CONTINUOUS PROCESS FOR MAKING POLYBUTYLENE TEREPHTHALATE USING PURIFIED TEREPHTHALIC ACID AND 1,4-BUTANE DIOL

Abstract

Disclosed is a continuous process and device for making polybutylene terephthalate (PBT) resin, particularly high molecular weight PBT resin. Also disclosed are a device for conducting the process, and a monitoring process for determining the carboxylic acid end group concentration of the resulting PBT.

Claims

1. A continuous process for preparing polybutylene terephthalate, comprising: (a) combining 1,4-butane diol (BDO) and purified terephthalic acid (PTA) in a slurry paste vessel to form a mixture; (b) continuously supplying the mixture from step (a) to a tower reactor having a plurality of reactor zones for at least one of esterification or transesterification; wherein the following conditions are maintained: (b 1) the mixture from step (a) is subjected to the esterification section with a treatment temperature in the range of 170 to 270° C. and a treatment pressure in the range of 0.5 to 1 bar; a first quantity of catalyst is supplied; (b2) the product of step (1)1) is transferred continuously into a pipe stretch while optionally a quantity of BDO is supplied; (b3) the product of step (b2) is transferred continuously to a cascade postesterification part of the tower reactor, comprising multiple cascades in series, wherein the pressure of each cascade is subsequently reduced to ultimately ≦0.25 bar, and optionally a second quantity of catalyst is supplied into the last cascade zone of the post-esterification part of the tower reactor; (c) the product obtained from step (b3) is continuously supplied to a first continuously stirred tank reactor, wherein the product of step (b3) is subjected to a melt temperature of 225 to 250° C., a pressure of 5 to 40 mbar, and a residence time between 10 and 60 minutes; (d) optionally, the product obtained from step (c) is continuously supplied to a second continuously stirred tank reactor, wherein the product of step (c) is subjected to a melt temperature of 230 to 260° C., a pressure of 0.1 to 35 mbar, and a residence time between 10 and 60 minutes; and (e) the obtained product from step (c) or, where a second continuously stirred tank reactor (d) is used, from step (d), is continuously transferred to a continuous polycondensation reactor wherein the product of step (d) is subjected to a melt temperature of 230 to 255° C., a pressure of 0.1 to 16 mbar, and a residence time of 30 minutes to 6 hours.

2. The process of claim 1 wherein the PTA comprises at least 99 weight percent terephthalic acid.

3. The process of claim 1 wherein the catalyst is selected from titanium alkoxides or reaction products thereof with a phosphorous compound; tin-containing compounds; zirconium-containing compounds, and/or combinations thereof.

4. The process of claim 1 wherein the catalyst is a alkoxide.

5. The process of claim 1 wherein the continuous polycondensation reactor (e) is a dual shafts disc ring reactor with independent revolutions per minute (rpm) control.

