A method for synthesizing sodium methylallyl sulfonate

Abstract

This invention relates to the field of acyclic or carbocyclic compounds and discloses a method for synthesizing sodium methyl methacrylate sulfonate. The method involves introducing an organic phase of methyl methacrylate and an aqueous phase of sodium sulfite into a microchannel reactor. A sulfonation reaction is carried out under the action of a phase transfer catalyst with a crown ether structure and a mixing unit. The reaction effluent is separated into layers by a continuous flow oil-water separator. The aqueous phase is concentrated and crystallized under reduced pressure. The mother liquor and oil phase are combined and extracted through a nanofiltration membrane for the phase transfer catalyst, which is then recycled. This method alleviates the limitations of two-phase mass transfer and local concentration segregation, reduces self-polymerization and eliminates side reactions, maintains the double bond structure of the product, and achieves closed-loop catalyst recycling.

Description

Technical Field

[0001] This invention relates to the field of acyclic or carbocyclic compounds, and discloses a method for synthesizing sodium methylpropenesulfonate. Background Technology

[0002] Sodium methacrylate sulfonate is an important polymerizing monomer, and its conventional synthetic route often involves the sulfonation reaction of methyl methacrylate with an aqueous solution of sodium sulfite. This reaction is a typical liquid-liquid two-phase system, where methyl methacrylate is dispersed in the aqueous phase in the form of microdroplets, and undergoes nucleophilic addition under heating conditions to generate the target product.

[0003] In existing batch reactor processes, a phase transfer catalyst is typically added to the system to promote mass transfer between the two phases. During operation, the raw materials and the phase transfer catalyst are fed into the reactor together, and the droplets are forcibly dispersed by mechanical stirring. After the reaction, the mixture is allowed to settle and separate into layers. The aqueous phase is then removed for concentration and crystallization, while the oil phase containing the phase transfer catalyst is recovered through distillation or simple filtration. This batch operation has a long cycle time, and the mixing intensity provided by stirring is limited.

[0004] The existing process described above suffers from technical problems such as limited mass transfer at the two-phase interface and localized concentration segregation leading to the destruction of double bond structures. In a batch reactor, the phase transfer catalyst and reactants cannot achieve microscopic homogeneous mixing under macroscopic stirring, which easily forms localized high-concentration regions on the droplet surface. This promotes the self-polymerization of methyl methacrylate or the elimination reaction of addition intermediates, resulting in irreversible loss of double bond structures in the product. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as limited mass transfer at the two-phase interface and damage to double bond structures due to local concentration segregation, this invention provides a method for synthesizing sodium methylpropenesulfonate.

[0006] To address the aforementioned technical problems, this invention provides a method for synthesizing sodium methacrylate sulfonate, comprising the following technical features: Methyl methacrylate organic phase and sodium sulfite aqueous phase are preheated and introduced into a microchannel reactor as independent feed streams; simultaneously, a phase transfer catalyst containing a crown ether structure is introduced into the methyl methacrylate organic phase; liquid-liquid dispersion and sulfonation reactions are carried out under the action of at least two sets of staggered mixing units within the microchannel reactor to obtain a reaction effluent containing sodium methacrylate sulfonate; the reaction effluent is introduced into a continuous flow oil-water separator for online static stratification, separating an aqueous phase rich in sodium methacrylate sulfonate and an oil phase containing the crown ether structure-containing phase transfer catalyst; the aqueous phase is collected and concentrated under reduced pressure to crystallize, precipitating crude sodium methacrylate sulfonate; the mother liquor after the crude product is precipitated is combined with the oil phase, and the crown ether structure-containing phase transfer catalyst is extracted by nanofiltration membrane, and the extracted crown ether structure-containing phase transfer catalyst is reintroduced into the methyl methacrylate organic phase for recycling.

