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 homogeneous ammoximation reaction on cyclohexanone, ammonia and hydrogen peroxide in an organic solvent; (2) extracting and distilling a product obtained by the homogeneous ammoximation reaction to obtain cyclohexanone-oxime; (3) contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst, and carrying out cyclohexanone-oxime gas-phase Beckmann rearrangement reaction; the cyclohexanone-oxime gas phase Beckmann rearrangement reaction is carried out under the condition of no carrier gas; the mixed raw materials comprise cyclohexanone-oxime, low-carbon alcohol and water; wherein based on the total weight of the cyclohexanone-oxime and the low-carbon alcohol, the content of the low-carbon alcohol is 70-90 wt%. According to the method, the selectivity of caprolactam can be guaranteed, gas-liquid separation can be simplified, and the technical economy of gas phase rearrangement can be greatly 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 prior art, and to provide a method for preparing caprolactam, which does not require the use of an inert carrier gas for heat transfer and can significantly reduce system energy consumption while ensuring a high caprolactam selectivity.

[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 homogeneous ammoximation reaction in an organic solvent;

[0007] (2) extracting and distilling the product obtained by the homogeneous ammoximation reaction to obtain cyclohexanone oxime;

[0008] (3) contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is carried out in the absence of a carrier gas; the mixed raw material comprises cyclohexanone oxime, a low-carbon alcohol and water; wherein the content of the low-carbon alcohol is 70-90 wt % based on the total weight of the cyclohexanone oxime and the low-carbon alcohol.

[0009] Preferably, the gas-phase Beckmann rearrangement reaction catalyst comprises an all-silicon molecular sieve having an MFI topological structure and a binder, and the binder is silicon dioxide.

[0010] According to the scanning electron microscope, the catalyst has an apple-shaped microsphere morphology, and there is only one large hole on the surface of the microsphere. The bulk density of the catalyst is not less than 0.64 g / cm 3 , the pore volume is not less than 0.3mL / g.

[0011] The method for preparing caprolactam by gas-phase Beckmann rearrangement of cyclohexanone oxime provided by the present invention is that under the rearrangement reaction atmosphere without carrier gas (nitrogen), a low-carbon alcohol solution of cyclohexanone oxime is directly contacted with a gas-phase Beckmann rearrangement reaction catalyst to obtain a low-carbon alcohol solution of crude caprolactam. During the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the conversion rate of cyclohexanone oxime is extremely high, which can reach more than 99.5%, and the selectivity of caprolactam can reach more than 96%. A large amount of nitrogen is omitted as a carrier gas for gas-phase rearrangement reaction to transfer heat, which is beneficial to saving raw material costs. At the same time, 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, which can greatly improve the technical and economic efficiency of the gas-phase rearrangement. DETAILED DESCRIPTION

[0012] 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.

[0013] The present invention provides a method for preparing caprolactam, the method comprising:

[0014] (1) in the presence of an oximation catalyst, subjecting cyclohexanone, ammonia and hydrogen peroxide to a homogeneous ammoximation reaction in an organic solvent;

[0015] (2) extracting and distilling the product obtained by the homogeneous ammoximation reaction to obtain cyclohexanone oxime;

[0016] (3) contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is carried out in the absence of a carrier gas; the mixed raw material comprises cyclohexanone oxime, a low-carbon alcohol and water; wherein the content of the low-carbon alcohol is 70-90 wt % based on the total weight of the cyclohexanone oxime and the low-carbon alcohol.

[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. Excessive temperature rise of the catalyst bed will seriously affect the catalyst life and the selectivity of caprolactam. 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 method provided by the present invention allows the low-carbon alcohol solution of cyclohexanone oxime to directly contact with the gas-phase Beckmann rearrangement reaction catalyst under the rearrangement reaction atmosphere without carrier gas (nitrogen) to obtain the low-carbon alcohol solution of crude caprolactam. During the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the conversion rate of cyclohexanone oxime is extremely high, which can reach more than 99.5%, and the selectivity of caprolactam can reach more than 96%.

