CN112048059B

CN112048059B - Method for catalytically synthesizing polyester by using titanium catalyst

Info

Publication number: CN112048059B
Application number: CN202010838357.2A
Authority: CN
Inventors: 杜玮辰; 汪绪兰; 刘雨; 张含; 陈爽; 刘明明
Original assignee: Haining Lanti New Material Co ltd
Current assignee: Haining Lanti New Material Co ltd
Priority date: 2020-08-19
Filing date: 2020-08-19
Publication date: 2023-02-14
Anticipated expiration: 2040-08-19
Also published as: CN112048059A

Abstract

The invention relates to the technical field of polyester synthesis, and discloses a method for catalytically synthesizing polyester by using a titanium catalyst, which comprises the following steps: adding a polyester synthetic substrate into a reaction vessel with a plate-frame type stirring paddle to perform polymerization reaction; and loading a heterogeneous titanium-silicon composite catalyst onto the plate-frame type stirring paddle before or during the polymerization reaction to prepare the polyester. According to the method, the titanium catalyst is loaded on the plate-frame type stirring paddle, so that the prepared polyester does not contain the catalyst, thereby preventing the polyester from alcoholysis under the action of the catalyst, and effectively solving the problem of viscosity reduction generated when the polyester is conveyed in a molten state; in addition, the method can also ensure that the catalyst is fully contacted with the substrate in the polyester preparation process, and is convenient for recycling the catalyst after the preparation is finished.

Description

Method for catalytically synthesizing polyester by using titanium catalyst

Technical Field

The invention relates to the technical field of polyester synthesis, in particular to a method for catalytically synthesizing polyester by using a titanium catalyst.

Background

Polyester is a general term for polymers obtained by polycondensation of polyhydric alcohol and polybasic acid, mainly includes polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like, is a kind of engineering plastics with excellent performance and wide application, and is widely applied to a plurality of fields such as fibers, films, packaging materials, engineering plastics and the like. The catalyst is an important link in polyester production, and not only influences the speed of esterification, ester exchange and polycondensation reaction in the polyester production process, but also has obvious influence on side reaction, thermal stability, product color and luster and the like.

At present, the most widely used polyester catalyst in industrial production is mainly an antimony compound, and the polyester catalyst has the advantages of mature process, low production cost, controllable catalytic activity, less side reaction and good hue. The general antimony compound is added into a reaction system in a pulping stage, and is uniformly mixed with the reaction system all the time along with the reaction, the antimony compound does not play a role in catalyzing the esterification stage, and mainly catalyzes the polycondensation reaction. Because the melt viscosity increases with the progress of the reaction, the catalyst is difficult to separate, and the catalytic polycondensation reaction is a reversible reaction, the polyester melt is easy to degrade under the conditions of non-negative pressure and the existence of dihydric alcohol and the catalyst. The reason is that viscosity reduction is easy to occur in the melt conveying process in the melt direct spinning production, so the melt conveying pipeline between the polymerization and spinning sections is not suitable to be too long, otherwise, the spinning cannot be performed due to the too large viscosity reduction of the melt. The titanium-based catalyst is used as an environment-friendly polyester polycondensation catalyst, the existing form in a reaction system in limited application examples is similar to that of an antimony-based catalyst, only the adding position is different (because part of the titanium-based catalyst is sensitive to water, a polymerization system needs to be added at the position even later than a diester), and the titanium-based catalyst has higher catalytic activity, so that the titanium-based catalyst has stronger degradation capability than the antimony-based catalyst under the condition of the same non-negative pressure and the presence of dihydric alcohol, and the melt viscosity is reduced more greatly, so that the spinning is not facilitated.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for synthesizing polyester by using a titanium catalyst. According to the method, the titanium catalyst is loaded on the plate-frame type stirring paddle, so that the prepared polyester does not contain the catalyst, and the problem of viscosity reduction caused by alcoholysis when the polyester is conveyed in a molten state is effectively solved.

The specific technical scheme of the invention is as follows:

a method for synthesizing polyester by using titanium catalyst comprises the following steps: adding a polyester synthetic substrate into a reaction vessel with a plate-frame type stirring paddle to perform polymerization reaction; and loading a heterogeneous titanium-silicon composite catalyst on the plate-frame type stirring paddle before or during the polymerization reaction to prepare the polyester.

The invention aims to load a titanium catalyst (heterogeneous titanium-silicon composite catalyst) on a plate-and-frame type stirring paddle: after the reaction is finished, the catalyst can be separated from the polyester melt, so that the obtained polyester product does not contain the catalyst, thereby preventing the polyester from alcoholysis under the action of the catalyst, effectively solving the problem of viscosity reduction generated when the polyester is conveyed in a molten state, and facilitating the subsequent spinning process.

While achieving the above objectives, loading the catalyst on the plate and frame type paddles also provides the following benefits: (1) A plate-frame type stirring paddle is selected, so that the catalyst can be fully contacted with a substrate through stirring in the reaction process, and the problem that the catalytic activity is influenced due to uneven dispersion of the catalyst in a reaction system can be solved; (2) In the cleaning process after the reaction is finished, due to the existence of the catalyst, the polyester adhered to the surface of the catalyst can be removed by alcoholysis by adding the dihydric alcohol, so that the catalyst loss is low, the aftertreatment is convenient, and the catalyst can be recycled conveniently.

