Green and efficient caprolactam production process and device

Abstract

The invention relates to the field of caprolactam production, and discloses a green and efficient production process and device. The process comprises the following steps: continuously oximating cyclohexanone and hydroxylamine in a microreactor under the catalysis of mesoporous silica solid acid; carrying out gas phase rearrangement on cyclohexanone-oxime in the presence of a ZSM-5 molecular sieve under the assistance of microwaves; coupling, rectifying and purifying the crude product through a four-stage molecular sieve membrane; and performing catalytic cracking on the by-product to obtain N2 / H2O and recycling. The device comprises a micro-reaction unit, a microwave-radial reactor, a membrane coupling rectifying tower group and a tail gas cracking unit. Zero emission of ammonium sulfate is achieved, the product purity is larger than or equal to 99.95%, and energy consumption is reduced by 45%.

Description

Technical Field

[0001] This invention relates to the field of caprolactam production, and more specifically, to a green and efficient caprolactam production process and apparatus. Background Technology

[0002] Caprolactam, a key monomer of nylon-6, has a global annual production exceeding ten million tons. Traditional industrial production primarily employs the cyclohexanone-hydroxylamine route (HPO method), which involves oxime conversion, Beckmann rearrangement, and multi-stage purification. However, existing technologies are limited by highly polluting catalysts, inefficient reactor design, and complex separation processes, resulting in high energy consumption and difficult-to-treat byproducts, making it difficult to meet the requirements of green chemical development. The specific shortcomings of existing technologies are as follows:

[0003] 1. The oxime process causes severe pollution.

[0004] Current processes commonly use sulfuric acid as the oxime catalyst, generating 2.8-3.5 tons of ammonium sulfate as a byproduct for every ton of caprolactam produced. The treatment of large amounts of sulfur-containing wastewater not only increases the cost of waste disposal but also wastes resources. Although solid acid catalysts have been researched, they suffer from low specific surface areas (typically <300 m²). 2 Problems such as the ease of dissolution of acid sites ( / g) prevent it from maintaining high activity in continuous production.

[0005] 2. The rearrangement and separation processes consume too much energy.

[0006] The Beckmann rearrangement requires a molten state at 120-130°C, relying on a large amount of steam to maintain the reaction temperature. Subsequent distillation purification necessitates 5-8 distillation columns in series due to the close boiling points of caprolactam and byproducts (e.g., the boiling point difference of methylcyclopentene is <5°C), resulting in energy consumption accounting for over 65% of the total production cost. Current molecular sieve membrane applications are limited to single dehydration processes, lacking effective solutions for the synergistic removal of light and heavy components.

[0007] 3. Insufficient utilization of by-products as resources

[0008] The light nitrogen-containing compounds generated in the reaction (such as cyclohexenylamine) are mostly incinerated, which wastes the value of nitrogen and increases CO2 emissions. Although catalytic cracking technology has been attempted, traditional fixed-bed reactors have drawbacks such as rapid catalyst deactivation due to carbon buildup (operation time <200 hours) and low nitrogen yield (<90%), making it impossible to achieve closed-loop recycling.

[0009] Therefore, a green and efficient caprolactam production process and apparatus are proposed to address the above problems. Summary of the Invention

[0010] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a green and efficient caprolactam production process and apparatus to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a green and efficient caprolactam production process and apparatus, comprising the following steps performed in sequence:

[0012] (a) Cyclohexanone and hydroxylamine solution undergo a continuous oxime reaction in the presence of a solid acid catalyst via a microreactor system to generate cyclohexanone oxime;

[0013] (b) Cyclohexanone oxime underwent a gas-phase Beckmann rearrangement reaction with molecular sieve catalyst and microwave energy field assistance to obtain crude caprolactam;

[0014] (c) Crude caprolactam is purified through four stages: removal of light components, dehydration, removal of heavy components and final product purification, with at least three stages integrating molecular sieve membrane separation technology.

[0015] (d) The nitrogen-containing byproducts generated during the reaction process are converted into nitrogen and water by catalytic cracking, and the resulting nitrogen is recycled for the hydroxylamine synthesis process.

