Method for continuously producing extinction chinlon 6 by recovering caprolactam monomer

Abstract

The invention relates to a method for continuously producing extinction chinlon 6 by recovering caprolactam monomers, and relates to the technical field of preparation of extinction chinlon 6, the method comprises the following steps: adding a flocculating agent into a to-be-recovered caprolactam monomer aqueous solution for physicochemical treatment to obtain a first caprolactam monomer aqueous solution; and carrying out filtration treatment and ion exchange treatment on the first caprolactam monomer aqueous solution to obtain a second caprolactam monomer aqueous solution, and the like. According to the method, the caprolactam-containing aqueous solution is subjected to purification, concentration, depolymerization, polymerization and other processes, the caprolactam monomer is completely recycled, and the continuous large-capacity production of the high-quality extinction chinlon 6 is realized, so that the technological process from recycling to polymerization of the caprolactam monomer is shortened, and the technological route for completely recycling the caprolactam monomer to produce the high-quality extinction chinlon 6 is innovated; the recovery rate and the finished product quality of the caprolactam monomer are improved, and the product types of a recovery production line are widened.

Description

Technical Field

[0001] The invention relates to the technical field of matte nylon 6 preparation, and in particular to a method for continuously producing matte nylon 6 by recycling caprolactam monomer. Background Art

[0002] Caprolactam is an important raw material for the synthetic chemical fiber nylon 6. Because nylon 6 polymer has unique excellent properties, such as electrical insulation, acid and alkali corrosion resistance, excellent mechanical strength and impact strength, excellent toughness and wear resistance, etc., it is widely used in civil silk, industrial silk, engineering plastic grade and composite materials.

[0003] In the process of continuous synthesis of nylon 6 polymer, according to the reaction mechanism, caprolactam monomer needs to go through hydrolysis ring opening, addition, polycondensation and other steps. When the chemical reaction equilibrium is reached, since the whole reaction process is reversible, the conversion rate of caprolactam is about 90%. Therefore, about 10% of monomers and oligomers will remain in the final polymer. In order to remove the low molecular weight substances in the slices, the extraction tower is usually used to remove them by hot water countercurrent extraction, thereby producing a large amount of extraction aqueous solution containing caprolactam monomer. If these monomer extraction aqueous solutions are not used, they will not only cause great harm to the environment, but also have a serious impact on the downstream processing process and product quality.

[0004] In industrial production, in order to recycle and reuse the caprolactam monomer in the aqueous extract solution, first, the extract water is usually physically filtered or settled to remove most of the suspended solids in the extract water, and then chemical adsorption or ion exchange is performed to remove a small amount of organic and inorganic groups or charged ions to achieve the purpose of purification; secondly, the purified aqueous extract solution is concentrated. The main methods include low-concentration concentration using membrane permeation technology and high-concentration concentration usually using multi-effect falling film evaporation or MVR falling film evaporation to concentrate the aqueous extract solution to different concentrations required by the back-end process; finally, the high-concentration caprolactam monomer concentrate can be utilized in the following ways: (1) directly reused in the polymerization section for hydrolysis and polymerization; (2) passing superheated steam into the depolymerization reactor to depolymerize and separate the oligomers, and then concentrating and distilling to finally obtain caprolactam monomer, and then depolymerizing; (3) conveying the monomer concentrate to a high-pressure depolymerization reactor for oligomer depolymerization to obtain a concentrate of low molecular weight substances, and then depolymerizing.

[0005] The existing problems in the process of recovering caprolactam monomer to synthesize nylon 6 high molecular polymer are as follows: (1) The purification process of the aqueous solution containing caprolactam monomer is imperfect. In some production processes, the aqueous solution is only subjected to two simple physical filtrations to remove impurities, which cannot effectively remove fine solid suspended matter and other charged groups or ions in the aqueous solution; in some production processes, the aqueous solution is physically filtered once and then anion and cation exchange is performed, which greatly reduces the service life of the anion and cation exchanger and increases the recycling cost; (2) There are technical shortcomings in the evaporation and concentration of the aqueous solution, such as: the membrane permeation technology cannot reach a higher concentration, and the multi-effect evaporation has high operating costs; (3) If the monomer concentrate is directly put into the polymerization for ring-opening hydrolysis, the product quality will be seriously reduced due to the presence of polymers in the concentrate; using superheated steam to depolymerize the polymers and then obtain the monomers through concentration and refining processes will generate a large amount of wastewater and waste solids during the recovery process, and the process is long and the investment and operating costs are high.

[0006] Therefore, in the process of recovering caprolactam monomers to synthesize nylon 6 high molecular polymers, the purification process of the extraction water solution must be fully considered to effectively remove impurities in the extraction water, simplify the operation process, increase the service life of the resin exchanger, and reduce additional energy and water consumption. In addition, in order to reduce the presence of oligomers in the monomer concentrate, shorten the treatment process, improve the recovery rate of monomers and the quality of polymer products, and reduce the production cost and environmental cost of the recovered monomers, it is necessary to boldly innovate the existing technical routes. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for recycling caprolactam monomer to continuously produce matte nylon 6. The present invention specifically provides a method for continuously and massively producing high-quality matte nylon 6 by fully recycling caprolactam monomer in a caprolactam-containing aqueous solution through purification, concentration, depolymerization and polymerization, which not only solves the problems of removing impurities in the purification process of the aqueous solution, but also innovates the process route of fully recycling caprolactam monomer to produce high-quality matte nylon 6, achieving energy saving and consumption reduction, reducing waste discharge, and reducing recycling costs and environmental costs.

