Title of Invention	"AN IMPROVED SINGLE STAGE PROCESS FOR THE PREPARATION OF ETHYL ACETATE"
Abstract	The present invention relates to an improved single stage process for the preparation of ethyl acetate.The invention relates to the preparation of lower esters of carboxylic acid using reactive distillation technique, which minimizes many of the problems, such as corrosion, waste disposal, generation of undesired side products, etc. In the present process a single catalytic distillation tower is used in which solid catalysts is supported in perforated cages woven bags of fibers or stainless steel mesh or monolith, which also served as packing material for distillation column. Acetic acid is fed from the top and distributed in the column with the help of a distribution plate. Ethanol is fed near the bottom of the reactor carboxylic acid ester as product is collected from the top of the catalytic column.

Title of Invention

"AN IMPROVED SINGLE STAGE PROCESS FOR THE PREPARATION OF ETHYL ACETATE"

Abstract

The present invention relates to an improved single stage process for the preparation of ethyl acetate.The invention relates to the preparation of lower esters of carboxylic acid using reactive distillation technique, which minimizes many of the problems, such as corrosion, waste disposal, generation of undesired side products, etc. In the present process a single catalytic distillation tower is used in which solid catalysts is supported in perforated cages woven bags of fibers or stainless steel mesh or monolith, which also served as packing material for distillation column. Acetic acid is fed from the top and distributed in the column with the help of a distribution plate. Ethanol is fed near the bottom of the reactor carboxylic acid ester as product is collected from the top of the catalytic column.

