U.S. patent number 3,692,863 [Application Number 04/769,723] was granted by the patent office on 1972-09-19 for dehydrogenation and dehydrocyclization method.
This patent grant is currently assigned to Ashland Oil & Refining Company. Invention is credited to Ronald A. Kmecak, Stephen M. Kovach.
United States Patent |
3,692,863 |
Kmecak , et al. |
September 19, 1972 |
DEHYDROGENATION AND DEHYDROCYCLIZATION METHOD
Abstract
A process for effecting a hydrogen transfer reaction involving
the dehydrogenation of at least a part of the feed material, such
as the dehydrocyclization of paraffinic hydrocarbons to produce
aromatics, and the dehydrogenation of low molecular weight
paraffins to produce hydrogen and monoolefins, including
contracting the feed material with a catalyst comprising a metal of
Group VIB of the Periodic System, in an amount between about 5 to
15 percent by weight of the finished catalyst, and a promotor of a
metal of Group IV of the Periodic System, such as tin and lead in
an amount of between about 1.0 and 10 percent by weight of the
finished catalyst, both deposited on an inert oxide support such as
gamma aluminas, silica-alumina, silica-magnesia, alumina-magnesia,
etc., at a temperature between about 550.degree. F. and
1,250.degree. F., a pressure between about 0.01 and 2,600 mm.
mercury absolute, and a liquid hourly space velocity between about
0.1 and 10. Where lower paraffins are dehydrogenated to olefins and
hydrogen, the hydrogen is separated from the olefins and contacted
with coal liquids in the presence of a hydrogenation catalyst,
preferably of the same character as the dehydrogenation catalyst,
and under conditions sufficient to a hydrogenate at least a part of
the coal liquids. An additional promotor selected from the group of
alkali metals, alkaline earth metals and rare earth metals may also
be added.
Inventors: |
Kmecak; Ronald A. (Ashland,
KY), Kovach; Stephen M. (Ashland, KY) |
Assignee: |
Ashland Oil & Refining
Company (Houston, TX)
|
Family
ID: |
25086340 |
Appl.
No.: |
04/769,723 |
Filed: |
October 22, 1968 |
Current U.S.
Class: |
208/143; 208/49;
502/242; 585/257; 585/365; 585/421; 585/663; 208/56; 502/300;
585/312; 585/420; 585/662 |
Current CPC
Class: |
B01J
23/24 (20130101); C10G 1/002 (20130101); C07C
5/3332 (20130101); C07C 5/322 (20130101); C07C
5/3332 (20130101); C07C 11/02 (20130101) |
Current International
Class: |
C07C
5/00 (20060101); C07C 5/32 (20060101); C10G
1/00 (20060101); C07C 5/333 (20060101); B01J
23/24 (20060101); B01J 23/16 (20060101); C07c
005/18 (); C07c 011/04 (); C10g 031/14 () |
Field of
Search: |
;260/683.3,673.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Schmitkons; G. E.
Claims
We claim:
1. A process for dehydrogenating hydrocarbons predominating in
aliphatic, paraffinic hydrocarbons having up to five carbon atoms
per molecule comprising: contacting the hydrocarbons with a
catalyst consisting essentially of about 5 to 15 percent by weight
of a metal of Group VI of the Periodic System and about 1.0 to 10
percent by weight of a metal selected from the group consisting of
lead oxide and tin oxide, both impregnated on an inert oxide
support, under conditions sufficient to effect said dehydrogenating
reaction, including, a temperature of about 550.degree. to
1,250.degree. F., a pressure of about 0.01 to 2,600 mm of mercury
and a liquid hourly space velocity of about 0.1 to 10.
2. A process in accordance with claim 1 wherein the inert oxide
support is a gamma alumina.
3. A process in accordance with claim 1 wherein the hydrocarbon is
ethane and the temperature is about 1,100.degree. to 1,250.degree.
F.
4. A process in accordance with claim 1 wherein the hydrocarbons
contain three through five carbon atoms per molecule and the
temperature is about 900.degree. to 1,150.degree. F.
5. A process in accordance with claim 1 wherein the paraffins are
converted to hydrogen and olefins, the hydrogen and olefins are
separated and coal liquids are contacted with the hydrogen in the
presence of a hydrogenation catalyst and under conditions
sufficient to hydrogenate at least a portion of said coal
liquids.
6. A process in accordance with claim 5 wherein the hydrogenation
catalyst is a catalyst of the same character as the dehydrogenation
catalyst.
