FORM 2 THE PATENT ACT 1970 (39 of 1970)& The Patents Rules, 2003 (See section 10 and rule 13)
TITLE OF THE INVENTION: "An efficient process for the production of high molecular weight polyester"
2 APPLICANT(a) Name : Reliance Industries Limited(b) Nationality: Indian company incorporated under the Companies Act 1956(c) Address : Reliance Technology Centre, B-4 MIDC Industrial Area,Patalganga- 410220, Dist- Raigad, Maharashtra, India. 3. INVENTORS(a) Name : Agarwal Uday Shankar(b) Nationality: Indian(c) Address : 501 Safal Aangan Plot No 3 and 4, Union Park, Chembur Mumbai400071, Maharashtra, India
(a) Name : Boon Wyndham Henry(b) Nationality: US Citizen(c) Address : 618 Rabbit Ridge CourtReno, Nevada USAUS Citizen: 618 Rabbit Ridge CourtReno, Nevada USA
(a)Name (b)Nationality (c) Address : Wadekar Shreeram AshokIndian: 204, Mohandeep Co-Op Housing Society Ltd. Almeida Road, Chandanwadi, Panchpakhadi Thane (West),400601, Maharashtra, India
(a) Name (b)Nationality (c) Address : Dubey Rajan:Indian : 201, Ambe Bhawan CHS, Plot No. 65 , Sector 12 Vashi, NaviMumbai-400703, Maharashtra, India
a)Name (b)Nationality: (c) Address : Tibude Ajay Ramlal Indian : 158, Teacher's Colony Nr Bharat Nagar, Kalumna Market Road, Nagpur-440 035 (MS), India Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION:
The invention relates to an efficient process for the production of high molecular weight polyester from low molecular weight prepolymer by solid state polymerization with reduced oligomer volatilization.
The invention also relates to a low molecular weight prepolymer having Intrinsic Viscosity (IV) of about 0.2 to about 0.45 dl/g prepared by the above process.
The invention also relates to a high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g produced from low molecular weight prepolymer having IV of about 0.2 to about 0.45 dl/g prepared by the above process.
BACKGROUND OF THE INVENTION:
Polyester resins such as polyethylene terephthalate (PET) are well known for making films, fibers and packaged container applications. A process for the production of high molecular weight polyesters comprises melt polymerization followed by solid-state polymerization (SSP).
In the melt polymerization process for producing PET, base prepolymer of Intrinsic Viscosity (IV) of about 0.4 to 0.65 dl/g is produced. The base prepolymer is either in the form of cylindrical chip or spherical chip and is amorphous in nature. The base chips are then subjected to solid-state polymerization after crystallizing it in a crystallizer so as to avoid sintering or lump formation in the solid-state polymerization reactor. Depending upon the end application, polyester with different IV is produced by solid-state polymerization (ref: US 3,405,098, 3,544,525, 4,245,253, 4,238,593, and 5,408,035).
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Another polymerization process which is different from the conventional polymerization process is disclosed in US 5,510,454, 5,532,333, 5,540,868, 5,714,262, 5,830,982, and 6,451,966 which are incorporated herein as reference in their entirety.
In this polymerization process, a crystalline hemispherical prepolymer having IV of about 0.1 to 0.4 dl/g is formed using particle former process. Such low IV prepolymer particles can also be produced with other techniques that are well known in the art and can be subjected to solid-state polymerization for producing higher molecular weight polyesters. Examples of such particle formation processes are given in US patents 4123207 and 7,008,203.
Prepolymer produced by these various techniques are then used as a precursor for solid-state polymerization process to increase the IV from about 0.5 dl/g to about 1 dl/g.
Solid-state polymerization process involves three steps namely preheating of low molecular weight prepolymer in a preheater section, attaining intermediate IV (0.4 to 0.6 dl/g) in an intermediate reactor termed conditioning vessel and then achieving final desired IV (0.7 to 1 dl/g) in a solid-state polymerization reactor. Preheater is a fluidized section in which prepolymer is heated at a temperature in the range of 210°C to 250°C under very high nitrogen gas flow.
