CN111363141B - Continuous hydrolysis polymerization method for green recycled caprolactam - Google Patents
Continuous hydrolysis polymerization method for green recycled caprolactam Download PDFInfo
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- CN111363141B CN111363141B CN202010092274.3A CN202010092274A CN111363141B CN 111363141 B CN111363141 B CN 111363141B CN 202010092274 A CN202010092274 A CN 202010092274A CN 111363141 B CN111363141 B CN 111363141B
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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
- C08G69/00—Macromolecular compounds obtained by reactions forming a carboxylic amide link in the main chain of the macromolecule
- C08G69/02—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids
- C08G69/08—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids derived from amino-carboxylic acids
- C08G69/14—Lactams
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
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- B01J19/0066—Stirrers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/18—Stationary reactors having moving elements inside
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/18—Stationary reactors having moving elements inside
- B01J19/1862—Stationary reactors having moving elements inside placed in series
Abstract
The invention relates to a continuous hydrolytic polymerization method for green recycled caprolactam, which is characterized in that reaction raw materials containing caprolactam are sequentially subjected to ring opening reaction, pre-polycondensation reaction and final polycondensation reaction to prepare polyamide 6, wherein a pre-polycondensation reaction device and a final polycondensation reaction device both contain a gas devolatilization space, and the gas devolatilization space is communicated with a vacuum condensation system; the vacuum condensing system, the condensing storage tank and the vacuum pump are communicated in sequence; the final polycondensation reaction device is a horizontal continuous reactor and is divided into a plurality of sections, and the pressure of each section is reduced progressively along the advancing direction of the melt during the final polycondensation reaction. The method can realize efficient green recovery of 8-10 wt% of hot water extractables generated by thermodynamic balance in the caprolactam hydrolytic polymerization process, the hot water extractables can be compounded with fresh caprolactam for direct recycling without triple effect evaporation, the content of the generated hot water extractables of the polyamide 6 slice is low, and the forming processing can be carried out without extraction.
Description
Technical Field
The invention belongs to the technical field of preparation of high polymer materials, and relates to a continuous hydrolytic polymerization method for green recycled caprolactam.
Background
The nylon fiber has excellent physical properties which cannot be compared with polyester fiber, such as higher breaking strength of the nylon fiber, wear resistance of the nylon fiber in the crown of general textile fiber, good moisture absorption, excellent elastic recovery rate and fatigue resistance, and excellent dyeing property. Nylon fibers have wide applications in other industries, such as the field of tire cord fabrics, automotive textiles, filter materials, and BCF carpet bulked yarns, in addition to apparel and decoration. The nylon fiber has many varieties, the main varieties are nylon 6 and nylon 66 fiber, and China mainly produces the nylon 6 fiber.
The PA6 polymerization is usually prepared by ring-opening polymerization of caprolactam as raw material, ring-opening agent, catalyst, molecular weight stabilizer and other auxiliary agents under certain temperature and pressure. In terms of the reaction mechanism, PA6 polymerization can be classified into hydrolytic polymerization, anionic polymerization, and anionic polymerization. The hydrolytic polymerization has the characteristics of high yield, high production continuity, stable product performance, strong controllability and the like, and is a PA6 polymerization mode commonly adopted in the industry at present. The monomer conversion rate reaches the maximum value (about 90 percent) after hydrolytic ring opening and addition polymerization, the molecular weight of the polymer is further improved after a period of amide ester bond exchange, the relative molecular mass of the polymer in the system is redistributed, finally, a certain dynamic balance is achieved according to reaction conditions (such as temperature, moisture, the dosage of a molecular weight stabilizer and the like), and the average relative molecular mass of the polymer also reaches a certain value.
The techniques commonly used in the industrial hydrolysis polymerization of PA6 can be classified into normal pressure continuous polymerization, two-stage continuous polymerization, intermittent high pressure polymerization, solid phase post polymerization, multi-stage continuous polymerization, etc. Wherein the normal pressure continuous polymerization is a production process widely used for producing civil silk in industry at present, and the relative viscosity of the obtained slices is 2.4-2.8; and the industrial yarn grade slices are produced by mainly adopting a two-stage continuous polymerization process, and the viscosity of the obtained slices is 2.8-4.0. The difference between the atmospheric continuous polymerization and the two-stage continuous polymerization is that the VK tube structure is different, and other procedures and process conditions are basically similar.
