CN117003648A

CN117003648A - Method for preparing hexamethylenediamine from caprolactam

Info

Publication number: CN117003648A
Application number: CN202210476451.7A
Authority: CN
Inventors: 张晓昕; 任艳红; 王宣; 孙敏
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-11-07

Abstract

The present disclosure relates to a process for preparing hexamethylenediamine from caprolactam, comprising the steps of: under the condition of catalytic ammonification, caprolactam and ammonia gas are contacted with a first catalyst to carry out ammonification and dehydration reaction, so as to obtain a first product containing 6-aminocapronitrile; under the condition of catalytic hydrogenation reaction, the first product, hydrogen and a second catalyst are contacted for hydrogenationReacting to obtain a second product containing hexamethylenediamine; the first catalyst comprises 5-95 wt% of a titanium-containing carrier, 2-30 wt% of vanadium oxide, 0.5-10 wt% of phosphorus pentoxide, 1-20 wt% of metal M oxide and/or 0-5 wt% of inorganic oxide on a dry basis and based on the total weight of the first catalyst; the titanium-containing carrier comprises TiO ₂ And a titanium-containing molecular sieve, the inorganic oxide comprising Al ₂ O ₃ And SiO ₂ One or two of them.

Description

Method for preparing hexamethylenediamine from caprolactam

Technical Field

The present disclosure relates to the technical field of hexamethylenediamine preparation, and in particular, to a method for preparing hexamethylenediamine from caprolactam.

Background

Hexamethylenediamine is an important chemical raw material and is commonly used for synthesizing important industrial products such as nylon 66, nylon 610, HDI and the like. The production device of adiponitrile, which is a synthesis raw material of hexamethylenediamine, is not available in China, and the requirement of adiponitrile is completely dependent on import, so that the development of a new synthesis method is very important.

The synthesis of hexamethylenediamine from caprolactam is less reported, and is originally reported by US2234566 and US 2181140. U.S. patent No. 2234566 reports the synthesis of 6-aminocapronitrile with silica-supported copper as dehydration catalyst, caprolactam at a reaction temperature of 360 ℃ and an ammonia/caprolactam molar ratio of 6, and separation of unreacted caprolactam by distillation followed by catalytic hydrogenation of aminocapronitrile over a nickel or cobalt catalyst to hexamethylenediamine with a caprolactam conversion of 21.7% and a 6-aminocapronitrile yield of 25%, and does not focus on hexamethylenediamine yield in this patent. U.S. patent No. 3855267 reports that 6-aminocapronitrile selectivity is 87% by passing a mixture of ammonia and caprolactam over an aluminum phosphate catalyst at an ammonia/caprolactam molar ratio of 75 to 100. The two methods for preparing 6-aminocapronitrile have the defects of low catalyst activity and high energy consumption.

Chinese patent No. CN107739318A reports a method and apparatus for preparing 6-aminocapronitrile by a caprolactam liquid phase method, which uses phosphoric acid or phosphate as a catalyst, and the reaction temperature is about 280 ℃, but the yield is not high, and the analysis from the examples shows that the yield is about 50%. The method has the defects of complicated separation of the catalyst and the solvent, high energy consumption, low caprolactam conversion rate and the like. The method for synthesizing 6-aminocapronitrile from caprolactam reported in Chinese patent No. CN107602416A is comparable with that reported in patent U.S. Pat. No. 3, 2234566. The reported method for preparing 6-aminocapronitrile by a caprolactam gas phase method has the reaction temperature of about 350 ℃, wherein the contact time of caprolactam and ammonia gas is less than 1 second, and the process is difficult to control.

In the reaction process of preparing 6-aminocapronitrile from caprolactam, firstly, the caprolactam and ammonia gas undergo an ammonification ring-opening reaction, and then are dehydrated to produce 6-aminocapronitrile. The gas phase systems reported at present are all carried out under the conditions of high temperature and high ammonia/caprolactam molar ratio, the surface of the catalyst simultaneously carries out ring opening and dehydration, besides 6-aminocapronitrile, the catalyst also has the advantages of cracking deamination products and polyamide oligomers, and the caprolactam conversion rate and the 6-aminocapronitrile selectivity are low.

Therefore, although the technical research on preparing 6-aminocapronitrile by ammonification of caprolactam is earlier, the used catalyst has the problems of low activity, low product yield and the like.

Disclosure of Invention

It is an object of the present disclosure to provide a process for preparing hexamethylenediamine from caprolactam, which can improve caprolactam conversion and 6-aminocapronitrile selectivity and increase hexamethylenediamine yield.

To achieve the above object, the present disclosure provides a process for preparing hexamethylenediamine from caprolactam, the process comprising the steps of:

s1, under the condition of catalytic ammonification, enabling caprolactam and ammonia gas to contact a first catalyst for ammonification and dehydration reaction to obtain a first product containing 6-aminocapronitrile;

S2, under the condition of catalytic hydrogenation reaction, enabling the first product and hydrogen to contact with a second catalyst for hydrogenation reaction to obtain a second product containing hexamethylenediamine;

wherein the first catalyst comprises, on a dry basis and based on the total weight of the first catalyst, 5 to 95 wt% of a titanium-containing support, 2 to 30 wt% of a vanadium oxide, 0.5 to 10 wt% of phosphorus pentoxide, 1 to 20 wt% of a metal M oxide, and/or 0 to 5 wt% of an inorganic oxide; wherein the titanium-containing carrier comprises TiO ₂ And a titanium-containing molecular sieve, wherein the metal M is selected from one or more of VB element, VIB element, VIII element and lanthanum element, and the inorganic oxide comprises Al ₂ O ₃ And SiO ₂ One or two of them.

Optionally, in step S1, the catalytic ammonification reaction conditions include: the reaction temperature is 120-700 ℃, and the molar ratio of ammonia gas to caprolactam is (0.1-100): 1, the partial pressure of ammonia is 0.1-5.0MPa, and the weight hourly space velocity of caprolactam is 0.1-100h ^-1 The method comprises the steps of carrying out a first treatment on the surface of the Preferably, the catalytic ammoniation reaction conditions include: the reaction temperature is 200-450 ℃, and the mole ratio of ammonia gas to caprolactam is (1-10): 1, the partial pressure of ammonia is 0.2-3.0MPa, and the weight hourly space velocity of caprolactam is 0.5-20h ^-1 The method comprises the steps of carrying out a first treatment on the surface of the Alternatively, the ammonification dehydration reaction is performed in a fixed bed reactor.

Optionally, in step S1, the first catalyst comprises 30-90 wt.% of a titanium-containing support, 4-15 wt.% of a vanadium oxide, 1-5 wt.% of phosphorus pentoxide, 2-10 wt.% of a metal M oxide and/or 0.1-2 wt.% of an inorganic oxide, on a dry basis and based on the total weight of the first catalyst.

