WO2009066310A2

WO2009066310A2 - An efficient process for the production of high molecular weight polyester from low molecular weight prepolymer

Info

Publication number: WO2009066310A2
Application number: PCT/IN2008/000451
Authority: WO
Inventors: Vikas Madhusudan Nadkarni; Sheeram Ashok Wadekar; Dubey Rajan; Sudan Pushap
Original assignee: Reliance Industries Limited
Priority date: 2007-07-19
Filing date: 2008-07-15
Publication date: 2009-05-28
Also published as: WO2009066310A3

Abstract

The present invention discloses 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 prepolymer having IV of about 0.2 dl/g to about 0.45 dl/g by adding the alkali metal salts of Lewis acid such as sulfonic acid selected from sodium para-toluenesulfonate or potassium para-toluene sulfonate at any steps during the esterification or the melt polymerization but before a particle former process. The process reduces the oligomer volatilization during melt polymerization and solid state polymerization and also increases the rate of polymerization and solid state polymerization. The present invention also discloses a low molecular weight crystalline prepolymer having IV of about 0.2 dl/g to about 0.45 dl/g and high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g produced by the above process.

Description

TITLE OF THE INVENTION An efficient process for the production of high molecular weight polyester from low molecular weight prepolymer

TECHNICAL FIELD OF THE INVENTION:

The invention relates is an efficient process for the production of high molecular weight polyester to reduce dust generation in melt polymerization and solid state polymerization and to reduce oligomer liberation in the solid state polymerization.

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).

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 namely US 4, 123,207 and US 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 1.2 dl/g.

Solid-state polymerization process involves three steps namely preheating of low molecular weight prepolymer in a preheater section, attaining intermediate IV (0.5 to 0.6 dl/g) in a reactor namely 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 210⁰C to 250°C under very high nitrogen gas flow.

In the melt polymerization process, hemispherical prepolymer particles are formed by dropping melt droplets on a preheated moving metal belt. Belt temperature is set between 100 to 200⁰C. Due to the very high temperature of melt droplet which is in the range of 260 to 300⁰C, 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 compared to top dome surface. These prepolymer particles break easily during handling e.g. during transfer/conveying to SSP, during SSP and during packaging/transportation and result in the 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 the 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 increases due to this bridging at a faster rate therefore demanding 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 tends to deposit on the internals 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 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 deposit get dislodged during the process, contaminating the final product in the form of black specks. Thus the product obtained is of not commercial quality.

Thus it is necessary to reduce dust generation and oligomer liberation during melt and 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 the 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 dust generation and oligomer volatilization during melt and solid-state polymerization process. Also, reactivity gain in the melt polymerization process with zinc p-toluene sulfonate compound is not discussed. 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 dust reduction and oligomer volatilization during polyester polymerization and also the problems associated with the same and hence the use of the Lewis acid by surface treatment for reducing oligomer volatilization during solid-state polymerization.

European patent application 745629 discloses the preparation of polyesters containing sulfonic acids such as para-toluene sulfonic acid. This patent however do not discuss about the problems associated with oligomer liberation in the melt polymerization or solid-state polymerization process.

US patent 5,644,019 discloses high activity catalyst system including para-toluene sulfonic acid for the production of polyethylene terephthalate. This patent is restricted to the melt phase polymerization only and does not discuss about the problems associated with the process described earlier.

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 reducing dust generation and oligomer volatilization during melt and solid-state polymerization process. US 4,418,188 describe 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 in cyclic oligomer content in polyethylene isophthalate (PEI) and copolymers thereof. This 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 can not be crystallized and thus can not be solid state polymerized. This patent also does not discuss the dust reduction and associated problems during polyester polymerization process.

According to our knowledge, the use of salts of Lewis acids such as sodium para-toluene sulfonate to reduce the volatilization of linear oligomers of polyester in the solid-state polymerization process and to reduce the dust generation in melt polymerization as well as solid-state polymerization 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. 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 process for the production of polyester by adding alkali metal salts of Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before a particle former step thereby reducing dust generation in melt polymerization and solid state polymerization and also reducing oligomer liberation in the solid state polymerization. Another object of the invention is to provide an efficient process for the production of polyester by adding alkali metal salts of Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before a particle former process thereby reducing dust generation in melt polymerization and solid state polymerization and also reducing oligomer liberation in the solid state polymerization which reduces waste generation during polyester polymerization process and also reduces 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 process for the production of polyester by adding alkali metal salts of Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before a particle former process thereby reducing the oligomer liberation in the solid state polymerization which reduces deposit formation on preheater nitrogen gas distribution plates, plenum and sidewalls of preheater, nitrogen gas circulation lines, conditioning vessel and reactor internals and therefore reducing shut down frequency for maintenance and increasing the productivity.

