Title of Invention

A CATALYST FOR PREPARATION OF PHTHALIC ANHYDRIDE AND PROCESS FOR PRODUCING PHTALIC ANHYDRIDE USING IT

Abstract The invention discloses a catalyst for the preparation of phthalic anhydride by gas-phase oxidation of o-xylene and/or naphthalene, wherein the catalyst comprises at least one first catalyst zone located towards the gas inlet, a second catalyst zone located closer to the gas outlet and a third catalyst zone located even closer to or at the gas outlet, with the catalyst zones preferably each having an active composition comprising TiO2, characterized in that the catalyst activity of the first catalyst zone is higher than the catalyst activity of the second catalyst zone. The invention is also for a process for preparation of phthalic anhydride using the said catalyst by reacting o-xylene and/or naphthalene and molecular oxygen at 25GPC to 490°C.
Full Text A CATALYST FOR PREPARATION OF PHTHAUC ANHYDRIDE
AND PROCESS FOR PRODUCING PHTHALIC ANHYDRIDE USING IT
DESCRIPTION
The invention relates to the use of a multizone (multi-layer)
catalyst, i.e. a catalyst having three or more different
zones (layers), for the preparation of phthalic anhydride
(PA) by gas-phase oxidation of o-xylene and/or naphthalene.
The industrial production of phthalic anhydride is carried out
by catalytic gas-phase oxidation of o-xylene and/or naphthalene.
For this purpose, a catalyst suitable for the reaction is
installed in a reactor, preferably a she11-and-tube reactor in
which a multiplicity of tubes are arranged in parallel, and a
mixture of the hydrocarbon(s) and an oxygen-containing gas, for
example air, is passed through it from above or below. Owing to
the evolution of a large amount of heat in such oxidation
reactions, it is necessary for a heat-transfer medium to be
passed around the reaction tubes and thus remove the heat
evolved so as to avoid hot spots. This energy can be utilized
for the production of steam. The heat-transfer medium used is
generally a salt melt, preferably a eutectic mixture of NaNO2
and KN03.
Multizone catalyst systems are used nowadays for the oxidation
of o-xylene and/or naphthalene to phthalic anhydride. The
objective is to match the activity of the individual catalyst
zones to the progress of the reaction along the reactor axis.
This makes it possible to achieve a high yield of the desired
product PA and at the same time to obtain a very low yield of
the undesirable intermediate phthalide. The 1st zone (= the zone
closest to the reactor inlet) usually has the lowest activity,
since the highest starting material concentrations and thus the
highest reaction rates occur in the region near the reactor
inlet. The heat liberated in the chemical reaction heats the
reaction gas up to the point at which the energy produced by the
reaction is just equal to the energy passed to the coolant. This
hottest point in the reaction tube is referred to as the hot
spot. An excessively high activity in the 1st zone would lead to
an uncontrolled increase in the hot spot temperature which
usually leads to a reduction in selectivity and can even lead to
a runaway reaction.
A further important aspect which has to be taken into account in
the design of the activity of the individual catalyst zones is
the position of the hot spot in the 1st catalyst zone. Since the
catalyst activity decreases with increasing time of operation,
the position of the hot spot moves ever further in the direction
of the reactor outlet. This can even continue so far that the
hot spot migrates from the 1st zone into the 2nd zone or even
into an even later zone. The associated significantly reduced PA
yield frequently makes it necessary in such a case for the
catalyst to be replaced, which leads to high production
downtimes.
E? 1 084 115 Bl describes a multizone catalyst for the oxidation
' of o-xylene and/or naphthalene to phthalic anhydride, in which
the activity of the individual catalyst zones increases
continuously from the reactor inlet to the reactor outlet. This
is achieved by increasing the amount of active composition and
at the same time decreasing the alkali metal content of the
catalyst so that the catalyst zone directly at the catalyst
inlet has the lowest active composition content and the highest
alkali metal content.
DE 103 23 818 Al describes a multizone catalyst for the
oxidation of o-xylene and/cr naphthalene to phthalic anhydride
which comprises at least three successive zones, in which the
activity of the individual catalyst zones increases continuously
from the reactor inlet to the reactor outlet. This is achieved
by use of TiO2 having a differing BET surface area so that the
BET surface area of the TiO2 used in the zone at the reactor
inlet is lower than that in the subsequent zones and is highest
in the last zone (reactor outlet).
DE 103 23 461 Al describes a multizone catalyst for the
oxidation of o-xylene and/or naphthalene to phthalic anhydride,
in which the activity of the individual catalyst zones increases
from the reactor inlet to the reactor outlet, with the ratio of
V2O5 to Sb23 in the first zone being from 3.5 : 1 to 5 : 1.
DE 103 23 817 Al describes a multizone catalyst for the
oxidation of o-xylene and/or naphthalene to phthalic anhydride
which comprises at least three successive zones, in which the
activity of the individual catalyst zones increases continuously
from the reactor inlet to the reactor cutlet and the last zone
closest to the reactor outlet contains more than 10% by weight
of V2O5 and is the only zone in which P is present.
¦A disadvantage of the catalysts described there is that despite
the use of such structured catalysts, the life of the catalyst
is not satisfactory, especially in respect of the increasing
migration of the hot spot in the direction of the gas stream.
Positioning of the hot spot in the (most active) catalyst zone
further towards the gas outlet also restricts the ability to
achieve fine adjustment of the selectivity of the catalyst so as
to avoid undesirable by-products.
There is therefore a continuing need for improved muitizone
catalysts for the preparation of phthalic anhydride and other
products obtained by partial oxidation of hydrocarbons.
It was therefore an object of the present invention to
provide an improved catalyst for the preparation of phthalic
anhydride by gas-phase oxidation of o-xylene and/or
naphthalene, which avoids the disadvantages of the prior art
and, in particular, makes advantageous positioning of the hot
spot and an improved life of the catalyst possible. A
particular objective of the present invention is to bring
about an increase in the catalyst life at a product yield
which is the same or even improved.
According to a first aspect of the invention, this object is
achieved by the use of the catalyst according to Claim 1.
Preferred embodiments are indicated in the subordinate
claims.
It has surprisingly been found that the object of the invention
can be achieved by using or introducing a first, very active
catalyst zone at the reactor inlet end (gas inlet end) . This
first catalyst zone which is located directly at the reactor
inlet and has a higher activity than the subsequent second
catalyst zone significantly increases the reaction rate in a
comparatively short region at the reactor inlet in which, owing
¦to the low temperature, only low reaction rates and thus low
chemical conversions usually occur. This finally results in
earlier positioning of the hot spot closer to the reactor inlet
than without the first catalyst zone according to the invention.
This is advantageous in respect of a long life (operating life)
as described above and also makes better fine adjustment of the
catalyst selectivity in the catalyst sections located downstream
of the abovementioned hot spot in the direction of the gas
outlet possible. Both yield and selectivity can be increased in
this way.
According to one aspect, the present invention thus provides the
use of a catalyst for the preparation of phthalic anhydride by
gas-phase oxidation of o-xylene and/or naphthalene, where the
catalyst comprises at least one first catalyst zone located
towards the gas inlet, a second catalyst zone located closer to
the gas outlet and a third catalyst zone located even closer to
or at the gas outlet, with the catalyst zones having different
compositions and preferably each having an active composition
comprising TiO2, characterized in that the catalyst activity of
the first catalyst zone is higher than the catalyst activity of
the second catalyst zone.
According to the invention, the individual catalyst zones have
different compositions. Here, the individual zones, in
particular the first and second catalyst zones, can also differ
only in that they have a different active composition content,
e.g. based on a particular reactor volume.
In a preferred embodiment according to the invention, the
particulate catalyst in the individual catalyst zones in each
case comprises inert ceramic supports and a layer comprising
catalytically active metal oxides which has been applied
thereto in a fluidized bed with the aid of suitable binders.
'In a preferred embodiment according to the invention, the
activity of the third catalyst zone is higher than that of
the second catalyst zone. Furthermore, the activity of a
fourth catalyst zone, if present, is preferably higher than
that of the third catalyst zone. If a fifth catalyst zone is
present, its activity is once again preferably higher than
the activity of the fourth catalyst zone. It has also been
found that it is particularly advantageous in terms of the
performance and life of the catalyst for the activity to
increase continuously (i.e. from catalyst zone to catalyst
zone) from the 2nd zone to the outlet end for the reaction
gas mixture, i.e. to the last catalyst zone.
According to the invention, the activity of the first
catalyst zone can be made higher than the activity of the