In the particle formation step, hemispherical prepolymer particles are formed by dropping melt droplets on a preheated moving metal belt. Belt temperature is set between 100 to 200°C. Due to the very high temperature of melt droplet which is in the range of 260 to 300°C, quenching effect occurs when it falls on low temperature metal belt. As a result, bottom surface of hemispherical prepolymer particle exhibits different crystalline morphology as compared to the top dome surface. It is observed that for every hemispherical crystalline prepolymer particle, the bottom surface remains weaker in terms of mechanical strength as
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compared to top dome surface. These prepolymer particles are weak and break easily during handling e.g. during transfer/conveying to SSP, during SSP and during packaging/transportation and thus result in formation of smaller particles, refered hereafter as 'dust particles'.
In the solid-state polymerization process, due to the lower prepolymer IV, more oligomers get liberated. These oligomers may be linear or cyclic in structures made up of the constituent units of the polyester. These oligomers can be low melting substances such as monohydroxy ethyl terephthalate (MHET), bishydroxyethyl terephthalate (BHET), etc. Due to very high nitrogen gas flow in preheater, oligomers get carried away along with dust particles into nitrogen circulation lines. This also leads to deposition of broken chips and dust particles on the vessel internals/walls as well as on the inert gas/vacuum line walls. It is also observed that broken chips, dust and oligomers stick to the preheater gas distribution plates, plenum and sidewalls. In addition, it is seen that, over a period of time, bridging of prepolymer, dust, broken particles or oligomers, hereafter referred as deposits, occur in the preheater nitrogen gas distribution plates, plenum and sidewalls of preheater and nitrogen gas circulation lines. This results in the partial or complete blocking of holes of preheater nitrogen gas distribution plate and thereby disturbing nitrogen gas flow / velocity and also the fluidization of prepolymer in the preheater. This manifests as a rapid increase in the pressure drop across the preheater nitrogen distribution plates leading to frequent shutdown of the plant to clean these deposits.
Similarly, oligomer liberation also seen in conditioning vessel, which is on the downstream of preheater in the solid-state polymerization process. Oligomers get liberated to a large extent in conditioning vessel where IV increases up to 0.6 dl/g. Oligomers get carried away along with nitrogen gas and tend to deposit on the internal and the surface of the conditioning vessel. Over a period of time, as a result of deposit formation, the pressure drop across conditioning vessel and nitrogen line increases and nitrogen gas flow becomes inconsistent. Therefore
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more and more nitrogen gas flow is required to achieve the same intrinsic viscosity and to remove the polymerization byproducts. Due to the higher nitrogen gas consumption, the polyester production cost increases.
Deposits are also formed on the nitrogen gas circulation lines, filters and heaters thereby reducing their life too. These deposits get degraded over a period of time due to very high temperature and residence time. These degraded deposits get dislodged during the process thereby contaminating the final product in the form of black specks. Thus the product quality is adversely affected.
Thus it is necessary to reduce oligomer liberation during solid-state polymerization process to overcome the problems associated with the process.
US 6,699,545 discloses the method for increasing polymerization rate of polyester polymers in the solid state by adding a catalytic amount of zinc p-toluene sulfonate to polyester melt that is essentially free of antimony and germanium, before solid sate polymerization. However, this patent does not disclose liberation of oligomer in the solid-state polymerization and the problems associated with the same and hence the use of the sulfonic acid compound for reducing oligomer volatilization during solid-state polymerization.
US 6,180,756 discloses the use of Lewis acid compounds such as p-Toluene sulfonic acid, methyl sulfonic acid and the like, to be introduced via a gas or liquid stream during solid-state polymerization using low molecular weight crystalline prepolymer. Patent mentions about the surface treatment of low molecular weight prepolymer with the Lewis acid compounds. These SSP rate-enhancing catalysts were chosen for their volatility to allow their introduction and/or removal by gas streams. This patent does not deal with either the oligomer content in polymer or with oligomer volatilization during solid-state polymerization and also the problems associated with the same and hence the use of the Lewis acid by
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surface treatment for reducing oligomer volatilization during solid-state polymerization.
