A method for preparing 6-aminocapronitrile

Abstract

The present invention provides a method for preparing 6-aminocapronitrile, with nylon 6 extract as raw material, comprising the following steps: S1: nylon 6 extract is subjected to triple-effect evaporation concentration treatment to improve the oligomer concentration in the extract; S2: nylon 6 concentrated extract and ammonia are preheated respectively; S3: nylon 6 concentrated extract steam and hot ammonia are fully mixed according to a certain mass ratio; S4: a mixture of polyamide oligomer steam and hot ammonia obtained by S3 is subjected to ammonia dehydration reaction under the action of a catalyst to obtain an ammonia reactant; S5: the ammonia reactant obtained by S4 is separated and purified to obtain the target product 6-aminocapronitrile. The preparation method of the present invention can effectively reduce production costs, the reactant conversion rate can reach more than 97%, and the purity of the obtained 6-aminocapronitrile is more than 99.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of aminocapronitrile, and in particular relates to a method for preparing 6-aminocapronitrile from nylon 6 extract. Background Art

[0002] 6-Aminocapronitrile is an important chemical intermediate. It can be hydrogenated to produce 1,6-hexanediamine. Most of 1,6-hexanediamine can be used to synthesize nylon 66 and nylon 610 resins. It can also be used to synthesize polyurethane resins, ion exchange resins and hexamethylene diisocyanate, as well as used as a curing agent for urea-formaldehyde resins, epoxy resins, etc., an organic cross-linking agent, etc. It is also used as a stabilizer and bleaching agent in the textile and papermaking industries, a corrosion inhibitor for aluminum alloys, and an emulsifier for chloroprene rubber.

[0003] At present, 6-aminocapronitrile is mainly prepared by partial hydrogenation of 1,6-adiponitrile, such as patents CN1238334C and CN101309897A. There are relatively few methods of preparing 6-aminocapronitrile using caprolactam as a raw material. For example, CN107602416A introduces a method for preparing 6-aminocapronitrile by a gas phase method, which uses caprolactam as a raw material. The ratio of ammonia to caprolactam added during the reaction is too high, resulting in high production costs, which is not conducive to industrial production.

[0004] The extract produced in the nylon 6 chip production process contains low concentrations of polyamide monomers and oligomers, and the oligomers are generally caprolactam dimers or trimers. On the one hand, if the extract is directly discharged as wastewater, its COD content exceeds the discharge standard, which will cause great environmental pollution and violate the sewage discharge standard; on the other hand, even if the organic matter content in the wastewater is reduced through sewage treatment, it is a waste of monomers and oligomers in the extract water, and it will also increase the cost of wastewater treatment. At present, the treatment of the extract is to first evaporate and concentrate the extract to increase the concentration to ≥95%, hydrolyze it in a preheater to generate caprolactam monomer, and directly add it to the caprolactam front section for reaction. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing 6-aminocapronitrile, which uses the extract produced in the production process of nylon 6 as raw material, can effectively reduce the cost of raw materials, and provide a reliable processing method for industrial production.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for preparing 6-aminocapronitrile by a gas phase method, using nylon 6-extract as a raw material, comprising the following steps:

[0008] S1: The nylon 6 extract is subjected to a triple-effect evaporation concentration treatment to increase the concentration of oligomers in the extract;

[0009] S2: preheating the nylon 6 concentrated extract and ammonia respectively, so that the concentrated extract is hydrolyzed into caprolactam monomer;

[0010] S3: fully mixing the nylon 6 concentrated extract vapor and the hot ammonia gas in a certain mass ratio;

[0011] S4: subjecting the mixture of the polyamide monomer vapor and the hot ammonia obtained in S3 to an amination-dehydration reaction under the action of a catalyst to obtain an amination reactant;

[0012] S5: Separate and purify the amination reaction product obtained in S4 to obtain the target product 6-aminocapronitrile.

[0013] Furthermore, in the step S1, in the triple-effect evaporation concentration, the triple-effect temperature is 120-130°C, the pressure is 0.1-0.15MPa, the second-effect temperature is 110-120°C, the pressure is 0.03-0.08MPa, and the first-effect temperature is 102-110°C, the pressure is ≤-20kPa.

[0014] Furthermore, in the step S1, the oligomer concentration is increased to ≥95% by triple-effect evaporation concentration treatment. Excessive water content will aggravate the reversible process during the aminocapronitrile reaction, which is not conducive to the forward reaction.

[0015] Furthermore, in step S2, the concentrated extract is preheated at a temperature of 265-370°C, and the ammonia gas is preheated at a temperature of 260-360°C.

[0016] Furthermore, in step S3, the concentrated extract vapor and the hot ammonia gas are fully mixed in a mass ratio of 1:1-7.

