Method and device for producing polymethoxydimethyl ether from polyformaldehyde production waste

Abstract

The application provides a method and device for producing polymethoxy dimethyl ether from polyformaldehyde production waste, and belongs to the technical field of polyformaldehyde. The production process of polyformaldehyde comprises a formaldehyde production step, a trioxymethylene production step and a polyformaldehyde production step; the method for producing polymethoxy dimethyl ether from polyformaldehyde production waste comprises: condensation reaction of formaldehyde-containing waste liquid generated in the formaldehyde production step, the trioxymethylene production step and the polyformaldehyde production step with methanol to generate methylal; condensation reaction of the heavy boiler produced in the trioxymethylene production step with the methylal to obtain polymethoxy dimethyl ether. The method and device for producing polymethoxy dimethyl ether from polyformaldehyde production waste can fully utilize the formaldehyde-containing waste liquid and the trioxymethylene heavy boiler in the polyformaldehyde production process, reduce the loss of production equipment, and ensure the product quality of polyformaldehyde.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyformaldehyde, and particularly relates to a method and device for producing polymethoxy dimethyl ether by using polyformaldehyde production waste. BACKGROUND

[0002] Polyformaldehyde is one of the five engineering plastics, has high friction resistance and self-lubricating performance, and is widely used in various mechanical and electrical, instrument, electronic and other fields.

[0003] At present, when polyformaldehyde is prepared, methanol is generally used as raw material, and the polyformaldehyde is obtained through a formaldehyde production step, a trioxane (1,3,5-Trioxane, TOX) production step and a polyformaldehyde production step.

[0004] In the formaldehyde production step, the trioxane production step and the polyformaldehyde production step, formaldehyde-containing waste liquid is generated, and at the same time, the trioxane production step also generates a reboiler. In addition to containing a large amount of TOX and a small amount of HCHO, the reboiler also contains a considerable amount of polyformaldehyde, epoxide compounds and acetal compounds and other substances, and cannot be directly used for the production of polyformaldehyde.

[0005] In order to fully utilize the raw materials, the formaldehyde-containing waste liquid and the reboiler in the polyformaldehyde production process are both recycled. However, when the formaldehyde-containing waste liquid is recycled by using the prior art, the formaldehyde will undergo disproportionation reaction to generate methanol and formic acid, which not only causes the loss of formaldehyde, but also causes the rectification equipment to be corroded by formic acid and unable to be used for a long time. At the same time, when the reboiler is recycled by using the prior art, the epoxide compounds and acetal compounds in the reboiler will be recycled and accumulated in the whole process, resulting in the existence of excessive impurities in the generated polymeric trioxane monomer, and further resulting in the reduction of the impact strength of the polyformaldehyde and the influence on the physical properties of the polyformaldehyde. SUMMARY

[0006] The purpose of the present application is to provide a method and device for producing polymethoxy dimethyl ether by using polyformaldehyde production waste, which can fully utilize the formaldehyde-containing waste liquid and the trioxane reboiler in the polyformaldehyde production process, reduce the damage to the production equipment, and ensure the product quality of the polyformaldehyde.

[0007] In a first aspect, the present application provides a method for producing polymethoxy dimethyl ether by using polyformaldehyde production waste. The production process of the polyformaldehyde comprises a formaldehyde production step, a trioxane production step and a polyformaldehyde production step, and the method for producing polymethoxy dimethyl ether by using polyformaldehyde production waste comprises:

[0008] The formaldehyde-containing waste liquid generated in the formaldehyde production step, the trioxane production step and the polyformaldehyde production step is subjected to condensation reaction with methanol to generate methylal;

[0009] The heavy boiler produced in the trioxymethylene production step is condensed with the methylal to obtain polymethoxy dimethyl ether.

[0010] Compared with the prior art, the method for producing polymethoxy dimethyl ether by using waste from the production of polymethylene provided by the present application condenses the methanol-containing waste liquid produced in the production of formaldehyde, the production of trioxymethylene and the production of polymethylene with methanol to produce methylal, and then oxidizes the methylal to prepare concentrated formaldehyde, without the need for pressurized rectification to separate dilute formaldehyde, so the energy consumption of the reaction is relatively low.

[0011] At the same time, when the methanol-containing waste liquid is condensed with methanol, the reaction temperature is relatively low, and the methanol will not be disulfuration to form formic acid, so the corrosion of the production equipment is relatively small, thereby prolonging the service life of the production equipment. In addition, most of the formaldehyde in the methanol-containing waste liquid can be condensed with methanol to form methylal, thereby ensuring high utilization of raw materials.

[0012] At the same time, when the heavy boiler produced in the trioxymethylene production step is condensed with methylal, the trioxymethylene and impurities in the heavy boiler can all eventually react to form the target product polymethoxy dimethyl ether (DMMn), thereby ensuring high utilization of raw materials while preventing the circulation of epoxide compounds and acetal compounds in the heavy boiler in the production process of polymethylene, and ensuring the physical properties of polymethylene.

[0013] As can be seen from the above, the method for producing polymethoxy dimethyl ether by using waste from the production of polymethylene provided by the present application can fully utilize the methanol-containing waste liquid and the trioxymethylene heavy boiler in the production process of polymethylene, reduce the wear of the production equipment, ensure the product quality of polymethylene, and reduce the production energy consumption.

[0014] In a second aspect, the present application also provides a device for producing polymethoxy dimethyl ether by using waste from the production of polymethylene. The polymethylene preparation unit comprises a formaldehyde production module, a trioxymethylene production module and a polymethylene production module.

[0015] The device for producing polymethoxy dimethyl ether by using waste from the production of polymethylene comprises a methylal preparation unit and a polymethoxy dimethyl ether preparation unit.

[0016] The feed inlet of the methylal preparation unit 2 is in communication with the methanol-containing waste liquid discharge outlets of the formaldehyde production module, the trioxymethylene production module and the polymethylene production module, and the feed inlet of the polymethoxy dimethyl ether reactor is in communication with the discharge outlet of the methylal preparation unit and the heavy boiler discharge outlet of the trioxymethylene production module.

[0017] Compared with the prior art, the device for producing polyoxymethylene dimethyl ethers from polyoxymethylene production waste provided by the present application has the same beneficial effects as the method for producing polyoxymethylene dimethyl ethers from polyoxymethylene production waste, which will not be repeated here.

[0018] In a third aspect, the present application further provides a method for co-producing polyoxymethylene and polyoxymethylene dimethyl ethers. The method comprises:

[0019] polyoxymethylene is produced from methanol as raw material through a formaldehyde production step, a trioxymethylene production step and a polyoxymethylene production step;

[0020] condensation reaction between the formaldehyde-containing waste liquid produced in the formaldehyde production step, the trioxymethylene production step and the polyoxymethylene production step and methanol to produce methylal;

[0021] condensation reaction between the heavy boiling liquid in the trioxymethylene production step and the methylal to obtain polyoxymethylene dimethyl ethers.

[0022] Compared with the prior art, the method for co-producing polyoxymethylene and polyoxymethylene dimethyl ethers provided by the present application has the same beneficial effects as the method for producing polyoxymethylene dimethyl ethers from polyoxymethylene production waste, which will not be repeated here.

