WO2009063483A2

WO2009063483A2 - Catalyst for the production of polyester

Info

Publication number: WO2009063483A2
Application number: PCT/IN2008/000457
Authority: WO
Inventors: Madhusudan Nadkarni Vikas; Shreeram Ashok Wadekar; Rajan Dubey; Sanjaya Kesarwani; Anil Kumar Satpathy
Original assignee: Reliance Industries Limited
Priority date: 2007-07-16
Filing date: 2008-07-16
Publication date: 2009-05-22
Also published as: WO2009063483A3

Abstract

The invention relates to a catalyst system for polyester synthesis, the catalyst system comprising at least 10 ppm of a group IV metal sulphonate and at least 50 ppm of antimony. The invention also relates to a process for polyester synthesis, to the polyester and to the articles prepared thereof.

Description

TITLE OF THE INVENTION

Catalyst for the production of polyester

TECHNICAL FIELD OF THE INVENTION:

The invention relates to a catalyst system comprising an antimony compound and a group IV metal sulphonate for the synthesis of polyester resins. The invention also relates to the process of polyester synthesis, to the polyester and to the articles prepared thereof .

BACKGROUND:

Polyesters such as polyethylene terephthalate (PET) are used in large quantities in the manufacture of textile fibers, packaging films and containers. Typically, such polyesters are synthesized by a catalysed two stage reaction. In the first stage, esterification reaction is carried out between a dicarboxylic acid and a polyol. The esterification reaction is followed by melt polymerization wherein the ester formed in the first stage undergoes polycondensation resulting in a polyester. Often the polyester obtained after melt polymerisation is further subjected to solid state polymerisation.

Conventionally, trivalent antimony compounds like antimony trioxide and its alcohol derivatives are used as ester polymerization catalysts. However, when used alone as the catalyst, the activity for polyester synthesis of antimony compounds is rather limited (Ben Duh, Polymer 43 (2002) 3147-3154). Lower catalyst activity would require longer residence times for synthesis of resins of desired molecular weight. This in turn affects the productivity, throughput and results in high production cost. There is a need for a catalyst system having improved activity for the synthesis of polyesters. DETAILED DESCRIPTION OF THE INVENTION:

Accordingly the invention provides a catalyst system comprising an antimony compound and a group IV metal sulphonate for the synthesis of polyester.

When used throughout this specification, the following terms have the meanings indicated:

The term "polyester", as used herein, is intended to include "copolyesters" and is understood to mean a synthetic polymer prepared by the polycondensation of one or more difunctional carboxylic acids with one or more difunctional hydroxyl compounds.

The term "low viscosity polyester", as used herein, is intended to mean polyester having intrinsic viscosity in the range of 0.2 dl/g to 0.6 dl/g.

In one embodiment, the invention provides a catalyst system for polyester synthesis, the catalyst system comprising at least 50 ppm of antimony wherein the antimony is present in the form of a compound and at least 10 ppm of a group IV metal sulphonate.

In another embodiment, the invention provides a catalyst system for polyester synthesis comprising antimony present in an amount ranging from 50 to 1500 ppm and a group IV metal sulphonate present in an amount ranging from 10 to 500 ppm, wherein the antimony is present in the form of a compound

In another embodiment, the invention provides a catalyst system for polyester synthesis comprising antimony present in an amount ranging from 50 to 1500 ppm and a group IV metal sulphonate present in an amount ranging from 10 to 500 ppm wherein the antimony is present in the form of a compound and the metal sulphonate is selected from tin methane sulphonate, titanium methane sulphonate, zirconium methane sulphonate and tin paratoluene sulphonate.

In another embodiment, the invention provides a process for synthesis of a polyester resin in the presence of catalyst system comprising antimony present in an amount ranging from 50 to 1500 ppm, the antimony being present in the form of a compound, and a group IV metal sulphonate present in an amount ranging from 10 to 500 ppm, the process comprising esterifying at least one organic dicarboxylic acid with a polyol at a temperature in the range of 250°C to 290°C to obtain a carboxylic acid ester and melt polymerizing the acid ester at a temperature in the range of 260°C to 300°C to obtain a low viscosity polyester;

In another embodiment the invention provides a polyester having an intrinsic viscosity in the range of 0.20 to 0.45 dl/g

In another embodiment the invention provides a polyester having an intrinsic viscosity in the range of 0.45 to 0.65 dl/g.

In another embodiment the invention provides a polyester having an intrinsic viscosity in the range of 0.70 to 1.20 dl/g.

In yet another embodiment the invention provides films, fibers, filaments and yarns prepared from the polyester.

