A system for the preparation of caprolactam by heterogeneous ammonoximation and gas-phase rearrangement

Abstract

This invention relates to the technical field of caprolactam preparation, and discloses a system for preparing caprolactam through heterogeneous ammonoximation and gas-phase rearrangement. The system includes a heterogeneous ammonoximation reaction unit and a gas-phase rearrangement reaction unit connected in series. A cyclohexanone oxime purification unit is connected between the heterogeneous ammonoximation reaction unit and the gas-phase rearrangement reaction unit. The cyclohexanone oxime purification unit has an inert solvent inlet. A solvent recycling unit is connected to the rear end of the gas-phase rearrangement reaction unit. The solvent recycling unit has an inert solvent outlet, which is connected to the inert solvent inlet of the cyclohexanone oxime purification unit. The solvent recycling unit also has a caprolactam outlet for producing caprolactam product. This invention, by using an inert solvent, eliminates the solvent removal step after the heterogeneous ammonoximation reaction, improves the ability to remove gas-phase rearrangement reaction gases, avoids the use of carrier gas, and saves energy.

Description

Technical Field

[0001] This invention relates to the technical field of caprolactam preparation, and in particular to a system for preparing caprolactam by heterogeneous ammonoximeation and gas-phase rearrangement. Background Technology

[0002] Caprolactam is a crucial raw material for the production of three major product lines: nylon, engineering plastics, and industrial tire cord. In recent years, the demand for caprolactam has been increasing annually. Caprolactam is generally synthesized from cyclohexanone directly with ammonia and hydrogen peroxide to obtain cyclohexanone oxime, which is then produced via the Beckmann rearrangement reaction. Currently, the main industrial method involves using cyclohexanone, ammonia, and hydrogen peroxide as raw materials, and tert-butanol as a solvent. First, an ammoniation reaction is carried out to generate cyclohexanone oxime, yielding a cyclohexanone oxime-tert-butanol-ammonia-aqueous solution. After removing tert-butanol by distillation, toluene is used as an extractant to extract the cyclohexanone oxime, resulting in a cyclohexanone oxime-toluene solution. Toluene is then removed by distillation to obtain the cyclohexanone oxime. Caprolactam is then produced via a liquid-phase rearrangement process using concentrated sulfuric acid or fuming sulfuric acid as a catalyst. The liquid-phase rearrangement process accounts for over 90% of the total caprolactam production capacity. However, the ammoniation reaction using tert-butanol as a solvent requires significant energy consumption during the removal process. In the liquid-phase rearrangement process, the large-scale use of concentrated sulfuric acid and fuming sulfuric acid causes severe equipment corrosion and environmental pollution, and a large amount of ammonia water is added to the system, producing ammonium sulfate as a byproduct. For every ton of caprolactam produced, 1.3–1.8 tons of ammonium sulfate are produced as a byproduct, resulting in high production costs. Therefore, developing green, environmentally friendly, and low-cost caprolactam production processes is crucial.

[0003] Chinese patent CN211339352U discloses an apparatus for preparing caprolactam, comprising a cyclohexanone amination oxime reaction system, a cyclohexanone oxime crystallization system, a rearrangement system, and a caprolactam purification system. The cyclohexanone oxime crystallization system replaces the toluene extraction, separation, and purification processes in the prior art to obtain cyclohexanone oxime crystals. While this method significantly improves the amination oxime process, replacing the toluene extraction, separation, and purification processes in the prior art with a crystallization system to purify cyclohexanone oxime can lead to problems such as pipeline blockage, lengthy processes, and operational difficulties.

[0004] In the Beckmann rearrangement process, the gas-phase Beckmann rearrangement of caprolactam based on a solid acid catalyst is a green, ammonium-sulfate-free process. This process is characterized by no equipment corrosion and no environmental pollution, and the separation and purification of the product are greatly simplified, attracting significant attention from industry professionals. A method for producing caprolactam via gas-phase rearrangement is proposed in Sumitomo Chemical's patent CN1273971A. This method uses a Pentasil-type zeolite catalyst as the catalyst, a lower alcohol with 1-6 carbon atoms as the reaction solvent, and nitrogen as the carrier gas. Cyclohexanone oxime undergoes a gas-phase rearrangement reaction in a series of fluidized bed and fixed bed reactors. This method avoids the use of concentrated sulfuric acid or fuming sulfuric acid as catalysts, thus preventing equipment corrosion and the formation of the byproduct ammonium sulfate. Patent CN101434569B, published by the Research Institute of Petroleum Processing at Sinopec, proposes a gas-phase rearrangement reaction of cyclohexanone oxime in a fixed-bed reactor. The reaction uses MFI-structured molecular sieves as a catalyst, straight-chain or branched fatty alcohols with 1-6 carbon atoms as the reaction solvent, and nitrogen as the carrier gas. This reaction yields caprolactam. Since the Beckmann rearrangement is a strongly exothermic reaction, removing the heat of reaction is a critical issue in the gas-phase rearrangement process. While the introduction of a carrier gas can remove some of the heat of reaction in the two methods described above, nitrogen has a low heat capacity, making the effective removal of the heat of reaction another very important problem.

[0005] The existing ammonium oxime process has the following shortcomings: 1. The process of removing tert-butanol is complex and consumes a lot of materials and energy; 2. Distillation and other steps are carried out at higher temperatures, and the oxime solution has relatively poor stability, which is not conducive to maintaining the selectivity of caprolactam in the rearrangement reaction; 3. When cyclohexanone oxime is transported in a molten state, all pipelines need to be insulated and heated, and are very prone to blockage, making production operations extremely inconvenient.