Alternatively, the TiO in the titanium-containing carrier, on a dry basis ₂ And titanium-containing molecular sieve in a weight ratio of 1: (0.01-10), preferably 1: (0.1-5); the titanium-containing molecular sieve comprises a titanium silicalite molecular sieve; the titanium silicalite molecular sieve is selected from one or more of HTS molecular sieve, TS-1 molecular sieve, TS-2 molecular sieve and TS-48 molecular sieve; optionally, the metal M is selected from one or more of tungsten, molybdenum, chromium, zinc, manganese, lanthanum, zirconium and iron; preferably one or more selected from tungsten, molybdenum and chromium, and more preferably one or two selected from molybdenum and tungsten.

Alternatively, the BET specific surface area of the first catalyst is 50-300m ² Per gram, the total pore volume is 0.1-0.4mL/g, and the micropore volume is 0.05-0.2mL/g; optionally, the shape of the first catalyst is selected from one or more of sphere, bar, cylinder, ring, clover, tetraleaf, honeycomb and butterfly.

Optionally, the first catalyst is prepared by a preparation method comprising the following steps: a. the vanadium source, water and acid are contacted to carry out oxidation-reduction reaction; adding a metal M source, a phosphorus source and a titanium-containing carrier into the reaction product to obtain a mixture; carrying out first drying treatment on the mixture to obtain an intermediate solid product; b. and sequentially carrying out forming treatment, second drying treatment and roasting treatment on the intermediate solid product.

Optionally, in step a, water: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is (0.5-2.0): (0.05-0.2): (0.05-0.5): (0.02-0.5): (0.01-1): 1, a step of; preferably (0.8-1.6): (0.05-0.1): (0.1-0.3): (0.04-0.3): (0.02-0.6): 1.

optionally, the vanadium source is selected from one or more of ammonium metavanadate, sodium metavanadate and vanadium pentoxide; the acid is one or more selected from oxalic acid, citric acid and nitric acid; the metal M in the metal M source is one or more selected from tungsten, molybdenum, chromium, zinc, manganese, lanthanum and iron; the metal M source is selected from one or more of nitrate, phosphate and chloride of metal M; preferably one or more selected from ammonium molybdate tetrahydrate, sodium tungstate, chromium nitrate and lanthanum nitrate; the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium hypophosphite, sodium dihydrogen phosphate and potassium dihydrogen phosphate.

Optionally, step a comprises: dissolving the vanadium source in water, and then adding the acid into the vanadium source solution to perform the oxidation reaction to obtain an oxidation reaction product; adding the metal M source and the phosphorus source into the oxidation reaction product, and performing first mixing to obtain a first mixture, wherein the temperature of the first mixture is optionally 50-100 ℃ for 60-300min; adding the titanium-containing carrier into the first mixture, and performing second mixing to obtain a second mixture, wherein the temperature of the second mixture is 30-80 ℃ and the time is 30-300min; carrying out the first drying treatment on the second mixture, and grinding the obtained product to obtain the intermediate solid product; optionally, the temperature of the first drying treatment is 80-150 ℃.

Optionally, the molding process in step b is extrusion molding; step b further comprises: extruding and mixing the intermediate solid product, a pore-expanding agent and an auxiliary agent, and then sequentially carrying out forming treatment, second drying treatment and roasting treatment; or the forming treatment in the step b is ball forming, and the step b further comprises: mixing the intermediate solid product with an inorganic oxide source, and then sequentially performing the molding treatment, the second drying treatment and the roasting treatment.

Alternatively, the pore-expanding agent is added in an amount of 0.5 to 10 wt%, preferably 1 to 5 wt%, on a dry basis and based on the added weight of the titanium-containing carrier; the extrusion aid is added in an amount of 0.5 to 4 wt%, preferably 0.5 to 2 wt%; the inorganic oxide source is added in an amount of 0.1 to 5% by weight, preferably 0.1 to 2.0% by weight, on a dry basis and based on the added weight of the titanium-containing carrier.

Optionally, in the step b, the pore-expanding agent is selected from one or more of sesbania powder, paraffin, stearic acid, glycerol, starch, polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyacrylamide, cellulose methyl ether, cellulose, polyalcohol and graphite; the extrusion aid is selected from one or more of organic acid, inorganic acid and inorganic base, preferably, the extrusion aid is selected from one or more of oxalic acid, tartaric acid, citric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, ammonia water, sodium hydroxide and potassium hydroxide; the addition form of the inorganic oxide source comprises inorganic oxide or inorganic oxide precursor; the inorganic oxide includes Al ₂ O ₃ And SiO ₂ One or two of the following components; the inorganic oxide precursor is selected from one or more of aluminum sol, silica sol and water glass.

Optionally, in step b, the conditions of the second drying process include: the temperature is 80-200deg.C, preferably 100-150deg.C; the time is 1-10h, preferably 2-4h; the roasting conditions include: the roasting temperature is 200-900 ℃, preferably 500-800 ℃; the calcination time is 0.5 to 10 hours, preferably 2 to 4 hours.

Optionally, in step S2, the catalytic hydrogenation reaction conditions include: the reaction temperature is 100-400 ℃, the reaction pressure is 0.5-20MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 0.1-1000:1, the weight hourly space velocity of the liquid feed is from 0.1 to 10h ^-1 The method comprises the steps of carrying out a first treatment on the surface of the PreferablyThe catalytic hydrogenation reaction conditions include: the reaction temperature is 150-350 ℃, the reaction pressure is 1.0-5.0MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 1-50:1, a weight hourly space velocity of the liquid feed of 0.5 to 5h ^-1 。

Optionally, in step S2, the catalytic hydrogenation reaction is performed in a slurry bed reactor, and the second catalyst comprises a Raney nickel hydrogenation catalyst; or the catalytic hydrogenation reaction is carried out in a fixed bed reactor, and the second catalyst is selected from supported hydrogenation catalysts; the supported hydrogenation catalyst is selected from one or more of nickel-based, cobalt-based and palladium-based catalysts; optionally, the nickel-based catalyst comprises 5-60 wt% nickel, 0-40 wt% cobalt, and 40-90 wt% first support; the cobalt-based catalyst comprises 5-60 wt% cobalt and 40-95 wt% second carrier; the palladium-based catalyst comprises 0.5 to 10 wt% palladium and 90 to 99.5 wt% of a third support; wherein the first support and the second support are each independently selected from one or both of silica and alumina; the third carrier is selected from one or two of activated carbon and alumina.

Optionally, the method further comprises: before step S2, carrying out first separation and purification treatment on the first product to obtain a 6-aminocapronitrile-rich product; then subjecting said 6-aminocapronitrile-rich product to said catalytic hydrogenation reaction; and after step S2, subjecting the second product to a second separation purification treatment.

