A method for continuously and efficiently synthesizing high-purity TMPTMA with a belt-free water agent

Abstract

This invention belongs to the field of organic synthesis technology, specifically relating to a method for the efficient continuous-flow synthesis of high-purity TMPTMA without the need for a water-carrying agent. The method employs a continuous-flow closed-loop reaction system, using trimethylolpropane (TMP) and methacrylic acid (MA) as raw materials, and SO42-. 2‑ Using a ZrO2-TiO2-Al2O3 composite solid acid as a dedicated catalyst and phenothiazine-hydroquinone-p-methoxyphenol as a composite polymerization inhibitor, this invention achieves efficient and continuous synthesis of TMPTMA through an integrated process encompassing raw material pretreatment, continuous flow reaction system construction and commissioning, continuous feeding and continuous flow reaction, in-situ pervaporation dehydration, catalyst separation and crude product purification, and product testing and collection. This invention generates no acidic wastewater, is a green, efficient, and stable process, and features a simple equipment structure, making it easy to scale up for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for efficient continuous flow synthesis of high-purity TMPTMA without the need for a water-carrying agent. Background Technology

[0002] Trimethylolpropane trimethacrylate (TMPTMA), as a high-performance multifunctional crosslinking monomer, plays a key role in high-end fields such as photocurable coatings, UV inks, electronic packaging resins, and 3D printing materials. Its purity, color, and stability directly affect the performance and quality of end products.

[0003] Currently, the industrial synthesis of TMPTMA commonly employs a traditional batch reaction process, relying on dehydrating agents such as toluene and cyclohexane to remove water generated during esterification via an azeotropic process. This traditional process suffers from several inherent drawbacks: the use of flammable and volatile organic dehydrating agents poses high safety risks; the reaction generates organic wastewater containing acidic catalysts, which is difficult and costly to treat, and environmentally unfriendly; the batch operation results in long reaction cycles, and auxiliary processes such as material loading and unloading, heating and cooling, and dehydrating agent recovery are time-consuming, making continuous and large-scale production difficult. Limited by the mass and heat transfer efficiency and side reaction control of traditional processes, product purity is typically no higher than 97%, yield is generally below 88%, and the color tends to be yellowish, failing to meet the stringent requirements of high-end applications for colorless transparency and high purity. The addition, separation, and recovery of dehydrating agents further increase operational steps, equipment investment, and energy consumption.

[0004] To avoid the problem of dehydrating agents, some improved processes have attempted to use batch synthesis without dehydrating agents, but they have not yet overcome the fundamental bottleneck of batch operation: low reaction efficiency, inaccurate process control, large fluctuations in product quality, and may still face the problem of incomplete dehydration leading to low conversion rate. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the efficient continuous-flow synthesis of high-purity TMPTMA without the need for a dehydrating agent, thereby overcoming the shortcomings of existing technologies. This method employs a continuous-flow closed-loop reaction system, using trimethylolpropane (TMP) and methacrylic acid (MA) as core raw materials, a sulfate / zirconia-titanium dioxide-alumina composite solid acid as a dedicated catalyst, and phenothiazine-hydroquinone-p-methoxyphenol as a composite polymerization inhibitor. No dehydrating agent is required. The efficient synthesis of TMPTMA is achieved through an integrated process encompassing raw material pretreatment, system setup and debugging, continuous reaction, separation and purification, and product testing and collection.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a method for efficient continuous flow synthesis of TMPTMA without water-carrying agent, wherein trimethylolpropane, methacrylic acid, composite solid acid catalyst and composite polymerization inhibitor are mixed evenly and continuously subjected to isothermal esterification reaction, and in-situ pervaporation dehydration is carried out during the reaction. The composite solid acid catalyst is SO4. 2- / ZrO2-TiO2-Al2O3 composite solid acid catalyst; The composite polymerization inhibitor is a phenothiazine-hydroquinone-p-methoxyphenol composite polymerization inhibitor.

[0008] In some other embodiments, the water content of the trimethylolpropane is ≤0.03 wt%, and the water content of the methacrylic acid is ≤0.02 wt%. The molar ratio of trimethylolpropane to methacrylic acid is 1:(3.3-3.7).

[0009] Specifically, the molar ratio of trimethylolpropane to methacrylic acid is any one of 1:3.3, 1:3.5, or 1:3.7, within which methacrylic acid is in appropriate excess to ensure that the hydroxyl groups of trimethylolpropane are fully and efficiently esterified, thereby obtaining the target esterified product with high yield, high purity, and controllable acid value.

