阅读说明：本技术 一种由己内酰胺生产己二胺的方法及其装置 (Method and device for producing hexamethylene diamine from caprolactam ) 是由 陈天然 虞新建 于 2021-02-08 设计创作，主要内容包括：本发明公开了一种由己内酰胺生产己二胺的方法及其装置,氨气、己内酰胺在催化剂作用下,进行氨化脱水反应,得到的氨化脱水反应产物经三级冷凝分离；将二级冷凝得到的己内酰胺、6-氨基己腈冷凝液在催化剂作用下进行加氢反应,反应得到的含己二胺和己内酰胺混合物经分离得己二胺,在加氢反应时加入该冷凝液总重量5%～500%的水用作加氢反应稀释剂。本发明利用己内酰胺水溶液作为6-氨基己腈加氢反应稀释剂,不需加入乙醇作为稀释剂,减少了副产物N-Et-HMD、BHT、焦油产生。由于不对氨化脱水反应液进行精馏分离,降低了能耗。(The invention discloses a method for producing hexamethylene diamine by caprolactam and a device thereof, ammonia gas and caprolactam are subjected to ammoniation dehydration reaction under the action of a catalyst, and the obtained ammoniation dehydration reaction product is separated by three-stage condensation; the caprolactam obtained by secondary condensation and 6-aminocapronitrile condensate are subjected to hydrogenation reaction under the action of a catalyst, the mixture containing hexamethylene diamine and caprolactam obtained by the reaction is separated to obtain hexamethylene diamine, and water accounting for 5-500% of the total weight of the condensate is added in the hydrogenation reaction to be used as a hydrogenation reaction diluent. The invention uses the caprolactam water solution as the 6-aminocapronitrile hydrogenation diluent without adding ethanol as the diluent, thereby reducing the generation of by-products of N-Et-HMD, BHT and tar. Because the ammonification dehydration reaction liquid is not rectified and separated, the energy consumption is reduced.)

1. A method for producing hexamethylene diamine from caprolactam mainly comprises the following steps:

s1: carrying out ammoniation dehydration reaction on ammonia gas and caprolactam under the action of a catalyst to obtain an ammoniation dehydration reaction product;

s2: carrying out primary condensation on the product of the S1 ammoniation dehydration reaction, cooling to 300-315 ℃, and separating out heavy components; carrying out secondary condensation on the primary condensed gas phase, cooling to 140-210 ℃, and separating out condensate containing caprolactam and 6-aminocapronitrile; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating out water, and returning uncondensed ammonia gas serving as a raw material to the ammoniation dehydration reaction;

s3: carrying out hydrogenation reaction on caprolactam obtained by secondary condensation in S2 and 6-aminocapronitrile condensate under the action of a catalyst, adding water accounting for 5-500% of the total weight of the condensate during the hydrogenation reaction, and carrying out the hydrogenation reaction to obtain a mixture containing hexamethylene diamine and caprolactam;

s4: separating the mixture containing the hexamethylene diamine and the caprolactam obtained in the step S3 to obtain the hexamethylene diamine and the caprolactam, and returning the caprolactam serving as a raw material to the ammoniation dehydration reaction.

2. The method for producing hexamethylenediamine from caprolactam according to claim 1, wherein the catalyst for the ammoniation dehydration reaction in step S1 is one of alkaline earth metal phosphate, transition metal phosphate, iiia metal phosphate or a combination of at least two thereof.

3. The method for producing hexamethylenediamine from caprolactam according to claim 1, wherein the ammoniation dehydration reaction is carried out in a fixed bed reactor or a fluidized bed reactor.

4. The method for producing hexamethylene diamine by using caprolactam as claimed in claim 1, wherein the ammonia gas and caprolactam have a molar ratio of 5-50: 1 in the ammonification dehydration reaction; the temperature of the ammoniation dehydration reaction is 300-500 ℃, the reaction pressure is 0-2.0 MPa, and the gas phase space velocity is 720-3600 h^-1。

5. The process for producing hexamethylenediamine from caprolactam according to claim 1, wherein the hydrogenation of caprolactam and 6-aminocapronitrile in step S3 is a selective hydrogenation, only 6-aminocapronitrile is hydrogenated, and caprolactam does not participate in the hydrogenation; the hydrogenation reactor is a fluidized bed reactor, a stirring reactor or a fixed bed reactor; the hydrogenation catalyst comprises one or the combination of at least two of metal supported catalyst, amorphous nickel, Raney nickel and Raney cobalt.

6. The method of producing hexanediamine from caprolactam of claim 1, wherein the 6-aminocapronitrile hydrogenation of step S3 is further added with a co-catalyst selected from NaOH, KOH and CH₃CH₂ONa、CH₃One or a combination of at least two of ONa; the mass ratio of the cocatalyst to the 6-aminocapronitrile is 0.001-0.2: 1; the molar ratio of the hydrogen to the 6-aminocapronitrile is 2-100: 1; the reaction temperature is 30-100 ℃, and the pressure is 0-10.0 MPaG; the mass concentration of the catalyst in the reaction section is 5-40%, and the flow rate of the liquid phase is 0.1-10.0 m/s.

7. The process for producing hexamethylenediamine according to claim 1, wherein the hexamethylenediamine and caprolactam mixture of step S4 is separated: the liquid phase overflowed from the hydrogenation reactor contains hexamethylene diamine, caprolactam, water, entrained catalyst, cocatalyst and the like, flows to a filter after being flashed by a flash tank, the entrained catalyst is removed by the filter, the liquid phase mixture is sent to an auxiliary agent decanter, the cocatalyst solution is separated from the mixture, and the mixture containing hexamethylene diamine and caprolactam is sent to a dehydration tower; the temperature of the top of the dehydration tower is 45-55 ℃, the pressure is 85-95 mmHgA, water and HMI are extracted from the top of the dehydration tower, and the mixture containing hexamethylene diamine and caprolactam at the bottom of the dehydration tower is sent to a de-weighting tower; separating heavy tar containing the auxiliary agent mud from the bottom of the heavy component removal tower, and sending a mixture containing hexamethylene diamine and caprolactam separated from the top of the tower to a light component removal tower; the temperature of the top of the light component removal tower is 90-100 ℃, the pressure is 10-40 mmHgA, light components are separated from the top of the tower, and a mixture containing hexamethylene diamine and caprolactam at the bottom of the tower is sent to a hexamethylene diamine tower; the temperature of the top of the hexamethylenediamine tower is 102-106 ℃, the pressure is 30-35mmHgA, caprolactam extracted from the bottom of the tower is recycled, refined hexamethylenediamine is extracted from the side line of the higher section of the tower, and the material discharged from the top of the tower returns to the lightness-removing tower.