[0016] Preferably, in step (a): the solid acid catalyst is a sulfonic acid-functionalized mesoporous silica material with a specific surface area of ​​not less than 800 m² / g, a pore size distribution of 2-10 nm, and a surface acid density of not less than 1.2 mmol / g. The microreactor system consists of 3-8 parallel microchannel reaction modules, each module is equipped with staggered static mixing units, the reaction temperature is controlled at 60-80℃, the material residence time does not exceed 30 seconds, and the cyclohexanone conversion rate is not less than 99.5%.

[0017] Preferably, in step (b): the gas-phase Beckmann rearrangement reaction is carried out in a radially flowing fixed-bed reactor, wherein an alumina protective layer and a ZSM-5 molecular sieve catalyst layer are sequentially arranged along the gas flow direction, wherein the silicon-aluminum molar ratio of the molecular sieve is 30-50, and microwave-assisted heating is used in pulse modulation mode, with electromagnetic waves at a frequency of 2.45 GHz acting on the catalyst bed to control the bed temperature in the range of 350-380°C, so that the selectivity of the rearrangement reaction is not less than 98%.

[0018] Preferably, the four-stage purification process in step (c) specifically includes: first-stage light component removal: removing light components below C5 using a NaA-type hydrophilic molecular sieve membrane under reduced pressure; second-stage dehydration: achieving deep dehydration by maintaining a high vacuum on the permeate side using a hydrophobic Silicalite-1 molecular sieve membrane; third-stage heavy component removal: separating high molecular weight heavy components under low temperature conditions using a scraped membrane evaporator; and fourth-stage purification: obtaining caprolactam product with a purity of not less than 99.95% through a zirconium oxide hollow fiber membrane.

[0019] Preferably, in step (d): the nitrogen-containing byproduct is contacted with a lanthanum-cobalt / cerium oxide bifunctional catalyst in a fluidized bed reactor and decomposed at a temperature of 450-500°C to generate nitrogen and water. The heat released in the decomposition reaction is recovered by a waste heat boiler to generate steam. The steam is supplied to the reboiler of the refining section, and the nitrogen generated is purified by pressure swing adsorption and returned to the hydroxylamine synthesis unit.

[0020] Preferably, the process system is mainly composed of four core units working together, with efficient linkage between materials and energy: the integrated micro-reaction unit completes the mixing and pre-reaction conversion of cyclohexanone and hydroxylamine solutions, and the intermediate products enter the microwave-radial flow rearrangement reactor, where the key rearrangement reaction is completed under the action of microwave electromagnetic field and layered catalyst bed; after preliminary separation, the rearranged products enter a four-stage membrane coupled distillation column group (passing through light oil removal, dehydration, heavy oil removal, and purification columns in sequence), with molecular sieve membrane separation integrated at the top of each column, and energy cascade utilization is achieved between columns through heat pump units; finally, the unreacted raw material gas and tail gas enter the tail gas recycling cracking unit, where waste heat is recovered after fluidized bed cracking, and nitrogen is purified and recycled back to the system, forming a closed loop.

[0021] Preferably, the online catalyst regeneration system includes: a catalyst switching chamber arranged in parallel for replacing deactivated catalysts without shutting down; a supercritical carbon dioxide cleaning module for removing carbon buildup on the catalyst surface by adjusting the pressure above the critical point; and a heat pump compressor unit with a two-stage compression configuration for increasing the heat of the low-temperature steam at the top of the light-light-removal tower and supplying it to the reboiler of the dehydration tower, thereby reducing the overall energy consumption of the system by 40-45%.

[0022] Preferably, the central intelligent control system includes an online mass spectrometer for real-time monitoring of the material composition at the outlet of each reactor; and an artificial intelligence optimization module that dynamically adjusts the following based on the monitoring data: the microreactor temperature control accuracy is within ±0.5℃, the microwave emission power is matched with the real-time catalyst activity, and the distillation column reflux ratio is automatically optimized based on the product purity feedback value.

[0023] The technical effects and advantages of this invention are as follows:

[0024] 1. Completely eliminate sulfur-containing pollutant emissions

[0025] By employing a sulfonic acid-functionalized mesoporous silica solid acid catalyst (specific surface area ≥800 m²), 2 This invention replaces traditional sulfuric acid with a cyclohexanone (acid density ≥1.2 mmol / g) solution, achieving a cyclohexanone conversion rate of over 99.5% within a microreactor, thus eliminating the generation of ammonium sulfate as a byproduct at the source. Compared to the traditional process that generates 2.8-3.5 tons of ammonium sulfate per ton of product, this invention achieves zero discharge of sulfur-containing waste and reduces waste treatment costs by over 92%.

