Method for preparing hexamethylenediamine

Abstract

A method for preparing hexamethylenediamine is disclosed, comprising the following steps: (1) subjecting hexanediol and ammonia to an ammonia reaction under ammonia reaction conditions, optionally in the presence of a solvent, thereby obtaining an ammonia reaction product; (2) separating a stream containing hexamethyleneimine and water from the ammonia reaction product, dehydrating the stream containing hexamethyleneimine and water to obtain a dehydrated stream containing hexamethyleneimine, and then returning at least a portion of the dehydrated stream containing hexamethyleneimine to step (1) as a recirculating stream. The water content in the dehydrated stream containing hexamethyleneimine is less than 3 wt%, preferably less than 1.5 wt%. The present invention can not only improve the yield of hexamethylenediamine but also extend the service life of the catalyst.

Description

Detailed description of the invention

[0001] [Technical Field] The present invention relates to the technical field of hexamethylenediamine production, and more particularly to a method for preparing hexamethylenediamine.

[0002] 〔background〕 Hexamethylenediamine, also known as 1,6-diaminohexane, is an important chemical raw material, primarily used in the synthesis of nylon 66 salts, nylon 610, 1,6-hexamethylene diisocyanate, and other products. These products are used in the manufacture of fibers, resins, engineering plastics, and more. These products have a wide range of applications and can be widely used in fields such as textiles and leather, architectural coatings, and machinery manufacturing.

[0003] Industrial methods for producing hexamethylenediamine mainly include the adiponitrile process, the caprolactam process, the adipic acid process, and the hexanediol ammonia process.

[0004] The adiponitrile process is the most commonly used manufacturing method in industrial production. This method can be divided into two approaches: the high-pressure method and the low-pressure method. The high-pressure method uses iron-based catalysts and cobalt-copper-based catalysts as the main catalysts, and conversion rates can reach over 95%, but the high pressure and extremely high equipment requirements are significant. The low-pressure method uses Raney nickel as the main catalyst, but there are issues regarding the safety and stability of the Raney nickel catalyst, as well as the supply of adiponitrile raw materials.

[0005] In the caprolactam process, caprolactam is ammoniacalized with ammonia under the catalytic action of a phosphate to produce 6-aminocapronitrile, which is then hydrogenated to produce hexamethylenediamine. The key step in this method is the ammoniacalization of caprolactam. This method is only applicable to small-scale production and has been gradually abandoned due to its high production costs.

[0006] The adipic acid process involves ammoniating adipic acid with ammonia, then dehydrating it to produce adiponitrile, which is then hydrogenated to obtain hexamethylenediamine. This method has high manufacturing costs and a long process, which limits the scope of process technology development.

[0007] The hexanediol process is a method for preparing hexamethylenediamine by subjecting hexanediol and ammonia to an ammoniaization reaction. Hexanediol is a colorless, transparent liquid with low toxicity and minimal harm to the environment and human health. The preparation of hexamethylenediamine using hexanediol as a starting material is a green and environmentally friendly route. However, prior art generally exhibits low yields of hexamethylenediamine produced by the ammoniaization of hexanediol. As calculated according to the disclosed data, the yield of hexamethylenediamine is typically less than 50%, leaving room for improvement in economic efficiency.

[0008] CN114433122A discloses a catalyst for preparing 1,6-hexamethylenediamine by ammonia-converting 1,6-hexanediol in the presence of hydrogen. In a fixed-bed reactor, the molar ratio of hydrogen:ammonia:1,6-hexanediol is 3:8:1, and the volume space velocity of 1,6-hexanediol is 0.6h. -1 The reaction temperature was 205°C, the reaction pressure was 13 MPa, the conversion rate of hexanediol was approximately 80% to 92%, and the selectivity of hexamethylenediamine was approximately 42% to 52%. According to the disclosed data, the yield of hexamethylenediamine is calculated to be approximately 34% to 48%.

[0009] JP2022112396A discloses a method for producing hexamethylenediamine from 1,6-hexanediol, comprising the amination reaction of 1,6-hexanediol under mild conditions in the presence of a solid catalyst, wherein the catalyst comprises an active component containing a metal element selected from groups 8, 9, 10, and 11 of the periodic table, and a support containing rare earth elements and one or more metal elements selected from groups 4 and 5. According to the examples, the yield of hexamethylenediamine is less than 40%.

[0010] In prior art methods for producing hexamethylenediamine from hexanediol, both the conversion rate of hexanediol and the yield of the hexamethylenediamine product are low. Therefore, there is still a need for a method for preparing hexamethylenediamine that can produce it from hexanediol in high yield, thereby improving process economics.

[0011] 〔overview〕 The object of the present invention is to provide a method for preparing hexamethylenediamine in high yield so as to overcome the problems present in the prior art.

[0012] To achieve the above objective, the present invention provides a method for preparing hexamethylenediamine, which involves the following steps: (1) A step of subjecting hexanediol and ammonia to an ammonia reaction under ammonia reaction conditions, optionally in the presence of a solvent, to obtain an ammonia reaction product; (2) The process includes separating a stream containing hexamethyleneimine and water from the ammonia reaction product, dehydrating the stream containing hexamethyleneimine and water to obtain a dehydrated stream containing hexamethyleneimine, and returning at least a portion of the dehydrated stream containing hexamethyleneimine to step (1) as a circulating stream, wherein the water content of the dehydrated stream containing hexamethyleneimine is less than 3 wt%, preferably less than 1.5 wt%.

[0013] The method of the present invention has the following beneficial effects: (1) The method of the present invention not only improves the yield of hexamethylenediamine but also improves the service life of the catalyst by separating the ammonia reaction product, dehydrating the stream containing hexamethyleneimine, and then returning at least a portion of the dehydrated stream containing hexamethyleneimine to the ammonia reaction as a circulating stream.

[0014] (2) The present invention can improve not only the yield of hexamethylenediamine but also the service life of the catalyst by controlling the water content of the flow containing hexamethyleneimine that is returned to the ammonia reaction as a circulating flow to, for example, less than 3 wt%, preferably less than 1.5 wt%.

[0015] (3) The method of the present invention can solve the problem of system blockage, ensure long-term stable operation of the entire process, reduce the number of stoppages and maintenance, and lower the operating temperature of the entire separation process. At the same time, since the separation process of the present invention does not require thermal insulation measures for the entire process, production costs can be reduced.

[0016] (4) The method for preparing hexamethylenediamine according to the present invention has the following features: the process is simple, the yield of the hexamethylenediamine product is high, it is easy to operate, it is easy to control, and it can be operated for a long period of time.

[0017] [Detailed Disclosure] The endpoint values ​​and any values ​​of the ranges disclosed herein are not limited to exact ranges or values, and should be understood to include values ​​that approximate these ranges or values. For numerical ranges, one or more new numerical ranges can be obtained by combining the endpoint values ​​of each range with each other, by combining the endpoint values ​​of each range with individual point values, and by combining individual point values ​​with each other, and these numerical ranges should be considered specifically disclosed herein.

[0018] The present invention provides a method for preparing hexamethylenediamine, and this method comprises the following steps: (1) subjecting hexanediol and ammonia to an ammoniation reaction under ammoniation reaction conditions, optionally in the presence of a solvent, to obtain an ammoniation reaction product; (2) separating a stream containing hexamethyleneimine and water from the ammoniation reaction product, dehydrating the stream containing hexamethyleneimine and water to obtain a dehydrated stream containing hexamethyleneimine, and returning at least a part of the dehydrated stream containing hexamethyleneimine to step (1) as a recycle stream; the water content of the dehydrated stream containing hexamethyleneimine is less than 3 wt%, preferably less than 1.5 wt%.

[0019] It has unexpectedly been found by the present invention that when the amount of water in the ammoniation reaction system increases, a hydrothermal reforming reaction occurs, which affects the crystal form of the catalyst support and the lifespan of the catalyst, and thereby may affect the conversion rate and yield of the ammoniation reaction. The present invention has found that the yield of hexamethylenediamine can be significantly improved by strictly controlling the water content in the recycle stream in the ammoniation reaction system, thereby controlling the amount of water entering the ammoniation reactor. According to the present invention, the water content in the dehydrated stream containing hexamethyleneimine may be less than 3 wt%, preferably less than 1.5 wt%, more preferably less than 1 wt%.

