A process for the preparation of 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl-diol

Abstract

The application belongs to the technical field of fine chemical synthesis, and particularly relates to a preparation method of 3,3',5,5'-tetra-tert-butyl-4,4'-diphenyl-diphenol, which comprises the following steps: S1 raw material pretreatment: after 2,6-di-tert-butyl phenol is vacuum dried, a nano zinc oxide-montmorillonite composite catalyst is added and uniformly mixed; in the scheme, by adopting a double-catalyst system composed of a nano zinc oxide-montmorillonite composite catalyst and a TiO2 photocatalyst modified by carbon nitride quantum dots, a synergistic process of microwave-assisted oxidative coupling and photocatalytic reduction is combined, key parameters such as reaction temperature, pressure and time are optimized, and a multi-stage purification process of supercritical CO2 extraction-recrystallization is matched, so that efficient recovery and recycling of the catalyst are realized, high-quality products with a purity of greater than or equal to 99.5% and a colority of less than or equal to 8 (APHA) are finally prepared, the total reaction time is shortened to 6-7 hours, the number of times of repeated use of the catalyst reaches 5-8 times, and the efficiency, economy and product quality stability of the process are significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fine chemical synthesis, and in particular to a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol. Background Art

[0002] 3,3',5,5'-Tetra-tert-butyl-4,4'-biphenol is an important hindered phenol antioxidant and polymer material additive with excellent thermal stability, oxidation resistance and weather resistance. It is widely used in plastics, rubber, coatings and other fields. Its product purity and color have a significant impact on the performance of downstream materials.

[0003] Traditional preparation processes have many shortcomings: First, catalysts mostly use single metal oxides or unmodified semiconductor materials, such as single nano-zinc oxide or ordinary TiO2, which have problems such as small specific surface area, low catalytic activity, and high photogenerated carrier recombination rate, resulting in incomplete oxidative coupling reactions (the content of intermediate products is often less than 80%), a large number of impurity residues in the reduction reaction, and the purity of the final product is difficult to exceed 98%; second, the reaction conditions are roughly controlled, such as large temperature fluctuations in the oxidation reaction and insufficient photocatalytic reduction time, which further aggravates the problems of low raw material conversion rate and increased by-products; third, the purification process mostly relies on single recrystallization or conventional extraction, and impurities are not completely removed, the product color is high (APHA ≥ 20), and the catalyst cannot be effectively recovered, which not only increases production costs but also easily introduces new impurities; fourth, the reaction efficiency is low, and the total reaction time of the traditional process often exceeds 8 hours, which is difficult to meet the needs of industrial continuous production.

[0004] In addition, a search revealed a Chinese patent application titled "3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol" (publication number CN117466715A). This invention first uses 2,6-di-tert-butylphenol as a raw material, undergoes an oxidative coupling reaction, and obtains the intermediate product, 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diquinone. The intermediate product is then reduced using Raney nickel as a catalyst and an alcohol reagent as a reducing agent to obtain 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol. The 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol produced using this invention's production process is a white powder with a maximum yield of 79.2%, a purity of 99.5%, a chromaticity value of 73.5, and excellent color. This process not only resolves the traditional contradiction of high purity but poor color, but also facilitates control of the reaction conditions, facilitating industrial production.

[0005] However, the oxidative coupling reaction of this invention relies on a single catalyst such as potassium hydroxide, which has a limited specific surface area, resulting in a low yield of intermediate products; although Raney nickel is used in the reduction reaction, it requires heating at 50-100°C, and the amount of alcohol reducing agent used is 30-50% of the raw material, which results in high energy consumption and cost; purification relies solely on ethanol beating, and impurities are not completely removed.

[0006] To this end, the present invention proposes a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol. By adopting a dual catalytic system consisting of a nano-zinc oxide-montmorillonite composite catalyst and a TiO2 photocatalyst modified with carbon nitride quantum dots, combining the synergistic process of microwave-assisted oxidative coupling and photocatalytic reduction, optimizing key parameters such as reaction temperature, pressure, and time, and coordinating with a multi-stage purification process of supercritical CO2 extraction-recrystallization, the efficient recovery and recycling of the catalyst are achieved. Finally, a high-quality product with a purity of ≥99.5% and a chroma of ≤8 (APHA) is prepared, and the total reaction time is shortened to 6-7 hours. The catalyst can be reused 5-8 times, which significantly improves the efficiency, economy and product quality stability of the process. Summary of the Invention

[0007] Technical problems solved: Solve the problems of low purity of traditional process products, poor catalyst efficiency, many impurities and high cost.

