CA1066302A - Process for making aromatic acids - Google Patents
Process for making aromatic acidsInfo
- Publication number
- CA1066302A CA1066302A CA250,254A CA250254A CA1066302A CA 1066302 A CA1066302 A CA 1066302A CA 250254 A CA250254 A CA 250254A CA 1066302 A CA1066302 A CA 1066302A
- Authority
- CA
- Canada
- Prior art keywords
- acid
- hydrolysis
- equilibrium
- reboiler
- aromatic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
Abstract
ABSTRACT OF THE DISCLOSURE
A process for making an aromatic carboxylic acid of high purity by feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distillation column operated at a temperature of from about 200°C. to about 325°C. at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, removing water vapor and ammonia from the top of the column, subjecting remaining equilibrium hydrolysis mixture to further hydrolysis and distill-ation in a reboiler, returning vapor from the reboiler to the distillation column, removing an aqueous solution of product acid from the reboiler, cooling said separated solution, and separating acid product. In one embodiment of the invention the hydrolysis mixture is obtained by subjecting a nitrile from the ammoxidation of an alkyl aromatic compound to aqueous hydrolysis in a closed reactor at about 200°C to about 325°C. until an essentially complete equilibrium is obtained.
A process for making an aromatic carboxylic acid of high purity by feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distillation column operated at a temperature of from about 200°C. to about 325°C. at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, removing water vapor and ammonia from the top of the column, subjecting remaining equilibrium hydrolysis mixture to further hydrolysis and distill-ation in a reboiler, returning vapor from the reboiler to the distillation column, removing an aqueous solution of product acid from the reboiler, cooling said separated solution, and separating acid product. In one embodiment of the invention the hydrolysis mixture is obtained by subjecting a nitrile from the ammoxidation of an alkyl aromatic compound to aqueous hydrolysis in a closed reactor at about 200°C to about 325°C. until an essentially complete equilibrium is obtained.
Description
It is known in the art to prepare aromatic carboxylic acids by hydrolysis of the corresponding nitriles which, in turn, are prepared by ammoxidation alkyl-substituted hydrocarbons. The acids obtained from such processes must generally have high purity and be essentially devoid of nitrogen containing by-products and, in the case of polycarboxylic acids, must also be free of any by--product monoacids. This is particularly true of aromatic dicar-~ boxylic acids such as terephthalic acid which is the well-known -~ intermediate to polyester fibers. In order to emply terephthalic acid for such use it must have a very high purity and, in particu-lar, be free of nitrogen containing bodies which will discolor the polymer made from such acid, and it must also be free of mono--acids such as p-toluic acid which might arise from incomplete ammoxidation since such a mono-acid would adversely affect poly-meri~ation of the acid in that the necessary high molecular weight polymer could not be obtained.
Thus, in accordance with the present teachings, a process is provided for producing an aromatic carboxylic acid which comprises the steps of feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distillation colu~n which is operated at a temperature from about 200C. to about 325C. at autogenous pressure whereby the equilibrium mixture ~` is subjected simultaneously to further hydrolysis and distillation of ammonia. Ammonia and water vapor are removed from the top of the column and the remaining equilibrium hydrolysis mixture is sub-jected to further hydrolysis and distillation in a reboiler at a temperature of from about 200C to about 325C. and returning vapors from the reboiler to the distillation column. An aqueous solution .
of product aromatic acid is removed from the reboiler and cool~d ~ ;
` 30 and the acid product which is now low in nitrogen impurities is separated.
.~ ~,,`i ~ .
.~ : .
, , 3~
More specifically, the novel process enables aroma-tic acids to be obtained essentially :Eree of unwanted by-products. In accord with the invention, a process is provided for making an aro-matic carboxylic acid of high purity from the hydrolysate of the corresponding nitrile preferably obtained by ammoxidation of an alkyl aromatic compound, by feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distilla-tion column operated at a temperature of from about 200C. to about 325C. and at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, concentrating ammonia by rectification in the upper portion of the column, removing the concentrated ~ aqueous ammonia vapor from the top of the column, subjecting :: the remaining ,.~
,.
~ ~
`'` . "
' ~. ,.: -: , ' .~' , ~ .
-2a-- . . .
