CN116410450A

CN116410450A - Preparation method of elastic fiber PBT resin and spun PBT product

Info

Publication number: CN116410450A
Application number: CN202310071436.9A
Authority: CN
Inventors: 孙卫杰; 刘建; 李平; 宋占尚; 张晓峰
Original assignee: Kanghui New Material Technology Co Ltd
Current assignee: Kanghui New Material Technology Co Ltd
Priority date: 2023-02-03
Filing date: 2023-02-03
Publication date: 2023-07-11

Abstract

The invention relates to a preparation method of elastic fiber PBT resin and a spun PBT product, which comprises the following steps: preparing dibasic acid and dihydric alcohol into slurry; preparing an additive solution by an additive and dihydric alcohol; preparing tetrabutyl titanate and dihydric alcohol into a catalyst solution, extracting a gas phase product into a process tower, mixing the dihydric alcohol which flows back to an esterification kettle from the process tower with the catalyst solution, adding 70-90ppm of effective component Ti, and sending into the esterification kettle; feeding the prepared slurry, additive solution and catalyst solution into an esterification kettle with load reduced to 60% -90% for esterification to obtain esterified substances; the esterified matter is sent to a prepolymerization kettle to prepare a precondensation reactant; the pre-polycondensation reactant is sent into a final polymerization kettle for liquid phase polycondensation to obtain a final polycondensation reactant; sending the final polycondensation reactant to a granulator for granulating, and sending the granulated material to a slicing bin for processing to obtain the spinning PBT resin with the intrinsic viscosity of 1.000-1.300 dL/g; the purpose is to ensure the uniformity and stability of the viscosity and meet the requirements of the spinning technology.

Description

Preparation method of elastic fiber PBT resin and spun PBT product

Technical Field

The invention belongs to the polyester product generation processing technology, and particularly relates to a preparation method of elastic fiber PBT resin and a spun PBT product.

Background

PBT (polybutylene terephthalate) is a novel engineering plastic with excellent comprehensive properties, excellent mechanical properties and electrical properties, chemical corrosion resistance, easy molding and low moisture absorption, and has been widely used in the fields of electronics, electricity, automobiles, mechanical manufacturing, spinning and the like.

The PBT spinning product has excellent elasticity, strength, modulus, color absorption and skin affinity, can be well fused with PET resin, and is very suitable for developing PBT-PET bi-component high-elasticity yarns so as to meet the requirements of the textile and clothing field on high-end elastic fabrics.

In order to ensure the stability of the PBT-PET bi-component melt spinning process, the spinning process has higher requirements on the production process control index of the PBT product, including the viscosity, molecular mass distribution, water content, carboxyl end value and the like of the PBT resin.

As the molecular chains are increased in the reaction process of the PBT product, and the degradation reaction is accompanied, the larger the molecular weight is, the longer the molecular chains are, and the more the degradation reaction is; the higher the intrinsic viscosity of the PBT product, the broader the molecular weight distribution. The spinning process requires that the molecular mass distribution index of the PBT product is as small as possible, the viscosity is stable, and the terminal carboxyl group is stable. The current liquid phase polycondensation process has an intrinsic viscosity below 1.000dL/g, and meets the requirements of spinning PBT products.

For the fiber PBT product with the intrinsic viscosity higher than 1.000dL/g, the viscosity amplitude is huge, the molecular mass distribution is extremely uneven, the carboxyl end of the product is higher, the hue is poor, and the requirement of the spinning process cannot be met.

As shown in fig. 1, the current PBT production process is mainly the PTA process (direct esterification process): with refined terephthalic acid HOOC-C ₆ H ₄ -COOH (PTA for short) and 1, 4-butanediol C ₄ H ₁₀ O ₂ (abbreviated asBD) is used as a raw material, tetrabutyl titanate is used as a catalyst, and polybutylene terephthalate HO- (CH) is generated through continuous esterification polycondensation reaction ₂ ) ₄ -OOC-C ₆ H ₄ -COO] _n -(CH ₂ ) ₄ -OH (i.e. PBT), and obtaining PBT slices by dicing with a dicing cutter. Wherein:

esterification reaction:

HOOC-C ₆ H ₄ -COOH+2C ₄ H ₁₀ O ₂ →HO-(CH ₂ ) ₄ -OOC-C ₆ H ₄ -COOH+2H ₂ O

polycondensation reaction:

nHO-(CH ₂ ) ₄ -OOC-C ₆ H ₄ -COOH→HO[-(CH ₂ ) ₄ -OOC-C ₆ H ₄ -COO] _n

-(CH ₂ ) ₄ -OH+(n-1)C ₄ H ₁₀ O ₂

the process flow comprises the following steps:

slurry preparation, esterification reaction kettle, pre-polycondensation kettle, pre-polymerization filter, final polycondensation kettle, final polymerization filter, melt conveying pipeline, casting belt head, granulating and drying, dynamic mixing and packaging.

The esterification reaction and the polycondensation reaction are both reversible reactions, and the reaction balance is determined by the concentrations of the reactants and the products, so that the reaction conditions are usually required to be controlled, the concentration of the products is regulated, and the reaction balance is pushed to move forward.

The product of the current liquid phase polymerization process has unstable intrinsic viscosity, large process fluctuation, unstable carboxyl end groups and uneven molecular weight distribution, and cannot be used as spinning materials. Most manufacturers now produce spun PBT products with an intrinsic viscosity higher than 1.000 dL/g: the liquid phase synthetic viscosity of the PBT resin is 1.000dL/g, and the viscosity of the PBT resin reaches 1.300dL/g after solid phase tackifying, so that the PBT resin is used as a spinning PBT product.

