Preparation method of low-color-value polyester and obtained polyester

Abstract

The invention discloses a preparation method of low-color-value polyester and the obtained polyester. The preparation method comprises the following steps: (1) carrying out esterification reaction on raw materials including aromatic dibasic acid, adipic acid and dihydric alcohol in the presence of a catalyst to obtain an esterification product; and (2) adding an alkaline substance and a phosphorus-containing compound into the esterification product, and carrying out condensation polymerization to obtain the low-color-value polyester. Alkaline substances are added in the later stage of esterification, decarboxylation cyclization and further polymerization side reaction of adipic acid or chain segments of adipic acid under the condition of high temperature in the polycondensation stage are inhibited, the a value and the b value of the product are reduced, and the quality of the polyester resin is improved.

Description

Technical Field

[0001] The present invention belongs to the field of polyesters, and particularly relates to the preparation of low-chromaticity polyesters. Background Art

[0002] The use of plastic materials has greatly improved the quality of human life. However, with the large increase in plastic waste, the soil and oceans on which humans depend for survival are also facing serious "white pollution". Therefore, it is extremely urgent to research and develop environmentally friendly biodegradable materials. Among a series of biodegradable polyesters, taking poly(butylene adipate-co-terephthalate) (PBAT) as an example, it has good ductility and elongation at break, as well as good heat resistance and impact resistance. At the same time, it can be degraded by microorganisms into water and carbon dioxide, and can be widely used in fields such as sheets, mulch films, packaging, and foaming. It is one of the most active and best market-applied biodegradable materials in the current research of biodegradable plastics.

[0003] In the preparation process of PBAT, adipic acid (AA) or its segments are prone to decarboxylation degradation under high-temperature conditions, as well as further polymerization of the degradation products, especially under the high-temperature conditions of polycondensation. This makes the obtained PBAT resin have a poor color and high a and b values, which greatly limits the application of PBAT.

[0004] CN 115286776A discloses a preparation method of PBAT. Terephthalic acid (PTA) and AA are respectively subjected to esterification reactions with 1,4-butanediol (BDO). In the esterification reaction of AA and BDO, a carbodiimide esterification activator is added. After the esterification is completed, the two esterified products are mixed and subjected to a polycondensation reaction under the action of a catalyst and an auxiliary agent to obtain a PBAT resin with good hue.

[0005] CN113667103A discloses a preparation method of a PBAT resin. A titanium EDTA composite catalyst, terephthalic acid, adipic acid, and 1,4-butanediol are subjected to an esterification reaction; after the esterification reaction is completed, a reducing agent 4,4′,4″-triaminotriphenylmethane and / or L-polylysine are added, and PBAT pellets are prepared by polycondensation. The PBAT shows low a and b values.

[0006] In the above technologies, the hue of the PBAT resin is improved by increasing the esterification rate of adipic acid or suppressing deacidification by reduction. However, there are still problems such as a large amount of esterification activator used, high cost of the reducing agent, and certain toxicity during the operation process. Summary of the Invention

[0007] In order to overcome the problems existing in the prior art, the present invention provides a method for preparing a polyester with low color value and the obtained polyester. Among them, by adding an alkaline substance in the later stage of esterification, the decarboxylation cyclization of adipic acid or its segments and further polymerization side reactions under high temperature conditions in the polycondensation stage are inhibited, the a and b values of the product are reduced, and the quality of the polyester (such as PBAT) resin is improved.

[0008] One of the purposes of the present invention is to provide a method for preparing a polyester with low chromaticity, including: (1) raw materials including aromatic dicarboxylic acid, adipic acid, and diol are subjected to an esterification reaction in the presence of a catalyst to obtain an esterification product; (2) an alkaline substance and a phosphorus-containing compound are added to the esterification product, and the polyester with low color value is obtained through a polycondensation reaction.

[0009] In a preferred embodiment, the aromatic dicarboxylic acid is selected from at least one of terephthalic acid and naphthalenedicarboxylic acid; and / or, the diol is selected from diols having 2 to 10 carbon atoms, preferably at least one of butanediol, propanediol, and ethylene glycol.