8. The process for producing hexamethylenediamine according to claim 1, wherein the hexamethylenediamine and caprolactam mixture of step S4 is separated: the liquid phase overflowed from the hydrogenation reactor contains hexamethylenediamine, caprolactam, water, entrained catalyst, cocatalyst and the like, flows to a filter after being flashed by a flash tank, the entrained catalyst is removed by the filter, the liquid phase mixture is sent to a cocatalyst decanter, the cocatalyst solution is separated from the mixture, and the mixture containing hexamethylenediamine and caprolactam is sent to a dehydration tower; the temperature of the top of the dehydration tower is 45-55 ℃, the pressure is 85-95 mmHgA, water and HMI are extracted from the top of the dehydration tower, and the mixture containing hexamethylene diamine and caprolactam at the bottom of the dehydration tower is sent to a light component removal tower; the temperature of the top of the light component removal tower is 90-100 ℃, the pressure is 10-40 mmHgA, light components are separated from the top of the tower, and a mixture containing hexamethylene diamine and caprolactam at the bottom of the tower is sent to a hexamethylene diamine tower; the temperature of the top of the hexamethylene diamine tower is 102-106 ℃, the pressure is 30-35mmHgA, refined hexamethylene diamine is extracted from the side line of the higher section of the tower, the material discharged from the top of the tower returns to a lightness-removing tower, the mixture containing caprolactam is extracted from the bottom of the tower and sent to a caprolactam evaporator in front of an ammoniation dehydration reactor, and heavy components are discharged from the bottom of the caprolactam evaporator.

9. The process of claim 1, wherein the hydrogenation of caprolactam and 6-aminocapronitrile in step S3 is carried out in a fixed bed reactor with a Catalyst of HTC NI 400 RP 2.5mm from johnson Matthey Catalyst, the Catalyst being packed in the fixed bed reactor, and water being added to the reaction feed: the mass ratio of (caprolactam + 6-aminocapronitrile) is 0.2-2: 1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-90 ℃, the reaction pressure is 0.5-3.0 MPa of gauge pressure, and the airspeed of the reaction liquid phase is 0.5-50h^-1。

10. A device for producing hexamethylene diamine by caprolactam mainly comprises an ammoniation dehydration reactor, a primary condenser, a secondary condenser, a tertiary condenser and a hydrogenation reactor, and is characterized in that the ammoniation dehydration reactor is provided with a feeding pipeline, and a gas phase outlet of the ammoniation dehydration reactor is connected with an inlet of the primary condenser; the gas phase outlet of the first-stage condenser is connected with the inlet of the second-stage condenser, and the first-stage condenser is provided with a liquid phase outlet; the gas phase outlet of the second-stage condenser is connected with the inlet of the third-stage condenser, and the liquid phase outlet of the second-stage condenser is connected with the inlet of the hydrogenation reactor; the third-stage condenser is provided with a gas phase outlet and a liquid phase outlet for discharging ammonia gas and waste water.

Technical Field

The invention belongs to the technical field of organic chemical industry, and relates to a method for producing hexamethylene diamine by using caprolactam, in particular to a method for producing hexamethylene diamine by hydrogenating a mixture of 6-aminocapronitrile and caprolactam and a device thereof.

Background

Hexamethylenediamine is a key raw material in the nylon industry, is usually used for synthesizing nylon 66 and nylon 610, and then is prepared into products such as nylon resin, nylon fibers, engineering plastics and the like. The industrial production method of the hexamethylene diamine is mainly a adiponitrile catalytic hydrogenation method, and the method produces impurity diaminocyclohexane which has large influence on the quality of nylon products while producing the hexamethylene diamine, and is difficult to separate. At present, with the increasing expansion of caprolactam production capacity and the decreasing price, the caprolactam method is expected to be popularized industrially. The caprolactam method takes caprolactam as a raw material to prepare 6-aminocapronitrile through catalytic ammoniation, and then the 6-aminocapronitrile is further subjected to catalytic hydrogenation to obtain the hexamethylene diamine.

Patent CN110423201A provides a method for synthesizing hexamethylenediamine from caprolactam as a raw material, which comprises mixing caprolactam, alkali and water, heating and refluxing to obtain 6-aminocaproate, further introducing amino protecting groups to protect terminal amino, then adding acid to neutralize and generate aminocaproic acid with amino protecting groups, drying, adding a dehydration catalyst for amide, heating and reacting in the presence of an ammonia source to convert carboxylic acid groups into cyano groups to obtain product nitrile, extracting and purifying the product nitrile, performing catalytic hydrogenation to generate corresponding amine, and removing the protecting groups to obtain hexamethylenediamine.

CN 112079725A discloses a method for producing hexamethylene diamine, ammonia, hydrogen and caprolactam are mixed and gasified to obtain mixed gas; adding a catalyst into the obtained mixed gas to perform a catalytic ammoniation reaction and a catalytic hydrogenation reaction; and then, condensing and separating the materials obtained by the reaction to obtain reaction liquid, and distilling the obtained reaction liquid to obtain the product hexamethylene diamine. The method integrates caprolactam ammoniation and hydrogenation, but has the defects of high reaction temperature and a plurality of byproducts, and has no industrial application value.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for producing hexamethylene diamine from caprolactam, which develops a method for producing hexamethylene diamine with low energy consumption, less byproducts and high product quality by organically combining the technologies of preparing 6-aminocapronitrile by ammoniating caprolactam and producing hexamethylene diamine by hydrogenating 6-aminocapronitrile.