[0008] The present invention provides a method for continuously producing matte nylon 6 by recycling caprolactam monomer, the method comprising the following steps:

[0009] adding a flocculant to the caprolactam monomer aqueous solution to be recovered for physicochemical treatment to obtain a first caprolactam monomer aqueous solution;

[0010] filtering and ion-exchanging the first aqueous caprolactam monomer solution to obtain a second aqueous caprolactam monomer solution;

[0011] The second caprolactam monomer aqueous solution is evaporated and concentrated to obtain a third caprolactam monomer aqueous solution;

[0012] The third caprolactam monomer aqueous solution is subjected to oligomer depolymerization treatment to obtain a fourth caprolactam monomer aqueous solution;

[0013] The fourth caprolactam monomer aqueous solution, fresh caprolactam monomer and matting agent are mixed and preheated, and then subjected to polymerization reaction to obtain matting nylon 6.

[0014] Furthermore, the method further comprises the following steps:

[0015] Collecting the extraction water and other aqueous solutions containing caprolactam monomers produced after the washed slices are stripped to obtain the caprolactam monomer aqueous solution to be recovered;

[0016] Wherein, the concentration of caprolactam monomer in the extraction water is 6 to 11% by weight;

[0017] In terms of weight percentage, the concentration of the caprolactam monomer in the other aqueous solution containing the caprolactam monomer is 0.6 to 3.5%;

[0018] The extraction water produced after the washed slices are stripped refers to the extraction aqueous solution formed by immersing the slices in water to extract the monomers in the slices into water; the other processes include filament pelletizing, slice drying and cation resin purification.

[0019] Furthermore, in terms of weight percentage, the concentration of caprolactam monomer in the first caprolactam monomer aqueous solution is 5-10%; the flocculant is a cationic polyacrylamide flocculant aqueous solution, and the weight percentage concentration of the cationic polyacrylamide flocculant aqueous solution is 1-5%; the added weight of the cationic polyacrylamide flocculant aqueous solution accounts for 0.01-0.05% of the weight of the caprolactam monomer aqueous solution to be recovered.

[0020] Furthermore, before filtering, the turbidity value of the aqueous solution of caprolactam monomer is 1.0 to 1.5 NTU; after filtering, the turbidity value of the aqueous solution of caprolactam monomer is 0.1 to 0.5 NTU;

[0021] The filtration process adopts a multi-media bed filter, which includes a first filter material layer, a second filter material layer, a third filter material layer and a fourth filter material layer from top to bottom. The property parameters of the filter material in the first filter material layer include: activated carbon, height 800mm, particle size 3.5-4.5mm; the property parameters of the filter material in the second filter material layer include: PP plastic, height 800mm, particle size 2.5-3.5mm; the property parameters of the filter material in the third filter material layer include: quartz sand, height 800mm, particle size 0.7-1.25mm;

[0022] The working condition parameters of the multi-media bed filter include: temperature 75-95°C, pressure 3.5-5.5 bar, and regeneration conditions: outlet water turbidity greater than 0.5 NTU or pressure difference before and after the filter greater than 0.5 bar.

[0023] Furthermore, before the ion exchange treatment, the conductivity value of the caprolactam monomer aqueous solution is ≥50 μs / cm; after the ion exchange treatment, the conductivity value of the caprolactam monomer aqueous solution is ≤10 μs / cm;

[0024] The ion exchange treatment uses a mixed bed ion exchanger containing anion resin and cationic resin, the filling amount of the anion resin in the mixed bed ion exchanger is 30-50% of the container volume, the filling amount of the cationic resin in the mixed bed ion exchanger is 20-40% of the container volume, and the flow rate of the caprolactam monomer aqueous solution in the mixed bed is 3-6 BV / h;

[0025] The working condition parameters of the ion exchange treatment include: temperature 80-100° C., pressure 3-5 bar, and regeneration conditions: outlet water conductivity greater than 10 μs / cm or pressure difference before and after the resin exchange bed greater than 0.5 bar.

[0026] Furthermore, the evaporation and concentration treatment includes sequentially using a first-stage falling film evaporator, a second-stage falling film evaporator and a third-stage falling film evaporator to perform step-by-step evaporation and concentration;

[0027] The working condition parameters of the one-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 15-25%, the temperature is 120-130° C., and the pressure is 2.0-3.0 bar;

[0028] The working condition parameters of the two-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 45-55%, the temperature is 110-120° C., and the pressure is 1.0-2.0 bar;

[0029] The working condition parameters of the three-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 65-85%, the temperature is 125-135° C., and the pressure is 2.0-3.0 bar.

[0030] Furthermore, the working condition parameters of the oligomer depolymerization treatment include: an operating temperature of 240 to 260° C. and an operating pressure of 20 to 30 bar.