Full Text	The present invention relates to an improved single stage process for the preparation of ethyl acetate. The present invention particularly relates to the preparation of lower esters of carboxylic acid using reactive distillation technique, which minimizes many of the problems, such as corrosion, waste disposal, generation of undesired side products, etc. The increase in the reaction yield provided by the process disclosed in the present invention can be obtained using a single column in which the heterogeneously catalysed reaction is combined with distillation over the catalyst packing. It substantially reduces the production cost as the purification step of separating the alcohol from the ester is eliminated. The lower esters find use as reagents for extraction processes in the food industry, as defatting agent and for the preparation of cosmetics, glues, lacquers and polymer solutions in the paper and foil industry. These are also used as a solvent and for the manufacture of artificial hair, leather, silk, transparent wrapping paper, plastic and varnish removers, cleaning preparation for textiles and also in the extraction of acetic acid from aqueous solutions. Esters of acetic acid and their derivatives are used for making coatings, adhesives, perfumes, plasticizers, etc. Ethyl acetate also finds application as an flavour component and as a solvent for nitro-cellulose. It is also used as a solvent and for the manufacture of artificial hair, leather, silk, transparent wrapping paper, plastic and varnish removers, cleaning preparation for textiles and also in the extraction of acetic acid from aqueous solutions. Reference may be made to US Patent No. 5, 536, 856, wherein, the esterification of carboxylic acid with an alcohol is carried out in two stages. In the first stage the alcohol vapour and the liquid acid flow counter currently and the product is collected from the bottom the reaction column. In the second stage, the product obtained from the first stage is again mixed with additional quantity of alcohol and passed through another column. The ester is obtained from lower part of the reactor. The acid to alcohol molar ratio ranged from 2.6:1 to 6.7:1 and the conversion of acid to ester was reported to be more than 90%. The referred patent describes the esterification of higher carboxylic acids; the process requires two column reactors and also an additional step of separating the excess acid which make the process less economical. The tolerance for water content of the alcohol is also limited to 5 mole %. Reference may also be made to another invention covered by the US Pat. No. 5998658. The process describe the use of two reactor system wherein the esterification of acetic acid with alcohol is first carried out in a fixed-bed reactor. The product from the first reactor is withdrawn from the bottom and is again fed near the bottom of second catalytic distillation column along with acetic acid, which is introduced from the top. Here again the use of two reactors makes the process more energy intensive. In another reference, US Pat. No. 5, 536, 556 esterification is carried out in two column reactors in which there is a plurality of esterification trays each having pre-determined liquid hold up. The esterification product is then fed in another reactor after mixing with more alcohol. This would further require a step to separate extra alcohol from the ester. References may be made to the US Pat. No. 493,9294 where in preparation of ultra high purity, methyl acetate has been reported using almost stoichiometric proportions of acetic acid alongwith 1-10% acetic anhydride and methanol in a single reactive distillation column, where in the methyl acetate is obtained at the top and water at the bottom. The main disadvantages of the above process is the utilization of homogeneous catalysts such as H2SO4, p-toluene sulfonic acid and phosphoric acid etc. which cannot be recycled and are associated with disposal problems. Another disadvantages of the above process is the material of construction of the reactor as the catalyst used is highly corrosive in nature. In the prior art processes almost water free alcohol is used as one of the reactant. This involves additional energy in enriching the alcohol. The inventors of the present invention have made intensive research in an attempt to improve the process for producing the lower esters of carboxylic acids by catalytic distillation using a single column. The main object of the present invention is to provide an improved process for the preparation of ethyl acetate. Another object of the present invention is production of lower esters of carboxylic acids through a single reactive distillation column packed with the solid acids as catalyst so as to eliminate above mentioned defects and post esterification separation steps and obtain maximum purity of the ester in single stage. Still another object of the present invention is to make the process commercially viable and reduce the production cost of ethyl acetate substantially. Yet another object of the present invention is to provide a process for the production of ethyl acetate in which aqueous ethanol without further enrichment is used as one of the reactants. Accordingly the present invention provides an improved single stage process for the preparation of ethyl acetate which comprises i) passing of lower carboxylic acids mainly acetic acid and anhydrous or aqueous ethyl alcohol in a molar ratio of alcohol to acid ranging from 1:1 - 1:5 in a countercurrent manner through an esterification zone in a single column containing a solid esterification catalyst held in bags of woven fabric, or stainless steel mesh or in the form of monolith, ii) separating the components present in the vapour phase using catalyst bags to allow the upcoming vapours of alcohols to come in contact with the downward flowing liquid acid and also to act as packing material in the distillation column iii) maintaining the temperature of the column reactor to a temperature of 50-150°C at a pressure ranging from 1-20 kg and controlling the parameters such that one of the reactants is present in the liquid phase and at least one of the products is also present in the liquid phase, whereas catalyst is present in solid phase, iv) collecting ethyl acetate as a liquid containing some alcohol by condensing the vapours