U.S. patent number RE34,804 [Application Number 08/002,221] was granted by the patent office on 1994-12-06 for method of producing high-strength high surface area catalyst supports.
This patent grant is currently assigned to Corning Incorporated. Invention is credited to Irwin M. Lachman, Lawrence A. Nordlie.
United States Patent |
RE34,804 |
Lachman , et al. |
December 6, 1994 |
Method of producing high-strength high surface area catalyst
supports
Abstract
A catalyst support having both substantial high strength and
high surface area can be produced by heating a shaped mixture of a
porous oxide having a surface area of at least 20 m.sup.2 /g and
the precursor of an inorganic binder for the porous oxide. The
binders are precursors of alumina, silica, or .[.titania,.].
.Iadd.zirconia .Iaddend.and are capable of imparting substantial
strength to the support at relatively low firing temperatures.
Inventors: |
Lachman; Irwin M. (Corning,
NY), Nordlie; Lawrence A. (Corning, NY) |
Assignee: |
Corning Incorporated (Corning,
NY)
|
Family
ID: |
24863911 |
Appl.
No.: |
08/002,221 |
Filed: |
January 8, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
712874 |
Mar 18, 1985 |
04631267 |
Dec 23, 1986 |
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Current U.S.
Class: |
502/64; 502/349;
502/439; 502/242; 502/263; 502/524; 502/527.19 |
Current CPC
Class: |
B01J
35/04 (20130101); B01J 37/0018 (20130101); B01J
37/0009 (20130101); Y10S 502/524 (20130101) |
Current International
Class: |
B01J
35/04 (20060101); B01J 35/00 (20060101); B01J
37/00 (20060101); B01J 029/04 (); B01J 020/28 ();
B01J 035/00 () |
Field of
Search: |
;502/527,439,64,263,351,355,524,349,242 |
References Cited
[Referenced By]
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Foreign Patent Documents
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0122572 |
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2554198 |
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DE |
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2658569 |
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DE |
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0138005 |
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JP |
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0017621 |
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JP |
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0045260 |
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JP |
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0095342 |
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Aug 1981 |
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JP |
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0035025 |
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Feb 1984 |
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JP |
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0035026 |
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Feb 1984 |
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JP |
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0035027 |
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Feb 1984 |
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JP |
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0035028 |
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Feb 1984 |
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JP |
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1064018 |
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Apr 1967 |
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GB |
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1315553 |
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May 1973 |
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GB |
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1474553 |
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May 1977 |
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GB |
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Other References
Walter Heinrich Stoepler, Investigations of the Correlation between
Structure and properties of Aluminum Oxides and their Extrusion
Behavior in the Fabrication of active, porous Aluminum Oxide
Substrates, Dissertation (1983)..
|
Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: Nwaneri; Angela N.
Claims
We claim:
1. A method of producing a monolithic catalyst support having
substantial strength and high surface area comprising:
(a) Mixing into a substantially homogeneous body
(i) a porous oxide having a surface area of at least 20 m.sup.2 /g
selected from the group consisting of zeolite, silica, alumina,
.Iadd.having a particle size of about 1-100 microns which when
calcined provides gamma-alumina or other transition alumina,
.Iaddend.spinel, .[.titania,.]. zirconia, and mixtures of
these;
(ii) a precursor of a permanent binder for the porous oxide
selected from the group consisting of alumina .[.precursors,.].
.Iadd.hydrate, aluminum propoxide, aluminum chlorohydrate,
.Iaddend.silica precursors, .[.titania precursors,.]. zirconia
.[.precursors,.]. .Iadd.hydrate, zirconium propoxide, .Iaddend.and
mixtures of these, .[.said binder precursor having a crystallite
size below 200 angstoms;.]. and
(iii) a temporary binder; and
(b) heating the body to a temperature of from
500.degree.-1000.degree. C. to result in substantial strength and
substantial surface area and to substantially completely burn off
said temporary binder.
2. The method of claim 1 in which the mixing step is performed
using 70-97 parts by weight of the porous oxide, 3-30 parts by
weight of the permanent binder precursor, and 1-20 parts by weight
of a temporary binder. .[.3. The method of claim 2 in which the
permanent binder precursor is a suspension of amorphous hydrated
titanium oxide in the form of a suspension of titanium hydrate or a
suspension of hydrolyzed titanium isopropoxide..]. .[.4. The method
of claim 2 in which the porous oxide is titania; the permanent
binder precursor is a suspension of hydrolyzed titanium
isopropoxide, aluminum chlorohydrate, or a silicone resin; and
the temporary binder is methyl cellulose..]. 5. The method of claim
2 in which the permanent binder precursor is a suspension of
amorphous hydrated zirconium oxide in the form of a suspension of
zirconium hydrate or a
suspension of hydrolyzed zirconium n-propoxide. 6. The method of
claim 2 in which the porous oxide is zirconia, the permanent binder
precursor is a suspension of hydrolyzed zirconium n-propoxide, and
the temporary binder
is methyl cellulose. 7. The method of claim 2 in which the porous
oxide has a surface are of at least 100 m.sup.2 /g and is selected
from the
group consisting of alumina, silica, zeolite, and spinels. 8. The
method of claim 7 in which the permanent binder precursor is a
suspension of hydrated alumina, aluminum chlorhydrate, or a
suspension of hydrolyzed
aluminum isopropoxide. 9. The method of claim 8 in which the porous
oxide is alumina; the permanent binder precurser is a suspension of
hydrated alumina, a suspension of hydrolyzed aluminum isopropoxide,
or aluminum
chlorohydrate; and the temporary binder is methyl cellulose. 10.
