessories, and materials of forms of the system, set forth in the following illustrative description, accompanying drawings, and examples, unless otherwise specifically stated herein. The apparatus, systems and methods disclosed herein can be practiced or implemented according to various other alternative forms and in various other alternative ways.

[0042] It is also to be understood that all technical and scientific words, terms, and/or phrases, used herein throughout the present disclosure have either the identical or similar meaning as commonly understood by one of ordinary skill in the art, unless otherwise specifically defined or stated herein. Phraseology, terminology, and, notation, employed herein throughout the present disclosure are for the purpose of description and should not be regarded as limiting.

Abbreviations and Definitions

[0043] The following abbreviations and definitions are used herein:

ADN = adiponitrile; AMC = 6-aminocapronitrile; BHMT = bis(hexamethylene) triamine; DCH = diaminocyclohexane; ESN = ethylsuccinonitrile; HMI = hexamethyleneimine; MCPD =

methylcyclopentanediamine; MGN = 2-methylglutaronitrile; 3- PIP = 3-methyipiperidine PMD = 2-methlypentamethylenediamine; organic dinitrile = an organic compound comprising two nitrile groups, for example ADN; ppm = parts per million by weight unless stated otherwise.

Detailed Description of Figure 1

[0044] The general flow of reactants and products through a system to convert dinitriles to diamines may be described with reference to Figure 1. Figure 1 is a diagram showing a four stage conversion process for hydrogenating dinitriles to produce diamines.

[0045] In Figure 1 , a source of ammonia is passed through line 2 into ammonia pump 10. A source of hydrogen is also passed through line 4 into hydrogen compressor 14. Ammonia from ammonia pump 10 passes through line 12 into line 18, and hydrogen from hydrogen compressor 14 passes through line 16 into line 18. The ammonia and hydrogen in line 18 is partially heated in heat exchanger 20 before it passes through line 22 to converter preheater 24. The heated ammonia and hydrogen from preheater 24 then passes through a series of four converters, depicted in Figure 1 as converters 42, 44, 46, and 48.

[0046] A source of dinitrile feed is fed from line 28 into dinitrile pump 30. Dinitrile feed from dinitrile pump 30 passes through line 32 to line 34. A portion of the dinitrile feed may pass through line 34 to the ammonia feed line 2. Dinitrile may also be introduced separately from ammonia through a pump dedicated to the dinitrile feed. A portion of the dinitrile feed may also pass from line 34 to line 26 via side stream 36 for introduction into the first stage converter 42. Similarly, side streams 38 and 40 provide fresh dinitrile feed to the second stage converter 44 and the third stage converter 46. Also fresh dinitrile feed in line 34 is introduced into the fourth stage converter 48, as depicted in Figure 1.

[0047] According to an embodiment not shown in Figure 1 , a portion of the hydrogen feed may be introduced downstream of the first stage converter 42, and optionally downstream of the second stage reactor 44, and the third stage reactor 46. According to another embodiment not shown in Figure 1 , fresh dinitrile feed need not be introduced into each converter. For example, all of the dinitrile feed may, optionally, be introduced at a point upstream of the first stage converter 42.

[0048] The effluent from the first stage converter 42 passes through line 50 to the second stage converter 44. At a point between the exit point from the first stage converter 42 and the point of introduction of fresh dinitrile feed to line 50 via line 38, the effluent from the first stage converter may be cooled in at least one heat exchanger or cooler not shown in Figure 1.

[0049] The effluent from the second stage converter 44 passes through line 52 to the third stage converter 46. At a point between the exit point from the second stage converter 44 and the point of introduction of fresh dinitrile feed to line 52 via line 40, the effluent from the first stage converter may be cooled in at least one heat exchanger or cooler not shown in Figure 1.

[0050] The effluent from the third stage converter 46 passes through line 54 to heat exchanger 20, where heat from third stage converter effluent is transferred to the coolant feed from line 18. The cooled effluent from the third stage converter 46 then passes through line 56 to the fourth stage converter 48. The cooled effluent from the third stage converter 46 may, optionally, pass through a cooler, not shown in Figure 1 , before passing to the fourth stage converter 48.

[0051] The effluent from the fourth stage converter 48 passes through line 58 to heat exchanger 60. The cooled effluent then passes from heat exchanger 60 through line 62 to product separator 64. Flash evaporation occurs in product separator 64. The liquid phase, comprising diamine, from the product separator 64 passes through line 66 to heat exchanger 60. The gas phase, comprising hydrogen and ammonia, from the product separator 64 passes through line 86 to gas circulation compressor 88 to promote flow of hydrogen and ammonia through line 18.

[0052] The liquid phase from the product separator 64, which is heated in heat exchanger

60, passes through line 68 to ammonia recovery system 70. The ammonia recovery system comprises an ammonia recovery column (not shown in Figure 1 ) and condenser (not shown in Figure 1 ). However, details of the ammonia recovery system, including the ammonia recovery column and the condenser, are shown in Figure 3, which is described hereinafter. A crude product comprising diamine is taken from the bottom of the ammonia column and exits the ammonia recovery system through line 72. The gas phase overhead from the ammonia recovery column passes into a condenser where a distillate phase comprising ammonia and a vapor phase comprising hydrogen is formed. A portion of the distillate phase may be returned to the ammonia recovery column as reflux. A portion of the distillate phase may be transported to at least one storage tank for storage. A portion of the distillate phase may also be recycled as ammonia feed to the hydrogenation reaction. In Figure 1 , this recycle of ammonia is represented by ammonia passing from the ammonia recovery system through line 74 to line 2.

[0053] The vapor phase from the condenser in the ammonia recovery system 70 passes through line 76 to ammonia absorber 78. This vapor phase comprises hydrogen and residual ammonia. The vapor phase is treated by scrubbing with water from line 80 in the ammonia absorber 78. Aqueous ammonia is removed from the ammonia absorber through line 82. A vapor phase comprising hydrogen exits the ammonia absorber 78 through line 84. Hydrogen in the stream in line 84 may be burned in a combustion device, such as a boiler or a flare. At least a portion of the vapor phase from the ammonia absorber 78 may be recycled as hydrogen feed, provided that water is removed from the stream. If water is not sufficiently removed from this stream, water may poison catalyst in the converters.

[0054] The vapor phase recovered from the product separator 64 comprises hydrogen.

This vapor phase may also comprise ammonia gas. This vapor phase may pass from the product separator 64 through line 86 to gas circulation compressor 88 for recycle into line 18.

[0055] In an optional embodiment, at least a portion of the vapor phase comprising hydrogen and ammonia in line 76 may be passed through a line not shown in Figure 1 as a feed to a catalyst activation unit for preparing a catalyst by reducing iron oxide with hydrogen.

Detailed Description of the Catalyst

[0056] The catalyst in the process is a hydrogenation catalyst suitable for hydrogenating a dinitrile to a diamine or a mixture of diamine and aminonitrile. Such catalysts may comprise Group VIII elements including iron, cobalt, nickel, rhodium, palladium, ruthenium and combinations thereof. The catalyst may also contain one or more promoters in addition to the Group VIII elements mentioned above, for example, one or more Group VIB elements such as chromium, molybdenum, and tungsten. The promoters may be present in concentrations 0.01 to 15 percent based on the weight of the catalyst, for example, from 0.5 to 5 percent. The catalyst may also be in the form of an alloy, including a solid solution of two or more metals, or an individual metal or a sponge metal catalyst. A "sponge metal" is one, which has an extended porous "skeleton" or "sponge-like" structure, preferably a base metal (e.g. iron, cobalt or nickel), with dissolved aluminum, optionally containing promoter(s). The amount of iron, cobalt or nickel present in the catalyst may vary.

Skeletal catalysts useful in the process of this invention contain iron, cobalt or nickel in an amount totaling from about 30 to about 97 weight % iron, cobalt and/or nickel, for example, from about 85 to about 97 weight % iron, cobalt or nickel, for example, 85-95% nickel. Sponge catalysts may be modified with at least one metal, for example, selected from the group consisting of chromium and molybdenum. The sponge metal catalysts may also contain surface hydrous oxides, adsorbed hydrogen radicals, and hydrogen bubbles in the pores. The instant catalyst, may also include aluminum, for example, from about 2 to 15 weight % aluminum, for example from about 4 to 10 weight % aluminum. Commercially available catalysts of the sponge type are promoted or unpromoted Raney® Ni or Raney® Co catalysts that can be obtained from the Grace Chemical Co. (Columbia, Md.). Catalysts comprising Group VIII metals are described in U.S. Patent No.

6,376,714.

[0057] The catalyst may be supported or unsupported.

[0058] A catalyst may be prepared by reducing an oxide of a Group VIII metal with hydrogen. For example, a catalyst may activated by reducing at least a part of iron oxide to metallic iron by heating it in the presence of hydrogen at a temperature above 200° C but not above 600° C. Activation may be continued until at least 80% by weight of the available oxygen in the iron has been removed and may be continued until substantially all, for example from 95 to 98% of the available oxygen has been removed. During the activation it is desirable to prevent back-diffusion of water-vapor formed. Examples of catalyst activation techniques are described in U.S. Patent No. 3,986,985.

[0059] At least a portion of the catalyst activation may take place in situ in one or more reactors for converting a dinitrile to a diamine. For example, referring to Figure 1 , an iron oxide catalyst precursor may be loaded in reactors 42, 44, 46 and 48. Hydrogen may then be passed over the catalyst precursor under conditions sufficient to reduce the iron oxide. When a sufficient degree of catalyst activation is achieved, dinitrile may included in the feed and the reactors may be maintained under conditions sufficient to convert dinitrile to diamine.

[0060] At least a portion of the catalyst activation may take place in a catalyst activation zone, which is separate from the reactors for converting dinitrile to diamine. An example of such a separate catalyst activation zone is described herein with reference to Figure 2, which is discussed in more detail below. When the catalyst precursor achieves a sufficient degree of activation, it may be transferred to one or more reactors for converting dinitrile to diamine.

[0061] Transfer of activated catalyst from a catalyst activation zone to a separate reactor may be problematic. For example, a reduced iron oxide catalyst is often pyrophoric and must be protected from atmospheric oxygen. According to one embodiment, the activated catalyst from the catalyst activation zone may be blanketed with an inert gas, such as nitrogen, and maintained in the inert atmosphere until the activated catalyst is loaded into one or more reactors for converting dinitrile into diamine. In another embodiment, the activated catalyst may be partially passivated prior to being transferred to a reaction zone for converting dinitrile to diamine. This passivation may take place by passing a source of oxygen over the activated catalyst in the activation zone before the catalyst is transferred. This passivation at least partially reoxidizes the external surface of catalyst particles, while maintaining the catalyst in a reduced state in the interior of the catalyst particles. After the passivated catalyst is loaded into reactors, for example, reactors 42, 44, 46 and 46 of Figure 1 , hydrogen may be passed over the passivated catalyst under conditions to reduce iron oxide on the surface of catalyst particles. Examples of catalyst passivation techniques are described in U.S. Patent No. 6,815,388.

[0062] Useful precursors for such an iron catalyst include iron oxides, iron hydroxides, iron oxyhydroxides or mixtures thereof. Examples include iron(lll) oxide, iron(ll, III) oxide, iron(ll) oxide, iron(ll) hydroxide, iron(lll) hydroxide or iron oxyhydroxide such as FeOOH. Synthetic or naturally occurring iron oxides, iron hydroxides or iron oxyhydroxides can be used, such as magnetite, which has the idealized formula of Fe₃0₄, brown ironstone, which has the idealized formula of Fe₂0₃ " H₂0, or red ironstone (hematite), which has the idealized formula of Fe₂0₃. Examples of sources of iron oxides for use as precursors for making a hydrogenation catalyst are described in U.S. Patent No. 6,815,388.

[0063] An example of an iron oxide precursor is Swedish magnetite. The composition of this magnetite is readily determinable by analysis using ICP spectrometry familiar to the skilled practitioner. The iron oxide catalyst precursor may comprise one or more selected from the group consisting of precursors having a total iron content greater than 65% by weight, Fe(ll) to Fe(lll) ratio between about 0.60 to about 0.75, total magnesium content greater than 800 ppm to less than 6000 ppm by weight, total aluminum content greater than about 700 ppm to less than 2500 ppm by weight, total sodium content less than about 400 ppm by weight, total potassium content less than about 400 ppm by weight, and a particle size distribution greater than about 90% in the range of 1.0 to 2.5 millimeters. Substantially similar iron oxide catalyst precursors are described in U.S. Patent Nos. 4,064,172 and 3,986,985 to Dewdney et al.

[0064] The reactors 42, 44, 46 and 48 of Figure 1 may be fixed bed reactors or other types of reactors. An example of a reactor, which does not use a fixed bed, is a slurry bubble column reactor with a riser and a downcomer as described in U.S. Published Application 201 1/0165029 to Zhang et al., U.S. Pat. No. 6,068,760 to Benham et al. and U.S. Patent 8,236,007 to Hou et al. The slurry bubble column reactor has an its ability to readily remove heat of reaction and to provide substantially isothermal operation.

[0065] A fixed bed reactor may have a cartridge, which includes the fixed bed of catalyst.

The catalyst cartridge may be moveable. In particular, the moveable cartridge may be capable of being loaded with a catalyst precursor, such as iron oxide, and placed in a catalyst activation unit. The catalyst precursor in the catalyst cartridge may then be activated in the catalyst activation unit. The cartridge, including activated catalyst, may then be moved to one or more of reactors 42, 44, 46 and 48. After shut down of the reaction in the reactors 42, 44, 46 and 48, the cartridge may then be removed from the one or more reactors and transported to a catalyst deactivation unit. The catalyst in the cartridge may be blanketed in an inert gas, such as nitrogen, when the cartridge is transported from the catalyst activation unit to a reactor or when the cartridge is transported from a reactor to a catalyst deactivation unit.

