Purified polyester resins and methods for making the same

Abstract

The application relates to the technical field of polyester resin processing, and discloses a purified polyester resin and a preparation method thereof, specifically, carbon dioxide supercritical fluid and polyester resin are contacted in the same direction; when the contact temperature T is 55-95 DEG C, the flow Q of the carbon dioxide supercritical fluid and the flow m of the polyester resin satisfy the following relationship: Q >= (m*CO) / [100*(0.001*T-0.041)], wherein CO is the initial content of migratable substances in the polyester resin, and R is the residence time; wherein Q is L / h, m is g / h, CO is wt%, and the method can realize continuous extraction, has high purification efficiency, and the obtained purified polyester resin has a low migration amount.

Description

Technical Field

[0001] This invention relates to the field of polyester resin processing technology, and more specifically to a purified polyester resin and its preparation method. Background Technology

[0002] Polybutylene succinate (PBS) is a polymer with good biodegradability. Compared with other biodegradable plastics such as polylactic acid, polyhydroxyalkanoates, and polycaprolactone, PBS is relatively inexpensive, has excellent mechanical properties, good heat resistance, and a heat distortion temperature close to 100℃. It is a key area of ​​research and development in biodegradable plastics both domestically and internationally.

[0003] However, during the production of polybutylene succinate (PBS), succinic acid and butanediol readily form monoesters, diesters, dimers, trimers, and cyclic compounds. The content of these oligomers and cyclic compounds typically exceeds 6000 μg / g, resulting in substandard total migration of the polyester material and failing to meet the requirements for polyester in the food packaging industry. Current technologies typically employ fixed-bed extraction of PBS, but this method can only be performed intermittently, leading to low purification efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of low production efficiency in the existing technology of purifying polyester resin by intermittent method, and to provide a method for purifying polyester resin and preparing the same. This method can achieve continuous extraction, has high purification efficiency, and the purified polyester resin obtained has low migration.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for purifying polyester resin, wherein supercritical carbon dioxide fluid is contacted with the polyester resin in the same direction.

[0006] When the contact temperature T = 55-95℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: Q ≥ (m × C0) / [100 × (0.001 × T - 0.041)], where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; m is g / h; and C0 is wt%.

[0007] A second aspect of the present invention provides a purified polyester resin obtained by the above-described method.

[0008] The purified polyester resin and its preparation method provided by the present invention have the following beneficial effects through the above technical solutions.

[0009] This invention achieves continuous extraction and improves purification efficiency by controlling the amounts of supercritical carbon dioxide fluid and polyester resin at a specific contact temperature, so that the supercritical carbon dioxide fluid and polyester resin flow in the same direction and come into contact; the resulting purified polyester resin has a low migration amount. Attached Figure Description

[0010] Figure 1 This is a process flow diagram for purifying polyester resin. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] The first aspect of the present invention provides a method for purifying polyester resin, wherein supercritical carbon dioxide fluid is contacted with the polyester resin in the same direction;

[0013] When the contact temperature T = 55-95℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: Q ≥ (m × C0) / [100 × (0.001 × T - 0.041)], where C0 is the initial content of migratable substances in the polyester resin, and R is the residence time; where Q is L / h, m is g / h, and C0 is wt%.

[0014] In this invention, at a specific contact temperature, the amounts of supercritical carbon dioxide fluid and polyester resin are controlled to make the supercritical carbon dioxide fluid and polyester resin flow in the same direction and come into contact; thereby achieving continuous extraction, improving purification efficiency, and obtaining purified polyester resin with low migration.

[0015] In this invention, (m×C0) / [100×(0.001×T-0.041)] does not introduce units in the calculation process. It can be understood that m is the flow rate of polyester resin and the value corresponding to the unit g / h; C0 is the initial content of migratable substances in polyester resin and the value corresponding to the unit wt%; T is the contact temperature and the value corresponding to the unit ℃.

[0016] Furthermore, when the contact temperature T = 70-90℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: Q ≥ (m × C0) / [100 × (0.001 × T - 0.041)].