[0006] The existing Beckmann rearrangement process has the following shortcomings: 1. The liquid-phase rearrangement process uses a large amount of concentrated sulfuric acid and fuming sulfuric acid, which causes serious equipment corrosion and environmental pollution. At the same time, it produces ammonium sulfate as a byproduct, resulting in high production costs. 2. The Beckmann rearrangement is a strongly exothermic reaction, and a large amount of heat of reaction needs to be removed promptly. When using a carrier gas to remove the heat of reaction, a large amount of carrier gas is required, resulting in high energy consumption, and an additional carrier gas recirculation booster is needed. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a system for the heterogeneous ammonoxime and gas-phase rearrangement preparation of caprolactam. The same inert solvent is used in both the cyclohexanone oxime and caprolactam production processes, eliminating the need for an inert solvent recovery system in the heterogeneous ammonoxime process. Furthermore, the inert solvent has a higher specific heat capacity than the carrier gas, allowing for the removal of more heat of reaction from the gas-phase rearrangement.

[0008] The objective of this invention is achieved through the following technical solution: a system for preparing caprolactam by heterogeneous ammonoximation and gas-phase rearrangement, the system comprising a heterogeneous ammonoximation reaction device and a gas-phase rearrangement reaction device connected in series; a cyclohexanone oxime purification device is connected between the heterogeneous ammonoximation reaction device and the gas-phase rearrangement reaction device; the cyclohexanone oxime purification device is provided with an inert solvent inlet; a solvent recycling device is connected to the rear end of the gas-phase rearrangement reaction device; the solvent recycling device is provided with an inert solvent outlet and is connected to the inert solvent inlet of the cyclohexanone oxime purification device; the solvent recycling device is also provided with a caprolactam outlet for producing caprolactam product.

[0009] Preferably, the heterogeneous ammonium oxime reaction apparatus is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oxime reaction under the action of a catalyst to generate cyclohexanone oxime.

[0010] Preferably, the molar ratio of cyclohexanone to hydrogen peroxide is 0.1 to 1:1; the molar ratio of cyclohexanone to ammonia is 0.1 to 5:1; the temperature of the heterogeneous ammonia oxime reaction is 80 to 100°C; and the catalyst is a titanium-silicon-aluminum molecular sieve catalyst.

[0011] Preferably, the cyclohexanone oxime refining apparatus includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence; the catalyst filter is connected to the cyclohexanone oxime outlet of the heterogeneous ammoniation reaction apparatus; the liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet; the filtrate inlet is connected to the catalyst filter; the aqueous phase outlet is connected to a wastewater treatment device; and the oil phase outlet is connected to the deammoniation tower.

[0012] Preferably, the deammoniation tower is provided with a mixed solution outlet, which is connected to the cyclohexanone oxime vaporization device via a pipeline. This pipeline also has a reaction solvent inlet; the reaction solvent inlet is connected to the reaction solvent outlet of the solvent recovery device. The mass ratio of the reaction solvent to the cyclohexanone oxime in the mixed solution at the reaction solvent inlet is 0.1–10:1.

[0013] The reaction solvent liquid is added to prevent cyclohexanone oxime from coking.

[0014] Preferably, the inert solvent is one or more of alkanes with 4 or more carbon atoms, cycloalkanes with 4 or more carbon atoms, and aromatic hydrocarbons with 4 or more carbon atoms; the reaction solvent is one or more of straight-chain fatty alcohols with 1 to 6 carbon atoms, branched-chain fatty alcohols with 1 to 6 carbon atoms, and aromatic hydrocarbons with 6 to 12 carbon atoms.

[0015] Preferably, a cyclohexanone oxime vaporization device is connected between the cyclohexanone oxime purification device and the gas-phase rearrangement reaction device; the cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulating pump circulated in connection with the cyclohexanone oxime evaporator; the cyclohexanone oxime evaporator is a falling film evaporator or a rising film evaporator, preferably a falling film evaporator; the circulating pump is used to send the unvaporized cyclohexanone oxime at the bottom of the evaporator to the mixed solution inlet of the evaporator.

[0016] Preferably, the cyclohexanone oxime evaporator is provided with a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet; the evaporator outlet is connected to the gas phase rearrangement reaction device through a pipeline, which is also provided with a reaction solvent vapor inlet II; both the reaction solvent vapor inlet I and the reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system.

[0017] The purpose of introducing reaction solvent vapor is to lower the partial pressure of cyclohexanone oxime, thereby aiding its vaporization. If the temperature of the cyclohexanone oxime gas decreases and liquefaction occurs, it is prone to coking. Introducing reaction solvent vapor can raise the temperature of the cyclohexanone oxime gas, preventing liquefaction and coking. At least one of the reaction solvent vapor inlet I and reaction solvent vapor inlet II should have ethanol vapor introduced; more preferably, both inlet II should have reaction solvent vapor introduced for better vaporization of cyclohexanone oxime.

[0018] Preferably, the evaporation temperature of cyclohexanone oxime in the cyclohexanone oxime evaporator is 135–190°C, and the evaporation pressure is 0–0.35 MPa(a); the mass fraction of cyclohexanone oxime in the mixed solution at the inlet of the cyclohexanone oxime evaporator is 15–85%; the mass ratio of the reaction solvent at the reaction solvent vapor inlet I of the cyclohexanone oxime evaporator to the cyclohexanone oxime in the cyclohexanone oxime evaporator is 0–10:1, and the mass ratio of the reaction solvent at the reaction solvent vapor inlet II to the cyclohexanone oxime at the evaporator outlet is 0–10:1.