reaching at the top of the column and the upcoming unreacted ethyl alcohol in the form of ethyl alcohol, ethyl acetate azeotrope come in contact with fresh acetic acid in presence of acidic catalyst and converted to get ethyl acetate, v) collecting the product formed by condensation without requiring any further purification where in purity of the product is above 95% due to the low alcohol content in the top product obtained in the one stage, vi) recovering the bottom product from the column containing mainly aqueous acetic acid for further recycling. In an embodiment of the present invention the process is a continuous process using a single reactor. In another embodiment of the present invention the acid used is glacial acetic acid. In yet another embodiment of the present invention the molar ratio of acetic acid to ethyl alcohol is preferably in the range of 1:1 to 2.5:1. In still another embodiment of the present invention an acidic catalyst is used for esterification reaction. In still another embodiment of the present invention the acidic catalyst used is either zeolites or cation exchange resin or a mixture thereof. In still another embodiment of the present invention the catalyst used is ZSM-5 zeolites. In still another embodiment of the present invention the cation exchange resin is macroreticular type or gel type. In still another embodiment of the present invention the system in step (ii) also acts as an extraction column wherein continuously extracting the water formed during esterification reaction from the water, alcohol & ethyl acetate ternary azeotrope by downward coming acetic acid, In still another embodiment of the present invention the reaction temperature is controlled such a manner that catalyst does not loses its activity due to over heating. In still another embodiment of the present invention the reaction temperature used varies from 50-150°C at 1-20 atm pressure. In still another embodiment of the present invention the alcohol vapours are fed below the catalyst zone and acid above the catalyst zone. Superior results have been obtained from the novel process disclosed in the present invention because of its high energy efficiency, high reaction yield and high purity of the product obtained in a single operation of esterification, the method disclosed in the present invention presents a very viable alternative to the well established commercial processes for the production of lower esters, mainly ethyl acetate. The reaction conditions are controlled such that acetic acid, and water are present as liquid phase and the alcohol and ester are present as vapour phase. In the present invention, a slight excess than stoichiometry of acid is always present so that very high conversion of the alcohol to the ester is obtained. invention, a slight excess than stoichiometry of acid is always present so that very high conversion of the alcohol to the ester is obtained. The fresh acetic acid entering in the system preferentially extracts and removes water formed during the reaction and present in one of the reactants thereby allowing the shifting of reaction equilibrium towards almost complete conversion of one of the reactants. The reaction conditions are controlled, such that the catalyst is always embedded in either of the reactants/product such that the catalyst temperature as always below the boiling points of highest boiling reactant/product. This helps to maintain relatively uniform temperature throughout the system and suppresses the formation of hot spots thereby reducing the chances of catalyst poisoning, minimizing the overheating/charring of the catalyst and preventing undesirable side reactions. This also helps to obtain a product of >95% purity so that the product can be utilized as such for certain applications without undergoing further purification steps or greatly simplifying the post esterification steps and minimizing the energy consumption. The present invention describes an improved single-stage process for the production of lower esters carboxylic acid preferentially acetic acid and lower alcohols e.g. ethanol, obviating the problems associated with the prior art process such as, requirement of more than one reactor systems, as described in many of the earlier patents, corrosion, use of large excess of one of the reactants, reducing the requirement of separation and recycling of excess reagent used, preventing undesirable side reactions. Other advantages of the present process are longer catalysts life, simultaneous removal of water from the product and excellent conversion even with aqueous alcohol to ester The process described in the present invention also achieves substantial energy saving by utilization of the heat of esterification reaction for the distillation of the product and energy required for post-esterification purification. In the present process a single catalytic distillation tower is used in which solid catalysts is supported in perforated cages woven bages of fibers or stainless steel mesh or monolith, which also served as packing material for distillation column. Acetic acid is fed from the top and distributed in the column with the help of a distribution plate. Ethanol is fed near the bottom of the reactor carboxylic acid ester as product is collected from the top of the catalytic column. The mole ratio of alcohol to acid varies for 1:1 - 1:5 preferential in the range of 1:1.5-2. Excess acetic acid along with extracted water is collected from the bottom. This acetic acid can be recycled. The key element of the process is in controlling the reaction conditions e.g. (reaction temperature and pressure. The temperature varies from 50-150°C at 1-20 kg pressure) in such a manner that all the three phases are present in the reaction system at any point of time and atleast one of the component of reaction mixture and atleast one of the components of the product streams always remain in the vapour phase. The system also provide efficient liquid vapour interaction in presence of catalyst resulting in high yield of the desired ester by maintaining continuous availability in more than stoichiometric ratio of fresh acetic acid (as liquid for) to the unreacted alcohol vapours. Out of the reaction product i.e water is continuously extracted from the water alcohol and ester ternary azeotrope with the help of fresh acid thereby shifting the equilibrium toward the desired product. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example -1 The reactor consist of a glass column, packed with the solid catalyst i.e. ion exchange resin macro reticular type, Amberlyst. About 30 g of the catalyst was packed in small cylinderal bags made up of stainless steel net. The packing was done in such a manner that there was enough space for vapour-liquid contact. The temperature of the column was maintained at reaction temperature 90°C. The alcohol vapour was fed from the bottom of the reaction zone and the acid from the top of the reaction zone, at predetermined rate. The flow rate of alcohol varied from 15ml/ hr to 30ml/hr whereas the flow rate of acid was kept at 30ml/hr. During the reaction, the overhead vapours from the reactor column were passed through a condenser and collected, the liquid product was analysed by G. C and unreacted acid along the water present in the reactants and formed during reaction was collected from the bottom of the reactor. The results are summarized in Table-1. Table-1 (Table Removed) Example - II All the reaction conditions and other reaction parameters were kept as in Example-l, except that the catalyst used is Tulsain. The procedure used is same as in Example-l. The results obtained are summarized in Table-2. Table-2 (Table Removed) Example - III All the reaction conditions and other reaction parameters were kept as in Example-l, except that the catalyst used is Zeolite, HZSM-6 catalyst. 40 g of the Zeolite catalyst was diluted with porcelain beads (40 gms.) and filled in the column. All the other reaction conditions were kept constant as in Example 1 & 2. The results are summarized in Table - 3. Table-3 (Table Removed) Example - IV All the reaction conditions and other reaction parameters were kept as in Example-l, except that the above experiment as in Example-l I were carried out using a mixture of 89% Ester and 11% alcohol. The ratio of alcohol & acid as calculated from the mixture was kept at 1:2. The results obtained are given in Table-4. Table-4 (Table Removed) Example - V All the reaction conditions and other reaction parameters were kept as in Example-l, except that the above experiment was carried out using aqueous alcohol (78%), as in Example-l. The results are tabulated as follows: Table - 5 (Table Removed) The main advantages of the present invention are: 1. High yield of the carboxylic acid esters is obtained in the invented single stage process against the two stage processes reported by most of the inventors 2. The invented process does not require pure ethanol for esterification reaction and aqueous ethanol can be used to produce ethyl acetate in high yields. 3. Under the present conditions water present either in the reactant or produced during the reaction is extracted with acetic acid and collected at the bottom product along with excess acetic acid used in the process. 4. The reaction system in the reactor at reaction temperature operates in state of vapour liquid in equilibrium and act as an isothermal system thus avoiding any possible over heating which may effect the catalyst activity. We Claim: 1 An improved single stage process for the preparation of ethyl acetate which comprises I) passing lower carboxylic acids mainly acetic acid and anhydrous or aqueous ethyl alcohol in a molar ratio of alcohol to acid ranging from 1:1 - 1:5 in a countercurrent manner through an esterification zone in a single column containing a solid esterification catalyst held in bags of woven fabric, or stainless steel mesh or in the form of monolith, II) separating the components present in the vapour phase using catalyst bags to allow the upcoming vapours of alcohols to come in contact with the downward flowing liquid acid and also to act as packing material in the distillation column, III) maintaining the temperature of the column reactor to a temperature of 50-150°C at a pressure ranging from 1-20 kg and controlling the parameters such that one of the reactants is present in the liquid phase and at least one of the products is also present in the liquid phase, whereas catalyst is present in solid phase, IV) collecting ethyl acetate as a liquid containing some alcohol by condensing the vapours reaching at the top of the column and the upcoming unreacted ethyl alcohol in the form of ethyl alcohol, ethyl acetate azeotrope come in contact with fresh acetic acid in presence of acidic catalyst and converted to get ethyl acetate, V) collecting the product formed by condensation without requiring any further purification where in purity of the product is above 95% due to the low alcohol content in the top product obtained in the one stage, VI) recovering the bottom product from the column containing mainly aqueous acetic acid for further recycling. 2 An improved process as claimed in claim-1 wherein the process is a continuous process using a single reactor. 3 An improved process as claimed in claims 1-2 wherein the acid used is glacial acetic acid. 4 An improved process as claimed in claims 1-3 wherein the molar ratio of acetic acid to ethyl alcohol is preferably in the range of 1:1 to 2.5:1. 5. An improved process as claimed in claims 1-4 wherein an acidic catalyst is used for esterification reaction. 6. An improved process as claimed in claims 1-5 wherein the acidic catalyst is either zeolites or cation exchange resin or a mixture thereof. 7. An improved process as claimed in claims 1-6 wherein the catalyst used is ZSM-5 zeolites. 8. An improved process as claimed in claims 1-7 wherein the cation exchange resin is macroreticular type or gel type. 9. A process as claimed in claims 1 to 8 wherein the system in step (ii) also acts as an extraction column wherein continuously extracting the water formed during esterification reaction from the water, alcohol & ethyl acetate ternary azeotrope by downward coming acetic acid, 10. An improved process as claimed in claims 1-9 wherein the reaction temperature 50-150°C is controlled in such a manner that catalyst does not loses its activity due to over heating. 11 An improved process as claimed in claims 1-10 wherein the alcohol vapours are fed below the catalyst zone and acid above the catalyst zone. 13. An improved single stage process for the preparation of ethyl acetate substantially as herein described with reference to the examples accompanying this specification

