Method for preparing acetoacetoxy ethyl methacrylate through efficient catalysis

Abstract

The invention relates to a method for preparing acetoacetoxy ethyl methacrylate through efficient catalysis, which belongs to the technical field of acetoacetoxy ethyl methacrylate production, and comprises the following steps: respectively preheating hydroxyethyl methylacrylate and ethyl acetoacetate to a target temperature, and then uniformly mixing the hydroxyethyl methylacrylate and the ethyl acetoacetate; introducing into a fixed reaction bed with a catalyst for complete reaction; after carrying out online separation through an online membrane separator, collecting a product and intercepting the catalyst for recycling; wherein the catalyst takes mesoporous silica nanospheres as a carrier, and adjacent Lewis acid sites and Lewis base sites are accurately constructed in a nanochannel of the carrier; the reaction activation energy is greatly reduced by using the catalyst for accurately constructing adjacent Lewis acid sites and Lewis base sites in the nano-channel of the carrier, and the carrier is stably combined with the active sites, so that the service life of the catalyst is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of acetoacetoxy ethyl methacrylate production, and particularly relates to a method for efficiently and catalytically preparing acetoacetoxy ethyl methacrylate. BACKGROUND

[0002] Acetoacetoxy ethyl methacrylate (AAEM) is a kind of methacrylic monomer, which is used to synthesize high solid content liquid acrylic resin and low VOC industrial and building paint acrylic emulsion. It can also be used for acetoacetate polymer, pesticide intermediate, photocuring reaction monomer, adhesive polymer, cosmetic polymer, pharmaceutical intermediate and self-crosslinking acrylic emulsion, which can replace N-hydroxymethyl acrylamide, diacetone acrylamide, hydroxyethyl methacrylate (HEMA) and the like, and has better reaction control and product performance.

[0003] The bifunctional catalyst in the prior art adopts a "random loading" strategy, and cannot realize atomic-level proximity regulation of Lewis acid sites and Lewis base sites (usually the distance is greater than 2 nm). This leads to long-distance migration of reactant molecules on the surface of the catalyst to complete the synergistic reaction of "acid activation-base attack", increases the reaction activation energy, makes the target reaction conversion rate low, and the proportion of side reactions is high.

[0004] The existing reaction device mainly adopts a kettle type reactor relying on batch heating and stirring, and has the problems of "local overheating" and "concentration gradient": high temperature easily causes HEMA self-polymerization (high proportion of polymerization inhibitor needs to be additionally added, increasing the purification cost), and uneven concentration leads to excessive reaction of EAA to generate byproduct ethanol aldehyde. The reaction condition is difficult to control and the product selectivity is low. SUMMARY

[0005] In order to overcome some of the problems mentioned in the background, the application provides a method for efficiently and catalytically preparing acetoacetoxy ethyl methacrylate, which at least partially solves the above problems.

[0006] According to the technical scheme of the application, a method for efficiently and catalytically preparing acetoacetoxy ethyl methacrylate is provided, which comprises the following steps: The hydroxyethyl methacrylate (HEMA) and the ethyl acetoacetate (EAA) are respectively preheated to a target temperature and then uniformly mixed to obtain a mixed solution; The mixed solution is introduced into a fixed reaction bed with a catalyst for complete reaction; After online separation by an online membrane separator, the product is collected and the catalyst is intercepted for recycling; Wherein the catalyst is a catalyst with adjacent Lewis acid sites and Lewis base sites precisely constructed in the nanochannel of the mesoporous silica nanosphere carrier, the Lewis acid sites are composed of single-atom Sn 4+ Species, and the Lewis base sites are composed of grafted nitrogen-doped carbon quantum dots.

[0007] Preferably, the preparation method of the mesoporous silica nanosphere carrier in the catalyst comprises the following steps: By Stober method combined with template method, using cetyltrimethylammonium bromide as a template agent and tetraethyl orthosilicate as a silicon source, stirring and reacting in an alkaline ethanol / water solution at 70-90°C, mesoporous silica is obtained; After centrifugal washing, the cetyltrimethylammonium bromide template is completely removed by refluxing with an acidic ethanol solution in a Soxhlet extractor; Dispersed in anhydrous toluene, an excess of 3-aminopropyltriethoxysilane is added, and refluxing reaction is carried out under nitrogen protection to obtain the mesoporous silica nanosphere carrier.

[0008] Preferably, the preparation of the Lewis acid sites comprises the following steps: The mesoporous silica nanosphere carrier is vacuum dried; The dried mesoporous silica nanosphere carrier powder is placed in an atomic layer deposition reaction chamber, heated to 80-90°C, and the following cycle is performed for 5-10 times to deposit the Lewis acid sites: Pulse A: pulse saturated tetrakis(dimethylamino)tin vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds; Pulse B: pulse saturated water vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds.