The technical scheme of the invention is as follows:

a method for producing hexamethylene diamine from caprolactam mainly comprises the following steps:

s1: carrying out ammoniation dehydration reaction on ammonia gas and caprolactam under the action of a catalyst to obtain an ammoniation dehydration reaction product;

s2: carrying out primary condensation on the product of the S1 ammoniation dehydration reaction, cooling to 300-315 ℃, and separating out heavy components; carrying out secondary condensation on the primary condensed gas phase, cooling to 140-210 ℃, and separating out condensate containing caprolactam and 6-aminocapronitrile; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating out water, and returning uncondensed ammonia gas serving as a raw material to the ammoniation dehydration reaction;

s3: carrying out hydrogenation reaction on caprolactam obtained by secondary condensation in S2 and 6-aminocapronitrile condensate under the action of a catalyst, adding water accounting for 5-500% of the total weight of the condensate during the hydrogenation reaction, and carrying out the hydrogenation reaction to obtain a mixture containing hexamethylene diamine and caprolactam;

s4: separating the mixture containing the hexamethylene diamine and the caprolactam obtained in the step S3 to obtain the hexamethylene diamine and the caprolactam, and returning the caprolactam serving as a raw material to the ammoniation dehydration reaction.

The ammoniation dehydration reaction catalyst in the step S1 is one or a combination of at least two of alkaline earth metal phosphate, transition metal phosphate and IIIA metal phosphate.

The ammoniation dehydration reaction is carried out in a fixed bed reactor or a fluidized bed reactor.

In the ammonification dehydration reaction, the molar ratio of ammonia gas to caprolactam is 5-50: 1; the temperature of the ammoniation dehydration reaction is 300-500 ℃, the reaction pressure is 0-2.0 MPa, and the gas phase airspeed is 720 ∞3600h^-1。

The hydrogenation of caprolactam and 6-aminocapronitrile in the step S3 is selective hydrogenation, only 6-aminocapronitrile is hydrogenated, and caprolactam does not participate in the hydrogenation reaction; the hydrogenation reactor is a fluidized bed reactor, a stirring reactor or a fixed bed reactor; the stirred reactor is preferably a continuous stirred reactor.

The hydrogenation catalyst of step S3 includes one or a combination of at least two of metal supported catalyst, amorphous nickel, raney nickel, and raney cobalt. The metal-supported catalyst is preferably a noble metal-supported catalyst in which the noble metal comprises at least one of platinum, palladium, nickel or rhodium and the support comprises any one of or a combination of at least two of activated carbon, silica or alumina.

The 6-aminocapronitrile hydrogenation reaction of step S3 is further added with a cocatalyst, wherein the cocatalyst is NaOH, KOH, CH₃CH₂ONa、CH₃One or a combination of at least two of ONa.

Hydrogenation reaction in step S3: the mass ratio of the cocatalyst to the 6-aminocapronitrile is 0.001-0.2: 1; the molar ratio of the hydrogen to the 6-aminocapronitrile is 2-100: 1; the reaction temperature is 30-100 ℃, and the pressure is 0-10.0 MPaG; the mass concentration of the catalyst in the reaction section is 5-40%, and the flow rate of the liquid phase is 0.1-10.0 m/s.

Separating the mixture of hexamethylene diamine and caprolactam in the step S4: the liquid phase overflowed from the hydrogenation reactor contains hexamethylene diamine, caprolactam, water, entrained catalyst, cocatalyst and the like, flows to a filter after being flashed by a flash tank, the entrained catalyst is removed by the filter, the liquid phase mixture is sent to an auxiliary agent decanter, the cocatalyst solution is separated from the mixture, and the mixture containing hexamethylene diamine and caprolactam is sent to a dehydration tower; the temperature of the top of the dehydration tower is 45-55 ℃, the pressure is 85-95 mmHgA, water and HMI are extracted from the top of the dehydration tower, and the mixture containing hexamethylene diamine and caprolactam at the bottom of the dehydration tower is sent to a de-weighting tower; separating heavy tar containing the auxiliary agent mud from the bottom of the heavy component removal tower, and sending a mixture containing hexamethylene diamine and caprolactam separated from the top of the tower to a light component removal tower; the temperature of the top of the light component removal tower is 90-100 ℃, the pressure is 10-40 mmHgA, light components are separated from the top of the tower, and a mixture containing hexamethylene diamine and caprolactam at the bottom of the tower is sent to a hexamethylene diamine tower; the temperature of the top of the hexamethylenediamine tower is 102-106 ℃, the pressure is 30-35mmHgA, caprolactam extracted from the bottom of the tower is recycled, refined hexamethylenediamine is extracted from the side line of the higher section of the tower, and the material discharged from the top of the tower returns to the lightness-removing tower.

Another separation scheme for the hydrogenated stream: separating the mixture of hexamethylene diamine and caprolactam in the step S4: the liquid phase overflowed from the hydrogenation reactor contains hexamethylenediamine, caprolactam, water, entrained catalyst, cocatalyst and the like, flows to a filter after being flashed by a flash tank, the entrained catalyst is removed by the filter, the liquid phase mixture is sent to a cocatalyst decanter, the cocatalyst solution is separated from the mixture, and the mixture containing hexamethylenediamine and caprolactam is sent to a dehydration tower; the temperature of the top of the dehydration tower is 45-55 ℃, the pressure is 85-95 mmHgA, water and HMI are extracted from the top of the dehydration tower, and the mixture containing hexamethylene diamine and caprolactam at the bottom of the dehydration tower is sent to a light component removal tower; the temperature of the top of the light component removal tower is 90-100 ℃, the pressure is 10-40 mmHgA, light components are separated from the top of the tower, and a mixture containing hexamethylene diamine and caprolactam at the bottom of the tower is sent to a hexamethylene diamine tower; the temperature of the top of the hexamethylene diamine tower is 102-106 ℃, the pressure is 30-35mmHgA, refined hexamethylene diamine is extracted from the side line of the higher section of the tower, the material discharged from the top of the tower returns to a lightness-removing tower, the mixture containing caprolactam is extracted from the bottom of the tower and sent to a caprolactam evaporator in front of an ammoniation dehydration reactor, and heavy components are discharged from the bottom of the caprolactam evaporator.

The light component removal tower is characterized in that the light component removal tower is formed by connecting two light component removal towers in series, steam from the heavy component removal tower is supplied from the bottom of the first light component removal tower, light components separated from the top of the first light component removal tower are sent out of a battery compartment, and tower bottom liquid is sent to the second light component removal tower through a second light component removal tower feeding tank; in the second lightness-removing tower, the light components remained in the feed are separated out at the top of the tower, the light components separated out at the top of the tower are returned to the first lightness-removing tower for further treatment, and the hexamethylenediamine and caprolactam liquid containing a small amount of heavy components at the bottom of the tower are sent to the hexamethylenediamine tower.

