Note: Descriptions are shown in the official language in which they were submitted.
- 2 -
The invention relates to silver catalysts for
the production of ethylene o~ide comprising silver
on a porous refractory support and also containing
one or more alkali compounds. The invention further
relates to a p~ocess for the preparation of these
catalysts and to a process for the production of
ethylene oxide in the presence of these catalysts.
Materials consisting of silver upon a support
are known to be useful catalysts for the production
of ethylene oxide by the controlled incomplete oxidation
of ethylene with molecu]ar oxygen. A great variety
o~ modi~ications have been proposed to improve the
activity and selectivity of these catalysts. These modifications
have involved, for example, the supports employed,
the method of production, the physical form of the silver
on the support and the addition of additives to the
catalyst.
The alkali metals and their salts have been repeatedly
proposed as additives for various silver catalysts
for the production of ethylene oxide~ U.S patent specification
2,125,333, an early pub~ication on this subject, discloses
"small amounts~' of alkali metals, including both sodium
or potassium, in silver catalysts Later patents elaborated
on this disclosure, but often with contradictory teachings.
For instance, U.S. patent specification 2,238,474 teaches
that while addition of 1000 ppm by weight to 24% by
weight of sodium improved silver catalysts, this amount
~8~
of potassium or cesium hydroxide ha~ a detrimental
ef~ect on catalyst performance. A large number of
promoters useful in broad weight ranges is cited in
U.S. patent specification 2,615,900, but no distinction
in the effectiveness of the various promoters is made.
The use of large amounts of alkali metal sulphates
is stated in U.S. patent specification 2,671,764. Further,
U.S. patent specification 2,765,283 discloses that
the addition from 1 to 2000 ppm by weight of an inorganic
chlorine compound (e.g. sodium chloride) to the catalyst
support prior to the addition of silver improves the
performance of the finished catalyst. However, U.S.
patent specification 2,799,687 discloses that when
from 20 ppm by weight to 1. 6% by weight of an inorganic
halide (sodium chloride or preferably potassium chloride)
are added as separate solid particles to a fluidized
bed of a supported silver catalyst, the halide acts
as a suppressant, inhibiting the catalyst activity.
In U.S. patent specification 3,144,416 a number of
promoter materials is cited, but no critical limitations
on their concentration is given. The use o~ alkali
and alkali earth metals as promoters is generally disclosed
in U.S.patent specification 3,563,913, listing specifically
lithium with no reference to cesium, rubidium or potassium.
These promoters are preferably added to the catalyst
support before the latter is impregnated with the solution
containing the silver compound. The use of aluminium
10~8(~
oxide supports having a pore volume between 0.15 and
0.30 m /g and a surface area below 10 m2/g is stated
in U.S.patent specification 3~575,888. The use of certain
organic amine solubilizing/reducing agents to produce
uniformly spaced, adherent, hemispherical deposits
of metallic silver on catalyst supports is disclosed
in U.S.patent speci~ication 3,702,259. According to
Netherlands patent application 7300162, catalysts may
be used that contain one or more of the alkali metals
potassium, rubidium and/or cesium in an amount of 0~35-3,0
milligramatom alkali metal (mgat) per kg catalyst,
which metals have been deposited simultaneously with
the silver on the catalyst support. Adding potassium,
rubidium and/or cesium in amounts outside the range
specified is not beneficial and addition of the alkali
prior to the;addition of silver offers little or no
advantage.
The prior art clearly recognizes that alkali metal
compound addition changes, for better or worse, the
character of a silver ekhylene oxide catalyst.
It has now been found that the deposition of ~otassium,
rubidium or cesium prior to the deposition of the silver
in critical amounts proportlonal to the support surface
area produces superior ethylene oxide catalysts.
The invention may be defined as relating to silver
catalysts for the production of ethylçne oxide comprising
silver and one or more alkali compounds on a porous
-- 5 --
0
refractory support, which catalysts have been prepared
by a process comprising the following steps:
(a) impregnating a porous refractory support having
a surface area from 0.03 m2/g to 10 m2/g with
a solution of a compound of an alkali metal having
an atomic number from 19 through 55 in such concentration
as to produce - optionally after extraction with
a solvent after either step (b) or (c) indicated
below - i.n the final catalyst a content from 0.25
to 16 milligram equivalent weights of the alkali
metal per kilogram total catalyst for each square
meter of support surface area per gram of catalyst
support((mgew/kg)/(m2/g));
(b) at least partially drying the impregnated support
f step ta);
(c) contacting the product of step (b) with a liquid
phase containing a dissolved silver compound or
a slurry of particles of silver or a silver compound
in an amount sufficient to deposit from 1 to 25
per cent by weight of silver, based on the total
catalyst, on the support surface, and
(d) ithermally treating the product of step (c), to
convert the silver compound to silver metal.
The catalysts according to the present invention
comprise a porous refractory support having deposited
on its exterior and interior tpore) surfaces from 1
to 25% by weight, based on total catalyst, of silver
6 --
~14~0~0
and certain amounts of potassium, rubidium and/or cesium
ions Of the alkali metals, i.e. lithium, sodium, potassium,
rubidium and cesium, only those alkali metals of atomic
number from 19 through 55 inclusive, i.e., potassium,
rubldium and cesium, are suitable. Unless otherwise
stated, these three suitable metals will hereinafter
be referred to as "the higher alkali metals". Excellent
results are achieved with each of the three higher
alkali metals. Potassium offers cost advantages, while
cesium gives the greatest catalyst improvement. Rubidium
gives a greater catalyst improvement than does potassium.
Mixtures of the higher alkali metals are also useful.
The higher alkali metals are present on the catalysts
in the f~rm of their cations, rather than as the extremely
active free alkali metals. Silverj on the other hand,
is present on the finished catalysts as silver metal.
