Preparation method of hydroxyanisole

Abstract

The invention belongs to the technical field of chemical production, and particularly relates to a preparation method of hydroxyanisole. A vertical segmented fixed bed reactor is adopted for reaction, the vertical segmented fixed bed reactor is divided into n reaction sections in the axial direction, and each reaction section independently controls the reaction temperature and is provided with a hydrogen peroxide feeding port; the method comprises the following steps: filling a catalyst in a reactor in a gradient manner, introducing an anisole solution from an anisole feed port of a first reaction section, introducing hydrogen peroxide from hydrogen peroxide feed ports of all reaction sections, decreasing the mass percent of the hydrogen peroxide introduced into all the reaction sections from the first reaction section to the nth reaction section, increasing the reaction temperature gradient of all the reaction sections, a hydroxyanisole product is obtained. According to the method provided by the invention, the utilization efficiency of the oxidant can be improved, side reactions are reduced, the controllability of the reaction process is enhanced, and the production efficiency and the product yield of the hydroxyanisole are optimized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical production, and particularly relates to a preparation method of hydroxyanisole. BACKGROUND

[0002] Hydroxyanisole (including p-hydroxyanisole and o-hydroxyanisole) is an important intermediate for the synthesis of medicines, spices and pesticides. The p-hydroxyanisole can be used as a polymerization inhibitor for acrylonitrile, acrylic acid and other vinyl monomers, and can be directly involved in the terpolymerization without removal after addition, which makes it irreplaceable in the polymer material industry and has high economic value.

[0003] At present, there are three main methods for preparing hydroxyanisole, namely, aminoanisole diazotization hydrolysis method, phenol methylation method and anisole hydroxylation method. The aminoanisole diazotization hydrolysis method has the characteristics of high pollution, low efficiency and high safety risk, and has been gradually replaced in industrial production. Compared with the phenol methylation method, the anisole hydroxylation method has the characteristics of low raw material cost, mild reaction conditions and good environmental protection. With the maturity of the preparation process of titanium silicalite molecular sieve, the advantages of the anisole hydroxylation method using titanium silicalite molecular sieve as a catalyst will be further highlighted, and it is expected to become the mainstream process for producing hydroxyanisole.

[0004] The related technology discloses a preparation method of TS-1 molecular sieve and application of the TS-1 molecular sieve in anisole hydroxylation reaction. The TS-1 molecular sieve with high catalytic activity is prepared by adding a surfactant and combining with a dry gel crystallization method. The TS-1 molecular sieve, anisole and a solvent are uniformly mixed, and hydrogen peroxide is added under stirring to perform a hydroxylation reaction, so that a good conversion rate and p-selectivity are obtained. The related technology discloses a method for synthesizing p-hydroxyanisole by catalyzing anisole oxidation with TS-1 titanium silicalite molecular sieve. The oxidant used is hydrogen peroxide, which reduces the generation of black tar and improves the yield. Acetonitrile and tert-butyl alcohol are used as system solvents to improve the selectivity of p-hydroxyanisole. The related technology discloses a method for co-producing p-hydroxyanisole and o-hydroxyanisole by anisole hydroxylation reaction. Anisole and hydrogen peroxide have the advantages of simple and efficient process flow, convenient and stable process operation, high product purity, low operating temperature in the separation process, small quality loss and the like, and are suitable for industrial application.

[0005] However, in actual production, the anisole hydrogen peroxide hydroxylation process still has the following technical bottlenecks:

[0006] 1. Low utilization efficiency of oxidant: the concentration of hydrogen peroxide is too high at the beginning of the reaction, and then decomposition side reactions occur (the effective utilization rate of hydrogen peroxide is only 30% to 40%). In addition, the local concentration of hydrogen peroxide is too high, which easily causes decomposition reactions or deep oxidation side reactions (phenolic oxidation, etc.), generates black tar, and reduces the selectivity and yield of the target product.

