An apparatus and method for preparing 6-aminocapronitrile using crude caprolactam as a raw material

Abstract

The present invention discloses an apparatus and method for preparing 6 - aminocapronitrile from crude caprolactam. After the crude caprolactam is dehydrated by a dehydration evaporator, it enters a caprolactam evaporator for evaporation. The caprolactam vapor is pressurized by an ammonia injector and introduced into a reaction feed mixer to be mixed with ammonia gas. After mixing, the reaction materials enter an ammoniation and dehydration reaction to prepare 6 - aminocapronitrile. The present invention realizes the preparation of 6 - aminocapronitrile from crude caprolactam through vacuum evaporation dehydration, vacuum evaporation of caprolactam, and ammonia injector pressurization technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic chemical industry, and relates to an apparatus and a method for preparing 6 - aminohexanenitrile from crude caprolactam as a raw material. Background Art

[0002] 6 - Aminohexanenitrile is an important chemical intermediate. It can be used to produce 1,6 - diaminohexane through complete hydrogenation, and 1,6 - diaminohexane can be used to produce the polymer nylon 66. Currently, 6 - aminohexanenitrile is mainly prepared by partial hydrogenation of 1,6 - dicyanohexane, such as in patents CN1238334 C and CN101309897 B, or by hydroformylation of pentenenitrile, such as in patent CN1100752C.

[0003] 6 - Aminohexanenitrile can be prepared from caprolactam through ammoniation and dehydration reaction. CN 107602416A discloses a gas - phase method for preparing 6 - aminohexanenitrile. This method uses caprolactam as a raw material and includes the following steps: mixing caprolactam vapor and hot ammonia gas in a certain mass ratio; performing an ammoniation and dehydration reaction on the mixture of caprolactam vapor and hot ammonia gas under catalyst conditions to obtain an ammoniated effluent; separating and purifying the obtained ammoniated effluent to obtain pure 6 - aminohexanenitrile.

[0004] However, as a polyamide monomer, caprolactam has a long production process flow and high costs. The industrial production of 6 - aminohexanenitrile using high - purity caprolactam as a raw material has relatively high costs.

[0005] Selecting relatively low - cost crude caprolactam, such as the crude caprolactam extraction liquid generated during the production of polyamide 6 from caprolactam, the heavy residue during caprolactam production, etc., as the raw material for preparing 6 - aminohexanenitrile can reduce the production cost of 6 - aminohexanenitrile, improve the product quality of polyamide 6, and reduce the production energy consumption of the source caprolactam device, having good industrial application prospects. Summary of the Invention

[0006] The present invention provides an apparatus and a method for preparing 6 - aminohexanenitrile from crude caprolactam as a raw material. Preparing 6 - aminohexanenitrile from crude caprolactam can reduce the production cost of 6 - aminohexanenitrile and the production energy consumption of the source caprolactam device.

[0007] The technical solution adopted by the present invention is:

[0008] An apparatus for preparing 6 - aminohexanenitrile from crude caprolactam mainly consists of a dehydration evaporator, a caprolactam evaporator, an ammonia gas ejector, a reaction feed mixer, and an ammoniation dehydration reactor. The crude caprolactam feed pipeline is connected to the inlet of the dehydration evaporator. The dehydration evaporator is provided with a gas phase outlet and a liquid phase outlet. The liquid phase outlet of the dehydration evaporator is connected to the caprolactam evaporator. The gas phase outlet of the caprolactam evaporator is connected to the inlet of the ammonia gas ejector. The outlet of the ammonia gas ejector is connected to the inlet of the reaction feed mixer. The outlet of the reaction feed mixer is connected to the ammoniation dehydration reactor.

[0009] A crude caprolactam storage tank can be arranged in front of the dehydration evaporator, and an alkali solution inlet is provided on the crude caprolactam feed pipe.

[0010] The alkali solution is one or more of NaOH, KOH, Ca(OH)₂, and Ba(OH)₂.

[0011] The gas phase outlet of the dehydration evaporator is connected to the dehydration evaporator condenser, and the condensate outlet of the dehydration evaporator is connected to the caprolactam evaporation and concentration device, and the condensate can return to the previous caprolactam evaporation and concentration device.

[0012] The caprolactam evaporator is provided with a liquid phase discharge outlet to discharge heavy components.

[0013] Both the dehydration evaporator and the caprolactam evaporator are connected to a vacuum system.

[0014] The technical scheme for preparing 6 - aminohexanenitrile by using the above - mentioned apparatus in the present invention is as follows:

[0015] A method for preparing 6 - aminohexanenitrile from crude caprolactam. After the crude caprolactam is dehydrated by the dehydration evaporator, it enters the caprolactam evaporator for evaporation. The caprolactam vapor is pressurized by the ammonia gas ejector and introduced into the reaction feed mixer to be mixed with ammonia gas. After mixing, the reaction materials enter the ammoniation dehydration reaction to prepare 6 - aminohexanenitrile.

