Polyester resin and method for purifying the same

Abstract

The application relates to the technical field of polyester resin processing, and discloses a polyester resin and a purification method thereof, which comprises the following steps: contacting polyester resin particles with a supercritical fluid; the polyester resin particles are a fixed phase, and the supercritical fluid is a flowing phase; wherein, taking the total weight of 100 polyester resin particles as a reference, the content of polyester resin particles with a weight m of less than or equal to 1.4 g is less than or equal to 5 wt%, the content of polyester resin particles with a weight of 1.4 g < m < 1.8 g is 20-40 wt%, the content of polyester resin particles with a weight of 1.8 g < m < 2.2 g is 20-60 wt%, the content of polyester resin particles with a weight of 2.2 g < m < 2.6 g is 20-40 wt%, and the content of polyester resin particles with a weight of 2.6 g < m is less than or equal to 5 wt%; the purification method has a high extraction rate, and the migration amount of the purified polyester resin is low.

Description

Technical Field

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

[0002] Polyesters are used in the food industry to make packaging bags, disposable tableware, straws, cups, plates, etc., and have excellent performance, showing great market potential. However, in the production of polybutylene succinate (PBS) and polybutylene adipate succinate resin (PBSA), succinic acid and butanediol easily form monoesters, diesters, dimers, trimers, and cyclic compounds. The content of these oligomers and cyclic compounds typically exceeds 6000 ug / g, resulting in substandard total migration of the polyester material, which fails to meet the requirements for polyester in the food packaging industry.

[0003] CN116217910A discloses a method for purifying polyester. Specifically, it uses supercritical carbon dioxide fluid to extract contaminants from polyester containing dicarboxylic acid 1,4-butanediol structural units, thus avoiding the use of organic solvent washing and high-temperature ultra-low-pressure degassing. This method offers milder operating conditions, lower operating costs, and fewer contaminant emissions. It can remove most oligomers and tetrahydrofuran from the polyester, yielding low-migration polyester that meets food contact safety requirements. However, when using supercritical extraction to extract polyester resin, the resin is packed in a fixed bed within the reactor. Fluid flows through the voids and is extracted. When the voids in the fixed bed are large, short circuits can easily occur, leading to uneven extraction. Conversely, when the voids are small, flow resistance is high, increasing system energy consumption. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of low extraction efficiency when using supercritical extraction to extract polyester resin, and to provide a polyester resin and its purification method. This purification method has a high extraction rate and low migration of the purified polyester resin.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for purifying polyester resin, wherein polyester resin particles are contacted with a supercritical fluid; the polyester resin particles are a stationary phase and the supercritical fluid is a mobile phase.

[0006] Based on the total weight of 100 polyester resin particles, the content of polyester resin particles with a weight m ≤ 1.4g is less than or equal to 5wt%, the content of particles with a weight of 1.4g < m ≤ 1.8g is 20-40wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g is 20-60wt%, the content of particles with a weight of 2.2g < m ≤ 2.6g is 20-40wt%, and the content of particles with a weight of 2.6g < m is less than or equal to 5wt%.

[0007] A second aspect of the present invention provides a polyester resin prepared by the above method.

[0008] The polyester resin and its purification method provided by the above technical solution have the following beneficial effects:

[0009] This invention controls the particle size distribution of polyester resin particles, making the pores inside the tank more uniform and dense after the polyester resin particles are filled. When supercritical fluid flows through the pores, no short circuits or dead zones are generated, resulting in more uniform extraction of polyester resin particles and improved extraction efficiency of supercritical fluid. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the extraction process of the present invention. 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] This invention provides a method for purifying polyester resin, wherein polyester resin particles are contacted with a supercritical fluid; the polyester resin particles are the stationary phase, and the supercritical fluid is the mobile phase.

[0013] Based on the total weight of 100 polyester resin particles, the content of polyester resin particles with a weight m ≤ 1.4g is less than or equal to 5wt%, the content of particles with a weight of 1.4g < m ≤ 1.8g is 20-40wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g is 20-60wt%, the content of particles with a weight of 2.2g < m ≤ 2.6g is 20-40wt%, and the content of particles with a weight of 2.6g < m is less than or equal to 5wt%.