[0019] Insufficient reaction solvent vapor introduction hinders vaporization and may cause coking, while excessive reaction solvent vapor introduction leads to high energy consumption. Furthermore, the reaction solvent at reaction solvent vapor inlet I and reaction solvent vapor inlet II do not both have a value of 0; that is, at least one reaction solvent vapor inlet must have reaction solvent vapor introduced.

[0020] Preferably, the gas-phase rearrangement reaction apparatus includes a reactor, a regenerator, a gas-catalyst separation device, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separation device is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The regenerator is cyclically connected to the reactor, and the deactivated catalyst in the reactor is passed into the regenerator for regeneration before being passed back into the reactor to ensure long-term operation of the apparatus.

[0021] Preferably, the reactor is one or more combinations of a fixed bed, a moving bed, and a fluidized bed, with a fluidized bed reactor being the most preferred. The regenerator is one or more combinations of a moving bed, a fixed bed, and a fluidized bed, with a fluidized bed regenerator being the most preferred. The gas-catalyst separation equipment is one or more combinations of a cyclone separator, a rapid separator, a metal filter, a ceramic filter, and a gravity settling device; the cooler is a tubular cooler or a plate cooler.

[0022] Preferably, the reactor temperature is 330–450°C, the reactor pressure is 0.1–1 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 0.01–20 h⁻¹. -1 The catalyst inside the reactor is a molecular sieve catalyst with an MFI topological structure. The temperature of the regenerator is 420–480 °C, and the pressure is 0.1–1 MPa(a).

[0023] Preferably, the solvent recycling device includes a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence; the reaction solvent recovery tower is provided with a reaction solvent outlet and a reaction solvent vapor outlet; the inert solvent recovery tower is provided with an inert solvent outlet, and the product in the tower bottom is caprolactam.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The inert solvent removal step after the heterogeneous ammonium oxime reaction is omitted, simplifying the process; (2) Cyclohexanone oxime undergoes a gas-phase rearrangement reaction to generate caprolactam, avoiding the use of concentrated sulfuric acid or fuming sulfuric acid as a catalyst, thus reducing equipment corrosion and the generation of the byproduct ammonium sulfate. (3) Using alkanes, cycloalkanes or aromatics with 4 or more carbon atoms as inert solvents improves the ability to remove gas-phase rearrangement reactions, avoids the use of carrier gas, saves energy, and eliminates the need for a carrier gas circulation booster. (4) After the gas-phase rearrangement reaction is completed, the inert solvent and the reaction solvent in the mixed solution are recovered and can be recycled. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement according to the present invention. Detailed Implementation

[0026] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto: The contents of rearranged products such as caprolactam, cyclohexanone oxime, light components, and heavy components in the crude caprolactam fraction after solvent recovery were calculated using the area normalization method, with the solvent not included in the integration. The relevant reaction evaluation parameters in the examples are defined as follows: Cyclohexanone oxime conversion rate (mol%) = [(100 - cyclohexanone oxime molar percentage in crude caprolactam) / 100] × 100%; Caprolactam selectivity (mol%) = [molar percentage of caprolactam in crude caprolactam / (100 - molar percentage of cyclohexanone oxime in crude caprolactam)] × 100%; Weight airspeed (h) -1 = Mass flow rate of cyclohexanone oxime (kg / h) / Mass of catalyst in fluidized bed reactor (kg).

[0027] Example 1 The heterogeneous ammonium oximation reactor is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oximation reaction in the presence of a catalyst (titanium-silicon-aluminum molecular sieve catalyst) to produce cyclohexanone oxime. Cyclohexanone, 27.5% (w / w) hydrogen peroxide, and 25% (w / w) ammonia are added to the heterogeneous ammonium oximation reactor. The molar ratio of cyclohexanone to hydrogen peroxide is 0.5:1, the molar ratio of cyclohexanone to ammonia is 1:1, and the oximation reaction temperature is 85℃.

[0028] After the reaction is complete, such as Figure 1 As shown, the reaction products are fed from the cyclohexanone oxime outlet of the heterogeneous ammoniation reactor into the cyclohexanone oxime purification unit. The cyclohexanone oxime purification unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence. The liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet. The reaction products are passed through the catalyst filter to separate the catalyst and filtrate. The catalyst is recycled back into the heterogeneous ammoniation reactor, while the filtrate is fed into the liquid-liquid separator from the filtrate inlet. Cyclohexane (inert solvent) enters from the inert solvent inlet, with a cyclohexane to cyclohexanone oxime mass ratio of 3:1. After liquid-liquid separation, the aqueous phase enters the wastewater treatment unit from the aqueous phase outlet, and the oil phase enters the deammoniation tower from the oil phase outlet for deammoniation treatment. The deammoniation tower has a mixed solution outlet, and the resulting mixed solution is a mixture of deammonised cyclohexanone oxime and inert solvent.