[0008] In view of the deficiencies in the prior art, the present invention provides a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol, thereby solving the technical problems mentioned in the background technology.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0010] A method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol comprises the following steps:

[0011] S1. Raw material pretreatment: vacuum-dry 2,6-di-tert-butylphenol, add 0.4-0.6% of nano zinc oxide-montmorillonite composite catalyst based on the raw material mass, and mix well to obtain pretreated raw material;

[0012] S2 microwave-assisted oxidative coupling reaction: the pretreated raw materials were mixed with cyclopentyl methyl ether in an amount of 20-40% of the raw material volume, and ozone-air mixed gas was introduced into a microwave reactor. The microwave power was controlled at 250-350 W, the reaction temperature was 100-120° C., the stirring speed was 400-600 rpm, the ozone concentration was 4-6%, the system pressure was 0.1-0.14 MPa, and the reaction time was 2.5-4.5 h. After the reaction, the catalyst was filtered and recovered to obtain an oxidation reaction filtrate;

[0013] S3 Photocatalytic Reduction Reaction: The oxidation reaction filtrate was transferred to a photocatalytic reactor, and a TiO2 photocatalyst modified with carbon nitride quantum dots accounting for 1.5-2.5% of the raw material mass and an ethylene glycol-water mixture were added. Photocatalytic reduction was carried out under nitrogen protection, and the reaction temperature was controlled at 60-70°C, the stirring speed at 500-700 rpm, and the light intensity at 50 mW / cm 2 365nm LED light source, reaction time 1.5-2.5h, after the reaction, filtering and recovering the catalyst to obtain a reduction reaction filtrate;

[0014] S4 multi-stage purification process: The reduction reaction filtrate is acidified, extracted with supercritical CO2, recrystallized and vacuum dried in sequence to obtain the target product;

[0015] S5 Catalyst recovery and circulation: The catalyst recovered in steps S2 and S3 is washed, dried or calcined and then reused.

[0016] In one possible implementation, the preparation method of the nano zinc oxide-montmorillonite composite catalyst is as follows: 3-8g of nano zinc oxide with a particle size of 30-50nm is dispersed in 150-250mL of deionized water, 8-15g of sodium montmorillonite with a cation exchange capacity of ≥100mmol / 100g is added, ultrasonic stirring is performed for 1.5-2.5h, and then filtered, dried at 120℃, and calcined at 500℃ for 3h, wherein the ZnO loading is 25-35wt% and the specific surface area is 160-240m 2 / g.

[0017] In one possible implementation, the ozone concentration in the ozone-air mixed gas is 4-6%, the system pressure is 0.1-0.14 MPa, the reaction time is 2.5-4.5 h, and the amount of cyclopentyl methyl ether added is 20-40% of the raw material volume.

[0018] In one possible implementation, the conditions for the photocatalytic reduction reaction are: the amount of TiO2 photocatalyst modified with carbon nitride quantum dots added is 1.5-2.5% of the mass of the raw material, and an ethylene glycol-water mixture is added with a volume ratio of 3:1 and 20-30% of the mass of the raw material.

[0019] In one possible implementation, in the multi-stage purification process, the supercritical CO2 extraction pressure is 10-14 MPa, the temperature is 35-45°C, the CO2 flow rate is 20-40 L / h, and the extraction time is 15-25 min; the recrystallization uses a 75% ethanol-ethyl acetate mixture with a material-liquid ratio w / v of 1:4-1:6, and the crystallization is carried out at 2-8°C for 1.5-3 h.