[0010] In a preferred embodiment, the molar ratio of the total molar amount of the aromatic dicarboxylic acid and adipic acid to the molar amount of the diol is 1:(1.1 - 2.0), preferably 1:(1.4 - 1:2.0), for example, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2.0;

[0011] In a further preferred embodiment, based on 100% of the total molar amount of the aromatic dicarboxylic acid and adipic acid, among them, the aromatic dicarboxylic acid accounts for 10 - 90%, and adipic acid accounts for 10 - 90%.

[0012] For example, based on 100% of the total molar amount of the aromatic dicarboxylic acid and adipic acid, among them, the aromatic dicarboxylic acid accounts for any point value or a range composed of any two point values among 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, and adipic acid accounts for any point value or a range composed of any two point values among 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

[0013] In a further preferred embodiment, based on 100% of the total molar amount of the aromatic dicarboxylic acid and adipic acid, among them, the aromatic dicarboxylic acid accounts for 40 - 60%, and adipic acid accounts for 40 - 60%.

[0014] In a preferred embodiment, the catalyst in step (1) is selected from any polyester esterification catalyst disclosed in the prior art, preferably but not limited to one or more selected from titanates.

[0015] In a further preferred embodiment, the general formula of the titanate is Ti(OR) 4 , wherein R is selected from alkyl groups having 1 to 10 carbon atoms.

[0016] In an even more preferred embodiment, the titanate is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate.

[0017] In a preferred embodiment, in step (1), based on the theoretical production amount of the polyester, the dosage of the catalyst is 50 to 200 mg / kg (for example, 50 mg / kg, 60 mg / kg, 80 mg / kg, 100 mg / kg, 120 mg / kg, 140 mg / kg, 160 mg / kg, 180 mg / kg, or 200 mg / kg), wherein the dosage of the catalyst is calculated based on the amount of the metal element, for example, based on the weight of the titanium element.

[0018] In a preferred embodiment, the conditions of the esterification reaction include: the pressure is atmospheric pressure - 0.5 MPa, and / or the temperature is 160 to 230 °C, and the time is 60 to 240 min.

[0019] For example, the conditions of the esterification reaction include: the pressure is atmospheric pressure, 0.2 MPa, 0.3 MPa, 0.4 MPa, or 0.5 MPa, and / or the temperature is 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, or 230 °C, and the time is 60 min, 80 min, 100 min, 120 min, 150 min, 180 min, 200 min, 220 min, or 240 min.

[0020] In a further preferred embodiment, the conditions of the esterification reaction include: the pressure is atmospheric pressure, and / or the temperature is 180 to 230 °C, and the time is 120 to 180 min.

[0021] In a preferred embodiment, the basic substance is selected from alkali metal compounds (preferably hydroxides and / or acetates).

[0022] Among them, the inventors conducted a large number of experiments and found that when the basic substance is selected from alkali metal compounds, the effect is significantly better than that of amine compounds.

[0023] In a further preferred embodiment, the basic substance is selected from at least one of hydroxides of alkali metals, organic acid salts of alkali metals (preferably C1 - C5 organic acid salts, such as acetates), and / or ammonia water.

[0024] In an even more preferred embodiment, the alkali metal is selected from at least one of lithium, sodium, and potassium.

[0025] For example, the basic substance is selected from at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium acetate, potassium acetate, and lithium acetate.

[0026] In the present invention, adding a basic substance in the later stage of esterification can play a role in stabilizing the carboxyl group and reduce decarboxylation under high-temperature conditions. The inventors also found in experiments that if the basic substance is added during the esterification process in step (1), the esterification rate of the polyester will decrease.

[0027] In a preferred embodiment, based on the theoretical production amount of the polyester being 100 wt%, the dosage of the basic substance is 0.0005 - 0.02 wt%, preferably 0.001 - 0.01 wt%, for example 0.001 wt%, 0.002 wt%, 0.003 wt%, 0.004 wt%, 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.009 wt% or 0.01 wt%.

[0028] Among them, the inventors found in a large number of experimental studies that when the dosage of the base is too high, it may promote the cleavage of the polyester main chain, resulting in a decrease in the viscosity of the polyester (such as PBAT resin).

