CA1079297A - Continuous process for producing therephthalic acid - Google Patents
Continuous process for producing therephthalic acidInfo
- Publication number
- CA1079297A CA1079297A CA286,555A CA286555A CA1079297A CA 1079297 A CA1079297 A CA 1079297A CA 286555 A CA286555 A CA 286555A CA 1079297 A CA1079297 A CA 1079297A
- Authority
- CA
- Canada
- Prior art keywords
- oxidation
- terephthalic acid
- mother liquor
- continuous process
- reactor
- 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.)
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-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
- C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
- C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
- C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
-
- 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
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
CONTINUOUS PROCESS FOR PRODUCING TEREPHTHALIC ACID
Abstract of Disclosure A process for producing terephthalic acid is disclosed in which p-xylene is oxidized in a liquid phase with molecular oxygen in the presence of a specific oxidation catalyst to obtain terephthalic acid slurry which is subjected to post-oxidation, then the slurry is separated into solid terephthalic acid and a mother liquor, while the solvent is recovered from the exhaust gas of the oxidation step by removing water, the mother liquor seperated and the solvent recovered being recycled to the oxidation step. thus, the process can be operated with the formation of much less undesirable by-products and with recycling the mother liquor to utilize the raw material of p-xylene as complete as possible.
Abstract of Disclosure A process for producing terephthalic acid is disclosed in which p-xylene is oxidized in a liquid phase with molecular oxygen in the presence of a specific oxidation catalyst to obtain terephthalic acid slurry which is subjected to post-oxidation, then the slurry is separated into solid terephthalic acid and a mother liquor, while the solvent is recovered from the exhaust gas of the oxidation step by removing water, the mother liquor seperated and the solvent recovered being recycled to the oxidation step. thus, the process can be operated with the formation of much less undesirable by-products and with recycling the mother liquor to utilize the raw material of p-xylene as complete as possible.
Description
1079Z~7 ~his invention relates to a process for producing terephthalic acid from p-xylene by oxidation. ;~
~here is a process already known, the so-called "SD process", in which p-xylene in acetic acid as a -~
solvent is oxidized with molecular oxygen in the presence of a heavy metal oxidation catalyst system. ~ -~he terephthalic acid produced is isolated from the slurry product b~ centrifugal separatlon and the mother~
liquor separated is usually subjected to distillation ...
to separate water and a residue containing the catalyæt ' and recover acetic acid for reuse. Because such mother liquor contains valuable materials, for example, t~e unreacted p-xylene, the catalyst and the oxidation intermediates, it is desirable from the commercial ~-point of view to recycle the mother liquor to the ~ oxidation step. However, the mother liquor also l contains small amounts of other materials which adversely affect the reaction, and, therefore, if the -mother liquor is recycled, then undesirable side reactions will occur to impair the quality of th~o -terephthalic acid product. ~hus, in practice, re-cycling the mother liquor has hitherto been impossible i~- without causing disadvantageæ as mentioned above.
Under these circumstances, we made intensive efforts to fi~d a process for producing terephthalic - -acid wherein the mother li~uor can be recycled to the reactor without cauæing deterioration of the reaction product, and, in consequence have found that, if the slurry product obtained in the oxidation reaction is 30 directly subjected to a post-oxidation treatment without :
~here is a process already known, the so-called "SD process", in which p-xylene in acetic acid as a -~
solvent is oxidized with molecular oxygen in the presence of a heavy metal oxidation catalyst system. ~ -~he terephthalic acid produced is isolated from the slurry product b~ centrifugal separatlon and the mother~
liquor separated is usually subjected to distillation ...
to separate water and a residue containing the catalyæt ' and recover acetic acid for reuse. Because such mother liquor contains valuable materials, for example, t~e unreacted p-xylene, the catalyst and the oxidation intermediates, it is desirable from the commercial ~-point of view to recycle the mother liquor to the ~ oxidation step. However, the mother liquor also l contains small amounts of other materials which adversely affect the reaction, and, therefore, if the -mother liquor is recycled, then undesirable side reactions will occur to impair the quality of th~o -terephthalic acid product. ~hus, in practice, re-cycling the mother liquor has hitherto been impossible i~- without causing disadvantageæ as mentioned above.
Under these circumstances, we made intensive efforts to fi~d a process for producing terephthalic - -acid wherein the mother li~uor can be recycled to the reactor without cauæing deterioration of the reaction product, and, in consequence have found that, if the slurry product obtained in the oxidation reaction is 30 directly subjected to a post-oxidation treatment without :
- 2 - ~ ~
separation of terephthalic acid, the mother liquor can be recycled to the oxidation reactor without causing any adverse effect on the oxidation reaction to obtain high quality terephthalic acid. This invention has been accomplished on the basis of this knowledge.
Accordingly, this invention provides a continuous process for producing terephthalic acid by oxidation of p-xylene in acetic acid as a solvent with molecular oxygen in the presence of an oxidation catal~st consisting essentially of a cobalt compound, a manganese compound and hydrogen bromide at a temperature of 150 to 250C under a pressure of atmospheric to 200 atm., which comprises (a) introducing at least a portion of the condensable gas discharged from an oxidation reactor to a distillation column to effect removal of water and recovery of the solvent, (b) effecting post-oxidation of the terephthalic acid slurry recovered from the oxidation reactor without addition of any p-xylene at a temperature ranging from the oxidation temperature to a temperature 50C lower than the oxidation temperature, (c) recovering terephthalic acid by centrifugal separation from the slurry obtained in the post-oxidation step (b), and (d) recycling the solvent recovered in the step (a) and the mother liquor obtained by separating the terephthalic acid in the step (c) into the oxidation reactor.
