Process for the production of thermoplastic polyester

Abstract

The present invention relates to a process for the production of a thermoplastic polyester using a reaction mixture comprising a dicarboxylic acid having a melting temperature of ≥200° C. wherein the dicarboxylic acid is introduced to the process in the form of particles having an average particle diameter of ≥100 μm. Such process results in a reduction of the polymerisation time. Furthermore, it allows for the production of thermoplastic polyesters having a desired balance of intrinsic viscosity and carboxylic end group content at a reduced polymerisation time.

Claims

1. Process for the production of a thermoplastic polyester using a reaction mixture comprising a dicarboxylic acid having a melting temperature of ≥200° C. wherein the dicarboxylic acid is introduced to the process in the form of particles having an average particle diameter of ≥100 μm; wherein the reaction mixture further comprising 1,4-butanediol.

2. Process according to claim 1 wherein the dicarboxylic acid particles have an average particle diameter of ≤200 μm.

3. Process according to claim 1 wherein a quantity of a tetra(C1-C8) titanate is used as catalyst.

4. Process according to claim 3 wherein the reaction mixture comprises 100-300 ppm of the catalyst.

5. Process according to claim 3, wherein the catalyst is tetraisopropyl titanate.

6. Process according to claim 1, wherein the dicarboxylic acid comprises a cyclic moiety.

7. Process according to claim 1 wherein the dicarboxylic acid is selected from isophthalic acid, terepthalic acid, furandicarboxylic acid, napthalenedicarboxylic acid, or combinations thereof.

8. Process according to claim 1 wherein the reaction mixture further comprises an aliphatic dicarboxylic acid selected from succinic acid, adipic acid, suberic acid, sebacic acid, or combinations thereof.

9. Process according to claim 1, wherein the reaction mixture comprises ≥95.0 wt % of a dicarboxylic acid selected from terephthalic, furandicarboxylic acid, or combinations thereof, with regard to the total weight of dicarboxylic acid present in the reaction mixture.

10. Process according to claim 1 wherein the thermoplastic polyester comprises ≥95.0 wt % of polymeric units derived from terephthalic acid and the 1,4-butanediol.

11. Process according to claim 1 comprising the following steps in this order: a. introducing a quantity of the dicarboxylic acid particles into a reactor vessel; b. introducing a quantity of the 1,4-butanediol into the reaction vessel; and c. introducing a quantity of a catalyst for the production of polyester into the reaction vessel.

12. Process according to claim 1 wherein the thermoplastic polyester is a poly(butylene terephthalate) comprising ≥95 wt % of units derived from terephthalic acid and 1,4-butanediol.

13. Process according to claim 1 wherein the dicarboxylic acid particles have an average particle diameter of ≥110 μm.

14. Process according to claim 1 wherein the dicarboxylic acid particles have an average particle diameter of 140 to 300 μm.

15. Process according to claim 1 wherein the 1,4-butanediol and thermoplastic polyester are combined in a molar ratio of 6:1 to 2:1.

16. Process for the production of a thermoplastic polyester using a reaction mixture; wherein the reaction mixture comprises terephthalic acid in the form of particles having an average particle diameter of 110 μm to 300 μm; 1,4-butanediol; wherein a molar ratio of the 1,4-butanediol to the terephthalic acid is 6:1 to 2:1; and a catalyst comprising a tetra(C1-C8) titanate.

Description

(1) The invention will now be illustrated by the following non-limiting examples.

(2) Preparation of Thermoplastic Polyesters

(3) In a 500 ml 3-necked round bottom flask, equipped with a condenser and a vacuum output, PBT polymers were prepared according to the process of the present invention. The flask was immersed in an oil bath which temperature was controlled by a Camile system.

(4) A reaction mixture of 74.8 g of 1,4-butanediol and 121.7 g of terephthalic acid flakes were introduced into the flask, equipped with mechanical stirrer and torque reader. The oil temperature was set to 240° C. after 10 minutes, 180 ppm of catalyst with regard to the total weight of the 1,4-butanediol and the terephthalic acid was assed to the flask. The catalyst was tetraisopropyl titanate. The temperature of the reaction mixture was maintained at 240° C. while stirring at 260 rpm under nitrogen atmosphere. An esterification reaction of the 1,4-butanediol and the terephthalic acid was performed at atmospheric pressure. When the reaction mixture reached its clearing point, i.e. the point where visual observation showed the reaction mixture to become a transparent liquid, the residence time was recorded. This marked the completion of the esterification stage of the polymerisation reaction.