subsequent second catalyst zone by any means with which those
skilled in the art are familiar.
In a preferred embodiment according to the invention, the
increased activity in the first catalyst zone can be achieved
by, for example:
- a higher content cf active composition than in the 2nd zone
- a higher BET surface area (in particular of the TiO2 used)
than in the 2nd zone
- a higher vanadium content than in the 2nd zone
- a lower Cs content than in the 2nd zone
- a lower Sb content than in the 2nd zone
- an increase in the bulk density in the first catalyst zone,
e.g. by use of a different (ring) geometry of the inert
shaped body used;
- the presence of or a larger amount of other activity-
increasing promoters compared to the second catalyst zone;
- the absence of or a smaller amount of activity-damping
-promoters compared to the second catalyst zone;
or combinations of two or more of the above measures.
Particular preference is given to the first catalyst zone
having a higher active composition content and/or a higher
BET surface area compared to the second catalyst zone. Since
the BET surface area of the catalyst zone depends first and
foremost on the BET surface area of the TiO2 used, a preferred
embodiment according to the invention provides for the BET
surface area of the TiC>2 in the first catalyst zone to be
higher than the BET surface area of the TiO2 in the second
catalyst zone.
The above measures for increasing the activity of the first
catalyst zone compared to the second catalyst zone can
naturally also be used for the preferred setting of the
activities of the subsequent catalyst zones (e.g. the third
and fourth catalyst zones).
In a preferred embodiment according to the invention, the
activity of the first catalyst zone is at least 5%, in
particular at least 10%, preferably at least 20%,
particularly preferably at least 30%, higher than the
activity of the subsequent second catalyst zone. A method of
determining or comparing the activity of catalysts (catalyst
zones) is indicated below in the method part.
The second catalyst zone is preferably the least active
catalyst zone in the total catalyst.
According to the invention, the length of the first catalyst
zone (1st zone) is preferably such that the hot spot occurs
in the subsequent second catalyst zone (2nd zone) and not in
¦the first catalyst zone itself under the desired reaction
conditions. Thus, the hot spot is preferably located in the
second catalyst zone, by means of which the above advantages
can be realized particularly well. For this reason, a
preferred length in the case of customary reactor tubes is 20
- 70 cm, particularly preferably 30 - 60 cm. Here, the
customary length of the reactor tubes and the catalyst bed
located therein is from about 2.5 to 3.5 m. The length of the
first catalyst zone is influenced not only by the volume flow
and the loading but also, in particular by the axial
temperature gradient in the surrounding coolant (salt bath).
In the case of a high axial temperature gradient which
occurs when coolant circulation is poor, the temperature of
the coolant at the reactor inlet is up to 10°C higher than at
the reactor outlet. In this case, the length of the first
catalyst zone is made shorter and its activity is made more
moderate than in the case of a small axial temperature
gradient in the coolant.
In a preferred embodiment according to the invention, the
length of the 1st zone is preferably 5 - 25%, particularly
preferably 10 - 25% of the total length of the catalyst or
catalyst bed. In addition to other factors, the height of the
axial temperature gradient in the surrounding cooling medium
also plays a role in the design of the length. In any case,
the length of the 1st zone is less than would correspond to
the position of a conceptual hot spot, measured as the
distance from the beginning of the catalyst bed to the point
at which the max. temperature is achieved, which would be
formed if, in place of the 1st zone, uhe corresponding region
were also to be filled with catalyst of the 2nd zone.
According to a particularly preferred embodiment, the ratio
of the length of the first zone to the length of the second
zone is less than or equal to 0.9. This ratio is more
preferably in the range from about 0.1 to 0.9, in particular
¦from 0.1 to 0.7, preferably from 0.15 to 0.5. This ensures
that the first zone is not too long compared to the second
" zone in which the hot spot is preferably located.
In a further, preferred embodiment according to the
invention, the individual catalyst zones each have at least
titanium and vanadium in the active composition. It has also
been found that particularly good results can be achieved in
the preparation of PA when the vanadium content of the active
composition in the first catalyst zone, calculated as V2O5, is
more than 4% by weight, in particular more than 5% by weight.
In addition, the individual catalyst zones preferably contain
no molybdenum and/or tungsten, in particular not in an atomic
ratio to vanadium in the range from 0.01 to 2. In a preferred
embodiment, no Ni or Co are used in the catalysts employed
either. In a preferred embodiment, the Na content of the
active composition is less than 500 ppm, in particular less
than 450 ppm.
Preference is also given to Cs and/or Sb being presenr in the
catalyst zones. In a particularly preferred embodiment
according to the invention, at least the second catalyst zone
contains Cs, with the first catalyst zone preferably having a
lower Cs content (or containing no Cs at all). It has been
found that the interplay of the first catalyst zone having a
desired high reaction rate for the primary conversion of the
smarting materials, in particular of starting materials, in
particular of o-xylene and/or naphthalene, directly at the
beginning of the bed at the gas inlet: end, and the second
catalyst zone having an early positioning of the hot spot
relatively near to the reactor inlet can be brought about
particularly well in this way.
The composition ranges of the catalysts (active composition)
used in the individual zones are preferably as follows:
Apart from the above components, the remainder of the active
composition comprises at least 90% by weight, preferably at
least 95% by weight, more preferably at least 98% by weight,
in particular at least 99% by weight, more preferably at
least 99.5% by weight, in particular 100% by weight of TiO2.
It has also been found in the context of the present
invention that particularly advantageous catalysts can, in
one embodiment, be produced when the active composition
content decreases from the second catalyst zone to the
catalyst zone nearest the gas outlet. In a preferred
embodiment, the second catalyst zone has an active
composition content of from about 6 to 12% by weight, in
particular from about 6 to 11% by weight, the third catalyst
zone has an active composition content of from about 5 to 11%
by weight, in particular from about 6 to 10% by weight, and
the fourth catalyst zone (if present) has an active
composition content of from about. 4 to 10% by weight, in
particular from about 5 to 9% by weight. However, catalysts
in which the active composition content remains constant or
increases from the 2nd zone to the last zone, i.e.:
Active composition content 2nd zone ^active composition content 3rd zone £¦¦• ^active
composition contention zane<.> are also possible in principle.
¦In an advantageous embodiment, at least the active
composition content cf the last zone is higher than that of
the 2nd zone.
In a particularly preferred embodiment according to the
invention, the catalyst according to the invention of the
first catalyst zone has an active composition content of from
about 6 to 20% by weight, preferably from about 7 to 15% by
weight.
The expressions first, second, third or fourth catalyst zone
are used as follows in the context of the present invention:
the first catalyst zone is the catalyst zone nearest the gas
inlet. In the direction of the gas outlet, at least two
further catalyst zones are present in the catalyst according
to the invention and these are referred to as second, third
or fourth catalyst zone. The third catalyst zone is located
closer to the gas outlet than the second catalyst zone. The
individual catalyst zones can be introduced with or without
mixing in the interface regions in order to obtain the
(multizone) catalyst.
In a particularly preferred embodiment according to the
invention, the catalyst used according to the invention has
four catalyst zones. The fourth catalyst zone is then at the
gas outlet end. However, the presence of additional catalyst
zones in a downstream direction is not ruled out. For
example, in an embodiment according to the invention, the
fourth catalyst zone as defined herein can be followed by a
fifth catalyst zone. Independently of this, the use of a
finishing reactor as described, for example, in DE-A-198 07
018 or DE-A-20 05 969 is also possible in the preparation of
phthalic anhydride.
In a preferred embodiment according to the invention, the BET
"surface area of the TiO2 used increases from the second
catalyst zone to the catalyst zone nearest the gas outlet. In
other words, preference is given to the BET surface area of
the TiC2 used in the second catalyst zone being lower than the
BET surface area of the TiO2 used in the catalyst zone nearest
the gas outlet (last catalyst zone). Preferred ranges for the
BET surface area of the TiO2 are from 15 to 30 m2/g for the
middle catalyst zones and from 15 to 45 m2/g for the catalyst
zone nearest the gas outlet (last catalyst zone).
Particularly advantageous catalysts are also obtained when
the BET surface areas of the TiC>2 of the middle catalyst zones
are identical while the BET surface area of the TiO2 in the
last catalyst zone is in comparison greater. The BET surface
area of the TiO2 of the first catalyst zone is preferably