This invention will be explained in detail.
~he process for producing terephthalic acid to 1079Z~7 which this invention is applicable may be any process in which p-xylene in acetic acid is reacted in a liquid phase with molecular oxygen in the presence of a catalyst containing heavy metals and bromine, so far as the above-mentioned requirements (a) to (d) are satisfied. Atypical example of such process i8 the so-called SD
process the details of which are disclosed i~ U~P
2,833,816.
The amount of the solvent to be used is usually 0.5 to 20, preferably 1 to 10, parts per part by weight of the p-xylene. The solvent may contain water or a reaction promoter, such as an aldehyde, a ketone, an alcohol or paraaldehyde.
The catalyst employed in this invention is a known Co-Mn-Br ternary catalyst system. Cobalt and -~
manganese compounds suitable for use in the catalyst system are disclosed in USP 2,833,816; for example, as a cobalt compound, cobalt acetate, cobalt bromide or cobalt naphthenate and, as a manganese compound, ~-t 20 man~anese acetate, manganese bromide or manganese naphthenate. It is essential that a portio~ or the whole of the bromine compound be hydrogen bromide. - -When cobalt bromide and/or manganese bromide are used, the amount of hydrogen bromide in the catalyst system -- 25 can be reduced since they contain bromine. -In the prior art oxidation of p-xylene with -molecular oxygen, sodium bromide is a typical bromine source in the catalyst. Due to the loss of a part of the bromine during the reaction the addition of a bromine compound is required in order to maintain the ., - , . . .
predetermined bromide concentration in the reaction system. However, the addition of sodium bromide increases the concentration of sodium ion in the mother liquor-which is recycled, since an amount of sodium ion corresponding to that of the lost bromine remains. Such excess sodium ion adversely affects the oxidation reaction. ~herefore, according to this invention, the use of hydrogen bromide as the bromine source is significant with respect to recycling the mother liquor to the oxidation step without adversely affecting the reaction. The amounts of catalyst components to be used are 200 to 5000 ppm, preferably ,j .
200 to 600 ppm, in terms of Co, 10 to 1000 ppm, preferably 100 to 600 ppm, in terms of Mn and 400 to 10,000 ppm, preferably 600 to 2000 ppm, in terms of Br, on the basis of the solvent. When the amount of catalyst used is within the above range, the oxidation reaction is ;~ successfully carried out while the mother liquor is i recycled.
The temperature at which the oxidation is carried out may be, in general, from 150 to 250C and, where the amount of catalyst used is within the above range, the temperature is from 170 to 230C, preferably 205 to , 225C. ~he pressure under which the oxidation is carried out is atmospheric to 200 atm., preferably up to 100 atm.
~ 25 The gas containing molecular oxygen to be supplied ; to the liquid phase containing p-xylene is usually air and the amount thereof to be supplied is from 1 to 100 moles, preferably 3 to 100 moles of oxygen, per mole of the material to be oxidized.
In the oxidation reactor, at least 95% by weight ~ 1079~:97 of p-xylene is oxidized, preferably more than 98%, especially more than 99%.
The reaction product slurry obtained from the oxidation reaction is then subjected to post-oxidation treatment without isolating terephthalic acid. The purpose of this treatment is to further oxidize the oxidation intermediates present in the slurry and the -oxygen content of a molecular oxygen-containing gas to be supplied to this treatment may be lower than that of the oxidation reaction. Usually, a portion of the exhaust gas from the oxidation reactor is conveniently used. ~he temperature range within which the post- ~-oxidation is carried out is from the oxidation temperature to a temperature 50C, preferably 30C, lower than that of the oxidation reaction. In the post-oxidation, no further catalyst may be required.
~he post-oxidation may be effected in a separate post-oxidation vessel or in a cooling crystallizer in which the post-oxidation and crystallization are concurrently carried out while cooling.
~ he slurry which has been subjected to the post-oxidation is cooled to effect crystallization, in the usual manner,and separated into the terephthalic acid and the mother liquor by a centrifugal separator.
It i8 essential according to this invention that the mother liquor be recycled as it is to the oxidation reactor. ~he amount of mother li~uor to be recycled is 20 to 80%, preferably 50 to 80%~ by weight.
It i8 preferred that the remaining mother liquor ~0 not being recycled be introduced into a distillation 1~79Z97 column in which water iæ removed and acetic acid is recovered. ~he recovered acetic acid may be reused in the oxidation step, if desired.
From the distillation residue, metallic catalyst components may be recovered by extracting the residue ' with water, followed by adding a carbonate compound to precipitate carbonates of metallic components, washing the precipitate with water and dissolving it in acetic ~ ~ -acid. ~he acetates thus recovered can be introduced into the oxidation step.
In order to recycle the mother liquor as it is to the oxidation reactor according to this invention, it is necessary to remove water which is formed during the reaction. ~ecause too high a water concentration adversely affects the reaction, it is preferred that, ! in general, the water concentration of the mother liquor !~ in the oxidation reaction mixture be maintained at less than 20% by weight. According to this invention, the water concentration is controlled in such a way that at i 20 least a portion of the condensable gas from the reactor ~ is removed and introduced into a distillation column, ''1 : wherein water is removed and the solvent is recovered for reuse. lt is not always necessary to install such distillation column separately from the reactor, and the distillation column used ma~ be of a type such that the column is directly connected with the top of the reactor so that water and a non-condensable gas are removed from the top of the column and a condensable gas is returned to the reactor. In general, the condensable gas discharged from the reactor is ' ` 1079Z97 condensed in the condenser, and most of the condensate is returned to the reactor and only a portion thereof is introduced into the distillation column.
