Process for the continuous catalytic oxidation preparation of p-menthane hydroperoxide

Abstract

The present application relates to the technical field of peroxide, and particularly relates to a process for preparing p-menthane hydroperoxide by continuous catalytic oxidation, comprising: mixing p-menthane after dehydration with a core-shell structure Fe-based heterogeneous catalyst and an initiator to obtain a homogeneous raw material solution; continuously feeding the homogeneous raw material solution and an oxygen-containing gas stream into the bottom of an oxidation reactor respectively to perform an oxidation reaction; separating a gas-liquid mixture obtained in the oxidation reaction, treating a gas phase, and discharging the treated gas phase; dividing a liquid phase into two paths, returning one path as a circulating stream to the reactor, and outputting the other path as a product extraction stream; performing at least one stage of vacuum concentration on the product extraction stream, recovering unreacted p-menthane, and obtaining p-menthane hydroperoxide crude product, and continuously performing the oxidation and separation steps. The components of the catalyst of the present application cooperate with each other and exhibit good performance in the process for preparing p-menthane hydroperoxide by continuous catalytic oxidation.

Description

Technical Field

[0001] This invention relates to the field of peroxide technology, and more particularly to a continuous catalytic oxidation process for preparing hydrogen peroxide-paraben. Background Technology

[0002] p-Mandane, an organic peroxide, is primarily used as a highly efficient free radical initiator in emulsion polymerization reactions. It can be used in the synthesis of various polymers such as styrene-butadiene rubber, acrylonitrile-butadiene-styrene copolymers, and styrene-acrylonitrile copolymers. It also plays a crucial role in the low-temperature curing of unsaturated polyester resins, often used in conjunction with accelerators such as cobalt salts to initiate the copolymerization and crosslinking reaction between the resin and vinyl monomers. p-Mandane, as the main raw material for the preparation of p-Mandane, is typically derived from the catalytic hydrogenation process of turpentine oil or other petrochemical routes. The tert-butyl and isopropyl substituents in its molecular structure endow it with specific oxidative reactivity. Continuous catalytic oxidation technology is an important process route for the preparation of p-Mandane. This technology uses air or oxygen-enriched air as a green oxidant, achieving selective oxidation of mentane by constructing a stable gas-liquid contact system in the reactor to generate the target peroxide product.

[0003] In terms of catalytic systems, transition metal salts such as cobalt salts and manganese salts are commonly used catalyst types. Some studies also use metal porphyrins, supported noble metals and other catalytic materials. These catalysts can promote the selective oxidation of specific carbon-hydrogen bonds in menthol molecules by regulating the free radical generation process in the reaction system. At the same time, some processes add a small amount of hydrogen peroxide as an initiator for menthol to accelerate the reaction start-up.

[0004] However, while homogeneous transition metal catalysts such as cobalt and manganese salts can be uniformly dispersed in the organic liquid system of menthol, rapidly initiating free radical chain oxidation reactions and adapting to continuous flow reaction kinetics, the dissolved catalyst flows out of the reactor simultaneously with the continuously entering and exiting reactants, unable to be retained and circulated in situ within the reaction system. This significant loss of catalyst directly increases raw material consumption and production costs. Simultaneously, residual transition metal ions in the product accelerate the thermal decomposition of menthol by hydrogen peroxide, reducing product storage stability, interfering with downstream polymer polymerization and cross-linking reactions, and causing polymer color differences, decreased aging resistance, and fluctuations in mechanical properties. Furthermore, free metal ions can disorderly induce free radical side reactions, exacerbating the generation of deep oxidation impurities, disrupting oxidation selectivity, and the continuous discharge mode can cause continuous fluctuations in the catalyst concentration, leading to unstable reaction rates and poor product quality uniformity. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a continuous catalytic oxidation process for preparing terane hydrogen peroxide.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A continuous catalytic oxidation process for preparing p-menthol peroxide includes the following steps:

[0008] S1. Dehydrate p-menthol and mix it with a heterogeneous catalyst and initiator to obtain a homogeneous feed solution; the p-menthol is dehydrated by distillation, and the water content of the p-menthol after dehydration is ≤0.05wt%; the amount of heterogeneous catalyst added is 0.8-1.2% of the total mass of p-menthol;

[0009] S2. The homogeneous feed liquid is continuously pumped into the bottom of the oxidation reactor, while oxygen-containing streams are continuously introduced into the bottom of the oxidation reactor through a gas distributor to carry out the oxidation reaction, resulting in a gas-liquid mixture containing hydrogen peroxide and para-menthol. The volume fraction of oxygen in the oxygen-containing stream is 90-99%, with the remainder being inert gases, selected from nitrogen or argon. The orifice diameter of the gas distributor is 10-50 μm, and the volume ratio of the gas flow rate to the homogeneous feed liquid pumping rate is (3-8):1. The oxidation reactor is a fixed-bed reactor, filled with inert packing material, selected from ceramic rings or quartz sand, with a packing particle size of 3-8 mm.

