1. A process for preparing 6-aminocapronitrile starting from caprolactam and ammonia, comprising the steps of:

s1, preheating caprolactam, mixing the caprolactam with a catalyst to obtain a mixed solution, and pumping the mixed solution into a main reactor through a temperature control metering pump;

s2, when the mixed solution in the step S1 is heated in the main reactor to reach 100-400 ℃, introducing preheated ammonia gas into the mixed solution;

s3, heating, aminating and dehydrating the reaction liquid obtained in the step S2 in a reaction area of a tube array in the middle of the main reactor to obtain a target product, overflowing the target product from a gas-phase outlet at the upper end of the main reactor in a gas-phase form, condensing the target product, and then entering a gas-liquid separation device, wherein excessive ammonia gas is separated from the gas-phase part for recycling;

and S4, carrying out vacuum rectification on the liquid phase reaction product subjected to gas-liquid separation in S3 by using a first rectifying tower, obtaining 6-aminocapronitrile from the gas phase part of the first rectifying tower, and carrying out vacuum rectification on the liquid phase part of the first rectifying tower by using a second rectifying tower to obtain caprolactam which is not completely reacted.

2. The method according to claim 1, wherein, in step S1,

the preheating temperature of caprolactam is 70-250 ℃, and preferably 80-150 ℃; and/or

The mass ratio of caprolactam to the catalyst is 1: 0.001-2, preferably 1: 0.002-0.1; and/or

The catalyst is phosphoric acid or phosphate, such as one or two or more selected from ammonium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, iron phosphate, zinc phosphate, manganese phosphate, cerium phosphate and zirconium phosphate, preferably phosphoric acid and ammonium phosphate.

3. The method according to claim 1, wherein the mixed solution is fed into the main reactor by a temperature-controlled metering pump set to a temperature of 70-140 ℃ in step S1.

4. The method according to claim 1, wherein in step S2, the mixed solution is heated in the main reactor to 150-300 ℃.

5. The method according to claim 1, wherein, in step S2,

the molar ratio of caprolactam to ammonia gas is 1: 1-100, preferably 1: 5-40; and/or

The preheating temperature of the ammonia gas is 100-300 ℃, and preferably 150-250 ℃.

6. The method according to claim 1, wherein, in step S3,

the heating temperature of the tubes in the middle of the main reactor is 100-500 ℃, and preferably 200-300 ℃; and/or

The temperature of the condenser for condensation is controlled to be 100-200 ℃, and preferably 120-150 ℃.

7. The method as claimed in claim 1, wherein the ammonia gas separated from the gas phase in step S3 is subjected to gas-liquid separation, then cooled to remove water, and then pressurized by an ammonia gas compressor and introduced into an ammonia gas preheater for recycling.

8. The method according to claim 1, wherein, in step S4,

the temperature of the vacuum rectification tower kettle of the first rectification tower is controlled to be 120-160 ℃, the vacuum pressure is 10-20 mmHg, the temperature of a gas phase at the top of the tower is 60-110 ℃, and the reflux ratio is 1-4: 1; and/or

The temperature of the tower bottom of the second rectifying tower is controlled to be 150-280 ℃, the vacuum pressure of the vacuum rectification is 10-20 mmHg, the temperature of the gas phase at the tower top is 120-150 ℃, and the reflux ratio is 1-4: 1.

9. The method of claim 1, wherein in step S4, the recovered caprolactam is recycled and pumped into the main reactor for reuse by a temperature-controlled metering pump.