[0019] The present invention has no particular limitation on the specific operating conditions of the homogeneous ammoximation reaction in step (1), which is the prior art of Sinopec and Enichem of Italy and is well known to those skilled in the art. For example, the homogeneous ammoximation reaction comprises: mixing cyclohexanone, ammonia and hydrogen peroxide in the presence of tert-butyl alcohol solvent for reaction, and the oximation catalyst used can be titanium silicon-1 molecular sieve having MFI topological structure.

[0020] The present invention does not particularly limit the conditions for extracting and distilling the product obtained by the homogeneous ammoximation reaction, and can be carried out by conventional methods in the art. For example, the product obtained by the reaction can be extracted with toluene and then distilled to obtain cyclohexanone oxime.

[0021] In the present invention, the use of low-carbon alcohol as a reaction solvent has an excellent heat transfer effect, can avoid the use of inert carrier gases such as nitrogen, and ensure a high cyclohexanone oxime conversion rate and caprolactam selectivity. Based on the total weight of the cyclohexanone oxime and the low-carbon alcohol, the content of the low-carbon alcohol is 70-90wt%, preferably 75-85wt%.

[0022] The usage amount of low-carbon alcohol in the existing gas phase Beckmann rearrangement reaction is usually below 70wt%, because excessive methanol or ethanol can react with caprolactam to generate methanol condensation products or ethanol condensation products, which affects the selectivity of caprolactam. Therefore, although the solvent can also be a good solvent for heat transfer, those skilled in the art usually do not use alcohol to transfer heat, but use a high nitrogen / oxime ratio to transfer heat through a large amount of nitrogen. However, in the present invention, by increasing the low-carbon alcohol solvent, the nitrogen heat transfer in the high nitrogen / oxime ratio is not used, which is conducive to the separation and reuse of the circulating gas, and can play an excellent heat transfer effect on the basis of ensuring a higher cyclohexanone oxime conversion rate and caprolactam selectivity, simplify the process, reduce equipment investment, and improve the economic efficiency of the gas phase rearrangement technology.

[0023] The present invention has no particular requirements for the specific type of the low-carbon alcohol, which can be selected conventionally in the art. Preferably, the solvent is C 1 -C 3 The alcohol is preferably methanol and / or ethanol.

[0024] According to some preferred embodiments of the present invention, the contacting method in step (3) includes: first mixing cyclohexanone oxime, low-carbon alcohol and water to obtain a mixed raw material liquid, then spraying and vaporizing the mixed raw material liquid, and then contacting the vaporized raw material with a gas-phase Beckmann rearrangement reaction catalyst. In the prior art, the content of cyclohexanone oxime in the vaporized raw material 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 high content of low-carbon alcohol, the mixed raw material liquid can be directly vaporized through an atomizing nozzle, and no additional inert gas needs to be introduced during the vaporization process.

[0025] 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.

[0026] According to some preferred embodiments of the present invention, the temperature of the spray vaporization is 155-180°C, preferably 160-175°C.

[0027] According to some preferred embodiments of the present invention, the pressure of the spray vaporization is 0.5-5 MPa, preferably 1-4 MPa.

[0028] According to some preferred embodiments of the present invention, in the mixed raw material, the molar ratio of water to cyclohexanone oxime is 0.01-0.5: 1. Controlling the molar ratio of water to cyclohexanone oxime within the above preferred range is conducive to inhibiting the alcoholysis reaction of caprolactam and helping to further improve the selectivity of caprolactam.

[0029] In some preferred embodiments, preferably, the low-carbon alcohol is methanol, and in the mixed raw material, the molar ratio of water to cyclohexanone oxime is 0.05-0.4:1, for example, it can be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1 and other typical but non-limiting molar ratios or ranges therebetween. Preferably, the molar ratio of water to cyclohexanone oxime is 0.05-0.1:1.

