DESC:FIELD
The present disclosure relates to a process for the preparation of a stable polyester polyol.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Polyester polyols: The term “Polyester polyols” refer to compounds formed by the condensation reaction of stoichiometric excess of glycol (diol, triol, or mixtures thereof) with a dicarboxylic acid.
Crude terephthalic acid: The term “Crude terephthalic acid (CTA)” refers to terephthalic acid having a purity of 99.7% which contains 0.3% impurities such as 4-carboxybenzaldehyde, and p-toluic acid.
Titanium Glycolate: The term “Titanium glycolate” refers to a chemical compound synthesized by the reaction of titanium butoxide with monoethylene glycol.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Polyester polyols are useful starting materials for the preparation of a variety of polymeric or resin compositions. Aromatic polyester polyols are widely used in the manufacture of polyurethane and polyurethane-poly isocyanurate foams and resins. It is also known in the art that, polyurethane plastics are prepared by reacting polyester polyols with di-isocyanates in the presence of a catalyst by addition polymerization process. Polyester polyols are commonly prepared from dicarboxylic acids such as terephthalic acid and glycols by melt condensation or by the transesterification of polyester derivatives.
The conventional processes for the preparation of polyester polyol, require the purification of terephthalic acid as an essential step which can add to the cost of manufacture of the polyols.
Further, it is preferable to obtain polyols in liquid form for usage in the manufacture of products such as polyurethane foams. However, using the conventional processes, the liquid polyols either solidify immediately after preparation or upon storage.
Therefore, there is felt a need for a process for preparing polyester polyols that mitigates the drawbacks mentioned herein above.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a polyester polyol having a stable liquid form at 25oC.
Still another object of the present disclosure is to provide a simple and cost effective process for preparing polyester polyols.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to a process for preparation of a stable polyester polyol. The process comprises mixing crude terephthalic acid with a mixture of glycols to obtain slurry, to which a catalyst is added. The slurry containing the catalyst is homogenized, and then the homogenized slurry is heated to a temperature in the range of 200 oC to 300 oC under stirring, for a time period in the range of 4 hours to 8 hours, to polyesterify the crude terephthalic acid and glycols in the slurry. The slurry comprising polyesterified crude terephthalic acid and glycols is cooled to obtain polyester polyol, having liquid form at 25 °C.
The molar ratio of crude terephthalic acid (CTA) to the mixture of glycols is in the range of 1:1.5 to 1:2.5. The glycols are selected from the group consisting of monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG), and polyethylene glycol.
The present disclosure further provides a stable polyester polyol in a liquid form at 25 °C. The stable polyester polyol has hydroxyl value in the range of 200-310 mg of KOH/gm, acid number in the range of 0.5 to 1.5 mg of KOH/gm and viscosity in the range of 4000-7000 centipoise.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
Polyester polyols are used to produce polyurethane (PU) foams which are suitable for electrical insulation, automotive applications, and manufacture of synthetic fabrics. The polyester polyols are preferred to be in stable liquid state, especially upon storage.
Further, the conventional processes for the preparation of polyester polyols require purification of starting materials such as terephthalic acid as an essential step which can add to the cost of manufacture of polyols.
The present disclosure provides a simple and economical process for the preparation of a stable polyester polyol. The process of the present disclosure provides an effective way to prepare polyester polyols from crude terephthalic acid, which gives a stable liquid polyol.
In one aspect, the present disclosure provides a process for the preparation of stable polyester polyols. The process is described in detail herein below:
The process comprises mixing crude terephthalic acid with a mixture of glycols to obtain slurry.
In accordance with the present disclosure, the crude terephthalic acid is production waste and/or post-consumer waste. In an embodiment, the crude terephthalic acid has a purity of 99.7% and contains 0.3% impurities such as 4-carboxy benzaldehyde and para-toluic acid.
The molar ratio of crude terephthalic acid (CTA) to the mixture of glycols is in the range of 1:1.5 to 1:2.5. In an exemplary embodiment, the molar ratio of crude terephthalic acid (CTA) to the mixture of glycols is 1:2.