greater than or equal to the BET surface area of the TiO2 of
the second catalyst zone or the middle catalyst zones and is
in particular in the range from about 15 to 4 5 m2/g. In an
embodiment according to the invention, the BET surface area
cf the TiO2 used is as follows:
BETi;02, 2nd zone ^ BET^ioa, 3rd zone ^ • ¦ • — BET7J.02, last zone. Even
greater preference is given to BETTiO2, isc zone ^ BETTiO2, 2nd zone.
The temperature management in the gas-phase oxidation of o-
xylene to phthalic anhydride is adequately known to a person
skilled in the art from the prior art, and reference may be
made, for example, to DE 100 40 827 Al.
When the catalyst of the invention is used for preparing
phthalic anhydride, it is usual practice to pass a mixture of
a gas containing molecular oxygen, for example air, and the
starting material to be oxidized (in particular o-xylene
and/or naphthalene; through a fixed-bed reactor, in
particular a shell-and-tube reactor which can comprise a
multiplicity of parallel tubes. A bed of at least one
catalyst is present in each of the reactor tubes. The
advantages of a bed composed of a plurality of (different)
catalyst zones have been discussed above.
When the catalysts described herein are employed for
preparing phthalic anhydride by gas-phase oxidation of o-
xylene and/or naphthalene, it has surprisingly been found
that use of the catalysts used according to the invention
results in very good PA yields with very low proportions of
phthalide and a position of the her spot close to the reactor
inlet, which makes an improved operating life of the catalyst
possible.
In a preferred embodiment according to the invention, the TiG;
used (usually in the anatase form) has a BET surface area of
at least 15 m2/g, preferably from 15 to 60 m2/g, in particular
from about 15 to 45 m2/g and particularly preferably from 15
to 40 m2/g. Furthermore, preference is given to at least 30%,
in particular at least 40%, and up to 80%, preferably up to
75%, in particular up to 70%, of the total pore volume of the
TiC>2 being formed by pores having a radius of from 60 to
400 run. The determination of the pore volumes and proportions
reported here is carried out, unless indicated otherwise, by
means of mercury porosimetry (in accordance with DIN 66133) .
The figure given for the total pore volume in the present
description is in each case based on the total pore volume
measured by means of mercury porosimetry in the pore radius
range from 7500 to 3.7 nm. Pores having a radius of more than
400 nm preferably make up less than about 30%, in particular
less than about 22%, particularly preferably less than 20%,
of the total pore volume of the TiO2 used. Furthermore,
preference is given to from about 50 to 75%, in particular
from about 50 to 70%, particularly preferably from 50 to 65%,
'of the total pore volume of the TiO2 being formed by pores
having a radius of from 60 to 400 nm and preferably from
about 15 to 25% of the total pore volume being formed by
pores having a radius of more than 400 nm. With regard to the
smaller pore radii, it is preferred that less than 30%, in
particular less than 20%, of the total pore volume of the TiO2
is formed by pores having a radius of from 3.7 to 60 nm. A
particularly preferred range for this pore size is from about
10 to 30% of the total pore volume, in particular from 12 to
20%.
In a further preferred embodiment, the TiO2 used has the
following particle size distribution: The D^ is preferably
0.5 urn or less; the D5o (i.e. the value at which half the
particles have a larger diameter and half the particles have
a smaller diameter) is preferably 1.5 urn or less; the D90 is
preferably 4 urn or less. The D90 of the TiC>2 used is
preferably in the range from about 0.5 to 20 um, in
particular from about 1 to 10 um, particularly preferably
from about 2 to 5 um. In electron micrographs, the TiC2 used
according to the invention preferably has an open-pored,
sponge-like structure in which more than 30%, in particular
more than 50%, of the primary particles or crystallites are
agglomerated to form open-pored agglomerates. It is assumed,
without the invention being restricted to this assumption,
that this particular structure of the TiC2 used, which is
reflected in the pore radius distribution, creates
particularly favourable reaction conditions for the gas-phase
oxidation.
In principle, another titanium dioxide having a different
specification than that described above, i.e. a different BET
surface area, porosimetry and/or particle size distribution, can
also be used in the catalyst of the invention. According to the
'invention, it is particularly preferred that at least 50%, in
particular at least "7 5%, particularly preferably all, of the
TiO2 used has a BET surface area and porosimetry as defined
herein and preferably also has the particle size distribution
described. Blends of different TiO2 materials can also be used.
Depending on the envisaged use of the catalyst, the customary
components known to those skilled in the art can be present
in the active composition of the catalyst in addition to TiO2.
The shape of the catalysts and its homogeneous or
heterogeneous structure are in principle also not subject to
any restrictions for the purposes of the present invention
and can have any variant which is known to those skilled in
the art and appears suitable for the respective application.
Coated catalysts have been found to be particularly useful
for the preparation of phthalic anhydride. Here, a support
which is inert under the reaction conditions, for example
silica (Si02) , porcelain, magnesium oxide, tin dioxide,
silicon carbide, rutile, alumina (AI2C3) , aluminium silicate,
magnesium silicate (steatite), zirconium silicate or cerium
silicate or mixtures of the above materials, is used. The
support can, for example, have the shape of rings, spheres,
shells or hollow cylinders. The catalytically active
composition is applied thereto in comparatively thin layers
(coatings). It is also possible for two or more layers of a
catalytically active composition having the same or different
composition to be applied.
With regard to the further components of the catalytically
active composition of the catalyst of the invention (in
addition to TiO2) , reference may basically be made to the
compositions or components which are described in the
relevant prior art and with which those skilled in the art
are familiar. These are mainly catalyst systems in which
'oxides cf vanadium are present in addition to titanium
cxide(s). Such catalysts are described, for example, in EP 0
964 744 Bl whose relevant disclosure is hereby expressly
incorporated by reference into the present description. In
many cases, it can be preferable to use a V2O5 material having
quite a small particle size for the individual catalyst zones cf
the catalyst of the invention in order to aid spraying onto the
TiOa- For example, at least 90% of the V205 particles used can
have a diameter of 20 urn or less. On this subject, reference may
be made, for example, to DE 10344846 Al.
In particular, a series of promoters to increase the
productivity cf the catalysts are described in the prior art
and these can likewise be used in the catalyst of the
invention. They include, inter alia, the alkali metals and
alkaline earth metals, thallium, antimony, phosphorus, iron,
niobium, cobalt, molybdenum, silver, tungsten, tin, lead
and/or bismuth and also mixtures cf two or more of the above
components. In a preferred embodiment according to the
invention, the catalysts used according to the invention thus
contain one or more of the above promoters. For example, DE
21 59 441 A describes a catalyst which comprises titanium
dioxide in the anatase modification together with from 1 to
30% by weight of vanadium pentoxide and zirconium dioxide. A
listing of suitable promoters may also be found in
WO2004/103561, page 5, lines 29 to 37, which is likewise
incorporated by reference. The individual promoters enable
the activity and selectivity of the catalysts to be
influenced, in particular by reducing or increasing the
activity. Selectivity-increasing promoters include, for
example, the alkali metal oxides and cxidic phosphorus
compounds, in particular phosphorus pentoxide. In a preferred
embodiment, the first catalyst zone and preferably also the
second catalyst zone contain(s) no phosphorus. It has been
found that a high activity can be achieved in this way, with
the selectivity in the subsequent catalyst zones (3rd and
further zone(s)) being able to be set advantageously by, for
example, the presence of phosphorus. In some cases it can be
advantageous for only the last zone to contain phosphorus. In
a further preferred embodiment, the ratio of vanadium,
calculated as V2O5, re antimony, calculated as Sb2O3, in the
catalyst of the 1st zone and/or in the catalyst of the 2nd zene
is from about 3.5 : 1 to 5 : 1, as described, for example, in DE
103 23 461 A.
In a further preferred embodiment, the alkali metal content,
preferably the Cs content, of the catalyst of the invention
remains constant or decreases from the 2nd zone to the last zone
(at the gas outlet end). In ether words:
CS content 2nd zone - Cs Content 3rd ZOne ^» • • S: C3 content last zone.
Particular preference is given to the last catalyst zone
containing no Cs.
Numerous suitable methods of producing the catalysts of the
invention are described in the prior art, so that a derailed
presentation here is basically unnecessary. For the
production of coated catalysts, reference may be made, for
example, to the process described in DE-A-16 42 938 or DE-A
17 69 998, in which a solution or suspension of the
components of the catalytically active composition and/or
their precursor compounds in water and/or an organic solvent
(frequently referred to as "slurry") is sprayed onto the
support material in a heated coating drum at elevated
