1, 3, 5-trioxane production system and process capable of recycling auxiliaries

Abstract

The invention discloses a 1, 3, 5-trioxane production system capable of recovering auxiliaries, which comprises a synthesis reaction rectifying tower, a light component removal tower kettle, a product concentration tower, an extraction tower, an extraction agent recovery dividing wall tower, membrane separation equipment and auxiliary extraction equipment, formaldehyde reacts in the synthesis reaction rectifying tower to obtain a 1, 3, 5-trioxane crude product, and the auxiliary extraction equipment is used for extracting the auxiliaries. The 1, 3, 5-trioxane is separated through the light component removal tower and the product concentration tower, and is purified through the extraction tower and the extraction agent recovery dividing wall tower, so that the 1, 3, 5-trioxane with the purity being greater than or equal to 99.99% is obtained; the membrane separation equipment and the assistant extraction equipment can be used for recovering an assistant and sending the recovered assistant to the synthesis reaction rectifying tower. The invention also discloses a 1, 3, 5-trioxane production process capable of recovering the auxiliary agent. According to the 1, 3, 5-trioxane process production system and process, the product yield can be effectively increased, the yield of formic acid in side reaction is reduced so as to reduce corrosion to equipment, and compared with a traditional sulfuric acid method process, the production cost and energy consumption are lower, and more economical efficiency is achieved.

Description

Technical Field

[0001] This invention relates to a system and process for producing 1,3,5-trioxane with recyclable additives. Background Technology

[0002] 1,3,5-Trioxane is an important chemical with a wide range of applications, including the preparation of pesticides, adhesives, disinfectants, and antibacterial agents. One of its most critical uses is in the synthesis of polyoxymethylene resins, where its usage is second only to polyamide-66 and polycarbonate. With the development of industries such as automobiles, electronics, industrial machinery, and medical devices, the demand for polyoxymethylene resins has been increasing year by year.

[0003] The existing 1,3,5-trioxane production process mainly consists of two processes: 1,3,5-trioxane synthesis and 1,3,5-trioxane separation. To produce 1,3,5-trioxane feedstock that meets the requirements for polyoxymethylene resin synthesis, the following specifications must be met: formaldehyde < 30 ppm; water < 40 ppm; sodium ions < 5 ppm; formic acid < 10 ppm; TOX purity ≥ 99.99%. Because this 1,3,5-trioxane production process involves a complex azeotropic system containing formaldehyde, water, and 1,3,5-trioxane, and the crude product is limited by the reaction equilibrium concentration, ordinary distillation methods cannot separate the high-purity 1,3,5-trioxane product required for polyoxymethylene resin synthesis.

[0004] Currently, the main methods for synthesizing 1,3,5-trioxane both domestically and internationally are as follows:

[0005] 1. Sulfuric Acid Process: The sulfuric acid process for synthesizing 1,3,5-trioxane was disclosed by DuPont in 1942. This method is simple and convenient, and is the most widely used in industry. In China, the sulfuric acid process is the mainstream technology for synthesizing 1,3,5-trioxane. Chongqing Yuntianhua's patent CN108273282 uses sulfuric acid as a catalyst, and the reaction is heated to 101-106℃ in a reboiler to obtain a gaseous mixture containing the product. Zhejiang Sanbo Polymer Co., Ltd.'s patent CN101121709 uses sulfuric acid as a catalyst, and concentrated formaldehyde is used to synthesize a gaseous mixture containing the product in a reactor at 85-140℃ and 0-1MPa. The disadvantages of the sulfuric acid process are: limited by reaction equilibrium, low yield of 1,3,5-trioxane, high content of formic acid as a byproduct, high energy consumption for subsequent product separation, and formic acid in the gaseous mixture can cause equipment corrosion.

[0006] 2. Solid Acid Method: Using solid acid instead of sulfuric acid is also a method for synthesizing 1,3,5-trioxane. Polyplastics Corporation and Asahi Kasei Corporation of Japan have applied for patents for solid acid process technology. In China, Chengdu Zhongke Kaitai Technology Co., Ltd.'s patent CN112174931 uses a solid acid catalyst to synthesize a gaseous mixture containing the product at a temperature of 80–150℃ and a pressure of 0.1–0.3 MPa. Suzhou Shuanghu Chemical Technology Co., Ltd.'s patent CN113582967 uses a solid acid catalyst to synthesize a gaseous mixture containing the product at a temperature of 100–102℃ and a pressure of -0.1–0.1 MPa. While the solid acid method reduces corrosiveness by using solid acid instead of sulfuric acid, the yield of 1,3,5-trioxane is lower than that of the sulfuric acid method, and the catalyst is prone to clogging and deactivation.

[0007] 3. Other methods: While ionic liquid methods combine the advantages of sulfuric acid and solid acid methods, high cost and difficulty in recycling have become their main limiting factors. Patents from China University of Petroleum (CN105175389) and Ordos University of Applied Technology (CN112237749) proposed a new approach: an acid-salt catalytic method for synthesizing 1,3,5-trioxane from formaldehyde. This method improves product yield and reduces formic acid formation, but it increases the cost of adding salts. The subsequent discharge of salts with the reaction residue increases environmental treatment costs, thus limiting its application due to economic constraints. While the idea of ​​adding salts in the sulfuric acid method is good, a satisfactory solution for salt recovery without adding extra costs to the process remains elusive.

[0008] Furthermore, the traditional sulfuric acid process for synthesizing 1,3,5-trioxane from concentrated formaldehyde requires a formaldehyde concentration higher than 60 wt%, and subsequent separation generates approximately 20 wt% dilute aldehydes. Traditional concentrated formaldehyde preparation utilizes the oxidation reaction of methanol and air in an iron-molybdenum catalyst to produce formaldehyde. This method only yields 45–55 wt% concentrated formaldehyde. To ultimately increase the concentration of this concentrated formaldehyde and the approximately 20 wt% dilute aldehydes to 60 wt%, vacuum concentration and pressure distillation are required, steps that consume significant energy.

[0009] There are many methods for separating 1,3,5-trioxane gas-phase mixtures both domestically and internationally, and the following two are the main ones that have been industrialized:

[0010] 1. Extraction Method: This method involves separating 1,3,5-trioxane by adding an extractant. Commonly used extractants include benzene and dichloroethane. The extractant can be recycled during production. Internationally, Celanese Corporation (USA) and P&ID Corporation (South Korea) both use extraction methods to separate 1,3,5-trioxane. In China, Yankuang Lunan Chemical Co., Ltd.'s patent CN113248469 uses benzene extraction to separate 1,3,5-trioxane. China National Chemical Engineering Co., Ltd.'s patent CN103420974 also uses benzene extraction to separate 1,3,5-trioxane.

[0011] 2. Crystallization Method: Yuntian uses a crystallization separation method to produce 1,3,5-trioxane, as shown in patent CN100528861C. BASF's patent CN1273462C also employs a crystallization process. Suzhou Shuanghu Chemical Technology Co., Ltd.'s patent discloses an apparatus and method for the continuous preparation of paraformaldehyde, including a reaction and concentration system, a crystallization system, and a purification system.

[0012] The above two separation methods struggle to achieve a 1,3,5-trioxane purity of 99.99%. This is primarily because during synthesis and separation, methanol reacts with formaldehyde aqueous solution under acidic conditions to generate trace amounts of 1,3-dioxopentane. This 1,3-dioxopentane then reacts with formaldehyde to form trioxone and other substances with boiling points close to the product, making subsequent distillation difficult and hindering product concentration. For example, in the extraction method, the 1,3-dioxopentane light component is not removed after synthesis distillation and is directly fed into the extraction tower, causing the 1,3-dioxopentane to accumulate in the system and form the difficult-to-separate trioxone, affecting product purity. While the crystallization method includes a light component removal and concentration step before entering the crystallization equipment, its purpose is to remove light components such as methyl formate and methyl acetal, not the 1,3-dioxopentane light component. Therefore, the formed trioxone remains unremoved, resulting in low final product purity. Summary of the Invention

[0013] Currently, the production of 1,3,5-trioxane is limited by technological constraints, with most processes suffering from the following problems: low product yield, low product purity, high formic acid content as a byproduct, high energy consumption in product separation, and severe equipment corrosion. This invention provides a 1,3,5-trioxane production system and process with recoverable additives. Based on the sulfuric acid process, suitable salt additives are added to adjust the product equilibrium concentration, effectively improving product yield, reducing the formic acid yield to mitigate equipment corrosion, and recovering the salts to reduce usage and processing costs. Secondly, methanol is reacted with recycled dilute formaldehyde to produce methylal, which is then oxidized to produce concentrated formaldehyde required for 1,3,5-trioxane synthesis. This process utilizes the characteristic of requiring dilute formaldehyde as feedstock, utilizing the dilute formaldehyde generated during the 1,3,5-trioxane synthesis separation, eliminating the need for vacuum concentration and pressure distillation processes in traditional dilute formaldehyde treatment. This process not only saves energy but also increases the upper limit of concentrated formaldehyde concentration. Secondly, during separation, components that may form trioxane (1,3-dioxane) are removed to ensure the final purity of the product meets the requirements: formaldehyde <30 ppm; water <40 ppm; sodium ions <5 ppm; formic acid <10 ppm; and 1,3,5-trioxane purity ≥99.99%. Simultaneously, the synthesized crude 1,3,5-trioxane product can have its light components removed and be concentrated to an azeotropic composition before entering the extraction tower, thus reducing the amount of benzene circulating in the extractant. Finally, for product extraction and separation, a partition wall tower is used for both extractant recovery and product separation, further saving energy.

