WO2009013623A2

WO2009013623A2 - Azeotropic distillation with entrainer regeneration

Info

Publication number: WO2009013623A2
Application number: PCT/IB2008/002698
Authority: WO
Inventors: Graham Robert Aird; Andrew Broadbent; Dena Ghiasy; Antony Peter John Limbach
Original assignee: Invista Technologies S.A.R.L.
Priority date: 2007-07-18
Filing date: 2008-06-27
Publication date: 2009-01-29
Also published as: TW200909408A; CN101854989A; SA08290441B1; WO2009013623A3; AR067614A1

Abstract

The present invention relates to a process for azeotropic distillation (Dl) of a feedstock (1), wherein the feedstock (1) comprises an aliphatic carboxylic acid and water, comprising conducting the azeotropic distillation (Dl) in the presence of an organic entrainer to produce a liquid phase component (2) comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock (1) and a vapor phase component (3) comprising the organic entrainer, an organic entrainer by-product and water, and either (i) returning a stream comprising the organic entrainer by-product to a point in the azeotropic distillation below where the feedstock is fed (9), wherein the organic entrainer by-product is converted to the organic entrainer or (ii) converting the organic entrainer by-product to the organic entrainer and then returning the organic entrainer to the azeotropic distillation.

Description

AZEOTROPIC DISTILLATION WITH ENTRAINER REGENERATION

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority from Provisional Application No.

60/950,426 filed July 18, 2007.

FIELD OF THE INVENTION

This invention relates to the separation of water from a liquid phase medium containing water and at least one organic component, more specifically the separation of water from a feed stream containing water and an aliphatic carboxylic acid.

BACKGROUND QF THE INVENTION

In the production of lerephthalic acid, for example, by the liquid phase oxidation of p-xylene in an aliphatic carboxylic acid solvent such as acetic acid, water and solvent are typically removed as an overhead vapor stream from the oxidation reactor as one means for controlling the temperature of reaction. The vapor stream is condensed to recover condensibles, some of which may be recycled as reflux to the oxidation reactor while other of the condensibles arc passed to a separation process which, in turn, allows for recovery of the aliphatic carboxylic acid solvent, such as acetic acid, having a reduced water content.

One convenient form of separation process comprises azeotropic distillation which is preferred over fractional distillation because of its improved energy efficient operation. However, the presence of an entrainer to accomplish the azeotropic distillation results in the formation of by-products of the entrainer, such as alcohols. The by-products are typically formed by the decomposition of the entrainer, especially by hydrolysis, at the conditions present in the distillation column. During the azeotropic distillation, these byproducts tend to stay in the top section of the distillation column solubilizing more water, which, in turn, increases energy consumption and the required diameter of the column. Additionally, as the entrainer degrades and forms by-product, more entrainer must be added to the azeotropic distillation column to effect separation, which increases the cost of operation.

Therefore, there exists a need in the art for a method of handling the entrainer by- products to enable operation of an inexpensive and efficient azeotropic distillation column for the dehydration of an aliphatic carboxylic acid solvent.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method has been found to manage and thereby reduce entrainer by-products produced in an azeotropic distillation column for the dehydration of an aliphatic carboxylic acid solvent. In this method, the reduction of the entrainer by-products results in the regeneration of the entrainer within the azeotropic distillation system or in an external vessel by conversion of the entrainer by-products. The present invention can be characterized by a process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; and either

(b) returning a stream comprising the organic entrainer by-product to a point in the azeotropic distillation below where the feedstock is fed, wherein the organic entrainer by- product is converted to the organic entrainer. or

(c) converting the organic entrainer by-product to the organic entrainer; and

(d) returning the organic entrainer to the azeotropic distillation. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic process diagram which illustrates one embodiment of the invention in which water is separated from an aliphatic carboxylic acid via azeotropic distillation, and the organic entrainer by-product is recycled.

Fig. 2 is a schematic diagram of an alternative embodiment of the invention.

Fig. 3 is a schematic diagram of another alternative embodiment of the invention.

Fig. 4 is a schematic diagram of another alternative embodiment of the invention in which esterification of the entrainer by-products takes place in an external reactor vessel.

Fig. 5 is a schematic diagram of a pilot scale configuration as described in Comparative Example 1.

Fig. 6 is a schematic diagram of another alternative embodiment of the invention in which esterification of the entrainer by-products takes place in an external reactor vessel.

