FIELD OF DISCLOSURE:
The present disclosure relates to a process for preparing purified dianhydrosugar alcohols. The present disclosure also relates to an integrated process for preparing a polymer from the purified dianhydrosugar alcohols.
BACKGROUND:
Dianhydrosugar alcohols are dehydration products of the sugar alcohols such as sorbitol, mannitol, galactitol, fucitol, iditol and the like. These are typically, used as co-monomers in polyester, as a plasticizers in PVC, and as an additives in pharmaceuticals. The increase in glass transition temperature with improved crystallinity in polyesters can also be obtained by adding low to moderate proportions of dianhydrosugar alcohols.
The known methods for the production of dianhydrosugar alcohol involve dehydration of hexitol with a catalyst or a cation exchange resin or aa zeolite.
WO2012165676 discloses a method for the preparation of dianhydrosugar alcohol by using hexitol and diol. More specifically, it relates to a method for the preparation of a dianhydrosugar alcohol which includes dehydration of hexitol with acids.
Catalytic dehydration of sugar is reported to be inexpensive and easy but, it often results in formation of colored by-products. Furthermore, such colored by-product may cause fouling and deactivation of the catalyst which may lead to high recovery cost and a low conversion rate of hexitol into dianhydrosugar alcohol. The polymer prepared from dianhydrosugar alcohol containing colored by-products or impurities may exhibit an unacceptable degree of color.
US 6,864,378 discloses an integrated continuous process for the manufacturing of polymer grade dianhydro sugar alcohols, such as isosorbide, by dehydration of corresponding sugar alcohols. The water vapors evolved during the

dehydration are used to separate dianhydrosugar alcohols from the high boiling by-products of the reaction mass.
US6670033 discloses an alternative process for the production of a purified anhydrosugar alcohol. In said process the anhydrosugar alcohol is purified by distillation, recrystallization from methanol, ethanol or ethylene glycol, melt recrystallization or a combination thereof.
However, recrystallization of dianhydrosugar alcohols with abovementioned solvents often gives a product of insufficient purity. Further, the yield of the process is low which renders the process non-economical. Furthermore, the presence of a residual amount of the crystallization solvent in the crystallized dianhydrosugar alcohol makes it unsuitable for certain applications, such as the manufacture of polyesters.
Therefore, there is a need to provide a method for purification of dianhydrosugar alcohol which can eliminate the additional step of crystallization and recrystallization.
OBJECTS:
Some of the objects of the present disclosure are described herein below:
It is an object of the present disclosure to provide an economic and simple process for the preparation and purification of dianhydrosugar alcohols.
It is another object of the present disclosure to provide a process for preparing dianhydrosugar alcohol which is less time consuming, selective and high yielding.
It is still another object of the present disclosure to provide a process for preparing a dianhydrosugar alcohol in a relatively high pure form.

It is yet another object of the present disclosure to provide a process for preparing a dianhydrosugar alcohol which is adapted to increase catalyst life.
It is a further object of the present disclosure to provide an environment friendly process for preparing a dianhydrosugar alcohol.
It is still further object of the present disclosure to provide a process for preparing a dianhydrosugar alcohol which can eliminate additional steps of crystallization and recrystallization.
It is another object of the present disclosure to provide an integrated process for the production of a polymer using a dianhydrosugar alcohol.
It is yet another object of the present disclosure to provide an integrated process for the production of a polymer which utilizes less amount of starting material.
It is still another object of the present disclosure to provide a polymer having improved glass transition temperature and crystallinity.
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:
In accordance with one aspect of the present disclosure there is provided a process for obtaining a purified dianhydrosugar alcohol; said process comprising the following steps:
a) dehydrating a sugar alcohol in the presence of at least one acid catalyst with simultaneous removal of water to obtain a reaction mixture;
b) subjecting the reaction mixture to distillation to obtain a crude dianhydrosugar alcohol;