[0007] 2. Reaction heat runaway risk: The reaction is a strong exothermic reaction, which makes it difficult to control the bed temperature, easy to form local hot spots, accelerate catalyst deactivation, and even exist safety hazards.

[0008] 3. Insufficient process flexibility: unable to adjust the concentration of oxidizing agent in real time according to the reaction progress, poor adaptability to catalysts with different activities and raw material purity, limiting the utilization rate of raw materials and production efficiency.

[0009] In summary, the existing technology disclosed in the prior art anisole hydroxylation process has the problems of low utilization efficiency of oxidizing agent, more side reactions, and poor controllability of the reaction process. SUMMARY

[0010] The purpose of the present application is to provide a preparation method of hydroxyanisole. The method provided by the present application can improve the utilization efficiency of oxidizing agent, reduce the occurrence of side reactions, and enhance the controllability of the reaction process, thereby optimizing the production efficiency and product yield of hydroxyanisole.

[0011] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0012] The present application provides a preparation method of hydroxyanisole, which uses a vertical sectional fixed bed reactor for reaction. The vertical sectional fixed bed reactor is divided into n reaction sections along the axial direction, n≥3, from bottom to top, the first reaction section, the second reaction section, …, the nth reaction section, each reaction section independently controls the reaction temperature and is provided with a hydrogen peroxide inlet, and the first reaction section is further provided with an anisole inlet; the first reaction section or the first reaction section and the second reaction section are filled with dilution catalyst, and the remaining reaction sections are filled with catalyst, wherein the dilution catalyst comprises a first molecular sieve catalyst and a dilution material, and the catalyst comprises a second molecular sieve catalyst.

[0013] The preparation method comprises the following steps:

[0014] An anisole solution is introduced from the anisole inlet of the first reaction section, and hydrogen peroxide is introduced from the hydrogen peroxide inlet of each reaction section. The mass percentage of hydrogen peroxide introduced into each reaction section decreases from the first reaction section to the nth reaction section. Anisole hydroxylation reaction is carried out in the vertical sectional fixed bed reactor. The reaction temperature of the first reaction section or the first reaction section and the second reaction section is lower than that of the remaining reaction sections, thereby obtaining the hydroxyanisole.

[0015] Preferably, the first molecular sieve catalyst and the second molecular sieve catalyst independently comprise one or more of TS-1, Ti-Beta, Ti-MWW and Ti-MSE.

[0016] Preferably, the dilution material comprises quartz sand and / or ceramic balls, and the volume ratio of the first molecular sieve catalyst to the dilution material is 1:1 to 1:2.

[0017] Preferably, the mass content of H2O2 in the hydrogen peroxide solution is 27.5 to 50 wt%.

[0018] Preferably, the anisole solution comprises anisole and an organic solvent; the organic solvent comprises one or more of methanol, ethanol, acetonitrile and acetone; and the mass ratio of the anisole to the organic solvent is 1:1.5 to 1:2.5.

[0019] Preferably, the molar ratio of anisole in the anisole solution to H2O2 in the hydrogen peroxide solution is 1:1.1 to 1:1.3.

[0020] Preferably, n is 3 to 5; when n is 3, the mass percentages of the hydrogen peroxide fed into the first reaction section, the second reaction section and the third reaction section are 50%, 30% and 20%, respectively; when n is 4, the mass percentages of the hydrogen peroxide fed into the first reaction section, the second reaction section, the third reaction section and the fourth reaction section are 40%, 30%, 20% and 10%, respectively; and when n is 5, the mass percentages of the hydrogen peroxide fed into the first reaction section, the second reaction section, the third reaction section, the fourth reaction section and the fifth reaction section are 30%, 25%, 20%, 15% and 10%, respectively.

[0021] Preferably, the anisole solution further comprises a preheating treatment before being fed into the first reaction section, and the temperature of the preheated anisole solution is 40 to 90°C.

[0022] Preferably, the reaction temperature of the first reaction section is 40 to 75°C, and the reaction temperatures of the remaining reaction sections are independently 80 to 100°C.