Solid phase tackifying techniques, also known as solid phase polycondensation, are polycondensation reactions that are carried out in the solid state. The polyester with certain molecular weight is heated to the temperature below the melting point and the glass transition temperature is reached, and the polycondensation reaction is continued by vacuumizing or inert gas partial pressure and taking away small molecules.

The solid-phase tackifying technology is adopted to produce the fiber PBT product, and the fiber PBT product has the inherent disadvantage. The reaction conditions for solid phase tackifying are temperature, vacuum or inert gas partial pressure, catalyst and residence time, and the particle core viscosity difference is positively correlated with the tackifying amplitude due to the difference between the temperature of the slice surface and the inside and the small molecule escape. As the viscosity of the product is increased from 1.000dL/g to 1.300dL/g, the viscosity difference of the surface core reaches 0.060-0.080dL/g, and the problems of high broken end rate, poor stability, uneven spinning, uneven dyeing and the like in the spinning process can not well meet the requirements of the spinning process.

Disclosure of Invention

The invention mainly aims at the problems and provides a preparation method of elastic fiber PBT resin and a spinning PBT product, which aim to ensure the uniformity and stability of viscosity and meet the requirements of a spinning process.

In order to achieve the above purpose, the invention provides a preparation method of elastic fiber PBT resin, which comprises the following steps:

preparation of the slurry: preparing dibasic acid and dihydric alcohol into slurry according to a certain proportion;

preparation of micro-additives: pre-preparing an additive and dihydric alcohol into an additive solution;

preparation of the catalyst solution: tetrabutyl titanate and dihydric alcohol are prepared into a catalyst solution with the Ti content of 6 percent according to the proportion, a gas phase product in an esterification kettle is extracted into a process tower, the dihydric alcohol which flows back to the esterification kettle from the process tower is mixed with the catalyst solution according to the proportion, the adding amount of an effective component T i is 70-90ppm, and the mixture is sent into the esterification kettle.

Esterification reaction: feeding the prepared slurry, additive solution and catalyst solution into an esterification kettle with load reduced to 60% -90% for esterification to obtain esterified substances;

pre-polycondensation reaction: the esterified matter is sent to a prepolymerization kettle to prepare a pre-polycondensation reactant;

and (3) final polymerization reaction: the pre-polycondensation reactant is sent to a final polymerization kettle for liquid phase polycondensation to obtain a final polycondensation reactant;

preparation of a spun PBT product: and (3) conveying the final polycondensation reactant to a granulator for granulating, conveying the granulated material to a slicing bin, and processing to obtain the spinning PBT product with the intrinsic viscosity of 1.000-1.300dL/g.

Further, the step of pre-formulating the additive with the glycol into an additive solution comprises: adding a certain amount of dihydric alcohol into an additive preparation tank, starting stirring and heating steam to heat the dihydric alcohol in the additive preparation tank to a proper position, adding the additive, and stirring at a constant temperature to completely dissolve the additive to obtain an additive solution with the concentration of 0.3%.

Further, the additive is an organic sodium salt, and acts as an anti-aging agent.

Further, the reaction conditions and vacuum conditions in the esterification kettle are as follows: the reaction temperature of the esterification kettle is 239-245 ℃, and the vacuum value of the esterification kettle is 350-450mbar/a; the reaction conditions and the vacuum conditions of the pre-polycondensation kettle are as follows: the temperature in the pre-polycondensation kettle is 248-252 ℃, and the vacuum value in the pre-polycondensation kettle is 12-16mbar/a; the viscosity of the pre-polycondensation reactants produced under the reaction conditions and vacuum conditions in the esterification kettle and the pre-polycondensation kettle is from 0.310 to 0.320dL/g.

Further, the pre-polymerization reaction further comprises the step of conveying the pre-polymerization reactant into a pre-polymer filter through a pre-polymer conveying pump to filter coarse particles, wherein the filtering precision of a filter element of the pre-polymer filter is 10-80 mu m.

Further, in the preparation of the spun PBT product, the step of feeding the final polycondensation reactant to a pelletizer comprises: the filtered final polycondensation reactant is sequentially conveyed to a viscometer, a final polycondensation filter, a melt distributing valve and a casting belt head through a gear pump connected with a single pipeline, cooled and then conveyed to a granulator for granulating, and the granulated material is conveyed to a dryer for drying.

Further, the pressure differential during operation of the melt filter is no greater than 95bar/g.

Further, in the preparation of the spun PBT product, the step of conveying the pelletized material to a slicing silo comprises: and conveying the material subjected to grain cutting into a slicing bin for static mixing treatment, adding a pipeline after a blanking gate valve of the slicing bin, enabling the slices subjected to static mixing treatment to enter a rotary valve to enable the slices to circulate at the bin, carrying out dynamic mixing, and finally weighing and packaging through a packaging machine.

Further, the molar mass ratio of the dibasic acid to the dihydric alcohol is 1:1.2.

Further, the dibasic acid is refined terephthalic acid, the dihydric alcohol is 1, 4-butanediol, and the catalyst is tetrabutyl titanate.

In order to achieve the above purpose, the invention provides a spinning PBT product, which is prepared by a preparation method of elastic fiber PBT resin, and the intrinsic viscosity of the prepared spinning PBT product is 1.000-1.300dL/g.

