Process for preparing methyl methacrylate by applying downer reactor through one-step oxidative esterification method

Abstract

The invention discloses a process for preparing methyl methacrylate by applying a downer reactor to a one-step oxidative esterification method, and a reaction system used in the process mainly comprises a particle conduit, a downer reactor, a bubble generator, a liquid-solid settling separator, a delivery pipe, a liquid-solid separator, a particle buffer bin and the like. A liquid raw material entering the downer reactor and a catalyst entering along a particle guide pipe flow downwards in parallel, are in countercurrent contact with oxidizing gas and are subjected to oxidative esterification reaction, after liquid-solid settling separation, catalyst particles are settled into a particle storage tank, then enter the bottom of a conveying pipe, are cleaned by conveying liquid and are conveyed into a liquid-solid separator, and the catalyst particles are separated by the liquid-solid separator. And after liquid-solid separation, the catalyst falls into the particle temporary storage bin to continuously participate in the next round of reaction. According to the process, backmixing in the reactor is basically eliminated, the reaction efficiency is improved, the reaction time is shortened, the conversion rate of methylacrolein and the selectivity of methyl methacrylate are increased, the utilization rate of oxygen is improved, and the process has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of methyl methacrylate production, and particularly relates to a process for preparing methyl methacrylate by one-step oxidative esterification in a down-flow bed reactor. BACKGROUND

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, mainly used for producing organic glass (polymethyl methacrylate, PMMA), paint and adhesive, etc. PMMA accounts for more than 70% of the MMA consumption market, has high transparency and weather resistance, and cannot be replaced by other materials, and is widely used in the fields of automobile lampshade, optical devices, furniture and household appliances, building and aviation, etc. As of 2024, the production capacity of methyl methacrylate in China is about 2,655,000 tons, and it is expected that the production capacity will exceed 3,000,000 tons in 2025. After nearly 100 years of development, there are three methods for synthesizing MMA, namely acetone cyanhydrin method (ACH method), C4 method and C2 method.

[0003] The acetone cyanhydrin method is widely used at home and abroad, but the raw material hydrogen cyanide used in this method is highly toxic, and concentrated sulfuric acid needs to be used in the production process, which requires high equipment, and a large amount of ammonium salt is also produced, which seriously pollutes the environment. At present, China has banned the construction of new industrial devices for producing methyl methacrylate by ACH method except for using methyl methacrylonitrile device by-product hydrogen cyanide. The C4 method is to produce methyl methacrylate by using isobutylene as raw material. This method was first developed by Asahi Kasei in Japan, and is the second largest production method next to the ACH method. The C4 route using isobutylene as raw material is a three-step method, that is, isobutylene is converted into methyl methacrylate through methyl methacrylate and methyl methacrylate. Later, on the basis of the three-step method of isobutylene, the three-step method was shortened to a two-step method, that is, isobutylene was directly oxidized and esterified to methyl methacrylate through methyl methacrylate. This process greatly shortens the process flow and avoids the production of methyl methacrylate, which can improve the production efficiency. The C2 method is to produce methyl methacrylate by using ethylene as raw material. This route is divided into two methods. One is the Alpha method, that is, ethylene is converted into methyl methacrylate through methyl propionate. This method has very high requirements for the performance of the catalyst, and only Lucite International Company has this technology and does not transfer it to others. The other is the BASF method, that is, ethylene is converted into methyl methacrylate through propionaldehyde-methyl methacrylate-methyl methacrylate. This process is green and environmentally friendly, but the equipment requirements are high due to the need to pass through methyl methacrylate, and the process is complex and the investment is large.

[0004] Through the above comparative analysis, ACH method will be gradually eliminated due to raw materials and environmental problems, and C2 and C4 routes, except Alpha method, all need to produce methyl methacrylate through methyl propionaldehyde, and it is difficult to break through the Alpha route in the short term. Therefore, the process of producing methyl methacrylate from ethylene or isobutene through methyl propionaldehyde is the key to developing new methyl methacrylate production processes.

[0005] Currently, the research and development of catalysts for the one-step oxidation esterification of methyl propionaldehyde to produce methyl methacrylate has made great progress. The Chinese invention patent with application number 202280057029.6 discloses the preparation of a catalyst for the oxidation esterification of methyl propionaldehyde to methyl methacrylate to extend the service life. The prepared heterogeneous noble metal-containing catalyst can maintain activity during operation and can extend the time between shutdown periods, achieving sustainable catalyst management. This method is simple, economical and environmentally friendly. The Chinese invention patent with application number 202310830405.7 discloses a method for synthesizing methyl methacrylate and a dual-functional oxidation esterification catalyst, as well as its preparation method and application. The catalyst includes an active component with the general formula AuRh a O n / MN b O x , where N is selected from Group IIA elements and M is a carrier element. The disclosed catalyst has high conversion rate and high single yield. The Chinese invention patent with application number 201811446361.3 discloses a low-cost and efficient catalyst for producing methyl methacrylate and its preparation method. The disclosed catalyst is a supported nanogold catalyst with a gold loading of only 0.05 wt%-0.98 wt%. The prepared catalyst has uniform gold particles, high activity for oxidation esterification, low cost, and is suitable for industrial production. The Chinese invention patent with application number 201910438644.1 discloses a catalyst for producing methyl methacrylate by one-step oxidation esterification, as well as its preparation method and application. The prepared catalyst uses a material containing electron-rich oxides as a composite carrier, metal palladium as an active component, rare earth metals as an active component, and a surfactant as an additive. When applied to the process of producing methyl methacrylate by one-step oxidation esterification of methyl propionaldehyde, it has high conversion rate and high selectivity, and the preparation process is simpler and the reaction conditions are milder.

