Polyoxymethylene production device

Abstract

The utility model provides a kind of polyformaldehyde production device, belong to polyformaldehyde production device technical field, including formaldehyde preparation unit, formaldehyde concentration unit and polymerization unit.Formaldehyde preparation unit is prepared crude aldehyde by multistage absorption tower and rectifying column combination, concentration unit realizes high concentration formaldehyde solution preparation using multistage flash evaporation and condensation recovery, and polymerization unit integrates trioxymethylene, dioxolane and polyformaldehyde reactor to complete continuous polymerization reaction.The utility model reduces the amount of use of absorbent water by optimizing process design, realizes solvent circulation, reduces energy consumption and wastewater discharge, while improving the tightness of reaction zone and separation zone, reducing intermediate product loss and byproduct accumulation, improving product purity and production efficiency, while significantly improving the uniformity of polymer molecular weight distribution, enhancing the mechanical strength and heat resistance of the product, suitable for large-scale industrial production, with high economic efficiency and environmental protection.

Description

Technical Field

[0001] This utility model belongs to the field of chemical production equipment technology, and specifically relates to a polyoxymethylene production device. Background Technology

[0002] Polyoxymethylene (POM) is a thermoplastic engineering plastic with excellent comprehensive performance. Its structure consists of highly crystalline, unbranched linear polymers, with the main repeating unit being —CH2O—, giving it both excellent physical and mechanical properties and chemical stability. As the third most widely used general-purpose engineering plastic after polyamide and polycarbonate, POM is known as "super steel" or "acetal" because its mechanical properties are closest to those of metallic materials. Within a wide temperature range of -40℃ to 100℃, POM maintains its creep resistance, fatigue resistance, wear resistance, and chemical corrosion resistance for extended periods. Combined with its outstanding self-lubricating properties and elasticity, it performs exceptionally well in harsh working conditions. With its metal-like hardness, strength, and rigidity, and significantly lower cost than non-ferrous metals and traditional engineering plastics, POM is gradually replacing brass, aluminum, zinc, and even steel, and is widely used in the automotive industry, electronics, machinery manufacturing, and other fields, and is also penetrating emerging applications such as medical devices, sports equipment, and consumer goods.

[0003] With the development of polyoxymethylene (POM) production technology, various preparation processes and equipment have been widely applied in the industrial field. However, under existing technologies, when using a low-concentration formaldehyde aqueous solution (30-50%) for POM production, excessive water in the system hinders the formation of products such as trioxymethylene, leading to a decrease in the polymerization rate and monomer conversion rate. Water in formaldehyde raw materials, as a highly polar medium, easily triggers chain transfer reactions, causing random breakage of polymer molecular chains, resulting in a wider molecular weight distribution and deterioration of the product's mechanical strength and heat resistance. To prepare high-concentration formaldehyde raw materials, the formaldehyde solution is usually concentrated twice. The multi-stage dehydration process used significantly increases energy consumption and equipment investment costs, generates large amounts of wastewater, and has low efficiency in treating high-concentration formaldehyde solutions. Utility Model Content

[0004] The technical problem to be solved by this utility model is to provide a polyoxymethylene production device that prepares high-concentration formaldehyde solution by combining multi-stage absorption and flash evaporation processes, reducing the amount of absorbent water used, and realizing solvent recycling through the recovery and reuse of condensate, which significantly reduces energy consumption and wastewater discharge. The integrated process design maintains high production capacity while reducing wastewater discharge and overall energy consumption during the production process, and can achieve product stability control without relying on complex external treatment systems, thereby improving resource utilization.

[0005] To solve the above-mentioned technical problems, an embodiment of this utility model provides a polyoxymethylene (POM) production device, characterized in that it includes a formaldehyde preparation unit, a formaldehyde concentration unit, and a polymerization unit, with each unit connected by pipelines to form an integrated process flow. The formaldehyde preparation unit includes a methanol oxidation reactor, a primary absorption tower, a secondary absorption tower, a crude aldehyde tank, a distillation tower, and a dilute aldehyde tank. A methanol preheater and an air compressor are respectively installed at the inlet of the methanol oxidation reactor, and a feed mixer is connected to the methanol oxidation reactor. The methanol oxidation reactor is connected to the bottom of the primary absorption tower, and the top of the primary absorption tower is connected to the bottom of the secondary absorption tower via a pipeline. The top of the secondary absorption tower is provided with a tail gas treatment interface. The bottom outlet of the absorption tower is connected to the inlet of the crude aldehyde tank, which is connected to the feed inlet in the middle of the distillation tower. The distillation tower returns one path to the top of the distillation tower via a reflux tank, and the other path is connected to methanol recovery. The bottom outlet of the distillation tower is connected to the dilute aldehyde tank, and the outlet of the dilute aldehyde tank is connected to the formaldehyde concentration unit. The formaldehyde concentration unit includes a multi-stage flash tank, a water recovery tank, and a concentrated aldehyde tank. The multi-stage flash tanks are interconnected by pipes and connected to the water recovery tank by pipes. The top outlet of the last stage flash tank of the multi-stage flash tank is connected to the concentrated aldehyde tank by a pipe. The polymerization unit includes a trioxymethylene reaction unit, a dioxinoxane reaction unit, and a polyoxymethylene reaction unit. The outlet of the concentrated aldehyde tank is connected to the trioxymethylene reaction unit and the dioxinoxane reaction unit by pipes, respectively.