[0026] 2. The overall energy consumption of the reaction-separation process is reduced by more than 50%.

[0027] This innovative approach combines gas-phase microwave-assisted rearrangement with four-stage membrane-coupled distillation: microwave radiation raises the Beckmann rearrangement temperature from 120°C in the molten state to 350-380°C in the gas phase, reducing the reaction time to 1 / 5 and steam consumption by 60%. The molecular sieve membrane (NaA / Silicalite-1 / ZnO2) works in synergy with the heat pump system to achieve simultaneous and efficient removal of light components, water, and heavy components. The distillation energy consumption is reduced from 65% of the total energy consumption in the traditional process to 30%, and the overall energy consumption of the entire process is ≤1.8 tons of standard coal / ton of product (compared to ≥3.6 tons in the traditional process).

[0028] 3. Product purity breaks through industry bottlenecks.

[0029] The four-stage purification system combines selective separation via molecular sieve membranes with low-temperature scraped-film evaporation: the hydrophobic Silicalite-1 membrane maintains a vacuum of ≤0.3 kPa on the permeate side, removing moisture to ≤10 ppm; the ZnO2 hollow fiber membrane precisely traps impurities such as cyclic dimers, resulting in a final product purity of 99.97% (higher than the national standard of 99.95%), and an ultraviolet absorbance of ≤0.03 (compared to 0.05-0.08 for traditional processes), meeting the production requirements of high-end nylon-6.

[0030] 4. By-product resource utilization rate exceeds 99%.

[0031] A nitrogen-containing tail gas full-cycle system is constructed: a lanthanum-cobalt / cerium oxide bifunctional catalyst decomposes byproducts into N2 and H2O at 450-500℃, with a nitrogen selectivity of ≥99.9%. The heat from the decomposition is recovered by a waste heat boiler to generate 0.8MPa steam, which meets 40% of the heat demand of the distillation column. The nitrogen purified from PSA is recycled for hydroxylamine synthesis, achieving a nitrogen utilization rate of 98.5% and reducing carbon emissions by 62% compared to the traditional incineration method. Attached Figure Description

[0032] Figure 1 This is a flowchart of the process of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] As attached Figure 1 As shown, (1) a green and efficient caprolactam production process and apparatus, comprising the following steps performed in sequence:

[0035] (a) Cyclohexanone and hydroxylamine solution undergo a continuous oxime reaction in the presence of a solid acid catalyst via a microreactor system to generate cyclohexanone oxime;

[0036] (b) Cyclohexanone oxime underwent a gas-phase Beckmann rearrangement reaction with molecular sieve catalyst and microwave energy field assistance to obtain crude caprolactam;

[0037] (c) Crude caprolactam is purified through four stages: removal of light components, dehydration, removal of heavy components and final product purification, with at least three stages integrating molecular sieve membrane separation technology.

[0038] (d) The nitrogen-containing byproducts generated during the reaction process are converted into nitrogen and water by catalytic cracking. The resulting nitrogen is recycled for the hydroxylamine synthesis process. First, cyclohexanone and a 25wt% hydroxylamine solution are fed into the microreactor system at a molar ratio of 1:1.05. This is followed by the addition of a sulfonic acid-based mesoporous silica catalyst (specific surface area 820 m²). 2 Cyclohexanone oxime was obtained by reacting in a microchannel at 70℃ and 0.8MPa for 28 seconds ( / g) to produce cyclohexanone oxime (conversion rate 99.6%). The oxime solution was then atomized and introduced into a radial flow reactor for gas-phase rearrangement under ZSM-5 molecular sieve (Si / Al = 35) catalysis and microwave power of 365℃ and 120W / g to produce crude caprolactam (selectivity 98.7%). The crude product was then passed sequentially through a four-stage distillation column: a primary light component removal column (0.8kPa, removing C5 light components to ≤40ppm) → a secondary dehydration column (Silicalite-1 membrane permeate side 0.25kPa, moisture ≤8ppm) → a tertiary scraped membrane heavy component removal column (145℃, heavy component ≤0.02%) → a quaternary purification column (ZnO2 membrane, purity 99.96%). Finally, the rearrangement tail gas and oxime treatment waste gas were combined and reacted with La in a fluidized bed. 0.8 Co 0.2 O x The / CeO2 catalyst was cracked at 480℃, and the resulting nitrogen gas was purified by PSA (99.99% purity) and returned to the hydroxylamine synthesis unit.

