Method for preparing aminocapronitrile from crude caprolactam

Abstract

The invention provides a method for preparing aminocapronitrile from crude caprolactam, the crude caprolactam is a mixture of polymerized state caprolactam and non-polymerized state caprolactam, and the method comprises the following steps: carrying out contact reaction on the crude caprolactam and ammonia gas in an ammonification reactor under the action of a catalyst to obtain a reaction mixture containing aminocapronitrile, and then carrying out post-treatment on the reaction mixture to obtain aminocapronitrile, the reaction temperature is 280 to 400 DEG C; the catalyst is a metal oxide or a molecular sieve catalyst. According to the invention, the refining and ammonification reactions of caprolactam are integrated and optimized, a plurality of unit steps for refining caprolactam, such as crystallization, water extraction and multi-effect water evaporation, are eliminated, the process flow is greatly simplified, and the production cost of 6-aminocapronitrile is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of green chemical preparation, and specifically is a method for directly preparing 6-aminocapronitrile by taking crude caprolactam liquid containing polymerized and non-polymerized states as raw material without purification. Background Art

[0002] Nylon 66 is a multi-purpose polymer material. With its excellent performance, the demand has been steadily increasing in recent years. Nylon 66 is made by polycondensation of hexamethylenediamine and adipic acid.

[0003] The existing production processes of hexamethylenediamine mainly include the butadiene method, the acrylonitrile method and the adipic acid method, but all of them have shortcomings (use of highly toxic chemicals, high energy consumption, low product selectivity, etc.). In comparison, the caprolactam method uses caprolactam as the raw material, generates 6-aminocapronitrile after ammonia dehydration, and then hydrogenates to generate hexamethylenediamine. The caprolactam method for producing hexamethylenediamine has the advantages of simple reaction steps, green process, sufficient raw material supply, and high product selectivity.

[0004] At present, the mainstream production process of caprolactam is to use benzene as raw material to make cyclohexanone, then use hydroxylamine to make cyclohexanone oxime, then use fuming sulfuric acid to perform Beckmann rearrangement to generate caprolactam sulfuric acid mixture, and finally generate crude caprolactam liquid containing ammonium sulfate through neutralization and crystallization. 60-70% of the crude caprolactam liquid containing ammonium sulfate is caprolactam, and the rest is impurities such as ammonium sulfate, water, cyclohexanone, benzene, toluene, and cyclohexanol.

[0005] Some processes utilize gas phase rearrangement or liquid phase rearrangement without sulfuric acid to obtain a crude caprolactam liquid containing polymerized and non-polymerized states after removing most of the impurities.

[0006] In order to improve the purity and quality of caprolactam, it is necessary to pass through a caprolactam refining unit to remove polymerized caprolactam and purify it to obtain refined caprolactam.

[0007] At present, the process flow of caprolactam refining includes benzene extraction, water back extraction, ion exchange, caprolactam hydrogenation, multi-effect evaporation, caprolactam distillation and other steps. Extraction refining is an important part of caprolactam refining. First, the crude caprolactam liquid containing ammonium sulfate is extracted with an organic solvent (usually benzene) to remove most of the water-soluble impurities, and then the caprolactam benzene solution is back extracted with water to remove some residual organic impurities to obtain a caprolactam aqueous solution; ion exchange and hydrogenation are used to further remove organic impurities containing unsaturated bonds; multi-effect evaporation is then used to remove water from the caprolactam aqueous solution, and finally caprolactam is distilled to obtain high-quality caprolactam products. It is not difficult to see from the above steps that the refining of caprolactam requires the distillation of the extractant benzene and water, and caprolactam also needs to be gasified, which requires a lot of energy consumption. In addition, the introduction of a large amount of water in the water washing and back extraction steps also leads to an increase in wastewater discharge.