[0010] In some other embodiments, the composite solid acid catalyst is used in an amount of 4-6% of the total mass; Specifically, the amount of composite solid acid catalyst used is any value or range of 4%, 5%, or 6% of the total mass of the mixture. Composite catalysts within this range provide sufficient and controllable catalytic activity for the reaction, ensuring efficient reaction acceleration while also considering process economy, ease of post-processing, and the potential value of catalyst recyclability.

[0011] The SO4 2- The preparation method of the ZrO2-TiO2-Al2O3 composite solid acid catalyst is as follows: Zirconium oxychloride octahydrate, titanium sulfate, and aluminum nitrate nonahydrate were dissolved in deionized water to prepare a mixed solution. The pH of the mixed solution was adjusted to 1.8-2.8, and the solution was hydrolyzed by stirring at room temperature. After standing for aging and drying to crystallize, the solution was immersed in sulfuric acid solution, filtered, dried, and calcined to obtain the final product.

[0012] In some other embodiments, the mixing mass ratio of zirconium oxychloride octahydrate, titanium sulfate and aluminum nitrate nonahydrate is 1: (0.4-0.6): (0.2-0.3); the hydrolysis time is 3-5 h, and the aging is carried out at a constant temperature of 25±2 ℃ for 14-18 h; The concentration of the sulfuric acid solution is 0.6-1.2 mol / L, and the impregnation time is 5-7 h; the calcination temperature is 550-650℃, and the time is 3-4 h.

[0013] Specifically, the mixing mass ratio of zirconium oxychloride octahydrate, titanium sulfate, and aluminum nitrate nonahydrate is any one or a range of 1:0.4:0.2, 1:0.4:0.3, 1:0.5:0.2, 1:0.5:0.3, 1:0.6:0.2, or 1:0.6:0.3; the hydrolysis time is any one or a range of 3, 4, or 5 h; and the aging is any one or a range of aging at a constant temperature of 25±2 ℃ for 14, 15, 16, or 18 h. The concentration of the sulfuric acid solution is any value or range of 0.6, 0.8, 1.0 or 1.2 mol / L, the immersion time is any value or range of 5, 6 or 7 h, the calcination temperature is any value or range of 550, 600 or 650℃, and the calcination time is any value or range of 3, 3.5 or 4 h.

[0014] In some other embodiments, the amount of the composite polymerization inhibitor added is 0.10%-0.15% of the mass of methacrylic acid.

[0015] The mass ratio of phenothiazine, hydroquinone, and p-methoxyphenol in the phenothiazine-hydroquinone-p-methoxyphenol composite polymerization inhibitor is 1:(0.8-1.2):(0.3-0.5).

[0016] Specifically, the amount of composite polymerization inhibitor added is any value or range between 0.10% and 0.15% of the mass of methacrylic acid. This value can effectively inhibit premature thermal polymerization or free radical polymerization of double bonds in methacrylic acid, ensuring the safety and stability of raw materials and reaction processes, while minimizing the negative impact of the polymerization inhibitor on the purity, color, and catalytic reaction of subsequent products.

[0017] In the phenothiazine-hydroquinone-p-methoxyphenol composite polymerization inhibitor, the mass ratio of phenothiazine, hydroquinone, and p-methoxyphenol is any value or range within the range of 1:0.8:0.3, 1:1:0.4, or 1:1.2:0.5. Phenothiazine, as the primary polymerization inhibitor, exhibits excellent high-temperature resistance; hydroquinone is a highly efficient room-temperature polymerization inhibitor that can rapidly capture free radicals; and p-methoxyphenol provides a supplementary effect in terms of moderate temperature and solubility. By adjusting the ratio of the three components, different temperature stages from room temperature storage to high-temperature reaction can be precisely covered, broadening the effective polymerization inhibition temperature window.

[0018] In some other embodiments, the isothermal esterification reaction is carried out at a temperature of 90-110°C for a time of 104-134 min.

[0019] Specifically, the isothermal esterification reaction is carried out at temperatures of 90, 100, or 110°C for 104, 110, 119, 125, 130, or 134 min. These values ​​provide a stable operating window, allowing for fine-tuning based on actual operating conditions (such as catalyst activity and feed ratio) while ensuring product quality and yield, thus achieving efficient, stable, and controllable production.

[0020] In some other embodiments, the following post-processing and material recycling steps are also included after the reaction is complete: The reaction material is subjected to solid-liquid separation to remove the composite solid acid catalyst and composite polymerization inhibitor, and a crude reaction product is obtained. The crude reaction product is then subjected to thin-film evaporation to separate and recover unreacted methacrylic acid. The crude product after thin-film evaporation is then subjected to adsorption and filtration to obtain trimethylolpropane trimethacrylate. The recovered methacrylic acid is then adsorbed and purified for reuse as a raw material.

