An apparatus and method for producing polybutylene terephthalate

Abstract

This invention discloses an apparatus and method for preparing polybutylene terephthalate (PPT). The apparatus includes an esterification reactor, a pre-condensation reactor, and a final condensation reactor. The inlet end of the final condensation reactor is equipped with alternating ordinary baffles and heating baffles. The height of the ordinary baffles is 1.2-3.0 times the height of the heating baffles. A weir plate is provided in the middle of the ordinary baffles, and its height decreases from the inlet end inwards. The method involves sequentially subjecting a mixed slurry of terephthalic acid and 1,4-butanediol to esterification, pre-condensation, and final condensation reactions in the apparatus. The catalyst is injected into the esterification reactor or partially injected into the pre-condensation reactor via a catalyst addition port. After the reaction, PPT with an average degree of polymerization of 130-200 is obtained. The high molecular weight PPT obtained by this invention using a specific apparatus and method exhibits a high average degree of polymerization, excellent spinning properties, and thermal stability.

Description

Technical Field

[0001] This invention relates to an apparatus for preparing polyester and a method for using the same, specifically to an apparatus for preparing polybutylene terephthalate and a method for using the same. Background Technology

[0002] Polybutylene terephthalate (PBT) is a crystalline thermoplastic polyester with excellent mechanical properties, heat resistance, and solvent resistance, and is one of the five major engineering plastics. The direct esterification polymerization process for PBT uses purified terephthalic acid (PTA) and 1,4-butanediol (BDO) as raw materials and tetrabutyl titanate (TBT) as a catalyst. Through three stages—esterification, pre-condensation, and final condensation—and under controlled conditions of temperature, pressure, residence time, and stirring speed, a PBT melt is generated. This melt is then pelletized and packaged to produce PBT chips. However, current technologies can only yield PBT polyester with an average degree of polymerization of 70-130. Summary of the Invention

[0003] Purpose of the invention: In order to solve the technical problems existing in the prior art, the present invention aims to provide a preparation apparatus for polybutylene terephthalate with stable and uniform catalyst feeding and high average degree of polymerization. The present invention also provides a method for preparing polybutylene terephthalate using the above apparatus.

[0004] Technical solution: The apparatus for preparing polybutylene terephthalate according to the present invention includes: an esterification kettle, a pre-shrinking kettle and a final shrinking kettle. The inlet end of the final shrinking kettle is equipped with alternating ordinary baffles and heating baffles, and a weir plate is provided in the middle of the ordinary baffles.

[0005] Furthermore, the height of the ordinary baffle is 1.2-3.0 times that of the heating baffle. The distance between the ordinary baffle and the heating baffle is directly proportional to the height of the ordinary baffle. The height of the weir plate decreases from the inlet end to the inside, which can ensure that the viscosity-enhancing reaction is completed at the front end. The gradually thickened polymer passes through the weir plate and climbs through the heating baffle. Its movement trajectory is sinusoidal. The heating baffle has a channel in the middle, and baffles and high-temperature heat medium are installed inside. The arrangement of multiple baffles can prevent short circuits of the heat medium and ensure uniform flow of the high-viscosity polymer.

[0006] Furthermore, the preferred arrangement of the ordinary baffle and the heating baffle is an alternating arrangement of the ordinary baffle at both ends and the heating baffle in the middle.

[0007] The method for preparing polybutylene terephthalate using the above-described apparatus according to the present invention includes the following steps:

[0008] (a) A mixed slurry of terephthalic acid and 1,4-butanediol is added to an esterification reactor for esterification reaction. The catalyst is injected into the esterification reactor through the catalyst addition port. The reaction yields an esterified melt with an average degree of polymerization of 5-20.

[0009] (b) The esterified melt is added to a pre-condensation reactor to carry out a pre-condensation reaction, and the reaction yields a pre-condensation melt with an average degree of polymerization of 30-60.

[0010] (c) The prepolymer melt is added to the final polymerization reactor. After the prepolymer melt is thickened by alternating ordinary baffles and heating baffles at the inlet end of the final polymerization reactor, the final polymerization reaction is carried out to obtain a final polymer melt with an average degree of polymerization of 130-200. Preferably, the average degree of polymerization of the final polymer melt is 135-195, which yields polybutylene terephthalate.

