Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21~31
12,439-1
This invention is concerned with silver catalysts,
their manufacture and their use in the manufacture of
ethylene oxide. The catalyst of this invention comprises
a supported silver catalyst. The catalyst contains a
combination of (a~ cesium and (b) at least one other alkali
metal selected from the group c~nsisting of lithium,
sodium, potassium and rubidium, wherein (a) and (b) are
present in amounts in relation to the amount of silver
therein sufficient to increase the efficiency of the
ethylene oxide manufac~ure to a value greater than the effi-
cienc~es obtainable under common operating conditions f~om
respective catalysts which are the same as said catalyst
except that instead of containing both (a) and (b), one
contains the respective amount of (a), and the other contains
the rcspective amount of (b). Thus, the catalyst, when
utilized in the manufacture of ethylene oxide, con-
tains a combination of cesium and one or more other
alkali metals (excluding francium) in an amount which
achieves a synergistic result as defined herein. In
addition, the process of this invention defines such
synergism as a function of the silver content of the
catalyst. Thus, for any given amount of silver in the
catalyst, the present invention provides the appropriate
correlation of alkali metal and silver whereby particular
combinations of cesium and one or more other alkali metals
may be selected which achieve efficiencies in the manu-
facture of ethylene oxide which exceed the higher
efficiency obtainable with such amount of silver when
in combination with the respective amount of either
cesium or the other alkali metals in such mixture.
~
~ 1 62~8~
12,439-1
The manufacture of ethylene oxide by the re-
action of oxygen or oxygen-conta.ining gases with ethylene
in the presence of a silver catalyst is an old and very
well developed art. For example, V. S. Patent No.
2,040,732, patented May 12, 1936, descrlbes the manu-
facture of ethylene oxide by the reaction oE oxygen with
ethylene in the presence of silver catalysts wb.ich con-
tain a class of metal promoters. In Reissue U. S. Patent
20,370, dated May 18, 1937, Leforte discloses that ~he
formation of olefin oxides may be effected by causing
olefins to combine directly with molecular oxygen in
the presence of a silver catalyst. From that point on,
the prior art has focused its efforts on improving the
catalyst's efficiency in producing ethylene oxide.
In characterizing this invention, the terms
"conversion", "selectivity", and "yield" are employed as
defined in U~ S. Patent No. 3,420,784, patented January 7,
1969, a~ column 3, lines 24-35 inclusive, This definition
of "selectivity" is consistent with that disclosed in
U. S. Patent No. 2,766,261 at column 6, lines 5-22, and
U. S. Patent No. 3,144,916, lines 5~-61. The definitions
of "yield" and "conversion" have more varied meaning
in the art and are not to be employed as defined, for
example, in the aforementioned U. S. Patent No. 2,766,261.
The terms "efficiency'` and "selectivity" as used throughout
the specification and claims are intended to be synonomous.
Silver catalysts employed in the manufacture
of ethylene oxide have undergone significant changes
since their initial period of development. As reported
181
12,439-l
by the art, silver particles were first deposited
upon support materials with little attention being paid to
support properties, such as surface area, pore volume
and chemical inertness. As the art evolved, there develop-
ed special ~echnologies related to carriers or supports con-
taining silver that were more effective for the reaction
of ethylene with oxygen to produce ethylene oxide. Today,~
most supports for the silver catalysts are particulate
materials which can be loaded in the interior of a reactor
wherein the reacting gases and the gaseous products of
the reaction are capable of flowing in and about these
particulate materials to pass through the reactor and
be recovered. The shape of the support is a variable
factor and the particular shape selected is peculiar to
the reactor employed, the gas flow required, and the
surface area which is desired for the optimization of
the reaction with other factors also being considered
The carriers that have been employed are
typically made of inorganic materials, generally of a
mineral nature. In most cases, the preferred carrier
is made of alpha-alumina, such as has been described in
the patent literature: see for example, U. S. Patents
2,294,383; 3,172,893; 3,332,887; 3,423,328; and 3,563,914.
The silver that is deposited on these carriers
is typically in the form of small particles. The patent
literature indicates that the size of the silver is a
factor in the elfectiveness of the catalyst and in most
cases fine particle silver i 5 obt2i.ned u~ilizing the
standard processes in the art; see or exa~.ple, U. S.
Patent Nos. 2,554,459; 2,831,870; 3,423,328 ~specifies
that silver particles of 150-400 angstroms are employed);
-- 4 --
~ ~2~
12,439-1
3,702,259 (disclosed a preparation procedure for forming
silver particles less than 1 micron in diameter) and
3,758,418 (discloses silver particles having a diameter
less than 1000 angstroms).
The deposition of silver onto the carrier
can be achieved by a number of techniques but the two
techniques which are most frequently employed involve,
in one case, the impregnation of the support with a silver
solution followed by heat treatment of the impregnated
support to effect deposition of the silver on the support
and, in the other case, the coating of the silver on the
support by ~he precipitation of silver or the preformation
of silver into a slurry such that the silver particles
are deposited on the support and adhere to the support
surface when the carrier or support is heated to remove
the liquids present. These various procedures are
exemplified in various U. S. Patents such as 2,773,844;
3,207,700; 3,501,407; and 3,664,970 (see British Patent
754,593), and 3,172,893.
The surface area provided by the suppor~ has
been the subject of considerable interest in the develop-
ment of silver catalysts. Disclosures concerning the
surface area of the catalyst carrier can be found in
U. S. Patent 2,766,261 (which discloses that a surface
area of 0.002-10 m2/gm is suitable); U. S. Patent
3,172,893 (which depicts a porosity of 35-65% and a
pore diameter of 80-200 microns); U. S. Patent 3,725,307
(which depicts a surface area of less than 1 m2/gm and
an average pore diameter of 10-15 microns); U. S. Patent
-- 5 --
~62~
12,439-1
3,664,970 (which utilizes a support having a minimum
porosity of about 30%, at least 90% of the pores having
diameters in the range of 1-30 microns, and the average
of such diameters being in the range of 4-10 microns);
and U. S. Paten~ 3,563,914 (which utilizes a catalyst
support having a surface area of less than 1 m2/gm, a
volume of 0.23 ml/gm and a particle size between 0.074
and 0.30 mm).
In the very earliest developments of silver
catalysts for the manufacture of ethylene oxide, it
has been determined that a number of metals when present
in combination with the silver could act as promoters of
the silver catalyst. These materials in themselves are
not catalysts but contribute to enhance the rate or amount
of oxide production. Cne of the problems in determining
whether or not these ~.etals act as promoters is the nature
of the reaction`itself. The reaction between oxygen and
ethylene to form ethylene oxide is a highly exothermic
reaction. However, even more exothermic than that re-
action is the combustion of ethylene or ethylene oxideto carbon dioxide. These reactions occur simultaneously
and the critical factor in determining the effectiveness
of the over,-all process is the measure of control
one has over these two competing reactions. Inevitably,
a material which enhances the production of ethylene oxide
might also be considered a material which inhibits the
complete combustion of ethylene to ethylene oxide to carbon
dioxide. Thus, there is a problem in defining whether that
material which is termed as a promoter is in fact an
inhibitor of the combustion reaction. It is well known
~3S218~
12,439-1
that there are materials which when added to the reaction
result in less carbon dioxide being formed and such
materials are termed inhibitors. There are also ~aterials
which when provided with the catalysts result in greater
production of ethylene oxide and those materials are
termed promoters. Whether the latter materials are in
reality inhibitors or promoters seems to be an irrelevant
issue. What is significant is that the outcome of the
reaction is favorable to the production of ethylene oxide.
For that reason, when determining or characterizing a
catalytic process for producing ethylene oxide a signifi-
cant factor entering into or qualifying that process is
the selectivity of the process to produce ethylene oxide,
selectivity being as defined previously.
The use of alkali metals as promoters for the
silver catalyzèd production of ethylene oxide is extremely
well known in the art. As far back as U. S. Patent
2,177,361 issued October 1939 there is found a teaching
of the use of alkali metals in silver catalysts. U. S.
Patent 2,238,471 discloses that lithium was very desirable
as a promoter but that potassium and cesium were detri-
mental The examples of that patent utilize essentially
10% by weight of potassium hydroxide or cesium hydroxide
to the silver oxide employed in making the catalyst. Later,
U. S. Patent 2,404,438 stated that sodium and lithium were
effective promoters for this reaction. Essentially the same
teaching could be found in U. S. Patent 2,424,084. U. S.
Patent 2,424,086 generalized about alkali metals as pro-
moters and specified sodium in particular. In U. S.
1~ 82~8~
12,439-1
Patent 2,671,764, the patentees believed that alkali metals
in the form of their sulfates would be effective as
promoters for such silver catalysts. In particular, the
patentees stated that sodium, potassium, lithium, rubidium
or cesium sulfates may be used as promoters. U. S. Patent
2,765,283 described the pretreatment of a support with a
dilute solution of a chlorine containing compo~nd and
indicated that such chlorine compounds should be inorganic.
Particular illustrations cited of suitable inorganic chlorine
compounds i~cluded sodium chloride, lithium chloride and
potassium chlorate. This patent specified that the amount
of the inorganic chlorine containing compound which is
deposited on the catalyst support is from 0.0001% to 0.2%
by weight, based on the weight of the support. U. S.
Patent 2,615,900 to Sears describes the use of metal
halide in the treatment of the supported catalyst and
specifies that such halides can be of alkali metals such
as lithium, sodium, potassium, and cesium. The metal
halide is present in the range of 0.01% to 50% based
upon the weight of metallic silver. The patent also
specif ies that mixtures of the individual metal halides
generally classified in the patent may be used to advan-
tage to enhance the break-in period of a new catalyst
composition while at the same time maintain a moderate
but steady activity of the catalyst over an extended
period of time during normal operation. Thus, one
particular metal halide treated catalyst would provide a
short-term high initial activity whereas another of the
metal halides would provide a longer term moderate
activity for the catalyst. This patent takes the position
1 ~ ~2 18 1
12,439-1
that the metal halides which are provided in the catalyst
serve to inhibit the combustion of ethylene to carbon
dioxide and thus classifies these materials as catalyst
depressants or anticatalytic materials. U. S Patent
2,709,173 describes the use of a silver catalyst for
making ethylene oxide in which there are provided
simultaneously with the introduction of the silver
catalyst to the solid support any of the alkali metal
halides such as lithium, sodium, potassium, and
rubidium compou~lds of chlorine, bromine and iodine, to
enhance the overall production of ethylene oxide. The
patent specifies small amounts "of less than about 0.5~/o
are desirable". In particular the patent emphasizes
"proportions of alkali metal halide within the range of
about 0.0001 to about 0.1%" are most preferred. The patent
states that "although the preferred catalyst composition
contains a separate promoter it is not always necessary
since during preparation of the catalyst the alkali
metal halide may be converted to some ex~ent to the
corresponding alkali metal oxide which acts as a promoter".
U. S. Patent 2,766,261 appears to draw from the teachings
of U. S. Patent 2,238,474 in that cesium and potassium are
said to be detrimental in silver catalysts; sodium and
lithium are suggested as useful promoters. However, U. S.
Patent 2,769,016 finds that sodium, po~assium and
lithium are promoters when used in the silver catalysts.
This latter patent also recommends the pretreatment cf
the support with dilute solutions of sodium chloride,
lithium chlcride or potassium chlorate. U. S. Patent
2,799,687 to Gould et al states that the addition of metal
1 1~2~81
12,439-1
halides within the range described by Sears in U. S.
Patent 2,615,900 is not productive of optimum results.
