Process for the preparation of aminocapronitrile from crude caprolactam

Abstract

The application provides a method for preparing aminocapronitrile from coarse caprolactam, wherein the coarse caprolactam is a mixture of polymerized caprolactam and non-polymerized caprolactam, and the method comprises the following steps: reacting the coarse caprolactam with ammonia gas in an ammoniation reactor under the action of a catalyst to obtain a reaction mixture containing aminocapronitrile, and then performing post-treatment on the reaction mixture to obtain aminocapronitrile; the reaction temperature is 280-400 DEG C; and the catalyst is a metal oxide or a molecular sieve catalyst. The method integrates and optimizes the refining and ammoniation reaction of caprolactam, eliminates multiple unit steps for refining caprolactam such as crystallization, water extraction and multi-effect evaporation of water, greatly simplifies the process flow, and greatly reduces the production cost of 6-aminocapronitrile.

Description

Technical Field

[0001] This invention belongs to the field of green chemical preparation technology, specifically a method for directly preparing 6-aminohexanonitrile from crude caprolactam liquid containing both polymerized and non-polymerized states without refining. Background Technology

[0002] Nylon 66 is a versatile polymer material, and its demand has been steadily increasing in recent years due to its excellent properties. Nylon 66 is made by the polycondensation of hexamethylenediamine and adipic acid.

[0003] Existing production processes for hexamethylenediamine mainly include the butadiene method, the acrylonitrile method, and the adipic acid method, but all have shortcomings (use of highly toxic chemicals, high energy consumption, and low product selectivity). In contrast, the caprolactam method uses caprolactam as a raw material, which is amination and dehydration to produce 6-aminohexanonitrile, and then hydrogenated to produce hexamethylenediamine. The caprolactam method for producing hexamethylenediamine has advantages such as simple reaction steps, environmentally friendly process, abundant raw material supply, and high product selectivity.

[0004] The current mainstream production process for caprolactam involves using benzene as a raw material to produce cyclohexanone, then using hydroxylamine to produce cyclohexanone oxime, followed by Beckmann rearrangement using fuming sulfuric acid to generate a caprolactam-sulfuric acid mixture. Finally, neutralization and crystallization produce a crude caprolactam solution containing ammonium sulfate. The crude caprolactam solution containing ammonium sulfate contains 60-70% caprolactam, with the remainder consisting of impurities such as ammonium sulfate, water, cyclohexanone, benzene, toluene, and cyclohexanol.

[0005] Some processes utilize gas-phase rearrangement or sulfuric acid-free liquid-phase rearrangement to remove most impurities, resulting in a crude caprolactam solution containing both polymeric and non-polymeric states.

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

[0007] The current caprolactam refining process includes steps such as benzene extraction, water back-extraction, ion exchange, caprolactam hydrogenation, multi-effect evaporation, and caprolactam distillation. Extraction refining is a crucial step in caprolactam refining. First, the crude caprolactam solution containing ammonium sulfate is extracted with an organic solvent (usually benzene) to remove most of the water-soluble impurities. Then, the caprolactam-benzene solution is back-extracted with water to remove some residual organic impurities, yielding an aqueous caprolactam 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 solution. Finally, caprolactam is distilled to obtain a high-quality caprolactam product. It is clear from these steps that caprolactam refining requires the distillation of the extractant benzene and water, and the caprolactam itself needs to be vaporized, both of which consume significant amounts of energy. Furthermore, the introduction of large amounts of water in the washing and back-extraction steps leads to increased wastewater discharge.

[0008] Existing technologies for caprolactam refining and caprolactam amination mainly focus on optimizing single-reaction processes or developing new catalysts. For example, patent CN201620239506.2 reports a caprolactam refining apparatus consisting of an extraction tower, a refining tower, a hydrogenation reactor, a light-weight removal tower, and a distillation unit, eliminating the need for water back-extraction, ion exchange, and evaporation steps; patent CN202220658386.5 reports a device for reducing steam consumption during caprolactam refining by fully utilizing the heat energy at the top of the tower to reduce steam and circulating water consumption; and patent CN201711000196.4 reports a method for caprolactam refining, including steps such as extractant extraction and hydrogen peroxide washing. The extraction process involves solvent extraction, water back-extraction, and ion exchange, which extends the lifespan of ion exchange resins. Patent CN201621187626.9 reports a low-energy caprolactam refining device, which, compared to traditional caprolactam refining processes, adds an alkali washing tower, an acid washing tower, and a de-heavy removal tower, while reducing water extraction, evaporation, and other processes, thus reducing wastewater generation. Patent CN113083270A reports the use of alkaline earth metal oxides, transition metal oxides, silicon oxide, and aluminum oxide as catalysts for the ammoniation of caprolactam to 6-aminohexanonitrile. Patent CN201910775834.2 reports the preparation of a catalyst for caprolactam ammoniation using phosphorus aluminum molecular sieves as a carrier by impregnating aluminum nitrate, magnesium nitrate, and nickel nitrate. CN16617690A reports an apparatus and method for preparing 6-aminohexanonitrile from crude caprolactam. The method uses crude caprolactam containing water and impurities to replace the currently refined caprolactam as raw material. 6-aminohexanonitrile is prepared by vacuum evaporation dehydration, vacuum evaporation of caprolactam and gaseous ammonia injection pressurization technology, which reduces the energy consumption of the single distillation and gasification purification of caprolactam.