7. A process for dehydrogenating hydrocarbons predominating in
aliphatic, paraffinic hydrocarbons having up to five carbon atoms
per molecule comprising: contacting the hydrocarbons with a
catalyst consisting essentially of about 5 to 15 percent by weight
of a metal of Group VI of the Periodic System, about 1.0 to 10
percent by weight of a metal selected from the group consisting of
lead oxide and tin oxide and about 1.0 to about 10 percent of a
second promoting metal selected from the group consisting of alkali
metals, alkaline earth metals, rare earth metals and mixtures
thereof, all impregnated on an inert oxide support, under
conditions sufficient to effect said dehydrogenating reaction,
including, a temperature of about 550.degree. to 1,250.degree. F.,
a pressure of about 0.01 to 2,600 mm of mercury and a liquid hourly
space velocity of about 0.1 to 10.
8. A process in accordance with claim 7 wherein the second promoter
is an alkali metal.
9. A process in accordance with claim 7 wherein the second promoter
is an alkaline earth metal.
10. A process in accordance with claim 7 wherein the second
promoter is a rare earth metal.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method for effecting reactions
involving the dehydrogenation of organic materials. In a more
specific aspect, the present invention relates to a method for the
dehydrogenation and dehydrocyclization of hydrocarbon
materials.
Numerous processes have been developed for the dehydrogenation of
organic materials and, particularly, for the dehydrogenation and
dehydrocyclization of non-aromatic hydrocarbons.
Among the dehydrocyclization type reactions are those involving the
treatment of a variety of feedstocks containing normal paraffins.
In these instances, normal paraffins, such as n-hexane and
n-heptane, or mixtures thereof, are dehydrogenated and cyclized to
produce aromatic hydrocarbons. This type reaction may also be
applied to hydrocarbon mixtures containing normal paraffins, such
as primary flash distillates and the products of the well-known
reforming process in which a naphtha fraction is contacted at
elevated temperature and pressure and in the presence of hydrogen
with a dehydrogenation catalyst, for example a catalyst consisting
essentially of platinum and alumina with or without combined
halogen to produce a gasoline fraction of increased octane number.
The dehydrocyclization reactions are, of course primarily confined
to the treatment of materials having five carbon atoms and
higher.
The dehydrogenation type of reaction without cyclization also is
primarily applied to paraffinic hydrocarbons. However, in this
case, the hydrocarbon feed is normally a hydrocarbon having five or
less carbon atoms per molecule. Specifically, in this latter case,
the petroleum industry now produces a wide variety of hydrocarbon
streams for use as fuels and chemicals. Two of the more important
chemicals are olefins which are utilized as chemical intermediates
and hydrogen which is used for the production and processing of
petrochemicals and fuels. At the present time, most of the
unsaturated light hydrocarbons are obtained as by-products of
cracking processes. While this is a relatively cheap source of
light olefins, the purity of the product does not generally meet
requirements where high purity is needed. One possible means of
obtaining relatively pure, unsaturated hydrocarbons is by the
dehydrogenation of the corresponding saturated hydrocarbons. This
is a relatively simple operation. Large quantities of the raw
material can be obtained at a reasonable price. Several processes
have been developed for light paraffin dehydrogenation. These
generally include cyclic, adiabatic, fixed-bed regenerative
processes requiring short cycle times due to coke deposition on the
catalyst. Therefore, for continuous operation, a minimum of three
reactors is required with one reactor on-stream, one being
regenerated, and one on standby. Multiples of this system can be
utilized to increase olefin production. Another method for
producing unsaturates is the pyrolysis of hydrocarbons. This is a
process which is used almost exclusively for the production of
acetylene, ethylene, and propylene. One drawback of this system is
the high temperature required and the low purity of the hydrogen
product stream. Yet another method which has been developed entails
the dehydrogenation of paraffins over precious metal catalysts.
However, conversions are very low, about 10 percent, and olefin
separation must be effected by aromatic alkylation. The production
of hydrogen for the petroleum-petrochemical industry is generally
through catalytic reforming of naphthas or the steam reforming of
light hydrocarbons. The hydrogen available from catalytic reforming
is rather limited and in short supply, so that more and more,
producers are resorting to steam reforming of light hydrocarbons to
satisfy the massive hydrogen requirements of today's
operations.
