Polymer devolatilization process and devolatilization system

Abstract

The invention provides a polymer devolatilization process and a devolatilization system. The devolatilization process comprises the following steps: heating a polymer raw material containing volatile components to obtain a molten polymer, pressurizing the molten polymer, mixing with an entrainer, and feeding into a falling film device; after sudden pressure drop and heating, the entrainer carries volatile components to be separated from the system, and a devolatilization product is obtained; the mass ratio of the polymer raw material to the entrainer is (10: 1)-(10000: 1). According to the polymer devolatilization process provided by the invention, the entrainer with a low boiling point is introduced into a reaction system, a large number of microbubbles are formed through vaporization of the entrainer and azeotropy of volatile components, removal of the volatile components in the material is enhanced through pressure swing flash evaporation, and extremely low pressure does not need to be reached in a devolatilization device.

Description

Technical Field

[0001] This invention relates to a polymer devolatilization process and system, belonging to the field of polymer devolatilization technology. Background Technology

[0002] In polymer production, the removal of low-molecular-weight volatile components is a crucial step. Polymers produced after reactor processing typically contain volatile organic compounds (VOCs) ranging from 10% to 80%. Depending on the intended use of the polymer, the VOC content needs to be reduced to the levels of several thousand ppm or even tens of ppm. To effectively remove these low-molecular-weight light components from the polymer, a devolatilization process is required.

[0003] Researchers have developed various devolatilization processes and equipment, which can be categorized into static and dynamic devolatilization equipment. Static devolatilization equipment mainly includes flash evaporators and drop-strip devolatilizers, while dynamic devolatilization equipment mainly includes extrusion-type, film-renewal-type, and surface-renewal-type devolatilizers. For most polymer devolatilization processes, as the lighter components are gradually removed, the polymer viscosity gradually increases, and its flowability deteriorates, requiring more energy to form a film to drive the timely removal of the lighter components. Therefore, in the later stages of devolatilization, there are often problems of high energy consumption and poor devolatilization efficiency.

[0004] Analysis of traditional devolatilization processes reveals two main reasons for poor devolatilization efficiency. Firstly, the poor flowability of the material results in poor film spreading. This can be addressed by designing special internal components or moving equipment to enhance film formation. Secondly, poor mass transfer is another major reason for the poor devolatilization effect. However, methods to enhance mass transfer are not yet perfect, leading to few reports on improvements to existing processes.

[0005] CN209734996U proposes a polymer devolatilization device. From top to bottom, the device comprises a feed distribution zone, a heating devolatilization zone, a first-stage falling film devolatilization zone, a second-stage falling film devolatilization zone, a third-stage falling film devolatilization zone, and a material collection zone. The first-stage falling film devolatilization zone is equipped with a liquid-collecting falling film distributor connected to an external motor at the bottom of the device via a rotating shaft. The material collection zone also includes a pusher device that moves the polymer downwards. The device is compact, small in size, and capable of performing static and dynamic multi-stage efficient devolatilization of polymers at suitable process temperatures. However, the driving force of this devolatilization process depends on the vacuum level; a high vacuum level is required to achieve high devolatilization efficiency.

[0006] CN101838354B proposes a method for devolatilization of aromatic vinyl polymers. This method involves pre-purging the chamber with nitrogen, heating the chamber, and then introducing the aromatic vinyl polymer into the chamber. A vacuum system is then used to perform three-stage devolatilization on the polymer within the chamber. However, this technology has a small mass transfer area and low volatile matter removal efficiency.

[0007] CN112339158B proposes a high-gravity rotating bed for polymer devolatilization and its application method. The device includes a shell, motor, liquid inlet chamber, multi-layer disc distributor, rotor, static guide, granulation assembly, unloading assembly, and gas outlet. The high-gravity environment generates a large and rapidly renewing phase interface, enhancing the polymer devolatilization process and reducing the volatile content in the polymer to below 500 ppm. This achieves an integrated process of volatile removal, granulation, and unloading of thermoplastic polymers under vacuum conditions, avoiding the series process of adding external granulation equipment in the traditional plastics industry, and significantly reducing floor space and energy consumption. However, this technology has a relatively simple devolatilization method, resulting in a relatively high residual volatile content.