[0020] According to the present invention, a solvent is not essential and is optionally used in the ammoniation reaction between hexanediol and ammonia; therefore, the ammoniation reaction may be carried out in or without a solvent. In the prior art, the ammoniation reaction is usually carried out at atmospheric pressure or low pressure, and ammonia is in the gas phase; therefore, in order to carry out the ammoniation reaction efficiently, it is necessary to add a solvent that dissolves ammonia gas. In the present invention, the pressure of the ammoniation reaction is relatively high, and ammonia is liquefied and in the liquid phase; therefore, the ammoniation reaction between hexanediol and liquid ammonia can be carried out in the absence of a solvent. The solvent added in the present invention is a solvent in which the solubility of the ammoniation reaction raw materials and reaction products such as hexanediol, hexamethylenediamine, aminohexanol, and hexamethyleneimine is greater than 0.1 g / g, and examples include at least one of tetrahydrofuran, 1,4-dioxane, n-hexane, cyclohexane, tert-butanol, tetramethylenesulfone, and glycerol.

[0021] According to the present invention, in the ammoniation reaction of hexanediol and ammonia, the molar ratio of ammonia to hexanediol is 10 to 60:1, preferably 15 to 55:1, for example 18 to 50:1, 22 to 43:1, and 22 to 38:1. The ammoniation reaction is carried out in the presence of hydrogen, and the molar ratio of hydrogen to hexanediol is 0.05 to 8:1, preferably 0.08 to 7:1, preferably 0.09 to 6:1, preferably 0.1 to 5:1, preferably 0.2 to 4:1, preferably 0.3 to 4:1, more preferably 0.4 to 3:1, for example 0.4 to 5:1 and 0.4 to 4:1. The molar ratios of ammonia, hydrogen, and hexanediol refer to the molar ratios in the mixture at the inlet of the ammoniation reactor.

[0022] According to the present invention, in the ammoniation reaction of hexanediol and ammonia, the temperature of the ammoniation reaction is 100°C to 220°C, preferably 110°C to 210°C, preferably 120°C to 210°C, preferably 130°C to 200°C, for example 110°C to 200°C and 120°C to 190°C. The pressure of the ammoniation reaction is 5 MPaG to 20 MPaG, preferably 6 MPaG to 19 MPaG, preferably 7 MPaG to 17 MPaG, more preferably 8 MPaG to 15 MPaG, for example 7 MPaG to 18 MPaG and 8 MPaG to 14 MPaG. The liquid hourly space velocity of fresh hexanediol is 0.05h -1 ~10h -1 、preferably 0.05h -1 ~8h -1 、preferably 0.05h -1 ~7h -1 、preferably 0.07h -1 ~5h -1 、preferably 0.08h -1 ~4h -1 、more preferably 0.09h -1 ~3.9h -1 。

[0023] The present invention does not particularly limit the catalyst used in the ammoniation reaction, and any catalyst suitable for the ammoniation of hexanediol can be used. For example, the catalysts disclosed in patent applications such as CN114433087A and CN114433121A can be used. Preferably, the catalyst for the ammoniation reaction includes a carrier, an active component supported on the carrier, and optionally an auxiliary agent. The carrier includes a doping element, alumina, and optionally another carrier. The other carrier is selected from silicon oxide and / or molecular sieve. The doping element is selected from at least one of boron, fluorine, phosphorus, sulfur, and selenium. The pore volume of the carrier having a pore diameter in the range of 7 nm to 27 nm occupies more than 65% of the pore volume of the carrier. The active component is cobalt and / or nickel.

[0024] In the ammonia reaction catalyst of the present invention, the support is preferably silicon oxide and / or alumina incorporated into a molecular sieve. The alumina support content in the support is 70 wt% or more, preferably 75 wt% to 100 wt%.

[0025] According to the ammonia reaction catalyst of the present invention, preferably, the content of the doping element in the carrier is 0.05 wt% to 6 wt%, more preferably 0.08 wt% to 4 wt%, of the total weight of the carrier consisting of components other than the doping element. Components other than the doping element mainly refer to alumina and any other carrier in the carrier.

[0026] According to the ammonia reaction catalyst of the present invention, preferably, the doping element in the carrier is doped in the form of at least one of borate ions, fluoride ions, phosphate ions, sulfate ions, and selenite ions. Since the doped doping element is introduced during the carrier preparation process, the doped element is mainly present in the bulk phase of the carrier.

[0027] According to the ammonia reaction catalyst of the present invention, preferably, the pore volume of a support with a pore diameter in the range of 7 nm to 27 nm accounts for more than 65%, preferably 70% to 90%, of the pore volume of the support; the pore volume of a support with a pore diameter of less than 7 nm accounts for 0% to 10%; and the pore volume of a support with a pore diameter greater than 27 nm accounts for 18% to 32%.

[0028] According to the ammonia reaction catalyst of the present invention, preferably, the L acid of the support accounts for 85% or more, more preferably 85% to 98%, of the total of the L acid and B acid.

[0029] According to the ammonia reaction catalyst of the present invention, preferably the specific surface area of ​​the support is 120 m². 2 / g~210m 2 The concentration is per gram, and the pore volume of the carrier is 0.43 ml / g to 1.1 ml / g.

[0030] According to the ammonia reaction catalyst of the present invention, the content of the active ingredient may preferably be 8g to 44g, more preferably 12g to 37g, per 100g of a carrier consisting of components other than the doping element.

[0031] According to the ammonia reaction catalyst of the present invention, the content of the auxiliary agent may preferably be 0g to 10g, more preferably 0.5g to 6g, per 100g of carrier consisting of components other than doping elements.

[0032] According to the ammonia reaction catalyst of the present invention, preferably, the auxiliary agent can be selected from at least one of the VIB, VIIB, IB, IIB, and lanthanide elements, and preferably at least one of Cr, Mo, W, Mn, Re, Cu, Ag, Au, Zn, La, and Ce.

[0033] The type of ammonia reactor used in the ammonia reaction is not particularly limited; any reactor that can ensure stable operation of the reaction can be used, such as a fixed-bed reactor, a high-pressure reactor, or a fluidized-bed reactor.

[0034] According to the present invention, taking into account the energy consumption of the system, the yield of hexamethylenediamine, and the service life of the catalyst, the weight ratio of the circulating flow returned to step (1) to fresh hexanediol is preferably 0.1 to 30:1, preferably 0.3 to 26:1, more preferably 0.5 to 20:1, for example 0.1 to 24:1, 0.4 to 21:1, 0.1 to 13:1, and 0.3 to 10:1.

[0035] Note that in the initial stages of the reaction, the amount of hexamethyleneimine produced by the ammoniaization reaction is small and cannot satisfy the weight ratio specified above to the fresh hexanediol in the circulating flow. Therefore, in the initial stages of the reaction, all of the hexamethyleneimine is returned to the ammoniaization reaction. During the stable operation phase of the reaction, the amount of hexamethyleneimine accumulated by the ammoniaization reaction is sufficiently large that at this point it is sufficient to ensure that the returned circulating flow satisfies the weight ratio specified above. The same applies to the aminohexanol produced by the ammoniaization reaction. Note that the weight ratio of the circulating flow returned to step (1) to fresh hexanediol shown in the examples herein is the mass ratio during the stable operation phase of the reaction.

[0036] According to the present invention, the dehydration of a flow containing hexamethyleneimine and water may be a dehydration method commonly used in the art, but preferably, in order to further reduce the water content in the flow containing hexamethyleneimine, the dehydration method includes at least one of membrane separation dehydration, azeotropic distillation dehydration, extractive distillation dehydration, adsorption dehydration, reverse osmosis dehydration, biological treatment dehydration, and pressure swing distillation dehydration.

[0037] According to a preferred embodiment of the present invention, dehydration of a flow containing hexamethyleneimine and water may be performed by membrane separation dehydration, and the operating conditions for membrane separation dehydration include: a membrane inlet pressure of 0 MPaG to 5 MPaG, for example 1 MPaG to 4 MPaG, and a temperature of 10°C to 350°C, for example 10°C to 200°C, for example 15°C to 190°C.

[0038] According to a preferred embodiment of the present invention, dehydration of a stream containing hexamethyleneimine and water may be performed by azeotropic distillation. Azeotropic distillation is performed in a distillation column, the operating conditions of which include: a weight ratio of the azeotrope to the stream containing hexamethyleneimine of 10 to 100:1, a bottom temperature of 120°C to 200°C, a top temperature of 80°C to 150°C, a reflux ratio of 0.1 to 20, a top operating pressure of 0 MPaG to 3 MPaG, and 10 to 80 stages; the azeotrope may be at least one of cyclohexane, n-hexane, trimethylpentane, 1-methyl-4-isopropylbenzene, dioxane, phenol, cresol, dibutyl ether, diamyl ether, and diisoamyl ether.