[0029] The mixed solution outlet is connected to the cyclohexanone oxime vaporization device via a pipeline. This pipeline also has a reaction solvent inlet, through which ethanol (the reaction solvent) is introduced. The reaction solvent inlet is connected to the reaction solvent outlet of the solvent recovery device. The mass fraction of cyclohexanone oxime in the solution after mixing the mixed solution and ethanol is 20%. The cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulation pump connected to the cyclohexanone oxime evaporator. The circulation pump is used to send unvaporized cyclohexanone oxime at the bottom of the evaporator to the mixed solution inlet of the evaporator. The cyclohexanone oxime evaporator has a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet. The evaporation temperature of the cyclohexanone oxime evaporator is 150°C, and the evaporation pressure of cyclohexanone oxime is 0.12 MPa(a). The evaporator outlet is connected to the gas-phase rearrangement reaction device via a pipeline. This pipeline also has a reaction solvent vapor inlet II. Both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system. The mass ratio of ethanol vapor at reaction solvent vapor inlet I to cyclohexanone oxime in the cyclohexanone oxime evaporator is 2:1, and the mass ratio of ethanol vapor at reaction solvent vapor inlet II to cyclohexanone oxime at the cyclohexanone oxime outlet is 1.5:1.

[0030] The mixed gas from the cyclohexanone oxime vaporization unit is fed into a gas-phase rearrangement reaction unit for a gas-phase rearrangement reaction. The gas-phase rearrangement reaction unit includes a reactor, a regenerator, a gas-catalyst separator, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separator is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The reactor temperature is 400℃, the pressure is 0.18 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 8 h⁻¹. -1 The regenerator temperature is 440℃ and the pressure is 0.18 MPa(a). Deactivated catalyst in the reactor enters the regenerator for regeneration and then returns to the reactor. The reactor outlet product undergoes gas-solid separation in a gas-catalyst separator, condensation in a cooler, and then is fed into a solvent recycling unit.

[0031] The solvent recycling unit comprises a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence. The reaction solvent recovery tower has a reaction solvent outlet and a reaction solvent vapor outlet. The vapor phase in the reaction solvent recovery tower is condensed and exits through the reaction solvent outlet, while the remaining vapor phase exits through the reaction solvent vapor outlet to the reaction solvent vapor inlets I and II of the cyclohexanone oxime evaporator. The liquid phase outlet of the reaction solvent recovery tower is a caprolactam-inert solvent solution, which is connected to the material inlet of the inert solvent recovery tower. The vapor phase at the top of the inert solvent recovery tower is condensed to obtain inert solvent, which is then connected through the inert solvent outlet to the inlet of the liquid-liquid separator in the cyclohexanone oxime purification unit. The bottom product of the inert solvent recovery tower is caprolactam.

[0032] Example 2 The heterogeneous ammonium oximation reactor is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oximation reaction in the presence of a catalyst (titanium-silicon-aluminum molecular sieve catalyst) to produce cyclohexanone oxime. Cyclohexanone, 27.5% (w / w) hydrogen peroxide, and 25% (w / w) ammonia are added to the heterogeneous ammonium oximation reactor. The molar ratio of cyclohexanone to hydrogen peroxide is 0.5:1, the molar ratio of cyclohexanone to ammonia is 1:1, and the oximation reaction temperature is 85℃.

[0033] After the reaction is complete, the reaction product is fed from the cyclohexanone oxime outlet of the heterogeneous ammoniation reactor into the cyclohexanone oxime purification unit. The cyclohexanone oxime purification unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence. The liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet. The reaction product is passed through the catalyst filter to separate the catalyst and filtrate. The catalyst is recycled back into the heterogeneous ammoniation reactor, while the filtrate is fed into the liquid-liquid separator from the filtrate inlet. Cyclohexane (inert solvent) enters from the inert solvent inlet, with a cyclohexane to cyclohexanone oxime mass ratio of 3:1. After liquid-liquid separation, the aqueous phase enters the wastewater treatment unit from the aqueous phase outlet, and the oil phase enters the deammoniation tower from the oil phase outlet for deammoniation treatment. The deammoniation tower has a mixed solution outlet, and the resulting mixed solution is a mixture of deammonised cyclohexanone oxime and the inert solvent.

[0034] The mixed solution outlet is connected to the cyclohexanone oxime vaporization device via a pipeline. This pipeline also has a reaction solvent inlet, through which ethanol (the reaction solvent) is introduced. The reaction solvent inlet is connected to the reaction solvent outlet of the solvent recovery device. The mass fraction of cyclohexanone oxime in the solution after mixing the mixed solution and ethanol is 25%. The cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulation pump connected to the cyclohexanone oxime evaporator. The circulation pump is used to send unvaporized cyclohexanone oxime from the bottom of the evaporator to the mixed solution inlet of the evaporator. The cyclohexanone oxime evaporator has a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet. The evaporation temperature of the cyclohexanone oxime evaporator is 150°C, and the evaporation pressure of cyclohexanone oxime is 0.12 MPa(a). The evaporator outlet is connected to the gas-phase rearrangement reaction device via a pipeline. This pipeline also has a reaction solvent vapor inlet II. Both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system. The mass ratio of ethanol vapor at reaction solvent vapor inlet I to cyclohexanone oxime in the cyclohexanone oxime evaporator is 2:1, and the mass ratio of ethanol vapor at reaction solvent vapor inlet II to cyclohexanone oxime at the cyclohexanone oxime outlet is 1.5:1.

