Method for preparing trimethyl phosphate without adding alkali

Abstract

The invention provides a method for preparing trimethyl phosphate without adding alkali, and relates to the technical field of trimethyl phosphate preparation, dimethyl phosphate and methanol are used as raw materials, a solid acid catalyst is added, and the dosage of the solid acid catalyst is 5-6 wt% of the mass of the dimethyl phosphate; the method comprises the following steps: mixing dimethyl phosphate, methanol and a solid acid catalyst to form a uniform reaction system, wherein the molar ratio of dimethyl phosphate to methanol is 1: (3-4); under the condition of normal pressure or pressurization, the temperature of the reaction system is kept at 25-130 DEG C through heating or illumination, and transesterification reaction is carried out for 20-60 minutes; after the reaction is finished, removing by-product water generated by the reaction, and recovering unreacted methanol; and carrying out vacuum reduced pressure distillation on the separated product, collecting trimethyl phosphate fraction, decolorizing and drying to obtain a trimethyl phosphate finished product.

Description

Technical Field

[0001] This invention relates to the field of trimethyl phosphate preparation technology, specifically a method for preparing trimethyl phosphate without adding alkali. Background Technology

[0002] The current industrial preparation of trimethyl phosphate (TMP) mainly employs alkaline-catalyzed transesterification processes, including inorganic and organic alkaline catalytic systems, or concentrated sulfuric acid catalysis. These traditional methods have significant drawbacks: alkaline catalysis involves reaction times of 4-6 hours, consumes large amounts of excess methanol, and generates substantial amounts of saline wastewater (5-8 cubic meters per ton of product produced). Furthermore, the catalyst cannot be recycled, leading to complex post-treatment, severe environmental pollution, and high production costs. While concentrated sulfuric acid catalysis offers high catalytic activity, its strong corrosiveness severely damages equipment, easily causing carbonization side reactions, requiring multiple neutralization and purification processes, and resulting in poor process safety. In addition, traditional heating methods suffer from low heat transfer efficiency and high energy consumption, typically producing products with a purity of only 97-98%, which is insufficient to meet the high-purity requirements of advanced fields such as pharmaceuticals and electronics. Therefore, developing an alkali-free, low-energy-consumption, high-efficiency, and environmentally friendly TMP preparation method, enabling catalyst recycling and clean production, has significant industrial application value. Summary of the Invention

[0003] To address the above problems, this invention proposes a method for preparing trimethyl phosphate without the addition of alkali, comprising the following steps: S1. Using dimethyl phosphate and methanol as raw materials, a solid acid catalyst is added, wherein the amount of the solid acid catalyst is 5-6 wt% of the mass of dimethyl phosphate; S2. Dimethyl phosphate, methanol and solid acid catalyst are mixed to form a homogeneous reaction system, wherein the molar ratio of dimethyl phosphate to methanol is 1:3-4. S3. Under normal or pressurized conditions, maintain the temperature of the reaction system at 25-130℃ by heating or light irradiation, and carry out the transesterification reaction for 20-60 minutes. S4. After the reaction is complete, remove the water, a byproduct of the reaction, and recover the unreacted methanol. S5. The separated product is subjected to vacuum distillation to collect the trimethyl phosphate fraction, which is then decolorized and dried to obtain the trimethyl phosphate product.

[0004] Furthermore, the solid acid catalyst is selected from one or more of solid acid resins, Ti-Zr oxides, or silica-sulfonic acid-based solid acids loaded with photosensitizers.

[0005] Furthermore, in step S3, microwave heating, continuous flow heating, or UV-LED photocatalysis is used to activate the reaction; wherein the reaction temperature is 110-130℃ when microwave heating or continuous flow heating is used, and the reaction temperature is 25-30℃ when UV-LED photocatalysis is used, and no external heating device is required.

[0006] Furthermore, the solid acid catalyst is supported on the surface with an ionic liquid promoter, wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride, and the amount of the ionic liquid is 10 wt% of the solid acid catalyst.

[0007] Furthermore, in step S4, 3A or 4A molecular sieves are used to adsorb and remove the by-product water for 30-40 minutes; methanol recovery is carried out by atmospheric distillation at a recovery temperature of 64-68℃, with a methanol recovery rate of ≥95%, and the recovered methanol is directly recycled.

[0008] Furthermore, in step S5, the vacuum distillation is carried out at a vacuum degree ≤10 mmHg, a distillation temperature of 70-80℃, a moisture content ≤0.04%, and a density of 1.065-1.075 g / cm³ at 25℃. 3 .

[0009] Furthermore, the solid acid resin is Amberlyst-15 type cation exchange resin with a particle size of 0.3-1.2 mm, and the mass ratio of TiO2 to ZrO2 in the Ti-Zr oxide is 1:0.5-2.

[0010] Furthermore, when microwave heating or continuous flow heating is used, nitrogen gas is introduced into the reaction system to stabilize the pressure to 5-8 bar, so that methanol remains in the liquid phase. When continuous flow heating is used, the reaction is carried out in a microporous bed reactor with a catalyst bulk density of 0.8 g / cm³ and a material residence time of 20-30 minutes through the catalyst bed.