Preferably, the preparation method of the heterogeneous titanium-silicon composite catalyst comprises the following steps:

(a) Mixing titanium dioxide sol and silicon dioxide sol to obtain mixed sol;

(b) Dropwise adding the mixed sol into an aqueous solution of a complexing agent, and uniformly mixing to obtain a complexing agent mixed sol;

(c) And (3) carrying out centrifugal treatment on the complexing agent mixed sol, taking the precipitate, washing and drying to obtain the heterogeneous titanium-silicon composite catalyst.

The invention uses silicon dioxide loaded titanium dioxide, and the prepared titanium catalyst (titanium-silicon composite catalyst) is a heterogeneous catalyst, can catalyze polyester synthesis in a solid state without being in the same phase with a reaction system, and can be loaded on a plate-frame type stirring paddle.

The method for preparing the titanium-silicon composite catalyst can obtain a heterogeneous catalyst, and also can ensure that the prepared catalyst has higher catalytic activity, and byproducts generated in the catalytic process are less, and the mechanism is as follows: compared with the traditional antimony catalyst, the titanium catalyst has higher catalytic activity, but the titanium catalyst is complexed with hydroxyl and ester oxygen in an esterification reaction product to form a multi-ring structure in the catalytic process, so that the structure can reduce the bond energy of carbon-oxygen bonds, the carbon-oxygen bonds are easy to break and generate thermal degradation, more byproducts are generated, and the hue of polyester is influenced; the titanium dioxide is loaded on the silicon dioxide, so that the catalytic activity of the titanium dioxide can be reduced, the occurrence of side reactions is reduced, and meanwhile, the complexing agent is adopted to be complexed with the titanium to occupy the active sites of the titanium, so that the formation of a multi-ring structure is reduced, and the side reactions are reduced.

Preferably, the plate-frame type stirring paddle comprises a stirring shaft and a frame type blade; a catalyst loading cage is arranged on the frame type blade; the catalyst loading cage is of a hollow structure, and through holes with the aperture smaller than the particle size of the heterogeneous titanium-silicon composite catalyst are formed in the wall of the cage.

The invention improves the structure of the plate-and-frame type stirring paddle in the prior art, and the loading of the catalyst on the plate-and-frame type stirring paddle can be realized by loading the heterogeneous titanium-silicon composite catalyst into the catalyst loading cage.

Preferably, in the step (a), the molar ratio of titanium atoms in the titania sol to silicon atoms in the silica sol is 1.

Further, in the step (a), the molar ratio of titanium atoms in the titania sol to silicon atoms in the silica sol is 1.

In consideration of the comprehensive performance of the catalyst, the ratio of titanium atoms in the titanium dioxide sol to silicon atoms in the silica sol needs to be strictly controlled, so that the ratio of titanium dioxide to silicon dioxide in the prepared heterogeneous titanium-silicon composite catalyst is controlled. Too high titanium content can cause severe side reaction in the polymerization process and poor polyester color; if the silicon content is too high, the specific surface area of the catalyst is reduced and the catalytic activity is too low. Therefore, in consideration of the catalytic by-product and the catalytic activity in combination, the molar ratio of titanium atoms to silicon atoms is selected from the range of 1.

Preferably, in the step (a), the titania sol is prepared as follows: and (2) dropwise adding the titanium compound into hydrochloric acid at the temperature of 20-30 ℃, and continuously stirring for 1-6 hours after dropwise adding to obtain the titanium dioxide sol.

Further, the titanium compound is at least one of tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisooctyl titanate and titanium tetrachloride.

Further, in the preparation process of the titanium dioxide sol, the concentration of the hydrochloric acid is 0.05-1 mol/L, and the molar ratio of the titanium compound to the hydrochloric acid is 1-10.

Hydrochloric acid acts as a precipitant in the preparation of the titanium dioxide sol. The titanium compound is not hydrolyzed completely due to the excessively low concentration and the excessively low consumption of the hydrochloric acid, so that the catalytic activity of the prepared catalyst is not controllable, and the hue of the polyester is influenced; too high concentration and too large amount of hydrochloric acid can cause too violent hydrolysis of the titanium compound, so that the grain diameter of the hydrolysate is larger and the catalytic activity is too small. Therefore, the molar ratio of the titanium compound to the hydrochloric acid is selected to be 1 to 10 in consideration of the catalytic activity and the hue of the polyester.

Preferably, in the step (a), the silica sol is prepared as follows: at the temperature of 20-30 ℃, dropwise adding a silicon compound into a mixed solution of hydrochloric acid and absolute ethyl alcohol, and continuously stirring for 1-6 h after dropwise adding to obtain the silica sol.

Further, the silicon compound is at least one of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate and tetrabutyl silicate.

