A benzil preparation process and equipment

Abstract

The invention discloses a benzil preparation process and equipment. The technical scheme thereof includes dissolving benzoin in anhydrous ethanol to prepare a benzoin solution, using a rare earth catalyst and hydrogen peroxide to perform preliminary oxidation on benzoin to generate benzophenone, and then performing deep oxidation on benzophenone by a palladium-based catalyst to generate benzil. After gas-liquid separation and distillation purification of the reaction liquid, benzil with a purity greater than 99.9% is obtained, and at the same time, the byproduct benzoic acid is catalytically hydrogenated and converted into benzyl alcohol, and unreacted benzoin is recovered for recycling. The preparation equipment includes a plurality of modules, which are respectively used for reaction, separation and purification, wherein the first reactor and the second reactor are respectively equipped with a rare earth catalyst mechanism and a palladium-based catalyst mechanism, and are provided with a temperature control system and a UV auxiliary light source module to improve reaction efficiency and control accuracy. The process of the invention has the characteristics of high yield, high purity and high resource recovery and utilization rate, and is suitable for the industrial production of benzil.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, and in particular to a benzil preparation process and equipment. Background Art

[0002] Benzil plays a wide range of roles in the production of medicines, fragrances, and daily chemicals, and is an important intermediate in organic synthesis. In current industrial production, benzil is mainly prepared by the benzoin oxidation method, which uses benzoin as a raw material and oxidizes it to benzil using an oxidant (such as nitric acid, potassium permanganate, or hydrogen peroxide).

[0003] However, in the actual production process, in the traditional oxidation reaction, the oxidation pathway of benzoin is relatively complex and easily generates by-products such as benzoic acid, phenol or carbon dioxide, which not only reduces the selectivity of benzoyl, but also increases the burden of subsequent separation and purification; and the strong oxidants used in the traditional process (such as nitric acid, potassium permanganate) will produce a large amount of toxic waste liquid, such as acidic wastewater containing nitrate and permanganate, which causes serious pollution to the environment and the cost of waste liquid treatment is high. Summary of the invention

[0004] The invention provides a benzil preparation process and equipment, which solves the problem that by-products and a large amount of toxic waste liquid are easily generated in the existing oxidation reaction.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a benzil preparation process, the steps are as follows: S1. Raw material preparation: preparing a dry benzoin raw material and dissolving it in a solvent to obtain a benzoin solution; S2, preliminary oxidation: sending the benzoin solution obtained in S1 into the first reaction chamber of the preparation equipment to be initially oxidized under the action of a rare earth catalyst and hydrogen peroxide to obtain a transition product benzophenone; S3, deep oxidation: transporting the transition product benzophenone obtained in S2 to the second reaction chamber, reacting it with a palladium-based catalyst to achieve deep oxidation, and obtaining a reaction solution containing benzil; S4, separation and purification: The gas phase and the liquid phase in the reaction liquid are separated by the gas-liquid separator of the preparation equipment, and the liquid phase is sent to the distillation tower of the preparation equipment for purification to obtain benzil with a purity greater than 99.9%; the gas phase is recovered to the storage tank for recycling; S5. By-product recovery: After the liquid phase in S4 is separated by a distillation tower, benzoic acid and unreacted benzoin are obtained. Benzoic acid is sent to the by-product recovery and conversion mechanism of the preparation equipment to generate benzyl alcohol under the action of catalytic hydrogenation; and unreacted benzoin is returned to the first reaction chamber.

[0006] The present invention is further configured such that the temperature in the first reaction chamber is set at 40-50° C., and the reaction time of the benzoin solution, hydrogen peroxide and rare earth catalyst in the first reaction chamber is 30 minutes.

[0007] The present invention is further configured such that the temperature in the second reaction chamber is set at 50-60° C., and the reaction time of the benzophenone solution and the palladium-based catalyst in the second reaction chamber is 1 hour.

[0008] The present invention is further configured such that the hydrogen peroxide is a 30% hydrogen peroxide solution, which is mixed with a benzoin solution at a volume ratio of 1:1.2 and then added into the first reaction chamber.

[0009] The present invention is further configured such that the rare earth catalyst is a catalyst in which cerium dioxide is supported on activated carbon, and the amount of the rare earth catalyst used is 0.5%-2% of the mass of benzoin.

[0010] The present invention is further configured such that the solvent is anhydrous ethanol, and the mass fraction of benzoin in the solution is 10%-15%.