[0006] The above patents all focus on the development of catalysts for the one-step oxidation esterification of methylacrolein to methyl methacrylate, and less on the development of processes and reactors. The raw materials for the one-step oxidation esterification of methylacrolein to methyl methacrylate are mainly methanol, methylacrolein and oxygen. Under the reaction conditions, methanol and methylacrolein are in liquid state, oxygen is in gaseous state, and the catalyst is in solid state. Therefore, a gas-liquid-solid three-phase reactor is required for the reaction process. Commonly used three-phase reactors include fixed bed reactors, continuous stirred tank reactors, slurry bed reactors and circulating fluidized bed reactors. In the fixed bed reactor, the particles of the catalyst are large, the concentration of the catalyst accumulation is relatively high, the reaction effect is poor, and the one-step oxidation esterification reaction of methylacrolein is a strong exothermic reaction, which is difficult to effectively control the temperature distribution in the reactor. Local hot spots not only affect the reaction effect, but also cause certain safety risks. The continuous stirred tank reactor can use micron-sized catalyst particles, and the high-efficiency mixing and heat and mass transfer rates in the reactor can be achieved by using stirring paddles, but the high-speed stirring paddles require higher strength of the catalyst. In experiments, it is found that continuous operation for more than 500 hours will cause a certain degree of catalyst breakage, which not only increases the production cost, but also affects the subsequent liquid-solid filtration system. The slurry bed reactor has the characteristics of simple structure and uniform mixing, but the back mixing in the slurry bed reactor is serious, the reaction rate is low, and the reaction material requires a longer residence time in the reactor. Methylacrolein is prone to polymerization, which not only reduces the utilization rate of raw materials but also reduces the service life of the catalyst. In order to realize the efficient conversion of the one-step oxidation esterification of methylacrolein to methyl methacrylate, a gas-liquid-solid three-phase circulating fluidized bed reactor can be used to realize the above reaction process in the riser, which can effectively shorten the reaction time and improve the reaction efficiency. However, in practical application, it is found that due to the three-phase reverse gravity field, there is still a certain amount of back mixing, and the gas phase and liquid-solid phase move upward, which is difficult to control the movement speed of the bubbles in the reactor, resulting in low oxygen utilization rate and high oxygen concentration at the outlet of the reactor, which can easily cause safety accidents. SUMMARY

[0007] In order to further improve the production efficiency of the reaction process of one-step oxidative esterification of methanol and methyl propyl aldehyde to prepare methyl methacrylate, aiming at the problems of slow transmission efficiency of fixed bed reactor, catalyst abrasion of stirred tank reactor, serious back mixing of slurry bed reactor and low oxygen utilization rate of gas movement speed difficult to control of three-phase circulating fluidized bed riser reactor, the purpose of the present application is to provide a process for preparing methyl methacrylate by one-step oxidative esterification method using down-flow bed reactor, the present application realizes high-efficiency conversion of one-step oxidative esterification for preparing methyl methacrylate by using gas-liquid-solid three-phase down-flow bed reactor, which combines the advantages of stirred tank reactor, slurry bed reactor and three-phase circulating fluidized bed reactor, and overcomes the existing problems and deficiencies, adopts liquid-solid phase downward movement in gravity field, significantly reduces the back mixing of liquid-solid phase, and the gas phase contacts with the liquid-solid phase in the form of bubbles, which not only increases the interphase transfer rate, but also can adjust the movement speed and residence time of the bubbles through the apparent liquid velocity, improves the reaction rate, shortens the reaction time, increases the oxygen utilization rate, increases the production performance of the device, improves the safety and stability of operation, and has wide industrial application prospect.