[0011] Furthermore, when using UV-LED photocatalysis, the particle size of the photosensitizer TiO2 in the silica-sulfonic acid solid acid loaded with photosensitizer is 20-50nm, the loading amount is 20wt% of the total mass of the catalyst, the wavelength of the UV-LED light source is 365nm, the light uniformity is ≥90%, and the temperature of the reaction system is naturally maintained at 25-30℃ through environmental heat dissipation.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention enables the green and efficient preparation of trimethyl phosphate without the need for the addition of amines or inorganic bases, completely eliminating the large amount of saline wastewater generated in traditional processes, avoiding equipment corrosion and environmental pollution, and achieving clean production.

[0013] By employing microwave, continuous flow, or photocatalytic activation technologies, the reaction time is shortened by several to tens of times compared to traditional methods, and the transesterification conversion rate and yield both reach high levels. The energy consumption is significantly lower than that of traditional processes, with the energy-saving effect of the photocatalytic route being particularly obvious. The solid acid catalyst can be recycled for a long time and maintains good activity, which greatly reduces the catalyst cost and significantly reduces the overall production cost.

[0014] The product has high purity, extremely low moisture and metal residue, and all indicators meet pharmaceutical-grade standards, satisfying the needs of high-end applications. The process parameters are standardized and have been verified to scale up to industrial scale. The reaction has excellent stability and has the potential for continuous production, combining the comprehensive advantages of being green, economical, and scalable. Detailed Implementation

[0015] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention. Example 1

[0016] This embodiment discloses a green method for preparing trimethyl phosphate (TMP) without the addition of alkali. It employs a transesterification reaction combined with solid acid catalysis and microwave / continuous flow heating technology to achieve efficient, low-consumption, and easily scalable production. The specific steps are as follows: 1. Preparation of raw materials and catalysts Industrial-grade dimethyl phosphate (DMP) was selected as the core raw material, with a purity ≥99.0% and a moisture content ≤0.1%, meeting the raw material requirements for industrial-scale production. It was combined with anhydrous analytical grade methanol (MeOH) with a moisture content ≤0.05% to avoid moisture affecting the transesterification equilibrium. The catalyst used was a solid acid resin (Amberlyst-15) or Ti-Zr oxide, which needed to be dried in a 120℃ vacuum drying oven for 4 hours before use to remove surface adsorbed water and improve catalytic activity. The catalyst loading was fixed at 5wt% of the DMP mass. For equipment, a 50L industrial-grade microwave reactor with a frequency of 2450MHz and a power adjustment range of 100-500W was used; or a continuous flow microwave heating module with a microporous bed diameter of 5cm, a length of 30cm, and a catalyst bulk density of 0.8g / cm³. 3 It is equipped with a 20L vacuum distillation unit with an ultimate vacuum of ≤5mmHg; and an online molecular sieve moisture separation unit with 3A molecular sieve and an adsorption capacity of ≥20%.

[0017] 2. Premix Mix 1 mol DMP with 3-4 mol excess methanol. Add DMP and methanol sequentially to a premixing vessel, start mechanical stirring at 300 rpm, and stir at room temperature (25-30℃) for 10 minutes to initially mix the raw materials. Then slowly add the pretreated solid acid catalyst and continue stirring for 15 minutes to form a homogeneous ester / alcohol / solid acid three-phase system. During the mixing process, maintain the pH of the system at 2-3 without additional adjustment. The excess methanol can promote the forward reversible transesterification reaction while inhibiting the self-polymerization side reaction of the raw materials.

[0018] 3. Catalytic transesterification Microwave mode: The premixed liquid is transferred to a microwave reactor, and nitrogen gas is introduced to stabilize the pressure at 5-8 bar, maintaining methanol in a liquid phase to increase the reaction rate. The microwave power is set to 300W, and the temperature is programmed to rise to 110-130℃, maintaining this temperature for 30 minutes. During the reaction, the built-in stirrer continuously stirs the mixture at 200 rpm to prevent localized overheating. Microwave heating allows the system temperature to reach the set value within 5 minutes, significantly shortening the heating time. Intermediate sampling and testing showed that the DMP conversion rate reached 85% after 15 minutes of reaction and ≥95% after 30 minutes.

[0019] Continuous flow mode: The premixed solution is dispensed via a metering pump at a rate of 0.5 mL / min. -1 The flow rate and control accuracy are ±0.02 mL·min. -1 A solid acid microporous bed preheated to 120°C is introduced, and the material stays in the bed for about 20 minutes. The fixed-bed catalytic structure of the microporous bed enables full contact between the raw material and the catalyst. When continuously discharged, the DMP conversion rate is stable at 95%-96%.

[0020] 4. Product separation After the reaction is complete, the reaction solution is cooled to room temperature (25°C) and transferred to an online moisture separation device. Water, a byproduct of transesterification, is removed by adsorption using a 3A molecular sieve (adsorption time 30 min, moisture removal rate ≥99%), thus disrupting the reaction equilibrium and increasing the TMP yield. Simultaneously, a methanol recovery system is activated to recover unreacted methanol through atmospheric distillation at 64-65°C, achieving a methanol recovery rate ≥95% and a methanol purity ≥99.8%. This recovered methanol can be directly recycled for the next batch of reaction, reducing raw material consumption.

