DESC:FIELD
The present disclosure relates to a process for the preparation of an ester.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
It is well-known that aromatic/ aliphatic carboxylic esters or anhydrides can be prepared by reacting organic acids with alcohols. In the esterification reactions, temperature-dependent equilibrium is formed between the starting materials (carboxylic acid and alcohol) and the products (ester and water). Conventionally, an entrainer is used to remove the water formed in the reaction, with the aim of shifting the equilibrium in favor of the product i.e. ester.
In some of the conventional processes, the starting material i.e. alcohol is used as an entrainer and after water is separated, it is recirculated back to the reaction. However, excess alcohol has the disadvantage that in the case of low-boiling alcohols, the reaction temperature at atmospheric pressure is so low that the reaction rate is too low for an industrial process. In order to counteract this effect, the reaction can be conducted under pressure, which leads to higher apparatus costs. Further, with excess of alcohol, the maximum possible concentration of the target product in the reaction vessel decreases and thus the batch yield decreases. Furthermore, the excess alcohol must be separated from the ester, which is time and energy consuming.
There is, therefore, felt a need for an improved process for preparation of aromatic/aliphatic carboxylic acid ester or anhydrides with shorter reaction times and high yields.

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.
Another object of the present disclosure is to provide a process for the preparation of aromatic and aliphatic carboxylic acid ester with shorter reaction time.
Still another object of the present disclosure is to provide a process for preparation of aromatic and aliphatic carboxylic acid ester with high batch yields of ester.
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 preparing an ester. The process comprises charging a reactor with one of a carboxylic acid or an anhydride and at least one alcohol to obtain a mixture. A catalyst is added to the mixture to obtain a resultant mixture. The resultant mixture is heated at a temperature in the range of 175 to 250?C to obtain a reaction mixture. Water and alcohol formed during the reaction is removed azeotropically from the reaction mixture to obtain a condensate comprising water and the alcohol. The alcohol is separated from the condensate and the separated alcohol is recycled to the reactor till the conversion of the acid or the anhydride to ester reaches to a range of 75 to 90% to obtain a reaction mass. The reaction is continued until the conversion of carboxylic acid or anhydride greater than 99% is achieved by azeotropically removing water and alcohol to obtain a product mixture comprising an ester. The ester is separated from the product mixture to obtain the ester having purity in the range of 95 to 99.5%.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a schematic representation of the reaction set up for esterification reaction of aromatic/aliphatic carboxylic acid.
List of Reference Numerals
REACTOR 1
OVERHEAD VAPOURS 2
CONDENSER 3
ORGANIC PHASE 4
AQUEOUS PHASE 5
REFLUX CONTROLLER 6
ETP (EFFLUENT TREATMENT PLANT) 7

DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
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.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Plasticizers are added to a resin composition to increase the flexibility of the resin composition. Common plasticizers include phthalates, in particular, ortho-phthalates, di-(2-ethylhexyl) phthalate (DEHP), di-iso-nonyl phthalate (DINP), di-isodecyl phthalate (DIDP), di-octyl phthalate (DOP), di-butyl phthalate (DBP), di-isobutyl phthalate (DIBP), di-isoheptyl phthalate (DIHP), di-octyl terephthalate (DOTP) and several other phthalates esters. The common aliphatic di-esters include Di-octyl adipate, Di-octyl sebacates, Di-octyl gluterates, Di-octyl aspartate Di-octyl azelates, Di-decyl adipate, Di-decyl sebacates and several other aliphatic carboxylic acid esters.
Di-(2-ethylhexyl) terephthalate, also known as di-octyl terephthalate or DOTP is used as a plasticizer in a variety of polymeric materials such as polyvinyl chloride. Conventionally, it can be prepared by the titanate-catalysed esterification of terephthalic acid (TPA) with 2-ethyl hexanol (2-EH) under elevated temperatures and pressures. However, these conventional processes are associated with drawbacks such as longer reaction time and low yields.
