A melt polycondensation reactor for a polyester

Abstract

This application provides a melt polycondensation reactor for polyester, belonging to the technical field of polymerization equipment. It includes a vertical shell, a top shell, a bottom shell, and a falling film element. The falling film element is disposed within the vertical shell. The top shell has a main feed pipe, and a branch feed pipe connects the main feed pipe to the falling film element. The top shell contains a heat transfer medium inlet box and a heat transfer medium outlet box. The falling film element includes a vertical circular tube, a spiral flow channel, and a return pipe. The top opening of the vertical circular tube communicates with the heat transfer medium inlet box. The spiral flow channel is disposed on the outer wall of the vertical circular tube and is connected to the branch feed pipe via a film distribution port, guiding the melt input from the main feed pipe spirally downwards. The heat transfer medium flows in an external-in, internal-out manner relative to the return pipe. This application achieves a uniform and stable increase in melt viscosity from low to high by changing the melt polycondensation path.

Description

Technical Field

[0001] This application relates to a melt polycondensation reactor for polyester, belonging to the field of polymerization equipment technology. Background Technology

[0002] Products made from high-viscosity polyesters exhibit significant advantages in strength, toughness, heat resistance, chemical resistance, and dimensional stability. They are particularly valuable for high-end engineering applications such as engineering plastics, industrial yarns, high-performance films, and pressure vessels, where high molecular weight is required. Industrial production of high-viscosity polyesters typically employs solid-state polycondensation and melt polycondensation. Melt polycondensation, with its superior heat transfer, high reaction efficiency, short polycondensation time, and low production cost, offers irreplaceable advantages in terms of product quality, production cost, environmental friendliness, and industrialization. Currently, many polyester materials in China are produced industrially using melt polycondensation, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), and polyamide (PA).

[0003] The core of melt polycondensation lies in the reactor design. During melt polycondensation, the polyester melt requires good heat transfer performance, short reaction residence time, and high reaction efficiency to obtain high-viscosity polyester with uniform quality. However, as the polycondensation process progresses and the polyester molecular weight increases to a certain level, the viscosity of the polyester melt increases rapidly. Byproducts of the polycondensation reaction become difficult to remove from the polycondensation system, severely hindering the reaction. Therefore, in the later stages of the polycondensation reaction, the mass transfer capacity of small-molecule byproducts becomes the main controlling factor. This necessitates a scientifically designed internal structure for the polycondensation reactor to improve the flow pattern of the polyester melt, optimize its film-forming properties, enhance the renewal efficiency of the polyester surface, and increase the devolatilization rate of small-molecule byproducts, thus enabling the industrial production of high-viscosity polyester products.

[0004] Vertical falling film melt polycondensation reactors are a new type of reactor for producing high-viscosity polyester products. They offer advantages such as simple structure, energy efficiency, environmental friendliness, and high reaction efficiency. The core of this type of reactor lies in the vertically arranged falling film elements inside the reactor. During the polycondensation reaction, the polyester material, under the influence of gravity, rapidly forms a film along the outer surface of the falling film elements and slides down. This results in excellent surface renewal efficiency and extremely high heat and mass transfer capabilities. Small molecule byproducts can be continuously extracted and removed from the reactor under vacuum conditions. Currently, most publicly available vertical melt polycondensation reactor falling film elements are vertical tubular types, such as corrugated tubes, U-shaped tubes, square tubes, and concave tubes. Some of these falling film elements have already been applied in industrial production.

[0005] However, in the use of these falling film elements, the polyester melt relies solely on adhesion to slide downwards, failing to provide sufficient constraint on its flow path. This results in varying residence times of the melt on the falling film element, leading to inconsistent quality of the final polycondensation product. Furthermore, in actual production, due to the large aspect ratio of the falling film element, under prolonged high-load and high-temperature conditions, it can undergo twisting and deformation. In severe cases, adjacent falling film elements may cross-contact, causing unpredictable flow behavior of the polyester melt, such as dead zones and melt cliff-like falls, significantly impacting the quality of the polycondensation product. Therefore, it is necessary to upgrade the current falling film elements. The aim is to retain the advantages of vertical falling film elements, such as good film-forming performance, high surface renewal efficiency, high polycondensation efficiency, and energy-saving and environmentally friendly gravity-based operation, while imposing constraints on the flow behavior of the polyester melt on the falling film element. This would ensure that the reaction residence time of the polyester melt on the falling film element is as consistent as possible, guaranteeing a more uniform quality of the final polycondensation product and improving overall product quality. Summary of the Invention

[0006] In view of this, this application provides a melt polycondensation reactor for polyester, which allows for diversified adjustments to the falling film element, optimizes the flow behavior of the polyester melt, improves the quality of high-viscosity polyester melt, and further enhances production efficiency and reduces production costs. It is applicable to the melt polycondensation reaction process of various polyester materials.