[0066] Deactivation of a pyrophoric catalyst in a cartridge may take place by passing an oxygen containing gas through the catalyst cartridge in a controlled manner. This deactivation may take place in a catalyst deactivation unit.

Detailed Description of Figure 2

[0067] The general flow of reactants and products through a system to prepare a reduced iron oxide catalyst may be described with reference to Figure 2. Figure 2 is a diagram showing a catalyst activation system for preparing a catalyst by reducing iron oxide with hydrogen.

[0068] In Figure 2, a first hydrogen source 100 and a second hydrogen source 104 are depicted. However, it will be understood that hydrogen may be supplied from a single source or more than two sources. Hydrogen from the first source 100 passes through line 102, and/or hydrogen from the second source 104 travels through line 106 to common hydrogen supply line 108. In one embodiment, the first hydrogen source 100 comprises at least a portion of vapor phase in line 76 exiting form the ammonia recovery system 70 shown in Figure 1. In another embodiment, the second hydrogen source 104 comprises hydrogen from a hydrogen pipeline. When a hydrogen pipeline is used, the hydrogen may be purified, for example, by a pressure swing adsorption treatment. When two sources of hydrogen are used, they may be used simultaneously or intermittently, by stopping the flow of hydrogen from the first source 100, when the second source 104 is used, and vice versa.

[0069] The hydrogen feed in line 108 is fed to preheater 110, and heated hydrogen is passed through line 112 to hydrogen/ammonia mixer 118. The ammonia feed to the

hydrogen/ammonia mixer 118 originates from ammonia source 114. The ammonia feed passes into the hydrogen/ammonia mixer 118 though line 1 16. The mixed hydrogen/ammonia feed passes through line 120 and line 122 into heat exchanger 124 to be heated. The heated

hydrogen/ammonia feed then passes through line 126 to preheater 128 for further heating to a temperature suitable for reducing iron oxide. This hydrogen/ammonia feed then passes through line 130 to catalyst activation unit 132 for reducing iron oxide. In catalyst activation unit 132, iron oxide is reduced, a portion of the hydrogen in the feed is converted to water (H₂0) and a portion of the ammonia ( H₃) is decomposed to form nitrogen (N₂) and hydrogen (H₂).

[0070] The effluent from the catalyst activation unit 132 passes through line 134 to heat exchanger 124, where heat from the effluent is transferred to the hydrogen/ammonia feed in line 122 and the effluent is cooled. The cooled effluent is then passed through line 136 to cooler 138 for further cooling. Cooler 138 may utilize refrigeration for all or a portion of the cooling in order to condense the maximum amount of water vapor in line 136. The effluent from cooler 138 passes through line 140 into separator 142, which includes a liquid phase comprising ammonia and water and a gas phase comprising hydrogen, ammonia and nitrogen. The liquid phase passes from separator 142 through line 1 8 and may be directed to storage tanks not shown in Figure 2.

[0071] At least a portion of the gas phase from separator 142 is passed by line 144 to compressor 146 and into line 122 for recycle to the catalyst activation unit 132. In order to minimize buildup of nitrogen in the recycle loop, a portion of the gas phase may also be taken from the separator 142 as a purge stream via line 150.

[0072] According to an optional embodiment not shown in Figure 2, preheater 110 and hydrogen/ammonia mixer 118 are not used. In this optional embodiment, ammonia from ammonia source is fed directly from line 120 into the system without first being mixed with hydrogen. Also, hydrogen from source 100 or source 104 is fed directly into cooler 138 without first being mixed with ammonia. Detailed Description of Figure 3

[0073] Figure 3 is a diagram showing details of the ammonia recovery system 70 shown in

Figure 1. In Figure 3, a heated stream 68, also shown in Figure 1 and comprising ammonia, hydrogen and diamine, is fed into ammonia recovery column 200. A diamine product stream 206 passes from the bottom of ammonia recovery column 200 into storage tank 210. The crude product in storage tank 210 may be further refined, for example, by steps illustrated in Figures 8A and 9. An overhead stream 202, comprising hydrogen and ammonia vapor, passes into condenser 220. A portion of the ammonia condensate is passed through line 204 as reflux into the ammonia recovery column 200. Another portion of the ammonia condensate is passed from condenser 220 through line 212 into storage tank 230. A portion of the ammonia condensate in storage tank 230 may be recycled through line 74 into line 2, as ammonia feed to the dinitrile conversion process as shown in Figure 1.

[0074] A vapor stream passes from condenser 220 through line 214 into ammonia absorber

78. A portion of this vapor stream may be taken as a side stream from line 214 into line 76 in order to be used as a hydrogen feed stream as described for the catalyst activation system shown in Figure 2.

[0075] A water stream is introduced into ammonia absorber 78 through line 80. An aqueous ammonia stream 82 passes from ammonia absorber 78 into storage tank 240. A vapor stream comprising hydrogen exits ammonia absorber 78 through line 84. Anhydrous ammonia may be recovered from the aqueous ammonia in storage tank 240 by distillation and recycled as an ammonia feed to the dinitrile hydrogenation process.

Summary of Figures 4-7

[0076] Figures 4-7 show a process for reacting adiponitrile with hydrogen in the presence of liquid ammonia to form hexamethylenediamine. Figures 4 and 5 show a reaction section for this reaction. Figure 4 shows the portion of the reaction section where the components of the feed are combined and heated to reaction temperature. Figure 5 shows the portion of the reaction section where the reaction of the feed components occurs. Figures 6 and 7 show a recovery section for recovering components of the product stream produced in the reaction section of Figures 4 and 5. Figure 6 shows a portion of the recovery section where a crude hexamethylenediamine product and unreacted hydrogen are recovered. Figure 7 shows a portion of the recovery section where ammonia is recovered. Overview of Figures 4 and 5

[0077] In Figures 4 and 5, fresh adiponitrile feed is introduced into the reaction section via line 301 , fresh hydrogen feed is introduced into the reaction section via line 309, and fresh liquid ammonia feed is introduced into the reaction section via line 313. These feeds are combined with various recycle feeds and are passed through line 308 to conservation heat exchanger 318 and preheater 323. The heated feed is then passed through line 326 into a series of reactors 327, 337 and 348. The reaction is exothermic. Heat generated in reactors 327, 337 and 348 is removed in heat reclaimers 329, 339 and 350 and coolers 334, 345 and 355. One reclaimer and one cooler is located downstream from each of the reactors 327, 337 and 348.

[0078] The product from the reaction section passes through line 356 to the recovery section shown in Figures 6 and 7.

[0079] Coolant for heat reclaimers 329, 339 and 350 passes from the recovery section into the reaction section via line 332. The coolant is a liquid stream from the recovery section. The liquid stream comprises liquid ammonia and hexamethylenediamine. This coolant passes into each of the heat reclaimers 329, 339 and 350 to form a vapor stream comprising ammonia and a liquid stream comprising ammonia and hexamethylenediamine. The vapor stream passes back into the recovery section through line 331 and the liquid stream passes back into the recovery section through line 333.

Detailed Description of Figures 4 and 5

[0080] Adiponitrile is introduced into the reaction section through line 301. At least a portion of the stream in line 301 may pass into adiponitrile pump 306 and then into line 307 for introduction into line 308. The stream in line 308 includes adiponitrile, hydrogen and liquid ammonia.

Adiponitrile pump 306 may be a reciprocating plunger pump or a multi-stage centrifugal pump. At least a portion of the adiponitrile feed may be diverted into line 302. The adiponitrile in line 302 is passed into recovery section illustrated in Figures 6 and 7. In particular, this feed is passed to pump 303 and then through line 304 and then into an adiponitrile absorber 361 , shown in Figure 6 (but not in Figures 4 or 5). The adiponitrile stream from the bottom of adiponitrile absorber 361 comprises adiponitrile and ammonia. The stream comprising adiponitrile and ammonia is returned to the reaction section via line 305 and is introduced into the adiponitrile feed stream in line 301.

[0081] A fresh hydrogen feed is introduced into the reaction section via line 309. At least a portion of the hydrogen feed may be passed into compression section 311 into line 312 and then into line 308 for introduction into the converters 327, 337 and 348. Compression section 311 may comprise, for example, two four-stage hydrogen compressors. At least one recycle stream of hydrogen may also be passed from the recovery section, illustrated in Figures 6 and 7, into line 309 of the reaction section. For example, hydrogen from the adiponitrile absorber 361 may be passed through line 310 to line 309. The combined fresh feed and recycled feed of hydrogen is then passed through compression section 311 to line 312 and into line 308. A hydrogen recycle stream may also be taken as an overhead from high pressure separator 357 through line 316 to gas circulating compressor 317 and then into line 308.

[0082] Fresh liquid ammonia feed is passed through line 313 into ammonia pump 314 to line 315 and then into line 308. Ammonia pump 314 may be a reciprocating plunger pump or a multi-stage centrifical pump. Some adiponitrile may be routed to the ammonia pump to aid in flow control and lubrication of pump components.

[0083] Feed comprising adiponitrlile, hydrogen and liquid ammonia is passed into conservation heat exchanger 318 through line 308. This feed is heated in conservation heat exchanger 318 by a liquid heating stream from the reaction section or the recovery section. This liquid stream is introduced into conservation heat exchanger 318 through line 319. An example of a liquid process stream is a liquid stream from a column used to separate hexamethylenediamine from lower boiling compounds. Such a stream is described with reference to Figure 8A as stream 463.

[0084] Conservation heat exchanger 318 may be a tube and shell type heat exchanger. Heating fluid may enter into conservation heat exchanger 318 through line 319 and pass through a shell section of a tube and shell type heat exchanger. A reactant fluid to be heated may enter into conservation heat exchanger 318 through line 308 and pass through a tube section of a tube and shell type heat exchanger. The cooled heating stream is returned to the reaction or recovery section through line 320.

[0085] The heated reactant stream from conservation heat exchanger 318 is then passed through line 321 to preheater 323. At least a portion of the stream in line 308 may be diverted from conservation heat exchanger 318 and introduced into line 321 via line 322. The amount of the stream in line 322, which is diverted around the conservation heat exchanger 318, may be used to control the temperature of the stream in line 321 , which is fed into preheater 323.

[0086] To heat the stream in line 321 , steam is introduced into preheater 323 through line

324. Cooled steam and/or condensate is recovered via line 325.

[0087] The heated reactant stream is then passed through line 326 into the first reactor or converter 327.

[0088] The effluent from reactor 327 passes through line 328 to heat reclaimer 329. A coolant stream, which comprises hexamethylenediamine and anhydrous, liquid ammonia, is passed into heat reclaimer 329 via line 332. In heat reclaimer 329, a portion of the liquid ammonia in the coolant stream vaporizes. A stream comprising vaporous ammonia is withdrawn from heat reclaimer 329 via line 331. A stream, which comprises hexamethylenediamine, liquid ammonia and dissolved hydrogen, is withdrawn from heat reclaimer 329 via line 333.

[0089] A cooled effluent stream from reactor 327 passes from heat reclaimer 329 through line 330. At least a portion of the stream in line 330 passes into cooler 334. Cooler 334 may be an air cooler or a water cooler. A portion of the stream in line 330 may also bypass cooler 334 by being diverted into line 336. By controlling the amount of the stream in line 330, which bypasses cooler 334, the temperature of the stream entering reactor 337 may be controlled. Feed, which passes through cooler 334 and any feed, which bypasses cooler 334, is passed into the second reactor 337 via line 335.

[0090] Although not shown in Figure 5, a portion of the stream in line 328 may bypass both reclaimer 329 and cooler 334, through a line not shown in Figure 5, as a way of controlling the temperature of the feed to converter 337.

[0091] Although not shown in Figure 5, an additional feed comprising hydrogen and/or adiponitrile may optionally be fed directly into reactor 337 or indirectly into reactor 337 by introduction, for example, into line 330, 335 or 336.

[0092] The effluent from reactor 337 passes through line 338 to heat reclaimer 339. A coolant stream, which comprises hexamethylenediamine and anhydrous, liquid ammonia is passed into heat reclaimer 339 via line 341. Line 341 is a side stream from line 332. In heat reclaimer 339, a portion of the liquid ammonia in the coolant stream vaporizes. A stream comprising vaporous ammonia is withdrawn from heat reclaimer 339 via line 342 and into line 331. A stream, which comprises hexamethylenediamine and liquid ammonia, is withdrawn from heat reclaimer 339 via line 343 to line 344 and then into line 333.

[0093] A cooled effluent stream from reactor 337 passes from heat reclaimer 339 through line 340. At least a portion of the stream in line 340 passes into cooler 345. Cooler 345 may be an air cooler or a water cooler. A portion of the stream in line 340 may also bypass cooler 345 by being diverted into line 347. By controlling the amount of the stream in line 340, which bypasses cooler 345, the temperature of the stream entering reactor 348 may be controlled. Feed, which passes through cooler 345 and any feed, which bypasses cooler 345, is passed into the third reactor 348 via line 346.

[0094] Although not shown in Figure 5, a portion of the stream in line 338 may bypass both reclaimer 339 and cooler 345, through a line not shown in Figure 5, as a way of controlling the temperature of the feed to converter 348. [0095] Although not shown in Figure 5, an additional feed comprising hydrogen and/or adiponitrile may optionally be fed directly into reactor 348 or indirectly into reactor 348 by introduction, for example, into line 340, 346 or 347.

[0096] The effluent from reactor 348 passes through line 349 to heat reclaimer 350. A coolant stream, which comprises hexamethylenediamine and anhydrous, liquid ammonia, is passed into heat reclaimer 350 via line 352. Line 352 is a side stream from line 332. In heat reclaimer 350, a portion of the liquid ammonia in the coolant stream vaporizes. A stream, which comprises vaporous ammonia, is withdrawn from heat reclaimer 350 via line 354 and into line 331. A stream, which comprises hexamethylenediamine, liquid ammonia and dissolved hydrogen is withdrawn from heat reclaimer 350 via line 353 to line 344 and then into line 333.

