Method for synthesizing antioxidant 168 by adopting micro-channel continuous flow process

Abstract

A method for synthesizing an antioxidant 168 by using a microchannel continuous flow process belongs to the technical field of chemical synthesis, adopts a microchannel esterification-microchannel ester exchange two-stage continuous process, and realizes the reaction of phosphorus trichloride and low-carbon chain alcohol to generate phosphorous acid dialkyl ester through the efficient mass transfer characteristic of a microchannel reactor in the esterification stage; hydrogen chloride generated by the reaction is immediately and directionally led out and recycled as industrial hydrochloric acid, a neutralizer does not need to be added, a microchannel reactor with an inner wall immobilized catalyst or a high-temperature and high-pressure strengthening process is adopted in the ester exchange stage, the reaction without catalyst residue or participation of the dialkyl phosphite and the 2, 4-di-tert-butylphenol is realized, no salt impurities are generated in the whole process, and the production cost is reduced. The method solves the problems of quality, cost, safety and the like caused by the use of a neutralizer, complex desalination, catalyst residue, salt-containing wastewater, remarkable amplification effect and the like in the traditional process, and has the industrial advantages of continuity, cleanness and high purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to antioxidant 168, and more particularly to a clean production process for synthesizing antioxidant 168 by using a micro-channel continuous flow process. BACKGROUND

[0002] Antioxidant 168 (tris(2,4-di-tert-butylphenyl) phosphite) is a widely used high-efficiency auxiliary antioxidant, which can produce a synergistic effect with the main antioxidant to significantly improve the thermal oxidation resistance of polymers such as polypropylene and polyethylene. Currently, the mainstream process for synthesizing antioxidant 168 in industry is still a batch kettle reaction. This process usually involves esterification of 2,4-di-tert-butylphenol with phosphorus trichloride in the presence of an organic solvent and a catalyst, and the chemical reaction formula is: 3C 14 H 22 O + PCl3→ C 42 H 63 O 3P + 3HCl↑. Although this route is mature, it has multiple technical bottlenecks that need to be solved due to the inherent defects of traditional reaction kettles.

[0003] First, the production efficiency is low and the energy consumption is high. Batch operation includes a large amount of non-productive time, such as material addition, heating and cooling of the reaction system, post-reaction treatment, and reaction kettle cleaning, etc. The equipment utilization rate and space-time yield are low. At the same time, the huge heat capacity of the reaction kettle leads to a slow heating and cooling process, resulting in significant energy waste.

[0004] Second, the product quality is unstable and there are many side reactions. The esterification reaction is a strong exothermic reaction, and in the presence of an alkaline catalyst, the raw material phosphorus trichloride and the product phosphite group are extremely sensitive to trace water and prone to hydrolysis and other side reactions. In a traditional stirred tank, the macro-mixing efficiency is low, and the mass transfer and heat transfer rates are slow, which can easily lead to local overheating or local high concentration. Local overheating can exacerbate product decomposition, discoloration, and other side reactions, while local accumulation of phosphorus trichloride can exacerbate its side reactions with trace water or phenol, generating substances such as dichlorides, acidic impurities, etc., resulting in high acid value, deep color, and decreased thermal stability of the final product. These factors cause fluctuations in product quality between different production batches, making it difficult to meet the requirements of high-end application fields.

[0005] Third, the production process has significant safety hazards. Phosphorus trichloride is a dangerous chemical with high reactivity and intense heat release when it comes into contact with water. The liquid holdup in a batch kettle is large, and once the reaction gets out of control, such as heat accumulation due to cooling failure or the introduction of trace moisture due to poor equipment sealing, it may cause material overflow and even explosions, posing a high risk of production safety.

[0006] Fourth, the process amplification effect is remarkable: from small test to industrial production of amplification process, with the increase of the volume of the reactor, mixing, heat transfer, mass transfer efficiency is further deteriorated, become the key to capacity and quality, amplification process is complex and full of uncertainty.

[0007] In recent years, continuous flow chemistry as a process intensification technology, in the field of fine chemicals synthesis shows great potential, its core lies in the use of micro-channel reactor high specific surface area, realize instant homogeneous mixing and efficient heat transfer of materials. However, how to apply this advanced process to the synthesis of antioxidant 168 this particular molecule, realize from laboratory preparation to industrial production of tons of stable, efficient, safe conversion, the prior art does not give a clear, systematic and industrial implementation of the solution.

[0008] Therefore, it has important practical significance to develop a new type of synthesis process which can fundamentally solve the above problems. SUMMARY

[0009] In order to solve the problems of the prior art, the present application provides a method for synthesizing antioxidant 168 by micro-channel continuous flow process, which realizes the continuous production of antioxidant 168.

