Process for polybutylene terephthalate production

Abstract

The present invention relates to a process of producing a polybutylene terephthalate comprising the steps of (a) reacting a terephthalic acid with a butanediol in an esterification reactor system (1) to obtain a first reaction product and (b) performing polycondensation of the first reaction product in a polycondensation reactor system (2) to obtain the polybutylene terephthalate, wherein, the step (a) is performed in the presence of ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2 to 25 W / cm2 to obtain the first reaction product.

Description

PROCESS FOR POLYBUTYLENE TEREPHTHALATE PRODUCTION

[0001] Thermoplastic polyesters are polymers that have found application spaces in a wide range of products. Particular species of thermoplastic polyesters, including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly(butylene terephthalate), have many desirable properties rendering them particularly useful for the production of many articles, including but not limited to good dimensional stability in injection molding, heat resistance and wear resistance. Such thermoplastic polyesters are commonly produced via esterification process followed by polycondensation. In such an esterification process, the reaction mixture may comprise terephthalic acid and dihydroxy alkane e.g., butanediol. The polybutylene terephthalate is prepared by the esterification of terephthalic acid with butanediol to form bis-hydroxybutyl terephthalate, followed by its polycondensation.

[0002] Manufacturing processes of polybutylene terephthalate has seen a paradigm shift from batch process to a continuous process and there is an increasing need to improve the production throughput with desired product properties. One of the problems associated with existing processes is the foaming during the esterification step that results in unreacted starting materials, un-utilized esterification catalyst(s) and incomplete reaction products. This problem impacts the overall performance of the polybutylene terephthalate process as it results in additional energy consumption, wastage of starting material and esterification catalyst(s), the yield and the properties of the produced polybutylene terephthalate.

[0003] Thus, for the foregoing reasons, there remains a need for developing a process that at least reduces the foaming in the manufacture of polybutylene terephthalate.

[0004] Therefore, an object of the present invention is to provide a process that addresses the issue of foaming during the production of polybutylene terephthalate.SUMMARY OF THE INVENTION

[0005] The present invention is related to a process for the manufacture of polybutylene terephthalate. Furthermore, the invention is related to the manufacturing of polybutyleneterephthalate having desired properties such as mechanical, chemical, thermal and flow properties.

[0006] The present invention provides an efficient process for the manufacturing of polybutylene terephthalate and addresses the problem of foaming during the manufacturing of polybutylene terephthalate.

[0007] The present invention is directed to a process of producing a polybutylene terephthalate comprising the steps of:a) reacting a terephthalic acid with a butanediol in an esterification reactor system (1) to obtain a first reaction product; andb) performing polycondensation of the first reaction product in a polycondensation reactor system (2) to obtain the polybutylene terephthalate,wherein, the step (a) is performed in the presence of ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2to 25 W / cm2to obtain the first reaction product.

[0008] In an embodiment of the invention, the frequency of the ultrasonic waves is from 80kHz to 1MHz, preferably 90kHz to 1MHz, preferably 100kHz to 1MHz, preferably 100kHz to 900kHz, more preferably 100kHz to 800kHz.

[0009] In an embodiment of the invention, the energy intensity of ultrasonic waves is from 1 W / cm2to 22 W / cm2, preferably from 4 W / cm2to 20 W / cm2, preferably from 5 W / cm2to 20 W / cm2, preferably from 5 W / cm2to 19 W / cm2, more preferably from 6 W / cm2to 19 W / cm2.

[0010] In another embodiment of the invention, the butanediol is selected from 1,2-butanediol, 1,3 -butanediol, 1,4-butanediol and combinations thereof. Preferably the butanediol is 1,4-butanediol.

[0011] In another embodiment of the invention, the first reaction product is obtained by reacting terephthalic acid with butanediol in the presence of a catalyst or a combination of catalysts. The esterification catalyst is selected from a titanium, a zirconium, a zinc and / or amagnesium, based catalyst. Preferably, the catalyst is a titanium-based catalyst. The titanium-based catalyst is a titanium alkoxy compound. The titanium alkoxy compound is selected from a titanium ethoxide, a titanium isopropoxide or a titanium butoxide, more preferably a titanium isopropoxide.

[0012] In a further embodiment of the invention, the esterification process is performed in an esterification reactor system (1) at a pressure of > 60000 and < 90000 Pa.