Furthermore, in the preparation process of the silica sol, the concentration of the hydrochloric acid is 0.05-1 mol/L, and the molar ratio of the silicon compound to the hydrochloric acid is 1.

Further, the molar ratio of the silicon compound to the absolute ethyl alcohol is 1 to 10.

Preferably, in step (b), the complexing agent is at least one of citric acid, lactic acid, tartaric acid, malic acid, α -pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methylhexalactam, N-ethylcaprolactam, e-caprolactam and 3-amino-2-caprolactam.

Preferably, in the step (b), the concentration of the aqueous solution of the complexing agent is 0.05 to 1mol/L.

Preferably, the molar ratio of the titanium atoms in the titania sol in step (a) to the complexing agent in step (b) is from 0.05 to 1.

In the heterogeneous titanium-silicon composite catalyst, the complexing agent is used for occupying active sites of titanium, so that the occurrence of side reactions is reduced. Too little complexing agent can result in too many byproducts and poor polyester color; too large a quantity of complex will result in too low a catalyst activity. Therefore, the molar ratio of the titanium atom to the complexing agent in the titanium dioxide sol is selected to be 0.05 to 1 in consideration of the catalytic activity and the catalytic by-products.

Preferably, step (a) is carried out at 20 to 30 ℃.

Preferably, step (b) is carried out at 20 to 30 ℃.

Preferably, in step (b), the mixing is performed by stirring for 0.5 to 5 hours.

Preferably, in step (c), the drying is carried out under vacuum at a temperature of 60 to 100 ℃.

Preferably, the method for catalytically synthesizing the polyester by using the titanium catalyst comprises the following steps:

scheme a:

(1) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-and-frame type stirring paddle, and loading the plate-and-frame type stirring paddle into a reaction vessel;

(2) Esterification: adding dicarboxylic acid and/or ester derivatives thereof and dihydric alcohol into a reaction vessel, starting a plate-and-frame stirring paddle, and carrying out esterification reaction at 230-260 ℃ under the pressure of less than or equal to 0.3MPa for 1-3 h to obtain a prepolymer;

(3) And (3) polycondensation: carrying out polycondensation reaction at 270-285 ℃ and under the pressure of less than 100Pa for 1-2.7 h to obtain polyester;

scheme B:

(1) Esterification: adding dicarboxylic acid and/or ester derivatives thereof and dihydric alcohol into a reaction vessel, and carrying out esterification reaction at 230-260 ℃ and under the pressure of less than or equal to 0.3MPa for 1-3 h to obtain a prepolymer;

(2) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle into a reaction container;

(3) Polycondensation: opening the plate-frame type stirring paddle, and carrying out polycondensation reaction at 270-285 ℃ and under the pressure of less than 100Pa for 1-2.7 h to obtain the polyester.

Preferably, the heterogeneous titanium silicon composite catalyst is used in an amount of 0.5 to 10ppm based on the polyester.

Further, the dosage of the heterogeneous titanium silicon composite catalyst is 1-6 ppm calculated by polyester.

Preferably, the dicarboxylic acid and/or its ester derivative is at least one of terephthalic acid, phthalic acid, isophthalic acid, biphenyldicarboxylic acid, oxalic acid, succinic acid, adipic acid, dimethyl terephthalate, and diethyl terephthalate.

Preferably, the dihydric alcohol is at least one of ethylene glycol, propylene glycol, butylene glycol and hexanediol.

Compared with the prior art, the invention has the following advantages:

(1) The titanium catalyst is loaded on the plate-frame type stirring paddle, so that the prepared polyester does not contain the catalyst, and the problem of viscosity reduction generated when the polyester is conveyed in a molten state is effectively solved;

(2) Loading a titanium catalyst on a plate-frame type stirring paddle, and fully contacting the catalyst with a substrate through stirring, wherein the catalytic activity is high;

(3) Loading a titanium catalyst on a plate-and-frame stirring paddle, so that polyester adhered to the surface of the catalyst can be removed conveniently, and the catalyst can be recycled;

(4) The titanium-silicon composite catalyst prepared by the method is a heterogeneous catalyst, can realize loading on a plate-and-frame stirring paddle, and has high catalytic activity, and the prepared polyester has good hue.

Drawings

FIG. 1 is a schematic perspective view of a plate and frame reactor used in the present invention;

FIG. 2 is a front view of FIG. 1;

the reference signs are: the stirring shaft 1, the frame type blade 2, the catalyst loading cage 3 and the kettle body 4.

Detailed Description

The present invention will be further described with reference to the following examples.

