U.S. patent application number 10/263324 was filed with the patent office on 2003-07-10 for integrated oxidative dehydrogenation/carbon filament production process and reactor therefor.
This patent application is currently assigned to Conoco Inc.. Invention is credited to Allison, Joe D., Carmichael, Lisa M., Meyer, Larry M., Ramani, Sriram, York, Kenneth M..
Application Number | 20030129121 10/263324 |
Document ID | / |
Family ID | 26949773 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030129121 |
Kind Code |
A1 |
Allison, Joe D. ; et
al. |
July 10, 2003 |
Integrated oxidative dehydrogenation/carbon filament production
process and reactor therefor
Abstract
The present invention includes an integrated process for the
production of carbon filaments, comprising converting a portion of
hydrocarbons to alkenes via oxidative dehydrogenation and further
converting a portion of the alkenes to carbon filaments via contact
with a metal catalyst. A portion of unconverted hydrocarbons
remaining after oxidative dehydrogenation may also be further
converted to carbon filaments via contact with the metal catalyst.
The conversion of hydrocarbons to alkenes via oxidative
dehydrogenation and further conversion of the alkenes and
unconverted hydrocarbons to carbon filaments via contact with a
metal catalyst may be carried out in the same or separate reactor
vessels. A plurality of reactor vessels arranged in parallel may be
used for the conversion of the alkenes and unconverted hydrocarbons
to carbon filaments.
Inventors: |
Allison, Joe D.; (Ponca
City, OK) ; Carmichael, Lisa M.; (Ponca City, OK)
; Meyer, Larry M.; (Ponca City, OK) ; York,
Kenneth M.; (Ponca City, OK) ; Ramani, Sriram;
(Ponca City, OK) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCOPHILLIPS COMPNAY
P.O. BOX 1267
PONCA CITY
OK
74602-1267
US
|
Assignee: |
Conoco Inc.
Houston
TX
|
Family ID: |
26949773 |
Appl. No.: |
10/263324 |
Filed: |
October 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60346573 |
Jan 4, 2002 |
|
|
|
Current U.S.
Class: |
423/447.3 |
Current CPC
Class: |
D01F 9/1271 20130101;
D01F 9/1273 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
423/447.3 |
International
Class: |
D01F 009/12 |
Claims
What is claimed is:
1. An integrated process for the production of carbon filaments,
comprising converting a portion of hydrocarbons to alkenes via
oxidative dehydrogenation and further converting a portion of the
alkenes to carbon filaments via contact with a metal catalyst.
2. The integrated process of claim 1 further comprising converting
a portion of unconverted hydrocarbons remaining after oxidative
dehydrogenation to carbon filaments via contact with the metal
catalyst.
3. The integrated process of claim 2 wherein the hydrocarbons
comprise greater than about 50% light alkanes.
4. The integrated process of claim 3 wherein the hydrocarbons
consist essentially of light alkanes.
5. The integrated process of claim 1 wherein the conversion of a
portion of the hydrocarbons to alkenes via oxidative
dehydrogenation and further conversion of a portion of the alkenes
to carbon filaments via contact with a metal catalyst are carried
out in the same reactor vessel.
6. The integrated process of claim 5 further comprising converting
an unconverted portion of hydrocarbons remaining after oxidative
dehydrogenation to carbon filaments via contact with the metal
catalyst.
7. The integrated process of claim 1 wherein the conversion of a
portion of the hydrocarbons to alkenes via oxidative
dehydrogenation is carried out in a first reactor vessel and the
further conversion of a portion of the alkenes to carbon filaments
via contact with a metal catalyst is carried out in a second
reactor vessel.
8. The integrated process of claim 7 further comprising converting
an unconverted portion of hydrocarbons remaining after oxidative
dehydrogenation to carbon filaments via contact with the metal
catalyst.
9. The integrated process of claim 7 wherein the further conversion
of a portion of the alkenes to carbon filaments via contact with a
metal catalyst is carried out in a plurality of reactor vessels
arranged in parallel.
10. The integrated process of claim 8 wherein the further
conversion of a portion of the alkenes and a portion of
hydrocarbons remaining after oxidative dehydrogenation to carbon
filaments via contact with a metal catalyst is carried out in a
plurality of reactor vessels arranged in parallel.