[0006] The trioxymethylene reaction unit includes a trioxymethylene reactor, a concentration tower, the top of a trioxymethylene extraction tower, a trioxymethylene light component removal tower, a methanol recovery tower, and a trioxymethylene recovery tower. The trioxymethylene reactor is connected to the bottom of the concentration tower via a pipeline. The top outlet of the concentration tower is connected to the top of the trioxymethylene extraction tower via a pipeline. The bottom outlet of the trioxymethylene extraction tower is connected to the trioxymethylene light component removal tower. The trioxymethylene light component removal tower is connected to a trioxymethylene phase separation tank via a pipeline. The upper outlet of the trioxymethylene phase separation tank is connected to the trioxymethylene extraction tower, and the lower outlet is connected to the methanol recovery tower. The methanol recovery tower is connected to the trioxymethylene recovery tower. The trioxymethylene recovery tower returns one path to the top of the trioxymethylene recovery tower via a reflux tank, and the other path is connected to the trioxymethylene extraction tower. The bottom outlet of the trioxymethylene recovery tower is connected to the trioxymethylene heavy component removal tower. The top outlet of the trioxymethylene heavy component removal tower is connected to a trioxymethylene storage tank. The bottom outlet of the trioxymethylene heavy component removal tower is connected to the waste solids treatment stage.

[0007] In the trioxymethylene reaction unit, the top outlet of the methanol recovery tower is connected to a condenser via a pipeline. The outlet of the condenser is connected to a reflux tank. The outlet of the reflux tank is divided into two paths: one path returns to the top of the methanol recovery tower, and the other path is connected to the formaldehyde preparation unit as raw material.

[0008] The dioxapentane reaction unit includes a dioxapentane reactor, a dioxapentane light-weight removal tower, a dioxapentane extraction tower, a reboiling tower, and a light-boiling tower. The dioxapentane reactor is connected to the bottom of the dioxapentane light-weight removal tower. The dioxapentane light-weight removal tower returns to the top of the tower via a reflux tank, and another path connects to the top of the dioxapentane extraction tower. The bottom outlet of the dioxapentane extraction tower is connected to the middle feed inlet of the reboiling tower. The reboiling tower returns to the top of the tower via a reflux tank, and another path connects to the middle feed inlet of the light-boiling tower. The bottom outlet of the light-boiling tower is connected to a dioxapentane storage tank.

[0009] In the dioxapentane reaction unit, the bottom outlet of the light boiling tower is connected to the dioxapentane storage tank via a pipeline, and the top outlet of the light boiling tower is connected to the condenser via a pipeline. The outlet of the condenser is connected to the reflux tank, and the outlet of the reflux tank is divided into two paths: one path returns to the top of the light boiling tower, and the other path is connected to the methanol recovery stage.

[0010] The polyoxymethylene (POM) reaction unit includes a POM reactor, a crusher, a centrifuge, and a dryer. Both the trioxymethylene (TOM) reaction unit and the dioxane (DOC) reaction unit are connected to the POM reactor. The POM reactor is connected to the crusher, and the crusher is connected to the centrifuge for separation. The solid outlet of the centrifuge is connected to the dryer inlet, and the liquid outlet is connected to the trioxymethylene recovery tower.

[0011] In the polyoxymethylene reaction unit, the top of the polyoxymethylene reactor is equipped with a cooling water system, which is connected to the inside of the reactor through pipes to prevent the polyoxymethylene polymer from deteriorating due to excessively high temperature in the polyoxymethylene reactor.

[0012] The formaldehyde preparation unit uses a packed tower structure for both the primary and secondary absorption towers, which are filled with either structured or random packing.

[0013] In the formaldehyde concentration unit, the multi-stage flash tank includes a primary flash tank and a secondary flash tank. The tops of both the primary and secondary flash tanks are connected to a condenser via pipes. The condenser outlet of the secondary flash tank is connected to a water recovery tank. The outlet of the water recovery tank is returned to the top of the secondary absorption tower via a pipe as a scrubbing liquid.

[0014] The beneficial effects of the above-mentioned technical solution of this utility model are as follows: In the formaldehyde preparation stage, this utility model collects formaldehyde products through a multi-stage absorption method to prepare a high-concentration dilute formaldehyde solution, reducing the use of absorbent water; the dilute formaldehyde solution is concentrated through a multi-stage flash evaporation device, and the condensate is rationally recycled and recycled back to the multi-stage formaldehyde absorption device, which can effectively realize the recycling of solvent and avoid the distillation and separation of large amounts of water, significantly reducing energy consumption; in addition, the polyoxymethylene product produced by this utility model has the advantages of narrow molecular weight distribution and regular crystal structure, and the product has a high heat distortion temperature. By designing a reaction system with higher concentration, it has the advantages of small volume, short dehydration process cycle, and low overall energy consumption. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the formaldehyde preparation unit and the formaldehyde concentration unit 2 in this utility model; Figure 2 This is a schematic diagram of the structure of the trioxymethylene reaction unit 3 in this utility model; Figure 3 This is a schematic diagram of the structure of the dioxapentane reaction unit 4 in this utility model; Figure 4 This is a schematic diagram of the structure of the polyoxymethylene polymerization unit 5 in this utility model.