[0016] The crude caprolactam is an aqueous caprolactam solution with a caprolactam mass content of more than 90%, which can be the caprolactam extraction liquid recovered from the polyamide device, or the residue from the distillation of the caprolactam production device, or other sources of crude caprolactam.

[0017] An alkali solution can be added to the crude caprolactam before entering the dehydration evaporation, and the addition amount of the alkali solution is 0.2% - 5.0% of the mass of the crude caprolactam.

[0018] Operating conditions of the dehydration evaporator: temperature 110 - 130 °C, absolute pressure 300 - 900 Pa.

[0019] Operating conditions of the caprolactam evaporator: temperature 130 - 150 °C, absolute pressure 900 - 3500 Pa.

[0020] Caprolactam vapor is pressurized to 0.1 - 0.5 MPa by an ammonia gas ejector, and is mixed with hot ammonia gas at 250 - 350 °C in a reaction feed mixer in a mass ratio of 1:2 - 1:10, then enters a fixed-bed reactor filled with a catalyst. The reaction temperature is controlled at 300 - 400 °C, the reaction pressure is 0.1 - 0.5 MPa, and the contact time between the mixture of caprolactam vapor and hot ammonia gas and the catalyst is 0.1 - 1 s.

[0021] The ammoniation and dehydration reaction materials enter a primary separation and rectification column. The top of the column is ammonia vapor containing water, and the bottom is ε-caprolactam, which is returned to the caprolactam evaporator; the middle part of the primary separation and rectification column is mainly a 6-aminocapronitrile stream that enters a secondary separation and rectification column. In the secondary separation and rectification column, light by-products are taken from the top, and 6-aminocapronitrile with a purity of over 99.6% is at the bottom; in the tertiary separation and rectification column, ammonia gas is returned from the top to the hot ammonia gas heater for heating and then returned to the ammoniation and dehydration reaction system. Water is taken from the middle of the column, and light by-products are at the bottom. The light by-products from the tertiary separation and rectification column can be separated together with the light by-products from the secondary separation and rectification column to obtain HN(5-hexenenitrile). After adding alkali to the water taken from the middle of the column to extract ammonia, it is neutralized and discharged to the wastewater treatment device.

[0022] Features and effects of the present invention:

[0023] 1. The present invention realizes the preparation of 6-aminocapronitrile from crude caprolactam through vacuum evaporation dehydration, vacuum evaporation of caprolactam, and ammonia gas ejector pressurization technology. The overall effective utilization rate of caprolactam is high, and the molar yield of 6-aminocapronitrile relative to caprolactam reaches 92%.

[0024] 2. The vacuum dehydration and vacuum evaporation of caprolactam in the present invention reduce the temperature of caprolactam during the dehydration and evaporation processes, preventing coking of the evaporator.

[0025] 3. The present invention uses an ammonia gas ejector to pressurize, increasing the pressure of the ammoniation and dehydration reaction. Brief Description of the Drawings

[0026] Figure 1 is a schematic diagram of an apparatus for preparing 6-aminocapronitrile from crude caprolactam according to the present invention

[0027] In the figure: 1 - crude caprolactam tank; 2 - dehydration evaporator; 3 - caprolactam transfer pump; 4 - caprolactam evaporator; 5 - dehydration evaporator condenser; 6 - caprolactam evaporator condenser; 7 - vacuum system; 8 - caprolactam separator; 9 - ammonia gas ejector pump; 10 - reaction feed mixer; 11 - ammonolysis reactor.

[0028] A - crude caprolactam; B - alkali solution; C - caprolactam containing water; D - dehydrated caprolactam; E - heavy components; F - caprolactam vapor; G - ammonia gas; H - mixed gas; I - ammoniation and dehydration reaction product. Embodiments

[0029] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0030] From Figure 1 It can be seen that the device of the present invention for preparing 6 - aminocapronitrile from crude caprolactam mainly consists of a dehydration evaporator, a caprolactam evaporator, an ammonia gas injector, a reaction feed mixer, and an ammoniation dehydration reactor. The crude caprolactam feed pipeline is connected to the inlet of the dehydration evaporator. The dehydration evaporator is provided with a gas phase outlet and a liquid phase outlet. The liquid phase outlet of the dehydration evaporator is connected to the caprolactam evaporator. The gas phase outlet of the caprolactam evaporator is connected to the inlet of the ammonia gas injector. The outlet of the ammonia gas injector is connected to the inlet of the reaction feed mixer. The outlet of the reaction feed mixer is connected to the ammoniation dehydration reactor. Examples

[0031] Crude caprolactam with a caprolactam mass content of 93% is added with sodium hydroxide in a mass ratio of 1.5%, and after mixing, it enters the dehydration evaporator, controlling the temperature at 120 - 130 °C and the absolute pressure at 300 - 900 Pa; the liquid phase enters the caprolactam evaporator for evaporation, controlling the temperature at 130 - 150 °C and the absolute pressure at 900 - 3500 Pa; the evaporated caprolactam vapor is pressurized to 0.1 - 0.5 MPa by the ammonia gas injector and introduced into the reaction feed mixer to be mixed with hot ammonia gas at 250 - 350 °C in a mass ratio of 1:2 - 1:10. After mixing, the reaction materials enter the ammoniation dehydration reaction to prepare 6 - aminocapronitrile.