'1~%
equilibrium hydrolysis mixture to further hydrolysis and distill-ation in a reboiler operated at about 200C to about 3~5C., returning vapors from the reboiler to a lower portion of the distillation column, removing an aqueous solution of product from the reboilder, cooling said separated solution, and separating acid product. In a preferred process~ the nitrile hydrolysate is obtained by an aqueous hydrolysis in a closed reactor at a temper-ature of from about 200C. to about 325C. until an essentially complete hydrolysis equilibrium is reached and the equilibrium ; hydrolysate i5 then fed to the reactive distillation unit.
The invention as described above involves a "reactive distillation" and such terminology is used herein to indicate the production of free aromatic carboxylic acid by the efficient removal of ammonia from a reaction zone where the normally equili-brium limited reaction of amide and ammonium salt is shifted to the salt which, in turn, yields free acid of high purity. Thus, for example, in the hydrolysis of terephthalonitrile in a closed system the chemistry is as follows:
:: `
'' ~OONH4 ~ CN\
CN ~O~H2 ~ ICOONH4 COONH4 [~ >(~
CN CN ~ CONH2 CONH2 COONH4 Terephthalonitrile ~ Ammonium Diammonium (TPN) O I Terephthalamate Terephthalate (ATA) (DAT) When such a hydrolysis mixture is subjected to reactive distill-ation -the equilibrium:
f OONH4 COONH~ COOH
> ~ ` ~ + 2NH3 is shifted to the right in the column because under the temperature conditions within the unit the ammonium salt is converted to the aromatic free acid and ammonia, the ammonia being removed contin-; uously from the reaction zone. Thus, all of the amide nitrogen eventually beco~es converted to ammonia and a high purity free acid results as product.
One of the major advantages of the process oE this inven-tion is that it enables in a sin~le step:
a) the concentration of ammonia, ,:
` b) its removal from the system, c) elimination of undesired nitrogen impurities and, -d) the making of high purity free acid. This is to be contrasted with prior art techniques which sweep ammonia from the ; system without concentration, thus requiring large volumes of steam. Furthermore, prior art methods yield the ammonium salts as intermediates and require one or more additional steps for conver-sion to the free acid.
The process of the invention is applicable to the produc-tion of a wide variety of aromatic carboxylic acids. The aromatic nitrile starting material may be selected from any of those compounds ~ .
... , . , . ... ...... . .... - ", , .. , .. , . .... . . . ~ .. . . ......... ~ .. ...... ... . - ~ .
3~2~
where one or more nitrile radicals are attached directly to an aromatic ring compound; preferably, a benzene or naphthalene ring.
Examples of nitriles falling within this class include benzonitrile, phthalonitrile, isophthalonitrile, terephthalonitrile~ the tolu-nitriles, naphthonitriles such as 1,5- and 2,6~dicyanonaphthalene, and the like. Preferred nitriles for use in the process are those of the benzene and naphthalene series such as the phthalonitriles, particularly terephthalonitrile and isoph~halonitrile, and 2,6-dicyanonaphthalene.
To explain more fully the invention reference is now made to the drawing where the preferred process will be illustrated with a hydroysate of terephthalonitrile. The terephthalonitrile to be hydrolyzed is fed into a closed hydrolytic chamber (11) where hydrolysis occurs at a temperature between about 200 and about 325C. under autogeneous pressure, the pressure actually rising to about 220 to about 1750 psia. In this reactor, the hydrolysis proceeds until an equilibrium is reached which at the preferred range of about 250C. to about 325C. requires from about 2 to about 0.1 hours. The hydrolysis products in the equilibrium mixture as shown above 7 will consist essentially of the diammonium salt of terephthalic acid and ammonium terephthalamate together with small amounts of the ammonium salt of 4-cyanobenzoic acid, 4-cyanobenza-mide, and terephthalamide. After the equilibrium is established the aqueous mixture is fed into a reactive distillation column (12) where hydrolysis of nitrogen-containing aromatics occur in a stripping section of the column and concentration of the resulting ammonia occurs in the upper section. It is in this way that the equilibrium is shifted by removal of ammonia taken overhead together with water vapor. The distillate product is recovered in the usual fashion with a portion of the overhead being returned to the column .: . 1. .'.':'."'.""1;"" ' - ~630~
as reflux. The reactor column is operated at a temperature between about 200C. and about 325C. preferably about 260C. to about 310C. and at autogenous pressure which will be a pressure of between about 220 and about 1750 psia. It is important that the residence time of materials within the column be longer than that found in simple distillation systems and a preferred method to accomplish an increased residence time is by means of an apparatus which employs liquid reservoirs between trays within the columns. In the process of this invention residence time will be preferably between about 15 and about 45 minutes. These long residence times are necessary to provide time to enable the amides in the equilibrium hydrolysis system to be shifted toward the salt as the ammonia is removed as explained above. To separate the ammonia effectively, only moderate reflux ratios on the order to 2 to 10 are required.