This is said to be especially true in the case of alkali
metal halides, particularly the chloride and fluoride of
sodium and potassium. The patentees recommend that the
inorganic halide component of the catalyst be maintained
within the range of 0.01-5 weight percent, preferably .01
to 0.1 weight percent, based on the weight of the "silver
oxidative catalytic component", i.e., the silver salt
transformed into elemental silver. U. S. Patent 3,144,416
mentions a variety of metals as promoters and one of
them is cesium. U. S. Patent 3,258,433 indicates th~t
sodium is an effective promoter. U. S. Patent 3,563,913
recommends the use of alkali me~als such as lithium
compounds as promoters. The preferred amount of promoting
material is said to be about 0.03 to 0.5%, by weight, of
metal oxide based on the weight of the support. U. S.
Patent 3,585,217 states that alkali metal chlorides "are
known to counteract the formation of carbon dioxide" and
"may be incorporated into the catalyst". U. S. Patent No.
3,125,538 discloses a supported silver catalyst contain-
ing a coincidentally deposited alkali metal selected from
among potassium, rubidium and cesium in a specified gram
atom ratio relative to silver. The weight of silver is
preferably 2-5% by weight, of the catalyst. The patentees
characterize this catalyst as being especially suitable
for the reaction of nitric oxide with propylene. U. S.
Patent ~os. 3,962,136 and 4,012,4~5 disclose the identical
catalyst as being useful for ethylene oxide production.
U. S. Patent 3,962,136 describes the coincidental
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1 J ~2181
12,439-1-C
deposition of al~ali metal with the silver on the support,
the alkali metals being present in their final form on the
support in the form of an oxide in which the oxide con-
sists of cesium, rubidium or mixtures of both, optionally
combined with a minor amount of an oxide of potassium.
The amount of such oxide is from about 4.0 x 10-5 gew/kg
to about 8.0 x 10-3 gew/kg of total catalyst. However,
U. S. Patent 4,010,115, patented March 1,1977, dis-
tinguishes itself by employing as the oxide of the alkali
etal the oxide of potassium optionally combined with a
parent
minor amount of an oxide rubidium or cesium. The/applica-
tion of U. S. Patents 3,962,136 and 4,010,115, and others,
contains some interesting data deserving of comment.
According to example 2 which contains some comparative
experiments, there is described the manufacture of a
catalyst which contains 310 parts per million by weight
of coincidentally-added potassium and that catalyst when
employed as an ethylene oxidation catalyst was found to
be inactive for the production of ethylene oxide. Even so,
we find that that amount of potassium in the catalyst lies
within the range disclosed in U. S. Patent 4,010,115 to
be effective for the production of ethylene oxide, although
no data is shown in the patent to support that view.
Belgium Patent 821,439, based upon British Patent
Specification 1,489,335, discloses that a catalyst can be
made that is equivalent to that produced in U. S. Patent
Nos. 3,962,136, 4,012,425, and Patent 4,010,115 to
Neilsen et al. by varying the procedure by which the alkali
1 1 6~81
12,14g-1-C
metal is supplied to the support. In the Belgium Patent
and its British equivalent, a porous refractory support
of a specified surface area is first impregnated with an
alkali metal to deposit it on the support metal in
specified quantities (both the quantities and the nature
of the porous support being equivalent to that which is
set forth in the aforementioned Nielsen et al U. S. Patents),
the support is then dried to fix the alkali metal and there-
after the silver is supplied to the support. This pro-
cedure is a sequential deposition of the alkali metal
promoter and the silver catalyst and yet essentially the
same type of catalyst was produced by the simultaneous
deposition of alkali metal and silver as evidenced by
a comparison of ~he data in the examples of the ~elgium
Patent with the data set forth in the aforementioned
Nielsen et al U. S. Patents. The criticality in the method
of deposition of alkali metal upon the support appears
doubtful in the face of that type of disclosure and the
disclosure of U. S. Patent Nos. 4,033,903 and 4,125,480
which describe subjecting a used silver-containing catalyst
with a post-addition of one or more of potassium, rubidium
or cesium. Apparently such treatment regenerates the
catalyst's ability to enhance selectivity to ethylene
oxide. Another patent which tends to indicate that a
post-addition of alkali metal such as cesium gives
results equivalent to either pre-addition or simultaneous
addition is U. S. Patent 4,066,575.
U. S. Patent 3,962,136 and its companion patents
were derived from a parent application filed
January 7, ]972, now abandoned, U. S.
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t 1 62~8~
12,439-1-C
Patent 3,962,136 discloses that the "highest level of
selectivity obtainable with potassium modified catalysts
at otherwise comparable conditions typically is lower
than that obtainable with rubidium or cesium-modified
catalysts" (see column 2, lines ~8-42). The parent
application contains a drawing which depicts the relative
effectiveness of rubidium, cesium and potassium to enhance
the selectivity of ethylene oxide when utilized in a
silver catalyst. The drawing shows that the curve C
which represents cesium addition provides the greatest
degree of enhancement of selectivity while curve B which
represents rubidium addition is intermediate and superior
to potassium addition represented by curve A. In an
amendment filed on April 11, 1975, in parent application
(filed June 19, 1974) to U. S. Patent 4,010,115, the
applicant urges that the invention and claims do not
involve "synergistic effects with the use of mixtures"
of the alkali metals. The same statement was made in
the amendment received on April 11, 1975 in the parent
application (filed May 20, 1974) to U. S. Patent 4,012,425.
German Offenlegungsschrift 2,640,540 discloses
in its examples a silver catalyst for ethylene oxide
production containing sodium and either potassium,
rubidium or cesium. Table I of this disclosure provides
the alkali content of all catalysts prepared in the
examples, many of which contain sodium, potassium and
cesium. A footnote
1 ~218~
12,439-1
to the Table states that the presence of potassium in
all catalysts tested (except for one which was free of
cesium) was due to impurities present in the support,
the level of such impurities being below that specified
as being useful for the invention. The disclosure does
not suggest that cesium may be combined with potassium
and/or sodium to advantage nor does the efficiency data
provided in the Table demonstrate any synergistic inter-
action of cesium with sodium or the potassium impurities
in the catalysts.
Japanese Application Publication Disclosure
No. 95213/75 is directed to a process for producing
ethylene oxide using a catalyst composition comprising
silver, barium, potassium and cesium in specified atomic
ratios. Table I of this disclosure summarizes the
efficiencies achieved with the various catalyst composi-
tions of the examples. No synergism with cesium and
potassium was demonstrated by any of the cesium-potassium-
barium mixtures of the examples. Indeed, a comparison of
some examples among Table I appears to demonstrate the
absencè of a cesium-potassium synergism, namely, the
efficiency achieved with a cesium-potassium mixture
is shown to be lower than the efficiency achieved with
the same amount of cesium in the absence of potassium.
For example, Examples 3 and 7 relate to catalysts having
an identical atomic ratio of cesium to silver (.05 atoms/
100 atoms Ag~, but differing potassium contents, the
atomic ratio of potassium in Example 3 being .001 atoms
K/lO0 atoms Ag and the corresponding ratio in Example 7
1 1 62181
12,439-1
being .05. The efficiency achieved in Example 3 was
76.4% and that of Example 7 was 75.9%. Thus, the
increased potassium content in E~ample 7 resulte~ in
a decrease in catalyst efficiency. Similarly, Examples
1 and 4 relate to catalysts havinv an identical atomic
ratio of cesium to silver, with the catalyst of Example 1
containing an amount of potassium one order of magnitude
greater than the catalyst of Example 4. Yet, the
efficiencies reported for both catalysts are essentially
the same, 76.7% and 76.6% for Examples 1 and 4,
respectively.
U. S. Patent 4,039,561 discloses a catalyst for
preparing ethylene oxide containing silver, tin, antimony,
thallium, potassium, cesium and oxygen in specified atomic
ratios. Mixtures of cesium and potassium are not dis-
closed to be desirable combinations. Indeed, Table I
of the patent discloses a silver-cesium-potassium com-
bination which is designated as a "control" example not
in accord with the disclosed invention and which achieved
a selectivity of 73.0%, a value markedly lower than the
selectivities achieved in the 45 Examples listed in
Tables 2 and 3. Moreover, the efficiencies provided in
Tables 2 and 3 for the various catalysts fail to demon-
strate the existence of any synergistic combination of
cesium and potassium among the numerous combination of
elements which were employed in the catalysts. It is also
note-worthy that the aforesaid U. S. Patent 4,039,561
claims the priority of a Japanese application filed in
1973, and that subsequent to such filing the same appli-
cant filed Japanese Application Publication No. 25703/77
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1 1 62181
12,439-1
which discloses a catalyst for ethylene oxide manufacture
comprised of the same metallic elements disclosed in
the U. S. Patent with the exception of cesium and
potassium. The efficiencies disclosed in the examples
of the latter Japanese Application are similar to those
shown in the U. S. Patent. The effect of cesium and
potassium in the catalyst composition disclosed in the U. S.
Patent is therefore presumably insignificant.
Belgium Patent 854,904 discloses silver catalysts
containing various mixtures of sodium and cesium. U. K.
Patent Application GB 2,002252A discloses, in Table 2,
supported silver catalysts containing various mixtures of
cesium and thallium, some of which additionally contain
potassium or antimony. U. S. Patent 4,007,135 broadly
discloses (in column 2, lines 25-30) silver catalysts for
alkylene oxide`production containing silver "together
with a promoting amount of at least one promoter selected
from lithium, potassium, sodium, rubidium, cesium, copper,
gold, magnesium, zinc, cadmium, strontium, calcium,
~ niobium, tantalum, molybdenum, tungsten, chromium, vana-
dium and barium...". European Patent Publication No.
0003642 discloses, in Table 3, silver-containing catalysts
~which include mixtures of potassium and cesium, and a
catalyst containing sodium and cesium. The above publica-
tions do not indicate a synergistic interaction of cesium
with otne~ alkali metals. !
Belgium Patent 867,045 discloses supported silver
catalysts containing what is referred to as an effective
proportion of lithium and a substantially lesser amount of
alkali metal selected from among cesium, rubidium and/or
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1 1 62~
12,439-1
potassi~n. Table I of the patent discloses three catalysts
all of which contain cesium, sodium, potassium and
lithium, the lithium concentration being at least one
order of magnitude greater than the concentration of
cesium or potassium. Referring to Table I, the catalysts
Ll, L2 and L3 have markedly different concentrations of
cesium, potassium and sodium, but are shown in Table II to
provide substantiallv similar selectivities. There is no
indication of a synergistic interaction of cesium with
either potassium or sodium in the silver catalysts dis-
closed.
Belgium Patent 867,185 discloses supported silver
catalysts for ethylene oxide production containing a
specified amount of potassium and at least one other alkali
metal selected from rubidium and cesium. Table I dis-
closes the composition of 14 potassium-containing catalysts,
two of which contain potassium in combination with cesium
(catalysts G and H). The selectivities of catalysts G and
H are shown to be identical at a pressure of 1.03 bars,
but differ slightly at the higher pressure of 16.55 bars.
No silver-potassium-cesium synergism can be discerned from
the data.
This invention distinguishes over the prior
art in the fact that the silver catalyst employed in
manufacturing ethylene oxide utilizes at least two alkali
metals (excluding francium~, one of which is cesium, each
of the alkali metals being present in an amount such that
the combination thereof in relation to the amount of silver
in the catalyst provides a synergy in terms of ethylene
oxide selectivity and a selectivity which is greater than
has been contemplated or disclosed by any prior art.
