|Title of Invention||
"LIQUID PHASE OXIDATION OF P-XYLENE TO TEREPHTHALIC ACID IN THE PRESENCE OF A CATALYST SYSTEM CONTAINING NICKEL, MANGANESE, AND BROMINE ATOMS"
|Abstract||A method for liquid phase oxidation of p-xylene with molecular oxygen to terephthalic acid that minimizes solvent loss through solvent burn and minimizes the formation of incomplete oxidation products such as 4-carboxybenzaldehyde (4-CBA). P-xylene is oxidized at a temperature in the range of 120°C to 250°C and in the presence of a source of molecular oxygen and a catalyst composition substantially free of zirconium atoms comprising a source of nickel (Ni) atoms, a source of manganese (Mn) atoms, and a source of bromine (Br) atoms, to form a crude reaction mixture comprising terephthalic acid and incompletely oxidized reaction products comprising 4-CBA, wherein the stoichiometric molar ratio of bromine atoms to manganese atoms is 1.5 or less, and the amount of nickel atoms is at least 500 ppm.|
|Full Text||Liquid Phase Oxidation of P-xylene To Terephthalic Acid In The
Presence of A Catalyst System Containing Nickel Manganese And
1. Field of the Invention
The invention pertains to the liquid phase oxidation of p-xylene,
more particularly to the liquid phase oxidation of p-xylene in the presence
of a catalyst system containing nickel, manganese, and bromine atoms
substantially free of zirconium atoms.
2. Background of the Invention
In typical known processes for producing terephthalic acid, p-xylene
is oxidized to the product terephthalic acid. P-xylene is continuously or
batchwise oxidized in a primary oxidation reactor in the liquid phase in the
presence of an oxygen containing gas such as air. P-xylene, an oxidation
catalyst, a molecular source of oxygen, and a solvent such as acetic acid
are combined in a reactor to produce a crude terephthalic acid
composition. A typical oxidation catalyst composition is made by
contacting a cobalt compound with a manganese compound, usually also
in combination with a promoter such as a bromine compound.
The resulting terephthalic acid product is not very soluble in a
solvent such as acetic acid under the reactor operating conditions, and
usually crystallizes out of the solvent as a solid to form a suspension. The
crude terephthalic acid composition in the primary oxidation reactor is a
reaction mixture which contains terephthalic acid solids, a solvent acting
as the suspending medium for the solids and containing a small amount of
terephthalic acid dissolved therein, catalyst, unreacted p-xylene,
incompletely oxidized intermediate oxidation products such as paratolualdehyde,
para-toluic acid, 4-carboxybenzaldehyde (4-CBA), and other
organic impurities which may cause discoloration dissolved in the solvent.
The crude terephthalic acid composition is discharged from the oxidation
zone and generally subjected to a variety of mother liquor exchange,
separation, purification, and recovery methods, resulting in recycling back
to the oxidation zone the recovered solvent and catalyst composition. It
would be desirable to reduce the amount of incompletely oxidized
intermediates ("intermediates"). By reducing the amount of intermediates,
primarily composed of 4-CBA, one may either improve the yield, reduce
the volume of mother liquor containing the intermediates which must be
separated from the terephthalic acid product, reduce the amount of
intermediates needed in a post oxidation reactor, or all the foregoing.
Other by-products of the liquid phase oxidation which are partially
or completely removed from the reaction mixture in the oxidation reactor
are the off-gases which include water, solvent, unreacted oxygen and
other unreacted gases found in the source of the molecular oxygen gas
such as n itrogen a nd carbon d ioxide, a nd additional a mounts of c arbon
dioxide and carbon monoxide produced by the catalytic decomposition of
the solvent under the oxidation conditions. The off-gases are vented at
the overhead of the oxidation reactor to a distillation column or a
condenser to separate the solvent from the other off-gases such as water,
carbon dioxide, carbon monoxide, nitrogen, methyl bromides, etc. The
solvent recovered in the distillation column or condensers is recycled back
to the oxidation reactor for further use. The hot uncondensed gases are
removed from the distillation column and sent to energy recovery devices,
such as turboexpanders and electric generators, or to heat exchangers, or
to steam generators, optionally before or after passing through catalytic
oxidation or other suitable equipment for neutralizing or removing acidic
and corrosive ingredients in the gaseous stream.
