Polymer devolatilization method

Abstract

The invention provides a polymer devolatilization method, and belongs to the technical field of polymer processing. The polymer devolatilization method comprises the following steps: adding a devolatilization auxiliary agent into a mixing section of an extruder, connecting the mixing section with a first ultrasonic generator, forming first ultrasonic waves in the mixing section by the first ultrasonic generator, and uniformly mixing the devolatilization auxiliary agent and a polymer melt under the action of the first ultrasonic waves so as to promote volatile components to be separated from the polymer melt. According to the polymer devolatilization method provided by the invention, more gas nuclei are formed in the mixing section through the ultrasonic cavitation effect, and the uniform mixing of the auxiliary agent and the polymer melt in the mixing section is enhanced by utilizing the ultrasonic turbulence effect, so that the devolatilization effect is improved, and the volatile component content in the devolatilized polymer is reduced.

Description

Technical Field

[0001] This invention belongs to the field of polymer processing technology and relates to a polymer devolatilization method. Background Technology

[0002] During polymer processing, the presence of volatile components such as moisture, gases, monomers, oligomers, and solvents in the raw materials can result in excessively high volatile content in the final product. This can lead to defects such as dull surface, dents, and internal bubbles, affecting product quality and potentially posing risks to human health, the natural environment, and industrial production. Therefore, it is necessary to remove volatile components from polymers, a process known as "volatilization removal."

[0003] Current devolatilization methods include increasing the mass transfer area, increasing the devolatilization temperature, and increasing the devolatilization vacuum.

[0004] For polymers, especially those with large molecular sizes, such as high-carbon α-olefins, the above method has limited devolatilization effect, and the devolatilized polymer has a high volatile content. Summary of the Invention

[0005] This invention provides a polymer devolatilization method to improve the devolatilization effect and reduce the volatile content in the polymer after devolatilization.

[0006] The polymer devolatilization method provided by the present invention includes adding a devolatilization aid in the mixing section of an extruder, the mixing section being connected to a first ultrasonic generator, the first ultrasonic generator generating a first ultrasonic wave in the mixing section, and under the action of the first ultrasonic wave, the devolatilization aid being uniformly mixed with the polymer melt to promote the separation of volatiles from the polymer melt.

[0007] According to one embodiment of the present invention, the exhaust section of the extruder is connected to a second ultrasonic generator, which generates a second ultrasonic wave within the exhaust section. Under the action of the second ultrasonic wave, the diffusion and rupture of bubbles within the exhaust section are accelerated.

[0008] According to one embodiment of the present invention, the frequency of the first ultrasonic wave is 20-100 kHz, and the power density of the first ultrasonic wave is 0.4-5 W / cm². 2 ;

[0009] And / or, the frequency of the second ultrasound is 20-100kHz, and the power density of the second ultrasound is 0.4-5W / cm². 2 .

[0010] According to one embodiment of the present invention, the extruder includes m exhaust sections, each exhaust section having an exhaust port, and each exhaust port being equipped with a vacuum system, wherein 3≤m≤5, and m is an integer;

[0011] The extruder includes n mixing sections, each mixing section being located before the corresponding venting section, and each mixing section having a devolatilization aid injection port at its front end, where 3≤n≤5 and n is an integer.

[0012] According to one embodiment of the present invention, the devolatilization aid enters the mixing section through the devolatilization aid injection port;

[0013] The devolatilization aids include gaseous devolatilization aids and / or liquid devolatilization aids;

[0014] According to one embodiment of the present invention, the gas devolatilization aid is one or more of high-purity nitrogen, high-purity carbon dioxide, high-purity helium and high-purity argon;

[0015] The liquid devolatilization aid is one or more of deionized water and low-boiling-point organic solvents.

[0016] According to one embodiment of the present invention, the low-boiling-point organic solvent is one or more of ethanol, diethyl ether, acetonitrile, acetone, propanol, ethyl acetate and chloroform.