[0010] The technical problem to be solved by the present application is solved by the following technical scheme: A method for synthesizing antioxidant 168 by micro-channel continuous flow process, comprising the following steps: (1) raw material pretreatment: select high purity raw materials, the purity of phosphorus trichloride is greater than or equal to 99%, the purity of low carbon chain alcohol is greater than or equal to 99.5%, phosphorus trichloride, low carbon chain alcohol and 2,4-di-tert-butyl phenol are respectively filtered through 5 μm precision filter to remove impurities, and 2,4-di-tert-butyl phenol is heated and melted to 75-85℃; The low carbon chain alcohol is preferably anhydrous ethanol.

[0011] (2) micro-channel esterification reaction: phosphorus trichloride and low carbon chain alcohol are pumped into a ceramic coating micro-channel reactor by a metering pump at a molar ratio of 1:(2.0-2.5) simultaneously, the reaction temperature is controlled at 0-5℃, the pressure is normal, the residence time is 10-20 min, the hydrogen chloride gas generated in the reaction is immediately discharged through the hydrophobic gas permeable membrane integrated in the inner wall of the reactor, and is recovered as 28-32% industrial hydrochloric acid by mass fraction through the water absorption system, and the reaction liquid is continuously discharged to obtain a dialkyl phosphite solution; The ceramic coating micro-channel reactor has a channel inner diameter of 0.5-1 mm, a channel number of 800-1200, and a total volume of 400-600 mL. The pump-in speed of the ceramic coating micro-channel reactor for pumping in phosphorus trichloride and low carbon chain alcohol by the metering pump is 40-60 mL / min.

[0012] (3) Microchannel transesterification reaction: The dialkyl phosphite solution obtained in step (2) is mixed with molten 2,4-di-tert-butylphenol at a molar ratio of 1:(3.0-3.2) and pumped into a microchannel transesterification reactor. The reaction temperature is controlled at 190-220℃, the pressure at -0.09~0.2 MPa, and the residence time at 30-40 min. The low-carbon chain alcohols produced by the reaction are recovered by condensation and recycled for use in step (2). The microchannel transesterification reactor is a ceramic microchannel reactor with a catalyst supported on the inner wall. The catalyst is tetraisopropyl titanate, the support is γ-Al2O3, the catalyst loading is 5-8 wt%, and the total volume is 700-900 mL. The catalyst is immobilized on the surface of a support using a sol-gel method and then coated onto the inner wall of the microchannel.

[0013] The microchannel transesterification reactor is used to pump diethyl phosphite solution and molten 2,4-di-tert-butylphenol at a rate of 25-35 mL / min. The reaction temperature of the microchannel ester exchange reactor is controlled at 190-200℃, the system is evacuated to -0.09MPa, and the residence time is 30-35 min. The byproduct, low-carbon chain alcohol, is condensed and recovered, then sent to a distillation column for purification to a purity of ≥97%, and then recycled for esterification reaction.

[0014] (4) Post-processing: The reaction solution from step (3) is fed into a continuous crystallizer, n-heptane is added for crystallization, filtered and vacuum dried to obtain antioxidant 168 product; In the crystallization process, the amount of n-heptane used is 1.2-1.8 times the mass of the reaction solution, the crystallization temperature is 0-5℃, the temperature of the vacuum drying process is 45-55℃, and the drying time is 6-8 h.

[0015] In this invention, in the microchannel transesterification reaction of step (3), the microchannel transesterification reactor with the catalyst immobilized on the inner wall can be replaced with a catalyst-free device. When the microchannel transesterification reactor without the catalyst participates in the microchannel transesterification reaction of step (3), the temperature is controlled at 210-220℃, the pressure at 0.1-0.2 MPa, and the residence time at 35-40 min.

[0016] In this invention, the process method, compared to existing technologies, eliminates the desalination step and employs a microchannel reactor. During the esterification reaction stage, the accumulation of HCl is fundamentally avoided due to the efficient mass transfer and directional separation capabilities of the microchannels: Firstly, mass transfer kinetics are enhanced, and the specific surface area of ​​the microchannel reactor reaches 5000-10000 m². 2 / m 3This process is 100-1000 times faster than traditional batch reactors. Phosphorus trichloride and ethanol flow in a plug flow within the microchannels, with no backmixing. The material mixing time is only in the millisecond range. After HCl is generated, it rapidly diffuses to the channel wall driven by the concentration gradient, avoiding the problem of local HCl enrichment in batch reactors, as well as the resulting equipment corrosion, product oxidation, and the formation of salt impurities from other amines. Then, a permeable membrane is used for directional separation. The inner wall of the esterification microchannel reactor is integrated with a hydrophobic permeable membrane. After HCl gas is generated, it is immediately discharged to the absorption tower through the permeable membrane. The HCl concentration in the reaction system is always maintained at an extremely low level, avoiding corrosion and side reactions without the need for a neutralizing agent. Furthermore, thermodynamic equilibrium control is applied. The immediate discharge of HCl is equivalent to removing the reaction product, which continuously promotes the forward esterification reaction (PCl3 + 2ROH → (RO)2POH + 2HCl↑), improving the conversion rate while completely eliminating the formation of salt impurities, thus eliminating the need for a desalination process in principle.