[0097] A cooled effluent stream from reactor 348 passes from heat reclaimer 350 through line 351. At least a portion of the stream in line 351 passes into cooler 355. Cooler 355 may be an air cooler or a water cooler. The cooled effluent from the third reactor 348 passes from cooler 355 through line 356 to the recovery section shown in Figures 6 and 7.

[0098] Each of heat reclaimers 329, 339 and 350 may be tube and shell type device similar to a tube and shell heat exchanger. The effluents from converters 327, 337 and 348 may enter into the tube side of the reclaimers, and cooling fluid may enter into the shell side of the reclaimers. Vapor generated in the shell side of a heat reclaimer may exit the reclaimer through a first line, and liquid from the shell side of the heat reclaimer may exit the reclaimer through a second line.

Overview of Figures 6 and 7

[0099] In the recovery section shown in Figures 6 and 7, ammonia and hydrogen are separated from hexamethylenediamine to provide a crude hexamethylenediamine product, which is recovered through line 385. This crude product also contains ammonia and other impurities, which are removed in refining steps not shown in Figure 6 and 7. However, examples of these refining steps are shown in Figures 8A and 9. The recovery section shown in Figures 6 and 7 also provides for the recovery of hydrogen and ammonia. Recovered hydrogen and ammonia may be recycled to the reaction section shown in Figures 4 and 5.

[00100] Most of the hydrogen in the stream entering the recovery section through line 356 is removed in high pressure separator 357 and intermediate pressure separator 359. The vapor stream from the high pressure separator 357 may be recycled directly to the conversion section. The vapor stream from the intermediate pressure separator 359 contains hydrogen and some ammonia. The vapor stream from the intermediate pressure separator 359 may be scrubbed with liquid adiponitrile in adiponitrile absorber 361 to provide a vapor stream enriched in hydrogen and a liquid stream comprising adiponitrile and dissolved ammonia. Both of these streams may be used as sources of feeds in the reaction section.

[00101] Liquid obtained from the intermediate pressure separator 359 is passed to reclaimer feed separator 364 to provide an ammonia vapor stream and a liquid stream partially depleted of ammonia. The liquid stream from reclaimer feed separator 364 is heated in heat reclaimers 329, 339 and 350, shown in Figure 5. Heated liquids and vapors from the heat reclaimers are passed to an ammonia recovery section comprising reclaimer tails tank 367, vapor cooler 375, flash evaporator 373, primary flash tank 380, and secondary flash tank 382. An anhydrous ammonia product is recovered as an overhead from vapor cooler 375. This anhydrous ammonia product is stored in anhydrous ammonia tank 398.

[00102] The crude hexamethylenediamine product is recovered from a liquid bottoms stream from the secondary flash tank 382. The overhead vapor stream from the secondary flash tank 382 comprises ammonia vapor. In Figure 7, this ammonia vapor is recovered as a liquid solution of aqueous ammonia in low pressure absorber 413. In low pressure absorber 413, ammonia vapor is scrubbed with water to form aqueous ammonia.

[00103] Figure 7 also shows a high pressure absorber 399, which also scrubs ammonia vapor with water to form a liquid solution of aqueous ammonia. In Figure 7, the ammonia feed to the high pressure absorber 399 comes from a vapor stream from adiponitrile absorber 361.

However, ojher sources of ammonia, not shown in Figure 7 may be fed to the high pressure absorber 399. Examples of such sources include vapor in line 360 obtained from intermediate pressure separator 359, and ammonia vapors vented from ammonia storage tank 398.

[00104] Aqueous ammonia solutions from the low pressure absorber 413 and the high pressure absorber 399 are fed to distillation column 424. A liquid bottoms water stream is recovered from distillation column 424 and is used as a water feed to low pressure absorber 413 and high pressure absorber 399. Anhydrous ammonia is obtained as a vaporous overhead from distillation column 424. A condensate of this overhead is passed to the anhydrous ammonia storage tank 398. Although not shown in Figure 7, the anhydrous ammonia in ammonia storage tank 398 may be used as a source of recycled ammonia feed in the conversion section shown in Figures 4 and 5.

Detailed Description of Figures 6 and 7

[00105] As shown in Figure 6, the cooled reactor effluent in line 356 passes into high pressure separator 357. An overhead stream comprising hydrogen and ammonia is passed through line 316 and returned to the converter section, shown in Figures 4 and 5. The stream in line 316 is used as a recycle hydrogen and ammonia feed.

[00106] A bottoms stream comprising hexamethylenediamine and liquid ammonia is passed from high pressure separator 357 through line 358 to intermediate pressure separator 359. An overhead vapor stream, which comprises ammonia and hydrogen, is passed from intermediate pressure separator 359 through line 360 to adiponitrile absorber 361. Adiponitrile is fed into adiponitrile absorber 361 through line 304. The adiponitrile scrubs the gasses in the absorber 361. Ammonia is dissolved in adiponitrile. A liquid phase comprising adiponitrile and dissolved ammonia passes from absorber 361 through line 305. As shown in Figure 4, the stream in line 305 is used as a feed for the conversion of adiponitrile to hexamethylenediamine.

[00107] A vapor phase stream is taken from absorber 361. This stream is enriched in hydrogen and depleted in ammonia, as compared to the vapor phase stream in line 360 entering the absorber 361. At least a portion of this hydrogen enriched stream may be passed through line 310 and used as a recycled hydrogen feed stream in the conversion process. At least a portion of the hydrogen enriched stream may also be passed through line 362 to high pressure absorber 399. In particular, the stream in line 362 may be a purge stream from the hydrogen stream from the adiponitrile absorber 361. The amount of hydrogen purged in this manner may be sufficient to keep the hydrogen purge at, for example, approximately 1% of the total hydrogen feed rate.

[00108] During start-up, shutdown, and normal operation, the adiponitrile absorber 361 may be optionally bypassed. During start-up, shutdown, and normal operation, vapors from the intermediate pressure separator 359 may be routed to high pressure absorber 399.

[00109] The liquid bottoms stream from intermediate pressure absorber 359 passes through line 363 to the reclaimer feed separator 364. In the reclaimer feed separator 364, the pressure of the liquid effluent from the intermediate pressure separator 359 in line 363 is reduced to provide a suitable vapor feed to the ammonia recovery section and to provide a suitable liquid coolant feed for use in heat reclaimers 329, 339 and 350. An overhead vapor stream passes from reclaimer feed separator 364 through line 365 to line 368 for introduction into vapor cooler 375. A liquid bottoms stream is passed from feed separator 364 through line 332 and into the heat reclaimers (i.e. heat reclaimers 329, 339 and 350) shown in Figure 5. A vapor stream from the heat reclaimers passes through line 331 to vapor cooler 375. A liquid stream from the heat reclaimers passes through line 333 to the reclaimer tails tank 367.

[00110] A vapor stream is taken as an overhead from the reclaimer tails tank 367 and is passed through line 368 to the vapor cooler 375. A liquid bottoms stream is taken from the reclaimer tails tank 367 and is passed through line 370 to pump 371 and then through line 372 to flash evaporator 373. An overhead vapor stream is taken from flash evaporator 373 and is passed through line 374 to line 368 and then into the vapor cooler 375.

[001 11] A liquid condensate is taken as a bottoms stream from the vapor cooler 375 and is passed through line 376 to pump 377 to line 378 and into flash evaporator 373. A liquid bottoms stream is taken from flash evaporator 373 through line 379 to primary flash tank 380. A liquid bottoms stream is taken from primary flash tank 380 through line 381 to secondary flash tank 382. The bottoms stream from secondary flash tank 382 flows through line 383 to pump 384 and then exits the recovery section through line 385.

[00112] The stream in line 385 comprises a crude hexamethylenediamine product, which is passed to a refining section, not shown in Figure 6. The crude product in line 385 may comprise, for example, 90 wt% hexamethylenediamine, 9 wt% ammonia and 1 wt% other impurities. The other impurities (i.e. those impurities other than ammonia) may comprise compounds having a boiling point lower than hexamethyenediamine and compounds having a boiling point higher than hexamethylenediamine. Examples of compounds having a boiling point lower than

hexamethylenediamine, include hydrogen, methane, diaminocyclohexane, hexamethyleneimine and water. Examples of compounds having a boiling point higher than hexamethylenediamine include 6-aminocapronitrile, adiponitrile and bis(hexamethylene) triamine.

[00113] A vaporous overhead stream is taken from primary flash tank 380 through line 386 to ammonia vapor compressor 387 and then to vapor cooler 375. At least a portion of the ammonia from this primary flash tank 380 may be vented through a scrubber (not shown in Figure 6), where hexamethylenediamine (HMD) is used to scrub out any diamine entrained with the escaping ammonia. The vaporous overhead stream from the vapor cooler 375 passes through line 390. This stream in line 390 is passed to partial or complete condenser 391 and then to line 392. Fluids in cooler 391 may be cooled with air, cooling water, or a chilled water/glycol stream from a

refrigeration unit. At least a portion of the stream in line 392 may be passed to trim separator 394. At least a portion of the stream in line 392 may also bypass the trim separator 394 by flowing through line 393 to ammonia receiver 396.

[001 14] In trim separator 394, phase separation occurs. Vapor phase is retained in the head (i.e. upper regions) of the trim separator 394, and a liquid phase collects in the bottoms regions of the trim separator 394. Ammonia vapors in the trim separator 394 may be vented into the high pressure absorber 399, the low pressure absorber 413 or the adiponitrile absorber 361. A liquid phase is taken from the bottoms of trim separator 394 through line 395 to ammonia receiver 396. Optionally, ammonia vapors in the ammonia receiver 396 may be vented through a line not shown in Figure 6 and passed to the high pressure absorber 399, the low pressure absorber 413 or the adiponitrile absorber 361.

[00115] The combined streams from line 393 and line 395 are collected in ammonia receiver 396. These combined streams are then passed through line 397 to anhydrous ammonia storage tank 398.

[00116] Ammonia storage tank 398 contains anhydrous ammonia, which is recovered without being contacted with water to form aqueous ammonia. However, there are various ammonia containing streams, which are contacted with water to scrub the vapors to remove ammonia from the vapors and produce solutions of aqueous ammonia. Aqueous ammonia may be distilled in one or more distillation steps to produce anhydrous ammonia. Anhydrous ammonia, produced from distillation of aqueous ammonia may be recovered and combined with anhydrous ammonia collected in anhydrous ammonia tank 398.

[00117] In Figure 7, aqueous ammonia is obtained from high pressure absorber 399 and from low pressure absorber 413. Water is introduced into high pressure absorber 399 through line 400. Ammonia vapor is introduced into high pressure absorber 399 through line 362. Ammonia vapor may also be introduced into high pressure absorber 399 from other sources through lines not shown in Figure 7. Examples of sources of ammonia vapor include vapors vented from trim separator 394, vapors vented from ammonia receiver, vapors vented from anhydrous ammonia storage tank 398, and vapors vented from aqueous ammonia storage tank 409.

[00118] In high pressure absorber 399, water is contacted with ammonia vapor in a counter current manner. As ammonia vapor dissolves in water, heat is generated. A vapor stream is taken from high pressure absorber 399 through line 401. Vapor in line 401 passes into purge separator 402. A portion of the content of purge separator 402 is returned to high pressure absorber 399 through line 403, and a portion of the content of purge separator 402 is taken as a purge stream in line 404. The purge stream comprises combustible gasses, such as hydrogen and methane. The combustible gasses may be burned in a combustion device, such as a boiler or a flare.

[00119] An aqueous ammonia stream is taken from the bottoms of the high pressure absorber 399 through line 405 to pump 406 and then into line 407. A portion of the stream in line 407 may be passed back into the high pressure absorber 399 through line 408. At least a portion of the stream in line 407 is also passed through line 408 to aqueous ammonia storage tank 409.

[00120] As shown in Figure 7, an overhead stream from the secondary flash tank 382 is passed through line 410 to low pressure absorber catch tank 411. A vaporous ammonia stream from low pressure catch tank 411 is passed through line 412 to low pressure absorber 413. Water is also passed to low pressure absorber through line 417. [00121] According to one optional embodiment not shown in Figures 6 and 7, at least a portion of the vapor in line 410 may be routed to ammonia vapor compressor 387 for recycle into vapor cooler 375.

[00122] A source of at least a portion of the water introduced into low pressure absorber 413 and high pressure absorber 399 may be distillation bottoms from aqueous ammonia distillation column 424. As shown in Figure 7, a liquid bottoms stream from column 424 passes through line 432 into process water tank 414. A water stream is taken from the process water tank 414 through line 415 to pump 416 and then into line 417. As shown in Figure 7, a portion of the water stream in line 417 is taken as a side stream in line 400 and passes as a water feed to high pressure absorber 399. Another portion of the water stream continues through line 417 and is introduced into low pressure absorber 413. Fresh or make up water may be added as needed, for example, to process water tank 414 or to any appropriate point upstream of high pressure absorber 399 or low pressure absorber 413.

[00123] Vapors from low pressure absorber 413 are passed through line 418. These vapors may comprise hydrogen or methane. These vapors in line 418 may be passed to a combustion device, such as a boiler or a flare.

[00124] Water is introduced into low pressure absorber 413 through line 417, and ammonia vapor is introduced into low pressure absorber 413 through line 412. Water and ammonia flow through low pressure absorber 413 in a counter current manner. The water collects ammonia by dissolving ammonia during the process. The dissolution of ammonia in water generates heat. The collected ammonia, in the form of aqueous ammonia, is passed from low pressure absorber 413 through line 419. The stream in line 419 passes through line 419 to pump 420 and then into line 421. A portion of the aqueous ammonia in line 421 may be passed through line 422 and back into low pressure absorber 413. At least a portion of the aqueous ammonia in line 421 is also passed through line 422 and then into aqueous ammonia storage tank 409.

