U.S. patent application number 10/323175 was filed with the patent office on 2003-10-09 for autothermal process for the production of olefins.
Invention is credited to Bearden, Mark D., Bharadwaj, Sameer S., Lazaruk, Gerald E., Maj, Joseph J., Murchison, Craig B., Siddall, Jonathan H..
Application Number | 20030191020 10/323175 |
Document ID | / |
Family ID | 27378717 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030191020 |
Kind Code |
A1 |
Bharadwaj, Sameer S. ; et
al. |
October 9, 2003 |
Autothermal process for the production of olefins
Abstract
A process and catalyst for the partial oxidation of paraffinic
hydrocarbons, such as ethane, propane, naphtha, and natural gas
condensates, to olefins, such as ethylene and propylene. The
process involves contacting a paraffinic hydrocarbon with oxygen in
the presence of hydrogen and a catalyst under autothermal process
conditions. Preheating the feed decreases oxygen consumption and
increases the net hydrogen balance. The catalyst comprises a Group
8B metal, preferably, a platinum group metal, and at least one
promoter selected from Groups 1B, 6B, 3A, 4A, and 5A, optionally
supported on a catalytic support, such as magnesia or alumina. In
preferred embodiments, the support is pretreated with a support
modifier selected from Groups 1A, 2A, 3B, 4B, 5B, 6B, 1B, 3A, 4A,
5A, the rare earth lanthanides, and the actinides. A modified
fluidized bed reactor is disclosed for the process.
Inventors: |
Bharadwaj, Sameer S.;
(Midland, MI) ; Siddall, Jonathan H.; (Midland,
MI) ; Maj, Joseph J.; (Midland, MI) ; Bearden,
Mark D.; (Lake Jackson, TX) ; Murchison, Craig
B.; (Midland, MI) ; Lazaruk, Gerald E.;
(Sanford, MI) |
Correspondence
Address: |
THE DOW CHEMICAL COMPANY
INTELLECTUAL PROPERTY SECTION
P. O. BOX 1967
MIDLAND
MI
48641-1967
US
|
Family ID: |
27378717 |
Appl. No.: |
10/323175 |
Filed: |
December 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10323175 |
Dec 17, 2002 |
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09388219 |
Sep 1, 1999 |
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60099041 |
Sep 3, 1998 |
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60111861 |
Dec 11, 1998 |
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60136003 |
May 26, 1999 |
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Current U.S.
Class: |
502/334 ;
502/303; 502/325; 502/328 |
Current CPC
Class: |
C07C 5/48 20130101; C07C
2521/12 20130101; B01J 37/18 20130101; B01J 21/04 20130101; B01J
23/40 20130101; B01J 23/8926 20130101; B01J 23/76 20130101; C07C
2523/04 20130101; B01J 35/04 20130101; B01J 21/10 20130101; B01J
23/8966 20130101; C07C 2521/14 20130101; C07C 2523/42 20130101;
B01J 35/06 20130101; B01J 37/0238 20130101; C07C 2527/224 20130101;
Y10S 502/514 20130101; B01J 37/0201 20130101; C07C 2523/44
20130101; C07C 2521/08 20130101; B01J 23/626 20130101; C07C 2523/50
20130101; C07C 2523/14 20130101; B01J 23/56 20130101; C10G 2400/20
20130101; C07C 2521/04 20130101; C07C 2521/10 20130101; C07C
2521/02 20130101; Y02P 20/584 20151101; C07C 2523/18 20130101; C07C
2523/08 20130101; B01J 23/6445 20130101; B01J 37/0207 20130101;
C07C 2521/06 20130101; B01J 23/54 20130101; C07C 2523/72 20130101;
Y02P 20/52 20151101; B01J 23/70 20130101; B01J 23/96 20130101; C07C
5/48 20130101; C07C 11/04 20130101; C07C 5/48 20130101; C07C 11/02
20130101 |
Class at
Publication: |
502/334 ;
502/325; 502/303; 502/328 |
International
Class: |
B01J 023/42 |
Claims
What is claimed is:
1. A catalyst composition comprising a Group 8B metal and at least
one promoter supported on a ceramic monolith support which has been
pretreated with a support modifier.
2. The composition of claim 1 wherein the Group 8B metal is a
platinum group metal.
3. The composition of claim 1 wherein the platinum group metal is
platinum.
4. The composition of claim 1 wherein the promoter is selected from
Groups 1B, 6B, 3A, 4A, 5A, and mixtures thereof.
5. The composition of claim 1 wherein the promoter is selected from
copper, tin, antimony, silver, indium, and mixtures thereof.
6. The composition of claim 1 wherein the support modifier is
selected from Groups 1A, 2A, 3B, 4B, 5B, 6B, 1B, 3A, 4A, 5A, the
lanthanide rare earths, and the actinide elements of the Periodic
Table, and mixtures of the aforementioned elements.
7. The composition of claim 1 wherein the support modifier is
selected from calcium, zirconium, tin, lanthanum, potassium,
lutetium, erbium, barium, holmium, cerium, silver, and
antimony.
8. The composition of claim 1 wherein the ceramic monolith is
selected from silica, alumina, silica-aluminas, aluminosilicates,
magnesia, magnesium aluminates, magnesium silicates, zirconia,
titania, boria, zirconia toughened alumina, lithium aluminum
silicates, silicon carbide, silicon nitride, and oxide-bonded
silicon carbide.
9. The composition of claim 8 wherein the ceramic monolith
comprises from 65 to 100 weight percent alpha alumina or gamma
alumina.
10. The composition of claim 1 wherein the support is in the form
of a foam, a fiber, or a pellet.
11. The composition of claim 10 wherein the ceramic monolith
comprises a foam having from 5 to 100 pores per linear inch (2 to
40 pores per linear cm) and a surface area greater than 0.001
m.sup.2/g and less than 10 m.sup.2/g.
12. The composition of claim 10 wherein the ceramic monolith is in
the form of a fiber having a diameter greater than 1 micron and
less than 20 microns, and a surface area greater than 0.001
m.sup.2/g and less than 1 m.sup.2/g.
13. The composition of claim 10 wherein the ceramic monolith is in
the form of pellets having a size between 30 and 1,000 microns.
14. The composition of claim 1 which is prepared by a process
comprising (a) contacting a ceramic support with a support modifier
to form a pretreated support, (b) optionally, calcining or reducing
the pretreated support, (c) depositing onto the pretreated support
a Group 8B metal and at least one promoter, (d) optionally,
calcining the metal loaded support, and (e) reducing the support
with a reducing agent under conditions sufficient to prepare the
catalyst composition.
15. The composition of claim 1 wherein the Group 8B metal is
platinum; the promoter is selected from copper, tin, antimony,
silver, indium, and mixtures thereof; the support is selected from
alumina, magnesia, and mixtures thereof; and the modifier is
selected from calcium, zirconium, tin, lanthanum, potassium,
lutetium, erbium, barium, holmium, cerium, silver, and
antimony.
16. The composition of claim 1 wherein the Group 8B metal is
platinum; the promoter is selected from tin, copper, and mixtures
thereof; the support is selected from alumina, magnesia, and
mixtures thereof; and the modifier is selected from tin, lanthanum,
and mixtures thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. application Ser.
No. 09/388,219, filed Sep. 1, 1999, U.S. Provisional Application
Serial No. 60/099,041, filed Sep. 3, 1998, U.S. Provisional
Application Serial No. 60/111,861, filed Dec. 11, 1998, and U.S.
Provisional Application Serial No. 60/136,003, filed May 26,
1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to the field of catalytic
oxidation of hydrocarbons. More particularly, the present invention
relates to the catalytic partial oxidation of paraffinic
hydrocarbons, such as ethane, propane, and naphtha, to produce
olefins, such as ethylene and propylene.
[0003] Olefins find widespread utility in industrial organic
chemistry. Ethylene is needed for the preparation of important
polymers, such as polyethylene, vinyl plastics, and
ethylene-propylene rubbers, and important basic chemicals, such as
ethylene oxide, styrene, acetaldehyde, ethyl acetate, and
dichloroethane. Propylene is needed for the preparation of
polypropylene plastics, ethylene-propylene rubbers, and important
basic chemicals, such as propylene oxide, cumene, and acrolein.
Isobutylene is needed for the preparation of methyl tertiary butyl
ether. Long chain mono-olefins find utility in the manufacture of
linear alkylated benzene sulfonates, which are used in the
detergent industry.
[0004] Low molecular weight olefins, such as ethylene, propylene,
and butylene, are produced almost exclusively by thermal cracking
(pyrolysis/steam cracking) of alkanes at elevated temperatures. An
ethylene plant, for example, typically achieves an ethylene
selectivity of about 85 percent calculated on a carbon atom basis
at an ethane conversion of about 60 mole percent. Undesired
coproducts are recycled on the shell side of the cracking furnace
to be burned, so as to produce the heat necessary for the process.
Disadvantageously, thermal cracking processes for olefin production
are highly endothermic. Accordingly, these processes require the
construction and maintenance of large, capital intensive, and
complex cracking furnaces. The heat required to operate these
furnaces at a process temperature of about 900.degree. C. is
frequently obtained from the combustion of methane which
disadvantageously produces undesirable quantities of carbon
dioxide. As a further disadvantage, the crackers must be shut down
periodically to remove coke deposits on the inside of the cracking
coils.
[0005] Catalytic processes are known wherein paraffinic
hydrocarbons are oxidatively cracked to form mono-olefins. In these
processes a paraffinic hydrocarbon is contacted with oxygen in the
presence of a catalyst consisting of a platinum group metal or
mixture thereof deposited on a ceramic monolith support.
Optionally, hydrogen may be a component of the feed. The process is
conducted under autothermal reaction conditions wherein the feed is
partially combusted, and the heat produced during combustion drives
the endothermic cracking process. Consequently, under these
autothermal process conditions there is no external heat source
required; however, the catalyst is required to support combustion
above the normal fuel-rich limit of flammability. Representative
references disclosing this type of process include the following
U.S. Pat. Nos. 4,940,826; 5,105,052; 5,382,741; and 5,625,111.
Disadvantageously, substantial amounts of deep oxidation products,
such as carbon monoxide and carbon dioxide, are produced, and the
selectivity to olefins remains too low when compared with thermal
cracking.
[0006] M. Huff and L. D. Schmidt disclose in the Journal of
Physical Chemistry, 97, 1993, 11,815, the production of ethylene
from ethane in the presence of air or oxygen under autothermal
conditions over alumina foam monoliths coated with platinum,
rhodium, or palladium. A similar article by M. Huff and L. D.
Schmidt in the Journal of Catalysis, 149, 1994, 127-141, discloses
the autothermal production of olefins from propane and butane by
oxidative dehydrogenation and cracking in air or oxygen over
platinum and rhodium coated alumina foam monoliths. The olefin
selectivity achieved in these processes is not comparable to that
achieved by steam cracking and therefore could be improved.
[0007] U.S. Pat. No. 5,639,929 teaches an autothermal process for
the oxidative dehydrogenation of C.sub.2-C.sub.6 alkanes with an
oxygen-containing gas in a fluidized catalyst bed of platinum,
rhodium, nickel, or platinum-gold supported on alpha alumina or
zirconia. Ethane produces ethylene, while higher alkanes produce
ethylene, propylene, and iso-butylene. Again, the olefin
selectivity could be improved.
[0008] C. Yokoyama, S. S. Bharadwaj and L. D. Schmidt disclose in
Catalysis Letters, 38, 1996, 181-188, the oxidative dehydrogenation
of ethane to ethylene under autothermal reaction conditions in the
presence of a bimetallic catalyst comprising platinum and a second
metal selected from tin, copper, silver, magnesium, cerium,
lanthanum, nickel, cobalt, and gold supported on a ceramic foam
monolith. This reference is silent with respect to co-feeding
hydrogen in the feedstream. While the use of a catalyst containing
platinum and tin and/or copper is better than a catalyst containing
a platinum group metal alone, the olefin selectivity should be
improved if the process is to be commercialized.
[0009] In view of the above, it would be desirable to discover a
catalytic process wherein a paraffinic hydrocarbon is converted to
an olefin in a conversion and selectivity comparable to commercial
thermal cracking processes. It would be desirable if the catalytic
process were to produce only small quantities of deep oxidation
products, such as, carbon monoxide and carbon dioxide. It would
also be desirable if the process were to achieve low levels of
catalyst coking. It would be even more desirable if the process
could be easily engineered without the necessity for a large,
capital intensive, and complex cracking furnace. Finally, it would
be most desirable if the catalyst for the process exhibited good
stability.
SUMMARY OF THE INVENTION
[0010] This invention is a process for the partial oxidation of
paraffinic hydrocarbons to form olefins. The process comprises
contacting a paraffinic hydrocarbon or mixture thereof with oxygen
in the presence of hydrogen and a catalyst. The contacting is
conducted under autothermal process conditions sufficient to form
the olefin. The catalyst employed in the process of this invention
comprises a Group 8B metal and at least one promoter.
[0011] The process of this invention efficiently produces olefins,
particularly mono-olefins, from paraffinic hydrocarbons, oxygen,
and hydrogen. Advantageously, the process of this invention
achieves a higher paraffin conversion and a higher olefin
selectivity as compared with prior art catalytic, autothermal
processes. More advantageously, the process of this invention
produces fewer undesirable deep oxidation products, such as carbon
monoxide and carbon dioxide, as compared with prior art catalytic,
autothermal processes. Even more advantageously, in preferred
embodiments, the process of this invention achieves a paraffin
conversion and olefin selectivity which are comparable to
commercial thermal cracking processes. As a further advantage, the
process produces little, if any, coke, thereby substantially
prolonging catalyst lifetime and eliminating the necessity to shut
down the reactor to remove coke deposits.
[0012] Most advantageously, the process of this invention allows
the operator to employ a simple engineering design and control
strategy, which eliminates the requirement for a large, expensive,
and complex furnace like that used in thermal cracking processes.
In one preferred embodiment, the reactor simply comprises an
exterior housing which contains a monolithic support onto which the
catalytic components are deposited. Since the residence time of the
reactants in the process of this invention is on the order of
milliseconds, the reaction zone operates at high volumetric
throughput. Accordingly, the reaction zone measures from about
one-fiftieth to about one-hundredth the size of a commercially
available steam cracker of comparable capacity. The reduced size of
the reactor lowers costs and simplifies maintenance procedures.
Finally, since the process of this invention is exothermic, the
heat produced can be harvested via integrated heat exchangers to
generate electricity or steam credits for other processes.