[0017] In the transesterification reaction of this invention, traditional transesterification processes use homogeneous Lewis acid catalysts. However, because these catalysts dissolve in the reaction solution and form a homogeneous system with the product, they must be separated by multiple washing processes, which can easily lead to residues and an increase in the acid value of the product. In contrast, the transesterification reaction of this invention uses a supported catalyst placed on the inner wall of a microchannel reactor. Tetraisopropyl titanate is immobilized on the surface of a γ-Al₂O₃ support using a sol-gel method, and then coated onto the inner wall of the microchannel. The immobilized catalyst forms a stable structure of active site-support-channel wall, with the catalytic active site Ti... 4+ Exposed to the inner wall surface of the channel, it does not enter the reaction liquid; when the reactants flow within the microchannel, they come into contact with the catalyst active sites on the channel wall, Ti 4+ Coordinated with oxygen atoms in the ester group, polarizing the ester bond -POR, reducing the activation energy of the transesterification reaction, promoting the substitution of alkoxy-OR by aryloxy-O-Ar, after the reaction is completed, the product flows directly out of the channel, and the catalyst remains immobilized on the wall, without the need for separation; the reaction conditions in the microchannel, such as temperature, pressure, and flow rate, are precisely controllable, the service life of the immobilized catalyst can reach more than 8000 hours, and the activity decay is uniform, without affecting the stability of the product.

[0018] In the transesterification reaction of this invention, a catalyst-free approach can also be adopted. Utilizing the pressure-resistant properties of the microchannels, high conversion rates can be achieved without a catalyst through transesterification under high temperature and pressure. In terms of reaction kinetics, the rate constant k of the transesterification reaction follows the Arrhenius equation k=Ae^(-k / k). -Ea / RTTraditional batch reactors suffer from low temperature control precision and cannot withstand high temperatures, requiring catalysts to lower the activation energy Ea. Microchannel technology offers high temperature control precision, stably controlling temperatures of 210-220℃, increasing the reaction rate constant by 3-5 times and offsetting the high activation energy effect without a catalyst. Thermodynamically, the pressure within the microchannel increases the partial pressure of the reactants, effectively increasing the concentration of the reaction system. According to the law of mass action, this drives the reversible transesterification reaction (RO)₂POH + 3ArOH ⇌ (ArO)₃P + 2ROH in the forward direction. Simultaneously, the reduced pressure side stream immediately distills off the byproduct ethanol, further disrupting the equilibrium and achieving a conversion rate of over 95%. In terms of product control, the plug flow characteristics of the microchannel prevent local overheating. At 210-220℃, the decomposition rate of antioxidant 168 is extremely low, and in the absence of a catalyst, product isomerization is not triggered, ensuring the product's acid value and color indicators.

[0019] In this invention, based on the precise coupling of transport and reaction within the microchannels, product loss is reduced, and the heat transfer coefficient within the microchannels reaches 1000-5000 W / (m²). 2 The flow rate (·K) is 10-50 times that of a batch reactor, rapidly removing the exothermic reaction ΔH=-128 kJ / mol and the endothermic reaction ΔH=+86 kJ / mol, avoiding side reactions caused by temperature fluctuations. Simultaneously, the plug flow ensures consistent residence time for all materials, increasing reaction selectivity by over 99% and reducing byproducts by 90%. The immediately discharged HCl is absorbed by water to obtain 28-32% industrial hydrochloric acid, achieving an atom utilization rate of 98%. The ethanol byproduct of transesterification is purified by distillation and recycled for the esterification reaction, achieving an ethanol recycling rate of ≥89%.