[0014] As one aspect of the invention, a 1,3,5-trioxane production system with recyclable additives is provided, comprising:

[0015] In the synthetic reactive distillation column, the additives (sodium benzenesulfonate), the catalyst (sulfuric acid), and formaldehyde undergo a catalytic reaction, and the synthesized crude product 1,3,5-trioxane is obtained at the top of the column.

[0016] The crude 1,3,5-trioxane product obtained from the top of the synthetic reactive distillation column is de-contaminated in the light component removal column to remove light components, and an aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane is obtained in the bottom of the column.

[0017] In the product concentration tower, the aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane obtained from the bottom of the light component removal tower is separated. The gas phase at the top of the tower is condensed to obtain a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope with methanol and formic acid.

[0018] An extraction column is used to extract a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope obtained from the top of the product concentration column with methanol and formic acid, and the extract phase is obtained at the top of the column.

[0019] An extractant recovery partition wall column is used, in which the extractant phase is separated and 1,3,5-trioxane is obtained on the column side;

[0020] The membrane separation device is used to separate the bottom liquid of the synthetic reactive distillation column into sodium benzenesulfonate, formic acid and 1,3,5-trioxane.

[0021] The auxiliary agent extraction device contains the retained sodium benzenesulfonate, formic acid, and 1,3,5-trioxane, which are then used to extract sodium benzenesulfonate, which is recycled back to the synthesis reactive distillation column as a circulating auxiliary agent.

[0022] In a specific embodiment, the 1,3,5-trioxane production system for recyclable additives further includes:

[0023] A methyl acetal reactive distillation column is used to catalytically react methanol and formaldehyde to produce methyl acetal.

[0024] A methyl acetal oxidation reactor, in which methyl acetal from the methyl acetal reactive distillation column undergoes an oxidation reaction to generate a reaction gas;

[0025] The formaldehyde absorption tower is used to absorb the formaldehyde in the reaction gas generated by the methyl acetal oxidation reactor. The formaldehyde obtained from the bottom of the tower is then transported to the synthesis reaction distillation tower.

[0026] In a specific embodiment, the synthetic reactive distillation column adopts a plate structure with 10 to 30 theoretical plates; the light component removal column adopts a plate structure with 7 to 20 theoretical plates; the product concentration column adopts a plate structure with 15 to 35 theoretical plates; the extraction column adopts a plate or packed column structure with 7 to 35 theoretical plates; and the extractant recovery partition wall column adopts a plate structure with 30 to 82 theoretical plates, with partition plates set in the middle 10 to 30 plates.

[0027] In a specific embodiment, the methyl acetal reactive distillation column is a plate type, a packed type, or a combination of both, with 20 to 50 theoretical plates; the methyl acetal oxidation reactor is a tubular reactor; and the formaldehyde absorption tower is a plate type, a packed type, or a combination of both, with 20 to 60 theoretical plates.

[0028] As another aspect of the invention, a process for producing 1,3,5-trioxane with recyclable additives is provided, operating on the aforementioned 1,3,5-trioxane production system with recyclable additives, comprising:

[0029] Formaldehyde solution was reacted in a synthetic reactive distillation column under the conditions of catalyst and additives to obtain crude 1,3,5-trioxane at the top of the column;

[0030] The crude 1,3,5-trioxane product obtained from the top of the synthetic reactive distillation column enters the light component removal column. After the light components are removed, an aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane is obtained in the bottom of the column.

[0031] The aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane obtained from the bottom of the light component removal tower is further separated in the product concentration tower. The gas phase at the top of the tower is condensed to obtain a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope with methanol and formic acid.

[0032] Benzene is added to the extraction tower as an extractant, and the product concentration tower tops a mixed solution of an azeotrope containing formaldehyde, 1,3,5-trioxane and water, methanol and formic acid is extracted to obtain the extract phase at the top of the extraction tower.

[0033] The extract phase obtained at the top of the extraction column is fed to the extractant recovery partition wall column, where 1,3,5-trioxane is obtained on the side of the extractant recovery partition wall column.

[0034] The reactive distillation column periodically discharges bottom liquid to maintain the sulfuric acid and sodium benzenesulfonate content in the bottom liquid phase. The discharged bottom liquid enters the membrane separation device for membrane separation. After membrane separation, the osmotic side yields a component containing sodium benzenesulfonate, formic acid and trioxymethylene, while the permeate side yields a component containing sulfuric acid, formaldehyde and water.

[0035] The component containing sodium benzenesulfonate, formic acid, and trioxymethylene obtained from the osmotic side of the membrane separation device enters the auxiliary agent extraction device, reacts with the oxidant to remove formic acid, and obtains an aqueous solution containing sodium benzenesulfonate and trioxymethylene, which is then recycled back to the synthesis reactive distillation column.

[0036] In a specific embodiment, the production process further includes:

[0037] Methanol and formaldehyde react in the methyl acetal reactive distillation column under resin catalyst conditions to produce methyl acetal.

[0038] The methyl acetal generated in the methyl acetal reactive distillation column undergoes an oxidation reaction with oxygen in the methyl acetal oxidation reactor under the condition of an iron-molybdenum catalyst to generate a reaction gas containing formaldehyde.

[0039] The formaldehyde-containing reaction gas generated by the methyl acetal oxidation reactor is cooled to 60-150°C and then enters the formaldehyde absorption tower. After circulation absorption, a formaldehyde solution is obtained in the bottom of the tower and then transported to the synthesis reaction distillation tower.

[0040] In a specific embodiment, the operating temperature of the synthetic reactive distillation column is 98–120°C, and the pressure is 0.01–0.05 MPaG; the operating temperature of the light component removal column is 80–120°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the product concentration column is 92–120°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the extraction column is 40–60°C, and the pressure is 0.1–0.6 MPaG; the operating temperature of the extractant recovery partition wall column is 70–90°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the membrane separation device is 98–120°C, the permeate side operating pressure is -0.01 to -0.05 MPaG, and the osmosis side operating pressure is 0.2–0.6 MPaG.

[0041] In a specific embodiment, in the synthetic reactive distillation column, the catalyst is sulfuric acid, the auxiliary agent is sodium benzenesulfonate, and the molar ratio of the auxiliary agent to the catalyst is 0.5 to 4:1; in the extractant recovery partition wall column, the mass ratio of the extractant to 1,3,5-trioxane in the feed is 0.4 to 4:1.

[0042] In a specific embodiment, the amount of benzene used in the extractant recovery interlayer tower is preferably benzene:1,3,5-trioxane mass ratio in the feed = 0.4-0.5:1.

[0043] In a specific embodiment, the operating temperature of the methyl acetal reactive distillation column is 60–120°C, and the pressure is 0.01–0.8 MPaG; the operating temperature of the methyl acetal oxidation reactor is 320–420°C, and the pressure is 0.1–0.3 MPaG; the operating temperature of the formaldehyde absorption tower is 100–150°C, and the pressure is 0.01–0.2 MPaG; in the methyl acetal reactive distillation column, the molar ratio of methanol to formaldehyde is 2–3:1; and in the methyl acetal oxidation reactor, the molar ratio of oxygen to methyl acetal is 1–2:1.

[0044] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0045] 1. The present invention provides a method and apparatus for producing 1,3,5-trioxane with recyclable additives. Based on the sulfuric acid process, a suitable salt additive, sodium benzenesulfonate, is added to adjust the reaction equilibrium concentration, which effectively improves the product yield and reduces the production of formic acid by-reaction, thereby reducing equipment corrosion.

[0046] 2. The present invention provides a high-yield, high-purity 1,3,5-trioxane production method and apparatus with recyclable additives. Besides improving reaction conversion rate and product yield, it also recovers the additive sodium benzenesulfonate to further reduce usage and processing costs, and is more economical than the traditional sulfuric acid process. With the same product output, due to the improved reaction conversion rate and product yield from the additive, 2.52 tons of steam can be saved per ton of product, resulting in energy savings of approximately RMB 453 per ton of product. Simultaneously, the additive and processing costs increase by approximately RMB 104 per ton. Ultimately, compared to the sulfuric acid process, production costs are reduced by RMB 349 per ton.

