Method for synthesizing aminocapronitrile from caprolactam

Abstract

The invention belongs to the technical field of fine chemical engineering, and provides a method for synthesizing hexamethylenediamine intermediate aminocapronitrile. By using the phosphoric acid modified ZSM-5 molecular sieve and utilizing the catalyst, vaporized caprolactam reacts with ammonia gas to obtain aminocapronitrile, the conversion rate exceeds 90%, the selectivity exceeds 99%, and the method is suitable for industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of 6-aminocapronitrile preparation, and in particular to a method for preparing aminocapronitrile by ammoniation and dehydration of caprolactam. Background Art

[0002] Hexamethylenediamine is an important organic chemical intermediate, mainly used in the production of polyamides, such as nylon 66 salt and nylon 610; it can also be used to synthesize diisocyanates or curing agents for epoxy resins and urea-formaldehyde resins, organic crosslinking agents, etc. With the continuous development of the synthetic fiber industry, the demand for hexamethylenediamine compounds has continued to increase worldwide, prices have continued to rise, and there is a large gap between market supply and demand.

[0003] At present, the main production processes of hexamethylenediamine include adiponitrile method, hexamethylenediol method, caprolactam method, adipic acid method, etc. Among them, the adiponitrile method is the most mainstream hexamethylenediamine production method in the world, but the key technologies are mostly monopolized by large foreign institutions, and the technical barriers are serious. The hexamethylenediol method has many processes and a large number of by-products, making it difficult to obtain hexamethylenediamine with high purity. At present, this method is basically not used to produce hexamethylenediamine. The adipic acid method technology is relatively mature, but due to high cost, long process, and unreasonable resource utilization, its process technology development is limited, and it has been basically eliminated abroad.

[0004] The caprolactam method for producing hexamethylenediamine requires the following three steps: the first step is the amination ring-opening reaction of caprolactam and ammonia to produce 6-aminocaproamide; the second step is the dehydration reaction of 6-aminocaproamide to remove oxygen atoms to produce 6-aminocapronitrile; the third step is the hydrogenation reaction of 6-aminocapronitrile and hydrogen to obtain hexamethylenediamine. The caprolactam method can bypass the barriers associated with the adiponitrile method.

[0005] The U.S. patent application with patent application publication number US2234566 uses silica gel supported copper as a dehydration catalyst to synthesize 6-aminocapronitrile under the conditions of a reaction temperature of 360°C and an ammonia / caprolactam molar ratio of 1:6. The caprolactam conversion rate is 21.7%, and the 6-aminocapronitrile yield is only 25%. The catalyst has the problem of low activity.

[0006] Patent CN107739318 has developed a method and device for preparing 6-aminocapronitrile from caprolactam by liquid phase method, wherein caprolactam, organic solvent and phosphate catalyst are put into a reactor, and reacted at 260-280°C to generate 6-aminocapronitrile, with a caprolactam conversion rate of 55% and a 6-aminocapronitrile selectivity of 97%. The batch process technology is used, which has the disadvantages of complex separation of catalyst and solvent in the later stage, high energy consumption, low production capacity and low caprolactam conversion rate.

[0007] CN107739318A discloses a method for preparing 6-aminocapronitrile by a caprolactam liquid phase method. In the method, caprolactam, a small amount of adiponitrile and phosphoric acid are put into a reaction kettle, and ammonia is introduced after the temperature is raised to 260°C to react and generate 6-aminocapronitrile. The caprolactam conversion rate of the method is only 58%, and adiponitrile is inevitably used, so the cost is high and the caprolactam conversion rate is low.

[0008] It is not difficult to see that although the technical research on the preparation of 6-aminocapronitrile by the amination of caprolactam was carried out early, problems such as low product yield and high energy consumption still exist. Therefore, it is urgent to develop a new preparation method. Summary of the invention

[0009] The main purpose of the present invention is to provide a method for preparing aminocapronitrile by amination and dehydration of caprolactam, so as to solve the problems of low yield and high energy consumption in the prior art of preparing 6-aminocapronitrile by amination of caprolactam.