[0009] Preferably, the preparation of the Lewis base sites comprises the following steps: Using citric acid as a carbon source and ethylenediamine as a nitrogen source, both are dissolved in deionized water, and placed in a high-pressure reaction kettle for reaction at 160-200°C for 6-10h, the obtained product is purified by dialysis to obtain nitrogen-doped carbon quantum dot particles; The mesoporous silica nanosphere carrier after preparation of the Lewis acid sites is dispersed in 2-morpholinoethanesulfonic acid buffer solution; Add the aqueous solution of the nitrogen-doped carbon quantum dots and the condensing agent, and stir until the reaction is complete; After the reaction is completed, the catalyst is obtained by centrifugation, repeated washing with water and ethanol, and vacuum drying.

[0010] Preferably, the method is carried out in a continuous flow microreactor system, which comprises the following units connected in sequence: Feed unit: contains 2 or more high-precision high-pressure liquid chromatography pumps or injection pumps; Pre-treatment and mixing unit: containing coil type online pre-heater placed in constant temperature oil bath and static micro-mixer; Reaction core unit: fixed bed micro-reactor with inner diameter of 2-4 mm and length of 20-50 cm, filled with catalyst inside and temperature control heating jacket outside; Pressure and temperature control system: containing back pressure regulator installed at the outlet of the system, Pt100 temperature sensor and PID temperature controller, which can maintain the system pressure at 1.5 MPa and the temperature control accuracy at ±0.5℃; Online monitoring unit: containing Fourier transform infrared flow cell or Raman spectrum probe connected to the outlet of the reactor, which is used for real-time monitoring of reaction progress; Product separation and collection unit: containing online membrane separator with built-in organic solvent resistant nanofiltration membrane, product receiving tank and tail gas absorption bottle.

[0011] Preferably, the mesoporous silica nanosphere carrier particle size is 95-105 nm, and the mesoporous pore size is 5-6 nm; the unreacted 3-aminopropyl triethoxysilane is removed by centrifugal washing 3-5 times with anhydrous ethanol.

[0012] Preferably, the particle size of the nitrogen-doped carbon quantum dots is 2-3 nm, and the pH value of the 2-morpholinoethanesulfonic acid buffer is 5.4-5.6. The condensing agent includes 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and the molar ratio of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride to N-hydroxysuccinimide is (1-1.2):1.

[0013] Preferably, in the pre-treatment and mixing unit, the target reaction temperature of the online pre-heater is 80-90℃, and the mixing time of the static micro-mixer is ≤100 ms. In the product separation and collection unit, the nanofiltration membrane material is polyimide, and the molecular weight cut-off is 1000-5000 Da; the tail gas absorption bottle is filled with cold water or 5%-10% mass fraction of sodium bisulfite solution.

[0014] Preferably, the online monitoring unit calculates the reaction conversion rate and selectivity by real-time detection of the hydroxyl characteristic peak intensity attenuation rate of hydroxyethyl methacrylate and the carbonyl characteristic peak intensity growth rate of the product acetoacetyl methyl methacrylate, and issues an alarm and stops running if the reaction conversion rate or selectivity is <88%.

[0015] Preferably, the reaction core unit can also be replaced by a channel type micro-reactor, and the catalyst is fixed on the inner wall of the micro-channel by coating process, the micro-channel inner diameter is 0.5-2 mm, and the length is 10-30 cm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention significantly reduces the activation energy of a reaction by using a catalyst that precisely constructs adjacent Lewis acid sites and Lewis base sites within nanochannels on a support, and the support and active sites are stably bound together, thus extending the catalyst lifetime. This invention achieves a synergistic effect through the high activity of the catalyst and the precise temperature control and efficient mass transfer of the microreactor: on the one hand, the efficient heat transfer of the microreactor avoids catalyst deactivation due to local overheating; on the other hand, the high selectivity of the catalyst greatly reduces pipeline blockage caused by the accumulation of by-products in the microreactor, and the product does not need to be refined to meet the purity requirements. Detailed Implementation

[0017] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0018] This invention provides a highly efficient catalytic method for preparing ethyl acetoacetate methacrylate, comprising the following steps: Hydroxyethyl methacrylate and ethyl acetoacetate were preheated to the target temperature and then mixed evenly to obtain a mixture. The mixture was passed into a fixed reaction bed containing a catalyst to allow for complete reaction. The catalyst loading was 0.5-1.5 g / cm³. 3 ; After online separation using an online membrane separator, the products are collected and the catalyst is retained for recycling. The catalyst is a catalyst in which adjacent Lewis acid sites and Lewis base sites are precisely constructed within the nanochannels of mesoporous silica nanospheres as a support. The Lewis acid sites are single-atom Sn anchored on the support. 4+ The species composition, wherein the Lewis base sites are composed of grafted nitrogen-doped carbon quantum dots.

