Cyclohexanone-oxime gas phase Beckmann rearrangement reaction method and reaction system

Abstract

The invention relates to the technical field of cyclohexanone-oxime gas-phase Beckmann rearrangement reaction, and discloses a cyclohexanone-oxime gas-phase Beckmann rearrangement reaction method and a reaction system, and the method comprises the following steps: (1) in the presence of carrier gas and an alcohol solvent, contacting cyclohexanone-oxime with a catalyst to carry out gas-phase Beckmann rearrangement reaction to obtain a product flow; (2) carrying out tar removal treatment on the product material flow to obtain a first material flow containing caprolactam; (3) carrying out gas-liquid separation on the first material flow to obtain alcohol-rich gas and a second material flow containing caprolactam; (4) carrying out light component removal treatment on the second material flow containing caprolactam to obtain crude caprolactam; the conditions of the cyclohexanone-oxime gas phase Beckmann rearrangement reaction, the tar removal treatment and the gas-liquid separation meet the following conditions: T1 > T2 > T3, P1 > P0 > P2 > P3, and P0 is standard atmospheric pressure, mmHg. According to the method, the purity and the yield of the crude caprolactam can be ensured, and temperature and pressure fluctuation is avoided, so that the process energy consumption is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and specifically relates to a method and a reaction system for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. Background Art

[0002] Caprolactam (CPL) is a large-volume and important basic organic raw material, mainly used for the production of nylon-6 fibers and nylon-6 engineering plastics, and is widely used in industries such as textiles, automobiles, electronics, ships, and packaging films. It is closely related to people's livelihood and occupies an important position in the national economy.

[0003] The Beckmann rearrangement reaction of cyclohexanone oxime is one of the core technologies for the industrial production of caprolactam. The gas-phase Beckmann rearrangement process has the advantages of no by-production of ammonium sulfate, low cost, and environmental friendliness, so it has received more and more extensive attention as a green production process for caprolactam.

[0004] In order to develop solid acid catalysts suitable for the gas-phase Beckmann rearrangement reaction, domestic and foreign researchers have conducted a large number of studies on two types of catalysts such as oxides, composite oxides, and zeolite molecular sieves. The results show that most catalysts have certain activities, but the common disadvantage is that the catalysts are prone to deactivation and the catalyst life is short and cannot meet the requirements of industrialization. Therefore, the fluidized bed gas-phase rearrangement process with continuous reaction-regeneration has received unanimous praise from experts.

[0005] Sumitomo Chemical Co., Ltd. of Japan began to engage in research on the gas-phase Beckmann rearrangement in 1982. They used high-silicon / aluminum ratio MFI structure molecular sieves as catalysts, and important progress has been made in the research work. In April 2003, Sumitomo Chemical achieved the industrialization of the gas-phase Beckmann rearrangement for the first time in Ehime, Japan with Silicalite-1 molecular sieves as catalysts. A new fluidized bed continuous reaction-regeneration process was adopted, solving the problems of easy deactivation of the catalyst and the engineering scale-up problem in crystallization purification. The reaction selectivity reached 96%. The initial production capacity of the factory was 60 kt / a, and then in November 2005, the production capacity was expanded to 85 kt / a by eliminating bottlenecks. So far, the caprolactam plant of Sumitomo Chemical in Japan is the only commercial caprolactam device using the gas-phase Beckmann rearrangement technology in the world.

[0006] For the post-treatment of the gas-phase Beckmann rearrangement product, the early research was combined with the existing liquid-phase rearrangement process route. The gas-phase rearrangement reaction product was cooled through multiple stages to obtain a methanol solution of crude caprolactam, and then operations such as methanol recovery, dehydration, removal of light and heavy impurities were carried out through distillation to obtain crude caprolactam, which was sent to the liquid-phase rearrangement separation and purification process for treatment. However, due to the large difference in the by-product composition between the liquid-phase rearrangement and the gas-phase rearrangement, it is difficult to obtain high-quality caprolactam by using the treatment method of the liquid-phase rearrangement.

[0007] In addition, the vapor-phase Beckmann rearrangement of cyclohexanone oxime is a strongly exothermic reaction, and the reaction product needs to undergo repeated cooling and heating processes after cooling, which undoubtedly greatly increases the energy consumption of the reaction system. Summary of the Invention

[0008] The object of the present invention is to overcome the problems of insufficient quality and yield of caprolactam and high energy consumption in the preparation process existing in the prior art, and to provide a method and a reaction system for the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime. This method can improve the quality and yield of caprolactam, efficiently utilize heat energy by means of a stepped cooling method, and has good economic benefits.