[0016] Figure labeling: 1. Formaldehyde preparation unit; 101. Methanol preheater; 102. Air compressor; 103. Methanol oxidation reactor; 104. Primary absorption tower; 105. Secondary absorption tower; 106. Crude aldehyde tank; 107. Distillation tower; 108. Dilute aldehyde tank; 2. Formaldehyde concentration unit; 201. Primary flash tank; 202. Secondary flash tank; 203. Concentrated aldehyde tank; 204. Water recovery tank; 3. Trioxymethylene reaction unit; 301. Trioxymethylene reactor; 302. Concentration tower; 303. Trioxymethylene extraction tower; 304. Trioxymethylene light component removal tower; 305. Methanol recovery tower; 306. Trioxymethylene recovery tower; 307. Trioxymethylene desulfurization tower; 308. Heavy tower; 309. Trioxymethylene phase separation tank; 4. Trioxymethylene storage tank; 401. Dioxapentane reaction unit; 402. Ethylene glycol tank; 403. Dioxapentane reactor; 404. Dioxapentane removal tower; 405. Dioxapentane extraction tower; 406. Light boiling tower; 407. Dealdehyde tower; 408. Dioxapentane phase separation tank; 409. Dioxapentane storage tank; 5. Polyoxymethylene polymerization unit; 501. Polyoxymethylene reactor; 502. Crusher; 503. Centrifuge; 504. Dryer; 6. Feed mixer; 7. Reboiler; 8. Discharge pump; 9. Condenser; 10. Reflux tank; 11. Preheater; 12. Cooling heat exchanger. Detailed Implementation

[0017] To make the technical problems, technical solutions and advantages of this utility model clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0018] An embodiment of this utility model provides a polyoxymethylene production device, which consists of a formaldehyde preparation unit 1, a formaldehyde concentration unit 2, and a polymerization unit. The units are connected by pipelines to form an integrated process flow.

[0019] Formaldehyde preparation unit 1 includes a methanol oxidation reactor 103, a primary absorption tower 104, a secondary absorption tower 105, a crude aldehyde tank 106, a distillation tower 107, and a dilute aldehyde tank 108, etc.; formaldehyde concentration unit 2 includes a primary flash tank 201, a secondary flash tank 202, a water recovery tank 204, and a concentrated aldehyde tank 203, etc.

[0020] The chemical reaction formula for the oxidation of methanol to formaldehyde is as follows: CH3OH (methanol) + 1 / 2O2 (oxygen) = CH2O (formaldehyde) + H2O (water).

[0021] In formaldehyde preparation unit 1, methanol oxidation reactor 103 is the starting part of the entire device. After the raw material methanol is pumped out from the methanol feed tank, the raw material formaldehyde, air, and steam are heated by methanol preheater 101 and vaporized by air compressor 102, and then connected to feed mixer 6 through pipeline. Feed mixer 6 is used to thoroughly mix the preheated methanol with compressed air before feeding it into methanol oxidation reactor 103. In feed mixer 6, the raw material formaldehyde, air, and steam are thoroughly mixed into a mixed gas before entering methanol oxidation reactor 103, where a vigorous exothermic oxidation reaction occurs under the catalysis of silver catalyst.

[0022] After the mixed gas reacts in the methanol oxidation reactor 103, the resulting product gas, at approximately 150°C, enters the bottom of the primary absorption tower 104 from the outlet of the methanol oxidation reactor 103. The top of the primary absorption tower 104 is connected to the bottom of the secondary absorption tower 105 via a pipeline. The top of the secondary absorption tower 105 is equipped with a tail gas treatment port to treat the partially unabsorbed formaldehyde gas and a large amount of air. The bottom outlet of the primary absorption tower 104 is connected to the crude aldehyde tank 106. Under condensation and rinsing with a formaldehyde solution containing a concentration of 26.6%, water vapor and some formaldehyde gas are absorbed into the aqueous solution, which is discharged from the bottom of the primary absorption tower 104 as a 45% formaldehyde aqueous solution, temporarily stored in the crude aldehyde tank 106. The outlet of the crude aldehyde tank 106 is connected to the feed inlet in the middle of the distillation column 107 via a pipeline. The formaldehyde aqueous solution pumped from the crude aldehyde tank 106 enters the distillation column 107 to separate the trace amount of formaldehyde contained in the material. The top of the distillation column 107 is equipped with a condenser 9, the outlet of which is connected to a reflux tank 10. The outlet of the reflux tank 10 splits into two paths: one path returns to the top of the distillation column 107 for reflux operation, and the other path connects to the methanol recovery stage to recover unreacted methanol, which is then returned to the methanol oxidation reactor 103 as a reaction feedstock. The formaldehyde flows to the bottom of the distillation column 107 and is temporarily stored in a dilute aldehyde tank 108. The outlet of the dilute aldehyde tank 108 is connected to the inlet of the primary flash tank 201 via a pipeline. The connections between these components ensure that the initial preparation and separation process of the formaldehyde solution can proceed efficiently.

[0023] In formaldehyde concentration unit 2, the inlet of the primary flash tank 201 is connected to the outlet of the discharge pump 8 of the dilute formaldehyde tank 108 via a pipeline. The formaldehyde aqueous solution in the dilute formaldehyde tank 108 is heated to 70°C by the preheater 11 before entering the primary flash tank 201. The gas enters the condenser 9 from above the primary flash tank 201, and after condensation, it is converted into a 3% formaldehyde aqueous solution, which is then sent to the formaldehyde removal tower 407 in the dioxane reaction unit 4 to recover the formaldehyde. The remaining liquid is pre-concentrated to a concentration of 50.2% by vacuum flash evaporation in the primary flash tank 201. The liquid outlet of the primary flash tank 201 is connected to the inlet of the secondary flash tank 202 via a pipeline. Before entering the secondary flash tank 202, the formaldehyde solution is preheated to 85°C by the preheater 11 to further improve the flash evaporation effect.