[0019] In a further embodiment of this example, the method for preparing the mesoporous silica nanosphere support in the catalyst includes the following steps: Mesoporous silica was obtained by combining the Stob process with a template method, using hexadecyltrimethylammonium bromide as a template agent and tetraethyl orthosilicate as a silicon source, and reacting in an alkaline ethanol / water solution at 70-90°C with stirring. After centrifugation and washing, the hexadecyltrimethylammonium bromide template was completely removed by reflux with acidic ethanol solution in a Soxhlet extractor; The mesoporous silica nanosphere carrier is dispersed in anhydrous toluene, an excess of 3-aminopropyl triethoxysilane is added, and reflux reaction is carried out under nitrogen protection to obtain the mesoporous silica nanosphere carrier, wherein the molar ratio of tetraethyl orthosilicate, cetyltrimethylammonium bromide and ethanol is 1: (0.1-0.2): (50-100).

[0020] In a further embodiment of the present example, the preparation of the Lewis acid sites comprises the following steps: The mesoporous silica nanosphere carrier is subjected to vacuum drying; The dried mesoporous silica nanosphere carrier powder is placed in an atomic layer deposition reaction chamber and heated to 80-90℃, and the following cycle is performed for 5-10 times to deposit the Lewis acid sites: Pulse A: pulse saturated tetrakis (dimethylamino) tin vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds; Pulse B: pulse saturated water vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds.

[0021] In a further embodiment of the present example, the preparation of the Lewis base sites comprises the following steps: Citric acid is used as a carbon source and ethylenediamine is used as a nitrogen source, which are dissolved in deionized water, wherein the molar ratio of the carbon source and the nitrogen source is (1-2): (1-2), and the obtained product is purified by dialysis to obtain nitrogen-doped carbon quantum dot particles; The mesoporous silica nanosphere carrier after the preparation of the Lewis acid sites is dispersed in a 0.05-0. molar 2-morpholinoethanesulfonic acid buffer solution; The nitrogen-doped carbon quantum dot particle aqueous solution and the condensing agent are added, and stirring is performed until the reaction is complete; After the reaction is completed, centrifugation is performed, and washing with water and ethanol is repeated, followed by vacuum drying to obtain the catalyst, wherein the mass ratio of the nitrogen-doped carbon quantum dot particles to the mesoporous silica nanosphere carrier is (0.2-0.5): 1, and the mass-volume ratio of the mesoporous silica nanosphere carrier to the 2-morpholinoethanesulfonic acid buffer solution is (1-5) mg: (1-2) mL.

[0022] In a further embodiment of the present example, the method is carried out in a continuous flow microreactor system, which comprises the following units connected in sequence: A feeding unit comprising 2 or more high-precision high-pressure liquid chromatography pumps or injection pumps; A pretreatment and mixing unit comprising a coil type online preheater placed in a constant temperature oil bath and a static micro-mixer; A reaction core unit, which is a fixed bed microreactor with an inner diameter of 2-4 mm and a length of 20-50 cm, and is internally filled with a catalyst and externally provided with a temperature control heating jacket; Pressure and temperature control system: including back pressure regulator installed at the outlet of the system, Pt100 temperature sensor and PID temperature controller, which can maintain the system pressure at 1.5 MPa and the temperature control accuracy at ±0.5℃; Online monitoring unit: including Fourier transform infrared flow cell or Raman spectroscopy probe connected to the outlet of the reactor, which is used for real-time monitoring of the reaction progress; Product separation and collection unit: including online membrane separator with built-in organic solvent-resistant nanofiltration membrane, product receiving tank and tail gas absorption bottle.

[0023] In further embodiments of the present embodiment, the mesoporous silica nanosphere carrier has a particle size of 95-105 nm and a mesoporous pore size of 5-6 nm; after the amination reaction, the unreacted 3-aminopropyltriethoxysilane is removed by centrifugal washing with anhydrous ethanol for 3-5 times.

[0024] In further embodiments of the present embodiment, the nitrogen-doped carbon quantum dots have a particle size of 2-3 nm, and the 2-morpholinoethanesulfonic acid buffer has a pH value of 5.4-5.6. The condensing agent includes 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and the molar ratio of the 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide is (1-1.2):1.

[0025] In further embodiments of the present embodiment, in the pretreatment and mixing unit, the target reaction temperature of the online preheater is 80-90℃, and the mixing time of the static micro-mixer is ≤100 ms. In the product separation and collection unit, the nanofiltration membrane material is polyimide, and the molecular weight cut-off is 1000-5000 Da; the tail gas absorption bottle is filled with cold water or a 5%-10% mass fraction sodium bisulfite solution.

[0026] In further embodiments of the present embodiment, the online monitoring unit calculates the reaction conversion rate and selectivity by real-time detection of the hydroxyl characteristic peak intensity attenuation rate of hydroxyethyl methacrylate and the carbonyl characteristic peak intensity growth rate of the product acetoacetyl methyl methacrylate.

[0027] In further embodiments of the present embodiment, the reaction core unit can also be replaced by a channel type microreactor, and the catalyst is fixed on the inner wall of the microchannel by a coating process. The microchannel has an inner diameter of 0.5-2 mm and a length of 10-30 cm.