11. The integrated process of claim 1 wherein hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons are recovered.
12. The integrated process of claim 2 wherein hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons are recovered.
13. The integrated process of claim 5 wherein hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons are recovered.
14. The integrated process of claim 7 wherein hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons are recovered.
15. The integrated process of claim 9 wherein hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons are recovered.
16. The integrated process of claim 1 wherein unconverted
hydrocarbons remaining after the oxidative dehydrogenation are
recycled and subjected to further oxidative dehydrogenation.
17. The integrated process of claim 2 wherein unconverted
hydrocarbons remaining after the oxidative dehydrogenation are
recycled and subjected to further oxidative dehydrogenation.
18. The integrated process of claim 5 wherein unconverted
hydrocarbons remaining after the oxidative dehydrogenation are
recycled and subjected to further oxidative dehydrogenation.
19. The integrated process of claim 7 wherein unconverted
hydrocarbons remaining after the oxidative dehydrogenation are
recycled and subjected to further oxidative dehydrogenation.
20. The integrated process of claim 9 wherein unconverted
hydrocarbons remaining after the oxidative dehydrogenation are
recycled and subjected to further oxidative dehydrogenation.
21. The integrated process of claim 1 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
22. The integrated process of claim 2 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
23. The integrated process of claim 5 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
24. The integrated process of claim 7 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
25. The integrated process of claim 9 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
26. The integrated process of claim 16 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
27. The integrated process of claim 17 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
28. The integrated process of claim 18 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
29. The integrated process of claim 19 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
30. The integrated process of claim 20 wherein unconverted alkenes,
unconverted hydrocarbons, or both remaining after the contact with
the metal catalyst are recycled and subjected to further contact
with the metal catalyst.
31. The integrated process of claim 1 further comprising
graphitizing the carbon filaments.
32. A reactor for the conversion of hydrocarbons to carbon
filaments, comprising a reactor vessel having an oxidative
dehydrogenation reaction zone and carbon filament reaction zone
downstream thereof.
33. The reactor of claim 32 wherein the oxidative dehydrogenation
reaction zone further comprises a bed of oxidative dehydrogenation
catalysts and the carbon filament reaction zone further comprises a
metal catalyst.
34. An integrated process unit for the conversion of hydrocarbons
to carbon filaments, comprising an oxidative dehydrogenation
reactor wherein a portion of the hydrocarbons is converted to
alkenes and a carbon filament reactor wherein a portion of alkenes
from the oxidative dehydrogenation reactor is converted to carbon
filaments.
35. The integrated process unit of claim 34 wherein a portion of
hydrocarbons remaining unconverted after oxidative dehydrogenation
is converted to carbon filaments via contact with the metal
catalyst.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims benefit of priority from U.S.
Provisional Application Serial No. 60/346,573, filed Jan. 4, 2002,
and entitled "Integrated Oxidative Dehydrogenation/Carbon Filament
Production Process and Reactor Therefor," which is incorporated
herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] This invention generally relates to the production of carbon
filaments. More specifically, the invention relates to an
integrated process employing oxidative dehydrogenation (ODH) to
convert alkanes to alkenes (also referred to as olefins) for use as
a feedstock in carbon filament production.
BACKGROUND OF THE INVENTION
[0005] Carbon filaments, especially when combined within a polymer
matrix to form an engineered composite material, are known for
their outstanding physical properties. However, the high cost of
manufacturing carbon filaments continues as an impediment to their
widespread use, and thus an ongoing need exists for efficient
methods for producing carbon filaments.
[0006] Alkanes are saturated hydrocarbons (compounds containing
hydrogen [H] and carbon [C]) whose molecules contain carbon atoms
linked together by single bonds. The simplest alkanes are methane
(CH.sub.4), ethane (CH.sub.3CH.sub.3), and propane
(CH.sub.3CH.sub.2CH.sub.3). Olefins, also called alkenes, are
unsaturated hydrocarbons whose molecules contain one or more pairs
of carbon atoms linked together by a double bond. Generally, olefin
molecules are commonly represented by the chemical formula
CH.sub.2.dbd.CHR, where C is a carbon atom, H is a hydrogen atom,
and R is an atom or pendant molecular group of varying composition.
Olefins containing two to four carbon atoms per molecule i.e.,
ethylene, propylene, and butylenes, are gaseous at ordinary
temperatures and pressure; those containing five or more carbon
atoms are usually liquid at ordinary temperatures.