6. The process of claim 1, comprising: (a) combining 1,4-butane diol (BDO) and purified terephthalic acid (PTA) in a mole ratio of 1.2:1 to 4:1 in a slurry paste vessel to form a mixture, wherein the temperature in the slurry paste vessel is in the range of 20 to 90° C., the pressure in the slurry paste vessel is in the range of 0.8 to 1.1 bar, and the residence time of the mixture in the slurry paste vessel is in the range of 1 to 4 hours; (b) continuously supplying the mixture from step (a) to a tower reactor having a plurality of reactor zones for at least one of esterification or transesterification, wherein the esterification or transesterification occurs continuously, simultaneously, and uninterruptedly until prepolycondensation occurs; wherein the following conditions are maintained: (b1) the mixture from step (a) is subjected to the esterification section with a treatment temperature in the range of 170 to 270° C. and a treatment pressure in the range of 0.4 to 1 bar; a first quantity of between 60 and 120 ppm of catalyst is supplied; the ratio of BDO to PTA is 1.6:1 to 3:1; and water, tetrahydrofuran (THF), and BDO are removed from the esterification section as overheads; (b2) the product of step (b1 ) is transferred continuously into a pipe stretch and maintained at a temperature in the range of 200 to 280° C. and a pressure in the range of 1 to 10 bar, while supplying 0.03 to 0.05 mol BDO; (b3) the product of step (b2) is transferred continuously to a cascade postesterification part of the tower reactor, which consists of four different cascades, wherein the pressure of each cascade is subsequently reduced to ≦0.25 bar, the temperature of each cascade is subsequently increased from 230 to 270° C., the residence time for each cascade is set between 2 and 30 minutes and a second quantity of TPT catalyst between 25 and 100 ppm diluted with 0.02 to 0.2 mol of BDO is supplied into the fourth cascade zone of the post-esterification part of the tower reactor; (b4) water, THF, byproducts, and excess BDO from steps (b1), (b2), and (b3) are removed and the BDO is purified and directed back again to the individual reaction steps; wherein the plurality of reactor zones in the tower reactor of step (b) are configured such that the lower third of the tower reactor is in the form of a hydrocyclone with attached heat exchanger, and wherein the hydrocyclone has a supply line from the mixer of step (a); the hydrocyclone is connected via a pressure pipe to the top side of the tower reactor; the top side of the tower reactor is configured in the form of a downflow cascade; and the cascade is in communication via a pipe with the central part of the tower reactor; (c) the product obtained from step (b3) is continuously supplied to a first continuously stirred tank reactor, wherein the product of step (b3) is subjected to a melt temperature of 225 to 250° C., a pressure of 5 to 70 mbar, and a residence time between 10 and 60 minutes; (d) the product obtained from step (c) is continuously supplied to a second continuously stirred tank reactor, wherein the product of step (c) is subjected to a melt temperature of 230 to 260° C., a pressure of 0.1 to 35 mbar, and a residence time between 10 and 60 minutes; (e) the product from step (d) is continuously transferred to a dual shafts disc ring reactor with independent revolutions per minute (rpm) control, wherein the product of step (d) is subjected to a melt temperature of 230 to 255° C., a pressure of 0.1 to 16 mbar, a rotation rate for each of the dual shafts that is independently 1 to 5 rpm, and a residence time of 30 minutes to 6 hours; and (f) the product of step (e) is continuously fed into a pelletizer and is pelletized.

7. The process of claim 1, wherein in step (a), BDO and PTA are combined in a mole ratio of 1.35:1 to 2.5:1; in step (b3), the residence time for each cascade is between 5 and 25 minutes.

8. The process of claim 1 wherein the temperature in the slurry paste vessel is maintained between 70° C. and 90° C., the pressure is maintained between 0.9 and 1.05 bar, and the residence time is 2.5 to 3.5 hours.

9. The process of claim 1, wherein the mixture from step (a) is subjected to the esterification section of the tower reactor of step (b) with a treatment temperature in the range of 240° C. to 250° C., a treatment pressure in the range of 0.6 to 0.8 bar, and a residence time of 80 to 120 minutes.

10. The process of claim 1, wherein the product of step (b3) has an intrinsic viscosity of between 0.1 and 0.2 dl/g and a carboxylic acid end group concentration of between 10 and 100 mmol/kg, with a conversion of between 95 and 99.5% based on free PTA.

11. The process of claim 1, wherein the product of step (b3) is subjected to a residence time of 30-50 minutes in the first and 30-50 minutes in the second continuously stirred tank reactors in series and is subjected to a melt temperature of 240 to 250° C.

12. The process of claim 1 wherein the obtained PBT has an intrinsic viscosity of 0.55 to 1.35 dl/g and a carboxylic acid end group concentration of 0.1 to 60 mmol/kg.

13. The process of claim 1 wherein the obtained PBT is characterized by the following intrinsic viscosity, carboxylic acid end group concentration, and melt viscosity values: (a) an intrinsic viscosity of 1.10 to 1.25 deciliters per gram, a carboxylic acid end group concentration of 35 to 45 millimoles per kilogram, and a melt viscosity of 750.0 to 950.0 Pa.Math.s (7500 to 9500 poise) measured at 265° C.; (b) an intrinsic viscosity of 0.95 to 1.0 deciliters per gram, a carboxylic acid end group concentration no greater than 40 millimoles per kilogram, and a melt viscosity of 350.0 to 450.0 Pa.Math.s (3500 to 4500 poise) measured at 265° C.; (c) an intrinsic viscosity of 0.78 to 0.82 deciliters per gram, a carboxylic acid end group concentration no greater than 40 millimoles per kilogram, and a melt viscosity of 145.0 to 185.0 Pa.Math.s (1450 to 1850 poise) measured at 265° C.; (d) an intrinsic viscosity of 0.68 to 0.72 deciliters per gram, a carboxylic acid end group concentration no greater than 24 millimoles per kilogram, and a melt viscosity of 74.0 to 90.0 Pa.Math.s (740 to 900 poise) measured at 265° C.; or (e) an intrinsic viscosity of 0.55 to 0.59 deciliters per gram, a carboxylic acid end group concentration no greater than 12 millimoles per kilogram, and a melt viscosity of 20.0 to 40.0 Pa.Math.s (200 to 400 poise) measured at 265° C.