[0017] Furthermore, in step S3, the concentrated extract vapor temperature is 265-370°C and the pressure is 3-15 MPa, the oligomers are hydrolyzed to generate caprolactam monomers at this temperature and pressure, and the hot ammonia temperature is 260-360°C.

[0018] Furthermore, in step S4, the reaction temperature of the ammoniation dehydration is 320-410°C, and the space velocity of the steam mixture passing through the catalyst is 3000-8500h -1 .

[0019] Furthermore, in step S4, the amination and dehydration reaction is carried out in a fixed bed.

[0020] Furthermore, in step S4, the catalyst is a microsphere catalyst, with silicon-phosphorus-aluminum molecular sieve as the main component and one or more of transition metal oxides and alkaline earth metal oxides as active ingredients.

[0021] Furthermore, the silicon-phosphorus-aluminum molecular sieve is one or a mixture of two or more of SAPO-5, SAPO-11, and SAPO-34 molecular sieves.

[0022] Furthermore, the transition metal oxide precursor is one or a mixture of two or more of the nitrates of iron, copper, zinc, nickel, manganese, cerium, and zirconium; the alkaline earth metal oxide precursor is one or a mixture of two or more of the nitrates of magnesium, calcium, and strontium.

[0023] Furthermore, in the catalyst, the ratio of metal oxide to molecular sieve is 0.1-3%.

[0024] Furthermore, in step S5, the method for separating the amination reactants is flash separation and distillation separation.

[0025] Furthermore, the distillation separation is a vacuum distillation purification, and the operating conditions are: the vacuum distillation bottom temperature is 150-160°C, the vacuum degree is 2-8mmHg, when the tower top temperature is 20-20°C, ammonia and water are evaporated, and when the tower top temperature is 120-140°C, 6-aminocapronitrile is evaporated. The operating conditions of the vacuum distillation here are typical laboratory distillation conditions, and the glass distillation tower used in the laboratory is 800mm high, 20mm inner diameter, and the filler is a Φ ring with a diameter of 3mm. The specific pilot scale-up process can be adjusted according to the specific situation.

[0026] The beneficial effects of the present invention are:

[0027] 1. Using nylon 6 extract as raw material, effectively utilize the polyamide oligomers therein to achieve resource utilization and reduce production costs.

[0028] 2. The concentrated extract steam and hot ammonia are added in a mass ratio of 1:1-7. The utilization rate of ammonia is high, which can further reduce production costs.

[0029] 3. The microsphere catalyst used has good wear resistance and high temperature hydrothermal resistance, which can ensure that the catalyst maintains the integrity of the structure during use. The catalyst size distribution is narrow, which is conducive to uniform reaction and has good catalytic performance. The conversion rate of the reactants can reach more than 97%, and the purity of the obtained 6-aminocapronitrile can reach more than 99.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0031] Figure 1 It is a schematic diagram of the process of the present invention:

[0032] Among them, 1. nylon 6 extract storage tank, 2. first-effect evaporator, 3. second-effect evaporator, 4. triple-effect evaporator, 5. concentrated extract storage tank, 6. concentrated extract preheater, 7. liquid ammonia tank, 8. ammonia preheater, 9. mixer, 10. amination reactor, 11. cooler, 12. gas-liquid separator, 13. ammonia absorption tank, 14. distillation tower, 15. 6-aminocapronitrile product tank. DETAILED DESCRIPTION

[0033] Embodiment 1:

[0034] The nylon 6 extract containing caprolactam monomer, dimer and trimer is pumped from the nylon 6 extract storage tank 1 into the first-effect evaporator 2, the temperature of the first-effect evaporator is 105°C, and the pressure is -0.02MPa. The extract is concentrated to 18% in the first-effect evaporator, and then pumped into the second-effect evaporator, the temperature of the second-effect evaporator is 112°C, and the pressure is 0.04MPa. The extract is further concentrated to 60% in the second-effect evaporator, and then pumped into the third-effect evaporator, the temperature of the third-effect evaporator is 125°C, and the pressure is 0.1MPa. The extract is further concentrated to 95% in the third-effect evaporator, and then pumped into the concentrated extract storage tank 5. The concentrated extract is heated to 280°C in the concentrated extract preheater 6. Ammonia is pumped from the liquid ammonia tank 7 into the ammonia preheater 8 and heated to 280°C. 0°C, the concentrated extract vapor and ammonia are fully mixed in the mixer 9, and transported to the ammoniation reactor 10 through a pipeline, and the ammoniation dehydration reaction is carried out at 360°C. The catalyst is SAPO-34 molecular sieve, manganese and cerium are active components, the proportion of active components to molecular sieve is 0.4%, and the contact time with the catalyst is 0.01s. The ammoniation reactants are cooled in the cooler 11 and separated in the gas-liquid separator 12. Ammonia and water enter the water ammonia storage tank 13, and the other part enters the distillation tower 14. The bottom temperature of the distillation tower is 155°C, the vacuum degree is 5mmHg, and the top temperature is 25°C. Ammonia and water are evaporated and transported to the ammonia absorption tower 13. When the top temperature is 135°C, 6-aminocapronitrile is evaporated and transported to the 6-aminocapronitrile product tank 15 through a pipeline. The reaction conversion rate is 80%, the selectivity is 98%, and the purity of 6-aminocapronitrile is 99.55%.

