CONTINUOUS PROCESS FOR PRODUCING POLY(TRIMETHYLENE TEREPHTHALATE) CONTAINING LOW LEVELS OF BY-PRODUCTS

Abstract

The present invention relates to a continuous process for producing poly(trimethylene terephthalate). According to the process of the present invention, it is possible to continuously produce poly(trimethylene terephthalate) containing low levels of toxic by-products such as acrolein and ally alcohol without additional additives.

Claims

1. A continuous process for producing poly(trimethylene terephthalate), comprising the steps of: forming a first esterification product by providing a raw material mixture including 1,3-propanediol and terephthalic acid or dimethyl terephthalate to a first esterification reactor, and then pressurizing and heating under a non-catalytic condition; forming a second esterification product by providing the first esterification product to a second esterification reactor and heating under non-catalytic and normal pressure conditions; forming a prepolymer of poly(trimethylene terephthalate) by providing the second esterification product to a first polymerization reactor and carrying out polycondensation; and forming a high molecular weight poly(trimethylene terephthalate) by providing the prepolymer together with a catalyst to a second polymerization reactor and carrying out polycondensation.

2. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the raw material mixture contains 1.0 to 1.5 mol of 1,3-propanediol with respect to 1 mol of terephthalic acid or dimethyl terephthalate.

3. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the formation of the first esterification product is carried out under a pressure of 1 to 4 kgf/cm.sup.2 and a temperature of 230 to 250° C.

4. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the formation of the second esterification product is carried out under normal pressure and a temperature of 240 to 260° C.

5. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the first and second esterification products each includes bis(3-hydroxypropyl)terephthalate, low molecular weight polyesters of 1,3-propanediol and terephthalic acid or dimethyl terephthalate, or a mixture thereof.

6. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the first polymerization reactor is maintained at a temperature of 230 to 270° C. and a pressure of 100 to 300 mmHg.

7. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the second polymerization reactor is maintained at a temperature of 230 to 270° C. and a pressure of 10 to 200 mmHg.

8. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the polycondensation reaction is further carried out by providing a stream discharged from the second polymerization reactor to the third polymerization reactor.

9. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the catalyst provided to the second polymerization reactor is an organic or inorganic compound including one or more active metals selected from the group consisting of titanium and tin.

10. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the catalyst provided to the second polymerization reactor is one or more compounds selected from the group consisting of tetraisopropyl titanate, tetrabutyl titanate, and dibutyltin oxide.

11. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the catalyst provided to the second polymerization reactor is added so that 20 to 250 ppm of the active metals are included based on the weight of the final polymer

12. The continuous process for producing poly(trimethylene terephthalate) according to claim 1, wherein the high molecular weight poly(trimethylene terephthalate) has an intrinsic viscosity of 0.8 to 1.2 dl/g or a weight average molecular weight of 70,000 to 130,000.

13. Poly(trimethylene terephthalate) produced by the process according to claim 1.

14. Poly(trimethylene terephthalate) according to claim 13, including 2.0 mol % or less of dipropylene glycol ether

15. Poly(trimethylene terephthalate) according to claim 13, including 20 ppm or less of acrolein and 10 ppm or less of allyl alcohol.

16. Poly(trimethylene terephthalate) according to claim 13, having a melting point of 227° C. or higher.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0075] FIG. 1 schematically illustrates an apparatus which can be used in the preparation method according to one embodiment of the invention.

EXPLANATION OF REFERENCE CHARACTERS

[0076] S: Slurry melting tank

[0077] E1, E2: Transesterification reactor

[0078] P1, P2, P3: Polymerization reactor

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0079] Hereinafter, preferable examples are presented to aid in understanding of the present invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited to or by them.

EXAMPLE 1

[0080] A raw material mixture of a homogeneous slurry phase was prepared by mixing 1,3-propanediol and terephthalic acid as raw materials in a slurry melting tank (S). At this time, about 1.3 mol of 1,3-propanediol per 1 mol of terephthalic acid was included in the raw material mixture.

[0081] The prepared raw material mixture was transferred from the slurry melting tank (S) to the first esterification reactor (E1), and the esterification was carried out under a pressure of about 2 kgf/cm.sup.2 and a temperature of about 245° C. As the esterification proceeded, a mixture of bis(3-hydroxypropyl)terephthalate and oligomers was formed.

[0082] Then, a stream discharged from the first esterification reactor (E1) was transferred to the second esterification reactor (E2), and the esterification was continuously carried out under a temperature of about 255° C. and normal pressure. At this time, gaseous by-product streams respectively generated at the first esterification reactor (E1) and the second esterification reactor (E2) were continuously evaporated and eliminated.

[0083] Subsequently, the esterification product was transferred to the first polymerization reactor (P1), and the polycondensation reaction was carried out while maintaining a temperature of about 255° C. and a reduced pressure condition of 100 to 200 mmHg. The stream discharged from the first polymerization reactor (P1) was provided to the second polymerization reactor (P2) after adding a catalyst thereto. At this time, tetraisopropyl titanate was used as the catalyst, and the content thereof was controlled so that about 180 ppm of titanium atoms were included therein based on the weight of the final polymer.