[0030] Preferably, the low-carbon alcohol is ethanol, and in the mixed raw material, the molar ratio of water to cyclohexanone oxime is 0.02-0.2:1, for example, it can be 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.2:1 and other typical but non-limiting molar ratios or ranges therebetween. Preferably, the molar ratio of water to cyclohexanone oxime is 0.03-0.08:1.

[0031] The use of the above preferred embodiment is conducive to further improving the selectivity of caprolactam and inhibiting the alcoholysis reaction of caprolactam.

[0032] In the present invention, the gas-phase Beckmann rearrangement reaction catalyst is an all-silicon or high-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 any catalyst 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 present invention also has no special restrictions on the source of the gas-phase Beckmann rearrangement reaction catalyst, which can be purchased from a commercial source or prepared by any known method, and those skilled in the art can select it according to actual needs.

[0033] According to some preferred embodiments of the present invention, the gas-phase Beckmann rearrangement reaction catalyst is the catalyst disclosed in Chinese patent application 202310595456.6, which is fully cited in the present invention.

[0034] The gas-phase Beckmann rearrangement reaction catalyst comprises an all-silicon molecular sieve with an MFI topological structure and a binder, wherein the binder is silicon dioxide; according to scanning electron microscopy, the catalyst has an apple-shaped microsphere morphology, and the microsphere surface has one and only one large hole, and the bulk density of the catalyst is not less than 0.64 g / cm 3 , the pore volume is not less than 0.3mL / g.

[0035] According to the present invention, preferably, the D50 of the gas-phase Beckmann rearrangement reaction catalyst is 50-100 μm, preferably 60-90 μm.

[0036] Preferably, the attrition index K of the gas-phase Beckmann rearrangement reaction catalyst is less than 3% / h, preferably 1.5-2.5% / h, and more preferably 1.5-2.2% / h.

[0037] According to the present invention, preferably, based on the dry weight of the catalyst, the content of the molecular sieve in the catalyst on a dry basis is 50-95% by weight, preferably 50-70% by weight, and the content of the binder on an oxide basis is 5-50% by weight, preferably 30-50% by weight.

[0038] The present invention has no particular limitation on the reactor used in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and those skilled in the art can select one according to test and production needs, for example, it can be a fixed bed reactor, a moving bed reactor or a fluidized bed reactor.

[0039] According to some preferred embodiments of the present invention, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in a fixed bed, a moving bed or a fluidized 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 0.05-0.5MPa, preferably 0.05-0.3MPa; a weight space velocity of cyclohexanone oxime of 0.1-5h -1 , preferably 0.4-2h -1 .

[0040] According to some other preferred embodiments of the present invention, 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 .

[0041] The present invention will be described in detail below through examples.

[0042] 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.

[0043] 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.

[0044] Cyclohexanone oxime conversion rate (mol%) = (100-cyclohexanone oxime molar percentage in the reaction product) / 100%;

[0045] Caprolactam selectivity (mol%) = mole percentage of caprolactam in the reaction product / (100-mole percentage of cyclohexanone oxime in the reaction product) × 100%;

[0046] WHSV(h -1 ) = cyclohexanone oxime flow rate in feed / catalyst mass in bed × 100%.

[0047] The spherical RBS-1 molecular sieve catalyst used in the following examples was prepared according to the method of Example 1 of Chinese patent application 202310595456.6.

[0048] Example 1

[0049] (1) carrying out a homogeneous ammoximation reaction by the method disclosed in CN1260241A, and then extracting and distilling the product obtained by the homogeneous ammoximation reaction to obtain cyclohexanone oxime;

[0050] (2) Cyclohexanone oxime is mixed with methanol and water to obtain a mixed raw material. Based on the total weight of cyclohexanone oxime and methanol, the content of methanol is 80 wt %, and the molar ratio of water to cyclohexanone oxime is 0.08:1.

[0051] 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 15cm, a length of 100cm, and a central sleeve diameter of 6cm. The radial moving bed reactor is equipped with a catalyst inlet, a central tube (small holes on the wall), a fan-shaped screen sleeve, a catalyst outlet, etc. The central tube set in the center of the reactor and the fan-shaped tube set 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 RBS-1 molecular sieve catalyst, and the catalyst bed height is 15-20cm.