[0008] Therefore, how to achieve a high volatile matter removal rate under relatively low vacuum conditions is an urgent problem to be solved. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide a polymer devolatilization process and system. To achieve the above objective, the present invention provides a polymer devolatilization process, wherein the devolatilization process includes:

[0010] (1) The polymer raw material containing volatiles is heated to obtain a molten polymer, which is then pressurized, mixed with an entrainer, and then fed into a falling film device.

[0011] (2) After a sudden pressure drop and heating, the entrainer carries the volatiles away from the system to obtain the devolatile product.

[0012] According to a specific embodiment of the present invention, preferably, the mass ratio of the polymer raw material to the entrainer is 10:1 to 10000:1, more preferably 50:1 to 1000:1.

[0013] According to a specific embodiment of the present invention, preferably, the devolatilization process further includes repeating the pressurization, mixing with an entrainer, and entering a falling film device of the devolatilized product in step (1), as well as the pressure drop and heating process in step (2). For example, when secondary devolatilization is involved, it specifically includes the following steps:

[0014] (1) The polymer raw material containing volatiles is heated to obtain a molten polymer, which is then pressurized, mixed with an entrainer, and then fed into a falling film device.

[0015] (2) After a sudden pressure drop and heating, the entrainer carries the volatiles away from the system to obtain a primary devolatilization product;

[0016] (3) Secondary devolatilization process: The product from the primary devolatilization is pressurized again, mixed with the entrainer, and then enters the falling film device; after a sudden pressure drop and heating, the entrainer carries the volatiles out of the system, yielding the secondary devolatilization product. In the secondary devolatilization process, the product from the primary devolatilization can be mixed with fresh raw materials that have not undergone devolatilization treatment and returned to the original reaction vessel, or it can be carried out in a new reaction vessel.

[0017] According to a specific embodiment of the present invention, preferably, in step (1), the pressure after pressurization is 500 kPaA to 1600 kPaA, more preferably 600 kPaA to 1000 kPaA.

[0018] According to a specific embodiment of the present invention, preferably, the pressure of the falling film device is 10 kPaA to 1 kPaA, more preferably 10 kPaA to 4 kPaA. The operation process of the present invention does not require high vacuum conditions and can be carried out under normal pressure or slightly negative pressure conditions.

[0019] According to a specific embodiment of the present invention, preferably, the molten polymer and the entrainer are mixed in a pipeline static mixer, and then transported to the falling film device via pipeline. The mixing refers to the molten polymer gradually flowing into the pipeline static mixer to mix with the entrainer online, and then flowing out of the pipeline static mixer into the falling film device after mixing.

[0020] According to a specific embodiment of the present invention, preferably, the polymer raw material includes polyester and / or polyolefin.

[0021] In some specific embodiments, preferably, the polyester includes one or more of the following: polybutylene succinate (PBS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate (PBST), polycaprolactone (PCL), and polyhydroxyalkanoates (PHA).

[0022] In some specific embodiments, preferably, the polyolefin includes one or more combinations of polyethylene, polypropylene, polyolefin elastomers, cyclic olefin polymers, etc. The cyclic olefin polymer includes one or more combinations of norbornene-ethylene copolymers, norbornene polymers, tetracyclododecene-ethylene copolymers, etc.

[0023] According to a specific embodiment of the present invention, preferably, the volatile components include one or more of the following: by-reaction products, monomeric small molecules, and solvents. The monomeric small molecules refer to small molecule monomer impurities that have not completed polymerization during polymer synthesis and / or small molecule monomers generated by side reactions, such as ethylene glycol. The by-reaction products are other products generated during the reaction process due to the occurrence of side reactions, such as tetrahydrofuran (THF).

[0024] In some specific embodiments, preferably, the solvent includes one or a combination of two or more of toluene, xylene, hexane, etc.

[0025] According to a specific embodiment of the present invention, preferably, the entrainer includes one or more of the following: inert gas, water, alcohols, esters, etc.

[0026] In some specific embodiments, preferably, the alcohols include ethanol and / or methanol; the esters include methyl acetate and / or ethyl acetate; and the inert gas includes nitrogen and / or nitrogen dioxide. In this invention, through a sudden pressure drop and the heating effect of the jacketed heat transfer oil, the entrainer can rapidly vaporize and evaporate in the form of microbubbles, carrying the volatiles out of the system under negative pressure.