Another object of the invention is to provide an efficient process for the production of polyester by adding alkali metal salts of Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before a particle former step thereby reducing the oligomer liberation in the solid state polymerization which reduces 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. Another object of the invention is to provide an efficient process for the production of polyester by adding alkali metal salts of Lewis acid such as a sulfonic acid in an esterification step or a melt polymerization step but before a particle former step thereby reducing 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 low molecular weight polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, alkali metal salts of Lewis acid such as sulfonic acid.

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, alkali metal salts of Lewis acid such as sulfonic acid.

Yet another object of the invention is to provide use of 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, alkali metal salts of sulfonic acid for the production of various packaging products such as performs, containers, films, sheets, fibers or yarns.

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 0.2 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 250⁰C to 290⁰C to obtain an esterified mixture; b) melt polymerizing the esterified mixture at temperature in the range of 260°C to 300⁰C 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 16O⁰C; d) adding alkali metal salts of Lewis acid such as sulfonic acid at any steps during the esterification step or melt polymerization step but before particle former process; and e) solid state polymerizing the prepolymer particles 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 dealt with the composition of the polyester of the invention or process for the production of polyester resin by using alkali metal salts of Lewis acid such as sulfonic acid for reducing dust generation in melt polymerization and solid-state polymerization process and reducing oligomer volatilization during solid-state polymerization process

The alkali metal salt of Lewis acid such as sulfonic acid is added in the range of about lOppm to lOOOppm based on alkali metal, preferably about 50 ppm to about 300 ppm by weight of polyester. The alkali metal salt of Lewis acid such as sulfonic acid is added as a powder or 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 monoalcohol, diol or polyol is selected from monoethylene glycol, diethylene glycol, Methylene glycol, propylene glycol, dipropylene glycol, butylenes glycol or 1,4-cyclohexane diol or any suitable polyol. The process is either continuous or batch process. 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 according to step 'C can be prepared by any of the particle former processes disclosed in the prior art. The addition of the alkali metal salt of Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces dust generation in the melt polymerization or in the solid-state polymerization process. The addition of the alkali metal salt of Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces oligomer volatilization in the solid-state polymerization process. The addition of the alkali metal salt of 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. The alkali metal salt of Lewis acid such as sulfonic acid is sodium para-toluenesulfonate or potassium para-toluene sulfonate. The alkali metal salt of Lewis acid such as sulfonic acid is preferably sodium para-toluene sulfonate. Sodium para-toluene sulfonate is added in the range of about lOppm to lOOOppm based on sodium, preferably about 50 ppm to about 300 ppm by weight of polyester. Sodium para-toluenesulfonate compound is added as a powder or 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 addition of the sodium para-toluene sulfonate at any steps during the esterification or melt polymerization but before particle former process reduces dust generation in the melt polymerization or in the solid-state polymerization process. The addition of the sodium para-toluene sulfonate at any steps during the esterification or melt polymerization but before particle former process reduces oligomer volatilization in the solid- state polymerization process. The addition of the sodium para-toluene sulfonate at any steps during the esterification or melt polymerization but before particle former process reduces frequency of shutdown of the plant.

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 alkali metal salts of Lewis acid such as sulfonic acid. The alkali metal salt of Lewis acid such as sulfonic acid is selected from sodium para-toluenesulfonate compound or potassium para-toluene sulfonate. The base polyester prepolymer chips produced by the above process are either crystalline or amorphous in nature. The shape of the prepolymer particles / chips obtained is either hemispherical or spherical or cylindrical. These prepolymer chips are used as a precursor for solid-state polymerization for increasing the IV.

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 alkali metal salts of Lewis acid such as sulfonic acid. The alkali metal salt of Lewis acid such as sulfonic acid is selected from sodium para-toluenesulfonate compound or potassium para-toluene sulfonate. The high molecular weight polyester resin may also comprise any suitable additives for the improvement of any 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 alkali metal salt of Lewis acid such as sulfonic acid, preferably sodium para-toluenesulfonate in an esterification or a melt polymerization but before a particle former process which has reduced dust generation in melt polymerization and solid state polymerization and also reduced oligomer liberation in the solid state polymerization. Therefore, the present process reduces waste generation during polyester polymerization process and 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. The process of the invention thus reduces shut down frequency for maintenance and increases the productivity. As the above process reduces 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 the consistency. Thus the process is efficient and cost-effective.

