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Патент USA US3071624

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United States Patent O?fice
1
3,071,614
Patented Jan. 1, 1963
2
Examples of aromatic hydrocarbon carboxylic acids,
3,071,614
,
and of typical aliphatic substituted aromatic feedstocks
which may be oxidized with molecular oxygen in the
presence of a metal oxidation catalyst (preferably in the
conjoint presence of an oxidation catalyst and bromine)
to produce them, are:
TABLE I
PURIFICATION OF AROMATIC ACIDS
James 0. Knobloch, Hobart, lind., assignoi- to Standard
Oil Company, Qhicago, HL, a corporation of Indiana
No Drawing. Filed Oct. 25, 1957, Ser. No. 692,272
7 Claims. (Cl. 260-525)
This invention relates to aromatic carboxylic acids.
More particularly it relates to the puri?cation of aromatic
hydrocarbon carboxylic acids (“aromatic acids") derived 10
from the metal-catalyzed liquid phase oxidation of ali
phatic-substituted aromatic compounds with molecular
Group
Benzene Carboxylic _______ __
Acid
Feedstocks
Benzoic _________ __
Toluene, ethylben
o-Phthalic- _. _____
o~Xylene, indene,
Isophthalic ______ __
m-Cyrnene, m
zene, stryene.
oxygen. Such aromatic acids are often contaminated
with traces of a tar-like yellowish or tan-colored oxida
o-toluic acid.
xylene, rn-diacetyl
tion byproduct which creates a troublesome puri?cation 15
problem in the recovery of pure aromatic acids. These
byproducts moreover inhibit crystallization when it is at
tempted to recrystallize aromatic acids from aqueous
benzene.
Terephthalic ____ __
p-Xylene, p-tolual
dehyde, hydroxy
cumic acid.
Pseudocumene.
Mesitylene.
solutions to such an extent that a byproduct-contaminated
Prehnitene.
Hexamethylbenzene.
solution containing ?ve times the saturation concentra 20
Alkyl-benzene Carboxylic-.tion of aromatic acids remains stable for Weeks despite
shock-chilling and seeding.
Durene.
m-Xylene.
Hemiinellitene.
phthalic.
An object of the present invention is to provide an im
proved process for purifying aromatic hydrocarbon car
t-Butyl-o-phthalic- t-Butyl-orthoxylene.
p-Cumic ________ __
phase molecular-oxygen oxidation of aliphatic-substituted
Polynuclear Aromatic _____ ._
aromatic compounds. A further object is to purify aque
ous solutions of aromatic acids. Yet another object is to
remove tar-like colored oxidation byproducts which in
p-Cymene.
m-Ethyl henzoic_. rn-- Iethylethyl
benzene.
Durylie___
Durene.
boxylic acids derived from the metal-catalyzed liquid 25
Diphenic ____ __
Phenanthrene.
Naphthalene 2,
dicarboxylic.
2,6-Dimethyl naph
Naphthoic ______ __
Methyl naph
thalene.
thalenes.
Naphthalic _____ -_ Acenaphthene.
hibit crystallization of aromatic acids from aqueous solu 30
tions. An additional object is to provide an aromatic acid
puri?cation process in which the treating agent may be
Liquid phase molecular-‘oxygen oxidation processes are
regenerated. Other objects will become more apparent
conducted according to known procedures at a tempera
‘as the description of this invention proceeds.
ture in the range of 60 to 275° C., and preferably 170
‘ In accordance with the objects above, it has now been 35 225° C. The pressure may be from atmospheric to about
discovered that aqueous solutions of aromatic hydrocar
bon carboxylic acids which are contaminated by colored
100 atmosphere or more, and is desirably about 28 atmos
pheres. Air, air containing a diluting proportion of an
byproducts of the metal-catalyzed liquid phase molecular
inert gas, commercially pure oxygen and ozone are com
oxygen oxidation of aliphatic-substituted aromatic com
mon sources of moleculartoxygen.
Oxidation catalysts
pounds may be puri?ed by treating the solution with 4-0 are soluble forms of one or more metals, preferably salts
adsorbent alumina. A major portion of the byproducts
of the known heavy metal oxidation catalysts such as
are thus adsorbed on the alumina, and the aromatic acids
may be recovered in a pure state from the treated solu
tion by such convenient means as crystallization and/or
cerium, cobalt, manganese, lead, chromium, nickel,
evaporation. Alumina treating may if desired be con
ducted continuously, and may also be integrated with
other aromatic acid separation and puri?cation steps.