[0023] In a fourth aspect, the present application further provides a system for co-producing polyoxymethylene and polyoxymethylene dimethyl ethers. The system comprises a polyoxymethylene preparation unit, a methylal preparation unit and a polyoxymethylene dimethyl ether preparation unit. The polyoxymethylene preparation unit comprises a formaldehyde production module, a trioxymethylene production module and a polyoxymethylene production module connected in series. The formaldehyde-containing waste liquid outlet of the formaldehyde production module, the trioxymethylene production module and the polyoxymethylene production module is in communication with the feed inlet of the methylal preparation unit. The outlet of the methylal preparation unit and the heavy boiling liquid outlet of the trioxymethylene production module are in communication with the feed inlet of the polyoxymethylene dimethyl ether preparation unit.

[0024] Compared with the prior art, the system for co-producing polyoxymethylene and polyoxymethylene dimethyl ethers provided by the present application has the same beneficial effects as the device for producing polyoxymethylene dimethyl ethers from polyoxymethylene production waste, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0025] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 A polyoxymethylene production process route in the prior art;

[0027] Figure 2A process route map of the method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste is provided for the embodiments of the present application.

[0028] Figure 3 A process route map of the separation and purification of polyoxymethylene dimethyl ethers is provided for the embodiments of the present application.

[0029] Figure 4 A structural schematic diagram of the device for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste is provided for the embodiments of the present application.

[0030] Figure 5 A flow schematic diagram of the polyformaldehyde co-production polyoxymethylene dimethyl ether system is provided for the embodiments of the present application.

[0031] Figure 6 A process route map of the method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste is provided for the embodiments of the present application.

[0032] Figure 7 A process route map of the preparation of polyformaldehyde from methanol as a raw material is provided for the embodiments of the present application.

[0033] Figure 8 A process route map of the refining of a mixture containing trioxymethylene is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0034] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects more clearly understood, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0035] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0036] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited. The meaning of "several" is one or more, unless otherwise explicitly and specifically limited.

[0037] In the description of the present application, it needs to be understood that the terms "upper", "lower", "front", "back", "left", "right" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0038] Polyformaldehyde is one of the five engineering plastics, which has good physical properties, chemical properties and mechanical properties, as well as high friction resistance and self-lubricating properties, and is one of the thermoplastics closest to metal. Therefore, polyformaldehyde is widely used in various mechanical and electrical, instrument, electronic and other fields. For example, polyformaldehyde is used to produce bearings, pipes, cams, pump impellers, valves, pump bodies, gears, pulleys and zippers.

[0039] The polyformaldehyde production process was invented by the American Celanese Company in 1960, and was successfully industrialized in 1962. The flow chart of the polyformaldehyde production process is shown in Figure 1 . Referring to Figure 1 , the polyformaldehyde production process mainly includes a formaldehyde production step, a trioxymethylene production step and a polyformaldehyde production step.

[0040] The formaldehyde production step mainly uses methanol as a raw material to oxidize methanol to formaldehyde.

[0041] The trioxymethylene production step mainly includes: obtaining a trioxymethylene mixture containing a concentrated formaldehyde aqueous solution under the action of a catalyst, and then separating and refining the trioxymethylene mixture containing to obtain a polymerization grade trioxymethylene.

[0042] The polyformaldehyde production step mainly includes: mixing the polymerization grade trioxymethylene with a comonomer and a catalyst, and then continuously copolymerizing the polymerization grade trioxymethylene in bulk to obtain a macromolecular substance with a hydroxyethyl ether or methoxy ether structure, i.e. polyformaldehyde. Then, after crushing and polymerization stabilization of the polyformaldehyde, the polyformaldehyde product is obtained.

[0043] The comonomer is dioxolane or ethylene oxide, and the —C—C— bond structure in dioxolane and ethylene oxide can effectively prevent the degradation of free radicals, thereby improving the stability of polyformaldehyde.

[0044] In the above polyformaldehyde production process, the formaldehyde production step, the trioxymethylene production step and the polyformaldehyde production step all produce formaldehyde-containing waste liquid. Generally, in the polyformaldehyde production process, the formaldehyde-containing waste liquid is recovered and utilized. The recovery efficiency of the formaldehyde-containing waste liquid means whether the raw materials can be fully utilized, and at the same time determines the energy consumption cost and product quality.

[0045] Due to the influence of the physical properties of formaldehyde, formaldehyde has a high affinity with water, therefore, in the dilute formaldehyde solution, formaldehyde mainly exists in the form of methylene glycol (CH2(OH)2). At the same time, the gas phase equilibrium of methylene glycol and water is very close, therefore, under normal pressure, it is difficult to separate formaldehyde and water.

[0046] At present, the dilute formaldehyde solution is mainly recovered and utilized by using the pressurized rectification process. However, since more than half of the dilute formaldehyde solution is water, the energy consumption of the scheme of recovering dilute formaldehyde by using the pressurized rectification process is extremely large. At the same time, since the dilute formaldehyde solution is continuously heated in the pressurized rectification process, the Cannizzaro disproportionation reaction of formaldehyde occurs to generate methanol and formic acid. This process not only causes the loss of formaldehyde, but also causes the rectification equipment to be corroded by formic acid and unable to be used for a long time, which brings a major safety hazard to normal production.

[0047] In the triformaldehyde production step of the above-mentioned production process of polyformaldehyde, the triformaldehyde refining is mainly to improve the purity of triformaldehyde. The process of preparing polyformaldehyde by polymerization of triformaldehyde has a very high requirement on the purity of triformaldehyde, which needs to reach 99.9%. If the purity does not reach this value, it will directly affect the efficiency of the polymerization reaction, and then affect the quality of the polyformaldehyde product, therefore, the synthesized triformaldehyde needs to be refined to obtain polymerization-grade triformaldehyde, and then the polymerization-grade triformaldehyde is used for polymerization reaction to obtain polyformaldehyde.

[0048] In the triformaldehyde refining process, in addition to obtaining polymerization-grade triformaldehyde monomer, reboiled material is also generated. In addition to containing a large amount of TOX and a small amount of HCHO, the reboiled material also contains a considerable amount of polyformaldehyde, epoxy compounds and acetal compounds and other substances. For example: 1,3,5 trioxaheptane trioxaoctane polyformaldehyde (CH2O) n tetraoxaoctane trioxanonane and polyoxymethylene dimethyl ether CH3(OCH2) n OCH3(n≥2), which causes the problem of insufficient use of raw materials in the production of polyformaldehyde, therefore, the reboiled material needs to be recovered and utilized to improve the raw material utilization rate of polyformaldehyde.

[0049] In a conventional polyformaldehyde production process, the treatment of the reboiler is to combine it with the dilute formaldehyde solution generated by the process, and then recover the crude TOX and 55% formaldehyde through rectification, and then reuse it for production, so that the epoxide compounds and acetal compounds in the reboiler will be recycled and accumulated in the entire process. When the reboiler content is high during polyformaldehyde production, the purity of TOX will be affected to a certain extent. Excessive impurities in the TOX monomer will cause molecular chain transfer during the polymerization reaction process, reduce the molecular weight of polyformaldehyde, increase the melt index range, increase the unstable end group, and further reduce the physical properties such as impact strength of polyformaldehyde.

[0050] Embodiment one

[0051] In order to fully utilize the formaldehyde-containing waste liquid and reboiler while reducing the damage to the production equipment and ensuring the product quality of polyformaldehyde, the present application provides a method for producing polyoxymethylene dimethyl ether from polyformaldehyde production waste. The production process of the polyformaldehyde includes a formaldehyde production step, a trioxymethylene production step, and a polyformaldehyde production step.