The method of claim 7 in which the porous oxide is a spinel, the
permanent binder precursor is a suspension of hydrated alumina, a
suspension of hydrolyzed aluminum isopropoxide, or aluminum
chlorohydrdate; and the
temporary binder is methyl cellulose. 11. The method of claim 7 in
which
the permanent binder precursor is a silicon resin. 12. The method
of claim 7 in which the porous oxide is silica; the permanent
binder precursor is a silicone resin, a suspension of a hydrated
alumina, a suspension of hydrolyzed aluminum isopropoxide, or
aluminum chlorohydrate; and the
temporary binder is methyl cellulose. 13. The method of claim 12 in
which
the permanent binder precursor is a silicone resin. 14. The method
of claim 7 in which the porous oxide is a zeolite; the permanent
binder precursor is a silicone resin, a suspension of a hydrated
alumina, aluminum chlorohydrate, or a suspension of hydrolyzed
aluminum
isopropoxide; and the temporary binder is methyl cellulose. 15. The
method of claim .[.4,.]. 6, 9, 10, 12, or 14 which further
comprises the step of
forming the mixed body of step (a) into the shape of a honeycomb.
16. A
catalyst support produced according to the method of claim 15. 17.
A catalyst support of claim 16 having at least 20 square meters of
surface area per gram of weight and a modulus of rupture of at
least 500 pounds
per square inch. 18. A catalyst support produced according to the
method
of claim 1 or 2. 19. A catalyst support of claim 18 which is in the
shape of a honeycomb and which has at least 20 square meters of
surface area per gram of weight and a modulus of rupture of at
least 500 pounds per square
inch. 20. A monolithic catalyst support having a modulus of rupture
of at least 500 psi, comprising 70-97 parts by weight of a high
surface area porous oxide phase and 3-30 parts by weight of a
permanent binder for the porous oxide phase dispersed throughout
wherein
(i) the porous oxide phase has a surface area of at least 20
m.sup.2 /g and consists of alumina, silica, zeolite, spinel,
zirconia, or mixtures of these; and
(ii) the binder results from heating in situ, at a temperature of
500.degree.-1,000.degree. C., a binder precursor consisting of
alumina precursors, silica precursors, zirconia precursors, or
mixtures of these,
said binder precursor having a crystallite size below 200 anstroms.
21. A catalyst support of claim 20 in which the porous oxide is a
spinel and the
binder results from an alumina precursor. 22. A catalyst support of
claim 20 in which the porous oxide is zirconia and the binder
results from a
zirconia precursor. 23. A catalyst support of claim 20 in which the
porous oxide is alumina having a surface area of at least 100
m.sup.2 /g and in which the binder results from an alumina
precursor or a silica precursor.
4. A catalyst support of claim 20 in which the porous oxide is
silica having a surface area of at least 100 m.sup.2 /g and in
which the binder
results from a silica precursor or an alumina precursor. 25. A
catalyst support of claim 20 in which the porous oxide is a zeolite
having a surface area of at least 100 m.sup.2 /g and in which the
binder results
from a silica precursor or an alumina precursor. 26. A catalyst
support of claim 20, 21, 22, 23, 24 or 25 which has a surface area
of at least 20 m.sup.2 /g and in which the binder has a crystallite
size of no greater
than about 2,000 angstroms. 27. A monolithic catalyst support
having a surface area of at least 20 m.sup.2 /g and a modulus of
rupture of at least 500 psi, comprising 70-97 parts by weight of a
high surface area porous oxide phase and 3-30 parts by weight of a
permanent binder for the porous oxide phase dispersed throughout
wherein (i) the porous oxide phase consists of alumina, silica,
zeolite, spinel, zirconia, or a mixture or these; and (ii) the
binder is alumina, silica, zirconia, or a mixture of these, the
binder having a crystalline size of no greater than about 2000
angstroms. 28. A catalyst support of claim 27 in which the porous
oxide is
a spinel and in which the binder is alumina. 29. A catalyst support
of claim 27 in which the porous oxide is zirconia and the binder is
zirconia.
0. A catalyst support of claim 27 in which the porous oxide is
alumina, having a surface area of at least 100 m.sup.2 /g, and in
which the binder
is alumina, silica, or a mixture of these. 31. A catalyst support
of claim 27 in which the porous oxide is silica, having a surface
area of at least 100 m.sup.2 /g, and in which the binder is silica,
alumina, or a mixture
of these. 32. A catalyst support of claim 28 in which the porous
oxide is a zeolite having a surface area of at least 100 m.sup.2
/g, and in which the binder is silica, alumina, or a mixture of
these.
Description
BACKGROUND OF THE INVENTION
This invention relates to ceramic monolithic supports for catalysts
and, in particular, to supports containing permanent inorganic
binding materials which can be fired at low temperatures, imparting
strength to the support while maintaining substantial surface
area.
The conventional ceramic monolithic catalyst support consists of a
ceramic support with a coating of a high surface material upon
which the catalyst is actually deposited. In order to obtain
substantial density and strength, the ceramic material normally
must be fired at a high temperature. Such high-temperature firing,
however, necessarily sinters the ceramic material and results in
its having a very small surface area. Consequently, the ceramic
must be coated with another material having a higher surface area,
as well as specific chemical characteristics on which to actually
deposit the catalyst. This procedure of depositing a high surface
area `washcoat` on the low surface area ceramic wall is disclosed,
for example, in U.S. Pat. Nos. 2,742,437 and 3,824,196.
In addition to requiring the second production step of applying the
washcoat, catalyst supports of this kind suffer from several
disadvantages in use. In service, the supports are exposed to a
flow of gases which often contain dusts or particulate matter,
which can cause the high surface area coating to flake off the
underlying ceramic support. This phenomenom can also occur where
the support is exposed to thermal cycling because the wash coat and
the underlying ceramic material often have different thermal
expansion coefficients.
