CN117247540A

CN117247540A - Production system and method for green and efficient preparation of polycaprolactam fibers

Info

Publication number: CN117247540A
Application number: CN202210657758.7A
Authority: CN
Inventors: 陈文兴; 吕汪洋; 王勇军; 陈世昌; 张先明
Original assignee: Shanghai Yuejian Material Technology Co ltd; Zhejiang Sci Tech University ZSTU
Current assignee: Shanghai Yuejian Material Technology Co ltd; Zhejiang Sci Tech University ZSTU
Priority date: 2022-06-10
Filing date: 2022-06-10
Publication date: 2023-12-19

Abstract

The invention relates to a production system and a method for preparing polycaprolactam fibers in a green and efficient manner. The production system comprises: the device comprises a VK tube reactor, an external falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. Continuously injecting a mixture of caprolactam, water, a molecular weight regulator and the like into a VK pipe for hydrolysis ring-opening polymerization reaction to prepare polycaprolactam base melt; then, the monomer and the oligomer in the basic melt are efficiently removed through an outside-tube falling film devolatilization reactor, and the melt is tackified at the same time, so that the obtained high-quality polycaprolactam melt can be directly spun to prepare polycaprolactam fibers. Compared with the traditional hot water extraction and fiber slice spinning process of polycaprolactam, the method realizes the preparation of polycaprolactam fibers by melt direct spinning, omits the processes of cooling and granulating, hot water extraction, drying and remelting and the like, greatly simplifies the process flow, effectively improves the production efficiency and obviously reduces the production energy consumption.

Description

Production system and method for green and efficient preparation of polycaprolactam fibers

Technical Field

The invention relates to the field of polyamide fiber materials, in particular to a production system and a method for preparing polycaprolactam fibers in a green and efficient manner.

Background

The polyamide material has good comprehensive properties such as mechanical property, heat resistance, abrasion resistance, self-lubricating property and the like, is a polymer material which is industrially produced in the world at the earliest time and is used for synthetic fibers, has been widely applied to the fields of textile clothing, cord, cables, tents, fishing nets and the like, and can be used as a parachute and other military fabrics in national defense. Polycaprolactam is the largest variety of polyamide, and the polymerization method mainly comprises hydrolysis polymerization, anion polymerization and solid-phase polymerization, and the main route of industrial production at home and abroad at present is caprolactam hydrolysis ring-opening polymerization, which comprises the processes of ring opening, polyaddition, polycondensation reaction and the like. Polycaprolactam has been widely used in various fields such as domestic yarns (relative viscosity 2.2-2.8), industrial canvas yarns (relative viscosity 2.7-3.0) and industrial yarns (relative viscosity greater than 3.5) according to the molecular weight or relative viscosity.

In the polymerization production of polycaprolactam materials, it is most common to prepare polycaprolactam by hydrolytic ring opening polymerization using one-stage or two-stage VK tube reactors. Polycaprolactam with different relative viscosities, including domestic filament grade polycaprolactam and industrial filament grade polycaprolactam, can be prepared by adjusting the process parameters and the reaction time of the VK pipe reactor. However, since the polymerization process of polycaprolactam is a reversible equilibrium process, about 10% of monomers and oligomers remain in the finally synthesized polycaprolactam, which cannot be directly used for spinning, regardless of whether a one-stage reactor or a two-stage reactor is used. At present, the hot water extraction process is mostly adopted in industry to reduce the content of monomers and oligomers in polycaprolactam, polycaprolactam slices are obtained after drying, and then polycaprolactam fibers are obtained by adopting the slice spinning process. In the past decades, a great deal of research is carried out around the structural design, slicing post-treatment and the like of a polyamide polymerization reactor at home and abroad, but no great breakthrough is made in the technical process of the industrial production of polyamide fibers.

Disclosure of Invention

The invention provides a production system and a method for preparing polycaprolactam fibers in a green and efficient way, aiming at solving the technical problems that the content of caprolactam monomers and oligomers in polycaprolactam melt prepared by a VK tube reactor is high and the fibers are difficult to prepare by direct spinning. The high-quality polycaprolactam with hot water extractables content less than 1.5wt% can be obtained by redesigning the process for removing monomers and oligomers in polycaprolactam melt and the production flow of polycaprolactam fiber, effectively connecting a VK tube reactor and an external falling film devolatilization reactor, designing a master control unit to adjust and match each part of process parameters, and carrying out real-time optimization control on a production system, and is directly applied to spinning preparation of polycaprolactam fiber, thereby omitting the processes of cooling granulating, hot water extraction, drying, remelting and the like.

In order to achieve the above object, the present invention provides the following specific technical solutions:

a production system for green and efficient preparation of polycaprolactam fibers, comprising: the device comprises a VK tube reactor, an external falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The working principle is as follows: the VK tube reactor is used for preparing polycaprolactam base melt, and the relative viscosity of the base melt is 2.0-3.6; the outside-tube falling film devolatilization reactor is connected with the VK tube reactor through a melt pipeline and is used for removing caprolactam monomers and oligomers in the basic melt, so that the content of hot water extractables in the polycaprolactam melt is less than 1.5wt%, and the viscosity of the polycaprolactam melt is increased to 2.2-4.0; the spinning unit is connected with the falling film devolatilization reactor outside the pipe through a melt pipeline and is used for preparing polycaprolactam fibers through spinning; the condensing heat exchange device is connected with the falling film devolatilization reactor outside the pipe, and exchanges heat between the extracted caprolactam monomer and oligomer steam and the condenser to condense the caprolactam monomer and oligomer steam; the collecting and recycling device is connected with the condensing heat exchange device and is used for collecting caprolactam monomers and oligomers condensed in the condensing heat exchange device; the vacuum system is connected with the condensation heat exchange device and provides vacuum power.