[00125] Aqueous ammonia from aqueous ammonia storage tank 409 is passed through line 423 to distillation column 424. A vaporous overhead stream comprising anhydrous ammonia is taken from distillation column 424 through line 425. The vaporous stream in line 425 is passed into condenser 426 and then into line 427. The stream in line 427 is passed to condenser tank 428. Liquid from condenser tank 428 is passed through line 429 and into pump 430. A portion of the stream from pump 430 may be returned to distillation column 424 as reflux. At least a portion of the stream from pump 430 is also passed through line 431 to anhydrous ammonia storage tank 398. [00126] Anhydrous ammonia in anhydrous ammonia storage tank 398 may be recycled to appropriate points in the reaction section, shown in Figures 4 and 5, through lines not shown in Figure 7.

[00127] Although the process depicted in Figures 4-7 is described above with respect to the production of hexamethylenediamine from adiponitrile, it will be understood that other diamines may be produced from other dinitriles in this process. For example, methylglutaronitrile may be substituted for adiponitrile to produce 2-methylpentamethylenediamine, instead of

hexamethylenediamine. Process conditions may be suitably adjusted when dinitriles other than hexamethylenediamine are produced.

Description of Process Conditions in Figures 4-7

[00128] The feed to the series of converters 327, 337 and 348 is heated and pressurized to sufficient levels. The temperature of the feed, e.g., in line 326, may be at least 75 °C.

[00129] Ammonia is added to the feed stream, which comprises hydrogen and adiponitrile, to provide a heat sink to control heat generated from the exothermic reaction of hydrogen with adiponitrile. By maintaining a sufficient amount of ammonia introduced to converters 327, 337 and 348, heat generated during the course of the hydrogenation may be dissipated. Ammonia also serves to dissolve hydrogen. The dissolved hydrogen distributes evenly over catalyst particles and blends with adiponitrile, thereby enhancing the hydrogenation reaction. When hydrogen is dissolved in liquid or supercritical phase ammonia, it is believed that hydrogen can penetrate a liquid film, which may comprise nitriles or amines, on the surface of the catalyst.

[00130] Ammonia also suppresses the formation of various undesirable byproducts in the converters. When adiponitrile is hydrogenated to form hexamethylenediamine, unwanted byproducts may include bis-(hexamethylene) triamine, diaminocyclohexane, and

hexamethyleneimine. When 2-methylglutaronitrile is hydrogenated to form

methylpentamethylenediamine, unwanted byproducts may include bis-(methylpentamethylene) triamine, methylcyclopentanediamine, and 3-methylpiperidine. The use of ammonia solvent to suppress the formation of byproducts during the hydrogenation of nitriles is described in U.S. Patent Application Publication No. 2009/0048466.

[00131] The temperature in converters 327, 337 and 348 is controlled to prevent the temperature in the converters from exceeding a temperature at which significant catalyst degradation and impurity formation occurs. For example, if the temperature of the catalyst becomes too high, sintering of catalyst particles may occur, resulting in loss of catalyst surface area and decreased activity and selectivity. This unwanted catalyst degradation may be minimized be controlling the temperature of the effluent from each of the converters, such that the temperature of the effluent does not exceed 200 °C. For example, if the temperature of the catalyst becomes too high, impurity formation may become too high resulting in a significant yield loss for the process. These unwanted impurity reactions may be minimized be controlling the temperature of the effluent from each of the converters, such that the temperature of the effluent does not exceed 200 °C. In one embodiment, for example, the temperature of the effluent from each of the converters is 190 °C or less. In another embodiment, for example, the temperature of the effluent from each of the converters is 180 °C or less.

[00132] The hydrogenation reaction in the converters of Figure 5, especially the first converter 327, may be initiated by introducing the feed stream to each converter at a temperature of at least 75 °C. For example, in the early stages of the process, the temperature of the feed stream in line 326 to converter 327 may be maintained at a temperature of 80 to 90 °C, the temperature of the feed stream in line 335 to converter 337 may be maintained at a temperature of 80 to 90 °C, and the temperature of the feed stream in line 346 to converter 348 may be maintained at a temperature of 100 to 150 °C.

[00133] Catalyst aging takes place over time. As the catalyst ages, the inlet temperature of the feed to the converters may be increased to compensate for loss of catalyst activity. Eventually, the catalyst will become fully aged, and the reaction must be discontinued and the catalyst replaced. Catalyst replacement may take place when the inlet or exit temperature to one of more converters exceeds a predetermined temperature or when byproduct formation due to increased temperatures make production no longer economical. For example, the hydrogenation process may be shut down for catalyst replacement, when the inlet temperature to one or more of the converters exceeds 150 °C, or when the exit temperature from one or more of the converters exceeds 190 °C.

[00134] Over the course of a reaction campaign, starting with the first introduction of feed into the converters and lasting until the catalyst is replaced, the temperature of the feed to each converter may fall in the range of 75 to 150 °C, and the temperature of the effluent from each converter may fall in the range of 30 to 190 °C.

[00135] The hydrogenation reaction which takes place in the converters is exothermic.

Consequently, the temperature of effluent from the converters will be greater than the feed to the converters. For example, the temperature of the effluent from the first converter 327 may be 160 to 180 °C, the temperature of the effluent from the second converter 337 may be 160 to 180 °C, and the temperature of the effluent from the third converter 348 may be 150 to 170 °C. [00136] The pressure in each of the converters should be sufficiently high to maintain anhydrous ammonia in a liquid or supercritical state, especially at the maximum temperature attained in each of the converters. The hydrogen, dinitrile reactants and diamine products should be dissolved or otherwise evenly dispersed throughout the ammonia phase. The pressure in each of the converters may be at least 2500 psig (31 ,128 kPa), for example, 4500 psig (34,575 kPa), for example, 5000 psig (34,575 kPa).

[00137] The effluent from the third converter 348 is in the form of a liquid or supercritical fluid comprising dissolved hexamethylenediamine, anhydrous ammonia and dissolved hydrogen. This fluid may have a pressure of at least 2500 psig (31 ,128 kPa) and a temperature of at least 150 °C. As shown in Figures 4, 5 and 6, at least a portion of the hydrogen in the effluent from converter 348 is first removed by cooling the effluent in heat reclaimer 350 and cooler 355 and then passing the cooled effluent to high pressure separator 357. The effluent may be cooled by at least 80 °C prior to being fed into high pressure separator 357. The high pressure separator 357 may be operated under conditions, such that overhead stream 316 comprises mostly hydrogen on a molar basis. The temperature of the feed introduced to the high pressure separator 357 may be less than 70 °C, for example, 50 °C. The pressure in the high pressure separator 357 may be less than 4500 psig (31 ,128 kPa), for example, 4200 psig (29,059 kPa).

[00138] The liquid bottoms stream from high pressure separator 357 comprises some dissolved hydrogen. Most of this remaining dissolved hydrogen is removed in the intermediate pressure separator 359. The intermediate pressure separator 359 may be operated under essentially the same temperature conditions as the high pressure separator 357. For example, the temperature of the feed introduced to the intermediate pressure separator 359 may be less than 70 °C, for example, 50 °C or less. The pressure in the intermediate pressure separator 359 may be from 1200 to 2500 psig (8,375 to 17,339 kPa), for example, from 1500 to 1800 psig (10,433 to 12,512 kPa).

[00139] The overhead vapor stream from the intermediate pressure separator 359 in line 360 comprises ammonia in addition to hydrogen. As shown in Figure 6, ammonia is recovered by scrubbing the vapor in line 360 with adiponitrile in adiponitrile absorber 361. In another

embodiment not shown in Figure 6, at least a portion of the overhead vapor stream from the intermediate pressure separator 359 may routed to high pressure absorber 399, where ammonia is recovered by scrubbing the vapor stream with water.

[00140] The pressure of the liquid effluent from the intermediate pressure separator 359 is then further reduced in feed separator 364 to a pressure at which ammonia will flash evaporate. As shown in Figure 6, vaporous ammonia is removed as an overhead stream from feed separator 364 through line 365. The temperature in feed separator 364 may be 50 °C or less, for example, from 15 to 50 °C. The pressure in feed separator 364 may be from 450 to 600 psig (3,204 to 4,238 kPa), for example, from 500 to 600 psig (3,549 to 4,238 kPa), for example, 550 psig (3,893 kPa).

[00141] To facilitate further removal of ammonia from the liquid bottoms stream from feed separator 364, the stream in line 332 is heated by at least 50 °C, for example, by at least 100 °C. As shown in Figures 5 and 6, this heating takes place by passing the stream in line 332 to heat reclaimers 329, 339 and 350. As liquid is heated in the heat reclaimers, a portion of the ammonia in the liquid is vaporized. This vaporized ammonia is passed through line 331 to vapor cooler 375. The heated liquid stream from the heat reclaimers is passed through line 333 to reclaimer tails tank 367. The temperature of the stream in line 333 may be from 75 to 180 °C, for example, 120 °C. Similarly, the temperature of liquids in reclaimer tails tank 367 and flash evaporator 373 may be from 130 to 180 °C, for example, 170 °C. According to an optional embodiment, not shown in Figures 5 and 6, steam may be used as a source of heat, in addition to or in replacement of one or more heat reclaimers. For example, vapor cooler 375 and flash evaporator 373 may be replaced with a distillation column, and stream may be introduced into a calandria or reboiler of the distillation column.

[00142] The temperature in the vapor cooler may be from 40 to 80 °C, for example, from 50 to 60 °C. The temperature in the primary flash tank 380 may be from 110 to 170 °C, for example, from 140 to 150 °C. The temperature in secondary flash tank 382 may be from 10 to 50 °C less than the temperature in the primary flash tank 380. The temperature in secondary flash tank 382 may be from 100 to 150 °C, for example, 140 °C. The temperature in the trim separator 394 and the ammonia receiver 396 may be from 15 to 45 °C, for example, 35 °C.

[00143] The pressure in the reclaimer tails tank 367, the flash evaporator 373, and the vapor cooler 375 may be from 5 to 70 psig (136 to 584 kPa) less than the pressure in the reclaimer feed separator 364. The pressure in the reclaimer tails tank 367, the flash evaporator 373, and the vapor cooler 375 may be from 400 to 550 psig (2,859 to 3,893 kPa), for example, from 475 to 500 psig (3,204 to 3,549 kPa). The pressure in the primary flash tank 380 may be from 25 to 50 psig (274 to 446kPa), for example, from 30 to 42 psig (308 to 391 kPa). The pressure in the secondary flash tank 382 may be from 0 to 25 psig (101 to 274 kPa), for example, from 0 to 10 psig (101 to 170 kPa).

[00144] The pressure in the ammonia receiver 396 may be from 300 to 600 psig (2, 170 to 4,238 kPa), for example, from 400 to 500 psig (2,859 to 3,549 kPa).

[00145] The high pressure absorber 399 is designed to treat high pressure vapor streams and the low pressure absorber 413 is designed to treat low pressure vapor streams. The pressure in the high pressure absorber 399 may be from 120 to 180 psig (929 to 1 ,342 kPa), for example, 150 psig (1 ,136 kPa). The pressure in the low pressure absorber 413 may be from 0 to 50 psig (101 to 446 kPa), for example, 0 to 10 psig (101 to 170 kPa).

[00146] Most of the ammonia that is used as a diluent in the conversion of adiponitrile (ADN) to hexamethylenediamine (HMD) is recovered as anhydrous ammonia from the overhead stream in line 390 from vapor cooler 375. Some of the ammonia, however, is recovered by scrubbing gasses comprising ammonia with water. The gasses, which are scrubbed may further comprise, for example, hydrogen and methane. The purpose of scrubbing is two-fold in that it reduces air pollution and recovers the ammonia.

[00147] Two systems are used to recover ammonia from the gas streams. One system uses the high pressure absorber (HPA) and the other system uses the low pressure absorber (LPA). In Figure 7, these absorbers are represented by HPA 399 and LPA 413.

[00148] An ammonia containing gas stream may enter the high pressure absorber below a bottom tray or packed section. Purified water and/or recycle water may be added and adjusted to control the temperature of gas exiting the high pressure absorber 399 through line 401 and the concentration of ammonia (NH₃) in the aqueous ammonia stream exiting the high pressure absorber 399 through line 405. A water stream in line 400 may enter the high pressure absorber 399 on the top of a scrubber above a distributor plate. This water flows down through packing and absorbs ammonia (NH₃). As ammonia is absorbed by water, heat is given off. The non- condensable gasses, such as hydrogen (H₂) and methane (CH₄), exit at the top of the scrubber. Any entrained liquid may be trapped out in an off-gas separator or purge gas separator 402, and the H₂ or CH₄ containing gas may be routed to a flare, an incinerator or a boiler, which may be located off-site.

[00149] The aqueous ammonia tails of the high pressure absorber 399 may be circulated through an air or water cooler (not shown in Figure 7) and sent to aqueous ammonia storage tank 409. A valve may be used to control the level of liquid in the high pressure absorber 399. Part of a cooled aqueous ammonia stream may be returned to the high pressure absorber 399 via lines 407 and 408. The aqueous ammonia stream, which is returned to high pressure absorber 399 through line 408, may be returned to the high pressure absorber 399 to remove the heat of absorption.

[00150] The concentration of ammonia (NH₃) in the aqueous ammonia solution exiting the high pressure absorber 399 through line 405 may be controlled to a predetermined level. For example, the concentration of ammonia in this solution may be 20 to 22 wt%. Depending upon the configuration of the equipment used in the process, an ammonia concentration below 20 wt% may cause excessive use of steam in the aqueous ammonia distillation column 424. Also, ammonia concentrations above 23 wt% may cause excess venting in the aqueous ammonia storage tank 409.