Liquid phase oxidations employing molecular oxygen
molybdenum, and tungsten. The metal catalyst may be
45
‘added to the reaction in elemental form, or as an ionic
compound such as cobalt acetate or ammonium molyb—
date, or in combined form such as tetraethyllead or cobalt
‘versene. Similarly bromine may be elemental, in an ionic
compound such as HBr or ammonium bromide, or as
tetrabromoethane or benzyl bromide. The oxidation re
50
tremely important in the commercial preparation of aro~
action is advantageously conducted in the presence of an
and a metal oxidation catalyst have recently become ex
matic acids. In these processes an aliphatic hydrocarbon
substituent on an aromatic ring is oxidized to a nuclear—
ly-attached carboxylic acid ‘group. The aliphatic sub
stituent may be methyl, normal, secondary, tertiary or
‘ inent solvent for the feedstock and catalyst; the solvent
preferably being a saturated monocarboxylic acid having
‘from 2 to about 8 carbon atoms in the molecule such as
acetic acid, but may be such diverse liquids as Water,
alicyclic and may be either saturated or unsaturated. An 55 benzophenone, benzonitrile, octyl alcohol, mineral oil, or
aromatic having more than one aliphatic substituent may
chlorinated hydrocarbons.
require the conjoint presence of a metal oxidation catalyst
Aromatic acids are separated in crude form from a
and bromine as the catalyst to effect the production of
reaction mixture by any one or more of a variety of
high yields of aromatic polycarboxylic acids. Since poly
carboxylic acids are more di?icult to produce than mono
carboxylic ‘acids, by control over the reaction conditions
it is possible to favor the oxidation of less than all of
the aliphatic substituents in order to produce alkyl-sub
stituted aromatic mono- or polycarboxylic acids.
Thus
the characterizations “aromatic hydrocarbon carboxylic
60 physical or chemical techniques. Insoluble aromatic acids
such as isophthalic or terephthalic may be ?ltered, centri
fuged, or decanted from the mixture at elevated tempera~
tures, and even the more soluble acids such as benzoic
and phthalic may be removed by these techniques from
a cooled reaction mixture. Aromatic acids may also be
acids” or “aromatic acids” as employed in the speci?ca
obtained in very impure form by merely evaporating Water
and the solvent, or by extraction with selective solvents.
tion and in the claims relate to mononuclear ‘and poly
nuclear aromatic compounds which have at least one
nuclearly-attached carboxylic acid group and which may
Since it is often more convenient to resolve mixtures of
isomeric aromatic acids than to separate isomers of the
in addition have one or more hydrocarbon substituent
such as an alkyl or alkenyl group.
feedstock, quite commonly an isomeric mixture of ali
phatic-substituted aromatic compounds is oxidized at one
time, and a combination of one or more physical and/ or
3,071,614
4
3
chemical separation techniques employed to resolve the
mixed aromatic acids in the reaction mixture.
In all of the foregoing separations—whether the aro
matic acid is recovered as a ?ltered solid, a distillation or
evaporation bottoms, or as an extract—the aromatic acids
are contaminated by deep yellow or tan-colored oxidation
byproducts. When concentrated, these byproducts have a
tar~like consistency. They boil within a very wide range
of temperature and hence‘ cannot be removed by distil
lation. Extensive investigation has shown that tar-like
byproducts from the oxidation of a single alkylbenzene
aqueous aromatic acid solutions are preferably either of
two types, the so-called “activated alumina” and “ac—
tivated bauxite.” Both are forms of aluminum oxide
which have ‘been heated to remove most of the bound
water and to provide an adsorbent having a surface area
between about 50 and 500 square meters per gram. “Ac
tivated alumina” is obtained by heating the product of
the Bayer process for the preparation of alumina. The
Bayer process involves extracting bauxite (aluminum ore)
with hot caustic, cooling and diluting the extract with cold
water to hydrolyze and precipitate the alumina, and cal
cining the precipitated alumina. “Activated bauxite” is
may have phenolic, acidic, ester, carbonyl, and ole?nic
merely heat-activated natural bauxite. Both products are
groups, and as a consequence are soluble to some extent
stable crystalline materials which are supplied commer
in most common solvents for aromatic acids.