[0020] Compared with the prior art, the present invention has the following advantages: (1) This application uses a microchannel reactor to immediately export and recover the hydrogen chloride generated by the esterification reaction through process design, without the need to add a neutralizing agent, thus eliminating the generation of salt impurities from the source, completely eliminating the desalination process, and discharging no salty wastewater. Only industrial hydrochloric acid that can be recycled is produced, which meets the requirements of green chemistry. (2) The low-carbon chain alcohols of the process by-products of this application are recycled, which improves the atom economy, has outstanding environmental benefits, eliminates neutralization and desalination, and reduces the overall production cost; (3) The process of this application provides two transesterification reaction schemes. In the catalyst-supported scheme, the catalyst is immobilized and there is no homogeneous catalyst residue. In the catalyst-free scheme, the use of catalyst is completely avoided. The product has low acid value, low color, and significantly better purity than the existing process. (4) The process of this application uses a microchannel reactor, which has a mass transfer efficiency 10-100 times higher than that of a batch reactor, high temperature control accuracy, no backmixing, a reduction of more than 90% in side reactions, a product yield of more than 95.5%, and an increase in production efficiency of more than 30%. Attached Figure Description

[0021] Figure 1 The infrared spectrum comparison diagram of the antioxidant 168 product of this application and the prior art; Figure 2 A comparison chart of the environmental protection and production efficiency indicators of the process of this application and the prior art; Figure 3 Characterization diagram of the transesterification microchannel supported catalyst in the process of this application (magnified comparison); Figure 4 This is a comparison chart of the quality of the antioxidant 168 product of this application with existing technology and scaled-up products. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0023] Example 1 This embodiment uses the supported catalyst scheme of this application to carry out small-scale pilot preparation.

[0024] 1. Equipment Preparation Precision filter: PTFE-5μm (Hangzhou Kelu), filtration accuracy 5 μm, material PTFE, flow rate 10-100mL / min, working pressure 0.1-0.3 MPa; Raw material melting tank: RG-5L (Zibo Youheng), volume 5 L, material 316L stainless steel, temperature control range from room temperature to 300℃, temperature control accuracy ±0.5℃; High-precision metering pump: BT300-2J (Baoding Lange), flow range 0.001-300 mL / min, accuracy ±0.5%, working pressure 0-0.6 MPa, material 316L+PTFE; Esterification microchannel reactor: MCR-100 (Wuhan Guoxin), channel inner diameter 0.8 mm, 1000 channels, total volume 500 mL, material 316L + ceramic coating, specific surface area 8000 m² 2 / m 3 ; Hydrophobic and breathable membrane module: PTFE-G2 (Shenzhen Membrane Technology), breathable pore size 0.2 μm, material PTFE, temperature range -20~150℃, gas flux 10-20 L / (m²) 2 ·min) HCl absorption tower: XF-50 (Weihai Xinyuan), packing type: θ ring, material: PP, tower diameter: 50 mm, tower height: 800 mm, absorption efficiency: ≥99%; Intermediate storage tank: CG-10L (Wuxi Xinlong), volume 10 L, material 316L stainless steel, with stirring device, stirring speed 60 r / min; Ester exchange microchannel reactor: MCR-100 (Wuhan Guoxin), with custom-supported catalyst, channel inner diameter 0.8 mm, total volume 800 mL, 316L material with ceramic coating, inner wall coated with γ-Al2O3 support (particle size 20-40 mesh, specific surface area 180 m²). 2 / g), supported tetraisopropyl titanate catalyst, with a loading of 6 wt% and a coating thickness of 50-80 μm; Ethanol condensation and recovery unit: LN-5L (Wuxi Guanya), condensation area 0.5 m² 2 Material: 316L; Temperature control range: -20~50℃; Condensation efficiency: ≥95%; Ethanol distillation column: JT-10L (Weihai Xinyuan), column diameter 80 mm, column height 1200 mm, packing type stainless steel θ rings, theoretical number of trays 15, distillation accuracy ≥97%; Continuous crystallizer: JJ-10L (Wuxi Guanya), volume 10 L, material 316L, temperature control range -10~100℃, stirring speed 40-100 r / min, temperature control accuracy ±0.5℃; Plate and frame filter: BK-0.1 (Hangzhou Kelu), filtration area 0.1 m² 2 Material: 316L; Working pressure: 0.1-0.3MPa; Filter cloth precision: 1 μm. Vacuum dryer: ZK-50 (Shanghai Vacuum Drying Equipment), volume 50 L, material 316L, temperature control range from room temperature to 200℃, vacuum degree ≤-0.095 MPa, temperature control accuracy ±1℃.

