A method for preparing caprolactam
By preparing caprolactam in a B-L biacid eutectic solvent-organic solvent two-phase system, the problems of poor reaction orientation, many side reactions and difficult catalyst circulation in the preparation of caprolactam in the prior art are solved, and a high yield and high purity synthesis and green and environmentally friendly process are achieved.
Patent Information
- Application Number
- CN202210926481.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-03
- Publication Date
- 2025-03-04
- Estimated Expiration
- 2042-08-03
AI Technical Summary
In the prior art, the preparation of caprolactam has problems such as poor reaction orientation, many side reactions, complicated product separation steps, and difficult catalyst separation, difficult to be easily separated, difficult to recycle and regenerate.
In the B-L biacid eutectic solvent-organic solvent two-phase system, caprolactam is prepared by rearrangement reaction using cyclohexanone oxime as the raw material. The molar ratio of eutectic solvent and cyclohexanone oxime is 25:1 to 1:25, the reaction temperature is 40 to 120°C, the reaction time is 2 to 8 hours, and the eutectic solvent and organic solvent are reused.
The synthesis of caprolactam with high yield and high purity was achieved, and side reactions such as raw material hydrolysis and product oligomerization were avoided, and the product separation and purification process was simplified. The yield of the obtained caprolactam was greater than 99.6%, the purity could reach 99.8%, and the eutectic solvent and organic solvent could be reused.
Abstract
Description
Technical Field
[0001] The invention relates to a method for preparing caprolactam, namely, to a method for preparing caprolactam in a BL double acidic low eutectic solvent-organic solvent two-phase system. Background Art
[0002] Caprolactam is one of the important organic chemical raw materials. It can be used to prepare nylon fiber, nylon-6 engineering plastics, medicine, coatings, plasticizers, artificial leather and other important raw materials. It has broad market applications in the fields of plastics, textiles, fine chemicals, etc. At present, industrial caprolactam is mostly prepared by Beckmann rearrangement reaction of cyclohexanone oxime catalyzed by concentrated sulfuric acid or fuming sulfuric acid. There are disadvantages such as poor reaction orientation, more side reactions, and complicated product separation steps. In particular, the catalyst sulfuric acid is not easy to separate, difficult to recycle and regenerate, and the waste acid is seriously discharged. Therefore, if a catalyst or catalytic system with mild reaction conditions, high conversion rate and selectivity, self-separation of products and no pollution to the environment can be found, it will inevitably provide new methods for caprolactam production technology and application. As a new type of green and recyclable reaction medium, low eutectic solvent has attracted extensive attention from researchers in recent years because of its easy availability of synthetic raw materials, simple preparation, good thermal stability, excellent solubility, adjustable structure and properties, easy separation and recovery, and reusability.
[0003] Therefore, the present invention applies for a method for preparing caprolactam, that is, it relates to a method for preparing caprolactam in a BL double acidic low eutectic solvent-organic solvent two-phase system. Compared with the traditional concentrated sulfuric acid or fuming sulfuric acid catalytic system, due to the difference in solubility of the low eutectic solvent and the organic solvent to the reactants and products, the hydrolysis of the raw material cyclohexanone oxime to form cyclohexanone is well avoided, and the polymerization of the product caprolactam to form caprolactam oligomers is suppressed, while the separation and purification process of the product are simplified, and the yield of the obtained caprolactam is greater than 99.6%, and the purity can reach 99.8%. In addition, the low eutectic solvent and the organic solvent used can be recycled and reused. The present invention provides a new green approach for the preparation of caprolactam. Summary of the invention
[0004] The purpose of the present invention is to replace the conventional method for preparing caprolactam under concentrated sulfuric acid or fuming sulfuric acid catalysis system and to develop a method for preparing caprolactam cleanly under mild reaction conditions.