c) mixing the crude dianhydrosugar alcohol with at least one diol to obtain a dispersion; and
d) contacting the dispersion with at least one adsorption aid to obtain a dispersion containing purified dianhydrosugar alcohol.
Typically, the step of neutralizing the reaction mixture by an alkali.
Typically, the method step of dehydration is carried out under continuous stirring at a temperature of 100 to 150°C and a pressure of 5 to 15 mmHg.
Typically, the sugar alcohol is at least one selected from the group consisting of sorbitol, mannitol, galactitol, fucitol and iditol.
Typically, the acid catalyst is at least one selected from the group consisting of sulfuric acid, phosphoric acid; alkyl, aryl, and arylalkylsulfonic acids, polymer bound sulfonic acids, trifluoromethanesulfonic acid, strong acid resins, acid forms of perfluorinated membranes, heteropoly acids and their acidic salts, zeolites and acid clays.
Typically, the acid catalyst is at least one phosphonate based catalyst selected from the group consisting of 2-aminoethylphosphonic acid (AEPn), dimethyl methylphosphonate (DMMP), 1-hydroxy ethylidene-l,l-diphosphonic acid (HEDP), amino tris(methylene phosphonic acid) (ATMP), ethylenediamine tetra(methylene phosphonic acid) (EDTMP), tetramethylenediamine tetra(methylene phosphonic acid) (TDTMP), hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), phosphonobutane-tricarboxylic acid (PBTC), N-(phosphonomethyl)iminodiacetic acid (PMIDA), 2-carboxyethyl phosphonic acid (CEPA), 2-hydroxyphosphonocarboxylic acid (HPAA), amino-tris-(methylene-phosphonic acid) (AMP) and diethylene triamine pentamethylene phosphonate (DTPMP/DETMP).

Typically, the amount of the acid catalyst ranges between 0.1 and 5 wt % with respect to the weight of the sugar alcohol.
Typically, the diol is at least one selected from the group consisting of monoethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane diol, 8-octane diol, 1,10 decanediol, 2,2-dimethyl-l,3-propanediol, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diol, cyclobutanediol, cyclobutane dimethanol, tetramethane cyclobutanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and their ester forming derivatives.
Typically, the adsorption aid is at least one selected from the group consisting of charcoal, activated carbon and fuller's earth.
Typically, the sugar alcohol is sorbitol, diol is monoethylene glycol and dianhydrosugar alcohol is isosorbide.
Typically, the purity of the dianhydrosugar alcohol is at least 99 %.
Typically, the yield of the dianhydrosugar alcohol is at least 75 %.
Typically, the formation of unwanted side products/polymers is less than 1 %.
In accordance with another aspect of the present disclosure there is provided a process for production of poly(alkylene-co-dianhydrosugar ester) dicarboxylate, said process comprising the following steps:
a) dehydrating a sugar alcohol in the presence of at least one acid catalyst with simultaneous removal of water to obtain a reaction mixture;
b) subjecting the reaction mixture to distillation to obtain a crude dianhydrosugar alcohol;

c) mixing the crude dianhydrosugar alcohol with at least one diol to obtain a dispersion;
d) contacting the dispersion with at least one adsorption aid to obtain a dispersion containing a purified dianhydrosugar alcohol;
e) subjecting the dispersion containing a purified dianhydrosugar alcohol with at least one dicarboxylic acid compound and optionally, at least one diol to esterification to obtain a pre-polymer; and
f) polycondensing the pre-polymer to obtain poly(alkylene-co-dianhydrosugar ester) dicarboxylate.
Typically, a step of neutralizing the reaction mixture by an alkali.
Typically, the method step of dehydration is carried out under continuous stirring at a temperature of 100 to 150°C and a pressure of 5 to 15 mmHg.
Typically, the sugar alcohol is at least one selected from the group consisting of sorbitol, mannitol, galactitol, fucitol and iditol.
Typically, the acid catalyst is at least one selected from the group consisting of sulfuric acid, phosphoric acid; alkyl, aryl, and arylalkylsulfonic acids, polymer bound sulfonic acids, trifluoromethanesulfonic acid, strong acid resins, acid forms of perfluorinated membranes, heteropoly acids and their acidic salts, zeolites and acid clays.
Typically, the acid catalyst is at least one phosphonate based catalyst selected from the group consisting of 2-aminoethyIphosphonic acid (AEPn), dimethyl methylphosphonate (DMMP), 1-hydroxy ethylidene-l,l-diphosphonic acid (HEDP), amino tris(methylene phosphonic acid) (ATMP), ethylenediamine tetra(methylene phosphonic acid) (EDTMP), tetramethylenediamine tetra(methylene phosphonic acid) (TDTMP), hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), phosphonobutane-tricarboxylic

