Preparation method and application of phosphoric acid modified molecular sieve catalyst for synthesizing hexamethylenediamine key intermediate

Abstract

The invention belongs to the technical field of fine chemical engineering, and provides a preparation method of a catalyst for synthesizing hexamethylenediamine intermediate aminocapronitrile and an application of the catalyst, the catalyst can be prepared by dipping a modified ZSM-5 molecular sieve with phosphoric acid, filtering, drying and calcining, vaporized caprolactam reacts with ammonia gas by using the catalyst to obtain aminocapronitrile, and then the hexamethylenediamine intermediate aminocapronitrile is synthesized. 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 relates to a preparation method of a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile and application of the catalyst. 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 institutions. 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 has been basically eliminated abroad.

[0004] The production of hexamethylenediamine by the caprolactam process requires the following three steps: the first step is the amination ring-opening reaction of caprolactam and ammonia to generate 6-aminocaproamide; the second step is the dehydration reaction of 6-aminocaproamide to remove oxygen atoms to generate 6-aminocapronitrile; the third step is the hydrogenation reaction of 6-aminocapronitrile and hydrogen to obtain hexamethylenediamine. At present, the core of this technology lies in the amination dehydration process, and the selection of catalysts in this process is very important.

[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] 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 relatively early, the catalysts used all had problems such as low activity, low product yield, and high energy consumption. Summary of the invention

[0008] The main purpose of the present invention is to provide a method for preparing a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile and the application of the catalyst, so as to solve the problem of low activity of the catalyst for preparing 6-aminocapronitrile by ammoniation of caprolactam in the prior art.

[0009] In order to achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing a phosphoric acid-modified molecular sieve catalyst for synthesizing a key intermediate of hexamethylenediamine is provided, wherein a molecular sieve catalyst for synthesizing a key intermediate of hexamethylenediamine is obtained by impregnating a ZSM-5 molecular sieve with phosphoric acid of different concentrations, performing solid-liquid separation, drying, and calcining.

[0010] Furthermore, the ZSM-5 molecular sieve is a spherical aggregate of 0.3-1 um, and the spherical aggregate contains primary particles with a particle size of 10-50 nm.

[0011] Furthermore, the relative degree of solidification of the ZSM-5 molecular sieve is 96% to 101%.

[0012] Furthermore, the ZSM-5 molecular sieve SiO 2 and Al 2 O 3 The molar ratio is 27:1 or 46:1.

[0013] Furthermore, the concentration of the phosphoric acid solution is 45-85%.

[0014] Furthermore, the immersion temperature is 25°C.

[0015] Furthermore, the solid-liquid separation method is vacuum filtration, and the temperature for vacuum removal of solvent is 80-150°C; the drying temperature is 100-120°C, preferably 120°C, and the drying time is 10-12h, preferably 8h; the roasting temperature is 300-450°C, preferably 400°C, and the roasting time is 10-24h, preferably 12h.

[0016] According to another aspect of the present invention, a method for synthesizing aminocapronitrile, an intermediate of hexamethylenediamine, is provided, wherein a catalyst obtained by any of the above-mentioned preparation methods is used to catalyze the amination of caprolactam to synthesize 6-aminocapronitrile.

[0017] In the above synthesis method, when the catalyst is heated to a certain temperature, ammonia and acetonitrile solution of caprolactam are introduced to react at a reaction temperature of 280-300°C and a space velocity of 0.8h -1 . Beneficial Effects

[0018] The phosphoric acid modified molecular sieve prepared by the method of the present invention is used as a catalyst for preparing 6-aminocapronitrile by a caprolactam liquid phase method. Caprolactam is used as a raw material, the phosphoric acid modified molecular sieve is used as a catalyst, and 6-aminocapronitrile is prepared by a gas phase method. The reaction conversion rate is high, the selectivity is good, the preparation process is simple, and the energy consumption is low. The reaction temperature is lower than 300° C., the energy consumption is low, the caprolactam conversion rate is greater than 90%, and the aminocapronitrile selectivity is greater than 99%, and the application value is high. Implementation

[0019] 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 1

[0020] Take 80g ZSM-5 molecular sieve, SiO 2 and Al 2 O 3 The molar ratio is 46:1. After impregnation with 85% phosphoric acid for 12 hours, the mixture is filtered, dried at 120°C for 8 hours, and calcined at 300°C for 8 hours, a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is finally obtained. Example 2

[0021] The difference between Example 2 and Example 1 is that SiO 2 and Al 2 O 3 The molar ratio is 27:1, and a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is finally prepared. Example 3

[0022] The difference between Example 3 and Example 1 is that the calcination temperature is 400° C., and a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is finally obtained. Example 4