[0013] As noted hereinbefore, thermal energy is needed to maintain
autothermal process conditions. Without preheating the feedstream,
the required thermal energy is totally supplied by the reaction of
the feedstream with oxygen, namely, alkane oxidative
dehydrogenation to form olefins and water, hydrogen oxidation to
form water, and carbon combustion to form carbon monoxide and
carbon dioxide. These processes can supply the heat necessary for
any endothermic dehydrogenation which takes place to form ethylene
and hydrogen. The prior art has recognized that a portion of the
required thermal energy can be obtained by preheating the
feedstream. The preheat can be conveniently supplied by condensing
high pressure saturated steam, or alternatively, by combusting
process off-gas or another fuel source. Surprisingly, it has now
been discovered that a high preheat temperature can be used without
loss in olefin selectivity, and further, that a high preheat
temperature provides advantages unrecognized heretofore.
Accordingly, in another aspect of this invention, the paraffinic
hydrocarbon and oxygen, which together comprise the reactant
feedstream, are preheated at a temperature greater than about
200.degree. C., but below the onset of reaction of the feedstream
components.
[0014] When the high preheat temperatures of this invention are
employed, advantageously less oxygen is required in the feedstream.
Since the cost of pure oxygen can be a significant cost component
of the feedstream, the decrease in oxygen employed translates
directly into economic savings. Moreover, since oxygen reacts with
hydrogen in the feedstream, the decrease in oxygen employed leads
to a decrease in hydrogen consumed and in the waste water produced.
As a consequence, more hydrogen is found in the product stream.
[0015] An increased yield of hydrogen in the product stream further
improves the economics of the autothermal oxidation process of this
invention. Since hydrogen is required for the process, hydrogen in
the product should be recycled and any deficit must be replaced by
importing hydrogen from an external source. Alternatively, hydrogen
can be made from off-gas streams, for example, a water-shift
reaction which converts carbon monoxide and water to hydrogen and
carbon dioxide. As a consequence of using the high preheat
temperature of this invention, the product stream is enriched in
hydrogen. Under optimal preheat conditions, the recycled hydrogen
substantially eliminates the need to import hydrogen or to derive
make-up hydrogen from other sources.
[0016] In a third aspect, the autothermal oxidation process of this
invention is beneficially conducted in a unique fluidized bed
reactor, characterized in that the reactor bed possesses an aspect
ratio of less than about 1:1, as measured during operation. For the
purposes of this invention, the aspect ratio is defined as the
ratio of the height (or depth) of the reactor bed to its
cross-sectional dimension (diameter or width). For use in this
fluidized bed, the catalyst comprises a support in the form of
pellets or spheres onto which the catalytic components are
deposited.
[0017] When operation of the process in the aforementioned unique
fluidized bed reactor is compared with operation in a fixed bed
reactor, several advantages become apparent. For example, ethylene
selectivity improves with use of the fluidized bed, while
selectivities to methane and deep oxidation products, such as
carbon monoxide and carbon dioxide, decrease. Significantly, the
selectivity advantages are achieved at ethane conversions which are
comparable to or better than those obtained in a fixed bed
reactor.
[0018] In a fourth aspect, this invention is a catalyst composition
comprising a Group 8B metal and at least one promoter supported on
a catalyst support which has been pretreated with at least one
support modifier.
[0019] The aforementioned composition is beneficially employed as a
catalyst in the autothermal partial oxidation of a paraffinic
hydrocarbon to an olefin. The catalyst composition beneficially
produces an olefin or mixture of olefins at conversions and
selectivities which are comparable to those of industrial thermal
cracking processes. Accordingly, the catalyst composition of this
invention produces low amounts of carbon monoxide and carbon
dioxide. Finally, the catalyst composition of this invention
advantageously exhibits good catalyst stability.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The process of this invention involves the partial oxidation
of a paraffinic hydrocarbon to form an olefin. The words "partial
oxidation" imply that the paraffin is not substantially oxidized to
deep oxidation products, specifically, carbon monoxide and carbon
dioxide. Rather, the partial oxidation comprises one or both of
oxidative dehydrogenation and cracking to form primarily olefins.
It is not known or suggested to what extent or degree either
process, oxidative dehydrogenation or cracking, predominates or
occurs to the exclusion of the other.
[0021] The partial oxidation process of this invention comprises
contacting a paraffinic hydrocarbon with oxygen in the presence of
a multi-metallic catalyst and in the presence of a hydrogen
co-feed. The contacting is conducted under autothermal process
conditions sufficient to form the olefin. The catalyst which is
employed in the process of this invention comprises a Group 8B
metal and at least one promoter, optionally supported on a catalyst
support. In a preferred embodiment of the process of this
invention, the paraffinic hydrocarbon is a paraffin selected from
ethane, propane, mixtures of ethane and propane, naphtha, natural
gas condensates, and mixtures of the aforementioned hydrocarbons;
and the preferred olefins produced are ethylene, propylene,
butylene, isobutylene, and butadiene.
[0022] In a preferred aspect of this invention, the feedstream
comprising the paraffinic hydrocarbon and oxygen is preheated
before introducing the feedstream into the autothermal oxidation
reactor. The preheat temperature is greater than about 200.degree.
C., but less than the temperature wherein reaction of the
feedstream components begins. Preferably, the upper limit on the
preheat temperature is less than about 900.degree. C.
[0023] In another preferred embodiment of this invention, the
reactor comprises an exterior housing which holds the catalyst, the
catalyst being provided in the form of a ceramic monolith support
onto which the catalytic components, including the Group 8B metal
and any promoter(s), have been deposited.
[0024] In another preferred aspect of this invention, the reactor
comprises a modified fluidized bed characterized by an aspect ratio
of less than about 1:1 in operating mode. As noted hereinbefore,
the aspect ratio is the ratio of the height (depth) of the reactor
to its cross-sectional dimension (diameter or width). In this
reactor, the catalyst is provided typically in the form of spheres
or granules.
[0025] In yet another preferred embodiment, the catalyst which is
employed in the process of this invention comprises a Group 8B
metal and at least one promoter supported on a catalytic support
which has been pretreated with at least one support modifier.
Preferably, the Group 8B metal is a platinum group metal. The
preferred platinum group metal is platinum. The preferred promoter
is selected from the elements of Groups 1B, 6B, 3A, 4A, 5A,
(equivalent to Groups 11, 6, 13, 14, and 15), and mixtures of the
aforementioned elements of the Periodic Table, as referenced by S.
R. Radel and M. H. Navidi, in Chemistry, West Publishing Company,
New York, 1990. The preferred support modifier is selected from
Groups 1A, 2A, 3B, 4B, 5B, 6B, 1B, 3A, 4A, 5A (equivalent Groups 1,
2, 3, 4, 5, 6, 11, 13, 14, 15), and the lanthanide rare earths and
actinide metals of the Periodic Table, as referenced by S. R. Radel
and M. H. Navidi, ibid.
[0026] In a most preferred embodiment of the catalyst composition,
the platinum group metal is platinum; the promoter is selected from
tin, copper, and mixtures thereof; the support is selected from
alumina, magnesia, and mixtures thereof; and the modifier is
selected from tin, lanthanum, and mixtures thereof.
[0027] Any paraffinic hydrocarbon or mixture of paraffinic
hydrocarbons can be employed in the process of this invention
provided that an olefin, preferably, a mono-olefin, is produced.
The term "paraffinic hydrocarbon," as used herein, refers to a
saturated hydrocarbon. Generally, the paraffin contains at least 2
carbon atoms. Preferably, the paraffin contains from 2 to about 25
carbon atoms, more preferably, from 2 to about 15 carbon atoms, and
even more preferably, from 2 to about 10 carbon atoms. The paraffin
can have a linear, branched, or cyclic structure, and can be a
liquid or gas at ambient temperature and pressure. The paraffin can
be supplied as an essentially pure paraffinic compound, or mixture
of paraffinic compounds, or as a paraffin-containing mixture of
hydrocarbons. Paraffin feeds which are suitably employed in the
process of this invention include, but are not limited to, ethane,
propane, butane, pentane, hexane, heptane, octane, and higher
homologues thereof, as well as complex higher boiling mixtures of
paraffin-containing hydrocarbons, such as naphtha, gas oil, vacuum
gas oil, and natural gas condensates. Additional feed components
may include methane, nitrogen, carbon monoxide, carbon dioxide, and
steam, if so desired. Minor amounts of unsaturated hydrocarbons may
also be present. Most preferably, the paraffin is selected from
ethane, propane, mixtures of ethane and propane, naphtha, natural
gas condensates, and mixtures thereof.
[0028] In the process of this invention, the paraffinic hydrocarbon
is contacted with an oxygen-containing gas. Preferably, the gas is
molecular oxygen or molecular oxygen diluted with an unreactive
gas, such as nitrogen, helium, carbon dioxide, or argon, or diluted
with a substantially unreactive gas, such as carbon monoxide or
steam. Any molar ratio of paraffin to oxygen is suitable provided
the desired olefin is produced in the process of this invention.
Preferably, the process is conducted fuel-rich and above the upper
flammability limit. Generally, the molar ratio of paraffinic
hydrocarbon to oxygen varies depending upon the specific paraffin
feed and autothermal process conditions employed. Typically, the
molar ratio of paraffinic hydrocarbon to oxygen ranges from about 3
to about 77 times the stoichiometric ratio of hydrocarbon to oxygen
for complete combustion to carbon dioxide and water. Preferably,
the molar ratio of paraffinic hydrocarbon to oxygen ranges from
about 3 to about 13, more preferably, from about 4 to about 11, and
most preferably, from about 5 to about 9 times the stoichiometric
ratio of hydrocarbon to oxygen for complete combustion to carbon
dioxide and water. These general limits are usually achieved by
employing a molar ratio of paraffinic hydrocarbon to oxygen greater
than about 0.1:1, preferably, greater than about 0.2:1, and by
using a molar ratio of paraffinic hydrocarbon to oxygen usually
less than about 3.0:1, preferably, less than about 2.7:1. For
preferred paraffins, the following ratios are more specific. For
ethane, the ethane to oxygen molar ratio is typically greater than
about 1.5:1, and preferably, greater than about 1.8:1. The ethane
to oxygen molar ratio is typically less than about 3.0:1,
preferably, less than about 2.7:1. For propane, the propane to
oxygen molar ratio is typically greater than about 0.9:1,
preferably, greater than about 1.1:1. The propane to oxygen molar
ratio is typically less than about 2.2:1, preferably, less than
about 2.0:1. For naphtha, the naphtha to oxygen molar ratio is
typically greater than about 0.3:1, preferably, greater than about
0.5:1. The naphtha to oxygen molar ratio is typically less than
about 1.0:1, preferably, less than about 0.9:1.
[0029] When a high preheat temperature is used, for example, above
200.degree. C., the limits on the molar ratio of paraffinic
hydrocarbon to oxygen can be shifted towards higher values. For
example, at high preheat the molar ratio of paraffinic hydrocarbon
to oxygen is typically greater than about 0.1:1 and less than about
4.0:1. Specifically, at high preheat the ethane to oxygen molar
ratio is typically greater than about 1.5:1, preferably, greater
than about 1.8:1, and typically less than about 4.0:1, preferably,
less than about 3.2:1. At high preheat, the molar ratio of propane
to oxygen is typically greater than about 0.9:1, preferably,
greater than about 1.1:1, and typically, less than about 3.0:1, and
preferably, less than about 2.6:1. At high preheat, the molar ratio
of naphtha to oxygen is typically greater than about 0.3:1,
preferably, greater than about 0.5:1, and typically, less than
about 1.4:1, and preferably, less than about 1.3:1. As an
advantageous feature of the process of this invention, hydrogen is
co-fed with the paraffin and oxygen to the catalyst. The presence
of hydrogen in the feedstream beneficially improves the conversion
of hydrocarbon and the selectivity to olefins, while reducing the
formation of deep oxidation products, such as, carbon monoxide and
carbon dioxide. The molar ratio of hydrogen to oxygen can vary over
any operable range provided that the desired olefin product is
produced. Typically, the molar ratio of hydrogen to oxygen is
greater than about 0.5:1, preferably, greater than about 0.7:1, and
more preferably, greater than about 1.5:1. Typically, the molar
ratio of hydrogen to oxygen is less than about 3.2:1, preferably,
less than about 3.0:1, and more preferably, less than about
2.7:1.
[0030] At high preheat the molar ratio of hydrogen to oxygen
typically is greater than about 0.1:1, preferably, greater than
about 0.7:1, and more preferably, greater than about 1.5:1. At high
preheat the molar ratio of hydrogen to oxygen is typically less
than about 4.0:1, preferably, less than about 3.2:1, and more
preferably, less than about 3.0:1.
[0031] Optionally, the feed may contain a diluent, which can be any
gas or vaporizable liquid which does not interfere with the process
of the invention. The diluent functions as a carrier of the
reactants and products and facilitates the transfer of heat
generated by the process. The diluent also helps to minimize
undesirable secondary reactions and helps to expand the
non-flammable regime for mixtures of the paraffin, hydrogen, and
oxygen. Suitable diluents include nitrogen, argon, helium, carbon
dioxide, carbon monoxide, methane, and steam. The concentration of
diluent in the feed can vary over a wide range. If a diluent is
used, the concentration of diluent is typically greater than about
0.1 mole percent of the total reactant feed including paraffin,
oxygen, hydrogen, and diluent. Preferably, the amount of diluent is
greater than about 1 mole percent of the total reactant feed.
Typically, the amount of diluent is less than about 70 mole
percent, and preferably, less than about 40 mole percent, of the
total reactant feed.
[0032] The catalyst which is employed in the process of this
invention beneficially comprises a Group 8B metal and at least one
promoter, described hereinbelow, optionally supported on a catalyst
support. The Group 8B metals include iron, cobalt, nickel, and the
platinum group metals, namely, ruthenium, rhodium, palladium,
osmium, iridium, and platinum. Mixtures of the aforementioned Group
8B metals may also be used. Preferably, the Group 8B metal is a
platinum group metal; preferably, the platinum group metal is
platinum. The catalyst also comprises at least one promoter, which
is suitably defined as any element or elemental ion which is
capable of enhancing the performance of the catalyst, as measured,
for example, by an increase in the paraffin conversion, an increase
in the selectivity to olefin, a decrease in the selectivities to
deep oxidation products, such as carbon monoxide and carbon
dioxide, and/or an increase in catalyst stability and lifetime. For
the purposes of this invention, the term "promoter" does not
include the platinum group metals. Preferably, the promoter is
selected from the elements of Groups 1B (Cu, Ag, Au), 6B (Cr, Mo,
W), 3A (for example, Al, Ga, In, Tl), 4A (for example, Ge, Sn, Pb),
and 5A (for example, As, Sb, Bi), and mixtures thereof. More
preferably, the promoter is selected from copper, tin, antimony,
silver, indium, and mixtures thereof. Most preferably, the promoter
is selected from copper, tin, antimony, and mixtures thereof.