The VK pipe reactor is a one-stage reactor or a two-stage reactor, and the reactors are provided with a feed inlet and a discharge outlet.

The external falling film devolatilization reactor is a vertical external falling film devolatilization reactor, the bottom of the reactor is a cone, a stirrer is arranged in the cone and used for uniformly material and cleaning the wall surface of the cone, the diameter of a used falling film pipe or the diameter of a maximum circumcircle is 5-100 mm, the pipe length is 3-20 m, and a hot coal flow passage is arranged in the falling film pipe and used for accurately controlling the reaction temperature.

The falling film tube used in the external falling film devolatilization reactor is preferably a corrugated tube or a star-shaped tube, and when the falling film tube is a star-shaped tube, the falling film tube is preferably a 3-12-angle star-shaped tube. The wave-joint pipe is a pipe with diameter change along the axial direction, and the pipe sections with large diameter and small diameter are alternately and smoothly transited and continuous in appearance, and each pipe section can be a straight pipe section or an arc pipe section along the axial direction. The star-shaped tube refers to a tube with a polygonal cross section, and the sides of the polygon can be plane sides or arc sides.

The number of the air outlets of the falling film devolatilization reactor outside the pipe is 1, 2 or more, the air outlets can be symmetrically distributed or distributed on one side, the number and the positions of the vacuum extraction openings are mainly set according to the content of specific volatile components, and the air outlets are connected with the condensation heat exchange device.

The condensation heat exchange device is a combination of condensers of 1 level, 2 levels or more (3-6 levels) connected in series or in parallel; the lower end of each stage of condensation heat exchange device is provided with a condensate outlet which is connected with the collection and recycling device. Caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe enters from the air inlet of the condensation heat exchange device, exchanges heat with the condenser, and condenses the monomer and oligomer steam into the collection and recycling device.

The condenser in the condensing heat-exchange device may be one or more of a spray condenser, a baffle condenser, a tube condenser, a filling condenser, a surface condenser, a spray condenser, or any device known in the art for this purpose.

The vacuum system is one or a plurality of series or parallel combination of a rotary vane vacuum pump, a steam jet pump, a liquid ring vacuum pump, a Roots vacuum pump, a reciprocating vacuum pump and a screw vacuum pump which are additionally provided with buffer tanks in front of the pump.

On the basis of using the production system in the technical scheme, the invention also provides a production method for preparing polycaprolactam fibers in a green and efficient way, which comprises the following steps:

(1) Mixing basic components caprolactam, water, a molecular weight regulator and additive components in proportion, preheating, continuously injecting into a VK tube reactor, and preparing polycaprolactam basic melt with relative viscosity of 2.0-3.6 through hydrolysis ring-opening polymerization;

(2) Conveying the basic melt to the upper part of a falling film devolatilization reactor outside a pipe through a melt pipeline, distributing the basic melt through a film distributor, performing a falling film reaction outside the falling film pipe, and enabling hot media in the falling film pipe to flow to precisely control the temperature to prepare high-quality polycaprolactam melt with the relative viscosity of 2.2-4.0 and the hot water extractables of less than 1.5wt%, so as to realize the relative viscosity increase value of 0.2-1.2, and omitting the steps of cooling granulating, hot water extraction, drying and remelting;

(3) And (3) conveying the high-quality polycaprolactam melt prepared by the pipe external falling film devolatilization reactor to a spinning unit for spinning through a melt pipeline to obtain polycaprolactam fibers.

In the method described above, in the step (1), the water content of the base component is 0.2 to 5wt% of caprolactam, and the molecular weight regulator content is 1.5wt% or less of caprolactam; the molecular weight regulator is one or a combination of more of organic monoacids, organic dibasic acids, monoamines and diamine. The organic acid is aliphatic H (CH) ₂ ) _n COOH, wherein n=1-10; or aromatic, benzoic acid or naphthoic acid. The monoamine is aliphatic H (CH) ₂ ) _m NH ₂ Wherein m=1 to 10; or aromatic, aniline. The organic dibasic acid is aliphatic dibasic acid HOOC (CH) ₂ ) _X COOH, wherein x=1-20; or aromatic dibasic acid, which is terephthalic acid, phthalic acid, isophthalic acid or naphthalene dicarboxylic acid; the diamine is aliphatic diamine H ₂ N(CH ₂ ) _y NH ₂ Wherein y=1-10; or aromatic diamine, which is p-phenylenediamine, naphthalene diamine, m-phenylenediamine, o-phenylenediamine or xylene diamine.

In the method, in the step (1), the additive component is one or more of a delustrant, an antioxidant and an anti-ultraviolet agent, and the addition amount of the additive component is not more than 5wt% relative to caprolactam in the basic component; wherein, the delustering agent is one or more of titanium dioxide, diatomite and silicon dioxide; the antioxidant is one or more of phenolic antioxidants, hindered phenolic antioxidants, semi-hindered phenolic antioxidants, phosphite antioxidants, tetramethyl piperidine amine antioxidants, benzofuranone antioxidants, hydroxylamine antioxidants, tertiary amine nitrogen oxides antioxidants, bisphenol monoacrylate antioxidants, bis salicylidene diamine antioxidants and thiopropionate antioxidants; the ultraviolet inhibitor is one or more of carbon black, zinc oxide, salicylate ultraviolet absorbent, benzophenone ultraviolet absorbent, benzotriazole ultraviolet absorbent, substituted acrylonitrile ultraviolet absorbent, triazine ultraviolet absorbent and hindered amine ultraviolet absorbent.