[0009] Although the above technologies have optimized the process flow and reduced energy consumption and raw material requirements in some areas, they still have drawbacks such as complicated process steps, large wastewater discharge, and high production costs. Summary of the Invention

[0010] To address the problems of the existing technologies mentioned above, this invention proposes a novel, simplified, low-energy-consumption, low-pollution, and highly feasible method for producing 6-aminohexanonitrile. This method directly uses crude caprolactam containing both polymeric and non-polymeric states as raw material. By increasing the amination reaction temperature, a reaction yield comparable to existing technologies is achieved. This process reduces overall energy consumption and wastewater discharge from the purification process by eliminating the purification steps, thereby reducing overall production costs and environmental impact.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing aminocaprolactam from crude caprolactam, wherein the crude caprolactam is a mixture of polymeric and non-polymeric caprolactam. The method is as follows: The crude caprolactam was reacted with ammonia in an ammoniation reactor under the action of a catalyst to obtain a reaction mixture containing aminohexanonitrile. The reaction mixture was then post-treated to obtain aminohexanonitrile. The reaction temperature is 280~400℃, and the preferred reaction temperature is 320~360℃; The catalyst is a metal oxide or a molecular sieve catalyst.

[0012] Preferably, the crude caprolactam contains at least 95% by mass of non-polymerized caprolactam, and more preferably at least 98% by mass.

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

[0014] Preferably, the post-processing further includes the step of recovering unreacted ammonia gas from the reaction mixture.

[0015] The post-processing steps can employ conventional techniques for processing aminohexanonitrile 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 for cyclohexanone oxime includes: Cyclohexanone oxime was rearranged in a solvent under the action of a liquid-phase rearrangement catalyst. After the reaction was completed, the crude caprolactam was obtained by purification to remove solid, light component impurities and solvent.

[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 component impurities are removed first, followed by the solvent; when the solvent is N,N-dimethylformamide, the solvent is removed first, followed by the light component impurities. Since DMSO and DMF have different densities, using different removal sequences helps to minimize the residual impurities and solvent content.

[0021] Preferably, the gas-phase rearrangement process of the cyclohexanone oxime includes: Cyclohexanone alcohol, methanol, and water in the gas phase are contacted with a gas phase rearrangement catalyst in a gas phase rearrangement reactor to carry out a rearrangement reaction. 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 this invention are as follows: This invention utilizes the characteristic that non-sulfur-containing impurities in crude caprolactam have virtually no impact on the amination reaction, eliminating multiple unit steps for refining caprolactam, such as crystallization, water extraction, and multi-effect evaporation of water. It also utilizes a higher reaction temperature to eliminate the adverse effects of polymerized caprolactam. While ensuring a reaction yield comparable to existing technologies, this invention greatly simplifies the process and significantly reduces the production cost of 6-aminohexanonitrile.

[0024] This invention directly ammoniates crude caprolactam obtained by simple purification of cyclohexanone oxime after non-sulfuric acid rearrangement at a higher temperature, bypassing the caprolactam refining process. Taking advantage of the fact that impurities in crude caprolactam have little impact on the ammoniation of caprolactam to prepare 6-aminohexanonitrile, this invention eliminates the crystallization, water extraction, and energy-intensive multi-effect evaporation and caprolactam vaporization distillation steps that generate wastewater. Under the premise of comparable reaction yield to existing technologies, the process is greatly simplified, the process is more environmentally friendly, and the production energy consumption and unit cost of 6-aminohexanonitrile are also effectively reduced.

[0025] Since the non-sulfuric acid liquid-phase rearrangement reaction of cyclohexanone oxime is almost anhydrous with a water content of less than 100 ppm, it is not easy to generate a large amount of polymer during the subsequent caprolactam evaporation and amination process. The reaction selectivity is high, the catalyst performance is stable, and the small amount of polymerized caprolactam generated will not affect the reaction yield at higher reaction temperatures, so there is no need for purification and removal before the reaction.

[0026] In this invention, caprolactam is vaporized only once before the amination reaction. In traditional processes, caprolactam needs to be vaporized once during the refining distillation process, and reflux is also required, resulting in high energy consumption.

