Crystallinity adjustment for PET solid state polymerization processes
By using a static container and inert gas design in the PET solid-state polymerization method, the problems of high cost and high energy consumption of mechanical crystallizers are solved, achieving low-cost and efficient control of PET crystallinity and reducing the risk of fragment fusion and agglomeration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UOP LLC
- Filing Date
- 2024-09-27
- Publication Date
- 2026-04-21
AI Technical Summary
In existing solid-state polymerization methods for PET, mechanical crystallizers are expensive, energy-intensive, and difficult to maintain, leading to severe fragment fusion and agglomeration, which affects production efficiency and cost.
By replacing expensive mechanical crystallizers with static containers, the maximum stress and chance of fusion between fragments are reduced through the design of the internal structure and inert gas flow of the static containers. Combined with the recirculation of inert gas and the design of internal baffles, good mobility of PET fragments at low crystallinity is ensured.
It reduces production costs and energy consumption, decreases the possibility of fragment fusion and agglomeration, achieves efficient control of PET crystallinity, and significantly reduces machinery and maintenance costs.
Smart Images
Figure CN121909232A_ABST
Abstract
Description
[0001] Related applications
[0002] This application claims priority to U.S. Nonprovisional Patent Application Serial No. 18 / 762,991, filed July 3, 2024, and U.S. Nonprovisional Patent Application Serial No. 63 / 587,732, filed October 4, 2023, the entire contents of each of which are incorporated herein by reference. Background Technology
[0003] Solid-state polymerization (SSP) of PET is designed to upgrade PET from melt-phase polymerization to produce high molecular weight materials. Over 90% of PET SSP products are bottle-grade PET resins. Applications of bottle-grade PET resins include mineral water bottles, carbonated soft drink (CSD) bottles, and hot-fill bottles.
[0004] The SSP process is accomplished by heating the polymer in solid fragment form at a temperature above its glass transition temperature (80°C) but below its melting point (approximately 240°C). In conventional SSP processes, fluidized bed heaters and two or more mechanical crystallizers are used to increase the crystallinity of PET to approximately 45% or higher. SSP processes are typically carried out in an inert gas environment, such as nitrogen, to prevent oxidative degradation of the polymer at elevated temperatures.
[0005] Increasing molecular weight by linking polymer molecules can occur through either of two main reactions: transesterification and esterification. These reactions are commonly referred to as polycondensation. After combining two PET molecules, transesterification produces one ethylene glycol (EG) molecule, while esterification produces one water molecule for each PET molecule.
[0006] PET exists in an amorphous or semi-crystalline state. The form of crystals depends on whether the material is oriented (mechanically strain-induced crystallinity) or produced by heating the amorphous material above its glass transition temperature.
[0007] Before PET becomes highly crystalline, the mobility or melting of PET molecules can lead to fusion or "stickiness" between two or more PET fragments. Lower crystallinity and higher temperature are the main factors causing agglomeration in the reactor. Additional factors that may contribute to the stickiness tendency include carboxyl content, comonomers, oligomers and fine powders, fragment properties, and maximum stress in the reactor.
[0008] To reduce the tendency for sticking in the reactor, conventional SSP methods utilize mechanical crystallizers to provide crystallization time while keeping the fragments mobile to minimize the chance of fragment fusion. Typical crystallizers include screw, mechanically stirred paddle shaft, paddle, vibrating bed, and moving bed types. Such machinery is typically expensive, difficult to maintain, and consumes a large amount of energy.
[0009] Therefore, there is a need for a low-cost, low-energy-density SSP method that minimizes fragment fusion. Attached Figure Description
[0010] Figure 1 This is a diagram of the standard SSP method.
[0011] Figure 2 This is a diagram of one embodiment of the method of the present invention.
[0012] Figure 3 This is a diagram of another embodiment of the method of the present invention.
[0013] Figure 4A This is a diagram of one implementation of the internal structure of a static container.
[0014] Figure 4B yes Figure 4A A top view of the implementation plan.
[0015] Figure 5 This is a graph showing the cohesive strength of PET fragments as a function of consolidation pressure. Detailed Implementation
[0016] This invention addresses this need by completely or partially replacing expensive crystallizers with small, static containers. Unlike crystallizers, static containers contain no moving parts, reducing mechanical and maintenance costs, as well as the energy used in the method. Through various container designs, static containers reduce maximum stress at the fragmentation sites, thereby minimizing the chance of agglomeration within the container, even at lower crystallinity levels. Such container design variations can include cone angles, surface smoothness, inert gas flow rates, internal container design, cross-sectional area variations, or combinations thereof.