[0021] On the other hand, the present invention provides a system for the efficient synthesis of TMPTMA through continuous flow without water-carrying agent. The system is a continuous flow closed-loop system, including a feeding device, a static mixer, a continuous flow reactor, an in-situ pervaporation dehydration device, a catalyst separation device, a thin film evaporation, an adsorption-filtration coupled purification device, and a product collection device connected in sequence.

[0022] In some other embodiments, the adsorption-filtration coupled purification device is connected to the feeding device.

[0023] The in-situ pervaporation dehydration device is a specialized device for real-time removal of water generated during esterification reactions. It is directly installed between the outlet of the continuous flow reactor and the catalyst separation device, and is seamlessly connected to the upstream and downstream devices through corrosion-resistant polytetrafluoroethylene pipelines, realizing continuous dehydration operation without interrupting material flow or introducing any impurities during the reaction process.

[0024] The in-situ pervaporation dehydration device is a specialized device for real-time removal of water generated during esterification reactions. It is directly installed between the outlet of the continuous flow reactor and the catalyst separation device, and is seamlessly connected to the upstream and downstream devices through corrosion-resistant polytetrafluoroethylene pipelines, realizing continuous dehydration operation without interrupting material flow or introducing any impurities during the reaction process.

[0025] In some other embodiments, the adsorption-filtration coupled purification device includes an adsorption column and a filter. The adsorbent used in the adsorption column is an activated carbon-activated alumina composite adsorbent with a particle size of 0.5-1 mm, and the filter is a ceramic membrane filter with a pore size of 0.05 μm.

[0026] The beneficial effects of this invention are: (1) This invention completely eliminates the safety risks, environmental pollution and product residue problems caused by traditional water-carrying agents by completely abandoning water-carrying agents and combining them with in-situ permeation vaporization real-time dehydration process. No acidic wastewater is generated during the reaction process, which is in line with the development trend of green chemical industry and clean production.

[0027] (2) An integrated continuous flow closed-loop reaction design is adopted to enhance mass and heat transfer efficiency, significantly shorten the reaction cycle (by more than 75% compared to traditional processes), support continuous and large-scale production, and significantly improve overall production efficiency. The process flow is simplified, equipment wear is low, and operation is convenient. The purification unit is highly compatible with the continuous flow system, requiring no complex post-processing, which facilitates rapid industrialization and large-scale application.

[0028] (3) By recycling raw materials and catalysts, optimizing continuous flow processes, and employing low-energy thin-film evaporation and adsorption-filtration coupled purification technologies, the system's energy consumption is reduced by 30–35%, and the overall production cost is reduced by 20–27%, resulting in significant economic benefits. Under the synergistic effect of a dedicated high-activity composite catalyst and a ternary composite polymerization inhibitor system, side reactions are effectively suppressed, and the product purity remains stable at ≥99.2% and the yield is ≥94.5%. Combined with the adsorption-filtration coupled purification method, precise color control can be achieved, and the product remains colorless and transparent for a long time, meeting the requirements of high-end application fields. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a schematic diagram of material flow in the continuous flow closed-loop reaction system of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the continuous flow closed-loop reaction system in Embodiment 1 of the present invention. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] As mentioned earlier, existing batch-type TMPTMA synthesis processes using a water-carrying agent are inefficient, produce poor product purity, involve numerous side reactions, pose significant environmental risks, and present substantial safety hazards. This invention provides a continuous-flow, high-efficiency method for synthesizing high-purity TMPTMA without a water-carrying agent. By optimizing the continuous-flow reaction system design, developing a dedicated high-efficiency catalyst, innovating an in-situ dehydration process, and optimizing reaction parameters, this method abandons the segmented structure and achieves continuous, efficient, and green synthesis of TMPTMA without a water-carrying agent. This improves product purity and yield, reduces energy consumption and environmental pressure, eliminates the safety hazards associated with water-carrying agents, simplifies equipment structure, and meets the needs of industrial-scale production and high-end applications.

[0033] Example 1 This embodiment provides a method for efficient continuous-flow synthesis of high-purity TMPTMA without the need for a water-carrying agent, specifically including the following steps: Step 1: Raw material pretreatment Trimethylolpropane (TMP) and methacrylic acid (MA) were subjected to deep dehydration treatment to control the water content of TMP to ≤0.03wt% and the water content of MA to ≤0.02wt%.