[0007] Specifically, this application is implemented through the following scheme:

[0008] A melt polycondensation reactor for polyester includes a vertical shell, a top shell, a bottom shell, and a falling film element. The falling film element is disposed inside the vertical shell, and the top shell is provided with a main feed pipe. A feed branch pipe is disposed between the main feed pipe and the falling film element.

[0009] The top shell is equipped with a heat transfer medium inlet box and a heat transfer medium outlet box.

[0010] The falling film element includes a vertical circular tube, a spiral flow channel, and a return pipe. The vertical circular tube is open at the top and sealed at the bottom, suspended in the inner cavity of the vertical shell. The top opening is connected to the heat transfer medium inlet box. The spiral flow channel is located on the outer wall of the vertical circular tube and is connected to the feed branch pipe via a film distribution port, guiding the melt input from the feed main pipe spiral downwards. The return pipe is located inside the vertical circular tube and is open at both ends. The top opening is connected to the heat transfer medium outlet box, and the bottom opening is connected to the vertical circular tube, allowing the heat transfer medium to operate in an external inlet and internal outlet manner relative to the return pipe.

[0011] After the low-viscosity polyester melt enters the reactor, it undergoes a melt polycondensation reaction while sliding down along the falling film element. The melt on each falling film element falls into the conical bottom shell of the reactor, where it is homogenized under the drive of a ribbon agitator, and finally the high-viscosity polyester melt is discharged. In this process, the falling film element of this application changes the flow path of the melt, causing the melt to flow downward along a spiral channel. While retaining the film-forming performance of traditional falling film elements and relying on gravity for energy saving and environmental protection, the spiral channel design also restricts the flow behavior of the polyester melt as it slides down, ensuring that the polyester melt does not experience cliff-like drops or dead zones, until it reaches the bottom of the falling film element to complete the polycondensation process and leaves the falling film element. The circular tube allows for the circulation of the heat transfer medium. The heat transfer medium flows into the circular tube of the falling film element from the inlet box, then enters the return pipe from the bottom of the circular tube, flows upward to the outlet box, and after leaving the reactor, it enters the heat transfer medium inlet box again through the external temperature control device. This achieves the circulation of the heat transfer medium in the falling film element. The external inlet and internal outlet flow method ensures that sufficient and uniform heat preservation and heating can still be achieved even when the melt path changes. The heat transfer system formed by the heat transfer medium and the melt flow path are coordinated to ensure that the reaction residence time of the polyester melt on the falling film element is as consistent as possible. The final polycondensation product has a more uniform quality, which improves the quality of the polycondensation product. The molecular weight and intrinsic viscosity of the polyester melt are continuously increased by 1 to 2 times, and the dynamic viscosity is increased by 8 to 10 times.

[0012] Furthermore, as a preferred option:

[0013] The ratio of the width L of the spiral channel to the diameter D of the vertical circular tube is 0.05~5, and the ratio of the helical pitch P of the spiral channel to the height H of the vertical circular tube is 0.2~10.

[0014] The spiral flow channel is formed by scanning a helical line around the surface of a circular tube using a cross-sectional pattern with optimized structural parameters. The helical pitch P of the spiral flow channel is either constant or set in a manner where the pitch is smaller at the top and larger at the bottom. This is based on the fact that the flow state of the polyester melt is completely different at the top and bottom of the falling film element.

[0015] The pitch of the spiral flow channel can be either a constant combined pitch or a variable pitch. A constant combined spiral flow channel allows multiple spiral flow channels with different pitches to be set on the same falling film element, i.e., a combined spiral flow channel. A variable pitch spiral flow channel allows a spiral flow channel with a continuously increasing pitch from top to bottom to be set on a single falling film element. That is, the spiral flow channel is composed of multiple spiral flow channels with different pitches, which is a combined spiral flow channel; or, the pitch P of the spiral flow channel increases sequentially from top to bottom, which is a variable pitch spiral flow channel.

[0016] To ensure the rationality and uniformity of the flow behavior of polyester melt in the spiral channel, the cross-sectional shape of the spiral channel is designed with optimized structural parameters. The cross-section of the spiral channel is flat, inclined, vertical baffle, inclined baffle, or horn-shaped.

