FORM 2
THE PATENT ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. Title of the invention:
"AN IMPROVED PROCESS FOR THE ESTERIFICATION OF POLYHYDRIC ALCOHOLS"
2. Applicant (s)
(a) Name: Godrej Industries Limited
(b) Nationality: Indian company incorporated under the Indian Companies
Act, 1956
(c) Address: Pirojshanagar, Eastern Express Highway, Vikroli (East),
Mumbai - 400079, Maharashtra, India.
3. Preamble to the description
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed.

Technical field:
The present invention envisages an improved method of manufacturing a mixture of esters, comprising reacting lower carbon chain carboxylic acids with a suitable mixture of monohydric, dihydric and trihydric alcohols, followed by subsequent separation of the mixture of esters by two stage distillation. This invention relates to a method of esterification and more particularly to a method of using an entrainer which is generated in situ, to facilitate the progress of the esterification reaction.
Background and Prior Art
In the prior art, a process for the esterification of lower chain carboxylic acids is known. The principles of this well knownorganic reaction have been well documentedin literature. (Kirk-OthmerEncyclopedia of Chemical Technology, Volume 10, 4th Edition, Pages 471-496). This process, when related specifically to the esterification of longer chain carboxylic acids, namely C6 - C24 fatty acids, has also been well documented in Fatty Acids, their Chemistry, Properties, Production & Uses, by Klare Markley, 2nd Edition, Volume 2, Pages 797-826. Over the years, the number of patents and publications relating to the esters and esterification of carboxylic acids and fatty acids, are too numerous to list, have come into public domain. Most of these include those related to fatty acid methyl esters, mainly used as biodiesel. This process is called trans-esterification and is base catalyzed, whereas, the direct esterification of fatty acids with an alcohol is acid catalyzed. Esters produced by the reaction of carboxylic acids with a monohydric alcohol are relatively simple reactions. The esters of carboxylic acids with di, tri and poly hydric alcohols are much more complex, in that, depending upon the molar ratio, they may form mono, di, tri & poly esters of the carboxylic acids.

One such alcohol is glycerol, commonly called glycerine, a trihydric alcohol.Esters
formed with glycerine are called glycerides, and on the basis the number of ester linkages,
they may be called as monoglycerides, diglycerides and triglycerides.
An esterification reaction is a reversible reaction, and on the basis of the reactivity of the
reactants, the reaction attains equilibrium after a specific degree of conversion. One of the
most critical factor needed to drive the reaction completion, is the removal of the water.
The water of reaction, formed when an acid reacts with an alcohol, must be driven out.
This can done by a number of processes -
Simple Distillation - At reduced pressure
Azeotropic Distillation - Using an Entrainer
Adsorption - Over a drying agent
By removing the water of reaction, the reaction will proceed In the forward direction. The
choice of Entrainer solvent ranges from hydrocarbons, both aliphatic and aromatic,
chlorinated hydrocarbons, aliphatic esters, ketones and long chain (> C4) alcohols. The
key to the choice of entrainer lies in its property of having limited ability to solubilize
water (azeotrope) and drive it out of the system.
Processes specific to the reaction of fatty acids with glycerol to produce mono, di and tri
glycerides are well documented {Journal of American Oil Chemists Society, Vol. 73 Page
347 (1996)} and the cross references therein}.
WO2011/001249 focuses primarily on method to prepare a mixture of lower carboxylic
acid esters of glycerol. It describes in great detail, the utilization of crude glycerol
generated from the process of the manufacture of biodiesel. It discusses a method to
overcome the impact of the impurities present in crude glycerol and a method to re-
esterify the mixture of glycerides so as to increase the yield of triglycerides in the final
product. As a process, it is essentially a typical esterification, utilizing an acid catalyst, an

entraining solvent to remove water and a suitable assembly to perform the said operation. The entrainers of choice, mentioned in this publication are esters, more specifically the acetate of lower alcohols, namely C2 to C4.
The drawbacks of this process are the use of sophisticated rectification columns to separate fractions having relatively wide gaps between their boiling points. Further, the use of esters, specifically acetates, while conducting a reaction with acetic acid, could also have been simplified and made more economical. Re-esterification, specifically with acetic anhydride, a banned and relatively costly reagent, further complicates matters. This processrequires very elaborate post reaction treatment steps, in order to remove the organic and inorganic impurities present in crude glycerol. These steps, if not taken, complicate matters to such an extent, that recovery of the products itself are at stake. Additionally, there is no mention of, whether there is complete removal of these impurities, or whether traces are carried over into the crude mixture of esters and also the final distilled mixture of esters.Furthermore, there is a neutralization step that not only increasesthe number of process stepsbut also results in overall yield of tri-ester product thereby affecting the process economics.
Therefore, the present invention seeks to simplify, minimize and/or eliminate the problems and omissions found in the prior art, for which the protection is sought.
Description of the invention
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