~he distillation is usually carried out under atmospheric pressure and at a bottom temperature of about 124C and at a top temperature of about 100C.
~he solvent recovered is recycled to the oxidation reactor.
The continuous proceæs according to this invention will be explained by referring to an accompanying drawing which is a block diagram illustrating one embodiment for the production of terephthalic acid. Supplied to oxidation reactor I are p-x~lene through pipe 10, a catalyst-containing solvent through pipe 12 and air through pipe 14 to effect oxidation reaction.
I The slurry is transferred through pipe 16 into --post-oxidation reactor II to which diluted air is blown .
through pipe 18 to effect the post-oxidation treatment.
The post-oxidized slurry is transferred through pipe 20 to cr~stallizer III in which crystallization is effected to precipitate thoroughly terephthalic acid, which is separated in centrifugal separator IV and is j recovered through pipe 22. ~he mother liquor is recycled through pipes 24 and 26 to oxidation vessel I, while a portion thereof is removed through pipe 28.
The condensable gas which is formed during the oxidation reaction and discharged through pipe 30 from the top of oxidation reactor I is condensed in condenser 32 and the most of the condensate is returned to the oxidation reactor and the remainder is introduced through ~.
1079Z~7 pipe 34 to distillation column V, in which water is removed through pipe 36 from the top and the solvent is recovered from the bottom and recycled through pipe 26 to oxidation reactor I.
hs mentioned above, the solvent and the mother liquor which have been recovered are rec~cled to oxidation reactor I through pipes 24 and 26, while a fresh catalyst and solvent are added through pipe l? ~ .:
to make up for what has been lost and removed whereby the operation is carried out continuously.
According to this invention, if the mother liquor of the slurry is recycled as it is to the oxidation reactor, the reaction is not adversely affected and high ~uality terephthalic acid can be obtained. ~urther, various valuable components in the mother liquor, such as the p-xylene, the oxidation intermediates and the catalyst, are completely utilized to make this process commercially attractive. The reason why the reaction is not impaired when the mother liquor i~ recycled is that, with the post-oxidation of the oxidation product slurry, the materials which would otherwise impair the reaction are substantially removed.
This invention will be explained in further detail by means of examples; however, it should be understood that this inve~tion is in no way limited by these e~amples.
~xample 1:
Into a 10 ~ capacity titanium autoclave reactDr I
equipped with a stirrer and an external heater was charged a mixture of 3 ~ of acetic acid (water content: ~h by weight), 4.43 g of cobalt acetate tetrahydrate, 4.68 g of manganese acetate tetrahydrate and 6.79 g of hydrobromic acid (47% aqueous solution), and then p-xylene was supplied through pipe 10 at a rate of 750 g~hr and air was supplied through pipe 14 at such a rate that the oxygen concentration of an exhaust gas from the reactor was 4 to 5% by volume, while the reaction conditions, reaction temperature of 210C and reaction pressure of ;-24 kg/cm2, were maintained for 1.5 hours to effect semicontinuous reaction. Then, a freshly prepared mixture of acetic acid and a catalyst having the above - -composition was supplied through pipe 12 at a rate of 2,250 g/hr, while the slurry was being discharged through pipe 16 at a rate of 3,600 g/hr to effect ,~ continuous oxidation reaction with the average residence time of 60 minutes. ~he slurry discharged from reactor I was supplied to a 10 ~ capacity titanium ,~ autoclave II (the post-oxidation vessel) equipped with ~ a stirrer and an external heater to which diluted air j~ having an o~gen concentration of 14% by volume was ' ? supplied through pipe 18 at such a rate that the oxygen concentration of an exhaust gas from the post-oxidation -vessel was maintained at 3 to 4% by volume, with the -reaction conditions of a temperature of 195C, a pressure of 19 kg/cm2 and an average residence time of 40 minutes. ~-The post-oxidized slurr~ was transferred to crystallizer ~
III in which crystallization was effected at 100C,and ; -terephthalic acid and, the reaction mother liquor were separated in oentrifugal separator IV.
After 3 hours from the start of the continuous ~0- oxidation reaction, a portion of the mother liquor to ~ - , 1079Zg7 which a fresh hydrogen bromide was added in an amount corresponding to that lost during the reaction was recycled to the reactor I through pipes 24 and 26 at a rate of 1250 g/hr (the recycling being 50%) and the remainder of mother liquor was removed through pipe 28.
~he amount of acetic acid solvent containing the catalyst supplied through pipe 12 was decreased to 1100 g/hr. In order to prevent the increase in the water content of the mother liquor in the reactor I
due to the recycling of the mother liquor, a portion of the condensate condensed from a condensable gas accompanying the exhaust gas from the reactor was withdrawn after 3 hours from the start of the continuous reaction through pipe 34, and acetic acid was supplied through pipe 26 in such an amount as contained in the condensate withdrawn to maintain the water concentration of the mother liquor in the reactor at 18% by weight (said acetic acid being one recovered from the dis-tillation column in commercial operation, but in this example the column was not used).
After continuing such mother liquor recycling for 30 hours, the terephthalic acid obtained by solid-liquid separation was suspended in acetic acid in an amount 3 times that of terephthalic acid and agitation was continued at a temperature of 80C for 20 minutes to effect washing. The properties of the terephthalic acid thus obtained are given in Table 1.