[0010] The main technical scheme of the present invention is a method for synthesizing aminocapronitrile from caprolactam, characterized in that the method comprises the following steps: S1: caprolactam is dissolved in anhydrous acetonitrile to prepare a caprolactam acetonitrile mixed solution, wherein the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-15:1; S2: passing ammonia gas and the mixed solution in S1 into a fixed bed reactor filled with a phosphoric acid-modified molecular sieve catalyst for ammonia dehydration reaction to obtain a product, the reaction temperature being 300-400°C; S3: After the reaction product is cooled, gas-liquid separation is performed, the separated ammonia gas is recovered, and the separated liquid is distilled to obtain the reaction product aminocapronitrile.

[0011] Preferably, the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-10:1.

[0012] Further preferably, the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-4:1.

[0013] Preferably, the mixed liquid feed temperature is room temperature.

[0014] Preferably, the mixed solution feeding rate is 0.1-0.3 mL / min.

[0015] Preferably, in step S2, the ammonia flow rate is 50-150 mL / min.

[0016] Further preferably, the ammonia flow rate is 80-100 mL / min.

[0017] Preferably, the reaction temperature in step S2 is 340-350°C.

[0018] Preferably, in step S3, the reaction product is cooled to 100-150°C.

[0019] Further preferably, in step S2, the reaction product is cooled to 100-120°C.

[0020] The method for synthesizing aminocapronitrile from caprolactam provided by the present invention has a caprolactam conversion rate greater than 92% and an aminocapronitrile selectivity greater than 99%. Beneficial Effects

[0021] The present invention discloses a method for preparing pure 6-aminocapronitrile by a liquid phase method using caprolactam as a raw material, wherein caprolactam is aminated and dehydrated to produce 6-aminocapronitrile. Compared with the prior art, the method for preparing 6-aminocapronitrile by a caprolactam liquid phase method disclosed in the present invention has the following advantages: The method for preparing 6-aminocapronitrile by a caprolactam liquid phase method of the present invention uses a gas phase method to prepare 6-aminocapronitrile, has high reaction conversion rate, good selectivity, simple preparation process and low energy consumption. The caprolactam conversion rate is greater than 92%, and the aminocapronitrile selectivity is greater than 99%, which has high application value. Implementation

[0022] In order to better understand the present invention, the content of the invention is further explained below in conjunction with the embodiments. It should be noted that, in the case of no conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments. Example

[0023] Example A method for synthesizing aminocapronitrile from caprolactam uses phosphoric acid-modified ZSM-5 molecular sieve as a catalyst for the dehydration amination reaction.

[0024] In the embodiment, the preparation method of the dehydration amination catalyst is as follows: the molar ratio of SiO2 and Al2O3 is 46:1, 75% phosphoric acid is used for impregnation for 12 hours and then filtered, dried at 120°C for 8 hours, and calcined at 300°C for 8 hours to finally obtain a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile. Example 1

[0025] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 80 mL / min, and the reaction temperature was 340°C. Example 2

[0026] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 80 mL / min, and the reaction temperature was 350°C. Example 3

[0027] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:4, the feed rate was 0.17 mL / min, the ammonia flow rate was 80 mL / min, and the reaction temperature was 340°C. Example 4

[0028] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:4, the feed rate was 0.17 mL / min, the ammonia flow rate was 80 mL / min, and the reaction temperature was 350°C. Example 5

[0029] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C, and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, and the reaction temperature was 340°C. Example 6

[0030] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:4, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, and the reaction temperature was 350°C. Example 7

[0031] Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, and the reaction temperature was 350°C.

[0032] Comparative Example 1 Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, the reaction temperature was 380°C, the reaction conversion rate was 95.6%, and the selectivity was 92.3%.

[0033] Comparative Example 2 Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, the reaction temperature was 300°C, the reaction conversion rate was 41.6%, and the selectivity was 99.8%.

[0034] Comparative Example 3 Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:10, the feed rate was 0.17 mL / min, the ammonia flow rate was 100 mL / min, the reaction temperature was 340°C, the reaction conversion rate was 90.6%, and the selectivity was 97.3%.