US 6,392,005 and 6,783,827 describe the use of phosphorus compounds or calcium phosphates or carboxy phosphonic acid in the conventional polymerization process to produce the polyesters of IV > 0.7 dl/g to control the production of cyclic oligomer and also to reduce regeneration of cyclic oligomer in the rear-stage melting process. The objective was to reduce the mold pollution during processing and to reduce contamination of goods packed in packages made there from. The patents are not concerned with use of these compounds in relation to oligomer volatilization during the SSP process itself.
US 4,418,188 describes the use of protonic acid catalysts selected from the group consisting of sulfuric, phosphoric, p-toluenesulfonic, sulfurous, sulfamic and trichloroacetic acid in an amount between 0.001 and 3 weight percent of the polymer formed to reduce cyclic oligomer content in polyethylene isophthalate (PEI) and copolymers thereof. The patent discloses melt polymerization process and does not deal with the SSP process or liberation of linear and oligomers during SSP process. Polyester with such a higher amount of IPA content cannot be crystallized and thus can not be solid state polymerized.
The use of sulfonic acids in polyesters is well known for reduction of cyclic oligomer liberation during downstream processing such as heat set blow moulding process and during fiber spinning.
According to our knowledge, the use of Lewis acids such as sulfonic acids to reduce the volatilization of linear oligomers of polyester in the solid-state polymerization process of the invention is not currently known in the art. However, when solid-state polymerization starts in some of the newer polyester technologies with unusually low molecular weight prepolymers, the volatilization of oligomers is substantially higher than conventional solid-state polymerization.
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These oligomers condense on many vessel and piping surfaces and cause many process and product problems including black speck formation, plugging of gas distributors/filters, over burdening of the nitrogen purification unit, etc. The present invention is intended to provide a solution to the above addressed issues.
OBJECTS OF THE INVENTION:
An object of the invention is to provide an efficient and cost-effective process for the production of polyester by adding a Lewis acid such as sulfonic acid in an esterification step or a melt polymerization step but before particle former process to reduce the oligomer liberation in the solid state polymerization.
Another object of the invention is to provide an efficient and cost-effective process for the production of polyester by adding a Lewis acid such as sulfonic acid in an esterification step or a melt polymerization step but before a particle former process to reduce the oligomer liberation in the solid state polymerization thereby reducing deposit formation on preheater nitrogen gas distribution plates, plenum and sidewalls of preheater, nitrogen gas circulation lines, conditioning vessel and reactor internals and thus requiring low maintenance of process plant.
Another object of the invention is to provide an efficient and cost-effective process for the production of polyester by adding a Lewis acid such as sulfonic acid in an esterification step or a melt polymerization step but before a particle former process to reduce the oligomer liberation in the solid state polymerization thereby reducing deposit formation on preheater nitrogen gas distribution plates, plenum and sidewalls of preheater, nitrogen gas circulation lines, conditioning vessel and reactor internals and thus reducing the shut down frequency for maintenance and increasing the productivity.
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Another object of the invention is to provide an efficient and cost-effective process for the production of polyester by adding a Lewis acid such as sulfonic acid in an esterification step or a melt polymerization step but before a particle former process to reduce the oligomer liberation in the solid state polymerization thereby reducing deposit formation on preheater nitrogen gas distribution plates, plenum and sidewalls of preheater, nitrogen gas circulation lines, conditioning vessel and reactor internals and subsequent degradation thus maintaining commercial quality of the product and consistency in maintaining the same.
Another object of the invention is to provide an efficient and cost-effective process for the production of polyester by adding a Lewis acid such as sulfonic acid in an esterification step or a melt polymerization step but before a particle former process to reduce the oligomer liberation in the solid state polymerization where the process plant reduces the problem associated with the prior art.
Yet another object of the invention is to provide a low molecular weight polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, a Lewis acid such as sulfonic acid prepared by the above process.
Yet another object of the invention is to provide high molecular weight polyester resins of IV of 0.5 dl/g to 1.2 dl/g produced from the low molecular weight polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, a Lewis acid such as sulfonic acid prepared by the above process.
Yet another object of the invention is to provide use of the high molecular weight polyester resins of IV of 0.5 dl/g to 1.2 dl/g produced from a low molecular weight crystalline polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, a Lewis acid such as sulfonic acid for the production of various packaging products such as performs, containers, films or sheets.