[0023] The difference between Example 4 and Example 1 is that the calcination temperature is 400° C. and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained. Example 5

[0024] The difference between Example 5 and Example 1 is that the calcination temperature is 400° C., the calcination time is 24 h, and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained. Example 6

[0025] The difference between Example 6 and Example 1 is that the calcination temperature is 400° C., the calcination time is 12 h, the phosphoric acid concentration is 75%, and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained. Example 7

[0026] The difference between Example 7 and Example 1 is that the calcination temperature is 400° C., the calcination time is 12 h, the phosphoric acid concentration is 65%, and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained. Example 8

[0027] The difference between Example 8 and Example 1 is that the calcination temperature is 400° C., the calcination time is 12 h, the phosphoric acid concentration is 55%, and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained. Example 9

[0028] The difference between Example 9 and Example 1 is that the calcination temperature is 400° C., the calcination time is 12 h, the phosphoric acid concentration is 45%, and the calcination time is 12 h, and finally a phosphoric acid-modified molecular sieve catalyst for synthesizing aminocapronitrile is obtained.

[0029] The phosphoric acid-modified molecular sieve catalysts for synthesizing aminocapronitrile prepared in Examples 1 to 9 were respectively heated at a space velocity of 0.8 h -1 The caprolactam was mixed with ammonia and passed through a catalyst bed at 280°C to undergo an amination reaction, with an ammonia / caprolactam molar ratio of 35:1 to generate 6-aminocapronitrile. The conversion rate of caprolactam was calculated and the results are listed in Table 1.

[0030] Comparative Example 1 Caprolactam and ammonia were fully mixed, the ammonia / caprolactam molar ratio was 35:1, the reaction temperature was 280°C, the catalyst was calcium phosphate, the reaction conversion rate was 45.6%, and the selectivity was 95.3%.

[0031] Comparative Example 2 Caprolactam and ammonia were fully mixed, the ammonia / caprolactam molar ratio was 35:1, the reaction temperature was 400°C, the catalyst was phosphoric acid modified molecular sieve, the reaction conversion rate was 91.6%, and the selectivity was 96.3%.

[0032] By comparing Comparative Example 1 with Examples 1-9, it can be seen that the conversion rate of the calcium phosphate catalyst is only 45.6%. By comparing Comparative Example 2 with Examples 1-9, it can be seen that although Comparative Example 2 finally obtains a higher conversion rate and selectivity, the reaction temperature is as high as 400° C., and the production cost is high. This shows that the phosphoric acid-modified molecular sieve catalyst of the present invention has a higher reaction selectivity and a better conversion rate under mild reaction conditions.

[0033] Table 1 Caprolactam conversion and aminocapronitrile selectivity

[0034] 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 preparing a phosphoric acid-modified molecular sieve catalyst for synthesizing a key intermediate of hexamethylenediamine, characterized in that: The molecular sieve catalyst for synthesizing the key intermediate of hexamethylenediamine is obtained by impregnating ZSM-5 molecular sieve with phosphoric acid of different concentrations, performing solid-liquid separation, drying and calcining.

2. The preparation method according to claim 1, characterized in that: The ZSM-5 molecular sieve is a spherical aggregate of 0.3-1 μm, and the spherical aggregate contains primary particles with a particle size of 10-50 nm.

3. The preparation method according to claim 1 or 2, characterized in that: The relative fineness of the ZSM-5 molecular sieve is 96% to 101%.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve is 27:1 or 46:

1.

5. The preparation method according to claim 1, characterized in that: The concentration of the phosphoric acid solution is 45-85%.

6. The preparation method according to claim 1, characterized in that: The immersion temperature is 25°C.

7. The preparation method according to claim 1, characterized in that: The solid-liquid separation method is vacuum filtration, and the temperature for vacuum solvent removal is 80-150°C; the drying temperature is 100-120°C, and the drying time is 10-12h; the calcination temperature is 300-450°C, and the calcination time is 10-24h.

8. The preparation method according to claim 1 or 7, characterized in that: The drying temperature is 120° C. and the drying time is 8 hours; the calcining temperature is 400° C. and the calcining time is 12 hours.

9. A method for synthesizing aminocapronitrile, an intermediate of hexamethylenediamine, characterized in that The catalyst obtained by the preparation method according to any one of claims 1 to 8 is used to catalyze the amination of caprolactam to synthesize 6-aminocapronitrile.

10. The synthesis method according to claim 9, characterized in that: When the catalyst is heated to a certain temperature, ammonia and acetonitrile solution of caprolactam are introduced to react at a temperature of 280-300°C and a space velocity of 0.8h -1 .

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