[0031] Furthermore, the weight of the fresh caprolactam monomer accounts for 20-80% of the weight of the caprolactam monomer in the fourth caprolactam monomer aqueous solution; the weight of the matting agent accounts for 0.25-1.6% of the sum of the weight of the fresh caprolactam monomer and the weight of the caprolactam monomer in the fourth caprolactam monomer aqueous solution;

[0032] The matting agent is at least one of titanium dioxide and silane compounds.

[0033] Furthermore, the preheating temperature before the polymerization reaction is 150-180°C, and the working condition parameters of the polymerization reaction include: pre-polymerization temperature 240-260°C, pressure 0.10-0.15Mpa, residence time 4-8 hours, post-polymerization temperature 245-270°C, pressure -0.05-0.05Mpa, residence time 12-18 hours.

[0034] The above technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0035] The embodiment of the present invention provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, specifically a method for continuously synthesizing high-quality matte nylon 6 in large volume by fully recycling caprolactam monomer in the process of purifying, concentrating, depolymerizing and polymerizing an aqueous solution containing caprolactam. The method of the present invention for continuously producing high-quality matte nylon 6 in large volume by fully recycling caprolactam monomer in the process of purifying, concentrating, depolymerizing and polymerizing an aqueous solution containing caprolactam shortens the process flow from recycling to polymerization of caprolactam monomer, innovates the process route of fully recycling caprolactam monomer to produce high-quality matte nylon 6, improves the recovery rate of caprolactam monomer and the quality of finished products, and broadens the product types of the recycling production line. At the same time, this process method achieves energy saving and consumption reduction, waste emission reduction, and automation of process operation and control. Specifically, the salient features of the present invention are:

[0036] (1) Effectively extend the service life of the deep filter and reduce the cleaning frequency. Under the same production capacity conditions, the service life of the filter unit is extended by more than 5 times;

[0037] (2) The exchange rate of anion and cation exchange resins was significantly improved, with the exchange rate per cycle increased by more than 2.5 times and the resin life increased by more than 1.5 times;

[0038] (3) The technical shortcomings in the evaporation and concentration of monomer aqueous solution were effectively solved by using MVR evaporation and split chamber falling film evaporator equipment to achieve the goal of energy saving and consumption reduction and saving operating costs;

[0039] (4) The use of a high-pressure depolymerization reactor to depolymerize the oligomers not only improves the monomer recovery rate and the quality of the polymer product, but also shortens the processing process and reduces the production cost and environmental cost of the recovered monomers;

[0040] (5) An integrated automatic control system is used, in which the filtration system determines whether to backwash and regenerate based on the online turbidity meter, the anion and cation exchange system determines whether acid-base regeneration is required based on the conductivity of the effluent, and the online concentration meter automatically controls the discharge concentration to reduce human error and achieve overall layout, unified management, and automatic centralized control to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0043] Figure 1 A flow chart of a method for continuously producing matte nylon 6 by recycling caprolactam monomer provided by the present invention;

[0044] Figure 2 This is a schematic diagram of the process of recycling caprolactam monomer to produce high-quality matte nylon 6 in an embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of the actual operation process system for recycling caprolactam monomer to produce high-quality matte nylon 6 in an embodiment of the present invention;

[0046] Figure 3 In: 1-caprolactam aqueous solution, 2-flocculant, 3-monomer aqueous solution collecting tank, 4-multi-media bed filter, 5-turbidity meter, 6-cationic resin mixed bed, 7-conductivity meter, 8-first-stage falling film evaporator, 9-first-stage separator, 10-second-stage falling film evaporator, 11-second-stage separator, 12-third-stage falling film evaporator, 13-third-stage separator, 14-compressor, 15-concentration meter, 16-cracker, 17-pre-polymerization kettle, 18-post-polymerization kettle, 19-high polymer nylon 6. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0049] The present invention provides a method for recycling caprolactam monomer to continuously produce matte nylon 6. Figure 1 As shown, the method comprises the following steps:

[0050] adding a flocculant to the caprolactam monomer aqueous solution to be recovered for physicochemical treatment to obtain a first caprolactam monomer aqueous solution;

[0051] filtering and ion-exchanging the first aqueous caprolactam monomer solution to obtain a second aqueous caprolactam monomer solution;

[0052] The second caprolactam monomer aqueous solution is evaporated and concentrated to obtain a third caprolactam monomer aqueous solution;

[0053] The third caprolactam monomer aqueous solution is subjected to oligomer depolymerization treatment to obtain a fourth caprolactam monomer aqueous solution;

[0054] The fourth caprolactam monomer aqueous solution, fresh caprolactam monomer and matting agent are mixed and preheated, and then subjected to polymerization reaction to obtain matting nylon 6.