A particular advantage of this portion of the process is that the actual water carried over is only a small fraction of the water in the feed. Thus, for ex~mple, a typical feed concentration to the column reactor may contain one mole of aromatic material to 50 moles of water and, even if the mole percent of water in the overhead is quite high (e.g., 50 mole %), the actual quantity of water carried over is only a small fraction of the feed (about 4%).
Likewise, the ammonia content is significantly concentrated.
For example, the ammonia concentration of the hydrolysate input is about 4 mole percent, but after concentration by rectification in the column it exits at no less than about 50 mole percent. Furthermore, there is no carry-over of i~
aromatic compounds in the overhead. It is thus clear that one major advantage of the process is that the utility requirements are low and thus a highly efficient process is achieved. This is .... ..... ...
., .
, ~.....
.. . .
in contrast to known techniques where ammonia is removed by steam sweeping which often requires that the quantity of steam be that or approach that of the feed itself and this high steam volume mitigates against an economical process.
The terephthalic acid product which flows to the bottom of the column is taken to a reboiler (13) where any residual intermediate materials are further converted by hydrolysis and removal of ammonia to terephthalic acid. The ammonia that is generated by this hydrolysis is returned to the column through line 14 where it is eliminated with the overhead stream. Residence time in the reboiler is about 0.5 to 3 hours. It will be under-stood that although the reboiler (13) is shown separate from the distillation column (12), the reboiler may be an integral part of the bottom portion of the column as is frPquently the case with industrial equipment. Finally, a solution of high purity tere-phthalic acid is taken from the reboiler and cooled and the acid crystals separated by filtration or other conventional means.
To exemplify further the operation and results oktained by the process, the following examples are given:
Examples An apparatus as illustrated in the drawing and described above is used to subject an equilibrium terephthalonitrile hydrol-ysis product to reactive distillation. Example 1 is operated in a batch precedure, the initial charge being made to the reboiler, while Examples 2, 3 and ~ are operated in a continuous mode. The table which follows indicates the conditions and results.
t) # ~ i3~3 r-l ~
t~ ci~
o\~
0 0~ o co H C) ~) CO
~) a) ~ r~ ~ ~ o~ c~
r~ ~ rl O
a) a) ~.) ~1 1~
o~o o 1}1 ~ !C O
O Q) r ~ r-l * O ~ x 5_1 C5 O ~ ~ ~ o r~ rl ~ ~ ~
u~ z o O ~) r-l ~ co oo ~
D3 ~ ~ , ~ I ~
~ ~ Z
H r~
u~ ~ ~
::~~ ~
~ ~ ~ ~ ~) . Q ~ O # ~ ~
~ O s l o r~
P~~I P4 ~ o O O O !4 ~ æ o o O ~ 00 p; ~1) r-l r-i ~ r~l z E~ ~ a) o ~ ~
O r~ ~ ~I _ r 51 a) ~ ~ Z r~
¦ 1 $ ~LI rl ~ ¦
E~ ~ ~H ~n o o o o O
.` Z O ~ O L~ O O ~
1~4 r~ ~r) r-l ~ ~ 1) O ~I) r~l ~ ~ ~ ~ ~ r~
(~ ~r Is') ~ ~ ~ (U
O r ~ ~r ~J N
. ~ r¢ 1~1 0 O
. . ~1 . H o $ r-l ` H ~1 ~ r~
r-l IJ (D
.' W rl 1~ O O t~
~ O ~ U~ ~ C~
H .4 : E~ P:; ~ 11 ~1 ,.
~ E~ ~ 4~
r~ U~
U~ ~ , . ..
h r-rl tU
., O ~ tJl O U~
~ tY;
) r-l ~ O
ul a) r~ ~ r~
a) J r-l O O O (U
rl 1:4 ~r t~ Q O ~0 00 h ~ ~1 r~ In ~ r~
O r-l ~ ~) ~; ~ ~ ~ z h ,_ ~ 0 O
.' rl a) ,~ r~ ~ rJ _~ r~
r~l ~ , ~;
O ~ O O O 0 0 0 x m ¦ L~ r-l t~l ~) ~ # 1:
1~6~
As can be seen from the above date, a significant reduction in amide nitrogen is readily achieved and the purity of the product terephthalic acid is quite high.
.. 9 .. .. ..