Prior to PA6 processing applications, where hot water extractables (consisting of caprolactam and its oligomers) of about 8-10 wt.% are produced due to thermodynamic equilibrium, they are removed from the matrix by industrial countercurrent extraction with superheated water for 8-16 h. After extraction is finished, the extraction water needs to be evaporated and concentrated, water in the concentrated solution is removed, and the concentrated solution is recycled into fresh caprolactam according to a certain proportion, so that the waste of raw materials is reduced. This part of the process requires a lot of time consuming resources and the stable morphology of oligomers in the concentrate of the extract water is changed, which leads to a reduction of the product quality when re-added to fresh caprolactam. Previous research has focused primarily on how to optimize the extraction process after PA6 product formation to reduce energy consumption and increase caprolactam and oligomer recovery, but has not investigated how to efficiently recover and dispose of the thermodynamic equilibrium portion of the process by forming it. Therefore, how to provide an efficient polymerization method in the research of the PA6 polymerization process at the present stage can collect and reasonably treat the recovered liquid in the polymerization process, reduce the subsequent treatment of the finished product, and become a research direction gradually changed at present.
Disclosure of Invention
The invention aims to overcome the defects of large energy resource consumption and limited content during recycling and compounding in the existing polyamide 6 polymerization technology, and provides a continuous hydrolytic polymerization method for green and efficient recycling of caprolactam.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a continuous hydrolytic polymerization method of green recycled caprolactam comprises the steps of sequentially carrying out ring opening reaction, pre-polycondensation reaction and final polycondensation reaction on reaction raw materials containing caprolactam to prepare polyamide 6, wherein a pre-polycondensation reaction device and a final polycondensation reaction device both comprise a gas devolatilization space, and the gas devolatilization space is communicated with a vacuum condensation system; the vacuum condensing system, a condensing storage tank (the condensing storage tank can be replaced and is used for receiving the extracted high-purity caprolactam and the oligomers thereof) and a vacuum pump are communicated in sequence; the final polycondensation reaction device is a horizontal continuous reactor (the multi-section vacuum gas phase is not communicated, a sealed spiral stirrer is used for division, physical spiral propulsion is carried out, a sealing baffle plate between each section can only pass through the stirrer and form sealing isolation with the stirrer), the final polycondensation reaction device is divided into a plurality of sections, the pressure of each section is reduced progressively along the advancing direction of a melt during the final polycondensation reaction (the horizontal continuous reactor is divided into a plurality of sections, the pressure of each section is different during the reaction, at present, the horizontal continuous reactor is realized, a falling film reactor with pores is used in the same vacuum degree area, the stirrer among different sections is converted into a solid sealed stirrer for division, the advancing mode of the melt is designed into a forward flow propulsion mode through the vertical angle of the stirrer, and the purpose of vacuum grading regulation is to prevent the flash evaporation phenomenon of the volatile hot water extractables when entering a high vacuum environment, the hot water extractables in the polyamide 6 melt were extracted by vacuum fractionation).