Hydrogen requirements are also extremely high in processes for the
treatment of liquids derived from coal. For example, coal liquids
may be obtained from coal in solid form by carbonization or
pyrolysis of the solid coal to produce coal tar products and the
solvent extraction of coal solids with solvents, such as tetralin,
decalin and the like, to produce a solvent extract. It is therefore
highly desirable that an integrated process for the production of
substantial volumes of hydrogen and the saturation and upgrading of
coal liquids with such hydrogen be provided.
It is therefore an object of the present invention to provide a
process for effecting reactions involving the dehydrogenation of
organic materials. Another object of the present invention is to
provide an improved process for effecting reactions involving the
dehydrogenation or dehydrocyclization of organic materials. Yet
another object of the present invention is to provide an improved
process for the saturation of highly unsaturated organic materials
derived from solids. Another and further object of the present
invention is to provide an integrated process for the saturation of
coal liquids including dehydrogenating paraffinic hydrocarbons to
produce mono-olefins and hydrogen, separating the hydrogen from the
mono-olefins and contacting the coal liquid with said hydrogen
under hydrogenation conditions. It is also an object of the present
invention to provide an improved process for the production of
olefins and hydrogen. Yet another object of the present invention
is to provide an improved process for the production of olefins and
hydrogen by the dehydrogenation of paraffins. A further object of
the present invention is to provide an improved process for the
production of olefins and hydrogen by the dehydrogenation of
paraffins which utilizes a novel catalyst system. A further object
of the present invention is to provide an improved process for the
conduct of dehydrogenation-type reactions which utilizes a catalyst
capable of high conversion rates. Another and further object of the
present invention is to provide an improved process for the conduct
of dehydrogenation-type reactions which utilizes a catalyst of high
selectivity. Still another object of the present invention is to
provide an improved process for the conduct of dehydrogenation-type
reactions which utilizes a catalyst having a low coking rate. These
and other objects and advantages of the present invention will be
apparent from the following detailed description.
SUMMARY OF THE INVENTION
Briefly, in accordance with the present invention, hydrocarbon
materials are dehydrogenated by contacting the hydrocarbon material
with a metal of Group VI of the Periodic System and a promoter of
Group IV of the Periodic System, and, if desired, an additional
promoter selected from the group consisting of oxides of alkali
metals, alkaline earth metals, rare earth metals, Group VIII metals
and mixtures thereof.
Suitable feedstocks for use in the dehydrocyclization of
non-aromatic hydrocarbons include those previously mentioned, such
as n-hexane and n-heptane and mixtures of these, as well as
hydrocarbon mixtures containing normal paraffins, such as
distillates and products of reforming operations.
The dehydrocyclization operation may be carried out at temperatures
varying all the way from 550.degree. F. to about 1,150.degree. F.,
at pressures between about 0.01 and 2,600 mm. mercury absolute, and
at liquid hourly space velocities of from 0.1 to 10.
Suitable feedstocks for use in the dehydrogenation include ethane,
propane, normal butane, iso-butane, normal pentane, iso-pentane,
etc.
Processing conditions for the dehydrogenation reaction are
dependent upon the feedstock employed. Generally, temperatures
between about 900.degree. F. and 1,250.degree. F., pressures
between about 100 and 2,500 mm. mercury absolute, and liquid hourly
space velocities from about 0.1 to 10 may be employed. More
specifically, if ethane is the feedstock, the temperature should be
between about 1,100.degree. F. and 1,250.degree. F. Where C.sub.3
to C.sub.5 paraffins are the feedstock, a temperature of
900.degree. to 1,150.degree. should be used.
The separation of the monoolefins and hydrogen produced in the
dehydrogenation reaction may be effected by selective adsorption
and other known separation techniques. The separated hydrogen is
then contracted with liquid materials of a highly unsaturated
nature such as coal liquids derived from solid coal. For example,
it is known that solid coal can be crushed or ground and subjected
to carbonization or pyrolysis at elevated temperatures to produce
liquid known as coal tar liquids. It is also known that crushed or
pulverized coal can be contacted with a suitable solvent, at
slightly elevated temperatures, such as tetralin, decalin and other
hydrogen transfer solvents, to thereby produce a solvent extract
which resembles coal tar liquids or heavy petroleum crudes. Both of
these crude materials, particularly the solvent extracts, are
highly unsaturated mixtures containing substantial volumes of
cyclic compounds, which must be saturated to some extent before
they can be further processed to produce fuels and chemicals. Such
saturation is effected in accordance with the present invention by
contacting the coal liquids with the hydrogen separated from the
monoolefins and recovering the hydrogenated coal liquids. The
hydrogenated coal liquids then resemble in substantially all
respects, except for aromaticity, hydrocarbon liquids derived from
petroleum crude oils; and, accordingly, they may be processed in
accordance with conventional refinery practices for the conversion
of petroleum oils.