[0035] The mixed gas from the cyclohexanone oxime vaporization unit is fed into a gas-phase rearrangement reaction unit for a gas-phase rearrangement reaction. The gas-phase rearrangement reaction unit includes a reactor, a regenerator, a gas-catalyst separator, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separator is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The reactor temperature is 400℃, the pressure is 0.18 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 8 h⁻¹. -1 The regenerator temperature is 440℃ and the pressure is 0.18 MPa(a). Deactivated catalyst in the reactor enters the regenerator for regeneration and then returns to the reactor. The reactor outlet product undergoes gas-solid separation in a gas-catalyst separator, condensation in a cooler, and then is fed into a solvent recycling unit.

[0036] The solvent recycling unit comprises a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence. The reaction solvent recovery tower has a reaction solvent outlet and a reaction solvent vapor outlet. The vapor phase in the reaction solvent recovery tower is condensed and exits through the reaction solvent outlet, while the remaining vapor phase exits through the reaction solvent vapor outlet to the reaction solvent vapor inlets I and II of the cyclohexanone oxime evaporator. The liquid phase outlet of the reaction solvent recovery tower is a caprolactam-inert solvent solution, which is connected to the material inlet of the inert solvent recovery tower. The vapor phase at the top of the inert solvent recovery tower is condensed to obtain inert solvent, which is then connected through the inert solvent outlet to the inlet of the liquid-liquid separator in the cyclohexanone oxime purification unit. The bottom product of the inert solvent recovery tower is caprolactam.

[0037] Example 3 The heterogeneous ammonium oximation reactor is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oximation reaction in the presence of a catalyst (titanium-silicon-aluminum molecular sieve catalyst) to produce cyclohexanone oxime. Cyclohexanone, 27.5% (w / w) hydrogen peroxide, and 25% (w / w) ammonia are added to the heterogeneous ammonium oximation reactor. The molar ratio of cyclohexanone to hydrogen peroxide is 0.5:1, the molar ratio of cyclohexanone to ammonia is 1:1, and the oximation reaction temperature is 85℃.

[0038] After the reaction is complete, the reaction product is fed from the cyclohexanone oxime outlet of the heterogeneous ammoniation reactor into the cyclohexanone oxime purification unit. The cyclohexanone oxime purification unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence. The liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet. The reaction product is passed through the catalyst filter to separate the catalyst and filtrate. The catalyst is recycled back into the heterogeneous ammoniation reactor, while the filtrate is fed into the liquid-liquid separator from the filtrate inlet. Cyclohexane (inert solvent) enters from the inert solvent inlet, with a cyclohexane to cyclohexanone oxime mass ratio of 3:1. After liquid-liquid separation, the aqueous phase enters the wastewater treatment unit from the aqueous phase outlet, and the oil phase enters the deammoniation tower from the oil phase outlet for deammoniation treatment. The deammoniation tower has a mixed solution outlet, and the resulting mixed solution is a mixture of deammonised cyclohexanone oxime and the inert solvent.

[0039] The mixed solution outlet is connected to the cyclohexanone oxime vaporization device via a pipeline. This pipeline also has a reaction solvent inlet, through which methanol (the reaction solvent) is introduced. The reaction solvent inlet is connected to the reaction solvent outlet of the solvent recovery device. The mass fraction of cyclohexanone oxime in the solution after mixing the mixed solution and methanol is 20%. The cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulation pump connected to the cyclohexanone oxime evaporator. The circulation pump is used to send unvaporized cyclohexanone oxime at the bottom of the evaporator to the mixed solution inlet of the evaporator. The cyclohexanone oxime evaporator has a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet. The evaporation temperature of the cyclohexanone oxime evaporator is 150°C, and the evaporation pressure of cyclohexanone oxime is 0.12 MPa(a). The evaporator outlet is connected to the gas-phase rearrangement reaction device via a pipeline. This pipeline also has a reaction solvent vapor inlet II. Both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system. The mass ratio of methanol vapor at reaction solvent vapor inlet I to cyclohexanone oxime in the cyclohexanone oxime evaporator is 2:1, and the mass ratio of methanol vapor at reaction solvent vapor inlet II to cyclohexanone oxime at the cyclohexanone oxime outlet is 1.5:1.

[0040] The mixed gas from the cyclohexanone oxime vaporization unit is fed into a gas-phase rearrangement reaction unit for a gas-phase rearrangement reaction. The gas-phase rearrangement reaction unit includes a reactor, a regenerator, a gas-catalyst separator, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separator is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The reactor temperature is 400℃, the pressure is 0.18 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 8 h⁻¹. -1The regenerator temperature is 440℃ and the pressure is 0.18 MPa(a). Deactivated catalyst in the reactor enters the regenerator for regeneration and then returns to the reactor. The reactor outlet product undergoes gas-solid separation in a gas-catalyst separator, condensation in a cooler, and then is fed into a solvent recycling unit.

[0041] The solvent recycling unit comprises a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence. The reaction solvent recovery tower has a reaction solvent outlet and a reaction solvent vapor outlet. The vapor phase in the reaction solvent recovery tower is condensed and exits through the reaction solvent outlet, while the remaining vapor phase exits through the reaction solvent vapor outlet to the reaction solvent vapor inlets I and II of the cyclohexanone oxime evaporator. The liquid phase outlet of the reaction solvent recovery tower is a caprolactam-inert solvent solution, which is connected to the material inlet of the inert solvent recovery tower. The vapor phase at the top of the inert solvent recovery tower is condensed to obtain inert solvent, which is then connected through the inert solvent outlet to the inlet of the liquid-liquid separator in the cyclohexanone oxime purification unit. The bottom product of the inert solvent recovery tower is caprolactam.