14. The process of claim 1 wherein the CEG is monitored via a process comprising the steps of: (a) dissolution of PBT polymer or oligomer in a mixture of solvents at room temperature; (b) suppression of ionic formation by adding a second substance for sharp equivalence point determination; and (c) titration of solution against potassium hydroxide using potentiometric or colorimetric method after addition of Bromophenol blue indicator; wherein mixture of solvents comprises hexafluoro-2-propanol, o-cresol, and dichloromethane; wherein second substance is selected from the group consisting of salts comprising a cation selected from the group consisting of sodium, potassium, calcium, and ammonium; and an anion selected from the group consisting of trifluoroacetate, trifluoropropionate, and trifluoroborate.

15. A device for operating the process of claim 1 comprising: (1) a slurry paste vessel, wherein 1,4-butane diol (BDO) and purified terephthalic acid (PTA) are combined to form a mixture; (2) a tower reactor to which the product from (1) is supplied, having a plurality of reactor zones configured such that the lower third of the tower reactor is in the form of a hydrocyclone with attached heat exchanger, and wherein the hydrocyclone has a supply line from the vessel (1), the hydrocyclone being connected to the top side of the tower reactor, the top side of the tower reactor being configured in the form of a downflow cascade; (3) a first continuously stirred tank reactor to which the product from (2) is supplied; (4) an optional second continuously stirred tank reactor to which the product from (3) is supplied; (5) a dual shaft ring reactor to which the product from (3) or, where a second continuous stirred tank reactor (4) is used, the product from (4), is supplied; (6) a pelletizer where the product from (5) is continuously fed and pelletized.

16. The process of claim 1 wherein in step (b3) the pressure of each cascade is subsequently reduced to ultimately <0.20 bar; the PTA comprises at least 99 weight percent terephthalic acid; and the catalyst is selected from tetraisopropyl titanate, tetraisobutyl titanate or tetra tert-butyl titanate.

17. The process of claim 16, wherein in step (a), BDO and PTA are combined in a mole ratio of 1.35:1 to 2.5:1; in step (b3), the residence time for each cascade is between 5 and 25 minutes; the temperature in the slurry paste vessel is maintained between 70° C. and 90° C., the pressure is maintained between 0.9 and 1.05 bar, and the residence time is 2.5 to 3.5 hours; the mixture from step (a) is subjected to the esterification section of the tower reactor of step (b) with a treatment temperature in the range of 240° C. to 250° C., a treatment pressure in the range of 0.6 to 0.8 bar, and a residence time of 80 to 120 minutes; and the product of step (b3) has an intrinsic viscosity of between 0.1 and 0.2 dl/g and a carboxylic acid end group concentration of between 10 and 100 mmol/kg, with a conversion of between 95 and 99.5% based on free PTA; and the product of step (b3) is subjected to a residence time of 30-50 minutes in the first and 30-50 minutes in the second continuously stirred tank reactors in series and is subjected to a melt temperature of 240 to 250° C.

18. The process of claim 6, wherein in step (b3) the pressure of each cascade is subsequently reduced to ultimately <0.20 bar; the PTA comprises at least 99 weight percent terephthalic acid; and the catalyst is selected from tetraisopropyl titanate, tetraisobutyl titanate or tetra tert-butyl titanate.