The amount of the higher alkali metal (or metals)
present on the catalyst surface is a critical function
of the surface area. The contents of higher alkali
metals of this invention are found to be directly proportional
to the surface area of the support with the optimum
content being preferably 5-4 and more preferably 5-3
milligram equivalent weight per kilogram total catalyst
for each square meter of surface area per gram of catalyst
support ((mgew/kg)/(m /gm)). In other words, the optimum
higher alkali metal content divided by the surface
area is approximately a constant value. It has been
~L~48~
found that as the alkali metal content is increased
from zero, the selectivity of the catalyst increases
to a maximum, and at contents beyond the maximum the
selectivity decreases again. The content at which this
maximum in the selectivity occurs is referred to herein
as the optimum alkali metal content. Further, since
the approach to the optimum selectivity is gradual
rather than a step function, there are alkali metal
contents both above and below the optimum that also
produce commercially significant improvements in catalyst
selectivity and are considered within the scope of
this invention. Hence, the alkali metal contents preferably
include contents that range from 25% to 175% of the
optimum content~ more preferably from 25% to 150%,
and most preferably from 50% to 150%. Expressed as
the operable range, the higher alkali metal contents,
relative to the support surface area range from 0.25
to 16, preferably from 0.25 to 14 and most preferably
from 0.5 to 14 milligram equivalent weights per kilogram
total catalyst for each square meter of surface area
per gram of catalyst support (mgew/kg)/(m ~gm). There
appears to be minor variations in the content range
of each of the higher alkali metals of this invention
wherein optimum selectivity is obtained when the catalysts
of this invention are employed in the partial oxidation
of ethylene to ethyl~ne oxide. It is thought, however,
that these minor differences are attributable to undetermined
experimental differences or other unknown variables,
-- 8 --
~Lai48~L0
but they are not considered to be significant. While
the optimum alkali metal content is directly proportional
to the surface area of the cata]yst support, not all
surface areas provide commercially useful catalysts.
The catalyst surface areas that have been found critical
for this invention range from 0.03 to 10 square meters
per gram (m2/g).
It must be made clear that the amounts of potassium,
rubidium and/or cesium deposited are not necessarily
the total amounts of these metals present in the catalysts.
They are the amounts of these alkali metals which are
present on the surface of the catalyst and which are
intentionally added to the catalysts prior to the addition
of silver. It is not unusual that substantial amounts,
often up to 1 %w, of higher alkali metals (usually
potassium) are present within the porous support, due
to use of support materials containing naturally occurring
alkali metals or inadvertent alkali metal addition
during support manufacture. These amounts of higher
alkali metal present in the support in non-leachable
form do not appear to contribute to the improved performance
of catalysts aocordin~ to this invention and are neglected
in determination of alkali metal concentrations. However,
amounts of higher alkali metal present in the support
in leachable form must be taken into account in determinlng
the amounts of higher alkali metal depos'ited on the
support. In fact, an alternate method of providing
all or part of the desired amounts of t~e higher alkall
metal is to incorporate the higher alkali metal in
the support in leachable form during the manufacture
of the support.
The catalysts according to the present invention
contain from 1 to 25% by weight, based on the total
catalyst, of silver as silver metal. Preferably, they
contain from 2 to 20 and most preferably from 4 to
16% by weight of silver. The use of amounts of silver
larger than 25% by weight is not excluded but is generally
economically unattractive. The silver is deposited
over the interior and exterior surfaces of the catalyst
support and should be evenly dispersed over these surfaces.
The exact physical form of the silver upon the
support can vary and does not appear to be critical
to the invention. Very excellent results are obtained
with the controlled surface alkali metal content catalyst
of this invention, however, when the silver is present
in the form of uniformly spaced, discontinuous, adherent,
discrete particles having a uni~orm diameter of less
than one micron (10,000 A). Best results are obtained
with this type of catalyst when the silver particles
have diameters of from 1000 to 10,000 A and most preferred
catalysts have silver particles of an average diameter-
in the range of from 1500 to 7500 A.
The support employed in the catalysts according
to the invention is selected from the large number
.
~8~0
of conventional porous refractory catalyst carriers or support materials which
are essentially inert in the presence of the ethylene oxidation feeds, pro-
ducts and reaction conditions. Such conventional materials may be of natural
or synthetic origin and preferably are of a macroporous structure, that is,
a structure having a surface area below 10 m2/g and preferably below 7 m /g.
These support materials typically have an apparent porosity of greater than
20%, Very suitable supports comprise those of siliceous and/or aluminous
composition. Specific examples of suitable supports are the aluminium oxides
~including the materials sold under the trade mark "Alundum"), charcoal,
pumice, magnesia, zirconia, kieselguhr, fuller's earth, silicon carbide,
porous agglomerates comprising silicon and/or silicon carbide, magnesia,
selected clays, artificial and natural zeolites and ceramics. Refractory
supports particularly useful in preparation of catalysts according to the
present invention comprise the aluminous materials, in particular those con-
taining alpha-alumina. In the case of alpha alumina-containing supports, pre-
ference is given to those having a specific surface area as measured by the
B.E.T. method of from 0.1 to 7 m2!g and an apparent porosity as measured by
conventional mercur~ or water absorption techniques of from 10% to 50% by
volume. The B.E.T. method for determining specific surface area is described
in detail in Brunauer,
-- 10 _
~.,
~[)4~3010
S., Emmett,P.H., and Teller,E., J.Am.Chem.Soc.,60
(1938), 309-319.