10. A process for preparing 6-aminocapronitrile starting from caprolactam and ammonia, comprising the steps of:

s1, preheating caprolactam to 70-250 ℃, preferably 80-150 ℃, mixing the caprolactam and a catalyst in a mass ratio of 1: 0.001-2, preferably 1: 0.002-0.1 to obtain a mixed solution, and pumping the mixed solution into a main reactor through a temperature control metering pump, wherein the temperature of the temperature control metering pump is set to be 70-140 ℃;

s2, heating the mixed solution in a main reactor, and when the mixed solution reaches 100-400 ℃, more preferably 150-300 ℃, introducing ammonia gas preheated to 100-300 ℃, preferably 150-250 ℃ into the mixed solution in S1 according to the molar ratio of caprolactam to ammonia gas of 1: 1-100, preferably 1: 5-40;

s3, introducing the ammonia gas introduced in the step S2 into an inlet at the upper end of a main reactor through an ammonia gas flowmeter, then bubbling at the bottom of the reactor, fully contacting with caprolactam and a catalyst, heating, aminating and dehydrating through a tube array reaction region in the middle of the main reactor to obtain a target product, overflowing the target product and excessive ammonia gas from an outlet at the upper end of the main reactor, entering a first condenser, cooling through the first condenser, entering a gas-liquid separator, entering a liquid phase reaction product into a temporary reaction liquid storage tank, entering a gas phase product into a second condenser, continuing to condense and separate, discharging and treating the obtained liquid wastewater, introducing the ammonia gas into an ammonia gas compressor, calculating the flow through the ammonia gas flowmeter, merging the ammonia gas into the front end of an ammonia gas preheater for recycling, wherein the temperature of the tube array reaction region arranged in the main reactor is controlled at 100-500 ℃, preferably 250-300 ℃, the temperature of the, preferably 120-150 ℃, controlling the temperature of the second condenser at 10-80 ℃, preferably 20-50 ℃;

s4, pumping a liquid phase product from the reaction liquid temporary storage tank into a first rectifying tower through a second temperature control metering pump for reduced pressure rectification, pumping a gas phase part into a rectified product 6-aminocapronitrile, pumping a liquid phase part of the first rectifying tower into a second rectifying tower through a third temperature control metering pump for reduced pressure rectification, pumping a gas phase part into a rectified product caprolactam, pumping the caprolactam obtained in a caprolactam receiving tank into a main reactor through a fourth temperature control metering pump for supplementary recycling as a reaction raw material, wherein the temperature of a tower bottom of the first rectifying tower is controlled at 120-160 ℃, the vacuum pressure of reduced pressure rectification is preferably 10-20 mmHg, the temperature of a gas phase at the tower top is preferably 60-110 ℃, the reflux ratio is preferably 1-4: 1, the temperature of the tower bottom of the second rectifying tower is controlled at 150-280 ℃, the vacuum pressure of reduced pressure is preferably 10-20 mmHg, the gas phase temperature at the tower top is preferably 120-150 ℃, the reflux ratio is preferably 1-4: 1.

Background

6-aminocapronitrile is an important chemical intermediate that can be used to produce 1, 6-hexamethylenediamine by complete hydrogenation, while 1, 6-hexamethylenediamine can be used to produce the polymer nylon 66. The preparation of 6-aminocapronitrile is currently mainly obtained by partial hydrogenation of 1, 6-adiponitrile, as in patent CN 1100752C. The patents for preparing 6-aminocapronitrile from caprolactam are not too many, and the current methods for preparing 6-aminocapronitrile from caprolactam can be divided into a gas phase method and a liquid phase method according to the reaction state of caprolactam, wherein the gas phase method has high reaction temperature and large energy consumption, such as the patent CN 107602416A. The liquid phase method has lower temperature and easier reaction, such as patent CN107739318A, but the patent is a batch kettle type reaction process, which contains solvent, has low efficiency, more byproduct impurities and low product purity.

Disclosure of Invention

The invention provides a continuous reaction process and a continuous reaction device for preparing a key intermediate 6-aminocapronitrile of hexamethylene diamine by a caprolactam liquid phase method, which solve a series of problems of low efficiency, a plurality of by-product impurities, high reaction temperature, high energy consumption and the like caused by the batch reaction for preparing 6-aminocapronitrile by the existing liquid phase method.