[0055] The embodiment of the present invention provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, specifically a method for continuously synthesizing high-quality matte nylon 6 in large volume by fully recycling caprolactam monomer in the process of purifying, concentrating, depolymerizing and polymerizing an aqueous solution containing caprolactam. The method of the present invention for continuously producing high-quality matte nylon 6 in large volume by fully recycling caprolactam monomer in the process of purifying, concentrating, depolymerizing and polymerizing an aqueous solution containing caprolactam shortens the process flow from recycling to polymerization of caprolactam monomer, innovates the process route of fully recycling caprolactam monomer to produce high-quality matte nylon 6, improves the recovery rate of caprolactam monomer and the quality of finished products, and broadens the product types of the recycling production line. At the same time, this process method achieves energy saving and consumption reduction, waste emission reduction, and automation of process operation and control. Specifically, the salient features of the present invention are:

[0056] (1) Effectively extend the service life of the deep filter and reduce the cleaning frequency. Under the same production capacity conditions, the service life of the filter unit is extended by more than 5 times;

[0057] (2) The exchange rate of anion and cation exchange resins was significantly improved, with the exchange rate per cycle increased by more than 2.5 times and the resin life increased by more than 1.5 times;

[0058] (3) The technical shortcomings in the evaporation and concentration of monomer aqueous solution were effectively solved by using MVR evaporation and split chamber falling film evaporator equipment to achieve the goal of energy saving and consumption reduction and saving operating costs;

[0059] (4) The use of a high-pressure depolymerization reactor to depolymerize the oligomers not only improves the monomer recovery rate and the quality of the polymer product, but also shortens the processing process and reduces the production cost and environmental cost of the recovered monomers;

[0060] (5) An integrated automatic control system is used, in which the filtration system determines whether to backwash and regenerate based on the online turbidity meter, the anion and cation exchange system determines whether acid-base regeneration is required based on the conductivity of the effluent, and the online concentration meter automatically controls the discharge concentration to reduce human error and achieve overall layout, unified management, and automatic centralized control to the greatest extent.

[0061] In some specific embodiments, Figure 2 As shown, the above method for recovering caprolactam monomer and continuously producing matte nylon 6 comprises the following steps:

[0062] a) Storage, mixing and flocculation of monomer aqueous solution: the extraction water produced after washing the slices and removing the monomers, with a concentration of 6-11%, and the aqueous solution containing caprolactam monomer produced in other processes, with a concentration of 0.6-3.5%, are collected in a monomer aqueous solution collection tank, and a flocculant is added under stirring for physical and chemical treatment, and the concentration of caprolactam monomer in the aqueous solution after mixing is finally 5-10%;

[0063] b) Removal of all flocculants, suspended solid particles, charged particles, groups and other impurities: (1) The collected, mixed and flocculated monomer aqueous solution is passed into a multi-media bed filter for step-by-step deep filtration to remove all flocculants and suspended solid particles and other impurities. The effluent from the multi-media bed filter is judged by an online turbidity meter to be qualified for backwashing and regeneration. The turbidity value of the monomer aqueous solution before filtration is 1.0-1.5 NTU, and the turbidity value after filtration is 0.1-0.5 NTU; (2) The monomer aqueous solution obtained in step (1) is passed through a mixed bed ion exchanger containing anion resin and cation resin to remove organic and inorganic charged particles, groups and other impurities. The effluent from the anion and cation resin exchange bed is judged by an online conductivity meter to be qualified for resin regeneration. The conductivity value of the monomer aqueous solution before ion exchange is ≥50 μs / cm, and the conductivity value after ion exchange is ≤10 μs / cm. The ion exchange resin is a macroporous resin, the anion resin product model is KIP214A, and the cation resin product model is KIP213A;

[0064] c) Evaporation and concentration of recovered monomer aqueous solution: the purified monomer aqueous solution obtained in step b) is preheated with secondary steam condensate and then enters the primary, secondary and tertiary falling film evaporators of the MVR system for gradual evaporation and concentration. The MVR compressor uses the secondary low-grade steam generated by the secondary and tertiary stages to pressurize and heat the steam to obtain high-grade, recyclable steam to heat the primary and tertiary falling film evaporators. The secondary steam generated by the primary falling film evaporator heats the secondary falling film evaporator, forming an efficient closed-loop steam system, wherein the secondary and tertiary falling film evaporators are split-chamber type high-efficiency energy-saving evaporators;

[0065] d) Depolymerization of oligomers in high-concentration monomer aqueous solution: The high-concentration monomer aqueous solution obtained in step c) is introduced into an existing cracker device, such as the cracker provided in the embodiment of the utility model patent "New cracker for nylon PA6 polymerization" with application number CN201020215410.5 obtained by the applicant, to depolymerize the oligomers, so that the oligomers are depolymerized into low-molecular caprolactam monomers, while reducing reaction by-products such as cyclic dimers and trimers, thereby obtaining a high-purity monomer concentrate;

[0066] e) Continuous, large-capacity polymerization of monomer concentrate: The high-purity monomer concentrate obtained in step d) is fed into existing polymerization equipment, such as the polymerization device provided in the embodiment of the applicant's invention patent "Continuous Polymerization Production Process for Nylon 6" with application number CN201010226541.8. The relatively high-purity recovered monomer concentrate is mixed with the new caprolactam monomer and the matting agent in a certain proportion and preheated, and then fed into a two-stage, continuous, large-capacity polymerization tube to synthesize high-quality matte nylon 6 polymer.

[0067] In some specific embodiments, the caprolactam monomer aqueous solution to be recovered mainly includes, by weight percentage: an extraction aqueous solution formed by immersing nylon 6 chips in water to extract the monomers in the chips into water, and a monomer-containing aqueous solution produced during the pelletization of nylon 6 filaments, chip drying, and purification of cation and anion resins.

[0068] In some specific embodiments, the concentration of the extracted water produced after washing the slices in step a is 6-11%, and the concentration of the aqueous solution containing caprolactam monomer produced in other processes is 0.6-3.5%. After mixing, the concentration of the caprolactam monomer in the aqueous solution is 5-10%.