[0007] Alkanes may be dehydrogenated to form olefins. Olefins have
traditionally been produced from alkanes by direct catalytic
dehydrogenation processes such as fluid catalytic cracking (FCC) or
steam cracking, depending on the size of the alkanes. Heavy olefins
are herein defined as containing at least five carbon atoms and are
typically produced by FCC. Light olefins are defined herein as
containing two to four carbon atoms and are typically produced by
steam cracking.
[0008] In the conversion of alkanes to olefins, fluid catalytic
cracking and steam cracking (also referred to as thermal cracking)
are known to have their drawbacks. For example, the processes are
endothermic, meaning that heat is absorbed by the reactions and the
temperature of the reaction mixtures decline as the reactions
proceed. This is known to lower the product yield, resulting in
lower value products. In addition, coke forms on the surface of the
catalyst during the cracking processes, covering active sites and
deactivating the catalyst. The regeneration cycle is very stressful
for the catalyst--temperatures are high and fluctuate and coke is
repeatedly deposited and burned off. Furthermore, the catalyst
particles are moving at high speed through steel reactors and
pipes, where wall contacts and interparticle contacts are
impossible to avoid. Catalyst damage and loss are serious problems
because the catalysts used in FCC units typically employ precious
metals and thus are quite expensive. Further, because FCC and steam
cracking units are large and require steam input, the overall
processes are expensive even before taking catalyst cost into
consideration.
[0009] Oxidative dehydrogenation (ODH) of alkanes to olefins is an
alternative to FCC and steam cracking. In ODH, an organic compound
is dehydrogenated in the presence of oxygen, typically in a short
contact time reactor containing an ODH catalyst. Although oxidative
dehydrogenation usually involves the use of a catalyst (referred to
herein as an ODH catalyst), and is therefore literally a catalytic
dehydrogenation, ODH is distinct from what is normally called
"catalytic dehydrogenation" in that the former involves the use of
an oxidant, and the latter does not. In the disclosure herein,
"oxidative dehydrogenation", though employing a catalyst, will be
understood as distinct from so-called "catalytic dehydrogenation"
processes in that the latter do not involve the interaction of
oxygen with the hydrocarbon feed. More effective ODH catalysts are
highly desirable and thus are under continued development. The
capital costs for olefin production via ODH is significantly less
than with the traditional processes because of simple fixed bed
catalyst reactor designs and high volume throughput. In addition,
ODH is an autothermal process, which requires no or very little
energy to maintain the reaction. Energy savings over traditional,
endothermal processes can be significant, especially through
recycling. Also, ODH reactions are comparable in selectivity and
conversion to steam cracking.
[0010] Olefins are useful as a feedstock for carbon filament
production via catalytic thermal decomposition. In a typical
process, filaments are produced by the thermal decomposition of
hydrocarbon gas on catalysts comprising metals such as iron,
cobalt, and nickel. The hydrocarbon gas is contacted with the metal
catalyst at a temperature in the range of about 500 to 900.degree.
C., wherein the hydrocarbon gas decomposes and resultant carbon
filaments grow. Carbon filaments produced from catalytic
decomposition of hydrocarbons may have a wide variety of diameters
(from tens of angstroms to tens of microns) and structures (e.g.,
twisted, straight, helical, branched, and mixtures thereof). The
following references, each of which is incorporated herein in its
entirety, contain additional disclosure regarding the formation of
carbon filaments: Baker et al, The Formation of Filamentous Carbon,
Chemistry and Physics of Carbon Vol. 14, p. 83, Marcel Dekker, NY
(1978); Baker, Catalytic Growth of Carbon Filaments, Vol. 27, No.
3, pp. 315-23 (1989); Tibbetts, Vapor Grown Carbon Fibers, NATO ASI
Series E: Applied Sciences, Vol. 177, pp. 73-94 (1989); and Bokx et
al, The Formation of Filamentous Carbon on Iron and Nickel
Catalysts, Parts I-III, Journal of Catalysis, Vol. 96, pp. 454-90
(1985).
