Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02173240 1998-12-1~
CATALYST CARRIER
This invention relates to catalyst carriers and
specifically to catalyst carriers based on alumina that may
be used as supports for metal and metal oxide catalyst
components of use in a variety of chemical reactions.
Background of the Invention
The use of alumina based catalyst carriers has
previously been described in a number of patents including
USPP 5,100,859; 5,055,442; 5,037,794; and 4,874,739. Such
carriers have a wide variety of potential applications in
the catalytic field and are especially useful where the
alumina base is alpha alumina.
A catalyst support needs to possess, in combination,
at least a minimum surface area on which the catalytic
component may be deposited, high water absorption and crush
strength. The problem is that usually an increase in one
can mean a reduction in another property. Thus high crush
strength may mean low porosity. Often the balance is
achieved by trial and error making the catalyst carrier art
even more unpredictable than other chemical process art.
A way has now been found to design carriers with more
confidence as to the final property balance. The carriers
of the invention have an excellent balance of crush
strength, abrasion resistance, porosity and catalytic
performance that make them ideal for a range of catalytic
applications. They are based on alpha alumina and the
novel process by which they are made assures high porosity
and excellent crush strength.
Descri~tion of the Invention
The present invention provides a novel alpha alumina
based catalyst carrier having a crush strength, (as
measured on a Compton Tensile Tester, model 50-OP), of at
least 51b (2.28N) and a settled packing density, (as
CA 02173240 1998-12-1~
.
measured by ASTM D-4699-87, modified by the use of cylinder
with an inside diameter of 3.75in (9.53cm) and a length of
18in (45.7cm), of at least 381b/ft3 (608kg/m3) which
comprises first and second alpha alumina components with a
first alpha alumina component in the form of particles
having an average crystallite size of from about 0.4 to
about 4 microns providing from about 95 to about 40% of the
total weight of alpha alumina in the carrier, and a second
alpha alumina component generated in situ by a sol-gel
process and providing the balance of the alpha alumina in
the carrier.
The alpha alumina generated in situ is readily
distinguished from the pre-formed alpha alumina particles
present in the carrier of the invention. In a
photomicrograph of the carrier the pre-formed alpha alumina
appears as clearly identifiable individual particles with
no internal porosity.
The invention also comprises a process for the
production of a catalyst carrier which comprises:
i) forming a mixture comprising:
a. at least one alpha alumina component with an
median particle size of 3 to 8 microns and:
b. a hydrated precursor of alpha alumina in an amount
sufficient to provide from 5 to 60% by weight of the
total weight of alpha alumina in the catalyst carrier
product;
c. from 5 to 40~, based on the weight of the alpha
alumina, of a burnout material; and
d. water in sufficient quantity to extrude the above
mixture;
ii) extruding the mixture into the desired shapes; and
iii) firing to convert the seeded precursor of alpha
alumina to alpha alumina so as to produce a catalyst
CA 02173240 1998-12-1~
carrier in which alpha alumina particles with a median
particle size of from 3 to 8 microns are dispersed in a
matrix of alpha alumina derived from the seeded precursor
material.
The catalyst carrier of the invention comprises a
number of alpha alumina components chosen to contribute to
the desired physical properties, including porosity, pore
volume, crush strength and the like. Often a combination
of two different alpha aluminas is preferred, one component
having larger particles mixed with a second component
having smaller particles, in weight ratios of from 10:90 to
90:10. The objective of this is to end up with a surface
area, (in this document a reference to "surface area" is
understood to mean the BET surface area measured using
nitrogen or krypton as the adsorbed gas), in the finished
product of from 0.4 to 5 m2/gm. The surface area in the
finished carrier is somewhat less than the free alumina
particles. Thus a convenient mixture may comprise for
example, two types of alpha alumina particles, the first
having a surface area of about 1 m2/gm and the second having
a surface area of 3 to 5 m2/gm.
The precursor of alpha alumina is preferably based on
boehmite but good results are also obtained if the
precursor comprises a mixture of boehmite with an aluminum
trihydrate such as gibbsite or bayerite. Where such a
mixture is used it is often preferred to use a weight ratio
of the monohydrate, (boehmite), to trihydrate of from 1:10
to 1:3 and more preferably from 1:8 to 1:4. It is often
preferred that, when a sol is formed from the precursor by
addition of water, a sub-micron particle sized see material
is also added. This has the effect of reducing the
temperature at which the transition to alpha alumina occurs
and reduces the crystal size of the alpha alumina produced
upon transformation.