1 ~ ~2 1 8 .t
In accordance with one aspect of the present
invention, there is provided a silver catalyst deposited
on a macroporous support having a surface area less than
lOm2/g and in a form and size for use in a fixed bed
tu~ular reactor used in a commercial operation for the
manufacture of ethylene oxide by vapor phase reaction
of ethylene and oxygen or an oxygen-containing gas in
gaseous admixture with diluent and inhibitor, which
catalyst contains 2 to 20 weight percent silver and a
combination of (a) cesium and (b) at least one other
alkali metal selected from the group consisting of lithium,
sodium, potassium and rubidium, which combination compri-
ses (a) and (b) in amounts in relation to the amount
of silver therein sufficient to increase synergistically
the efficiency of the ethylene oxide manufacture to
a value greater than the efficiencies obtainable under
common conditions from respective catalysts which are
the same as the catalyst except that instead of containing
both (a) and (b), one contains the respective amount
of (a), and the other contains the respective amount
o (b).
In the detailed description of the invention
which follows, reference will be made to the graphical
representation of the accompanying drawings, wherein:
Figures 1 and 2 show contour lines drawn at
constant efficiency and temperature in the potassium~
cesium concentration space with the darker lines represen-
ting selectivity contours (selectivity values indicated
for each line) and with the lighter, broken lines repre-
senting temperature contours (temperatures indicatedfor each line).
- 17A -
116218~
The catalysts of the invention are characterized
by a combination of (a) cesium and (b) at least one other
alkali metal selected from the group consisting of lithium,
sodium, potassium and rubidium so as to achieve a syner-
gistic result, i.e., an efficiency greater than the greater
value obtainable under common conditions from respective
catalysts which are the same as said catalyst except
that instead of containing both (a) and (b), one contains
the respective amount of (a), and the other contains
the respective amount of (b). Catalysts in accord with
the invention are comprised of silver, cesium and at
least one other alkali metal (excluding francium) deposited
onto the surface of a porous support, the particular
mixture of silver and alkali metals being correlated
to produce a synergistic result.
The invention as hereinafter described defines
the binary alkali metal combinations of cesium-lithium,
cesium-sodium, cesium-potassium and cesium-rubidium,
which in co~bination with silver provide a synergistic
result for a particular catalyst carrier and catalyst
preparation. The catalysts of the invention are not,
however, restricted to binary combinations of alkali
metal. Other alkali metals may advantageously be added
to any of the aforementioned synergistic binary co~bina-
tions for the purpose of raising or lowering the catalyst
operating temperature, improving the initial catalyst
activity during the start-up period and/or improving
the aging characteristics of the catalyst over prolonged
periods of operation. In some
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` ~62181
12,439-1
instances, the addition of a third or even a fourth alkali
metal to an otherwise synergistic binary combination will
effect a further increase in catalyst efficiency.
The mathematical relation.ships from which are
derived the synergistic binary a~kali metal co~binations
of the invention are set forth below and described, for
purposes of illustration, in terms of a cesium-potassium
combination. Binary combinations of cesium with any of
the other alkali metals in accordance with the invention are
readily determined by an analogous procedure wherein the
particular alkali metal of interest is substituted for
potassium in the procedure described below.
The relationship of cesium, potassium and silver
to ach.Fve a synergistic result as herein defLned is
characterized with the aid of a mathematical equation, or
model, which correlates efficiency as a function of weight
percent silver, weight percent cesium and weight percent
potassium deposited on the catalyst support. Thus,
synergism with mixtures of cesium and potassium
can be obtained at any concentration of silver in the
finished catalyst.
The general form of the mathematical equation,
hereinafter referred to as the "Efficiency ~odel", defines
efficiency (or selectivity) as a function of weight per-
cents (wt. %) of silver, cesium and potassium deposited
on the catalyst support as follows:
Efficiency, % = bo + bl(BG) + b2(BCs) + b3(BK)
+ b4(BG)2 + b5(BCs)2 + b6(BK)2
+ b7(BG x BCs) + b8(BG x BK)
+ b9(BCs x BK)
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1 1 62181
12,439-1
where:
o' 1' b2~ b3~ b4~ bs~ b6, b7, b8 and bg are the
respective coefficients for each term of the Efficiency
Model, and comprise a set of constants determined for a
particular catalyst carrier and a particular~method of
catalyst preparation following a designed se~ of experi-
ments as hereinafter described. The value of some of
these coefficients may be zero.
BG = (wt. % Ag - wt. % Ag);
0 where, wt. % Ag = average value of wt. % Ag used in .he
designed set of experiments.
BCs = (wt. % Cs - wt % Cs);
where, wt. % Cs = average value of wt. % Cs used in the
designed se; of experiments.
BK = (wt. % K - wt. % K);
where, wt. % K = ave-age value of wt. % K used in the
designed set of experiments.
The designed set of experiments is most con-
veniently planned in the format of a Composite Design in
three independent variables as described by 0. L. Davies,
"The Design and Analysis ~f Industrial Experiments",
Hafner Publishing Company, 1960, P. 532-535. For this
purpose, the three independent v,~riables are the weight
percents of silver, cesium and potassium, respectively.
The ranges of each variable are chosen so that selec-
tivity al:' activity of all catalysts in the designed -`
set of experimen s can be measured under the desired
test conditions. It is therefore desirable to first
conduct a few preliminary range finding experiments to
- 20 -
1~82181
12,439-1
determine the appropriate ranges of cesium and potassium
for this purpose. Zero perc~llt cesium and/or potassium
is a convenient lower limit for use in the Composite
Design The upper concentration limit of cesium and
potassium can be readily determined by a series of experi-
- ments with catalysts containing successively larger amounts
of either cesium or potassium as follows: An initial
catal-,ist is prepared (using a preparation procedure,
if desired, such as hereinafter disclosed in the Examples)
containing a small amount (on the order of about 0.001
percent by weight) of either cesium or potassium with a
fixed amount, say 7 percent by weight, of silver, and
its selectivity then determined for the pro.iuction of
ethylene oxide at the desired test conditions. This
experiment is then repeated with a catalyst containing
double the amount ~0.002 percent by weight) of the
alkali metal and the experiment thus repeated in a series of
experiments wherein eac~ succeeding experiment uses a
catalyst containing double the alkali metal content of
the catalyst of the previous experiment, until the
measured selectivity of the last catalyst tested is
less than that of the initial catalyst. The upper limit
of cesium or potassium concentration is thus defined for
the Composite Design.
The above-described interative procedure may be
advantageously altered so as to more quickly determine the
upper limit of concentration in the event it is observed
that a two-fold increase in the alkali metal content of the
catalyst does not produce a significant change in catalyst
- 21 -
13162181
12,439-1
selectivity. This is particularly likely to occur, for
example, with catalysts containing lithium or sodium
(depending upon the particular carrier and preparation
procedure employed) in contrast to catalysts containing
other alkali metals where, as a general rule, the efficiency
response is more sensitive to increasing alkali con-
centration. Accordingly, in the event the catalyst
efficiency is virtually unchanged when the alkali content
of the catalyst has been doubled, a ten-fold increase in
alkali content should be employed in the above-described
iteration until the measured efficiency of the last catalyst
is less than that of the initial catalyst. Thereafter it may
be desirable to repeat the last iterative step using a
lower level of alkali, such as, a three or five-fold increase
of alkali ~etal content, in order to more accurately deter-
mine the upper limit of alkali metal concentration for ~he
Composite Design.
The range of silver concentration in the
Composite Design may typically be 6-16 weight percent,
giving an average value of silver (wt. % ~) of 11 weight
percent. Similarly, the ranges of cesium and potassium
concentrations are typically from 0.0 to 0.02 weight percent
For rubidium, the range is also typically from 0.0 to 0.02
weight percent, while for lithium and sodium, the ranges are
typically 0.0 to 0.1 weight percent. For some carriers, the
upper concentration limit of cesium and/or potassium may be
5 to 10 times greater. This is particularly likely to
occur for carriers which contain exchangeable cations.
- 22 -
1 ~ ~21~
12,439-1
Table 11.5 on page 533 of the aforementioned
Davies Publication depicts a three-variable Composite
Design scaled in units of - ~ , -1, 0, +1 and +C~
where -1 represents a "low level" of the respective
variable; +l represents a "high level" of such variable;
O represents the average level of the variable; -o~
represents a level which is somewhat lower in value than
that which is represented by -1; and +Cy~represents a
level which is somewhat higher than that represented
by +1. The particular choice of -~C and + o(is not
critical. However, Table 11.6 on page 534 of the Davies
Publication suggests values of -OC and + ~ which are
particularly useful for a Composite Design in accordance
with the present invention. The designed set of experi-
ments is thus typically comprised of 16 to 20 experiments
wherein catalysts of varying concentrations of silver,
cesium, and potassium are tested. Thus, for example, a
preferred Composlte Design in which the weight percent
silver ranges from 7.0 to 15.0%; the weight percent
cesium ranges from 0.0 to .02%; and the weight percent
potassium ranges from 0.0 to 0.01% ..s c follows:
Wt. % Silver Wt. % Cesium Wt. % Potassium
9 0.005 0.002
13 0.005 0.002
9 0.015 0.002
13 0.015 0.002
9 0.005 0.~08
13 0.005 0.008
9 0.015 0.008
13 0.015 0.008
l 0.010 0.005
11 0.010 0.005
7 0.010 0.005
0.010 0.005
11 0.0 0.005
11 0.020 0.005
11 0 . 010 0 . O
11 O. 010 0 . 010
- 23 -
t 1 62181
12,439-1
The catalysts of the designed set of experi-
Ments are tested by means well known in the art for
measuri~g their selectivity and activity. A convenient
measure of activity, i.e., the degree of conversion of
reactant to product per unit time, is ~he temperature
required to o~tain either a fixed ethylene oxide pro-
duction or to achieve a chosen level of mole percent
ethylene (or oxygen) conversion. Thus, a mathematical
equation for catalyst temperature (Temperature Model)
can be developed in a manner similar to the Efficiencv
Model. That is, for each catalyst there is obtained
two responses (selectivity and temperature) which are re-
lated to the three controlled variables (weight percents
of silver, cesium, and potassium). The relationship
between each response and the controlled variables is
obtained by fitting these data to equations, or
mathematical models, by the method of least squares
as described in Chapter 8 of "Statistical Methods in
Research and Production", O.L. Davies and P.L. Golds.,ith,
Long~an Group, Ltd., London, 4th Ed., 1976. In prac-
tice, the fitting of mathematical models to such data
is routinely done with the aid of a digital computer
as described in "Applied Regression Analysis", N. R.
Draper and H. Smith, John Wiley and Sons, Inc., 1965.
The resulting models (the Efficiency Model and the
Temperature Model) describe the relationship between
the responses and the controlled variables.
It is well known in the art that the nu..ber
of experiments required to establish mathematical re-
- 24 -
1 1 62~81
12,439-1
lationships among several variables is dependent upon
the reproducibility of the data. Thus, for a Composite
Design containing approximately 16 experiments it may
occasionally be necessary to repeat all or part of tne
set of designed experiments in order to fir~ly establish
the relationship between efficiency and weight percents
of silver, cesium and potassium to an acceptable level
of statistical confidence. In practice, it has been
found that for a designed set of about 16 experiments
wherein the weight percent of silver is varied from
about 7% to about 15%, one complete replication of the
designed experiments is usually sufficient to establish
this relationship provided that the standard deviation
of a single experimental test result is no greater than
about 0.7% efficiency units. During the course of ex-
perimentation, data other than from the designed set of
experiments may be acquired which is useful for develop-
ing the model as described above. For example, data
acquired from the aforementioned preliminary range
finding experiments as well as any additional experi-
mental data which is available with regard to the
particular catalyst carrier and method of preparation
of interest is desirably included with that derived
from the Composite Design, and the equations thus
fitted to the data. Consequently, as a practical
matter, data from about 30 to 60 experiments may be
available for developing the Efficiency and Temperature
~odels.
