CN111732699A - Polyformaldehyde production process - Google Patents
Polyformaldehyde production process Download PDFInfo
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- CN111732699A CN111732699A CN202010487011.2A CN202010487011A CN111732699A CN 111732699 A CN111732699 A CN 111732699A CN 202010487011 A CN202010487011 A CN 202010487011A CN 111732699 A CN111732699 A CN 111732699A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
- C08G2/18—Copolymerisation of aldehydes or ketones
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
- C08G2/04—Polymerisation by using compounds which act upon the molecular weight, e.g. chain-transferring agents
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
- C08G2/28—Post-polymerisation treatments
Abstract
The invention relates to the technical field of polyformaldehyde production and manufacture, in particular to a polyformaldehyde production process, which comprises the steps of feeding quantitative trioxymethylene, comonomers, initiators and molecular weight regulators into a plurality of polymerization reactors which are connected in series, feeding materials from a previous polymerization reactor to a next polymerization reactor for continuous reaction, arranging an external circulation at a discharge port of the polymerization reactors, arranging a temperature control system on an external circulation pipeline, feeding crude polyformaldehyde reacted by the multistage polymerization reactors from an outlet of a last polymerization reactor into a grinder to grind the polyformaldehyde into powdery particles; the polymer thermal stabilization adopts a mode of combining a flash devolatilization device and a screw extruder to stabilize the end group and remove volatile components, can provide enough retention time and gas-liquid phase contact space, ensures that the volatile components in polyformaldehyde are completely removed, ensures that the product performance is better, can reduce the devolatilization port number of the double screw extruder, and ensures that the equipment structure is simpler.
Description
Technical Field
The invention relates to the technical field of production and manufacturing of polyformaldehyde, and particularly relates to a polyformaldehyde production process.
Background
Polyformaldehyde is one of common engineering plastics, has the characteristics of high mechanical strength, good abrasion resistance, good fatigue resistance and good chemical corrosion resistance, and is widely applied to the field of engineering materials. The alloy can replace metal and alloy materials in many occasions and is widely applied to the fields of automobiles, electronics, machinery and the like. Polyformaldehyde is divided into formaldehyde and copolyformaldehyde, which are more widely used because of their better thermal stability than homopolyformaldehyde.
The existing production process of the copolyoxymethylene takes trioxymethylene as a polymerization monomer and dioxolane (or ethylene oxide, trioxymethylene and the like) as a copolymerization monomer to carry out copolymerization reaction in a polymerization reactor. The copolymerization process includes chain initiation, chain growth, chain transfer, chain termination. In the early stage of polymerization, the reaction rate is high, in the polymerization process of the polymerization degree of the product, some active centers are on the surface of the polymer, and some active centers are shielded along with the polymerization, so that the polymerization reaction rate is reduced, the polymerization degree distribution of the polymerization product is wide, and the quality of the product is poor. During the copolymerization, impurities such as water, methanol, formic acid and the like in the raw materials can cause chain transfer, so that unstable hemiacetal terminal hydroxyl structure is formed at the terminal of the copolymer. Part of formaldehyde and trioxymethylene exist in the polymer, so that the obtained polyformaldehyde needs to be passivated, and volatile substances such as formaldehyde and the like in the polyformaldehyde are removed, so that the thermal stability of the polyformaldehyde is improved. At present, crude polyformaldehyde is generally dried by nitrogen and then sent to a double-screw extruder for melting treatment, a stabilizer is added to convert unstable terminal groups at the tail end into stable terminal groups, and volatile components are removed by vacuum pumping under reduced pressure. The devolatilization capability of the extruder will directly affect the end-cap stabilization effect. Because the twin-screw extruder devolatilizes a mouthful screw rod department area of contact less, need design more devolatilizing mouthful just can guarantee the desorption effect, devolatilizing mouthful a lot of heat transfer area that can influence the barrel, heating efficiency also can reduce.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a polyformaldehyde production process, and aiming at the defects of the prior art, the design scheme has the advantages of improving the reaction rate, reducing subsequent processing units, having lower production cost and high finished product quality, and solves the problems of lower reaction rate, more subsequent processing units, high production cost and low finished product quality of the conventional equipment.