[0047] 3. Methylal is produced by reacting methanol with recycled dilute formaldehyde. The methylal is then oxidized to produce concentrated formaldehyde required for the synthesis of 1,3,5-trioxane. This process utilizes the characteristic that dilute formaldehyde is required as feedstock, allowing the dilute formaldehyde produced during the 1,3,5-trioxane synthesis separation to be utilized, eliminating the need for vacuum concentration and pressure distillation processes required in traditional dilute formaldehyde treatment. This process not only saves energy but also increases the upper limit of concentrated formaldehyde concentration. Traditional iron-molybdenum method for concentrated formaldehyde preparation requires vacuum concentration and pressure distillation processes to increase the concentration of the 45-55 wt% concentrated formaldehyde and recycled dilute formaldehyde produced by the iron-molybdenum method to over 60 wt%. The methylal oxidation process can produce 60-70 wt% concentrated formaldehyde, and the dilute formaldehyde directly reacts with methanol to synthesize methylal, resulting in a 48% energy saving compared to traditional methods.

[0048] 4. Before entering the extraction tower, the crude 1,3,5-trioxane product should be separated to remove components that may form trioxane heptacyclic rings (1,3-dioxane) as much as possible. At the same time, it should be concentrated to the azeotropic composition before entering the extraction tower. This ensures that the final purity of the product can still meet the requirements, i.e., formaldehyde <30ppm; water <40ppm; sodium ion <5ppm; formic acid <10ppm; 1,3,5-trioxane purity ≥99.99%, even with a relatively small benzene circulation volume.

[0049] 5. Regarding product extraction and separation, the use of a partition wall column for extractant recovery and product separation can further save energy. In the traditional process, a dual-column separation is used here. The extractant is recovered at the top of the first column, the bottom liquid is sent to the second column, the product is produced at the top of the second column, and the bottom liquid is sent to the product recovery column. In comparison, a single partition wall column replaces the dual columns, which can save 10-20% of energy consumption. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0051] Figure 1 This is a schematic diagram of the production process of 1,3,5-trioxane, a recyclable auxiliary agent disclosed in an embodiment of the present invention.

[0052] Figure 2 This is a schematic diagram of the production process for preparing 1,3,5-trioxane using the traditional sulfuric acid method, as shown in Comparative Example 1. Detailed Implementation

[0053] The process flow for Examples 1-5 can be found here. Figure 1 .

[0054] Example 1

[0055] 1) The added methanol, recycled methanol from the top of the methanol recovery tower, recycled dilute formaldehyde from the bottom of the product concentration tower, and recycled dilute formaldehyde from the top of the formaldehyde recovery tower are mixed and fed into the methyl acetal reactive distillation tower. The molar ratio of total methanol to total formaldehyde is 3:1. Inside the methyl acetal reactive distillation tower, methanol and formaldehyde react under catalytic conditions to produce methyl acetal. The catalyst used is a resin catalyst. The operating temperature of the methyl acetal reactive distillation tower is 70℃, and the operating pressure is 0.4 MPaG. The methyl acetal reactive distillation tower adopts a plate and packed composite type, with 20 theoretical plates. The bottom of the methyl acetal reactive distillation tower is wastewater, which is discharged to a wastewater treatment device. Methyl acetal is collected from the top of the tower. The methyl acetal synthesis reaction formula is as follows:

[0056]

[0057] 2) Methyl acetal from the top of the methyl acetal reactive distillation column, along with circulating air and fresh air from the circulating blower, are mixed at a molar ratio of oxygen:methyl acetal = 1.8:1 and enter the methyl acetal oxidation reactor. The methyl acetal oxidation reactor is a tubular reactor; the oxidation reaction occurs on the catalyst within the tubes. The catalyst is an iron-molybdenum catalyst. The reactor is set at a temperature of 380℃ and a pressure of 0.15 MPaG. The shell side of the methyl acetal oxidation reactor is filled with heat transfer oil to remove some of the heat generated by the reaction. The methyl acetal oxidation reaction formula is as follows:

[0058]

[0059] 3) After the reaction gas generated in the methyl acetal oxidation reactor is cooled to 60℃, it enters the formaldehyde absorption tower. The formaldehyde absorption tower is a composite type with plates and packing, with a theoretical configuration of 30 plates. The operating temperature is 130℃ and the pressure is 0.01 MPaG. After absorption by the circulating liquid in the bottom of the tower, a 60wt% concentrated formaldehyde solution is obtained. Part of the tail gas exiting from the top of the formaldehyde absorption tower is returned as circulating air to the inlet of the circulating blower, where it is pressurized and participates in the mixing of raw materials in the methyl acetal oxidation reactor. The outlet pressure of the circulating blower is 0.05 MPaG. The other part enters the ECS reactor, where it passes through the ECS catalyst bed and is oxidized and decomposed, converting the organic matter in the tail gas into CO2 and H2O, ultimately meeting emission requirements. The ECS catalyst used is a molecular sieve catalyst containing a small amount of Pt. The reactor is set at a temperature of 380℃ and a pressure of 0.15 MPaG.

[0060] 4) Sodium benzenesulfonate (auxiliary agent) and sulfuric acid (catalyst) are mixed in a molar ratio of 1.5:1, and then fed together with concentrated formaldehyde solution from the bottom of formaldehyde absorption tower 3 and a small amount of bottom liquid containing 1,3,5-trioxane from the bottom of the light component distillation tower into the synthesis reactive distillation column for catalytic reaction. The synthesized crude 1,3,5-trioxane product is collected from the top of the synthesis reactive distillation column. The synthesis reactive distillation column adopts a plate structure with 12 theoretical plates, an operating temperature of 98℃, and a pressure of 0.01 MPaG. The synthesis reaction formula is as follows:

[0061]

[0062] 2CH2O + H2O → HCOOH (formic acid) + CH4O

[0063] HCOOH + CH4O → HCOOCH3 (methyl formate) + H2O

[0064] 5) In the synthetic reactive distillation column, the bottom liquid needs to be periodically discharged to maintain the content of sulfuric acid and sodium benzenesulfonate in the bottom liquid, ensuring conversion rate and selectivity. The sulfuric acid content is controlled at 4 wt%, and the sodium benzenesulfonate content is controlled at 11 wt%. The discharged bottom liquid enters the membrane separation unit 15 for membrane separation. Following the pervaporation desalination process, the retained sodium benzenesulfonate, formic acid, and 1,3,5-trioxane enter the auxiliary agent extraction unit 16. The sulfuric acid, water, and other organic components, such as formaldehyde, on the permeate side after membrane separation are cooled and sent to the downstream sewage treatment plant for treatment. The membrane separation unit 15 operates at a temperature of 110℃, with a permeate side operating pressure of -0.01 MPaG and a residual side operating pressure of 0.4 MPaG. Sodium benzenesulfonate, formic acid, and 1,3,5-trioxane from membrane separation unit 15 are mixed with an oxidant, wherein hydrogen peroxide is used as the oxidant. Formic acid reacts with hydrogen peroxide under normal pressure and cobalt catalyst conditions to produce CO2 and water. The final remaining aqueous solution of sodium benzenesulfonate and 1,3,5-trioxane (1,3,5-trioxane does not react) can be recycled back to the synthesis reactive distillation column. The total recovery rate of the additives can reach 91%. This step can realize the recycling and reuse of additives to reduce their use and treatment costs.

[0065] 6) The crude 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 47.43 wt% 1,3,5-trioxane, 11.86 wt% formaldehyde, 0.09 wt% formic acid, and 38.69 wt% water (at this point, the formaldehyde conversion rate in the synthetic distillation reaction is 80%, and the yield of 1,3,5-trioxane is 79%). It is sent from the top of the synthetic reactive distillation column to a light component removal column for further removal of light components (the light components contain 1,3-dioxapentane, which easily forms trioxaheptacyclic rings, and the boiling point of trioxaheptacyclic rings is close to that of the product, affecting the final product separation purity. Other embodiments follow the same principle and will not be repeated). The light component removal column operates at a temperature of 90°C and a pressure of 0.006 MPaG, using a plate column structure with 10 theoretical plates. After condensation of the vapor phase at the top of the light component removal column, the liquid enters the light component distillation column at 65°C. The organic waste liquid separated at the top of the light component distillation column is incinerated. The organic waste liquid contains 9 wt% 1,3-dioxane, 62 wt% methyl formate, 10 wt% methanol, and methyl acetal, etc. The liquid phase at the bottom of the light component distillation column is returned to the synthesis reactive distillation column. The operating temperature of the light component distillation column is 40°C, the pressure is 0.005 MPaG, and it is a plate column with 10 theoretical plates. The aqueous solution containing methanol, formaldehyde, formic acid, and 1,3,5-trioxane in the bottom of the light component removal column is sent to the product concentration column for further separation. The operating temperature of the product concentration column is 92°C, the pressure is 0.005 MPaG, and it is a plate column with 18 theoretical plates. The dilute formaldehyde at the bottom of the product concentration tower is returned to the inlet of the methyl acetal reactive distillation tower. The vapor phase at the top of the product concentration tower is condensed into a liquid phase at 75°C. This liquid phase is an azeotrope of formaldehyde, 1,3,5-trioxane, and water, of which 1,3,5-trioxane accounts for 60 wt%, formaldehyde accounts for 6 wt%, and the remainder consists of water, methanol, formic acid, and other trace organic compounds. This liquid phase is then sent to the extraction tower.

