A process for the preparation of caprolactam

Abstract

The application relates to a method for preparing caprolactam, characterized by using an acidic compound with temperature-controlled phase transfer catalysis characteristics as a catalyst to catalyze a cyclohexanone oxime rearrangement reaction for preparing caprolactam, and recycling and reusing the catalyst; the rearrangement reaction conditions are as follows: the molar ratio of cyclohexanone oxime to the catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to an organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h. The method has the following characteristics: the acidic compound with temperature-controlled phase transfer catalysis characteristics as the catalyst catalyzes the cyclohexanone oxime rearrangement reaction for preparing caprolactam, and has the characteristics of 'high-temperature homogeneous reaction-low-temperature two-phase separation'; the reaction conditions are mild, the catalyst has good catalytic activity, the product yield is high, the solvent and the catalyst are easy to separate and can be reused.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing caprolactam, i.e. to a method for preparing caprolactam with the feature of temperature-controlled phase transfer catalysis An acidic compound is used as a catalyst for preparing caprolactam by rearrangement reaction of cyclohexanone oxime. BACKGROUND

[0002] Nylon series chemical fibers have an important strategic role in national economy, social development and national security. Caprolactam is an important raw material for the synthesis of nylon-6, which is prepared by Beckmann rearrangement reaction of cyclohexanone oxime using concentrated sulfuric acid or fuming sulfuric acid as a catalyst. The catalyst has many defects in the catalytic reaction process, such as multiple side reactions, poor product selectivity, complex product separation operation, and difficult separation / reuse of the catalyst after use, which has become a technical bottleneck restricting the development of caprolactam industry and seriously affects the transformation and upgrading of nylon fiber industry in China. Therefore, it has important academic significance and potential application prospect to create a new type of catalytic system with high catalytic activity, good selectivity, easy separation and recovery, and recyclable use, to realize efficient conversion of caprolactam under mild conditions and separation, recovery and reuse of the catalytic system.

[0003] The temperature-controlled phase separation catalytic system combines the advantages of homogeneous catalysis and heterogeneous separation together, fully embodies the feature of "high-temperature homogeneous reaction-low-temperature two-phase separation", and has been well applied in organic reactions such as catalytic alkylation, hydrodeoxygenation and oxidative desulfurization. Therefore, the present application invents a method for preparing caprolactam with the feature of temperature-controlled phase transfer catalysis An acidic compound is used as a catalyst for preparing caprolactam by rearrangement reaction of cyclohexanone oxime. The present application has the advantages of mild reaction conditions, high catalytic activity and good stability, and the reaction process has the feature of "high-temperature homogeneous reaction-low-temperature two-phase separation". The catalyst can be separated automatically after the reaction and can be reused, realizing the integration of reaction and separation and the separation, recovery and recycling of the catalyst. The present application provides a clean new way for the preparation of caprolactam. SUMMARY

[0004] The purpose of the present application is to replace the traditional preparation method of caprolactam using concentrated sulfuric acid or fuming sulfuric acid as a catalyst, and to develop a method for clean preparation of caprolactam under mild reaction conditions.

[0005] Based on the above, the present application relates to a method for preparing caprolactam, characterized by using a temperature-controlled phase transfer catalytic system The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure. The acid compound alkylsultone and single-alkoxy polyoxyethylene ether are dissolved in ethyl acetate with a mass number of 2 times of the two, and refluxed at normal pressure for 3 h, and then distilled off the ethyl acetate under reduced pressure to prepare; the single-alkoxy polyoxyethylene ether is one of single-methoxyl polyoxyethylene ether with a molecular weight of 400-800, single-ethoxyl polyoxyethylene ether with a molecular weight of 400-800 or single-dodecyl polyoxyethylene ether with a molecular weight of 600-1400, the alkylsultone is one of 1,3-propane sulfone or 1,4-butane sulfone, and the organic solvent is one of toluene, cyclohexane or a mixture of the two with a volume ratio of 1:9-9:1.