In the above method, in the step (1), when the VK tube reactor is a one-stage reactor, the reaction temperature is 220-280 ℃, the absolute reaction pressure is 0.05-0.8 MPa, and the relative viscosity of the polycaprolactam base melt is 2.0-3.4.

In the above method, in the step (1), when the VK tube reactor is a two-stage reactor, the reaction temperature of the pre-polymerization reactor is 220-280 ℃, the absolute reaction pressure is 0.05-1.0 MPa, the reaction temperature of the post-polymerization reactor is 235-280 ℃, the absolute reaction pressure is 0.02-0.4 MPa, and the relative viscosity of the polycaprolactam base melt is 2.1-3.6.

In the method, in the step (2), the reaction temperature of the falling film devolatilization reactor outside the pipe is 240-280 ℃ and the absolute reaction pressure is 20-500 Pa.

In the method, in the step (3), the spinning temperature of the spinning unit is 245-300 ℃, and the spinning winding speed is 2500-6000m/min.

A method for producing polycaprolactam fiber in green and high efficiency, which is characterized in that the method further comprises the following steps: caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe are subjected to heat exchange in a condensation heat exchange device, the monomer and the oligomer are condensed to a collection and recycling device, and the obtained condensate can be directly recycled as a basic component or can be recycled as the basic component after evaporation concentration and/or pyrolysis to replace part of caprolactam raw materials in the basic component. The apparatus for the concentration by evaporation may be all the apparatuses known in the art for this purpose, preferably a three-effect multistage evaporator; the apparatus for the cleavage may be all apparatuses known in the art for this purpose.

In the process described above, in step (1), the caprolactam in the base may be fresh caprolactam feed, may be a caprolactam mixture comprising fresh caprolactam and all/part of the recycled caprolactam monomer or oligomer, or may be a caprolactam mixture comprising fresh caprolactam and all/part of the recycled caprolactam monomer or oligomer cleavage product. That is, the obtained condensate may be directly transferred to the VK tube reactor or other VK tube reactor in step (1) for polymerization, or may be transferred to the VK tube reactor or other VK tube reactor in step (1) for polymerization after evaporation concentration and/or cleavage.

The temperature of the condenser in the condensing heat exchange device is set to be 5-120 ℃.

The caprolactam monomer and oligomer collected in the collecting and recycling device can be recycled after being treated by an evaporation concentration device and/or a cracking device, and the equipment used for evaporation concentration and/or cracking can be all the equipment known in the prior art for the purpose.

When the condensation heat exchange device is a combination of 2 or more stages (3-6 stages) of condensers connected in series or in parallel, mixed steam of caprolactam monomer and oligomer obtained by devolatilization of the falling film devolatilization reactor outside the pipe enters the first stage condensation heat exchange device for heat exchange, and the gas which is not condensed yet can enter the next stage condensation heat exchange device for heat exchange.

The invention connects the VK tube reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device and the vacuum system in turn, adjusts and matches the process parameters of each part by designing the total control unit, carries out real-time optimization control on the production system, can realize the efficient removal of monomers and oligomers in the basic melt prepared by the VK tube reactor, and tackifies the basic melt, and the obtained high-quality polycaprolactam melt with the hot water extractables content less than 1.5wt% can be directly spun into polycaprolactam fibers. In the invention, the lower the content of the molecular weight regulator in the VK pipe reactor is, the higher the melt viscosity increasing potential of the falling film devolatilization reactor outside the pipe is, and the melt with higher relative viscosity is easier to prepare; the higher the polymerization temperature (more than 280 ℃) in the VK tube reactor, the more the content of monomers and oligomers, and the more difficult the devolatilization of the monomers and oligomers in the off-tube falling film devolatilization reactor; the higher the vacuum degree of the falling film devolatilization reactor outside the pipe (namely the smaller the absolute pressure of the reaction), the better the devolatilization effect of caprolactam monomer and oligomer, the lower the vacuum degree (more than 500 Pa) or the shorter the falling film pipe (less than 2 m), the poorer the devolatilization effect of caprolactam monomer and oligomer, and the higher the hot water extractables content in the final melt can be caused, which can affect the quality of polycaprolactam melt. In addition, excessive reaction temperatures (greater than 280 ℃) in the off-line falling film devolatilization reactor can lead to side reactions that degrade the melt. Therefore, the proportion of each raw material component, especially the addition amount of a molecular weight regulator, needs to be comprehensively regulated, the polymerization reaction temperature in the VK tube reactor is controlled, the related parameters and reaction conditions of the outside-tube falling film devolatilization reactor are designed to realize the efficient removal of monomers and oligomers in the basic melt prepared by the VK tube reactor, and meanwhile, the viscosity increasing rule of the outside-tube falling film devolatilization reactor is utilized to effectively control the relative viscosity of the polycaprolactam melt in a required range.

Compared with the prior art, the invention has the beneficial effects that:

(1) The polycaprolactam production system and method designed by the invention are used for effectively removing high-content caprolactam monomer and oligomer with the weight percentage of about 10% in polycaprolactam basic melt prepared by a VK tube reactor through the combination of a falling film devolatilization reactor outside the tube and a condensation heat exchange device, and the key points are as follows: the difficult-to-devolatilize cyclic oligomer with higher boiling point, especially cyclic dimer, can be efficiently and azeotropically removed from a melt film formed by falling film outside a pipe in the coexistence of low boiling point substances such as caprolactam, and finally, high-quality polycaprolactam melt with hot water extractables less than 1.5wt% and stable relative viscosity can be obtained, and the production stability and continuity of the falling film process and the subsequent melt direct spinning preparation of polyamide fibers are maintained.

