Note: Descriptions are shown in the official language in which they were submitted.
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CHROMIA ALUMINA CATALYSTS FOR ALKANE DEHYDROGENATION
TECHNICAL FIELD
[0001] The present invention relates generally to the field of catalysts.
In
particular, the invention relates to catalysts comprising bayerite and silica
for use in
alkane dehydrogenation.
BACKGROUND
[00021 The CATOFINO process converts aliphatic hydrocarbons to their
corresponding olefins over a fixed-bed chromia alumina catalyst. For example,
it can
be used to produce isobutylene, propylene or amylenes from isobutane, propane
or
isopentanes, respectively. The process is an adiabatic, cyclic process. Each
cycle
comprises several steps, including catalyst reduction, dehydrogenation,
purging of the
the remaining hydrocarbon from the reactor, and finally a regeneration step
with air.
The cycle then starts again with the reduction step.
100031 The dehydrogenation reaction is highly endothermic. Therefore, the
temperature of the catalyst bed decreases during the dehydrogenation step.
This
decrease in temperature causes a decrease in paraffin conversion. In order to
reheat
the catalyst bed and remove coke that has deposited on the catalyst during the
dehydrogenation step, the reactor is purged of hydrocarbon and then undergoes
a
regeneration step with air. Heat is provided to the bed by the hot air that
passes
through the bed and also by the combustion of the coke deposits on the
catalyst.
Reduction of the catalyst, with a reducing gas such as hydrogen, prior to
dehydrogenation step also provides some additional heat. As flow in the
reactor is
usually from top to bottom and coke deposits to a larger amount at the reactor
inlet,
there is a tendency for the top of the bed to be hotter than the bottom of the
bed. Also,
the coke distribution in the catalyst bed, which is not easily controlled,
affects the
amount of heat added at each location and the resulting catalyst bed
temperature
profile. These factors make control of the temperature profile in the bed
difficult.
Hydrothermal stability of catalysts used in the CATOFIN process is usually
the
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limiting factor for their lifetime use, and thermal stability as well as high
selectivity to
the olefin are desired qualities.
100041 Aluminum oxide, or alumina, is a commonly used catalyst carrier.
The
properties it displays vary, depending on its preparation, purity and thermal
history.
There is_ia variety of types of alumina, with varying surface areas, pore size
distributions, surface acidic properties and crystal structures. Examples
include
gibbsite (along with its three structural polymorphs bayerite, doyleite and
nordstrandite), boehmite and diaspore. Boehmite alumina crystals dehydrate and
form a variety of polymorphs depending on the temperature of heating. Alumina
produced by dehydration of boehmite exists as 7-alumina between approximately
500
and 850 C, 8-alumina between 850 and 1050 C, 0-alumina between 1050 and 1150 C
and a-alumina above 1150 C. Bayerite is. a trihydrate form of alumina with
dehydrates to malumina between approximately 300 and 500 C, 0-alumina between
850 and 1150 C and a-alumina above 1150 C.
[0005] There are also various stabilizers that can be used with alumina.
This
includes alkaline earth metals and rare earth metals, as well as other
elements such as
zirconium. For example, the use of alkaline earth metal oxides is discussed in
US
Patent Publication No. US 2010/0312035.
SUMMARY
[0006] One aspect of the invention relates to a method of making a
dehydrogenation catalyst support, the method comprising doping bayerite with
silica,
wherein the bayerite is doped by spray-drying bayerite powder in the presence
of
silica; shaping the silica-doped bayerite; and calcining the shaped silica-
doped
bayerite to form alumina. In one embodiment of this aspect, the method further
comprises adding a chromium compound to the support to provide a catalyst
composite. hi another embodiment, the concentration of silica has a range of
about
0.1%, to about 10% by weight of the total support. In a more specific
embodiment,
the concentration of silica has a range of about 0.2% to about 7% by weight of
the
total support. In an even more specific embodiment, the concentration of
silica is
about 0.3% by weight of the total support. Alternatively, the concentration of
silica is
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about 1.5% by weight of the total support. In another embodiment, the silica-
doped
bayerite is shaped by extrusion.
[0007] Another aspect of the invention relates to a method of making a
dehydrogenation catalyst support, the method comprising mixing bayerite with a
silica source; shaping the bayerite mixed with the silica source; and
calcining the
shaped mixture to form alumina. In a particular embodiment, the silica source
is
colloidal silica, and the bayerite mixed with the colloidal silica are co-
extruded. In
another embodiment, the bayerite mixed with the silica source are shaped by
extrusion. Alternatively, mixing bayerite with a silica source may comprise
impregnating bayerite with silica. In yet another embodiment, the silica
source is an
alkali silicate, and bayerite is mixed with the alkali silicate before
extrusion. In a
more specific embodiment, the alkali silicate is sodium silicate. In one
embodiment
of this aspect, the method further comprises adding a chromium compound to the
support to provide a catalyst composite. In other embodiments, the
concentration of
silica has a range of about 0.1%, to about 10% by weight of the total support.
In a
more specific embodiment, the concentration of silica has a range of about
0.2% to
about 7% by weight of the total support. In a yet more specific embodiment,
the
concentration of silica is about 0.4% by weight of the total support.
Alternatively, the
concentration of silica may be about 1.6% by weight of the total support.
10008] A third aspect of the invention relates to a method of making a
dehydrogenation catalyst support, the method comprising mixing a silica source
and a
bayerite slurry to form a mixture; precipitating silica with an acid; shaping
the
mixture; and calcining the shaped mixture to form alumina. In one embodiment,
the
acid is acetic acid, propionic acid, formic acid, oxalic acid or nitric acid.
In another
embodiment, the silica source is an alkali silicate. In a further embodiment,
the alkali
silicate is sodium silicate. In other embodiments, the concentration of silica
has a
range of about 0.1%, to about 10% by weight of the total support, or the
concentration
of silica has a range of about 0.1%, to about 10% by weight of the total
support. In
more specific embodiments, the concentration of silica is about 0.4% by weight
of the
total support or the concentration of silica is about 1% by weight of the
total support.
