A low ammonia ratio fixed bed catalyst for preparing 6-aminocapronitrile by a vapor phase process and preparation method thereof

Abstract

The present invention relates to a low-ammonia ratio fixed-bed catalyst for preparing 6-aminocapronitrile by a vapor phase process and a preparation method thereof. The fixed-bed catalyst comprises the following components, based on 100 wt% of the total weight of the catalyst: a) 15-50 wt% of silicalite-1 molecular sieve; b) 10-30 wt% of aluminum nitride; c) 5-25 wt% of silicon oxide provided as silica sol; d) 5-10 wt% of aluminum oxide provided as pseudo-boehmite; and e) 5-10 wt% of attapulgite. The catalyst of the present invention exhibits high conversion and selectivity in the vapor phase process for preparing 6-aminocapronitrile under low ammonia ratio conditions, thereby improving the competitiveness of the device.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic science and chemical technology. Specifically, the present invention relates to a method for preparing a catalyst for preparing 6-aminocapronitrile by a vapor phase process, the catalyst prepared by the method, and the use of the catalyst in the preparation of 6-aminocapronitrile. Background Art

[0002] Hexamethylenediamine (HMDA) is an important chemical raw material and intermediate in organic synthesis, primarily used in the production of nylon 66, nylon 610, and polyurethane (PU) materials. In recent years, due to the continuous increase in caprolactam production capacity and a significant caprolactam oversupply, the route of ammonia dehydration of caprolactam to produce 6-aminocapronitrile, followed by hydrogenation to produce 1,6-hexamethylenediamine has attracted considerable attention. The preparation of 6-aminocapronitrile is a key step in the hexamethylenediamine production line. To improve caprolactam conversion and aminocapronitrile selectivity, many research and production units increase the ammonia mass ratio to achieve this goal. However, this significantly increases the energy consumption and product cost of the equipment. The high total space velocity also significantly limits the reactor configuration and catalyst shape.

[0003] The ammonia ratios in patent applications JP33-10790, JP41-14092, and JP43-18687 are all above 25, which results in a very high total space velocity. This leads to high energy consumption for material preheating and ammonia circulation. This reaction is endothermic, and high space velocities place high demands on both reactor design and catalyst configuration.

[0004] In patent application CN 107602416A, when the ammonia molar ratio is 16, the conversion rate is 57.3% and the selectivity is 97.8%. When the conversion rate is too low, it will cause a lot of trouble in separating the reaction materials and the raw material cost will also be greatly increased.

[0005] Therefore, in order to reduce costs and increase the maximum profit of manufacturers, a fixed bed catalyst with high conversion rate, high selectivity and low ammonia ratio is urgently needed. Summary of the Invention

[0006] In response to the technical deficiencies, the present invention provides a catalyst with a low ammonia ratio for preparing 6-aminocapronitrile by the ammoniation of caprolactam. The catalyst has high caprolactam conversion, high 6-aminocapronitrile selectivity, a low ammonia ratio, and can achieve the level of fixed-bed operation.

[0007] To achieve the above object, in one aspect, the present invention provides a fixed bed catalyst comprising the following components based on 100 wt% of the total weight of the catalyst:

[0008] a) 15-50 wt% silicalite-1 molecular sieve;

[0009] b) 10-30 wt% aluminum nitride;

[0010] c) 5-25 wt% of silicon oxide provided as silica sol;

[0011] d) 5-10 wt% of alumina provided as pseudo-boehmite;

[0012] e) 5-10 wt% of attapulgite.

[0013] In a specific embodiment, the aluminum nitride is macroporous aluminum nitride with a pore size of ≥20 nm.

[0014] In a specific embodiment, the catalyst can be further treated with an aqueous solution of ammonia and ammonium phosphate to ammoniate the catalyst surface, and the surface loading of phosphorus is 0.5-5 wt% of the total weight of the catalyst.

[0015] In a specific embodiment, based on 100 wt% of the total weight of the catalyst, the catalyst comprises the following components:

[0016] a) 40-45 wt% silicalite-1 all-silicon molecular sieve;

[0017] b) 20-25 wt% aluminum nitride;

[0018] c) 10-15 wt% of silicon oxide provided as silica sol;

[0019] d) 5-10 wt% of alumina provided as pseudo-boehmite;

[0020] e) 5-10 wt% of attapulgite;

[0021] f) 0.5-1 wt% surface-loaded phosphorus.