cially in hard grains, lumps, balls, and tablets of various
Attempts to remove these byproducts from aromatic
mesh sizes. Other heat or chemically activated alumina
acids by prior-art methods have failed to suggest a proc—
containing materials which are insoluble in water may be
.ess suitable for commercial adaptation. For example,
employed with somewhat lesser e?ectiveness.
aromatic acids produced by the Willgerodt oxidation of
In the practice of the present invention, the initial step
an alkylbenzene with ammonium sul?de, ammonium sul
fate, and water are decolorized by passing the reaction 20 is obtaining an equeous solution of the aromatic acid
or the mixture of aromatic acids. This may be done
mixture thru activated charcoal, but When it was at
either by dissolving the acid in water, extracting a soluble
tempted to purify byproduct-contaminated ammonium
acid from a less-soluble one with Water, extracting a
phthalate solutions with charcoal or with alumina, it was
distillation bottoms with water, or inherently by conduct
found that the phthalic acid could not be recovered from
ing the oxidation in Water or a water-containing inert
the treated solution in an acceptable yield. Adsorbent
solvent. The aqueous solvent used for dissolving the
alumina will not purify aqueous solutions of alkali metal
salts or aromatic acids, and of course only the very vola
aromatic acid may be Water alone or may be water with
tile aromatic acids may be puri?ed by distillation. Treat
ing aqueous solutions of alkali metal salts of liquid-phase
minor amounts of solubilizing agents such as the lower
alcohols, e.g. methanol, or the lower saturated aliphatic
acids as acetic, but these are not essential.
catalytic aromatic acids with charcoal is extremely ef
fective, but requires the use of stoichiometric amounts
of alkalies to dissolve the aromatic acids and then equal
quantities of mineral acids to “spring” the treated aro
matic acids.
In contrast to the methods described above, the process
of this invention, i.e., purifying aqueous aromatic acid
solutions by treating with adsorbent alumina, is simple,
?exible, highly effective, and very economical. It is also
the only process which permits regeneration of the ad
The necessary quantity and temperature of the dissolv
ing water depends upon the solubility of the aromatic acid
and also on whether a single aromatic acid or a mixture
of acids is to be dissolved. As will be shown hereinafter,
aromatic acids are more soluble in water containing other
aromatic acids than in pure water. Since most aromatic
acids are comparatively insoluble it is desirable to conduct
the dissolving and alumina treating at an elevated tem
perature, ie from about 20 to 300° C. or higher, and
sorbent. No extraneous reagents are necessary, except 40 preferably from 50 to 100° C. At temperature substan
tially above 100° C. pressure containing equipment is re
for a small amount of an alkali used for adsorbent re
quired. Table II below presents the solubility data at
generation, which affords appreciable cost savings and
various temperatures for some of the more common aro
reduces sources of possible contamination. Moreover,
matic acids, together with the vapor pressure (in pounds
the process may be integrated with aromatic acid separa
tion processes such as water extraction of orthophthalic 45 per square inch absolute) of pure water at the respective
temperatures shown. In the table benzoic acid is desig
acid from orthophthalic-isophthalic-terephthalic mixtures,
nated BA, ortho-phthalic acid PA, phthalic anhydride
or the extraction of an isophthalic acid concentrate from
isophthalic-terephthalic mixtures with hot water wherein
PAN, isophthalic acid IA, terephthalic acid TA, and
the extract solutions may be puri?ed by alumina treat
trimellitic acid TMLA.
TABLE II
Solubility in grams per 100 grams Water
Pressure,
Temp, ‘’ C.
p.s.i.a.
IA + TA
BA
PA
PAN
IA
TA
_ TMLA
IA
TA
0. 011
0. 0014
1. 75
0.0046
______ __
0.037
0.32
.
