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Патент USA US3042733

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tes Patent "
mu
3,042,717
Fatented July 3, 1962
2
1
able alkali metal salts, especially alkali metal carbonates,
3,042,717
under the conditions above set forth.
'
PRQCESS F011 TEE ?RQDUCTION 0F ARO
IWA'I‘IC DICARBOXYLIC AND PGLYCARBOX
YLIC ACIDS
Such mixtures
need not contain the alkali metal salt'forming components
in exact stoichiometric proportions; one or the other
component may be present in excess.
Walter Schenk, Heidelberg, Germany, assignor to Henkel
While I have indicated that the starting salts may be
& (lie G.m.b.H., Dusseldorf-Holthausen, Germany, a
produced prior to the reaction by neutralizing aromatic
corporation of Germany
No Drawing. Filed Feb. 15, 1961, Ser. No. 89,344
12 Claims. (Cl. 260—522)
polycarboxylic acids with an alkali metal hydroxide, or
in situ from aromatic polycarboxylic acids and alkali
metal salts, such as alkali metal carbonates, it is not'
This invention relates to a process for the production
possible to conduct the reaction in the presence of alkali
of aromatic dicarboxylic and polycarboxylic acids, and
metal hydroxides. Thus, such strong alkalis cannot be in
more particularly to the production of aromatic dicar
the reaction chamber during the reaction.
boxylic and polycarboxylic acids from alkali metal’ salts
The presence of strong alkali in the reaction chamber
of other aromatic carboxylic acids having at least three 15 produces an aromatic monocarboxylic salt. I have found
carboxyl groups in the molecule.
that the reaction may be controlled by the precise con
I have found that industrially useful aromatic dicar
ditions of my process to prevent splitting off of all but
boxylic and polycarboxylic acids are obtained in a very
one carboxyl group so that an aromatic dicarboxylic acid
simple fashion by heating alkali metal salts of aromatic
carboxylic acids having at least three carboxyl groups 20
in the molecule to temperatures above 300° C. up to
about 500° C., and thereafter converting the alkali metal
smts obtained thereby into the corresponding free acids
salt is obtained.
'
The best results are obtained if the starting material
is provided in a thoroughly dry state. If the alkali metal
salts of the aromatic carboxylic acids serving as the
starting materials are produced, for example, by neu-,
tralizing aqueous solutions of the carboxylic acids with
Aromatic polycarboxylic acids which may be employed
alkali metal hydroxide, the dissolved alkali metal salts
as starting materials for the process according to the pres
formed thereby may be transformed into dry powders
ent invention are, for example, hemi-mellitic acid, tri
by any suitable drying process, for instance by spray
drying, drum-drying and the like. If necessary, the sub
mellitic acid, trimesitinic acid, mellophanic acid, prehnitic
acid pyromellitic acid, benzene-pentacarboxylic acid and
stantially dry powder may then be subjected to a further
mellitic acid, as well as mixtures of such acids. Mixtures 30 drying procedure just prior to its use in the present proc
containing these acids are produced, for instance, by oxi
ess, especially if the powder has been stored, in order
dation of alkylbenzenes or by oxidation-degradation of
to remove small residual amounts of moisture.
higher, possibly alkylated, ring systems, or from car~
I have further found that the reaction according to
the present invention is favorably in?uenced by the pres
bonaceous substances such as graphite, mineral coal,
ence of catalysts. Metals and their compounds in gen
brown coal, peat, wood, lignin, coal extracts, tars, pitch,
eral have proved to be suitable catalysts, especially zinc,
asphalts, coke, petroleum residues or their transformation
products by treatment with nitric acid or oxygen and
cadmium, mercury, iron, lead, manganese and cesium
and their compounds, such as their oxides, inorganic
alkalis. When benzene polycarboxylic acids are used, the
product is predominantly terephthalic acid.
40 or organic acid salts, complexes and metal organic com
pounds. The amount of catalyst added to the starting
Further suitable as starting materials for the process
or various salts of such acids.
material to produce the desired catalytic e?ect may vary
within rather wide limits, namely from ‘0 to 15% by
weight, but preferably from 0.5 to 5% by weight, based
ring systems, especially bicyclic aromatic ring systems,
such as diphenyl-2,3,4’-tricarboxylic acid, naphthalene 45 on the Weight of starting material. Most advantageously,
the catalyst is provided in a ?nely divided state and uni
l,4,5-tricarboxylic acid, diphenyl-Z,3,5,6-tetracarboxylic
according to the present invention are those aromatic
polycarboxylic acids which are derived from polycyclic
acid, diphenyl-3,4,3’,4'-tetracarboxylic acid, naphthalene
formly distributed throughout the starting material, which
may, for example, be accomplished by dissolving or
l,4,5,8-tetracarboxylic acid and the like.
