High-yield preparation method of methyl methoxyacrylate
The method uses ultrafiltration, pervaporation, and nanofiltration membranes with a nanoscale gold catalyst to produce methyl methoxyacrylate with high yield and purity, addressing decomposition and purity issues in traditional distillation methods while reducing costs and environmental impact.
Patent Information
- Application Number
- CN202510530391.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-07-15
AI Technical Summary
In the traditional preparation method of methyl methoxyacrylate, under-pressure distillation may cause product decomposition or insufficient purity due to improper temperature control.
The separation and purification method of ultrafiltration membrane, permeable evaporation membrane and nanofiltration membrane was used to combine nano-gold catalysts and gas chromatographs to monitor the reaction conditions in real time, and use analytical pure methanol washing catalysts to carry out the recovery and regeneration of the catalyst.
It realizes efficient separation and purification of methyl methoxyacrylate under mild conditions, improves yield and purity, reduces production costs, and reduces the impact of catalyst waste on the environment.
Smart Images
Figure CN120309479A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of methyl methoxyacrylate preparation, specifically to a method for preparing methyl methoxyacrylate with high yield. Background Art
[0002] Methyl methoxyacrylate is an important organic synthesis intermediate with the chemical formula C5H8O3 and the structural formula CH2=C(OMe)COOCH3. Its molecular structure contains a methyl acrylate backbone, and a methoxy group is introduced at the α-position, endowing it with unique chemical activity. This compound is usually a colorless to light yellow transparent liquid, with certain volatility, soluble in organic solvents such as ethanol and ether, and slightly soluble in water. As an α,β-unsaturated ester compound, the double bond structure of methyl methoxyacrylate makes it prone to addition, polymerization and other reactions, and the electron-donating effect of the methoxy group further enhances its reactivity. It is commonly used in the synthesis of complex organic molecules or polymer materials. In the industrial field, it can be used as a monomer to participate in polymerization reactions to prepare polymers or copolymers with excellent properties, and is widely used in the research and development of coatings, adhesives and functional materials. In addition, the ester group and methoxy group in its structure also make it a key raw material for the synthesis of pharmaceutical and pesticide intermediates, for example, used to construct bioactive heterocyclic compounds. Methyl methoxyacrylate plays an important role in the fields of organic synthesis and materials science by virtue of its unique chemical properties.
[0003] Traditional methods for preparing methyl methoxyacrylate often use vacuum distillation for separation. However, even in vacuum distillation, in some cases, problems such as product decomposition or insufficient purity may still occur due to improper temperature control or other factors. Summary of the Invention
[0004] In view of the deficiencies of the prior art, the present invention provides a method for preparing methyl methoxyacrylate with high yield, which solves the problems that traditional methods for preparing methyl methoxyacrylate often use vacuum distillation for separation, but even in vacuum distillation, in some cases, problems such as product decomposition or insufficient purity may still occur due to improper temperature control or other factors.
[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for preparing methyl methoxyacrylate with high yield, including the following steps: S1. Production preparation: Prepare methacrolein, methanol, catalyst, ultrafiltration membrane, pervaporation membrane, nanofiltration membrane and gas chromatograph; S2. Pretreatment: Activate the catalyst in a muffle furnace; S3. Reaction: Put the activated catalyst, methacrolein and methanol into a reaction kettle for reaction, and use a gas chromatograph to observe in real time; S4. Separation and purification: The reaction mixture is preliminarily filtered through an ultrafiltration membrane, then methyl methacrylate is separated through a pervaporation membrane, and then the separated methyl methacrylate is purified using a nanofiltration membrane. S5. Catalyst recovery: The catalyst separated by preliminary filtration is washed and reused. S6. Membrane regeneration: The ultrafiltration membrane and the pervaporation membrane are cleaned with an organic solvent, and the nanofiltration membrane is regenerated by acid-base cleaning.
[0006] Preferably, in S1, the purity of methacrolein is ≥99%, the purity of methanol is ≥99.7%, the catalyst is a nano-gold catalyst, the particle size of the nano-gold catalyst is 2 - 10 nm, the dosage of the nano-gold catalyst is 0.1% - 1% of the mass of methacrolein, and the cut-off molecular weight of the ultrafiltration membrane is controlled at 10 - 100 kDa.
[0007] Preferably, in S2, the activation temperature is controlled at 200 - 300 °C, the activation time is controlled at 2 - 4 hours, and the heating rate of the muffle furnace is controlled at 5 - 10 °C / min.
