FIELD OF DISCLOSURE
The present disclosure relates to a process for producing aromatic carboxylic acids.
Particularly, the present disclosure relates to a process for producing terepthalic acids
by oxidation of para-xylene.
BACKGROUND
Aromatic carboxylic acid, preferably terepthalic acid is widely used in the industry
mainly in the manufacture of polyethylene terephthalate (PET). PET finds
applications in fibers, films, containers, packaging materials, molded articles and
household consumable goods. Therefore, there is a huge demand for terepthalic acid
in the industry.
US 2833816 discloses the preparation of terepthalic acid by oxidation of para-xylene.
Oxidation is carried out in the presence of a bromide-promoted homogeneous catalyst
such as cobalt (II) acetate, manganese (II) acetate and hydrobromic acid and in the
presence of acetic acid as a solvent. The oxidation reaction is exothermic and yields
terepthalic acid together with by-products such as environmentally hazardous methyl
bromide and acetic acid over and above the oxidation gaseous products, such as
carbon dioxide and carbon monoxide.
WO 20071133978 discloses the use of expensive reactors constructed using titanium
and other corrosion-resistant metals or alloys to obviate the drawback associated with
the use of hydrobromic acid as a promoter in the oxidation reaction.
In the absence of a hydrobromic acid promoter, it is observed that para-xylene
oxidation is very slow and gives an unacceptably low yield of the desired product and
hence is not practical for commercial production. Additionally, oxidation of acetic
acid to carbon dioxide and carbon monoxide tends to increase in the absence of a
bromide promoter.
Several alternative promoters have been tested as a potential replacement for
hydrobromic acid in the conventional cobalt-manganese homogeneous catalytic
system. US 3361803 discloses the use of methylethyl ketone and acetaldehyde as an
alternative oxidation promoter, Saha et al, in the Journal of Physical Chemistry, 2004,
108, 425-531 discloses N-hydroxypthalimide and Saha et al. in the Journal of
Molecular catalysis, 2004, 207, 12 1- 127; WO 2005/000779 A2 discloses the use of
bromoanthracenes as an alternative oxidation promoter, however these alternatives are
not practical either because of their high consumption or decomposition. In the later
cases, N-hydroxypthalimide and bromoanthracenes are reported to decompose during
the oxidation process and hence continuous addition of these promoters are
recommended, which makes the process less feasible.
WO 20071133978 A2 discloses the use of Group IV, V and VI metal components or
their combinations for the para-xylene oxidation in the absence of a bromide
promoter. However, the process leads to an extremely low selectivity of the desired
terepthalic acid.
German Patent No. 2804158 discloses a bromide-free catalyst process for the
manufacture of terepthalic acid using a conventional cobalt, manganese catalyst.
US 6169170 discloses the oxidation of aromatic feed materials to the corresponding
carboxylic acids in a liquid phase reaction mixture using a homogeneous catalytic
system containing a Group IIIA metal in combination with either a Group VIIB metal
and/or cerium or a Group IVA metal, preferably zirconium or hafnium. Catalyst
compositions such as cerium acetate and zirconium acetate, ruthenium oxide and
zirconium acetate are disclosed in the '170 patent. However, practical applications of
this catalyst are limited because the water formed as a byproduct rapidly converts
zirconium (IV) acetate to zirconium (IV) oxide, and the latter easily contaminates the
solid carboxylic acid product.
Although homogeneous catalysts have been tested and commercially applied for
aerobic oxidation of methylated arenes to aromatic carboxylic acids, the literature
using heterogeneous catalysis for similar oxidation processes is very limited.
Ratnasamy et al. (Journal of Catalysis 2001, 204, 409-4 19) discloses a liquid phase
selective oxidation of para-xylene to terepthalic acid using oxo-bridged cobaltmanganese
complexes encapsulated in zeolite-Y, in acetic acid solvent. The article
discloses a moderate to high activity of the catalyst, depending on their encapsulated
nature, with appreciable selectivity in the desired product at high temperature.