Full Text

The present invention relates to an improved single stage process for the preparation of ethyl acetate.
The present invention particularly relates to the preparation of lower esters of carboxylic acid using reactive distillation technique, which minimizes many of the problems, such as corrosion, waste disposal, generation of undesired side products, etc. The increase in the reaction yield provided by the process disclosed in the present invention can be obtained using a single column in which the heterogeneously catalysed reaction is combined with distillation over the catalyst packing. It substantially reduces the production cost as the purification step of separating the alcohol from the ester is eliminated.
The lower esters find use as reagents for extraction processes in the food industry, as defatting agent and for the preparation of cosmetics, glues, lacquers and polymer solutions in the paper and foil industry. These are also used as a solvent and for the manufacture of artificial hair, leather, silk, transparent wrapping paper, plastic and varnish removers, cleaning preparation for textiles and also in the extraction of acetic acid from aqueous solutions.
Esters of acetic acid and their derivatives are used for making coatings, adhesives, perfumes, plasticizers, etc. Ethyl acetate also finds application as an flavour component and as a solvent for nitro-cellulose. It is also used as a solvent and for the manufacture of artificial hair, leather, silk, transparent wrapping paper, plastic and varnish removers, cleaning preparation for textiles and also in the extraction of acetic acid from aqueous solutions.
Reference may be made to US Patent No. 5, 536, 856, wherein, the esterification of carboxylic acid with an alcohol is carried out in two stages. In the first stage the alcohol vapour and the liquid acid flow counter currently and the product is collected from the bottom the reaction column. In the second stage, the product obtained from the first stage is again mixed with additional quantity of alcohol and passed through another column. The ester is obtained from lower part of the reactor. The acid to alcohol molar ratio ranged from 2.6:1 to 6.7:1 and the conversion of acid to ester was reported to be more than 90%. The referred patent describes the esterification of higher carboxylic acids; the process requires two column reactors and also an additional step of