The technical scheme of the invention has the following advantages: on the one hand, the higher the polymerization degree, the more degradation reaction occurs in the melt conveying process, and the additive is added into the system as an anti-aging agent, so that the thermal degradation in the polycondensation reaction process and the melt conveying process can be reduced to a certain extent, the uniformity and stability of the viscosity can be ensured, and the product quality can be improved; on the other hand, compared with the prior art, the method adopts a mode of increasing the catalyst to increase the polymerization speed, and the method properly reduces the load, prolongs the residence time of the reaction, reduces the adding amount of the catalyst, can compensate the influence of low reaction speed of the low catalyst, avoids the high catalyst from accelerating the positive reaction and simultaneously accelerating the reverse reaction speed, reduces the process stability, simultaneously avoids the high catalyst from accelerating the degradation reaction in a melt conveying link, and leads the quality of the post-processed product to be poor as the degradation reaction of the PBT resin is more.

Drawings

FIG. 1 is a process flow diagram of a spun PBT product disclosed in the prior art.

FIG. 2 is a process flow diagram of one of the presently disclosed processes for making a spun PBT product.

FIG. 3 is a flow chart of an additive formulation disclosed herein.

Fig. 4 is a schematic structural diagram of a dynamic blending system disclosed in the present application.

Fig. 5 is a schematic diagram of a discharge system disclosed in the prior art.

FIG. 6 is a schematic diagram of an optimally designed outfeed system as disclosed herein.

Fig. 7 is a schematic perspective view of a pre-or final-condensation filter as disclosed herein.

In the figure: 1. BD pipeline; 2. a hopper; 3. preparing a tank; 4. a feed tank; 5. a feed pump; 6. a bottom valve; 7. a polycondensation kettle; 8. a gear pump; 9. a viscometer; 10. a final aggregation filter; 11. a melt distribution valve; 12. casting a belt head; 13. slicing bin; 14. discharging gate valve; 15. a rotary valve.

Detailed Description

The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

In one aspect of the invention, a method for preparing an elastic fiber PBT resin is provided. The spinning PBT product prepared by the method for preparing the elastic fiber PBT resin has the physical and chemical characteristics of high viscosity, good high elasticity, soft hand feeling, good wear resistance and fiber crimping property, good stretching elasticity and compression elasticity, bright color absorption and stable dyeing.

In the method of the invention, the viscosity of the formed spinning PBT product is increased by 1.000-1.300dL/g by reducing the addition amount of the catalyst, adding the anti-aging agent, regulating and controlling the proportion of the blending mixture, greatly optimizing the esterification kettle and the pre-polycondensation kettle, and the like. In addition, the method can stabilize the spinning formation, and can obtain the spinning PBT product with the full-roll rate reaching 95%, high fiber strength and good elasticity. The spun PBT product fiber prepared by the method has high strength and good high elasticity, so that the spun PBT product fiber is the best material for manufacturing high-elasticity textiles such as sportswear, tights, medical bandages and the like.

The above-mentioned preparation method of the elastic fiber PBT resin, as shown in FIG. 2, may include the following steps, but is not limited to.

Preparation of slurry S100: the dibasic acid and the dibasic alcohol are prepared into slurry according to the proportion.

Specifically, in this example, as an example of the dibasic acid and the dibasic alcohol, purified terephthalic acid HOOC-C ₆ H ₄ -COOH (PTA for short) and 1, 4-butanediol C ₄ H ₁₀ O ₂ (BD for short) is used as a raw material for the subsequent esterification reaction.

Wherein, the concrete steps for preparing the slurry comprise: the raw material refined terephthalic acid (PTA) is white powdery crystal, and 1, 4-Butanediol (BD) is low-volatility liquid with good fluidity under normal temperature and normal pressure; the two are not mutually soluble. The molar mass ratio of PTA to BD entering the slurry preparation unit is 1:1.2, a proportion adjustment system is generally adopted, automatic proportioning of PTA and BD is ensured, and recycling BD is adopted in slurry preparation. In order to ensure the proportioning ratio, PTA is metered by a mass scale, controlled by a screw feeder, and BD is metered by a mass flowmeter and controlled by a regulating valve. The sizing agent prepared according to the proportion is stirred uniformly in a sizing agent preparation tank, and the sizing agent preparation tank is provided with an external coil pipe for heating, so that the sizing agent temperature is ensured to be stable. The prepared sizing agent is discharged from the bottom of the sizing agent tank and is conveyed into the esterification kettle through a sizing agent pump. In order to ensure that the slurry meets the requirements, a mass flowmeter is arranged on a slurry pump outlet pipeline, and the slurry flow is controlled through slurry pump frequency conversion and the mass flowmeter.

Preparation of micro-additives S200: the additive and the dihydric alcohol are prepared into an additive solution in advance.

The additive is an organic sodium salt which is added to the system as an anti-aging agent and which acts to reduce thermal degradation during the polycondensation reaction and during melt transfer. The additive and BD are added into a slurry tank to be mixed uniformly, wherein the concentration of the additive in the final product is 0-10ppm. The anti-aging agent is added in a trace amount, so that the spinning process of the product is not influenced. The higher the polymerization degree, the more degradation reaction occurs in the melting and conveying process, and the thermal degradation can be reduced to a certain extent by adding a trace amount of anti-aging agent, so that the product quality is improved.