[0008] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: The application provides a process for preparing methyl methacrylate by one-step oxidation esterification using a gas-liquid-solid three-phase down-flow bed reactor, wherein the gas-liquid-solid three-phase down-flow bed reactor mainly comprises a raw material inlet 1, a particle guide pipe 2, a down-flow bed reactor 3, a bubble generator 4, a reaction liquid outlet 5, a liquid-solid sedimentation separator 6, a particle storage tank 7, an auxiliary conveying liquid inlet 8, a conveying liquid inlet 9, a conveying pipe 10, a liquid-solid separator 11, a conveying liquid outlet 12, a particle buffer bin 13, a loosening liquid inlet 14, a loosening liquid distribution plate 15, a gas outlet 16, a gas partition plate 17; the down-flow bed reactor 3, the liquid-solid sedimentation separator 6, the particle storage tank 7, the conveying pipe 10, the liquid-solid separator 11 and the particle buffer bin 13 are sequentially connected; the down-flow bed reactor 3 and the particle buffer bin 13 are separated by the gas partition plate 17; the down-flow bed reactor 3 and the particle buffer bin 13 are connected by the particle guide pipe 2 which penetrates the gas partition plate 17 and the loosening liquid distribution plate 15 in the vertical direction; the sidewall top of the down-flow bed reactor 3 is provided with the gas outlet 16; the other sidewall of the down-flow bed reactor 3 is provided with the raw material inlet 1; the cross section of the bottom of the down-flow bed reactor 3 is provided with the bubble generator 4; the bubble generator 4 is connected with the gas inlet; the sidewall bottom of the down-flow bed reactor 3 is provided with the reaction liquid outlet 5; the bubble generator 4 is located above the reaction liquid outlet 5; the bottom of the down-flow bed reactor 3 is connected with the top of the liquid-solid sedimentation separator 6; the bottom of the liquid-solid sedimentation separator 6 is connected with the particle storage tank 7; the sidewall of the particle storage tank 7 is connected with the bottom sidewall of the conveying pipe 10 through a discharging inclined pipe; the bottom sidewall of the conveying pipe 10 is provided with the auxiliary conveying liquid inlet 8 and the conveying liquid inlet 9; the top of the conveying pipe 10 is connected with the inlet of the liquid-solid separator 11 through a pipeline; the top of the liquid-solid separator 11 is provided with the conveying liquid outlet 12; the bottom of the liquid-solid separator 11 is connected with the particle buffer bin 13; the sidewall bottom of the particle buffer bin 13 is provided with the loosening liquid inlet 14; the cross section of the particle buffer bin 13 above the loosening liquid inlet 14 is provided with the loosening liquid distribution plate 15 for uniformly distributing the loosening liquid. The process comprises the following steps: (1) the mixed liquid of liquid raw materials methanol and methylacrolein enters the down-flow bed reactor 3 through the raw material inlet 1; the catalyst in the particle buffer bin 13 enters the top of the down-flow bed reactor 3 along the particle guide pipe 2 under the action of the loosening liquid inputted through the loosening liquid inlet 14; under the action of gravity and the liquid raw materials, the catalyst moves downward along the down-flow bed reactor 3, contacts with the oxidation gas which is inputted from the bottom of the down-flow bed reactor 3 in countercurrent and occurs oxidation esterification reaction, and the remaining gas is discharged from the gas outlet 16 at the top of the down-flow bed reactor 3; (2) the liquid phase after reaction and the catalyst enter the liquid-solid sedimentation separator 6 through the bottom of the down-flow bed reactor 3, and the separation of the catalyst and the liquid phase is carried out; the liquid phase containing the reaction product is discharged from the reaction liquid outlet 5, and the catalyst particles are settled in the particle storage tank 7; (3) The catalyst particles in the particle storage tank 7 enter the bottom of the conveying pipe 10 through the discharge inclined pipe, move upward along the conveying pipe 10 under the carrying action of the conveying liquid, and clean the reactants and reaction products on the surface and in the pores of the catalyst, the catalyst and the conveying liquid enter the liquid-solid separator 11 through the top of the conveying pipe 10, after liquid-solid separation, the conveying liquid is discharged from the system through the conveying liquid outlet 12, and the catalyst falls into the particle buffer bin 13 to continue to participate in the next round of reaction.

[0009] Based on the above technical scheme, further, the down-flow bed reactor 3 and the conveying pipe 10 are in the shape of a cylinder; the particle storage tank 7 is in the shape of a cone.

[0010] Based on the above technical scheme, further, the raw material inlet 1 is located above the outlet end of the particle guide pipe 2; the auxiliary conveying liquid inlet 8 is located above the conveying liquid inlet 9.

[0011] Based on the above technical scheme, further, the liquid-solid separator 11 for separating the catalyst particles and the conveying liquid is one of a settling type separator, a liquid-solid cyclone separator, and a filter type separator, or a combination of two or more thereof.

[0012] Based on the above technical scheme, further, the structure of the bubble generator 4 is one of a Venturi type, a double tangential type, a cyclone type, a dissolved gas-released gas type, a jet type, a porous mode, a vortex type, and an injector array type, or a combination of two or more thereof.

[0013] Based on the above technical scheme, further, the molar ratio of methanol and methyl acrylaldehyde in the liquid raw material is 1:1~100:1, the conveying liquid, the auxiliary conveying liquid, and the loosening liquid are one of methanol, ethanol, and methyl acrylaldehyde, or a combination of two or more thereof.

[0014] Based on the above technical scheme, further, the oxidizing gas is oxygen or a mixture of oxygen and nitrogen, wherein the volume fraction of oxygen is 5%~100%.