It is therefore an object of the present invention to provide a
monolithic support having a high surface area which is not easily
abraded. It is a further object of the invention to provide a
monolithic support which develops substantial strength at
temperatures below those at which the high surface area of the
constituent materials would be adversely affected.
SUMMARY OF THE INVENTION
The present invention provides a method of producing a catalyst
support having both high strength and high surface area. The method
comprises (a) mixing into a substantially homogeneous body (1) a
porous oxide having a surface area of at least 20 m.sup.2 /g
selected from the group consisting of zeolites, silica, alumina,
spinel, .[.titania,.]. zirconia, and mixtures of these; (2) a
precursor of a permanent binder for the porous oxide selected from
the group consisting of alumina precursors, silica percursors,
.[.titania precursors,.]. zirconia precursors, and mixtures of
these; and (3) a temporary binder, and (b) heating the body to a
temperature from 500-1000.degree. C. to result in substantial
strength and surface area. The permanent binders of this invention,
incorporated into the support in their precursor-form, enable the
support to develop substantial strength at firing temperatures
lower than those normally required. The use of a lower firing
temperature substantially eliminates the problem of
temperature-induced loss of surface area by the porous oxide. The
binder materials, in addition to imparting strength to the support,
provide surface area of their own. As a result, a high strength
support is provided which exhibits high surface area as well.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a method is provided to form a
catalyst support structure in which a high surface area support
phase of a porous oxide is bound into a strong cohesive mass by
permanent binders which are uniformally mixed into the support
structure itself. The porous oxide, precursors for the permanent
binders, and a temporary binder are mixed into a substantially
homogeneous body, which can be formed into any desired shape, and
then heated according to conventional techniques of the ceramic
arts. The method of the present invention, however, by virture of
the permanent binders employed, permits the use of lower
temperatures, generally below 1000.degree. C., to form the support
structure. Strength and density of the support structure,
previously attained only at temperatures which led to reduction in
surface area, are obtainable through the present method at
relatively low temperatures, at which the surface area of the
porous oxide phase is not seriously affected. It has been found,
surprisingly, that better strength is gained by the use of the
binders in precursor form than if an equal weight of the actual
binder material (silica, alumina, .Iadd.or .Iaddend.zirconia.[., or
titania.].) had been incorporated into the support directly.
The porous oxides suitable for use as the support phase material
herein are those which, after calcining, have a surface area of at
least 20 square meters per gram, preferably at least 100 square
meters per gram, and most preferably at least 200 square meters per
gram. (As used herein "calcining" means heating a material to a
temperature sufficiently high to substantially eliminate any
volatiles but below that at which the material begins to lose
substantial porosity.) Preferably, the oxide is alumina, silica,
spinel, .[.titania,.]. zirconia or a zeolite. Mixtures of the
oxides can also be used. The invention is not limited to these
particular oxides, however, and as those skilled in the art will
recognize, the invention contemplates the use of other materials
which are commonly used as catalyst supports and which have the
above-described characteristics.
The aluminas useful in the preparation of the high surface area
support phase of this invention are those which, upon calcining,
provide gamma-alumina or other transition aluminas having the
specified surface area. Colloidal gamma-alumina can be used
directly, or materials which generate a transition alumina upon
calcining, such as alpha-alumina monohydrate, or alumina trihydrate
can also be used. When alpha-alumina monohydrate or alumina
trihydrate is used, the particle size can be from less than 1
micron up to about 100 microns. Suitable commercially available
materials of this kind are Kaiser SA substrate alumina, available
from the Kaiser-Chemical Division of Kaiser Aluminum Corporation,
and the Catapal.RTM. aluminas available from the chemical division
of Conoco Corporation. The colloidal gamma-alumina is generally in
the form of particles not exceeding 1 micron.
Spinels useful in the present invention are the magnesium aluminate
spinels heretofore used as catalyst supports, including spinel
solid solutions in which magnesium is partially replaced by such
other metals as manganese, cobalt, zirconium, or zinc. Preferred
spinels are magnesium aluminate spinels having 1-7 percent by
weight alumina in excess of 1:1 MgO.Al.sub.2 O.sub.3 spinel; that
is, those having about 72.0-73.5 weight percent Al.sub.2 O.sub.3
(balance MgO). Spinels of this kind are available on order from
Baikowski International Corporation of Charlotte, North Carolina,
or can be prepared by co-precipitation or wet-mixing precursor
powders of alumina and magnesia, followed by drying and calcining.
Such a procedure is described in U.S. Pat. No. 4,239,656, the
disclosure of which is hereby incorporated by reference. As a
supplement to this disclosure, however, it has been found that
calcining of the spinels should normally not exceed 1300.degree. C.
for 2-2.5 hours. Calcining temperatures below 1200.degree. C. are
preferred. Suitable alumina precursor powders for preparation of
the spinels are commercially available as Kaiser SA hydrated
alumina. Magnesium oxide component powders found to be suitable are
magnesium hydroxide slurry, about 40 weight percent MgO, available
from Dow Chemical Company, or hydrated magnesium carbonate.
High surface area silicas that can be used in the practice of the
present invention are the amorphous silicas of about 1-10 microns
or sub-micron particle size such as Cabosil.RTM. EH-5 colloidal
silica, available from Cabot Corporation. Colloidal silica derived
from gels, such as Grade 952 from the Davison Chemical Division of
W. R. Grace & Co. can also be used. .[.High surface area
titanias suitable for use in the high surface area support phase
are also commercially available, such as P25 TiO.sub.2 available
from DeGussa Corporation..].
The use of zeolites to provide high surface area in various
catalytic and molecular sieving operations is well known.