[0017] This method can be used with a variety of polyesters. Suitable polyesters include, but are not limited to, polyethylene terephthalate (PET), polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polypropylene naphthalene (PNT), polycyclohexyl terephthalate (PCT), polyethylene naphthalate (PEN), polyethylene furanate (PEF), or combinations thereof.
[0018] For ease of discussion, PET will be used as the polyester in the following discussion. Those skilled in the art will understand that the invention is not limited to PET.
[0019] like Figure 1 As shown, in the conventional SSP method 100, the PET feed stream 105 is fed to the buffer container 110. The PET feed stream 115 leaving the buffer container 110 has a crystallinity in the range of 0% to 35%, depending on the upstream granulation mechanism.
[0020] The PET feed stream 115 from the buffer container 110 is fed to a precrystallizer (such as a fluidized bed heater) 120, in which the PET feed stream is heated to a temperature above the glass transition temperature but below the melting point. The heated PET feed stream 125 leaving the precrystallizer 120 has a crystallinity in the range of 35% to 40%.
[0021] The heated PET feed stream 125 is fed to the first crystallizer 130 and then to the second crystallizer 135. The portion of the crystallized PET feed stream 140 leaving the second crystallizer 135 has a crystallinity of 45% or higher.
[0022] A portion of the crystallized PET feed stream 140 is fed to the SSP reactor 145, where the crystallinity is further increased to 50% or greater. The PET stream 150 exiting the SSP reactor is cooled in a cooler 155, and the PET product stream 160 is recovered.
[0023] The inert gas purification system 165 removes impurities and water through oxidation. The purified inert gas stream 170 is divided into three parts 175, 180, and 185. Inert gas stream 175 is sent to the SSP reactor 145. Inert gas stream 180 is sent to the second crystallizer 135. Using inert gas stream 185 as a booster gas, a portion of the crystallized PET feed stream 140 from the second crystallizer 135 is sent to the SSP reactor 145. Inert gas stream 190 from the second crystallizer 135 is sent to the first crystallizer 130 and then to the pre-crystallizer 120. Recycled inert gas stream 195 from the pre-crystallizer 120 is recycled back to the pre-crystallizer 120. A second inert gas stream 197 from the pre-crystallizer 120 is sent to the inert gas purification system 165.
[0024] exist Figure 2 In the illustrated embodiment, a static container follows a single crystallizer to further crystallize and heat the PET fragments before the SSP reactor.
[0025] exist Figure 2 In method 200, the PET feed stream 205 is fed to a buffer container 210. The PET feed stream 215 leaving the buffer container 210 has a crystallinity in the range of 0% to 35%.
[0026] The PET feed stream 215 from buffer container 210 is fed to precrystallizer 220, where it is heated to a temperature above the glass transition temperature but below the melting point. Suitable precrystallizers 220 include, but are not limited to, fluidized bed heaters, stirred / agglomerated heaters (with a stirred container acting as a heater), batch heaters, heat exchangers, or combinations thereof. The heated PET feed stream 225 exiting precrystallizer 220 has a crystallinity in the range of about 35% to 40%.
[0027] A valve (not shown) may be present between the buffer container 210 and the pre-crystallizer 220 to maintain a consistent flow of solids and prevent unobstructed passage of gas between the containers.
[0028] The heated PET feed stream 225 is fed to a single crystallizer 230. The crystallinity of the portion of the crystallized PET feed stream 235 leaving the single crystallizer 230 is in the range of 37% to 42%.
[0029] A portion of the crystallized PET feed stream 235 from a single crystallizer 230 is fed to a static container 240, in which the crystallinity is increased to 45% or higher.
[0030] The PET stream 245 from static container 240 is fed to SSP reactor 250, where the crystallinity is further increased to 50% or greater. Any type of conveying system can be used to convey the PET stream to SSP reactor 250. Suitable conveying systems include, but are not limited to, gravity feed conveying systems and pneumatic conveying systems.
[0031] The PET stream 255 leaving the SSP reactor is cooled to 60°C or lower in a cooler 260, and the PET product stream 265 is recovered.