be produced by well known methods, such as by neu- '
suspending the catalyst in an aqueous solution of the
salts serving as the starting material and thereafter spray
drying, drum-drying or otherwise evaporating the sus
pension or solution to produce a dry, ?nely divided,
tralization of the particular aromatic carboxylic acid with
homogeneous powder. However, the catalyst may also
The above indicated aromatic carboxylic acids or the
mixtures thereof are employed as starting materials in
the form of their alkali metal salts. These salts may
be added to the starting material in conjunction with
an alkali metal hydroxide to form the salt which is to be
later used as the starting material. The potassium and 55 well known carrier substances, such as kieselguhr.
In addition to catalysts, the reaction mixture may also ‘
sodium salts are especially suitable, because they are
readily accessible and relatively inexpensive to produce.
comprise inert liquid or solid additives. For example, the
reaction in accordance with the present invention maybe
carried out in the presence of sand, metal powders, metal
shavings, kieselguhr, activated charcoal and inert salts
such as potassium carbonate, sodium carbonate, or sodi
While the lithium, rubidium and cesium salts, as well as
thallium salts, produce equally satisfactory results, their
use as starting materials for the process herein disclosed
is of only secondary importance because of their rela
um sulfate. The addition of such inert materials in many
tively high cost. In some cases itis advantageous to
employ the acid alkali metal salts of the aromatic poly
carboxylic acids as the starting material in place of the
neutral alkali metal salts.
7
cases improves the physical properties of the reaction mix
In place of the inert solids, inert liquids may also ‘
ture.
65
be present during the rearrangement reaction, provided
such liquids do not decompose under‘ the conditions of
It is not necessary that the starting material contain
elevated temperature’ and pressure. Such suitable inert ;
the ?nished alkali metal salts of aromatic carboxylic
liquids are, for example, diphenyloxide,‘ diphenyl, benzene, .
acids. Equally suitable are reaction mixtures which,
naphthalene and the like.
under the conditions of the reaction, produce the alkali
metal salts in situ. For example, I have, found that the 70 The rearrangement reaction according to the’ present
invention takes place upon heating the starting material '”
desired results are also produced by heating mixtures
to temperaturesabove 300° C. up to the temperaturev at of aromatic carboxylic anhydrides or esters and suit
3,042,717
3
4
which ‘the salts of the aromatic carboxylic acids and the
reaction products begin to decompose, but below the
temperature of substantial decomposition most advan
Example II '
180 parts of benzene polycarboxylic acid mixture ob
tained from nitric acid oxidation of coal, which consisted
largely of mellitic acid and had an acid number of 881,
were partially neutralized with 70 parts of potassium hy
droxide. After evaporating the water, the resulting solid
tageously by’ heating the starting material to between
340° C. and 450° C. At temperatures above 500° C. the
starting material as well as the reaction products de
compose to' an excessive extent, so that the yields are
substantially reduced.
was ?rst heated to 150° C., as described in Example I.
Consequently, it ‘is not advanta
. Thereafter, the dry product was treated for an hour and
a half in a ?uidized bed at a temperature of’ 390° C. and
geous to carry out the reaction ‘at such extremely elevated
temperatures.
a carbon dioxide pressure of 80 atmospheres. The car
bon dioxide was recycled with the aid of a recycling
pump. The reaction product was then worked up as
In order to avoid local overheating and sinterin g of the
reaction mixture, it is advantageous to agitate the starting
materials, for example by heating the reaction mixture in'
autoclaves provided with a stirring device, in rotary auto
described in Example I and yielded 65.5 parts terephthalic
claves, in rotary furnaces or in ?uidized bed systems. 15
Similarly, adequate uniform heat distribution may be pro
vided by distributing the reaction mixture in thin layers,
0 either in conjunction with or without agitation. However,
good yields vare also obtained without the application of
any of these measures, as long as means are provided to
prevent local overheating.
'
The best results are obtained if oxygen is substantially
excluded from the reaction space during the rearrange
ment reaction according to the present invention. For
this purpose it is advantageous to heat the starting mate
rial in the presence of inert gases such as carbon dioxide,
nitrogen, methane,~benzene, carbon monoxide and the
like. Particularly good yields are obtained if the rear
acid.
