Process for purifying polyester resins

Abstract

The application relates to the technical field of polyester resin processing, and discloses a method for purifying polyester resin, which comprises the following steps: when the mass of polyester resin is m, after the polyester resin is contacted with a supercritical fluid for a contact residence time t1; the purified polyester resin flows out at a rate v1, and the polyester resin flows into an extraction reactor at the rate v1, so that the average contact residence time t2 of the polyester resin and the supercritical fluid satisfies t2=m / v1>=t1; and the method can realize continuous feeding and discharging and has high production efficiency.

Description

Technical Field

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

[0002] Polyesters, as a class of high-performance polymers, are widely used in the food packaging field and have broad market prospects. Currently, they are used in packaging bags, disposable tableware, straws, cups, and plates. However, during the production process, polyester inevitably generates some oligomers, such as polybutylene succinate (PBS) and polybutylene adipate succinate (PBSA). During production, due to the poor thermal stability of succinic acid, the macromolecular polymers easily undergo chain scission to form monoesters, diesters, dimers, trimers, and cyclic compounds. Furthermore, the content of these oligomers and cyclic compounds is high, typically exceeding 6000 μg / g. This limits their application in specific fields, especially food packaging, where the total migration limits of materials are strictly controlled to avoid potential threats to human health. To solve this problem, high-purity resins can be prepared during the production process; alternatively, the polymer can be purified through post-treatment to remove harmful impurities.

[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, removing most oligomers and tetrahydrofurans from the polyester to obtain low-migration polyester that meets food contact safety requirements. However, this method can only be operated intermittently and cannot be run continuously, limiting its large-scale production application.

[0004] US5478921A discloses a method for purifying materials containing bioresorbable polymers. The method involves contacting the polymer with an extractant under supercritical conditions of specific temperature and pressure to extract residual impurities from the polymer, followed by recovery of the purified polymer. This significantly reduces the level of residual monomers in bioresorbable polymers without altering the polymer's viscosity or melting point. However, this method also operates intermittently and cannot be run continuously.

[0005] Supercritical fluid extraction can effectively reduce oligomers in resins and ensure that their migration levels meet the requirements. However, most current extraction processes rely on batch reaction devices, which cannot achieve continuous operation, resulting in low production efficiency and severely limiting large-scale production applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem that intermittent supercritical extraction cannot achieve continuous operation and has low production efficiency, and to provide a method for purifying polyester resin that can achieve continuous feeding and continuous discharge with high production efficiency.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for purifying polyester resin, wherein the method comprises: having a mass of polyester resin m, allowing the polyester resin to be in contact with a supercritical fluid for a residence time t1; allowing the purified polyester resin to flow out at a rate v1, while simultaneously allowing polyester resin to flow into an extraction reactor at a rate v1, such that the average residence time t2 between the polyester resin and the supercritical fluid satisfies t2=m / v1≥t1.

[0008] The method for purifying polyester resin provided by the present invention, through the above technical solution, has the following beneficial effects.

[0009] In this invention, after the polyester resin has been in contact with the supercritical fluid for a residence time t1, the outflow rate and inflow rate of the purified polyester resin are adjusted so that the average residence time t2 between the polyester resin and the supercritical fluid satisfies t2 = m / v1 and t2 ≥ t1, thereby achieving continuous extraction of polyester resin and improving production efficiency. 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 the method includes: the mass of the polyester resin is m, and after the polyester resin is in contact with a supercritical fluid for a residence time t1; the purified polyester resin is discharged at a rate v1, while simultaneously flowing into an extraction reactor at a rate v1, such that the average residence time t2 between the polyester resin and the supercritical fluid satisfies t2=m / v1≥t1.

[0013] In this invention, after the polyester resin has been in contact with the supercritical fluid for a residence time t1, the outflow rate and inflow rate of the purified polyester resin are adjusted so that the average residence time t2 between the polyester resin and the supercritical fluid satisfies t2 = m / v1 and t2 ≥ t1, thereby achieving continuous extraction of polyester resin and improving production efficiency.

[0014] According to the present invention, the method further includes: performing solid-liquid separation on the extracted material to obtain purified polyester resin and liquid phase.

[0015] In this invention, the extracted material includes purified polyester resin and a liquid phase, wherein the liquid phase is the extracted supercritical fluid. In this invention, the outflow rate v1 of the purified polyester resin differs from the flow rate of the supercritical fluid. For example, by adding a filter valve system to the outlet of the extraction system, the outflow rate of the purified polyester resin can be adjusted by regulating the opening of the gate of the filter valve system; simultaneously, the flow rate of the supercritical fluid can be controlled by a circulating pump, thereby achieving a difference between the outflow rate of the purified polyester resin and the flow rate of the supercritical fluid.