[0011] It has been found that ODH reaction conditions (and olefins
produced there from) are particularly well suited for integration
with carbon filament formation to achieve an efficient, integrated
process according to the present invention. In terms of product
composition, products exiting the ODH catalyst contain primarily
olefins and hydrogen with small amount of CO, CO.sub.2 and alkanes,
of which the olefins form a preferred precursor for the carbon
filament growth. In terms of energy integration, ODH reactions
result in exit gas temperatures of 800-1200.degree. C., which
decrease to the preferred range of 500-900.degree. C. by optimizing
the location of the carbon filament catalyst downstream of the ODH
catalyst. Thus, no separate heat input is needed for the carbon
filament growth. Furthermore, traditional olefin production
processes are endothermic and any subsequent (downstream) processes
that require heat input are expensive and so, avoided. This is
especially true for carbon filament production, which usually
proceeds by pyrolysis of hydrocarbons (mostly alkanes) at higher
temperatures. In contrast, an integrated process according to the
present invention is a novel, exothermal process.
SUMMARY OF THE INVENTION
[0012] The present invention includes an integrated process for the
production of carbon filaments, comprising converting a portion of
hydrocarbons to alkenes via oxidative dehydrogenation and further
converting a portion of the alkenes to carbon filaments via contact
with a metal catalyst. A portion of unconverted hydrocarbons
remaining after oxidative dehydrogenation may also be further
converted to carbon filaments via contact with the metal catalyst.
The conversion of a portion of hydrocarbons to alkenes via
oxidative dehydrogenation and further conversion of a portion of
the alkenes and unconverted hydrocarbons to carbon filaments via
contact with a metal catalyst may be carried out in the same or
separate reactor vessels. A plurality of reactor vessels arranged
in parallel may be used for the conversion of the alkenes and
unconverted hydrocarbons to carbon filaments. Hydrogen and carbon
monoxide produced during the oxidative dehydrogenation of the
hydrocarbons may be recovered as product gases. Hydrocarbons
remaining unconverted following initial oxidative dehydrogenation
may be recycled and subjected to further oxidative dehydrogenation.
Likewise, any alkenes and unconverted hydrocarbons remaining
unconverted following initial contact with a metal catalyst may be
recycled and subjected to further contact with the metal catalyst.
The integrated process may further comprise graphitizing the carbon
filaments.
[0013] The present invention further includes a reactor for the
conversion of alkanes to carbon filaments, comprising a reactor
vessel having an oxidative dehydrogenation reaction zone and carbon
filament reaction zone downstream thereof. The oxidative
dehydrogenation reaction zone further comprises a bed of oxidative
dehydrogenation catalysts and the carbon filament reaction zone
further comprises a metal catalyst. The present invention further
includes an integrated process unit for the conversion of alkanes
to carbon filaments, comprising an oxidative dehydrogenation
reactor wherein alkanes are converted to alkenes and a carbon
filament reactor wherein alkenes from the oxidative dehydrogenation
reactor are converted to carbon filaments.
DESCRIPTION OF DRAWINGS
[0014] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings in which:
[0015] FIG. 1 is a process flow diagram of the present
invention.
[0016] FIG. 2 is a process flow diagram of a preferred embodiment
of the present invention.
[0017] FIGS. 3 and 4 are scanning electron microscopy (SEM) photos
of carbon filaments produced according to the present
invention.
[0018] FIGS. 5 and 6 are transmission electron microscopy (TEM)
photos of carbon filaments produced according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Referring to FIG. 1, feed stream 5 comprising hydrocarbons
and feed stream 7 comprising oxygen are fed to ODH reactor 10,
wherein a portion of the hydrocarbons undergo oxidative
dehydrogenation in the presence of an ODH catalyst to produce
effluent stream 15 comprising CO, CO.sub.2, H.sub.2, H.sub.2O,
olefins, and unconverted hydrocarbons. Product gases may be
separated and recovered. For example, H.sub.2 and CO may be
separated by a separator (not shown), recovered via stream 35, and
used in other industrial processes. Hydrocarbon conversion within
the CF reactor typically is less than 100 percent in a single pass,
and thus the unconverted hydrocarbons may optionally be separated
by a separator (for example, a hydrocarbon splitter, not shown) and
recycled via stream 30, preferably following removal of H.sub.2 and
CO, if applicable. Alternatively, the unconverted hydrocarbons may
be fed to the CF reactor as discussed below.
[0020] Hydrocarbons and oxygen may be fed to the ODH in separate
streams as shown or may be combined into a single feed stream.