[0015] Based on the above technical scheme, further, the catalyst is a supported catalyst, the active component of which is one of copper oxide, zinc oxide, gold, palladium, gold-palladium alloy, and palladium-copper alloy, or a combination of two or more thereof, the particle size of the catalyst is 20~5000 μm; the particle density is 1000~8000 kg / m 3 .

[0016] Based on the above technical scheme, further, the diameter of the down-flow bed reactor is 20~600 mm, and the height is 0.5~50 m.

[0017] Based on the above technical scheme, further, the liquid superficial velocity in the downflow bed reactor is 0.1-1000 m / h, the catalyst concentration is 0.05-30 wt%, and the superficial liquid velocity in the conveying pipe is 10-50000 m / h.

[0018] Based on the above technical scheme, further, the pressure of the reaction system is normal pressure-50 MPa, and the temperature is 0-200 DEG C.

[0019] Compared with the prior art, the present application has the following beneficial effects: (1) In the process of preparing methyl methacrylate by one-step oxidation esterification method using the three-phase downflow bed reactor, the liquid-solid phase is in the order of gravity field, almost no back mixing, the reaction rate is improved, the reaction time is shortened, the space utilization of the reactor is increased, and it is more beneficial to large-scale production.

[0020] (2) In the process of preparing methyl methacrylate by one-step oxidation esterification method using the three-phase downflow bed reactor, the oxygen is in the form of bubbles and countercurrently contacted with the liquid-solid phase, the degree of turbulence is increased, the mixing degree and contact efficiency between the three phases are improved, the reaction effect is further improved, the apparent liquid velocity can also realize the precise control of the bubble movement speed and residence time, the oxygen utilization rate is increased, the device operation benefit is increased and the device operation safety is improved.

[0021] (3) In the process of preparing methyl methacrylate by one-step oxidation esterification method using the three-phase downflow bed reactor, the reaction rate is improved, the reaction time is shortened, the conversion rate of methyl methacrylate and the selectivity of methyl methacrylate are improved, and the self-polymerization degree of methyl methacrylate is reduced, the device operation efficiency and economy are increased.

[0022] (4) In the process of preparing methyl methacrylate by one-step oxidation esterification method using the three-phase downflow bed reactor, the conveying pipe not only conveys the catalyst particles, but also uses the high-speed conveying liquid flow to clean the reactants and reaction products on the surface and in the pores of the catalyst, and timely realizes the renewal of the active surface of the catalyst, prolonging the service life of the catalyst.

[0023] (5) In the whole system for preparing methyl methacrylate by one-step oxidation esterification method using the three-phase downflow bed reactor, no moving equipment is used, the failure rate of the device operation is reduced, the wear of the equipment on the catalyst is reduced, the catalyst consumption is reduced, the continuous stability of the device operation is increased, the operation cycle of the device is prolonged, and the production benefit is improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced below.

[0025] Figure 1 The structural schematic diagram of the one-step oxidative esterification method for producing methyl methacrylate by using the three-phase down-flow bed reactor in Example 1 is shown in the figure, wherein, 1 is a raw material inlet, 2 is a particle guide pipe, 3 is a down-flow bed reactor, 4 is a bubble generator, 5 is a reaction liquid outlet, 6 is a liquid-solid settling separator, 7 is a particle storage tank, 8 is an auxiliary conveying liquid inlet, 9 is a conveying liquid inlet, 10 is a conveying pipe, 11 is a liquid-solid separator, 12 is a conveying liquid outlet, 13 is a particle buffer bin, 14 is a loosening liquid inlet, 15 is a loosening liquid distribution plate, 16 is a gas outlet, and 17 is a gas baffle.

[0026] Figure 2 The structural schematic diagram of the one-step oxidative esterification method for producing methyl methacrylate by using the riser reactor in Comparative Example 1 is shown in the figure, wherein, 201 is a liquid inlet, 202 is a gas-liquid mixing inlet, 203 is a riser reactor, 204 is a three-phase rapid separator, 205 is a settling separator, 206 is a gas outlet, 207 is a particle baffle, 208 is a liquid outlet, 209 is a particle return pipe, and 210 is a particle control valve.

[0027] Figure 3 The structural schematic diagram of the one-step oxidative esterification method for producing methyl methacrylate by using the gas-liquid-solid three-phase slurry bed reactor in Comparative Example 2 is shown in the figure, wherein, 301 is a liquid phase feed inlet, 302 is a gas inlet, 303 is a bubble generator, 304 is a gas outlet, 305 is a liquid outlet, and 306 is a catalyst filter.