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Detailed Description of the invention:
According to the invention there is provided an efficient process for the production of high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g from low molecular weight crystalline prepolymer having IV of about 0.1 dl/g to about 0.45 dl/g; the process comprising :
a) esterifying at least one dicarboxylic acid or mono-esters thereof or di-ester thereof and at least one polyol at temperature in the range of 250°C to 290°C to obtain an esterified mixture;
b) melt polymerizing the esterified mixture at temperature in the range of 260°C to 300°C to obtain polyester prepolymer having IV of about 0.2 to about 0.45 dl/g;
c) producing prepolymer particles of polyesters by a particle former process at a temperature in the range of 110 to 160°C;
d) adding a suitable Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process; and
e) solid state polymerizing the prepolymer to obtain a high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g.
The term "polyester" as used herein means polyethylene terephthalate (PET), which intends to cover polymer and copolymers of polyethylene terephthalate.
The basic process comprising particle former process and solid-state polymerization is disclosed in US 5,510,454 (herein after referred as '454 patent), US 5,532,333, US 5,540,868, US 5,714,262, US 5,830,982, and US 6,451,966. However, none of these patents disclose the composition of the polyester of the present invention or a process for the production of polyester resin by using a Lewis acid such as sulfonic acid e.g. methane sulfonic acid, para-toluene sulfonic
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acid or any other sulfonic acid for reducing oligomer liberation during solid-state polymerization process.
The sulfonic acid is selected from methane sulfonic acid, para-toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid or any suitable sulfonic acid. Preferably, the sulfonic acid is selected from methane sulfonic acid or para-toluene sulfonic acid. The sulfonic acid is added in the range of about 0.001 wt % to 3 wt %, preferably about 0.01wt % to about 0.1wt % by weight of polyester. The sulfonic acid is added as a powder, a liquid or a slurry in ethylene glycol at any stage of esterification or melt polymerization such as slurry mixing tank, oligomer line and column reactor particularly in the column reactor, but before the particle former process. The dicarboxylic acid is selected from terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic or any suitable dicarboxylic acids or mono-esters thereof or di-esters thereof. The dicarboxylic acid is preferably isophthalic acid or mono-ester thereof or di-ester thereof. The term polyol is intended to cover any suitable alcohol containing two or more hydroxyl groups known to those skilled in the art. The polyol is selected from monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylenes glycol or 1,4-cyclohexane diol or any suitable polyol. The prepolymer particles obtained are either crystalline or amorphous in nature. The shape of the prepolymer particles obtained is either hemispherical or spherical or cylindrical. The process is either continuous process or batch process. The prepolymer particles obtained can be prepared by any of the particle former processes disclosed in the prior art. The addition of the Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces oligomer volatilization during solid-state polymerization process. The addition of the Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces frequency of plant shutdown.
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According to the present invention there is provided prepolymer having IV of about 0.2 to about 0.45 dl/g comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and a Lewis acid such as sulfonic acid. The base polyester prepolymer chips produced by the above process are crystalline or amorphous in nature. The prepolymer produced by the above process is either hemispherical or spherical or cylindrical in shape. These prepolymer chips are used as a precursor for solid-state polymerization for increasing the IV. The sulfonic acid is selected from methane sulfonic acid, para-toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid or any suitable sulfonic acid.
According to the invention there is provided a high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g produced from low molecular weight prepolymer having IV of about 0.2 to about 0.45 dl/g comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and a Lewis acid such as sulfonic acid. The sulfonic acid is selected from methane sulfonic acid, para-toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid or any suitable sulfonic acid. The high molecular weight polyester resin may also comprise any suitable additives for the improvement of the performance of polyester article.
According to the present invention there is provided a use of the resin for the production of polyester articles such as preforms, containers, fibers or filaments, films or sheets.
Thus the present invention provided a process for the production of polyester by adding a Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before particle former process which has reduced substantially the oligomer liberation in the solid state polymerization. This substantially reduces the deposit formation on preheater nitrogen gas distribution plates, plenum and sidewalls of preheater, nitrogen gas circulation lines and
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conditioning vessels. Thus the process plant using the above process requires low maintenance as well as lower frequency of shut down for maintenance and increasing the productivity. The reduction in deposit formation also substantially eliminates degradation thus maintaining commercial quality of the product and the consistency for maintaining the same. Thus the present process is an efficient and cost-effective process.