1 J 62181
12,439-l
The general form of the mathematical equation,
hereinafter referred as the "Temperature Model" defines
~e~perature as a function of weight percents of silver,
cesium and potassium deposited on the catalyst support
as follows: ~
Temp., C = aO + al(BG) + a2(BCs) + a3(BK)
+ a4(BG)2 + as~BCs)2 + a6(BK)2
~ a7(BCs x BG) + ag(BG x BK) + ag(BCs x BK)
where:
aO, al, a2, a3, a4, a5, a6, a7, a8 and a9 are the re-
spective coefficients for each term in ~he Temperature
Model which comprise a set of constants determined for
a particular carrier and a particular method of catalyst
preparation following the designed set of experiments as
described above. The value of some of these coeffic-
ients may be zero. BG, BCs, and B~ are as defined
above.
The most convenient use of the Efficiency and
Temperature Models for defining the area of synergism
for any selected weight percent of silver in the catalyst
is to depict efficiency and temperature responses in a
graphical form, commonly referred to as contour ~aps,
as described in Chapter 11 of the aforementioned "Design
and Analysis of Industrial Experiments". Thus, Figures
1 and 2 depict the contour maps of efficiency and temp-
erature for a selected carrier and catalyst preparation
procedure at 7 and 13 weight percent silver~ respectively.
The contour maps were derived from a designed set of
experiments in which the percent silver ranged from
5.88 to 16~05~/o; the percent cesium ran~ed from 0.00
~ ~ ~2181
12,439-1
to 0.019%; and the percent potassium ranged from 0.00
to 0.021%. Table I below summa.izes the experimental
data which was available for the selected carrier and
catalyst preparation procedure and from which the con-
tour maps were derived. The experiments were conducted
in two different test reactors in accordance with the
standard test procedure hereinafter described under the
heading "Catalyst Comparisons". Two similar, but slight-
ly different,carriers were used in the experiments.
10 Table I represents the experimental data on a common
basis, namely, the data was adjusted to ccmpensate for
observed differences between the reactors snd catalyst
carriers employed.
621~1
12, 439- 1
TAgLE I
wt% A~ wt~ S w~e~p (~C)Efficienc~
11.14 0.00477 0.00158256.0 73.9
10.53 0.00897 0.0256.4 77.5
11.14 0.00479 0.0256.0 72.9
11.01 0.00941 0.00312256.0 ~7.4
11.21 0.00240 0.00080258.0 70,7
10.9~ 0.01865 0.0282.2 74,3
11.04 0.009~1 0.0257.~ 76.3
011.0'1 0.009~1 0.0255,0 76.3
11.09 0.01421 0.00412270.7 7j.7
10.41 0.0 0.0 263.068.5
10.1 0.0 0.0 265.068.-
11.16 0.01909 0.00633292.6 72.G
10.9~ 0.01403 0.0267.0 76.7
10.70 0.01128 0.00379262.0 77.5
9.08 0.0190Q 0.00315293.0 71.8
9.31 0.00968 0.00645269.9 76.6
13.17 0.00617 0.00102254.9 74.2
20 9,10 0.00323 0.00214260.0 7~,7
13.14 O.OO91S 0.00613259.1 77.5
11.11 0.00950 0.00315259.6 77.6
11.31 0.0120~ 0.0260.3 77.4
11.05 0.00236 0.00078260.4 70.1
12.72 0.00311 0.0020725S.8 71.6
16.05 0.00941 0.00313263.0 77.7
5.88 0.00924 0.00306269.1 76.8
11.04 0,01421 0.00157268.9 76.7
10.89 0.00462 0,00450256.4 75.4
10.80 0.0 0.00613 260.5 69.9
B.93 0.00630 0.00105260.4 74.4
15.51 0.01288 0,0266.4 77.2
6.03 0.01341 0.0280.3 73.7
13.11 0.00897 0.00810266.2 77.1
- 28 ~
1 1 62181
12, 439-1
IA.B L F
(continued)
Ef f lc ienc
w~t% AR wt% Cs w~/. X S~p. (-C~ %
16.00 0.00888 0.00800 264.3 77. ~3
10.93 0.0 0.01230 263.6 73.3
12.95 0.01562 0.00469 277.1 76~0
13.12 0.01313 0.00336 268.1 77.0
12.85 0.00150 0.0 26L.4 68.2
0 13.12 0.01047 0.00297 257.3 78.3
13.26 0.0178! 0.00540 282.3 74 ~ 5
12.91 0.0138' 0.00407 269.4 77.
12.91 0.0138' 0.00407 269.8 77.2
12.91 0.01038 0.0029j 257.0 7~.3
12.91 0.0103S 0.00'95 257.2 76.-.
13.00 0.00150 0,07100 299.0 6-~.
13.00 0,01036 O.OljO0 290.7 72.'
6.88 0.00150 0.01470 28~.6 73.7
7.14 0.01056 0,01220 289.' 7~.3
/.06 O.OOj94 0.01010 280.4 75~'
8.00 0.00727 0.00192 263.3 75.7
8.00 0.01153 0.00330 274.4 76.9
8.15 0.01171 0.00339 272.7 77.6
8.30 0,00749 0.00199 262.2 76.5
3.03 0.00150 0.0 268.0 69.0
7.00 0.01056 0.0 264.0 75.5
7.00 O.OlOS6 0,0~400 271.0 76.2
- 29 -
i ~ 62181
12,439-1
The specific Efficiency and Temperature Models
derived from the sbove data by the aforementioned method
of least square are as follows:
Efficiency, % ~ ~7.19 ~ 0.196(BG) + 133.4(BCs)
+ 120.5(BK) - 63787.0 rBCs)2
- 47229.0 (BK)2 ~ 52.1 (BG x BCs)
- 60823.0 (~Cs x BK); and
Temperature, C - 259.44 - 1.279(BG) + 1555.8(BCs)
1 794.1(BK) ~ 0.346$(BG)2
+ 168544.0(BCs)2 ~ 147856.0(BI;)2
+ 132807.0(BCs x BK)
where: BG - (wt.% Ag - 11.0)
BCs ~ (wt.~/o Cs - 0.01)
BK ~ (wt.% K - 0.003)
Figures 1 and 2 show contour lines of constant
eff.ciency and temperature in potassium-cesium concen-
tration space. The darker lines represent selectivit-
contours with selectivity values being indicated for
each line. The lighter, broken lines represent temp-
erature contours with temperatures indicated in degrees
centigrade. The efficiency and temperature for points
in between the designated contour lines can be inter-
polated. The maximum selectivity achievable for any
combination of cesium and potassium as a function of
cesium concentration is indicated by the curve labelled
Se ~ ax This ~urve represents the maximum synergism
achievable for any given level of cesium. The synergism
curve (designated "A" in Figures 1 and 2) separates the
region of synergism, as herein defined, and regions of
- 30 -
~6~81
12,439-1
additive and antagonistic effec~:s. Additive effects occur
when the efficiency obtained with a combination of cesium
and potassium is a weighted average of the efficiencies
obtainable under common conditions from respective catalysts
which are the same as the catalyst containing said combina-
tion except that instead of containing both potassi~m and
cesium, one contains the respective amount of cesium, and
the other contains the respective amount of potassium. Anta-
gonistic effects occur when the efficiency obtainable with a
mixture of cesium and potassium is less than the efficiencies
obtainable with corresponding catalysts which contain the
respective amount of cesium, and the respective amount of
potassium, individually, as described above. The area bound
by ordinate, the abscissa and the synergism curve (curve "A")
defines the area of synergism in accordance with the present
invention. The area to the right of the synergism curve "A",
represents the area of additive and antagonistic effects as
described above, and thus defines mixtures not in accord with
the present invention. For any given contour map the pre-
ferred combinations of cesium and potassium are those whichproduce selectivities on or about the SelMax curve. However,
in general, preferred mixtures are those wherein cesium and
potassium are present in a weight ratio of from about 100:1
to 1:100 depending upon the particular catalyst carrier and
preparation procedure of choice. For mixtures of cesium
and lithium, or cesium and sodium, preferred mixtures are
usually those wherein the alkali metals are present in a
weight ratio of from about 1000:1 to 1:1000.
Referring to Figure 1, a catalyst containing
for example, 0.003% Cs and 0% K has an efficiency of about
73%. The addition of approximately 0.008% K to this
- 31 -
12,439-1
catalyst results in an increase in efficiency to about
76.0%, the maximum selectivity at this level of cesium
(i.e., the value on the SelMax curve). Further additions
of potassium up to about .016% K (i.e., the value on curve
"A"~ would yield efficiencies equal to or gr~ater ~han those
obtainable with the given amount (0.003%) of cesium alone
(i.e., no alkali metal other than cesi~l~ being present);
potassium additions beyond .016% K result in efficiencies
lower than those obtainable with 0.003% of cesium
alone, i.e., in the region of either additive or anta-
gonistic effects. Yet, such amount of potassium which
causes such antagonistic effects can still yield a catalyst
with reasonably desirable selectivity and activity for a
given mode of operation.
The region of synergism varies with the silver .
content of the catalyst as described by the Efficiency
Model. Figure 2 illustrates the region of synergism at
13% silver. The SelMax curve and synergism curve (curve
"A") of Figure 2 are as previously defined with reference
to Figure l. Comparison of Figures 1 and 2 show that
the efficiency contour lines are similar but are dis-
placed with respect to the cesium and potassium axes. For
example, the 76% efficiency contour line in Figure l
envelops an area which is smaller than the area covered by
the corresponding contour line in Figure 2. Further, the
maximum value of selectivity obtainable at 7 weight
percent silver, i.e., the maximum along the SelMax line,
is slightly above 76% (Figure l) while the corresponding
maximum for 13 weight percent silver is slightly above 77.8%
~Figure 2).
The Efficiency Model and th~ Temperature Model
which are developed are specific to a particular method of
- 32 -
~ 3 621~
catalyst preparation, a particular carrier and a particu-
lar binary alkali metal combination. Variations in either
the method of preparation or the carrier or the particular
binary combination may change the coefficients of the
Models, and hence, the shape of the contour maps derived
therefrom. Thus, the curves "A" and SelMa~ may comprise
straight lines or curves, and may intercept one or both
axes (viz., the cesium axis and that of the other alkali
metal in the binary combination). For example, in Figures
l and 2, curve "A" and SelMax intercept both axes, and
intercept the cesium axis at an angle greater than 90.
However, for a different carrier, a different method
of preparation or a different binary alkali metal combin-
ation with cesium, the resultant curves "A" and SelMax
may intercept the cesium axis at an angle less than 90,
or may be parallel to one of the axes. The coefficlients
of the Model and the resultant contour maps can be readily
determined for any-of the aforementioned variations using
the designed set of experiments as described above.
The concentration of silver in the finished
catalyst may vary from about 2 to 20 weight percent,
the preferred range being from about 6% to about 16%
by weight of silver. Lo~-er silver concentrations are
preferred from an economic standpoint. However, the
optimum silver concentration for any particular catalyst
will be dependent upon economic factors as well as per-
formance characteristics, such as, catalyst efficiency,
rate of catalyst aging and reaction temperature.