[0052] Figure 2 A flowchart of the method for producing polyoxymethylene dimethyl ether from polyformaldehyde production waste is shown. Referring to Figure 2 , the method comprises:

[0053] S100: The formaldehyde-containing waste liquid generated in the formaldehyde production step, the trioxymethylene production step, and the polyformaldehyde production step is subjected to a condensation reaction with methanol to generate methylal.

[0054] It should be noted that the condensation reaction of the formaldehyde-containing waste liquid with methanol to generate methylal can be selected according to the actual situation, as long as methylal can be generated. For example, liquid phase condensation process can be used, or reaction rectification process can be used. In the embodiments of the present application, the liquid phase condensation of formaldehyde and methanol to generate methylal (DMM) in the presence of an acidic catalyst can effectively recycle dilute formaldehyde without the need for a special dilute formaldehyde recovery device. The process route is mature, the reaction conditions are mild, the reaction temperature is controlled at 45℃-90℃, and the generation of a large amount of formic acid is avoided; under the condition of stoichiometric ratio of raw materials methanol and formaldehyde 2:1, formaldehyde is almost completely converted into methylal, reducing the generation of formaldehyde-containing wastewater. Compared with the dilute formaldehyde pressurized rectification recovery process, the entire process has the advantages of low energy consumption, low corrosion, and green environmental protection.

[0055] S200: The reboiler generated in the trioxymethylene production step is subjected to a condensation reaction with the methylal to obtain polyoxymethylene dimethyl ether.

[0056] It should be noted that the trioxymethylene production step includes: synthesizing formaldehyde into a trioxymethylene-containing mixture, and then refining the trioxymethylene-containing mixture. Refining the trioxymethylene-containing mixture includes: the trioxymethylene crude product prepared by concentrating formaldehyde is subjected to alkali washing, benzene extraction, re-alkali washing, benzene-water separation, light boiling tower separation and purification, and heavy boiling tower purification separation, etc. steps, so that the polymeric grade trioxymethylene can be obtained at the top of the heavy boiling tower. The material discharged from the bottom of the heavy boiling tower is the heavy boiling material. The heavy boiling material includes 60% to 80% trioxymethylene, 5% to 20% DMM3, 0.1% to 1.0% H2O, epoxy compounds, polyoxymethylene, and polyoxymethylene dimethyl ethers (DMMn, n>1) with a polymerization degree greater than 1. Among them, the epoxy compounds include tri-octacyclic, tri-octacyclic and tri-octacyclic.

[0057] The heavy boiling material is mixed with methylal, and the trioxymethylene in the heavy boiling material reacts with the methylal under the action of the catalyst to generate polyoxymethylene dimethyl ethers (DMMn). At the same time, other impurities in the heavy boiling material can also be decomposed under the action of the catalyst to release formaldehyde (HCHO), which further reacts with methylal to generate polyoxymethylene dimethyl ethers (DMMn), so that the impurities in the heavy boiling material can be fully utilized. At the same time, DMMn is a high-performance diesel clean additive, which can significantly improve the engine combustion performance and reduce diesel engine exhaust pollutant emissions when added to diesel. DMMn can also be used as an environmentally friendly green solvent to partially or completely replace aromatic hydrocarbons, alcohol ethers and their acetate, ketones, esters and other solvents, and has good economic benefits and application prospects.

[0058] In the method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste provided in the present application, the condensation reaction of the formaldehyde-containing waste liquid generated in the formaldehyde production step, the trioxymethylene production step and the polyformaldehyde production step with methanol to generate methylal can occur without pressure rectification, so the energy consumption of the reaction is relatively low.

[0059] At the same time, the reaction temperature is relatively low when the formaldehyde-containing waste liquid reacts with methanol, so the formaldehyde will not be disulfided to generate formic acid, so the corrosion of the production equipment is relatively small, thereby prolonging the service life of the production equipment. In addition, most of the formaldehyde in the formaldehyde-containing waste liquid can react with methanol to generate methylal, thereby ensuring high utilization of raw materials.

[0060] At the same time, when the heavy boiling material generated in the trioxymethylene production step reacts with methylal, the trioxymethylene and impurities in the heavy boiling material can ultimately react to generate the target product polyoxymethylene dimethyl ethers (DMMn), thereby ensuring high utilization of raw materials while preventing the circulation of epoxy compounds and acetal compounds in the heavy boiling material in the production process of polyformaldehyde, and ensuring the physical properties of polyformaldehyde.

[0061] From the above, the method for producing polymethoxy dimethyl ether from polyformaldehyde production waste provided by the application can fully utilize the formaldehyde-containing waste liquid and the trioxane reboiler in the polyformaldehyde production process, reduce the loss of the production equipment, ensure the product quality of the polyformaldehyde, and reduce the production energy consumption.

[0062] Specifically, the equipment used in the condensation reaction in S100 can be selected according to actual conditions. For example, the equipment can be a tank reactor, a fixed bed reactor, or a reaction distillation column.

[0063] In some possible implementation manners, the formaldehyde-containing waste liquid and the methanol need to be condensed and reacted under the action of a first catalyst to obtain methylal. It should be noted that the type of the first catalyst can be selected according to actual conditions, as long as the first catalyst can catalyze the condensation reaction of the formaldehyde in the formaldehyde-containing waste liquid and the methanol to generate methylal.

[0064] Specifically, the first catalyst can be an acidic catalyst. Further, the first catalyst is a solid catalyst, and the first catalyst can be one or a mixture of several of an acidic cationic resin, a molecular sieve, a supported ionic liquid, and aluminum oxide.

[0065] Specifically, the equipment used in the condensation reaction of the formaldehyde-containing waste liquid and the methanol can also be selected according to actual conditions. For example, a tank reactor, a fixed bed reactor, or a reaction distillation column can be used.

[0066] Regardless of which equipment is used in the condensation reaction of the formaldehyde-containing waste liquid and the methanol, the reaction temperature and the reaction pressure are not changed. Generally, the temperature of the condensation reaction should be 0 ℃ to 200 ℃, and the pressure of the condensation reaction should be -0.1 MPa to 3.0 MPa.

[0067] Specifically, the concentration of the formaldehyde in the formaldehyde-containing waste liquid is generally determined by the production process during the production of the polyformaldehyde. Generally, the mass concentration of the formaldehyde in the formaldehyde-containing waste liquid is 5% to 40%.

[0068] In order to ensure that the formaldehyde in the formaldehyde-containing waste liquid can fully react with the methanol, the molar ratio of the formaldehyde to the methanol in the formaldehyde-containing waste liquid is 1:(1-3). Preferably, the molar ratio of the formaldehyde to the methanol in the formaldehyde-containing waste liquid is 1:(1.5-2.5).

[0069] In some possible implementation manners, the reboiler and the methylal need to be condensed and reacted under the action of a second catalyst. The type of the second catalyst can be selected according to actual conditions, as long as the second catalyst can catalyze the condensation reaction of the TOX in the reboiler and the methylal to generate polymethoxy dimethyl ether.

[0070] Specifically, the second catalyst can be an acidic catalyst, and the acid amount of the B acid center of the second catalyst accounts for 80% or more of the total acid amount. Preferably, the second catalyst is a solid acidic catalyst.