[0010] S3. Separate the gas-liquid mixture. The resulting gas phase is treated and discharged, while the resulting liquid oxidation product stream is divided into two streams. The first stream is returned to the oxidation reactor as a circulating stream to participate in the reaction, and the second stream is output as the product outflow. The gas-liquid separation uses a gas-liquid separator with a separation temperature of 30-40℃ and a separation pressure of atmospheric pressure. The gas phase treatment uses activated carbon adsorption with an adsorption temperature of 25-35℃ and an adsorption time of 0.5-1h. After treatment, the organic matter content in the gas phase is ≤50mg / m³. 3 ;

[0011] S4. The product effluent is subjected to at least one stage of vacuum concentration to separate and recover unreacted p-mentholane, yielding crude p-mentholane hydroperoxide. The recovered unreacted p-mentholane is purified by distillation and returned to step S1 for reuse. The distillation conditions are: 15-25 theoretical plates in the distillation column, reflux ratio of 3-5:1, top temperature of 160-170℃, bottom temperature of 180-190℃, and operation at atmospheric pressure; the purity of the crude p-mentholane hydroperoxide is ≥85 wt%.

[0012] Steps S2 and S3 are performed consecutively.

[0013] The heterogeneous catalyst has a core-shell structure, consisting of an inner core with an Fe-NC coordination structure and an outer layer of hydrophobically modified inorganic shell. A mesoporous isolation shell is provided between the inner core and the hydrophobically modified inorganic shell. The heterogeneous catalyst is an Fe-based catalyst.

[0014] Further, in step S1, the amount of initiator added is 0.6-1.0% of the total mass of p-menthol, and the initiator is selected from purified p-menthol with a mass fraction ≥50%; the mixing process is carried out under inert gas protection and constant temperature conditions of 20-30℃, and the stirring speed is controlled at 120-180 rpm during mixing, and stirring is continued for 15-25 min; the inert gas is selected from one or a mixture of nitrogen and argon, and the inert gas introduction rate is 0.5-1 L / min; the mixing is carried out by mechanical stirring; the purity of purified p-menthol with hydrogen peroxide is ≥98 wt%.

[0015] Furthermore, the heterogeneous catalyst in step S1 is prepared by the following steps:

[0016] A1. Under inert gas protection, acetylenyl ferrocene and melamine are dissolved in an organic solvent, heated to 120-140℃, and stirred in the dark for 4-8 hours to carry out liquid-phase prepolymerization reaction to obtain Fe-NC coordination structure organic core sol.

[0017] A2. Add mesoporous precursor and dispersant to organic core sol, and react at 50-60℃ and 100-150rpm for 8-14h to obtain core complex coated with mesoporous layer; the temperature is controlled by constant temperature water bath during the reaction.

[0018] A3. Mix the core complex with the hydrophobic modifier and the inorganic shell precursor, add solvent and ultrasonically disperse evenly, then stir and react at 70-80℃ for 1-3 hours. After centrifugation, washing and vacuum drying, a heterogeneous catalyst is obtained.

[0019] Furthermore, in step S2, the oxidation reaction temperature is 80-130℃, the reaction pressure is atmospheric pressure to 0.3MPa, and the residence time of the homogeneous feed liquid in the oxidation reactor is 4-8h.

[0020] Furthermore, in step S3, the reflux ratio of the circulating flow to the product outflow is (5-20):1, and the concentration of hydrogen peroxide to monane in the oxidation reactor is controlled at 15-20%.

[0021] Furthermore, the reduced-pressure concentration process in step S4 is carried out continuously using a two-stage or multi-stage falling film evaporator; wherein, the first-stage concentration conditions are: vacuum degree (-0.095) - (-0.085) MPa, temperature 50-70℃; the second-stage concentration conditions are: vacuum degree (-0.098) - (-0.095) MPa, temperature 70-90℃; a buffer tank is provided between the two stages of concentration, with a buffer tank temperature of 40-50℃ and a pressure of -0.080--0.070 MPa; the evaporation rate during the concentration process is 0.1-0.3 kg / (m³). 2 ·h).

[0022] Further, in step A1, the mass ratio of acetylenoid ferrocene to melamine is (1-1.5):(4-8), and the volume ratio of acetylenoid ferrocene to organic solvent is 1g:(60-100)mL, with the organic solvent selected from dimethyl sulfoxide or N,N-dimethylformamide.

[0023] Furthermore, in step A1, the inert gas is selected from one or a mixture of nitrogen and argon, and the introduction rate is 0.3-0.8 L / min; light protection is achieved by wrapping the reaction vessel with black cloth; stirring is done by magnetic stirring at a speed of 200-300 rpm.

[0024] Further, in step A2, the mesoporous precursor is selected from tetraethyl orthosilicate or sodium silicate, and the dispersant is selected from anhydrous ethanol; the amount of mesoporous precursor added is 10-20% of the mass of the organic core sol; the amount of dispersant added is 30-50% of the volume of the organic core sol.

[0025] Further, in step A3, the inorganic shell precursor is selected from magnesium aluminum hydrotalcite or zinc aluminum hydrotalcite, and the hydrophobic modifier is selected from stearic acid or sodium stearate; the mass ratio of the core complex, the hydrophobic modifier, and the inorganic shell precursor is 100:(5-10):(20-30); the magnesium-aluminum molar ratio of magnesium aluminum hydrotalcite is (2-4):1, and the zinc-aluminum molar ratio of zinc aluminum hydrotalcite is (2-3):1.