3.3
51
>100
After dissolving the aromatic acid (together with con
ment. Further, equipment corrosion is negligible in con
taminating oxidation byproducts and any oxidation cat
trast to acid-springing techniques. Process control is sim
alyst) in water, the resulting solution is advantageously
pli?ed by the use of White adsorbent alumina crystals
?ltered to remove insoluble polymers and any undissolved
since adsorbent eifectiveness ‘and capacity may be moni
tored visually by observing the color of the alumina. 70 aromatic acid. This operation may be conducted in a
conventional pressure ?lter as for example a Shriver plate
And ?nally the product may be recovered merely by
and-frame ?lter press employing canvas ?lter cloths.
cooling the puri?ed solution to crystallize the aromatic
The adsorbent alumina may be disposed either in one
carboxylic acids, or by evaporating the water, or by a
or more ?xed “percolation process” beds or it may be
combination employing both.
Aluminas suitable for treating byproduct-contaminated 75 slurried with the solution either ‘batchwise, continuously,
5
3,071,614
or intermittently in a “contact process.” In a percolation
operation the adsorbent preferably has a mesh size
between about 5 and 90 US. standard screen size, and
the solution is passed through the bed either up?ow or
downflow. Since adsorbent alumina is normally a glassy
white solid, if the adsorption vessel is provided with
portholes or other viewing means it is possible to visually
monitor the saturation of the alumina by following the
progression of color through the bed, and discontinuing
the flow of solution when the bed becomes completely
colored. 'Flow rates through the bed are regulated to
give between about 5 minutes and 1 hour or more con
tact time, preferably a time in excess of 10 minutes. The
necessary quantity of alumina depends on the amount of
none of the sensible heat content of the solution can be
recovered by heat exchange, as may be accomplished
when aromatic acids are recovered by cooling or evap
orating the solution.
As a. preferred embodiment of the aromatic acid re
covery step, the puri?ed solution is cooled by indirect
heat exchange with the water used for initially dissolv
ing the crude aromatic acid. The temperature of the
cooled puri?ed solution may be any temperature at
which the aromatic acid has a solubility less than its
saturation concentration in the aqueous solvent. Cooling
may be quite rapid in which event the aromatic acid
crystallizes in the form of tiny crystals, or may be gradual,
e.g. over several hours, to “grow" the aromatic acid
byproducts present and the degree of byproducts re 15 crystals. The cooling rate and/or temperature may be
moval desired; it may range from 1A0, to 10 parts by
regulated if it is desired to separate more than one dis
weight per part of dissolved acid, ‘but is preferably from
solved‘ aromatic acid by selective crystallization. Since
1/2 to 2 parts. The percolation temperature may range
crystallization from a treated solution may commence
from the temperature used for dissolving the aromatic
almost immediately upon reaching the saturation temper
acid to as low as the saturation temperature; although, as 20 ature, it is desirable to effect cooling and crystallization in
will be shown by the examples hereinafter presented, per
a scraped-surface jacketed tank or scraped-wall tube
colation can be employed with supersaturated solutions,
type heat exchanger to prevent crystal accumulation on
this procedure is undesirable in a percolation process as
the vessel walls. Filtration, centrifugation, decantation,
crystallization of aromatic acids from supersaturated solu
or hydrocyclones may be used to separate the aromatic
tions inevitably occurs in the bed. Percolation adsorption 25 acid crystals from the mother liquor. The mother liquor
is very advantageously used when operating at pressures
may be evaporated entirely or in part to recover addi
substantially in excess of atmospheric.
tional aromatic acids or, and preferably, is recycled to
As an alternate to percolation, the contact process may
the aromatic acid dissolving step.
be employed wherein ?nes (approximately l00-200
The recovered aromatic acid crystals are pure white
mesh) or larger particles of the adsorbent are held in 30 or only slightly tinged with yellow and may be air dried
suspension in a fluid stream from which they are sep
arated by ?ltration after a sufficient time of contact. The
or dried under vacuum to obtain pure aromatic acids of
commerce.
contact process may be conducted either by slurrying
The adsorbent alumina employed for purifying the
?nes or larger adsorbent particles with the solution in an
aqueous aromatic acid solution may be regenerated and
open tank or in a pressure vessel or by injecting ?nes into 35 reused by washing with a solvent for the colored oxida
a pipeline carrying the solution, which pipeline is of suf
ficient length to provide a suitably long contact time.
Again the contact time is preferably within 5 minutes
to 1 hour, optimally more than 10 minutes, and quan
tion byproducts.