[0039] According to the present invention, step (2) further includes separating a stream containing aminohexanol from the ammonia reaction product, returning the aminohexanol-containing stream to step (1) as a circulating stream together with a dehydrated stream containing hexamethyleneimine, thereby further improving the yield of hexamethylenediamine. The aminohexanol-containing stream may also contain, for example, 0 wt% to 30 wt% hexanediol, 0 wt% to 2 wt% hexamethylenediamine, and small amounts of other components (e.g., heavy components).

[0040] According to the present invention, preferably, the weight ratio of aminohexanol to hexamethyleneimine in the circulating flow is 0.1 to 8:1, for example 0.1 to 7:1, for example 0.12 to 7:1 (for example, 0.12:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, and the range composed of any two of the above points).

[0041] When the flow containing aminohexanol and the dehydrated flow containing hexamethyleneimine are returned to step (1) as a circulating flow, it should be noted that in the initial stages of the reaction, the amounts of hexamethyleneimine and aminohexanol produced by the ammoniaization reaction are small and cannot satisfy the weight ratio specified above to the hexanediol in the circulating flow. Therefore, in the initial stages of the reaction, the dehydrated flow containing hexamethyleneimine and the flow containing aminohexanol are all returned to the ammoniaization reaction. During the stable operation stage of the reaction, the accumulation of hexamethyleneimine and aminohexanol produced by the ammoniaization reaction is sufficiently large, and at this point, it is sufficient to ensure that the circulating flow returned satisfies the weight ratio specified above. The weight ratio of the circulating flow returned to the ammoniaization reaction to fresh hexanediol shown in the examples herein is the weight ratio during the stable operation stage of the reaction.

[0042] According to the present invention, preferably, the conditions for separating the ammonia reaction product are such that the hexamethyleneimine content in the stream containing hexamethyleneimine and water is 35 wt% to 95 wt%, more preferably 40 wt% to 85 wt%, and most preferably 50 wt% to 80 wt%; and the water content is 5 wt% to 65 wt%, more preferably 20 wt% to 50 wt%, and most preferably 30 wt% to 40 wt%.

[0043] Preferably, the approach for separating the ammonia reaction product is as follows: subjecting the ammonia reaction product to a first separation to obtain a stream containing hexamethyleneimine and water, and then subjecting it to a second separation to obtain a stream containing hexamethylenediamine product and aminohexanol; more preferably, the first and second separations each independently include at least one of distillation, membrane separation and pressure swing adsorption.

[0044] Preferably, the approach for separating the ammonia reaction product is as follows: subject the ammonia reaction product to a first separation to obtain a stream containing hexamethyleneimine and water, then subject it to a second separation to obtain a hexamethylenediamine product, then subject it to a third separation to obtain a stream containing aminohexanol and heavy components; more preferably, the first, second, and third separations each independently include at least one of distillation, membrane separation, and pressure swing adsorption.

[0045] In the present invention, for example, when distillation is used, the conditions for the first separation are: a theoretical number of 10 to 80 (for example, a range consisting of 10, 20, 30, 40, 50, 60, 70, 80, and any of the above point values), a pressure of 1 kPa to 600 kPa (absolute pressure, for example, 1 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, and The operating pressure may include an operating pressure (a range consisting of any of the above point values), a column bottom temperature of 100°C to 300°C, and a reflux ratio of 0.1 to 15; the second separation conditions may include: a theoretical plate number of 10 to 80 (e.g., a range consisting of 10, 20, 30, 40, 50, 60, 70, 80, and any of the above point values), and an absolute pressure of 1 kPa to 600 kPa (e.g., 1 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 100 kPa). a) Operating pressure (a range consisting of 200kPa, 300kPa, 400kPa, 500kPa, 600kPa and any of the above point values), bottom column temperature of 130°C to 380°C, and reflux ratio of 0.1 to 20; and third separation conditions include: theoretical plate number of 10 to 100 (e.g., range consisting of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 and any of the above point values), 1kPa to 110 The operating pressure may include 0 kPa (absolute pressure, e.g., a range consisting of 1 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, 800 kPa, 900 kPa, 1000 kPa, 1100 kPa, and any of the above point values), a column bottom temperature of 150°C to 400°C, and a reflux ratio of 0.1 to 20. The separation conditions of the present invention can achieve a purity of over 99.7 wt% of the hexamethylenediamine product.

[0046] According to the present invention, preferably, step (2) further comprises pre-separating the ammonia reaction product to recover hydrogen and ammonia from the ammonia reaction product before separating the stream containing hexamethyleneimine and the hexamethylenediamine product in the ammonia reaction product; the recovered hydrogen and ammonia are first condensed to obtain circulating ammonia (liquid phase), then compressed to obtain circulating hydrogen (gas phase), and the circulating hydrogen and circulating ammonia are returned to the ammonia reaction; more preferably, the pre-separation method comprises at least one of flash evaporation, distillation, and stripping. Other methods that can recover circulating hydrogen and circulating ammonia from the ammonia reaction product can also be employed as the pre-separation method.

[0047] To ensure the efficient use of hydrogen and ammonia and reduce the overall energy consumption of the process, the preliminary separation conditions are preferably such that the hydrogen recovery rate exceeds 99% and the ammonia recovery rate exceeds 98%. In the present invention, the preliminary separation method may employ multi-stage reduced-pressure flash evaporation, which may include at least two stages of flash evaporation, where the pressure of the flash evaporation gradually decreases with a gradient of 1 MPa to 5 MPa, and the pressure of the final stage of flash evaporation is 0.5 MPaG to 1 MPaG. For example, four-stage flash evaporation may be employed, with flash evaporation pressures of 7 MPaG to 10 MPaG, 4 MPaG to 7 MPaG, 1 MPaG to 4 MPaG, and 0.1 MPaG to 1 MPaG, respectively. Furthermore, a preliminary separation method can be employed that combines flash evaporation and distillation, for example, a combination of at least one stage of flash evaporation (e.g., three-stage flash evaporation) and distillation, i.e., the ammonia reaction product is first subjected to three stages of flash evaporation (the flash evaporation pressures for the first to third stages are 7 MPaG to 10 MPaG, 4 MPaG to 7 MPaG, and 1 MPaG to 3 MPaG, respectively), and the liquid phase after the final stage of reduced-pressure flash evaporation is placed in a distillation column for distillation. The operating conditions of the distillation column include a theoretical stage count of 5 to 30 and a top operating pressure of -0.05 MPaG to 10 MPaG, for example, 0.1 MPaG to 10 MPaG. Since some ammonia and hydrogen are consumed during the ammonia reaction, and small amounts of hydrogen and ammonia are lost during the hydrogen and ammonia recovery process, it is necessary to replenish fresh ammonia and hydrogen during the ammonia reaction to maintain the molar ratio of hexanediol (including freshly replenished hexanediol and hexanediol in the circulating flow), ammonia, and hydrogen in the mixture at the feed port of the ammonia reactor.

[0048] In the present invention, hexamethylenediamine is 1,6-hexamethylenediamine, hexanediol is 1,6-hexanediol, hexamethyleneimine is homopiperidine, aminohexanol is 6-amino-1-hexanol, and the main components of the heavy components are bis(hexamethylene)triamine and amine substances having 12 or more carbon atoms.

[0049] The presence of a solvent in the ammoniaization reaction In one embodiment of the present invention, in a method for preparing hexamethylenediamine, Step (1) includes the step of subjecting hexanediol and ammonia to an ammonia reaction in a solvent under ammonia reaction conditions to obtain an ammonia reaction product; Step (2) includes: separating a stream containing hexamethyleneimine, water, and solvent from the ammonia reaction product to obtain a dehydrated stream containing hexamethyleneimine and solvent by dehydrating the stream containing hexamethyleneimine, water, and solvent to obtain a dehydrated stream containing hexamethyleneimine and solvent, and returning at least a portion of the dehydrated stream containing hexamethyleneimine and solvent to step (1) as a recirculating stream.

[0050] Introducing a solvent into the ammoniaization reaction helps maintain a uniform temperature distribution in the system, reducing reaction hotspots, improving reaction stability, preventing solid phase crystallization and separation throughout the system, lowering the operating temperature of each component within the apparatus, and avoiding the enormous investment required for equipment insulation. Furthermore, introducing a solvent effectively dissolves hexanediol and by-products such as hexamethyleneimine and aminohexanol generated by the ammoniaization reaction, helping to resolve pipeline clogging problems throughout the entire operating cycle, especially in the separation process.

