Production method of caprolactam

Abstract

The invention relates to the technical field of caprolactam preparation, and discloses a caprolactam production method, which comprises: (1) in a fluidized bed reactor, contacting cyclohexanone-oxime with a catalyst to carry out a cyclohexanone-oxime gas phase Beckmann rearrangement reaction; (2) when the conversion rate of the cyclohexanone-oxime is reduced to 96%, performing regeneration treatment on the contacted catalyst in an oxygen-containing atmosphere to obtain a regenerated catalyst; the carbon content of the regenerated catalyst is not higher than 3wt%, the nitrogen content is not higher than 0.3 wt%, and the recovery rate of the BET specific surface area of the regenerated catalyst is not lower than 88%; and (3) at least part of the regenerated catalyst is used for providing the catalyst in the step (1). According to the production method, the gas-phase Beckmann rearrangement reaction and the regeneration treatment are coupled, and the active center of the regenerated catalyst is fully recovered by controlling the carbon and nitrogen contents in the regenerated catalyst and the recovery rate of the BET specific surface area, so that the service life of the catalyst is prolonged.

Description

Technical Field

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

[0002] ε-caprolactam is one of the important raw materials for synthetic fibers and synthetic resins, and is mainly used to manufacture polyamide fibers (nylon 6), resins, and films. The industrial method for producing caprolactam is to use fuming sulfuric acid as a catalyst and solvent, and to obtain it by a liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime. The vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime on a solid acid catalyst is a new method for achieving the non-sulfammoniumization of ε-caprolactam, which has the advantages of no equipment corrosion and no environmental pollution, and the separation and purification of the product is also greatly simplified. However, the disadvantage is that the catalyst is easily deactivated, and the catalyst life is short and cannot meet the requirements of industrialization. Therefore, it is difficult to apply industrially.

[0003] The method of producing ε-caprolactam by gas-phase Beckmann rearrangement reaction using fluidized bed technology is to treat the deactivated solid catalyst with oxygen-containing gas at high temperature to regenerate the catalyst.

[0004] CN1269360A discloses a method for producing ε-caprolactam by gas-phase Beckmann rearrangement reaction using fluidized bed process, wherein a deactivated solid catalyst is treated with oxygen-containing gas at high temperature to regenerate the catalyst. The nitrogen content of the catalyst during the process from the regeneration step to the reaction step reaches the range of 10ppm-2500ppm. The method continuously performs Beckmann rearrangement reaction and catalyst regeneration, and has high conversion rate and high selectivity.

[0005] CN1680331A reports a method for regenerating a gas-phase Beckmann rearrangement catalyst, which comprises: regenerating a zeolite catalyst in an atmosphere of an oxygen-containing gas; during the reaction process and the catalyst regeneration process, the carbon content and nitrogen content of the solid catalyst should be maintained within the range of 0.5-2% (by weight) and 0.01-0.2% (by weight), respectively. The method adopts intermittent reaction-regeneration and is only applicable to fluidized bed processes. By improving the durability of the catalyst activity, in order to reduce the nitrogen and carbon contents of the catalyst, it is necessary to shorten the residence time of the catalyst in the reactor and reduce the heat treatment temperature.

[0006] In these conventional regeneration methods, the catalyst activity cannot be fully maintained at all times, and therefore, when the catalyst is operated for a long period of time, there are problems with the conversion rate of cyclohexanone oxime and the selectivity of caprolactam. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems of short service life and high cost of the catalyst for the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime in the prior art, and to provide a method for producing caprolactam. The method couples the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime with catalyst regeneration, so that the catalyst has a long service life, low regeneration cost and good production stability of caprolactam.