The oxidative decomposition of the solvent in the primary oxidation
reactor resulting in the generation of carbon dioxide and carbon monoxide
gas is referred to as the solvent burn, and results in the loss of solvent. It
is desirable to recover and recycle back to the oxidation reactor as much
solvent as possible for further use. However, once the solvent is
decomposed in the primary oxidation reactor into its constituent gaseous
products, such as carbon monoxide and carbon dioxide when acetic acid
is the solvent, there no longer exists solvent to recover resulting in the
permanent loss of solvent and requiring a fresh source of make-up
solvent. R educing t he amount o f solvent b urn w ould s ignificantly I ower
the operating costs in the oxidation zone by allowing a greater amount of
solvent to be recovered and recycled back to the oxidation zone and by
lowering the amount of fresh make-up feed. H owever, the reduction in
solvent burn should not come at the expense increasing the amount of 4-
CBA in the crude mixture, and if possible, it would be desirable to
simultaneously reduce the solvent burn and reduce the amount of 4-CBA
generated in the crude oxidation mixture.
3. Summary of the Invention
We have found that the decomposition of a solvent in an oxidation
process and the production of 4-CBA can be controlled by a combination
of an appropriate selection of reaction conditions and catalyst
composition. There is now provided a process for the oxidation of pxylene
to terephthalicacid comprising oxidizing in the liquid phase a pxylene
composition comprising at least 80 wt.% p-xylene based on the
weight of liquid reactants, at a temperature in the range of 120°C to 250°C
and in the presence of a source of molecular oxygen and a catalyst
composition substantially free of zirconium atoms comprising a source of
nickel (Ni) atoms, a source of manganese (Mn) atoms, and a source of
bromine (Br) atoms, to form a crude reaction mixture comprising
terephthalic acid and incompletely oxidized reaction products comprising
4-carboxybenzaldehyde compounds, wherein the stoichiometric molar
ratio of bromine atoms to manganese atoms is 1.5 or less, and the amount
of nickel atoms is at least 500 ppm.
There is also provided a catalyst composition substantially free of
zirconium atoms comprising a source of nickel atoms, a source of
manganese atoms, and a source of bromine atoms, wherein the molar
ratio of bromine atoms to each of nickel atoms and manganese atoms are
1.5 or less, and the amount of nickel atoms are at least 500 ppm. The
catalyst composition is also preferably substantially free of cobalt atoms.
4. Brief Description of the Drawings
Figure 1 illustrates a process flow of crude terephthalic acid
streams and the overhead of an oxidation unit.
5. Detailed Description Of The Invention
It is to be understood that the word comprising is open ended and
may include any number and type of unstated steps, processes, or
ingredients. The description of method steps does not preclude
intervening steps and is not restricted to carrying out the steps in a
particular order unless otherwise stated. Numerical ranges include each
integer and all fractions thereof between the end points of the stated
The process comprises oxidizing p-xylene in the liquid phase. The
liquid phase may at any moment comprise the feed reactants, or the
carboxylic acid reaction product dissolved or suspended in the reaction
mixture, or both, especially in a continuous process.
The product of the oxidation of p-xylene includes terephthalic acid
solids as the predominant product (at least 50 wt.% of the solids), and
incomplete oxidation products which may be found in the solids, in the
liquid phase, or in both. P-xylene fed to the oxidation reactor may be
purified of contaminants which may interfere with the oxidation reaction.
The reactant feed may be pure or a mix of the compounds isomers or
lower or higher homologues, as well as some saturated alicyclic or
aliphatic compounds having similar boiling points to the aromatic or fused
ring compounds. However, at least 80 wt.% , preferably at least 95 wt.%,
or at least 98 wt.% of the liquid reactants is p-xylene.