[0026] Further, in step A3, the solvent is selected from anhydrous ethanol, and the amount added is 5-10 times the mass of the core complex; the ultrasonic dispersion power is 200-300W, and the ultrasonic time is 15-30min; the centrifugation speed is 8000-10000rpm, and the centrifugation time is 10-20min; the washing is performed with anhydrous ethanol 3-5 times; the vacuum drying temperature is 60-80℃, the drying time is 8-12h, and the water content of the catalyst after drying is ≤0.5wt%.

[0027] The beneficial effects of this invention are:

[0028] 1. The core of the catalyst of this invention is a polymer nanophase formed by covalent cross-linking of acetylene-based ferrocene and melamine. Fe atoms are anchored in the conjugated heterocyclic polymer framework through both coordination and covalent bonds, which helps to improve the problem of easy loss of existing homogeneous cobalt and manganese salt catalysts. The covalent anchoring method allows the Fe active centers to be firmly bound to the polymer framework, reducing the probability of them flowing out of the reactor simultaneously with the reactants. This allows them to remain in situ within the reaction system and be recycled, thereby helping to reduce catalyst raw material consumption and production costs.

[0029] 2. The mesoporous isolation shell of the catalyst's intermediate layer in this invention is formed in situ by hydrolysis and condensation of a mesoporous precursor. It possesses a regular and interconnected nanoporous structure. This structural feature not only enables efficient mass transfer between reactants and products but also provides excellent physical isolation. The mesoporous channels provide rapid diffusion pathways for reactants such as menthol and oxygen, allowing them to more efficiently contact the core Fe active center. Simultaneously, it promotes the rapid diffusion of hydrogen peroxide generated from the reaction out of the active region. The mesoporous isolation shell effectively separates the acidic Fe active core from the basic outer inorganic shell, reducing passivation and poisoning deactivation of the Fe active center caused by acid-base interface contact, thus contributing to the stability of the catalyst's catalytic performance during long-term operation.

[0030] 3. The outer layer of the catalyst is a hydrophobically modified layered hydrotalcite inorganic shell, prepared by in-situ modification of the inorganic shell precursor with a hydrophobic modifier. This modification transforms the catalyst surface from hydrophilic to hydrophobic, facilitating uniform dispersion of the catalyst in the organic feed liquid and forming a relatively stable suspension system. This increases the gas-liquid-solid three-phase interface area, improving oxygen dissolution efficiency and reaction rate, and better adapting to the kinetic characteristics of continuous catalytic oxidation processes. Simultaneously, the hydrophobic shell can, to some extent, block trace amounts of water in the system, reducing the intrusion of water molecules into the core and their disruption of the peroxy bond of menthol by hydrogen peroxide, thereby inhibiting the occurrence of hydrolysis and thermal decomposition side reactions. The mildly alkaline sites inherent in the hydrotalcite layers can gently quench excess active free radicals in the system, reducing the possibility of deep oxidation of menthol and menthol by hydrogen peroxide, thus decreasing the formation of byproducts such as alcohols, ketones, and organic acids.

[0031] 4. The core-shell structure of the catalyst in this invention gives it good suspension stability. It is not prone to agglomeration, sedimentation, or wear and breakage under continuous reflux conditions, and can participate in the reaction stably for a long time, ensuring the smooth operation of continuous production. The high efficiency and stability of the catalyst's active center help reduce the amount of initiator used, thereby reducing production energy consumption and costs. At the same time, the catalyst is not prone to metal ion loss, which is beneficial to improving product purity and storage stability, enabling it to better meet the requirements of downstream polymer material synthesis. There is no need to add an additional metal ion removal process, which simplifies the process and reduces production costs. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the following examples and comparative examples, p-menthol was industrial grade with a purity ≥99.0 wt% and a water content ≤0.5 wt%; acetylenyl ferrocene (CAS No.: 1271-47-2) and melamine (CAS No.: 108-78-1) were analytical grade with a purity ≥99%; dimethyl sulfoxide (CAS No.: 67-68-5) and N,N-dimethylformamide (CAS No.: 68-12-2) were analytical grade with a purity ≥99.7%; tetraethyl orthosilicate (CAS No.: 78-10-4) and sodium silicate (CAS No.: 1344-09-8) were analytical grade with a purity ≥98.0%; stearic acid (CAS No.: 57-11-4) and sodium stearate (CAS No.: 822-16-2) were analytical grade with a purity ≥99.0%.

[0034] Example 1

[0035] A continuous catalytic oxidation process for preparing p-menthol peroxide includes the following steps:

[0036] S1. Take 1000g of p-mentholane and dehydrate it by distillation. The water content of the dehydrated p-mentholane is 0.05wt%. Add 7.996g of heterogeneous catalyst (0.8% of the total mass of 999.5g of dehydrated p-mentholane) and 5.997g of initiator (0.6% of the total mass of 999.5g of dehydrated p-mentholane) to the dehydrated p-mentholane. Stir continuously at 120rpm for 15min under nitrogen protection at 20℃ to obtain a homogeneous feed solution. The initiator is 50% by mass of purified hydrogen peroxide p-mentholane.

