Method for preparing caprolactam

Abstract

The invention relates to the technical field of caprolactam preparation, and discloses a caprolactam preparation method, which comprises: (1) in the presence of an oximation catalyst, carrying out a heterogeneous ammoximation reaction on cyclohexanone, ammonia and hydrogen peroxide in an aqueous solution; (2) extracting the product obtained in the step (1) by adopting a solvent A to obtain a cyclohexanone-oxime-A solution; (3) mixing a solvent B with the cyclohexanone oxime-A solution to obtain a mixed raw material, and then contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst; the cyclohexanone-oxime gas phase Beckmann rearrangement reaction is carried out under the condition of no carrier gas; the solvent A is C5-C8 alkane, and the solvent B is low-carbon alcohol; the mass ratio of the solvent A to the solvent B is 1: (0.4-1). According to the method, the heterogeneous ammoximation product can be directly utilized, additional separation and purification of cyclohexanone-oxime are not needed, a large amount of nitrogen used as carrier gas of a gas-phase rearrangement reaction for heat removal is omitted, and the technical economy of gas-phase rearrangement can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of caprolactam, and in particular to a method for preparing caprolactam. Background Art

[0002] Caprolactam is the main raw material for the production of three major series of products: nylon, industrial cord and nylon engineering plastics. Its demand has always been strong. It is generally prepared by the Beckmann rearrangement reaction of cyclohexanone oxime. At present, the industry usually adopts the liquid phase rearrangement process with concentrated sulfuric acid or fuming sulfuric acid as a catalyst. The caprolactam produced by this process accounts for about 90% of the total caprolactam production in the world. However, this process consumes a large amount of sulfuric acid and ammonia water. Generally, 1.3-1.8 tons of ammonium sulfate will be produced as a by-product for every ton of caprolactam produced. The production cost is high, and the use of sulfuric acid will also cause problems such as equipment corrosion and environmental pollution.

[0003] The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime under solid acid catalyst conditions is a new process for realizing the non-sulfurization of caprolactam. It has the problems of no equipment corrosion and no environmental pollution, and the separation and purification of the product will also be greatly simplified. Therefore, the gas-phase Beckmann rearrangement reaction process without sulfurization has attracted great attention from industry insiders. However, in the gas-phase Beckmann rearrangement fixed bed and moving bed processes, due to the strong exothermic characteristics of the rearrangement reaction, the temperature rise of the catalyst bed in the fixed bed and moving bed reactors reaches 150°C. In the prior art, a large amount of inert carrier gas such as nitrogen is required to transfer heat, so the nitrogen / oxime molar ratio is sometimes as high as about 30-50, and the nitrogen usage, circulation volume and consumption are all very large, resulting in a very thick circulating gas pipeline, high energy consumption, high investment (high-power nitrogen compressor), and complex process. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of large catalyst bed temperature rise, large inert carrier gas consumption and high energy consumption in the gas-phase Beckmann rearrangement reaction in the prior art, and to provide a method for preparing caprolactam. The method couples the heterogeneous ammoximation reaction with the gas-phase Beckmann rearrangement reaction, does not require the use of an inert carrier gas, and greatly reduces the energy consumption of the reaction system.

[0005] In order to achieve the above object, the present invention provides a method for preparing caprolactam, the method comprising:

[0006] (1) in the presence of an oximation catalyst, subjecting cyclohexanone, ammonia and hydrogen peroxide to a heterogeneous ammoximation reaction in an aqueous solution;

[0007] (2) extracting the product obtained in step (1) with solvent A to obtain a cyclohexanone oxime-A solution;

[0008] (3) mixing solvent B with cyclohexanone oxime-A solution to obtain a mixed raw material, and then contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to perform a cyclohexanone oxime gas-phase Beckmann rearrangement reaction; the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is performed in the absence of a carrier gas;

[0009] Wherein, the solvent A is C 6 -C 8 The solvent A is an alkane, and the solvent B is a low-carbon alcohol; the mass ratio of solvent A to solvent B is 1:(0.4-1).

