Polymerization vessel for high viscosity PBT and method for preparing high viscosity PBT / low viscosity pet bicomponent elastic fibers by melt direct spinning

Abstract

A polymerization vessel for high viscosity PBT and a method for preparing high viscosity PBT / low viscosity PET bicomponent elastic fibers by melt direct spinning. The polymerization vessel (14) is provided with front and rear dual shafts (8), and multiple circular tray reactors (9) are arranged on said shafts; a plurality of homogenizers (20) are circumferentially arranged as spaced apart along the outer periphery of combination trays in a low viscosity zone. During the preparation of bicomponent elastic fibers, two production lines are used to separately produce a high viscosity PBT melt and a low viscosity PET melt, and then spinning is carried out. The high viscosity PBT production line comprises a first esterification vessel (10), a second esterification vessel (20), a first pre-polymerization vessel (12), a second pre-polymerization vessel (13), and a high viscosity PBT polymerization vessel (14); the low viscosity PET production line comprises a first esterification vessel (10), a second esterification vessel (20), a first pre-polymerization vessel (12), a second pre-polymerization vessel (13), and a low viscosity PET final polymerization vessel (14). By using the present method, low costs and high productivity are achieved, and the process is significantly shortened; the prepared elastic fibers have a fiber strength that may be 2.6-3.2 cN / dtex, a crimp contraction that may be 25-75%, and a crimp stability that may be 62-75%.

Description

Polymerization kettle for high-viscosity PBT and method for preparing melt-spun high-viscosity PBT / low-viscosity PET bicomponent elastic fiber Technical Field

[0001] The invention relates to a polymerization kettle for high-viscosity PBT and a method for preparing melt-spun high-viscosity PBT / low-viscosity PET bicomponent elastic fibers. Background Art

[0002] The application scope of elastic fibers in the modern chemical fiber industry is becoming wider and wider. Especially in recent years, with the rapid development of the theory of bicomponent elastic fibers, we have a deeper understanding of the forming mechanism and elasticity generation mechanism of parallel bicomponent elastic fibers, and the varieties of elastic fibers and original technologies have also made great progress. Starting in the 1970s, DuPont first launched single-component spandex elastic fiber, which quickly became popular in the market for its unique style and characteristics. In the late 1970s, it launched the two-component parallel elastic fiber T800, which uses PBT / PET parallel composite to produce good elastic effect. However, due to the low glass transition temperature (26-42°C) of the PBT component of PBT / PET elastic fiber, the fiber undergoes rapid crystallization under stress, and the elastic recovery rate and shape retention of T800 fiber are poor. In the 21st century, with the successful industrialization of PDO by chemical and biological fermentation methods, PTT polyester has a unique molecular structure and excellent elastic recovery properties. DuPont's T400, PTT / PET two-component elastic fiber, was launched. The PTT / PET two-component parallel composite fiber has excellent elastic recovery rate and shape retention. The fabric will not deform after repeated stretching. Its elastic sustained-release effect overcomes the restraining feeling of spandex elastic fiber. With its excellent resistance to chlorine bleaching and light exposure, it has become the best elastic fiber variety in the fabric industry.

[0003] The development of bicomponent elastic fibers has been a key area of ​​industry development over the past decade. The latest advances utilize the differing orientation and crystallization behaviors of PET polyester components of varying viscosity. During the spinning process, the high-viscosity and low-viscosity components undergo elastic curling due to the varying speeds and percentages of transition from the oriented state to the crystallized state, forming a spring-like structure that exhibits excellent elastic properties on the fabric. Patents such as CN111101237A, CN101126180A, CN106337212A, CN107964690A, CN101851812A, and CN115613159A disclose a series of PET / PET, PBT / PET, and PTT / PET composite elastic fibers and their preparation methods, as well as methods for preparing easily or deeply dyed elastic fibers using modified PET fibers with retained elasticity, such as high-viscosity ECDP, high-viscosity high-shrinkage polyester, high-viscosity disperse dye-friendly polyester, and high-viscosity CDP cationic polyester, with low-viscosity PET polyester.

[0004] The preparation methods of the above-mentioned elastic fibers are all based on a chip spinning production process in which high-viscosity chips and low-viscosity chips are pre-crystallized and melted by a drying screw, and then formed into a composite spinning box and a composite parallel spinneret. Although this process solves the basic technical problems of parallel composite spinning, the chip spinning technology has obvious defects such as a long process, high cost, low production capacity, and poor product quality stability.

[0005] PBT / PET bicomponent composite elastic fibers offer moderate elasticity, a low price, and excellent clothing comfort. Their cost is only half that of PTT / PET bicomponent fibers, while their crimp shrinkage is significantly higher than that of composite elastic fibers like PET / PET. Combined with their stress-relieving properties, these fibers have promising market applications. While their crimp stability is inferior to that of PTT / PET elastic fibers, their stability meets the requirements for rapid fashion changes, thus offering broad application prospects. However, the crimp shrinkage, crimp stability, and quality stability of existing PBT / PET bicomponent fibers are insufficient, leaving significant room for improvement. Furthermore, during the synthesis of PBT, the dehydration and cyclization of the 1,4-butanediol raw material in the polymerization system produces a large amount of tetrahydrofuran as a byproduct. This byproduct significantly impacts both the polymerization system and the resulting PBT product. Controlling the content of this byproduct is a key challenge in the PBT synthesis process.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a high-viscosity PBT polymerization kettle, which is used to prepare a high-viscosity PBT melt. The high-viscosity PBT melt prepared by the polymerization kettle has a very high viscosity. When it is used to prepare melt-spun high-viscosity PBT / low-viscosity PET two-component elastic fiber, the performance of the fiber can be significantly improved.

[0008] The present invention aims to provide a melt-spun high-viscosity PBT / low-viscosity PET bicomponent elastic fiber, which has significantly improved curl shrinkage, curl stability and quality stability.

[0009] Another object of the present invention is to provide a method for preparing melt-spun high-viscosity PBT / low-viscosity PET bicomponent elastic fibers, which has significantly reduced costs, high production capacity, and a significantly shortened process flow. The curl shrinkage rate, curl stability, and quality stability of the prepared elastic fibers are significantly improved.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A high-viscosity PBT polymerization kettle, which is used to prepare a high-viscosity PBT melt, wherein the high-viscosity PBT melt is used to prepare a high-viscosity PBT / low-viscosity PET two-component elastic fiber. The high-viscosity PBT polymerization kettle is a horizontal polymerization kettle and includes a main body containing a chamber inside. The main body includes a low-viscosity area, a medium-high-viscosity area, and a high-viscosity area arranged in sequence along the axial direction of the high-viscosity PBT polymerization kettle. The viscosity of the PBT melt in the low-viscosity area, the medium-high-viscosity area, and the high-viscosity area increases in sequence. The high-viscosity PBT polymerization kettle also includes two stirring shafts, one of which is arranged at the low-viscosity area. The stirring shaft is arranged in the low viscosity zone and part of the medium and high viscosity zone, and the other stirring shaft is arranged in the high viscosity zone and the remaining medium and high viscosity zones; a plurality of disc reactors are arranged on the two stirring shafts, the disc reactor in the low viscosity zone is a 3-10-piece combination disc; the disc reactor in the medium and high viscosity zone is a double-piece combination disc; the disc reactor in the high viscosity zone is a single disc; a plurality of homogenizers are arranged at intervals along the outer edge of each group of combination discs in the low viscosity zone of the PBT high viscosity final polymerization kettle, and the homogenizers extend along the axial direction of the high viscosity PBT polymerization kettle and are used to hang the PBT melt in the low viscosity zone on the surface of the disc reactor.

[0012] By adopting this setting, the devolatilization efficiency in the low-viscosity zone (front chamber) can be improved by 20% to 35%. When the characteristic viscosity of the inlet position of the medium-high viscosity zone and the high-viscosity zone (back chamber) is determined, the length of the front chamber can be shortened by 18% to 28% compared with the conventional disc reactor, the full volume of the high-viscosity PBT polymerization kettle can be reduced by 15% to 20%, the material residence time can be reduced by 15% to 20%, the material mixing is more uniform, and the product quality is effectively improved.