In one embodiment of this aspect, the method further comprises adding a
chromium
compound to the support to provide a catalyst composite.
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[0009] A fourth aspect of the invention relates to a dehydrogenation
catalyst
comprising Cr203, an alkali metal oxide, Si02, and A1203, wherein the Cr203 is
present in a range of greater than 0% and about 30%; the alkali metal oxide is
present
in a range of greater than 0% and about 1% by weighthe Si02 is present in a
range
of about 0.1% to about 10% by weight; and the A1203 is in the eta-phase, theta-
phase,
or combinations thereof, and substantially free of the alpha- and gamma-
phases. In a
particular embodiment, Si02 is present in a range of about 0.2% to about 0.7%
by
weight. In a more specific embodiment, Si02 is present in a range of about
0.3% to
about 1.5% by weight. In a yet more specific embodiment, the Si02 is present
in an
amount of about 0.3% by weight. In another embodiment, the dehydrogenation
catalyst further comprises a stabilizer selected from the group consisting of
alkaline
earth metals, rare earth metals, zirconium and combinations thereof. In
another
embodiment, the alkali metal oxide is Na20.
[0010] The catalyst composite according to various embodiments of the
invention may be contacted with aliphatic hydrocarbons under suitable
conditions to
facilitate a dehydrogenation reaction. Accordingly, another aspect of the
invention
relates to a method of dehydrogenating a dehydrogenatable hydrocarbon
comprising
contacting the dehydrogenatable hydrocarbon with a dehydrogenation catalyst
composite. The catalyst composite comprises Cr203, an alkali metal oxide,
Si02, and
A1203, wherein the Cr203 is present in a range of greater than 0% and about
30%; the
alkali metal oxide is present in a range of greater than 0% and about 1% by
weight;
the Si02 is present in a range of about 0.1% to about 10% by weight; and the
A1203 is
in the eta-phase, theta-phase, or combinations thereof. The catalyst composite
is
substantially free of the alpha- and gamma-phases. In a particular embodiment
the
Si02 is present in a range of about 0.2% to about 0.7% by weight.
[0011] Alternatively, another aspect of the invention relates to a method
of
making an olefin comprising contacting ail alkane comprising from about 2 to
about
12 carbon atoms with a dehydrogenation catalyst composite. The dehydrogenation
catalyst composite comprises Cr203, an alkali metal oxide, Si02, and A1203,
wherein
the Cr203 is present in a range of greater than 0% and about 30%; the alkali
metal
oxide is present in a range of greater than 0% and about 1% by weight and the
Si02 is
present in a range of about 0.1% to about 10% by weight. The A1203 is in the
eta-
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phase, theta-phase, or combinations thereof, and substantially free of the
alpha- and
gamma-phases. This
method provides a dehydrogenated hydrocarbon at a
temperature of about 400 degrees Celsius to about 700 degrees Celsius and a
pressure
from about 2 pia to about 20 psia to provide the olefin. In a particular
embodiment,
the alkane comprises propane or isobutane, and the olefin comprises propylene
or
isobutylene.
DETAILED DESCRIPTION
100121 Before
describing several exemplary embodiments of the invention, it
is to be understood that the invention is not limited to the details of
construction or
process steps set forth in the following description. The invention is capable
of other
embodiments and of being practiced or being carried out in various ways.
[0013] As used
herein, a catalyst "support" is the material to which a catalyst
is affixed to or dispersed on. As used herein, a "composite" refers to the
support and
catalytically active material. Catalytically active material, such as chromium
oxide, is
added to a support to provide a catalyst composite.
[0014] As used
herein, a "silica source" refers to any compound that will form
silica when used in the processes for making a catalyst described herein.
[0015] As used
herein, a "stabilizer" refers to a compound that aids in the
maintenance of catalytic activity over the catalyst's lifetime. This may be
the result
of preservation of active surface area, prevention of the creation of a
catalytically
inactive phase (such as alpha-Cr-alumina in the case of Cr203 catalysts), or
related
features.
[0016] It has
been found that catalysts using silica-stabilized alumina provide
superior alkane conversion and alkylene selectivity after aging. In
particular, it has
been discovered that silica-stabilized alumina powder, prepared by spray
drying of
bayerite powder or by precipitation of silica onto a bayerite slurry with an
acid,
exhibits such superior properties. Additionally, it has been found that co-
extrusion,
precipitations of silica onto the bayerite or impregnation of bayerite with
silica
compounds also provides superior alkane conversion and alkylene selectivity
after
aging. Related to this, catalysts produced by these methods also show lower
rates of
alpha-Cr-alumina production, as compared to the current CATOFIN catalysts.
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Alpha-Cr-alumina is catalytically inactive, and thus inhibits the overall
activity of the
catalyst. These are surprising results, as silica would be expected to be too
acidic to
produce these beneficial results. The acidity is a very critical aspect of the
catalyst, as
iffects the selectivity of the _____________________________________
dehydrogenation process. Catalysts prepared witlythese
silica-containing support materials have higher hydrothermal stability than
current
CATOFINO catalysts.
[0017] The
catalysts can be evaluated for stability using accelerated aging
tests, which simulate the normal aging process but over much shorter periods
of time.
These are well known in the art, and usually involve heat treatment at
elevated
temperatures with elevated humidity conditions. In one embodiment, conditions
of
the heat treatment are at 800 degrees Celsius for 96 hours with air/steam
(6%/94%,
800 seem). In another embodiment, conditions of the heat treatment are at 850
degrees Celsius for 24 hours with air/steam (6%/94%, 800 sccm). In yet another
embodiment, conditions of the heat treatment are at 850 degrees Celsius for 72
h with
air/steam (20%/80%, 1000 sccm). Samples may also be evaluated by performing
cyclic oxidation-reduction reaction aging tests, which simulate plant
operation.
[0018]
Furthermore, stability of the catalysts can be measured using other
parameters. Aside from performance tests, the physical-chemical properties of
the
aged catalysts, such as the alpha-Cr-alumina phase content, and surface area
can be
determined. As the reduction of surface area and the appearance of alpha-Cr-
alumina
in catalysts occur as a result of the aging process, they can be used as
indirect
indicators of catalyst stability. Thus, lower alpha-Cr-alumina content and/or
higher
surface area in the aged catalysts indicates higher stability of the
catalysts.