[0010] The present invention couples heterogeneous ammoximation with the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and directly utilizes the extract phase containing cyclohexanone oxime obtained by heterogeneous ammoximation to carry out the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. 6 -C 8 The alkane is used as an extractant (solvent A) and acts in synergy with the low-carbon alcohol to further control the mass ratio of solvent A and solvent B. Under the condition of ensuring that the conversion rate and selectivity of the gas-phase rearrangement reaction are equivalent, the extractant in the heterogeneous ammoximation can be directly used without the need for additional separation and purification of cyclohexanone oxime, eliminating the need for a large amount of nitrogen as a carrier gas for the gas-phase rearrangement reaction to transfer heat, which can greatly improve the technical and economic efficiency of the gas-phase rearrangement. In addition, the inventors of the present invention have also found that without introducing a carrier gas, it is beneficial to separate the circulating gas of the gas-phase rearrangement reaction, that is, the separation of the solvent alcohol and the non-condensable gas becomes simple. DETAILED DESCRIPTION

[0011] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0012] The present invention provides a method for preparing caprolactam, the method comprising:

[0013] (1) in the presence of an oximation catalyst, subjecting cyclohexanone, ammonia and hydrogen peroxide to a heterogeneous ammoximation reaction in an aqueous solution;

[0014] (2) extracting the product obtained in step (1) with solvent A to obtain a cyclohexanone oxime-A solution;

[0015] (3) mixing solvent B with cyclohexanone oxime-A solution to obtain a mixed raw material, and then contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to perform a cyclohexanone oxime gas-phase Beckmann rearrangement reaction; the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is performed in the absence of a carrier gas;

[0016] Wherein, the solvent A is C 6 -C 8 The solvent A is an alkane, and the solvent B is a low-carbon alcohol; the mass ratio of solvent A to solvent B is 1:(0.4-1).

[0017] In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime in a fixed bed, a moving bed or a fluidized bed, the temperature rise of the catalyst bed is relatively large. The reaction heat Q of the Beckmann rearrangement reaction of cyclohexanone oxime under standard conditions is 185 kJ / mol oxime. The temperature rise of the catalyst bed in a fixed bed or a moving bed reactor is as high as 150°C. Therefore, in the prior art, a large amount of nitrogen needs to be introduced as a carrier gas for the reaction to transfer heat. The nitrogen / oxime molar ratio is sometimes as high as about 30-50, and the nitrogen usage, circulation amount and consumption are all very large. In addition, with the introduction of nitrogen, the storage of the carrier gas, the separation of the solvent alcohol and the non-condensable gas, etc., undoubtedly increase the load of the device system.

[0018] The present invention couples heterogeneous ammoximation with the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and directly utilizes the extract phase containing cyclohexanone oxime obtained by heterogeneous ammoximation to carry out the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. 6 -C 8 The alkane is used as the extractant (solvent A) and works synergistically with the low-carbon alcohol to further control the mass ratio of solvent A to solvent B. Under the condition of ensuring the conversion rate and selectivity level of the gas-phase rearrangement reaction are equivalent, the extractant in the heterogeneous ammoximation can be directly utilized without the need for additional separation and purification of cyclohexanone oxime, thus eliminating the need for a large amount of nitrogen as a carrier gas for heat transfer in the gas-phase rearrangement reaction, thereby greatly improving the technical and economic benefits of the gas-phase rearrangement.

[0019] According to some preferred embodiments of the present invention, solvent A is at least one of a substituted or unsubstituted chain alkane or cycloalkane with 5-8 carbon atoms, and a substituted or unsubstituted aromatic hydrocarbon with 6-8 carbon atoms. The chain alkane may be a straight-chain alkane or a branched alkane, and the H atom in the cycloalkane may also be substituted by an alkyl group. The substituent in the substituted aromatic hydrocarbon with 6-8 carbon atoms may be at least one of a halogen atom, a methyl group, and an ethyl group. Preferably, solvent A is selected from at least one of n-hexane, cyclohexane, cyclopentane, methylcyclohexane, n-heptane, n-octane, benzene, toluene, xylene, and halogenated benzene, more preferably at least one of cyclohexane, n-heptane, benzene, and toluene, more preferably cyclohexane. Using the above-mentioned preferred solvent A as an extractant and cooperating with solvent B can further improve the catalyst stability and caprolactam selectivity of gas phase rearrangement.

