Note: Descriptions are shown in the official language in which they were submitted.
~L~34~5i9
This invention relates to a process ~or producing a
phthalic acid which comprises oxidizing the corresponding
tolualdehyde with molecular oxygen or a molecular oxygen-
containing gas in a liquid phase by using a lower aliphaticmonocarboxylic acid as a solvent and heavy metal salt(s)
containing as at least one manganese salt and at least one
bromine compound as catal~st and more particularly relates
to a process for producing a phthalic acid from the cor-
responding tolualdehyde, characterized in that the watercontent o~ the reaction solution into which the tolualdehyde
is introduced is maintained at less than 10% by weight based
on the weight of the solution9 thereby preventing blackening
of t~e resulting phthalic acid.
Japanese Patent Publication No. 2666/1959 filed on
May 4, 1955 discloses that when an at least one aliphatic
group-substituted aromatic compound is oxidized with molecular
oxygen or a molecular oxygen-containing gas in a liquld phase
by using a lower aliphatic monocarboxylic acid as a solvent
and a heavy metal salt containing a manganese salt and a
bromine compound as a catalyst, the corresponding aromatic
carboxylic acid is formed. Terephthalic acid and iso-
phthalic acid have been prepared from p-xylene and m-xylene,
respectively, on an industrial scale by using the above
mentioned process.
Japanese Patent Publication No. 2666/1959 discloses
that a manganese salt is an excellent catalyst for producing
an aromatic carboxylic acid ~rom the corresponding aliphatic
group-substituted aromatic compound. The publication dis-
closes that a cobalt salt also is an excellent catalyst~
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In case of oxidizing p-xylene with molecular oxygen or a
molecular oxygen-containing gas in a liquid phase by using
acetic acid, etc. as a solvent, and a catalyst consisting
of a heavy metal salt and a brom:ine sompound to obtain
terephthalic acid, Journal of Industrial Chemistry~ Vol,
70, 1967, page 1155 discloses that a cobalt salt i~ the most
effective ca-talyst of the heavy metal salts~ and that a
manganese salt ranks next. Also, Organic Oxidation Reaction,
written by Yoshio Kamiya, published by Gihodo in 1974 dis-
closes that the heavy metal salts obtained by adding a
manganese salt to a cobalt salt have a synergistic effect
as a catalyst for producing terephthalic ac~d ~rom p-xylene.
Japanese Patent Publication No~ 367~2/1970 filed on June 26,
1967 discloses that polymerizable terephthalic acid of high
i~ 15 purity can be ob-tained by oxidizing p-xylene and that a
cobalt salt has an excellent catalytic action for the oxi-
dization reaction. Considering these prior art technlques
together, it was known that a mixture of a cobalt salt and
a manganese salt have excellent catalytic action ~or oxidiz-
ing p-xylene with molecular oxygen or a molecular oxygen-
containing gas in a liquid phase by using a lower aliphatic
monocarboxylic acid as a solvent, and a bromine compound
- and a heavy metal salt as a catalyst to obtain terephthalic
acid.
Journal of Industrial Chemistry, Vol. 67, 19649 page
1396 discloses that when p-xylene is oxidized in a system
comprising a manganese salt as a metal component p-xylene
is oxidized to terephthalic acid via p-toluic acid and 4-
carboxy benzaldehyde (hereinunder abbreviated as 4CBA~.
