WO2024000848A1

WO2024000848A1 - Caprolactam synthesis method free of by-production of ammonium sulfate

Info

Publication number: WO2024000848A1
Application number: PCT/CN2022/120386
Authority: WO
Inventors: 庄大为; 刘文刚; 杨琦武; 刘新伟; 王聪; 杨克俭
Original assignee: 中国天辰工程有限公司
Priority date: 2022-06-29
Filing date: 2022-09-22
Publication date: 2024-01-04
Also published as: CN115073343A; CN115073343B

Abstract

Provided in the present invention is a caprolactam synthesis method free of by-production of ammonium sulfate. By designing a special process route, selecting a specific solvent, and using cyclohexanone oxime as a raw material, a Beckmann rearrangement reaction is catalyzed by means of fuming sulfuric acid, thereby producing a caprolactam product. After the Beckmann rearrangement reaction, separating a caprolactam-sulfuric acid phase from a solvent phase may also reduce the reaction heat in the reaction process. In addition, by optimizing the reaction process route, no ammonia is consumed and the sulfuric acid is consumed only once, so that during long-period operation, the consumption of the sulfuric acid is basically zero. Finally, no ammonium sulfate is produced, and gentle reaction conditions and a high product yield are allowed.

Description

A method for synthesizing caprolactam without by-product ammonium sulfate

Technical field

The invention belongs to the technical field of chemical synthesis, and in particular relates to a catalyst for preparing caprolactam through Beckmann rearrangement and a preparation method thereof.

Background technique

Caprolactam is an important organic chemical raw material. Due to its special structure, it is mainly used as a monomer of polymers to produce polyamide 6 (PA6) chips through polymerization. Different brands of PA6 have different slice properties and their application fields are also different. After processing, PA6 is widely used in textiles, packaging, automobiles, electronics, machinery and other fields.

The raw material routes for the production of caprolactam in the world are mainly benzene, phenol and toluene. Among the three raw materials, the toluene route accounts for the highest production capacity and is the most important caprolactam production method in the world. Represented by the technology of Dutch company DSM, cyclohexanone is synthesized from cyclohexanone oxime, and caprolactam is obtained through Beckmann rearrangement. In recent years, my country's caprolactam production technology has made great progress, and domestic production capacity has been greatly expanded.

The Beckmann rearrangement reaction (Beckmann rearrangement reaction) is an acid-catalyzed rearrangement reaction. The reactant oxime is rearranged into an amide under the catalysis of acid. There are now a variety of Beckmann rearrangement catalysts, including inorganic acids, organic acids, acidic molecular sieves, ionic liquids, etc.

In the industrial production of caprolactam, sulfuric acid or fuming sulfuric acid is often used as a catalyst. Caprolactam is produced by the Beckmann rearrangement reaction of cyclohexanone oxime in the presence of sulfuric acid or fuming sulfuric acid. The process generally adopts the method of external circulation of materials to transfer heat, that is, fuming sulfuric acid is added from the circulation pump inlet of the rearrangement reactor to the system to mix with the rearrangement liquid, and the heat is removed from the reaction system through the circulation pipeline heat exchanger. After the temperature is lowered, The circulating liquid enters the mixer and is quickly mixed with the added cyclohexanone oxime to react to form a rearrangement liquid. The process is mature and simple, so this method is basically used in industry to produce caprolactam.

The rearrangement reaction of cyclohexanone oxime in the presence of fuming sulfuric acid is a strongly exothermic reaction with fast reaction speed and violent reaction. Poor system configuration will lead to the generation of a large number of impurities, seriously affecting the quality of caprolactam products. What's more serious is that this process also produces a large amount of ammonium sulfate by-product. Every ton of caprolactam produced will produce 1.4 to 1.8 tons of ammonium sulfate by-product. Ammonium sulfate is a kind of chemical fertilizer, and its selling price is lower than the cost price. A large amount of ammonium sulfate by-product will cause the cost to rise. Therefore, the process needs to be improved to reduce the consumption of sulfuric acid and ammonia, and reduce the output of by-product ammonium sulfate to reduce production costs.

In patent US4257950, cyclohexanone oxime is dissolved in a solvent that is inert to niacin and insoluble in water and nicotinic acid, and nicotinic acid is used as a catalyst to perform Beckmann rearrangement to produce caprolactam, but the by-product ammonium sulfate is not reduced.

Patent CN1508128A also discloses a method for preparing caprolactam using cyclohexanone oxime and nicotinic acid or anhydrous sulfuric acid in the presence of a solvent inert to nicotinic acid or sulfuric acid, but ammonium sulfate is still a by-product.