A variety of procedures may be employed for
preparing catalysts containing combinations of cesium
and one or more other alkali metals (excluding francium)
- 33 -
~ ~ 6~181
in accordance with the present invention. In accordance
with a further aspect of this invention, which constitutes
a preferred catalyst preparation procedure, there is
provided a process for preparing a supported silver cata-
lyst for the commercial operation for the production
of ethylene oxide by the vapor phase oxidation of ethylene
with oxygen or an oxygen-containing gas in gaseous ad-
mixture with diluent and inhibitor in a fixed bed tubular
reactor, comprising: (1) impregnating a macroporous
catalyst having a surface area less than 10 m2/g and
in a form and size for use in a reactor used in the
commercial operation with a solution comprising a solvent
or solubilizing agent, silver salt sufficient to deposit
the desired amount of silver on the support of 2 to 20
weight percent silver, and salts of (a) cesium and (b)
at least one other alkali metal selected from the group
consisting of lithium, sodium, potassium and rubidium,
sufficient to deposit respective amounts of (a) and (b)
on the support such that the efficiency of ethylene oxide
manufacture in the commercial operation using the finished
catalyst is increased to a value greater than the effic-
iencies obtainable under common conditions from respective
catalysts which are the same as the catalyst except that
instead of containing both (a) and (b), one contains
the respective amount of (a) and the other contains the
respective amount of (b); and (2) treating the impregna-
ted support to convert at least a fraction of the silver
salt to silver metal and effect deposition of silver,
(a) and (b), respectively, on surfaces of the support.
Silver and alkali metal deposition are generally
accomplished by heating the carrier at elevated tempera-
- 34 -
.,~ .,:i1
~ 1 621~1
tures to evaporate the liquid within the support and
effect deposition of the silver and alkali metal onto
the interior and exterior carrier surfaces. Alternatively,
a coating of silver and alkali metals may be formed on
the carrier from an emulsion or slurry containing the
same followed by heating the carrier as described above.
Impregnation of the carrier is generally the preferred
technique for silver deposition because it utilizes silver
more efficiently than coating procedures, the latter
being generally unable to effect substantial silver depo-
sition into the interior surfaces of the carrier. In
addition, coated catalysts
- 34A -
1 1 621~1
12,439-1
are more susceptible to silver loss by mechanical
abrasion.
The sequence of impregnating or depositing the
surfaces of the carrier with silver and alkali metals is
optional. Thus, impregnation and deposition~of silver
and alkali metals may be effected coincidentally or se-
quentially, i.e., the alkali metals may be deposited prior
to, during, or subsequent to silver addition to the carrier.
The alkali metals may be deposited together or sequentially.
For example, cesium may be deposited first followed by the
coincidental or sequential deposition of silver and
the other alkali metal(s), or such other alkali metal(s)
may be deposited first followed by coincidental or se-
quential deposition of silver and cesium.
Impregnation of the catalyst carrier is effected
using one or more solutions containing silver and alkali
metal compounds in accordance with well-known procedures
for coincidental or sequential depositions. For coinci-
dental deposition, following impregnation the impregnated
carrier is heat or chemically treated ~o reduce the silver
compound to silver metal and deposit the alkali metals onto
the catalyst surfaces. For sequential deposition, the
carrier is initially impregnated with silver or alkali
metal (depending upon the sequence employed) and then
heat or chem cally treated as described above. This
is followed by a second impregnation step and a correspond-
ing heat or chemical treatment to produce the finished
catalyst -ontaining silver and alkali metals.
The silver solution used to impregnate the
carrier is comprised of a silver salt or compound in a
- 35 -
1 ~ ~21~1
12,439-1
solvent or complexing/solubilizing agent such as the silver
solutions disclosed in the art. The particular silver
salt employed is not critical and may be chosen, for
e~ample, from among silver nitrate, silver oxide or
silver carboxylates, such as, silver acetate, oxalate,
citrate, phthalate, lactate, propionate, butyrate and
higher fatty acid salts.
A wide variety of solvents or complexing/
solubilizing agents may be employed to solubilize silver
to the desired concentration in the impregnating medium.
Among those disclosed in the art as being s~itable
for this purpose are lactic acid (U. S. Patent Nos.
2,477,435 to Aries; and 3,501,417 to DeMaio); ammonia
~ U. S. Patent 2,463,228 to West et al); alcohols,
such as ethylene glycol (U. S. Patent Nos. 2,825,701 to
Endler et al; and 3,563,914 to Wattimena); and amines
and aqueous mixtures of amines (U. S. Patent Nos. 2,459,896
to Schwarz; 3,563,914 to Wattimena; 3,702,259 to Nielsen;
and 4,097,414 to Cavitt).
Suitable alkali metal salts include all those
soluble in the particular solvent or solubilizing agent
employed. Accordingly, inorganic and organic salts of
alkali metals, such as, nitrates, halides, hydroxides,
sulfates and carboxylates may be used. When coincidentally
deposited with silver, the alkali metal salt employed is
preferably one which does not react with silver salt in
solution in order to avoid premature silver precipitation
from same. Thus, ~or example, alkali metal halides are
preferably not used in lactic acid solution because they
react with silver ions present therein.
- 36 -
1 1 62181
Following impregnation of the catalyst carrier
with silver and alkali metal salts, the impregnated carrier
particles are separated from any remaining non-absorbed
solution or slurry. This is conveniently accomplished
by draining the excess impregnating medium or alternatively
by using separation techniques, such as, filtration or
centri~ugation. The impregnated carrier is then generally
heat treated (e.g., roasted)to effect decomposition and
reduction of the silver metal salt to metallic silver
and the deposition of alkali metal ion. Such roasting
may be carried out at a temperature of from about 100C
to 900C, preferably from 200 to 700C, for a period
of time sufficient to convert substantially all of the
silver salt to silver metal. In general, the higher
the temperature, the shorter the required reduction period.
For example, at a temperature of from about 400C to
900C, reduction may be accomplished in about 1 to 5
minutes. Although a wide range of heating periods have
been suggested in the art to thermally treat the impreg-
nated support, (e.g., U.S. Patent 3,563,914 suggests
heating for less than 300 seconds to dry but not roast
reduce the catalyst; U.S. Patent 3,702,259 discloses
heating from 2 to 8 hours at a temperature of from 100
to 375C to reduce the silver salt in the catalyst; and
U.S. Patent 3,962,136 suggests ~ to 8 hours for the same
temperature range) it is only important that the reduction
time be correlated with temperature such that substantially
complete reduction of the silver salt to metal is accom-
plished. A continuous or step-wise heating program may
be used for this purpose.
I 1 62181
12,439-1
Heat treatment is preferably carried out in
air, but a nitrogen or carbon dioxide atmosphere may
also be employed. The equipment used for such heat
treatment may use a static or flowing atmosphere of
such gases to effect reduction.
The particle size of silver metal deposited
upon the carrier is a function of the catalyst prepara-
tion procedure employed. Thus, the particular choice of
solvent and/or comple~ing agent, silver salt, heat treat-
ment conditions and catalyst carrier may affect, to vary-
ing degrees, the size of the resulting silver particle.
For carriers of general interest for the production of
ethylene oxide, a distribution of silver particle sizes
in the range of .05 to 2.0 microns is typically obtained.
However, the role of particle size of the silver catalyst
upon the effectiveness of the catalyst in making ethylene
oxide is not clearly understood. In view of the fact that
the silver particles are known to migrate on the surface
of the catalyst when used in the cat.alytic reaction re-
sulting in a marked change in their size and shape, silverparticle size may not be a significant factor in affecting
catalytic performance.
CARRIER SELECTION
The catalyst carrier employed in practicing
the invention may be selP,cted from conventional, porous,
refractory materials which are essentially inert to
ethylene, ethylene oxide and other reactants and products
at reaction conditions. These materials are generally
labelled as "macroporous" and consist of porous materials
- 38 -
1 1 B2181
12,439-1
having surface areas less than 10 m2/g (square meters
per gm of carrier) and preferably less than 1 m2/g. The
surface area is measured by the conventional B.E.T. method
described by Brunauer, S., Emmet, P., and Teller, E., in
J. Am. Chem. Soc. Vol. 60, pp309-16, (1938). They are
further characterized by pore -~olumes ranging from about
0.15 - 0.8 cc/g, preferably from about 0.2 - 0.6 cc/g.
Pore volumes may be measured by conventional mercury
porosimetry or water absorption techniques. Median pore
diameters for the above-descr;.bed carriers range from
about 0.01 to lO0 microns, a more preferred range being
from about 0.5 to 50 mi_rons.
The carrier should preferably not contain ions
which are exchangeable with the alkali metals
supplied to the catalyst, either in the preparation or use
of the catalyst, so as to upset the amount of alkali metal
which provides the desired synergism. If the carrier
contains such ion, the ion should be removed by standard
chemical techniques such as leaching. Moreover, if the
carrier contains an amount of alkali metal, which is
transferable to the silver whereby the synergistic
combination is upset, then the carrier should be treated
to remove such excess alkali metal or the amount of alkali
metal supplied to the catalyst should be less than the
synergistic amount, allowing the transferred alkali metal
to effect the desired synergistic amounts.
The chemical composition of the carrier is not
narrowly critical. Carriers may be composed, for example,
of alpha-a~umina, silicon carbide, silicon dioxide,
zirconia, magnesia and various clays. In general,
- 39 -
~ 1 S~
alpha-alumina based materials are preferred. These alpha-
alumina based materials may be of very high purity, i.e.,
98 + wt.% alpha-alumina, the remaining components being
silica, alkali metal oxides (e.g., sodium oxide) and
trace amounts of other metal and non-metal impurities;
or they may be of lower purity, i.e., about 80 wt.% alpha-
alumina, the balance being a mixture of silicon dioxide,
various alkali oxides, alkaline earth oxides, iron oxide,
and other metal and non-metal oxides. The lower purity
carriers are formulated so as 'o be inert under catalyst
preparation and reaction conditions. A wide variety
of such carriers are commercially available. The carriers
may be in the form of pellets, extruded particles, spheres,
rings and the like. The si~ze of the carriers may vary
from about l/16" to ~". The carrier size is chosen to
be consistent with the type of reactor employed. In
general, for fixed bed reactor applications, sizes in
the range of 1/8" to 3/8" have been found to be most
suitable in the typical tubular reactor used in commercial
operations.
The silver catalysts of the invention are par-
ticularly suitable for use in the production of ethylene
oxide by the vapor phase oxidation of ethylene with molec-
ular oxygen. In accordance with another aspect of the
present invention, there is provided in the continuous
process for the production of ethylene oxide in a com-
mercial operation wherein ethylene and oxygen provided
as oxygen or as an oxygen-containing gas are reacted
in vapor phase admixture with diluent and inhibitor at
a temperature of from about 200C to 300C in the presence
of a supported silver catalyst in a fixed bed tubular
- 40 -
. ' , .
~6~181
reactor to form ethylene oxide, the improvement which
comprises employing a supported silver catalyst which
catalyst has a macroporous support having a surface area
less than lO m2~g and is in a form and size for use in
a reactor used in the commercial operation and which
catalyst contains 2 to 20 weight percent silver a combina-
tion of (a) cesium and (b) at least one other alkali
metal selected from the group consisting of lithium,
sodium, potassium and rubidium, which combination comprises
(a) and (b) in amounts in relation to the amount of silver
therein sufficient to increase the efficiency of ethylene
oxide manufacture in the commercial operation to a value
greater than the efficiencies obtainable under common
conditions from respective catalysts which are the same
as the catalyst except that instead of containing both
(a) and (b), one contains the respective amount of (a),
and the other contains the respective amount of (b).
The reaction conditions for carrying out the
vapor phase oxidation reaction to produce ethylene oxide
are well-known and extensively described in the prior
art. This applies to reaction conditions, such as, tempera-
ture, pressure, residence time, concentration of reactants,
diluents (e.g., nitrogen, methane and CO2), inhibitors
(e.g., ethylene dichloride) and the like. In addition,
the desirability of recycling unreacted feed, or employing
a single-pass system, or using successive reactions to
increase ethylene conversion by employing reactors in
series arrangement can be readily determined by those
skilled in the art. The particular mode of operation
selected will usually be dictated by process economics.