In order to achieve the above object, the present invention provides a process for preparing 6-aminocapronitrile, starting from caprolactam and ammonia, comprising the steps of:

s1, preheating caprolactam, mixing the caprolactam with a catalyst to obtain a mixed solution, and pumping the mixed solution into a main reactor through a temperature control metering pump;

s2, when the mixed solution in the step S1 is heated in the main reactor to reach 100-400 ℃, introducing preheated ammonia gas into the mixed solution;

s3, heating, aminating and dehydrating the reaction liquid obtained in the step S2 in a reaction area of a tube array in the middle of the main reactor to obtain a target product, overflowing the target product from a gas-phase outlet at the upper end of the main reactor in a gas-phase form, condensing the target product, and then entering a gas-liquid separation device, wherein excessive ammonia gas is separated from the gas-phase part for recycling;

and S4, carrying out vacuum rectification on the liquid phase reaction product subjected to gas-liquid separation in S3 by using a first rectifying tower, obtaining 6-aminocapronitrile from the gas phase part of the first rectifying tower, and carrying out vacuum rectification on the liquid phase part of the first rectifying tower by using a second rectifying tower to obtain caprolactam which is not completely reacted.

Further, the caprolactam preheating temperature in step S1 is preferably 70 to 250 ℃, more preferably 80 to 150 ℃; the mass ratio of the caprolactam to the catalyst is preferably 1: 0.001-2, more preferably 1: 0.002-0.1, and the catalyst is preferably phosphoric acid or phosphate, such as one or two or more selected from ammonium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, iron phosphate, zinc phosphate, manganese phosphate, cerium phosphate and zirconium phosphate, and is preferably phosphoric acid or ammonium phosphate.

Further, in step S1, the mixed solution is pumped into the main reactor through a temperature-controlled metering pump, wherein the temperature of the temperature-controlled metering pump is set to 70-140 ℃ to ensure that caprolactam is not solidified during the transportation process.

Further, in step S2, the mixed solution is heated in the main reactor, preferably, the temperature of the mixed solution is 150-300 ℃.

Further, the molar ratio of the caprolactam and the ammonia gas in the step S2 is preferably 1: 1-100, and more preferably 1: 5-40; the preheating temperature of the ammonia gas is preferably 100-300 ℃, and more preferably 150-250 ℃.

Further, in the step S3, the heating temperature of the tubes in the middle of the main reactor is preferably 100-500 ℃, and more preferably 200-300 ℃; the temperature of the condenser for condensation is preferably controlled to be 100-200 ℃, and more preferably to be 120-150 ℃.

Further, preferably, the ammonia gas separated from the gas phase part in step S3 is cooled to remove water after gas-liquid separation, and then pressurized by an ammonia gas compressor and introduced into an ammonia gas preheater for recycling.

Further, in the step S4, the temperature of the vacuum distillation tower kettle of the first distillation tower is controlled to be 120-160 ℃, the vacuum pressure is preferably 10-20 mmHg, the gas phase temperature at the top of the tower is preferably 60-110 ℃, and the reflux ratio is preferably 1-4: 1; the temperature of the bottom of the second rectifying tower is controlled to be 150-280 ℃, the vacuum pressure of the vacuum rectification is preferably 10-20 mmHg, the gas phase temperature at the top of the tower is preferably 120-150 ℃, and the reflux ratio is preferably 1-4: 1.

Further, preferably, in step S4, the recovered caprolactam is pumped into the main reactor for recycling through a temperature-controlled metering pump. The temperature of the temperature-controlled metering pump is set to 70-140 ℃ to ensure that caprolactam does not solidify during the conveying process.

In one embodiment, the present invention provides a process for preparing 6-aminocapronitrile starting from caprolactam and ammonia comprising the steps of:

s1, preheating caprolactam to 70-250 ℃, preferably 80-150 ℃, mixing the caprolactam and a catalyst in a mass ratio of 1: 0.001-2, preferably 1: 0.002-0.1 to obtain a mixed solution, and pumping the mixed solution into a main reactor through a temperature control metering pump, wherein the temperature of the temperature control metering pump is set to be 70-140 ℃;