[0011] A benzil preparation device comprises a first reactor, a second reactor, a gas-liquid separator, a multi-effect distillation tower and a by-product conversion device which are connected in sequence; a rare earth catalyst mechanism is arranged in a first reaction chamber of the first reactor, and a palladium-based catalyst mechanism is arranged in a second reaction chamber of the second reactor; a temperature control mechanism and a control mechanism are also arranged in the first reaction chamber and the second reaction chamber, and the temperature control mechanism is connected to the control mechanism and is used for adjusting the temperature in the first and second reaction chambers; the control mechanism is used for monitoring the working parameters of the control device.

[0012] The present invention is further configured as follows: the first reactor includes a cavity with a feed port and a discharge port, the feed port is connected to a metering pump, and the discharge port is connected to a second reactor via an electromagnetic valve; the rare earth catalytic mechanism includes a placement frame arranged in the first reaction chamber, the placement frame is used to place the rare earth catalyst; it also includes stirring blades that are rotatably arranged on the upper and lower sides of the placement frame, a pair of the stirring blades are connected to a motor via a rotating shaft that passes through the placement frame; a UV auxiliary light source module connected to a control mechanism is arranged on the top of the first reaction chamber, and the UV auxiliary light source module is used to assist the reaction between the solution and the rare earth catalyst.

[0013] The present invention is further configured such that a guide pipe connected to the feed port is provided in the cavity of the first reactor, the guide pipe divides the first reaction cavity into an outer cavity and an inner cavity, the lower ends of the outer cavity and the inner cavity are connected through a one-way through hole, and the one-way through hole is used for allowing the liquid in the inner cavity to flow unidirectionally to the outer cavity; the placement frame and a pair of stirring blades are arranged in the inner cavity.

[0014] The present invention is further configured such that the second reactor includes a shell with a second reaction chamber, the palladium-based catalyst mechanism includes a support mesh arranged in the second reaction chamber, a catalyst bed is arranged on the support mesh, and the catalyst bed is loaded with palladium metal and has a honeycomb structure.

[0015] In summary, the beneficial effects of the present invention are: Compared with the prior art, the present application preliminarily completes the mild oxidation reaction of benzoin to benzophenone through the synergistic effect of rare earth catalyst and hydrogen peroxide, realizes the high selectivity control of the oxidation reaction, and avoids the phenomenon that benzoin generates byproducts such as benzoic acid due to the action of strong oxidants in the traditional oxidation process. At the same time, the introduction of palladium-based catalyst, using its efficient oxidation catalytic properties, completes the deep oxidation of benzophenone at a lower temperature, which not only effectively improves the yield and purity of benzil, but also inhibits the occurrence of side reactions, thereby further reducing the generation ratio of byproducts.

[0016] Moreover, by using hydrogen peroxide as an oxidant to replace traditional nitric acid and potassium permanganate, not only the amount of waste liquid generated during the reaction is reduced, but also the environmental pollution caused by acidic wastewater and difficult-to-treat precipitates is avoided, significantly reducing the cost of waste treatment. Combined with the efficient separation and recovery design of the cyclone gas-liquid separator and the multi-effect distillation tower, unreacted benzoin and oxidant can be recycled, thereby maximizing resource utilization. The by-product benzoic acid is converted into benzyl alcohol through catalytic hydrogenation reaction, achieving a high value-added conversion of resources, which not only reduces the burden of the process on the environment, but also further improves economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of embodiment 1.

[0018] Figure 2 It is a schematic diagram of device connection of the second embodiment.

[0019] Figure 3 is a perspective view of the first reactor.

[0020] Figure 4 This is a diagram of the internal structure of the first reactor.

[0021] Figure 5 It is a half-section view of the first reactor.

[0022] Figure 6 This is a method diagram of the UV auxiliary light source module.

[0023] Figure 7 This is an enlarged view of a one-way through hole.

[0024] Figure 8 is a cross-sectional view of the second reactor.

[0025] : 100, first reactor; 200, second reactor; 300, gas-liquid separator; 301, gas phase outlet; 302, liquid phase outlet; 400, multi-effect distillation tower; 500, by-product conversion device; 1, first reaction chamber; 11, feed inlet; 12, discharge port; 13, metering pump; 14, solenoid valve; 15, guide pipe; 16, outer chamber; 17, inner chamber; 18, one-way through hole; 19, sealing film; 20, discharge port; 2, rare earth catalyst mechanism; 21, placement frame; 22, stirring blade; 23, rotating shaft; 24, motor; 3, second reaction chamber; 4, palladium-based catalyst mechanism; 41, support net; 42, palladium-based catalyst bed; 5, temperature control mechanism; 51, cooling coil; 52, temperature sensor; 6, UV auxiliary light source module. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention. Example