[0033] Any atomic ratio of Group 8B metal to promoter can be
employed in the catalyst, provided the catalyst is operable in the
process of this invention. The optimal atomic ratio will vary with
the specific Group 8B metal and promoter(s) employed. Generally,
the atomic ratio of the Group 8B metal to promoter is greater than
0.10 (1:10), preferably, greater than about 0.13 (1:8), and more
preferably, greater than about 0.17 (1:6). Generally, the atomic
ratio of the Group 8B metal to promoter is less than about 2.0
(1:0.5), preferably, less than about 0.33 (1:3), and more
preferably, less than about 0.25 (1:4). Although the promoter is
used in a gram-atom amount equivalent to or greater than the Group
8B metal, the promoter nonetheless functions to enhance the
catalytic effect of the catalyst. Compositions prepared with
promoter alone, in the absence of Group 8B metal, are typically
(but not necessarily always) catalytically inactive in the process.
In contrast, the Group 8B metal is catalytically active in the
absence of promoter, albeit with lesser activity.
[0034] The catalyst can be suitably employed in the form of a
metallic gauze. More specifically, the gauze can comprise an
essentially pure Group 8B metal or an alloy of Group 8B metals onto
which the promoter is deposited. Suitable gauzes of this type
include pure platinum gauze and platinum-rhodium alloy gauze coated
with the promoter. The method used to deposit or coat the promoter
onto the gauze can be any of the methods described hereinafter.
Alternatively, a gauze comprising an alloy of a Group 8B metal and
the promoter can be employed. Suitable examples of this type
include gauzes prepared from platinum-tin, platinum-copper, and
platinum-tin-copper alloys.
[0035] In another embodiment, the Group 8B metal and promoter are
supported on a catalytic support. The loading of the Group 8B metal
on the support can be any which provides for an operable catalyst
in the process of this invention. In general, the loading of the
Group 8B metal is greater than about 0.001 weight percent,
preferably, greater than about 0.1 weight percent, and more
preferably, greater than about 0.2 weight percent, based on the
total weight of the Group 8B metal and support. Preferably, the
loading of the Group 8B metal is less than about 80 weight percent,
preferably, less than about 60 weight percent, and more preferably,
less than about 10 weight percent, based on the total weight of the
Group 8B metal and the support. Once the Group 8B metal loading is
established, the desired atomic ratio of Group 8B metal to promoter
determines the loading of the promoter.
[0036] The catalytic support comprises any material which provides
a surface to carry the Group 8B metal, the promoter(s), and any
support modifiers. Preferably, the support is thermally and
mechanically stable under autothermal process conditions.
Preferably, the catalytic support is a ceramic, such as, a
refractory oxide, carbide, or nitride. Non-limiting examples of
suitable ceramics include alumina, silica, silica-aluminas,
aluminosilicates, including cordierite, magnesia, magnesium
aluminate spinels, magnesium silicates, zirconia, titania, boria,
zirconia toughened alumina (ZTA), lithium aluminum silicates,
silicon carbide, oxide-bonded silicon carbide, and silicon nitride.
Mixtures of the aforementioned refractory oxides, nitrides, and
carbides may also be employed, as well as washcoats of the
aforementioned materials on a support. Preferred ceramics include
magnesia, alumina, silica, and amorphous or crystalline
combinations of magnesia, alumina and silica, including mullite.
Alpha (.alpha.) and gamma (.gamma.) alumina are preferred forms of
alumina. Preferred combinations of alumina and silica comprise from
about 65 to about 100 weight percent alumina and from essentially 0
to about 35 weight percent silica. Other refractory oxides, such as
boria, can be present in smaller amounts in the preferred alumina
and silica mixtures. Preferred zirconias include zirconia fully
stabilized with calcia (FSZ) and zirconia partially stabilized with
magnesia (PSZ), available from Vesuvius Hi-Tech Ceramics, Inc.
Magnesia is the most preferred support, because it produces fewer
cracking products and less carbon monoxide. Moreover, the
hydrocarbon conversion and olefin selectivity tend to be higher
with magnesia. The catalytic support may take a variety of shapes
including that of porous or non-porous spheres, granules, pellets,
irregularly shaped solid or porous particles, or any other shape
which is suitable for catalytic reactors, including fixed bed,
transport bed, and fluidized bed reactors. In a preferred form, the
catalyst is a monolith. As used herein, the term "monolith" means
any continuous structure, including for example, honeycomb
structures, foams, and fibers, including fibers woven into fabrics
or made into non-woven mats or thin paper-like sheets. Monoliths do
not, in general, contain significant microporosity. Foams have a
sponge-like structure. More preferably, the support is a foam or
fiber monolith. Fibers tend to possess higher fracture resistance
as compared with foams and honeycombs. Preferred ceramic foams,
available from Vesuvius Hi-Tech Ceramics, Inc., comprise magnesia,
alpha alumina, zirconia, or mullite with a porosity ranging from
about 5 to about 100 pores per linear inch (ppi) (2 to 40 pores per
linear cm (ppcm)). Foams having about 45 ppi (18 ppcm) are more
preferred. The term "porosity," as used herein, refers to channel
size or dimension. It is important to note that the foam supports
are not substantially microporous structures. Rather, the foams are
macroporous, meaning that they are low surface area supports with
channels ranging in diameter from about 0.1 mm to about 5 mm. The
foams are estimated to have a surface area less than about 10
m.sup.2/g, and preferably, less than about 2 m.sup.2/g, but greater
than about 0.001 m.sup.2/g. Preferred ceramic fibers, available
from 3M Corporation as Nextel.TM. brand ceramic fibers, typically
have a diameter greater than about 1 micron (.mu.m), preferably,
greater than about 5 .mu.m. The diameter is suitably less than
about 20 .mu.m, preferably, less than about 15 .mu.m. The length of
the fibers is generally greater than about 0.5 inch (1.25 cm),
preferably, greater than about 1 inch (2.5 cm), and typically less
than about 10 inches (25.0 cm), preferably, less than about 5
inches (12.5 cm). The surface area of the fibers is very low, being
generally less than about 1 m.sup.2/g, preferably, less than about
0.3 m.sup.2/g, but greater than about 0.001 m.sup.2/g. Preferably,
the fibers are not woven like cloth, but instead are randomly
intertwined as in a mat or matted rug. Most preferred are
Nextel.TM. brand 440 fibers which consist of gamma alumina (70
weight percent), silica (28 weight percent), and boria (2 weight
percent) and Nextel.TM. brand 610 fibers which consist of alpha
alumina (99 weight percent), silica (0.2-0.3 weight percent) and
iron oxide (0.4-0.7 weight percent).
[0037] The deposition of the Group 8B metal and promoter(s) onto
the support can be made by any technique known to those skilled in
the art, for example, impregnation, ion-exchange,
deposition-precipitation, vapor deposition, sputtering, and ion
implantation. In one preferred method, the Group 8B metal is
deposited onto the support by impregnation. Impregnation is
described by Charles N. Satterfield in Heterogeneous Catalysis in
Practice, McGraw-Hill Book Company, New York, 1980, 82-84,
incorporated herein by reference. In this procedure, the support is
wetted with a solution containing a soluble Group 8B compound,
preferably, to the point of incipient wetness. The contacting
temperature typically ranges from about ambient, taken as
23.degree. C., to about 100.degree. C., preferably, from about
23.degree. C. to about 50.degree. C. The contacting is conducted
usually at ambient pressure. Non-limiting examples of suitable
Group 8B compounds include the Group 8B nitrates, halides,
sulfates, alkoxides, carboxylates, and Group 8B organometallic
compounds, such as halo, amino, acetylacetonate, and carbonyl
complexes. Preferably, the Group 8B compound is a platinum group
halide, more preferably, a chloride, such as chloroplatinic acid.
The solvent can be any liquid which solubilizes the Group 8B
compound. Suitable solvents include water, aliphatic alcohols,
aliphatic and aromatic hydrocarbons, and halo-substituted aliphatic
and aromatic hydrocarbons. The concentration of the Group 8B
compound in the solution generally ranges from about 0.001 molar
(M) to about 10 M. After contacting the support with the solution
containing the Group 8B compound, the support may be dried under
air at a temperature ranging from about 23.degree. C. to a
temperature below the decomposition temperature of the Group 8B
compound, typically, a temperature between about 23.degree. C. and
about 100.degree. C.
[0038] The deposition of the promoter can be accomplished in a
manner analogous to the deposition of the Group 8B metal.
Accordingly, if impregnation is used, then the support is wetted
with a solution containing a soluble compound of the promoter at a
temperature between about 23.degree. C. and about 100.degree. C.,
preferably, between about 23.degree. C. and about 50.degree. C., at
about ambient pressure. Suitable examples of soluble promoter
compounds include promoter halides, nitrates, alkoxides,
carboxylates, sulfates, and organometallic compounds, such as
amino, halo, and carbonyl complexes. Suitable solvents comprise
water, aliphatic alcohols, aliphatic and aromatic hydrocarbons, and
chloro-substituted aliphatic and aromatic hydrocarbons. Certain
promoter compounds, such as compounds of antimony and tin, may be
more readily solubilized in the presence of acid. For example,
hydrochloric acid (5-25 weight percent) can be suitably employed.
The concentration of the promoter compound in the solution
generally ranges from about 0.01 M to about 10 M. Following
deposition of the soluble promoter compound or mixture thereof, the
impregnated support may be dried under air at a temperature between
about 23.degree. C. and a temperature below the temperature wherein
vaporization or decomposition of the promoter compound occurs.
Typically, the drying is conducted at a temperature between about
23.degree. C. and about 100.degree. C.
[0039] In one method of preparing the catalyst, the Group 8B metal
is deposited onto the support first, and thereafter the promoter is
deposited onto the support. In an alternative method, the promoter
is deposited first, followed by the deposition of the Group 8B
metal. In a preferred method of preparing the catalyst, the Group
8B metal and the promoter are deposited simultaneously onto the
support from the same deposition solution. In any of these methods,
following one or more of the depositions, a calcination under
oxygen is optional. If performed, the calcination is conducted at a
temperature ranging from about 100.degree. C. to below the
temperature at which volatilization of the metals becomes
significant, typically, less than about 1,100.degree. C.
Preferably, the calcination is conducted at a temperature between
about 100.degree. C. and about 500.degree. C.
[0040] As a final step in the preparation of the catalyst, the
fully-loaded support is reduced under a reducing agent, such as
hydrogen, carbon monoxide, or ammonia, at a temperature between
about 100.degree. C. and about 900.degree. C., preferably between
about 125.degree. C. and about 800.degree. C., so as to convert the
Group 8B metal substantially to its elemental form. The promoter
may be reduced fully or partially, or not reduced at all, depending
upon the specific promoter chosen and the reduction conditions. In
addition, reduction at elevated temperatures may produce alloys of
the Group 8B metal and the promoter. Alloys may provide enhanced
catalyst stability by retarding vaporization of the promoter during
the process of this invention.
[0041] In another preferred embodiment, the support is pretreated
with a support modifier prior to loading the Group 8B and
promoter(s). The support modifier can be any metal ion having a
charge of +1 or greater. Preferably, the support modifier is
selected from Groups 1A (Li, Na, K, Rb, Cs), 2A (for example, Mg,
Ca, Sr, Ba), 3B (Sc, Y, La), 4B (Ti, Zr, Hf), 5B (V, Nb, Ta), 6B
(Cr, Mo, W), 1B (Cu, Ag, Au), 3A (for example, Al, Ga, In), 4A (for
example, Ge, Sn, Pb), 5A (for example, As, Sb, Bi), and the
lanthanide rare earths (for example, Ce, Er, Lu, Ho) and actinide
elements (specifically Th) of the Periodic Table previously
identified. More preferably, the support modifier is selected from
calcium, zirconium, tin, lanthanum, potassium, lutetium, erbium,
barium, holmium, cerium, antimony, and mixtures thereof. Most
preferably, the support modifier is selected from lanthanum, tin,
antimony, calcium, and mixtures thereof. Certain elements, such as
tin, antimony, and silver, may function as both promoter and
support modifier simultaneously.
[0042] The procedure to modify the support comprises contacting the
support with a solution containing a soluble compound of the
support modifier. The contacting can involve ion-exchange or
impregnation methods. Preferably, the modification procedure
involves submerging the support in the solution such that
essentially all of the surface area of the support is contacted
with an excess of the solution. Compounds suitable for preparing
the solution of support modifier include modifier nitrates,
halides, particularly the chlorides, alkoxides, carboxylates, and
organometallic complexes including amino, halo, alkyl, and carbonyl
complexes. Suitable solvents include water, aliphatic alcohols,
aromatic hydrocarbons, and halo-substituted aliphatic and aromatic
hydrocarbons. Typically, the concentration of modifier compound in
the solution ranges from about 0.001 M to about 10 M. Acidified
solutions, for example, of hydrochloric acid and diluted solutions
thereof, may be beneficially employed. The contact time generally
ranges from about 1 minute to about 1 day. The contacting
temperature suitably ranges from about 23.degree. C. to about
100.degree. C., and pressure is generally ambient. Alternatively,
slurries of mixed oxides containing promoter and/or modifier
elements, such as magnesium stannate (Mg.sub.2SnO.sub.4), can be
deposited onto the support. The modified support is typically
calcined, as noted hereinabove, or reduced under a reducing agent,
such as hydrogen, at a temperature between about 100.degree. C. and
about 900.degree. C., preferably, between about 200.degree. C. and
about 800.degree. C. The choice of calcination or reduction depends
on the element used to pretreat the support. If the element or its
oxide is readily vaporizable, the pretreated support is reduced. If
the element or its oxide is not readily vaporizable, then the
pretreated support is calcined. As a guideline, the words "readily
vaporizable" may be taken to mean that greater than about 1 weight
percent of any metal component in the catalyst is vaporized in a
period of about 24 hours under calcination conditions at about
200.degree. C. The term "readily vaporizable" may be given a
narrower or broader definition, as desired.