[0008] Preferably, in S3, the molar ratio of methacrolein to methanol is controlled at 1:2 - 1:5, the reaction temperature in the reaction kettle is controlled at 50 - 100 °C, oxygen is introduced into the reaction kettle, and after introducing oxygen, the pressure inside the reaction kettle is controlled at 0.1 - 1 MPa, and the stirring speed of the reaction kettle is controlled at 200 - 500 revolutions per minute.
[0009] Preferably, in S3, the chromatographic column of the gas chromatograph uses a HP-5 capillary column with a column length of 30 m, an inner diameter of 0.25 mm, a film thickness of 0.25 μm. The column temperature uses a programmed temperature rise method. The initial temperature is controlled at 40 - 60 °C and maintained for 2 - 5 minutes, and then it is heated at a rate of 5 - 10 °C / min to 150 - 200 °C and maintained for 5 - 10 minutes. The inlet temperature of the gas chromatograph is controlled at 200 - 250 °C, nitrogen is used as the carrier gas, the carrier gas flow rate is controlled at 1 - 2 mL / min, a hydrogen flame ionization detector is used, the detector temperature is set at 250 - 300 °C, and the injection volume of the gas chromatograph is controlled at 0.1 - 1 μL.
[0010] Preferably, in S4, the ultrafiltration membrane is made of polyethersulfone, the operating pressure of the preliminary filtration is controlled at 0.1 - 0.5 MPa, the temperature during filtration is controlled at 20 - 40 °C, and the flow rate of the reaction mixture is controlled at 1 - 5 m / s; The pervaporation membrane is made of polydimethylsiloxane, the operating temperature during separation is controlled at 40 - 60 °C, and the vacuum degree on the permeation side is controlled at <10 kPa; The nanofiltration membrane is made of polyamide, with the molecular weight cut-off controlled at 200 - 1000 Da. The operating pressure during purification is controlled at 0.5 - 2 MPa, the temperature during purification is controlled at 20 - 40 °C, and the feed flow rate is controlled at 0.5 - 2 m / s.
[0011] Preferably, in S5, the detergent is methanol of analytical reagent grade. The liquid-solid ratio of the methanol to the catalyst is controlled at 5:1 - 20:1. The catalyst and the detergent are put into a magnetic stirrer for washing. The temperature of the magnetic stirrer is controlled at 20 - 50 °C, the stirring speed of the magnetic stirrer is controlled at 100 - 300 revolutions per minute, the washing time is controlled at 10 - 30 minutes, and the number of washing times is 2 - 5 times. The washed catalyst is activated in a muffle furnace at 200 - 300 °C for 2 - 4 hours.
[0012] Preferably, in S6, the organic solvent for cleaning the ultrafiltration membrane is ethanol with a purity ≥ 90%. The soaking cleaning method is adopted, and the cleaning temperature is controlled at 30 - 50 °C, and the soaking time is 1 - 3 hours; The organic solvent for cleaning the ultrafiltration membrane is ethanol with a purity ≥ 95%. The stirring and soaking cleaning method is adopted, the stirring speed is controlled at 50 - 150 revolutions per minute, the cleaning temperature is controlled at 35 - 55 °C, and the soaking time is 1.5 - 4 hours; The nanofiltration membrane is first pickled with citric acid with a concentration of 1% - 3%. The pickling temperature is controlled at 25 - 40 °C, and the pickling time is 1 - 2 hours. The flow rate of citric acid is controlled at 0.1 - 0.3 cubic meters per hour. Then, it is rinsed with pure water at a flow rate of 0.1 - 0.3 cubic meters per hour. The temperature during rinsing is controlled at 20 - 30 °C, and the continuous rinsing time is 30 - 60 minutes. The rinsing pressure is controlled at 0.1 - 0.3 MPa. Then, it is alkali-washed with sodium hydroxide with a concentration of 0.1% - 2%. The alkali-washing temperature is controlled at 25 - 40 °C, and the alkali-washing time is 1 - 2 hours. The flow rate of sodium hydroxide is controlled at 0.1 - 0.3 cubic meters per hour.
