U.S. patent application number 12/518662 was filed with the patent office on 2010-01-21 for process for production of terephthalic acid.
This patent application is currently assigned to Mitsubishi Gas Chemical Company, Inc.. Invention is credited to Hideaki Fujita, Masato Inari, Nobuo Namiki, Fumiya Zaima.
Application Number | 20100016629 12/518662 |
Document ID | / |
Family ID | 39511581 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100016629 |
Kind Code |
A1 |
Zaima; Fumiya ; et
al. |
January 21, 2010 |
PROCESS FOR PRODUCTION OF TEREPHTHALIC ACID
Abstract
The invention provides a method for producing terephthalic acid,
characterized by including subjecting a p-phenylene compound to
liquid-phase oxidation reaction by use of a
molecular-oxygen-containing gas in the presence of a catalyst at
least containing a heavy metal compound and a bromine compound, and
hydrous acetic acid having a water content of 1 to 15 mass %, to
thereby yield a slurry; regulating the temperature of the slurry to
35 to 140.degree. C., to thereby cause terephthalic acid to
precipitate; removing the terephthalic acid through solid-liquid
separation, to thereby recover a mother liquor; and recovering the
catalyst from the mother liquor through a series of the following
steps (1) to (4) for reusing at least a portion of the catalyst in
the liquid-phase oxidation reaction: (1) an adsorption step
including regulating the ratio "amount by mole of bromide ions in
the mother liquor/total amount by mole of heavy metal ions in the
mother liquor" to 0.6 to 3, and then exposing the mother liquor to
a pyridine-ring-containing chelate resin which has been heated to
35 to 140.degree. C., so that the resin adsorbs catalyst-derived
heavy metal ions and bromide ions, and also adsorbs a carboxylic
acid mixture which has been by-produced through the liquid-phase
oxidation reaction, (2) an elution step (A) of exposing hydrous
acetic acid having a water content of 1 to 15 mass % to the
pyridine-ring-containing chelate resin which has undergone the
adsorption step, thereby yielding an eluate containing the
by-produced carboxylic acid mixture, (3) an elution step (B) of
exposing water or hydrous acetic acid having a water content of 20
mass % or more to the pyridine-ring-containing chelate resin which
has undergone the elution step (A), thereby yielding an eluate
containing catalyst-derived heavy metal ions and bromide ions, and
(4) a displacement step of exposing hydrous acetic acid having a
water content of 1 to 15 mass % to the pyridine-ring-containing
chelate resin which has undergone the elution step (B), serving as
a displacement liquid, thereby regenerating the resin.
Inventors: |
Zaima; Fumiya; (Okayama,
JP) ; Inari; Masato; (Okayama, JP) ; Fujita;
Hideaki; (Okayama, JP) ; Namiki; Nobuo;
(Okayama, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Mitsubishi Gas Chemical Company,
Inc.
Tokyo
JP
Toyobo Co., Ltd.
Osaka
JP
Mizushima Aroma Company, Ltd.
Okayama
JP
|
Family ID: |
39511581 |
Appl. No.: |
12/518662 |
Filed: |
December 7, 2007 |
PCT Filed: |
December 7, 2007 |
PCT NO: |
PCT/JP2007/073650 |
371 Date: |
June 11, 2009 |
Current U.S.
Class: |
562/414 |
Current CPC
Class: |
C07C 51/47 20130101;
C07C 51/47 20130101; C07C 63/26 20130101; B01J 45/00 20130101; B01J
49/50 20170101 |
Class at
Publication: |
562/414 |
International
Class: |
C07C 51/265 20060101
C07C051/265 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2006 |
JP |
2006-333240 |
Claims
1. A method for producing terephthalic acid comprising: subjecting
a p-phenylene compound to a liquid-phase oxidation reaction by the
use of a molecular-oxygen-containing gas in the presence of a
catalyst at least containing a heavy metal compound and a bromine
compound, and hydrous acetic acid having a water content of 1 to 15
mass %, to thereby yield a slurry; regulating the temperature of
the slurry to 35 to 140.degree. C., to thereby cause terephthalic
acid to precipitate; removing the terephthalic acid through
solid-liquid separation, to thereby recover a mother liquor; and
recovering the catalyst from the mother liquor through a series of
operations (1) to (4) for reusing at least a portion of the
catalyst in the liquid-phase oxidation reaction: (1) an adsorption
operation including regulating the amount by mole of bromide ions
in the mother liquor/total amount by mole of heavy metal ions in
the mother liquor ratio to 0.6 to 3, and then exposing the mother
liquor to a pyridine-ring-containing chelate resin which has been
heated to 35 to 140.degree. C., so that the resin adsorbs
catalyst-derived heavy metal ions and bromide ions, and also
adsorbs a by-produced carboxylic acid mixture which has been
by-produced through the liquid-phase oxidation reaction, (2) an
elution operation (A) of exposing hydrous acetic acid having a
water content of 1 to 15 mass % to the pyridine-ring-containing
chelate resin which has undergone the adsorption operation, thereby
yielding an eluate containing the by-produced carboxylic acid
mixture, (3) an elution operation (B) of exposing water or hydrous
acetic acid having a water content of 20 mass % or more to the
pyridine-ring-containing chelate resin which has undergone the
elution operation (A), thereby yielding an eluate containing
catalyst-derived heavy metal ions and bromide ions, and (4) a
displacement operation of exposing hydrous acetic acid having a
water content of 1 to 15 mass % to the pyridine-ring-containing
chelate resin which has undergone the elution operation (B),
serving as a displacement liquid, thereby regenerating the
resin.
2. The method for producing terephthalic acid as described in claim
1, wherein hydrous acetic acid is recovered from the mother liquor
which has undergone the adsorption operation, from the eluate
obtained through the elution operation (A), and from the
displacement liquid employed in the displacement operation, and the
recovered hydrous acetic acid is reused in the liquid-phase
oxidation reaction as at least a portion of hydrous acetic acid
having a water content of 1 to 15 mass %.
3. The method for producing terephthalic acid as described in claim
1, wherein hydrous acetic acid is recovered from the mother liquor
which has undergone the adsorption operation, from the eluate
obtained through the elution operation (A), and from the
displacement liquid employed in the displacement operation, and the
recovered hydrous acetic acid is reused in the elution operation
(A) as at least a portion of hydrous acetic acid having a water
content of 1 to 15 mass %.
4. The method for producing terephthalic acid as described in claim
1, wherein hydrous acetic acid is recovered from the mother liquor
which has undergone the adsorption operation, from the eluate
obtained through the elution operation (A), and from the
displacement liquid employed in the displacement operation, and the
recovered hydrous acetic acid is reused in the displacement
operation as a displacement liquid.
5. The method for producing terephthalic acid as described in claim
1, wherein the eluate obtained through the elution operation (B) is
returned to the liquid-phase oxidation reaction, and reused as at
least a portion of the catalyst.
6. The method for producing terephthalic acid as described in claim
1, wherein a regenerated pyridine-ring-containing chelate resin
which has been obtained through the displacement operation is
reused in the adsorption operation as the pyridine-ring-containing
chelate resin.
7. The method for producing terephthalic acid as described in claim
1, wherein the hydrous acetic acid having a water content of 1 to
15 mass % and employed in the elution operation (A) contains
bromide ions in an amount of 1 to 1,000 mass ppm.
8. The method for producing terephthalic acid as described in claim
1, wherein the hydrous acetic acid having a water content of 1 to
15 mass % and employed in the displacement operation as a
displacement liquid contains bromide ions in an amount of 1 to
1,000 mass ppm.