[0035] Comparative Example 4 Caprolactam was dissolved in anhydrous acetonitrile at 25-30°C and then introduced into a fixed bed reactor containing 100 mL of an acid-modified molecular sieve catalyst. Ammonia was introduced into the fixed bed reactor for reaction, and the product was cooled to 80°C and then distilled to obtain aminocapronitrile; the mass ratio of caprolactam to acetonitrile was 1:1, the feed rate was 0.17 mL / min, the ammonia flow rate was 50 mL / min, the reaction temperature was 340°C, the reaction conversion rate was 82.4%, and the selectivity was 77.8%.

[0036] The caprolactam conversion rate and 6-aminocapronitrile selectivity of the above-mentioned embodiment and comparative example products were detected and calculated, and the calculation formula is as follows: Caprolactam conversion rate = (1-mass of caprolactam in the product / feed amount of caprolactam) * 100%; Aminocapronitrile selectivity=(mass of 6-aminocapronitrile in the product / 112) / (caprolactam conversion rate in the product*feed amount of caprolactam / 113)*100%.

[0037] The test results are shown in the table below.

[0038] Comparative Example 1 and Comparative Example 2 significantly increase / decrease the reaction temperature, respectively. It can be seen that increasing the temperature is beneficial to the conversion of caprolactam, but it will also bring about side reactions, affecting the selectivity of aminocapronitrile, and the higher the temperature, the worse the selectivity; while lowering the reaction temperature is just the opposite, the lower the temperature, the lower the conversion rate.

[0039] Comparative Example 3 increases the acetonitrile content during feeding, which dilutes the caprolactam solution, reduces the reaction efficiency, and also slightly decreases the conversion rate and selectivity.

[0040] In Comparative Example 4, the ammonia flow rate was reduced, and it was found that the caprolactam conversion rate and the aminocapronitrile selectivity decreased significantly. This was because the ammonia was insufficient and the water generated by the reaction could not be effectively removed, making it difficult for the reaction to proceed in the forward direction.

[0041] It can be seen from the above comparative data that by adopting the amination dehydration reaction conditions provided by the present invention, especially the appropriate selection of raw material ratio, reaction temperature and ammonia feed rate, the caprolactam conversion rate is greater than 92%, and the aminocapronitrile selectivity is greater than 99%, taking into account both the raw material conversion rate and the product selectivity, and achieving the optimal synthesis effect.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations, such as changing the type of solvent and the catalyst for further reaction of the common TMQ, temperature / time, different reaction modes, such as intermittent and continuous, etc. Any modification, equivalent substitution, improvement, etc. (such as the use of acetone derivatives, etc.) made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for synthesizing aminocapronitrile from caprolactam, characterized in that The method comprises the following steps: S1: caprolactam is dissolved in anhydrous acetonitrile to prepare a caprolactam acetonitrile mixed solution, wherein the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-15:1; S2: passing ammonia gas and the mixed solution in S1 into a fixed bed reactor filled with a phosphoric acid-modified molecular sieve catalyst for ammonia dehydration reaction to obtain a product, the reaction temperature being 300-400°C; S3: After the reaction product is cooled, gas-liquid separation is performed, the separated ammonia gas is recovered, and the separated liquid is distilled to obtain the reaction product aminocapronitrile.

2. The method according to claim 1, characterized in that In step S1, the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-10:

1.

3. The method according to claim 1 or 2, characterized in that: In step S1, the mass ratio of anhydrous acetonitrile to caprolactam is 1:1-4:

1.

4. The method according to claim 1, characterized in that: In step S2, the mixed liquid feed temperature is room temperature.

5. The method according to claim 1, characterized in that: In step S2, the mixed solution feeding rate is 0.1-0.3 mL / min.

6. The method according to claim 1, characterized in that: In step S2, the ammonia flow rate is 50-150 mL / min.

7. The method according to claim 1 or 6, characterized in that: In step S2, the ammonia flow rate is 80-100 mL / min.

8. The method according to claim 1, characterized in that: The reaction temperature in step S2 is 340-350°C.

9. The method according to claim 1, characterized in that: In step S3, the reaction product is cooled to 100-150°C.

10. The method according to claim 1 or 9, characterized in that: In step S3, the reaction product is cooled to 100-120°C.

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