[0066] 7) In the extraction tower, benzene is used as the extractant to extract the azeotrope. The operating temperature is 60℃, and the pressure is 0.4 MPaG. It is a plate tower with 22 theoretical plates. The mass ratio of benzene to 1,3,5-trioxane in the feed is 0.4:1. Sodium hydroxide solution is added to the extraction tower to neutralize the formic acid. The newly added benzene is mainly used to compensate for losses during the extractant recovery process. The raffinate at the bottom of the extraction tower is sent to the product recovery tower, and the extractant at the top is sent to the extractant recovery partition wall tower. This extractant recovery partition wall tower operates at 80℃ and 0.005 MPaG. It is a plate tower with 82 theoretical plates, and the middle 30 plates are equipped with partition plates. The condensate at the top of the extractant recovery interlayer column is mixed with water, and then the aqueous phase is separated by a water-oil separator and sent to the methanol recovery column for further separation of methanol and trace products. The methanol recovery column has a pressure of 0.005 MPaG, a plate column structure, and 20 theoretical plates. The methanol at the top of the methanol recovery column is recycled back to the inlet of the methyl acetal reactive distillation column, and the aqueous solution containing trace products at the bottom of the methanol recovery column is sent to the product recovery column. The oil phase of benzene extracted by the water-oil separator in the extractant recovery interlayer column is recycled back to the extraction column. The purity of the recycled benzene is 94%, and the yield is 99%. Qualified products are collected from the side of the extractant recovery interlayer column, of which 1,3,5-trioxane has a purity of 99.99%. The heavy components separated at the bottom of the column are sent to the product recovery column. In addition to the raffinate from the extraction tower, the bottom liquid from the extractant recovery interlayer tower, and the bottom liquid from the methanol recovery tower, the product recovery tower feed also includes a recycled liquid containing 18 wt% 1,3,5-trioxane from the downstream polymerization process (1,3,5-trioxane enters the polymerization process to synthesize polyoxymethylene resin, part of which is converted into polyoxymethylene resin, and the unreacted portion is returned to the product recovery tower as polymerization recycled liquid. Other embodiments are similar and will not be repeated). The purpose of the product recovery tower is mainly to recover a small amount of product from the above feed to improve the product yield. The concentrated product aqueous solution at the top of the product recovery tower is returned to the inlet of the extraction tower. The product recovery tower operates at a temperature of 105°C and a pressure of 0.006 MPaG, with a plate tower structure and a theoretical plate size of 25. The formaldehyde-containing aqueous solution in the bottom of the product recovery tower is sent to the formaldehyde recovery tower. Dilute formaldehyde is separated at the top of the formaldehyde recovery tower and returned to the inlet of the methyl acetal reactive distillation tower. The aqueous solution containing heavy organic components and sodium formate is collected from the bottom of the formaldehyde recovery tower and discharged as wastewater to the wastewater treatment unit. The formaldehyde recovery tower operates at a temperature of 135℃ and a pressure of 0.25 MPaG. It is a plate tower with a theoretical plate count of 32.

[0067] Example 2

[0068] Steps 1), 2), and 3) are the same as in Example 1.

[0069] 4) Sodium benzenesulfonate (auxiliary agent) and sulfuric acid (catalyst) are mixed at a molar ratio of 0.75:1, and then fed together with concentrated formaldehyde solution from the bottom of formaldehyde absorption tower 3 and a small amount of bottom liquid containing 1,3,5-trioxane from the bottom of the light component distillation tower into the synthesis reactive distillation column for catalytic reaction. The synthesized crude 1,3,5-trioxane product is collected from the top of the synthesis reactive distillation column. The synthesis distillation column 6 adopts a plate structure with 12 theoretical plates, an operating temperature of 98℃, and a pressure of 0.01 MPaG. The synthesis reaction formula is as follows:

[0070]

[0071] 2CH2O + H2O → HCOOH (formic acid) + CH4O

[0072] HCOOH + CH4O → HCOOCH3 (methyl formate) + H2O

[0073] Step 5) is the same as in Example 1.

[0074] 6) The 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 41.78 wt% 1,3,5-trioxane, 15.94 wt% formaldehyde, 0.10 wt% formic acid, and 38.69 wt% water (at this point, the formaldehyde conversion rate in the synthetic distillation reaction is 73%, and the 1,3,5-trioxane yield is 70%). This product is sent from the top of the synthetic reactive distillation column to a light component removal column for further removal of light components. The light component removal column operates at a temperature of 90°C and a pressure of 0.006 MPaG, using a plate column structure with 10 theoretical plates. After condensation of the vapor phase at the top of the light component removal column, the liquid enters the light component distillation column at 65°C. The organic waste liquid separated at the top of the light component distillation column is incinerated. The organic waste liquid contains 9 wt% 1,3-dioxane, 65 wt% methyl formate, 10 wt% methanol, and methyl acetal, etc. The liquid phase at the bottom of the light component distillation column is returned to the synthesis reactive distillation column. The operating temperature of the light component distillation column is 40°C, the pressure is 0.005 MPaG, and it is a plate column with 10 theoretical plates. The aqueous solution containing methanol, formaldehyde, formic acid, and 1,3,5-trioxane in the bottom of the light component removal column is sent to the product concentration column for further separation. The operating temperature of the product concentration column is 92°C, the pressure is 0.005 MPaG, and it is a plate column with 18 theoretical plates. The dilute formaldehyde solution at the bottom of the product concentration tower is returned to the inlet of the methyl acetal reactive distillation tower. The vapor phase at the top of the product concentration tower is condensed into a liquid phase by a condenser. The liquid phase at 75°C is an azeotrope of formaldehyde, 1,3,5-trioxane and water, of which 1,3,5-trioxane accounts for 60 wt%, formaldehyde accounts for 6 wt%, and the remainder consists of water, methanol, formic acid and other trace organic compounds, which are then sent to the extraction tower.

[0075] Step 7) is the same as in Example 1.

[0076] With the same product output, due to the reduced feed amount of additives, the conversion rate of the synthetic distillation reaction and the product yield also decrease. Therefore, energy consumption can be reduced by 1.68 tons of steam per ton of product produced, resulting in energy savings of approximately 302 yuan / ton of product. However, the added costs for additives and processing are approximately 52 yuan / ton. Ultimately, compared to the sulfuric acid process, production costs can be reduced by 250 yuan / ton.

[0077] Example 3

[0078] Steps 1) and 2) are the same as in Example 1.

[0079] 3) After the reaction gas generated in the methyl acetal oxidation reactor is cooled to 60℃, it enters the formaldehyde absorption tower. The formaldehyde absorption tower is a plate tower with 20 theoretical plates, an operating temperature of 110℃, and a pressure of 0.01 MPaG. After absorption by the circulating liquid in the bottom of the tower, a 57% concentrated formaldehyde solution is obtained in the bottom of the formaldehyde absorption tower. Part of the tail gas exiting from the top of the formaldehyde absorption tower is returned as circulating air to the inlet of the circulating blower, where it is pressurized and participates in the mixing of raw materials in the methyl acetal oxidation reactor. The outlet pressure of the circulating blower is 0.05 MPaG. The other part enters the ECS reactor, passing through the ECS catalyst bed and being oxidized and decomposed. The ECS catalyst used is a molecular sieve catalyst containing a small amount of Pt. The reactor is set at a temperature of 380℃ and a pressure of 0.15 MPaG.

[0080] 4) Sodium benzenesulfonate (auxiliary agent) and sulfuric acid (catalyst) are mixed in a molar ratio of 2:1, and then fed together with concentrated formaldehyde solution from the bottom of formaldehyde absorption tower 3 and a small amount of bottom liquid containing 1,3,5-trioxane from the bottom of the light component distillation tower into the synthesis reactive distillation column for catalytic reaction. The synthesized crude 1,3,5-trioxane product is collected from the top of the synthesis reactive distillation column. The synthesis reactive distillation column adopts a plate structure with 12 theoretical plates, an operating temperature of 98℃, and a pressure of 0.01 MPaG. The synthesis reaction formula is as follows:

[0081]

[0082] 2CH2O + H2O → HCOOH (formic acid) + CH4O

[0083] HCOOH + CH4O → HCOOCH3 (methyl formate) + H2O

[0084] Step 5) is the same as in Example 1).

