WO2009087651A2

WO2009087651A2 - An improved solid-state polymerization process for the production of high molecular weight polyethylene terephthalate

Info

Publication number: WO2009087651A2
Application number: PCT/IN2008/000678
Authority: WO
Inventors: Vikas Madhusudan Nadkarni; Shreeram Ashok Wadekar; Srinivasacharya Ramacharya Ayodhya; Pushap Sudan; Anil Kumar Satpathy
Original assignee: Reliance Industries Limited
Priority date: 2007-10-16
Filing date: 2008-10-16
Publication date: 2009-07-16
Also published as: WO2009087651A3

Abstract

The invention relates to an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290 °C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300 °C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3- propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240 °C, under an inert atmosphere. The invention also relates to the polyester resin to the compositions containing the resin and to the shaped articles prepared from the composition.

Description

An improved solid-state polymerization process for the production of high molecular weight polyethylene terephthalate

Field of invention

The invention relates to an improved process for polyester resin synthesis, to the polyester resin and to the compositions containing the resin.

Background

Thermoplastic polyester resins such as PET (Polyethylene terephthalate) resins find applications in the manufacture of containers for food and beverage packaging and in the production of films and industrial yarns. For such applications, it is desirable to have PET resins having high molecular weight. To obtain resins having high molecular weight, resin synthesis is usually carried out by a multi stage polymerization reaction. In the first stage, polymerization is carried out in the molten state resulting in a prepolymer having intrinsic viscosity of around 0.6 dl/g and subsequently the prepolymer is polymerized in the solid state to obtain polyester having higher intrinsic viscosity. Quality of the products such as preforms and bottles prepared from a PET resin is largely determined by their clarity and to improve the product clarity, comonomers are used during the resin synthesis. Conventionally, isophthalic acid is used as the comonomer for improving clarity of the resin products. The overall rate of polymerization and resin productivity of the conventional polymerization process depends upon the rate of solid state polymerization that is slower and rate limiting. It is desirable to improve the productivity of the PET resin synthesis. Moreover, there is scope for further improvement in the clarity of the conventional resin products. Detailed Description

Accordingly, the invention provides an improved process for polyester synthesis comprising reacting ester oligomers with alkyl substituted I₅ 3 -propane diol.

In one embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of * 250 to 2900 C to obtain an ester oligomer, then reacting the oligomer in molten state at a temperature in the range of 260 to 300⁰C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3-propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C, under an inert atmosphere.

In another embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3-propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C, under an inert atmosphere wherein the first reaction is carried out in the presence of 200 to 300 ppm of antimony trioxide

In another embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3-propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to

240⁰C, under an inert atmosphere wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic acid and the polyol is selected from the group consisting of monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol or 1,4-cyclohexane diol.

In another embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0.2 to 5 percentage by weight of at least one alkyl substituted 1,3 -propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C₅ under an inert atmosphere.

In another embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3-propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C, under an inert atmosphere wherein the propane diol is selected from neopentyl glycol and 2-methyl-l,3 propanediol

In another embodiment, the invention provides an improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0,01 to 10 percentage by weight of at least one alkyl substituted 1,3-propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C, under an inert atmosphere wherein the inert atmosphere is maintained by nitrogen gas having a temperature in the range of 200 to 240 ⁰C.

In another embodiment the invention provides a polyester resin having intrinsic viscosity upto 1.2 dl/g.

In another embodiment, the invention provides a preform having percentage haze not greater than 4.

In a further embodiment, the invention provides a composition comprising the polyester resin

In a still further embodiment, the invention provides shaped articles prepared from polyester resin composition.

The invention provides an improved process for the synthesis of polyester resins. The process of invention utilizes an alkyl substituted 1,3- propane diol as a comonomer. The process of invention involves three reaction stages- a first esterification stage, a second melt polymerization stage and a third solid state polymerization stage. During the first reaction stage, a dicarboxylic acid is reacted with a polyol resulting in an ester oligomer. The first stage reaction is usually carried out in the presence of 200 - 300 ppm of an antimony trioxide catalyst. The dicarboxylic acid that can be used for the first stage reaction include, but is not limited to, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic acid. The polyol that can be used for the first stage reaction is selected from the group consisting of monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylenes glycol, 1 ,4-cyclohexane diol or neopentyl glycol. The esterification reaction is often carried out in the presence of a catalyst. The catalysts that can be used for the esterification, include but are not limited to, chlorides, bromides, oxides, acetates and sulfates of cobalt (Co), antimony (Sb) and manganese (Mn) metals.