The hydrogenation of the coal liquids may be carried out in the
presence of the same catalysts employed for the dehydrogenation
reaction. However, any known hydrogenation catalysts may also be
employed, such as Group VIII metals, for example, platinum,
palladium, rhodium and nickel and cobalt and Group VI metals, such
as molybdenum or tungsten or various combinations of these metals,
deposited on a carrier such as alumina or silica. Hydrogenation
conditions may include temperatures from about 450.degree. to
800.degree. F., preferably about 500.degree. to 800.degree. F.,
pressures of about 400 to 10,000 psig., liquid hourly space
velocities from about 0.1 to 10, and hydrogen-to-hydrocarbon mole
ratios from about 1 to 20 to 1.
The novel catalysts of the present invention include an active
metal from Group VIB of the Periodic System, and specifically,
chromium, molybdenum and tungsten, in a concentration of about 5 to
15 percent by weight based on the finished catalyst. The promoter
of the present invention includes a Group IV metal, in its oxide
form, and if desired, alkali metals, such as potassium, rubidium
and cesium, alkaline earth metals, such as calcium, strontium and
barium, Group VIII metals, such as platinum, rhodium, ruthenium,
palladium and nickel, and rare earth metals, such as cerium or
thorium in a concentration of about 1 to 10 percent by weight based
on the finished catalyst product. The promoter is preferably in its
oxide form. Both of these materials are deposited on an inert oxide
support, preferably an alumina of a gamma type, such as the
bayerite, beta, etc., and boehmite crystalline forms. Other
suitable supports of this character may be used also, such as other
aluminas, silica-alumina, silica, silica-magnesia,
alumina-magnesia, silica-zirconia, etc.
The catalysts may be prepared by techniques well known in the art.
For example, such preparation includes known impregnation
techniques. One can employ extrudates or pellets for impregnation
or powders followed by pellitization or extrusion to yield the
finished catalyst. The active metal and the promoter are added
through the use of water-soluble salts, such as their halides,
nitrates, sulfates, acetates, etc. Easily hydrolyzed salts can be
kept in solution without decomposition by employing the appropriate
inorganic acids. Well-known procedures for drying and calcination
of the catalysts may also be employed, such as vacuum drying and
calcination in oxidative, neutral and reductive atmospheres,
utilizing calcination temperatures of about 800.degree. to
1,200.degree. F.
The following examples illustrate the preparation of the catalysts
of this invention.
EXAMPLE I
To 900 ml. of distilled water was added 81 g. of stannous sulfate
and 30 ml. of concentrated sulfuric acid. The sulfuric acid was
required to bring the insolubles from the stannous sulfate into
solution. This was believed to be tin hydroxide. This solution was
added to 900 ml. of a boehmite alumina as pellets and after contact
for 15 minutes, the unadsorbed liquid was decanted from the
catalyst pellets. The resulting impregnated catalyst was dried at
250.degree. F. for 1 hour and calcined in air at 950.degree. F. for
16 hours in a muffle furnace. This yielded a catalyst of the
following composition:
4% SnO--Al.sub.2 O.sub.3.
A solution containing 150 ml. of distilled water, 45 g. of chromic
acid, and 9.5 g. of potassium nitrate was added to 150 ml. of 4%
SnO--Al.sub.2 O.sub.3 pellets from above. Catalyst and solution was
in contact for 15 minutes and the unadsorbed liquid was decanted.
The resulting catalyst was dried at 250.degree. F. for 1 hour can
calcined in air at 950.degree. F. in a muffle furnace for 16 hours.
This yielded a catalyst of the following composition:
15% Cr.sub.2 O.sub.3 --2% K.sub.2 O--4% SnO--Al.sub.2 O.sub.3.
EXAMPLE II
To 600 ml. of distilled water was added 20 g. of lead nitrate. This
solution was added to 600 ml. of a boehmite alumina as pellets and
after contact for 15 minutes, the unadsorbed liquid was decanted
from the catalyst pellets. The resulting impregnated catalyst was
dried at 250.degree. F. for 1 hour and calcined in air at
950.degree. F. in a muffle furnace for 16 hours. This yielded a
catalyst of the following composition:
2% PbO--Al.sub.2 O.sub.3.