Comparative Example 1:
Procedures similar to those of Example 1 were repeated to carry out continuous oxidation excepting 1079Z~'7 that recycling the mother liquor and withdrawing a portion of the condensate were omitted. ~he properties of the terephthalic acid obtained are given in ~able 1. '' ' As is clear from ~,xample 1 and Comparative ~xample 1, the properties of terephthalic acid obtained by effecting post-oxidation and recycling the mother liquor to the oxidation reactor are comparable with those of the terephthalic acid in Comparative Example 1 which does not involve recycling the mother liquor and which gives good results.
~xample 2:
, Procedures similar to those of ~xample 1 were repeated excepting that the amount of acetic acid ,- containing the catalyst supplied through pipe 12 was 680 g/hr and the amount of mother liquor recycled ~,, through pipes 24 and 26 was 1730 g/hr (recycling being 7~/0 of the mother liquor separated). ~he properties of the terephthalic acid obtained are given in Table 1.;
, ~rom the results, it is clear that in Example 2 the amount of mother liquor to be recycled can be increased to 70y by weight without deteriorating the ,, .
., properties of the terephthalic acid compared with those in Example 1 (recycling being 50%) and Comparative ' E~ample 1 (no recycling). '' - 25 Comparative xample 2:
Procedures similar to those of Comparative Example 1 were repeated to carry out continuous oxidation reaction for 30 hours excepting that p-xylene was supplied at 500 g~hr, the semicontinuous reaction time was 2 hours, acetic acid containing the cata,lyst was .
.JI.. : ~ '. '' - : . .
! . . ' ~ . .
supplied in the continuous reaction at 1500 g/hr and the average residence time in rea.ctor I was 90 minutes;
. and no post-oxidation was carried out. ~he properties of the terephthalic acid obtained are given in Table 1.
i 5 Comparative EXample 3:
.~ Procedures similar to those of Comparative ! Example 2 were repeated excepting that, after 4 hours from the start of the continuous reàction, the reaction mother liquor was recycled through pipes 24 and 2~ at a rate of 830 g/hr and the amount of acetic acid solvent containing the catalyst supplied through pipe 12 was decreased to 750 g/hr, while the water concentration of the mother liquor in reactor I was maintained at 18% in the same manner as in ~xample 1 and recycling the mother liquor was continued for 30 hours. ~he properties of the terephthalic acid thus obtained are given in Table 1.
As is clear from the results, the terephthalic ~ acid produced by recycling to the reactor the mother - liquor which does not subject to post-oxidation (Com-parative Example 3) contains much more 4-carboxybenz-aldehyde of oxidation intermediate impurity and its transmittance is lower in comparison with terephthalic acid produced without recycling the mother liquor and effecting post-oxidation (Comparative ~xample 2).
~xample 3:
Procedures similar to those of Example 1 were repeated excepting that p-x~lene was supplied at a rate of 500 g/hr, the semicontinuous reaction time was 2 hours, acetic acid containing the catalyst was supplied in the continuous reaction at 1500 g~hr, the average .
~ - - 13 -residence time in the reactor I was 90 minuteæ, and, a~ter 3 hours from the start of continuous reaction~ the mother liquor was recycled at 830 g/hr and the acetic acid containing the catalyst was supplied at 750 g/hr.
~he properties of the tereph~halic acid thus obtained are given in ~able 1.
Comparative ~ample 4:
~ he reaction was carried out as in Example 3 but recycling the mother liquor and withdrawing a portion of the condensate were omitted. The propertieæ
of the resulting terephthalic acid are given in ~able 1.
Table 1 - ~ .
I :' ¦ Comp. Comp.¦ Comp. Comp.
Ex. 1 ~x. 2l-~x. 1 ~. 2 ~x. 3 ~x. 3 ~x. 4 . _ 4-CBA*
concentration in the product 460 460 450 400 580 280 270 -~
terephthalic acid (ppm) :.. _ . .' Transmittance 340 m~ 88 87.5 89 84 ?7 91. o 91. 5 400 m~ 98. 5 98.0 98.5 98-5 97- 5 99.0 99.o ~ .
Residence 60 60 60 9o 9o 9o 9o . __ .
.
Post-oxidation done done done none none done done ~ , . ._ ,.
mother liquor done done none none done done none __ . ~ . ~
Amount of mother liquor 5o 7o _ _ 5o 5o _ (% by weight) l ~_ ~ _ *Note 4-CBA: 4-Carboxybenzaldehyde
separation of terephthalic acid, the mother liquor can be recycled to the oxidation reactor without causing any adverse effect on the oxidation reaction to obtain high quality terephthalic acid. This invention has been accomplished on the basis of this knowledge.
Accordingly, this invention provides a continuous process for producing terephthalic acid by oxidation of p-xylene in acetic acid as a solvent with molecular oxygen in the presence of an oxidation catal~st consisting essentially of a cobalt compound, a manganese compound and hydrogen bromide at a temperature of 150 to 250C under a pressure of atmospheric to 200 atm., which comprises (a) introducing at least a portion of the condensable gas discharged from an oxidation reactor to a distillation column to effect removal of water and recovery of the solvent, (b) effecting post-oxidation of the terephthalic acid slurry recovered from the oxidation reactor without addition of any p-xylene at a temperature ranging from the oxidation temperature to a temperature 50C lower than the oxidation temperature, (c) recovering terephthalic acid by centrifugal separation from the slurry obtained in the post-oxidation step (b), and (d) recycling the solvent recovered in the step (a) and the mother liquor obtained by separating the terephthalic acid in the step (c) into the oxidation reactor.