[0027] like Figure 1-2 As shown, this embodiment discloses a process for preparing benzil, and the steps are as follows: S1. Raw material preparation: preparing a dry benzoin raw material and dissolving it in a solvent to obtain a benzoin solution; The solvent is anhydrous ethanol, and the mass fraction of benzoin in the solution is 10%-15%. Anhydrous ethanol can effectively dissolve benzoin and ensure that when hydrogen peroxide reacts with it, it will not inhibit the catalyst; and as an organic synthesis intermediate, benzoin (Benzoin) has a hydroxyl group (-OH) that is very easy to participate in the oxidation reaction. After being dissolved in anhydrous ethanol, benzoin molecules can be evenly distributed, and ethanol as a solvent can provide appropriate solubility and low-temperature reaction conditions for the reaction, thereby helping to improve the efficiency and selectivity of the reaction; at the same time, the mass fraction of benzoin in the solution is maintained at 10%-15%, which can ensure that the oxidant in the reaction process can efficiently react with the benzoin molecules and improve the conversion rate and selectivity of the reaction.

[0028] S2, preliminary oxidation: sending the benzoin solution obtained in S1 into the first reaction chamber of the preparation equipment to be initially oxidized under the action of a rare earth catalyst and hydrogen peroxide to obtain a transition product benzophenone; First, the benzoin solution obtained by mixing S1 with anhydrous ethanol and a 30% hydrogen peroxide solution are mixed in a ratio of 1:1.2, and then introduced into a first reaction chamber in a first reactor, wherein the first reaction chamber carries a rare earth catalyst supported on activated carbon, and the rare earth catalyst may be cerium dioxide, which activates hydrogen peroxide to generate highly active oxygen species (such as ·OH or O 2 ⁻), these oxygen species react with the hydroxyl group (-OH) of benzoin to produce the transition product benzophenone and a small amount of by-product benzoic acid.

[0029] At the same time, the temperature in the first reaction chamber is set at 45°C under the control of the temperature control mechanism. This temperature significantly improves the selectivity of the reaction, improves the efficiency of the transition product benzophenone, avoids excessive oxidation of benzoin, and reduces the generation of by-products. Allowing the benzoin solution mixed with hydrogen peroxide to react in the first reaction chamber for 30 minutes can ensure uniform mixing of the solution and sufficient reaction with the rare earth catalyst.

[0030] The following table is a comparison data table of the optimal temperature in the first reaction chamber: parameter Recommended range (40-50℃) Below range (<40℃) Above range (>50℃) Reaction time 30 minutes The reaction time is extended to more than 60 minutes, which reduces the efficiency The reaction time is shortened to 20 minutes, but the by-products increase Product purity (benzophenone) >95% Below 80%, oxidation is incomplete and impurities increase 80%-90%, peroxidation byproducts increase Catalyst consumption Standard catalyst dosage (0.5%-2% of benzoin mass) Catalyst utilization rate decreases, and the dosage may need to be increased The catalyst is partially deactivated and needs to be replaced more frequently Equipment load Normal temperature operation, stable equipment Equipment efficiency decreases, and low temperatures require additional heating and energy consumption High temperature can easily cause fatigue or damage to equipment materials By-product ratio <5% <10%, the recovery of incompletely reacted benzoin increases >15%, complex impurities are generated, increasing the difficulty of purification According to the above table, it can be seen that: too low temperature will reduce efficiency, and too high temperature will affect the reaction selectivity and equipment stability of the initial oxidation. Therefore, it must be controlled within the recommended range to ensure the effective oxidation of benzoin and the inhibition of by-products.

[0031] S3, deep oxidation: transporting the transition product benzophenone obtained in S2 to the second reaction chamber, reacting it with a palladium-based catalyst to achieve deep oxidation, and obtaining a reaction solution containing benzil; The benzophenone solution obtained by the preliminary oxidation will be transported to the second reaction chamber of the second reactor, and a palladium-based catalyst is placed in the second reaction chamber. The palladium-based catalyst further oxidizes the carbonyl group of benzophenone to generate benzil through a catalytic reaction; at the same time, the temperature in the second reaction chamber is controlled at 55°C by a temperature control mechanism. Keeping the reaction temperature at 55°C allows the palladium-based catalyst to efficiently catalyze the oxidation reaction at a lower temperature, while avoiding thermal decomposition of benzil caused by excessively high temperature, thereby allowing the yield of benzil to reach more than 90%, and the formation of the by-product benzoic acid is effectively suppressed, ensuring the formation of high-purity benzil.

[0032] If the temperature in the second reaction chamber is too high, it will easily cause catalyst deactivation and product quality degradation, while if the temperature is too low, the reaction time will be prolonged, the oxidation efficiency will be reduced, and the energy consumption of the equipment will be increased. Therefore, keeping it within the recommended range can maximize the efficiency of deep oxidation and the high purity of the target product.