[0043] Following the pretreatment modification, the Group 8B metal
and promoter(s) are loaded onto the support. Then, the support is
reduced as described hereinbefore. Alternatively, the metal-loaded
support may be calcined first and then reduced. Whether the
modified support is calcined or not depends again upon the
vaporization potential of the modifier metal(s) and promoter(s)
employed. Supports modified with metals or metal oxides which tend
to vaporize readily are typically not calcined. Supports modified
with metals or metal oxides which do not vaporize readily can be
calcined.
[0044] The process of this invention is advantageously conducted
under autothermal process conditions. The term "autothermal process
conditions" means that the heat generated by reaction of the feed
is sufficient to support the catalytic process which converts the
paraffin to the olefin. Accordingly, the need for an external
heating source to supply the energy for the process can be
eliminated. In order to maintain autothermal conditions, the
catalysts of the prior art are required to support combustion
beyond the normal, fuel-rich limit of flammability. This is not a
requirement in the present invention. Here, autothermal conditions
can also be maintained with a catalyst which does not support
combustion beyond the normal, fuel-rich limit of flammability,
provided that hydrogen and optionally a preheat are supplied to the
process.
[0045] Ignition can be effected by preheating the feed to a
temperature sufficient to effect ignition when contacted with the
catalyst. Alternatively, the feed can be ignited with an ignition
source, such as a spark or flame. Upon ignition, the
reaction-generated heat causes the temperature to take a step
change jump to a new steady state level that is herein referred to
as the autothermal reaction.
[0046] While running autothermally, the paraffin feed does not have
to be preheated, so long as the feed contains hydrogen or the
catalyst supports combustion beyond the normal, fuel-rich limit of
flammability. (The word "combustion," as used herein, means the
reaction of the hydrocarbon with oxygen unaided by hydrogen.)
Preheating the feedstream, however, has certain advantages. The
advantages comprise a decrease in oxygen and hydrogen consumed, an
increase in the paraffin concentration in the feed, an increase in
the operating paraffin to oxygen molar ratio, and a net increase in
recycle hydrogen in the product stream. In addition, catalysts can
be used which do not support combustion beyond the normal fuel-rich
limit of flammability. These advantages are particularly
significant when the preheating is conducted at a temperature
greater than about 200.degree. C. and less than the temperature
wherein reaction of the feedstream components begins. Suitable
preheat temperatures are typically greater than about 40.degree.
C., preferably, greater than about 125.degree. C., and even more
preferably, greater than about 200.degree. C. In another preferred
embodiment, the preheat temperature is greater than about
400.degree. C. Suitable preheat temperatures are typically less
than about 900.degree. C., preferably, less than about 800.degree.
C., and more preferably less than about 600.degree. C.
[0047] As a general rule, the autothermal process operates at close
to the adiabatic temperature (that is, essentially without loss of
heat), which is typically greater than about 750.degree. C., and
preferably, greater than about 925.degree. C. Typically, the
autothermal process operates at a temperature less than about
1,150.degree. C., and preferably, less than about 1,050.degree. C.
Optionally, the temperature at the reactor exit can be measured,
for example, by using a Pt/Pt--Rh thin wire thermocouple. With a
monolith catalyst, the thermocouple can be sandwiched between the
monolith and the downstream radiation shield. Measurement of
temperature close to the reactor exit may be complicated by the
high temperature involved and the fragility of the thermocouple.
Thus, as an alternative, one skilled in the art can calculate the
adiabatic temperature at the reactor exit from a knowledge of the
preheat temperature and the exit stream composition. The "adiabatic
temperature" is the temperature of the product stream without any
heat loss, that is, when all of the heat generated by the process
is used to heat the products. Typically, the measured temperature
is found to be within about 25.degree. C. of the calculated
adiabatic temperature.
[0048] The operating pressure is typically equal to or greater than
about 1 atmosphere absolute (atm abs) (100 kPa abs). Typically, the
pressure is less than about 20 atm abs (2,000 kPa abs), preferably,
less than about 10 atm (1,000 kPa abs), and more preferably, less
than about 7 atm abs (700 kPa abs).
[0049] Since the products of this process must be removed rapidly
from the reaction zone, gas hourly space velocities are very high.
The specific gas hourly space velocity employed will depend upon
the choice of reactor cross sectional dimension (for example,
diameter) and the form and weight of the catalyst particles.
Generally, the gas hourly space velocity (GHSV), calculated as the
total flow of the hydrocarbon, oxygen, hydrogen, and optional
diluent flows, is greater than about 50,000 ml total feed per ml
catalyst per hour (h.sup.-1) measured at standard temperature and
pressure (0.degree. C., 1 atm) (STP). Preferably, the GHSV is
greater than about 80,000 h.sup.-1, and more preferably, greater
than 100,000 h.sup.-1. Generally, the gas hourly space velocity is
less than about 6,000,000 h.sup.-1, preferably, less than about
4,000,000 h.sup.-1, more preferably, less than 3,000,000 h.sup.-1,
measured as the total flow at STP. Gas flows are typically
monitored in units of liters per minute at standard temperature and
pressure (slpm). The conversion of gas flow from "slpm" units to
gas hourly space velocity units (h.sup.-1) is made as follows: 1
GHSV h - 1 = slpm .times. 1000 cm 3 / min .times. 60 min / h cross
- sectional area of catalyst ( cm 2 ) .times. length ( cm )
[0050] The residence time of the reactants in the reactor is simply
calculated as the inverse of the gas hourly space velocity. At the
high space velocities employed in the process of this invention,
the residence time is on the order of milliseconds. Thus, for
example, a gas hourly space velocity of 100,000 h.sup.-1 measured
at STP is equivalent to a residence time of 36 milliseconds at
STP.
[0051] The process of this invention may be conducted in any
reactor designed for use under adiabatic, autothermal process
conditions. In one preferred design, the catalyst is prepared on a
monolith support which is sandwiched between two radiation shields
inside a reactor housing. Alternatively, fixed bed and fluidized
bed reactors can be used with catalysts in the form of pellets,
spheres, and other particulate shapes. Continuous and intermittent
flow of the feedstream are both suitable. It is noted that
fluidized bed reactors of the prior art typically possess an aspect
ratio in static mode of greater than 1:1, and more preferably,
greater than about 5:1. Static mode is defined as the unfluidized
or fixed bed configuration. Fluidized bed reactors are generally
operated in a bubbling, turbulent, or fast-fluidized regime with
expanded beds measuring from about 1.5 to 15 times the static
depth. Typically, the aspect ratio in operating mode is greater
than about 5:1 to 10:1. For full fluidization, a catalyst particle
size ranging between about 30 and 1,000 microns is
satisfactory.
[0052] It is believed that the oxidation reaction of this invention
occurs predominantly at the reactor entry, which in the case of a
stationary catalyst is at the front edge of the catalyst. Such a
theory should not be binding or limiting of the invention in any
manner. In view of this theory, the optimal reactor for the process
of this invention should possess a large cross-sectional dimension
and a short height (or depth). On a commercial scale, for example,
a catalyst bed of diameter about 5 to 8 feet (1.5 m to 2.4 m) and a
height of about 1 inch (2.5 cm) may be suitably employed.
Additionally, it is believed that catalyst located at the front
edge of a stationary bed can deactivate more quickly with time. As
a consequence, longer catalyst lifetime and better selectivities
can be achieved by circulating particles of the catalyst, rather
than using a stationary bed.
[0053] A preferred reactor design for the process of this invention
comprises a modified fluidized bed reactor, characterized in that
its aspect ratio in operating mode, and preferably also in static
mode (unfluidized or fixed bed configuration), is less than 1:1,
and more preferably, less than about 0.1:1, but greater than about
0.001:1. Most preferably, the aspect ratio is about 0.01:1. This
unique fluidized bed is operated above the minimum fluidization
flow with an expanded bed on the order of about 2 or 3 times the
static depth, and preferably, less than about 1.5 times the static
depth. For the purposes of this invention, "minimum fluidization
flow" is defined as the minimum gas velocity at which the catalyst
particles are suspended under operating conditions. The velocity
necessary to achieve minimum fluidization depends upon the density
and viscosity of the gas phase and the catalyst particle size and
density. One skilled in the art would know how to calculate the
minimum fluidization flow for any given gas composition and
catalyst particle. A suitable authority on the subject is found in
Fluidization Engineering, by D. Kunii and O. Levenspeil, 2.sup.nd
ed., Butterworth-Heineman, 1989, incorporated herein by reference.
A catalyst particle size of between about 500 and about 850 microns
(23-30 US mesh) is suitable for feed velocities of about 0.05 to 5
meters per second (mps) at standard temperature and pressure. An
advantage of the modified fluidized bed reactor may result from its
continuous circulation (fluidization), which results in continuous
renewal of catalyst particles at the reactor entry. This
configuration produces substantially better product yields than a
stationary catalyst.
[0054] When a paraffinic hydrocarbon is contacted with oxygen under
autothermal process conditions in the presence of a co-feed of
hydrogen and in the presence of the multi-metallic catalyst
described hereinabove, an olefin, preferably a mono-olefin, is
produced. Ethane is converted primarily to ethylene. Propane and
butane are converted primarily to ethylene and propylene. Isobutane
is converted primarily to isobutylene and propylene. Naphtha and
other higher molecular weight paraffins are converted primarily to
ethylene and propylene.
[0055] The conversion of paraffinic hydrocarbon in the process of
this invention can vary depending upon the specific feed
composition, catalyst composition, reactor, and process conditions
employed. For the purposes of this invention, "conversion" is
defined as the mole percentage of paraffinic hydrocarbon in the
feed which is converted to products. Generally, at constant
pressure and space velocity, the conversion increases with
increasing temperature. Typically, at constant temperature and
pressure, the conversion does not change significantly over a wide
range of high space velocities employed. In this process, the
conversion of paraffinic hydrocarbon is typically greater than
about 50 mole percent, preferably, greater than about 60 mole
percent, and more preferably, greater than about 70 mole
percent.
[0056] Likewise, the selectivity to products will vary depending
upon the specific feed composition, catalyst composition, reactor,
and process conditions employed. For the purposes of this
invention, "selectivity" is defined as the percentage of carbon
atoms in the converted paraffin feed which react to form a specific
product. For example, the olefin selectivity is calculated as
follows: 2 Moles of olefin formed .times. Number of carbon atoms in
olefin Moles of paraffin converted .times. Number of carbon atoms
in paraffin .times. 100
[0057] Generally, the olefin selectivity increases with increasing
temperature up to a maximum value and declines as the temperature
continues to rise. Usually, the olefin selectivity does not change
substantially over a wide range of high space velocities employed.
In the process of this invention, the olefin selectivity is
typically greater than about 50 carbon atom percent, preferably,
greater than about 60 carbon atom percent, more preferably, greater
than about 70 carbon atom percent, and even more preferably,
greater than about 80 carbon atom percent. Other products formed in
smaller quantities include methane, carbon monoxide, carbon
dioxide, propane, butenes, butadiene, propadiene, acetylene,
methylacetylene, and C.sub.6+hydrocarbons. Acetylene can be
hydrogenated to ethylene downstream to increase the overall
selectivity to olefin. At least part of the carbon monoxide, carbon
dioxide, and methane formed may be recycled to the reactor.
[0058] Water is also formed in the process of this invention from
the reaction of hydrogen or hydrocarbon. The presence of hydrogen
in the feed minimizes the formation of carbon oxides by reacting
with the oxygen to produce water and energy. Accordingly, it is
advantageous to recycle the hydrogen in the product stream,
obtained from the dehydrogenation of the paraffin, back to the
reactor. Optimally, the hydrogen needed to meet the demands of the
process essentially equals the hydrogen formed during conversion of
the paraffin to olefin. Under these balanced conditions, the
hydrogen forms a closed loop wherein there is essentially no demand
for additional hydrogen to be added to the feed. Such conditions
are more easily met when the feed is preheated and a higher
hydrocarbon to oxygen molar ratio is employed.
[0059] The invention will be further clarified by a consideration
of the following examples, which are intended to be purely
illustrative of the use of the invention. Other embodiments of the
invention will be apparent to those skilled in the art from a
consideration of this specification or practice of the invention as
disclosed herein. Unless otherwise noted, all percentages are given
on a mole percent basis. Selectivities are given on a carbon atom
percent basis.
EXAMPLE 1 (E-1)
Oxidation of Ethane to Ethylene--Hydrogen and Pt/Sn Catalyst
[0060] A catalyst comprising platinum and tin supported on an
alumina monolith was prepared by the following method. Platinum and
tin were codeposited on a foam monolith (92 weight percent alpha
alumina, 8 weight percent silica; 1.8 cm diameter.times.1 cm thick,
45 ppi (18 ppcm)) by impregnation with an aqueous solution of
platinum and tin in a Pt:Sn atomic ratio of 1:5. The impregnation
solution was prepared from a stock aqueous solution of
hexachloroplatinic acid (0.193 M H.sub.2PtCl.sub.6) and a stock
aqueous solution of stannous chloride (0.372 M SnCl.sub.2)
acidified with 5 weight percent hydrochloric acid. Sufficient
impregnation solution was used to obtain a platinum loading of 1.3
weight percent. The impregnated monolith was dried in ambient air
and then reduced under flowing hydrogen (5 volume percent in
nitrogen) at a flow rate of 1 cubic foot per hour (cfh) (473
cm.sup.3/min) using the following temperature profile: 1 h from
ambient to 125.degree. C., then 1 h from 125.degree. C. to
300.degree. C.; 1 h from 300.degree. C. to 450.degree. C., held for
30 min at 450.degree. C., and then cooled to room temperature.
[0061] The catalyst was sandwiched between two inert alpha alumina
monoliths which acted as radiation shields. The monoliths were
sealed in a quartz tube using FiberFrax.TM. brand alumina-silica
cloth (FiberFrax is a trademark of and available from Unifrax
Corporation), and the reactor was insulated by wrapping the quartz
tube with high temperature insulation. A feed comprising ethane
(2.6 standard liters per minute (slpm)), oxygen (1.3 slpm),
hydrogen (2.6 slpm) and nitrogen (1.147 slpm) was fed to the
reactor. Total flow was 7.647 slpm (GHSV 180,305 h.sup.-1) at 15
volume percent dilution with nitrogen. The ethane to oxygen molar
ratio was 2:1; the hydrogen to oxygen molar ratio was 2:1.