The seed used can be any material that is effective
.
CA 02173240 1998-12-1~
to produce nucleation sites in the precursor so as to
reduce the transition temperature at which a transition
alumina converts to alpha alumina. Seeds that accomplish
this goal generally have the same crystal lattice type as
alpha alumina itself and lattice dimensions that do not
differ by too much from those of alpha alumina. Clearly
the most convenient seed is alpha alumina itself and sub-
micron sized particles of alpha alumina are the preferred
seed. It is however possible to use other seeds such as
alpha ferric oxide and chromium oxide and certain complex
oxides of titanium.
The alpha alumina formed from the preferred seeded
precursor when the extruded mixture is fired generally has
a much finer crystal size than the alpha alumina particles
with which the seeded precursor is mixed unless, during
firing, it is maintained at a high temperature for a
prolonged period. As produced, the seeded sol-gel material
has a sub-micron crystal structure but if it is held at
temperatures over 1400~C for extended periods, crystal
growth begins and the size differentiation may become less
apparent.
The carrier of the invention preferably has a porosity
of at least 50~ and more desirably from 60 to 75~. The
porosity is related to the surface area which is preferably
from 0.4 to 5, and more preferably from 0.6 to 1.2 square
meters/gram.
It is often found advantageous to add titania to the
mixture to be extruded in an amount that represents from
0.05 to 1.0~, and more preferably from 0.08 to 0.6~ of the
weight of the fired carrier. Certain forms of alumina and
bond material may also contain titania as impurities or
components. The contribution of such forms of titania are
not included in the amounts specified above. The titania
can be added as the dioxide, as a titanate or as a
precursor of titania.
~ H--2630/1 . 217~2~0
In the ~ollowing description all the above options are
understood to be included under the term "titania" It
is believed that the titania may function as a form of
crystai growth inhibitor in the alpha alumina formed as a
result of the conversion of the seeded precursor.
The titania is preferably in the form of a powder
with a relatively high surface area such from 8 to 300
square meters/gram. In practice the preferred titanias
have an amorphous or anatase structure as the rutile
structure commonly has a much smaller surface area.
Commercial pigment grades of titania can often give good
results.
When the carrier comprises a titania component, it
is often found that surface areas are in the lower end of
the ranges discussed above. In spite of this lower
surface area such carriers give good results in terms of ~ -
the performance of catalysts supported on the carrier. 7~ t~
While it would appear that the alpha alumina formed ,
from the seeded precursor acts in some sense as a matrix
binder holding the rest of the alpha alumina particles
together,~ ~s~usu~lly preferred~to add a ceramic bond
material to the mixture to give added strength to the
fired carrier. Conventional ceramic bond materials can
be used and after firing these typically comprise -~
components, (expressed as the oxides), such as silica,
alumina, alkaline earth metal oxides, alkali metal
oxides, iron oxide and titanium oxide, with the first two
being the dominant components.
Pescription of Preferred Em~odiments
The invention is further described with reference to
the following examples which are for the purposes of
' illustration only and are not intended to imply any
necess~ry-limitation an t~e essential scope of the
invention .,~
21 7324~
W096/08309 T~/US94/09775
Example 1 - ; I
This Example details the preparation of the carriers
made using the formulations described in the following
Examples.
The ceramic components are mixed with a bhrn-out
material, (walnut shell flour), and boric acid for about
a minute. Water and the seed component are added, the
water being in an amount that is necessary to make the
mixture extrudable. Generally this is about 3jO% by
weight. The mixture is mixed for about two tolfour
minutes and then about 5% by weight based on the weight
of the ceramic components, of vaseline is added as an
extrusion aid. The mixture is then mixed for a further 2
to 4 minutes before being extruded in the ~orm o~ hollow
cylinders and dried to less than 2~ uncombined water.
These were then fired in a tunnel kiln with a maximum
temperature of about 1500~C for about 4 hours.
Exam~le 2
In this Example three carriers according to the
invention are described in terms of their formulation,
(Table 1) and their physical properties and catalytic
performance when used in conjunction with a standard
commercial catalyst to produce ethylene oxide, (Table 2 ) .
The performance is compared against a standard commercial
catalyst/carrier combination using the same catalyst.
6 1.