[0009] To achieve the above object, on the one hand, the present invention provides a method for the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, the method comprising:

[0010] (1) In the presence of a carrier gas and an alcohol solvent, contacting cyclohexanone oxime with a catalyst to carry out a vapor-phase Beckmann rearrangement reaction to obtain a product stream;

[0011] (2) Subjecting the product stream to de-tar treatment to obtain a first stream containing caprolactam;

[0012] (3) Separating the first stream into a gas rich in alcohol and a second stream containing caprolactam by gas-liquid separation;

[0013] (4) Subjecting the second stream containing caprolactam to light component removal treatment to obtain crude caprolactam;

[0014] Wherein, the temperature of the vapor-phase Beckmann rearrangement reaction is T1, °C, the reaction pressure is P1, mmHg; the temperature of the de-tar treatment is T2, °C, and the pressure is P2, mmHg; the temperature of the gas-liquid separation is T3, °C, and the pressure is P3, mmHg. The conditions of the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, de-tar treatment, and gas-liquid separation satisfy: T1 > T2 > T3, P1 > P0 > P2 > P3, and P0 is the standard atmospheric pressure, mmHg.

[0015] On the other hand, the present invention provides a reaction system for the method of the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, the reaction system comprising a raw material supply unit 1, a reaction unit 2, a de-tar tower 3, a gas-liquid separation tower 4, and a light component removal unit 5 connected in series in sequence along the material flow direction;

[0016] The raw material supply unit 1 includes a falling film evaporator for supplying a vapor-phase raw material including a carrier gas, an alcohol solvent, and cyclohexanone oxime to the reaction unit;

[0017] The reaction unit 2 is used for carrying out the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime;

[0018] The bottom of the de-tar tower 3 is provided with a feed inlet communicating with the outlet of the reaction unit 2, the top of the tower is provided with a first logistics outlet, and the bottom of the tower is provided with a tar outlet;

[0019] The bottom of the gas-liquid separation tower 4 is provided with a feed inlet communicating with the first logistics outlet of the de-tar tower 3, the top of the tower is provided with a rich alcohol gas outlet, and the bottom of the tower is provided with a second logistics outlet;

[0020] Preferably, the light component removal unit 5 includes a series-connected primary light component removal tower 501 and a secondary light component removal tower 502;

[0021] Preferably, the rich alcohol gas outlet of the gas-liquid separation tower 4 is communicated with the raw material supply unit 1, and at least part of the rich alcohol gas is returned to the raw material supply unit 1.

[0022] In the prior art, the post-treatment of the gas-phase rearrangement reaction product needs to be cooled in multiple stages to obtain a methanol solution of crude caprolactam, and then operations such as methanol recovery, dehydration, light component removal, and heavy component removal are carried out through distillation. The repeated processes of cooling and heating are not only unfavorable for the yield of crude caprolactam, but also cause a large amount of heat waste, greatly increasing the process cost. The reaction method provided by the present invention integrates the gas-phase rearrangement reaction and the separation process. The product logistics of the gas-phase Beckmann rearrangement reaction are successively subjected to de-tar treatment, gas-liquid separation to recover the alcohol solvent, and then light component removal treatment. By adopting the separation and purification steps in a specific order, it is beneficial to avoid temperature and pressure fluctuations while ensuring the purity and yield of crude caprolactam, thereby greatly reducing the process energy consumption. Moreover, the inventors of the present invention found in the research that the temperature of the reaction product of the gas-phase rearrangement is relatively high, and the reaction product can be used as a heat source. In the case of the post-treatment steps in a specific order, a stepped cooling method is adopted to efficiently utilize the heat energy, save energy and reduce consumption, and obtain good economic benefits. Description of the Drawings

[0023] Figure 1 is a schematic diagram of a reaction system in an embodiment of the present invention.

[0024] Description of the Reference Numerals

[0025] 1 Raw material supply unit 2 Reaction unit 201 Fluidized bed reactor

[0026] 202 Regenerator 203 Fixed bed reactor 3 De-tar tower

[0027] 4 Gas-liquid separation tower 5 Light component removal unit 501 Primary light component removal tower

[0028] 502 Secondary light component removal tower 6 Alcohol solvent refining tower Detailed Embodiments

[0029] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. 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, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0030] The first aspect of the present invention provides a method for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the method comprising:

[0031] (1) In the presence of a carrier gas and an alcohol solvent, contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction to obtain a product stream;

[0032] (2) Subjecting the product stream to de-tar treatment to obtain a first stream containing caprolactam;

[0033] (3) Separating the first stream into a gas rich in alcohol and a second stream containing caprolactam by gas-liquid separation;

[0034] (4) Subjecting the second stream containing caprolactam to light component removal treatment to obtain crude caprolactam;

[0035] Wherein, the temperature of the gas-phase Beckmann rearrangement reaction is T1, °C, the reaction pressure is P1, mmHg; the temperature of the de-tar treatment is T2, °C, the pressure is P2, mmHg; the temperature of the gas-liquid separation is T3, °C, the pressure is P3, mmHg, and the conditions of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the de-tar treatment and the gas-liquid separation satisfy: T1 > T2 > T3, P1 > P0 > P2 > P3, where P0 is the standard atmospheric pressure, mmHg.