[0028] It should be noted that: the preparation process of catalyst combined with atomic layer deposition and covalent fixation precisely constructs Sn-N paired active sites with a distance of 0.5-1.0 nm in the single channel of mesoporous silica nanospheres, realizes the atomic level spatial proximity control of Lewis acid and base sites, greatly reduces the reaction activation energy, and greatly improves the target reaction conversion rate compared with traditional non-adjacent bifunctional catalysts.

[0029] By depositing Sn-based Lewis acid sites through 5-10 ALD cycles, it is ensured that Sn is dispersed in the form of single atoms or ultra-small SnO x clusters with a particle size of ≤2 nm, and no agglomerated nanoparticles are generated; N-CQDs, i.e. N-doped carbon quantum dots, are covalently fixed through EDC (1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride) and NHS (N-hydroxysuccinimide) activated amidation reaction, also maintaining a high dispersion state, maximizing the exposure rate of active sites, and reducing the waste of active sites.

[0030] The MSN carrier is pretreated with amino groups to provide strong binding sites for Sn-based LAS through coordination adsorption and N-CQDs through amide bonds, avoiding the shedding of active sites during the reaction; and the mesoporous structure of MSN with a pore size of 5-6 nm has high specific surface area and regular channels, which is beneficial for the diffusion of reactants and the desorption of products. After the catalyst is used for several cycles, the activity retention rate can still reach more than 90%.

[0031] The reaction system realizes ±0.5℃ temperature control through Pt100 sensor and PID temperature controller, and back pressure regulator maintains 1.5 MPa stable system pressure to avoid reactant vaporization or local overheating at high temperature; high-precision HPLC pump / injection pump precisely controls the raw material ratio with an error of ≤0.1 mL / min, greatly reducing the occurrence of side reactions, and the selectivity of target product is significantly improved compared with traditional kettle reaction.

[0032] The reactor outlet is integrated with online FTIR flow cell or Raman spectrum probe, which can monitor the intensity change of HEMA hydroxyl peak at 3200-3600 cm -1 and AAEM carbonyl peak at 1700-1750 cm -1 in real time, calculate the conversion rate and selectivity in real time, adjust the feeding rate, temperature and other parameters based on data feedback, and avoid raw material waste caused by "blind reaction".

[0033] The online membrane separator adopts polyimide nanofiltration membrane with a pore size of 1000-5000 Da to accurately intercept impurities, and a static micro-mixer is used to realize instantaneous uniform mixing of raw materials within 100 ms to avoid local concentration unevenness. The fixed bed micro-reactor with an inner diameter of 2-4 mm has a narrow space and high specific surface area, which can improve the heat transfer efficiency compared with traditional kettle type reaction, so that the reaction heat can be removed in time, and the contact distance between the reactants and the catalyst is shortened, and the reaction time is shortened from several hours to tens of minutes.

[0034] The detection methods in the following examples and comparative examples include: Sn atomic dispersion: observed by high-angle annular dark-field scanning transmission electron microscopy, and the proportion of Sn bright spots was counted; combined with X-ray absorption fine structure analysis of Sn coordination number.

[0035] Lewis acid site, hereinafter referred to as LAS, Lewis base site, hereinafter referred to as LBS, LAS / LBS site number and strength: ammonia temperature programmed desorption quantifies LAS; CO2 temperature programmed desorption quantifies LBS.

[0036] Catalyst life: continuously recycle the catalyst, detect the reaction conversion rate after each cycle, and record the cycle number when the conversion rate decreases by >10% compared with the initial value.

[0037] HEMA conversion rate and AAEM selectivity: Agilent 1260 type high performance liquid chromatography is used for detection: ZORBAX SB-C18 (4.6×250mm) is used as the chromatographic column, the mobile phase is methanol and water with a volume ratio of 6:4, the flow rate of the mobile phase is 1.0 mL / min, and the detection wavelength is 210 nm; Conversion rate = (1-reaction HEMA peak area / initial HEMA peak area) × 100%; Selectivity = (AAEM peak area / (total product peak area-unreacted raw material peak area)) × 100%.

[0038] Product purity: Thermo TRACE 1310-ISQ QD type gas chromatography-mass spectrometry analysis is used, and the purity of the target product AAEM = (AAEM peak area / total peak area) × 100%.

[0039] Example 1 Catalyst preparation method: In a 500 mL three-necked flask, 120 mL of deionized water and 300 mL of anhydrous ethanol were added, 0.2 g of NaOH was added under stirring at 300 rpm, and then the temperature was raised to 80°C. After the NaOH was completely dissolved, 1.0 g of CTAB was added, and stirring was continued for 30 min until the solution was clear and the CTAB was completely dissolved to form micelles. The temperature was maintained at 80°C, and stirring was continued at 300 rpm. Then, 5.0 mL of TEOS was slowly added to the reaction system at a rate of 0.5 mL / min using a constant-pressure dropping funnel. After the addition was completed, the temperature was maintained and stirring was continued for 6 h. During this process, the solution gradually changed from clear to milky white, and MSN particles were generated. After the reaction was completed, the mixture was transferred to a centrifuge tube and centrifuged at 8000 rpm for 15 min. The supernatant was discarded. The precipitate was washed with anhydrous ethanol three times, each time at 8000 rpm for 15 min to remove unreacted TEOS and free CTAB.