[0006] The present application solves the technical problem by the following technical scheme:

[0007] The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure. The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure. The acid catalyst is named as [MPEG600-C3SO3H], and other acid catalysts are named in the same way. The acid catalyst is named as [MPEG600-C3SO3H], and other acid catalysts are named in the same way.

[0008] The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure. The acid catalyst is named as [MPEG600-C3SO3H], and other acid catalysts are named in the same way.

[0009] The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure. The acid compound is used for preparing caprolactam by catalyzing rearrangement reaction of cyclohexanone oxime, and the catalyst is recycled and reused; the rearrangement reaction is carried out under the following conditions: the molar ratio of cyclohexanone oxime to catalyst is 10:1-200:1, the mass ratio of cyclohexanone oxime to organic solvent is 1:1-1:5, the reaction temperature is 40-150 DEG C, and the reaction time is 1-8 h; the acid catalyst is prepared by dissolving equal molar 1,3-propane sulfone and single-methoxyl polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times of the two, and refluxing at normal pressure for 3 h, and then distilling off the ethyl acetate under reduced pressure.

[0010] The present application has the following characteristics compared with the conventional method:

[0011] 1. The present application has the following characteristics compared with the conventional method: The acid compound has the characteristics of "high-temperature homogeneous reaction and low-temperature two-phase separation" in catalyzing the rearrangement reaction of cyclohexanone oxime to prepare caprolactam.

[0012] 2. The reaction condition is mild, the catalytic activity of the catalyst is good, the yield of the product is high, and the solvent and the catalyst are easy to separate and can be reused. Specific implementation method

[0013] The method of the present application will be further described below in conjunction with examples, which are not limitations of the present application.

[0014] Example 1: Dissolve equal molar amounts of 1,3-propane sulfone lactone and monomethoxy polyoxyethylene ether with a molecular weight of 600 in ethyl acetate with a mass number of 2 times that of the two, reflux at normal pressure for 3 h, and distill off the ethyl acetate under reduced pressure to obtain The acid catalyst [MPEG600-C3SO3H].

[0015] Put 0.1 mol of cyclohexanone oxime, 0.003 mol of The acid catalyst [MPEG600-C3SO3H] and toluene with a mass number of 3 times that of the raw material cyclohexanone oxime into a pressure reactor equipped with magnetic stirring and a thermometer, seal the reactor, replace the air in the reactor with nitrogen for 3 times, heat the material in the reactor to 110°C and keep it at this temperature for 4 h of stirring reaction, after the reaction is completed, quickly cool the reactor in a water bath to room temperature, and transfer the reaction mixture to a separatory funnel for standing and layering, the upper layer is the organic phase of the product and toluene, and the lower layer is the catalyst phase; after the upper layer product phase is distilled off under reduced pressure to remove the solvent toluene, the product caprolactam is obtained, with a yield of 99.5%; the lower layer catalyst phase is directly used for recycling experiments.

[0016] Comparative Example 1: Put 0.1 mol of cyclohexanone oxime, 0.003 mol of 70% concentrated sulfuric acid and toluene with a mass number of 3 times that of the raw material cyclohexanone oxime into a pressure reactor equipped with magnetic stirring and a thermometer, seal the reactor, replace the air in the reactor with nitrogen for 3 times, heat the material in the reactor to 110°C and keep it at this temperature for 4 h of stirring reaction, after the reaction is completed, quickly cool the reactor in a water bath to room temperature, and transfer the reaction mixture to a separatory funnel for standing and layering, the upper layer is the organic phase of the product, and the lower layer is the waste acid phase, the waste acid phase is extracted with toluene with the same mass as cyclohexanone oxime for three times, the product organic phase is combined and distilled off under reduced pressure to remove the solvent, to obtain the product caprolactam, with a yield of 85.1%.