In one embodiment of the invention, the liquid phase oxidation
process is carried out in the presence of a solvent. Suitable solvents are
those which are solvents for the p-xylene under the oxidation reaction
conditions, wherein the p-xylene is sufficiently soluble in the solvent so as
to be completely soluble therein or sufficiently soluble to form a pumpable
crude flow discharged from the oxidation reactor. Suitable solvents
include water and the aliphatic solvents. The preferred aliphatic solvents
are aliphatic carboxylic acids which include, but are not limited to,
aqueous solutions of C2 to Ce monocarboxylic acids, e.g., acetic acid,
propionic acid, n- butyric acid, isobutyric acid, n-valeric acid,
trimethylacetic acid, caprioic acid, and mixtures thereof. Preferably, the
solvent is volatile under the oxidation reaction conditions to allow it to be
taken as an off-gas from the oxidation reactor. It is also preferred that the
solvent selected is also one in which the catalyst composition is soluble
under the reaction conditions.
The most common solvent used for the oxidation of p-xylene is an
aqueous acetic acid solution, typically having a concentration of 80 to 99
wt.%. In especially preferred embodiments, the solvent comprises a
mixture of water and acetic acid which has a water content of about 2.5%
to about 15% by weight. Additionally, a portion of the solvent feed to the
primary oxidation reactor may be obtained from a recycle stream obtained
by displacing about 80 to 90% of the mother liquor taken from the crude
reaction mixture stream discharged from the primary oxidation reactor with
fresh, wet acetic acid containing about 2.5to 15% water. This exchange
may be accomplished in any convenient apparatus but can most easily be
accomplished in a centrifuging apparatus, such as one or more cyclones.
The amount of solvent used in not limited. It is not generally
necessary to use large amounts. Suitable amounts of solvent range from
0.1 wt.% to 20 wt.%, or 1 wt.% to 10 wt.%, or even small amounts in the
range of 1 wt.% to 5 wt.%, based on the weight of all feeds to the
oxidation reaction zone.
The oxidation of p-xylene is conducted in the presence of a source
of oxygen. This is easily accomplished be feeding an oxygen containing
gas to the primary oxidation reactor to allow the gas to contact the liquid
reaction mixture in the reactor. Preferred oxygen containing gases include
air and other mixtures of nitrogen and oxygen. One such convenient
mixture which can be used in the process of the present invention is the
vent gas from the primary oxidation which ordinarily comprises about 5 to
20% oxygen. By reducing the amount of oxygen in the gas to a level less
than found in air, the extent of solvent burn can be further reduced in the
primary oxidation zone and also in secondary post oxidation reactors
further downstream designed to complete the oxidation of intermediate
products produced in the primary oxidation reactor.
The relation between the temperature and pressure in the primary
oxidation reactor is regulated to ensure that the reaction proceeds
essentially in the liquid phase rather than completely in the gaseous
phase, while allowing the reaction to proceed towards the oxidation of the
reactants. The p-xylene feed should not be mostly vaporized. Thus, the
oxidation reaction proceeds at elevated temperatures and pressures. It is
desirable to ensure that at least 70% of the reactants remain in the liquid
phase, more preferably at least 80%. The oxidation reaction desirably
proceeds at a temperature ranging from 80°C to 250°C, and the heat of
reaction will generate pressures ranging from 70 psig to 800 psig. For
example, as p-xylene is oxidized to produce TPA using the catalyst
composition of the invention in a liquid phase oxidation carried out at a
temperature ranging from 120-200°C and a pressure in the range of about
90 to 270 psig. Lowering the oxidation temperature also helps to reduce
the extent of solvent burn, all other conditions and ingredients being equal.
The process of the invention is particularly well suited for oxidizing pxylene
at low t emperatures without generating excessive amounts of 4-
CBA. Thus, more preferred oxidation temperatures are within the range of
140°C to 190°C.
The catalyst system employed in the process of the invention is
substantially free of zirconium atoms and comprises a source of nickel
atoms, a source of manganese atoms, and a source of bromine atoms.
The catalyst composition is preferably soluble in the solvent under
reaction conditions, or it is soluble in the reactants fed to the oxidation
zone. More preferably, the catalyst composition is soluble in the solvent at
40°C and 1 atm., and is soluble in the solvent under the reaction
The source of nickel may be provided in ionic form as inorganic
nickel salts, such as nickel nitrate, nickel chloride, or organic nickel
compounds such as nickel salts of aliphatic or aromatic acids having 2-22
carbon atoms, including nickel acetate, nickel octanoate, nickel benzoate,
and nickel naphthalate. The weight amount of each of nickel, manganese,
bromine, or other atoms are based on the atomic weight of the atom,
whether or not the atom is in elemental form or in ionic form. The weight
percentage of a catalyst component includes the counter-cation or anion
only if the weight percentage is used in the context of the source of the
atom. For example, the amount of nickel refers to the amount of nickel
atoms, whether elemental or ionic, and not the amount of nickel acetate.