19. The process of claim 18, wherein in step (a), BDO and PTA are combined in a mole ratio of 1.35:1 to 2.5:1; in step (b3), the residence time for each cascade is between 5 and 25 minutes. the temperature in the slurry paste vessel is maintained between 70° C. and 90° C., the pressure is maintained between 0.9 and 1.05 bar, and the residence time is 2.5 to 3.5 hours; the mixture from step (a) is subjected to the esterification section of the tower reactor of step (b) with a treatment temperature in the range of 240° C. to 250° C., a treatment pressure in the range of 0.6 to 0.8 bar, and a residence time of 80 to 120 minutes; the product of step (b3) has an intrinsic viscosity of between 0.1 and 0.2 dl/g and a carboxylic acid end group concentration of between 10 and 100 mmol/kg, with a conversion of between 95 and 99.5% based on free PTA; and the product of step (b3) is subjected to a residence time of 30-50 minutes in the first and 30-50 minutes in the second continuously stirred tank reactors in series and is subjected to a melt temperature of 240 to 250° C.

20. The process of claim 7, wherein the temperature in the slurry paste vessel is maintained between 70° C. and 90° C., the pressure is maintained between 0.9 and 1.05 bar, and the residence time is 2.5 to 3.5 hours; the mixture from step (a) is subjected to the esterification section of the tower reactor of step (b) with a treatment temperature in the range of 240° C. to 250° C., a treatment pressure in the range of 0.6 to 0.8 bar, and a residence time of 80 to 120 minutes; the product of step (b3) has an intrinsic viscosity of between 0.1 and 0.2 dl/g and a carboxylic acid end group concentration of between 10 and 100 mmol/kg, with a conversion of between 95 and 99.5% based on free PTA; and the product of step (b3) is subjected to a residence time of 30-50 minutes in the first and 30-50 minutes in the second continuously stirred tank reactors in series and is subjected to a melt temperature of 240 to 250° C.

Description

EXAMPLES

[0231] The following examples illustrate the scope of the invention. The examples and preparations which follow are provided to enable those skilled in the art to more clearly understand and to practice the present invention. They should not be considered as limiting the scope of the invention, but merely as being illustrative and representative thereof.

[0232] Example Alternative Process for Determining CEG Concentration

[0233] Complete dissolution of the polymer sample is critical in order to obtain reproducible and accurate values.

[0234] The samples were prepared offline and transferred into disposable beakers before placing them onto the sample changer of automated titrator. CEG values for both process samples as well as the Resin grades mentioned in the table below were determined using the titration procedure.

[0235] About 0.25 grams of sample was weighed accurately and transferred into a 2 oz. glass bottle. 2 ml of hexafluoro-2-propanol was dispensed into the 2 oz. glass bottle along with a 25 mL of o-cresol/dichloromethane (75%/25% in volume ratio) mixture and the bottle was capped. The bottle was placed in an ultrasonic sonicator until the samples are completely dissolved. It is observed that samples of higher molecular weight species of polyesters required longer dissolution time compared to the lower molecular weight species. Once the dissolution was complete, samples were transferred to a disposable 150 mL polypropylene beaker. 25 ml of o-cresol/dichloromethane (75%/25% in volume ratio) mixture was added to the 2 oz. bottle to completely transfer the contents. 20 mL of dichloromethane in two aliquots is used further to rinse the bottle and completely transfer without loss to the disposable polypropylene beaker. No precipitation was observed during dilution with dichloromethane. To this 200 pL of the 500 mM sodium trifluoroacetate solution in methanol is added and mixed well. To this solution was pipetted 5 drops of bromophenol blue indicator solution. (The bromophenol blue indicator is prepared by dissolving approx. 0.25 g bromophenol blue in 50 mL methanol). The titration is performed potentiometrically or colorimetrically. The probe used in this colorimetric titration was an Optrode colorimetric probe (Metrohm), which monitors color change for equivalence point determination. The best results were obtained using 610 nm wavelength setting on the probe. Metrohm automated titration equipment was attached to a sample changer system (Metrohm USA, Riverview, Fla.) in this example.

[0236] The results are shown in the following table, where the comparative examples are representative of commercial PBT grades.

TABLE-US-00002 PBT CEG (mmol/Kg) C. Ex. 1 7 C. Ex. 2 7 C. Ex. 3 20 C. Ex. 4 41 Process Sample 1 99 Process Sample 2 164

Example 1

[0237] A series of experiments 1.1-1.10 were performed in a continuously operating process according to the conditions set out here below.