temperature until the desired content of catalytically active
composition, based en the total weight of the catalyst, has
been achieved. The application of the catalytically active
composition to the inert support ;coating process) can also
be carried out in fiuidized-bed coaters as described in DE 21
06 796.
Coated catalysts are preferably produced by applying a thin
layer of from 50 to 500 um of the active component to an inert
support (cf. US 2,035,606). Spheres or hollow cylinders have
been found to be particularly useful as supports. These shaped
bodies give a high packing density with a low pressure drop and
reduce the risk of formation of packing defects when the
catalyst is introduced into the reaction tubes.
The molten and sintered shaped bodies have to be heat-resistant
within the temperature range of the reaction which occurs. As
indicated above, possibilities are, for example, silicon
carbide, steatite, silica, porcelain, Si02, AI2O3 or alumina.
The advantage of carrying out the coating of support bodies in a
fiuidized bed is the high uniformity of the layer thickness
which plays a critical role in the catalytic performance of the
catalyst. A particularly uniform coating is obtained by spraying
a suspension or solution of the active components onto the
heated support at from 80 to 200°C in a fluidized bed, for
example as described in DE 12 30 756, CE 198 28 583 or DE 197 CS
589. In contrast to coating in a coating drum, when hollow
cylinders are used as supports, the inside of the hollow
cylinder can also be coated uniformly in the fluidized-bed
processes described. Among the fluidized-bed processes described
above, the process cf DE 197 09 589 is particularly advantageous
since the predominantly horizontal, circular motion of the
supports enables net only uniform coating but also low abrasion
of apparatus components to be achieved.
In the coating procedure, the aqueous solution or suspension of
the active components and an organic binder, preferably a
copolymer of vinyl acetate-vinyl laurate, vinyl acetate-ethylene
or styrene-acrylate, is sprayed by means of one or more nozzles
onto the heated, fluidized support. It is particularly
advantageous to introduce the spray liquid at the point of
greatest product velocity where the sprayed material can be
distributed uniformly in the bed- The spraying procedure is
continued until either the suspension has been used up or the
required amount of active components has been applied to the
support.
In a particularly preferred embodiment according to the
invention, the catalytically active composition of the
catalyst of the invention is applied in a moving bed or
fluidized bed with che aid of suitable binders so that a
coated catalyst is produced. Suitable binders encompass
organic binders with which those skilled in the art are
familiar, preferably copolymers, advantageously in the form
of an aqueous dispersion, of vinyl acetate-vinyl laurate,
vinyl acetate-acrylate, styrene-acrylate, vinyl acetate-
maleate and vinyl acetate-ethylene. Particular preference is
given to using an organic polymeric or copolymeric adhesive,
in particular a vinyl acetate copolymer adhesive, as binder.
The binder used is added to the catalytically active
composition in customary amounts, for example from about 10
to 20% by weight, based on the solids content of the
catalytically active composition. For example, reference may
be made to EP 744 214. If the application of the
catalytically active composition is carried out at elevated
temperatures of about 150°C, application to the support
without organic binders is also possible, as is known from
the prior art. Coating temperatures which can be employed
when using the abovementioned binders are, according to
DE 21 06 796, in the range from, for example, about 50 to
450°C. The binders used burn out within a short time when the
catalyst is heated during start-up of the charged reactor.
The binders serve first and foremost to strengthen the
adhesion of the catalyticaliy active composition to the
support and to reduce attrition during transport and charging
of the catalyst.
Further possible processes for producing coated catalysts for
the catalytic gas-phase oxidation of aromatic hydrocarbons to
carboxylic acids and/or carboxylic anhydrides have been
described, for example, in WO 93/00778 and EP-A 714 700.
According to this, a powder is firstly produced from a
solution and/or suspension of the catalyticaliy active metal
oxides and/or their precursor compounds, if appropriate in
the presence of auxiliaries for catalyst production, and this
is subsequently, in order to produce the catalyst, applied in
the form of a coating to the support, if appropriate after
conditioning and if appropriate after heat treatment to
produce the catalyticaliy active metal oxides, and the
support which has been coated in this way is subjected to
heat treatment to produce the catalyticaliy active metal
oxides or a treatment to remove volatile constituents.
Suitable conditions for carrying out a process for the
preparation of phthalic anhydride from o-xylene and/or
naphthalene are likewise known to those skilled in the art
from the prior art. In particular, reference may be made to
the summary presentation in K. Towae, W. Enke, R. Jackh, N.
Bhargana "Phthalic Acid and Derivatives" in Ullmann's
Encyclopedia of Industrial Chemistry Vol. A. 20, 1992, 181,
and this is hereby incorporated by reference. For example,
the boundary conditions known from the above reference WO-A
98/37967 or WC 99/61433 can be selected for steady-state
operation of the oxidation.
For this purpose, the catalysts are firstly introduced into
the reaction tubes of the reactor, which are thermostatted
from the outside to the reaction temperature, for example by
means of salt melts. The reaction gas is passed at
temperatures of generally from 300 to 450°C, preferably from
320 to 420°C and particularly preferably from 340 to 400°C,
and a gauge pressure of generally from 0.1 to 2.5 bar,
preferably frcm 0.3 to 1.5 bar, over the catalyst bed
prepared in this way at a space velocity of generally from
750 to 5000 h"1.
The reaction gas passed over the catalyst is generally
produced by mixing a gas containing molecular oxygen, which
can comprise oxygen together with suitable reaction
moderators and/or diluents such as steam, carbon dioxide
and/or nitrogen, with the aromatic hydrocarbon to be
oxidized. The gas containing molecular oxygen can generally
comprise from 1 to 100 mol%, preferably frcm 2 to 50 mol% and
particularly preferably from 10 to 30 mol%, of oxygen, from 0
to 30 mol%, preferably from 0 to 10 mol%, of water vapour and
from 0 to 50 mol%, preferably frcm 0 ~o 1 mol%, of carbon
dioxide, with the balance being nitrogen. To produce the
reaction gas, the gas containing the molecular oxygen is
generally admixed with from 30 to 150 g of the aromatic
hydrocarbon to be oxidized per standard m3 of gas.
In a particularly preferred embodiment according to the
invention, the active composition (catalytically active
composition) of the catalyst of the first catalyst zone
comprises from 5 to 16% by weight of V2O5, from 0 to 5% by
weight of Sb2O3, from 0.2 to 0.75% by weight of Cs, from 0 to
3% by weight of Nb205, from 0 to 1% by weight of P. The
remainder of the active composition comprises at least 90% by
weight, preferably at least 95% by weight, more preferably at
'least 38% by weight:, in particular at leasz 99% by weight,
1 more preferably at least 99.5% by weight, in particular 100%
by weight, of TiG2. In a particularly preferred embodiment
according to the invention, the EET surface area of the TiO2
is from 15 to about 45 m2/g. Furthermore, preference is given
to such a first catalyst zone making up 5 - 25%, particularly
preferably 10 - 25%, of the total length of ail catalyst zones
present (total length of the catalyst bed present).
In a particularly preferred embodiment according to the
invention, the active composition of the catalyst of the
second catalyst zone comprises from 5 to 25% by weight of
V205, from 0 to 5% by weight of Sb2O3, from 0.2 to 0.75% by
weight of Cs, from 0 to 2% by weight of Nb20=, from 0 to 1% by
weight of P. The remainder of the active composition
comprises at least 90% by weight, preferably at least 95% by
weight, more preferably at least 98% by weight, in particular
at least 99% by weight, more preferably at least 99.5% by
weight, in particular 100% by weight, of TiO2. In a
particularly preferred embodiment according to the invention,
the BET surface area of the TiC2 is from 15 to about 25 m2/g.
Furthermore, preference is given to such a second catalyst zone
making up from about 15 to 60%, in particular from 20 to 60% or
from 20 to 50%, of the total length of all catalyst zones
present (total length of the catalyst bed present).
In a particularly preferred embodiment according to the
invention, the active composition of the catalyst of the
third catalyst zone comprises from 5 to 15% by weight of V2Os,
from 0 to 4% by weight of Sb2C>3, from 0.05 to 0.5% by weight of
Cs, from 0 to 2% by weight of Nb205, 0 - 1% by weight of P. The
remainder of the active composition comprises at least 90% by
weight, preferably at least 95% by weight, more preferably at
least 98% by weight, in particular at least 99% by weight,
more preferably at least 99.5% by weight, in particular 100%
by weight, of TiO2. The TiO2 preferably has a BET surface area
in the range from about 15 to 25 m2/g. Furthermore, preference
is given to this third zone making up from about 10 to 30% of
the total length of all catalyst zones present, in particular if
the third zone is followed by at least one further catalyst
zone. If the third zone is the last zone, i.e. the zone nearest
the reactor cutlet, the 3rd zone preferably makes up 20 - 50% of
the total length.
In a particularly preferred embodiment according to the
invention, the active composition of the catalyst of the