In one embodiment: the hydrogenation reaction of caprolactam and 6-aminocapronitrile in step S3 is carried out in a fixed bed reactor, the Catalyst is HTC NI 400 RP 2.5mm sold by Johnson Matthey Catalyst company, the Catalyst is filled in the fixed bed reactor, and the reaction feed liquid is addedWater, water: the mass ratio of (caprolactam + 6-aminocapronitrile) is 0.2-2: 1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-90 ℃, the reaction pressure is 0.5-3.0 MPa of gauge pressure, and the airspeed of the reaction liquid phase is 0.5-50h^-1. Separating a mixture containing hexamethylene diamine and caprolactam, wherein a liquid phase overflowing from a hydrogenation reactor contains hexamethylene diamine, caprolactam, water, an entrained catalyst and the like, flows to a filter feeding tank after being flashed by a flash tank, the liquid phase is separated from the mixture containing hexamethylene diamine and caprolactam by a filter after the entrained catalyst is removed by the filter, the liquid phase containing hexamethylene diamine and caprolactam is sent to a dehydration tower, water and HMI are separated from crude hexamethylene diamine and caprolactam under the conditions that the temperature of the top of the tower is 45-55 ℃ and the pressure of the top of the tower is 85-95 mmHgA, the liquid phase is extracted from the top of the tower and sent to a wastewater pretreatment system, the liquid phase of the mixture containing hexamethylene diamine and caprolactam is sent to a lightness-removing tower for treatment, light components such as DCH are separated from the top of the tower under the conditions that the temperature of the top of the tower is 90-100 ℃ and the; extracting caprolactam from the bottom of a hexamethylenediamine tower under the conditions that the temperature of the top of the hexamethylenediamine tower is 102-106 ℃ and the pressure of the top of the hexamethylenediamine tower is 30-35mmHgA, sending the caprolactam to a caprolactam evaporator fed by an ammoniation dehydration reaction, and discharging heavy components from the bottom of the caprolactam evaporator; and (3) collecting refined hexamethylene diamine at the side line of the higher section of the tower, sending the refined hexamethylene diamine to a hexamethylene diamine storage tank in a tank field, and returning the discharged material at the top of the hexamethylene diamine tower to a light component removal tower feeding tank for retreatment.

The device for producing hexamethylene diamine by caprolactam, which is realized by the invention, mainly comprises an ammoniation dehydration reactor, a primary condenser, a secondary condenser, a tertiary condenser and a hydrogenation reactor, and is characterized in that the ammoniation dehydration reactor is provided with a feeding pipeline, and a gas phase outlet of the ammoniation dehydration reactor is connected with an inlet of the primary condenser; the gas phase outlet of the first-stage condenser is connected with the inlet of the second-stage condenser, and the first-stage condenser is provided with a liquid phase outlet; the gas phase outlet of the second-stage condenser is connected with the inlet of the third-stage condenser, and the liquid phase outlet of the second-stage condenser is connected with the inlet of the hydrogenation reactor; the third-stage condenser is provided with a gas phase outlet and a liquid phase outlet for discharging ammonia gas and waste water.

The ammoniation dehydration reactor is a fixed bed reactor or a fluidized bed reactor.

The hydrogenation reactor is a fluidized bed reactor, a stirring reactor or a fixed bed reactor; the reactor is provided with a liquid-solid separator which is provided with an overflow port.

The hydrogenation reactor is composed of two or three similar reaction tubes, is a gas-liquid-solid three-phase boiling type fluidized bed reactor, the reaction tubes are lifted to a gas-liquid separator, unreacted hydrogen and liquid in the gas-liquid separator are separated, the hydrogen enters a hydrogen washing tower to wash out entrained solvent, then the hydrogen is pressurized and recycled by a hydrogen circulating compressor, and the washed solvent is returned to the hydrogenation reactor; the lower part of the gas-liquid separator is provided with a liquid-solid separator which is provided with a waste catalyst discharge port and an overflow port; the reaction material and the hydrogen from the hydrogen pressure boosting compressor and the hydrogen circulation compressor are supplied from the bottom of the reaction tube, respectively, and the hydrogen and the reaction liquid rise together from the reaction tube to the gas-liquid separator.

The overflow port of the liquid-solid separator is connected with a dehydration tower, water is produced at the top of the dehydration tower, the bottom of the dehydration tower is connected with a heavy component removal tower, heavy components are produced at the bottom of the heavy component removal tower, and the top of the heavy component removal tower is connected with a light component removal tower; separating out light components from the top of the light component removal tower, and connecting the bottom of the light component removal tower with a hexamethylenediamine tower; separating out the hexamethylene diamine product at the top of the hexamethylene diamine tower, and arranging a caprolactam material flow outlet at the bottom of the hexamethylene diamine tower.

In one embodiment, the overflow port of the liquid-solid separator is connected with a dehydration tower, water is produced at the top of the dehydration tower, and the bottom of the dehydration tower is connected with a light component removal tower; separating out light components from the top of the light component removal tower, and connecting the bottom of the light component removal tower with a hexamethylenediamine tower; separating out the hexamethylene diamine product from the top of the hexamethylene diamine tower, arranging a caprolactam material flow outlet at the bottom, and returning the caprolactam to a caprolactam feeding evaporator before the ammoniation dehydration reactor.

The dehydration tower is provided with a flash tank in front, the inlet of the flash tank is connected with the overflow port of the liquid-solid separator, the gas outlet of the flash tank is connected with the hydrogen washing tower, and the liquid outlet of the flash tank is connected with the dehydration tower.

The front of the dehydration tower is provided with a desolventizing tower which is connected with an overflow port of a liquid-solid separator, a solvent outlet at the top of the desolventizing tower is connected with a hydrogenation reactor, and a tower bottom outlet of the desolventizing tower is connected with the dehydration tower. The front of the desolventizing tower is provided with a flash tank, the inlet of the flash tank is connected with the overflow port of the liquid-solid separator, the gas outlet of the flash tank is connected with the hydrogen washing tower, and the liquid outlet of the flash tank is connected with the feeding pipe of the desolventizing tower.

The light component removing tower is characterized in that two light component removing towers are connected in series, steam from a heavy component removing tower enters the bottom of a first light component removing tower, light components are separated from the top of the tower, and the bottom of the tower is sent to a second light component removing tower; light components separated from the top of the second lightness-removing tower return to the first lightness-removing tower, and a mixture of hexamethylene diamine and caprolactam containing a small amount of heavy components at the bottom of the second lightness-removing tower is sent to a hexamethylene diamine tower.