100191
Accordingly, one aspect of the invention relates to a method of making
a dehydrogenation catalyst support, the method comprising doping bayerite with
silica, wherein the bayerite is doped by spray-drying bayerite powder in the
presence
of silica; shaping the silica-doped bayerite; and calcining the shaped silica-
doped
bayerite to form alumina. In one embodiment, the concentration of silica may
be in
the range of about 0.1%, to about 10% by weight of the total support. In a
more
specific embodiment, the concentration of silica is in the range of about 0.2%
to
about 7% by weight of the total support. In a yet more specific embodiment,
the
concentration of silica is about 0.3% by weight of the total support.
Alternatively,
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the concentration of silica may be about 1.5% by weight of the total support.
The
catalyst composite may comprise Cr203 to constitute a catalyst composite.
[0020] Another aspect
of the invention relates to a method of making a
dehydrogenation ____ catalyst -------------------------------------- support,
the method comprising: mixing a silica source and
a bayerite slurry to form a mixture; precipitating silica with an acid;
shaping the
mixture; and calcining the shaped mixture to form alumina. Suitable acids
include,
but are not limited to, acetic acid, propionic acid, formic acid, oxalic acid
and/or
nitric acid. In one embodiment, the mixture is precipitated with acetic acid.
In
another embodiment, the silica source is an alkali silicate. In a further
embodiment,
the alkali silicate is sodium silicate. The concentration of silica may be
about 0.4%
by weight of the total support. In another embodiment, the concentration of
silica is
about 1.5% by weight of the total support. This method may also further
comprise
adding a chromium compound to provide a composite.
[0021] Shaping of the
catalyst support can occur via any of the methods well
known in the art and into any suitable shape. The shape chosen can vary
substantially, and generally corresponds to the shape of the resultant
catalyst support.
Examples of forming machines include, but are not limited to, molding
machines,
tableting machines, rolling granulators, marumarizers, and pelletors. The
shape of the
formed alumina mixture includes spheres, tablets, cylinders, stars, tri-lobes,
quadra-
lobes, pellets, pills, granules, honeycombs, and cubes. The shapes, generally
referred
to as "particulates," may have any suitable size. However, in one embodiment,
the
sizes of the shapes are substantially uniform. The shaped material has its
components
mixed therein. In another embodiment, the shaped material has its components
uniformly mixed therein.
[0022] In one
embodiment, shaping occurs via extrusion. In another
embodiment, the alumina mixture is extruded in a continuous manner over a
broad
range of diameters and shapes. Examples of forming or extrusion machines
include
extrusion molding machines, single screw extruders, twin screw extruders, co-
extruders, pin extruders, linear extruders, and monofilament extruders.
[0023] After forming
the material into a desired shape, the alumina mixture is
optionally dried to remove any remaining liquid (and typically to remove
remaining
water). Drying is conducted in at least one of a desiccator, under a vacuum
(reduced
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pressure), and/or elevated temperature (baking) for a sufficient period of
time to
remove any remaining liquid from the shaped material.
[0024] The
manner in which the shaped alumina mixture is dried is not
critical. In one embodiment, the ___________________________________ dried
aluminanixture contains less than about-3%
by weight free moisture. In another embodiment, the dried alumina mixture
contains
less than about 1% by weight free moisture.
[0025] In one
embodiment, drying involves at least one of maintaining an
elevated temperature (above about 35 C) overnight, desiccation overnight, and
under
a vacuum overnight. When employing elevated temperatures, in one embodiment,
the
shaped alumina mixture is heated from about 35 C to about 150 C for a time
from
about 5 seconds to about 6 hours.
[0026] Another
aspect of the invention relates to a method of making a
dehydrogenation catalyst support, the method comprising mixing bayerite with a
silica source; shaping the bayerite mixed with the silica source; and
calcining the
shaped mixture to form alumina. Regarding this aspect of the invention, silica
may be
added via various methods and at other stages of catalyst preparation, as
well. For
example, in one embodiment, the method comprises impregnating bayerite with
silica
and shaping the bayerite impregnated with silica. In a variant of this method,
the
silica source is colloidal silica, and the bayerite mixed with colloidal
silica are co-
extruded. Bayerite may be mixed with the silica source via impregnation or co-
extrusion in various embodiments. Generally, a silica source may also be added
during various steps of the catalyst preparation. In one embodiment, alkali
silicate
may be added during preparation. Again, shaping may be accomplished by any of
the
suitable methods discussed above.
[0027]
Accordingly, one embodiment of the invention relates to a method of
making a dehydrogenation catalyst support, the method comprising: mixing
bayerite
with colloidal silica; co-extruding the bayerite mixed with the colloidal
silica. The
method may further comprise calcining the co-extruded mixture to form alumina.
In
one embodiment, the silica source comprises a colloidal silica. In
another
embodiment, the silica source is an alkali silicate. Examples of suitable
alkali
silicates include, but are not limited to, sodium silicate and potassium
silicate. In one
embodiment, the catalyst composite contains Cr203.
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[0028] In another embodiment, the method of making a catalyst support
comprises impregnating bayerite with silica, shaping the bayerite mixed with
the
silica source and calcining the shaped mixture to form alumina. In yet another
embodiment, the __________ silica source is an alkali silicate, and
bayerite-is mixed-with-the -
alkali silicate by impregnation.
[0029] The concentration of silica may vary. In one embodiment, the
concentration of silica is from about 0.1%, to about 10% by weight of the
total
support. In a further embodiment, the concentration of silica is in the range
of about
0.2% to about 7% by weight of the total support. In a specific embodiment, the
concentration of silica is about 0.4% by weight of the total support.
Alternatively, in
another embodiment, the concentration of silica is about 1.6% by weight of the
total
support.