However oxidation of acetic acid to unwanted gas emission remains an issue in this
process.
WO 2007/133976 discloses the use of heterogeneous catalysts consisting of
palladium, antimony and molybdenum loaded on titania support in combination with
o
several other metal acetates for the aerobic oxidation of para-xylene at 181-220 C
and 25-30 Bar. Although the '976 patent claims relatively high conversion of paraxylene
and high selectivity of terepthalic acid product, the recyclability of the catalyst
remains a concern in the process. The catalyst being costly, the overall process
becomes costly and less feasible on a large scale.
Thus, there is felt a need to develop an economically feasible and environmentally
friendly process for the production of terepthalic acid.
OBJECT
Some of the objects of the present disclosure, which at least one embodiment herein
satisfies, are as follows:
The main object of the present disclosure is to provide an economically feasible and
environmentally friendly process for the production of aromatic carboxylic acids.
Another object of the present disclosure is to provide a process for the production of
aromatic carboxylic acids using a recyclable heterogeneous catalyst.
SUMMARY
The present disclosure provides a process for producing aromatic carboxylic acids by
oxidation of methyl arenes, the process comprising the following step: reacting a
methyl arene compound with an oxidizing gas in the presence of an oxidation reaction
medium containing water and a heterogeneous catalyst to form a product mixture
containing an aromatic carboxylic acid.
o o
Typically, the process is carried out at a temperature in the range of 35 C to 220 C
and pressure in the range of 1-30 bar.
Typically, the heterogeneous catalyst is a cerium oxide compound.
Typically, the cerium oxide compound is in the form of nano- crystalline particles
having controlled spherical morphology and particle size in the range of 1 -30 nm.
Typically, the methyl arene compound is selected from the group containing paraxylene,
meta-xylene, ortho-xylene, 2,6-dimenthynapthalene and 1,5-dimethyl
naphthalene.
Typically, the oxidizing gas is oxygen gas or air.
In a preferred embodiment of the present disclosure, the methyl arene compound is
para-xylene and the aromatic carboxylic acid is terepthalic acid.
•
Typically, the oxidation reaction medium contains water. Monocarboxylic acids of
carbon content CpCg can also be used as solvents. Further metals of groups IV, V, VI
and VIII can be preferably used as a co-catalyst for enhancing the oxidation reaction.
Another aspect of the present disclosure is directed to a process for preparing the
cerium oxide compound as claimed in any one of the preceding claim, the process
comprising the following steps:
a) forming a micro emulsion solution by mixing eerie chloride in a
solvent system containing at least one solvent selected from the
group of Triton X, n-hexane/1-dodecanol, water and ethanol;
b) stirring said micro emulsion at a temperature in the range of 20 to
o
40 C till a clear micro emulsion is obtained;
c) adding at least one nitrogen compound selected from the group
containing ammonia and ethylene diamine to said clear emulsion
under vigorous stirring to yield a reacted solution;
d) heating the reacted solution at a temperature in the range of 120 to
o
200 C for a time period in the range of 10-40 hours, followed by
cooling the solution at room temperature to obtain a product solution
containing cerium oxide; and
e) isolating and further purifying the isolated cerium oxide to obtain
nano crystalline cerium oxide particles having controlled spherical
morphology and particle size in the range of 1 -30 nm.
Typically, the formation of micro emulsion in step a) is optionally carried out in the
presence of a phase transfer agent.
Typically, the phase transfer agent is Cetyltrimethylammonium bromide.
Typically, the solvent system contains a mixture of Triton X, n-hexane and 1-
dodecanol.
Typically, the solvent system contains a mixture of water and ethanol.
6
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates XRD patterns of Ce02 nanoparticle synthesized in accordance with
the present disclosure, 1(a) represents bulk XRD pattern of cubic Ce02, 1(b)
represents XRD pattern of synthesized Ce02 nanoparticles catalyst 1, and 1(c)
represents XRD pattern of synthesized Ce02 nanoparticles catalyst 2.