This invention will be explained in detail.
~he process for producing terephthalic acid to 1079Z~7 which this invention is applicable may be any process in which p-xylene in acetic acid is reacted in a liquid phase with molecular oxygen in the presence of a catalyst containing heavy metals and bromine, so far as the above-mentioned requirements (a) to (d) are satisfied. Atypical example of such process i8 the so-called SD
process the details of which are disclosed i~ U~P
2,833,816.
The amount of the solvent to be used is usually 0.5 to 20, preferably 1 to 10, parts per part by weight of the p-xylene. The solvent may contain water or a reaction promoter, such as an aldehyde, a ketone, an alcohol or paraaldehyde.
The catalyst employed in this invention is a known Co-Mn-Br ternary catalyst system. Cobalt and -~
manganese compounds suitable for use in the catalyst system are disclosed in USP 2,833,816; for example, as a cobalt compound, cobalt acetate, cobalt bromide or cobalt naphthenate and, as a manganese compound, ~-t 20 man~anese acetate, manganese bromide or manganese naphthenate. It is essential that a portio~ or the whole of the bromine compound be hydrogen bromide. - -When cobalt bromide and/or manganese bromide are used, the amount of hydrogen bromide in the catalyst system -- 25 can be reduced since they contain bromine. -In the prior art oxidation of p-xylene with -molecular oxygen, sodium bromide is a typical bromine source in the catalyst. Due to the loss of a part of the bromine during the reaction the addition of a bromine compound is required in order to maintain the ., - , . . .
predetermined bromide concentration in the reaction system. However, the addition of sodium bromide increases the concentration of sodium ion in the mother liquor-which is recycled, since an amount of sodium ion corresponding to that of the lost bromine remains. Such excess sodium ion adversely affects the oxidation reaction. ~herefore, according to this invention, the use of hydrogen bromide as the bromine source is significant with respect to recycling the mother liquor to the oxidation step without adversely affecting the reaction. The amounts of catalyst components to be used are 200 to 5000 ppm, preferably ,j .
200 to 600 ppm, in terms of Co, 10 to 1000 ppm, preferably 100 to 600 ppm, in terms of Mn and 400 to 10,000 ppm, preferably 600 to 2000 ppm, in terms of Br, on the basis of the solvent. When the amount of catalyst used is within the above range, the oxidation reaction is ;~ successfully carried out while the mother liquor is i recycled.
The temperature at which the oxidation is carried out may be, in general, from 150 to 250C and, where the amount of catalyst used is within the above range, the temperature is from 170 to 230C, preferably 205 to , 225C. ~he pressure under which the oxidation is carried out is atmospheric to 200 atm., preferably up to 100 atm.
~ 25 The gas containing molecular oxygen to be supplied ; to the liquid phase containing p-xylene is usually air and the amount thereof to be supplied is from 1 to 100 moles, preferably 3 to 100 moles of oxygen, per mole of the material to be oxidized.
In the oxidation reactor, at least 95% by weight ~ 1079~:97 of p-xylene is oxidized, preferably more than 98%, especially more than 99%.
The reaction product slurry obtained from the oxidation reaction is then subjected to post-oxidation treatment without isolating terephthalic acid. The purpose of this treatment is to further oxidize the oxidation intermediates present in the slurry and the -oxygen content of a molecular oxygen-containing gas to be supplied to this treatment may be lower than that of the oxidation reaction. Usually, a portion of the exhaust gas from the oxidation reactor is conveniently used. ~he temperature range within which the post- ~-oxidation is carried out is from the oxidation temperature to a temperature 50C, preferably 30C, lower than that of the oxidation reaction. In the post-oxidation, no further catalyst may be required.
~he post-oxidation may be effected in a separate post-oxidation vessel or in a cooling crystallizer in which the post-oxidation and crystallization are concurrently carried out while cooling.
~ he slurry which has been subjected to the post-oxidation is cooled to effect crystallization, in the usual manner,and separated into the terephthalic acid and the mother liquor by a centrifugal separator.
It i8 essential according to this invention that the mother liquor be recycled as it is to the oxidation reactor. ~he amount of mother li~uor to be recycled is 20 to 80%, preferably 50 to 80%~ by weight.
It i8 preferred that the remaining mother liquor ~0 not being recycled be introduced into a distillation 1~79Z97 column in which water iæ removed and acetic acid is recovered. ~he recovered acetic acid may be reused in the oxidation step, if desired.
From the distillation residue, metallic catalyst components may be recovered by extracting the residue ' with water, followed by adding a carbonate compound to precipitate carbonates of metallic components, washing the precipitate with water and dissolving it in acetic ~ ~ -acid. ~he acetates thus recovered can be introduced into the oxidation step.
In order to recycle the mother liquor as it is to the oxidation reactor according to this invention, it is necessary to remove water which is formed during the reaction. ~ecause too high a water concentration adversely affects the reaction, it is preferred that, ! in general, the water concentration of the mother liquor !~ in the oxidation reaction mixture be maintained at less than 20% by weight. According to this invention, the water concentration is controlled in such a way that at i 20 least a portion of the condensable gas from the reactor ~ is removed and introduced into a distillation column, ''1 : wherein water is removed and the solvent is recovered for reuse. lt is not always necessary to install such distillation column separately from the reactor, and the distillation column used ma~ be of a type such that the column is directly connected with the top of the reactor so that water and a non-condensable gas are removed from the top of the column and a condensable gas is returned to the reactor. In general, the condensable gas discharged from the reactor is ' ` 1079Z97 condensed in the condenser, and most of the condensate is returned to the reactor and only a portion thereof is introduced into the distillation column.