[0023] Alternatively, the reaction temperatures of the first reaction section and the second reaction section are independently 40 to 75°C, and the reaction temperatures of the remaining reaction sections are independently 80 to 100°C.

[0024] Preferably, each reaction section is provided with a temperature control system, which monitors the actual reaction temperature of each reaction section in real time and links to the frequency converter of the hydrogen peroxide pump.

[0025] The temperature control system controls the absolute value of the difference between the actual reaction temperature and the set reaction temperature of each reaction section to be ≤5°C.

[0026] When the temperature of a reaction section exceeds 110°C, the temperature control system of the reaction section automatically cuts off the hydrogen peroxide feed of the reaction section, and simultaneously starts the jacket circulating water quenching to reduce the temperature to the set value ±10°C within 5 minutes.

[0027] The application provides a preparation method of hydroxyanisole, which adopts a vertical sectional fixed bed reactor for reaction, the vertical sectional fixed bed reactor is divided into n reaction sections along the axial direction, n is greater than or equal to 3, and the reaction sections are sequentially the first reaction section, the second reaction section,..., and the n-th reaction section from bottom to top, each reaction section is independently controlled in reaction temperature and is provided with a hydrogen peroxide feeding port, and the first reaction section is further provided with an anisole feeding port; the first reaction section or the first reaction section and the second reaction section are filled with dilution catalyst, and the remaining reaction sections are filled with catalyst, the dilution catalyst comprises a first molecular sieve catalyst and a dilution material, and the catalyst comprises a second molecular sieve catalyst; the preparation method comprises the following steps: anisole solution is introduced from the anisole feeding port of the first reaction section, hydrogen peroxide is introduced from the hydrogen peroxide feeding port of each reaction section, the mass percentage of hydrogen peroxide introduced by each reaction section decreases from the first reaction section to the n-th reaction section, anisole hydroxylation reaction is carried out in the vertical sectional fixed bed reactor, the reaction temperature of the first reaction section or the first reaction section and the second reaction section is lower than that of the remaining reaction sections, and the hydroxyanisole is obtained.

[0028] Compared with the prior art, the application has the following advantages:

[0029] The preparation method provided by the application improves the effective utilization rate of hydrogen peroxide and the selectivity of the target product: by implementing the strategy of adding hydrogen peroxide in sections and batches, the application effectively avoids the abnormal increase of local concentration, thereby reducing the decomposition side reaction of hydrogen peroxide, so that the effective utilization rate of hydrogen peroxide is improved to more than 60%; at the same time, by reducing the deep oxidation side reaction, the selectivity of the target product can also reach more than 95%.

[0030] The preparation method provided by the application optimizes the controllability of the reaction temperature: by accurately matching the independently segmented temperature control system with the catalytic activity gradient, the application effectively controls the temperature difference of the catalyst bed, effectively inhibits the formation of hot spots, reduces the deactivation rate of the catalyst, and thus prolongs the service life of the catalyst to more than 1200 hours.

[0031] The preparation method provided by the application improves the safety of the preparation process and the flexibility of the operation: by segmenting the delivery of hydrogen peroxide, the application significantly reduces the risk of the reaction system; in addition, the application can flexibly adjust the number of sections and the feeding ratio according to the characteristics of raw materials and catalysts to adapt to different production modes with different capacity demands. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Reaction principle diagram for decomposition reaction or deep oxidation side reaction (phenolic oxidation) caused by too high local concentration of hydrogen peroxide when anisole reacts with H2O2. DETAILED DESCRIPTION

[0033] The present application provides a preparation method of hydroxyanisole, which adopts a vertical sectional fixed bed reactor for reaction, the vertical sectional fixed bed reactor is divided into n reaction sections along the axial direction, n≥3, from bottom to top, the reaction sections are the 1st reaction section, the 2nd reaction section, …, the nth reaction section, the reaction temperature of each reaction section is independently controlled and a hydrogen peroxide feeding port is arranged, the 1st reaction section is further provided with an anisole feeding port; the 1st reaction section or the 1st reaction section and the 2nd reaction section are filled with a dilution catalyst, and the remaining reaction sections are filled with a catalyst, the dilution catalyst comprises a first molecular sieve catalyst and a dilution material, and the catalyst comprises a second molecular sieve catalyst;