[0029] In a preferred embodiment, the basic substance is added to the esterification product in the form of a solution, preferably an alcohol / water mixed solution.

[0030] The inventors found through experiments that using an alcohol / water mixed solution not only improves the solubility of the basic substance but also reduces the flash evaporation degree during feeding.

[0031] In a further preferred embodiment, in the alcohol / water mixed solution, the weight ratio of alcohol to water is 9 - 5; and / or the concentration of the basic substance in the solution is 0.1 - 1 wt%.

[0032] For example, in the alcohol / water mixed solution, the weight ratio of alcohol to water is 9, 8, 7, 6 or 5; and / or the concentration of the basic substance in the solution is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%.

[0033] In a further preferred embodiment, the alcohol is selected from diols, preferably the same diol as in step (1).

[0034] In a preferred embodiment, the phosphorus-containing compound is selected from at least one of phosphate esters, preferably trihydrocarbyl phosphate, and the hydrocarbyl group is selected from an alkyl group having 1 - 10 carbon atoms or an aryl group having 6 - 15 carbon atoms.

[0035] In a further preferred embodiment, the phosphorus-containing compound is selected from at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, dibutyl phosphate, and triphenyl phosphate.

[0036] Among them, the phosphorus compound can form a specific compound with the metal in the esterification catalyst (such as titanium in titanate) under high-temperature conditions, reducing the coordination ability of the metal (such as titanium) to the ester carbonyl oxygen, thereby able to reduce the thermal degradation reaction rate of the polyester to a certain extent and also helpful for improving the hue of the polyester. When the content of the phosphorus-containing compound is too low, the inhibition of the side reaction degree catalyzed by titanium is limited and cannot effectively improve the catalyst performance. When the content of the phosphorus-containing compound is too high, although the hue and thermal degradation rate are effectively improved, the activity of the titanium catalyst is also severely inhibited.

[0037] In a preferred embodiment, based on the theoretical production amount of the raw polyester being 100 wt%, the dosage of the phosphorus-containing compound is 0.002 - 0.2 wt%, preferably 0.002 - 0.12 wt%, wherein the dosage of the phosphorus-containing compound is based on the dosage of phosphorus element.

[0038] For example, based on the theoretical production amount of the polyester being 100 wt%, the dosage of the phosphorus-containing compound is 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.02 wt%, 0.04 wt%, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.16 wt%, 0.18 wt%, or 0.2 wt%, wherein the dosage of the phosphorus-containing compound is based on the dosage of phosphorus element.

[0039] In a preferred embodiment, the conditions of the polycondensation reaction in step (2) include: the temperature is 210 - 250 °C, and / or the pressure is an absolute pressure of 30 - 500 Pa, and / or the time is 1 - 8 h.

[0040] For example, the conditions of the polycondensation reaction in step (2) include: the temperature is 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, or 250 °C, and / or the pressure is an absolute pressure of 30 Pa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, 250 Pa, 300 Pa, 350 Pa, 400 Pa, 450 Pa, or 500 Pa, and / or the time is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h.

[0041] In the present invention, by adding an alkaline substance after esterification, the stability of carboxyl groups is effectively improved, side reactions such as decarboxylation are inhibited, and a PBAT resin with low a and b values is prepared in combination with a phosphorus-containing compound.

[0042] The second object of the present invention is to provide a polyester obtained by the preparation method described in the first object of the present invention, and its intrinsic viscosity > 1.2 dl / g.

[0043] In a preferred embodiment, the L value of the polyester > 80, preferably > 82.

[0044] In a preferred embodiment, the a value of the polyester is < 2.

[0045] In a preferred embodiment, the b value of the polyester < 10, preferably < 8.

[0046] In the present invention, the endpoints and any values within the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following text, in principle, the various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed herein.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) By adding an alkaline substance in the later stage of esterification, the present invention can, with a relatively low dosage, well improve the hue of the resin, obtain a PBAT resin with a low color value, and at the same time have a relatively small impact on the polymerization activity, and can obtain a resin with an intrinsic viscosity > 1.2 dl / g, having good technical effects.