[0014] In this invention, by controlling the particle size distribution of polyester resin particles, the pores inside the tank are made more uniform and dense after the polyester resin particles are filled in the tank. When the supercritical fluid flows through the pores, no short circuit or dead zone will be generated. This not only makes the extraction of polyester resin particles more uniform, but also improves the extraction efficiency of supercritical fluid.

[0015] In this invention, the total weight of the 100 polyester resin particles is simply referred to as the weight per 100 particles.

[0016] In this invention, the sum of the contents of polyester resin particles with weights m≤1.4g, 1.4g<m≤1.8g, 1.8g<m≤2.2g, 2.2g<m≤2.6g, and 2.6g<m is 100wt%.

[0017] Furthermore, based on the total weight of 100 polyester resin particles, the content of polyester resin particles with a weight m ≤ 1.4g is less than or equal to 1wt%, the content of particles with a weight of 1.4g < m ≤ 1.8g is 25-35wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g is 35-45wt%, the content of particles with a weight of 2.2g < m ≤ 2.6g is 25-35wt%, and the content of particles with a weight of 2.6g < m is less than or equal to 1wt%.

[0018] According to the present invention, the polyester resin particles are spherical and / or near-spherical particles.

[0019] According to the present invention, the density of the polyester resin particles is 0.85-1.6 kg / m³. 3 .

[0020] Furthermore, the density of the polyester resin particles is 1.15-1.55 kg / m³. 3 .

[0021] According to the present invention, the number average molecular weight of the polyester resin is 20,000-200,000 g / mol.

[0022] In this invention, when the number-average molecular weight of the polyester resin meets the above-mentioned range, the purified polyester resin not only meets the practical application requirements, but also has a high extraction efficiency during the extraction process.

[0023] Furthermore, the number-average molecular weight of the polyester resin is 30,000-100,000 g / mol.

[0024] According to the present invention, the polyester resin is selected from at least one of polybutylene succinate, polybutylene adipate, polybutylene terephthalate, polybutylene sebacic acid, and polybutylene adipate.

[0025] Furthermore, the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

[0026] According to the present invention, the critical temperature T of the supercritical fluid is related to the initial melting point T of the polyester resin. s Satisfying 10℃≤T s -T.

[0027] According to the present invention, the initial melting point T of the polyester resin is... s The temperature ranges from 100 to 250℃.

[0028] In this invention, the initial melting point of the polyester resin refers to the temperature at which the polyester begins to melt.

[0029] In this invention, T s The temperature difference between -T and -T can vary over a wide range, as long as the temperature difference is greater than or equal to 10℃.

[0030] According to the present invention, the supercritical fluid is selected from at least one of carbon dioxide, nitrous oxide, nitrogen, methane, ethane, ethylene, propane, butane, and pentane;

[0031] In this invention, when the type of supercritical fluid meets the above-mentioned range, it is beneficial to improve the extraction efficiency and obtain polyester resin with lower migration.

[0032] Furthermore, the supercritical fluid is selected from carbon dioxide and / or nitrogen.

[0033] According to the present invention, the flow rate of the supercritical fluid is 20-200 L / (h·kg polyester).

[0034] In this invention, when the flow rate of the supercritical fluid meets the above-mentioned range, the supercritical fluid can promptly remove the target extractant from the polyester resin, thereby improving the extraction efficiency and avoiding an increase in energy consumption.

[0035] Furthermore, the flow rate of the supercritical fluid is 60-150 L / (h·kg polyester).

[0036] According to the present invention, the pressure of the supercritical fluid is 10-50 MPa.

[0037] In this invention, when the pressure of the supercritical fluid meets the above-mentioned range, it can, on the one hand, enable the gas to form a supercritical state, and on the other hand, improve the wetting ability of the supercritical fluid in the polyester resin and the solubility of the target extract in the supercritical fluid, thereby improving the extraction efficiency and obtaining a polyester resin with lower migration.

[0038] Furthermore, the pressure of the supercritical fluid is 20-35 MPa.

[0039] According to the present invention, the contact temperature T j Satisfy: T s ≥T j ≥T.