A solution containing 150 ml. of distilled water, 36 g. of chromic
acid, and 5.5 g. of cesium nitrate was added to 150 ml. of 2%
PbO--Al.sub.2 O.sub.3 pellets from above. Catalyst and solution was
in contact for 15 minutes and the unadsorbed liquid was decanted.
The resulting catalyst was dried at 250.degree. F. for 1 hour and
calcined in air at 950.degree. F. for 16 hours in a muffle furnace.
This yielded a catalyst of the following composition:
12% Cr.sub.2 O.sub.3 --2% Cs.sub.2 O--2% PbO--Al.sub.2 O.sub.3.
EXAMPLE III
By employing the techniques and procedures outlined in Examples I
and II other catalytic compositions were prepared. A solution
containing 600 ml. of distilled water, 54 g. of stannous sulfate
and 20 ml. of concentrated sulfuric acid was added to 600 ml. of a
boehmite alumina. Drying and calcination yielded the following
composition:
3% SnO--Al.sub.2 O.sub.3.
A solution containing 150 ml. of distilled water, 29 g. of ammonium
molybdate, 10 g. of potassium nitrate, and 5 ml. of concentrated
ammonium hydroxide was added to 150 ml. of 3% SnO--Al.sub.2 O.sub.3
pellets. Drying and calcination yielded the following
composition:
12% MoO.sub.3 --2% K.sub.2 O--3% SnO--Al.sub.2 O.sub.3.
EXAMPLE IV
To 600 ml. of distilled water was added 54 g. of stannous sulfate
and 20 ml. of concentrated sulfuric acid. The tin sulfate was
partially insoluble and the sulfuric acid brought it into solution.
This insolubility was probably due to the presence of tin
hydroxide. This solution was added to 600 ml. of a boehmite alumina
and after contact for 15 minutes, the unadsorbed liquid was
decanted from the catalyst pellets. The resulting impregnated
catalyst was dried at 250.degree. F. for 1 hour and calcined at
950.degree. F. for 16 hours to yield a catalyst of the following
composition:
4% SnO--Al.sub.2 O.sub.3.
A solution containing 150 ml. of distilled water and 30 g. of
chromic acid was added to 150 ml. of 4% SnO--Al.sub.2 O.sub.3
pellets (prepared as above) and allowed to remain in contact for 15
minutes before decanting the unadsorbed liquid. The impregnated
catalyst was dried at 250.degree. F. for 1 hour and calcined in air
at 950.degree. F. for 16 hours in a muffle furnace. This yielded a
catalyst of the following composition:
10% Cr.sub.2 O.sub.3 --4% SnO--Al.sub. 2 O.sub.3.
EXAMPLE V
A 4% SnO--Al.sub. 2 O.sub.3 catalyst was prepared according to the
procedure described in Example IV. To 150 ml. of 4% SnO--Al.sub. 2
O.sub.3 pellets was added a solution containing 150 ml. of
distilled water and 1 g. of rhodium trichloride. The unadsorbed
liquid was decanted and the catalyst dried and calcined according
to the procedure outlined in Example I. To the rhodium oxide-tin
oxide-alumina catalyst was added a solution containing 150 ml. of
distilled water and 45 g. of chromic acid. The catalyst was dried
and calcined (see Example I) to yield the following
composition:
15% Cr.sub.2 O.sub.3 --0.5% Rh--4% SnO--Al.sub. 2 O.sub.3.
EXAMPLE VI
To 400 ml. of distilled water was added 18 g. of stannous sulfate.
This solution was added to 200 ml. of bayerite alumina (similar to
beta) and 200 ml. of boehmite alumina in separate impregnation
vessels. The solution remained in contact with the aluminas for 15
minutes and was then decanted. The resulting catalysts were dried
for 1 hour at 250.degree. F. and calcined in air in a muffle
furnace for 16 hours at 950.degree. F. This yielded two 4 percent
tin oxide on alumina catalysts. To each tin oxide-alumina catalyst
was added a solution containing 200 ml. of distilled water and 40
g. of chromic acid. The solution and catalyst remained in contact
for 15 minutes and the remaining solution removed by decantation.