[0037] Heterogeneous catalysts are prepared by the following steps:

[0038] A1. Under nitrogen protection, take 1g of acetylated ferrocene and 8g of melamine, dissolve them in 60mL of dimethyl sulfoxide, wrap the reaction vessel with black cloth to protect it from light, stir magnetically at 200rpm, heat to 120℃, stir and react for 4h to carry out liquid phase prepolymerization reaction to obtain organic core sol.

[0039] A2. Add 0.9g of tetraethyl orthosilicate and 18mL of anhydrous ethanol to the above 9g organic core sol. Under the conditions of 50℃ and stirring speed of 100rpm, the temperature is controlled by a constant temperature water bath for 8h to obtain the core complex.

[0040] A3. Take 5g of core complex, 0.25g of stearic acid, and 1g of magnesium aluminum hydrotalcite, mix them evenly, add 25mL of anhydrous ethanol, ultrasonically disperse at 200W power for 15min, then stir and react at 70℃ for 1h, centrifuge at 8000rpm for 10min, collect the precipitate, wash it 3 times with anhydrous ethanol, and then vacuum dry at 60℃ for 8h to obtain the heterogeneous catalyst.

[0041] S2. A fixed-bed oxidation reactor with a volume of 5L is selected and filled with 2000g of ceramic ring inert packing with a particle size of 3mm. The homogeneous raw material liquid obtained above is continuously pumped into the bottom of the oxidation reactor. At the same time, oxygen-containing gas is continuously introduced into the bottom of the oxidation reactor through a gas distributor with a pore size of 10μm. The oxidation reaction is carried out at 80℃ and atmospheric pressure. The residence time of the homogeneous raw material liquid in the reactor is controlled to be 4h to obtain a gas-liquid mixture.

[0042] S3. The above gas-liquid mixture is fed into a gas-liquid separator and separated at 30°C and atmospheric pressure. After separation, approximately 2252.4 mL of gas phase and approximately 1010 g of liquid phase are obtained. The obtained gas phase is treated by activated carbon adsorption. An adsorption column filled with 50 g of activated carbon is selected, and the adsorption temperature is controlled at 25°C for 0.5 h. The gas phase is collected after treatment. The 1010 g liquid phase oxidation product stream is divided into two streams. The first stream is returned to the oxidation reactor as a circulating stream (841.7 g) to participate in the reaction, and the second stream is output as a product outflow (168.3 g).

[0043] S4. The 168.3g product effluent is continuously concentrated under reduced pressure using a two-stage falling film evaporator, with a 1L buffer tank between the two concentration stages. The first-stage concentration conditions are: vacuum degree -0.095MPa, temperature 50℃, and evaporation rate 0.1kg / (m³). 2 ·h), with a heat transfer area of ​​0.1m². 2 A falling film evaporator was used, with a concentration time of approximately 1.7 hours, separating approximately 134.6 g of unreacted p-menthane. The secondary concentration conditions were: vacuum -0.098 MPa, temperature 70℃, and evaporation rate 0.1 kg / (m²). 2 The concentration time was approximately 0.3 h, and a small amount of unreacted p-menthol was further separated, approximately 8.4 g. A total of approximately 143 g of unreacted p-menthol was recovered from the two separations. The recovered unreacted p-menthol was purified by distillation to obtain approximately 140 g of qualified p-menthol, which was returned to step S1 for reuse. Finally, 16.9 g of hydrogen peroxide p-menthol was obtained.

[0044] Example 2

[0045] A continuous catalytic oxidation process for preparing p-menthol peroxide includes the following steps:

[0046] S1. Take 1000g of p-mentholane and dehydrate it by distillation. The water content of the dehydrated p-mentholane is 0.03wt%. Add 9.997g of heterogeneous catalyst (1.0% of the total mass of 999.7g of dehydrated p-mentholane) and 7.998g of initiator (0.8% of the total mass of 999.7g of dehydrated p-mentholane) to the dehydrated p-mentholane. Stir continuously at 150rpm for 20min under argon protection at 25℃ to obtain a homogeneous feed solution. The initiator is 70% by mass of purified hydrogen peroxide p-mentholane.

[0047] Heterogeneous catalysts are prepared by the following steps:

[0048] A1. Under argon protection, 1.25g of acetylenyl ferrocene and 6g of melamine were dissolved in 100mL of N,N-dimethylformamide. The reaction vessel was wrapped in black cloth to protect it from light. The mixture was magnetically stirred at 250rpm and heated to 130℃. The reaction was stirred for 6h to carry out liquid-phase prepolymerization reaction to obtain organic core sol.

[0049] A2. Add 1.0875g sodium silicate and 40mL anhydrous ethanol to the above 7.25g organic core sol. Under the conditions of 55℃ and stirring speed of 125rpm, the temperature is controlled by a constant temperature water bath for 11h to obtain the core complex.