The present invention is further exemplified by the following non-limiting examples.
Example 1:
PET prepolymer having IV of 0.26 dl/g was prepared by melt-phase polymerization process. Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1:2 ratio in reactor. 2 wt % Isophthalic acid and 1.5 wt % diethylene glycol (DEG) were added in the reactor. Esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 dl/g. About 150 ppm of antimony was added as a catalyst and 10 ppm P was added as a thermal stabilizer. About 0.03% wt p-toluene sulfonic acid was added in the middle of the column reactor. 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. The prepolymer throughput was 72-kg/ hour. Carboxyl end groups in the prepolymer were 140 meq/kg.
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Example 2:
PET prepolymer of IV of 0.26 dl/g was prepared by melt-phase polymerization process.
Purified terephthalic acid and MEG were charged in 1:2 ratio in reactor. 1.5wt % Isophthalic acid and 1.5 wt % DEG were added in the reactor. Esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 dl/g. About 150 ppm of antimony was added as a catalyst and 10 ppm P was added as a thermal stabilizer. About 0.015% wt methane sulfonic acid was added in the middle of the column reactor. 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. The prepolymer throughput was 72 kg/ hour. Carboxyl end groups in the prepolymer were 140 meq/kg.
Example 3:
PET prepolymer of IV of 0.26 dl/g was prepared by melt-phase polymerization process.
Purified terephthalic acid and MEG were charged in 1:2 ratio in reactor. 1.5wt % Isophthalic acid and 1.5 wt % DEG were added in the reactor. Esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 dl/g. About 150 ppm of antimony was added as a catalyst and 10 ppm P was added as a thermal stabilizer. About 0.03% wt methane sulfonic acid was added in the middle of the column reactor. 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
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collected for carrying out solid-state polymerization. The prepolymer throughput was 72 kg/ hour. Carboxyl end groups in the prepolymer were 140 meq/kg.
Example 4: Comparative
PET prepolymer of IV of 0.26 dl/g was prepared by melt-phase polymerization process.
Purified terephthalic acid and MEG were charged in 1:2 ratio in reactor. 1.5wt % Isophthalic acid and 1.5 wt % DEG were added in the reactor. Esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 dl/g. About 290ppm of antimony was added as a catalyst and 10 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 160°C and then collected for carrying out solid-state polymerization. The prepolymer throughput was 72 kg/ hour. Carboxyl end groups in the prepolymer were 140 meq/kg. This prepolymer was considered as "Control".
Example 5:
Solid state polymerization
Crystalline prepolymer having IV of 0.26 dl/g obtained in the examples 1 to 4, was solid-state polymerized under inert atmosphere to raise the IV up to 1 dl/g. The prepolymer was passed through fluid bed heater at a temperature 236°C at least for 5 minutes residence time. This was further passed through crystallizer maintained at 224°C and then through a reactor of stage 1 maintained at 232°C, by maintaining gas / solid ratio 0.6 with at least two hours residence time. The reaction mixture was further passed through a reactor of stage 2 maintained at
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221 °C temperature for at least 23 hours residence time by maintaining gas to solid ratio 0.5 to obtain high molecular weight resin.
Oligomer volatilization measurements were carried out by heating the desired amount of prepolymer in a fixed bed reactor at 230°C for desired time under nitrogen flow. The byproduct leaving with the nitrogen was condensed in a collection pot and weighed. The weight of the oligomers as % of the prepolymer weight was taken as the % oligomer volatilization. IV of prepolymer used for oligomer volatilization experiment was 0.26dl/g.
Reduction in oligomer volatilization from low molecular weight crystalline prepolymer with and without sulfonic acid compounds is given in the table 1 and 2.