[0008] In order to achieve the above object, the present invention provides a method for producing caprolactam, the method comprising:

[0009] (1) in a fluidized bed reactor, contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime;

[0010] (2) when the conversion rate of cyclohexanone oxime drops to 96%, regenerating the contacted catalyst in an oxygen-containing atmosphere to obtain a regenerated catalyst;

[0011] Wherein, the carbon content of the regenerated catalyst is not higher than 3wt%, the nitrogen content is not higher than 0.3wt%, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not lower than 88%;

[0012] (3) At least part of the regenerated catalyst is used to provide the catalyst of step (1).

[0013] Preferably, the time t of the regeneration process is determined by formula (I),

[0014] t=0.36×MHSV×t r Formula (I),

[0015] Where t is the regeneration time, in h; MHSV is the mass space velocity of cyclohexanone oxime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in h -1 ;t r is the reaction time of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in hours; 0.36 represents MHSB×t r The duration is 0.36 times of the time, in h.

[0016] Due to the high temperature of the gas-phase Beckmann rearrangement reaction, the carbon deposits on the gas-phase rearrangement catalyst appear in the form of a film formed by the aggregation of particles with a diameter less than 10nm. For high-silicon molecular sieves, it is generally believed that the ortho-silanol groups and silanol groups on the outer surface of the molecular sieve are the active centers of the cyclohexanone oxime rearrangement reaction, among which the silanol groups are the most suitable active centers. The pore diameter of the all-silicon-1 molecular sieve with the MFI topological structure and the existence of the "cage" in the molecular sieve structure cause the coking precursors to accumulate on the catalyst surface, which easily covers the active center of the catalyst and causes the molecular sieve catalyst to be rapidly deactivated due to coking.

[0017] The method for producing caprolactam provided by the present invention couples a cyclohexanone oxime gas-phase Beckmann rearrangement reaction with a catalyst regeneration process. When the conversion rate of cyclohexanone oxime in the reaction drops to 96%, the deactivated catalyst is regenerated. By controlling the carbon and nitrogen contents in the regenerated catalyst and the recovery rate of the BET specific surface area of ​​the regenerated catalyst, the active center of the regenerated catalyst is fully exposed, which is beneficial to improving the service life of the catalyst. Under preferred conditions, after more than 40 reaction-regeneration processes, the catalyst still maintains good catalytic activity. DETAILED DESCRIPTION

[0018] 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.

[0019] The present invention provides a method for producing caprolactam, the method comprising:

[0020] (1) in a fluidized bed reactor, contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime;

[0021] (2) when the conversion rate of cyclohexanone oxime drops to 96%, regenerating the contacted catalyst in an oxygen-containing atmosphere to obtain a regenerated catalyst;

[0022] Wherein, the carbon content of the regenerated catalyst is not higher than 3wt%, the nitrogen content is not higher than 0.3wt%, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not lower than 88%;

[0023] (3) At least part of the regenerated catalyst is used to provide the catalyst of step (1).

[0024] In the present invention, "fresh catalyst" refers to a catalyst that has not been subjected to the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, "regenerated catalyst" refers to a catalyst after regeneration treatment, and "deactivated catalyst" refers to a catalyst after the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0025] In the present invention, the "recovery rate of the BET specific surface area of ​​the regenerated catalyst" refers to the percentage of the BET specific surface area of ​​the regenerated catalyst to the BET specific surface area of ​​the fresh catalyst.

[0026] In the gas-phase Beckmann rearrangement reaction, thermal cracking and thermal condensation reactions can occur in the gas phase, and "gas-phase carbon" may be deposited on the catalyst surface. Carbon deposits on gas-phase rearrangement catalysts usually appear in the form of a thin film composed of particles with a diameter of less than 10nm. Coking precursors accumulate on the catalyst surface and easily cover the active centers of the catalyst. Carbon deposition and coking of high-boiling-point precursors lead to catalyst deactivation. In the regeneration process of carbon-deactivated catalysts, the most important problem is to minimize the temperature rise caused by the exothermic oxidation reaction when converting carbon deposits into CO2 and CO to prevent thermal sintering of the catalyst.