[0238] BDO and PTA were mixed in a mole ratio as presented in table 1A in a slurry paste vessel to form a mixture. The temperature, pressure and residence time in the mixer are presented in table 1A.

TABLE-US-00003 TABLE 1A conditions slurry paste vessel and esterification section of tower reactor Example 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 Mole ratio BDO/PTA in 1.43 1.43 1.43 1.44 1.43 1.43 1.42 1.41 1.35 1.32 mixer Temperature mixer (° C.) 80 80 79 80 80 80 80 81 79 81 Pressure mixer (bar) 1.03 1.03 1.04 1.03 1.04 1.04 1.04 1.04 1.04 1.04 Residence time mixer 3.2 3.0 2.7 3.0 2.8 3.1 3.4 3.7 3.0 3.9 (hours) Mole ratio BPD/PTA 2.92 2.87 2.75 2.87 2.74 2.90 2.69 3.23 2.55 2.43 entering tower First catalyst quantity 100 90 90 90 90 100 70 70 70 70 (ppm) Temperature esterification 245 244 246 244 246 243 247 245 244 244 (° C.) Treatment pressure (bar) 0.79 0.79 0.79 0.79 0.79 0.79 0.79 0.79 0.79 0.79 Residence time tower 1.46 1.46 1.28 1.45 1.31 1.44 1.65 1.59 1.45 1.92 reactor (hours)

[0239] The slurry paste from the mixer was mixed with additional BDO such that the BDO:PTA ratio was as listed in table 1B before being transferred to a tower reactor where an esterification process occurred in the lower section of the reactor. A first quantity of TPT catalyst as presented in table 1B was supplied in the esterification section. The treatment temperatures, pressure and residence time in the esterification section are listed in table 1B.

[0240] The product from the esterification section was transferred continuously to the cascade post-esterification part of the tower reactor which consisted of four different cascades. The temperature and residence time in each cascade are listed in table 1B. The pressure in the top cascade and the pressure in the fourth-from-top cascade are listed in table 1B. The pressure of the post-esterification section was gradually decreased from the top cascade to the bottom cascade. In the fourth from top cascade, a second quantity of TPT catalyst diluted with 0.2 mole of BDO as listed in table 1B was supplied. The IV and CEG of the product at the end of the post-esterification section are listed in table 1B.

TABLE-US-00004 TABLE 1B conditions cascade post-esterification section tower reactor and product properties Example 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 Temperature top cascade 241 241 239 240 239 241 242 242 242 244 (° C.) Residence time top 14 14 12 13 12 13 15 15 14 18 cascade (min) Temp. second from top 242 242 240 241 240 242 242 243 243 244 cascade (° C.) Res. time second from top 10 10 8 9 8 10 10 11 10 13 cascade (min) Temp. third from top 242 242 244 244 244 244 245 245 246 245 cascade (° C.) Res. time third from top 10 10 8 9 8 9 10 10 10 13 cascade (min) Temp. fourth from top 245 245 247 245 247 245 246 246 246 245 cascade (° C.) Res. time fourth from top 15 14 16 13 15 14 18 17 17 17 cascade (min) Pressure top cascade 0.30 0.28 0.29 0.28 0.29 0.31 0.28 0.29 0.28 0.26 (bar) Pressure fourth from top 0.22 0.23 0.23 0.22 0.22 0.23 0.22 0.23 0.25 0.22 cascade (bar) Second catalyst quantity 80 80 80 80 80 70 100 100 100 100 (ppm) IV of product from post- 0.14 0.15 0.15 0.14 0.14 0.14 0.14 0.14 0.15 esterification (dl/g) CEG of product from post- 25 22 35 22 35 31 20 25 21 28 esterification (mmol/kg)

[0241] The product from the post-esterification section was continuously supplied to the first continuously stirred tank reactor (CSTR 1). The melt temperature, pressure and residence time in CSTR 1 are listed in table 1C. The product from CSTR 1 was continuously supplied to a second continuously stirred tank reactor (CSTR 2). The melt temperature, pressure and residence time in CSTR 2 are listed in table 1C. The IV and CEG of the product leaving CSTR 2 are listed in table 1C.