(2) The wave-length tube or 3-12-pointed star-shaped falling film tube preferably used in the invention has unique falling film diversion structure and high-efficiency film forming characteristic, can prevent the phenomenon of discontinuous or uneven thickness and the like of the falling film outside the polycaprolactam melt tube, can continuously and efficiently remove caprolactam monomers and oligomers in the polycaprolactam melt, obviously improves the product quality of the polycaprolactam melt after the falling film outside the tube is devolatilized, and meets the production requirement of direct spinning of the high-quality polycaprolactam melt.

(3) The invention can fully wet the extraction pipeline and the condensation heat exchange device by utilizing the high-content caprolactam removed from the polycaprolactam base melt, fully exert the characteristic of better dissolving caprolactam oligomer of caprolactam at high temperature, and prevent vaporized oligomer molecules from being separated and enriched on the solid wall surface, thereby prolonging the cleaning period of the falling film devolatilization reactor outside the pipe, the condensation heat exchange device and the extraction pipeline.

(4) According to the invention, the heat exchange is carried out between the condensation heat exchange device and the mixed steam extracted from the falling film devolatilization reactor outside the pipe, the steam is condensed into the collecting device, and the condensed liquid containing caprolactam monomer and oligomer is collected and obtained, and can be directly used as a basic component for recycling or used as a basic component for recycling after evaporation concentration and/or pyrolysis, so that the efficient recycling of the monomer and oligomer is realized.

(5) Compared with the hot water extraction process for preparing polycaprolactam by using a traditional VK tube reactor, the production system and the method provided by the invention can effectively remove monomers and oligomers in a basic melt in a shorter time by optimizing the reaction temperature and the pressure of the outside falling film devolatilization reactor, can efficiently prepare a high-quality polycaprolactam melt, can remove processes such as extraction, drying and the like which take tens to hundreds of hours, saves a great amount of time, and improves the production efficiency.

(6) The technology of the invention can be directly connected with the current main flow polycaprolactam VK pipe reactor, is suitable for removing caprolactam monomers and oligomers in polycaprolactam melt in different application fields, can produce polycaprolactam in different target viscosity ranges according to requirements in a wider range, so that the invention can be applied to different fields, and the prepared high-quality polycaprolactam melt can be directly spun into products such as nylon civil fibers, industrial yarns and the like.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a schematic diagram of the connection of a one-stage VK tube reactor and an off-tube falling film devolatilization reactor according to the present invention;

FIG. 3 is a schematic diagram of the connection of a two-stage VK tube reactor and an off-tube falling film devolatilization reactor according to the present invention;

FIG. 4 is a schematic diagram showing the connection of the falling film devolatilization reactor outside the tube to the condensing heat exchanger in the present invention;

FIG. 5 is a schematic diagram showing the connection of the outside-tube falling film devolatilization reactor to the spinning unit in the present invention;

FIG. 6 is a schematic view of a falling film tube used in the external falling film devolatilization reactor of the present invention;

the reference numerals are:

VK tube reactor:

a one-stage VK pipe reactor 1, a feed inlet 2 and a discharge outlet 3;

two-stage VK tube reactor: a pre-polymerization reactor 4, a post-polymerization reactor 5, a feed inlet 6 of the pre-polymerization reactor and a discharge outlet 7 of the post-polymerization reactor;

an external falling film devolatilization reactor: the vertical type outside pipe falling film devolatilization reactor 8, a feed inlet 9, a discharge outlet 10, a melt cavity 11, a film distributor 12, a falling film pipe 13, a heating medium inlet 14, a heating medium outlet 15, a stirrer 16, an air outlet 17 and a gear pump 18;

condensing heat exchange device: a condenser 19, an air inlet 20, an air outlet 21, and a condensate outlet 22;

and (3) collecting and recycling devices: a collection tank 23 and a feed inlet 24;

and (3) a vacuum system: a buffer tank 25; a vacuum pump unit 26;

spinning unit 27.

Detailed Description

In order to further illustrate the present invention, a system and method for producing polycaprolactam fibers in a green and efficient manner is provided in the following detailed description, which is not to be construed as limiting the scope of the invention.

In the invention, the data of the relative viscosity of polycaprolactam and the content of hot water extractables are obtained according to the national standard GB/T38138-2019 test, and the test sample of the polycaprolactam is a sample prepared by a VK tube reactor or an external falling film reactor after cooling and granulating; the polycaprolactam fiber breaking strength value is obtained according to the national standard GB/T14344-2008 test.