acid (PBTC), N-(phosphonomethyl)iminodiacetic acid (PMIDA), 2-carboxyethyl phosphonic acid (CEPA), 2-hydroxyphosphonocarboxylic acid (HPAA), amino-tris-(methylene-phosphonic acid) (AMP) and diethylene triamine pentamethylene phosphonate (DTPMP/DETMP).
Typically, the amount of the acid catalyst ranges between 0.1 and 5 wt % with respect to the weight of the sugar alcohol.
Typically, the diol is at least one selected from the group consisting of monoethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane diol, 8-octane diol, 1,10 decanediol, 2,2-dimethyl-l,3-propanediol, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diol, cyclobutanediol, cyclobutane dimethanol, tetramethane cyclobutanediol, diethylene glycol and their ester forming derivatives.
Typically, the adsorption aid is at least one selected from the group consisting of charcoal, activated carbon and fuller's earth.
Typically, the dicarboxylic acid compound is at least one selected from the group consisting of terephthalic acid, isophthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, naphthalene dicarboxylic acid and cyclohexane dicarboxylic acid, the corresponding diester with a lower alcohol and their ester forming derivatives.
Typically, the esterification is carried out at a temperature ranging between 200°C and 300°C
Typically, the polycondensation is carried out at a temperature ranging between 200°C and 300°C
Typically, the dianhydrosugar is isosorbide, the dicarboxylic acid compound is terephthalic acid, diol is monoethylene glycol and the poly(alkylene-co-

dianhydrosugar ester) dicarboxylate is poly(ethylene-co-isosorbide)
terephthalate.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
The disclosure will now be described with reference to accompanying drawing.
Figure 1 illustrates a process for the preparation of a purified dianhydrosugar
alcohol.
Figure 2 illustrates a process for the preparation of poly (alkylene- co-
dianhydro sugar ester) dicarboxylate using the purified dianhydrosugar alcohol
of the present disclosure.
DETAILED DESCRIPTION:
The prior art reveals that processes for the preparation of dianhydrosugar alcohols, which involve dehydration of sugar alcohols in the presence of one or more acid catalysts, are economical and preferred. However, these processes further require purification and/or recrystallization steps in order to reduce the presence of the colored impurities and other by-products. Further, the resulting products obtained after crystallization or purification are still not suitable for manufacturing of polymers.
Therefore, in order to obviate the limitations of the prior art processes the inventors of the present disclosure have developed a simple and selective method for the preparation of purified dianhydrosugar alcohols. After conducting several experiments and trials the inventors of the present disclosure have found that the colored impurities formed in the preparation of the dianhydrosugar alcohol can effectively be eliminated by first dispersing the dianhydrosugar alcohol in a suitable diol and then adsorbing the colored impurities by means of adsorption aids. It is found that separating colored impurities by using adsorption aids in order to obtain a dispersion containing

purified dianhydrosugar alcohol is advantageous over the crystallization
processes of the prior art.
Further, the inventors of the present disclosure surprisingly have found that the
polymer prepared using the dispersion containing purified dianhydrosugar
alcohol exhibits high crystallinity and glass transition temperature.
In accordance with one aspect of the present disclosure there is provided a
process for the preparation of the purified dianhydrosugar alcohols. The process
involves the following steps:
In the first step, sugar alcohol is dehydrated in the presence of one or more acid
catalysts with simultaneous removal of water, which is formed as a by-product
of the dehydration reaction, at a temperature of 100 to 150°C and at a pressure
of 5 to 15 mmHg to obtain a reaction mixture containing a crude
dianhydrosugar alcohol and unreacted acid catalyst. The reaction mixture is then
subjected to a distillation process in order to separate the unreacted acid catalyst
and crude dianhydrosugar alcohol.
Typically, the sugar alcohol includes but is not limited to at least one of sorbitol,
mannitol, galactitol, fucitol and iditol. The amount of acid catalyst is maintained
in the range of 0.1 and 5 wt % with respect to the mass of the sugar alcohol. In
accordance with one embodiment of the present disclosure the reaction mixture
is neutralized by using an alkali.
Typically, the acid catalyst includes but is not limited to at least one of sulfuric acid, phosphoric acid; alkyl, aryl, and arylalkylsulfonic acids, polymer bound sulfonic acids, trifluoromethanesulfonic acid, strong acid resins, acid forms of perfluorinated membranes, heteropoly acids and their acidic salts, zeolites and acid clays.
Typically, the phosphonate based acid catalyst includes but is not limited to 2-aminoethylphosphonic acid (AEPn), dimethyl methylphosphonate (DMMP), 1-hydroxy ethylidene-l,l-diphosphonic acid (HEDP), amino tris(methylene