[0020] Beneficial effects compared with existing technologies:

[0021] In this scheme, by using a dual catalytic system consisting of a nano zinc oxide-montmorillonite composite catalyst and a TiO2 photocatalyst modified with carbon nitride quantum dots, and combining the synergistic process of microwave-assisted oxidative coupling and photocatalytic reduction, the efficient preparation and high-purity output of 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol were achieved. Specifically, the nano zinc oxide-montmorillonite composite catalyst has a ZnO loading of 25-35wt% and a 160-240m 2 The high surface area of ​​1000 nm / g provides ample active sites for the oxidative coupling reaction. Combined with microwave-assisted technology (250-350 W power, 100-120°C), the ozone activation efficiency and reaction rate are significantly improved, allowing the intermediate product content to reach over 88% within 2.5-4.5 hours. The carbon nitride quantum dot-modified TiO2 photocatalyst suppresses photogenerated electron-hole recombination, keeping the residual intermediate product in the reduction reaction below 0.3% under a 365 nm LED light source. This overcomes the issues of insufficient activity and incomplete reaction caused by traditional single catalysts. Furthermore, the multi-stage purification process combines supercritical CO2 extraction (10-14 MPa pressure, 35-45°C temperature) with recrystallization (75% ethanol-ethyl acetate mixture) to effectively remove residual raw materials and by-products, maintaining a stable product purity above 99.5% with a color ≤8 (APHA). In addition, the two catalysts can be reused 4-9 times after simple washing and calcination, with an activity retention rate of more than 85%, which greatly reduces production costs, takes into account process efficiency and economy, and has significant improvements in product quality and sustainability compared to traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

[0023] Figure 1 This is the infrared spectrum of 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol prepared in Example 1 of the present invention;

[0024] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol prepared in Example 1 of the present invention;

[0025] Figure 3 This is the carbon nuclear magnetic resonance spectrum of 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described in detail. However, the present invention can be implemented in various forms, so the present invention is not limited to the embodiments described below.

[0027] The technical solution in the embodiments of the present application is to solve the problems of the above-mentioned background technology, and the overall idea is as follows:

[0028] Example 1:

[0029] This embodiment introduces a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol, comprising the following steps:

[0030] 1. Raw material selection and components

[0031] 1.1 Main raw materials

[0032] 2,6-di-tert-butylphenol with a purity of ≥99.5% and a moisture content of ≤0.05%, white crystalline powder, melting point 69-71°C, and color APHA ≤10;

[0033] 1.2 Catalyst system

[0034] Add 0.5% (by mass) of nano zinc oxide-montmorillonite composite catalyst, disperse 5g of nano zinc oxide (particle size 30-50nm) in 200mL of deionized water, add 10g of sodium montmorillonite (cation exchange capacity ≥100mmol / 100g), stir ultrasonically for 2h, filter, dry at 120℃, and calcine at 500℃ for 3h.

[0035] ZnO loading 30wt%, specific surface area 180-220m 2 / g.

[0036] Carbon nitride quantum dot modified TiO2 photocatalyst: 5g P25 TiO2 was dispersed in 100mL melamine ethanol solution (0.1mol / L), refluxed for 2h, centrifuged, and calcined at 600℃ for 2h to obtain g-C3N4@TiO2 composite material (loading amount 5wt%).

[0037] 1.3 Solvents and additives

[0038] Anhydrous cyclopentyl methyl ether (CPME) with a water content of ≤0.01% and an acid value of ≤0.01 mgKOH / g;

[0039] An ethylene glycol-water mixture with a volume ratio of 3:1, analytical grade, was used for photocatalytic reduction;

[0040] Supercritical CO2 with purity ≥99.99% and water content ≤5ppm;

[0041] 2. Equipment selection and parameters

[0042] 2.1 Oxidation reaction equipment

[0043] MARS6 (CEMCorporation) microwave reactor, volume: 500mL, pressure ≥10MPa, microwave frequency 2450MHz, equipped with magnetic stirring (100-1500rpm), infrared temperature sensor, and pressure transmitter;

[0044] 2.2 Photocatalytic reduction equipment

[0045] Photocatalytic reactor, borosilicate glass material, jacketed temperature control, 365nm LED array (light intensity 50mW / cm 2 ) light source, equipped with mechanical stirring (300-800rpm), circulating cooling water system (temperature control accuracy ±1℃);

[0046] 2.3 Separation and purification equipment

[0047] HA221-50-06 (Nantong Hua'an) supercritical extraction unit, 5L extraction kettle volume, maximum working pressure 50MPa, temperature range 30-80℃, CO2 flow rate 0-50L / h;

[0048] 3. Complete process flow

[0049] S1. Raw material pretreatment

[0050] 2,6-di-tert-butylphenol was placed in a vacuum drying oven and dried at 60°C and -0.09 MPa for 4 hours. After cooling to room temperature, 0.5% (by mass) of nano zinc oxide-montmorillonite composite catalyst was added and mixed evenly.