[0017] Comparative Example 2: 0.1 mol of cyclohexanone oxime, 0.003 mol of 1-ethyl-3- propylsulfonyl chloride imidazole hexafluoroborate and 3 times the mass of cyclohexanone oxime of toluene were put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, the material in the reactor was heated to 110°C and kept stirring for 4 hours, after the reaction was completed, the reactor was quickly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel for standing and layering, the upper layer was the product organic phase and the lower layer was the catalyst phase, the toluene in the upper layer product organic phase was distilled off to obtain the product caprolactam with a yield of 87.6%.

[0018] Example 2: equimolar 1,4-butane sultone and methoxy polyoxyethylene ether with a molecular weight of 600 were dissolved in 2 times the mass of ethyl acetate, refluxed at normal pressure for 3 hours, and then distilled under reduced pressure to remove the ethyl acetate, to obtain acidic catalyst [MPEG600-C4SO3H].

[0019] 0.1 mol of cyclohexanone oxime, 0.003 mol of 1-ethyl-3-propylsulfonyl chloride imidazole hexafluoroborate and 3 times the mass of cyclohexanone oxime of toluene were put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, the material in the reactor was heated to 110°C and kept stirring for 4 hours, after the reaction was completed, the reactor was quickly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel for standing and layering, the upper layer was the product organic phase and the lower layer was the catalyst phase, the toluene in the upper layer product organic phase was distilled off to obtain the product caprolactam with a yield of 87.6%. acidic catalyst [MPEG600-C4SO3H] and 3 times the mass of cyclohexanone oxime of toluene were put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, the material in the reactor was heated to 110°C and kept stirring for 4 hours, after the reaction was completed, the reactor was quickly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel for standing and layering, the upper layer was the product organic phase and the lower layer was the catalyst phase, the toluene in the upper layer product organic phase was distilled off to obtain the product caprolactam with a yield of 87.6%.

[0020] Example 3: equimolar 1,3-propane sultone and methoxy polyoxyethylene ether with a molecular weight of 400 were dissolved in 2 times the mass of ethyl acetate, refluxed at normal pressure for 3 hours, and then distilled under reduced pressure to remove the ethyl acetate, to obtain acidic catalyst [MPEG400-C3SO3H].

[0021] 0.1 mol of cyclohexanone oxime, 0.003 mol of 1-ethyl-3-propylsulfonyl chloride imidazole hexafluoroborate and 3 times the mass of cyclohexanone oxime of toluene were put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, the material in the reactor was heated to 110°C and kept stirring for 4 hours, after the reaction was completed, the reactor was quickly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel for standing and layering, the upper layer was the product organic phase and the lower layer was the catalyst phase, the toluene in the upper layer product organic phase was distilled off to obtain the product caprolactam with a yield of 87.6%. The acidic catalyst [MPEG400-C3SO3H] and toluene with the same mass number as the raw material cyclohexanone oxime were put into a pressure reaction kettle equipped with magnetic stirring and a thermometer. After the kettle was sealed and the air in the kettle was replaced with nitrogen three times, the materials in the kettle were heated to 150°C and kept stirring for 1 h. After the reaction was completed, the reaction kettle was rapidly cooled to room temperature in a water bath, and the product was extracted three times with toluene with the same mass as cyclohexanone oxime. The combined extract was distilled under reduced pressure to remove the extractant, and the product caprolactam was obtained with a yield of 99.1%. The acidic catalyst [MPEG400-C3SO3H] in the raffinate phase could be reused after the residual extractant toluene was removed by distillation under reduced pressure.

[0022] Example 4: Equal molar 1,4-propane sultone and methoxy polyoxyethylene ether with a molecular weight of 800 were dissolved in ethyl acetate with a mass number twice that of the two, and refluxed at atmospheric pressure for 3 h. The ethyl acetate was removed by distillation under reduced pressure to obtain The acidic catalyst [MPEG800-C4SO3H].