[0008] The existing technologies for caprolactam refining and caprolactam amination are mainly aimed at the process optimization of a single reaction or the development of new catalysts. For example, patent CN201620239506.2 reports a caprolactam refining device, which consists of an extraction tower, a refining tower, a hydrogenation reactor, a light removal tower, and a distillation device, and does not require water back extraction, ion exchange, evaporation and other steps; patent CN202220658386.5 reports a device for reducing steam consumption in the process of caprolactam refining, which reduces steam and circulating water consumption by making full use of the heat energy at the top of the tower; patent CN201711000196.4 reports a method for refining caprolactam, the process of which includes extraction with an extractant, washing with hydrogen peroxide, and washing with water. The extractant is washed with water, back-extracted with water, and ion exchange is performed to extend the life of the ion exchange resin; Patent CN201621187626.9 reports a low-energy caprolactam refining device, which adds an alkali washing tower, an acid washing tower, and a deweighting tower compared to the traditional caprolactam refining process, reduces water extraction, evaporation and other processes, and reduces wastewater generation; Patent CN113083270A reports the use of alkaline earth metal oxides, transition metal oxides, silicon oxide, and aluminum oxide as catalysts for the amination of caprolactam to produce 6-aminocapronitrile; Patent CN201910775834.2 reports the use of phosphate aluminum molecular sieve as a carrier, and the catalyst for the amination of caprolactam is prepared by impregnation of aluminum nitrate, magnesium nitrate, and nickel nitrate. CN16617690A reports a device and method for preparing 6-aminocapronitrile using crude caprolactam as raw material, using crude caprolactam containing water and impurities to replace the currently refined caprolactam as raw material, and preparing 6-aminocapronitrile through vacuum evaporation dehydration, vacuum evaporation of caprolactam and gas ammonia injection pressurization technology, thereby reducing the energy consumption of primary distillation and gasification refining of caprolactam.

[0009] Although the above technology has been optimized for the process flow and partially reduced energy consumption and raw material requirements, it still has the defects of complicated process steps, large amount of wastewater discharge and high production cost. Summary of the invention

[0010] In view of the problems of the prior art, the present invention proposes a novel, simplified, low-energy, low-pollution and highly feasible method for producing 6-aminocapronitrile. The method directly uses a crude caprolactam liquid containing polymerized and non-polymerized states as a raw material, and achieves a reaction yield equivalent to that of the prior art by increasing the temperature of the amination reaction. The process reduces the refining step of caprolactam, reduces the overall energy consumption, reduces the wastewater discharge caused by the refining step, and reduces the production cost as a whole, reducing the environmental pressure.

[0011] To achieve the above object, the present invention adopts the following technical solution: A method for preparing aminocapronitrile from crude caprolactam, wherein the crude caprolactam is a mixture of polymerized caprolactam and non-polymerized caprolactam. The method is: The crude caprolactam is contacted with ammonia in an ammoniation reactor under the action of a catalyst to react to obtain a reaction mixture containing aminocapronitrile, and then the reaction mixture is post-treated to obtain aminocapronitrile; The reaction temperature is 280-400°C, preferably 320-360°C; The catalyst is a metal oxide or a molecular sieve catalyst.

[0012] Preferably, in the crude caprolactam, the content of non-polymerized caprolactam is greater than 95% by mass, preferably greater than 98% by mass.

[0013] Preferably, the crude caprolactam is first converted into a gaseous state and mixed with ammonia before entering the reactor for reaction.

[0014] Preferably, the post-treatment further comprises the step of recovering the unreacted ammonia in the reaction mixture.

[0015] The post-treatment step can adopt conventional processes for treating aminocapronitrile reaction mixtures in the art.

[0016] Preferably, the crude caprolactam is obtained by a non-sulfuric acid liquid phase rearrangement process of cyclohexanone oxime, or a gas phase rearrangement process of cyclohexanone oxime.

[0017] Preferably, the non-sulfuric acid liquid phase rearrangement process of cyclohexanone oxime comprises: Cyclohexanone oxime is subjected to rearrangement reaction in a solvent under the action of a liquid phase rearrangement catalyst, and after the reaction is completed, solids, light component impurities and solvents are removed by purification to obtain the crude caprolactam.

[0018] Preferably, the liquid phase rearrangement catalyst is a solid sulfonic acid resin.

[0019] Preferably, the solvent is dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF).

[0020] Preferably, when the solvent is dimethyl sulfoxide, the light impurities are removed first and then the solvent; when the solvent is N,N-dimethylformamide, the solvent is removed first and then the light impurities. Due to the different densities of DMSO and DMF, using different removal orders is beneficial to minimize the residual impurities and solvent content.

[0021] Preferably, the gas phase rearrangement process of cyclohexanone oxime comprises: The gas phase cyclohexanone alcohol, methanol and water are contacted with a gas phase rearrangement catalyst in a gas phase rearrangement reactor to carry out a rearrangement reaction, and after the reaction is completed, unreacted methanol, water and light component impurities are removed by purification to obtain the crude caprolactam.