[0024] Under reduced pressure, flash evaporation is performed in the secondary flash tank 202. The gas is piped from the top of the secondary flash tank 202 to the cooling heat exchanger 12, where it is condensed and converted into a 15% formaldehyde aqueous solution, which is recovered by the water recovery tank 204. The recovered formaldehyde aqueous solution is returned to the top of the secondary absorption tower 105 as a scrubbing liquid through the outlet of the water recovery tank 204, thus realizing the recycling of the condensate. The bottom of the secondary flash tank 202 receives the concentrated formaldehyde solution, which is temporarily stored in the concentrated formaldehyde tank 203 through a pipe. After two flash evaporations, the formaldehyde solution concentration is approximately 65.2%, which can be used as a raw material for subsequent polymerization units.

[0025] When the formaldehyde solution concentration is increased to over 60%, the reduction in water content in the raw material not only accelerates the spontaneous condensation process of trioxymethylene but also inhibits water-involved side reaction pathways, thereby improving the selectivity of the polymerization reaction and increasing the single-pass conversion rate. This reduces the subsequent purification pressure on the trioxymethylene raw material in the polyoxymethylene production unit and reduces the volume of the polymerization unit.

[0026] In the formaldehyde concentration unit 2 described above, the multi-stage flash tank design allows for the gradual concentration of high-concentration formaldehyde solution. Simultaneously, the cooperation of condenser 9 and water recovery tank 204 enables solvent recovery and reuse, significantly reducing energy consumption and wastewater discharge. This not only optimizes the formaldehyde solution concentration process but also reduces resource waste.

[0027] The polymerization unit includes a trioxymethylene reaction unit 3, a dioxane reaction unit 4, and a polyoxymethylene polymerization unit 5. The concentrated aldehyde tank 203 in the formaldehyde preparation unit 1 is connected in series to the trioxymethylene reaction unit 3 and the dioxane reaction unit 4 via pipes.

[0028] The chemical reaction formula for the synthesis of trioxymethylene is as follows: 3CH2O (formaldehyde) = C3H6O3 (trioxymethylene). The trioxymethylene reaction unit 3 includes a trioxymethylene reactor 301, a concentration tower 302, a trioxymethylene extraction tower 303, a trioxymethylene light component removal tower 304, a methanol recovery tower 305, a trioxymethylene recovery tower 306, and a trioxymethylene heavy component removal tower 307. The concentrated aldehyde tank 203, under the action of the discharge pump 8, enters the trioxymethylene reactor 301 through a pipeline. It undergoes gasification and high-speed circulation through the preheater 11, and reacts with sulfuric acid catalyst to synthesize trioxymethylene. The gas after the reaction contains trioxymethylene, which, after cooling with hot water, becomes a liquid trioxymethylene solution, which is then connected to the concentration tower 302 through a pipeline. In concentration tower 302, the component mainly composed of trioxymethylene enters the gas phase, while the component mainly composed of formaldehyde condenses and goes to the bottom of concentration tower 302. Thus, the top output of concentration tower 302 is an aqueous solution of trioxymethylene and formaldehyde. The top outlet of concentration tower 302 is connected to the top of trioxymethylene extraction tower 303 through a pipeline for extraction. At the same time, the bottom output of concentration tower 302 is an aqueous solution of formaldehyde, which is connected to the dilute aldehyde tank 108 in formaldehyde concentration unit 2 through a pipeline and is combined with the dilute aldehyde solution in dilute aldehyde tank 108.

[0029] An aqueous solution of trioxymethylene and formaldehyde is fed from the top of the trioxymethylene extraction tower 303. Benzene extract for recycling is fed from the bottom of the trioxymethylene extraction tower 303. After extraction, the trioxymethylene-benzene solution is piped from the top of the trioxymethylene extraction tower 303 to a feed mixer 6 containing liquid sodium hydroxide, and then piped to the inlet of the trioxymethylene light component removal tower 304. Additionally, the bottom of the trioxymethylene extraction tower 303 is connected to the trioxymethylene recovery tower 306 via a pipe.

[0030] In the trioxymethylene light-weight removal tower 304, benzene vapor from the feed mixer 6 first passes through the condenser 9 and cooler, then flows into the trioxymethylene phase separator 308 via the reflux tank 10. Benzene and water in the material are immiscible, forming two layers. The upper benzene outlet of the trioxymethylene phase separator 308 is returned to the trioxymethylene extraction tower 303 via a pipeline, while the lower water outlet of the trioxymethylene phase separator 308 is connected to the feed inlet of the methanol recovery tower 305 via a pipeline. The bottom of the trioxymethylene light-weight removal tower 304 contains crude trioxymethylene with trace amounts of reboiling matter, which is connected to the trioxymethylene heavy-weight removal tower 307 via a pipeline.

[0031] After the two phases are separated in the trioxymethylene phase separator 308, the lower aqueous solution is sent to the methanol recovery tower 305, where it is separated by atmospheric distillation. The methanol is then condensed and cooled at the top of the methanol recovery tower 305 and recovered as raw material for formaldehyde preparation unit 1. The bottom outlet of the methanol recovery tower 305 is connected to the feed inlet of the trioxymethylene recovery tower 306 via a pipeline.