[0027] In the prior art, in order to pursue higher selectivity of caprolactam, more attention is paid to lower nitrogen and carbon content in the regenerated catalyst. In this case, it is often necessary to shorten the time of gas phase Beckmann rearrangement reaction or reduce the heat treatment temperature. However, this may lead to incomplete and incomplete catalyst regeneration, thus requiring frequent catalyst regeneration treatment, increasing the cost of industrial production. The inventors of the present invention have found in their research that the nitrogen and carbon content on the deactivated catalyst can be reflected by the fresh / regenerated catalyst space velocity (the amount of cyclohexanone oxime treated), and then the recovery rate of the BET specific surface area of ​​the regenerated catalyst and the appropriate nitrogen and carbon content can be controlled, which can be beneficial to the activity recovery of the regenerated catalyst and help to improve the service life of the catalyst.

[0028] In the present invention, the carbon content of the regenerated catalyst is not higher than 3wt%, the nitrogen content is not higher than 0.3wt%, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not less than 88%; preferably, the carbon content of the regenerated catalyst is 0.2-3wt%, preferably 0.25-1wt%; the nitrogen content is 0.001-0.3wt%, preferably 0.002-0.01wt%; preferably, the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not less than 92%, more preferably 95-100%. The inventors of the present invention have realized in a large number of experiments that for the same catalyst, due to the different amounts of cyclohexanone oxime treated, the amount of carbon deposits and specific surface areas on the catalyst are different. If the same conditions are used for regeneration, the regeneration effect will be unsatisfactory. In the prior art, due to the inappropriate regeneration process conditions (regeneration time, regeneration temperature, regeneration gas volume), the recovery rate of the BET surface area of ​​the regenerated catalyst is insufficient. Although the regeneration agent requirements can be met in a short period of time, it is not conducive to the long-term repeated regeneration of the catalyst.

[0029] For the gas-phase Beckmann rearrangement reaction with fast reaction characteristics, the side effect is coking on the molecular sieve catalyst. The generation of coking will cause the catalyst activity to decrease and also affect the selectivity of the product. However, the regeneration temperature is sensitive to the catalyst coking. The regeneration temperature is an important factor in improving the coking intensity. If the regeneration temperature is too high, it will have an irreversible effect on the catalyst performance and reduce the catalyst selectivity. Therefore, the gas-phase Beckmann rearrangement reaction is closely related to the regeneration conditions of the catalyst.

[0030] According to the present invention, when the conversion rate of cyclohexanone oxime drops to 96%, the contacted catalyst is regenerated in an oxygen-containing atmosphere to obtain a regenerated catalyst. It is understandable that as the reaction time is longer, the conversion rate of cyclohexanone oxime is lower, and the catalyst deactivation degree is higher. Those skilled in the art can regenerate the catalyst at any time when the conversion rate is not less than 96% according to the actual operation situation. In order to improve the regeneration effect of the catalyst and improve the production economy, preferably, when the conversion rate of cyclohexanone oxime drops to 98%, the contacted catalyst is regenerated. More preferably, when the conversion rate of cyclohexanone oxime drops to 99.8%, the preferred conversion rate is 99-99.8%, and the contacted catalyst is regenerated. The timing of the catalyst regeneration treatment is controlled by the conversion rate of cyclohexanone oxime, and the above preferred embodiment is adopted, which is conducive to the regeneration effect of the catalyst and prolongs the stability of the catalyst.

[0031] If the fluidized bed conversion rate is low, it is difficult to maintain for a long period. In addition, a low conversion rate can easily make the catalyst carbon deposition and coking more serious, and regeneration may require longer time and higher temperature. Maintaining the cyclohexanone oxime conversion rate in the fluidized bed reactor within the above preferred range is conducive to increasing the service life of the catalyst and improving the overall production operation cycle.

[0032] The inventors of the present invention have found in their research that coupling the gas-phase Beckmann rearrangement reaction and the regeneration treatment of the catalyst and matching appropriate gas-phase Beckmann rearrangement reaction conditions and regeneration treatment conditions are beneficial to ensuring the regeneration effect of the regenerated catalyst.