The stated concentration of catalyst components are based on the
quantity of catalyst components in the reaction zone of the oxidation
reactor. The catalyst component concentrations can be measured by
sampling the oxidation reactor underflow.
Nickel in the catalyst composition may be present in a
concentration of about 500 to 5000 ppm, based on the weight of all liquid
and solid feeds. Preferably, the concentration of nickel is about 500 to
4000 ppm. Even more preferably, the concentration of nickel is about
1500 to 3000 ppm. The oxidation state of nickel when added as a
compound to the reaction mixture is not limited, and includes +2 or +3.
The source of manganese may be provided as inorganic
manganese salts, such as manganese borates, manganese halides,
manganese nitrates, or organometallic manganese compounds such as
the manganese salts of lower aliphatic carboxylic acids, including
manganese acetate, and manganese salts of beta-diketonates, including
manganese acetylacetonate. Manganese in the catalyst composition may
be present in a concentration of about 100 to 3000 ppm. Preferably, the
concentration of manganese is about 200 to 2500 ppm.
The bromine component may be added as elemental bromine, in
combined form or as an anion. Suitable sources of bromine include
hydrobromic acid, sodium bromide, ammonium bromide, potassium
bromide, tetrabromoethane, benzyl bromide, 4- bromopyridine, alphabromo-
p-toluic acid, and bromoacetic acid. Hydrogen bromide and alphabromo-
p-toluic acid are preferred bromine sources. Bromine in the
catalyst composition may be present in an amount ranging from 150 to
3000 ppm, based on the total liquid.
The catalyst composition of the invention is substantially free of
zirconium, and preferably also substantially free from cobalt. In one
embodiment, the catalyst composition is free of any metals other than
nickel and manganese. We have found that zirconium added to the
catalyst composition impairs the reduction of solvent burn. For example,
the solvent burn in an oxidation reaction is much higher using a catalyst
composition containing Mn, Ni, Zr, and Br compared to the solvent burn
observed when only Mn, Ni, Br are used the catalyst composition. Thus,
the catalyst composition is devoid of Zr in a quantity which would increase
the solvent burn by more than 10% relative to the same catalyst
composition devoid of Zr. In one embodiment, the catalyst composition
contains less than 5 ppm Zr, or 2 ppm or less of Zr, or 0 ppm Zr.
Likewise, in another embodiment, the catalyst composition further
contains less than 5 ppm cobalt, or 2 ppm or less of cobalt, or 0 ppm
The relative amounts of elements in the catalyst composition are
not particularly limited, other than molar amount of bromine relative to
manganese atoms is 1.5 or less. Normalizing the molar quantity of
manganese to 1, the molar amount of bromine is 1.5 or less, preferably
1 .1 or less, or 1 .0 or less, and even 0.9 or less.
In a preferred embodiment, the molar amount of bromine relative to
each of nickel and manganese is 1.5 or less, or 1.1 or less, or 1.0 or less,
or 0.9 or less.. The molar amount of bromine is desirably at least 0.3, or
0.5 relative to the molar amount of each of nickel and manganese in order
to maximize the yield of the desired acid.
Suitable molar stoichiometric ratios of the nickel atoms to
manganese atoms range from 0.2:1 to 4:1, preferably about 0.5:1 to 2.5:1.
Non-limiting examples of catalyst component molar ratios suitable
for use in the invention include the following: molar stoichiometric ratios of
nickel atoms to bromine atoms ranging from about 0.66:1 to 5:1, or about
0.9:1 to 4:1, or about 1.0:1 to 3.5:1, or about 1 .1:1 to 3.5:1; and molar
stoichiometric ratio of manganese atoms to bromine atoms ranging from
about 0.67:1 to 5:1, or 0.9:1 to 2.5:1, or about 1.0:1 to 2:1, or about 1.1:1
to 1.8:1. Other suitable ranges include, by way of example, molar
stoichiometric ratios of the following metals: Nii.2.5Mni-2Bro.3-i.5 or Nh-
The particular amount of nickel used in the catalyst composition is
at least 500 ppm Ni to be effective to maximize the yield of the desired
acid. Below this amount, the yield to the desired acid suffers significantly.