[0032] The trioxymethylene recovery tower 306 has three inlets: the bottom water layer of the trioxymethylene extraction tower 303, the bottom aqueous solution of the methanol recovery tower 305, and the material recovered by the centrifugal separator in the polyoxymethylene polymerization unit 5. The three materials are fed into the trioxymethylene recovery tower 306 and heated by the reboiler 7. The top output of the trioxymethylene recovery tower 306 is a high-concentration trioxymethylene solution, which is cooled by the condenser 9 set at the top of the trioxymethylene recovery tower 306 and returned to the trioxymethylene extraction tower 303 for extraction and purification by the reflux tank 10. The bottom output of the trioxymethylene recovery tower 306 is a formaldehyde aqueous solution, which is sent to the crude formaldehyde tank 106 in the formaldehyde concentration unit 2 by the discharge pump 8 for formaldehyde purification and concentration.

[0033] Crude paraformaldehyde is piped to paraformaldehyde de-weighing tower 307. The paraformaldehyde is heated by reboiler 7 and distilled off from the top of tower 307. After condensation, it enters paraformaldehyde storage tank 309 as a polymerization feedstock for polyoxymethylene polymerization unit 5. High-boiling-point substances are discharged from the bottom of paraformaldehyde de-weighing tower 307 and enter the waste solids treatment stage. Furthermore, the paraformaldehyde storage tank is sealed with nitrogen to prevent paraformaldehyde from combining with oxygen in the air to produce formic acid impurities.

[0034] The chemical reaction formula for the reaction of ethylene glycol with formaldehyde to produce dioxapentane is as follows: CH2O (formaldehyde) + HOCH2CH2OH (ethylene glycol) = C3H6O2 (dioxapentane) + H2O (water). The dioxapentane reaction unit 4 includes an ethylene glycol tank 401, a dioxapentane reactor 402, a dioxapentane light-light-removal tower 403, a dioxapentane extraction tower 404, a reboiling tower 405, a light-boiling tower 406, and a formaldehyde removal tower 407, etc.

[0035] Ethylene glycol, the raw material, is pumped from ethylene glycol tank 401 and heated by preheater 11. It is then mixed with methanol prepared by formaldehyde concentration unit 2 in feed mixer 6 to form an aqueous solution of methanol and ethylene glycol. This solution enters dioxane reactor 402, where dioxane is generated under the action of sulfuric acid as a catalyst. The reaction temperature inside dioxane reactor 402 is 100°C. The generated dioxane, water, formaldehyde, and trace impurities are vaporized. Due to the high corrosiveness of sulfuric acid, the reaction equipment uses corrosion-resistant material (Zr). The top product of dioxane reactor 402 contains a high concentration of dioxane and, after cooling, enters dioxane removal tower 403.

[0036] The dioxapentane removal tower 403 is equipped with a condenser 9 at the top and a reboiler 7 at the bottom. The dioxapentane solution produced by the dioxapentane reactor 402 is distilled and separated in the dioxapentane removal tower 403. The dioxapentane gas containing water at the top of the dioxapentane removal tower 403 is condensed by the condenser 9 to obtain a dioxapentane solution, which is then sent to the dioxapentane extraction tower 404. The material at the bottom of the dioxapentane removal tower 403 consists of formaldehyde, water, and a small amount of ethylene glycol, and is pumped into the formaldehyde removal tower 407. The formaldehyde removal tower 407 removes a small amount of formaldehyde from the formaldehyde-containing wastewater and recovers it to the crude formaldehyde tank 106. After the formaldehyde content in the wastewater is lower than 0.1%, it enters the wastewater treatment stage.

[0037] The dioxapentane solution, concentrated in dioxapentane removal tower 403, is sent to dioxapentane extraction tower 404, where sodium hydroxide is used as the extractant to separate water and dioxapentane. The solution then flows into dioxapentane phase separation tank 408. After phase separation, the upper dioxapentane solution is further purified by passing it through a pipeline to reboiling tower 405. The lower water and sodium hydroxide solution is separated to remove a small amount of methanol and then the alkali solution is recovered.

[0038] The dioxapentane solution in the upper layer of the dioxapentane extraction tower 404 is pumped to the reboiling tower 405. The feed is introduced from the middle of the reboiling tower 405. The reboiling tower 405 is used to separate dioxapentane from the reboiling point substance. The crude dioxapentane after being condensed by the condenser 9 enters the light boiling tower 406 through the reflux tank 10. The reboiled substance at the bottom of the reboiling tower 405 is returned to the dioxapentane extraction tower 404.

[0039] A small amount of methanol is distilled from the crude dioxapentane obtained from the distillation column 405 in the light boiling column 406 and then distilled off from the top and recovered as raw material for formaldehyde preparation unit 1. A high-purity dioxapentane solution is distilled from the bottom of the light boiling column 406 and pumped to the dioxapentane storage tank 409 as polymerization raw material for polyoxymethylene polymerization unit 5.

[0040] The connection relationships between the components of the above-mentioned trioxymethylene reaction unit 3 and dioxane reaction unit 4 ensure the efficient synthesis and separation and purification of trioxymethylene and dioxane.

[0041] The chemical reaction formula for the copolymerization of trioxymethylene and dioxapentane is as follows: mC3H6O3 (trioxymethylene) + nC3H6O2 (dioxapentane) + C3H8O2 (methyl acetal) = CH3O-(C3H6O3)m-(C3H6O2) n The polyoxymethylene (POM) polymerization unit 5 includes a POM reactor 501, a crusher 502, a centrifuge 503, a dryer 504, etc.