The present disclosure provides a rapid, efficient, economical, and environment friendly process for the preparation of an ester that mitigates the drawbacks mentioned herein above.
The present disclosure provides a process for preparing an ester. The process is described in detail herein below.
Initially, one of a carboxylic acid or an anhydride is added to at least one alcohol to obtain a resultant mixture.
The carboxylic acid is at least one selected from the group consisting of terephthalic acid, phthalic acid, isophthalic acid, benzoic acid, p-toluic acid, adipic acid, glutamic acid, sebacic acid, aspartic acid, succinic acid, malonic acid, azelaic acid, 2-Furoic acid, 5-Formyl-2-furancarboxylic acid, 2,5-Furan dicarboxylic acid, tetrahydrofuroic acid, tetrahydropyroncarboxylic acid, and levulinic acid. In an exemplary embodiment, the carboxylic acid used is terephthalic acid.
The anhydride is at least one selected from the group consisting of phthalic anhydride, benzoic anhydride, isophthalic anhydride, 4-methylbenzoic anhydride, acetic anhydride, and maleic anhydride. In an exemplary embodiment, the anhydride used is phthalic anhydride.
The alcohol is at least one selected from the group consisting of 2-ethyl hexanol, 2-methyl-1-octanol, 2-methyl-1-butanol, 2-methyl-1-decanol, 2-methyl-1-heptanol, benzyl alcohol, and phenyl ethyl alcohol. In an exemplary embodiment, the alcohol is 2-ethyl hexanol.
In accordance with the present disclosure, the 2-ethyl hexanol is at least one selected from fresh 2-ethyl hexanol and recycled 2-ethyl hexanol.
The mole ratio of carboxylic acid or an anhydride to alcohol is in the range of 1:1 to 1:4.
In the next step, a catalyst is added to the mixture to obtain a resultant mixture.
The catalyst is selected from a homogenous catalyst and a heterogeneous catalyst.
In accordance with the present disclosure, the catalyst is a heterogeneous catalyst selected from the group consisting of tin powder, tin (IV) oxide, tin (II) oxalate, zirconium tetra-alkoxides and zirconium dioxide. In an exemplary embodiment, the catalyst is tetra isopropyl titanate.
In accordance with the present disclosure, the catalyst is a homogeneous catalyst selected from the group consisting of titanium tetra-alkoxides, sulphuric acid, phosphoric acid, methane sulphonic acid, and para-toluene sulphonic acid.
The resultant mixture is further heated gradually at a temperature in the range of 175 to 250?C to obtain a reaction mixture.
Typically, the reaction mixture is heated at a temperature in the range of 140 to 300 °C and at a pressure in the range of 1 to 10 bar absolute.
Water and alcohol is removed azeotropically from the reaction mixture to obtain a condensate comprising water and alcohol. The alcohol obtained is separated from the condensate and recycled to the reactor until the conversion of the acid or the anhydride to ester reaches to a range of 75 to 90% to obtain a reaction mass. This results in further shift of the reaction equilibrium towards forward direction which results into a significant reduction in the batch time as compared to the conventional process. Further, water and alcohol from the reaction mass is azeotropically removed until the conversion of carboxylic acid or anhydride is greater than 99% to obtain product mass comprising ester. The product mixture is separated to obtain the ester having purity in the range of 95 to 99.5%.
The amount of catalyst is in the range of 100 to 1000 ppm with respect to total reaction mass.
In accordance with one embodiment the present disclosure, the aromatic carboxylic acid ester prepared is benzoate or substituted benzoate. In one embodiment, the aromatic carboxylic acid ester prepared is at least one selected from octyl benzoate, 2-Ethylhexyl p-toluate, 2-Ethylhexyl 4-formyl benzoate, Methyl benzoate, and Methyl 4-formyl benzoate.