[0025] 2. Raw material preparation Phosphorus trichloride (PCl3): Industrial grade, 99.2% purity after distillation and purification, moisture ≤0.05%, single batch continuous feed 1.25 kg (9.25 mol); Anhydrous ethanol (C2H5OH): Industrial grade, purity 99.7%, moisture ≤0.03%, single batch continuous feed 1.01 kg (21.96 mol); 2,4-Di-tert-butylphenol: Industrial grade, purity 99.5%, melting point 52-54℃, single batch continuous feed 2.59 kg (12.13 mol); n-Heptane: Industrial grade, purity 99.0%, moisture ≤0.05%, single batch dosage 7.5 kg (based on 1.5 times the mass of the reaction solution); Tetraisopropyl titanate: Industrial grade, 98.0% purity, immobilized on the inner wall of the reactor, no additional feeding required; γ-Al₂O₃ support: particle size 20-40 mesh, specific surface area 180 m² 2 / g, pore size 5-10 nm, the amount of coating used on the inner wall of the reactor is about 50 g.

[0026] 3. Catalyst immobilization process ① Carrier pretreatment: γ-Al2O3 powder was placed in a muffle furnace and calcined for 4 h to remove surface adsorbed water and impurities; ② Sol preparation: Dissolve 10 g of tetraisopropyl titanate in 50 mL of anhydrous ethanol, stir well, and slowly add 5 mL of deionized water. Hydrolyze at room temperature for 2 h to form a transparent titanium sol. ③ Coating onto the substrate: Titanium sol was uniformly coated onto the inner wall of the transesterification microchannel reactor, with a coating thickness controlled at 50-80 μm. After air-drying at room temperature, it was dried at 120℃ for 4 h, and then calcined at 550℃ for 3 h to allow tetraisopropyl titanate to form stable chemical bonds with γ-Al2O3. The catalyst loading was 6 wt%. ④ Activation: Rinse the reactor channel with anhydrous ethanol to remove unsupported free catalyst on the surface, and purge with nitrogen for 30 min before use.

[0027] 4. Preparation process ① Raw material pretreatment: Phosphorus trichloride and anhydrous ethanol are filtered through a precision filter to remove impurities at a flow rate of 50 mL / min; 2,4-di-tert-butylphenol is added to the raw material melting tank, heated to 80℃ to melt, kept at the temperature for later use, and then filtered through a precision filter to remove impurities after melting.

[0028] ② Microchannel esterification reaction: Start the esterification microchannel reactor, introduce chilled brine into the jacket, and pre-cool to 0℃; simultaneously pump phosphorus trichloride (flow rate 50 mL / min) and anhydrous ethanol (flow rate 45 mL / min) into the reactor at a molar ratio of 1:2.2 using a metering pump; control the reaction temperature at 0-5℃ and atmospheric pressure, and the material residence time at 15 min; the HCl gas generated by the reaction is immediately discharged through the hydrophobic and permeable membrane on the inner wall of the reactor and enters the HCl absorption tower, where it is absorbed by countercurrent circulating water to obtain industrial hydrochloric acid with a mass fraction of 30.2% and a recovery rate of 0.18 kg / h; the reaction liquid is continuously discharged from the outlet of the esterification reactor as a pale yellow and clear diethyl phosphite solution, which is directly pumped into the intermediate storage tank.

[0029] ③ Microchannel transesterification reaction: Start the transesterification microchannel reactor, introduce heat transfer oil into the jacket, preheat to 195℃, start the vacuum system, and pump the pressure inside the transesterification reactor to -0.09 MPa; mix the diethyl phosphite solution in the intermediate storage tank with molten 2,4-di-tert-butylphenol at a molar ratio of 1:3.1 using a metering pump, and pump it into the transesterification reactor at a flow rate of 30 mL / min; control the reaction temperature at 195±2℃, the pressure at -0.09 MPa, and the material residence time at 32 min; collect the ethanol by-product of the reaction through a condensation recovery device, send it to a distillation column for purification, and obtain recovered ethanol with a purity of 97.5% at a recovery rate of about 0.085 kg / h, which is recycled for the esterification reaction; the reaction liquid is continuously discharged from the outlet of the transesterification reactor as a white turbid crude antioxidant 168 solution.

[0030] ④ Post-processing: Pump the crude product solution into a continuous crystallizer, add n-heptane, stir at 60 r / min, cool to 0-5℃ and crystallize for 2 h; send the crystallized liquid into a plate and frame filter for filtration, the filter cake does not need to be washed with water, and is directly sent into a vacuum dryer to dry at 50℃ and -0.095 MPa for 6 h to obtain white powdered antioxidant 168 product.

[0031] 5. Test Results Yield (HPLC): 96.8%; Melting point: 183-184℃; Acid value: 0.025 mg KOH / g; APHA color: 22; Catalyst residue: Not detected (ICP-MS detection limit 0.001%); Salt impurities: Not detected (ion chromatography detection); Single batch yield: 3.85 kg.

[0032] Example 2 This embodiment uses the catalyst-free scheme of this application to carry out small-scale pilot preparation.