Example 1

The embodiment provides a production system for preparing polycaprolactam fibers in a green and efficient way, and the process flow of the production system is shown in figure 1, and the production system comprises a VK tube reactor, an outside-tube falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a one-stage reactor 1, and is provided with 1 feed inlet 2 and 1 discharge outlet 3; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for precisely controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 3 of the one-section type VK pipe reactor, as shown in figure 2; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 2 condensers 19, wherein each condenser is provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with a feed inlet 24 of a collecting and recycling device 23, the air inlet of the former stage condenser is connected with the air outlet of the falling film devolatilization reactor outside the tube, the air outlet is connected with the air inlet of the latter stage condenser, and the air outlet of the latter stage condenser is connected with a vacuum system; the vacuum system is a series combination of a screw vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube 13 used in the falling film devolatilization reactor outside the tube is a 3-angle star-shaped tube, the maximum circumcircle diameter is 50mm, and the tube length is 10m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

By using the production system in the technical scheme, the embodiment also provides a production method for preparing polycaprolactam fibers in a green and efficient way, which comprises the following steps:

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant N, N' -bis (2, 6-tetramethyl-4-piperidinyl) -1, 3-benzenedicarboxamide (SEED) at 100:2:0.4: mixing in proportion of 0.5, preheating, continuously injecting into a VK tube reactor, setting one-stage normal pressure polymerization with the absolute reaction pressure of 0.1MPa in the VK tube reactor, wherein the upper part of the reactor has the reaction temperature of 245 ℃, the lower part of the reactor has the reaction temperature of 260 ℃, and obtaining polycaprolactam base melt with the relative viscosity of 2.23 through hydrolysis ring-opening polymerization;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 265 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.47 and the hot water extractables content of 0.91 weight percent is prepared, so that the relative viscosity increment value is 0.24;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 270 ℃, the spinning winding speed is 4500m/min, and the polycaprolactam fibers with the breaking strength of 4.5cN/dtex and the breaking elongation of 23% are obtained.

Setting the temperature of the condenser to 75 ℃, condensing caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe into a collecting and recycling device through the condenser, and directly recycling condensate serving as a basic component to replace part of fresh caprolactam raw materials in the basic component.

Example 2

The embodiment provides a production system for preparing polycaprolactam fibers in a green and efficient way, and the process flow of the production system is shown in figure 1, and the production system comprises a VK tube reactor, an outside-tube falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a two-stage reactor and comprises a pre-polymerization reactor 4 and a post-polymerization reactor 5, wherein 1 feed inlet 6 and 1 discharge outlet 7 are respectively arranged; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for accurately controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 7 of the post polymerization reactor in the two-stage VK pipe reactor, as shown in figure 3; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 3 condensers 19, wherein each condenser is provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with a feed inlet 24 of a collecting and recycling device 23, the air inlet of the first-stage condenser is connected with the air outlet of the falling film devolatilization reactor outside the tube, the air outlet is connected with the air inlet of the subsequent-stage condenser, and the air outlet of the final-stage condenser is connected with a vacuum system; the vacuum system is a series combination of a liquid ring vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube 13 used in the falling film devolatilization reactor outside the tube is a 3-angle star-shaped tube, the maximum circumcircle diameter is 60mm, and the tube length is 10m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant SEED at 100:2:0.3:0.3: mixing in proportion of 0.8, preheating, continuously injecting into a pre-polymerization reactor in a VK tube reactor, setting the absolute reaction pressure of the pre-polymerization reactor to be 0.3MPa, setting the upper reaction temperature to be 250 ℃, setting the lower reaction temperature to be 270 ℃, setting the absolute reaction pressure of the post-polymerization reactor to be 0.06MPa, setting the upper reaction temperature to be 270 ℃, setting the lower reaction temperature to be 245 ℃, and carrying out hydrolysis ring-opening polymerization to obtain polycaprolactam base melt with the relative viscosity of 2.35;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 260 ℃, the absolute reaction pressure is set to be 60Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.81 and the hot water extractables content of 0.96wt% is prepared, so that the relative viscosity increment value is 0.46;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 275 ℃, the spinning winding speed is 4300m/min, and the polycaprolactam fibers with the breaking strength of 4.9cN/dtex and the breaking elongation of 22% are obtained.

Example 3

The embodiment provides a production system for preparing polycaprolactam fibers in a green and efficient way, and the process flow of the production system is shown in figure 1, and the production system comprises a VK tube reactor, an outside-tube falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a one-stage reactor 1, and is provided with 1 feed inlet 2 and 1 discharge outlet 3; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for precisely controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 3 of the one-section type VK pipe reactor, as shown in figure 2; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 2 spray condensers 19, wherein each spray condenser 19 is provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with a feed inlet 24 of a collecting and recycling device 23, the air inlet of the first-stage spray condenser is connected with the air outlet of the falling film devolatilization reactor outside the pipe, the air outlet is connected with the air inlet of the later-stage spray condenser, and the air outlet of the last-stage spray condenser is connected with a vacuum system; the vacuum system is a series combination of a screw vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube used in the falling film devolatilization reactor outside the tube is a node tube, the maximum circumcircle diameter is 40mm, and the tube length is 12m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant SEED, matting agent titanium dioxide in an amount of 100:2:0.22:0.5: mixing in proportion of 0.27, preheating, continuously injecting into a VK tube reactor, setting one-stage normal pressure polymerization with the absolute reaction pressure of 0.1MPa in the VK tube reactor, wherein the upper part of the reactor has the reaction temperature of 245 ℃, the lower part of the reactor has the reaction temperature of 260 ℃, and obtaining polycaprolactam base melt with the relative viscosity of 2.65 through hydrolysis ring-opening polymerization;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 260 ℃, the absolute reaction pressure is set to be 40Pa, and high-quality polycaprolactam melt with the relative viscosity of 3.22 and the hot water extractables content of 0.89wt% is prepared, so that the relative viscosity increment value is 0.57;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 275 ℃, the spinning winding speed is 3700m/min, and the polycaprolactam fibers with the breaking strength of 6.3cN/dtex and the breaking elongation of 21% are obtained.

The spray liquid of the spray condenser is water, the temperature is 10 ℃, caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe is condensed into a collecting and recycling device through the spray condenser, and condensed liquid can be used as a basic component for recycling after being evaporated, concentrated and cracked through a three-effect multistage evaporator to replace part of fresh caprolactam raw materials in the basic component.