[0051] S2. Microwave-assisted oxidative coupling reaction

[0052] The pretreated raw materials were added to a microwave reactor, and cyclopentyl methyl ether (30% of the raw material volume) was added, and the reactor was sealed and replaced with nitrogen three times;

[0053] Set the microwave power to 300 W, raise the temperature to 110 °C, and start stirring (500 rpm);

[0054] An ozone-air mixture (ozone concentration 5%) was introduced, the system pressure was maintained at 0.12 MPa, and the reaction was continued for 3.5 h;

[0055] After the reaction is completed, the mixture is cooled to 40°C, the catalyst is recovered by filtration, and the filtrate is fed into the next step;

[0056] In-process control indicators: intermediate product content ≥92% (HPLC area normalization method);

[0057] S3. Photocatalytic reduction reaction

[0058] The oxidation reaction filtrate was transferred to a photocatalytic reactor, and 2% (by mass) of g-C3N4@TiO2 catalyst and 25% of the raw material mass of ethylene glycol-water mixture were added;

[0059] Nitrogen was introduced to replace the air three times, and a slight positive nitrogen pressure (0.02 MPa) was maintained;

[0060] Turn on the LED light source and circulating cooling water, control the reaction temperature to 65°C, stir at 600 rpm, and react for 2 h. Use a 365 nm LED array light source with a light intensity of 50 mW / cm2.

[0061] After the reaction is completed, the light source is turned off, the mixture is cooled to room temperature, and the catalyst is recovered by filtration through a ceramic membrane;

[0062] In-process control index: intermediate product residue ≤ 0.1% (HPLC detection);

[0063] S4, multi-stage purification process

[0064] Acidification: Slowly add 10% hydrochloric acid solution to the filtrate to adjust the pH to 3, and a white solid will precipitate;

[0065] Supercritical extraction: transfer the solid material to a supercritical extraction reactor, set the pressure to 12 MPa, the temperature to 40°C, the CO2 flow rate to 30 L / h, extract for 20 minutes, and then reduce the pressure for separation;

[0066] Recrystallization: Add the crude product obtained from extraction into a mixture of 75% ethanol and ethyl acetate (solid-liquid ratio 1:5, w / v), heat to reflux to dissolve, cool to 5°C to crystallize for 2 hours, and filter;

[0067] Drying: The filter cake was vacuum dried at 60°C and -0.09 MPa for 6 h to obtain a pure white product;

[0068] S5. Catalyst recovery and circulation

[0069] Oxidation catalyst: Wash with cyclopentyl methyl ether 3 times, dry at 120℃ and reuse 5 times;

[0070] Photocatalyst: The catalyst retained by the ceramic membrane is washed with deionized water and calcined at 500°C for 1 hour, and can be reused 8 times.

[0071] like Figure 1 The infrared spectrum showed that 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol had a broad phenolic hydroxyl peak at 3000-3500 cm⁻¹, a biphenyl skeleton vibration peak at 1450-1600 cm⁻¹, and a tert-butyl characteristic peak at 1000-1300 cm⁻¹, proving that it contained the target functional group.

[0072] like Figure 2As shown in the hydrogen spectrum, the strong peak at δ1-2ppm is tert-butyl methyl hydrogen, indicating that a large amount of tert-butyl groups are retained; the simplified peak at δ6-8ppm is biphenyl hydrogen, which is equivalent to the symmetrical substitution environment, indicating that the product structure matches the target.

[0073] like Figure 3 The carbon spectrum shows that δ20-60ppm is tert-butyl carbon, δ120-160ppm is biphenyl carbon, and δ150-160ppm is phenolic hydroxyl-linked carbon. The characteristic peaks are consistent with the carbon skeleton and functional group positions of the target product, confirming that it is the target product.