The total amount of catalyst present in the primary oxidation
reactor, based on the ppm by weight of Ni, Mn, and Br atoms, and any
other added metal atoms relative to the weight of the solvent is effective
to obtain the desired degree of .conversion at the operation temperature.
In general, suitable amounts of catalyst range from 2000 ppm to 9000
ppm of total combined metal and bromine atoms, although more can be
used if desired, especially if the oxidation reaction is conducted at lower
temperatures. Suitable amounts of catalyst based on their compound
weight will vary widely depending on the counter ion molecular weight, but
for most common anions, the amounts would generally range from 0.1 to
10 wt%, or 0.1 to 5 wt.%, or 0.1 to 3 wt.%, based on the weight of the
Other organic or non-metallic catalyst components can be included
in the catalyst composition of the invention. For example, the catalyst
composition may include a source pyridine. The pyridine component of the
catalyst s ystem m ay b e a dded t o a p rimary oxidation r eactor o r t o p ost
oxidation reactors. The pyridine component can be in the form of pyridine
per se or the form of a compound of pyridine. For example, 4-
bromopyridine may be used as both a source of pyridine and bromine
The catalyst composition can be formed by adding each source of
metal and bromine atoms of the catalyst composition to the oxidation
reactor separately in sequence or simultaneously, or a prepared
composition may be added to the oxidation reactor, and in either case, the
addition may be made as an initial batch or continuously during the course
of the oxidation reaction. The catalyst composition prepared as a batch
may be dissolved in the solvent to form a catalyst feed followed by adding
the catalyst feed to the primary oxidation reactor. Each component, or the
catalyst composition batch, can be added to the primary oxidation reactor
before or after or during addition of the solvent. In a continuous process,
the catalyst components or the catalyst composition are added
simultaneous with the solvent feed, or in the solvent feed, or separately
metered as required for fresh make-up.
After the initial charge of catalyst composition in a continuous
process, the residual mother liquor from the primary oxidation supplies a
portion of the necessary catalyst components to the primary oxidation
reactor by partial displacement of the primary oxidation mother liquor with
fresh solvent. The remainder can be made up with a continuous fresh feed
of make-up catalyst.
By using the catalyst composition of the invention, the extent of
solvent burned and rendered unusable in a recycle stream is reduced
relative to other catalyst compositions containing zirconium, or other
catalyst compositions containing the same metal atoms with molar
quantities of bromine in excess of 1.5 with respect to manganese, under
identical operating conditions. While the absolute amount of solvent burn
in the present invention is quite low, this reduction is not achieved at the
expense of yield. Obtaining a low amount of solvent is possible by
running the reaction at low oxidation temperatures or using a catalyst
which has a lower degree of conversion or selectivity, but this negatively
impacts other results such as lowered yields and increased quantities of
intermediates. The catalyst composition of the invention has the
advantage of a m aintaining a low ratio of solvent burn to yield, thereby
minimizing the impact on yield to obtain the low solvent burn relative to
other catalyst compositions while simultaneously generating low quantities
of incomplete intermediate oxidations products.
In a preferred embodiment, the ratio of solvent burn (in moles of
CO and CO2 expressed as COx, per mole of terephthalic acid produced) is
0.80 moles COx/mol TPA or less, or 0.70 or less, or 0.55 or less.
The catalyst composition of the invention is also capable of
reducing the quantity of incomplete intermediate oxidation products
produced in the reaction mixture. In the process of the invention, the
quantity of the 4-carboxybenzaldehyde (4-CBA) isolated intermediates in
the reaction mixture is preferably below 60,000 ppm, more preferably
below 50,000, or below 40,000, or below 30,000. The levels of 4-CBA
listed are measured as the cumulative amount of 4-CBA in the solid and
liquid phase and reported relative to the total weight of solid isolated. In
the solid phase alone, the amount of 4-CBA produced by the process of
the invention may be 10,000 or less.
