Synthesis method of trioxymethylene

Abstract

The invention relates to a trioxymethylene synthesis method, which comprises: S1, adding a formaldehyde aqueous solution, a solvent and a composite catalyst into a reaction kettle, and uniformly stirring and mixing to obtain a mixed solution; s2, heating the mixed solution obtained in the step S1 to 110-150 DEG C, and reacting for 1-4 hours to obtain a reaction solution; s3, cooling the reaction liquid obtained in the step S2 to 70-80 DEG C, standing for layering, separating out a water phase and a catalyst, and then washing the organic phase twice; and S4, feeding the washed organic phase obtained in the step 3 into a rectifying tower for rectification to obtain the product trioxymethylene, and recycling the solvent. The synthesis method disclosed by the invention is high in conversion rate and high in yield, and the purity of the obtained product is greater than 99.9%.

Description

Technical Field

[0001] The invention relates to the field of trioxymethylene preparation, in particular to a method for synthesizing trioxymethylene. Background Art

[0002] Trioxane, also known as trioxane, is an important organic chemical raw material. It is primarily used in the production of polyoxymethylene (POM). With its excellent mechanical properties, chemical resistance, and self-lubrication, POM is widely used in the automotive, electronics, and machinery industries.

[0003] Traditional methods for synthesizing triformaldehyde typically use aqueous formaldehyde as the raw material, undergoing a condensation reaction in the presence of an acidic catalyst. However, these methods have several drawbacks. For example, the reaction has low selectivity, resulting in the production of a large number of byproducts and low triformaldehyde yields. Furthermore, traditional catalysts such as sulfuric acid are highly corrosive, requiring high equipment requirements and causing environmental pollution. Furthermore, the reaction process is energy-intensive and requires demanding reaction conditions, making it unsuitable for large-scale industrial production.

[0004] In recent years, although some improved synthesis methods have been proposed, there are still some problems to be solved. It is of great practical significance to develop an efficient, environmentally friendly and low-cost synthesis method of triformaldehyde.

[0005] CN 105669639 B provides a method for synthesizing trioxymethylene through the cyclization reaction of a formaldehyde aqueous solution catalyzed by an ionic liquid. The method comprises the steps of distilling the reactants, formaldehyde aqueous solution, and ionic liquid at 97°C-102°C and atmospheric pressure 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, and the anion is p-ClPhSO3-. Using an ionic liquid formed by 4-chlorobenzenesulfonate as an anion as a catalyst, formaldehyde is cyclized to trioxymethylene. The catalyst has high catalytic activity, requires little usage, and after the reaction, the trioxymethylene concentration is high, the content of byproducts such as methanol and formic acid is low, and the selectivity is good. However, the production cost is high. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method for synthesizing trioxymethylene, comprising the following steps:

[0007] S1. The formaldehyde aqueous solution, solvent and composite catalyst were added to the reactor and stirred to obtain a mixture;

[0008] S2. The mixed solution obtained in step S1 is heated to 110 to 150°C and reacted for 1 to 4 hours to obtain a reaction solution;

[0009] S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, allowed to stand for stratification, the aqueous phase and the catalyst were separated, and the organic phase was washed with water twice;

[0010] S4. The washed organic phase obtained in step 3 is sent to a distillation tower for rectification to obtain trioxymethylene, and the solvent can be recycled.

[0011] Furthermore, 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 solution. The solvent can not only play a solvent role, but also adjust the acidity of the reaction system, change the chemical environment of the reaction, and guide the growth of the triformaldehyde lattice through the hydrogen bond network to reduce the generation of oligomers. At the same time, it synergizes with the composite catalyst, plays the role of the catalyst, and improves the selectivity and yield of the reaction. The phosphorus atom in the additive has a lone pair of electrons, which can interact with the reactant molecules and the catalyst surface, promote the reaction, and suppress the occurrence of 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, and the amount of the composite catalyst added is 0.5-3% of the mass of the formaldehyde aqueous solution. The active sites on the surfaces of the zinc oxide and titanium oxide can interact with the reactant molecules, catalytically promoting the reaction and optimizing the reaction environment. The catalytic activity of the zinc oxide and titanium oxide further improves the efficiency and selectivity of the reaction. A more preferred technical solution is to use the zinc oxide and titanium oxide in the form of nanoparticles. Nanoparticles can increase catalytic sites, reduce the activation energy of formaldehyde polymerization, and accelerate the reaction.