9. The method for producing terephthalic acid as described in claim
1, wherein, in the adsorption operation, the amount by mole of
bromide ions in the mother liquor/total amount by mole of heavy
metal ions in the mother liquor ratio is regulated to 1.6 to
2.5.
10. The method for producing terephthalic acid as described in
claim 1, wherein when Q represents the total amount (g) of hydrous
acetic acid having a water content of 1 to 15 mass % supplied in
the elution operation (A), and V represents the volume (mL) of a
pyridine-ring-containing chelate resin layer, the ratio Q/V is 0.5
to 10.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
terephthalic acid. Terephthalic acid is effectively employed as,
for example, a starting material for polyethylene
terephthalate.
BACKGROUND ART
[0002] Generally, terephthalic acid is produced through
liquid-phase oxidation reaction of a p-phenylene compound (e.g.,
p-xylene) in acetic acid serving as a solvent in the presence of a
catalyst (e.g., cobalt or manganese), or in the presence of a
catalyst together with a promoter (e.g., a bromine compound or
acetaldehyde). A slurry containing crude terephthalic acid produced
through such liquid-phase oxidation reaction is generally subjected
to crystallization at ambient pressure and lowered temperature,
followed by solid-liquid separation.
[0003] A mother liquor recovered through the solid-liquid
separation contains catalyst-derived useful catalyst components
such as heavy metal ions and bromide ions, and an industrial
process requires recycling of these catalyst components for
reduction of production cost. In the most convenient recycling
method, the mother liquor is returned, as it is, to and reused in
the reaction system. However, as has been known, since the mother
liquor contains, for example, various organic impurities
by-produced through liquid-phase oxidation reaction, and inorganic
impurities derived from corrosion of an employed apparatus, when
the mother liquor is reused as it is in the reaction system, the
concentration of these impurities is gradually increased in the
reaction system, and an increase in impurity concentration beyond a
predetermined level adversely affects liquid-phase oxidation
reaction. For example, in the case of production of terephthalic
acid, the mother liquor is generally returned to the reaction
system in a proportion of 70 to 98%, and the remaining portion (2
to 30%) of the mother liquor (i.e., a portion of the mother liquor
which is not reused in the reaction system) is fed to a step of
recovering acetic acid serving as a solvent. In view of the
foregoing, various methods have been proposed for recovering
catalyst components from the mother liquor fed to such an acetic
acid recovery step, and reusing the catalyst components.
[0004] For example, such known methods include a method in which
water and an alkali metal carbonate salt are added to a residue
obtained through recovery of a solvent from a mother liquor, to
thereby cause a catalyst component in the form of carbonate salt to
precipitate, and the catalyst component is dissolved in a
predetermined amount of acetic acid serving as a solvent, and
reused for reaction (see Patent Document 1); and a method in which
oxalic acid and an alkali metal hydroxide are added to a mother
liquor, to thereby cause a catalyst component in the form of
oxalate salt to precipitate, and the catalyst component is
dissolved in acetic acid serving as a solvent, followed by
oxidation for recovery of the catalyst component (see Patent
Document 2). There have also been known methods for recovering a
catalyst component from a mother liquor by use of an anion exchange
resin (see Patent Documents 3 to 11), including a method in which a
bromide-ion-type anion exchange resin is exposed to a mother liquor
for adsorption of cobalt ions and manganese ions on the resin,
hydrous acetic acid having a water content of 2 mass % and water
are caused to pass through the resin, to thereby recover cobalt
ions and manganese ions through elution, a
lower-aliphatic-monocarboxylate-ion-type weakly basic anion
exchange resin is exposed to an eluate obtained through the
aforementioned adsorption for adsorption of bromide ions and nickel
ions on the resin, and hydrous acetic acid having a water content
of 2 mass % and water are caused to pass through the resin, to
thereby recover bromide ions and nickel ions through elution (see
Patent Document 3); a method in which the cobalt concentration and
the bromine/cobalt ratio of a mother liquor are respectively
regulated so as to fall within specific ranges, followed by
adsorption of cobalt and bromine on a strongly basic anion exchange
resin, and cobalt and bromine are eluted from the strongly basic
anion exchange resin with hydrous acetic acid having a water
content of 10 mass % or more, to thereby recover a cobalt catalyst
(see Patent Document 4); a method in which cobalt ions, manganese
ions, and bromide ions are caused to be adsorbed together on an
anion exchange resin containing a pyridine ring serving as an ion
exchange group, and these ions are recovered through elution by a
known technique (see Patent Document 5); and a method in which a
catalyst component is recovered from a mother liquor by use of an
anion-exchange-type chelate resin (see Patent Document 7). [0005]
Patent Document 1: Japanese Patent Application Laid-Open (kokai)
No. S48-066090 [0006] Patent Document 2: Japanese Patent
Application Laid-Open (kokai) No. H02-203939 [0007] Patent Document
3: Japanese Patent Application Laid-Open (kokai) No. S53-104590
[0008] Patent Document 4: Japanese Patent Application Laid-Open
(kokai) No. S53-133574 [0009] Patent Document 5: Japanese Patent
Application Laid-Open (kokai) No. S53-102290 [0010] Patent Document
6: Japanese Patent Application Laid-Open (kokai) No. H10-015390
[0011] Patent Document 7: Japanese Patent Application Laid-Open
(kokai) No. H11-152246 [0012] Patent Document 8: Japanese Patent
Application Laid-Open (kokai) No. 2002-012573 [0013] Patent
Document 9: Specification of US Patent No. 4162991 [0014] Patent
Document 10: Specification of US Patent No. 4238294 [0015] Patent
Document 11: Japanese Kohyo Patent Publication No. 2003-507160
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0016] The method described in Patent Document 1 or 2 requires, for
example, an alkali metal carbonate salt or oxalic acid in an amount
equivalent to or greater than that of a catalytic metal, and thus
is economically disadvantageous. In addition, the method requires
an intricate process and a great deal of labor for recovery of a
catalyst component in the form of carbonate salt or oxalate salt,
which is not preferred.
[0017] The anion exchange resins described in Patent Documents 3 to
6 and 8 to 11 exhibit low heat resistance (allowable temperature
limit: 80 to 100.degree. C.), and thus may undergo chemical
degradation (reduction in exchange capacity) or physical
degradation (e.g., breakage of the resin) depending on the
temperature of a mother liquor which has been caused to pass
through the resins, which is not preferred. When a
pyridine-ring-containing anion exchange resin described in Patent
Document 5 is employed, elution of cobalt ions, manganese ions, and
bromide ions adsorbed on the resin requires a liquid containing,
for example, sulfuric acid, nitric acid, alkylsulfuric acid, or
hydroxide ions, and, in practice, difficulty is encountered in
reusing the thus-recovered liquid as is in the reaction system.
[0018] The method described in Patent Document 7 employs an
anion-exchange-type "chelate resin," and is advantageous in that,
unlike the case of the pyridine-ring-containing anion exchange
resin described in Patent Document 5, cobalt ions, manganese ions,
and bromide ions adsorbed on the chelate resin can be eluted with
hydrous acetic acid having a water content of 1 to 15 mass %.
However, when a mother liquor recovered through the method of the
present invention (i.e., a mother liquor recovered through
solid-liquid separation of a slurry produced by liquid-phase
oxidation reaction of a p-phenylene compound) is caused to pass
through the chelate resin, a carboxylic acid mixture which has been
by-produced (hereinafter may be referred to as a "by-produced
carboxylic acid mixture") is adsorbed on the chelate resin, and,
upon elution of cobalt ions, manganese ions, and bromide ions, the
by-produced carboxylic acid mixture is eluted and recovered
together with these ions. When the by-produced carboxylic acid
mixture concentration of the mother liquor is increased, a catalyst
is deactivated, and reaction yield is reduced. Therefore, a
catalyst recovery method employing the anion-exchange-type chelate
resin has not yet been put into practice on an industrial
scale.