The catalyst was dried at 250.degree. F. for 1 hour and calcined in
air in a muffle furnace for 16 hours at 950.degree. F. This yielded
the following composition:
10% Cr.sub.2 O.sub.3 --2% SnO--Al.sub. 2 O.sub.3.
EXAMPLE VII
To 600 ml. of a boehmite alumina was added a solution containing
600 ml. of distilled water, 80 g. of stannous sulfate and 20 ml. of
concentrated sulfuric acid. The stannous sulfate was not completely
water soluble and the sulfuric acid dissolved all insolubles to
give a clear solution. The insolubles are believed to be tin
hydroxide which are converted to the soluble sulfate. These
insolubles were not noted in Example I. The solution and catalyst
remained in contact for 15 minutes and the remaining solution then
removed by decantation. The catalyst was dried at 250.degree. F.
for 1 hour and calcined in air in a muffle furnace for 16 hours at
950.degree. F. This yielded a 6 percent tin oxide on alumina
catalyst.
To 150 ml. of 6 percent tin oxide on alumina pellets was added a
solution containing 150 ml. of distilled water and 15 g. of chromic
acid. The solution and catalyst remained in contact for 15 minutes
and the unadsorbed solution removed by decantation. The catalyst
was dried at 250.degree. F. for 1 hour and calcined in air in a
muffle furnace for 16 hours at 950.degree. F. This yielded the
following composition:
5% Cr.sub.2 O.sub.3 --6% SnO--Al.sub. 2 O.sub.3.
EXAMPLE VIII
To 600 ml. of distilled water was added 54 g. of stannous sulfate
and 20 ml. of concentrated sulfuric acid. The stannous sulfate was
not completely water soluble and the sulfuric acid dissolved all
insolubles to give a clear solution. The insolubles are believed to
be tin hydroxide which are converted to the soluble sulfate. The
solution was added to 600 ml. of boehmite alumina extrudate. The
solution and catalyst remained in contact for 15 minutes and the
unadsorbed solution was removed by decantation. The catalyst was
dried at 250.degree. F. for 1 hour and calcined in air in a muffle
furnace for 16 hours at 950.degree. F. This yielded a 3 percent tin
oxide on alumina catalyst.
To 300 ml. of 3 percent tin oxide on alumina pellets was added a
solution containing 300 ml. of distilled water and 10 g. of
potassium nitrate. The solution and catalyst remained in contact
for 15 minutes and the unadsorbed liquid was removed by
decantation. The catalyst was dried at 250.degree. F. for 1 hour
and calcined in air in a muffle furnace for 16 hours at 950.degree.
F. This yielded the following composition:
12% Cr.sub.2 O.sub.3 --1% K.sub.2 O--3% SnO--Al.sub. 2 O.sub.3.
The following Tables illustrate the present invention. ##SPC1##
TABLE II
Feed: Propane
Conditions: 1110.degree.F, 810 mm Hg absolute, 5 LHSV
Run 4 5 9 10 8 11 12
__________________________________________________________________________
Catalyst Commercial Chromia 12 10 10 10 15 15 15 Potassia 2MgO 2 --
2 4 -- 4 Tin Oxide -- -- 2 2 -- 4 2 Conversion 25.3 38.3 30.7 31.4
32.5 28.7 29.5 Selectivity 88.8 90.4 91.7 93.6 90.7 90.8 93.7
.DELTA.Conversion 24.7 6.0 7.4 0.79 18.4 2.9 0.6 Gm. Carbon/ 20 g.
Catalyst 0.77 1.31 1.23 0.36 1.23 0.44 0.14
__________________________________________________________________________
As shown in Table II, the data derived from catalysts combining the
promoters (potassia and tin oxide) are not the average values one
expects to obtain by summation of results obtained from catalysts
utilizing each promoter separately. Instead, a synergistic effect
is observed which produces a highly selective catalyst with
excellent coke inhibiting properties and very little deactivation.
This may be attributed to the formation of a completely different
promoter, e.g., potassium stannate, potassium tin chromate,
etc.
The superior performance achieved with chromia-potassia-tin oxide
on alumina led to a study on the effect of potassia concentration,
holding chromia and tin oxide constant.