[0084] The polycondensation at the second polymerization reactor (P2) was carried out while maintaining a temperature of about 260° C. and a reduced pressure condition of 10 to 100 mmHg, and the viscosity of the reaction product gradually increased. The stream discharged from the second polymerization reactor (P2) was transferred to the third polymerization reactor (P3), and the polycondensation was carried out while maintaining a temperature of about 260° C. and a reduced pressure condition of 1 mmHg or less.

[0085] PTT (intrinsic viscosity: about 0.94 dl/g, weight average molecular weight: 98,900) was obtained by the above method, and the final polymer was obtained in a pelletized solid form.

EXAMPLE 2

[0086] PTT (intrinsic viscosity: about 0.95 dl/g, weight average molecular weight: 99,900) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 250° C. under normal pressure.

COMPARATIVE EXAMPLE 1

[0087] PTT (intrinsic viscosity: about 0.96 dl/g, weight average molecular weight: 101,300) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 255° C. under a pressure of about 1.5 kgf/cm.sup.2.

COMPARATIVE EXAMPLE 2

[0088] PTT (intrinsic viscosity: about 0.96 dl/g, weight average molecular weight: 101,500) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 255° C. under a pressure of about 2.0 kgf/cm.sup.2.

COMPARATIVE EXAMPLE 3

[0089] PTT (intrinsic viscosity: about 0.95 dl/g, weight average molecular weight: 99,800) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 255° C. under a pressure of about 2.5 kgf/cm.sup.2.

COMPARATIVE EXAMPLE 4

[0090] PTT (intrinsic viscosity: about 0.94 dl/g, weight average molecular weight: 94,000) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 255° C. under a pressure of about 3.0 kgf/cm.sup.2.

COMPARATIVE EXAMPLE 5

[0091] PTT (intrinsic viscosity: about 0.95 dl/g, weight average molecular weight: 99,600) was obtained in the same manner as in Example 1, except that the second esterification reactor (E2) was operated at a temperature of about 250° C. under a pressure of about 2 kgf/cm.sup.2.

EXPERIMENTAL EXAMPLES

[0092] The physical properties of PTT prepared by the examples and comparative examples were tested by the following methods, and the results are listed in Tables 1 and 2 below.

[0093] 1) Content of acrolein and allyl alcohol: 0.5 g of a powdery specimen prepared by cryo-milling was collected and sealed in a glass bottle, and the content of acrolein and allyl alcohol was quantitatively analyzed through gas chromatography after heating the same at 150° C. for 30 min.

[0094] 2) Intrinsic viscosity (IV): After dissolving PTT in o-chlorophenol to have a concentration of 1.2 g/dl, the intrinsic viscosity was measured at 35° C. by using an Ubbelohde viscometer.

[0095] 3) Quantification of dipropylene glycol ether (DPG): Confirmed by NMR analysis (converting the average value of peaks at 2.2 ppm, 3.8 ppm, and 4.5 ppm as analyzed by 600 MHz H NMR to mol %).

[0096] 4) Melting point (Tm): The sample was filled in an aluminum pan using a differential scanning calorimeter (DSC), heated up to 280° C. at 10° C./min, held at 280° C. for 2 min, and then cooled at −150° C./min. Then, when the temperature was raised up to 280° C. at 10° C./min, the temperature at the position of the apex of the endothermic curve was defined as the melting point (Tm).

TABLE-US-00001 TABLE 1 E2 reactor E2 reactor DPG content Temperature Pressure in E2 product (° C.) (kgf/cm.sup.2) (mol %) Example 1 255 1.0 1.2 Example 2 250 1.0 1.1 Comparative 255 1.5 2.0 Example 1 Comparative 255 2.0 2.0 Example 2 Comparative 255 2.5 2.1 Example 3 Comparative 255 3.0 2.3 Example 4 Comparative 250 2.0 2.3 Example 5

TABLE-US-00002 TABLE 2 Allyl DPG Acrolein alcohol content in content in content in Polymer Polymer polymer polymer polymer IV Tm (mol %) (ppm) (ppm) (dl/g) (° C.) Example 1 1.6 15 8 0.94 227.2 Example 2 1.5 14 9 0.95 227.3 Comparative 2.9 30 10 0.96 225.6 Example 1 Comparative 2.4 25 9 0.95 226.2 Example 2 Comparative 2.4 32 10 0.94 226.2 Example 3 Comparative 2.6 28 10 0.94 226.0 Example 4 Comparative 2.7 27 9 0.95 225.9 Example 5

[0097] As shown in Tables 1 and 2, it was confirmed that the content of dipropylene glycol ether (DPG) in the esterification product (E2 product) formed by the processes of the examples was as low as 1.2 mol % or less, and the content of DPG in the final polymer was as low as 1.6 mol % or less.

[0098] In particular, it was confirmed that PTT formed by the processes of the examples contained low levels of dipropylene glycol ether (DPG), causing less reduction in the melting point (Tm), and had a melting point of 227° C. or higher. In addition, PTT formed by the processes of the examples contained 15 ppm or less of acrolein and 9 ppm or less of allyl alcohol, and showed low levels of by-products compared with PTT according to the comparative examples.