A preferred process in accordance with the present invention
comprises contacting crude terephthalic acid which is produced by the
oxidation of para-xylene with a mixture of nitrogen and oxygen comprising
about 5 to 20% oxygen at a temperature of about 120°C to 190°C. and a
pressure of 100 psig to 400 psig. The purification is conducted in the
presence of a solvent which is preferably obtained by displacing about 80
to 90% of the mother liquor from the primary oxidation with fresh, wet,
acetic acid containing about 4-12% water. The residual mother liquor from
the p rimary oxidation supplies m ost, if n ot a II, of the n ecessary catalyst
The invention will b e further illustrated by the following examples
although it will be understood that these examples are included merely for
purposes of illustrating some of the embodiments within the scope of the
Referring to the accompanying FIG. 1, p-xylene is introduced v ia
conduit 10 into primary oxidation reactor 12, and aqueous acetic acid
solvent having 4-12% water having dissolved therein the catalyst
composition of the invention is fed through line 11 to the reactor 12. If
desired, the p-xylene, solvent, and catalyst composition charges may be
fed to reactor 12 at a plurality of points along the side of the reactor, or fed
together through one line. An oxygen-containing gas under pressure is
introduced near the bottom of the reactor 12 via conduit 14. The preferred
oxygen-containing gas is air or oxygen-enriched air. The flow rate of the
oxygen-containing gas to reactor 12 is controlled to maintain between
about 2 and 9 volume percent oxygen (calculated on a dry, solvent free
basis) in the off-gas which exits the reactor via conduit 16. The reactants
in reactor 12 are maintained at an elevated pressure of about 50 to 175
psia to maintain a contained, volatizable reaction medium substantially in
the liquid state at the reaction temperature of about 120 to 190°C.
During the course of the oxidation reaction, exothermic heat of
reaction and water generated by t he o xidation of p -xylene are removed
from reactor 12 by vaporization of a portion of the liquid reaction medium.
These vapors, known as reactor off-gas, comprise vaporized acetic acid
solvent, about 5 to 30 weight percent water, and oxygen-depleted process
gas containing minor amounts of decomposition products including
catalyst residue, as well as additional carbon dioxide and carbon
monoxide generated by the decomposition of acetic acid. The reactor offgas
passes upwardly through the reactor 12 and is conveyed via conduit
16 to the lower portion of water removal column 18 for distillation and
recovery of the acetic acid back to the primary oxidation reactor. The
crude reaction mixture is discharged from the primary oxidation reactor to
a solid/liquid separator 20 into which is fed fresh acetic acid through line
22 to exchange the mother liquor discharged through line 24. The mother
liquor containing acetic acid and the catalyst composition is subjected to
conventional purification and purging techniques to recover and recycle
the catalyst composition to the primary oxidation reactor 12.
The catalyst composition is effective as a catalyst not only in the
primary oxidation zone, but also to effectuate post oxidation in secondary
reactors to further increase the yield of product.
The following procedure was used as a representative procedure
for examples 1-7, with variations noted on the table.
Each of the catalyst solutions set forth in the Table, containing 80 g
of a 96% aqueous acetic acid (92% aqueous acetic acid in examples 7)
and the noted concentrations of nickel (as Ni(OAc)2 4 H2O), manganese
(as Mn(OAc)2 4 HaO) and bromine (as HBr), were charged to a 300-mL
titanium autoclave equipped with a high pressure condenser and an Isco
pump. Once the autoclave was pressurize up to 100 psig with nitrogen,
the contents were heated to about 160'C, or 163°C in the case of
examples 7, in a closed system (i.e., with no gas flow). Thereafter, the
pressure was increased b y an a dditional 2 40 p si-250 psi using a 50/50
vol% mix of nitrogen and air at a flow rate of about 500 seem each. Once
the autoclave was pressurized to about 340 to 350 psig, the pressure was
further increased up to 700 psig using only nitrogen.
At the target pressure, a flow of nitrogen at about 500 seem and air
at about 500 seem was started and continued to maintain the target
pressure throughout the experiment. Once the flow of nitrogen/air at the
target pressure was commenced, p-xylene was pumped into the autoclave
at a rate of 0.034 mL/min for 136 min. The reaction conditions noted on
Table 1 were maintained throughout the experiment. Off-gas samples
were taken at 90 min after starting the pumping of p-xylene.