[0005] Based on the above, the present invention relates to a method for preparing caprolactam, characterized in that cyclohexanone oxime is used as a raw material in a two-phase reaction system consisting of a BL double acidic low eutectic solvent and an organic solvent, and a rearrangement reaction is performed to prepare caprolactam, the molar ratio of the low eutectic solvent to cyclohexanone oxime is 25:1-1:25, the organic solvent is 1-30 mL, the reaction temperature is 40-120°C, and the reaction is performed for 2-8 hours to prepare caprolactam, and the low eutectic solvent and the organic solvent are recovered and reused; the low eutectic solvent is a two-component low eutectic solvent or a three-component low eutectic solvent, and the two-component low eutectic solvent is a hydrogen A three-component eutectic solvent having a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 4:1 to 1:4 is prepared by reacting a hydrogen bond acceptor, a hydrogen bond donor and a third component in a molar ratio of 4:1:1 to 1:4:1 at 60°C for 0.5 to 2.5 hours, wherein the hydrogen bond acceptor is one of ferric chloride, chromium chloride, scandium chloride, zinc dichloride or indium chloride, the hydrogen bond donor is one of formic acid, acetic acid, propionic acid, phenylpropionic acid, trichloroacetic acid or trifluoroacetic acid, the third component is one of choline chloride, urea or glycerol, and the organic solvent is one of toluene, acetonitrile or cyclohexane.
[0006] The invention is characterized in that the reaction conditions for preparing caprolactam from cyclohexanone oxime are preferably a molar ratio of cyclohexanone oxime to a low eutectic solvent of 15:1 to 1:15, 5 to 10 mL of an organic solvent, a reaction temperature of 60 to 100° C., and a reaction time of 3 to 6 hours.
[0007] The present invention solves this technical problem through the following technical solutions:
[0008] The specific technical scheme is illustrated by taking the BL bis-acidic low eutectic solvent prepared by the molar ratio of zinc chloride, choline chloride and trichloroacetic acid of 1:1:2 as an example, wherein the BL bis-acidic low eutectic solvent is named [ZnCl2][ChCl][TCA]2, and the naming method of other low eutectic solvents is similar.
[0009] Zinc chloride, choline chloride and trichloroacetic acid were added into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1:2, heated to 60°C and stirred for 2 hours to obtain a low eutectic solvent [ZnCl2][ChCl][TCA]2.
[0010] 0.01mol cyclohexanone oxime, 0.02mol low eutectic solvent [ZnCl2][ChCl][TCA]2 and 10mL acetonitrile were put into a pressure reactor equipped with a stirrer and a thermometer. After the reactor was sealed and the air in the reactor was replaced by nitrogen three times, the materials in the reactor were heated to 40°C and stirred for 8h. After the reaction, the resulting mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. Among them, the low eutectic solvent phase was extracted three times with an equal volume of toluene, and the organic product phase and the extraction phase were combined, and the toluene was recovered by distillation and recycled to obtain the product caprolactam, and the yield and purity were 99.8% and 99.8% respectively; the residual phase low eutectic solvent was distilled to remove the residual toluene and can be reused.
[0011] Compared with the traditional method, the present invention has the following characteristics:
[0012] 1. The BL double acidic low eutectic solvent-organic solvent two-phase system can achieve high yield and high purity synthesis of caprolactam.
[0013] 2. The difference in solubility between BL double acidic low eutectic solvent and organic solvent for reactants and products effectively avoids the hydrolysis of raw material cyclohexanone oxime and inhibits the polymerization of product caprolactam and other side reactions.
[0014] 3. The reaction conditions are mild, the product is easy to separate and the treatment is simple, and the BL double acidic low eutectic solvent and organic solvent used are easy to recycle and can be reused. Specific implementation methods
[0015] The method of the present invention is further described below in conjunction with embodiments, which are not intended to limit the present invention.
[0016] Example 1: Zinc chloride, choline chloride (ChCl) and trichloroacetic acid (TCA) were put into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1:2, heated to 60°C and stirred for 2 hours to obtain a low eutectic solvent [ZnCl2][ChCl][TCA]2. 0.01 mol of cyclohexanone oxime, 0.02 mol of a low eutectic solvent [ZnCl2][ChCl][TCA]2 and 10 mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 40°C and stirred for 8 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with an equal volume of toluene, the organic product phase and the extraction phase are combined, the toluene is recovered by distillation and recycled, and the product caprolactam is obtained, and the yield and purity are 99.8% and 99.8% respectively; the low eutectic solvent of the raffinate phase can be reused after the residual toluene is removed by distillation.
[0017] Comparative Example 1: 0.01 mol of cyclohexanone oxime and 10 mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer. The reactor was sealed and the air in the reactor was replaced with nitrogen three times. The materials in the reactor were heated to 40°C and kept stirring for 8 hours. After the reaction, the resulting mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification. The organic product phase was obtained by phase separation. The toluene was recovered by distillation and recycled. No product was obtained after the reaction.