Fig. 7 is a schematic diagram of another alternative embodiment of the invention in which esterification of the entrainer by-products takes place in an external reactor vessel.

Fig. 8 is a schematic diagram of another alternative embodiment of the invention in which esterification of the entrainer by-products takes place in an external reactor vessel.

Fig. 9 is a schematic diagram of another alternative embodiment of the invention in which esterification of the entrainer by-products takes place in an external reactor vessel.

DETAILED DESCRIPTION

The present invention can be characterized by a process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising: (a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; and

(b) returning a stream comprising the organic entrainer by-product to a point in the azeotropic distillation below where the feedstock is fed, wherein the organic entrainer byproduct is converted to the organic entrainer.

Another embodiment of the present invention can be characterized by a process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water;

(b) converting the organic entrainer by-product to the organic entrainer; and

(c) returning the organic entrainer to the azeotropic distillation.

In all above embodiments of the present invention step (a) can further comprise (i) removing the vapor phase component of step (a) from the distillation process; (ii) condensing it to form an organic liquid phase and an aqueous liquid phase; (iii) recycling the organic phase to the distillation process; (iv) stripping the aqueous phase to recover organic entrainer and organic entrainer by-product and form a second vapor phase. Additionally, in all above embodiments step (a) can further comprise (v) condensing the second vapor phase; and (vi) recycling at least some of the condensate from step (v) to said stripping step (iv).

Another embodiment of the present invention can be characterized by a process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising: (a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; (b) condensing the vapor phase component under conditions whereby the organic entrainer, organic entrainer by-product and water condense and form an organic phase and an aqueous phase;

(c) returning the organic phase from step (b) to the top of the azeotropic distillation as a reflux; (d) conducting purification of the aqueous phase from step (b) to remove the organic entrainer and organic entrainer by-product from the water; and

(e) returning the organic entrainer and the organic entrainer by-product to a point in the azeotropic distillation below where the feedstock is fed, wherein the organic entrainer by-product is converted to the organic entrainer.

In the above embodiment of the present invention step (b) can further comprise (i) separating the organic phase from the aqueous phase; and the conducting purification of step (d) can comprise (i) forming a stream comprising organic entrainer, organic entrainer by-product and water, and (ii) separating the stream into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase comprising the water. Alternatively, the conducting purification of step (d) can comprise (i) stripping the aqueous phase from step (b) to produce a vapor phase comprising the organic entrainer, organic entrainer by-product and water, (ii) condensing the vapor phase under conditions whereby the organic entrainer, organic entrainer by-product and water condense and (iii) separating the organic entrainer, organic entrainer by-product and water into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase comprising the water.

Another embodiment of the present invention can be characterized by a process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising: (a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; (b) condensing the vapor phase component from step (a) under conditions whereby the organic entrainer, organic entrainer by-product and water condense;

(c) separating the organic entrainer, organic entrainer by-product and water condensate from step (b) into an organic phase and an aqueous phase;

(d) returning the organic phase from step (c) to the top of the azeotropic distillation as a reflux;

(e) conducting purification of the aqueous phase from step (c) to produce a stream comprising organic entrainer, organic entrainer by-product and water;

(f) separating the organic entrainer, organic entrainer by-product and water stream from step (e) into an organic phase and an aqueous phase; and (g) returning the organic phase from step (f) to a point in the azeotropic distillation below where the feedstock is fed, wherein the organic entrainer by-product is converted to the organic entrainer.

(b) condensing the vapor phase component from step (a) under conditions whereby the organic entrainer, organic entrainer by-product and water condense;

(c) separating the organic entrainer, organic entrainer by-product and water condensate from step (b) into an organic phase and an aqueous phase; (d) returning the organic phase from step (c) to the top of the azeotropic distillation as a reflux; (e) stripping the aqueous phase from step (c) to produce a vapor phase comprising the organic entrainer, organic entrainer by-product and water;

(f) condensing the vapor phase from step (e) under conditions whereby the organic entrainer, organic entrainer by-product and water condense; (g) separating the organic entrainer, organic entrainer by-product and water condensate from step (f) into an organic phase and an aqueous phase; and

(h) returning the organic phase from step (g) to a point in the azeotropic distillation below where the feedstock is fed, wherein the organic entrainer by-product is converted to the organic entrainer.