Regardless of the character of the support used,
it is preferably shaped into particles, chunks, pieces,
pellets, rings, spheres, and the like, of a size suitable
for employent in fixed bed applications. Conventional
commercial fixed bed ethylene oxidation reactors are
typically in the form of a plurality of parallel elongated
tubes (in a suitable shell) approximately 2.5 to 5
cm in diameter and 7 to 14 m long filled with catalyst.
In such reactors, it is desirable to employ a support
formed into a rounded shape, such as, for example,
spheres, pellets, rings, tablets, and the like,having
diameters of from 2.5 to 20 mm.
The catalysts of the invention are prepared by
a technique in which the desired higher alkali metal
is deposited on the catalyst support surface prior
to the deposition o~ the silver. Accordingly, the invention
also relates to a process for the preparation of silver
catalysts according to the invention, which comprises:
(a) impregnating a porous refractory support having
a surface area from 0.03 m2/g to 10 m2/g with
a solution of a compound of an alkali metal having
an atomic number from 19 through 55 in such concentration
as to produce - optionally after extraction with
a solvent after either step (b) or (c) indicated
below - in the final catalyst a content from
- 12 ~-
~4~
0.25 to 16 milligram equivalent weights of zhe
alkali metal per kilogram total catalyst for each
square metre of support surface area per gram
of catalyst support ((mgew/kg)/(m2/g));
(b) at least partially drying the impregnated support
of step (a);
(c) contacting the product of step (b) with a liquid
phase containing a dissolved silver compound or
a slurry of particles of silver or a silver compound
to deposit from 1 to 25 per cent by weight of
silver, based on the total catalyst, on the support
surface, and
(d) thermally treating the product of step (c); to
convert the silver compound to silver metal.
The exact concentrations of higher alkali metal
compounds and silver compounds employed in the impregnatin~
solution used in the above-mentioned steps (a) and
(c) may generally require some routine experimentation
since the amount of higher alkali metal compounds and
silver compounds deposited will depend in part on
the porosity and surface area of the catalyst support.
However, methods of varying the amount of a higher
alkali metal and silver deposited are conventional,
as is the analytical determination of the amount of
5 the materials actually present.
Preferably the impregnating liquid in step (a)
above contains the higher alkali metal compound in
such concentration as to produce in the final product
a higher alkali metal content from 0.25 to 14 and most
preferably from 0O50 to 14 milligram equivalent weights
per kilogram total catalyst for each square meter of
support surface area.
Another method involves deposition of larger then
required amounts of the higher alkali metal salts according
to step (a) in the general procedure described above
followed by contacting the catalyst particles so obtained
after either step (b) or step (d) of the procedure
described above with a suitable solvent, for example
an anhydrous alkanol of 1 or 2 carbon atoms per molecule,
methyl or ethyl acetate or tetrahydrofuran. The higher
alkali metals are soluble in the solvents described
to a sufficient degree that one or more washings with
these solvents will selectively remove the excess higher
alkali metal such that the amount remaining intact
on the support surface falls within the concentration
range critical to the invention. This method then provides
a ready means of adjus~ing the higher alkali metal
concentration from levels in excess of the content
of 16 (mgew/kg)/(m2/g), whether the result of purposeful
or inadvertent actions~ to specific concentrations
within the range of from 0.25 to 16 (mgew/kg)/(m2/g),
by a process whîch is readily applicable to large plant
scale operations.
- 14 -
~L~4~ O
An excellent method for adding the desired higher
alkali metals ls to dissolve a compound thereof in
an aqueous phase in an amount regulated to give the
required alkali metal addition to the finished catalyst
when the support is contacted therewith. Suitable higher
alkali metal compounds generally include all those
which are soluble in an aqueous phase. In this regard,
no unusual effectiveness is observed with use of any
particular anion in the alkali metal compounds. For
example, hydroxides, nitrates, nitrites~ chlorides,
iodidesl bromates, bicarbonates, oxalates, acetates,
tartrates, lactates or isopropoxides, may be used.
The support after impregnation with the higher alkali
metal may be dried in any suitable manner, preferably
by increasing the temperature to a value between 100C
and 200C, for example for a time from 0.5 to 8 and
particularly from 0.5 to 4 hours with multiple temperatures
being suitable and conducting an inert gas over the
heated support. Suitable inert gases are nitrogen,
air, hydrogen, noble gases, carbon dioxide, methane
and mixtures of these gases. Drying can be performed
at atmospheric, sub-, and super-atmospheric pressures.
Vacuum- and freeze-drying may also suitably be employed.
A great variety of methods for adding silver to
supports are known. In a typical method, the support
may be impregnated with an a~ueous solution of silver
nitrate, dried, and the silver reduced with hydrogen
- 15
~L~48~1~
or hydrazine as described in U.S. Patent Specification
3,575,888. In another technique the support may be
impregnated with an ammoniacal solution of silver oxalate
or carbonate and the silver metal formed by thermally
5 decomposing the salt. Silver may be added as well by
the technique disclosed in U.S. Patent Specification
3,702,259, wherein the support is impregnated with
special aqueous solutions of silver salts and combinations
of ammonia, vicinal alkanolamines and/or vicinal alkyldiamines,
and then thermally treated. Other possible methods
for adding silver include impregnating a support with
an ethanolamine-containing solution of a silver salt
and then reducing, as disclosed by Japanese Patent
Specification 19606/1971, or by adding a slurry of
~ine particles of silver carbonate to the support and
thermally decomposing as described in U.S.Patent Specification
3,043,854 or adding silver in the form of "cluster"
silver as by the process described in U.S.Patent Specification
3,781,317~ In each of these techniques, silver is added
to the support when the support is contacted with a
liquid phase containing either a silver solution or
a slurry of particles o~ silver or a silver compound.
A particularly effective method of depositing
the silver is where the silver is added to the support
from a basic solution, particularly from a nitrogenous
base-containing basic solution. Examples of these nitrogenous
bases are ammonia, the alkylamines and the alkanolamines.
