Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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"LAYERED CATALYST COMPOSITION AND PROCESSES
FOR PREPARING AND USING THE COMPOSITION"
BACKGROUND OF THE INVENTION
Hydrocarbon conversion processes are carried out using catalysts
including zeolites and supports containing catalytic components. Platinum
based catalysts with or without promoters and modifiers are commonly used.
One such hydrocarbon conversion process is the dehydrogenation of
hydrocarbons, particularly alkanes such as isobutane, which are converted to
isobutylene. For example, US-A-3,878,131 (and related US-A-3,632,503 and
US-A-3,755,481) discloses a catalyst comprising a platinum metal, a tin oxide
component and a germanium oxide component. All components are uniformly
dispersed throughout the alumina support. US-A-3,761,531 (and related US-A-
3,682,838) discloses a catalytic composite comprising a platinum group
component, a Group NA metallic component, e.g., germanium, a Group VA
metallic component, e.g., arsenic, antimony and an alkali or alkaline earth
component all dispersed on an alumina carrier material. Again all the
components are evenly distributed on the carrier.
US-A-3,558,477, US-A-3,562,147, US-A-3,584,060 and US-A-3,649,566
all disclose catalytic composites comprising a platinum group component and a
rhenium component on a refractory oxide support. However, as before, these
references disclose that the best results are achieved when the platinum group
component and rhenium component are uniformly distributed throughout the
catalyst.
It is also known that for certain processes selectivity towards desirable
products is inhibited by excessive residence time of the feed or the products
at
the active sites of the catalyst: Thus, US-A-4,716,143 describes a catalyst in
which the platinum group metal is deposited in an outer layer (400 m) of the
support. No preference is given to how the modifier metal should be
distributed
throughout the support. Similarly US-A-4,786,625 discloses a catalyst in which
the platinum is deposited on the surface of the support whereas the modifier
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metal is evenly distributed throughout the support.
US-A-3,897,368 describes a method for the production of a noble metal
catalyst where the noble metal is platinum and the platinum is deposited
selectively upon the external surface of the catalyst. However, this
disclosure
describes the advantages of impregnating only platinum on the exterior layer
and utilizes a specific type of surfactant to achieve the surface impregnation
of
the noble metal.
The art also discloses several references where a catalyst contains an
inner core and an outer layer or shell. For example, US-A-3,145,183 discloses
spheres having an - impervious center and a- porous shell. Although it is
disclosed that the impervious center can be small, the overall diameter is
1/8" or
larger. It is stated that for smaller diameter spheres (less than 1/8"),
uniformity
is hard to control. US-A-5,516,740 discloses a thin outer shell of catalytic
material bonded to an inner core of catalytically inert material. The outer
core
can have catalytic metals such as platinum dispersed on it. US 5,516,740
further discloses that this catalyst is used in an isomerization process.
Finally,
the outer layer material contains the catalytic metal prior to it being coated
onto
the inner core.
US-A-4,077,912 and US-A-4,255,253 disclose a catalyst having a base
support having deposited thereon a layer of a catalytic metal oxide or a
combination of a catalytic metal oxide and an oxide support. W098/14274
discloses a catalyst which comprises a catalytically inert core material on
which
is deposited and bonded a thin shell of material containing active sites.
Applicants have developed a layered catalyst composition which differs
from the prior art in several ways. The composition comprises an inner core
such as alpha alumina and an outer layer such as gamma alumina or a zeolite.
The outer layer optionally has uniformly distributed thereon at least one
platinum
group metal such as platinum and a modifier metal such as tin. The platinum
group metal to modifier metal atomic ratio varies from 0.1 to 5. The outer
layer
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has a thickness of 40 to 400 microns. A modifier metal, e.g., lithium, can
also
optionally be present on the catalyst composition and may be present either
entirely in the layer or distributed throughout the catalyst composition.
Finally,
the composition is prepared using an organic bonding agent such as polyvinyl
alcohol which increases the bond between the layer and the inner core thereby
reducing loss of the layer by attrition.
SUMMARY OF THE INVENTION
The present invention relates to a layered catalyst composition, a process
for preparing the composition and hydrocarbon conversion processes using the
composition. One embodiment is a layered catalyst composition comprising an
inner core, an outer layer bonded to said inner core, the outer layer
comprising
an outer refractory inorganic oxide optionally having uniformly dispersed
thereon
at least one platinum group metal, optionally a promoter metal and the
catalyst
composition further optionally having dispersed thereon a modifier metal and
where the inner core is selected from the group consisting of alpha alumina,
theta alumina, silicon carbide, metals, cordierite, zirconia, titania and
mixtures
thereof. '
Another embodiment of the invention is a hydrocarbon conversion
process comprising contacting a hydrocarbon fraction with the layered
composition described above under hydrocarbon conversion conditions to give a
. converted product.
Another hydrocarbon conversion process is the alkylation of aromatic
hydrocarbons using a layered composition comprising an inner core and an
outer layer comprising a zeolite and a binder.
A still further embodiment of the invention is a process for preparing the
layered catalyst composition described above, the process comprising:
a) coating an inner core with a slurry comprising the outer refractory
inorganic oxide and an organic bonding agent, said outer oxide having
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uniformly dispersed thereon at least one promoter metal, drying the
coated core and calcining at a temperature of 400 C to 900 C for a
time sufficient to bond the outer layer to the inner core and provide a
layered composition.