[0013] The present invention provides a method for preparing methyl methacrylate with a high yield. It has the following beneficial effects: 1. In the present invention, by combining the ultrafiltration membrane, pervaporation membrane and nanofiltration membrane for separation and purification, the use of vacuum distillation is avoided. The ultrafiltration membrane can preliminarily filter the reaction mixture to remove some macromolecular impurities. The pervaporation membrane can effectively separate methyl methacrylate from the mixture. The nanofiltration membrane further purifies the separated methyl methacrylate. Through the combination of these membrane separation technologies, the high-efficiency separation and purification of the product can be achieved under mild conditions, thus solving the problem that the traditional method for preparing methyl methacrylate often uses vacuum distillation for separation, but even in vacuum distillation, in some cases, the product may still decompose or the purity may be insufficient due to improper temperature control or other factors.
[0014] 2. In the present invention, by using analytically pure methanol for washing, under appropriate temperature, stirring speed and time conditions, impurities on the surface of the catalyst can be effectively removed, the activity of the catalyst can be restored, and the washing and activation process is used to recycle the catalyst, reducing the production cost and at the same time reducing the impact of catalyst waste on the environment.
[0015] 3. In the present invention, by controlling the molar ratio of methacrolein to methanol at 1:2 - 1:5 to make methanol in excess, promoting the full reaction of methacrolein and increasing its conversion rate, and at the same time controlling the reaction temperature at 50 - 100 °C, pressure at 0.1 - 1 MPa and stirring speed at 200 - 500 revolutions per minute, a suitable reaction environment can be provided, the reaction rate can be accelerated, and the reaction efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 It is a preparation flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative work belong to the scope of protection of the present invention.
[0018] Please refer to the attached Figure 1 , the embodiment of the present invention provides a method for preparing methyl methacrylate with high yield, including the following steps: S1. Production preparation: Prepare methacrolein, methanol, catalyst, ultrafiltration membrane, pervaporation membrane, nanofiltration membrane and gas chromatograph; S2. Pretreatment: Activate the catalyst in a muffle furnace; S3. Reaction: Put the activated catalyst, methacrolein and methanol into a reaction kettle for reaction, and at the same time use a gas chromatograph for real-time observation; S4. Separation and purification: Preliminarily filter the reaction mixture through an ultrafiltration membrane, then separate methyl methacrylate through a pervaporation membrane, and then purify the separated methyl methacrylate using a nanofiltration membrane; S5. Catalyst recovery: Wash and reuse the catalyst preliminarily filtered and separated; S6. Membrane regeneration: Clean the ultrafiltration membrane and pervaporation membrane with an organic solvent, and regenerate the nanofiltration membrane by cleaning with acid and alkali.
[0019] In S1, the purity of methacrolein is ≥99%, the purity of methanol is ≥99.7%, the catalyst is a nano-gold catalyst, the particle size of the nano-gold catalyst is 2 - 10 nm, the dosage of the nano-gold catalyst is 0.1% - 1% of the mass of methacrolein, and the cut-off molecular weight of the ultrafiltration membrane is controlled at 10 - 100 kDa.
[0020] Specifically, with the purity of methacrolein ≥99% and the purity of methanol ≥99.7%, the interference of impurities to the reaction can be reduced, the reaction can be ensured to proceed as expected, the yield and selectivity of the target product methyl methacrylate can be improved, the probability of side reactions can be reduced, and the product quality can be enhanced; the nano-gold catalyst with a particle size of 2 - 10 nm has a large specific surface area and many active sites, which can significantly improve the reaction activity and catalytic efficiency and accelerate the reaction rate; the dosage of the nano-gold catalyst is 0.1% - 1% of the mass of methacrolein, within this range, effective catalysis of the reaction can be achieved, and the increase in cost and difficulty in separation caused by excessive catalyst dosage can be avoided; the cut-off molecular weight of the ultrafiltration membrane is controlled at 10 - 100 kDa, which can effectively retain the nano-gold catalyst, realize the separation of the catalyst from the reaction product, facilitate the recovery and recycling of the catalyst, reduce the production cost, and ensure the product purity at the same time.
[0021] In S2, the activation temperature is controlled at 200 - 300 °C, the activation time is controlled at 2 - 4 hours, and the heating rate of the muffle furnace is controlled at 5 - 10 °C / min.