[0030] Another component of the catalyst support may be an alkali oxide. A
compound containing the desired alkali metal is added, which converts to the
alkali
oxide during heating. Any suitable alkali .metal may be used, although
preferred
alkali oxides are lithium oxide, sodium oxide and potassium oxide. The most
preferred alkali metal oxide is sodium oxide. General examples of alkali
compounds
include alkali salts, organoalkali compounds and alkali oxides.
[0031] Thus, for example, where sodium oxide is the desired alkali oxide,
a
sodium compound may be added during catalyst composite preparation. The sodium
compound is a molecule containing at least one atom of sodium. The sodium
compound can be converted to sodium oxide during heating. General examples of
sodium compounds include sodium salts, sodium chromates, organosodium
compounds, and sodium oxide. Specific examples of sodium compounds include,
but
are not limited to sodium oxide, sodium fluoride, sodium chloride, sodium
bromide,
sodium iodide, sodium chromate, sodium dichromate, sodium acetate, sodium
bicarbonate, sodium carbonate, sodium formate, sodium hydroxide, sodium
metasilicate, sodium nitrate, sodium nitrite, sodium phosphate, sodium
sulfate,
sodium sulfite, and the like.
[0032] Where lithium oxide is desired, the lithium compound, can be
converted to lithium oxide during heating. The lithium compound is a molecule
containing at least one atom of lithium. General examples of lithium compounds
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include lithium salts, organolithium compounds, lithium, and lithium oxide.
Specific
examples of lithium compounds include lithium metal powder, lithium acetate,
lithium amide, lithium borates, lithium carbonate, lithium formate, lithium
halides
such as lithium fluoride, lithium chloride, lithium bromide, and lithium
iodide, lithium
hydride, lithium hydroxide, lithium hypochlorite, lithium nitrate, lithium
nitride,
lithium phosphate, lithium silicate, lithium zirconate, lithium perchlorate,
lithium
peroxide, lithium metasilicate, lithium sulfate, lithium butyllithium, lithium
rnethyllithium, lithium phenyllithium, and the like.
[0033] Many
CATOFIN catalysts utilize Cr203 as the catalytically active
metal oxide. Accordingly, a chromium compound may be added to the catalyst. A
chromium compound is a compound containing chromium that will convert to
catalytically active chromium oxide. The chromium compound is converted to
chromium oxide during heating (one or more of chromium (III) oxide and
chromium
(VI) oxide). General examples of chromium compounds include, but are not
limited
to, chromium, chromium salts, chromates, chromic acid, and chromium oxides.
Specific examples of chromium compounds include chromium, sodium chromate,
sodium dichromate, potassium chromate, potassium dichromate, ammonium
dichromate, chromic acid, chromic chloride, chromic acetylacetonate, chromic
potassium sulfate, chromium (III) oxide, chromium (VI) oxide, barium chromate,
chromyl chloride, barium chromate, strontium chromate, lead chromate, chromium
nitride, chromium nitrate, chromium fluoride, and the like. In one
specific
embodiment, calcined alumina extrudates are impregnated to incipient wetness
with
an aqueous solution of chromic acid, sodium dichromate solution and water. The
catalyst can then be dried and calcined. Alternatively, catalytically active
chromium
oxide may be added during any stage of catalyst support preparation.
[0034] It is
critical that the alumina used does not have a gamma-A1203 crystal
structure, because it is highly acidic. Acidity can adversely affect
selectivity, as
discussed above. Calcination will expose a catalyst to high temperature during
catalyst preparation. Thus, as bayerite will exist in eta and theta form, it
produces
superior results to aluminas with the gamma phase. Thus, in one embodiment,
bayerite is used as the alumina source for the catalyst. By extension of this
principle,
boehmite should not be used, as it. leads to formation of the gamma-phase.
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[0035] Accordingly, another aspect of the invention relates to a
dehydrogenation catalyst comprising Cr203, alkali metal oxide, Si02, and
A1203,
wherein the Cr203 is present in a range of greater than 0% and about 30%; the
alkali
metal oxide is present in-a range of greater than-0%-and about-1%by weight;
the Si027
is present in a range of about 0.1% to about 10% by weight. The A1203 is in
the eta-
phase, theta-phase, or combinations thereof, and substantially free of the
alpha-phase
and optionally includes a stabilizer. In one embodiment, Si02 is present in
the range
of about 0.2% to about 0.7% by weight. In another embodiment, the Si02 is
present
in the range of about 0.3% to about 1.5% by weight. In a specific embodiment,
the
Si02 is present in amount of about 0.3%. In one embodiment, the alkali metal
oxide
is preferably chosen from lithium oxide, sodium oxide and potassium oxide. In
a
different embodiment, the alkali oxide is Na20. In another embodiment,
mixtures of
alkali oxides may be used.
[0036] Any suitable stabilizer (in addition to the silica compound) may be
used. This includes, but is not limited to alkaline earth metals, rare earth
metals,
zirconium, magnesium, strontium, barium and combinations and compounds thereof
General examples of alkaline earth metal compounds include alkaline earth
metal
salts, organo alkaline earth metal compounds, alkaline earth metals, and
alkaline earth
metal oxides. Examples of alkaline earth metal compounds include alkaline
earth
metal powder, alkaline earth metal acetate, alkaline earth metal amide,
alkaline earth
metal borates, alkaline earth metal carbonate, alkaline earth metal formate,
alkaline
earth metal halides such as alkaline earth metal fluoride, alkaline earth
metal chloride,
alkaline earth metal bromide, and alkaline earth metal iodide, alkaline earth
'metal
hydride, alkaline earth metal hydroxide, alkaline earth metal hypochlorite,
alkaline
earth metal nitrate, alkaline earth metal nitride, alkaline earth metal
phosphate,
alkaline earth metal silicate, alkaline earth metal zirconate, alkaline earth
metal
perchlorate, alkaline earth metal peroxide, alkaline earth metal metasilicate,
alkaline
earth metal sulfate, alkaline earth metal monohydrogen orthophosphate,
trialkaline
earth metal orthophosphate, alkaline earth metal hypophosphate, alkaline earth
metal
pyrophosphate, alkaline earth metal sulfite, alkaline earth metal oxalate,
alkaline earth
metal citrate, alkaline earth metal methylate, alkaline earth metal propylate,
alkaline
earth metal pentylate, alkaline earth metal ethoxide, or the like.