Fig. 3 is a formulation flow of additive solution: closing an additive preparation tank bottom valve 6, adding quantitative BD (usually 340 kg) into an additive preparation tank 3 through a BD pipeline 1, heating BD in the additive preparation tank 3 to 60 ℃ by starting stirring and heating steam, adding 1kg of additive through a hopper 2 after heating to a proper temperature, and stirring at the constant temperature of 60 ℃ for 1 hour to completely dissolve; opening an additive preparation tank bottom valve 6, and discharging the prepared additive solution into an additive supply tank 4; the constant temperature of the feed tank 4 is controlled, the stirring condition is controlled, the power is provided by the feed pump 5, the flow is controlled by the flowmeter and the regulating valve, the prepared additive solution is added into the slurry tank, and the additive solution is uniformly stirred and dispersed into the materials in the slurry tank.

Preparation of catalyst solution S300: the step of preparing the catalyst solution by tetrabutyl titanate and dihydric alcohol according to the proportion comprises the following steps: mixing quantitative tetrabutyl titanate and quantitative dihydric alcohol in proportion, starting stirring and heating steam, heating to a proper position and uniformly mixing to fully react the tetrabutyl titanate and the dihydric alcohol to obtain a catalyst solution with T i content of 6 percent.

Extracting gas phase products in the esterification kettle to a process tower, uniformly mixing dihydric alcohol which flows back to the esterification kettle from the process tower with a catalyst solution, wherein the adding amount of an effective component T i is 70-90ppm, and adding the effective component into the esterification kettle.

Specifically, a common catalyst for PBT production is tetrabutyl titanate, which is mixed with BD in proportion in advance to prepare a catalyst solution with stable titanium content, and the catalyst solution is put into a catalyst feed tank for use. The BD mixed with tetrabutyl titanate in proportion is BD from part of the bottom of a process tower to be refluxed to an esterification kettle, water, tetrahydrofuran THF and other components are separated from the top of the tower, the bottom of the tower is BD with higher purity, after the catalyst tetrabutyl titanate is uniformly mixed with the part of BD, a catalyst solution in a feed tank is added into a reaction system by a catalyst pump at a stable flow rate, and the catalyst flow rate is controlled by a mass flowmeter and a catalyst pump frequency conversion arranged in a pipeline.

Notably, are: current PBT production process technology, when the intrinsic viscosity is higher than 1.000dL/g, tends to suffer from several problems: 1. as the viscosity increases, the process fluctuation becomes large, the common amplitude is about 0.100dL/g, the viscosity is uncontrolled, the product index greatly fluctuates, and the spinning process cannot be used; 2. the physical and chemical indexes of the product, such as carboxyl end groups, color values, tensile strength, elongation at break and the like, are unstable, the dyeing is uneven, the elasticity is unstable, and the product cannot be used for processing after spinning.

Under the current technical conditions, the catalyst used for PBT esterification polycondensation is tetrabutyl titanate, which is a high-efficiency transesterification catalyst, is added in an esterification stage to participate in esterification reaction and polycondensation reaction, and according to the reaction mechanism of the tetrabutyl titanate complexing catalysis terephthalic acid beta-bis-hydroxybutyrate (BHBT) to synthesize PBT, the titanium catalyst and a monomer BHBT are complexed to generate CAT.BHBT, CAT.BHBT and BHBT to form an unstable intermediate complex, namely, the unstable intermediate complex is decomposed into stable PBT chains through CAT. PBT, and BD is released, so that the PBT chains are increased into PBT products with stable polymerization degree through the circulation of CAT. BHBT in the systemUnder steady state conditions: k (k) ₂ [CAT.BHBT][BHBT]＝k ₃ [CAT.PBT][BHBT]The method comprises the steps of carrying out a first treatment on the surface of the And the complexing constant k of the catalyst and the BHBT ₁ ＝[CAT.BHBT]/[CAT][BHBT]；

Then [ CAT. PBT ]]＝k ₁ k ₂ /k ₃ [CAT][BHBT]The method comprises the steps of carrying out a first treatment on the surface of the From this the kinetic equation is obtained: d [ PBT ]]/dt＝k ₃ [CAT.PBT][BHBT]＝k ₁ k ₂ [CAT][BHBT] ² 。

It can be seen that the polycondensation reaction rate is proportional to the square of the catalyst concentration and monomer concentration.

When a continuous polyester plant produces a PBT product with an intrinsic viscosity of 1.000dL/g, a catalyst addition amount of 70 to 90ppm (the content of Ti as an active ingredient in the final product, the same applies hereinafter) is generally added, and the higher the product intrinsic viscosity, the higher the plant load, the higher the catalyst is required. In theory, the PBT resin with the intrinsic viscosity higher than 1.000dL/g is produced, the required catalyst is higher, about 90-120ppm can be achieved, the catalyst concentration is increased, the reaction speed can be accelerated, the esterification and polycondensation reactions are more severe, meanwhile, the reaction residence time is short, the residence time can be shortened, and the reaction balance is pushed to move towards the positive direction. However, high catalysts also have the following adverse effects:

(1) Because the esterification reaction and the polycondensation reaction are reversible reactions, the high catalyst accelerates the forward reaction and simultaneously accelerates the reverse reaction speed, so that the process control difficulty is increased, and the stable process is not facilitated.