separating the excess acid which make the process less economical. The tolerance for water content of the alcohol is also limited to 5 mole %.
Reference may also be made to another invention covered by the US Pat. No. 5998658. The process describe the use of two reactor system wherein the esterification of acetic acid with alcohol is first carried out in a fixed-bed reactor. The product from the first reactor is withdrawn from the bottom and is again fed near the bottom of second catalytic distillation column along with acetic acid, which is introduced from the top. Here again the use of two reactors makes the process more energy intensive.
In another reference, US Pat. No. 5, 536, 556 esterification is carried out in two column reactors in which there is a plurality of esterification trays each having pre-determined liquid hold up. The esterification product is then fed in another reactor after mixing with more alcohol. This would further require a step to separate extra alcohol from the ester.
References may be made to the US Pat. No. 493,9294 where in preparation of ultra high purity, methyl acetate has been reported using almost stoichiometric proportions of acetic acid alongwith 1-10% acetic anhydride and methanol in a single reactive distillation column, where in the methyl acetate is obtained at the top and water at the bottom.
The main disadvantages of the above process is the utilization of homogeneous catalysts such as H2SO4, p-toluene sulfonic acid and phosphoric acid etc. which cannot be recycled and are associated with disposal problems. Another disadvantages of the above process is the material of construction of the reactor as the catalyst used is highly corrosive in nature.
In the prior art processes almost water free alcohol is used as one of the reactant. This involves additional energy in enriching the alcohol.
The inventors of the present invention have made intensive research in an attempt to improve the process for producing the lower esters of carboxylic acids by catalytic distillation using a single column.
The main object of the present invention is to provide an improved process for the preparation of ethyl acetate.
Another object of the present invention is production of lower esters of carboxylic acids through a single reactive distillation column packed with the solid acids as catalyst so as to eliminate above mentioned defects and post esterification separation steps and obtain maximum purity of the ester in single stage.
Still another object of the present invention is to make the process commercially viable and reduce the production cost of ethyl acetate substantially.
Yet another object of the present invention is to provide a process for the production of ethyl acetate in which aqueous ethanol without further enrichment is used as one of the reactants.
Accordingly the present invention provides an improved single stage process for the
preparation of ethyl acetate which comprises
i) passing of lower carboxylic acids mainly acetic acid and anhydrous or aqueous ethyl alcohol in a molar ratio of alcohol to acid ranging from 1:1 - 1:5 in a countercurrent manner through an esterification zone in a single column containing a solid esterification catalyst held in bags of woven fabric, or stainless steel mesh or in the form of monolith,
ii) separating the components present in the vapour phase using catalyst bags to allow the upcoming vapours of alcohols to come in contact with the downward flowing liquid acid and also to act as packing material in the distillation column
iii) maintaining the temperature of the column reactor to a temperature of 50-150°C at a pressure ranging from 1-20 kg and controlling the parameters such that one of the reactants is present in the liquid phase and at least one of the products is also present in the liquid phase, whereas catalyst is present in solid phase,
iv) collecting ethyl acetate as a liquid containing some alcohol by condensing the vapours reaching at the top of the column and the upcoming unreacted ethyl alcohol in the form of ethyl alcohol, ethyl acetate azeotrope come in contact with fresh acetic acid in presence of acidic catalyst and converted to get ethyl acetate,
v) collecting the product formed by condensation without requiring any further purification where in purity of the product is above 95% due to the low alcohol content in the top product obtained in the one stage,

vi) recovering the bottom product from the column containing mainly aqueous acetic
acid for further recycling.
In an embodiment of the present invention the process is a continuous process using a single reactor.
In another embodiment of the present invention the acid used is glacial acetic acid. In yet another embodiment of the present invention the molar ratio of acetic acid to ethyl alcohol is preferably in the range of 1:1 to 2.5:1.
In still another embodiment of the present invention an acidic catalyst is used for esterification reaction.
In still another embodiment of the present invention the acidic catalyst used is either zeolites or cation exchange resin or a mixture thereof.
In still another embodiment of the present invention the catalyst used is ZSM-5 zeolites. In still another embodiment of the present invention the cation exchange resin is macroreticular type or gel type.
In still another embodiment of the present invention the system in step (ii) also acts as an extraction column wherein continuously extracting the water formed during esterification reaction from the water, alcohol & ethyl acetate ternary azeotrope by downward coming acetic acid,
In still another embodiment of the present invention the reaction temperature is controlled such a manner that catalyst does not loses its activity due to over heating. In still another embodiment of the present invention the reaction temperature used varies from 50-150°C at 1-20 atm pressure.
In still another embodiment of the present invention the alcohol vapours are fed below the catalyst zone and acid above the catalyst zone.
Superior results have been obtained from the novel process disclosed in the present invention because of its high energy efficiency, high reaction yield and high purity of the product obtained in a single operation of esterification, the method disclosed in the present invention presents a very viable alternative to the well established commercial processes for the production of lower esters, mainly ethyl acetate.
The reaction conditions are controlled such that acetic acid, and water are present as liquid phase and the alcohol and ester are present as vapour phase. In the present invention, a slight excess than stoichiometry of acid is always present so that very high conversion of the alcohol to the ester is obtained.