[0013] In another embodiment of the invention, the polybutylene terephthalate is prepared using a batch process or a continuous process. Preferably, the polybutylene terephthalate is prepared using a continuous process.

[0014] In another embodiment of the invention, the polycondensation is performed in at least two sub-steps. The polycondensation process comprises:(bl) subjecting the first reaction product from esterification step to a first polycondensation in one or more reactors to obtain a second reaction product; and(b2) subjecting the second reaction product from step (bl) to a second polycondensation in one or more reactors to obtain the polybutylene terephthalate.

[0015] In a further embodiment of the present invention, polycondensation reactor (2) is a vertical stirred bed reactor, a horizontal stirred bed reactor, a plug flow reactor, a stirred tank polymerization reactor and a combination thereof, preferably a vertical stirred bed reactor.

[0016] In another embodiment of the invention, the ultrasonic waves were produced using at least one ultrasonic device provided in the esterification section (12) or post esterification section (13) of the esterification reactor system (1). Preferably, in the esterification section (12) of the esterification reactor system (1).

[0017] In another embodiment of the invention, the ultrasonic device is provided in a reboiler section (11) of the esterification reactor system (1).

[0018] In a further embodiment of the invention, the ultrasonic waves are produced using at least one ultrasonic device provided in the esterification section (12) of the esterification reactor system (1) and at least one ultrasonic device provided in the reboiler section (11) of the esterification reactor system.

[0019] In yet another embodiment of the invention, the polybutylene terephthalate comprises > 95.0 wt.%, preferably > 99.0 wt.%, of polymeric units derived from the terephthalic acid and butanediol.

[0020] In a further embodiment of the invention, the polybutylene terephthalate comprises > 99 wt.% of units derived from the terephthalic acid and 1,4-butanediol.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 illustrates a polybutylene terephthalate production process that includes an esterification reactor system (1) and a polycondensation reactor (2) system.

[0022] Figure 2 illustrates different sections of an esterification reactor system (1) that includes a reboiler section (11), an esterification section (12) and a post esterification section (13).DETAILED DESCRIPTION OF EMBODIMENTS

[0023] The following definitions are used in the present description and claims to define the stated subject matter. Other terms not cited below are meant to have the generally accepted meaning in the field.“polymer” as used in the present description means: a chemical compound comprising repeating structural units, wherein the structural units are monomers.“reactor” as used in the present description means: a reaction vessel in which the reaction is performed.

[0024] The present invention will now be described below in greater detail. All embodiments described with respect to one aspect of the present invention are also applicable to other aspects of the invention, unless otherwise stated.

[0025] Thermoplastic polyesters such as polybutylene terephthalate are manufactured by the esterification of terephthalic acid with butanediol in presence of an esterification catalyst. Water, being the byproduct formed during the esterification is distilled out along with tetrahydrofuran which is produced either by cyclization of excess 1,4 butanediol or backbiting reaction of bis-hydroxybutyl terephthalate. Excess amount of 1,4 butanediol is also separated during the esterification reaction to drive the reaction forward. One problem associated with this process is the foaming of the reaction mixture which tends to entrain some catalyst, unreacted starting materials, and some oligomers. This disturbs the reactor performance and foamy material ends up in the polybutylene terephthalate produced that impacts the mechanical, chemical, thermal and flow properties of a produced grade. Thus, there is a need to find a solution to the problem of foaming during esterification. The present invention provides a solution to the foaming problem and at least avoids or reduces the amount of unreacted starting materials, un-utilized esterification catalyst(s) and incomplete reaction products produced during the manufacturing of polybutylene terephthalate. The present invention provides a solution that can at least reduce process wastage, improve process performance, improve the yield and the properties of the produced polybutylene terephthalate.

[0026] Surprisingly, the inventors of the present invention found that usage of ultrasonic waves of specific frequency and energy intensity results in the foam level reduction during the production of polybutylene terephthalate. Particularly, using ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2to 25 W / cm2during the esterification step have significant impact on the reduction of foam level in the esterification reactor system.