In the prior art, the polyamide 6 polymerization process is carried out under normal pressure through a VK tube, and the method for recovering caprolactam and caprolactam oligomer generally comprises the following steps: after slicing and granulating, carrying out hot water countercurrent extraction on the slices until the content of caprolactam and oligomers in the slices meets the spinning requirement, carrying out triple effect evaporation after obtaining an extract liquid, obtaining a caprolactam concentrated solution, and then adding part of the caprolactam concentrated solution into fresh caprolactam for production;
the polyamide 6 polymerization process is carried out under the vacuum condition by a pre-polymerization reaction device and a final polymerization reaction device, wherein the pre-polymerization reaction device and the final polymerization reaction device both comprise a gas devolatilization space, the gas devolatilization space is communicated with a vacuum condensation system, the vacuum condensation system, a condensation storage tank and a vacuum pump are sequentially communicated, and the method for recovering caprolactam comprises the following steps: in the process of synthesizing polyamide 6 from caprolactam, extracting solution is obtained from a polyamide 6 melt by using a vacuum extraction method, and the extracting solution is heated to be molten and then filtered to remove floccules for recycling to obtain unreacted high-purity caprolactam;
the prior art needs triple effect evaporation because the caprolactam concentration in the extract liquid is extremely low, and most of water in the extract liquid needs to be removed to obtain caprolactam concentrated solution which can be used for production again;
the prior art is not only complex in operation, but also the content of cyclic dimer in the product is often higher when the obtained caprolactam concentrated solution is polymerized, mainly because: the extract liquid contains a large amount of water, the cyclic dimer can be converted from a needle-shaped alpha crystal form to a blocky beta crystal form under the condition of water, the melting point of the alpha crystal form in the cyclic dimer is only about 240 ℃ and is lower than the polycondensation temperature, the melting point of the beta crystal form is 348 ℃, the beta crystal form is insoluble in a melt, and the cyclic dimer of the beta crystal form is difficult to participate in polymerization reaction;
the cyclic dimer content in the product is relatively low without triple effect evaporation, and the main reason is that the method adopts a vacuum extraction mode, water does not exist in the extraction liquid, triple effect evaporation is not needed to remove water, and meanwhile, the cyclic dimer in the extraction liquid is an alpha crystal form with low melting point and is easy to participate in polymerization reaction, so that the cyclic dimer content in the polymerization product is relatively low;
in the prior art, polyamide 6 is carried out in a normal pressure process, caprolactam flash evaporation caused by pressure difference is hardly considered in conception, in the actual industrial production, influence of the caprolactam flash evaporation on pipeline equipment and conversion rate is not considered unrealistic, the thermodynamic balance of caprolactam hydrolytic polymerization is only 90 percent, namely 8-10 percent by weight of hot water extractables are contained in a system, the hot water extractables consist of caprolactam and caprolactam oligomers, the caprolactam and the caprolactam oligomers are easy to evaporate at room temperature, if the caprolactam flash evaporation is changed into a vacuum system, the pressure difference can quickly flash the caprolactam flash evaporation system out to be condensed in the pipeline wall and the inner wall of the equipment to form crystals, the polyamide 6 is expected to realize transition from ring opening to pre-polycondensation at a relatively gentle pressure through multi-stage regulation, the invention is expected to remove the caprolactam oligomers, but is not expected to be removed through a flash evaporation mode, because the flash evaporation can be quickly condensed and condensed in the equipment and the damage to the equipment is irreversible, the invention firstly uses the vacuum degree with slower gradient to realize the stable transition from ring opening to pre-condensation, and then carries out vacuum degree adjustment along with the reaction, thereby realizing devolatilization efficiency and simultaneously preventing the flash evaporation after reaching the specified vacuum degree;
in the prior art, although the molecular weight of polyamide 6 is improved by using a vacuum means, the used fixed process pressure is controlled to be more than 0.5MPa, and most of used equipment is vertical discontinuous devices which only remove water molecules; the multistage vacuum devolatilization aims at removing caprolactam and small molecules thereof generated by water and thermodynamic equilibrium in a system, and aims to realize the recovery of hot water extractables in a green polymerization process so as to replace the traditional hot water post-treatment recovery.
As a preferable scheme:
in the continuous hydrolytic polymerization method for the green recycled caprolactam, the ring opening reaction device is a VK tube reactor or a vertical reactor; the pre-polycondensation reaction device is a horizontal disc reactor or a vertical reactor; the final polycondensation reaction device is a horizontal disc reactor; the horizontal disc reactor consists of a horizontal reactor body and a disc stirrer; the horizontal reactor body is of a cylinder-like structure, and the cylinder-like structure is different from a cylinder only in that the cross section of the cylinder-like structure is in an oblong shape, the oblong shape consists of two semicircles and two line segments, and the long symmetry axis of the oblong shape is parallel to the vertical direction; the disc stirrer consists of a rotating shaft and a plurality of discs sleeved on the rotating shaft, and the rotating shaft is parallel to the central shaft of the horizontal reactor body; the disc stirrer is positioned in the horizontal reactor body and is close to the bottom of the horizontal reactor body, and the diameter of the semicircle is equal to that of the disc; the top space of the horizontal reactor body is communicated with a vacuum condensing system.