General examples

Preparing a heterogeneous titanium-silicon composite catalyst by the following steps:

(a) Preparing titanium dioxide sol: dropwise adding a titanium compound into hydrochloric acid at the temperature of 20-30 ℃, and continuously stirring for 1-6 hours after dropwise adding to obtain titanium dioxide sol; the titanium compound is at least one of tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisooctyl titanate and titanium tetrachloride; the concentration of the hydrochloric acid is 0.05-1 mol/L, and the molar ratio of the titanium compound to the hydrochloric acid is 1-10;

(b) Preparing a silica sol: dropwise adding a silicon compound into a mixed solution of hydrochloric acid and absolute ethyl alcohol at the temperature of 20-30 ℃, and continuously stirring for 1-6 hours after dropwise adding to obtain silicon dioxide sol; the silicon compound is at least one of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate and tetrabutyl silicate; the concentration of the hydrochloric acid is 0.05-1 mol/L, and the molar ratio of the silicon compound to the hydrochloric acid is 1; the molar ratio of the silicon compound to the absolute ethyl alcohol is 1-10;

(c) Mixing the titanium dioxide sol and the silicon dioxide sol at the temperature of 20-30 ℃ to obtain mixed sol; the molar ratio of titanium atoms in the titanium dioxide sol to silicon atoms in the silica sol is 1;

(d) Dropwise adding the mixed sol into the aqueous solution of the complexing agent at the temperature of between 20 and 30 ℃, and continuously stirring for 0.5 to 5 hours to obtain the mixed sol of the complexing agent; the complexing agent is at least one of citric acid, lactic acid, tartaric acid, malic acid, alpha-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methylhexalactam, N-ethylcaprolactam, epsilon-caprolactam and 3-amino-2-caprolactam; the concentration of the water solution of the complexing agent is 0.05-1 mol/L; the molar ratio of the titanium atoms in the titanium dioxide sol in the step (c) to the complexing agent in the step (d) is 0.05-1;

(e) And (3) carrying out centrifugal treatment on the complexing agent mixed sol, taking the precipitate, washing with deionized water to remove chloride ions, and carrying out vacuum drying at the temperature of 60-100 ℃ to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

The heterogeneous titanium-silicon composite catalyst is utilized to prepare polyester through the following steps:

scheme a:

(1) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle (the structure is shown in figures 1 and 2, the structure comprises a stirring shaft 1 and a frame type blade 2, a hollow catalyst loading cage 3 is arranged on the frame type blade 2, and a through hole with the aperture smaller than the particle size of the heterogeneous titanium-silicon composite catalyst is arranged on the wall of the cage) into a plate-frame type reaction kettle (the structure is shown in figure 2, the structure comprises the plate-frame type stirring paddle and a kettle body 4); the dosage of the heterogeneous titanium silicon composite catalyst is 0.5-10 ppm calculated by polyester;

(2) Esterification: adding dicarboxylic acid and/or ester derivatives thereof and dihydric alcohol into a plate-and-frame type reaction kettle, starting a plate-and-frame type stirring paddle, and carrying out esterification reaction at 230-260 ℃ and under the pressure of less than or equal to 0.3MPa for 1-3 h to obtain a prepolymer; the dicarboxylic acid and/or ester derivatives thereof are at least one of terephthalic acid, phthalic acid, isophthalic acid, diphenic acid, oxalic acid, succinic acid, adipic acid, dimethyl terephthalate and diethyl terephthalate; the dihydric alcohol is at least one of ethylene glycol, propylene glycol, butanediol and hexanediol;

(3) Polycondensation: carrying out polycondensation reaction at 270-285 ℃ under the pressure of less than 100Pa for 1-2.7 h to obtain polyester;

scheme B:

(1) Esterification: adding dicarboxylic acid and/or ester derivatives thereof and dihydric alcohol into a plate-and-frame reactor, and carrying out esterification reaction at 230-260 ℃ and under the pressure of less than or equal to 0.3MPa for 1-3 h to obtain a prepolymer; the dicarboxylic acid and/or ester derivatives thereof are at least one of terephthalic acid, phthalic acid, isophthalic acid, diphenic acid, oxalic acid, succinic acid, adipic acid, dimethyl terephthalate and diethyl terephthalate; the dihydric alcohol is at least one of ethylene glycol, propylene glycol, butanediol and hexanediol;

(2) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle (the structure is shown in figures 1 and 2, and comprises a stirring shaft 1 and a frame type blade 2, wherein a hollow catalyst loading cage 3 is arranged on the frame type blade 2, and through holes with the pore diameter smaller than the particle diameter of the heterogeneous titanium-silicon composite catalyst are arranged on the wall of the cage) into a plate-frame type reaction kettle (the structure is shown in figure 2, and comprises the plate-frame type stirring paddle and a kettle body 4); the dosage of the heterogeneous titanium silicon composite catalyst is 0.5-10 ppm calculated by polyester;

(3) Polycondensation: starting a plate-frame type stirring paddle, and carrying out polycondensation reaction at the temperature of 270-285 ℃ and under the pressure of less than 100Pa for 1-2.7 h to obtain the polyester.