[0032] The method includes an inert gas purification system 270. A fresh inert gas stream 275 exits the inert gas purification system 270. A portion 280 of the fresh inert gas stream 275 is fed to an SSP reactor 250. A second portion 285 is fed to a static container 240 to remove oligomers and fine powder from the debris and to facilitate debris mobility. One or more inlets are present in the static container 240 for the second portion 285 of the fresh inert gas stream 275. The inlets may be located at different heights in the static container 240. A third portion 290 of the fresh inert gas stream 275 is used to convey a PET stream 245 from the static container 240 to the SSP reactor 250.
[0033] An inert gas stream 295 from static container 240 is fed to pre-crystallizer 220, which helps fluidize the stream and remove fine particles and oligomers. A recirculated inert gas stream 300 from pre-crystallizer 220 is recycled back to pre-crystallizer 220. A second inert gas stream 305 from pre-crystallizer 220 is fed to inert gas purification system 270.
[0034] A single crystallizer 230 is optional, depending on the crystallinity of the feed from the precrystallizer 220. In either case, the heated PET feed stream 225 from the precrystallizer 220 will enter the static container 240.
[0035] Figure 3 The design is similar, but the inert gas streams are different. In method 200', a portion 280 of the fresh inert gas stream 275 is fed to the SSP reactor, and a portion 290 is used to feed the PET stream 245 from the static container 240 to the SSP reactor 250. The inert gas stream 295 from the static container 240 is fed to the pre-crystallizer 220. The recirculated inert gas stream 300 from the pre-crystallizer 220 is recycled back to the pre-crystallizer 220. A second inert gas stream 305 from the pre-crystallizer 220 is fed to the inert gas purification system 270.
[0036] However, fresh inert gas is not sent to the static container 240. Instead, a portion 310 of the recirculated inert gas stream 300 is sent to the static container 240.
[0037] Recirculating the inert gas reduces the load on the inert gas purification system 270. While recirculated inert gas may be acceptable for increasing crystallinity, it may allow oligomers and dust to re-enter the system. Fresh inert gas does not present this problem.
[0038] Static containers typically take the form of hoppers, where the most significant stress concentration occurs at the junction of the cylindrical and conical sections. The mass within the cylindrical section of the static container should be controlled to limit stress at the tangential. The fusion of PET fragments in the hopper is primarily determined by temperature, crystallinity, and stress on the fragments. This risk can also be mitigated if sufficient movement exists between particles. Particle flow in the hopper or bin can be modeled using appropriate software, such as a DEM (Discrete Element Method) model. The static container was modeled using standard PET physics, a 900 tonnes / day unit, a 4 m diameter static container, and residence times of 0.5 h and 1 h for each case. Simulations show that the maximum stress in each case is very low, at 7 kPa and 11 kPa, due to the lower required levels. This is significantly lower than typical reactor containers. Furthermore, high radial velocities were recorded, indicating strong particle movement between PET fragments in the bottom cylindrical and conical sections. Reducing stress within the hopper minimizes the physical deformation of the PET particles and their contact areas. The dynamics of particle movement exert forces that disrupt any potential bonding, thereby reducing the likelihood of particle agglomeration. Furthermore, supplying a heated gas after the static vessel adds additional force to break up any fused fragments that may form, and the static vessel can be operated at a lower temperature if necessary. These measures collectively reduce the likelihood of agglomeration within the vessel.
[0039] The residence time in a static container typically ranges from 30 minutes to 6 hours, or 30 minutes to 5 hours, or 30 minutes to 4 hours, or 30 minutes to 3 hours, or 30 minutes to 2 hours, or 30 minutes to 1 hour.
[0040] To maintain the mobility of the fragments, strategies such as adjusting the internal structure or altering the cross-sectional profile can be employed. The aim is to ensure that the fragments move unimpeded throughout the container. By fine-tuning these parameters, PET fragments can achieve optimal crystallinity levels without any tendency to stick together.
[0041] Achieving the desired crystallinity depends on various factors within the actual PET composition, including the presence of components such as copolymers, catalyst effects, and carboxyl-hydroxyl content. The choice of analytical techniques also plays a crucial role, such as X-ray diffraction, ATR-FTIR, DSC, gravity-based methods, or measuring PET density by injecting helium to measure volume and weight. As a general approximation, the target level for optimal crystallinity before reactor preparation is typically around 45%.
