DESC:FIELD
The present disclosure relates to a process for preparing a stable polyester polyol.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Aromatic polyols, derived from polyester, are important intermediates for the manufacture of polyurethane based foams, useful for insulation applications. Polyethylene terephthalate is an important substrate for preparing polyols. The polyols are preferred to be obtained in liquid form for usage in most applications. The polyols are obtained in liquid form by achieving an optimum value of viscosity, acid value and/or hydroxyl value.
However, it is difficult to obtain polyols in liquid form by using conventional methods. In addition, the polyols obtained in liquid state precipitate upon storage, making it impractical for usage in further applications.
There is, therefore, felt a need for a process for preparing polyols that mitigates the drawbacks mentioned hereinabove.
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 ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for preparing polyols from polyester flakes.
Still another object of the present disclosure is to provide polyols having desired viscosity, acid value, and hydroxyl value.
Yet another object of the present disclosure is to provide polyols having comparatively better storage stability.
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 provides a process for preparing a stable polyester polyol. The process comprises a step of forming a slurry of polyester flakes and glycols. The weight ratio of polyester flakes and the glycols is in the range of 1:1 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 (PEG). Zinc acetate is added to the slurry and the slurry is homogenized under stirring. The homogenized slurry is heated at a temperature in the range of 200 °C to 300 °C for a time period in the range of 3 hours to 7 hours to transesterify the polyester with glycols, followed by cooling the transesterified slurry to obtain a stable polyester polyol in liquid form.
The present disclosure further provides a stable polyester polyol in liquid form at 25 °C, having hydroxyl value in the range of 200 to 300 mgKOH/gm, acid value of less than 2 mgKOH/gm and viscosity in the range of 3500 to 5000 centipoise at 25 °C.
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 conventionally prepared by polyesterification of dicarboxylic acids or by transesterification of polyester. The polyols are used for the manufacture of polyurethane foams which are suitable in applications such as insulation, automotive applications and manufacture of synthetic fabrics.
One of the limitations of the present process is the difficulty in obtaining polyester polyols in liquid state. Moreover, even if the polyols are liquid in nature, they tend to lack stability and usually solidify upon storage.
The present disclosure provides a simple and economical process for preparing a stable polyester polyol. The polyol so obtained is stable and does not precipitate upon storage.
In one aspect, the present disclosure provides a process for preparing a stable polyester polyol. The process comprises a step of forming slurry of polyester flakes and glycols.
In an embodiment, the polyester is in the form of flakes.
In an embodiment, the polyester flakes are recycled from post-consumer waste, which are used in the same state or is pre-treated before use. In an embodiment, the pre-treatment includes removal of color or additives from the polyester flakes.
In an exemplary embodiment, the polyester is in the form of flakes obtained from waste bottles. In an embodiment, the polyester flakes are subjected to bleaching before using in the process.
In an exemplary embodiment, the polyester is polyethylene terephthalate.
The glycols are selected from the group consisting of monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG) and polyethylene glycol (PEG).
In an embodiment, the glycols are diethylene glycol (DEG) and triethylene glycol (TEG). The molar ratio of DEG and TEG is in the range of 1:0.9 to 1:1.2. In an exemplary embodiment, the molar ratio of DEG and TEG is 1:1.
The molar ratio of glycols i.e. diethylene glycol (DEG) and triethylene glycol (TEG), which is in the range of 1:0.9 to 1:1.2, is very important, because when the ratio is lower than the given range, the obtained polyol tends to solidify, whereas when the ratio is greater than given range, the desired properties of polyol are not obtained.
In accordance with the present disclosure, the weight ratio of the polyester flakes to the glycols is in the range of 1:1 to 1:2.5. In an exemplary embodiment, the weight ratio of the polyester flakes to the glycols is 1:1.3.
In the next step, zinc acetate is added to the slurry and the slurry containing zinc acetate is homogenized.
The zinc acetate is used as a catalyst in an amount in the range of 0.5 wt.% to 1 wt.% with respect to the polyester flakes. In an exemplary embodiment, the zinc acetate is used in an amount of 0.75 wt.%, with respect to the polyester flakes.
In the next step the homogenized slurry containing zinc acetate is heated to a temperature in the range of 200 °C to 300 °C, under stirring, for a time period in the range of 3 hours to 7 hours, to transesterify the polyester with glycols.
The temperature range of the step of heating the homogenized slurry i.e. 200 °C to 300 °C, is very significant, as below 200 °C, the reaction does not proceed to completion, whereas above 300 °C, the product tends to undergo degradation.
In an embodiment, the homogenized slurry is heated to a temperature in the range of 200 °C to 250 °C. In an exemplary embodiment, the homogenized slurry is heated at 225 °C.