These and other objects and embodiments will become more clear after a
detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The layered catalyst composition comprises an inner core composed of a
material which has substantially lower adsorptive capacity for catalytic metal
precursors, relative to the outer layer. Some of the inner core materials are
also
not substantially penetrated by liquids, e.g., metals. Examples of the inner
core
material include, but are not limited to, refractory inorganic oxides, silicon
carbide and metals. Examples of refractory inorganic oxides include without
limitation alpha alumina, theta alumina, cordierite, zirconia, titania and
mixtures
thereof. A preferred inorganic oxide is alpha alumina.
These materials which form the inner core can be formed into a variety of
shapes such as pellets, extrudates, spheres or irregularly shaped particles
although not all materials can be formed into each shape. Preparation of the
inner core can be done by means known in the art such as oil dropping,
pressure molding, metal forming, pelletizing, granulation, extrusion, rolling
methods and marumerizing. A spherical inner core is preferred. The inner core
whether spherical or not has an effective diameter of 0.05 mm to 5 mm and
preferably from 0.8 mm to 3 mm. For a non-spherical inner core, effective
diameter is defined as the diameter the shaped article would have if it were
molded into a sphere. Once the inner core is prepared, it is calcined at a
temperature of 400 C to 1500 C.
The inner core is now coated with a layer of a refractory inorganic oxide
which is different from the inorganic oxide which may be used as the inner
core
and will be referred to as the outer refractory inorganic oxide. This outer
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refractory oxide is one which has good porosity, has a surface area of at
least
20m2/g, and preferably at least 50m2/g, an apparent bulk density of 0.2g/ml to
1.0g/ml and is chosen from the group consisting of gamma alumina, delta
alumina, eta alumina, theta alumina, silica/alumina, zeolites, non-zeolitic
molecular sieves (NZMS), titania, zirconia and mixtures thereof. It should be
pointed out that silica/alumina is not a physical mixture of silica and
alumina but
means an acidic and amorphous material that has been cogelled or
coprecipitated. This term is well known in the art, see e.g., U.S.-A-
3,909,450;
3,274,124 and 4,988,659. Examples of zeolites include, but are not limited to,
zeolite Y, zeolite X, zeolite L, zeolite beta, ferrierite, MFI, mordenite and
erionite.
Non-zeolitic molecular sieves (NZMS) are those molecular sieves which contain
elements other than aluminum and silicon and include silicoaluminophosphates
(SAPOs) described in U.S.-A-4,440,871, ELAPOs described in U.S.-A-
4,793,984, MeAPOs described in U.S.-A- 4,567,029. Preferred refractory
inorganic oxides are gamma and eta alumina.
A preferred way of preparing a gamma alumina is by the well-known oil drop
method which is described in U. S-A- 2, 620,314. The oil drop method comprises
forming an aluminum hydrosol by any of the techniques taught in the art and
preferably by reacting aluminum metal with hydrochloric acid; combining the
hydrosol with a suitable gelling agent, e. g., hexamethylenetetraamine; and
dropping
the resultant mixture into an oil bath maintained at elevated temperatures (93
C).
The droplets of the mixture remain in the oil bath until they set and form
hydrogel
spheres. The spheres are then continuously withdrawn from the oil bath and
typically subjected to specific aging and drying treatments in oil and
ammoniacal
solutions to further improve their physical characteristics. The resulting
aged and
gelled spheres are then washed and dried at a relatively low temperature of 80
C
to 260 C and then calcined at a temperature of 455 to 705 C for a period of 1
to
20 hours. This treatment effects conversion of the hydrogel to the
corresponding
crystalline gamma alumina.
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The layer is applied by forming a slurry of the outer refractory oxide and
then coating the inner core with the slurry by means well known in the art.
Slurries of inorganic oxides can be prepared by means well known in the art
which usually involve the use of a peptizing agent. For example, any of the
transitional aluminas can be mixed with water and an acid such as nitric,
hydrochloric, or sulfuric to give a siurry. Alternatively, an aluminum sol can
be
made by for example, dissolving aluminum metal in hydrochloric acid and then
mixing the aluminum sol with the alumina powder.
It is,also required that the slurry contain an organic bonding agent which
aids in the adhesion of the layer material to the inner core. Examples of this
organic bonding agent include but are not limited to polyvinyl alcohol (PVA),
hydroxy propyl cellulose, methyl cellulose and carboxy methyl cellulose. The
amount of organic bonding agent which is added to the slurry will vary
considerably from 0.1 wt. % to 3 wt. % of the slurry. How strongly the outer
layer is bonded to the inner core can be measured by the amount of layer
material, lost during an attrition test, i.e., attrition loss. Loss of the
second
refractory oxide by attrition is measured by agitating the catalyst,
collecting the
fines and calculating an attrition loss. It has been found that by using an
organic
bonding agent as described above, the attrition loss is less than 10 wt. % of
the
outer layer. Finally, the thickness of the outer layer varies from 40 to 400
microns, preferably from 40 microns to 300 microns and more preferably from
45 microns to 200 microns.
Depending on the particle size of the outer refractory inorganic oxide, it
may be necessary to mill the slurry in order to reduce the particle size and
simultaneously give a narrower particle size distribution. This can be done by
means known in the art such as ball milling for times of 30 minutes to 5 hours
and preferably from 1.5 to 3 hours. It has been found that using a slurry with
a
narrow particle size distribution improves the bonding of the outer layer to
the
inner core.
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Without wishing to be bound by any particular theory, it appears that
bonding agents such as PVA aid in making an interlocking bond between the
outer layer material and the inner core. Whether this occurs by the PVA
reducing the surface tension of the core or by some other mechanism is not
clear. What is clear is that a considerable reduction in loss of the outer
layer by
attrition is observed (See examples 8 and 9).