invention, a slight excess than stoichiometry of acid is always present so that very high conversion of the alcohol to the ester is obtained.
The fresh acetic acid entering in the system preferentially extracts and removes water formed during the reaction and present in one of the reactants thereby allowing the shifting of reaction equilibrium towards almost complete conversion of one of the reactants.
The reaction conditions are controlled, such that the catalyst is always embedded in either of the reactants/product such that the catalyst temperature as always below the boiling points of highest boiling reactant/product. This helps to maintain relatively uniform temperature throughout the system and suppresses the formation of hot spots thereby reducing the chances of catalyst poisoning, minimizing the overheating/charring of the catalyst and preventing undesirable side reactions. This also helps to obtain a product of >95% purity so that the product can be utilized as such for certain applications without undergoing further purification steps or greatly simplifying the post esterification steps and minimizing the energy consumption.
The present invention describes an improved single-stage process for the production of lower esters carboxylic acid preferentially acetic acid and lower alcohols e.g. ethanol, obviating the problems associated with the prior art process such as, requirement of more than one reactor systems, as described in many of the earlier patents, corrosion, use of large excess of one of the reactants, reducing the requirement of separation and recycling of excess reagent used, preventing undesirable side reactions.
Other advantages of the present process are longer catalysts life, simultaneous removal of water from the product and excellent conversion even with aqueous alcohol to ester
The process described in the present invention also achieves substantial energy saving by utilization of the heat of esterification reaction for the distillation of the product and energy required for post-esterification purification.
In the present process a single catalytic distillation tower is used in which solid catalysts is supported in perforated cages woven bages of fibers or stainless steel mesh or monolith, which also served as packing material for distillation column. Acetic acid is fed from the top and distributed in the column with the help of a distribution plate.

Ethanol is fed near the bottom of the reactor carboxylic acid ester as product is collected from the top of the catalytic column. The mole ratio of alcohol to acid varies for 1:1 - 1:5 preferential in the range of 1:1.5-2. Excess acetic acid along with extracted water is collected from the bottom. This acetic acid can be recycled.
The key element of the process is in controlling the reaction conditions e.g. (reaction temperature and pressure. The temperature varies from 50-150°C at 1-20 kg pressure) in such a manner that all the three phases are present in the reaction system at any point of time and atleast one of the component of reaction mixture and atleast one of the components of the product streams always remain in the vapour phase. The system also provide efficient liquid vapour interaction in presence of catalyst resulting in high yield of the desired ester by maintaining continuous availability in more than stoichiometric ratio of fresh acetic acid (as liquid for) to the unreacted alcohol vapours.
Out of the reaction product i.e water is continuously extracted from the water alcohol and ester ternary azeotrope with the help of fresh acid thereby shifting the equilibrium toward the desired product.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
Example -1
The reactor consist of a glass column, packed with the solid catalyst i.e. ion exchange resin macro reticular type, Amberlyst. About 30 g of the catalyst was packed in small cylinderal bags made up of stainless steel net. The packing was done in such a manner that there was enough space for vapour-liquid contact. The temperature of the column was maintained at reaction temperature 90°C. The alcohol vapour was fed from the bottom of the reaction zone and the acid from the top of the reaction zone, at predetermined rate. The flow rate of alcohol varied from 15ml/ hr to 30ml/hr whereas the flow rate of acid was kept at 30ml/hr. During the reaction, the overhead vapours from the reactor column were passed through a condenser and collected, the liquid product was analysed by G. C and unreacted acid along the water present in the reactants and formed during reaction was collected from the bottom of the reactor. The results are summarized in Table-1.

Table-1
(Table Removed)

Example - II
All the reaction conditions and other reaction parameters were kept as in Example-l, except that the catalyst used is Tulsain. The procedure used is same as in Example-l. The results obtained are summarized in Table-2.
Table-2

(Table Removed)
Example - III
All the reaction conditions and other reaction parameters were kept as in Example-l, except that the catalyst used is Zeolite, HZSM-6 catalyst. 40 g of the Zeolite catalyst was diluted with porcelain beads (40 gms.) and filled in the column. All the other reaction conditions were kept constant as in Example 1 & 2. The results are summarized in Table - 3.
Table-3

(Table Removed)
Example - IV
All the reaction conditions and other reaction parameters were kept as in Example-l, except that the above experiment as in Example-l I were carried out using a mixture of 89% Ester and 11% alcohol. The ratio of alcohol & acid as calculated from the mixture was kept at 1:2. The results obtained are given in Table-4.
Table-4