s2, heating the mixed solution in a main reactor, and when the mixed solution reaches 100-400 ℃, more preferably 150-300 ℃, introducing ammonia gas preheated to 100-300 ℃, preferably 150-250 ℃ into the mixed solution in S1 according to the molar ratio of caprolactam to ammonia gas of 1: 1-100, preferably 1: 5-40;

s3, introducing the ammonia gas introduced in the step S2 into an inlet at the upper end of a main reactor through an ammonia gas flowmeter, then bubbling at the bottom of the reactor, fully contacting with caprolactam and a catalyst, heating, aminating and dehydrating through a tube array reaction region in the middle of the main reactor to obtain a target product, overflowing the target product and excessive ammonia gas from an outlet at the upper end of the main reactor, entering a first condenser, cooling through the first condenser, entering a gas-liquid separator, entering a liquid phase reaction product into a temporary reaction liquid storage tank, entering a gas phase product into a second condenser, continuing to condense and separate, discharging and treating the obtained liquid wastewater, introducing the ammonia gas into an ammonia gas compressor, calculating the flow through the ammonia gas flowmeter, merging the ammonia gas into the front end of an ammonia gas preheater for recycling, wherein the temperature of the tube array reaction region arranged in the main reactor is controlled at 100-500 ℃, preferably 250-300 ℃, the temperature of the first condenser is controlled at 100-200 ℃, preferably 120-150 ℃, controlling the temperature of the second condenser at 10-80 ℃, preferably 20-50 ℃;

s4, pumping a liquid phase product from the reaction liquid temporary storage tank into a first rectifying tower through a second temperature control metering pump for reduced pressure rectification, pumping a gas phase part into a rectified product 6-aminocapronitrile, pumping a liquid phase part of the first rectifying tower into a second rectifying tower through a third temperature control metering pump for reduced pressure rectification, pumping a gas phase part into a rectified product caprolactam, pumping the caprolactam obtained in a caprolactam receiving tank into a main reactor through a fourth temperature control metering pump for supplementary recycling as a reaction raw material, wherein the temperature of a tower bottom of the first rectifying tower is controlled at 120-160 ℃, the vacuum pressure of reduced pressure rectification is preferably 10-20 mmHg, the temperature of a gas phase at the tower top is preferably 60-110 ℃, the reflux ratio is preferably 1-4: 1, the temperature of the tower bottom of the second rectifying tower is controlled at 150-280 ℃, the vacuum pressure of reduced pressure is preferably 10-20 mmHg, the gas phase temperature at the tower top is preferably 120-150 ℃, the reflux ratio is preferably 1-4: 1.

Compared with the prior art, the continuous reaction method for preparing 6-aminocapronitrile by using the caprolactam liquid phase method has the following advantages:

1. the invention relates to a method for preparing 6-aminocapronitrile by a caprolactam liquid phase method, which takes caprolactam and ammonia gas as raw materials, takes phosphoric acid or phosphate as a catalyst, and prepares 6-aminocapronitrile by liquid phase reaction, and has the advantages of no solvent, low temperature, low energy consumption, high reaction conversion rate, high selectivity and simple preparation process.

2. According to the continuous reaction process for preparing 6-aminocapronitrile by the caprolactam liquid-phase method, the reaction is carried out in the tubular bubble tower, the inside of the reactor is uniformly heated, the material coking is effectively avoided, meanwhile, the target product 6-aminocapronitrile and the byproduct water generated by the reaction can be timely separated from the reaction system, the reaction is carried out in the forward direction, the open-loop polymerization of caprolactam caused by water at high temperature is avoided, the possibility of further coking and carbonization is avoided, and the reaction conversion rate and the selectivity are effectively improved.

The present invention has been described in detail hereinabove, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. Furthermore, there is no intention to be bound by any theory presented in the preceding prior art or the summary or the following examples.

Unless expressly stated otherwise, a numerical range throughout this specification includes any sub-range therein and any numerical value incremented by the smallest sub-unit within a given value. Unless expressly stated otherwise, numerical values throughout this specification represent approximate measures or limitations to the extent that such deviations from the given values, as well as embodiments having approximately the stated values and having the exact values stated, are included. Other than in the operating examples provided at the end of the detailed description, all numbers expressing quantities or conditions of parameters (e.g., quantities or conditions) used in the specification (including the appended claims) are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the number. "about" means that the numerical value so stated is allowed to be somewhat imprecise (with some approach to exactness in that value; about or reasonably close to that value; approximately). As used herein, "about" refers to at least variations that can be produced by ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" can include variations of less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%.