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[0037] The catalyst composite according to various embodiments of the
invention may be contacted with aliphatic hydrocarbons under suitable
conditions to
facilitate a dehydrogenation reaction. Accordingly, another aspect of the
invention
-relates to-a-metho-d -of-dehydrogenating- a-dehydrogenatable-hydrocarbon-
comprising -
contacting the dehydrogenatable hydrocarbon with a dehydrogenation catalyst
composite to provide a dehydrogenated hydrocarbon. The catalyst composite
comprises Cr203, an alkali metal oxide, Si02, and A1203, wherein the Cr203 is
present
in a range of greater than 0% and about 30%; the alkali metal oxide is present
in a
range of greater than 0% and about 1% by weight; the Si02 is present in a
range of
about 0.1% to about 10% by weight; and the A1203 is in the eta-phase, theta-
phase, or .
combinations thereof. The catalyst composite is substantially free of the
alpha- and
gamma-phases. In a particular embodiment the Si02 is present in a range of
about
0.2% to about 0.7% by weight.
[0038] General examples of dehydrogenatable hydrocarbons include, but are
not limited to, aliphatic compounds containing from about 2 to about 30 carbon
atoms
per molecule, alkylaromatic hydrocarbons where the alkyl group contains from
about
2 or to about 6 carbon atoms, and naphthenes or alkyl-substituted naphthenes
where
the alkyl group contains from about 2 to about 6 carbon atoms. Specific
examples of
dehydrogenatable hydrocarbons include ethane, propane, n-butane, isobutane, n-
pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, 2,2-
dimethylbutane, n-heptane, 2-methyl hexane, 2,2,3-trimethylbutane,
cyclopentane,
cyclohexane, methylcyclopentane, ethylcyclopentane, n-propylcyclopentane, 1,3-
dimethylcyclohexane, ethylbenzene, n-butylbenzene, 1,3,5-triethylbenzene,
isopropylbenzene, isobutylbenzene, ethylnaphthalene, and the like.
[0039] Alternatively, another aspect of the invention relates to a method
of
making an olefin comprising contacting an alkane comprising from about 2 to
about
12 carbon atoms with a dehydrogenation catalyst composite. The dehydrogenation
catalyst composite comprises Cr203, an alkali metal oxide, Si02, and A1203,
wherein
the Cr203 is present in a range of greater than 0% and about 30%; the alkali
metal
oxide is present in a range of greater than 0% and about 1% by weight and the
Si02 is
present in a range of õabout 0.1% to about 10% by weight. The A1203 is in the
eta-
phase, theta-phase, or combinations thereof, and substantially free of the
alpha- and
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gamma-phases. This
method provides a dehydrogenated hydrocarbon at a
temperature from about 400 degrees Celsius to about 700 degrees Celsius and a
pressure from about 2 psia to about 20 psia to provide the olefin. In a
particular
-emb-o-diment, the alkane¨comprises-propane-or -isobutane,--and-the- olefin
comprises
propylene or isobutylene.
[0040] Generally
speaking, the feedstocks suitable for use with the subject
innovation generally contain paraffinic hydrocarbons having from about 2 to
about 20
carbon atoms. In another embodiment, the feedstocks contain paraffinic
hydrocarbons
having from about 3 to about 12 carbon atoms. In one embodiment, the
feedstocks
boil at a temperature of about 400 degrees Celsius or less at atmospheric
pressure. In
another embodiment, the feedstocks boil at a temperature of about 250 degrees
=
Celsius or less at atmospheric pressure.
[0041] The
dehydrogenation process optionally begins with preheating a
hydrocarbon feedstock. The feedstock can be preheated in feed/reactor effluent
heat
exchangers prior to entering a furnace or contacting other high temperature
waste heat
as a means for final preheating to a targeted catalytic reaction zone inlet
temperature.
Suitable final preheating means include, for example, waste heat from other
refinery
processes such as a fluid catalytic cracking unit, a fluidized or delayed
coking unit, a
catalytic hydrocracker, a crude distillation unit, a catalytic reforming unit,
and/or
hydrotreating units found in conventional petroleum refineries.
10042] The
reaction zone can include one or more fixed bed reactors
containing the same or different catalysts, a moving bed reactor, or a
fluidized bed
reactor. The feedstock may be contacted with the catalyst bed in one or more
of an
upward, downward, or radial flow fashion. The reactants may be in the liquid
phase,
mixed liquid and vapor phase, or the vapor phase.
[0043] In
embodiments where a fixed bed reactor is employed, a
dehydrogenation reaction zone may contain one or at least two fixed bed
reactors.
Fixed bed reactors in accordance with the subject innovation can also contain
a
plurality of catalyst beds. The plurality of catalyst beds in a single fixed
bed reactor
can also contain the same or different catalysts.
[0044] Since
dehydrogenation reactions are generally endothermic, interstage
heating, consisting of heat transfer devices between fixed bed reactors or
between
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catalyst beds in the same reactor shell, can be employed. Heat sources can
include
conventional process heaters such as one or more process furnaces or can
include
internally produced heat such as that produced from catalyst regeneration
within a
-fluidized -catalytic-processHeating- requirements- may--also-be-met -from-
heating
sources available from other refinery process units.
[0045] The dehydrogenation reaction zone effluent is generally cooled and
the
effluent stream is directed to a separator device such as a stripper tower
where light
hydrocarbons and hydrogen formed during the reaction- step can be removed and
directed to more appropriate hydrocarbon pools. Where the process is performed
in
the presence of supplemental hydrogen or sufficient internally generated
hydrogen is
produced, a separate hydrogen separation step can be performed upstream of and
prior
to light hydrocarbon separation. Some of the recovered hydrogen can be
recycled
back to the process while some of the hydrogen can be purged to external
systems
such as plant or refinery fuel.
[0046] The stripper liquid effluent product is then generally conveyed to
downsteam processing facilities. The olefin product optionally can be directed
to a
polymerization facility or to an isomerization process for isomerization and
thereafter
directed to an ether facility for conversion, in the presence of an alkanol,
to an ether.