[0034] The dedicated composite solid acid catalyst for TMPTMA synthesis is a sulfate / zirconia-titanium dioxide-alumina composite catalyst (SO4). 2- The preparation method of the / ZrO2-TiO2-Al2O3 composite catalyst is as follows: Zirconium oxychloride octahydrate (ZrOCl2·8H2O), titanium sulfate (Ti(SO4)2), and aluminum nitrate nonahydrate (Al(NO3)3·9H2O) were dissolved in deionized water at a mass ratio of 1:0.5:0.25. The pH was slowly adjusted to 2.3 using dilute nitric acid or dilute ammonia. The mixture was hydrolyzed at room temperature with stirring for 4 hours. It was then placed in a constant temperature incubator and aged at 25±2℃ for 15 hours. After drying and crystallization, the crystals were immersed in 0.9mol / L sulfuric acid (H2SO4) solution for 6 hours. The crystals were then filtered, dried, and calcined (600℃, 3.5 hours) to obtain the final product.

[0035] The composite polymerization inhibitor is phenothiazine-hydroquinone-p-methoxyphenol, wherein the mass ratio of phenothiazine, hydroquinone, and p-methoxyphenol is 1.0:1.0:0.4.

[0036] Step 2: Construction and commissioning of the continuous flow reaction system like Figure 1 and Figure 2As shown, the continuous flow reaction system, arranged in the material flow direction, includes a feed device, a static mixer, a continuous flow reactor, an in-situ pervaporation dehydration device, a catalyst separation device, a thin-film evaporation-adsorption-filtration coupled purification device, and a product collection device, connected sequentially via corrosion-resistant polytetrafluoroethylene pipelines. All components of the continuous flow reaction system can utilize existing, corresponding equipment. The specific structural composition and parameters are as follows: (1) Feeding device Structure: The storage tank adopts a double-layer jacket structure, with an outer insulation layer and an inner layer made of 316L stainless steel. The inner wall of the tank is polished (roughness Ra≤0.8μm) to avoid raw material residue and contamination.

[0037] Performance limitations: Metering pump accuracy ≤ ±0.5%, feed flow rate adjustment range 0.5-5 mL / min, enabling continuous and stable feeding; storage tank volume 5-10L, working pressure 0.1-0.3MPa, resistant to MA, TMP and catalyst corrosion, leak-free; pre-filter can trap solid impurities with a particle size ≥ 0.2μm, ensuring feed purity and meeting the purity requirements after raw material pretreatment.

[0038] (2) Static mixer Structure: It adopts a static mixer made of 316L stainless steel. The two ends of the mixer are connected by flanges, which are compatible with the polytetrafluoroethylene pipelines at the outlet of the feed device and the inlet of the continuous flow reactor.

[0039] Performance limitations: Mixing efficiency ≥98%, capable of rapidly and uniformly mixing TMP, MA, catalyst and polymerization inhibitor without material stratification; operating temperature range 50-150℃, operating pressure 0.1-0.5MPa, strong corrosion resistance, no material adsorption residue; pressure drop ≤0.02MPa, does not affect continuous material flow, suitable for subsequent continuous flow reaction requirements.

[0040] (3) Continuous flow reactor Structure: The reactor is a tubular continuous flow reactor made of 316L stainless steel. It adopts a serpentine tube structure (to meet the needs of industrial mass and heat transfer). The reactor is equipped with a constant temperature jacket with heat transfer oil flowing through it to achieve precise temperature control. A material distributor is installed at the reactor inlet and a pressure buffer is installed at the outlet to prevent material backflow and pressure fluctuations. The reactor has a built-in temperature sensor to monitor the reaction temperature in real time.

[0041] Performance limitations: Operating temperature range 80-130℃, with precise temperature control (accuracy ±1℃), suitable for reaction requirements of 90-110℃; operating pressure 0.1-0.6MPa, leak-free and deformation-free; serpentine tube structure enhances mass and heat transfer, reduces side reactions, and material residence time can be adjusted by flow rate to meet residence time requirements of 104-134min; resistant to corrosion in esterification reaction systems, with a service life ≥5000h.

[0042] (4) In-situ pervaporation dehydration device Structure: The membrane shell is made of 316L stainless steel. The feed chamber and the permeation chamber are separated by a sealing gasket to prevent the material from mixing with the permeation water. The device is equipped with a feed preheating module, and the preheating temperature is the same as the reaction temperature.

[0043] Performance limitations: Dehydration temperature 100-110℃, vacuum degree 0.092-0.095MPa, dehydration rate ≥0.8g / (m²·h), dehydration rate ≥99%, capable of removing water generated in the reaction in real time, promoting the forward reaction; the pervaporation membrane has a water selectivity of ≥99.5%, does not adsorb TMP, MA and TMPTMA products, and has no product loss; the dual membrane modules can be used alternately, which is convenient for maintenance, and the membrane module service life is ≥1000h.