Readily-available zeolites useful in the present invention include
the crystalline aluminosilicate zeolites with the art-recognized
designations A, X, and Y, and silicalite which is virtually 100%
silica. Zeolites A, X, and Y, and their methods of preparation, are
disclosed in U.S. Pat. Nos. 2,882,243; 2,882,244; and 3,130,007,
respectively. The disclosures of these patents are incorporated by
reference. Silicalite is described in NATURE (Vol. 271), No. 5645
(1978).
Composites of alumina and silica also can form the basis for the
high surface area porous oxide phase. Alumina-silica composites are
commercially available from Davison Chemical Division of Grace
Chemical Company and from the Norton Chemical Company, or can be
prepared by the gel processes as described, for example, in U.S.
Pat. Nos. 4,129,522 and 4,039,474. Alternatively, alumina and
silica can be mixed directly in the preparation of the catalyst
support as described below.
When the high surface area porous oxide material is an alumina,
spinel, or a mixture of alumina and silica, it is preferred to add
up to about 20 percent by weight (based on the alumina, spinel, or
alumina-silica mixture weight) of a rare earth oxide. The preferred
rare earth oxides are those of the "cerium subgroup", that is,
elements of atomic number 57-62, particularly cerium and lanthanum.
Cerium oxide is most preferred. Particularly useful spinels, for
example, are those in which about 1 to 20 percent by weight, based
on the total spinel weight, of cerium oxide is present. Cerium
oxide is incorporated by adding, for example, cerium acetate,
cerium carbonate, or cerium nitrate to the other precursor powders
during the spinel preparation after calcining, or during formation
of the catalyst support itself. In like manner, particularly useful
mixtures of alumina and silica are those in which about 5 percent
by weight, based on the total alumina and silica dry weight, of
cerium oxide is present.
The preferred porous oxides for use in the high surface area
support phase are the transition aluminas, particularly
gamma-alumina, zeolites, silica, .Iadd.and .Iaddend.zirconia.[.,
and titania.]..
The permanent binders integrated into the catalyst support
structures of this invention are silica, alumina, .Iadd.or
.Iaddend.zirconia.[., or titania.].. These binders are used in the
presently described method in the form of "precursors" for the
binders, meaning herein materials which, at or below the firing
temperature of the green support structure, generate the actual
binder component. The precursors are mixed with the high surface
area porous oxide and with a temporary binder, to be described
below, to form a plasticized mass which can be molded into the
desired shape and then heated (fired).
It will be noted that the precursors to be described below are
generally in the form of a dispersion, suspension, or solution in a
liquid diluent. It is generally preferred that the precursors be in
such form before being mixed with the porous oxide powders and
temporary binder. However, binder precursors in solid form can be
used directly, although they must be well mixed into either the
water used in the batch plasticizing step (described below) or a
diluent introduced into the batch as the carrier of some other
component. In this dispersed, suspended, or dissolved form, the
binder precursors are distinguished from the usual ceramic
materials by size. When dispersed or suspended, the binder
particles are broken down to virtually crystallite size below 200
angstroms and preferably below 100 angstroms. When the binder
precursor is dissolved, the crystallites derived from the solute
are of the same order of size. In contrast, ordinary ceramic
materials are about three orders of magnitude coarser, usually
greater than 20 microns in size. The binder particles substantially
retaih this characteristic of small size in the final monolith
support itself. Although some sintering of the binder can take
place during the heating or firing of the monolith, it is expected
that the crystallite size of the binder in the fired support will
be no greater than about 2000 angstroms. Crystallite size can be
determined by electron microscopy.
The porous oxides are generally of the same crystallite size as the
binders, but are normally agglomerated into particles on the order
of micron size, which, under ordinary conditions, do not adhere
well to each other. The binders act as a "cement" for the
agglomerated porous oxides in the final support structures and
thereby provide substantial strength to the structure.
The preferred precursors for the permanent alumina binders are the
hydrated aluminas, hydrolyzed aluminum isopropoxide, and aluminum
chlorohydrate. The hydrated aluminas are most preferably in the
form of aqueous suspensions. Aqueous suspensions are commercially
available, such as from the Ethyl Corp., but are also easily
prepared from commercially available alumina monohydrate and
alumina trihydrate powders by dispersing these powders in water in
the presence of an organic acid. Aluminum isopropoxide is
commercially available as a dispersion in alcohol. For example, a
dispersion of aluminum isopropoxide, 30-35 percent by weight in
isobutanol, is available from the Alpha Products Division of Morton
Thiokol Inc. The aluminum isopropoxide is hydrolyzed by refluxing
the alcohol dispersion of the compound with water in the presence
of an acid. Aluminum chlorohydrate is available in the form of an
aqueous solution (for example, as CHLORHYDROL 50% or REHABOND
CB-65S from Reheis Chemical Co. of Berkeley Heights, New Jersey) or
as an organic derivative (such as REHYDROL II aluminum chlorohydrex
from Reheis Chemical Co.). The latter is soluble in anhydrous
alcohols, and is preferably used in this form. Aluminum
chlorohydrate is also available in solid particulate form, as
CHLORHYDROL Powder from Reheis Chemical Co., and can be
pre-dissolved before mixing with the porous oxides or can be
dissolved in the water used in the batch plasticizing step, to be
described hereinafter.
Examples of preparations of precursors for alumina binders are as
follows:
EXAMPLE A
Alumina Monohydrate Suspension
Ten parts by weight of alumina monohydrate powder is added to a
solution of 89 parts of water and one part concentrated acetic
acid. A suspension is obtained with moderate agitation.
EXAMPLE B
Hydrolyzed Aluminum Isopropoxide
To 516 ml of distilled water, at a temperature of
85.degree.-90.degree. C., is added 120 ml of a 30-35 weight percent
dispersion of aluminum isopropoxide in isobutanol. This mixture is
refluxed for one hour at a maximum temperature of 88.degree. C.,
resulting in the formation of a thin gel-like slurry. 10 ml of 1.32
molar HCl is slowly added with stirring, and this mixture is
refluxed for an additional 24 hours, resulting in a thin milky
slurry. Ammonium hydroxide is added dropwise until a pH of 7-7.5 is
reached. The result is a thick slurry which does not settle out on
standing.
The preferred precursors for the permanent silica binders are
silicone resins such as those disclosed in U.S. Pat. No. 3,090,681
issued to Weyer. The most preferred silicone resin is a hydroxyl
functional silicone resin available from the Dow-Corning Co. as
Resin 6-2230. The silicone resins, as the precursor, can be mixed
directly with the porous oxide powders, in which case a solvent
should be used during the plasticizing step to dissolve the resin.
The resin can be predissolved in an appropriate organic solvent.
Suitable solvents are alcohols such as methyl alcohol, ethyl
alcohol, or isopropyl alcohol, which is preferred. Whether they are
predissolved in a solvent or mixed directly with the porous oxide
powders, the silicone resins are preferably milled first to a
particle size finer than 20 microns, and more preferably finer than
10 microns.
The preferred precursor for the permanent zirconia binder is a
suspension of an amorphous hydrated zirconium oxide, which can be
in the form of hydrolyzed zirconium n-propoxide or a slurry of
zirconium hydrate. Hydrolyzed zirconium n-propoxide is preferred
and can be prepared by mixing the n-propoxide with an excess volume
of water, preferably 400% excess, at room temperature for 10 days.
After this time, the liquid is decanted and the solid washed with
distilled water to yield a slurry of hydrated amorphous zirconium
oxide.
.[.The preferred precursor for the permanent titania binders is a
suspension of an amorphous hydrated titanium oxide. This can be in
the form of hydrolyzed titanium isopropoxide or a slurry of
titanium hydrate. Slurries of titanium hydrate are commercially
available, such as from SCM Corp. It is preferred to neutralize
such slurries, as may be necessary if they are acidic, so that they
will be compatible with the temporary binders used in the
invention. The preferred precursor of a permanent titania binder is
a suspension of hydrolyzed titanium isopropoxide, an example of
which is shown immediately below in Example C.
EXAMPLE C
Hydrolyzed Titanium Isopropoxide
To one gallon of water was added 298 ml of titanium isopropoxide.
This mixture was stirred, and then allowed to sit for ten days at
room temperature, after which time the resultant mixture was
centrifuged, the liquid decanted, and the solid washed with
distilled water. The resultant suspension was neutralized to a pH
of 8.05. The titania content of the suspension is 0.1334 g of
titania per gram of suspension..].
Although any of the permanent binders described herein are
generally compatible with any of the porous oxides contemplated for
use in this invention, certain combinations are nevertheless
preferred. When the porous oxide is an alumina or a spinel, the
preferred binders are suspensions of hydrolyzed aluminum
isopropoxide, suspensions of hydrated alumina, and solutions of
aluminum chlorohydrate. For silica as the porous oxide, the
preferred binders are a silicone resin, aluminum chlorohydrate
solutions, and suspensions of hydrated aluminas. .[.For titania,
the preferred binders are based on slurries of hydrolyzed titanium
isopropoxide, silicone resin, suspensions of hydrated alumina, and
aluminum chlorohydrate solutions..]. For zeolites, the preferred
binders are based on silicone resins, suspensions of hydrated
alumina, and aluminum chlorohydrate solutions. For zirconia as the
porous oxide, the preferred binder is hydrolyzed zirconium
n-propoxide.
In the practice of the present method, the porous oxide powders are
mixed with the precursors for the permanent binder and with a
temporary binder; that is, one which is completely or substantially
completely burned off at the temperature at which the support
structure is fired. The temporary binder has the primary function
of forming a plasticized mass with the oxide powders and the
permanent binder precursor, and can be any of the well-known
materials commonly used in the ceramic art for such purposes.
Suitable temporary binding agents are disclosed in:
"Ceramics Processing Before Firing," ed. by George Y. Onoda, Jr.
& L. L. Hench, John Wiley & Sons, New York
"Study of Several Groups of Organic Binders Under Low-Pressure
Extrusion," C. C. Treischel & E. W. Emrich, Jour. Am. Cer.
Soc., (29), pp. 129-132, 1946
"Organic (Temporary) Binders for Ceramic Systems," S. Levine,
Ceramic Age, (75) No. 1, pp. 39+, January 1960
Temporary Organic Binders for Ceramic Systems" S. Levine, Ceramic
Age, (75) No. 2, pp. 25+, February 1960
The most preferred binder is methyl cellulose, available as
Methocel A4M from the Dow Chemical Co.
Generally, about 70-97 parts by weight of the porous oxide and 1-20
parts by weight of the temporary binder are mixed with sufficient
permanent binder precursor to provide 3-30 parts by weight of the
permanent binder material itself. For example, when the permanent
binder precursor is a solution of aluminum chlorohydrate, the
solution must be added in such amounts as will generate 3-30 parts
by weight of alumina itself in the final support structure. This
amount of alumina, of course, is independent of any alumina added
as the high surface area porous oxide. Up to about 1 percent by
weight, based upon total mixture weight, of a surfactant, such as
sodium stearate, can also be used to facilitate mixing and flow for
subsequent processing. The mixture is further plasticized by the
addition of water and possibly a solvent, such as isopropyl
alcohol, as well. When the permanent binder precursor is a silicone
resin, it is preferred to use a 50/50 volume mixture of water and
isopropyl alcohol to plasticize the batch. The silicone resin can
be predissolved in the alcohol.
The mixture can also contain up to 20 percent by weight, based upon
the total weight of the porous oxide powder and the permanent
binder itself, of a clay such as kaolin. The clay provides
additional binding action and imparts additional hardness and
strength to the final support structure. The presence of clay is
most useful in supports in which the porous oxide is alumina. A
preferred kaolin clay is available from the Georgia-Kaolin Co. as
HYDRITE MP kaolin.
The high surface area porous oxide powders can be substituted with
substantial amounts of a compatible low surface area oxide powder
to facilitate formation and drying so long as the average overall
surface area of the oxide powders does not fall below 20 square
meters per gram weight of oxide powder generally about 20 percent
by weight of the porous oxide can be replaced by the low surface
area powder, but in the particular case of silica, up to 80 percent
of the high surface area silica can be replaced by low surface area
silica. For example, 20 parts by weight of high surface area silica
such as CABOSIL EH-5 silica (Cabot Corp.) can be combined with 80
parts by weight of low surface area silicas such as SUPERSIL silica
(Pennsylvania Glass Sands Co.) in the preparation of catalyst
supports according to the present invention. The total surface area
per gram weight of the silicas is still in excess of 20 m.sup.2 /g
because of the high surface area of the CABOSIL silica (400 m.sup.2
/g).
The components are combined to form a homogeneous or substantially
homogeneous mixture. Normally, the dry ingredients are first
premixed, preferably in an intensive mixer, and then combined with
the wet ingredients (i.e., binder precursors in suspensions or
solutions, water, alcohols). It is critical that the high surface
area porous oxide powder be well mixed into a plasticized mass with
the permanent binder precursor. Conventional mixing equipment can
be used, but the use of a mix muller is preferred. To effect
further mixing, the batch can subsequently be extruded through a
"noodling" die one or more times. Ultimately, the batch is formed
into the desired support shape, preferably by extrusion through a
die. The method of this invention is particularly well suited to
the preparation of catalyst support structures in the shape of a
honeycomb.
The "green" catalyst support shapes are heated (fired) at a
temperature of about 500.degree.-1000.degree. C. for a period of
about 4-6 hours. It is preferred to employ the lower temperatures
within this range when the porous oxide is a zeolite. Optionally,
the firing step can be preceeded by drying the support shapes at
about 100.degree.-120.degree. C., preferably by steam heat.
However, when a silicone resin is used as the precursor for the
permanent binder, a drying temperature of 50.degree. C. may be used
initially to drive off solvent such as alcohol. This can be
followed by steam-heat drying. The resulting monolithic support of
this invention is comprised of 70-97 parts by weight of the porous
oxide and 3-30 parts by weight of a permanent binder for the oxide
dispersed throughout.
An advantage of the catalyst support structures of the present
invention is the substantial strength obtained at relatively low
firing temperatures; that is, temperatures of about 1000.degree. C.
or below. At these lower firing temperatures, sintering does not
occur to an extent which adversely affects the surface area of the
porous oxide phase of the support, or which causes excessive firing
shrinkage. Substantial overall surface area of at least 20 m.sup.2
/g, preferably greater than 100 m.sup.2 /g, and most preferably
greater than 150-200 m.sup.2 /g is normally retained, and firing
shrinkage is normally held to less than 5 percent, preferably less
than 6 percent. Nevertheless, the use of the binder precursors of
the invention contributes to the development of substantial
strength in the support structure. The material preferably should
obtain a flexural strength, measured as the modulus of rupture, of
greater than 500 pounds per square inch (psi), more preferably
greater than 1000 psi, and most preferably greater than 1500 psi.
Accordingly, the support structures of the invention attain the
combination of needed strength and high surface area without high
temperature firing and the disadvantages that generally attend such
procedures.
To determine the modulus of rupture, an extruded, fired rod of the
material is supported at two points along its length and a load
applied to the rod midway between the two supports. The load is
gradually increased until the rod breaks. The modulus of rupture is
calculated as ##EQU1## where "M" is modulus of rupture; "L" is the
load applied when the rod breaks (pounds); "a" is one-half the
distance between the two supports (inches), and "d" is the rod
diameter (inches).
The support structures of this invention may have some catalytic
activity of their own by virtue of the chemistry and structure
provided by the high surface area porous oxide and the permanent
binder components. The support may further carry additional
catalytically active ingredients dispersed throughout. These
additional ingredients can be incorporated into the structure by
methods well known in the art. The support structures of this
invention, particularly those in the shape of honeycombs, are
useful in most applications in which it is necessary to
catalytically convert undesirable components in a gas stream prior
to the stream's further processing or exhaustion to the atmosphere.
Examples of such use are the catalytic converter in automotive
exhaust systems and the conversion of fluids in the chemical or
petroleum industries.
The following examples illustrate various embodiments of the
invention. The examples are intended to be illustrative, but not
limiting, of the invention.
EXAMPLES 1-5
In Examples 1-5, the ingredients listed in corresponding Tables 1A,
2A, 3A, .Iadd.and .Iaddend.4A.[., and 5A.]. were combined according
to their indicated weight parts, as follows. The dry ingredients
were first intensively mixed to substantial homogeneity in a
Littleford blender. The dry mixture was transferred to a mix muller
into which were further added the "wet" components (the slurries of
permanent binder precursors, water, alcohol). The resultant batch
was mixed in the muller until a well-plasticized batch was
attained. Each batch composition was extruded through a die to form
rods having a diameter of 5/16-inch. The rods were heated at
various temperatures between 500.degree. C. and 1000.degree. C. for
a period of six hours. Measurements of overall surface area, firing
shrinkage (linear), and modulus of rupture (according to the
procedure described earlier herein) were taken. The results were
recorded, for each example, in the corresponding "B" Table.
Examples 1-3 contain a control example (indicated) in which the
catalyst support shape is comprised entirely of the high surface
area porous alumina, no permanent binder precursor having been
incorporated in precursor form into the green batch. These examples
are presented for purposes of comparison. Among the examples,
particularly preferred embodiments relating to alumina, .Iadd.and
.Iaddend.silica.[., and titania.]. (as the high surface area
oxides) are shown in Examples 1G, .Iadd.and .Iaddend.4C, .[.and
5D,.]. respectively.