[0049] (2) The preparation method described in the present invention is simple and easy to implement, and can be applied to large-scale production. Specific Embodiments

[0050] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0051] In addition, it should be noted that, among the various specific technical features described in the following specific embodiments, they can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0052] In addition, any combination can be made among various different embodiments of the present invention, as long as it does not violate the idea of the present invention. The technical solutions thus formed belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0053] If there is no special limitation, the raw materials used in the examples and comparative examples are those disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0054] In the present invention, the intrinsic viscosity, hue, etc. of the polyester are tested by the following methods:

[0055] (1) Intrinsic viscosity: Using a phenol-tetrachloroethane mixture as a solvent, it is measured with an Ubbelohde viscometer at a temperature of 25°C.

[0056] (2) Hue: After treating the pellet sample at 80°C for 1 hour, its Hunter L value (brightness), a value (hue of red-green), and b value (hue of yellow-blue) are measured with a color-view automatic color difference meter from BYK Gardner. Among them, the higher the L value, the greater the brightness; the higher the a value, the redder the polyester chip, and the higher the b value, the yellower the polyester chip. For the present invention, it is desired to pursue a high L value and a low a / b value.

[0057] (3) Acid value: The esterified product is dissolved with dichloromethane, using phenolphthalein as an indicator, and titrated with a KOH / ethanol solution. The average value is taken after measuring 3 times.

[0058]

Example 1

[0059] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 °C to 230 °C at atmospheric pressure, and the reaction time was 150 min. The water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and 0.1 wt% of a NaOH BDO (1,4-butanediol) / water mixed solution (the addition amount of NaOH was 0.002 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 wt% based on the amount of polyester produced) were added. After stirring for 10 min, the pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually increased to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0060] The test results are listed in Table 1.

[0061]

Example 2

[0062] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and 0.1 wt% of a NaOH BDO / water mixed solution (the addition amount of NaOH was 0.004 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 wt% based on the amount of polyester produced) were added. The pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually increased to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0063] The test results are listed in Table 1.

[0064]

Example 3

[0065] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and a 0.1 wt% BDO / water mixed solution of sodium hydroxide (the addition amount of sodium hydroxide was 0.008 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 wt% based on the amount of polyester produced) were added. The pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0066] The test results are listed in Table 1.

[0067]

Example 4

[0068] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and a 0.1 wt% BDO / water mixed solution of sodium acetate (the addition amount of sodium acetate was 0.004 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 wt% based on the amount of polyester produced) were added. The pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0069] The test results are listed in Table 1.

[0070]

Example 5

[0071] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and a 0.1 wt% KOH BDO / water mixed solution (the addition amount of potassium hydroxide was 0.004 w% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 w% based on the amount of polyester produced) were added. The pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0072] The test results are listed in Table 1.

[0073]

Example 6

[0074] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and a 0.1 wt% ammonia water BDO / water mixed solution (the addition amount of ammonia water was 0.004 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element was 0.006 wt% based on the amount of polyester produced) were added. The pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time, the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0075] The test results are listed in Table 1.

[0076]

Example 7

[0077] 274 g of terephthalic acid, 161 g of adipic acid, 480 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 °C to 230 °C, the pressure was atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and 0.1 wt% KOH BDO (1,4-butanediol) / water mixed solution (the addition amount of potassium hydroxide was 0.006 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and tributyl phosphate (the addition amount of tributyl phosphate in terms of phosphorus element was 0.005 wt% based on the amount of polyester produced) were added. After stirring for 10 min, the pressure was reduced by vacuum to a system pressure below 150 Pa, and at the same time, the temperature was gradually increased to 240 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0078] The test results are listed in Table 1.

[0079]

Example 8

[0080] 182 g of terephthalic acid, 240 g of adipic acid, 480 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 °C to 220 °C, the pressure was atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, and 0.1 wt% KOH BDO (1,4-butanediol) / water mixed solution (the addition amount of potassium hydroxide was 0.006 wt% based on the amount of polyester produced, and the weight ratio of BDO to water was 9:1) and dibutyl phosphate (the addition amount of dibutyl phosphate in terms of phosphorus element was 0.005 wt% based on the amount of polyester produced) were added. After stirring for 10 min, the pressure was reduced by vacuum to a system pressure below 150 Pa, and at the same time, the temperature was gradually increased to 240 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0081] The test results are listed in Table 1.