- 16 -
~(~148~
In a particularly preferred modification, the
silver addition to the catalyst support is rnade by
techniques such as those disclosed in U.S.Patent Specification
3,702,259. This preferred preparation method involves
impregnation of an alumina support with certain aqueous
silver salt solutions and a subsequent thermal reduction
of the silver salt. The silver impregnation solution
consists essentially of:
A.a silver salt of a carboxylic acid,
B. an organic amine alkaline solubilizing/reducing
agent, and
C. an additional aqueous solvent as is required
to
achieve the desired silver level.
Suitable carboxylic acid silver salts include
silver carbonate and the silver salts of mono- and
polybasic carboxylic and hydroxycarboxylic acids of
up to about 16 carbon atoms per molecule. Silver carbonate
and silver oxalate are particularly useful silver salts,
with silver oxalate being most preferred.
An organic amine solubilizing/reducing agent is
present in the impregnating solution used in this prepration
method. Suitable organic amine silver-solubilizing/reducing
agents include lower alkylenediamines of from 1 to
5 carbon atoms per molecule, mixtures of a lower alkanolamine
of from 1 to 5 carbon atoms with a lower alkylenediamine
of from 1 to 5 carbon atoms, as well as mixtures of
~0480~(~
ammonia with lower alkanolamines or lower alkylene-diamines
of from 1 to 5 carbons. Four groups of organic amine
solubilizing/reducing agents are preferred. They are
the following:
A. vicinal alkylenediamines of from 2 to 4 carbon
atoms,
B. mixtures of (1) vicinal alkanolamines of from
2 to 4;carbon atoms and (2) vicinal alkylenediamines
of from 2 to 4 carbon atoms;
C. mixtures of vicinal alkylenediamines of from 2
to 4 carbon atoms and ammonia; and
D. mixtures of vicinal alkanolamines of from 2 to
4 carbon atoms and ammonia.
These preferred solubilizing/reducing agents are generally
added in the amount of from 0.1 to 10 moles per mole
of silver present.
~ ery preferred as solubilizing/reducing agents
are:
A. ethylenediamine,
. ethylenediamine in combination with ethanolamine,
C. ethylenediamine in combination with ammonia and
D. ethanolamine in combination with ammonia.
Ethylenediamine, alone or in combination with
ethanolamine, is most preferred.
When ethy]enediamine is used as the sole solubilizlng/r~luci~g
agent, it is necessary to add amounts of the amine
- 18 -
in the range of from 0.1 to 5.0 moles of ethylenediamine
per mole of silver.
When ethylenediamine and ethanolamine together
are used as solubllizing/reducing agent, it is suitable
to employ from 0 1 to 3.0 moles of ethylenediamine
per mole of silver and from 0.1 to 2.0 moles of ethanolamine
per mole of silver.
When ethylenediamine or ethanolamine is used with
ammonia, it is generally useful to add at least about
two moles of ammonia per mole of silver and very suitable
to add from about 2 to about 10 moles of ammonia per
mole of silver. The amount of ethylenediamine or ethanolamine
employed is suitably from 0.1 to 2.0 moles per mole
of silver.
As already noted, it is essential that only certain
controlled amounts of the hi~her alkali metals of the
invention be present, these amounts being a function
of the surface area of the catalyst support. These
amounts are achieved by either controlled addition
of alkali metal to the support in the first impregnation
step or by controlled removal of excess alkali metal
from the impregnated catalyst support either before
or after the silver impregnation step.
The thermal treatment of step (d) may be carried
out at a temperature of from 100 to 500C, preferably
to 375C, and more preferably from 125 to 325C, for
the time, typically 0.5 to 8 hours, required to decompose
- 19 -
~L~348~:~0
the silver salt and form the adherent particulate deposit
of metallic silver o~ the surfaces. Lower temperatures
do not adequately decompose the silver salt and ~hould
be avoided. More than one temperature may be employed.
The higher alkali metal-promoted silver catalysts
have been shown to be particularly selective catalysts
in the direct oxidation of ethylene with molecular
oxygen to ethylene oxide. The conditions for carrying
out such an oxidation reaction in the presence of the
silver catalysts of the present invention broadly comprise
those described in the prior art. This applies, for
example, to suitable temperatures, pressures, residence
times, diluent materials such as nitrogen, carbon dioxide,
steam, argon, methane or other saturated hydrocarbons,
the presence or absence of moderating agents to control
the catalytic action, for example 1,2-dichloroethane,
vinyl chloride or chlorinated polyphenyl compounds,
the desirability of employing recycle operations or
applying successive conversions in different reactors
to increase the yields of ethylene oxide, and any other
special conditions which may be selected in processes
- for preparing ethylene oxide. Pressures in the range
of from about atmospheric to about 35 bar abs. are
generally employed. Higher pressures may, however,
be emplyed within the scope of the invention. Molecular
oxygen employed as reactant is obtained from conventional
sources. The suitable oxygen charge may consist essentially
:`
~o~
of relatively pure oxygenl a concentrated oxygen stream comprising oxygen
in major amounts with lesser amounts of one or more diluents, such as
nitrogen, argon, etc., or another oxygen-containing stream, such as air. The
use of the present novcl silver catalysts in ethylene oxidation reactions
is in no way limited to the use of specific conditions among those which are
known to be effective.
In a preferred application of the silver catalysts of the invention
ethylene oxide is produced when an oxygen-containing gas of not less than
95% oxygen is contacted with ethylene in the presence of the present
catalysts at a temperature in the range of from 210C to 285C and preferably
225C to 270C. Accordingly, the present invention also provides a process
for the production of ethylene oxide by direct oxidation of ethylene in the
vapour phase with molecular oxygen at ethylene oxide forming conditions at a
temperature in the range from 210C to 285C in the presence of a fixed bed
of a silver catalyst, which process is conducted in the presence of a silver
catalyst as previously described.