[0007] This synthesis method is carried out in a microchannel reactor. The sulfonation reaction of methyl methacrylate (MMA) with sodium sulfite is a nucleophilic addition, requiring sulfite ions to cross the liquid-liquid interface to attack the carbon-carbon double bond of MMA. A phase transfer catalyst containing a crown ether structure binds to the sulfite ions, transferring them from the aqueous phase to the organic phase interface. The mixing unit within the microchannel reactor shears macroscopic droplets into micron-sized droplets, ensuring uniform distribution of the phase transfer catalyst over a large specific surface area. This avoids elimination reactions or free radical self-polymerization caused by excessively high local concentrations of sulfite ions or MMA, thus protecting the double bond structure of the product. The reaction effluent undergoes online stratification via a continuous flow oil-water separator, shortening the product's residence time in the high-temperature system. A nanofiltration membrane separates the crown ether from small-molecule inorganic salts and water based on molecular weight differences, achieving a closed-loop circulation of the phase transfer catalyst.

[0008] Furthermore, in the above technical solution, before being introduced into the microchannel reactor, the methyl methacrylate organic phase and the sodium sulfite aqueous phase are respectively flowed through independent preheating modules for temperature adjustment, so that the preheating temperature of the methyl methacrylate organic phase is lower than that of the sodium sulfite aqueous phase, and the temperature difference between the methyl methacrylate organic phase and the sodium sulfite aqueous phase when they converge into the microchannel reactor is controlled between 5°C and 15°C, so as to form an interface disturbance based on temperature gradient at the inlet of the microchannel reactor.

[0009] In practice, when the two feed streams merge, there is a temperature difference. The contact between the high-temperature fluid and the low-temperature fluid generates a local surface tension gradient, which triggers the Marangoni effect. This interface disturbance based on the temperature gradient spontaneously breaks the static equilibrium of the phase interface in the initial stage of fluid merging, accelerating the interfacial mass transfer of the catalyst through interface renewal and phase transfer.

[0010] Furthermore, in the above technical solution, the phase transfer catalyst containing the crown ether structure is a complex crown ether system comprising benzo15-crown-5 and dibenzo18-crown-6, wherein the molar ratio of benzo15-crown-5 to dibenzo18-crown-6 is 1:2 to 2:1, and the complex crown ether system is enriched at the interface between the sodium sulfite aqueous phase and the methyl methacrylate organic phase.

[0011] In practice, the cavity of benzo15-crown-5 is matched with sodium ions, and dibenzo18-crown-6 provides stronger lipophilicity. After the two are combined, a stable sulfite ion complex is formed at the liquid-liquid interface, which is anchored to the organic phase side through hydrophobic interaction, increasing the effective reactant concentration at the interface.

[0012] Furthermore, in the above technical solution, the at least two sets of staggered mixing units arranged in the microchannel reactor are an asymmetric static micro-mixing structure. The asymmetric static micro-mixing structure includes a main channel and a branch pipe connected to the main channel at an asymmetric angle. The methyl methacrylate organic phase and the sodium sulfite aqueous phase are sheared and subdivided in the branch pipe and then collide and merge in the main channel.

[0013] In practice, the fluid is forced to be distributed into non-uniform micro-flow bundles in the branch pipe with an asymmetric angle. When it merges into the main channel, the difference in velocity and momentum generates strong transverse secondary flow and eddies. This asymmetric collision further tears the macroscopic droplets into submicron-sized droplets, improving the degree of micro-mixing between the two phases.

[0014] Furthermore, in the above technical solution, the continuous flow oil-water separator is equipped with a hydrophilic and oleophobic composite hollow fiber membrane module. The reaction effluent flows through the outside of the hydrophilic and oleophobic composite hollow fiber membrane module. The aqueous phase permeates into the inside of the hydrophilic and oleophobic composite hollow fiber membrane module and is discharged under the drive of capillary force and pressure difference. The oil phase is trapped on the outside of the hydrophilic and oleophobic composite hollow fiber membrane module and discharged.