[0011] Further, in step (a), the molar ratio of terephthalic acid to 1,4-butanediol is 1:2.0-1:3.2.

[0012] Further, in step (a), the esterification reaction conditions are: reaction temperature 236-246℃, reaction pressure 35-55kPa, residence time 1.5-3.5h, and stirrer speed 90-160rpm.

[0013] Furthermore, in step (a), after the catalyst is prepared with fresh BDO, it is injected into the esterification reactor through the catalyst addition port at a speed of 10-30 m / s. This addition method can make the amount of catalyst added more stable and dispersed evenly in the reactor, effectively ensuring the esterification reaction. The catalyst is a titanium-based catalyst, which is added alone in the esterification reactor or added in batches in the esterification reactor and the pre-shrinking reactor.

[0014] Further, in step (b), the conditions for the pre-condensation reaction are: reaction temperature 245-255℃, reaction pressure 1.0-3.0kPa, residence time 1.5-3.0h, and stirrer speed 40-80rpm.

[0015] Furthermore, in step (c), the conditions for the final polycondensation reaction are: reaction temperature 245-255℃, reaction pressure 40-150kPa, residence time 0.8-2.0h, and stirrer speed 2-10rpm.

[0016] Invention Principle: First, this invention features multiple sets of special baffles at the inlet of the final shrinkage reactor to create a special flow channel for the melt. This special flow channel design provides the required residence time and temperature for thickening, while also ensuring the fluidity of the high molecular weight polymer. Second, in this invention, bis(4-hydroxybutyl) terephthalate is generated by an alkydation reaction between terephthalic acid and 1,4-butanediol in an esterification reactor. Then, in two tandem condensation reactors, bis(4-hydroxybutyl) terephthalate molecules undergo a condensation reaction to remove butanediol molecules, ultimately yielding the product with a degree of polymerization of 130-200 required in this invention.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0018] (1) The polybutylene terephthalate produced by the three-reactor direct esterification method of the present invention has an average degree of polymerization of 130-200. Compared with the polyester with a low average degree of polymerization in the prior art, it has the outstanding advantages of excellent spinning performance and high thermal stability.

[0019] (2) The final shrinkage vessel structure described in this invention has a unique design, with alternating ordinary baffles and heating baffles. Through the design of its height and structure, it can ensure that the thickening reaction is completed at the front end.

[0020] (3) The catalyst is added by spraying from the catalyst addition port. Compared with the traditional spray method, the catalyst addition amount is more stable and the catalyst is mixed more evenly with the material in the reactor, which effectively ensures the occurrence of the esterification reaction.

[0021] (4) The process and equipment used in this invention are simple and can greatly avoid the problem of thermal degradation of materials due to prolonged residence time in the reactor, resulting in waste. At the same time, the high production efficiency also reduces the waste of recycled BDO. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the apparatus for preparing polybutylene terephthalate according to the present invention;

[0023] Figure 2 This is a schematic diagram of the alternating baffles of the present invention;

[0024] Figure 3 This is a side view of the ordinary baffle of the present invention;

[0025] Figure 4 This is a side view of the heating baffle of the present invention.

[0026] Detailed Description of Embodiments with Drawings

[0027] The present invention will now be further described with reference to specific embodiments.

[0028] The apparatus for preparing polybutylene terephthalate described in this invention is as follows: Figure 1 As shown, it includes, in sequence, an esterification reactor 1, a pre-shrinking reactor 2, and a final shrinking reactor 3. The final shrinking reactor 3, as shown... Figure 2 As shown, the inlet end of the final shrinkage vessel 3 is equipped with alternating ordinary baffles 31 and heating baffles 32. The preferred arrangement is an alternating arrangement of ordinary baffles 31 at both ends and heating baffles 32 in the middle. The height of the ordinary baffles 31 is 1.2-3.0 times the height of the heating baffles 32. Figure 3 As shown, a weir plate 33 is provided in the middle of the ordinary baffle 31. The height of the weir plate 33 decreases from the inlet end to the inside, ensuring that the thickening reaction is completed at the front end. The gradually thickened polymer body passes through the weir plate 33, climbs through the heated baffle 32, and its movement trajectory is sinusoidal. Figure 4 As shown, the heating baffle 31 has a channel 34 in the middle, and a baffle 35 and a high-temperature heat medium are provided inside. The arrangement of multiple baffles 34 can prevent short circuits of the heat medium. The distance between the ordinary baffle 31 and the heating baffle 32 is directly proportional to the height of the ordinary baffle 31.