In a further embodiment the invention provides a process for synthesis of a polyester resin in the presence of catalyst system comprising antimony present in an amount ranging from 50 to 1500 ppm wherein the antimony is present in the form of a compound and a group IV metal sulphonate present in an amount ranging from 10 to 500 ppm, the process comprising esterifying at least one dicarboxylic acid with a polyol at temperature in the range of 250°C to 290°C to obtain a carboxylic acid ester, melt polymerizing the acid ester at a temperature in the range of 260⁰C to 300°C to obtain a low viscosity polyester and reacting the low viscosity polyester in the solid state at a temperature in the range of 200 to 240⁰C to form a polyester having intrinsic viscosity in the range of 0.70 to 1.2 dl/g

In a still further embodiment the invention provides shaped articles prepared from the polyester

The invention provides a catalyst system comprising an antimony compound and a group IV metal sulphonate. The total metal content of the catalyst system is in the range of 10 ppm to 1000 ppm. Advantageously, the catalyst system has a metal content in the range of 100 to 400 ppm. Typically, an antimony compound in combination with tin methane sulphonate or tin para toluene sulphonate is used in the catalyst system.

The invention also provides a process for synthesis of polyester resins in the presence of the catalyst system. Usually the process is carried out in two stages, resulting in a low molecular weight polyester. In the first stage an organic dicarboxylic acid is reacted with polyol at around 250 to 290°C to obtain an acid ester. The organic dicarboxylic acid used in the esterification stage is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 4,4'-biphenyl dicarboxylic or any suitable dicarboxylic acids or derivatives thereof. The polyol used is selected from monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, 1 ,4-cyclohexane diol or any other suitable polyol. The first stage reaction results in carboxylic acid ester which is melt polymerise at around 260 to 300° C to obtain a low viscosity polyester. Typically the intrinsic viscosity of the polyester formed after melt polymerization is in the range of 0.2 dl/g to 0.65 dl/g. Depending upon the process conditions, the melt polymerization yields polyester having different intrinsic viscosities. In one aspect of the invention, a polyester having intrinsic viscosity of around 0.60 dl/g is obtained. The low viscosity polyesters can be crystalline, semicrystalline or amorphous. The low viscosity polyester is either used directly in the manufacture of films, fibers or filaments or is further polymerised in the solid state to form higher molecular weight polyester. After melt polymerization the low viscosity is either drained and cut into granular form or is passed through an orifice to form droplets on a steel conveyor belt of a particle former. The catalyst system is added at any stage during esterification or melt polymerization but before particle former stage or before solid state polymerization. The solid state polymerization is catalysed by the catalyst system used in the melt polymerization stage. The solid state polymerization usually results in polyester having intrinsic viscosity in the range of 0.70 to 1.20 dl/g.. The polyester may be linear or branched and may be a homo-polyester or contain co-monomers upto 10 wt%.

The catalyst system used in the process of the invention can be used either in the supported or unsupported form. The polyester resins synthesized by the process of the invention can be used for the manufacture articles such as preforms, molded parts, containers, fibers or filaments, films or sheets or technical yarn in various sizes and shapes. The polymerization process can be a continuous process or a batch process. The resin can also be combined with additives to impart I specific functional characteristics.

The invention is further illustrated by way of the following examples. In the examples, the melt polymerization synthesis of polyester resin having intrinsic viscosity around 0.26 dl/g is carried out at atmospheric pressure under nitrogen flow. Consequently, the reactivity or the catalyst activity is 5 measured in terms of the amount of nitrogen gas that flows into the reactor at a fixed nitrogen gas temperature. The lesser the requirement of the nitrogen gas the higher the catalyst activity and reactivity. The catalyst activity and reactivity during the synthesis of polyester resins of higher viscoity is measured in terms of the residence time. The lesser the residence time, the higher the activity. The residence time is measured as the time required to obtain a polyester of desired intrinsic viscosity from the beginning of polymerization reaction.

Example 1:

Synthesis of polyester having intrinsic viscosity (IV) of around 0.60 dl/g using the catalyst system comprising antimony trioxide and tin methane sulfonate.

Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1 :2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid, 290 ppm of antimony trioxide catalyst based on antimony and 25 ppm NaOH were added. The esterification reaction was carried out at 256°C. Tin methanesulfonate based on 50ppm as metallic tin was added at the end of esterification reaction. The oligomer obtained was then subjected to polycondensation in the presence of 25 ppm of cobalt as Cobalt acetate and 25 ppm of phosphorous as phosphoric acid at temperature of 285⁰C to obtain a prepolymer having IV up to 0.60 dl/g. After achieving the desired prepolymer IV, the polyester was drained and cut in a granular form for further processing.