[0071] For example, the second catalyst can be one or more of a molecular sieve, a resin, a supported ionic liquid, and alumina.

[0072] As an embodiment, the equipment used for the condensation reaction between the reboiled material and the methylal can be selected according to actual conditions, as long as the condensation reaction between the methylal and the trioxane in the reboiled material can be ensured. For example, the equipment can be a tank reactor or a fixed bed reactor.

[0073] Regardless of the reaction equipment used for the condensation reaction between the methylal and the trioxane, the reaction temperature and the reaction pressure do not change. The reaction temperature of the condensation reaction is 30°C to 200°C, and the reaction pressure is 0 MPa to 2.0 MPa.

[0074] Specifically, in order to ensure that the methylal in the azeotrope and the trioxane in the reboiled material can fully react, the molar ratio of the methylal to the trioxane is (0.5-10):1, and preferably, the molar ratio of the methylal to the trioxane is (1-6):1.

[0075] As a possible implementation manner, in order to further improve the purity of the polymethyl ether dimethyl ether, see Figure 2 After S200, the method for producing the polymethyl ether dimethyl ether from the polymethylal production waste further includes:

[0076] S300: The polymethyl ether dimethyl ether is separated and purified to obtain a polymethyl ether dimethyl ether DMM with a polymerization degree of 3-6. 3～6 At this time, the polymethyl ether dimethyl ether with a higher or lower polymerization degree is removed, and the obtained polymethyl ether dimethyl ether has a polymerization degree of 3-6, which is more suitable for application.

[0077] Specifically, see Figure 3 In S300, the separation and purification of the polymethyl ether dimethyl ether specifically includes:

[0078] S310: The polymethyl ether dimethyl ether mixture is subjected to light reboiled material removal to obtain a polymethyl ether dimethyl ether with a polymerization degree of 3 or more.

[0079] It should be noted that the light reboiled material herein refers to a component in the polymethyl ether dimethyl ether, which has a boiling point lower than that of the polymethyl ether dimethyl ether with a polymerization degree of 3. In the polymethyl ether dimethyl ether mixture of the present application, the light reboiled material mainly includes DMM, DMM2, and a small amount of formaldehyde, water, methanol, and TOX.

[0080] The light boiler removal can be performed in a light boiler column, and the product in the column bottom of the light boiler column is dimethyl ether with a polymerization degree of 3 or more. The product in the column top of the light boiler column is the light boiler, which can be fed into S200 to participate in the reaction. The removed light boiler is recycled to S200 to participate in the condensation reaction as raw material, thereby further improving the utilization rate of the raw material.

[0081] S320: removing the heavy boiler from the dimethyl ether with a polymerization degree of 3 or more to obtain dimethyl ether with a polymerization degree of 3-6.

[0082] It should be noted that the heavy boiler mentioned herein refers to dimethyl ether with a polymerization degree of more than 6. For example, the heavy boiler can be DMM7 and DMM8.

[0083] The heavy boiler removal can be performed in a heavy boiler column, and the product in the column bottom of the heavy boiler column is the heavy boiler. At this time, the heavy boiler can be recycled to S200 to participate in the condensation reaction as a reactant. The product in the column top of the heavy boiler column is dimethyl ether with a polymerization degree of 3-6.

[0084] Embodiment Mode Two

[0085] The application also provides a device for producing dimethyl ether from polyformaldehyde production waste. The polyformaldehyde preparation unit 1 comprises a formaldehyde production module 11, a trioxane production module 12 and a polyformaldehyde production module 13.

[0086] The structure diagram of the device for producing dimethyl ether from polyformaldehyde production waste provided by the application is shown in Figure 4 . As shown in Figure 4 , the device comprises a methylal preparation unit 2 and a dimethyl ether preparation unit 3. The feed inlet of the methylal preparation unit 2 is in communication with the formaldehyde-containing waste liquid outlets of the formaldehyde production module 11, the trioxane production module 12 and the polyformaldehyde production module 13, and the feed inlet of the dimethyl ether preparation unit 3 is in communication with the outlet of the methylal preparation unit 2 and the heavy boiler outlet of the trioxane production module 12.

[0087] It should be noted that the type of the methylal reactor can be selected according to the actual situation. For example, the methylal reactor can be a kettle reactor, a fixed bed reactor or a reactive distillation column.

[0088] When the methylal reactor is a reactive distillation column, the feed inlet of the reactive distillation column is in communication with the formaldehyde-containing waste liquid outlet of the polyformaldehyde production device, and the product in the column top of the reactive distillation column is an azeotrope containing methylal. The waste in the column bottom of the reactive distillation column comprises formaldehyde, methanol and water, which can be discharged to a waste water treatment unit.

[0089] The polyoxymethylene dimethyl ethers reactor 31 can be selected according to actual conditions. For example, the polyoxymethylene dimethyl ethers reactor 31 can be a tank reactor or a fixed bed reactor.

[0090] When the polyoxymethylene dimethyl ethers reactor 31 is a fixed bed reactor, the fixed bed reactor should be equipped with a Beta molecular sieve. The feed inlet of the fixed bed reactor is in communication with the outlet of the methylal reactor, and the outlet of the fixed bed reactor obtains a condensation product containing DMM 2-8 .

[0091] Compared with the prior art, the device for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste provided by the present application has the same beneficial effects as the method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste provided in the first embodiment, which will not be described here.

[0092] As a feasible embodiment, see Figure 4 , the polyoxymethylene dimethyl ethers preparation unit 3 comprises a polyoxymethylene dimethyl ethers reactor 31 and a separation and purification module. The feed inlet of the polyoxymethylene dimethyl ethers reactor 31 is in communication with the outlet of the methylal preparation unit 2 and the heavy boiling reboiler outlet of the polyformaldehyde production module 12. The feed inlet of the separation and purification module is in communication with the outlet of the polyoxymethylene dimethyl ethers reactor 31. The separation and purification device is mainly used for removing polyoxymethylene dimethyl ethers with a polymerization degree less than 3 and a polymerization degree greater than 6, so as to obtain polyoxymethylene dimethyl ethers with a polymerization degree of 3-6.

[0093] Specifically, the separation and purification module comprises a first light boiling tower 32 and a first heavy boiling tower 33. The feed inlet of the first light boiling tower 32 is in communication with the outlet of the polyoxymethylene dimethyl ethers reactor 31, the outlet at the bottom of the first light boiling tower 32 is in communication with the feed inlet of the first heavy boiling tower 33, and the product at the top of the first heavy boiling tower 33 is polyoxymethylene dimethyl ethers with a polymerization degree of 3-6.

[0094] The product at the bottom of the first light boiling tower 32 is polyoxymethylene dimethyl ethers with a polymerization degree greater than or equal to 3, and the product at the bottom of the first light boiling tower 32 enters the first heavy boiling tower 33 for reboiler removal. The product at the top of the first light boiling tower 32 is mainly DMM, DMM2, and a small amount of formaldehyde, water, methanol and TOX. At this time, the outlet at the top of the first light boiling tower 32 can be in communication with the feed inlet of the polyoxymethylene dimethyl ethers reactor 31, so that the product at the top of the first light boiling tower 32 is recycled to the polyoxymethylene dimethyl ethers reactor 31 to undergo condensation reaction as the raw material in S200, thereby further improving the utilization rate of the raw material.