Preferably the solvent comprises an
aqueous solution of an alkali metal hydroxide or other base
compound such as a carbonate. A caustic solution con
taining from about 1 to 10% sodium potassium or lith
ium hydroxide is very effective for this purpose. After
regeneration, the adsorbent bed is washed with de
mineralized water to obviate the possibility of contaminat
ing the aromatic acids with the hydroxide. The regen
observed in the contact process is that it may be em
erated bed is washed with water to a neutral pH prior to
ployed with cold supersaturated solutions yet, because
returning the bed on stream. Organic solvents such as
colored by-products removal is not quite complete,‘ 45 methanol, pyridine, chloroform, benzene, or hexane are
crystallization does not commerce instantaneously.
not effective for desorbing colored byproducts.
The treated solution may contain dissolved metal
Various embodiments of the present invention are
tities of alumina similar to those in percolation are
required. Separation of the adsorbent particles may be
accomplished by ?ltration, centrifugation, or settling, or
by the use of hydrocyclones. An interesting phenomenon
oxidation catalyst, traces of dissolved alumina, and/or
further illustrated by the examples below.
bromides. These may be removed by passing the solu
tion through a strong acid-acting cation exchange resin 50
Example I
to remove the metal catalyst and alumina and by passing
the solution through a weakly basic anion exchange resin
Adsorbent alumina was employed in a contact process
to purify a byproduct-contaminated supersaturated ortho
to remove the bromide. With ion exchange resins (par
ticularly of the anion type) temperatures substantially
phthalic acid solution. The solution was obtained by heat
ing 70 g. of o-phthalic acid that was contaminated by
in excess of about 150° C. are undesirable because of
some solubility of the resin in hot water.
colored oxidation byproducts of the bromine~promoted
metal-catalyzed air oxidation of orthoxy-lene in an acetic
The alumina treated and preferably deionized solu
tion may then be treated for recovery of the aromatic
acid medium in 1 liter of water to boiling, cooling to 25 °
C. and ?ltering off solids.
acid. While a variety of chemical and physical separa
tion means are available, two physical methods are out 60
By titration with a standard base, the solution, having
standing with respect to economy and ef?ciency of opera
a deep yellow color, was found to contain 3.69 grams of
tion. In the ?rst, the solution is cooled in order to
ortho-phthalic acid per 100 ml. of solution at 25° C.
crystallize the aromatic acid therefrom, while in the
Since saturation at this temperature is a concentration of
second, a part or all of the water is evaporated to effect
only 0.74 gram per 100 ml., the solution had 400% more
crystallization. Both methods may be employed simul
aromatic acid than at saturation, yet was quite stable.
taneously or concurrently; for example the solution may
Evaporating an aliquot portion‘ con?rmed the ortho
phthalic acid concentration. The solids obtained on
evaporation had an acid number of 667; the theoretical
acid number of phthalic acid is 675.
lization and evaporation ,the solution is ?ashed into a 70
A 100 ml. sample of the original solution was added to a
lower pressure region where part or all of the water is
beaker containing 1.4 grams of adsorbent alumina manu
evaporated, leaving crystals or a crystal-containing con
factured by the Fischer Scienti?c Company and designated
centrated slurry of cold water and aromatic acids. Flash
grade A—54~l/ 2, 80-200 mesh. The suspension was stirred
ing has the advantage of reducing equipment costs but is
for 20 minutes at room temperature and then ?ltered
somewhat expensive in terms of heat requirements as 75 through a tared M~porosity fritted glass crucible. The re
be cooled to crystallize aromatic acids which are then
?ltered off, and the mother liquor evaporated to recover
additional aromatic acids. By concurrent use of crystal
3,071,814
covered alumina weighed 1.497 grams after air drying and
was light yellow in color.
of glass wool. The alumina ?lled the column to a depth
of 15 inches above the supporting glass wool. The col
- The ?ltrate was almost colorless.
umn was heated to 94° C. by circulating oil from a con
Standing overnight
at room temperature caused phthalic acid to precipitate.
The solid material was ?ltered off and found to weigh
2.566 grams after air drying. This represents a 69%
recovery of phthalic acid. The solids had an acid num
ber of 673 (theoretical is ‘675) and contained only a trace
of ‘the original yellow color. The ?ltrate was evaporated
to dryness and 0.965 gram (26% of the original ortho 10
phthalic acid) of very white ortho-phthalic acid was re
covered.
'
Thus a 96% recovery of white almost pure ortho
phthalic acid was obtained.
stant temperature bath through the jacket.