According to the technical scheme, the method for preparing hexamethylenediamine from caprolactam is provided, the hexamethylenediamine is prepared from caprolactam serving as a raw material through ammonification and dehydration reaction and hydrogenation reaction, the caprolactam conversion rate and the 6-aminocapronitrile selectivity in the ammonification and dehydration reaction are high, and the catalyst has high catalytic stability under the long-time ammonification reaction event; in the hydrogenation reaction process, the yield of the hexamethylenediamine product is high; in addition, the HCN raw material adopted in the traditional process is not used in the reaction process of the method, and the reaction process is environment-friendly.

Additional features and advantages of the present disclosure will be set forth in the detailed description which follows.

Detailed Description

The following describes specific embodiments of the present disclosure in detail. It should be understood that the detailed description and specific examples, while indicating and illustrating the disclosure, are not intended to limit the disclosure.

The present disclosure provides a process for preparing hexamethylenediamine from caprolactam, the process comprising the steps of:

In the method provided by the disclosure, caprolactam is used as a raw material to prepare hexamethylenediamine through ammonification and dehydration reaction and hydrogenation reaction, the caprolactam conversion rate and the 6-aminocapronitrile selectivity in the ammonification and dehydration reaction are high, and the catalyst has higher catalytic stability under the long-time ammonification reaction event; in the hydrogenation reaction process, the yield of the hexamethylenediamine product is high; in addition, the HCN raw material adopted in the traditional process is not used in the reaction process of the method, and the reaction process is environment-friendly.

In addition, the inorganic oxide is added into the first catalyst adopted by the method, so that the strength of the catalyst can be improved, and the service life of the catalyst is prolonged; the first catalyst is also added with metal M oxide, so that the conversion rate of the first catalyst in the reaction of preparing 6-aminocapronitrile by ammonification of caprolactam and the selectivity of the target product 6-aminocapronitrile can be further improved, and the generation of byproducts is reduced.

In a preferred embodiment, in step S1, the first catalyst comprises, on a dry basis and based on the total weight of the first catalyst, 30-90 wt.% of a titanium-containing support, 4-15 wt.% of a vanadium oxide, 1-5 wt.% of phosphorus pentoxide, 2-10 wt.% of a metal M oxide and/or 0.1-2 wt.% of an inorganic oxide. When the content of each component of the first catalyst in the present disclosure meets the present embodiment, the conversion rate and the target product selectivity of the first catalyst in the reaction for preparing 6-aminocapronitrile by ammonification of caprolactam can be further improved.

In the present disclosure, the content of each component in the first catalyst is determined using an X-ray fluorescence spectrometer. The content of the titanium-containing carrier in the catalysts of the present disclosure was calculated as the total Ti element oxide obtained by XRF testing.

In one embodiment, the titanium-containing support comprises TiO on a dry basis ₂ And titanium-containing molecular sieve in a weight ratio of 1: (0.01-10), preferably 1: (0.1-5). The weight ratio of titanium dioxide to titanium-containing molecular sieve in the present disclosure is calculated as the mass ratio of the two materials added during the preparation process.

According to the present disclosure, tiO ₂ As is well known to those skilled in the art, rutile and anatase titania, preferably rutile, may be employed for the support of the catalytic material.

Titanium-containing molecular sieves are well known to those skilled in the art, and include titanium silicalite molecular sieves, in light of the present disclosure; the titanium silicalite molecular sieve is selected from one or more of HTS molecular sieve, TS-1, TS-2 and TS-48 molecular sieve.

In one embodiment, the metal M is selected from one or more of tungsten, molybdenum, chromium, zinc, manganese, lanthanum and iron; preferably one or more selected from tungsten, molybdenum and chromium, and more preferably one or two selected from molybdenum and tungsten.

In one embodiment, the BET specific surface area of the first catalyst is 50-300m ² Preferably 50 to 100m ² /g; total pore volume of 0.1-0.4mL/g, preferably 0.1-0.3 mL/g; the micropore volume is 0.05-0.2mL/g, preferably 0.05-0.1 mL/g.

In one embodiment, the first catalyst is a particulate shaped catalyst, the shape of the catalyst being selected from one or more of sphere, bar, cylinder, ring, clover, tetraleaf, honeycomb and butterfly, preferably in the form of a bar or a pellet with a diameter of 0.5-5.0 mm.

The first catalyst in the present disclosure may be used in various reactors, such as a fixed bed reactor, a moving bed reactor, or a fluidized bed reactor.

In one embodiment, the first catalyst is prepared by a preparation method comprising the steps of:

a. the vanadium source, water and acid are contacted to carry out oxidation-reduction reaction; adding a metal M source, a phosphorus source and a titanium-containing carrier into the reaction product to obtain a mixture; carrying out first drying treatment on the mixture to obtain an intermediate solid product;

b. and sequentially carrying out forming treatment, second drying treatment and roasting treatment on the intermediate solid product.

The method comprises the steps of firstly carrying out oxidation reaction on a vanadium source and acid to obtain an oxidation product (for example, carrying out oxidation reaction on the vanadium source and oxalic acid to obtain vanadyl oxalate), then mixing the oxidation product with a metal M source, a phosphorus source and a titanium-containing carrier, and drying to remove moisture to enable the vanadyl oxalate, the metal M source and the phosphorus source to be loaded on the titanium-containing carrier to obtain an intermediate solid product.

In one embodiment, in step a, water: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is (0.5-2.0): (0.05-0.2): (0.05-0.5): (0.02-0.5): (0.01-1): 1, a step of; preferably (0.8-1.6): (0.05-0.1): (0.1-0.3): (0.04-0.3): (0.02-0.6): 1.

in one embodiment, the vanadium source is selected from one or more of ammonium metavanadate, sodium metavanadate and vanadium pentoxide;

the acid is one or more selected from oxalic acid, citric acid and nitric acid;

the metal M in the metal M source is one or more selected from tungsten, molybdenum, chromium, zinc, manganese, lanthanum and iron; the metal M source is selected from one or more of nitrate, phosphate and chloride of metal M; preferably one or more of ammonium molybdate tetrahydrate, sodium tungstate, chromium nitrate and lanthanum nitrate;

the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium hypophosphite, sodium dihydrogen phosphate and potassium dihydrogen phosphate.

In a specific embodiment, step a comprises:

dissolving the vanadium source in water, and then adding the acid into the vanadium source solution to perform the oxidation reaction to obtain an oxidation reaction product;

adding the metal M source and the phosphorus source into the oxidation reaction product, and performing first mixing to obtain a first mixture, wherein the temperature of the first mixture is optionally 50-100 ℃ for 60-300min;

Adding the titanium-containing carrier into the first mixture, and performing second mixing to obtain a second mixture, wherein the temperature of the second mixture is 30-80 ℃ and the time is 30-300min;

carrying out the first drying treatment on the second mixture, and grinding the obtained product to obtain the intermediate solid product; optionally, the temperature of the first drying treatment is 80-150 ℃. Alternatively, it may be milled to a particle size of 30 μm or less. Wherein the abrasive particle size is the maximum particle size of the abrasive particles.