[0018] Comparative Example 2: 0.01 mol of cyclohexanone oxime, 0.02 mol of 70% concentrated sulfuric acid and 10 mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer. The reactor was sealed and the air in the reactor was replaced with nitrogen three times. The materials in the reactor were heated to 40°C and stirred for reaction for 8 hours. After the reaction, the resulting mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification. The organic product phase was obtained by phase separation. The toluene was recovered by distillation and recycled to obtain the product caprolactam, and the yield and purity were 99.4% and 98.5%, respectively.
[0019] Example 2: Zinc chloride and formic acid (FA) were put into a reaction flask equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:4, heated to 60°C and stirred for 0.5h to obtain a low eutectic solvent [ZnCl2][FA]2. 0.01mol of cyclohexanone oxime, 0.25mol of a low eutectic solvent [ZnCl2][FA]2 and 30mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 60°C and stirred for 6h. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with an equal volume of toluene, the organic product phase and the extraction phase are combined, the toluene is recovered by distillation and recycled, and the product caprolactam is obtained, and the yield and purity are 99.7% and 99.6% respectively; the low eutectic solvent of the raffinate phase can be reused after the residual toluene is removed by distillation.
[0020] Example 3: Ferric chloride and acetic acid (AA) are put into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1, heated to 60°C and stirred for 2 hours to obtain a low eutectic solvent [FeCl3][AA]. 0.02 mol of cyclohexanone oxime, 0.01 mol of a low eutectic solvent [FeCl3][AA] and 5 mL of toluene are put into a pressure reactor equipped with a stirrer and a thermometer, the reactor is sealed, and the air in the reactor is replaced by nitrogen three times, and the materials in the reactor are heated to 80°C and stirred for 4 hours. After the reaction, the resulting mixture is quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase are obtained by phase separation. Among them, the low eutectic solvent phase is extracted three times with an equal volume of toluene, the organic product phase and the extraction phase are combined, the toluene is recovered by distillation and recycled, and the product caprolactam is obtained, and its yield and purity are 99.5% and 99.6% respectively; the residual phase low eutectic solvent can be reused after distillation to remove the residual toluene.
[0021] Example 4: Chromium chloride and acetic acid were added to a reaction flask equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 4:1, heated to 60°C and stirred for 2.5 hours to obtain a low eutectic solvent [CrCl3]4[AA]. 0.25 mol of cyclohexanone oxime, 0.01 mol of a low eutectic solvent [CrCl3]4[AA] and 1 mL of toluene were added to a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 60°C and stirred for 2 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with an equal volume of toluene, the organic product phase and the extraction phase are combined, the toluene is recovered by distillation and recycled, and the product caprolactam is obtained, and the yield and purity are 99.6% and 99.7% respectively; the low eutectic solvent of the raffinate phase can be reused after the residual toluene is removed by distillation.
[0022] Example 5: Scandium chloride and propionic acid (PA) were put into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1, heated to 60°C and stirred for 1.5 hours to obtain a low eutectic solvent [ScCl3][PA]. 0.01 mol of cyclohexanone oxime, 0.15 mol of a low eutectic solvent [ScCl3][PA] and 5 mL of acetonitrile were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 60°C and stirred for 3 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with equal volumes of acetonitrile, the organic product phase and the extraction phase are combined, the acetonitrile is recovered by distillation and recycled, and the product caprolactam is obtained, and the yield and purity are 99.4% and 99.6%, respectively; the low eutectic solvent of the raffinate phase can be reused after the residual acetonitrile is removed by distillation.
[0023] Example 6: Indium chloride and phenylpropionic acid (PPA) were put into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:3, heated to 60°C and stirred for 1 hour to obtain a low eutectic solvent [InCl3][PPA]3. 0.15 mol of cyclohexanone oxime, 0.01 mol of low eutectic solvent [InCl3][PPA]3 and 8 mL of acetonitrile were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 60°C and stirred for 4 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separatory funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with equal volumes of acetonitrile, the organic product phase and the extraction phase are combined, the acetonitrile is recovered by distillation and recycled, and the product caprolactam is obtained, and the yield and purity are 99.8% and 99.5%, respectively; the low eutectic solvent of the raffinate phase can be reused after the residual acetonitrile is removed by distillation.