Example 4

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid at 100:2: mixing in proportion of 0.18, preheating, continuously injecting into a pre-polymerization reactor in a VK tube reactor, setting the absolute reaction pressure of the pre-polymerization reactor to be 0.3MPa, setting the upper reaction temperature to be 250 ℃, setting the lower reaction temperature to be 265 ℃, setting the absolute reaction pressure of the post-polymerization reactor to be 0.06MPa, setting the upper reaction temperature to be 265 ℃, setting the lower reaction temperature to be 255 ℃, and carrying out hydrolysis ring-opening polymerization to obtain polycaprolactam base melt with the relative viscosity of 2.96;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 265 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 3.58 and the hot water extractables content of 1.06 weight percent is prepared, so that the relative viscosity increment value is 0.62;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 280 ℃, the spinning winding speed is 3300m/min, and the polycaprolactam fibers with the breaking strength of 8.6cN/dtex and the breaking elongation of 20% are obtained.

Example 5

The embodiment provides a production system for preparing polycaprolactam fibers in a green and efficient way, and the process flow of the production system is shown in figure 1, and the production system comprises a VK tube reactor, an outside-tube falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a two-stage reactor and comprises a pre-polymerization reactor 4 and a post-polymerization reactor 5, wherein 1 feed inlet 6 and 1 discharge outlet 7 are respectively arranged; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for accurately controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 7 of the post polymerization reactor in the two-stage VK pipe reactor, as shown in figure 3; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 3 condensers 19, wherein the condensers are respectively provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with a feed inlet 24 of a collecting and recycling device 23, the air inlet of the first-stage condenser is connected with the air outlet of the falling film devolatilization reactor outside the tube, the air outlet is connected with the air inlet of the subsequent-stage condenser, and the air outlet of the final-stage condenser is connected with a vacuum system; the vacuum system is a series combination of a liquid ring vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube 13 used in the falling film devolatilization reactor outside the tube is a 3-angle star-shaped tube, the maximum circumcircle diameter is 40mm, and the tube length is 12m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid at 100:2: mixing in proportion of 0.15, preheating, continuously injecting into a pre-polymerization reactor in a VK tube reactor, setting the absolute reaction pressure of the pre-polymerization reactor to be 0.3MPa, setting the upper reaction temperature to be 255 ℃, setting the lower reaction temperature to be 270 ℃, setting the absolute reaction pressure of the post-polymerization reactor to be 0.06MPa, setting the upper reaction temperature to be 270 ℃, setting the lower reaction temperature to be 255 ℃, and carrying out hydrolysis ring-opening polymerization to obtain polycaprolactam base melt with the relative viscosity of 3.35;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is 270 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 3.88 and the hot water extractables content of 1.19 weight percent is prepared, so that the relative viscosity increment value is 0.53;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 285 ℃, the spinning winding speed is 2900m/min, and the polycaprolactam fibers with the breaking strength of 9.5cN/dtex and the breaking elongation of 18% are obtained.

Example 6

The embodiment provides a production system for preparing polycaprolactam fibers in a green and efficient way, and the process flow of the production system is shown in figure 1, and the production system comprises a VK tube reactor, an outside-tube falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a one-stage reactor 1, and is provided with 1 feed inlet 2 and 1 discharge outlet 3; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for precisely controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 3 of the one-section type VK pipe reactor, as shown in figure 2; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 3 condensers 19, wherein each condenser 19 is provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with the collecting and recycling device, the air inlet of the first-stage condenser is connected with the air outlet of the falling film devolatilization reactor outside the pipe, and the air outlet of the last-stage condenser is connected with the vacuum system; the vacuum system is a series combination of a screw vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube used in the falling film devolatilization reactor outside the tube is a 6-angle star-shaped tube, the maximum circumcircle diameter is 50mm, and the tube length is 10m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant SEED, matting agent titanium dioxide in an amount of 100:2:0.4:0.5:2.3, continuously injecting the mixture into a VK tube reactor after preheating, setting the reaction absolute pressure of the one-stage VK tube reactor to be 0.1MPa for normal pressure polymerization, wherein the upper part of the reactor is at 245 ℃, the lower part of the reactor is at 260 ℃, and obtaining polycaprolactam base melt with the relative viscosity of 2.18 through hydrolysis ring-opening polymerization;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 265 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.45 and the hot water extractables content of 0.90 weight percent is prepared, so that the relative viscosity increment value is 0.27;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 270 ℃, the spinning winding speed is 4300m/min, and the polycaprolactam fibers with the breaking strength of 4.2cN/dtex and the breaking elongation of 23% are obtained.

Setting the temperature of the condenser to 75 ℃; caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe are condensed into a collecting and recycling device through a condenser, and condensate can be directly used as a basic component for recycling to replace part of fresh caprolactam raw materials in the basic component.