[0022] Specifically, by controlling the activation temperature at 200 - 300 °C, suitable energy conditions can be provided for the activation of the nano-gold catalyst, causing specific changes in the internal structure of the nano-gold catalyst, such as the breaking and recombination of chemical bonds, thereby improving its reaction activity, and at the same time avoiding over-reaction or structural damage of the nano-gold catalyst due to too high temperature, or insufficient activation due to too low temperature; controlling the activation time at 2 - 4 hours can ensure that the nano-gold catalyst has enough time for sufficient activation reaction at a suitable temperature, making the activation process more thorough, ensuring that the nano-gold catalyst reaches the expected activation state to obtain good performance; controlling the heating rate of the muffle furnace at 5 - 10 °C / min can make the nano-gold catalyst uniformly heated, avoiding local overheating caused by too fast heating rate, resulting in non-uniform changes in the internal structure of the substance and affecting the consistency and stability of the activation effect. The appropriate heating rate helps to precisely control the activation process and improve the stability and reproducibility of the product quality.
[0023] In S3, the molar ratio of methacrolein to methanol is controlled at 1:2 - 1:5, the reaction temperature in the reaction kettle is controlled at 50 - 100 °C, oxygen is introduced into the reaction kettle, after introducing oxygen, the internal pressure of the reaction kettle is controlled at 0.1 - 1 MPa, and the stirring speed of the reaction kettle is controlled at 200 - 500 revolutions per minute.
[0024] Specifically, by controlling the molar ratio of methacrolein to methanol within the range of 1:2 - 1:5, it can ensure that methanol is in excess in the reaction system, enabling methacrolein to react fully, thereby increasing its conversion rate, and further enhancing the selectivity and yield of the target product. By controlling the reaction temperature within the range of 50 - 100 °C, it provides suitable energy conditions for the reaction. This temperature range allows the reaction to have a relatively high rate, while avoiding an excessive increase in side reactions and a decrease in product selectivity due to too high a temperature, or an overly slow reaction rate and an overly long reaction time due to too low a temperature. Oxygen is introduced into the reaction kettle and the pressure is controlled within the range of 0.1 - 1 MPa. As an oxidant, oxygen participates in the reaction, which can promote the oxidation reaction between methacrolein and methanol. An appropriate pressure helps to maintain the phase stability of the reaction system, increases the solubility of the reactants and oxygen in the reaction medium, enabling the reaction to proceed more efficiently in a homogeneous system, and thus enhancing the reaction rate and product yield. The stirring speed of the reaction kettle is controlled within the range of 200 - 500 revolutions per minute, which can ensure that the reactants, oxygen, and catalyst are fully and evenly mixed in the reaction kettle, improving the mass transfer efficiency, and avoiding inconsistent reaction rates or an increase in side reactions caused by uneven local concentrations. At the same time, stirring also promotes heat transfer, making the reaction temperature more uniform, which is conducive to improving the stability and repeatability of the reaction.
[0025] In S3, the chromatographic column of the gas chromatograph uses a HP-5 capillary column with a column length of 30 m, an inner diameter of 0.25 mm, and a film thickness of 0.25 μm. The column temperature is controlled using a programmed temperature method. The initial temperature is controlled within the range of 40 - 60 °C and maintained for 2 - 5 minutes, and then it is heated at a rate of 5 - 10 °C per minute to 150 - 200 °C and maintained for 5 - 10 minutes. The inlet temperature of the gas chromatograph is controlled within the range of 200 - 250 °C. Nitrogen is used as the carrier gas, and the carrier gas flow rate is controlled within the range of 1 - 2 mL per minute. A hydrogen flame ionization detector is used, and the detector temperature is set within the range of 250 - 300 °C. The injection volume of the gas chromatograph is controlled within the range of 0.1 - 1 μL.
