Note: Descriptions are shown in the official language in which they were submitted.
--1
~;æ~7~
IMPROVED CARBONATE-SUPPORTED
CATALYTIC SYSTEM FOR
EPOXIDATION OF ALRENES
Technical Field-
The pre~ent lnvention i~ directed to an lmproved
~y~tem for the preparation of alkene oxide from al-
kene and an oxygen-containing ga~ employing a BUp-
ported sllver catalyst and to the catalysts used ln
the ~ystem. More particularly, the present invention
relates to the oxidation of alkene~ to the cor-
re~ponding epoxides in which enhanced per~ormance i~attained by comblnation of a gaseou~ member of a
redox-half reaction palr pre~ent in the gaseous ml~-
ture of oxygen and alkene, a salt of a member of a
redox-half reaction pair ln comblnation wlth the
cataly~t and use of a ~tablllty-~nhanclng carbonate
salt ~upport.
Background Art:
The productlon of alkene oxlde~, or epoxide~,
partlcularly ethylene oxide by the dlrect oxldatlon
of the correspondlng alkene ln the pre~ence of a
sllver-containlng catalyst ha~ been known for many
year~. For example, the basic process was described
by ~efort ln U. S. Patent 1,998,878 ~nd by Van Peskl
-
Si~82772
ln U. S. Patent 2,040,782. The basic reaction pro-
ceed~, a~ illu~trated for ethylene, according to the
equation:
0
2 CH2-CH2 1 2 ~ 2 CH2 CH2 (I)
and production of an unwanted by-product according to
the reactlon:
CH2-CH2 + 3 2 - ~- 2 C02 ~ 2 H20 (II)
or by further oxidation Oe the epo~lde.
ln the year~ between the Van Peskl patent and
15 the present inventions, re~earch efforts have been
directed to lmproving both the activity and longevity
or useful llfe of the catalyst and the efficiency of
; the overall catalytic reactlon. AB 1S indicated by
¦ reaction~ I and Il, the oxldatlon oE an alkene may
? 20 produce either the alkene oxide ~I) sought in the
! proce~s or the by-product~ C02 and ~2-
Several tér~s are commonly ueed to descrlbe some
of the parameters of the catalytlc system. For ln-
~tance, ~conver~lon~ has been deflned as the percent-
25 age of alkene fed to the reactor which undergoe~
reaction. The ~efflciencyR or, a~ lt is sometime~
called, the ~aelectivity~ of the o~erall proces~ i~
an indication o~ the proportlon, u~ually repre~ented
by a percent~ge, of the converted materlal or product
30 which iB alkene oxide. The commercial ~uccefi~ of a
reactlon ~ystem depend~ in large mea~ure on the effl-
clency of the syQtem. At pre~ent, maximum eficlen-
cles in commerciai production of ethylene oxlde by
epoxidation are in the low 805, e.g., 80 or 81 per-
35 cent. Even a very ~mall increase ln efflclency will
3--
~2a~7'72
proviae &ub~tantial cost benefit~ ln large-~cale
operatlon. For example, taking 100,000 metric ton~
as a typical yearly yield for a conventlonal ethylene
oxl~e plant ~nd as~uming 80 percent conver~ion~ an
increaqe ln eff iciency of from 80 to 84 percent, all
other thing~ being equal, would re~ult ln ~ savings
of 3790 metric tons of ethylene per year. In ~ddi-
tion, the heat of reaction for reactlon II (formation
of carbon dloxide) is much greater than that of reac-
tion I (formation of ethylene oxide) BO heat-remov~l
problem~ are more burdensome as the efficiency de-
crea~e~. Furthermore, as the efficiency decrease~,
there i~ the potential for a greater amount of impur-
itie~ to be pre~ent ln the reactor effluent whlch can
complicate ~eparation of the de~ired alkene oxide
product. It would be desirable, therefore, to de-
velop a proce~s for the epoxidatlon of alkene ln
which the eef iclency ~B greater than that obtained in
conventional commerclal proces~es, e.g., wlth ethy-
lene, efficiencies of B4 percent or greater, whllemalntalnlng other performance characterlstlc~, partl-
cularly the activlty, as descrlbed below, ln A ~atl~-
factory range.
The product of the efflclency and the conversion
i~ equal to the yleld, or the percentage o~ the al-
kene fed that i~ converted lnto the corre3pondlng
oxide.
The ~activity~ of the cataly~t 1B a term used to
indic~te the amount of alkene oxlde contalned in the
outlet ~tream of the reactor relative to that ln the
lnlet ~tream. Actlvlty i~ generally expre~ed ln
terms of poundfi of alkene oxlde produced per ~ubic
foot of catalyst per hour at speclfied reactlon con-
ditlons and rate of feed. The activlty may ~180 be
stated ln terms of the amount of ethylene oxlde ln
~8~:77~
the outlet stream or the d~fference between the ethy-
lene ox~de content of the lnlet and outlet ~treams.