(2) After the reaction is completed, the catalyst can remain in the PBT finished product, so that the catalyst addition amount is large, the catalyst remained in the PBT finished product is also large, the catalyst addition amount is small, and the catalyst remained in the PBT finished product is also small. After the polycondensation reaction is completed, in the sections of PBT melt conveying process, spinning and the like, the temperature of the PBT slice rises to reach a molten state, at the moment, the conditions of high vacuum, stirring and the like for pushing the polycondensation reaction are not existed, the degradation reaction is uncontrolled, if more catalyst is added, in the melt conveying link, the catalyst accelerates the degradation reaction, the more the degradation reaction of the PBT resin occurs, and the quality of the post-processed product is poorer.

(3) The high catalyst increases the reaction speed, the viscosity in the final polymerization stage increases fast, the liquid level of the final polycondensation kettle is low, the stirring rotation speed is low and the vacuum is relatively high in order to control the balance of the polycondensation reaction, under the condition, the materials are unevenly mixed, the materials are unevenly stirred and pulled, the viscosity fluctuation of the final product is large, and the spinning process requirement cannot be met.

Therefore, in order to solve the technical problems caused by the addition of the high catalyst, the catalyst is properly lowered, so that the adverse effects of the three points can be weakened, and the method is beneficial to solving the problems of producing the elastic fiber PBT resin. Therefore, in this example, the amount of the catalyst used for producing a PBT resin having an intrinsic viscosity of 1.000dL/g to 1.300dL/g was about 70 to 90ppm, while the amount of the catalyst used for producing a PBT resin having a tackiness of 1.300dL/g was about 75ppm, and the amount was not increased but slightly decreased.

Esterification reaction S400: and (3) feeding the prepared slurry, the additive solution and the catalyst solution into an esterification kettle with the load reduced to 60% -90% for esterification to obtain an esterified substance.

Specifically, the slurry delivered from the slurry preparation unit into the inner chamber of the esterification kettle is uniformly mixed under the action of a stirrer, the temperature is raised to 240-245 ℃ by a heater in the kettle, a bubbling liquid level meter is arranged in the esterification kettle, the liquid level of the reaction kettle is controlled to be 650-750mm, the esterification reaction is carried out under vacuum conditions, the pressure of the reaction kettle is controlled to be 350-450mbar/a, preferably 400mbar/a (bar is a common engineering pressure unit, 1 bar=0.1 mpa,1 bar=1000 bar, a represents absolute pressure, g represents gauge pressure, 400mbar/a represents absolute pressure 40kPa, and the same applies below), and the pressure is controlled by a regulating valve and a vacuum gauge; the reaction conditions of the esterification kettle are slightly adjusted due to the difference of variety viscosities. PTA and BD in slurry in an esterification reactor are subjected to esterification reaction under the action of a catalyst to generate an esterified product (BHBT), and simultaneously, side reactions of polycondensation reaction and BD cyclodehydration to generate Tetrahydrofuran (THF) are also carried out. Under the vacuum condition, water, THF and part of BD steam generated by the reaction are distilled out from a gas phase pipeline at the top of the reactor, so that the esterification reversible reaction is developed towards the direction favorable for positive reaction. The materials stay in the esterification kettle for about 1 hour, and the esterified substances after the esterification reaction flow out from the outer chamber and are sent to the next working procedure by an esterification pump. The pipeline at the outlet of the esterification pump is provided with a flowmeter and a regulating valve, controls the discharge flow and controls the liquid level of the esterification kettle in cascade.

In the above-described implementation, the catalyst is lowered, which results in a problem of slow reaction rate, so that it is necessary to appropriately lower the load and to lengthen the residence time while lowering the reaction rate, so as to compensate for the effect of low catalyst reaction rate. For example, the operating load of the device is reduced to 60% -90%; assuming an 80% device load feed, the esterification residence time can be extended from 60 minutes to 75 minutes and the pre-polycondensation residence time can be extended from 30 minutes to 40 minutes.

Pre-polycondensation reaction S500: and (3) conveying the esterified product to a prepolymerization kettle to prepare a pre-polymerization reactant.

Final polymerization reaction S600: and (3) conveying the pre-polycondensation reactant into a final polymerization kettle for liquid phase polycondensation to obtain a final polycondensation reactant.

The polycondensation reaction is a reaction that occurs between butanediol ester groups, i.e., two butanediol ester groups polycondense and produce one molecule of butanediol. In the initial stage of the reaction, the oligomer is formed which has reactive difunctional groups (butanediol ester groups) at both ends of each molecule, so that the reaction can proceed. In fact, the polycondensation reaction starts to occur when a certain amount of BHBT is produced in the system soon after the esterification reaction starts. In the latter stage of the esterification, the monomers substantially disappear, producing oligomers of different degrees of polymerization. The oligomers formed can be condensed with the starting monomers or with one another until PBT macromolecules are formed. The polycondensation reaction is a reversible reaction, and it is seen from the reaction equation that lowering the BD concentration in the reactant system allows the reaction to proceed toward the production of the polymer. Therefore, in the actual production process, we try to remove the small molecules BD in the system as much as possible. Under the high temperature condition, along with the increase of the molecular weight of the polymer, various side reactions such as thermal degradation, thermal oxygen degradation, cyclization of the polymer and the like can occur at the same time, so that the molecular weight of the polymer is reduced, the melting point is reduced, the hue is poor, and the quality of the final product is influenced. In the general process for producing PBT, the polycondensation reaction is divided into two steps, namely, pre-polycondensation and final polycondensation.