fourth catalyst zone comprises from 5 to 25% by weight of
V205, from 0 to 5% by weight of Sb2O3, from 0 to 0.2% by weight
cf Cs, from 0 to 2% of P, from 0 to 1% by weight of Nb2C5. The
remainder of the active composition comprises at least 90% by
weight, preferably at least 95% by weight, more preferably at
least 98% by weight, in particular at least 99% by weight,
more preferably at least 99.5% by weight, in particular 100%
by weight, of TiO2. If the fourth zone represents the catalyst
zone nearest the gas outlet of the reactor (last catalyst zone),
preference is given to a BET surface area of the TiO2 which is
somewhat higher than that of the zones closer to the gas inlet,
in particular in the range from about 15 to about 45 m2/g.
Furthermore, preference is given to such a fourth catalyst zone
making up from about 10 to 50%, particularly preferably from 10
to 40%, of the total length cf ail catalyst zones present. A
fifth catalyst zone is then generally not necessary, but is
possible.
It has also been found that, in a preferred embodiment,
catalysts used according to the invention which have no
phosphorus in the catalytically active composition in the
middle catalyst zone and, if appropriate, in the first catalyst
zone, display particularly good activities combined with a very
high selectivity. Furthermore, preference is given to at least
0.05% by weight of the catalytically active composition in the
first catalyst zone and the middle catalyst zones being formed
by at least one alkali metal, calculated as alkali metal(s).
Caesium is particularly preferred as alkali metal.
The catalysts used according to the invention can be heat
treated or calcined (conditioned) in a customary manner before
use. It has here been found to be advantageous for the catalyst
to be calcined for at least 24 hours at at least 390°C, in
particular from 24 to 72 hours at > 4C0°C, in an 02-ccntaining
gas, in particular in air. The temperature should preferably not
exceed 500°C, in particular 470°C. However, other calcination
conditions which appear suitable to a person skilled in the arc
are not ruled out in principle.
According to a further aspect, the present invention provides a
process for producing a catalyst as described herein, which
comprises the following steps:
a. provision of a catalytically active composition as
defined herein,
b. provision of an inert support, in particular an inert
support shaped body;
c. application of the catalytically active composition
to the inert support, in particular in a fluidized
bed or a moving bed.
The individual catalysts are subsequently introduced in the
desired order as catalyst zones into the reactor in order to
obtain the multizone catalyst.
According to a further aspect, the invention also provides a
process for the preparation of phthalic anhydride by gas-phase
oxidation of o-xylene and/or naphthalene, in which a three-zone
or multizone catalyst as defined in the above description is
used. In this process, a gaseous stream comprising o-xylene
and/or naphthalene and also molecular oxygen is generally
passed at elevated temperature, in particular from about 250 to
490"C, over a three-zone or multizone catalyst as defined in the
preceding claims.
METHODS
The following methods are used for determining the parameters
of the catalysts according to the invention:
1. BET surface area:
The determination is carried out by the BET method in
accordance with DIN 66131; the BET method is also published
in J. Am. Chem. Sec. 60, 309 (1938).
2. Pore radius distribution:
The determination of the pore radius distribution of the TiO2
used was carried out by mercury porosimetry in accordance
with DIN 66133; maximum pressure: 2,000 bar, Porosimeter 4000
(from Porotec, Germany), in conformity with the
manufacturer's instructions.
3. Particle sizes:
The determination of the particle sizes was carried out by
the laser scattering method using a Fritsch Particle Sizer
Analysette 22 Economy (from Fritsch, Germany) in conformity
with the manufacturer's instructions, including sample
pretreatment: the sample is homogenized in deionized water
without addition of auxiliaries and treated with ultrasound
for 5 minutes.
The determination of the BET surface area, the pore radius
distribution or the pore volume and the particle size
distribution was in the case of titanium dioxide in each case
carried out on the uncalcined material dried at 150°C under
reduced pressure.
The figures quoted in the present description for the BET
surface areas of the catalysts or catalyst zones also refer
to the BET surface areas of the TiOs material used in each
case (dried at 150°C under reduced pressure, uncalcined, cf.
above).
In general, the BET surface of the catalyst is determined by
the BET surface area of the TiO2 used, with the addition of
further catalyticaliy active components changing the BET
surface area to a certain extent. A person skilled in the art
will know this.
The active composition content (proportion of catalyticaliy
active composition without binder) is in each case the
proportion (in % by weight) of the total weight of the
catalyst including support which is made up by the
catalyticaliy active composition in the respective catalyst
zone, measured after conditioning at 400°C for 4 hours in
air.
4. Catalyst activity:
For the purposes of the invention, the activity of the
catalyst in a catalyst zone is the ability of the catalyst to
react the starting material used within a defined volume (=
balance space), for example a reaction tube cf defined length
and internal diameter (e.g. 25 mm internal diameter, 1 m
length), under prescribed reaction conditions (temperature,
pressure, concentration, residence time). The catalyst under
consideration accordingly has a higher activity than another
catalyst when it achieves a higher conversion of starting
material in this prescribed volume under in each case
identical reaction conditions. In the case of o-xylene or
naphthalene as starting material, the catalyst activity is
thus given by the magnitude of the conversion of o-xylene or
naphthalene into the oxidation products. The cause of a
higher catalyst activity can be either an optimized nature /
quality of the active sites for the desired reaction (cf.,
for example, "turnover frequency") or an increased number of
active sites in the same balance space, which is the case
when, for example, a larger mass of catalyst having otherwise
identical properties is present in the balance space.
Operational quantification of the activity:
According to the invention, the activity of the 1st zone is
higher than that of the 2nd zone. This means firstly that, in
accordance with the present exposition, the conversion of
starting material at the end of a reaction space (= reaction
tube of defined length and internal diameter, e.g. 25 mm
internal diameter, 1 m length) which is charged with "zone 1
catalyst" and through which the feed mixture flows is higher
than in an otherwise identical comparative experiment in
which the identical reaction space has been filled with "zone
2 catalyst".
Such a test is advantageously carried out using conditions
within the following ranges:
Length of reaction tube:
1 m
Internal diameter of reaction tube: 25 mm
Temperature of cooling medium: 380 - 420 °C
Pressure: 1-1.5 bar absolute
o-Xylene loading in feed mixture: 60 g of o-xylene/
standard m3 of air
The activity of the first catalyst zone compared to the activity
of the second catalyst zone can then be quantified as follows
with the aid of the following definition according to the
invention of a "catalyst having a 10% higher activity" used for
zone 1 compared to a catalyst used for zone 2:
The feed mixture is passed through the comparative catalyst
(= zone 2 catalyst having the intended composition) under the
abcvementioned conditions, with the total volume flow through
the reaction tube being set sc that the o-xylene conversion
after passage through the reaction space is very close to 50%.
In a second experiment, the same reaction volume is filled with
zone 1 (test) catalyst which differs from the zone 2 catalyst
only in that the active composition content is 10% higher.
Thus, 10% more active composition is present in the reaction
volume than in the case of the comparative catalyst. The o-
xylene conversion after passage through the reaction space
filled with zone 1 catalyst is then determined under identical
reaction conditions. This is higher than that obtained using the
comparative catalyst, i.e. higher than 50%. The difference
between the o-xylene conversion obtained in this way and the 50%
conversion obtained using the comparative catalyst is used as a
relative figure corresponding to a 10% increase in activity. The
change made to the catalyst to achieve such an effect is
immaterial. Accordingly, a catalyst which differs from the
intended zone 2 catalyst only in that the active composition
content is 20% higher can, for example, be used to determine a
figure for a 20% higher activity of the catalyst, etc.
In the present description, the hot spot is the maximum
temperature measured in the entire catalyst bed. Furthermore,
there are also (secondary) hot spots, i.e. maximum
temperatures, in the further catalyst zones under
consideration.
The invention is illustrated by the following noniimiting
examples:
EXAMPLES
Example 1: (Comparative Example):
A 3-zone catalyst system having the composition and zone
lengths shown below was introduced into a tube reactor which
had an internal diameter of 25 mm and was cooled by means of
a salt bath. A 3 mm thermocouple sheath having an installed
movable element was arranged centrally in the reaction tube
to measure the temperature. 4 standard m3/h of air having a
loading of 30 - 100 g of o-xylene / standard m3 of air (o-
xylene purity > 99%) were passed through the tube from the
top downwards at a total pressure of about 1450 mbar.