[0032] The ammoniation dehydration reactor is a fixed - bed reactor filled with a catalyst, controlling the reaction temperature at 300 - 400 °C, the reaction pressure at 0.1 - 0.5 MPa, and the contact time between the mixture of caprolactam vapor and hot ammonia gas and the catalyst at 0.1 - 1 s.

[0033] The ammoniation dehydration reaction materials enter the first - stage separation rectification column. The top of the column is ammonia - containing steam with water, and the bottom is ε - caprolactam, which returns to the caprolactam evaporator; the middle part of the first - stage separation rectification column is mainly a 6 - aminocapronitrile stream that enters the second - stage separation rectification column. In the second - stage separation rectification column, light by - products are taken at the top, and the bottom is 6 - aminocapronitrile with a purity of over 99.8%; in the third - stage separation rectification column, ammonia gas at the top returns to the hot ammonia gas heater for heating and then returns to the ammoniation dehydration reaction system. Water is taken from the middle of the column, and the bottom is light by - products, which can be separated together with the light by - products of the second - stage separation rectification column to obtain HN(5 - hexenenitrile). After adding alkali to the water taken from the middle of the column to extract ammonia, it is neutralized and discharged to the wastewater treatment device.

[0034] Throughout the whole process, the molar yield of 6 - aminocapronitrile relative to caprolactam reaches 95.3%. Examples

[0035] Add sodium hydroxide to the extract of the caprolactam mass content 90% polyamide plant at a mass ratio of 2.5%. After mixing, it enters the dehydration evaporator, and the temperature is controlled at 120 - 130 °C, and the absolute pressure is 300 - 900 Pa; the liquid phase enters the caprolactam evaporator for evaporation, and the temperature is controlled at 130 - 150 °C, and the absolute pressure is 900 - 3500 Pa; after evaporation, the caprolactam vapor is pressurized to 0.1 - 0.5 MPa by an ammonia injector, and is introduced into the reaction feed mixer to be mixed with hot ammonia gas at 250 - 350 °C at a mass ratio of 1:2 - 1:10. After mixing, the reaction material enters the ammoniation dehydration reaction to prepare 6 - aminocapronitrile.

[0036] The ammoniation dehydration reactor is a fixed - bed reactor equipped with a catalyst. The reaction temperature is controlled at 300 - 400 °C, the reaction pressure is 0.1 - 0.5 MPa, and the contact time of the mixture of caprolactam vapor and hot ammonia gas with the catalyst is 0.1 - 1 s.

[0037] The ammoniation dehydration reaction material enters the first - stage separation rectification column. The top of the column is ammonia - containing water vapor, and the bottom of the column is ε - caprolactam, which returns to the caprolactam evaporator; the middle part of the first - stage separation rectification column is mainly the 6 - aminocapronitrile stream, which enters the second - stage separation rectification column. In the second - stage separation rectification column, light by - products are taken from the top, and the bottom is 6 - aminocapronitrile with a purity of more than 99.8%; in the third - stage separation rectification column, ammonia gas at the top returns to the hot ammonia gas heater for heating and then returns to the ammoniation dehydration reaction system. Water is taken from the middle of the column, and the bottom is light by - products, which can be separated together with the light by - products of the second - stage separation rectification column to obtain HN(5 - hexenenitrile). After adding alkali to the water taken from the middle of the column to extract ammonia, it is neutralized and discharged to the wastewater treatment device.

[0038] Throughout the process, the molar yield of 6 - aminocapronitrile relative to caprolactam reaches 92.0%. Example

[0039] Add sodium hydroxide to the caprolactam production residue with a caprolactam mass content of 98% at a mass ratio of 1.0%. After mixing, it enters the dehydration evaporator, and the temperature is controlled at 120 - 130 °C, and the absolute pressure is 300 - 900 Pa; the liquid phase enters the caprolactam evaporator for evaporation, and the temperature is controlled at 130 - 150 °C, and the absolute pressure is 900 - 3500 Pa; after evaporation, the caprolactam vapor is pressurized to 0.1 - 0.5 MPa by an ammonia injector, and is introduced into the reaction feed mixer to be mixed with hot ammonia gas at 250 - 350 °C at a mass ratio of 1:2 - 1:10. After mixing, the reaction material enters the ammoniation dehydration reaction to prepare 6 - aminocapronitrile.