Fig 2 illustrates low magnification TEM image, SAED pattern and HRTEM image of
the catalyst synthesized in accordance with the present disclosure, TEM image 2(a),
SAED pattern 2(b) and HRTEM image 2(c) is for catalyst 1 and TEM image 2(d),
SAED pattern 2(e) and HRTEM image 2(f) is for catalyst 2.
Fig 3 illustrates product distribution of para xylene oxidation carried out in accordance
with the present disclosure.
DETAILED DESCRIPTION
The embodiments herein and the various features and advantageous details thereof are
explained with reference to the non-limiting embodiments in the following
description. Descriptions of well-known components and processing techniques are
omitted so as to not unnecessarily obscure the embodiments herein. The examples
used herein are intended merely to facilitate an understanding of the ways in which the
embodiments herein may be practiced and to further enable those of skill in the art to
practice the embodiments herein. Accordingly, the examples should not be construed
as limiting the scope of the embodiments herein.
The description herein after, of the specific embodiments will so fully reveal the
general nature of the embodiments herein that others can, by applying current
knowledge, readily modify and/or adapt for various applications such specific
embodiments without departing from the generic concept, and, therefore, such
adaptations and modifications should and are intended to be comprehended within the
7
meaning and range of equivalents of the disclosed embodiments. It is to be understood
that the phraseology or terminology employed herein is for the purpose of description
and not of limitation. Therefore, while the embodiments herein have been described in
terms of preferred embodiments, those skilled in the art will recognize that the
embodiments herein can be practiced with modification within the spirit and scope of
the embodiments as described herein.
The present disclosure is directed to a process for the producing aromatic carboxylic
acids by oxidation of methyl arenes.
Methyl arenes are methyl benzene and methyl naphthalene derivatives and include
compounds like para-, ortho-, meta- xylene, 2,6-dimethyl naphthalene and 1,5-
dimethyl naphthalene. The present disclosure is therefore directed to a process for
producing several aromatic carboxylic acids which includes but is not limited to
terepthalic acid, isopthalic acid, pthalic acid, 2,6-napthalene dicarboxylic acid and 1,5-
napthalene dicarboxylic acid.
In a preferred embodiment of the present disclosure the oxidation catalyst used is
cerium oxide nano-particulate catalyst. Cerium oxide nano-particulate catalyst of
various controlled sizes and shapes are prepared.
One aspect of the disclosure deals with the preparation of Cerium oxide nanoparticulate
catalyst of controlled sizes and shapes preferably in the range of 1 -30 nm.
In accordance with the present disclosure, cerium oxide nano-particulate is prepared
from eerie chloride CeCl3.7H20. The process steps include forming a micro emulsion
solution by mixing Ceric chloride in a solvent system containing at least one solvent
selected from the group of Triton X, n-hexane/1-dodecanol, water and ethanol, stirring
said micro emulsion at a temperature in the range of 20 to 40°C till a clear micro
emulsion is obtained, adding at least one nitrogen compound selected from the group
8
containing ammonia and ethylene diamine to said clear emulsion under vigorous
stirring to yield a reacted solution, heating the reacted solution at a temperature in the
range of 120 to 200°C for a time period in the range of 10-40 hours, followed by
cooling the solution at room temperature to obtain a product solution containing
cerium oxide, and isolating and further purifying the isolated cerium oxide to obtain
nano crystalline cerium oxide particles.
In one of the embodiments of the present disclosure, the solvent system contains a
mixture of Triton X, n-hexane and 1-dodecanol. The most preferred ratio of Triton X-
100: n-hexanol: 1 -Dodecanol is found to be 3:8:2 wt/wt.
In another embodiment the solvent system contains a mixture of water and ethanol
having a ratio 1:1 v/v.