At a loading of 60 - 65 g of o-xylene / standard m3 of air
and a salt bath temperature of from 370 to 375°C, the hot
spot was measured in zone 1 at a position of 90 - 100 cm
(from the beginning of the bed in the direction of the
reactor outlet).
Example 2: (Example according to the invention):
A 4-zone catalyst system having the composition and zone
lengths shown below was introduced into a tube reactor which
had an internal diameter of 25 mm and was cooled by means of
a salt bath. A 3 mm thermocouple sheath having an installed
movable element was arranged centrally in the reaction tube
to measure the temperature. 4 standard m3/h of air having a
loading of 30 - 100 g of o-xylene / standard m3 of air (o-
xylene purity > 99%) were passed through the tube from the
top downwards at a total pressure of about 1450 mbar.
At a loading of 60 - 65 g of o-xylene / standard m3 of air
and a salt bath temperature of from 365 to 375°C, the hot
spot described in Example 1 was now measured in zone 2 at a
position of 75 - 85 cm (from the beginning of the bed in the
direction of the reactor outlet).
The position of the hot spot described in Example 2 according
to the invention is thus significantly closer to the reactor
inlet than in Comparative Example 1.
This leads to the following advantages for the catalyst
according to the invention, with these applying not only to
the specific example but generally for the present invention:
- Longer life since the hot spot is located closer to the
reactor inlet at the beginning of the reaction and
accordingly also as deactivation progresses; in particular it
remains longer in the 2nd zone (formerly 1st zone).
- A lower content of phthalide in the reaction gas leaving
the reactor since the reaction has moved further upstream.
- The (secondary) hot spot in the 3rd zone is lower than in
the equivalent 2nd zone of the comparative example since more
o-xylene is reacted in the two preceding zones 1 and 2 than
in zone 1 in the comparative example.
When Example 2 was repeated using a catalyst which was
identical except for the absence of phosphorus in the first
zone, the salt bath temperatures at the same loading could be
reduced somewhat and the hot spot was located somewhat closer
still to the gas inlet end (position: about 70 cm).
The influence of an upstream catalyst zone in which the Cs
content has been reduced to increase the catalyst activity is
described below.
Example 3: (Comparative Example):
A 3-zone catalyst system having the composition and zone
lengths shown below was introduced into a tube reactor which
had an internal diameter of 25 mm and was cooled by means of
a salt bath. A 3 mm thermocouple sheath having an installed
moveable element was arranged centrally in the reaction tube
to measure the temperature. 4 standard m3/h of air having a
loading of 30 - 100 g of o-xyisne / standard m3 of air
(o-xyiene purity > 99%) were passed through the tube from the
top downwards at a total pressure of 1450 mbar.
At a loading of 60 - 65 g of c-xylene / standard m3 of air and
a salt bath temperature of from 358 to 362°C, the hot spot
was measured in zone 1 at a position of 90 cm measured from
the beginning of the bed in the direction of the reactor
outlet.
Example 4: (Example according to the invention):
A 4-zone catalyst system having the composition and zone
lengths shown below was introduced into a tube reactor which
had an internal diameter of 25 mm and was cooled by means of
a salt bath. A 3 mm thermocouple sheath having an installed
moveable element was arranged centrally in the reaction tube
to measure the temperature. 4 standard m3/h of air having a
loading of 30 - 100 g of o-xylene / standard m3/h of air
(c-xylene purity > 99%) were passed through the tube from the
top downwards at a total pressure of about 1450 mbar.
At a loading of 60 - 65 g of o-xyiene / standard m3 of air and
a salt bath temperature of from 352 to 356°C, the hot spot
was measured in zone 1 at a position of 80 cm from the
beginning of the bed in the direction of the reactor outlet.
The position of the hot spot in Example 4 according to the
invention is thus about 10 cm closer to the reactor inlet
than in Comparative Example 3.
WE CLAIM:
1. A catalyst for the preparation of phthalic anhydride by gas-phase oxidation of o-
xylene and/or naphthalene, wherein the catalyst comprises at least one first
catalyst zone located towards the gas inlet, a second catalyst zone located closer to
the gas outlet and a third catalyst zone located even closer to or at the gas outlet,
with the catalyst zones preferably each having an active composition comprising
TiO2, characterized in that the catalyst activity of the first catalyst zone is higher
than the catalyst activity of the second catalyst zone.
2. Catalyst as claimed in claim 1, wherein the catalyst activity increases from the
second to the third catalyst zone.
3. Catalyst as claimed in either of the preceding claims, wherein the catalyst activity
increases from the third to the fourth catalyst zone and, if appropriate, further to
the fifth catalyst zone.
4. Catalyst as claimed in any of the preceding claims, wherein a total of four or five
catalysts zones, in particular four catalyst zones, are present.
5. Catalyst as claimed in any of the preceding claims, wherein the length of the first
catalyst zone is from 5 to 30%, in particular from 10 to 25%, particularly
preferably from 10 to 20%, of the total length of the total catalyst bed.
6. Catalyst as claimed in any of the preceding claims, wherein the first catalyst zone
has
a. a higher active composition content and/or
b. a higher vanadium content and/or
c. a TiO2 having a higher BET surface area and/or
d. a lower Sb content and/or
e. a lower Cs content and/or
f. a higher content of promoters which increase the activity and/or
g. a higher bulk density, in particular as a result of the use of a different
geometry of the shaped bodies, and/or
h. a lower content of promoters which lower the activity
than the second catalyst zone.
7. Catalyst as claimed in any of the preceding claims, wherein the first catalyst zone
comprises a higher content of promoters which increase the activity.
8. Catalyst as claimed in any of the preceding claims, wherein the first zone has a
higher bulk density than the second catalyst zone, in particular as a result of the
use of a different geometry of the shaped body.
9. Catalyst as claimed in any of the preceding claims, wherein the individual catalyst
zones are composed of coated catalysts in which an active composition has been
applied to an inert support.
10. Catalyst as claimed in any of the preceding claims, wherein the individual catalyst
zones comprise as active composition at least:
Composition Range
V2O5 /% by wt. 1 - 25
Sb2O3 /% by wt. 0-4
Cs /% by wt. 0-1
P /% by wt. 0-2
with the remainder of the active composition comprising at least 90% by weight,
preferably at least 95% by weight, more preferably at least 98% by weight, in
particular at least 99% by weight, more preferably at least 99.5% by weight, in
particular 100% by weight, of TiO2 and the BET surface area of the TiO2 used
being in the range from 10 to 50 m2/g and the active composition making up from
4 to 20% by weight of the total weight of the catalyst.
11. Catalyst as claimed in any of the preceding claims, wherein the catalyst of the first
catalyst zone has an active composition content of from 6 to 20% by weight,
preferably from 7 to 15% by weight, and the active composition preferably
comprises from 5 to 16% by weight of V2O5, from 0 to 5% by weight of SteCb,
from 0.2 to 0.75% by weight of Cs, from 0 to 3% by weight of NteOs, 0 to 1% by
weight of P and TiO2 as balance.
12. Catalyst as claimed in any of the preceding claims, wherein the second catalyst
zone has an active composition content of from 6 to 12% by weight, preferably
from 6 to 11% by weight, with the active composition preferably comprising from
5 to 15% by weight of V2O5, from 0 to 5% by weight of Sb2O3, from 0.2 to 0.75%
by weight of Cs, from 0 to 2% by weight of ISfeOs, 0 to 1% by weight of P and
TiO2 as balance.
13. Catalyst as claimed in any of the preceding claims, wherein the third catalyst zone
has an active composition content of from 5 to 11% by weight, preferably from 6
to 10% by weight, with the active composition preferably comprising from 5 to
15% by weight of V2O5, from 0 to 4% by weight of SteCh, from 0.05 to 0.5% by
weight of Cs, from 0 to 2% by weight of NbOs, 0 to 1% by weight of P and TiO2
as balance.
14. Catalyst as claimed in any of the preceding claims, wherein the fourth catalyst
zone has an active composition content of from 5 to 25% by weight of V2O5, from
0 to 5% by weight of Sb2O3, from 0 to 0.2% by weight of Cs, from 0 to 1% by
weight of Nb2O5, from 0 to 2% by weight of P and TiO2 as balance.
15. Catalyst as claimed in any of the preceding claims, wherein the first catalyst zone
has an active composition content of from 7 to 20% by weight,
the second catalyst zone has an active composition content of from 7 to 12% by
weight, with the active composition content of the second catalyst zone preferably
being less than or equal to the active composition content of the first catalyst zone;
the third catalyst zone has an active composition content in the range from 6 to
11% by weight, with the active composition content of the third catalyst zone
preferably being less than or equal to the active composition content of the second
catalyst zone, and
the fourth catalyst zone has an active composition content in the range from 5 to
10% by weight, with the active composition content of the fourth catalyst zone
preferably being less than or equal to the active composition content of the third
catalyst zone.
16. Catalyst as claimed in any of the preceding claims, wherein the BET surface area
of the last catalyst zone nearest the gas outlet is higher than the BET surface area
of the preceding (upstream) catalyst zones.