[0017] In this invention, in order to improve the extraction efficiency of polyester resin, preferably, when the contact temperature T = 55-95℃, the flow rate Q of supercritical carbon dioxide fluid and the flow rate m of polyester resin satisfy the following relationship: (2m×C0) / [100×(0.001×T-0.041)]≥Q≥(m×C0) / [100×(0.001×T-0.041)].

[0018] According to a preferred embodiment of the present invention, when the contact temperature T = 70-90℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: (2m×C0) / [100×(0.001×T-0.041)]≥Q≥(m×C0) / [100×(0.001×T-0.041)].

[0019] According to a more preferred embodiment of the present invention, when the contact temperature T = 70-90°C, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: (1.5m×C0) / [100×(0.001×T-0.041)]≥Q≥(m×C0) / [100×(0.001×T-0.041)].

[0020] According to the present invention, the polyester resin has a cylindrical and / or spherical morphology.

[0021] In this invention, there are no special restrictions on the height and bottom radius of the cylindrical polyester resin; in this invention, the sphere includes ellipsoids and / or quasi-spheres.

[0022] According to the present invention, the polyester resin is polybutylene succinate and / or polybutylene adipate.

[0023] In this invention, there are no special requirements for the flow rate of the polyester resin, which can be adjusted according to actual production needs. However, to further improve production efficiency, preferably, the flow rate m of the polyester resin is 100-10000 g / h. More preferably, the flow rate m of the polyester resin is 500-5000 g / h.

[0024] According to the present invention, the total weight of 100 polyester resin particles is less than or equal to 2.5g.

[0025] According to the present invention, the density of the polyester resin is 0.85-1.6 kg / m³. 3 .

[0026] In this invention, by limiting the density of the polyester resin and the total weight of 100 polyester resin particles, the polyester resin has specific specifications, and the supercritical carbon dioxide fluid can have a higher wetting ability on the polyester resin, resulting in higher extraction efficiency.

[0027] Furthermore, the total weight of 100 polyester resin particles is 1.8-2.2g.

[0028] Furthermore, the density of the polyester resin is 1.15-1.55 kg / m³. 3 .

[0029] According to the present invention, the number average molecular weight of the polyester resin is 20,000-200,000 g / mol.

[0030] In this invention, when the number-average molecular weight of the polyester resin meets the above-mentioned range, the purified polyester resin can not only meet the practical application requirements, but also has a high extraction efficiency during the extraction process.

[0031] Furthermore, the number-average molecular weight of the polyester resin is 30,000-100,000 g / mol.

[0032] According to the present invention, the pressure of the supercritical carbon dioxide fluid is 10-50 MPa.

[0033] In this invention, when the pressure of the supercritical carbon dioxide fluid meets the above-mentioned range, the wetting ability of the supercritical fluid in the polyester resin and the solubility of the target extract in the supercritical fluid can be improved, thereby increasing the extraction efficiency.

[0034] Furthermore, the pressure of the supercritical carbon dioxide fluid is 30-40 MPa.

[0035] According to the present invention, the dwell time is 2-5 hours.

[0036] Furthermore, the stay time is 2-3 hours.

[0037] According to the present invention, the initial content of migratable substances C0 in the polyester resin is 0.6wt%-2wt%.

[0038] Furthermore, the initial content of migratable substances (C0) in the polyester resin is 0.8 wt%-1 wt%.

[0039] According to the present invention, the contact takes place within a coil reactor.

[0040] A second aspect of the present invention provides a purified polyester resin obtained by the above-described method.

[0041] According to the present invention, the migration amount of the purified polyester resin is less than or equal to 10 mg / dm³. 2 .

[0042] The invention will be further described below with reference to the accompanying drawings, such as... Figure 1 As shown, the method for purifying polyester resin includes:

[0043] Carbon dioxide gas from a gas cylinder or a separator is stored in a gas storage tank. The carbon dioxide gas in the storage tank is pressurized to a specific pressure by a booster pump, causing the carbon dioxide gas to form a supercritical state. The formed supercritical carbon dioxide fluid has its temperature regulated by heat exchange system I. The temperature-regulated supercritical carbon dioxide fluid comes into contact with polyester resin in a coil reactor. The polyester resin continuously enters the coil reactor from the resin feeding system, where impurities are extracted. The product after contact continuously enters the solid-liquid separation system from the coil reactor for solid-liquid separation, obtaining purified polyester resin and a liquid phase. The purified polyester resin is stored in the finished product system. The liquid phase is cooled by heat exchange system II and then enters the separator for depressurization to obtain supercritical carbon dioxide fluid and impurities. The supercritical gas is then stored in the gas storage tank.