~he distillation is usually carried out under atmospheric pressure and at a bottom temperature of about 124C and at a top temperature of about 100C.
~he solvent recovered is recycled to the oxidation reactor.
The continuous proceæs according to this invention will be explained by referring to an accompanying drawing which is a block diagram illustrating one embodiment for the production of terephthalic acid. Supplied to oxidation reactor I are p-x~lene through pipe 10, a catalyst-containing solvent through pipe 12 and air through pipe 14 to effect oxidation reaction.
I The slurry is transferred through pipe 16 into --post-oxidation reactor II to which diluted air is blown .
through pipe 18 to effect the post-oxidation treatment.
The post-oxidized slurry is transferred through pipe 20 to cr~stallizer III in which crystallization is effected to precipitate thoroughly terephthalic acid, which is separated in centrifugal separator IV and is j recovered through pipe 22. ~he mother liquor is recycled through pipes 24 and 26 to oxidation vessel I, while a portion thereof is removed through pipe 28.
The condensable gas which is formed during the oxidation reaction and discharged through pipe 30 from the top of oxidation reactor I is condensed in condenser 32 and the most of the condensate is returned to the oxidation reactor and the remainder is introduced through ~.
1079Z~7 pipe 34 to distillation column V, in which water is removed through pipe 36 from the top and the solvent is recovered from the bottom and recycled through pipe 26 to oxidation reactor I.
hs mentioned above, the solvent and the mother liquor which have been recovered are rec~cled to oxidation reactor I through pipes 24 and 26, while a fresh catalyst and solvent are added through pipe l? ~ .:
to make up for what has been lost and removed whereby the operation is carried out continuously.
According to this invention, if the mother liquor of the slurry is recycled as it is to the oxidation reactor, the reaction is not adversely affected and high ~uality terephthalic acid can be obtained. ~urther, various valuable components in the mother liquor, such as the p-xylene, the oxidation intermediates and the catalyst, are completely utilized to make this process commercially attractive. The reason why the reaction is not impaired when the mother liquor i~ recycled is that, with the post-oxidation of the oxidation product slurry, the materials which would otherwise impair the reaction are substantially removed.
This invention will be explained in further detail by means of examples; however, it should be understood that this inve~tion is in no way limited by these e~amples.
~xample 1:
Into a 10 ~ capacity titanium autoclave reactDr I
equipped with a stirrer and an external heater was charged a mixture of 3 ~ of acetic acid (water content: ~h by weight), 4.43 g of cobalt acetate tetrahydrate, 4.68 g of manganese acetate tetrahydrate and 6.79 g of hydrobromic acid (47% aqueous solution), and then p-xylene was supplied through pipe 10 at a rate of 750 g~hr and air was supplied through pipe 14 at such a rate that the oxygen concentration of an exhaust gas from the reactor was 4 to 5% by volume, while the reaction conditions, reaction temperature of 210C and reaction pressure of ;-24 kg/cm2, were maintained for 1.5 hours to effect semicontinuous reaction. Then, a freshly prepared mixture of acetic acid and a catalyst having the above - -composition was supplied through pipe 12 at a rate of 2,250 g/hr, while the slurry was being discharged through pipe 16 at a rate of 3,600 g/hr to effect ,~ continuous oxidation reaction with the average residence time of 60 minutes. ~he slurry discharged from reactor I was supplied to a 10 ~ capacity titanium ,~ autoclave II (the post-oxidation vessel) equipped with ~ a stirrer and an external heater to which diluted air j~ having an o~gen concentration of 14% by volume was ' ? supplied through pipe 18 at such a rate that the oxygen concentration of an exhaust gas from the post-oxidation -vessel was maintained at 3 to 4% by volume, with the -reaction conditions of a temperature of 195C, a pressure of 19 kg/cm2 and an average residence time of 40 minutes. ~-The post-oxidized slurr~ was transferred to crystallizer ~
III in which crystallization was effected at 100C,and ; -terephthalic acid and, the reaction mother liquor were separated in oentrifugal separator IV.
After 3 hours from the start of the continuous ~0- oxidation reaction, a portion of the mother liquor to ~ - , 1079Zg7 which a fresh hydrogen bromide was added in an amount corresponding to that lost during the reaction was recycled to the reactor I through pipes 24 and 26 at a rate of 1250 g/hr (the recycling being 50%) and the remainder of mother liquor was removed through pipe 28.
~he amount of acetic acid solvent containing the catalyst supplied through pipe 12 was decreased to 1100 g/hr. In order to prevent the increase in the water content of the mother liquor in the reactor I
due to the recycling of the mother liquor, a portion of the condensate condensed from a condensable gas accompanying the exhaust gas from the reactor was withdrawn after 3 hours from the start of the continuous reaction through pipe 34, and acetic acid was supplied through pipe 26 in such an amount as contained in the condensate withdrawn to maintain the water concentration of the mother liquor in the reactor at 18% by weight (said acetic acid being one recovered from the dis-tillation column in commercial operation, but in this example the column was not used).
After continuing such mother liquor recycling for 30 hours, the terephthalic acid obtained by solid-liquid separation was suspended in acetic acid in an amount 3 times that of terephthalic acid and agitation was continued at a temperature of 80C for 20 minutes to effect washing. The properties of the terephthalic acid thus obtained are given in Table 1.