[0033] According to some preferred embodiments of the present invention, the temperature of the regeneration treatment is 40-80°C higher than the temperature of the cyclohexanone oxime gas-phase Beckmann rearrangement reaction, for example, the temperature difference can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., which are typical but not limiting temperature differences or ranges therebetween. The above preferred embodiments are used to facilitate the treatment of carbon and nitrogen deposits on the catalyst, obtain better regeneration agents, and thus facilitate the improvement of the service life of the catalyst.

[0034] Preferably, the temperature of the regeneration treatment is 400-550°C, preferably 420-480°C, more preferably 440-470°C.

[0035] In order to further ensure the regeneration effect of the regenerated catalyst and ensure the economy of the overall process, the inventors of the present invention creatively proposed to determine the duration of the regeneration treatment of the deactivated catalyst based on the time the catalyst participates in the gas-phase Beckmann rearrangement reaction and the unit catalyst space velocity (i.e., reflecting the amount of cyclohexanone oxime treated). In the present invention, the "time the catalyst participates in the gas-phase Beckmann rearrangement reaction" can be determined by the residence time of the catalyst in the reactor of the gas-phase Beckmann rearrangement reaction.

[0036] According to some preferred embodiments of the present invention, the time t of the regeneration process is determined by formula (I):

[0037] t=0.36×MHSV×t r Formula (I),

[0038] Where t is the regeneration time, in h; MHSV is the mass space velocity of cyclohexanone oxime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in h -1 ;t r is the reaction time of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in hours, and 0.36 represents MHSV×t r The duration is 0.36 times of the time, in h.

[0039] The prior art still lacks in-depth research on the regeneration treatment conditions of the gas-phase Beckmann rearrangement reaction catalyst. In order to ensure low carbon content and nitrogen content, a long regeneration time is usually required, which lacks specificity. Formula (I) effectively relates the catalyst space velocity, reaction time and regeneration time. By adopting the above preferred embodiment, different catalyst regeneration treatment conditions are matched for different catalysts and the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, which can not only ensure the regeneration effect of the deactivated catalyst, but also control the regeneration cost, thereby improving the economy of the overall process.

[0040] According to the present invention, the regeneration treatment is carried out in an oxygen-containing atmosphere, which can be provided by a mixture of oxygen and an inert gas or air. According to some preferred embodiments of the present invention, the volume content of oxygen in the oxygen-containing atmosphere is 5-50%, preferably 20-30%. Considering the economy and convenience of the method, it is preferably carried out in the presence of air.

[0041] According to some preferred embodiments of the present invention, the oxygen-containing atmosphere is introduced in an amount of 200-2000 L / kgcat·h, preferably 500-1000 L / kgcat·h.

[0042] According to some preferred embodiments of the present invention, in step (1), the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in the presence of a solvent. Preferably, the solvent comprises alcohol and water, and the alcohol is methanol and / or ethanol, preferably ethanol.

[0043] According to some preferred embodiments of the present invention, the mass ratio of the alcohol, water and cyclohexanone oxime is (0.5-5):(0.001-0.1):1, preferably (0.8-3):(0.01-0.06):1.

[0044] According to some preferred embodiments of the present invention, the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in the presence of a carrier gas. Preferably, the carrier gas is provided by an inert gas, such as nitrogen.

[0045] Preferably, the molar ratio of the carrier gas to cyclohexanone oxime is 0.5-20:1, preferably 0.5-5:1.

[0046] The present invention has no particular limitation on the conditions for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and the reaction can be carried out under conventional reaction conditions in the art. Preferably, the conditions for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime include: a temperature of 300-400°C, preferably 360-400°C; a pressure of 0.005-0.8MPa, preferably 0.05-0.5MPa; a mass space velocity of cyclohexanone oxime of 0.1-15h -1 , preferably 1-8h -1 The combination of the above-mentioned preferred vapor-phase Beckmann rearrangement reaction conditions and the catalyst regeneration treatment conditions is beneficial to improving the conversion rate of cyclohexanone oxime and the selectivity of caprolactam, and prolonging the life of the catalyst.

