A method for treating methyl methacrylate wastewater

Abstract

The application discloses a kind of methyl methacrylate wastewater treatment methods, belong to chemical wastewater treatment technical field.The methyl methacrylate wastewater containing acetic acid mass concentration 10-15% as reactant and extraction agent, with methanol in the reaction section of reaction rectifying column Counter-current contact and occur esterification under the catalysis of solid acid.The reaction section is loaded with the catalysis-water absorption dual-functional packing system consisting of solid acid catalytic particles, acid-resistant composite water-absorption particles and supporting packing;The method uses acid-resistant composite water-absorption particles to selectively adsorb water generated by esterification, reduces the water activity of micro area on the surface of catalytic particles, reduces the inhibition of high water content on esterification equilibrium, reduces the molar ratio of methanol and acetic acid to 1.2:1-1.8:1, and the mass fraction of methyl acetate product obtained at the top of the column is not less than 99%.

Description

Technical Field

[0001] This invention belongs to the field of chemical wastewater treatment technology, and specifically relates to a method for treating methyl methacrylate wastewater. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material widely used in plexiglass, coatings, adhesives, and plastics processing aids. Industrially, it is mostly produced using the isobutylene oxidation process, where air oxidizes isobutylene in two stages in the presence of a molybdenum catalyst, first to methacrolein, then further to methacrylic acid, which is then esterified with methanol. The production of methacrylic acid generates a large amount of acidic wastewater with acetic acid as the main organic pollutant. Acetic acid accounts for approximately 10-15% of the wastewater, with the remainder consisting mainly of water and trace organic impurities. This wastewater is highly acidic and has a high concentration of organic matter. Incineration requires a large amount of fuel to maintain combustion, resulting in high energy consumption and operating costs, and the organic matter is not recycled. Directly feeding it into a biological treatment system leads to excessively high acetic acid concentrations and chemical oxygen demand (COD) exceeding emission standards, making it difficult to meet discharge requirements.

[0003] Acetic acid and methanol can undergo esterification under the action of an acidic catalyst to produce methyl acetate. This reaction is reversible. Simple batch reaction is limited by the equilibrium conversion rate. It not only requires a large excess of one reactant, but also requires multiple distillation columns for product separation. The process is lengthy, the equipment investment is large, and the energy consumption is high.

[0004] Reactive distillation technology couples the reaction process with the distillation process, allowing the product to leave the reaction zone with the rising vapor as it is generated, thus suppressing the reverse reaction and effectively improving the conversion rate of acetic acid. For example, Chinese patent application CN1796358A discloses a method for synthesizing methyl acetate using reactive distillation; Chinese patent application CN101328119A further discloses a process for synthesizing methyl acetate using a reactive distillation partitioned column, integrating the esterification reaction, product separation, and excess methanol recovery into a single partitioned column. Excess methanol is drawn off via a side stream for recycling, eliminating the need for a subsequent distillation column and resulting in higher thermodynamic efficiency.

[0005] When existing reactive distillation technology is applied to the treatment of methyl methacrylate (Mmethacrylate) production wastewater, the following objective technical problems still exist: the wastewater has a low acetic acid mass fraction but a high water content. Water, as one of the products of the esterification reaction, according to the law of mass action, continuously inhibits the forward shift of the esterification equilibrium from the product side, limiting the actual achievable acetic acid conversion depth within the reaction zone. Existing reactive distillation relies solely on rising vapor to remove methyl acetate and water vapor from the gas phase out of the reaction zone, failing to reduce the water activity at the liquid-phase catalytic sites. Therefore, to improve acetic acid conversion and recovery, the molar ratio of methanol to acetic acid must be increased to 3:1 or even 6:1, significantly increasing the side-stream methanol recovery load and the reboiler energy consumption, thus weakening the economic viability of waste-to-waste treatment. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for treating methyl methacrylate wastewater. The aim is to break the inhibition of esterification equilibrium through in-situ dehydration, reduce the alcohol-acid ratio, and achieve low-energy continuous operation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for treating methyl methacrylate wastewater, wherein the method is carried out in a reactive distillation column, which is provided from top to bottom with a rectification section, an extraction section, a reaction section, and a stripping section, and is divided into a side-stream rectification section by a baffle at the bottom of the column and a common stripping section at the bottom of the column, and includes the following steps: (1) Feeding: Methyl methacrylate wastewater is added from above the reaction section and flows from top to bottom; methanol is added from the middle of the reaction section; the two are in countercurrent contact within the reaction section; (2) Reaction and dehydration: The reaction section is filled with a catalytic-water-absorbing dual-function packing system, which consists of solid acid catalytic particles, acid-resistant composite water-absorbing particles and supporting packing. (3) Extraction and distillation purification: The methyl acetate generated in step (2) enters the extraction section with the rising vapor and is extracted by the acetic acid in the wastewater to remove the methanol and water it carries. After the trace amount of acetic acid is removed by the distillation section, the methyl acetate product is collected at the top of the tower. (4) Distillation, side stream recovery and bottom product: The liquid phase below the reaction section is stripped of a small amount of methyl acetate in the distillation section, and a mixture containing water and methanol is obtained at the bottom of the partition; one of the mixture is recycled back to the methanol feed in step (1) by collecting methanol at the top of the side stream through the side stream rectification section; the other is recycled back to the bottom of the tower by collecting wastewater through the common distillation section. The molar ratio of methanol to acetic acid in the methyl methacrylate wastewater is 1.2:1 to 1.8:1.