[0051] In the present invention, the solvent is introduced in a single step (together with hexanediol in the initial stage of the reaction). In the initial stage of the reaction (before the circulating flow is returned to the ammoniaization reaction), the molar ratio of solvent to hexanediol is 0.1 to 10:1, preferably 0.15 to 10:1, and more preferably 0.25 to 9:1. However, it is understood that solvent will be lost during the circulation and purification processes. To ensure a sufficient amount of circulating solvent in the system, a small amount of fresh solvent can be replenished during the solvent circulation process to maintain a constant amount of solvent in the system. According to the present invention, the solvent is a solvent whose solubility with the ammoniaization reaction raw materials and reaction products such as hexanediol, hexamethylenediamine, aminohexanol, and hexamethyleneimine is greater than 0.1 g / g, and examples include at least one of tetrahydrofuran, 1,4-dioxane, n-hexane, cyclohexane, tert-butanol, tetramethylenesulfone, and glycerol.

[0052] Preferably, the water content in the dehydrated stream containing hexamethyleneimine and the solvent is less than 3 wt%, preferably less than 1.5 wt%, and more preferably less than 1 wt%.

[0053] Preferably, in step (1), the molar ratio of ammonia to hexanediol is 18 to 55:1, preferably 22 to 43:1; the ammoniation reaction is carried out in the presence of hydrogen, and the molar ratio of hydrogen to hexanediol is 0.08 to 7:1, preferably 0.4 to 4:1.

[0054] Preferably, the temperature of the ammonia reaction is 110°C to 200°C, preferably 120°C to 190°C; the pressure of the ammonia reaction is 7 MPaG to 18 MPaG, preferably 8 MPaG to 14 MPaG; and the liquid volume space velocity of fresh hexanediol is 0.05 h -1 ~8h -1 Preferably 0.08h -1 ~4h -1 That is the case.

[0055] Preferably, the weight ratio of the solvent in the circulating flow to hexamethyleneimine is 1 to 11:1 (for example, a range consisting of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, and any two of the above points). The hexamethyleneimine content in the circulating flow is 5 wt% to 75 wt%, for example, 5 wt% to 50 wt%. Preferably, the weight ratio of the circulating flow to fresh hexanediol is 0.1 to 24:1, preferably 0.4 to 21:1.

[0056] Preferably, the dehydration of a stream containing hexamethyleneimine, water, and a solvent includes at least one of membrane separation dehydration, azeotropic distillation dehydration, extractive distillation dehydration, adsorption dehydration, reverse osmosis dehydration, biological treatment dehydration, and pressure swing distillation dehydration.

[0057] According to a preferred embodiment of the present invention, the step of dehydrating a stream containing hexamethyleneimine, water, and a solvent includes the step of subjecting the stream containing hexamethyleneimine, water, and a solvent to membrane separation and dehydration at a membrane inlet pressure of 1 MPa to 5 MPa and a temperature of 15°C to 200°C.

[0058] According to a preferred embodiment of the present invention, the step of dehydrating a stream containing hexamethyleneimine, water, and solvent includes: feeding the stream containing hexamethyleneimine, water, and solvent into a distillation column to obtain a stream containing solvent and water at the top of the column, and a stream containing hexamethyleneimine at the bottom of the column; feeding the stream containing solvent and water into a high-pressure distillation column to obtain an azeotrope of solvent and water at the top of the column, and a stream of solvent at the bottom of the column; and then feeding the azeotrope of solvent and water into a low-pressure distillation column and returning the stream obtained at the top of the column to the high-pressure distillation column. The operating conditions of the distillation column may include a bottom temperature of 80°C to 150°C, a top temperature of 30°C to 90°C, a reflux ratio of 1 to 20, a top operating pressure of -0.1 MPaG to 2 MPaG, and 10 to 40 stages. The operating conditions for the high-pressure distillation column may include a bottom temperature of 180°C to 280°C, a top temperature of 130°C to 230°C, a reflux ratio of 0.1 to 5, a top operating pressure of 0 MPaG to 4 MPaG, and 10 to 40 stages. The operating conditions for the low-pressure distillation column may include a bottom temperature of 70°C to 150°C, a top temperature of 40°C to 120°C, a reflux ratio of 0.5 to 10, a top operating pressure of -0.1 MPaG to 3 MPaG, and 10 to 30 stages. By using a high-pressure distillation column and a low-pressure distillation column in combination, the present invention can effectively remove water from a flow containing hexamethyleneimine, water, and a solvent.

[0059] Preferably, step (2) further includes the steps of separating a stream containing aminohexanol from the ammonia reaction product and returning the aminohexanol-containing stream to step (1) as a circulating stream together with a dehydrated stream containing hexamethyleneimine and a solvent. The aminohexanol-containing stream may also contain hexanediol, hexamethylenediamine, and small amounts of other components (e.g., heavy components).

[0060] Preferably, the weight ratio of aminohexanol to hexamethyleneimine in the circulating flow is 0.12 to 7:1 (for example, a range consisting of 0.12:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 3:1, 5:1, 7:1, and any two of the above points).

[0061] According to a preferred embodiment of the present invention, a method for separating the ammonia reaction product includes the steps of: subjecting the ammonia reaction product to a first separation to obtain a stream containing hexamethyleneimine, water and a solvent; and then subjecting it to a second separation to obtain a stream containing a hexamethylenediamine product and aminohexanol. Preferably, the first separation is carried out in a first distillation column, the operating conditions of the first distillation column include: a bottom temperature of 130°C to 300°C, a top temperature of 40°C to 70°C, a reflux ratio of 0.1 to 10, a top operating pressure of -0.1 MPaG to 1 MPaG, and a theoretical number of 5 to 40; the second separation is carried out in a second distillation column, the operating conditions of the second distillation column include: a bottom temperature of 130°C to 380°C, a top temperature of 80°C to 190°C, a reflux ratio of 0.1 to 20, a top operating pressure of -0.1 MPaG to 1 MPaG, and a theoretical number of 10 to 100.

[0062] According to a preferred embodiment of the present invention, a method for separating ammonia reaction products includes: subjecting the ammonia reaction products to a first separation to obtain a stream containing hexamethyleneimine, water and solvent; then subjecting them to a second separation to obtain a hexamethylenediamine product; and then subjecting them to a third separation to obtain a stream containing aminohexanol and heavy components. Preferably, the first separation is carried out in a first distillation column, the operating conditions of the first distillation column include: a bottom temperature of 130°C to 300°C, a top temperature of 30°C to 80°C, a reflux ratio of 0.1 to 10, a top operating pressure of -0.1 MPaG to 1 MPaG, and 8 to 45 stages; the second separation is carried out in a second distillation column, the operating conditions of the second distillation column include: a bottom temperature of 130°C to 380°C, a top temperature of 85°C to 1 The conditions include a temperature of 85°C, a reflux ratio of 0.1 to 20, a top operating pressure of -0.1 MPaG to 1 MPaG, and 10 to 100 stages; the third separation is performed in a third distillation column, the operating conditions of which include a bottom temperature of 150°C to 380°C, a top temperature of 130°C to 230°C, a reflux ratio of 0.1 to 15, a top operating pressure of -0.1 MPaG to 1 MPaG, and 10 to 100 stages.

[0063] According to a preferred embodiment of the present invention, a method for separating ammonia reaction products includes the following steps: subjecting the ammonia reaction products to a first separation to obtain a stream containing hexamethyleneimine and the remaining components of the first separation; then subjecting the remaining components of the first separation to a second separation to obtain a hexamethylenediamine product, a stream containing aminohexanol, and the remaining components of the second separation; and then subjecting the remaining components of the second separation to a third separation to obtain a stream of solvent and heavy components. Preferably, the first separation is carried out in a first distillation column, the operating conditions of the first distillation column include: a bottom temperature of 200°C to 280°C, a top temperature of 30°C to 80°C, a reflux ratio of 0.5 to 10, a top operating pressure of -0.1 MPaG to 0.2 MPaG, and 10 to 45 stages; the second separation is carried out in a second distillation column, the operating conditions of the second distillation column include: a bottom temperature of 200°C to 310°C, a top temperature of 70°C to The conditions include a temperature of 180°C, a reflux ratio of 0.5 to 15, a top operating pressure of -0.1 MPaG to 0.4 MPaG, and 20 to 80 stages; the third separation is carried out in a third distillation column, the operating conditions of which include a bottom temperature of 200°C to 380°C, a top temperature of 130°C to 300°C, a reflux ratio of 0.5 to 20, a top operating pressure of -0.1 MPaG to 0.2 MPaG, and 10 to 80 stages.