phosphonic acid) (ATMP), ethylenediamine tetra(methylene phosphonic acid)
(EDTMP), tetramethylenediamine tetra(methylene phosphonic acid) (TDTMP),
hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP),
phosphonobutane-tricarboxylic acid (PBTC), N-
(phosphonomethyl)iminodiacetic acid (PMIDA), 2-carboxyethyl phosphonic acid (CEPA), 2-hydroxyphosphonocarboxylic acid (HPAA), amino-tris-(methylene-phosphonic acid) (AMP) and diethylene triamine pentamethylene phosphonate (DTPMP/DETMP).
In the second step, the crude dianhydrosugar alcohol is mixed with at least one diol to obtain a dispersion. Said dispersion is then contacted with adsorption aids such as charcoal, activated carbon, and Fuller's earth to obtain a purified dispersion containing a purified dianhydrosugar alcohol. Typically, the purified dianhydrosugar alcohol obtained in accordance with the present disclosure is characterized by having at least 99% of purity.
Typically, the diol includes but is not limited to monoethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane diol, 8-octane diol, 1,10 decanediol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diol, cyclobutanediol, cyclobutane dimethanol, tetramethane cyclobutanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and their ester forming derivatives. In accordance with one exemplary embodiment of the present disclosure the sugar alcohol is sorbitol, the diol is monoethylene glycol and the dianhydrosugar alcohol is isosorbide.
In accordance with another aspect of the present disclosure there is provided a process for preparing poly(alkylene-co-dianhydrosugar ester) dicarboxylate by using the purified dispersion obtained herein above. The process involves the following steps:

In the first step, the dispersion containing the purified dianhydrosugar alcohol is mixed with a dicarboxylic acid and then subjected to the esterification to obtain a pre-polymer. In accordance with one of the embodiments of the present disclosure the dispersion is mixed with excess of diol along with the dicarboxylic acid and then esterified to obtain a pre-polymer. The pre-polymer is then polycondensed to obtain a poly(alkylene-co-dianhydrosugar ester) dicarboxylate.
In accordance with one of the embodiments of the present disclosure water and the unreacted diol present in the pre-polymer are separated before the method step of polycondensation.
In accordance with one of the exemplary embodiments of the present disclosure the dianhydrosugar is isosorbide, the dicarboxylic acid compound is terephthalic acid, diol is monoethylene glycol and the poly(alkylene-co-dianhydrosugar ester) dicarboxylate is poly(ethylene-co-isosorbide) terephthalate.
The process for the preparation of purified dianhydrosugar alcohols is further illustrated in accordance with Figure 1 of the accompanying drawings. A sugar alcohol is dehydrated in a reaction zone (14) by using an acid catalyst to obtain a reaction mixture. Water formed due to dehydration of the sugar alcohol is simultaneously separated at a temperature of 100 to 150°C and at a pressure of 5 to 15 mmHg and collected through line (18). The reaction mixture containing a crude dianhydrosugar and an unreacted acid catalyst is then passed to a distillation zone (22) through line (20), wherein the distillation of the reaction mixture is carried out to separate the unreacted acid catalyst and the crude dianhydrosugar alcohol. In accordance with one embodiment of the present disclosure the separated acid catalyst is recycled to the reaction zone (14) via line (24).