[0009] In this scheme, during the reaction and dehydration process, acetic acid and methanol undergo esterification under the action of the solid acid catalyst particles to produce methyl acetate and water. The water generated in the reaction is selectively adsorbed and removed by adjacent acid-resistant composite water-absorbing particles. This reduces the water activity around the liquid phase catalytic site and forms a synergistic effect with the continuous vapor stripping and water separation in the reactive distillation phase. This doubly weakens the inhibition of the product water on the reversible esterification equilibrium, causing the esterification equilibrium to shift towards the product direction, thereby obtaining a high acetic acid conversion rate at a low methanol ratio close to stoichiometry.

[0010] Furthermore, the acetic acid concentration in the methyl methacrylate wastewater is 10-15%.

[0011] Furthermore, the acid-resistant composite absorbent particles comprise a continuous phase matrix and acid-resistant microporous molecular sieve microparticles uniformly distributed therein. The continuous phase matrix is ​​one of the following: (A) a silica inorganic binder phase formed by calcination and solidification of silica sol; (B) a sulfonated polystyrene-divinylbenzene network formed by copolymerization of styrene sulfonate and divinylbenzene. The acid-resistant microporous molecular sieve microparticles are high-silica chalcogenide (CHA structure) or SAPO-34 silica-phosphorus-alumina molecular sieve. In the acidic hydrothermal phase of this process, the acid-resistant microporous molecular sieve microparticles can maintain their crystal structure and adsorption capacity for a long time, providing deep selective water absorption capacity; the continuous phase matrix provides large-capacity, rapid hydrophilic water absorption capacity.

[0012] Further, when the continuous phase matrix is ​​a silica inorganic binder phase, the preparation method of the acid-resistant composite absorbent particles includes the following steps: (a) calcining and activating the acid-resistant microporous molecular sieve microparticles at 400-550℃ for later use; (b) mixing the activated molecular sieve microparticles with silica sol at a molecular sieve to silica dry basis mass ratio of (1-4):1, adding a pore-forming agent and deionized water to form a formable slurry; (c) granulating or extruding the slurry, drying it at 80-120℃, and then calcining it at 500-550℃ for 2-4 hours to obtain the acid-resistant composite absorbent particles.

[0013] Further, when the continuous phase matrix is ​​a sulfonated polystyrene-divinylbenzene network, the preparation method of the acid-resistant composite absorbent particles includes the following steps: (a) calcining and activating the acid-resistant microporous molecular sieve microparticles at 400-550℃ for later use; (b) preparing a monomer phase containing sodium styrene sulfonate, divinylbenzene and a free radical initiator, wherein divinylbenzene accounts for 12-20% of the total monomer content, and dispersing the activated molecular sieve microparticles in the monomer phase; (c) molding the particles into particles by suspension polymerization; (d) washing the particles with dilute acid to convert them to the hydrogen form, washing them with water until neutral, and drying them at 60-90℃ to obtain acid-resistant composite absorbent particles.

[0014] Furthermore, the acid-resistant composite absorbent particles undergo initial activation before loading and use, namely, vacuum insulation and dehydration for 2-4 hours to remove water adsorbed during preparation and storage, thus restoring their working absorbent capacity. When the continuous phase matrix is ​​a silica inorganic binder phase, the initial activation temperature is 130-180℃; when the continuous phase matrix is ​​a sulfonated polystyrene-divinylbenzene network, the initial activation temperature is no higher than 130℃.