[0029] Example 1: The method of using the apparatus for preparing polybutylene terephthalate according to the present invention is as follows:

[0030] (a) A mixed slurry of terephthalic acid and 1,4-butanediol in a molar ratio of 3.1 was added to esterification reactor 1 for esterification reaction. The reaction conditions were: reaction temperature 238℃, reaction pressure 50kPa, residence time 2h, and stirrer speed 140rpm. After the reaction was completed, the esterified melt was obtained.

[0031] After the titanium-based catalyst is prepared with fresh BDO, it is injected into the esterification reactor 1 through the catalyst addition port at a speed of 20 m / s.

[0032] (b) The esterified melt is added from the outer chamber to the pre-condensation reactor 2 for pre-condensation reaction. The reaction conditions are: reaction temperature 245℃, reaction pressure 2.0kPa, residence time 1.5h, and stirrer speed 60rpm. After the reaction is completed, the pre-condensation melt is obtained.

[0033] (c) The prepolymer melt is produced from the inner chamber of the prepolymer reactor and added to the final polymerization reactor 3. After the prepolymer melt is thickened by alternating ordinary baffles 31 and heating baffles 32 at the inlet end of the final polymerization reactor 3, the final polymerization reaction is carried out. The reaction conditions are: reaction temperature 250℃, reaction pressure 80kPa, residence time 1h, and stirrer speed 9.0rpm. The final polymerization melt obtained after the reaction is polybutylene terephthalate.

[0034] Example 2: The method of using the apparatus for preparing polybutylene terephthalate according to the present invention is as follows:

[0035] (a) A mixed slurry of terephthalic acid and 1,4-butanediol in a molar ratio of 3.1 was added to esterification reactor 1 for esterification reaction. The reaction conditions were: reaction temperature 238℃, reaction pressure 50kPa, residence time 2h, and stirrer speed 140rpm. After the reaction was completed, the esterified melt was obtained.

[0036] After the titanium-based catalyst is prepared with fresh BDO, it is injected into the esterification reactor 1 through the catalyst addition port at a speed of 20 m / s.

[0037] (b) The esterified melt is added from the outer chamber to the pre-condensation reactor 2 for pre-condensation reaction. The reaction conditions are: reaction temperature 245℃, reaction pressure 2.0kPa, residence time 1.5h, and stirrer speed 60rpm. After the reaction is completed, the pre-condensation melt is obtained.

[0038] (c) The prepolymer melt is produced from the inner chamber of the prepolymer reactor and added to the final polymer reactor 3. After the prepolymer melt is thickened by alternating ordinary baffles 31 and heating baffles 32 at the inlet end of the final polymer reactor 3, the final polymerization reaction is carried out. The reaction conditions are: reaction temperature 250℃, reaction pressure 80kPa, residence time 1h, and stirrer speed 7.5rpm. The final polymer melt obtained after the reaction is polybutylene terephthalate.

[0039] Example 3: The method of using the apparatus for preparing polybutylene terephthalate according to the present invention is as follows:

[0040] (a) A mixed slurry of terephthalic acid and 1,4-butanediol in a molar ratio of 3.1 was added to esterification reactor 1 for esterification reaction. The reaction conditions were: reaction temperature 238℃, reaction pressure 50kPa, residence time 2h, and stirrer speed 100rpm. After the reaction was completed, the esterified melt was obtained.

[0041] After the titanium-based catalyst is prepared with fresh BDO, it is injected into the esterification reactor 1 through the catalyst addition port at a speed of 20 m / s.