[0039] (2) In step (a): the solid acid catalyst is a sulfonic acid-functionalized mesoporous silica material with a specific surface area of ​​not less than 800 m² / g, a pore size distribution of 2-10 nm, and a surface acid density of not less than 1.2 mmol / g. The microreactor system consists of 3-8 parallel microchannel reaction modules, each module containing staggered static mixing units. The reaction temperature is controlled at 60-80℃, and the material residence time does not exceed 30 seconds, achieving a cyclohexanone conversion rate of not less than 99.5%. The sulfonic acid-functionalized mesoporous silica is prepared by a sol-gel method: tetraethyl orthosilicate, hexadecyl trioxide, and other organic compounds are mixed. Methylammonium bromide and 3-mercaptopropyltrimethoxysilane were mixed in a molar ratio of 10:2:1, hydrolyzed, and then oxidized with hydrogen peroxide to obtain a catalyst with a pore size of 6.5 nm and an acid density of 1.28 mmol / g. This catalyst was then packed into six parallel microchannel modules (each module measuring 200 × 100 × 10 mm). Each module contained 20 sets of titanium alloy static mixing units (diamond-shaped with a staggered angle of 45°). The cyclohexanone feed flow rate was controlled at 15 L / min, the hydroxylamine injection pressure differential was 0.3 MPa, and the reaction temperature was maintained at 70 ± 0.3 °C using a PID temperature control system. Online NIR spectroscopy confirmed that the residual amount of cyclohexanone was 0.25%.

[0040] (3) In step (b): the gas-phase Beckmann rearrangement reaction is carried out in a radially flowing fixed-bed reactor. The reactor is sequentially equipped with an alumina protective layer and a ZSM-5 molecular sieve catalyst layer along the gas flow direction. The silicon-aluminum molar ratio of the molecular sieve is 30-50. Microwave-assisted heating is used with pulse modulation. Electromagnetic waves at a frequency of 2.45 GHz are applied to the catalyst bed to control the bed temperature in the range of 350-380℃, so that the selectivity of the rearrangement reaction is not less than 98%. The radially flowing reactor is layered along the gas flow direction: the lower layer is a γ-Al2O3 protective layer (particle size 3-5 mm). The catalyst bed is 50cm high, with the upper layer being ZSM-5 molecular sieve (particle size 1-2mm, bed height 120cm). Cyclohexanone oxime solution is preheated to 280℃ and then sprayed into the reactor as atomized particles with a diameter of 50μm. The carrier gas nitrogen flow rate to material volume ratio is 1.8:1. The microwave system uses a magnetron array (total power 30kW), and the working cycle is controlled by a pulse modulator (5s on / 1s off). The power density is adjusted to 115W / g using a fiber optic temperature probe in the bed to ensure that the catalyst bed temperature gradient is ≤3℃ / m. After the rearranged products are collected in a cold trap, HPLC analysis shows that the ε-caprolactam content is 98.9%.

[0041] (4) The four-stage purification process in step (c) specifically includes: First-stage light component removal: removing light components below C5 using a NaA-type hydrophilic molecular sieve membrane under reduced pressure; Second-stage dehydration: achieving deep dehydration by maintaining a high vacuum on the permeate side using a hydrophobic Silicalite-1 molecular sieve membrane; Third-stage heavy component removal: separating high molecular weight heavy components under low temperature conditions using a scraped membrane evaporator; Fourth-stage purification: obtaining caprolactam product with a purity of not less than 99.95% through a zirconium oxide hollow fiber membrane. The operation of the four-stage purification system is as follows: First-stage light component removal: crude caprolactam enters a light component removal tower with a diameter of 1.2m, and a NaA molecular sieve membrane (membrane area 15m²) is integrated at the top of the tower. 2 Operating pressure: 0.8 kPa; reboiler temperature: 85℃; condensate content at the top of the column: ≤35 ppm cyclopentene; Secondary dehydration: Reboiler liquid is pumped into a dehydration column (1.0 m diameter); Silicalite-1 membrane module (10 m² membrane area) is installed at the top of the column. 2 The permeate side is maintained under a vacuum of 0.25 kPa. The moisture content of the bottom product is determined to be 6 ppm by Karl Fischer method. Three-stage deweighting: The material enters a scraped film evaporator (evaporation area 5 m²). 2 The rotor speed was controlled at 15 rpm and the temperature at 145℃. The content of cyclic dimers in the bottom residue was 0.015%. Four-stage refining: the evaporated fraction entered the refining tower (diameter 0.8m), and a ZnO2 hollow fiber membrane (fiber inner diameter 0.5mm) was coupled in the middle of the tower. The reflux ratio was 1.8. The absorbance of the product produced in the tower bottom was measured by ultraviolet spectrophotometer and was 0.022 (280nm).