[0022] Preferably, the gas phase rearrangement catalyst is a ZSM-5 type zeolite molecular sieve catalyst with a high silicon / aluminum ratio.

[0023] The beneficial effects of the present invention are: The invention utilizes the characteristic that non-sulfur-containing impurities in crude caprolactam have substantially no influence on the amination reaction, eliminates a plurality of unit steps for refining caprolactam such as crystallization, water extraction, and multi-effect water evaporation, utilizes a relatively high reaction temperature to eliminate the adverse influence of polymerized caprolactam, greatly simplifies the process flow while ensuring that the reaction yield is equivalent to that of the prior art, and significantly reduces the production cost of 6-aminocapronitrile.

[0024] The invention directly performs an amination reaction on crude caprolactam obtained by simple purification after non-sulfuric acid rearrangement of cyclohexanone oxime at a relatively high temperature, bypasses the caprolactam refining process, utilizes the characteristic that impurities in crude caprolactam have substantially no influence on the preparation of 6-aminocapronitrile by amination of caprolactam, eliminates the crystallization and water extraction which generate waste water, and the high-energy consumption multi-effect evaporation and caprolactam gasification and distillation steps, greatly simplifies the process, makes the process more environmentally friendly, and effectively reduces the production energy consumption and unit cost of 6-aminocapronitrile, while the reaction yield is comparable to that of the prior art.

[0025] Since the non-sulfuric acid liquid phase rearrangement reaction process of cyclohexanone oxime is almost water-free and the water content is below 100 ppm, it is not easy to produce a large amount of polymer in the subsequent caprolactam evaporation and amination process. The reaction selectivity is high and the catalyst performance is stable. The small amount of polymerized caprolactam produced will not affect the reaction yield at a higher reaction temperature and does not need to be refined and removed before the reaction.

[0026] In the present invention, caprolactam is gasified only once before the amination reaction, while in the conventional process, caprolactam needs to be gasified only once during the distillation process of refining, and furthermore, reflux is required, so the energy consumption is high.

[0027] In summary, the process of the present invention is simple, can be flexibly adjusted according to different processes, has low energy consumption, is environmentally friendly, and has good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a schematic diagram of the process flow of Example 1.

[0029] Figure 2 This is a schematic diagram of the process flow of Example 2.

[0030] Figure 3 This is a schematic diagram of the process flow of Example 3.

[0031] Figure 4 It is the chromatogram of crude caprolactam in Example 1.

[0032] Figure 5 1 is a chromatogram of the reaction mixture containing aminocapronitrile in Example 1.

[0033] Figure 6 It is the chromatogram of fine caprolactam in Example 1.

[0034] Figure 7 This is a chromatogram of the reaction mixture obtained by the amination reaction of pure caprolactam as a raw material in Example 1.

[0035] Among them, 1 is a liquid phase rearrangement reactor, 2 is a sedimentation separator, 3 is a filter, 4 is a lightness removal tower, 5 is a first desolventizing tower, 6 is a second desolventizing tower, 7 is a gasification evaporator, 8 is an amination reactor, 9 is a gas phase rearrangement reactor, 10 is a methanol removal tower, and 11 is a dehydration tower. DETAILED DESCRIPTION

[0036] Example 1 like Figure 1 As shown, a mixed solution with a cyclohexanone oxime content of 16.7% and a DMSO content of 83.3% is used as a raw material and enters a liquid phase rearrangement reactor. Under the action of a solid sulfonic acid resin catalyst, a caprolactam DMSO mother liquor with a similar concentration is generated. After filtration, the mother liquor enters a lightness removal tower. The lightness removal tower is operated under negative pressure. The top pressure of the tower is 10 KPa and the temperature is 110°C. Cyclohexanone and other by-products and a small amount of DMSO are evaporated. The desolventizing tower removes DMSO and recovers it. The top pressure of the first desolventizing tower is 2 KPa and the temperature is 80.9°C. High-purity DMSO is evaporated, accounting for 70-95% of the total solvent usage. The bottom temperature of the tower is 148°C. The material enters the second desolventizing tower for caprolactam purification. The top pressure of the second desolventizing tower is 1.5 KPa and the temperature is 84.5°C. The material containing DMSO is returned to the bottom feed port of the first desolventizing tower. Through the precise distillation of the double towers in series, the DMSO content in the caprolactam in the bottom of the second desolventizing tower is ensured to be less than 10 ppm. The mass fraction of caprolactam was 98.02%, and the impurities were mainly some polycondensates of caprolactam at high temperature ( Figure 4 ).