Example 1

(a) Preparing titanium dioxide sol: dropwise adding 4.5mmol of tetrabutyl titanate into 20mL of 0.1mol/L hydrochloric acid at the temperature of 25 ℃, and continuously stirring for 3 hours after dropwise adding is finished to obtain titanium dioxide sol;

(b) Preparing a silica sol: dropwise adding 20mmol of tetramethyl silicate into a mixed solution of 30mL of 0.2mol/L hydrochloric acid and 3mL of absolute ethyl alcohol at 25 ℃, and continuously stirring for 3 hours after dropwise adding to obtain silicon dioxide sol;

(c) Mixing the titanium dioxide sol and the silicon dioxide sol at 25 ℃ to obtain mixed sol;

(d) Dropwise adding the mixed sol into 150mL of 0.15mol/L epsilon-caprolactam water solution at 25 ℃, and continuously stirring for 5h to obtain a complexing agent mixed sol;

(e) And (3) centrifuging the mixed sol of the complexing agent, taking the precipitate, washing with deionized water to remove chloride ions, and drying at 70 ℃ in vacuum to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

(1) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle (the structure is shown in figures 1 and 2, the structure comprises a stirring shaft 1 and a frame type blade 2, a hollow catalyst loading cage 3 is arranged on the frame type blade 2, and a through hole with the aperture smaller than the particle size of the heterogeneous titanium-silicon composite catalyst is arranged on the wall of the cage) into a plate-frame type reaction kettle (the structure is shown in figure 2, the structure comprises the plate-frame type stirring paddle and a kettle body 4);

(2) Esterification: adding terephthalic acid and ethylene glycol into a plate and frame type reaction kettle, starting a plate and frame type stirring paddle, and carrying out esterification reaction at 255 ℃ and 0.25MPa for 3 hours to obtain a prepolymer;

(3) And (3) polycondensation: the polycondensation reaction is carried out at the temperature of 280 ℃ and under the condition of 60Pa to obtain the polyester.

And (3) adding ethylene glycol into the kettle for alcoholysis washing after discharging, and adding the next batch of substrate after washing to perform polymerization reaction.

Example 2

(a) Preparing titanium dioxide sol: at 25 ℃, dropwise adding 30mmol tetraisopropyl titanate into 20mL of 0.5mol/L hydrochloric acid, and continuously stirring for 5 hours after dropwise adding to obtain titanium dioxide sol;

(b) Preparing a silica sol: dropwise adding 60mmol of tetramethyl silicate into a mixed solution of 30mL of 1mol/L hydrochloric acid and 6mL of absolute ethyl alcohol at 25 ℃, and continuously stirring for 4 hours after dropwise adding to obtain silicon dioxide sol;

(d) Dropwise adding the mixed sol into 200mL of 0.3mol/L citric acid aqueous solution at 25 ℃, and continuously stirring for 5 hours to obtain complexing agent mixed sol;

(e) And (3) centrifuging the mixed sol of the complexing agent, taking the precipitate, washing with deionized water to remove chloride ions, and drying at 100 ℃ in vacuum to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

(2) Esterification: adding terephthalic acid and ethylene glycol into a plate and frame type reaction kettle, starting a plate and frame type stirring paddle, and carrying out esterification reaction at 250 ℃ and 0.28MPa for 2.5 hours to obtain a prepolymer;

(3) And (3) polycondensation: the polycondensation reaction is carried out at 278 ℃ and 80Pa to obtain the polyester.

And after discharging, adding ethylene glycol into the kettle for alcoholysis washing, and after washing, adding the next batch of substrate to perform polymerization reaction.

Example 3

(a) Preparing titanium dioxide sol: at 25 ℃, 14.5mmol of tetrapropyl titanate is added into 10mL of 1mol/L hydrochloric acid drop by drop, and stirring is continued for 1.5h after the dropwise addition is finished, so as to obtain titanium dioxide sol;

(b) Preparing a silica sol: at 25 ℃, dropwise adding 30mmol of tetrapropyl silicate into mixed solution of 40mL of 0.8mol/L hydrochloric acid and 4mL of absolute ethyl alcohol, and continuously stirring for 3 hours after dropwise adding to obtain silicon dioxide sol;

(d) Dropwise adding the mixed sol into 100mL of 0.8mol/L N-methylpyrrolidone aqueous solution at the temperature of 25 ℃, and continuously stirring for 4 hours to obtain a complexing agent mixed sol;

(e) And (3) centrifuging the mixed sol of the complexing agent, taking the precipitate, washing with deionized water to remove chloride ions, and drying in vacuum at 60 ℃ to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

(1) Esterification: adding terephthalic acid and ethylene glycol into a plate-and-frame type reaction kettle, and carrying out esterification reaction at 240 ℃ and 0.25MPa for 2.5 hours to obtain a prepolymer;

(2) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle (the structure is shown in figures 1 and 2, and comprises a stirring shaft 1 and a frame type blade 2, wherein a hollow catalyst loading cage 3 is arranged on the frame type blade 2, and through holes with the pore diameter smaller than the particle diameter of the heterogeneous titanium-silicon composite catalyst are arranged on the wall of the cage) into a plate-frame type reaction kettle (the structure is shown in figure 2, and comprises the plate-frame type stirring paddle and a kettle body 4);

(3) And (3) polycondensation: and opening a plate-frame type stirring paddle, and carrying out polycondensation reaction at 285 ℃ under the condition of 70Pa to obtain the polyester.