[0035] Embodiment 2:

[0036] The nylon 6 extract containing caprolactam monomer, dimer and trimer is pumped from the nylon 6 extract storage tank 1 into the first-effect evaporator 2, the temperature of the first-effect evaporator is 108°C, and the pressure is -0.02MPa. The extract is concentrated to 25% in the first-effect evaporator, and then pumped into the second-effect evaporator, the temperature of the second-effect evaporator is 114°C, and the pressure is 0.05MPa. The extract is further concentrated to 70% in the second-effect evaporator, and then pumped into the third-effect evaporator, the temperature of the third-effect evaporator is 127°C, and the pressure is 0.12MPa. The extract is further concentrated to 95% in the third-effect evaporator, and then pumped into the concentrated extract storage tank 5. The concentrated extract is heated to 320°C in the concentrated extract preheater 6. Ammonia is pumped from the liquid ammonia tank 7 into the ammonia preheater 8 and heated to 2 90°C, the concentrated extract vapor and ammonia are fully mixed in the mixer 9, and transported to the ammoniation reactor 10 through a pipeline, and the ammoniation dehydration reaction is carried out at 370°C. The catalyst is SAPO-11 molecular sieve, iron and magnesium are active components, the active components account for 1% of the molecular sieve, and the contact time with the catalyst is 0.03s. The ammoniation reactants are cooled in the cooler 11 and separated in the gas-liquid separator 12. Ammonia and water enter the water ammonia storage tank 13, and the other part enters the distillation tower 14. The bottom temperature of the distillation tower is 156°C, the vacuum degree is 5.5mmHg, and the top temperature is 26°C. Ammonia and water are evaporated and transported to the ammonia absorption tower 13. When the top temperature is 134°C, 6-aminocapronitrile is evaporated and transported to the 6-aminocapronitrile product tank 15 through a pipeline. The reaction conversion rate is 90%, the selectivity is 98.1%, and the purity of 6-aminocapronitrile is 99.6%.

[0037] Embodiment 3:

[0038] The nylon 6 extract containing caprolactam monomer, dimer and trimer is pumped from the nylon 6 extract storage tank 1 into the first-effect evaporator 2, the temperature of the first-effect evaporator is 109°C, and the pressure is -0.03MPa. The extract is concentrated to 25% in the first-effect evaporator, and then pumped into the second-effect evaporator, the temperature of the second-effect evaporator is 115°C, and the pressure is 0.06MPa. The extract is further concentrated to 50% in the second-effect evaporator, and then pumped into the third-effect evaporator, the temperature of the third-effect evaporator is 127°C, and the pressure is 0.12MPa. The extract is further concentrated to 85% in the third-effect evaporator, and then pumped into the concentrated extract storage tank 5. The concentrated extract is heated to 320°C in the concentrated extract preheater 6. Ammonia is pumped from the liquid ammonia tank 7 into the ammonia preheater 8 and heated to 290°C. The concentrated extract vapor and ammonia are fully mixed in the mixer 9 and transported to the ammoniation reactor 10 through a pipeline. The ammoniation dehydration reaction is carried out at 380°C. The catalyst is SAPO-11 molecular sieve, and manganese, cerium and zirconium are active components. The proportion of active components to molecular sieve is 0.6%. The contact time with the catalyst is 0.02s. The ammoniation reactants are cooled in the cooler 11 and separated in the gas-liquid separator 12. Ammonia and water enter the water ammonia storage tank 13, and the other part enters the distillation tower 14. The bottom temperature of the distillation tower is 156°C, the vacuum degree is 5.5 mmHg, and the top temperature is 26°C. Ammonia and water are evaporated and transported to the ammonia absorption tower 13. When the top temperature is 134°C, 6-aminocapronitrile is evaporated and transported to the 6-aminocapronitrile product tank 15 through a pipeline. The reaction conversion rate is 95%, the selectivity is 98.2%, and the purity of 6-aminocapronitrile is 99.65%.