If the activ1ty of a reaction system ls low,
th~n, all other thlngs belng equal, the commerclal
value of that system will be low. The lower the
activity of a reactlon ~ystem, the le~ product pro-
duced in a unit time for a given feed rate, reactor
temperature/ cataly~t, surface area, etcetera. A low
activity can render even a high efflciency process
commercially impractical. ~or production of ethylene
oxide, an activity below 4 pound~ of ethylene oxide
per hour per cubic ~oot of catalyst i8 unacceptable
for commercial practlce. The activity 1~ preferably
greater than 8 pounds, and in ~ome lnstance~ an acti-
vity greater than ll pound~ of alkene oxlde per hourper cubic foot of catalyst i~ deslred.
In some lnstances, activity is measured over a
period of time ln terms of the amount of alkene oxlde
produced at A ~peclfled constant temperature. Alter-
natively, ~ctivity may be measured as a function ofthe temperature required to sustain production of a
specified constant amount of alkene oxide. Plots of
such mea~urements yleld ~aglng rates~ whlch reflect
the stability or useful llfe of the cataly~t. The
useful life of ~ reaction system ls the length of
time that reactants can be passed through the reac-
tion sy~tem during whlch acceptable activlty 1~ ob-
~erved. The area under a plot of activity versus
time iB equAl to the number of pounds of ~lkene o~lde
produced durlng the u~eful llfe of the catalyst per
~ublc ~oot of catalyst. The greater the ~r~a under
such a plot, the more valuable the proce~ lnce
regeneratlon or replacement of the catalyst lnvolves
a number of expense~, sometlme~ referred to a~ turn-
around costs. The rate at whlch activlty decreases,
i2827;~
l.e., the rate of deactivatlon at a glven polnt int~me, can be repre~ented by the 810pe of the actlvlty
plot, l.e., the der~vatlve of activity wlth re~pect
to t~me:
deac~ivatlon ~ dlactlvlty]/dt.
The average rate of deactivation over a perlod
o~ time can be represented then by the change in
act.iv~ty divided by the time periods
average deactivation ~ a activity/ ~
At ~ome polnt, the act~vity decrease~ to an
unacceptable level, for example, the temperature
required to maintain the ~ctivity of the ~ystem be-
comes unacceptably high or the rate of production
become~ unacceptably low. At thls point, the cata-
lyst mu~t either be regenerated or replaced. Some of
these deflnltions may be represented as set ou~ be-
low:
ConverYlon O moles alkene reacted x 100
mole~ alkene fed
Efflclency ~ moles alkene oxide Produced x 100
moles alkene reacted
Yleld , moles alkene oxlde Produced ~ 100
moles alkene fed
Typically, ln commercial productlon, ~ince the
outlet or effluent stream emanatlng from the reactor
may contaln Jubstantial nmounts of unreacted alkene,
the effluent ~tream 18 recycled and comblned wlth the
~2~n2
feedstream after removal of at lea~t a portion of ~he
alkene oxide. Geneeally, a~ the activlty o~ a cata-
lyst decreases with time, ln order to obtain the same
ultimate yleld of epoxlde product, the effluent
stream must elther be recycled 2 greater number of
time~ or the ~emperature wlthln the reactor mu~t be
raised to lncrease the activity of the catalyst. The
former approach to increasing the yield of product
require~ additional energy e~penditures and the lat-
ter, which i~ most frequently used, causes faseercataly~t deterloration.
~ s used herein, an activity-reduclng comp~und
refer~ to a co~pound which, when present in an acti-
vity-reduc~ng amount, cau~es a reductlon ln actlvlty,
gome or all of whlch actlvlty may subsequently be
regained by returning to a situatlon ln whlch the
concentration o~ the compound ls below the minlmum
actlvlty-reducing amount. The mlnlmum actlvlty-
reduclng amount varles dependlng on the partlcular
sy~tem, the feedstream and the actlvity-reduclng
compound.
Conversely, deactivatlon, as u3ed hereln, refers
to a permanent 1085 of actlvlty, l.e., a decrea~e ln
activity which cannot be recovered~ As noted above,
act~vity can be lncreased b~ ealslng the temperAture,
but the need to operate at a higher temperature to
malntaln a particular actlvity i~ representative of
deactlvatlon. Furthermoce, cataly~t~ tend to deactl-
vate more rnpldly when reactlon i8 carrled out at
higher temperatures.
In contrast to problems assoclated wlth low or
decre~sing cat~lyAt activitle~, less than ~atisfac-
tory efflclencies result in los~ of starting mater-
lal, the alkene, as the unwanted product C02. Ultl
mately, thls also lncreases product costs.