[0028] Figure 4 The structural schematic diagram of the one-step oxidative esterification method for producing methyl methacrylate by using the gas-liquid-solid three-phase stirred tank reactor in Comparative Example 3 is shown in the figure, wherein, 401 is a liquid phase feed inlet, 402 is a gas inlet, 403 is a bubble generator, 404 is a gas outlet, 405 is a liquid outlet, 406 is a catalyst filter, 407 is a stirring paddle, and 408 is a motor. DETAILED DESCRIPTION

[0029] The application will be described in detail below with reference to the examples, but the embodiments of the application are not limited thereto. Obviously, the examples described below are only some of the embodiments of the application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0030] Example 1 This example provides a process for producing methyl methacrylate by using the gas-liquid-solid three-phase down-flow bed reactor one-step oxidative esterification method, and the structural schematic diagram is as shown in Figure 1As shown in the figure, the main structure of the reactor and the inlets and outlets of related materials are displayed. This gas-liquid-solid three-phase descending bed reactor mainly includes the following components and units: raw material inlet 1, particle conduit 2, descending bed reactor 3, bubble generator 4, reaction liquid outlet 5, liquid-solid sedimentation separator 6, particle storage tank 7, auxiliary conveying liquid inlet 8, conveying liquid inlet 9, conveying pipe 10, liquid-solid separator 11, conveying liquid outlet 12, particle buffer bin 13, loosening liquid inlet 14, loosening liquid distribution plate 15, gas outlet 16, and gas baffle 17. The descending bed reactor 3, liquid-solid sedimentation separator 4, and other components and units are also shown. The separator 6, particle storage tank 7, conveying pipe 10, liquid-solid separator 11, and particle buffer chamber 13 are connected in sequence. The descending bed reactor 3 and particle buffer chamber 13 are separated by a gas baffle 17 and connected by a vertical particle conduit 2 that passes through the gas baffle 17 and loose liquid distribution plate 15. The descending bed reactor 3 is cylindrical. A gas outlet 16 is provided at the top of the side wall of the descending bed reactor 3, and a raw material inlet 1 is provided on the other side wall of the descending bed reactor 3. The raw material inlet 1 is located above the outlet end of the particle conduit 2. A bubble generator 4 is installed on the bottom cross-section of the reactor 3, and the bubble generator 4 is connected to the gas inlet. A reaction liquid outlet 5 is installed on the bottom side wall of the descending bed reactor 3, and the bubble generator 4 is located above the reaction liquid outlet 5. The bottom of the descending bed reactor 3 is connected to the top of the liquid-solid sedimentation separator 6. The liquid-solid sedimentation separator 6 is a sedimentation type liquid-solid separator. The bottom of the liquid-solid sedimentation separator 6 is connected to the particle storage tank 7. The particle storage tank 7 is conical, and the side wall of the particle storage tank 7 is connected to the bottom side wall of the conveying pipe 10 through a feed inclined pipe. An auxiliary delivery liquid inlet 8 and a delivery liquid inlet 9 are provided on the wall. The auxiliary delivery liquid inlet 8 is located above the delivery liquid inlet 9. The delivery pipe 10 is connected to the inlet of the liquid-solid separator 11 through a pipe. The liquid-solid separator 11 is a liquid-solid hydrocyclone separator. The top of the liquid-solid separator 11 is provided with a delivery liquid outlet 12. The bottom of the liquid-solid separator 11 is connected to the particle buffer chamber 13. A loosening liquid inlet 14 is provided on the bottom side wall of the particle buffer chamber 13. A loosening liquid distribution plate 15 is provided on the cross-section of the particle buffer chamber 13 above the loosening liquid inlet 14 for uniformly distributing the loosening liquid. The liquid feedstock is a mixture of methanol and methacrolein, with a molar ratio of methanol to methacrolein of 10:1. The auxiliary transport liquid, transport liquid, and loosening liquid are all made of methanol. The gas used in the reaction is a mixture of oxygen and nitrogen, with an oxygen volume fraction of 50% and a flow rate of 10 ml / min. The catalyst used in the reaction is supported gold nanoparticles with a median particle size of 85 μm and a particle density of 2100 kg / m³. 3The diameter of the down-flow bed reactor is 50 mm, the height of the reactor is 10 m, the inner diameter of the conveying pipe is 10 mm, and the height of the conveying pipe is 12 m; the superficial liquid velocity in the down-flow bed reactor is 30 m / h, the catalyst concentration is 15 wt%, and the superficial liquid velocity in the conveying pipe is 100 m / h; the pressure of the reaction system is controlled at 0.5 MPa, and the temperature of the down-flow bed reactor is 80 ℃.