[0047] According to some preferred embodiments of the present invention, the method for producing caprolactam provided by the present invention is carried out in at least one fluidized bed reactor. The gas-phase Beckmann rearrangement reaction and the regeneration treatment can be carried out in the same fluidized bed reactor or in two different fluidized bed reactors. Those skilled in the art can make a selection according to the actual device.

[0048] According to some preferred embodiments of the present invention, the production method adopts an intermittent reaction mode, the production method is carried out in a fluidized bed reaction system, the fluidized bed reaction system includes a fluidized bed reactor, and the production method includes: passing cyclohexanone oxime into the fluidized bed reactor, contacting with the catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; when the conversion rate of cyclohexanone oxime drops to 96%, stopping the cyclohexanone oxime feeding, and regenerating the contacted catalyst in an oxygen-containing atmosphere to obtain a regenerated catalyst. After regeneration, the raw material feeding is switched again, and the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is repeated.

[0049] According to some other preferred embodiments of the present invention, the production method adopts a continuous reaction mode, and the production method is carried out in a fluidized bed reaction system, the fluidized bed reaction system includes a fluidized bed reactor and a fluidized bed regenerator, the fluidized bed reactor and the fluidized bed regenerator are respectively loaded with a first catalyst and a second catalyst, cyclohexanone oxime is introduced into the fluidized bed reactor, and is contacted with the first catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; when the conversion rate of cyclohexanone oxime drops to 96%, the first catalyst is sent to the fluidized bed regenerator for regeneration treatment, and the second catalyst in the fluidized bed regenerator is sent to the fluidized bed reactor; then the above-mentioned gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is repeated. Wherein, the first catalyst and the second catalyst have the same definition as the above-mentioned catalyst in the present invention, and the "first" and "second" are only used to distinguish the catalysts in the fluidized bed reactor and the fluidized bed regenerator.

[0050] In a further preferred embodiment, the packing volume ratio of the first catalyst to the second catalyst is 1:1-5.

[0051] The present invention has a wide selection range for the catalyst. Conventional solid acid catalysts in the art that can be used to catalyze the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime can be applied to the production method of caprolactam provided by the present invention, and can be purchased from commercial sources or prepared by any known method.

[0052] According to some preferred embodiments of the present invention, the catalyst is a microsphere catalyst, and the catalyst comprises an all-silicon molecular sieve with an MFI structure and a binder.

[0053] The present invention has no particular limitation on the source of the all-silicon molecular sieve with the MFI topological structure, and the molecular sieve may be purchased from a commercial source or prepared by a method known in the prior art, for example, the molecular sieves disclosed in CN111847472A, CN109775714A, CN102233277A, CN102050464A, CN111847472A, and CN107337213A or prepared by the preparation methods disclosed therein may be used.

[0054] Preferably, the binder is silicon dioxide.

[0055] The present invention has a wide selection range for the content of molecular sieve and binder in the catalyst. Preferably, 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.

[0056] Preferably, the particle size of the microsphere catalyst is 20-300 μm.

[0057] According to some preferred embodiments of the present invention, the catalyst is selected from the catalyst disclosed in Chinese patent application 202310595456.6, and the content of this application is incorporated herein by reference.

[0058] Preferably, the catalyst comprises an all-silicon molecular sieve having 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.

[0059] The present invention will be described in detail below through examples.

[0060] Example 1

[0061] The microsphere catalyst used is the catalyst prepared in Example 1 of 202310595456.6, and the catalyst has an apple-shaped microsphere morphology, and the surface of the microsphere has one and only one large hole. The catalyst includes 60.2% by weight of MFI topological structure silicon molecular sieve, 39.8% by weight of binder calculated as SiO2, D50 is 86.78 μm, wear index is 1.8% / h, and bulk density is 0.658 g / cm 3 , the pore volume is 0.429mL / g.