[0013] In the present invention, a composite disc refers to two or more adjacent disc reactors fixedly connected together to form a composite disc. The disc reactor can be a conventional disc reactor used in polyester synthesis. For example, the disc reactor includes a central circular hollow portion and an annular reactor portion around the outer edge of the hollow portion, wherein the reactor portion is provided with multiple sieve holes.

[0014] In some embodiments, the cross section of the homogenizer is wedge-shaped; the thick end of the wedge faces the rotation direction of the disc reactor.

[0015] In some embodiments, the number of the homogenizers is 8 to 12.

[0016] In some embodiments, the homogenizers are evenly distributed along the circumference of the disc reactor.

[0017] The present invention adopts the above-mentioned homogenizer setting, combined with a special melt material flow channel design, to achieve an enhanced mixing effect in the bottom material area, push more material to a higher position along the rotation direction, increase the residence time of the material on the disc reactor, and improve the devolatilization efficiency of the disc reactor.

[0018] In some embodiments, the total number of disc reactors in the low viscosity zone is 25-35, the total number of disc reactors in the medium-high viscosity zone and the high viscosity zone is 20-30, and the total number of disc reactors in the high viscosity zone is 8-12.

[0019] In some embodiments, the length of the low viscosity zone is half the length of the high viscosity PBT polymerization kettle, the total length of the medium-high viscosity zone and the high viscosity zone is half the length of the high viscosity PBT polymerization kettle; the ratio of the length of the medium-high viscosity zone to the high viscosity zone is 2:1.

[0020] In some embodiments, the length of the stirring shaft arranged in the low viscosity zone and part of the medium and high viscosity zone is two-thirds of the length of the high viscosity PBT polymerization kettle, and the length of the stirring shaft arranged in the high viscosity zone and the remaining medium and high viscosity zone is one-third of the length of the high viscosity PBT polymerization kettle.

[0021] In the present invention, one half, two thirds, and one third are not the exact mathematical values ​​of one half, two thirds, and one third, but refer to values ​​approximately between one half, two thirds, and one third, and approximately equal to one half, two thirds, and one third.

[0022] In some embodiments, the high-viscosity PBT polymerization kettle further includes a prepolymer inlet located at the bottom of the front end of the low-viscosity zone and a high-viscosity PBT melt outlet located at the bottom of the rear end of the high-viscosity zone, and the high-viscosity PBT melt outlet is in a bell-mouth shape.

[0023] In some embodiments, the spacing between the two discs in the medium- and high-viscosity zones, as well as between the discs themselves, gradually increases from front to back. The diameter of the disc reactors in the high-viscosity zone decreases from front to back, with the diameter of the last disc reactor in the high-viscosity zone being 88%-92% of the diameter of the first. The high-viscosity zone is also equipped with composite scrapers, including an axial scraper for scraping melt from the stirring shaft, a wall scraper for scraping melt from the inner wall of the high-viscosity PBT polymerizer, a disc scraper for scraping melt from the disc reactor, and a bottom scraper. The disc scrapers are arranged in two layers, controlling the material thickness on the disc reactor to no more than 30 mm. This scraper arrangement allows for the membrane rupture of high-viscosity materials on the discs and allows for efficient mixing with fresh, low-viscosity materials. One layer of the scrapers ensures effective separation of the high-viscosity materials, while the other layer controls the material thickness on the discs. This effectively controls the separation of the high-viscosity melt after scraping, and the material thickness on the two disc reactors is kept below 30 mm, preferably 10-30 mm.

[0024] In some embodiments, the aspect ratio of the high-viscosity PBT polymerization kettle is 3.0 to 3.6:1.0. This high aspect ratio is conducive to distributing more disc reactors to increase the effective devolatilization area and improve the vacuum degree of the reactor, thereby increasing the viscosity of the PBT melt and reducing the level of side reactions. It can also be combined with a high vacuum design to quickly increase the viscosity of the high-viscosity PBT melt.

[0025] In some embodiments, the stirring shafts are respectively fixed to fixed seats at the front and rear ends of the high-viscosity PBT polymerization kettle. In addition, a support seat for supporting two stirring shafts can be fixed to the inner wall of the main body in the middle of the final polymerization kettle. The rear end of the stirring shaft located in the low-viscosity zone and part of the medium-high viscosity zone is fixed to the support seat, while the front end of the stirring shaft located in the high-viscosity zone and the remaining medium-high viscosity zone is fixed to the support seat.

[0026] The present invention also provides a method for preparing a high-viscosity PBT / low-viscosity PET bicomponent elastic fiber using the aforementioned high-viscosity PBT polymerization kettle, wherein the bicomponent elastic fiber contains a high-viscosity PBT component and a low-viscosity PET component, the viscosity of the high-viscosity PBT component being greater than the viscosity of the low-viscosity PET component, and the preparation method comprises the steps of separately preparing a high-viscosity PBT melt and a low-viscosity PET melt, and spinning the high-viscosity PBT melt and the low-viscosity PET melt through the same parallel composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PBT melt is greater than the viscosity of the low-viscosity PET melt; the step of preparing the high-viscosity PBT melt comprises sequentially passing terephthalic acid and 1,4-butanediol through a first esterification kettle, The second esterification kettle carries out esterification reaction, the first prepolymerization kettle and the second prepolymerization kettle carry out prepolymerization reaction to obtain PBT prepolymer, and the PBT prepolymer is polymerized in the aforementioned high-viscosity PBT polymerization kettle to obtain the high-viscosity PBT melt; the step of preparing the low-viscosity PET melt includes the steps of sequentially passing terephthalic acid and ethylene glycol through the first esterification kettle and the second esterification kettle for esterification reaction, the first prepolymerization kettle and the second prepolymerization kettle for prepolymerization reaction to obtain PET prepolymer, and the PET prepolymer is polymerized in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

[0027] In the present invention, PBT refers to poly(1,4-butylene terephthalate), and PET refers to polyethylene terephthalate.

[0028] The high-viscosity PBT / low-viscosity PET bicomponent elastic fiber of the present invention comprises a high-viscosity and a low-viscosity bicomponent. The high-viscosity PBT / low-viscosity PET bicomponent elastic fiber is prepared by a melt-spinning method, whereby the melt obtained from polymerization is directly used for spinning, without undergoing the melt cooling and slicing steps before remelting and spinning.

[0029] In some embodiments, the bicomponent elastic fiber contains 30% to 70% of a high-viscosity PBT component and 70% to 30% of a low-viscosity PET component.

[0030] In some embodiments, the high-viscosity PBT melt has an intrinsic viscosity of 0.98 to 1.20 and a dynamic viscosity of 225 to 615 Pa.s; the low-viscosity PET melt has an intrinsic viscosity of 0.45 to 0.55 and a dynamic viscosity of 90 to 240 Pa.s.

[0031] In some embodiments, the high-viscosity PBT melt has an intrinsic viscosity of 0.95 to 1.10 and a dynamic viscosity of 430 to 900 Pa·s.

[0032] In some embodiments, the high-viscosity PBT melt has an intrinsic viscosity of 0.97 to 1.05 and a dynamic viscosity of 500 to 750 Pa·s.

[0033] In some embodiments, in the same parallel composite spinning assembly, the high-viscosity PBT melt has a dynamic viscosity of 200 to 520 Pa.s, and the low-viscosity PET melt has a dynamic viscosity of 70 to 220 Pa.s. This indicates that the high-viscosity PBT melt of the present invention experiences a minimal viscosity drop upon reaching the spinning assembly after being transported.

[0034] In the present invention, the intrinsic viscosity is the result of measurement in a mixed solvent of phenol and tetrachloroethane at a volume ratio of 3:2.

[0035] In some embodiments, when preparing a high-viscosity PBT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before the esterification reaction. The esterification catalyst is selected from tetrabutyl titanate, tetraisopropyl titanate, or tetra(2-ethylhexyloxy) titanate. Tetra(2-ethylhexyloxy) titanate is preferred because it is less susceptible to hydrolysis and more stable, thereby facilitating stable polymerization of PBT.