[00151] The low pressure absorber 413 (LPA) may receive vapors from one or more of the primary flash tank 380 and the secondary flash tank 382. Ammonia filters (for removing particulates from the ammonia recycle stream) and ammonia pumps may also be depressured to the LPA 413 when they are taken out of service.

[00152] Ammonia in vapors introduced to the low pressure absorber 413 is scrubbed out in the low pressure absorber 413. A large circulating flow of aqueous ammonia may be maintained by means of a circulation pump 420, which pumps liquid from the base of the low pressure absorber 413, through air or water coolers (not shown in Figure 7), and then back into the top of the low pressure absorber 413 through a distributor. Liquid flows down through packing and absorbs the ammonia (NH₃) vapor coming up through the packing.

[00153] The liquid level at the base of the low pressure absorber 413 may be controlled to allow a portion of the aqueous ammonia solution to flow to the aqueous ammonia storage tank 409.

[00154] The concentration of ammonia (NH₃) in the aqueous ammonia solution exiting the low pressure absorber 413 through line 419 may be controlled to the same predetermined level of the concentration in the high pressure absorber 399. For example, the concentration of ammonia in this solution may be 20 to 22 wt%.

[00155] Vapor may flow through a vent scrubber located at the top of the low pressure absorber 413. Recycle water from the process water storage tank 414 may be fed to the top of the vent scrubber, and may flow down through packing to the base of the column. The liquid from the base of the low pressure absorber 413 may be pumped by the tails pump 420 to low pressure absorber coolers (not shown in Figure 7).

[00156] Unabsorbed gasses off the top of the vent scrubber may be routed through line 418 to a flare, boiler, or other combustion device.

Detailed Description of Figure 8A

[00157] Figure 8A shows an example of a way of recovering a purified diamine product from a crude diamine product. It will be understood that the features represented in Figure 8A are schematic and not drawn to scale. The recovery scheme shown in Figure 8A is especially applicable to the recovery of hexamethylenediamine.

[00158] In Figure 8A, the crude diamine product is passed into low boiler distillation section 451 via line 450. The diamine feed stream in line 450 may correspond to the effluent stream in line 385 of Figure 6. In low boiler distillation section 451 , the compounds in line 450 are separated into two streams, represented in Figure 8A by lines 452 and 454. Compounds in line 452 comprise compounds having a boiling point lower than the boiling point of the diamine in line 450.

Compounds in line 454 comprise compounds having boiling points both lower and higher than the boiling point of the diamine in line 450. At least a portion of these compounds in line 454, having a boiling point lower than the diamine, may have a boiling point within 50 °C of the boiling point of the diamine.

[00159] The stream in line 450 comprises compounds, defined hereinafter as "low boilers," "intermediate boilers," diamine and "high boilers." The stream in line 450 may comprise at least 95 wt%, for example, at least 97 wt% of the diamine produced in the hydrogenation of the dinitrile. Examples of low boilers include ammonia and water. Examples of high boilers include oligomers of the diamine and aminonitriles, such as the hydrogenation product produced when only one of the two nitrile groups on a dinitrile is hydrogenated.

[00160] When the diamine is hexamethylenediamine (HMD), high boilers include

bis(hexamethylene) triamine. When the diamine is hexamethylenediamine (HMD), intermediate boilers include one or more isomers of diaminocyclohexane (DCH). An example of an isomer of diaminocyclohexane (DCH) is 1,2-diaminocyclohexane.

[00161] When the diamine is 2-methylpentamethylenediamine (MPMD), high boilers include bis(2-methylpentamethylene) triamine. When the diamine is 2-methylpentamethylenediamine (MPMD), intermediate boilers include one of more isomers of methylcyclopentanediamine (MCPD).

[00162] The effluent stream in line 385 of Figure 6 corresponds to the feed in line 450 of Figure 8A. The effluent stream in line 385 may pass through one or more heating stages prior to being introduced to low boiler distillation section 451 through line 450. For example, the stream in line 385 may pass through a first heat exchanger where it comes in thermal contact with effluent stream 454 from low boiler distillation section 451. This heat exchanger serves to both heat the stream from line 385 and cool the stream in line 454. The heated effluent from the first heat exchanger may then be passed through a second heat exchanger. Steam may be used in the second heat exchanger to further heat the feed to low boiler distillation section 451.

[00163] Low boiler distillation section 451 may operate under atmospheric or vacuum conditions. The temperature profile in the first of one or more columns in low boiler distillation section 451 may be such that compounds having the boiling point of water or less, i.e. 100°C or less, tend to flash off as soon as they enter the column. When such a column is operated at atmospheric conditions, this flash evaporation may be facilitated by heating the effluent stream in line 385 to a temperature of 110 to 150 °C, for example, 130 °C. Any column in low boiler distillation section 451 may be in fluid connection with a heat exchanger, calandria or reboiler (not shown in Figure 8A) to supply at least a portion of the heat for the distillation.

[00164] The distillation conditions in low boiler distillation section 451 may be such that at least 95 % of the diamine entering into the low boiler distillation section 451 through one or more streams represented by line 450 is withdrawn in stream 454. The distillation conditions may also be such that at least 99 wt%, for example, at least 99.5 wt%, of compounds have a boiling point of 100°C or less are withdrawn in one or more overhead vapor streams in line 452. The low boiler distillation section 451 may be operated under conditions such that a maximum of 5 %, for example, from 0.1 to 1 %, of the diamine entering into low boiler distillation section 451 passes into one or more overhead streams, represented in Figure 8A as line 452. In this way, the loss of diamine in line 452 is minimized.

[00165] One or more streams comprising one or more high boilers are taken from low boiler distillation section 451 through one or more conduits, represented by line 454, to intermediate boiler distillation section 460. The stream in line 454 may also contain diamine, intermediate boilers and low boilers entrained with the high boilers. The stream in line 484 contains diamine and high boilers, which are separated in the high boiler distillation section 455. A stream comprising compounds with high boilers passes from the high boiler distillation section 455 through line 456. A stream comprising the diamine passes from the high boiler distillation section 455 through line 458.

[00166] A stream comprising diamine and intermediate boilers is taken from low boiler distillation section 451 through line 454 to intermediate boiler distillation column 460.

[00167] Intermediate boiler distillation column 460 may operate under vacuum conditions. The head pressure in the intermediate boiler distillation column 460 may be from 40 to 120 mm Hg (6.7 to 16 kPa), for example, from 50 to 70 mm Hg (10.7 to 13.3 kPa).

[00168] A liquid phase is withdrawn from the bottom section of the intermediate boiler distillation column 460 through line 484. A portion of the stream in line 484 may pass through a pump and into a calandria (not shown in Figure 8A). Steam may be used as a source of heat for the calandria. The calandria may be of forced circulation loop design or thermosiphon design. The pump may provide steady flow of material and sufficient backpressure (for example from 20 to 30 psig, i.e. 239 to 308 kPa) so as not to boil material. Heated liquid from the calandria may be returned to the intermediate boiler distillation column 460. The liquid stream from the calandria may pass into the intermediate boiler distillation column 460 through a restricting orifice. The

compounds with the lowest boiling point will vaporize up into the column, and higher boiling compounds will be returned to the base of the intermediate boiler distillation column 460. [00169] Near the top of the intermediate boiler distillation column 460, two trays are installed. The lower tray is a liquid collector tray 461. This tray 461 collects liquid from above and interfaces with vapors traveling up the column. Liquid from above, which is collected in liquid collection tray 461 , includes a return flow from heat exchanger 466 introduced through line 467 and reflux introduced through 487. The approximate temperature on the liquid collection tray 461 may be from 115 to 125 °C, for example, 121 °C. The liquid is pumped from line 463 through pump 464 to line 465 and into heat exchanger 466.

[00170] Heat exchanger 466 may be located in close proximity or in a relatively remote location from intermediate boiler distillation column 460. For example, heat exchanger 466 and intermediate boiler distillation column 460 may be located in the same or different buildings or enclosures.

[00171] The temperature of the liquid in the stream entering the heat exchanger 466 may be reduced by an amount of from 15 to 35 °C, for example, from 20 to 30 °C, in heat exchanger 466 before the liquid is returned to the intermediate boiler distillation column 460 through line 467. The return flow through line 467 may enter the intermediate boiler distillation column 460 at a point above the top liquid return tray 462. Reflux may also enter intermediate boiler distillation column 460 at a point above the top liquid return tray 462. This reflux may enter intermediate boiler distillation column 460 through line 487.

[00172] The overhead vapors from intermediate boiler distillation column 460 pass through the top liquid return tray 462 and then into a condenser, for example, a barometric spray condenser 475 where they are condensed. The transport of these vapors from intermediate boiler distillation column 460 to barometric spray condenser 475 is represented in Figure 8A by line 474. Line 474 in Figure 8A enters the rectangle depicting barometric spray condenser 475 at the bottom of the rectangle. However, this depiction is only a diagrammatic representation. The vapors from intermediate boiler distillation column 460 may enter the barometric spray condenser 475 through a variety of locations. For example, these vapors may enter the barometric spray condenser 475 near the top or near the bottom of the condenser 475. The barometric spray condenser 475 may be operated in a cocurrent or a counter current fashion as described below. The barometric spray condenser 475 may be operated under atmospheric or vacuum conditions.

[00173] Condensed vapors exit from barometric spray condenser 475 pass through line 476, then through pump 477 to line 478 and into heat exchanger 480. The liquid entering into heat exchanger 480 through line 478 may be cooled by at least 5 °C, for example, from 5 to 20 °C, before exiting heat exchanger 480 through line 481. The liquid entering the heat exchanger 480 through line 478 may be at a temperature of from 75 to 90 °C, for example, from 80 to 90 °C. The liquid exiting the heat exchanger 480 through line 481 may be at a temperature of from 65 to 85 °C, for example, from 70 to 80 °C.

[00174] Cooling fluid is introduced into heat exchanger 480 through line 482. The cooling fluid may be air or water. For example, liquid water may be introduced into heat exchanger 480 through line 482 at a temperature of from 35 to 50 °C, for example, from 40 to 45 °C. The temperature of the cooling water entering heat exchanger 480 through line 482 may be increased by 2 to 20 °C, for example, by 2 to 10 °C in heat exchanger 480 before exiting through line 483.

[00175] The process stream in line 481 is sprayed into barometric spray condenser 475. Line 481 in Figure 8A enters the rectangle depicting barometric spray condenser 475 at the top of the rectangle. However, this depiction is only a diagrammatic representation. The liquid spray may enter the barometric spray condenser 475 through a variety of locations. For example, these vapors may enter the barometric spray condenser 475 near the top or near the bottom of the condenser 475. The barometric spray condenser 475 may be operated in a cocurrent or a counter current fashion. When the barometric spray condenser 475 is operated in a cocurrent fashion, the spray may be introduced into the condenser 475 at a point below or equal to the point of entry of the vapor introduced through line 474. When the barometric spray condenser 475 is operated in a counter current fashion, the spray may be introduced into the condenser 475 at a point above the point of entry of the vapor introduced through line 474. An example of a cocurrent barometric spray condenser is described in U.S. Patent No. 5,516,922. An example of a counter current barometric spray condenser is described in U.S. Patent No. 2,214,932.

[00176] As shown in Figure 8A, a distillate stream comprising intermediate boilers, such as diaminocyclohexane (DCH), is removed in stream 479 from line 478.

[00177] A distillate stream may be taken off the liquid (either before or after the air/water cooler) and used as column reflux. For example, this distillate stream may be taken from line 476, line 478, line 479 or line 481. The reflux liquid in this distillate stream may be introduced into intermediate boiler distillation column 460 at a point above the top liquid return tray 462. The stream for returning reflux to the intermediate boiler distillation column 460 is depicted in Figure 8A, as passing through line 487.

[00178] Hexamethylenediamine has a boiling point of 205 °C. When adiponitrile is hydrogenated to make hexamethylenediamine, various isomers of diaminocyclohexane, such as ,2-diaminocyclohexane, are formed as byproducts. These isomers of diaminocyclohexane may have boiling points, for example, within the range of 185 to 195 °C. These isomers of

diaminocyclohexane are intermediate boilers. In a process for hydrogenating adiponitrile to make hexamethylenediamine, these isomers of diaminocyclohexane are mostly separated from hexamethylenediamine in intermediate boiler distillation column 460.

[00179] Methylpentamethylenediamine has a boiling point of 194 °C. When

methylglutaronitrile is hydrogenated to make methylpentamethylenediamine, various isomers of methylcyclopentanediamine are formed as byproducts. These isomers of

methylcyclopentanediamine may have boiling points, for example, within the range of 180 to 187 °C. These isomers of methylcyclopentanediamine are intermediate boilers. In a process for hydrogenating methylglutaronitrile to make methylpentamethylenediamine, these isomers of methylcyclopentanediamine are mostly separated from methylpentamethylenediamine in intermediate boiler distillation column 460.

[00180] A stream comprising a refined diamine product is taken as a distillate stream from high boiler distillation column 455 through line 458. Although not shown in Figure 8A, a portion of the stream in line 484 may be pumped into a heat exchanger, caldaria or reboiler and heated. The heated stream from the heat exchanger, calandria or reboiler may be returned to the intermediate boiler distillation column 460 at a point above the draw point for line 484. Intermediate boilers are concentrated in purge concentrator column 485, and exit the system as overhead stream 486. The bottoms from column 485 are returned as reflux to column 460 through line 488.

[00181] Heat exchanger 466 in Figure 8A corresponds to heat exchanger 318 in Figure 4. The feed introduced through line 468 to heat exchanger 466 in Figure 8A corresponds to the feed introduced into heat exchanger 318 through line 308 in Figure 4. The feed introduced through line 465 to heat exchanger 466 in Figure 8A corresponds to the feed introduced into heat exchanger 318 through line 319 in Figure 4.