Thus, in accordance with the present teachings, a process is provided for producing an aromatic carboxylic acid which comprises the steps of feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distillation colu~n which is operated at a temperature from about 200C. to about 325C. at autogenous pressure whereby the equilibrium mixture ~` is subjected simultaneously to further hydrolysis and distillation of ammonia. Ammonia and water vapor are removed from the top of the column and the remaining equilibrium hydrolysis mixture is sub-jected to further hydrolysis and distillation in a reboiler at a temperature of from about 200C to about 325C. and returning vapors from the reboiler to the distillation column. An aqueous solution .
of product aromatic acid is removed from the reboiler and cool~d ~ ;
` 30 and the acid product which is now low in nitrogen impurities is separated.
.~ ~,,`i ~ .
.~ : .
, , 3~
More specifically, the novel process enables aroma-tic acids to be obtained essentially :Eree of unwanted by-products. In accord with the invention, a process is provided for making an aro-matic carboxylic acid of high purity from the hydrolysate of the corresponding nitrile preferably obtained by ammoxidation of an alkyl aromatic compound, by feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distilla-tion column operated at a temperature of from about 200C. to about 325C. and at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, concentrating ammonia by rectification in the upper portion of the column, removing the concentrated ~ aqueous ammonia vapor from the top of the column, subjecting :: the remaining ,.~
,.
~ ~
`'` . "
' ~. ,.: -: , ' .~' , ~ .
-2a-- . . .
'1~%
equilibrium hydrolysis mixture to further hydrolysis and distill-ation in a reboiler operated at about 200C to about 3~5C., returning vapors from the reboiler to a lower portion of the distillation column, removing an aqueous solution of product from the reboilder, cooling said separated solution, and separating acid product. In a preferred process~ the nitrile hydrolysate is obtained by an aqueous hydrolysis in a closed reactor at a temper-ature of from about 200C. to about 325C. until an essentially complete hydrolysis equilibrium is reached and the equilibrium ; hydrolysate i5 then fed to the reactive distillation unit.
The invention as described above involves a "reactive distillation" and such terminology is used herein to indicate the production of free aromatic carboxylic acid by the efficient removal of ammonia from a reaction zone where the normally equili-brium limited reaction of amide and ammonium salt is shifted to the salt which, in turn, yields free acid of high purity. Thus, for example, in the hydrolysis of terephthalonitrile in a closed system the chemistry is as follows:
:: `
'' ~OONH4 ~ CN\
CN ~O~H2 ~ ICOONH4 COONH4 [~ >(~
CN CN ~ CONH2 CONH2 COONH4 Terephthalonitrile ~ Ammonium Diammonium (TPN) O I Terephthalamate Terephthalate (ATA) (DAT) When such a hydrolysis mixture is subjected to reactive distill-ation -the equilibrium:
f OONH4 COONH~ COOH
> ~ ` ~ + 2NH3 is shifted to the right in the column because under the temperature conditions within the unit the ammonium salt is converted to the aromatic free acid and ammonia, the ammonia being removed contin-; uously from the reaction zone. Thus, all of the amide nitrogen eventually beco~es converted to ammonia and a high purity free acid results as product.
One of the major advantages of the process oE this inven-tion is that it enables in a sin~le step:
a) the concentration of ammonia, ,:
` b) its removal from the system, c) elimination of undesired nitrogen impurities and, -d) the making of high purity free acid. This is to be contrasted with prior art techniques which sweep ammonia from the ; system without concentration, thus requiring large volumes of steam. Furthermore, prior art methods yield the ammonium salts as intermediates and require one or more additional steps for conver-sion to the free acid.
The process of the invention is applicable to the produc-tion of a wide variety of aromatic carboxylic acids. The aromatic nitrile starting material may be selected from any of those compounds ~ .
... , . , . ... ...... . .... - ", , .. , .. , . .... . . . ~ .. . . ......... ~ .. ...... ... . - ~ .
3~2~
where one or more nitrile radicals are attached directly to an aromatic ring compound; preferably, a benzene or naphthalene ring.
Examples of nitriles falling within this class include benzonitrile, phthalonitrile, isophthalonitrile, terephthalonitrile~ the tolu-nitriles, naphthonitriles such as 1,5- and 2,6~dicyanonaphthalene, and the like. Preferred nitriles for use in the process are those of the benzene and naphthalene series such as the phthalonitriles, particularly terephthalonitrile and isoph~halonitrile, and 2,6-dicyanonaphthalene.