[0027] Unlike existing devolatilization processes, this invention introduces a small amount of low-boiling-point entrainer that azeotropically interacts with volatiles into the system. This reduces the system's viscosity, improves the flowability of high-viscosity polymer materials, and facilitates film formation. The viscosity of polymer polymerization systems is typically above 5000 cp (medium viscosity) or even above 50000 cp (high viscosity). Adding 0.1% to 1% of a liquid entrainer can reduce the viscosity of medium-viscosity fluids to around 1600 cp. For high-viscosity fluids above 50000 cp, adding an appropriate proportion and type of entrainer can reduce the viscosity by an order of magnitude. Furthermore, the entrainer's evaporation upon heating and azeotropic interaction with volatiles generates numerous microbubbles within the system. As these bubbles grow and escape from the system, a large amount of volatiles is simultaneously removed, effectively reducing the volatile content in the system.

[0028] According to a specific embodiment of the present invention, preferably, in steps (1) and (2), the heating temperatures are 90°C to 270°C.

[0029] In some specific embodiments, preferably, the heating temperature in steps (1) and (2) is higher than the solidification point of the polymer and higher than the boiling point of the entrainer under the same pressure, more preferably 135-260°C, and even more preferably 230-260°C. The heating is achieved through jacketed heat transfer oil.

[0030] According to a specific embodiment of the present invention, preferably, the volatile content of the secondary devolatification product is less than 30 ppm, more preferably 20 ppm.

[0031] The present invention also provides a polymer devolatilization system for implementing the above-mentioned polymer devolatilization process, the system comprising at least: a polymer melting unit, a devolatilization unit, and a product collection device;

[0032] The polymer melting unit includes at least a melting tank; the melting tank is provided with at least a polymer raw material inlet, a gas inlet, and a molten polymer outlet;

[0033] The devolatilization unit includes at least a falling film device, a cold trap, and a vacuum pump; the falling film device is provided with at least a material inlet, a devolatilization product outlet, and a volatile matter outlet.

[0034] The molten polymer outlet of the melting tank is connected to the material inlet of the falling film device via a pipeline; the devolatilization product outlet of the falling film device is connected to the product collection device via a pipeline; and the volatile matter outlet of the falling film device is connected in sequence to a cold trap and a vacuum pump via pipelines.

[0035] In some specific implementations, preferably, the product collection device includes at least a product tank; the product tank is provided with at least a product inlet and a product outlet.

[0036] According to a specific embodiment of the present invention, preferably, a pipeline static mixer is provided on the pipeline connecting the molten polymer outlet of the melting tank and the material inlet of the falling film device.

[0037] In some specific embodiments, preferably, the material inlet of the falling film device is a throttling structure; inside the falling film device, a liquid distributor is provided at the top and a falling film element composed of multiple metal wire meshes is provided at the bottom; the liquid distributor enables the material to be evenly distributed on the metal wire mesh to form a film and move downward.

[0038] In some specific embodiments, preferably, the pipeline at the volatiles outlet of the falling film device is a volatiles exhaust pipeline; the volatiles exhaust pipeline is used to connect the cold trap and the falling film device to discharge the volatiles from the system.

[0039] In some specific embodiments, preferably, the liquid distributor is a porous plate trough structure; in this invention, after the molten polymer flows into the porous plate trough structure through the overflow baffle, it can be evenly distributed on the metal wire mesh connected to the distributor.

[0040] In some specific embodiments, preferably, the falling film device is provided with a heating jacket on the outside; the heating jacket is used to heat the polymer, promote the vaporization of the entrainer and the escape of light components.

[0041] According to a specific embodiment of the present invention, preferably, the system further includes a circulation unit; the circulation unit includes at least a polymer circulation pipeline; the polymer circulation pipeline is used to connect the devolatilization product outlet of the falling film device with the polymer raw material inlet of the melting tank. In the present invention, the polymer after the above-mentioned devolatilization process can be transported to a product tank by a melt pump for subsequent processing, or it can be transported back to the melting tank for repeated devolatilization, achieving a multi-stage devolatilization effect and realizing deep devolatilization.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The polymer devolatilization process provided by the present invention introduces an entrainer with a low boiling point into the reaction system. Through the vaporization of the entrainer and the azeotropic reaction with the volatiles, a large number of microbubbles are formed, which effectively promotes the removal of volatiles.