Oxygen may be fed to the ODH reactor as pure oxygen, air,
oxygen-enriched air, oxygen mixed with a diluent, and so forth. The
hydrocarbon feedstock may be any gaseous hydrocarbon having a low
boiling point, such as ethane, natural gas, associated gas, or
other sources of light hydrocarbons having from 1 to 10 carbon
atoms. In addition, hydrocarbon feeds including naphtha and similar
feeds may be employed. The hydrocarbon feedstock may be a gas
arising from naturally occurring reserves of ethane which contain
carbon dioxide. Preferably, the feed comprises at least 50% by
volume light alkanes (.ltoreq.C.sub.10).
[0021] Any suitable reactor configuration may be employed in order
to contact the reactants with the ODH catalyst. One suitable
configuration is a fixed catalyst bed, in which the ODH catalyst is
retained within a reaction zone in a fixed arrangement. ODH
catalysts may be employed in the fixed bed regime using fixed bed
reaction techniques well known in the art. Preferably, a
short-contact time reactor (SCTR) is used, for example a
millisecond contact time reactor of the type used in synthesis gas
production. A general description of major considerations involved
in operating a reactor using millisecond contact times is given in
U.S. Pat. No. 5,654,491, which is incorporated herein by reference.
Additional disclosure regarding suitable ODH reactors and the ODH
process is provided in Schmidt et al, New Ways to Make Old
Chemicals, Vol. 46, No. 8 AIChE Journal p.1492-95 (August 2000);
Bodke et al, Oxidative Dehydrogenation of Ethane at Millisecond
Contact Times: Effect of H.sub.2 Addition, 191 Journal of Catalysis
p. 62-74 (2000); Iordanoglou et al, Oxygenates and Olefins from
Alkanes in a Single-Gauze Reactor at Short Contact Times, 187
Journal of Catalysis P. 400-409 (1999); and Huff et al, Production
of Olefins by Oxidative Dehydrogenation of Propane and Butane over
Monoliths at Short Contact Times, 149 Journal of Catalysis p.
127-141 (1994), each of which is incorporated by reference herein
in its entirety.
[0022] Within ODH reactor 10, the hydrocarbon feedstock is
contacted with the ODH catalyst as a gaseous phase mixture with an
oxygen-containing gas in a reaction zone that is maintained at
conversion-promoting conditions effective to produce the effluent
stream 15 comprising olefins. The process is operated at
atmospheric or super atmospheric pressures, the latter being
preferred. The pressures may be from about 100 kPa to about 12,500
kPa, preferably from about 130 kPa to about 5,000 kPa. The process
of the present invention may be operated at catalyst temperatures
of from about 400.degree. C. to about 1200.degree. C., preferably
from about 500.degree. C. to about 900.degree. C. The hydrocarbon
feedstock and the oxygen-containing gas are preferably pre-heated
before contact with the ODH catalyst. The hydrocarbon feedstock and
the oxygen-containing gas are passed over the ODH catalyst at any
of a variety of space velocities.
[0023] Gas hourly space velocities (GHSV) for the process, stated
as normal liters of gas per liters of catalyst per hour, are from
about 20,000 to at least about 100,000,000 hr.sup.-1, preferably
from about 50,000 to about 50,000,000 hr.sup.-1, and more
preferably from about 50,000 to about 5,000,000 hr.sup.-1.
Residence time is inversely proportional to space velocity, and
high space velocity indicates low residence time on the catalyst.
In a preferred millisecond contact time reactor, the reactant gas
mixture residence time with the ODH catalyst is no more than about
100 milliseconds.
[0024] ODH catalysts may be of any suitable form, including foam,
monolith, gauze, noodles, spheres, pills or the like, for operation
at the desired gas velocities with minimal back pressure.