[0085] 6) The crude 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 39.63 wt% 1,3,5-trioxane, 14.83 wt% formaldehyde, 0.12 wt% formic acid, and 38.69 wt% water (at this point, the formaldehyde conversion rate in the synthetic distillation reaction is 74%, and the 1,3,5-trioxane yield is 70%). It is sent from the top of the synthetic reactive distillation column to a light component removal column for further removal of light components. The light component removal column operates at a temperature of 90℃ and a pressure of 0.006 MPaG, using a plate column structure with 10 theoretical plates. After condensation of the vapor phase at the top of the light component removal column, the liquid enters the light component distillation column at 65°C. The organic waste liquid separated at the top of the light component distillation column is incinerated. The organic waste liquid contains 9 wt% 1,3-dioxane, 65 wt% methyl formate, 10 wt% methanol, and methyl acetal, etc. The liquid phase at the bottom of the light component distillation column is returned to the synthesis reactive distillation column. The operating temperature of the light component distillation column is 40°C, the pressure is 0.005 MPaG, and it is a plate column with 10 theoretical plates. The aqueous solution of methanol, formaldehyde, formic acid, and 1,3,5-trioxane at the bottom of the light component removal column is sent to the product concentration column for further separation. The operating temperature of the product concentration column is 92°C, the pressure is 0.005 MPaG, and it is a plate column with 18 theoretical plates. The dilute formaldehyde at the bottom of the product concentration tower is returned to the inlet of the methyl acetal reactive distillation tower. The vapor phase at the top of the product concentration tower is condensed into a liquid phase by a condenser. The liquid phase at 75°C is an azeotrope of formaldehyde, 1,3,5-trioxane and water, of which 1,3,5-trioxane accounts for 60 wt%, formaldehyde accounts for 6 wt%, and the remainder consists of water, methanol and formic acid and other trace organic compounds, which are then sent to the extraction tower.

[0086] Step 7) is the same as in Example 1).

[0087] With the same product output, due to the decrease in concentrated formaldehyde concentration and the increase in the amount of auxiliary materials, the conversion rate and product yield of the synthetic distillation reaction are not much different from those in Example 2. However, the energy consumption can only be reduced by 0.956t of steam per ton of product, resulting in an energy saving of approximately 172 yuan / ton of product. At the same time, the cost of auxiliary materials and processing increases by approximately 138 yuan / ton. Ultimately, compared with the sulfuric acid method, the production cost can be reduced by 33.54 yuan / ton.

[0088] Example 4:

[0089] 1) Newly added methanol, recycled methanol from the top of the methanol recovery tower, recycled formaldehyde from the bottom of the product concentration tower, and recycled dilute formaldehyde from the top of the formaldehyde recovery tower are mixed and fed into the methyl acetal reactive distillation tower. The molar ratio of total methanol to total formaldehyde is 2:1. Inside the methyl acetal reactive distillation tower, methanol and formaldehyde react under catalytic conditions to produce methyl acetal. The catalyst used is a resin catalyst. The operating temperature of the methyl acetal reactive distillation tower is 60℃, and the operating pressure is 0.01 MPaG. The methyl acetal reactive distillation tower is a plate type, with a theoretical plate configuration of 50 plates. The bottom of the methyl acetal reactive distillation tower is wastewater, which is discharged to a wastewater treatment device. Methyl acetal is collected from the top of the tower. The methyl acetal synthesis reaction formula is as follows:

[0090]

[0091] 2) Methyl acetal from the top of the methyl acetal reactive distillation column, along with circulating air and fresh air from the circulating blower, are mixed in a molar ratio of oxygen:methyl acetal = 1:1 and enter the methyl acetal oxidation reactor. The methyl acetal oxidation reactor is a tubular reactor; the oxidation reaction occurs on the catalyst within the tubes. An iron-molybdenum catalyst is used. The reactor is set at a temperature of 320℃ and a pressure of 0.1 MPaG. The shell side of the methyl acetal oxidation reactor is filled with heat transfer oil to remove some of the heat generated by the reaction. The methyl acetal oxidation reaction formula is as follows:

[0092]

[0093] 3) After the reaction gas generated in the methyl acetal oxidation reactor is cooled to 150℃, it enters the formaldehyde absorption tower. The formaldehyde absorption tower uses packed bed material with 60 theoretical plates, operating at 100℃ and 0.2 MPaG. After absorption by the circulating liquid in the bottom of the tower, a 60wt% concentrated formaldehyde solution is obtained. Part of the tail gas exiting the top of the formaldehyde absorption tower is returned as circulating air to the inlet of the circulating blower, where it is pressurized and participates in the mixing of raw materials in the methyl acetal oxidation reactor. The outlet pressure of the circulating blower is 0.03 MPaG. The other part enters the ECS reactor, passing through the ECS catalyst bed and being oxidized and decomposed. The ECS catalyst used is a molecular sieve catalyst containing a small amount of Pt. The reactor is set at 320℃ and 0.1 MPaG.

[0094] 4) Sodium benzenesulfonate (auxiliary agent) and sulfuric acid (catalyst) are mixed at a molar ratio of 0.5:1, and then fed together with concentrated formaldehyde solution from the bottom of formaldehyde absorption tower 3 and a small amount of bottom liquid containing 1,3,5-trioxane from the bottom of the light component distillation tower into the synthesis reactive distillation column for catalytic reaction. The synthesized crude 1,3,5-trioxane product is collected from the top of the synthesis reactive distillation column. The synthesis reactive distillation column adopts a plate structure with 10 theoretical plates, a temperature of 120℃, and a pressure of 0.05 MPaG. The synthesis reaction formula is as follows:

[0095]

[0096] 2CH2O + H2O → HCOOH (formic acid) + CH4O

[0097] HCOOH + CH4O → HCOOCH3 (methyl formate) + H2O

[0098] 5) In the synthetic reactive distillation column, the bottom liquid phase needs to be periodically discharged to maintain the content of sulfuric acid and sodium benzenesulfonate in the bottom of the column, ensuring conversion rate and selectivity. The sulfuric acid content is controlled at 2 wt%, and the sodium benzenesulfonate content is controlled at 1 wt%. The discharged bottom liquid enters the membrane separation unit 15 for membrane separation. Following the pervaporation desalination process, the retained sodium benzenesulfonate, formic acid, and 1,3,5-trioxane enter the auxiliary agent extraction unit 16. The sulfuric acid, water, and other organic components, such as formaldehyde, on the permeate side after membrane separation are cooled and sent to the downstream sewage treatment plant for treatment. The membrane separation unit 15 operates at a temperature of 98℃, with a permeate side operating pressure of -0.05 MPaG and a residual side operating pressure of 0.2 MPaG. Sodium benzenesulfonate, formic acid, and 1,3,5-trioxane from membrane separation unit 15 are mixed with an oxidant, wherein hydrogen peroxide is used as the oxidant. Formic acid reacts with hydrogen peroxide under normal pressure and cobalt catalyst conditions to produce CO2 and water. After the reaction, the final remaining components are an aqueous solution of sodium benzenesulfonate and 1,3,5-trioxane (1,3,5-trioxane does not react). The total recovery rate of the additives can reach 90%, and they can be recycled back to the synthesis reactive distillation column.

[0099] 6) The crude 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 38.2 wt% 1,3,5-trioxane, 21.09 wt% formaldehyde, 0.14 wt% formic acid, and 38.64 wt% water (at this point, the formaldehyde conversion rate in the synthetic distillation reaction is 64.85%, and the 1,3,5-trioxane yield is 63.66%). This product is sent from the top of the synthetic reactive distillation column to a light component removal column for further removal of light components. The light component removal column operates at a temperature of 80℃ and a pressure of 0.005 MPaG, using a plate column structure with 7 theoretical plates. After condensation of the vapor phase at the top of the light component removal column, the product enters the light component distillation column at 60°C. The organic waste liquid separated at the top of the light component distillation column is incinerated. The organic waste liquid contains 9 wt% 1,3-dioxane, 62 wt% methyl formate, 10 wt% methanol, and methyl acetal, etc. The liquid phase at the bottom of the light component distillation column is returned to the synthesis reactive distillation column. The operating temperature of the light component distillation column is 35°C, the pressure is 0.02 MPaG, and it is a plate column with 7 theoretical plates. The aqueous solution containing methanol, formaldehyde, formic acid, and 1,3,5-trioxane in the bottom of the light component removal column is sent to the product concentration column for further separation. The operating temperature of the product concentration column is 120°C, the pressure is 0.02 MPaG, and it is a plate column with 15 theoretical plates. The dilute formaldehyde at the bottom of the product concentration tower is returned to the inlet of the methyl acetal reactive distillation tower. The vapor phase at the top of the product concentration tower is condensed into a liquid phase by a condenser. The liquid phase at 70°C is an azeotrope of formaldehyde, 1,3,5-trioxane and water, of which 1,3,5-trioxane accounts for 60 wt%, formaldehyde accounts for 6 wt%, and the remainder is water, methanol and formic acid and other trace organic substances, which are sent to the extraction tower.