[0015] Furthermore, in the catalytic-water-absorbing bifunctional packing system, the volume ratio of solid acid catalytic particles, acid-resistant composite water-absorbing particles and supporting packing is (30-50):(30-50):(10-20).

[0016] Preferably, the volume ratio of the acid-resistant composite water-absorbing particles gradually increases from top to bottom along the reaction section; this is because the residual acetic acid concentration is low in the lower part of the reaction section, the reaction is closest to equilibrium, and it is most inhibited by water, so concentrating the water absorption capacity in the lower part of the reaction section has the highest marginal gain for promoting the deep reaction.

[0017] Preferably, the support packing is a ceramic Raschig ring or a metal Pall ring.

[0018] Preferably, the solid acid catalyst particles are selected from zirconium oxide sulfate or heteropolyacid supported particles with a temperature resistance of not less than 180°C; the use of high-temperature resistant solid acids can ensure the stability of the catalyst activity under repeated high-temperature regeneration conditions.

[0019] Furthermore, the reaction section is divided along the column height into an independently separable upper reaction zone and a lower reaction zone, each equipped with independent gas-phase bypass pipes, liquid-phase bypass pipes, and regeneration medium inlet and outlet pipelines. When the acid-resistant composite water-absorbing particles in one reaction zone approach water saturation, that reaction zone is isolated from the main gas-liquid flow in the column and its bypass pipe is cut off. This allows the rising vapor and falling liquid phase of the entire column to flow continuously through the bypass pipe, maintaining the continuous distillation process within the column. Simultaneously, the other reaction zone undertakes the esterification reaction online. The isolated reaction zone is regenerated by introducing the regeneration medium, and the two reaction zones alternate in operation. The gas-phase bypass pipe and liquid-phase bypass pipe can be filled with inert structured packing to compensate for the mass transfer capacity of that section during bypass and maintain the stability of the distillation balance within the column.

[0020] Furthermore, the regeneration is determined according to the type of continuous phase matrix: when it is a silica inorganic binder phase, superheated methanol vapor or inert hot gas at 130-180℃ is introduced and vacuumed to 1-10 kPa to remove water from the silica mesopores and molecular sieve channels; when it is a sulfonated polystyrene-divinylbenzene network, competitive displacement desorption is first performed with superheated methanol vapor at 100-120℃, followed by vacuuming to 1-10 kPa at a temperature not exceeding 130℃; the desorbed water is condensed and stratified, and the methanol is recycled, while the water is incorporated into the tower bottom wastewater. Because this invention uses a low methanol ratio, reduces the amount of water produced in the reaction, and lowers the saturation rate of the acid-resistant composite water-absorbing particles, the switching cycle is long (the switching cycle between the two reaction zones is 12-24 hours), the regeneration frequency is low, and the disturbance to continuous operation is small.

[0021] Furthermore, the method is operated at atmospheric pressure and satisfies one or more of the following conditions: the upper temperature of the reaction section is 70-75℃, the lower temperature is 80-90℃; the top temperature of the column is 50-70℃, and the top reflux ratio is 0.5-10; the top temperature of the side stream is 62-66℃, and the side stream reflux ratio is 1-3; the bottom temperature of the column is 90-110℃; both the wastewater and methanol are liquid-phase feeds with a feed temperature of 20-50℃; and the liquid hourly space velocity is 2-6 h⁻¹. - ¹.

[0022] Furthermore, the methanol is industrial pure methanol or industrial recycled crude methanol with a purity greater than 80%.

[0023] Furthermore, the baffles in the reactive distillation column are eccentrically arranged inside the column, so that the ratio of the cross-sectional area of ​​the stripping section to the side stream rectification section is 2:1-8:1, which can also be determined according to the specific flow rate of the material inside the column.

[0024] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention introduces acid-resistant composite water-absorbing particles into the reaction section to remove water generated during the esterification reaction in situ, thereby reducing the water activity of the micro-regions on the surface of the catalytic particles and weakening the inhibitory effect of water on the esterification equilibrium from the perspectives of reaction kinetics and thermodynamics. Under these conditions, the molar ratio of methanol to acetic acid can be significantly reduced from 3:1-6:1 in the existing process to 1.2:1-1.8:1, reducing the amount of methanol circulating and the amount of reboiler steam consumed, thus reducing operating energy consumption.