[0026] Specifically, by using an HP-5 capillary column with a column length of 30 m, an inner diameter of 0.25 mm, and a film thickness of 0.25 μm, a relatively large separation space and appropriate partition coefficients can be provided, effectively separating various components in the mixed sample and achieving good separation effects and high separation efficiency. The initial temperature is controlled at 40 - 60 °C and maintained for 2 - 5 minutes, which helps in the focusing and separation of low-boiling components, enabling them to have better peak shapes at lower temperatures. Then, it is heated at a rate of 5 - 10 °C / minute to 150 - 200 °C and maintained for 5 - 10 minutes, allowing high-boiling components to flow out sequentially at gradually increasing temperatures. Such a temperature programming method can take into account components in different boiling point ranges, improving the resolution and analysis efficiency, and enabling good separation and detection of each component. By controlling the inlet temperature at 200 - 250 °C, it can ensure that the sample vaporizes instantaneously and enters the chromatographic column in a gaseous form, guaranteeing the injection effect and repeatability of the sample, and avoiding problems such as peak broadening or tailing caused by incomplete vaporization of the sample. Nitrogen is selected as the carrier gas. Its chemical properties are stable, providing a stable mobile phase environment for the separation process. The carrier gas flow rate is controlled at 1 - 2 mL / minute, enabling the sample to move at an appropriate speed in the chromatographic column, fully interacting with the stationary phase to achieve effective separation of each component while ensuring a reasonable analysis time. A hydrogen flame ionization detector is used, which has high sensitivity and selectivity for organic compounds. The detector temperature is set at 250 - 300 °C, ensuring the stability and accuracy of detection, enabling the ionization process to proceed smoothly, effectively detecting each separated component, reducing baseline noise, and improving the quality of the detection signal. The injection volume is controlled at 0.1 - 1 μL, making the amount of sample entering the chromatographic column appropriate. It not only ensures that enough sample is detected but also avoids overloading the chromatographic column due to excessive injection volume, which may affect the separation effect and the shape of the chromatographic peak, ensuring the accuracy and reliability of the analysis results.
[0027] In S4, the ultrafiltration membrane is made of polyethersulfone. The operating pressure for preliminary filtration is controlled at 0.1 - 0.5 MPa, the temperature during filtration is controlled at 20 - 40 °C, and the flow rate of the reaction mixture is controlled at 1 - 5 m / s. The pervaporation membrane is made of polydimethylsiloxane. The operating temperature during separation is controlled at 40 - 60 °C, and the vacuum degree on the permeate side is controlled at < 10 kPa. The nanofiltration membrane is made of polyamide. The molecular weight cut-off is controlled at 200 - 1000 Da. The operating pressure during purification is controlled at 0.5 - 2 MPa, the temperature during purification is controlled at 20 - 40 °C, and the feed flow rate is controlled at 0.5 - 2 m / s.
[0028] Specifically, the ultrafiltration membrane made of polyethersulfone has good chemical stability, thermal stability and mechanical strength. It can maintain stable performance within a wide pH range, and has strong anti-pollution ability, effectively retaining macromolecular substances. The operating pressure for preliminary filtration is controlled at 0.1 - 0.5 MPa, providing a driving force for the mixed liquid to pass through the ultrafiltration membrane, enabling small molecule substances to smoothly pass through the membrane, while ensuring the service life of the membrane and avoiding membrane damage or increased membrane pollution caused by excessive pressure. The filtration temperature for preliminary filtration is controlled at 20 - 40 °C, which can maintain the fluidity of the mixed liquid, reduce its viscosity, improve the filtration efficiency, and at the same time avoid adverse effects of too high or too low temperature on the membrane performance and separation effect. For example, too high temperature may cause membrane material aging, and too low temperature may cause precipitation of some components in the mixed liquid. The flow rate of the reaction mixed liquid for preliminary filtration is controlled at 1 - 5 m / s, which can prevent the occurrence of concentration polarization phenomenon, avoid the formation of excessive concentration boundary layers on the membrane surface, ensure the stability of the separation effect, improve the membrane flux, reduce the deposition of impurities on the membrane surface, and extend the membrane cleaning cycle. The pervaporation membrane made of polydimethylsiloxane has good selectivity and permeability for organic substances, and can effectively separate different components in the organic mixture. The temperature during separation is controlled at 40 - 60 °C, which helps to increase the diffusion rate of molecules, increase the solubility and diffusion coefficient of organic substances in the membrane, thereby improving the pervaporation flux and separation factor, and enabling the target component to more efficiently permeate from one side of the membrane to the other side. The vacuum degree on the permeate side during separation is controlled at <10 kPa, which can reduce the partial pressure of the target component on the permeate side, form a large concentration difference across the membrane, provide a strong driving force for the permeation of components, promote the separation process, and improve the separation efficiency and separation effect. The nanofiltration membrane made of polyamide has good separation performance and chemical corrosion resistance, and has specific retention characteristics for substances with different molecular weights, enabling fine separation of different components in the mixed liquid. The retention molecular weight of the nanofiltration membrane is controlled at 200 - 1000 Da, which can accurately retain substances within the target molecular weight range, effectively separate different components in the mixed liquid, and achieve the purpose of purification. The operating pressure during purification is controlled at 0.5 - 2 MPa, providing sufficient driving force for the nanofiltration process, enabling small molecule substances to pass through the membrane while retaining the substances to be separated, and at the same time ensuring the stability and separation efficiency of the membrane, avoiding damage to the membrane or affecting the separation effect due to too high or too low pressure. The temperature during purification is controlled at 20 - 40 °C, which can maintain the physical properties of the mixed liquid stable, ensure the stable performance of the nanofiltration membrane, improve the separation effect and separation efficiency, and prevent changes in the membrane pore size or the properties of some components in the mixed liquid due to temperature changes, affecting the separation effect. The feed flow rate is controlled at 0.5 - 2 m / s, which helps to optimize the hydrodynamic conditions on the membrane surface, reduce the occurrence of concentration polarization and membrane pollution phenomena, improve the membrane flux and separation effect, and ensure the stability and repeatability of the nanofiltration process.