A total of
400 cc. of a deep yellow aqueous solution of ortho-phthalic
acid containing 6.10 grams of acid per 100 ml. (24.40
grams ortho-phthalic acid in all) was eluted through the
column in 5i0—55 minutes at 94° C. with 2 p.s.i.g. nitrogen
pressure.
At this temperature, the solution was not
saturated with respect to phthalic acid.
After the yellow solution had been eluted through the
column, the color band extended about 11/: inches down
from the top of the column, suggesting an ultimate ef
:Eective adsorbent life of 160 cc. of solution per gram of
15 alumina. The solution left the column having only a
Example [I
trace of a very light green color. On cooling to 20° 0.,
An alumina percolation operation at room temperature
10.143 grams (41.5%) of ortho-phthalic acid having a
was employed to purify the supersaturated solution of Ex
faint trace of yellow color was deposited. The cooled
ample I.
solution was ?ltered to separate the solid ortho-phthalic
The bed was prepared by slurrying 25 grams of Fischer 20 acid, and the water-White ?ltrate evaporated to yield
A-541/2 alumina with 98 cc. of water saturated with
an additional 9.69 grams (37%) quantity of ortho
reagent grade ortho-phthalic acid at 25° C., and the sus
phthalic acid that showed no trace of any color.
pension poured into a glass column to form a bed 13%
The adsorbent bed was washed with three 100 ml. por
inches high by % inch I.D. which was full of liquid. To
tions of water at 94° C. The wash water had only a
this column was added 100 ml. of the deep-yellow-colored 25 trace of a very light green color. The color band on
byproduct - contaminated supersaturated ortho - phthalic
the alumina appeared unaffected by the hot wash water.
solution of Example I. With nitrogen pressure (4 p.s.i.g.)
The wash water eluted 3.05 grams (12.5%) of ortho
this yellow solution was eluted down through the column
phthalic ‘acid.
.
in 10 minutes, leaving a color band at the very top of
Thus a total of 22.88 grams of almost colorless ortho
the column. An additional 100 ml. of the same contami 30 phthalic acid was recovered. This represents 914% of the
nated solution was added to the column. After 17 hours
vortho-phthalic acid charged.
'
under the same nitrogen pressure only 88 grams of solu
Example V
tion had been eluted ‘from the second 10 ml. charge. This
A
byproduobcontaminated
aqueous trimellitic acid solu
indicated that the supersaturated solution was depositing
solid ortho-phthalic acid within the column which was 35 tion was alumina treated in a percolation operation at
26° C. The solution was unsaturated with respect to
plugging the adsorbent bed.
The eluted solutions were water White and were evap
orated to recover 3.22 grams of perfectly White ortho
trimellitic acid at the treating temperature.
The trimellitic acid was prepared by oxidizing pseudo
cumene with air in an acetic acid solvent and in the pres
phthalic acid crystals. A total of 7.82 grams of ortho
40 ence of a cobalt-manganese~bromine catalyst. The tri
phthalic acid had been added to the column.
mellitic acid was ?ltered from the oxidation reaction mix
Example III
ture and given an initial puri?cation by recrystallization
from water. Sixteen grams of the recrystallized acid
A deep yellow supersaturated aqueous ortho-phthalic
(acid number 798; theoretical acid number is 801) having
acid solution was alumina treated in a contact operation
45 a APHA color in excess of 500 (solution color in di
at 70° C.
methylformamide) was dissolved in one liter of water
The original solution was prepared as in Example I
at 26° C.
and found by titration to contain 3.64 grams of ortho
Fischer alumina (A-541/2, 80-200 mesh, 25.0 grams)
phthalic acid per 100 ml. of solution, representing super
was prepared by slurrying 25.0 grams of the alumina with
saturation at room temperature to the extent of about
2.94 grams per 1100 ml. solution. It was very deep yellow 50 5 successive portions of 100 ml. of water, allowing the
coarser material to settle, and decanting the suspension
in color.
of ?nes. The coarse alumina particles were then slurried
A 100 ml. sample of this solution was slurried with
with 250 ml. of water and poured into a 25 inch high by
1.3660 grams of Fischer A-54-1/2 adsorbent alumina.