[0025] (2) The acid-resistant composite absorbent particles used in this invention have excellent chemical and mechanical stability. A continuous phase provides large-capacity rapid water absorption, while an acid-resistant microporous molecular sieve provides selective deep water absorption, selectively adsorbing and removing the water generated immediately during the reaction. The continuous phase matrix is ​​based on silica inorganic binder phase or sulfonated polystyrene-divinylbenzene network, which has good resistance to heat and acid hydrolysis.

[0026] (3) The present invention preferably divides the reaction section into upper and lower double reaction zones that can be independently bypassed, and adopts an alternating operation and regeneration strategy to realize in-situ regeneration of water-absorbing particles without interrupting the main reaction process, thus solving the problem of continuous operation in the industrial application of solid adsorbents and ensuring the production efficiency and operational reliability of the device. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0028] Unless otherwise specified, the raw materials and equipment used in the embodiments and comparative examples are commercially available.

[0029] Preparation of acid-resistant composite absorbent granules Preparation Example 1 High-silica chalcogenide (CHA structure, silica-alumina ratio of about 12, pore size of about 0.38 nm) microparticles (particle size of about 5 μm) were activated at 500℃ for 3 hours for later use. They were then mixed with acidic silica sol (silica mass fraction of 30%) at a molecular sieve to silica dry basis mass ratio of 2:1. Polyethylene glycol 4000 (accounting for 8-12% of silica dry basis mass) and deionized water (accounting for 20-30% of the total mass of solid materials) were added to prepare an extrudable slurry. After extrusion molding, the slurry was dried at 110℃ for 6 hours and then calcined at 530℃ for 3 hours. After cooling to room temperature in the furnace, acid-resistant composite water-absorbing particles were obtained.

[0030] The acid-resistant composite absorbent granules are activated for the first time at 160℃ and approximately 5kPa under vacuum for 3 hours before use.

[0031] Preparation Example 2 High-silica chalcogenide (CHA structure, silica-alumina ratio of about 12, pore size of about 0.38 nm) microparticles (particle size of about 5 μm) were activated at 500℃ for 3 hours for later use. Preparation of the monomer phase: Sodium styrene sulfonate (purity ≥99%) was dissolved in a mixed solvent of deionized water and anhydrous ethanol (volume ratio 1:1) to prepare a solution with a mass fraction of approximately 45%; divinylbenzene (industrial grade, purity ≥80%) (divinylbenzene accounts for 15wt% of the total mass of sodium styrene sulfonate and divinylbenzene) was added to this solution; benzoyl peroxide (BPO) (BPO accounts for 0.8wt% of the total mass of sodium styrene sulfonate and divinylbenzene) was added, and the mixture was stirred until completely dispersed; the activated molecular sieve particles were dispersed in the above monomer phase at a mass ratio of molecular sieve:(sodium styrene sulfonate + divinylbenzene) = 1:2, and the mixture was ultrasonically dispersed for 15 min to achieve uniform dispersion; Preparation of the aqueous phase: Add polyvinyl alcohol (PVA-1788) and NaCl to deionized water and dissolve completely to obtain the aqueous phase (polyvinyl alcohol mass concentration 2.0 wt%, NaCl mass concentration 5.0 wt%). The monomer phase was slowly added to the aqueous phase (volume ratio of aqueous phase to monomer phase was 3:1) under stirring at 800 r / min. Nitrogen gas was introduced for protection, and the temperature was raised to 75℃ and maintained for polymerization for 6 hours. Then the temperature was raised to 90℃ and maintained for 2 hours for ripening. After polymerization, spherical particles were filtered out and washed repeatedly with deionized water. The particles were placed in 1.0 mol / L hydrochloric acid and stirred and soaked at room temperature for 2 hours to convert them to the hydrogen form. Then they were washed with deionized water until the pH of the washing solution was 5-7. They were dried in a vacuum drying oven at 80℃ to constant weight to obtain acid-resistant composite water-absorbing particles.

[0032] The acid-resistant composite absorbent granules are activated for the first time at 120℃ and approximately 5kPa under vacuum for 3 hours before use.

[0033] Example 1 The method for treating methyl methacrylate wastewater in this embodiment uses a reactive distillation column that is sequentially provided from top to bottom with a rectification section, an extraction section, a reaction section, and a stripping section. A baffle is provided at the bottom of the column to separate a side-stream rectification section and a common stripping section.