[0069] In some specific embodiments, the flocculant added in step a is cationic polyacrylamide, the brand is FLOPAMFO4650, the concentration of the prepared aqueous solution is 1-5%, and the added mass accounts for 0.01-0.05% of the monomer aqueous solution.

[0070] In some specific embodiments, in step b, the multi-media bed filter comprises three layers of filter materials: upper, middle and lower; wherein, the upper filter material: activated carbon, height 800 mm, particle size 3.5-4.5 mm; the middle filter material: PP plastic, height 800 mm, particle size 2.5-3.5 mm; the lower filter material: quartz sand, height 800 mm, particle size 0.7-1.25 mm.

[0071] In some specific embodiments, in step b, the operating conditions of the multi-media bed filter are: temperature 75-95°C, pressure 3.5-5.5 bar, and regeneration conditions: effluent turbidity is greater than 0.5 NTU or the pressure difference before and after the filter is greater than 0.5 bar.

[0072] In some specific embodiments, in step b, the operating conditions of the anion and cation exchange resins are: temperature 80-100°C, pressure 3-5 bar, and regeneration conditions: effluent conductivity greater than 10 μs / cm or the pressure difference before and after the resin exchange bed is greater than 0.5 bar.

[0073] In some specific embodiments, in step c, the discharge of the first-stage falling film evaporator: concentration 15-25%, temperature 120-130°C, pressure 2.0-3.0 bar; the discharge of the second-stage falling film evaporator: concentration 45-55%, temperature 110-120°C, pressure 1.0-2.0 bar; the discharge of the third-stage falling film evaporator (automatically controlled by the online concentration meter to discharge): concentration 65-85%, temperature 125-135°C, pressure 2.0-3.0 bar.

[0074] In some specific embodiments, in step d, the operating temperature of the cracker is 240-260° C. and the operating pressure is 20-30 bar.

[0075] In some specific embodiments, in step e, the mass ratio of the neocaprolactam monomer to the recovered monomer is 20-80%; the mass ratio of the matting agent to the total recovered monomer is 0.25-1.6%.

[0076] In some specific embodiments, the actual operation process system for recycling caprolactam monomer to produce high-quality matte nylon 6 in the embodiments of the present invention is as follows Figure 3 As shown; Figure 3 In: 1-caprolactam aqueous solution, 2-flocculant, 3-monomer aqueous solution collecting tank, 4-multi-media bed filter, 5-turbidity meter, 6-cationic resin mixed bed, 7-conductivity meter, 8-first-stage falling film evaporator, 9-first-stage separator, 10-second-stage falling film evaporator, 11-second-stage separator, 12-third-stage falling film evaporator, 13-third-stage separator, 14-compressor, 15-concentration meter, 16-cracker, 17-pre-polymerization kettle, 18-post-polymerization kettle, 19-high polymer nylon 6.

[0077] Description of the entire material system: The monomer aqueous solution 1 produced in the entire process section is added to the monomer aqueous solution collection tank 3 together with the flocculant 2 for storage, mixing and flocculation; the monomer aqueous solution after mixing and flocculation passes through the multi-media bed filter 4 to remove all flocculants and suspended solid particles and other impurities, and the online turbidity meter 5 is used to judge whether the effluent of the multi-media bed filter is qualified and backwashed for regeneration; the monomer aqueous solution then passes through the mixed bed ion exchanger 6 where anion resin and cation resin exist to remove organic and inorganic charged particles, groups and other impurities, and the online conductivity meter 7 is used to judge whether the effluent of the anion and cation resin exchange bed is qualified and the resin is regenerated; the monomer aqueous solution enters the MVR evaporation device after purification, and is evaporated by the first-stage falling film evaporator 8, the second-stage falling film evaporator 10, and the third-stage falling film evaporator 12 for falling film evaporation. The gas and liquid are separated by the primary separator 9, the secondary separator 11 and the tertiary separator 13. The secondary steam generated by the primary separator provides heat to the secondary falling film evaporator. The low-quality secondary steam generated by the second and third separators is pressurized and heated by the compressor 14, and the high-quality steam generated provides heat to the primary and third falling film evaporators. Each effect performs falling film circulation evaporation through the bottom pump. The high-concentration monomer aqueous solution after evaporation and concentration is transported to the cracker 16 through the pump after being tested and qualified by the online concentration meter 15, and the polymer is depolymerized to obtain a high-purity monomer concentrate; the high-purity monomer concentrate and the fresh caprolactam monomer 20, as well as the matting agent 21, enter the pre-polymerization kettle 17 for preliminary polymerization; after the preliminary polymerization, it enters the post-polymerization kettle 18 to synthesize the polymer 19 nylon 6.

[0078] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0079] Example 1

[0080] This example provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, the method comprising the following steps:

[0081] (1) Monomer solution collection

[0082] The extracted water produced by washing nylon 6 slices with circulating water in the process of producing matte nylon 6 slices, with a concentration of 8.3%, and the monomer-containing dilute solution produced in other production processes, with a concentration of 1.3%, are collected together in a monomer solution collection tank for storage and mixing. After mixing and stabilization, the concentration of the monomer solution is 8.1%. At the same time, a flocculant with a concentration of 5% of the prepared aqueous solution is added, and the mass ratio of the monomer aqueous solution is 0.03%. The linear speed of the blade end of the stirrer is 3m / s to form a uniform and stable suspension.