[0044] (5) Catalyst separation unit Structure: It adopts a ceramic membrane filter made of silicon carbide ceramic to achieve efficient separation of catalyst and reaction liquid. The separated catalyst can be recycled after activation.

[0045] Performance requirements: Filtration efficiency ≥ 99.8%, capable of completely separating SO4 from the reaction system. 2- / ZrO2-TiO2-Al2O3 composite catalyst (particle size ≥0.5μm), catalyst residue in the filtered material ≤0.01wt%; operating temperature 40-120℃, operating pressure 0.1-0.4MPa, strong corrosion resistance, can withstand the erosion of catalyst and reaction system; backwashing cycle ≥24h, filtration efficiency restored to ≥99.5% after backwashing, suitable for continuous production requirements.

[0046] (6) Thin-film evaporation-adsorption-filtration coupled purification device The device is an integrated structure, consisting of a thin-film evaporation unit and an adsorption-filtration unit, which are connected in series. ① Thin-film evaporation unit: Employs a 316L stainless steel scraped-film evaporator with heat transfer oil heating. Equipped with a steam condensation chamber and unreacted MA recovery pipeline, it efficiently recovers unreacted raw materials, preventing material carbonization. Performance specifications: Evaporation temperature 80-100℃, vacuum degree 0.08-0.09MPa, unreacted MA recovery rate ≥98%, MA residue in crude product after evaporation ≤0.5wt%, uniform heating, and no material carbonization.

[0047] ② Adsorption-Filtration Unit: Composed of a 316L stainless steel fixed-bed adsorption column (filled with activated carbon-activated alumina composite adsorbent) connected in series with a high-precision ceramic membrane filter, it effectively removes residual polymerization inhibitors, colored impurities, and trace solid particles, ensuring material clarity. Performance Limitations: Adsorption column feed flow rate 1-2 mL / min, adsorption temperature 40-50℃, adsorption efficiency ≥99%, effectively removing residual polymerization inhibitors, trace impurities, and colored substances from crude products; ceramic membrane filtration accuracy ≤0.05μm, removing adsorbent dust and trace solid impurities, resulting in a clear and transparent material free of suspended solids.

[0048] (7) Product collection device Structure: It adopts a 316L stainless steel double-layer jacketed storage tank with polished inner wall. The top is equipped with a feed port and a vacuum exhaust port, and the bottom is equipped with a discharge port and a sampling port. Cooling water is circulated through the jacket to achieve cooling storage, and a liquid level sensor is installed inside the tank to monitor the storage volume in real time.

[0049] Performance limitations: Operating temperature 20-40℃, can cool the purified product to room temperature for storage to prevent product deterioration; operating pressure 0.1MPa (atmospheric pressure storage), no leakage, no volatilization; resistant to TMPTMA corrosion, no product adsorption residue, sampling port can achieve sampling and testing at any time; liquid level sensor accuracy ±1%, can provide real-time feedback on product collection volume, adaptable to continuous discharge requirements.

[0050] (8) Corrosion-resistant polytetrafluoroethylene pipeline Structure: The pipeline material is polytetrafluoroethylene (PTFE), and PTFE gaskets and flanges are used at pipeline connections to prevent material leakage; the pipeline length is reasonably set according to the equipment layout, and curved elbows are used at bends to avoid material stagnation.

[0051] Performance limitations: Temperature range -20~200℃, adaptable to the operating temperature requirements of various devices in the system; resistant to corrosion by MA, TMP, catalysts and TMPTMA products, with no swelling or aging; smooth inner wall of pipeline, no material adsorption residue, low pressure drop, and does not affect the continuous flow of materials; service life ≥3000h, good sealing performance, and leakage rate ≤0.001mL / h.

[0052] After the system is built, airtightness testing and parameter debugging are carried out to ensure that the system is leak-free, temperature is stable, and material flow is smooth. The dehydration efficiency of the in-situ pervaporation dehydration device, the membrane evaporation separation effect, and the adsorption-filtration coupling purification effect of the adsorption-filtration coupling purification device all meet the reaction and product quality requirements, ensuring that the product purity meets the standards and is colorless and transparent.

[0053] Before using the continuous flow reaction system, an airtightness test and parameter adjustment are performed to ensure that the system is leak-free, temperature is stable, and material flow is smooth. This ensures that the dehydration efficiency of the in-situ pervaporation dehydration device, the membrane evaporation separation, and the adsorption-filtration effect of the adsorption-filtration coupled purification device all meet the requirements of the reaction and product quality, ensuring that the product purity meets the standards and is colorless and transparent.