[0044] According to a particularly preferred embodiment of the present invention, the method for purifying polyester resin includes: contacting the polyester resin with supercritical carbon dioxide fluid in the same direction;

[0045] When the contact temperature T = 70-90℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: Q ≥ (m × C0) / [100 × (0.001 × T - 0.041)], where C0 is the initial content of migratable substances in the polyester resin, and R is the residence time; where Q is L / h; m is g / h; and C0 is wt%.

[0046] The pressure of the supercritical carbon dioxide fluid is 30-40 MPa.

[0047] The present invention will be described in detail below through embodiments.

[0048] Initial content of migratable substances (C0) in polyester resin and migration amount of purified polyester resin: Polyester resin raw material or purified polyester resin was injection molded into small square test pieces. The size of the test pieces conformed to type D1 of GB / T17037.3-2003 "Preparation of Injection Molded Test Specimens for Thermoplastic Plastics - Part 3: Small Square Test Pieces". The test pieces were tested according to the method in GB31604.8-2016. Test conditions: 50 vol% ethanol aqueous solution as the simulated solution, temperature 70℃, 2 hours, every 6 dm²... 2 The small square sample was immersed in 1L of simulated solution, and the migration amount was calculated according to Formula 1 in 6.1, with units of mg / dm³. 2 .

[0049] Resin 1: Polybutylene succinate (PSS) was purchased from Yizheng Chemical Fiber Co., Ltd. as a commercially available product with brand name AS009; the initial content of migratable substances (C0) in PSS was 1.0 wt%, the PSS was spherical, and the density was 1.26 kg / m³. 3The number average molecular weight is 100,000 g / mol, and the total weight of 100 polybutylene succinate particles is 2.0 g.

[0050] Resin 2: Polybutylene succinate (Polybutylene succinate) was prepared via a two-step melt polymerization method, namely, esterification followed by polycondensation. The specific reaction conditions were as follows: In a 20L reactor, 5.4 kg of butanediol, 3.54 kg of succinic acid, and 4.4 g of tetrabutyl titanate catalyst were added. Esterification was carried out at atmospheric pressure at a temperature of 210℃. After esterification, polycondensation was performed at a temperature of 250℃ and a pressure of 80 Pa. The reactor was discharged after the stirring power reached the target value. The weight of 100 Polybutylene succinate particles was adjusted by controlling the discharge pressure and regulating the melt strip thickness. The specific parameters of the obtained Polybutylene succinate were as follows: the total weight of 100 polyester resin particles was 2.5 g, the initial content of migratable substances (C0) was 1.0 wt%, the Polybutylene succinate was cylindrical, and the density was 1.25 kg / m³. 3 The number-average molecular weight is 50,000 g / mol.

[0051] Resin 3: Polybutylene succinate (PBS) was prepared via a two-step melt polymerization method, namely, esterification followed by polycondensation. The specific reaction conditions were as follows: In a 20L reactor, 5.4 kg of butanediol, 3.54 kg of succinic acid, and 4.4 g of tetrabutyl titanate catalyst were added. Esterification was carried out at atmospheric pressure and a temperature of 230℃. After esterification, polycondensation was performed at 230℃ and a pressure of 80 Pa. The reactor was discharged after the stirring power reached the target value. The weight of 100 PBS particles was adjusted by controlling the discharge pressure and regulating the melt strip thickness. The specific parameters of the obtained PBS were as follows: the total weight of 100 PBS particles was 3.0 g, the initial content of migratable substances (C0) was 1.0 wt%, the PBS was cylindrical, and the density was 1.25 kg / m³. 3 The number-average molecular weight is 30,000 g / mol.