[0034] Methyl methacrylate wastewater (acetic acid concentration of 13%) was added from the top of the reaction section at a rate of 5000 kg / h; industrial-grade methanol was added from the middle of the reaction section at a rate of 520 kg / h, with a molar ratio of methanol to acetic acid of approximately 1.5:1; the feed temperature for both was 30°C. The reaction section was filled with a catalytic-water-absorbing bifunctional packing system, repeatedly filled from bottom to top in the order of "supporting packing layer - bifunctional packing layer - supporting packing layer - bifunctional packing layer," with adjacent bifunctional packing layers separated by supporting packing layers. The bifunctional packing layer consisted of a mixture of solid acid catalytic particles and acid-resistant composite water-absorbing particles, with a volume ratio of 40:40:20 for the solid acid catalytic particles (zirconia sulfate with a temperature resistance of not less than 180°C), the acid-resistant composite water-absorbing particles (preparation example 1, filled after initial activation), and the supporting packing (ceramic Raschig rings). In this embodiment, the reactive distillation column has a diameter of 1.0m and a total height of 6m in the reaction section (3m each in the upper and lower reaction zones). Based on theoretical plates, there are approximately 8 rectification plates, 6 extraction plates, 12 reaction plates, 10 stripping plates, and 8 side-stream rectification plates. The combined volumetric flow rate of wastewater and methanol liquid feed is approximately 5.8 m³ / h, and the liquid hourly space velocity (LHSV, based on the feed volumetric flow rate and the volume of solid acid catalyst particles packed) is approximately 3.1 h⁻¹. - ¹, The residence time of the liquid phase in the reaction section is approximately 10-15 minutes. Operation is at atmospheric pressure. The temperature at the top of the reaction section is 72℃, and the temperature at the bottom is 85℃; the reflux ratio at the top of the column is 3, and the temperature at the top of the column is 58℃; the reflux ratio at the side stream is 1.5, and the temperature at the top of the side stream is 64℃; the temperature at the bottom of the column is 100-105℃; the cross-sectional area ratio of the stripping section to the rectification section is 3.4:1.

[0035] After approximately 16 hours of operation, the lower reaction zone reached near-saturation (based on the water content at the lower reaction zone outlet). It was then isolated and connected to the gas and liquid phase bypass pipes, allowing the upper reaction zone to handle the reaction online. Subsequently, the acid-resistant composite absorbent particles underwent single-stage regeneration: 160°C superheated methanol vapor was introduced, and the pressure in the zone was reduced to approximately 5 kPa. Desorption was carried out for approximately 0.8 hours, removing water from the silica mesopores and molecular sieve channels. The desorbed water was led to the regeneration condenser via an independent regeneration loop, while methanol was recycled and the water was added to the bottom of the column. The entire process lasted approximately 1.5 hours, during which the purity of the top product and the acetic acid conversion rate remained relatively stable. The upper and lower reaction zones were operated alternately.

[0036] In this example, the acetic acid conversion rate was measured to be approximately 92.0%, and the mass fraction of methyl acetate product at the top of the column was approximately 99.0%.

[0037] Examples 2-4 Examples 2-4 are basically the same as Example 1, except that the feed rate is adjusted to change the liquid hourly space velocity. The acetic acid conversion rates of each example are shown in Table 1.

[0038] Table 1. Variation of acetic acid conversion rate with liquid hourly space velocity in Examples 1-4

[0039] As shown in Table 1, in Examples 1-4, the acetic acid conversion rate increased with decreasing liquid hourly space velocity (prolonged residence time), reaching a peak at approximately 3.1 h. - ¹(Example 1) After that, it tends to level off and approach the equilibrium conversion level driven by dehydration.

[0040] Example 5 Example 5 is basically the same as Example 1, except that the molar ratio of methanol to acetic acid is reduced to 1.2:1 (wastewater feed 5000 kg / h, industrial methanol feed 416 kg / h), and the volume ratio of solid acid catalyst particles (zirconia sulfate with a temperature resistance of not less than 180℃), acid-resistant composite water-absorbing particles (preparation example 1, loaded after initial activation) and supporting filler (ceramic Raschig ring) in the catalytic-water-absorbing bifunctional packing system is 30:50:20.