[0017] According to one embodiment of the present invention, the liquid devolatilization aid is injected into the mixing section through the first-stage devolatilization aid injection port;

[0018] The gas devolatilization aid is injected into the mixing section through the devolatilization aid injection port of the 2nd to nth stage.

[0019] According to one embodiment of the present invention, the amount of the gas devolatilization aid added is 6-14 wt% of the polymer mass; the amount of the liquid devolatilization aid added is 0.2-5 wt% of the polymer mass.

[0020] According to one embodiment of the present invention, after the polymer is treated by the polymer devolatilization method, the volatile content is measured to be <50ppm according to PV3341 standard and ASTM D4322 standard.

[0021] The party room de-vaporization method provided by this invention has at least the following beneficial effects:

[0022] The polymer devolatilization method provided by this invention involves installing a first ultrasonic generator in the mixing section of an extruder to generate first ultrasonic waves within the mixing section. A devolatilization aid is added to the mixing section. The first ultrasonic waves have a cavitation effect, causing cavitation bubbles or nuclei to form in the polymer melt and the devolatilization aid. This reduces the gas phase partial pressure of volatiles, making them easier to diffuse. The cavitation bubbles or nuclei grow and break down with the periodic changes of the first ultrasonic waves, thereby removing more volatiles. Furthermore, the mechanical effect generated by ultrasonic cavitation induces macroscopic turbulence and high-speed collisions of internal molecular chains in the polymer melt, enhancing eddy diffusion and promoting the mixing of the devolatilization aid with the melt. This improves the devolatilization effect of the aid and reduces the volatile content in the polymer after devolatilization.

[0023] Furthermore, the polymer devolatilization method provided by this invention generates a second ultrasonic wave in the exhaust section. The cavitation of the second ultrasonic wave impacts, peels off, and erodes the interface between the melt and the gas phase, causing the interface to be continuously renewed and increasing its mass transfer area. As a result, in the devolatilization exhaust section, more bubbles or gas nuclei break down, and more volatiles diffuse into the gas phase space, thereby further improving the polymer devolatilization effect. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] The reason why devolatilization methods that increase the mass transfer area, raise the devolatilization temperature, and increase the devolatilization vacuum have poor devolatilization effects is that their devolatilization efficiency has a limit, and the closer the devolatilization efficiency is to this limit, the higher the energy consumption and cost become. This is especially true for polymers with large molecular sizes, where the volatility of volatiles is poor and the diffusion rate is slow, resulting in poor devolatilization efficiency. Furthermore, regarding methods that increase the devolatilization temperature, polymers with large molecular sizes have large molecular sizes and correspondingly high boiling points. The boiling points of the volatiles are higher than the decomposition temperature of the polymer, making it impossible to achieve devolatilization by simply increasing the temperature.

[0026] Based on this, the present invention provides a polymer devolatilization method, which forms more gas nuclei in the mixing section through the ultrasonic cavitation effect and enhances the uniform mixing of additives with polymer melt in the mixing section by utilizing the ultrasonic turbulence effect, thereby improving the devolatilization effect and reducing the volatile content in the polymer after devolatilization, so as to achieve devastating of polymers, especially polymers with large molecular size.

[0027] The polymer devolatilization method provided by this invention includes the following steps: adding a devolatilization aid to the mixing section of an extruder; the mixing section is connected to a first ultrasonic generator; the first ultrasonic generator generates first ultrasonic waves within the mixing section; under the action of the first ultrasonic waves, the devolatilization aid is uniformly mixed with the polymer melt to promote the separation of volatiles from the polymer melt. The extruder can be a single-screw extruder, a twin-screw extruder, or a multi-screw extruder; this invention does not limit the type of extruder.