[00182] The heated feed exiting heat exchanger 466 through line 469 in Figure 8A corresponds to the heated feed exiting heat exchanger 318 through line 321 in Figure 4. The cooled feed exiting heat exchanger 466 through line 467 in Figure 8A corresponds to the cooled feed exiting heat exchanger 318 through line 320 in Figure 4.

[00183] The temperature of the feed in line 468 may be increased by 27 to 47 °C, for example, from 32 to 42 °C, in heat exchanger 466 to heat the feed exiting the heat exchanger 466 through line 469.

[00184] Heat exchanger 470 in Figure 8A corresponds to heat exchanger 323 in Figure 4. The feed introduced through line 469 to heat exchanger 470 in Figure 8A corresponds to the feed introduced into heat exchanger 323 through line 321 in Figure 4. The temperature of the feed in line 469 may be increased by 2 to 10 °C, for example, from 1 to 5 °C in heat exchanger 470 to heat the feed exiting the heat exchanger 470 through line 473. The heated feed may then be introduced into converter 327 through line 326, as shown in Figure 4 and Figure 5.

[00185] The amount of heat energy, for example, in terms of kilowatt hours, imparted by heat exchanger 466 to heat the feed in line 468 in order to produce the heated feed in line 473 may be from 80 to 99 %, for example, from 90 to 99 %, for example, from 92 to 98 %, of the total heat energy imparted to the feed by both heat exchanger 468 and heat exchanger 470.

Detailed Description of Figure 8B

[00186] Figure 8B shows one embodiment of the low boiler distillation section 451 of Figure 8A. The particular distillation section in Figure 8B comprises two distillation columns 490 and 492. However, it will be understood that the low boiler distillation section 451 of Figure 8A may comprise a different configuration of distillation columns including a single distillation column or more than two distillation columns.

[00187] As shown in Figure 8B, a crude diamine stream passes through line 450 into a first distillation column 490. At least a portion of the low boilers in the stream from line 450 are removed from the first distillation column 490 as an overhead stream through line 452.

[00188] A bottoms stream comprising diamine, intermediate boilers and high boilers is taken from the first distillation column 490 and is passed to the second distillation column 492 through line 491. In the second distillation column 492, the diamine and intermediate boilers are separated from high boilers. The diamine and intermediate boilers are taken from the second distillation column 492 as an overhead steam through line 454. As shown in Figure 8A, the stream in line 454 is fed to the intermediate boiler distillation column 460.

[00189] A side draw stream is taken from the second distillation column 492 through line 453A. A bottoms stream is taken from the second distillation column 492 through line 453B. Both of these streams are introduced into the high boiler distillation section 455 (shown in Figure 8A). As shown in Figure 8B, a recycle stream from the high boiler distillation section is introduced into the second distillation column 492 through line 496. The stream in line 496 may be introduced into the second distillation column 492 at a point below the draw point of the side draw stream 453A and above the draw point of the bottoms stream 453B.

[00190] Although not shown in Figure 8B, it will be understood that a portion of the overhead vapor stream in line 452 may be passed to a condenser and at least a portion of the condensate may be returned to the first distillation column 490 as reflux. Also not shown in Figure 8B are calandrias or reboilers for supplying heat for the distillation. For example, a portion of the stream in line 491 may be pass through a calandria or a reboiler and the heated fluid may be introduced into the first distillation column at a point below the point of introduction of the feed stream in line 450.

Detailed Description of Figure 8C

[00191] Figure 8C shows one embodiment of the high boiler distillation section 455 of Figure 8A. The particular distillation section in Figure 8C comprises two distillation columns 493 and 495. However, it will be understood that the high boiler distillation section 455 of Figure 8A may comprise a different configuration of distillation columns including a single distillation column or more than two distillation columns.

[00192] In Figure 8C, a first feed stream comprising at least one intermediate boiler, diamine and at least one high boiler is introduced in a first distillation column 493 through line 453A. As shown in Figure 8B, the stream in line 453A is taken as a side draw stream from distillation column 492. A second feed stream comprising diamine and at least one high boiler is introduced in a second distillation column 495 through line 453B. As shown in Figure 8B, the stream in line 453B is taken as a bottoms stream from distillation column 492.

[00193] A vaporous overhead stream comprising at least one intermediate boiler is taken from the first distillation column 493 of Figure 8C through line 457. A liquid side draw stream comprising diamine may be taken from the first distillation column 493 through line 458A.

[00194] A liquid bottoms stream is taken from the first distillation column 493 of Figure 8C through line 496 and is returned to the second distillation column 492 of Figure 8B. As shown in Figure 8B, the stream in line 496 is introduced at a point above the draw point of the bottoms stream in line 453B and below the draw point of the side stream in line 453A.

[00195] The stream in line 453B is introduced into the second distillation column 495 at a point above the draw point of the bottoms stream in line 456 and below the draw point of the overhead vapor stream in line 458B. The bottoms stream in line 456 of Figure 8C corresponds to the stream in line 456 of Figure 8A. The stream in line 456 comprises at least one high boiler. The high boilers in the stream in line 456 may be further refined to separate various components in the stream in steps not shown in Figures 8A and 8C.

[00196] The overhead vapor stream in line 485B may be passed to a diamine storage tank not shown in Figure 8C. Similarly, the stream line 485A in Figure 8C may be passed to a diamine storage tank not shown in Figure 8C. Also, the stream in line 484 of Figure 8A may be passed to a diamine storage tank not shown in Figure 8A. The storage tanks for storing the contents of these three streams may be the same or different. For example, these three streams may be passed to a common storage tank. [00197] A portion of any of the streams in lines 458A, 458B and 484 may be returned to any of column 460 (shown in Figure 8A), column 493 (shown in Figure 8B) and column 495 (shown in Figure 8C). For example, all three of these streams may be stored in a common storage tank, and a portion of this commonly stored diamine may be returned along with reflux to distillation column 495 in Figure 8C.

[00198] The overhead vapor streams in lines 457 and 458B may pass through condensers (not shown in Figure 8C) and portions of the condensate may be returned to distillation columns 493 and 458B as reflux. Also, portions of the bottoms streams in lines 496 and 456 may pass through heat exchangers, reboilers or calandria (not shown in Figure 8C) and portions of the heated fluid may be returned to distillation columns 493 and 458B at a point below the point of introduction of feed streams 453A and 453B.

Detailed Description of Figure 9

[00199] Figure 9 shows a modified version of the process shown in Figure 8A. In particular, features from Figure 8A are omitted in Figure 9. These omitted features include tray 461 , tray 462, line 463, pump 464, line 465, heat exchanger 466, and line 467. In Figure 9, fluid in line 468 passes directly into heat exchanger 470 without first being preheated in heat exchanger 466.

Moveable Catalyst Cartridge and Converter Vessel

[00200] As mentioned previously, the hydrogenation catalyst may be contained in a movable catalyst cartridge. An example of such a catalyst cartridge and its use in a converter vessel is described below with reference to Figures 10-16.

Detailed Description of Figure 10

[00201] Figure 10 is a plan view of the catalyst cartridge having a cylindrical casing 600, which has a top end 602, a base 604 including an inlet orifice 610 for a central standpipe 611 (not shown in Figure 10, but shown in Figures 12 and 13) for incoming chemical reactants and one or more exit orifices 608 for the chemical products. The chemical reaction occurs entirely within cartridge 600, from which ambient air can be readily excluded.

Detailed Description of Figure 11 and Figure 12

[00202] Figure 1 1 is a side view of the structure of Figure 10, and Figure 12 is a cutaway view of Figure 1 1 along line 3-3, revealing internal structures of the catalyst cartridge. A mating inlet pipe 613 is inserted into standpipe 611 through the inlet orifice 610. Chemical reactants are flow upward through standpipe 611 to the top portion of the reactor cartridge 600. The upper end of the reactor cartridge 600 is capped with a head, which is bolted on to the top of the cartridge. The head and bolts are not shown for clarity.

[00203] The upper end of standpipe 611 extends nearly to the top of the cartridge and above the top of the catalyst bed (not shown for clarity), such that the chemical reactants entering the cartridge are transported to the top of the catalyst bed, through which they may percolate by gravity, and are forced by the pressure of the reactant feed. In order to equally distribute the incoming reactant feed across the top of the catalyst bed, the upper end of standpipe 611 may be equipped with an inverted conical screen 612, such that the chemical reactants exit the top of the standpipe 611 and are distributed through the inverted conical screen 612. Alternatively, the upper end of standpipe 611 is closed and an array of holes 614 drilled around the circumference of the upper end of the standpipe provide a fluid exit, such that the chemical reactants are equally distributed across the top of the catalyst bed. In the latter embodiment, the array of holes 614 are

advantageously surrounded with screening (not shown for clarity), such that the reactants can exit the standpipe but no catalyst pellets or granules can enter and clog it. At least a portion of holes 614 extend above the level of the catalyst bed. At least a portion of holes 614 may also be positioned below the top level of the catalyst bed.

[00204] After passing through the catalyst bed, the chemical reactants are reacted and transformed into chemical products, which exit the cartridge by passing first through perforations or screens in the exit distributor pipes 618, then downward into a collection channel (not shown in Figures 11 and 12) attached to the bottom of base 604 of the cartridge 600. Exit distributor pipes 618 may comprise holes surrounded by screeneing. The products then exit through one or more discharge pipes (not shown in Figures 11 and 12) and into the void space between the bottom of the cartridge and the inside bottom head of the converter (as shown in Figure 15B). The chemical products are subsequently collected and processed further.

Detailed Description of Figure 13A

[00205] Figure 13A is a plan view of the converter 630 vessel (hereinafter referred to as the "converter") for using the catalyst cartridge in a hydrogenation reaction. The converter is shown from the bottom.

[00206] The converter provides reinforcement of the walls of the cartridge during the hydrogenation reaction, which takes place at high temperature and pressure. The walls of the cartridge are designed to provide sufficiently light weight, because the walls must only withstand the differential pressure across the catalyst bed. If the walls of the cartridge were designed to withstand the temperature and pressure conditions of the hydrogenation reaction without reinforcement, the cartridge would, as a practical matter, be too heavy to insert, transport and remove.

[00207] The converter 630 as a whole is substantially cylindrical, having a bottom portion 632, a central portion 638 and a top portion 640. This top portion 640 may be of somewhat larger diameter than the rest of the device. Bottom portion 632 is penetrated by a centrally located inlet pipe 634 and at least one exit orifice 636.

Detailed Description of Figure 13B

[00208] Figure 13B is an exploded view of the converter of Figurel 3A, which additionally illustrates that the inlet pipe 634 is comprised of at least three distinct portions; an inlet pipe connection flange 634a for connection to incoming piping for chemical reactant fluids; a reduced diameter inlet pipe insertion portion 634b configured to fit inside a central standpipe 652 of the catalyst cartridge; and a connection flange 634c by which the inlet pipe is bolted to the bottom of the converter 630. The top portion 640 of the converter has a retainer ring 644 with breech lock thread teeth 646 on an outer circumference thereof.

Detailed Description of Figure 14A and Figure 14B

[00209] Figure 14A is a side view of the converter 630, and Figurel 4B is a cutaway view of Figure 14A, which illustrates the entire converter system in more detail. For example, in Figure 14b, the fluid connection between exit orifice 636 with an internal void 632a of lower portion 632 is visible, as is the overall arrangement of inlet pipe 634. Likewise the interior arrangement of top portion 640 can be seen in the cross-sectional view. A converter top head 620 is positioned above catalyst cartridge 600. A centrally disposed standpipe 652 is disposed within the converter, such that the lower end of standpipe 652 fits over the upper end 634b of inlet pipe 634, the combination providing a fluidly sealed inlet for chemical reactants to the catalyst (not shown for clarity).

Converter top head 620 is secured into position by retainer ring 644 of breech lock mechanism 648, as described below.

[00210] Exit orifices 650 empty into a collection channel (not shown in Figure 14B) at the bottom of the catalyst cartridge provide an exit for chemical products.

[00211] Converter top portion 640 contains a breech lock mechanism 648 which comprises the combination of breech lock teeth 642 formed on the interior circumference of top portion 640 and retainer ring 644 having coacting breech lock teeth 646 formed on its outer circumference. When engaged and rotated in a first direction, breech lock mechanism 648 locks the converter top head 620 in place. When rotated in the opposite direction, the breech lock mechanism 648 releases converter top head 620 and retainer ring 644 and converter top head 620 can be lifted out of converter 630, providing access to a spent catalyst cartridge 600.

Detailed Description of Figure 15

[00212] Figure 15 is a plan view of the locking mechanism of the converter, which is comprised of an outer shell 660 and an inner insert, in this case a retainer ring 662 configured to be inserted into the shell and partially rotated for locking. Shell 660 has a cylindrical inner surface and a first flat end surface 666 at one end. The cylindrical inner surface contains a first breech lock thread 672 comprised of 2 to 20 equidistant lock rings, each comprising m columns of teeth 672a and m interspaces 672b being alternately arranged around the cylindrical inner surface.

[00213] Retainer ring 662 has a second breech lock thread 668 which comprises a number m interspaces 668b and m columns of teeth 668a, equivalent in number to those of the pipe, alternately arranged around the cylindrical outer surface 670 thereof, wherein m is 2 to 12. Upon insertion of retainer ring 662 into the void of shell 660, the columns of teeth 668a on the retainer ring 662 are aligned with the interspaces 672b on the inner surface of the shell 660, permitting the retainer ring 662 to be axially moved into shell 660. In order to lock the breech lock mechanism so- formed, the retainer ring 662 is partially rotated such that the breech lock thread/teeth 668a thereof pass into and between the breech lock thread/teeth 672a of the pipe, thus coacting to hold the retainer ring 662 in the axial direction into shell 660.