In yet another embodiment of the present disclosure, the formation of micro emulsion
is carried out in the presence of a phase transfer agent, preferably
Cetyltrimethylammonium bromide.
The phase purity of the catalyst products obtained under different experimental
conditions shows high purity of the Ce02 cubic phase. The XRD patterns suggest that
the as-prepared Ce02 nanoparticles are nano crystalline in nature having an average
crystalline size in the range of 1 nm to 30 nm. The morphologies of the nano crystals
for the samples analyzed by TEM shows that the nanoparticles are close to spherical.
No peaks of any other phases or any other impurities are detected indicating the high
purity of the Ce02 cubic phase.
In accordance with the present disclosure the oxidation of methyl arenes to aromatic
carboxylic acid is carried out using the nano crystalline cerium oxide particles having
controlled morphology and average particle size in the range of 1 nm to 30 nm, as a
catalyst.
In a preferred embodiment of the present disclosure, para-xylene is oxidized to
terepthalic acid using nano crystalline cerium oxide particles having controlled
morphology and average particle size in the range of 1 nm to 30 nm, as a catalyst.
Partially oxidized derivatives such as para-toluic acid, para-tolualdehyde,
terepthaldehyde etc., may also be used as the starting substrates for preparing
terepthalic acid.
The process in accordance with the present disclosure involves the step of reacting a
methyl arene compound with oxygen/air in the presence of an oxidation reaction
medium containing water and a cerium oxide nano-particulate having controlled
morphology and particle size of 1 to 30 nm, to form a product mixture containing an
aromatic carboxylic acid. The process is carried out at a temperature in the range of 35
o o
C to 220 C and pressure in the range of 1-30 bar.
The use of heterogeneous catalysts for the oxidation reaction of methyl arenes is not
limited to the cerium oxide catalysts. Similar cerium oxide catalysts supported with
Au, Pt, Pd, metals. GroupVIIIB and Group VIII metals can also be used for this
oxidation reaction.
Although the reaction medium does not require the presence of any additives, a small
quantity of monocarboxylic acids of carbon content 1-8 may be used to test increase
the effectiveness of the process. Oxidation intermediates and other suitable cocatalysts
may be suitably added to enhance the reactivity of the oxidation process in
water medium.
The present disclosure is further supported herein with working examples, which do
not limit the scope of the present disclosure.
EXAMPLES:
Example 1: Preparation of Cerium oxide nanoparticles Catalyst 1
10
A micro emulsion solution was prepared by adding 15 ml of 0.5 mmol CeCl3.7H20
aqueous solution (0.033M) into a solvent system containing a mixture of Triton X-
100/n-hexane/l -Dodecanol in the ratio of 3:8:2 wt/wt, the micro emulsion was stirred
for 20 min at room temperature until the micro emulsion became transparent. 2 ml
NH3 solution was added drop wise to the clear micro emulsion under vigorous stirring
over a period of 20 minutes. The stirring was maintained till the clear solution turned
gray and finally yellow. The solution was then transferred into a Teflon-lined stainless
steel sealed autoclave and the solution was heated to 160°C for 36 hours. The solution
was then cooled and the white precipitate so obtained was centrifuged and washed
o
with distilled water, absolute ethanol and acetone repeatedly and dried in air at 40 C.
The product catalyst 1 was dispersed in 2 ml of ethanol and stored for further
characterization.
Example 2: Preparation of catalyst 2
1.5 mmol Cetyltrimethylammonium bromide was dissolved in a polar solvent system
containing a mixture of water and ethanol (15 ml each), 0.5 mmol of CeCl3.7H20 was
added to this solution (CTAB to CeCl3.7H20 ratio was 3:1). The reaction mixture was
continuously stirred for 1 hour by a magnetic stirrer, 15 ml of ethylene diamine was
added drop wise under vigorous stirring and the stirring was maintained for another 1
hour till yellow color appeared. The yellow solution was transferred into a Teflonlined
stainless steel autoclave and the solution was heated to 160°C for 36 hours. The
solution was then cooled and the white precipitate so obtained was centrifuged and
washed with distilled water, absolute ethanol and acetone repeatedly and dried in air at
o
40 C. The product catalyst 2 was dispersed in 2ml of ethanol and stored for further
characterization.