The resulting ethylene oxide is separated and recovered from the
reaction products by conventional methods known and used in the art. Use of
the silver catalysts of the invention in ethylene oxide production processes
gives higher overall ethylene oxidation selectivities to ethylene oxide at
a given ethylene conversion than is possible with conventional ca~alysts.
While the reason for these higher selectivities observed with
catalysts of this invention is not fully understood, experiments have
indicated that conventional silver catalysts ~not containing higher alkali
metals) cause ethylene oxide to combust after formation while silver
catalysts containing higher alkali metals according to this invention do not
cause as extensive ethylene oxide comhustion.
- 20 -
,~'
- 21 - ~4~
The invention is ~urther illustrated by means
of the ~ollowing Examples.
EXAMPLE I
~_ . .
A series of catalysts were prepared using alumina
supports with different surface areas. The physical
properties o~ these supports are shown in table I.
- 22 -
~4~ 0
Table I
Catalyst support A B C D E
Trade name -Carborun- Norton Girdler Péchiney
dum Company SRS 6
SAHT-96 LA-4102
Sur~ace area, m2g 0.19 0.51 1.07 1.32 6.55
Form of particles rings spheres, cylin- rings, spheres,
8 mm diam. 5 mm ders,diam. diam. diam.2 to
5 mm 15 mm 5 mm
Sodium content,%w 0.02 0.13 0.24 o.40 0.52
Zinc content, %w - - 0.24 0. 23
Silica content,%w 0. 26 2.37 0.15 0.28 2.5
Iron content, %w 0.09 0.45 o.o4 0.03 0.05
Trace metals other
than Na, Zn, Si and Fe,
%w oxides 0.33 0.85 0.25 0.3 0.3
Apparent porosity~),%v 24 50 25 25 40
Median pore diameter,
micron 3.9 2 o.8 0.6 0.25
80% of the pores had
diameters in the
range of from
.. to .. ~micron 1.5-15 0.3-10 0.4-1.2 0.2-1.5 0.1-0.9
Pore volume"),ml/g0.23 0.25 0.22 0.45
_______
') from water adsorption
~') determined by means of the mercury porosimeter
2~ 480~L0
C fl ti fl ly r~ ti F~ d rl lJ ~ n a li (3 (~ A ~ 1., /~ - 2, .... ~ J., r3 t; c .
Wr.)r~ marl~3 'Lrl aC'COrdflrlCe Wl.t;tl t~l:i.f3 invr?nti:lon~ that if~,
h ,y t h e c3 ~ n ~, .l. fl :1 cl r? l~ r.) [~; :l. t, i c) ~ o L~ t, f l ~,' .a :l. k f~ i rnc ti a l. a nd
tihr,~ ~I.l3.vr.?r. C'flt;l'l.y).~ rlc!fJ.i p;rlr.ll;ed M/\-O, f;~l3-0, . . ., ~ ~0,
r3t;c, wrlrr3 n~t :Ln acc,c)rclfln~le w:i.t;h th(? :invr~nt;ir.?-n ln that
th~?y cont;fl.:i.n~d no alka:l i rnet,f~ a.tia3yf3t,f^~ c1r~F;.i~nati~d
N~ M~\-2, . . . ) Nl.~-'l, rnkc~ wt~re~ f.;l~.f~;O not; :I.n accordanc
w.lt;h th;l.)i,; .lnvf~nt:ioll in that t,h~J d~pof~lt.lorl o-f' thre alka:L
m~3t~.1 an(l ti^lr.~ Fsl,`l.vc.~r~ w~!:rr~ marlr.,~ r3Lmult,anc!c)uf.~ Ly.
J,O '.L'o L'lLul~.;krak,f? thr~ prr?r~flrflt,:lon o~ crlt,lll$rFitf.~ in
~coorclflnc~ w.l. kh th.lf~ Invr.?nl;lon th~ pr~paratii.on o.f catalyst~
rna~ wl~h ~upport C .1~ El~`ti out; he:low. rrhe other catalyf3t~
:ln accorfl~n~o wllih thf3 Inv~?nl~ion w~,rf~ prc!p~lred ln a
a lm.l la:r ~fJh:l orl .
~1'3 An amc)unti o;f` 30 ~; ot` ~mppo:rk C h~vLn~, a ~ur.~ac~
~r~Q o~ L . 07 m /~, wQr~ .f~;ir~3t :imprf?~n~t;f?~ un~lf~?r a prf~?ssurf~
o~E` O . 04 ba.r ab~ . .In a rot~ry ~vapo:r ator wi th ~ . 5 ml
o.~ an acluf~oufl ~30:luki:Lon c,~ontaln Inp 3 m~ ce~,.iunl hyclroxide
p~x~ ml ~lo~ t:lon, '.['h~ :i.mpre~n~ll;t~(.l sl~pport wa~ clr:1~d
2t~ by h~lt~tlp~ ror 3t) m:i.tl ak :llQC, and kh~n Ior tiwo hour~t
at ~50C .ln ~1 ~.ttre~lm ol` n:i t;ro~;en.