[0082]

Comparative Example 1

[0083] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, triethyl phosphate was added (the addition amount of triethyl phosphate based on the amount of polyester produced was 0.006 wt% in terms of phosphorus element), the pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0084] The test results are listed in Table 1.

[0085]

Comparative Example 2

[0086] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, the pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0087] The test results are listed in Table 1.

[0088]

Comparative Example 3

[0089] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol, tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) and sodium hydroxide (the addition amount of sodium hydroxide based on the amount of polyester produced was 0.004 wt%, and the weight ratio of BDO to water was 9:1) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, the reaction time was 150 min, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed, the pressure was reduced to atmospheric pressure, triethyl phosphate was added (the addition amount of triethyl phosphate based on the amount of polyester produced was 0.006 wt% in terms of phosphorus element), the pressure was reduced by vacuum to a system pressure below 130 Pa, and at the same time the temperature was gradually raised to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0090] The test results are listed in Table 1.

[0091]

Comparative Example 4

[0092] Mix 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) to form a slurry, add it to a polymerization kettle, and carry out an esterification reaction. The esterification temperature rises from 190 to 230 °C, the pressure is atmospheric pressure, the reaction time is 150 min, and the water generated by the reaction is discharged through a rectification device. After the esterification is completed, the pressure is reduced to atmospheric pressure, and a 0.1 wt% NaOH BDO / water mixed solution (the addition amount of NaOH is 0.02 wt% based on the amount of polyester produced, and the weight ratio of BDO to water is 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element is 0.006% based on the amount of polyester produced) are added. The pressure is reduced to less than 130 Pa by vacuum, and at the same time, the temperature is gradually raised to 250 °C. When the system reaction reaches 150 min, the reaction is stopped. Then, the product is extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0093] The test results are listed in Table 1.

[0094]

Comparative Example 5

[0095] Mix 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) to form a slurry, add it to a polymerization kettle, and carry out an esterification reaction. The esterification temperature gradually rises from 190 °C to 230 °C, the pressure is atmospheric pressure, the reaction time is 150 min, and the water generated by the reaction is discharged through a rectification device. After the esterification is completed, the pressure is reduced to atmospheric pressure, and a 0.1 wt% dopamine BDO (1,4-butanediol) / water mixed solution (the addition amount of dopamine is 0.004 wt% based on the amount of polyester produced, and the weight ratio of BDO to water is 9:1) and triethyl phosphate (the addition amount of triethyl phosphate in terms of phosphorus element is 0.006 wt% based on the amount of polyester produced) are added. After stirring for 10 min, the pressure is reduced to less than 130 Pa by vacuum, and at the same time, the temperature is gradually raised to 250 °C. When the system reaction reaches 150 min, the reaction is stopped. Then, the product is extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0096] The test results are listed in Table 1.

[0097] Table 1:

[0098]

[0099] It can be seen from Table 1 that:

[0100] (1) Compared with Example 2, in Comparative Example 1, sodium hydroxide was not added after esterification, and the a and b values of the obtained PBAT resins were relatively high, indicating that the addition of sodium hydroxide can effectively stabilize carboxyl groups and inhibit side reactions such as decarboxylation.

[0101] (2) Compared with Example 2, in Comparative Example 3, sodium hydroxide was added in the esterification stage. The premature addition of sodium hydroxide affected the progress of the esterification reaction, resulting in a relatively high acid value of the esterified product (indicating that the base inhibited esterification) and promoting hydrolysis. Under high-temperature conditions in the polycondensation stage, the esterified product with a relatively high acid value may be more prone to reactions such as decarboxylation, thus leading to a worse color of the resin.

[0102] (3) Compared with Example 2, in Comparative Example 4, an excessive amount of sodium hydroxide was added. Although it can improve the color of the resin, too much sodium hydroxide also reduces the intrinsic viscosity of the resin.