[0019] In view of the foregoing, an object of the present invention
for solving the aforementioned problems is to provide a method for
producing, in an industrially advantageous manner, terephthalic
acid by use of a specific chelate resin while suppressing an
increase in concentration of a by-produced carboxylic acid mixture
in a reaction system and a mother liquor.
Means for Solving the Problems
[0020] In order to attain the aforementioned object, the present
inventors have conducted extensive studies, and as a result have
found that, in the production of terephthalic acid, when catalyst
components are recovered from a mother liquor by use of an
anion-exchange-type pyridine-ring-containing chelate resin through
a series of the below-described steps (1) to (4), heavy metal ions
and bromide ions (i.e., catalyst components) can be separated from
a by-produced carboxylic acid mixture, and, even in the case where
liquid-phase oxidation reaction is carried out continuously, an
increase in concentration of the by-produced carboxylic acid
mixture can be suppressed in the reaction system and the mother
liquor, and therefore the catalyst components can be recovered and
reused a maximum number of times in liquid-phase oxidation reaction
without being deactivated. The present invention has been
accomplished on the basis of this finding.
[0021] Accordingly, the present invention provides: [0022] [1] a
method for producing terephthalic acid, characterized by
comprising:
[0023] subjecting a p-phenylene compound to liquid-phase oxidation
reaction by use of a molecular-oxygen-containing gas in the
presence of a catalyst at least containing a heavy metal compound
and a bromine compound, and hydrous acetic acid having a water
content of 1 to 15 mass %, to thereby yield a slurry;
[0024] regulating the temperature of the slurry to 35 to
140.degree. C., to thereby cause terephthalic acid to
precipitate;
[0025] removing the terephthalic acid through solid-liquid
separation, to thereby recover a mother liquor; and
[0026] recovering the catalyst from the mother liquor through a
series of the following steps (1) to (4) for reusing at least a
portion of the catalyst in the liquid-phase oxidation reaction:
[0027] (1) an adsorption step including regulating the ratio
"amount by mole of bromide ions in the mother liquor/total amount
by mole of heavy metal ions in the mother liquor" to 0.6 to 3, and
then exposing the mother liquor to a pyridine-ring-containing
chelate resin which has been heated to 35 to 140.degree. C., so
that the resin adsorbs catalyst-derived heavy metal ions and
bromide ions, and also adsorbs a carboxylic acid mixture which has
been by-produced through the liquid-phase oxidation reaction
(hereinafter the carboxylic acid mixture will be referred to as a
"by-produced carboxylic acid mixture"),
[0028] (2) an elution step (A) of exposing hydrous acetic acid
having a water content of 1 to 15 mass % to the
pyridine-ring-containing chelate resin which has undergone the
adsorption step, thereby yielding an eluate containing the
by-produced carboxylic acid mixture,
[0029] (3) an elution step (B) of exposing water or hydrous acetic
acid having a water content of 20 mass % or more to the
pyridine-ring-containing chelate resin which has undergone the
elution step (A), thereby yielding an eluate containing
catalyst-derived heavy metal ions and bromide ions, and
[0030] (4) a displacement step of exposing hydrous acetic acid
having a water content of 1 to 15 mass % to the
pyridine-ring-containing chelate resin which has undergone the
elution step (B), serving as a displacement liquid, thereby
regenerating the resin; [0031] [2] the method for producing
terephthalic acid as described in [1] above, wherein hydrous acetic
acid is recovered from the mother liquor which has undergone the
adsorption step, from the eluate obtained through the elution step
(A), and from the displacement liquid employed in the displacement
step, and the recovered hydrous acetic acid is reused in the
liquid-phase oxidation reaction as at least a portion of hydrous
acetic acid having a water content of 1 to 15 mass %; [0032] [3]
the method for producing terephthalic acid as described in [1] or
[2] above, wherein hydrous acetic acid is recovered from the mother
liquor which has undergone the adsorption step, from the eluate
obtained through the elution step (A), and from the displacement
liquid employed in the displacement step, and the recovered hydrous
acetic acid is reused in the elution step (A) as at least a portion
of hydrous acetic acid having a water content of 1 to 15 mass %;
[0033] [4] the method for producing terephthalic acid as described
in any one of [1] to [3] above, wherein hydrous acetic acid is
recovered from the mother liquor which has undergone the adsorption
step, from the eluate obtained through the elution step (A), and
from the displacement liquid employed in the displacement step, and
the recovered hydrous acetic acid is reused in the displacement
step as a displacement liquid; [0034] [5] the method for producing
terephthalic acid as described in any one of [1] to [4] above,
wherein the eluate obtained through the elution step (B) is
returned to the liquid-phase oxidation reaction, and reused as at
least a portion of the catalyst; [0035] [6] the method for
producing terephthalic acid as described in any one of [1] to [5]
above, wherein a regenerated pyridine-ring-containing chelate resin
which has been obtained through the displacement step is reused in
the adsorption step as the pyridine-ring-containing chelate resin;
[0036] [7] the method for producing terephthalic acid as described
in any one of [1] to [6] above, wherein the hydrous acetic acid
having a water content of 1 to 15 mass % and employed in the
elution step (A) contains bromide ions in an amount of 1 to 1,000
mass ppm; [0037] [8] the method for producing terephthalic acid as
described in any one of [1] to [7] above, wherein the hydrous
acetic acid having a water content of 1 to 15 mass % and employed
in the displacement step as a displacement liquid contains bromide
ions in an amount of 1 to 1,000 mass ppm; [0038] [9] the method for
producing terephthalic acid as described in any one of [1] to [8]
above, wherein, in the adsorption step, the ratio "amount by mole
of bromide ions in the mother liquor/total amount by mole of heavy
metal ions in the mother liquor" is regulated to 1.6 to 2.5; and
[0039] [10] the method for producing terephthalic acid as described
in any one of [1] to [9] above, wherein when Q represents the total
amount (g) of hydrous acetic acid having a water content of 1 to 15
mass % supplied in the elution step (A), and V represents the
volume (mL) of a pyridine-ring-containing chelate resin layer, the
ratio Q/V is 0.5 to 10.
EFFECTS OF THE INVENTION
[0040] In the method for producing of terephthalic acid, a
by-produced carboxylic acid mixture can be effectively separated
from catalyst-derived heavy metal ions and bromide ions, and the
thus-recovered heavy metal ions and bromide ions can be reused, as
it is, as a catalyst in liquid-phase oxidation reaction. Therefore,
terephthalic acid can be produced stably in a more economically
advantageous manner while high reaction yield is maintained over a
long period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 shows an exemplary process for producing terephthalic
acid.