SL~BSlmJ~~ S~P~VI~ ~
~ W096/08309 ~ ~ 7 3 2 ~ ~ PCT~S94/09775
TABLE 1
CARRIER COMPOSITION CARRIER A CARRIER B CARRIER C
ALPHA #1 * 46.6% 45.2~ 46.6%
. ALPHA #2 * 18.7~ 18.7% 28.0%
ALPHA #3 * (SEED) 0.9% 0.9% 0.9%
GIBBSITE * 28.0% 28.0% 18.7%
BOEHMITE * 4.5% 4.5% 4.5%
CERAMIC BOND * 1.3% 2.7% 1.3%
ORGANIC BURNOUT ** 11% 16% 11%
10 PETROLEUM JELLY ** 5~ 5% 5%
BORIC ACID ** 0.15% 0.15% 0.15%
WATER about 30% about 30% about 30%
* indicates "ceramic components" and percentages given
are based on î~o% of the ceramic components.
** percentages are based on total weight of ceramic
components.
Water is added in an amount to make the above mixture
extrudable.
"Alpha #l" is a commercial alpha alumina that has a
median particle size of 3 to 3.4 microns, a BET surface
area of about 0.9 to about 1.4 m2/gm~ a crystallite size
of 1.6 to 2.2 microns and a soda content of 0.02 to
0.06%.
"Alpha #2" is an alpha alumina with a median particle
25 size of 4.0 to 8.0 microns, a surface area of 3.0 to 5.0
m2/gm, a crystallite size of from 0.4 to 0.8 micron and a
soda content of 0.1 to 0.3%
"Alpha #3" is an alpha alumina that was used as the seed
for the gibbsite and boehmite precursors of alpha
alumina. Its median particle size was less than 0.1
micron.
The gibbsite had a median particle size of from 4.0 to 20
microns and the boehmite was dispersible as a sol.
The ceramic bond contained components, (expressed as the
oxides), in the following approximate proportions: 60%
silica, 29% alumina, 3% of calcium oxide, 2% of magnesia,
4% of alkali metal oxides and less than 1% each of ferric
UTE S~T ~R~
CA 02l73240 l998-l2-l~
The gibbsite had a median particle size of from 4.0 to 20
microns and the boehmite was dispersible as a sol. The
ceramic bond contained components, (expressed as the
oxides), in the following approximate proportions: 60
silica, 29~ alumina, 3~ of calcium oxide, 2~ of magnesia,
4~ of alkali metal oxides and less than 1~ each of ferric
oxide and titania.
TABLE 2
PROPERTY CARRIER A CARRIER B CARRIER C
Select. (1) +1.05/-0.05 +1. 05/-6.5 +1.25/-2
Surface Area 1.15 m2/gm 0. 912 m2/gm 0. 97 m2/gm
Pack. Density 733. 7 kg/m3 775. 4 kg/m3 736.9 kg/m3
Crush Strength 6 .18 N 6. 94 N 8.10 N
Attrition 21. 7% 18.09~ 19.8~
The above Table includes certain measurement criteria
that are used throughout this specification to describe the
results obtained. Where these are not further explained in
the context, they have the meanings described below:
(1) "Selectivity" This is measured using a standard
catalyst formulation deposited on the carrier and assessed
against the selectivity shown by the same standard catalyst
on a standard carrier. In each case a standard gas flow
containing ethylene, oxygen and inert gases and comprising
25~ by volume of ethylene was passed over the catalyst.
The standard conditions are those to achieve a conversion
of 40~ of the oxygen content of the flow. Clearly if the
selectivity of the standard can be exceeded by even a small
amount, this is an advantage. This is even more attractive
if it can be achieved at a lower temperature.
The standard catalyst/carrier combination, under the
conditions of the evaluation had a selectivity of 81. 2~
~ ~1173240
W096/08309 PCT~S94/09775
"Pack. Density" is the settled packing density as
measured by ASTM D-4699-87, modified as described above,
or the equivalent.
The "Crush Strength", (occasionally called "C.S."), of
the carrier is measured as described above.
"Attrition" is the amount of catalyst weight loss
measured using ASTM D-4058-92.
The "surface area" is the BET surface area measured using
nitrogen or krypton as the adsorbate.
As can be seen, the carriers in accordance with the
invention allow a higher degree of selectivity to the
desired product while operating at a lower temperature.
These improvements are considered extremely significant.
Example 3
In the pair of experiments that comprise this
Example, the effect of the presence of the sol-gel
derived component is determined.
The formulations that were used to make the carriers
is set forth in Table 3 and the physical properties and
selectivity, (assessed as in Example 2) are described in
Table 4.