The time duration of heating the homogenized slurry i.e. 3 hours to 7 hours, is very significant, as below 3 hours, the reaction does not complete, whereas beyond 7 hours, the reaction does not progress any further and hence is not economically viable.
In an embodiment, the homogenized slurry is heated for 4 hours to 6 hours. In an exemplary embodiment, the homogenized slurry is heated for 5 hours.
In an embodiment, the process comprises a step of recovering unreacted glycols.
In an embodiment, the process comprises subjecting the polyol to the removal of residual moisture.
In another aspect, the present disclosure provides a stable polyester polyol in liquid form at 25 °C.
The polyester polyol having hydroxyl value in the range of 200-300 mgKOH/gm, acid value of less than 2 mgKOH/gm and viscosity in the range of 3500-5000 centipoise at 25 °C.
In an exemplary embodiment, the polyol composition has hydroxyl value of 234 mgKOH/gm, acid value of 0.9 mgKOH/gm and viscosity of 3600 centipoise.
The process of the present disclosure is simple, environmentally friendly and economical. The polyester polyol obtained by the process of the present disclosure, advantageously, remains in liquid form at ambient temperature even upon long storage.
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 laboratory scale experiment which is set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiment can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTAL DETAIL
Experiment-1: Preparation of polyols
Polyethylene terephthalate (3.84 kg) was taken in the form of flakes, to which a glycols (5.12 kg) (mixture of diethylene glycol and polyethylene glycol in a molar ratio of 1:1) was added to obtain a slurry. Zinc acetate catalyst (28.8g) was added to the slurry. The slurry containing zinc acetate catalyst was homogenized under stirring. The homogenized slurry was heated at 225 °C for 5 hours to transesterify the polyester with glycols. The transesterified slurry was cooled to obtain polyester polyol in liquid form (sample 1). The polyester polyol was subjected to nitrogen bubbling followed by applying vacuum to remove the residual moisture.
The sample 1 was characterized for determining the hydroxyl value, acid value and viscosity which is summarized in Table 1.
Table 1: Characteristics of the polyester polyol sample (sample 1)
Sample 1 Hydroxyl value (OHV) (in mgKOH/g) Acid value (AV) (in mgKOH/g) Viscosity at 25 °C
(in centipoise) Appearance
234 0.9 3600 Dark yellowish clear liquid even after 60 days
As observed in Table 1, the hydroxyl value, acid value and viscosity is in the desired range.
The process of the present disclosure is simple, economical and environmental friendly. The polyol obtained by using the process of the present disclosure, is stable and remains in liquid form at 25 °C, even upon long term storage.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing a stable polyester polyol that:
? is simple and economical;
? provides polyol with desired characteristics; and
? provides polyols which remain in liquid form upon storage.
The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications 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.
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” or “a’ 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 a 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.
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 components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure 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 preparing a stable polyester polyol, said process comprising the following steps:
(i) forming a slurry of polyester flakes and glycols, wherein the weight ratio of the polyester flakes and the glycols is in the range of 1:1 to 1:2.5; wherein the glycols are selected from the group consisting of monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG) and polyethylene glycol (PEG);
(ii) adding zinc acetate to said slurry;
(iii) homogenizing the slurry containing zinc acetate;
(iv) heating the homogenized slurry to a temperature in the range of 200 °C to 300 °C, under stirring, for a time period in the range of 3 hours to 7 hours to transesterify the polyester with glycols; and
(v) cooling the transesterified slurry to obtain polyester polyol in liquid form.
2. The process as claimed in claim 1, wherein the glycols are diethylene glycol (DEG) and triethylene glycol (TEG).
3. The process as claimed in claim 2, wherein the molar ratio of DEG to TEG is in the range of 1:0.9 to 1:1.2.
4. The process as claimed in claims 2 or 3, wherein the molar ratio of DEG to TEG is 1:1.
5. The process as claimed in claim 1, wherein the zinc acetate is present in an amount in the range of 0.25 wt% to 0.75 wt.% with respect to the polyester flakes.
6. The process as claimed in claim 1, which further includes a step of removing residual moisture.
7. The process as claimed in claim 6, wherein the step of removing residual moisture is performed by bubbling nitrogen through the liquid polyester polyol obtained, followed by applying vacuum.
8. A stable polyester polyol in liquid form at 25 °C.
9. The stable polyester polyol as claimed in claim 8, having hydroxyl value in the range of 200-300 mgKOH/gm, acid value of less than 2 mgKOH/gm and viscosity in the range of 3500-5000 centipoise at 25 °C.