[0028] By installing a first ultrasonic generator in the mixing section of the extruder, first ultrasonic waves are generated within the mixing section. A devolatilization aid is added to the mixing section. The first ultrasonic wave exhibits a cavitation effect. Under the action of the ultrasonic wave, the medium can generate a large number of small bubbles and gas nuclei. These bubbles and gas nuclei form along the ultrasonic wave propagation path, grow larger in negative pressure areas, and rapidly collapse in positive pressure areas, thus tearing the liquid apart under the action of positive and negative pressure to form cavities. As the bubbles grow and collapse, enormous instantaneous pressure and high temperature and high pressure effects are generated.

[0029] The cavitation effect of the first ultrasound wave causes cavitation bubbles or nuclei to form in the polymer melt and devolatilization aid, reducing the partial pressure of volatiles in the gas phase and thus making them easier to diffuse. The cavitation bubbles or nuclei grow and break down with the periodic changes of the first ultrasound wave, thereby removing more volatiles.

[0030] The turbulent effect of ultrasound refers to the mechanical effects of microjets, shock waves, and acoustic jets generated by cavitation, which can induce macroscopic turbulence in liquid flow and high-speed collisions of solid particles, enhancing eddy diffusion. Firstly, the turbulent effect of ultrasound can induce macroscopic turbulence in polymer melts and high-speed collisions of internal molecular chains, enhancing eddy diffusion, thereby promoting the mixing of devolatilization aids with the melt, improving the devolatilization effect of the aids, and reducing the volatile content in the polymer after devolatilization.

[0031] Applying devolatilization aids and ultrasound to the polymer extrusion devolatilization process can promote the removal of volatiles, ultimately yielding high-quality polyolefin products with weak odor and low volatile content. This fills the demand gap in high-end fields such as aerospace, pharmaceutical packaging, and electronics, and is of great significance to the field of polymer devolatilization and other material processing.

[0032] In one specific embodiment, the exhaust section of the extruder is connected to a second ultrasonic generator, which generates a second ultrasonic wave within the exhaust section. Under the action of the second ultrasonic wave, the diffusion and rupture of bubbles within the exhaust section are accelerated.

[0033] A second ultrasonic wave is generated in the exhaust section. This second ultrasonic wave has a surface effect, which is the impact, peeling, and erosion effect of ultrasonic cavitation on the interface between the melt and the gas phase, causing the interface to be constantly renewed. This increases the mass transfer area in the exhaust section, resulting in more bubbles or gas nuclei breaking up and more volatiles diffusing into the gas phase space, thereby further improving the polymer devolatilization effect.

[0034] In one specific embodiment, the frequency of the first ultrasonic wave is 20-100 kHz, and the power density of the first ultrasonic wave is 0.4-5 W / cm². 2 For example, the frequency of the first ultrasonic wave can be a range of 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, or any combination thereof. Preferably, the frequency of the first ultrasonic wave is 40-80 kHz. For example, the power density of the first ultrasonic wave can be 0.4 W / cm². 2 1W / cm 2 2W / cm 2 3W / cm 2 4W / cm 2 5W / cm 2 Or a range consisting of any two of them. Preferably, the power of the first ultrasound wave is 1-3 W / cm. 2 By setting the frequency and power density of the first ultrasonic wave within the aforementioned range, the cavitation and turbulence effects generated by the first ultrasonic wave can improve the polymer devolatilization effect. Furthermore, it avoids noise caused by excessively high ultrasonic wave frequency and power density, and reduces production costs.

[0035] In one possible implementation, the frequency of the second ultrasonic wave is 20-100 kHz, and the power density of the second ultrasonic wave is 0.4-5 W / cm². 2 For example, the frequency of the second ultrasonic wave can be a range of 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, or any combination thereof. Preferably, the frequency of the second ultrasonic wave is 40-80 kHz. For example, the power density of the second ultrasonic wave can be 0.4 W / cm². 2 1W / cm 2 2W / cm 2 3W / cm 2 4W / cm 2 5W / cm 2 Or a range consisting of any two of them. Preferably, the power of the second ultrasound is 1-3 W / cm. 2By setting the frequency and power density of the second ultrasound within the aforementioned range, the surface effect generated by the second ultrasound can improve the polymer devolatilization effect. Furthermore, it avoids noise caused by excessively high ultrasound frequency and power density, and reduces production costs.