Example 2:

I Synthesis of polyester having intrinsic viscosity of around 0.26 dl/g using the catalyst system comprising antimony trioxide and tin methanesulfonate

Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1 :2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid and 1.5 wt % diethylene glycol (DEG) were added. i The esterification reaction was carried out at 280⁰C. The oligomer obtained was polymerized at

290⁰C to raise the IV up to 0.26 dl/g. Tin methanesulfonate having 50 ppm as metallic tin was added during the melt polymerization. About 290 ppm of antimony was added as a catalyst and 15 ppm P was added as a thermal stabilizer. A static mixer was put after every injection nozzle for adding any suitable additive, co-monomer for better dispersion. The low IV prepolymer melt was then passed through the 1.5 mm diameter orifice to form droplets on a continuous moving steel belt of particle former. These droplets were then crystallized on the particle former maintained at a temperature between 110 to 160⁰C and then collected for carrying out solid-state polymerization.

Example 3:

Synthesis of polyester having intrinsic viscosity of around 0.6 dl/g using antimony trioxide catalyst

Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1 :2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid, Antimony trioxide catalyst containing 290 ppm antimony and 25 ppm of sodium hydroxide were added. The esterification reaction was carried out at 256°C. The oligomer obtained was then subjected to polycondensation in the presence of Cobalt acetate containing 25 ppm of cobalt and phosphoric acid containing 25 ppm of phosphorous at temperature of 285°C to obtained a prepolymer having IV up to 0.6 dl/g. This prepolymer was considered as "Control" for the prepolymer prepared according to Example 1. After achieving desired prepolymer IV, the polyester was drained and cut in a granular form for further processing. )

Example 4:

Synthesis of polyester having intrinsic viscosity of around 0.26 dl/g using antimony trioxide catalyst

5 Purified terephthalic acid and monoethylene glycol were charged in 1 :2 molar ratio. To the above reaction mixture, 1.5wt % Isophthalic acid and 1.5 wt % diethylene glycol were added. The esterification reaction was carried out at 280⁰C. The oligomer obtained was polymerized at 290°C to raise the IV up to 0.26 dl/g. About 290ppm of antimony was added as a catalyst and 15 ppm Phosphorous was added as a thermal stabilizer. A static mixer was put after every injection nozzle for adding any suitable additive, co-monomer for better dispersion. The low IV prepolymer melt was then passed through the 1.5 mm diameter orifice to form droplets on a continuous moving steel belt of particle former. These droplets were then crystallized on the particle former maintained at a temperature between 110 to 160°C and then collected for carrying out solid-state polymerization. This prepolymer particles was considered as "Control" for the prepolymer particles prepared according to Example 2.

Example 5:

Comparative study of the activity of the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide catalyst for solid state polymerization of low viscosity polymer formed in examples 1 and 3

Amorphous chips obtained in the example 1 & 3 were precrystallized in a tumbler dryer at a temperature of usually 100 to 200°C for a period of two hours. These precrystallized chips desirably have 20 to 40 % crystallinity. These chips were then used as a precurser of solid-state polymerization. 20kg Crystallized prepolymer chips were subjected to solid-state polymerization at nitrogen gas temperature of 210⁰C. Samples were drawn every hour to monitor IV rise for each recipe. After achieving desired IV, the reaction was terminated and polymer was drained and collected. Example 6:

Comparative study of the activity of the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide catalyst during solid state polymerization of low viscosity polymer formed in examples 2 and 4

Crystalline prepolymer having IV of 0.26 dl/g obtained in the example 2 and 4, was solid-state polymerized under inert atmosphere to raise the IV up to 0.76 dl/g. The solid-state polymerization reaction was carried out at 235⁰C of nitrogen gas temperature. After achieving desired IV, the reaction terminated and polymer drained and collected.

Example 7: Manufacture of preforms and bottles

Resin produced by SSP process was used for producing preforms using two cavity Arburg injection moulding machine (Model: Allrounder 420C). Before moulding, resins were dried for 6 hrs at 175°C in a dryer. Preform weight was 48g. Processing temperatures were in the range of 280 - 300°C and the cycle time was 34.5 seconds. These preforms were then used for producing bottles having volume of 1.5L. Bottles were produced using SIDEL SBOl single cavity blow moulding machine. Blowing temperature was maintained at 105⁰C.