[0042] Comparative Example 1 The heterogeneous ammonium oximation reactor is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oximation reaction in the presence of a catalyst (titanium-silicon-aluminum molecular sieve catalyst) to produce cyclohexanone oxime. Cyclohexanone, 27.5% (w / w) hydrogen peroxide, and 25% (w / w) ammonia are added to the heterogeneous ammonium oximation reactor. The molar ratio of cyclohexanone to hydrogen peroxide is 0.5:1, the molar ratio of cyclohexanone to ammonia is 1:1, and the oximation reaction temperature is 85℃.

[0043] After the reaction is complete, the reaction product is fed from the cyclohexanone oxime outlet of the heterogeneous ammoniation reactor into the cyclohexanone oxime purification unit. The cyclohexanone oxime purification unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence. The liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet. The reaction product is passed through the catalyst filter to separate the catalyst and filtrate. The catalyst is recycled back into the heterogeneous ammoniation reactor, while the filtrate is fed into the liquid-liquid separator from the filtrate inlet. Cyclohexane (inert solvent) enters from the inert solvent inlet, with a cyclohexane to cyclohexanone oxime mass ratio of 3:1. After liquid-liquid separation, the aqueous phase enters the wastewater treatment unit from the aqueous phase outlet, and the oil phase enters the deammoniation tower from the oil phase outlet for deammoniation treatment. The deammoniation tower has a mixed solution outlet, and the resulting mixed solution is a mixture of deammonised cyclohexanone oxime and the inert solvent. The mixed solution is fed into a distillation column to remove cyclohexane. The vapor phase at the top of the column is condensed to obtain liquid cyclohexane, which is then recycled to the liquid-liquid separator. The liquid phase at the bottom of the column is cyclohexanone oxime.

[0044] Cyclohexanone oxime is introduced into a cyclohexanone oxime vaporization device. The pipeline also includes a reaction solvent inlet, which allows ethanol (the reaction solvent) to pass through. This reaction solvent inlet is connected to the reaction solvent outlet of a solvent recovery system. The mass fraction of cyclohexanone oxime in the solution after mixing cyclohexanone oxime and ethanol is 60%. The cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulation pump connected to the evaporator. The circulation pump is used to send unvaporized cyclohexanone oxime from the bottom of the evaporator to the mixed solution inlet of the evaporator. The cyclohexanone oxime evaporator has a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet. The evaporation temperature of the cyclohexanone oxime evaporator is 150°C, and the evaporation pressure of cyclohexanone oxime is 0.12 MPa(a). The evaporator outlet is connected to a gas-phase rearrangement reaction device via a pipeline, which also includes a reaction solvent vapor inlet II. Both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system. The mass ratio of ethanol vapor at reaction solvent vapor inlet I to cyclohexanone oxime in the cyclohexanone oxime evaporator is 2:1, and nitrogen is simultaneously introduced as a carrier gas with a molar ratio of nitrogen to cyclohexanone oxime of 3:1. The mass ratio of ethanol vapor at reaction solvent vapor inlet II to cyclohexanone oxime at the outlet of the cyclohexanone oxime evaporator is 1.5:1, and nitrogen is simultaneously introduced as a carrier gas with a molar ratio of nitrogen to cyclohexanone oxime of 2:1.

[0045] The mixed gas from the cyclohexanone oxime vaporization unit is fed into a gas-phase rearrangement reaction unit for a gas-phase rearrangement reaction. The gas-phase rearrangement reaction unit includes a reactor, a regenerator, a gas-catalyst separator, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separator is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The reactor temperature is 400℃, the pressure is 0.18 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 8 h⁻¹. -1 The regenerator temperature is 440℃ and the pressure is 0.18 MPa(a). Deactivated catalyst in the reactor enters the regenerator for regeneration and then returns to the reactor. The reactor outlet product undergoes gas-solid separation in a gas-catalyst separator, condensation in a cooler, and then is fed into a solvent recycling unit.

[0046] The solvent recycling unit comprises a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence. The reaction solvent recovery tower has a reaction solvent outlet and a reaction solvent vapor outlet. The vapor phase in the reaction solvent recovery tower is condensed and exits through the reaction solvent outlet, while the remaining vapor phase exits through the reaction solvent vapor outlet to the reaction solvent vapor inlets I and II of the cyclohexanone oxime evaporator. The liquid phase outlet of the reaction solvent recovery tower is a caprolactam-inert solvent solution, which is connected to the material inlet of the inert solvent recovery tower. The vapor phase at the top of the inert solvent recovery tower is condensed to obtain inert solvent, which is then connected through the inert solvent outlet to the inlet of the liquid-liquid separator in the cyclohexanone oxime purification unit. The bottom product of the inert solvent recovery tower is caprolactam.

[0047] Comparative Example 2 The heterogeneous ammonium oximation reactor is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oximation reaction in the presence of a catalyst (titanium-silicon-aluminum molecular sieve catalyst) to produce cyclohexanone oxime. Cyclohexanone, 27.5% (w / w) hydrogen peroxide, and 25% (w / w) ammonia are added to the heterogeneous ammonium oximation reactor. The molar ratio of cyclohexanone to hydrogen peroxide is 0.5:1, the molar ratio of cyclohexanone to ammonia is 1:1, and the oximation reaction temperature is 85℃.