[0015] In practice, the hydrophilic layer on the surface of the hollow fiber membrane allows water molecules to wet and penetrate the pores, while the oleophobic layer blocks the penetration of organic phase molecules. Under the synergistic drive of capillary force and transmembrane pressure difference, the aqueous phase continuously permeates to achieve phase separation, avoiding the thermal degradation of products caused by the long time required for traditional static stratification.

[0016] Furthermore, in the above technical solution, in the step of collecting the aqueous phase for vacuum concentration and crystallization, an ultrasonic-coupled falling film evaporator is used. The aqueous phase forms a falling film on the tube wall of the falling film evaporator, and an ultrasonic field with a frequency of 20kHz to 40kHz is applied to the falling film. During the vacuum concentration process, methanol is added to the aqueous phase as an antisolvent to promote the nucleation and growth of sodium methyl propylene sulfonate crystals under the action of the ultrasonic field.

[0017] In practice, methanol lowers the dielectric constant of the aqueous phase, disrupts the solvation layer of sodium methacrylate, breaks the dissolution-precipitation equilibrium, and promotes crystal precipitation. The cavitation effect generated by the ultrasonic field provides the energy barrier required for nucleation, while falling film evaporation achieves uniform heating and rapid desolvation of the material. The three factors work together to control the density and growth rate of the crystal nuclei.

[0018] Furthermore, in the above technical solution, in the step of extracting the phase transfer catalyst containing the crown ether structure by nanofiltration membrane, a polyamide composite nanofiltration membrane with a molecular weight cutoff of 200 to 400 Daltons is used. After the combined mother liquor and the oil phase are pretreated to remove residual methyl methacrylate, they pass through the polyamide composite nanofiltration membrane in a cross-flow manner. The phase transfer catalyst containing the crown ether structure is retained on the concentration side, while small molecule inorganic salts and water permeate through the polyamide composite nanofiltration membrane into the permeation side.

[0019] In practice, the pore size of the polyamide composite nanofiltration membrane is between that of the reverse osmosis membrane and the ultrafiltration membrane, and the surface has charged groups. Based on steric hindrance and the Donnan effect, the crown ether macromolecules are physically intercepted, while small molecules of inorganic salts and water pass through the membrane pores under pressure, thus achieving molecular-level sieving of catalysts and impurities.

[0020] Furthermore, in the above technical solution, the methyl methacrylate organic phase also contains a polar aprotic solvent as a diluent, the polar aprotic solvent being dimethyl sulfoxide or N-methylpyrrolidone, the volume ratio of the methyl methacrylate to the polar aprotic solvent being between 1:0.5 and 1:1.5, and the polar aprotic solvent being miscible with the phase transfer catalyst containing the crown ether structure.

[0021] In practice, polar aprotic solvents can dissolve crown ether-complexed sulfite ions, providing a highly polar reaction microenvironment without proton donors for nucleophilic addition reactions, reducing the solvation energy of sulfite ions and increasing their nucleophilic attack activity.

[0022] Furthermore, in the above technical solution, a water-soluble macromolecular polymer is pre-dissolved in the aqueous phase of sodium sulfite as an anti-self-polymerization barrier agent. The water-soluble macromolecular polymer is polyvinylpyrrolidone (PVP), and the mass ratio of PPVP to sodium sulfite is between 1:100 and 1:500. The PPVP is uniformly dispersed in the aqueous phase of sodium sulfite.

[0023] In practice, the long-chain macromolecules of polyvinylpyrrolidone form a spatial network structure inside the microdroplets, which blocks the collisions between methyl methacrylate monomers through steric hindrance, thus blocking the free radical chain transmission pathway and inhibiting thermally initiated polymerization side reactions at the microscale.

[0024] Furthermore, in the above technical solution, in the step of reintroducing the extracted crown ether-containing phase transfer catalyst into the methyl methacrylate organic phase for recycling, an online conductivity monitor is set up to detect the concentration of the crown ether-containing phase transfer catalyst in the recycling pipeline in real time. When the concentration is lower than a set threshold, fresh crown ether-containing phase transfer catalyst is added to the recycling pipeline to maintain the constant phase transfer catalytic activity in the microchannel reactor.