[0095] The overhead product of the first reboiler column 33 is a polymethyl oxide dimethyl ether with a polymerization degree of 3-6, and the polymethyl oxide dimethyl ether with a polymerization degree of 3-6 is discharged from the overhead of the first reboiler column 33. The bottom product of the first reboiler column 33 is a polymethyl oxide dimethyl ether with a polymerization degree greater than 6. At this time, the bottom outlet of the first reboiler column 33 can be connected to the feed inlet of the polymethyl oxide dimethyl ether reactor 31, so that the bottom product of the first reboiler column 33 can be recycled to the polymethyl oxide dimethyl ether reactor 31 to undergo condensation reaction as the raw material of S200, thereby further improving the utilization rate of the raw material.

[0096] Embodiment three

[0097] The present application provides a method for co-producing polymethyl alcohol and polymethyl oxide dimethyl ether. Referring to Figure 6 The method for co-producing polymethyl alcohol and polymethyl oxide dimethyl ether comprises:

[0098] S400: producing polymethyl alcohol from methanol as a raw material through a formaldehyde production step, a trioxymethylene production step and a polymethyl alcohol production step.

[0099] It should be noted that the formaldehyde production step, the trioxymethylene production step and the polymethyl alcohol production step all produce formaldehyde-containing waste liquid. The trioxymethylene production step produces reboiler.

[0100] S500: condensation reaction of the formaldehyde-containing waste liquid produced in the formaldehyde production step, the trioxymethylene production step and the polymethyl alcohol production step with methanol to produce methylal.

[0101] S600: condensation reaction of the reboiler in the trioxymethylene production step with the methylal to obtain polymethyl oxide dimethyl ether.

[0102] Compared with the prior art, the beneficial effects of the present embodiment are the same as those of the above-mentioned embodiments, which will not be repeated here.

[0103] As a possible implementation, referring to Figure 7 The above method for preparing polymethyl alcohol from methanol as a raw material mainly comprises the following steps:

[0104] S410: oxidizing methanol to formaldehyde.

[0105] It should be noted that there are many methods for oxidizing methanol to formaldehyde.

[0106] For example: methanol can be mixed with air, and formaldehyde can be prepared under the action of a catalyst, and then concentrated formaldehyde aqueous solution can be obtained by water absorption. The concentration of formaldehyde in the above-mentioned concentrated formaldehyde aqueous solution is greater than 50%.

[0107] The overhead product of the first light boiling tower 32 can also be mixed with methanol and evaporated, mixed with air, and reacted with a catalyst to produce formaldehyde, which is absorbed with water to obtain a concentrated formaldehyde aqueous solution. In this process, the catalyst is an oxidation catalyst, and the effective metal elements in the oxidation catalyst are one or more of silver, iron, molybdenum, bismuth, chromium, tungsten, cobalt, and nickel. For example, the catalyst can be an iron-molybdenum catalyst. The reaction pressure is normal pressure, and the reaction temperature is 260°C.

[0108] In the embodiments of the present application, the overhead product of the first light boiling tower 32 is mixed with methanol and evaporated to obtain formaldehyde. At this time, the overhead product of the light boiling tower can be recycled to further improve the utilization rate of raw materials.

[0109] The dilute formaldehyde aqueous solution produced by the formaldehyde production unit can be used as a formaldehyde-containing waste liquid to participate in the condensation reaction in S500.

[0110] S420: The concentrated formaldehyde aqueous solution produced by the formaldehyde production unit is reacted with a cyclization catalyst to form trioxane, and a trioxane-containing mixture is collected in the gas phase. The concentration of trioxane in the trioxane-containing mixture is 17.53%, and the rest is methanol, methyl formate, methylal, formaldehyde, water, and formic acid. Among them, methanol, methyl formate, methylal, and formic acid are by-products of the reaction, and formaldehyde is an unreacted raw material.

[0111] It should be understood that the type of cyclization catalyst described above can be selected according to actual conditions.

[0112] Specifically, the cyclization catalyst described above can be a solid acid catalyst. For example, one or a mixture of several of an acidic cationic resin, a molecular sieve, a supported ionic liquid, and alumina.

[0113] The equipment used to synthesize trioxane from the concentrated formaldehyde aqueous solution described above can be selected according to actual conditions. For example, it can be a tank reactor or a fixed bed reactor.

[0114] Regardless of the equipment used to synthesize trioxane from the concentrated formaldehyde aqueous solution, the reaction temperature and the reaction pressure remain unchanged. For example, the reaction temperature can be 80°C to 150°C, and the pressure can be -0.1 MPa to 0.5 MPa.

[0115] S430: The trioxane-containing mixture is refined to obtain polymer-grade trioxane.

[0116] It should be noted that the trioxane-containing mixture needs to be refined to increase the purity of trioxane in the trioxane-containing mixture to 99.9% to obtain polymer-grade trioxane.

[0117] S440: mixing the polymerization grade of trioxane with the comonomer and the catalyst, so that the polymerization grade of trioxane is subjected to bulk continuous copolymerization to obtain the polyoxymethylene.

[0118] It should be noted that the above-mentioned comonomer should have a -C-C- bond structure, so that the -C-C- bond structure in the comonomer can effectively prevent the degradation of free radicals in the polyoxymethylene, further improving the stability of the polyoxymethylene.

[0119] The above-mentioned comonomer can be selected according to the situation. For example, the above-mentioned polyoxymethylene can be dioxolane or oxirane.

[0120] The polymerization process of the polymerization grade of trioxane can be selected according to the actual situation, as long as it can ensure that the polymerization grade of trioxane can be subjected to bulk continuous copolymerization to obtain the polyoxymethylene. For example, batch polymerization can be used for polymerization, or a kneader continuous reaction extrusion method can be used for polymerization. In the embodiments of the present application, a screw polymerization reactor is mainly used as a polymerization device, and a continuous reaction extrusion method is used to make the polymerization grade of trioxane polymerize.

[0121] S450: crushing and polymerization stabilizing the above-mentioned polyoxymethylene to obtain a polyoxymethylene product.

[0122] Further, in order to improve the refining efficiency of the trioxane-containing mixture in S430, referring to Figure 8 In the embodiments of the present application, the following steps are mainly used to refine the trioxane-containing mixture:

[0123] S431: concentrating the trioxane-containing mixture to increase the concentration of trioxane, to obtain a trioxane crude product. The concentration of trioxane in the trioxane crude product is 64.71%, and the rest is methanol, methyl formate, methylal, formaldehyde, and formic acid.

[0124] It should be noted that the above-mentioned trioxane-containing mixture can be concentrated in the concentration column 122. During the concentration process, the overhead outlet of the concentration column 122 is the trioxane crude product, and the product in the column bottom of the concentration column 122 is a formaldehyde-containing mixture, which is composed of methanol, formaldehyde, water, and formic acid. At this time, the formaldehyde-containing mixture in the column bottom of the concentration column 122 can be used as a formaldehyde-containing waste liquid, which flows out through the column bottom discharge port of the concentration column 126 and is used as a raw material to participate in the condensation reaction in S500. The formaldehyde-containing mixture flowing out of the column bottom discharge port of the concentration column 122 can also be used as a raw material to participate in the reaction in S420.