% inch diameter glass tube which had a glass wool plug
The suspension was heated in a beaker to 70° C. and held
between 70 and 80° C. for 10 minutes with stirring. The 55 sealing the bottom thereof.
All of the byproduct-contaminated trimellitic acid solu
alumina was ?ltered o?‘ at 70° C. and was tan in color.
tion was eluted downward from the bed over a 11/: hour
On cooling the ?ltrate to 40° C., crystallization com
period. No attempt was made to wash the bed free of
menced. The solution was permitted ‘to remain at room
occluded solution.
temperature for about 15 hours and produced coarse
crystalline ortho-phthalic acid having a lemon~yellow 60 After elutriation, a color band extended about 4 inches
down from the top of the column and was most intense in
color. 2.213 grams (61%) of ortho-phthalic acid was re
the ?rst 1/2 inch, thereafter tapering in intensity.
covered by ?ltration, and an additional 1.24 grams (34%)
The eluted solution was ?ltered from a small amount
by evaporation of the water-white ?ltrate.
of suspended alumina and was evaporated under vacuum
Example I V
65 at 45° C.
A deep yellow solution of ortho-phthalic acid (derived
The trimellitic acid recovered by vacuum evaporation
[from the air oxidation of orthoxylene in acetic acid in the
weighed 12.9 grams and represented 80.7% of the tri
presence of a cobalt bromide catalyst) was treated by
mellitic acid charged. It had an APHA color of approxi~
percolation through an adsorbent alumina bed at 94° C.
mately 15.
The adsorbent bed was prepared by slurrying a mixture
From the discussion and examples above, it is seen that
of 25.0 grams of Fischer A-54l/2 adsorbent alumina in
adsorbent alumina is extremely effective for removing
92 cc. of room-temperature-saturated aqueous ortho
colored tar-like byproducts from aqueous aromatic acid
phthalic acid (reagent grade) solution into a jacketed
solutions. By either percolating or slurrying the solution
glass tube. The jacketed column was 24 inches long by
with alumina it is possible to adsorb practically all of the
% inch ID. and was plugged at the bottom with a wad 75 tar-like materials from solution and permit recovery of
8,071,614
high purity aromatic acids. The process of the invention
furthermore allows the use of relatively low cost ad
sorbents and also permits of their regeneration merely by
Washing with a basic solution.
Having described the invention, I claim:
1. In a process for purifying an aromatic hydrocarbon
10
tion and crystallizing aromatic hydrocarbon carboxylic
acid therefrom.
6. Process of claim 1 wherein the temperature of said
contacting step is from about 20 to 300° C.
7. Process of claim 6 wherein the temperature of said
5
contacting step is from 50—-100° C.
carboxylic acid which is contaminated with traces of tar
like byproducts of the heavy-metal-catalyzed liquid-phase
References Cited in the ?le of this patent
molecular-oxygen oxidation of an aliphatic substituted
UNITED STATES PATENTS
aromatic compound, the improvement of contacting an 10
2,154,626
Koch ________________ __ Apr. 18, 1939
aqueous solution containing aromatic hydrocarbon car
2,726,262
Grosskinsky et a1 _______ __ Dec. 6, 1955
boXylic acid and said byproducts with adsorbent alumina,
2,744,938
Urban ________________ .__ May 8, 1956
whereby said byproducts are selectively adsorbed onto the
2,862,958
Goreau _______________ __ Dec. 2, 1958
alumina.
2. Process of claim 1 wherein said aromatic hydrocar 15
OTHER REFERENCES
bon carboxylic acid is a benzene polycarboxylic acid.
Weissberger,
Technique
of Organic Chemistry, vol. V,
3. Process of claim 2 wherein said benzene polycar
Adsorption and Chromatograph, pages 189-90 and 206
boxylic acid is ortho-phthalic acid.
(1951). (Copy in Library.)
4. Process of claim 2 wherein said benzene polycar
National Bureau of Standards, Bibliography of Solid
boxylic acid is trimellitic acid.
5. Process of claim 1 wherein aromatic hydrocarbon 20 Adsorbents, 1943 to 1953, article Nos. 3232, 919, 4498,
4611, 4667, 8977, 9038, 9081, 7920, 12747, 4835, 2689
carboxylic acid is recovered from said aqueous solution
subsequent to said contacting step by cooling said solu
and 3785. (Circular 566.)
(Copy in Division 31.)
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