[0029] In S5, analytical grade methanol is used as the detergent, and the liquid-to-solid ratio of methanol to the catalyst is controlled at 5:1-20:1. The catalyst and the detergent are placed in a magnetic stirrer for washing. The temperature of the magnetic stirrer is controlled at 20-50°C, the stirring speed of the magnetic stirrer is controlled at 100-300 rpm, the washing time is controlled at 10-30 minutes, the washing times are 2-5 times, and the washed catalyst is activated in a muffle furnace at 200-300°C for 2-4 hours.
[0030] Specifically, analytical grade methanol is used, which has high purity and few impurities. It can effectively dissolve organic impurities on the surface of the catalyst and will not introduce new impurities to contaminate the catalyst, thereby ensuring the purity of the catalyst; the liquid-solid ratio of methanol to catalyst is controlled at 5:1-20:1, which can make the catalyst fully contact with the detergent, provide sufficient solvent for the dissolution of impurities, ensure that the impurities are effectively removed, and avoid solvent waste; the temperature of the magnetic stirrer is controlled at 20-50°C. Properly increasing the temperature can enhance the solubility and molecular diffusion rate of methanol, accelerate the dissolution and desorption process of impurities, but avoid the loss of active components of the catalyst or structural changes due to excessive temperature; the stirring speed is controlled at 100-300 rpm, which can fully mix the catalyst and the detergent , promote the dissolution and desorption of impurities, and avoid mechanical damage to the catalyst particles caused by excessive stirring speed, affecting its structure and activity; the washing time is controlled at 10-30 minutes, which can not only ensure that the impurities have enough time to be dissolved and desorbed, but also avoid the waste of time and solvent caused by long-term washing; the number of washings is controlled at 2-5 times. Through multiple washings, the impurity content on the catalyst surface can be gradually reduced to ensure the washing effect. The number of washings can be flexibly adjusted according to the initial content of impurities on the catalyst surface and the washing effect; the washed catalyst is activated in a muffle furnace at 200-300℃ for 2-4 hours to remove residual washing solvent, further activate the active sites on the catalyst surface, and restore the activity of the catalyst so that it can participate in the reaction efficiently again.
[0031] In S6, the organic solvent for cleaning the ultrafiltration membrane is ethanol with a purity of ≥90%, and the immersion cleaning method is adopted. The cleaning temperature is controlled at 30 - 50°C, and the immersion time is 1 - 3 hours; the organic solvent for cleaning the ultrafiltration membrane is ethanol with a purity of ≥95%, and the stirring immersion cleaning method is adopted. The stirring speed is controlled at 50 - 150 revolutions per minute, the cleaning temperature is controlled at 35 - 55°C, and the immersion time is 1.5 - 4 hours; the nanofiltration membrane is first pickled with citric acid with a concentration of 1% - 3%, the pickling temperature is controlled at 25 - 40°C, pickling is carried out for 1 - 2 hours, the flow rate of citric acid is controlled at 0.1 - 0.3 cubic meters per hour, and then rinsed with pure water at a flow rate of 0.1 - 0.3 cubic meters per hour. The temperature during rinsing is controlled at 20 - 30°C, continuous rinsing is carried out for 30 - 60 minutes, and the rinsing pressure is controlled at 0.1 - 0.3 MPa. Then, it is alkali-washed with sodium hydroxide with a concentration of 0.1% - 2%, the alkali-washing temperature is controlled at 25 - 40°C, alkali-washing is carried out for 1 - 2 hours, and the flow rate of sodium hydroxide is controlled at 0.1 - 0.3 cubic meters per hour.