[0013] Furthermore, before heating in step S2, oxygen in the reaction kettle and the mixed liquid is replaced with nitrogen. By removing oxygen from the system, the production of by-products such as formic acid can be reduced.

[0014] Furthermore, after the replacement in step S2, the pressure of the reactor is maintained at 0.12 to 0.20 MPa. The reaction is carried out at a temperature of 110 to 150° C. and a pressure of 0.12 to 0.20 MPa. During the reaction, the formaldehyde molecules undergo a condensation reaction under the action of the composite catalyst to gradually form trioxymethylene molecules. The specific solvent and the composite catalyst act synergistically to improve the selectivity and yield of the reaction and reduce the formation of by-products. Another advantage of controlling the reaction at 110 to 150° C. is that the trioxymethylene produced by the reaction can exist in the reactor in a gaseous form, 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] Furthermore, the trioxymethylene product obtained after distillation in step S4 is dissolved in deionized water 4 times its mass at a temperature between 30 and 45°C, and then sodium chloride 0.5 times its mass is slowly added, and the temperature is slowly lowered to 0 to 5°C, filtered, washed, and dried to obtain a trioxymethylene product. A high-purity product can be obtained by the salting-out purification method, with a purity greater than 99.9%.

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

[0018] The synthesis method of the present invention has high conversion rate, high yield, simple process, is suitable for promotion and application, and the purity of the prepared product is greater than 99.9%, the product quality is stable, and can be applied to various application scenarios. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] Example 1

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

[0022] S1. 100kg of 37wt% aqueous formaldehyde solution, 150kg of di(2-ethylhexyl) phosphate, 0.5kg of zinc oxide and 0.5kg of titanium oxide were added to the reactor and stirred to obtain a uniform mixture;

[0023] S2. The mixed solution obtained in step S1 was heated to 110-120°C and reacted at normal pressure for 2h to obtain a reaction solution;

[0024] S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, allowed to stand for stratification, the aqueous phase and the catalyst were separated, and the organic phase was washed twice with water. The conversion rate of the organic phase was measured by sampling before washing at 91.2%;

[0025] S4. The washed organic phase obtained in step 3 was fed into a distillation tower for rectification to obtain 32.1 kg of trioxymethylene 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 comprises the following steps:

[0028] S1. 100kg of 37wt% aqueous formaldehyde solution, 150kg of di(2-ethylhexyl) phosphate, 0.5kg of zinc oxide and 0.5kg of titanium oxide were added to the reactor and stirred to obtain a uniform mixture;

[0029] S2. The mixed solution obtained in step S1 is first replaced with nitrogen in the reactor and the mixed solution, and then heated to 140-150°C, pressure 0.15-0.20 MPa, and reacted for 2 h to obtain a reaction solution;

[0030] S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, separated by static layering, the aqueous phase and the catalyst were separated, and then the organic phase was washed twice with water. The conversion rate of the organic phase was measured by sampling before washing at 92.4%;

[0031] S4. The washed organic phase obtained in step 3 was fed into a distillation tower for rectification to obtain 33.04 kg of trioxymethylene 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 comprises the following steps:

[0034] S1. 100kg of 37wt% formaldehyde solution, 150kg of di(2-ethylhexyl) phosphate, 0.5kg of nano-zinc oxide and 0.5kg of nano-titanium oxide were added to the reactor and stirred to obtain a uniform mixture;