DESCRIPTION OF REFERENCE NUMERALS
[0042] 1: Reactor [0043] 2: Crystallization step [0044] 3:
Solid-liquid separator [0045] 4: Mother liquor receiving tank
[0046] 5: Pyridine-ring-containing chelate resin column [0047] 6:
Hydrobromic acid tank [0048] 7: Tank for storing hydrous acetic
acid having a water content of about 12 mass % (also called
"displacement liquid tank") [0049] 8: Tank for storing hydrous
acetic acid having a water content of about 35 mass % [0050] 9:
Intermediate tank [0051] 10: Raw material tank [0052] 11: Conduit
for cake of crude terephthalic acid crystals [0053] 12: Conduit for
mother liquor [0054] 13: Conduit for hydrobromic acid [0055] 14:
Conduit for prepared mother liquor [0056] 15: Conduit over column
[0057] 16: Conduit under column [0058] 17: Conduit for purged
liquid [0059] 18: Conduit for hydrous acetic acid having a water
content of about 12 mass % (also called "displacement liquid
conduit") [0060] 19: Conduit for hydrous acetic acid having a water
content of about 35 mass % [0061] 20: Conduit for recovered
catalyst liquid [0062] 21: Conduit for recovered catalyst liquid
[0063] 22: Conduit for raw material mixture
BEST MODES FOR CARRYING OUT THE INVENTION
[0064] In the present invention, firstly, a p-phenylene compound is
subjected to liquid-phase oxidation reaction by use of a
molecular-oxygen-containing gas in the presence of a catalyst at
least containing a heavy metal compound and a bromine compound, and
hydrous acetic acid having a water content of 1 to 15 mass %
(preferably 1 to 12 mass %, more preferably 1 to 9 mass %), to
thereby yield a slurry (hereinafter the thus-obtained slurry may be
referred to as an "oxidation reaction slurry"). As used herein, the
term "p-phenylene compound" refers to a phenylene compound having
substituents at positions 1 and 4 of the benzene ring. Examples of
such a substituent include alkyl groups such as methyl, ethyl,
propyl, and butyl. A particularly preferred p-phenylene compound is
p-xylene.
[0065] At least one of a cobalt compound and a manganese compound
is essentially employed as a heavy metal compound (i.e., a catalyst
component), and optionally, for example, a nickel compound, a
cerium compound, or a zirconium compound may be employed together
with such an essential heavy metal compound. Examples of the cobalt
compound, manganese compound, nickel compound, cerium compound, and
zirconium compound include organic acid salts, hydroxides, halides,
and carbonates of the respective metals. Particularly, acetic acid
salts and bromides of the respective metals are preferably
employed. Specific examples of such a heavy metal compound include
cobalt acetate, cobalt hydroxide, cobalt fluoride, cobalt chloride,
cobalt bromide, cobalt iodide, cobalt carbonate, manganese acetate,
manganese hydroxide, manganese fluoride, manganese chloride,
manganese bromide, manganese iodide, manganese carbonate, nickel
acetate, nickel hydroxide, nickel fluoride, nickel chloride, nickel
bromide, nickel iodide, nickel carbonate, cerium acetate, cerium
hydroxide, cerium fluoride, cerium chloride, cerium bromide, cerium
iodide, cerium carbonate, zirconium acetate, zirconium hydroxide,
zirconium fluoride, zirconium chloride, zirconium bromide,
zirconium iodide, and zirconium carbonate.
[0066] No particular limitation is imposed on the bromine compound
employed as a catalyst component, so long as it dissolves in
hydrous acetic acid and generates bromide ions in the reaction
system. Examples of the bromine compound include inorganic bromine
compounds such as hydrogen bromide, sodium bromide, and cobalt
bromide; and organic bromine compounds such as bromoacetic acid and
tetrabromoethane. Of these, hydrogen bromide, cobalt bromide, and
manganese bromide are preferably employed. More preferably,
hydrobromic acid prepared by dissolving hydrogen bromide in an
aqueous solution is employed.
[0067] The liquid-phase oxidation reaction is preferably performed
at 160 to 230.degree. C., more preferably 180 to 210.degree. C.
When the reaction temperature falls within the above range, the
amount of a reaction intermediate remaining in the oxidation
reaction slurry can be reduced, and excessive loss of hydrous
acetic acid having a water content of 1 to 15 mass % (i.e., a
solvent) by combustion is prevented. No particular limitation is
imposed on the reaction pressure, so long as the reaction system
can be maintained in a liquid phase at the aforementioned reaction
temperature. Generally, the reaction pressure is preferably 0.78 to
3.04 MPa, more preferably 0.98 to 1.86 MPa.
[0068] Examples of a molecular-oxygen-containing gas include air,
oxygen gas diluted with an inert gas, and oxygen-enriched air.
Generally, air is preferred, from the viewpoints of facility and
cost.
[0069] Preferably, the oxidation reaction slurry obtained through
the aforementioned liquid-phase oxidation reaction is fed to the
subsequent reactor connected in series, so as to thoroughly
complete oxidation reaction by use of a molecular-oxygen-containing
gas.
[0070] The thus-obtained oxidation reaction slurry is subjected to
pressure reduction and cooling (35 to 140.degree. C.) through flash
evaporation in one or more stages in a crystallization step
employing one or more crystallization tanks, to thereby thoroughly
crystallize crude terephthalic acid, and then the slurry is fed to
the below-described solid-liquid separator.
[0071] The oxidation reaction slurry obtained through the
aforementioned liquid-phase oxidation reaction is separated into
crude terephthalic acid crystals and a mother liquor by means of a
solid-liquid separator. This solid-liquid separation is generally
performed at atmospheric pressure. No particular limitation is
imposed on the separation temperature, but this separation is
generally performed at a temperature lower than the boiling point
of hydrous acetic acid at atmospheric pressure (e.g., 35 to
110.degree. C). Examples of the solid-liquid separator include a
centrifugal separator, a centrifugal filter, and a vacuum filter.
This solid-liquid separation is preferably performed so that the
crystal content of the mother liquor is 1 mass % or less, more
preferably 0.1 mass % or less.
[0072] The thus-obtained crude terephthalic acid crystals may be
appropriately subjected to a known purification process, such as
catalytic hydrogenation (see, for example, Japanese Patent
Publication (kokoku) No. S41-16860), oxidation treatment, or
recrystallization, to thereby yield terephthalic acid crystals of
high purity.
<Adsorption Step>
[0073] The mother liquor recovered through separation of crude
terephthalic acid crystals from the oxidation reaction slurry by
the aforementioned procedure contains catalyst-derived heavy metal
ions and bromide ions, and a by-produced carboxylic acid mixture.
These heavy metal ions are ions of the heavy metals constituting
the aforementioned heavy metal compounds. The by-produced
carboxylic acid mixture includes aromatic polycarboxylic acids each
having carboxyl groups which are ortho to each other. Examples of
such an aromatic polycarboxylic acid include trimellitic acid
compounds (e.g., trimellitic acid, hemimellitic acid, and
5-methyltrimellitic acid); pyromellitic acid; and phthalic acid
compounds (e.g., phthalic acid, 3-methylphthalic acid, and
4-methylphthalic acid). The mother liquor contains, in addition to
the aforementioned ions and by-produced carboxylic acid mixture,
various organic compounds (e.g., terephthalic acid, acetic acid,
unreacted raw materials, reaction intermediates, and reaction
by-products), and a considerable amount of water (i.e., a reaction
product).
[0074] In the present invention, the ratio "amount by mole of
bromide ions in the mother liquor/total amount by mole of heavy
metal ions in the mother liquor" (hereinafter the ratio may be
referred to as "the bromide ratio (of the mother liquor)") is
regulated, and then a pyridine-ring-containing chelate resin is
exposed to the mother liquor, to thereby selectively adsorb
catalyst-derived heavy metal ions, bromide ions, and a by-produced
carboxylic acid mixture on the pyridine-ring-containing chelate
resin, whereby a liquid (hereinafter the thus-obtained liquid may
be referred to as a "residual mother liquor") is recovered
[adsorption step]. When crude terephthalic acid crystals recovered
through separation by means of a solid-liquid separator are washed
with water or hydrous acetic acid, a liquid obtained through this
washing may be mixed with the mother liquor, and the resultant
mixture may be subjected to the adsorption step.