[0125] The above-mentioned concentration column 122 can be a plate column, a wall column or a packed column, and the middle part or the column bottom of the concentration column 122 is provided with an inlet for receiving the trioxane-containing mixture in the gas phase collected in S420. The operating pressure of the concentration column 126 is -0.1 MPa to 0.2 MPa.

[0126] S432: After the crude trioxane product is subjected to alkali washing, benzene extraction, re-alkali washing, and benzene-water separation, the upper phase (organic phase) is subjected to light boiler removal and heavy boiler removal to obtain polymerization-grade trioxane. At this time, the content of trioxane in the polymerization-grade trioxane is greater than 99.9%.

[0127] It should be noted that when the crude trioxane product is subjected to alkali washing, benzene extraction, re-alkali washing, and benzene-water separation, it can be performed in the extraction column 123. After the benzene-water separator 124, the lower phase (aqueous phase) obtained can be recycled to the feed inlet of the extraction column 123 in the S432 step.

[0128] The upper phase (organic phase) can be subjected to light boiler removal in a light boiler column. After the upper phase (organic phase) is separated and purified in the light boiler column, the product in the light boiler column column stillage is subjected to subsequent heavy boiler removal. The light boiler column overhead product is mainly benzene and a small amount of methanol, and the benzene can be recycled to S432 for recycling as an extractant, and the methanol can be recycled to S400 as a raw material to prepare methylal.

[0129] The light boiler column column stillage product is mainly a trioxane mixture containing epoxide compounds, acetal compounds, and paraformaldehyde, and the light boiler column column stillage product can be subjected to heavy boiler removal by a heavy boiler column. The heavy boiler column overhead product is the polymerization-grade trioxane, and the heavy boiler column column stillage product includes trioxane, DMM3, water, epoxide compounds, and paraformaldehyde. At this time, the heavy boiler column column stillage product needs to be recycled to S600 as a raw material to participate in the condensation reaction in S600.

[0130] Embodiment Four

[0131] The present application provides a polyformaldehyde co-production polymethoxydimethyl ether system. Referring to Figure 5 The polyformaldehyde co-production polymethoxydimethyl ether system includes a polyformaldehyde preparation unit 1, a methylal preparation unit 2, and a polymethoxydimethyl ether preparation unit 3. The polyformaldehyde preparation unit 1 includes a formaldehyde production module 11, a trioxane production module 12, and a polyformaldehyde production module 13. The formaldehyde-containing waste liquid discharge outlets in the formaldehyde production module 11, the trioxane production module 12, and the polyformaldehyde production module 13 are in communication with the feed inlet of the methylal preparation unit 2, the heavy boiler discharge outlet of the trioxane production module 12 is in communication with the methylal preparation unit 2, and the discharge outlet of the methylal preparation unit 2 is in communication with the feed inlet of the polymethoxydimethyl ether preparation unit 3.

[0132] In the above polyformaldehyde co-production of polymethyloxymethyl ether system, the formaldehyde production module 11 mainly uses methanol as raw material to produce concentrated formaldehyde aqueous solution with a concentration greater than 55%. The trioxane production module 12 mainly uses concentrated formaldehyde aqueous solution to produce polymeric trioxane with a purity higher than 99.9%. The polyformaldehyde production module 13 mainly uses polymeric trioxane to produce polyformaldehyde product. The above methylal preparation unit 2 is used to produce methylal by reacting with methanol using the formaldehyde-containing waste liquid generated in the polyformaldehyde production module 13, the trioxane production module 12 and the polyformaldehyde production module 13 as raw material. The polymethyloxymethyl ether unit uses the above methylal and the reboiler produced by the trioxane production module 12 as raw material to produce polymethyloxymethyl ether.

[0133] Compared with the prior art, the polyformaldehyde co-production of polymethyloxymethyl ether system provided by the embodiment of the present application has the same beneficial effects as the above-mentioned embodiment three, which will not be repeated here.

[0134] As a possible implementation, the above trioxane production module 12 includes a trioxane reactor 121 and a trioxane refining module. The feed inlet of the trioxane reactor 121 is in communication with the outlet of the above formaldehyde production module 11, and the outlet of the trioxane reactor 121 is in communication with the feed inlet of the trioxane refining module. In the above trioxane production module 12, the formaldehyde-containing waste liquid outlet is located in the trioxane refining module.

[0135] It should be noted that the above trioxane reactor 121 can be a kettle reactor or a fixed bed reactor.

[0136] The above trioxane reactor 121 mainly uses concentrated formaldehyde solution to produce a trioxane-containing mixture. The trioxane refining module is used to refine the trioxane-containing mixture, so as to increase the purity of trioxane to 99.9% and obtain polymeric trioxane.

[0137] For example, in order to ensure the refining efficiency of the trioxane mixture, the trioxane refining module includes a concentration column 122, an extraction column 123, a benzene water separator 124, a second light boiling column 125, and a second heavy boiling column 126. The feed inlet of the concentration column 122 is in communication with the outlet of the trioxane reactor 121, the bottom outlet of the concentration column 122 is a formaldehyde-containing waste liquid outlet, which is in communication with the feed inlet of the methylal preparation unit 2, the top outlet of the concentration column 122 is in communication with the feed inlet of the extraction column 123. The top outlet of the extraction column 123 is in communication with the feed inlet of the benzene water separator 124, the upper phase outlet of the benzene water separator 124 is in communication with the feed inlet of the second light boiling column 125, the bottom outlet of the second light boiling column 125 is in communication with the feed inlet of the second heavy boiling column 126, the top outlet of the second heavy boiling column 126 is in communication with the feed inlet of the polyoxymethylene production module 13, and the bottom outlet of the second heavy boiling column 126 is a heavy boiling material outlet.

[0138] Specifically, in order to further improve the utilization rate of methanol in the raw material, the trioxane refining module further includes a methanol recovery column 127. The feed inlet of the methanol recovery column 127 is in communication with the tail outlet of the formaldehyde production module 11, so that the methanol-containing waste liquid generated by the formaldehyde production module 11 can be separated and used as raw material into the formaldehyde production module 11, further improving the utilization rate of methanol.

[0139] Specifically, in order to further improve the utilization rate of trioxane, the trioxane refining module further includes a trioxane recovery column 128. The feed inlet of the trioxane recovery column 128 is in communication with the bottom outlet of the extraction column 123 and the waste outlet of the crusher 132, so that the trioxane-containing waste in the extraction column 123 and the crusher 132 can enter the trioxane recovery column 128 for recovery. The bottom outlet of the trioxane recovery column 128 is in communication with the feed inlet of the methylal preparation unit 2, so that the separated formaldehyde can be used as raw material to participate in the reaction of the methylal preparation unit 2, improving the utilization rate of trioxane.

[0140] Specifically, in order to further improve the utilization rate of the raw material, the bottom outlet of the concentration column 122 can be in communication with the feed inlet of the trioxane reactor 121, so that the bottom product of the concentration column 122 can be used as raw material to participate in the synthesis of the trioxane mixture.

[0141] The top methanol outlet of the second light boiling column 125 can also be in communication with the feed inlet of the formaldehyde production module 11, so that the top product of the second light boiling column 125 can be used as raw material to participate in the production of formaldehyde.