In the second stage reaction, the ester oligomer formed in the first stage is reacted with an alkyl substituted 1, 3- propane diol that is added as a comonomer. Advantageously, neopentyl glycol or 2-methyl-l,3 propanediol is added as the comonomer. The alkyl substituent of the propane diol can be a linear or a branched alkyl. Advantageously, the substituent is a C i. ₈ alkyl. The substituted propane diol is usually added after the first reaction stage and before the melt polymerization (polycondensation) stage. Usually the propane diol is added in 0.01 to 10% by weight of the total weight of the reactants. Advantageously, the propane diol is added in 0.2 to 5% by weight of the reactants. During the melt polymerization, the ester oligomers react with the comonomer and undergo condensation to form a prepolymer having comonomer residue in the polymer backbone. The condensation reaction is accompanied by an increase in intrinsic viscosity (IV). After an IV of around 0.65 dl /g is reached, the melt polymerization is terminated.

The solid state polymerization of the prepolymer is carried out at a temperature in the range of 200 - 24O⁰C under an inert atmosphere. Inert atmosphere is maintained by nitrogen gas having a temperature in the range of 200-240⁰C. The solid state polymerization results in a polyester resin having higher intrinsic viscosity. After solid-state polymerization, PET resin having an IV up to 1.2 dl/g is obtained. The invention also provides a composition comprising the polyester resin. The composition of the invention can contain one or more additives including colorants, pigments, glass fibers, crystallization aids, impact modifiers, surface lubricants, denesting agents, stabilizing agents, antioxidants, ultraviolet light absorbing agents, metal deactivators, nucleating agents, acetaldehyde lowering compounds, flame retardants, recycling release aids, oxygen scavenging materials, platelet particles, reheat rate enhancing aids such as elemental antimony or reduced antimony or reducing agents to form such species in situ, silicon carbide, carbon black, graphite, activated carbon, titanium nitride, black iron oxide, red iron oxide and the like, sticky bottle additives such as talc, and fillers and the like. The resin composition may also contain small amounts of branching agents such as trifunctional or tetrafunctional carboxylic acids or their derivatives or alcohols such as trimellitic anhydride, trim-ethylol propane, pyromellitic dianhydride, pentaerythritol, and other polyester forming polyacids or polyols generally known in the art. The stabilizing agents that can be used in the composition include phosphorous- containing stabilizing agents, for example, phosphoric acid and phosphates, phosphonic acids and esters thereof, polyphosphoric acids and salts of esters thereof, and similar phosphorus, compounds. The nucleating agents that can be used in the resin composition include metal powders such as zinc and aluminium, metal oxides such as the oxides of zinc, magnesium, titanium and silicon, clays, mixed metal oxides and hydrated variations thereof; inorganic salts such as sodium carbonate and the carbonates, silicates and phosphates of calcium; polymers such as polytetrafluoroethylene powder (PTFE); organic compounds such as sorbitol; and organic salts, for example, the sodium salts of carboxylic acids such as benzoic acid, tartaric acid and stearic acid.

The polyester resin synthesized by the process of the invention is used in large quantities for the manufacture of containers. The polyester resin of the invention can also be used to make sheets, films, trays, rods, tubes, lids, fibers, filaments (such as bulk continuous filaments), other injection molded articles, and any other appropriate molded, extruded, or thermoformed article.

The invention is further illustrated by the following non limiting examples.

In the examples and the results that follow, intrinsic viscosity (IV) was determined by using ASTM D 4603 method. According to the procedure, 0.125g of resin was dissolved in Phenol / tetrachloroethane (40/60 w/w) solution. Intrinsic viscosity measurements were carried out in Ubbelohde viscometer at 25°C.

Melting point was determined using Perkin-Elmer's DSC-7 instrument. Heating and cooling rates were 10⁰C / minute.

Measurement of percentage haze was done in the following manner. Resin obtained after solid state polymerization was used for producing preforms using 2 cavity Arburg injection moulding machine (Model: Allrounder 420C). Before moulding, resins were dried for 5 hrs at 175⁰C in a dryer. The weight of the preform 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 checking percentage haze using Hunterlab spectrophotometer (Model: ColorQuest XE).

Example 1: Synthesis of PET resins (Comparative)

^■PET prepolymer having IV of 0.60 dl/g was prepared in a batch reactor by melt-phase polymerization process. Purified terephthalic acid (PTA) and monoethylene glycol (MEG) were charged in 1 :2 molar ratio in the reactor. To the above reaction mixture, 290 ppm of antimony trioxide catalyst based on antimony and 25 ppm NaOH were added. 2 wt % Isophthalic acid was also added along with PTA. Esterification reaction was carried out at 255°C. 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 a temperature of 285°C to obtain a prepolymer having IV of 0.6 dl/g.

The prepolymer was then polymerized in the solid state under an inert atmosphere to raise the IV up to 1 dl/g. Solid state polymerization (SSP) was carried out in a batch reactor. Nitrogen gas temperature for solid state polymerization was 205°C and target SSP exit IV was 0.76± 0.02 dl/g.