[0021] 5. Purification and finished product The supernatant after dehydration and methanol recovery was fed into a vacuum distillation apparatus. The vacuum was set to 10 mmHg, and the temperature was programmed to rise to 70-80℃ at a rate of 5℃ / min. The target fraction with a boiling point of approximately 73℃ was collected, with temperature fluctuations within ±1℃, to remove a small amount of high-boiling impurities. Subsequently, 0.5 wt% activated carbon was added to the fraction, and the mixture was stirred and decolorized at room temperature for 30 min. After filtering to remove the activated carbon, the product was deeply dried using molecular sieves for 4 h to obtain a high-purity TMP product. The product had a moisture content ≤0.03% and a density of 1.065-1.075 g / cm³ at 25℃. 3 It meets the standards for industrial solvent-grade products.

[0022] 6. Quality Inspection and Process Validation use 1 H / 31 Batch quality verification was performed using PNMR, GC-MS, and ICP-OES. 1 HNMR detection was performed using CDCl3 as solvent. The chemical shift of the methyl characteristic peak was δ = 3.75 ppm, with no interference from impurity peaks. 31 The PNMR chemical shift δ = -1.8 ppm is a characteristic peak for TMP. GC-MS analysis shows a product purity of ≥99.5% with no significant organic impurities. ICP-OES analysis indicates a residual metal content of ≤0.0001%, meeting the requirements for pharmaceutical and pesticide-grade solvents. In industrial scale-up validation, the reactor volume was expanded from 50 L to 500 L while maintaining the same process parameters. The transesterification conversion rate remained ≥95%, and the TMP yield stabilized at 92-94%. After 10 catalyst cycles, the conversion rate only decreased from 96% to 95.2%, with an activity retention rate of 99%, demonstrating excellent potential for large-scale application.

[0023] This method uses no amine or inorganic bases throughout the process, avoiding the generation of salt waste liquid. The catalyst can be recycled, the reaction time is shortened by more than 87.5% compared with the traditional process, and the energy consumption is only 1 / 3 to 1 / 4 of the traditional process. It has significant advantages of being green and environmentally friendly, highly efficient and low-consumption, and easy to scale up. Example 2

[0024] This embodiment, based on Example 1, introduces an ionic liquid as a synergistic agent. Through the synergistic catalytic effect of the solid acid and the ionic liquid, the efficiency of the transesterification reaction and the product yield are further improved, achieving the efficient and green preparation of TMP. The specific steps are as follows: 1. Preparation of raw materials and catalysts Industrial-grade dimethyl phosphate (DMP) was selected as the reaction raw material, with a purity ≥99.2%, moisture content ≤0.08%, and acid value ≤0.05 mg KOH / g, meeting the raw material standards for large-scale production. Anhydrous analytical grade methanol (MeOH) with a purity ≥99.9% and moisture content ≤0.05% was used to avoid moisture interference with the transesterification equilibrium. The catalyst was Amberlyst-15 solid acid resin with a particle size of 0.3-1.2 mm and a specific surface area ≥45 m². 2 / g, before use, it needs to be dried in a vacuum drying oven at 110℃ for 6 hours to remove surface adsorbed water and residual impurities to ensure catalytic activity. The catalyst loading should be strictly controlled to 5wt% of the DMP mass.

[0025] The ionic liquid additive used is 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), with a purity ≥99.5% and a moisture content ≤0.1%. Its dosage is 10 wt% of the catalyst mass, i.e., 0.5 wt% of the DMP mass. Equipment includes a 50L industrial-grade microwave reactor with a frequency of 2450MHz, a power adjustment range of 50-500W, and a temperature control accuracy of ±1℃; a high-efficiency distillation column with 30 trays and an adjustable reflux ratio of 1:1-5:1; a ceramic membrane separation device with a pore size of 50nm and a molecular weight cutoff of 500Da; an online sampling and detection device; and a vacuum distillation system with an ultimate vacuum ≤5mmHg.

[0026] 2. Premix A mixture of 1 mol DMP and 3.5 mol methanol was prepared. First, methanol and DMP were added sequentially to a 20L premixing vessel. A variable frequency stirrer was turned on, and the mixture was stirred at 350 rpm for 8 minutes at room temperature (25-28℃) to form a homogeneous solution. Then, the pretreated Amberlyst-15 solid acid resin and [BMIM]Cl ionic liquid were placed in a planetary ball mill and ground at 200 rpm for 10 minutes to uniformly coat the solid acid surface with the ionic liquid, forming a composite catalytic system. The composite catalyst was slowly added to the raw material solution in the premixing vessel, and stirring continued for 15 minutes to form a stable ester / alcohol / composite catalyst three-phase system. The pH of the system was maintained at 2.1-2.3. Laser particle size analysis showed that the catalyst dispersion particle size was ≤5 μm, with no obvious agglomeration.

[0027] 3. Catalytic transesterification The premixed three-phase system was transferred to a microwave reactor, and the air inside the reactor was purged three times with high-purity nitrogen (≥99.99% purity). The pressure was then stabilized at 6 bar, a pressure that ensures methanol remains in the liquid phase throughout the reaction and prevents the ionic liquid from evaporating. The microwave power was set to 280W, and the programmed temperature rise was initiated, increasing to 110°C at a rate of 8°C / min, and held at this temperature for 25 minutes. During the reaction, the built-in anchor-type stirrer continuously stirred at 250 rpm to ensure uniform mixing of the system.

[0028] Online sampling and testing showed that the DMP conversion rate reached 90% after 10 minutes of reaction, rose to 96% after 20 minutes, and stabilized at ≥97% after 25 minutes, which is 4-6% higher than the conversion rate at the same time point in Example 1.