[0100] 7) In the extraction tower, benzene is used as the extractant to extract the azeotrope. The operating temperature is 40℃, and the pressure is 0.1 MPaG. It is a packed tower with 7 theoretical plates. The mass ratio of benzene to 1,3,5-trioxane in the feed is 4:1. Sodium hydroxide solution is added to the extraction tower to neutralize the formic acid in the tower. The newly added benzene is mainly used to replenish the losses during the extraction process. The raffinate at the bottom of the extraction tower is sent to the product recovery tower, and the extract phase at the top is sent to the extractant recovery partition tower. This partition tower operates at 70℃ and 0.02 MPaG. It is a plate tower with 30 theoretical plates and 10 partition plates in the middle. The condensate at the top of the extractant recovery interlayer column is mixed with water, and then the aqueous phase is separated by a water-oil separator and sent to the methanol recovery column. The methanol recovery column has a pressure of 0.02 MPaG, a plate column structure, and a theoretical plate size of 35. It can separate methanol and trace products. The methanol at the top of the methanol recovery column is recycled back to the inlet of the methyl acetal reactive distillation column, and the aqueous solution containing trace products at the bottom of the methanol recovery column is sent to the product recovery column. The oil phase of benzene extracted by the water-oil separator in the extractant recovery interlayer column is recycled back to the extraction column. The purity of the recycled benzene is 94%, and the yield is 99%. Qualified products are collected from the side of the extractant recovery interlayer column, of which 1,3,5-trioxane has a purity of 99.99%. The heavy components separated at the bottom of the column are sent to the product recovery column. The product recovery tower feeds the raffinate from the extraction tower, the bottom liquid from the extractant recovery interlayer tower, and the bottom liquid from the methanol recovery tower, as well as a recycled liquid containing 18 wt% 1,3,5-trioxane from the downstream polymerization process. The purpose of the product recovery tower is primarily to recover small amounts of product from the feed to improve product yield. The concentrated product aqueous solution at the top of the product recovery tower is returned to the inlet of the extraction tower. The product recovery tower operates at a temperature of 80°C and a pressure of 0.005 MPaG, using a plate tower structure with 12 theoretical plates. The formaldehyde aqueous solution in the bottom of the product recovery tower is sent to the formaldehyde recovery tower. Dilute formaldehyde separated at the top of the formaldehyde recovery tower is returned to the inlet of the methyl acetal reactive distillation tower. The formaldehyde recovery tower bottom yields an aqueous solution containing heavy organic components and sodium formate, which is discharged as wastewater to the wastewater treatment unit. The formaldehyde recovery tower operates at a temperature of 110°C and a pressure of 0.15 MPaG, using a plate tower structure with 30 theoretical plates.

[0101] With the same product output, the sodium benzenesulfonate additive improves the conversion rate and product yield of the synthetic distillation reaction, resulting in a saving of 0.534 tons of steam per ton of product. This energy saving amounts to approximately 93 yuan per ton of product, while increasing the cost of additives and processing by approximately 34 yuan per ton. Ultimately, compared to the sulfuric acid process, this saves 59 yuan per ton in production costs. Furthermore, the extractant recovery utilizes a partitioned wall tower; under the aforementioned operating conditions, energy consumption can be reduced by 10% compared to the traditional dual-tower process.

[0102] Example 5:

[0103] 1) Newly added methanol, recycled methanol from the top of the methanol recovery tower, recycled dilute formaldehyde from the bottom of the product concentration tower, and recycled dilute formaldehyde from the top of the formaldehyde recovery tower are mixed and fed into the methyl acetal reactive distillation tower. The molar ratio of total methanol to total formaldehyde is 2.5:1. Inside the methyl acetal reactive distillation tower, methanol and formaldehyde react under catalytic conditions to produce methyl acetal. The catalyst used is a resin catalyst. The operating temperature of the methyl acetal reactive distillation tower is 120℃, and the operating pressure is 0.8 MPaG. The methyl acetal reactive distillation tower is packed with 40 theoretical plates. The bottom of the methyl acetal reactive distillation tower is wastewater, which is discharged to a wastewater treatment unit. Methyl acetal is collected from the top of the tower. The methyl acetal synthesis reaction formula is as follows:

[0104]

[0105] 2) Methyl acetal from the top of the methyl acetal reactive distillation column, along with circulating air and fresh air from the circulating blower, are mixed at a molar ratio of oxygen:methyl acetal = 2:1 and enter the methyl acetal oxidation reactor. The methyl acetal oxidation reactor is a tubular reactor; the oxidation reaction occurs on the catalyst within the tubes. An iron-molybdenum catalyst is used. The reactor is set at a temperature of 420℃ and a pressure of 0.3 MPaG. The shell side of the methyl acetal oxidation reactor is filled with heat transfer oil to remove some of the heat generated by the reaction. The methyl acetal oxidation reaction formula is as follows:

[0106]

[0107] 3) After the reaction gas generated in the methyl acetal oxidation reactor is cooled to 70℃, it enters the formaldehyde absorption tower. The formaldehyde absorption tower uses packed bed material with 60 theoretical plates, operating at 100℃ and 0.2 MPaG. After absorption by the circulating liquid in the bottom of the tower, a 60wt% concentrated formaldehyde solution is obtained. Part of the tail gas exiting the top of the formaldehyde absorption tower is returned as circulating air to the inlet of the circulating blower, where it is pressurized and participates in the mixing of raw materials in the methyl acetal oxidation reactor. The outlet pressure of the circulating blower is 0.25 MPaG. The other part enters the ECS reactor, passing through the ECS catalyst bed where it is oxidized and decomposed. The ECS catalyst used is a molecular sieve catalyst containing a small amount of Pt. The reactor is set at 420℃ and 0.3 MPaG.

[0108] 4) Sodium benzenesulfonate (auxiliary agent) and sulfuric acid (catalyst) are mixed in a molar ratio of 4:1, and then fed together with concentrated formaldehyde solution from the bottom of formaldehyde absorption tower 3 and a small amount of bottom liquid containing 1,3,5-trioxane from the bottom of the light component distillation tower into the synthesis reactive distillation column for catalytic reaction. The synthesized crude 1,3,5-trioxane product is collected from the top of the synthesis reactive distillation column. The synthesis reactive distillation column adopts a plate structure with 30 theoretical plates, a temperature of 102℃, and a pressure of 0.02 MPaG. The synthesis reaction formula is as follows:

[0109]

[0110] 2CH2O + H2O → HCOOH (formic acid) + CH4O

[0111] HCOOH + CH4O → HCOOCH3 (methyl formate) + H2O

[0112] 5) In the synthetic reactive distillation column, the bottom liquid needs to be periodically discharged to maintain the content of sulfuric acid and sodium benzenesulfonate in the bottom liquid, ensuring conversion rate and selectivity. The sulfuric acid content is controlled at 5 wt%, and the sodium benzenesulfonate content is controlled at 15 wt%. The discharged bottom liquid enters the membrane separation unit 15 for membrane separation. Following the pervaporation desalination process, the retained sodium benzenesulfonate, formic acid, and 1,3,5-trioxane enter the auxiliary agent extraction unit 16. The sulfuric acid, water, and other organic components, such as formaldehyde, on the permeate side after membrane separation are cooled and sent to the downstream sewage treatment plant for treatment. The membrane separation unit 15 operates at a temperature of 120℃, with a permeate side operating pressure of -0.02 MPaG and a residual side operating pressure of 0.6 MPaG. Sodium benzenesulfonate, formic acid, and 1,3,5-trioxane from membrane separation unit 15 are mixed with an oxidant, wherein hydrogen peroxide is used as the oxidant. Formic acid reacts with hydrogen peroxide under normal pressure and cobalt catalyst conditions to produce CO2 and water. After the reaction, the final remaining components are an aqueous solution of sodium benzenesulfonate and 1,3,5-trioxane (1,3,5-trioxane does not react). The total recovery rate of the additives can reach 90.5%, which can be recycled back to the synthesis reactive distillation column.

[0113] 6) The crude 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 47.43 wt% 1,3,5-trioxane, 11.86 wt% formaldehyde, 0.09 wt% formic acid, and 38.69 wt% water (at this point, the formaldehyde conversion rate in the synthetic distillation reaction is 80%, and the 1,3,5-trioxane yield is 79%). It is sent from the top of the synthetic reactive distillation column to a light component removal column for further removal of light components. The light component removal column operates at a temperature of 120℃ and a pressure of 0.02 MPaG, using a plate column structure with 20 theoretical plates. After condensation of the vapor phase at the top of the light component removal column, the product enters the light component distillation column at 80°C. The organic waste liquid separated at the top of the light component distillation column is incinerated. The organic waste liquid contains 9 wt% 1,3-dioxane, 62 wt% methyl formate, 10 wt% methanol, and methyl acetal, etc. The liquid phase at the bottom of the light component distillation column is returned to the synthesis reactive distillation column. The light component distillation column operates at a temperature of 80°C and a pressure of 0.02 MPaG. It is a plate column with a theoretical plate of 25. The aqueous solution containing methanol, formaldehyde, formic acid, and 1,3,5-trioxane at the bottom of the light component removal column is sent to the product concentration column for further separation. The product concentration column operates at a temperature of 120°C and a pressure of 0.02 MPaG. It is a plate column with a theoretical plate of 35. The dilute formaldehyde at the bottom of the product concentration tower is returned to the inlet of the methyl acetal reactive distillation tower. The vapor phase at the top of the product concentration tower is condensed into a liquid phase by a condenser. The liquid phase at 80°C is an azeotrope of formaldehyde, 1,3,5-trioxane and water, of which 1,3,5-trioxane accounts for 60 wt%, formaldehyde accounts for 6 wt%, and the remainder consists of water, methanol and formic acid and other trace organic compounds, which are then sent to the extraction tower.