Comparative example 1

The production system adopted in the embodiment is the same as that adopted in the embodiment 1, and the process flow is shown in fig. 1, and comprises a VK tube reactor, an external falling film devolatilization reactor, a spinning unit, a condensation heat exchange device, a collection and recycling device, a vacuum system and a general control unit. The VK pipe reactor is a one-stage reactor 1, and is provided with 1 feed inlet 2 and 1 discharge outlet 3; the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor 8, which is provided with 1 feed inlet 9, 1 discharge outlet 10 and 1 air outlet 17, the falling film pipe is internally provided with a heating medium flow for precisely controlling the temperature, the heating medium enters from a heating medium inlet 14 and flows out from a heating medium outlet 15, and the feed inlet 9 is connected with the discharge outlet 3 of the one-section type VK pipe reactor, as shown in figure 2; the condensation heat exchange device and the collection and recycling device are sequentially connected after the outside falling film devolatilization reactor 8, as shown in figure 4; the condensing heat exchange device comprises a series combination of 2 condensers 19, wherein each condenser is provided with 1 air inlet 20, 1 air outlet 21 and 1 lower condensate outlet 22, the lower condensate outlets 22 are connected with a feed inlet 24 of a collecting and recycling device 23, the air inlet of the former stage condenser is connected with the air outlet of the falling film devolatilization reactor outside the tube, the air outlet is connected with the air inlet of the latter stage condenser, and the air outlet of the latter stage condenser is connected with a vacuum system; the vacuum system is a series combination of a screw vacuum pump and a Roots vacuum pump, and a buffer tank 25 is arranged in front of a vacuum pump 26; the spinning unit 27 is connected with the discharge port 10 of the falling film devolatilization reactor outside the pipe through a melt pipe, as shown in fig. 5; the main control unit is used for adjusting and matching the process parameters of each part of the VK pipe reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, so as to realize the optimal control of the production system.

The falling film tube 13 used in the falling film devolatilization reactor outside the tube is a 3-angle star-shaped tube, and is different in that the maximum circumcircle diameter is 120mm, and the tube length is 2m; the bottom of the tube external falling film devolatilization reactor is a cone, and a spiral belt stirrer 16 is arranged in the cone for uniformly feeding materials and cleaning the wall surface of the cone; the melt pipes are each provided with a gear pump 18 for conveying the material.

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant SEED at 100:2:0.4: mixing in proportion of 0.5, preheating, continuously injecting into a VK tube reactor, setting one-stage normal pressure polymerization with the absolute reaction pressure of 0.1MPa in the VK tube reactor, wherein the upper part of the reactor has the reaction temperature of 245 ℃, the lower part of the reactor has the reaction temperature of 260 ℃, and obtaining polycaprolactam base melt with the relative viscosity of 2.23 through hydrolysis ring-opening polymerization;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 265 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.28 and the hot water extractables content of 2.58 weight percent is prepared, so that the relative viscosity increment value is 0.05;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 270 ℃, the spinning winding speed is 3000m/min, and the polycaprolactam fibers with the breaking strength of 2.3cN/dtex and the breaking elongation of 18% are obtained.

Comparative example 2

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12 and then subjected to falling film reaction outside the falling film pipe, wherein the difference is that the reaction temperature of the falling film devolatilization reactor outside the pipe is 245 ℃, the absolute reaction pressure is 1500Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.26 and the hot water extractables content of 3.71 weight percent is prepared, so that the relative viscosity increment value is 0.03;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is 270 ℃, the spinning winding speed is 2800m/min, and the polycaprolactam fibers with the breaking strength of 1.9cN/dtex and the breaking elongation of 19% are obtained.

The difference is that the temperature of the condenser is set to be 125 ℃, caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe is condensed into a collecting and recycling device through the condenser, and condensate can be directly used as a basic component for recycling to replace part of fresh caprolactam raw materials in the basic component.

Comparative example 3

(1) Caprolactam (including fresh caprolactam and recycled caprolactam monomers and oligomers), water, terephthalic acid, antioxidant SEED at 100:2:0.4: mixing in proportion of 0.5, preheating, continuously injecting into a VK tube reactor, setting a one-stage VK tube reactor for normal pressure polymerization with reaction absolute pressure of 0.1MPa, wherein the difference is that the upper part of the reactor has a reaction temperature of 260 ℃, the lower part of the reactor has a reaction temperature of 290 ℃, the lower part of the reactor has a reaction temperature of 280 ℃, and obtaining polycaprolactam base melt with relative viscosity of 2.13 through hydrolysis ring-opening polymerization;

(2) The basic melt is conveyed into a melt cavity 11 at the upper part of the falling film devolatilization reactor outside the pipe through a pipeline, and is distributed by a film distributor 12, and then falling film reaction is carried out outside the falling film pipe, the reaction temperature of the falling film devolatilization reactor outside the pipe is set to be 265 ℃, the absolute reaction pressure is 50Pa, and the high-quality polycaprolactam melt with the relative viscosity of 2.25 and the hot water extractables content of 1.83 weight percent is prepared, so that the relative viscosity increment value is 0.12;

(3) The high-quality polycaprolactam melt obtained in the outside-tube falling film devolatilization reactor is conveyed to a spinning unit through a pipeline for preparing polycaprolactam fibers by direct spinning, the spinning temperature of the spinning unit is set to 270 ℃, the spinning winding speed is 3800m/min, and the polycaprolactam fibers with the breaking strength of 3.6cN/dtex and the breaking elongation of 22% are obtained.

From the results of the above examples and comparative examples, it was found that a high quality polycaprolactam melt having a hot water extractables of less than 1.5wt% could not be obtained and a relative viscosity increase of 0.2 or more could not be achieved in an external falling film devolatilization reactor in which the diameter of the falling film tube was too large and the length of the falling film tube was too short (in comparative example 1), the reaction absolute pressure of the external falling film devolatilization reactor and the temperature of the condenser were too high (in comparative example 2), and the reaction temperature of the VK tube reactor was too high (in comparative example 3). Therefore, the invention connects the VK tube reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device and the vacuum system in turn, adjusts and matches the technological parameters of each part through designing the master control unit, carries out real-time optimization control on the production system, optimizes the reaction temperature and the reaction absolute pressure of the outside falling film devolatilization reactor through designing the relevant parameters such as the diameter and the length of the falling film tube of the outside falling film devolatilization reactor, and can obtain the high-quality polycaprolactam melt with the relative viscosity of 2.2-4.0 and the hot water extractables of less than 1.5 weight percent. Further matching the spinning temperature and the spinning winding speed of the spinning unit to obtain the high-quality polycaprolactam fiber.