According to preferred embodiment, the invention describes an optimized method of manufacturing a mixture of high boiling esters, by esterification of polyhydric alcohols with excess of low carbon chain carboxylic acids, comprising a lower boiling ester as an entraining solvent, generated in situ, followed by a simple two stage distillation, wherein, said method is devoid of neutralization .
In this process, acetic acid is used to increase the percentage of triester instead of using
mixture of acetic acid and acetic anhydride.
The water is collected in Dean Stark apparatus. In the side arm of the Dean Stark, water
forms the lower layer (since the density of butyl acetate is < 1). The water is drained out,
from the bottom vaive of the Dean Stark. The water and solvent that collects in the side
arm is warm. At such times, some amount of the butyl acetate is carried out with the
water, even after it has been drained out of the Dean Stark. After cooling, if the water has
a layer of butyl acetate, this water is taken in a separatory funnel and a thorough
separation of the water and butyl acetate is carried out. The butyl acetate recovered by
this step, is added back to the reaction mixture through an addition or dropping funnel.
The process of esterification is discussed herein below in greater details with regard to the use of reagents and reactants like acids, alcohols, entrainer, equipment, catalysts and reaction conditions.
Lower Carboxylic Acid
The lower carbon chain carboxylic acids include those having carbon numbers C2 to C4, namely acetic acid, propionic acid and butyric acid. In a particular embodiment of this invention, the process aims at obtaining a mixture of the acetates mono-, di- and triesters,

respectively from high purity (>98%), as well as commercial grade (94 to 98%) acetic
acid (RN: 64-19-7).
Another very advantageous aspect of the patent is the use of only acetic acid, and the
avoidance of acetic anhydride as a primary or re-esterification reagent, meant to increase
the percentage of the tri ester.
The preferred amount of acetic acid taken is 1 molar excess of the stoichiometric
requirement,on the basis of the quantity of the polyhydric alcohol. In addition, a
stoichiometric amount is also taken for the in situ generation of the entrainer.
Polyhydric Alcohol
The polyhydric alcohols 'include those having carbon numbers C2 to C4, with 2 to 3 hydroxyl groups per molecule, in a particular embodiment of this invention, the process aims at obtaining a mixture of mono-, di- and triesters, of acetic acid. Advantageously, not imposing any limitation to the invention, the claimed process is optimized to obtain a mixture of monoacetin (glycerol mono acetate or 1 -propanediol monoacetate, RN: 106-61- 6), diacetin (glycerol di acetate or 1,3-propanetriol diacetate RN: 25395-31-7) and triacetin (glycerol tri acetate or 1,2,3-propanetriol triacetate. RN: 102-76-l)from high purity (> 99%) glycerol.
Entrainer
As can be seen from the description mentioned above, both, the C2 to C4 carboxylic acid, as well as the C2 to C3 polyhydric alcohol are infinitely soluble in water It thus is imperative that a water immiscible entrainer be used, so as to drive the reaction to completion. The lower carbon chain C4 to C6 esters, namely, ethyl, propyl, isopropyl and butyl esters of acetic acid are all immiscible in water. But their boiling points are 78°C,

and 140°C. With the higher boiling point and very slight miscibility, butyl acetate is the better of the three esters, it has been established in the prior art, that butyl acetate, having boiling point 140°C, can very optimally be used as an entrainer. Therefore, The process of the present invention has made an improvement over the prior art by generating the butyl acetate in situ by using butanol as the entraining solvent precursor. The reaction of butanol with the required excess of acetic acid is so vigorous, that even before the esterification of acetic acid with glycerol begins, the butyl acetate is generated. This butyl acetate, formed in situ, then begins to act as the entrainer, effectively removing the water of reaction generated by the esterification of glycerol and acetic acid.. The water is collected in Dean Stark, apparatus and water forms the lower layer (since the density of butyl acetate is < 1), which drained out, from the bottom valve of the Dean Stark. If any amount of the butyl acetate is carried out with the water, can be separated using a separatory funnel, where thorough separation of the water and butyl acetate is carried out. The butyl acetate recovered is added back to the reaction mixture through an addition or dropping funnel.
The preferred amount of the entrainer required, in accordance with this invention, is the molar equivalent of the polyol taken. It is important to note that the said amount is sufficient to effectively remove all the water generated in the course of the reaction.
Another aspect of this invention is that the mixture of un-reacted acetic acid and butyl acetate, generated as part of one reaction, can be used as part of the input for the next reaction, and so forth. This would further economize the process, since these recycled reagents will be complementing a part of the amount of the high purity, fresh reagents. Catalysts