[0025] In practice, the concentration of crown ether in aqueous solution corresponds to the conductivity of the system. The online conductivity monitor converts the physical signal into concentration data. When the concentration decreases due to circulation loss, the replenishment mechanism is automatically triggered to ensure the dynamic balance of the mass transfer driving force at the liquid-liquid interface.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. By introducing the organic phase of methyl methacrylate and the aqueous phase of sodium sulfite into a microchannel reactor and supplementing it with a phase transfer catalyst containing a crown ether structure, the local concentration segregation phenomenon in the batch reaction was mitigated. The mixing unit within the microchannel reactor refines the droplet size, increases the specific surface area of ​​the two-phase contact, and allows the phase transfer catalyst to be uniformly distributed at the interface, avoiding high-concentration aggregation of reactants in localized areas, reducing self-polymerization and eliminating side reactions, and maintaining the double bond structure in the product. The combination of continuous flow oil-water separation and nanofiltration membrane retention and recovery allows the phase transfer catalyst to circulate in a closed-loop system, maintaining a constant catalyst concentration within the reaction system.

[0028] 2. The preheating temperature difference of the feed stream is set at the microchannel inlet to create interfacial disturbance, accelerating interfacial renewal in the initial mixing stage. The branch pipes of the asymmetric static micromixing structure shear and subdivide the fluid, enhancing mass transfer efficiency at the microscale of mixing. The hydrophilic-oleophobic composite hollow fiber membrane module utilizes capillary force and pressure difference to achieve online separation of the aqueous and oil phases, shortening the residence time of the product at high temperatures. The ultrasonically coupled falling film evaporator, combined with methanol antisolvent, makes the nucleation process uniform and controllable, avoiding the phenomenon of impurity encapsulation during crystallization. The cross-flow filtration of the polyamide composite nanofiltration membrane separates crown ethers from small molecule inorganic salts. The addition of polar aprotic solvent and polyvinylpyrrolidone improves the dissolution environment of the organic phase and the anti-self-polymerization ability of the aqueous phase, respectively. Online conductivity monitoring ensures the stability of catalyst activity during circulation. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0030] Example 1: Methyl methacrylate (MMA) organic phase and sodium sulfite aqueous phase were used as independent feed streams. The MMA organic phase was composed of MMA and dimethyl sulfoxide at a volume ratio of 1:1, and a crown ether-containing phase transfer catalyst was introduced into it. This phase transfer catalyst was a composite crown ether system composed of benzo[15-crown-5] and dibenzo[18-crown-6] at a molar ratio of 1.5:1. The sodium sulfite aqueous phase had a sodium sulfite mass concentration of 30%, and polyvinylpyrrolidone (PVP) was dissolved in it as an anti-self-polymerization barrier agent. The mass ratio of PPV to sodium sulfite was 1:200. The two feed streams flowed through independent preheating modules. The preheating temperature of the MMA organic phase was 50°C, and the preheating temperature of the sodium sulfite aqueous phase was 60°C. The temperature difference between the two when they converged into the microchannel reactor was controlled at 10°C. The microchannel reactor contains two sets of staggered mixing units. Each mixing unit is an asymmetric static micro-mixing structure, comprising a main channel and branch pipes connected to it at an asymmetric angle. The methyl methacrylate organic phase and the sodium sulfite aqueous phase are sheared and subdivided within the branch pipes before colliding and merging in the main channel, undergoing liquid-liquid dispersion and sulfonation reactions to obtain a reaction effluent containing sodium methacrylate sulfonate. This reaction effluent is introduced into a continuous flow oil-water separator, which contains a hydrophilic-oleophobic composite hollow fiber membrane module. As the reaction effluent flows past the outside of this membrane module, the aqueous phase permeates into the inside of the membrane module under capillary force and pressure difference and is discharged, while the oil phase is retained on the outside of the membrane module and discharged, achieving online static stratification. Aqueous phase rich in sodium methyl methacrylate was collected and concentrated under reduced pressure using an ultrasonic-coupled falling film evaporator. A falling film formed on the tube wall of the evaporator, and an ultrasonic field with a frequency of 30 kHz was applied to the falling film. During the reduced pressure concentration process, methanol was added to the aqueous phase as an antisolvent, precipitating crude sodium methyl methacrylate. The mother liquor after the crude product was precipitated was combined with the oil phase, pretreated to remove residual methyl methacrylate, and then passed through a polyamide composite nanofiltration membrane with a molecular weight cutoff of 300 Daltons in a cross-flow manner. The phase transfer catalyst containing the crown ether structure was retained on the concentration side, while small molecule inorganic salts and water permeated through the nanofiltration membrane into the permeate side. The phase transfer catalyst containing the crown ether structure extracted from the concentration side was reintroduced into the methyl methacrylate organic phase for recycling. An online conductivity monitor was installed on the recycling pipeline to detect the concentration in real time. When the concentration fell below a set threshold, fresh phase transfer catalyst containing the crown ether structure was added.