The slurry may also contain an inorganic bonding agent selected from an
alumina bonding agent, a silica bonding agent or mixtures thereof. Examples of
silica bonding agents include silica sol and silica gel, while examples of
alumina
bonding agents include alumina sol, boehmite and aluminum nitrate. The
inorganic bonding agents are converted to alumina or silica in the finished
composition. The amount of inorganic bonding agent varies from 2 to 15 wt. %
as the oxide, and based on the weight of the slurry. The use of an inorganic
binder is preferred when the outer refractory oxide is a zeolite.
Coating of the inner core with the slurry can be accomplished by means
such as rolling, dipping, spraying, etc. One preferred technique involves
using a
fixed fluidized bed of inner core particles and spraying the slurry into the
bed to
coat the particles evenly. The thickness of the layer can vary considerably,
but
usually is from 40 to 400 microns preferably from 40 to 300 microns and most
preferably from 50 microns to 200 microns. It should be pointed out that the
optimum layer thickness depends on the use for the catalyst and the choice of
the outer refractory oxide. Once the inner core is coated with the layer of
outer
refractory inorganic oxide, the resultant layered composition is dried at a
temperature of 100 C to 320 C for a time of 1 to 24 hours and then calcined at
a
temperature of 400 to 900 C for a time of 0.5 to 10 hours to effectively bond
the outer layer to the inner core and provide a layered calcined composition.
Of
course, the drying and calcining steps can be combined into one step.
When the inner core is composed of a refractory inorganic oxide (inner
refractory oxide), it is necessary that the outer refractory inorganic oxide
be
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different from the inner refractory oxide. Additionally, it is required that
the inner
refractory inorganic oxide have a substantially lower adsorptive capacity for
catalytic metal precursors relative to the outer refractory inorganic oxide.
When the outer refractory inorganic oxide is a zeolite (with or without an
inorganic binder) the iayered composition can be used to catalyze the
alkylation
of aromatic hydrocarbons, as will be further detailed below. However, for
other
processes catalytic metals need to be dispersed onto the layered composition.
Catalytic metals can be dispersed on the layered support by means known in
the art. Thus, a platinum group metal, a promoter metal and a modifier metal
can be dispersed on the outer layer. The platinum group metals include
platinum, palladium, rhodium, iridium, ruthenium and osmium. Promoter metals
are selected from the group consisting of tin, germanium, rhenium, gallium,
bismuth, lead, indium, cerium, zinc and mixtures thereof, while modifier
metals
are selected from the group consisting of alkali metals, alkaline earth metals
and mixtures thereof.
These catalytic metal components can be deposited on the layered
support in any suitable manner known in the art. One method involves
impregnating the layered support with a solution (preferably aqueous) of a
decomposable compound of the metal or metals. By decomposable is meant
that upon heating the metal compound is converted to the metal or metal oxide
with the release of byproducts. Illustrative of the decomposable compounds of
the platinum group metals are chloroplatinic acid, ammonium chloroplatinate,
bromoplatinic acid, dinitrodiamino platinum, sodium tetranitroplatinate,
rhodium
trichoride, hexa-amminerhodium chloride, rhodium carbonylchloride, sodium
hexanitrorhodate, chloropalladic acid, palladium chloride, palladium nitrate,
diamminepalladium hydroxide, tetraamminepalladium chloride, hexachloroiridate
(IV) acid, hexachloroiridate (III) acid, ammonium hexachloroiridate (III), '
ammonium aquohexachloroiridate (IV), ruthenium tetrachloride,
hexachlororuthenate, hexa-ammineruthenium chloride, osmium trichloride and
ammonium osmium chloride. Illustrative of the decomposable promoter metal
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compounds are the halide salts of the promoter metals. A preferred promoter is
tin and preferred decomposable compounds are stannous chloride or stannic
chloride.
The alkali and alkaline earth metals which can be used as modifier
metals in the practice of this invention include lithium, sodium, potassium,
cesium, rubidium, beryllium, magnesium, calcium, strontium and barium.
Preferred modifier metals are lithium, potassium, sodium and cesium with
lithium and sodium being especially preferred. Illustrative of the
decomposable
compounds of the alkali and alkaline earth metals are the halide, nitrate,
carbonate or hydroxide compounds, e.g., potassium hydroxide, lithium nitrate.
All three types of metals can be impregnated using one common solution
or they can be sequentially impregnated in any order, but not necessarily with
equivalent results. A preferred impregnation procedure involves the use of a
steam-jacketed rotary dryer. The support composition is immersed in the
impregnating solution containing the desired metal compound contained in the
dryer and the support is tumbled therein by the rotating motion of the dryer.
Evaporation of the solution in contact with the tumbling support is expedited
by
applying steam to the dryer jacket. The resultant composite is allowed to dry
under ambient temperature conditions, or dried at a temperature of 800 to
110 C, followed by calcination at a temperature of 200 C to 700 C for a time
of
1 to 4 hours, thereby converting the metal compound to the metal or metal
oxide. It should be pointed out that for the platinum group metal compound, it
is
preferred to carry out the calcination at a temperature of 400 C to 700 C.
In one method of preparation, the promoter metal is first deposited onto
the layered support composition and calcined as described above and then the
modifier metal and platinum group metal are simultaneously dispersed onto the
layered support composition by using an aqueous solution which contains a
compound of the modifier metal and a compound of the platinum group metal.
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The composition is impregnated with the solution as described above and then
calcined at a temperature of 400 C to 700 C for a time of 1 to 4 hours.