According to the continuous hydrolysis polymerization method of the green recycled caprolactam, the length of the line segment is 2-30 cm, the diameter of the semicircle is 20-150 cm, and the half height of the cylinder (namely, the half length along the axial direction) is 30-180 cm; the disc stirrer is a horizontal falling film type disc stirrer, a plurality of small holes are uniformly distributed in the disc, and the rotating speed of the disc stirrer ranges from 1 r/min to 40 r/min.
According to the continuous hydrolytic polymerization method for the green recycled caprolactam, the vacuum condensation system is a scraper condensation system and is provided with a hot water heat tracing system, the temperature of hot water is 70-95 ℃, the scraper and the hot water heat tracing system are used in a vacuum pipeline, because the melting point of caprolactam is about 60 ℃, the melting point of caprolactam is increased after the caprolactam is mixed with oligomer, the hot water heat tracing ensures that the pipeline temperature can freely flow into a storage tank before the melting point of caprolactam, and the scraper is used for scraping some non-melting enriched substances into the storage tank.
The continuous hydrolysis polymerization method for the green recycled caprolactam comprises the steps that the vacuum pump is an ethylene glycol vacuum pump or a water circulating pump and is provided with a multistage filtering device.
According to the continuous hydrolysis polymerization method for the green recycled caprolactam, the reaction raw materials comprise caprolactam, deionized water and a molecular weight regulator, the addition amount of the deionized water is 2-3 wt% of the addition amount of the caprolactam, the addition amount of the molecular weight regulator is 0.05-0.5 wt% of the addition amount of the caprolactam, and the proportions are within the conventional polyamide 6 polymerization process proportion range.
According to the continuous hydrolysis polymerization method for the green recycled caprolactam, the molecular weight regulator is terephthalic acid, terephthalic acid diacetate, adipic acid, malonic acid, succinic acid or glutaric acid, the molecular weight regulator can be short-chain aliphatic and aromatic dibasic acid, and the carboxylic acid and the amide are reacted to carry out end capping to control the molecular weight of the product.
According to the continuous hydrolytic polymerization method for the green recycled caprolactam, the ring opening reaction temperature is 230-250 ℃, the time is 3-5 h, the pressure is 0.3-1 MPa, and the ring opening temperature, the time and the pressure are all the conditions of the conventional polyamide 6 ring opening process; the polyamide 6 oligomer obtained by the ring-opening reaction has a number average molecular weight of 1000-5000 and a hot water extractables content of 8-10 wt%.
According to the continuous hydrolysis polymerization method for the green recycled caprolactam, the temperature of the pre-polycondensation reaction is 240-270 ℃, the time is 0.5-1.5 h, the pressure is 12500-17500 Pa, the time of the pre-polycondensation temperature is a conventional polymerization reaction condition, and the pressure greater than 10000Pa is selected as the initial pressure to prevent the flash evaporation of the oligomer; the polyamide 6 oligomer obtained by the pre-polycondensation reaction has the number average molecular weight of 10000-14000 and the content of hot water extractables of 2-4 wt%.
In the continuous hydrolytic polymerization method of the green recycled caprolactam, the final polycondensation reaction is carried out at the temperature of 240-270 ℃ for 10-50 min (in the final polycondensation stage, the time is controlled to be 10-50 min, the polycondensation time is not too long because the molecular weight of hot water extractables and water is rapidly removed and the molecular weight is rapidly increased under a high vacuum environment), the final polycondensation reaction device is divided into A, B, C three sections which are sequentially arranged along the melt advancing direction, and during the final polycondensation reaction, the pressure of the section A is 7500 +/-2500 Pa, the pressure of the section B is 2000 +/-500 Pa, the pressure of the section C is 500 +/-100 Pa, the whole final polycondensation reaction is not suitable to be kept in a high vacuum environment, the molecular weight can be increased out of control, therefore, the gradient vacuum degree is adopted, the materials are discharged after the high vacuum devolatilization is finished, the pressure of each section is controlled to be reduced in a gradient manner, so that the devolatilization efficiency is gradually increased, and finally, the pressure is reduced to about 500Pa to finish the polycondensation; the polyamide 6 obtained by the final polycondensation has a number average molecular weight of 16000-19000, a hot water extractables content of 1-2 wt% and a relative viscosity of 2.4-2.8.