[0034] The preparation method comprises the following steps:

[0035] The anisole solution is introduced from the anisole feeding port of the 1st reaction section, the hydrogen peroxide is introduced from the hydrogen peroxide feeding port of each reaction section, the mass percentage of the hydrogen peroxide introduced by each reaction section decreases from the 1st reaction section to the nth reaction section, the anisole hydroxylation reaction is carried out in the vertical sectional fixed bed reactor, the reaction temperature of the 1st reaction section or the 1st reaction section and the 2nd reaction section is lower than that of the remaining reaction sections, and the hydroxyanisole is obtained.

[0036] In the present application, all the preparation raw materials / components are commercially available products well known to those skilled in the art, unless otherwise specified.

[0037] The preparation method provided by the present application adopts a vertical sectional fixed bed reactor. In the present application, n can be 3, 4 or 5. In the present application, the vertical sectional fixed bed reactor can have an inner diameter of 20-25 mm and a height of 3-4 m. The catalyst in the vertical sectional fixed bed reactor is filled by a gradient filling method. The first molecular sieve catalyst preferably comprises one or more of TS-1, Ti-Beta, Ti-MWW and Ti-MSE. The dilution material preferably comprises quartz sand and / or ceramic balls. The volume ratio of the first molecular sieve catalyst to the dilution material is preferably 1:1-1:2, and in the examples, can be 1:1.5, 1:1.3 or 1:1.2. In the present application, the dilution catalyst is filled in the first reaction section, and the remaining reaction sections are filled with the catalyst. Alternatively, in the present application, the dilution catalyst is filled in the first reaction section and the second reaction section, and the remaining reaction sections are filled with the catalyst. Thus, the present application can reduce the initial reaction activity in the initial reaction stage of the first reaction section or the first reaction section and the second reaction section, and avoid excessive decomposition of hydrogen peroxide. At the same time, the present application fills the remaining reaction sections with the catalyst (not diluted), which can improve the subsequent reaction efficiency, thereby forming a gradient distribution of catalytic activity in the vertical sectional fixed bed reactor, which is beneficial to improving the effective utilization rate of hydrogen peroxide and the selectivity of the target product.

[0038] In the present application, the mass content of H2O2 in the hydrogen peroxide is preferably 27.5-50 wt%, and in the examples, can be 35 wt%. In the present application, when n is 3, the mass percentages of hydrogen peroxide fed into the first reaction section, the second reaction section and the third reaction section are preferably 50%, 30% and 20%, respectively. When n is 4, the mass percentages of hydrogen peroxide fed into the first reaction section, the second reaction section, the third reaction section and the fourth reaction section are preferably 40%, 30%, 20% and 10%, respectively. When n is 5, the mass percentages of hydrogen peroxide fed into the first reaction section, the second reaction section, the third reaction section, the fourth reaction section and the fifth reaction section are preferably 30%, 25%, 20%, 15% and 10%, respectively.

[0039] In the present application, the anisole solution preferably comprises anisole and an organic solvent. The organic solvent preferably comprises one or more of methanol, ethanol, acetonitrile and acetone. The mass ratio of the anisole to the organic solvent is preferably 1:1.5-1:2.5, and in the examples, can be 1:2 or 1:2.5.

[0040] In the present application, the anisole solution is preferably continuously fed, and the feeding amount of the anisole solution is preferably 0.75-0.88 kg / h, and in the examples, can be 0.75 kg / h or 0.88 kg / h.