[0027] In summary, the present invention has a simple process, can be flexibly adjusted according to different processes, and is energy-efficient, environmentally friendly, and economical. Attached Figure Description

[0028] The present invention will be 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 for Example 1.

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

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

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

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

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

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

[0035] 1 is a liquid phase rearrangement reactor, 2 is a sedimentation separator, 3 is a filter, 4 is a light component removal tower, 5 is a first solvent removal tower, 6 is a second solvent removal tower, 7 is a vaporization evaporator, 8 is an ammoniation reactor, 9 is a gas phase rearrangement reactor, 10 is a methanol removal tower, and 11 is a dehydration tower. Detailed Implementation

[0036] Example 1 For example Figure 1 As shown, a mixed solution containing 16.7% cyclohexanone oxime and 83.3% DMSO was used as raw material and fed into a liquid-phase rearrangement reactor. Under the action of a solid sulfonic acid resin catalyst, a caprolactam-DMSO mother liquor with a similar concentration was generated. After filtration, the mother liquor was fed into a light-light ... The yield was 98.02% caprolactam by mass, with impurities mainly consisting of high-temperature condensation polymers of caprolactam. Figure 4 ).

[0037] Crude caprolactam containing polymerized caprolactam is vaporized and then fed into an ammoniation reactor. The catalyst is activated alumina, the reaction temperature is 320℃, the feed molar ratio of ammonia to crude caprolactam is 24:1, and the space velocity is 0.8 h⁻¹. -1The single-pass caprolactam conversion rate was 60.4%, and the selectivity for 6-aminohexanonitrile was 96.9%. In the mixture obtained from the amination reaction, the caprolactam condensate in the raw material was largely depolymerized. The mixture consisted of aminohexanonitrile (peak at 11.68 min), caprolactam (peak at 14.402 min), and polyaminohexanonitrile (peak at 20.646 min). The impurities were mainly heavy byproducts (aminohexanonitrile dimers) that appeared during the reaction, with a content of 1.75%. Figure 5 ).

[0038] Existing technologies use caprolactam in an amination reaction, such as... Figure 6 As shown, the purified caprolactam obtained after the purification step has eliminated caprolactam condensate impurities and has a high purity. The chromatogram of the resulting reaction mixture obtained by the amination reaction of this purified caprolactam is shown below. Figure 7 As shown. The main components were aminocaproic acid (11.7 min), caprolactam (14.38 min), and aminocaproic acid dimer (20.63 min). The conversion rate of caprolactam was 62.7%, and the selectivity of aminocaproic acid was 97.6%.

[0039] As can be seen from the comparison, the present invention uses crude caprolactam as raw material. Due to the use of a specific reaction temperature, the impact of heavy component impurities on the reaction conversion rate and selectivity is very small, which can meet the needs of industrialization and is comparable to the effect of the existing technology using refined caprolactam.

[0040] In existing technologies, the preparation of refined caprolactam from crude caprolactam (including caprolactam, polycaprolactam, etc.) typically involves multiple complex and energy-intensive process steps, such as extraction, back-extraction, ion exchange, multi-effect evaporation, hydrogenation, and distillation. This results in numerous steps, a complex process, high energy consumption, and the generation of significant industrial waste. Therefore, the method of this invention can significantly reduce the energy consumption of the caprolactam refining process while ensuring reaction yield and selectivity. This reduces overall production costs and environmental impact.

[0041] The reacted aminohexanonitrile product liquid is fed into the distillation and purification system. At this point, the caprolactam content in the reaction liquid is about 39.8%. This unreacted caprolactam is returned from the bottom of the column to the vaporization system before the ammoniation reaction after the aminohexanonitrile product is distilled to participate in the reaction again.

[0042] Example 2

[0043] like Figure 2As shown, a mixed solution containing 15% cyclohexanone oxime and 85% DMF was used as raw material and fed into a liquid-phase rearrangement reactor. Under the action of a solid sulfonic acid resin catalyst, a caprolactam-DMF mother liquor with a similar concentration was generated. After filtration, the mother liquor was fed into a desolventizing tower, which operated under negative pressure with a top pressure of 3 kPa and a temperature of 59°C. DMF was distilled off, and the bottom material was fed into a light component removal tower with an operating pressure of 1.5 kPa and a top temperature of 75.8°C. The top material contained residual DMF, cyclohexanone, 5-cyano-1-pentene, and n-hexanonitrile, which were then separated into by-products and a DMF recovery system. The bottom temperature was [not specified]. The caprolactam mass fraction was 99.9%, and the impurities were mainly some high-temperature condensation products of caprolactam.

[0044] Crude caprolactam containing polymerized caprolactam is vaporized and then fed into an ammoniation reactor. The catalyst is a phosphate-based catalyst, the reaction temperature is 360℃, the feed molar ratio of ammonia to caprolactam is 24:1, and the space velocity is 0.85 h⁻¹. -1 The single-pass caprolactam conversion rate was 58.5%, and the selectivity for 6-aminohexanonitrile was 96.9%.