[0083] (2) Multi-media bed filtration

[0084] The suspension obtained in step (1) is transported to a multi-media bed filter for deep filtration to remove all impurities such as flocculants and suspended solid particles. The turbidity value of the initial monomer aqueous solution before filtration is 1.2 NTU, and the turbidity value after filtration is 0.2 NTU;

[0085] (3) Anion exchange resin

[0086] The monomer aqueous solution obtained in step (2) is passed through an anion resin and a cation resin exchanger to remove impurities such as organic and inorganic charged particles and groups, wherein the anion resin is a macroporous resin, and the conductivity value of the initial monomer aqueous solution before ion exchange is 83 μs / cm, and the conductivity value after ion exchange is 4.0 μs / cm;

[0087] (4) MVR multi-stage evaporation concentration

[0088] The purified monomer aqueous solution obtained in step (3) is concentrated by MVR multi-stage falling film evaporation, with an initial concentration of 8.1% and concentrated to 80.2%, wherein the discharge of the first-stage falling film evaporator has a concentration of 17%, a temperature of 127°C, and a pressure of 2.5 bar; the discharge of the second-stage falling film evaporator has a concentration of 50.2%, a temperature of 117°C, and a pressure of 1.5 bar; and the discharge of the third-stage falling film evaporator has a concentration of 80.2%, a temperature of 128°C, and a pressure of 2.5 bar;

[0089] (5) Depolymerization and homogenization treatment of monomer concentrate

[0090] The concentrated monomer aqueous solution obtained in step (4) is fed into a cracker for depolymerization and homogenization treatment at an operating temperature of 250° C. and an operating pressure of 24 bar;

[0091] (6) Two-stage polymerization of monomer recovery

[0092] The high-purity, homogenized recovered monomer solution obtained in step (5) is mixed and preheated with fresh caprolactam monomer and a matting agent in a certain proportion, and then subjected to polymerization reaction to obtain matte nylon 6; wherein the mass ratio of new caprolactam monomer to recovered monomer is 60%, and the mass ratio of matting agent to total recovered monomer is 1.6%; the preheating temperature before the polymerization reaction is 160°C, and the working condition parameters of the polymerization reaction include: preferably a pre-polymerization temperature of 240-260°C, a pressure of 0.15Mpa, and a residence time of 6 hours, and a post-polymerization temperature of 245-270°C, a pressure of 0.01Mpa, and a residence time of 16 hours; the matting agent is preferably titanium dioxide.

[0093] After testing, the relative viscosity of the matte nylon 6 produced in this embodiment is 2.6.

[0094] Example 2

[0095] This example provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, the method comprising the following steps:

[0096] (1) Monomer solution collection

[0097] The extracted water produced by washing nylon 6 slices with circulating water in the process of producing matte nylon 6 slices, with a concentration of 9.3%, and the dilute monomer solution produced in other production processes, with a concentration of 1.1%, are collected together in a monomer solution collection tank for storage and mixing. After mixing and stabilization, the concentration of the monomer solution is 9.0%. At the same time, a flocculant with a concentration of 5% of the prepared aqueous solution is added, and the mass ratio of the monomer aqueous solution is 0.04%. The linear speed of the blade end of the stirrer is 4m / s to form a uniform and stable suspension.

[0098] (2) Multi-media bed filtration

[0099] The suspension obtained in step (1) is transported to a multi-media bed filter for deep filtration to remove all impurities such as flocculants and suspended solid particles. The turbidity value of the initial monomer aqueous solution before filtration is 1.3 NTU, and the turbidity value after filtration is 0.3 NTU;

[0100] (3) Anion exchange resin

[0101] The monomer aqueous solution obtained in step (2) is passed through an exchanger containing an anion resin and a cation resin to remove impurities such as organic and inorganic charged particles and groups. The conductivity value of the initial monomer aqueous solution before ion exchange is 88 μs / cm, and the conductivity value after ion exchange is 4.2 μs / cm;

[0102] (4) MVR multi-stage evaporation concentration

[0103] The purified monomer aqueous solution obtained in step (3) is concentrated by MVR multi-stage falling film evaporation, with an initial concentration of 9.0% and concentrated to 82.2%, wherein the discharge of the first-stage falling film evaporator is 19% in concentration, 129°C in temperature and 2.5 bar in pressure; the discharge of the second-stage falling film evaporator is 53.2% in concentration, 119°C in temperature and 1.5 bar in pressure; the discharge of the third-stage falling film evaporator is 82.2% in concentration, 131°C in temperature and 2.5 bar in pressure; (5) Depolymerization and homogenization of monomer concentrated solution The concentrated monomer aqueous solution obtained in step (4) is fed into a cracker for depolymerization and homogenization, with the operating temperature of the depolymerization being 250°C and the operating pressure being 24 bar;

[0104] (6) Two-stage polymerization of monomer recovery

[0105] The high-purity, homogenized recovered monomer solution obtained in step (5) is mixed and preheated with fresh caprolactam monomer and a matting agent in a certain proportion, and then subjected to polymerization reaction to obtain matte nylon 6, wherein the mass ratio of fresh caprolactam monomer to recovered monomer is 40%, the mass ratio of matting agent to total recovered monomer is 0.25%, the preheating temperature before the polymerization reaction is 160°C, and the working condition parameters of the polymerization reaction include: preferably a pre-polymerization temperature of 240-260°C, a pressure of 0.15Mpa, and a residence time of 6 hours, and a post-polymerization temperature of 245-270°C, a pressure of 0.01Mpa, and a residence time of 16 hours; the matting agent is preferably titanium dioxide.