[0032] Specifically, by using ethanol with a purity of ≥90%, the organic pollutants on the surface of the ultrafiltration membrane can be effectively dissolved. The high purity ensures the cleaning effect and avoids secondary pollution of the membrane by impurities; the immersion method enables ethanol to fully contact the membrane surface, allowing pollutants to dissolve and diffuse in the solvent; the cleaning temperature of 30 - 50°C enhances the dissolution ability of ethanol and the molecular diffusion rate, accelerating the removal of pollutants and preventing damage to the membrane material due to excessive temperature; the immersion time of 1 - 3 hours ensures that pollutants have sufficient time to be dissolved and detached from the membrane surface; Ethanol with a purity of ≥95% can further improve the cleaning ability and more thoroughly remove stubborn organic pollutants; the stirring speed of 50 - 150 revolutions per minute enables ethanol to be fully mixed with the membrane, reducing concentration polarization on the membrane surface and improving the cleaning efficiency; the temperature range of 35 - 55°C further enhances the cleaning effect and is within the tolerance range of the membrane material; the immersion of 1.5 - 4 hours can ensure deep cleaning and effectively remove pollutants even in the case of more severe pollution; The 1% - 3% citric acid solution can effectively dissolve pollutants such as inorganic scale and metal oxides on the membrane surface, and is relatively mild, reducing corrosion of the membrane; the pickling temperature of 25 - 40°C increases the reaction rate between citric acid and pollutants, enhancing the pickling effect and avoiding high temperature accelerating the corrosion of the membrane by acid; the pickling time of 1 - 2 hours ensures that pollutants fully react with the acid and dissolve; the flow rate of 0.1 - 0.3 cubic meters per hour makes the citric acid solution flow uniformly on the membrane surface, improving the mass transfer effect and ensuring comprehensive cleaning; The performance of the membrane can be maintained stable by a flushing temperature of 20 - 30 °C, avoiding the influence of temperature change on the membrane structure; a flow rate of 0.1 - 0.3 cubic meters per hour and a pressure of 0.1 - 0.3 MPa can effectively flush out the residual citric acid and dissolved pollutants in the membrane, while preventing damage to the membrane due to excessive pressure; a flushing time of 30 - 60 minutes ensures thorough flushing. The organic and microbial pollutants on the membrane surface can be removed by a sodium hydroxide solution of 0.1% - 2%, and the damage to the membrane is relatively small at a suitable concentration; an alkali washing temperature of 25 - 40 °C promotes the reaction between the alkali and the pollutants, improving the cleaning effect; an alkali washing time of 1 - 2 hours allows the pollutants to fully react with the alkali and be removed; a flow rate of 0.1 - 0.3 cubic meters per hour ensures the uniform distribution of the alkali solution on the membrane surface, achieving efficient cleaning.
[0033] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing methyl methacrylate with high yield, characterized in that: It includes the following steps: S1. Production preparation: Prepare methacrolein, methanol, catalyst, ultrafiltration membrane, pervaporation membrane, nanofiltration membrane and gas chromatograph; S2. Pretreatment: Activate the catalyst in a muffle furnace; S3. Reaction: Put the activated catalyst, methacrolein and methanol into a reaction kettle for reaction, and use a gas chromatograph to observe in real time; S4. Separation and purification: Preliminarily filter the reaction mixture through an ultrafiltration membrane, then separate methyl methacrylate through a pervaporation membrane, and then purify the separated methyl methacrylate using a nanofiltration membrane; S5. Catalyst recovery: Wash and reuse the catalyst preliminarily filtered and separated; S6. Membrane regeneration: Clean the ultrafiltration membrane and pervaporation membrane with an organic solvent, and regenerate the nanofiltration membrane by cleaning with acid and alkali.
2. The method for preparing methyl methacrylate with high yield according to claim 1, characterized in that, In S1, the purity of the methacrolein is ≥99%, the purity of the methanol is ≥99.7%, the catalyst is a nano-gold catalyst, the particle size of the nano-gold catalyst is 2–10 nm, the dosage of the nano-gold catalyst is 0.1%–1% of the mass of methacrolein, and the cut-off molecular weight of the ultrafiltration membrane is controlled at 10–100 kDa.
3. The method for preparing methyl methacrylate with high yield according to claim 1, characterized in that, In S2, the activation temperature is controlled at 200-300 °C, the activation time is controlled at 2-4 hours, and the heating rate of the muffle furnace is controlled at 5-10 °C / min.