[0022] On the other hand, the present invention also provides a method for preparing the fixed bed catalyst, the method comprising the following steps:

[0023] 1) Calcinate the silicalite-1 all-silicon molecular sieve powder to remove the template agent to prepare H-type silicalite-1 molecular sieve;

[0024] 2) The H-type silicalite-1 molecular sieve obtained in step 1), aluminum nitride, attapulgite, pseudo-boehmite, and Tianqing powder are added to a mixer in a certain proportion and mixed, and then the acidic silica sol and acetic acid aqueous solution are added to the mixer for mixing, extrusion molding, drying, and calcination.

[0025] In a specific embodiment, the method further comprises the following step 3) after step 2):

[0026] The product obtained in step 2) is subjected to hydrothermal treatment, washed with deionized water, dried and calcined.

[0027] In a specific embodiment, the method further comprises the following step 4) after step 3):

[0028] The product obtained in step 3) and an aqueous solution of (NH4)3PO4 and NH3·H2O are added to a hydrothermal reaction kettle to carry out a hydrothermal reaction, washed with deionized water, dried, and calcined.

[0029] In a specific embodiment, in step 1), silicalite-1 molecular sieve is added to a 10wt% aqueous solution of ammonium chloride and stirred at 70-90°C for 0.5-4 hours, followed by filtration. The filter cake is stirred with deionized water, filtered, and washed until the pH value is 6.5-7.0. The filter cake is then dried in air at 100-120°C for 8 hours and calcined at 450-550°C for 4 hours. The above steps are repeated three times, and finally tablets are formed.

[0030] In a specific embodiment, in step 2), the H-type silicalite-1 molecular sieve, aluminum nitride, attapulgite, pseudo-boehmite, and Tianqing powder obtained in step 1 are added to a mixer in a certain proportion and mixed for 10-15 minutes. Then, the acidic silica sol and the acetic acid aqueous solution are added to the mixer and mixed for 20-30 minutes, extruded into four-leaf clover strips with a diameter of 2.5-3 mm, dried at 120°C for 6-8 hours, and then crushed into four-leaf clover particles of 3-8 mm, and calcined at 550°C for 3-5 hours.

[0031] In a specific embodiment, in step 2), the silica sol contains 25-45% silicon oxide, and the concentration of the acetic acid aqueous solution is 5-25%.

[0032] In a specific embodiment, in step 3), the product obtained in step 2) is crushed into pieces with a length of 3-8 mm, deionized water is added thereto, and the pieces are hydroheated at 90-120° C. for 2 hours, filtered, washed with deionized water, dried at 100-120° C. for 8-12 hours, and calcined at 450-550° C. for 4-5 hours.

[0033] In a specific embodiment, in step 4), the product obtained in step 3) and the aqueous solution of (NH4)3PO4 and NH3·H2O are added to a hydrothermal reactor, hydrothermally heated at 90-110°C for 2 hours, filtered, washed with deionized water, dried in air at 100-120°C for 4-8 hours, and then calcined at 400-600°C for 3-5 hours.

[0034] In a specific embodiment, in step 4), the aqueous solution of (NH4)3PO4 and NH3·H2O is a mixed solution of a 10 wt% aqueous solution of (NH4)3PO4 and a 10-26 wt% aqueous solution of NH3·H2O in a mass ratio of 1:1-5.

[0035] In another aspect, the present invention provides use of the fixed-bed catalyst in the vapor phase preparation of 6-aminocapronitrile.

[0036] In another aspect, the present invention provides a method for preparing 6-aminocapronitrile by a vapor phase process, the method comprising carrying out an amination reaction of caprolactam with ammonia under the catalytic action of the above-mentioned fixed bed catalyst to prepare 6-aminocapronitrile.

[0037] In a specific embodiment, in the amination reaction, the reaction temperature is 320-400°C, the caprolactam space velocity is 2.75-3.8h -1 , the molar ratio of ammonia to caprolactam is 3-10, preferably, the molar ratio of ammonia to caprolactam is 4-6.

[0038] The present invention has the following beneficial technical effects:

[0039] 1. The fixed-bed catalyst provided by the present invention has a simple molding process and inexpensive materials. Moreover, the fixed-bed catalyst provided by the present invention still has high conversion rate and selectivity under low ammonia ratio conditions. The fixed-bed catalyst of the present application has a lower ammonia ratio than that reported in the prior art in the preparation of 6-aminocapronitrile from caprolactam.