[0036] According to the present invention, the product stream of the gas-phase Beckmann rearrangement reaction is successively subjected to de-tar treatment and gas-liquid separation to recover the alcohol solvent, and then light component removal treatment is carried out. Adopting the separation and purification steps in a specific order is beneficial to improving the purity and yield of crude caprolactam. Moreover, the inventors of the present invention found in the research that the reaction product temperature of the gas-phase rearrangement is relatively high, and the reaction product can be used as a heat source. In the case of the post-treatment steps in a specific order, by coordinating the temperatures and pressures of each step in the overall process and adopting a step-by-step cooling method, the heat energy can be efficiently utilized, energy can be saved and consumption can be reduced, and good economic benefits can be obtained.

[0037] In the present invention, the de-tar treatment and the gas-liquid separation can be carried out by rectification. The "temperature of the de-tar treatment" and the "temperature of the gas-liquid separation" in the present invention both refer to the separation temperature of the material. When separated by a separation column, it refers to the top temperature of the separation column.

[0038] According to some preferred embodiments of the present invention, 160°C ≤ T1 - T2 ≤ 200°C, 900 mmHg ≤ P1 - P2 ≤ 2100 mmHg.

[0039] Preferably, 70°C ≤ T2 - T3 ≤ 160°C, 80 mmHg ≤ P2 - P3 ≤ 150 mmHg, wherein the temperature of the gas-phase Beckmann rearrangement reaction is T1, °C; the reaction pressure is P1, mmHg; the temperature of the de-tar treatment is T2, °C; the pressure is P2, mmHg; the temperature of the gas-liquid separation is T3, °C, and the pressure is P3, mmHg. Controlling the above preferred temperature difference range is beneficial to the removal of tar and reduces the loss of caprolactam.

[0040] In the present invention, P0 is the standard atmospheric pressure, which is 760 mmHg. In the present invention, unless otherwise specified, the pressures involved refer to absolute pressures.

[0041] The present invention does not particularly limit the specific conditions of the gas-phase Beckmann rearrangement reaction, and conventional reaction conditions in the art can be adopted.

[0042] In order to improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam, and further match with the subsequent treatment process, according to some preferred embodiments of the present invention, the conditions of the gas-phase Beckmann rearrangement reaction include: 360°C ≤ T1 ≤ 400°C, 1500 mmHg ≤ P1 ≤ 2660 mmHg, and the mass space velocity of cyclohexanone oxime is 0.2 - 10 h -1 . In the present invention, preferably, in the initial stage of the reaction, the catalyst bed is preheated by an auxiliary start-up heat source, preferably preheated to 220 - 250°C, and then the gas-phase cyclohexanone oxime is brought into contact with the catalyst bed, and the reactor is heated to the temperature T1 by the heat released from the gas-phase reaction. The reaction process can be in the form of a fixed bed, a moving bed, and a fluidized bed, and the fluidized bed process form is preferred. By adopting the above preferred embodiments, the heat released from the reaction is fully utilized, and the excessive temperature rise of the catalyst bed can be avoided.

[0043] According to the present invention, the cyclohexanone oxime contacts the catalyst in a gas phase. Preferably, the gas-phase raw material of cyclohexanone oxime is provided by a falling film evaporation method. According to some preferred embodiments of the present invention, step (1) includes: evaporating cyclohexanone oxime in the coexistence of a carrier gas and an alcohol solvent to obtain a raw material gas containing cyclohexanone oxime, the carrier gas, and the gas-phase alcohol solvent, and then bringing the raw material gas into contact with the catalyst to carry out the gas-phase Beckmann rearrangement reaction to obtain a product stream. The present invention does not particularly limit the specific conditions of the falling film evaporation, and conventional methods in the art can be adopted to obtain the gas-phase raw material.

[0044] The present invention has no particular limitation on the specific selection of the carrier gas and the alcohol solvent, and conventional selections in the art can be used. Preferably, the carrier gas is nitrogen. Preferably, the alcohol solvent is a lower alcohol, preferably methanol.

[0045] Preferably, the mass ratio of the carrier gas to cyclohexanone oxime is 0.02 - 0.4:1.

[0046] According to some preferred embodiments of the present invention, based on the total amount of the cyclohexanone oxime and the alcohol solvent, the content of the cyclohexanone oxime is 20 - 70 wt%, preferably 25 - 50 wt%.