An alternative method of preparation involves adding one or more of the
metal components to the outer refractory oxide prior to applying it as a layer
onto the inner core. For example, a decomposable salt of the promoter metal,
e.g., tin (IV) chloride can be added to a slurry composed of gamma alumina and
aluminum sol. Further, either the modifier metal or the platinum group metal
or
both can be added to the slurry. Thus, in one method, all three catalytic
metals
are deposited onto the outer refractory oxide prior to depositing the second
refractory oxide as a layer onto the inner core. Again, the three types of
catalytic metals can be deposited onto the outer refractory oxide powder in
any
order although not necessarily with equivalent results.
One preferred method of preparation involves first impregnating the
promoter metal onto the outer refractory oxide and calcining as described
above. Next, a slurry is prepared (as described above) using the outer
refractory oxide containing the promoter metal and applied to the inner core
by
means described above. Finally, the modifier metal and platinum group metal
are simultaneously impregnated onto the layered composition which contains
the promoter metal and calcined as described above to give the desired layered
catalyst. This method of preparation is preferred when the catalyst is used in
a
dehydrogenation process. Other methods, as described above, may be
preferred when the catalyst is to be used for other processes.
As a final step in the preparation of the layered catalyst composition, the
catalyst composition is reduced under hydrogen or other reducing atmosphere in
order to ensure that the platinum group metal component is in the metallic
state
(zero valent). Reduction is carried out at a temperature of 100 C to 650 C for
a
time of 0.5 to 10 hours in a reducing environment, preferably dry hydrogen.
The
state of the promoter and modifier metals can be metallic (zero valent), metal
oxide or metal oxychloride.
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The layered catalyst composition can also contain a halogen component
which can be fluorine, chlorine, bromine, iodine or mixtures thereof with
chlorine
and bromine preferred. This halogen component is present in an amount of
0.03 to 1.5 wt. % with respect to the weight of the entire catalyst
composition.
The halogen component can be applied by means well known in the art and can
be done at any point during the preparation of the catalyst composition
although
not necessarily with equivalent results. It is preferred to add the halogen
component after all the catalytic components have been added either before or
after treatment with hydrogen.
Although in the preferred embodiments all three metals are uniformly
distributed, throughout the outer layer of the outer refractory oxide and
substantially present only in the outer layer, it is also Within the bounds of
this
invention that the modifier metal can be present both in the outer layer and
the
inner core. This is owing to the fact that the modifier metal can migrate to
the
inner core, when the core is other than a metallic core.
Although the concentration of each metal component can vary
substantially, it is desirable that the platinum group metal be present in a
concentration of 0.01 to 5 weight percent on an elemental basis of the entire
weight of the catalyst and preferably from 0.05 to 2.0 wt.%. The promoter
metal
is present in an amount from 0.05 to 10 wt.% of the entire catalyst while the
modifier metal is present in an amount from 0.1 to 5 wt.% and preferably from
2
to 4 wt.% of the entire catalyst. Finally, the atomic ratio of the platinum
group
metal to modifier metal varies from 0.05 to 5. In particular when the modifier
metal is tin, the atomic ratio is from 0.1:1 to 5:1 and preferably from 0.5:1
to 3:1.
When the modifier metal is germanium the ratio is from 0.25:1 to 5:1 and when
the promoter metal is rhenium, the ratio is from 0.05:1 to 2.75:1.
The various layered compositions described above can be used in a
variety of hydrocarbon conversion process. For example, a layered composition
in which the outer layer comprises azeolite and an inorganic binder has
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particular use for,the alkylation of aromatic hydrocarbons by olefins. The
alkylation and preferably the monoalkylation of aromatic compounds involves
reacting an aromatic compound with an olefin using the above described layered
composition. The olefins which can be used in the instant process are any of
those which contain from 2 up to 20 carbon atoms. These olefins may be
branched or linear olefins and either terminal or internal olefins. Preferred
olefins are ethylene, propylene and those olefins which are known as detergent
range olefins. Detergent range olefins are linear olefins containing from 6 up
through 20 carbon atoms which have either internal or terminal double bonds.
Linear olefins containing from 8 to 16 carbon atoms are preferred and those
containing from 10 up to 14 carbon atoms are especially preferred.
The alkylatable aromatic compounds may be selected from the group
consisting of benzene, naphthalene, anthracene, phenanthrene, and substituted
derivatives thereof, with benzene and its derivatives being the most preferred
aromatic compound. By alkylatable is meant that the aromatic compound can
be alkylated by an olefinic compound. The alkylatable aromatic compounds
may have one or more f the substituents selected from the group consisting of
alkyl groups (having from 1 to 20 carbon atoms), hydroxyl groups, and alkoxy
groups whose alkyl group also contains from 1 up to 20 carbon atoms. Where the
substituent is an alkyl or alkoxy group, a phenyl group can also can be
substituted
on the alkyl chain. Although unsubstituted and monosubstituted benzenes,
naphthalenes, anthracenes, and phenanthrenes are most often used in the
practice of this invention, polysubstituted aromatics also may be employed.
Examples of suitable alkylatable aromatic compounds in addition to those cited
above include biphenyl, toluene, xylene, ethylbenzene, propylbenzene,
butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, octylbenzene, etc.;
phenol, cresol, anisole, ethoxy-, propoxy-, butoxy-, pentoxy-, hexoxybenzene,
etc.