[0040] 2. The catalyst of the present application improves the conversion rate and selectivity of the catalyst through the active components of all-silicon S-1 molecular sieve and macroporous aluminum nitride.

[0041] 3. In this application, the characteristic of aluminum nitride being slightly soluble in water is utilized, and the all-silicon S-1 molecular sieve and aluminum nitride are mixed and formed and then subjected to hydrothermal treatment, which further increases the pore structure of the catalyst, thereby further improving the conversion rate and selectivity.

[0042] 4. The catalyst of this application is also treated with aqueous ammonia and ammonium phosphate solution to increase the weakly acidic sites on the catalyst surface and ammoniate the catalyst surface. This allows the reaction conversion rate to reach over 90%, greatly improving the reaction efficiency, reducing subsequent separation costs, and enhancing the competitiveness of the device. DETAILED DESCRIPTION

[0043] The technical solutions of this application are described in detail below through specific examples to facilitate a better understanding of the present invention by those skilled in the art. These examples are not intended to limit the scope of this application, which encompasses any equivalent or alternative forms made by those skilled in the art based on their understanding of this application. The silicalite-1 molecular sieve was prepared in the laboratory using patent CN107337213A. Aluminum nitride was purchased from Hunan Xiangci Science and Technology Co., Ltd., and silica sol was purchased from Qingdao Ocean Chemical Co., Ltd.

[0044] Preparation Example 1

[0045] 1000g of silicalite-1 molecular sieve was added to a 5L round-bottom flask, followed by 2L of a 10wt% aqueous solution of ammonium chloride, stirred at 80°C for 30 minutes, and filtered. The filter cake was added to the original round-bottom flask, and 2L of deionized water was added, stirred for 15 minutes, filtered, and washed until the pH was 6.5. The filter cake was then dried in air at 105°C for 8 hours and calcined at 550°C for 4 hours. This process was repeated three times to obtain the active silicalite-1 molecular sieve, which was pressed into tablets as Catalyst A.

[0046] Preparation Example 2

[0047] The purchased aluminum nitride powder is pressed into tablets and used as catalyst B.

[0048] Preparation Example 3

[0049] 450 g of the catalyst A prepared in Preparation Example 1, 200 g of aluminum nitride, 60 g of attapulgite, 130 g of pseudo-boehmite, and 50 g of Tianqing powder were first added to a mixer and mixed. After 15 minutes, 500 g of acidic silica sol (40% silicon oxide) and 100 g of a 10% acetic acid aqueous solution were added to the mixer and mixed for 30 minutes. The mixture was extruded into four-leaf clover strips with a diameter of 2.5 mm, dried at 120°C for 6 hours, and then crushed into four-leaf clover particles of 3-8 mm. The catalyst C was calcined at 550°C for 4 hours.

[0050] Preparation Example 4

[0051] 2L of deionized water and 900g of catalyst C crushed to 3-8mm in length were added to the hydrothermal autoclave, and the mixture was hydrothermaled at 110°C for 4 hours, filtered, washed 4 times with 8L of deionized water, dried at 120°C for 8 hours, and calcined at 550°C for 4 hours to obtain catalyst D.

[0052] Preparation Example 5

[0053] 500 g of catalyst D obtained in Example 4 and 1 L of a mixed solution of 10 wt% (NH4)3PO4 and 15 wt% NH3·H2O in a mass ratio of 1:1 were added to a hydrothermal reactor, hydroheated at 90°C for 2 hours, filtered, washed four times with 4 L of deionized water, dried in air at 120°C for 8 hours, and then calcined at 500°C for 4 hours to obtain modified catalyst E.

[0054] Preparation Example 6

[0055] Except that the hydrothermal temperature in Example 5 was changed to 110° C., other conditions remained unchanged to obtain modified catalyst F.

[0056] Examples 1-6

[0057] In Examples 1-6, the catalysts prepared in Examples 1-6 were used in fixed-bed reactors to carry out the amination of caprolactam to produce 6-aminocapronitrile. The reaction conditions were: catalyst loading of 500 g, reaction temperature of 350° C., caprolactam space velocity of 3.8 h-1 / 2. -1 The molar ratio of ammonia to caprolactam was 6. The material after the reaction was subjected to chromatographic analysis, and the peaks before caprolactam were called light impurities, and the peaks after caprolactam were called heavy impurities. The reaction results are shown in Table 1 below.