In the second step, the crude dianhydrosugar alcohol and a diol are mixed in a purification zone (28) to obtain a dispersion. The dispersion so obtain is further treated with an adsorption aid to obtain a purified dianhydrosugar alcohol. The process for the preparation of poly(alkylene-co-dianhydrosugar ester) dicarboxylate by using the purified dianhydrosugar alcohol obtained herein above is further illustrated in accordance with the Figure 2. The process involves the following steps:
In the first step, the dispersion containing purified dianhydrosugar alcohol is mixed with a dicarboxylic acid and then esterified in an ester interchange zone (32) via line (30) in order to obtain a pre-polymer. In accordance with one of the embodiments of the present disclosure the purified dispersion is esterified with excess diol and dicarboxylic acid to obtain a pre-polymer. The pre-polymer is then introduced in a polymerization zone (38) via line (36) and then polycondensed to obtain a poly(alkylene-co-dianhydrosugar ester) dicarboxylate.
Water formed as a by-product of esterification of the purified dianhydrosugar alcohol is separated from the pre-polymer in the ester interchange zone (32) and then introduced to a distillation zone (46) via line (44). The distillation zone (46) is adapted to fractionate water and the unreacted diol via line (48) and (50) respectively. In accordance with one of the embodiment of the present disclosure the unreacted diol is recycled to the purification zone (28).
Hereinafter, the present disclosure will be described in more detail with reference to the following Examples, but the scope of the present disclosure is not limited thereto.

Example 1:
100 gm of sorbitol was dehydrated in the presence of 1.0 gm of 1-Hydroxyethylidene 1,1 -Diphosphonic acid catalyst under continuous stirring to obtain isosorbide along with water and unreacted acid catalyst. Water obtained due to dehydration of sorbitol was simultaneously fractionated at a temperature of 100 C and a pressure 15 mmHg to obtain a first mixture containing crude isosorbide and unreacted acid catalyst. The first mixture was then distilled to separate unreacted acid catalyst.
60 gm of crude isosorbide so obtained was then mixed with 60 ml of monoethylene glycol and 12 gm of charcoal to obtain purified isosorbide dispersed in a monoethylene glycol. Yields and purity are 75% and 99 %
respectively.
Example 2:
100 gm of sorbitol was dehydrated in the presence of 1.0 gm of 1-Hydroxyethylidene 1,1 -Diphosphonic acid catalyst under continuous stirring to obtain isosorbide along with water and acid catalyst. Water obtained due to dehydration of sorbitol was simultaneously fractionated at a temperature of 150 °C and a pressure 5 mmHg to obtain a first mixture containing isosorbide and unreacted acid catalyst. The first mixture was then distilled to separate unreacted acid catalyst.
60 gm of crude isosorbide so obtained was then mixed with 60.ml of monoethylene glycol and 9 gm of activated carbon to obtain purified isosorbide dispersed in a monoethylene glycol. Yields and purity are 75% and 99 % respectively.
Example 3:
Purified terephthalic acid (PTA) was esterified with Isosorbide- monoethylene glycol (MEG) solution obtained from Example 1.

PTA and MEG was maintained at a molar ratio of 1:2 molar ratio of PTA and MEG was maintained. The isosorbide is maintained at 5 wt % based on final polymer was targeted. Tin oxalate (40 ppm as a metallic tin (Sn) based on final polymer) in the form of slurry was added as catalyst. The esterification was carried out at around 260°C to obtain oligomer. The oligomer obtained was further melt polymerized at 290°C to obtain polyester polymer having intrinsic viscosity (IV) up to 0.6 dl/g. Antimony trioxide (290ppm as elemental antimony (Sb) based on final polymer) was added as catalyst and 25 ppm Phosphorus (P) and 25 ppm of Cobalt (Co) (based on final polymer) was added as a thermal stabilizer and colorant respectively. The polymer melt was then extruded out from the reactor in the form of amorphous cylindrical chips. These amorphous chips were analyzed for intrinsic viscosity (IV), Color and carboxylic acid (COOH) content. These amorphous polymer particles were used as precursor for solid-state polymerization. The solid state polymerization was carried out to obtain polymer of 0.8 IV
Melt Polymerization:-