[0040] According to the present invention, the contact temperature is 35-220°C, and the contact time is 2-5 hours.

[0041] In this invention, when the conditions for contact between polyester resin particles and supercritical fluid meet the above-mentioned range, on the one hand, the gas is in a supercritical state, and on the other hand, the wetting ability of supercritical fluid in polyester resin and the solubility of target extract in supercritical fluid are improved, thereby improving extraction efficiency and obtaining polyester resin with lower migration.

[0042] Furthermore, the contact temperature is 70-90℃, and the contact time is 3-4 hours.

[0043] In this invention, when the flow rate, pressure, and contact temperature of the supercritical fluid are within the preferred range of this invention, not only is the extraction efficiency high, but the energy consumption is also low, thus improving production safety.

[0044] According to the present invention, the polyester resin particles are placed in a reactor.

[0045] In this invention, polyester resin particles are filled into the reactor and kept fixed to prevent particle movement.

[0046] According to the present invention, the reactor is a fixed-bed reactor.

[0047] 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 storing gas from a gas cylinder or a separator in a gas storage tank. The gas in the storage tank is pressurized to a specific pressure by a booster pump, causing the gas to form a supercritical state and thus a supercritical fluid. The supercritical fluid passes through a heat exchange system I to regulate its temperature. The temperature-regulated supercritical fluid comes into contact with polyester resin particles in an extraction tank to extract impurities from the polyester resin particles, thereby purifying the polyester resin. The supercritical fluid flowing out of the extraction tank enters a heat exchange system II to cool the supercritical fluid, causing the impurities in the supercritical fluid to transform into a liquid or solid state. The supercritical fluid containing impurities enters a separator and is depressurized into a gas, separating the gas from the impurities.

[0048] According to a particularly preferred embodiment of the present invention, a method for purifying polyester resin includes: contacting polyester resin particles with a supercritical fluid; wherein the polyester resin particles are a stationary phase and the supercritical fluid is a mobile phase;

[0049] Based on the total weight of 100 polyester resin particles, the content of polyester resin particles with a weight m ≤ 1.4g is less than or equal to 1wt%, the content of particles with a weight of 1.4g < m ≤ 1.8g is 25-35wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g is 35-45wt%, the content of particles with a weight of 2.2g < m ≤ 2.6g is 25-35wt%, and the content of particles with a weight of 2.6g < m is less than or equal to 1wt%; the density of the polyester resin particles is 1.15-1.55 kg / m³.3 ;

[0050] The supercritical fluid has a flow rate of 60-150 L / (h·kg polyester) and a pressure of 20-35 MPa; the contact temperature T j Satisfies: The initial melting point T of the polyester resin s ≥T j ≥ Critical temperature T of supercritical fluid.

[0051] A second aspect of the present invention provides a polyester resin prepared by the above method.

[0052] According to the present invention, the migration amount of the polyester resin is less than or equal to 10 mg / dm³. 2 .

[0053] The present invention will be described in detail below through embodiments.

[0054] Migration of polyester resin: Purified polybutylene diacid 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 materials - Part 3: Small square test specimens". Migration was tested according to GB31604.8-2016. The test conditions were: 50 vol% ethanol aqueous solution as the simulated solution, temperature 70℃, 2 hours, per 6 dm². 2 The small square sample was immersed in 1L of simulated solution, and the migration amount Q was calculated according to Formula 1 in 6.1, in mg / dm³. 2 .

[0055] Polyester resin: Polybutylene succinate (PBS resin) was purchased from Yizheng Chemical Fiber Company as AS009, a commercially available product. The granules are spherical, and the density of the polyester resin granules is 1.26 kg / m³. 3 The number-average molecular weight of the polyester resin is 100,000 g / mol, and the initial melting point is 114℃.

[0056] Example 1

[0057] Polyester resin particles (PBS resin) were mixed uniformly according to the following composition. Based on the total weight of 100 polyester resin particles (m), the content of particles with a weight of 1.4g < m ≤ 1.8g was 30wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g per 100 particles was 30wt%, and the content of particles with a weight of 2.2g < m ≤ 2.6g per 100 particles was 40wt%. The mixed polyester resin particles were packed into an extraction vessel, and supercritical fluid (carbon dioxide) was introduced to contact the polyester resin particles. The supercritical fluid flow rate was 60 L / (h·kg polyester), the contact temperature was 85℃, the contact pressure was 30 MPa, and the contact time was 3 h. Purified polyester resin was obtained. The test results of the purified polyester resin are shown in Table 2.