Useful esterification catalysts, according to the invention, but not excluding any other, are chosen from inorganic acids, such as sulfuric and hydrochloric, and sulfonic, such as methanesulfonic, xylenesulfonic and p-toluene sulfonic acids. The quantity required can range from 1 to 3% w/w based on the amount of Glycerol taken for esterification, preferably, 1.5 to 2.5%, most preferably from 2.1 to 2.5%.
Process of the Invention
a. In a suitable vessel equipped with an overhead stirrer, two addition funnels, a
thermometer pocket and a water entraining assembly, fitted with adequate water
cooled condenser, charge the total required amounts of lower carboxylic acid, the
precursor of the entrainer (lower aliphatic alcohol) and freshly vacuum dried
catalyst.
b. Simultaneously charge only 70% of the required amount of the polyol, and start
the heating and stirring.
c. When the reaction mixture attains a steady state of reflux, its temperature is
109°C. This takes about 60 minutes. At this temperature, the entrainer, which has
already formed in situ, begins to azeotropically carry out the water that is
generated by the esterification reaction. The water and entrainer are separated, and
the entrainer is transferred back into the reaction vessel, through one of the
addition funnels.
d. As the reaction progresses, the temperature keeps rising. After about 120 minutes
of collecting the water, the reaction mixture temperature reaches close to 120°C.
e. At this point in time, the balance 30% of the polyol, is transferred into the second
additional funnel, and dosed at such a rate, that the entire addition takes about 120
minutes. The multi stage dosing of polyol increases the conversion rate and

reduces the reaction period. The collection of water, its separation from the entrainer and transfer of the entrainer back into the reaction vessel continues undisturbed
f. After the total amount of the polyol has been added, the temperature of the reaction mixture is now close to 130°C. Continue the reaction until all water of reaction has stopped getting generated. This takes an additional 180 minutes.
g. At this point, the temperature of the reaction mixture is close to 140°C.
h. The entire reaction cycle, from dosing of reagents to the end of water generation, takes almost 480 minutes.
i. The final 180 minutes is the time that determines the distribution of the esters across the polyol. After achieving, a very high degree of conversion, it is the percentage of mono-, di- and tri esters, formed at the end of the reaction that is more critical. Different applications require varying amounts of the mono, di and tri esters of the polyol.
j. The amount of water collected at the end of the reaction is close to 45% more than that theoretically expected. This phenomenon is explained by the fact that this additional amount is the lower carboxylic acid which has been carried over, due to its solubility in water and vice versa.
k. At the end of the reaction, the water entraining assembly is replaced with a simple downward distillation assembly. Without neutralizing the catalyst the mixture consisting of the un-reacted lower carboxyiic acid and entrainer are distilled out at atmospheric pressure. More than 90% of this mixture is collected in this manner.
l. The last traces of the above mixture are removed as part of a pre-cut, taken before
the distillation of the polyol ester. This operation is performed under reduced pressure (<10 mm of Hg).

m. The yield of the distilled polyol ester is about 95%, in addition to the 3% pre-cut, rich in the mixture of lower carboxylic acid and enlrainer. The advantage of taking a pre-cut is twofold. Firstly, it ensures that the final distillate polyol ester has very low acidity. Secondly, it is a means of recovering almost 100% of the entrainer and excess lower carboxylic acid, which can be recycled.
n. The residue is < 3%, and hence, allowing for < 1% of vapour losses, the material balance has been achieved.
o. By not neutralizing the catalyst intact, there is an advantage. All through the distillation process the esterification continues, resulting into a polyol ester having a higher percentage of Tri Ester.
p. The composition of the polyol ester has been determined by Gas Liquid Chromatography, and tabulated as under-

Composition of Polyol Ester Percentage
Mono Ester < 1
Di Ester <20
Tri Ester >80
There are a number of factors that determine the composition of the polyol esters. They are the use of excess lower carboxylic acid, the mode of adding the polyol and the total reaction time. This process described above has been designed such that the percentages of the Mono, Di and Tri Esters will always be as in the above mentioned table. Such products have useful applications as binders in foundry resins, as plasticizers for cellulosic filters and as solubilizers in flavor and fragrance products.