Therefore, it seems self-evident that terephthalic acid can
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- . -
be easily produced from p~tolualdehyde using the same catalyst
as the one for producing terephthalic acid from p-xylene in
the same way as -the prior artO
The inventors of`-the present invention, however,
have found that when p-tolualdehyde is oxidized in place
of p-xylene under the same continuous oxidizing conditions
as those under which p-xylene is oxidized to terephthalic
acid, dark gray terephthalic acid is surprisingly ~ormed~
In other words, we have found that a technical problem which
does not occur in case of producing terephthalic acid from
p-xylene occurs when terephthalic acid is prodùced from
"
p-tolualdehyde. We have also found that blackening of the
resulting terephthalic acid is caused by mixing o~ the
manganese salt employed as one component of the catalyst
in the resulting terephthalic acid. I-t is a matter o~
course that even if the dark gray terephthalic acid produced
from p-tolualdehyde reacts wi-th glycols, polyesters having
high whiteness can not be obtained. It was also ~ound that
even i~ the dark gray terephthalic acid is washed with
acetic acid, etc. the dark gray color can not be removed
from the terephthalic acid. Similarly, we have ~ound that
neither recrystallization of the dark gray terephthalic
acid in acetic acid or water, nor particular recrystalliza-
tion as disclosed in Japanese Patent Publication No. 16860/
1966 on March 27, 1964 removes the dark gray from the
terephthalic acid. In other words, it was found that
industrially valuable terephthalic acid can not be obtained
from p-tolualdehyde as it is when p-xylene is oxidized to
tereph-thalic acid.
In the prior art, terephthalic acid has been produced
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s~
from p-xylene as a starting material on an industrial scale,
because the technique o~ producing terephthalic acid from
p-xylene has progressed by practicing the inventions dis
closed in Japanese Patent Publication Nos. 2666/1959 and
36732/1970.
P-xylene which is employed as a starting material
for the production of terephthallc acid is produced b~ com-
plicated processes, such as isomerlzation of xylenes and
separation of xylenes. On the other hand, it was known
-that p-tolualdehyde can be easily produced from toluene
and carbon monoxide. Recently, p-tolualdehyde has been
produced by reac-ting -toluene with carbon mopo~ide in the
presence of hydrogen fluoride and boron tri~luoride as a
catalyst as disclosed in Japanese Patent Publication No~
29760/1964. Toluene can be more easily produced on an
industrial scale than xylene. For example, separation of "
toluene ~rom aromatic hydrocarbons and purification of
toluene are easier than those of p-xylene. Also, toluene
is cheaper than p-xylene. Therefore, it is advantageous -~
that p-tolualdehyde produced from toluene can be used as a
starting material ~or the production of terephthalic acid
However, as mentioned above9 the technique for the production
o~ terephthalic acid from p-xylene can not be applied to the
technique for the production o~ terephthalic acid ~rom p-
~5 tolualdehyde as it is.
The inventors of this invention have carried out awide range of research to ~ind an industrially valuable
process for producing a phthalic acid which comprises
oxidizing the corresponding tolualdehyde with molecular
,~; ~ , .
oxygen or a molecular oxygen-containing gas in a liquid
phase by using a lower aliphatic monocarboxylic acid as a
solvent, and heavy metal salt(s) containing at least one
manganese salt and at least one bromine co`mpound as a catalyst.
As a result, we have found that in case of oxidizing p-
tolualdehyde with molecular oxygen or a molecular oxygen-
containing gas in a liquid phase by using lower aliphatic
monocarboxylic acid as a solvent in the presence of heavy
metal salt containing at leas-t one manganese salt to ~or~
terephthalic acid, the water content in the lower aliphatic
monocarboxylic acid has a great influence on the bYackening
of terephthalic acid caused by mixing of manganese ~herein.
We have found that when p-tolualdehyde i~ oxidized
in the liquid monocarboxylic acid by maintaining the w~ter
content in a reaction solution into which p-tolualdehyde
is introduced at less than 10% by weight based on the
com~ined weight of the solvent and water in the reaction
solution~ terephthalic acid which has high whiteness and
is industrially ~aluable can be produced. This in~ent~on
is based on these discovery.
Therefore, an object of this invention is to provide
a process for producing a non-blackened phthalic acid from
the corresponding tolualdehyde.
This invention relates to a process ~or producing a
non-blackened phthalic acid from the corresponding tolu-
aldehyde which comprises oxidizing the tolualdehyde with
molecular oxygen or a molecular oxygen-containing gas in
a liquid phase by using a lower aliphatic monocarboxylic
acid as a solvent, and heavy metal salt(s) containing at
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1.. ~ , ,
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least one rnanganese sal-t, especially bo-th manganese and
cobalt sal-ts, and a bromine compound as a catalyst, charac~
terized in that the water content in a reaction solution
into which -the tolualdehyde is introduced is maintained at
less than 10% by weight based on the combined weight of the
solvent and water in the solu-tion.
