A process for the synthesis of trioxane

Abstract

The present application relates to a kind of synthesis method of trioxane, comprising the following steps: S1.formaldehyde aqueous solution, solvent and composite catalyst are added to reaction kettle, and stirring is mixed uniformly to obtain mixed liquor;S2.the mixed liquor obtained in step S1 is heated to 110~150 ℃, and reaction is 1~4h, to obtain reaction liquid;S3.the reaction liquid obtained in step S2 is cooled to 70~80 ℃, and static stratification is separated, and water phase and catalyst are then separated, and then organic phase is washed 2 times;S4.the washed organic phase obtained in step 3 is sent into rectifying column rectification, to obtain product trioxane, and solvent can be recycled.The synthesis method of the present application has high conversion rate, high yield, and the purity of the obtained product is greater than 99.9%.

Description

Technical Field

[0001] This invention relates to the field of trioxymethylene preparation, specifically a method for synthesizing trioxymethylene. Background Technology

[0002] Trioxane, also known as trioxane, is an important organic chemical raw material. It is mainly used in the production of polyoxymethylene (POM), which has good mechanical properties, chemical resistance, and self-lubricating properties, and is widely used in the automotive, electronics, and machinery industries.

[0003] Traditional methods for synthesizing trioxymethylene typically use aqueous formaldehyde solution as a raw material, undergoing a condensation reaction under the action of an acidic catalyst. However, these methods have several drawbacks. For example, the reaction selectivity is low, and a large number of byproducts are generated, resulting in low trioxymethylene yields. Furthermore, traditional catalysts such as sulfuric acid are highly corrosive, requiring sophisticated equipment and easily causing environmental pollution. In addition, the reaction process involves high energy consumption and demanding reaction conditions, which is not conducive to large-scale industrial production.

[0004] In recent years, although some improved synthesis methods have been proposed, some problems still need to be solved. Developing an efficient, environmentally friendly, and low-cost method for synthesizing trioxymethylene is of great practical significance.

[0005] CN 105669639 B discloses a method for synthesizing trioxymethylene via the cyclization reaction of formaldehyde aqueous solution using an ionic liquid catalyzed by an ionic liquid. The method includes a step of distilling an aqueous formaldehyde solution and an ionic liquid under atmospheric pressure at 97℃-102℃ to synthesize trioxymethylene. The amount of formaldehyde aqueous solution added is 30wt%-80wt%, the amount of ionic liquid added is 0.1wt%-6wt%, and the remainder is water. The ionic liquid is a liquid composed of anions and cations, with the anion being p-ClPhSO3-. Using an ionic liquid with 4-chlorobenzenesulfonate as the anion as a catalyst to cyclize formaldehyde into trioxymethylene exhibits high catalytic activity, requires a small amount of catalyst, results in a high concentration of trioxymethylene after the reaction, and low content of byproducts such as methanol and formic acid, demonstrating good selectivity. However, the production cost is relatively high. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for synthesizing paraformaldehyde, comprising the following steps:

[0007] S1. Add formaldehyde aqueous solution, solvent and composite catalyst to the reaction vessel, stir and mix evenly to obtain a mixture;

[0008] S2. Heat the mixture obtained in step S1 to 110-150℃ and react for 1-4 hours to obtain the reaction solution;

[0009] S3. Cool the reaction solution obtained in step S2 to 70-80℃, let it stand and separate into layers, separate the aqueous phase and the catalyst, and then wash the organic phase with water twice.

[0010] S4. The organic phase obtained after washing with water in step 3 is sent to a distillation column for distillation to obtain the product trioxymethylene. The solvent can be recycled.

[0011] Further, in step S1, the solvent is di(2-ethylhexyl) phosphate (P204) or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507), and the amount of solvent added is 1 to 2 times the mass of the formaldehyde aqueous solution. The solvent not only functions as a solvent but also adjusts the acidity of the reaction system, altering the chemical environment of the reaction. It guides the growth of paraformaldehyde lattice through hydrogen bonding networks, reducing the formation of oligomers. Simultaneously, it synergistically interacts with the composite catalyst, acting as a catalyst to improve the selectivity and yield of the reaction. The phosphorus atoms in the additive possess lone pairs of electrons, enabling them to interact with reactant molecules and the catalyst surface, promoting the reaction while inhibiting side reactions.

[0012] Furthermore, in step S1, the composite catalyst is a mixture of zinc oxide and titanium oxide in a mass ratio of 1:1. The amount of composite catalyst added is 0.5-3% of the mass of the formaldehyde aqueous solution. The active sites on the surfaces of zinc oxide and titanium oxide can interact with reactant molecules, catalyzing and promoting the reaction, optimizing the reaction environment. Zinc oxide and titanium oxide possess catalytic activity, further improving the efficiency and selectivity of the reaction. A better technical solution is that the zinc oxide and titanium oxide are nanoparticles. Nanoparticles can increase catalytic sites, reduce the activation energy of formaldehyde polymerization, and accelerate the reaction.