Example III
15 parts of the tripotassium salt of hemimellitic acid,
admixed with 0.75 part cadmium oxide, were heated at
470° C. for ?ve minutes in a glass vessel on an aluminum
block (the temperature was measured in the aluminum
block). During the run, carbon dioxide was passed over
V
the reaction mixture. The raw product thus obtained
was extracted with boiling water and after ?ltration the
‘resulting solution was admixed with hydrochloric acid.v
25 .The precipitated terephthalic acid was repeatedly washed
with hot Water and subsequently dried at 130° C. The
. yield was 4.2 parts of terephthalic acid.
Example IV
rangement reaction above described is carried ‘out in an
atmosphere of carbon dioxide under pressure. However, 30
elevated pressures are not essential to satisfactory yields;
the rearrangement reaction will also proceed at subatrnos
pheric and atmospheric pressures.‘
15 parts of the tripotassium salt of trimellitic acid, ad
mixed with 0.75 part cadium carbonate, were heated for
?ve minutes at 420° C., as described in Example III. The
~
raw product was then worked up in the manner described
The various dicarboxylic and polycarboxylic acid alkali -
in that example and yielded 4.2 parts of terephthalic acid.
metal salts formed by the rearrangement reaction may be 35
Example V
separated from each other, from untransformed starting
material and from the catalyst by a number of known
methods.
' v40 parts of the tripotassium salt of hemimellitic acid
in admixture with 4 parts cadmium benzoate were heated
for one hour at 420° C. in a rotary autoclave in an atmos
For example, a .very suitable method com-7
prises dissolving the reaction product mixture in water,
?ltering ofI' insoluble components, precipitating the acids
or their acid alkali metal salts by acidifying the ?ltrate
with acid agents such as ‘sulfuric acid, hydrochloric acid
or carbon dioxide, and separating the precipitated acids
or acid salts from each other, for example by extraction
40 phere of carbon dioxide under pressure. The initial pres
. sure of carbon dioxide was 58yatmospheres and the ?nal
pressure was 194 atmospheres. Upon'working up the re-V
action product in the above described manner, 12.5 parts
terephthalic acid were obtained.
'
with hot water.
Any untransformed starting materials 45,.
Example Vl
may readily be recovered from the aqueous solution and
10.0 gm. trimesitinic acid, together with 30.0 ‘gm. potas-.
may be reused as starting materials for subsequent re
arrangement reactions, The free acids or their alkali
metalsalts may, vif desired, be-transformed into their
derivatives such as their methyl esters by methods well
known in chemical industry.
.
The, following examples will further illustrate my in
' vention and enable persons skilled in the art to understand
sium carbonate and 2.0. gm. cadmium ?uoride, were
’ milled and the resulting mixture was heated in an auto
clave at. an initial carbon dioxide pressure of 50 atmos
pheres for four hours at 420° C. Upon working up the
reaction mixture in the, above described manner, 6.3 gm.
_ terephthalic acid were obtained. r
the invention more completely; It is understood, ‘how
ever, that the invention is not limited to these particular
examples.
e
'
'
'
Example
I
Example VII
10.0 gm. trimesitinic acid were milled with 30 gm.
sodium carbonate and 2.0 gm. cadmium ?uoride, and the
mixture was heated for ,four hours at 420° C. in an auto
clave at an initial carbon dioxide pressure of 50 atmos
165 parts of the dipotassium salt'of pyromellitic'acid ‘
and 5 parts potassium carbonate were heated for one hour
pheres. The reaction mixture was worked up in the above
at about 150° C. in a rotary autoclave in order to remove 60 described manner and yielded 2.7. gm. terephthalic acid.
traces‘ of moisture. Thereafter, carbon dioxide was intro
duced to a pressure of 50' atmospheres gauge and the‘
autoclave was heated'pto about 400° C. ‘for six hours.
During this time, the pressure rose 'to about 122 atmos
’' ' pheres. After cooling, the reaction mixture was dissolved 65
in 1007parts water and‘ the terephthalic acid was precipi
tated-from the solution by' acidi?cation thereof with sul
' {uric acid. . The precipitated acid wasseparated from the
hot solution, which contained the untransformed carbox
, ylic‘ acid mixture.
61.5 parts terephthalic acid were ob; , 70
tained from'this' ?rst run, and by subjecting the benzene
polycarboxylic acid mixture to-the above ‘reaction a second -
'time,17.9 ‘additional parts of; ‘terephthalic acid were ob
a
' Example VIII
An intimate mixture of 25.0 gm. of, the tripotassium
salt of trimesitinic acid with 25.0 gm. potassium carbon
ate and 4.0 gm. zinc ?uoride was heated for three hours
at 340° C. at an initialcarbon dioxide pressure of 50
atmospheres. The reaction mixture was worked up in
the above described manner and yielded 7.3 gm. tereph
thalicracid.