Where at least a portion of the olefin from the process of the subject
innovation is iso-
olefin, the stream can be sent directly to an ether facility or to a
polymerization
facility. Prior to direction to an ether facility, the product stream can be
purified by
removing unconverted paraffinic hydrocarbon from the product. This unconverted
product can be recycled back to the reaction zone or further manipulated in
other
process units. The olefin product can be directed to an alkylation process for
reaction
with isoparaffin to form higher octane, lower volatility gasoline blending
components.
The olefin product can be directed to a chemical manufacture process for
conversion
to other commodity chemical products or process streams. Methods for
integration of
the process of the subject innovation with other conventional refinery or
chemical
plant processes or products are known to those skilled in the art.
[00471 The catalyst composite is used at a temperature to facilitate
catalytic
dehydrogenation processes. In one embodiment, the temperature during catalytic
dehydrogenation is from about 250 degrees Celsius to about 750 degrees
Celsius. In
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another embodiment, the temperature during catalytic dehydrogenation is from
about
400 degrees Celsius to about 650 degrees Celsius. Reaction temperatures below
these
ranges can result in reduced paraffin conversion and lower olefin yield.
Reaction
- temperatures above-these - ranges -can- result - in -reduced -olefin-
selectivity and lower-
olefin yields.
[0048] The
catalyst composite is used at a pressure to facilitate catalytic
dehydrogenation processes. In one embodiment, the pressure during catalytic
dehydrogenation is from about 0 psia (vacuum pressure) to about 500 psia. In
another
embodiment, the pressure during catalytic dehydrogenation is from about 2 psia
to
about 20 psia. In another embodiment, the pressure during catalytic
dehydrogenation
is from about 20 psia to about 300 psia. Excessively high reaction pressures
increase
energy and equipment costs and provide diminishing marginal benefits.
Excessively
high hydrogen circulation rates can also influence reaction equilibrium and
drive the
reaction undesirably towards reduced paraffin conversion and lower olefin
yield.
[0049] The
catalyst composite is used at a weight hourly space velocity
(WHSV) to facilitate catalytic dehydrogenation processes. In one embodiment,
the
WHSV is from about 0.1 hr -I to about 100 hr -1. In another embodiment, the
WHSV
is from about 0.5 hr -1 to about 50 hr -1. Feed space velocities exceeding the
levels
described herein generally result in a decline in paraffin conversion which
overwhelms any gain in olefin selectivity, thereby resulting in lower olefin
yield. Feed
space velocities short of the levels described herein are generally costly in
terms of
capital requirements.
[0050] General
examples of dehydrogenated hydrocarbons that are
catalytically yielded from the feedstock materials include olefin compounds
containing from about 2 to about 30 carbon atoms per molecule, alkenylaromatic
hydrocarbons where the alkenyl group contains from about 2 to about 6 carbon
atoms,
and naphthenes or alkenyl-substituted naphthenes where the alkenyl group
contains
from about 2 to about 6 carbon atoms. Specific examples of dehydrogenated
hydrocarbons include ethylene, propylene, butene, isobutylene, pentene,
isopentene,
hexene, 2-methylpentene, 3-methylpentene, 2,2-dimethylbutene, heptene, 2-
methylhexene, 2,2,3-trimethylbutene, cyclopentene,
cyclohexene,
methylcyclopentene, ethylcyclopentene, n-propyleyclopentene,
propylenylpentane,
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1,3-dimethylcyclohexene, styrene, butenylbenzene, triethenylbenzene,
methylstyrene,
isobutenylbenzene, ethenyinaphthalene, and the like.
EXAMPLES
Comparative example Cl (No silica):
100511 Cl was prepared according the method described in US Patent No.
7,012,038, and was impregnated with Cr and sodium. US Patent No. 7,012,038 by
Alerasool et al. is herein incorporated by reference. This example is
comparative
example because it does not contain silica and is a commercially available
catalyst.
[0052] Alumina trihydrate (2700.4 grams) was loaded into a 10 L EIRICH
mixer and a solution containing water (150.2 grams) was added to the mixer. A
solution containing water (210.5 grams), nitric acid (132.0 grams), and
lithium nitrate
(25.9 grains) was added to the mixer. The blend was mixed for a total of 23
minutes.
An additional 9.9 grams of water was added to the blend and the blend was
mixed for
one more minute. The blend was formed into cylindrical extrudates (1/8"
diameter),
dried at 90 degrees Celsius overnight, and then calcined at 800 degrees
Celsius for 2
hours in air. The calcined extrudates were allowed to cool in the furnace
without
external cooling.
[0053] A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(82.4
grams), sodium dichromate solution (12.4 grams, 69% sodium dichromate
dihydrate),
and water (58.8 grams). The sample was dried and calcined in air at 750.
degrees
Celsius for 2 hours. The impregnated extrudates were allowed to cool in the
furnace
without external cooling.
Example 2 (impregnated with 0.4% SiQ2Na-silicate)
[0054] Alumina trihydrate (2700.4 grams) was loaded into a 10 L EIRICHO
mixer. A solution of 24.5g Sodium silica (PQ; 28.7% Si02) in 80 ml water was
added
to the mixer. After 2 minutes of mixer operation, a solution containing water
(200
grams) and nitric acid (198.0 grams) was added to the mixer. The blend was
mixed
for a total of approximately 20 minutes. The blend was formed into cylindrical
extrudates (1/8" diameter), dried at 90 degrees Celsius overnight, and then
calcined at
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800 degrees Celsius for 2 hours in air. The calcined extrudates were allowed
to cool in
the furnace without external cooling.
[0055] A portion of the calcined alumina extrudates (250 grams) were
- impregnated to incipient -wetness -with-an -aqueous solution of¨chromic-
acid (8-8
grams), sodium dichromate solution (7.7 grams, 69% sodium dichromate
dihydrate),
and water (52 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
Example 3 (impregnated with 1.6% SiO, Na-silicate)
[0056] Alumina trihydrate (2700.4 grams) was loaded into a 10 L EIRICHS
mixer.. A solution of 98.3g Sodium silica (PQ; 28.7% Si02) was added to the
mixer.