The pre-shrinking kettle is a vertical reactor, an inner chamber and an outer chamber are of structures, and heating coils are arranged in the inner chamber and the outer chamber to ensure the temperature required by the reaction; the inner chamber is provided with a stirrer. The reaction condition of the pre-shrinking kettle is controlled to be 250+/-2 ℃, the liquid level is controlled to be 65+/-10%, the vacuum condition is 10-20mbara, and the pre-polymerization reaction condition is slightly adjusted due to the difference of the variety viscosity. The esterified substance is conveyed to a preshrinking kettle by an esterification pump and enters the outer chamber of the reactor. The esterified substance surrounds the outer chamber for a circle, enters the inner chamber from the overflow port, and finally is discharged from the bottom of the reaction kettle. The esterification substance gradually evaporates from the outer chamber to the inner chamber in the preshrinking kettle, the BD in the material pushes the reaction balance to move, the reaction balance is converted into a polymer with lower polymerization degree, and the rest esterification reaction is finished at the same time, so that the preparation is made for final polycondensation.

Fig. 7 is a schematic perspective view of a pre-polycondensation filter: after discharging the prepolymer, conveying the prepolymer to a prepolymer filter through a gear pump; the filtering precision is adjusted according to the difference of the variety viscosity, and impurities such as cokes, catalyst hydrolysis particles and the like in the prepolymer are removed by a filter. A cooler is arranged behind the prepolymer filter to prevent side reactions such as degradation and the like from occurring when the temperature of the prepolymer is higher, and the quality of products is influenced. The cooled prepolymer is fed to a final polymerization vessel.

And (3) final polycondensation kettle: the final-shrinkage reactor is horizontal, a double-shaft multi-layer disc-ring stirrer is arranged in the final-shrinkage reactor, a plurality of baffle plates are arranged among stirring discs, the final-shrinkage reactor is divided into a plurality of small chambers, and holes are formed in the baffle plates among the small chambers. The stirrer pulls the bottom material into a film shape when rotating, so that the specific surface area of the material is increased as much as possible, thereby facilitating the removal of small molecules such as BD generated by the reaction, and simultaneously, the material in the kettle moves forwards in a piston flow direction under the pushing of the stirring disc, so that the polycondensation reaction is promoted to be carried out in the direction of generating the high-polymerization-degree PBT. The precondensate enters a final polycondensation kettle from the bottom of the inlet end of the reaction kettle, the polycondensation reaction is completed under the high vacuum condition, and the material stays in the final polycondensation kettle for about 2-2.5 hours to generate the PBT melt with higher polymerization degree. And the mixture enters a gear pump at the outlet end of the final polymerization kettle and enters a melt conveying pipeline.

The temperature of heating medium of the final polycondensation kettle in the general process is 245 ℃, the vacuum of the reaction kettle is 1-2mbara, and the stirring rotation speed of the inlet end is 1-10rpm; the stirring rotation speed of the outlet end ranges from 1 rpm to 5rpm (the rpm is a rotation speed unit, namely, each minute, and represents the rotation times of equipment per minute, mainly adopted in Japan Europe, and the same applies below), the liquid level of the reaction kettle is 10-40%, the viscosity range of the product is larger, the product with the inherent viscosity of 0.700-1.000dL/g in the common device can be produced more stably, and the product with the inherent viscosity higher than 1.000dL/g in the section can not be produced stably.

And (3) a final aggregation filter: the PBT melt is powered by a gear pump, enters a final polymerization filter through a viscometer, filters agglomerated particles, carbonized particles and other impurity coarse particles in the melt, and then is sent to a granulating unit for granulation. The final-aggregation filter is a candle core type, a plurality of filter cores are arranged in each cavity, and the filtering precision is 10-80 mu m. When the pressure difference of the online platform rises to a specified value, switching operation is carried out on site, meanwhile, the original online platform is disassembled and cleaned, and the online platform is assembled on site for standby after cleaning is finished.

In the prior art, in the production device of PBT, the variety with the intrinsic viscosity of more than 1.000dL/g is produced, stable production is difficult, and when the high-viscosity product is produced, the common method is to strengthen the reaction conditions of a pre-polycondensation kettle and a final polycondensation kettle simultaneously, so that the discharge viscosity of the pre-polycondensation kettle is increased, and the final polycondensation can be continuously thickened, so that the intrinsic viscosity is increased to a target value. However, in the production, the process scheme can not stabilize the process of the final product, the viscosity amplitude is huge, the process is not controlled seriously, and the product can not meet the spinning process requirement at all.

The reason that the intrinsic viscosity of the produced product fluctuates greatly is that the material viscosity at the inlet end of the final polymerization kettle is high, the material reaction speed in the final polymerization kettle is high under the condition that the reaction condition of the final polymerization kettle is also enhanced, the molecular chain grows fast, the fluidity of the material in the kettle is poor, the liquid level distribution is changed, the liquid level in the middle part is gradually increased, the liquid level at the outlet end is gradually reduced, so that the residence time of the material in the middle part is prolonged, the degradation reaction speed is accelerated, the liquid level at the outlet end is reduced, even the liquid level is emptied, part of the material is repeatedly coated under the stirring effect, the viscosity fluctuation is large, and even the discharging is difficult. The fluctuation seriously causes difficult discharging of the reaction kettle, and the production is forced to be interrupted; the light weight is changed into periodic fluctuation, so that the intrinsic viscosity and quality index of the product fluctuate greatly and the spinning can not be performed.