[0106] After testing, the relative viscosity of the matte nylon 6 produced in this embodiment is 2.6.

[0107] Example 3

[0108] This example provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, the method comprising the following steps:

[0109] (1) Monomer solution collection

[0110] The extracted water produced by washing nylon 6 slices with circulating water in the process of producing matte nylon 6 slices, with a concentration of 10.1%, and the dilute monomer solution produced in other production processes, with a concentration of 1.0%, are collected together in a monomer solution collecting tank for storage and mixing. After mixing and stabilization, the concentration of the monomer solution is 9.8%. At the same time, a flocculant with a concentration of 5% of the prepared aqueous solution is added, and the added mass accounts for 0.05% of the monomer aqueous solution. The linear speed of the blade end of the stirrer is 5m / s to form a uniform and stable suspension.

[0111] (2) Multi-media bed filtration

[0112] The suspension obtained in step (1) is transported to a multi-media bed filter for deep filtration to remove all impurities such as flocculants and suspended solid particles. The turbidity value of the initial monomer aqueous solution before filtration is 1.3 NTU, and the turbidity value after filtration is 0.3 NTU. When the online turbidity meter determines that the turbidity value of the outlet water of the multi-media bed filter is greater than 0.5 NTU, the backwash regeneration process is started. The regeneration process uses 80° C. hot water for backwash regeneration, and the operating pressure is 4.5 bar;

[0113] (3) Anion exchange resin

[0114] The monomer aqueous solution obtained in step (2) is passed through an anion resin and a cation resin exchanger to remove impurities such as organic and inorganic charged particles and groups. The conductivity value of the initial monomer aqueous solution before ion exchange is 91 μs / cm, and the conductivity value after ion exchange is 5.2 μs / cm. When the online conductivity meter determines that the conductivity value of the effluent from the anion and cation resin exchange bed is greater than 10 μs / cm, the acid-base regeneration process is started. The temperature of the regenerated acid-base solution is 80° C., and the regeneration operation pressure is 4.0 bar.

[0115] (4) MVR multi-stage evaporation concentration

[0116] The purified monomer aqueous solution obtained in step (3) is concentrated by MVR multi-stage falling film evaporation, with an initial concentration of 9.8% and concentrated to 85.2%, wherein the discharge of the first-stage falling film evaporator has a concentration of 21%, a temperature of 131°C, and a pressure of 2.5 bar; the discharge of the second-stage falling film evaporator has a concentration of 55.2%, a temperature of 120°C, and a pressure of 1.5 bar; and the discharge of the third-stage falling film evaporator has a concentration of 85.2%, a temperature of 135°C, and a pressure of 2.5 bar;

[0117] (5) Depolymerization and homogenization treatment of monomer concentrate

[0118] The concentrated monomer aqueous solution obtained in step (4) is fed into a cracker for depolymerization and homogenization. The operating temperature for depolymerization is 250° C. and the operating pressure is 26 bar.

[0119] (6) Two-stage polymerization of monomer recovery

[0120] The high-purity, homogenized recovered monomer solution obtained in step (5) is mixed and preheated with fresh caprolactam monomer and a matting agent in a certain proportion, and then subjected to polymerization reaction to obtain matte nylon 6, wherein the mass ratio of new caprolactam monomer to recovered monomer is 20%, and the mass ratio of matting agent to total recovered monomer is 0.25%; the preheating temperature before the polymerization reaction is 160° C., and the working condition parameters of the polymerization reaction include: preferably a pre-polymerization temperature of 240-260° C., a pressure of 0.15 MPa, and a residence time of 6 hours, and a post-polymerization temperature of 245-270° C., a pressure of 0.01 MPa, and a residence time of 16 hours; and the matting agent is preferably titanium dioxide.

[0121] After testing, the relative viscosity of the matte nylon 6 produced in this embodiment is 2.6.

[0122] In summary, the embodiment of the present invention provides a method for recycling caprolactam monomer to continuously produce matte nylon 6, specifically a method for continuously synthesizing high-quality matte nylon 6 in large capacity by fully recycling caprolactam monomer from a caprolactam aqueous solution through purification, concentration, depolymerization and polymerization. The method of the present invention for continuously producing high-quality matte nylon 6 in large capacity by fully recycling caprolactam monomer from a caprolactam aqueous solution through purification, concentration, depolymerization and polymerization shortens the process flow from recycling to polymerization of caprolactam monomer, innovates the process route of fully recycling caprolactam monomer to produce high-quality matte nylon 6, improves the recovery rate of caprolactam monomer and the quality of finished products, and broadens the product types of the recycling production line. At the same time, this process method achieves energy saving and consumption reduction, waste reduction, and automation of process operation and control.