Contents of the invention

This method discloses a caprolactam synthesis method without ammonium sulfate by-product. This method uses cyclohexanone oxime as raw material and catalyzes the Beckmann rearrangement reaction through fuming sulfuric acid to obtain the caprolactam product. Compared with the existing process, this method has the advantages of no ammonium sulfate by-product, mild reaction conditions, and high yield, and is suitable for industrial production.

Specifically, a caprolactam synthesis method without ammonium sulfate by-product of the present invention includes the following steps:

(1) Slowly add caprolactam to fuming sulfuric acid and stir until fully dissolved to form caprolactam-sulfate;

(2) Place cyclohexanone oxime in the solvent and stir until dissolved;

(3) Preheat the cyclohexanone oxime solution obtained in step (2), preheat the caprolactam-sulfate obtained in step (1), and then add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase Mix the liquid, stir until evenly mixed and keep warm for a period of time;

(3) Separate the two-phase reaction obtained in step (2) to obtain a lighter solvent phase and a heavier caprolactam-sulfuric acid phase;

(4) Distillate and separate the solvent phase obtained in step (3) to obtain a caprolactam product. The solvent obtained by distillation can be reused; the distillation is vacuum distillation, and the pressure is an absolute pressure of 2 to 12 kPa, preferably 4 to 8 kPa. The distillation temperature of caprolactam is 130-190°C, preferably 162-183°C.

(5) Collect the caprolactam-sulfate obtained in step (3), and remove a small amount of entrained solvent through flash evaporation purification. The caprolactam-sulfate can be reused as a catalyst. The caprolactam-sulfate flash evaporation temperature is 50 to 120°C, preferably 80 to 100°C, and the flash evaporation pressure is an absolute pressure of 2 to 36 kPa, preferably 10 to 20 kPa.

In the step (2), the selected solvent is carbon tetrachloride, chlorobenzene, dichlorobenzene, propyl ether, ethyl propyl ether, butyl ether, 1-chloropropane, ethylene glycol dimethyl ester, propyl propionate. One or more of the esters are preferably one or more of carbon tetrachloride, chlorobenzene, dichlorobenzene, propyl ether, ethyl propyl ether and butyl ether.

In the step (1), the concentration of fuming sulfuric acid used is 3 to 40%, and the preferred concentration is 8 to 20%.

The mass ratio of caprolactam to oleum is 0.5-3, and the preferred mass ratio is 0.8-2.

The adding step is to heat the caprolactam to 80°C to fully melt it, and gradually add it to the oleum. The adding time is not less than 10 minutes. When adding, stir the oleum quickly, and cool the oleum to maintain the temperature. Below 100℃. After the addition is complete, continue to stir the caprolactam-sulfuric acid mixture until a uniform liquid forms;

In the step (2), the mass concentration of cyclohexanone oxime is 5-30wt%, and the preferred concentration is 5-20wt%.

In the step (3), the preheating temperature of the cyclohexanone oxime solution is 50-250°C, preferably 100-180°C, and the preheating temperature of caprolactam-sulfate is 50-250°C, preferably 100-180°C. The mass ratio of caprolactam-sulfate to cyclohexanone oxime is 0.5-20, preferably 3-10, the reaction temperature is 50-170°C, preferably 100-130°C, and the reaction time is 0.5-30min, preferably 5-15min ;

In the step (4), the rectification is vacuum distillation, the pressure is an absolute pressure of 2 to 12 kPa, preferably 4 to 8 kPa, and the caprolactam fraction temperature is 130 to 190°C, preferably 162 to 183°C;

In the step (5), the caprolactam-sulfate flash evaporation temperature is 50-120°C, preferably 80-100°C, and the flash evaporation pressure is an absolute pressure of 2-36 kPa, preferably 10-20 kPa.

Beneficial effects:

The invention provides a caprolactam synthesis method that does not produce ammonium sulfate by-product. By designing a special process route and selecting a specific solvent to separate the caprolactam-sulfuric acid phase from the solvent phase, the reaction heat can also be reduced during the reaction process; and By optimizing the reaction process route, there is no need to consume ammonia gas, and the sulfuric acid consumption is one-time. During long-term operation, the sulfuric acid consumption is basically zero; ultimately, no by-product ammonium sulfate can be achieved, the reaction conditions are mild, and the product yield is high.

Description of drawings

Figure 1 is a schematic process flow diagram of a caprolactam synthesis method without ammonium sulfate by-product according to the present invention.

Detailed ways

The present invention will be described in detail below with reference to examples.

Example 1

Heat 8kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 6 kg of oleum with a concentration of 10%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 4kg of cyclohexanone oxime in 27.5kg of carbon tetrachloride and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 140°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixed solution. Stir quickly until the mixture is uniform, and keep the temperature at 140°C. Maintain the temperature and the reaction time is 15min. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is rectified, the distillation pressure is an absolute pressure of 4kPa, and the caprolactam fraction temperature is 170°C to obtain a caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 98.2%, the yield of caprolactam after distillation was 3.86kg, and the yield was 96.5%.