[0040] The MSN wet precipitate obtained by centrifugation was dispersed in 100 mL of a mixed solution composed of 10 mL of concentrated hydrochloric acid and 90 mL of anhydrous ethanol, and then transferred to the sample chamber of a Soxhlet extractor. 200 mL of the same mixed solution was added as an extractant, and the solution was heated to boiling and maintained under reflux for 48 h. The CTAB was extracted into the solution by destroying the interaction between CTAB and SiO2 with acidic ethanol. Then, the MSN precipitate was collected by centrifugation, washed with deionized water until the pH of the supernatant was 7, and then dried at 60°C under vacuum for 12 h to obtain white MSN powder with a particle size of 100 nm and a pore size of 5.5 nm.

[0041] In a 250 mL three-necked flask, 2.0 g of dry MSN powder and 200 mL of anhydrous toluene were added and ultrasonically dispersed for 30 min to ensure uniform dispersion of the MSN. Then, high-purity nitrogen gas with a purity specification of 99.999% was introduced to replace the air in the flask for 30 min to exclude the interference of moisture and oxygen. The flask was heated to 110°C under stirring at 300 rpm in a nitrogen atmosphere, and 2.0 mL of APTES was added. The temperature was maintained under reflux for 12 h to allow the ethoxy group of APTES to undergo a silanization reaction with the hydroxyl group on the surface of the MSN, and -NH2 to be grafted to the inner wall of the pore. Then, the temperature was cooled to room temperature, and the solid was collected by centrifugation at 8000 rpm for 15 min. The solid was washed with anhydrous ethanol three times to remove unreacted APTES, and finally dried at 80°C under vacuum for 6 h to obtain amino-functionalized MSN, which was denoted as MSN-NH2 powder.

[0042] 1.0 g of MSN-NH2 powder was placed in an ALD sample boat and placed in a vacuum drying oven. The sample boat was dried at 120°C under a vacuum degree of ≤10 Pa for 6 h to completely remove the adsorbed water on the surface and in the pores of the substrate, and a dried MSN-NH2 sample boat was obtained. The dried MSN-NH2 sample boat was placed in a Beneq TFS 200 ALD reaction chamber, the reaction chamber was closed, and vacuum was applied until the pressure was ≤ 5 x 10 -3 Pa, the reaction chamber temperature was set to 90°C, and the temperature was held for 30 min to stabilize the sample temperature; the TDMASn precursor bottle was connected to the deionized water precursor bottle in a 5°C water bath, and the pipeline sealing was checked.

[0043] The TDMASn valve was opened, and TDMASn vapor was pulsed into the reaction chamber for 0.1 s; the valve was closed; high-purity nitrogen gas with a flow rate of 50 sccm was introduced to purge the reaction chamber for 30 s to remove unchemisorbed TDMASn and byproducts (such as dimethylamine) until the reaction chamber pressure returned to ≤ 5 x 10 -3 Pa.

[0044] The water valve was opened, and water vapor was pulsed into the reaction chamber for 0.1 s, and the water vapor reacted with the chemisorbed TDMASn to generate SnO x and dimethylamine, and the valve was closed; high-purity nitrogen gas with a flow rate of 50 sccm was introduced again to purge for 30 s to remove byproducts generated during the reaction and excess water vapor, and one ALD cycle was completed. After 10 ALD cycles were completed, the reaction chamber heating was turned off, and the sample boat was removed after natural cooling to room temperature to obtain the MSN-Sn functionalized with Sn-based LAS.

[0045] In the inner lining reaction kettle, 1.0 g of citric acid, 0.5 mL of ethylenediamine, and 20 mL of deionized water were added, and ultrasonic stirring was performed for 30 min until the citric acid was completely dissolved to form a clear yellow solution; the reaction kettle was sealed and placed in an oven, and the temperature was increased to 180°C for 10 h of constant temperature reaction to allow the citric acid to dehydrate and carbonize, and the ethylenediamine to participate in N-doping to form N-CQDs; after the reaction was completed, the oven was turned off and naturally cooled to room temperature, and the reaction kettle was removed to obtain a brown-yellow N-CQDs crude solution; the crude solution was centrifuged at 10,000 rpm for 20 min to remove unreacted solid impurities; the supernatant after centrifugation was transferred to a 3500 Da dialysis bag and placed in 500 mL of deionized water for dialysis for 72 h, and the deionized water was replaced every 12 hours during this period to remove small molecule impurities; after dialysis was completed, a 10 mg / mL N-CQDs aqueous solution was obtained.