17. Catalyst as claimed in any of the preceding claims, wherein at least 40%, in
particular at least 50%, particularly preferably at least 60%, of the total pore
volume of the TiO2 used is formed by pores having a radius in the range from 60
to 400 nm.
18. Catalyst as claimed in any of the preceding claims, wherein up to 75%, in
particular up to 70% of the total pore volume of the TiCfe used is formed by pores
having a radius in the range from 60 to 400 nm.
19. Catalyst as claimed in any of the preceding claims, wherein the catalytically active
composition is applied in a moving bed or fluidized bed.
20. Catalyst as claimed in any of the preceding claims, wherein at least 0.05% by
weight of the catalytically active composition of at least one catalyst zone is made
up of at least one alkali metal, calculated as alkali metal(s).
21. Catalyst as claimed in any of the preceding claims, wherein an organic polymer or
copolymer, in particular a vinyl acetate copolymer, is used as adhesive for the
catalytically active composition.
22. Catalyst as claimed in any of the preceding claims, wherein the catalyst is calcined
or conditioned for at least 24 hours at > 390°C, preferably from 24 to 72 hours at
> 400°C, in an Cb-containing gas, in particular air.
23. Catalyst as claimed in any of the preceding claims, wherein niobium is present in
an amount of from 0.1 to 2% by weight, in particular from 0.5 to 1% by weight, of
the catalytically active composition in at least one catalyst zone.
24. Catalyst as claimed in any of the preceding claims, wherein only one TiO2 source
is used and all of the TiO2 used has the BET surface area or pore radius
distribution defined in one or more of the preceding claims.
25. Catalyst as claimed in any of the preceding claims, wherein phosphorous is
present in the active composition at least in the last catalyst zone.
26. Catalyst as claimed in any of the preceding claims, wherein the first catalyst zone
has an activity which is at least 5%, in particular at least 10%, preferably at least
20%, particularly preferably at least 30%, higher than that of the subsequent
second catalyst zone.
27. Process for the preparation of phthalic anhydride, in which a gaseous stream
comprising o-xylene and/or naphthalene and also molecular oxygen is passed at a
temperature from 250°C to 490°C over a multizone catalyst, wherein the catalyst
comprises at least one first catalyst zone located towards the gas inlet, a second
catalyst zone located closer to the gas outlet and a third catalyst zone located even
closer to or at the gas outlet, with the catalyst zones preferably each having an
active composition comprising TiO2, wherein the catalyst activity of the first
catalyst zone is higher than the catalyst activity of the second catalyst zone.
28. Process as claimed in claim 27, wherein the multizone catalyst is a three-zone
catalyst.
29. Process as claimed in claims 27 to 28, wherein the catalyst activity increases from
the second to the third catalyst zone.
30. Process as claimed in claims 27 to 29, wherein the catalyst activity increases from
the third to the fourth catalyst zone and, if appropriate, further to the fifth catalyst
zone.
31. Process as claimed in claims 27 to 30, wherein a total of four or five catalyst
zones, in particular four catalyst zones, are present.
32. Process as claimed in claims 27 to 31, wherein the length of the first catalyst zone
is from 5 to 30%, in particular from 10 to 25%, particularly preferably from 10 to
20%, of the total length of the total catalyst bed.
33. Process as claimed in claims 27 to 32, wherein the first catalyst zone has
a. a higher active composition content and/or
b. a higher vanadium content and/or
c. a TiO2 having a higher BET surface area and/or
d. a lower Sb content and/or
e. a lower Cs content and/or
f. a higher content of promoters which increase the activity and/or
g. a higher bulk density, in particular as a result of the use of a different geometry
of the shaped bodies, and/or
h. a lower content of promoters which lower the activity
than the second catalyst zone.
34. Process as claimed in claims 27 to 33, wherein the first catalyst zone comprises a
higher content of promoters which increase the activity.
35. Process as claimed in claims 27 to 34, wherein the first zone has a higher bulk
density than the second catalyst zone, in particular as a result of the use of a
different geometry of the shaped body.
36. Process as claimed in claims 27 to 35, wherein the individual catalyst zones are
composed of coated catalysts in which an active composition has been applied to
an inert support.
37. Process as claimed in claims 27 to 36, wherein the individual catalyst zones
comprise as active composition at least:
Composition Range
V2O5 /% by wt. 1-25
Sb2O3 /% by wt. 0-4
Cs /% by wt. 0-1
P /% by wt. 0-2
with the remainder of the active composition comprising at least 90% by weight,
preferably at least 95% by weight, more preferably at least 98% by weight, in
particular at least 99% by weight, more preferably at least 99.5% by weight, in
particular 100% by weight, of TiO2 and the BET surface area of the TiO2 used
being in the range from 10 to 50 m2/g and the active composition making up from
4 to 20% by weight of the total weight of the catalyst.
38. Process as claimed in claims 27 to 37, wherein the catalyst of the first catalyst
zone has an active composition content of from 6 to 20% by weight, preferably
from 7 to 15% by weight, and the active composition preferably comprises from 5
to 16% by weight of V2O5, from 0 to 5% by weight of SteCb, from 0.2 to 0.75%
by weight of Cs, from 0 to 3% by weight of NbOs, 0 to 1% by weight of P and
TiO2 as balance.
39. Process as claimed in claims 27 to 38, wherein the second catalyst zone has an
active composition content of from 6 to 12% by weight, preferably from 6 to 11%
by weight, with the active composition preferably comprising from 5 to 15% by
weight of V2O5, from 0 to 5% by weight of Sb2O3, from 0.2 to 0.75% by weight of
Cs, from 0 to 2% by weight of Nb2O5, 0 to 1% by weight of P and TiO2 as
balance.
40. Process as claimed in claims 27 to 39, wherein the third catalyst zone has an
active composition content of from 5 to 11% by weight, preferably from 6 to 10%
by weight, with the active composition preferably comprising from 5 to 15% by
weight of V2O5, from 0 to 4% by weight of SbaOs, from 0.05 to 0.5% by weight of
Cs, from 0 to 2% by weight of Nb2O5, 0 to 1% by weight of P and TiO2 as
balance.
41. Process as claimed in claims 27 to 40, wherein the fourth catalyst zone has an
active composition content of from 5 to 25% by weight of V2O5, from 0 to 5% by
weight of Sb2O3, from 0 to 0.2% by weight of Cs, from 0 to 1% by weight of
Nb2O5, from 0 to 2% by weight of P and TiO2 as balance.
42. Process as claimed in claims 27 to 41, wherein the first catalyst zone has an active
composition content of from 7 to 20% by weight,
the second catalyst zone has an active composition content of from 7 to 12% by
weight, with the active composition content of the second catalyst zone preferably
being less than or equal to the active composition content of the first catalyst zone;
the third catalyst zone has an active composition content in the range from 6 to
11% by weight, with the active composition content of the third catalyst zone
preferably being less than or equal to the active composition content of the second
catalyst zone, and
the fourth catalyst zone has an active composition content in the range from 5 to
10% by weight, with the active composition content of the fourth catalyst zone
preferably being less than or equal to the active composition content of the third
catalyst zone.
43. Process as claimed in claims 27 to 42, wherein the BET surface area of the last
catalyst zone nearest the gas outlet is higher than the BET surface area of the
preceding (upstream) catalyst zones.
44. Process as claimed in claims 27 to 43, wherein at least 40%, in particular at least
50%, particularly preferably at least 60%, of the total pore volume of the TiO2
used is formed by pores having a radius in the range from 60 to 400 nm.
45. Process as claimed in claims 27 to 44, wherein up to 75%, in particular up to 70%
of the total pore volume of the TiO2 used is formed by pores having a radius in the
range from 60 to 400 nm.
46. Process as claimed in claims 27 to 45, wherein the catalytically active
composition is applied in a moving bed or fluidized bed.
47. Process as claimed in claims 27 to 46, wherein at least 0.05% by weight of the
catalytically active composition of at least one catalyst zone is made up of at least
one alkali metal, calculated as alkali metal(s).
48. Process as claimed in claims 27 to 47, wherein an organic polymer or copolymer,
in particular a vinyl acetate copolymer, is used as adhesive for the catalytically
active composition.
49. Process as claimed in claims 27 to 48, wherein the catalyst is calcined or
conditioned for at least 24 hours at > 390°C, preferably from 24 to 72 hours at >
400°C, in an O2-containing gas, in particular air.
50. Process as claimed in claims 27 to 49, wherein niobium is present in an amount of
from 0.1 to 2% by weight, in particular from 0.5 to 1% by weight, of the
catalytically active composition in at least one catalyst zone.
51. Process as claimed in claims 27 to 50, wherein only one TiO2 source is used and
all of the TiO2 used has the BET surface area or pore radius distribution defined in
one or more of the preceding claims.
52. Process as claimed in claims 27 to 51, wherein phosphorous is present in the
active composition at least in the last catalyst zone.
53. Process as claimed in claims 27 to 52, wherein the first catalyst zone has an
activity which is at least 5%, in particular at least 10%, preferably at least 20%,
particularly preferably at least 30%, higher than that of the subsequent second
catalyst zone.