~]~ 1UppOrti W~1~3 th~n .impr~ .rnat~cl w:i ~h an aclueou~3
~tolutlon o.~` ~tl.~ltrer ~ rrh:lS ~C)lUkiOtl wa't prep~recl
by the ro'1lowit~ t~ohr~ u~. 6 Qram~3 anhy(lrou~t sllv~r
~5 n:l~.r~t~ nnd 3.3 gr~ s pc~t~3~.nLllm ox~lat~,e (K~C204.1 ~120)
w~r~ ~p~rat~ly ct.l.ssolv~?d i.n ClUf~l'lt:itt:i~?S Or l~Q ml of
w~t~.r~ ~rt~ 30 ~ ob~ d W(?~ m:i~x(?d ~ d h~ .t~d
24 ~
on a steam bath. The silver oxalate precipitate was
centrifuged and the supernata~t liquid decanted. Subsequently,
the precipitate was washed five times with 100 ml hot
(60-9oC) distilled water. The precipitate was centrifuged
and the water decanted after each washing. The precipitate
was then dissolved in 10 ml of a mixture consisting
of 75 %v of 1,2-diaminoethane and 25 %v of waterg the
mixture being cooled in ice. A quantity of 30 grams
of the cesium-containing support was then consecutively
impregnated at a pressure of 0.04 bar abs. in a rotary
evaporator, with 8.5 ml of the latter liquid, warmed
up by indirect heat exchange with hot water to a temperature
of 60C with rotation, again at 0.04 bar abs, to partially
remove the solvent, poured out onto a large filter
paper and gently shaken to remove any excess moisture,
heated in a stream of nitrogen for a period of two
hours until a temperature of 300C was attained and
kept at 300C for a further two hours. The catalyst
was then cooled to ambient temperature. The silver
content of the catalyst was 7.8 % by weight. The cesium
content amounted to 3.35 mgew per kg catalyst. Examination
of the catalyst with an electron microscope revealed
that the silver had been deposited on the support as
discrete particles with a uniform diameter of from
5 to 0.3 microns (500 to 3000 A). The silver particles
were uniformly spaced over the surface of the ~upport.
- 25 -
4~1~9 0
To prepare the NA-0, ..., NI-O series of catalysts
which did not contain any alkali metal, the first impregnation
step with the cesium hydroxide solution described above
was omitted with the subsequent steps being substantially
the same.
To prepare the NA-1, NA-2, ..., N~-5, series of
catalysts not in accordance with the invention, the
first impregnation step with the cesium hydroxide described
above was also omitted. The subsequent steps were followed
in a substantially similar fashion with the exception
that cesium hydroxide was added to the silver ethylenediamine-water
solution in su~ficient quantities to provide the desired
alkali metal content in the final catalyst product.
The catalysts prepared above were comparatively
tested for the production of ethylene oxide. The reactor
consisted of a tube with an internal diameter of 5
mm and was in each experiment rilled over a length
of 12 cm with catalyst particles whose dimensions were
in the range between 0.4 and o.8 mm. These catalyst
particles were obtained by crushing the catalyst particles
prepared as described in the above.
A mixture containing oxygen and ethylene was conducted
through the catalyst bed in the presence of a small
amount of vinyl chloride as a moderator under the following
conditions:
-- 2 6
~L~4801(~
Pressure ~ . . . . . . . . . . . . . . . . . . . 14.5 bar abs
space velocity . . . . . . . . . . . . . . . . .3300 h 1
ethylene in feed ............................. 30 %m
oxygen in feed . . . . . . . . . . . . . . . . . 8.5 ~m
nitrogen in feed . . . . . . . . . . . . . . . . 61.5 %m
moderator concentration, parts of vinyl chloride
per million parts of feed (vol). . . . . . . . . 10 ppm
The reaction temperature was adjusted to provide
for an oxygen conversion of 52% and the selectivity
to ethylene oxide was determined. The selectivity to
ethylene oxide~ expressed as a percentage, is defined
as the number of moles of ethylene oxide formed out
of 100 moles converted ethylene. The results of the
above described experiments are shown in Tables II
through VI. As can be noted from these tables, at the
lowest support surface areas used, the sequential deposition
method of this invention give similar results to the
simultaneous deposition method. However, with the more
desirable hi~her surface area supports, the technique
of this invention produces far superior catalyst to
those not produced in accordance with this invention.
.
.~ - 27 -
109~81~10
Table II
Catalyst prepared with supports having surface areas of 0.19 m /g
Cat. Silver Cesium content Reactor Oxidation
content mgew7kg ppmw temp to selectivity to
achieve ethylene
52% O oxide, %
conve~-
_____ _~______ ________ _________ _ionlC
A-1') 7.0 0.86 114 259 79.9
A-2 7.6 1.01 134 255 80 3
A-3 7.9 1.11 148 259 80.7
A-4 7.6 1.49 198 265 79.8
A-5 8.2 1.65 220 261 79.0
NA-O 7.8 0 0 - 251 69.5
NA-1 8.3 0.77.103 254 80.3
NA-2 8.3 1.08 143 258 80 6
NA-3 7.7 1,25 166 263 80.2
NA-4 7.8 1.64 218 264 79 7
NA-5 8.o 1 89 252 295 76.1
======--==================================
A-1. A-2,..., B-1, etc, are catalysts prepared according to
this invention.
NA-O, NB~O, etc, are catalysts not according to this invention
and with no alkali metal additionO
NA-1, NA-2,... , NB 1, etc, are catalysts not according to
this invention and prepared by the simultaneous deposition
of alkali metal with the silver.
- 2~ - ~
Table III
Catalyst prepared with supports having sur~ace areas o~ 0.51 m /g.
Catalyst Silver Cesium_content Reactor Oxidation
Content mgew7kg ppmw temp.to selectivity to
achieve to ethylene
52% O~ oxide,%
conve -
__ ____ _______ ________ ________ _ion~C
B-1~) 7.7 o.89118 254 74.5
B-2 7.9 1.53204 252 77.8
B-3 7.7 2.79371 258 78.2
B-4 7.5 3.77502 259 76.5
B-5 7.9 5.50732 , 300 70.4
NB-O 7.7 0 0 251 71.0
NB-1 7.1 2.64351 261 77.6
NB-2 7.4l 3.78503 274 76.1
NB-3 8~0 5.47728 > 300 64
====_==_=================================================_======
7) See footnote ~) of Table II.