[0042] (5) In step (d): the nitrogen-containing byproducts are contacted with a lanthanum-cobalt / cerium oxide bifunctional catalyst in a fluidized bed reactor and decomposed at a temperature of 450-500℃ to generate nitrogen and water. The heat released during the decomposition reaction is recovered by a waste heat boiler to generate steam, which is supplied to the reboiler in the refining section. The nitrogen generated is purified by pressure swing adsorption and returned to the hydroxylamine synthesis unit. The nitrogen-containing byproducts (mainly cyclohexenylamine and unreacted hydroxylamine) are discharged at 120m 3 A flow rate of [flow rate] / h is fed into a fluidized bed reactor (bed diameter 0.8m), where it reacts with a lanthanum-cobalt / cerium oxide catalyst (La:Co:Ce molar ratio 1:0.2:5) at a fluidization number of 1.8 and a temperature of 485℃. Mass spectrometry analysis of the outlet gas shows an N2 content of 99.95%. The pyrolysis gas is then passed through a waste heat boiler (heat exchange area 50m²). 2 The temperature is lowered to 150℃, generating 1.3t / h of saturated steam at 0.8MPa. This steam is directly fed into the reboiler of the dehydration tower (100% heat load matching). After cooling, the cracked gas enters the PSA module (filled with lithium-modified 13X molecular sieve adsorbent), where 99.995% high-purity nitrogen is obtained at an adsorption pressure of 1.2MPa and a desorption pressure of 0.01MPa. The nitrogen is then pressurized by a compressor to the operating pressure of 1.5MPa for the hydroxylamine synthesis unit and reused.

[0043] (6) The process system is mainly composed of four core units working together, with efficient linkage between materials and energy: the integrated micro-reaction unit completes the mixing and pre-reaction conversion of cyclohexanone and hydroxylamine solution feed, and the intermediate product enters the microwave-radial flow rearrangement reactor, where the key rearrangement reaction is completed under the action of microwave electromagnetic field and layered catalyst bed; after preliminary separation, the rearranged product enters a four-stage membrane coupled distillation tower group (passing through light removal, dehydration, heavy removal, and purification towers in sequence), with molecular sieve membrane separation integrated at the top of each tower, and energy cascade utilization is achieved between the towers through heat pump units; finally, the unreacted raw material gas and tail gas enter the tail gas recycling cracking unit, where waste heat is recovered after fluidized bed cracking, and nitrogen is purified and recycled back to the system to form a closed loop. The device is constructed as follows: Micro-reaction unit: cyclohexanone is fed by a gear metering pump (accuracy ± The system includes a 316L stainless steel main channel (Φ25mm) with a 0.5% input, and hydroxylamine solution injected through a high-pressure injection valve (opening time 0.1s). The microchannel array consists of 6 sets of reaction plates (200×100mm) connected in parallel, with serpentine channels etched to a depth of 0.8mm within the plates. The microwave-radial reactor features an 8mm thick quartz shield, a microwave resonant cavity equipped with 8 magnetrons (single tube power 3.75kW), a catalyst bed divided into upper and lower zones, and temperature difference sensors spaced 30cm apart. The four-stage distillation column group is connected to the light-light removal column and the dehydration column via a downcomer. The heat pump unit uses R245fa working fluid with a compression ratio of 3.5. The tail gas cracking unit has a gas distribution plate (35% opening rate) at the bottom of the fluidized bed reactor, and the PSA module contains 4 adsorption towers (Φ0.6m×3m).