Generally, the process is carried out by con-
- 41 -
~ ~ 6~181
tinuously introducing a feed stream containing ethylene
and oxygen to a catalyst-containing reactor at a tempera-
ture of from about 200 to 300C, and a pressure which
may vary from one atmosphere to about 30 atmospheres
depending upon the mass velocity and productivity desired.
Residence times in large-scale reactors are generally
on the order of about 1-5 seconds. Oxygen may be supplied
to the reaction in an oxygen~containing stream, such
as, air or as commercial oxygen. The resulting ethylene
oxide is separated and recovered from the reaction pro-
ducts using conventional methods.
The invention is illustrated further by the
catalyst comparisons which are now discussed in relation
to Tables II to VI and the experimental results set forth
therein.
The catalysts cited in the Tables below were
all evaluated for comparison purposes under standard
test conditions using backmixed, bottom-agitated "Magne-
drive" autoclaves as described in Figure 2 of the paper
by J.M. Berty entitled "Reactor for Vapor Phase Catalytic
Studies", in Chemical Engineering Progress, Vol. 70,
No. 5,
- 41A -
; ~
,~,,, d
~6~1Bl
12,439-1
pages 78-84, lg74. The reactor was operated at 1.0
mole % ethylene oxide in the outlet gas under the
following standard inlet conditions:
Component Mole %
Oxygen 6.0
Ethylene 8.0
Ethane 0.50
Carbon Dioxide 6.5
Nitrogen Balance of Gas
Parts per million Ethylene
Chloride = 7.5
The pressure was maintained constant at 275
psig and the total outlet flow maintained at 22.6 SCFH.(l)
The outlet ethylene oxide concentration was maintained
at 1.0% by adjusting the reaction temperature. Thus,
temperature (C) and catalyst efficiency are obtained
as the responses describing the catalyst performance.
A typical catalvst test procedure is comprised
of the following steps:
1. 80 cc of catalyst is charged to a backmixed
autoclave The volur,le of catalyst is measured in a 1"
I.D. graduated cylinder after tapping the cylinder several
times to thoroughly pack the catalyst. The weight of
the catalyst is noted.
2. The backmixed autoclave is heated to about
reaction temperature in a nitrogen flow of 20 SCFH with
the fan operating at 1500 rpm. The nitrogen flow is
then discontinued and the above-described feed stream
is introduced into the reactor. The total gas outlet
-
(1~ SCFH refers to cubic feet per hour at standard temper-
ature and pressure, namely, 0C and one atmosphere.
- 42 -
~ ~ 6;~181
12,439-1
flow is adjusted to 22.6 SCFH. The temperature is
adjusted over the next few hours so that the ethylene
oxide concentration in the outlet gas is approximately
1.0%
3. The outlet oxide concentration is monitored
over the next 4-6 days to make certain that the catalyst
has reached its peak steady state performance. The
temperature is periodically adjusted to achieve 1%
outlet oxide. The selectivity of the catalyst to
ethylene oxide and the temperature are thus obtained.
The standard deviation of a single test result
reporting catalyst efficiency in accordance with the
procedure described above is 0.7% efficiency units.
Tables II through VI below summarize test re-
sults obtained with silver catalysts in the absence of
additives and those containing cesium in combination with
one or more alkali metals selected from among lithium,
sodium, potassium and rubidium. Tests were carried out
using a variety of catalyst carriers and different
2Q preparation procedures. Catalysts which were prepared
by the same method of preparation on a similar ca-;rier
are identified in the Tables by a common number
- 43
1 3 62181
TABLE II
B PERIMENT Wt.~g Wt.%Cs Wt.%X ~EFF** TEMP.(CC)
1 A 11.14 0.00479 0.0000 71.7 256
1 B 11.14 0.00477 0.00158 73.9 256
1 C 10.8g 0.00461 0.00450 75.4 256
1 D 10.41 0.0000 0.0000 68.4 265
1 E 10.80 0.0000 0.00613 69.9 261
1 F 10.93 0.0000 0.0123 73.3 264
1 G 10.90 0.0000 0.0210 66.6 299
1 H 11.04 0.00941 0.0000 75.6 256
1 I 11.06 0.00941 0.00313 76.9 258
1 J 10.92 0.0186 0.0000 73.1 283
1 K 11.16 0.0191 0.00633 72.0 293
1 L 8.04 0.004 0.008 76.0 269.3
1 M 7.84 -- 0.0078 75.0 263.8
1 N 8.28 0.0041 -- 73.8 258.3
1 O 8.07 -- __ 67.3 260.0
1 P 14.97 -- -- 66.7 252.9
1 Q 15.19 0.00405 -- 72.6 252.0
1 R 14.80 -- 0.0079 75~5 255.5
1 S 15.10 0.004 0.0081 77.9 256.6
2 A 17.4 0.000 0.093 73.5 278
2 B 16.6 0.0044 0.088 74.7 279
2 C 16.5 0.0085 0.089 74.2 278
2 D 17.3 0.000 0.000 ~8-67* 284-299
2 E 17.0 0.0044 0.0016 70.8 276
2 F 15.7 0.0044 0.069 74.1 280
2 G 16.5 0.0092 0.0028 72.2 275
2 H 16.5 0.0092 0.088 73.2 287
* Due to rapid deactivation of this catalyst, initial and final
perform~nces, respectively, are given.
**"EFF" is the abbreviation for efficiency as previously defined.
81
12,439-l
Experiments lB and lC demonstrate the synergism
achieved with silver catalysts containing mixtures of
cesium and potassium in accordance with the invention
relative to the "cesium only" catalyst of lA which con-
tained essentially the same concentratlon of silver and
cesium but contained no potassium. As used herein, the term
"cesium only" refers to a catalyst wherein cesium is the
only alkali metal deposited upon the carrier. The terms
"potassium only", "lithium only", and "sodium only" are
correspondingly defined for the respective catalysts. Thus,
the efficiency achieved with combination of alkali metals
in experiment lB was about 2% higher than that achieved
with the corresponding cesium only catalyst of experiment
lA. The further addition of K from a level of .00158%
(Example lB) to a level of 0.~045% K (experiment lC) while
maintaining Ag and Cs essentially constant provided an
even greater improvement in efficiency relative to lA,
namely, about 3.7%. The catalyst of experiment lD con-
tained no cesium or potassium and provided a relatively
low 68.4% efficiency. Experiments lE, F, and G demon-
strate that "potassium only" catalysts which con-
tained essentially the same amount of silver as catal-
ysts lB and lC achieved a selectivity no higher
than 73.3%, significantly below that achieved with the
catalysts of lB and lC containing mixtures of cesium
and potassium. It should also be noted that in addition
to providing higher efficiency, the catalysts of the
invention (lB and lC) operated at lower tempe~atures
than the potassium only catalysts (lE, lF and lG), thus
indicating higher catalyst activity. Although the
cesium only catalyst (lA) operated at the same low
temperature as catalysts lB and lC, it provided a sub-
stantially lower efficiency.
- ~5 -
1162181
12,439-1
The catalyst of experiment lH was a cesium
only catalys~ containing Cs at a level nearly double
that of catalysts lA, B and C. The addition of .0031%
potassium to a catalyst of such composition produced
an efficiency improvement of greater than 1% as shown
in Example 1.
Experiments lJ and lK are illustrative of a
non-synergistic combination of Cs and K. Thus, the
addition of K to the cesium only catalyst of lJ contain-
ing about 11% Ag and a relatively high Cs concentration of0.0186% resulted in a catalyst (lK) having a lower
efficiency and higher operating temperature. That is to
say, the combination of K and Cs in experiment lK did not
produce a synergistic result. Consequently, such cesium-
potassium mixture is not in accord with the present
invention.
Experiments lL through 10 demonstrate the
synergism of the present invention for catalysts con-
taining approximately 8% silver. The efficiency of
catalyst lL which contained a synergistic combination of
cesium and potassium was 1% higher than the potassium
only catalyst of lM, and more than 2% higher than the
efficiency of the cesium only catalyst of lN. Silver
catalyst lO which contained no cesium or potassium
achieved an efficiency nearly 9% below that of catalyst
lL.
Experiments lP through lS demonstrate the
synergism of the present invention for catalyst con-
taining approximately 15% silver. The efficiency of
catalyst lS which contained a synergistic mixture of
- 46 -
1 16~181
12,439~1
cesium and potassium was ~ore than 5% higher than the
cesium only catalyst of lQ which contained the respective
amount of cesium in such mixture, and about 2.5% higher
than the potassium only catalyst of lR which contained ~he
respective amount of potassium in s~ch mixture. Catalyst
lP which contained no additives achieved an efficiency
about 11% lower than catalyst lS.
Experiments 2B and 2C demonstrate the efficiencies
achieved with potassium-cesium mixtures for a catalyst
containing about 17% silver compared to the potassium
only catalyst of experiment 2A. The addition of .0044%
cesium in experiment 2B resulted in an improved effi-
ciency of 74.7% compared to the 73.5% efficiency achieved
in experiment 2A. The silver catalyst of 2D which had no
alkali metal deposited on the carrier is provided in the
Table for comparative purposes.
A comparison of experiments 2E and 2F show that
when the K concentration was increased from .0016% to
.06~% while maintaining the Cs level constant, a greater
than 3% improvement in efficiency was achieved. Li~e-
wise, a comparison of experiments 2G and 2H demonstrates
that when the potassium concentration was increased
while maintaining the silver and cesium levels constant,
a 1% improvement in efficiency resulted.
Three catalysts containing 7% Ag were prepared
containing the optimum cesium concentration as determined
from the Efficiency Model, supra, obtained from a designed
set of experiments. The catalysts (experiments 3A, B and C)
- 47 -
~ 1 621~1
12,439-1
all contained about 7.0 w~. % silver and 0.00906 wt. %
cesium, with no potassium being present. To demonstrate
the operation of the Efficiency Model, three additional
catalysts were prepared (experiments 3D, E and F), each
containing about 7.0% silver, 0 00906% cesium and 0.004%
potassium. The difference in the performance of the cesium/
potassium catalysts relative to the cesium only catalysts
was predicted from the Efficiency Model ~o be about 0.6%
efficiency units. As noted below in Table III, the actual
observed difference in performance was found to be 0.7%,
which is regarded to reflect agreement with the prediction
of the Efficiency Model. Experiment 3G provides the effi-
ciency of a potassium only catalyst containing silver and
potassium at the same concentration as the catalysts of
experiments 3D, E and F, thus demonstrating the synergism
achieved with the cesium-potassium combination.
- 48 -
I 1 B2181
12,439-1
TABLE III
Cesium Only Catalysts: 7.0~/O A~, 0.00906% Cs
Experiment /O Eff. T, C
3A 75.4 263.9
3B 75.7 ~ 261.4
3C 75.4 266.1
Average: 75.5 + 0.17-'~
Cesium Plus Potassium Catalysts: 7.0% Ag,
0.00906% Cs, 0.004% K
3D 76.0 271.4
3E 76.1 271.5
3F 76.4 270.9
Average: 76.2 + 0.21*
Potassium Only Catalyst: 7.0% A~, 0.0040% K
3G 72.8 265.3
* Values reflect standard deviations.
Table IV below demonstrates the synergism
achieved with a combination of cesium and lithium
(experiment 4C) relative to the corresponding cesium only
catalyst of experiment 4A and the corresponding lithium
only catalyst of experiment 4B. Thus, the catalyst of 4C
was about 10% more efficient than the lithium only catalyst
of 4B and about 3.5% more efficient than the cesium only
catalyst of 4A.