[0020] According to some preferred embodiments of the present invention, the solvent B is C 1 -C 3The alcohol is preferably methanol and / or ethanol.

[0021] According to a particularly preferred embodiment of the present invention, the solvent A is cyclohexane and the solvent B is ethanol. In the above preferred case, it is beneficial to further improve the selectivity of caprolactam and reduce the types and quantities of by-products.

[0022] The present invention has no particular limitation on the specific operating conditions of the heterogeneous ammoximation reaction in step (1), and can be carried out using conditions known in the art, for example, the heterogeneous ammoximation reaction method disclosed in CN105837507A can be used. The oximation catalyst is a titanium silicon molecular sieve catalyst, which can be the titanium silicon molecular sieve catalyst disclosed in CN105837507A, and will not be described in detail here.

[0023] In the present invention, there is no particular limitation on the amount of solvent A used for extraction in step (2), as long as cyclohexanone oxime can be fully extracted from the product, and those skilled in the art can select it according to actual needs. Preferably, the amount of solvent A is such that the content of solvent A in the cyclohexanone oxime-A solution obtained in step (2) is 60-80wt%, more preferably 65-75wt%.

[0024] According to the present invention, the mass ratio of solvent A to solvent B in the mixed raw material is 1:(0.5-0.8). By controlling the mass ratio of solvent A to solvent B, it is beneficial to the reaction heat transfer and can ensure a higher conversion rate and selectivity of the cyclohexanone oxime gas-phase Beckmann rearrangement reaction.

[0025] According to some preferred embodiments of the present invention, based on the total amount of the mixed raw material, the content of cyclohexanone oxime is 10-30wt%, preferably 15-25wt%. Controlling the content of cyclohexanone oxime in the mixed raw material within the above preferred range is conducive to reducing the partial pressure of cyclohexanone oxime and improving the vaporization effect.

[0026] It can be understood that, in the present invention, the contents of solvent A and solvent B are adjusted to ensure that the content of cyclohexanone oxime in the mixed raw material is within the above preferred range.

[0027] According to the present invention, the mixed raw material may further contain water. Preferably, the mixed raw material further contains water, and the water content does not exceed 5wt%, preferably 0.2-3wt%, based on the total amount of the mixed raw material.

[0028] According to some preferred embodiments of the present invention, the contacting method in step (3) includes: spraying and vaporizing the mixed raw material, and then contacting the vaporized mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst. In the prior art, the vaporized raw material is usually an alcohol solution of cyclohexanone oxime, wherein the content of cyclohexanone oxime is relatively high. In order to reduce the partial pressure of cyclohexanone oxime in the vaporized raw material, it is usually necessary to introduce an inert gas such as nitrogen to assist in vaporization. In the present invention, due to the presence of solvent A and solvent B in the mixed raw material, the mixed raw material can be directly vaporized through an atomizing nozzle, and no additional inert gas needs to be introduced during the vaporization process. Further, by controlling the ratio of solvent A and solvent B, it is beneficial to ensure a better vaporization effect.

[0029] In the present invention, there is no particular limitation on the operating conditions of the spray vaporization, and the spray vaporization can be carried out in a conventional manner in the art.

[0030] According to some preferred embodiments of the present invention, the temperature of the spray vaporization is 155-180°C, preferably 160-175°C.

[0031] According to some preferred embodiments of the present invention, the pressure of the spray vaporization is 0.5-5 MPa, preferably 1-4 MPa.

[0032] In some preferred embodiments, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in a fixed bed or moving bed reactor. Preferably, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction conditions include: reaction temperature of 300-500°C, preferably 350-420°C; reaction pressure of 0.05-0.5MPa, preferably 0.05-0.3MPa; weight space velocity of cyclohexanone oxime of 0.1-5h -1 , preferably 0.4-2h -1 .

[0033] In some other preferred embodiments, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in a fluidized bed reactor. Preferably, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction conditions include: a reaction temperature of 300-500°C, preferably 350-400°C; a reaction pressure of 0.05-0.5MPa, preferably 0.05-0.3MPa; a weight space velocity of cyclohexanone oxime of 2-8h -1 , preferably 3-6h -1 .