The particular conditions under which the monoalkylation reaction is
conducted depends upon the aromatic compound and the olefin used. One
necessary condition is that the reaction be conducted under at least partial
liquid
phase conditions. Therefore, the reaction pressure is adjusted to maintain the
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olefin at least partially dissolved in the liquid phase. For higher olefins
the reaction
may be conducted at autogenous pressure. As a practical matter the pressure
normally is in the range between 200 and 1,000 psig (1379-6985 kPa) but
usually
is in a range between 300-600 psig (2069-4137 kPa). The alkylation of the
alkylatable aromatic compounds with the olefins in the C2-C20 range can be
carried out at a temperature of 60 C to 400 C, and preferably from 90 C to 250
C,
for a time sufficient to form the desired product. In a continuous process
this time
can vary considerably, but is usually from 0.1 to 3 hr'weight hourly space
velocity
with respect to the olefin. In particular, the alkylation of benzene with
ethylene can
be carried out at temperatures of 200 C to 250 C and the alkylation of benzene
by
propylene to give cumene at a temperature of 90 C to 200 C: The ratio of
alkylatable aromatic compound to olefin used in the instant process will
depend
upon the degree of selective monoalkylation desired as well as the relative
costs
of the aromatic and olefinic components of the reaction mixture. For
alkylation of
benzene by propylene, benzene-to-olefin ratios may be as low as 1 and as high
as 10, with a ratio of 2.5-8 being preferred. Where benzene is alkylated with
ethylene a benzene-to-olefin ratio between 1:1 and 8:1 is preferred. For
detergent
range olefins of C6-C20, a benzene-to-olefin ratio of between 5:1 up to as
high as
30:1 is generally sufficient to ensure the desired monoalkylation selectivity,
with a
range between 8:1 and 20:1 even more preferred.
The zeolites of this invention can also be used to catalyze transalkylation
which is included in the general term "alkylation". By "transalkylation" is
meant
that process where an alkyl group on one aromatic nucleus is intermolecularly
transferred to a second aromatic nucleus. A preferred transalkylation process
is
one where one or more alkyl groups of a polyalkylated aromatic compound is
transferred to a nonalkylated aromatic compound, and is exemplified by
reaction
of diisopropylbenzene with benzene to give two molecules of cumene. Thus,
transalkylation often is utilized to add to the selectivity of a desired
selective
monoalkylation by reacting the polyalkylates invariably formed during
alkylation
with nonalkylated aromatic to form additional monoalkylated products. For the
purposes of this process, the polyalkylated aromatic compounds are those
formed
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in the alkylation of alkylatable aromatic compounds with olefins as described
above, and the nonalkylated aromatic compounds are benzene, naphthalene,
anthracene, and phenanthrene. The reaction conditions for transalkylation are
similar to those for alkylation, with temperatures being in the range of 100
to 250 ,
pressures in the range of 100 to 750 psig, and the molar ratio of unalkylated
aromatic to polyalkylated aromatic in the range from 1 to 10. Examples of
polyalkylated aromatics which may be reacted with, e.g., benzene as the
nonalkylated aromatic include diethylbenzene, diisopropylbenzene,
dibutylbenzene, triethylbenzene, triisopropylbenzene etc.
When the layered compositions of this invention contain catalytic metals
and optionally promoters and modifiers, they can be used in hydrocarbon
conversion processes such as alkylation of isoparaffins, hydrocracking,
cracking
isomerization, hydrogenation, dehydrogenation and oxidation. The conditions
for carrying out these processes are well known in the art and are presented
here for completeness.
Hydrocracking conditions typically include a temperature in the range of
240 C to 649 C (400 F-1200 F), preferably between 316 C and 510 C (600-
950 F). Reaction pressures are in the range of atmospheric to 24,132 kPag
(3,500 psig), preferably between 1,379 and 20,685 kPag (200 - 3,000 psig).
Contact times usually correspond to liquid hourly space velocities (LHSV) in
the
range of 0.1 hr 1 to 15 hr 1, preferably between 0.2 and 3 hr 1. Hydrogen
circulation rates are in the range of 178 to 8,888 standard cubic meters per
cubic meter 'of charge (1,000 to 50,000 standard cubic feet (scf) per barrel
of
charge) preferably between 355 to 5,333 std. m3/m3 (2,000 and 30,000 scf per
barrel of charge). .
The reaction zone effluent is normally removed from the catalyst bed,
subjected to partial condensation and vapor-liquid separation and then
fractionated to recover the various components thereof. The hydrogen, and if
desired some or all of the unconverted heavier materials, are recycled to the
reactor. Alternatively, a two-stage flow may be employed with the unconverted
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material being passed into a second reactor. Catalysts of the subject
invention
may be used in just one stage of such a process or may be used in both reactor
stages.
Catalytic cracking processes are preferably carried out with the catalyst
composition using feedstocks such as gas oils, heavy naphthas, deasphalted
crude oil residua, etc. with gasoline being the principal desired product.
Temperature conditions of 454 C to 593 C (850 to 1100 F,) LHSV values of
0.5 to 10 hr' and pressure conditions of from 0 to 345 kPag (50 psig) are
suitable.
tsomerization reactions are carried out in a temperature range of 371 C
to 538 C (700 - 1000 F). Olefins are preferably isomerized at temperatures of
260 C to 482 C (500 F to 900 F), while paraffins, naphthenes and alkyl
aromatics are isomerized at temperatures of 371 C to 538 C (700 F to 1000 F).
Hydrogen pressures are in the range of 689 to 3,445 kPag (100 to 500 psig).
Contact times usually correspond to liquid hourly space velocities (LHSV) in
the
range of 0.1 hr"' to 10 hr'. Hydrogen to hydrocarbon molar ratios are in the
range of 1 to 20, preferably between 4 and 12.