[0047] Preferably, the gaseous raw material further contains water, and based on the total amount of the cyclohexanone oxime, the alcohol solvent and water, the content of water is 0.1 - 5 wt%.

[0048] In the present invention, the de-tar treatment is used to separate, from the product stream, impurity components with boiling points higher than that of caprolactam, to obtain a first stream containing caprolactam. The first stream contains caprolactam, alcohol solvent, nitrogen, by-products, etc. Tar mainly comes from falling film evaporation and catalyst regeneration for burning coke, and a small amount of heavy components are generated in the gas-phase rearrangement reaction. The present invention has a relatively wide selection range for the specific conditions of the de-tar treatment, with the above temperature gradient being met and the caprolactam gas not being liquefied as the principle.

[0049] According to some preferred embodiments of the present invention, the conditions for the de-tar treatment include: 195°C ≤ T2 ≤ 210°C, 550 mmHg ≤ P2 ≤ 600 mmHg.

[0050] According to some specific embodiments of the present invention, the de-tar treatment is carried out in a distillation column. As described above, the top temperature of the distillation column at this time is the temperature of the de-tar treatment, which means that the product stream is cooled from the bottom temperature to the top temperature, enabling comprehensive energy utilization. Specifically, the top temperature of the distillation column is 196 - 210°C, the bottom temperature of the column kettle is 203 - 212°C, and the pressure is 550 - 600 mmHg. In the present invention, unless otherwise specified, the pressure refers to the absolute pressure.

[0051] According to the present invention, preferably, the method does not include the step of cooling the product stream, and directly performs the de-tar treatment on the high-temperature product stream. By adopting the above preferred embodiments, the high temperature of the reaction product can be utilized for de-tar, which is beneficial to energy utilization.

[0052] In the present invention, the gas-liquid separation is used to recover the alcohol solvent from the first stream containing caprolactam. The alcohol-rich gas includes alcohol, non-condensable gas, etc. The present invention has a relatively wide selection range for the specific conditions of the gas-liquid separation to meet the above temperature gradient and ensure that the alcohol solvent is not liquefied. According to some preferred embodiments of the present invention, the conditions of the gas-liquid separation include: 50°C ≤ T3 ≤ 60°C, 450 mmHg ≤ P3 ≤ 550 mmHg.

[0053] According to some specific embodiments of the present invention, the gas-liquid separation is carried out in a gas-liquid separation column. According to the foregoing, the top temperature of the gas-liquid separation column at this time is the temperature of the gas-liquid separation. Specifically, the top temperature of the gas-liquid separation column is 50 - 55°C, the bottom temperature is 130 - 135°C, the pressure is 450 - 550 mmHg, and the inlet temperature of the gas-phase material is 170 - 190°C.

[0054] According to the present invention, preferably, the alcohol-rich gas includes alcohol, carrier gas, and optional impurity gas, and the impurity gas includes ammonia and / or trimethylamine.

[0055] According to the present invention, the alcohol-rich gas can be recycled as a raw material to improve the utilization rate of the raw material. According to some preferred embodiments of the present invention, the method further includes: returning at least part of the alcohol-rich gas to step (1), and subjecting the remaining part of the alcohol-rich gas to gas-liquid separation to remove non-condensable gas, and the obtained liquid-phase alcohol can be returned to the raw material supply unit for recycling. By adopting the above preferred embodiment, it can ensure that most of the methanol and nitrogen are recycled.

[0056] According to some preferred embodiments of the present invention, based on the total amount of the alcohol-rich gas, the content of the part of the alcohol-rich gas returned to step (1) is 80 - 95 vol%, preferably 85 - 92 vol%.

[0057] In the present invention, through the light component removal treatment described in step (4), by-products and impurities such as water, cyclohexanone, 5-hexenenitrile, cyclohexenone, AMH, and oxime in the second stream are removed to obtain crude caprolactam.

[0058] According to some preferred embodiments of the present invention, the light component removal treatment includes primary light component removal and secondary light component removal, and the top temperature of the primary light component removal is 50 - 80°C lower than the top temperature of the secondary light component removal. According to the present invention, cyclohexanone, 5-hexenenitrile, etc. in the light components are separated during the primary light component removal process, and after optional oil-water separation, they are sent to the sewage treatment device for treatment; AMH and oxime are separated during the secondary light component removal process. By adopting the above preferred embodiment, it is beneficial to the recovery and reuse of AMH and oxime.

[0059] Preferably, the conditions of the primary light component removal include: the top temperature is 35 - 38°C, the bottom temperature is 143 - 145°C, and the pressure is 45 - 55 mmHg.

[0060] Preferably, the conditions for the secondary light component removal include: the top temperature is 105 - 110 °C, the bottom temperature is 140 - 142 °C, and the pressure is 5 - 12 mmHg.