[0044] (7) The online catalyst regeneration system includes: a catalyst switching chamber set in parallel for replacing deactivated catalysts without shutting down the system; a supercritical carbon dioxide cleaning module for removing carbon buildup on the catalyst surface by adjusting the pressure above the critical point; and a heat pump compressor unit with a two-stage compression configuration to increase the heat of the low-temperature steam at the top of the light-light-removal tower and supply it to the reboiler of the dehydration tower, thereby reducing the overall energy consumption of the system by 40-45%. The catalyst switching chamber is equipped with a dual-valve structure (ball valve + gate valve). When switching, the feed valve of the backup chamber is opened first, and the main chamber valve is closed after 0.5 seconds to ensure that the pressure fluctuation is ≤0.05MPa. The operating conditions of the supercritical CO2 cleaning module are: CO2 pressure 12MPa, temperature 38℃, and circulation flow rate 8m. 3 / h, after cleaning, the acid density of the catalyst is restored to 98.2% of the initial value; the heat pump system adopts a two-stage centrifugal compressor (first stage compression ratio 2.2, second stage 1.6), which heats the 45℃ steam at the top of the light precipitator to 85℃ and supplies it to the reboiler of the dehydration tower. The total energy consumption of the system is reduced to 1.82 tons of standard coal / ton of product (42% lower than the traditional process).

[0045] (8) The central intelligent control system includes an online mass spectrometer that monitors the composition of the material at the outlet of each reactor in real time; an artificial intelligence optimization module that dynamically adjusts the following based on the monitoring data: the temperature control accuracy of the microreactor is within ±0.5℃, the microwave emission power is matched with the real-time activity of the catalyst, and the reflux ratio of the distillation column is automatically optimized based on the product purity feedback value. The central control system (50) connects each device through the Modbus protocol: the online mass spectrometer (501) collects the reactor outlet component data every 30 seconds; the AI ​​optimization module (502) establishes a dynamic model based on the LSTM neural network and performs the following controls: the temperature of the microreactor is adjusted according to the real-time feedback of the cyclohexanone conversion rate, and the opening of the heat transfer oil valve is adjusted (accuracy ±0.3℃); the microwave power is dynamically adjusted according to the change of the dielectric loss factor of the ZSM-5 catalyst (measured every 8 hours), and the output of the magnetron (±5kW) is dynamically adjusted; the reflux ratio of the distillation column is automatically optimized according to the product absorbance value detected by UV online, according to the preset algorithm (for every 0.01 increase in absorbance, the reflux ratio increases by 0.2).

[0046] Example 1:

[0047] Step 1: Solid acid-catalyzed continuous oxime catalysis

[0048] 1. Catalyst loading: Sulfonic acid-functionalized mesoporous silica catalyst (specific surface area 820 m²) is loaded. 2 (1.25 mmol / g, acid density 1.25 mmol / g) was filled into 6 parallel microchannel modules of the microreactor system. Each module contained a titanium alloy static mixing unit (channel diameter 1.5 mm, mixing unit spacing 10 mm).

[0049] 2. Raw material feeding:

[0050] Cyclohexanone was fed into the main feed pipe at a flow rate of 12.5 L / min via a metering pump;

[0051] Hydroxylamine solution (25 wt%) was injected at 3.2 L / min via a side-line injector, and the two streams of material merged at the microchannel inlet.

[0052] 3. Reaction control:

[0053] Maintain the reaction temperature at 68±0.5℃ (controlled by jacket heat transfer oil circulation);

[0054] Residence time: 25 seconds; System pressure: 0.8 MPa;

[0055] The residual amount of cyclohexanone at the outlet is monitored by an online infrared analyzer to be ≤0.3% (conversion rate ≥99.7%).

[0056] Step 2: Microwave-assisted gas-phase rearrangement

[0057] 1. Catalyst activation:

[0058] The lower layer of the radial flow reactor is filled with a γ-Al2O3 protective layer (particle size 3-5 mm, bed height 0.5 m); the upper layer is filled with ZSM-5 molecular sieve (Si / Al = 35, particle size 1-2 mm, bed height 1.2 m), and activated with nitrogen at 400℃ for 2 hours.

[0059] 2. Feed vaporization:

[0060] The cyclohexanone oxime solution produced in step 1 is preheated to 280°C and then sprayed into the inlet of the rearrangement reactor through an atomizing nozzle.

[0061] The carrier gas (nitrogen) flow rate is controlled at 1.5 times the material volume ratio.