[0031] Example 2: Based on Example 1, the molar ratio of benzo[15-crown-5] to dibenzo[18-crown-6] in the phase transfer catalyst containing the crown ether structure was adjusted to 1:2, and the other conditions were the same as in Example 1.

[0032] Example 3: Based on Example 1, the molar ratio of benzo[15-crown-5] to dibenzo[18-crown-6] in the phase transfer catalyst containing the crown ether structure was adjusted to 2:1, and the other conditions were the same as in Example 1.

[0033] Example 4: Based on Example 1, the polar aprotic solvent was replaced with N-methylpyrrolidone, the volume ratio of methyl methacrylate to N-methylpyrrolidone was kept at 1:1, and the other conditions were the same as in Example 1.

[0034] Example 5: Based on Example 1, the volume ratio of methyl methacrylate to dimethyl sulfoxide was adjusted to 1:0.5, and the other conditions were the same as in Example 1.

[0035] Example 6: Based on Example 1, the volume ratio of methyl methacrylate to dimethyl sulfoxide was adjusted to 1:1.5, and the other conditions were the same as in Example 1.

[0036] Example 7: Based on Example 1, the mass ratio of polyvinylpyrrolidone to sodium sulfite in the aqueous phase of sodium sulfite was adjusted to 1:100, and the other conditions were the same as in Example 1.

[0037] Example 8: Based on Example 1, the mass ratio of polyvinylpyrrolidone to sodium sulfite in the aqueous phase of sodium sulfite was adjusted to 1:500, and the other conditions were the same as in Example 1.

[0038] Example 9: Based on Example 1, the preheating temperature of the organic phase of methyl methacrylate was adjusted to 55°C, and the preheating temperature of the aqueous phase of sodium sulfite was adjusted to 60°C. The temperature difference between the two phases when they were introduced into the microchannel reactor was controlled at 5°C. All other conditions were the same as in Example 1.

[0039] Example 10: Based on Example 1, the preheating temperature of the organic phase of methyl methacrylate was adjusted to 50°C, and the preheating temperature of the aqueous phase of sodium sulfite was adjusted to 65°C. The temperature difference between the two phases when they were introduced into the microchannel reactor was controlled at 15°C. The other conditions were the same as in Example 1.

[0040] Example 11: Based on Example 1, the frequency of the ultrasonic field applied to the falling film during the vacuum concentration and crystallization process was adjusted to 20kHz, and the other conditions were the same as in Example 1.

[0041] Comparative Example 1: Based on Example 1, polyvinylpyrrolidone in the sodium sulfite aqueous phase was removed, i.e., no anti-self-polymerization barrier agent was added, and the other conditions were the same as in Example 1.

[0042] Comparative Example 2: Using a traditional batch process, methyl methacrylate, sodium sulfite aqueous solution, and a phase transfer catalyst containing a crown ether structure were added to a mechanically stirred reactor at once and heated to 60°C for reaction. After the reaction was completed, the mixture was allowed to stand and separate into layers. The aqueous phase was then collected and concentrated and crystallized by conventional vacuum distillation without performing nanofiltration membrane interception and catalyst recovery.