[0058] Table 1

[0059] Example catalyst Initial conversion rate % Initial selectivity% Heavy impurity content% Light impurity content% 1 A 55.5 97.9 1.9 0.2 2 B 60.2 97.3 0.2 1.5 3 C 76.2 98.5 1.0 0.5 4 D 85.5 99.1 0.5 0.4 5 E 92.1 99.0 0.5 0.5 6 F 92.4 98.9 0.5 0.6

[0060] The following conclusions can be drawn from the reaction results of the above Examples 1-6:

[0061] S-1 all-silicon molecular sieve is used as a catalyst (such as preparation example 1), and the amount of light impurities generated is very low. However, due to the small pore size, the reaction materials are not conducive to timely desorption and further react to generate heavy impurities, and the conversion rate is low.

[0062] When aluminum nitride alone is used as a catalyst (such as Preparation Example 2), the amount of heavy impurities generated is relatively low, but the light impurity content is relatively high due to the weak acidity of the surface, and the conversion rate is relatively low due to the large pore size and the lack of micropore effect.

[0063] Catalyst C, obtained by mixing and molding S-1 all-silicon molecular sieve, aluminum nitride, and various binders, exhibits high conversion and selectivity, with significantly reduced carbon deposits. Furthermore, to further enhance catalyst performance, the present invention further hydrothermally treats the molded composite catalyst, leveraging the hydrolysis properties of aluminum nitride to create more macropores in the catalyst, further facilitating material diffusion. The resulting catalyst, Catalyst D, exhibits even higher performance. Catalyst E, which undergoes surface amination and phosphorus modification, further improves conversion and reduces caprolactam circulation. This is likely due to the ammonia coating of some of the strong acidic sites on the catalyst surface, while phosphorus provides a further portion of weaker acidic sites, further enhancing conversion. This further reduces energy consumption and separation costs.

[0064] In summary, the present application adopts S-1 all-silicon molecular sieve and weakly acidic macroporous aluminum nitride as the main active bodies, adds silica sol and a binder, mixes and prepares four-leaf clover-shaped particles, and then hydrolyzes the aluminum nitride and modifies the surface with phosphorus ammoniate to obtain a new type of fixed bed catalyst. The catalyst exhibits high conversion rate and selectivity, low ammonia ratio, and reduced content of heavy and light impurities in the reaction of preparing 6-aminocapronitrile by vapor phase method. Therefore, the fixed bed catalyst provided by the present application has great application and promotion prospects in the preparation of 6-aminocapronitrile by amination of caprolactam.

Claims

1. A fixed-bed catalyst for preparing 6-aminocapronitrile by an aminating reaction of caprolactam with ammonia, comprising the following components based on 100 wt % of the total weight of the catalyst: a) 40-50 wt% silicalite-1 molecular sieve; b) 20-30 wt% aluminum nitride, wherein the aluminum nitride is macroporous aluminum nitride with a pore size of ≥20 nm; c) 5-25 wt% of silicon oxide provided as silica sol; d) 5-10 wt% alumina provided as pseudo-boehmite; and e) 5-10 wt% attapulgite, in, The fixed bed catalyst is prepared by a method comprising the following steps: 1) Calcination of silicalite-1 molecular sieve powder to remove the template to prepare H-type silicalite-1 molecular sieve; 2) adding the H-type silicalite-1 molecular sieve, aluminum nitride, attapulgite, pseudo-boehmite, and Tianqing powder obtained in step 1) to a mixer in a certain proportion and mixing them, then adding the acidic silica sol and acetic acid aqueous solution to the mixer and mixing them, extruding, drying, and calcining; as well as 3) The product obtained in step 2) is subjected to hydrothermal treatment, washed with deionized water, dried and calcined.

2. The fixed bed catalyst according to claim 1, wherein The catalyst is further treated with an aqueous solution of ammonia and ammonium phosphate to ammoniate the surface of the catalyst, and the surface loading of phosphorus is 0.5-5 wt % of the total weight of the catalyst.