According to the continuous hydrolytic polymerization method for the green recycled caprolactam, after the final polycondensation reaction is finished, the content of caprolactam and oligomers in a condensation storage tank is 96-98 wt%, the balance is water (the water is generated in the reaction process and is very little and only accounts for 2-4 wt% of vacuum extraction), and the mass of the caprolactam and the oligomers in the condensation storage tank is 10-15 wt% of the addition amount of the caprolactam in a ring opening reaction device (obtained according to the conversion rate in thermodynamic equilibrium).
Has the advantages that:
(1) according to the continuous hydrolytic polymerization method for the green recycled caprolactam, the recycled caprolactam and the low polymer thereof can be directly mixed with fresh caprolactam for recycling without triple effect evaporation, the crystal form of the cyclic low polymer is not changed due to the reduction of the water content, the cyclic low polymer is easier to open the ring and participate in the reaction again, and the recycling adjustable proportion accounts for 1-30 wt% of the fresh caprolactam;
(2) according to the continuous hydrolytic polymerization method for the green recycled caprolactam, the recycled oligomers mainly comprise cyclic oligomers and linear oligomers, wherein the cyclic dimers mainly comprise cyclic oligomers, and because the cyclic oligomers can be changed into stable substances which are difficult to recycle after contacting with water, compared with the caprolactam and the oligomers thereof recycled by traditional extraction water, the low water content in the recycled substances of the hydrolytic polymerization method can effectively avoid the crystal transformation of the caprolactam and the oligomers thereof;
(3) the method can realize efficient green recovery of 8-10 wt% of hot water extractables generated by thermodynamic balance in the caprolactam hydrolysis polymerization process, caprolactam and low polymers thereof can be compounded with fresh caprolactam for direct recycling without triple effect evaporation, the content of the generated hot water extractables of the polyamide 6 slices is low, molding processing can be performed without extraction, and the hot water extractables can also be directly connected with a melt spinning system for processing at that time after a post-polycondensation reactor.
Drawings
FIG. 1 is a schematic diagram of a continuous hydrolytic polymerization unit for green recycled caprolactam of the present invention;
FIG. 2 is a schematic structural view of a horizontal disc reactor;
the method comprises the following steps of 1-a batching kettle, 2-an adding kettle, 3-a ring-opening reaction device, 4-a pre-polycondensation reaction device, 5-a final polycondensation reaction device, 5.1-a horizontal reactor body, 5.2-a disc stirrer, 6-a vacuum condensation system, 6.1-a cleaning scraper, 6.2-a hot water heat tracing system, 7-a condensation storage tank, 8-a partition switch I, 9-a partition switch II, 10-a vacuum pump and 11-a granulator.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
A continuous hydrolytic polymerization method of green recycled caprolactam comprises the steps of sequentially carrying out ring opening reaction (as shown in figure 1, reaction raw materials enter a ring opening reaction device 3 through a batching kettle 1 and an adding kettle 2), pre-polycondensation reaction and final polycondensation reaction (final polycondensation reaction products are fusant which is cooled and cut into slices by a granulator 11) on a mixture of caprolactam, deionized water and a molecular weight regulator to prepare polyamide 6;
the molecular weight regulator is terephthalic acid, terephthalic acid diacetate, adipic acid, malonic acid, succinic acid or glutaric acid; the adding amount of the deionized water is 2-3 wt% of the adding amount of the caprolactam, and the adding amount of the molecular weight regulator is 0.05-0.5 wt% of the adding amount of the caprolactam;