[0042] Figure 4A Figure 4B5 illustrates one design of the internal structure of the static container 400. The inert gas flow in the static container is designed to ensure uniform flow through the reactor at each height to ensure effective removal of oligomers and to balance the temperature from the heat of crystallization.
[0043] The static container 400 has a conical portion with a diameter D1 and a conical portion with a diameter D2 smaller than D1. Inert gas inlets 405, 410, and 415 are located at three different locations on the static container 400. One or more locations may have inert gas inlets on the static container 400. At each location on the static container 400, one or more inert gas inlets 405, 410, and 415 may be present. Figure 4B Four inert gas inlets 415 are shown.
[0044] There are internal baffles 420, 425, and 430. The height of these internal baffles in the middle of the static container 400 is higher than their height on the sides. Figure 4A As shown. The baffles facilitate movement between PET fragments by utilizing changes in cross-sectional area. The internal baffles 420, 425, and 430 can be solid. Alternatively, they can be perforated tubes connected to the inert gas inlet, allowing inert gas to flow through them.
[0045] Example
[0046] Example 1
[0047] A techno-economic analysis was conducted on the existing 550 t / d PET solid-state polymerization unit. The simulation was performed using proprietary software. It showed an 8% reduction in total capital costs and a 6% reduction in utilities. This does not include any reduction in maintenance work due to having only one (or no) crystallizer.
[0048]
[0049] Example 2
[0050] Standard PET feedstock was subjected to solid-state polymerization and subsequently tested on a shear tester to evaluate its cohesive strength under different consolidation pressures. Samples were continuously exposed to a nitrogen flow at 210°C for 4 or 16 hours, effectively replicating real-world container conditions. Results are illustrated in… Figure 5 middle.
[0051] This comparison evaluated the properties of PET samples with similar intrinsic viscosity and crystallinity. The results showed that the sample tested for 4 hours under similar loads exhibited lower cohesive strength compared to the sample tested for 16 hours. Therefore, the tendency for aggregation was significantly less in smaller containers.
[0052] Specific implementation plan
[0053] While the following description is presented in conjunction with specific embodiments, it should be understood that the description is intended to be illustrative and not to limit the scope of the foregoing description and the appended claims.
[0054] A first embodiment of the present invention is an apparatus for producing solid crystalline polymer particles, the apparatus comprising a precrystallizer containing a first inert gas for heating a polyester feedstock produced by a melt-phase polyester polymerization unit to obtain a crystallization level in the range of 35% to 40%; a static container connected to the outlet of the precrystallizer, the static container having a countercurrent flow of a second inert gas to obtain a crystallization level greater than or equal to 45%, the static container having a residence time of 30 minutes to 6 hours; and an SSP reactor container connected to the static container, the SSP reactor having a countercurrent flow of a third inert gas. One embodiment of the present invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, further comprising a single crystallizer located between the outlet of the precrystallizer and the inlet of the static container to obtain a crystallization level in the range of 37% to 42%. Another embodiment of the present invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the static container has a first inert gas inlet at a first height and a second inert gas inlet at a second height above the first height. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the static container has a residence time of 30 minutes to 1 hour. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the static container includes an internal baffle, or wherein the static container has varying cross-sectional dimensions, or both. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the static container includes a plurality of perforated pipes connected to a plurality of inert gas inlets. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the first inert gas, or the second inert gas, or the third inert gas, or a combination thereof, is nitrogen. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, wherein the pre-crystallizer includes a fluidized bed heater. One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, and the embodiment further includes a buffer container for feeding polyester feed, the outlet of which is connected to the inlet of the pre-crystallizer.One embodiment of the invention is one, any, or all of the embodiments described in the preceding embodiments to the first embodiment described in this paragraph, and the embodiment further includes a conveying system for connecting the static container to the SSP reactor vessel.