In table 1, the melt polymersation (polycondensation) activity using the catalyst system of the invention is compared with that using antimony trioxide alone as the catalyst. Table 1 : Comparison of activity using the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide alone as the catalyst during polycondensation of ester to achieve an intrinsic viscosity of 0.6 dl/g

From Table 1, it is clear that the time required for melt polymerization to achieve a target IV of 0.6 dl/g is substantially less for the catalyst system of the invention (catalyst system of Example 1). In other words the melt polymerization rate is significantly improved with the catalyst system of the invention.

Table 2 compares the activity of the catalyst system of the invention with antimony trioxide catalyst during melt polymerization to obtain polyester having intrinsic viscosity of 0.26 dl/g.

Table 2: Comparison of activity using the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide alone as the catalyst during polycondensation of ester to achieve an intrinsic viscosity of 0.26 dl/g

From Table 2 it is clear that in the experiment (experiment No 1) using the catalyst system of the invention, the nitrogen gas flow in the column reactor is lowered as compared to the nitrogen gas flow in the reactor of experiment No 2 that uses antimony trioxide alone as the catalyst, The lowering of nitrogen gas flow in the reactor is indicative of the increase in solid state polymerization rate.

In Table 3, the solid state polymerization activity using catalyst system of the invention is compared with that using antimony trioxide alone as the catalyst. Table 3 : Comparison of activity using the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide catalyst during solid state polymerization of low viscosity polymers formed in examples 1 and 3

From table 3 it is clear that by using the catalyst system (antimony trioxide and tin methane sulphonate) of the invention, the residence time for solid state polymerization to obtain polyester of intrinsic viscosity 0.920 dl/g is lowered.

In table 4, the solid state polymerization activity using the catalyst system of the invention is compared with that using antimony trioxide alone as the catalyst.

Table 4 : Comparison of activity using the catalyst system comprising antimony trioxide and tin methane sulphonate with antimony trioxide catalyst during solid state polymerization of low viscosity polymers formed in examples 2 and 4

When antimony trioxide alone is used as the catalyst, a residence time of 16 hours as required to obtain a polyester having intrinsic viscosity of 0.764 dl/g. In comparison, polyester having higher intrinsic viscosity (0.778 dl/g) was obtained at a lesser residence time (9 hours) using the catalyst system of the invention.

As evident from the foregoing, the catalyst system of the invention has improved activity that enables synthesis of polyester with high productivity and throughput. Thus the synthesis becomes more efficient and cost effective. Moreover, due to the improved catalyst activity and to the consequent increase in productivity the reaction temperatures can be kept low to avoid unwanted side reactions.

The above description is illustrative only and is not limiting. The present invention is defined by the claims that follow and their full range of equivalents.

Claims

CLAIMS :

1. A catalyst system for polyester synthesis, the catalyst system comprising at least 10 ppm of a group IV metal sulphonate and at least 50 ppm of antimony wherein the antimony is present in the form of a compound

2. The catalyst system as claimed in claim 1 wherein the antimony is present in an amount ranging from 50 to 1500 ppm and the metal sulphonate is present in an amount ranging from 10 to 500 ppm.

3. The catalyst system as claimed in claim 1 wherein the metal sulphonate is selected from tin methane sulphonate, titanium methane sulphonate, zirconium methane sulphonate and tin paratoluene sulphonate.

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4. A process for synthesis of a polyester resin in the presence of catalyst system as claimed any one of the claims 1 to 3, the process comprising esterifying at least one dicarboxylic acid or derivatives thereof with a polyol at a temperature in the range of 250°C to 290°C to obtain a carboxylic acid ester and melt polymerizing the acid ester at a temperature in the range of 26O⁰C to 300°C to obtain a low viscosity polyester.

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5. The process as claimed in claim 4 wherein the dicarboxylic acid is terephthalic acid and the polyol is ethylene glycol.

6. A polyester having an intrinsic viscosity in the range of 0.20 to 0.45 dl/g synthesized by the process as claimed in claim 4.

7. A polyester having an intrinsic viscosity in the range of 0.45 to 0.65 dl/g synthesized by the process as claimed in claim 4.

8. The process as claimed in claim 4 further comprising reacting the low viscosity polyester in the solid state at a temperature in the range of 200 to 240⁰C to form a polyester having intrinsic viscosity in the range of 0.70 to 1.20 dl/g

9. A polyester having intrinsic viscosity in the range of 0.70 to 1.20 dl/g prepared by the process as claimed in claim 8.

10. j, Films, fibers, filaments and yarns prepared from the polyester as claimed in any one of the claims 7 or 9

11. Shaped articles prepared from the polyester as claimed in claim 9.