[0242] The product from CSTR 2 was continuously transferred to a dual shafts ring reactor with independent revolutions per minute (rpm). The melt temperature, pressure and residence time in the ring reactor are listed in table 1C. Each of the two disc ring reactor shaft rotation rates was independently between 1 and 5 rpm. The IV and CEG of the resulting products are listed in table 1C.

TABLE-US-00005 TABLE 1C conditions CSTR's and ring reactor and product properties Example 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 Melt temp CSTR 1 (° C.) 240 240 242 240 242 242 241 241 241 240 Pressure CSTR 1 (mbar) 32 32 32 32 32 32 32 32 32 32 Residence time CSTR 1 38 41 27 41 28 40 49 48 48 60 (min) Melt temp CSTR 2 (° C.) 240 241 242 241 242 242 242 242 242 241 Pressure CSTR 2 (mbar) 27 27 27 27 27 27 27 27 27 27 Residence time CSTR 2 46 45 40 45 41 45 52 49 62 58 (min) IV of product from CSTR 0.27 0.24 0.25 0.24 0.25 0.26 0.26 0.26 0.25 0.28 2 (dl/g) CEG of product from 15 10 16 10 16 9 16 11 16 15 CSTR 2 (mmol/kg) Melt temp. ring reactor 239 239 240 241 240 240 240 240 240 240 (° C.) Pressure ring reactor 4.4 4.3 4.8 0.5 0.5 0.7 0.8 0.9 0.5 0.9 (mbar) Residence time ring 3.0 2.5 3.0 3.0 2.5 3.0 2.0 1.5 2.5 1.5 reactor (hours) IV of product from ring 0.70 0.70 0.69 1.14 1.17 1.03 0.98 0.97 1.07 0.87 reactor (dl/g) CEG of product from ring 33 27 34 43 45 36 33 32 37 33 reactor (mmol/kg)

Comparative Example 2

[0243] A series of experiments 2.1-2.3 were performed using a butylene terephthalate oligomer produced using dimethylterephthalate and butanediol, having an IV of 0.13 dl/g and a CEG of 7 mmol/kg. This oligomer, being a product of the post-esterification section of the PBT production process, was subjected to polycondensation via two CSTR's in series and a subsequent ring reactor similar to examples 1.1-1.10.

[0244] The oligomer was continuously supplied to the first continuously stirred tank reactor (CSTR 1). The melt temperature, pressure and residence time in CSTR 1 are listed in table 2.

[0245] The product from CSTR 1 was continuously supplied to a second continuously stirred tank reactor (CSTR 2). The melt temperature, pressure and residence time in CSTR 2 are listed in table 2. The IV and CEG of the product leaving CSTR 2 are listed in table 2.

[0246] The product from CSTR 2 was continuously transferred to a dual shafts ring reactor with independent revolutions per minute (rpm). The melt temperature, pressure and residence time in the ring reactor are listed in table 2. Each of the two disc ring reactor shaft rotation rates was independently between 1 and 5 rpm. The IV and CEG of the resulting products are listed in table 2.

TABLE-US-00006 TABLE 2 conditions CSTR's and ring reactor and product properties of comparative examples Example 2.1 2.2 2.3 Melt temp CSTR 1 (° C.) 230 230 230 Pressure CSTR 1 (mbar) 53 53 53 Residence time CSTR 1 (min) 40 40 40 Melt temp CSTR 2 (° C.) 240 240 240 Pressure CSTR 2 (mbar) 26 26 26 Residence time CSTR 2 (min) 40 40 40 IV of product from CSTR 2 0.30 0.30 0.30 (dl/g) CEG of product from CSTR 2 10 10 10 (mmol/kg) Melt temp. ring reactor (° C.) 239 242 242 Pressure ring reactor (mbar) 4 2.75 2.6 Residence time ring reactor 2.0 2.5 3.0 (hours) IV of product from ring reactor 0.78 0.96 1.15 (dl/g) CEG of product from ring 27 45 49 reactor (mmol/kg)

[0247] The above examples demonstrate that the process according to the current invention, wherein the conditions of the polycondensation section, in particular the lower pressure of the first CRST, allow for the production of PBT with desired high IV and desired low CEG using an oligomer produced based on PTA and butanediol having a higher CEG.