[0029] Preferably, the pretreated Amberlyst-15 solid acid resin and [BMIM]Cl ionic liquid are composited in an optimized ratio, preferably 10 wt% of the catalyst mass. Ball milling is used to uniformly coat the solid acid surface with the ionic liquid, forming a composite system with dual catalytic functions. In this system, [BMIM]Cl not only enhances methanol adsorption through a hydrogen bonding network but also regulates the acidic site distribution of the solid acid through ion exchange and surface modification, achieving a synergistic catalytic effect.

[0030] The interaction between the ionic liquid [BMIM]Cl and the Amberlyst-15 solid acid resin is a complex, multi-effect process. First, the imidazole cations of [BMIM]Cl can partially replace protons on the surface of the solid acid through ion exchange, forming new active sites. At the same time, chloride ions, as hydrogen bond acceptors, can form a hydrogen bond network with methanol molecules, enhancing the concentration of methanol on the catalyst surface.

[0031] This synergistic effect not only increases the local reactant concentration but also lowers the activation energy by altering the microenvironment on the catalyst surface. The π-electron system of the imidazole ring may interact π-π with the aromatic structure of the solid acid, further stabilizing the composite catalytic system.

[0032] 4. Product separation After the reaction was completed, microwave heating was turned off, and the reaction solution was rapidly cooled to room temperature (25°C) through a cooling jacket. It was then transferred to a ceramic membrane separator for cross-flow filtration at 0.3 MPa pressure. The byproduct water was separated within 30 minutes, with a water removal rate ≥99.5%. The filtered organic phase was fed into a high-efficiency distillation column with a bottom temperature of 68°C, a top temperature of 64.5°C, and a reflux ratio of 2:1. Methanol and ionic liquid were separated and recovered based on their boiling point differences. Methanol has a boiling point of 64.7°C, and [BMIM]Cl has a boiling point >300°C. The methanol recovery rate was ≥96%, and the recovery purity was ≥99.8%. The ionic liquid was collected at the bottom of the distillation column, with a recovery rate ≥98.5% and a purity maintained above 99.2%, allowing for recycling without additional purification.

[0033] 5. Purification and finished product The crude product, after removal of moisture, methanol, and recovered ionic liquid, is transferred to a vacuum distillation apparatus. A vacuum of 10 mmHg is set, and the temperature is increased to 72-78°C at a rate of 4°C / min. The target fraction at 73-75°C is collected, with a collection volume percentage of 92%, removing a small amount of high-boiling impurities. 0.4 wt% of columnar activated carbon (1-2 mm particle size, specific surface area ≥1000 m²) is added to the collected fraction. 2 / g, stir and decolorize at room temperature for 30 min, filter to remove activated carbon, and then deep dry through 4A molecular sieve for 5 h to obtain high-purity TMP product. The product has a moisture content ≤0.02%, a density of 1.068-1.072 g / cm³ at 25℃, and a refractive index of 1.396-1.398, which meets the standards for pharmaceutical-grade solvents.

[0034] 6. Quality Inspection and Cyclic Performance Verification Multiple methods are used for quality verification: 1 HNMR detection was performed using CDCl3 as solvent. The chemical shift of the methyl characteristic peak was δ=3.74ppm, and the peak shape was symmetrical with no impurity peaks. 31 The PNMR chemical shift δ = -1.78 ppm showed no residual peaks from the raw material. GC-MS analysis was performed using an HP-5 column (30 m × 0.32 mm × 0.25 μm) with a column temperature program of initial 40 °C for 2 min, followed by a ramp-up to 200 °C at a rate of 10 °C / min. The product purity was ≥99.7%. ICP-OES analysis showed that the residual metal content was ≤0.001%, which is far below the industrial control standard.

[0035] In the performance verification, the recovered solid acid catalyst and ionic liquid were dried at 110℃ for 4 hours and then reused in the reaction. After 8 cycles, the DMP conversion rate was still ≥95%, and the TMP yield remained above 93%, only decreasing by 2.5% compared to the first use. The purity of the ionic liquid remained above 98.8%, with no obvious degradation. Calculations showed that due to the shortened reaction time, increased yield, and recycling of the additives, the overall cost per unit product in this example was 8-10% lower than in Example 1 and more than 35% lower than the traditional alkaline catalytic process, demonstrating both high efficiency and economy. Table 1 shows the experimental data for optimizing the ionic liquid dosage. Table 2 shows the catalyst-ionic liquid cycle performance data. Table 3 shows the effect of different reaction temperatures on the performance of Example 2.

[0036] Table 1 Amount of ionic liquid used (relative to catalyst mass %) DMP conversion rate (%) TMP yield (%) Product purity (%) 5 93.2 89.7 99.3 10 97.5 95.2 99.7 15 97.8 95.4 99.6 20 96.9 94.1 99.5 Table 2 Loop count DMP conversion rate (%) TMP yield (%) Ionic liquid recovery rate (%) Activity retention rate (%) 1 97.5 95.2 98.8 100.0 2 97.2 94.8 98.5 99.7 4 96.5 93.7 98.1 98.9 6 95.8 92.9 97.6 98.2 8 95.1 92.3 97.2 97.5 10 94.3 91.5 96.8 96.7 Table 3 Reaction temperature (°C) DMP conversion rate (%) TMP yield (%) Product purity (%) 90 88.6 83.5 99.4 100 94.3 90.1 99.6 110 97.5 95.2 99.7 120 97.9 95.5 99.6 130 98.1 95.3 99.5 Example 3