In accordance with another embodiment of the present disclosure, the aromatic carboxylic acid ester prepared is alkyl/ di-alkyl terephthalate. In one embodiment, the aromatic carboxylic acid ester prepared is at least one selected from mono (2-ethylhexyl) terephthalate or di-alkyl terephthalate e.g. di-octyl terephthalate, di-octyl phthalate, di-octyl isophthalate and similar compounds preferably di-octyl terephthalate (DOTP). In an exemplary embodiment, the aromatic carboxylic acid ester is DOTP.
In one embodiment, the aliphatic carboxylic acid ester prepared is at least one selected from Di-octyl adipate, Di-octyl sebacates, Di-octyl gluterates, Di-octyl aspartate Di-octyl azelates, Di-decyl adipate, Di-decyl sebacates and several other aliphatic carboxylic acid esters
In accordance with the present disclosure, the process is selected from batch process and continuous process. The process is carried out in a reactor system selected from the group consisting of a batch reactor, a continuous flow reactor, a cascade of stirred tank reactors, fixed bed reactor, fluidized bed reactor and any combination thereof.
The process of the present disclosure further comprises separation and product recovery from the product mixture. Any unreacted reactant is removed by at least one method selected from filtration, neutralization using caustic aqueous solution and distillation.
The product mixture after esterification includes ester product(s) along with any of the reactants including alcohol, catalyst, intermediate and side products. The downstream process may include combination of the steps such as separating off the excess alcohol and any low boilers, neutralizing the acids present, caustic or water wash of the neutralized products, performing distillation, converting the catalyst into a readily filterable residue, addition of filter aid and/or solid treating agents, separating off the solids, and drying, if required.
The present disclosure provides a simple and economical process for preparation of aromatic or aliphatic carboxylic acid ester, which results in significant reduction in batch time.
The present disclosure is further explained with the help of Figure 1.
According to FIG. 1, aromatic carboxylic acid is introduced in the reactor (1) and mixed with alcohol and a catalyst. The reactor is heated to a temperature ranging from 140 to 300 °C.
Water formed during the reaction is removed azeotropically as overhead vapours (2) along with alcohol. The so obtained overhead vapours (2) are condensed in condenser (3) and further separated in to aqueous phase (5) and organic phase (4) in a separator. The separated organic phase (4) containing alcohol is recycled back to reactor (1) through reflux controller (6). The aqueous phase (5) is sent to some other process or effluent treatment plant (7).
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 scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Experiment 1: Preparation of di-octyl terephthalate from terephthalic acid and 2-ethyl hexanol in accordance with the present disclosure
100 ml round bottom flask equipped with magnetic stirring for agitation and Dean-Stark apparatus with overhead condenser for continuous removal of water from the reaction. Round bottom flask was charged with terephthalic acid and 2-ethyl hexanol in mole ratio of 1:2.6 to obtain a mixture. Tetra-isopropyl titanate (600 ppm) was added as catalyst to the mixture to obtain a resultant mixture. The resultant mixture was heated from room temperature to 184 oC, which increased during the course of the reaction and reached up to 230 oC, towards the end of reaction under constant stirring at atmospheric pressure to obtain a reaction mixture.
The water formed during the reaction was removed azeotropically as overhead vapour comprising water and 2-ethyl hexanol. The overhead vapours were condensed and water was separated from 2-ethyl hexanol using a Dean-Stark apparatus / decanter. The separated 2-ethyl hexanol was recycled to the reactor till conversion of terephthalic acid reaches 79 %. When the conversion of terephthalic acid reached 79%, the recycling of 2-ethyl hexanol was stopped and the overhead vapour was continuously removed from the reactor until conversion of terephthalic acid reached 99% to obtain a product mixture comprising di-octyl terephthalate (DOTP) product.
The total batch time for this experiment was 6 hours. After completion of reaction, the reaction mixture was cooled to room temperature and then product was filtered to separate unreacted terephthalic acid. The filtrate was then purified to obtain the DOTP product, which was analyzed by HPLC. The selectivity towards DOTP was 99.4% based on HPLC analysis data.