[0023] 0.1 mol of cyclohexanone oxime, 0.01 mol of The acidic catalyst [MPEG800-C4SO3H] and a mixture of toluene with a mass number five times that of the raw material cyclohexanone oxime and cyclohexane (volume ratio 1:9) were put into a pressure reaction kettle equipped with magnetic stirring and a thermometer. After the kettle was sealed and the air in the kettle was replaced with nitrogen three times, the materials in the kettle were heated to 40°C and kept stirring for 8 h. After the reaction was completed, the reaction kettle was rapidly cooled to room temperature in a water bath, and the product was extracted three times with a mixture of toluene and cyclohexane (volume ratio 1:9) with the same mass as cyclohexanone oxime. The combined extract was distilled under reduced pressure to remove the extractant, and the product caprolactam was obtained with a yield of 99.0%. The acidic catalyst [MPEG800-C4SO3H] in the raffinate phase could be reused after the residual extractant toluene was removed by distillation under reduced pressure.

[0024] Example 5: Equal molar 1,3-propane sultone and monoethoxy polyoxyethylene ether with a molecular weight of 400 were dissolved in ethyl acetate with a mass number twice that of the two, and refluxed at atmospheric pressure for 3 h. The ethyl acetate was removed by distillation under reduced pressure to obtain The acidic catalyst [EPEG400-C3SO3H].

[0025] 0.2 mol of cyclohexanone oxime, 0.001 mol of The acidic catalyst [EPEG400-C3SO3H] and cyclohexane with 5 times the mass of cyclohexanone oxime are put into a pressure reaction kettle provided with magnetic stirring and a thermometer, the kettle is sealed and the air in the kettle is replaced with nitrogen for three times, then the materials in the kettle are heated to 100°C and kept stirring for 3 hours, after the reaction is completed, the reaction kettle is rapidly cooled to room temperature in a water bath, and cyclohexane with the same mass as cyclohexanone oxime is used for extraction three times, the combined extract is subjected to vacuum distillation to remove the extractant, and the product caprolactam is obtained, with a yield of 99.0%; the acidic catalyst [EPEG400-C3SO3H] in the raffinate can be reused after the residual extractant toluene is removed by vacuum distillation.

[0026] Example 6: Equal molar 1,4-propane sultone and monoethoxypolyoxyethylene ether with a molecular weight of 600 are dissolved in ethyl acetate with 2 times the mass of the two, and subjected to atmospheric reflux reaction for 3 hours, and vacuum distillation to remove ethyl acetate, to prepare The acidic catalyst [EPEG600-C4SO3H].

[0027] 0.2 mol of cyclohexanone oxime, 0.01 mol of The acidic catalyst [EPEG600-C4SO3H] and cyclohexane with 3 times the mass of cyclohexanone oxime are put into a pressure reaction kettle provided with magnetic stirring and a thermometer, the kettle is sealed and the air in the kettle is replaced with nitrogen for three times, then the materials in the kettle are heated to 110°C and kept stirring for 3 hours, after the reaction is completed, the reaction kettle is rapidly cooled to room temperature in a water bath, and toluene with the same mass as cyclohexanone oxime is used for extraction three times, the combined extract is subjected to vacuum distillation to remove the extractant, and the product caprolactam is obtained, with a yield of 99.0%; the acidic catalyst [EPEG600-C4SO3H] in the raffinate can be reused after the residual extractant cyclohexane is removed by vacuum distillation.

[0028] Example 7: Equal molar 1,3-propane sultone and monoethoxypolyoxyethylene ether with a molecular weight of 800 are dissolved in ethyl acetate with 2 times the mass of the two, and subjected to atmospheric reflux reaction for 3 hours, and vacuum distillation to remove ethyl acetate, to prepare The acidic catalyst [EPEG800-C3SO3H].