[0033] S4, separation and purification: The gas phase and the liquid phase in the reaction liquid are separated by the gas-liquid separator of the preparation equipment, and the liquid phase is sent to the distillation tower of the preparation equipment for purification to obtain benzil with a purity greater than 99.9%; the gas phase is recovered to the storage tank for recycling; Among them, the gas-liquid separator is a cyclone gas-liquid separator, which can perform gas-liquid separation on the reaction liquid with benzil generated in S2. The gas phase is unreacted hydrogen peroxide, which will be recycled to the storage tank for reuse, and the liquid phase is crude benzil. The crude benzil will be sent to the multi-effect distillation tower for fractionation. The multi-effect distillation tower separates these components by precisely controlling the distillation temperature and using the different boiling points of benzil, by-products, benzophenone and solvent. Benzil has a high boiling point and can be effectively separated from other low-boiling components. Finally, benzil, benzophenone and solvent are obtained. The purity of the separated benzil can reach more than 99.9% and is collected and used; while the unreacted benzophenone will be sent back to the first reactor for recycling, thereby reducing the waste of raw materials. The by-product benzoic acid will be separated from the middle distillate of the distillation tower and enter the by-product recovery and conversion mechanism.

[0034] S5. Recovery of by-products: After the liquid phase in S4 is separated by a distillation tower, benzoic acid, unreacted benzoin and solvent are obtained. Benzoic acid is sent to the by-product conversion device of the preparation equipment to generate benzyl alcohol under the action of catalytic hydrogenation; and unreacted benzoin is returned to the first reaction chamber.

[0035] The benzoic acid separated in the multi-effect distillation tower will be sent to the by-product conversion mechanism for processing; the by-product recovery and conversion mechanism includes a liquid-liquid separation device and a catalytic hydrogenation reaction device. Benzoic acid and the solvent are separated by the liquid-liquid separation device. Benzoic acid will be sent to the catalytic hydrogenation reaction device for further conversion. The hydrogenation reaction uses a cobalt-based catalyst and is carried out at 60°C and 1.5MPa. In the hydrogenation reaction, hydrogen molecules react with the carboxyl groups of benzoic acid through the catalyst surface to generate benzyl alcohol and water. The role of the catalyst is to reduce the energy required for the reaction and ensure the efficient reaction. The cobalt-based catalyst can effectively promote the hydrogenation process of benzoic acid, allowing the reaction to proceed under mild conditions with a conversion rate of up to 95%.

[0036] Through catalytic hydrogenation, the carboxyl group in benzoic acid is reduced to an alcohol group to produce benzyl alcohol. Benzyl alcohol is a high value-added chemical widely used in pharmaceuticals, fragrances, synthetic resins and other fields. Through the above reaction, the conversion rate of benzoic acid is as high as 95%, and the purity of benzyl alcohol reaches 99.5%. Through this process, the by-products are not only effectively recovered and converted, but also the overall economic benefits of the process are increased.

[0037] The following table compares the effects of the existing process and the process of this application Comparison Dimensions Prior art The technology of the present invention Process Single oxidation reaction, no preliminary oxidation and deep oxidation steps Step oxidation: preliminary oxidation (benzoin to benzophenone) and deep oxidation (benzophenone to benzil) Initial oxidation yield not applicable 85% Deep oxidation yield 60%-70% 80% Benzil purity ≤98% ≥99.9% Catalyst use Limited catalyst selection and low efficiency Rare earth catalyst (initial oxidation) + palladium-based catalyst (deep oxidation) By-product recovery (benzoic acid conversion) By-product conversion rate ≤80% By-product conversion rate ≥ 90% Unreacted benzoin recovery The recovery rate is about 5% Recovery rate ≥12% Reaction conditions Wide temperature and time range, low control accuracy Initial oxidation: 45°C, 30 minutes; Deep oxidation: 55°C, 1 hour Environmental friendliness Imperfect by-product treatment leads to waste of resources By-product recycling (benzoic acid converted into benzyl alcohol), raw material recycling According to the above table content, it can be known that the benzil preparation process of the present invention significantly improves the yield, purity and by-product recovery efficiency by introducing step-by-step oxidation (primary oxidation and deep oxidation) and optimizing the reaction conditions and the selection of catalysts. At the same time, the optimization of the process greatly improves the recovery rate of by-product conversion and unreacted raw materials, reduces resource waste, and improves overall economic benefits and environmental protection. Compared with the existing process, the present invention not only improves the yield and purity of the main product benzil, but also makes significant improvements in by-product recovery and resource utilization, and has stronger market competitiveness and environmental advantages. Therefore, the process of the present invention has a wide range of application prospects in actual industrial production. Example