[0041] In this embodiment, thanks to enhanced dehydration, the acetic acid conversion rate still reached 88.5% at near stoichiometric ratios, the mass fraction of methyl acetate product at the top of the tower was about 99.0%, the dual-zone switching cycle was about 20 hours, and the methanol circulation load was further reduced compared to Example 1.

[0042] Example 6 Example 6 is basically the same as Example 1, except that the methanol is replaced with industrially recovered crude methanol (actual composition: 85% methanol, 14% water, 1% impurities).

[0043] In this embodiment, the acetic acid conversion rate is approximately 91.0%, and the mass fraction of methyl acetate product at the top of the column is approximately 99.0%. Due to the water introduced by the crude methanol, the water absorption load increases slightly, and the switching cycle is shortened from approximately 16 hours to approximately 13 hours, but it is still within the range of 12-24 hours of continuous operation. The use of industrial recovery of crude methanol can reduce raw material costs.

[0044] Example 7 Example 7 is basically the same as Example 1, except that the volume ratio of acid-resistant composite absorbent particles increases from 30% to 50% along the reaction section from top to bottom (Example 1 is a uniform 40%).

[0045] In this example, the acetic acid conversion rate was approximately 93.5%, and the mass fraction of methyl acetate product at the top of the column was approximately 99.2%.

[0046] Example 8 Example 8 is basically the same as Example 1, except that: the acid-resistant composite water-absorbing particles are the same as those prepared in Example 2; in order to adapt to the upper limit of the temperature resistance of the acid-resistant composite water-absorbing particle matrix of about 130°C, the acid-resistant composite water-absorbing particles and solid acid catalyst particles are layered and filled, and the regeneration is carried out in stages: the first stage is competitive replacement with superheated methanol vapor at 110°C, and the second stage is extended desorption by vacuuming at 125°C.

[0047] In this embodiment, the acid-resistant composite water-absorbing particles prepared in Preparation 2 are used with sulfonated polystyrene-divinylbenzene as the matrix. Due to their high water absorption, a high acetic acid conversion rate of 94.0% is obtained, the mass fraction of methyl acetate product at the top of the tower is about 99.0%, and the dual-zone switching cycle is about 20 hours.

[0048] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that: the reaction section is only filled with solid acid catalyst particles and supporting filler, without filling with acid-resistant composite water-absorbing particles, and there is no dual reaction zone switching.

[0049] In this comparative example, under the condition of methanol:acetic acid = 1.5:1, the water activity in the reaction zone was high, the acetic acid conversion rate was only about 77.6%, and the mass fraction of methyl acetate product at the top of the column was about 95.8%. To achieve the same effect as in Example 1, the methanol:acetic acid ratio needs to be increased to 3:1 or higher, which would lead to an increase in the side-stream methanol recovery load and the reboiler energy consumption.

[0050] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that: single acid-resistant high-silica zeolite molded particles are used instead of acid-resistant composite water-absorbing particles.

[0051] In this comparative example, the acetic acid conversion rate was approximately 88.5%, the mass fraction of methyl acetate product at the top of the column was approximately 99.0%, the switching cycle was shortened to approximately 6 hours, and regeneration was frequent.

[0052] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that the acid-resistant composite absorbent particles are replaced by a single sulfonated polystyrene-divinylphenyl body (without acid-resistant molecular sieve particles).

[0053] In this comparative example, single sulfonated polystyrene-divinylphenyl body was used as the acid-resistant composite water-absorbing particles. Although its water absorption capacity was high, it lacked the polar sieving effect of molecular sieves, resulting in increased non-selective methanol entrainment. This led to increased methanol recycling losses and a heavier burden on the overhead distillation separation. The acetic acid conversion rate was approximately 89.0%, and the mass fraction of methyl acetate product at the top of the column dropped to approximately 97.0%. The dual-zone switching cycle was approximately 22 hours.