[0017] The falling film element is provided with one or more spiral channels.

[0018] The falling film element is provided in multiple ways. When multiple falling film elements are used at the same time, they are arranged in a rectangular grid, a triangular grid, or a concentric ring within the vertical housing.

[0019] To ensure that the polyester melt falls quickly and evenly onto the spiral flow channel, the film-making port is located at the top of the vertical shell and is connected to the feed branch pipe, located directly above the spiral flow channel. The film-making port can be circular, elliptical, square, polygonal, or slotted.

[0020] The top shell is provided with an upper partition and a lower partition. The space between the upper partition and the lower partition is the heat transfer medium outlet box, and the space between the lower partition and the bottom plate of the top shell is the heat transfer medium inlet box.

[0021] The height H of the falling film element is 1~40m, and the diameter D of the vertical circular tube is 10~500mm.

[0022] The main feed pipe and the feed branch pipes are connected by a melt distributor. More preferably, at least three sets of feed branch pipes are provided.

[0023] The vertical shell has a shell jacket on its outer wall. A heat transfer medium inlet is located on one lower side of the shell jacket, and a heat transfer medium outlet is located on the other upper side, so as to achieve heat transfer medium coiling and insulation with one side in and the other side out on both sides of the vertical shell.

[0024] The vertical housing is provided with a vacuum extraction port, which is located at the upper part of the vertical housing and communicates with the inner cavity of the vertical housing.

[0025] The outer wall of the bottom shell is provided with a bottom shell jacket. A heat transfer medium inlet is provided on one side of the bottom shell jacket at a lower position, and a heat transfer medium outlet is provided on the other side at a higher position, so that the heat transfer medium can be coiled and insulated on both sides of the bottom shell with one side in and the other side out.

[0026] A ribbon agitator is installed inside the bottom shell, with its bottom connected to the bottom plate of the bottom shell and its upper part suspended.

[0027] The innovation of this invention lies in the improvement of the traditional structure of the falling film element, which optimizes the flow path of the polyester melt on the falling film element. In addition to ensuring the advantages of traditional vertical falling film elements such as good film-forming performance, high surface renewal efficiency, high polycondensation efficiency, and energy saving and environmental protection by relying on gravity, it can also constrain the flow behavior of the polyester melt on the falling film element to a certain extent, so that the reaction residence time of the polyester melt on the falling film element is as consistent as possible, thereby improving the quality of the final polycondensation product.

[0028] Compared to traditional vertical falling film elements, the spiral falling film element disclosed in this invention has the following advantages:

[0029] The first advantage lies in the ability of the spiral falling film element to restrict the flow behavior of the polyester melt on the falling film element. In traditional vertical falling film elements, the polyester melt relies solely on the adhesive force between itself and the falling film element to slide vertically downwards. However, in actual production, the following situations arise: fluctuations in production volume cause instability in the flow behavior of the polyester melt on the vertical falling film element; the adhesive force alone is insufficient to restrict the polyester melt from sliding downwards along the falling film element, causing the melt to detach from the falling film element and fall prematurely into the conical bottom shell; over long-term use, the vertical falling film element may bend, twist, or cross, altering the vertical flow path of the polyester melt, and in severe cases, even creating dead zones. All of these situations affect the uniformity of the molecular weight and viscosity of the polycondensation product, seriously impacting the quality of the polycondensation product.

[0030] The falling film element disclosed in this invention can effectively improve the above situation. It optimizes the vertical sliding of polyester melt along the vertical falling film element to sliding down on a nearly vertical spiral channel. It not only retains the advantages of traditional falling film elements such as good film-forming performance, high surface renewal efficiency, high polycondensation efficiency, and energy saving and environmental protection by relying on gravity, but also restricts the flow behavior of polyester melt when it slides down through the rational design of the spiral channel, ensuring that the polyester melt will not fall off a cliff or have dead zones.

[0031] The second advantage lies in its ability to optimize the flow behavior of the polyester melt throughout the spiral falling film element. In traditional vertical falling film elements, low-viscosity polyester melt flows in from the top and then slides down the element under gravity until it reaches the bottom, where it completes the polycondensation process and leaves. During this process, the molecular weight and intrinsic viscosity of the polyester melt increase by 1-2 times, while the dynamic viscosity increases by 8-10 times. Therefore, the flow state of the polyester melt at the top and bottom of the falling film element is completely different. At the top, the melt viscosity is low, and the vertical sliding speed is fast; at the bottom, the melt viscosity is very high, and the vertical sliding speed is slow. This indicates that for vertical falling film elements, the sliding behavior of the polyester melt on its surface is unstable and uncontrollable.