Drawings

FIG. 1 is a schematic diagram showing an apparatus for carrying out the continuous reaction process for producing 6-aminocapronitrile by the liquid phase process of caprolactam of the present invention.

Reference numerals:

1-a main reactor; 2-a tubular reaction zone; 3-a feed zone; 4-gas-liquid separation discharge area; 5-ammonia preheater; 6-ammonia gas feed pipe; 7-an ammonia gas flow meter; an 8-caprolactam preheater; a 9-caprolactam feed pipe; 10-a first temperature-controlled metering pump; 11-ammonia cylinder; 12-a first condenser; 13-a gas-liquid separator; 14-a second condenser; 15-a first recovery line; 16-a reaction liquid temporary storage tank; 17-a second temperature-controlled metering pump; 18-a first rectification column; 19-a second rectification column; 20-a third condenser; 21-a fourth condenser; a 22-6-aminocapronitrile receiver tank; a 23-caprolactam receiving tank; 24-a third temperature control metering pump; 25-a second recovery line; 26-fourth temperature-controlled metering pump.

Detailed Description

Hereinafter, the present invention will be described in detail by examples. However, the examples provided herein are for illustrative purposes only and are not intended to limit the present invention.

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Medicine information:

caprolactam, CAS number: 105-60-2, industrial super grade, Cangzhou Asahi chemical Co., Ltd;

liquid ammonia, CAS No.: 7664-41-7, industrial grade superior, Hebei Xuyang coking Co., Ltd;

phosphoric acid, CAS No.: 7664-38-2, reagent AR grade, Beijing Wacko Biotech limited;

ammonium phosphate, CAS number: 7722-76-1, reagent AR grade, national drug group chemical reagents, Inc.

Instrument information:

a temperature control metering pump CP050T, a temperature control range of 30-140 ℃, and Technological development Limited company of Tianjin Gechan Keyuan;

gas chromatograph: agilent 7890B, chromatography column: HP-5, 30m 320um 0.25 um.

Caprolactam conversion and 6-aminocaproamide selectivity were calculated as follows:

metering of the total mass M of caprolactam_{Step 1}And the number of moles R and the total mass M of the discharged sample_{Go out 1}(including sampling port samples and materials collected by a condensation recovery system), and testing the mass percentage content of the 6-aminocaproamide and the caprolactam of the discharged sample by a GC external standard method, thereby calculating the mole number G of the 6-aminocaproamide and the mole number H of the caprolactam of the discharged sample.

The 6-aminocaproamide conversion and 6-aminocapronitrile selectivity were calculated as follows:

metering of the total mass M of 6-aminocaproamide_{Step 2}And the number of moles N and the total mass M of the discharged sample_{Go out 2}(including sampling port samples and materials collected by a condensation recovery system), and testing the mass percentage content of the 6-aminocapronitrile and the 6-aminocaproamide in the discharged sample by a GC external standard method, thereby calculating the mole number D of the 6-aminocapronitrile and the mole number E of the 6-aminocaproamide in the discharged sample.