SU~ttTl~E Sff~T t~ULE ~6
W096/~8309 ~1 7 3 ~ ~ O PCTIS9Jl~9775
TABLE 3
COMPONENT WITH SOL-GEL NO SOL-GEL
C0MPONENT Wt% COMPON:NT Wt%
ALPHA ALUMINA #1 48.7 50.6
ALPIA ALUMINA #2 42.25 48.1
ALPHA ALUMINA SEED 0.5 0
DISPERSIBLE BOEHMITE 7.25 o
CERAMIC BOND 1.3 1.3
ORGANIC BURNOUT 20 20
PETROLEUM JELLY 5.0 5.0
FORMIC ACID 2.4 2.4
BORIC ACID 0.15 0.15
The carrier cont~ ning the sol-ge_ component, (shown
in the first column), is a carrier according to the
invention. The other is given for comparative purposes.
The all7~;n.7s used are as indicated in Table 1. In both
formulations water was added to make the mixture
extrudable, (about 30~). The weights of the last three
components in the chart are based on 100 parts by weight
of the ceramic components.
SUBSTITUTE SHEET (RULE 26)
CA 02173240 1998-12-1
TABLE 4
INVENTION INVENTION
WATER ABSORPTION ~ 41.5 47.8
PACK, DENSITY (KG/M3) 756.1 719.3
CRUSH STRENGTH (N) 6.90 5.11
SURFACE AREA (M2/GM) 1.18 1.47
FIRING TEMPERATURE 1482 1482
( o C )
ACID LEACHABLES (ppm)
sodium
potassium 138 174
calcium 80 104
aluminum 132 188
394 460
SELECTIVITY +0.2 -1
The packing density, crush strength, selectivity and
surface area were measured as described in Table 2. The
water absorption is a measure of the increase in weight of
the carrier after being immersed in water and weighed.
The results indicate that the crush strength of the
carrier of the invention is significantly increased by the
presence of the sol-gel component while maintaining the
surface area at over 1.1 m2/gm. The selectivity of a
standard catalyst supported on the carrier of the invention
is slightly better than the standard but significantly
better than the same catalyst supported on a carrier
without the sol-gel component. The carrier can therefore
be expected to have a longer life than carriers made
without the seed component.
Example 4
This Example illustrates the performance of a carrier
evaluated in the same way as is described in Example 2.
-11--
~ H-2630/l ~ 1 7 3 2 ~ O
The carrier comprised:
40~ by weight of alpha alumina particles with a median
particle size of about 3 to 3.5 microns and a surface
area of about 1 */gm;
52.1% by weight of gibbsite;
o.9% of alpha alumina seed particles with a median
particle size of less than about 0.1 micron; ''
6% by weight of boehmite;
1% by weight of a ceramic bond; and
2.4% of formic acid.
The formulation comprised in addition the additives
described in Example 2, (burnout material, petroleum
jelly and boric acid), and water is added to make the
formulation extrudable.
The carrier had a surface area of 1.06 m2/gm., a
crush strength of 15.4..-lb (6.90.N) and packing density of
51.2 lb/ft3 (820.2 kg/m3). All these properties are
measured as described in Example 2. . ~ ;
The carrier, when evaluated as described in Example
2 had a selectivity increase of 0.5 which was obtained at
- a.temper~tllr~that was.?3~C lower.. than for the.. standard.~ c
S.
Exam~le 5
." This Example describes the effect of adding titania to a
carrier formulation according to the invention. The
formulations used are set out in Table 5 and the
properties are described in Table 6.
:-,-'.: .. ' '~1 .', .
, ;~ ~ . s
. .
A?A~?, ~ ~?~ ?~ .
CA 02l73240 l998-l2-l~
TABLE 5
CARRIER COMPOS. CARRIER D CARRIER E CARRIER F CARRIER G
ALPHA #1 * 46.6~ 46.6% 46.6~ 46.6
ALPHA #2 * 28% 28~ 28% 28%
ALPHA #3 * 0.9% 0.9% 0.9% 0.9%
(SEED)
GIBBSITE * 18.7% 18.7~ 18.7~ 18.7
BOEHMITE * 4.5% 4.5~ 4.5% 4.5
CERAMIC BOND * 1.3~ 1.3% 1.3~ 1.3%
TiO2 * 0.1~ 0.2~ 0.1~ 0.2
ORG. BURNOUT ~ 11% 11
PET. JELLY ~ 5~ 5~ 5~ 5
BORIC ACID ~ 0.15~ 0.15% 0.15% 0.15
WATER (to make about 30~ about 30% about 30~ about 30
extrudable)
* indicates "ceramic components" and percentages given
are based on lO0~ of the ceramic components.