[0045] The reacted aminohexanonitrile product liquid is fed into the distillation and purification system. At this point, the caprolactam content in the reaction liquid is about 41.2%. This unreacted caprolactam is returned from the bottom of the column to the vaporization system before the ammoniation reaction after the aminohexanonitrile product is distilled to participate in the reaction again.

[0046] Example 3

[0047] like Figure 3 As shown, a mixed solution of cyclohexanone oxime (35% by mass) and methanol (65% by mass) was used as raw material. After vaporization, it entered a gas-phase rearrangement reactor, and a certain amount of water (3% by mass of raw material) was introduced. Under the catalysis of a high silica / alumina ratio ZSM-5 zeolite molecular sieve catalyst, caprolactam product liquid was generated and entered a methanol removal tower. The methanol removal tower operated at atmospheric pressure, with a top temperature of 68°C, and methanol was distilled off. The bottom temperature of the tower was approximately 140°C. The bottom solution entered a dehydration tower, with an operating pressure of 20 kPa and a top temperature of 70°C. At ℃, the distillate from the top of the column contains water, cyclohexanone (cyclohexanone forms an azeotrope with water at 95℃, with an azeotropic composition of 38.4% cyclohexanone), 5-cyano-1-pentene, and other azeotropes formed with water. These are then separated into by-products and treated by a water environmental protection system. The bottom temperature of the column is 132℃. The bottom material enters a light component removal column for further removal of small amounts of water and light components. The column operating pressure is 1.3 kPa, the top temperature is 83℃, and the bottom temperature is 147℃. The caprolactam mass fraction is 99.3%, with impurities mainly consisting of high-temperature condensation polymers of caprolactam.

[0048] Crude caprolactam containing polymerized caprolactam is vaporized and then fed into an ammoniation reactor. A titanium-silicon molecular sieve catalyst is used, the reaction temperature is 400℃, the feed molar ratio of ammonia to caprolactam is 18:1, and the space velocity is 0.6 h⁻¹. -1 The single-pass caprolactam conversion rate was 55.7%, and the selectivity for 6-aminohexanonitrile was 96.2%.

[0049] The reacted aminohexanonitrile product liquid is fed into the distillation and purification system. At this time, the caprolactam content in the reaction liquid is about 43.3%. This unreacted caprolactam is returned from the bottom of the column to the vaporization system before the ammoniation reaction after the aminohexanonitrile product is distilled to participate in the reaction again.

Claims

1. A method for preparing aminohexanonitrile from crude caprolactam, characterized in that, The crude caprolactam is a mixture of polymeric and non-polymeric caprolactam, wherein the content of non-polymeric caprolactam in the crude caprolactam is between 95% and 98.02% by mass. The method is as follows: The crude caprolactam was reacted with ammonia in an ammoniation reactor under the action of a catalyst to obtain a reaction mixture containing aminohexanonitrile. The reaction mixture was then post-treated to obtain aminohexanonitrile. The reaction temperature is 320~360℃; The catalyst is activated alumina; 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. The non-sulfuric acid liquid-phase rearrangement process for cyclohexanone oxime includes: Cyclohexanone oxime was rearranged in a solvent under the action of a liquid-phase rearrangement catalyst. After the reaction was completed, the crude caprolactam was obtained by purification to remove solid, light component impurities and solvent. The vapor-phase rearrangement process for the cyclohexanone oxime includes: Cyclohexanone alcohol, methanol, and water in the gas phase are contacted with a gas phase rearrangement catalyst in a gas phase rearrangement reactor to carry out a rearrangement reaction. After the reaction is completed, unreacted methanol, water, and light component impurities are removed by purification to obtain the crude caprolactam.

2. The method according to claim 1, characterized in that, The crude caprolactam contains more than 98% by mass of non-polymerized caprolactam.

3. The method according to claim 1, characterized in that, The post-processing also includes the step of recovering unreacted ammonia from the reaction mixture.

4. The method according to claim 1, characterized in that, The liquid-phase rearrangement catalyst is a solid sulfonic acid resin.

5. The method according to claim 1, characterized in that, The solvent is dimethyl sulfoxide or N,N-dimethylformamide.

6. The method according to claim 5, characterized in that, When the solvent is dimethyl sulfoxide, the light component impurities are removed first, and then the solvent is removed; when the solvent is N,N-dimethylformamide, the solvent is removed first, and then the light component impurities are removed.

7. The method according to claim 1, characterized in that, The gas-phase rearrangement catalyst is a ZSM-5 type zeolite molecular sieve catalyst with a high silicon / aluminum ratio.

Images