[0016] In this invention, the mass of the polyester resin can be adjusted according to the size of the extraction device used. The unit of mass of the polyester resin is kilograms.

[0017] According to the present invention, the liquid phase is subjected to heat exchange and cooling and depressurization in sequence to obtain supercritical gas and impurities.

[0018] According to the present invention, the supercritical gas, after being pressurized and heated by heat exchange, is used to purify polyester resin.

[0019] According to the present invention, 1h≤t1≤5h.

[0020] In this invention, when the contact residence time t1 between the polyester resin and the supercritical fluid meets the above-mentioned range, a polyester resin with low migration can be obtained.

[0021] Furthermore, 2h≤t1≤4h.

[0022] According to the present invention, the ratio of the flow rate Q of the supercritical fluid to the mass m of the polyester resin satisfies 35-700 L / h.

[0023] In this invention, when the flow rate of the supercritical fluid and the mass m of the polyester resin satisfy the above relationship, 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.

[0024] Furthermore, the ratio of the flow rate Q of the supercritical fluid to the mass m of the polyester resin satisfies 40-350 L / h.

[0025] 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.

[0026] Furthermore, the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

[0027] 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.

[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 initial melting point T of the polyester resin is... s The temperature ranges from 100 to 250℃.

[0031] According to the present invention, in step (1), the pressure of the supercritical fluid is 10-50 MPa.

[0032] 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.

[0033] Furthermore, in step (1), the pressure of the supercritical fluid is 30-40 MPa.

[0034] According to the present invention, the temperature T in which the polyester resin contacts the supercritical fluid is... j Satisfy: T s ≥T j ≥T.

[0035] According to the present invention, the temperature of the contact is 35-100°C.

[0036] In this invention, when the contact temperature meets the above-mentioned range, not only is the gas in a supercritical state, but the wetting ability of the supercritical fluid in the polyester resin and the solubility of the target extract in the supercritical fluid are also improved, thereby improving the extraction efficiency and obtaining a polyester resin with low migration.

[0037] Furthermore, the temperature of the contact is 55-95°C.

[0038] According to the present invention, the supercritical fluid is selected from at least one of carbon dioxide, nitrous oxide, nitrogen, methane, ethane, and ethylene.

[0039] In this invention, when the above-mentioned type of supercritical fluid is used, the supercritical fluid is easy to recycle and can improve the extraction efficiency.

[0040] Furthermore, the supercritical fluid is carbon dioxide and / or nitrogen.

[0041] According to the present invention, the number average molecular weight of the polyester resin is 10,000-200,000 g / mol.

[0042] Furthermore, the number-average molecular weight of the polyester resin is 20,000-100,000 g / mol.

[0043] According to the present invention, the total weight of 100 polyester resin particles is 1.5-2.5g.

[0044] According to the present invention, the density of the polyester resin is 0.85-1.6 kg / m³. 3 .

[0045] In this invention, by limiting the density of the polyester resin and the total weight of 100 polyester resin particles, the polyester resin has a specific particle size range. The supercritical fluid can have better wetting ability on the polyester resin, resulting in higher extraction efficiency and high removal uniformity of the same batch of products.

[0046] Furthermore, the total weight of 100 polyester resin particles is 1.8-2.2g.

[0047] Furthermore, the density of the polyester resin is 1.15-1.55 kg / m³. 3 .

[0048] According to the present invention, when the temperature T in contact with the supercritical fluid is... j When the temperature is between 55-95℃ and the supercritical fluid is carbon dioxide, the flow rate Q of the supercritical carbon dioxide fluid and the effluent rate v1 of the purified polyester resin satisfy the following relationship: Q ≥ (10v1 × C0) / (0.001 × T) j -0.041), where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; v1 is kg / h; C0 is wt%; and the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

[0049] In this invention, when the flow rate Q of the supercritical carbon dioxide fluid and the outflow rate v1 of the purified polyester resin satisfy the above relationship at a specific contact temperature, the polyester resin can be extracted more effectively.

[0050] In this invention, (10v1×C0) / (0.001×T) j-0.041) No units are introduced in the calculation. It can be understood that v1 is the effluent rate of the purified polyester resin, expressed in kg / h; C0 is the initial content of migratable substances in the polyester resin, expressed in wt%; T j This represents the temperature at which the polyester resin comes into contact with the supercritical fluid, expressed in °C.