TABLE 1 - Oligomer volatilization for 50g prepolymer during 2 hrs of
residence time at 230°C

Resin p-toluenesulfonic acid(wt %) Methanesulfonicacid (wt %) % Reductionin oligomervolatilization
PET
prepolymer ------ ------ ---------
(according to
Example 4
PET
prepolymer (according to 0.03 — 50
Example 1
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TABLE 2 - Oligomer volatilization for 4kg prepolymer during 4 hrs of
residence time at 230°C

Resin p-toluenesulfonic acid(wt %) Methanesulfonic acid(wt %) % Reductionin oligomervolatilization
PETprepolymer(according toExample 4 — — —
PETprepolymer(according toExample 1 0.03 — 39.3
PETprepolymer(according toExample 2 — 0.015 25.0
PETprepolymer(According toExample 3 — 0.03 39.3
As seen from the table - 1 and 2, substantial reduction in oligomer volatilization
was observed with the use of methane sulfonic acid and para-toluene sulfonic
acid.
According to the present invention, no adverse effect on the perform clarity was
observed due to the addition of sulfonic acid compounds.
Bottles of 1.5 L volume were produced using SIDEL SB01 single cavity blow moulding machine. Performance of the bottles produced with sulfonic acid
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compounds was comparable to the bottles produced without sulfonic acid compounds.
We claim:
1. An efficient process for the production of high molecular weight polyester
resin having IV of about 0.5 dl/g to about 1.2 dl/g from low molecular
weight crystalline prepolymer having IV of about 0.2 dl/g to about 0.45
dl/g;
the process comprising :
a) esterifying at least one dicarboxylic acid or mono-esters thereof or di-esters thereof and at least one polyol at temperature in the range of 250°C to 290°C to obtain an esterified mixture;
b) melt polymerizing the esterified mixture at temperature in the range of 260°C to 300°C to obtain polyester prepolymer having IV of about 0.2 to about 0.45 dl/g;
c) producing prepolymer particles of polyesters by a particle former process at a temperature in the range of 110 to 160°C;
d) adding a Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process; and
e) solid state polymerizing the prepolymer to obtain a high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g.

2. The process as claimed in claim 1, wherein the Lewis acid such as sulfonic acid is selected from methane sulfonic acid, para toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid.
3. The process as claimed in claim 1, wherein the sulfonic acid is added as a powder, a liquid or a slurry by mixing it in ethylene glycol at any stage of esterification or melt polymerization such as slurry mixing tank, oligomer
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line and column reactor particularly in the column reactor, but before the particle former process.
4. The process as claimed in claim 1, wherein the sulfonic acid is added in the range of about 0.001 wt % to 3 wt % by weight of polyester.
5. The process as claimed in claim 1, wherein the polyol is selected from monoethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylenes glycol or 1,4-cyclohexane diol.
6. The process as claimed in claim 1, wherein the dicarboxylic acid is selected from terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic acid or mono-esters thereof or di-ester thereof.
7. The process as cliamed in any of the preceding claims, wherein the process is either continuous or batch process.
8. The process as claimed in any of the preceding claims, wherein the addition of the Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces oligomer volatilization during solid-state polymerization process.
9. The process as claimed in any of the preceding claims, wherein the addition of the Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces frequency of shutdown of the plant.
10. The prepolymer having IV of about 0.2 to about 0.45 dl/g; the prepolymer comprising at least one dicarboxylic acid or mono-esters thereof or di-
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esters thereof or anhydrides, at least one polyol and a Lewis acid such as sulfonic acid.
11. The prepolymer as cliamed in claim 10, wherein the prepolymer is either crystalline or amorphous in nature.
12. The prepolymer as cliamed in claim 10, wherein the prepolymer is either hemispherical or spherical or cylindrical in nature.
14. The prepolymer as claimed in claim 10, wherein the Lewis acid such as sulfonic acid is selected from methane sulfonic acid, para toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid.
13. A high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g produced from low molecular weight prepolymer having IV of about 0.2 to about 0.45 dl/g; the resin comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and a Lewis acid such as sulfonic acid.
14. High molecular weight polyester resin as claimed in claim 13, wherein the Lewis acid such as sulfonic acid is selected from methane sulfonic acid, para toluene sulfonic acid, toluene sulfonic acid, benzene sulfonic acid or xylene sulfonic acid.
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15. High molecular weight polyester resin as claimed in claim 13, wherein the resin is used for the production of polyester articles such as preforms, containers, fibers or filaments, films or sheets.
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