[0027] The present invention provides an efficient process for the manufacturing of polybutylene terephthalate by addressing the problem of foaming during esterification of terephthalic acid with butanediol. The process to produce polybutylene terephthalate comprises the steps of:a) reacting a terephthalic acid with a butanediol in an esterification reactor system (1) to obtain a first reaction product; andb) performing polycondensation of the first reaction product in a polycondensation reactor system (2) to obtain the polybutylene terephthalate,wherein, the step (a) is performed in the presence of ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2to 25 W / cm2to obtain the first reaction product.

[0028] In an embodiment of the present invention, the esterification process to obtain first reaction product is performed in the presence of ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2to 25 W / cm2. Preferably ultrasonic waves of frequency from 30kHz to 1MHz, from 40kHz to 1MHz, from 50kHz to 1MHz, from 60kHz to 1MHz, from 70kHz to 1MHz, from 80kHz to 1MHz, from 90kHz to 1MHz. More preferably, ultrasonic waves of frequency from 100kHz to 1MHz, from 100kHz to 900 kHz, from 100kHz to 800 kHz.

[0029] In an embodiment of the present invention, the esterification process to obtain first reaction product is performed in the presence of ultrasonic waves of energy intensity from 1 W / cm2to 25 W / cm2. Preferably, ultrasonic waves of energy intensity from 1 W / cm2to 22 W / cm2, from 2 W / cm2to 20 W / cm2, from 3 W / cm2to 20 W / cm2, from 4 W / cm2to 22 W / cm2, preferably from 5 W / cm2to 22 W / cm2. More preferably, the energy intensity of ultrasonic waves is from 5 W / cm2to 20 W / cm2, from 5 W / cm2to 19 W / cm2, from 6 W / cm2to 19 W / cm2.

[0030] In an embodiment of the present invention, the butanediol is selected from 1,2-butanediol, 1,3 -butanediol, 1,4-butanediol and combinations thereof. Preferably the butanediol is 1,4-butanediol. Other substituted butanediols could also be used for the esterification of terephthalic acid to obtain the first reaction product.

[0031] In another embodiment of present invention, the first reaction product is obtained by reacting the terephthalic acid with the butanediol in the presence of a catalyst or combination of catalysts. Different kinds of esterification catalysts can be used. The esterification catalyst is selected from a titanium, a zirconium, a zinc and / or a magnesium, based catalyst. Preferably, the catalyst is a titanium-based catalyst. The titanium-based catalyst is a titanium alkoxy compound. The titanium alkoxy compound is selected from a titanium ethoxide, a titanium isopropoxide or a titanium butoxide, more preferably a titanium isopropoxide.

[0032] In another embodiment of the present invention, the esterification of the terephthalic acid with a butanediol is performed in an esterification reactor system (1) at a pressure of > 60000 and < 90000 Pa to obtain a first reaction product.

[0033] The esterification reactor system at least includes reboiler section (11) and esterification section (12). The reboiler in the reboiler section (11) facilitates the heat transfer and mixing of the reactants through the thermosiphon effect in the esterification reactor system (I) and some amount of foaming occurs in this section. The reaction stream in reboiler section (I I) is in fluid communication with esterification section (12) of esterification reactor system where majority of the esterification occurs, and a great amount of foaming is seen. The esterification reactor system further includes a post esterification section (13).

[0034] In an embodiment of the present invention, the ultrasonic waves are produced using at least one ultrasonic device provided in the esterification section (12) or post esterification section (13) of the esterification reactor system. Preferably, in the esterification section (12) of the esterification reactor system. More preferably, at the entrance of esterification section (12) of the esterification reactor system.

[0035] In yet another embodiment of the present invention, the ultrasonic device is provided in a reboiler section (11) of the esterification reactor system (1). Preferably, at the reboiler exit section of the esterification reactor system (1).

[0036] In another embodiment of the present invention, the ultrasonic waves are produced using at least one ultrasonic device provided in the esterification section (12) of the esterification reactor system (1) and at least one ultrasonic device provided in the reboiler section (11) of the esterification reactor system (1).

[0037] In an embodiment of the present invention, the ultrasonic waves are produced using at least one ultrasonic device provided at the reboiler exit section of the esterification reactor system (1) and at least one ultrasonic device provided at the entrance of the esterification section (12) of the esterification reactor system (1).

[0038] In another embodiment of the present invention, the polybutylene terephthalate is prepared using a batch process or a continuous process. Preferably polybutylene terephthalate is prepared using a continuous process.