In a dehydrogenation process, dehydrogenatable hydrocarbons are
contacted with the catalyst of the instant invention in a dehydrogenation zone
maintained at dehydrogenation conditions. This contacting can be
accomplished in a fixed catalyst bed system, a moving catalyst bed system, a
fluidized bed system, etc., or in a batch-type operation. A fixed bed system
is
preferred. In this fixed bed system the hydrocarbon feed stream is preheated
to
the desired reaction temperature and then flowed into the dehydrogenation zone
containing a fixed bed of the catalyst. The dehydrogenation zone may itself
comprise one or more separate reaction zones with heating means there
between to ensure that the desired reaction temperature can be maintained at
the entrance to each reaction zone. The hydrocarbon may be contacted with
the catalyst bed in either upward, downward or radial flow fashion. Radial
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of the hydrocarbon through the catalyst bed is preferred. The hydrocarbon may
be in the liquid phase, a mixed vapor-liquid phase or the vapor phase when it
contacts the catalyst. Preferably, it is in the vapor phase.
Hydrocarbons which can be dehydrogenated include hydrbcarbons with 2
to 30 or more carbon atoms including paraffins, isoparaffins, alkylaromatics,
naphthenes and olefins. A preferred group of hydrocarbons is the group of
norrnal paraffins with 2 to 30 carbon atoms. Especially preferred normal
paraffins are those having 2 to 15 carbon atoms.
Dehydrogenation conditions include a temperature of from 400 C to
900 C, a pressure of from 1 to 1013 kPa and a liquid hourly space velocity
(LHSV) of from 0.1 to 100 hr'. Generally for normal paraffins the lower the
molecular weight the higher the temperature required for comparable
conversion. The pressure in the dehydrogenation zone is maintained as low as
practicable, 'consistent with equipment limitations, to maximize the chemical
equilibrium advantages.
The effluent stream from the dehydrogenation zone generally will contain
unconverted dehydrogenatable hydrocarbons, hydrogen and the products of
dehydrogenation reactions. This effluent stream is typically cooled and passed
to a hydrogen separation zone to separate a hydrogen-rich vapor phase from a
hydrocarbon-rich liquid phase. Generally, the hydrocarbon-rich liquid phase is
further separated by means of either a suitable selective adsorbent, a
selective
solvent, a selective reaction or reactions or by means of a suitable
fractionation
scheme. Unconverted dehydrogenatable hydrocarbons are recovered and may
be recycled to the dehydrogenation zone. Products of the dehydrogenation
reactions are recovered as final products or as intermediate products in the
preparation of other compounds.
The dehydrogenatable hydrocarbons may be admixed with a diluent
material before, while or after being flowed to the dehydrogenation zone. The
diluent material may be hydrogen, steam, methane, ethane, carbon dioxide,
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nitrogen, argon and the like or a mixture thereof. Hydrogen is the preferred
diluent. Ordinarily, when hydrogen is utilized as the diluent it is utilized
in
amounts sufficient to ensure a hydrogen to hydrocarbon mole ratio of 0.1:1 to
40:1, with best results being obtained when the mole ratio range is 1:1 to
10:1.
The diluent hydrogen stream passed to the dehydrogenation zone will typically
be recycled hydrogen separated from the effluent from the dehydrogenation
zone in the hydrogen separation zone.
Water or a material which decomposes at dehydrogenation conditions to
form water such as an alcohol, aldehyde, ether or ketone, for example, may be
added to the dehydrogenation zone, either continuously or intermittently, in
an
amount to provide, caiculated on the basis of equivalent water, i to 20,000
weight ppm of the hydrocarbon feed stream. Adding 1 to 10,000 weight ppm of
water gives best results when dehydrogenating paraffins having from 2 to 30 or
more carbon atoms.
Hydrogenation processes can be carried out using reactors and
hydrogenation zones similar to the dehydrogenation process described above.
Specifically, hydrogenation conditions include pressures of 0 kPag to 13,789
kPag, temperatures of 30 C to 280 C, H2 to hydrogenatable hydrocarbon mole
ratios of 5:1 to 0.1:1 and LHSV of 0.1 to 20 hr 1.
The layered compositions of this invention can also be used in oxidation
reactions. These oxidation reactions include:
1) partial oxidation of hydrocarbon streams, such as naphtha or
methane, to generate synthesis gas (CO +H2);
2) selective oxidation of hydrogen produced from endothermic
dehydrogenation reactions such as ethylbenzene to styrene; and,
3) oxidation of methane, ethane or carbon monoxide to clean up flue gas
emissions from combustion processes.
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The layered sphere catalyst will be of most benefit to processes where
the activity or selectivity of the catalyst is_ limited by intraparticle
diffusional
resistance of product or reactants.
The conditions for the oxidation process depend on the individual process
application but are generally 350 C to 800 C, 40 kPa to 2030 kPa, with a
diluent
present in the feedstream such as N2, CO2, HO to control the reaction.
Hydrogen may also be present as a diluent and also a reactant. For the
selective oxidation of hydrogen, the molar ratio of oxygen to H2 may vary from
0.05 to 0.5. The diluent level is generally from 0.1 to 10 moles of diluent
per
mole of hydrocarbon. For example, the steam to ethylbenzene molar ratio may
be from 5:1 to 7:1 during the dehydrogenation of ethylbenzene. Typical space
velocity for oxidation is between 0.5 to 50 hr' LHSV.
The following examples are presented in illustration of this invention and
are not intended as undue limitations on the generally broad scope of the
invention as set out in the appended claims.
EXAMPLE 1
Alumina spheres were prepared by the well known oil drop method which is
described in U. S.-A- 2, 620,314. This process involves forming an aluminum
hydrosol by dissolving aluminum in hydrochloric acid. Hexamethylene tetraamine
was added to the sol to gel the sol into spheres when dispersed as droplets
into an
oil bath maintained at 93 C. The droplets remained in the oil bath until they
set and
formed hydrogel spheres. After the spheres were removed from the hot oil, they
were pressure aged at 135 C and washed with dilute ammonium hydroxide
solution,
dried at 110 C and calcined at 650 C for about 2 hours to give gamma alumina
spheres. The calcined alumina was now crushed into a fine powder having a
particle
size of less than 200 microns.