In one embodiment, the molding process in step b is extrusion molding; step b further comprises: and extruding and mixing the intermediate solid product with a pore-expanding agent and an auxiliary agent, and then sequentially carrying out the forming treatment, the second drying treatment and the roasting treatment.

In a preferred embodiment, the pore-expanding agent is added in an amount of 0.5 to 10 wt%, preferably 1 to 5 wt%, on a dry basis and based on the weight of the titanium-containing carrier; the extrusion aid is added in an amount of 0.5 to 4% by weight, preferably 0.5 to 2% by weight.

In a specific embodiment, the pore-expanding agent is selected from one or more of sesbania powder, paraffin, stearic acid, glycerol, starch, polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyacrylamide, cellulose methyl ether, cellulose, polyalcohol and graphite;

The extrusion aid is one or more selected from oxalic acid, tartaric acid, citric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, ammonia water, sodium hydroxide and potassium hydroxide. In the method, the pore expanding agent and the extrusion assisting agent are added in the step b, so that the forming treatment of the first catalyst can be facilitated, and the pore channels of the first catalyst can be increased.

In another embodiment, the forming process in step b is ball forming, and step b further includes: mixing the intermediate solid product with an inorganic oxide source, and then sequentially performing the molding treatment, the second drying treatment and the roasting treatment.

According to the present disclosure, the inorganic oxide serves as a binder to bond the titanium-containing support and the vanadium oxide, metal M oxide powder particles to each other at the time of extrusion to improve the strength and life of the first catalyst.

In a preferred embodiment, the inorganic oxide source is added in an amount of 0.1 to 5 wt%, preferably 0.1 to 2.0 wt%, on a dry basis and based on the weight of the titanium-containing carrier, and an appropriate amount of the inorganic oxide source is added in the present disclosure, so that the phenomenon that the first catalyst is difficult to mold, even if the first catalyst is barely molded, and is broken when leaving the molding machine is avoided; but also avoid the defect that the spherical product becomes soft and sticky due to excessive addition of the inorganic oxide source.

According to the present disclosure, the inorganic oxide in the first catalyst may be added in the form of an inorganic oxide, including Al, or in the form of a precursor thereof ₂ O ₃ And SiO ₂ One or two of the following components; the inorganic oxide precursor is selected from one or more of aluminum sol, silica sol and water glass.

In the present disclosure, the inorganic oxide as an inert substance can withstand corrosion of strong acid and strong alkali, so that the molded particles are not crushed during the alkali extraction process.

In a further embodiment, if silica sol is used as the binder, it may be an acidic silica sol or an alkaline silica sol, which may be commercially available or may be prepared according to any of the prior art. Other inorganic oxide precursors known to those skilled in the art to have binding properties may also be added during the first catalyst preparation process.

In one embodiment, in the step b, the conditions of the second drying process include: the temperature is 80-200deg.C, preferably 100-150deg.C; the time is 1-10h, preferably 2-4h;

the roasting conditions include: the roasting temperature is 200-900 ℃, preferably 500-800 ℃; the calcination time is 0.5 to 10 hours, preferably 2 to 4 hours. According to the present disclosure, the strength of the first catalyst can be improved by performing the drying treatment and the calcination treatment after extrusion molding.

In one embodiment, in step S1, the catalytic ammonification reaction conditions include: the reaction temperature is 120-700 ℃, and the weight ratio of ammonia gas to caprolactam is (0.1-100): 1, the partial pressure of ammonia is 0.1-5.0MPa, and the weight hourly space velocity of caprolactam is 1-100h ^-1 。

In a preferred embodiment, in step S1, the catalytic ammonification reaction conditions include: the reaction temperature is 200-450 ℃, and the mole ratio of ammonia gas to caprolactam is (1-10): 1, the partial pressure of ammonia is 0.2-3.0MPa, and the weight hourly space velocity of caprolactam is 0.5-20h ^-1 . The preferred catalytic ammonification reaction conditions provided by the present disclosure can further increase the caprolactam conversion and 6-aminocapronitrile selectivity of the catalytic ammonification.

In a specific embodiment, in step S1, the ammonification dehydration reaction is performed in a fixed bed reactor. The use of a fixed bed reactor in the present disclosure allows for continuous reactions.

In another specific embodiment, in step S1, the ammonification and dehydration reaction is performed in a reaction kettle. The batch reaction can be performed by using the reaction kettle as a reactor in the present disclosure.

In accordance with the present disclosure, in an ammonification dehydration reaction, either liquid phase or gas phase embodiments known in the art may be employed.

In the disclosure, after step S1 is completed, before step S2, performing a first separation and purification treatment on the first product to obtain a product rich in 6-aminocapronitrile; the 6-aminocapronitrile-rich product is then subjected to the catalytic hydrogenation reaction.

In the present disclosure, the purity of 6-aminocapronitrile in the 6-aminocapronitrile-rich product obtained by the first separation and purification is 90 wt% or more.

In one embodiment, the first separation and purification method is to perform flash separation and/or rectification separation on the first product; preferably, the obtained first product is subjected to vacuum rectification and purification to obtain pure 6-aminocapronitrile, wherein the operation conditions and the process of the vacuum rectification are as follows: the temperature of the bottom of the vacuum rectification tower is 150-160 ℃, the vacuum degree is 2-4torr, ammonia gas and water are distilled off when the temperature of the top of the tower is 20-40 ℃, and 6-aminocapronitrile is distilled off when the temperature of the top of the vacuum rectification tower is 130-140 ℃.

In one embodiment, in step S2, the catalytic hydrogenation reaction conditions include: the reaction temperature is 100-400 ℃, the reaction pressure is 0.5-20MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 0.1-1000:1, the weight hourly space velocity of the liquid feed is from 0.1 to 10h ^-1 。

In a preferred embodiment, the catalytic hydrogenation reaction conditions comprise: the reaction temperature is 150-350 ℃, the reaction pressure is 1.0-5.0MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 1-50:1, a weight hourly space velocity of the liquid feed of 0.5 to 5h ^-1 。

In one embodiment, in step S2, the catalytic hydrogenation reaction may be performed in a slurry bed reactor, and the second catalyst is selected from Raney nickel hydrogenation catalysts.

In another embodiment, the catalytic hydrogenation reaction may be carried out in a fixed bed reactor, the second catalyst being selected from supported hydrogenation catalysts; the supported hydrogenation catalyst is selected from one or more of nickel-based, cobalt-based and palladium-based catalysts.