[0037] This embodiment utilizes photocatalysis technology combined with a supported solid acid composite system to achieve alkali-free transesterification preparation of TMP at room temperature. The key advantages of this technology are low energy consumption and environmental friendliness. The specific steps are as follows: 1. Preparation of raw materials and catalysts Industrial-grade dimethyl phosphate (DMP) was selected as the reaction raw material, with a purity ≥99.0%, moisture content ≤0.1%, and acid value ≤0.06mgKOH / g, meeting the raw material stability requirements for large-scale production; it was combined with anhydrous analytical grade methanol (MeOH), with a purity ≥99.9% and moisture content ≤0.05%, to avoid moisture inhibiting the forward esterification reaction.

[0038] The catalyst is a silica gel-SO3H solid acid supported on TiO2 as a photosensitizer, wherein the silica gel support has a specific surface area ≥300m². 2 TiO2 (particle size 20-50 nm) with a pore size of 10-20 nm was loaded onto a silica gel surface via a sol-gel method, followed by sulfonation to introduce -SO3H. On the supported silica gel-SO3H solid acid surface, photogenerated electrons were captured by surface defects or adsorbed oxygen, inhibiting electron-hole recombination. Simultaneously, photogenerated holes migrated to the catalyst surface, promoting the formation of surface protons (H+). +The migration and activation of SO3H enhance the proton-donating capacity of its acidic sites. The photosensitizer TiO2 accounts for 20 wt% of the total catalyst mass, and the total acid content of the solid acid is ≥2.5 mmol / g. Before use, the catalyst must be dried in a vacuum oven at 80℃ for 8 hours to remove surface adsorbed water, ensuring photosensitivity and exposure of acidic sites. Its loading is strictly controlled at 6 wt% of the DMP mass (photocatalytic activity experiments have verified that this loading achieves the optimal balance between light efficiency and catalytic effect).

[0039] To verify the true contribution of photocatalysis to the reaction, the following control experiment was designed, as shown in Table 4, which compares photocatalysis with simple thermal catalysis, with a fixed reaction time of 60 min.

[0040] Table 4 condition Reaction temperature (°C) DMP conversion rate (%) TMP yield (%) No light exposure, only thermal catalysis 30 42.3 38.5 UV-LED illumination, no catalyst required 30 <5 – UV-LED + catalyst (Implementation 3) 30 94.0 91.2 UV-LED + catalyst (Implementation 3) 40 (Heating Assist) 96.8 94.5 Experimental results show that the conversion rate of simple thermocatalysis at the same temperature is only 42.3%, indicating that photocatalysis significantly improves the reaction efficiency. Combining the photothermal effect and the proton migration enhancement mechanism, this method achieves a balance between high conversion rate and high energy efficiency under ambient temperature and pressure conditions.

[0041] In terms of equipment, it is equipped with a 50LUV-LED photocatalytic reactor with an array of LED beads arranged at a wavelength of 365nm, a single bead power of 1W, a total power of 30W, and an illumination uniformity of ≥90%; a high-speed centrifuge with a speed of 8000r / min; a 4A molecular sieve drying device with an adsorption capacity of ≥25%; an atmospheric pressure distillation column with 25 trays; and a vacuum distillation system with an ultimate vacuum of ≤5mmHg, and an online ultraviolet-visible spectrophotometer for monitoring the reaction process.

[0042] 2. Premix A mixture of 1 mol DMP and 4 mol methanol was prepared and added sequentially to a 30L premixing reactor. A variable frequency stirrer was turned on and stirred at 400 rpm for 12 minutes at room temperature (25-30℃) to form a homogeneous and transparent solution. Then, the pretreated supported solid acid catalyst was slowly added, and stirring continued for 20 minutes. Through mechanical stirring and adjustment of the catalyst surface's hydrophilicity / hydrophobicity, the catalyst was uniformly dispersed in the reaction system without significant sedimentation. Laser particle size analysis showed that the catalyst particle size was ≤8μm, and the system pH was maintained at 2.0-2.2, providing a stable reaction environment for room temperature esterification.

[0043] 3. Catalytic transesterification Transfer the premixed homogeneous solution into the UV-LED photocatalytic reactor, maintaining atmospheric pressure (no pressurization required, reducing equipment operating costs), ensuring no air bubbles block the light. Turn on the UV-LED light source, set the light power to 30W, and allow the reaction temperature to remain naturally at 25-30℃ for a total reaction time of 60 minutes.

[0044] During the reaction, the built-in stirrer continuously stirred at 300 r / min to ensure uniform illumination of the system. Online sampling and testing showed that the DMP conversion rate reached 58.7% after 15 min, increased to 79.2% after 30 min, reached 91.5% after 45 min, and stabilized at ≥94% after 60 min. The catalytic mechanism is as follows: under UV-LED irradiation, the TiO2 photosensitizer absorbs photons to generate photogenerated electron-hole pairs. These photogenerated holes promote proton migration and activation, enhancing the proton supply capacity of acidic sites, thereby efficiently catalyzing the transesterification reaction of DMP and methanol, avoiding the dependence on high-temperature heating in traditional processes.