After 2 minutes of mixer operation, a solution containing water (200 grams)
and nitric
acid (198.0 grams) was added to the mixer. The blend was mixed for a total of
approximately 20 minutes. The blend was formed into cylindrical extrudates
(1/8"
diameter), dried at 90 degrees Celsius overnight, and then calcined at 800
degrees
Celsius for 2 hours in air. The calcined extrudates were allowed to cool in
the furnace
without external cooling.
[0057] A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(87.7
grams), sodium dichromate solution (3 grams, 69% sodium dichromate dihydrate),
and water (49 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
Example 4 (co-extruded with colloidal silica 0.5% Si02)
[0058] Alumina trihydrate (2700.4 grams) was loaded into a 10 L EIRICHO
mixer. A solution of 33.75g colloidal silica (NALCO 2327) in 50 ml water was
added to the mixer. After 2 minutes of mixer operation, a solution containing
water
(290 grams) and nitric acid (132.0 grains) was added to the mixer. The blend
was
mixed for a total of approximately 20 minutes. The blend was formed into
cylindrical
extrudates (1/8" diameter), dried at 90 degrees Celsius overnight, and then
calcined at
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800 degrees Celsius for 2 hours in air. The calcined extrudates were allowed
to cool in
the furnace without external cooling.
[00591 A portion
of the calcined alumina extrudates (250 grams) were
impregn6ted to incipient wetness with an ___________________________ aqueous
solution of chromic -acid- (82A
grams), sodium dichromate solution (12.4 grams, 69% sodium dichromate
dihydrate),
and water (58.8 grams). The sample was dried and calcined in air at 750
degrees
Celsius for 2 hours. The impregnated extrudates were allowed to cool in the
furnace
without external cooling.
Example 5 (co-extruded with colloidal silica 3% SiO2j
[0060] Alumina
trihydrate (2700.4 grams) was loaded into a 10 L EIRICH
mixer. A solution of 202.5g colloidal silica (NALCO 2327) in 50 ml water was
added to the mixer. After 2 minutes of mixer operation, a solution containing
water
(210 grams) and nitric acid (132.0 grams) was added to the mixer. The blend
was
mixed for a total of approximately 20 minutes. The blend was formed into
cylindrical
extrudates (1/8" diameter), dried at 90 degrees Celsius overnight, and then
calcined at
800 degrees Celsius for 2 hours in air. The calcined extrudates were allowed
to cool in
the furnace without external cooling.
[0061] A portion
of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(82.4
grams), sodium dichromate solution (12.4 grams, 69% sodium dichromate
dihydrate),
and water (58.8 grams). The sample was dried and calcined in air at 750
degrees
Celsius for 2 hours. The impregnated extrudates were allowed to cool in the
furnace
without external cooling.
Example 6 NO, modified Al-trihydrate 0.3% SiO2)
[0062] Alumina
trihydrate (2700.4 grams) spray dried with 0.3% Si02 and
0.15% Na20 was loaded into a 10 L EIRICHO mixer. A solution containing water
(450 grams), nitric acid (198.0 grams) was added to the mixer. The blend was
mixed
for a total of approximately 20 minutes. The blend was formed into cylindrical
extrudates (1/8" diameter), dried at 90 degrees Celsius overnight, and then
calcined at
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800 degrees Celsius for 2 hours in air. The calcined extrudates were allowed
to cool in
the furnace without external cooling.
[00631 A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid (88
¨
grams), sodium dichromate solution (7.7 grams, 69% sodium dichromate
dihydrate),
and water (52 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
Example 7 (Si02 modified Al-trihydrate 1.5% Si02)
[0064] Alumina trihydrate (2700.4 grams) spray dried with 1.5% Si02 and
0.4% Na20 was loaded into a 10 L EIRICHO mixer. A solution containing water
(400
grams), nitric acid (198.0 grams) was added to the mixer. The blend was mixed
for a
total of approximately 20 minutes. The blend was formed into cylindrical
extrudates
(1/8" diameter), dried at 90 degrees Celsius overnight, and then calcined at
800
degrees Celsius for 2 hours in air. The calcined extrudates were allowed to
cool in the
furnace without external cooling.
[00651 A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(87.7
grams), sodium dichromate solution (3 grams, 69% sodium dichromate dihydrate),
and water (49 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
=
Example 8 (Precipitation with acetic acid)
[00661 Alumina trihydrate (2700.4 grams) with 0.4% Si02 added as sodium
silicate to a slurry of Bayerite and precipitated with acetic acid was loaded
into a 10 L
EIRICH mixer. A solution containing water (340 grams), nitric acid (198.0
grams)
was added to the mixer. The blend was mixed for a total of approximately 20
minutes.
The blend was formed into cylindrical extrudates (1/8" diameter), dried at 90
degrees
Celsius overnight, and then calcined at 800 degrees Celsius for 2 hours in
air. The
calcined extrudates were allowed to cool in the furnace without external
cooling.
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100671 A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(87.9
grams), sodium dichromate solution (6.1 grams, 69% sodium dichromate
dihydrate),
and water (49 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
Example 9 (Precipitation with acetic acid)
[0068] Alumina trihydrate (2700.4 grams) with 1% Si02 added as sodium
silicate to a slurry of Bayerite and precipitated with acetic acid was loaded
into a 10 L
EIRICH mixer. A solution containing water (340 grams), nitric acid (198.0
grams)
was added to the mixer. The blend was mixed for a total of approximately 20
minutes.
The blend was formed into cylindrical extrudates (1/8" diameter), dried at 90
degrees
Celsius overnight, and then calcined at 800 degrees Celsius for 2 hours in
air. The
calcined extrudates were allowed to cool in the furnace without external
cooling.
[00691 A portion of the calcined alumina extrudates (250 grams) were
impregnated to incipient wetness with an aqueous solution of chromic acid
(87.7
grams), sodium dichromate solution (3.1 grams, 69% sodium dichromate
dihydrate),
and water (49 grams). The sample was dried and calcined in air at 750 degrees
Celsius
for 2 hours. The impregnated extrudates were allowed to cool in the furnace
without
external cooling.