The term "reaction solution" means a mixture of the
lower aliphatic monocarboxylic acid and water in the reaction
system. In other words, when the oxidization reaction is
contlnuously carried out in a reaction vessel of continuously
agitating type, the term l'water content in a reaction solu-
tion" means the concentration of water contained in ~he
reaction solution which contacts with the tolualdehyde at
the time it is introduced into the reaction system. The
term "blackening of terephthalic acid" means that terephthalic
acid in black, dark gray or gra~ish brown, etc~ is ~or~edO
Water which is present in the reaction solution comprises
water contained in the solvent and water formed during
oxidizing the tolualdehyde.
Even when the oxidization of p-tolualdehyde is carried
out at such a high concentration of manganese at ~hich the
oxidization of p-xylene is conventionally carried out~ -
manganese is not mixed in the reaction terephthalic acid by
maintaining the water content in the reaction solution at
less 10% by weight based on the comblned weight of the
solvent and water in the solution according -to this inven-
tion. Therefore~ according to this invention, white tere-
phthalic acid can be obtained.
The history of the tolualdehyde is not of a limiting
~0 nature to the process of this invention. In other words,
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all tolualdehydes which have been prepared by a variety of
methods can be used in the process of this invention. The
tolualdehyde obtained by reaction o~ toluene wi-th carbon
monoxide in the presence of hydrogen fluoride and boron
trifluoride as a catalyst is preferably used as a starting
material in the present process.
The catalyst employed in this invention may consist
of heavy metal salt containing one or more manganese salt
and one or more bromine compound. The catalyst may also
consist of heavy metal salts containing one or more manganese
salt and one or more cobalt salt, and one or more bromine -
compound. The heavy metal salt includes inorganic salt
or organic salt of manganese and inorganic or organic salt
of cobalt. It is preferred that the heavy metal salt be
soluble in the lower aliphatic monocarboxylic acid employed
as a solvent. The proportion o~ the components constituting
the catalyst of this invention in the reaction system is not
critical in this invention. Independent of the amount o~
the components constituting the ca-talyst, a non-blackened
phthalic acid can be obtained from the corresponding tolu-
aldehyde by limiting the water content in the solution to
a specific value. The manganese sal-t may be used in such
amoun-t that the manganese atoms in the reaction solution
ranges from 0.005% to 0.5% by weight based on the weight of
the solvent. The cobalt salt may be used in such an amount
that the proportion o~ cobalt atoms in the solution ranges
from 0.01% to 0~3% by weight based on the weight o~ the
solvent. The bromine compound includes an inorganic salt9
such as, for example ammonium bromide, sodium bromide,
potassium bromide or hydrogen bromide, etc. and an organic
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4S9
bromide, such as, for example te~rabromoe-thane or tetrabromo
p-xylene, etc. The bromine compound may be used in such an
amount that the proportion of bromine atoms in the solution
ranges from 0.05% to 0.5% by weight based on the weight o~
the solvent.
Solution temperature is not critical. However,
elevated temperature speeds the process and a temperature
ranging from about 120CC to about 240C is advantageously
employed. The oxidization reaction o~ this invention is
carried out in the liquid phase. Therefore, it is preferred
that the oxidization reaction be carried out under one or
superatmosphere so as to keep the tolualdehyde and the
solvent introduced into the reaction system in the liquid
state~ The oxidization reac-tion is conveniently carried
out under a pressure ranging from 1 to 50 atoms.
Molecular oxygen or a molecular oxygen-containing
; gas is used as an oæidizing agent. From an economic point
; of viaw air is the preferred oxidizing agent.
A lower aliphatic noncarboxylic acid9 such as acetic
acid, propionic acid or butyric acid, etc. is conveniently
used as the solvent. Acetic acid is preferred. The amount
of lower aliphatic monocarboxylic acid used is conveniently
at least two times as much as the tolualdehyde on the
weight basis.