[0013] Furthermore, in step S2, before heating, the oxygen in the reactor and the mixture is replaced with nitrogen. By removing oxygen from the system, the production of byproducts such as formic acid can be reduced.

[0014] Further, in step S2, the pressure in the reactor is maintained at 0.12–0.20 MPa after displacement. The reaction is carried out at a temperature of 110–150°C and a pressure of 0.12–0.20 MPa. During the reaction, formaldehyde molecules undergo a condensation reaction under the action of the composite catalyst, gradually forming trioxymethylene molecules. The synergistic effect of the specific solvent and the composite catalyst improves the selectivity and yield of the reaction and reduces the formation of byproducts. Another advantage of controlling the reaction at 110–150°C is that the trioxymethylene produced in the reaction can exist in gaseous form in the reactor, reducing the concentration of trioxymethylene in the liquid phase, promoting the reaction to move in the forward direction, and improving the conversion rate and yield.

[0015] Furthermore, the concentration of the formaldehyde aqueous solution in step S1 is between 35 and 40 wt%.

[0016] Further, the trioxymethylene product obtained after distillation in step S4 is dissolved in four times its mass of deionized water at a temperature between 30 and 45°C. Then, sodium chloride at 0.5 times its mass is slowly added, and the temperature is slowly lowered to 0-5°C. The mixture is then filtered, washed, and dried to obtain purified trioxymethylene. High-purity products with a purity greater than 99.9% can be obtained through salting-out purification.

[0017] Furthermore, the aqueous phase separated in step S2, after being concentrated, can be used as a raw material for the next reaction.

[0018] The synthesis method of this invention has high conversion rate, high yield, and simple process, making it suitable for widespread application. The prepared product has a purity of over 99.9%, stable product quality, and can be applied to various application scenarios. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1

[0021] A method for synthesizing trioxymethylene, comprising the following steps:

[0022] S1. Add 100 kg of 37 wt% formaldehyde aqueous solution, 150 kg of di(2-ethylhexyl) phosphate, 0.5 kg of zinc oxide and 0.5 kg of titanium oxide to the reaction vessel, and stir to mix evenly to obtain a mixture;

[0023] S2. Heat the mixture obtained in step S1 to 110-120°C and react at normal pressure for 2 hours to obtain the reaction solution;

[0024] S3. Cool the reaction solution obtained in step S2 to 70-80℃, let it stand and separate into layers, separating the aqueous phase and the catalyst. Then wash the organic phase twice with water. Before washing the organic phase, take a sample and determine the conversion rate, which is 91.2%.

[0025] S4. The organic phase obtained after washing with water in step 3 is sent to a distillation column for distillation to obtain 32.1 kg of trioxymethylene product, with a yield of 86.8% and a purity of 98.5%. The solvent can be recycled.

[0026] Example 2

[0027] A method for synthesizing trioxymethylene, comprising the following steps:

[0028] S1. Add 100 kg of 37 wt% formaldehyde aqueous solution, 150 kg of di(2-ethylhexyl) phosphate, 0.5 kg of zinc oxide and 0.5 kg of titanium oxide to the reaction vessel, and stir to mix evenly to obtain a mixture;

[0029] S2. First, replace the oxygen in the reaction vessel and the mixture obtained in step S1 with nitrogen, then raise the temperature to 140-150℃ and the pressure to 0.15-0.20MPa, and react for 2 hours to obtain the reaction solution;

[0030] S3. Cool the reaction solution obtained in step S2 to 70-80℃, let it stand and separate into layers, separating the aqueous phase and the catalyst. Then wash the organic phase twice with water. Before washing the organic phase, take a sample and determine the conversion rate, which is 92.4%.

[0031] S4. The organic phase obtained after washing with water in step 3 is sent to a distillation column for distillation to obtain 33.04 kg of trioxymethylene product, with a yield of 89.3% and a purity of 99.1%. The solvent can be recycled.

[0032] Example 3

[0033] A method for synthesizing trioxymethylene, comprising the following steps:

[0034] S1. Add 100 kg of 37 wt% formaldehyde aqueous solution, 150 kg of di(2-ethylhexyl) phosphate, 0.5 kg of nano zinc oxide and 0.5 kg of nano titanium oxide to the reaction vessel, stir and mix evenly to obtain a mixture;

[0035] S2. First, replace the oxygen in the reaction vessel and the mixture obtained in step S1 with nitrogen, then raise the temperature to 140-150℃ and the pressure to 0.15-0.20MPa, and react for 2 hours to obtain the reaction solution;

[0036] S3. Cool the reaction solution obtained in step S2 to 70-80℃, let it stand and separate into layers, separating the aqueous phase and the catalyst. Then wash the organic phase twice with water. Before washing the organic phase, take a sample and determine the conversion rate, which is 93.8%.