[0048] After the reaction is complete, the reaction product is fed from the cyclohexanone oxime outlet of the heterogeneous ammoniation reactor into the cyclohexanone oxime purification unit. The cyclohexanone oxime purification unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence. The liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet. The reaction product is passed through the catalyst filter to separate the catalyst and filtrate. The catalyst is recycled back into the heterogeneous ammoniation reactor, while the filtrate is fed into the liquid-liquid separator from the filtrate inlet. Cyclohexane (inert solvent) enters from the inert solvent inlet, with a cyclohexane to cyclohexanone oxime mass ratio of 3:1. After liquid-liquid separation, the aqueous phase enters the wastewater treatment unit from the aqueous phase outlet, and the oil phase enters the deammoniation tower from the oil phase outlet for deammoniation treatment. The deammoniation tower has a mixed solution outlet, and the resulting mixed solution is a mixture of deammonised cyclohexanone oxime and the inert solvent. The mixed solution is fed into a distillation column to remove cyclohexane. The vapor phase at the top of the column is condensed to obtain liquid cyclohexane, which is then recycled to the liquid-liquid separator. The liquid phase at the bottom of the column is cyclohexanone oxime.

[0049] Cyclohexanone oxime is introduced into a cyclohexanone oxime vaporization device. The pipeline also includes a reaction solvent inlet, which is methanol (the reaction solvent). This reaction solvent inlet is connected to the reaction solvent outlet of a solvent recovery system. The mass fraction of cyclohexanone oxime in the solution after mixing cyclohexanone oxime and methanol is 60%. The cyclohexanone oxime vaporization device includes a cyclohexanone oxime evaporator and a circulation pump connected to the evaporator. The circulation pump is used to send unvaporized cyclohexanone oxime from the bottom of the evaporator to the mixed solution inlet of the evaporator. The cyclohexanone oxime evaporator has a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet. The evaporation temperature of the cyclohexanone oxime evaporator is 150°C, and the evaporation pressure of cyclohexanone oxime is 0.12 MPa(a). The evaporator outlet is connected to a gas-phase rearrangement reaction device via a pipeline, which also includes a reaction solvent vapor inlet II. Both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system. The mass ratio of methanol vapor at reaction solvent vapor inlet I to cyclohexanone oxime in the cyclohexanone oxime evaporator is 2:1, and nitrogen is simultaneously introduced as a carrier gas with a molar ratio of nitrogen to cyclohexanone oxime of 3:1. The mass ratio of methanol vapor at reaction solvent vapor inlet II to cyclohexanone oxime at the cyclohexanone oxime outlet is 1.5:1, and nitrogen is simultaneously introduced as a carrier gas with a molar ratio of nitrogen to cyclohexanone oxime of 2:1.

[0050] The mixed gas from the cyclohexanone oxime vaporization unit is fed into a gas-phase rearrangement reaction unit for a gas-phase rearrangement reaction. The gas-phase rearrangement reaction unit includes a reactor, a regenerator, a gas-catalyst separator, and a cooler. The material inlet of the reactor is connected to the evaporator outlet of the cyclohexanone oxime evaporator, and the gas-solid two-phase inlet of the gas-catalyst separator is connected to the gas-solid two-phase outlet of the reactor. The separated catalyst solid is returned to the reactor. The reactor temperature is 400℃, the pressure is 0.18 MPa(a), and the mass hourly space velocity (HSV) of cyclohexanone oxime in the reactor is 8 h⁻¹. -1 The regenerator temperature is 440℃ and the pressure is 0.18 MPa(a). Deactivated catalyst in the reactor enters the regenerator for regeneration and then returns to the reactor. The reactor outlet product undergoes gas-solid separation in a gas-catalyst separator, condensation in a cooler, and then is fed into a solvent recycling unit.

[0051] The solvent recycling unit comprises a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence. The reaction solvent recovery tower has a reaction solvent outlet and a reaction solvent vapor outlet. The vapor phase in the reaction solvent recovery tower is condensed and exits through the reaction solvent outlet, while the remaining vapor phase exits through the reaction solvent vapor outlet to the reaction solvent vapor inlets I and II of the cyclohexanone oxime evaporator. The liquid phase outlet of the reaction solvent recovery tower is a caprolactam-inert solvent solution, which is connected to the material inlet of the inert solvent recovery tower. The vapor phase at the top of the inert solvent recovery tower is condensed to obtain inert solvent, which is then connected through the inert solvent outlet to the inlet of the liquid-liquid separator in the cyclohexanone oxime purification unit. The bottom product of the inert solvent recovery tower is caprolactam.

[0052] Quantitative analysis of caprolactam products was performed using a GC8000 chromatograph with FID detection. An OV-1 capillary column with a diameter of 0.25 mm and a diameter of 30 m was used. The vaporization chamber temperature was 248 °C, and the detection chamber temperature was 240 °C. The column temperature was programmed, with a constant temperature of 110 °C for 8 min, a rate of 15 °C / min to 230 °C, and then a constant temperature for 14 min.

[0053] Table 1 As shown in Table 1, the device in this patent can produce caprolactam products with high conversion rate and high selectivity, and has low energy consumption and low cost.

[0054] Comparative Examples 1-2 employ a traditional process method, where cyclohexane is removed before the mixed solution enters the gas-phase rearrangement unit. However, using nitrogen as the carrier gas not only affects product conversion and selectivity but also results in very high energy consumption. Furthermore, an additional circulating carrier gas compressor is required due to the need for a carrier gas in the system. Additionally, because cyclohexane removal leaves molten cyclohexanone oxime as the bottom liquid product of the cyclohexane removal tower, it is prone to causing blockages during pipeline transportation, making long-term operation of the unit difficult.