The glycols are selected from the group consisting of monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG), and polyethylene glycol.
In an embodiment, the glycols are a mixture of diethylene glycol (DEG) and triethylene glycol (TEG). The molar ratio of DEG to TEG is in the range of 1:0.8 to 1:1.5. In an exemplary embodiment, the molar ratio of DEG to TEG is 1:1.
The aforestated molar ratio of DEG to TEG used in the process of the present disclosure is significant, as beyond the mentioned range, the prepared polyols tend to solidify either immediately after preparation or upon storage.
In an embodiment, the catalyst is titanium glycolate, wherein the moisture content in the titanium glycolate is in the range of 20% to 30%. In an exemplary embodiment, the moisture content in the titanium glycolate is 26%.
The amount of the catalyst is in the range of 10 to 100 ppm with respect to the crude terephthalic acid. In an exemplary embodiment, the amount of the catalyst is 50 ppm with respect to the crude terephthalic acid.
In an embodiment, the temperature in the step of heating the homogenized slurry is in the range of 220 oC to 230 oC. In an exemplary embodiment, the temperature in the step of heating the homogenized slurry is 225 oC.
In an embodiment, the time period for the step of heating the homogenized slurry is in the range of 5 hours to 7 hours. In an exemplary embodiment, the time period for the step of heating the homogenized slurry is 5 hours.
In one embodiment, the process of the present disclosure is a continuous process. In another embodiment, the process of the present disclosure is a batch process.
In another aspect, the present disclosure provides a stable polyester polyol having a liquid form at 25 °C. The polyol has hydroxyl value in the range of 200-310 mg of KOH/gm, acid number in the range of 0.5 to 1.5 mg of KOH/gm and viscosity in the range of 4000-7000 centipoise.
In an exemplary embodiment, the polyester polyol has hydroxyl value of 254 mg of KOH/gm, acid number of 0.6 mg of KOH/gm and viscosity of 6900 centipoise.
In an embodiment, the polyester polyol is a transparent liquid.
The polyester polyol obtained by the process of the present disclosure is transparent, has stable liquid form at 25°C and does not precipitate even upon storage.
The present disclosure provides a rapid process for the preparation of polyester polyols that avoids purification of crude terephthalic acid that makes the process economical and environment friendly.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be tested to scale up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

Experimental Details:
Example 1: Preparation of polyester polyol (Sample 1)
Crude terephthalic acid (125 g, 99.7% pure) and a mixture of diethylene glycol and triethylene glycol (190 g, molar ratio of 1:1) were mixed under nitrogen, in a reactor, to obtain slurry. Titanium glycolate having moisture content of 26% (50 ppm with respect to CTA) was added to the slurry. The slurry containing the titanium glycolate was homogenized at 225 °C for 5 hours to obtain homogenized slurry containing yellowish brown colored polyester polyols. The slurry containing polyester polyol is cooled to 25 °C to obtain polyester polyols in liquid form.
Example 2: Preparation of polyester polyol (Sample 2):
Sample 2 was prepared by using the experimental process as given in Experiment 1, except that the crude terephthalic acid used was obtained from a different source.
Comparative Example A: Preparation of polyol (Sample 3)
Sample 2 was prepared by using the experimental process as given in Experiment 1, except that only DEG was used instead of a mixture of DEG and TEG.
Comparative Example B: Preparation of polyol (Sample 4)
Sample 2 was prepared by using the experimental process as given in Experiment 1, except that the molar ratio of CTA to glycol was 1:1.8 instead of 1:2.
The polyester polyols, prepared in accordance to the present disclosure (Samples 1 and 2) were tested for measuring the acid values, viscosity and hydroxyl values, which was compared with Samples 3 and 4 (prepared as per the comparative examples A and B). The results are presented in Table-1.