[0050] A3. Take 7g of core complex, 0.525g of sodium stearate, and 1.75g ​​of zinc aluminum hydrotalcite, mix them evenly, add 52.5mL of anhydrous ethanol, ultrasonically disperse at 250W for 22min, then stir and react at 75℃ for 2h, centrifuge at 9000rpm for 15min, collect the precipitate, wash it 4 times with anhydrous ethanol, and then vacuum dry at 70℃ for 10h to obtain the heterogeneous catalyst;

[0051] S2. A fixed-bed oxidation reactor with a volume of 5L is selected and filled with 2000g of quartz sand inert packing material with a particle size of 5.5mm. The homogeneous feed liquid obtained above is continuously pumped into the bottom of the oxidation reactor. At the same time, oxygen-containing gas is continuously introduced into the bottom of the oxidation reactor through a gas distributor with a pore size of 30μm. The oxidation reaction is carried out at 105℃ and 0.15MPa. The residence time of the homogeneous feed liquid in the reactor is controlled to be 6h to obtain a gas-liquid mixture.

[0052] S3. The above gas-liquid mixture is fed into a gas-liquid separator and separated at 35°C and atmospheric pressure. After separation, approximately 6214.2 mL of gas phase and approximately 1014 g of liquid phase are obtained. The obtained gas phase is treated by activated carbon adsorption. An adsorption column filled with 50 g of activated carbon is selected, the adsorption temperature is controlled at 30°C, and the adsorption time is 0.75 h. The treated gas phase is collected. The obtained 1014 g of liquid phase oxidation product stream is divided into two streams. The first stream is returned to the oxidation reactor as a circulating stream (892.1 g) to participate in the reaction, and the second stream is output as a product outflow stream (121.9 g).

[0053] S4. The 121.9g product effluent is continuously concentrated under reduced pressure using a two-stage falling film evaporator, with a 1L buffer tank between the two concentration stages. The first-stage concentration conditions are: vacuum degree -0.090MPa, temperature 60℃, and evaporation rate 0.2kg / (m³). 2 ·h), with a heat transfer area of ​​0.1m². 2 A falling film evaporator was used, with a concentration time of approximately 0.6 hours, separating approximately 97.5 g of unreacted p-menthane. The secondary concentration conditions were: vacuum degree -0.0965 MPa, temperature 80℃, and evaporation rate 0.2 kg / (m³). 2 The concentration time was approximately 0.1 h, and a small amount of unreacted p-menthol was further separated, approximately 2.4 g. A total of approximately 99.9 g of unreacted p-menthol was recovered from the two separations. The recovered unreacted p-menthol was purified by distillation to obtain approximately 97 g of qualified p-menthol, which was returned to step S1 for reuse. Finally, 12.2 g of hydrogen peroxide p-menthol was obtained.

[0054] Example 3

[0055] A continuous catalytic oxidation process for preparing p-menthol peroxide includes the following steps:

[0056] S1. Take 1000g of p-mentholane and dehydrate it by distillation. The water content of the dehydrated p-mentholane is 0.01wt%. Add 11.999g of heterogeneous catalyst (1.2% of the total mass of 999.9g of dehydrated p-mentholane) and 9.999g of initiator (1.0% of the total mass of 999.9g of dehydrated p-mentholane) to the dehydrated p-mentholane. Stir continuously at 180rpm for 25min under nitrogen and argon gas mixture (volume ratio 1:1) at 30℃ to obtain a homogeneous feed liquid. The initiator is 98% purified p-mentholane peroxide.

[0057] Heterogeneous catalysts are prepared by the following steps:

[0058] A1. Under nitrogen protection, take 1.5g of acetylenol ferrocene and 4g of melamine, dissolve them in 150mL of dimethyl sulfoxide, wrap the reaction vessel with black cloth to protect it from light, stir magnetically at 300rpm, heat to 140℃, stir and react for 8h to carry out liquid phase prepolymerization reaction to obtain organic core sol.

[0059] A2. Add 1.1g of tetraethyl orthosilicate and 75mL of anhydrous ethanol to the above 5.5g organic core sol. React at 60℃ and 150rpm using a constant temperature water bath for 14h to obtain the core complex.

[0060] A3. Take 8g of core complex, 0.8g of stearic acid, and 2.4g of magnesium aluminum hydrotalcite, mix them evenly, add 80mL of anhydrous ethanol, ultrasonically disperse at 300W for 30min, then stir and react at 80℃ for 3h, centrifuge at 10000rpm for 20min, collect the precipitate, wash it 5 times with anhydrous ethanol, and then vacuum dry at 80℃ for 12h to obtain the heterogeneous catalyst.

[0061] S2. A fixed-bed oxidation reactor with a volume of 5L is selected and filled with 2000g of ceramic ring inert packing with a particle size of 8mm. The homogeneous feed liquid obtained above is continuously pumped into the bottom of the oxidation reactor. At the same time, oxygen-containing gas is continuously introduced into the bottom of the oxidation reactor through a gas distributor with a pore size of 50μm. The oxidation reaction is carried out at 130℃ and 0.3MPa. The residence time of the homogeneous feed liquid in the reactor is controlled to be 8h to obtain a gas-liquid mixture.