[0037] The crude caprolactam containing polymerized caprolactam is gasified and then enters the ammoniation reactor. The catalyst is activated alumina, the reaction temperature is 320°C, the feed molar ratio of ammonia to crude caprolactam is 24:1, and the space velocity is 0.8h -1, the single-pass caprolactam conversion rate was 60.4%, and the selectivity of 6-aminocapronitrile was 96.9%. In the mixture obtained by the amination reaction, the caprolactam polycondensate in the raw material was basically depolymerized, and the composition of the mixture was aminocapronitrile (peak at 11.68min), caprolactam (peak at 14.402min), and polyaminocapronitrile (peak at 20.646min). The impurities were mainly heavy by-products (aminocapronitrile dimers) produced in the reaction, with a content of 1.75% ( Figure 5 ).

[0038] The prior art uses refined caprolactam to enter the amination reaction, such as Figure 6 As shown, the purified caprolactam obtained after the purification step has eliminated the impurities of caprolactam polycondensate and has a high purity. The purified caprolactam is subjected to an amination reaction, and the chromatogram of the obtained reaction mixture is as shown in Figure 7 The main components are aminocapronitrile (11.7 min), caprolactam (14.38 min) and aminocapronitrile dimer (20.63 min), the conversion rate of caprolactam is 62.7%, and the selectivity of aminocapronitrile is 97.6%.

[0039] By comparison, it can be seen that the present invention uses crude caprolactam as raw material. Due to the use of a specific reaction temperature, the influence of heavy component impurities on the reaction conversion rate and selectivity is very small, which can meet industrial needs and is equivalent to the effect of using refined caprolactam in the prior art.

[0040] In the prior art, the preparation of refined caprolactam from crude caprolactam (including caprolactam, polycaprolactam, etc.) usually involves multiple complex and energy-intensive process steps, such as extraction, stripping, ion exchange, multi-effect evaporation, hydrogenation, distillation, etc., resulting in many steps in the caprolactam refining process, complex flow, high energy consumption, and a large amount of industrial waste. Therefore, the method of the present invention can greatly reduce the energy consumption of the caprolactam refining step while ensuring the reaction yield and selectivity. The overall production cost is reduced and the environmental pressure is reduced.

[0041] The aminocapronitrile product liquid after the reaction enters the distillation and refining system. At this time, the caprolactam content in the reaction liquid is about 39.8%. This part of unreacted caprolactam returns from the bottom of the tower to the gasification system before the amination reaction after the aminocapronitrile product is evaporated to participate in the reaction again.

[0042] Example 2

[0043] like Figure 2As shown, a mixed solution of 15% cyclohexanone oxime mass content and 85% DMF mass content is used as a raw material and enters a liquid phase rearrangement reactor. Under the action of a solid sulfonic acid resin catalyst, a caprolactam DMF mother liquor with a similar concentration is generated. After filtration, the mother liquor enters a desolventizing tower. The desolventizing tower is operated at a negative pressure. The tower top pressure is 3 KPa and the temperature is 59°C. DMF is evaporated. The bottom material enters a light component removal tower. The tower operating pressure is 1.5 KPa and the tower top temperature is 75.8°C. Residual DMF, cyclohexanone, 5-cyano-1-pentene, hexanenitrile and other light components are obtained at the top of the tower. The by-product separation and DMF recovery system are removed. The bottom temperature is 99.9% caprolactam mass fraction, wherein the impurities are mainly some caprolactam polycondensates at high temperature.

[0044] The crude caprolactam containing polymerized caprolactam is gasified and then enters the ammoniation reactor. The catalyst is phosphate, the reaction temperature is 360°C, the feed molar ratio of ammonia to caprolactam is 24:1, and the space velocity is 0.85h -1 The single-pass caprolactam conversion rate was 58.5%, and the 6-aminocapronitrile selectivity was 96.9%.

[0045] The aminocapronitrile product liquid after the reaction enters the distillation and refining system. At this time, the caprolactam content in the reaction liquid is about 41.2%. This part of unreacted caprolactam returns from the bottom of the tower to the gasification system before the amination reaction after the aminocapronitrile product is evaporated to participate in the reaction again.