[0123] Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present invention; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0124] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for recovering caprolactam monomer and continuously producing matte nylon 6, characterized in that: The method comprises the following steps: adding a flocculant to the caprolactam monomer aqueous solution to be recovered for physicochemical treatment to obtain a first caprolactam monomer aqueous solution; filtering and ion-exchanging the first aqueous caprolactam monomer solution to obtain a second aqueous caprolactam monomer solution; The second caprolactam monomer aqueous solution is evaporated and concentrated to obtain a third caprolactam monomer aqueous solution; The third caprolactam monomer aqueous solution is subjected to oligomer depolymerization treatment to obtain a fourth caprolactam monomer aqueous solution; The fourth caprolactam monomer aqueous solution, fresh caprolactam monomer and matting agent are mixed and preheated, and then subjected to polymerization reaction to obtain matting nylon 6.

2. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: The method further comprises the following steps: Collecting the extraction water and other aqueous solutions containing caprolactam monomers produced after the washed slices are stripped to obtain the caprolactam monomer aqueous solution to be recovered; Wherein, the concentration of caprolactam monomer in the extraction water is 6 to 11% by weight; In terms of weight percentage, the concentration of the caprolactam monomer in the other aqueous solution containing the caprolactam monomer is 0.6-3.5%.

3. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: In terms of weight percentage, the concentration of caprolactam monomer in the first caprolactam monomer aqueous solution is 5-10%; the flocculant is a cationic polyacrylamide flocculant aqueous solution, and the weight percentage concentration of the cationic polyacrylamide flocculant aqueous solution is 1-5%; the added weight of the cationic polyacrylamide flocculant aqueous solution accounts for 0.01-0.05% of the weight of the caprolactam monomer aqueous solution to be recovered.

4. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: Before filtering, the turbidity value of the aqueous solution of caprolactam monomer is 1.0-1.5 NTU; after filtering, the turbidity value of the aqueous solution of caprolactam monomer is 0.1-0.5 NTU; The filtration process adopts a multi-media bed filter, which includes a first filter material layer, a second filter material layer, a third filter material layer and a fourth filter material layer from top to bottom. The property parameters of the filter material in the first filter material layer include: activated carbon, height 800mm, particle size 3.5-4.5mm; the property parameters of the filter material in the second filter material layer include: PP plastic, height 800mm, particle size 2.5-3.5mm; the property parameters of the filter material in the third filter material layer include: quartz sand, height 800mm, particle size 0.7-1.25mm; The working condition parameters of the multi-media bed filter include: temperature 75-95°C, pressure 3.5-5.5 bar, and regeneration conditions: outlet water turbidity greater than 0.5 NTU or pressure difference before and after the filter greater than 0.5 bar.

5. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: Before the ion exchange treatment, the conductivity value of the caprolactam monomer aqueous solution is ≥50μs / cm; after the ion exchange treatment, the conductivity value of the caprolactam monomer aqueous solution is ≤10μs / cm; The ion exchange treatment uses a mixed bed ion exchanger containing anion resin and cationic resin, the filling amount of the anion resin in the mixed bed ion exchanger is 30-50% of the container volume, the filling amount of the cationic resin in the mixed bed ion exchanger is 20-40% of the container volume, and the flow rate of the caprolactam monomer aqueous solution in the mixed bed is 3-6 BV / h; The working condition parameters of the ion exchange treatment include: temperature 80-100° C., pressure 3-5 bar, and regeneration conditions: outlet water conductivity greater than 10 μs / cm or pressure difference before and after the resin exchange bed greater than 0.5 bar.

6. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: The evaporation and concentration treatment includes sequentially using a first-stage falling film evaporator, a second-stage falling film evaporator and a third-stage falling film evaporator to perform gradual evaporation and concentration; The working condition parameters of the one-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 15-25%, the temperature is 120-130° C., and the pressure is 2.0-3.0 bar; The working condition parameters of the two-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 45-55%, the temperature is 110-120° C., and the pressure is 1.0-2.0 bar; The working condition parameters of the three-stage falling film evaporator include: the weight percentage concentration of the caprolactam monomer aqueous solution is 65-85%, the temperature is 125-135° C., and the pressure is 2.0-3.0 bar.

7. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: The working condition parameters of the oligomer depolymerization treatment include: an operating temperature of 240 to 260° C. and an operating pressure of 20 to 30 bar.

8. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 1, characterized in that: The weight of the fresh caprolactam monomer accounts for 20-80% of the weight of the caprolactam monomer in the fourth caprolactam monomer aqueous solution; the weight of the matting agent accounts for 0.25-1.6% of the sum of the weight of the fresh caprolactam monomer and the weight of the caprolactam monomer in the fourth caprolactam monomer aqueous solution; The matting agent is at least one of titanium dioxide and silane compounds.

9. The method for continuously producing matte nylon 6 by recycling caprolactam monomer according to claim 8, characterized in that: The preheating temperature before the polymerization reaction is 150-180°C, and the working condition parameters of the polymerization reaction include: pre-polymerization temperature 240-260°C, pressure 0.10-0.15Mpa, residence time 4-8 hours, post-polymerization temperature 245-270°C, pressure -0.05-0.05Mpa, residence time 12-18 hours.

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