[0036] In some embodiments, the esterification reaction in the first esterification kettle for preparing the high-viscosity PBT melt is carried out at a pressure of 40 to 60 kPa.

[0037] In some embodiments, the esterification reaction in the second esterification kettle for preparing the high-viscosity PBT melt is carried out under normal pressure.

[0038] In some embodiments, the second esterification kettle used to prepare the high-viscosity PBT melt is a horizontal reactor and includes three chambers arranged in sequence front to back. When preparing the high-viscosity PBT melt, the preparation method further includes the step of adding a side reaction inhibitor to the first chamber from the front to the back of the second esterification kettle, and the side reaction inhibitor is a Lewis base.

[0039] In some embodiments, the Lewis base is selected from a combination of one or more of triethanolamine, quaternary ammonium salts, ethylenediaminetetraacetic acid, sodium acetate, sodium benzoate, sodium formate, potassium succinate, lithium acetate, and zinc acetate.

[0040] In some embodiments, the mass of the Lewis base is 30 to 300 ppm based on the mass of the high-viscosity PBT melt.

[0041] In some embodiments, the mass of the Lewis base is 75 to 240 ppm based on the mass of the high-viscosity PBT melt.

[0042] In some embodiments, the mass of the Lewis base is 100 to 160 ppm based on the mass of the high-viscosity PBT melt.

[0043] In some embodiments, the first esterification kettle and the second esterification kettle for preparing high-viscosity PBT melt are both provided with distillation towers at their upper ends, and the preparation method further includes the steps of extracting a mixture of water and tetrahydrofuran from the tops of the two distillation towers and extracting 1,4-butanediol from the bottoms of the towers.

[0044] Preferably, the preparation method further comprises the step of separating the mixture of water and tetrahydrofuran by three-tower distillation to obtain pure tetrahydrofuran.

[0045] Preferably, the preparation method further comprises the step of recovering the extracted 1,4-butanediol.

[0046] Preferably, the distillation tower is made of SUS316L.

[0047] The process tower provided on the first esterification kettle of the present invention adopts a reduced pressure design. The first esterification kettle is a reduced pressure esterification kettle, and its operating pressure is controlled at 40-60 kPa (absolute pressure). The top of the tower is equipped with a by-product reflux system, a production system (esterified water+tetrahydrofuran) and a liquid ring vacuum pump. The second esterification kettle is a multi-chamber normal pressure design and a separately designed rectification tower. A side reaction inhibitor is injected into the first subchamber of the second esterification kettle. The inhibitor is a Lewis base. The inhibitor improves the pH value environment of the second esterification kettle under weakly acidic conditions and suppresses the reaction degree of etherification reaction of 1,4-butanediol raw material to generate tetrahydrofuran. The comprehensive effect can effectively reduce the amount of tetrahydrofuran generated by 15%-20%.

[0048] In some embodiments, a distillation column is installed at the top of each of the first and second esterification reactors used to prepare a high-viscosity PBT melt. The preparation method further includes the step of recovering 1,4-butanediol from the bottom of the distillation column. This recovery can be performed using a specialized recovery device. After recovery, impurities in the 1,4-butanediol are removed and the 1,4-butanediol is refined. The refined 1,4-butanediol can be added back to the raw material slurrying system for subsequent esterification and polymerization reactions.

[0049] Preferably, the distillation tower at the upper end of the second esterification kettle is arranged in the third sub-chamber from the front to the back of the second esterification kettle.

[0050] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.280 to 0.350.

[0051] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.290 to 0.325.

[0052] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.295 to 0.310.

[0053] In some embodiments, when preparing a high-viscosity PBT melt, the preparation method further includes the step of injecting a polymerization catalyst into the third sub-chamber from the front to the rear of the second esterification kettle.

[0054] In some embodiments, the polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the resultant in 1,4-butanediol.

[0055] In some embodiments, the titanate is selected from tetrabutyl titanate, tetraisopropyl titanate, or tetra(2-ethylhexyloxy) titanate.

[0056] In some embodiments, the protonic acid is selected from a combination of one or more of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid, and polyphosphoric acid.

[0057] In some embodiments, the mass ratio of the titanate to the protonic acid is 1:0.5-2.0.

[0058] In some embodiments, the mass percentage of titanium element in the polymerization catalyst is 1.0%-3.0%.

[0059] In some embodiments, the mass of the titanium element in the esterification catalyst accounts for 30 to 40 ppm of the mass of the high-viscosity PBT melt.

[0060] In some embodiments, the mass of the titanium element in the polymerization catalyst accounts for 30 to 80 ppm of the mass of the high-viscosity PBT melt.

[0061] In some embodiments, when used to prepare a high-viscosity PBT melt, the preparation method further includes the step of introducing a heat stabilizer, an antioxidant, or a colorant into the second esterification kettle before conducting the second esterification reaction; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

[0062] In some embodiments, the amount of the heat stabilizer or antioxidant is 30 to 300 ppm based on the total mass of the high-viscosity PBT melt.

[0063] To ensure the high-viscosity PBT melt's excellent resistance to heat and thermal-oxidative degradation during esterification and polymerization melt transport, a thermal stabilizer and antioxidant are compounded. To enhance the stability of the high-viscosity PBT melt, these additives can be added to improve the melt's thermal stability and oxidation resistance, respectively. These thermal stabilizers and antioxidants are added to control the level of polymerization side reactions under high-temperature conditions. The antioxidant further reduces the risk of thermal degradation during melt transport caused by trace oxygen.

[0064] Thermal stabilizers and antioxidants are beneficial to reducing the viscosity drop level during the melt conveying process. For high-viscosity PBT melt conveying process, the pipeline residence time is 30 to 40 minutes, and the viscosity drop of high-viscosity PBT melt is effectively controlled between 0.050 and 0.105. The more optimized viscosity drop level is 0.075 to 0.095. Combined with the short-process melt conveying design, the optimal viscosity drop is 0.085 to 0.090. Compared with the existing viscosity drop of 0.150 to 0.235 of thickened high-viscosity PBT polyester, it can greatly reduce the original intrinsic viscosity of the melt and effectively improve product quality.

[0065] In some embodiments, the high-viscosity PBT polymerization kettle further includes steam inlets for introducing superheated 1,4-butanediol vapor, located at the top of the main body in the middle of the medium-high viscosity zone, at the rear end of the medium-high viscosity zone, and at the rear end of the high viscosity zone. The preparation method further includes the step of metering the superheated 1,4-butanediol vapor using a metering system and introducing it into the high-viscosity PBT polymerization kettle. This serves to form a gel-like crosslinked carbonization at the upper rear end of the high-viscosity PBT polymerization kettle after a period of operation. The 1,4-butanediol vapor inlet facilitates regular cleaning of the entire polymerization apparatus without stopping the entire apparatus (no downtime), thereby maintaining the apparatus's long-term operational capability.

[0066] In some embodiments, the high-viscosity PBT polymerization kettle is connected to a vacuum pump with a maximum vacuum level of 60-75 Pa. The preparation method controls the vacuum pump's suction capacity to 85-230 kg / h, and the vacuum level within the high-viscosity PBT polymerization kettle to 90-150 Pa. The vacuum pump's suction capacity can meet a production capacity of 30,000-100,000 tons / year.

[0067] According to experimental research data, the amount of volatile matter generated in a high-viscosity (intrinsic viscosity of 1.05-1.16) PBT final polymerization kettle is 1.5-2.2 times that of a conventional PBT polyester unit with a viscosity level of 0.92 (intrinsic viscosity). The higher the high-viscosity outlet viscosity, the higher the amount of non-condensable gas generated. Therefore, the vacuum pump exhaust design is 1.5-2.5 times that of a conventional polyester unit of the same production capacity. The vacuum pump exhaust capacity is based on the production capacity of 30,000-100,000 tons / year, and the selection range is 70-220kg / h. The vacuum system design of the unit takes into account the harmful effects of acrolein and allyl alcohol and adopts a fully enclosed design. A wastewater and exhaust gas neutralization device is also designed, and the wastewater and exhaust gas are sent to the stripping tower for treatment to meet emission standards.