[0074] Example 2:

[0075] This embodiment introduces a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol, comprising the following steps:

[0076] 1. Raw material selection and components

[0077] 1.1 Main raw materials

[0078] 2,6-di-tert-butylphenol with a purity of ≥99.5% and a moisture content of ≤0.05%, a white crystalline powder, a melting point of 69-71°C, and a color of APHA ≤10 (the dosage is 60% of that in Example 1);

[0079] 1.2 Catalyst system

[0080] Nano zinc oxide-montmorillonite composite catalyst: 3g nano zinc oxide (particle size 30-50nm) was dispersed in 150mL deionized water, and 8g sodium montmorillonite (cation exchange capacity ≥100mmol / 100g) was added. After ultrasonic stirring for 1.5h, the mixture was filtered, dried at 120℃, and calcined at 500℃ for 3h. The ZnO loading was 25wt% and the specific surface area was 160-190m 2 / g;

[0081] Carbon nitride quantum dot-modified TiO2 photocatalyst: 3 g of P25 TiO2 was dispersed in 80 mL of 0.1 mol / L melamine ethanol solution, refluxed for 1.5 h, centrifuged, and calcined at 600 °C for 2 h to obtain a g-C3N4@TiO2 composite material (loading 5 wt%).

[0082] 1.3 Solvents and additives

[0083] Anhydrous cyclopentyl methyl ether (CPME): water content ≤ 0.01%, acid value ≤ 0.01 mgKOH / g (the dosage is 60% of that in Example 1);

[0084] Ethylene glycol-water mixture (volume ratio 3:1): analytical grade (the amount used is 60% of that in Example 1); supercritical CO2: purity ≥99.99%, water content ≤5 ppm (the amount used is 60% of that in Example 1);

[0085] 2. Equipment selection and parameters

[0086] Same as Example 1 (the equipment model remains unchanged, only the operating parameters are adjusted);

[0087] 3. Complete process flow

[0088] S1. Raw material pretreatment: 2,6-di-tert-butylphenol was dried at 60°C and -0.09 MPa for 3.5 h, and 0.4% (by mass) of nano zinc oxide-montmorillonite composite catalyst was added;

[0089] S2. Microwave-assisted oxidative coupling reaction: Add cyclopentyl methyl ether (20% by volume of the raw material), microwave power 250 W, heat to 100°C, stir at 400 rpm, introduce ozone-air mixture (ozone concentration 4%), maintain pressure at 0.1 MPa, and react for 2.5 h. In-process control indicator: intermediate product content ≥88% (HPLC);

[0090] S3. Photocatalytic reduction reaction: Add 1.5% (by mass) g-C3N4@TiO2 catalyst and 20% (by mass) of ethylene glycol-water mixture to the reaction mixture at 60°C, stirring at 500 rpm, and react for 1.5 h. Use a 365 nm LED array light source with a controlled light intensity of 50 mW / cm3. In-process control indicator: Residual intermediate product ≤ 0.3% (HPLC).

[0091] S4, multi-stage purification process:

[0092] Acidification: adjust pH to 3.5;

[0093] Supercritical extraction: pressure 10 MPa, temperature 35°C, CO2 flow rate 20 L / h, extraction 15 min;

[0094] Recrystallization: material-liquid ratio 1:4 (w / v), cool to 8°C and crystallize for 1.5h;

[0095] Drying: vacuum drying at 55°C and -0.09 MPa for 5 h;

[0096] S5. Catalyst recovery: The oxidation catalyst was reused 4 times; the photocatalyst was reused 6 times.

[0097] Example 3:

[0098] This embodiment introduces a method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol, comprising the following steps:

[0099] 1. Raw material selection and components

[0100] 1.1. Main raw material: 2,6-di-tert-butylphenol (the amount used is 140% of that in Example 1), and the rest is the same as in Example 1;

[0101] 1.2 Catalyst system

[0102] Nano zinc oxide-montmorillonite composite catalyst: 8g nano zinc oxide (particle size 30-50nm) was dispersed in 250mL deionized water, 15g sodium montmorillonite was added, ultrasonically stirred for 2.5h, filtered, dried at 120℃, and calcined at 500℃ for 3h; ZnO loading 35wt%, specific surface area 200-240m 2 / g;

[0103] Carbon nitride quantum dot-modified TiO2 photocatalyst: 8 g of P25 TiO2 was dispersed in 120 mL of melamine ethanol solution, refluxed for 2.5 h, centrifuged, and calcined at 600 °C for 2 h to obtain g-C3N4@TiO2 (loading 5 wt%).