[0062] S3. The above gas-liquid mixture is fed into a gas-liquid separator and separated at 40°C and atmospheric pressure. After separation, approximately 12096 mL of gas phase and approximately 1018 g of liquid phase are obtained. The obtained gas phase is treated by activated carbon adsorption. An adsorption column filled with 50 g of activated carbon is selected, the adsorption temperature is controlled at 35°C, and the adsorption time is 1 h. The treated gas phase is collected. The obtained 1018 g of liquid phase oxidation product stream is divided into two streams. The first stream is returned to the oxidation reactor as a circulating stream (967.6 g) to participate in the reaction, and the second stream is output as a product collection stream (50.4 g).

[0063] S4. The 50.4g product stream is continuously concentrated under reduced pressure using a two-stage falling film evaporator, with a 1L buffer tank between the two stages. The first-stage concentration conditions are: vacuum degree -0.085MPa, temperature 70℃, and evaporation rate 0.3kg / (m³). 2 ·h), with a heat transfer area of ​​0.1m². 2 A falling film evaporator was used, with a concentration time of approximately 0.2 hours, separating approximately 40.3 g of unreacted p-menthane. The secondary concentration conditions were: vacuum degree -0.095 MPa, temperature 90℃, and evaporation rate 0.3 kg / (m²).2 The concentration time is approximately 0.03 h, and a small amount of unreacted p-menthol is further separated, approximately 1.0 g. A total of approximately 41.3 g of unreacted p-menthol is recovered from the two separations. The recovered unreacted p-menthol is purified by distillation to obtain approximately 40 g of qualified p-menthol, which is returned to step S1 for reuse. Finally, hydrogen peroxide p-menthol is obtained.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that acetylenyl ferrocene is not added; the remaining steps are the same as in Example 1.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 2 is that melamine is not added, while the remaining steps are the same as in Example 2.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 3 is that tetraethyl orthosilicate is not added; the remaining steps are the same as in Example 3.

[0070] Comparative Example 4

[0071] The difference between this comparative example and Example 1 is that stearic acid is not added, while the remaining steps are the same as in Example 1.

[0072] Comparative Example 5

[0073] The difference between this comparative example and Example 2 is that zinc-aluminum hydrotalcite is not added; the remaining steps are the same as in Example 2.

[0074] Collect the hydrogen peroxide-paramonene products obtained from the process steps of Examples 1-3 and Comparative Examples 1-5, and record the product quality;

[0075] The catalysts used in Examples 1-3 and Comparative Examples 1-5 were recycled 5 times according to the corresponding process. After each cycle, the above process steps were repeated, and the product quality and purity of each cycle were recorded.

[0076] The purity of hydrogen peroxide-derived para-menthol and the residual amount of unreacted para-menthol in the final products of each scheme were determined by gas chromatography. The specific detection parameters are as follows: Column: SE-54 capillary column (30m×0.32mm×0.25μm); Column temperature program: initial temperature 80℃, hold for 2 min, increase to 180℃ at a rate of 10℃ / min, hold for 5 min; Detector temperature: 250℃; Injector temperature: 200℃; Carrier gas: nitrogen, flow rate 1.0mL / min; Injection volume: 1μL; Injection mode: split injection (split ratio 10:1); Detection time: 20 min for each sample.

[0077] Calculate the conversion of menthol, the yield of menthol from hydrogen peroxide, and the product yield and retention rate of the fifth cycle. The formulas are as follows:

[0078] p-Mandane conversion rate = (initial p-Mandane mass - unreacted p-Mandane mass) / initial p-Mandane mass × 100%;

[0079] Hydrogen peroxide yield to menthol = (actual mass of hydrogen peroxide to menthol obtained / theoretically obtainable mass of hydrogen peroxide to menthol) × 100%;

[0080] The product yield retention rate of the fifth cycle = (fifth cycle yield / first cycle yield) × 100%.

[0081] The results are shown in Table 1:

[0082] Table 1. Experimental results of purity and yield in different examples and comparative examples

[0083]

[0084] As shown in Table 1, Examples 1-3 outperformed Comparative Examples 1-5 in terms of menthol conversion, hydrogen peroxide yield of menthol, product purity, and catalyst yield retention after 5 cycles. This indicates that the catalyst structure and preparation process designed in this invention have significant advantages in the continuous catalytic oxidation preparation of hydrogen peroxide of menthol.

[0085] In Example 1, the addition of acetylenic ferrocene resulted in a 17.8% conversion rate of menthol, a 16.5% yield of menthol from hydrogen peroxide, a product purity of 98.7%, and a catalyst yield retention rate of 88.9% after 5 cycles. In Comparative Example 1, without the addition of acetylenic ferrocene, all indicators decreased significantly, with a menthol conversion rate of only 3.3%, a hydrogen peroxide yield of menthol of 2.7%, a product purity of 82.4%, and a catalyst yield retention rate of 44.8% after 5 cycles. The acetylenic ferrocene covalently crosslinks with melamine to form a polymer nanophase. Fe atoms are anchored in the conjugated heterocyclic polymer backbone through both coordination and covalent bonds, ensuring that the Fe active centers are firmly bound to the polymer backbone. This reduces the probability of Fe atoms flowing out of the reactor simultaneously with the reactants, allowing them to remain in situ within the reaction system and be recycled. This improves the catalyst's stability and activity, which is beneficial for increasing the menthol conversion rate and the hydrogen peroxide yield of menthol, while ensuring product purity and catalyst recyclability.