(5) The polymerisation reaction was initiated by reduction of the pressure in the flask to 0.2 mbar. The increase in torque at given speed of the mechanical stirrer was observed. The time needed to reach a particular torque level at given speed was determined. The increase in torque is an indicator for the polymer chain build-up that occurs during the polymerisation reaction. The higher the torque, the higher the degree of polymerisation that is reached. The faster a particular torque level is reached, the faster the polymerisation reaction is performed.

(6) The polymerisation was performed stepwise: first, the stirrer was set to 260 rpm. When a torque level of 3.40 N.Math.m was reached, the residence time was registered and the stirrer speed decreased to 130 rpm. This reduced torque of the stirrer. When again after polymer build-up a torque of 3.40 N.Math.m was reached, the residence time was registered and the stirrer speed further decreased to 65 rpm. Again when after further polymer build-up a torque of 3.40 N.Math.m was reached, the residence time was registered and the stirrer speed further reduced to 32 rpm. Again when a torque of 3.40 N.Math.m was reached, the residence time was registered. The obtained product was cooled to obtain poly(butylene terephthalate) polymer samples.

(7) In the below table, the total residence time to reach a particular torque level at given stirrer speed is presented using different size terephthalic acid flakes.

(8) TABLE-US-00001 TABLE I polymerisation times Experiment 1 2 3 TPA size 74 μm 120 μm 141 μm Esterification time 35 33 28 Time to 3.40@260 76 63 45 Time to 3.40@130 94 70 48 Time to 3.40@65 100 75 51 Time to 3.40@32 107 81 56

(9) In the above table, the TPA size is the average particle size of the terephthalic acid flakes introduced to the polymerisation reaction. The esterification time is the time between the addition of the catalyst to the reaction flask and the observance of the clearing point. The time to 30@260 is the time between the addition of the catalyst and the observance of a torque of 3.40 N.Math.m at 260 rpm stirrer speed; equally, time to 3.40@130, 3.40@65 and 3.40@32 is the time between addition of the catalyst and the observance of a torque of 3.40 N.Math.m at 130 rpm, 65 rpm and 32 rpm, respectively.

(10) The poly(butylene terephthalate) polymer samples obtained from the reaction were subjected to material characterisations to determine the intrinsic viscosity and the carboxylic end group content.

(11) The intrinsic viscosity was determined in accordance with ASTM D2857-95 (2007) using an automatic Viscotek Microlab 500 Relative Viscometer Y501. 0.200 g of a sample was dissolved in a 60/40 vol/vol % solution of phenol and 1,1,2,2-tetrachloroethane. Intrinsic viscosity was expressed in dl/g.

(12) The carboxylic end group content of the samples was determined in accordance with ASTM D7409-15 using a Metrohm-Autotitrator Titrando 907, using a 800 Dosino 2 ml dosing unit and a 814 USB sample processor. All the units are controlled from a PC using Tiamo 2.0 Full version. 1.5-2.0 g of sample was fully dissolved in 50 ml of o-cresol at 80° C. After dissolving, the sample was cooled to room temperature and 50 ml of o-cresol and 1 ml of water were added. The blank was prepared along the same procedure. The electrodes and titrant dosing were dipped into the sample solution and the titration was started. The equivalence point of the titration was used for the calculation of the carboxylic end group value according to the equation:
CEG=(Q.sub.S−Q.sub.B)*N.sub.NaOH*1000

(13) wherein:

(14) CEG=the carboxylic end group content in mmol/kg;

(15) Q.sub.S=the titrated quantity of the sample in ml;

(16) Q.sub.B=the titrated quantity of the blank in ml; and

(17) N.sub.NaOH=the concentration of NaOH in mol/l.

(18) The intrinsic viscosity (I.V.) and the carboxylic end group content (CEG) of the samples are presented in table II:

(19) TABLE-US-00002 TABLE II material properties of sample poly(butylene terephthalates) Experiment 1 2 3 I.V. 1.05 1.10 1.11 CEG 21 29 28

(20) This demonstrates that the intrinsic viscosity and the carboxylic end group content of the sample polymers differ only marginally and all comply to the desired specifications of the poly(butylene terephthalate) products that are desired to be produced.

(21) By comparing the results from the polymerisation time data in table 2, it is demonstrated that the process according to the present invention, in which terephthalic acid having an average particle size of ≥100 μm is used, results in a faster process whilst still, as demonstrated by the results in table 3, resulting in a desired product.