[0046] 1.0 g of MSN-Sn powder was added to 100 mL of MES buffer with a concentration of 0.1 mol / L, and ultrasonic dispersion was performed for 30 min to form a uniform suspension; 0.22 g of EDC and 0.2 g of NHS were added to the suspension, and stirring was performed at room temperature for 30 min; 50 mL of an N-CQDs aqueous solution was slowly dropped at a rate of 10 mg / mL, and stirring was continued at room temperature for 24 h; after the reaction was completed, the mixture was centrifuged at 8000 rpm for 15 min, and the supernatant was discarded; the precipitate was washed with deionized water for 3 times, and then washed with anhydrous ethanol for 2 times to remove the physically adsorbed N-CQDs; then, vacuum drying was performed at 60°C for 12 h to obtain the target LBS functionalized product, namely the catalyst.

[0047] Product reaction process: The raw materials HEMA and EAA containing a polymerization inhibitor were accurately delivered through a feeding unit, wherein the flow rate ratio of HEMA:EAA was 1:1.2, the total flow rate was 1.0 mL / min, the material pipeline was first passed through an online preheater to be heated to 85°C, and then immediately entered a static micro-mixer for instantaneous and efficient convective diffusion mixing to form a uniform reactant solution.

[0048] In a fixed bed micro-reactor with an inner diameter of 3 mm and a length of 35 cm, the micro-reactor was filled with a catalyst with a catalyst amount of 1 g / cm 3 The pre-mixed reactants were contacted with the catalyst at 85°C and 1.5 MPa to perform a catalytic reaction. The narrow space of the micro-reactor ensures excellent heat transfer efficiency, and the reaction heat can be removed in time to avoid local overheating.

[0049] A back pressure regulator was installed at the outlet end of the system to maintain the entire reaction system operating at 1.5 MPa to prevent the reactants or products from being vaporized at high temperature. A temperature sensor was used to monitor the reactor temperature in real time, and the power of the heating jacket was adjusted through a PID controller to achieve accurate temperature control of ± 0.5°C.

[0050] The reaction process was monitored in real time by monitoring the weakening of the hydroxyl characteristic peak 3450 cm -1 of HEMA and the enhancement of the carbonyl characteristic peak 1725 cm -1 of AAEM, and the conversion rate and selectivity were calculated and recorded in real time, and an alarm was issued and the work was stopped when the conversion rate and selectivity were less than 88%.

[0051] After the reaction was completed, the reaction liquid flowed out and the catalyst was separated from the product through a membrane separator. Acetaldehyde that may be produced by a side reaction can be absorbed and treated by a tail gas absorption bottle, and the product is directly detected without storage.

[0052] The detection results are as follows: catalyst: Sn monatomic dispersion rate is 98%, LAS amount is 0.8 mmol / g, LBS amount is 0.75 mmol / g; conversion retention rate is 92% after 10 cycles.

[0053] Product reaction: conversion rate of HEMA is 92%, selectivity of AAEM is 95%; reaction reaches stable time is 12 min; purity of AAEM is 98.5%.

[0054] Example 2 The difference from example 1 is that: ALD cycle is 5 times.

[0055] The detection results are as follows: catalyst: Sn monatomic dispersion rate is 95%, LAS amount is 1.1 mmol / g, LBS amount is 0.73 mmol / g; conversion retention rate is 91% after 10 cycles.

[0056] Reaction: conversion rate of HEMA is 93%, selectivity of AAEM is 94%; reaction reaches stable time is 12 min; purity of AAEM is 96.5%.

[0057] Example 3 The difference from example 1 is that: 1.0 g of citric acid, 0.5 mL of ethylenediamine and 20 mL of deionized water are added in the inner lining reaction kettle, ultrasonic stirring for 30 min until the citric acid is completely dissolved to form a clear yellow solution; the reaction kettle is sealed and put into the oven, heated to 170 DEG C constant temperature reaction 10 h to make citric acid dehydrated carbonization, ethylenediamine participates in N-doping, forms N-CQDs.

[0058] The detection results are as follows: catalyst: Sn monatomic dispersion rate is 97%, LAS amount is 0.8 mmol / g, LBS amount is 0.68 mmol / g; conversion retention rate is 90% after 10 cycles.

[0059] Product reaction: conversion rate of HEMA is 91%, selectivity of AAEM is 95%; reaction reaches stable time is 12 min; purity of AAEM is 96.0%.

[0060] Example 4 The difference from example 1 is that: reaction temperature is 80 DEG C.

[0061] The detection results are as follows: catalyst: Sn monatomic dispersion rate is 94%, LAS amount is 1.03 mmol / g, LBS amount is 0.68 mmol / g; conversion retention rate is 86% after 10 cycles.

[0062] Reaction: conversion of HEMA was 87%, selectivity of AAEM was 96%; time to reach steady state was 13 min; purity of AAEM was 97.5%.

[0063] Example 5 The difference from Example 1 is that the reaction temperature is 85°C.

[0064] The test results are as follows: catalyst: dispersion of Sn monomers is 94%, LAS amount is 1.03 mmol / g, LBS amount is 0.68 mmol / g; conversion retention rate after 10 cycles is 86%.