The solid state polymerization reaction rates in terms of rate of increase in intrinsic viscosity are given in table 1.

Example 2: Synthesis of PET resins using 2-methyl-l,3 propanediol as the comonomer

Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1:2 molar ratio. To the above reaction mixture, 290 ppm of antimony trioxide catalyst based on antimony and 25 ppm NaOH were added. The esterification reaction was carried out at 255°C. 2 wt% 2-methyl- 1,3 propanediol was added at the end of the 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 285°C to obtain a prepolymer having IV of 0.6 dl/g. The prepolymer having IV of 0.6 dl/g was polymerized in the solid state under an inert atmosphere to raise the IV up to 1 dl/g. Solid state polymerization was carried out in a batch reactor. Nitrogen gas temperature for solid state polymerization was 205°C and target SSP exit IV was 0.76± 0.02 dl/g.

Example 3: Manufacture of preforms and bottles from PET resin

Resins produced by examples 1 and 2 were used for producing preforms using 2 cavity Arburg injection moulding machine (Model: Allrounder 420C). Before moulding, resins were dried for 6 hrs at 175⁰C 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.

Table 1 below compares the solid state polymerisation rate in terms of rate of increase of intrinsic viscosity during synthesis of PET resin described in example 1 and example 2. TABLE 1:

Rate of increase in intrinsic viscosity of PET resins during solid state polymerization of prepolymer

From table 1 it is clear that the rate of increase in intrinsic viscosity during solid state polymerization of the process (illustrated in example 2) is higher (0.030 dl/g/hr) as compared to the rate of increase in intrinsic viscosity (0.021 dl/g/hr) during solid state polymerization of the conventional process (illustrated in the comparative example 1). The rate of increase in intrinsic viscosity is indicative of the solid-state polymerisation rate and, therefore, of the overall polymersation rate. The higher rate observed in the process of the invention (illustrated in example 1) would lead to improvement in the resin productivity. Further, the conventional process utilizes, as a clarity-inducing co-monomer, isophthalic acid that is less available. In contrast, the substituted propanediol used as the comonomer in the process of the invention is easily available.

Table 2 displays the intrinsic viscosity and the melting point of PET resins and table 3 displays the percentage haze values of PET preforms prepared using the resins synthesized by example 1 and example 2. TABLE 2:

Intinsic viscosity and melting point of PET resins at a residence time of 6 hours during solid state polymerization according to the processes illustrated in example 1 and example

2.

TABLE 3:

Percentage Haze of the preforms prepared from the PET resins synthesized by the processes illustrated in example 1 and example 2.

From table 2 it is clear that the PET resin synthesized by the process of the invention (illustrated in example 2) has lower melting point (247.6⁰C) as compared to the resins synthesised by the conventional process (illustrated in example 1). From table 3 it is clear that the preform obtained from the PET resin synthesized by the process of the invention (illustrated in example 2) has lower value of haze (4.0 %). Lower value of haze signifies better clarity while lower melting point enables easier and more energy efficient processing of the resin during the manufacture of various structures and shaped articles.

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

Claims

1. An improved process for polyester synthesis, the process comprising first reacting a dicarboxylic acid and a polyol at a temperature in the range of 250 to 290⁰C to obtain an ester oligomer, then reacting the oligomer in the molten state at a temperature in the range of 260 to 300⁰C with 0.01 to 10 percentage by weight of at least one alkyl substituted 1,3 -propane diol resulting in a prepolymer having intrinsic viscosity up to 0.65 dl/g and finally reacting the prepolymer in the solid state at a temperature in the range of 200 to 240⁰C, under an inert atmosphere.

2. The process as claimed in claim 1 wherein the first reaction is carried out in the presence of 200-300 ppm of antimony tri oxide

3. The process as claimed in anyone of the claims 1 or 2 wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic acid and the polyol is selected from the group consisting of monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylenes glycol or 1,4-cyclohexane diol.

4. The process as claimed in anyone of the claims 1 to 3 wherein the oligomer is reacted with 0.2 to 5% by weight of the propanediol.

5. The process as claimed in anyone of the claims 1 to 4 wherein the propane diol is selected from neopentyl glycol and 2-methyl -1,3-propanediol.

6. The process as claimed in anyone of the claims 1 to 5 wherein the inert atmosphere is maintained by nitrogen gas having a temperature in the range of 200 to 240⁰C.

7. Polyester resin having intrinsic viscosity upto 1.2 dl/g synthesized by the process as claimed in any one of the claims 1 to 6.

8. A preform having a percentage haze not greater than 4 prepared from the polyester resin as claimed in claim 7

9. A composition comprising the polyester resin as claimed in claim 7.

10. Shaped articles prepared from the composition as claimed in claim 9.