[0038] like Figure 2-8 As shown, in order to implement the preparation steps of Example 1, the present application additionally provides a benzil preparation device, including a first reactor 100, a second reactor 200, a gas-liquid separator 300, a multi-effect distillation tower 400 and a by-product conversion device 500 connected in sequence; a rare earth catalyst mechanism 2 is arranged in the first reaction chamber 1 of the first reactor 100, and a palladium-based catalyst mechanism 4 is arranged in the second reaction chamber 3 of the second reactor 200; a temperature control mechanism 5 and a control mechanism are also arranged in the first reaction chamber 1 and the second reaction chamber 3, and the temperature control mechanism 5 is connected to the control mechanism for adjusting the temperature in the first and second reaction chambers; the control mechanism is used to monitor and control the working parameters of the control device, wherein the control mechanism is a PLC controller and a control panel connected to the PLC controller, and the control panel can display the working status of each device and adjust the device parameters.

[0039] The first reactor 100 is used to complete the initial oxidation of the benzoin solution to generate a transition product, benzophenone; Figure 3-4As shown, the first reactor 100 includes a cavity with a feed port 11 and a discharge port 12, the feed port 11 is connected to a metering pump 13, and the discharge port 12 is connected to a second reactor 200 through a solenoid valve 14; the rare earth catalytic mechanism includes a placement frame 21 arranged in the first reaction chamber 1, and the placement frame 21 is used to place the rare earth catalyst; it also includes stirring blades 22 that are rotatably arranged on the upper and lower sides of the placement frame 21, and a pair of stirring blades 22 are connected to a motor 24 through a rotating shaft 23 that penetrates the placement frame 21; wherein, the first reactor 100 is provided with two feed ports 11, which are respectively connected to containers for storing hydrogen peroxide solution and benzoin solution, and a metering pump 13 is arranged between the container and the feed port 11, and the metering The pump 13 can add the hydrogen peroxide solution and the benzoin solution into the first reaction chamber 1 for a mixed reaction according to a preset ratio. At the same time, a placement frame 21 loaded with a rare earth catalyst is also provided in the first reaction chamber 1. The placement frame 21 is detachably arranged in the first reaction chamber 1. Its specific structure is that an annular support bar 25 is provided on the inner wall of the first reaction chamber 1, and a magnet is provided on the support bar 25. A magnetic attraction piece that is attracted to the magnet is provided at the bottom of the placement frame 21. The installation and fixation of the placement frame 21 is achieved by the mutual attraction between the magnet and the magnetic attraction piece. As for the rare earth catalyst in the placement frame 21, it is loaded on the activated carbon. Therefore, the user can replace the rare earth catalyst by disassembling and assembling the placement frame 21.

[0040] At the same time, after the mixed benzoin solution flows through the placement frame 21, it will react with the rare earth catalyst in the placement frame 21, thereby realizing the preliminary oxidation of the benzoin solution; and the temperature control mechanism 5 arranged on the first reactor 100 includes a cooling coil 51 arranged on the side of the first reactor 100, one end of the cooling coil 51 is connected to the cooling water by a water pump, the water pump is connected to the control mechanism, and the other end is connected to the cooling water collection tank, and also includes a temperature sensor 52 and a heating tube arranged in the first reaction chamber 1, the heating tube is connected to the power supply. The heating tube is arranged on the inner wall of the first reactor 100, and the power supply and the temperature sensor 52 are also connected to the control mechanism. When the equipment is started, the control mechanism will first start the heating tube through the power supply, so that the heating tube cooperates with the temperature sensor 52 to control the temperature in the first reaction chamber 1 between 40-50°C, thereby ensuring that when the solution does not undergo an oxidation reaction, its reaction temperature can also be maintained at an optimal state. When the benzoin solution reacts with the rare earth catalyst to release heat, the temperature sensor 52 detects that the temperature is higher than the set value, and then controls the power supply to turn off the power supply to the heating tube, and starts the water pump at the same time to allow cooling water to flow through the cooling coil 51, thereby achieving cooling in the first reaction chamber 1 and avoiding side reactions in the oxidation reaction caused by high temperature.

[0041] In order to ensure the uniform mixing of hydrogen peroxide and benzoin solution, Figure 4-5As shown, stirring blades 22 located on the upper and lower sides of the placement frame 21 are also rotatably arranged in the first reaction chamber 1, and a pair of the stirring blades 22 are connected to the motor 24 through the rotating shaft 23 that penetrates the placement frame 21. The stirring blades 22 located above the placement frame 21 will rotate at a high speed, so that the liquid forms a strong turbulent state in the first reaction chamber 1, thereby promoting the uniform mixing of the benzoin solution and the oxidant, that is, the hydrogen peroxide solution, and the mixed reaction liquid will pass through the placement frame 21 under the rotation guidance of the lower stirring blades, and fully contact and react with the rare earth catalyst, thereby achieving the initial oxidation of benzoin. The design of the upper and lower sides of the stirring blades 22 allows the liquid to always maintain a uniform flow state, avoid the local "dead zone" phenomenon of the catalyst basket, and improve the utilization efficiency of the catalyst.