[0075] The pyridine-ring-containing chelate resin employed in the
present invention is an anion-exchange-type chelate resin having a
pyridine ring and obtained through polymerization of
4-vinylpyridine and divinylbenzene serving as main raw materials.
In general, a chelate resin is a water-insoluble polymer base
having a ligand which can coordinate with metal ions to form a
complex, and exhibits a function of selectively
adsorbing/separating specific metal ions. Particularly, a
`pyridine-ring-containing` chelate resin is advantageous in that it
effectively adsorbs heavy metal ions. Such a
pyridine-ring-containing chelate resin may be a commercially
available one. Examples of commercially available
pyridine-ring-containing chelate resins include "REILLEX
(registered trademark) 425 Polymer" (trade name, product of Reilly)
and "Sumichelate (registered trademark) CR-2" (trade name, product
of Sumitomo Chemical Co., Ltd.).
[0076] No particular limitation is imposed on the method for
exposing the mother liquor to a pyridine-ring-containing chelate
resin, and, for example, the chelate resin is impregnated with the
mother liquor, or the mother liquor is caused to pass through the
chelate resin. From the viewpoint of adsorption efficiency, more
preferably, the mother liquor is caused to pass through a
pyridine-ring-containing chelate resin. From the viewpoints of heat
resistance and adsorption performance of a pyridine-ring-containing
chelate resin, the chelate resin must be heated to 35 to
140.degree. C. before being exposed to the mother liquor. The
chelate resin is preferably heated to 45 to 130.degree. C., more
preferably 70 to 120.degree. C., much more preferably 85 to
110.degree. C.
[0077] The residual mother liquor obtained by exposing the mother
liquor to a pyridine-ring-containing chelate resin contains hydrous
acetic acid having a water content of 1 to 15 mass %. Therefore,
preferably, the hydrous acetic acid is recovered from the residual
liquid through, for example, distillation, and at least a portion
of the thus-recovered hydrous acetic acid is reused in liquid-phase
oxidation reaction, or employed as a displacement liquid for the
below-described regeneration of the pyridine-ring-containing
chelate resin.
[0078] In the present invention, the mother liquor obtained through
liquid-phase oxidation reaction and solid-liquid separation
generally has a water content of 7 to 16 mass %. Therefore, when
the mother liquor is applied to a pyridine-ring-containing chelate
resin column, in many cases, the water content of the mother liquor
is not particularly required to be regulated. However, when the
water content of the mother liquor is increased by, for example,
mixing the mother liquor with a liquid obtained through the
aforementioned washing of crude terephthalic acid crystals
recovered by solid-liquid separation, the water content is
preferably regulated to 16 mass % or less (more preferably 1 to 14
mass %, much more preferably 5 to 12 mass %) through, for example,
distillation. When the water content of the mother liquor exceeds
16 mass %, in the adsorption step, catalyst-derived heavy metal
ions and bromide ions and a by-produced carboxylic acid mixture are
less likely to be sufficiently adsorbed on a
pyridine-ring-containing chelate resin.
[0079] The pyridine-ring-containing chelate resin which has not
undergone any preliminary treatment may be exposed to the mother
liquor. However, preferably, the mother liquor is brought into
contact with a bromide-type chelate resin prepared by exposing a
pyridine-ring-containing chelate resin to, for example, an acetic
acid solution containing bromide ions in advance. No particular
limitation is imposed on the method for preparing a bromide-type
pyridine-ring-containing chelate resin, and, for example, the
chelate resin may be prepared by exposing a
pyridine-ring-containing chelate resin to an aqueous solution of
any of the aforementioned bromine compounds (e.g., sodium bromide
and hydrogen bromide) or a liquid mixture of the aqueous solution
and acetic acid, followed by removal of excess bromide through
washing with glacial acetic acid or hydrous acetic acid having a
water content of 15 mass % or less. This washing is preferably
performed with hydrous acetic acid having a water content lower
than that of the mother liquor.
[0080] From the viewpoint of efficient elution of a by-produced
carboxylic acid mixture adsorbed on a pyridine-ring-containing
chelate resin, the bromide ratio of the mother liquor is 0.6 to 3,
preferably 0.7 to 2.8, more preferably 0.9 to 2.5, much more
preferably 1.6 to 2.5, particularly preferably 2 to 2.5. When the
bromide ratio is high, percent adsorption of the aforementioned
heavy metal ions is increased, and percent adsorption of a
by-produced carboxylic acid mixture tends to be reduced. Therefore,
when the bromide ratio is increased particularly in the adsorption
step, in the below-described elution step (A), a by-produced
carboxylic acid mixture can be effectively separated from catalyst
components (i.e., heavy metal ions and bromide ions). The bromide
ratio is regulated by, for example, adding, to the mother liquor,
an aqueous solution of any of the aforementioned bromine compounds
(e.g., hydrobromic acid) serving as a bromide source.
<Elution Steps (A) and (B)>
[0081] In the present invention, the pyridine-ring-containing
chelate resin which has undergone the aforementioned adsorption
step is subjected to an elution step (A); i.e., a step of exposing
the resin to hydrous acetic acid having a water content of 1 to 15
mass % (preferably 1 to 12 mass %, more preferably 1 to 9 mass %),
thereby selectively eluting a by-produced carboxylic acid mixture,
and then is subjected to an elution step (B); i.e., a step of
exposing the resin to water or hydrous acetic acid having a water
content of 20 mass % or more, thereby recovering catalyst-derived
heavy metal ions and bromide ions.
[0082] The pyridine-ring-containing chelate resin which has
undergone the aforementioned adsorption step contains, in addition
to catalyst-derived heavy metal ions and bromide ions, a
by-produced carboxylic acid mixture. When the
pyridine-ring-containing chelate resin is subjected to the elution
step (B) without being subjected to the elution step (A), so as to
recover the heavy metal ions and bromide ions (i.e., catalyst
components), the by-produced carboxylic acid mixture is contained
in the catalyst components. In such a case, when the catalyst
components are returned to and reused in the reaction system, the
concentration of the by-produced carboxylic acid mixture is
gradually increased in the reaction system and the mother liquor,
which causes deactivation of the catalyst. Such a process results
in an economic disadvantage when being put into practice on an
industrial scale. In order to suppress an increase in concentration
of the by-produced carboxylic acid mixture, the elution step (A) is
required; i.e., the by-produced carboxylic acid mixture is
selectively eluted, with heavy metal ions and bromide ions being
adsorbed on the pyridine-ring-containing chelate resin.
[0083] The hydrous acetic acid having a water content of 1 to 15
mass % and employed in the elution step (A) preferably contains
bromide ions in an amount of 1 to 1,000 mass ppm, more preferably
10 to 1,000 mass ppm, for rapidly eluting the by-produced
carboxylic acid mixture adsorbed on the pyridine-ring-containing
chelate resin. In the elution step (A), there may be employed
acetic acid (water content: 4 to 11 mass %, bromide ion content: 1
to 50 mass ppm) recovered from the bottom of a distillation column
upon removal of water (through evaporation) from the residual
mother liquor obtained through the adsorption step, an eluate
obtained through the elution step (A), or a displacement liquid
employed in the below-described displacement step.
[0084] When Q represents the total amount (g) of hydrous acetic
acid supplied in the elution step (A), and V represents the volume
(mL) of a pyridine-ring-containing chelate resin layer, the ratio
Q/V is preferably 0.5 to 10, more preferably 1 to 6, much more
preferably 3 to 4.5. When the ratio Q/V falls within the above
range, the by-produced carboxylic acid mixture can be effectively
and selectively eluted from the pyridine-ring-containing chelate
resin.