[0051] In this invention, to improve the extraction efficiency of polyester resin while reducing energy consumption, preferably, the temperature T when the polyester resin contacts the supercritical fluid is... j When the temperature is between 55-95℃ and the supercritical fluid is carbon dioxide, the flow rate Q of the supercritical carbon dioxide fluid and the effluent rate v1 of the purified polyester resin satisfy the following relationship: (20v1×C0) / (0.001×T-0.041)≥Q≥(10v1×C0) / (0.001×T) j -0.041), where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; v1 is kg / h; C0 is wt%; and the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

[0052] According to a preferred embodiment of the present invention, when the temperature T in contact with the supercritical fluid is... j When the temperature is 70-95℃ and the supercritical fluid is carbon dioxide, the flow rate Q of the supercritical carbon dioxide fluid and the effluent rate v1 of the purified polyester resin satisfy the following relationship: (20v1×C0) / (0.001×T-0.041)≥Q≥(10v1×C0) / (0.001×T) j -0.041), where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; v1 is kg / h; C0 is wt%; and the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

[0053] According to the present invention, the method for purifying polyester resin employs a series reaction vessel or a fluidized bed reactor.

[0054] According to the present invention, the number of the series reactors is 1-5.

[0055] 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:

[0056] (1) With the filter valve system closed, supercritical gas is pumped to form supercritical fluid. The supercritical fluid is then regulated by heat exchange system I and enters the extraction system. The polyester resin is in contact with the supercritical fluid in the extraction system for a residence time of t1. The filter valve system is then opened, and the purified polyester resin is allowed to flow out at a rate of v1 by controlling the gate opening of the filter valve system. At the same time, the polyester resin in the resin feeding system flows into the extraction reactor at a rate of v1, so that the average residence time t2 between the polyester resin and the supercritical fluid satisfies t2=m / v1≥t1. The material flowing out of the extraction system is subjected to solid-liquid separation in the solid-liquid separation system to obtain purified polyester resin and liquid phase.

[0057] (2) The purified polyester resin enters the finished product system; the liquid phase is cooled by heat exchange system II and then enters the separation tank for depressurization to obtain supercritical gas and impurities; the supercritical gas is stored in the storage tank and then returned to the extraction system for purification of polyester resin after passing through the booster pump and heat exchange system I.

[0058] In this invention, when the filter valve system is closed, the outflow rate of the purified polyester resin is 0. Because the gate of the filter valve system has pores, the supercritical fluid can pass smoothly through the filter valve system. In this invention, the outflow rate v1 of the purified polyester resin is controlled by controlling the opening degree of the gate of the filter valve system.

[0059] The present invention will be described in detail below through embodiments.

[0060] 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 .

[0061] Polybutylene succinate (PBS resin) is a commercially available product from Yizheng Chemical Fiber Co., Ltd., brand name AS009; PBS is spherical with a density of 1.26 kg / m³. 3 The number average molecular weight is 100,000 g / mol, the total weight of 100 polybutylene succinate particles is 2 g, and the initial melting point is 114 °C; the initial content of migratable substances C0 in the polyester resin is 1.0 wt%.

[0062] Example 1

[0063] (1) With the filter valve system closed (the outflow rate of the purified polyester resin is 0), 30 kg of polybutylene succinate is fed into a 200 L vertical stirred reactor. The contact residence time t1 between the polyester resin and the supercritical fluid is 2.5 h. The filter valve system is then opened, and the polyester resin is introduced into the extraction system. By controlling the opening of the gate of the filter valve system, the outflow rate v1 of the purified polyester resin is made to be 12 kg / h. At the same time, polyester resin flows into the extraction reactor at a rate of v1, so that the average contact residence time t2 of the polyester resin in the extraction system is 2.5 h. The material flowing out of the extraction system is subjected to solid-liquid separation in the solid-liquid separation system to obtain purified polyester resin and liquid phase.

[0064] The ratio of the supercritical fluid velocity Q to the polyester resin mass m is 150 L / h, the pressure of the supercritical fluid is 40 MPa, and the contact temperature T is... j The temperature is 85℃.

[0065] (2) The purified polyester resin enters the finished product system; the liquid phase is cooled by heat exchange system II and then enters the separation tank for depressurization to obtain supercritical gas and impurities; the supercritical gas is stored in the storage tank and then returned to the extraction system for purifying polyester resin after passing through the booster pump and heat exchange system I. The test results of the purified polybutylene succinate are shown in Table 1.