(b) condensing the vapor phase component under conditions whereby the organic entrainer, organic entrainer by-product and water condense and form an organic phase and an aqueous phase;

(c) returning the organic phase from step (b) to the azeotropic distillation;

(d) conducting purification of the aqueous phase from step (b) to remove the organic entrainer and organic entrainer by-product from the water;

(e) converting the organic entrainer by-product to the organic entrainer; and (f) returning the organic entrainer to the azeotropic distillation.

(a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; (b) condensing the vapor phase component from step (a) under conditions whereby the organic entrainer, organic entrainer by-product and water condense;

(f) separating the organic entrainer, organic entrainer by-product and water stream from step (e) into an organic phase and an aqueous phase; (g) converting the organic entrainer by-product in the organic phase to organic entrainer; and

(h) returning the organic entrainer to the azeotropic distillation.

(e) stripping the aqueous phase from step (c) to produce a vapor phase comprising the organic entrainer, organic entrainer by-product and water;

(f) condensing the vapor phase from step (e) under conditions whereby the organic entrainer, organic entrainer by-product and water condense; (g) separating the organic entrainer, organic entrainer by-product and water condensate from step (f) into an organic phase and an aqueous phase;

(h) converting the organic entrainer by-product in the organic phase to organic entrainer; and

(i) returning the organic entrainer to the azeotropic distillation.

The vapor phase component of step (a) in all embodiments, which comprises the organic entrainer, organic entrainer by-product and water, is removed from the distillation process as a tops product, for example as an overhead vapor stream, from the distillation column and can be condensed into a liquid stream and a first vapor stream. The first vapor stream can be passed to a second distillation column in which the first vapor stream comprising the organic entrainer, organic entrainer by-product and water pass into the column and undergo further distillation whereby the organic entrainer, organic entrainer by-product and water arc condensed and recovered from the column as a liquid phase, and any other impurities remain in the vapor phase. The recovered organic entrainer/organic entrainer by-product/water liquid phase can then be allowed to phase separate into organic and aqueous phases. In all embodiments of the present invention the organic entrainer can be at least one ester selected from n-butyl acetate, isobutyl acetate, n-propyl acetate, isopropyl acetate or mixtures thereof, for example isobutyl acetate, n-propyl acetate or isopropyl acetate; n- propyl acetate or isopropyl acetate; or n-propyl acetate. The organic entrainer can be an entrainer with a boiling point in the range of from about the boiling point of isopropyl acetate to about the boiling point of n-butyl acetate, for example from about 88 ⁰C to about 126 ⁰C. The organic entrainer by-product can be at least one member selected from propanol, butanol, an alcohol corresponding to the organic ester entrainer or mixtures thereof.

In all embodiments of the present invention the conversion of organic entrainer byproducts to organic entrainer can comprise esterification of the organic entrainer byproduct with aliphatic carboxylic acid. Aliphatic carboxylic acid for this purpose should be in relatively high concentration to favour the esterification reaction rather than hydrolysis. Aliphatic carboxylic acid exists in such concentrations below the distillation column feed point. The esterification can take place either within the distillation column using the aliphatic carboxylic acid present, or else in a separate reactor vessel outside of the column. The reactant aliphatic carboxylic acid can be fresh or derived from the column bottoms product. The stream to be reacted can be a relatively high concentration of entrainer byproduct to facilitate its esterification.

In all embodiments of the present invention the recycled organic phase or reflux to the azeotropic distillation column can comprise organic entrainer by-product at a concentration in the range of from about 1 weight % to about 15 weight % of the total composition, for example from about 2 weight % to about 15 weight % or from about 1 weight % to about 10 weight % or from about 2 weight % to about 10 weight % or from about 2 weight % to about 8 weight % or from about 2 weight % to about 6 weight %.

The aromatic carboxylic acid production processes in which the instant invention can be most applicable are those processes employed on a commercial scale for production of terephthalic acid and isophthalic acid in which the aliphatic carboxylic acid solvent is typically acetic acid. The present invention can be better understood by reference to Figures 1, 2, 3, 4, 6, 7, 8 and 9 which illustrate azeotropic distillation processes for the separation of an aliphatic carboxylic acid and water.