Example 2

Heat 14kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 18%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 6kg of cyclohexanone oxime in 50kg of dichlorobenzene and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 170°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixed solution. Stir quickly until the mixture is uniform, and keep the temperature at 170°C. Maintain the temperature and the reaction time is 8 minutes. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is rectified, the distillation pressure is an absolute pressure of 7kPa, and the caprolactam fraction temperature is 183°C to obtain a caprolactam product. After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 99.3%, the yield of caprolactam after distillation was 5.87kg, and the yield was 97.8%.

Example 3

Heat 18kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 15%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 2.9kg of cyclohexanone oxime in 25kg of chlorobenzene and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 170°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixture. Stir quickly until the mixture is even, and keep the temperature at 170°C. Maintain the temperature and the reaction time is 10min. After the reaction is completed, stop stirring and separate the two phases to obtain the solvent phase and the caprolactam-sulfate phase. The solvent phase is subjected to rectification. The distillation pressure is an absolute pressure of 6 kPa and the caprolactam fraction temperature is 175°C to obtain the caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 98.3%, the yield of caprolactam after distillation was 2.82kg, and the yield was 97.2%.

Example 4

Heat 20kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 20%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 10kg of cyclohexanone oxime in 180kg of propyl ether and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 150°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixed solution. Stir quickly until the mixture is uniform, and keep the temperature at 150°C. Maintain the temperature and the reaction time is 15min. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is rectified, the distillation pressure is an absolute pressure of 6kPa, and the caprolactam fraction temperature is 162°C to obtain a caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 99.9%, the selectivity of caprolactam was 97.8%, the yield of caprolactam after distillation was 9.55kg, and the yield was 95.5%.

Example 5

Heat 8kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 15%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 4kg of cyclohexanone oxime in 32kg of butyl ether and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 130°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixed solution. Stir quickly until the mixture is uniform, and keep the temperature at 130°C. Maintain the temperature and the reaction time is 15min. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is rectified, the distillation pressure is an absolute pressure of 8kPa, and the caprolactam fraction temperature is 170°C to obtain a caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 94.8%, the yield of caprolactam after distillation was 3.56kg, and the yield was 89.3%.

Example 6

Heat 10kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 10%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 5kg of cyclohexanone oxime in 90kg of diethyl propyl ether and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 100°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixture. Stir quickly until the mixture is even, and keep the temperature at 100°C. Maintain the temperature and the reaction time is 12min. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is rectified, the distillation pressure is an absolute pressure of 7kPa, and the caprolactam fraction temperature is 168°C to obtain a caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 98.9%, the yield of caprolactam after distillation was 4.91kg, and the yield was 98.2%.

Comparative example 1

Preheat 10kg of cyclohexanone oxime to 100°C, take 10kg of fuming sulfuric acid with a concentration of 10%, and preheat it to 100°C. Slowly spray the cyclohexanone oxime solution into the fuming sulfuric acid, continue to stir and keep the reaction temperature at 100°C, stop the reaction after 5 minutes, and obtain the caprolactam-sulfuric acid phase. Place the caprolactam-sulfuric acid phase in 20kg of saturated ammonium sulfate aqueous solution, keep the temperature at 45°C, start stirring and gradually introduce ammonia gas into it. After the introduction, the liquid is divided into three phases, and the pH value of the lower water phase is 6.0 . Take a total of 16kg of the upper caprolactam phase, place it in 15kg of benzene, keep the temperature at 45°C, and stir until the extraction is completed. Take a total of 27.1kg of the caprolactam-benzene phase in the upper layer, place it in 10kg of water, keep the temperature at 30°C, and stir until the extraction is completed to obtain an aqueous solution of caprolactam.

After analysis, the conversion rate of cyclohexanone oxime is 100%, the selectivity of caprolactam is 98.7%, the output of caprolactam after neutralization crystallization-extraction treatment is 38.7kg, the yield is 96.8%, and the amount of by-product ammonium sulfate is 55.1kg , 1.42kg of ammonium sulfate is produced per kilogram of caprolactam.

Comparative example 2

Heat 12kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 10 kg of oleum with a concentration of 10%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 3kg of cyclohexanone oxime in 25kg of tert-butyl alcohol and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 80°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixture. Stir quickly until the mixture is even, and keep the temperature at 80°C. Maintain the temperature and the reaction time is 5min. After the reaction is completed, the stirring is stopped, the reaction product is a single phase, and both caprolactam and caprolactam-sulfate are dissolved in the solvent. It is impossible to obtain a sulfuric acid-free caprolactam solution, and it is impossible to obtain caprolactam without producing ammonium sulfate by-product.

