DESC:FIELD OF DISCLOSURE
The present disclosure relates to a process for manufacturing polyester. The present disclosure specifically relates to a membrane separation process for selective removal of condensates produced during condensation polymerization reaction.

BACKGROUND
Polyesters may be produced by esterification of a diol and a dicarboxylic acid or a diester, using condensation polymerization. A condensate is produced as a by-product of the reaction. In prior art processes, the condensate by-product is removed by distillation process, involving the use of tall columns, pumps, heaters, collection receivers and the like, leading to high capital costs and high operating costs.
Therefore there is a need for a polyester manufacturing process wherein the condensate is removed without the use of expensive equipment in an easy and efficient manner.
Also it is observed that the conventional distillation process is energy intensive as energy is required to run the distillation equipment which includes pumps, heaters, and receivers amongst other equipment.
Therefore there is a need to provide a process which consumes less energy while separating the condensate.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

An object of the present disclosure is to provide a process for selectively removing at least one component of the condensate from a mixture of vapours formed during the condensation polymerization.

Another object of the present disclosure is to provide an energy efficient process for the production of polyesters.
Still another object of the present disclosure is to provide a process for manufacture of polyester wherein the process does not use distillation columns.

Another object of the present disclosure is to provide a process for the manufacture of polyester wherein the process has reduced capital cost.

Another object of the present disclosure is to provide a process for the manufacture of polyester wherein the process has reduced operating costs.

Another object of the present disclosure is to provide a process for manufacture of polyester with reduced diol feeding.

Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

SUMMARY
A process for manufacturing polyester wherein the reactants which include diacids or diesters, diols and optionally a catalyst are heated in a reactor and a mixture and condensate vapours are obtained. The condensate vapours are passed through a membrane and at least one component of the condensate is selectively removed from the reactor. The mixture is further heated at low pressure to obtain polyester. The membrane is placed either in the vapour phase of the reactor or outside the reactor in a chamber. The membrane is a ceramic type permeable membrane. The reactants are heated in the temperature range of 250oC to 300oC. The temperature of the membrane is kept at a temperature range of 200oC to 300oC. The temperature of the membrane is kept higher than the boiling point of the diol. The diol is atleast one selected from the group consisting of ethylene glycol, butane diol and propane diol. The condensate comprises at least one of water vapour, monoethylene glycol vapour, terephthalic acid vapour, methanol and oligomer. The process of manufacturing the polyester is either a batch or a continuous process. The condensate is selectively removed by applying vacuum on the membrane. A mist eliminator is placed upstream of the membrane before passing the condensate vapour through the membrane.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 illustrates a schematic representation of an esterifier, in one embodiment of the present disclosure, with the membrane being placed outside the esterifier, in a chamber.

Figure 2 illustrates a schematic representation of an esterifier in another embodiment of the present disclosure with the membrane being inside the esterifier.

DETAILED DESCRIPTION
A preferred embodiment of the present disclosure will now be described in detail with reference to the accompanying drawings. The preferred embodiment does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiment herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiment in the following description. Description of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiment herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiment herein may be practiced and to further enable those of skill in the art to practice the embodiment herein. Accordingly, the example should not be construed as limiting the scope of the embodiment herein.
In accordance with one of the exemplary embodiments of the present disclosure, there is disclosed a process for manufacture of high viscosity polyester resin.
In the manufacture of polyester, condensation polymerization is an important step. The reactants, which include diacids or diesters, diols and optionally a catalyst, are heated in a reactor to produce a mixture and condensate vapours, due to an esterification reaction. The condensate comprises at least one of water vapour, monoethylene glycol vapour, terephthalic acid vapour, methanol and oligomer. This esterification reaction is reversible, and in order to drive the reversible reaction in the forward direction, it is important to remove the condensate as quickly as possible. In prior processes, the mixed vapour is generally removed by distillation process using distillation columns. The remaining mixture is further heated at low pressure to obtain high viscosity polyester.
In one embodiment of the present disclosure, the esterification reaction takes place between terephthalic acid and a diol.
The diol is at least one selected from the group consisting of ethylene glycol, butane diol and propane diol. The condensate vapour comprises water vapour, diol vapour, and some purified terephthalic acid, alcohol and oligomers, sometimes as entrapped liquid or solid droplets. The polyester produced is Polyethylene Terephthalate (PET).
In another embodiment of the present disclosure, the polyester produced is Poly Trimethylene Terephthalate (PTT).
In yet another embodiment of the present disclosure, the polyester produced is PolyButylene Terephthalate (PBT).
In one embodiment of the present disclosure, the polyester was produced by an esterification reaction.
In another embodiment of the present disclosure, the polyester produced was produced by a transesterification reaction.
Generally in conventional processes, the condensate which primarily comprises water vapour or alcohol, is removed by distillation in distillation columns using tall columns, pumps, heaters, collection receivers and the like. This equipment leads to high capital cost as well as high operating costs. The present disclosure is an alternative to the use of distillation column.
In the present disclosure, membrane separation is used for removal of condensates like water or alcohol formed during esterification. In a preferred embodiment of the present disclosure, the membrane selectively removes water vapour. In other embodiments of the present disclosure, compounds like methyl alcohol are removed. The water vapour generated in the reactor passes through the membrane which selectively allows only water vapour or alcohol to pass through and not the reactants. This prevents the need for reheating the condensed vapours of monoethylene glycol. The membrane separation is particularly advantageous in case of polymers whose viscosity is high. The membrane used is a ceramic type permeable membrane.
The use of membrane separation method to selectively remove water vapour or alcohol from the mixture of vapours without condensing other vapours helps in saving energy.
In prior art process excess diol is fed, and the excess evaporated diol is condensed and is then distilled. This results in a lot of heat energy being expended. The energy saved in the process of the present disclosure is in the range of 10,000-70,000 k Cals per MT of polyester. Since the present disclosure does not require addition of extra diol, additional latent heat for vaporization of the excess diol is not needed.
The membrane is placed in the vapour phase and not dipped in the reaction mixture when dealing with high viscosity material or material with potential to choke the membrane, or material capable of degrading or dissolving the membrane, such as oligomers in the reaction mixture.
The vapour also carries the polymer or the oligomer as a vapour or as a suspension, which is removed by a mist eliminator placed between the melt phase and the membrane. In the absence of a mist eliminator, the polymer deposits on the membrane and chokes it. During the reaction process, since the membrane is maintained at high temperature, the deposits are further oligomerised or depolymerised. The deposits are solubilised by water in the preferred embodiment or by methanol or diol in other embodiments. These deposits then fall back from the membrane and return to the reaction mixture.
Figure 1 and Figure 2 illustrate different embodiments of the present disclosure.
Figure 1 illustrates an esterifier, in one embodiment of the present disclosure, with the membrane being placed outside the esterifier in a chamber.
Referring to Figure 1, the membrane 6, is placed after the mist eliminator 7, outside the esterification reactor 4, in a chamber such that the condensate first passes through the mist eliminator and then through the membrane in the chamber. The mist eliminator 7, eliminates the suspended droplets so that they don’t reach the membrane. The reaction components 1, are fed into the esterifier 4, and the products are separated into two phases, namely, liquid 2, and the vapour phase 3. The vapour phase 3, consists of a condensate comprising water vapour or alcohol. The condensate is passed first through the mist eliminator 7, and then through the membrane 6. The membrane 6, used for separation is a ceramic type permeable membrane. The membrane 6, does not allow the diol to pass through, while the water vapour or alcohol 8, is selectively passed through and is separated. During this transfer there is not much cooling. Oligomers flow up to the mist eliminator and dissolve in glycol and fall back into the vapour phase and then into the liquid phase.
Figure 2 illustrates an esterifier, in another embodiment of the present disclosure, with the membrane being placed inside the esterifier.
Referring to Figure2, the mist eliminator 7, along with the membrane 6, is placed inside the esterification reactor 4, such that the condensate first passes through the mist eliminator 7, and then through the membrane 6, which is a ceramic type permeable membrane. The reactants 1, are fed into the esterification reactor 4 where the products are separated into the liquid phase 2, and the gaseous phase 3. The glycol and the condensate, are fed into the mist eliminator 7, which consists of a membrane 6. The condensate 8, passes through the membrane 6, and the diol does not pass through the membrane.
While dealing with high viscosity materials or with materials with potential to choke the membrane or with material that is capable of degrading or dissolving the membrane such as oligomers in the reaction mixture, it is preferred that the membrane is placed in the vapour phase and not dipped in the reaction mixture.
Water vapour or alcohol is taken out of the reactor by applying vacuum on the membrane while the diol remains in the reactor. The proportion of diol and the terephthalic acid is the same as that in the product, in an amount of 1:1.
EXAMPLES
Example 1
Polyester manufacturing process using pure terephthalic acid and ethylene glycol:
The reaction components terphthalic acid and ethylene glycol, are fed into the esterifier, and the products are separated into two phases, namely, liquid and the vapour phase. The vapour phase consists of a condensate comprising water vapour. The condensate is passed first through the mist eliminator, and then through the ceramic permeable membrane. The ceramic permeable membrane, does not allow the ethylene glycol to pass through, while the water vapour, is selectively passed through and is separated.
Example 2
Polyester manufacturing process using di-methyl terephthalate and ethylene glycol:
The reaction components di-methyl terephthalate and ethylene glycol, are fed into the esterifier, and the products are separated into two phases, namely, liquid and the vapour phase. The vapour phase consists of a condensate comprising methanol vapour. The condensate is passed first through the mist eliminator, and then through the ceramic permeable membrane. The ceramic permeable membrane, does not allow the ethylene glycol to pass through, while the methanol vapour, is selectively passed through and is separated.
TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The process of separation of condensate produced during condensation polymerization, in accordance with the present disclosure has several technical advantages including but not limited to the realization of:
• Selective removal of the condensate formed during condensation polymerisation.
• Energy efficient process for production of polyester.
• A process which does not use distillation columns for production of polyester.
• Reduced capital cost during the production process of polyester.
• Reduced operating costs during the production of polyester.
• Reduced diol feeding during the manufacture of the polyester.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