Features and effects of the invention

According to the invention, 6-aminocapronitrile and caprolactam mixture flow is subjected to 6-aminocapronitrile hydrogenation reaction, the caprolactam aqueous solution is favorable for 6-aminocapronitrile hydrogenation, and can control caprolactam not to be hydrogenated, the caprolactam aqueous solution is used as a 6-aminocapronitrile hydrogenation reaction diluent, ethanol is not required to be added as a diluent, and the generation of byproducts N-Et-HMD (N-ethylhexanediamine), BHT (dicyclohexylenetriamine) and tar is reduced.

According to the invention, a caprolactam ammoniation dehydration reactant is separated in a condensation mode, ammonia gas is recovered, the 6-aminocapronitrile and a caprolactam mixture are directly hydrogenated without rectification separation, and only the 6-aminocapronitrile is hydrogenated and the caprolactam is not hydrogenated by adding water.

The invention saves the energy consumption of rectification separation of ammoniated dehydration reactants, reduces byproducts of hydrogenation reaction, and reduces the consumption of 1.5t/t of hexamethylene diamine product in hexamethylene diamine production. The one-way conversion rate of caprolactam can reach 50-70%, and the selectivity of hexamethylene diamine can reach 99%.

In a preferred embodiment of the invention, the separation of hydrogenation products is carried out without a de-weighting tower, and caprolactam containing heavy components is fed into a caprolactam evaporator through an ammoniation dehydration reaction and is evaporated through caprolactam, so that the separation process is simplified, and the steam consumption can be reduced by 0.5t/t of products.

Drawings

FIG. 1 is a schematic diagram of an apparatus for producing hexamethylenediamine from caprolactam according to the present invention;

wherein: 1-an ammoniation dehydration reactor, 2-a first-stage condenser, 3-a second-stage condenser, 4-a third-stage condenser and 5-a hydrogenation reactor;

a-ammoniation dehydration reaction feed stream, B-heavy components condensed by a primary condenser, C-tertiary condenser condensate and D-tertiary condenser gas-phase ammonia gas.

Detailed Description

The invention is further illustrated below with reference to examples and figures, but the invention is not limited to these examples.

The invention relates to a method for producing hexamethylene diamine by caprolactam, which adopts a device in figure 1 and consists of an ammoniation dehydration reactor, a primary condenser, a secondary condenser, a tertiary condenser and a hydrogenation reactor, and is characterized in that the ammoniation dehydration reactor is provided with a feeding pipeline, and a gas phase outlet of the ammoniation dehydration reactor is connected with an inlet of the primary condenser; the gas phase outlet of the first-stage condenser is connected with the inlet of the second-stage condenser, and the first-stage condenser is provided with a liquid phase outlet; the gas phase outlet of the second-stage condenser is connected with the inlet of the third-stage condenser, and the liquid phase outlet of the second-stage condenser is connected with the inlet of the hydrogenation reactor; the third-stage condenser is provided with a gas phase outlet and a liquid phase outlet for discharging ammonia gas and waste water. The ammoniation dehydration reactor is a fixed bed reactor or a fluidized bed reactor.

The hydrogenation reactor is a fluidized bed reactor, a stirring reactor or a fixed bed reactor; the reactor is provided with a liquid-solid separator which is provided with an overflow port.

The hydrogenation reactor is composed of two or three similar reaction tubes, is a gas-liquid-solid three-phase boiling type fluidized bed reactor, the reaction tubes are lifted to a gas-liquid separator, unreacted hydrogen and liquid in the gas-liquid separator are separated, the hydrogen enters a hydrogen washing tower to wash out entrained solvent, then the hydrogen is pressurized and recycled by a hydrogen circulating compressor, and the washed solvent is returned to the hydrogenation reactor; the lower part of the gas-liquid separator is provided with a liquid-solid separator which is provided with a waste catalyst discharge port and an overflow port; the reaction material and the hydrogen from the hydrogen pressure boosting compressor and the hydrogen circulation compressor are supplied from the bottom of the reaction tube, respectively, and the hydrogen and the reaction liquid rise together from the reaction tube to the gas-liquid separator.

The overflow port of the liquid-solid separator is connected with a dehydration tower, water is produced at the top of the dehydration tower, the bottom of the dehydration tower is connected with a heavy component removal tower, heavy components are produced at the bottom of the heavy component removal tower, and the top of the heavy component removal tower is connected with a light component removal tower; separating out light components from the top of the light component removal tower, and connecting the bottom of the light component removal tower with a hexamethylenediamine tower; separating out the hexamethylene diamine product at the top of the hexamethylene diamine tower, and arranging a caprolactam material flow outlet at the bottom of the hexamethylene diamine tower.

In one embodiment, the overflow port of the liquid-solid separator is connected with a dehydration tower, water is produced at the top of the dehydration tower, and the bottom of the dehydration tower is connected with a light component removal tower; separating out light components from the top of the light component removal tower, and connecting the bottom of the light component removal tower with a hexamethylenediamine tower; separating out the hexamethylene diamine product from the top of the hexamethylene diamine tower, arranging a caprolactam material flow outlet at the bottom, and returning the caprolactam to a caprolactam feeding evaporator before the ammoniation dehydration reactor.

The dehydration tower is provided with a flash tank in front, the inlet of the flash tank is connected with the overflow port of the liquid-solid separator, the gas outlet of the flash tank is connected with the hydrogen washing tower, and the liquid outlet of the flash tank is connected with the dehydration tower.

The front of the dehydration tower is provided with a desolventizing tower which is connected with an overflow port of a liquid-solid separator, a solvent outlet at the top of the desolventizing tower is connected with a hydrogenation reactor, and a tower bottom outlet of the desolventizing tower is connected with the dehydration tower. The front of the desolventizing tower is provided with a flash tank, the inlet of the flash tank is connected with the overflow port of the liquid-solid separator, the gas outlet of the flash tank is connected with the hydrogen washing tower, and the liquid outlet of the flash tank is connected with the feeding pipe of the desolventizing tower.