I
?
,
,
.
,
Example IX _‘
‘A’ mixture ‘of 25.0 gm. of the potassium 'salt of
trimesitinic acid with 25.0, gm. potassium carbonate and
2.0 gm. cadmium ?uoride, was heated for three hours at
tainedin such pure form that‘it could'be used for the‘
75 430° C. at an'initial nitrogen pressure of 100 atmospheres.
' production of polyesters without further puri?cation.
3,042,717
5
6
The reaction mixture was worked up in the above de
scribed manner and yielded 9.0 gm. terephthalic acid.
benzene polycarboxylic acid with at least three carboxyl
While I have disclosed certain speci?c embodiments
of my invention, it will be apparent to persons skilled in
and the decomposition temperature of said starting ma
terial and the reaction product in a substantially anhy
drous, substantially oxygen-free atmosphere of an inert
groups in the molecule to a temperature between 300° C.
the art that the invention is not limited to these embodi
ments and that various changes and modi?cations may be
' made without departing from the spirit of the invention
or the scope of the appended claims.
This application is a continuation-in-part of my pre
gas, in the presence of a catalyst containing a metal se
'lected from the group consisting of zinc, cadmium, mer
cury, iron, lead, cerium, manganese, converting the alkali
metal salts of terephthalic acid formed thereby into the
vious application Serial Number 582,087, ?led May 2, 10 corresponding free acid, and separating said free acid
from the reaction mass.
1956, now abandoned.
7. The method of producing terephthalic acid from
I claim:
mixed aromatic polycarboxylic acids having at least three
1. The process of producing terephthalic acid, which
carboxyl groups per aromatic ring, which consists essen
consists essentially of heating an alkali metal salt of a
benzene polycarboxylic acid with at least three carboxyl 15 tially of converting said aromatic polycarboxy-lic acids
into the corresponding alkali metal salts thereof, heating
groups in the molecule to a temperature between 300° C.
said salts to above 300° C. and below the temperature at
and the decomposition temperature of said starting ma
which substantial decomposition takes place, in a substan
terial and the reaction products in a substantially anhy
tially dry inert atmosphere, to convert said salts into alkali
drous, substantially oxygen-free atmosphere of an inert
gas converting the alkali metal salts of terephthalic acid 20. metal salts of terephthalic acid and separating the tereph
thalic acid from the remainder of the reaction mixture
formed thereby into the corresponding free acid, and sep
by dissolving said mixture in water and acidifying said
arating said free acid from the reaction mass.
mixture to precipitate terephthalic acid therefrom.
2. The process according to claim 1, wherein the inert
8. The process according to claim 1 wherein the ben
gas is carbon dioxide.
3. The process according to claim 1, wherein the inert 25 zene polycarboxylic acid is pyromellitic acid.
gas is nitrogen.
9. The process according to claim 1 wherein the ben
4. The process according to claim 1, wherein the inert
zene polycarboxylic acid is mellitic acid.
gas is selected from the group consisting of carbon diox
10. The process according to claim 1 wherein the ben
ide, nitrogen, methane, benzene and carbon monoxide.
zene polycarboxylic acid is hemimellitic acid.
5. The process of producing terephthalic acid, which 30 11. The process according to claim 1 wherein the ben
consists essentially of heating an alkali metal salt of a
zene polycarboxylic acid is trimellitic acid.
benzene polycarboxylic acid with at least three carboxyl
12. The process according to claim 1 wherein the ben
groups in the molecule to a temperature above 300° C.
zene polycarboxylic acid is trimesitinic acid.
but below the decomposition temperature of said starting
material and the reaction products in a substantially an
hydrous, substantially oxygen-free atmosphere of an inert
References Cited in'the ?le of this patent
gas, at elevated pressures, converting the alkali metal salts
UNITED STATES PATENTS
of terephthalic acid formed thereby into the correspond
ing free acid, and separating said free acid from the reac
tion mass.
6. The process of producing terephthalic acid, which
consists essentially of heating an alkali metal salt of a
40
1,885,834
Jaeger _______________ __ Nov. 1, 1932
2,020,505
2,734,914
Jaeger _-_‘ ___________ _._ Nov. 12, 1935
McKinnis ____________ __ Feb. 14, 1956
2,863,913
Raecke et al ___________ _._ Dec. 9, 1958
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