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. Sodium para- toluenesulfonate having 200ppm as sodium was added in a slurry form in MEG in oligomer line. Esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290⁰C to raise the IV up to 0.26 dl/g. About 290ppm 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 2: 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 280⁰C. The oligomer obtained was further polymerized at 29O⁰C to raise the IV up to 0.26 dl/g. About 290ppm 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 16O⁰C and then collected for carrying out solid- state polymerization. This prepolymer was considered as "Control".

Example 3:

Solid state polymerization

Crystalline prepolymer having IV of 0.26 dl/g obtained in the example 1 and 2, was solid-state polymerized under inert atmosphere to raise the IV up to 0.76 +/- 0.02 dl/g. The solid-state polymerization reaction carried out at 235°C of nitrogen gas temperature in a 50kg fluidized bed batch reactor. Oligomer volatilization measurements were carried out by heating desired amount of prepolymer in a fixed bed reactor at 230⁰C for 4 hours 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.

TABLE - 1 : data of reduction in dust generation and oligomer volatilization by suing sodium para- toluene sulfonate

pph = Pounds per hour

As seen from Table — 1, substantial reduction in dust generation and oligomer volatilization was observed with sodium para-toluene sulfonate. According to the present invention, no adverse effect on the perform clarity was observed due to the addition of sodium para-toluene sulfonate.

Bottles of 1.5 L volume were produced using SIDEL SBOl single cavity blow moulding machine. Performance of the bottles produced with sodium para-toluene sulfonate was comparable to the bottles produced without sodium para-toluene sulfonate.

Claims

Claims:

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 25O⁰C to 290°C to obtain an esterified mixture; b) melt polymerizing the esterified mixture at temperature in the range of 260⁰C 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 alkali metal salts of Lewis acid such as sulfonic acid at any steps during the esterification step or melt polymerization step but before particle former process; and e) solid state polymerizing the prepolymer particles 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 2, wherein the alkali metal salts of Lewis acid such as sulfonic acid is added in the range of about lOppm to lOOOppm based on alkali metal by weight of polyester,

3. The process as claimed in claim 1, wherein the alkali metal salts of Lewis acid such as sulfonic acid is added as a powder or 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.

4. 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 or mono- esters thereof or di-esters thereof.

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 any of the preceding claims wherein the process is either continuous or batch process.

7. The process as claimed in any of the preceding claims, wherein the addition of the alkali metal salts of Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces dust generation in the melt polymerization or in the solid-state polymerization process.

8. The process as claimed in any of the preceding claims, wherein the addition of the alkali metal salts of Lewis acid such as sulfonic acid at any steps during the esterification or melt polymerization but before particle former process reduces oligomer volatilization in the solid- state polymerization process.

9. The process as claimed in any of the preceding claims, wherein the addition of the alkali metal salts of 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 process as claimed in any of the preceding claims, wherein the alkali metal salts of Lewis acid such as sulfonic acid is selected from sodium para-toluenesulfonate or potassium para- toluene sulfonate.

11. The process as claimed in any of the preceding claims, wherein the alkali metal salts of Lewis acid such as sulfonic acid is preferably sodium salt of para-toluene sulfonate.

12. 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-esters thereof or anhydrides, at least one polyol and the alkali metal salts of Lewis acid such as sulfonic acid.

13. The prepolymer as claimed in claim 12, wherein the prepolymer is either crystalline or amorphous in nature.

14. The prepolymer as claimed in claim 12, wherein the shape of the prepolymer is either hemispherical or spherical or cylindrical.

15. The prepolymer as claimed in claim 12, wherein the alkali metal salts of Lewis acid such as sulfonic acid is selected from sodium para-toluenesulfonate or potassium para-toluene sulfonate.

16. The 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 alkali metal salts of Lewis acid such as sulfonic acid.

17. The high molecular weight polyester resin as claimed in claim 16, wherein the alkali metal salts of Lewis acid such as sulfonic acid is selected from sodium para-toluenesulfonate or potassium para-toluene sulfonate.

18. High molecular weight polyester resin as claimed in claim 16, wherein the resin is used for the production of polyester articles such as preforms, containers, fibers or filaments, films or sheets.