[0062] The catalyst was operated autothermally and the heat
generated by the reaction was sufficient to sustain the process.
However, heat was needed initially to ignite the process. The
procedure for light-off involved establishing the flows of
nitrogen, ethane, and hydrogen, then adding the oxygen flow; and
then heating the feed to 200.degree. C. until ignition. This
procedure ensured a fuel-rich feed for safety considerations. The
light-off conditions were 7 slpm total gas flow, 2.24 slpm of
ethane, 2.24 slpm of hydrogen, 1.12 slpm of oxygen, 1.40 slpm of
nitrogen, 20 percent dilution with nitrogen, an ethane to oxygen
molar ratio of 2:1, a hydrogen to oxygen molar ratio of 2:1, and a
pressure of 1.34 atm abs (136 kPa abs). After light-off, the
external heat source was removed, and the gas flow rates and
pressure were adjusted to the desired conditions, as shown in Table
1. Pressure was maintained at 1.34 atm abs (136 kPa abs). Shutdown
of the reactor was accomplished by turning off oxygen prior to
alkane and hydrogen.
[0063] The product gases were analyzed on a Carle gas chromatograph
designed for refinery gas analyses of components up to C.sub.6
hydrocarbons. For quantitative determination of concentrations,
standards were used for all species except water, which was
obtained from an oxygen atom balance. Nitrogen was used as an
internal GC calibration standard. Results are set forth in Table
1.
1TABLE 1 Oxidation of Ethane to Ethylene with Pt Catalysts Examples
vs. Comparative Experiments.sup.a,b % Carbon Atom Selectivities Ex.
# % C.sub.2H.sub.6 Catalyst Conv. C.sub.2H.sub.4 CO CO.sub.2
CH.sub.4 C3+ CE-1a 62.3 61.1 22.60 7.75 4.05 4.50 Pt - No H.sub.2
CE-1b 62.2 71.1 16.92 1.40 6.10 4.48 Pt - H.sub.2 CE-1c 65.9 67.6
17.65 6.40 3.80 4.55 Pt--Sn No H.sub.2 E-1 69.6 81.1 7.29 0.34 6.28
4.99 Pt--Sn H.sub.2 CE-2 68.0 68.3 17.70 6.40 3.95 3.65 Pt--Sb No
H.sub.2 E-2 69.5 81.5 7.56 0.27 6.32 4.35 Pt--Sb H.sub.2 CE-3 66.5
68.0 17.03 6.57 3.87 4.53 Pt--Sn--Sb No H.sub.2 E-3 68.5 80.6 8.27
0.46 6.10 4.57 Pt--Sn--Sb H.sub.2 .sup.aFeed with hydrogen: ethane
(2.6 slpm), oxygen (1.3 slpm), hydrogen (2.6 slpm) and nitrogen
(1.147 slpm); total flow = 7.647 slpm (GHSV = 180,305 h.sup.-1);
15% N.sub.2 dilution; molar ratios: C.sub.2H.sub.6/O.sub.2 = 2:1;
H.sub.2/O.sub.2 2:1; autothermal conditions; pressure = 1.34 atm
abs (136 kPa abs); no preheat. .sup.bFeed without hydrogen: ethane
(2.6 slpm); oxygen (1.3 slpm); nitrogen (2.1 slpm); total flow: 6.0
slpm (GHSV 141,471 h.sup.-1); 35% N.sub.2 dilution; molar ratio
C.sub.2H.sub.6/O.sub.2 = 2:1; autothermal conditions; pressure =
1.34 atm abs (136 kPa abs); no preheat.
[0064] It was seen that a catalyst comprising platinum and tin
supported on a ceramic monolith was active in the partial oxidation
of ethane in the presence of hydrogen to produce ethylene. The
catalyst achieved an ethane conversion of 69.6 percent and an
ethylene selectivity of 81.1 percent. The ethane conversion and
ethylene selectivity achieved were comparable to those obtained
from commercial thermal cracking furnaces. Very low amounts of
carbon monoxide (7.29 percent) and carbon dioxide (0.34 percent)
were found, as well as comparable amounts of methane and C3+
products. Carbon monoxide, carbon dioxide, and methane, at least in
part, can be recycled to the reactor along with the hydrogen
produced in the process.
Comparative Experiment 1
(CE-1a) and (CE-1b)
[0065] The oxidation of ethane was conducted under autothermal
process conditions with a catalyst consisting of platinum supported
on a ceramic monolith support. The catalyst was prepared as in E-1,
with the exception that no tin was added to the catalyst. The
process was conducted first in the absence of hydrogen (CE-1a) as
noted hereinafter, and then, in the presence of hydrogen (CE-1b) in
a manner similar to E-1. For the part of the experiment without
hydrogen, the flow rates of the reactant feed were adjusted as
follows: ethane (2.6 slpm); oxygen (1.3 slpm); nitrogen (2.1 slpm).
Total flow was 6 slpm (GHSV=141,471 h.sup.-1) at 35 volume percent
nitrogen dilution. Molar ratio of ethane to oxygen was 2:1. This
flow adjustment ensured that identical absolute amounts of ethane
and oxygen were used with and without hydrogen. The level of
nitrogen dilution was adjusted to ensure equivalent ethane
conversions with and without hydrogen. Processes were conducted
autothermally in the manner described in E-1 with the results shown
in Table 1 (CE-1a and CE-1b).
[0066] It was seen that a catalyst consisting of pure platinum on
an alumina monolith achieved an ethylene selectivity of 61.1
percent in the absence of hydrogen (CE-1a) and 71.1 percent in the
presence of hydrogen (CE-1b) at similar ethane conversions. Thus,
the addition of hydrogen improved ethylene selectivity. More
significantly, when CE-1a and CE-1b were compared with E-1, it was
found that the combined use of hydrogen in the feed and tin in the
catalyst resulted in the highest ethane conversion and ethylene
selectivity at significantly lower selectivities to carbon
oxides.
(CE-1c)
[0067] The oxidation of ethane was conducted as in E-1 with the
exception that no hydrogen was used in the process, and the feed
flow rates were adjusted as described in CE 1a. The catalyst used
was identical to the catalyst of E1. Results are shown in Table 1
(CE-1c). When the process of E-1, using a catalyst containing
platinum and tin, was repeated in the absence of hydrogen, an
ethylene selectivity of 67.6 percent was achieved at an ethane
conversion of 65.9 percent. When E-1 was compared with CE-1c, it
was seen that the combined use of hydrogen in the feed and tin in
the catalyst gave the highest ethane conversion, the highest
ethylene selectivity, and the lowest selectivities to carbon
oxides.
EXAMPLE 2 (E-2)
Oxidation of Ethane to Ethylene--Hydrogen and Pt/Sb Catalyst
[0068] A catalyst comprising platinum and antimony supported on an
alumina monolith was prepared in a manner similar to that described
in Example 1. The monolith of Example 1 was impregnated with an
aqueous solution of platinum and antimony in a Pt:Sb atomic ratio
of 1:5. The impregnation solution was prepared from a stock aqueous
solution of hexachloroplatinic acid (0.193 M H.sub.2PtCl.sub.6) and
a stock aqueous solution of antimony triacetate (0.182 M
Sb(OAc).sub.3) containing hydrochloric acid sufficient to dissolve
the antimony salt. Sufficient impregnation solution was used to
obtain a platinum loading of 1.3 weight percent. The impregnated
monolith was dried in ambient air, then reduced under flowing
hydrogen in the manner described in E-1 hereinabove.
[0069] The catalyst was tested in the oxidation of ethane to
ethylene in the presence of hydrogen and under autothermal process
conditions as described in E-1 with the results shown in Table 1
hereinabove. It was seen that under autothermal process conditions
a catalyst comprising platinum and antimony supported on a ceramic
monolith achieved an ethane conversion of 69.5 percent and an
ethylene selectivity of 81.5 percent. Selectivities to carbon
monoxide and carbon dioxide were low. The results are comparable to
those achieved in commercial thermal cracking furnaces.
Comparative Experiment 2 (CE-2)
[0070] The catalyst of E-2 comprising platinum and antimony
supported on an alumina monolith was tested in the oxidation of
ethane as described in E-2, with the exception that no hydrogen was
used in the feedstream. Process conditions were as described in
CE-1a. Results are set forth in Table 1 (CE-2).
[0071] When E-2 was compared with CE-2 or any of CE-1a and CE-1b,
it was seen that the combined use of antimony in the catalyst and
hydrogen in the feedstream as shown in E-2 gave the highest ethane
conversion and ethylene selectivity and the lowest levels of carbon
oxides.
EXAMPLE 3 (E-3)
Oxidation of Ethane to Ethylene--Hydrogen and Pt/Sn/Sb Catalyst
[0072] A catalyst comprising platinum, tin, and antimony supported
on an alumina monolith was prepared in a manner similar to that
described in Examples 1 and 2. The metals were codeposited by
impregnation of the support with an aqueous solution of Pt, Sn, and
Sb salts in a Pt:Sn:Sb atomic ratio of 1:5:0.26. The impregnation
solution was prepared from a stock aqueous solution of platinum
hexachloroplatinic acid (0.193 M), a stock aqueous solution of
stannous chloride (0.372 M) containing hydrochloric acid (5 weight
percent), and a stock aqueous solution of antimony triacetate
(0.182 M) containing hydrochloric acid (50 weight percent).
Sufficient impregnation solution was used to obtain a platinum
loading of 1.3 weight percent. The impregnated monolith was dried
in ambient air and reduced under hydrogen as described in E-1
hereinabove.
[0073] The catalyst was tested in the oxidation of ethane to
ethylene in the presence of hydrogen and under autothermal process
conditions as described in E-1 with the results shown in Table 1
hereinabove. It was seen that a catalyst comprising platinum, tin,
and antimony supported on a ceramic monolith achieved an ethane
conversion of 68.5 percent and an ethylene selectivity of 80.6
percent. Carbon monoxide and carbon dioxide were produced only at
low levels. The results are comparable to those achieved in
commercial thermal cracking furnaces.
Comparative Experiment 3 (CE-3)
[0074] The catalyst of E-3 comprising platinum, tin, and antimony
on an alumina monolith was evaluated in the oxidation of ethane as
described in E-3, with the exception that no hydrogen was used in
the feedstream. Process conditions were as described in CE-1a.
Results are set forth in Table 1 (CE-3). When E-3 was compared with
CE-3 and any of CE 1a and CE-1b, it was seen that the combined use
of antimony and tin in the catalyst and hydrogen in the feedstream
as shown in E-3 gave the highest conversion of ethane, the highest
selectivity to ethylene, and the lowest levels of carbon
oxides.
EXAMPLE 4 (E-4)
Oxidation of Ethane to Ethylene--Pt/Cu/Fiber Monolith Catalyst
[0075] An aqueous impregnation solution was prepared containing
platinum and copper in a Pt:Cu atomic ratio of 1:5. The
impregnation solution was prepared from stock solutions of
chloroplatinic acid (0.193 M H.sub.2PtCl.sub.6) and cupric chloride
(1.49 M CuC1.sub.2). A ceramic fiber mat (Nextel.TM. 440 brand
fiber mat, 2 cm square.times.1 cm thick, weighing 0.25 g) was
precalcined in air at 900.degree. C., cooled, and then impregnated
with the impregnation solution to saturation. Sufficient solution
was used to obtain a calculated platinum loading of 16 weight
percent in the finished mat. The impregnated fiber mat was dried in
ambient air, then reduced in flowing hydrogen, as described in
E-1.
[0076] The catalyst was sandwiched between two inert foam monoliths
(1.8 cm dia by 1 cm thick, 18 ppcm alumina or mullite), wrapped in
FiberFrax.TM. brand alumina-silica cloth, and packed into a quartz
tube reactor (Inner Diameter (I.D.) 1.9 cm). The feed to the
reactor was preheated with a heating tape wrapped around the quartz
tube upstream of the catalyst. The catalyst zone was not heated,
but was insulated with high temperature insulation material to
minimize heat losses. Ethane, hydrogen, and nitrogen were preheated
to 200.degree. C. and fed to the reactor. Oxygen was then
introduced to the reactor which resulted in catalyst ignition. Upon
ignition the temperature rose within a few seconds to 1000.degree.
C., and the reactor operated autothermally. Process conditions and
results are shown in Table 2.
2TABLE 2 Ethane Oxidation to Ethylene Over Catalyst of Pt/Cu on
Fiber Monolith E-4 Run 1.sup.a Run 2.sup.a Total Feed Flow, slpm
6.75 8.0 GHSV, h.sup.-1 318,471 377,448 N.sub.2 Dilution 12% 30%
Molar Ratio C.sub.2H.sub.6/O.sub.2 2.2 2.0 Molar Ratio
H.sub.2/O.sub.2 2.2 2.0 % C.sub.2H.sub.6 Conv 70.0 71.2 % CO Sel
7.5 7.8 % CO.sub.2 Sel 0.6 0.7 % C.sub.2H.sub.4 Sel 80.0 80.4 %
C.sub.2H.sub.2 Sel 1.0 1.2 % Total C.sub.2H.sub.4 Sel 81.0 81.6
.sup.aFeed preheated at 200.degree. C.; pressure = 1.35 atm abs
(137 kPa).
[0077] It was found that a catalyst comprising platinum and copper
supported on a ceramic fiber monolith achieved an ethane conversion
of about 70 percent and an ethylene selectivity of 80 percent.
Carbon monoxide and carbon dioxide were produced only at low
levels. The results are comparable to those achieved in commercial
thermal cracking furnaces.
EXAMPLE 5 (E-5)
Oxidation of Ethane to Ethylene--Catalyst Stability
[0078] Five catalysts were prepared as follows:
[0079] Catalyst A comprised platinum and copper in a Pt:Cu atomic
ratio of 1:1 supported on an alumina foam monolith. The monolith of
E-1 was impregnated with an aqueous impregnation solution (1 ml)
prepared from stock solutions of hexachloroplatinic acid (0.193 M)
and cupric chloride (1.49 M). Sufficient stock solutions were used
to achieve a Pt:Cu atomic ratio of 1:1. Calculated platinum loading
was 1.2 weight percent. The impregnated monolith was dried and
reduced under hydrogen in the manner described in E-1.
[0080] Catalyst B comprised platinum and copper in a Pt:Cu atomic
ratio 1:1 supported on a Nextel.TM. 440 ceramic fiber mat. The
catalyst was prepared in the manner described in E-4 hereinabove,
with the exception that the amounts of stock solutions used were
adjusted to provide the Pt:Cu atomic ratio of 1:1. Calculated
platinum loading was 20 weight percent.