TABLE 1A
__________________________________________________________________________
Alumina Alumina Monohy- Aluminum.sup.2 Aluminum Aluminum.sup.3
Kaiser Monohy- drate Chloro- Isoprop- Chloro- SA.sup.1 drate.sup.8
Slurry hydrate oxide hydrate Alpha-Alumina.sup.4 Methyl EX. NO.
Alumina Slurry (Ex. A) Macrospheres (Ex. B.) Solution Monohydrate
Clay.sup.5 Cellulose Water
__________________________________________________________________________
1A (control) 100.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.0 90.8 1B 90.0
109.1 0.0 0.0 0.0 0.0 0.0 0.0 6.0 0.0 1C 92.0 119.0 0.0 8.0 0.0 0.0
0.0 0.0 6.0 0.0 1D 84.0 0.0 0.0 8.0 8.0 0.0 0.0 0.0 6.0 85.0 1E
82.0 100.0 0.0 8.0 0.0 0.0 0.0 10.0 6.0 2.0 1F 66.0 0.0 0.0 0.0 0.0
14.0 10.0 10.0 6.0 53.8 1G 76.0 0.0 0.0 0.0 7.25 8.2 9.5 0.0 6.0
66.3 1H 76.0 0.0 0.0 0.0 14.5 0.0 9.5 0.0 6.0 60.5 1I 76.0 0.0 0.0
0.0 0.0 14.5 9.5 0.0 6.0 69.1
__________________________________________________________________________
TABLE 1B ______________________________________ Firing Modules of
BET Linear Temper- Rupture Surface Area Shrinkage EX. NO. ature
(.degree.C.) (psi) (m.sup.2 /g) (%)
______________________________________ 1A 500 1740 219 1.45 750
2200 147 2.1 1000 2000 82 5.1 1B 500 2030 235 1.47 750 1950 186
2.04 1000 2020 92 4.8 1C 500 1230 268 2.2 750 2900 179 2.4 1000
2230 77 6.0 1D 500 490 279 2.2 750 550 198 2.5 1000 600 87 5.6 1E
500 2260 227 1.9 750 1900 166 2.3 1000 3020 84 5.3 1F 500 2500 200
-- 750 2600 140 -- 10000 2800 70 -- 1G 500 2630 256 1.9 750 2140
168 2.4 1000 2410 91 4.8 1H 500 -- 220 1.7 750 -- 157 2.4 1000 --
92 -- 1I 500 1530 250 -- ______________________________________
TABLE 2A
__________________________________________________________________________
Aluminum.sup.3 Alumina- Alpha-Alumina Chlorohydrate Monohydrate
Methyl EX. NO. Boehmite.sup.6 Monohydrate.sup.4 Solution
Slurry.sup.8 Cellulose Clay.sup.5 Water
__________________________________________________________________________
2A (Control) 100 0.0 0.0 0.0 6.0 0.0 41.0 2B 76 9.5 13.1 0.0 6.0
0.0 34.1 2C 90 0.0 0.0 44.5 6.0 0.0 0.0 2D 66 10.0 14.0 0.0 6.0
10.0 28.8
__________________________________________________________________________
TABLE 2B ______________________________________ Firing Modulus of
BET Linear Temper- Rupture Surface Area Shrinkage EX. NO. ature
(.degree.C.) (psi) (m.sup.2 /g) (%)
______________________________________ 2A 500 370 201 0.29 750 280
147 0.5 1000 140 42 1.2 2B 500 650 215 0.69 750 600 130 0.86 1000
400 48 1.80 2C 500 1230 203 0.39 750 1720 137 0.49 1000 1090 40
1.11 2D 500 530 165 0.48 750 680 130 0.89 1000 570 52 1.60
______________________________________
TABLE 3A
__________________________________________________________________________
Alumina-.sup.8 Aluminum.sup.3 Alumina.sup.7 MonoTrihydrate
Chlorohydrate Alpha-Alumina.sup.4 Methyl EX. NO. Trihydrate Slurry
Solution Monohydrate Cellulose Water
__________________________________________________________________________
3A (Control) 100 0.0 0.0 0.0 6.0 55.4 3B 90 64.4 0.0 0.0 6.0 0.0 3C
76 0.0 9.7 9.5 6.0 32.4 3D 76 0.0 14.5 9.5 6.0 55.0 3E 50 0.0 14.5
34.5 6.0 35.0
__________________________________________________________________________
TABLE 3B ______________________________________ BET Firing Modulus
of Surface Linear Temper- Rupture Area Shrinkage EX. NO. ature
(.degree.C.) (psi) (m.sup.2 /g) (%)
______________________________________ 3A (Control) 500 1540 204
1.2 750 1500 124 1.4 1000 1250 45 3.3 3B 500 2080 275 0.98 750 1810
167 1.25 1000 1740 50 2.44 3C 500 1130 189 0.82 750 1050 149 1.30
1000 800 49 2.50 3D 500 1580 146 1.1 750 1670 148 1.5 1000 850 59
2.4 3E 500 1260 246 1.3 750 1190 154 1.8 1000 1470 70 3.4
______________________________________
TABLE 4A ______________________________________ High Low Sili-
Isopropyl EX. Surface Surface.sup.10 cone.sup.11 Methyl Alcohol NO.