[0045] 4. Product separation After the reaction was completed, the UV-LED light source was turned off, and the reaction solution was transferred to a high-speed centrifuge at 8000 r / min for 15 min to achieve rapid separation of the solid acid catalyst, with a catalyst recovery rate ≥98%. The supernatant after centrifugation was sent to a 4A molecular sieve drying device to adsorb and remove the by-product water for 40 min, with a water removal rate ≥99.2%, thus breaking the reaction equilibrium to improve the TMP yield. Subsequently, the dehydrated organic phase was sent to an atmospheric distillation column, with the bottom temperature set at 67℃, the top temperature at 64.6℃, and the reflux ratio at 1.5:1, to recover excess methanol, with a methanol recovery rate ≥95.5% and a recovery purity ≥99.7%, which can be directly recycled for the next batch of reaction.

[0046] 5. Purification and finished product The crude product, after dehydration and methanol recovery, is transferred to a vacuum distillation apparatus. A vacuum of 10 mmHg is set, and the temperature is increased to 71-79°C at a rate of 3°C / min. The target fraction at 73-76°C is precisely collected, with a collection volume percentage of 90%, removing a small amount of high-boiling impurities. 0.6 wt% of powdered activated carbon (particle size ≤ 50 μm, specific surface area ≥ 1200 m²) is added to the collected fraction. 2 / g, stirred and decolorized at room temperature for 40 min, filtered to remove activated carbon, and then vacuum dried at 50℃ and -0.09MPa for 6 h to obtain refined TMP product. The product has a moisture content ≤0.04%, a density of 1.066-1.074 g / cm³ at 25℃, and a refractive index of 1.395-1.397, which meets the standards for industrial solvent grade and pharmaceutical excipient grade.

[0047] 6. Quality Inspection and Process Validation Multi-dimensional testing methods are used to confirm product quality: 1 HNMR detection was performed using CDCl3 as solvent. The chemical shift of the methyl characteristic peak was δ=3.75ppm, and the peak shape was sharp with no interference from other peaks. 31 The PNMR chemical shift δ = -1.81 ppm showed no residual peaks from the raw material. GC-MS analysis was performed using a DB-5 column (30 m × 0.32 mm × 0.25 μm) with a column temperature program of initial 50 °C for 3 min, followed by ramping to 180 °C at a rate of 8 °C / min. The product purity was ≥99.5%. ICP-OES analysis showed a residual metal content of ≤0.0002%, meeting the requirements for high-purity applications.

[0048] In the catalyst cycling performance verification, the recovered solid acid was dried at 80℃ for 4 hours and then reused. After 6 cycles, the DMP conversion rate was still ≥80%, the activity retention rate was 85.1%, and the TMP yield remained above 89%. BET characterization showed that after 6 cycles, the catalyst specific surface area increased from 302 m² / m³ to 302 m² / m³. 2 / g decreased to 268m 2 The slight decrease in activity is mainly due to the / g, but it still possesses highly efficient catalytic capabilities. Energy consumption calculations show that the energy consumption per unit product in this embodiment is only 38% of that of the traditional heating process, resulting in energy savings of over 62%. Furthermore, it eliminates the need for investment and maintenance costs for heating equipment. When produced on a large scale, the overall cost per unit product is reduced by 5-7% compared to Example 1 and by over 32% compared to the traditional alkaline catalytic process, providing a feasible solution for low-energy and green production.

[0049] Comparative Example 1 A conventional method for preparing TMP using K2CO3 alkali catalysis combined with oil bath heating. This comparative example uses a traditional inorganic alkali catalyst and oil bath heating, a conventional industrial preparation process, with the following steps: Industrial-grade dimethyl phosphate (DMP) and anhydrous methanol (MeOH) are selected; the catalyst is anhydrous potassium carbonate (K2CO3), and the dosage is 8 wt% of the mass of DMP; it is equipped with a conventional oil bath reactor, a vacuum distillation device, a water washing and neutralization device, and a wastewater treatment system.

[0050] Mix 1 mol DMP with 4 mol methanol, add anhydrous K2CO3, and stir at room temperature for 30 min to form a heterogeneous base catalytic system, in which K2CO3 partially dissolves.

[0051] The reactor was placed in an oil bath and heated to 130°C, maintaining atmospheric pressure for 4 hours. Due to uneven heat transfer in the oil bath, continuous stirring was necessary to ensure a uniform reaction. K₂CO₃ catalyzed the production of a large amount of carbonate ions, promoting transesterification.

[0052] After the reaction is completed and cooled to room temperature, deionized water is added to dissolve the generated potassium salt byproduct. After standing and separating the layers, the aqueous phase is separated, and the alkaline wastewater containing potassium salt is separated. The organic phase is washed three times with water to remove residual alkali and salt. The washing wastewater needs to be treated separately.

[0053] The organic phase after water washing is first distilled at atmospheric pressure to recover methanol, and then distilled under reduced pressure at 10 mmHg to collect the fraction at 70-82℃. The fraction is then dehydrated with a desiccant to obtain the TMP product.

[0054] GC-MS analysis showed the product purity to be 98.2-98.8%. 1 H / 31 The structure was confirmed by PNMR; the transesterification conversion rate was 90-92%, and the TMP yield was 83-86%.

[0055] This comparative example generates a large amount of alkaline wastewater containing potassium salts, resulting in high treatment costs; the energy consumption of oil bath heating is more than 3 times that of Example 1, and the reaction time is extended by 7 times; the catalyst is not recyclable, and the purity of the product is lower than 99.5% of that of Example 1.