[0086] In Example 2, the addition of melamine resulted in a 15.7% conversion rate of menthol, a 15.1% yield of menthol from hydrogen peroxide, a product purity of 99.2%, and a 91.8% yield retention rate after 5 catalyst cycles. In Comparative Example 2, without the addition of melamine, the menthol conversion rate decreased to 4.5%, the menthol yield from hydrogen peroxide was 3.6%, the product purity was 85.7%, and the yield retention rate after 5 catalyst cycles was 52.1%. Melamine and acetylenyne-ferrocene covalently cross-link to form a polymer nanophase, providing anchoring sites for Fe atoms and constructing a stable catalyst core structure. Without melamine, an effective polymer framework cannot be formed to fix the Fe active centers, making it easy for the active centers to be lost during the reaction, thus failing to fully exert the catalytic effect and affecting the conversion of menthol, the yield of menthol from hydrogen peroxide, the product purity, and the catalyst's recyclability.

[0087] Example 3, with the addition of tetraethyl orthosilicate, showed a menthol conversion rate of 8.9%, a menthol yield of 8.2% from hydrogen peroxide, a product purity of 99.3%, and a catalyst yield retention rate of 93.4% after 5 cycles. Comparative Example 3, without the addition of tetraethyl orthosilicate, showed a menthol conversion rate of 5.4%, a menthol yield of 4.5% from hydrogen peroxide, a product purity of 88.6%, and a catalyst yield retention rate of 63.2% after 5 cycles. Tetraethyl orthosilicate (Examples 1 and 3) or sodium silicate (Example 2) were grown in situ via hydrolysis and polycondensation to form a mesoporous isolation shell layer in the catalyst's intermediate layer. This shell layer possesses a regular and interconnected nanoporous structure, enabling efficient mass transfer between reactants and products, allowing reactants to more efficiently contact the core Fe active centers and promote the reaction. It also provides excellent physical isolation, effectively separating the acidic Fe active core from the basic outer inorganic shell layer, reducing passivation and poisoning deactivation of Fe active centers caused by acid-base interface contact, and maintaining the stability of the catalyst's catalytic performance during long-term operation. Without this component, an effective mesoporous isolation shell cannot be formed, affecting the stability and activity of the catalyst and causing a decline in various indicators.

[0088] In Example 1, the addition of stearic acid resulted in a 17.8% conversion rate of menthol, a 16.5% yield of menthol from hydrogen peroxide, a product purity of 98.7%, and a yield retention rate of 88.9% after 5 catalyst cycles. In Comparative Example 4, without the addition of stearic acid, the menthol conversion rate decreased to 10.7%, the menthol yield of menthol from hydrogen peroxide was 9.4%, the product purity was 89.8%, and the yield retention rate after 5 catalyst cycles was 70.9%. Stearic acid (Examples 1 and 3) or sodium stearate (Example 2) was used to in-situ modify the inorganic shell precursor, resulting in a hydrophobically modified layered hydrotalcite inorganic shell layer on the outer layer of the catalyst. This change from hydrophilic to hydrophobic to facilitate uniform dispersion of the catalyst in the organic phase feed liquid, forming a relatively stable suspension system, increasing the gas-liquid-solid three-phase contact interface area, improving oxygen dissolution efficiency and reaction rate, and adapting to the kinetic characteristics of continuous catalytic oxidation processes. Meanwhile, the hydrophobic outer shell can block trace amounts of water in the system, reducing the damage of hydrogen peroxide to the peroxy bond of menthol by water molecules penetrating the core, and inhibiting the occurrence of hydrolysis and thermal decomposition side reactions of the product. Without stearic acid or sodium stearate, the outer layer of the catalyst cannot be hydrophobically modified, thus failing to effectively perform the above-mentioned functions, resulting in poor reaction efficiency and catalyst performance.

[0089] In Example 2, the addition of zinc-aluminum hydrotalcite resulted in a 15.7% conversion rate of menthol, a 15.1% yield of menthol from hydrogen peroxide, a product purity of 99.2%, and a 91.8% yield retention rate after 5 catalyst cycles. In Comparative Example 5, without the addition of zinc-aluminum hydrotalcite, the menthol conversion rate was 9.6%, the menthol yield of menthol from hydrogen peroxide was 8.5%, the product purity was 91.6%, and the yield retention rate after 5 catalyst cycles was 72.7%. The mildly alkaline sites inherent in the zinc-aluminum hydrotalcite (Example 2) or magnesium-aluminum hydrotalcite (Examples 1 and 3) layers can mildly quench excess reactive free radicals in the system, reducing the possibility of deep oxidation of menthol and menthol from hydrogen peroxide, thereby reducing the formation of byproducts such as alcohols, ketones, and organic acids, and improving product purity. Simultaneously, it also has a positive impact on the recyclability of the catalyst. The absence of this component prevents the effective quenching of excess free radicals, leading to an increase in byproducts, a decrease in product purity, and a certain impact on catalyst performance.