[0044] (2) The polymer devolatilization process provided by this invention increases the pressure of the material in the devolatilization system by pressurizing the melting tank. Therefore, when the material is pumped to a falling film device under normal or slightly negative pressure, an effect similar to flash evaporation is achieved, enhancing the removal of volatiles from the material through pressure-switching flash evaporation. This invention overcomes the limitation of devolatilization efficiency in traditional processes, which is constrained by the vacuum level within the device. It eliminates the need for extremely low pressures within the devolatilization device, significantly reducing the stringent requirements for operating conditions and lowering energy consumption.

[0045] (3) The polymer devolatilization process provided by the present invention realizes multi-stage devolatilization operation through cyclic operation, which saves the process floor space, simplifies the production equipment, reduces energy consumption, and reduces design and manufacturing costs and production operation costs.

[0046] (4) The polymer devolatilization process provided by this invention, after secondary devolatilization, results in a lower volatile content in the product (preferredly below 30 ppm), achieving a significantly better devolatilization effect than traditional processes. The devolatilization system of this invention solves the problems of traditional devolatilization processes and equipment failing to effectively remove light components and consuming excessive energy; it also solves the problem of poor film formation caused by poor material flowability in traditional static devolatilization devices. The devolatilization system of this invention can be used in the devolatilization process of various polymers, significantly improving the heat and mass transfer efficiency of the polymer devolatilization process, reducing product production costs, and possessing broad industrial application prospects. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the polymer devolatilization system provided by the present invention.

[0048] Explanation of icon numbers:

[0049] 1-Melting tank; 2-Falling film device; 3-Product tank; 4,5-Mel pump; 6,7,8-Flow meter; 9-Vacuum pump; 10-Cold trap; 11-Polymer feed line; 12-Pipeline static mixer; 13-Nitrogen line; 14-Discharge line; 15-Polymer circulation line. Detailed Implementation

[0050] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0051] Example 1

[0052] This embodiment provides a polymer devolatilization system, such as Figure 1 As shown, the devolatilization system includes: a polymer melting unit, a devolatilization unit, a product collection device, and a circulation unit;

[0053] The polymer melting unit includes at least a melting tank 1; the melting tank 1 is provided with at least a polymer raw material inlet, a gas inlet, and a molten polymer outlet; the polymer raw material inlet of the melting tank 1 is connected to a polymer feed pipeline 11, and the gas inlet is connected to a nitrogen pipeline 13;

[0054] The devolatilization unit includes at least a falling film device 2, a cold trap 10, and a vacuum pump 9; the falling film device 2 is provided with at least a material inlet, a devolatilization product outlet, and a volatile matter outlet.

[0055] The product collection device includes at least a product tank 3; the product tank 3 is provided with at least a product inlet and a product outlet;

[0056] The circulation unit includes at least a polymer circulation pipeline 15.

[0057] The molten polymer outlet of the melting tank 1 is connected to the material inlet of the falling film device 2 via a pipeline. A melt pump 4, a flow meter 6, and a pipeline static mixer 12 are sequentially installed on the pipeline. The devolatilization product outlet of the falling film device 2 is connected to the melt pump 5 and then to two branch pipelines. One branch pipeline is the discharge pipeline 14, which connects the devolatilization product outlet to the product inlet of the product tank 3. A flow meter 8 is installed on the discharge pipeline 14 to control the flow rate. The other branch pipeline is the polymer circulation pipeline 15, which connects the devolatilization product outlet of the falling film device 2 to the polymer raw material inlet of the melting tank 1. A flow meter 7 is installed on the polymer circulation pipeline 15 to control the flow rate. The volatile matter outlet of the falling film device 2 is sequentially connected to a cold trap 10 and a vacuum pump 9 via a pipeline.

[0058] Example 2

[0059] This embodiment provides a polymer devolatilization process using the polymer devolatilization system provided in Example 1. The specific steps are as follows:

[0060] (1) A PBS polymer with a volatile THF content of 450 ppm is added to a melting tank 1 through a polymer feed line 11, and nitrogen is introduced through a nitrogen line 13. The reaction raw materials are heated to 800 kPaA in the melting tank 1 by the jacket heat transfer oil at 135°C, and then transported to the inlet of the pipeline static mixer 12 on the material pipeline by a melt pump 4. At the same time, water is pumped to the inlet of the pipeline static mixer 12 on the material pipeline using water as an entrainer. The mass ratio of PBS to water is 1000:1. After the two are fully mixed in the pipeline static mixer 12, the viscosity can be reduced from 8000 cp to about 3000 cp. Then it enters a falling film device 2 at 5 kPaA and 135°C.