3. The fixed bed catalyst according to claim 1, wherein Based on 100 wt% of the total weight of the catalyst, the catalyst comprises the following components: a) 40-45 wt% silicalite-1 all-silicon molecular sieve; b) 20-25 wt% aluminum nitride; c) 10-15 wt% of silicon oxide provided as silica sol; d) 5-10 wt% alumina provided as pseudo-boehmite; e) 5-10 wt% attapulgite; and f) 0.5-1 wt% surface-loaded phosphorus.

4. A method for preparing the fixed bed catalyst according to any one of claims 1 to 3, comprising the following steps: 1). Calcinate the silicalite-1 all-silicon molecular sieve powder to remove the template agent and prepare H-type silicalite-1 molecular sieve; 2) The step 1) obtained H-type silicalite-1 molecular sieve, aluminum nitride, attapulgite, pseudo-boehmite, Tian Qing powder according to a certain proportion was added to the mixer and mixed, after which the acidic silica sol and aqueous acetic acid solution were added to the mixer and mixed, extruded, dried, and calcined; 3) The product obtained in step 2) is subjected to hydrothermal treatment, washed with deionized water, dried and calcined.

5. The method according to claim 4, wherein The method further comprises the following step 4) after step 3): The product obtained in step 3) and an aqueous solution of (NH4)3PO4 and NH3·H2O are added to a hydrothermal reaction kettle to carry out a hydrothermal reaction, washed with deionized water, dried, and calcined.

6. The method according to claim 5, wherein In step 1), adding silicalite-1 molecular sieve to a 10 wt% aqueous solution of ammonium chloride, stirring at 70-90° C. for 0.5-4 hours, and then filtering with suction. The filter cake is stirred with deionized water, filtered with suction, and the filter cake is washed until the pH value is 6.5-7.

0. The filter cake is then dried in air at 100-120° C. for 8 hours, calcined at 450-550° C. for 4 hours, and the above steps are repeated three times before tableting; and / or In step 2), the H-type silicalite-1 molecular sieve, aluminum nitride, attapulgite, pseudo-boehmite, and Tianqing powder obtained in step 1 are added to a mixer in a certain proportion and mixed for 10-15 minutes, and then the acidic silica sol and acetic acid aqueous solution are added to the mixer and mixed for 20-30 minutes, extruded into four-leaf clover strips with a diameter of 2.5-3 mm, dried at 120° C. for 6-8 hours, and then crushed into four-leaf clover particles of 3-8 mm, and calcined at 550° C. for 3-5 hours; and / or In step 3), the product obtained in step 2) is crushed into pieces having a length of 3-8 mm, deionized water is added thereto, and the mixture is hydrothermaled at 90-120° C. for 2 hours, filtered, washed with deionized water, dried at 100-120° C. for 8-12 hours, and calcined at 450-550° C. for 4-5 hours; and / or In step 4), the product obtained in step 3) and the aqueous solution of (NH4)3PO4 and NH3·H2O are added to a hydrothermal reactor, hydrothermally heated at 90-110°C for 2 hours, filtered, washed with deionized water, dried in air at 100-120°C for 4-8 hours, and then calcined at 400-600°C for 3-5 hours.

7. The method according to claim 6, wherein: In step 2), the silica sol contains 25-45% silicon oxide, and the concentration of the acetic acid aqueous solution is 5-25%.

8. The method according to claim 6, wherein: In step 4), the aqueous solution of (NH4)3PO4 and NH3·H2O is a mixed solution of a 10 wt% aqueous solution of (NH4)3PO4 and a 10-26 wt% aqueous solution of NH3·H2O in a mass ratio of 1:1-5.

9. Use of the fixed bed catalyst according to any one of claims 1 to 3 in the gas phase preparation of 6-aminocapronitrile, wherein The gas phase method for preparing 6-aminocapronitrile comprises subjecting caprolactam to an amination reaction with ammonia to prepare 6-aminocapronitrile.

10. A method for preparing 6-aminocapronitrile by a vapor phase process, the method comprising subjecting caprolactam to an amination reaction with ammonia under the catalytic action of the fixed bed catalyst according to any one of claims 1 to 3 to prepare 6-aminocapronitrile.

11. The method according to claim 10, wherein In the amination reaction, the reaction temperature is 320-400°C, and the caprolactam space velocity is 2.75-3.8 h -1 , the molar ratio of ammonia to caprolactam is 3-10.

12. The method according to claim 11, wherein: The molar ratio of ammonia to caprolactam is 4-6.