Experiment 2-5: Preparation of di-octyl terephthalate from terephthalic acid and 2-ethyl hexanol at various reflux stop time.
100 ml round bottom flask equipped with magnetic stirring for agitation and Dean-Stark apparatus with overhead condenser for continuous removal of water from the reaction. Round bottom flask was charged with terephthalic acid (16.62gm) and 2-ethyl hexanol (33.85gm) in mole ratio of 1:2.6 to obtain a mixture. Tetra-isopropyl titanate (600 ppm (w/w)) was added as catalyst to obtain a resultant mixture. The resultant mixture was heated from 32? C to 184 oC, which increased during the course of reaction and reached up to 230 oC, towards the end of reaction under constant stirring at atmospheric pressure to obtain a reaction mixture.
After completion of the reaction, reaction mixture was cooled to room temperature and then reaction mixture was filtered to separate unreacted terephthalic acid. Final conversion of terephthalic acid was calculated based upon unreacted terephthalic acid after filtration & drying. The filtrate was then purified to obtain the DOTP product, which was analyzed by HPLC.
In all the experiments, the selectivity towards DOTP was found to be 99.4% based on HPLC analysis data. Results are showed in Table 1.
Table 1:
Experiment No. Catalyst loading (ppm) Reflux stop time (hours) Conversion of PTA at reflux stop time (%) Selectivity of DOTP (%) at reflux stop time Reaction stop time (hours) Final Conversion of PTA (%) Final Selectivity of DOTP (%)
2 600 2 61 99.4 6 70 99.4
3 600 3 70 99.4 6 88 99.4
4 600 4 79 99.4 6 99 99.4
5 600 5 85 99.4 7 99.5 99.4

It is observed from Table 1 that the conversion of terephthalic acid varies when the reflux was stopped at particular time. It is also found that varied reflux stop time did not affect the DOTP selectivity. The final conversion of terephthalic acid was found to be 70% for reflux stop at 2 h and total reaction time is 6 h; 88% for reflux stop at 3 h and total reaction time is 6 h; 99% for reflux stop at 4 h and total reaction time is 6 h & 99.5 % for reflux stop at 5 h and total reaction time is 7 h.
Experiment 6: Preparation of di-octyl phthalate from phthalic anhydride and 2-ethyl hexanol in accordance with the present disclosure
100 ml round bottom flask was equipped with magnetic stirring for agitation and Dean-Stark apparatus with overhead condenser for continuous removal of water from the reaction. Round bottom flask was charged with phthalic anhydride and 2-ethyl hexanol in mole ratio of 1:2.6 to obtain a mixture. Tetra-isopropyl titanate (600 ppm) was added as catalyst to obtain a resultant mixture. The resultant mixture was heated from room temperature to 184 oC, which increased during the course of reaction and reached up to 230 oC, towards the end of reaction under constant stirring at atmospheric pressure to obtain a reaction mixture.
The water formed during the reaction was removed azeotropically as overhead vapour comprising water and 2-ethyl hexanol. The overhead vapours were condensed and water was separated from 2-ethyl hexanol using a Dean-Stark apparatus / decanter. The separated 2-ethyl hexanol was recycled to the reactor till the conversion of phthalic anhydride reached 85 %. The recycling of 2-ethyl hexanol was stopped when the conversion of phthalic anhydride reached 85% and the overhead vapour was continuously removed from the reactor until the conversion of phthalic anhydride reached 99.5 % to obtain a product mixture comprising di-octyl phthalate (DOP) product.
The total batch time for the experiment was 2 hours. After completion of the reaction, the reaction mixture was cooled to 32?C and the product was filtered out to separate unreacted phthalic anhydride.
The filtrate was then purified to obtain the DOP product, which was analyzed by HPLC. The selectivity towards DOP was greater than 99% based on HPLC analysis data.
Experiment 7: Comparative example for preparation of DOTP from terephthalic acid and 2-ethyl hexanol.