Wherever a range of values is specified, a value up to 10% below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the disclosure.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiment without departing from the principles of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. ,CLAIMS:1. In the manufacture of polyester, the process of separating constituents from the condensate, comprising the following steps:
• Subjecting at least one diacid or diester, at least one diol and optionally one or more catalyst to esterification in a reactor by heating under pre-determined temperature to obtain a mixture and condensate vapours;
• passing the condensate vapours through a membrane for selectively removing atleast one component selected from water vapour and alcohol from the condensate vapours.
2. The process as claimed in claim 1, which includes the step of placing the membrane in the vapour phase of the reactor.
3. The process as claimed in claim 1, which includes the step of placing the membrane in a chamber outside the reactor and passing the condensate vapours though the said chamber.
4. The process as claimed in claim 1, wherein said reaction mixture is heated to a temperature in the range between 2500 C to 3000 C.
5. The process as claimed in claim 1, which includes the step of maintaining the temperature of the membrane in the range between 2000 C to 3000 C, which is higher than the boiling point of the diol.
6. The process as claimed in claim 1, wherein the process is a continuous process.
7. The process as claimed in claim1, wherein the process is a batch process.
8. The process as claimed in claim 1, which includes the step of removing the condensate selected from water vapour and alcohol by applying vacuum on the membrane.
9. The process as claimed in claim 1, wherein the said alcohol is methanol.
10. The process as claimed in claim 1, which includes the step of removing mist upstream of the membrane before passing the condensate vapour through the membrane.