The catalyst samples 1 & 2 were characterized using powder X-ray diffractometer
(XRD) scanned at a rate of I*' per minute over the 29 range from 10 to 80° using a
Rigaku Miniflex diffractometer employing CuKa, radiation. TEM images and
selected-area electron diffraction (SPIED) were taken with a Philips Tecnai G"^ 30
11
transmission electron microscope with 300 kV accelerating voltage. The optical
properties were studied using a UV-visible Spectroscopy System (Perkin-Elmer
spectrophotometer, Lamda 35).The phase purity of the catalyst products 1 &2 was
examined by the x-ray diffraction (XRD) pattern.
Figure I show XRD patterns of the two samples. As shown in Figure 1, the
characteristic peaks located at 20 = 28.55, 33.08, 47.49, 56.35, 59.09, 69.42, 76.71 and
79.08 corresponds to (111), (200), (220), (311), (222), (400), (331) and (420) planes,
respectively. All these peaks can be indexed to a face-centered cubic (fee)
pure phase of Ce02 fluorite structure, which matches with the bulk XRD pattern and
to the reported value (space group = Fm3m , space group no=225, a= 5.411A° A,
JCPDS card #34-0394;.
The calculated lattice parameter of both the samples has been found to be 5.4107 A°,
which is in good agreement with the standard values. No peaks of any other phases or
any other impurities have been detected, indicating the high purity of the Ce02 cubic
phase. The broad and sharp reflections in the XRD patterns suggest that the
synthesized Ce02 nanoparticles were nano crystalline in nature. The average
crystalline size calculated using the Scherrer formula was found to be 6 nm for
catalyst 1 and 13 nm for catalyst 2.
Figure 2 shows the morphologies of the Ce02 catalyst products 1 &2 analyzed by
TEM.
Figure 2a shows mono dispersed particles of Ce02 nanoparticles of catalyst 1 with
close spherical morphology. The average particle size was calculated around 4-5 nm
which is consistent with the average size obtained from XRD measurements.
The morphology and structure of Ce02 nanoparticles catalyst 1 was further
investigated by HRTEM. Figure 2c shows the HRTEM image of a single nanoparticle
12
with lattice spacing of 0.267nm, corresponding to (200) lattice planes, which clearly
indicate the single crystalline nature of Ce02 nanoparticles.
The spotty SAED pattern of Ce02 nanoparticles catalyst 1 as in Figure 2b reveals the
poly crystalline nature of the catalyst particles with cubic fluorite structure, with (111),
(200), (220), (311), (222), (400) and (331) lattice planes clearly indexed.
Figure 2d represents the TEM image of catalyst 2. The average particle size of the
mono dispersed particles of catalyst 2 was found to be 12-15 nm.
The SAED pattern in Figure 2e shows rings corresponding to different lattice planes
of cubic Ce02.
Figure 2f represents the lattice and high crystallinity of Ce02 nano crystals.
Distinctive set of fringes can be unambiguously identified, such as those
corresponding to (200) the plane of bulk Ce02 (d200CeO2 = 0.27nm). The clear lattice
fringes from the HRTEM image indicates that catalyst 2 as prepared was free from
dislocations and stacking faults.
Example 3: General Reaction for Oxidation of para-xylene
100 mmole para-xylene, water (5-10ml), Ce02 catalyst 2 (2 to 10 mg) was charged in
a glass reactor equipped with an impeller and a manometer. The solution was heated
and maintained at a temperature 70 °C to 95*^C under atmospheric pressure of ©2(1-2
bar). The progression of reaction was monitored by the volume of O2 consumption as
a function of time. The initial change in the volume of O2 against time was linear. The
slope of the linear plot, when converted into concentration unit, gave the initial
reaction rate as, v,. To confirm this catalytic effectiveness, a blank experiment was
also performed for para xylene oxidation without Ce02 catalyst 2, which showed no
oxygen consumption in 10 hrs under identical reaction conditions. Thus, the observed
13
initial reaction rate in presence of the Ce02 material validated its catalytic
effectiveness.