Concentrations of CO and COa were determined by GC. At the expiration
of 136 minutes, the autoclave was cooled under a flow of nitrogen and
vent. The reaction mixture was analyzed for the concentration of 4-
carboxybenzaldehyde, as determined by high pressure liquid phase
chromatography, observed in the solids isolated and in the filtrate. The
results are reported in Table 1.
(Table Removed) The stoichiometric molar ratio of nickel, manganese and bromine in
Examples 1 was 2.3:1.0:0.6 molar (or 1.0:0.4:0.3 molar normalized to
nickel), in Examples 4 was 0.9:1.0:0.7 molar (or 1.0:1.1:0.8 molar
normalized to nickel), and in Example 6 was 0.3:1.0:0.7 molar (or 1:3.3:2.3
normalized to nickel).
Examples 1a-1e, 4a-c and 6, which all use a catalyst system
consisting of nickel, manganese and bromine, show a marked reduction in
solvent burn as seen by the reduced amount of CO and CO2 produced in
the course of the oxidation of p-xylene to terephthalic acid, relative to a
reaction performed under comparable conditions with a catalyst system
consisting of cobalt, manganese and bromine used as a benchmark
(Comparative examples 7a-7c). The amount of CO and CO2 released in
p-xylene oxidation is proportional to the extent of solvent loss through
Comparative Example 2 shows that terephthalic acid is not
produced, under the conditions evaluated (temperature and pressure), in
the absence of manganese.
Comparative Examples 3a-3b and 5 show that the addition of
zirconium as a fourth catalyst component, even when added to a Ni/Mn/Br
based catalyst system with a Br:Mn ratio of less than 1.5, leads to an
increase in the amount of CO and CO2 produced, relative to that observed
in the absence of Zr (Ex. 1a-1e and 4a-4c and 6).
Examples 8-16 illustrate the effect of stoichiometric molar ratios of
the elements nickel, manganese, and bromine on solvent burn and
intermediate production, in particular 4-CBA.
Data for Examples Comp 8, Comp 9, 10, Comp 11, Comp 12, and
13 are predicted values obtained from models derived from experiments
performed in the same manner as in examples 1-7 using 96% aqueous
acetic acid. Results for Examples Comp 14, Comp 15 and 16 are values
obtained by an average of 3-4 data points generated in the same manner
as in Examples 1 through 7, except that these examples were prepared
using 88 wt.% aqueous acetic acid.
(Table Removed)In each of the comparative examples, the molar stoichiometric ratio
of bromine to nickel or of bromine to manganese was higher than 1.05.
Example 10 achieved a simultaneous reduction in solvent bum and 4-CBA
content relative to Comparative Examples 8 and 9 having a
bromine:manganese ratio higher than 1.5, under the same temperature of
Example 13 also achieved a simultaneous reduction in solvent burn
per gram of solid isolated and 4-CBA content relative to Comparative
examples 11 and 12 at slightly lower reaction temperatures of 155°C.
Likewise, Example 16 achieved a simultaneous reduction in solvent
burn per gram of solid isolated and 4-CBA content, and a lower absolute
amount of solvent burn, relative to Comparative examples 14 and 15, both
of which had a bromine:manganese ratio higher than 1.5, under a more
dilute concentration of acetic acid and at a higher oxidation temperature of
A comparison of the relatively small variation in solvent burn results
between Examples 10,13, and 16 indicates that the catalyst composition
of the invention allows for wide latitude of nickel concentrations.
1. A process for the oxidation of p-xylene to terephthalic acid comprising oxidizing in the
liquid phase a p-xylene composition comprising at least 80 wt.% p-xylene based on the
weight of liquid reactants, at a temperature in the range of 120°C to 250°C and in the
presence of a source of molecular oxygen and a catalyst composition comprising less
than 5 ppm of zirconium atoms, a source of nickel (Ni) atoms, a source of manganese
(Mn) atoms, and a source of bromine (Br) atoms, to form a crude reaction mixture
comprising terephthalic acid and incompletely oxidized reaction composition comprising
4-carboxybenzaldehyde (4-CBA) compounds, wherein the stoichiometric molar ratio of
bromine atoms to manganese atoms is 1.5 or less, and the amount of nickel atoms is at
least 500 ppm.