The light component removing tower is characterized in that two light component removing towers are connected in series, steam from a heavy component removing tower enters the bottom of a first light component removing tower, light components are separated from the top of the tower, and the bottom of the tower is sent to a second light component removing tower; light components separated from the top of the second lightness-removing tower return to the first lightness-removing tower, and a mixture of hexamethylene diamine and caprolactam containing a small amount of heavy components at the bottom of the second lightness-removing tower is sent to a hexamethylene diamine tower.

The production process of the invention comprises the following steps:

s1: carrying out ammoniation dehydration reaction on ammonia gas and caprolactam under the action of a catalyst to obtain an ammoniation dehydration reaction product;

s2: carrying out primary condensation on the ammoniated dehydration reaction product obtained in the step S1, cooling to 300-315 ℃, and separating out heavy components; carrying out secondary condensation on the primary condensed gas phase, cooling to 140-210 ℃, and separating out condensate containing caprolactam and 6-aminocapronitrile; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating out water, and returning gas-phase ammonia gas to the ammoniation dehydration reaction to be used as a raw material for recycling;

s3: carrying out hydrogenation reaction on caprolactam obtained by secondary condensation in S2 and 6-aminocapronitrile condensate under the action of a catalyst to obtain a mixture containing crude hexamethylene diamine and caprolactam;

s4: and (3) separating the mixture containing the crude hexamethylene diamine and the caprolactam obtained in the step (S3) to obtain the hexamethylene diamine and the caprolactam, and returning the caprolactam to the ammoniation dehydration reaction to be used as a raw material for recycling.

Example 1:

production of hexamethylenediamine from caprolactam

Evaporating caprolactam in an evaporator, and mixing the caprolactam with hot ammonia gas according to a mol ratio of 1: 30, mixing the mixture, putting the mixture into a fixed bed reactor filled with a magnesium phosphate catalyst, controlling the temperature to be 300-400 ℃, and controlling the reaction pressure to be 0-1.0 MPa; the gas phase space velocity is 720-3600 h^-1；

Carrying out primary condensation on the ammoniation dehydration reaction product obtained above, cooling to 300-315 ℃, and separating out heavy components; carrying out secondary condensation on the primary condensed gas phase, cooling to 140-210 ℃, and separating out condensate containing caprolactam and 6-aminocapronitrile; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating out water, and returning gas-phase ammonia gas to the ammoniation dehydration reaction to be used as a raw material for recycling;

and (3) carrying out hydrogenation reaction on caprolactam obtained by secondary condensation and 6-aminocapronitrile condensate under the action of a catalyst to obtain a mixture containing crude hexamethylene diamine and caprolactam. The hydrogenation reaction is carried out in a fluidized bed reactor consisting of three reaction tubes, the hydrogenation catalyst is of a Raney nickel type, the cocatalyst is NaOH, and water are added into reaction feed liquid: the mass ratio of (caprolactam + 6-aminocapronitrile) is 0.5:1, the mass ratio of the cocatalyst to 6-aminocapronitrile is 0.001-0.1: 1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-100 ℃, the reaction pressure is gauge pressure of 1.5-3.0 MPa, the concentration of the catalyst in the reaction section is 25%, and the flow rate of the reaction liquid phase is 2.0-4.0 m/s;

the method comprises the following steps of (1) enabling a liquid phase overflowing from a hydrogenation reactor to contain hexamethylenediamine, caprolactam, water, an entrained catalyst, NaOH and the like to flow to a filter feeding tank after being flashed by a flash tank, removing the entrained catalyst through a filter, feeding a hexamethylenediamine and caprolactam mixture of the liquid phase solution into an NaOH decanter, separating the NaOH solution from the hexamethylenediamine and caprolactam solution, feeding a crude hexamethylenediamine and caprolactam solution into a dehydration tower, separating water and HMI (cyclohexylimine) from the hexamethylenediamine and caprolactam mixture under the conditions that the temperature of the tower top is 45-55 ℃ and the pressure of the tower top is 85-95 mmHgA, pumping out the mixture from the tower top, feeding the mixture into a wastewater pretreatment system, feeding a hexamethylenediamine and caprolactam mixture flow liquid at the tower bottom into a de-weighting tower for treatment, and separating heavy tar containing NaOH slurry from the hexamethylenediamine and caprolactam liquid at the tower bottom of the de-; sending the crude hexamethylenediamine and caprolactam liquid at the top of the tower to a lightness removing tower for treatment, separating light components such as DCH (diaminocyclohexane) from the top of the tower under the conditions that the temperature at the top of the tower is 90-100 ℃ and the pressure at the top of the tower is 10-40 mmHgA, and sending the solution containing hexamethylenediamine and caprolactam at the bottom of the tower to a hexamethylenediamine tower; under the conditions that the temperature of the top of the hexamethylenediamine tower is 102-106 ℃ and the pressure of the top of the hexamethylenediamine tower is 30-35mmHgA, extracting caprolactam from the bottom of the hexamethylenediamine tower for cyclic utilization; and (3) collecting refined hexamethylene diamine at the side line of the higher section of the tower, sending the refined hexamethylene diamine to a hexamethylene diamine storage tank in a tank field, and returning the discharged material at the top of the hexamethylene diamine tower to a light component removal tower feeding tank for retreatment.

The conversion per pass of the ammonification and dehydration of the caprolactam is 50-70 percent, the purity of the hexamethylene diamine product is 99.9 percent, the generation of a by-product N-Et-HMD (N-ethylhexamethylene diamine) is reduced because ethanol is not used as a solvent, the N-Et-HMD cannot be detected, meanwhile, a caprolactam water solution plays a role of a diluent in the hydrogenation reaction process, the hydrogenation selectivity of the 6-aminocapronitrile is improved, the selectivity reaches 99 percent, and the consumption of the raw material caprolactam is reduced. Conventionally, ethanol is used as a diluent, and the amount of N-Et-HMD in a hydrogenation product reaches 1.5-2.5%.

Because the rectification separation of the caprolactam ammoniation dehydration reaction material flow is not needed, the steam consumption can be reduced by 1.5 t/t.