Referring to Figure 1 , a feed line 1 to dehydration column D 1 (which can be a packed or a tray type distillation column) comprises the water draw off obtained from the oxidation reactor overheads condenser system associated with the oxidation reactor for the production of terephthalic acid. For example, but not limited to, the composition of feed line 1 can comprise 1 wt%-40 wt% water and 99 wt%-60 wt% acetic acid. Other feeds can also be supplied to the column such as crystallizer vapour streams. Heat to column Dl is supplied via reboiler EL A low boiling point organic entrainer, such as n-propyl acetate, isopropyl acetate iso-butyl acetate or n-butyl acetate, can be supplied to the column via the reflux line 5, and the column is operated so as to insure penetration of the entrainer to a level below feed 1 whereby feed 1 enters the column at an entrainer-rich region.

The bottoms product withdrawn from the base of column Dl via line 2 comprises, for example, acetic acid having relatively low water content relative to the incoming feed line 1 and is suitable for recycle to the oxidation reaction. For example, but not limited to, the bottoms product can comprise 1 wt%-20 wt% water and 99 wt%-80 wt% acetic acid. The tops product at the head of column Dl is cooled against a suitable medium, such as, but not limited to, cooling water, steam or heat transfer fluid in a column overheads condenser system E2. The condensate is supplied to a primary decanter Fl where condensate is separated into an organic phase (primarily organic entrainer with a small quantity of organic entrainer by-product, water and some methyl acetate, paraxylene and other organics) and an aqueous phase containing organic entrainer by-product and a small quantity of organic entrainer. The organic phase comprising mainly organic entrainer is reintroduced into the distillation column via line 5. The aqueous phase is passed via line 6 to a recovery column D2 for recovery of the organic entrainer and organic entrainer by- product via line 8 to recycle decanter F2. Primary decanter Fl can also used to introduce any additional entrainer required in the system. Recovery column D2 is heated by steam (either by direct sparging or through a reboiler) and the vapor line 8 out of the column goes through a condenser E3. Recovery column D2 comprises packed or trayed sections. The bottoms product withdrawn from the base of recovery column D2 via line 7 comprises water having a relatively low organics content (for example, but not limited to, less than about 1 wt%) relative to the incoming feed stream 6.

Recycle decanter F2 is fed via line 8 from recovery column D2 through condenser E3. Feed stream 8 comprises primarily organic entrainer and organic entrainer by-product. Any water in feed stream 8 can be separated out in recycle decanter F2 and fed via line 10 back either to primary decanter Fl or to recovery column D2. Organic entrainer and organic entrainer by-product is fed via line 9 to dehydration column Dl below feed line 1 . The organic entrainer by-products are converted within dehydration column D 1 back to the organic entrainer by esterification.

Figure 2 illustrates an alternative configuration to Figure 1 wherein the condenser E3 is internal to the recovery column D2. Non-condensable lights can be fed to recovery column D2 via line 1 1 from E2 to a feed point between upper and lower packed or trayed sections in column D2. Separator devices can be provided within recovery column D2 above the upper and lower packer or trayed sections. Feed line 6 from primary decanter Fl feeds recovery column D2 at a point between the lower separator device and lower packed or trayed section. Line 8 feeding recycle decanter F2 exits recovery column D2 at a point just above the lower separator device and below the upper packed or trayed section.

Figure 3 illustrates an alternative configuration to Figure 2 wherein the recycle decanter F2 is internal to recovery column D2.

Figure 4 illustrates an alternative configuration to Figures 1 -3 wherein the esterification of the entrainer by-products can take place in esterification reactor Rl instead of within the azeotropic distillation column Dl . The internal decanter of Figure 3 can also be used in this configuration to conduct the phase separation duty.

Figure 6 illustrates an alternative configuration to Figure 4 wherein line 8 can be cooled by an additional heat exchanger E4. Figure 7 illustrates an alternative configuration to Figure 4 wherein line 8 feeding recycle decanter F2 exits recovery column D2 at a point within the upper packed or trayed section. Additionally, line 15 feeding primary decanter Fl exits recovery column D2 at a point between upper and lower packed or trayed sections in column D2.

Figure 8 illustrates an alternative configuration to Figure 7 wherein line 8 is cooled by an additional heat exchanger E4.

Figure 9 illustrates an alternative configuration to Figure 4 wherein line 16 can feed entrainer by-product into line 9 prior to esterification reactor R 1.

The following examples further illustrate the present invention.

COMPARATIVE EXAMPLE 1

A pilot scale dehydration column system was run in the configuration of Figure 5 to demonstrate the problematic build up of organic entrainer by-product in the overheads.