[0068] In some embodiments, a melt pump is used to transport high-viscosity PBT melt and low-viscosity PET melt, and a melt cooler is provided at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PBT melt to 252-253°C after cooling by the melt cooler; a filter and a booster pump are provided between the melt pump and the parallel composite spinning assembly; the preparation method controls the transport time of the high-viscosity PBT melt to 30-40 minutes.

[0069] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization vessel is 0.280 to 0.350. This range effectively reduces the overall material loading on the polymerization vessel plate, optimizes material residence time, significantly reduces the reaction level in the polymerization vessel, and, in combination with thermal stabilizers and thermal oxygen stabilizers, minimizes the generation of non-condensable gases.

[0070] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.290 to 0.325.

[0071] In some embodiments, the intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.295 to 0.310.

[0072] In some embodiments, the low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its aspect ratio is 2.2-2.8:1.0.

[0073] In some embodiments, the preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PBT melt before the high-viscosity PBT melt passes through the filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, atmospheric pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, and polypropylene terephthalate PBT.

[0074] Furthermore, the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt, preferably 0.5 to 2.0%, and more preferably 0.8 to 1.5%. Adding the viscosity reducer can significantly reduce the kinematic viscosity of the high-viscosity melt, improve the melt conveying efficiency, and reduce process degradation.

[0075] In some embodiments, the molar ratio of terephthalic acid to 1,4-butanediol is 1:1.05-1.65.

[0076] In some embodiments, the esterification reaction in the first esterification kettle for preparing the high-viscosity PBT melt is carried out at 245°C to 247°C.

[0077] In some embodiments, when used to prepare a high-viscosity PBT melt, the esterification reaction in the second esterification kettle is carried out at 248° C. to 252° C.

[0078] In some embodiments, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at 250°C to 252°C.

[0079] In some embodiments, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at a pressure of 7 to 102 kPa.

[0080] In some embodiments, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at 251°C to 252°C.

[0081] In some embodiments, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at a pressure of 0.5 to 1.5 kPa.

[0082] In some embodiments, the same spinning assembly is a composite spinning beam.

[0083] In some embodiments, the composite spinning beam includes a composite spinneret.

[0084] The present invention also provides a high-viscosity PBT / low-viscosity PET two-component elastic fiber prepared by the above preparation method.

[0085] In some embodiments, the bicomponent elastic fiber has a strength of 2.6 to 3.2 cN / dtex, a crimp shrinkage of 25% to 75%, and a crimp stability of 82% to 90%.

[0086] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0087] The high-viscosity PBT polymerization kettle of the present invention adopts an unconventional disc reactor design. The front chamber (low-viscosity zone) adopts a combined disc design and a split homogenizer is designed on the outer edge of the disc group. The rear chamber (medium-high viscosity zone and high viscosity zone) adopts a combined disc combined with a single disc and a composite scraper design. This can achieve the slow release of the material in the low-viscosity zone - hanging on the surface of the disc reactor, greatly improving the viscosity of the high-viscosity PBT melt, effectively reducing the level of side reactions during the polymerization of high-viscosity PBT, and ultimately achieving significant improvements in various properties of the two-component elastic fiber.

[0088] The present invention utilizes two different polyester production lines to produce high-viscosity PBT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PBT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-direct spinning high-viscosity PBT / low-viscosity PET parallel elastic fibers.

[0089] In the present invention, a special polymerization catalyst is adopted. The polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the catalyst in 1,4-butanediol. The polymerization catalyst does not contain a Ti-OH group. The catalyst can significantly inhibit the hydrolysis of ordinary titanium-based catalysts in the polymerization stage, and further significantly inhibit the occurrence of side reactions in the polymerization stage, which is beneficial to improving the high-viscosity PBT melt performance and the final two-component elastic fiber performance.

[0090] In the present invention, the intrinsic viscosity of the high-viscosity PBT melt can reach 0.98-1.20, and the intrinsic viscosity of the low-viscosity PET melt is 0.45-0.55. The viscosity of the high-viscosity PBT melt is much higher than that of the prior art.

[0091] The bicomponent elastic fiber of the present invention has a strength of 2.6 to 3.0 cN / dtex, a crimp shrinkage of 20 to 55 percent, and a crimp stability of 62 to 75 percent, far exceeding the performance of existing bicomponent elastic fibers. The bicomponent elastic fiber of the present invention can be in various varieties, including FDY, POY, and DTY.

[0092] The preparation method of the present invention is used for industrial production of two-component elastic fibers, which can achieve a low-viscosity PET melt production capacity of 30,000 to 80,000 tons / year and a high-viscosity PBT melt production capacity of 30,000 to 80,000 tons / year. When the product is melt-spun high-viscosity PBT / low-viscosity PET two-component elastic fiber, the comprehensive device production capacity is 60,000 to 160,000 tons / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] FIG1 is a schematic diagram of a two-line polymerization system used in the embodiment;

[0094] FIG2 is a schematic structural diagram of a combined tray in a low viscosity zone of a high viscosity PBT polymerization kettle used in the embodiment;

[0095] FIG3 is a schematic cross-sectional view of a composite tray in a low-viscosity zone of a high-viscosity PBT polymerization kettle used in the examples;

[0096] FIG4 is a schematic structural diagram of a high-viscosity PBT polymerization kettle used in the examples;

[0097] FIG5 is a schematic structural diagram of a composite scraper in a high-viscosity PBT polymerization reactor used in the embodiment;

[0098] Among them, 1- low viscosity zone, 2- medium and high viscosity zone, 3- high viscosity zone, 4- composite scraper, 5- disk scraper, 6- axial scraper, 7- wall scraper, 8- stirring shaft, 9- disc reactor, 10- first esterification kettle, 11- second esterification kettle, 12- first prepolymerization kettle, 13- second prepolymerization kettle, 14- high viscosity PBT polymerization kettle, 15- low viscosity PET final polymerization kettle, 16- melt pump, 17- prepolymer inlet, 18- high viscosity PBT melt outlet, 19- steam feed port, 20- homogenizer, 21- support seat, 22- sieve hole. DETAILED DESCRIPTION

[0099] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the basic principles, main features, and advantages of the present invention, and the present invention is not limited in scope by the following examples. The implementation conditions used in the examples can be further adjusted according to specific requirements. The implementation conditions not specified are generally those used in routine experiments. Unless otherwise specified in the following examples, all raw materials were purchased commercially or prepared by conventional methods in the art.

[0100] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

[0101] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments of the present invention. In the following embodiments, it should be noted that the "front" and "rear" directions in the terms are based on the flow direction of the material, and the direction in which the material flows first is the front, and the direction in which the material flows later is the rear. For example, in Figure 1, the "front" in the term refers to the left side in Figure 1, and the "rear" in the term refers to the right side in Figure 1. For example, in Figure 4, the "front" in the term refers to the right side in Figure 1, and the "rear" in the term refers to the left side in Figure 1. Therefore, the directions and positional relationships described in the present invention are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, only have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation of the present invention.

[0102] As shown in FIG1 , when preparing high-viscosity PBT / low-viscosity PET two-component elastic fibers in the embodiment, two production lines are used. The first production line prepares a high-viscosity PBT melt. As shown in the first row of FIG1 , the production line includes a five-reactor device system consisting of a first esterification reactor 10, a second esterification reactor 11, a first prepolymerization reactor 12, a second prepolymerization reactor 13, and a high-viscosity PBT polymerization reactor 14. The five reactors are connected by necessary pipelines, and necessary vacuum systems, etc. are connected to the five reactors. Among them, a melt pump 16 and filters A and B are provided between the second prepolymerization reactor 13 and the high-viscosity PBT polymerization reactor 14. In the actual production process, filters A and B are not turned on at the same time. For example, filter A can be turned on first, and after the device has been running for a period of time, filter B can be switched to use. At this time, filter A can be cleaned.