ID Sb (ppm) Sn (ppm) Co (ppm) P(ppm) Isosorbide (%) Esterification Time (Min) Polycondensation Time (Min)
3 290 40 25 25 5 202 99
Amorphous chips:

ID IV(dl/g) L* a* b*
3 0.590 67.3 0.52 2.21
*scale, 'L' representing white and black colours, 'a' representing red and green colours and 'b' representing yellow and blue colours

Thermal Behavior

Recipe glass transition temperature Tg(°C)
3 83.8
Solid State Polymerization: -

ID IV(dl/g) L* a* b*
3 0.803 80.2 0.29 2.8
*scale, 'L' representing white and black colours, 'a' representing red and green colours and 'b' representing yellow and blue colours
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 "a", "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.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure and the claims unless there is a statement in the specification to the contrary.

While certain embodiments of the disclosure have been described, these embodiments have been presented by way of examples only, and are not intended to limit the scope of the disclosure. Variations or modifications in the process of this disclosure, within the scope of the disclosure, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this disclosure.

We claim,
1. A process for obtaining a purified dianhydrosugar alcohol; said process
comprising the following steps:
a) dehydrating a sugar alcohol in the presence of at least one acid catalyst with simultaneous removal of water to obtain a reaction mixture;
b) subjecting the reaction mixture to distillation to obtain a crude dianhydrosugar alcohol;
c) mixing the crude dianhydrosugar alcohol with at least one diol to obtain a dispersion; and
d) contacting the dispersion with at least one adsorption aid to obtain a dispersion containing purified dianhydrosugar alcohol.

2. The process as claimed in claim 1, further comprises the step of neutralizing the reaction mixture by an alkali.
3. The process as claimed in claim 1, wherein the method step of dehydration is carried out under continuous stirring at a temperature of 100 to 150°C and a pressure of 5 to 15 mmHg.
4. The process as claimed in claim 1, wherein the sugar alcohol is at least one selected from the group consisting of sorbitol, mannitol, galactitol, fucitol and iditol.
5. The process as claimed in claim 1, wherein the acid catalyst is at least one selected from the group consisting of sulfuric acid, phosphoric acid; alkyl, aryl, and arylalkylsulfonic acids, polymer bound sulfonic acids, trifluoromethanesulfonic acid, strong acid resins, acid forms of

perfluorinated membranes, heteropoly acids and their acidic salts, zeolites and acid clays.
6. The process as claimed in claim 1, wherein the acid catalyst is at least one phosphonate based catalyst selected from the group consisting of 2-aminoethylphosphonic acid (AEPn), dimethyl methylphosphonate (DMMP), 1-hydroxy ethylidene-l,l-diphosphonic acid (HEDP), amino tris(methylene phosphonic acid) (ATMP), ethylenediamine tetra(methylene phosphonic acid) (EDTMP), tetramethylenediamine tetra(methylene phosphonic acid) (TDTMP), hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), phosphonobutane-tricarboxylic acid (PBTC), N-(phosphonomethyl)iminodiacetic acid (PMIDA), 2-carboxyethyl phosphonic acid (CEPA), 2-hydroxyphosphonocarboxylic acid (HPAA), amino-tris-(methylene-phosphonic acid) (AMP) and diethylene triamine pentamethylene phosphonate (DTPMP/DETMP).
7. The process as claimed in claim 1, wherein the amount of the acid catalyst ranges between 0.1 and 5 wt % with respect to the weight of the sugar alcohol.
8. The process as claimed in claim 1, wherein the diol is at least one selected from the group consisting of monoethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane diol, 8-octane diol, 1,10 decanediol, 2,2-dimethyl-l,3-propanediol, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diol, cyclobutanediol, cyclobutane dimethanol, tetramethane cyclobutanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and their ester forming derivatives.