[0052] Example 1

[0053] Polybutylene succinate (resin 1) and supercritical carbon dioxide were continuously fed into a coil reactor from one end. The flow rate of polybutylene succinate was 900 g / h, the pressure of the supercritical carbon dioxide was 40 MPa, the contact temperature T was 85℃, and the flow rate Q of the supercritical carbon dioxide was 210 L / h. The polybutylene succinate and supercritical carbon dioxide were held in the coil reactor for 2.5 hours. The extracted product continuously flowed out from the other end of the reactor and was separated into purified polyester resin and liquid phase by solid-liquid separation. The separated supercritical fluid could be recycled after removing the extract. The test results of the purified polyester resin are shown in Table 1.

[0054] Examples 2-6

[0055] The polyester resin was purified according to the method in Example 1, and the specific extraction conditions are shown in Table 1. The test results of the purified resin are shown in Table 1.

[0056] Example 7

[0057] The polyester resin was purified according to the method in Example 1, except that resin 2 was extracted. The specific extraction conditions are shown in Table 1. The test results of the purified resin are shown in Table 1.

[0058] Example 8

[0059] The polyester resin was purified according to the method in Example 1, except that resin 3 was extracted. The specific extraction conditions are shown in Table 1. The test results of the purified resin are shown in Table 1.

[0060] Comparative Examples 1-2

[0061] The polyester resin was purified according to the method in Example 1, and the specific extraction conditions are shown in Table 1. The test results of the purified resin are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] As can be seen from the results in Table 1, when the flow rates of the supercritical carbon dioxide fluid and the polyester resin meet the relationship defined in this invention at a specific contact temperature, the resin can be extracted more effectively, ensuring a sufficient amount of supercritical fluid and preventing the oligomers from becoming saturated in the supercritical carbon dioxide fluid and thus unable to be further extracted. When the flow rate Q of the supercritical fluid is less than the flow rate calculated by (m×C0) / [100×(0.001×T-0.041)] (Comparative Example 1), the amount of polyester resin migration cannot be further reduced even if the residence time is extended due to the gradual saturation of the extract in the supercritical fluid, resulting in a poorer extraction effect.

[0066] In Comparative Example 2, the excessively high contact temperature caused the PBS resin to stick and clump together during its flow within the reactor, affecting operation. At the same time, the increased particle size after clumping made it difficult for oligomers to migrate out, resulting in a high migration rate in the obtained product.

[0067] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying polyester resin, characterized in that, Supercritical carbon dioxide fluid and polyester resin are in contact in the same direction; When the contact temperature T = 55-95℃, the flow rate Q of the supercritical carbon dioxide fluid and the flow rate m of the polyester resin satisfy the following relationship: Q ≥ (m × C0) / [100 × (0.001 × T - 0.041)], where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; m is g / h; and C0 is wt%.

2. The method according to claim 1, wherein, The flow rate m of the polyester resin is 100-10000 g / h, preferably 500-5000 g / h; Preferably, the polyester resin has a cylindrical and / or spherical morphology; Preferably, the polyester resin is polybutylene succinate and / or polybutylene adipate.

3. The method according to claim 1 or 2, wherein, The total weight of 100 polyester resin particles is less than or equal to 2.5g, preferably 1.8-2.2g.

4. The method according to any one of claims 1-3, wherein, The density of the polyester resin is 0.85-1.6 kg / m³. 3 The preferred value is 1.15-1.55 kg / m³. 3 .

5. The method according to any one of claims 1-4, wherein, The number average molecular weight of the polyester resin is 20,000-200,000 g / mol, preferably 30,000-100,000 g / mol.

6. The method according to any one of claims 1-5, wherein, The pressure of the supercritical carbon dioxide fluid is 10-50 MPa, preferably 30-40 MPa.

7. The method according to any one of claims 1-6, wherein, The dwell time is 2-5 hours, preferably 2-3 hours.

8. The method according to any one of claims 1-7, wherein, The initial content of migratable substances (C0) in the polyester resin is 0.6wt%-2wt%, preferably 0.8wt%-1wt%.

9. The method according to any one of claims 1-8, wherein, The contact takes place inside a coil reactor.

10. A purified polyester resin prepared by the method according to any one of claims 1-9; Preferably, the migration amount of the purified polyester resin is less than or equal to 10 mg / dm³. 2 .

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