[0062] 3. Microwave rearrangement operation:

[0063] Start the 2.45GHz microwave generator in pulse mode (5s operation / 1s interval), with a power density of 120W / g catalyst;

[0064] The catalyst bed temperature was controlled at 365±5℃, and the reaction pressure at 0.3MPa.

[0065] Gas chromatography online monitoring shows rearrangement selectivity ≥98.5%.

[0066] Step 3: Quadruple membrane coupled distillation purification

[0067] 1. Level 1 remission:

[0068] Crude caprolactam enters the light component removal tower (operating pressure 0.8 kPa), with a NaA molecular sieve membrane integrated at the top of the tower; the temperature at the bottom of the tower is controlled at 85℃ and the temperature at the top of the tower is controlled at 45℃ to remove light components below C5 (content ≤50ppm).

[0069] 2. Secondary dehydration:

[0070] The liquid from the light-weight removal tower is pumped into the dehydration tower, and a Silicalite-1 hydrophobic membrane is installed at the top of the tower.

[0071] The vacuum level on the permeation side is maintained at 0.25 kPa, and the moisture content of the material collected from the bottom of the tower is ≤8 ppm.

[0072] 3. Three-stage weight removal:

[0073] The liquid in the bottom of the dehydration tower enters the scraped film evaporator (operating temperature 145℃), with an evaporation surface linear velocity of 2.5 m / s;

[0074] Heavy components (such as cyclic dimers) are discharged from the bottom residue port (content ≤0.02%).

[0075] 4. Fourth-level refinement:

[0076] The deweighted material enters the refining tower and is coupled with a ZnO2 hollow fiber membrane (pore size 0.4nm);

[0077] With a top reflux ratio of 1.8, the bottom product is caprolactam with a purity of 99.97% (UV absorbance 0.025).

[0078] Step 4: Byproduct pyrolysis and resource recycling

[0079] 1. Pyrolysis reaction:

[0080] The nitrogen-containing tail gas from the oxime / rearrangement process is collected and fed into a fluidized bed reactor;

[0081] with La 0.8 Co 0.2 O x / CeO2 catalyst (particle size 80-100μm) reacted in contact at 480℃;

[0082] At a space velocity of 2000 h⁻¹, the outlet N₂ concentration is ≥99.93%.

[0083] 2. Energy recovery:

[0084] The pyrolysis gas is cooled to 150℃ in a waste heat boiler to produce 0.8MPa saturated steam (yield 1.2t / h);

[0085] Steam is delivered to the dehydration tower reboiler, replacing 40% of the externally supplied steam.

[0086] 3. Nitrogen reuse:

[0087] The pyrolysis gas enters the PSA purification module (the adsorbent is lithium-modified 13X molecular sieve);

[0088] Purified nitrogen (99.995% purity) is pressurized to 1.0 MPa and returned to the hydroxylamine synthesis unit. Step 5: Catalyst regeneration and system maintenance

[0089] 1. Solid acid regeneration:

[0090] Supercritical CO2 cleaning is initiated every 500 hours:

[0091] ① Switch to the backup catalyst compartment;

[0092] ② CO2 is introduced into the main chamber and pressurized to 10MPa, and the temperature is raised to 35℃;

[0093] ③ Circulate and clean for 2 hours to dissolve and remove carbon deposits (activity recovery ≥98%).

[0094] 2. Catalyst rearrangement replacement:

[0095] When the rearrangement selectivity drops to 97%, the reactor is shut down;

[0096] The molecular sieve was removed under nitrogen protection and regenerated by air roasting at 550°C for 4 hours.

[0097] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0098] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0099] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A green and efficient caprolactam production process and apparatus, characterized in that, This includes the following steps performed sequentially: (a) Cyclohexanone and hydroxylamine solution undergo a continuous oxime reaction in the presence of a solid acid catalyst via a microreactor system to generate cyclohexanone oxime; (b) Cyclohexanone oxime underwent a gas-phase Beckmann rearrangement reaction with molecular sieve catalyst and microwave energy field assistance to obtain crude caprolactam; (c) Crude caprolactam is purified through four stages: removal of light components, dehydration, removal of heavy components, and final product purification. At least three of these stages integrate molecular sieve membrane separation technology. (d) The nitrogen-containing byproducts generated during the reaction process are converted into nitrogen and water by catalytic cracking, and the resulting nitrogen is recycled for the hydroxylamine synthesis process.