[0054] Step 3: Continuous Feeding and Continuous Flow Reaction Pretreated TMP and MA (molar ratio 1:3.5), a composite polymerization inhibitor (0.12% of MA mass), and a special composite solid acid catalyst (5% of the total reaction system mass) are continuously pumped into a static mixer via a feeding device. After uniform mixing, the mixture is continuously fed into a continuous flow reactor. The reaction temperature is controlled at 100 ℃ and the residence time at 119 min for isothermal esterification. The water generated during the reaction is removed in real time by an in-situ pervaporation dehydration device without the need for a dehydrating agent, continuously driving the reaction forward.

[0055] Step 4: Catalyst separation and crude product purification After the reaction is complete, the material continuously flows out of the reactor and enters the catalyst separation unit to completely separate the special composite solid acid catalyst from the crude reaction product. The separated catalyst can be recycled up to 10 times after simple washing and reactivation, effectively reducing production costs. The crude reaction product after catalyst separation is continuously pumped into a thin-film evaporation and adsorption-filtration coupled purification unit, the specific operation of which is as follows: The crude reaction product is continuously passed through a thin-film evaporator to separate and reuse unreacted MA. It then enters an adsorption column filled with a specialized adsorbent (preferably an activated carbon-activated alumina composite adsorbent with a particle size of 0.5 mm). The feed flow rate is controlled at 1 mL / min, and the adsorption temperature is 45°C. The adsorbent adsorbs residual color from the crude product. The adsorbed material is then continuously filtered through a high-precision ceramic membrane filter (0.05 μm pore size) to remove adsorbent dust and trace solid impurities, yielding a high-purity TMPTMA product. Unreacted MA, after desorption and purification in the adsorption column, can be recycled back to the reaction system, improving raw material utilization. This method is compatible with the continuous flow process of this invention, requiring no significant modifications to existing continuous flow closed-loop systems. It is simple to operate, energy-efficient, and can accurately remove trace impurities that affect product color, ensuring a colorless and transparent product.

[0056] Test results: The product is a colorless and transparent liquid with a purity of 99.5%, an acid value of 0.07 mg KOH / g, a water content of 0.02 wt%, a TMP conversion rate of 99.4%, a TMPTMA yield of 94.8%, and no acidic wastewater is generated throughout the process.

[0057] Example 2 Unlike Example 1, in step 1, TMP and MA are subjected to deep dehydration treatment, with water contents controlled at 0.03wt% and 0.02wt%, respectively. In step 3, the molar ratio of TMP to MA is 1:3.3, and 4% of a special catalyst and 0.10% of a composite polymerization inhibitor (phenothiazine, hydroquinone, and p-methoxyphenol in a mass ratio of 1:0.8:0.3) are added to the reaction system. After the materials are mixed evenly, they are continuously fed into the reactor, with the reaction temperature controlled at 90℃ and the residence time at 104 min. The reaction water is removed in real time through an in-situ pervaporation device. In step 4, after the reaction is completed, the catalyst is separated, and the crude product is purified by thin-film evaporation and adsorption-filtration coupled purification method. Finally, the product performance and color are tested. The adsorption-filtration coupled purification method strictly controls the feed flow rate to 1mL / min and the adsorption temperature to 40℃. Activated carbon-activated alumina composite adsorbent is selected. The operation is simple, and it can efficiently remove trace impurities and polymerization inhibitor residues, completely avoiding abnormal product color. It is suitable for continuous flow industrial production. The other steps are the same as in the embodiments.

[0058] Test results: The product is a colorless and transparent liquid with a purity of 99.2%, an acid value of 0.08 mg KOH / g, a water content of 0.03wt%, a TMP conversion rate of 99.2%, a TMPTMA yield of 94.5%, and no acidic wastewater is generated throughout the process.

[0059] Comparative Example 1 This comparative example uses a traditional batch process with a water-carrying agent to prepare TMPTMA. The specific steps are as follows: Using TMP and MA in a molar ratio of 1:3.5 as raw materials, p-toluenesulfonic acid as a catalyst (2.5% of the total reaction system), cyclohexane as a dehydrating agent (200g), and phenothiazine as a polymerization inhibitor (0.10% of MA by mass), the above materials were added to a four-necked flask, stirred and mixed thoroughly, and then heated to 100℃ for an azeotropic dehydration reaction for 8 hours. After the reaction was completed, the mixture was neutralized to neutral with alkali solution, washed with water until salt-free, and then the dehydrating agent, unreacted raw materials, and byproducts were removed by vacuum distillation to obtain the TMPTMA product.