[0036] In one specific embodiment, the extruder includes m venting sections, each with an exhaust port, where 3 ≤ m ≤ 5, and m is an integer. For example, m can be 3, 4, or 5. The exhaust ports are used to discharge volatile gases.

[0037] In one possible implementation, each exhaust port is equipped with a vacuum system, setting the vacuum level at the exhaust port to 0.02-0.095 MPaG. Exemplary settings include 0.02 MPaG, 0.05 MPaG, 0.07 MPaG, 0.09 MPaG, or 0.095 MPaG. Preferably, the vacuum level is set to 0.07-0.09 MPaG. For example, the exhaust port is connected to a vacuum pump to maintain a vacuum environment within the exhaust section, facilitating the movement of volatiles from the high-pressure region of the polymer melt to the low-pressure region of the exhaust section, thereby facilitating volatile removal and further improving the devolatilization effect.

[0038] The extruder includes n mixing sections, each mixing section is located before the corresponding venting section, and each mixing section has a devolatilization aid injection port at its front end, where 3≤n≤5 and n is an integer.

[0039] In this embodiment, the exhaust section and the mixing section located within the exhaust section form a devolatilization unit. The number of devolatilization units is 3, 4, or 5. This ensures that the devolatilization aid and polymer melt are uniformly mixed within the mixing section and the corresponding exhaust section. Fewer than 3 devolatilization units will result in insufficient exhaust of volatile gases, leading to poor devolatilization performance. More than 5 devolatilization units will increase the number of vacuum pumps required to form the vacuum system, increasing the cost of the vacuum pumps, but the improvement in exhaust performance of the devolatilization units located at the rear is not significant.

[0040] In one possible implementation, the extruder temperature is 100-300°C. For example, 100°C, 200°C, or 300°C, preferably 180-240°C.

[0041] The temperature of the mixing section of the extruder is set to 160-240℃. For example, 160℃, 200℃, or 220℃, preferably 190-220℃.

[0042] The exhaust temperature is set to 200-260℃. For example, 200℃, 240℃, or 260℃, preferably 220-240℃.

[0043] In one possible implementation, the devolatilization aid enters the mixing section through a devolatilization aid injection port, thereby adding the devolatilization aid in the mixing section. The devolatilization aid can reduce the partial pressure of volatile components in the gas phase space, thereby increasing the driving force for volatile component diffusion and making it easier for them to escape from the polymer. The devolatilization aid can increase bubble nucleation sites, providing more opportunities for bubble formation and accelerating the release of volatile components. The devolatilization aid can also improve the interaction between the polymer and volatile components, reducing the interaction forces between the polymer and volatile components, making them easier to separate. This, in turn, improves the devolatilization effect and reduces the content of volatile components after devolatilization.

[0044] Deviation aids include gaseous devolatilization aids and / or liquid devolatilization aids. Deviation aids may include only gaseous devolatilization aids, only liquid devolatilization aids, or both gaseous and liquid devolatilization aids.

[0045] In one possible implementation, the gas devolatilization aid is one or more of high-purity nitrogen, high-purity carbon dioxide, high-purity helium, and high-purity argon. The purity of the high-purity nitrogen, carbon dioxide, helium, and argon is greater than or equal to 99.99%.

[0046] Liquid devolatilization aids are one or more of deionized water and low-boiling-point organic solvents. The low-boiling-point organic solvent can be an organic solvent with a boiling point lower than the boiling point of the volatile components in the material; for example, a low-boiling-point organic solvent with a boiling point below 100 degrees Celsius. It should be noted that the boiling point requirements for the low-boiling-point organic solvent vary depending on the different polymers and the different volatile components.

[0047] Preferably, the low-boiling-point organic solvent is one or more of ethanol, diethyl ether, acetonitrile, acetone, propanol, ethyl acetate, and chloroform.