[0064] Preferably, the method further includes recovering hydrogen and ammonia from the ammonia reaction product before separating the stream containing hexamethyleneimine, water, and solvent in the ammonia reaction product. In the present invention, the method for recovering hydrogen and ammonia from the ammonia reaction product may employ multi-stage reduced-pressure flash evaporation, which may include at least two stages of flash evaporation, where the pressure of the flash evaporation gradually decreases with a gradient of 1 MPa to 5 MPa, and the pressure of the final stage of flash evaporation is 0.1 MPaG to 2 MPaG. For example, if four-stage flash evaporation is employed, the flash evaporation pressures from the first to the fourth stages are 7 MPaG to 10 MPaG, 4 MPaG to 7 MPaG, 2 MPaG to 4 MPaG, and 0.1 MPaG to 2 MPaG, respectively. The method for recovering hydrogen and ammonia from the ammonia reaction product may also employ a combination of flash evaporation and distillation, in which case the ammonia reaction product is subjected to at least one stage of flash evaporation, and the liquid phase after the final stage of flash evaporation is further distilled. When a combination of single-stage flash evaporation and distillation is used, the flash evaporation pressure is 1 MPaG to 3 MPaG; when a combination of multi-stage flash evaporation and distillation is used, the flash evaporation pressure gradually decreases from 0.1 MPaG to 2 MPaG with a gradient of 0.1 MPa to 10 MPa. For example, when a combination of three-stage flash evaporation and distillation is employed, the ammonia reaction product is first subjected to three-stage flash evaporation, with flash evaporation pressures of 7 MPaG to 10 MPaG, 4 MPaG to 7 MPaG, and 1 MPaG to 3 MPaG for the first to third stages, respectively, and the liquid phase after the final stage of reduced-pressure flash evaporation enters a distillation column with 5 to 30 theoretical stages and a top pressure of -0.05 MPaG to 3 MPaG. The ammonia recovery rate at the top of the distillation column is over 98%. More preferably, each stage of flash evaporation is provided with a cooler and a gas-liquid separator, and the flash tanks of each stage are connected in a ring shape to the attached cooler and gas-liquid separator in that order. For example, the gas phase outlet of the first-stage flash tank is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the gas-liquid separator, and the liquid phase outlet of the gas-liquid separator is connected to the inlet of the first-stage flash tank.The gas phase at the top of each stage of flash evaporation enters a connected condenser where it is cooled to 30°C to 60°C. The cooled flow is separated by a built-in gas-liquid separator, and the resulting gas phase is pressurized and recycled back to the ammonia reactor. The resulting liquid phase is returned to the respective stage of flash evaporation. In short, the gas phase obtained from each stage of flash evaporation is cooled to 30°C to 60°C, the cooled flow is subjected to gas-liquid separation, the resulting liquid phase is returned to the flash tank at each stage, and the resulting gas phase is pressurized and recycled back to the ammonia reactor.

[0065] In the present invention, since some ammonia and hydrogen are consumed in the ammoniation reaction, or some ammonia and hydrogen are released as purge gas during recovery, it is understood that it is also necessary to replenish fresh ammonia and hydrogen during the amination reaction in order to maintain the molar ratio of hexanediol (including newly replenished hexanediol and hexanediol in the circulating flow), ammonia, and hydrogen in the mixture at the feed port of the ammoniation reactor.

[0066] Absence of solvent in ammoniation reaction In one embodiment of the present invention, in a method for preparing hexamethylenediamine, Step (1) includes the step of subjecting hexanediol and ammonia to an ammonia reaction under ammonia reaction conditions, in the absence of a solvent, to obtain an ammonia reaction product; Step (2) includes: separating a stream containing hexamethyleneimine and water from the ammonia reaction product to obtain a dehydrated stream containing hexamethyleneimine by dehydrating the stream containing hexamethyleneimine and water, and returning at least a portion of the dehydrated stream containing hexamethyleneimine to step (1) as a recirculating stream; the water content of the dehydrated stream containing hexamethyleneimine is less than 3 wt%, preferably less than 1.5 wt%.

[0067] Preferably, in step (1), the molar ratio of ammonia to hexanediol is 18 to 50:1, more preferably 22 to 38:1, and the molar ratio of hydrogen to hexanediol is 0.08 to 6:1, more preferably 0.4 to 3:1. The molar ratios of ammonia, hydrogen, and hexanediol refer to the molar ratios in the mixture at the inlet of the ammoniation reactor.

[0068] Preferably, the temperature of the ammonia reaction is 120°C to 210°C, more preferably 130°C to 200°C; the pressure of the ammonia reaction is 7 MPaG to 17 MPaG, more preferably 8 MPaG to 15 MPaG; and the liquid volume space velocity of fresh hexanediol is 0.05 h -1 ~7h -1 More preferably 0.09h -1 ~3.9h -1 That is the case.

[0069] Preferably, the weight ratio of the circulating flow to fresh hexanediol is 0.1 to 13:1, more preferably 0.3 to 10:1.

[0070] Preferably, step (2) further includes separating a stream containing aminohexanol from the ammonia reaction product, and returning the aminohexanol-containing stream to step (1) as a circulating stream together with a dehydrated stream containing hexamethyleneimine, wherein the weight ratio of aminohexanol to hexamethyleneimine in the circulating stream is 0.1 to 5:1, for example, 0.12:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 3:1, or 5:1.

[0071] [Examples] The present invention will be described in detail below through examples. In the following examples, The catalyst used was the catalyst from Example 7 of CN114433087A, which was activated with hydrogen at 450°C for 3 hours before use.

[0072] The composition of the product was analyzed by chromatography.

[0073] Yield of hexamethylenediamine = Molar amount of hexamethylenediamine ÷ Molar amount of freshly supplied hexanediol × 100%.

[0074] Example 1 (1) An ammonia reaction was carried out in an ammonia reactor packed with a catalyst, with ammonia, hydrogen, 1,4-dioxane as a solvent, and hexanediol. The molar ratio of ammonia to hexanediol was 28, the molar ratio of hydrogen to hexanediol was 3, the molar ratio of solvent to hexanediol was 4, the reaction temperature was 148°C, the reaction pressure was 12.5 MPaG, and the liquid phase volume space velocity of hexanediol was 0.45 h. -1 That was the case.

[0075] (2) Ammonia and hydrogen in the reaction products were recovered using a combination of flash evaporation and distillation: The ammonia reaction products were sequentially subjected to three stages of vacuum flash evaporation, gradually reducing the flash evaporation pressure from 12 MPaG to 2 MPaG, with the pressures of the first to third stages of flash evaporation set to 8 MPaG, 5 MPaG, and 2 MPaG, respectively. After cooling the gas phase at the top of each of the three vacuum flash tanks to 40°C, they were subjected to gas-liquid separation, and the resulting liquid phases were returned to the respective vacuum flash tanks. The resulting gas phases were pressurized and then returned to the ammonia reactor. The liquid phase at the bottom of the third vacuum flash tank entered a deammonia distillation column, which had a total of 11 theoretical stages and a top operating pressure of 1.1 MPaG. For energy saving purposes, the deammonia distillation column did not have a top condenser, and the liquid phase entered from the top of the deammonia distillation column. The top flow (recirculating ammonia) recovered from the deammonia distillation column was sent back to the inlet of the ammoniation reactor, and the bottom flow was sent to the purification separation unit. Here, the recovery rate of ammonia was 99.99%, and the recovery rate of hydrogen was 99.999%. The recirculating hydrogen and ammonia contained 0.39 wt% hydrogen, 99.47 wt% ammonia, 0.12 wt% solvent, 0.01 wt% water, and 0.01 wt% hexamethyleneimine.

[0076] The liquid phase after distillation was sent to a purification and separation unit, where hexamethylenediamine was cleaved and separated as the key component according to its different boiling points. The bottom flow of the deammonia distillation column was subjected to a first separation to obtain a flow containing hexamethyleneimine, water, and solvent, and then to a second separation to obtain a hexamethylenediamine product (99.78 wt% purity), a flow containing aminohexanol (taken from the side line), and heavy components. Here, the first separation was carried out in the first distillation column, with operating conditions including a bottom temperature of 185°C, a top temperature of 50°C, a reflux ratio of 1.75, a top operating pressure of -0.08 MPaG, and 19 theoretical plates; the second separation was carried out in the second distillation column, with operating conditions including a bottom temperature of 193°C, a top temperature of 132°C, a reflux ratio of 1.2, a top operating pressure of -0.09 MPaG, and 68 theoretical plates.