[0032] The spiral falling film element disclosed in this invention allows for controllable adjustment of the helical pitch of its spiral flow channel. A smaller pitch can be set at the top of the falling film element to control the flow rate of low-viscosity melts, while a larger pitch can be set at the bottom to increase the flow rate of high-viscosity melts. This allows for better control of the polyester melt flow rate throughout the falling film element, optimizing the overall flow behavior and making it more stable and controllable.

[0033] The third advantage is that by changing the flow path of the polyester melt from vertically downward to spirally downward, the vertical height of the falling film element will be significantly reduced, thereby reducing the height of the reactor, reducing the space occupancy of the polycondensation reactor and production costs.

[0034] The fourth advantage is that it allows multiple identical spiral channels to be set on a single falling film element, transforming the polycondensation region based on the "toroidal surface" in traditional vertical falling film elements into a "toroidal" polycondensation region based on spiral channels in falling film elements. This will greatly improve the production efficiency of a single falling film element and further reduce the production cost of melt falling film polycondensation.

[0035] This invention optimizes the core component of the vertical melt polycondensation reactor—the falling film element. Compared with the traditional vertical falling film element, the falling film element of this invention consists of a vertical circular tube and a spiral flow channel extending downward around the vertical circular tube. While retaining the advantages of the vertical falling film element, such as good film-forming performance, high surface renewal efficiency, high polycondensation efficiency, and energy saving and environmental protection relying on gravity, it can also constrain the flow behavior of the polyester melt on the falling film element to a certain extent, preventing dead zones and melt drop during the falling film melt polycondensation process. This ensures that the reaction residence time of the polyester melt on the falling film element is as consistent as possible, guaranteeing a more uniform quality of the final polycondensation product and improving the quality of the polycondensation product. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application.

[0037] Figure 1 This is a schematic diagram of the melt polycondensation reactor of this application;

[0038] Figure 2 This is a schematic diagram of the flat-plate falling film element in this application.

[0039] a) Front view, b) AA direction view (2:1), c) BB direction cross section view;

[0040] Figure 3This is a schematic diagram of the inclined plate falling film element in this application.

[0041] a) Front view, b) AA direction view (2:1), c) BB direction cross section view;

[0042] Figure 4 This is a schematic diagram of the vertical baffle-shaped falling film element in this application.

[0043] a) Front view, b) BB direction section view, c) AA direction view (2:1);

[0044] Figure 5 This is a schematic diagram of the inclined plate baffle-shaped falling film element in this application.

[0045] a) Front view, b) BB direction section view, c) AA direction view (2:1);

[0046] Figure 6 This is a schematic diagram of the horn-shaped falling film element in this application.

[0047] a) Front view, b) BB direction section view, c) AA direction view (2:1);

[0048] Figure 7 This is a schematic diagram of different types of membrane openings in this application;

[0049] Figure 8 This is a schematic diagram of the falling film element structure with a double helix flow channel in this application.

[0050] a) Front view, b) Sectional view along the AA direction;

[0051] Figure 9 This is a schematic diagram of the falling film element structure with four helical channels in this application.

[0052] a) Front view, b) Sectional view along the AA direction;

[0053] Figure 10 This is a schematic diagram of the falling film element structure with dual combined spiral flow channels in this application.

[0054] a) Front view, b) Sectional view along the AA direction;

[0055] Figure 11 This is a schematic diagram of the falling film element structure with three combined spiral channels in this application.

[0056] a) Front view, b) Sectional view along the AA direction;

[0057] Figure 12 This is a schematic diagram of the structure of the pitch-gradient flow channel falling film element in this application.

[0058] a) Front view, b) Sectional view along the AA direction;

[0059] Figure 13 This is a planar schematic diagram of the arrangement of the falling film elements in this application.

[0060] a) Rectangular grid arrangement, b) Triangular grid arrangement, c) Concentric circular arrangement;

[0061] Figure 14 This is a structural comparison diagram of three types of falling film elements.

[0062] (a) Vertical circular tube shape, (b) Concave tube shape, (c) Spiral flow channel shape of this application.