[0041] In the present application, the molar ratio of anisole in the anisole solution to H2O2 in the hydrogen peroxide is preferably 1:1.1-1:1.3, and in the embodiments, it can be 1:1.1 or 1:1.2. The molar ratio of anisole in the anisole solution to H2O2 in the hydrogen peroxide in the present application refers to the molar ratio of anisole in the anisole solution to the total amount of H2O2 in the hydrogen peroxide fed into the n reaction sections.

[0042] In the present application, the anisole solution preferably further comprises a preheating process before being fed into the first reaction section, and the temperature of the preheated anisole solution is preferably 40-90°C, and in the embodiments, it can be 55°C or 60°C.

[0043] In the present application, the reaction temperature of the first reaction section is preferably 40-75°C, and in the embodiments, it can be 50°C, 55°C, 70°C or 75°C; and the reaction temperature of the remaining reaction sections is independently preferably 80-100°C, and in the embodiments, it can be 80°C or 90°C.

[0044] Alternatively, the reaction temperature of the first reaction section and the second reaction section is independently preferably 40-75°C, and in the embodiments, it can be 50°C, 55°C, 70°C or 75°C, and the reaction temperature of the remaining reaction sections is independently preferably 80-100°C, and in the embodiments, it can be 80°C or 90°C.

[0045] In the present application, the reaction temperature of each reaction section is preferably: the reaction temperature of the first reaction section < the reaction temperature of the second reaction section < the reaction temperature of the third reaction section < … < the reaction temperature of the n reaction section. In the present application, when n is preferably 3, the reaction temperature of the first reaction section is preferably 50-55°C. The reaction temperature of the second reaction section is preferably 70-75°C. The reaction temperature of the third reaction section is preferably 80-90°C. In the present application, when n is preferably 4, the reaction temperature of the first reaction section is preferably 50-55°C. The reaction temperature of the second reaction section is preferably 70-75°C. The reaction temperature of the third reaction section is preferably 80-90°C. The reaction temperature of the fourth reaction section is preferably 90°C.

[0046] In the present application, by controlling the reaction temperature of the first reaction section or the first reaction section and the second reaction section to be preferably 40-75°C, the decomposition of H2O2 in the hydrogen peroxide can be effectively inhibited in the initial stage of the reaction; at the same time, by controlling the temperature of the remaining reaction sections to be 80-100°C, the reaction rate of the anisole hydroxylation reaction can be effectively improved, and the yield of the target product is increased.

[0047] In this invention, the anisole solution passes through the vertical segmented fixed-bed reactor from bottom to top, contacting hydrogen peroxide in the catalyst bed of each reaction section to carry out the anisole hydroxylation reaction. In this invention, the pressure of the anisole hydroxylation reaction in the vertical segmented fixed-bed reactor is preferably 0.6–1 MPa, and in the examples it can be 0.8 MPa, 0.6 MPa, or 1 MPa.

[0048] In this invention, each reaction section is preferably equipped with a temperature control system, which preferably includes thermocouples. The temperature control system preferably monitors the actual reaction temperature of each reaction section in real time and links it to the frequency converter of the hydrogen peroxide pump. The temperature control system preferably controls the absolute value of the difference between the actual reaction temperature and the set reaction temperature of each reaction section to be ≤5℃. This invention preferably uses a temperature control system to maintain the actual reaction temperature of each reaction section at an absolute value ≤5℃ from the set reaction temperature, which can effectively suppress the formation of local hot spots during the reaction process, reduce the catalyst deactivation rate, and further extend the catalyst's service life.

[0049] In this invention, when the temperature of a certain reaction section exceeds 110°C, the temperature control system of that reaction section preferably automatically cuts off the hydrogen peroxide feed to that reaction section and starts the jacket circulating water rapid cooling, cooling down to the set value ±10°C within 5 minutes.

[0050] In summary, the preparation method provided by this invention achieves the production of hydroxyanisole through staged addition of hydrogen peroxide, catalytic activity gradient matching, and precise temperature control via a segmented fixed-bed reactor, solving the problems of low selectivity, high risk of thermal runaway, and poor operational flexibility in traditional processes.