Silica.sup.9 Silica Resin Cellulose (cc) Water
______________________________________ 4A 83 0 17 6 97.0 97.0 4B 50
50 20 6 52.5 52.5 4C 30 70 20 6 36.5 36.5 4D 20 80 20 6 24.0 24.0
______________________________________
TABLE 4B ______________________________________ Modulus of BET
Firing Rupture Surface Area EX. NO. Temperature (.degree.C.) (psi)
(m.sup.2 /g) ______________________________________ 4A 500 330 272
600 -- 253 700 -- 202 1000 -- 45 4B 500 --* 163 600 -- 141 700 --
129 1000 -- 44 4C 500 700 155 600 575 121 700 510 119 4D 500 860
131 600 620 121 700 790 98 1000 660 12
______________________________________ *Not suitable for strength
tests.
.[.TABLE 5A
__________________________________________________________________________
Hydrolyzed Titanium.sup.12 Titanium Aluminum.sup.3 Methyl
Silicone.sup.11 Hydrate Isopropoxide Chlorohydrate i-Propyl EX. NO.
TiO.sub.2 Cellulose Resin Slurry (Ex. C.) Solution Alcohol (cc)
Water
__________________________________________________________________________
5A (Control) 100 7.2 0.0 0.0 0.0 0.0 0.0 52.5 5B 83 4.0 17.0 0.0
0.0 0.0 23.5 23.5 5C 86.2 6.2 0.0 77.4 0.0 0.0 0.0 9.8 5D 88.4 6.4
0.0 0.0 87.2 0.0 0.0 0.0 5E 84.6 4.0 0.0 0.0 0.0 0.0 0.0 23.1 5F
83.0 4.0 17.0 0.0 0.0 15.3 17.2 17.2.].
__________________________________________________________________________
1
.[.TABLE 5B ______________________________________ Modules of BET
Firing Rupture Surface Area EX. NO. Temperature (.degree.C.) (psi)
(m.sup.2 /g) ______________________________________ 5A 500 265 37
640 940 21 810 -- 3.9 1000 11,000 -- 5B 500 1,000 50 640 1,200 80
810 -- 45 1000 3,100 30 5C 500 360 54 640 900 33 810 -- 6 1000
22,300 0.1 5D 500 650 48 640 2,200 27 810 -- 7 1000 20,300 0.3 5E
500 1,160 48 640 900 45 810 -- 11 1000 -- 2 5F 500 1,130 112 640
1,090 -- 1000 -- 22.]. ______________________________________
.sup.1 Kaiser S. A. substrate alunmina, a hydrated alumina which,
after heat treatment at 600.degree. C. for one hour, has a weight
losson-ignition of 27% and provides gammaalumina, surface area 300
m.sup. /g. .sup.2 Reheis Chemical Company, CHLORHYDROL aluminum
chlorohydrate. .sup.3 Fifty percent by weight is water, alumina
content 24%, Reheis Chemical Company. .sup.4 CATAPAL 5B from Conoco
Chemicals. After calcination at 900.degree. F. for three hours
provides surface area of 250 m.sup.2 /g. .sup.5 HYDRITE MP kaolin,
GeorgiaKactin Company. .sup.6 Alcoa Company F1 alumina, particle
size less than 100mesh, surface area 2.2 m.sup.2 /g. .sup.7
Reynolds Company high surface area alumina trihydrate. .sup.8 Ethyl
Corporation Alumina Monohydrate slurry. .sup.9 W. R. Grace Co.
Grade 952 (Ex. 4A), CABOSIL EH5 from Cabot Corporation surface area
400 m.sup.2 /g. median particle size 0.007 micro (Exs. 4B, 4C, 4D).
.sup.10 SUPERSIL silica, particles finer than 200 mesh. Pa. Glass
Sands Co. .sup.11 Dow Corning Company, Resin Q62230 .[. .sup.12 SCM
Corporation.].
EXAMPLE 6
A preferred zeolite-based catalyst support was prepared from the
following batch, figures indicating weight parts:
______________________________________ Methyl Cellulose 5 Sodium
Stearate 0.5 Silicone Resin (Dow Corning Q6-2230) 22 Zeolite (Union
Carbide Corp. - 13X) 78 Distilled Water 12.4 Isopropyl Alcohol 12.4
______________________________________
The materials were first dry mixed and then plasticized with the
water and alcohol. The batch was extruded as a honeycomb and as
rods for measurement of flexural strength. After heating at
500.degree. C. for six hours, the material had a flexural strength,
measured as the modulus of rupture, of 750 psi. X-ray diffraction
analysis shows the same zeolite structure in the fired structure as
in the raw batch.
EXAMPLE 7
A preferred zeolite-based catalyst support was prepared from the
following batch, figures indicating weight parts:
______________________________________ Methyl Cellulose 6 Silicone
Resin (Dow Corning Q6-2230) 17 Silicalite (Union Carbide Corp.
S-115 83 Silicalite zeolite) Distilled Water 11.3 Isopropyl Alcohol
33.9 ______________________________________
The materials were first dry mixed and then plasticized with the
water and alcohol. The batch was extruded as a honeycomb and as
rods for the measuremet of flexural strength. After heating at
500.degree. C. for six hours, the material had a flexural strength,
measured as the modulus of rupture, of 1020 psi. X-ray diffraction
analysis shows the same crystalline silicalite structure as in the
S-115 raw material.
EXAMPLE 8
A preferred zeolite-based catalyst support was prepared from the
following batch, figures indicating weight parts:
______________________________________ Methyl Cellulose 5 Silicone
Resin (Dow Corning Q6-2230) 17 Linde LZY-62 Y-Zeolite (Union
Carbide Corp.) 83 Distilled Water 21 Isopropyl Alcohol 21
______________________________________
The materials were first dry mixed and then plasticized with the
water and alcohol. The batch was extruded as a honeycomb and as
rods for the measurement of flexural strength. After heating at
500.degree. C. for six hours, the material had a flexural strength,
measured as the modulus of rupture, of 1230 psi. X-ray diffraction
showed the same Y-zeolite structure as in the raw materials.
* * * * *