[0042] The trioxymethylene storage tank 309 and the dioxin storage tank 409 are connected to the polyoxymethylene reactor 501 via pipelines. The outlet of the polyoxymethylene reactor 501 is connected to the crusher 502 via a pipeline. The outlet of the crusher 502 is connected to the inlet of the centrifuge 503 via a pipeline. The solid outlet of the centrifuge 503 is connected to the inlet of the dryer 504 via a pipeline, and the liquid outlet is connected to the feed inlet of the trioxymethylene extraction tower 303 in the trioxymethylene reaction unit 3 via a pipeline. The outlet of the dryer is connected to the polyoxymethylene powder storage tank via a pipeline, and the outlet of the polyoxymethylene powder storage tank is connected to the subsequent granulation and packaging stages via a pipeline. The above structural design enables the final preparation process of polyoxymethylene to be completed efficiently and ensures the purity and quality of the product.

[0043] The reaction raw materials for the polyoxymethylene (POM) polymerization unit 5 consist of trioxymethylene, dioxane, and methylal. These are uniformly mixed under nitrogen protection by the feed mixer 6 and then injected into the POM reactor 501. Boron trifluoride is injected into another inlet of the POM reactor 501 as a catalyst for the exothermic polymerization reaction. It should also be noted that the POM reactor 501 has a cooling water system to prevent excessively high temperatures from degrading the POM polymer.

[0044] After the reaction is complete, the polyoxymethylene (POM) flakes are discharged from below the POM reactor 501, yielding POM containing unstable unterminated groups. Triethanolamine aqueous solution is injected into the feed mixer 6 below the discharge port of the POM reactor 501, preserving the POM flakes in an alkaline solution. The POM-containing flakes are fed into a crusher 502 for crushing and then pumped into a centrifuge 503 for solid-liquid separation, yielding POM powder and an aqueous solution containing trioxymethylene, formaldehyde, and water. The aqueous solution is recycled to the trioxymethylene extraction tower 303 in the trioxymethylene reaction unit 3. The wet POM powder is fed into a dryer 504, where nitrogen is used as a circulating carrier to remove moisture from the POM powder at 120–125°C. The dried POM powder, at approximately 120°C, is cooled to 80°C and then blown by a blower into a POM powder storage tank for subsequent granulation and packaging processes.

[0045] The operation process of this utility model is as follows: First, the methanol feedstock, after preheating, is fully mixed with compressed air in the feed mixer 6, and then enters the methanol oxidation reactor 103 for oxidation reaction to generate formaldehyde gas. The generated formaldehyde gas enters the bottom of the primary absorption tower 104, where it forms a dilute formaldehyde solution through condensation and rinsing with the aldehyde-containing solution returned from the primary absorption tower. The unabsorbed gas enters the secondary absorption tower 105 for further absorption, and the remaining tail gas is discharged through the tail gas treatment interface. The dilute formaldehyde solution at the bottom of the primary absorption tower 104 enters the crude formaldehyde tank 106, and then is sent to the distillation tower 107 for separation. Part of the condensate at the top of the distillation tower 107 is returned to the top of the distillation tower 107, and the other part of the crude formaldehyde is sent to the methanol recovery stage. The dilute formaldehyde solution at the bottom enters the dilute formaldehyde tank 108. The dilute formaldehyde solution in the dilute formaldehyde tank 108 is concentrated sequentially through a primary flash tank 201 and a secondary flash tank 202. The condensate is recycled through a condenser 9 and a water recovery tank 204, ultimately yielding a high-concentration formaldehyde solution which is stored in the concentrated formaldehyde tank 203.

[0046] The high-concentration formaldehyde solution in the concentrated aldehyde tank 203 is fed into the trioxymethylene reactor 301 and the dioxin reactor 402 for reaction. The generated trioxymethylene and dioxin are then separated and purified through multiple stages and stored in the trioxymethylene storage tank and the dioxin storage tank, respectively. The trioxymethylene and dioxin are then fed into the polyoxymethylene reactor for polymerization. The generated polyoxymethylene is crushed, centrifuged, dried, and stored in the polyoxymethylene powder storage tank. Finally, the finished product is prepared through granulation and packaging.

[0047] This invention achieves efficient preparation and continuous polymerization of high-concentration formaldehyde solution through the above-described specific embodiments. The combination of multi-stage absorption and flash evaporation processes reduces the amount of absorbent water used, and solvent recycling through the recovery of condensate significantly reduces energy consumption and wastewater discharge. The integrated reaction and separation design improves the tightness of the connection between the reaction and separation zones, reduces intermediate product loss and by-product accumulation, and improves product purity and production efficiency. Furthermore, the polyoxymethylene product produced by this invention has the advantages of narrow molecular weight distribution, regular crystal structure, and high heat distortion temperature. By designing a reaction system with higher concentrations, the device boasts advantages such as small size, short dehydration process cycle, and low overall energy consumption.

[0048] In actual operation, the methanol preheater 101 and air compressor 102 are first started to heat the methanol to a suitable temperature and then mix it thoroughly with compressed air through the feed mixer 6. The mixed gas then enters the methanol oxidation reactor 103, where the reaction temperature is maintained stable with the assistance of the reboiler 7 to ensure the efficiency of methanol oxidation to formaldehyde gas. The generated formaldehyde gas enters the bottom of the primary absorption tower 104 from the outlet of the methanol oxidation reactor 103, where it forms a dilute formaldehyde solution through the action of the absorbent water. The unabsorbed gas enters the secondary absorption tower 105 for further absorption, and the remaining tail gas is discharged through the tail gas treatment interface. During this process, the dilute formaldehyde solution at the bottom of the primary absorption tower 104 flows into the crude aldehyde tank 106 and is transported through pipeline to the feed inlet in the middle of the distillation tower 107. Part of the condensate at the top of the distillation tower 107 is returned to the top of the distillation tower 107 to maintain separation efficiency, and the other part is sent to the methanol recovery stage to recover unreacted methanol. The dilute formaldehyde solution at the bottom of the distillation tower 107 enters the dilute aldehyde tank 108 to provide raw material for the subsequent concentration process.