Comparative Example 1:
Procedures similar to those of Example 1 were repeated to carry out continuous oxidation excepting 1079Z~'7 that recycling the mother liquor and withdrawing a portion of the condensate were omitted. ~he properties of the terephthalic acid obtained are given in ~able 1. '' ' As is clear from ~,xample 1 and Comparative ~xample 1, the properties of terephthalic acid obtained by effecting post-oxidation and recycling the mother liquor to the oxidation reactor are comparable with those of the terephthalic acid in Comparative Example 1 which does not involve recycling the mother liquor and which gives good results.
~xample 2:
, Procedures similar to those of ~xample 1 were repeated excepting that the amount of acetic acid ,- containing the catalyst supplied through pipe 12 was 680 g/hr and the amount of mother liquor recycled ~,, through pipes 24 and 26 was 1730 g/hr (recycling being 7~/0 of the mother liquor separated). ~he properties of the terephthalic acid obtained are given in Table 1.;
, ~rom the results, it is clear that in Example 2 the amount of mother liquor to be recycled can be increased to 70y by weight without deteriorating the ,, .
., properties of the terephthalic acid compared with those in Example 1 (recycling being 50%) and Comparative ' E~ample 1 (no recycling). '' - 25 Comparative xample 2:
Procedures similar to those of Comparative Example 1 were repeated to carry out continuous oxidation reaction for 30 hours excepting that p-xylene was supplied at 500 g~hr, the semicontinuous reaction time was 2 hours, acetic acid containing the cata,lyst was .
.JI.. : ~ '. '' - : . .
! . . ' ~ . .
supplied in the continuous reaction at 1500 g/hr and the average residence time in rea.ctor I was 90 minutes;
. and no post-oxidation was carried out. ~he properties of the terephthalic acid obtained are given in Table 1.
i 5 Comparative EXample 3:
.~ Procedures similar to those of Comparative ! Example 2 were repeated excepting that, after 4 hours from the start of the continuous reàction, the reaction mother liquor was recycled through pipes 24 and 2~ at a rate of 830 g/hr and the amount of acetic acid solvent containing the catalyst supplied through pipe 12 was decreased to 750 g/hr, while the water concentration of the mother liquor in reactor I was maintained at 18% in the same manner as in ~xample 1 and recycling the mother liquor was continued for 30 hours. ~he properties of the terephthalic acid thus obtained are given in Table 1.
As is clear from the results, the terephthalic ~ acid produced by recycling to the reactor the mother - liquor which does not subject to post-oxidation (Com-parative Example 3) contains much more 4-carboxybenz-aldehyde of oxidation intermediate impurity and its transmittance is lower in comparison with terephthalic acid produced without recycling the mother liquor and effecting post-oxidation (Comparative ~xample 2).
~xample 3:
Procedures similar to those of Example 1 were repeated excepting that p-x~lene was supplied at a rate of 500 g/hr, the semicontinuous reaction time was 2 hours, acetic acid containing the catalyst was supplied in the continuous reaction at 1500 g~hr, the average .
~ - - 13 -residence time in the reactor I was 90 minuteæ, and, a~ter 3 hours from the start of continuous reaction~ the mother liquor was recycled at 830 g/hr and the acetic acid containing the catalyst was supplied at 750 g/hr.
~he properties of the tereph~halic acid thus obtained are given in ~able 1.
Comparative ~ample 4:
~ he reaction was carried out as in Example 3 but recycling the mother liquor and withdrawing a portion of the condensate were omitted. The propertieæ
of the resulting terephthalic acid are given in ~able 1.
Table 1 - ~ .
I :' ¦ Comp. Comp.¦ Comp. Comp.
Ex. 1 ~x. 2l-~x. 1 ~. 2 ~x. 3 ~x. 3 ~x. 4 . _ 4-CBA*
concentration in the product 460 460 450 400 580 280 270 -~
terephthalic acid (ppm) :.. _ . .' Transmittance 340 m~ 88 87.5 89 84 ?7 91. o 91. 5 400 m~ 98. 5 98.0 98.5 98-5 97- 5 99.0 99.o ~ .
Residence 60 60 60 9o 9o 9o 9o . __ .
.
Post-oxidation done done done none none done done ~ , . ._ ,.
mother liquor done done none none done done none __ . ~ . ~
Amount of mother liquor 5o 7o _ _ 5o 5o _ (% by weight) l ~_ ~ _ *Note 4-CBA: 4-Carboxybenzaldehyde
Claims (5)
1. A continuous process for producing terephthalic acid by oxidation of p-xylene in acetic acid as a solvent with molecular oxygen in the presence of an oxidation catalyst consisting essentially of a cobalt compound, a manganese compound and hydrogen bromide at a temperature of 150 to 250°C under a pressure of atmospheric to 200 atm., which comprises (a) introducing at least a portion of the condensable gas discharged from an oxidation reactor to a distillation column to effect removal of water and recovery of the solvent, (b) effecting post-oxidation of the terephthalic acid slurry recovered from the oxidation reactor without addition of any p-xylene at a temperature ranging from the oxidation reaction temperature to a temperature 0 to 50°C lower than the reaction temperature, (c) recovering terephthalic acid by centrifugal separation from the slurry obtained in the post-oxidation step (b), and (d) recycling the solvent recovered in the step (a) and the mother liquor obtained by separating the terephthalic acid in the step (c) into the oxidation reactor.
2. A continuous process for producing terephthalic acid according to Claim 1, wherein 20 to 80% by weight of the mother liquor from which the terephthalic acid produced has been separated is recycled to the oxidation reactor.