[0103] The second production line produces low-viscosity PET melt, as shown in the second row of Figure 1. This line comprises a five-vessel system: a first esterification vessel 10, a second esterification vessel 11, a first prepolymerization vessel 12, a second prepolymerization vessel 13, and a low-viscosity PET final polymerization vessel 15. The five vessels are interconnected by necessary piping and are connected to the necessary vacuum systems. A melt pump 16 and filters A and B are located between the second prepolymerization vessel 13 and the low-viscosity PET final polymerization vessel 15. In actual production, filters A and B are not operated simultaneously. For example, filter A can be activated first, and after a period of operation, filter B can be switched to the system, allowing filter A to be cleaned.

[0104] As shown in Figure 1, the second esterification reactor 11, used to prepare a high-viscosity PBT melt, is a horizontal reactor comprising three compartments arranged in a tandem arrangement. Both the first and second esterification reactors 10, 11, used to prepare a high-viscosity PBT melt, are equipped with distillation towers at their tops. Each tower features a water and tetrahydrofuran (THF) mixture recovery system, which can be connected to a three-tower distillation recovery system to purify and recover the THF.

[0105] As for the high-viscosity PBT polymerization kettle 14, as shown in Figure 4, it is also a horizontal polymerization kettle and includes a main body containing a chamber inside. The main body includes a low-viscosity zone 1, a medium-high-viscosity zone 2, and a high-viscosity zone 3 arranged in sequence along the axial direction of the high-viscosity PBT polymerization kettle 14. The viscosity of the PBT melt in the low-viscosity zone 1, the medium-high-viscosity zone 2, and the high-viscosity zone 3 increases in sequence; the high-viscosity PBT polymerization kettle 14 also includes two stirring shafts 8, one of which is arranged in the low-viscosity zone 1 and part of the medium-high-viscosity zone 2, and the other stirring shaft 8 is arranged in the high-viscosity zone 3 and the remaining medium-high-viscosity zone 2.

[0106] Multiple disc reactors 9 are mounted on both agitator shafts 8. The disc reactors 9 in the low-viscosity zone 1 consist of 3-10 discs; the disc reactors 9 in the medium-high viscosity zone 2 consist of two discs; and the disc reactors 9 in the high-viscosity zone 3 consist of a single disc. The total number of disc reactors 9 in the low-viscosity zone 1 is 25-35, the total number of disc reactors 9 in the medium-high viscosity zone 2 and the high-viscosity zone 3 is 20-30, and the total number of disc reactors 9 in the high-viscosity zone 3 is 8-12.

[0107] As shown in Figure 4 , the length of low-viscosity zone 1 is one-half the length of high-viscosity PBT polymerizer 14, and the combined length of medium-high-viscosity zone 2 and high-viscosity zone 3 is one-half the length of high-viscosity PBT polymerizer 14. The ratio of the lengths of medium-high-viscosity zone 2 to high-viscosity zone 3 is 2:1. The length of the stirring shaft 8 located within low-viscosity zone 1 and a portion of medium-high-viscosity zone 2 is two-thirds the length of high-viscosity PBT polymerizer 14, while the length of the stirring shaft 8 located within high-viscosity zone 3 and the remaining medium-high-viscosity zone 2 is one-third the length of high-viscosity PBT polymerizer 14. It should be emphasized that the terms "one-half," "two-thirds," and "one-third" herein do not refer to exact values ​​of one-half, two-thirds, and one-third, but rather refer to values ​​approximately between one-half, two-thirds, and one-third, or thereabouts, and are sufficient to be approximately equal to one-half, two-thirds, and one-third.

[0108] The high-viscosity PBT polymerization kettle 14 also includes a prepolymer inlet 17 located at the front bottom of the low-viscosity zone 1 and a high-viscosity PBT melt outlet 18 located at the rear bottom of the high-viscosity zone 3. The high-viscosity PBT melt outlet 18 is in a bell-mouth shape.

[0109] As shown in Figures 2-3, a plurality of homogenizers 20 are circumferentially spaced apart on the outer edge of each set of combined disks in the low-viscosity zone 1 of the PBT high-viscosity final polymerization kettle 14. The homogenizers 20 extend along the axial direction of the high-viscosity PBT polymerization kettle 14 and are used to drip the PBT melt in the low-viscosity zone 1 onto the surface of the disc reactor 9. The thick end of the wedge faces the direction of rotation of the disc reactor 9; the number of homogenizers 20 is 8 to 12. Although the example in Figure 3 shows 8 homogenizers, it does not mean that the present invention must have 8 homogenizers 20. Preferably, the homogenizers 20 are evenly distributed along the circumference of the disc reactor 9.

[0110] As shown in Figure 4, in the double-piece combination disk in the medium and high viscosity area 2, the distance between the combination disk groups and the two disks themselves gradually increases from front to back; the diameter of the disc reactor 9 in the high viscosity area 3 decreases from front to back, and the diameter of the last disc reactor 9 in the high viscosity area 3 is 88%-92% of the diameter of the first disc reactor 9.

[0111] As shown in Figures 4-5, the high viscosity area 3 is also provided with a composite scraper 4, which includes an axial scraper 6 for scraping the melt on the stirring shaft, a wall scraper 7 for scraping the melt on the inner wall of the high viscosity PBT polymerization kettle 14, and a disk scraper 5 for scraping the melt on the disc reactor 9, as well as a bottom scraper. The disk scraper 5 is provided with two layers, and the material thickness on the disc reactor 9 is controlled to be no more than 30 mm.

[0112] High-viscosity PBT polymerizer 14 also includes steam inlets for superheated 1,4-butanediol vapor, located at the top of the main body in the middle of medium-high viscosity zone 2, at the rear end of medium-high viscosity zone 2, and at the rear end of high viscosity zone 3. High-viscosity PBT polymerizer 14 is connected to a vacuum pump with a maximum vacuum of 60-75 Pa. A melt pump is used to transport the high-viscosity PBT melt and the low-viscosity PET melt, and a melt cooler is installed at the melt pump outlet.

[0113] As shown in FIG1 , the low-viscosity PET final polymerization reactor 15 is a horizontal polymerization reactor, and its aspect ratio is 2.2-2.8:1.0.

[0114] The high-viscosity PBT polymerization kettle 14 is connected to a vacuum pump, which is a liquid ring pump with a chilled water device at its inlet for cooling the gas. A melt pump transports the high-viscosity PBT melt and the low-viscosity PET melt, and a melt cooler is provided at the melt pump outlet.

[0115] After the high-viscosity PBT polymerization kettle 14 and before the same spinning assembly, a dynamic mixer and a filter are set; before the dynamic mixer, a viscosity reducer injection system is set.

[0116] Necessary melt pumps, vacuum pumps, conveying pipelines, etc. can be installed on the pipeline that serves as a connection between the five kettles on the two production lines.

[0117] The same spinning assembly is a composite spinning manifold, and a high-viscosity PBT polymerization kettle 14 is set on the top of the composite spinning manifold to shorten the conveying distance of the melt, especially the high-viscosity PBT melt. The composite spinning manifold contains a spinneret.

[0118] Example 1

[0119] This embodiment provides a method for preparing a high-viscosity PBT / low-viscosity PET bicomponent elastic fiber, and the specific steps are as follows:

[0120] The preparation method of the polymerization catalyst used in this embodiment is as follows:

[0121] Tetrabutyl titanate and acetic acid are mixed and subjected to an exothermic reaction in a mass ratio of 1:1. After the reaction, a titanium tetraacetate complex and a large amount of n-butanol by-product are generated. The reaction system is vacuum-purified at 50° C. for 2.0 hours to remove the generated n-butanol. The system is cooled to room temperature, and 1,4-butanediol is injected into the reaction system with stirring to prepare a 1,4-butanediol solution of a polymerization catalyst. The injection amount of 1,4-butanediol is controlled so that the titanium content in the polymerization catalyst solution is 1.0%.

[0122] The polymerization devices of the above two production lines are used to synthesize high-viscosity PBT melt and low-viscosity PET melt respectively.

[0123] For the high-viscosity PBT melt production line, the equipment includes a beating kettle, a first esterification kettle (with a distillation tower at the top), a second esterification kettle (three-chamber structure, with a distillation tower at the top), a first prepolymerization kettle, a second prepolymerization kettle, a high-viscosity PBT polymerization kettle, and a matching vacuum system and melt conveying system.