[0065] Reaction: conversion of HEMA was 94%, selectivity of AAEM was 93%; time to reach steady state was 10 min; purity of AAEM was 97.0%.

[0066] Example 6 The difference from Example 1 is that the system pressure is 1.2 MPa.

[0067] The test results are as follows: catalyst: dispersion of Sn monomers is 94%, LAS amount is 1.03 mmol / g, LBS amount is 0.68 mmol / g; conversion retention rate after 10 cycles is 86%.

[0068] Reaction: conversion of HEMA was 91%, selectivity of AAEM was 95 3%; time to reach steady state was 11 min; purity of AAEM was 96.8%.

[0069] Example 7 The difference from Example 1 is that the system pressure is 1.8 MPa.

[0070] The test results are as follows: catalyst: dispersion of Sn monomers is 94%, LAS amount is 1.03 mmol / g, LBS amount is 0.68 mmol / g; conversion retention rate after 10 cycles is 86%.

[0071] Reaction: conversion of HEMA was 92%, selectivity of AAEM was 95%; time to reach steady state was 12 min; purity of AAEM was 97.8%.

[0072] Comparative Example 1 Catalyst Preparation: The catalyst is co-impregnated with SnCl4 and ethylenediamine on amorphous SiO2, Sn loading is the same as Example 1, there is no MSN mesoporous structure, LAS-LBS spacing is > 2 nm.

[0073] The reaction process was carried out in a 500 mL three-necked flask simulation autoclave reactor, a heating jacket was set to control the temperature difference within ±2°C, the reaction temperature was 85°C, and mechanical stirring was carried out at a speed of 500 rpm; after the reaction, the catalyst was centrifuged, and the remaining conditions were the same as in Example 1.

[0074] The detection results are as follows: the Sn agglomerate particles with a particle size of 5-8 nm accounted for 60%, the LAS number was 0.4 mmol / g; the conversion retention rate was 55% after 3 cycles.

[0075] Reaction: HEMA conversion rate 60%, AAEM selectivity 72%; reaction reached stable time 60 min; AAEM purity 90% needs rectification.

[0076] Comparative Example 2 The catalyst used was the catalyst of Example 1; the reaction device was the same as in Comparative Example 1, and the process was the same as in Comparative Example 1.

[0077] The detection results are as follows: the Sn single atom dispersion rate was 98%, the LAS number was 0.8 mmol / g, and the LBS number was 0.75 mmol / g; the conversion retention rate was 85% after 3 cycles, and the conversion retention rate was 70% after 5 cycles.

[0078] Reaction: HEMA conversion rate 78%, AAEM selectivity 88%; reaction reached stable time 40 min; AAEM purity 94.5%.

[0079] In summary, both Example 1 and Example 2 achieved high activity, indicating that 5-10 ALD cycles can meet the demand, and 5 cycles can achieve Sn single atom dispersion, avoiding excessive cycles leading to agglomeration; the conversion rate of Examples 4, 1, and 5 is between 87% and 94%, and the selectivity is between 93% and 96%, indicating that 80-90°C is the optimal temperature range, and the performance is stable within a temperature difference of ±5°C.

[0080] The Sn single atom dispersion rate of Example 1 is much higher than that of Comparative Example 1, and the cycle life of Example 1 is significantly improved to 10 times compared to 3 times of Comparative Example 1, proving that the "ALD + covalent fixation" process can solve the agglomeration and shedding problems of traditional catalysts.

[0081] The conversion rate, selectivity, and stable time of Example 1 are better than those of Comparative Examples 1-2, proving that the "precise temperature control + real-time monitoring + membrane circulation" system can solve the problems of poor mass transfer, difficult temperature control, and difficult recovery in the autoclave reactor.

[0082] The performance of Comparative Example 2 is still lower than that of Example 1, indicating that the synergistic effect of "this catalyst + continuous flow microreactor" is the key to improving overall performance, and both are indispensable.

[0083] The catalyst of the application realizes the substantial improvement of HEMA conversion rate, the improvement of AAEM selectivity, and the prolongation of catalyst circulation life, compared with the traditional technology, by precisely regulating the LAS-LBS spatial distribution and high dispersity, combining the precise temperature control, real-time monitoring, and catalyst circulation function of the continuous flow microreactor, fully meeting the needs of industrialization of "high efficiency, stability, and greenness".

[0084] The above merely describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate, characterized in that, The method comprises the following steps: The hydroxyethyl methacrylate and ethyl acetoacetate are preheated to a target temperature and then mixed uniformly to obtain a mixed solution; The mixed solution is introduced into a fixed reaction bed with a catalyst for complete reaction; After online separation by an online membrane separator, the product is collected and the catalyst is recycled; Wherein the catalyst is a catalyst with mesoporous silica nanospheres as a carrier, and adjacent Lewis acid sites and Lewis base sites are precisely constructed in the nanochannels of the carrier, the Lewis acid sites are composed of single-atom Sn 4+ Species, and the Lewis base sites are composed of grafted nitrogen-doped carbon quantum dots.

2. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 1, characterized in that, The preparation method of the mesoporous silica nanosphere carrier in the catalyst comprises the following steps: Mesoporous silica is obtained by stirring and reacting in an alkaline ethanol / water solution at 70-90 DEG C by a Stober method combined with a template method, using cetyltrimethylammonium bromide as a template agent and tetraethyl orthosilicate as a silicon source; After centrifugal washing, the cetyltrimethylammonium bromide template is completely removed by refluxing with an acidic ethanol solution in a Soxhlet extractor; The mesoporous silica nanosphere carrier is dispersed in anhydrous toluene, an excess of 3-aminopropyltriethoxysilane is added, and refluxing reaction is performed under nitrogen protection to obtain the mesoporous silica nanosphere carrier.

3. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 2, characterized in that, The preparation of the Lewis acid site comprises the following steps: The mesoporous silica nanosphere carrier is dried in a vacuum; The dried mesoporous silica nanosphere carrier powder is placed in an atomic layer deposition reaction chamber, heated to 80-90 DEG C, and subjected to the following cycle for 5-10 times to deposit the Lewis acid site: Pulse A: pulse saturated tetrakis (dimethylamino) tin vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds; Pulse B: pulse saturated water vapor into the reaction chamber for 0.1 seconds, and purge with high-purity nitrogen for 30 seconds.

4. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 3, characterized in that, The preparation of the Lewis base site comprises the following steps: Nitrogen-doped carbon quantum dot particles are obtained by dissolving citric acid as a carbon source and ethylenediamine as a nitrogen source in deionized water, placing them in a high-pressure reaction kettle, and reacting at 160-200 DEG C for 6-10 h, and then purifying the obtained product by dialysis. The mesoporous silica nanosphere carrier after the preparation of the Lewis acid site is dispersed in a 2-morpholinoethanesulfonic acid buffer solution; The nitrogen-doped carbon quantum dot particle aqueous solution and a condensing agent are added, and stirring reaction is performed until completion; After the reaction is completed, the catalyst is obtained by centrifugal washing, repeated washing with water and ethanol, and vacuum drying.

5. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 1, characterized in that, The method is performed in a continuous flow microreactor system, and the system comprises the following units connected in sequence: A feeding unit comprising 2 or more high-precision high-pressure liquid chromatography pumps or injection pumps; A pretreatment and mixing unit comprising a coil type online preheater placed in a constant temperature oil bath and a static micro-mixer; A reaction core unit, which is a fixed bed microreactor with an inner diameter of 2-4 mm and a length of 20-50 cm, is internally filled with a catalyst and externally provided with a temperature control heating jacket; A pressure and temperature control system comprising a back pressure regulator, a Pt100 temperature sensor and a PID temperature controller installed at the outlet of the system, which can maintain the system pressure at 1.5 MPa and the temperature control accuracy at ± 0.5 DEG C; An online monitoring unit comprising a Fourier transform infrared flow cell or a Raman spectrum probe connected to the outlet of the reactor, which is used for real-time monitoring of the reaction progress; A product separation and collection unit comprising an online membrane separator with built-in organic solvent-resistant nanofiltration membranes, a product receiving tank and a tail gas absorption bottle.

6. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 2, characterized in that, The mesoporous silica nanosphere carrier has a particle size of 95-105 nm and a mesoporous pore size of 5-6 nm; the mesoporous silica nanosphere carrier is centrifugally washed with anhydrous ethanol for 3-5 times to remove unreacted 3-aminopropyl triethoxysilane.

7. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 4, characterized in that, The nitrogen-doped carbon quantum dots have a particle size of 2-3 nm, and the 2-morpholinoethanesulfonic acid buffer has a pH value of 5.4-5.

6. The condensing agent comprises 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and the molar ratio of the 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride to the N-hydroxysuccinimide is (1-1.2):

1.

8. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 5, characterized in that, In the pretreatment and mixing unit, the target reaction temperature of the inline preheater is 80-90 ℃, and the mixing time of the static micro-mixer is ≤100 ms. In the product separation and collection unit, the nanofiltration membrane material is polyimide, and the molecular weight cut-off is 1000-5000 Da; the tail gas absorption bottle is filled with cold water or a 5%-10% sodium bisulfite solution.

9. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 5, characterized in that, The online monitoring unit calculates the reaction conversion rate and selectivity by detecting the hydroxyl characteristic peak intensity attenuation rate of hydroxyethyl methacrylate and the carbonyl characteristic peak intensity growth rate of the product acetoacetyl methyl methacrylate in real time, and issues an alarm and stops running if the reaction conversion rate or selectivity is <88%.

10. The process for the efficient catalytic preparation of acetoacetoxy ethyl methacrylate according to claim 5, characterized in that, The reaction core unit can also be replaced by a channel type microreactor, and the catalyst is fixed on the inner wall of the microchannel through a coating process, the microchannel has an inner diameter of 0.5-2 mm and a length of 10-30 cm.