[0114] 7) In the extraction tower, benzene is used as the extractant to extract the azeotrope. The operating temperature is 50℃, and the pressure is 0.6 MPaG. It is a packed tower with 35 theoretical plates. The mass ratio of benzene to 1,3,5-trioxane in the feed is 0.5:1. Sodium hydroxide solution is added to the extraction tower to neutralize the formic acid. The newly added benzene is mainly used to replenish the losses during the extraction process. The raffinate at the bottom of the extraction tower is sent to the product recovery tower, and the extract phase at the top is sent to the extractant recovery partition tower. This extractant recovery partition tower operates at 90℃ and 0.02 MPaG. It is a plate tower with 82 theoretical plates and 30 partition plates in the middle. The condensate at the top of the extractant recovery interlayer column is mixed with water, and then the aqueous phase is separated by a water-oil separator and sent to the methanol recovery column for further separation of methanol and trace products. The methanol recovery column has a pressure of 0.02 MPaG, a plate column structure, and a theoretical plate size of 35. The methanol at the top of the methanol recovery column is recycled back to the inlet of the methyl acetal reactive distillation column, and the aqueous solution containing trace products at the bottom of the methanol recovery column is sent to the product recovery column. The oil phase of benzene extracted by the water-oil separator in the extractant recovery interlayer column is recycled back to the extraction column. The purity of the recycled benzene is 94%, and the yield is 99%. Qualified products are collected from the side of the extractant recovery interlayer column, of which 1,3,5-trioxane has a purity of 99.99%. The heavy components separated at the bottom of the column are sent to the product recovery column. The product recovery tower feeds the raffinate from the extraction tower, the bottom liquid from the extractant recovery interlayer tower, and the bottom liquid from the methanol recovery tower, as well as a recycled liquid containing 18 wt% 1,3,5-trioxane from the downstream polymerization process. The purpose of the product recovery tower is primarily to recover small amounts of product from the feed to improve product yield. The concentrated product aqueous solution at the top of the product recovery tower is returned to the inlet of the extraction tower. The product recovery tower operates at a temperature of 130°C and a pressure of 0.02 MPaG, using a plate tower structure with a theoretical plate size of 30. The formaldehyde aqueous solution in the bottom of the product recovery tower is sent to the formaldehyde recovery tower. Dilute formaldehyde separated at the top of the formaldehyde recovery tower is returned to the inlet of the methyl acetal reactive distillation tower. The formaldehyde recovery tower bottom yields an aqueous solution containing heavy organic components and sodium formate, which is discharged as wastewater to the wastewater treatment unit. The formaldehyde recovery tower operates at a temperature of 145°C and a pressure of 0.55 MPaG, using a plate tower structure with a theoretical plate size of 60.

[0115] With the same product output, the sodium benzenesulfonate additive improves the conversion rate and product yield of the synthetic distillation reaction, resulting in a saving of 2.52 tons of steam per ton of product. This energy saving amounts to approximately 453 yuan per ton of product, while increasing the cost of additives and processing by approximately 141 yuan per ton. Ultimately, this results in a cost saving of 312 yuan per ton compared to the sulfuric acid process. Furthermore, the extractant recovery utilizes a partitioned wall tower, and under the aforementioned operating conditions, energy consumption can be reduced by 20% compared to the traditional dual-tower process.

[0116] Comparative Example 1

[0117] This comparative example uses the traditional sulfuric acid process; the specific process flow can be found in [reference needed]. Figure 2 .

[0118] 1) A conventional formaldehyde oxidation method is used to prepare 60wt% concentrated formaldehyde feedstock: newly added methanol, recycled methanol from the top of the methanol recovery tower, and recycled air from the circulating blower are mixed with fresh air in excess of oxygen (methanol to oxygen molar ratio of 0.96:1) and fed into the formaldehyde oxidation reactor. The formaldehyde oxidation reactor is a tubular reactor, where the oxidation reaction occurs on the catalyst within the tubes. An iron-molybdenum catalyst is used. The reactor is set at a temperature of 268℃ and a pressure of 0.1 MPaG. The formaldehyde oxidation reaction formula is as follows:

[0119]

[0120] 2) After the reaction gas generated in the formaldehyde oxidation reactor is cooled to 120℃, it enters the formaldehyde absorption tower. The formaldehyde absorption tower is a composite type with plates and packing, with a theoretical configuration of 30 plates. The operating temperature is 55℃ and the pressure is 0.03 MPaG. After absorption by the circulating liquid in the bottom of the tower, a 45-55 wt% concentrated formaldehyde solution is obtained from the bottom of the formaldehyde absorption tower. Part of the tail gas exiting from the top of the formaldehyde absorption tower is returned as circulating air to the inlet of the circulating blower, where it is pressurized and participates in the raw material mixing. The outlet pressure of the circulating blower is 0.077 MPaG. The other part enters the ECS reactor, passing through the ECS catalyst bed where it is oxidized and decomposed. The ECS catalyst used is a molecular sieve catalyst containing a small amount of Pt. The reactor is set at a temperature of 380℃ and a pressure of 0.15 MPaG.

[0121] 3) A 45-55 wt% concentrated formaldehyde solution is fed into a vacuum concentration unit at an operating pressure of 25 kPaA and an operating temperature of 68°C, yielding a 60 wt% concentrated formaldehyde liquid phase, which is then fed into a synthesis reactive distillation column. The gaseous dilute formaldehyde obtained from the vacuum concentration is fed into a pressure distillation unit at an operating pressure of 350 kPaA and an operating temperature of 135°C, using 28 theoretical plates. The top of the pressure distillation unit yields a concentrated formaldehyde solution with a concentration similar to the circulating dilute formaldehyde concentration at the top of the formaldehyde recovery tower. The two solutions are mixed and recycled back to the inlet of the vacuum concentration unit. Wastewater is discharged from the bottom of the pressure distillation unit.

[0122] 4) Using the traditional sulfuric acid process, sulfuric acid and concentrated formaldehyde from a vacuum concentration unit are fed together into a synthetic reactive distillation column for the synthesis reaction. The synthesized crude 1,3,5-trioxane is collected from the top of the synthetic reactive distillation column. The synthetic reactive distillation column adopts a plate structure with 12 theoretical plates, an operating temperature of 98℃, and a pressure of 0.01 MPaG.

[0123] 5) In the reactive distillation column, the liquid phase containing sulfuric acid in the bottom layer needs to be periodically drained to maintain its concentration in the column and ensure conversion rate and selectivity. The sulfuric acid content in the liquid phase should be controlled at 4 wt%.

[0124] 6) The crude 1,3,5-trioxane product collected from the top of the synthetic reactive distillation column contains 36.14 wt% 1,3,5-trioxane and 0.19 wt% formic acid (at this time, the formaldehyde conversion rate of the synthetic distillation reaction is 67%, and the yield of 1,3,5-trioxane is 60%), and is sent from the top of the synthetic reactive distillation column to the extraction column.

[0125] 7) In the extraction tower, benzene is used as the extractant to extract the crude 1,3,5-trioxane. The operating temperature is 60℃, the pressure is 0.4 MPaG, and the tower has a plate structure with 22 theoretical plates. The mass ratio of benzene to 1,3,5-trioxane in the feed is 1.11:1. The raffinate at the bottom of the extraction tower is sent to the product recovery tower, and the extractant at the top is sent to the extractant recovery tower. This extractant recovery tower operates at 80℃ and 0.005 MPaG, and has a plate structure with 61 theoretical plates. Water is added to the condensate at the top of the extractant recovery tower, and the aqueous phase is separated by a water-oil separator and sent to the methanol recovery tower. The methanol recovery tower operates at 0.005 MPaG, has a plate structure with 20 theoretical plates, and can separate methanol and trace products. The methanol at the top of the methanol recovery tower is recycled back to the inlet of the formaldehyde oxidation reactor, and the aqueous solution containing trace products at the bottom of the methanol recovery tower is sent to the product recovery tower. The oil phase benzene extracted by the water-oil separator in the extractant recovery tower is recycled back to the extraction tower. The purity of the recycled benzene is 94%, and the yield is 99%. The bottom liquid of the extractant recovery tower is sent to the product tower. Qualified product is collected from the top of the product tower, of which 1,3,5-trioxane has a purity of 99.9%. Heavy components are separated from the bottom of the tower and enter the product recovery tower. In addition to the raffinate from the extraction tower, the bottom liquid from the product tower, and the bottom liquid from the methanol recovery tower, the feed to the product recovery tower also includes a circulating liquid containing 18wt% 1,3,5-trioxane from the downstream polymerization process. The purpose of the product recovery tower is mainly to recover a small amount of product from the above feed to improve the product yield. The concentrated product aqueous solution at the top of the product recovery tower is returned to the inlet of the extraction tower. The product recovery tower operates at a temperature of 105℃ and a pressure of 0.006MPaG. It is a plate tower with a theoretical plate size of 25. The formaldehyde-containing aqueous solution in the bottom of the product recovery tower is sent to the formaldehyde recovery tower. Dilute formaldehyde is separated at the top of the formaldehyde recovery tower and returned to the inlet of the vacuum concentration equipment. The aqueous solution containing heavy organic components and sodium formate is collected from the bottom of the formaldehyde recovery tower and discharged as wastewater to the wastewater treatment unit. The formaldehyde recovery tower operates at a temperature of 135℃ and a pressure of 0.25 MPaG. It is a plate tower with a theoretical plate count of 32.