The results as summarized in Table 1 (Examples 4-10 with varying catalyst
concentration and temperature parameters) for oxidation amounting to about 15-25%
with respect to the initial para xylene concentration, showed an increase in v, from 17
X 10'^ mol L'' Min"' to 31 x 10"^ mol L"' Min"' upon increasing the catalyst loading
o
from 5 mg to 10 mg. Increase in the temperature from 70 to 85 C also shows an
increase in Vj.
Table 1
Examples
4
5
6
7
8
9
10
Catal>ia
CaiaJj^ 2
Caialy:^ 2
Calaly« 2
Calalysl I
Caialysi 2
Caial>'si 2
Calal>si 2
CcOj, mg
5
7.6
10
10
10
10
10
Temperature. *C
"'O
•^0
. 70
' ?0
40
50
S5
i>* I 0 - ^ m o ! l . ' M i n '
17
27
31
29
16
27
41
EXAMPLE 11
Oxidation of Para-xylene using catalyst 1.
100 mmole para-xylene, water (6 ml), Ce02 catalyst 1(10 mg) was charged in a glass
reactor equipped with an impeller and a manometer. The solution was heated and
maintained at a temperature 85°C under atmospheric pressure of oxygen (1 bar) for a
period of 7hr to yield 18% terepthalic acid along with partially oxidized intermediates.
Table 2 shows the results of the desired oxidation product along with partially
oxidized intermediates.
14
EXAMPLE 12
Oxidation of Para-xylene using catalyst 1.
100 mmole para-xylene, water (6ml), Ce02 catalyst 1 (8.5 mg) was charged in a glass
reactor equipped with an impeller and a manometer. The solution was heated and
o
maintained at a temperature of 70 C under atmospheric pressure of O2 (1 bar) for a
period of 25 hr to yield 35% terepthalic acid along with partially oxidized
intermediates. Table 2 shows the results of the desired oxidation product along with
partially oxidized intermediates.
Table 2
Ex«nplc No.
11
12
Oxidation com}i!ion$
Cfttaiysl I « lOmg
Ptra-xyloie • 100 mM
Tem:p«ntt«re = 85 X^
Pressure of oxMfpri = 1 bar
WaSbet • 6 mL
RcaK:f foil time - 7 hr
CaialyjH 1 = 8.5 mg
ftira-xylene » 100 mM
Tamperatene » 70 *€
Pratsurc ofx>i>citt8ldchydc •= 27%
Tonephtfialdtelddiyde • 6%
Tcfcphihatk; K W " 35%
p-toNic scid « $7%
4-carbox;^nMlcfehyde ~ 9%
EXAMPLE 13.
Oxidation of Para-xylene at higher temperature.
100 mmole para-xylene, water (6ml) and Ce02 catalyst 1 (8.5 mg) were charged in a
glass reactor equipped with an impeller and a manometer. The solution was heated
under reflux and maintained at a temperature of 100 C (reflux) under atmospheric
pressure of O2 (1 bar) for a period of 8 hr. Figure 3 shows the product distribution of
terepthalic acid along with other partially oxidized intermediates of para-xylene.
Reaction at high temperature yields 35% terepthalic acid along with partially oxidized
intermediates, 38% para-toluic acid, 28% 4-carboxybenzaldehyde and 6-7%
terepthaldialdehyde.