[0052] The mixed raw materials were fed by gas atomization spraying, the vaporizer temperature was controlled at 175°C, and the pipeline was kept at 200°C. At normal pressure, the reaction temperature was 380°C, and the weight space velocity (WHSV) of cyclohexanone oxime was 2h -1After 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 RBS-1 molecular sieve catalyst can be unloaded from the lower end of the reactor for regeneration, and 50 grams of fresh or regenerated spherical RBS-1 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, and the product composition is analyzed.

[0053] After running for 96 hours, the composition of the methanol solution containing crude caprolactam was analyzed, and the conversion of cyclohexanone oxime was calculated to be 99.8%, the selectivity of caprolactam was 95.6%, and the selectivity of methanol condensate (methyl-ε-caprolactam) was 1%.

[0054] Example 2

[0055] The method of Example 1 is followed, except that an equal mass of ethanol is used to replace methanol, and based on the total weight of cyclohexanone oxime and ethanol, the content of ethanol is 80wt%, and the molar ratio of water to cyclohexanone oxime is 0.05:1.

[0056] The reactor temperature was set at 385°C, and the catalyst bed temperature was measured to be 390-395°C after 24 hours of operation, indicating good heat removal effect. The product composition was analyzed after 96 hours of operation, and the cyclohexanone oxime conversion was 99.8%, the caprolactam selectivity was 96.3%, and the selectivity of ethanol condensation product (ethyl-ε-caprolactimide) was 0.6%.

[0057] Example 3

[0058] The method of Example 1 is followed, except that the gas-phase Beckmann rearrangement reaction is carried out in a fixed bed reactor having an inner diameter of 28 mm and a catalyst bed height of 15 cm.

[0059] Based on the total weight of cyclohexanone oxime and methanol, the content of methanol is 80wt%, and the molar ratio of water to cyclohexanone oxime is 0.0625:1.

[0060] Feeding by gas atomization spray, vaporizer temperature control 175℃; pipeline insulation 200℃; reaction pressure: 0.1MPa; reaction temperature: 380℃, weight space velocity (WHSV) 2h -1 After 24 hours of operation, the catalyst bed temperature was measured to be 395-398° C. After 72 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was greater than 99.8%, the caprolactam selectivity was 95.9%, and the selectivity of the methanol condensate (methyl-ε-caprolactimide) was 1.1%.

[0061] Example 4

[0062] The method of Example 3 is followed, except that the content of methanol in the mixed raw material is 75wt% based on the total weight of cyclohexanone oxime and methanol, and the molar ratio of water to cyclohexanone oxime is 0.0625:1.

[0063] After 24 hours of operation, the catalyst bed temperature was measured to be 396-400° C. After 72 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was greater than 99.8%, the caprolactam selectivity was 95.6%, and the selectivity of the methanol condensate (methyl-ε-caprolactimide) was 0.9%.

[0064] Example 5

[0065] The method of Example 3 is followed, except that the content of methanol in the mixed raw material is 90wt% based on the total weight of cyclohexanone oxime and methanol, and the molar ratio of water to cyclohexanone oxime is 0.0625:1.

[0066] After 24 hours of operation, the catalyst bed temperature was measured to be 395-398° C. After 72 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was greater than 99.8%, the caprolactam selectivity was 95.5%, and the selectivity of the methanol condensate (methyl-ε-caprolactimide) was 1.2%.

[0067] Example 6

[0068] The method of Example 3 is followed, except that an equal mass of ethanol is used to replace methanol, and based on the total weight of cyclohexanone oxime and ethanol, the content of ethanol is 80wt%, and the molar ratio of water to cyclohexanone oxime is 0.03:1.

[0069] After 24 hours of operation, the catalyst bed temperature was measured to be 395-398° C. After 96 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was greater than 99.8%, the caprolactam selectivity was 95.9%, and the selectivity of ethanol condensate (ethyl-ε-caprolactimide) was 1.1%.