[0048] In one specific embodiment, the liquid devolatilization aid is injected into the mixing section via the first-stage devolatilization aid injection port.

[0049] The gaseous devolatilization aid is injected into the mixing section through the 2nd to nth stage devolatilization aid injection ports. The first stage devolatilization aid injection port is the first devolatilization aid injection port along the flow direction of the polymer, the second stage devolatilization aid injection port is the second devolatilization aid injection port along the flow direction of the polymer, and the nth stage devolatilization aid injection port is the nth devolatilization aid injection port along the flow direction of the polymer.

[0050] In one specific embodiment, the amount of gas devolatilization aid added is 6-14 wt% of the polymer mass, for example, 6 wt%, 8 wt%, 10 wt%, 12 wt%, or 14 wt%. Preferably, the amount of gas devolatilization aid added is 10-12 wt% of the polymer mass.

[0051] The amount of liquid devolatilization aid added is 0.2-5 wt% of the polymer mass, for example, 0.2 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Preferably, the amount of liquid devolatilization aid added is 1-2 wt% of the polymer mass.

[0052] This allows the gaseous deflaking aid and liquid devolatilization aid to be fully mixed with the polymer, thereby improving the devolatilization effect of the devolatilization aid.

[0053] In one specific embodiment, after the polymer is treated by a polymer devolatilization method, the volatile content is measured to be <50 ppm according to PV3341 and ASTM D4322 standards.

[0054] The polymer devolatilization method provided by the present invention will be described in detail below through specific embodiments.

[0055] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0056] Example 1

[0057] This embodiment provides a polymer devolatilization method, the process of which is as follows:

[0058] High-density polyethylene (HDPE) material containing a certain amount of octene was prepared. The octene content of the material before devolatilization was analyzed by headspace gas chromatography according to PV3341 and ASTM D4322 standards. The twin-screw extruder was started, with the exhaust section temperature set to 230℃, the vacuum level set to 0.09 MPaG for each stage, and the screw speed set to 60 rpm. The insertion ultrasonic generators in each mixing and exhaust section were turned on, with the frequency adjusted to 40 kHz and the power density to 1 W / cm³. 2 HDPE material is fed into a twin-screw extruder at a feed rate of 1 kg / h. After the twin-screw extruder is running stably, high-purity nitrogen is injected at a rate of 1.2 L / min into the first to third stage devolatilization aid injection ports. The extruded devolatilized polyolefin melt strand is then drawn into a pelletizer for granulation to obtain devolatilized HDPE granules. The residual octene content is tested by headspace gas chromatography according to PV3341 and ASTM D4322 standards.

[0059] Example 2

[0060] This embodiment provides a polymer devolatilization method, which is basically the same as that in Example 1. The difference is that after the twin-screw extruder is running stably, ethanol is injected at a rate of 25 g / h into the first to third stage devolatilization aid injection ports.

[0061] Example 3

[0062] This embodiment provides a polymer devolatilization method, which is basically the same as that in Example 1. The difference is that after the twin-screw extruder is running stably, ethanol is injected at a rate of 25 g / h into the first-stage devolatilization aid injection port, and high-purity nitrogen is injected at a rate of 1.2 L / min into the second and third-stage devolatilization aid injection ports.

[0063] Comparative Example 1

[0064] The process in this embodiment is basically the same as that in embodiment 1, except that no devolatilization aid is injected after the twin-screw extruder has been running stably.

[0065] Comparative Example 2

[0066] The process of this comparative example is basically the same as that of Example 1, except that the insertion ultrasonic generators of each mixing section and exhaust section are turned off.

[0067] Comparative Example 3

[0068] The process of this comparative example is basically the same as that of Example 2, except that the insertion ultrasonic generators of each mixing section and exhaust section are turned off.

[0069] Comparative Example 4

[0070] The process of this comparative example is basically the same as that of Example 3, except that the insertion ultrasonic generators of each mixing section and exhaust section are turned off.