[0033] 1. Equipment Preparation Consistent with Example 1, except that the ester exchange microchannel reactor is a custom-designed general-purpose model without a catalyst, the rest of the structure and parameters are the same as in Example 1.

[0034] 2. Raw material preparation Consistent with Example 1, the amounts of phosphorus trichloride, anhydrous ethanol, and 2,4-di-tert-butylphenol remain unchanged, and no catalyst or support is required.

[0035] 3. Preparation process ① Raw material pretreatment: Same as in Example 1; ② Microchannel esterification reaction: The molar ratio of phosphorus trichloride to ethanol is 1:2.3. The pump flow rate is adjusted to 45 mL / min (PCl3) and 42 mL / min (ethanol). The reaction temperature is 2-5℃ and the residence time is 18 min. The remaining parameters are the same as in Example 1 to obtain a diethyl phosphite solution. ③ Microchannel transesterification reaction: Start the catalyst-free transesterification microchannel reactor, preheat the jacket to 215℃, adjust the system pressure to 0.15 MPa (gauge pressure), and keep the other feeding methods and molar ratios the same as in Example 1. The flow rate of the mixture is 28 mL / min; control the reaction temperature at 215±2℃, the pressure at 0.15 MPa, the material residence time at 38 min, and the ethanol recovery and purification parameters the same as in Example 1. The purity of the recovered ethanol is 97.2%. ④ Post-processing: The amount of n-heptane was adjusted to 8.0 kg, which is 1.6 times the mass of the reaction solution. The drying temperature was 52℃. The remaining parameters were the same as in Example 1.

[0036] 4. Test Results Yield (HPLC): 95.6%; Melting point: 182-184℃; Acid value: 0.028 mg KOH / g; APHA color: 24; Catalyst residue: None (no need to detect); Salt impurities: Not detected (ion chromatography); Single batch yield: 3.78 kg.

[0037] Example 3 This embodiment sets up a comparative experiment, with Example 1 as experimental group 1, Example 2 as experimental group 2, and the traditional batch process as control group 1.

[0038] 1. Control Group 1 Process Control group 1 equipment: 10 L four-necked flask with stirrer, dropping funnel, condenser, 5 L neutralization vessel, plate and frame filter, water washing tank, vacuum dryer.

[0039] The raw materials for control group 1 were phosphorus trichloride, anhydrous ethanol, and 2,4-di-tert-butylphenol, which were the same as in Example 1, with the addition of 0.93 kg (9.25 mol) of triethylamine as a neutralizing agent and 12.95 kg (0.5 wt%) of tetraisopropyl titanate as a homogeneous catalyst.

[0040] Specific steps for control group 1: ① Esterification reaction: Add anhydrous ethanol to a 10 L four-necked flask, cool to 0-5℃ in an ice-water bath, add phosphorus trichloride dropwise, and simultaneously add triethylamine to neutralize HCl to generate triethylamine hydrochloride; after the addition is complete, heat to 25℃ and react for 2 h, filter to remove triethylamine hydrochloride, and obtain diethyl phosphite solution. ② Transesterification reaction: 2,4-di-tert-butylphenol and tetraisopropyl titanate were added to the above solution, the temperature was raised to 195℃, the pressure was reduced to -0.09 MPa and the reaction was carried out for 8 h, and the ethanol was distilled off for recovery. ③ Post-processing: After the reaction solution is cooled, it is added to a water washing tank and washed three times with 5 kg of deionized water to remove residual triethylamine hydrochloride and catalyst. The organic phase is separated and then added to n-heptane for crystallization. After filtration and drying, the product is obtained.

[0041] 2. Result Comparison Table 1 compares the results of process experimental groups 1 and 2 of this application with those of the existing technology process control group 1. Item Experiment Group 1 Experiment Group 2 Control Group 1 Yield (HPLC, %) 96.8 95.6 91.5 Product acid value (mgKOH / g) 0.025 0.028 0.12 Product APHA color 22 24 43 Catalyst residue (%) Not detected No 0.08 Neutralizer usage No No Triethylamine, 0.93 kg Desalination process No No Filtering + 3 times water washing Salt-containing wastewater generation (kg / t product) 0 0 5200 Production mode Continuous (24h uninterrupted) Continuous (24h uninterrupted) Batch (single batch 12h) Single batch production cycle (h) 0.78 (47 min) 0.93 (56 min) 12 Raw material loss rate (%) 2.1 2.5 6.8 The comparison results show that the product yield and purity of experimental group 1 (Example 1) and experimental group 2 (Example 2) of this application are significantly better than those of the traditional batch process (control group 1), and the use of neutralizing agent, desalination process and discharge of saline wastewater are completely avoided. The problem of catalyst residue is completely solved, and the overall advantages are obvious.