FIG. 1 is a schematic diagram showing an apparatus for carrying out the continuous reaction process for producing 6-aminocapronitrile by the liquid phase process of caprolactam of the present invention. Ammonia (NH) as shown in fig. 1₃) And Caprolactam (CPL) are respectively preheated, then respectively introduced into the main reactor 1 from a top feed inlet and a bottom feed inlet of the main reactor 1 according to a certain proportion through an ammonia gas flowmeter 7 and a first temperature control metering pump 10, and the catalyst and the caprolactam are mixed according to a certain proportion in advance and then preheated. The reaction material discharged from the upper end of the main reactor 1 is cooled by the first condenser 12 and then enters the gas-liquid separator 13, the liquid phase reaction product enters the reaction liquid temporary storage tank 16, the gas phase product enters the second condenser 14 to continue condensation and separation, the obtained liquid wastewater is discharged for treatment, the ammonia gas enters the ammonia gas compressor arranged on the first recovery pipeline 15 through the first recovery pipeline 15 and then is subjected to flow calculation through the ammonia gas flowmeter 7, and the ammonia gas is converged to the front end of the ammonia gas preheater for recycling. The liquid phase product is pumped into a first rectifying tower 18 through a second temperature control metering pump 17 after coming out of a reaction liquid temporary storage tank 16, the gas phase part is condensed and refluxed through a third condenser 20 to obtain a rectified product 6-aminocapronitrile (6-ACN) and enters a 6-aminocapronitrile receiving tank 22, and the 6-ACN receiving tank 22 is connected with a vacuum system. The liquid phase part of the first rectifying tower 18 is pumped into a second rectifying tower 19 through a third temperature control metering pump 24, and the gas phase is pumped into a third rectifying towerThe product is condensed and refluxed by a fourth condenser 21 to obtain a rectified product Caprolactam (CPL), the rectified product caprolactam enters a caprolactam receiving tank 23, the CPL receiving tank 23 is connected with a vacuum system, and the residue of the rectifying still of the second rectifying tower 19 is discharged and treated as solid waste. The caprolactam obtained from the caprolactam receiving tank 23 is pumped into the main reactor 1 through a second recovery pipeline 25 and a fourth temperature control metering pump 26 arranged thereon, and is used as a reaction raw material for supplement and recycling.

Example 1

Preheating caprolactam to 80 ℃ in a preheater 8, wherein the caprolactam is in a liquid state, adding phosphoric acid (based on the mass of the caprolactam) with the mass ratio of 0.002% as a catalyst into the caprolactam, fully mixing the caprolactam and the liquid caprolactam, and pumping the caprolactam into a main reactor 1 through a first temperature control metering pump 10, wherein the temperature of the first temperature control metering pump is 70-140 ℃, and the temperature of the main reactor is controlled to be 250 ℃; the preheating temperature of ammonia gas is 250 ℃, the ammonia gas is introduced into an inlet at the upper end of the main reactor 1 through an ammonia gas flowmeter 7, then bubbling is carried out at the bottom of the reactor, the ammonia gas is fully contacted with caprolactam and a catalyst, the temperature of the tubular reaction area 2 is controlled at 300 ℃, and the molar ratio of the introduced amount of the ammonia gas to the caprolactam is 40: 1.

Reaction products and excessive ammonia gas overflow from an outlet at the upper end of the main reactor 1 and enter a first condenser 12, the temperature of the first condenser 12 is controlled at 130 ℃, the reaction products enter a gas-liquid separator 13 after being cooled by the first condenser 12, liquid-phase reaction products enter a temporary reaction liquid storage tank 16, gas-phase products enter a second condenser 14, the temperature of the second condenser 14 is controlled at 20 ℃, condensation and separation are continued, obtained liquid wastewater is discharged for treatment, and the ammonia gas enters an ammonia gas compressor, then the flow is calculated by an ammonia gas flowmeter 7, and the ammonia gas is converged into the front end of an ammonia gas preheater for recycling.

And (3) after the liquid phase product is discharged from the reaction liquid temporary storage tank 16, pumping the liquid phase product into a first rectifying tower 18 through a second temperature control metering pump 17, wherein the temperature of the second temperature control metering pump is set to be 70-140 ℃, the temperature of the tower bottom of the first rectifying tower is controlled to be 120-160 ℃, the vacuum pressure is 15mmHg, the temperature of the gas phase at the tower top is 90-100 ℃, and the reflux ratio is 4:1, so that the rectified product 6-aminocapronitrile enters a 6-aminocapronitrile receiving tank 22.