[0066] Examples 2-9

[0067] 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 polyester resin are shown in Table 1.

[0068] Comparative Example 1

[0069] (1) With the filter valve system open, the polyester resin is introduced into the extraction system. By controlling the opening of the gate of the filter valve system, the outflow rate v1 of the purified polyester resin is made to be 12 kg / h. At the same time, the polyester resin flows into the extraction reactor at a rate of v1. The average residence time of the polyester resin in the extraction system is t2, which is 0 h. The material flowing out of the extraction system is subjected to solid-liquid separation in the solid-liquid separation system to obtain purified polyester resin and liquid phase.

[0070] The flow rate, pressure, and contact temperature of the supercritical fluid are the same as in Example 1.

[0071] (2) The purified polyester resin enters the finished product system; the liquid phase is cooled by heat exchange system II and then enters the separation tank for depressurization to obtain supercritical gas and impurities; the supercritical gas is stored in the storage tank and then returned to the extraction system for purifying polyester resin after passing through the booster pump and heat exchange system I. The test results of the purified polybutylene succinate are shown in Table 1.

[0072] Table 1

[0073]

[0074] As can be seen from the results in Table 1, the method for purifying polyester resin using the present invention can achieve continuous resin extraction, thereby improving production efficiency. The preferred embodiment of the present invention not only yields polyester resin with low migration, but also results in relatively low energy loss due to the relatively low flow rate of the supercritical fluid during extraction. In Comparative Example 1, because no polyester resin was introduced into the extraction system and the contact residence time between the polyester resin and the supercritical fluid did not meet t1, the polyester resin had virtually no residence time in the extraction system, making extraction impossible.

[0075] 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, The method includes: having a mass of polyester resin m, allowing the polyester resin to contact and reside with the supercritical fluid for a time t1; allowing the purified polyester resin to flow out at a rate v1, while simultaneously allowing polyester resin to flow into the extraction reactor at a rate v1, such that the average contact and residence time t2 between the polyester resin and the supercritical fluid satisfies t2=m / v1≥t1.

2. The method according to claim 1, wherein, 1h≤t1≤5h; Preferably, 2h≤t1≤4h.

3. The method according to claim 1 or 2, wherein, The ratio of the flow rate Q of the supercritical fluid to the mass m of the polyester resin is 35-700 L / h, preferably 40-350 L / h. Preferably, 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.

4. The method according to any one of claims 1-3, 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℃.

5. The method according to any one of claims 1-4, wherein, The pressure of the supercritical fluid is 10-50 MPa, preferably 30-40 MPa; Preferably, the temperature T in which the polyester resin contacts the supercritical fluid is... j Satisfy: T s ≥T j ≥T; Preferably, the contact temperature is 35-100℃, and more preferably 55-95℃.

6. The method according to any one of claims 1-5, wherein, The supercritical fluid is selected from at least one of carbon dioxide, nitrous oxide, nitrogen, methane, ethane, and ethylene, preferably carbon dioxide and / or nitrogen.

7. The method according to any one of claims 1-6, wherein, The number average molecular weight of the polyester resin is 10,000-200,000 g / mol, preferably 20,000-100,000 g / mol; Preferably, the total weight of 100 polyester resin pellets is 1.5-2.5g, more preferably 1.8-2.2g; Preferably, 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 .

8. The method according to any one of claims 1-7, wherein, When the polyester resin comes into contact with the supercritical fluid, the temperature T j When the temperature is between 55-95℃ and the supercritical fluid is carbon dioxide, the flow rate Q of the supercritical carbon dioxide fluid and the effluent rate v1 of the purified polyester resin satisfy the following relationship: Q ≥ (10v1 × C0) / (0.001 × T) j -0.041), where C0 is the initial content of migratable substances in the polyester resin; where Q is L / h; v1 is kg / h; C0 is wt%; and the polyester resin is selected from polybutylene succinate and / or polybutylene adipate.

9. The method according to any one of claims 1-8, wherein, The method further includes: performing solid-liquid separation on the extracted material to obtain purified polyester resin and liquid phase; Preferably, the liquid phase is subjected to heat exchange and cooling, and depressurization in sequence to obtain supercritical gas and impurities; Preferably, the supercritical gas is pressurized and heated by heat exchange before being used to purify polyester resin.

10. The method according to any one of claims 1-9, wherein, The method for purifying polyester resin employs a series reaction vessel or a fluidized bed reactor. Preferably, the number of the series reactors is 1-5.

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