The pilot system was operated over a period of several days at an overheads pressure of 4 bara. Samples from SPl, going into dehydration column Dl were taken to demonstrate an increase in organic entrainer by-product in the overheads. The organic entrainer used was

99% pure n-propyl acetate with less than 1% propanol impurity. The results are in Table 1 below.

Table 1

EXAMPLE 2

A laboratory scale batch autoclave was ran a number of times to demonstrate the conversion of an organic entrainer by-product back to organic entrainer. Conditions in the autoclave were designed to be similar to the lower portion of an azeotropic distillation column. To demonstrate the conversion n-propyl acetate (nPA) was used as an entrainer and propanol (PrOH) was used as an entrainer by-product in the feed to the batch autoclave. Water and acetic acid were also fed to the batch autoclave as detailed in Table 2. Concentrations of propanol were monitored by sampling the liquor from the autoclave following each run. The feed composition, percent reduction of propanol in the system, residence time, and temperature of the batch autoclave were recorded. The results are in Table 2 below.

Table 2

EXAMPLE 3

An Aspen simulation and a kinetics model were used to demonstrate the effectiveness of the eslerification reactor Rl. The esterifier feed concentrations were generated by the Aspen simulation and were applied to a kinetics model of n-propyl acetate hydrolysis / esterification. From this the rates of n-propanol conversion were determined. The configuration of the Aspen simulation used to generate an esterifϊcation reactor Rl feed composition was broadly as in Figure 4, with the following differences:

• Methyl acetate recovery column D2 modeled in two separate sections (top and bottom)

• Only a fraction of organics from recycle decanter (line 9) goes through the esterifier. The rest is mixed with line 5 prior to going back to the column as reflux.

• There is a PX purge column in the ASPEN model

« There are hydrolysis blocks to simulate entrainer hydrolysis in various places.

Standing concentration of propanol in the reflux (line 5) is controlled by the value of fractional conversion specified in the esterifier block. The Aspen simulation consisted of the following main unit operations:

« Dehydration column Dl and re-boiler El : Specifications: Top P = 3.8 bara, Bottom

P = 4 bara, Controlled by a "design spec" on bottom product « Dehydration column condenser E2: Specifications: T — 1 15-1 16 C

• Methyl acetate recovery columns: P = 3.65 - 4 bara

• Esterifier Rl : Specifications: P = 7 bara, T= 160 C The rate of esterification was calculated using:

dt \ 5 J

Results of the simulation and kinetics model are in Table 3 below.

Table 3

EXAMPLE 4

An Aspen simulation and a kinetics model were used to demonstrate the effectiveness of the esterification reactor Rl . The Aspen simulation was run in the configuration of Figure 6 and generated esterifier feed concentrations for the kinetics model as in Example 3. The simulation configuration differences, the unit operation descriptions and the rate calculation are the same as in Example 3. Results are in Table 4 below.

Table 4

EXAMPLE 5

An Aspen simulation and a kinetics model were used to demonstrate the effectiveness of the esterification reactor Rl . The Aspen simulation was run in the configuration of Figure 7 and generated esterifier feed concentrations for the kinetics model as in Example 3. The simulation configuration differences, the unit operation descriptions and the rate calculation are the same as in Example 3. Results are in Table 5 below.

Table 5

EXAMPLE 6

An Aspen simulation and a kinetics model were used to demonstrate the effectiveness of the esterification reactor R l . The Aspen simulation was run in the configuration of Figure 8 and generated esterificr feed concentrations for the kinetics model as in Example 3. The simulation configuration differences, the unit operation descriptions and the rate calculation are the same as in Example 3. Results are in Table 6 below.

Table 6

EXAMPLE 7 A laboratory scale tubular reactor system was run to demonstrate the effectiveness of the esterification reactor R l and to verify results of the Aspen simulations and kinetics model in Examples 3-6. The laboratory scale tubular reactor system had a pump with 10 ml head to pump the Feed Composition into a 1/16" O. D. pre-heater coil, then to a 1/2" O.D. pipe reactor fitted with HlTRAN inserts, then to a 1/16" O. D. cooler coil, and finally into a sample container. The pre-heater coil and pipe reactor were in an oil bath set at a temperature of about 16O⁰C. The cooler coil was in a cooling bath set at a temperature of about 2O⁰C. The system had a back pressure regulator set at a pressure of about 1 1 bara (to suppress boiling) located just before the sample container. Reactor residence time was about 25 minutes.

