Continuous process for making polybutylene terephthalate using purified terephthalic acid and 1,4-butane diol

Abstract

A device for making polybutylene terephthalate includes (1) a slurry paste vessel; (2) a tower reactor to which a mixture of 1,4-butane diol and terephthalic acid from vessel (1) is supplied, the tower reactor having a plurality of reactor zones wherein the lower third of the tower reactor is in the form of a hydrocyclone with attached heat exchanger, and the hydrocyclone has a supply line from vessel (1), the hydrocyclone being connected to the top side of the tower reactor; (3) a first continuously stirred tank reactor to which the product from tower reactor (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 stirred tank reactor (3) or (4), is supplied; and (6) a pelletizer where the product from dual shaft ring reactor (5) is continuously fed and pelletized.

Claims

1. A device for operating a continuous process for preparing polybutylene terephthalate, the device 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 mixture from the slurry paste vessel (1) is supplied for at least one of esterification or transesterification, the tower reactor having a plurality of reactor zones configured that a 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 slurry paste vessel (1), the hydrocyclone being connected to a top side of the tower reactor, the top side of the tower reactor being configured in the form of a downflow cascade, wherein the following conditions are maintained: (b1) the mixture from the slurry paste vessel (1) is subjected to an 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 (b1) is transferred continuously into a pipe stretch while optionally a quantity of BDO is supplied; (b3) the product of (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; (3) a first continuously stirred tank reactor to which the product from (b3) is supplied, wherein the product from (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; (4) an optional second continuously stirred tank reactor to which the product from the first continuously stirred tank reactor (3) is supplied, wherein the product from the first continuously stirred tank reactor (3) 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; (5) a dual shaft ring reactor to which the product from the first continuously stirred tank reactor (3) or, where the second continuously stirred tank reactor (4) is used, the product from the second continuously stirred tank reactor (4), is supplied, wherein the product from the tank reactor (3) or the product from the tank reactor (4) 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; and (6) a pelletizer where the product from the dual shaft ring reactor (5) is continuously fed and pelletized.

Description

EXAMPLES

(1) 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.

(2) Example Alternative Process for Determining CEG Concentration

(3) Complete dissolution of the polymer sample is critical in order to obtain reproducible and accurate values.

(4) 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.

(5) 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 L 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.

(6) The results are shown in the following table, where the comparative examples are representative of commercial PBT grades.

(7) 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

(8) A series of experiments 1.1-1.10 were performed in a continuously operating process according to the conditions set out here below.

(9) 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.

(10) 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 mixer 1.43 1.43 1.43 1.44 1.43 1.43 1.42 1.41 1.35 1.32 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 (hours) 3.2 3.0 2.7 3.0 2.8 3.1 3.4 3.7 3.0 3.9 Mole ratio BPD/PTA entering 2.92 2.87 2.75 2.87 2.74 2.90 2.69 3.23 2.55 2.43 tower First catalyst quantity (ppm) 100 90 90 90 90 100 70 70 70 70 Temperature esterification ( C.) 245 244 246 244 246 243 247 245 244 244 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 reactor 1.46 1.46 1.28 1.45 1.31 1.44 1.65 1.59 1.45 1.92 (hours)

(11) 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.

(12) 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.

(13) 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 ( C.) 241 241 239 240 239 241 242 242 242 244 Residence time top cascade 14 14 12 13 12 13 15 15 14 18 (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 cascade 242 242 244 244 244 244 245 245 246 245 ( C.) Res. time third from top 10 10 8 9 8 9 10 10 10 13 cascade (min) Temp. fourth from top cascade 245 245 247 245 247 245 246 246 246 245 ( C.) Res. time fourth from top 15 14 16 13 15 14 18 17 17 17 cascade (min) Pressure top cascade (bar) 0.30 0.28 0.29 0.28 0.29 0.31 0.28 0.29 0.28 0.26 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 (ppm) 80 80 80 80 80 70 100 100 100 100 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)

(14) 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.

(15) 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.

(16) 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 (min) 38 41 27 41 28 40 49 48 48 60 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 (min) 46 45 40 45 41 45 52 49 62 58 IV of product from CSTR 2 0.27 0.24 0.25 0.24 0.25 0.26 0.26 0.26 0.25 0.28 (dl/g) CEG of product from CSTR 2 15 10 16 10 16 9 16 11 16 15 (mmol/kg) Melt temp. ring reactor ( C.) 239 239 240 241 240 240 240 240 240 240 Pressure ring reactor (mbar) 4.4 4.3 4.8 0.5 0.5 0.7 0.8 0.9 0.5 0.9 Residence time ring reactor 3.0 2.5 3.0 3.0 2.5 3.0 2.0 1.5 2.5 1.5 (hours) IV of product from ring reactor 0.70 0.70 0.69 1.14 1.17 1.03 0.98 0.97 1.07 0.87 (dl/g) CEG of product from ring 33 27 34 43 45 36 33 32 37 33 reactor (mmol/kg)

Comparative Example 2

(17) 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.

(18) 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. 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.

(19) 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.

(20) 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 0.78 0.96 1.15 reactor (dl/g) CEG of product from ring 27 45 49 reactor (mmol/kg)

(21) 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.