[0061] The present invention does not particularly limit the specific method for the gas-phase Beckmann rearrangement reaction. As long as the above reaction temperature is satisfied, conventional methods and reactors in the art can be used.

[0062] According to some preferred embodiments of the present invention, the gas-phase Beckmann rearrangement reaction is carried out in a series of fluidized bed reactor and fixed bed reactor. Adopting the above preferred embodiments is beneficial to further improve the conversion rate of cyclohexanone oxime.

[0063] The present invention has a wide selection range for the catalyst used in the gas-phase Beckmann rearrangement reaction. Any known catalyst in the art that can catalyze the gas-phase Beckmann rearrangement of cyclohexanone oxime can be applied to the present invention, and those skilled in the art can select according to actual needs.

[0064] Preferably, the fluidized bed reactor is filled with a microsphere all-silica-1 molecular sieve catalyst with an MFI structure, and the fixed bed reactor is filled with a spherical all-silica-1 molecular sieve catalyst with an MFI structure. The particle size of the microsphere all-silica-1 molecular sieve catalyst is 50 - 300 μm. For example, it can be a microsphere catalyst obtained by spray forming, such as the catalyst disclosed in Chinese Patent Application 202310595456.6. The particle size of the spherical all-silica-1 molecular sieve catalyst is 1.3 - 2.2 mm, and it can be obtained by rolling forming, such as the catalysts disclosed in Chinese Patent Application 201210592676.5 or 201610285300.8.

[0065] Preferably, the volume ratio of the microsphere all-silica-1 molecular sieve catalyst to the spherical all-silica-1 molecular sieve catalyst is (10 - 40):1, preferably (15 - 30):1.

[0066] In a further preferred embodiment, the method includes: regenerating the microsphere all-silica-1 molecular sieve catalyst in the fluidized bed reactor. The regeneration treatment can be carried out in a regenerator, and a circulating fluidized bed catalytic reaction device composed of a fluidized bed reactor and a regenerator is formed to realize the circulation of the catalyst.

[0067] Preferably, the temperature of the regeneration treatment is 50 - 100 °C higher than the temperature of the gas-phase Beckmann rearrangement reaction.

[0068] In the present invention, hot air can be provided to the regenerator through an external heat source such as a combustion furnace, thereby providing a heat source and an oxygen-containing gas for the spent catalyst at the same time. After the catalyst coked with carbon in the reactor is circulated to the regenerator, it burns and releases heat, keeping the regenerator at a constant temperature up to the regeneration temperature, so that the reaction-regeneration system reaches a normal operating state. At the same time, a part of the reaction heat in the fluidized bed reactor can be used to heat the deactivated catalyst during the regeneration process. The deactivated catalyst burns to remove carbon deposits in the oxygen-containing atmosphere in the regenerator, is regenerated and heated, and then returns to the reactor, while transferring the heat from the former to the latter to provide at least part of the reaction heat, thereby realizing the circulation of heat between the reactor and the regenerator.

[0069] To ensure the long-term stability of the performance of the molecular sieve catalyst and prevent the catalyst from being poisoned and permanently deactivated. Preferably, the temperature of the regeneration treatment is 400-550 °C.

[0070] On the other hand, the present invention provides a reaction system for the above-mentioned method of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The reaction system includes a raw material supply unit 1, a reaction unit 2, a de-tar column 3, a gas-liquid separation column 4, and a light-component removal unit 5 connected in series in the direction of the material flow;

[0071] The raw material supply unit 1 includes a falling film evaporator for supplying a gas-phase raw material including a carrier gas, an alcohol solvent, and cyclohexanone oxime to the reaction unit;

[0072] The reaction unit 2 is used for carrying out the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime;

[0073] The bottom of the de-tar column 3 is provided with a feed port communicating with the outlet of the reaction unit 2, the top of the column is provided with a first material flow outlet, and the bottom of the column is provided with a tar outlet;

[0074] The bottom of the gas-liquid separation column 4 is provided with a feed port communicating with the first material flow outlet of the de-tar column 3, the top of the column is provided with a rich-alcohol gas outlet, and the bottom of the column is provided with a second material flow outlet;

[0075] Preferably, the light-component removal unit 5 includes a first-stage light-component removal column 501 and a second-stage light-component removal column 502 connected in series;

[0076] Preferably, the rich-alcohol gas outlet of the gas-liquid separation column 4 is connected to the raw material supply unit 1, and at least part of the rich-alcohol gas is returned to the raw material supply unit 1.

[0077] According to some preferred embodiments of the present invention, the reaction unit 2 includes a fluidized bed reactor 201 and a fixed bed reactor 203 connected in series. Preferably, the fixed bed reactor is an adiabatic reactor, and there is no need to provide an additional heat source. It can be heated by using the heat of the product obtained from the fluidized bed reactor. By adopting the above preferred embodiments, while ensuring the complete conversion of the remaining small amount of cyclohexanone oxime, it is beneficial to improve the heat utilization rate and avoid energy waste.