[0049] The dilute formaldehyde solution in dilute aldehyde tank 108 sequentially enters the primary flash tank 201 and the secondary flash tank 202 for gradual concentration. The steam at the top of the primary flash tank 201 is connected to the condenser 9 via a pipeline. The condensed liquid enters the water recovery tank 204 and is then returned to the top of the secondary absorption tower 105 as scrubbing liquid, thus achieving condensate recycling. The concentrated liquid at the bottom of the primary flash tank 201 enters the secondary flash tank 202 for further concentration. The steam at the top of the secondary flash tank 202 is also recycled through the condenser 9 and the water recovery tank 204. Finally, the high-concentration formaldehyde solution at the bottom of the secondary flash tank 202 flows into the concentrated aldehyde tank 203, completing the efficient concentration process of the formaldehyde solution. This multi-stage flash evaporation process significantly reduces the amount of absorbent water used and achieves solvent recycling through condensate recovery, thereby reducing energy consumption and wastewater discharge.

[0050] The high-concentration formaldehyde solution in the concentrated formaldehyde tank 203 is transported via pipelines to the trioxymethylene reactor 301 and the dioxin reactor 402 for reaction. In the trioxymethylene reactor 301, the reboiler 7 at the top is used to control the reaction temperature. The trioxymethylene produced is transported via pipelines to the bottom of the concentration tower 302 for preliminary separation. The light components at the top of the concentration tower 302 enter the top of the trioxymethylene extraction tower 303, while the heavy components at the bottom of the trioxymethylene extraction tower 303 enter the middle feed inlet of the trioxymethylene light component removal tower for further separation. The light components at the top of the trioxymethylene light component removal tower enter the trioxymethylene phase separation tank 308. The liquid in the upper layer of the trioxymethylene phase separation tank 308 returns to the top of the trioxymethylene extraction tower 303, while the liquid in the lower layer enters the middle feed inlet of the methanol recovery tower 305. Part of the condensate at the top of the methanol recovery tower 305 is returned to the top of the methanol recovery tower 305, and the other part is returned to the formaldehyde preparation unit 1 as raw material. The heavy components at the bottom of methanol recovery tower 305 enter the middle inlet of trioxymethylene recovery tower 306. After further separation, the light components at the top return to the top of trioxymethylene extraction tower 303, while the heavy components at the bottom enter the middle inlet of trioxymethylene de-heavy component tower 307. The trioxymethylene product at the top of trioxymethylene de-heavy component tower 307 enters the trioxymethylene storage tank, while the waste solids at the bottom enter the waste solids treatment stage.

[0051] In the dioxapentane reactor 402, the dioxapentane produced in the reaction is transported via pipeline to the bottom of the dioxapentane light component removal tower 403 for preliminary separation. The light component at the top of the dioxapentane light component removal tower 403 enters condenser 9. Part of the condensed liquid is returned to the top of the dioxapentane light component removal tower 403, and the other part enters the top of the dioxapentane extraction tower 404 for further separation. The heavy component at the bottom of the dioxapentane extraction tower 404 enters the middle feed inlet of the reboiler tower 405. The light component at the top of the reboiler tower 405 enters condenser 9. Part of the condensed liquid is returned to the top of the reboiler tower 405, and the other part enters the middle feed inlet of the light boiling tower 406. The light component at the top of the light boiling tower 406 enters condenser 9. Part of the condensed liquid is returned to the top of the light boiling tower 406, and the other part is returned to the methanol recovery stage. The dioxapentane product at the bottom of the light boiling tower 406 enters the dioxapentane storage tank.

[0052] The products from the trioxymethylene storage tank 309 and the dioxin storage tank 409 are respectively transported through pipelines to the polyoxymethylene reactor 501 for polymerization. A cooling water system at the top of the polyoxymethylene reactor 501 is used to control the reaction temperature. The polyoxymethylene produced is transported through pipelines to the inlet of the crusher 502 for preliminary crushing. The crushed material enters the centrifuge 503; the solid portion enters the dryer 504 for drying, while the liquid portion is returned to the feed inlet in the middle of the trioxymethylene recovery tower 306 for recycling. The dried polyoxymethylene powder enters the polyoxymethylene powder storage tank, and finally, the finished product is prepared through granulation and packaging.

[0053] The above description is the preferred embodiment of this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.