[0124] For the low-viscosity PET melt production line, the equipment includes a beating kettle, a first esterification kettle, a second esterification kettle, a first prepolymerization kettle, a second prepolymerization kettle, a low-viscosity PET final polymerization kettle, and a matching vacuum system and melt conveying system.

[0125] Synthetic high-viscosity PBT melt:

[0126] Purified terephthalic acid and 1,4-butanediol are sequentially subjected to esterification reactions in the first and second esterification reactors, followed by prepolymerization reactions in the first and second prepolymerization reactors to produce a PBT prepolymer. The PBT prepolymer is then polymerized in a high-viscosity PBT polymerization reactor to produce a high-viscosity PBT melt. The molar ratio of purified terephthalic acid to 1,4-butanediol is 1:1.25. The esterification temperature in the first esterification reactor is 245°C to 247°C, and the esterification is carried out at a pressure of 40 to 60 kPa (this pressure refers to the actual pressure in the first esterification reactor, which is lower than atmospheric pressure, meaning that the first esterification reactor is actually a reduced-pressure reaction). The esterification temperature in the second esterification reactor is 248°C to 252°C, and the esterification is carried out at atmospheric pressure. An esterification catalyst was added to the first esterification kettle: TOT catalyst (tetrakis(2-ethylhexyloxy)titanate) produced by Japan Soda Co., Ltd., in an amount such that the mass of the titanium element therein was 30 ppm of the mass of the melt. The polymerization catalyst prepared above was introduced into the third compartment from the front to the back of the second esterification kettle, in an amount such that the mass of the titanium element therein was 70 ppm of the mass of the melt. No matting agent was added. The reaction temperature of the first prepolymerization kettle was 250-252°C, and the vacuum degree was 9.9 kPa; the reaction temperature of the second prepolymerization kettle was 251-252°C, and the vacuum degree was 1.05 kPa; the melt outlet temperature of the high-viscosity PBT polymerization kettle was 252.2°C, and the vacuum degree in the high-viscosity PBT polymerization kettle was 133 Pa. Superheated 1,4-butanediol is injected into the steam feed port of the high-viscosity PBT polymerization reactor via a steam jet pump. To precisely separate the large amount of tetrahydrofuran produced during the polymerization process, a large-capacity chilled water exchanger is placed upstream of the vacuum liquid ring pump. The high-viscosity PBT melt discharged from the reactor has an intrinsic viscosity of 1.149 and a dynamic viscosity of 505 Pa.s. These intrinsic viscosities were measured in a 3:2 volume ratio of phenol and tetrachloroethane. The dynamic viscosity is measured at 252°C.

[0127] Synthetic low-viscosity PET melt:

[0128] Purified terephthalic acid and ethylene glycol are sequentially subjected to esterification in a first and second esterification reactors, followed by prepolymerization in a first and second prepolymerization reactors to produce a PET prepolymer. The PET prepolymer is then polymerized in a low-viscosity PET final polymerization reactor to produce a low-viscosity PET melt. The catalysts for both esterification and polymerization are ethylene glycol antimony, used in an amount such that the antimony content is 210 ppm relative to the total mass of the PET melt. This catalyst is added to the reaction system in the first esterification reactor. The first esterification reactor operates under pressure, while the second esterification reactor operates under atmospheric pressure. No matting agent is added. By adjusting the reaction conditions (including the vacuum level, stirring rate, and polymerization temperature of the low-viscosity PET final polymerization kettle, controlling the vacuum level to 180-220 Pa, stirring rates in the low-viscosity zone (front chamber) to 4.0-6.0 rpm, and stirring rates in the medium-high viscosity zone and high viscosity zone (back chamber) to 1.5-3.5 rpm; and polymerization temperature to 272-275°C), a low-viscosity PET melt with an intrinsic viscosity of 0.450 and a dynamic viscosity of 90 Pa.s was obtained. This intrinsic viscosity was measured in a mixed solvent of phenol and tetrachloroethane in a volume ratio of 3:2. The dynamic viscosity is measured at 270°C.

[0129] Spinning:

[0130] Finally, the high-viscosity PBT melt and the low-viscosity PET melt are transported to the composite spinning manifold at a mass ratio of 5:5, and spun through a composite spinning spinneret to obtain a high-viscosity PBT / low-viscosity PET two-component elastic fiber.

[0131] The reaction conditions, parameters for high-viscosity PBT melt, and low-viscosity PET melt are shown in Tables 1-5. "-" indicates none. Melt chip properties were tested according to GB / T 14190-2017. Intrinsic viscosity was measured in a 3:2 volume ratio of phenol and tetrachloroethane. Water, ash, iron, and agglomerated particles refer to the mass fractions of water, ash, iron, and agglomerated particles in the polyester, respectively. The unit of intrinsic viscosity is dL / g.

[0132] Example 2-13

[0133] Example 2-13 provides a method for preparing a high-viscosity PBT / low-viscosity PET bicomponent elastic fiber. The specific steps are essentially the same as those in Example 1, with the only difference being that: when synthesizing the high-viscosity PBT melt, the parameters of the high-viscosity PBT melt are adjusted by adjusting the reaction conditions (including the vacuum level of the high-viscosity PBT polymerization kettle, the stirring rate in the low-viscosity zone, the stirring rates in the medium-high-viscosity zone and the high-viscosity zone, the inlet temperature of the PBT prepolymer melt (PBT low-viscosity melt), and the residence time of the material in the final polymerization kettle). When synthesizing the low-viscosity PET melt, the parameters of the low-viscosity PET melt are adjusted by adjusting the reaction conditions (including the vacuum level of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, and the polymerization temperature of the low-viscosity PET final polymerization kettle). Furthermore, during polymerization, triethanolamine, a Lewis base and side reaction inhibitor, is introduced into the first chamber from the front to the rear of the second esterification kettle, with the mass of triethanolamine accounting for 160 ppm of the mass of the high-viscosity PBT melt. The reaction conditions, parameters of the high-viscosity PBT melt, and parameters of the low-viscosity PET melt are shown in Tables 1-5.

[0134] Example 14

[0135] Example 14 provides a method for preparing a high-viscosity PBT / low-viscosity PET two-component elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing a high-viscosity PBT melt, the parameters of the high-viscosity PBT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PBT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high viscosity zone and the high-viscosity zone, the inlet temperature of the PBT prepolymer melt (PBT low-viscosity melt), the residence time of the material in the final polymerization kettle, etc.); when synthesizing a low-viscosity PET melt, the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate ... The parameters of the low-viscosity PET melt were adjusted by adjusting the polymerization temperature of the high-viscosity PET final polymerization vessel. During polymerization, a Lewis base, triethanolamine, was introduced into the first chamber of the second esterification vessel (from front to back) to suppress side reactions. The amount of triethanolamine, representing 160 ppm of the mass of the high-viscosity PBT melt, was also introduced from the viscosity reducer injection system. The specific type of viscosity reducer was an amorphous polyester with an intrinsic viscosity of 0.55 (measured using a 3:2 volume ratio of phenol:tetrachloroethane). The dosage was 0.5% of the total melt mass. The reaction conditions, parameters of the high-viscosity PBT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0136] Example 15

[0137] Example 15 provides a method for preparing a high-viscosity PBT / low-viscosity PET two-component elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing a high-viscosity PBT melt, the parameters of the high-viscosity PBT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PBT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high viscosity zone and the high-viscosity zone, the inlet temperature of the PBT prepolymer melt (PBT low-viscosity melt), the residence time of the material in the final polymerization kettle, etc.); when synthesizing a low-viscosity PET melt, the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate ... The parameters of the low-viscosity PET melt were adjusted by adjusting the polymerization temperature of the high-viscosity PET final polymerization vessel. During polymerization, a Lewis base, triethanolamine, was introduced into the first chamber of the second esterification vessel (from front to back) to suppress side reactions. The amount of triethanolamine, representing 160 ppm of the mass of the high-viscosity PBT melt, was also introduced from the viscosity reducer injection system. The specific type of viscosity reducer was an amorphous polyester with an intrinsic viscosity of 0.58 (measured using a 3:2 volume ratio of phenol:tetrachloroethane). The amount of the viscosity reducer was 0.8% of the total melt mass. The reaction conditions, parameters of the high-viscosity PBT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0138] Comparative Example 1

[0139] Comparative Example 1 provides a preparation method for melt-spinning high-viscosity PET / low-viscosity PET two-component elastic fiber. The preparation method adopts a six-reactor polymerization device, which includes a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, and a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor respectively connected to the second prepolymerization reactor. The high-viscosity PET melt obtained by the high-viscosity final polymerization reactor and the low-viscosity PET melt obtained by the low-viscosity final polymerization reactor are simultaneously transported to the same spinning assembly for parallel spinning. Among them, the second esterification reactor is provided with three sub-chambers. The high-viscosity final polymerization reactor and the low-viscosity final polymerization reactor both adopt conventional structures in the prior art.