To explain more fully the invention reference is now made to the drawing where the preferred process will be illustrated with a hydroysate of terephthalonitrile. The terephthalonitrile to be hydrolyzed is fed into a closed hydrolytic chamber (11) where hydrolysis occurs at a temperature between about 200 and about 325C. under autogeneous pressure, the pressure actually rising to about 220 to about 1750 psia. In this reactor, the hydrolysis proceeds until an equilibrium is reached which at the preferred range of about 250C. to about 325C. requires from about 2 to about 0.1 hours. The hydrolysis products in the equilibrium mixture as shown above 7 will consist essentially of the diammonium salt of terephthalic acid and ammonium terephthalamate together with small amounts of the ammonium salt of 4-cyanobenzoic acid, 4-cyanobenza-mide, and terephthalamide. After the equilibrium is established the aqueous mixture is fed into a reactive distillation column (12) where hydrolysis of nitrogen-containing aromatics occur in a stripping section of the column and concentration of the resulting ammonia occurs in the upper section. It is in this way that the equilibrium is shifted by removal of ammonia taken overhead together with water vapor. The distillate product is recovered in the usual fashion with a portion of the overhead being returned to the column .: . 1. .'.':'."'.""1;"" ' - ~630~
as reflux. The reactor column is operated at a temperature between about 200C. and about 325C. preferably about 260C. to about 310C. and at autogenous pressure which will be a pressure of between about 220 and about 1750 psia. It is important that the residence time of materials within the column be longer than that found in simple distillation systems and a preferred method to accomplish an increased residence time is by means of an apparatus which employs liquid reservoirs between trays within the columns. In the process of this invention residence time will be preferably between about 15 and about 45 minutes. These long residence times are necessary to provide time to enable the amides in the equilibrium hydrolysis system to be shifted toward the salt as the ammonia is removed as explained above. To separate the ammonia effectively, only moderate reflux ratios on the order to 2 to 10 are required.
A particular advantage of this portion of the process is that the actual water carried over is only a small fraction of the water in the feed. Thus, for ex~mple, a typical feed concentration to the column reactor may contain one mole of aromatic material to 50 moles of water and, even if the mole percent of water in the overhead is quite high (e.g., 50 mole %), the actual quantity of water carried over is only a small fraction of the feed (about 4%).
Likewise, the ammonia content is significantly concentrated.
For example, the ammonia concentration of the hydrolysate input is about 4 mole percent, but after concentration by rectification in the column it exits at no less than about 50 mole percent. Furthermore, there is no carry-over of i~
aromatic compounds in the overhead. It is thus clear that one major advantage of the process is that the utility requirements are low and thus a highly efficient process is achieved. This is .... ..... ...
., .
, ~.....
.. . .
in contrast to known techniques where ammonia is removed by steam sweeping which often requires that the quantity of steam be that or approach that of the feed itself and this high steam volume mitigates against an economical process.
The terephthalic acid product which flows to the bottom of the column is taken to a reboiler (13) where any residual intermediate materials are further converted by hydrolysis and removal of ammonia to terephthalic acid. The ammonia that is generated by this hydrolysis is returned to the column through line 14 where it is eliminated with the overhead stream. Residence time in the reboiler is about 0.5 to 3 hours. It will be under-stood that although the reboiler (13) is shown separate from the distillation column (12), the reboiler may be an integral part of the bottom portion of the column as is frPquently the case with industrial equipment. Finally, a solution of high purity tere-phthalic acid is taken from the reboiler and cooled and the acid crystals separated by filtration or other conventional means.
To exemplify further the operation and results oktained by the process, the following examples are given:
Examples An apparatus as illustrated in the drawing and described above is used to subject an equilibrium terephthalonitrile hydrol-ysis product to reactive distillation. Example 1 is operated in a batch precedure, the initial charge being made to the reboiler, while Examples 2, 3 and ~ are operated in a continuous mode. The table which follows indicates the conditions and results.