2. The process as claimed in claim 1, wherein said solvent comprises an acetic acid
3. The process as claimed in claim 2, wherein said acetic acid composition comprises 2.5 to
15 wt.% water.
4. The process as claimed in claim 1, wherein the molar ratio of Br to Ni and the molar ratio
of Br to Mn are each 1.5 or less and at least 0.3.
5. The process as claimed in claim 4, wherein the molar ratio of Br to Ni and the molar ratio
of Br to Mn are each 1.1 or less.
6. The process as claimed in claim 5, wherein the molar ratio of Br to Ni and the molar ratio
of Br to Mn are each 1.0 or less.
7. The process as claimed in claim 6, wherein the molar ratio of Br to Ni is 0.9 or less.
8. The process as claimed in claim 1, wherein the molar ratio of nickel atoms to manganese
atoms ranges fiom 0.2:l to 4:l.
9. The process as claimed in claim 8, wherein the molar ratio of nickel atoms to manganese
atoms ranges from 0.5:l to 2.5:l.
10. The process as claimed in claim 1 , wherein the molar ratio of Br to Mn is 1.1 or less.
11. The process as claimed in claim 10, wherein the molar ratio of Br to Mn is 1.0 or less.
12. The process as claimed in claim 1, wherein the oxidation temperature is within a range of
140°C to 190°C and the oxidation reaction is conducted under a pressure in the range of
50 to 175 psig.
13. The process as claimed in claim 1, wherein the catalyst composition contains less than 2
14. The process as claimed in claim 1, wherein the catalyst composition contains less than 5
15. The process as claimed in claim 15, wherein the reaction mixture comprises 40,000 pprn
4-CBA or less.
16. The process as claimed in claim 1 , wherein the 4-CBA content in the solids is 10,000
pprn or less.
17. The process as claimed in claim 1, wherein the ratio of solvent burn is 0.80 moles COX
per mole of terephthalic acid produced or less.
18. The process as claimed in claim 18, wherein said ratio is 0.70 or less.
19. The process as claimed in claim 1, wherein the catalyst composition is fiee of cobalt
20. The process as claimed in claim 1, wherein the ratio of solvent burn is 0.60 moles COX
per mole of terephthalic acid or less, and the total quantity of 4-CBA in the solid and
liquid phase is 40,000 pprn or less.
21. The process as claimed in claim 20, wherein the total quantity of 4-CBA is 10,000 pprn
22. A catalyst composition for performing the process as claimed in claim 1, comprising less
than 5 ppm of zirconium atoms, a source of nickel ( Ni) atoms, a source of manganese
(Mn) atoms, and a source of bromine (Br) atoms, wherein the stoichiometric molar ratio
of bromine atoms to manganese atoms is 1.5 or less, and the amount of nickel atoms is at
least 500 ppm.
23. The catalyst composition as claimed in claim 22, wherein the molar ratio of Br to Ni and
the molar ratio of Br to Mn are each 1.5 or less and at least 0.3.
24. The catalyst composition as claimed in claim 23, wherein the molar ratio of Br to Ni and
the molar ratio of Br to Mn are each 1.0 or less.
25. The catalyst composition as claimed in claim claim 22, wherein the molar ratio of nickel
atoms to manganese atoms ranges fiom 0.5:1 to 2.5:l.
26. The catalyst composition as claimed in claim claim 22, wherein the molar ratio-of Br to
Mn is 1.0 or less.
27. The composition as claimed in claim 22, wherein the catalyst composition is represented
by the formula: Nil-2.~~l-2Bro.3-1.5.
28. The composition as claimed in claim 22, wherein the catalyst composition is represented
by the formula: Nil-2.~khl-2Br0.6-1.
|Indian Patent Application Number||5091/DELNP/2006|
|PG Journal Number||37/2013|
|Date of Filing||04-Sep-2006|
|Name of Patentee||GRUPO PETROTEMEX, S.A. DE C.V.|
|Applicant Address||RICARDO MARGAIN NO. 444, TORRE SUR, PISO 16 COL VALLE DEL CAMPESTRE 66265 SAN PEDRO GARZA GARCIA, NUEVO LEON (81) 8748 1500, MEXICO|
|PCT International Classification Number||C07C 51/265|
|PCT International Application Number||PCT/US2005/011848|
|PCT International Filing date||2005-04-08|