[0060] Test results: The product is yellowish in color, with a purity of 96%, an acid value of 0.36 mg KOH / g, a TMP conversion rate of 92.3%, and a TMPTMA yield of 88.1%. The reaction process generates a large amount of acidic wastewater, and the reaction cycle is long with low production efficiency.

[0061] Comparative Example 2 This comparative example uses a conventional batch process without water-carrying agent to synthesize TMPTMA. The specific steps are as follows: The types and amounts of raw materials, catalyst (p-toluenesulfonic acid), and polymerization inhibitor (phenothiazine) were the same as in Comparative Example 1. No dehydrating agents were added. The materials were directly added to a four-necked flask, and the temperature was raised to 110°C for a dehydration reaction, which lasted for 10 hours. After the reaction was completed, the TMPTMA product was obtained through neutralization, water washing, and vacuum distillation purification.

[0062] Test results: The product is yellowish in color, with a purity of 95.1%, an acid value of 0.42 mg KOH / g, a TMP conversion rate of 89.7%, a TMPTMA yield of 85.6%, and produces acidic wastewater during the reaction. The raw materials also show slight carbonization, and there are many side reactions.

[0063] Comparative Example 3 Unlike Example 1, the catalyst is a sulfate / zirconia-titanium dioxide composite catalyst (SO4). 2- The ZrO2-TiO2 composite catalyst was prepared as follows: zirconium oxychloride octahydrate (ZrOCl2·8H2O) and titanium sulfate (Ti(SO4)2) were dissolved in deionized water at a mass ratio of 1:0.5. The pH was slowly adjusted to 2.3 with dilute nitric acid, and the mixture was hydrolyzed by stirring at room temperature for 4 hours. The mixture was then placed in a constant temperature incubator and aged at 25°C for 16 hours. After drying and crystallization, the catalyst was impregnated in a 0.9 mol / L sulfuric acid (H2SO4) solution for 6 hours. The catalyst was then filtered, dried, and calcined (600°C, 3.5 hours) to obtain the final product. The amount of catalyst used was still 5% of the total mass of the reaction system, and the other steps were the same as in Example 1.

[0064] The results showed that the catalyst activity and selectivity were significantly lower than in Example 1, the reaction rate was slower, and the material residence time needed to be extended to 150 min to achieve a similar reaction progress. The final product purity was 98.3%, the acid value was 0.15 mg KOH / g, the TMP conversion rate was 97.2%, and the TMPTMA yield was 90.5%. Moreover, the catalyst activity significantly decreased after 5 cycles of use and could not be used stably. The main reason was the lack of alumina component, which reduced the catalyst stability and catalytic selectivity, increased side reactions, and led to a decrease in product purity and yield.

[0065] Comparative Example 4 Unlike Example 1, the catalyst is a sulfate / zirconia composite catalyst (SO4). 2-The preparation method of the / ZrO2 composite catalyst is as follows: Zirconium oxychloride octahydrate (ZrOCl2·8H2O) is dissolved in deionized water, the pH is slowly adjusted to 2.3 with dilute nitric acid, and hydrolyzed by stirring at room temperature for 4 hours. It is then placed in a constant temperature incubator and aged at 25°C for 16 hours. After drying and crystallization, it is impregnated in 0.9 mol / L sulfuric acid (H2SO4) solution for 6 hours, filtered, dried, and calcined (600°C, 3.5 hours) to obtain the catalyst. The amount of catalyst used is still 5% of the total mass of the reaction system, and other steps are the same as in Example 1.

[0066] The results showed that the catalyst activity decreased significantly, the reaction rate slowed down considerably, and even with the material residence time extended to 180 min, the reaction progress of Example 1 could not be achieved. The final product had a purity of 97.5%, an acid value of 0.21 mg KOH / g, a TMP conversion rate of 95.8%, and a TMPTMA yield of 88.7%. The catalyst activity decreased sharply after being recycled three times, and the product turned slightly pale yellow. The main reason was the lack of titanium dioxide and aluminum oxide components, which significantly reduced the catalyst's catalytic activity, selectivity, and stability. The increase in side reactions (such as double bond polymerization and raw material carbonization) led to a significant reduction in product quality and yield.

[0067] Comparative Example 5 Unlike Example 1, the polymerization inhibitor was phenothiazine-hydroquinone (mixed in a mass ratio of 1:1), and the amount used was still 0.12% of the mass of MA. There was no p-methoxyphenol component. The other steps were the same as in Example 1.