[0104] 1.3. Solvent and additives: the dosage is 140% of that in Example 1, and the rest is the same as in Example 1;

[0105] 2. Equipment selection and parameters

[0106] Same as Example 1;

[0107] 3. Complete process flow

[0108] S1. Raw material pretreatment: drying for 6 hours, adding 0.6% (by mass) oxidation catalyst;

[0109] S2. Microwave-assisted oxidative coupling reaction: microwave power 350 W, temperature raised to 120°C, stirring at 600 rpm, ozone concentration 6%, pressure 0.14 MPa, reaction time 4.5 h; in-process control index: intermediate product content ≥ 90% (HPLC);

[0110] S3. Photocatalytic reduction reaction: Add 2.5% (by mass) photocatalyst and 30% (by mass) ethylene glycol-water mixture of the raw material mass. The reaction temperature was 70°C, stirring was 700 rpm, and the reaction was carried out for 2.5 h. A 365 nm LED array light source was used with a light intensity controlled at 50 mW / cm. The intermediate product residue was ≤ 0.2% (HPLC).

[0111] S4, multi-stage purification process:

[0112] Acidification: adjust pH to 2.5;

[0113] Supercritical extraction: pressure 14 MPa, temperature 45°C, CO2 flow rate 40 L / h, extraction 25 min;

[0114] Recrystallization: material-liquid ratio 1:6 (w / v), cool to 2°C and crystallize for 3 hours;

[0115] Drying: vacuum drying at 65°C and -0.09 MPa for 7 h;

[0116] S5. Catalyst recovery: The oxidation catalyst was reused 6 times; the photocatalyst was reused 9 times.

[0117] Comparative Example 1:

[0118] Compared with Example 1, this comparative example replaces the catalyst type with a single catalyst

[0119] 1. Raw material selection and components

[0120] 1.1. The main raw materials, solvents and additives are the same as those in Example 1;

[0121] 1.2. Catalyst system: Only 5g of nano zinc oxide (particle size 30-50nm) was used as the oxidation catalyst (without montmorillonite loading), and the photocatalyst was the same as in Example 1;

[0122] 2. Equipment selection and parameters

[0123] Same as Example 1;

[0124] 3. Complete process flow

[0125] S1, raw material pretreatment: adding 0.5% (by mass) of single nano zinc oxide catalyst, and the rest is the same as Example 1;

[0126] S2. Microwave-assisted oxidative coupling reaction: Due to the low activity of the single catalyst, the intermediate product content was only 78% (HPLC) after 3.5 h of reaction. The other parameters were the same as those in Example 1.

[0127] S3, photocatalytic reduction reaction, multi-stage purification process, catalyst recovery and circulation are the same as in Example 1.

[0128] Comparative Example 2:

[0129] Compared with Example 1, the oxidation reaction temperature of this comparative example is too low.

[0130] 1. Raw material selection and components

[0131] Same as Example 1;

[0132] 2. Equipment selection and parameters

[0133] Same as Example 1;

[0134] 3. Complete process flow

[0135] S1, raw material pretreatment, catalyst system are the same as in Example 1;

[0136] S2. Microwave-assisted oxidative coupling reaction: microwave power was set to 300 W, the temperature was raised to 80° C. (lower than 110° C. in Example 1), and stirring was performed at 500 rpm. An ozone-air mixture (ozone concentration 5%) was introduced, the pressure was maintained at 0.12 MPa, and the reaction was carried out for 3.5 h. After the reaction, the intermediate product content was only 72% (HPLC), and the rest was the same as in Example 1.

[0137] S3, photocatalytic reduction reaction, multi-stage purification process, catalyst recovery and circulation are the same as in Example 1.