Exper,ment 4D demonstrates that when the lithium
concentration of catalyst 4C was increased about ten-fold,
~,9 _
1 162181
12,439-1
the resulting efficiency was reduced by more than 3%.
However, a comparison of catalysts 4D and 4E discloses that
the efficiency obtained with catalyst 4D was increased
by increasing the cesium concentration from 0~0053% to
0.0300%. It should be noted .hat the cesium only catalyst
of experiment 4G (corresponding to the cesium concentration
of 4E~ was inactive; that is, at that concentration of
cesium, no ethylene oxide was produced. Yet, the com-
bination of this concentration of cesium with 0.0300%
lithium resulted in a very active catalyst (4E).
Similarly, the lithium only catalyst of 4F (corresponding
to the lithium concentration of 4E) provided a relatively
low efficiency of 65.4%. Thus, the synergism achieved
in catalyst 4E is underscored by the sharp contrast of
its efficiency relative to the poor results achieved with
catalysts 4F and 4G.
- 50 -
1 162~81
12, 439- 1
_, o~
,_ ,~ I~ ~o oo ~o
.
E ~ c~
E~ ~r
~1 . ,,
~ 4~ ~ Cr~ 0 03 'D ~
E~ ~ . . . . . u
~ ~ c~
~ ~ r~
H
U~
~ ~ O O C`l O O
0 1~) ~'1 0 0 0 0
O O O ~ ~ ~ O
O O O O O O O
U~ .
J~ O O O O O O O
U~
~ ¢
,_1 H
E-~ ~ ~ O O
~ U~ O U~ U~ O O O
C_~ O O O O ~'1 0 ~ ::~
. o o o o o o o 5
E~ ~ . . . . . . O
u~ 3 o o o o o o o
~ CL
U~
U~
~ ¢~ o
~ oo ~ ~ ~ O O a~
¢ ~ ~ ~ ~ ~ ~ C
z 3
~ al
U~
¢ 3
C~ ~ U~
C
,, e
S~ ¢ ~ C~ ~ tsl ~ C~ o
Z
x
k~
- 51 -
8 1
12,439-1 -
Table V below demonstrates the synergism
achieved with the catalyst of experiment SC relatlve to
the corresponding cesium only catalyst of experiment 5A
and the corresponding sodium only catalyst of experiment
5B. Thus, the catalyst of 5C was 6% more e~ficient
than the cesium only catalyst of 5A and 7.2V~ more
efficient than the sodium only catalyst of 5B. Experiment
5D discloses that increasing the sodium concentration
ten-fold relative to the concentration in catalyst 5C
had the effect of lowering the catalyst efficiency.
- 52 -
~ 1 62181
12, 439-1
/
C~
O I~ a~
U~
b ~
E~l
.
r~
C~
Z o o o o
~ o ~ ~ o
O a~ o o o ~
U~ . o o o o
,_
C~ ~
:~ ~ a
F~ E~ O tn
~_ ~ ~ ~ O Ul U~
~ C~ ~ o o o o
¢ ~ :~; ?~ O O O O
E~ ~ ~
o o o o
z
Eo
C~ ¢
U~ oo o o
E~
U~ ~ ~ .
~ 3
e
.
U) ~ U~
x
- 53 -
1 ~ ~21# 1
12,439-1
Table VI below demonstrates the synergism
achieved with a catalyst containing silver and cesium
in combination with potassium, sodiu~ and lithium as
indicated in experiment 6A. The presence of chloride
ion in the catalyst concentrations of 6A, B and C
indicates that at least a portion of the alkali metal
salts used in the catalyst preparation procedure were
in the form of chlorides. The efficiency achieved with
the synergistic combination of experir,~ent 6A was about
1.2% greater than the efficiency of the corresponding
cesium only catalyst of 6C and about 9% greater than
the corres?onding combination of potassiu~, sodium and
lithium of catalyst 6B.
- 54 -
1 ~S2181 12,439-1
c~
o
. ~ ,~ ~
E~
~ ~ ~ ~ c~
~ ~ 0 ~ r~
r~
~n
u~
¢ c~
o
o o o
c"
~: ~ `D ~D O
o 8 o
o o o
o ~ ta E
oa z ~ ~ o ~
:~ ¢ ¢ ~ o, o, o,
Ei~ z ~ 3 o o o
¢ ~ V~ ~ ~, ~ o
E~ ~ O, o, o,
u~ 3 o o o
C~
~:
C~ ~ o
_~ o _~
~ o O o
æ 3 o o o tn
¢ u~
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C~ ¢ ~ o _~
E~
V~ ~ ~ ~
. ~ ~ ~ :~
¢ 3
8 ~
. ¢ ~ ~,
~o ~o
.
~ ~6~181
12,439-l
The catalysts of the invention can be prepared
with a variety of carriers and preparation procedures.
The defined synergism obtainable with combinations of
cesium with the other alkali metals is not restricted, for
example, to a particular type or chemical composition of
catalyst carrier, to a particular sequence of silver and
alkali metal deposition, or to a special class of solvents
or solubilizing agents used in the preparation procedure.
In the following examples detailed procedures
are provided as illustrative of methods and carriers
which are useful for preparing catalysts according to
the invention. These examples are by way of illustra-
tion only, and are not to be construed as limiting the
scope of the invention described herein.
- 56 -
1 8 1
EXAMPLE 1
A catalyst containing 11.14 wt.% Ag, .00477
wt.~ Cs and .00158 wt.~ K was prepared as hereinafter
described on an alpha-alumina carrier "A" having the
following chemical composition and physical properties:
Chemical Composition of Carrier "A"
Alpha~Alumina 98.5 wt.%
Silicon Dioxide 0.74 wt.%
Calcium Oxide0.22 wt.%
Sodium Oxide0.16 wt.%
Ferric Oxide0.14 wt.%
Potassium Oxide 0.04 wt.%
Magnesium Oxide 0.03 wt.%
Physical Properties of Carrier "A"
Surface Area (1) ~ 0.3 m~/g
Pore Volume (2) ~~ 0.50 cc/g
~or water absorption)
Packing Density (3) 0.70 g/ml
Median Pore Diameter (4) 21 microns
Pore Size Distr~b~tion, % Total Pore Volume (4)
Pore Size, Microns % TPV
0.1 - 1.0 1.5
1.0 - 10.0 38.5
10.0 - 30.0 20.0
30 - 100 32.0
> 100 8.0
(1) Method of measurement described in "Adsorption, Surface
Area and Porosity", S.J. Gregg and X.S.W. Sing,
Academic Press (1967), pages 316-321.
(2) Method of Measurement as described in ASTM C20-46.
(3) Calculated value based on conventional measurement
of the weight of the carrier in a known volume container.
(4) Method of measurement described in "Application of
Mercury Penetration to Materials Analysis", C.Orr
Jr., Powder Technology, Vol. 3, pp. 117-123 (1970).
- 57 -
~~3
1 162181
The carrier "A" was impregnated under vacuum
as hereinafter described with a solution of silver salts
and alkali me~tals. The impregnating solution was prepared
at a concentration such that the finished catalyst contained
the desired amounts of silver, cesium and potassium.
The required concentration of silver, cesium and potassium
in solution for the given carrier is calculated from
the packing density (grams/cc) and pore volume of the
carrier which are either known or readily determined.
Assuming that all of the silver in the impregnating solu-
tion contained in the pores of the carrier is deposited
upon the carrier, approximately 21 wt.% silver in solution
is necessary to prepare a catalyst containing about 11
wt.% silver on the catalyst. The required concentration
of alkali metal in solution is obtained by dividing the
solution silver concentration by the ratio of silver
to cesium or potassium desired in the finished catalyst.
Thus, to obtain 11.0 wt.% Ag and .0047 wt.% Cs, the ratio
is approximately `2330 and the required cesium concentra-
tion in solution is .009 wt.%. In like manner, thesolution concentration of potassium was calculated to
be .003 wt.%. The solution containing the desired concen-
trations of silver and alkali metals was prepared as
described below:
Impregnating Solution Preparation
80.16 gms of ethylenediamine (high purity grade)
was mixed with 176 g of distilled water. 60.06 gms of
anhydrous oxalic acid (reagent grade) was then added
slowly to the solution at ambient temperature (23C)
while continuous3y stirring. During this addition of
oxalic acid, the solution temperature rose to about
- 58 -
?, :1 62181
40C due to the reaction exotherm. 147.25 gms of silver
oxide powder (Handy and Harmon, 850 Third Avenue, New
York, N.Y. 10022) was then added to the diamine-oxalic
acid-water solution. Finally, 29.30 gms of monoethanolamine,
13.26 gms of aqueous Cs solution as hydroxide (.00444
g Cs/ml soln, or 0.0589 g Cs), 34.28 gms of aqueous K
solution as carbonate (.0005669 K/ml soln, or .0194 gms
K) and 120.6 gms of distilled water were added to complete
the solution. The solution was filtered and 0.9 grams
of undissolved silver was recovered. The specific gravity
of the resulting solution was about 1.328 g/ml.
Catalyst Preparation
125 g of Carrier "A" was impregnated in a 12"
long x 2" I.D. glass cylindrical vessel equipped with
a side arm and suit~ble stopcocks for impregnating the
carrier under va~uum. A 500 ml separatory funnel for
containing the impregnating solution was inserted through
a rubber stopper into the top of the impregnating vessel.
The impregnating vessel containing the carrier was evacu-
ated to approximately 2 inches of mercury pressure for
about 20 minutes after which the impregnating solution
was slowly added to the carrier by opening the stopcock
between the separatory funnel and the impregnating vessel
until the carrier was completely immersed in solution,
the pressure within the vessel being maintained at approx-
imately 2 inches of mercury. Following addition ~f the
solution, the vessel was opened to the atmosphere to
attain atmospheric pressure, the carrier then remaining
immersed in the impregnating solution at ambient conditions
for about 1 hour, and thereafter drained of excess solu-
tion for about 30 minutes. The impregnated carrier was
- 59 -
~J6~181
then heat treated as follows to effect reduction of silver
salt and deposition of cesium and potassium ions on the
catalyst surface. The impregnated carrier was spread
out in a single layer on a 2-5/8" wide endless stainless
steel belt (spiral weave) and transported through a 2"
x 2" square heating zone for 2.5 minutes, the heating
zone being maintained at 500C by passing hot air upward
th~ough the belt and about the catalyst particles at
the rate of 266 SCFH. The hot air was generated by passing
it through a 5 f~. long x 2" I.D. stainless steel pipe
which was externally heated by an electric furnace (Lind-
bergTM tubular furnace: 2-~" I.D., 3 feet long heating
zone) capable of delivering 5400 watts. The heated air
in the pipe was discharged from a square 2" x 2" discharge
port located immediately beneath the moving belt carrying
the catalyst carrier. After being roasted in the heating
zone, the finished catalyst was weighed, and based upon
the weight gain of the carrier, and the known ratios
of silver to cesium and potassium in the impregnating
solution, it was calculated to contain 11.14 wt.% of
silver, 0.00477 wt.~ cesium and .00158 wt.% potassium.
By chemical analysis, described below, this catalyst
was found to contain 10.88% Ag, in close agreement with
the calculated value.