In one embodiment, the nickel-based catalyst comprises 5-60 wt% nickel, 0-40 wt% cobalt, and 40-90 wt% first support; the cobalt-based catalyst comprises 5-60 wt% cobalt and 40-95 wt% of a second support; the palladium-based catalyst comprises 0.5 to 10 wt% palladium and 90 to 99.5 wt% of a third support; wherein the first support and the second support are each independently selected from one or both of silica and alumina; the third carrier is selected from one or two of activated carbon and alumina.

The second catalyst employed in the hydrogenation reaction of the present disclosure may be a catalyst conventionally employed in the art; or a catalyst prepared by a known method.

The hydrogenation reaction in step S2 may also be operated as a batch reaction in accordance with the present disclosure. The batch reaction generally adopts a reaction kettle as a reactor, 6-aminocapronitrile and a second catalyst are put into the reaction kettle, hydrogen is introduced into the reaction kettle for reaction at a certain temperature and under a certain pressure, reaction products are discharged from the reaction kettle after the reaction is finished, the products are separated, and then the products are put into the next batch of materials for reaction.

The hydrogenation reaction in step S2 may also be operated as a continuous reaction in accordance with the present disclosure. The continuous hydrogenation reaction can be carried out by using a shell-and-tube reactor, wherein the second catalyst is fixed in the tube, and the heat released by the reaction is removed by cooling water in the shell side.

In a specific embodiment, the method further comprises: after step S2, subjecting the second product to a second separation purification treatment; preferably, the purity of the hexamethylenediamine after the second separation and purification treatment is more than 99% by weight. The 6-aminocapronitrile hydrogenation reaction product mainly contains hexamethylenediamine, and can also contain a certain amount of unreacted 6-aminocapronitrile and a small amount of high-boiling substances, and the mixture can be separated by a rectification method, preferably by rectification separation. The rectification separation may be carried out batchwise or continuously. The second separation and purification in the present disclosure may employ process parameters conventional in the art.

In the following examples, all reagents used were commercially available ones unless otherwise specified.

In the following examples and comparative examples, the pressures are gauge pressures unless otherwise specified.

In the following examples and comparative examples, BET specific surface area, total pore volume, and micropore volume of the catalyst were measured by an automatic adsorbent of Micromeritics ASAP-2020, the specific surface area was calculated using a two-parameter BET equation, the pore distribution was calculated by BJH method, and the micropore specific surface area and pore volume were calculated by t method.

The content of each component in the catalyst was determined using an X-ray fluorescence spectrometer (XRF).

Preparation example 1

Preparation of vanadyl oxalate: 40g of ammonium metavanadate was dissolved in 500g of water, then heated in a water bath at 80℃and 80g of oxalic acid crystals were slowly added with stirring, and the reaction was carried out at 80℃for 120min until the color of the slurry changed from yellow to purple to a clear solution.

Then, 80g of ammonium molybdate tetrahydrate and 18g of ammonium dihydrogen phosphate were added, and heating was continued on a water bath for 30 minutes to obtain a mixed solution containing vanadyl oxalate, ammonium molybdate and phosphoric acid.

Continuously stirring the solution under the water bath condition of 70 ℃, and adding 500g of TiO into the solution under the continuous stirring ₂ (DuPont R900) and 50g of titanium silicalite molecular sieve (HTS 3 molecular sieve, hunan Jian Long product) were aged for 4 hours with stirring. The resulting product was dried in an oven at 110℃for 4h. And (3) adding the dried material into a grinder, and grinding for 30min to obtain an intermediate solid product with the maximum particle size of less than 30 microns.

Water in the steps: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is 0.909:0.073:0.145:0.145:0.027:1.

continuously adding 15g of sesbania powder (purchased from an orchid plant gum factory) and 20g of 20 wt% nitric acid aqueous solution (4 g of nitric acid) into the intermediate solid product for full mixing, wherein the adding amount of the sesbania powder is 2.7 wt% and the adding amount of the nitric acid is 0.73 wt% based on the adding weight of the titanium-containing carrier on a dry basis; then extruding the bar catalyst with the diameter of 2.5mm by a bar extruder, drying for 4 hours at 120 ℃, and roasting for 4 hours at 750 ℃ to obtain the bar catalyst, which is named CAT-1.

The catalyst CAT-1 was dried and the strength was determined to be 40N/cm by means of an intensity meter.

Catalyst CAT-1 had a composition of 83.3% by weight of TiO ₂ V4.7 wt% ₂ O ₅ 9.9 wt% MoO ₃ 1.7 wt% P ₂ O ₅ And 0.4 wt% SiO ₂ 。

Preparation of comparative example 1

The same procedure as in preparation example 1 was employed, except that preparation example 1 was used:

10g of ammonium metavanadate and 20g of oxalic acid crystal are adopted; 10g of ammonium molybdate tetrahydrate and 2g of ammonium dihydrogen phosphate; the rest of the procedure is the same as in the preparation example. The resulting product was designated DCAT-1.

The catalyst DCAT-1 was dried and measured for strength by an intensity meter at 30N/cm.

Catalyst DCAT-1 had a composition of 96.5 wt% TiO ₂ V at 1.4 wt% ₂ O ₅ 1.4 wt% MoO ₃ 0.2 wt% of P ₂ O ₅ 0.4 wt% SiO ₂ 。

Preparation of comparative example 2

The same procedure as in preparation example 1 was employed, except that preparation example 1 was used: the procedure was the same as in preparation example 1 except that ammonium molybdate tetrahydrate was not added. The resulting product was designated DCAT-2.

The catalyst DCAT-2 was dried and measured for strength using an intensity meter at 25N/cm.

Catalyst DCAT-2 had a composition of 92.5 wt% TiO ₂ V5.3 wt% ₂ O ₅ 1.9 wt% of P ₂ O ₅ 0.4 wt% SiO ₂ 。

Preparation example 2

Preparation of vanadyl oxalate: 40g of ammonium metavanadate was dissolved in 500g of water, then heated in a water bath at 80℃and 110g of oxalic acid crystals were slowly added with stirring, and the reaction was carried out at 80℃for 120min until the color of the slurry changed from yellow to purple to a clear solution.

Then, 80g of ammonium molybdate tetrahydrate and 18g of ammonium dihydrogen phosphate were added, and heating was continued on the water bath for 30 minutes to obtain a mixed aqueous solution containing vanadyl oxalate, ammonium molybdate and phosphoric acid.

Continuously stirring the solution at 70 ℃, and adding 500g of TiO into the solution under continuous stirring ₂ (DuPont R900) and 50g of titanium silicalite molecular sieve (HTS-3, a product of Hunan Jian Long Co., ltd.) were further stirred and aged for 4 hours. The resulting product was dried in an oven at 110℃for 4h. The dried material was added to a mill and milled for 30min to give an intermediate solid product (maximum particle size below 30 microns).