[0078] Preferably, the reaction system further includes a regeneration reactor 202, and the regeneration reactor 202 is connected in parallel with the fluidized bed reactor 201 for regenerating the catalyst from the fluidized bed reactor 201.

[0079] Preferably, the reaction system further includes an alcohol solvent refining tower 6. The alcohol solvent refining tower 6 is communicated with the rich alcohol gas outlet of the gas-liquid separator 4 to perform gas-liquid separation on the remaining rich alcohol gas, remove the non-condensable gas, and the obtained liquid-phase alcohol can be returned to the raw material supply unit for recycling.

[0080] Preferably, the reaction system further includes a heating device, and the heating device can be, for example, a combustion furnace to provide low, medium and high pressure steam and hot water to the reaction system.

[0081] The present invention will be described in detail below through examples.

[0082] Example 1

[0083] Using the reaction system as Figure 1 shown to carry out the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The reaction system includes a raw material supply unit 1, a reaction unit 2, a de-tar tower 3, a gas-liquid separation tower 4, and a light component removal unit 5 connected in series along the material flow direction; the raw material supply unit 1 includes a falling film evaporator, the reaction unit 2 includes a fluidized bed reactor 201 and a fixed bed reactor 203 connected in series, and the regeneration reactor 202 is connected in parallel with the fluidized bed reactor 201; the bottom of the de-tar tower 3 is provided with a feed port communicated with the outlet of the fixed bed reactor 203, the top is provided with a first material flow outlet, and the bottom is provided with a tar outlet; the bottom of the gas-liquid separation tower 4 is provided with a feed port communicated with the first material flow outlet of the de-tar tower 3, the top is provided with a rich alcohol gas outlet, and the bottom is provided with a second material flow outlet; the light component removal unit 5 includes a primary light component removal tower 501 and a secondary light component removal tower 502 connected in series; the rich alcohol gas outlet of the gas-liquid separation tower 4 is communicated with the raw material supply unit 1 to return at least part of the rich alcohol gas to the raw material supply unit 1. The alcohol solvent refining tower 6 is communicated with the rich alcohol gas outlet of the gas-liquid separator 4 to perform gas-liquid separation on the remaining rich alcohol gas, and the refined liquid-phase alcohol is returned to the raw material supply unit. The reaction system further includes a heating device, and the heating device can be, for example, a combustion furnace to provide low, medium and high pressure steam and hot water to the reaction system.

[0084] The catalyst in the catalyst bed of the fluidized bed reactor is the microsphere all-silica-1 molecular sieve catalyst with MFI structure in Example 1 of Chinese Patent Application No. 202310595456.6. The catalyst in the catalyst bed of the fixed bed reactor is the spherical all-silica-1 molecular sieve catalyst with MFI structure in Example 1 of Chinese Patent Application No. 201210592676.5. The volume ratio of the microsphere molecular sieve catalyst to the spherical molecular sieve catalyst for loading the catalyst is 20:1.

[0085] The reaction conditions of the fluidized bed reactor include: temperature of 380 °C, absolute pressure of 1520 mmHg, and mass space velocity of cyclohexanone oxime of 4.2 h -1 , the feed mass composition, cyclohexanone oxime: methanol: nitrogen: water = 31.85: 60.04: 5: 1.75. The conditions of the fixed bed reactor include: temperature of 380 °C and absolute pressure of 1380 mmHg.