In order to achieve the above object, the present invention provides a process for producing polyoxymethylene, comprising the steps of,
s01, feeding quantitative trioxymethylene, comonomer, initiator and molecular weight regulator into a plurality of polymerization reactors connected in series, and feeding materials from the previous polymerization reactor to the next polymerization reactor for continuous reaction;
s01-1, arranging an external circulation at a discharge hole of the polymerization reactor, and arranging a temperature control system on an external circulation pipeline;
s02, feeding the crude polyformaldehyde reacted by the multistage polymerization reactor from the outlet of the final polymerization reactor to a grinder to grind the polyformaldehyde into powdery particles;
s03, feeding the ground powdery polyformaldehyde into a dryer for drying and preheating;
s04, conveying the dried and preheated polyformaldehyde into a flash devolatilization device, and connecting the top of the flash devolatilization device with a vacuum pumping device to continuously pump out light components of the polyformaldehyde;
and S05, conveying the devolatilized polyformaldehyde to a double-screw extruder through a gear pump or a screw feeder.
In the above technical solution, preferably, the method further comprises the following steps,
the number of the polymerization reactors connected in series in the step S01 is 3 to 4, and the polymerization reactor can be any one of a double-screw reactor, a kettle type reactor and a tubular reactor;
wherein, the polymerization reactor needing to be provided with the external circulation in the step S01-1 can be any one or more, partial materials at the outlet of the polymerization reactor return to the inlet of the polymerization reactor at the current stage, and the circulation amount of the materials accounts for 0-50% of the total discharge amount.
In the above technical solution, preferably, in the step S04, the molten polyoxymethylene is injected into the flash devolatilizer so that the polyoxymethylene has a sufficient degassing surface area to separate the gas bubbles from the polyoxymethylene, and the flash devolatilizer may be disposed before or after the twin screw extruder, and the number of the flash devolatilizers is 1 to 2.
In the above technical solution, preferably, the initiator in step S01 is a cationic initiator, and is any one of boron trifluoride and its complex, carbon tetrachloride and phosphorus trifluoride, and the addition amount of the initiator is determined according to the reaction result, and is 1ppm to 300 ppm.
In the above technical solution, preferably, the molecular weight regulator in step S01 is methylal, and the addition amount is 1ppm to 1000 ppm.
In the above technical scheme, preferably, the reaction temperature of the polymerization reactor in the step S01 is 80-180 ℃, and the reaction pressure is 0.1-10 MPa.
In the above technical solution, preferably, the number of the screw extruders in the step S05 is 1-2, and the screw extruders are provided with 1-3 devolatilization ports.
In the technical scheme, preferably, the total retention time of the materials in the melting post-treatment process is 5-20 minutes, and the retention time of the flash devolatilization device is 0.5-5 minutes.
In the technical scheme, preferably, the process pressure of the dried powdery particles is-10 to-90 kPa in the process of entering the flash devolatilization device and the double-screw extruder, and the process temperature is 160 to 220 ℃.
Compared with the prior art, the invention has the following beneficial effects:
1. in the invention, the polymerization process is formed by connecting a plurality of polymerization reactors with external circulation in series, so that the reaction residence time and the polymerization degree distribution of polymerization products are effectively controlled, when a single reactor is circulated externally, the back mixing of materials is accelerated, the material residence time distribution is widened, the polymerization degree distribution of the polymerization products is widened, when a plurality of reactors are circulated externally, the external circulation can narrow the material residence time distribution and narrow the polymerization degree distribution of the polymerization products, meanwhile, part of unreacted trioxymethylene and low polymerization degree polymers are circulated and then return to the polymerization reactors for further reaction, the loads of a subsequent processing unit and a trioxymethylene recovery unit are reduced, the energy consumption in the whole process is further reduced, the product quality is higher, and the method is particularly suitable for producing the polyformaldehyde with large molecular weight.
2. According to the invention, the polymer thermal stabilization adopts a mode of combining a flash devolatilization device and a screw extruder to stabilize the end group and remove volatile components, so that sufficient retention time and gas-liquid phase contact space can be provided, the volatile components in polyformaldehyde can be completely removed, the product performance is better, the number of devolatilization ports of the double screw extruder can be reduced, and the equipment structure is simpler.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:
FIG. 1 is a schematic flow diagram of a polyoxymethylene production process disclosed in an embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation, numerous implementation details are set forth in order to provide a thorough understanding of the various embodiments of the present invention. It should be understood, however, that these implementation details are not to be interpreted as limiting the invention. That is, in some embodiments of the invention, such implementation details are not necessary. In addition, some conventional structures and components are shown in simplified schematic form in the drawings.