3. A continuous process for producing terephthalic acid according to Claim 1, wherein the oxidation reaction is carried out while the water concentration of the mother liquor in the oxidation reaction mixture is maintained at less than 20% by weight.
4. A continuous process for producing terephthalic acid according to Claim 3, wherein 20 to 80% by weight of the mother liquor from which the terephthalic acid produced has been separated is recycled to the oxidation reactor.
5. A continuous process for producing terephthalic acid according to Claim 1, wherein said cobalt compound is cobalt acetate and said manganese compound is manganese acetate.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP51111015A JPS5949212B2 (en) | 1976-09-16 | 1976-09-16 | Manufacturing method of terephthalic acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079297A true CA1079297A (en) | 1980-06-10 |
Family
ID=14550224
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA286,555A Expired CA1079297A (en) | 1976-09-16 | 1977-09-12 | Continuous process for producing therephthalic acid |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5949212B2 (en) |
| BE (1) | BE858814A (en) |
| CA (1) | CA1079297A (en) |
| DE (1) | DE2741382A1 (en) |
| ES (1) | ES462370A1 (en) |
| GB (1) | GB1589310A (en) |
| IT (1) | IT1090868B (en) |
| PH (1) | PH12993A (en) |
| PT (1) | PT67039B (en) |
Families Citing this family (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5555138A (en) * | 1978-10-19 | 1980-04-22 | Mitsubishi Chem Ind Ltd | Preparation of highly pure terephthalic acid |
| US4334086A (en) * | 1981-03-16 | 1982-06-08 | Labofina S.A. | Production of terephthalic acid |
| JPS5992295A (en) * | 1982-11-15 | 1984-05-28 | Mitsubishi Heavy Ind Ltd | Steering gear |
| JPS59143790A (en) * | 1983-02-05 | 1984-08-17 | Hitachi Zosen Corp | Rolling control device for high-speed boat |
| JP2581979B2 (en) * | 1989-07-12 | 1997-02-19 | 川崎重工業株式会社 | Emergency landing attitude control device for hydrofoil ship |
| US5087741A (en) * | 1990-11-29 | 1992-02-11 | Eastman Kodak Company | Continuous production of aromatic carboxylic acids |
| US7276625B2 (en) | 2002-10-15 | 2007-10-02 | Eastman Chemical Company | Process for production of a carboxylic acid/diol mixture suitable for use in polyester production |
| US7193109B2 (en) | 2003-03-06 | 2007-03-20 | Eastman Chemical Company | Process for production of a carboxylic acid/diol mixture suitable for use in polyester production |
| US7214760B2 (en) | 2004-01-15 | 2007-05-08 | Eastman Chemical Company | Process for production of a carboxylic acid/diol mixture suitable for use in polyester production |
| US7816556B2 (en) | 2006-03-01 | 2010-10-19 | Eastman Chemical Company | Polycarboxylic acid production system employing enhanced multistage oxidative digestion |
| US7326807B2 (en) | 2006-03-01 | 2008-02-05 | Eastman Chemical Company | Polycarboxylic acid production system with enhanced heating for oxidative digestion |
| US7501537B2 (en) | 2006-03-01 | 2009-03-10 | Eastman Chemical Company | Polycarboxylic acid production system employing oxidative digestion with reduced or eliminated upstream liquor exchange |
| US7772424B2 (en) | 2006-03-01 | 2010-08-10 | Eastman Chemical Company | Polycarboxylic acid production system employing enhanced evaporative concentration downstream of oxidative digestion |
| US7420082B2 (en) | 2006-03-01 | 2008-09-02 | Eastman Chemical Company | Polycarboxylic acid production system employing hot liquor removal downstream of oxidative digestion |
| US7326808B2 (en) | 2006-03-01 | 2008-02-05 | Eastman Chemical Company | Polycarboxylic acid production system employing cooled mother liquor from oxidative digestion as feed to impurity purge system |
| US7393973B2 (en) * | 2006-03-01 | 2008-07-01 | Eastman Chemical Company | Polycarboxylic acid production system with enhanced residence time distribution for oxidative digestion |
| US20070208194A1 (en) | 2006-03-01 | 2007-09-06 | Woodruff Thomas E | Oxidation system with sidedraw secondary reactor |
-
1976
- 1976-09-16 JP JP51111015A patent/JPS5949212B2/en not_active Expired
-
1977
- 1977-09-12 CA CA286,555A patent/CA1079297A/en not_active Expired
- 1977-09-14 ES ES462370A patent/ES462370A1/en not_active Expired
- 1977-09-14 DE DE19772741382 patent/DE2741382A1/en not_active Ceased
- 1977-09-14 PH PH20225A patent/PH12993A/en unknown
- 1977-09-14 IT IT69032/77A patent/IT1090868B/en active
- 1977-09-15 GB GB38606/77A patent/GB1589310A/en not_active Expired
- 1977-09-15 PT PT67039A patent/PT67039B/en unknown
- 1977-09-16 BE BE181004A patent/BE858814A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| GB1589310A (en) | 1981-05-13 |
| JPS5337636A (en) | 1978-04-06 |
| PT67039A (en) | 1977-10-01 |
| PH12993A (en) | 1979-10-29 |
| DE2741382A1 (en) | 1978-03-23 |
| PT67039B (en) | 1979-02-15 |
| IT1090868B (en) | 1985-06-26 |
| JPS5949212B2 (en) | 1984-12-01 |
| ES462370A1 (en) | 1978-06-01 |
| BE858814A (en) | 1978-01-16 |
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