[0051] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1:

[0053] This embodiment provides a method for preparing hydroxyanisole using a vertical segmented fixed-bed reactor. The reactor is divided into three reaction sections along the axial direction: reaction section 1, reaction section 2, and reaction section 3 from bottom to top. Each reaction section has independently controlled reaction temperature and a hydrogen peroxide inlet. The reaction section 1 also has an anisole inlet. The vertical segmented fixed-bed reactor has an inner diameter of 20 mm and a total height of 3 m. The reaction section 1 is filled with a diluting catalyst composed of TS-1 and ceramic balls in a volume ratio of 1:1.5. The reaction sections 2 and 3 are filled with TS-1 molecular sieves. Feed distribution of 35wt% hydrogen peroxide (mass percentage): 50% in reaction zone 1, 30% in reaction zone 2, and 20% in reaction zone 3; feed rate of anisole solution: 0.75 kg / h (mass ratio of anisole to solvent acetone: 1:2, preheated to 55℃); molar ratio of anisole to H2O2 in hydrogen peroxide: 1:1.1; temperature control scheme: 50℃ in reaction zone 1, 75℃ in reaction zone 2, and 95℃ in reaction zone 3; operating pressure: 0.8 MPa.

[0054] Example 2:

[0055] This embodiment provides a method for preparing hydroxyanisole using a vertical segmented fixed-bed reactor. The reactor is divided into three reaction sections along the axial direction: reaction section 1, reaction section 2, and reaction section 3 from bottom to top. Each reaction section has independently controlled reaction temperature and a hydrogen peroxide inlet. The reaction section 1 also has an anisole inlet. The vertical segmented fixed-bed reactor has an inner diameter of 20 mm and a total height of 3 m. The reaction section 1 is filled with a diluting catalyst composed of TS-1 and ceramic balls in a volume ratio of 1:1.3. The reaction sections 2 and 3 are filled with TS-1 molecular sieves. Feed distribution of 35wt% hydrogen peroxide (mass percentage): 50% in reaction zone 1, 30% in reaction zone 2, and 20% in reaction zone 3; feed rate of anisole solution: 0.75 kg / h (mass ratio of anisole to methanol solvent: 1:2, preheated to 55℃); molar ratio of anisole to H2O2 in hydrogen peroxide: 1:1.2; temperature control scheme: 50℃ in reaction zone 1, 70℃ in reaction zone 2, and 90℃ in reaction zone 3; operating pressure: 0.6 MPa.

[0056] Example 3:

[0057] This embodiment provides a method for preparing hydroxyanisole using a vertical segmented fixed-bed reactor. The reactor is divided into four reaction sections along the axial direction: reaction section 1, reaction section 2, reaction section 3, and reaction section 4, from bottom to top. Each reaction section has independently controlled reaction temperature and a hydrogen peroxide inlet. Reaction section 1 also has an anisole inlet. The vertical segmented fixed-bed reactor has an inner diameter of 25 mm and a total height of 4 m. Reaction sections 1 and 2 are filled with a diluting catalyst composed of TS-1 and ceramic balls in a volume ratio of 1:1.3. Reaction sections 3 and 4 are filled with TS-1 molecular sieves. Feed distribution of 35wt% hydrogen peroxide (mass percentage): 40% in reaction zone 1, 30% in reaction zone 2, 20% in reaction zone 3, and 10% in reaction zone 4; feed rate of anisole solution: 0.88 kg / h (mass ratio of anisole to solvent acetone: 1:2.5, preheated to 60℃); molar ratio of anisole to H2O2 in hydrogen peroxide: 1:1.1; temperature control scheme: 55℃ in reaction zone 1, 70℃ in reaction zone 2, 80℃ in reaction zone 3, and 90℃ in reaction zone 4; operating pressure: 0.8 MPa.