TABLE III
Feed: Propane
Conditions: 1110.degree.F, 810 mm Hg absolute, 5 LHSV
Run 13 14 15 16 17 18
__________________________________________________________________________
Catalyst Chromia 10 10 10 12 12 12 Potassia 1 2 4 2 3 5 Tin Oxide 2
2 2 2 2 2 Conversion 32.1 31.4 20.3 31.0 29.5 27.5 Selectivity 93.7
93.6 90.8 94.7 94.3 95.1 .DELTA.Conversion 4.5 0.8 0 2.3 1.8 2.1
Gm. Coke/ 20 g. Catalyst 0.25 0.36 0.19 0.19 0.11 0.27
__________________________________________________________________________
The data establishes that a balance must be maintained between the
three components. At the 10 percent chromia level, this balance is
approximated at 2 percent potassia and 2 percent tin oxide. A
slightly higher average conversion with 1 percent potassia hardly
justifies its higher rate of deactivation. The composition
utilizing 4 percent potassia has catalyst fouling properties;
however, low conversion and selectivity indicates an overload
effect which inhibits dehydrogenation activity. At the 12 percent
chromia level, the conversion drops as potassia concentration on
catalyst is increased from 2 to 5 percent. With respect to catalyst
fouling, 3 percent potassia is near optimum.
Thus, if the amount of tin oxide on the catalyst is held constant,
an increase in chromia content must be accomplished by an increased
potassia concentration to achieve desirable performance.
A series of compositions were also prepared to determine the ideal
tin oxide concentration. The results with these catalysts are shown
in Table IV.
TABLE IV
Feed: Propane
Conditions: 1110.degree.F, 810 mm Hg absolute, 5 LHSV
Run 19 20 21 22
__________________________________________________________________________
Catalyst Chromia 10 10 12 12 Potassia 2 2 3 3 Tin 2 4 1 2
Conversion 31.4 26.3 36.4 29.5 Selectivity 93.6 94.1 94.6 94.3
.DELTA.Conversion 0.8 1.8 4.7 1.8 Gm. Coke/ 20 g. Catalyst 0.36
0.16 0.38 0.11
__________________________________________________________________________
There is little advantage to going to higher than 2 percent tin
oxide with the 10 chromia - 2 percent potassia composition. The
additional tin oxide minimizes carbon on catalyst and improves
selectivity; however, lower conversion and greater deactivation
rate indicates the catalyst is unable to withstand much fouling. In
the 12 percent chromia - 3 percent potassia, a definite improvement
in catalyst life is observed with 2 percent tin oxide as opposed to
1 percent. The general trend with the data in Table V and the other
tables indicates little incremental performance with greater than 2
percent tin oxide on catalyst.
In all catalysts tested, higher conversions are obtained with
increased temperatures accompanied by poorer selectivities, greater
coke laydown on catalyst, and consequently higher deactivation
rates.
Increased yield is also achieved at lower space velocities.
In addition, selectivities decreased slightly while the change in
conversion with time and carbon on catalyst deposition rates became
nil.
Data was compiled to determine stability characteristics of these
compositions. This included aging and regeneration properties.
These catalysts were processed and regenerated with air for many
cycles without any loss in initial and final activities. The
commercial catalyst deactivated at a very rapid rate, while the
catalyst compositions of this invention have a very shallow
deactivation slope.
Other combinations are shown in Table V.
TABLE V
Feed: Propane
Conditions: 1110.degree.F, 810 mm Hg absolute, 5 LHSV
Run 23 24 25 26 27 28
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Catalyst Commercial Metal Oxide 12Cr 15Cr 12Mo 12Cr 12Cr 10Cr
Promoter 1 2MgO 2Cs 2K 2K 2Cs 2Pb Promoter 2 -- 2Sn 3Sn 2Pb 2Pb 2Sn
Conversion 25.3 33.6 11.2 33.9 34.9 28.4 Selectivity 88.8 93.2 73.9
92.8 90.9 93.1 .DELTA.Conversion 24.7 2.9 5.0 11.8 11.2 3.8 Gm.
Coke/ 20 g. Catalyst 0.77 0.41 1.09 0.90 1.28 0.93
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The results in Table V show that molybdena can be substituted for
chromia; however, a lower activity catalyst is obtained. As to
promoter 1, any alkali metal oxide, alkaline earth metal oxide, or
rare earth metal oxide can be utilized without a decrease in
conversion or selectivity. Tin oxide or lead oxide are
interchangeable.
When reference is made herein to the Periodic System of elements,
the particular groupings referred to are as set forth in the
Periodic Chart of the Elements, in "The Merck Index," Seventh
Edition, Merck & Co., Inc., 1960.
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