[0043] Comparative Example 3: Based on Example 1, the preheating temperature of the organic phase of methyl methacrylate was adjusted to 40°C, and the preheating temperature of the aqueous phase of sodium sulfite was adjusted to 60°C. The temperature difference between the two phases when they were introduced into the microchannel reactor was controlled at 20°C, which is outside the specified temperature difference range. The other conditions were the same as in Example 1.

[0044] Comparative Example 4: Based on Example 1, no ultrasonic field was applied in the reduced pressure concentration and crystallization step. Instead, a falling film evaporator was used for reduced pressure concentration and methanol was added as a solvent. The other conditions were the same as in Example 1.

[0045] Test method:

[0046] The sodium methyl methacrylate products prepared in Examples 1-11 and Comparative Examples 1-4 were subjected to performance tests. The test indicators included: double bond retention rate (calculated by integral area of ​​nuclear magnetic resonance hydrogen spectrum), color of reaction effluent (using platinum-cobalt colorimetric method), amount of by-product polymer generated (determined by mass percentage using gel permeation chromatography), and content of inorganic salt impurities in the product (determined by mass percentage using ion chromatography).

[0047] Double bond retention rate test: determined by the ¹H-NMR integral method.

[0048] (1) Take 10 mg of dried sodium methylpropenesulfonate sample and dissolve it in 0.5 mL of heavy water (D2O).

[0049] (2) Nuclear magnetic resonance spectroscopy was used for testing, with a scanning range of 0-10 ppm;

[0050] (3) Integrate the double bond hydrogen signal (5.5-6.5ppm) and the reference hydrogen signal to calculate the double bond retention rate: Double bond retention rate (%) = (sample double bond hydrogen integral / standard double bond hydrogen integral) × 100; Three parallel samples are tested in each group, and the arithmetic mean is taken.

[0051] Colorimetric test of the reaction effluent: determined by the platinum-cobalt colorimetric method.

[0052] (1) Filter the reaction effluent to remove solid impurities;

[0053] (2) The absorbance was measured at a wavelength of 456 nm using a spectrophotometer, in accordance with the standard GB / T11903-1989.

[0054] (3) Calculate the colorimetric value (platinum cobalt number) based on the platinum cobalt standard curve; test 3 parallel samples for each group and take the arithmetic mean.

[0055] Byproduct polymer formation test: determined by gel permeation chromatography (GPC).

[0056] (1) Take the sample aqueous solution and filter it through a 0.22μm filter membrane;

[0057] (2) Chromatographic conditions: gel chromatography column, differential refractive index detector, mobile phase is 0.1 mol / L sodium nitrate aqueous solution, flow rate is 1.0 mL / min;

[0058] (3) Calculate the polymer mass fraction based on the peak area; test 3 parallel samples for each group and take the arithmetic mean.

[0059] Inorganic salt impurity content in the product was determined by ion chromatography.

[0060] (1) Accurately weigh 1.0 g of sample, dissolve and dilute to 100 mL, and filter through a 0.22 μm filter membrane;

[0061] (2) Ion chromatography conditions: anion chromatography column, conductivity detector, and eluent is a sodium carbonate / sodium bicarbonate mixed solution;

[0062] (3) Quantitative analysis using the external standard method, calculating the mass fraction of inorganic salt impurities; three parallel samples were tested in each group, and the arithmetic mean was taken.

[0063] The test results are shown in Table 1.