Typically, ODH catalysts contain a precious metal, such as
platinum, which promotes alkane conversion to alkenes. For example,
U.S. Pat. No. 6,072,097 and WO Pub. No. 00/43336 describe the use
of platinum and chromium oxide-based monolith ODH catalysts for
ethylene production with SCTRs; U.S. Pat. No. 6,072,097 describes
the use of Pt-coated monolith ODH catalysts for use in SCTRs; and
WO Patent No. 0043336 describes the use of Cr, Cu, Mn or this mixed
oxide-loaded monolith as the primary ODH catalysts promoted with
less than 0.1% Pt, each of these references being incorporated
herein in their entirety. Alternative ODH catalysts are available
that do not contain any unoxidized metals and are activated by
higher preheat temperatures. Examples of preferred alternative ODH
catalysts that do not contain any unoxidized metal are disclosed in
copending U.S. Pat. Applications 60/309,427, filed Aug. 1, 2001 and
entitled "Oxidative Dehydrogenation of Alkanes to Olefins Using an
Oxide Surface" and 60/324,346, filed Sep. 24, 2001 and entitled
"Oxidative Dehydrogenation of Alkanes to Olefins Using Non-Precious
Metal Catalyst", which are incorporated by reference herein in
their entirety.
[0025] In a preferred embodiment of the present invention, light
alkanes and pure O.sub.2 are converted to the corresponding light
olefins in a short-contact time reactor employing a metal oxide ODH
catalyst.
[0026] In some embodiments, ODH is carried out using the
hydrocarbon and/or oxygen feed mixed with an appropriate oxidant,
steam, CO.sub.2, or various combinations thereof. Appropriate
oxidants may include, but are not limited to I.sub.2, O.sub.2, and
SO.sub.2. Use of the oxidant shifts the equilibrium of the
dehydrogenation reaction towards complete conversion through
formation of compounds containing the abstracted hydrogen (e.g.
H.sub.2O, HI, H.sub.2S). Steam may be used to activate the
catalyst, remove coke from the catalyst via a water-gas shift
reaction, or serve as a diluent for temperature control. CO.sub.2
may be present as part of the source hydrocarbon stream (for
example, natural gas) and may be beneficial in serving as a diluent
for temperature control and limiting CO.sub.2 production in the ODH
reactor.
[0027] According to the present invention, the ODH conversion is
integrated with carbon filament (CF) production to achieve an
integrated ODH/CF production process. More specifically, effluent
stream 15 comprising olefins is fed from the ODH reactor 10 to a CF
reactor 20 wherein the olefins are contacted with a metal catalyst
and a portion thereof is converted to carbon filaments, which are
recovered via stream 25. Effluent stream 15 may further comprise
unconverted hydrocarbons remaining following the ODH reaction, in
particular in the absence of a hydrocarbon splitter and recycle
stream 30 as discussed previously. Like the olefins, the
unconverted hydrocarbons are contacted with the metal catalyst and
a portion thereof converted to carbon filaments, which are
recovered via stream 25. Hydrocarbon conversion within the CF
reactor typically is less than 100 percent in a single pass, and
thus unconverted hydrocarbons and unconverted olefins from CF
reactor 20 may be further processed via recycle stream 32 to the CF
reactor.
[0028] The CF catalyst may be any known catalyst for the production
of carbon filaments from olefins and/or hydrocarbons, and is
preferably a metal catalyst, defined herein as comprising elemental
iron, nickel, cobalt, or chromium; alloys comprising the foregoing
metals; oxides of the forgoing metals and alloys; and combinations
of the foregoing metals, alloys, and oxides. The CF catalyst may
comprise any appropriate structure such as a wire, gauze, mesh,
sheets, spheres, rods, or coated supports. Preferred CF catalysts
include Ni gauzes, a nickel-copper alloy screen or wire known as
MONEL.RTM. alloy 400 available from Marco Specialty Steel Inc., and
a nickel-chromium alloy known as Nichrome.RTM. available from Parr
Instruments, Inc.
[0029] The CF reactor 20 is configured to support the particular CF
catalyst being used and accommodate harvesting of the carbon
filaments upon completion of their growth cycle. The CF reactor 20
is further configured such that the carbon filaments can be removed
from the metal catalyst and/or reactor vessel. The CF reactor 20
may be either a batch or continuous reactor, and is preferably a
continuous reactor, thus allowing the integrated ODH/CF production
process to operate continuously. A suitable continuous reactor is
shown in FIG. 6 of Tibbetts, Vapor Grown Carbon Fibers, NATO ASI
Series E: Applied Sciences, Vol. 177, pp. 78 (1989). Alternatively,
one or more reactors such as second carbon filament reactor 40 may
be placed in parallel with carbon filament reactor 20, allowing for
the integrated ODH/CF production process to operate continuously by
switching feed stream 15 between the two reactors as needed for
reactor servicing, carbon filament product recovery, etc. While not
shown, recycle may be employed with additional reactors as shown
and discussed for CF reactor 20.