The raw materials and equipment used in the invention are common raw materials and equipment in the field unless specified otherwise; the methods used in the present invention are conventional in the art unless otherwise specified.

The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that modifications and variations can be made by those skilled in the art without departing from the principles of the present invention, and such modifications and variations are also to be considered as being within the scope of the present invention.

Claims

1. A production system for green and efficient preparation of polycaprolactam fibers, which is characterized by comprising:

VK tube reactor: the relative viscosity of the basic melt is 2.0-3.6;

an external falling film devolatilization reactor: the device is connected with a VK pipe reactor through a melt pipeline and is used for removing caprolactam monomers and oligomers in the basic melt, so that the content of hot water extractables in the polycaprolactam melt is less than 1.5wt%, and the viscosity of the polycaprolactam melt is increased to 2.2-4.0;

spinning unit: the melt pipeline is connected with an external falling film devolatilization reactor for spinning to prepare polycaprolactam fibers;

Condensing heat exchange device: the caprolactam monomer and oligomer vapor is connected with a falling film devolatilization reactor outside the tube, and the extracted caprolactam monomer and oligomer vapor is subjected to heat exchange with a condenser to condense the caprolactam monomer and oligomer vapor;

and (3) collecting and recycling devices: the device is connected with the condensation heat exchange device and is used for collecting caprolactam monomers and oligomers condensed in the condensation heat exchange device;

and (3) a vacuum system: the device is connected with a condensation heat exchange device to provide vacuum power;

and the general control unit: the method is used for adjusting and matching the process parameters of each part of the VK tube reactor, the outside falling film devolatilization reactor, the spinning unit, the condensation heat exchange device, the collection and recycling device and the vacuum system, and realizing the optimal control of the production system.

2. The production system of claim 1, wherein: the external falling film devolatilization reactor is a vertical external falling film devolatilization reactor, the bottom of the reactor is a cone, a stirrer is arranged in the cone and used for uniformly material and cleaning the wall surface of the cone, the diameter of a used falling film pipe or the diameter of a maximum circumcircle is 5-100 mm, the pipe length is 3-20 m, and a hot coal flow passage is arranged in the falling film pipe and used for accurately controlling the reaction temperature.

3. The production system of claim 1, wherein: the falling film tube used in the external falling film devolatilization reactor is preferably a corrugated tube or a star-shaped tube, and when the falling film tube is a star-shaped tube, the falling film tube is preferably a 3-12-angle star-shaped tube.

4. The production system of claim 1, wherein: the condensation heat exchange device is a combination of 1-stage, 2-stage or more stages of condensers which are connected in series or in parallel, and the lower end of each stage of condensation heat exchange device is provided with a condensate outlet which is connected with the collection and recycling device.

5. The production system of claim 1, wherein: the vacuum system is one or a plurality of series or parallel combination of a rotary vane vacuum pump, a steam jet pump, a liquid ring vacuum pump, a Roots vacuum pump, a reciprocating vacuum pump and a screw vacuum pump which are additionally provided with buffer tanks in front of the pump.

6. A method for producing polycaprolactam fiber in green and high efficiency, using the production system of any one of claims 1 to 5, characterized by comprising the following steps:

7. The production method according to claim 6, wherein in step (1): the water content of the basic component is 0.2-5 wt% of caprolactam, and the molecular weight regulator content is less than 1.5wt% of caprolactam; the molecular weight regulator is one or a combination of more of organic monoacids, organic dibasic acids, monoamines and diamine;

the additive component is one or more of a delustrant, an antioxidant and an anti-ultraviolet agent, and the addition amount of the additive component is not more than 5wt% relative to caprolactam in the basic component.

8. The method of claim 6, wherein in step (1): when the VK pipe reactor is a one-stage reactor, the reaction temperature is 220-280 ℃, the absolute reaction pressure is 0.05-0.8 MPa, and the relative viscosity of the polycaprolactam base melt is 2.0-3.4; when the VK pipe reactor is a two-stage reactor, the reaction temperature of the pre-polymerization reactor is 220-280 ℃, the absolute reaction pressure is 0.05-1.0 MPa, the reaction temperature of the post-polymerization reactor is 235-280 ℃, the absolute reaction pressure is 0.02-0.4 MPa, and the relative viscosity of the polycaprolactam base melt is 2.1-3.6.

9. The method of claim 6, wherein in step (2): the reaction temperature of the falling film devolatilization reactor outside the pipe is 240-280 ℃, and the absolute reaction pressure is 20-500 Pa.

10. The method of claim 6, wherein in step (3): the spinning temperature of the spinning unit is 245-300 ℃, and the spinning winding speed is 2500-6000m/min.

11. The production method according to claim 6, characterized in that the production method further comprises: caprolactam monomer and oligomer steam extracted from the falling film devolatilization reactor outside the pipe are subjected to heat exchange in a condensation heat exchange device, the monomer and the oligomer are condensed to a collection and recycling device, and the obtained condensate can be directly recycled as a basic component or can be recycled as the basic component after evaporation concentration and/or pyrolysis to replace part of caprolactam raw materials in the basic component.