[0034] According to the present invention, the gas-phase Beckmann rearrangement reaction catalyst can be any catalyst in the art that can catalyze the gas-phase Beckmann rearrangement reaction. The present invention has no particular limitation on the source of the gas-phase Beckmann rearrangement reaction catalyst, and the catalyst can be purchased from a commercial source or prepared by any known method. Those skilled in the art can select the catalyst according to actual needs.

[0035] Preferably, the gas-phase Beckmann rearrangement reaction catalyst is an all-silicon molecular sieve catalyst with an MFI topological structure. The present invention has no special requirements for the composition of the molecular sieve catalyst, and the catalysts known in the art that can be used for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime can be applied to the present invention. The molecular sieve catalyst generally includes a molecular sieve with an MFI topological structure and a binder, and the molecular sieve with an MFI topological structure can be prepared, for example, by the method disclosed in CN102050464A. Those skilled in the art can perform optional molding according to different reactors and different test needs to obtain a molecular sieve catalyst.

[0036] For example, when used in a fixed bed, the spherical molecular sieve catalyst formed by rolling balls disclosed in 201210592676.5 or 201610285300.8 can be used; when used in a moving bed or a fluidized bed, the spray-formed microsphere molecular sieve catalyst disclosed in 202310595456.6, 202310594134.X, and 202310703580.X can be used.

[0037] The present invention will be described in detail below through examples.

[0038] In the following examples, the reaction products were quantitatively analyzed using an Agilent 6890 gas chromatograph (hydrogen flame ionization detector, PEG20M capillary column, column length 50 m), with a vaporization chamber temperature of 521 ° K, a detection chamber temperature of 513 ° K, and a column temperature program of 383 ° K for 8 minutes, 15 ° K / min to 503 ° K and then constant temperature for 14 minutes. The content of the rearrangement product was calculated using the area normalization method, and the solvent was not involved in the integration.

[0039] The molar percentage of cyclohexanone oxime in the reaction product and the molar percentage of caprolactam in the reaction product were obtained through the above analysis, and the cyclohexanone oxime conversion rate and caprolactam selectivity were calculated according to the following formula.

[0040] Cyclohexanone oxime conversion rate (mol%) = (100-cyclohexanone oxime molar percentage in the reaction product) / 100%;

[0041] Caprolactam selectivity (mol%) = mole percentage of caprolactam in the reaction product / (100-mole percentage of cyclohexanone oxime in the reaction product) × 100%;

[0042] WHSV(h -1 ) = cyclohexanone oxime flow rate in feed / catalyst mass in bed × 100%.

[0043] The spherical gas-phase Beckmann rearrangement reaction catalyst used in the following examples was prepared according to the method disclosed in Example 1 of CN103908980A. The microsphere molecular sieve catalyst used was prepared according to the method disclosed in Example 1 of Chinese patent application 202310595456.6.

[0044] Example 1

[0045] (1) using the method disclosed in Example 1 of CN105837507A to carry out a heterogeneous ammoximation reaction to obtain a cyclohexanone oxime aqueous solution;

[0046] (2) extracting the cyclohexanone oxime aqueous solution with a certain amount of cyclohexane to obtain a cyclohexane solution containing 25 wt% of cyclohexanone oxime;

[0047] (3) A 25 wt % cyclohexanone oxime solution in cyclohexane is mixed with ethanol to obtain a mixed raw material. In the mixed raw material, the content of cyclohexanone oxime is 17.2 wt %, the mass ratio of cyclohexane to ethanol is 1:0.6, and the water content is 0.4 wt %.