[0086] Cyclohexanone oxime, nitrogen, water and methanol are vaporized through a falling film evaporator at 155 - 170 °C, and the raw material gas is heated to about 220 - 250 °C by medium-pressure steam heated by a combustion furnace and enters the fluidized bed reactor in gaseous form. At the same time, the catalyst bed of the circulating fluidized catalytic reaction device is heated to about 220 - 250 °C by using the auxiliary start-up heat source, and the reactor is quickly heated to the predetermined reaction temperature by the reaction heat release of the vaporized raw materials. The regenerator is heated by the combustion furnace, and the catalyst with carbon deposition and coking in the reactor is circulated to the regenerator and burned to release heat, so that the regenerator is kept at a constant temperature of 460 °C, so that the reaction-regeneration system reaches the normal operation state. The gaseous products of the gas-phase rearrangement reaction pass through an adiabatic small fixed bed to completely convert cyclohexanone oxime, and then the gaseous reaction products are subjected to de-tar treatment through a de-tar tower. The conditions of the de-tar tower are set as 209 °C at the top of the tower, 212 °C at the bottom of the tower, and 575 mmHg absolute pressure. The first stream containing caprolactam flowing out from the top of the de-tar tower is sent to a gas-liquid separation tower for gas-liquid separation. The top temperature of the tower is set at 52 °C, the bottom temperature of the tower is 134 °C, and the absolute pressure is 485 mmHg. The rich alcohol gas is obtained from the top of the tower. 90 vol% of the rich alcohol gas is returned to the falling film evaporator to supplement the gas-phase raw materials, and the remaining 10 vol% of the rich alcohol gas is sent to an alcohol solvent refining tower 6 for refining to remove non-condensable gas, and the liquid-phase methanol obtained is then returned to the falling film evaporator. The second stream containing caprolactam collected at the bottom of the gas-liquid separation tower is sent to a primary light component removal tower, and by-products and impurities such as water, cyclohexanone, 5-hexenenitrile, cyclohexenone, AMH and oxime are removed through a secondary light component removal tower respectively. The conditions of the primary light component removal tower are 37 °C at the top of the tower, 143 °C at the bottom of the tower, and 50 mmHg absolute pressure. The secondary light component removal tower is 108 °C at the top of the tower, 141 °C at the bottom of the tower, and 6.5 mmHg absolute pressure. The effluent flowing out from the bottom of the secondary light component removal tower is collected and its composition is analyzed by chromatography. The purity of the crude caprolactam is 99.3%.

[0087] Comparative Example 1

[0088] According to the method of Example 1, the difference is that the gaseous reaction product obtained from the reaction unit is first cooled by water, and then further cooled by circulating an ethylene glycol solution at -10°C. The reaction product is collected to obtain a methanol solution mixture containing caprolactam; it is sent to a methanol solvent recovery column. The top temperature of the column is set at 65°C, the bottom temperature is 115°C, and the pressure is atmospheric. The liquid-phase product obtained at the bottom of the column is dehydrated, and the dehydration is carried out in a dehydration column. The conditions of the dehydration column include: 58°C at the top, 112°C at the bottom, and 150 mmHg absolute pressure. The product flowing out from the bottom of the dehydration column is subjected to light-component removal treatment, and the light-component removal is carried out in a light-component removal column. The conditions of the light-component removal column include: 88°C at the top, 140°C at the bottom, and 9.75 mmHg absolute pressure. The product flowing out from the bottom of the light-component removal column is subjected to heavy-component removal treatment. The conditions of the heavy-component removal column include: 130°C at the top, 155°C at the bottom, and 9.75 mmHg absolute pressure. The overhead product of the heavy-component removal column is collected to obtain crude caprolactam, and its composition is analyzed by chromatography. The purity of the crude caprolactam is 99.45%.

[0089] Since the crude caprolactam still needs to be further purified through subsequent crystallization and refining processes, for the existing crystallization process, a purity of the crude caprolactam above 99% can meet the process requirements. Through the comparison between Example 1 and Comparative Example 1, it can be seen that the crude caprolactam obtained by the method provided by the present invention can reach a level comparable to the existing post-treatment process and can meet the needs in actual process production. At the same time, compared with the existing post-treatment process, the method provided by the present invention adopts a brand-new post-treatment route, which can significantly reduce the fluctuations in temperature and pressure during the process while ensuring the purity of the crude caprolactam, improve the utilization rate of heat, and has the significant advantages of energy conservation and consumption reduction.

[0090] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, characterized in that The method includes: (1) In the presence of a carrier gas and an alcohol solvent, contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction to obtain a product stream; (2) Subjecting the product stream to de-tar treatment to obtain a first stream containing caprolactam; (3) Separating the first stream into a gas-rich alcohol and a second stream containing caprolactam by gas-liquid separation; (4) Subjecting the second stream containing caprolactam to light component removal treatment to obtain crude caprolactam; wherein, the temperature of the gas-phase Beckmann rearrangement reaction is T1, °C, and the reaction pressure is P1, mmHg; the temperature of the de-tar treatment is T2, °C, and the pressure is P2, mmHg; the temperature of the gas-liquid separation is T3, °C, and the pressure is P3, mmHg. The conditions of the cyclohexanone oxime gas-phase Beckmann rearrangement reaction, de-tar treatment, and gas-liquid separation satisfy: T1 > T2 > T3, P1 > P0 > P2 > P3, where P0 is the standard atmospheric pressure, mmHg.

2. The method according to claim 1, wherein 160°C ≤ T1 - T2 ≤ 200°C, 900 mmHg ≤ P1 - P2 ≤ 2100 mmHg, and / or, 70°C ≤ T2 - T3 ≤ 160°C, 80 mmHg ≤ P2 - P3 ≤ 150 mmHg, wherein, the temperature of the gas-phase Beckmann rearrangement reaction is T1, °C, and the reaction pressure is P1, mmHg; the temperature of the de-tar treatment is T2, °C, and the pressure is P2, mmHg; the temperature of the gas-liquid separation is T3, °C, and the pressure is P3, mmHg.