[0042] And, if Figure 7 As shown, in order to improve the sufficient reaction contact between the solution and the catalyst, a guide pipe 15 connected to the feed port 11 is provided in the cavity of the first reactor 100, and the guide pipe 15 divides the first reaction chamber 1 into an outer chamber 16 and an inner chamber 17. The lower ends of the outer chamber 16 and the inner chamber 17 are connected through a one-way through hole 18. A placement frame 21 and a pair of stirring blades 22 are arranged in the inner chamber 17, and a discharge port 20 connecting the outer chamber 16 and the inner chamber 17 is also provided at the lower end of the guide pipe 15. The discharge port 20 flows from the outer chamber 16 to the inner chamber 17 in one direction; the guide pipe 15 is located in the cavity and is divided into the inner chamber 17 and the outer chamber 16. The inner chamber 17 is the main reaction zone, and the outer chamber 16 is the fluid reflux zone. The bottoms of the inner chamber 17 and the outer chamber 16 are connected through a one-way through hole 18 to ensure that the liquid circulates continuously during the reaction process, enhance the uniformity of the material, and ensure the sufficient reaction of the reaction liquid and the liquid. The one-way through hole 18 connects the outer cavity 16 and the inner cavity 17, and a sealing film 19 is provided at the through hole. The sealing film 19 covers one side of the hole and can only be deformed in one direction. When there is pressure in the inner cavity 17 relative to the outer cavity 16, the sealing film 19 will deform and open the one-way through hole 18, so that the liquid in the inner cavity 17 can flow to the outer cavity 16. After the internal solution completes the reaction, the solenoid valve 14 between the first reactor 100 and the second reactor 200 will be opened, so that the reaction liquid can enter the second reactor 200 through the discharge port 12 of the first reactor 100; at the same time, after the reaction liquid in the inner cavity 17 is discharged, the reaction liquid in the outer cavity 16 will enter the inner cavity 17 through the discharge port 20, and then enter the second reactor 200 through the discharge port 12; when the first reaction chamber 1 is in normal working state, since there is still reaction liquid in both the inner and outer cavities 16, the discharge port 20 is in a closed state, and the opening and closing of the discharge port 20 is controlled by the one-way valve.

[0043] like Figure 6As shown, a UV auxiliary light source module 6 connected to the control mechanism is also provided at the top of the first reaction chamber 1. In the photocatalytic process, UV light can provide energy to make the electrons on the catalyst surface transition from the valence band to the conduction band to form electron-hole pairs. This excited electron-hole pair is highly active and can promote the occurrence of chemical reactions. For rare earth catalysts, the energy of UV light can excite the special electron orbits present in rare earth metal oxides, thereby enhancing their catalytic ability. And when UV light acts on reactant molecules, it can directly or indirectly destroy chemical bonds, activate or dissociate reactants, and form more free radicals or reactive intermediates. These active intermediates can significantly accelerate the reaction rate. At the same time, by optimizing the wavelength and intensity of UV light, certain reaction paths can be activated in a targeted manner, thereby suppressing the occurrence of side reactions and improving the selectivity of target products.

[0044] like Figure 8 As shown, the benzophenone solution obtained by the reaction in the first reactor 100 will be sent to the second reactor 200 after the solenoid valve 14 is opened. The second reactor 200 includes a shell with a second reaction chamber 3, wherein the second reactor 200 is an existing fixed bed catalytic reactor, and a temperature control mechanism 5 is arranged on the shell. The temperature control mechanism 5 is the same as the temperature control mechanism 5 of the first reactor 100, including a cooling coil 51 arranged on the shell and connected to cooling water, a temperature sensor 52 arranged in the second reaction chamber 3 and a heating pipe connected to the control mechanism, and the temperature control mechanism 5 The temperature in the second reaction chamber 3 can be controlled at 50-60°C, thereby avoiding the thermal decomposition reaction of benzil; and the palladium-based catalyst mechanism 4 includes a support mesh 41 arranged in the second reaction chamber 3, and the support mesh 41 is a porous metal mesh, and the support mesh 41 is distributed up and down, and the palladium-based catalyst bed 42 is fixed in the reactor to ensure that the catalyst will not be displaced during the reaction. The catalyst bed is loaded with palladium metal and has a honeycomb structure. The catalyst bed adopts a honeycomb structure and is loaded with palladium metal, which increases the density of catalytic active sites and improves the deep oxidation efficiency of benzophenone.