[0042] (b) The esterified melt is added from the outer chamber to the pre-condensation reactor 2 for pre-condensation reaction. The reaction conditions are: reaction temperature 245℃, reaction pressure 2.0kPa, residence time 1.5h, and stirrer speed 60rpm. After the reaction is completed, the pre-condensation melt is obtained.

[0043] (c) The prepolymer melt is produced from the inner chamber of the prepolymer reactor 2 and added to the final polymer reactor 3. After the prepolymer melt is thickened by alternating ordinary baffles 31 and heating baffles 32 at the inlet end of the final polymer reactor 3, the final polymerization reaction is carried out. The reaction conditions are: reaction temperature 250℃, reaction pressure 80kPa, residence time 1h, and stirrer speed 9.0rpm. The final polymer melt obtained after the reaction is polybutylene terephthalate.

[0044] Comparative Example 1: The difference from Example 1 is that this comparative example uses an esterification reactor stirrer speed of 100 rpm and a final shrinkage reactor stirrer speed of 7.5 rpm, and the catalyst is added by spraying it into the esterification reactor through the catalyst addition port. The actual degree of polymerization of the products from Examples 1, 2, 3 and Comparative Example 1 described in this invention is shown in Table 1.

[0045] Table 1 Production Parameters and Product Aggregation Degree

[0046]

Claims

1. An apparatus for preparing polybutylene terephthalate, comprising: Esterification vessel (1), pre-shrinking vessel (2), and final shrinking vessel (3), characterized in that the inlet end of the final shrinking vessel (3) is equipped with alternating ordinary baffles (31) and heating baffles (32), and the middle part of the ordinary baffles (31) is provided with a weir plate (33); the height of the ordinary baffles (31) is 1.2-3.0 times the height of the heating baffles (32); the distance between the ordinary baffles (31) and the heating baffles (32) is directly proportional to the height of the ordinary baffles (31); the height of the weir plate (33) decreases from the inlet end to the inside; the middle part of the heating baffles (32) is provided with a channel (34), and the inside is provided with a baffle plate (35) and a high-temperature heat medium.

2. A method for preparing polybutylene terephthalate using the apparatus of claim 1, characterized in that, Includes the following steps: (a) A mixed slurry of terephthalic acid and 1,4-butanediol is added to an esterification reactor (1) for esterification reaction. The catalyst is injected into the esterification reactor through the catalyst addition port. The reaction yields an esterified melt with an average degree of polymerization of 5-20. (b) The esterified melt is added to the pre-condensation reactor (2) to carry out a pre-condensation reaction, and a pre-condensation melt with an average degree of polymerization of 30-60 is obtained. (c) The prepolymer melt is added to the final shrinkage vessel (3). After the prepolymer melt is thickened by alternating ordinary baffles (31) and heating baffles (32) at the inlet end of the final shrinkage vessel (3), the final shrinkage reaction is carried out to obtain a final shrinkage melt with an average degree of polymerization of 130-200, which is polybutylene terephthalate.

3. The method according to claim 2, characterized in that, In step (a), the molar ratio of terephthalic acid to 1,4-butanediol is 1:2.0-1:3.

2.

4. The method according to claim 2, characterized in that, In step (a), the catalyst is prepared with 1,4-butanediol and then injected into the esterification vessel through the catalyst addition port.

5. The method according to claim 2, characterized in that, The catalyst is injected at a rate of 10-30 m / s.

6. The method according to claim 5, characterized in that, In steps (a) to (c), the esterification reaction conditions are: reaction temperature 236-246℃, reaction pressure 35-55kPa, residence time 1.5-3.5h, and stirrer speed 90-160rpm; the pre-condensation reaction conditions are: reaction temperature 245-255℃, reaction pressure 1.0-3.0kPa, residence time 1.5-3.0h, and stirrer speed 40-80rpm; and the final condensation reaction conditions are: reaction temperature 245-255℃, reaction pressure 40-150kPa, residence time 0.8-2.0h, and stirrer speed 2-10rpm.

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