[0085] Preferably, hydrous acetic acid having a water content of 1
to 15 mass % is recovered, through distillation or a similar
technique, from the eluate obtained through the elution step (A),
which contains the by-produced carboxylic acid mixture, and at
least a portion of the thus-recovered hydrous acetic acid is reused
in liquid-phase oxidation reaction, or employed in the elution step
(A) or in the below-described displacement step.
[0086] In the elution step (B), metal impurities other than
catalyst-derived heavy metal ions and bromide ions are not
virtually adsorbed on the pyridine-ring-containing chelate resin.
Therefore, through exposing the resin to water or hydrous acetic
acid having a water content of 20 mass % or more (preferably 20 to
70 mass %, more preferably 25 to 50 mass %, much more preferably 25
to 40 mass %), hydrous acetic acid which contains heavy metal ions
and bromide ions, and which can be reused, as it is, in
liquid-phase oxidation reaction (hereinafter the thus-obtained
hydrous acetic acid may be referred to as a "recovered catalyst
liquid") can be produced.
[0087] Alternatively, a condensate (water content: 20 to 50 mass %)
recovered in liquid-phase oxidation reaction by means of a reflux
condenser attached to the reactor may be employed in the elution
step (B) as hydrous acetic acid.
<Displacement Step>
[0088] In this step, from the viewpoint of adsorption efficiency of
catalyst components, the pyridine-ring-containing chelate resin
which has undergone the elution step (B) is brought into contact
with a displacement liquid; i.e., hydrous acetic acid having a
water content of 1 to 15 mass % (preferably 1 to 12 mass %, more
preferably 1 to 9 mass %), to thereby regenerate the
pyridine-ring-containing chelate resin. The thus-regenerated
pyridine-ring-containing chelate resin can be reused in the
adsorption step. Through the displacement step, the water content
of hydrous acetic acid present around the chelate resin is reduced
to a level equal to the water content of the displacement liquid,
so that heavy metal ions and bromide ions are rapidly adsorbed on
the chelate resin in the subsequent adsorption step. In contrast,
when the displacement step is not performed, since the chelate
resin layer is surrounded by hydrous acetic acid having a high
water content immediately after the elution step (B), in the
adsorption step, adsorption efficiency of catalyst components is
reduced at an early stage of exposure of the chelate resin to the
mother liquor, and percent recovery of the catalyst components is
reduced, resulting in an economic disadvantage.
[0089] In order to facilitate adsorption of cobalt ions, manganese
ions, and bromide ions on the pyridine-ring-containing chelate
resin, more preferably, hydrous acetic acid having a water content
of 1 to 15 mass % and containing bromide ions in an amount of 1 to
1,000 mass ppm is employed as a displacement liquid.
[0090] There may be employed, as a displacement liquid, acetic acid
(water content: 4 to 11 mass %, bromide ion content: 1 to 50 mass
ppm) recovered from the bottom of a distillation column upon
removal of water (through evaporation) from the residual mother
liquor obtained through the adsorption step, the eluate obtained
through the elution step (A), or the displacement liquid employed
in the displacement step.
[0091] The overall flow of the method of the present invention will
next be briefly described with reference to FIG. 1, which shows an
exemplary process for producing terephthalic acid. However, the
present invention is not limited to the process shown in FIG.
1.
[0092] As shown in FIG. 1, a mixture of raw materials (a
p-phenylene compound, a heavy metal compound, a bromine compound,
and hydrous acetic acid) is fed through a conduit 22 to a reactor
1, and liquid-phase oxidation reaction is performed in the presence
of a molecular-oxygen-containing gas. The reaction product is in
the form of slurry obtained through crystallization of a portion of
crude terephthalic acid. The reaction product is subjected to
pressure reduction and cooling through flash evaporation in several
stages in a crystallization step 2, followed by separation by means
of a solid-liquid separator 3, to thereby yield a cake of crude
terephthalic acid crystals. The thus-obtained cake is transferred
through a conduit 11. The mother liquor recovered through
separation by means of the solid-liquid separator 3 is fed via a
conduit 12 to a mother liquor receiving tank 4, and hydrobromic
acid is fed from a hydrobromic acid tank 6 through a conduit 13 to
the mother liquor receiving tank 4, to thereby appropriately
regulate the bromide ratio of the mother liquor. Subsequently, the
mother liquor is caused to pass through conduits 14 and 15, and
then subjected to the adsorption step; i.e., the mother liquor is
introduced to a pyridine-ring-containing chelate resin column 5
through the top of the column and caused to pass therethrough. A
substance which is not adsorbed on the pyridine-ring-containing
chelate resin is discharged from the bottom of the column, and then
purged via conduits 16 and 17. The substance is appropriately
subjected to, for example, distillation for recovery of hydrous
acetic acid, and the thus-recovered hydrous acetic acid is
transferred (for reuse) to a raw material tank 10 or a tank 7 for
storing hydrous acetic acid having a water content of about 12 mass
%.
[0093] The pyridine-ring-containing chelate resin which has
undergone the adsorption step is subjected to the elution step (A).
Specifically, hydrous acetic acid having a water content of about
12 mass % is fed from the tank 7 through a conduit 18 and the
conduit 15, and introduced to the pyridine-ring-containing chelate
resin column 5 through the top of the column and caused to pass
therethrough. An eluate containing a by-produced carboxylic acid
mixture is discharged from the bottom of the column, and then
purged via the conduits 16 and 17. The eluate is appropriately
subjected to, for example, distillation for recovery of hydrous
acetic acid, and the thus-recovered hydrous acetic acid is
transferred (for reuse) to the raw material tank 10 or the tank 7
for storing hydrous acetic acid having a water content of about 12
mass %.
[0094] After completion of the elution step (A), the elution step
(B) is carried out. Specifically, hydrous acetic acid having a
water content of about 35 mass % is fed from a tank 8 through a
conduit 19 and the conduit 16, and introduced to the
pyridine-ring-containing chelate resin column 5 so as to pass
therethrough for elution of heavy metal ions and bromide ions
adsorbed on the pyridine-ring-containing chelate resin. The
thus-recovered catalyst liquid is transferred through a conduit 20
to an intermediate tank 9. Subsequently, the recovered catalyst
liquid is fed through a conduit 21 to the raw material tank 10, and
reused as a catalyst for liquid-phase oxidation reaction.
[0095] After completion of the elution step (B), the displacement
step is carried out. Specifically, hydrous acetic acid having a
water content of about 12 mass %, serving as a displacement liquid,
is fed from the displacement liquid tank 7 through the conduit 18
and the conduit 15, and introduced to the pyridine-ring-containing
chelate resin column 5 so as to pass therethrough. The resultant
eluate is purged via the conduits 16 and 17. The eluate is
appropriately subjected to, for example, distillation for recovery
of hydrous acetic acid, and the thus-recovered hydrous acetic acid
is transferred (for reuse) to the raw material tank 10 or the tank
7 for storing hydrous acetic acid having a water content of about
12 mass %. After completion of the displacement step, the
aforementioned adsorption step may be carried out.
Examples
[0096] The present invention will next be described in more detail
by way of examples, which should not be construed as limiting the
invention thereto.
<Preliminary Treatment of Pyridine-Ring-Containing Chelate
Resin>
[0097] In each of the Examples and the Comparative Example, there
was employed a pyridine-ring-containing chelate resin prepared
through the following procedure: an acetic acid solution (200 mL)
containing 10 mass % hydrobromic acid was caused to pass through a
pyridine-ring-containing chelate resin ["Sumichelate (registered
trademark) CR-2" (trade name, product of Sumitomo Chemical Co.,
Ltd.)] so as to prepare a bromide-type pyridine-ring-containing
chelate resin, and excess hydrobromic acid was rinsed out the
chelate resin with an acetic acid solution having a water content
of 12 mass %.