Water in the steps: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is 0.909:0.073:0.2:0.145:0.033:1.

then adding 20g of aluminum sol (Hunan Jian Long product) and fully and uniformly mixing, wherein the adding amount of the aluminum sol is 3.6 weight percent based on the adding weight of the titanium-containing carrier on a dry basis; then turning into a small ball catalyst in a ball rolling machine, screening out small balls with the diameter of 2.0-3.0mm in the obtained small ball catalyst, drying the small balls at 120 ℃ for 4 hours, and roasting the small balls at 550 ℃ for 4 hours to obtain the small ball catalyst, which is named CAT-2.

The catalyst CAT-2 was dried and the intensity was determined to be 60N/cm by means of an intensity meter.

Catalyst CAT-2 had a composition of 82.8% by weight of TiO ₂ V4.7 wt% ₂ O ₅ 9.9 wt% MoO ₃ 1.7 wt% P ₂ O ₅ 0.4 wt% SiO ₂ And 0.5 wt% Al ₂ O ₃ 。

Preparation example 3

10g of ammonium metavanadate and 30g of oxalic acid crystals are adopted; 60g of ammonium molybdate tetrahydrate and 18g of ammonium dihydrogen phosphate; the rest of the procedure is the same as in the preparation example. The resulting product was designated CAT-3.

In this embodiment, the vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is 0.018:0.055:0.109:0.033:1.

The catalyst CAT-3 was dried and the strength was determined to be 40N/cm by means of an intensity meter.

Catalyst CAT-3 had a composition of 77.9% by weight of TiO ₂ V2.4 wt% ₂ O ₅ 15.4 wt% MoO ₃ 3.5 wt% P ₂ O ₅ And 0.8 wt% SiO ₂ 。

Preparation example 4

Then, 25g of lanthanum nitrate and 30g of sodium hypophosphite were added, and heating was continued on a water bath for 30 minutes to obtain a mixed aqueous solution containing vanadyl oxalate, lanthanum nitrate and sodium hypophosphite.

The vanadium source in the above steps: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is 0.073:0.2:0.045:0.055:1. then adding 20g of aluminum sol (Hunan Jian Long product) and fully and uniformly mixing, wherein the adding amount of the aluminum sol is 3.6 weight percent based on the adding weight of the titanium-containing carrier on a dry basis; then turning into a small ball catalyst in a ball rolling machine, screening out small balls with the diameter of 2.0-3.0mm in the obtained small ball catalyst, drying the small balls at 120 ℃ for 4 hours, and roasting the small balls at 550 ℃ for 4 hours to obtain the small ball catalyst, which is named CAT-4.

After the catalyst CAT-4 is dried, the intensity is measured to be more than 40N/particle by an intensity measuring instrument.

Catalyst CAT-4 had a composition of 88.2% by weight of TiO ₂ V5.0 wt% ₂ O ₅ 2.0 wt% La ₂ O ₃ 3.9 wt% P ₂ O ₅ 0.4 wt% SiO ₂ And 0.5 wt% Al ₂ O ₃ 。

Preparation example 5

The same procedure as in preparation example 4 was employed, except that preparation example 4 was: 40g of ammonium metavanadate was dissolved in 500g of water; 110g of oxalic acid crystals are added; adding 30g of lanthanum nitrate; the remaining preparation parameters were the same as in example 4. Wherein the vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is 0.073:0.2:0.055:0.055:1. the product obtained was designated CAT-5.

After the catalyst CAT-5 was dried, the intensity was measured to be 50N/particle by an intensity measuring instrument.

Catalyst CAT-5 had a composition of 87.8% by weight TiO ₂ V5.0 wt% ₂ O ₅ 2.4 wt% La ₂ O ₃ 3.9 wt% P ₂ O ₅ 0.4 wt% SiO ₂ And 0.5 wt% Al ₂ O ₃ 。

Structural test data for the catalyst products obtained in the above examples and comparative examples are listed in table 1 below.

TABLE 1

	BET specific surface area/m ² /g	Total pore volume/mL/g	Micropore volume/mL/g
				CAT-1	86	0.18	0.08
DCAT-1	59	0.16	0.06
				DCAT-2	65	0.17	0.06
CAT-2	85	0.25	0.07
				CAT-3	71	0.12	0.08
CAT-4	82	0.23	0.06
				CAT-5	91	0.24	0.07

The following reaction examples are presented to illustrate the performance of the catalysts prepared as described above in the preparation of 6-aminocapronitrile by ammonification and dehydration of caprolactam

Reaction example 1

10g of catalyst CAT-1 were chargedThe middle part in the stainless steel reactor with the jacket and the two ends are filled with inert gasesAnd (5) sex quartz sand. 10g/h (0.088 mol/h) of Caprolactam (CPL) are thoroughly mixed with 7.5g/h (0.44 mol/h) of hot ammonia (molar ratio CPL to ammonia 1:5) at a temperature of 100 ℃. The mixture of caprolactam and ammonia gas is contacted with catalyst to react at 250 deg.c and CPL space velocity of 1.0 hr ^-1 The partial pressure of ammonia is 1MPa. This example measures and calculates caprolactam conversion and 6-aminocapronitrile selectivity at 20h and 200h, respectively. The specific data are shown in Table 2. Deamination, dehydration and vacuum rectification are carried out on the ammoniation reactant to obtain the 6-aminocapronitrile with the purity of 99.0 weight percent. />

Comparative examples 1 to 2

The same ammonification dehydration reaction as in reaction example 1 was employed, except that the reaction example 1 was as follows: the catalyst CAT-1 is replaced by DCAT-1 to DCAT-2 respectively.

Reaction examples 2 to 9

The same ammonification dehydration reaction as in reaction example 1 was employed, and the specific reaction conditions and reaction results are shown in Table 2 below.

TABLE 2

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As can be seen from table 2 above:

compared with reaction comparative examples 1-2 adopting DCAT-1 and DCAT-2, the first catalyst provided by the disclosure is adopted to carry out ammonification catalytic reaction in reaction examples 1 and 6-8, and under the same reaction conditions, the reaction examples 1 and 6-8 can obtain higher caprolactam conversion rate and 6-aminocapronitrile selectivity in caprolactam ammonification reaction; and the caprolactam conversion rate and 6-aminocapronitrile selectivity change between reaction 200h and reaction 20h are smaller, and the stability is higher.

Further, comparing reaction example 1 with reaction example 3, it is understood that catalyst CAT-1 used in reaction example 1 satisfies "in step a, water: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is (0.8-1.6): (0.05-0.1): (0.1-0.3): (0.04-0.3): (0.02-0.6): 1", and the composition of CAT-1 satisfies the conditions" 30-90% by weight of titanium-containing support, 4-15% by weight of vanadium oxide, 1-5% by weight of phosphorus pentoxide, 2-10% by weight of metal M oxide and/or 0.1-2% by weight of inorganic oxide ", reaction example 1 enables higher caprolactam conversion and 6-aminocapronitrile selectivity in the caprolactam ammoniation reaction.