[0030] As an alternative to separate ODH and CF reactors, a single,
combined-process reactor as shown in FIG. 2 may be employed. The
combined ODH/CF reactor may be arranged vertically, as shown in
FIG. 2, or horizontally. Feed stream 5 comprising hydrocarbons and
feed stream 7 comprising oxygen are fed to combined ODH/CF reactor
50. Composition and configuration of the hydrocarbon and oxygen
feed streams may be varied as discussed previously with regard to
the embodiment shown in FIG. 1.
[0031] The oxygen and hydrocarbon feed come into contact with ODH
catalyst bed 52, wherein a portion of the hydrocarbon and oxygen
feed is converted to olefins. Upon exiting the ODH catalyst bed,
the reactor contents comprise unconverted hydrocarbons and oxygen
feed, mixed olefins corresponding to the composition of the
hydrocarbon feedstream, hydrogen, carbon monoxide, carbon dioxide,
and water. A CF catalyst 54 is positioned in the reactor downstream
from the ODH catalyst bed. As the reactor contents flow through the
reactor, the olefins produced in the ODH catalyst bed and
unconverted hydrocarbons come into contact with the CF catalyst,
resulting in carbon filament growth thereon. Carbon filaments are
removed from the reactor via carbon filament product stream 56. The
carbon filaments may be removed as a continuous operation, or two
or more batch type ODH/CF reactors can be employed in parallel,
with carbon filament production and recovery alternating among the
reactors as described previously to maintain a continuous CF
production process. Downstream from the CF catalyst, the reactor
contents exit the reactor via effluent stream 58 and comprise
unconverted hydrocarbon and oxygen feed, mixed olefins (if any
remain following conversion to carbon filaments), hydrogen, carbon
monoxide, carbon dioxide, and water. Prior to exiting the ODH/CF
reactor 50, the reactor contents are optionally quenched (i.e.,
rapidly cooled), for example though use of a cooling jacket 60.
Unconverted hydrocarbons and unconverted olefins (if any) in
effluent stream 58 may be further processed via recycle stream 62.
Optionally, product gases such as H.sub.2 and CO may be recovered
from effluent stream 58 via a separation process (not shown)
located either upstream (i.e., in line 58a) or downstream (i.e., in
line 58b) of the recycle stream 62, as appropriate.
EXAMPLES
[0032] The examples were carried out using a bench scale combined
ODH/CF reactor of the type shown in FIG. 2 and configured without a
recycle. The reactor comprised a 0.5 inch inside diameter quartz
tube approximately 18 inches in length and arranged vertically with
a single hydrocarbon/oxygen feed stream into the top and an
effluent stream exiting the bottom. An ODH catalyst bed was
positioned in the upper third of the reactor near the feed inlet
and a CF catalyst was positioned near the middle of the reactor,
downstream of the ODH catalyst bed. The bottom third of the
reactor, below the CF catalyst, was cooled with a cooling jacket.
The ODH catalyst used was a platinum/gold catalyst. The CF catalyst
used was a nickel-copper alloy screen or wire known as MONEL.RTM.
alloy 400 available from Marco Specialty Steel Inc. The wire was
looped back and forth into a bundle and held in place by friction
against the reactor walls. A preferred feed to the reactor
consisted essentially of a combined ethane and pure oxygen stream
of about 4-5 normal liters per minute, resulting in ethylene as a
preferred olefin following the ODH reaction. Preferably, the feed
stream was preheated to about 150-300.degree. C. before entering
the reactor. Temperatures across the ODH catalyst bed ranged from
about 800 to 1000.degree. C. upon the ODH reaction being lit off.