[0058] Example 2-13

[0059] The polyester resin was purified according to the method of Example 1. The composition and contact conditions of 100 polyester resin particles are shown in Table 1, and the test results of the purified polyester resin are shown in Table 2.

[0060] Comparative Examples 1-3

[0061] The polyester resin was purified according to the method of Example 1. The composition and contact conditions of 100 polyester resin particles are shown in Table 1, and the test results of the purified polyester resin are shown in Table 2.

[0062] Table 1

[0063]

[0064]

[0065] Table 2

[0066] Example number <![CDATA[Migration amount, mg / dm 2 > Example 1 3.0 Example 2 2.0 Example 3 3.1 Example 4 5.0 Example 5 4.8 Example 6 5.2 Example 7 3.1 Example 8 4.3 Example 9 5.0 Example 10 1.0 Example 11 9.5 Example 12 7.5 Example 13 6.0 Comparative Example 1 20.0 Comparative Example 2 18.0 Comparative Example 3 12.0

[0067] The results show that when the contact time between the polyester resin and the supercritical fluid is the same, the migration amount of the polyester resin purified by this invention is lower, indicating that the extraction efficiency of the method of this invention is high.

[0068] 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, Polyester resin particles are in contact with a supercritical fluid; the polyester resin particles are the stationary phase and the supercritical fluid is the mobile phase. Based on the total weight of 100 polyester resin particles, the content of polyester resin particles with a weight m ≤ 1.4g is less than or equal to 5wt%, the content of particles with a weight of 1.4g < m ≤ 1.8g is 20-40wt%, the content of particles with a weight of 1.8g < m ≤ 2.2g is 20-60wt%, the content of particles with a weight of 2.2g < m ≤ 2.6g is 20-40wt%, and the content of particles with a weight of 2.6g < m is less than or equal to 5wt%.

2. The method according to claim 1, wherein, Based on the total weight of 100 polyester resin granules, the content of polyester resin granules with a weight m ≤ 1.4g is less than or equal to 1wt%, the content of 1.4g < m ≤ 1.8g is 25-35wt%, the content of 1.8g < m ≤ 2.2g is 35-45wt%, the content of 2.2g < m ≤ 2.6g is 25-35wt%, and the content of 2.6g < m is less than or equal to 1wt%.

3. The method according to claim 1 or 2, wherein, The polyester resin particles are spherical and / or near-spherical particles.

4. The method according to any one of claims 1-3, wherein, The density of the polyester resin particles 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 polyester resin is selected from at least one of polybutylene succinate, polybutylene adipate, polybutylene terephthalate, polybutylene sebacic acid and polybutylene adipate. Preferably, the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

7. The method according to any one of claims 1-6, wherein, The critical temperature T of the supercritical fluid is related to the initial melting point T of the polyester resin. s Satisfying 10℃≤T s -T; Preferably, the initial melting point T of the polyester resin is... s The temperature ranges from 100 to 250 degrees Celsius. Preferably, the supercritical fluid is selected from at least one of carbon dioxide, nitrous oxide, nitrogen, methane, ethane, ethylene, propane, butane, and pentane; Preferably, the supercritical fluid is selected from carbon dioxide and / or nitrogen.

8. The method according to any one of claims 1-7, wherein, The flow rate of the supercritical fluid is 20-200 L / (h·kg polyester), preferably 60-150 L / (h·kg polyester); Preferably, the pressure of the supercritical fluid is 10-50 MPa, and more preferably 20-35 MPa; Preferably, the contact temperature T j Satisfy: T s ≥T j ≥T; Preferably, the contact temperature is 35-220℃, more preferably 70-90℃; Preferably, the contact time is 2-5 hours, and more preferably 3-4 hours.

9. The method according to any one of claims 1-8, wherein, The polyester resin particles are placed in the reactor; Preferably, the reactor is a fixed-bed reactor.

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

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