[0063] Numbered in the diagram: 1. Vertical shell; 11. Shell jacket; 12. First inlet; 13. First outlet; 14. Vacuum extraction port; 15. Film distribution port; 2. Top shell; 21. Top shell bottom plate; 22. Upper partition plate; 23. Lower partition plate; 24. Second inlet; 25. Second outlet; 2A. Heat transfer medium inlet box; 2B. Heat transfer medium outlet box; 3. Bottom shell; 31. Bottom shell jacket; 32. Third inlet; 33. Third outlet; 34. Bottom shell bottom plate; 4. Main feed pipe; 41. Melt distributor; 42. First feed branch pipe; 43. Second feed branch pipe; 44. Third feed branch pipe; 5. Falling film element; 51. Vertical circular tube; 52. Spiral flow channel; 521. Flat plate; 522. Inclined plate; 523. Baffle; 53. Return pipe; 6. Discharge port; 7. Ribbon agitator. Detailed Implementation

[0064] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the technical solutions in the embodiments of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0065] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to that other component. The terms "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or position based on the orientation or position shown in the accompanying drawings, and are only for ease of description and should not be construed as limiting the present technical solution.

[0066] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or specifying the number of technical features. "A plurality of" means two or more, unless otherwise explicitly defined.

[0067] This embodiment provides a melt polycondensation reactor for polyester, which enables the polyester melt to grow uniformly and stably from an intrinsic viscosity of 0.50~0.80 dL / g to 1.00~1.20 dL / g.

[0068] Figure 1 This is a schematic diagram of the melt polycondensation reactor for polyester in this application. It mainly consists of a vertical shell 1, a circular top shell 2, and a conical bottom shell 3, which are installed in sequence.

[0069] The top of the top shell 2 is provided with a main feed pipe 4, which is connected to three feed branch pipes via a melt distributor 41: a first feed branch pipe 42, a second feed branch pipe 43, and a third feed branch pipe 44. The top shell 2 is provided with an upper partition plate 22 and a lower partition plate 23, which together with the bottom plate 21 of the top shell form two boxes: the bottom plate 21 of the top shell and the lower partition plate 23 form a heat transfer medium inlet box 2A, which is provided with a second inlet 24; the upper partition plate 22 and the lower partition plate 23 form a heat transfer medium outlet box 2B, which is provided with a second outlet 25.

[0070] A housing jacket 11 is provided around the vertical housing 1. The housing jacket 11 is provided with a first inlet 12 and a first outlet 13, and a vacuum extraction port 14 is provided at the upper position. The vacuum extraction port 14 is connected to the cavity of the vertical housing 1. Multiple falling film elements 5 are installed in the vertical shell 1. Each falling film element 5 includes a vertical circular tube 51, a spiral flow channel 52, and a return pipe 53. The upper end of the vertical circular tube 51 has an opening that connects to the top shell bottom plate 21 and is connected to the heat transfer medium inlet box 2A. The lower end is domed and suspended in the cavity of the vertical shell 1. The spiral flow channel 52 extends spirally downward around the vertical circular tube 51. The top of the vertical shell 1 has a film distribution port 15 that is connected to the feed branch pipe and is located directly above the spiral flow channel 52 to ensure that the polyester melt falls quickly and evenly onto the spiral flow channel 52. The return pipe 53 is installed inside the vertical circular tube 51. The return pipe 53 passes through the heat transfer medium inlet box 2A, with its upper opening connected to the heat transfer medium outlet box 2B and its lower opening suspended inside the vertical circular tube 51. The heat transfer medium enters the heat transfer medium inlet box 2A through the second inlet 24, then enters the vertical circular pipe 51 through the upper opening, then enters the return pipe 53 through the lower opening, and finally enters the heat transfer medium outlet box 2B through the upper opening of the return pipe 53, and exits from the second outlet 25, realizing that the heat transfer medium is discharged at the return pipe. Figure 1The external inflow and internal outflow, as indicated by the arrow, are followed by the heat transfer medium inlet box 2A after leaving the reactor via an external temperature control device, thereby realizing the circulation of the heat transfer medium in the falling film element 5.

[0071] A bottom shell jacket 31 is provided around the bottom shell 3. A third inlet 32 ​​and a third outlet 33 are provided on the bottom shell jacket 31. A ribbon agitator 7 is provided inside the bottom shell 3. It is installed on the bottom plate 34 of the bottom shell. Power is transmitted from the bottom of the bottom shell 3. A discharge port 6 is provided at the bottom of the bottom shell 3.

[0072] The falling film element 5 can be of various specifications, and its cross-sectional shape can be as follows: Figure 2 The flat plate shape shown Figure 3 The inclined plate shape shown Figure 4 The vertical baffle shape shown Figure 5 The inclined plate baffle shape shown Figure 6 The bull horn shape shown is an example.