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Next, a siurry was prepared by mixing 258 g of an aluminum sol (20 wt. %
A12 03) and 6.5 g of a 50% aqueous solution of tin chloride and 464 g of
deionized water and agitated to uniformly distribute the tin component. To
this
mixture there were added 272 g of the above prepared alumina powder, and the
slurry was ball milled for 2 hours thereby reducing the maximum particle size
to
less than 40 microns. This slurry (1,000 g) was sprayed onto 1 kg of alpha
alumina cores having an average diameter of 1.05 mm by using a granulating
and coating apparatus for 17 minutes to give an outer layer of 74 microns. At
the end of the process, 463 g of slurry were left which did not coat the
cores.
This layered spherical support was dried at 150 C for 2 hours and then
calcined
at 615 C for 4 hours in order to convert the pseudoboehmite in the outer layer
into gamma alumina and convert the tin chloride to tin oxide.
The calcined layered support (1150 g) was impregnated with lithium using
a rotary impregnator by contacting the support with an aqueous solution (1:1
solution: support volume ratio) containing lithium nitrate and 2 wt.% nitric
acid
based on support weight. The impregnated catalyst was heated using the rotary
impregnator until no solution remained, dried, and then calcined at 540 C for
2
hours.
The tin and lithium containing composite was now impregnated with
platinum by contacting the above composite with an aqueous solution (1:1
solution: support volume ratio) containing chloroplatinic acid and 1.2 wt.%
hydrochloric acid (based on support weight). The impregriated composite was
heated using the rotary impregnator until no solution remained, dried and
calcined at 540 C for 21/2 hours and reduced in hydrogen at 500 C for 2 hours.
Elemental analysis showed that this catalyst contained 0.093 wt.% platinum,
0:063 wt.% tin and 0.23 wt.% lithium with respect to the entire catalyst. This
catalyst was identified as catalyst A. The distribution of the platinum was
determined by Electron Probe Micro Analysis (EPMA) using a Scanning Electron
Microscope which showed that the platinum was evenly distributed throughout
the outer layer only.
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EXAMPLE 2
The procedure of Example 1 was repeated, except that a slurry was
prepared by mixing 275 g of an alumina sol into 431 g of deionized water with
sufficient agitation, and then adding 289 g of gamma alumina powder, 5.36 g of
a 50% aqueous solution of tin chloride was used, and after granulation and
coating, the layered spherical support had an outer layer of 99 microns in
thickness. There were 248 g of slurry left after the coating was carried out.
Elemental analysis (wt.% based on the entire catalyst) showed that this
catalyst
contained 0.09 wt.% platinum, 0.09 wt.% tin and 0.23 wt.% lithium and was
identified as catalyst B. Catalyst B was analyzed by EPMA which showed that
the platinum was evenly distributed throughout the outer layer only.
COMPARATIVE EXAMPLE 1
A catalyst was prepared in a similar way to that of example II of U.S.-A-
4,786,625 except that the solution was sprayed onto the support. The catalyst
was analyzed and found to contain 0.43 wt.% platinum, 1.7 wt.% tin and 0.62
wt.% lithium. This catalyst was identified as catalyst C. Catalyst C was
analyzed by EPMA which showed that the platinum was on the surface of the
support.
COMPARATIVE EXAMPLE 2
A catalyst was prepared according to example I of U.S.-A- 4,786,625.
This catalyst was analyzed and found to contain 0.43 wt. /d platinum, 0.48
wt.%
tin and 0.58 wt. % lithium. This catalyst was identified as catalyst D. All
the
metals were evenly distributed throughout the support.
EXAMPLE 3
A gamma .alumina slurry (1000g) was prepared as in example 1 except
that no tin chloride was added to the slurry. This slurry was applied to 1000g
of
alpha alumina cores having a diameter of 1.054mm as in example 1 and
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calcined as in example 1 to give a layered support with an outer gamma-alumina
layer of 74 microns in thickness.
The layered support (202g) was contacted with an aqueous solution
prepared by diluting a 50% tin chloride 'solution (Sn content: 0.144g based on
metal) and nitric acid (HNO3 content: 18.2g) with deionized water to a volume
of
150 ml. The mixture was dried in a rotary evaporator at a temperature of 150 C
for 2 hours, following by calcination at a temperature of 615 C for 4 hours.
The tin containing layered composition of the previous paragraph was
now impregnated with lithium and platinum using a rotary impregnator by
contacting the composition with an aqueous solution containing chloroplatinic
acid (Pt = 0.188g), lithium nitrate (Li = 0.54g) and nitric acid. The
impregnated
catalyst composition was heated in the rotary evaporator until no solution
remained, calcined at 540 C for 2 1/2 hours and then reduced in hydrogen at
500 C for 2 hours. The platinum and tin were determined by EPMA to be evenly
distributed throughout the outer layer. Elemental analysis showed that this
layered catalyst composition contained 0.093 wt.% platinum, 0.071 wt.% tin and
0.268 wt. % lithium calculated as the metal and based on the entire catalyst
weight. This catalyst was identified as catalyst E.
EXAMPLE 4
A sample of 600 ml. of spherical alumina was prepared as in example 1.
This alumina was impregnated using a rotary impregnator with an aqueous
solution prepared by diluting 9.55 g of a 50% tin chloride solution and 49.6 g
of a
61 % nitric acid solution with deionized water to a volume of 420 mi. The
impregnated alumina spheres were dried in the rotary evaporator and then
calcined at 540 C for 2'/2 hours.