[0048] The gas-phase Beckmann rearrangement reaction is carried out in a radial moving bed reactor. The semi-continuous radial moving bed reactor made of 316L stainless steel has a diameter of 15 cm, a length of 100 cm, and a central sleeve diameter of 6 cm. The radial moving bed reactor is provided with a catalyst inlet, a central tube (small holes on the wall), a fan-shaped screen sleeve, and a catalyst outlet. The central tube arranged in the center of the reactor, the fan-shaped tube arranged on the wall, and their connectors realize the radial uniform flow of oil and gas, and the axial flow of the catalyst from top to bottom. The material passes through the catalyst bed from the central tube of the upper reactor, and the reaction product flows out of the reactor from the lower outlet of the reactor after being distributed in the fan-shaped tube. The initial catalyst loading amount is 800 grams of spherical molecular sieve catalyst, and the catalyst bed height is 15-20 cm.

[0049] The mixed raw materials were fed by gas atomization spray, the vaporizer temperature was controlled at 175°C, and the pipeline was kept at 200°C. The materials were fed from the central sleeve of the radial moving bed reactor, the reaction pressure was 0.05MPa, the reaction setting temperature was 380°C, and the weight hourly space velocity (WHSV) of cyclohexanone oxime was 2h -1 After 24 hours of operation, the catalyst bed temperature was measured to be 390-396°C, indicating a good heat transfer effect. When the reaction conversion rate is less than 99.8%, 50 grams of partially deactivated spherical gas-phase rearrangement molecular sieve catalyst can be unloaded from the lower end of the reactor for regeneration, and 50 grams of fresh or regenerated spherical gas-phase rearrangement molecular sieve catalyst can be added at the same time. The reaction product is cooled by an ice-water mixture and enters a collection bottle for gas-liquid separation. After 96 hours of operation, the product composition is analyzed, and the cyclohexanone oxime conversion rate is 99.8%, and the total caprolactam selectivity is 96%.

[0050] Example 2

[0051] The method of Example 1 was followed, except that an equal mass of methanol was used to replace ethanol, and the water content was 0.8 wt %.

[0052] The reactor temperature was set at 380°C, and the catalyst bed temperature was measured to be 390-395°C after 24 hours of operation, indicating good heat removal effect. After 96 hours of operation, the product composition was analyzed, and the cyclohexanone oxime conversion rate was 99.8%, and the total caprolactam selectivity was 95.5%.

[0053] Example 3

[0054] The method of Example 1 is followed, except that the cyclohexanone oxime vapor-phase Beckmann rearrangement reaction is carried out in a stainless steel fixed bed reactor. The reactor has an inner diameter of 5 mm, contains 0.469 g of a 40-60 mesh catalyst, and a 30 mm high 30 mesh coarse quartz sand is filled above the catalyst bed, and a 50 mesh fine quartz sand is filled below the catalyst bed.

[0055] In step (3), the cyclohexanone oxime-cyclohexane solution is mixed with ethanol to obtain a mixed raw material. In the mixed raw material, the content of cyclohexanone oxime is 17wt%, the mass ratio of cyclohexane to ethanol is 1:0.625, and the water content is 0.4wt%.

[0056] The fixed bed reaction conditions included: reaction pressure 0.05 MPa, reactor set temperature 380°C, cyclohexanone oxime weight space velocity (WHSV) 16 h -1 After running for 2 hours, the catalyst bed temperature was measured to be 380-382°C, indicating a good heat transfer effect. The reaction product was cooled by ice-water mixture and then entered the collection bottle for gas-liquid separation. After running for 6 hours, the product composition was analyzed, and the cyclohexanone oxime conversion rate was 99.42%, and the total caprolactam selectivity was 96.14%.

[0057] Example 4

[0058] The method of Example 2 is followed, except that the amounts of cyclohexane and methanol added are such that, in the mixed raw material, the content of cyclohexanone oxime is 14.3 wt %, the mass ratio of cyclohexane to methanol is 1:1, and the water content is 0.3 wt %.

[0059] The mixed raw materials were fed by gas atomization spraying, the temperature of the vaporizer was controlled at 175°C, and the pipeline was kept at 200°C. The materials were fed from the central sleeve of the radial moving bed reactor, the reaction pressure was 0.05MPa, the reaction temperature was 380°C, and the weight hourly velocity (WHSV) of cyclohexanone oxime was 2h -1. When the reaction conversion rate is less than 99.8%, 50 grams of partially deactivated spherical gas-phase rearrangement molecular sieve catalyst can be discharged from the lower end of the reactor for regeneration, and 50 grams of fresh or regenerated spherical gas-phase rearrangement molecular sieve catalyst can be added at the same time. The reaction product is cooled by ice-water mixture and enters the collection bottle for gas-liquid separation. After running for 24 hours, the catalyst bed temperature is measured to be 390-394°C. After running for 96 hours, the product composition is analyzed, and the cyclohexanone oxime conversion rate is 99.9%, and the total caprolactam selectivity is 96.32%.