[0138] Comparative Example 3:

[0139] Compared with Example 1, the photocatalyst of this comparative example is not modified

[0140] 1. Raw material selection and components

[0141] The main raw materials, solvents and auxiliary agents are the same as those in Example 1; catalyst system: the photocatalyst is replaced by unmodified P25 TiO2 (5g), and the oxidation catalyst is the same as that in Example 1;

[0142] 2. Equipment selection and parameters

[0143] Same as Example 1;

[0144] 3. Complete process flow

[0145] S1, raw material pretreatment, microwave-assisted oxidative coupling reaction are the same as in Example 1;

[0146] S2. Photocatalytic reduction reaction: Due to the low photocatalytic efficiency of unmodified TiO2, the residual amount of the intermediate product still reached 1.5% (HPLC) after 2 h of reaction. The other parameters were the same as those in Example 1.

[0147] S3, multi-stage purification process, catalyst recovery and circulation are the same as in Example 1.

[0148] Comparative Example 4:

[0149] Compared with Example 1, the supercritical extraction pressure of this comparative example is insufficient.

[0150] 1. Raw material selection and components

[0151] Same as Example 1;

[0152] 2. Equipment selection and parameters

[0153] Same as Example 1;

[0154] 3. Complete process flow

[0155] S1, raw material pretreatment, microwave-assisted oxidative coupling reaction, and photocatalytic reduction reaction are the same as in Example 1;

[0156] S2, multi-stage purification process: supercritical extraction set pressure 5MPa (lower than 12MPa in Example 1), temperature 40°C, CO2 flow rate 30L / h, extraction 20min; due to insufficient pressure, impurities were not completely removed, and the remaining steps were the same as in Example 1;

[0157] S3. Catalyst recovery and circulation are the same as in Example 1.

[0158] Comparative Example 5:

[0159] Compared with Example 1, the catalyst in this comparative example was not recycled and new catalyst was used directly.

[0160] 1. Raw material selection and components

[0161] Same as Example 1;

[0162] 2. Equipment selection and parameters

[0163] Same as Example 1;

[0164] 3. Complete process flow

[0165] S1, raw material pretreatment, microwave-assisted oxidative coupling reaction, and photocatalytic reduction reaction are the same as in Example 1;

[0166] S2. Catalyst recovery and recycling: The catalyst recovery step is eliminated and new catalyst is used for each reaction. Due to the introduction of trace impurities by the new catalyst, the product color increases (APHA ≥ 25);

[0167] S3. The multi-stage purification process is the same as in Example 1.

[0168] Experimental example:

[0169] Parallel experiments were conducted on the preparation methods of Examples 1-3 and Comparative Examples 1-5 to test product purity (HPLC), yield, catalyst reusability stability, and product chromaticity. The results are shown in the following table:

[0170]

[0171] Experimental results analysis

[0172] Product purity and yield:

[0173] The product purities of Examples 1-3 were all ≥99.5%, and the yields were ≥88%, which were significantly higher than those of Comparative Examples 1-5 (purity ≤97.0%, yield ≤85%).

[0174] Comparative Example 1 uses a single oxidation catalyst (without montmorillonite loading) with a low specific surface area (80-100m 2 / g), insufficient catalytic activity, resulting in decreased purity and yield;

[0175] In Comparative Example 2, the oxidation reaction temperature was too low (80°C), the ozone solubility was reduced, the reaction was incomplete, and the yield was only 70%;

[0176] In Comparative Example 3, since the photocatalyst was not modified (no carbon nitride quantum dots), the photogenerated carrier recombination rate was high, the reduction efficiency was low, and the impurities remained, resulting in a decrease in purity;

[0177] Product color:

[0178] The products of Examples 1-3 all had a chromaticity of ≤8 (APHA) and were pure white. Comparative Examples 1-5 all had a chromaticity of ≥15 (APHA) due to insufficient catalyst activity or incomplete removal of impurities, and some products were slightly yellow (e.g., Comparative Example 5 had a chromaticity of 28 APHA).

[0179] Catalyst stability:

[0180] The activity retention rate of the oxidation catalyst of Example 1 was still 90% after being reused 5 times, and the activity of the photocatalyst did not decrease significantly after being reused 8 times;

[0181] The single oxidation catalyst of Comparative Example 1 has no carrier to fix it, so the active components are easily lost, and the activity retention rate after 5 repeated uses is only 60%;

[0182] In Comparative Example 5, since the catalyst was not recycled, trace impurities were introduced each time a new catalyst was used, which not only increased the cost but also led to unstable product quality.