Claims

1. A polyoxymethylene (POM) production apparatus, characterized in that, The system includes a formaldehyde preparation unit, a formaldehyde concentration unit, and a polymerization unit, all connected by pipelines to form an integrated process flow. The formaldehyde preparation unit comprises a methanol oxidation reactor, a primary absorption tower, a secondary absorption tower, a crude aldehyde tank, a distillation tower, and a dilute aldehyde tank. The methanol oxidation reactor is equipped with a methanol preheater and an air compressor at its inlet, connected to a feed mixer. The methanol oxidation reactor is connected to the bottom of the primary absorption tower, and the top of the primary absorption tower is connected to the bottom of the secondary absorption tower via a pipeline. The top of the secondary absorption tower has a tail gas treatment interface, and the bottom outlet of the primary absorption tower is connected to the inlet of the crude aldehyde tank. The feed inlet is connected to the middle of the distillation column. One path from the distillation column returns to the top of the column via a reflux tank, while the other path connects to methanol recovery. The bottom outlet of the distillation column is connected to a dilute aldehyde tank, and the outlet of the dilute aldehyde tank is connected to a formaldehyde concentration unit. The formaldehyde concentration unit includes a multi-stage flash tank, a water recovery tank, and a concentrated aldehyde tank. The multi-stage flash tanks are interconnected via pipes and also connected to the water recovery tank via pipes. The top outlet of the last-stage flash tank is connected to the concentrated aldehyde tank via a pipe. The polymerization unit includes a trioxymethylene reaction unit, a dioxapentane reaction unit, and a polyoxymethylene reaction unit. The outlet of the concentrated aldehyde tank is connected to the trioxymethylene reaction unit and the dioxapentane reaction unit via pipes, respectively.

2. The polyoxymethylene production apparatus according to claim 1, characterized in that, The trioxymethylene reaction unit includes a trioxymethylene reactor, a concentration tower, the top of a trioxymethylene extraction tower, a trioxymethylene light component removal tower, a methanol recovery tower, and a trioxymethylene recovery tower. The trioxymethylene reactor is connected to the bottom of the concentration tower via a pipeline. The top outlet of the concentration tower is connected to the top of the trioxymethylene extraction tower via a pipeline. The bottom outlet of the trioxymethylene extraction tower is connected to the trioxymethylene light component removal tower. The trioxymethylene light component removal tower is connected to a trioxymethylene phase separation tank via a pipeline. The upper outlet of the trioxymethylene phase separation tank is connected to the trioxymethylene extraction tower, and the lower outlet is connected to the methanol recovery tower. The methanol recovery tower is connected to the trioxymethylene recovery tower. The trioxymethylene recovery tower returns one path to the top of the trioxymethylene recovery tower via a reflux tank, and the other path is connected to the trioxymethylene extraction tower. The bottom outlet of the trioxymethylene recovery tower is connected to the trioxymethylene heavy component removal tower. The top outlet of the trioxymethylene heavy component removal tower is connected to a trioxymethylene storage tank. The bottom outlet of the trioxymethylene heavy component removal tower is connected to the waste solids treatment stage.

3. The polyoxymethylene production apparatus according to claim 2, characterized in that, In the trioxymethylene reaction unit, the top outlet of the methanol recovery tower is connected to a condenser via a pipeline. The outlet of the condenser is connected to a reflux tank. The outlet of the reflux tank is divided into two paths: one path returns to the top of the methanol recovery tower, and the other path is connected to the formaldehyde preparation unit as raw material.

4. The polyoxymethylene production apparatus according to claim 1, characterized in that, The dioxapentane reaction unit includes a dioxapentane reactor, a dioxapentane light-weight removal tower, a dioxapentane extraction tower, a reboiling tower, and a light-boiling tower. The dioxapentane reactor is connected to the bottom of the dioxapentane light-weight removal tower. The dioxapentane light-weight removal tower returns to the top of the tower via a reflux tank, and another path connects to the top of the dioxapentane extraction tower. The bottom outlet of the dioxapentane extraction tower is connected to the middle feed inlet of the reboiling tower. The reboiling tower returns to the top of the tower via a reflux tank, and another path connects to the middle feed inlet of the light-boiling tower. The bottom outlet of the light-boiling tower is connected to a dioxapentane storage tank.

5. The polyoxymethylene production apparatus according to claim 4, characterized in that, In the dioxapentane reaction unit, the bottom outlet of the light boiling tower is connected to the dioxapentane storage tank via a pipeline, and the top outlet of the light boiling tower is connected to the condenser via a pipeline. The outlet of the condenser is connected to the reflux tank, and the outlet of the reflux tank is divided into two paths: one path returns to the top of the light boiling tower, and the other path is connected to the methanol recovery stage.

6. The polyoxymethylene production apparatus according to claim 1, characterized in that, The polyoxymethylene (POM) reaction unit includes a POM reactor, a crusher, a centrifuge, and a dryer. Both the trioxymethylene (TRI) reaction unit and the dioxane (DI) reaction unit are connected to the POM reactor. The POM reactor is connected to the crusher, and the crusher is connected to the centrifuge for separation. The solid outlet of the centrifuge is connected to the dryer inlet, and the liquid outlet is connected to the trioxymethylene recovery tower.

7. The polyoxymethylene production apparatus according to claim 6, characterized in that, In the polyoxymethylene reaction unit, a cooling water system is provided at the top of the polyoxymethylene reactor. The cooling water system is connected to the inside of the reactor through pipes to prevent the polyoxymethylene polymer from deteriorating due to excessively high temperature in the polyoxymethylene reactor.

8. The polyoxymethylene production apparatus according to claim 1, characterized in that, Both the primary and secondary absorption towers in the formaldehyde preparation unit adopt a packed tower structure, and the packed towers are filled with either structured packing or random packing.

9. The polyoxymethylene production apparatus according to claim 1, characterized in that, In the formaldehyde concentration unit, the multi-stage flash tank includes a primary flash tank and a secondary flash tank. The tops of both the primary and secondary flash tanks are connected to a condenser via pipes. The condenser outlet of the secondary flash tank is connected to a water recovery tank, and the outlet of the water recovery tank is returned to the top of the secondary absorption tower via a pipe as a scrubbing liquid.

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