[0060] Example 5

[0061] The method of Example 1 is followed, except that the amounts of cyclohexane and ethanol added are such that, in the mixed raw material, the content of cyclohexanone oxime is 19.2 wt %, the mass ratio of cyclohexane to ethanol is 1:0.4, and the water content is 0.5 wt %.

[0062] The mixed raw materials were fed by gas atomization spraying, the temperature of the vaporizer was controlled at 175°C, and the pipeline was kept at 200°C. The materials were fed from the central sleeve of the radial moving bed reactor, the reaction pressure was 0.05MPa, the reaction temperature was 380°C, and the weight hourly velocity (WHSV) of cyclohexanone oxime was 2h -1 . When the reaction conversion rate is less than 99.0%, 50 grams of partially deactivated spherical gas-phase rearrangement molecular sieve catalyst can be discharged from the lower end of the reactor for regeneration, and 50 grams of fresh or regenerated spherical gas-phase rearrangement molecular sieve catalyst can be added at the same time. The reaction product is cooled by ice-water mixture and enters the collection bottle for gas-liquid separation. After running for 24 hours, the catalyst bed temperature is measured to be 392-397°C. After running for 96 hours, the product composition is analyzed, and the cyclohexanone oxime conversion rate is 99.0%, and the total caprolactam selectivity is 95.84%.

[0063] Example 6

[0064] The method of Example 1 was followed, except that an equal mass of n-heptane was used to replace cyclohexane.

[0065] The mixed raw materials were fed by gas atomization spraying, the temperature of the vaporizer was controlled at 175°C, and the pipeline was kept at 200°C. The materials were fed from the central sleeve of the radial moving bed reactor, the reaction pressure was 0.05MPa, the reaction temperature was 380°C, and the weight hourly velocity (WHSV) of cyclohexanone oxime was 2h -1 . When the reaction conversion rate is less than 99.5%, 50 grams of partially deactivated spherical gas-phase rearrangement molecular sieve catalyst can be discharged from the lower end of the reactor for regeneration, and 50 grams of fresh or regenerated spherical gas-phase rearrangement molecular sieve catalyst can be added at the same time. The reaction product is cooled by ice-water mixture and enters the collection bottle for gas-liquid separation. After running for 24 hours, the catalyst bed temperature is measured to be 390-396°C. After running for 96 hours, the product composition is analyzed, and the cyclohexanone oxime conversion rate is 99.5%, and the total selectivity of caprolactam is 95.78%.

[0066] Example 7

[0067] (1) using the method disclosed in Example 1 of CN105837507A to carry out a heterogeneous ammoximation reaction to obtain a cyclohexanone oxime aqueous solution;

[0068] (2) extracting the cyclohexanone oxime aqueous solution with a certain amount of cyclohexane to obtain a cyclohexane solution containing 25 wt% of cyclohexanone oxime;

[0069] (3) A 25 wt % cyclohexanone oxime solution in cyclohexane is mixed with ethanol. In the mixed raw material, the content of cyclohexanone oxime is 17.5 wt %, the mass ratio of cyclohexane to ethanol is 1:0.6, and the water content is 0.3 wt %.

[0070] The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime was carried out in a homemade fixed fluidized bed reactor. The vertical 316L stainless steel reactor had an upper diameter of 20 cm and a lower diameter of 10 cm. The lengths of the upper and lower sections were 60 and 80 cm, respectively. The microsphere molecular sieve catalyst (prepared by the method of Example 1 of Chinese patent application 202310595456.6) was loaded in an amount of 260 g. The microsphere particle size was 50-150 μm, and the specific surface area was 336 m 2 ·g -1 The micropore specific surface area is 284m 2 ·g -1 The non-microporous specific surface area is 52m 2 ·g -1 ; Pore volume 0.429mL / g, micropore volume 0.136mL / g.