[0024] Example 7: Zinc chloride, urea (Urea) and trifluoroacetic acid (TFA) were added to a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1:4, heated to 60°C and stirred for 0.5h to obtain a low eutectic solvent [ZnCl2][Urea][TFA]4. 0.01mol of cyclohexanone oxime, 0.01mol of low eutectic solvent [ZnCl2][Urea][TFA]4 and 8mL of cyclohexane were added to a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 80°C and stirred for 3h. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with an equal volume of toluene, the organic product phase and the extraction phase are combined, and the cyclohexane is recovered by distillation and recycled to obtain the product caprolactam, with a yield and purity of 99.8% and 99.6% respectively; the low eutectic solvent of the raffinate phase can be reused after the residual cyclohexane is removed by distillation.
[0025] Example 8: Zinc chloride, glycerol (Gl) and trichloroacetic acid were put into a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 4:1:1, heated to 60°C and stirred for 2.5 hours to obtain a low eutectic solvent [ZnCl2]4[Gl][TCA]. 0.01 mol of cyclohexanone oxime, 0.01 mol of a low eutectic solvent [ZnCl2][Gl][TCA]4 and 8 mL of cyclohexane were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, and then the materials in the reactor were heated to 120°C and stirred for 5 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. The low eutectic solvent phase is extracted three times with an equal volume of toluene, and the organic product phase and the extraction phase are combined. The cyclohexane is recovered by distillation and recycled to obtain the product caprolactam, and the yield and purity are 99.7% and 99.5% respectively; the low eutectic solvent of the raffinate phase can be reused after the residual cyclohexane is removed by distillation.
[0026] Example 9: The low eutectic solvent [ZnCl2][ChCl][TCA]2 recovered in Example 1, 0.01 mol of cyclohexanone oxime and 10 mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced by nitrogen for 3 times, and the materials in the reactor were heated to 40°C and stirred for 8 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. Among them, the low eutectic solvent phase was extracted three times with an equal volume of toluene, and the organic product phase and the extraction phase were combined. The toluene was recovered by distillation and recycled to obtain the product caprolactam, and its yield and purity were 99.8% and 99.7%, respectively; and the low eutectic solvent [ZnCl2][ChCl][TCA]2 recovered in this example was reused 10 times under the same experimental conditions, and the product caprolactam obtained by 10 repeated uses had a yield and purity greater than 99.6% and 99.5%, respectively.
[0027] Example 10: The low eutectic solvent [ZnCl2][FA]2 recovered in Example 2, 0.01 mol of cyclohexanone oxime and 30 mL of toluene were put into a pressure reactor equipped with a stirrer and a thermometer, the reactor was sealed, and the air in the reactor was replaced by nitrogen for 3 times, and the materials in the reactor were heated to 60°C and stirred for 6 hours. After the reaction, the obtained mixture was quickly cooled to room temperature and transferred to a separating funnel for standing and stratification, and the organic product phase and the low eutectic solvent phase were obtained by phase separation. Among them, the low eutectic solvent phase was extracted three times with an equal volume of toluene, and the organic product phase and the extraction phase were combined. The toluene was recovered by distillation and recycled to obtain the product caprolactam, and its yield and purity were 99.7% and 99.5%, respectively; and the low eutectic solvent [ZnCl2][FA]2 recovered in this example was reused 10 times under the same experimental conditions, and the product caprolactam obtained by 10 repeated uses had a yield and purity greater than 99.5% and 99.4%, respectively.
Claims
1. A method for preparing caprolactam, characterized in that In a two-phase reaction system consisting of a BL double acidic low eutectic solvent and an organic solvent, cyclohexanone oxime is used as a raw material to prepare caprolactam through a rearrangement reaction, the molar ratio of the low eutectic solvent to cyclohexanone oxime is 25:1-1:25, the organic solvent is 1-30 mL, the reaction temperature is 40-120°C, the reaction is performed for 2-8 hours to prepare caprolactam, and the low eutectic solvent and the organic solvent are recovered and reused; the low eutectic solvent is a two-component low eutectic solvent or a three-component low eutectic solvent, and the two-component low eutectic solvent is a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 4:1 A three-component eutectic solvent is prepared by reacting a hydrogen bond acceptor, a hydrogen bond donor and a third component at a molar ratio of 4:1:1 to 1:4:1 at 60°C for 0.5 to 2.5 hours, wherein the hydrogen bond acceptor is one of ferric chloride, chromium chloride, scandium chloride, zinc dichloride or indium chloride, the hydrogen bond donor is one of formic acid, acetic acid, propionic acid, phenylpropionic acid, trichloroacetic acid or trifluoroacetic acid, the third component is one of choline chloride, urea or glycerol, and the organic solvent is one of toluene, acetonitrile or cyclohexane.