[0039] Embodiment 4:

[0040] The nylon 6 extract containing caprolactam monomer, dimer and trimer is pumped from the nylon 6 extract storage tank 1 into the first-effect evaporator 2, the temperature of the first-effect evaporator is 108°C, and the pressure is -0.02MPa. The extract is concentrated to 25% in the first-effect evaporator, and then pumped into the second-effect evaporator, the temperature of the second-effect evaporator is 114°C, and the pressure is 0.05MPa. The extract is further concentrated to 65% in the second-effect evaporator, and then pumped into the third-effect evaporator, the temperature of the third-effect evaporator is 130°C, and the pressure is 0.14MPa. The extract is further concentrated to 95% in the third-effect evaporator, and then pumped into the concentrated extract storage tank 5. The concentrated extract is heated to 330°C in the concentrated extract preheater 6. Ammonia is pumped from the liquid ammonia tank 7 into the ammonia preheater 8, and the temperature is heated to 310°C. The extract vapor and ammonia are fully mixed in the mixer 9 and transported to the ammoniation reactor 10 through a pipeline, and the ammoniation dehydration reaction is carried out at 390°C. The catalyst is a mixture of SAPO-5 and SAPO-11 molecular sieves, copper and calcium are active components, the proportion of active components to molecular sieves is 2%, and the contact time with the catalyst is 0.04s. The ammoniation reactants are cooled in the cooler 11 and separated in the gas-liquid separator 12. Ammonia and water enter the water ammonia storage tank 13, and the other part enters the distillation tower 14. The bottom temperature of the distillation tower is 156°C, the vacuum degree is 5.5mmHg, and the top temperature is 26°C. Ammonia and water are evaporated and transported to the ammonia absorption tower 13. When the top temperature is 134°C, 6-aminocapronitrile is evaporated and transported to the 6-aminocapronitrile product tank 15 through a pipeline. The reaction conversion rate is 98%, the selectivity is 98.3%, and the purity of 6-aminocapronitrile is 99.75%.

[0041] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing 6-aminocapronitrile, characterized in that, The method uses nylon 6 extract as raw material and comprises the following steps: S1: The nylon 6 extract is subjected to triple-effect evaporation concentration treatment; in the triple-effect evaporation concentration, the third-effect temperature is 120-130℃, the pressure is 0.1-0.15MPa, the second-effect temperature is 110-120℃, the pressure is 0.03-0.08MPa, the first-effect temperature is 102-110℃, and the pressure is ≤-20kPa; through the triple-effect evaporation concentration treatment, the oligomer concentration increases to more than 95% S2: preheating the nylon 6 concentrated extract and ammonia respectively, and heating the concentrated extract to 280°C-330°C; S3: fully mixing the nylon 6 concentrated extract vapor and the hot ammonia gas in a certain mass ratio; S4: subjecting the mixture of the polyamide oligomer vapor obtained in S3 and the hot ammonia gas to an amination-dehydration reaction under the action of a catalyst to obtain an amination reactant; S5: Separate and purify the amination reaction product obtained in S4 to obtain the target product 6-aminocapronitrile.

2. A method for preparing 6-aminocapronitrile as claimed in claim 1, characterized in that, In the step S3, the concentrated extract vapor and the hot ammonia gas are fully mixed in a mass ratio of 1:1-7.

3. A method for preparing 6-aminocapronitrile as claimed in claim 1, characterized in that, In step S3, the concentrated extract vapor temperature is 265-370°C, the pressure is 3-15 MPa, and the hot ammonia temperature is 260-360°C.

4. A method for preparing 6-aminocapronitrile as claimed in claim 1, characterized in that, In step S4, the reaction temperature of the ammoniation dehydration is 320-410°C, and the space velocity of the steam mixture passing through the catalyst is 3000-8500h -1 .

5. A method for preparing 6-aminocapronitrile as claimed in claim 1, characterized in that, In the step S4, the amination and dehydration reaction is carried out in a fixed bed.

6. A method for preparing 6-aminocapronitrile as claimed in claim 1, characterized in that, In step S4, the catalyst is a microsphere catalyst, with silicon-phosphorus-aluminum molecular sieve as the main component and one or more of transition metal oxides and alkaline earth metal oxides as active components.

7. A method for preparing 6-aminocapronitrile as claimed in claim 6, characterized in that, In the step S4, the proportion of active ingredients to molecular sieve is 0.1-3%.

8. A method for preparing 6-aminocapronitrile as claimed in claim 6, characterized in that, The silicon-phosphorus-aluminum molecular sieve is one or a mixture of two or more of SAPO-5, SAPO-11, and SAPO-34 molecular sieves.

9. A method for preparing 6-aminocapronitrile as claimed in claim 6, characterized in that, The precursor of the transition metal oxide is one or a mixture of two or more of the nitrates of iron, copper, zinc, nickel, manganese, cerium and zirconium; the precursor of the alkaline earth metal oxide is one or a mixture of two or more of the nitrates of magnesium, calcium and strontium.

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