[0061] (2) After the mixture enters the falling film device 2, under the sudden change of pressure, the liquid water immediately undergoes a phase change and forms an azeotrope with the volatile THF, generating a large number of bubbles that carry out most of the volatiles; then the PBS raw material passes through the liquid distributor and forms a film on the falling film wire mesh, continuously generating bubbles that carry out the remaining THF, thus obtaining the primary devolatilization product; the primary devolatilization product is transported to the product tank 3 through the melt pump 5 and the discharge pipeline 14, with a volatile content of 120-130 ppm;

[0062] (3) The product after the first devolatilization is transported back to the melting tank 1 through the melt pump 5 and the polymer circulation pipeline 15, and then undergoes a second devolatilization process through the same steps to obtain the second devolatilization product; after the two devolatilization processes, the volatile content in the PBS product is reduced to 20 ppm.

[0063] Example 3

[0064] This embodiment provides a polymer devolatilization process using the polymer devolatilization system provided in Example 1. The specific steps are as follows:

[0065] (1) A cyclic olefin polymer COC with a volatile xylene content of 1000 ppm is added to a melting tank 1 through a polymer feed line 11, and nitrogen is introduced through a nitrogen line 13. The reaction raw materials are heated to 1600 kPaA in the melting tank 1 by the jacket heat transfer oil at 260°C, and then transported to the inlet of the pipeline static mixer 12 on the material pipeline by a melt pump 4. At the same time, nitrogen is transported to the inlet of the pipeline static mixer 12 on the material pipeline using nitrogen as an entrainer. The mass ratio of COC to nitrogen is 10:1. After the two are fully mixed in the pipeline static mixer 12, they enter the falling film device 2 at 1 kPaA and 260°C.

[0066] (2) After the mixture enters the falling film device 2, under the sudden change of pressure, nitrogen gas generates a large number of bubbles in COC and carries out most of the volatile matter; then the cyclic olefin polymer forms a film on the falling film wire after passing through the liquid distributor, and continuously generates bubbles to carry out the remaining xylene, thus obtaining the primary devolatilization product; the primary devolatilization product is transported to the product tank 3 through the melt pump 5 and the discharge pipeline 14, with a volatile matter content of 60 ppm;

[0067] (3) The product after the first devolatilization is transported back to the melting tank 1 through the melt pump 5 and the polymer circulation pipeline 15, and then undergoes a second devolatilization process through the same steps to obtain the second devolatilization product; after the two devolatilization processes, the volatile content in the COC product is reduced to 30ppm.

[0068] Example 4

[0069] This embodiment provides a polymer devolatilization process using the polymer devolatilization system provided in Example 1. The specific steps are as follows:

[0070] (1) PBT polymer with a volatile THF content of 750 ppm is added to the melting tank 1 through the polymer feed line 11 and nitrogen is introduced through the nitrogen line 13. The reaction raw materials are heated to 800 kPaA in the melting tank 1 under the heating action of the jacket heat transfer oil at 250°C, and then transported to the inlet of the pipeline static mixer 12 on the material pipeline by the melt pump 4. At the same time, nitrogen is used as an entrainer to transport nitrogen to the inlet of the pipeline static mixer 12 on the material pipeline. The mass ratio of PBT to nitrogen is 8000:1. After the two are fully mixed in the pipeline static mixer 12, they enter the falling film device 2 at 5 kPaA and 250°C.

[0071] (2) After the mixture enters the falling film device 2, under the sudden change of pressure, the nitrogen bubbles dispersed in the liquid immediately detach and carry away most of the volatiles; then the PBS raw material passes through the liquid distributor and forms a film on the falling film wire mesh, continuously removing the residual micro bubbles and carrying away the remaining THF, to obtain the primary devolatilization product; the primary devolatilization product is transported to the product tank 3 through the melt pump 5 and the discharge pipeline 14, with a volatile content of 320 ppm;

[0072] (3) The product after the first devolatilization is transported back to the melting tank 1 through the melt pump 5 and the polymer circulation pipeline 15, and then undergoes a second devolatilization process through the same steps to obtain the second devolatilization product; after the two devolatilization processes, the volatile content in the PBT product is reduced to 120ppm.