The analysis for silver was carried out by the
following method: An approximately 50 g sample of catalyst
was powdered in a mill and 10 g of the powdered sample
weighed to the nearest 0.1 mg. The silver (and cesium,
etc.) in the catalyst sample was dissolved in hot (80C)
50%, by volume, nitric acid solution. The insoluble
alumina particles were filtered and washed with distilled
- 60 -
f 7l
1 1 6~
water to remove all a &ering nitrate salts of Ag, Cs,
etc. This solution was made up to 250 ml in a volumetric
flask using distilled water. A 25 ml aliquot of this
solution was titrated according to standard procedures
using a 0.1 Normal solution of ammonium th~xyanate and
ferric nitrate as indicator. The amount of Ag so determined
in 250 ml solution was then used to calculate the weight
percent silver in the catalyst sample.
Silver and alkali metal concentrations for all
catalysts described in the specification are calculated
values as described above.
Example 2
A catalyst containing 16.6 wt.% Ag, 0.0044 wt.%
Cs and 0.088 wt.% K was prepared as hereinafter described
on a carrier "B" having the following characteristics:
Chemical Composition of Carr_er "B"
Alpha-Alumina 86.0 wt.%
Silicon Dioxide 11.8 wt.%
Calcium Oxide 0.24 wt.%
Sodium Oxide 0.69 wt.%
Ferr~ic Oxide 0.30 wt.%
Potassium Oxide 0.54 wt.%
Titanium Dioxide 0.34 wt.%
Physical Properties of Carrier "B"
Surface Area (1) 0.10 m2/g
Pore Volume (2) 0.40 cc/g
(or water absorption)
Packing Density (3) 0.72 g/ml
Median Pore Diameter (4) 22 microns
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Pore Size D istribution (4)
Pore Size, microns % Total Pore Volume
0.1 - 1.0 0.0
1.0 - 10.0 12
10.0 - 30 55
30 - 100 33
> 1.00 0.0
(1) Method of measurement described in "Adsorption, Surface
Area and Porosity", S.J. Gregg and K.S.W. Sing,
Academic Press (1967), pages 316-321.
(2) Method of Measurement as described in ASTM C20-46.
(3) Calculated value based on conventional measurement of
the weight of the carrier in a known volume container.
(4) Method of measurement described in "Application of
Mercury Penetration to Materials Analysis", C.Orr Jr.,
Powder Technology, Vol. 3, pp. 117-123 (1970).
The preparation procedure consisted of the
following steps:
li) 333.5 g of lactic acid (88% in water) was
heated to about 75C and 1.44 g K2CO3 and 4.86
g of aqueous CsOH solution (containing .008
g/ml or .039 g Cs) added to the heated lactic
acid, while stirring the solution.
(ii) 163.75 g Ag2O (Metz Metallurgical Corp.,
3900 So. Clinton Ave., So. Plainfield, N.J.
07080) was incrementally added to the heated
lactic acid with stirring so that the heat genera-
ted from the exothermic reaction of Ag2O with
lactic acid did not exceed about 85C. Most
Ag2O and/or silver was left suspended in solution.
This suspension was dark brownlsh grey in colour.
(iii) Hydrogen peroxide (3.3 ml.) was incrementally
added to the above Ag2O lactic acid solution
while rapidly stirring to assist complete
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dissolution of the suspended matter. A clear
yellow solution was obtained, the solution temper-
ature belng about 80C. (Small amounts of lactic
acid or water were added to make up for any
evaporation losses). This solution contained
about 30.4% silver, 0.12~ K and .0078% Cs.
(iv) 189 grams of carrier "B" was evacuated and
impregnated with the solution prepared in ~iii)
while it was at its elevated temperature of
aout 80C. The method of impregnating the carrier
was as described in Example 1 with an additional
step being that the cylindrical impregnating
vessel containing the carrier was surrounded
by a heating jacket which maintained the carrier
temperature at about 80C during the impregnation
procedure to insure that silver lactate remained
in solution.
(v) The impregnated carrier of (iv) was heat
treated at 400C for four minutes using the
apparatus and general method described in Example
1.
Example 3
A catalyst containing 13.4 wt.% Ag, 0.0091 wt.~
Cs and 0.0027 wt.% K was prepared by the following procedure
on Carrier "A" (described in Example 1).
Impregnating Solution Preparation
78.6 grams of triethylenetetramine (high purity
grade) was mixed with 80 g of distilled water. 51.57
grams of oxalic acid dihydrate (reagent grade) was then
added slowly to the continuously stirred amine solution.
During this addition, the temperature of the solution
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increased to 60C due to the reaction exotherm. 5.83
g of aqueous cesium hydroxide solution (0.009728 g Cs/g
solution) and 4.46 g of aqueous potassium carbonate solution
(0.00369 of K/g solution) were then added to the solution
followed by the addition of 89.26 g of silver oxide (Metz
Metallurgical Corp.). Finally 15.28 g of monoethanolamine
was added to the solution along with additional distilled
water to produce a total solution volume of 250 nl. The
solution was filtered and about 5 g of undissolved silver
was recovered.
Catalyst Preparation
150 g of Carrier "A" was evacuated at room
temperature and impregnated with the above-described
impregnation solution in accordance with the procedure
of Example 1. Following impregnation, heat treatment
of the carrier was carried out at 500C for 2.5 minutes
using the apparatus and method described in Example 1.
The composition of the finished catalyst, calcu~
lated from the weight gain of the carrier, was as stated
~o abo~e.
Example 4
A catalyst containing 13.04 wt.% Ag, 0.0089
wt.% Cs and 0.0026 wt.% K was prepared by the following
procedure on Carrier "A" (described in Example 1).
Impregnating Solution Preparation
114.25 gams of aminoethylethanolamine (high
purity grade) was mixed with 80 g of distilled water.
50.42 grams of oxalic acid dihydrate (reagent grade)
was then slowly added to the continuously stirred amine
solution~ the solution temperature rising to about 60C
due to the reaction exotherm. 5.84 g of aqueous cesium
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hydroxide solution (0.009723 g Cs/g solution) and 4.52
g of aqueous potassium carbonate solution (0.00369 g
K/g solution) were then added to the solution followed
by the addition of 89 g of silver oxide (Metz Metallurgical
Corp.). Additional distilled water was then added to
the solution to produce a total volume of 250 ml.
Catalyst Preparation
150 :g of Carrier "A" was evacuated and impreg-
nated with the above-described solution in accordance
with the procedure of Example 1. Heat treatment of the
impregnated carrier was then carried out at 500C for
2.5 minutes using the apparatus and method as described
in Example 1.
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12,439-1
Example 5
A catalyst having nominally the same composition
as the catalyst of Example 1 (specifically, 11.1 wt. % ~g,
0.0048 wt. % Cs and 0.0016 wt. % K) was prepared as
described in Example 1 except that the preparation of the
impregnating solution was carried out using aq~eous solu-
tions of cesium chloride and potassium chloride instead of
cesium hydroxide and potassium carbonate, respectively.
Upon addition of such chloride salts to the silver-con-
taining impregnating solution, the solution remained clear,i.e., no precipitation of silver chloride was observed.
Example 6
A catalyst having nominally the same composition
as the catalyst of Example 1 except for the substitution of
lithium for potassium (specifically 11.0 wt. %
Ag, 0.0047 wt. % Cs and 0.003 wt. % Li) was prepared as
describèd in Example 1, the solution concentration of
lithium being calculated to be 0.00573 wt. %. Accordingly,
the preparation procedure of Example 1 was followed except
that instead of adding potassium carbonate solution to the
impregnating solution, 34 grams of an aqueous lithium
solution as carbonate (0.001094 g lithium/ml, or 0.0372 g
lithium) were added.
Example 7
A catalyst having nominally the same composition
as the catalyst of Example 1 except for the substitution
of sodium for potassium (specifically 11.0 wt. %
Ag, 0.0047 wt. % Cs and 0.01 wt. % sodium) was prepared
in accordance with the procedure of Example 1, the solution
concentration of sodium being calculated to be 0.0191 wt. %.
Thus, the procedure of Example 1 was followed except that
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12,439-1
instead of adding potassium carbonate to the impregnating
solution, 34 grams of an aqueous sodium solution as
carbonate (0 00365 g sodium/ ml, or 0.12415 gram sodium)
were added.
Example 8
A catalyst containing 12.59 wt. % Ag, 0.0088 wt.
/. Cs and 0.0025 wt. % K was prep~red on Carrier "A"
(described in Example 1) by a sequential impregnation
method whereby potassi~m and cesium were deposited upon
the carrier prior to the deposition of silver, as follows:
146.1 grams of Carrier "A" was impregnated with 250 ~1 of
an aqueous solution containing 0.05696 g of cesiu~ as
hydroxide and 0.1674 g of potassium as carbonate follow-
ing the general method of impregnation described in
Exa~ple 1. The impregnated carrier was then heat treaeed
at 400C for 2.5 minutes in accordance with the procedure
of Example 1 to deposit cesium and potassium ions on the
carrier surface. Following this heat treatment, the
carrier was impregnated with the silver-containing im-
pregnating solution as described below:
Preparation of Silver-Containing ImPre~natin~ Solution
48.9 grams of ethylenediamine (high purity
grade) was mixed with 80 cc of distilled water. 50.6g of
oxalic acid dihydrate (reagent grade) was then added
slowly to the solution over a period of one hour while conti-
nuo~sly 6tirring. During this addition of oxalic acid,
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the solution temperature rose to about 40C due to the
reaction exotherm. 89.34 grams of silver oxide powder
(Metz Metallurgical Corp.) was then added to the diamine-
oxalic acid-water solution. Finally, 17.84~grams of
monoethanolamine was added to the solu~ion along with
add~tional distllled water to provide a total solution
volume of 250 ml.
CstalYst Preparation
The aforementioned Csrrier "A" was impregnated
with the above-descrlbed impregnating solution snd then
heat treated at 400C for 2.5 minutes in accordance with
the method described in Example 1.
Example 9
A catalyst containing 13.09 wt. % Ag, 0.00&9 wt. %
Cs and 0.0026 wt. % X was prepared on Carrier "A" (des-
cribed in Example 1) by a sequential impregnation method
whereby silver was deposited upon the carrier prior to
the deposition of potassium and cesium, as follows:
Preparation of Silver-Containlng ImPre~nating Solution
48.43 grams of ethylenediamine (high purity
grade) was mixed with 100 grams of distilled water. 50.75
grams of oxalic acid dihydrate (reagent grade) was then
added slowly to the solution at ambient temperature while
continuously stirring,the solut~on temperature rising to
about 60C due to the reaction exotherm. 88.97 grams of
silver oxide power (Metz Metallurgical Corp.) was then
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added to the diamine-oxalic acid-water solution. Finally
i7.7 grams of monoethanolamine and 44.0 grams of distilled
water were added to complete the solution. The specific
gravity of the solution was 1.3957.
Catalvst Preparation
lS0 grams of Carrier "A" was impregnated with
the above-described solution and then heat treated at
500C for 2.5 minutes in accordance with the method
described in Example l. Following this heat treatment,
the carrier was impregnated with the impregnating sol~tion
as described belo~:
Pre~ n of Impre~natin~_Sol~ltion Containin~ Cesiu-
and Potassium
5.791 grams of aqueous cesium hydroxide solu-
tion (0.009723 grams Cs/g solution) and 4.415 ~rams of
aqueous p~tassium carbonate solution (0.00369 grams K/g
solution) were added to a 250 ml volumetric cylinder and
n-butanol then added to fill the cylinder to the 25Q ml
mark. The cylinder was heated to 40C, sealed and shaken
vigorously until a clear solution was obtained.
~'~
The above described silver-containing Carrier "A"
was impregnated under vacuum with the impregnating solution
containing cesium and potassium for a period of 15
minutes, and then drained of excess solution using the
method described in Example l. Heae treatment of ~he
carrier was then carried out at 500C for 2.5 minutes in
accordance wleh the method of EXample l.
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