The invention discloses a catalyst for the preparation of phthalic anhydride by gas-phase
oxidation of o-xylene and/or naphthalene, wherein the catalyst comprises at least one first
catalyst zone located towards the gas inlet, a second catalyst zone located closer to the gas
outlet and a third catalyst zone located even closer to or at the gas outlet, with the catalyst
zones preferably each having an active composition comprising TiO2, characterized in
that the catalyst activity of the first catalyst zone is higher than the catalyst activity of the
second catalyst zone.
The invention is also for a process for preparation of phthalic anhydride using the said
catalyst by reacting o-xylene and/or naphthalene and molecular oxygen at 25GPC to
490°C.

Documents:

02142-kolnp-2007-abstract.pdf

02142-kolnp-2007-assignment.pdf

02142-kolnp-2007-claims.pdf

02142-kolnp-2007-correspondence others 1.1.pdf

02142-kolnp-2007-correspondence others.pdf

02142-kolnp-2007-description complete.pdf

02142-kolnp-2007-form 1.pdf

02142-kolnp-2007-form 3 1.1.pdf

02142-kolnp-2007-form 3.pdf

02142-kolnp-2007-form 5.pdf

02142-kolnp-2007-international publication.pdf

02142-kolnp-2007-international search report.pdf

02142-kolnp-2007-pct request form.pdf

02142-kolnp-2007-priority document.pdf

2142-kolnp-2007-abstract.pdf

2142-KOLNP-2007-ANEXURE TO FORM 3.pdf

2142-KOLNP-2007-ASSIGNMENT 1.1.pdf

2142-kolnp-2007-assignment1.1.pdf

2142-kolnp-2007-claims.pdf

2142-KOLNP-2007-CORRESPONDENCE 1.2.pdf

2142-kolnp-2007-correspondence1.1.pdf

2142-kolnp-2007-description (complete).pdf

2142-kolnp-2007-examination report.pdf

2142-kolnp-2007-form 1.pdf

2142-kolnp-2007-form 13.pdf

2142-kolnp-2007-form 18.pdf

2142-KOLNP-2007-FORM 3.1.2.pdf

2142-kolnp-2007-form 3.3.pdf

2142-kolnp-2007-form 5.pdf

2142-KOLNP-2007-FORM-27.pdf

2142-kolnp-2007-gpa.pdf

2142-kolnp-2007-reply to examination report.pdf

2142-kolnp-2007-specification.pdf


Patent Number 244690
Indian Patent Application Number 2142/KOLNP/2007
PG Journal Number 52/2010
Publication Date 24-Dec-2010
Grant Date 15-Dec-2010
Date of Filing 12-Jun-2007
Name of Patentee SÜD-CHEMIE AG
Applicant Address LENBACHPLATZ 6, 80333, MÜNCHEN
Inventors:
# Inventor's Name Inventor's Address
1 GÜCKEL CHRISTIAN 10 B FORSYTHIA LANE, PARAMUS, NJ 07652-4307
2 ESTENFELDER, MARVIN C/O FA. MEISSNER ELFENWEG 24, D-76199 KARLSRUHE
3 PITSCHI, WERNER JUSTUS-VON-LIEBIG-STRASSE 28, D-83052 BRUCKMÜHL
4 DIALER, HARALD FEILITZSTR. 21, D-81545, MÜNCHEN
PCT International Classification Number B01J 35/00
PCT International Application Number PCT/EP2006/001915
PCT International Filing date 2006-03-02
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10 2005 009 473.2 2005-03-02 Germany