[0062] The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime was carried out in a fixed fluidized bed reactor. The vertical 316L stainless steel fluidized bed reactor had an upper diameter of 20 cm, a lower diameter of 10 cm, and upper and lower lengths of 60 and 80 cm, respectively. The loading amount of the microsphere molecular sieve catalyst in the fixed fluidized bed reactor was 250 g. The reaction conditions in the fluidized bed reactor included: reaction pressure 0.1 MPa, fluidized bed reaction temperature 385 ° C, gas atomization spray feeding, vaporization chamber temperature control 190 ° C, vaporizer minimum temperature point 160 ° C, outlet pipeline insulation 200 ° C, cyclohexanone oxime WHSV 4.2h -1 , cyclohexanone oxime accounts for 35 weight% of the total amount of cyclohexanone oxime and ethanol, water accounts for 0.8 weight% of the total amount of water, ethanol and cyclohexanone oxime, and the molar ratio of nitrogen to cyclohexanone oxime is 2.

[0063] After 10 hours of reaction, the conversion rate of cyclohexanone oxime was 99.69%. The feeding of cyclohexanone oxime, ethanol and water was stopped, and nitrogen was continued to be introduced into the fluidized bed reactor at a rate of 450 L / h for 30 minutes. Then the nitrogen was switched to air at a rate of 180 L / h. After the temperature of the fluidized bed reactor was increased from 385°C to 450°C, the catalyst regeneration was started.

[0064] The time t of the regeneration process is determined by the following formula:

[0065] t=0.36×MHSV×t r ,

[0066] Wherein, t is the regeneration time, in h; MHSV is the mass space velocity of cyclohexanone oxime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in h -1 ;t r is the reaction time of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in hours, and 0.36 represents MHSV×t r The duration is 0.36 times of the time, in h.

[0067] The regeneration time was determined to be 15 h. After the regeneration was completed, the carbon content and nitrogen content of the regenerated catalyst were tested, the specific surface area was tested by the BET method, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst was calculated. The results are shown in Table 1.

[0068] The air was switched to nitrogen, and the raw materials were introduced into the fluidized bed reactor to start the next reaction. After 10 hours of reaction, regeneration was performed. In this way, a reaction-regeneration cycle was completed, and the conditions and time of each reaction were controlled to be the same.

[0069] The above reaction-regeneration cycle was repeated for 40 reaction-regeneration cycles. After the 40th reaction, the carbon content and nitrogen content on the microsphere catalyst were 2.0% and 0.2% by weight, respectively. After regeneration, the carbon content and nitrogen content on the microsphere catalyst were 0.6% and 0.02% by weight, respectively. The reaction results are shown in Table 1.

[0070] The product obtained after the above-mentioned gas-phase Beckmann rearrangement reaction is subjected to heat exchange (first by water cooling, and then by circulating ethylene glycol solution at -10°C for cooling), and the reaction products are collected to obtain an ethanol solution mixture containing caprolactam. The gas-phase rearrangement reaction is run for a total of 400 hours, the reaction conversion rate of cyclohexanone oxime is 98.57%, the single-pass selectivity of caprolactam is about 96.62%, the ethyl-ε-caprolactam condensate is ~1.0 wt% (converted to caprolactam through hydrolysis reaction), and the light components (substances with lower boiling points than caprolactam) in the ethanol solution mixture containing caprolactam account for ~2.0 wt%, and the heavy components (substances with higher boiling points than caprolactam) account for ~0.5 wt%.