[0073] Example 5

[0074] This embodiment provides a polymer devolatilization process using the polymer devolatilization system provided in Example 1. The specific steps are as follows:

[0075] (1) PET polymer with a volatile ethylene glycol content of 600 ppm is added to the melting tank 1 through the polymer feed line 11, and nitrogen is introduced through the nitrogen line 13; the reaction raw materials are heated to 800 kPaA in the melting tank 1 under the heating action of jacket heat transfer oil at 270°C, and then transported to the inlet of the pipeline static mixer 12 on the material pipeline by the melt pump 4; at the same time, water is used as an entrainer and pumped to the inlet of the pipeline static mixer 12 on the material pipeline. The mass ratio of PET to water is 1500:1. After the two are fully mixed in the pipeline static mixer 12, they enter the falling film device 2 at 5 kPaA and 270°C.

[0076] (2) After the mixture enters the falling film device 2, under the sudden change of pressure, the liquid water immediately undergoes a phase change and evaporates together with the volatile ethylene glycol, generating a large number of bubbles that carry away most of the volatiles; then the PET raw material passes through the liquid distributor and forms a film on the falling film wire mesh, continuously generating bubbles that carry away the remaining ethylene glycol, thus obtaining the primary devolatilization product; the primary devolatilization product is transported to the product tank 3 through the melt pump 5 and the discharge pipeline 14, with a volatile content of 220 ppm;

[0077] (3) The product after the first devolatilization is transported back to the melting tank 1 through the melt pump 5 and the polymer circulation pipeline 15, and then undergoes a second devolatilization process through the same steps to obtain the second devolatilization product; after the two devolatilization processes, the volatile content in the PET product is reduced to 50ppm.

[0078] Comparative Example 1

[0079] This comparative example provides a polymer devolatilization process, the specific steps of which are as follows:

[0080] A PBS polymer with a volatile THF content of 489 ppm was added to a melting tank 1. The mixture was stirred and vacuumed to 5 kPaA under the heating effect of jacketed heat transfer oil at 235°C. The resulting PBS product had a volatile content of 445 ppm.

[0081] It can be seen that the volatile content is not reduced after using the traditional devolatilization process in Comparative Example 1.

[0082] Comparative Example 2

[0083] This comparative example provides a polymer devolatilization process, the specific steps of which are as follows:

[0084] A PBS polymer with a THF content of 489 ppm was added to a melting tank 1 and pressurized to 800 kPaA. The mixture was stirred under the heating effect of jacketed heat transfer oil at 235°C, and then piped into a falling film device 2 under a negative pressure of 5 kPaA. After a single devolatilization under the heating effect of jacketed heat transfer oil at 235°C, the PBS product obtained had a volatile content of approximately 337 ppm. Repeating the above steps, a second devolatilization process yielded a PBS product with a volatile content of approximately 281 ppm.

[0085] Therefore, compared with Comparative Example 1, the devolatilization effect can be improved by using the falling film device 2.

[0086] Comparative Example 3

[0087] This comparative example provides a polymer devolatilization process, the specific steps of which are as follows:

[0088] A PBS polymer with a volatile THF content of 489 ppm and an entrainer were added to a melting tank 1 and pressurized to 800 kPaA. The mixture was stirred under the heating effect of jacketed heat transfer oil at 235°C to mix the PBS raw material with the entrainer (the entrainer was water, and the mass of the entrainer was one-thousandth of the PBS raw material). After mixing, the viscosity decreased from 8000 cp to below 3000 cp. After mixing, the pressure of the melting tank 1 was changed to 5 kPaA. The volatile content of the obtained PBS product was about 347 ppm.

[0089] Therefore, it can be seen that, compared with Comparative Example 1, adding an entrainer can improve the devolatilization effect.