[0140] Specifically, terephthalic acid, ethylene glycol, and an antimony ethylene glycol catalyst are sequentially subjected to an esterification reaction in a first esterification kettle and a second esterification kettle, followed by a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to produce an ethylene terephthalate prepolymer. Prior to the second esterification reaction in the second esterification kettle, a conventional titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, with titanium dioxide accounting for 10% by weight and ethylene glycol accounting for 90% by weight) is added to a chamber of the second esterification kettle via a corresponding pipeline. The molar ratio of terephthalic acid to ethylene glycol is 1:1.25, the catalyst is used in an amount such that the antimony element accounts for 210 ppm of the total mass of the melt, and the matting agent is used in an amount such that the titanium dioxide accounts for 0.3% of the total mass of the melt. The ethylene terephthalate prepolymer was then passed through a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor for polymerization, respectively, to produce a high-viscosity PET melt and a low-viscosity PET melt. Finally, the high-viscosity PET melt and the low-viscosity PET melt were directly passed through the same parallel composite spinning beam at a mass ratio of 5:5 for spinning, yielding a PET bicomponent elastic fiber. The parameters of the high-viscosity PET melt and the low-viscosity PET melt are shown in Tables 3-5. The fiber properties of the present invention were tested in accordance with the GBT 8960-2015 testing standard.

[0141] Comparative Example 2

[0142] Comparative Example 2 provides a method for preparing a chip-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fiber. Specifically, high-viscosity PTT and low-viscosity PET melt chips are pre-crystallized and then melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 to produce the chip-spun bicomponent elastic fiber. The properties of the corresponding chips are shown in Tables 3-5. Both the high-viscosity PTT and low-viscosity PET chips were commercially available and contained a titanium dioxide matting agent, which constituted 0.32% of the mass of the chips.

[0143] Comparative Example 3

[0144] Comparative Example 3 provides a method for preparing a chip-spun bicomponent elastic fiber composed of high-viscosity EDDP (disperse dye atmospherically metadyed polyester) and low-viscosity PET. Specifically, high-viscosity EDDP and low-viscosity PET melt chips are pre-crystallized and melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 for spinning, yielding the chip-spun bicomponent elastic fiber. The properties of the resulting chips are shown in Tables 3-5.

[0145] Table 1 Test indicators of high viscosity PBT polyester ester materials

[0146] Table 2 Test indexes of high viscosity PBT prepolymer second kettle materials

[0147] Table 3 Test indexes of high viscosity PBT polyester chips

[0148] Table 4 Physical and chemical indicators of low-viscosity PET polyester chips

[0149] Table 5 High viscosity PBT polymerization kettle control data and high viscosity PBT, low viscosity PET related indicators

[0150] The properties of the composite elastic fibers obtained by spinning the high-viscosity melts and low-viscosity PET melts corresponding to Examples 1-15 and Comparative Examples 1-3 are shown in Table 6. The fiber type is FDY, with a specification of 83 dtex / 36 f. The fiber properties in this invention were tested in accordance with the GBT 8960-2015 test standard.

[0151] Table 6 Physical and chemical indicators of PBT / PET two-component composite elastic fibers

[0152] It can be seen that the present invention utilizes two different polyester production lines to produce high-viscosity PBT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PBT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-spinning high-viscosity PBT / low-viscosity PET parallel elastic fibers, and the obtained fibers have excellent performance.

[0153] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications based on the spirit and essence of the present invention are intended to be encompassed by the scope of protection of the present invention.

Claims

1. A high-viscosity PBT polymerization kettle, which is used to prepare high-viscosity PBT melt, and the high-viscosity PBT melt is used to prepare high-viscosity PBT / low-viscosity PET bicomponent elastic fibers, and is characterized in that: The high-viscosity PBT polymerization kettle is a horizontal polymerization kettle, and includes a main body with a chamber inside. The main body includes a low-viscosity zone, a medium-high viscosity zone, and a high-viscosity zone arranged in sequence along the axis of the high-viscosity PBT polymerization kettle. The viscosity of the PBT melt in the low-viscosity zone, medium-high viscosity zone, and high-viscosity zone increases in sequence. The high-viscosity PBT polymerization kettle also includes two stirring shafts. One stirring shaft is arranged in the low-viscosity zone and part of the medium-high viscosity zone, and the other stirring shaft is arranged in the high-viscosity zone and the remaining medium-high viscosity zone. A plurality of disk reactors are arranged on the two stirring shafts. The disk reactors in the low-viscosity zone are 3-10-piece combined disks; the disk reactors in the medium-high viscosity zone are double-piece combined disks; the disk reactors in the high-viscosity zone are single-piece disks. A plurality of homogenizers are arranged at intervals in the circumferential direction of the outer edge of each group of combined disks in the low-viscosity zone of the PBT high-viscosity final polymerization kettle. The homogenizers extend along the axis of the high-viscosity PBT polymerization kettle and are used to drip and hang the PBT melt in the low-viscosity zone on the surface of the disk reactor.

2. The high-viscosity PBT polymerization kettle according to claim 1, wherein: The cross-section of the homogenizer is wedge-shaped; the thick end of the wedge faces the rotation direction of the disk reactor; and / or, the number of the homogenizers is 8-12, and preferably, the homogenizers are evenly distributed along the circumferential direction of the disk reactor.

3. The high-viscosity PBT polymerization kettle according to claim 1, characterized in that: The total number of disk reactors in the low-viscosity zone is 25-35, the total number of disk reactors in the medium-high viscosity zone and the high-viscosity zone is 20-30, and the total number of disk reactors in the high-viscosity zone is 8-12.

4. The high-viscosity PBT polymerization kettle according to claim 1, characterized in that: The length of the low-viscosity zone is one-half of the length of the high-viscosity PBT polymerization kettle, and the combined length of the medium-high viscosity zone and the high-viscosity zone is one-half of the length of the high-viscosity PBT polymerization kettle; the length ratio of the medium-high viscosity zone to the high-viscosity zone is 2:

1.

5. The high-viscosity PBT polymerization kettle according to claim 1, wherein: The length of the stirring shaft arranged in the low-viscosity zone and part of the medium-high viscosity zone is two-thirds of the length of the high-viscosity PBT polymerization kettle, and the length of the stirring shaft arranged in the high-viscosity zone and the remaining medium-high viscosity zone is one-third of the length of the high-viscosity PBT polymerization kettle; and / or, the high-viscosity PBT polymerization kettle also includes a prepolymer inlet at the bottom of the front end of the low-viscosity zone and a high-viscosity PBT melt outlet at the bottom of the rear end of the high-viscosity zone. The high-viscosity PBT melt outlet is in the shape of a flared mouth.

6. The high-viscosity PBT polymerization kettle according to claim 1, wherein: In the double-piece combined disks in the medium-high viscosity zone, the distance between the combined disk groups and the distance between the two disks of each group gradually increase from front to back; the diameters of the disk reactors in the high-viscosity zone gradually decrease from front to back. The diameter of the last disk reactor in the high-viscosity zone is 88%-92% of the diameter of the first disk reactor in the high-viscosity zone. A composite scraper is also arranged in the high-viscosity zone. The composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high-viscosity PBT polymerization kettle, a disk scraper for scraping the melt on the disk reactor, and a bottom scraper. The disk scraper is arranged in two layers, and the thickness of the material on the disk reactor is controlled not to exceed 30 mm.