[0070] Example 7

[0071] The method of Example 1 is followed, except that the cyclohexanone oxime vapor-phase Beckmann rearrangement reaction is carried out in a homemade fixed fluidized bed reactor. The vertical 316L stainless steel reactor has an upper section diameter of 20 cm, a lower section diameter of 10 cm, an upper section length of 60 cm, and a lower section length of 80 cm, respectively. The RBS-1 molecular sieve catalyst loading amount is 280 g.

[0072] Based on the total weight of cyclohexanone oxime and ethanol, the content of ethanol is 75wt%, and the molar ratio of water to cyclohexanone oxime is 0.04:1.

[0073] The above mixed raw materials were fed by gas atomization spraying, the vaporizer temperature was controlled at 190°C, the vaporizer core was 190°C, and the pipeline was kept at 190°C. The reaction pressure was 0.1MPa, the fluidized bed reaction temperature was 380°C, and the cyclohexanone oxime WHSV was 4.1h -1 After 12 hours of operation, the catalyst bed temperature was measured to be 380-385° C. After 10 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was 99.5%, the caprolactam selectivity was 96.4%, and the selectivity of the ethanol condensate (ethyl-ε-caprolactimide) was about 0.8%.

[0074] Example 8

[0075] The method of Example 7 was followed, except that an equal amount of methanol was used to replace ethanol, the content of methanol was 75wt% based on the total weight of cyclohexanone oxime and methanol, and the molar ratio of water to cyclohexanone oxime was 0.06:1. The catalyst bed temperature was measured to be 380-385°C after running for 12 hours. The reaction was carried out for 10 hours, and the product composition was analyzed. The cyclohexanone oxime conversion rate was 99.8%, the caprolactam selectivity was 95.5%, and the selectivity of the methanol condensate (methyl-ε-caprolactimide) was about 1%.

[0076] Example 9

[0077] The method of Example 3 was followed, except that the content of methanol was 55 wt %, and the molar ratio of water to cyclohexanone oxime was 0.25:1. The catalyst bed temperature was measured to be 400-405° C. after 24 h of operation. The reaction was carried out for 72 hours, and the product composition was analyzed. The cyclohexanone oxime conversion was greater than 98%, the caprolactam selectivity was 94.2%, and the selectivity of the methanol condensate (methyl-ε-caprolactimide) was 0.4%.

[0078] Comparative Example 1

[0079] Cyclohexanone oxime vapor-phase Beckmann rearrangement reaction was carried out in a stainless steel fixed-bed reactor with an inner diameter of 5 mm and loaded with 0.60 g of 40-60 mesh RBS-1 molecular sieve catalyst, about 30 mm high 30 mesh coarse quartz sand was filled on the catalyst bed, and 50 mesh fine quartz sand was filled below the catalyst bed.

[0080] The rearrangement reaction conditions are: normal pressure; reaction temperature 380°C; cyclohexanone oxime weight space velocity (WHSV) 2h -1 The reaction solvent is methanol, the weight of the cyclohexanone oxime is 40% of the weight of the reaction raw material, and the water content of the reaction raw material is: 1.6% (m); carrier gas (N 2) flow rate was 66mL / min, and the catalyst bed temperature was measured to be 390-396°C after running for 2h. The reaction product was cooled by ice-water mixture and then entered the collection bottle for gas-liquid separation, and the product composition was analyzed. The reaction was carried out for 10 hours, and the product composition was analyzed. The cyclohexanone oxime conversion rate was close to 100%, the caprolactam selectivity was 96.4%, and the methanol condensate (methyl-ε-caprolactimide) selectivity was 0.9%.

[0081] Comparative Example 2

[0082] According to the method of comparative example 1, the difference is that ethanol is used to replace methanol, the weight of cyclohexanone oxime is 35% of the weight of the reaction raw material, and the water content of the reaction raw material is: 1.0% (m). After running for 2 hours, the catalyst bed temperature is measured to be 380-383°C, the reaction is carried out for 10 hours, and the product composition is analyzed. The conversion rate of cyclohexanone oxime is close to 100%, the selectivity of caprolactam is 96.5%, and the selectivity of ethanol condensation product (ethyl-ε-caprolactimide) is 0.6%.