[0071] Feeding method: gas atomization spray, vaporizer temperature control 190℃, pipeline insulation 190℃, reaction pressure 0.05MPa, reaction temperature 380℃, cyclohexanone oxime WHSV 3h -1 The reaction product was cooled by ice-water mixture and then entered into a collection bottle for gas-liquid separation. After running for 6 hours, the catalyst bed temperature was measured to be 380-390°C. After reacting for 10 hours, the product composition was analyzed. The cyclohexanone oxime conversion rate was 99.95%, and the total caprolactam selectivity was 96.53%.

[0072] Example 8

[0073] The method of Example 7 was followed, except that an equal amount of methanol was used to replace ethanol, and the water content was 0.6 wt %. After 6 h of operation, the catalyst bed temperature was measured to be 380-392° C. After 10 h of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was 99.8%, and the total caprolactam selectivity was 96.5%.

[0074] Comparative Example 1

[0075] The method of Example 1 is followed, except that the cyclohexanone oxime vapor phase Beckmann rearrangement reaction is carried out in a stainless steel fixed bed reactor, the reactor has an inner diameter of 5 mm, is loaded with 0.469 g of 40-60 mesh catalyst, the catalyst bed is filled with about 30 mm high 30 mesh coarse quartz sand, and the catalyst bed is filled with 50 mesh fine quartz sand. The rearrangement reaction conditions are: normal pressure, reaction temperature 380°C; cyclohexanone oxime weight space velocity (WHSV) is 16h -1 ; The reaction solvent is ethanol, the weight of the ethanol is 65% of the weight of the reaction raw material, and the water content of the reaction raw material is: 1.2% (m); carrier gas (N 2 ) flow rate was 45 mL / min. After running for 2 hours, the catalyst bed temperature was measured to be 380-382°C. The reaction product was cooled by ice-water mixture and then entered into a collecting bottle for gas-liquid separation. After reacting for 6 hours, the product composition was analyzed. The cyclohexanone oxime conversion rate was 99.5%, and the total caprolactam selectivity was 96.4%.

[0076] Comparative Example 2

[0077] The method of comparative example 1 is followed, except that methanol is used instead of ethanol, and the water content of the reaction raw material is 1.8% (m). After running for 2 hours, the catalyst bed temperature is measured to be 380-382°C.

[0078] After 6 hours of reaction, the product composition was analyzed and the cyclohexanone oxime conversion was 99.25% and the total caprolactam selectivity was 96.23%.

[0079] Comparative Example 3

[0080] The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime was carried out in a homemade fixed fluidized bed reactor. The vertical 316L stainless steel reactor had an upper diameter of 20 cm and a lower diameter of 10 cm. The lengths of the upper and lower sections were 60 and 80 cm, respectively. The microsphere molecular sieve catalyst (prepared by the method of Example 1 of Chinese patent application 202310595456.6) was loaded in an amount of 260 g. The microsphere particle size was 50-150 μm, and the specific surface area was 336 m 2 ·g -1 The micropore specific surface area is 284m 2 ·g -1 The non-microporous specific surface area is 52m 2 ·g -1 ; Pore volume 0.429mL / g, micropore volume 0.136mL / g.

[0081] The feed was fed by gas atomization spraying, the temperature of the vaporizer was controlled at 190°C, the pipeline was kept at 190°C, the reaction solvent was ethanol, the weight of the ethanol was 65% of the weight of the reaction raw material, and the water content of the reaction raw material was: 1.2% (m); the carrier gas (N 2) flow rate is 6.6L / min, nitrogen / oxime molar ratio is 2, reaction pressure is 0.05MPa, reaction temperature is 380℃, cyclohexanone oxime WHSV is 3h -1 The reaction product was cooled by ice-water mixture and then entered into a collection bottle for gas-liquid separation. After running for 6 hours, the catalyst bed temperature was measured to be 380-390°C. After reacting for 10 hours, the product composition was analyzed. The cyclohexanone oxime conversion rate was 99.90%, and the total caprolactam selectivity was 96.60%.