[0031] The specific process of preparing methyl methacrylate by one-step oxidative esterification using the gas-liquid-solid three-phase down-flow bed reactor is as follows: The catalyst particles in the particle buffer tank 13 enter the top of the down-flow bed 3 under the action of the loosening liquid methanol, move downward along the down-flow bed reactor 3 under the action of gravity and the liquid raw material (a mixture of methanol and methylacrolein in a molar ratio of 10:1), and react with the mixed gas (oxygen in a volume fraction of 50%) from the bottom of the down-flow bed reactor 3 in a countercurrent manner in the process of movement. The remaining gas is discharged from the gas outlet 16 at the top, and the liquid phase containing the reaction products is discharged from the reaction liquid outlet 5 and then enters the separation system, while the catalyst particles return to the particle storage tank 7. The nano gold catalyst particles in the particle storage tank 7 enter the bottom of the conveying pipe 10 and move upward along the conveying pipe 10 under the carrying action of the conveying liquid methanol. The circulation amount of the catalyst particles in the conveying pipe 10 is controlled by adjusting the flow rate of the auxiliary conveying liquid methanol. The conveying pipe 10 is connected to the liquid-solid separator 11 at the top, which can realize rapid separation of the catalyst particles and the conveying liquid methanol. The conveying liquid is discharged from the conveying liquid outlet 12 at the top of the liquid-solid separator 11, and the catalyst particles fall into the particle buffer tank 13 to participate in the next round of reaction. After the device is stably operated for 2 hours, liquid phase samples are taken from the reaction liquid outlet, the composition of the liquid phase is analyzed by chromatography, and the oxygen concentration of the gas phase sample is analyzed at the gas phase outlet 16. According to the above analysis results, the conversion rate of methylacrolein, the selectivity of methyl methacrylate, and the utilization rate of oxygen are calculated, and the specific results are shown in Table 1.

[0032] The conveying pipe 10 not only plays a role in conveying the catalyst particles, but also can clean the reaction products on the surface of the catalyst particles, preventing the generated methyl methacrylate and the remaining methylacrolein from covering the active centers of the catalyst particles, thereby prolonging the service life of the catalyst.

[0033] Comparative Example 1 This comparative example provides a process for preparing methyl methacrylate by one-step oxidative esterification using a riser reaction system, and the schematic diagram is as follows: Figure 2, the main structure of the reactor and the inlet and outlet of the related materials are shown, and the reactor mainly includes a liquid inlet 201, a gas-liquid mixing inlet 202, a riser reactor 203, a three-phase rapid separator 204, a settling separator 205, a gas outlet 206, a particle baffle 207, a liquid outlet 208, a particle return pipe 209 and a particle control valve 210 and the like. The riser reactor 203, the three-phase rapid separator 204, the settling separator 205 and the particle return pipe 209 are connected in series. The bottom end of the riser reactor 203 is provided with the gas-liquid mixing inlet 202, and the gas-liquid mixing inlet 202 is provided with a liquid-driven bubble generator. The connecting pipeline of the particle return pipe 209 and the riser reactor 203 is provided with the liquid inlet 201, and the bottom of the particle return pipe 209 is provided with the particle control valve 210. The inlet of the three-phase rapid separator 204 is connected with the top end outlet of the riser reactor 203, and the outlet of the three-phase rapid separator 204 is located in the inside of the settling separator 205. The settling separator 205 is composed of a hollow cylinder with a sealed top and a conical bottom. The top of the settling separator 205 is provided with the gas outlet 206, and the sidewall of the settling separator 205 is provided with the liquid outlet 208. The liquid outlet 208 is provided with the particle baffle 207, and the bottom of the settling separator 205 is connected with the particle return pipe 209. The liquid phase in the reactor is a mixture of methanol and methylacrolein, and the molar ratio of methanol to methylacrolein is 10:1. The gas used in the reaction is a mixture of oxygen and nitrogen, and the volume fraction of oxygen is 50%. The gas feed flow rate is 10 ml / min, most of the bubble diameter is controlled in 50-500 μm, the catalyst used in the reaction is a supported nano-gold catalyst, the particle size of the catalyst is 50-200 μm, the median particle size is about 85 μm, and the particle density of the catalyst is 2100 kg / m 3 ; the inner diameter of the riser reactor is 50 mm, and the height is 15 m; the superficial liquid velocity of the liquid in the riser reactor is 30 m / h, and the catalyst concentration is 15wt%; the use pressure of the riser reactor is 0.5 MPa, and the temperature controlled by the reactor is 80℃; The specific process of applying the riser reactor to one-step oxidation esterification to prepare methyl methacrylate is as follows: The mixture of methanol and methylacrolein (methylacrolein and methanol were mixed in a molar ratio of 10:1) was divided into two streams, one fifth of which was introduced into the reactor through the liquid inlet 201 downstream of the particle control valve 202 for feeding the catalyst particles into the bottom of the riser reactor 203, and the remaining mixture was introduced into the bottom of the riser reactor 203 through the gas-liquid mixing inlet 202. The catalyst concentration in the reactor was controlled by the particle control valve 210 to maintain a catalyst concentration of 15 wt% in the riser reactor. After the system was stabilized, the gas-liquid mixture (the volume ratio of oxygen to nitrogen in the mixed gas was 5:5) was introduced into the bottom of the riser reactor 203 through the gas-liquid mixing inlet 202, mixed thoroughly, and moved upward along the riser while being in contact with the reaction. The pressure of the reactor was controlled at 0.5 MPa, and the temperature of the reactor was controlled at 80°C. After the gas-liquid-solid three-phase preliminary separation was achieved by the three-phase rapid separator 204 at the top of the riser reactor, the mixture was introduced into the settling separator 205 for further settling separation. The gas was discharged from the gas outlet 206 at the top, the liquid phase passed over the particle baffle 207 and was discharged from the liquid outlet 208 to enter the subsequent separation system, and the catalyst particles were returned to the reactor through the particle return pipe 209 at the bottom of the settling separator 205 to participate in the reaction again. After the device was continuously operated for 1 hour, samples were taken at the gas outlet 206 and the liquid outlet 208 for analysis of their compositions, and the reaction effect was calculated, including the conversion of methylacrolein, the selectivity of methyl methacrylate, and the utilization rate of oxygen. The device was continuously operated for more than 24 hours, and sampling and analysis were performed once every hour. The final test results were averaged, and the specific results are shown in Table 1.