[0071] Comparative Example 5

[0072] The process of this comparative example is basically the same as that of comparative example 1, except that the insertion ultrasonic generators of each mixing section and exhaust section are turned off.

[0073] The octene content before and after devolatilization in the above embodiments and comparative examples are shown in Table 1.

[0074] Table 1

[0075]

[0076] The following conclusions can be drawn from Table 1:

[0077] The results from Examples 1-3 and Comparative Example 1 show that the addition of a devolatilization aid effectively enhances the devolatilization effect of the polymer. Adding a liquid devolatilization aid in the first stage and a gaseous devolatilization aid in stages 2-n further improves the removal of volatiles. The results from Examples 1-3, Comparative Examples 2-4, and Comparative Examples 1 and 5 show that introducing ultrasonic waves into the devolatilization process can further remove volatiles from the polymer melt. The results from Examples 1-3 show that combining ultrasonic waves and a devolatilization aid can achieve a high standard of less than 50 ppm of volatiles after devolatilization, resulting in a high-quality product with weak odor and low volatile content.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polymer devolatilization method, characterized in that, include: A devolatilization aid is added to the mixing section of an extruder. The mixing section is connected to a first ultrasonic generator, which generates a first ultrasonic wave within the mixing section. Under the action of the first ultrasonic wave, the devolatilization aid is uniformly mixed with the polymer melt to promote the separation of volatiles from the polymer melt.

2. The polymer devolatilization method according to claim 1, characterized in that, The exhaust section of the extruder is connected to a second ultrasonic generator, which generates a second ultrasonic wave within the exhaust section. Under the action of the second ultrasonic wave, the diffusion and rupture of bubbles within the exhaust section are accelerated.

3. The polymer devolatilization method according to claim 2, characterized in that, The frequency of the first ultrasonic wave is 20-100kHz, and the power density of the first ultrasonic wave is 0.4-5W / cm². 2 ; And / or, the frequency of the second ultrasound is 20-100kHz, and the power density of the second ultrasound is 0.4-5W / cm². 2 .

4. The polymer devolatilization method according to claim 2 or 3, characterized in that, The extruder includes m exhaust sections, each exhaust section is provided with an exhaust port, and each exhaust port is equipped with a vacuum system, where 3≤m≤5, and m is an integer; The extruder includes n mixing sections, each mixing section being located before the corresponding venting section, and each mixing section having a devolatilization aid injection port at its front end, where 3≤n≤5 and n is an integer.

5. The polymer devolatilization method according to claim 4, characterized in that, The devolatilization aid enters the mixing section through the devolatilization aid injection port; The devolatilization aids include gaseous devolatilization aids and / or liquid devolatilization aids.

6. The polymer devolatilization method according to claim 5, characterized in that, The gas devolatilization aid is one or more of high-purity nitrogen, high-purity carbon dioxide, high-purity helium, and high-purity argon. The liquid devolatilization aid is one or more of deionized water and low-boiling-point organic solvents.

7. The polymer devolatilization method according to claim 6, characterized in that, The low-boiling-point organic solvent is one or more of ethanol, diethyl ether, acetonitrile, acetone, propanol, ethyl acetate, and chloroform.

8. The polymer devolatilization method according to claim 5, characterized in that, The liquid devolatilization aid is injected into the mixing section through the first-stage devolatilization aid injection port; The gas devolatilization aid is injected into the mixing section through the devolatilization aid injection port of the 2nd to nth stage.

9. The polymer devolatilization method according to claim 5, characterized in that, The amount of the gas devolatilization aid added is 6-14 wt% of the polymer mass; the amount of the liquid devolatilization aid added is 0.2-5 wt% of the polymer mass.

10. The polymer devolatilization method according to any one of claims 1-3, characterized in that, After the polymer is treated by the polymer devolatilization method, the volatile content is measured to be <50ppm according to PV3341 and ASTM D4322 standards.

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