[0039] In another embodiment of the present invention, the polycondensation is performed in at least two sub-steps. The polycondensation process comprises:(bl) subjecting the first reaction product from esterification step to a first polycondensation in one or more reactors to obtain a second reaction product; and(b2) subjecting the second reaction product from step (bl) to a second polycondensation in one or more reactors to obtain the polybutylene terephthalate.

[0040] In an embodiment of the present invention, the polycondensation of the esterification product is performed as per the procedures known in the art. Preferably, the polycondensation of the esterification product is performed in a polycondensation reactor (2) at a temperature of 230 to 260 °C, a pressure of 10 to 3500 Pa, and a residence time between 10 and 60 minutes to obtain the polybutylene terephthalate. Depending upon the polybutylene terephthalate grade to be produced, specific temperature, pressure and residence time can be used.

[0041] In a further embodiment of the present invention, the polycondensation reactor (2) is a vertical stirred bed reactor, a horizontal stirred bed reactor, a plug flow reactor, a stirred tank polymerization reactor and a combination thereof, preferably a vertical stirred bed reactor.

[0042] In another embodiment of the present invention, the polybutylene terephthalate comprises > 95.0 wt.%, preferably > 99.0 wt.%, of polymeric units derived from the terephthalic acid and butanediol. In a further embodiment of the present invention, the polybutylene terephthalate comprises > 99 wt.% of units derived from the terephthalic acid and the 1,4-butanediol.

[0043] It is to be noted that the invention relates to all possible combinations of features recited in the claims. Features described in the description may further be combined. Although the invention has been described in detail for purposes of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the claims. It is further noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product comprising certain components also discloses a product consisting of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps.

[0044] The invention will now be further elucidated with the following examples without being limited hereto. The present experiments were performed by using an ultrasonic probe from Hielscher Ultrasonics GmbH, Germany, purified terephthalic acid from INEOS having a purity of 99.98%, 1, 4 butanediol from BASF having a purity of 99.84% and tetraisopropyl titanate from Dorf Ketal with a Ti content of- 16.8 %.EXAMPLES

[0045] In a 3.0 litre slurry tank equipped with a mechanical stirrer, a reaction mixture of 740.8 g of 1,4-butanediol and 1217 g of terephthalic acid flakes were added. After thorough mixing of the reaction mixture, the slurry was transferred to a continuous reactor system that is equipped with a heating blanket, a stirrer, a condenser, and a pressure transducer. The reactor temperature was maintained at 240 °C, 180 ppm of catalyst with regards to the total weight of the 1,4-butanediol and the terephthalic acid was added. Tetraisopropyl titanate was used as the catalyst. The temperature of the reaction mixture was maintained at 240 °C, while stirring at 260 rpm under nitrogen atmosphere. The reaction was performed at a pressure of 8000 Pa. Foaming of the reaction was observed through the sight glass in the reactor. The level of foaming was assessed by measuring the foam height in centimetres (cm). The ultrasonic probe was inserted to the top section of the reactor system, where there is a heavy vapor trafficventing through the condenser. Table 1 indicates the effect of ultrasonic vibration on the reduction of foam level. The polycondensation of obtained reaction product of 1,4-butanediol and terephthalic acid is performed at a temperature of 240 °C, a pressure of 900 Pa, and a residence time of 45 minutes to obtain the polybutylene terephthalate.Table 1 - Effect of ultrasonic vibration on foam level reduction # Frequency (kHz) Energy Intensity (W / cm2) Foam Level Reduction (%) 1 nil nil 02 100 5 83 200 7.2 184 400 11.1 415 500 12.8 656 600 14 687 800 18.1 70*Esterification process conditions - 240 °C, 8000 PaTable 2 - Effect of energy intensity on foam level reduction # Frequency (kHz) Energy Intensity (W / cm2) Foam Level Reduction (%) 2 100 5 82a 100 7.2 123 200 7.2 183a 200 11.1 334 400 11.1 41*Esterification process conditions - 240 °C, 8000 Pa

[0046] Table 1 shows that the use of ultrasonic waves during the esterification, results in the reduction of foam level. In example-2, there is an 8% reduction of foam level at a frequency of 100 kHz as compared to the case where there’s no ultrasonic frequency used (example-1).It is also obvious from Table 1 that there is a concomitant increase in the foam level reduction with increasing ultrasonic frequency.Table 2 demonstrates the role of energy intensity in reducing foam levels at similar frequencies. Examples 2 & 2a demonstrate this aspect of the invention. At similar frequencies, there is at least a 50% increase in the foam reduction level with a higher energy intensity as compared to a lower energy intensity. Among an increase of frequency and an increase of energy intensity, the increase of energy intensity seems to be playing a greater role in the foam reduction level.