as shown in FIG. 1, the ring-opening reaction apparatus 3 is a vertical reactor (or VK tube reactor); the temperature of the ring-opening reaction is 230-250 ℃, the time is 3-5 h, and the pressure is 0.3-1 MPa; the number average molecular weight of polyamide 6 oligomer obtained by ring-opening reaction is 1000-5000, and the content of hot water extractables is 8-10 wt%;
the pre-polycondensation reaction device 4 and the final polycondensation reaction device 5 both contain gas devolatilization spaces, and the gas devolatilization spaces are communicated with a vacuum condensation system 6; a vacuum condensing system 6 (a scraper type condensing system, which comprises a cleaning scraper 6.1 and a hot water heat tracing system 6.2, the temperature of hot water is 70-95 ℃), a condensing storage tank 7 (an inlet of which is provided with a cut-off switch I8) and a vacuum pump 10 (an ethylene glycol vacuum pump or a water circulating pump, which is provided with a multistage filtering device, and an inlet of which is provided with a cut-off switch II 9) are sequentially communicated;
as shown in FIG. 1, the pre-polycondensation reaction device 4 is a vertical reactor (which may be a horizontal disc reactor); the temperature of the pre-polycondensation reaction is 240-270 ℃, the time is 0.5-1.5 h, and the pressure is 12500-17500 Pa; the polyamide 6 oligomer obtained by the pre-polycondensation reaction has the number average molecular weight of 10000-14000 and the content of hot water extractables of 2-4 wt%;
as shown in fig. 1 and fig. 2, the final polycondensation reaction device 5 is a horizontal disc reactor, and the horizontal disc reactor consists of a horizontal reactor body 5.1 and a disc stirrer 5.2; the horizontal reactor body 5.1 is of a cylindrical structure, and the similar cylinder (with the half height of 30-180 cm) is different from a cylinder only in that the cross section of the similar cylinder is in an oblong shape, the oblong shape consists of two semicircles (with the diameter of 20-150 cm and the same diameter) and two line segments (with the length of 2-30 cm and the same length), and the long symmetry axis of the oblong shape is parallel to the vertical direction; the disc stirrer 5.2 is a horizontal falling film type disc stirrer, a plurality of small holes are uniformly distributed in the disc, and the rotating speed of the disc stirrer 5.2 is 1-40 r/min; the disc stirrer 5.2 consists of a rotating shaft and a plurality of discs sleeved on the rotating shaft, and the rotating shaft is parallel to the central shaft of the horizontal reactor body 5.1; the disc stirrer 5.2 is positioned in the horizontal reactor body 5.1 and is close to the bottom of the horizontal reactor body 5.1, and the diameter of the semicircle is equal to that of the disc; the top space of the horizontal reactor body 5.1 is communicated with a vacuum condensing system 6; the temperature of the final polycondensation reaction is 240-270 ℃, the time is 10-50 min, the final polycondensation reaction device 5 is divided into A, B, C three sections which are sequentially arranged along the advancing direction of the melt, the pressure of the section A is 7500 +/-2500 Pa, the pressure of the section B is 2000 +/-500 Pa, and the pressure of the section C is 500 +/-100 Pa during the final polycondensation reaction; the polyamide 6 obtained by the final polycondensation has the number average molecular weight of 16000-19000, the hot water extractables content of 1-2 wt% and the relative viscosity of 2.4-2.8; after the final polycondensation reaction is finished, the content of caprolactam and oligomer in a condensation storage tank 7 is 96-98 wt%, the balance is water, and the mass of the caprolactam and oligomer in the condensation storage tank 7 is 10-15 wt% of the addition amount of caprolactam in the ring-opening reaction device 3.