In addition, the descriptions related to the first, the second, etc. in the present invention are only used for description purposes, do not particularly refer to an order or sequence, and do not limit the present invention, but only distinguish components or operations described in the same technical terms, and are not understood to indicate or imply relative importance or implicitly indicate the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
The invention is described in further detail below with reference to the accompanying drawings;
referring to fig. 1, a process for producing polyoxymethylene according to the present invention includes the following steps,
s01, feeding quantitative trioxymethylene, comonomer, initiator and molecular weight regulator into a plurality of polymerization reactors connected in series, and feeding materials from the previous polymerization reactor to the next polymerization reactor for continuous reaction;
s01-1, arranging an external circulation at a discharge hole of the polymerization reactor, and arranging a temperature control system on an external circulation pipeline;
s02, feeding the crude polyformaldehyde reacted by the multistage polymerization reactor from the outlet of the final polymerization reactor to a grinder to grind the polyformaldehyde into powdery particles;
s03, feeding the ground powdery polyformaldehyde into a dryer for drying and preheating;
s04, conveying the dried and preheated polyformaldehyde into a flash devolatilization device, and connecting the top of the flash devolatilization device with a vacuum pumping device to continuously pump out light components of the polyformaldehyde;
and S05, conveying the devolatilized polyformaldehyde to a double-screw extruder through a gear pump or a screw feeder.
In the above embodiment, preferably, the method further includes the steps of:
the number of the polymerization reactors connected in series in the step S01 is 3 to 4, and the polymerization reactor can be any one of a double-screw reactor, a kettle type reactor and a tubular reactor;
wherein, the polymerization reactor needing to be provided with the external circulation in the step S01-1 can be any one or more, partial materials at the outlet of the polymerization reactor return to the inlet of the polymerization reactor at the current stage, and the circulation amount of the materials accounts for 0-50% of the total discharge amount.
In the above embodiment, it is preferable that the molten polyoxymethylene is introduced into the flash devolatilizer by spraying in the step S04 so that the polyoxymethylene has a sufficient degassing surface area to separate the gas bubbles from the polyoxymethylene, and the flash devolatilizer may be provided before or after the twin screw extruder in an amount of 1 to 2 flash devolatilizers.
In the above embodiment, preferably, the initiator described in step S01 is a cationic initiator, and is any one of boron trifluoride and its complex, carbon tetrachloride and phosphorus trifluoride, and the amount of the initiator added is determined according to the reaction result, and is 1ppm to 300 ppm.
In the above examples, it is preferable that the molecular weight modifier described in step S01 is methylal, and the amount added is 1ppm to 1000 ppm.
In the above embodiment, preferably, the polymerization reactor in step S01 has a reaction temperature of 80 to 180 ℃ and a reaction pressure of 0.01 to 10 MPa.
In the above embodiment, it is preferable that the number of the screw extruders in the step S05 is 1 to 2, and the screw extruder is provided with 1 to 3 devolatilization ports.
In the above embodiment, preferably, the total residence time of the materials in the melt post-treatment process is 5 to 20 minutes, and the residence time of the flash devolatilizer is 0.5 to 5 minutes.
In the above embodiment, preferably, the process pressure of the dried powdery particles in the process of entering the flash devolatilizer and the twin-screw extruder is-10 to-90 kPa, and the process temperature is 160 to 220 ℃.
As shown in figure 1, when in use, trioxymethylene, dioxolane and an initiator are added into a polymerization reactor, the reaction temperature is set to be 50 ℃, the reaction pressure is set to be 0.5Mpa, 4 polymerization reactors are operated in series, the reactor 1, the reactor 2 and the reactor 3 are provided with external circulation, and part of materials at the outlet of the reactor 1 are returned to the inlet of the reactor 1 again, and so on, and meanwhile, a molecular weight regulator methylal is added according to the needs of products; and (3) grinding polyformaldehyde into powdery particles by a grinder for materials at the outlet of the reactor 4, drying and preheating the powdery particles, conveying the powdery particles to a flash evaporation devolatilization device and a double-screw extruder, wherein the pressure is 70kPa, the process temperature is 180 ℃, triethylamine can be added for stabilizing polyformaldehyde, light components such as formaldehyde can be removed by vacuumizing, the vacuum degree of each devolatilization port is gradually increased from front to back, and finally the obtained polyformaldehyde particles are dried and screened to obtain qualified products.