After analysis, the conversion rate of cyclohexanone oxime was 98.5%, and the selectivity of caprolactam was 93.9%.

Comparative example 3

Heat 8kg caprolactam to 80°C to fully melt it. Slowly add the melted caprolactam to 6 kg of oleum with a concentration of 10%, and stir until uniform to obtain caprolactam-sulfate. Dissolve 4kg of cyclohexanone oxime in 27.5kg of cyclooctane and stir until fully dissolved. Preheat the cyclohexanone oxime solution and caprolactam-sulfate to 140°C respectively. Add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain a two-phase mixed solution. Stir quickly until the mixture is uniform, and keep the temperature at 140°C. Maintain the temperature and the reaction time is 15min. After the reaction is completed, the stirring is stopped and the two phases are separated to obtain a solvent phase and a caprolactam-sulfate phase. The obtained solvent phase is distilled to obtain caprolactam product.

After analysis, the conversion rate of cyclohexanone oxime was 100%, the selectivity of caprolactam was 94.2%, the yield of caprolactam after distillation was 0.058kg, and the yield was 1.45%.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection.

Claims

A method for synthesizing caprolactam without by-product ammonium sulfate, characterized in that it includes the following steps:

(1) Slowly add caprolactam to fuming sulfuric acid and stir until fully dissolved to form caprolactam-sulfate;

(2) Place cyclohexanone oxime in the solvent and stir until dissolved to form a cyclohexanone oxime solution;

(3) Preheat the cyclohexanone oxime solution obtained in step (2), preheat the caprolactam-sulfate solution obtained in step (1), and then add the cyclohexanone oxime solution to the caprolactam-sulfate to obtain two phase mixture, stir until evenly mixed and keep warm;

(3) Separate the two-phase reaction obtained in step (2) to obtain a lighter solvent phase and a heavier caprolactam-sulfuric acid phase;

(4) Distillate and separate the solvent phase obtained in step (3) to obtain caprolactam product, and the solvent obtained by distillation can be reused;

(5) Collect the caprolactam-sulfate obtained in step (3) and purify it by flash evaporation. The caprolactam-sulfate can be reused as a catalyst.
The caprolactam synthesis method according to claim 1, characterized in that: the solvent in the step (2) is carbon tetrachloride, chlorobenzene, dichlorobenzene, propyl ether, ethyl propyl ether, butyl ether, 1-chloro One or more of propane, ethylene glycol dimethyl ester, propyl propionate, preferably one or more of carbon tetrachloride, chlorobenzene, dichlorobenzene, propyl ether, ethyl propyl ether, butyl ether .
The caprolactam synthesis method according to claim 1, characterized in that in the step (1), the concentration of fuming sulfuric acid used is 3 to 40%, and the preferred concentration is 8 to 20%.
The caprolactam synthesis method according to claim 1, characterized in that: in the step (1), the mass ratio of caprolactam to oleum is 0.5-3, and the preferred mass ratio is 0.8-2.
The caprolactam synthesis method according to claim 1, characterized in that: in the step (1), the adding step is to heat the caprolactam to 80°C to fully melt it, and gradually add it to the fuming sulfuric acid. The adding time No less than 10 minutes. When adding the oleum, stir the oleum quickly and cool the oleum to keep the temperature below 100°C. After the addition is complete, continue to stir the caprolactam-sulfuric acid mixture until a uniform liquid is formed.
The caprolactam synthesis method according to claim 1, characterized in that: in the step (2), the mass concentration of cyclohexanone oxime is 5-30wt%, and the preferred concentration is 5-20wt%;
The caprolactam synthesis method according to claim 1, characterized in that: in the step (3), the preheating temperature of the cyclohexanone oxime solution is 50-250°C, preferably 100-180°C, and the preheating temperature of the caprolactam-sulfate is The heat temperature is 50 to 250°C, preferably 100 to 180°C;
The caprolactam synthesis method according to claim 1, characterized in that: in the step (3), the mass ratio of caprolactam-sulfate and cyclohexanone oxime is 0.5 to 20, preferably 3 to 10, and the reaction temperature is 50 ~250°C, preferably 100~180°C, and the reaction time is 0.5~30min, preferably 5~15min.
The caprolactam synthesis method according to claim 1, characterized in that: in the step (4), the rectification is vacuum distillation, the pressure is an absolute pressure of 2 to 12 kPa, preferably 4 to 8 kPa, and the distillation temperature of the caprolactam is 130 to 190°C, preferably 162 to 183°C.
The caprolactam synthesis method according to claim 1, characterized in that: in the step (5), the caprolactam-sulfate flash evaporation temperature is 50-120°C, preferably 80-100°C, and the flash pressure is an absolute pressure of 2 ~36kPa, preferably 10~20kPa.