[0183] in conclusion

[0184] This experiment shows that the preparation method of Example 1 (optimized composite catalyst system, precise reaction parameters and multi-stage purification process) can stably prepare high-purity and high-yield 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol, and has excellent catalyst recycling performance, and the overall benefits are significantly better than other comparative schemes.

[0185] Finally, it should be noted that the above embodiments are merely examples for the purpose of illustrating the present invention and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all embodiments. However, obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol, characterized in that: The following steps are involved: S1. Raw material pretreatment: 2,6-di-tert-butylphenol is used as raw material, after vacuum drying, 0.4-0.6% of nano zinc oxide-montmorillonite composite catalyst is added to the raw material by weight and mixed evenly to obtain a pretreated raw material; S2 microwave-assisted oxidative coupling reaction: the pretreated raw materials were mixed with cyclopentyl methyl ether in an amount of 20-40% of the raw material volume, and ozone-air mixed gas was introduced into a microwave reactor. The microwave power was controlled at 250-350 W, the reaction temperature was 100-120° C., the stirring speed was 400-600 rpm, the ozone concentration was 4-6%, the system pressure was 0.1-0.14 MPa, and the reaction time was 2.5-4.5 h. After the reaction, the catalyst was filtered and recovered to obtain an oxidation reaction filtrate; S3 Photocatalytic Reduction Reaction: The oxidation reaction filtrate was transferred to a photocatalytic reactor, and a TiO2 photocatalyst modified with carbon nitride quantum dots accounting for 1.5-2.5% of the raw material mass and an ethylene glycol-water mixture were added. Photocatalytic reduction was carried out under nitrogen protection, and the reaction temperature was controlled at 60-70°C, the stirring speed at 500-700 rpm, and the light intensity at 50 mW / cm 2 365nm LED light source, reaction time 1.5-2.5h, after the reaction, filtering and recovering the catalyst to obtain a reduction reaction filtrate; S4 multi-stage purification process: The reduction reaction filtrate is acidified, extracted with supercritical CO2, recrystallized and vacuum dried in sequence to obtain the target product; S5 Catalyst recovery and circulation: The catalyst recovered in steps S2 and S3 is washed, dried or calcined and then reused.

2. The method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol according to claim 1, wherein: The preparation method of the nano zinc oxide-montmorillonite composite catalyst is as follows: 3-8g of nano zinc oxide with a particle size of 30-50nm is dispersed in 150-250mL of deionized water, 8-15g of sodium montmorillonite with a cation exchange capacity of ≥100mmol / 100g is added, ultrasonic stirring is performed for 1.5-2.5h, and then filtering is performed, drying is performed at 120°C, and calcining is performed at 500°C for 3h. The ZnO loading is 25-35wt% and the specific surface area is 160-240m 2 / g.

3. The method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyl diphenol according to claim 1, wherein: The ozone concentration in the ozone-air mixed gas is 4-6%, the system pressure is 0.1-0.14 MPa, the reaction time is 2.5-4.5 hours, and the amount of cyclopentyl methyl ether added is 20-40% of the raw material volume.

4. The method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol according to claim 1, wherein: The conditions for the photocatalytic reduction reaction are as follows: the amount of TiO2 photocatalyst modified with carbon nitride quantum dots added is 1.5-2.5% of the mass of the raw material, and an ethylene glycol-water mixture with a volume ratio of 3:1 is added, and the mass of the mixture is 20-30% of the mass of 2,6-di-tert-butylphenol.

5. The method for preparing 3,3',5,5'-tetra-tert-butyl-4,4'-biphenyldiphenol according to claim 1, wherein: In the multi-stage purification process, the supercritical CO2 extraction pressure is 10-14 MPa, the temperature is 35-45°C, the CO2 flow rate is 20-40 L / h, and the extraction time is 15-25 min; the recrystallization uses a 75% ethanol-ethyl acetate mixture with a material-liquid ratio w / v of 1:4-1:6, and crystallization is carried out at 2-8°C for 1.5-3 h.

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