[0142] As a possible implementation, the polyformaldehyde production module 13 comprises a polyformaldehyde reactor 131, a pulverizer 132 and a polymerization stabilizing device 133. The feed inlet of the polyformaldehyde reactor 131 is in communication with the overhead outlet of the second reboiler column 126, and the outlet of the polyformaldehyde reactor 131 is in communication with the feed inlet of the pulverizer 132. The polyformaldehyde outlet of the pulverizer 132 is in communication with the feed inlet of the polymerization stabilizing device 133, and the waste outlet of the polymerization stabilizing device 133 is the formaldehyde-containing waste outlet, which is in communication with the feed inlet of the methylal preparation unit 2, and the product outlet of the polymerization stabilizing device 133 is the polyformaldehyde product.

[0143] The polyformaldehyde production module 13 provided by the present application can produce polyformaldehyde and improve the physical and chemical stability of the polyformaldehyde product, thereby further improving the performance of the polyformaldehyde product.

[0144] As a possible implementation, the methylal preparation unit 2 comprises a methylal reactor. The feed inlet of the methylal reactor is in communication with the tail outlet of the formaldehyde production, the bottom outlet of the concentration column 126, the bottom outlet of the trioxane recovery column 128 and the formaldehyde aqueous solution outlet of the polymerization stabilizing device 133, the overhead outlet of the methylal reactor is in communication with the feed inlet of the polyoxymethylene ether preparation unit 3, and the bottom outlet of the methylal reactor is the waste outlet, which is directly connected to the wastewater unit.

[0145] It should be noted that the methylal reactor can be a reactive distillation column. The overhead outlet of the methylal reactor can be used to collect a mixture of methanol and methylal in gas phase, which can be directly used as raw material for the polyoxymethylene ether preparation unit 3, or after separation and purification, the pure methylal can be obtained. The bottom outlet of the methylal reactor is an aqueous solution containing less than 0.05% of formaldehyde and methanol, which can be directly sent to the wastewater treatment unit.

[0146] As a possible implementation, the polyoxymethylene ether preparation unit 3 comprises a polyoxymethylene ether reactor 31, a first light reboiler column 32 and a first heavy reboiler column 33. The feed inlet of the polyoxymethylene ether reactor 31 is in communication with the outlet of the methylal reactor and the bottom outlet of the second reboiler column 125, the outlet of the polyoxymethylene ether reactor 31 is in communication with the feed inlet of the first light reboiler column 32, and the bottom outlet of the first light reboiler column 32 is in communication with the feed inlet of the first heavy reboiler column 33.

[0147] It should be noted that the polyoxymethylene ether reactor 31 is a fixed bed reactor equipped with Beta molecular sieve.

[0148] At this time, the methylal generated in the methylal reactor and the column bottom product in the second reboiling column 125 enter the polyoxymethylene dimethyl ethers reactor 31 to perform a condensation reaction, to obtain a polyoxymethylene dimethyl ethers crude product. The polyoxymethylene dimethyl ethers crude product enters the first light boiling column 32 to remove light boiling substances, and then enters the first reboiling column 33 to remove reboiling substances, to obtain polyoxymethylene dimethyl ethers with a polymerization degree of 3-6.

[0149] Specifically, in order to further improve the utilization rate of raw materials, the bottom discharge port of the first reboiling column 33 is in communication with the feed inlet of the polyoxymethylene dimethyl ethers reactor 31, so that the column bottom product of the first reboiling column 33 can be recycled to the polyoxymethylene dimethyl ethers reactor 31 to participate in the reaction, to improve the utilization rate of raw materials.

[0150] The top discharge port of the first light boiling column 32 is in communication with the feed inlet of the polyoxymethylene dimethyl ethers reactor 31 and the feed inlet of the formaldehyde production module 11, so that the column top product of the first light boiling column 32 can participate in the reaction of the polyoxymethylene dimethyl ethers reactor 31 and the formaldehyde production module 11 as raw materials, to further improve the utilization rate of raw materials.

[0151] Embodiment one

[0152] The embodiment of the present application provides a method for co-producing polyformal and polyoxymethylene dimethyl ethers, which comprises a formaldehyde preparation section, a polyformal preparation section, a methylal synthesis section and a DMMn synthesis section.

[0153] The formaldehyde preparation section (1) comprises the following steps:

[0154] The mixture of methanol (stream A) and methylal (stream S) from the DMMn synthesis section is evaporated, mixed with air, and reacted at 260°C under normal pressure in the presence of an iron-molybdenum oxidation catalyst to generate formaldehyde, and a concentrated formaldehyde aqueous solution (stream C) with a concentration of 55.0% is obtained by water absorption.

[0155] The polyformal preparation section (2) comprises the following steps:

[0156] The concentrated formaldehyde aqueous solution (stream C) enters the TOX reactor 121 containing a resin catalyst, and the catalyst is used in an amount of 5% of the mass of the concentrated formaldehyde aqueous solution, and the reaction is carried out at a temperature of 115°C under normal pressure. The gas phase (stream D) collected at the outlet of the TOX reactor 121 comprises 0.86% of methanol, 0.07% of methyl formate, 0.09% of methylal, 17.55% of trioxymethylene, 38.40% of formaldehyde, 42.85% of water and 0.18% of formic acid. Among them, methanol, methyl formate, methylal and formic acid are by-products of the reaction, and formaldehyde is unreacted raw material.

[0157] The gas phase (stream D) from the trimerization reactor 121 is concentrated in the concentration column 122. The crude product of the trimerization (stream E) is obtained at the top of the concentration column 122 and has the following composition: methanol: 0.70%, methyl formate: 0.14%, methylal: 0.30%, trimer: 64.71%, formaldehyde: 3.71%, water: 30.44%, formic acid: 0.003%. The aqueous solution of formaldehyde (stream F) is obtained at the bottom of the concentration column 122 and has the following composition: methanol: 0.99%, formaldehyde: 55.11%, water: 43.64%, formic acid: 0.26%. This stream is recycled to the TOX reactor 121 or to the methylal synthesis section.

[0158] The crude product of the trimerization (stream E) obtained at the top of the concentration column 122 is washed with a base, extracted with benzene, washed again with a base and separated from the benzene. The lower phase (aqueous phase) is recycled to the TOX extraction column 123 and the upper phase (organic phase) is separated and purified in a second light boiling column 125 and a second heavy boiling column 126. The polymer grade TOX (stream G) is obtained at the top of the second heavy boiling column 126 and has the following composition: trimer: 99.93%, formaldehyde: 0.0057%, water: 0.0020%, formic acid: 0.0023%, heptoxide: 0.052%, DMM3: 0.0080%. This stream is introduced into the screw polymerization reactor 131. The heavy boiling residue (stream H) is obtained at the bottom of the second heavy boiling column 126 and has the composition shown in Table 1. This stream is introduced into the polyoxymethylene dimethyl ethers reactor 31 in step (4).

[0159] Table 1 Composition of the main substances in the TOX heavy boiling residue

[0160]

[0161] The polymer grade TOX (stream G) obtained at the top of the second heavy boiling column 126 is polymerized in the screw polymerization reactor 131 in the presence of other comonomers and of auxiliary agents. After being ground and polymerization stabilized, the polyformaldehyde product is obtained. The unreacted TOX (stream I) from the grinder 132 is recycled to the trimer recovery column 128. The dilute formaldehyde (stream J) from the polymerization stabilization reactor is introduced into the methylal synthesis section.