At the beginning of each test water was pumped through the system and the oil bath was set to the required temperature. When the set temperature was reached, water was replaced by feed solution. The unit was run for a sufficient period of time before samples were taken to ensure that the liquid flowing though the unit was representative of feed solution and all the water had been pumped out. Three 7-8 ml samples were collected for each experiment. Samples of the feed and product were analysed on a Gas Chromatograph. Water concentrations were measured by a Karl Fischer test using a standard KF titration solution on 10Dl injected samples. Results of propanol (PrOH) conversion are in Table 7 below.

Table 7

0

While the invention has been described in conjunction with specific embodiments thereof, it is evident that the many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall 5 within the spirit and scope of the claims.

Claims

What is claimed is:

1. A process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(a) conducting the azeotropic distillation in the presence of an organic enlrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; and

2. The process of claim 1 wherein the organic entrainer has a boiling point in the range of from about the boiling point of isopropyl acetate to about the boiling point of n-butyl acetate.

3. The process of claim 1 wherein the organic entrainer has a boiling point in the range of from about 88 ⁰C to about 126 ⁰C.

4. The process of claim 1 wherein the organic entrainer is at least one ester selected from the group consisting of n-butyl acetate, isobutyl acetate, n-propyl acetate, isopropyl acetate and mixtures thereof.

5. The process of claim 1 wherein the organic entrainer by-product is at least one member selected from the group consisting of propanol, butanol, an alcohol corresponding to the organic entrainer and mixtures thereof.

6. The process of claim 1 comprising the additional steps of (i) removing the vapor phase component of step (a) from the distillation process; (ii) condensing it to form an organic phase and an aqueous phase; (iii) recycling the organic phase to the distillation process; (iv) stripping the aqueous phase to recover organic entrainer and organic entrainer byproduct and form a second vapor phase.

7. The process of claim 6 wherein the organic phase of step (iii) comprises an organic entrainer by-product in a concentration of from about 1 weight % to about 15 weight %.

8. The process of claim 6 comprising the additional steps of (v) condensing the second vapor phase; and (vi) recycling at least some of the condensate from step (v) to said stripping step (iv).

9. The process of claim 1 wherein the conversion in step (b) comprises esterification of the organic entrainer by-product.

10. A process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(a) conducting the azeotropic distillation in the presence of an organic entrainer to produce a liquid phase component comprising said aliphatic carboxylic acid having a reduced water content relative to the water content in the feedstock and a vapor phase component comprising the organic entrainer, an organic entrainer by-product and water; (b) converting the organic entrainer by-product to the organic entrainer; and

(c) returning the organic entrainer to the azeotropic distillation.

1 1 . The process of claim 10 wherein the organic entrainer has a boiling point in the range of from about the boiling point of isopropyl acetate to about the boiling point of n-butyl acetate.

12. The process of claim 10 wherein the organic entrainer has a boiling point in the range of from about 88 ⁰C to about 126 ⁰C.

13. The process of claim 10 wherein the organic entrainer is at least one ester selected from the group consisting of n-butyl acetate, isobutyl acetate, n-propyl acetate, isopropyl acetate and mixtures thereof.

14. The process of claim 10 wherein the organic entrainer by-product is at least one member selected from the group consisting of propanol, butanol, an alcohol corresponding to the organic entrainer and mixtures thereof.

15. The process of claim 10 comprising the additional steps of (i) removing the vapor phase component of step (a) from the distillation process; (ii) condensing it to form an organic phase and an aqueous phase; (iii) recycling the organic phase to the distillation process; (iv) stripping the aqueous phase to recover organic entrainer and organic entrainer by-product and form a second vapor phase.

16. The process of claim 15 wherein the organic phase of step (iii) comprises an organic entrainer by-product in a concentration of from about 2 weight % to about 15 weight %.

17. The process of claim 15 comprising the additional steps of (v) condensing the second vapor phase; and (vi) recycling at least some of the condensate from step (v) to said stripping step (iv).

18. The process of claim 10 wherein the conversion in step (b) comprises esteriflcation of the organic entrainer by-product.

19. A process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(c) returning the organic phase from step (b) to the azeotropic distillation; (d) conducting purification of the aqueous phase from step (b) to remove the organic entrainer and organic entrainer by-product from the water; and

20. The process of claim 19 wherein the organic entrainer has a boiling point in the range of from about the boiling point of isopropyl acetate to about the boiling point of n-butyl acetate.

21. The process of claim 19 wherein the organic entrainer has a boiling point in the range of from about 88 ⁰C to about 126 ⁰C.