Example 4

(a) Preparing titanium dioxide sol: at 25 ℃, dropwise adding 5mmol of tetraethyl titanate into 5mL of 1mol/L hydrochloric acid, and continuously stirring for 1h after dropwise adding to obtain titanium dioxide sol;

(b) Preparing a silica sol: at 25 ℃, dropwise adding 50mmol of tetraethyl silicate into a mixed solution of 25mL of 0.5mol/L hydrochloric acid and 5mL of absolute ethyl alcohol, and continuously stirring for 6 hours after dropwise adding to obtain silicon dioxide sol;

(d) Dropwise adding the mixed sol into 100mL of a 1mol/L tartaric acid aqueous solution at 25 ℃, and continuously stirring for 5 hours to obtain a complexing agent mixed sol;

(e) And (3) centrifuging the mixed sol of the complexing agent, taking the precipitate, washing with deionized water to remove chloride ions, and drying in vacuum at 80 ℃ to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

(1) Esterification: adding terephthalic acid and ethylene glycol into a plate-and-frame type reaction kettle, and carrying out esterification reaction at 260 ℃ and 0.3MPa for 2.5 hours to obtain a prepolymer;

(2) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle (the structure is shown in figures 1 and 2, the structure comprises a stirring shaft 1 and a frame type blade 2, a hollow catalyst loading cage 3 is arranged on the frame type blade 2, and a through hole with the aperture smaller than the particle size of the heterogeneous titanium-silicon composite catalyst is arranged on the wall of the cage) into a plate-frame type reaction kettle (the structure is shown in figure 2, the structure comprises the plate-frame type stirring paddle and a kettle body 4);

(3) And (3) polycondensation: and opening a plate-frame type stirring paddle, and carrying out polycondensation reaction at 285 ℃ under the condition of 90Pa to obtain the polyester.

Example 5

(a) Preparing titanium dioxide sol: at 25 ℃, dropwise adding 50mmol of titanium tetrachloride into 10mL of 0.5mol/L hydrochloric acid, and continuously stirring for 5 hours after dropwise adding to obtain titanium dioxide sol;

(b) Preparing a silica sol: at 25 ℃, 5mmol of tetrabutyl silicate is dropwise added into a mixed solution of 10mL of 0.5mol/L hydrochloric acid and 1mL of absolute ethyl alcohol, and stirring is continued for 1h after dropwise addition is finished to obtain silicon dioxide sol;

(d) Dropwise adding the mixed sol into 50mL 1mol/L N-methyl caprolactam water solution at 25 ℃, and continuously stirring for 4h to obtain complexing agent mixed sol;

(1) Esterification: adding terephthalic acid and ethylene glycol into a plate-and-frame type reaction kettle, and carrying out esterification reaction at 260 ℃ and 0.3MPa for 2.5h to obtain a prepolymer;

(3) Polycondensation: and opening a plate-frame type stirring paddle, and carrying out polycondensation reaction at 285 ℃ under the condition of 90Pa to obtain the polyester.

Comparative example 1

(e) And (3) centrifuging the mixed sol of the complexing agent, taking the precipitate, washing with deionized water to remove chloride ions, and drying in vacuum at 70 ℃ to constant weight to obtain the heterogeneous titanium-silicon composite catalyst.

(1) Adding a catalyst: dispersing a heterogeneous titanium-silicon composite catalyst into ethylene glycol to obtain ethylene glycol catalyst dispersion liquid;

(2) Esterification: adding terephthalic acid and ethylene glycol catalyst dispersion liquid into a plate-and-frame type reaction kettle, starting a plate-and-frame type stirring paddle, and carrying out esterification reaction at 255 ℃ and 0.25MPa for 3h to obtain a prepolymer;

Comparative example 2

(a) Preparing titanium dioxide sol: dropwise adding 20mmol of tetrabutyl titanate into 15mL of 0.1mol/L hydrochloric acid at 25 ℃, and continuously stirring for 3h after dropwise adding to obtain titanium dioxide sol;

(b) Preparing a silica sol: at 25 ℃, dropwise adding 80mmol of tetrabutyl silicate into a mixed solution of 30mL of 1mol/L hydrochloric acid and 7mL of absolute ethyl alcohol, and continuously stirring for 3 hours after dropwise adding to obtain silicon dioxide sol;

(d) Dropwise adding the mixed sol into 150mL of 0.5mol/L tartaric acid aqueous solution at 25 ℃, and continuously stirring for 2h to obtain a complexing agent mixed sol;

(2) Esterification: adding terephthalic acid and ethylene glycol catalyst dispersion liquid into a plate-and-frame type reaction kettle, starting a plate-and-frame type stirring paddle, and carrying out esterification reaction at 255 ℃ and under the pressure of 0.25MPa to obtain a prepolymer;

(3) And (3) polycondensation: the polycondensation reaction is carried out at the temperature of 280 ℃ and under the condition of 60Pa, the reaction time is 2.5h, and the polyester is obtained.

Comparative example 3

Comparative example 3 differs from example 4 in that: in the step (b), the dosage of the tetraethyl silicate is 70mmol, the dosage of 0.5mol/L hydrochloric acid is 35mL, and the dosage of the absolute ethyl alcohol is 7mL. The remaining parameters and operations were as in example 4.

Comparative example 4

Comparative example 4 differs from example 5 in that: in the step (b), the dosage of tetrabutyl silicate is 3mmol, the dosage of 0.5mol/L hydrochloric acid is 6mL, and the dosage of absolute ethyl alcohol is 0.6mL. The remaining parameters and operations were as in example 5.

Comparative example 5

Comparative example 5 differs from example 4 in that: in the step (a), the amount of 1mol/L hydrochloric acid used is 8mL. The remaining parameters and operation were as in example 4.

Comparative example 6

Comparative example 6 differs from example 5 in that: in the step (a), the amount of 0.5mol/L hydrochloric acid used was 8mL. The remaining parameters and operations were as in example 5.

Comparative example 7

Comparative example 7 differs from example 4 in that: in the step (d), the amount of the 1mol/L aqueous tartaric acid solution was 150mL. The remaining parameters and operations were as in example 4.

Comparative example 8

Comparative example 8 differs from example 5 in that: in step (d), 1mol/L of an aqueous solution of N-methylhexalactam is used in an amount of 30mL. The remaining parameters and operation were as in example 5.

The polyester chips obtained in examples 1 to 3 and comparative examples 1 to 8 were tested for viscosity, hue, melting point, and diethylene glycol content, and the results are shown in Table 1. After the polyester chip is subjected to heat treatment for 3 hours at 100 ℃ in an air atmosphere, the viscosity and the hue of the polyester chip are tested, and the data of the viscosity change and the hue change are shown in a table 2.

TABLE 1

TABLE 2

Example 1 is different from comparative example 1 in that a plate and frame type reaction kettle is used in example 1, the catalyst is loaded on a plate and frame type stirring paddle, and the catalyst is directly dispersed in the reaction system in comparative example 1, and other conditions are the same. From the data in Table 2, the polyester chips obtained in example 1 exhibited significantly less viscosity change after heat treatment than those obtained in comparative example 1. The reason why the problem of viscosity drop during the transportation of polyester in a molten state can be effectively solved by loading a titanium-based catalyst in a plate-and-frame type stirring paddle is presumed to be as follows: in the embodiment 1, after the reaction is finished, the catalyst in the plate-and-frame type stirring paddle can be separated from the polyester melt, so that the obtained polyester product does not contain the catalyst, thereby preventing the alcoholysis of the polyester under the action of the catalyst and effectively improving the problem of viscosity reduction of the polyester melt.

In example 4 and comparative example 3, the molar ratio of the titanium compound in step (a) to the silicon compound in step (b) was 1; in example 5 and comparative example 4, the molar ratio of the titanium compound in step (a) to the silicon compound in step (b) was 1. From the data in Table 1, it can be seen that the polycondensation time is significantly increased in the process of preparing the polyester of comparative example 3 compared to example 4; the polyester chip obtained in comparative example 4 was significantly inferior in hue to example 5. The reason why the molar ratio of the peptide compound to the silicon compound is controlled in the range of 1.1 to 10 and that too high or too low affects the catalyst performance is presumed to be as follows: the use amount of the peptide compound is too large, so that side reaction is severe in the polymerization process, and the color of the slice is poor; if the amount of the silicon compound used is too large, the specific surface area of the catalyst is lowered and the catalytic activity is too low.

Example 4 and comparative example 5, in step (a), the molar ratios of titanium compound to hydrochloric acid were 1 and 0.625, respectively, and the other conditions were the same; in example 5 and comparative example 6, the molar ratio of the titanium compound to hydrochloric acid in step (a) was 10. From the data in Table 1, it can be seen that the polycondensation time is significantly increased in the process of preparing the polyester of comparative example 5 compared to example 4; the polyester chip obtained in comparative example 6 had a significantly poorer hue than that of example 5. It is shown that the molar ratio of the titanium compound to the hydrochloric acid (i.e. the molar ratio of titanium atoms in the titanium dioxide sol to silicon atoms in the silica sol) needs to be controlled within the range of 1 to 10, and that too high or too low will affect the catalyst performance, and the reason is presumed as follows: in the process of preparing titanium dioxide sol, hydrochloric acid is used as a precipitator to play a role, so that the titanium compound is incompletely hydrolyzed due to the excessively low concentration and the excessively small dosage of the hydrochloric acid, the catalytic activity of the prepared catalyst is uncontrollable, and the hue of polyester is influenced; too high concentration and too large amount of hydrochloric acid can cause too violent hydrolysis of the titanium compound, so that the grain diameter of the hydrolysate is larger and the catalytic activity is too small.