[0055] A second embodiment of the present invention is a method for preparing polyester granules, the method comprising providing a polyester feed stream; heating the polyester feed stream in a pre-crystallizer containing a first inert gas to obtain a crystallization level in the range of 35% to 40% and forming a heated polyester stream; feeding the heated polyester stream to a countercurrent static container containing a second inert gas to obtain a second polyester stream having a crystallization level greater than or equal to 45%; and feeding the second polyester stream to an SSP to increase the crystallinity of the second polyester stream to a crystallinity level greater than or equal to 50%. One embodiment of the present invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, which further includes partially crystallizing the heated polyester stream in a single crystallizer to obtain a crystallization level in the range of 37% to 42% before feeding the heated polyester stream to the static container. One embodiment of the present invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, which further includes passing a third inert gas countercurrently through an SSP reactor. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the third inert gas comprises nitrogen. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the first inert gas, or the second inert gas, or a combination thereof comprises nitrogen. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein at least a portion of the second inert gas in the static container is a recirculated inert gas. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the static container has a residence time of 30 minutes to 6 hours. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the static container has a residence time of 30 minutes to 1 hour. One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, which further includes feeding the polyester feed stream to a buffer container before heating the polyester feed stream. Another embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the static container includes an internal baffle, or wherein the static container has varying cross-sectional dimensions, or both.One embodiment of the invention is one, any, or all of the embodiments described in the preceding to the second embodiments of this paragraph, wherein the static container includes a plurality of perforated tubes connected to a plurality of inert gas inlets.
[0056] Although no further detailed description has been provided, it is believed that those skilled in the art will be able to make full use of the invention by employing the foregoing description and will be able to readily identify the essential features of the invention without departing from its spirit and scope, and to make various changes and modifications to adapt it to various uses and situations. Therefore, the foregoing preferred embodiments should be understood as illustrative only and not as limiting the remainder of this disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
[0057] In the foregoing, all temperatures are expressed in degrees Celsius, and all portions and percentages are by weight unless otherwise specified.
Claims
1. A method for preparing polyester granules, the method comprising: Provide polyester feed stream (205); The polyester feed stream (205) is heated in a pre-crystallizer (220) containing a first inert gas to obtain a crystallization level in the range of 35% to 40% and to form a heated polyester stream (225). The heated polyester stream (225) is conveyed to a countercurrent static container (240) with a second inert gas to obtain a second polyester stream (245) having a crystallinity level greater than or equal to 45%; and The second polyester stream (245) is fed into the SSP reactor vessel (250) to increase the crystallinity of the second polyester stream (245) to a crystallinity level greater than or equal to 50%.
2. The method according to claim 1, further comprising: Before the heated polyester stream (225) is conveyed to the static container (240), the heated polyester stream (225) is partially crystallized in a single crystallizer (230) to obtain a crystallization level in the range of 37% to 42%.
3. The method according to any one of claims 1 to 2, further comprising: A third inert gas is passed through the SSP reactor vessel (250) in a countercurrent manner.
4. The method according to any one of claims 1 to 2, wherein the first inert gas, or the second inert gas, or a combination thereof, comprises nitrogen.
5. The method according to any one of claims 1 to 2, wherein at least a portion of the second inert gas in the static container (240) is a recirculated inert gas.
6. The method according to any one of claims 1 to 2, further comprising: Before heating the polyester feed stream (205), the polyester feed stream (205) is conveyed to the buffer container (210).
7. The method according to any one of claims 1 to 2, wherein the static container (240) includes internal baffles (420, 425, 430), or wherein the static container (240) has varying cross-sectional dimensions, or wherein the static container (240) includes a plurality of perforated tubes connected to a plurality of inert gas inlets, or a combination thereof.
8. The method according to any one of claims 1 to 2, wherein the static container (240) has a residence time of 30 minutes to 6 hours.
9. An apparatus for producing solid crystalline polymer particles, the apparatus comprising: A pre-crystallizer (220) containing a first inert gas is used to heat the polyester feed (205) generated by the molten phase polyester polymerization unit to obtain a crystallization level in the range of 35% to 40%. A static container (240) connected to the outlet of the pre-crystallizer (220) has a countercurrent flow of a second inert gas to achieve a crystallization level of greater than or equal to 45%, and the static container (240) has a residence time of 30 minutes to 6 hours. as well as An SSP reactor vessel (250) is connected to the static vessel (240), the SSP reactor vessel (250) having a countercurrent flow of a third inert gas; as well as Optionally, a single crystallizer (230) is located between the outlet of the pre-crystallizer (220) and the inlet of the static container (240) to achieve a crystallization level in the range of 37% to 42%.
10. The device according to claim 9: The static container (240) has a first inert gas inlet at a first height and a second inert gas inlet at a second height above the first height; or The static container (240) includes internal baffles (420, 425, 430), or the static container has varying cross-sectional dimensions, or both; or The static container (240) includes multiple perforated pipes connected to multiple inert gas inlets; or Their combination.