[0090] Comparative Example 4

[0091] This comparative example provides a polymer devolatilization process, the specific steps of which are as follows:

[0092] A PBS polymer with a THF content of 489 ppm and an entrainer were added to a melting tank 1 and pressurized to 800 kPaA. The mixture was stirred under heating with jacketed heat transfer oil at 235°C to mix the PBS raw material and the entrainer (water, with a mass of 1 / 1000 of the PBS raw material). After mixing, the viscosity decreased from 8000 cp to below 3000 cp. The mixture was then piped into a falling film device 2 under a negative pressure of 5 kPaA. After a single devolatilization process under heating with jacketed heat transfer oil at 235°C, the PBS product obtained had a volatile content of approximately 287 ppm. Repeating the above steps, a second devolatilization process yielded a PBS product with a volatile content of approximately 144 ppm.

[0093] Therefore, compared with Comparative Examples 2-3, adding an entrainer and simultaneously using the falling film device 2 can achieve a better devolatilization effect.

Claims

1. A polymer devolatilization process, wherein, The devolatilization process includes: (1) The polymer raw material containing volatiles is heated to obtain a molten polymer, which is then pressurized, mixed with an entrainer, and then fed into a falling film device. (2) After a sudden pressure drop and heating, the entrainer carries the volatiles away from the system to obtain the devolatile product; The mass ratio of the polymer raw material to the entrainer is from 10:1 to 10000:

1.

2. The devolatilization process according to claim 1, wherein, The devolatilization process also includes repeating the process of pressurizing the devolatilized product in step (1), mixing it with the entrainer, and entering the falling film device, as well as the process of pressure drop and heating in step (2).

3. The devolatilization process according to claim 1, wherein, In step (1), the pressure after pressurization is 500 kPaA to 1600 kPaA.

4. The devolatilization process according to claim 1, wherein, The pressure of the falling film device is 10 kPaA to 1 kPaA.

5. The devolatilization process according to claim 1, wherein, The molten polymer and entrainer are mixed in a pipeline static mixer and then transported to the falling film device via pipeline.

6. The devolatilization process according to claim 1, wherein, The polymer raw materials include polyester and / or polyolefin.

7. The devolatilization process according to claim 6, wherein, The polyester includes one or more of the following: polybutylene succinate, polyethylene terephthalate, polybutylene terephthalate, polybutylene adipate, polycaprolactone, and polyhydroxyalkanoates.

8. The devolatilization process according to claim 6, wherein, The polyolefin includes one or more of polyethylene, polypropylene, polyolefin elastomers, and cyclic olefin polymers.

9. The devolatilization process according to claim 1, wherein, The volatile components include one or more of the following: by-reaction products, monomeric small molecules, and solvents.

10. The devolatilization process according to claim 9, wherein, The solvent includes one or more of toluene, xylene, and hexane.

11. The devolatilization process according to claim 1, wherein, The entrainer includes one or more of the following: inert gas, water, alcohol, and ester.

12. The devolatilization process according to claim 11, wherein, The alcohols include ethanol and / or methanol; the esters include methyl acetate and / or ethyl acetate; the inert gases include nitrogen and / or nitrogen dioxide.

13. The devolatilization process according to claim 1, wherein, In steps (1) and (2), the heating temperatures are 90°C to 270°C, respectively.

14. A polymer devolatilization system for implementing the polymer devolatilization process according to any one of claims 1-13, said system comprising at least: Polymer melting unit, devolatilization unit, product collection device; The polymer melting unit includes at least a melting tank; the melting tank is provided with at least a polymer raw material inlet, a gas inlet, and a molten polymer outlet; The devolatilization unit includes at least a falling film device, a cold trap, and a vacuum pump; the falling film device is provided with at least a material inlet, a devolatilization product outlet, and a volatile matter outlet. The molten polymer outlet of the melting tank is connected to the material inlet of the falling film device via a pipeline; the devolatilization product outlet of the falling film device is connected to the product collection device via a pipeline; and the volatile matter outlet of the falling film device is connected in sequence to a cold trap and a vacuum pump via pipelines.

15. The devolatilization system according to claim 14, wherein, A pipeline static mixer is installed on the pipeline connecting the molten polymer outlet of the melting tank to the material inlet of the falling film device.

16. The devolatilization system according to claim 14, wherein, The system further includes a circulation unit; the circulation unit includes at least a polymer circulation pipeline; the polymer circulation pipeline is used to connect the devolatilization product outlet of the falling film device to the polymer raw material inlet of the melting tank.

Images