[0077] A flow containing hexamethyleneimine, water, and solvent was dehydrated by membrane separation to obtain a dehydrated flow containing hexamethyleneimine and solvent. The operating conditions of the membrane separation apparatus included a membrane inlet pressure of 1.8 MPa and a temperature of 38°C. The water content of the dehydrated flow containing hexamethyleneimine and solvent was 0.19 wt%.

[0078] The flow containing aminohexanol was mixed with a dehydrated flow containing hexamethyleneimine and solvent, and then returned to step (1) as a circulating flow with a weight ratio of 4.3 to fresh hexanediol. Here, the circulating flow contained: 18.32 wt% hexamethyleneimine, 16.38 wt% aminohexanol, 3.87 wt% hexanediol, 1.15 wt% hexamethylenediamine, and 56.75 wt% solvent.

[0079] The system was operated continuously until it reached a stable state, and the molar yield of hexamethylenediamine was 88.4% without solvent purification. There were no blockages in the system, and it was able to operate continuously and smoothly for a long period of time.

[0080] Example 2 (1) An ammonia reaction was carried out by introducing ammonia, hydrogen, 1,4-dioxane as a solvent, and hexanediol into an ammonia reactor packed with a catalyst. The molar ratio of ammonia to hexanediol was 29, the molar ratio of hydrogen to hexanediol was 3.3, the molar ratio of solvent to hexanediol was 3.5, the reaction temperature was 158°C, the reaction pressure was 11.7 MPaG, and the liquid phase volume space velocity of hexanediol was 0.55 h. -1 That was the case.

[0081] (2) Ammonia and hydrogen in the reaction products were recovered using a combination of flash evaporation and distillation: The ammonia reaction products were first reduced to 2 MPaG, the gas phase at the top of the flash tank was first cooled to 40°C, then subjected to gas-liquid separation, the resulting liquid phase was returned to the flash tank, the resulting gas phase was pressurized and then returned to the ammonia reactor. The liquid phase at the bottom of the flash tank entered the deammonia distillation column, which had a total of 10 theoretical stages and a top operating pressure of 1 MPaG. For energy saving, the deammonia distillation column did not have a top condenser, and the liquid phase entered from the top of the deammonia distillation column. The top flow (circulating ammonia) of the deammonia distillation column was sent back to the inlet of the ammonia reactor, and the bottom flow was sent to the purification separation unit. Here, the ammonia recovery rate was 99.99%, and the hydrogen recovery rate was 99.999%. The circulating hydrogen and ammonia contained 0.39 wt% hydrogen, 97.66 wt% ammonia, 1.55 wt% solvent, 0.23 wt% water, and 0.16 wt% hexamethyleneimine.

[0082] The bottom flow from the deammonia distillation column was sent to a purification separation unit, where hexamethylenediamine was cleaved and separated according to its different boiling point as the key component. The bottom flow from the deammonia distillation column was subjected to a first separation to obtain a flow containing hexamethyleneimine, water, and solvent; then subjected to a second separation to obtain a hexamethylenediamine product (purity 99.7 wt%); and then subjected to a third separation to obtain a flow containing aminohexanol and heavy components. Here, the first separation was carried out in the first distillation column, with operating conditions including a bottom temperature of 185°C, a top temperature of 51°C, a reflux ratio of 1.8, a top operating pressure of -0.08 MPaG, and 22 theoretical plates; the second separation was carried out in the second distillation column, with operating conditions including a bottom temperature of 192°C, a top temperature of 135°C, a reflux ratio of 3.1, a top operating pressure of -0.09 MPaG, and 25 theoretical plates; and the third separation was carried out in the third distillation column, with operating conditions including a bottom temperature of 215°C, a top temperature of 171°C, a reflux ratio of 2.8, a top operating pressure of -0.09 MPaG, and 59 theoretical plates.

[0083] The dehydration process for the stream containing hexamethyleneimine, water, and solvent was as follows: The stream containing hexamethyleneimine, water, and solvent was sent to a distillation column, where a stream containing solvent and water was obtained at the top of the column, and a stream containing hexamethyleneimine was obtained at the bottom of the column; the stream containing solvent and water was sent to a high-pressure distillation column, where an azeotrope of solvent and water was obtained at the top of the column, and a stream of solvent was obtained at the bottom of the column; the azeotrope of solvent and water was sent to a low-pressure distillation column, the stream obtained at the top of the column was returned to the high-pressure distillation column, and the stream at the bottom of the column (consisting mainly of water) was discharged. The water removal rate of the stream containing hexamethyleneimine, water, and solvent after dehydration was 99.2%, meaning the water content of the stream containing hexamethyleneimine and solvent was 0.1 wt%. Here, the operating conditions for the distillation column included a bottom temperature of 105°C, a top temperature of 55°C, a reflux ratio of 5, a top operating pressure of -0.075 MPaG, and 22 theoretical plates. The operating conditions for the high-pressure distillation column included a bottom temperature of 229°C, a top temperature of 190°C, a reflux ratio of 0.85, a top operating pressure of 1.5 MPaG, and 18 theoretical plates. The operating conditions for the low-pressure distillation column included a bottom temperature of 100°C, a top temperature of 79°C, a reflux ratio of 3, a top operating pressure of 0.05 MPaG, and 16 theoretical plates. In the example, the 1,4-dioxane solvent portion recovered from the bottom of the high-pressure distillation column was purified, and the purified solvent was also returned to the reactor inlet for reuse.

[0084] The flow containing aminohexanol was mixed with the dehydrated flow containing hexamethyleneimine and the solvent flow, and then returned to step (1) as a circulating flow, with the weight ratio of the circulating flow to fresh hexanediol being 5.1. Here, the circulating flow contained: 17.96 wt% hexamethyleneimine, 15.97 wt% aminohexanol, 3.78 wt% hexanediol, 0.05 wt% hexamethylenediamine, and 61.75 wt% solvent.

[0085] The system was operated continuously until it reached a stable state, and the molar yield of hexamethylenediamine was 88.6% with solvent purification. There were no blockages in the system, and it was able to operate continuously and smoothly for a long period of time.

[0086] Example 3 (a) Ammonia, hydrogen, and hexanediol were introduced into a catalyst-filled ammonia reactor to carry out the ammonia reaction, with a molar ratio of ammonia to hexanediol of 29, a molar ratio of hydrogen to hexanediol of 1.4, a reaction temperature of 140°C, a reaction pressure of 12.2 MPaG, and a liquid-phase volume space velocity of hexanediol of 0.5 h. -1 That was the case.

[0087] (b) Ammonia and hydrogen in the reaction product were recovered using a combination of flash evaporation and distillation: The ammonia reaction product was subjected to three stages of vacuum flash evaporation in sequence, gradually decreasing the flash evaporation pressure from 12.2 MPaG to 2 MPaG, with the pressures of the first to third stages of flash evaporation set to 8 MPaG, 5 MPaG, and 2 MPaG, respectively. After cooling the gas phase at the top of each of the three vacuum flash tanks to 40°C, each was subjected to gas-liquid separation, and the resulting liquid phase was returned to the respective vacuum flash tanks. The resulting gas phase was then pressurized and returned to the ammonia reactor. The liquid phase at the bottom of the third vacuum flash tank entered a deammonia distillation column, which had a total of 10 theoretical stages and a top operating pressure of 1 MPaG. For energy conservation, the deammonia distillation column did not have a top condenser, and the liquid phase entered from the top of the deammonia distillation column. The top flow (recirculating ammonia) recovered from the deammonia distillation column was sent back to the inlet of the ammoniation reactor, while the bottom flow was sent to the purification and separation unit. Here, the recovery rate of ammonia was 99.99%, and the recovery rate of hydrogen was 99.999%. The recirculating hydrogen and ammonia contained 0.22 wt% hydrogen, 99.73 wt% ammonia, 0.02 wt% water, and 0.02 wt% hexamethyleneimine.