[0058] Example 4:

[0059] This embodiment provides a method for preparing hydroxyanisole using a vertical segmented fixed-bed reactor. The reactor is divided into four reaction sections along the axial direction: reaction section 1, reaction section 2, reaction section 3, and reaction section 4, from bottom to top. Each reaction section has independently controlled reaction temperature and a hydrogen peroxide inlet. Reaction section 1 also has an anisole inlet. The vertical segmented fixed-bed reactor has an inner diameter of 25 mm and a total height of 4 m. Reaction sections 1 and 2 are filled with a diluting catalyst composed of TS-1 and ceramic balls in a volume ratio of 1:1.2. Reaction sections 3 and 4 are filled with TS-1 molecular sieves. Feed distribution of 35wt% hydrogen peroxide (mass percentage): 40% in reaction zone 1, 30% in reaction zone 2, 20% in reaction zone 3, and 10% in reaction zone 4; feed rate of anisole solution: 0.88 kg / h (mass ratio of anisole to methanol solvent: 1:2.5, preheated to 60℃); molar ratio of anisole to H2O2 in hydrogen peroxide: 1:1.2; temperature control scheme: 55℃ in reaction zone 1, 70℃ in reaction zone 2, 80℃ in reaction zone 3, and 90℃ in reaction zone 4; operating pressure: 1.0 MPa.

[0060] Comparative Example 1:

[0061] This embodiment provides a method for preparing hydroxyanisole, using a vertical, non-segmented fixed-bed reactor with an inner diameter of 20 mm and a height of 3 m, filled with TS-1 molecular sieves. Feed: 35% hydrogen peroxide is uniformly mixed with an anisole solution preheated to 55°C (mass ratio of anisole to solvent acetone is 1:2, feed rate of anisole solution (excluding hydrogen peroxide) is 0.75 kg / h), and then passed from bottom to top through the catalyst bed. The molar ratio of anisole to hydrogen peroxide is 1:1.1; the temperature is controlled at 85°C; the operating pressure is 0.8 MPa.

[0062] Test example:

[0063] In the embodiments and comparative examples of the present invention, an Agilent gas chromatograph was used, and the contents of anisole, o-hydroxyanisole and p-hydroxyanisole in the system were determined by external standard method, and hydrogen peroxide was determined by iodometric method.

[0064] The conversion rate of anisole, the selectivity of p-hydroxyanisole, and the effective utilization rate of hydrogen peroxide are calculated using the following formulas:

[0065]

[0066]

[0067]

[0068] Table 1. Reaction results of different embodiments

[0069]

[0070] Table 1 shows the optimal data for each example and comparative example experiment (the reaction between reactants and catalyst requires a certain period of time, and the time for the conversion rate to reach the optimal value may vary slightly for each example). Furthermore, Example 1 maintained a high anisole conversion rate, hydroxyanisole selectivity, and hydrogen peroxide utilization rate (greater than 42.0%, 95.2%, and 62.0%, respectively) after 1200 hours of reaction. In contrast, Comparative Example 1 showed a significant decrease in anisole conversion rate, hydroxyanisole selectivity, and hydrogen peroxide utilization rate after approximately 960 hours of reaction (26.7%, 80.6%, and 27.2%, respectively). These experimental results demonstrate that using a segmented fixed-bed reactor and rationally controlling the process parameters of each segment, such as feed distribution, temperature, and pressure, can significantly improve the anisole conversion rate, hydroxyanisole selectivity, and hydrogen peroxide utilization rate compared to a non-segmented reactor. Different temperature control schemes and variations in the molar ratio of anisole to hydrogen peroxide in the feed also resulted in different reaction effects in each example. These data indicate that the segmented fixed-bed reactor and corresponding process parameter optimization proposed in this invention are of great significance for the production process of hydroxyanisole, enabling better utilization of raw materials and reduction of production costs while improving production efficiency and product quality.

[0071] As can be seen from the above embodiments, the preparation method provided by the present invention can improve the utilization efficiency of oxidant, reduce the occurrence of side reactions, enhance the controllability of the reaction process, and optimize production efficiency and product yield.