4. The method for preparing methyl methacrylate with high yield according to claim 1, wherein In S3, the molar ratio of methacrolein to methanol is controlled at 1:2-1:5, the reaction temperature in the reaction kettle is controlled at 50-100 °C, oxygen is introduced into the interior of the reaction kettle, and after introducing oxygen, the pressure inside the reaction kettle is controlled at 0.1-1 MPa, and the stirring speed of the reaction kettle is controlled at 200-500 revolutions per minute.
5. The method for preparing methyl methacrylate with high yield according to claim 1, characterized in that, In S3, the chromatographic column of the gas chromatograph uses a HP–5 capillary column, the column length is 30 m, the inner diameter is 0.25 mm, the film thickness is 0.25 μm, the column temperature uses a programmed temperature rise method, the initial temperature is controlled at 40-60 °C, maintained for 2-5 minutes, and then heated at a rate of 5-10 °C per minute to 150-200 °C and maintained for 5-10 minutes. The inlet temperature of the gas chromatograph is controlled at 200-250 °C, nitrogen is used as the carrier gas, the carrier gas flow rate is controlled at 1-2 mL / min, a hydrogen flame ionization detector is used, the detector temperature is set at 250-300 °C, and the injection volume of the gas chromatograph is controlled at 0.1-1 μL.
6. The method for preparing methyl methacrylate with high yield according to claim 1, characterized in that, In S4, the ultrafiltration membrane is made of polyethersulfone, the operating pressure of the preliminary filtration is controlled at 0.1-0.5 MPa, the temperature during filtration is controlled at 20-40 °C, and the flow rate of the reaction mixture is controlled at 1-5 m / s; The pervaporation membrane is made of polydimethylsiloxane, the operating temperature during separation is controlled at 40-60 °C, and the vacuum degree on the permeation side is controlled at <10 kPa; The nanofiltration membrane is made of polyamide, the cut-off molecular weight is controlled at 200-1000 Da, the operating pressure during purification is controlled at 0.5-2 MPa, the temperature during purification is controlled at 20-40 °C, and the feed flow rate is controlled at 0.5-2 m / s.
7. The method for preparing methyl methacrylate with high yield according to claim 1, characterized in that, In S5, the detergent is analytical grade methanol, and the liquid-solid ratio of the methanol to the catalyst is controlled at 5:1 - 20:
1. The catalyst and the detergent are placed in a magnetic stirrer for washing. The temperature of the magnetic stirrer is controlled at 20 - 50 °C, the stirring speed of the magnetic stirrer is controlled at 100 - 300 revolutions per minute, the washing time is controlled at 10 - 30 minutes, and the number of washing times is 2 - 5 times. The washed catalyst is activated in a muffle furnace at 200 - 300 °C for 2 - 4 hours.
8. The method for preparing methyl methacrylate with high yield according to claim 1, wherein In S6, the organic solvent for ultrafiltration membrane cleaning is ethanol with a purity ≥ 90%. The immersion cleaning method is adopted, and the cleaning temperature is controlled at 30 - 50 °C, and the immersion time is 1 - 3 hours. The organic solvent for ultrafiltration membrane cleaning is ethanol with a purity ≥ 95%. The stirring immersion cleaning method is adopted, the stirring speed is controlled at 50 - 150 revolutions per minute, the cleaning temperature is controlled at 35 - 55 °C, and the immersion time is 1.5 - 4 hours. The nanofiltration membrane is first pickled with citric acid with a concentration of 1% - 3%. The pickling temperature is controlled at 25 - 40 °C, pickling is carried out for 1 - 2 hours, and the flow rate of citric acid is controlled at 0.1 - 0.3 cubic meters per hour. Then, it is rinsed with pure water at a flow rate of 0.1 - 0.3 cubic meters per hour. The temperature during rinsing is controlled at 20 - 30 °C, and continuous rinsing is carried out for 30 - 60 minutes. The rinsing pressure is controlled at 0.1 - 0.3 MPa. Then, it is alkali-washed with sodium hydroxide with a concentration of 0.1% - 2%. The alkali-washing temperature is controlled at 25 - 40 °C, alkali-washing is carried out for 1 - 2 hours, and the flow rate of sodium hydroxide is controlled at 0.1 - 0.3 cubic meters per hour.