The presen-t process is particularly suitable ~or
oxidizing p-tolualdehyde to form terephthalic acid. This
is because not only p tolualdehyde is commercially available
and the resulting terephthalic acid is useful, but also the
effect of this invention is advantageous in case o~ the
oxidation of p--tolualdehyde. This invention is more
~ : .
sui-table for continous or semi-continuous oxidizatlon of p-
tolualdehyde.
The present invention is ~urther illustrated by the
following Examples and Compara-tive Examples, However, this
invention should not be limited by these examples7 and the
changes and modifications wi-thin the spirit and scope of
this invention can be effected. The percent and parts in
the Examples are based on weight unless otherwise speci~ied.
~LL
Continuous oxidization of p ~olualdehyde was carried
out in an apparatus for continuous oxidization reaction
comprising a 2.5 ~ pressure reactor made o~ ti-tanium equipped
with reflux condenser, stirring means, hea-ting means~ inlet
for raw material, inlet for raw material gas, exit ~or gas
exit for reaction product, and two receivers for the reaction
product connected to the exit for reaction product of the
reactor.
500 gr of acetic acid (having water content of 5%)
containing 0.598 gr of cobalt acetate tetrahydrate, 1,265 gr
o~ manganese acetate and 0.654 gr of tetrabromoethane was
charged into the reactor. The pressure in the reactor was
- raised to 10 Kg/cm2 by blowing nitrogen gas into the reactor9
and thereafter the temperature in the reactor was raised to
210C. Feeding solution having the following components
was prepared in another container:
cobalt acetate te-tra hydrate (Co content in the
feeding solution 0.0283%~
manganese acetate (Mn content in the feeding
solution 0.0567%)
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tetrabromo ethane ( Br content in the feeding solution
0.121%)
balance of acetic acid (having water con-tent of
0.03%~
The feeding solution was continuously fed into the
reactor at the rate of 1120 gr/hr, and p-tolualdehyde was
continuously fed into the reactor at the rate o~ 225 gr/hr
at 210C and at 18.0 Kg/cm2 gauge. At the same time9 air
was blown into the reactor at such a rate as to maintain
oxygen content in the gas withdrawn from the exit for gas
of the reactor at 3%. The water content in the reaction
solution was 9.80% in the stationary sta-te. The reaction
product in the slurry state was continuously withdrawn from
the reactor to the receiver. The reaction product was
filtered, and cake was separated from the filtrate. The
cake was washed twice with acetic acid solution twice as
much as the cake and then was washed twice with water twice
as much as the cake, and was dried to obtain terephthalic ~-
acid. The yield of terephthalic acid was 96.6/~ on the mol
basis.
The resulting terephthalic acid had the following
properties:
Appearance white
4CBA contained the terephthalic acid 1420 ppm
Alkaline color* 0.637
Ash contained in the terephthalic acid 8.0 ppm
* 2 gr of the terephthalic acid was dissolved in
25 ml of a 2 normal solution of potassium hydroxide. The
resulting solution was placed in 50 mm cell~ The cell was
exposed to light having wavelength of 340 m~ to determine
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4~9
optical density. The alkaline color expresses the resulting
optical density.
The resulting terephthalic~ acid was hydrogenated with
molecular hydrogen in the presence of a catalyst and was
recrystallized in hot water as disclosed in Japanese Patent
Publication No. 16860/1966. The solution was lowerad to a
room temperature, and the terephthalic acid was removed
from the solution. The resulting terephthalic acid had
the following properties:
Appearance white
4CBA contained in the terephthalic acid less than
10 ppm
alkaline color 0~090
The resulting terephthalic acid reacted with ethylene
glycol to form polyethylene terephthalate. The resulting
polyethylene terephthalate was clear.