** percentages are based on total weight of ceramic
components.
The "D" and "E" carriers were fired at 1420~C and the
"F" and "G" carriers were fired at 1480~C. The components
were all as described in Example 2. The titanium oxide was
in a hydrated form and had a surface area of about 250
m2/gm.
TABLE 6
CARRIER D CARRIER E CARRIER F CARRIER G
SELECTIVITY +0.7/-7 +0.8/-11 +0.7/-8 +1.3/-8
S.A. (M2/GM) 1.15 1.01 0.86 0.70
P.D. (KG/M3) 770.7 815.9 848.1 770.7
C.S.(N) 5.64 6.67 8.06 6.90
-13-
wo ~G,~a~3 ~ 1 7 3 2 4 ~ PCT~S94/09775 -
at elevated temperatures. There are many such processes
in the petrochemical industry but the present carrier has
proved itself particularly suitable in the catalytic
formation of ethylene oxide from a gas streamlcomprising
s ethylene and oxygen. The utility of the present
invention is however not so limited.
Example 6
This Example details the preparation of the carriers.
The exact identification of the components is~ given in
Table 7 below. The mixing process used was as follows.
The ceramic components are mixed with a burn-out
material, (walnut shell flour), and boric acid for about
a minute. Water and the seed component are added, the
w~ter being in an amount that is necessary to make the
mixture extrudable. Generally this is about 30~ by
weight. The mixture is mixed for about two to four
minutes and then about 5% by weight based on the weight
of the ceramic components, of vaseline is added as an
extrusion aid. The mixture is then mixed for a further 2
to 4 minutes before being extruded in the form of hollow
cylinders and dried to less than 2% uncombined water.
These were then fired in a tunnel kiln with a maximum
temperature of about 1500~C for about 4 hours.
SUBSllTUTE SHEET (RULE ~5
I
~ W096/08309 i~ 7 3 2 g O PCT~S94/09775
TABLE 7
CARRIER COMPOS. CARRIER H CARRIER I CARRIER J
ALPH~ #1 * 45.5% 46.0% 46.0%
ALPH~ #2 * 28% 27.6% 27.6%
ALPHA #3 * (SEED) 2.0% 2.2% 2.2%
GIBBSITE * 18.7% 18.4% 18.4%
BOEHMITE * 4.5% 4.5% 4.5%
CERAMIC BOND * 1.3~ 1.3% 1.3%
Tio2 * 0.6% 0.4% 0.4%
ORG. BURNOUT ** 11% 15% 11%
PET. JELLY ** 5% 5% 24~
BORIC ACID ** 0.15% 0.15% 0.15%
WATER (to make about 30% about 30% about 30%
extrudable)
x indicates "ceramic components" and percentages given
are based on 100% of the ceramic components.
** percentages are based on total weight of ceramic
components.
Water is added in an amount to make the above mixture
extrudable.
"Alpha #1" is a commercial alpha alumina that has a
median particle size of 3 to 3.4 microns, a BET surface
area of about 0.9 to about 1.4 m2/gm, a crystallite size
of 1.6 to 2.2 microns and a soda content of 0.02 to
0.06%.
"Alpha #2" is an alpha alumina with a median particle
size of 4.0 to 8.0 microns, a surface area of 3.0 to 5.0
m2/gm, a crystallite size of from 0.4 to 0.8 micron and a
soda content of 0.1 to 0.3%
"Alpha~3i' is an~a12ph~ alumina that was used as the seed
for the gibbsite and boehmite precursors of alpha
alumina. Its median particle size was less than 0.1
SUBSTITUTE SHE~T (RULE 26)
~ H-2630/1
~3~
micron.
The gibbsite had a median particle size of from 4.0 to 20
microns and the boehmite was dispersible as a sol.
The titanium oxide was in a hydrated form and had a
surface area of about 250 m2/gm.
The ceramic bond contained components, (expressed as the
oxides), in the following approximate proportions: 60%
silica, 29% alumina, 3% of calcium oxide, 2% of magnesia,
4% of alkali metal oxides and less than 1% each of ferric
oxide and titania.
All the carriers were fired at 1390~C.
TABLE 8
CARRIER H . CARRIER I CARRIER J
SELECTIVITY +1.2/-12 +1.3/-8 +1.2/-6
S.A. (M2/GM) 0.66 0.78 0.72
P.D. (LB/FT3) 50.14 51.8 48.6
C.S. (LB) 17.9 18.5 15.3
. . . :~ - - i;
16