9. The process as claimed in claim 1, wherein the adsorption aid is at least one selected from the group consisting of charcoal, activated carbon and fuller's earth.
10.The process as claimed in claim 1, wherein the sugar alcohol is sorbitol, diol is monoethylene glycol and dianhydrosugar alcohol is isosorbide.
1 l.The process as claimed in claim 1, wherein the purity of the dianhydrosugar alcohol is at least 99 %.
12.The process as claimed in claim 1, wherein the yield of the dianhydrosugar alcohol is at least 75 %.
13. The process as claimed in claim 1, wherein the formation of unwanted side products/polymers is less than 1 %.
14. A process for production of poly(alkylene-co-dianhydrosugar ester) dicarboxylate, said process comprising the following steps:

a) dehydrating a sugar alcohol in the presence of at least one acid catalyst with simultaneous removal of water to obtain a reaction mixture;
b) subjecting the reaction mixture to distillation to obtain a crude dianhydrosugar alcohol;
c) mixing the crude dianhydrosugar alcohol with at least one diol to obtain a dispersion;
d) contacting the dispersion with at least one adsorption aid to obtain a dispersion containing a purified dianhydrosugar alcohol;
e) subjecting the dispersion containing a purified dianhydrosugar alcohol with at least one dicarboxylic acid compound and

optionally, at least one diol to esterification to obtain a pre-polymer; and f) polycondensing the pre-polymer to obtain poly (alkylene-co-dianhydrosugar ester) dicarboxylate.
15.The process as claimed in claim 14, further comprises a step of neutralizing the reaction mixture by an alkali.
16.The process as claimed in claim 14, wherein the method step of dehydration is carried out under continuous stirring at a temperature of 100 to 150°C and a pressure of 5 to 15 mmHg.
17.The process as claimed in claim 14, wherein the sugar alcohol is at least one selected from the group consisting of sorbitol, mannitol, galactitol, fucitol and iditol.
18.The process as claimed in claim 14, wherein the acid catalyst is at least one selected from the group consisting of sulfuric acid, phosphoric acid; alkyl, aryl, and arylalkylsulfonic acids, polymer bound sulfonic acids, trifluoromethanesulfonic acid, strong acid resins, acid forms of perfluorinated membranes, heteropoly acids and their acidic salts, zeolites and acid clays.
19.The process as claimed in claim 14, wherein the acid catalyst is at least one phosphonate based catalyst selected from the group consisting of 2-aminoethylphosphonic acid (AEPn), dimethyl methylphosphonate (DMMP), 1-hydroxy ethylidene-l,l-diphosphonic acid (HEDP), amino tris(methylene phosphonic acid) (ATMP), ethylenediamine tetra(methylene phosphonic acid) (EDTMP), tetramethylenediamine tetra(methylene phosphonic acid)

(TDTMP), hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), phosphonobutane-tricarboxylic acid (PBTC), N-(phosphonomethyl)iminodiacetic acid (PMIDA), 2-carboxyethyl phosphonic acid (CEPA), 2-hydroxyphosphonocarboxylic acid (HPAA), amino-tris-(methylene-phosphonic acid) (AMP) and diethylene triamine pentamethylene phosphonate (DTPMP/DETMP).
20.The process as claimed in claim 14, wherein the amount of the acid catalyst ranges between 0.1 and 5 wt % with respect to the weight of the sugar alcohol.
21.The process as claimed in claim 14, wherein the diol is at least one selected from the group consisting of monoethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane diol, 8-octane diol, 1,10 decanediol, 2,2-dimethyl-l,3-propanediol, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diol, cyclobutanediol, cyclobutane dimethanol, tetramethane cyclobutanediol, diethylene glycol and their ester forming derivatives.
22.The process as claimed in claim 14, wherein the adsorption aid is at least one selected from the group consisting of charcoal, activated carbon and fuller's earth.
23.The process as claimed in claim 14, wherein the dicarboxylic acid compound is at least one selected from the group consisting of terephthalic acid, isophthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, naphthalene dicarboxylic acid and cyclohexane dicarboxylic acid, the corresponding diester with a lower alcohol and their ester forming derivatives.

24.The process as claimed in claim 14, wherein the esterification is carried out at a temperature ranging between 200°C and 300 °C.
25.The process as claimed in claim 14, wherein the polycondensation is carried out at a temperature ranging between 200 °C and 300 °C.
26. The process as claimed in claim 14, wherein the dianhydrosugar is isosorbide, the dicarboxylic acid compound is terephthalic acid, diol is monoethylene glycol and the poly(alkylene-co-dianhydrosugar ester) dicarboxylate is poly(ethylene-co-isosorbide) terephthalate.