[0029] 0.1 mol of cyclohexanone oxime, 0.001 mol of The acid catalyst [EPEG800-C3SO3H] and the mixture of toluene and cyclohexane (volume ratio 1:9) with 3 times the mass of the raw material cyclohexanone oxime were put into a pressure reaction kettle equipped with magnetic stirring and a thermometer, the kettle was sealed and the air in the kettle was replaced with nitrogen for 3 times, then the material in the kettle was heated to 120°C and kept stirring for 2 hours, after the reaction was completed, the reaction kettle was quickly cooled to room temperature in a water bath, and the mixture of toluene and cyclohexane (volume ratio 1:9) with the same mass as the cyclohexanone oxime was extracted three times, the combined extract was distilled under reduced pressure to remove the extractant, and the product caprolactam was obtained, with a yield of 99.0%; the acid catalyst [EPEG800-C3SO3H] in the raffinate phase was reused after the residual extractant was removed by reduced pressure distillation.

[0030] Example 8: Equal molar amounts of 1,3-propane sultone and monododecyl polyoxyethylene ether with a molecular weight of 600 were dissolved in ethyl acetate with 2 times the mass of the two, refluxed at atmospheric pressure for 3 hours, and distilled under reduced pressure to remove the ethyl acetate, to obtain The acid catalyst [DPEG600-C3SO3H].

[0031] 0.1 mol of cyclohexanone oxime, 0.003 mol of The acid catalyst [DPEG600-C3SO3H] and the mixture of toluene and cyclohexane (volume ratio 1:1) with 3 times the mass of the raw material cyclohexanone oxime were put into a pressure reaction kettle equipped with magnetic stirring and a thermometer, the kettle was sealed and the air in the kettle was replaced with nitrogen for 3 times, then the material in the kettle was heated to 80°C and kept stirring for 4 hours, after the reaction was completed, the reaction kettle was quickly cooled to room temperature in a water bath, and toluene with the same mass as the cyclohexanone oxime was extracted three times, the combined extract was distilled under reduced pressure to remove the extractant, and the product caprolactam was obtained, with a yield of 99.0%; the acid catalyst [DPEG600-C3SO3H] in the raffinate phase was reused after the residual extractant cyclohexane was removed by reduced pressure distillation.

[0032] Example 9: Equal molar amounts of 1,3-propane sultone and monododecyl polyoxyethylene ether with a molecular weight of 1400 were dissolved in ethyl acetate with 2 times the mass of the two, refluxed at atmospheric pressure for 3 hours, and distilled under reduced pressure to remove the ethyl acetate, to obtain The acid catalyst [DPEG1400-C3SO3H].

[0033] 0.1 mol of cyclohexanone oxime, 0.003 mol of The mixture of the acidic catalyst [DPEG 1400-C3SO3H] and the raw material cyclohexanone oxime, 3 times the mass of toluene and cyclohexane (volume ratio 1:1) was put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the material in the reactor was heated to 80°C and kept stirring for 4 hours. After the reaction was completed, the reactor was rapidly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel to separate into two layers. The upper layer was the organic phase of the product and toluene, and the lower layer was the catalyst phase. The product was obtained by removing the solvent toluene from the upper layer by vacuum distillation, and the yield was 99.0%. The acidic catalyst [DPEG 1400-C3SO3H] in the lower layer could be reused after removing the residual solvent cyclohexane by vacuum distillation.

[0034] Example 10: 1,3-propane sulfone and monododecyl polyoxyethylene ether with a molecular weight of 1000 were dissolved in 2 times the mass of ethyl acetate, and the mixture was refluxed at atmospheric pressure for 3 hours. The ethyl acetate was removed by vacuum distillation to obtain The acidic catalyst [DPEG 1000-C3SO3H].