[0056] Comparative Example 2 A conventional method for the preparation of TMP using Et3N amine catalysis combined with batch reactor heating. This comparative example employs an organic amine base catalyst and batch reactor heating, a common process in traditional fine chemical plants. The steps are as follows: Industrial-grade DMP and anhydrous methanol are used; the catalyst is triethylamine (Et3N), and the dosage is 1.2 times the molar amount of DMP; it is equipped with a conventional stainless steel reactor, distillation column, water washing and neutralization device and organic waste liquid recovery system.

[0057] A homogeneous amine catalytic system is formed by slowly adding triethylamine dropwise with 1 mol DMP and 5 mol excess methanol, and stirring for 20 min. Triethylamine forms a weak complex with methanol to promote the reaction.

[0058] Shut down the reactor, raise the temperature to 140°C, and maintain the pressure at 10 bar for 5 hours. Triethylamine is volatile, so the pressure must be strictly controlled to prevent catalyst loss. For reactor heating, a gradient temperature increase is necessary to avoid localized overheating.

[0059] After the reaction is completed, the temperature and pressure are reduced. First, methanol (containing a small amount of triethylamine) is recovered by distillation. The remaining crude product is added to dilute hydrochloric acid to neutralize the excess triethylamine, generating triethylamine hydrochloride. The solid salt is separated by filtration, and the filtrate is washed twice with water to remove residual salt and acid.

[0060] The organic phase after washing with water was distilled under reduced pressure at a vacuum of 10 mmHg, and the fraction at 71-83℃ was collected. The product was obtained by decolorization with activated carbon and drying with molecular sieve.

[0061] The product purity was found to be 98.0-98.5%; ICP-OES analysis showed no metal residue, but the content of organic impurities was higher than that in Example 1; the transesterification conversion rate was 89-91%, and the TMP yield was 81-84%.

[0062] The triethylamine used in this comparative example is volatile and pollutes the environment, and the amine salt waste liquid generated during neutralization is difficult to treat; the reaction time is 10 times that of Example 1, and the excessive amount of methanol leads to high energy consumption for recovery; the catalyst is not recyclable, and the overall production cost is more than 30% higher than that of Example 1.

[0063] Comparative Example 3 This comparative example uses a traditional TMP preparation method combining concentrated sulfuric acid catalysis and conventional heating. It employs a liquid strong acid catalyst and conventional heating with a heating mantle, representing an earlier TMP preparation process. The steps are as follows: Industrial-grade DMP and anhydrous methanol are used; the catalyst is 98% concentrated sulfuric acid, and the dosage is 6 wt% of the DMP mass; the reaction flask is equipped with an electric heating mantle, a neutralization vessel, a vacuum distillation apparatus, and acid-resistant equipment.

[0064] Mix 1 mol DMP with 4.5 mol methanol, slowly add concentrated sulfuric acid dropwise under ice bath conditions, stir for 15 min, and control the system temperature to not exceed 30℃ to avoid methanol carbonization.

[0065] Place the reaction flask in a heating mantle and heat to 120°C. React at atmospheric pressure for 6 hours. Due to the highly corrosive nature of concentrated sulfuric acid, glass or special alloy equipment must be used. Continuous stirring is required during the reaction to prevent localized carbonization side reactions.

[0066] After the reaction is completed and cooled to room temperature, sodium hydroxide aqueous solution is slowly added to neutralize concentrated sulfuric acid, and the pH is adjusted to neutral to generate sodium sulfate byproduct. The solid salt is separated by filtration, and the organic phase is taken after the filtrate is allowed to stand and separate into layers. The organic phase is washed twice with water to remove residual salt.

[0067] The organic phase is first distilled at atmospheric pressure to recover methanol, and then the fraction at 70-85℃ is collected by vacuum distillation (10 mmHg). Because it contains a small amount of carbonized impurities, it needs to be purified by multiple distillations to obtain the TMP product.

[0068] GC-MS analysis showed that the product purity was 97.5-98.0%; trace amounts of carbonization byproducts were present; the transesterification conversion rate was 88-90% and the TMP yield was 79-82%.

[0069] The concentrated sulfuric acid in this comparative example severely corrodes the equipment, generates a large amount of sodium sulfate wastewater during neutralization, and poses a significant environmental burden. The reaction time is 12 times that of Example 1, and carbonization side reactions easily occur, leading to lower purity. The catalyst is not recyclable, and post-processing requires multiple distillations, resulting in significantly higher energy consumption and production costs compared to Examples 1-3. Table 5 shows a comparison of the core performance of the examples and the comparative examples.