Detailed Description of Figure 16

[00214] In Figure 16, a breech lock mechanism is incorporated onto a chemical reactor containment vessel 660 having disposed inside of it a catalyst cartridge 600, in fluid communication with inlet and exit connections on the bottom of the cartridge. A converter top head 620 is disposed below the bottom of retainer ring 662 such that rotation and locking of the breech lock mechanism acts to hold retainer ring 662 within the shell 660. Net fluid flow into and out of the cartridge is represented by the arrows in Figure 16.

Recovery of Hydrogen, Ammonia and Diamine

[00215] The product stream, which exits the last converter 348 in Figure 5 through line 349, comprises hydrogen, diamine and ammonia at very high pressure, e.g., as high as 5500 pisg (38,022 kPa), and high temperature, e.g., as high as 190 °C. It is necessary, to remove and recover as much hydrogen and ammonia, as reasonably possible, while stepping down the temperature and pressure of the mixture. [00216] As described herein with reference to Figures 4-7, much of the hydrogen in the product stream is recovered and recycled by operation of high pressure separator 357, intermediate pressure separator 359 and adiponitrile absorber 361. Once this hydrogen is removed, a liquid stream, which comprises ammonia and diamine, is obtained from intermediate pressure separator 359. However, this liquid is still at high pressure, e.g., as high as 1500 psig (10,433 kPa), and elevated temperature, e.g., as high as 70 °C. A challenge remains to recover ammonia from this liquid. In particular, it is desirable to recover as much of the ammonia as reasonable possible in anhydrous form, with the remaining ammonia being recovered as aqueous ammonia.

[00217] As described herein with reference to Figures 4-7, a first portion of the ammonia in the liquid stream from intermediate pressure separator 359 is removed by flash evaporation in separator 364. The liquid bottom stream from separator 364 has a reduced pressure of, e.g., 550 psig (3,893 kPa), but this liquid still contains a considerable amount of ammonia, which is ultimately recovered by distillation.

[00218] At least portion of the heat needed to distill anhydrous ammonia from the liquid stream exiting separator 364 via line 332 is supplied by heat reclaimers 329, 339 and 350.

[00219] As shown in Figure 6, the first distillation zone, from which vaporous anhydrous ammonia is recovered, comprises a collection of distillation vessels. These vessels comprise recovery tails tank 367, flash evaporator 373 and vapor cooler 375. However, it will be understood that different distillation equipment may be substituted for these vessels. For example, these vessels may be replaced by a single distillation column suitably configured to accomplish the desired distillation. In Figure 6, an anhydrous ammonia stream is taken from the distillation zone as an overhead stream from vapor cooler 375 through line 390. The liquid bottoms from the distillation zone exit flash evaporator 373 through line 379.

[00220] These liquid bottoms from the first distillation zone are at elevated pressure, e.g., as high as about 500 psig (3,549 kPa), and include ammonia. Accordingly, ammonia in this liquid is recoverable by flash evaporation. However, it has been discovered that, if the pressure in the liquid is reduced to near atmospheric pressure, e.g., 2 psig (115 kPa), in one stage, a considerable amount of the desired diamine product, e.g., HMD, will be carried overhead with the ammonia vapors. It has further been discovered that if these vapors are passed to an ammonia compressor, then as many as four compressor stages are needed.

[00221] As shown in Figure 6, two flash evaporation stages are used. A first flash evaporation stage takes place in primary flash tank 380, which is part of the second distillation zone for removing ammonia from a mixture of ammonia and diamine. Primary flash tank 380 may be operated at a pressure, e.g., from about 30 to 50 psig (308 to 446 kPa) sufficiently high to minimize the amount of diamine carried over in the overhead vapors and to maximize the amount of anhydrous ammonia, which is recycled to the first distillation zone via ammonia compressor 387.

[00222] The liquid bottoms from the primary flash tank 380 pass through line 381 to the secondary flash tank 382, which is part of the third distillation zone for removing ammonia from a mixture of ammonia and diamine. This secondary flash tank 382 may operate at near atmospheric pressure, e.g., about 2 psig (1 15 kPa). The amount and pressure of the ammonia in this stream are such that it is not economical to pass through a compressor for recycle to the first distillation zone. Ammonia in the overhead stream from the secondary flash tank 382 may be recovered by scrubbing with water, e.g., in low pressure absorber 413 (shown in Figure 7), followed by distillation of the aqueous ammonia, e.g., in distillation column 424.

[00223] The liquid bottoms stream from the secondary flash tank 382 still contains ammonia. However, this stream also contains byproducts having boiling points higher and lower than the diamine. A refined diamine product is ultimately recovered, for example, using distillation steps described above with reference to Figures 8A and 9.

[00224] The overhead stream from the primary flash tank 380 has sufficient properties, such that it may be compressed in a three-stage ammonia compressor. Thus, the two-stage flash evaporation process has an advantage over a single stage flash evaporation process in that the size of the ammonia compressor, e.g., represented in Figure 6 as ammonia compressor 387, used for recycling ammonia from the second distillation zone to the first distillation zone, may be reduced in size (e.g., from four stages to three stages).

[00225] It has further been discovered, however, that the overhead from the primary flash evaporator 380 still contains a small amount of diamine, e.g., HMD.

[00226] A multi-stage ammonia compressor typically contains cooling stages between compression stages. If the compressed gas is cooled below the melting point of the diamine in one or more of these cooling stages, diamine may solidify. Solidification of the diamine could clog the interstage coolers or even lead to total failure of a compressor.

[00227] The problem of dinitrile solidification in a multi-stage compressor is solved by maintaining the temperature of cooling water used in interstage coolers at a temperature of at least 1 °C above the melting point of the diamine. Hexamethylenediamine (HMD) has a melting point of 40.6 °C. Accordingly, when the diamine is HMD, the temperature of the cooling water used in the multi-stage ammonia compressor 387 may be at least 41 .6 °C. By keeping the compressed gas in the ammonia compressor above the melting point of the dinitrile, diamine in the liquid state may be generated in the cooling stages of the compressor. This liquid diamine may be collected in suction separators located downstream of interstage coolers and then passed along with liquid in line 385 for further refinement, for example, as described herein with reference to Figures 8A and 9.

EXAMPLES

[00228] The Examples which follow describe methods for hydrogenating dinitriles to produce diamines and methods for preparing catalysts for this hydrogenation reaction.

EXAMPLE 1

[00229] This Example describes the conversion of methylglutaronitrile (MGN) to 2- methylpentamethylenediamine (MP D). Referring to Figure 1 , feed streams comprising MGN and both fresh feed and recycled hydrogen and ammonia are passed into a series of four converters 42, 44, 46 and 48. The MGN feed may have the following composition:

MGN = 99.1 wt% min

ESN = 0.4 wt% max

HCN = 20 ppm max

Water = 0.12 wt%max

Ethylene glycol = 50 ppm max

Phosphorus = 15 ppm

Others = 0.7 wt% max

[00230] The pressure of the feed to the first converter 42 may be at least 3500 psig (24,233 kPa), for example, at least 4000 psig (27,680 kPa), for example, at least 4500 psig (31 ,128 kPa). The temperature of the feed to the first converter may be at least 100 °C, for example at least 105 °C, for example, at least 1 10 °C. The reaction of hydrogen with MGN in the first converter 42 is exothermic. Therefore, the temperature of the effluent stream exiting the first converter 42 may be at least 5 °C, for example, at least 10 °C, greater than the temperature of the stream entering the first converter 42. The temperature of the stream exiting the first converter 42 should preferably not exceed 200 °C, for example, 190 °C, for example, 180 °C.

[00231] Before the effluent stream from the first converter 42 is introduced into the second converter 44, it is preferably cooled by at least 5 °C, for example, at least 10 °C. This cooling may take place at least in part by passing the effluent from converter 42 into at least one heat exchanger or cooler (not shown in Figure 1 ) and by introducing a fresh feed of MGN (having a temperature less than that of the effluent from converter 42) into line 50 via line 38.

[00232] The pressure of the feed to the second converter 44 may be at least 3500 psig (24,233 kPa), for example, at least 4000 psig (27,680 kPa), for example, at least 4500 psig (31 ,128 kPa). The temperature of the feed to the second converter 44 may be at least 100 °C, for example at least 105 °C, for example, at least 110 °C. The reaction of hydrogen with MGN in the second converter 44 is exothermic. Therefore, the temperature of the effluent stream exiting the second converter may be at least 5 °C, for example, at least 10 °C, greater than the temperature of the stream entering the second converter 44. The temperature of the stream exiting the second converter 44 should preferably not exceed 200 °C, for example, 190 °C, for example, 180 °C.

[00233] Before the effluent stream from the second converter 44 is introduced into the third converter 46, it is preferably cooled by at least 5 °C, for example, at least 10 °C. This cooling may take place at least in part by passing the effluent from third converter 46 into at least one heat exchanger or cooler (not shown in Figure 1 ) and by introducing a fresh feed of MGN (having a temperature less than that of the effluent from second converter 44) into line 52 via line 40.

[00234] The pressure of the feed to the third converter 46 may be at least 3500 psig (24,233 kPa), for example, at least 4000 psig (27,680 kPa), for example, at least 4500 psig (31 ,128 kPa). The temperature of the feed to the third converter may be at least 100 °C, for example at least 105 °C, for example, at least 1 10 °C. The reaction of hydrogen with MGN in the third converter 46 is exothermic. Therefore, the temperature of the effluent stream exiting the third converter 46 may be at least 5 °C, for example, at least 10 °C, greater than the temperature of the stream entering the third converter 46. The temperature of the stream exiting the third converter 46 should preferably not exceed 200 °C, for example, 190 °C, for example, 180 °C.

[00235] Before the effluent stream from the third converter 46 is introduced into the fourth converter 48, it is preferably cooled by at least 5 °C, for example, at least 10 °C. This cooling may take place at least in part by passing the effluent from third converter 46 through line 54 and heat exchanger 20 into line 56. The temperature of the stream in line 56 may be further reduced by introducing a fresh feed of MGN (having a temperature less than that of the effluent from third converter 46) into line 56 via line 34.

[00236] The pressure of the feed to the fourth converter 48 may be at least 3500 psig (24,233 kPa), for example, at least 4000 psig (27,680 kPa), for example, at least 4500 psig (31 ,128 kPa). The temperature of the feed to the fourth converter may be at least 90 °C, for example, at least 95 °C. The reaction of hydrogen with MGN in the fourth converter 48 is exothermic.

Therefore, the temperature of the effluent stream exiting the fourth converter 48 may be at least 5 °C, for example, at least 10 °C, greater than the temperature of the stream entering the fourth converter 48. The temperature of the stream exiting the fourth converter 48 should preferably not exceed 200 °C, for example, 190 °C, for example, 180 °C. For example, the stream exiting the fourth converter 48 may have a temperature within the range of 130 to 180 °C and a pressure within the range of 4100 to 4500 psig (28,370 to 31 ,128 kPa).

[00237] The effluent from the fourth stage converter 48 passes through line 58 to heat exchanger 60. The effluent from fourth converter may be reduced to a temperature range of 30 to 60 °C at a pressure of 4100 to 4500 psig (28,370 to 31 ,128 kPa) in heat exchanger 60. The cooled effluent then passes from heat exchanger 60 through line 62 to product separator 64. Flash evaporation occurs in product separator 64. In the product separator 64, the pressure of the effluent from the fourth converter 48 may be reduced to a range of 450 to 500 psig (3,204 to 3,549 kPa) to cause separation of at least one liquid phase and at least one vapor phase.

[00238] The liquid phase, comprising MPMD, from the product separator 64 passes through line 66 to heat exchanger 60. The liquid phase may be heated to a temperature of about 65 to 85 °C in the heat exchanger 60. The feed stream in line 68 entering the ammonia recovery system 70 may have a temperature of 65 to 85 °C and a pressure of 465 to 480 psig (3,307 to 3,41 kPa). The stream in line 68 may comprise from 55 to 65 wt % ammonia, from 35 to 45 wt % MPMD and less than 1 wt %, for example, from 0.1 to 0.5 wt %, hydrogen.

[00239] The ammonia recovery system 70 comprises an ammonia recovery column (not shown in Figure 1) and condenser (not shown in Figure 1). The ammonia recovery column may have a base temperature of 150 °C and a head temperature of 67 °C. The column may operate under super atmospheric pressure. A crude product comprising MPMD is taken from the bottom of the ammonia column and exits the ammonia recovery system through line 72. This crude product may comprise at least 90 wt % MPMD. The crude product may be further refined to remove impurities.

[00240] The gas phase overhead from the ammonia recovery column passes into a condenser where a distillate phase comprising ammonia and a vapor phase comprising hydrogen is formed. A portion of the distillate phase may be returned to the ammonia recovery column as reflux. A portion of the distillate phase may transported to at least one storage tank for storage. A portion of the distillate phase may also be recycled as ammonia feed to the hydrogenation reaction. In Figure 1 , this recycle of ammonia is represented by ammonia passing form the ammonia recovery system through line 74 to line 2.

[00241] The gas phase, comprising hydrogen and ammonia, from the product separator 64 passes through line 86 to gas circulation pump 88 to promote flow of hydrogen and ammonia through line 18. The gas in line 86 may comprise from 92 to 96 wt % hydrogen (H₂) and 4 to 8 wt % ammonia (NH₃). [00242] A source of ammonia is passed through line 2 and ammonia pump 10 via line 12 into a hydrogen/ammonia recycle stream in line 18. The source of ammonia may also include recycled ammonia introduced into line 2 through line 74. A source of hydrogen is also passed through line 4 into hydrogen compressor 14. Ammonia from ammonia pump 10 passes through line 12 into line 18, and hydrogen from hydrogen compressor passes through line 16 into line 18. The stream comprising ammonia and hydrogen in line 18 is partially heated in heat exchanger 20 before it passes through line 22 to converter preheater 24. The heated ammonia and hydrogen from preheater 24 then passes through a series of four converters, depicted in Figure 1 as converters 42, 44, 46, and 48.