Further, comparing reaction example 1 with reaction example 9, it is known that the ammonification catalysis condition of reaction example 1 satisfies "the reaction temperature is 200-450 ℃, the mole ratio of ammonia to caprolactam is (1-10): 1", reaction example 1 enables a higher caprolactam conversion and 6-aminocapronitrile selectivity in the caprolactam ammoniation reaction.

Reaction examples 10 to 15

A process for the synthesis of hexamethylenediamine by hydrogenation of 6-aminocapronitrile is described.

20gNi-Co/Al ₂ O ₃ The hydrogenation catalyst is filled in the middle part of a stainless steel reactor with phi 24 multiplied by 4 multiplied by 800mm, and inert quartz sand is filled at two ends. Introducing hydrogen, reducing for 24 hours at 300 ℃ and 1.0MPa, and reducing to the temperature and the pressure of hydrogenation reaction. And pumping 6-aminocapronitrile obtained by ammonification of caprolactam into a reactor by a metering pump for reaction. And (3) taking a product sample after the reaction for 20 hours, condensing, and performing off-line chromatographic analysis to calculate the conversion rate of 6-aminocapronitrile and the selectivity of hexamethylenediamine from the product composition. The specific data are shown in Table 3.

Hexamethylenediamine yield = 6-aminocapronitrile conversion x hexamethylenediamine selectivity

Wherein the hydrogenation catalyst Ni-Co/Al is adopted ₂ O ₃ The specific synthetic steps of (the second catalyst) include:

(1) Nickel nitrate (Ni (NO) ₃ ) ₂ ) Preparing cobalt nitrate and aluminum nitrate solution: to a 1L beaker was added 285mL of deionized water, stirring was started, heating was performed to 50-60℃and 97g of nickel nitrate crystals, 136g of cobalt nitrate and 295g of aluminum nitrate were added to prepare a mixed solution having a concentration of about 30% by weight.

(2) Sodium carbonate (Na) ₂ CO ₃ ) Preparing a solution: to ensure complete precipitation of metal ions, the precipitant sodium carbonate was dosed 1.05 times. 1200mL of deionized water was added to a 2L beaker, stirring was started, heating was performed to 50-60℃and 208g of anhydrous sodium carbonate solid was added to prepare a sodium carbonate solution having a concentration of about 15% by weight.

Adding the aqueous sodium carbonate solution and the metal salt solution slurry into a 5L reaction kettle for contact at the temperature of 80 ℃, filtering to obtain a solid after the contact for 4 hours, drying the obtained solid, and roasting the solid in a muffle furnace at the temperature of 500 ℃ for 6 hours to obtain a roasted solid; the roasted solid is subjected to programmed temperature reduction, then the reduced solid is firstly cooled to 60 ℃ under the atmosphere of argon and then is continuously cooled to 40 ℃ under the atmosphere of a mixed gas of argon and oxygen with the oxygen concentration of 5 volume percent under the atmosphere of the argon and the oxygen to obtain Ni-Co/Al ₂ O ₃ A catalyst, as a hydrogenation catalyst.

The composition of the hydrogenation catalyst was 35.0 wt% Co as measured by XRF ₃ O ₄ 25 wt% NiO,40 wt% Al ₂ O ₃ 。

Reaction example 16

Hexamethylenediamine was prepared using the reaction conditions of reaction example 15, differing from reaction example 15 in that the hydrogenation catalyst was replaced with a palladium-based catalyst; the palladium-based catalyst is Pd/Al ₂ O ₃ A catalyst. The preparation method comprises the following steps:

(1) And (3) carrier modification: weighing 100g gamma-Al with phi 3mm multiplied by 8mm ₂ O ₃ Particles (Hunan Jian feldspar Co., ltd., surface area 150 m) ² Per g, pore volume of 0.4 mL/g), saturated water absorption of 70mL, according to P ₂ O ₅ /Al ₂ O ₃ 3.25g of monoammonium phosphate is weighed according to the mass ratio of 0.02, added into 70mL of deionized water required by weighing to prepare corresponding ammonium phosphate solution, mixed and stirred uniformly with active alumina, and then transferred into an oven to be dried for 4 hours at 120 ℃. And roasting the dried sample at 550 ℃ for 8 hours to obtain the required carrier.

(2) And (3) preparing a catalyst: 100mL of aqueous solution with the palladium chloride concentration of 15g/L is measured, 75g of the carrier obtained in the step (1) is taken, the carrier is added into the palladium chloride solution, the carrier is immersed for 12h at room temperature under stirring, 12.5mL of NaOH solution with the concentration of 5 wt% is added dropwise, and the temperature is kept for 2-10h to obtain a suspension. Hydrogen gas with the flow rate of 30ml/min is introduced into the suspension at 30 ℃ and the suspension is subjected to reduction activation for 4h under stirring. Filtering and washing with deionized water to Cl ^- Concentration is less than 10 ^-6 M, then at 70℃and vacuum degree of 1.013X10 ^-3 ～1.013×10 ^-4 Drying for 4h under Pa, and preserving under nitrogen protection to obtain the catalyst.

The composition of the palladium-based catalyst was 2.0 wt% Pd,98.0 wt% Al as measured by XRF ₂ O ₃ . The reaction results are shown in Table 3.

TABLE 3 Table 3

In the hydrogenation reaction examples, the hydrogenation reaction conditions of the reaction examples 11 to 13 and 15 and 16 satisfy the conditions of "the reaction temperature is 150 to 350 ℃, the reaction pressure is 1.0 to 5.0MPa, and the molar ratio of the hydrogen to the 6-aminocapronitrile is 1 to 50:1", the conversion of 6-aminocapronitrile, the selection of hexamethylenediamine and the yield of hexamethylenediamine were higher in the hydrogenation reaction of reaction examples 11 to 13 and 15, 16 than in reaction examples 10 and 14.

The preferred embodiments of the present disclosure have been described in detail above, but the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solutions of the present disclosure within the scope of the technical concept of the present disclosure, and all the simple modifications belong to the protection scope of the present disclosure.

In addition, the specific features described in the above embodiments may be combined in any suitable manner without contradiction. The various possible combinations are not described further in this disclosure in order to avoid unnecessary repetition.

Moreover, any combination between the various embodiments of the present disclosure is possible as long as it does not depart from the spirit of the present disclosure, which should also be construed as the disclosure of the present disclosure.