According to the analysis of the polycondensation mechanism, the technical scheme for conventionally producing high-viscosity products is that the reinforced pre-polycondensation kettle and the final polycondensation kettle are wrong and do not accord with the polycondensation process. Most of the polycondensation reaction is completed in the final polycondensation reactor, so that the scheme of the embodiment adopting the independent reinforced final polycondensation reactor accords with the polycondensation reaction mechanism.

The temperature and vacuum conditions of the esterification kettle and the pre-polycondensation kettle are properly adjusted according to the data in the table 1, so that the molecular weight distribution of materials entering the final polycondensation kettle is uniform, indexes such as carboxyl end groups are stable, the viscosity is about 0.310-0.320dL/g, the fluidity is good, and good conditions are created for stable and controllable final polycondensation reaction. According to the following table 1, the liquid level and stirring conditions of the final polymerization kettle are properly improved, the residence time is prolonged to about 2.5-3.0 hours, the materials are stirred and pushed to move from a low-viscosity end to a high-viscosity end, the molecular chain of the product is gradually increased, the molecular weight is gradually increased, the polycondensation reaction is stable and controllable, the final product has stable intrinsic viscosity and qualified quality index, the spinning process requirement can be met, and the full-package rate can reach 95%.

Preparation of spun PBT product S700: and (3) conveying the final polycondensation reactant to a granulator for granulating, conveying the granulated material to a slicing bin, and processing to obtain the spinning PBT product with the intrinsic viscosity of 1.000-1.300dL/g.

Referring to fig. 4-6, the step of feeding the final polycondensation reactant to the pelletizer includes: the filtered final polycondensation reactant is sequentially conveyed to a viscometer 9, a final polycondensation filter 10, a melt distributing valve 11 and a casting belt head 12 through a gear pump 8 connected with a single pipeline, is cooled and then conveyed to a granulator for granulating treatment, and the granulated material is conveyed to a dryer for drying treatment; the materials subjected to the granulating treatment and the drying treatment are conveyed into a slicing bin 13 for static mixing treatment, a pipeline is added after a blanking gate valve 14 of the slicing bin 13, and slices subjected to static mixing treatment are led to enter a rotary valve 15 and return to the slicing bin, so that dynamic mixing is realized, the purposes of further homogenizing product indexes and improving the product quality are achieved. And finally weighing and packaging by a packaging machine.

As shown in fig. 5, when the elastic fiber PBT resin is produced, the high viscosity of the product causes the high pressure of the discharging system, the gear pump 8 and the viscometer 9 are blocked, and the risk of serious accidents such as overpressure of the final-polymerization filter 10 is increased; in addition, as the intrinsic viscosity of the product is high, the more thermal degradation occurs in the melt conveying process, the longer the residence time of the original discharging system, the more degradation occurs in the final discharging product, and the product quality is affected.

In order to further improve the running stability of the equipment and the product quality, the discharging system is optimally designed, as shown in fig. 6, the double gear pump 8 is changed into a single pump, and the length of a pipeline is shortened. The elevation of the gear pump 8 is raised, the length of a pipeline between the final polycondensation kettle 7 and the gear pump 8 is greatly shortened, and the volume of the discharging pipe can be greatly reduced due to the thick and short pipe diameter of the section. Because the discharge pressure of the gear pump 8 is high when the elastic fiber PBT resin is produced, the pressure difference of the final-polymerization filter 10 is too high, and the filtering area of the final-polymerization filter 10 is enlarged by 30%, so that the pressure difference of the filter is reduced, and the discharge pressure of the gear pump 8 is reduced.

Through the optimized design of the discharging system, firstly, the discharging pressure of the melt pump is reduced from original 230-200bar to 190-160bar, and the discharging system equipment such as the gear pump 8, the viscometer 9 and the like is operated in a safe state; the pressure difference of the final aggregation filter 10 is reduced from 100-80bar to 95-70bar, the service life of the filter element is prolonged, and the filter switching period is prolonged from 4 days to 8 days, thereby greatly reducing the production cost. Second, because the double pumps are changed into single pumps, the gear pump is lifted, the volume of the discharging system is reduced to 67% of the original volume, the theoretical residence of the high polymer in the discharging system is reduced to 12 min from 18 min, the thermal degradation of the high polymer in the melt conveying pipe is greatly reduced, and the product quality is effectively improved.

Because the spinning grade product is prepared, coarse particles in the product are strictly stopped, and the filter element cleaning requirement is strict. On the other hand, because the device produces the elastic fiber PBT resin for a long time, each reaction kettle is serious in coking, the filter designed by the traditional technology is short in switching period and frequent in switching, on one hand, the stable product quality cannot be ensured, and in addition, the production cost is high, so that the production requirement of the elastic fiber PBT resin cannot be met.

As a preferable scheme of the embodiment, the filter core of the prepolymer filter is increased by 20 percent, so that the area of the filter is enlarged by 20 percent, thereby prolonging the switching period of the prepolymer filter and reducing the production cost.

The impurities such as cokes and carbon black particles generated in the final polycondensation kettle are removed through a final polymerization filter, the switching time of the final polymer filter is greatly shortened in the production process of the elastic fiber PBT resin, the average switching time is about 4 days, the production cost is greatly increased, the number of filter elements of the final polymerization filter is increased by 30%, the switching period of the final polymer filter is prolonged from 4 days to 8 days, and the production cost is greatly reduced.