[0103] In summary, it can be seen that adding a certain amount of alkaline substance and phosphorus-containing compound after esterification as described in the present invention effectively improves the color of the resin, can obtain a polyester with a low color value, and has good technical effects.

[0104] The present invention has been described in detail above in combination with specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing a low-chromaticity polyester, comprising: (1) Reacting raw materials including aromatic dicarboxylic acid, adipic acid, and diol in the presence of a catalyst to obtain an esterification product; (2) Adding an alkaline substance and a phosphorus-containing compound to the esterification product and subjecting it to a polycondensation reaction to obtain the low-chromaticity polyester.

2. The preparation method according to claim 1, wherein, the aromatic dicarboxylic acid is selected from at least one of terephthalic acid and naphthalenedicarboxylic acid; and / or, the diol is selected from C2-C10 diols, preferably at least one of butanediol, propanediol, and ethylene glycol.

3. The preparation method according to claim 1, wherein, the ratio of the total molar amount of the aromatic dicarboxylic acid and adipic acid to the molar amount of the diol is 1:(1.1-2.0), preferably 1:(1.4-1:2.0); and / or, based on 100% of the total molar amount of the aromatic dicarboxylic acid and adipic acid, among which, the aromatic dicarboxylic acid accounts for 10-90%, preferably 40-60%, and adipic acid accounts for 10-90%, preferably 40-60%.

4. The preparation method according to claim 1, wherein, The catalyst described in step (1) is selected from catalysts for polyester esterification, preferably one or more of titanates; more preferably, the general formula of the titanate is Ti(OR) 4 , wherein R is selected from alkyl groups having 1 to 10 carbon atoms; more preferably, in step (1), based on the theoretical production amount of the polyester, the dosage of the catalyst is 50-200 mg / kg.

5. The preparation method according to claim 1, wherein, the conditions of the esterification reaction include: the pressure is normal pressure - 0.5 MPa, and / or, the temperature is 160-230 °C, and the time is 60-240 min; preferably, the pressure is normal pressure, and / or, the temperature is 180-230 °C, and the time is 120-180 min.

6. The preparation method according to claim 1, wherein, the alkaline substance is selected from at least one of hydroxides of alkali metals, organic acid salts of alkali metals (preferably C1-C5 organic acid salts), and / or ammonia water, preferably, the alkali metal is selected from at least one of lithium, sodium, and potassium; more preferably, based on 100 wt% of the theoretical production amount of the polyester, the dosage of the alkaline substance is 0.0005-0.02 wt%, preferably 0.001-0.01 wt%.

7. The preparation method according to claim 1, wherein, the alkaline substance is added to the esterification product in the form of a solution, preferably an alcohol / water mixed solution; more preferably, the alcohol is selected from diols, preferably the same diol as in step (1).

8. The preparation method according to claim 1, wherein, the phosphorus-containing compound is selected from at least one of phosphate esters, preferably trihydrocarbyl phosphates, and the hydrocarbyl group is selected from C1-C10 alkyl groups or C6-C15 aryl groups; more preferably, the phosphorus-containing compound is selected from at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, dibutyl phosphate, and triphenyl phosphate.

9. The preparation method according to claim 1, wherein, Based on the theoretical production amount of the raw material polyester being 100 wt%, the dosage of the phosphorus-containing compound is 0.002 - 0.2 wt%, preferably 0.002 - 0.12 wt%, wherein the dosage of the phosphorus-containing compound is based on the amount of phosphorus element.

10. According to the preparation method described in claim 1, characterized in that the conditions of the polycondensation reaction in step (2) include: the temperature is 210 - 250 °C, and / or the pressure is an absolute pressure of 30 - 500 Pa, and / or the time is 1 - 8 h.

11. A polyester obtained by using the preparation method described in any one of claims 1 - 11.

12. According to the polyester described in claim 11, characterized in that the intrinsic viscosity of the polyester > 1.2 dl / g; and / or the a value of the polyester is < 2; and / or the b value of the polyester < 10, preferably < 8.

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