(Table Removed)
Example - V
All the reaction conditions and other reaction parameters were kept as in Example-l, except that the above experiment was carried out using aqueous alcohol (78%), as in Example-l. The results are tabulated as follows:
Table - 5

(Table Removed)
The main advantages of the present invention are:
1. High yield of the carboxylic acid esters is obtained in the invented single
stage process against the two stage processes reported by most of the
inventors
2. The invented process does not require pure ethanol for esterification reaction
and aqueous ethanol can be used to produce ethyl acetate in high yields.
3. Under the present conditions water present either in the reactant or produced
during the reaction is extracted with acetic acid and collected at the bottom
product along with excess acetic acid used in the process.
4. The reaction system in the reactor at reaction temperature operates in state
of vapour liquid in equilibrium and act as an isothermal system thus avoiding
any possible over heating which may effect the catalyst activity.

We Claim:
1 An improved single stage process for the preparation of ethyl acetate which comprises
I) passing lower carboxylic acids mainly acetic acid and anhydrous or aqueous ethyl alcohol in a molar ratio of alcohol to acid ranging from 1:1 - 1:5 in a countercurrent manner through an esterification zone in a single column containing a solid esterification catalyst held in bags of woven fabric, or stainless steel mesh or in the form of monolith,
II) separating the components present in the vapour phase using catalyst bags to allow the upcoming vapours of alcohols to come in contact with the downward flowing liquid acid and also to act as packing material in the distillation column,
III) maintaining the temperature of the column reactor to a temperature of 50-150°C at a pressure ranging from 1-20 kg and controlling the parameters such that one of the reactants is present in the liquid phase and at least one of the products is also present in the liquid phase, whereas catalyst is present in solid phase,
IV) collecting ethyl acetate as a liquid containing some alcohol by condensing the vapours reaching at the top of the column and the upcoming unreacted ethyl alcohol in the form of ethyl alcohol, ethyl acetate azeotrope come in contact with fresh acetic acid in presence of acidic catalyst and converted to get ethyl acetate,
V) collecting the product formed by condensation without requiring any further purification where in purity of the product is above 95% due to the low alcohol content in the top product obtained in the one stage,
VI) recovering the bottom product from the column containing mainly aqueous acetic acid for further recycling.

2 An improved process as claimed in claim-1 wherein the process is a continuous process using a single reactor.
3 An improved process as claimed in claims 1-2 wherein the acid used is glacial acetic acid.
4 An improved process as claimed in claims 1-3 wherein the molar ratio of acetic acid to ethyl alcohol is preferably in the range of 1:1 to 2.5:1.

5. An improved process as claimed in claims 1-4 wherein an acidic catalyst is used for esterification reaction.
6. An improved process as claimed in claims 1-5 wherein the acidic catalyst is either zeolites or cation exchange resin or a mixture thereof.
7. An improved process as claimed in claims 1-6 wherein the catalyst used is ZSM-5 zeolites.
8. An improved process as claimed in claims 1-7 wherein the cation exchange resin is macroreticular type or gel type.
9. A process as claimed in claims 1 to 8 wherein the system in step (ii) also acts as an extraction column wherein continuously extracting the water formed during esterification reaction from the water, alcohol & ethyl acetate ternary azeotrope by downward coming acetic acid,
10. An improved process as claimed in claims 1-9 wherein the reaction temperature 50-150°C is controlled in such a manner that catalyst does not loses its activity due to over heating.
11 An improved process as claimed in claims 1-10 wherein the alcohol vapours are fed below the catalyst zone and acid above the catalyst zone.
13. An improved single stage process for the preparation of ethyl acetate substantially as herein described with reference to the examples accompanying this specification

Documents:

« Previous Patent

Next Patent »

Patent Number

222257

Indian Patent Application Number

409/DEL/2002

PG Journal Number

34/2008

Publication Date

22-Aug-2008

Grant Date

04-Aug-2008

Date of Filing

28-Mar-2002

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RENU AGGARWAL	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA.
2	AJAY KUMAR BHATNAGAR	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA.
3	ASHOK KUMAR GUPTA	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA.

PCT International Classification Number

C11C 001/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA