U.S. patent application number 10/135087 was filed with the patent office on 2002-12-05 for supported perovskite-type oxides and methods for preparation thereof.
Invention is credited to Acharya, Divyanshu R., Bulow, Martin, Fitch, Frank R., Tamhankar, Satish S., Wolf, Rudolph J., Zeng, Yongxian.
Application Number | 20020179887 10/135087 |
Document ID | / |
Family ID | 26832969 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020179887 |
Kind Code |
A1 |
Zeng, Yongxian ; et
al. |
December 5, 2002 |
Supported perovskite-type oxides and methods for preparation
thereof
Abstract
Supported perovskite-type oxides are described. The
perovskite-type oxides have the general formula of
A.sub.xA'.sub.x'B.sub.yB'.sub.y'O.sub.3-.sub.- .sup..delta.,
wherein A is an ion of a metal of Group IIIa or IIIb of the
periodic table of elements or mixtures thereof; A' is an ion of a
metal of Groups Ia or IIa of the periodic table or mixtures
thereof; B and B' are ions of a d-block transition metal of the
periodic table or mixtures thereof; x, x', y and y' vary from 0 to
1; 0.95<x+x'<1.05; 0.95<y+y'<1.05; .delta. is the
deviation from ideal oxygen stoichiometry. This invention also
provides for the selection of support materials and the shapes of
supported perovskite-type oxides as well as the methods for making
them.
Inventors: |
Zeng, Yongxian; (North
Plainfield, NJ) ; Wolf, Rudolph J.; (Lebanon, NJ)
; Fitch, Frank R.; (Bedminster, NJ) ; Bulow,
Martin; (Basking Ridge, NJ) ; Tamhankar, Satish
S.; (Scotch Plains, NJ) ; Acharya, Divyanshu R.;
(Bridgewater, NJ) |
Correspondence
Address: |
Philip H. Von Neida
Intellectual Property Dept.
The BOC Group, Inc.
100 Mountain Ave.
Murray Hill
NJ
07974
US
|
Family ID: |
26832969 |
Appl. No.: |
10/135087 |
Filed: |
April 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60287924 |
May 1, 2001 |
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Current U.S.
Class: |
252/373 ;
502/325; 502/406; 95/96 |
Current CPC
Class: |
B01J 23/83 20130101;
B01D 2253/306 20130101; B01J 20/3042 20130101; B01J 20/3289
20130101; B01J 37/03 20130101; C01B 2203/043 20130101; Y02P 20/52
20151101; B01D 53/053 20130101; B01D 53/02 20130101; B01D 2253/304
20130101; B01J 2523/00 20130101; B01J 20/103 20130101; B01D 2253/25
20130101; B01D 53/0462 20130101; B01D 2253/106 20130101; B01D
2253/342 20130101; B01J 20/28057 20130101; B01J 2220/42 20130101;
B01J 20/28042 20130101; B01J 20/28004 20130101; C01B 2203/1088
20130101; C01B 2203/82 20130101; B01J 20/0207 20130101; C01B 3/40
20130101; B01J 2523/24 20130101; B01J 2523/842 20130101; B01J
2523/845 20130101; B01J 2523/3706 20130101; B01J 2523/24 20130101;
B01J 2523/845 20130101; B01J 2523/842 20130101; B01J 2523/3706
20130101; B01J 2523/847 20130101; C01B 2203/1064 20130101; C01B
2203/1241 20130101; C01B 3/382 20130101; B01J 20/3007 20130101;
B01J 23/002 20130101; B01J 20/0233 20130101; B01J 20/3078 20130101;
B01J 20/305 20130101; C01B 2203/142 20130101; B01J 37/0009
20130101; B01J 2523/00 20130101; B01J 20/28019 20130101; B01D
2253/112 20130101; B01D 2253/104 20130101; C01B 2203/1047 20130101;
C01B 3/386 20130101; C01B 2203/1082 20130101; B01D 2253/308
20130101; B01J 20/041 20130101; B01J 20/06 20130101; B01J 20/08
20130101; B01J 20/28045 20130101; B01J 20/3236 20130101; B01J
2523/00 20130101; C01B 2203/0244 20130101; B01J 20/3021 20130101;
C01B 2203/1052 20130101; B01J 20/0225 20130101; C01B 2203/0205
20130101; B01J 20/3204 20130101; C01B 2203/0844 20130101 |
Class at
Publication: |
252/373 ; 95/96;
502/406; 502/325 |
International
Class: |
C01B 003/26; B01J
023/00; B01J 020/02; B01D 053/047 |
Claims
Having thus described the invention, what we claim is:
1. A composition comprising a supported perovskite-type oxide
having a general formula
A.sub.xA'.sub.x'B.sub.yB'.sub.y'O.sub.3-.sub..sup..delta.- ,
wherein: A is an ion of a metal of Group IIIa or IIIb of the
periodic table of elements or mixtures of these; A' is an ion of a
metal of Groups Ia or IIa of the periodic table of elements or
mixtures of these; B and B' are ions of a d-block transition metal
of the periodic table of elements or mixtures of these; x, x', y
and y' range from 0 to 1.05; 0.95<x+x'<1.05;
0.95<y+y'<1.05; and .delta. is the deviation from ideal
oxygen stoichiometry:
2. The composition as claimed in claim 1 wherein A is an La ion, A'
is an Sr ion; and B and B' are selected from the group consisting
of Ni, Co and Fe ions.
3. The composition as claimed in claim 1 wherein said supported
perovskite-type oxide has the formula
La.sub.xSr.sub.x'Ni.sub.yCo.sub.y'
Fe.sub.y"O.sub.3-.sub..sup..delta., wherein x, x', y, y' and y" are
all smaller than 1.05 but greater than 0.
4. The composition as claimed in claim 3 wherein 0.5<x<1,
0.1<x'<0.5, 0.2<y<0.8, 0.2<y'<0.6 and
0.1<y"<0.5.
5. The composition as claimed in claim 1 wherein said
perovskite-type oxide has particle sizes in the range of about 0.01
to 100 microns.
6. The composition as claimed in claim 1 wherein said
perovskite-type oxide has particle sizes in the range of about 0.1
to 50 microns.
7. The composition as claimed in claim 1 wherein said support is
selected from the group consisting of porous inorganic materials,
which are stable at temperatures in the range of 600-1200.degree.
C.
8. The composition as claimed in claim 1 wherein said support is
selected from the group consisting of: (1) metal oxides; (2)
aluminates; (3) metal aluminum silicates, and (4) metals.
9. The composition as claimed in claim 8 wherein said metal oxides
are selected from the group consisting of alpha-Al.sub.2O.sub.3,
gamma-Al.sub.2O.sub.3, eta-Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2,
MgO, CeO.sub.2, CaO and SiO.sub.2.
10. The composition as claimed in claim 8 wherein said aluminate is
selected from the group consisting of MgAl.sub.2O.sub.4 and
CaAl.sub.2O.sub.4.
11. The composition as claimed in claim 8 wherein said metal
aluminum silicate is a cordierite.
12. The composition as claimed in claim 8 wherein said metal is a
porous high nickel containing alloy.
13. The composition as claimed in claim 1 wherein said support is
selected from the group consisting of alpha-Al.sub.2O.sub.3,
gamma-Al.sub.2O.sub.3 and eta-Al.sub.2O.sub.3 or mixtures of
these.
14. The composition as claimed in claim 1 wherein said support is
selected from the group of cordierites consisting of
Mg.sub.2Al.sub.3 [AlSi.sub.5O.sub.18] and Fe.sub.2Al.sub.3
[AlSi.sub.5O.sub.18].
15. The composition as claimed in claim 1 wherein said support is
MgAl.sub.2O.sub.4.
16. The composition as claimed in claim 1 wherein said support has
particle sizes in the range of about 1 to 10,000 microns.
17. The composition as claimed in claim 16 wherein said support has
particle sizes in the range of about 10 to 1,000 microns.
18. The composition as claimed in claim 1 which is prepared by
dispersing perovskite-type oxides onto the selected support with or
without the aid of a liquid solvent; and treating the mixture of
perovskite-type oxide and support at a temperature of
600-1,500.degree. C.
19. The composition as claimed in claim 1 wherein said supported
perovskite-type oxide has the shape selected from the group
consisting of beads, rings, extrudates with any cross sectional
shapes with or without holes, honey-comb with uniform channels and
monolith with random porosity and foam structure.
20. The composition as claimed in claim 19 wherein the shape is
selected from the group consisting of monolith or extrudates with
cylindrical shape.
21. The composition as claimed in claim 1 further comprising
additives useful in the forming process and useful to control the
pore structure.
22. The composition as claimed in claim 21 wherein said additives
are selected from the group consisting of water, organic solvents,
cellulose, polymers, synthetic and naturally formed fibers, starch
and metal oxides.
23. The composition as claimed in claim 22 wherein said additives
are selected from the group consisting of water, cellulose, about
0.1 to 1 wt % MgO and about 0.1 to 0.5 wt % TiO.sub.2.
24. The composition as claimed in claim 1 having pore sizes in the
range of about 0.001 to 10 microns, and surface area in the range
of 1 to 200 m.sup.2/g.
25. The composition as claimed in claim 1 can be coated on one or
more support materials to achieve an increase in performance, and
enhancement of thermal and mechanical properties.
26. The composition as claimed in claim 1 be further coated or
impregnated with metals selected from transition and noble metals
selected from the group consisting of Rh, Pt, and Ag.
27. The composition as claimed in claim 24 having pore size in the
range of 0.01-1 microns and surface area in the range of 1 to 50
m2/g.
28. The composition as claimed in claim 1, which is formed by
extrusion.
29. The composition as claimed in claim 28 wherein said extrusion
is performed using screw extrusion methods.
30. The composition as claimed in claim 1, which is formed by
pressing procedures.
31. A method of separating a gas component from a mixture of gases
by either of pressure swing adsorption or thermal swing adsorption
comprising passing said gas mixture through the composition as
claimed in claim 1.
32. A method for converting hydrocarbons into hydrogen and carbon
monoxide by contacting said hydrocarbons with a composition as
claimed in claim 1.
33. The method as claimed in claim 32 wherein reactions of partial
oxidation, steam reforming, or auto-thermal reforming, take place
in either continuous or cyclic operations.
Description
[0001] This application claims priority from U.S. Provisional
Patent Application Serial No. 60/287,924 filed May 1, 2001.
FIELD OF THE INVENTION
[0002] This invention relates generally to supported
perovskite-type oxides, for hydrocarbon oxidation, steam methane
reforming, auto-thermal reforming, cyclical auto-thermal reforming
(CAR) and high temperature air separation. More particularly, this
invention relates to perovskite-type oxides displaying significant
oxygen storage capability and high oxygen exchange rate at high
temperature. Even more particularly, the present invention relates
to the methods of making the supported perovskite-type oxides
having the general formula of A.sub.xA'.sub.x'B.sub.yB'.sub.y'O.su-
b.3-.sub..sup..delta..
BACKGROUND OF THE INVENTION
[0003] Most perovskite-type ceramic materials with a general
formula of ABO.sub.3-.sub..sup..delta. are mixed electronic and
oxygen ion conductors at high temperature and are known to be
suitable materials for making dense oxygen semi-permeable
membranes. These membranes hold promising applications in air
separation and partial oxidation of hydrocarbons to hydrogen and
carbon monoxide. Despite tremendous interest and efforts from both
academic institutes and industrial companies, the applications of
dense ceramic membranes made of perovskite-type oxides are still
facing many technical challenges. These include fabrication of
pin-hole free dense membranes, developing high temperature sealing
and joining techniques to integrate a particular membrane with
other parts of the reactor system, and controlling the chemical and
mechanical stability of the membrane during the harsh operating
conditions. In addition, there are issues related to safety and
economy of ceramic membrane reactor applications.
[0004] It has been discovered by the present inventors that
perovskite-type oxides in non-membrane form exhibit both good
oxygen storage capability and/or catalytic properties for
high-temperature air separation, total combustion, partial
oxidation and steam reforming reactions. Historically,
perovskite-type oxides in non-membrane form for a high-temperature
air separation process as well as in a cyclic auto-thermal
reforming (CAR) process have been disclosed. In the CAR process,
air and natural gas/steam mixture are contacted alternately with
perovskite-type oxides. The present inventors have further
discovered that perovskite-type oxides, when supported by porous
support, show higher reactivity and faster oxygen exchange rate
than the unsupported ones.
SUMMARY OF THE INVENTION
[0005] The present invention relates to perovskite-type oxides in
non-membrane form with high oxygen-storage capability and oxygen
exchange rate at high temperature while having good catalytic
properties for oxidation reactions. Further, the present invention
provides for supported perovskite-type oxides with improved
performance compared to that of the unsupported ones. These
supported perovskite-type oxides are particularly useful for high
temperature air separation processes, via pressure swing adsorption
(PSA) or thermal swing adsorption (TSA), and for the conversion of
hydrocarbons into products that contain hydrogen and carbon
monoxide, via partial oxidation, steam reforming, or auto-thermal
reforming, in continuous or cyclical operations (CAR process).
Methods for making supported perovskite-type oxides also forms part
of the present invention.
[0006] The perovskite-type oxides having a general formula of
A.sub.1-xA'.sub.xB.sub.1-yB'.sub.yO.sub.3-.sub..sup..delta., where
A is an ion of a metal of Groups IIIa or IIIb of the periodic table
of elements; A' is an ion of a metal of Groups Ia or IIa of the
periodic table; B and B' are ions of a d-block transition metal of
the periodic table; x and y vary from 0 to 1.05; .delta. is the
deviation from ideal oxygen stoichiometry. The perovskite-type
materials can be A-site or B-site rich compositions as long as the
perovskite phase structure is maintained. For a general composition
of A.sub.xA'.sub.xB.sub.yB'.sub.y'O- .sub.3-.sub..sup..delta.,
A-site rich means x+x'>1 while y+y'<or=1, and B-site rich
means x+x'<or=1 while y+y'>1.
[0007] In a preferred embodiment, the perovskite-type oxides have
A-sites containing La and Sr ions and B-sites containing Ni, Co and
Fe ions. In a more preferred embodiment, the perovskite-type oxides
have a formula of La.sub.xSr.sub.x'Ni.sub.yCo.sub.y'
Fe.sub.y"O.sub.3-.sub..sup..delta., in which x, x', y, y' and y"
are all smaller than 1.05 but greater than 0. In the most preferred
embodiment, the perovskite-type oxides have a formula of
La.sub.xSr.sub.x'Ni.sub.yCo.sub.y' Fe.sub.y"O.sub.3-.sub..sup.-
.delta., in which 0.5<x<1, 0.1<x'<0.5, 0.2<y<0.8,
0.2<y'<0.6 and 0.1<y"<0.5.
[0008] In a preferred embodiment, the perovskite-type oxides have
particle sizes in the range of about 0.01 to 100 microns. In a more
preferred embodiment, the perovskite-type oxides have particle
sizes in range of about 0.1 to 50 microns.
[0009] The present invention further comprises appropriate carriers
that vary widely in their porosity, for supporting perovskite-type
oxides. In a preferred embodiment, the support materials are
selected from: (1) metal oxides such as alpha-Al.sub.2O.sub.3,
gamma-Al.sub.2O.sub.3, eta-Al.sub.2O.sub.3, ZrO.sub.2, MgO,
CeO.sub.2, CaO and SiO.sub.2; (2) aluminates such as
MgAl.sub.2O.sub.4 and CaAl.sub.2O.sub.4; (3) metal aluminum
silicates such as cordierites; (4) metals such as porous high
nickel containing alloy. In a more preferred embodiment, the
support materials are selected from alpha-Al.sub.2O.sub.3,
gamma-Al.sub.2O.sub.3 and eta-Al.sub.2O.sub.3 or mixtures thereof.
In another more preferred embodiment, the support materials are
selected from cordierites such as Mg.sub.2Al.sub.3
[AlSi.sub.5O.sub.18] and Fe.sub.2Al.sub.3 [AlSi.sub.5O.sub.18], or
related derivatives stable at high temperature. In yet another more
preferred embodiment, the support material is MgAl.sub.2O.sub.4.
The thermal expansion properties of the supports have to be
controlled carefully to ensure stability of the final product with
regard to temperature changes.
[0010] In a preferred embodiment, the supported perovskite-type
oxides can be further coated on one or more other support materials
to achieve an increase in performance, and enhancement of thermal
and mechanical properties.
[0011] In another preferred embodiment of the present invention,
the support material has particle sizes in the range of about 0.1
to 10,000 microns. In a more preferred embodiment, the support
material has particle sizes in the range of about 5 to 1,000
microns.
[0012] The present invention also provides for methods of preparing
supported perovskite-type oxides. The methods comprise dispersing
perovskite-type oxides onto the selected support with or without
the aid of a liquid solvent. The methods further comprise treating
the mixture of perovskite-type oxide and support at a high
temperature to form close bonding between adjacent particles of
perovskite-type oxides and the support.
[0013] Another object of the present invention is to provide the
supported perovskite-type oxides with appropriate macroscopic
particle shapes. In a preferred embodiment, the shapes of the
supported perovskite-type oxides are selected from beads, rings,
extrudates, pellets with any cross-sectional shapes with or without
holes, honeycomb-type structures with uniform channels and
monolithic ones with random porosity and/or foam structure. In a
more preferred embodiment, the shapes of the supported
perovskite-type oxides are selected from those of monolithic
structures and extrudates particularly with cylindrical shape. The
extrudates are formed by extrusion, particularly screw extrusion.
Alternatively, there are various pressing procedures, which can be
utilized to shape the perovskite-type oxides, and these procedures
provide good mechanical stability of the resulting shaped
material.
[0014] Appropriate additives will help the shape forming process
and control the desired pore structure within the shape. In a
preferred embodiment, the additives are selected from water,
organic solvents, cellulose, polymers, synthetic and naturally
formed fibers, starch and metal oxides. In a more preferred
embodiment, the additives are water, various types of cellulose
with particle sizes compatible with those of the components to be
shaped, about 0.1 to 1 wt % MgO and about 0.1 to 0.5 wt %
TiO.sub.2.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention relates to a composition of
perovskite-type materials supported by a solid carrier, methods for
fabricating the perovskite-type material on the carrier and their
use in high-temperature air separation, total combustion, partial
oxidation and steam reforming reactions. The perovskite-type
materials have a general formula of
A.sub.1-xA'.sub.xB.sub.1-yB'.sub.yO.sub.3-.sub..sup..delta., where
A is an ion of a metal of Group IIIa and IIIb of the periodic table
of elements; A' is an ion of a metal of Groups la and Ha of the
periodic table; B and B' are ions of a d-block transition metal of
the periodic table; x and y vary from 0 to 1.05; .delta. is the
deviation from ideal oxygen stoichiometry. The perovskite-type
materials can be A-site or B-site rich compositions as long as the
perovskite phase structure is maintained. For a general composition
of A.sub.xA'.sub.x'B.sub.yB'.sub.y'- O.sub.3-.sub..sup..delta.,
A-site rich means x+x'>1 while y+y'<or=1, and B-site rich
means x+x'<or=1 while y+y'>1. In general, most
perovskite-type oxides have certain oxygen storage and catalytic
properties. It was found that the compositions of perovskite-type
oxides were critical to their oxygen storage capacity and catalytic
properties. For example, the perovskite-type oxides with A-site
containing La and Sr ions and B-sites containing Ni, Co and Fe ions
showed very good oxygen storage and catalytic properties for cyclic
auto-thermal reforming (CAR) process.
[0016] The methods for synthesis of perovskite-type materials are
well known in literature. The commonly used methods are: (1)
solid-state reaction; (2) combustion synthesis; (3) citrate method;
(4) co-precipitation method; (5) sol-gel method, and (5)
spray-pyrolysis method. Although different synthesis methods may
result in different particle sizes and surface properties, they
produce the perovskite-type oxides with the same phase structure,
i.e. perovskite-type structure, which can be characterized by X-ray
diffraction measurement. The appropriate particle sizes of
perovskite-type oxide powders for making supported perovskite-type
oxides are in the range of 0.01 to 100 microns.
[0017] The requirement on the support materials include: (1)
resistant to high temperature, i.e., 600 to 1200.degree. C.; (2)
maintaining appropriate pore structure at high temperature; (3)
good affinity for perovskite-type oxides but not having significant
reactions with perovskite-type oxides; (4) good mechanical strength
at both low and high temperatures; (5) low thermal expansion. The
suitable support materials include: (1) metal oxides such as
alpha-Al.sub.2O.sub.3, gamma-Al.sub.2O.sub.3, eta-Al.sub.2O.sub.3,
ZrO.sub.2, TiO2, MgO, CeO.sub.2, CaO and SiO.sub.2; (2) aluminates
such as MgAl.sub.2O.sub.4 and CaAl.sub.2O.sub.4; (3) metal aluminum
silicates, such as cordierites; (4) metals such as porous high
nickel containing alloy. The preferred selections are
alpha-Al.sub.2O.sub.3, gamma-Al.sub.2O.sub.3 and
eta-Al.sub.2O.sub.3 and mixtures thereof. The other class of
preferred supports are cordierites such as Mg.sub.2Al.sub.3
[AlSi.sub.5O.sub.18] and Fe.sub.2Al.sub.3 [AlSi.sub.5O.sub.18], or
related derivatives stable at high temperature. The particle size
of the supports should be compatible with the particle size of the
perovskite powder. The appropriate particle size range is about 1
to 10,000 microns.
[0018] In a preferred embodiment, the supported perovskite-type
oxides can be further coated on one or more other support materials
to achieve an increase in performance, thermal and mechanical
properties. In another preferred embodiment, the supported
perovskite-type oxides can be further coated or impregnated with
metals selected from transition and noble metals, such as Rh, Pt,
Ag, etc.
[0019] Once a perovskite-type powder has been synthesized and the
support selected, the task is to coat the perovskite-type powder
onto the support. The methods to do this include: (1) dry coating;
and (2) wet coating. In dry coating, the perovskite-type powders
and support particles are physically mixed together and uniformly
distributed. This mixture is then subjected to high temperature
sintering, resulting in strong bonding between the perovskite and
the support. In wet coating method, both perovskite and support are
dispersed in a liquid solvent to form a uniform suspension. The
solid mixture after filtration is then dried and sintered. The wet
coating method also includes sol-gel method in which the
perovskite-type oxides (or precursors) are synthesized in a form of
sol. The perovskite-type oxides in the form of sol are then coated
or impregnated onto the support. The preferred coating method of
this invention is that of dry coating.
[0020] It is necessary that the supported perovskite-type oxides
are formed into appropriate shapes to achieve higher mass and heat
transfer rates, higher surface area, enhanced resistance to
attrition and fluidization compared to those features of the
perovskite-type oxides without support. These shapes include beads,
rings, extrudates, pellets with any cross-sectional shapes with or
without holes, honeycomb structures with uniform channels and
monolithic ones with random porosity and/or foam structure. The
preferred shapes of this invention are extrudates and monolithic
structures. The monolithic and honeycomb structures can be used
either in a single piece or stacked pieces packed randomly in a
reactor bed. There are many forming methods to fabricate those
shaped structures, such as extrusion using dies with differently
shaped channels, agglomeration, tape casting, foam casting, etc.
The preferred shape forming method in this invention is extrusion,
particularly screw extrusion. Alternatively, there are a number of
pressing procedures which also provide good mechanical stability
which can be utilized to shape the perovskite-type oxides.
[0021] In many cases, solvents, binders, sintering aids and
pore-forming additives are added into the supported perovskite-type
oxide powders before shaping the material. This is to optimize the
plasticity of the materials and to control the green strength of
the shaped material as well as to promote the sintering and to
control the pore structure of the final products. These additives
and aids include: water, organic solvents, various types of
celluloses with particle sizes compatible with those of the
components to be shaped, polymers, fibers of both synthetic and
naturally formed, starches and small amount of metal oxides such as
MgO and TiO.sub.2. The selected combination and the amounts of
these additives and aids are critical to achieve desired products.
After shape forming, the green body is subjected to drying,
calcination and sintering to remove the organic additives and gain
good bonding and mechanical strength.
[0022] The pore size distribution and surface area of the supported
perovskite-type oxides are critical to the performance. The
preferred pore size and the surface area are respectively in the
range of about 0.001 to 10 microns and a surface area in the range
of about 1 to 200 m.sup.2/g. In a preferred embodiment, the
supported perovskite oxides have a pore size in the range of about
0.01 to 1 microns and a surface area in the range of about 1 to 50
m.sup.2/g.
[0023] The following represent examples of making perovskite-type
oxide powders and supported perovskite-type oxide extrudates: They
should be considered merely as examples of the present invention
and not as limiting the scope thereof.
EXAMPLE 1
Preparation of 6.56 g
La.sub.0.5Sr.sub.0.5Co.sub.0.5Fe.sub.0.5O.sub.3-.sub- ..sup..delta.
Perovskite-type Oxide by Co-precipitation Method.
[0024] The preparation started with respectively dissolving 4.87 g
La(NO.sub.3).sub.3, 3.17 g Sr(NO3)2, 4.36 g Co(NO3)2.6H2O, 6.06 g
Fe(NO3)3 into 50 ml deionised water and 15.13 g oxalic acid into
100 ml deionised water. The above-made metal nitrate solution was
dropped into above-made oxalic acid solution at a rate of 0.5
drop/second while stirring until finished. The solid precipitate
was collected by filtration and dried at 100.degree. C. overnight
in an oven, and then placed in a furnace and heated up at
20.degree. C./min up to 600.degree. C. The solid was held at
600.degree. C. for 1 hour, resulting in pyrolysis. The residual was
calcined at 900.degree. C. for 2 hours. The perovskite-type powder
of La.sub.0.5Sr.sub.0.5Co.sub.0.5Fe.sub.0.5O.sub.3-
-.sub..sup..delta. was thus produced. Its XRD pattern is shown in
FIG. 1.
EXAMPLE 2
Preparation of 12.2 g
La.sub.0.2Sr.sub.0.8Co.sub.0.5Fe.sub.0.5O.sub.3-.sub- ..sup..delta.
Perovskite-type Oxide by Citrate Method.
[0025] The preparation was started by dissolving 3.9 g
La(NO.sub.3).sub.3, 10.16 g Sr(NO.sub.3).sub.2, 8.73 g
Co(NO.sub.3).sub.26H2O, 12.12 g Fe(NO.sub.3).sub.3 into 800 ml
dilute HNO.sub.3 solution (720 ml deionised water and 80 ml
concentrated HNO.sub.3). 34.6 g citric acid was added to the
above-made metal nitrate solution. The solution was then heated to
90-110.degree. C. with reflux for 3 hours. After that, water was
gradually removed from the solution by evaporation until a gel-like
"polymer" was formed. This gel was collected and dried at
90.degree. C. overnight in an oven, and then subjected to a
temperature of 500.degree. C. for 1 hour. The charred material was
collected, ground and sintered at 900.degree. C. for 10 hour. The
perovskite-type powder of
La.sub.0.5Sr.sub.0.5Co.sub.0.5Fe.sub.0.5O.sub.3-.sub..sup..delta.
was thus produced. Its XRD pattern is shown in FIG. 2.
EXAMPLE 3
Preparation of 20 g
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.su-
b.3-.sub..sup..delta. Perovskite-type Oxide by Combustion Synthesis
Method.
[0026] The preparation was started by dissolving 29.5 g
La(NO.sub.3).sub.3,6H2O, 3.60 g Sr(NO.sub.3).sub.2, 9.91 g
Ni(NO.sub.3)2.6H2O, 9.91 g Co(NO.sub.3).sub.26H2O, and 6.88 g
Fe(NO.sub.3).sub.3,9H2O into 400 ml deionised water. 32.0 g glycine
(H.sub.2NCH.sub.2CO.sub.2H) was then added to the above-made
solution. This solution was heated up to 90-100.degree. C. while
stirring for about 3 hours with reflux. The water was then
evaporated and a concentrated solution of about 100 ml was
obtained, which was transferred into an alumina crucible and placed
into a box furnace pre-heated at 250.degree. C. The solution was
further concentrated and formed a gel-like material, which was
quickly combusted as the furnace temperature was increased to
400.degree. C. The residue was collected and ground into powder.
This powder was then sintered at 900.degree. C. for 8 hours. The
perovskite-type powder of
La.sub.0.8Sr.sub.0.2CO.sub.0.4Ni.sub.0.4Fe.sub.-
0.2O.sub.3-.sub..sup..delta. was thus produced. Its XRD pattern is
shown in FIG. 3.
EXAMPLE 4
Preparation of 500 g
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.s-
ub.3-.sub..sup..delta. Perovskite-type Oxide by Solid State
Reaction Method.
[0027] The powder of perovskite-type oxide was prepared first by
mixing of corresponding metal oxides and then under repeated steps
of sintering, ball-milling and filtration for three times. The
sintering steps lasted for 8 hours at ramp and cooling rates of
3.degree. C./min. The sintering temperatures in 3 repeat steps
were, respectively, 1000.degree. C., 1250.degree. C. and
1300.degree. C., and the sintering time was 8 hours. The first
sintering was conducted right after dry-mixing of La.sub.2O.sub.3,
Sr(OH).sub.28H.sub.2O, Ni.sub.2O.sub.3, Co.sub.2O.sub.3 and
Fe.sub.2O.sub.3. The ball milling of the material was carried out
with grinding the media and water after each sintering. The solid
was collected by filtration after ball milling. The filtration cake
was dried at 100.degree. C. over night before it was subjected to
the next sintering. After the last ball-milling, the dried
filtration cake was crushed and ground into fine powder. The powder
had a perovskite-type phase structure as shown in FIG. 4.
EXAMPLE 5
Fabrication of
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.-
sub..sup..delta. Perovskite-type Oxide Extrudates without
Support.
[0028] The perovskite-type oxide powder made in Example 4 was
transferred into a slurry after addition of about 5 wt %
hydroxyethyl cellulose and 14.5 wt % water. The cellulose was added
first and well mixed with the solid. Water was then sprayed in,
little by little, with intermediate stirring and mixing to preserve
the homogeneity of the mixture and to avoid agglomeration. Thus
obtained slurry was aged overnight before it was loaded into an
extruder and transformed into extrudates (1/8" diameter and 1/4"
long). The extrudates were dried in an oven at 90.degree. C. for
about 2 hr. They were then heated at 3.degree. C./min to
600.degree. C. and kept at this temperature for 5 hr. After the
cellulose was burned out, the extrudates were further sintered at
1350.degree. C. for 8 hours. The final product of
La.sub.0.8Sr.sub.0.2Co.-
sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.sub..sup..delta. extrudes
appeared to be dense and mechanically strong.
EXAMPLE 6
Fabrication of 50 wt % alpha-Al.sub.2O.sub.3 Supported
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.sub..sup..delt-
a. Perovskite-type Oxide Extrudates with Support.
[0029] The perovskite-type oxide powder made in Example 4 was well
mixed with equal amount of alpha-Al.sub.2O.sub.3 powder (100 mesh).
The mixture was then sintered at 1300.degree. C. for 8 h with ramp
and cooling rates of 3.degree. C./min. After sintering, the color
of the mixture changed from black to dark blue. The resulting
powder was turned into a slurry after addition of about 5 wt %
hydroxyethyl cellulose and 20.5 wt % water. The cellulose was added
first and well mixed with the solid. Water was then sprayed in,
little by little, with intermediate stirring and mixing to preserve
the homogeneity of the mixture and to avoid agglomeration. Thus
obtained slurry was aged overnight before it was loaded into an
extruder and transformed into extrudates (1/8" diameter and 1/4"
long). The extrudates were dried in an oven at 90.degree. C. for
about 2 hr. They were then heated at 3.degree. C./min to
600.degree. C. and held at this temperature for 5 hr. After
cellulose was burned out, the extrudates were further sintered at
1350.degree. C. for 8 h. The final product of 50 wt %
LSNCF-82442/alpha-Al.sub.2O.sub.3 extrudes appeared to be porous
and mechanically strong.
EXAMPLE 7
Fabrication of 30 wt % alpha-Al.sub.2O.sub.3 and 10 wt %
Gamma-Al203 supported
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.sub.-
.sup..delta. Perovskite-type Oxide Extrudates with Support.