[0081] Catalyst C comprised platinum and copper in an atomic ratio
of 1:2 supported on a Nextel.TM. 440 ceramic fiber mat. The
catalyst was prepared in the manner described in E-4 hereinabove,
with the exception that the amounts of stock solutions used were
adjusted to give the Pt:Cu atomic ratio of 1:2. Calculated platinum
loading was 24 weight percent.
[0082] Catalyst D comprised platinum, tin, and copper in an atomic
ratio 1:1:1 supported on a Nextel.TM. 440 ceramic fiber mat. The
catalyst was prepared by calcining the fiber mat at 900.degree. C.,
cooling, then impregnating the calcined mat to wetness with an
impregnation solution prepared from stock solutions of
hexachloroplatinic acid (0.193 M), cupric chloride (1.49 M), and
stannous chloride (0.372 M) acidified with 5 weight percent
hydrochloric acid. Calculated platinum loading was 18 weight
percent. The impregnated fiber mat was dried in ambient air and
reduced under hydrogen, as described in E-1 hereinbefore.
[0083] Catalyst E comprised platinum and tin in an atomic ratio of
1:5 supported on a Nextel.TM. 440 brand ceramic fiber mat. The
catalyst was prepared by calcining the fiber mat at 900.degree. C.,
cooling, and impregnating the fiber mat to saturation with an
aqueous impregnation solution prepared from stock solutions of
hexachloroplatinic acid (0.193 M) and stannous chloride (0.372 M)
acidified with hydrochloric acid (5 weight percent). Calculated
platinum loading was 8.5 weight percent. The impregnated fiber mat
was dried and reduced as described in E-1 hereinbefore.
[0084] The catalysts were tested in the oxidation of ethane to
ethylene in the presence of hydrogen and under autothermal reaction
conditions. Process conditions and results are set forth in Table
3.
3TABLE 3 Oxidation of Ethane to Ethylene - Stability of
Catalysts.sup.a Flow GHSV % C.sub.2H.sub.6 TOS.sup.b Catalyst slpm
h.sup.-1 % N.sub.2 % C.sub.2H.sub.4 Sel Conv h A: Pt--Cu 7.33
172,830 20.5 79.1 63.1 2.0 (1:1) 78.9 63.0 13.7 on Al.sub.2O.sub.3
foam B: Pt--Cu 8.33 392,959 30 82.2 58.5 1 (1:1) 81.1 56.5 8 on
fiber mat C: Pt--Cu 8.33 392,959 30 82.5 60.9 0.5 (1:2) 81.6 59.3
17.3 on fiber mat D: Pt--Sn--Cu 8.33 392,959 30 83.7 61.2 0.3
(1:1:1) 81.6 59.3 18 on fiber mat E: Pt--Sn 8.33 392,959 30 83.2
59.4 2 (1:5) 82.0 55.1 18 on fiber mat .sup.aFeed: ethane, oxygen,
hydrogen, nitrogen. Total flow as shown; % N.sub.2 = mole
percentage of feedstream which is nitrogen; molar ratios:
C.sub.2H.sub.6/O.sub.2 = 2:1, H.sub.2/O.sub.2 2:1; no preheat;
autothermal process conditions; pressure = 1.34 atm abs (136 kPa).
.sup.bTOS = time on stream.
[0085] It was found that catalysts comprising platinum and tin,
copper, or a mixture thereof, supported on a ceramic foam or fiber
mat achieved a high ethane conversion, a high ethylene selectivity,
and good catalyst stability in a process of oxidizing ethane to
ethylene in the presence of hydrogen.
EXAMPLE 6 (E-6)
Oxidation of Ethane to Ethylene--Variation in Pt/Cu Ratio
[0086] Catalysts comprising platinum and copper supported on
Nextel.TM. 440 brand ceramic fiber mats were prepared in the manner
described in E-4 hereinabove. The atomic ratio of platinum to
copper was varied from 1:0.1 to 1:5. The catalysts were tested in
the oxidation of ethane to ethylene in the presence of hydrogen and
under autothermal process conditions, with the results shown in
Table 4.
4TABLE 4 Oxidation of Ethane to Ethylene Variation in Pt/Cu
Ratio.sup.a Pt:Cu Pt loading TOS.sup.b % C.sub.2H.sub.4 %
C.sub.2H.sub.6 ratio (wt %) h Sel. Conv. 1:0.1 21 2.1 79.3 55.1
1:0.5 21 8.5 80.3 56.2 1:1 20 8.0 81.1 56.5 1:2 24 16.3 81.6 59.3
1:3 21 16.5 81.7 59.4 1:5 18 15.5 82.1 59.3 .sup.aFeed: ethane,
oxygen, hydrogen, nitrogen. Total Flow = 8.33 slpm (GHSV = 392,959
h.sup.-1), 30% nitrogen dilution; molar ratios:
C.sub.2H.sub.6/O.sub.2 = 2:1, H.sub.2/O.sub.2 = 2:1; no preheat;
autothermal conditions; pressure = 1.32 atm abs (134 kPa).
.sup.bTOS = time on stream (h).
[0087] Samples run out to 8 or less hours would have given slightly
lower conversion and selectivity if run out to 16 hours. Thus, it
was found that as the atomic ratio of platinum to copper decreased
from 1:0.1 to 1:5, the ethane conversion and ethylene selectivity
increased. It was also found that at the higher concentrations of
copper, the catalyst did not remain lit in the absence of
hydrogen.
EXAMPLE 7 (E-7)
Oxidation of Ethane to Ethylene--Variation in Space Velocity
[0088] A catalyst comprising platinum and copper in an atomic ratio
of 1:1 supported on a Nextel.TM. 440 brand ceramic fiber mat was
prepared in a manner similar to that described in E-4 hereinabove.
The catalyst was evaluated in the oxidation of ethane to ethylene
in the presence of hydrogen under autothermal process conditions.
The gas hourly space velocity of the total feed was progressively
increased at constant pressure with the results shown in Table
5.
5TABLE 5 Oxidation of Ethane to Ethylene Variation in Space
Velocity.sup.a Flow rate GHSV % C.sub.2H.sub.4 % C.sub.2H.sub.6
slpm h.sup.-1 Sel. Conv. 7 330,100 80.6 54.3 14 660,200 81.0 55.7
21 990,300 81.7 55.5 28 1,320,400 81.6 55.7 35 1,650,500 82.4 53.0
42 1,980,600 81.9 52.4 .sup.aFeed: ethane, oxygen, hydrogen,
nitrogen; 25% nitrogen dilution; molar ratios:
C.sub.2H.sub.6/O.sub.2 = 2:1, H.sub.2/O.sub.2 = 2:1; no preheat,
autothermal conditions; pressure = 1.68 atm abs (170 kPa).
[0089] Over a wide range of space velocities tested, it was found
that the ethane conversion and ethylene selectivity did not change
significantly.
EXAMPLE 8 (E-8)
Oxidation of Ethane to Ethylene--Modified Support
[0090] Four catalysts were prepared comprising platinum supported
on a modified ceramic foam monolith (92 weight percent alpha
alumina, 8 weight percent silica; 45 ppi (18 ppcm); 1.8 cm dia by 1
cm thick; average weight 2.8 g). The preparation was characterized
by first modifying the support with a support modifier,
specifically tin or antimony, and then depositing platinum and
optionally copper on the modified support. In this example, the
same element (Sn) that modifies the support also functions as a
promoter. Details of the preparation were as follows:
[0091] Catalyst A comprised platinum on a tin-modified alumina
monolith. The monolith of E-1 was impregnated to wetness with an
aqueous solution of stannous chloride (0.372 M) containing 5 weight
percent hydrochloric acid. The impregnated support was air dried
and then reduced at 700.degree. C. under flowing hydrogen at a flow
rate of 1 cfh (473 cm.sup.3/min). The modified support was
impregnated with an aqueous solution (1 ml) of hexachloroplatinic
acid (0.193 M), then dried in ambient air and reduced under
hydrogen as described in E-1.
[0092] Catalyst B comprised platinum and copper (1:1) on a
tin-modified alumina monolith. The monolith was impregnated to
wetness with an aqueous solution of stannous chloride (0.372 M)
containing hydrochloric acid (5 weight percent). The
tin-impregnated monolith was air dried and reduced at 700.degree.
C. for 2 h in flowing hydrogen (5 volume percent in nitrogen) at a
flow rate of 1 cfh (473 cm.sup.3/min). The modified monolith was
impregnated with an aqueous solution (1 ml) prepared from stock
solutions of hexachloroplatinic acid (0.193 M) and cupric chloride
(1.49 M). The impregnated monolith was air dried and reduced under
flowing hydrogen as described in E-1.
[0093] Catalyst C comprised platinum and copper (1:5) on a
tin-modified alumina monolith. The catalyst was prepared as in "B"
hereinabove with the exception that sufficient stock solutions were
used to give a Pt:Cu atomic ratio of 1:5.
[0094] Catalyst D comprised platinum and copper (1:5) on an
antimony-modified alumina monolith. In this example, the monolith
comprised alpha alumina (99.5 weight percent). The monolith was
impregnated to wetness with a solution of antimony triacetate
(0.182 M) dissolved in hydrochloric acid. The monolith was air
dried and reduced for 2 h at 700.degree. C. under flowing hydrogen
(5 volume percent in nitrogen) at a flow rate of 1 cfh (473
cm.sup.3/min). The reduced monolith was impregnated with an aqueous
impregnation solution (1 ml) prepared from a stock solution of
hexachloroplatinic acid (0.193 M, 1 ml) and a stock solution of
cupric chloride (1.49 M, 0.65 ml). The monolith was dried in air
and reduced as in E-1.
[0095] The catalysts were evaluated in the oxidation of ethane in
the presence of hydrogen and under autothermal reaction conditions
with the results shown in Table 6.
6TABLE 6 Oxidation of Ethane to Ethylene - Modified Support.sup.a %
% Flow GHSV C.sub.2H.sub.6 H.sub.2 Pre- C.sub.2H.sub.4
C.sub.2H.sub.6 TOS.sup.b Catalyst slpm h.sup.-1 % N.sub.2 O.sub.2
O.sub.2 heat .degree. C. Sel. Conv h A: Pt 11 259,364 5 2.1 2.1 150
78.3 68.1 0.5 Sn--Al.sub.2O.sub.3 150 76.6 67.5 7.5 foam B: Pt--Cu
(1:1) 11 259,364 5 2.1 2.1 150 79.8 71.1 0.5 Sn--Al.sub.2O.sub.3
150 78.8 69.7 15 foam C: Pt--Cu (1:5) 7 159,155 12 2.2 2.2 200 81.4
69.8 5 Sn--Al.sub.2O.sub.3 200 81.0 69.1 21 foam D: Pt--Cu 7
165,050 10 2.3 2.3 250 82.0 67.8 2.5 (1:5) 250 81.8 67.4 15
Sb--Al.sub.2O.sub.3 foam .sup.aFeed: ethane, oxygen, hydrogen,
nitrogen; total flow, nitrogen dilution, and molar ratios of
C.sub.2H.sub.6/O.sub.2 and H.sub.2/O.sub.2 as shown; preheat as
shown; autothermal conditions; pressure = 1.34 atm abs (136 kPa).
.sup.bTOS = time on stream (h).
[0096] It was found that a catalyst comprising platinum and
optionally copper supported on a ceramic foam monolith modified
with tin or antimony achieved a high conversion of ethane, a high
selectivity to ethylene, and good catalyst stability. Results are
comparable to those obtained from a commercial cracking
furnace.
EXAMPLE 9 (E-9)
Oxidation of a Natural Gas Liquid Feed
[0097] A catalyst comprising platinum and copper (1:2) on a
tin-modified alumina monolith (92 weight percent alumina) was
prepared in the manner described in Example 8B, with the exception
that the atomic ratio of Pt:Cu was adjusted to 1:2. This catalyst
was evaluated in the oxidation of a natural gas liquid (NGL) feed
in the presence of hydrogen under autothermal process conditions.
The liquid feed composition, an Algerian condensate, comprised on a
weight percent basis a mixture of 42.1 percent paraffins, 34.4
percent isoparaffins, 7.3 percent aromatics, 12.3 percent
naphthenes, 0.2 percent oxygenates, and the balance (about 3-4
percent) unidentified components. The alkanes comprised C.sub.1-19
alkanes having a maximum molar concentration in the C.sub.5-8
range. Feed was preheated at 200.degree. C. Total gas flow was
about 8 slpm (GHSV 200,000 h.sup.-1). Process conditions and
results are set forth in Table 7.
7TABLE 7 Oxidation of Natural Gas Liquid Feed (NGL).sup.a,b Liq.
feed O.sub.2 H.sub.2 N.sub.2 CH.sub.4 C.sub.2H.sub.4 C.sub.3H.sub.6
C.sub.4H.sub.8 C.sub.4H.sub.6 C.sub.6+ gm/min slpm slpm slpm NGL
NGL NGL NGL NGL NGL 3.2 1.2 3.2 2.0 0.17 0.38 0.10 0.026 0.033 0.09
3.2 1.1 3.2 2.0 0.135 0.33 0.14 0.050 0.039 0.11 3.15 1.3 3.2 2.6
0.176 0.39 0.08 0.021 0.031 0.092 3.15 1.2 3.2 2.6 0.149 0.36 0.13
0.043 0.039 0.099 .sup.aFeed composition: C.sub.1-19 alkanes (76.5
wt %), maximum molar range C.sub.5-8; autothermal conditions;
200.degree. C. preheat; pressure = 1.34 atm abs (136 kPa); GHSV =
200,000 h.sup.-1. .sup.bSelectivities given in g product per g NGL
in the feed.
[0098] It was seen that a catalyst comprising platinum and copper
on a ceramic monolith support was capable of oxidizing a natural
gas liquid feed in the presence of hydrogen under autothermal
conditions to a mixture of low molecular weight olefins,
specifically, ethylene, propylene, butylene, and butadiene.