[0073] Combination Figure 2 The spiral flow channel 52 of the flat-plate falling film element has a constant pitch. The height H of the vertical circular tube 51 is 1~40m, and the diameter D is 10-500mm. The ratio of the pitch P of the spiral flow channel 52 to the height H of the vertical circular tube 51 is 0.2~10, and the ratio of the width L of the flat plate 521 to its thickness d is 1~10. The falling film element 5 that meets these structural parameters can further control the flow path of the polyester melt, so that the polyester melt falls uniformly along the spiral flow channel, homogenizes the residence time and reaction degree of the polyester melt, and achieves a stable and uniform increase in the intrinsic viscosity of the polyester melt. For example, when the ratio of the pitch P to the height H is specifically set to 5 and the ratio of the width L to the thickness d is specifically set to 3, the viscosity of the melt entering from the feed pipe 4 with a viscosity of 0.65 dL / g increases stably to 1.05 dL / g at the discharge port 6, and the viscosity fluctuates almost no between batches.

[0074] Combination Figure 3 The inclined plate falling film element is an improvement on the flat plate falling film element. Using the contact point between the flat plate 521 and the vertical circular tube 51 as the center, the flat plate 521 is rotated by a certain angle to obtain the inclined plate 522. The horizontal angle α between the tangent at the contact point of the inclined plate 522 and the vertical circular tube 51 is allowed to be 30°~90° (when α is 90°, it is a flat plate falling film element). At this time, the ratio of the width L of the inclined plate 522 to its thickness d is 1~10. This structure of the falling film element 5 further optimizes the flow path of the polyester melt in the spiral channel, preventing the polyester melt from falling directly from the outside when it slides down the spiral channel. When the α value is specifically set to 60°, the intrinsic viscosity of the polyester melt can be increased from 0.60~0.80 dL / g at the feed pipe 4 to 1.10~1.20 dL / g at the discharge port 6.

[0075] Combination Figure 4 The vertical baffle-shaped falling film element is an improvement on the flat plate falling film element 521. A baffle 523 is added to the outside of the flat plate 521. The baffle 523 is set vertically, and the ratio of the height h of the baffle 523 to its thickness d is 0.5~3.0. This structure of the falling film element 5 also optimizes the flow path of the polyester melt in the spiral channel, restricting the polyester melt from falling directly from the outside when it slides down the spiral channel, which can increase the intrinsic viscosity of the melt by about 0.3~0.6 dL / g.

[0076] Combination Figure 5 The inclined plate baffle-shaped falling film element is an improvement on the flat plate of the inclined plate falling film element. A vertical baffle 523 is added to the outside of the inclined plate 522, and the ratio of the height h of the baffle 523 to its thickness d is 0.5~3.0. This structure of the falling film element 5 combines the advantages of the inclined plate and vertical baffle-shaped falling film elements, further restricting the polyester melt from falling directly from the outside when it slides down the spiral channel, and can increase the intrinsic viscosity of the melt by about 0.35~0.50 dL / g.

[0077] Combination Figure 6 In the cross-section of the spiral flow channel of the horn-shaped falling film element, the ratio of the width L of the spiral flow channel 52 to the diameter D of the vertical circular tube 51 is 0.1~1; the ratio of the thickness H at the intersection of the spiral flow channel 52 and the vertical circular tube 51 to the width L of the spiral flow channel 52 is 0.1~1; and the ratio of the radius R of the arc on the upper side of the spiral flow channel 52 to the diameter D of the vertical circular tube 51 is 0.1~1.0. This falling film element 5, while ensuring that the polyester melt does not fall off the outside as it slides down the spiral flow channel, further optimizes the flow characteristics of the polyester melt in the spiral flow channel, ensuring the uniform distribution of the polyester melt in the spiral flow channel, and can increase the intrinsic viscosity of the melt by approximately 0.4~0.5 dL / g.

[0078] To optimize the film distribution morphology of the low-viscosity melt as it falls from the feed pipe into the spiral channel 52, combined with... Figure 7 The shape of the membrane opening 15 can be set to various forms such as circle, oval, square / rectangular, slotted, polygonal, etc.