[0030] The perovskite-type oxide powder made in Example 4 was well
mixed with alpha-Al.sub.2O.sub.3 powder (100 mesh) at a ratio of
6:3 by weight. The mixture was sintered at 1050.degree. C. for 8 h
with ramp and cooling rates of 3.degree. C./min. After sintering,
the color of the mixture changed from black to dark blue. The
resulting powder was well mixed with gamma-Al203 at a ratio of 9:1
by weight. The mixture was then turned into a slurry after addition
of about 5 wt % hydroxyethyl cellulose and 20.5 wt % water. The
cellulose was added first and well mixed with the solid. Water was
then sprayed in, little by little, with intermediate stirring and
mixing to preserve the homogeneity of the mixture and to avoid
agglomeration. Thus obtained slurry was aged overnight before it
was loaded into an extruder and transformed into extrudates (1/8"
diameter and 1/4" long). The extrudates were dried in an oven at
90.degree. C. for about 2 hr. They were then heated at 3.degree.
C./min to 600.degree. C. and held at this temperature for 5 hr.
After cellulose was burned out, the extrudates were further
sintered at 1350.degree. C. for 8 h. The final product of 60 wt %
LSNCF-82442/30 wt % alpha-Al.sub.2O.sub.3/10 wt % gamma-Al203
extrudes appeared to be porous and mechanically strong.
EXAMPLE 8
Comparison of the Performance of Unsupported and Supported
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.sub..sup..delt-
a. Perovskite-type Oxide Extrudates for Cyclic Auto-thermal
Reforming (CAR) Process.
[0031] 200 cc of unsupported and alpha-Al.sub.2O.sub.3-supported
La.sub.0.8Sr.sub.0.2Co.sub.0.4Ni.sub.0.4Fe.sub.0.2O.sub.3-.sub..sup..delt-
a. perovskite-type oxide extrudates prepared in Example 5 and
Example 6 were loaded separately in a fixed bed reactor for two
comparison experiments. For cyclic auto-thermal reforming process,
a flow of air and a flow of methane/steam mixture were fed
alternately into the reactor. Oxygen was retained by the
perovskite-type oxide during the air step in the form of solid
phase lattice oxygen, which was reacted with methane/steam mixture
in the subsequent step to form a product containing hydrogen and
carbon monoxide. Table 1 gives the results of the experiments over
unsupported and supported extrudates. As shown in the table, the
supported extrudates had much higher methane conversion and
hydrogen and carbon monoxide concentration in the product.
1TABLE 1 CAR Process over LSNCF-82442 with and without Support
Furnace Temp. H2O/ Product Composition (%) Carbon Conversion
(H.sub.2 + CO)/CH.sub.4 .degree. C. CH4 H.sub.2 CH.sub.4 CO.sub.2
CO Balance CH.sub.4 H.sub.2O Real Ideal 50 wt %
LaSrNiCoFe-82442/Al.sub.2O.sub.3 825 (Co) 2.1 69.0 3.22 8.65 19.1
3.17 89.6 17.1 2.84 3.17 825 (Re) 2.1 68.2 3.66 9.58 18.6 -6.18
88.5 11.3 2.73 3.08 825 (Co) 1.5 67.3 4.52 7.25 20.9 -1.57 86.2
20.4 2.70 3.13 825 (Re) 1.5 66.0 4.60 8.48 20.9 -2.26 86.4 11.1
2.55 2.95 800 (Co) 2.1 66.5 5.37 7.46 20.6 -1.02 83.9 19.4 2.60
3.10 800 (Re) 2.1 65.7 5.41 8.55 20.3 -1.42 84.2 13.9 2.51 2.98 800
(Co) 2.1 66.3 5.87 7.25 20.5 0.18 82.6 21.7 2.58 3.13 Pure
LaSrNiCoFe-82442 perovskite 800 (Co) 2.1 64.5 9.0 12.5 14.0 0.9
74.8 16.2 2.2 3.0 800 (Re) 2.1 62.7 10.7 12.6 13.9 0.6 71.2 12.9
2.1 2.9 800 (Co) 3.3 61.8 11.4 14.7 12.1 2.7 70.1 7.7 1.9 2.8 800
(Re) 3.3 59.8 13.5 14.7 12.0 0 66.4 4.8 1.8 2.7 Note: ideal
(H.sub.2 + CO)/CH.sub.4 was under assumption of 100% CH.sub.4
conversion Co: Co-current flow; Re: Reverse flow
[0032] While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications of the invention will be obvious to those
skilled in the art. The appended claims in this invention generally
should be construed to cover all such obvious forms and
modifications which are within the true spirit and scope of the
present invention.
* * * * *