[0034] Comparative Example 2 This comparative example used a gas-liquid-solid three-phase slurry bed reactor, and the structure of the reactor was as follows: Figure 3The reactor diameter is 200 mm, and the effective volume (below the liquid outlet) is the same as that of the downflow bed reactor in Comparative Example 1. The liquid raw material enters from the liquid phase feed port 301 at the bottom of the reactor, and the gas enters from the gas inlet 302 at the side wall of the bottom of the reactor, forms bubbles through the bubble generator 303, and then enters the reactor to mix with the liquid. The catalyst is uniformly mixed in the reactor under the action of the bubbles and catalyzes the oxidative esterification reaction. After the reaction, the gas is discharged from the gas outlet 304 at the top of the reactor, and the liquid after the reaction is discharged from the liquid outlet 305. A catalyst filter 306 is installed at the liquid outlet position, and the catalyst can remain in the reactor. In this comparative example, in order to ensure a high conversion rate of methacrolein, a liquid residence time of 60 min is required, and the feed amount of the liquid raw material is 6.25 L / h. The raw material ratio, catalyst concentration, reaction temperature and pressure and other parameters are consistent with those of Example 1. The gas and liquid phase outlets are sampled and analyzed, and the conversion rate of methacrolein, the selectivity of methyl methacrylate and the utilization rate of oxygen are calculated. The specific results are shown in Table 1.

[0035] Comparative Example 3 In this comparative example, a gas-liquid-solid three-phase stirred tank reactor is used. The structure of the reactor is shown in Figure 4 The basic structure of the reactor is the same as that of the slurry bed reactor used in Comparative Example 2, except that a stirring paddle 407 driven by a motor 408 is added in the reactor. The liquid raw material enters from the liquid phase feed port 401 at the bottom of the reactor, and the gas enters from the gas inlet 402 at the side wall of the bottom of the reactor, forms bubbles through the bubble generator 403, and then enters the reactor to mix with the liquid. The catalyst is uniformly mixed in the reactor under the action of the bubbles and stirring, and catalyzes the oxidative esterification reaction. After the reaction, the gas is discharged from the gas outlet 404 at the top of the reactor, and the liquid after the reaction is discharged from the liquid outlet 405. A catalyst filter 406 is installed at the liquid outlet position, and the catalyst can remain in the reactor. The raw material ratio, feed speed, catalyst concentration, reaction temperature and pressure and other parameters are consistent with those of Example 1. The gas and liquid phase outlets are sampled and analyzed, and the conversion rate of methacrolein, the selectivity of methyl methacrylate and the utilization rate of oxygen are calculated. The specific results are shown in Table 1.

[0036] Table 1. Comparison of reaction effects of one-step oxidative esterification of methanol methacrolein to methyl methacrylate using different reactors

[0037] As shown in Table 1, the conversion rate of methylpropylaldehyde is as high as 89.2%, the selectivity of methyl methacrylate is as high as 98.7%, and the oxygen utilization rate can be increased to 75.3% by using the gas-liquid-solid three-phase down-flow bed reactor to perform the process of one-step oxidation esterification of methylpropylaldehyde to prepare methyl methacrylate. Compared with the existing continuous stirred tank reactor, slurry bed reactor and riser reactor, the reaction time is significantly shortened, the reaction effect is obviously improved, and in particular, the oxygen utilization rate is significantly improved, thereby avoiding the safety risk caused by the excessively high oxygen concentration in the gas phase space at the top of the reactor.