[0054] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating methyl methacrylate wastewater, characterized in that, The method is carried out in a reactive distillation column, which is provided from top to bottom with a rectification section, an extraction section, a reaction section, and a stripping section, and is divided into a side-stream rectification section by a baffle at the bottom of the column and a common stripping section at the bottom of the column. The method includes the following steps: (1) Feeding: Methyl methacrylate wastewater is added from above the reaction section and flows from top to bottom; methanol is added from the middle of the reaction section; the two are in countercurrent contact within the reaction section; (2) Reaction and dehydration: The reaction section is filled with a catalytic-water-absorbing dual-function packing system, which consists of solid acid catalytic particles, acid-resistant composite water-absorbing particles and supporting packing. (3) Extraction and distillation purification: The methyl acetate generated in step (2) enters the extraction section with the rising vapor and is extracted by the acetic acid in the wastewater to remove the methanol and water it carries. After the trace amount of acetic acid is removed by the distillation section, the methyl acetate product is collected at the top of the tower. (4) Distillation, side stream recovery and bottom product: The liquid phase below the reaction section is stripped of a small amount of methyl acetate in the distillation section, and a mixture containing water and methanol is obtained at the bottom of the partition; one of the mixture is recycled back to the methanol feed in step (1) by collecting methanol at the top of the side stream through the side stream rectification section; the other is recycled back to the bottom of the tower by collecting wastewater through the common distillation section. The molar ratio of methanol to acetic acid in the methyl methacrylate wastewater is 1.2:1 to 1.8:

1.

2. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The acetic acid concentration in the methyl methacrylate wastewater is 10-15%.

3. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The acid-resistant composite absorbent particles comprise a continuous phase matrix and acid-resistant microporous molecular sieve particles uniformly distributed therein; the continuous phase matrix is ​​one of the following: (A) a silica inorganic binder phase formed by calcination and solidification of silica sol; (B) a sulfonated polystyrene-divinylbenzene network formed by copolymerization of styrene sulfonate and divinylbenzene; the acid-resistant microporous molecular sieve particles are high-silica zeolite or silica-alumina molecular sieves.

4. The method for treating methyl methacrylate wastewater according to claim 3, characterized in that, When the continuous phase matrix is ​​a silica inorganic binder phase, the preparation method of the acid-resistant composite absorbent particles includes the following steps: (a) activating the acid-resistant microporous molecular sieve microparticles at 400-550℃ for 2-4 hours, and setting them aside; (b) mixing the activated molecular sieve microparticles with silica sol at a molecular sieve to silica dry basis mass ratio of (1-4):1, adding a pore-forming agent and deionized water to form a formable slurry; (c) granulating or extruding the slurry, drying it at 80-120℃, and then calcining it at 500-550℃ for 2-4 hours to obtain the acid-resistant composite absorbent particles.

5. The method for treating methyl methacrylate wastewater according to claim 3, characterized in that, When the continuous phase matrix is ​​a sulfonated polystyrene-divinylbenzene network, the preparation method of the acid-resistant composite absorbent particles includes the following steps: (a) activating the acid-resistant microporous molecular sieve microparticles at 400-550℃ for later use; (b) preparing a monomer phase containing sodium styrene sulfonate, divinylbenzene and a free radical initiator, wherein divinylbenzene accounts for 12-20% of the total monomer content, and dispersing the molecular sieve microparticles in the monomer phase; (c) molding the particles into particles by suspension polymerization; (d) washing the particles with dilute acid to convert them to the hydrogen form, washing them with water until neutral, and drying them to obtain the acid-resistant composite absorbent particles.

6. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, In the catalytic-water-absorbing bifunctional packing system, the volume ratio of solid acid catalytic particles, acid-resistant composite water-absorbing particles and supporting packing is (30-50):(30-50):(10-20).

7. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The volume percentage of the acid-resistant composite absorbent particles gradually increases from top to bottom along the reaction section.

8. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The solid acid catalyst particles are selected from zirconium oxide sulfate or heteropolyacid supported particles with a temperature resistance of not less than 180℃.

9. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The reaction section is divided into an upper reaction zone and a lower reaction zone along the height of the tower. The upper and lower reaction zones are independently isolated and bypassed. Each zone is equipped with an independent gas phase bypass pipe, a liquid phase bypass pipe, and regeneration medium inlet and outlet pipelines.

10. The method for treating methyl methacrylate wastewater according to claim 1, characterized in that, The method is operated at atmospheric pressure and meets one or more of the following conditions: the upper temperature of the reaction section is 70-75℃, the lower temperature is 80-90℃; the top temperature of the column is 50-70℃, and the top reflux ratio is 0.5-10; the top temperature of the side stream is 62-66℃, and the side stream reflux ratio is 1-3; the bottom temperature of the column is 90-110℃; both the wastewater and methanol are liquid-phase feeds with a feed temperature of 20-50℃; and the liquid hourly space velocity is 2-6 h⁻¹. - ¹.

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