15
EXAMPLE 14
Oxidation of Para-xylene using recovered catalyst
Catalyst 1 used in example 11 was recovered, washed and dried. Experiment was
carried out under similar reaction conditions as mentioned in Example 11 using 8 mg
of recovered catalyst and 2 mg of fresh catalyst 1. After 7 hr reaction the sample was
collected and analyzed by HPLC method. The oxidation yielded 16% terepthalic acid
along with other partially oxidized intermediates of para-xylene.
Throughout this specification the word "comprise", or variations such as "comprises"
or "comprising", will be understood to imply the inclusion of a stated element, integer
or step, or group of elements, integers or steps, but not the exclusion of any other
element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more
elements or ingredients or quantities, as the use may be in the embodiment of the
invention to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been
included in this specification is solely for the purpose of providing a context for the
invention. It is not to be taken as an admission that any or all of these matters form
part of the prior art base or were common general knowledge in the field relevant to
the invention as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the specific steps of the
preferred process, it will be appreciated that many steps can be made and that many
changes can be made in the preferred steps without departing from the principles of
the disclosure. These and other changes in the preferred steps of the disclosure will be
apparent to those skilled in the art from the disclosure herein, whereby it is to be
distinctly understood that the foregoing descriptive matter is to be interpreted merely
as illustrative of the disclosure and not as a limitation.
16

We claim:
1. A process for producing aromatic carboxylic acids by oxidation of methyl arenes,
said process comprising the following step:
reacting a methyl arene compound with an oxidizing gas in the presence of an
oxidation reaction medium containing water and a heterogeneous catalyst, to
form a product mixture containing an aromatic carboxylic acid.
2. The process as claimed in claim 1, wherein the process is carried out at a
temperature in the range of 35 °C to 220°C and pressure in the range of 1-30 bar.
3. The process as claimed in claim 1, wherein the heterogeneous catalyst is a cerium
oxide compound.
4. The process as claimed in claim 1, wherein cerium oxide compound is in the form
of nano- crystalline particles having controlled spherical morphology and
particle size in the range of 1 -30 nm.
5. The process as claimed in claim 1, wherein the methyl arene compound is at least
one selected from the group containing para-xylene meta-xylene, ortho-xylene,
2,6-dimenthynapthalene and 1,5-dimethyl naphthalene.
6. The process as claimed in claim 1, wherein the oxidizing gas is oxygen or air.
7. The process as claimed in claim 1, wherein the methyl arene compound is paraxylene
and the aromatic carboxylic acid is terepthalic acid.
8. The process as claimed in claim 1, wherein the oxidation reaction medium further
comprises monocarboxylic acids of carbon content 1-8 and a metal additive as cocatalyst
from groups IV, V, VI or VIII.
9. A process for preparing the cerium oxide compound as claimed in any one of the
preceding claims, said process comprising the following steps:
a. forming a micro emulsion solution by mixing eerie chloride in a solvent
system containing at least one solvent selected from the group of Triton
X, n-hexane/1-dodecanol, water and ethanol;
b. stirring said micro emulsion at a temperature in the range of 20 to 40°C
till a clear micro emulsion is obtained;
17
c. adding at least one nitrogen compound selected from the group
containing ammonia and ethylene diamine to said clear emulsion under
vigorous stirring to yield a reacted solution;
d. heating the reacted solution at a temperature in the range of 120 to
200°C for a time period in the range of 10-40 hr, followed by cooling
the solution at room temperature to obtain a product solution containing
cerium oxide; and
e. isolating and further purifying the isolated cerium oxide to obtain nano
crystalline cerium oxide particles having controlled spherical
morphology and particle size in the range of 1 -30 nm.
10. The process as claimed in claim 9, wherein the formation of micro emulsion in
step a) is optionally carried out in the presence of a phase transfer agent.
11. The process as claimed in claim 10, wherein the phase transfer agent is
Cetyltrimethylammonium bromide.
12. The process as claimed in claim 9, wherein the solvent system contains a mixture
of Triton X, n-hexane and 1-dodecanol.
13. The process as claimed in claim 9, wherein the solvent system contains a mixture
of water and ethanol.