[0070] Table 5 Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2) Comparative Example 3 Catalyst type Solid acid resin / titanium-based Solid acid, [BMIM]Cl <![CDATA[TiO2 silica gel - SO3H supported]]> <![CDATA[Anhydrous K2CO3 (inorganic base)]]> Triethylamine (organic amine) 98% concentrated sulfuric acid (liquid acid) reaction temperature 110-130℃ 110℃ 25-30℃ (normal temperature) 130℃ 140℃ 120℃ reaction time 30min 25min 60min 4 hours (240 minutes) 5 hours (300 minutes) 6 hours (360 minutes) Reaction pressure 5-8 bar 6bar Atmospheric pressure Atmospheric pressure 10 bar Atmospheric pressure Transesterification conversion rate ≥95% ≥97% ≥94% 90-92% 89-91% 88-90% TMP yield 90-94% 93-96% 89-92% 83-86% 81-84% 79-82% Product purity (GC-MS) ≥99.5% ≥99.7% ≥99.5% 98.2-98.8% 98.0-98.5% 97.5-98.0% Catalyst cycle number ≥10 times ≥8 times ≥6 times Non-recyclable Non-recyclable Non-recyclable Wastewater generation No (only trace amounts of water byproducts) none none Large amounts (containing potassium salts) Large amounts (containing amine salts) Large amounts (containing sulfates) Relative energy consumption (baseline value) 1.0 (Baseline) 0.9 0.4 (60% energy saving) 3.2 3.8 4.5 Catalyst type none none none Low-medium Low High (strong corrosion) Unit product comprehensive cost (yuan / ton) 18000-19000 19500-20500 18500-19500 25000-26500 27000-28500 30000-32000 Catalyst cost percentage 3-5% 6-8% 5-7% 12-15% 18-22% 10-13% Wastewater treatment cost (RMB / ton of product) 0 0 0 3500-4000 4000-4500 5000-5500 The relative energy consumption is based on Example 1 (1.0) and is calculated comprehensively by considering reaction time, heating method, and equipment operating load. Wastewater generation is calculated per ton of TMP produced. The example produces no additional wastewater; only byproduct water is recyclable. The comparative example requires 5-8 m³ of wastewater. 3 Wastewater containing salinity and organic matter. Data are derived from process parameters and test results of each embodiment and comparative example, visually demonstrating the technical effectiveness.

[0071] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

[0072] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for preparing trimethyl phosphate without adding alkali, characterized in that, Includes the following steps: S1. Using dimethyl phosphate and methanol as raw materials, a solid acid catalyst is added, wherein the amount of the solid acid catalyst is 5-6 wt% of the mass of dimethyl phosphate; S2. Dimethyl phosphate, methanol and solid acid catalyst are mixed to form a homogeneous reaction system, wherein the molar ratio of dimethyl phosphate to methanol is 1:3-4. S3. Under normal or pressurized conditions, maintain the temperature of the reaction system at 25-130℃ by heating or light irradiation, and carry out the transesterification reaction for 20-60 minutes. S4. After the reaction is complete, remove the water, a byproduct of the reaction, and recover the unreacted methanol. S5. The separated product is subjected to vacuum distillation to collect the trimethyl phosphate fraction, which is then decolorized and dried to obtain the trimethyl phosphate product.

2. The method for preparing trimethyl phosphate without adding alkali according to claim 1, characterized in that, The solid acid catalyst is selected from one or more of solid acid resins, Ti-Zr oxides, or silica-sulfonic acid-based solid acids supported on photosensitizers.

3. The method for preparing trimethyl phosphate without adding alkali according to claim 1, characterized in that, In step S3, microwave heating, continuous flow heating, or UV-LED photocatalysis is used to activate the reaction; the reaction temperature is 110-130℃ when microwave heating or continuous flow heating is used, and the reaction temperature is 25-30℃ when UV-LED photocatalysis is used, without the need for an external heating device.

4. The method for preparing trimethyl phosphate without adding alkali according to claim 1, characterized in that, The solid acid catalyst is supported on the surface with an ionic liquid promoter, wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride, and the amount of the ionic liquid is 10 wt% of the mass of the solid acid catalyst.

5. The method for preparing trimethyl phosphate without adding alkali according to claim 1, characterized in that, Step S4 uses 3A or 4A molecular sieves to adsorb and remove the by-product water for 30-40 minutes; methanol recovery is carried out by atmospheric distillation at 64-68℃ with a methanol recovery rate of ≥95%, and the recovered methanol is directly recycled.

6. The method for preparing trimethyl phosphate without adding alkali according to claim 1, characterized in that, In step S5, the vacuum distillation is carried out at a vacuum degree ≤10 mmHg, a distillation temperature of 70-80℃, a moisture content ≤0.04%, and a density of 1.065-1.075 g / cm³ at 25℃. 3 .

7. The method for preparing trimethyl phosphate without adding alkali according to claim 2, characterized in that, The solid acid resin is Amberlyst-15 type cation exchange resin with a particle size of 0.3-1.2 mm, and the mass ratio of TiO2 to ZrO2 in the Ti-Zr oxide is 1:0.5-2.

8. The method for preparing trimethyl phosphate without adding alkali according to claim 3, characterized in that, When microwave heating or continuous flow heating is used, nitrogen gas is introduced into the reaction system to stabilize the pressure to 5-8 bar, so that methanol remains in the liquid phase. When continuous flow heating is used, the reaction is carried out in a microporous bed reactor with a catalyst bulk density of 0.8 g / cm³ and a material residence time of 20-30 minutes through the catalyst bed.

9. The method for preparing trimethyl phosphate without adding alkali according to claim 3, characterized in that, When using UV-LED photocatalysis, the particle size of the photosensitizer TiO2 in the silica-sulfonic acid solid acid loaded with photosensitizer is 20-50nm, the loading amount is 20wt% of the total mass of the catalyst, the wavelength of the UV-LED light source is 365nm, the light uniformity is ≥90%, and the temperature of the reaction system is naturally maintained at 25-30℃ through environmental heat dissipation.