[0040] The ammoniation dehydration reactor is a fixed - bed reactor equipped with a catalyst. The reaction temperature is controlled at 300 - 400 °C, the reaction pressure is 0.1 - 0.5 MPa, and the contact time of the mixture of caprolactam vapor and hot ammonia gas with the catalyst is 0.1 - 1 s.

[0041] The ammoniation dehydration reaction materials enter the primary separation rectification column. The overhead of the column is ammonia vapor containing water, and the bottom of the column is ε-caprolactam, which is returned to the caprolactam evaporator. The middle part of the primary separation rectification column is mainly the 6-aminocapronitrile stream, which enters the secondary separation rectification column. In the secondary separation rectification column, the light by-products are taken from the overhead, and the bottom is 6-aminocapronitrile with a purity of over 99.8%. In the tertiary separation rectification column, the ammonia gas from the overhead is returned to the hot ammonia gas heater for heating and then returned to the ammoniation dehydration reaction system. Water is taken from the middle of the column, and the bottom is light by-products, which can be separated together with the light by-products from the secondary separation rectification column to obtain HN(5-hexenenitrile). After adding alkali to the water taken from the middle of the column to extract ammonia, it is neutralized and discharged to the wastewater treatment device.

[0042] Throughout the process, the molar yield of 6-aminocapronitrile relative to caprolactam reaches 96.5%.

[0043] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing 6 - aminohexanenitrile from crude caprolactam, characterized in that: The production device mainly consists of a dehydration evaporator, a caprolactam evaporator, an ammonia gas injector, a reaction feed mixer, and an ammoniation dehydration reactor. The caprolactam evaporator is provided with a liquid discharge port. The crude caprolactam feed pipeline is connected to the inlet of the dehydration evaporator. The dehydration evaporator is provided with a gas phase outlet and a liquid phase outlet. The liquid phase outlet of the dehydration evaporator is connected to the caprolactam evaporator. The gas phase outlet of the caprolactam evaporator is connected to the inlet of the ammonia gas injector. The outlet of the ammonia gas injector is connected to the inlet of the reaction feed mixer. The outlet of the reaction feed mixer is connected to the ammoniation dehydration reactor; A crude caprolactam storage tank is arranged in front of the dehydration evaporator, and the crude caprolactam feed pipe is provided with an alkali liquor feed port. The gas phase outlet of the dehydration evaporator is connected to a dehydration evaporator condenser, and the condensate outlet of the dehydration evaporator is connected to a caprolactam evaporation and concentration device. Both the dehydration evaporator and the caprolactam evaporator are connected to a vacuum system; The method is that after the crude caprolactam is dehydrated by the dehydration evaporator, it enters the caprolactam evaporator for evaporation. The caprolactam vapor is pressurized by the ammonia gas injector and introduced into the reaction feed mixer to be mixed with ammonia gas. After mixing, the reaction material enters the ammoniation dehydration reaction to prepare 6 - aminocapronitrile. An alkali liquor is added to the crude caprolactam before entering the dehydration evaporation. The alkali liquor is one or more of NaOH, KOH, Ca(OH)2, and Ba(OH)2, and the addition amount of the alkali liquor is 0.2% - 5.0% of the mass of the crude caprolactam.

2. The method for preparing 6-aminocapronitrile using crude caprolactam as a raw material according to claim 1, characterized in that The crude caprolactam is an aqueous caprolactam solution with a caprolactam mass content of more than 90%, or / and a caprolactam extraction solution recovered from a polyamide device, or / and a residue from the distillation of a caprolactam production device.

3. The method for preparing 6 - amino - capronitrile using crude caprolactam as raw material according to claim 1, characterized in that The operating conditions of the dehydration evaporator are: temperature 110 - 130°C, absolute pressure 300 - 900 Pa; the operating conditions of the caprolactam evaporator are: temperature 130 - 150°C, absolute pressure 900 - 3500 Pa.

4. The method for preparing 6 - amino - capronitrile using crude caprolactam as a raw material according to claim 1, characterized in that The caprolactam vapor is pressurized to 0.1 - 0.5 MPa by the ammonia gas injector and mixed with hot ammonia gas at a mass ratio of 1:2 - 1:10 and at a temperature of 250 - 350°C in the reaction feed mixer, and then enters a fixed - bed reactor equipped with a catalyst. The reaction temperature is controlled at 300 - 400°C, the reaction pressure is 0.1 - 0.5 MPa, and the contact time between the mixture of caprolactam vapor and hot ammonia gas and the catalyst is 0.1 - 1 s.

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