Claims

CLAIMS1. A process to produce a polybutylene terephthalate comprising the steps of:(a) reacting a terephthalic acid with a butanediol in an esterification reactor system (1) to obtain a first reaction product; and(b) performing polycondensation of the first reaction product in a polycondensation reactor system (2) to obtain the polybutylene terephthalate,wherein, the step (a) is performed in the presence of ultrasonic waves of frequency from 20kHz to 1MHz and energy intensity from 1 W / cm2to 25 W / cm2to obtain the first reaction product.

2. The process according to claim 1, wherein frequency of the ultrasonic waves is from 80kHz to 1MHz, preferably 90kHz to 1MHz, preferably 100kHz to 1MHz, preferably 100kHz to 900kHz, more preferably 100 kHz to 800kHz.

3. The process according to any one of the claims 1-2, wherein energy intensity of ultrasonic waves is from 1 W / cm2to 22 W / cm2, preferably from 4 W / cm2to 20 W / cm2, preferably from 5 W / cm2to 20 W / cm2, preferably from 5 W / cm2to 19 W / cm2, more preferably from 6 W / cm2to 19 W / cm2.

4. The process according to any one of the claims 1-3, wherein the butanediol is selected from 1,2-butanediol, 1,3 -butanediol, 1,4-butanediol and combinations thereof, preferably, 1,4- butanediol.

5. The process according to any one of the claims 1-4, wherein the first reaction product is obtained by reacting the terephthalic acid with the butanediol in the presence of a titanium, a zirconium, a zinc and / or a magnesium, based catalyst, preferably a titanium-based catalyst.

6. The process according to claim 5, wherein the titanium-based catalyst is a titanium alkoxy compound, preferably a titanium ethoxide, a titanium isopropoxide or a titanium butoxide, more preferably a titanium isopropoxide.

7. The process according to any one of the claims 1-6, wherein the polybutylene terephthalate is prepared using a batch process or a continuous process, preferably a continuous process.

8. The process according to any one of the claims 1-7, wherein the pressure of the esterification reactor system (1) is > 60000 and < 90000 Pa.

9. The process according to any one of the claims 1-8, wherein the step (b) is performed in at least two sub-steps comprising:• (bl) subjecting the first reaction product from step (a) to a first polycondensation in one or more reactors to obtain a second reaction product; and• (b2) subjecting the second reaction product from step (bl) to a second polycondensation in one or more reactors to obtain the polybutylene terephthalate.

10. The process according to any one of the claims 1-9, wherein the polycondensation reactor (2) is a vertical stirred bed reactor, a horizontal stirred bed reactor, a plug flow reactor, a stirred tank polymerization reactor and a combination thereof, preferably a vertical stirred bed reactor.

11. The process according to any one of the claims 1-10, wherein the ultrasonic waves are produced using at least one ultrasonic device provided in an esterification section (12) or a post esterification section (13) of the esterification reactor system (1), preferably in the esterification section (12) of the esterification reactor system (1).

12. The process according to any one of the claims 1-11, wherein the ultrasonic device is provided in a reboiler section (11) of the esterification reactor system (1).

13. The process according to any one of the claims 1-12, wherein the ultrasonic waves are produced using at least one ultrasonic device provided in the esterification section (12) of the esterification reactor system (1) and at least one ultrasonic device provided in the reboiler section (11) of the esterification reactor system (1).

14. The process according to any one of the claims 1-13, wherein the polybutylene terephthalate comprises > 95.0 wt.%, preferably > 99.0 wt.%, of polymeric units derived from the terephthalic acid and butanediol.

15. The process according to any one of the claims 1-14, wherein the polybutylene terephthalate comprises > 99 wt.% of units derived from the terephthalic acid and the 1,4- butanediol.

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