[0042] The infrared spectra of the three sets of products are compared as follows: Figure 1 As shown, experimental groups 1 and 2 did not have the impurity peak (3600 cm⁻¹) found in the traditional process (control group 1). -1 Residual phenolic groups and 1700 cm -1 The presence of oxidized impurities (C=O) demonstrates the high purity advantage brought by the process of this application; the characteristic peaks of the products in experimental group 1 and experimental group 2 are sharper and the baseline is more stable, which corroborates the technical effects of acid value reduction and color optimization. Moreover, the spectral curves of the products in experimental group 1 and experimental group 2 are basically the same, proving that both the catalyst-supported and catalyst-free schemes can produce high-purity products.

[0043] The process comparison of the three product groups Figure 2 As shown, the core environmental protection effect of zero saline wastewater in Experimental Group 1 and Experimental Group 2 is clearly demonstrated, which, compared with the heavy pollution of the traditional process in Control Group 1, proves the advantages of clean production. It also shows that the production cycle of the proposed solution is shortened by more than 93% compared with the traditional process, proving the efficiency improvement of continuous production. Combined with the raw material loss rate data, it proves the technical value of the proposed solution in both cost reduction and environmental protection. Moreover, the process comparison between Experimental Group 1 and Experimental Group 2 is not significantly different, proving that the two solutions, one with a catalyst and the other without a catalyst, perform equally well in both cost reduction and environmental protection.

[0044] Example 4 This embodiment is based on Example 1 and is a scaled-up experiment, with a scale of 10 times.

[0045] 1. Equipment Preparation Both the esterification microchannel reactor and the ester exchange microchannel reactor were model MCR-1000 (Wuhan Guoxin), which was scaled up 10 times in Example 1. All other supporting equipment were scaled-up models of the equipment corresponding to Example 1.

[0046] 2. Test Plan Using the process parameters of the supported catalyst in Example 1, five batches of continuous production were carried out, with a production cycle of 8 hours for each batch. The key indicators of each batch of products were recorded, the average value was calculated, and this was recorded as Experiment Group 3. The results were compared with those of Example 1 (1 L-level).

[0047] 3. Scale up the experimental data and comparison table ① Test results of single batches in the five batch method tests (Table 2) Batch Yield (HPLC, %) Acid value (mgKOH / g) APHA color Catalyst residue Salt impurities Single batch yield (kg) 1 96.9 0.024 21 Not detected Not detected 38.6 2 97.0 0.026 22 Not detected Not detected 38.7 3 96.7 0.025 23 Not detected Not detected 38.4 4 96.9 0.023 22 Not detected Not detected 38.6 5 96.8 0.027 21 Not detected Not detected 38.5 Average value 96.86 0.025 21.8 Not detected Not detected 38.56 ② Comparison table of scale-up test and small-scale test (Example 1, Experimental group 1) (Table 2) Item Experiment Group 1 Experiment Group 3 Difference rate (after amplification) Yield (HPLC, %) 96.8 96.86 +0.06% Product acid value (mgKOH / g) 0.025 0.025 0% Product APHA color 22 21.8 -0.9% Catalyst residue (%) Not detected Not detected No Salt impurities Not detected Not detected No Single batch yield (kg) 3.85 38.56 999.5% Index fluctuation range (yield) - ±0.3% - The data results show that the average indicators of the five batches of products produced continuously in the 10 L-level microchannel are basically consistent with the results of the 1 L-level pilot test. The fluctuation range of key indicators such as yield, acid value, and color is ≤0.3%, and there is no catalyst residue or salt impurities. This proves that the process parameters of this scheme have a good scale-up effect, and the equipment selection and process design are suitable for industrial production needs. It can be further scaled up to a 5000 L-level industrial production line.

[0048] Figure 3 X-ray diffraction (XRD) spectra of the catalyst immobilized on the inner wall of the transesterification microchannel reactor are shown. The XRD pattern of the γ-Al₂O₃ / Ti(OiPr)₄ immobilized catalyst shows the characteristic diffraction peaks before and after the experiment in Example 4. Since the two lines are basically coincident, it proves the rationality of the structure of the immobilized catalyst and proves that it does not fall off or enter the reaction system, providing structural evidence for the absence of catalyst residue. The Ti 2p XPS spectra of the immobilized catalyst show the energy spectrum before and after the experiment in Example 4. Comparing the binding energy of Ti elements before and after practical application, it also proves that the catalyst structure is stable and does not fall off after use, proving the stability of the immobilized catalyst in industrial application and supporting the scale-up feasibility conclusion of Example 4.