[0071] Example 2

[0072] The method of Example 1 is followed, except that the loading amount of the microsphere molecular sieve catalyst in the fixed fluidized bed reactor is 300 g, and the reaction conditions in the fluidized bed reactor include: reaction pressure 0.1 MPa, fluidized bed reaction temperature 385°C, gas atomization spray feeding, vaporization chamber temperature control 190°C, vaporizer minimum temperature point 160°C, outlet pipeline insulation 200°C, cyclohexanone oxime WHSV 2.2h -1 , cyclohexanone oxime accounts for 35 weight% of the total amount of cyclohexanone oxime and ethanol, water accounts for 0.4 weight% of the total amount of water, ethanol and cyclohexanone oxime, and the molar ratio of nitrogen to cyclohexanone oxime is 3.

[0073] After 14 hours of reaction, the conversion rate of cyclohexanone oxime was 99.74%. The feeding of cyclohexanone oxime, ethanol and water was stopped, and nitrogen was continued to be introduced into the fluidized bed reactor at a rate of 420 L / h for 30 min. Then the nitrogen was switched to air at 150 L / h, the temperature of the fluidized bed reactor was raised to 465°C, and the catalyst regeneration was started.

[0074] The time t of the regeneration process is determined by the following formula:

[0075] t=0.36×MHSV×t r ,

[0076] Wherein, t is the regeneration time, in h; MHSV is the mass space velocity of cyclohexanone oxime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in h -1 ;t r is the reaction time of the gas-phase Beckmann rearrangement of cyclohexanone oxime, in h.

[0077] The regeneration time was determined to be 11 h. After the regeneration was completed, the carbon content and nitrogen content of the regenerated catalyst were tested, the specific surface area was tested by the BET method, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst was calculated. The results are shown in Table 1.

[0078] The air was switched to nitrogen, and the raw materials were introduced into the fluidized bed reactor to start the next reaction. After 14 hours of reaction, regeneration was performed, thus completing a reaction-regeneration cycle. The conditions and time of each reaction were controlled to be the same.

[0079] The above reaction-regeneration cycle was repeated for 40 times, and the results are shown in Table 1.

[0080] Example 3

[0081] The method of Example 1 was followed, except that the temperature of each catalyst regeneration was 480° C. After regeneration, the carbon content and nitrogen content of the regenerated catalyst were tested, the specific surface area was tested by the BET method, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst was calculated. The results are shown in Table 1.

[0082] The above reaction-regeneration cycle was repeated for 20 times, and the results are shown in Table 1.

[0083] Example 4

[0084] The method of Example 1 was followed, except that each regeneration treatment lasted for 10 h. After the regeneration was completed, the carbon content and nitrogen content of the regenerated catalyst were tested, the specific surface area was tested by the BET method, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst was calculated. The results are shown in Table 1.

[0085] The above reaction-regeneration cycle was repeated for 10 times, and the results are shown in Table 1.

[0086] Comparative Example 1

[0087] The method of Example 1 is followed, except that the temperature of each regeneration treatment is 360° C. and the regeneration treatment time is 20 h.

[0088] The carbon content and nitrogen content of the regenerated catalyst were tested, the specific surface area was tested by the BET method, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst was calculated. The above reaction-regeneration cycle was repeated. After 4 reaction-regeneration cycles, the results are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] *Due to the use of alkaline buffer solution containing nitrogen compounds for post-treatment in the catalyst preparation, there is a certain amount of nitrogen on the surface of the fresh catalyst.

[0093] As can be seen from the results of Table 1, the production method of caprolactam provided by the present invention couples the cyclohexanone oxime gas phase Beckmann rearrangement reaction and the regeneration treatment of the catalyst. By controlling the regeneration temperature and time, it is possible to ensure the regeneration effect of the deactivated catalyst, effectively extend the service life of the catalyst, and control the regeneration cost, thereby improving the economy of the overall process. By comparing Examples 1 and 2 with Examples 3 and 4, it can be seen that when the regeneration temperature is too high or the regeneration time is too short, the activity of the catalyst can be maintained in a short-term cycle. By comparing Example 1 with Comparative Example 1, it can be seen that the regeneration temperature is too low. Although the carbon and nitrogen contents can reach a considerable level in the first regeneration, the catalyst has a low specific surface recovery rate. After the third regeneration, the carbon and nitrogen contents of the catalyst are too high, and the recovery rate of the BET specific surface area is less than 85%. This is because the regeneration temperature is lower than the reaction temperature, and the organic impurities adsorbed on the catalyst surface cannot be removed, resulting in rapid carbon deposition and coking deactivation of the catalyst, and this deactivation is not easy to restore activity.