[0072] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing hydroxyanisole, characterized in that, The reaction is carried out in a vertical segmented fixed-bed reactor, which is divided into n reaction sections along the axial direction, where n≥3, and from bottom to top are reaction section 1, reaction section 2, ..., reaction section n. Each reaction section independently controls the reaction temperature and is equipped with a hydrogen peroxide inlet. The first reaction section is also equipped with an anisole inlet. The first reaction section, or the first and second reaction sections, is filled with a dilution catalyst, and the remaining reaction sections are filled with catalyst. The dilution catalyst includes a first molecular sieve catalyst and a dilution material, and the catalyst includes a second molecular sieve catalyst. The preparation method includes the following steps: An anisole solution is introduced through the anisole inlet of the first reaction section, and hydrogen peroxide is introduced through the hydrogen peroxide inlets of each reaction section. The mass percentage of hydrogen peroxide introduced into each reaction section decreases from the first reaction section to the nth reaction section. The anisole hydroxylation reaction is carried out in a vertical segmented fixed-bed reactor. The reaction temperature of the first reaction section or the first and second reaction sections is lower than the reaction temperature of the remaining reaction sections to obtain the hydroxyanisole.

2. The preparation method according to claim 1, characterized in that, The first molecular sieve catalyst and the second molecular sieve catalyst independently include one or more of TS-1, Ti-Beta, Ti-MWW and Ti-MSE.

3. The preparation method according to claim 1 or 2, characterized in that, The diluting material includes quartz sand and / or ceramic balls, and the volume ratio of the first molecular sieve catalyst to the diluting material is 1:1 to 1:

2.

4. The preparation method according to claim 1, characterized in that, The hydrogen peroxide contains 27.5–50 wt% H2O2.

5. The preparation method according to claim 1, characterized in that, The anisole solution comprises anisole and an organic solvent; the organic solvent comprises one or more of methanol, ethanol, acetonitrile and acetone; the mass ratio of the anisole to the organic solvent is 1:1.5 to 1:2.

5.

6. The preparation method according to claim 1, 4, or 5, characterized in that, The molar ratio of anisole in the anisole solution to H2O2 in the hydrogen peroxide is 1:1.1 to 1:1.

3.

7. The preparation method according to claim 1 or 4, characterized in that, The value of n is 3 to 5; when n is 3, the mass percentages of hydrogen peroxide introduced into the first, second, and third reaction sections are 50%, 30%, and 20%, respectively; when n is 4, the mass percentages of hydrogen peroxide introduced into the first, second, third, and fourth reaction sections are 40%, 30%, 20%, and 10%, respectively; when n is 54, the mass percentages of hydrogen peroxide introduced into the first, second, third, fourth, and fifth reaction sections are 30%, 25%, 20%, 15%, and 10%, respectively.

8. The preparation method according to claim 1 or 5, characterized in that the anisole solution is further subjected to a preheating treatment before being introduced into the first reaction section, and the temperature of the preheated anisole solution is 40-90°C.

9. The preparation method according to claim 1, characterized in that the reaction temperature of the first reaction zone is 40-75°C, and the reaction temperature of the remaining reaction zones is independently 80-100°C; Alternatively, the reaction temperatures of the first and second reaction zones can be independently set at 40–75°C, and the reaction temperatures of the remaining reaction zones can be independently set at 80–100°C.

10. The preparation method according to claim 1 or 9, characterized in that each reaction section is equipped with a temperature control system, wherein the temperature control system monitors the actual reaction temperature of each reaction section in real time and links the hydrogen peroxide pump frequency converter. The temperature control system ensures that the absolute value of the difference between the actual reaction temperature and the set reaction temperature in each reaction zone is ≤5℃. When the temperature of a certain reaction section exceeds 110℃, the temperature control system of that reaction section automatically cuts off the hydrogen peroxide feed to that reaction section and simultaneously starts the jacket circulating water rapid cooling, cooling down to the set value ±10℃ within 5 minutes.

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