[0082] By comparing the above embodiments and comparative examples, it can be seen that the present invention adopts C 6 -C 8 The alkane is used as the extractant (solvent A) and works synergistically with the low-carbon alcohol to further control the mass ratio of solvent A to solvent B. Under the condition of ensuring the conversion rate and selectivity of the gas-phase rearrangement reaction are at the same level, the extractant in the heterogeneous ammoximation can be directly utilized without the need for additional separation and purification of cyclohexanone oxime, and a large amount of nitrogen is saved as the carrier gas for heat transfer in the gas-phase rearrangement reaction. The temperature rise of the catalyst bed is controllable, which can greatly improve the technical and economic benefits of the gas-phase rearrangement.

[0083] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing caprolactam, It is characterized in that The method comprises: (1) in the presence of an oximation catalyst, subjecting cyclohexanone, ammonia and hydrogen peroxide to a heterogeneous ammoximation reaction in an aqueous solution; (2) extracting the product obtained in step (1) with solvent A to obtain a cyclohexanone oxime-A solution; (3) mixing solvent B with cyclohexanone oxime-A solution to obtain a mixed raw material, and then contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to perform a cyclohexanone oxime gas-phase Beckmann rearrangement reaction; the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is performed in the absence of a carrier gas; Wherein, the solvent A is C 5 -C 8 The solvent A is an alkane, and the solvent B is a low-carbon alcohol; in the mixed raw material, the mass ratio of solvent A to solvent B is 1: (0.4-1).

2. The method according to claim 1, in, Solvent A is at least one of a substituted or unsubstituted chain alkane or cycloalkane having 5 to 8 carbon atoms, and a substituted or unsubstituted aromatic hydrocarbon having 6 to 8 carbon atoms; Preferably, the solvent A is selected from at least one of n-hexane, cyclohexane, cyclopentane, methylcyclohexane, n-heptane, n-octane, benzene, toluene, xylene and halogenated benzene, more preferably at least one of cyclohexane, n-heptane, benzene and toluene, more preferably cyclohexane; And / or, the solvent B is C 1 -C 3 alcohol, preferably methanol and / or ethanol; Preferably, the amount of solvent A used is such that the content of solvent A in the cyclohexanone oxime-A solution obtained in step (2) is 60-80 wt %, more preferably 65-75 wt %.

3. The method according to claim 1 or 2, in, In the mixed raw material, the mass ratio of solvent A to solvent B is 1:(0.5-0.8).

4. The method according to any one of claims 1 to 3, in, The contacting method in step (3) includes: spraying and vaporizing the mixed raw material, and then contacting the vaporized mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst.

5. The method according to claim 4, in, The temperature of the spray vaporization is 155-180°C.

6. The method according to any one of claims 1 to 5, in, In step (3), based on the total amount of the mixed raw materials, the content of cyclohexanone oxime is 10-30wt%, preferably 15-25wt%.

7. The method according to any one of claims 1 to 6, in, The mixed raw material further contains water. Based on the total amount of the mixed raw material, the water content does not exceed 5wt%, preferably 0.2-3wt%.

8. The method according to any one of claims 1 to 7, in, The cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in a fixed bed or moving bed reactor. Preferably, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction conditions include: a reaction temperature of 300-500° C., preferably 350-420° C.; a reaction pressure of 0.05-0.5 MPa, preferably 0.05-0.3 MPa; a weight space velocity of cyclohexanone oxime of 0.1-5 h -1 , preferably 0.4-2h -1 .

9. The method according to any one of claims 1 to 7, in, The cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in a fluidized bed reactor. Preferably, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction conditions include: a reaction temperature of 300-500°C, preferably 350-400°C; a reaction pressure of 0.05-0.5MPa, preferably 0.05-0.3MPa; a weight space velocity of cyclohexanone oxime of 2-8h -1 , preferably 3-6h -1 .

10. The method according to any one of claims 1 to 9, in, The gas-phase Beckmann rearrangement reaction catalyst is an all-silicon molecular sieve catalyst with an MFI topological structure.