And pumping the liquid phase part of the first rectifying tower 18 into a second rectifying tower 19 through a third temperature control metering pump 24, wherein the temperature of the third temperature control metering pump is set to be 70-140 ℃, the temperature of the tower bottom of the second rectifying tower is controlled to be 150-280 ℃, the vacuum pressure is 15mmHg, the gas phase temperature at the tower top is 130-140 ℃, the reflux ratio is 4:1, the rectified caprolactam is obtained and enters a caprolactam receiving tank, the receiving tank is connected with a vacuum system, and the residue of the rectifying tower of the second rectifying tower 19 is discharged and treated as solid waste.

And pumping caprolactam obtained from a caprolactam receiving tank into the main reactor 1 through a fourth temperature control metering pump 26 to be supplemented and recycled as a reaction raw material, wherein the setting temperature of the fourth temperature control metering pump is 70-140 ℃.

The caprolactam conversion was calculated to be 89.3% and the selectivity 98.6%.

Example 2

Preheating caprolactam to 80 ℃ in a preheater 8, wherein the caprolactam is in a liquid state, adding phosphoric acid (based on the mass of the caprolactam) with the mass ratio of 0.01% as a catalyst, fully mixing the caprolactam with the liquid caprolactam, and pumping the caprolactam into a main reactor through a first temperature control metering pump 10, wherein the temperature of the first temperature control metering pump is 70-140 ℃, and the temperature of the main reactor is controlled to be 200 ℃; the preheating temperature of ammonia gas is 200 ℃, ammonia gas is introduced into an inlet at the upper end of the main reactor 1 through an ammonia gas flowmeter 7, then bubbling is carried out at the bottom of the reactor, the ammonia gas is fully contacted with caprolactam and a catalyst, the temperature of the tubular reaction area 2 is controlled to be 250 ℃, and the molar ratio of the introduced amount of ammonia gas to the caprolactam is 30: 1.

Reaction products and excessive ammonia gas overflow from an outlet at the upper end of the main reactor 1 and enter a first condenser 12, the temperature of the first condenser 12 is controlled at 130 ℃, the reaction products enter a gas-liquid separator 13 after being cooled by the first condenser 12, liquid-phase reaction products enter a temporary reaction liquid storage tank 16, gas-phase products enter a second condenser 14, the temperature of the second condenser 14 is controlled at 20 ℃, condensation and separation are continued, obtained liquid wastewater is discharged for treatment, and the ammonia gas enters an ammonia gas compressor, then the flow is calculated by an ammonia gas flowmeter 7, and the ammonia gas is converged into the front end of an ammonia gas preheater for recycling.

And (3) after the liquid phase product is discharged from the reaction liquid temporary storage tank 16, pumping the liquid phase product into a first rectifying tower 18 through a second temperature control metering pump 17, wherein the temperature of the second temperature control metering pump is set to be 70-140 ℃, the temperature of the tower bottom of the first rectifying tower is controlled to be 120-160 ℃, the vacuum pressure is 15mmHg, the temperature of the gas phase at the tower top is 90-100 ℃, and the reflux ratio is 4:1, so that the rectified product 6-aminocapronitrile enters a 6-aminocapronitrile receiving tank 22.

And pumping the liquid phase part of the first rectifying tower 18 into a second rectifying tower 19 through a third temperature control metering pump 24, wherein the temperature of the third temperature control metering pump is set to be 70-140 ℃, the temperature of the tower bottom of the second rectifying tower is controlled to be 150-280 ℃, the vacuum pressure is 15mmHg, the gas phase temperature at the tower top is 130-140 ℃, the reflux ratio is 4:1, the rectified caprolactam is obtained and enters a caprolactam receiving tank, the receiving tank is connected with a vacuum system, and the residue of the rectifying tower of the second rectifying tower 19 is discharged and treated as solid waste.

And pumping caprolactam obtained from a caprolactam receiving tank into the main reactor 1 through a fourth temperature control metering pump 26 to be supplemented and recycled as a reaction raw material, wherein the setting temperature of the fourth temperature control metering pump is 70-140 ℃.

The caprolactam conversion was calculated to be 91.7% and the selectivity 97.1%.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.