<Method for Determining Heavy Metal Ion Concentration>
[0098] Heavy metal ion concentration was determined by means of an
atomic absorption spectrophotometer having the following
specification. [0099] Model: Polarized Zeeman atomic absorption
spectrophotometer Z-2300 (product of Hitachi High-Technologies
Corporation) [0100] Wavelength: Cobalt ion: 240.7 nm, Manganese
ion: 279.6 nm Flame: Acetylene-air [0101] Determination method: An
appropriate amount of a sample is placed in a 100-mL glass
container (mass of the sample is measured by means of a balance),
and the sample is diluted with pure water and 20 mass %
hydrochloric acid (constant boiling point, iron-free) for accurate
analysis (about 2 mL) so that the concentration of heavy metal ions
to be measured is about 1 ppm (the mass of the diluted sample is
measured for determination of a dilution factor). The heavy metal
ion concentration of the diluted sample is determined on the basis
of a calibration curve prepared by use of standard samples having
heavy metal ion concentrations of 0 ppm, 1 ppm, and 2 ppm. The
heavy metal ion concentration of the undiluted sample is determined
by multiplying the heavy metal ion concentration of the diluted
sample by the dilution factor.
<Method for Determining Bromide Ion Concentration>
[0102] Bromide ion concentration was determined under the following
conditions. [0103] Titrator: Automatic potentiometric titrator
AT-510 (product of Kyoto Electronics Manufacturing Co., Ltd.)
[0104] Titration liquid: 1/250 N aqueous silver nitrate solution
[0105] Detection electrodes:
[0106] Composite glass electrode C-172
[0107] Silver electrode M-214
[0108] Temperature compensation electrode T-111 [0109]
Determination method: A Teflon (registered trademark) stirrer chip
is placed in a 200-mL beaker, and an appropriate amount of a sample
is placed therein (the mass of the sample is measured by means of a
balance). Pure water is added to the beaker so that the volume of
the liquid in the beaker is about 150 mL, and 60 mass % nitric acid
(about 2 mL) is added thereto. Bromide ion concentration is
determined through precipitation titration by means of the
aforementioned automatic potentiometric titrator.
<Method for Determining By-Produced Carboxylic Acid Mixture
Concentration>
[0110] Concentration of each of the aforementioned phthalic acid
compounds and trimellitic acid compounds was determined through gas
chromatography under the following conditions. [0111] Model:
Agilent 6890N (product of Agilent Technologies) [0112] Column
employed: DB-1 (product of Agilent Technologies) [0113] Column
temperature: 100 to 280.degree. C. [0114] Detector: Flame
ionization detector (FID)
[0115] Percent recovery of catalyst components and percent
inclusion of a by-produced carboxylic acid mixture were calculated
through the following methods.
<Cobalt Ion>
[0116] Percent recovery of cobalt ions was determined by
calculating the ratio (%) of the amount of cobalt ions contained in
a recovered catalyst liquid to that of cobalt ions contained in a
mother liquor.
<Manganese Ion>
[0117] Percent recovery of manganese ions was determined by
calculating the ratio (%) of the amount of manganese ions contained
in the recovered catalyst liquid to that of manganese ions
contained in the mother liquor.
<Bromide Ion>
[0118] Percent recovery of bromide ions was determined by
calculating the ratio (%) of the amount of bromide ions contained
in the recovered catalyst liquid to that of bromide ions contained
in the mother liquor.
<By-Produced Carboxylic Acid Mixture>
[0119] Percent inclusion of a by-produced carboxylic acid mixture
was determined by calculating the ratio (%) of the amount of a
phthalic acid compound or trimellitic acid compound contained in
the recovered catalyst liquid to that of a phthalic acid compound
or trimellitic acid compound contained in the mother liquor.
Example 1
[0120] p-Xylene was subjected to liquid-phase oxidation reaction
(reaction temperature: 200.degree. C., reaction pressure: 1.62 MPa)
by use of air in hydrous acetic acid having a water content of 9
mass % in the presence of cobalt acetate, manganese acetate, and
hydrobromic acid, to thereby yield a slurry containing crude
terephthalic acid. Subsequently, the slurry was subjected to a
crystallization step, followed by pressure release and cooling to
100.degree. C. Thereafter, the terephthalic acid was removed
through solid-liquid separation with a glass filter, to thereby
recover crude terephthalic acid crystals and a mother liquor of
about 80.degree. C. The mother liquor was found to contain cobalt
ions in an amount of 610 mass ppm, manganese ions in an amount of
360 mass ppm, bromide ions in an amount of 810 mass ppm,
trimellitic acid compounds in an amount of 2,500 mass ppm, phthalic
acid compounds in an amount of 2,100 mass ppm, and water in an
amount of 12 mass %. The bromide ratio of the mother liquor was
found to be 0.6.
[0121] The above-preliminarily treated pyridine-ring-containing
chelate resin (90 mL) was charged into a double-tube glass column.
Hot water of 80.degree. C. was circulated through a jacket of the
pyridine-ring-containing chelate resin column, to thereby maintain
the pyridine-ring-containing chelate resin at 80.degree. C.
[0122] The aforementioned mother liquor was introduced to the
pyridine-ring-containing chelate resin column through the top of
the column and was caused to pass downward therethrough at a flow
rate of 360 g/hour for 50 minutes [adsorption step]. Thereafter,
hydrous acetic acid having a water content of 12 mass % was
introduced to the column through the top and caused to pass
downward therethrough at a flow rate of 360 g/hour for 20 minutes
(Q/A=120 g/90 mL=about 1.33) [elution step (A)]. After completion
of the elution step (A), hydrous acetic acid having a water content
of 35 mass % was introduced to the column through the bottom and
caused to pass upward therethrough at a flow rate of 360 g/hour for
90 minutes [elution step (B)]. After completion of the elution step
(B), an displacement liquid (hydrous acetic acid having a water
content of 12 mass %) was introduced to the column through the top
and caused to pass downward therethrough at the same flow rate as
described above for 20 minutes [displacement step]. A cycle
consisting of the adsorption step, the elution step (A), the
elution step (B), and the displacement step (and return to the
adsorption step) was repeated at 180 minutes/cycle.
[0123] Hydrous acetic acid having a water content of about 12 mass
% was recovered, through distillation, from the residual mother
liquor obtained through the adsorption step, from the eluate
obtained through the elution step (A), and from the displacement
liquid employed in the displacement step. The thus-recovered
hydrous acetic acid was reused as hydrous acetic acid in the
liquid-phase oxidation reaction, as hydrous acetic acid in the
elution step (A), and as a displacement liquid in the displacement
step. Also, a catalyst liquid recovered through the elution step
(B) and containing cobalt ions, manganese ions, and bromide ions
was reused as a catalyst for liquid-phase oxidation reaction.
[0124] Table 1 shows data of percent recovery of cobalt ions,
manganese ions, and bromide ions, and percent inclusion of phthalic
acid compounds and trimellitic acid compounds, as determined by use
of a catalyst liquid recovered on day 4 of the experiment.
[0125] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00001 TABLE 1 Percent recovery Cobalt ions 88% Manganese
ions 68% Bromide ions 92% Percent inclusion Trimellitic acid
compounds 50% Phthalic acid compounds 9%
Comparative Example 1
[0126] The experiment and measurement were performed in the same
manner as employed in Example 1, except that the elution step (A)
was not performed, and the cycle consisting of the adsorption step,
the elution step (B), and the displacement step (and return to the
adsorption step) was repeated at 160 minutes/cycle. The results are
shown in Table 2.