Table 1 process parameters of the PBT resin of the elastic fiber during the production process; table 2 shows the physical and chemical indexes of the produced elastic fiber PBT product; table 3 shows physical properties such as tensile strength, elongation at break, bending stress of the produced elastic fiber PBT product, and specifically, the physical properties are shown in tables 1, 2 and 3.

Table 1: main technological parameters of elastic fiber PBT resin

Note that: m represents the central value of the intrinsic viscosity of the product and ranges from 1.000dL/g to 1.300dL/g.

Table 2: physicochemical index of elastic fiber PBT product

Analysis item	Unit (B)	Elastic fiber
			Intrinsic viscosity	dL/g	1.000-1.300
Terminal carboxyl group content	mol/t	15-30
			L value	\	≥90
b value	\	1.8-4.0
			Melting point	℃	≥222
Ash content	mg/kg	≤300
			Moisture content	％	≤0.20
Hundred grain weight	g	2.1±0.1
			Powder scraps	mg/kg	0-30

Note that: m represents the center value of the intrinsic viscosity of the product.

Table 3: physical indexes such as tensile strength, elongation at break, bending stress and the like

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As can be seen from Table 3, with the increase of the intrinsic viscosity of the PBT resin, the elongation at break becomes significantly larger, and the elastic fiber PBT resin produced by the technical scheme of the embodiment has high intrinsic viscosity and high elasticity, can be elongated by about 400%, and has very stable other physical and chemical indexes.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that modifications and variations can be made without departing from the technical principles of the present invention, and these modifications and variations should also be regarded as the scope of the invention.

Claims

1. The preparation method of the elastic fiber PBT resin is characterized by comprising the following steps of:

preparation of the catalyst solution: preparing tetrabutyl titanate and dihydric alcohol into a catalyst solution with the Ti content of 6 percent according to a proportion, extracting a gas phase product in an esterification kettle into a process tower, mixing the dihydric alcohol which flows back to the esterification kettle from the process tower with the catalyst solution according to a proportion, and feeding the catalyst solution into the esterification kettle, wherein the adding amount of the effective component Ti is 70-90 ppm;

and (3) final polymerization reaction: the pre-polycondensation reactant is sent into a final polymerization kettle for liquid phase polycondensation to obtain a final polycondensation reactant;

2. The method for preparing the elastic fiber PBT resin according to claim 1, wherein the step of preparing an additive solution from an additive and a glycol in advance comprises: adding a certain amount of dihydric alcohol into an additive preparation tank, starting stirring and heating steam to heat the dihydric alcohol in the additive preparation tank to a proper position, adding the additive, and stirring at a constant temperature to completely dissolve the additive to obtain an additive solution with the concentration of 0.3%.

3. The method for preparing the elastic fiber PBT resin according to claim 1, wherein the reaction conditions and the vacuum conditions in the esterification kettle are as follows: the reaction temperature of the esterification kettle is 239-245 ℃, and the vacuum value of the esterification kettle is 350-450mbar/a; the reaction conditions and the vacuum conditions of the pre-polycondensation kettle are as follows: the temperature in the pre-polycondensation kettle is 248-252 ℃, and the vacuum value in the pre-polycondensation kettle is 12-16mbar/a; the viscosity of the pre-polycondensation reactants produced under the reaction conditions and vacuum conditions in the esterification kettle and the pre-polycondensation kettle is from 0.310 to 0.320dL/g.

4. The method for producing a PBT resin for elastic fibers according to claim 1, wherein the pre-polycondensation further comprises feeding the pre-polycondensation reactant into a prepolymer filter by a prepolymer feeding pump to filter coarse particles, wherein the filter element of the prepolymer filter has a filtration accuracy of 10 to 80. Mu.m.

5. The method for producing an elastic fiber PBT resin according to claim 4, wherein in the production of the spun PBT product, the step of feeding the final polycondensation reactant to a pelletizer comprises: the filtered final polycondensation reactant is sequentially conveyed to a viscometer, a final polycondensation filter, a melt distributing valve and a casting belt head through a gear pump connected with a single pipeline, cooled and then conveyed to a granulator for granulating, and the granulated material is conveyed to a dryer for drying.

6. The process for producing a PBT resin with elastic fibers according to claim 5, wherein the pressure difference during the operation of the melt filter is not more than 95bar/g.

7. The method for producing an elastic fiber PBT resin according to claim 1, wherein in the production of the spun PBT product, the step of transporting the pelletized material to a dicing hopper comprises: and conveying the material subjected to grain cutting into a slicing bin for static mixing treatment, adding a pipeline after a blanking gate valve of the slicing bin, enabling the slices subjected to static mixing treatment to enter a rotary valve to enable the slices to circulate at the bin, carrying out dynamic mixing, and finally weighing and packaging through a packaging machine.

8. The method for producing a PBT resin with elastic fibers according to claim 1, wherein the molar mass ratio of the dibasic acid to the dibasic alcohol is 1:1.2.

9. The method for preparing the elastic fiber PBT resin according to claim 1, wherein the dibasic acid is refined terephthalic acid, the dihydric alcohol is 1, 4-butanediol, and the catalyst is tetrabutyl titanate.

10. A spun PBT product, characterized in that the spun PBT product is prepared by the method of any of claims 1 to 9, and the intrinsic viscosity of the prepared spun PBT product is 1.000 to 1.300dL/g.