Table-1: Properties of polyester polyol
Sample No. Molar ratio of CTA:Glycols (DEG+TEG) Glycols used and their molar ratio Hydroxy Value (in mg KOH/g) Acid Value (in mg KOH/g) Viscosity (in Cp) at 25 °C Product nature
Sample 1 (Example-1) 1:2 DEG and TEG
1:1 254 0.6 6900 Yellowish brown colored liquid even after 60 days
Sample 2 (Example-2) 1:2 DEG and TEG
1:1 242.6 0.8 4451 Dark brown colored liquid even after 60 days
Sample 3 (Comparative Example-A) 1:2 DEG 305 1 NA White, solid in room temperature (forms solid in 4 days)
Sample (Comparative Example-B) 1:1.8 DEG and TEG
1:0.8 248 1.4 6570 Yellowish brown (forms solid after 60 days)

As observed in Table 1, the polyols prepared as per the present disclosure (Examples 1 and 2), are obtained in liquid form, which does not solidify upon storage.
The process of the present disclosure does not require the step of purification of crude terephthalic acid thereby rendering the process economical. Further, the process of the present disclosure provides polyester polyol, which is a stable and transparent liquid at 25 °C.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of a stable polyester polyol, which
• is simple and economical; and
• provides a stable and clear liquid at 25 °C
The embodiments as described herein above, and various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description.
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.
The foregoing description of specific embodiments so fully reveal the general nature of the embodiments herein, that others can, by applying current knowledge, readily modify and/or adapt for various applications of such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Further, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
Having described and illustrated the principles of the present disclosure with reference to the described embodiments, it will be recognized that the described embodiments can be modified in arrangement and detail without departing from the scope of such principles.
While considerable emphasis has been placed herein on the particular features of this disclosure, 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 disclosure. These and other modifications in the nature of the disclosure 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 disclosure and not as a limitation. ,CLAIMS:WE CLAIM:

1. A process for the preparation of a stable polyester polyol, said process comprising the following steps:
(a) mixing crude terephthalic acid with a mixture of glycols to obtain slurry; and
(b) adding catalyst to the slurry;
(c) homogenizing the slurry containing the catalyst;
(d) heating the homogenized slurry to a temperature in the range of 200 oC to 300 oC under stirring, for a time period in the range of 4 hours to 8 hours to polyesterify the crude terephthalic acid and glycols in the slurry;
(e) cooling the polyesterified slurry to obtain polyester polyols in liquid form.
2. The process as claimed in claim 1, wherein the molar ratio of said crude terephthalic acid (CTA) to said glycols is in the range of 1:1.5 to 1:2.5.
3. The process as claimed in claims 1 or 2, wherein the molar ratio of said crude terephthalic acid (CTA) to said glycols is 1:2.
4. The process as claimed in claim 1, wherein said glycols are selected from the group consisting of monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG), and polyethylene glycol.
5. The process as claimed in claim 1, wherein said glycols are a mixture of diethylene glycol (DEG) and triethylene glycol (TEG).
6. The process as claimed in claim 5, wherein the molar ratio of said diethylene glycol (DEG) to triethylene glycol (TEG) is in the range of 1:0.8 to 1:1.5.
7. The process as claimed in claim 6, wherein the molar ratio of said diethylene glycol (DEG) to triethylene glycol (TEG) is 1:1.
8. The process as claimed in claim 1, wherein the amount of said catalyst is in the range of 10 to 100 ppm with respect to the crude terephthalic acid.
9. The process as claimed in claim 1, wherein said catalyst is titanium glycolate.
10. The process as claimed in claim 9, wherein titanium glycolate has moisture content in the range of 20% to 30%.
11. The process as claimed in claim 1, wherein the homogenized slurry is heated to a temperature in the range of 220 oC to 230 oC.
12. The process as claimed in claim 1 or 11, wherein the homogenized slurry is heated for a time period in the range of 5 to 6 hours.
13. A stable polyester polyol being liquid at 25 °C.
14. The stable polyester polyol as claimed in claim 13, having hydroxyl value in the range of 200-310 mg of KOH/gm, acid number in the range of 0.5 to 1.5 mg of KOH/gm and viscosity in the range of 4000-7000 centipoise.