22. The process of claim 19 wherein the organic entrainer is at least one ester selected from the group consisting of n-butyl acetate, isobutyl acetate, n-propyl acetate, isopropyl acetate and mixtures thereof.

23. The process of claim 19 wherein the organic entrainer by-product is at least one member selected from the group consisting of propanol, butanol, an alcohol corresponding to the organic entrainer and mixtures thereof.

24. The process of claim 19 wherein the conversion in step (e) comprises esterification of the organic entrainer by-product.

25. The process of claim 19 wherein the organic phase of step (c) comprises an organic entrainer by-product in a concentration of from about 1 weight % to about 15 weight %.

26. The process of claim 19 wherein step (b) further comprises (i) separating the organic phase from the aqueous phase; and wherein the conducting purification of step (d) comprises (i) forming a stream comprising organic entrainer, organic entrainer by-product and water, and (ii) separating the stream into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase.

27. The process of claim 19 wherein step (b) further comprises (i) separating the organic phase from the aqueous phase; and wherein the conducting purification of step (d) comprises (i) stripping the aqueous phase from step (b) to produce a vapor phase comprising the organic entrainer, organic entrainer by-product and water, (ii) condensing the vapor phase under conditions whereby the organic entrainer, organic entrainer byproduct and water condense and (iii) separating the organic entrainer, organic entrainer byproduct and water into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase.

28. A process for azeotropic distillation of a feedstock, wherein the feedstock comprises an aliphatic carboxylic acid and water, comprising:

(b) condensing the vapor phase component under conditions whereby the organic entrainer, organic entrainer by-product and water condense and form an organic phase and an aqueous phase; (c) returning the organic phase from step (b) to the azeotropic distillation;

(e) converting the organic entrainer by-product to the organic entrainer; and (i) returning the organic entrainer to the azeotropic distillation.

29. The process of claim 28 wherein the organic entrainer has a boiling point in the range of from about the boiling point of isopropyl acetate to about the boiling point of n-butyl acetate.

30. The process of claim 28 wherein the organic entrainer has a boiling point in the range of from about 88 ⁰C to about 126 ⁰C.

31. The process of claim 28 wherein the organic entrainer is at least one ester selected from the group consisting of n-butyl acetate, isobutyl acetate, n-propyl acetate, isopropyl acetate and mixtures thereof.

32. The process of claim 28 wherein the organic entrainer by-product is at least one member selected from the group consisting of propanol, butanol, an alcohol corresponding to the organic entrainer and mixtures thereof.

33. The process of claim 28 wherein the converting of step (e) comprises esterification of the organic entrainer by-product.

34. The process of claim 28 wherein the organic phase of step (c) comprises an organic entrainer by-product in a concentration of from about 2 weight % to about 15 weight %.

35. The process of claim 28 wherein step (b) further comprises (i) separating the organic phase from the aqueous phase; and wherein the conducting purification of step (d) comprises (i) forming a stream comprising organic entrainer, organic entrainer by-product and water, and (ii) separating the stream into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase.

36. The process of claim 35 wherein step (d) further comprises cooling the stream prior to the separating.

37. The process of claim 35 wherein the stream of step (d) exits a recovery column at a point within an upper packed or trayed section.

38. The process of claim 35 wherein additional organic entrainer by-product is added to the organic phase of step (d) (ii).

39. The process of claim 28 wherein step (b) further comprises (i) separating the organic phase from the aqueous phase; and wherein the conducting purification of step (d) comprises (i) stripping the aqueous phase from step (b) to produce a vapor phase comprising the organic entrainer, organic entrainer by-product and water, (ii) condensing the vapor phase under conditions whereby the organic entrainer, organic entrainer byproduct and water condense and (iii) separating the organic entrainer, organic entrainer byproduct and water into an organic phase comprising the organic entrainer and organic entrainer by-product and an aqueous phase.

40. The process of claim 39 wherein step (d)(ii) further comprises cooling the organic entrainer, organic entrainer by-product and water after they condense.

41. The process of claim 39 wherein the organic entrainer, organic entrainer by-product and water of step (d)(ii) exit a recovery column at a point within an upper packed or trayed section.

42. The process of claim 39 wherein additional organic entrainer by-product is added to the organic phase of step (d)(iii).

43. The process of any one of claims 1, 10, 19 or 28 wherein the aliphatic carboxylic acid is acetic acid.