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CN-121974824-A - Treatment method of reaction residues of synthesis of 6-aminocapronitrile from caprolactam

CN121974824ACN 121974824 ACN121974824 ACN 121974824ACN-121974824-A

Abstract

The invention provides a treatment method of reaction residues of synthesizing 6-aminocapronitrile from caprolactam, which comprises the steps of firstly, feeding the reaction residues of synthesizing 6-aminocapronitrile from caprolactam and fresh water into a stirred tank reactor for preliminary hydrolysis reaction, fixing a catalyst on a stirring paddle through a wire mesh, then, feeding reaction liquid and ammonia gas into a multistage gas-liquid two-phase tower reactor, and sequentially passing through a reaction section filled with metal oxide, a molecular sieve and a solid base catalyst to realize deep hydrolysis of a polymer, decomposition of aminocaproic acid and ammonolysis of caprolactam. The method has the advantages of high hydrolysis rate of 94% or more, high 6-aminocapronitrile yield of 90% or more, capability of deeply hydrolyzing residues, simple flow and continuous operation, solves the problems of insufficient hydrolysis and intermittent operation in the prior art, greatly reduces the solid waste discharge in the production process of hexamethylenediamine, reduces the cost, improves the economic benefit and provides guarantee for green safety and safety production.

Inventors

  • WANG XIAODA
  • GE XUEHUI
  • LIU YAN
  • LIU ZHIYONG
  • ZHOU CAIJIN
  • JIANG LILONG
  • PAN DEBIAO
  • WANG JIANHUA

Assignees

  • 福建省恒申化工科技有限公司
  • 福州大学

Dates

Publication Date
20260505
Application Date
20251215

Claims (7)

  1. 1. A method for treating reaction residues of synthesizing 6-aminocapronitrile from caprolactam is characterized by comprising the following steps: Step (1) delivering reaction residues generated in synthesis of 6-aminocapronitrile from caprolactam and fresh water into a stirred tank reactor for preliminary hydrolysis reaction, wherein the obtained reaction liquid contains water, polymer, aminocaproic acid, caprolactam and 6-aminocapronitrile, and a solid catalyst is filled in the reactor, the operating pressure range of the stirred tank reactor is 0.1-1.0 MPa, the reaction temperature range is 250-400 ℃, the stirring speed range is 50-1500 rpm, the residence time range is 30-360 min, the catalyst volume fraction range is 10% -40%, and the mass ratio of the fresh water to the residues is 1-20; The reaction liquid and fresh ammonia which leave the stirred tank reactor in the step (2) are respectively sent into a gas-liquid two-phase tower reactor, three different types of solid catalysts are arranged in the tower reactor, and the three different types of solid catalysts are respectively subjected to residue deep hydrolysis reaction, aminocaproic acid decomposition and caprolactam ammonolysis reaction, so that 6-aminocapronitrile is finally obtained from the tower reactor; The tower reactor comprises a partial condenser, a partial reboiler and a tower body provided with tower plates with different structures, wherein the tower body is divided into six parts, and comprises three separation sections and three reaction sections, namely a first separation section, a first reaction section, a second separation section, a third reaction section and a third separation section from top to bottom; The reaction liquid and fresh ammonia gas leaving the stirred tank reactor enter the tower reactor from the top of the first reaction section and the bottom of the third reaction section respectively, the steam leaving from the top of the tower is subjected to partial condenser to obtain ammonia gas and water, the ammonia gas returns to the tower reactor from the bottom of the third reaction section, the water returns to the tower reactor from the top of the first separation section and the bottom of the first reaction section respectively, the liquid leaving from the bottom of the tower reactor is subjected to partial reboiler to obtain steam and liquid phase, the steam returns to the tower reactor from the bottom, and the liquid phase is extracted as a product; The operating pressure of the tower reactor ranges from 0.1 MPa to 1.0MPa, the mass ratio of the reaction liquid to the fresh ammonia gas ranges from 1 (0.1-10), the mass ratio of water returned to the top of the first separation section to water returned to the bottom of the first reaction section ranges from 0.1-10, and the mass ratio of gas phase to liquid phase leaving part of the reboiler ranges from 1-20.
  2. 2. A process for treating the reaction residue of synthesizing 6-aminocapronitrile from caprolactam according to claim 1, wherein the residue is above 50% based on 6-aminocapronitrile dimer, dimer of 6-aminocapronitrile and caprolactam polymer.
  3. 3. The method for treating 6-aminocapronitrile reaction residue in caprolactam synthesis according to claim 1, wherein the catalyst in the stirred tank reactor is metal oxide solid particles.
  4. 4. The method for treating 6-aminocapronitrile reaction residue in caprolactam synthesis according to claim 1, wherein solid catalyst particles in the stirred tank reactor are wrapped in a wire mesh and fixed on a stirring paddle to avoid catalyst loss, and insoluble solid waste in the stirred tank reactor is discharged from the bottom thereof.
  5. 5. The method for treating 6-aminocapronitrile reaction residues generated in the synthesis of caprolactam according to claim 1, wherein the number of theoretical plates in the first, second and third separation sections of the tower reactor ranges from 1 to 10, from 1 to 15 and from 1 to 10 respectively, and the number of theoretical plates in the first, second and third reaction sections ranges from 5 to 20, from 5 to 20 and from 5 to 15 respectively.
  6. 6. The method for treating 6-aminocapronitrile reaction residue in caprolactam synthesis according to claim 1, wherein the column internals of the column reactor are trays including at least one of bubble cap trays, valve trays and sieve trays.
  7. 7. The method for treating 6-aminocapronitrile reaction residues in caprolactam synthesis according to claim 1, wherein a metal basket filled with catalyst particles is placed on a tower plate of three reaction sections of a tower reactor, the volume fraction of the catalyst particles is 5% -30%, and the catalysts in the first reaction section, the second reaction section and the third reaction section are respectively metal oxide solid particles, a molecular sieve and solid alkali.