[00243] A source of MGN feed is fed from line 28 into dinitrile pump 30. MGN feed from dinitrile pump 30 passes through line 32 to line 34. A portion of the MGN feed may pass through line 34 to the ammonia feed line 2. A portion of the MGN feed may also pass from line 34 to line 26 via side stream 36 for introduction into the first stage converter 42. Similarly, side streams 38 and 40 provide fresh MGN feed to the second stage converter 44 and the third stage converter 46. Also, fresh MGN feed in line 34 is introduced into the fourth stage converter 48, as depicted in Figure 1.

[00244] In an optional embodiment, at least a portion of the vapor phase comprising hydrogen and ammonia in line 76 is passed through a line not shown in Figure 1 as a feed to a catalyst activation unit for preparing a catalyst by reducing iron oxide with hydrogen. This stream may comprise 55 to 65 wt % hydrogen (H₂) and 35 to 45 wt % ammonia (NH₃).

EXAMPLE 2

[00245] This Example describes an embodiment where a catalyst is formed by reducing iron oxide with hydrogen in the presence of ammonia.

[00246] Referring to Figure 2, hydrogen is supplied from source 100. In this Example, hydrogen source 104 is not used. The hydrogen supplied from source 100 comes from a hydrogen pipeline, which has been purified by a pressure swing adsorption treatment.

[00247] The hydrogen in source 100 is pressurized to a pressure of from 200 to 400 psig (1 ,480 to 2,859 kPa), for example, from 250 to 350 psig (1 ,825 to 2,515 kPa), for example, 300 psig (2,170 kPa). Hydrogen from source 100 is passed, sequentially, through line 102 and line 108 to preheater 110. Heated hydrogen is passed through line 112 to hydrogen/ammonia mixer 118. The ammonia feed to the hydrogen/ammonia mixer 118 originates from ammonia source 114. The ammonia in source 1 4 is anhydrous, liquid ammonia, pressurized to a pressure of 300 to 500 psig (2,170 to 3,549 kPa), for example, 350 to 450 psig (2,515 to 3,204 kPa), for example, 400 psig 2,859 kPa). The ammonia feed passes into the hydrogen/ammonia mixer 118 though line 116.

[00248] The liquid ammonia fed to the hydrogen/ammonia mixer 118 vaporizes in the presence of hydrogen to form a gaseous hydrogen/ammonia mixture. This mixture may comprise from 96 to 98 mol %, for example, 97 mol %, hydrogen and 2 to 4 mol%, for example, 3 mol %, ammonia. The liquid ammonia may be introduced into the hydrogen/ammonia mixer 118 at an ambient temperature, for example, a temperature of less than 30 °C. The hydrogen in preheater 110 is heated to a temperature sufficient to sustain the gaseous state of ammonia in the hydrogen/ammonia mixer 118 and in streams downstream of the hydrogen/ammonia mixer 118. For example, the temperature of hydrogen in line 112 may be at least 120 °C, for example, from 120 to 140 °C, for example, 130 °C. The temperature of the hydrogen/ammonia mixture exiting the hydrogen/ammonia mixer 1 18 to line 120 may be at least 30 °C, for example, from 30 to 50 °C, for example, 40 °C.

[00249] As shown in Figure 2, the temperature of the hydrogen/ammonia mixture is ramped up to a suitable reaction temperature in two heating steps. In a first heating step, the mixture passes from line 120 to line 122 into heat exchanger 124. The temperature of the

hydrogen/ammonia mixture exiting the heat exchanger 124 through line 126 may be, for example, at least 50 °C, for example, from 60 to 350 °C. The temperature of the hydrogen/ammonia mixture exiting preheater 128 into line 130 and into catalyst activation unit 132 may be from 375 to 425 °C, for example from 385 to 415 °C, for example, 400 °C. The pressure of the hydrogen/ammonia mixture entering the catalyst activation unit 132 may be at least 25 psig (274 kPa), for example, from 50 to 200 psig (446 to 1 ,480 kPa), for example, 120 psig (929 kPa).

[00250] The reaction of iron oxide with hydrogen in the catalyst activation unit 132 produces water (H₂0) as a byproduct. Also, some decomposition of ammonia (NH₃) takes place to produce hydrogen (H₂) and nitrogen (N₂). Therefore the gaseous effluent, which exits the catalyst activation unit 132 and enters line 134 comprises a mixture of hydrogen, ammonia, water and nitrogen. The composition of this gaseous mixture depends at least in part on the purity of the hydrogen charged to the catalyst activation unit, and may vary based upon this and the selection of operating conditions.

[00251] The reduction reaction, which takes place in the catalyst activation unit 132, is endothermic. The temperature of the effluent exiting catalyst activation unit 132 may be at least 10 °C less, for example, from 15 to 40 °C less, for example, 25 °C less than the temperature of the feed to the catalyst activation unit 132. The temperature of the effluent exiting catalyst activation unit 132 may be from 300 to 450 °C, for example, from 350 to 425 °C, for example, from 360 to 400 °C, for example, 375 °C. The pressure of the effluent exiting the catalyst activation unit 132 may be at least 25 psig (274 kPa), for example, from 50 to 200 psig (446 to 1 ,480 kPa), for example, 100 psig (791 kPa).

[00252] The temperature of the effluent from the catalyst activation unit is reduced in two steps. In a first step, the temperature of this effluent is partially reduced by passing the effluent through line 134 and through heat exchanger 124. In this way, heat is supplied to the

hydrogen/ammonia mixture entering the heat exchanger 124 through line 122 and exiting the heat exchanger 124 through line 126. In a second cooling step the partially cooled effluent from the catalyst activation unit 132 is cooled in cooler 138. In this way, the temperature of the effluent is reduced to a temperature sufficient to permit the phase separation, which takes place in separator 142.

[00253] The cooled effluent from the catalyst activation unit 132 is passed from cooler 138 through line 140 into separator 142. In separator 142, the effluent from the catalyst activation unit 132 separates at atmospheric pressure into a liquid phase comprising ammonia and water and a gas phase comprising hydrogen and ammonia. In order to maximize the amount of water in the liquid phase and to minimize the amount of water which remains in the gaseous phase, the effluent entering separator 142 may be cooled to a temperature of 10 °C or less, for example, 5 °C or less, by means of the heat exchanger 124 and cooler 138.

[00254] Water, mixed with ammonia, is removed as the liquid phase from separator 142 through line 148. At least a portion of the gas phase in separator 142 is removed from the separator through line 144 for recycle to the catalytic activation unit 132. The temperature of the gas in line 144 may be 10 °C or less, for example, 5 °C or less, for example, 2 °C. A portion of the gas phase in separator 142 may also be removed via line 150 as a purge stream. By taking a purge from the gas phase of separator 142, the build-up of nitrogen in the recycle loop may be minimized.

[00255] The gas phase used for recycle passes through line 144 and through compressor 146. In this way the pressure of the gas is increased to the pressure of the gas in lines 120 and 122.

EXAMPLE 3

[00256] This Example describes a process for separating a diamine from ammonia using a distillation process.

[00257] Referring to Figures 4-7, a first distillation zone comprises recovery tails tank 367, flash evaporator 373 and vapor cooler 375. A liquid comprising hexamethylenediamine (HMD) enters into the recovery tails tank 367 of the first distillation zone through line 333. The liquid entering recovery tails tank 367 comprises 80 wt% HMD and 20 wt% ammonia. The pressure in recovery tails tank 367, flash evaporator 373 and vapor cooler 375 is maintained at 500 psig (3,549 kPa). The temperature in recovery tails tank 367, flash evaporator 373 and vapor cooler 375 is between 100 C to 140 °C.

[00258] Liquid in the first distillation zone is distilled. A first overhead vapor stream enriched in ammonia is obtained from vapor cooler 375. This first overhead vapor stream exits vapor cooler 375 via line 390. A first liquid bottoms stream enriched in diamine is obtained from flash evaporator 373. This first liquid bottoms stream exits flash evaporator 373 via line 379.

[00259] A second distillation zone comprises primary flash tank 380. Liquid from the first liquid bottoms stream is introduced into the primary flash tank 380 through line 379. The pressure in primary flash tank 380 is maintained at 30 to 50 psig (308 kPa). The temperature in primary flash tank 380 is maintained at 120 to 160 °C.

[00260] Liquid in the primary flash tank 380 is distilled by flash evaporation. A second overhead vapor stream enriched in ammonia is obtained. This second overhead vapor stream exits primary flash tank 380 through line 386. A second liquid bottoms stream enriched in diamine is obtained. This second liquid bottoms stream exits primary flash tank 380 through line 386.

[00261] Vapor from the second overhead vapor stream passes through line 386 and through multi-stage, ammonia vapor compressor 387. Compressed vapor from ammonia vapor compressor 387 passes through line 388 and into the vapor cooler 375 of the first distillation zone.

[00262] Multi-stage ammonia vapor compressor 387 has three compression stages. The first compression stage includes a suction separator to remove any liquid that could enter the compressor and cause damage. This is followed by a suction pulsation damper, 1st stage compression cylinder, discharge pulsation damper, and interstage cooler.

[00263] The second compression stage of ammonia vapor compressor 387 includes a suction separator to remove any liquid that may have condensed in the interstage cooler and that could enter the compressor and cause damage. This is followed by a suction pulsation damper, compression cylinder, discharge pulsation damper, and interstage cooler.

[00264] The third compression stage includes a suction separator to remove any liquid that may have condensed in the interstage cooler and that could enter the compressor and cause damage. This is followed by a suction pulsation damper, compression cylinder, and discharge pulsation damper.

[00265] Ammonia vapor compressor 387 is designed so that each stage of compression will not exceed 150 °C in order to prevent compressor damage. After each stage of compression the gas is cooled down to approximately 41-45 °C, before compressing in the next stage. The intercoolers are mounted next to the compressor. The cooling water for the intercoolers is a closed loop cooling water system, so the water that exits the intercoolers returns to a storage tank or vessel. The temperature of the cooling water used in the interstage coolers is maintained at a temperature above 41.6 °C.

[00266] The bottoms stream from the primary flash tank 380, which is part of the above- mentioned second distillation zone is passed through line 381 and is introduced into a third distillation zone. Secondary flash tank 382 is part of this third distillation zone. Distillation takes place in secondary flash tank 382 by flash evaporation. The pressure in secondary flash tank 382 is maintained at 2 psig to 10 psig (1 15 kPa to 171 kPa). The temperature in secondary flash tank 382 is maintained at 110 to 130 °C.

[00267] A third overhead vapor stream enriched in ammonia and a third liquid bottoms stream enriched HMD are obtained. The third overhead vapor stream exits secondary flash tank 382 through line 410. The third liquid bottoms stream exits secondary flash tank 382 through line 383. The third liquid bottoms stream comprises greater than 90 wt% diamine and less than 10 wt% ammonia.

[00268] The claims and terms used therein are to be taken as variants of the invention described. These claims are not restricted to such variants but are to be read as covering the full scope of the invention implicit within the disclosure herein.

Claims

1. A process for separating a diamine from ammonia, said process comprising the steps of:

(a) introducing a liquid comprising diamine and ammonia into a first distillation zone;

(b) distilling the liquid in the first distillation zone of step (a) to obtain a first overhead vapor stream enriched in ammonia and a first liquid bottoms stream enriched in diamine;

(c) introducing liquid from the first liquid bottoms stream from step (b) into a second distillation zone;

(d) distilling the liquid in the second distillation zone of step (c) to obtain a second overhead vapor stream enriched in ammonia and a second liquid bottoms stream enriched in diamine;

(e) passing vapor from the second overhead vapor stream of step (d) through a multistage compressor and then into said first distillation zone;

(f) introducing the second bottoms stream from step (d) into a third distillation zone;

(g) distilling the liquid in the third distillation zone of step (f) to obtain a third overhead vapor stream enriched in ammonia and a third liquid bottoms stream enriched in diamine,

wherein the pressure in the second distillation zone of step (d) is less than the pressure in the first distillation zone of step (b), and

wherein the pressure in the third distillation zone of step (g) is less than the pressure in the second distillation zone of step (d).

2. The process of claim 1 , wherein the first distillation zone comprises a distillation column, and wherein both the second distillation zone and the third distillation zone comprise a flash tank.

3. The process of claim 1 , wherein the liquid introduced into the first distillation zone of step (a) comprises less than 80 wt% diamine and more than 20 wt% ammonia, based on the total weight of diamine and ammonia in the liquid;

wherein the liquid introduced into the second distillation zone of step (c) comprises from 70 to 95 wt% diamine and from 5 to 30 wt% ammonia, based on the total weight of diamine and ammonia in the liquid; and wherein the liquid introduced into the third distillation zone of step (c) comprises more than 85 wt% diamine and less than 15 wt% ammonia, based on the total weight of diamine and ammonia in the liquid.

4. The process of claim 1 , wherein fluid which is passed through the compressor of step (e) is heated to maintain the temperature of the fluid passing through this compressor above the freezing point of diamine passing through the compressor.

5. The process of claim 5, wherein the compressor of step (e) comprises at least one intercooler cooler, which is cooled by charging cooling water into the intercooler; and

wherein the cooling water is maintained at a temperature at least 1 °C above the freezing point of the diamine.

6. The process of claim 1 , wherein the diamine is hexamethylenediamine (HMD).

7. The process of claim 1 , wherein the diamine is 2-methylpentamethylenediamine (MPMD).

8. The process of claim 1 , wherein the pressure in the first distillation zone of step (b) is at least 400 psig;

wherein the pressure in the second distillation zone of step (d) is between 20 psig and 100 psig; and

wherein the pressure in the third distillation zone of step (g) is less than 0 psig.