Example
The following example, with specifically named polyol, lower carboxylic acid, entrainer
and catalyst, demonstrates the various embodiments of this invention, but which does in no way impose limitations to the invention, other than what is described in the claims attached to this document.
Glacial Acetic Acid. 450 gm (7.5 moles), Butanol, 111 gm (1.5 moles) and p-Toluene Sulfonic Acid, 3 gm (2.1% w/w basis Glycerine), were charged into a 5-necked, flanged, round bottom flask. The vessel was fitted with an overhead stirrer, a thermometer pocket, two 100 ml dropping funnels and a water entraining system, fitted with an appropriate condenser. Glycerine, 100 gm (1.08 moles), amounting to only 70% of the total, was charged into the vessel. The reaction was started, and within 60 minutes, the reaction mixture reached a steady state of reflux, with the temperature attaining 109°C. The water collection started, it was separated from the entrainer and which in turn was transferred back into the vessel through one of the dropping funnels. The reaction was continued for 120 minutes, the temperature of the reaction mixture rising to about 120°C. In the meanwhile, the balance 30%) of the Glycerine, 40 gm (0.43 moles) was transferred into the second dropping funnel.The Glycerine was dosed at a rate such that it took 120 minutes to complete. The water collection continued, separating it from the entrainer and transferring the entrainer back into the vessel through the first dropping funnel. After complete addition of all the Glycerine, at which time the reaction mixture had attained a temperature of 130°C, the reaction was continued for another 180 minutes. At the end of a total reaction time of 480 minutes, and the temperature touching 140°C, the water collection had stopped. The water collected amounted to 151gm. which is about 45% more than the theoretical amount. This water contained acetic acid, both having mutual

solubility in each other. Without neutralization of the catalyst, the solvent mixture, consisting of the un-reacted acetic acid and butyl acetate, was distilled at atmospheric pressure, using a simple downward distillation assembly. The bottom temperature rose from 140 to 180° C, the vapour temperature rose from 120 to 150°C. The total solvent mixture collected was about 180 gm. The last traces of the solvent mixture were removed at the next stage. With the total reaction mass reduced to less than half (346 gm), it was transferred into a 2 necked 500 ml round bottom flask, fitted with a distillation assembly. A pre-cut amounting to about 10 gm (3%) was taken, so as to ensure complete removal of the solvent mixture, specifically acetic acid. The acidity imparted by even traces of acetic acid, would render the Triacetin unusable in certain food, pharmaceutical and personal care applications.
Finally the Triacetin fraction (310 gm) was collected at a bottom temperature of 112 to 118°C at 6 mm of Hg. This amounted to a yield of 94.8%, on the basis of the theoretical amount of Triacetin. The composition of the Triacetin fraction, as determined by GLC, is tabulated below -

Composition of Triacetin Fraction Percentage
Monoacetin 0.66
Diacetin 18.91
Triacetin 80.42
The characteristics of 80% Triacetin are tabulated below.

Analytical Parameters Results
Acidity % (As Acetic Acid) <0.05
Moisture % <0.2
Saponification Value >260
Purity % (Based on SV) >99

We Claim:
1. An optimized method of manufacturing a mixture of high boiling esters, by esterification of polyhydric alcohols with excess of low carbon chain carboxylic acids, comprising a lower boiling ester as an entraining solvent, generated in situ, followed by a simple two stage distillation, wherein, said method is devoid of neutralization.
2. The method as claimed in claim 1, wherein the first stage distillation comprising of the mixture of lower boiling entraining solvent and excess of the low carbon chain carboxylic acid, and the second stage comprising the mixture of higher boiling esters.
3. The method, as claimed in Claim I, wherein the low carbon chain carboxylic acids are having 2-4 carbon atoms, having purity > 90% but < 98%.
4. The method, as claimed in Claim 1, wherein the polyhydric alcohols are having 2 - 4 carbon atoms, having purity > 99%.
5. The method, as claimed in Claim 1, wherein the lower boiling entrainer is generated in situ, prior to the process of esterification.
6. The method, as claimed in Claim 1, wherein the lower boiling entrainer is an ester, having about 4-6 carbon atoms.
7. The method, as claimed in Claim 1, wherein the lower boiling ester is obtained in situ from low boiling, low carbon chain monohydric alcohols having about 2-4 carbon atoms.

8. The method, as claimed in Claim 1, wherein the polyhydric alcohol is added in
multiple stages, during the course of the process of esterification.
9. The mixture of high boiling esters manufactured according to the method
described in Claim 1.