[0083] Comparative Example 3

[0084] The method of Example 3 is followed, except that the mixed raw material does not contain water.

[0085] After 24 hours of operation, the catalyst bed temperature was measured to be 398-403° C. After 72 hours of reaction, the product composition was analyzed, and the cyclohexanone oxime conversion was greater than 99.4%, the caprolactam selectivity was 93.4%, and the selectivity of methanol condensate (methyl-ε-caprolactimide) was 3.6%.

[0086] From the comparison of the above embodiments and comparative examples, it can be seen that the method for preparing caprolactam provided by the present invention can avoid the use of nitrogen heat transfer in a high nitrogen / oxime ratio, can obtain excellent heat transfer effect, and on the basis of ensuring a high cyclohexanone oxime conversion rate and caprolactam selectivity, simplify the process flow, reduce equipment investment, and improve the economic efficiency of gas phase rearrangement technology.

[0087] 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 homogeneous ammoximation reaction in an organic solvent; (2) extracting and distilling the product obtained by the homogeneous ammoximation reaction to obtain cyclohexanone oxime; (3) contacting the mixed raw material with a gas-phase Beckmann rearrangement reaction catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is carried out in the absence of a carrier gas; the mixed raw material comprises cyclohexanone oxime, a low-carbon alcohol and water; Wherein, based on the total weight of the cyclohexanone oxime and the low-carbon alcohol, the content of the low-carbon alcohol is 70-90wt%.

2. The method according to claim 1, in, Low carbon alcohol is C 1 -C 3 alcohol, preferably methanol and / or ethanol; Preferably, based on the total weight of the cyclohexanone oxime and the lower alcohol, the content of the lower alcohol is 75-85wt%.

3. The method according to claim 1 or 2, in, The contacting method in step (3) includes: firstly mixing cyclohexanone oxime, low-carbon alcohol and water to obtain a mixed raw material liquid, then spraying and vaporizing the mixed raw material liquid, and then contacting the vaporized raw material with a gas-phase Beckmann rearrangement reaction catalyst.

4. The method according to claim 3, in, The temperature of the spray vaporization is 155-180°C.

5. The method according to any one of claims 1 to 4, in, In the mixed raw material, the molar ratio of water to cyclohexanone oxime is 0.01-0.5:1; Preferably, the low-carbon alcohol is methanol, and the molar ratio of water to cyclohexanone oxime in the mixed raw material is 0.05-0.4:1, preferably 0.05-0.1:1; Preferably, the low-carbon alcohol is ethanol, and in the mixed raw material, the molar ratio of water to cyclohexanone oxime is 0.02-0.2:1, preferably 0.03-0.08:

1.

6. The method according to any one of claims 1 to 5, in, The gas-phase Beckmann rearrangement reaction catalyst comprises an all-silicon molecular sieve having an MFI topological structure and a binder, wherein the binder is silicon dioxide; According to the scanning electron microscope, the catalyst has an apple-shaped microsphere morphology, and there is only one large hole on the surface of the microsphere. The bulk density of the catalyst is not less than 0.64 g / cm 3 , the pore volume is not less than 0.3mL / g.

7. The method according to claim 6, in, The D50 of the gas-phase Beckmann rearrangement reaction catalyst is 50-100 μm, preferably 60-90 μm; Preferably, the attrition index K of the gas-phase Beckmann rearrangement reaction catalyst is less than 3% / h, preferably 1.5-2.5% / h, and more preferably 1.5-2.2% / h.

8. The method according to claim 6 or 7, in, Based on the dry weight of the catalyst, the content of the molecular sieve in the catalyst is 50-95% by weight, preferably 50-70% by weight, and the content of the binder in terms of oxide is 5-50% by weight, preferably 30-50% by weight.

9. The method according to any one of claims 1 to 8, 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 .

10. The method according to any one of claims 1 to 8, 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 .