- 29 - ~ ~4~0
Table IV
Catalyst prepared with supports having sur~ace areas of I.07 m2/~
Catalyst Silver Cesium content Reactor Oxidation
content mgew7kg ppmw temp.to selectivity to
achieve ethylene
52% O oxide, %
conve~-
sion,C
.______.__ ________ . ______________
C-1")8,4 1,56 208 237 77.7
C-2 8.83.52 468 249 78,4
C-3 10,7 6,o3 802 255 79.5
C-4 8,76.59 877 256 77.5
C-5 10,6 7.95 1058 268 76,4
NC-O 8,o 0 0 260 71,9
NC-1 8,o 1,87 249 251 75,1
NC-2 8,o 3.11 430 260 75,9
NC-3 8,4 4,08 543 252 76.2
NC-4 9,2 4,80 639 257 74.7
NC-5 8.o 5.43 722 320 67.8
================================_=====================.
') See footnote of table II.
,
.~
~04813~
Table V
Catalyst Prepared with Supports having surface are,as of 1.32 m2/g
Catalyst Silver Cesium content Reactor Oxidation
content mgew7kg ppmw temp.to selectivity to
achieve ethylene
52% O oxide,%
conve~-
,________ _______ ________ ________ __onl_C__ ____.____ _____
D-1l) 6.6 4.19 557 260 67.0
D-2 6.o 6.35 844 265 73.2
D-3 6.9 7.691024 264 75.4
D-4 7.2 9.561272 261 74.3
ND-0 5.4 0 0 257 66.o
ND-1 5.4 4. o8543 ' 293 65.6
ND-2 5O4 4.69 624 289 63.2
=_====_======================================================._=
~) See footnote ~) of table II
Table VI
Catalyst prepared with supports having surface areas of 6.~55 m2/g
Catalyst Silver Cesium content Reactor Oxidation
content mgew7kg ppmw temp.to selectivity to
achieve ethylene
52% O~ oxide,%
conve~-
__ ____ ________ _______ ___ _ sion~C
E-17) 11.5 25.73420 207 73~3
E-2 11.0 35.34690 205 75,4
E-3 11,2 39.55250 205 75.1
NE-0 9.4 0 0 220 50.0
NE-1 11.9 42.35621 277 42.4
=====================_=========================================
') See footnote') Or table II.
- 31 ~
The above~mentioned results are also represented
in the accompanying graph, where the cesium contents
; of the catalysts, in ppm, are plotted along the horizontal
axis and the selectivities to ethylene oxide, in %,
5 along the vertical axis. The selectivities of the catalysts
made from the five different aluminas mentioned in
Table I are indicated in the graph with five different
; symbols. The five lines based on each set of symbols
represent the selectivity as a function of the cesium
content for the surface area stated near each line.
The four lines for the surface areas 0.19, 0.51, 1.07
and 1. 32 m /g are based on the left hand and lower
scales, whereas the line for the surface area 6.55
m /g is based on the left hand and upper scales. The
vertical arrows pointed to each of the five curves
indicate the optimum cesium content of each of the
four catalysts. These optimum cesium contents are stated
in Table VII.
Table VII
Alumina surface Optimum cesium Selectivity at Optimum cesium
area, m2/g content, mgew/ optimum cesium content divided
kg content, % by surface a~ea
________________ ______________ ______________ (mg_w!kg)/(m /g~
0.19 1.12 80.7 5.9
0.51 2.26 78.4 4.5
1.07 6.02 79.5 5.6
1.32 8.13 75.5 6.1
6.55 35.7 75.4 5.4
=_======== = ======================================================
- 32 - ~0480~
EXAMPLE II
Catalysts in accordance with this invention containing
varying amounts of potassium as the higher alkali metal
component were prepared using the feedstocks and general
preparative t;echniques c-f Example I. Instead of adding
cesium to the first impregnating solution, potassium
as potassium hydroxide was added. The catalyst compositions,
so prepared, were tested as ethylene oxide catalysts
using the apparatus and technique of Example I. The
compositions of these catalysts along with the results
are given in Table VIII.
Table III
Catalyst prepared with supports having surface areas of 0,19 m /g
Catalyst Silver Potassium content Reactor Oxidation
content mgew7kg ppmw temp.to selectivity to
achieve ethylene
52% O oxide,%
conve~
sion C
________ _______ ______ ________ ____~___ ______________
F-1') 7.8 1.7468 256 79.8
NF-0 7.8 0 _ 251 69.5
======_=======___==_=====_===_=====_=_===========_==========_==
') See footnote ') of table II.
EXAMPLE III
Catalysts in accordance with this invention cotaining
varying amounts of rubidium as the higher alkali metal
component were prepared using the feedstocks and general
preparative techniques of Example I. Instead of adding
cesium hydroxide to the first impregnating solution,
~C~48~1~
rubidium as rubidium hydroxide was added. The catalyst
compositions so prepared were tested as ethylene oxide
catalyst using the apparatus and technique of Example I.
The compositions of the catalysts along with the results
are given in Table IX.
Table IX
Catalyst prepared with supports having surface areas of 0.19 m /g.
Catalyst Silver Rubidium Content Reactor Oxidation
content mgew/kg ppmw temp. selectivity
to achie- to ethylene
ve 52% 2 oxide, %
conver-
sion C
__ _____ _______ ______,_ _________ ____~____ ___________
G~1l) 7.8 1.0690 252 76.7
NG-O 7.8 0 0 251 69.5
========================================================= = .
~) See footnote') of Table II.