Similar experimental procedure as disclosed in experiment 1 was carried out, except the reaction was carried with continuous recycling of the 2-ethyl hexanol to the reactor until the conversion of terephthalic acid reached 99%.
The total batch time required to achieve around 99% conversion of terephthalic acid was 16 hours. The selectivity towards DOTP was 99.35% based on HPLC analysis data.
Experiment 8: Comparative example for preparation of DOP from phthalic anhydride and 2-ethyl hexanol.
Similar experimental procedure as disclosed in experiment 6 was carried out, except the reaction was carried with continuous recycling of the 2-ethyl hexanol to the reactor until the conversion of phthalic anhydride reached 99.5 %.
The total batch time required to achieve around 99.5 % conversion of phthalic anhydride was 6 hours. The selectivity towards DOP was 99.3 % based on HPLC analysis data.
From the comparative examples 7 and 8, it is evident that the process of preparing an ester of the present disclosure requires lesser reaction time and capable of producing ester in high yield.
TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of an ester, which is characterized by:
-short reaction time; and
-high batch yields.
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 reveal 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.
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 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 an ester, said process comprising the following steps:
(i) charging a reactor with one of a carboxylic acid or an anhydride and at least one alcohol to obtain a mixture;
(ii) adding a catalyst to the mixture to obtain a resultant mixture;
(iii) heating the resultant mixture at a temperature in the range of 175 to 250?C to obtain a reaction mixture;
(iv) azeotropically removing water from the reaction mixture to obtain a condensate comprising water and the alcohol;
(v) separating the alcohol from the condensate and recycling the separated alcohol to the reactor till the conversion of the acid or the anhydride to ester reaches to a range of 75 to 90% to obtain a reaction mass;
(vi) azeotropically removing water and alcohol from the reaction mass until the conversion of carboxylic acid or anhydride is greater than 99% to obtain a product mixture comprising ester; and
(vii) separating the ester from the product mixture to obtain the ester having purity in the range of 95 to 99.5%.
2. The process as claimed in claim 1, wherein in process step (iii), the resultant mixture is heated gradually.
3. The process as claimed in claim 1, wherein the catalyst is a heterogeneous catalyst selected from the group consisting of tin powder, tin (IV) oxide, tin (II) oxalate, zirconium tetra-alkoxides and zirconium dioxide.
4. The process as claimed in claim 1, wherein the catalyst is a homogeneous catalyst selected from the group consisting of titanium tetra-alkoxides, sulphuric acid, phosphoric acid, methane sulphonic acid, and para-toluene sulphonic acid.
5. The process as claimed in claim 1, wherein the carboxylic acid is at least one selected from the group consisting of terephthalic acid, phthalic acid, isophthalic acid, benzoic acid, p-toluic acid, adipic acid, glutamic acid, sebacic acid, aspartic acid, succinic acid, malonic acid, azelaic acid, 2-Furoic acid, 5-Formyl-2-furancarboxylic acid, 2,5-Furan dicarboxylic acid, tetrahydrofuroic acid, tetrahydropyroncarboxylic acid, and levulinic acid.
6. The process as claimed in claim 1, wherein the anhydride is at least one selected from the group consisting of phthalic anhydride, benzoic anhydride, isophthalic anhydride, 4-methylbenzoic anhydride, acetic anhydride, and maleic anhydride.
7. The process as claimed in claim 1, wherein the alcohol is at least one selected from the group consisting of 2-ethyl hexanol, 2-methyl-1-octanol, 2-methyl-1-butanol, 2-methyl-1-decanol, 2-methyl-1-heptanol, benzyl alcohol, and phenyl ethyl alcohol.
8. The process as claimed in claim 1, wherein the mole ratio of carboxylic acid or an anhydride to alcohol is in the range of 1:1 to 1:4.

9. The process as claimed in claim 1, wherein the amount of catalyst of step (ii) is in the range of 100 to 1000 ppm.