[0079] The ratio of the width of the membrane opening 15 to the width D of the spiral flow channel 52 is 0.3~0.8. Among them, in... Figure 7In this context, "width" refers to the transverse width, such as the diameter of a circle, the major axis of an ellipse, or the length of a rectangle. The ratio of the width of the fabric opening 15 to the width D of the spiral flow channel 52 primarily affects the uniformity of polyester melt distribution as it falls from the fabric opening onto the spiral flow channel. If the ratio is too large, the polyester melt will fall directly from the outside of the spiral flow channel 52. If the ratio is too small, the initial distribution of the polyester melt as it slides down the spiral flow channel 52 will be uneven. Depending on the type of fabric opening, a ratio of 0.3 to 0.8 ensures that the polyester melt does not fall from the outside of the spiral flow channel 52 while maintaining its uniform distribution within the spiral flow channel 52.

[0080] In the above-described falling film element 5, multiple spiral flow channels 52 can be arranged on a single falling film element 5 to form a multi-channel falling film element, thereby improving production efficiency and production capacity. For example... Figure 8 It is a flat-plate falling film element with a double-helix flow channel. Figure 9 The four-helix flow channel is a flat-plate falling film element. In a multi-channel falling film element, each helix flow channel must be identical and uniformly distributed.

[0081] In the above-described falling film element 5, the pitch P of the spiral flow channel 52 on the falling film element 5 can be combined and adjusted to form a combined flow channel falling film element or a pitch-gradient flow channel falling film element. Wherein:

[0082] As the polyester melt slides down from the falling film element 5, its viscosity increases rapidly. Therefore, the pitch of the upper end of the falling film element in the combined spiral flow channel must be smaller than the pitch of the lower end to ensure the uniformity of the polyester melt's velocity throughout the entire falling process. Figure 10 The dual-combination spiral flow channel falling film element requires P1 < P2. For example, if the height H of the falling film element 5 is 10m, P1 can be set to 10m and P2 can be set to 50m, which can increase the intrinsic viscosity of polyester melt from 0.60dL / g at the feed main pipe 4 to 1.15dL / g at the discharge port 6. Figure 11 The three-combination spiral flow channel falling film element requires P3 < P4 < P5. For example, if the height H of the falling film element 5 is 10m, P3 can be set to 10m, P4 can be set to 20m, and P5 can be set to 50m. This can further optimize the uniform flow of polyester melt on the falling film element 5 and increase the intrinsic viscosity of polyester melt from 0.60dL / g at the feed main pipe 4 to 1.20dL / g at the discharge port 6. The same principle applies to more combination spiral flow channels.

[0083] When the pitch of the spiral flow channel gradually increases from the top to the bottom of the falling film element, it is considered to be... Figure 12 The pitch-gradient flow channel falling film element shown is illustrated.

[0084] When multiple falling film elements are installed inside the vertical housing 1, their arrangement on the top plate of the same vertical housing 1 can be configured as follows: Figure 13 As shown, the grid can be arranged as a) rectangular grid, b) triangular grid, or c) concentric circular grid.

[0085] In the above structure, the heat transfer system is set up as follows:

[0086] Part 1: The heat transfer medium is continuously injected into the shell jacket 11 from the first inlet 12 to provide heat to the vertical shell 1, and then flows out through the first outlet 13 and enters the heat transfer medium circulation system for circulation after temperature regulation.

[0087] Part Two: The heat transfer medium is continuously injected from the second inlet 24, enters the heat transfer medium inlet box 2A, flows into the vertical circular tube 51 of the falling film element 5, provides heat to the falling film element 5, and then flows upward through the return pipe 53 into the heat transfer medium outlet box 2B in the top shell 2, and then flows out from the second outlet 25, enters the heat transfer medium circulation system, and circulates after temperature regulation.

[0088] Part 3: The heat transfer medium is continuously injected into the bottom shell jacket 31 from the third inlet 32 ​​to provide heat to the bottom shell 3, and then flows out through the third outlet 33 and enters the heat transfer medium circulation system for circulation after temperature regulation.

[0089] The melt is transported in the following manner:

[0090] Low-viscosity melt continuously enters from the feed main pipe 4 of the top shell 2. After passing through the melt distributor 41, it is divided by the first feed branch pipe 42, the second feed branch pipe 43, and the third feed branch pipe 44. It then falls through the film distribution port 15 onto the spiral flow channel 52 of the falling film element corresponding to each feed branch pipe. After sliding down the spiral flow channel 52 to the bottom end of the vertical circular pipe 51, it falls into the bottom shell 3. After further homogenization by the ribbon agitator 7, the resulting high-viscosity melt flows out from the discharge port 6, completing the polycondensation process.