Claims (9)
1. A continuous hydrolysis polymerization method of green recycled caprolactam is characterized by comprising the following steps: carrying out ring-opening reaction, pre-polycondensation reaction and final polycondensation reaction on reaction raw materials containing caprolactam in sequence to prepare polyamide 6, wherein the pre-polycondensation reaction device and the final polycondensation reaction device both comprise a gas devolatilization space, and the gas devolatilization space is communicated with a vacuum condensation system; the vacuum condensing system, the condensing storage tank and the vacuum pump are communicated in sequence; the final polycondensation reaction device is a horizontal continuous reactor and is divided into a plurality of sections, and the pressure of each section is reduced progressively along the advancing direction of the melt during the final polycondensation reaction;
the ring-opening reaction device is a VK tube reactor or a vertical reactor; the pre-polycondensation reaction device is a horizontal disc reactor or a vertical reactor; the final polycondensation reaction device is a horizontal disc reactor; the horizontal disc reactor consists of a horizontal reactor body and a disc stirrer; the horizontal reactor body is of a cylinder-like structure, and the cylinder-like structure is different from a cylinder only in that the cross section of the cylinder-like structure is in an oblong shape, the oblong shape consists of two semicircles and two line segments, and the long symmetry axis of the oblong shape is parallel to the vertical direction; the disc stirrer consists of a rotating shaft and a plurality of discs sleeved on the rotating shaft, and the rotating shaft is parallel to the central shaft of the horizontal reactor body; the disc stirrer is positioned in the horizontal reactor body and is close to the bottom of the horizontal reactor body, and the diameter of the semicircle is equal to that of the disc; the top space of the horizontal reactor body is communicated with a vacuum condensing system.
2. The continuous hydrolytic polymerization method of green recycled caprolactam according to claim 1, wherein the length of the line segment is 2-30 cm, the diameter of the semicircle is 20-150 cm, and the half height of the cylinder is 30-180 cm; the disc stirrer is a horizontal falling film type disc stirrer, a plurality of small holes are uniformly distributed in the disc, and the rotating speed of the disc stirrer ranges from 1 r/min to 40 r/min.
3. The continuous hydrolysis polymerization method of green recycled caprolactam according to claim 1, wherein the vacuum condensing system is a scraper type condensing system and is provided with a hot water heat tracing system, and the temperature of hot water is 70-95 ℃; the vacuum pump is a glycol vacuum pump or a water circulating pump and is provided with a multistage filtering device.
4. The continuous hydrolysis polymerization method of green recycled caprolactam of claim 1, wherein the reaction raw material comprises caprolactam, deionized water and a molecular weight regulator, the addition amount of the deionized water is 2-3 wt% of the addition amount of the caprolactam, and the addition amount of the molecular weight regulator is 0.05-0.5 wt% of the addition amount of the caprolactam.
5. The continuous hydrolysis polymerization method of green recycled caprolactam of claim 4, wherein the molecular weight regulator is terephthalic acid, terephthalic acid diacetate, adipic acid, malonic acid, succinic acid or glutaric acid.
6. The continuous hydrolytic polymerization method of green recycled caprolactam according to claim 5, characterized in that the temperature of the ring opening reaction is 230-250 ℃, the time is 3-5 h, and the pressure is 0.3-1 MPa; the polyamide 6 oligomer obtained by the ring-opening reaction has a number average molecular weight of 1000-5000 and a hot water extractables content of 8-10 wt%.
7. The continuous hydrolysis polymerization method of green recycled caprolactam according to claim 6, wherein the temperature of the pre-polycondensation reaction is 240-270 ℃, the time is 0.5-1.5 h, and the pressure is 12500-17500 Pa; the polyamide 6 oligomer obtained by the pre-polycondensation reaction has the number average molecular weight of 10000-14000 and the content of hot water extractables of 2-4 wt%.
8. The continuous hydrolytic polymerization method of green recycled caprolactam according to claim 7, characterized in that the final polycondensation reaction temperature is 240-270 ℃, the time is 10-50 min, the final polycondensation reaction device is divided into A, B, C three sections which are arranged in sequence along the melt advancing direction, the pressure of the section A is 7500 +/-2500 Pa, the pressure of the section B is 2000 +/-500 Pa, and the pressure of the section C is 500 +/-100 Pa during the final polycondensation reaction; the polyamide 6 obtained by the final polycondensation has a number average molecular weight of 16000-19000, a hot water extractables content of 1-2 wt% and a relative viscosity of 2.4-2.8.
9. The continuous hydrolytic polymerization method of green recycled caprolactam according to claim 8, wherein after the final polycondensation reaction is finished, the content of caprolactam and oligomers in a condensation storage tank is 96-98 wt%, the balance is water, and the mass of the caprolactam and oligomers in the condensation storage tank is 10-15 wt% of the addition amount of caprolactam in a ring opening reaction device.
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