Temperatures across the CF catalyst ranged from about 500 to
900.degree. C., and preferably about 600 to 800.degree. C. The
pressure within the reactor was about 4 psig, with minimal (i.e.,
less than about 1 psig) pressure drop across the reactor. The
reactor was typically run in cycles of about 4-8 hours following
the ODH reaction being lit off, resulting in typical yields of
about 1-2 g of carbon filaments. The carbon filaments typically
adhered to the CF catalyst and were harvested by removing the
bottom fitting from the reactor tube and shaking and/or removing
the wire CF catalyst from the reactor. The CF catalyst was
optionally polished between cycles with an emery cloth, especially
when moderate to heavy tarnish existed on the wire following a
cycle. In Examples 1-5, operation of the experimental reactor as
described above produced the following results summarized in Table
1:
1TABLE 1 Carbon Carbon Reactor Fila- Exit Gas Carbon ODH Filament
Inlet ment Dry Duration Filament Ethane/O2 N2 Feed GHSV Preheat
Growth Temp Pressure Yield Composition Example (hrs) Catalyst Feed
Ratio (mol %) (.times.10.sup.6 hr.sup.-1) Temp (.degree. C.) Range
(.degree. C.) (psig) (grams) (mol %) 1 6 Ni--Cr 2.0 16 2.59 350 750
5.3 1.57 H.sub.2 = 31.6 C.sub.2H.sub.2 = 0.59 C.sub.3H.sub.8 = 0.05
C.sub.3H.sub.6 = 0.34 O.sub.2 = 0.33 N.sub.2 = 12.9 CO.sub.2 = 2.2
C.sub.2H.sub.4 = 22.7 C.sub.2H.sub.6 = 5.3 CH.sub.4 = 5.2 CO = 19.2
2 6 Ni--Cr 2.0 10 1.96 350 550-900 4.4 1.15 Not Available 3 7 Ni
2.1 10 1.96 350 500-900 4.1 0.75 H.sub.2 = 30.8 C.sub.2H.sub.2 =
0.64 C.sub.3H.sub.8 = 0.08 C.sub.3H.sub.6 = 0.32 O.sub.2 = 0.24
N.sub.2 = 8.6 CO.sub.2 = 3.3 C.sub.2H.sub.4 = 25.8 C.sub.2H.sub.6 =
8.2 CH.sub.4 = 5.0 CO = 17.0 4 6 Ni 2.0 10 2.44 350 500-900 5.0
0.68 H.sub.2 = 31.9 C.sub.2H.sub.2 = 0.88 C.sub.3H.sub.8 = 0.07
C.sub.3H.sub.6 = 0.32 O.sub.2 = 0.29 N.sub.2 = 8.6 CO.sub.2 = 2.0
C.sub.2H.sub.4 = 25.0 C.sub.2H.sub.6 = 6.2 CH.sub.4 = 5.4 CO = 19.5
5 6 Monel .RTM. 2.0 10 2.44 350 500-900 6.7 1.4 Not Available
[0033] A representative sample of the carbon filaments produced
during the experiments had the following physical properties
as-synthesized: diameters in the range of about 10-200 nm; length
of about 10-20 microns; surface area of about 200-350 m.sup.2/g;
real density of about 1.9-2.1 g/cc; bulk density of about 0.3-0.34
g/cc; Lc (plane thickness) by XRD of about 3-5 nm; d-spacing of
about 0.33-0.35 nm, and physical structures as shown in the
electron microscopy photographs of FIGS. 3-6. Following
graphitization under nitrogen flow at 2500.degree. F. for 30
minutes, the properties are: diameters in the range of about 10-200
nm; length of about 10-20 microns; surface area of about 25-35
m.sup.2/g; real density of about 2.0-2.2 g/cc; bulk density of
about 0.32-0.34 g/cc; Lc (plane thickness) by XRD of about 10-14
nm; d-spacing of about 0.34-0.36 nm. As can be seen from FIGS. 3-4,
which are SEM photos, the carbon filaments having a variety of
physical structures are produced, including straight, twisted, and
helical carbon filaments. FIGS. 5 and 6 are TEM photos showing that
the carbon filaments may be solid filaments as shown in FIG. 5 or
may have a tubular structure (also referred to as carbon nanotubes)
as shown in FIG. 6. Carbon filaments produced in accordance with
the present invention are useful, for example, in engineered
composite materials as described previously.
[0034] While the preferred embodiments of the invention have been
shown and described, modifications thereof can be made by one
skilled in the art without departing from the spirit and teachings
of the invention. Reactor design criteria, pendant hydrocarbon
processing equipment, and the like for any given implementation of
the invention will be readily ascertainable to one of skill in the
art based upon the disclosure herein. The embodiments described
herein are exemplary only, and are not intended to be limiting.
Many variations and modifications of the invention disclosed herein
are possible and are within the scope of the invention.
Accordingly, the scope of protection is not limited by the
description set out above, but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims.
* * * * *