EXAMPLE 10 (E-10)
Oxidation of Ethane to Ethylene--Pt--Cu Catalyst on Modified
Support
[0099] Catalysts were prepared comprising platinum and copper
supported on a modified ceramic foam monolith. The preparation was
characterized by first modifying the support with tin and
optionally a second modifier, and thereafter depositing platinum
and copper on the modified support. The support comprised a foam
monolith, either 92 or 99.5 weight percent alumina [1.8 cm
dia.times.1 cm thick; 45 ppi (18 ppcm)]. Preparations were as
follows:
[0100] Catalyst A comprising platinum and copper (1:2) on a
tin-modified alumina (92 weight percent) was prepared in the manner
described in Example 8B, with the exception that the atomic ratio
of Pt:Cu was adjusted to 1:2. Catalyst B comprising platinum and
copper (1:5) on a tin-modified alumina (92.0 weight percent) was
prepared as in Example 8C. Catalyst C comprising platinum and
copper (1:4) on a tin-modified alumina (99.5 weight percent) was
prepared in the manner described in Example 8B, with the exception
that the atomic ratio of Pt:Cu was adjusted to 1:4. Catalyst D
comprising platinum and copper (1:5) on a tin-modified alumina
(99.5 weight percent) was prepared as in Example 8C.
[0101] Catalyst E comprised platinum and copper (1:5) on a tin and
calcium-modified alumina monolith (99.5 weight percent). The
monolith was immersed in a saturated aqueous solution of calcium
hydroxide for 24 h. Then, the monolith was rinsed several times
with distilled water, air dried, and calcined at 900.degree. C. for
1 h. The calcined monolith was immersed in an aqueous solution of
stannous chloride (0.372 M) containing hydrochloric acid (5 weight
percent) for several hours, after which the monolith was air dried
and reduced under flowing hydrogen (1 cfh; 473 cm.sup.3/min) at
700.degree. C. for 2 h. An aqueous impregnation solution having a
Pt:Cu atomic ratio of 1:5 was prepared from stock solutions
comprising hexachloroplatinic acid (1 ml, 0.193 M) and cupric
chloride (0.65 ml, 1.49 M). The monolith was impregnated with the
impregnation solution (1 ml). The impregnated monolith was dried in
ambient air and reduced as in E-1.
[0102] Catalyst F comprised platinum and copper (1:5) on a tin and
zirconium-modified alumina monolith (99.5 weight percent). The
monolith was immersed for 24 h in an aqueous solution of zirconium
oxychloride (ZrOCl.sub.2, 1M) containing 1 weight percent
hydrochloric acid. The monolith was rinsed with distilled water,
air dried, and calcined at 900.degree. C. for 1 h. The calcined
monolith was immersed for several hours in an aqueous solution of
stannous chloride (0.372 M) containing hydrochloric acid (5 weight
percent), after which the monolith was air dried and reduced under
flowing hydrogen (1 cfh; 473 cm.sup.3/min) at 700.degree. C. for 2
h. An impregnation solution containing platinum and copper (1:5)
was prepared from stock solutions of hexachloroplatinic acid (1 ml,
0.193 M) and cupric chloride (0.65 ml, 1.49 M). The monolith was
impregnated with the impregnation solution (1 ml), dried in air,
and reduced as in E-1.
[0103] Catalyst G comprised platinum and copper (1:5) on a tin and
lanthanum-modified alumina foam monolith (99.5 weight percent). The
monolith was immersed for 24 h in an aqueous solution of lanthanum
chloride (1 M) containing 1 weight percent hydrochloric acid. The
monolith was rinsed with distilled water several times, air dried,
and then calcined at 900.degree. C. for 1 h. The calcined monolith
was cooled and then immersed in an aqueous solution of stannous
chloride (0.372 M) containing hydrochloric acid (5 weight percent)
for several hours, after which the monolith was air dried and
reduced under flowing hydrogen (1 cfh; 473 cm.sup.3/min) at
700.degree. C. for 2 h. The modified monolith was impregnated with
an impregnation solution (1 ml) containing platinum and copper
(1:5) prepared from the stock solutions noted hereinbefore. The
impregnated monolith was reduced under hydrogen as in E-1.
[0104] The catalysts were evaluated in the oxidation of ethane in
the presence of hydrogen under autothermal reaction conditions with
the results shown in Table 8.
8TABLE 8 Oxidation of Ethane to Ethylene Catalyst of Pt--Cu on
Modified Support.sup.a Pre- % % Flow GHSV % heat C.sub.2H.sub.4
C.sub.2H.sub.6 TOS.sup.b Catalyst slpm h.sup.-1 N.sub.2 .degree. C.
Sel. Conv. h A: Pt--Cu (1:2) 7.0 165,050 10 300 79.9 71.3 7.2
Sn--Al.sub.2O.sub.3 (92%) B: Pt--Cu (1:5) 7.0 165,050 10 300 80.2
71.6 13 Sn--Al.sub.2O.sub.3 (92.0%) C: Pt--Cu (1:4) 8.3 196,409 5
300 81.0 71.9 4.5 Sn--Al.sub.2O.sub.3 (99.5%) D: Pt--Cu (1:5) 7.0
165,050 10 300 80.7 72.4 12 Sn--Al.sub.2O.sub.3 (99.5%) E: Pt--Cu
(1:5) 8.3 196,409 5 250 81.5 71.4 0.3 Sn--Ca--Al.sub.2O.sub.3
(99.5%) F: Pt--Cu (1:5) 8.3 196,409 5 250 81.0 71.7 0.3
Sn--Zr--Al.sub.2O.sub.3 (99.5%) G: Pt--Cu (1:5) 8.3 196,409 5 250
81.7 71.2 0.5 Sn--La--Al.sub.2O.sub.3 (99.5%) .sup.aFeed: ethane,
oxygen, hydrogen, and nitrogen. Total flow and nitrogen dilution as
shown; molar ratios: C.sub.2H.sub.6/O.sub.2 = 2.3:1,
H.sub.2/O.sub.2 = 2.3:1; preheat as shown; autothermal conditions;
pressure = 1.34 atm abs (136 kPa). .sup.bTOS = time on stream
(h).
[0105] It was seen that a catalyst comprising platinum and copper
supported on an alumina monolith which had been pretreated with at
least one of tin, calcium, zirconium, and lanthanum achieved a high
ethane conversion, a high ethylene selectivity, and good stability
in the oxidation of ethane to ethylene in the presence of hydrogen.
Results of this invention are comparable to those obtained from
commercial thermal cracking furnaces.
EXAMPLE 11 (E-11)
Oxidation of Ethylene--Variation with Pressure
[0106] The catalyst of E-7 was evaluated in the partial oxidation
of ethane to ethylene in the presence of hydrogen in the manner
described in E-7, with the exception that the pressure in the
reactor was varied from about 2 atm abs (200 kPa abs) to about 4
atm abs (400 kPa abs). As in E-7, the catalyst comprised platinum
and copper in an atomic ratio 1:1 supported on a Nextel.TM. 440
brand fiber mat. Process conditions and results are set forth in
Table 9.
9TABLE 9 Oxidation of Ethane-Variation in Pressure.sup.a, b Flow
rate GHSV % N.sub.2 Pressure % C.sub.2H.sub.4 % C.sub.2H.sub.6 slpm
h.sup.-1 dilution kPa Sel. Conv. 49 2,310,770 25 214 80.8 55.6 56
2,640,800 25 249 79.6 57.6 61 2,886,017 23 406 76.4 60.2 45
2,122,071 20 406 76.1 62.4 40 1,886,286 10 406 72.9 67.3
.sup.aFeed: ethane, oxygen, hydrogen, nitrogen; 25% nitrogen
dilution; molar ratios: C.sub.2H.sub.6O.sub.2 = 2:1,
H.sub.2/O.sub.2 = 2:1; no preheat, autothermal conditions.
.sup.bCatalyst: Pt/Cu (1:1) supported on Nextel .TM. 440 fiber
mat.
[0107] It was seen that as the pressure of the process increased,
the ethane conversion increased and the ethylene selectivity
decreased.
EXAMPLE 12 (E-12)
Partial Oxidation of Propane to Ethylene and Propylene
[0108] Two catalysts were evaluated in the partial oxidation of
propane to ethylene and propylene in the presence of hydrogen.
Catalyst A, identical to Catalyst E-1 hereinabove, comprised
platinum and tin in an atomic ratio 1:5 supported on an alumina
foam monolith (92 weight percent). Feed comprised a mixture of
ethane (70 volume percent) and propane (30 volume percent) at a
nitrogen dilution of 21 percent. Other process conditions and
results are shown in Table 10.
[0109] Catalyst B, identical to Catalyst E-3 hereinabove, comprised
platinum, tin, and antimony in an atomic ratio of 1:5:0.26
supported on an alumina foam monolith (92 weight percent). Feed
comprised propane at a nitrogen dilution of 30 percent. Process
conditions and results are shown in Table 10.
10TABLE 10 Partial Oxidation of Propane to Propylene and Ethylene
With Hydrogen and Multi-Metallic Catalyst Mol % Conversion Feed %
C.sub.2H.sub.6 % C.sub.3H.sub.8 % Carbon Atom Selectivities
Conditions.sup.a, b Conv Conv C.sub.2H.sub.4 C.sub.3H.sub.6 CO
CO.sub.2 CH.sub.4 C4+ A.sup.a. 70/30 71.8 94.6 65.2 3.5 12.6 0.6
14.2 3.0 C.sub.2H.sub.6/C.sub.3H.sub.8 B.sup.b. 100% C.sub.3H.sub.8
(1) Comparative.sup.b -- 71.9 35.0 22.8 12.3 8.2 14.2 5.1 (2).sup.b
-- 77.5 41.5 20.7 10.1 1.0 18.0 5.5 (3).sup.b -- 67.8 39.5 25.4 8.6
1.1 16.8 5.7 .sup.aCatalyst A: Pt/Sn (1:5) on alumina foam
monolith; feed: ethane (70 vol %) and propane (30 vol %); 21%
nitrogen dilution; total flow = 10 slpm; molar ratios:
C.sub.2H.sub.6/O.sub.2 = 1.05:1, C.sub.3H.sub.8/O .sub.2 = 0.45:1,
H.sub.2/O 2 = 1.5:1. .sup.bCatalyst B: Pt/Sn/Sb (1:5:0.26) on
alumina foam monolith; (1) Propane feed; 30% nitrogen dilution;
total flow = 7 slpm; molar ratio: C.sub.3H.sub.8/O.sub.2 = 1.3:1;
comparative: no hydrogen. (2) Propane feed; 23% nitrogen dilution;
total flow = 9 slpm; molar ratios: C.sub.3H.sub.8/O.sub.2 = 1.3:1,
H.sub.2/O.sub.2 = 1.0:1. (3) Propane feed; 23% nitrogen dilution;
total flow = 9 slpm; molar ratios: C.sub.3H.sub.8/O.sub.2 = 1.4:1,
H.sub.2/O.sub.2 = 1.0:1.
[0110] It was seen that propane is converted primarily to ethylene
and propylene in the presence of hydrogen and a multi-metallic
catalyst supported on an alumina monolith. When the Comparative
Experiment 12-B1 is compared with Examples 12-B2 and 12-B3, it is
seen that the total selectivity to ethylene and propylene is higher
when hydrogen is co-fed.
EXAMPLE 13 (E-13)
Ethane to Ethylene with Preheat
[0111] A catalyst comprising platinum and copper on a tin and
lanthanum-modified alumina monolith support was prepared as in
Example E-10G. The catalyst was evaluated in the autothermal
partial oxidation of ethane to ethylene under the conditions shown
in Table 11. The feed comprising ethane, oxygen, hydrogen, and
nitrogen was preheated to temperatures ranging from 281.degree. C.
to 589.degree. C. At preheat temperatures above 400.degree. C., the
molar ratio of ethane to oxygen was raised to 2.7:1 and higher.
Results are set forth in Table 11.
11TABLE 11 Autothermal Oxidation of Ethane to Ethylene Using
Preheat.sup.a T (.degree. C.) % C.sub.2H.sub.6 % C.sub.2H.sub.4 %
CH.sub.4 % CO % CO.sub.2 Net C.sub.2H.sub.6/O.sub.2 H.sub.2/O.sub.2
Preheat Conv Sel Sel Sel Sel H.sub.2/C.sub.2H.sub.4 2.3 2.3 281
70.4 80.00 6.67 8.20 0.55 0.004 2.7 2.7 488 67.7 81.80 6.30 6.90
0.53 0.12 2.7 2.7 538 70.1 81.22 6.66 7.33 0.53 0.18 2.8 2.8 589
69.7 81.46 6.65 7.23 0.53 0.21 .sup.aFeedstream:
C.sub.2H.sub.6/O.sub.2 and H.sub.2/O.sub.2 molar ratios as shown;
10% nitrogen dilution; pressure = 1.35 bar abs (135 kPa); GHSV, in
the range 180,000 to 200,000 h.sup.-1; flow rate in the range 7.7
to 8.4 slpm; autothermal process conditions.
[0112] It was found that by preheating the feed to temperatures
above 400.degree. C., substantially the same ethane conversion and
product selectivities were obtained at higher hydrocarbon to oxygen
molar ratios, as were obtained at lower preheat and lower
hydrocarbon to oxygen ratios. Compare, for example, the run at
281.degree. C. preheat with the run at 538.degree. C. preheat. The
ethane conversion and ethylene selectivity were similar while
oxygen usage dropped from 0.88 g O.sub.2 per g ethylene
(ethane/oxygen molar ratio of 2.3:1) to 0.76 g O.sub.2 per g
ethylene (ethane/oxygen molar ratio 2.7:1.) Likewise, the net
hydrogen balance per mole ethylene improved from about zero (0.004)
at 281.degree. C. to 0.18 at 538.degree. C.
EXAMPLE 14 (E-14)
Autothermal Oxidation of Ethane to Ethylene Using Pt/Cu on Magnesia
Pellets
[0113] A catalyst was prepared as in Example E-4 hereinabove, with
the exception that magnesia pellets (Norton; 3 mm dia.times.5 mm
length cylinders) were used in place of the alumina fiber mat
support. The magnesia pellets were heated to 1200.degree. C. for 16
h to reduce the surface area to less than 1 m.sup.2/g. A solution
containing platinum and copper in an atomic ratio of 1:5 was
prepared using hexachloroplatinic acid and cupric chloride. The
pellets were loaded with the solution, dried at 80.degree. C.
overnight, and reduced at 450.degree. C. under hydrogen (5 volume
percent) in nitrogen. Pt:Cu atomic ratio was 1:5.6. Pt loading,
0.57 weight percent; copper loading, 1.03 weight percent; balance
magnesia.