7. A preparation method of a high-viscosity PBT / low-viscosity PET bicomponent elastic fiber. The bicomponent elastic fiber contains a high-viscosity PBT component and a low-viscosity PET component, and the viscosity of the high-viscosity PBT component is greater than that of the low-viscosity PET component. It is characterized in that: the preparation method includes the steps of separately preparing a high-viscosity PBT melt and a low-viscosity PET melt, and spinning the high-viscosity PBT melt and the low-viscosity PET melt through the same side-by-side composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PBT melt is greater than that of the low-viscosity PET melt; the step of preparing the high-viscosity PBT melt includes the steps of subjecting terephthalic acid and 1,4-butanediol to esterification reaction in a first esterification kettle and a second esterification kettle in sequence, and subjecting them to prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PBT prepolymer, and subjecting the PBT prepolymer to polymerization reaction in a high-viscosity PBT polymerization kettle to obtain the high-viscosity PBT melt, and the high-viscosity PBT polymerization kettle is the high-viscosity PBT polymerization kettle according to any one of claims 1-6; the step of preparing the low-viscosity PET melt includes the steps of subjecting terephthalic acid and ethylene glycol to esterification reaction in a first esterification kettle and a second esterification kettle in sequence, and subjecting them to prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PET prepolymer, and subjecting the PET prepolymer to polymerization reaction in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

8. The preparation method according to claim 7, characterized in that: By mass percentage, the bicomponent elastic fiber contains 30%-70% of the high-viscosity PBT component and 70%-30% of the low-viscosity PET component; and / or, the intrinsic viscosity of the high-viscosity PBT melt is 0.98-1.20, and the dynamic viscosity is 225-615 Pa·s; the intrinsic viscosity of the low-viscosity PET melt is 0.45-0.55, and the dynamic viscosity is 90-240 Pa·s.

9. The preparation method according to claim 7, characterized in that: In the same side-by-side composite spinning assembly, the dynamic viscosity of the high-viscosity PBT melt is 200-520 Pa·s, and the dynamic viscosity of the low-viscosity PET melt is 70-220 Pa·s.

10. The preparation method according to claim 7, wherein: When preparing the high-viscosity PBT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before the esterification reaction, and the esterification catalyst is selected from tetrabutyl titanate, tetraisopropyl titanate or tetra(2-ethylhexoxy) titanate.

11. The preparation method according to claim 7, characterized in that: The esterification reaction in the first esterification kettle for preparing the high-viscosity PBT melt is carried out under a pressure of 40-60 kPa; and / or, the esterification reaction in the second esterification kettle for preparing the high-viscosity PBT melt is carried out at atmospheric pressure; and / or, the second esterification kettle for preparing the high-viscosity PBT melt is a horizontal reaction kettle and includes three compartments arranged in sequence from front to back. When preparing the high-viscosity PBT melt, the preparation method further includes the step of adding a side reaction inhibitor to the first compartment from front to back of the second esterification kettle, and the side reaction inhibitor is a Lewis base.

12. The preparation method according to claim 11, wherein: The Lewis base is selected from a combination of one or more of triethanolamine, quaternary ammonium salt, ethylenediaminetetraacetic acid, sodium acetate, sodium benzoate, sodium formate, potassium succinate, lithium acetate and zinc acetate; and / or the mass of the Lewis base is 30 to 300 ppm of the mass of the high-viscosity PBT melt.

13. The preparation method according to claim 7, characterized in that: The first esterification kettle and the second esterification kettle for preparing high-viscosity PBT melt are both provided with distillation towers at their upper ends, and the preparation method further includes the steps of extracting a mixture of water and tetrahydrofuran from the tops of the two distillation towers and extracting 1,4-butanediol from the bottoms of the towers; preferably, the preparation method further includes the step of separating the mixture of water and tetrahydrofuran by three-tower distillation to obtain pure tetrahydrofuran; preferably, the preparation method further includes the step of recovering the extracted 1,4-butanediol.

14. The preparation method according to claim 7, characterized in that: The intrinsic viscosity of the PBT prepolymer introduced into the high-viscosity PBT polymerization kettle is 0.280 to 0.

350.

15. The preparation method according to claim 11, wherein: When preparing the high-viscosity PBT melt, the preparation method further comprises the step of injecting a polymerization catalyst into the third sub-chamber from the front to the rear of the second esterification kettle.

16. The preparation method according to claim 15, characterized in that: The polymerization catalyst is prepared by reacting titanate with protonic acid under anhydrous conditions, removing alcohol byproducts, and dissolving the reactants in 1,4-butanediol.

17. The preparation method according to claim 16, wherein: The titanate is selected from tetrabutyl titanate, tetraisopropyl titanate or tetra(2-ethylhexyloxy) titanate; and / or the protonic acid is selected from a combination of one or more of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid and polyphosphoric acid; and / or the mass ratio of the titanate to the protonic acid is 1:0.5-2.0; and / or the mass percentage of titanium element in the polymerization catalyst is 1.0%-3.0%.

18. The preparation method according to claim 10 or 15, characterized in that: The mass of the titanium element in the esterification catalyst accounts for 30 to 40 ppm of the mass of the high-viscosity PBT melt; and / or the mass of the titanium element in the polymerization catalyst accounts for 30 to 80 ppm of the mass of the high-viscosity PBT melt.

19. The preparation method according to claim 7, wherein: The high-viscosity PBT polymerization kettle also includes steam feed ports for introducing superheated 1,4-butanediol steam, which are arranged at the middle of the medium-high viscosity zone, the rear end of the medium-high viscosity zone, and the rear end of the high viscosity zone. The preparation method also includes the step of using a metering system to meter the superheated 1,4-butanediol steam and introducing it into the high-viscosity PBT polymerization kettle.

20. The preparation method according to claim 7, characterized in that: The high-viscosity PBT polymerization kettle is connected to a vacuum pump, the ultimate vacuum degree of the vacuum pump is 60-75 Pa, and the preparation method controls the suction volume of the vacuum pump to 85-230 kg / h; and controls the vacuum degree in the high-viscosity PBT polymerization kettle to 90-150 Pa.

21. The preparation method according to claim 7, characterized in that: A melt pump is used to transport high-viscosity PBT melt and low-viscosity PET melt, and a melt cooler is arranged at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PBT melt to 252-253° C. after being cooled by the melt cooler; a filter and a booster pump are arranged between the melt pump and the parallel composite spinning assembly; the preparation method controls the transport time of the high-viscosity PBT melt to 30-40 minutes.

22. The preparation method according to claim 7, characterized in that: The low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its aspect ratio is 2.2-2.8:1.

0.

23. The preparation method according to claim 7, wherein: The preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PBT melt before the high-viscosity PBT melt passes through the filter; the viscosity reducer is selected from one or a combination of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye easily dyeable polyester ECDP, normal pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, and poly-1,3-propanediol terephthalate PBT.

24. The preparation method according to claim 7, characterized in that: The molar ratio of terephthalic acid to 1,4-butanediol is 1:1.05 to 1.65; and / or, the esterification reaction in the first esterification kettle for preparing the high-viscosity PBT melt is carried out at 245°C to 247°C.

25. The preparation method according to claim 7, characterized in that: When preparing the high-viscosity PBT melt, the esterification reaction in the second esterification kettle is carried out at 248°C to 252°C; and / or, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at 250°C to 252°C; and / or, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBT melt is carried out under a pressure of 7 to 102 kPa; and / or, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBT melt is carried out at 251°C to 252°C; and / or, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBT melt is carried out under a pressure of 0.5 to 1.5 kPa.

26. A high-viscosity PBT / low-viscosity PET bicomponent elastic fiber prepared by the preparation method according to any one of claims 7 to 25.

27. The high-viscosity PBT / low-viscosity PET bicomponent elastic fiber according to claim 26, wherein: The strength of the bicomponent elastic fiber is 2.6 to 3.0 cN / dtex, the crimp shrinkage rate is 20% to 55%, and the crimp stability is 62% to 75%.

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