[0035] 0.1 mol of cyclohexanone oxime, 0.003 mol of The mixture of the acidic catalyst [DPEG 1000-C3SO3H] and the raw material cyclohexanone oxime, 3 times the mass of toluene and cyclohexane (volume ratio 1:1) was put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the material in the reactor was heated to 80°C and kept stirring for 4 hours. After the reaction was completed, the reactor was rapidly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel to separate into two layers. The upper layer was the organic phase of the product and toluene, and the lower layer was the catalyst phase. The product was obtained by removing the solvent toluene from the upper layer by vacuum distillation, and the yield was 99.0%. The acidic catalyst [DPEG 1000-C3SO3H] in the lower layer could be reused after removing the residual solvent cyclohexane by vacuum distillation.

[0036] Example 11: The recovered The mixture of the acidic catalyst [MPEG 600-C3SO3H], 0.1 mol of cyclohexanone oxime, and 3 times the mass of toluene was put into a pressure reactor equipped with magnetic stirring and a thermometer, the reactor was sealed and the air in the reactor was replaced with nitrogen for 3 times, then the material in the reactor was heated to 110°C and kept stirring for 4 hours. After the reaction was completed, the reactor was rapidly cooled to room temperature in a water bath, and the reaction mixture was transferred to a separatory funnel to separate into two layers. The upper layer was the organic phase of the product and toluene, and the lower layer was the catalyst phase. The product was obtained by removing the solvent toluene from the upper layer by vacuum distillation, and the yield was 99.2%. The recovered The acidic catalyst [MPEG600-C3SO3H] was repeatedly used for 10 times under the same experimental conditions, and the yield of the product caprolactam was greater than 98.1% in each time.

[0037] Example 12: the product recovered in Example 2 The acidic catalyst [MPEG600-C4SO3H], 0.1 mol of cyclohexanone oxime, and toluene with 3 times the mass of the raw material cyclohexanone oxime were put into a pressure reaction kettle equipped with magnetic stirring and a thermometer. After the kettle was sealed and the air in the kettle was replaced with nitrogen for 3 times, the materials in the kettle were heated to 110°C and kept stirring for 4 h. After the reaction was completed, the reaction kettle was quickly cooled to room temperature in a water bath, and the product was extracted with toluene with the same mass as the cyclohexanone oxime for 3 times. The combined extract was distilled under reduced pressure to remove the extractant, and the product caprolactam was obtained with a yield of 99.1%. The product recovered in this example The acidic catalyst [MPEG600-C4SO3H] was repeatedly used for 10 times under the same experimental conditions, and the yield of the product caprolactam was greater than 97.8% in each time.

Claims

1. A method for preparing caprolactam, characterized in that: An acidic compound with temperature-controlled phase transfer catalysis is used as a catalyst to catalyze the rearrangement reaction of cyclohexanone oxime to prepare caprolactam, and the catalyst is recovered and reused; The rearrangement reaction conditions are as follows: a molar ratio of cyclohexanone oxime to the catalyst of 10:1 to 200:1, a mass ratio of cyclohexanone oxime to the organic solvent of 1:1 to 1:5, a reaction temperature of 40 to 150° C., and a reaction time of 1 to 8 hours; The rearrangement reaction was carried out in a pressure reactor equipped with a magnetic stirrer and a thermometer. After adding the raw materials, the reactor was sealed and the air in the reactor was replaced with nitrogen three times. After heating to the reaction temperature, the reactor was kept warm and stirred. The acidic catalyst is prepared by dissolving equimolar amounts of an acidic compound, an alkyl sultone, and a monoalkoxy polyoxyethylene ether, in ethyl acetate (2 times the mass of the acidic compound), subjecting the mixture to reflux reaction at normal pressure for 3 hours, and then removing the ethyl acetate by vacuum distillation. The monoalkoxy polyoxyethylene ether is one of monomethoxy polyoxyethylene ether with a molecular weight of 400-800, monoethoxy polyoxyethylene ether with a molecular weight of 400-800, or monododecyl polyoxyethylene ether with a molecular weight of 600-1400; the alkyl sultone is one of 1,3-propane sultone or 1,4-butane sultone; and the organic solvent is one of toluene, cyclohexane, or a mixture of the two in a volume ratio of 1:9 to 9:1.

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