[0045] Through the arrangement of the first reactor 100 and the second reactor 200, compared with the existing preparation using a single catalytic system, a dual catalytic system is used. The synergistic effect of the dual catalytic system effectively improves the selectivity of the oxidation reaction, reduces the generation of by-products, and increases the yield of benzil (selectivity greater than 98%), which is significantly improved compared with the single catalyst system in the prior art; at the same time, the staged reaction process can better control the reaction conditions so that each stage of the reaction is carried out under the optimal conditions. This design not only improves the selectivity of the reaction, but also effectively avoids the generation of by-products and avoids the overreaction in the traditional method.

[0046] like Figure 2As shown, the solution after the reaction in the second reactor 200 will contain benzil and a small amount of by-product benzoic acid. The mixed solution of the two compounds will be transported to the gas-liquid separator 300 by a pipeline. The gas-liquid separator 300 is a cyclone gas-liquid separator 300, which is a prior art, such as the Hydro-Flow gas-liquid separator 300; it mainly includes a cyclone separation chamber with an inlet and a gas phase outlet 301 and a liquid phase outlet 302. The solution after the reaction enters the cyclone separation chamber through the inlet. The cyclone separation chamber is provided with cyclone blades. When the solution passes through the cyclone separation chamber, the gas phase and the liquid phase are separated under the action of centrifugal force, wherein the gas phase is mainly unreacted hydrogen peroxide gas, and the gas phase outlet 301 is connected to a recovery device, which can recycle the unreacted hydrogen peroxide gas; and the liquid phase mainly includes benzil and a small amount of benzophenone, benzoic acid and solvent liquid, and the liquid phase outlet 302 is connected to a distillation tower through a conveying pipeline to achieve further processing.

[0047] The distillation tower is a multi-effect distillation tower 400, which also belongs to the prior art, such as a multi-effect distillation device, which is mainly composed of a tower body composed of multiple sections of tower plates, and the upper and lower parts of the tower plates are filled with fillers. By controlling the distillation temperature of the distillation tower, the liquid phase solution separated from the gas-liquid separator 300 will be fractionated after entering the distillation tower, thereby separating benzil, benzophenone, benzoic acid and solvent; wherein the temperature gradient in the distillation tower is helpful to separate benzil (higher boiling point) and low boiling point solvent, benzophenone, while benzoic acid is concentrated in the middle distillate due to its lower volatility, thereby achieving effective separation from benzil. The separated benzil has a purity of more than 99.9% and is collected, while the unreacted solvent and benzoin are recycled and reused, and the benzoic acid in the middle distillate is sent to the by-product conversion device 500 for treatment through a conveying pipeline. In order to separate benzoic acid from the solvent, before being sent to the by-product conversion device 500, the benzoic acid and the solvent can be sent to a liquid-liquid separation device. The liquid-liquid separation device separates the benzoic acid and the solvent according to the difference in solubility between the components. The separated benzoic acid will be sent to the by-product conversion device 500.

[0048] The byproduct conversion device 500 is a catalytic hydrogenation reactor, which is a prior art. A cobalt-based catalyst bed is provided inside the reactor, and a hydrogen inlet and a temperature control mechanism 5 are provided. For example, the Swiss Thaletec hydrogenation reactor, after entering the catalytic hydrogenation reactor, benzoic acid undergoes a hydrogenation reaction under the action of hydrogen and a cobalt-based catalyst to generate benzyl alcohol. The temperature and pressure are controlled at 60°C and 1.5 MPa, respectively, and the byproduct water is discharged synchronously. The conversion of the byproduct benzyl alcohol turns the original waste into a valuable product, thereby improving the economic return of the entire production process. As a solvent, fragrance and chemical intermediate, benzyl alcohol has a high market demand, and the improvement of the conversion rate further optimizes the overall economic benefits of the process. Moreover, through the setting of the device, by effectively recovering and converting byproducts, not only waste emissions are reduced, but also the utilization efficiency of resources is improved, which is in line with the concept of green chemistry. By converting benzoic acid into benzyl alcohol through catalytic hydrogenation, direct waste of benzoic acid is avoided, and environmental pollution is reduced.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the design concept of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for preparing benzil, characterized in that: Here are the steps: S1. Raw material preparation: preparing a dry benzoin raw material and dissolving it in a solvent to obtain a benzoin solution; S2, preliminary oxidation: the benzoin solution obtained in S1 is fed into the first reaction chamber (1) of the preparation equipment to be subjected to preliminary oxidation under the action of a rare earth catalyst and hydrogen peroxide to obtain a transition product, benzophenone; S3, deep oxidation: transporting the transition product benzophenone obtained in S2 to the second reaction chamber (3), allowing it to react with a palladium-based catalyst to achieve deep oxidation, thereby obtaining a reaction solution containing benzil; S4, separation and purification: The gas phase and the liquid phase in the reaction liquid are separated by the gas-liquid separator (300) of the preparation equipment, and the liquid phase is sent to the distillation tower of the preparation equipment for purification to obtain benzil with a purity greater than 99.9%; the gas phase is recovered to the storage tank for recycling; S5, by-product recovery: After the liquid phase in S4 is separated by a distillation tower, benzoic acid and unreacted benzoin are obtained. The benzoic acid is sent to the by-product recovery and conversion mechanism of the preparation equipment to generate benzyl alcohol under the action of catalytic hydrogenation; and the unreacted benzoin is returned to the first reaction chamber (1).