Example 2

Production of hexamethylenediamine from caprolactam

Evaporating caprolactam in an evaporator, and mixing the caprolactam with hot ammonia gas according to a mol ratio of 1: 30, mixing and feeding the mixture into a fixed bed reactor filled with a magnesium phosphate catalyst, controlling the temperature at 300 ℃ and the temperature at 400 ℃, and controlling the reaction pressure at 0-1.0 MPa; the gas phase space velocity is 730-3600 h^-1；

Performing primary condensation on the ammoniation dehydration reaction product obtained above, cooling to the temperature of 300 ℃ and 315 ℃, and separating out heavy components; then the primary condensed gas phase is subjected to secondary condensation, cooled to 140 ℃ and 210 ℃, and condensed liquid containing caprolactam and 6-aminocapronitrile is separated; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating water, and returning gas-phase ammonia gas to the ammoniation dehydration reaction to be used as a raw material for recycling;

and (3) carrying out hydrogenation reaction on caprolactam obtained by secondary condensation and 6-aminocapronitrile condensate under the action of a catalyst to obtain a mixture containing crude hexamethylene diamine and caprolactam. The hydrogenation reaction is carried out in a continuous stirring reactor, the hydrogenation catalyst is of a Raney nickel type, the concentration and mass concentration of the catalyst are 5% -30%, the cocatalyst is NaOH, and water are added into the reaction solution: the mass ratio of (caprolactam + 6-aminocapronitrile) is 0.8:1, the mass ratio of the cocatalyst to 6-aminocapronitrile is 0.001-0.1: 1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-80 ℃, and the reaction pressure is 1.5-3.0 MPa of gauge pressure;

the method comprises the following steps of (1) enabling a liquid phase overflowing from a hydrogenation reactor to contain hexamethylenediamine, caprolactam, water, an entrained catalyst, NaOH and the like to flow to a filter feeding tank after being flashed by a flash tank, removing the entrained catalyst through a filter, feeding a hexamethylenediamine and caprolactam mixture of the liquid phase solution into an NaOH decanter, separating the NaOH solution from crude hexamethylenediamine and caprolactam solution, feeding the crude hexamethylenediamine and caprolactam solution into a dehydration tower, separating water and HMI (human machine interface) from the crude hexamethylenediamine and caprolactam mixture under the conditions that the temperature of the tower top is 45-55 ℃ and the pressure of the tower top is 85-95 mmHgA, pumping out the mixture from the tower top, feeding the mixture into a wastewater pretreatment system, feeding a hexamethylenediamine and caprolactam mixture flow liquid at the tower bottom into a de-weighting tower for treatment, and separating heavy tar containing NaOH mud from the hexamethylenediamine and caprolactam liquid at the tower; sending the crude hexamethylenediamine and caprolactam liquid at the top of the tower to a lightness-removing tower for treatment, separating light components such as DCH from the top of the tower under the conditions that the temperature at the top of the tower is 90-100 ℃ and the pressure at the top of the tower is 10-40 mmHgA, and sending the solution containing hexamethylenediamine and caprolactam at the bottom of the tower to a hexamethylenediamine tower; under the conditions that the temperature of the top of the hexamethylenediamine tower is 102-106 ℃ and the pressure of the top of the hexamethylenediamine tower is 30-35mmHgA, extracting caprolactam from the bottom of the hexamethylenediamine tower for cyclic utilization; and (3) collecting refined hexamethylene diamine at the side line of the higher section of the tower, sending the refined hexamethylene diamine to a hexamethylene diamine storage tank in a tank field, and returning the discharged material at the top of the hexamethylene diamine tower to a light component removal tower feeding tank for retreatment.

The conversion per pass of the ammonification and dehydration of the caprolactam is 50-70 percent, the purity of the hexamethylene diamine product is 99.9 percent, the generation of a by-product N-Et-HMD (N-ethylhexamethylene diamine) is reduced because ethanol is not used as a solvent, the N-Et-HMD cannot be detected, meanwhile, a caprolactam water solution plays a role of a diluent in the hydrogenation reaction process, the hydrogenation selectivity of the 6-aminocapronitrile is improved, the selectivity reaches 99 percent, and the consumption of the raw material caprolactam is reduced.

The steam consumption can be reduced by 1.5t/t because the rectification separation of caprolactam ammonification dehydration reaction material flow is not needed.

Example 3

Production of hexamethylenediamine from caprolactam

Evaporating caprolactam in an evaporator, and mixing the caprolactam with hot ammonia gas according to a mol ratio of 1: 30, mixing the mixture, putting the mixture into a fixed bed reactor filled with a magnesium phosphate catalyst, controlling the temperature to be 300-400 ℃, and controlling the reaction pressure to be 0-1.0 MPa; the gas phase space velocity is 730-3600 h^-1；

Performing primary condensation on the ammoniation dehydration reaction product obtained above, cooling to the temperature of 300 ℃ and 315 ℃, and separating out heavy components; then the primary condensed gas phase is subjected to secondary condensation, cooled to 140 ℃ and 180 ℃, and condensed liquid containing caprolactam and 6-aminocapronitrile is separated; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating water, and returning gas-phase ammonia gas to the ammoniation dehydration reaction to be used as a raw material for recycling;

the caprolactam obtained by secondary condensation and the 6-aminocapronitrile condensate are subjected to hydrogenation reaction under the action of a catalyst,a mixture containing crude hexamethylenediamine and caprolactam is obtained. The hydrogenation reaction is carried out in a fixed bed reactor, the hydrogenation catalyst is a Raney nickel type forming catalyst, the catalyst is filled in the fixed bed reactor, the cocatalyst is NaOH, and water are added into reaction feed liquid: the mass ratio of (caprolactam + 6-aminocapronitrile) is 0.5:1, the mass ratio of the cocatalyst to 6-aminocapronitrile is 0.001-0.1: 1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-90 ℃, the reaction pressure is 0.5-3.0 MPa of gauge pressure, and the airspeed of the reaction liquid phase is 0.5-50h^-1；