[0126] As can be seen from the above examples and comparative examples, the yield of 1,3,5-trioxane in Examples 1-5 reached 63.66-79%, which is higher than the yield of the conventional sulfuric acid method in Comparative Example 1; the formic acid content in the products of Examples 1-5 was 0.09-0.14%, which is lower than the formic acid content in Comparative Example 1, indicating that the method of the present invention can effectively improve the yield of 1,3,5-trioxane and reduce the yield of formic acid by side reaction; the production cost of Examples 1-5 is 33.54-349 yuan / ton lower than the production cost of the conventional sulfuric acid method in Comparative Example 1; furthermore, In Examples 1-3 and Example 5, the amount of benzene used as the extractant in step 7) was 0.4-0.5:1 (benzene:feed mass ratio = 0.4-0.5). Compared to Comparative Example 1, where the traditional sulfuric acid method used benzene as the extractant in a mass ratio of 1.11:1, this method achieved the required final product purity with a smaller benzene recycling rate: formaldehyde < 30 ppm; water < 40 ppm; sodium ions < 5 ppm; formic acid < 10 ppm; and 1,3,5-trioxane purity ≥ 99.99%.

Claims

1. A 1,3,5-trioxane production system of a recyclable aid, characterized by, include: In the synthetic reactive distillation column, the additives, catalysts and formaldehyde undergo a catalytic reaction, and the synthesized crude product 1,3,5-trioxane is obtained at the top of the column; The crude 1,3,5-trioxane product obtained from the top of the synthetic reactive distillation column is de-contaminated in the light component removal column to remove light components, and an aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane is obtained in the bottom of the column. In the product concentration tower, the aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane obtained from the bottom of the light component removal tower is separated. The gas phase at the top of the tower is condensed to obtain a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope with methanol and formic acid. An extraction column is used to extract a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope obtained from the top of the product concentration column with methanol and formic acid, and the extract phase is obtained at the top of the column. An extractant recovery partition wall column is used, in which the extractant phase is separated to obtain 1,3,5-trioxane on the column side; The membrane separation device is used to separate the bottom liquid of the synthetic reactive distillation column into sodium benzenesulfonate, formic acid and 1,3,5-trioxane. The auxiliary agent extraction device is used to extract sodium benzenesulfonate, formic acid and 1,3,5-trioxane, which are then recycled back to the synthesis reactive distillation column as a circulating auxiliary agent.

2. The 1,3,5-trioxane production system of the recyclable adjuvant of claim 1, characterized by, Also includes: A methyl acetal reactive distillation column is used to catalytically react methanol and formaldehyde to produce methyl acetal. A methyl acetal oxidation reactor, in which methyl acetal from the methyl acetal reactive distillation column undergoes an oxidation reaction to generate a reaction gas; The formaldehyde absorption tower is used to absorb the formaldehyde in the reaction gas generated by the methyl acetal oxidation reactor. The formaldehyde obtained from the bottom of the tower is then transported to the synthesis reaction distillation tower.

3. The 1,3,5-trioxane production system of the recyclable adjuvant of claim 1, characterized by, The synthetic reactive distillation column adopts a plate structure with 10-30 theoretical plates; the light component removal column adopts a plate structure with 7-20 theoretical plates; the product concentration column adopts a plate structure with 15-35 theoretical plates; the extraction column adopts a plate or packed column structure with 7-35 theoretical plates; the extractant recovery partition wall column adopts a plate structure with 30-82 theoretical plates, and the middle 10-30 plates are equipped with partition plates.

4. The 1,3,5-trioxane production system of the recyclable adjuvant of claim 2, characterized by, The methyl acetal reactive distillation column adopts a plate type, a packed type, or a combination of both, with 20 to 50 theoretical plates; the methyl acetal oxidation reactor is a tubular reactor; the formaldehyde absorption tower adopts a plate type, a packed type, or a combination of both, with 20 to 60 theoretical plates.

5. A process for producing 1,3,5-trioxane with recyclable additives, characterized in that, Operating on a 1,3,5-trioxane production system with a recyclable adjuvant as described in any of claims 1-4, comprising: Formaldehyde solution was reacted in a synthetic reactive distillation column under the conditions of catalyst and additives to obtain crude 1,3,5-trioxane at the top of the column; The crude 1,3,5-trioxane product obtained from the top of the synthetic reactive distillation column enters the light component removal column. After the light components are removed, an aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane is obtained in the bottom of the column. The aqueous solution containing methanol, formaldehyde, formic acid and 1,3,5-trioxane obtained from the bottom of the light component removal tower is further separated in the product concentration tower. The gas phase at the top of the tower is condensed to obtain a mixed solution of formaldehyde, 1,3,5-trioxane and water azeotrope with methanol and formic acid. Benzene is added to the extraction tower as an extractant, and the product concentration tower tops a mixed solution of an azeotrope containing formaldehyde, 1,3,5-trioxane and water, methanol and formic acid is extracted to obtain the extract phase at the top of the extraction tower. The extract phase obtained at the top of the extraction column is fed to the extractant recovery partition wall column, where 1,3,5-trioxane is obtained on the column side of the extractant recovery partition wall column. The reactive distillation column periodically discharges the bottom liquid to maintain the content of sulfuric acid and sodium benzenesulfonate in the bottom liquid phase. The discharged bottom liquid enters the membrane separation device for membrane separation. After membrane separation, the osmotic side yields a component containing sodium benzenesulfonate, formic acid and trioxymethylene, while the permeate side yields a component containing sulfuric acid, formaldehyde and water. The component containing sodium benzenesulfonate, formic acid, and trioxymethylene obtained from the osmotic side of the membrane separation device enters the auxiliary agent extraction device, reacts with the oxidant to remove formic acid, and obtains an aqueous solution containing sodium benzenesulfonate and trioxymethylene, which is then recycled back to the synthesis reactive distillation column.

6. The production process according to claim 5, characterized in that, Also includes: Methanol and formaldehyde react in the methyl acetal reactive distillation column under resin catalyst conditions to produce methyl acetal. The methyl acetal generated in the methyl acetal reactive distillation column undergoes an oxidation reaction with oxygen in the methyl acetal oxidation reactor under the condition of an iron-molybdenum catalyst to generate a reaction gas containing formaldehyde. The formaldehyde-containing reaction gas generated by the methyl acetal oxidation reactor is cooled to 60-150°C and then enters the formaldehyde absorption tower. After circulation absorption, a formaldehyde solution is obtained in the bottom of the tower and then transported to the synthesis reaction distillation tower.

7. The production process according to claim 5, characterized in that, The operating temperature of the synthetic reactive distillation column is 98–120°C, and the pressure is 0.01–0.05 MPaG; the operating temperature of the light component removal column is 80–120°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the product concentration column is 92–120°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the extraction column is 40–60°C, and the pressure is 0.1–0.6 MPaG; the operating temperature of the extractant recovery partition wall column is 70–90°C, and the pressure is 0.005–0.02 MPaG; the operating temperature of the membrane separation equipment is 98–120°C, the permeate side operating pressure is -0.01 to -0.05 MPaG, and the osmosis side operating pressure is 0.2–0.6 MPaG.

8. The production process according to claim 5, characterized in that, In the synthesis reactive distillation column, the catalyst is sulfuric acid, the auxiliary agent is sodium benzenesulfonate, and the molar ratio of the auxiliary agent to the catalyst is 0.5 to 4:1; in the extractant recovery partition wall column, the mass ratio of the extractant to 1,3,5-trioxane in the feed is 0.4 to 4:

1.

9. The production process according to claim 5, characterized in that, In the extractant recovery interlayer tower, the mass ratio of the extractant to 1,3,5-trioxane in the feed is 0.4 to 0.5:

1.

10. The production process according to claim 6, characterized in that, The methyl acetal reactive distillation column operates at a temperature of 60–120°C and a pressure of 0.01–0.8 MPaG; the methyl acetal oxidation reactor operates at a temperature of 320–420°C and a pressure of 0.1–0.3 MPaG; the formaldehyde absorption column operates at a temperature of 100–150°C and a pressure of 0.01–0.2 MPaG; in the methyl acetal reactive distillation column, the molar ratio of methanol to formaldehyde is 2–3:1; in the methyl acetal oxidation reactor, the molar ratio of oxygen to methyl acetal is 1–2:1.

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