2. A benzil preparation process according to claim 1, characterized in that, The temperature in the first reaction chamber (1) is set at 40-50° C., and the reaction time of the benzoin solution, hydrogen peroxide and rare earth catalyst in the first reaction chamber (1) is 30 minutes.

3. A benzil preparation process according to claim 1, characterized in that, The temperature in the second reaction chamber (3) is set at 50-60° C., and the benzophenone solution reacts with the palladium-based catalyst in the second reaction chamber (3) for 1 hour.

4. A benzil preparation process according to claim 2, characterized in that, The hydrogen peroxide is a 30% concentration hydrogen peroxide solution, which is mixed with a benzoin solution at a volume ratio of 1:1.2 and then added into the first reaction chamber (1).

5. A process for preparing benzil according to claim 2, characterized in that: The rare earth catalyst is a catalyst in which cerium dioxide is supported on activated carbon, and the amount of the rare earth catalyst used is 0.5%-2% of the mass of benzoin.

6. A process for preparing benzil according to claim 1, characterized in that: The solvent is anhydrous ethanol, and the mass fraction of benzoin in the solution is 10%-15%.

7. A benzil preparation device for implementing the benzil preparation process according to any one of claims 1 to 6, characterized in that: The invention comprises a first reactor (100), a second reactor (200), a gas-liquid separator (300), a multi-effect distillation tower (400) and a by-product conversion device (500) which are connected in sequence; a rare earth catalyst mechanism (2) is arranged in a first reaction chamber (1) of the first reactor (100), and a palladium-based catalyst mechanism (4) is arranged in a second reaction chamber (3) of the second reactor (200); a temperature control mechanism (5) and a control mechanism are also arranged in the first reaction chamber (1) and the second reaction chamber (3); the temperature control mechanism (5) is connected to the control mechanism and is used to adjust the temperature in the first and second reaction chambers; the control mechanism is used to monitor the working parameters of the control device.

8. A benzil preparation device according to claim 7, characterized in that: The first reactor (100) comprises a cavity having a feed port (11) and a discharge port (12), wherein the feed port (11) is connected to a metering pump (13), and the discharge port (12) is connected to a second reactor (200) via a solenoid valve (14); the rare earth catalyst mechanism comprises a placement frame (21) arranged in the first reaction chamber (1), wherein the placement frame (21) is used to place the rare earth catalyst; and further comprises stirring blades (22) rotatably arranged on the upper and lower sides of the placement frame (21), wherein a pair of the stirring blades (22) are connected to a motor (24) via a rotating shaft (23) penetrating the placement frame (21); and a UV auxiliary light source module (6) connected to a control mechanism is arranged at the top of the first reaction chamber (1), wherein the UV auxiliary light source module (6) is used to assist the reaction between the solution and the rare earth catalyst.

9. A benzil preparation device according to claim 8, characterized in that: A guide pipe (15) connected to the feed port (11) is arranged in the cavity of the first reactor (100); the guide pipe (15) divides the first reaction cavity (1) into an outer cavity (16) and an inner cavity (17); the lower ends of the outer cavity (16) and the inner cavity (17) are connected via a one-way through hole (18); the one-way through hole (18) is used to allow liquid in the inner cavity (17) to flow in one direction toward the outer cavity (16); the placement frame (21) and a pair of stirring blades (22) are arranged in the inner cavity (17).

10. The benzil preparation device according to claim 9, characterized in that: The second reactor (200) comprises a shell with a second reaction chamber (3), and the palladium-based catalyst mechanism (4) comprises a support mesh (41) arranged in the second reaction chamber (3), a catalyst bed layer being arranged on the support mesh (41), and the catalyst bed layer being loaded with palladium metal and presenting a honeycomb structure.

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