[0035] S2. The mixed solution obtained in step S1 is first replaced with nitrogen in the reactor and the mixed solution, and then heated to 140-150°C, pressure 0.15-0.20 MPa, and reacted for 2 h to obtain a reaction solution;

[0036] S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, allowed to stand for stratification, the aqueous phase and the catalyst were separated, and the organic phase was washed twice with water. The conversion rate of the organic phase was measured by sampling before washing at 93.8%;

[0037] S4. The washed organic phase obtained in step 3 was fed into a distillation tower for rectification to obtain 33.8 kg of trioxymethylene 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 comprises the following steps:

[0040] S1 37wt% formaldehyde solution 100kg, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester 150kg, 0.5kg of nano zinc oxide and 0.5kg of nano titanium oxide were added to the reactor and stirred to obtain a mixture;

[0041] S2. The mixed solution obtained in step S1 is first replaced with nitrogen in the reactor and the mixed solution, and then heated to 140-150°C, pressure 0.15-0.20 MPa, and reacted for 2 h to obtain a reaction solution;

[0042] S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, separated by static layering, the aqueous phase and the catalyst were separated, and then the organic phase was washed twice with water. The conversion rate of the organic phase was measured by sampling before washing at 93.5%;

[0043] S4. The washed organic phase obtained in step 3 was fed into a distillation tower for rectification to obtain 33.7 kg of trioxymethylene 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 4 times its mass at a temperature between 30 and 45° C., and then sodium chloride 0.5 times its mass was slowly added, and the temperature was slowly lowered to 0 to 5° C., filtered, washed, and dried to obtain 30.3 kg of trioxymethylene fine product with a purity of 99.91%.

[0045] Comparative Example 1

[0046] The solvent in Example 1 was replaced with heavy aromatic hydrocarbons. Other details were the same as in Example 1 and 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 the rest was the same as in Example 1, which will not be described again. The final conversion rate was 32.1%, and the yield was 26.2%.

[0049] The data from Examples 1 to 4 demonstrate that pressurization, appropriate reaction temperature, and nanocatalysts remove oxygen from the system; salting-out further yields a high-purity product. The data from Comparative Example 1 demonstrate that only the specific solvent of the present invention can achieve the technical effects of the present invention, and that the synergistic effect of the solvent and catalyst of the present invention can achieve the optimal technical effects.

Claims

1. A method for synthesizing trioxymethylene, characterized in that: The following steps are involved: S1. The formaldehyde aqueous solution, solvent and composite catalyst were added to the reactor and stirred to obtain a mixture; S2. The mixed solution obtained in step S1 is heated to 110 to 150°C and reacted for 1 to 4 hours to obtain a reaction solution; S3. The reaction solution obtained in step S2 was cooled to 70-80 ° C, allowed to stand for stratification, the aqueous phase and the catalyst were separated, and the organic phase was washed with water twice; S4. The organic phase after washing obtained in step 3 is sent to a distillation tower for rectification to obtain trioxymethylene, and the solvent can be recycled.

2. The method for synthesizing trioxymethylene according to claim 1, wherein In step S1, the solvent is di(2-ethylhexyl) phosphate or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester), and the amount of the solvent added is 1 to 2 times the mass of the formaldehyde aqueous solution.

3. The method for synthesizing trioxymethylene according to claim 1, wherein 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 the composite catalyst added is 0.5-3% of the mass of the formaldehyde aqueous solution.

4. The method for synthesizing trioxymethylene according to claim 1, wherein Before heating in step S2, oxygen in the reaction kettle and the mixed liquid is replaced with nitrogen.

5. The method for synthesizing trioxymethylene according to claim 4, wherein After the replacement in step S2, the pressure of the reactor is maintained at 0.12-0.20 MPa.

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

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

8. The method for synthesizing trioxymethylene according to claim 3, wherein In step S1, the zinc oxide and titanium oxide are nanoparticles.

9. The method for synthesizing trioxymethylene according to claim 1, wherein The aqueous phase separated in step S2 can be concentrated and used as a raw material for the next reaction.