EXAMPLE IV
A series of catalysts were prepared in the same
manner as described in Example I starting from the
supports B, C, D and E listed in Table I, but using
cesium nitrate instead of cesium hydroxide. The catalysts
A, F, K and P containing no cesium were included in
Table X for comparative purposes. The catalysts had
the properties stated in Table X. The catalysts prepared
were comparatively tested for the production of ethylene
oxide in fixed beds. The reactor consisted of a tube
with an internal diameter of 5 mm and was in each experiment
filled over a length of 16 cm with catalyst particles
whose largest dimensions varied between 0.4 and o.8 mm.
- 34 ~ q~4~0
A mixture containing oxygen and ethylene was conducted
through the catalyst bed in the presence of a small
amount of 1,2-dichloroethane as a moderator under the
following conditions:
pressure . , . . , , . . . . . . . . 14.5 bar abs.
space velocity , , . . , , . . . . . 3000 h 1
ethylene in feed . . . . . . . . . . 30 %m
oxygen in feed . . . . . . . . . . . 7,8 %m
nitrogen in feed . . . . . . . . . . 62.2 %m
mode~ator concentration, parts of
chlorine per million parts of feed(w) 1.5 ppm
. The reaction temperature was adjusted to provide
for an oxygen conversion of 40% and the selectivity
to ethylene oxide was determined. The values of S40
and T40 thus obtained are presented in Table X, together
with the number of run hours elapsed at the moment
of determination.
~~ - 35 -
Table ~
Exp, Cat. Sur~ace Silver Ceslum diameter S40~ T o~ Run
No, area of content,content silver % ~hours
a~umina, %w Or cat,, particles,
m /g mgat/kg microns
_____ _ __ ___ ___ _______ _ ____ _ _________ _____ ____ _____
1 A 0.51 12,8 0 0,1-0,4 76,3 214 100
2 B 0,51 12,1 0,72 0,05-0.5 78,7 220 95
3 C~) 0.51 9,4 1,07 0,1-0,6 79.o 235 120
4 D') 0.51 11.0 1.24 0,1-0.6 79.0 235 120
E 0.51 9.6 1.30 0.05-0.4 79.0 222*) 65
6 F 1,07 9.7 0 0.1-0.4 75.4 210 40
7 G 1.07 8.5 0.32 0,05-0.3 75.9 210 115
8 H 1,07 8.4 C,68 0,1-0.3 76.3 209 117
9 I 1,07 9,0 2.21 0,1-0,4 80,6 209 75
80,5 220 103
79.7 228 260
J 1.07 7.8 3.35 0.05-0.3 79.3 211*) 60
11 K 1,32 8,o 0 0.05-0,2 73,9 205 85
12 L 1,32 9.5 1.07 0.05-0.2 75.6 212 150
13 M 1,32 7,5 2,19 0,05-0,3 76.8 215 145
14 N 1,32 7.8 2,26 0.05-0,3 77,1 208 50
77,5 223 116
77.5 222 215
0 1,32 7.3 2.49 0.05-0.3 77.5 227 167
16 p 6,55 9.4 0 0.05-0.3 50 215 30
17 Q 6.55 8.5 15 0,05-0,3 74,8 200 90
18 R 6.55 8.7 21 0,05-0.2 77,6 191 30
= = = _ = = = = = = = = = = = = = = = = = = _ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ~r = =
*) In this case an amount of 3 instead of 1.5 ppm 1,2-dichloroethane
was used, temperature corrected to 1.5 ppm from 3 ppm.
') This catalyst was prepared by a single simultaneous impregnation
and heated in air at 300C,
3L048~10
s not in acccrdance with the_present invention.
Series A:
.
Catalysts containing varying amounts of lithium,
an alkali metal not falling within the scope of this
invention, were prepared using the feedstocks and
general preparative techniques of Example I. Instead
of adding cesium hydroxide to the first impregnating
solution, lithium as lithium hydroxide was added. The
catalyst compositions so prepared were tested as ethylene
oxide catalysts using the apparatus and technique of
Example I. The composition of these catalysts along
with the results are given in Table XI.
Table XI
Lithium c~talyst prepared with supports having surface areas
of 0.19 m /g.
Catalyst Silver Lithium content Reactor Oxidation
content mgew7kg ppmw temp. to selectivity to
achieve ethylene
52% 0~ oxide, %
conve~sion,
C
________ _______ _________ ________________ _______ ______
NH-O') 7.8 0 0 25169.5
NH-l 6.928 200 25073.5
NH-2 6.956 390 25072.4
NH-3 6.972 500 25272.8
====================_=_==============================_========
') See footnote ') of Table II.
Series B:
Catalysts containing varying amounts of sodi.um,
an alkali metal not falling within the scope of this
- 37 ~ O
invention were prepared using the feedstocks and general
preparative techniques of Example I. Instead o'~ adding
cesium hydroxide to the first impregnation solution,
sodium as sodium hydroxide was added. The catalyst
compositions so prepared were tested as ethylene oxide
catalysts using the apparatus techniques o~ example
I. The composition of these catalysts along with the
results are given in Table XII below.
Table XII
Sodium ca~alyst prepared with supports having surface areas
of 0.19 m /g,
Catalyst Silver Sodium content_ Reactor Oxidation
content mgew7kg ppmw temp. to selectivity to
achieve ethylene
52% O oxide, %
conve~sion,
________ _______ ________ ______ ________.. _ ______________
NI-O 7.8 0 0 , 251 69.5
NI-1 7,1 1.22 28 252 72.3
NI-2 7.1 2.17 50 251 74.1
NI-3 7.1 3.22 74 249 75.7
NI-4 7,1 3.57 82 254 75.5
NI-5 7.1 4.39 101 254 75.5
=============_=== ==============================_============