[0091] Compared with conventional falling film elements, the above-described melt polycondensation reactor for polyester provides better control over the flow behavior of the polyester melt on the falling film element, ensuring that the reaction residence time of the polyester melt on the falling film element is as consistent as possible, thus guaranteeing a more uniform quality of the final polycondensation product and improving the quality of the polycondensation product.

[0092] Taking polyester PET as an example, this application combines the spiral flow channel shape with conventional falling film elements (represented by vertical circular tubes and concave tubes). Figure 14 As shown in Table 1.

[0093] Table 1: Effect of different falling film elements on the tackifying properties of polyester

[0094] .

[0095] Figure 14 The vertical cylindrical falling film element shown in (a) relies on gravity for energy conservation and environmental protection. As the polyester material slides down the falling film element, it exhibits strong surface renewal efficiency, resulting in a rapid increase in the viscosity of the polyester melt. However, the polyester melt falls solely due to adhesion to the vertical cylindrical tube, making the entire process uncontrolled and prone to melt spillage. Simultaneously, cross-flow occurs between different positions on the vertical cylindrical tube, deteriorating the uniformity of the polyester melt's molecular weight, which is above 1.80.

[0096] The structure of the concave tubular falling film element, which is an improvement on the vertical circular tubular falling film element, is as follows: Figure 14 As shown in (b), the polyester melt falls along the concave area designed on the falling film element, which effectively avoids cross-flow of polyester melt at different positions on the falling film element and is conducive to improving the uniformity of the polyester melt molecular weight. However, the constraint force on the melt is insufficient, and the uniformity of the melt molecular weight is still above 1.75.

[0097] Taking a spiral flow channel falling film element as an example, this application retains the advantages of vertical falling film elements, such as energy saving and environmental protection relying on gravity, high surface renewal efficiency, and high polycondensation efficiency. It can also constrain the flow path and flow mode of polyester melt on the falling film element, which can avoid dead zones and melt drop during the falling film melting and polycondensation process. This ensures that the reaction residence time of polyester melt on the falling film element is consistent, and guarantees that the molecular weight of the final polycondensation product is more uniform. The molecular weight uniformity is reduced to below 1.75, which can further improve the quality of polycondensation products.

[0098] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A melt polycondensation reactor for polyester, comprising a vertical shell, a top shell, a bottom shell, and a falling film element, wherein the falling film element is disposed within the vertical shell, the top shell is provided with a main feed pipe, and a feed branch pipe is disposed between the main feed pipe and the falling film element, characterized in that: The top shell is equipped with a heat transfer medium inlet box and a heat transfer medium outlet box. The falling film element includes a vertical circular tube, a spiral channel, and a return pipe. The top opening of the vertical circular tube is connected to the heat transfer medium inlet box. The spiral channel is set on the outer wall of the vertical circular tube and is connected to the feed branch pipe through a film distribution port to guide the melt input from the feed main pipe spiral downward. The return pipe is set inside the vertical circular tube and has openings at both ends. The top opening is connected to the heat transfer medium outlet box, and the bottom opening is connected to the vertical circular tube, so that the heat transfer medium runs in an external inlet and internal outlet manner relative to the return pipe. The falling film element is provided with one or more spiral channels, which are composed of multiple spiral channels with different pitches, or the pitch P of the spiral channels increases sequentially from top to bottom; the cross-section of the spiral channel is flat, inclined, vertical baffle, inclined baffle or bull horn. The ratio of the width L of the spiral channel to the diameter D of the vertical circular tube is 0.05~5, the ratio of the helical pitch P of the spiral channel to the height H of the vertical circular tube is 0.2~10, the height H of the falling film element is 1~40m, and the diameter D of the vertical circular tube is 10~500mm.

2. The melt polycondensation reactor for polyester according to claim 1, characterized in that: The helical pitch P of the spiral flow channel is either constant or set in a manner where the pitch is smaller at the top and larger at the bottom.

3. The melt polycondensation reactor for polyester according to claim 1, characterized in that: Multiple falling film elements are provided, which are arranged in a rectangular grid, a triangular grid, or a concentric ring within the vertical housing.

4. The melt polycondensation reactor for polyester according to claim 1, characterized in that: The opening of the membrane can be circular, elliptical, square, polygonal, or slotted.

5. A melt polycondensation reactor for polyester according to claim 1, characterized in that: The top shell is provided with an upper partition and a lower partition. The space between the upper partition and the lower partition is the heat transfer medium outlet box, and the space between the lower partition and the bottom plate of the top shell is the heat transfer medium inlet box.

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