2. The green and efficient caprolactam production process and apparatus according to claim 1, characterized in that, In step (a): the solid acid catalyst is a sulfonic acid-functionalized mesoporous silica material with a specific surface area of ​​not less than 800 m² / g, a pore size distribution of 2-10 nm, and a surface acid density of not less than 1.2 mmol / g. The microreactor system consists of 3-8 parallel microchannel reaction modules, each module is equipped with staggered static mixing units, the reaction temperature is controlled at 60-80℃, the material residence time does not exceed 30 seconds, and the cyclohexanone conversion rate is not less than 99.5%.

3. The green and efficient caprolactam production process and apparatus according to claim 1, characterized in that: In step (b), the gas-phase Beckmann rearrangement reaction is carried out in a radially flowing fixed-bed reactor. The reactor is sequentially equipped with an alumina protective layer and a ZSM-5 molecular sieve catalyst layer along the gas flow direction. The silicon-aluminum molar ratio of the molecular sieve is 30-50. Microwave-assisted heating is performed using pulse modulation, with electromagnetic waves at a frequency of 2.45 GHz acting on the catalyst bed to control the bed temperature in the range of 350-380°C, so that the selectivity of the rearrangement reaction is not less than 98%.

4. The green and efficient caprolactam production process and apparatus according to claim 1, characterized in that: Step (c) includes the following four purification processes: First-stage light component removal: removing light components below C5 using a NaA-type hydrophilic molecular sieve membrane under reduced pressure; Second-stage dehydration: achieving deep dehydration by maintaining a high vacuum on the permeate side using a hydrophobic Silicalite-1 molecular sieve membrane; Third-stage heavy component removal: separating high molecular weight heavy components under low temperature conditions using a scraped membrane evaporator; Fourth-stage purification: obtaining caprolactam product with a purity of not less than 99.95% through a zirconium oxide hollow fiber membrane.

5. The green and efficient caprolactam production process and apparatus according to claim 1, characterized in that: In step (d): the nitrogen-containing byproducts are contacted with a lanthanum-cobalt / cerium oxide bifunctional catalyst in a fluidized bed reactor and decomposed at a temperature of 450-500°C to generate nitrogen and water. The heat released in the decomposition reaction is recovered by a waste heat boiler to generate steam. The steam is supplied to the reboiler in the refining section. The nitrogen generated is purified by pressure swing adsorption and returned to the hydroxylamine synthesis unit.

6. A green and efficient caprolactam production process and apparatus for implementing any one of claims 1-5, characterized in that, The process system is mainly composed of four core units working together, with efficient linkage between materials and energy: the integrated micro-reaction unit completes the mixing and pre-reaction conversion of cyclohexanone and hydroxylamine solutions, and the intermediate products enter the microwave-radial flow rearrangement reactor, where the key rearrangement reaction is completed under the action of microwave electromagnetic field and layered catalyst bed; after preliminary separation, the rearranged products enter a four-stage membrane coupled distillation column group (passing through light oil removal, dehydration, heavy oil removal, and purification columns in sequence), with molecular sieve membrane separation integrated at the top of each column, and energy cascade utilization is achieved between columns through heat pump units; finally, the unreacted raw material gas and tail gas enter the tail gas recycling cracking unit, where waste heat is recovered after fluidized bed cracking, and nitrogen is purified and recycled back to the system, forming a closed loop.

7. The green and efficient caprolactam production process and apparatus according to claim 6, characterized in that: The online catalyst regeneration system includes: a catalyst switching chamber set in parallel for replacing deactivated catalysts without stopping the system; a supercritical carbon dioxide cleaning module for removing carbon buildup on the catalyst surface by adjusting the pressure above the critical point; and a heat pump compressor unit with a two-stage compression configuration for increasing the heat of the low-temperature steam at the top of the light-light-removal tower and supplying it to the reboiler of the dehydration tower, thereby reducing the overall energy consumption of the system by 40-45%.

8. The green and efficient caprolactam production process and apparatus according to claim 6, characterized in that: The central intelligent control system includes an online mass spectrometer that monitors the composition of the material at the outlet of each reactor in real time; and an artificial intelligence optimization module that dynamically adjusts the microreactor temperature control accuracy within ±0.5℃ range, matches the microwave emission power with the real-time catalyst activity, and automatically optimizes the distillation column reflux ratio based on the product purity feedback value.

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