[0049] Figure 4The products from Example 1 (Experimental Group 1), Example 2 (Experimental Group 2), scale-up test product (Experimental Group 3), and conventional process product (Control Group 1) were compared to demonstrate the performance of each product and process in terms of yield, acid value, color, and catalyst residue. Specifically, the yields of Experimental Groups 1-3 were all ≥95.6%, higher than the 91.5% of Control Group 1, proving the efficiency advantage of the process. The acid values ​​of Experimental Groups 1-3 were ≤0.0028 mg KOH / g, and the color was ≤24, with the scale-up test data being largely consistent with the small-scale test data, demonstrating the stability of the quality and no degradation during scale-up. The conventional process (Control Group 1) had 0.08% catalyst residue, while this method (Experimental Groups 1-3) showed no detectable / no residue, directly verifying the core innovation of this method: no catalyst residue.

Claims

1. A method for synthesizing antioxidant 168 using a microchannel continuous flow process, characterized in that, Includes the following steps: (1) Raw material pretreatment: Select high-purity raw materials, with phosphorus trichloride purity ≥99% and low-carbon chain alcohol purity ≥99.5%. Phosphorus trichloride, low-carbon chain alcohol and 2,4-di-tert-butylphenol are filtered through 5 μm precision to remove impurities. 2,4-di-tert-butylphenol is heated and melted to 75-85℃. (2) Microchannel esterification reaction: Phosphorus trichloride and low-carbon chain alcohol are simultaneously pumped into the ceramic-coated microchannel reactor at a molar ratio of 1:(2.0-2.5) using a metering pump. The reaction temperature is controlled at 0-5℃, atmospheric pressure, and residence time at 10-20 min. The hydrogen chloride gas generated by the reaction is immediately discharged through the hydrophobic and breathable membrane integrated on the inner wall of the reactor and recovered by the water absorption system as industrial hydrochloric acid with a mass fraction of 28-32%. The reaction solution is continuously discharged to obtain a dialkyl phosphite ester solution. (3) The dialkyl phosphite solution obtained in step (2) is mixed with molten 2,4-di-tert-butylphenol at a molar ratio of 1:(3.0-3.2) and pumped into a microchannel transesterification reactor. The reaction temperature is controlled at 190-220℃, the pressure at -0.09~0.2MPa, and the residence time at 30-40 min. The low-carbon chain alcohols produced by the reaction are recycled for step (2) after being condensed and recovered. (4) Post-processing: The reaction solution from step (3) is fed into a continuous crystallizer, n-heptane is added for crystallization, filtered and vacuum dried to obtain antioxidant 168 product.

2. The method according to claim 1, characterized in that, The low-carbon chain alcohol in step (1) is anhydrous ethanol.

3. The method according to claim 1, characterized in that, In step (2), the inner diameter of the ceramic-coated microchannel reactor is 0.5-1 mm, the number of channels is 800-1200, and the total volume is 400-600 mL.

4. The method according to claim 1, characterized in that, In step (3), the microchannel transesterification reactor is a ceramic microchannel reactor with a catalyst supported on the inner wall. The catalyst is tetraisopropyl titanate, the support is γ-Al2O3, the catalyst loading is 5-8wt%, and the total volume is 700-900 mL.

5. The method according to claim 4, characterized in that: The catalyst is immobilized on the surface of a support using a sol-gel method and then coated onto the inner wall of the microchannel.

6. The method according to claim 1, characterized in that: In step (2), the ceramic-coated microchannel reactor is pumped with phosphorus trichloride and low-carbon chain alcohol at a rate of 40-60 mL / min using a metering pump. In step (3), the microchannel transesterification reactor is pumped with diethyl phosphite solution and molten 2,4-di-tert-butylphenol at a rate of 25-35 mL / min.

7. The method according to claim 1, characterized in that, In step (3), the reaction temperature of the microchannel ester exchange reactor is controlled at 190-200℃, the system is evacuated to -0.09 MPa, and the residence time is 30-35 min.

8. The method according to claim 1, characterized in that, In step (4), the amount of n-heptane used in the crystallization step is 1.2-1.8 times the mass of the reaction solution, the crystallization temperature is 0-5℃, the temperature of the vacuum drying step is 45-55℃, and the drying time is 6-8 h.

9. The method according to claim 1, characterized in that, In step (3) microchannel transesterification reaction, the microchannel transesterification reactor with catalyst immobilized on the inner wall can be replaced with a catalyst-free device. When the microchannel transesterification reactor without catalyst participates in step (3) microchannel transesterification reaction, the temperature is controlled at 210-220℃, the pressure at 0.1-0.2 MPa, and the residence time at 35-40 min.

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