3. The method according to claim 1 or 2, characterized in that, The conditions for the gas-phase Beckmann rearrangement reaction include: 360°C ≤ T1 ≤ 400°C, 1500 mmHg ≤ P1 ≤ 2660 mmHg, and the mass space velocity of cyclohexanone oxime is 0.2 - 10 h -1 ; Preferably, the conditions of the de-tar treatment include: 195°C ≤ T2 ≤ 210°C, 550 mmHg ≤ P2 ≤ 600 mmHg; Preferably, the conditions of the gas-liquid separation include: 50°C ≤ T3 ≤ 60°C, 450 mmHg ≤ P3 ≤ 550 mmHg.

4. The method according to any one of claims 1-3, characterized in that, The gas-rich alcohol includes alcohol, carrier gas, and optional impurity gas, and the impurity gas includes ammonia and / or trimethylamine; Preferably, the method further includes: returning at least part of the gas-rich alcohol to step (1), and subjecting the remaining part of the gas-rich alcohol to refining to remove non-condensable gas; Preferably, based on the total amount of the gas-rich alcohol, the content of the part of the gas-rich alcohol returned to step (1) is 80 - 95 vol%.

5. The method according to any one of claims 1-4, characterized in that The method does not include a step of cooling the product stream.

6. The method according to any one of claims 1-5, characterized in that, The light component removal treatment includes primary light component removal and secondary light component removal, and the top temperature of the primary light component removal is 50 - 80°C lower than the top temperature of the secondary light component removal; Preferably, the conditions of the primary light component removal include: the top temperature is 35 - 38°C, the bottom temperature is 143 - 145°C, and the pressure is 45 - 55 mmHg; Preferably, the conditions of the secondary light component removal include: the top temperature is 105 - 110°C, the bottom temperature is 140 - 142°C, and the pressure is 5 - 12 mmHg.

7. The method according to any one of claims 1-6, wherein The gas-phase Beckmann rearrangement reaction is carried out in a series of fluidized bed reactors and fixed bed reactors; Preferably, the fluidized bed reactor is filled with a microsphere all-silica-1 molecular sieve catalyst with an MFI structure, and the fixed bed reactor is filled with a spherical all-silica-1 molecular sieve catalyst with an MFI structure; Preferably, the volume ratio of the microsphere all-silica-1 molecular sieve catalyst to the spherical all-silica-1 molecular sieve catalyst is (10 - 40):1, preferably (15 - 30):

1.

8. The method according to claim 7, characterized in that The method includes: regenerating the microsphere all-silica-1 molecular sieve catalyst in the fluidized bed reactor; Preferably, the temperature of the regeneration treatment is 50 - 100 °C higher than the temperature of the gas-phase Beckmann rearrangement reaction.

9. A reaction system for the method of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime according to any one of claims 1-8, characterized in that, The reaction system includes a raw material supply unit (1), a reaction unit (2), a de-tar column (3), a gas-liquid separation column (4), and a de-light component unit (5) connected in series along the material flow direction; The raw material supply unit (1) includes a falling film evaporator for supplying a gas-phase raw material including a carrier gas, an alcohol solvent, and cyclohexanone oxime to the reaction unit; The reaction unit (2) is used for carrying out the gas-phase Beckmann rearrangement reaction on cyclohexanone oxime; The bottom of the de-tar column (3) is provided with a feed port communicated with the outlet of the reaction unit (2), the top is provided with a first material flow outlet, and the bottom is provided with a tar outlet; The bottom of the gas-liquid separation column (4) is provided with a feed port communicated with the first material flow outlet of the de-tar column (3), the top is provided with a rich alcohol gas outlet, and the bottom is provided with a second material flow outlet; Preferably, the de-light component unit (5) includes a first-stage de-light component column (501) and a second-stage de-light component column (502) connected in series; Preferably, the rich alcohol gas outlet of the gas-liquid separation column (4) is communicated with the raw material supply unit (1) to return at least part of the rich alcohol gas to the raw material supply unit (1).

10. The reaction system according to claim 9, characterized in that, The reaction unit (2) includes a fluidized bed reactor (201) and a fixed bed reactor (203) connected in series; Preferably, the reaction system further includes a regeneration reactor (202), and the regeneration reactor (202) is connected in parallel with the fluidized bed reactor (201) for regenerating the catalyst from the fluidized bed reactor (201); Preferably, the reaction system further includes an alcohol solvent refining column (6), and the alcohol solvent refining column (6) is communicated with the rich alcohol gas outlet of the gas-liquid separator (4) to refine the remaining part of the rich alcohol gas to remove non-condensable gas.

Images