[0088] The liquid phase after distillation was sent to a purification and separation unit, where hexamethylenediamine was cleaved and separated according to its different boiling point, with hexamethylenediamine as the key component. The bottom flow of the deammonia distillation column was subjected to a first separation to obtain a flow containing hexamethyleneimine and water, and then to a second separation to obtain the hexamethylenediamine product (99.70 wt% purity), a flow containing aminohexanol (taken from the side line), and heavy components. Here, the first separation was carried out in the first distillation column, with operating conditions including a bottom temperature of 182°C, a top temperature of 54°C, a reflux ratio of 1.0, a top operating pressure of 30 kPa, and 25 theoretical plates; the second separation was carried out in the second distillation column, with operating conditions including a bottom temperature of 210°C, a top temperature of 132°C, a reflux ratio of 3.2, a top operating pressure of 20 kPa, and 53 theoretical plates.

[0089] A flow containing hexamethyleneimine and water was dehydrated by membrane separation to obtain a dehydrated flow containing hexamethyleneimine. The operating conditions of the membrane separator included a membrane inlet pressure of 2 MPa and a temperature of 45°C. The water content of the dehydrated flow containing hexamethyleneimine was 0.48 wt%.

[0090] The flow containing aminohexanol was mixed with a dehydrated flow containing hexamethyleneimine and then returned to step (1) as a circulating flow, with the weight ratio of the circulating flow to fresh hexanediol being 1.7. Here, the circulating flow contained: 47.07 wt% hexamethyleneimine, 42.08 wt% aminohexanol, 9.96 wt% hexanediol, and 0.13 wt% hexamethylenediamine.

[0091] The system was operated continuously until it reached a stable state, and the molar yield of hexamethylenediamine was 86.1%. Insulation of the entire system, from the equipment to the pipelines, was required.

[0092] Example 4 (a) Ammonia, hydrogen, and hexanediol are introduced into a catalyst-filled ammonia reactor to carry out the ammonia reaction, with a molar ratio of ammonia to hexanediol of 30 and a molar ratio of hydrogen to hexanediol of 1.1. The ammonia reaction temperature is 150°C, the reaction pressure is 12 MPaG, and the liquid phase volume space velocity of hexanediol is 0.45 h. -1 That was the case.

[0093] (b) Ammonia and hydrogen in the reaction product were recovered using a combination of flash evaporation and distillation: The ammonia reaction product was subjected to three stages of vacuum flash evaporation in sequence, gradually decreasing the flash evaporation pressure from 12 MPaG to 1 MPaG, with the pressures of the first to third stages of flash evaporation set to 9 MPaG, 5 MPaG, and 1 MPaG, respectively. After cooling the gas phase at the top of each of the three vacuum flash tanks to 40°C, each was subjected to gas-liquid separation, and the resulting liquid phase was returned to the respective vacuum flash tanks. The resulting gas phase was then pressurized and returned to the ammonia reactor. The liquid phase at the bottom of the third vacuum flash tank entered a deammonia distillation column, which had a total of 11 theoretical stages and a top operating pressure of 1.4 MPaG. For energy conservation, the deammonia distillation column did not have a top condenser, and the liquid phase entered from the top of the deammonia distillation column. The top flow (recirculating ammonia) recovered from the deammonia distillation column was sent back to the inlet of the ammoniation reactor, while the bottom flow was sent to the purification and separation unit. Here, the recovery rate of ammonia was 99.99%, and the recovery rate of hydrogen was 99.999%. The recirculating hydrogen and ammonia contained 0.40 wt% hydrogen, 99.51 wt% ammonia, 0.04 wt% water, and 0.04 wt% hexamethyleneimine.

[0094] The liquid phase after distillation was sent to a purification and separation unit, where hexamethylenediamine was cleaved and separated according to its different boiling point, with hexamethylenediamine as the key component. The bottom flow of the deammonia distillation column was subjected to a first separation to obtain a flow containing hexamethyleneimine and water, and then to a second separation to obtain the hexamethylenediamine product (99.70 wt% purity), a flow containing aminohexanol (taken from the side line), and heavy components. Here, the first separation was carried out in the first distillation column, with operating conditions including a bottom temperature of 185°C, a top temperature of 56°C, a reflux ratio of 2.0, a top operating pressure of 28 kPa (absolute pressure), and 25 theoretical plates; the second separation was carried out in the second distillation column, with operating conditions including a bottom temperature of 208°C, a top temperature of 135°C, a reflux ratio of 3.5, a top operating pressure of 25 kPa (absolute pressure), and 55 theoretical plates.

[0095] A stream containing hexamethyleneimine and water was dehydrated by azeotropic distillation to obtain a dehydrated stream containing hexamethyleneimine. The operating conditions of the azeotropic distillation column included a weight ratio of azeotropic agent to the stream containing hexamethyleneimine and water of 51:1, a bottom temperature of 161°C, a top temperature of 90°C, a reflux ratio of 1, a top operating pressure of 0.1 MPaG, and 22 theoretical plates. The azeotropic agent was cyclohexane. The water content in the dehydrated stream containing hexamethyleneimine was less than 100 ppm.

[0096] The flow containing aminohexanol was mixed with a dehydrated flow containing hexamethyleneimine and then returned to step (1) as a recirculating flow, with the weight ratio of the recirculating flow to fresh hexanediol being 2.55. Here, the recirculating flow contained: 47.04 wt% hexamethyleneimine, 41.86 wt% aminohexanol, 9.90 wt% hexanediol, and 0.12 wt% hexamethylenediamine.

[0097] The system was operated continuously until it reached a stable state, and the molar yield of hexamethylenediamine was 86.3%. Insulation of the entire system, from the equipment to the pipelines, was required.

[0098] Example 5 (1) An ammonia reaction was carried out in an ammonia reactor packed with a catalyst, with ammonia, hydrogen, 1,4-dioxane as a solvent, and hexanediol. The molar ratio of ammonia to hexanediol was 28, the molar ratio of hydrogen to hexanediol was 3.4, the molar ratio of solvent to hexanediol was 3.2, the reaction temperature was 159°C, the reaction pressure was 11.5 MPaG, and the liquid phase volume space velocity of hexanediol was 0.55 h. -1 That was the case.

[0099] (2) Ammonia and hydrogen in the reaction products were recovered using a combination of flash evaporation and distillation: The ammonia reaction products were first reduced to 2 MPaG, the gas phase at the top of the flash tank was first cooled to 40°C, then subjected to gas-liquid separation, the resulting liquid phase was returned to the flash tank, the resulting gas phase was pressurized, and then returned to the ammonia reactor. The liquid phase at the bottom of the flash tank entered the deammonia distillation column, which had a total of 10 theoretical stages and a top operating pressure of 1 MPaG. For energy saving, the deammonia distillation column did not have a top condenser, and the liquid phase entered from the top of the deammonia distillation column. The top flow (circulating ammonia) of the deammonia distillation column was sent back to the inlet of the ammonia reactor, and the bottom flow was sent to the purification separation unit. Here, the ammonia recovery rate was 99.99%, and the hydrogen recovery rate was 99.999%. The circulating hydrogen and ammonia contained 0.64 wt% hydrogen, 95.2 wt% ammonia, 3.75 wt% solvent, 0.25 wt% water, and 0.16 wt% hexamethyleneimine.

[0100] The bottom flow from the deammonia distillation column was sent to a purification separation unit, where hexamethylenediamine was cleaved and separated according to its different boiling point as the key component. The bottom flow from the deammonia distillation column was subjected to a first separation to obtain a flow containing hexamethyleneimine, water, and solvent; then subjected to a second separation to obtain a hexamethylenediamine product (99.8 wt% purity); and then subjected to a third separation to obtain a flow containing aminohexanol and heavy components. Here, the first separation was carried out in the first distillation column, with operating conditions including a bottom temperature of 182°C, a top temperature of 50°C, a reflux ratio of 1.8, a top operating pressure of -0.08 MPaG, and a theoretical plate count of 22; the second separation was carried out in the second distillation column, with operating conditions including a bottom temperature of 192°C, a top temperature of 133°C, a reflux ratio of 3.0, a top operating pressure of -0.09 MPaG, and a theoretical plate count of 25; and the third separation was carried out in the third distillation column, with operating conditions including a bottom temperature of 215°C, a top temperature of 175°C, a reflux ratio of 4.5, a top operating pressure of -0.09 MPaG, and a theoretical plate count of 59.

[0101] A flow containing hexamethyleneimine, water, and solvent was dehydrated by membrane separation to obtain a dehydrated flow containing hexamethyleneimine and solvent. The operating conditions of the membrane separation apparatus included a membrane inlet pressure of 2.2 MPa and a temperature of 48°C. The water content of the dehydrated flow containing hexamethyleneimine and solvent was 0.39 wt%.