The resulting tin-containing catalyst was impregnated with an aqueous
solution containing platinum and lithium, prepared by diluting a
chloroplatinic
acid solution (Pt content: 1.71 g), a lithium nitrate solution (Li content:
1.16 g)
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and 6.61 g of a 61 % nitric acid solution with deionized water to a volume of
420
ml. The obtained spherical catalyst was dried in a rotary evaporator untit no
solution remained and then calcined at a temperature of 540 C for 2.5 hours.
The platinum and tin were evenly distributed throughout the sphere.
A slurry was prepared by mixing 600 ml of the above spherical catalyst
with 4.0 g of P-sait (dinitrodiammineplatinum in nitric acid) 0.641 g of meta
stannic acid and 202 g of alumina sol (20 wt.% A(203) with 1204 g of deionized
water and ball milling the mixture for 4 hours. This slurry was now used to
apply
a layer onto an alpha-alumina core having a diameter of 1.054 mm as in
example 1. A layered catalyst was obtained which had a layer of 50 microns.
This layered catalyst composition was dried at 150 C for 2 hrs. and then
calcined at 615 C for 4 hours to convert the pseudoboehmite in the. outer
layer
to gamma alumina. Finally, the catalyst composition was reduced in hydrogen
at 500 C for 2 hours. Elemental analysis showed that this catalyst contained
0.089 wt.% platinum, 0.113 wt. % tin and 0.05 wt.% lithium, all calculated on
an
elemental basis and based on the weight of the entire catalyst. This catalyst
was identified as catalyst F.
EXAMPLE 5
The catalysts of examples 1-4 and comparative examples 1 and 2 were
tested for dehydrogenation activity. In a 1.27 cm (1/2") reactor; 10 cc of
catalyst
was placed and a hydrocarbon feed composed of 8.8 wt. % n-C10, 40.0 wt. % n-
C11, 38.6 wt. % n-C12, 10.8 wt. % n-C13, 0.8 wt. % n-C14 and 1 vol. % non-
normals was flowed over the catalyst under a pressure of 138 kPa (20 psig), a
H2: hydrocarbon molar ratio of 6:1 and a liquid hourly space velocity (LHSV)
of
20 hr 1. Water at a concentration of 2000 ppm based on hydrocarbon weight
was injected. The total normal olefin concentration in the product (% TNO) was
maintained at 15 wt. % by adjusting reactor temperature.
The results of the testing are presented in Table 1. What is presented is
the deactivation rate (slope) which is obtained by plotting temperature ( F)
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needed to maintain 15% TNO versus time. Selectivity for TNO at 120 hours on
stream is also presented and is calculated by dividing % TNO by total
conversion. Finally, non-TNO selectivity is 100% - %TNO.
Table 1
Comparison of Layered versus Non-Layered Catalysts
Deactivation TNO Non-TNO
Catalyst I.D. Rate( F/hr) Selectivity Selectivity
wt.% wt.%
A 0.052 94.6 5.4
B 0.032 94.0 6.0
C 0.067 93.5 6.5
D 0.05 91.1 8.9
E 0.050 94.4 5.6
F 0.033 94.0 6.0
The results show that the layered catalysts of the invention have both
lower deactivation rates and increased selectivity to normal olefins versus
catalysts of the prior art. Specifically, comparing catalysts A, B, E and F
with
catalyst C (platinum on the surface), it is observed that the deactivation
rate is
smaller for catalysts A, B, E and F. Additionally, selectivity is better for
the
layered catalysts of the invention. It must be pointed out that when
selectivities
are this high, one must look at the residual amount left or the non-TNO
selectivity. Here, the amount of non-TNO for catalysts A and E are 17 wt.% and
14 wt. % less, respectively, than for catalyst C which is a substantial
improvement.
Comparing catalysts A, B, E and F with catalyst D (uniform platinum)
what is observed is that catalysts B and F have a much lower deactivation rate
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than catalyst D, while catalysts A and E have a much higher selectivity (39
and
37 wt.% less non-TNO make, respectively) than catalyst D. Again, this shows a
marked improvement in stability and selectivity.
EXAMPLE 6
The procedure set forth in example 1 was used to prepare a catalyst with
the modification that polyvinyl alcohol (PVA) at a concentration of 2 wt. % of
the
gamma alumina was added to the sfurry. This catalyst was identified as
catalyst G.
EXAMPLE 7
The procedure set forth in example 1 was used to prepare a catalyst with
the modification that hydroxy propyl cellulose (HPC) at a concentration of, 2
wt.
% of the gamma alumina was added to the slurry. This catalyst was identified
as catalyst H.
EXAMPLE 8
The procedure in example 1 was used to prepare-a catalyst with a layer
thickness of 90 microns. This catalyst was identified as catalyst I.
EXAMPLE 9
Catalysts G, H and I were tested for loss of layer material by attrition
using the following test.
A sample of the catalyst was placed in a vial which in turn was placed in a
blender mill along with tvvo other vials containing the same amount of
catalyst
sample. The vials were milled for ten (10) minutes, the vials removed and then
sieved to separate the powder from the spheres. The powder was weighed and
an attrition loss (wt.%) was calculated.
The results of the attrition test are summarized in Table 2.
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Table 2
Effect of Organic Binding Agent on Attrition
Catalyst I.D. Weight Percent Loss '
Based on Total Amount Based On Layer
G (PVA) 1.0 4.3
H (HPC) 1.9 8.5
I (No Additive) 3.7 17.9
The date is Table 2 show that using an organic binding agent greatly
improves the attrition loss of a layered catalyst.