[0046] Example 3

[0047] like Figure 3 As shown, a mixed solution of 35% cyclohexanone oxime and 65% methanol is used as a raw material, which is gasified and enters a gas phase rearrangement reactor, and a certain amount of water (raw material 3%, mass composition) is introduced. Under the action of a high silicon / aluminum ratio ZSM-5 zeolite molecular sieve catalyst, a caprolactam product liquid is generated and enters a de-methanolation tower. The de-methanolation tower is operated at normal pressure, with a tower top temperature of 68°C, methanol is evaporated, and a tower bottom temperature of about 140°C. The tower bottom solution enters a dehydration tower with a tower operating pressure of 20KPa and a tower top temperature of 70 ℃, water, cyclohexanone (cyclohexanone and water have azeotropy, the azeotropic point is 95℃, and the azeotropic composition is 38.4% of cyclohexanone), 5-cyano-1-pentene and other azeotropes with water are distilled out from the top of the tower, and the by-product separation and water environmental protection treatment systems are removed. The bottom temperature of the tower is 132℃, and the bottom material enters the light component removal tower to continue to remove a small amount of water and light components. The tower operating pressure is 1.3KPa, the top temperature is 83℃, the bottom temperature is 147℃, and the mass fraction of caprolactam is 99.3%, among which the impurities are mainly some condensation products of caprolactam at high temperature.

[0048] The crude caprolactam containing polymerized caprolactam is gasified and then enters the ammoniation reactor. Titanium-silicon molecular sieve catalyst is used. The reaction temperature is 400°C, the feed molar ratio of ammonia to caprolactam is 18:1, and the space velocity is 0.6h -1 The single-pass caprolactam conversion rate was 55.7%, and the 6-aminocapronitrile selectivity was 96.2%.

[0049] The aminocapronitrile product liquid after the reaction enters the distillation and refining system. At this time, the caprolactam content in the reaction liquid is about 43.3%. This part of unreacted caprolactam returns from the bottom of the tower to the gasification system before the amination reaction after the aminocapronitrile product is evaporated to participate in the reaction again.

Claims

1. A method for preparing aminocapronitrile from crude caprolactam, characterized in that: The crude caprolactam is a mixture of polymerized caprolactam and non-polymerized caprolactam. The method is: The crude caprolactam is contacted with ammonia in an ammoniation reactor under the action of a catalyst to react to obtain a reaction mixture containing aminocapronitrile, and then the reaction mixture is post-treated to obtain aminocapronitrile; The reaction temperature is 280-400°C, preferably 320-360°C; The catalyst is a metal oxide or a molecular sieve catalyst.

2. The method according to claim 1, characterized in that In the crude caprolactam, the content of non-polymerized caprolactam is greater than 95% by mass, preferably greater than 98% by mass.

3. The method according to claim 1, characterized in that The post-treatment further comprises the step of recovering the unreacted ammonia in the reaction mixture.

4. The method according to claim 1, characterized in that: The crude caprolactam is obtained by a non-sulfuric acid liquid phase rearrangement process of cyclohexanone oxime or a gas phase rearrangement process of cyclohexanone oxime.

5. The method according to claim 4, characterized in that The non-sulfuric acid liquid phase rearrangement process of cyclohexanone oxime comprises: Cyclohexanone oxime is subjected to rearrangement reaction in a solvent under the action of a liquid phase rearrangement catalyst, and after the reaction is completed, solids, light component impurities and solvents are removed by purification to obtain the crude caprolactam.

6. The method according to claim 5, characterized in that The liquid phase rearrangement catalyst is a solid sulfonic acid resin.

7. The method according to claim 5, characterized in that The solvent is dimethyl sulfoxide or N,N-dimethylformamide.

8. The method according to claim 7, characterized in that When the solvent is dimethyl sulfoxide, the light component impurities are removed first and then the solvent; when the solvent is N,N-dimethylformamide, the solvent is removed first and then the light component impurities are removed.

9. The method according to claim 4, characterized in that The gas phase rearrangement process of cyclohexanone oxime comprises: The gas phase cyclohexanone alcohol, methanol and water are contacted with a gas phase rearrangement catalyst in a gas phase rearrangement reactor to carry out a rearrangement reaction, and after the reaction is completed, unreacted methanol, water and light component impurities are removed by purification to obtain the crude caprolactam.

10. The method according to claim 9, characterized in that The gas phase rearrangement catalyst is a ZSM-5 type zeolite molecular sieve catalyst with a high silicon / aluminum ratio.

Images