The method comprises the following steps of (1) enabling a liquid phase overflowing from a hydrogenation reactor to contain hexamethylenediamine, caprolactam, water, an entrained catalyst, NaOH and the like to flow to a filter feeding tank after being flashed by a flash tank, removing the entrained catalyst through a filter, feeding a hexamethylenediamine and caprolactam mixture of the liquid phase solution into an NaOH decanter, separating the NaOH solution from crude hexamethylenediamine and caprolactam solution, feeding the crude hexamethylenediamine and caprolactam solution into a dehydration tower, separating water and HMI (human machine interface) from the crude hexamethylenediamine and caprolactam mixture under the conditions that the temperature of the tower top is 45-55 ℃ and the pressure of the tower top is 85-95 mmHgA, pumping out the mixture from the tower top, feeding the mixture into a wastewater pretreatment system, feeding a hexamethylenediamine and caprolactam mixture flow liquid at the tower bottom into a de-weighting tower for treatment, and separating heavy tar containing NaOH mud from the hexamethylenediamine and caprolactam liquid at the tower; sending the crude hexamethylenediamine and caprolactam liquid at the top of the tower to a lightness-removing tower for treatment, separating light components such as DCH from the top of the tower under the conditions that the temperature at the top of the tower is 90-100 ℃ and the pressure at the top of the tower is 10-40 mmHgA, and sending the solution containing hexamethylenediamine and caprolactam at the bottom of the tower to a hexamethylenediamine tower; under the conditions that the temperature of the top of the hexamethylenediamine tower is 102-106 ℃ and the pressure of the top of the hexamethylenediamine tower is 30-35mmHgA, extracting caprolactam from the bottom of the hexamethylenediamine tower for cyclic utilization; and (3) collecting refined hexamethylene diamine at the side line of the higher section of the tower, sending the refined hexamethylene diamine to a hexamethylene diamine storage tank in a tank field, and returning the discharged material at the top of the hexamethylene diamine tower to a light component removal tower feeding tank for retreatment.

The conversion per pass of the ammonification and dehydration of the caprolactam is 40-50 percent, the purity of the hexamethylene diamine product is 99.9 percent, the generation of a by-product N-Et-HMD (N-ethylhexamethylene diamine) is reduced because ethanol is not used as a solvent, the N-Et-HMD cannot be detected, meanwhile, a caprolactam water solution plays a role of a diluent in the hydrogenation reaction process, the hydrogenation selectivity of the 6-aminocapronitrile is improved, the selectivity reaches 99 percent, and the consumption of the raw material caprolactam is reduced.

The steam consumption can be reduced by 1.5t/t because the rectification separation of caprolactam ammonification dehydration reaction material flow is not needed.

Example 4

Production of hexamethylenediamine from caprolactam

Evaporating caprolactam in an evaporator, and mixing the caprolactam with hot ammonia gas according to a mol ratio of 1: 30, mixing the mixture, putting the mixture into a fixed bed reactor filled with a magnesium phosphate catalyst, controlling the temperature to be 300-400 ℃, and controlling the reaction pressure to be 0-1.0 MPa; the gas phase space velocity is 730-3600 h^-1；

Carrying out primary condensation on the ammoniation dehydration reaction product obtained above, cooling to 300-315 ℃, and separating out heavy components; carrying out secondary condensation on the primary condensed gas phase, cooling to 140-210 ℃, and separating out condensate containing caprolactam and 6-aminocapronitrile; carrying out third-stage condensation on the gas phase of the second-stage condensation, cooling to 40-60 ℃, separating out water, and returning gas-phase ammonia gas to the ammoniation dehydration reaction to be used as a raw material for recycling;

and (3) carrying out hydrogenation reaction on caprolactam obtained by secondary condensation and 6-aminocapronitrile condensate under the action of a catalyst to obtain a mixture containing crude hexamethylene diamine and caprolactam. The hydrogenation reaction was carried out in a fixed bed reactor, the Catalyst was HTC NI 400 RP 2.5mm sold by johnson Matthey Catalyst company, the Catalyst was loaded in the fixed bed reactor, water: the mass ratio of (caprolactam + 6-aminocapronitrile) is 1.5:1, and the molar ratio of hydrogen to 6-aminocapronitrile is 2-8: 1; the reaction temperature is 60-90 ℃, the reaction pressure is 0.5-3.0 MPa of gauge pressure, and the airspeed of the reaction liquid phase is 0.5-50h^-1；

Separating a mixture containing hexamethylene diamine and caprolactam, wherein a liquid phase overflowing from a hydrogenation reactor contains hexamethylene diamine, caprolactam, water, an entrained catalyst and the like, flows to a filter feeding tank after being flashed by a flash tank, the liquid phase is separated from the mixture containing hexamethylene diamine and caprolactam by a filter after the entrained catalyst is removed by the filter, the liquid phase containing hexamethylene diamine and caprolactam is sent to a dehydration tower, water and HMI are separated from crude hexamethylene diamine and caprolactam under the conditions that the temperature of the top of the tower is 45-55 ℃ and the pressure of the top of the tower is 85-95 mmHgA, the liquid phase is extracted from the top of the tower and sent to a wastewater pretreatment system, the liquid phase of the mixture containing hexamethylene diamine and caprolactam is sent to a lightness-removing tower for treatment, light components such as DCH are separated from the top of the tower under the conditions that the temperature of the top of the tower is 90-100 ℃ and the; extracting caprolactam from the bottom of a hexamethylenediamine tower under the conditions that the temperature of the top of the hexamethylenediamine tower is 102-106 ℃ and the pressure of the top of the hexamethylenediamine tower is 30-35mmHgA, sending the caprolactam to a caprolactam evaporator fed by an ammoniation dehydration reaction, and discharging heavy components from the bottom of the caprolactam evaporator; and (3) collecting refined hexamethylene diamine at the side line of the higher section of the tower, sending the refined hexamethylene diamine to a hexamethylene diamine storage tank in a tank field, and returning the discharged material at the top of the hexamethylene diamine tower to a light component removal tower feeding tank for retreatment.

The conversion per pass of the ammonification and dehydration of the caprolactam is 40-50 percent, the purity of the hexamethylene diamine product is 99.9 percent, the generation of a by-product N-Et-HMD (N-ethylhexamethylene diamine) is reduced because ethanol is not used as a solvent, the N-Et-HMD cannot be detected, meanwhile, a caprolactam water solution plays a role of a diluent in the hydrogenation reaction process, the hydrogenation selectivity of the 6-aminocapronitrile is improved, the selectivity reaches 99 percent, and the consumption of the raw material caprolactam is reduced.

In the embodiment, because a fixed bed reactor is used, a novel catalyst is simultaneously selected, and a cocatalyst is not required to be added, caprolactam fed by an ammoniation dehydration reaction can be used for evaporating to remove heavy components, a de-weighting tower in the separation of hydrogenation products is omitted, and the steam consumption of each ton of products can be reduced by 0.5t/t of hexamethylene diamine. Thus, compared with the prior separation process, the method can reduce the steam consumption by 2.0t/t and simultaneously reduce the separation strength of the catalyst.