Example 10 (accelerated aging)
[00701 Catalyst from comparative example Cl and examples 2-9 were loaded
into an inconel tube located in a 2" id. quartz tube which was mounted in a
vertical
tube furnace. The catalysts were treated in alternating reducing and oxidizing
atmosphere at high temperature to simulate cycles experienced in a CATOFINO
reactor. The samples were cooled in a nitrogen flow. The samples were
characterized
by BET surface area and x-ray diffraction (XRD) measurement. Results are shown
in
Table 1 below. As seen in Table 1, the surface area after aging in inventive
examples
2 through 9 are far superior to that of comparative example Cl. The average
surface
area of the inventive examples is 53.9, which is far above the 29 of the
comparative
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example Cl. Even more striking results are seen in with the percentage of
catalytically inactive alpha-Cr-alumina. While comparative example Cl is at
92%,
the highest of the inventive examples is 60%. Furthermore, example 9 was a
mere
2%. These results show the superior nature of the silica-stabilized catalysts.
Table 1: Characterization Results For Catalysts
Catalyst % Surface area % Cr as alpha-
Si02 _ after aging Cr-alumina
Comparative Example CI 0 29 92
Example 2 0.4 52 60
Example 3 1.6 61 45
Example 4 0.5 46 44
Example 6 0.3 48 60
Example 7 1.5 52 30
Example 8 0.4 58.6 13
Example 9 1.0 60 2
Example 11 (Catalyst testin )
[0071] Results from accelerated aging tests and fresh performance tests
during
propane dehydrogenation for examples 6, 7 and 8 are shown in Table 2 below.
The
performance of examples 6, 7 and 8 after aging is given in Table 2, as propane
conversion and selectivity comparisons to standard Comparative Example Cl, as
described above. Accordingly, a positive number in the conversion and
selectivity
comparison columns correlate to higher conversion and higher selectivity than
Comparative Example Cl, and a negative number correlates to lower conversion
and
selectivity. A value of zero indicates equal conversion and selectivity.
[0072] The silica-containing samples yielded close to zero or positive
numbers in both columns. This indicates that they are effective catalysts in
the fresh
state, which is obviously a prerequisite for commercial use. Thus, silica-
containing
materials are promising options for catalysts used in propane dehydrogenatiCm,
particularly if the silica is added during spray drying or by precipitation to
the alumina
powder as sodium silicate.
Table 2: Fresh Performance of Samples in Propane Dehydrogenation
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Description Propane conversion Selectivity vs.
vs. Comparative Comparative
Example Cl Example Cl
03% Si02 spray dried -0.8 -1.3
1.5% Si02 spray dried +1.1 +1.1
0.4% Si02 precipitated +1.2 -1.1
Comparative Example Cl 0 0
[0073] Catalyst tests were performed in a fixed bed continuous flow
reactor.
The catalyst charge was 150 ml. The reactor tube was heated in a tube furnace
to 590
degrees Celsius in flowing nitrogen. Once the desired temperature was
achieved, a
feed consisting of 100% propane was passed over the catalyst bed at a gas
hourly
superficial velocity (GHSV) of 530 hr-I at 0.33 atm. The entire product stream
was
analyzed on-line using sampling valves and an HP 5890 chromatograph (TCD)/HP
5971 mass selective detector.
[0074] Test results are summarized in Table 3. The inventive examples
combine high fresh propane conversion and selectivity with improved aged
performance when compared to existing technology.
Table 3: Performance Testing Results For Catalysts
Fresh catalysts Aged catalysts
Catal yst %Si02 Propane Propylene Propane % of Propylene % of
conversion Selectivity cony. fresh Selectivity fresh
cony. sel.
Comparative 0 54.4 90.6 42.9 78.8 82.4 90.9
Example Cl
Example 2 0.4 53.7 86.9 49.0 91.2 87.2 100.3
Example 3 1.6 52.9 90.1 40.3 76.2 93.3 103.6
Example 4 0.5 53.9 87.3 45.7 84.8 91.7 105.0
Example 5 3 49.7 90.6
Example 6 0.3 55.6 90.5 46.4 83.5 82.8 91.5
Example 7 1.5 53 92.1 42.6 80.4 93.9 102.0
Example 8 0.4 55.6 89.5 50.2 90.3 88.7 99.1
Example 9 1.0 52.5 87.4 44.9 85.5 90.9 104.0
[0075] As is seen in Table 3, comparative example Cl provides the
baseline
for propane conversion and propylene selectivity with propane conversion after
aging
at about 78.8% of the fresh conversion and propane selectivity after aging at
about
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90.1% of the fresh selectivity. The results show that propane selectivity
performance
after aging is much better in the inventive examples than in comparative
example Cl.
In fact, propane selectivity actually increases after aging in all the
inventive examples,
__except_for_ Examples 6 and 8. As the lifetime of catalysts is
usually_limited by _the_
drop in the observed selectivity, this feature represents a marked improvement
in
lifetime over the comparative example. In addition, the conversion of the
inventive
examples is higher than for comparative example Cl for all catalysts besides
example
3.
[00761 Reference throughout this specification to "one embodiment,"
"certain
embodiments," "one or more embodiments" or "an embodiment" means that a
particular feature, structure, material, or characteristic described in
connection with
the embodiment is included in at least one embodiment of the invention. Thus,
the
appearances of the phrases such as "in one or more embodiments," "in certain
embodiments," "in one embodiment" or "in an embodiment" in various places
throughout this specification are not necessarily referring to the same
embodiment of
the invention. Furthermore, the particular features, structures, materials, or
characteristics may be combined in any suitable manner in one or more
embodiments.
[0077] Although the invention has been described with reference to
particular
embodiments, it is to be understood that these embodiments are merely
illustrative of
the principles and applications of the present invention. It will be apparent
to those
skilled in the art that various modifications and variations can be made to
the method
and apparatus of the present invention without departing from the spirit and
scope of
the invention. Thus, it is intended that the present invention include
modifications
and variations that are within the scope of the appended claims and their
equivalents.