[0055] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A system for preparing caprolactam by heterogeneous ammonoximation and gas-phase rearrangement, characterized in that, The system includes a heterogeneous ammonium oxime reaction unit and a gas-phase rearrangement reaction unit connected in series. A cyclohexanone oxime purification unit is connected between the heterogeneous ammoniation reaction unit and the gas-phase rearrangement reaction unit; the cyclohexanone oxime purification unit is equipped with an inert solvent inlet; a cyclohexanone oxime vaporization unit is connected between the cyclohexanone oxime purification unit and the gas-phase rearrangement reaction unit; the cyclohexanone oxime vaporization unit includes a cyclohexanone oxime evaporator; the cyclohexanone oxime evaporator is equipped with a mixed solution inlet, a reaction solvent vapor inlet I, and an evaporator outlet; the evaporator outlet is connected to the gas-phase rearrangement reaction unit via a pipeline, which is also equipped with a reaction solvent vapor inlet II; both reaction solvent vapor inlet I and reaction solvent vapor inlet II are connected to the reaction solvent vapor outlet of the solvent recovery system; The gas-phase rearrangement reaction apparatus is connected to a solvent recycling device at its rear end; the solvent recycling device is provided with an inert solvent outlet and is connected to the inert solvent inlet of the cyclohexanone oxime purification apparatus; the solvent recycling device is also provided with a caprolactam outlet for producing caprolactam products.

2. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 1, characterized in that, The heterogeneous ammonium oxime reaction apparatus is equipped with a cyclohexanone inlet, a hydrogen peroxide inlet, and an ammonia inlet. Cyclohexanone, hydrogen peroxide, and ammonia undergo a heterogeneous ammonium oxime reaction under the action of a catalyst to generate cyclohexanone oxime.

3. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 2, characterized in that, The molar ratio of cyclohexanone to hydrogen peroxide is 0.1~1:1; the molar ratio of cyclohexanone to ammonia is 0.1~5:1; the temperature of the heterogeneous ammonia oxime reaction is 80~100℃; and the catalyst is a titanium-silicon-aluminum molecular sieve catalyst.

4. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in any one of claims 1-3, characterized in that, The cyclohexanone oxime refining unit includes a catalyst filter, a liquid-liquid separator, and a deammoniation tower connected in sequence; the catalyst filter is connected to the cyclohexanone oxime outlet of the heterogeneous ammoniation reaction unit; the liquid-liquid separator has a filtrate inlet, an inert solvent inlet, an aqueous phase outlet, and an oil phase outlet; the filtrate inlet is connected to the catalyst filter; the aqueous phase outlet is connected to a wastewater treatment unit; and the oil phase outlet is connected to the deammoniation tower.

5. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 4, characterized in that, The deammoniation tower is provided with a mixed solution outlet, which is connected to the cyclohexanone oxime vaporization device via a pipeline. The pipeline is also provided with a reaction solvent inlet. The reaction solvent inlet is connected to the reaction solvent outlet of the solvent recovery device. The mass ratio of the reaction solvent at the reaction solvent inlet to the cyclohexanone oxime in the mixed solution is 0.1~10:

1.

6. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 5, characterized in that, The inert solvent is one or more of alkanes with 4 or more carbon atoms, cycloalkanes with 4 or more carbon atoms, and aromatic hydrocarbons with 4 or more carbon atoms; the reaction solvent is one or more of straight-chain fatty alcohols with 1 to 6 carbon atoms, branched fatty alcohols with 1 to 6 carbon atoms, and aromatic hydrocarbons with 6 to 12 carbon atoms.

7. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in any one of claims 1-3, characterized in that, The cyclohexanone oxime vaporization device includes a circulating pump that is circulated in connection with the cyclohexanone oxime evaporator.

8. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 7, characterized in that, The evaporation temperature of cyclohexanone oxime in the cyclohexanone oxime evaporator is 135~190 ℃, and the evaporation pressure is 0~0.35 MPa(a); the mass fraction of cyclohexanone oxime in the mixed solution at the inlet of the cyclohexanone oxime evaporator is 15~85%; the mass ratio of the reaction solvent at the reaction solvent vapor inlet I to the cyclohexanone oxime in the cyclohexanone oxime evaporator is 0~10:1, and the mass ratio of the reaction solvent at the reaction solvent vapor inlet II to the cyclohexanone oxime at the evaporator outlet is 0~10:

1.

9. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 1, characterized in that, The gas-phase rearrangement reaction apparatus comprises a reactor, a gas-catalyst separation device, and a cooler connected in sequence; the reactor temperature is 330~450 ℃, the reactor pressure is 0.1~1 MPa(a), and the cyclohexanone oxime mass hourly space velocity in the reactor is 0.01~20 h⁻¹. -1 The catalyst inside the reactor is a molecular sieve catalyst with an MFI topology.

10. The system for preparing caprolactam by heterogeneous ammoniation and gas-phase rearrangement as described in claim 1, characterized in that, The solvent recycling device includes a reaction solvent recovery tower and an inert solvent recovery tower connected in sequence; the reaction solvent recovery tower is provided with a reaction solvent outlet and a reaction solvent vapor outlet; the inert solvent recovery tower is provided with an inert solvent outlet.

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