[0064] Table 1 Performance test results of each embodiment and comparative example

[0065] serial number Double bond retention rate (%) Color of the reaction effluent (platinum-cobalt grade) Byproduct polymer formation rate (%) Inorganic salt impurity content (%) in the product Example 1 99.2 10 0.08 0.04 Example 2 98.5 15 0.12 0.05 Example 3 98.8 12 0.10 0.05 Example 4 98.9 12 0.09 0.06 Example 5 98.4 18 0.15 0.07 Example 6 98.6 16 0.13 0.06 Example 7 98.7 14 0.11 0.05 Example 8 98.2 20 0.18 0.08 Example 9 98.0 22 0.20 0.09 Example 10 97.5 28 0.25 0.10 Example 11 98.6 15 0.14 0.08 Comparative Example 1 90.5 85 1.50 0.12 Comparative Example 2 82.3 150 3.20 1.50 Comparative Example 3 95.0 60 0.80 0.15 Comparative Example 4 98.8 25 0.15 0.15

[0066] Results analysis:

[0067] Example 1 employed a microchannel reactor combined with a phase transfer catalyst containing a crown ether structure and an asymmetric static micromixing structure to refine droplets and achieve uniform mass transfer at the interface, avoiding localized concentration segregation. The double bond retention rate reached 99.2%, and the byproduct polymer was only 0.08%, far superior to Comparative Example 2 (82.3% double bond retention, 3.20% polymer retention), which suffered from macroscopically uneven mixing due to conventional stirred tank mixing. This demonstrates the decisive role of continuous flow microscale mixing in suppressing self-polymerization and eliminating side reactions. Nanofiltration membrane extraction reduced the inorganic salt impurities in Example 1 to as low as 0.04%, while Comparative Example 2, without nanofiltration membrane separation, had inorganic salt impurities as high as 1.50%.

[0068] Comparative Example 1 removed the polyvinylpyrrolidone (PVP) anti-self-polymerization barrier agent from the aqueous phase. The absence of microscopic steric hindrance allowed for unimpeded free radical chain propagation, leading to a surge in byproduct polymer content to 1.50% and a sharp drop in double bond retention to 90.5%, confirming the crucial role of this macromolecular polymer in inhibiting self-polymerization. Comparative Example 3 expanded the feed temperature difference to 20°C, exceeding the set temperature range. While the excessive temperature difference increased initial interfacial disturbance, it also triggered severe local thermal stress imbalance, resulting in decreased fluid mixing homogeneity and localized thermally induced self-polymerization. The color increased to 60, and the double bond retention dropped to 95.0%, demonstrating the necessity of limiting the temperature difference to 5°C to 15°C for balancing the formation of moderate interfacial disturbance with maintaining the system's thermal stability. Comparative Example 4 omitted the ultrasonic field during the crystallization process and relied solely on falling film evaporation and antisolvent. Due to insufficient nucleation density and uneven crystal growth rate, the inorganic salt impurities embedded in the mother liquor could not be effectively released, and the content of inorganic salt impurities in the product increased to 0.15%. This demonstrates the necessity of the nucleation barrier overcoming capability provided by ultrasonic cavitation for crystallization purification.

Claims

1. A method for synthesizing sodium methylpropene sulfonate, characterized in that, Includes the following steps: Methyl methacrylate organic phase and sodium sulfite aqueous phase are preheated as independent feed streams and then introduced into a microchannel reactor. At the same time, a phase transfer catalyst with a crown ether structure is introduced into the methyl methacrylate organic phase. Liquid-liquid dispersion and sulfonation reaction are carried out under the action of at least two sets of staggered mixing units in the microchannel reactor to obtain a reaction effluent containing sodium methacrylate. The reaction effluent is introduced into a continuous flow oil-water separator for online static stratification, separating an aqueous phase rich in sodium methylpropene sulfonate and an oil phase containing the crown ether-containing phase transfer catalyst. The aqueous phase was collected and concentrated under reduced pressure to crystallize, precipitating crude sodium methylpropene sulfonate. The mother liquor after the crude product is precipitated is combined with the oil phase, and the phase transfer catalyst containing the crown ether structure is extracted by nanofiltration membrane. The extracted phase transfer catalyst containing the crown ether structure is then reintroduced into the methyl methacrylate organic phase for recycling.

2. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, Before being introduced into the microchannel reactor, the methyl methacrylate organic phase and the sodium sulfite aqueous phase are respectively flowed through independent preheating modules for temperature adjustment, so that the preheating temperature of the methyl methacrylate organic phase is lower than that of the sodium sulfite aqueous phase, and the temperature difference between the methyl methacrylate organic phase and the sodium sulfite aqueous phase when they converge into the microchannel reactor is controlled between 5°C and 15°C, so as to form an interface disturbance based on temperature gradient at the inlet of the microchannel reactor.

3. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, The phase transfer catalyst containing the crown ether structure is a complex crown ether system comprising benzo15-crown-5 and dibenzo18-crown-6, wherein the molar ratio of benzo15-crown-5 to dibenzo18-crown-6 is 1:2 to 2:1, and the complex crown ether system is enriched at the interface between the sodium sulfite aqueous phase and the methyl methacrylate organic phase.

4. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, The at least two sets of staggered mixing units arranged in the microchannel reactor are an asymmetric static micro-mixing structure. The asymmetric static micro-mixing structure includes a main channel and branch pipes connected to the main channel at an asymmetric angle. The methyl methacrylate organic phase and the sodium sulfite aqueous phase are sheared and subdivided in the branch pipes and then collide and merge in the main channel.

5. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, The continuous flow oil-water separator is equipped with a hydrophilic and oleophobic composite hollow fiber membrane module. The reaction effluent flows through the outside of the hydrophilic and oleophobic composite hollow fiber membrane module. The aqueous phase permeates into the inside of the hydrophilic and oleophobic composite hollow fiber membrane module and is discharged under the drive of capillary force and pressure difference. The oil phase is trapped on the outside of the hydrophilic and oleophobic composite hollow fiber membrane module and discharged.

6. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, In the step of collecting the aqueous phase for vacuum concentration and crystallization, an ultrasonic-coupled falling film evaporator is used. The aqueous phase forms a falling film on the tube wall of the falling film evaporator, and an ultrasonic field with a frequency of 20kHz to 40kHz is applied to the falling film. During the vacuum concentration process, methanol is added to the aqueous phase as an antisolvent to promote the nucleation and growth of sodium methyl propylene sulfonate crystals under the action of the ultrasonic field.

7. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, In the step of extracting the phase transfer catalyst containing the crown ether structure by nanofiltration membrane, a polyamide composite nanofiltration membrane with a molecular weight cutoff of 200 to 400 Daltons is used. After the combined mother liquor and the oil phase are pretreated to remove residual methyl methacrylate, they are passed through the polyamide composite nanofiltration membrane in a cross-flow manner. The phase transfer catalyst containing the crown ether structure is retained on the concentration side, while small molecule inorganic salts and water permeate through the polyamide composite nanofiltration membrane into the permeate side.

8. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, The methyl methacrylate organic phase further includes a polar aprotic solvent as a diluent, wherein the polar aprotic solvent is dimethyl sulfoxide or N-methylpyrrolidone, and the volume ratio of the methyl methacrylate to the polar aprotic solvent is between 1:0.5 and 1:1.

5. The polar aprotic solvent is miscible with the phase transfer catalyst containing the crown ether structure.

9. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, The aqueous phase of sodium sulfite contains a water-soluble macromolecular polymer as an anti-self-polymerization barrier agent, wherein the water-soluble macromolecular polymer is polyvinylpyrrolidone, and the mass ratio of polyvinylpyrrolidone to sodium sulfite is between 1:100 and 1:500, and the polyvinylpyrrolidone is uniformly dispersed in the aqueous phase of sodium sulfite.

10. The method for synthesizing sodium methylpropene sulfonate according to claim 1, characterized in that, In the step of reintroducing the extracted crown ether-containing phase transfer catalyst into the methyl methacrylate organic phase for recycling, an online conductivity monitor is set up to detect the concentration of the crown ether-containing phase transfer catalyst in the recycling pipeline in real time. When the concentration is lower than a set threshold, fresh crown ether-containing phase transfer catalyst is added to the recycling pipeline to maintain the constant phase transfer catalytic activity in the microchannel reactor.