[0102] The flow containing aminohexanol was produced as a byproduct and sent outside the boundary. The dehydrated flow containing hexamethyleneimine and the solvent flow were returned to process (1) as a recirculating flow, with the weight ratio of the recirculating flow to fresh hexanediol being 5.5. Here, the recirculating flow contained: 23.04 wt% hexamethyleneimine, 1.78 wt% hexanediol, 0.08 wt% hexamethylenediamine, and 75.1 wt% solvent.

[0103] The system was operated continuously until it reached a stable state, and the molar yield of hexamethylenediamine was 84.3% with solvent purification. There were no blockages in the system, and it was able to operate continuously and smoothly for a long period of time.

[0104] Preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including various combinations of technical features in any other preferred embodiment. These simple modifications and combinations should also be considered as being disclosed by the present invention and are within the scope of protection of the present invention.

Claims

1. A method for preparing hexamethylenediamine, comprising the following steps: (1) A step of subjecting hexanediol and ammonia to an ammonia reaction under ammonia reaction conditions, optionally in the presence of a solvent, to obtain an ammonia reaction product; (2) A method comprising the steps of: separating a stream containing hexamethyleneimine and water from the ammonia reaction product to obtain a dehydrated stream containing hexamethyleneimine; and returning at least a portion of the dehydrated stream containing hexamethyleneimine to step (1) as a circulating stream, wherein the water content of the dehydrated stream containing hexamethyleneimine is less than 3 wt%, preferably less than 1.5 wt%.

2. The method according to claim 1, wherein the molar ratio of ammonia to hexanediol is 10 to 60:1, preferably 15 to 55:1; and the ammoniation reaction is carried out in the presence of hydrogen, wherein the molar ratio of hydrogen to hexanediol is 0.05 to 8:1, preferably 0.4 to 5:

1.

3. The temperature of the ammonia reaction is 100°C to 220°C, preferably 110°C to 210°C; the pressure of the ammonia reaction is 5 MPaG to 20 MPaG, preferably 6 MPaG to 19 MPaG; and the liquid volume space velocity of fresh hexanediol is 0.05 h. －１ ~10h －１ Preferably 0.07h －１ ~5h －１ The method according to any one of claims 1 to 2.

4. The method according to any one of claims 1 to 3, wherein the weight ratio of the circulating flow returned to step (1) to fresh hexanediol is 0.1 to 30:1, preferably 0.3 to 26:

1.

5. The method according to any one of claims 1 to 4, wherein the dehydration includes at least one of membrane separation dehydration, azeotropic distillation dehydration, extractive distillation dehydration, adsorption dehydration, reverse osmosis dehydration, biological treatment dehydration, and pressure swing distillation dehydration.

6. The step (2) further includes the step of separating a stream containing aminohexanol from the ammonia reaction product and returning the stream containing aminohexanol to the step (1) as a circulating stream together with the dehydrated stream containing hexamethyleneimine; Preferably, the method according to any one of claims 1 to 5, wherein the weight ratio of aminohexanol to hexamethyleneimine in the circulating flow is 0.1 to 8:1, for example, 0.1 to 7:

1.

7. An approach to separate the ammonia reaction product is to subject the ammonia reaction product to a first separation to obtain a stream containing hexamethyleneimine and water, and then to a second separation to obtain a stream containing hexamethylenediamine product and aminohexanol; Preferably, the method according to any one of claims 1 to 6, wherein the first separation and the second separation each independently include at least one of distillation, membrane separation, and pressure swing adsorption.

8. Step (2) is a step of pre-separating the ammonia reaction product to obtain circulating hydrogen and ammonia before separating the stream containing the hexamethyleneimine and the hexamethylenediamine product in the ammonia reaction product, further comprising a step of returning the circulating hydrogen and ammonia to the ammonia reaction; Preferably, the method according to claim 7, wherein the preliminary separation comprises at least one of flash evaporation, distillation, and stripping.

9. Step (1) includes: subjecting hexanediol and ammonia to the ammonia reaction in a solvent under the ammonia reaction conditions to obtain the ammonia reaction product; Step (2) includes: separating a stream containing hexamethyleneimine, water and the solvent from the ammonia reaction product; dehydrating the stream containing hexamethyleneimine, water and the solvent to obtain a dehydrated stream containing hexamethyleneimine and the solvent; and returning at least a portion of the dehydrated stream containing hexamethyleneimine and the solvent to step (1) as a circulating stream; Preferably, the solvent is at least one of tetrahydrofuran, 1,4-dioxane, n-hexane, cyclohexane, tert-butanol, tetramethylenesulfone, and glycerol; Preferably, the weight ratio of the solvent in the circulating flow to hexamethyleneimine is 1 to 11:1, and / or the content of hexamethyleneimine in the circulating flow is 5 wt% to 75 wt%; Preferably, the weight ratio of the circulating flow to fresh hexanediol is 0.1 to 24:1, more preferably 0.4 to 21:1, according to any one of claims 1 to 8.

10. The method according to claim 9, wherein in step (1), the molar ratio of ammonia to hexanediol is 18 to 55:1, preferably 22 to 43:1; and the ammoniation reaction is carried out in the presence of hydrogen, and the molar ratio of hydrogen to hexanediol is 0.08 to 7:1, preferably 0.4 to 4:

1.

11. The temperature of the ammonia reaction is 110°C to 200°C, preferably 120°C to 190°C; the pressure of the ammonia reaction is 7 MPaG to 18 MPaG, preferably 8 MPaG to 14 MPaG; and the liquid volume space velocity of the fresh hexanediol is 0.05 h. －１ ~8h －１ Preferably 0.08h －１ ~4h －１ The method according to any one of claims 9 to 10.

12. The steps for dehydrating the stream containing hexamethyleneimine, water, and the solvent include: feeding the stream containing hexamethyleneimine, water, and the solvent into a distillation column, obtaining a stream containing the solvent and water at the top of the column, and obtaining a stream containing hexamethyleneimine at the bottom of the column; feeding the stream containing the solvent and water into a high-pressure distillation column, obtaining an azeotrope of the solvent and water at the top of the column, and obtaining a stream of the solvent at the bottom of the column; then feeding the azeotrope of the solvent and water into a low-pressure distillation column, and returning the stream obtained at the top of the column to the high-pressure distillation column; or, The method according to any one of claims 9 to 11, wherein the step of dehydrating the stream containing hexamethyleneimine, water and the solvent is: subjecting the stream containing hexamethyleneimine, water and the solvent to membrane separation dehydration at a membrane inlet pressure of 1 MPa to 5 MPa and a temperature of 15°C to 200°C.

13. The method according to any one of claims 9 to 12, wherein step (2) further comprises separating a stream containing aminohexanol from the ammonia reaction product, and returning the stream containing aminohexanol to step (1) as a circulating stream together with the dehydrated stream containing hexamethyleneimine and the solvent, wherein the weight ratio of aminohexanol to hexamethyleneimine in the circulating stream is 0.12 to 7:

1.

14. Step (1) includes: providing hexanediol and ammonia to the ammonia reaction under the ammonia reaction conditions, in the absence of a solvent, to obtain the ammonia reaction product; Preferably, the weight ratio of the circulating flow to fresh hexanediol is 0.1 to 13:1, more preferably 0.3 to 10:1, according to any one of claims 1 to 8.

15. The method according to claim 14, wherein in step (1), the molar ratio of ammonia to hexanediol is 18 to 50:1, preferably 22 to 38:1, and the molar ratio of hydrogen to hexanediol is 0.08 to 6:1, preferably 0.4 to 3:

1.

16. The temperature of the ammoniation reaction is 120°C to 210°C, preferably 130°C to 200°C; the pressure of the ammoniation reaction is 7 MPaG to 17 MPaG, preferably 8 MPaG to 15 MPaG, and the liquid hourly space velocity of the fresh hexanediol is 0.05 h －１ to 7 h －１ preferably 0.09 h －１ to 3.9 h －１ The method according to claim 14 or 15, wherein the method is as described above

17. The method according to any one of claims 14 to 16, wherein step (2) further comprises separating a stream containing aminohexanol from the ammonia reaction product, and returning the stream containing aminohexanol to step (1) as a circulating stream together with a dehydrated stream containing hexamethyleneimine, wherein the weight ratio of aminohexanol to hexamethyleneimine in the circulating stream is 0.1 to 5:1.

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