[0038] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A process for the preparation of methyl methacrylate by one step oxidation esterification process using gas-liquid-solid three phase down flow bed reactor characterized in that, The gas-liquid-solid three-phase down-flow bed reactor mainly comprises a raw material inlet, a particle guide pipe, a down-flow bed reactor, a bubble generator, a reaction liquid outlet, a liquid-solid sedimentation separator, a particle storage tank, an auxiliary conveying liquid inlet, a conveying liquid inlet, a conveying pipe, a liquid-solid separator, a conveying liquid outlet, a particle buffer bin, a loosening liquid inlet, a loosening liquid distribution plate, a gas outlet and a gas partition plate; the down-flow bed reactor, the liquid-solid sedimentation separator, the particle storage tank, the conveying pipe, the liquid-solid separator and the particle buffer bin are sequentially connected; the down-flow bed reactor and the particle buffer bin are divided by the gas partition plate; the down-flow bed reactor and the particle buffer bin are connected by the vertical particle guide pipe penetrating through the gas partition plate and the loosening liquid distribution plate; the top of the side wall of the down-flow bed reactor is provided with the gas outlet; the other side wall of the down-flow bed reactor is provided with the raw material inlet; the bottom of the down-flow bed reactor is provided with the bubble generator on the cross section; the bubble generator is connected with the gas inlet; the bottom side wall of the down-flow bed reactor is provided with the reaction liquid outlet; the bubble generator is above the reaction liquid outlet; the bottom of the down-flow bed reactor is connected with the top of the liquid-solid sedimentation separator; the bottom of the liquid-solid sedimentation separator is connected with the particle storage tank; the side wall of the particle storage tank is connected with the bottom side wall of the conveying pipe through the discharging inclined pipe; the bottom side wall of the conveying pipe is provided with the auxiliary conveying liquid inlet and the conveying liquid inlet; the top of the conveying pipe is connected with the inlet of the liquid-solid separator through a pipeline; the top of the liquid-solid separator is provided with the conveying liquid outlet; the bottom of the liquid-solid separator is connected with the particle buffer bin; the bottom side wall of the particle buffer bin is provided with the loosening liquid inlet; the cross section of the particle buffer bin above the loosening liquid inlet is provided with the loosening liquid distribution plate for uniformly distributing the loosening liquid. The process comprises the following steps: (1) the mixed liquid of liquid raw materials methanol and methyl acrylal is introduced into the down-flow bed reactor through the raw material inlet; the catalyst in the particle buffer bin is introduced into the top of the down-flow bed reactor under the action of the loosening liquid introduced through the loosening liquid inlet along the particle guide pipe; the catalyst moves downward along the down-flow bed reactor under the action of gravity and the liquid raw materials; the catalyst is in countercurrent contact with the oxidizing gas introduced through the gas inlet at the bottom of the down-flow bed reactor and reacts; the remaining gas is discharged through the gas outlet at the top of the down-flow bed reactor; (2) the liquid phase after the reaction and the catalyst are introduced into the liquid-solid sedimentation separator through the bottom of the down-flow bed reactor; the catalyst and the liquid phase are separated; the liquid phase containing the reaction product is discharged through the reaction liquid outlet; the catalyst particles are deposited into the particle storage tank; (3) the catalyst particles in the particle storage tank are introduced into the bottom of the conveying pipe through the discharging inclined pipe; the catalyst particles move upward along the conveying pipe under the carrying action of the conveying liquid; the catalyst particles are cleaned; the catalyst and the conveying liquid are introduced into the liquid-solid separator through the top of the conveying pipe; the conveying liquid is discharged through the conveying liquid outlet after the liquid-solid separation; the catalyst falls into the particle buffer bin to participate in the next round of reaction.

2. The process according to claim 1, characterized in that, The down-flow bed reactor and the delivery pipe are in the shape of a cylinder; the particle storage tank is in the shape of a cone; the raw material inlet is located above the outlet end of the particle guide pipe; and the auxiliary delivery liquid inlet is located above the delivery liquid inlet.

3. The process of claim 1, wherein, The liquid-solid separator is used for separating the catalyst particles from the delivery liquid, and is one of a settling type separator, a liquid-solid cyclone separator, a filtering type separator, or a combination of two or more thereof.

4. The process of claim 1, wherein, The bubble generator is one of a Venturi type, a double tangential type, a cyclone type, a dissolved gas-released gas type, a jet type, a porous pattern type, a vortex type, and an injector array type, or a combination of two or more thereof.

5. The process of claim 1, wherein, The molar ratio of methanol to methyl acrylaldehyde in the liquid raw material is 1:1 to 100:1, and the delivery liquid, the auxiliary delivery liquid, and the loosening liquid are one of methanol, ethanol, and methyl acrylaldehyde, or a combination of two or more thereof.

6. The process of claim 1, wherein, The oxidizing gas is oxygen or a mixture of oxygen and nitrogen, wherein the volume fraction of oxygen is 5% to 100%.

7. The process of claim 1, wherein, The catalyst is a supported catalyst, the active component of which is one or a combination of two or more of copper oxide, zinc oxide, gold, palladium, gold-palladium alloy, palladium-copper alloy, the particle size of the catalyst is 20-5000 μm, and the particle density is 1000-8000 kg / m 3 .

8. The process of claim 1, wherein, The diameter of the down-flow bed reactor is 20 to 600 mm, and the height is 0.5 to 50 m.

9. The process of claim 1, wherein, The liquid superficial flow velocity in the down-flow bed reactor is 0.1 to 1000 m / h, the catalyst concentration is 0.05 to 30 wt%, and the superficial liquid velocity in the delivery pipe is 10 to 50000 m / h.

10. The process of claim 1, wherein, The pressure of the reaction system is normal pressure to 50 MPa, and the temperature is 0 to 200℃.

Images