[0094] 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 producing caprolactam, characterized in that: The method comprises: (1) in a fluidized bed reactor, contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; (2) when the conversion rate of cyclohexanone oxime drops to 96%, regenerating the contacted catalyst in an oxygen-containing atmosphere to obtain a regenerated catalyst; Wherein, the carbon content of the regenerated catalyst is not higher than 3wt%, the nitrogen content is not higher than 0.3wt%, and the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not lower than 88%; (3) At least part of the regenerated catalyst is used to provide the catalyst of step (1).

2. The method according to claim 1, wherein: The regenerated catalyst has a carbon content of 0.2-3 wt%, preferably 0.25-1 wt%; a nitrogen content of 0.001-0.3 wt%, preferably 0.002-0.01 wt%; Preferably, the recovery rate of the BET specific surface area of ​​the regenerated catalyst is not less than 92%, preferably 95-100%.

3. The method according to claim 1 or 2, wherein: The temperature of the regeneration treatment is 40-80° C. higher than the temperature of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime; Preferably, the temperature of the regeneration treatment is 400-550°C, preferably 420-480°C.

4. The method according to any one of claims 1 to 3, wherein: The time t of the regeneration process is determined by formula (I), t=0.36×MHSV×t r Formula (I), Where t is the regeneration time, in h; MHSV is the mass space velocity of cyclohexanone oxime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in h -1 ; t r is the reaction time of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in hours; 0.36 represents MHSV×t r The duration is 0.36 times of the time, in h.

5. The method according to any one of claims 1 to 4, wherein: In step (2), the oxygen-containing atmosphere is provided by a mixture of oxygen and an inert gas or air; Preferably, the volume content of oxygen in the oxygen-containing atmosphere is 5-50%; Preferably, the oxygen-containing atmosphere is introduced in an amount of 200-2000 L / kgcat·h.

6. The method according to any one of claims 1 to 5, wherein: In step (1), the cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in the presence of a solvent; Preferably, the solvent comprises alcohol and water, the alcohol is methanol and / or ethanol, preferably ethanol; Preferably, the mass ratio of the alcohol, water and cyclohexanone oxime is (0.5-5):(0.001-0.1):

1.

7. The method according to any one of claims 1 to 6, wherein: The cyclohexanone oxime gas-phase Beckmann rearrangement reaction is carried out in the presence of a carrier gas; Preferably, the carrier gas is provided by an inert gas, preferably nitrogen; Preferably, the molar ratio of the carrier gas to cyclohexanone oxime is 0.5-20:1, preferably 0.5-5:

1.

8. The method according to any one of claims 1 to 7, wherein: The conditions for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime include: a temperature of 300-400° C., preferably 360-400° C.; a pressure of 0.005-0.8 MPa, preferably 0.05-0.5 MPa; a mass space velocity of cyclohexanone oxime of 0.1-15 h -1 , preferably 1-8h -1 .

9. The method according to any one of claims 1 to 8, wherein: The catalyst is a microsphere catalyst, and the catalyst comprises an all-silicon molecular sieve with an MFI structure and a binder; Preferably, based on the total amount of the catalyst, the content of the MFI structured all-silicon molecular sieve on a dry basis is 50-95wt%, and the content of the binder is 5-50wt%; Preferably, the particle size of the microsphere catalyst is 20-300 μm.

10. The method according to any one of claims 1 to 9, wherein: When the conversion rate of cyclohexanone oxime drops to 98%, the contacted catalyst is subjected to the regeneration treatment.

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