[0114] The catalyst particles were sandwiched between two inert
alumina monoliths in a quartz tube reactor. Catalyst bed dimensions
were 17 mm (dia) by 15 mm (depth). The catalyst was evaluated in
the autothermal oxidation of ethane to ethylene in the manner
described hereinbefore. Process conditions and results are set
forth in Table 12.
12TABLE 12 Ethane Autothermal Oxidation to Ethylene with Pt/Cu/MgO
Pelleted Catalyst.sup.a Time % C.sub.2H.sub.6 % C.sub.2H.sub.4 %
CH.sub.4 % CO % CO.sub.2 h C.sub.2H.sub.6/O.sub.2 H.sub.2/O.sub.2
Cony Sel Sel Sel Sel Preheat, 250.degree. C.; 8 slpm.sup.b 0.9 2.3
2.3 73.6 79.6 7.5 5.4 2.2 4.5 2.3 2.3 73.5 80.0 7.0 5.4 2.0 6.2 2.3
2.3 73.7 79.4 6.9 5.5 2.0 7.2 2.3 2.3 73.7 79.5 7.0 5.6 2.0
Preheat, 275.degree. C.; 6 slpm.sup.b; stable after 10 h 10.3 2.3
2.3 73.3 80.0 6.6 5.6 2.2 Preheat, 250.degree. C. at 2.5 h and
275.degree. C. at 3.5 h; 8 slpm.sup.b 2.5 2.4 2.4 69.3 82.0 6.4 4.7
1.8 3.5 2.4 2.4 70.8 81.5 6.6 4.9 1.8 .sup.aFeedstream:
C.sub.2H.sub.6/O.sub.2 and H.sub.2/O.sub.2 as shown; 5% N.sub.2
dilution; preheat as shown; pressure 1.35 bar abs (135 kPa);
calculated adiabatic temperature = 950-1,050.degree. C.;
autothermal process conditions. .sup.b6 slpm = GHSV 94,314
h.sup.-1; 8 slpm = 125,752 h.sup.-1.
[0115] It was found that magnesia pellets can be suitably employed
as a catalyst support in the autothermal oxidation process of this
invention.
EXAMPLE 15 (E-15)
Oxidation of Ethane to Ethylene Using Catalyst of Pt--Cu on
Magnesia Monolith Support
[0116] A catalyst comprising platinum and copper on a ceramic
monolith was prepared in the manner described in Example E-4, with
the exception that a magnesia monolith (Hi-Tech Ceramics, 17 mm
dia.times.10 mm width, 45 ppi) was used in place of the alumina
fiber mat. Pt:Cu atomic ratio was 1:5, and the total metal loading
was 5.67 weight percent. The catalyst was evaluated in the
autothermal oxidation of ethane to ethylene as described
hereinbefore, with the results shown in Table 13.
13TABLE 13 Autothermal Oxidation of Ethane to Ethylene Using Pt/Cu
on MgO Monolitha Time % C.sub.2H.sub.6 % C.sub.2H.sub.4 % CH.sub.4
% CO % C0.sub.2 (h) Conv Sel Sel Sel Sel 0.5 75.1 80.0 6.7 6.0 1.8
1.5 75.1 80.7 6.5 5.9 1.5 2.5 74.6 81.2 6.3 5.9 1.4 4.5 74.5 81.4
6.3 6.1 1.3 5.5 74.4 81.2 6.3 6.1 1.3 6.5 74.5 81.4 6.3 6.2 1.2
.sup.aFeedstream: molar ratios: C.sub.2H.sub.6/O.sub.2 = 2.3:1,
H.sub.2/O.sub.2 = 2.3:1; 5% N.sub.2 dilution; preheat = 275.degree.
C.; pressure = 1.35 bar abs (135 kPa); GHSV = 125,752 h.sup.-1;
flow rate = 8 slpm; autothermal process conditions; calculated
adiabatic temperature = 935.degree. C.
[0117] It was found that a magnesia monolith can be suitably
employed as a support in the autothermal oxidation process of this
invention.
EXAMPLE 16 (E-16)
Oxidation of Ethane to Ethylene in Modified Fluidized Bed
Reactor
[0118] Alumina beads were used to prepare a catalyst. A solution
containing platinum, copper, and tin in an atomic ratio of 1:5:5
was prepared by mixing hexachloroplatinic acid (0.659 ml, 0.193 M),
cupric chloride (0.427 ml, 1.48 M), and stannous chloride (9.97 ml,
0.064 M, HCl to dissolve). Alumina beads (Norton, 590-850 .mu.m, 28
g) were suspended in the solution with excess deionized water. The
mixture was stirred and heated until almost all of the water was
evaporated. The resulting solids were dried at 80.degree. C. The
total metals loading was 0.5 weight percent. The catalyst was
loaded into the reactor and reduced under hydrogen (5 volume
percent in nitrogen) at 300.degree. C.
[0119] A reactor was used comprising a quartz tube (19 mm dia) into
which the catalyst (6 g) was loaded to a bed height of 1.5 cm
(static aspect ratio 0.8). A quartz frit was used to support the
catalyst and evenly distribute the gas flow. The feed was preheated
and the reactor insulated in the manner described hereinbefore.
Ethane, hydrogen, oxygen, and nitrogen were preheated to
275.degree. C. and fed to the reactor at a flow rate which
disengaged the particles and circulated them within the bed. The
flow rate was set for slightly above minimal fluidization at
operating conditions (5 slpm). The bed expanded to a height of 3.0
cm (operating aspect ratio 1.6). Oxygen was introduced which
resulted in catalyst ignition. Upon light-off, the catalyst
operated autothermally. Process conditions and results are shown in
Table 14.
14TABLE 14 Autothermal Oxidation of Ethane to Ethylene Using
Modified Fluidized Bed Reactor.sup.a Time % C.sub.2H.sub.6 %
C.sub.2H.sub.4 % CH.sub.4 % CO % CO.sub.2 (h) Conv Sel Sel Sel Sel
4 70.6 82.7 5.8 3.6 0.72 5 70.8 82.8 5.9 3.5 0.71 6 70.5 83.0 5.8
3.4 0.68 7 70.7 83.0 5.9 3.3 0.68 8 70.3 83.1 5.8 3.3 0.67
14.5.sup.b 71.1 81.9 6.4 4.0 1.0 36.5.sup.b 71.6 81.7 6.4 4.0 0.8
.sup.aFeedstream: molar ratios: C.sub.2H.sub.6/O.sub.2 = 2.3:1,
H.sub.2/O.sub.2 = 2.3:1; 10% N.sub.2 dilution; preheat =
275.degree. C.; pressure = 1.35 bar abs (135 kPa); GHSV = 78,600
h.sup.-1 static bed; flow rate 5 slpm; autothermal process
conditions; calculated adiabatic temperature = 975.degree. C.
.sup.bConditions as in (a), with exception of the following molar
ratios: C.sub.2H.sub.6/O.sub.2 = 2.4:1, H.sub.2/O.sub.2 = 2.2:1;
calculated adiabatic temperature = 932.degree. C.
[0120] It was seen that a reactor operating at slightly above
minimal fluidization could be used for the autothermal oxidation of
ethane to ethylene to achieve high selectivity to ethylene and low
selectivities to methane, carbon monoxide, and carbon dioxide. In
this laboratory example, the aspect ratio during operation was
greater than 1:1, because of the smaller reactor diameter; however,
the same results are expected with a commercial scale reactor
having a diameter of 1.5 or more meters and the same bed depth of 3
cm during operation, which results in an aspect ratio less than
1:1.
EXAMPLE 17 (E-17)
Ethane Oxidation to Ethylene Using Pelleted Alumina Support in
Fixed Bed Reactor
[0121] The catalyst (6 g) from Example 16, prepared with alumina
pellets, was evaluated in the oxidation of ethane to ethylene in a
fixed bed reactor. The pellets were sandwiched between an inert
alumina monolith and a quartz frit to retain the pellets in a fixed
bed. Results are set forth in Table 15.
15TABLE 15 Autothermal Oxidation of Ethane to Ethylene in Fixed Bed
Reactor.sup.a Time % C.sub.2H.sub.6 % C.sub.2H.sub.4 % CH.sub.4 %
CO % CO.sub.2 (h) Conv Sel Sel Sel Sel 2.5 70.8 80.4 6.7 5.8 0.94
3.5 70.6 80.6 6.6 5.9 0.95 4.5 70.4 80.6 6.5 6.0 0.95 5.5 70.2 80.7
6.5 6.0 0.93 .sup.aFeedstream molar ratios: C.sub.2H.sub.6/O.sub.2
= 2.3:1, H.sub.2/O.sub.2 = 2.3:1; 10% N.sub.2 dilution; preheat,
275.degree. C.; pressure = 1.35 bar abs (135 kPa); GHSV = 78,600
h.sup.-1 static bed; flow rate = 5 slpm; autothermal process
conditions; calculated adiabatic temperature = 960.degree. C.
[0122] It was found that ethane could be oxidized to ethylene in a
fixed bed reactor over a catalyst prepared on alumina pellets. When
Example 16 was compared with Example 17, it was concluded that
although both the fixed bed and the modified fluidized bed reactors
were suitable, the selectivities were more favorable in the
modified fluidized bed reactor. Less methane, carbon monoxide, and
carbon dioxide were obtained, and more ethylene was obtained at
closely similar conversions.
EXAMPLE 18 (E-18)
Ethane Oxidation Using Catalyst of Pt--Cu on Sn modified MgO
Support
[0123] A magnesia monolith support (Hi-Tech Ceramics, Inc.; 17 mm
dia.times.10 mm thick) was treated with an aqueous solution of tin
(IV) chloride (0.24 M), then dried at 90.degree. C. and reduced at
about 875.degree. C. under hydrogen (5 percent in nitrogen). Tin
loading was 1 weight percent. The tin-treated support was
impregnated with an aqueous solution of platinum and copper (Pt/Cu
atomic ratio 1:5) prepared using solutions of hexachloroplatinic
acid (0.19 M) and cupric chloride (1.49 M). Then, the monolith was
dried at 80.degree. C. and reduced at 450.degree. C. under the
aforementioned hydrogen flow. Pt loading was 3.26 weight
percent.
[0124] The catalyst was evaluated in the oxidation of ethane under
autothermal conditions as shown in Table 16.
16TABLE 16 Ethane Oxidation Using Pt--Cu on Sn-Treated MgO
Support.sup.a TOS % Conv % Sel % Sel % Sel % Sel (h) C.sub.2H.sub.6
C.sub.2H.sub.4 CH.sub.4 CO CO.sub.2 1.33 76.8 79.9 7.1 4.8 1.8 2.66
76.5 80.3 6.9 5.0 1.7 4.00 76.4 80.4 6.7 5.1 1.6 6.66 76.6 80.3 6.7
5.4 1.4 18.66 75.7 80.8 6.5 5.8 1.2 34.25 75.6 80.4 6.5 6.3 1.1
50.33 74.3 81.0 6.3 6.5 1.0 .sup.aFeedstream molar ratios:
C.sub.2H.sub.6/O.sub.2 = 2.3:1, H.sub.2/O.sub.2 = 2.3:1; 5% N.sub.2
dilution; preheat, 280.degree. C.; pressure = 1.35 bar abs (135
kPa); GHSV = 125,752 h.sup.-1; flow rate 8 slpm; autothermal
process conditions; calculated adiabatic temperature = 960.degree.
C.
[0125] It was found that the catalyst of Example 18 with a
tin-modified magnesia support achieved somewhat higher conversion
and higher selectivity than the related catalyst of Example 15
which used an unmodified magnesia support.
EXAMPLE 19
[0126] A solution containing nickel and copper in an atomic ratio
of 1:1 was prepared from an aqueous solution of nickel (II)
chloride hexahydrate (0.2 M) and an aqueous solution of copper (II)
chloride (1.49 M). An alumina monolith (99.5 weight percent
alumina; 17 mm diameter.times.10 mm length) was loaded with the
Ni--Cu solution, dried at 80.degree. C. overnight, and then reduced
at 450.degree. C. in hydrogen (5 volume percent) in nitrogen. The
total metal loading was 1.48 weight percent. The catalyst was
evaluated in the autothermal oxidation of ethane to ethylene in the
manner previously described. The catalyst required at least
400.degree. C. preheat for ignition. Upon ignition, the preheat was
reduced, and the catalyst remained ignited under the process
conditions employed; however, the catalyst extinguished in the
absence of hydrogen in the feedstream.
17TABLE 17 Autothemial Oxidation of Ethane Over
Ni--Cu/Al.sub.2O.sub.3 Catalyst.sup.a,b T Mol % Mol % Mol % Mol %
Mol % Run Time preheat C.sub.2H.sub.6 C.sub.2H.sub.6 CH.sub.4 CO
CO.sub.2 #19 (h) (.degree. C.) Conv. Sel. Sel Sel Sel (a) 2.5 250
79.7 73.2 7.3 12.3 1.01 (b) 3.5 125 72.9 75.0 6.2 11.7 0.90 (c) 5.5
200 64.4 79.6 5.4 8.7 0.91 (d) 7.4 250 68.4 78.1 5.9 9.2 0.94 (e)
8.2 275 69.5 77.7 6.1 9.3 0.93 (f) 17.5 275 68.6 76.3 6.6 10.9 0.59
(g) 27.0 275 68.1 76.2 6.3 11.4 0.56 .sup.aRuns 1(a), 1(b): molar
ratios C.sub.2H.sub.6/O.sub.2 = 2.0:1; H.sub.2/O.sub.2 = 2.0:1;
9.76% N.sub.2 dilution; flow rate = 7.167 slpm; GHSV = 112,658
h.sup.-1; 1.35 bar abs; adiabatic temperature = (a) 975.degree. C.,
(b) 950.degree. C. .sup.bRuns 1(c)-1(g): molar ratios,
C.sub.2H.sub.6/O.sub.2 = 2.3:1; H.sub.2/O.sub.2 = 2.3:1; 10%
N.sub.2 dilution; flow rate = 8.0 slpm; GHSV = 125,752 h.sup.-1;
1.35 bar abs; adiabatic temperature = 925-975.degree. C.
[0127] It was observed that a catalyst comprising copper and nickel
on an alumina monolith is capable of oxidizing ethane to ethylene
under autothermal conditions. As shown in Examples 19(a) versus
19(b) and Examples 19(c)-19(e), the catalyst is more active at a
higher preheat temperature. As shown in Examples 19(e)-19(g) the
catalyst is relatively stable for several hours.
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