It should be noted that, the polymer thermal stabilization adopts a mode of combining a flash devolatilizer and a screw extruder to stabilize the end group and remove volatile components, can provide enough residence time and gas-liquid phase contact space, ensure the complete removal of the volatile components in polyformaldehyde, make the product performance better, and simultaneously can reduce the number of devolatilization ports of the double screw extruder, make the equipment structure simpler, and simultaneously can add a polymerization terminator in polyformaldehyde in the thermal stabilization process, the terminator inactivates an initiator, and simultaneously the unstable end group of polyformaldehyde is hydrolyzed, and is removed from formaldehyde and becomes stable end group, and various additives such as an antioxidant, a whitening agent and the like can be added according to the product requirements.
It should be noted that the external circulation is provided at the outlet of the polymerization reactor for the purpose of increasing the reaction time of the materials, i.e., the larger the circulation amount, the longer the average residence time of the system, and the larger the degree of polymerization of the product polyoxymethylene, and the temperature control system is provided on the external circulation line for the purpose of ensuring that the materials can be adjusted in temperature when the circulation reaction is performed.
The above description is only an embodiment of the present invention, and is not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (9)
1. A production process of polyformaldehyde is characterized by comprising the following steps: the method comprises the following steps:
s01, feeding quantitative trioxymethylene, comonomer, initiator and molecular weight regulator into a plurality of polymerization reactors connected in series, and feeding materials from the previous polymerization reactor to the next polymerization reactor for continuous reaction;
s01-1, arranging an external circulation at a discharge hole of the polymerization reactor, and arranging a temperature control system on an external circulation pipeline;
s02, feeding the crude polyformaldehyde reacted by the multistage polymerization reactor from the outlet of the final polymerization reactor to a grinder to grind the polyformaldehyde into powdery particles;
s03, feeding the ground powdery polyformaldehyde into a dryer for drying and preheating;
s04, conveying the dried and preheated polyformaldehyde into a flash devolatilization device, and connecting the top of the flash devolatilization device with a vacuum pumping device to continuously pump out light components of the polyformaldehyde;
and S05, conveying the devolatilized polyformaldehyde to a double-screw extruder through a gear pump or a screw feeder.
2. The process for producing polyoxymethylene according to claim 1, wherein: the number of the polymerization reactors connected in series in the step S01 is 3 to 4, and the polymerization reactor can be any one of a double-screw reactor, a kettle type reactor and a tubular reactor;
wherein, the polymerization reactor needing to be provided with the external circulation in the step S01-1 can be any one or more, partial materials at the outlet of the polymerization reactor return to the inlet of the polymerization reactor at the current stage, and the circulation amount of the materials accounts for 0-50% of the total discharge amount.
3. The process for producing polyoxymethylene according to claim 1, wherein: in the step S04, the molten polyformaldehyde enters a flash devolatilizer in a spraying mode, so that the polyformaldehyde has enough degassing surface area to separate bubbles from the polyformaldehyde, the flash devolatilizer can be arranged before or after a double-screw extruder, and the number of the flash devolatilizers is 1-2.
4. The process for producing polyoxymethylene according to claim 1, wherein: the initiator in the step S01 is a cationic initiator, is any one of boron trifluoride and a complex thereof, carbon tetrachloride and phosphorus trifluoride, and is added in an amount of 1ppm to 300ppm according to the reaction result.
5. The process for producing polyoxymethylene according to claim 1, wherein: the molecular weight regulator in the step S01 is methylal, and the addition amount is 1ppm-1000 ppm.
6. The process for producing polyoxymethylene according to claim 1, wherein: in the step S01, the reaction temperature of the polymerization reactor is 80-180 ℃, and the reaction pressure is 0.1-10 MPa.
7. The process for producing polyoxymethylene according to claim 1, wherein: in the step S05, the number of the screw extruders is 1-2, and the screw extruders are provided with 1-3 devolatilization ports.
8. The process for producing polyoxymethylene according to claim 1, wherein: the total retention time of the materials in the melting post-treatment process is 5-20 minutes, and the retention time of the flash evaporation devolatilization device is 0.5-5 minutes.
9. The process for producing polyoxymethylene according to claim 1, wherein: and (3) feeding the dried powdery particles into a flash devolatilization device and a double-screw extruder, wherein the process pressure is-10 to-90 kPa, and the process temperature is 160 to 220 ℃.
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| CN202010487011.2A CN111732699A (en) | 2020-06-01 | 2020-06-01 | Polyformaldehyde production process |
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| CN202010487011.2A CN111732699A (en) | 2020-06-01 | 2020-06-01 | Polyformaldehyde production process |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113307923A (en) * | 2021-04-14 | 2021-08-27 | 兖矿鲁南化工有限公司 | High-efficiency devolatilization method and system for copolyformaldehyde |
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