t) # ~ i3~3 r-l ~
t~ ci~
o\~
0 0~ o co H C) ~) CO
~) a) ~ r~ ~ ~ o~ c~
r~ ~ rl O
a) a) ~.) ~1 1~
o~o o 1}1 ~ !C O
O Q) r ~ r-l * O ~ x 5_1 C5 O ~ ~ ~ o r~ rl ~ ~ ~
u~ z o O ~) r-l ~ co oo ~
D3 ~ ~ , ~ I ~
~ ~ Z
H r~
u~ ~ ~
::~~ ~
~ ~ ~ ~ ~) . Q ~ O # ~ ~
~ O s l o r~
P~~I P4 ~ o O O O !4 ~ æ o o O ~ 00 p; ~1) r-l r-i ~ r~l z E~ ~ a) o ~ ~
O r~ ~ ~I _ r 51 a) ~ ~ Z r~
¦ 1 $ ~LI rl ~ ¦
E~ ~ ~H ~n o o o o O
.` Z O ~ O L~ O O ~
1~4 r~ ~r) r-l ~ ~ 1) O ~I) r~l ~ ~ ~ ~ ~ r~
(~ ~r Is') ~ ~ ~ (U
O r ~ ~r ~J N
. ~ r¢ 1~1 0 O
. . ~1 . H o $ r-l ` H ~1 ~ r~
r-l IJ (D
.' W rl 1~ O O t~
~ O ~ U~ ~ C~
H .4 : E~ P:; ~ 11 ~1 ,.
~ E~ ~ 4~
r~ U~
U~ ~ , . ..
h r-rl tU
., O ~ tJl O U~
~ tY;
) r-l ~ O
ul a) r~ ~ r~
a) J r-l O O O (U
rl 1:4 ~r t~ Q O ~0 00 h ~ ~1 r~ In ~ r~
O r-l ~ ~) ~; ~ ~ ~ z h ,_ ~ 0 O
.' rl a) ,~ r~ ~ rJ _~ r~
r~l ~ , ~;
O ~ O O O 0 0 0 x m ¦ L~ r-l t~l ~) ~ # 1:
1~6~
As can be seen from the above date, a significant reduction in amide nitrogen is readily achieved and the purity of the product terephthalic acid is quite high.
.. 9 .. .. ..
Claims (7)
- Claim 1. A process for making an aromatic carboxylic acid which comprises the step of:
(1) feeding an essentially equilibrium hydrolysis mixture of an aromatic nitrile to a reactive distillation column operated at a temperature of from about 200°C. and about 325°C.
at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, (2) removing ammonia and water vapor from the top of said column, (3) subjecting remaining equilibrium hydrolysis mixture to further hydrolysis and distillation in a reboiler at a temperature of from about 200°C. to about 325°C. and returning vapors from the reboiler to the column, (4) removing an aqueous solution of product aromatic acid from the reboiler, (5) cooling said separated solution of acid product and, (6) separating an acid product low in nitrogen impurities. - Claim 2. The process of Claim 1 where the aromatic nitrile is of the benzene or naphthalene series.
- Claim 3. The process of Claim 2 where the aromatic nitrile is a phthalonitrile.
- Claim 4. The process of Claim 2 where the aromatic nitrile is terephthalonitrile and the acid produced is terephthalic acid.
- 5. A process for making an aromatic dicarbo-xylic acid of the benzene or naphthalene series which comprises the steps of.
(1) subjecting an aromatic dinitrile of the benzene or naphthalene series to an aqueous hydrolysis in a closed reactor at a temperature of from about 200°C. to about 325°C.
until an essentially complete equilibrium mixture is obtained, (2) feeding said equilibrium hydrolysis mixture to a reactive distillation column operated at a temperature of from about 250°C. and about 325°C. at autogenous pressure where the equilibrium mixture is subjected simultaneously to further hydrolysis and distillation of ammonia, (3) removing ammonia and water vapor from the top of said column, (4) subjecting remaining equilibrium hydrolysis mixture to further hydrolysis and distillation in a reboiler at a temperature of from about 200°C. to about 325°C. and re-turning vapors from the reboiler to the column, (5) removing an aqueous solution of product aro-matic acid from the reboiler, (6) cooling said separated solution of acid product and, (7) separating an acid product low in nitrogen impurities. - 6. The process of Claim 5 where the nitrile is a phthalonitrile and the product a benzene dicarboxylic acid.
- 7. The process of Claim 5 where the nitrile is terephthalonitrile and the acid product is terephthalic acid.
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA250,254A CA1066302A (en) | 1976-04-14 | 1976-04-14 | Process for making aromatic acids |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA250,254A CA1066302A (en) | 1976-04-14 | 1976-04-14 | Process for making aromatic acids |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066302A true CA1066302A (en) | 1979-11-13 |
Family
ID=4105714
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA250,254A Expired CA1066302A (en) | 1976-04-14 | 1976-04-14 | Process for making aromatic acids |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1066302A (en) |
-
1976
- 1976-04-14 CA CA250,254A patent/CA1066302A/en not_active Expired
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