f~
500 gr o~ acetic acid (having water content of 15%)
containing 0.598 gr of cobalt acetate tetrahydrate, 1.265 gr
of manganese acetate and 0.654 gr o~ tetrabromoethane was
charged into the reactor employed in Example 1. The pressure
in the reactor was raised to 10 Kg/cm2 by blowing nitrogen
gas into the reactor, and thereafter the temperature in the
reactor was raised to 220C. Feeding solution having the
following components was prepared in another container:
cobalt acetate tetra hydra-te (Co content in the
feeding solution 0.0283%)
manganese acetate (Mn content in the feeding
solution 0.0567%)
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2~9
tetrabromo ethane (Br content in the feeding
solution 0.121%)
balance o~ ace-tic acid (having wa-ter content o~ 5%)
The feeding solution was continuously ed into the
reactor at the rate of 782 gr/hr, and p-tolualdehyde was
continuously fed into the reactor at the rate of 295 ~r/hr
at 220C and at 23.8 Kg/cm2 Gauge. At the same time alr
was blown into the reactor at such a rate as to maintain
the oxygen content in the gas wi-thdrawn from the exit for
gas in the reactor at 3%. The water content in the reaction
solution was 13~2% in the stationary state. The reaction
product in a slurry state was continuously withdrawn from
the reactor. The resulting product was treated in the same
way as in Example 1.
The resulting terephthalic acid had the following
propertieso
Appearance dark gray
4CBA contained in the terephthalic acid 1210 ppm ;
Alkaline color
Ash contained in the terephthalic acid 1100 ppm
Mn304 in the ash (based on the weight of
~ the terephthalic acid) 765 ppm
; The yield of terephthalic acid was 88.1% on the mole
basis. However, even if the terephthalic acid was re~rystal-
lized in hot water, the black color of the terephthalic acid
caused by manganese remained. The terephthalic acid was
- hydrogenated and was recrystallized in hot water in the
same way as that of Example 1. The resulting terephthalic
acid was dark gray. The terephthalic acid which was hydro-
genated and recrystallized reacted with ethylene glycol to
,.,; .. . . . . . . . .
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455~
form polyethylene -terephthalate. The resul-ting polyethylene
terephthalate was dark gray.
Example 2
The procedure of Example 1 was repeated except that
500 gr of acetic acid (having water conten-t of 5%) contain-
ing 1~52 gr of cobalt acetate tet;rahydrate, 0.402 gr o~
manganese acetate and 0.654 gr of tetrabromoethane was
charged into the reactor before introducing p-tolualdehyde
into the reactor, the feeding solution (containing 720 ppm
of Co, 180 ppm of Mn and 280 ppm o~ Br) was continuously
introduced into the reactor, the temperature of the rea~tor
was 206C, and the feeding rate of p-tolualdehyde is 217 gr/hr
and the feeding rate of the feeding solution was 108~ gr/hr.
The water content in the reaction solution was 7.80%
in the stationary state.
The resulting terephthalic acid had the following
propertieso
Appearance white
4CBA contained in the terephthalic acid 1160 ppm
Alkaline color 0.650
Ash contained in the terephthalic acid 10 ppm
The yield of terephthalic acid was 96.8% on the mole
basis. The terephthalic acid was hydrogenated and recrystal-
lized in the same way as in Example 1. The resulting tere-
phthalic acid had the same properties as those of Example 1.The polyethylene terephthalate obtained by reacting ethylene
glycol therewi-th was clear.
~L ' ,.
The procedure of Example 2 was repeated except that
the water content of the acetic acid charged into the
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reaction sys-tem before introducing p-tolualdehyde into the
reactor was 10%, the ~eeding rate o~ p-tolualdehyde was
296 gr/hr and the feeding rate o~ the feeding solution wa8
786 gr/hr, and the pressure in the reactor Was 17.5 Kg/cm2
Gauge. The water con-tent in the reaction solution was 11.2%
in the stationary state.
The resulting terephthalic acid had the following
propertles~
Appearance - dark gray
4CBA contained in the terephthalic acid lZ10 ppm
Alkaline color ~-~O
Ash contained in the terephthalic acid 500 ppm
And the yield of terephthalic acid was 92.3% on the
mole basisO The terephthalic acid was hy~rogenated and
recrystallized in the same way as in Example 1. The result-
ing terephthalic acid was black. The terephthalic acld
which was hydrogenated and recrystallized reacted with
ethylene glycol to form polyethylene terephthalate. The
resulting polyethylene terephthalate was dark gray,
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