[0127] The experiment was further continued. The catalytic activity
was gradually reduced, and the yield of terephthalic acid produced
through liquid-phase oxidation reaction was considerably
reduced.
TABLE-US-00002 TABLE 2 Percent recovery Cobalt ions 89% Manganese
ions 79% Bromide ions 93% Percent inclusion Trimellitic acid
compounds 77% Phthalic acid compounds 38%
Example 2
[0128] The experiment and measurement were performed in the same
manner as employed in Example 1, except that the elution step (A)
was performed for 60 minutes (Q/A=360 g/90 mL=4), and the cycle
consisting of the adsorption step, the elution step (A), the
elution step (B), and the displacement step (and return to the
adsorption step) was repeated at 220 minutes/cycle. The results are
shown in Table 3.
[0129] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00003 TABLE 3 Percent recovery Cobalt ions 88% Manganese
ions 67% Bromide ions 91% Percent inclusion Trimellitic acid
compounds 34% Phthalic acid compounds 5%
Example 3
[0130] The experiment and measurement were performed in the same
manner as employed in Example 1, except that hydrobromic acid was
added to the recovered mother liquor so as to attain a bromide
ratio of 0.9, and then the mother liquor was subjected to the
adsorption step. The results are shown in Table 4.
[0131] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00004 TABLE 4 Percent recovery Cobalt ions 96% Manganese
ions 72% Bromide ions 92% Percent inclusion Trimellitic acid
compounds 43% Phthalic acid compounds 7%
Example 4
[0132] The experiment and measurement were performed in the same
manner as employed in Example 1, except that hydrobromic acid was
added to the recovered mother liquor so as to attain a bromide
ratio of 1.2, and then the mother liquor was subjected to the
adsorption step. The results are shown in Table 5.
[0133] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00005 TABLE 5 Percent recovery Cobalt ions 98% Manganese
ions 77% Bromide ions 92% Percent inclusion Trimellitic acid
compounds 38% Phthalic acid compounds 6%
Example 5
[0134] The experiment and measurement were performed in the same
manner as employed in Example 1, except that hydrobromic acid was
added to the recovered mother liquor so as to attain a bromide
ratio of 1.5, and then the mother liquor was subjected to the
adsorption step. The results are shown in Table 6.
[0135] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00006 TABLE 6 Percent recovery Cobalt ions 99% Manganese
ions 81% Bromide ions 91% Percent inclusion Trimellitic acid
compounds 32% Phthalic acid compounds 5%
Example 6
[0136] The procedure of Example 1 was repeated. However, in Example
6, a pyridine-ring-containing chelate resin "REILLEX (registered
trademark) 425 Polymer" (trade name, product of Reilly) (90 mL) was
used; the mother liquor was fed to the adsorption step after the
bromide ratio had been adjusted to 2.5 through addition of
hydrobromic acid; and a cycle [adsorption step (120 min), elution
step (A) (20 min, Q/A=120 g/90 mL=about 1.33), elution step (B) (80
min), and displacement step (20 min)] was repeated at 240
minutes/cycle. Also, hydrous acetic acid (water content: 8 mass %,
bromide ion level: 10 mass ppm) recovered from the bottom of a
distillation column upon removal of water (through evaporation) at
125.degree. C. (ambient pressure) from an eluate obtained through
the elution step (A) was employed as the hydrous acetic acid in the
elution step (A) and as the displacement liquid in the displacement
step. Table 7 shows data of percent recovery of cobalt ions,
manganese ions, and bromide ions, and percent inclusion of phthalic
acid compounds and trimellitic acid compounds, as determined by use
of a catalyst liquid recovered on day 180 of the experiment.
[0137] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00007 TABLE 7 Percent recovery Cobalt ions 99.9% Manganese
ions 90% Bromide ions 96% Percent inclusion Trimellitic acid
compounds 3% Phthalic acid compounds 0%
Example 7
[0138] The experiment was performed in the same manner as employed
in Example 6, except that the recovered mother liquor was heated to
90.degree. C., and then subjected to the adsorption step. Table 8
shows data of percent recovery of cobalt ions, manganese ions, and
bromide ions, and percent inclusion of phthalic acid compounds and
trimellitic acid compounds, as determined by use of a catalyst
liquid recovered on day 10 of the experiment.
[0139] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00008 TABLE 8 Percent recovery Cobalt ions 99.9% Manganese
ions 98% Bromide ions 99% Percent inclusion Trimellitic acid
compounds 1.8% Phthalic acid compounds 0%
Example 8
[0140] The experiment was performed in the same manner as employed
in Example 6, except that the recovered mother liquor was cooled to
40.degree. C. so as to remove a precipitated solid content, and
then subjected to the adsorption step, and that the
pyridine-ring-containing chelate resin was employed at 40.degree.
C. Table 9 shows data of percent recovery of cobalt ions, manganese
ions, and bromide ions, and percent inclusion of phthalic acid
compounds and trimellitic acid compounds, as determined by use of a
catalyst liquid recovered on day 7 of the experiment.
[0141] The experiment was further continued. However, liquid-phase
oxidation reaction was effectively performed without reducing
catalytic activity.
TABLE-US-00009 TABLE 9 Percent recovery Cobalt ions 84% Manganese
ions 63% Bromide ions 81% Percent inclusion Trimellitic acid
compounds 5% Phthalic acid compounds 0%
[0142] As is clear from the data obtained in Examples 1 to 8,
according to the method of the present invention, percent inclusion
of trimellitic acid compounds is reduced to 50% or less, and
percent inclusion of phthalic acid compounds is reduced to 10% or
less. In addition, under certain conditions, the percent inclusion
is reduced to 5% or less. Particularly when the time of the elution
step (A) (i.e., Q/A) is regulated as described in Example 2, or
when the bromide ratio of a mother liquor is modified before the
adsorption step (Examples 3 to 5), percent inclusion of trimellitic
acid compounds and phthalic acid compounds is further reduced, as
compared with the case of Example 1. In contrast, according to the
method of Comparative Example 1, which does not include the elution
step (A) and thus is similar to a conventional production method,
percent inclusion of trimellitic acid compounds is 77%, and percent
inclusion of phthalic acid compounds is increased to 38%. That is,
this method encounters difficulty in continuously performing
liquid-phase oxidation reaction over a long period of time while
reusing recovered catalyst components. In Examples 6 to 8, the
bromide ratio before the adsorption step was adjusted to 2.5, and
the bromide ion level of the hydrous acetic acid employed in the
elution step (A) and in the displacement step was adjusted to 10
mass ppm. In these Examples, percent inclusion of trimellitic acid
compounds can be successfully reduced to a very low level, and
percent inclusion of phthalic acid compounds can be reduced to
substantially zero. Thus, remarkable effects can be attained. When
the temperature of a mother liquor is increased to 90.degree. C.
(Example 7), percent recovery of heavy metal ions is increased, and
percent inclusion of trimellitic acid compounds and phthalic acid
compounds is reduced.
[0143] A difference in percent inclusion of a by-produced
carboxylic acid mixture by some tens % greatly affects production
of terephthalic acid. Thus, the present invention realizes
economically advantageous and long-term reliable production of
terephthalic acid.
INDUSTRIAL APPLICABILITY
[0144] Terephthalic acid produced through the method of the present
invention can be employed as, for example, a starting material for
polyethylene terephthalate.
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