Claims

1. A process for preparing hexamethylenediamine from caprolactam, characterized in that it comprises the following steps:

2. The method according to claim 1, wherein in step S1, the catalytic ammonification reaction conditions comprise: the reaction temperature is 120-700 ℃, and the molar ratio of ammonia gas to caprolactam is (0.1-100): 1, the partial pressure of ammonia is 0.1-5.0MPa, and the weight hourly space velocity of caprolactam is 0.1-100h ^-1 ；

Preferably, the catalytic ammoniation reaction conditions include: the reaction temperature is 200-450 ℃, and the mole ratio of ammonia gas to caprolactam is (1-10): 1, the partial pressure of ammonia is 0.2-3.0MPa, and the weight hourly space velocity of caprolactam is 0.5-20h ^-1 ；

Alternatively, the ammonification dehydration reaction is performed in a fixed bed reactor.

3. The method according to claim 1, characterized in that in step S1, the first catalyst comprises, on a dry basis and based on the total weight of the first catalyst, 30-90 wt.% of a titanium-containing support, 4-15 wt.% of vanadium oxide, 1-5 wt.% of phosphorus pentoxide, 2-10 wt.% of metal M oxide and/or 0.1-2 wt.% of an inorganic oxide.

4. The method of claim 1, wherein the TiO in the titanium-containing carrier, on a dry basis ₂ And titanium-containing molecular sieve in a weight ratio of 1: (0.01-10), preferably 1: (0.1-5);

the titanium-containing molecular sieve comprises a titanium silicalite molecular sieve; the titanium silicalite molecular sieve is selected from one or more of HTS molecular sieve, TS-1 molecular sieve, TS-2 molecular sieve and TS-48 molecular sieve;

optionally, the metal M is selected from one or more of tungsten, molybdenum, chromium, zinc, manganese, lanthanum, zirconium and iron; preferably one or more selected from tungsten, molybdenum and chromium, further preferably one or both selected from molybdenum and tungsten.

5. A process according to claim 1, wherein the BET specific surface area of the first catalyst is 50-300m ² Per gram, the total pore volume is 0.1-0.4mL/g, and the micropore volume is 0.05-0.2mL/g;

optionally, the shape of the first catalyst is selected from one or more of sphere, bar, cylinder, ring, clover, tetraleaf, honeycomb and butterfly.

6. The method of claim 1, wherein the first catalyst is prepared by a preparation method comprising the steps of:

7. The method of claim 6, wherein in step a, water: vanadium source: acid: metal M source: phosphorus source: the weight ratio of the titanium-containing carrier is (0.5-2.0): (0.05-0.2): (0.05-0.5): (0.02-0.5): (0.01-1): 1, a step of; preferably (0.8-1.6): (0.05-0.1): (0.1-0.3): (0.04-0.3): (0.02-0.6): 1.

8. the method according to claim 6, wherein the vanadium source is selected from one or more of ammonium metavanadate, sodium metavanadate and vanadium pentoxide;

the acid is one or more selected from oxalic acid, citric acid and nitric acid;

9. The method of claim 6, wherein step a comprises:

carrying out the first drying treatment on the second mixture, and grinding the obtained product to obtain the intermediate solid product; optionally, the temperature of the first drying treatment is 80-150 ℃.

10. The method of claim 6, wherein the molding process in step b is extrusion molding; step b further comprises: extruding and mixing the intermediate solid product, a pore-expanding agent and an auxiliary agent, and then sequentially carrying out forming treatment, second drying treatment and roasting treatment; or alternatively

The forming process in the step b is ball forming, and the step b further comprises: mixing the intermediate solid product with an inorganic oxide source, and then sequentially performing the molding treatment, the second drying treatment and the roasting treatment.

11. The method according to claim 10, wherein the pore-expanding agent is added in an amount of 0.5-10 wt%, preferably 1-5 wt%, on a dry basis and based on the added weight of the titanium-containing carrier; the extrusion aid is added in an amount of 0.5 to 4 wt%, preferably 0.5 to 2 wt%;

the inorganic oxide source is added in an amount of 0.1 to 5% by weight, preferably 0.1 to 2.0% by weight, on a dry basis and based on the added weight of the titanium-containing carrier.

12. The method of claim 11, wherein, in step b,

the pore-expanding agent is one or more selected from sesbania powder, paraffin, stearic acid, glycerol, starch, polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyacrylamide, cellulose methyl ether, cellulose, polyalcohol and graphite;

the extrusion aid is selected from one or more of organic acid, inorganic acid and inorganic base, preferably, the extrusion aid is selected from one or more of oxalic acid, tartaric acid, citric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, ammonia water, sodium hydroxide and potassium hydroxide;

the addition form of the inorganic oxide source comprises inorganic oxide or inorganic oxide precursor; the inorganic oxide includes Al ₂ O ₃ And SiO ₂ One or two of the following components; the inorganic oxide precursor is selected from one or more of aluminum sol, silica sol and water glass.

13. The method according to claim 6, wherein in step b, the conditions of the second drying process include: the temperature is 80-200deg.C, preferably 100-150deg.C; the time is 1-10h, preferably 2-4h;

the roasting conditions include: the roasting temperature is 200-900 ℃, preferably 500-800 ℃; the calcination time is 0.5 to 10 hours, preferably 2 to 4 hours.

14. The method according to claim 1, wherein in step S2, the catalytic hydrogenation reaction conditions include: the reaction temperature is 100-400 ℃, the reaction pressure is 0.5-20MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 0.1-1000:1, the weight hourly space velocity of the liquid feed is from 0.1 to 10h ^-1 ；

Preferably, the catalytic hydrogenation reaction conditions include: the reaction temperature is 150-350 ℃, the reaction pressure is 1.0-5.0MPa, and the molar ratio of hydrogen to 6-aminocapronitrile is 1-50:1, a weight hourly space velocity of the liquid feed of 0.5 to 5h ^-1 。

15. The process of claim 1, wherein in step S2, the catalytic hydrogenation reaction is carried out in a slurry bed reactor, and the second catalyst comprises a Raney nickel hydrogenation catalyst; or alternatively

The catalytic hydrogenation reaction is carried out in a fixed bed reactor, and the second catalyst is selected from supported hydrogenation catalysts; the supported hydrogenation catalyst is selected from one or more of nickel-based, cobalt-based and palladium-based catalysts;

optionally, the nickel-based catalyst comprises 5-60 wt% nickel, 0-40 wt% cobalt, and 40-90 wt% first support; the cobalt-based catalyst comprises 5-60 wt% cobalt and 40-95 wt% of a second support; the palladium-based catalyst comprises 0.5 to 10 wt% palladium and 90 to 99.5 wt% of a third support; wherein the first support and the second support are each independently selected from one or both of silica and alumina; the third carrier is selected from one or two of activated carbon and alumina.

16. The method according to claim 1, characterized in that the method further comprises:

before step S2, carrying out first separation and purification treatment on the first product to obtain a 6-aminocapronitrile-rich product; then subjecting said 6-aminocapronitrile-rich product to said catalytic hydrogenation reaction; and

after step S2, the second product is subjected to a second separation purification treatment.