Description

Treatment method of reaction residues of synthesis of 6-aminocapronitrile from caprolactam Technical Field The invention relates to the technical field of organic chemical industry, in particular to a treatment method of reaction residues of synthesizing 6-aminocapronitrile from caprolactam. Background Hexamethylenediamine is mainly used for producing polyamides such as nylon 66, nylon 610, etc. About 90% of hexamethylenediamine is used in the nylon 66 industry, the remainder being mainly used in the preparation of high performance polyurethanes and epoxy curing agents. According to the technical route and the difference of raw materials, the synthesis method of hexamethylenediamine is mainly divided into a1, 4-butadiene hydrocyanation method, an acrylonitrile electrolytic dimerization method, a1, 6-adipic acid ammonification dehydration method, a caprolactam ammonification dehydration method, a1, 6-hexanediol ammonification method, a1, 6-adipic acid ester ammonification method, a1, 6-hexanedialdehyde ammonification method and the like. The butadiene hydrocyanation method is a main technique for producing hexamethylenediamine, and only a few nationwide companies such as foreign english-wida, oshi and the like grasp the industrialization technique, so that the technical barrier is high. In addition, in recent years, the domestic caprolactam industry is faced with serious surplus capacity problems, and searching for new downstream products for caprolactam has become urgent. For the two reasons mentioned above, the route for producing hexamethylenediamine starting from caprolactam has been attracting attention. The caprolactam route was first proposed by dupont in patents US2181140 and US 2234566. The method has two main reaction steps, namely ring-opening ammoniation dehydration reaction of caprolactam and ammonia at high temperature to generate 6-aminocapronitrile and hydrogenation of 6-aminocapronitrile to generate 1, 6-hexamethylenediamine. Wherein the ammoniated dehydration of caprolactam is a key step in this route. The ammonification and dehydration of caprolactam to 6-aminocapronitrile can be classified into a liquid phase method and a gas phase method. The liquid phase method is to perform gas-liquid two-phase reaction between liquid caprolactam and excessive ammonia gas at 260-280 deg.c for 0.5-2 hr. The caprolactam conversion was about 65%. For example, patent CN107739318a employs a liquid phase process to prepare 6-aminocapronitrile. The gas phase method is to make the vaporized caprolactam and excessive ammonia gas undergo the gas phase reaction at about 300-400 deg.C, the reaction time is very short (about 1 s), and the conversion rate can be up to above 98%. For example, patent CN107602416a employs a gas phase process to prepare 6-aminocapronitrile. The gas phase method has high conversion rate and more application, but the caprolactam with higher reaction temperature is polymerized in a series under the action of water generated by ammonification and dehydration reaction, so that the condensate obtained after condensation of the reaction gas contains a large amount of polymer residues. For example, patent CN111635330B hydrolyzes the residue to perform a depolymerization reaction, then hydrogenates the obtained hydrolysis reaction liquid, and after the reaction is completed, distills the obtained hydrogenation reaction liquid under negative pressure, and dehydrates the reaction liquid to obtain products such as aminocaproic acid, n-valeric acid, and n-caproic acid. For example, CN111747877a, the residue and water are put into a reaction vessel to carry out depolymerization reaction, and then distilled under negative pressure to obtain aminocapronitrile and caprolactam. The above treatment method has problems in that hydrolysis of residue is insufficient, the flow is complicated and batch operation is required. Disclosure of Invention The invention aims to solve the technical problem of providing a treatment method for the reaction residues of synthesizing 6-aminocapronitrile from caprolactam, which has the advantages of deep hydrolysis of the residues, simple flow and continuous operation, greatly reduces the solid waste discharge in the production process of hexamethylenediamine, reduces the cost, improves the economic benefit and provides guarantee for green safety production. The invention is realized in the following way: A method for treating reaction residues of synthesizing 6-aminocapronitrile from caprolactam comprises the following steps: Step (1) delivering reaction residues generated in synthesis of 6-aminocapronitrile from caprolactam and fresh water into a stirred tank reactor for preliminary hydrolysis reaction, wherein the obtained reaction liquid contains water, polymer, aminocaproic acid, caprolactam and 6-aminocapronitrile, and a solid catalyst is filled in the reactor, the operating pressure range of the stirred tank reactor is 0.1-1.0 MPa, the reaction temperature range is 25