[0090] In summary, the components of the catalyst of this invention cooperate with each other to construct a core-shell structure catalyst with specific structure and function, which exhibits good performance in the continuous catalytic oxidation process for the preparation of termonane with hydrogen peroxide.

[0091] In the description of this specification, the reference to terms such as "embodiment," "various embodiments," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or preparation example is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0092] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A continuous catalytic oxidation process for preparing p-menthol peroxide, characterized in that, Includes the following steps: S1. Dehydrate the p-menthol and mix it with the heterogeneous catalyst and initiator to obtain a homogeneous feed liquid; S2. The homogeneous raw material liquid is continuously pumped into the bottom of the oxidation reactor, and oxygen-containing gas is continuously introduced into the bottom of the oxidation reactor through the gas distributor to carry out the oxidation reaction, thereby obtaining a gas-liquid mixture containing hydrogen peroxide and para-menthol. S3. Separate the gas-liquid mixture. The gas phase is treated and discharged, while the liquid phase oxidation product stream is divided into two streams. The first stream is returned to the oxidation reactor as a circulating stream to participate in the reaction, and the second stream is output as the product outflow. S4. The product outflow is subjected to at least one stage of vacuum concentration treatment to separate and recover unreacted p-mentholane, and to obtain crude p-mentholane peroxide. Steps S2 and S3 are performed consecutively. The heterogeneous catalyst has a core-shell structure, consisting of an inner core with an Fe-NC coordination structure and an outer layer of hydrophobically modified inorganic shell. A mesoporous isolation shell is provided between the inner core and the hydrophobically modified inorganic shell. The heterogeneous catalyst is an Fe-based catalyst.

2. The process for continuous catalytic oxidation to prepare p-menthol peroxide according to claim 1, characterized in that, In step S1, the amount of initiator added is 0.6-1.0% of the total mass of p-menthol, and the initiator is selected from purified p-menthol with a mass fraction of ≥50%. The mixing process is carried out under inert gas protection and constant temperature conditions of 20-30℃. During mixing, the stirring speed is controlled at 120-180 rpm and the stirring is continued for 15-25 min.

3. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 1, characterized in that, The heterogeneous catalyst in step S1 is prepared by the following steps: A1. Under inert gas protection, acetylenyl ferrocene and melamine are dissolved in an organic solvent, heated to 120-140℃, and stirred in the dark for 4-8 hours to carry out liquid-phase prepolymerization reaction to obtain Fe-NC coordination structure organic core sol. A2. Add mesoporous precursor and dispersant to organic core sol, and react at 50-60℃ and 100-150rpm for 8-14h to obtain core complex coated with mesoporous layer. A3. Mix the core complex with the hydrophobic modifier and the inorganic shell precursor, add solvent and ultrasonically disperse evenly, then stir and react at 70-80℃ for 1-3 hours. After centrifugation, washing and vacuum drying, a heterogeneous catalyst is obtained.

4. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 1, characterized in that, In step S2, the oxidation reaction temperature is 80-130℃, the reaction pressure is atmospheric pressure to 0.3MPa, and the residence time of the homogeneous feed liquid in the oxidation reactor is 4-8h.

5. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 1, characterized in that, In step S3, the reflux ratio of the circulating flow to the product outflow is (5-20):1, and the concentration of hydrogen peroxide to monane in the oxidation reactor is controlled at 15-20%.

6. The process for continuous catalytic oxidation to prepare p-menthol peroxide according to claim 1, characterized in that, In step S4, the vacuum concentration process is carried out continuously using a two-stage or multi-stage falling film evaporator. The first-stage concentration conditions are: vacuum degree (-0.095) - (-0.085) MPa, temperature 50-70℃; the second-stage concentration conditions are: vacuum degree (-0.098) - (-0.095) MPa, temperature 70-90℃.

7. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 3, characterized in that, In step A1, the mass ratio of acetylenoid ferrocene to melamine is (1-1.5):(4-8), and the volume ratio of acetylenoid ferrocene to organic solvent is 1g:(60-100)mL. The organic solvent is selected from dimethyl sulfoxide or N,N-dimethylformamide.

8. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 3, characterized in that, In step A2, the mesoporous precursor is selected from tetraethyl orthosilicate or sodium silicate, and the dispersant is selected from anhydrous ethanol; the amount of mesoporous precursor added is 10-20% of the mass of the organic core sol; the amount of dispersant added is 30-50% of the volume of the organic core sol.

9. The process for continuous catalytic oxidation to prepare terpinene hydrogen peroxide according to claim 3, characterized in that, In step A3, the inorganic shell precursor is selected from magnesium aluminum hydrotalcite or zinc aluminum hydrotalcite, and the hydrophobic modifier is selected from stearic acid or sodium stearate; the mass ratio of the core complex, the hydrophobic modifier, and the inorganic shell precursor is 100:(5-10):(20-30).

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