[0068] The results showed that the polymerization inhibition effect was poor, and slight polymerization side reactions occurred during the reaction. The crude product was pale yellow in color. After purification by adsorption-filtration coupling, the product still had a slight yellow tinge, with a purity of 98.8%, an acid value of 0.11 mgKOH / g, a TMP conversion rate of 98.5%, and a TMPTMA yield of 92.3%. Moreover, unreacted MA polymerized during the recovery process, and the recovery rate dropped to below 85%. The main reason was the lack of p-methoxyphenol component, which destroyed the synergistic polymerization inhibition effect of the ternary polymerization inhibition system and failed to effectively inhibit the double bond polymerization side reaction, resulting in abnormal product color, decreased purity and yield, and reduced raw material recovery rate.

[0069] In summary, the continuous flow synthesis method without water-carrying agent, which adopts thin-film evaporation and adsorption-filtration coupled purification method, is significantly superior to existing processes in terms of production efficiency, product purity, yield, and environmental friendliness. It effectively solves the core defects of existing processes and has outstanding technical advantages and industrial application value.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for efficient continuous flow synthesis of TMPTMA without the need for a water-carrying agent, characterized in that, Trimethylolpropane, methacrylic acid, composite solid acid catalyst and composite polymerization inhibitor are mixed evenly to form a mixture. The mixture is continuously subjected to a constant temperature esterification reaction. During the reaction, in-situ pervaporation dehydration is carried out. The composite solid acid catalyst is SO4. 2- / ZrO2-TiO2-Al2O3 composite solid acid catalyst; The composite polymerization inhibitor is a phenothiazine-hydroquinone-p-methoxyphenol composite polymerization inhibitor.

2. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 1, characterized in that, The trimethylolpropane has a water content ≤0.03 wt%, and the methacrylic acid has a water content ≤0.02 wt%. The molar ratio of trimethylolpropane to methacrylic acid is 1:(3.3-3.7).

3. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 1, characterized in that, The amount of the composite solid acid catalyst used is 4-6% of the mass of the mixture; The SO4 2- The preparation method of the ZrO2-TiO2-Al2O3 composite solid acid catalyst is as follows: Zirconium oxychloride octahydrate, titanium sulfate, and aluminum nitrate nonahydrate were dissolved in deionized water to prepare a mixed solution. The pH of the mixed solution was adjusted to 1.8-2.8, and the solution was hydrolyzed by stirring at room temperature. After standing for aging and drying to crystallize, the solution was immersed in sulfuric acid solution, filtered, dried, and calcined to obtain the final product.

4. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 3, characterized in that, The mass ratio of zirconium oxychloride octahydrate, titanium sulfate, and aluminum nitrate nonahydrate is 1: (0.4-0.6): (0.2-0.3); the hydrolysis time is 3-5 h, and the aging is carried out at a constant temperature of 25±2 ℃ for 14-18 h. The concentration of the sulfuric acid solution is 0.6-1.2 mol / L, and the impregnation time is 5-7 h; the calcination temperature is 550-650℃, and the time is 3-4 h.

5. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 1, characterized in that, The amount of the composite polymerization inhibitor added is 0.10%-0.15% of the mass of methacrylic acid; The mass ratio of phenothiazine, hydroquinone, and p-methoxyphenol in the phenothiazine-hydroquinone-p-methoxyphenol composite polymerization inhibitor is 1:(0.8-1.2):(0.3-0.5).

6. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 1, characterized in that, The isothermal esterification reaction is carried out at a temperature of 90-110℃ for a time of 104-134 min.

7. The method for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 1, characterized in that, After the reaction is complete, the following post-processing and material recycling steps are also included: The reaction material is subjected to solid-liquid separation to remove the composite solid acid catalyst and composite polymerization inhibitor, and a crude reaction product is obtained. The crude reaction product is then subjected to thin-film evaporation to separate and recover unreacted methacrylic acid. The crude product after thin-film evaporation is then subjected to adsorption and filtration to obtain trimethylolpropane trimethacrylate. The recovered methacrylic acid is then adsorbed and purified for reuse as a raw material.

8. A system for the efficient continuous flow synthesis of TMPTMA without the need for a water-carrying agent, characterized in that, The system is a continuous flow closed-loop system, which includes a feeding device, a static mixer, a continuous flow reactor, an in-situ pervaporation dehydration device, a catalyst separation device, a thin film evaporation, an adsorption-filtration coupled purification device, and a product collection device connected in sequence.

9. The system for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 8, characterized in that, The adsorption-filtration coupled purification device is connected to the feeding device.

10. The system for efficient continuous flow synthesis of TMPTMA without water-carrying agent according to claim 8, characterized in that, The adsorption-filtration coupled purification device includes an adsorption column and a filter. The adsorbent used in the adsorption column is an activated carbon-activated alumina composite adsorbent with a particle size of 0.5-1 mm. The filter is a ceramic membrane filter with a pore size of 0.03-0.06 μm.

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