[0037] S4. The organic phase obtained after washing with water in step 3 is sent to a distillation column for distillation to obtain 33.8 kg of trioxymethylene product, with a yield of 91.4% and a purity of 99.1%. The solvent can be recycled.

[0038] Example 4

[0039] A method for synthesizing trioxymethylene, comprising the following steps:

[0040] S1. Add 100 kg of 37 wt% formaldehyde aqueous solution, 150 kg of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, 0.5 kg of nano zinc oxide and 0.5 kg of nano titanium oxide to the reaction vessel, stir and mix evenly to obtain a mixed solution;

[0041] S2. First, replace the oxygen in the reaction vessel and the mixture obtained in step S1 with nitrogen, then raise the temperature to 140-150℃ and the pressure to 0.15-0.20MPa, and react for 2 hours to obtain the reaction solution;

[0042] S3. Cool the reaction solution obtained in step S2 to 70-80℃, let it stand and separate into layers, separating the aqueous phase and the catalyst. Then wash the organic phase twice with water. Before washing the organic phase, take a sample and determine the conversion rate to be 93.5%.

[0043] S4. The organic phase obtained after washing with water in step 3 is sent to a distillation column for distillation to obtain 33.7 kg of trioxymethylene product, with a yield of 91.3% and a purity of 99.1%. The solvent can be recycled.

[0044] The trioxymethylene product obtained after distillation in step S4 was dissolved in deionized water at a temperature between 30 and 45°C, with a mass of 4 times its weight. Then, sodium chloride at a mass of 0.5 times its weight was slowly added, and the temperature was slowly lowered to 0-5°C. After filtration, washing, and drying, 30.3 kg of high-purity trioxymethylene was obtained with a purity of 99.91%.

[0045] Comparative Example 1

[0046] The solvent in Example 1 was replaced with a heavy aromatic hydrocarbon, and everything else was the same as in Example 1, so it will not be repeated here. The final conversion rate was 58.3% and the yield was 53.2%.

[0047] Comparative Example 2

[0048] The composite catalyst in Example 1 was removed, and everything else remained the same as in Example 1, so it will not be repeated here. The final conversion rate was 32.1%, and the yield was 26.2%.

[0049] Data from Examples 1 to 4 show that pressurization, a suitable reaction temperature, and a nano-catalyst are effective in removing oxygen from the system. Salting out can further yield a high-purity product. Data from Comparative Example 1 indicates that the specific solvent required to achieve the technical effects of this invention is essential, and that the synergistic effect of the solvent and catalyst is crucial for achieving the optimal technical results.

Claims

1. A method for synthesizing trioxymethylene, characterized in that, Includes the following steps: S1. Add formaldehyde aqueous solution, solvent and composite catalyst to the reaction vessel, stir and mix evenly to obtain a mixture; S2. Heat the mixture obtained in step S1 to 110~150℃ and react for 1~4 hours to obtain the reaction solution; S3. Cool the reaction solution obtained in step S2 to 70~80℃, let it stand and separate into layers, separate the aqueous phase and the catalyst, and then wash the organic phase with water twice. S4. The washed organic phase obtained in step 3 is fed into a distillation column for distillation to obtain the product trioxymethylene. The solvent can be recycled. In step S1, the solvent is di(2-ethylhexyl) phosphate or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, and the amount of solvent added is 1 to 2 times the mass of the formaldehyde aqueous solution. In step S1, the composite catalyst is a mixture of zinc oxide and titanium oxide in a mass ratio of 1:1, and the amount of composite catalyst added is 0.5 to 3% of the mass of the formaldehyde aqueous solution.

2. The method for synthesizing trioxymethylene according to claim 1, characterized in that, Before heating in step S2, the oxygen in the reactor and the mixture is replaced with nitrogen.

3. The method for synthesizing trioxymethylene according to claim 2, characterized in that, In step S2, the pressure of the reactor is maintained at 0.12~0.20 MPa after displacement.

4. The method for synthesizing trioxymethylene according to claim 1, characterized in that, The concentration of the formaldehyde aqueous solution in step S1 is between 35 and 40 wt%.

5. The method for synthesizing trioxymethylene according to claim 1, characterized in that, The trioxymethylene product obtained after distillation in step S4 is dissolved in deionized water at a temperature between 30 and 45°C, with 4 times its mass of the product being dissolved in deionized water. Then, sodium chloride at 0.5 times its mass of the trioxymethylene product is slowly added, and the temperature is slowly lowered to 0-5°C. The product is then filtered, washed, and dried to obtain the refined trioxymethylene product.

6. The method for synthesizing trioxymethylene according to claim 1, characterized in that, The aqueous phase separated in step S2, after being concentrated, can be used as a raw material for the next reaction.