[0162] (3) Methylal synthesis section

[0163] The dilute formaldehyde (stream K) produced in the formaldehyde preparation section, the bottom of the concentration tower 126 (stream L) and the bottom of the trioxymethylene recovery tower 128 (stream M) in the polyoxymethylene preparation section, and the dilute formaldehyde (stream J) produced in the polymerization stabilization process are mixed to obtain a formaldehyde concentration of 30.0%. This stream is then mixed with methanol (stream B) and enters a methyl acetal reactor containing a resin catalyst. The methyl acetal reactor is a reactive distillation column, with a reaction temperature of 100°C and a reaction pressure of atmospheric pressure. By controlling the top temperature of the column to 41–42°C, an azeotrope (stream N) with a mass fraction of 92% methyl acetal and 8% methanol is obtained at the top of the reactive distillation column. The bottom of the reactive distillation column yields an aqueous solution (stream O) with a formaldehyde and methanol content of less than 0.05%, which is sent to the wastewater treatment unit.

[0164] (4) DMMn Synthesis Section

[0165] The acetal-methanol azeotrope (stream N) obtained from the top of the acetal reactor is mixed with the reboiler of the second reboiler (stream H, composition shown in Table 1) at a acetal-to-TOX molar ratio of 5:1, and then fed into the polyoxymethylene dimethyl ether reactor 31, which is equipped with Beta molecular sieves. The polyoxymethylene dimethyl ether reactor 31 is a fixed-bed reactor with a reaction temperature of 100℃, a reaction pressure of 1.0 MPa, and a space velocity of 3 h⁻¹. -1 DMM-containing products were obtained at the outlet of polyoxymethylene dimethyl ether reactor 31. 2-8 The condensation product (stream P) was analyzed by gas chromatography. TOX, HCHO, and other reboilers reacted almost completely to form DMMn, of which DMMn... 2-8 The content is 37.88%, and the main components are shown in Table 2.

[0166] Table 2. Main material composition of condensation products

[0167]

[0168] The crude polyoxymethylene dimethyl ether (P stream) is separated and purified by the first light boiling column 32. The top product (Q stream) mainly consists of DMM, DMM2, and small amounts of formaldehyde, water, methanol, and TOX. This stream can be recycled to the inlet of the polyoxymethylene dimethyl ether reactor 31 (R stream) or sent to the formaldehyde preparation section (S stream). The bottom product (T stream) is a mixture of polyoxymethylene dimethyl ethers with n≥3.

[0169] A mixture of polyoxymethylene dimethyl ethers with n≥3 (stream T) was further purified by a first reboiler 33, and the top of the column (stream U) yielded a polyoxymethylene dimethyl ether mixture DMM with a concentration greater than 99.5%. 3-6 The reboiler residue (stream V) discharged from the reboiler is mainly polyoxymethylene dimethyl ether with n>6, which is recycled to the inlet of polyoxymethylene dimethyl ether reactor 31.

[0170] Comparative Example 1

[0171] The traditional polyformaldehyde production process is mainly composed of two systems of polyformaldehyde preparation and dilute formaldehyde recovery. Compared with Example 1, the preparation process of polyformaldehyde in the two processes is the same, and the difference lies in the recovery and utilization of dilute formaldehyde and TOX reboiler.

[0172] In the traditional polyformaldehyde production process, the function of the dilute formaldehyde recovery system is to concentrate formaldehyde, refine TOX, and recover the dilute formaldehyde solution generated in the polyformaldehyde post-treatment process and the reboiler generated in the TOX refining process through rectification to obtain crude TOX and 55% formaldehyde, which are reused for production. The aldehyde-containing wastewater generated in the dilute formaldehyde recovery process needs to be further treated by sewage treatment to meet the discharge standard, and the accumulated reboiler needs to be treated by incineration.

[0173] Compared with Example 1, in the traditional polyformaldehyde production process, the recovery of dilute formaldehyde and TOX reboiler has high energy consumption, low utilization rate of raw material HCHO, poor economic benefit, and is not green and environmentally friendly.

[0174] In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0175] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. Process for the production of polymethoxydimethyl ether from polyformaldehyde production waste, characterized in that, The production process of polyformaldehyde comprises a formaldehyde production step, a trioxymethylene production step and a polyformaldehyde production step, the method for producing polyoxymethylene dimethyl ether from polyformaldehyde production waste comprises: carrying out condensation reaction of the formaldehyde-containing waste liquid generated in the formaldehyde production step, the trioxymethylene production step and the polyformaldehyde production step with methanol to generate methylal; the molar ratio of formaldehyde to methanol in the formaldehyde-containing waste liquid is 1: (1-3); carrying out condensation reaction of the reboiler generated in the trioxymethylene production step with the methylal to obtain polyoxymethylene dimethyl ether; the reboiler contains, in addition to a large amount of trioxymethylene and a small amount of formaldehyde, polyoxymethylene, epoxide compounds and acetal compounds, the molar ratio of the methylal to the trioxymethylene in the reboiler is (0.5-10): 1, and the condensation reaction of the reboiler and the methylal is carried out under the action of a second catalyst, the second catalyst being one or more of molecular sieves, resins, supported ionic liquids and alumina; the production process of polyformaldehyde uses production units including a formaldehyde production module, a trioxymethylene production module and a polyformaldehyde production module; the method for producing polyoxymethylene dimethyl ether from polyformaldehyde production waste uses devices including a methylal preparation unit and a polyoxymethylene dimethyl ether preparation unit; the feed inlet of the methylal preparation unit is in communication with the formaldehyde-containing waste liquid outlets of the formaldehyde production module, the trioxymethylene production module and the polyformaldehyde production module, and the feed inlet of the polyoxymethylene dimethyl ether preparation unit is in communication with the outlet of the methylal preparation unit and the reboiler outlet of the trioxymethylene production module.

2. The method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste according to claim 1, characterized in that, the condensation reaction of the formaldehyde-containing waste liquid and methanol is carried out under the action of a first catalyst, the first catalyst being one or more of acidic cationic resins, molecular sieves, supported ionic liquids and alumina.

3. The method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste according to claim 1, characterized in that, the mass concentration of formaldehyde in the formaldehyde-containing waste liquid is 5%-40%.

4. The method for producing polymethoxy dimethyl ether from polyformaldehyde production waste according to claim 1, characterized in that, when the formaldehyde-containing waste liquid and methanol are subjected to condensation reaction, the reaction temperature is 30°C-200°C, and the pressure of the condensation reaction is -0.1 MPa-3.0 MPa; and / or when the reboiler and the methylal are subjected to condensation reaction, the reaction temperature is 30°C-200°C, and the reaction pressure is 0 MPa-2.0 MPa.

5. The method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste according to claim 1, characterized in that, after the polyoxymethylene dimethyl ether is obtained, the method further comprises: carrying out separation and purification of the polyoxymethylene dimethyl ether to obtain polyoxymethylene dimethyl ether with a polymerization degree of 3-6.

6. The method for producing polyoxymethylene dimethyl ethers from polyformaldehyde production waste according to claim 5, characterized in that, carrying out separation and purification of the polyoxymethylene dimethyl ether comprises: carrying out light reboiler removal of the polyoxymethylene dimethyl ether mixture to obtain polyoxymethylene dimethyl ether with a polymerization degree of ≥3; carrying out reboiler removal of the polyoxymethylene dimethyl ether with a polymerization degree of ≥3 to obtain polyoxymethylene dimethyl ether with a polymerization degree of 3-6.

Images