In example 4 and comparative example 7, the molar ratios of the silicon compound in step (c) to the complexing agent in step (d) were 0.05; in example 4 and comparative example 8, the molar ratios of the silicon compound in step (c) to the complexing agent in step (d) were 1 and 1.67, respectively, and the other conditions were the same. From the data in Table 1, it can be seen that the polycondensation time is significantly increased in the process of preparing the polyester of comparative example 7 compared to example 4; the polyester chip obtained in comparative example 8 was significantly inferior in hue to example 5. It is shown that the molar ratio of the silicon compound to the complexing agent (i.e. the molar ratio of the titanium atoms in the titanium dioxide sol to the complexing agent) needs to be controlled within the range of 0.05 to 1, and that too high or too low will affect the catalyst performance, presumably for the following reasons: the complexing agent occupies the active site of titanium, so that the occurrence of side reaction is reduced, and the consumption of the complexing agent is too low, so that the by-product is too much, and the color difference of polyester is caused; the catalyst activity is too low due to the excessive complex dosage, and the raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modifications, alterations and equivalent changes made to the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for synthesizing polyester by using titanium catalyst is characterized by comprising the following steps:

scheme A:

(1) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-frame type stirring paddle, and loading the plate-frame type stirring paddle into a reaction container;

(2) Esterification: adding dicarboxylic acid and/or ester derivatives thereof and dihydric alcohol into a reaction container, opening a plate-and-frame stirring paddle, and carrying out esterification reaction at 230-260 ℃ under the pressure of less than or equal to 0.3MPa for 1-3 h to obtain a prepolymer;

(3) Polycondensation: carrying out polycondensation reaction at the temperature of 270 to 285 ℃ and under the pressure of less than 100Pa for 1 to 2.7h to obtain polyester;

scheme B:

(2) Loading a catalyst: loading a heterogeneous titanium-silicon composite catalyst on a plate-and-frame type stirring paddle, and loading the plate-and-frame type stirring paddle into a reaction vessel;

(3) Polycondensation: opening a plate-frame type stirring paddle, and carrying out polycondensation reaction at the temperature of 270 to 285 ℃ under the pressure of less than 100Pa for 1 to 2.7h to obtain polyester;

in the scheme A and the scheme B, the plate-frame type stirring paddle comprises a stirring shaft and a frame type blade; a catalyst loading cage is arranged on the frame type blade; the catalyst loading cage is of a hollow structure, and through holes with the aperture smaller than the particle size of the heterogeneous titanium-silicon composite catalyst are formed in the wall of the cage; the preparation method of the heterogeneous titanium-silicon composite catalyst comprises the following steps:

(a) Mixing titanium dioxide sol and silicon dioxide sol to obtain mixed sol;

(b) Dropwise adding the mixed sol into an aqueous solution of a complexing agent, and uniformly mixing to obtain a mixed sol of the complexing agent;

2. The method for catalytically synthesizing a polyester by using a titanium-based catalyst according to claim 1, wherein in the step (a), the molar ratio of titanium atoms in the titania sol to silicon atoms in the silica sol is from 1 to 0.1 to 10.

3. The method for catalytically synthesizing polyester by using titanium-based catalyst according to claim 1, wherein:

in the step (a), the titania sol is prepared as follows: dropwise adding a titanium compound into hydrochloric acid at the temperature of 20-30 ℃, and continuously stirring for 1-6 hours after dropwise adding to obtain titanium dioxide sol; and/or

In the step (a), the silica sol is prepared as follows: and (3) dropwise adding the silicon compound into a mixed solution of hydrochloric acid and absolute ethyl alcohol at the temperature of 20-30 ℃, and continuously stirring for 1-6 hours after dropwise adding to obtain the silicon dioxide sol.

4. The method for synthesizing polyester by using titanium catalyst as claimed in claim 3, wherein:

the titanium compound is at least one of tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisooctyl titanate and titanium tetrachloride; and/or

The silicon compound is at least one of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate and tetrabutyl silicate; and/or

In the preparation process of the titanium dioxide sol, the concentration of the hydrochloric acid is 0.05 to 1mol/L, and the molar ratio of the titanium compound to the hydrochloric acid is 1 to 10; and/or

In the preparation process of the silica sol, the concentration of the hydrochloric acid is 0.05 to 1mol/L, and the molar ratio of the silicon compound to the hydrochloric acid is 1; and/or

The molar ratio of the silicon compound to the absolute ethyl alcohol is 1 to 10.

5. The method for catalytically synthesizing polyester with titanium based catalyst according to claim 1, wherein in the step (b), the complexing agent is at least one selected from citric acid, lactic acid, tartaric acid, malic acid, α -pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methylhexalactam, N-ethylcaprolactam, e-caprolactam and 3-amino-2-caprolactam.

6. The method for catalytically synthesizing polyester by using a titanium-based catalyst according to claim 1, wherein the molar ratio of the titanium atom in the titanium dioxide sol in the step (a) to the complexing agent in the step (b) is from 0.05 to 1.

7. The method for catalytically synthesizing polyester by using titanium-based catalyst according to claim 1, wherein:

the dicarboxylic acid and/or ester derivatives thereof are at least one of terephthalic acid, phthalic acid, isophthalic acid, diphenic acid, oxalic acid, succinic acid, adipic acid, dimethyl terephthalate and diethyl terephthalate; and/or

The dihydric alcohol is at least one of ethylene glycol, propylene glycol, butanediol and hexanediol.