1~8;~2
To be considered 6ati~factory, a cataly~t must
not only have ~ 5uf f i~ient activlty ~nd the catalytlc
system provide an acceptable efficiencyr but the
cataly~t mu~t also demonstrate a minimum u~eful llfe
¦ 5 or 6tability. When a cataly~t 1~ spent, typic~lly
! the reactor must be shut down and partlally di~man-
¦ tled to remove the spent catalyst. This re~ults ln
lo~ses in time and productivity. In addition, the
catalyst must be replaced and the silvet salvaged or,
where pos~ible, regenerated. Even when a cataly3t 1~
! capable of regeneration in situ, generally productlon
must be halted for some perlod of tlme. At be~t,
replacement or regener~tion of cataly~t requires
additional lo~es ln tlme to treat the ~pent cataly~t
and, at worst, requlre~ replacement of the cataly~t
wlth the ~socl~ted costs.
Since even ~mall improvements in actlvity, ef-
ficiency or u~eful life may have slgnificance ln
large ~cale commercial productlon, such lmprovement
have been the ob~ect of a great deal of research ln
the direct epoxidation of alkenes. The focu~ of
attempt~ to improve performance, such 8~ the ~ctlvity
and useful life of the catalyst and the efficiency of
the sy~tem, has lncluded such areas ~ feed~tream
additlve~ or removal of components therefeomt method~
of prep~ration of the cataly~t~ depo~ltlon or impreg-
natlon of ~ partlcul~e type or form of ~llvee~ com-
po~ltlon, formation, phy~ic~l propertles nnd morpho-
logy of the support~ additlves deposited on or lm-
pregn~ted ln the support~ shape of ~upport aggreg~tesused ln the reactor~ and varlous types of re~ctors
and bed designs, ~uch ~ ~tatlonary and fluldlzed
beds.
;8-
~B2~7~
Early work on the ~ilver-catalyzed direct oxlda-
eion of alkene~ to alkene oxldesi ln many ln~tances
resulted in lmprovement~ in activity and particularly
thel~electively of the sy~tem, in many case~ the
efficlency lncrea~ing by ~everal percent. Recent
modiflcation~ in such ~y~tem~ have resulted ln only
small incremental improvements in efficiency; how-
ever, in term-Q of operating costs, even fractions of
a percent improvement in efficlency can translate
into large ~avlngs in production. Accordlngly, cur-
rent reaearch i8 still being directed to improvements
in the activity and u~eul life of the catalyst and
~electlvity of the system.
Although a vast number of elementfi and compounds
are known to have effective catalytic propertles in
variou~ ceaction~, many have at least one shortcom-
ing, such as very high cost and/or llmited avail~bil-
ity, thermal inqtability in the temperature range in
which the reaction is to be conducted, low mechanlcal
strength, small sueface area per unlt of volume,
~usceptibillty to poisoning, short useful lifetime,
etcetera. Suc~ undesirable characterl~tics make ~uch
substances of limited utility as cataly3ts. Some of
these shottcomlngs, however, may be overcome and in
~ome instances the e~eectiveness o~ the c~tnly~t may
Ibe improved by applying the sub~tance to ~ c~rrler or
support.
New support materlals are continuously being
tried. How~ver, many of those which were employed in
i 30 the early development of the ~llver-bearlng cataly~t~
are, with some modifications, still being u~ed.
Material~ which have found mo~t wldespread use are
typlcally inorganic and generally are of a mlneral
nature. Such materials commonly include alumlna,
flre brick, clay, bauxlte, bentonite, kleselguhr,
~32~72
carbon, ~lllcate~, ~ilic~, ~ilicon carbide, zlrconla,
dlatomaceous earth, and pumice.
In addition to the physical strength of the
~upport materlals, other physical properties, ~uch as
S ~urface area, pore volume, pore dlmensions, and cata-
ly~t slze have drawn considerable attentlon. The~e
propertles have been examined with great scrutiny
when evldence indlcated that there was a correlation
between the size of the catalyst and the efficiency
of the ove~all ~ystem or useful life of the cata-
lyst. Some materials are also preferred for their
chemical properties, l.e., their ~inertne~s~ or ~pro-
moting~ properties.
The support serves a number of functions in a
heterogeneous catalytic system. Ease of handllng
facilitated by a support which generally takes the
form o di~crete particles or aggregates of varying
~hape or eize which, depending on usage, have a ma~or
dimen~ion of about 1 millimeter to about 20 mlll~-
meter~. Thus it 18 not necessary for the catalyst toform a permanent or ~emi-permanent part of the reac-
tor.
The support, however, serves pr~marily to in-
crease the surface area of the ~active~ component of
the catalyst, ~llver, which 1~ important in that mo~t
epoxldation occurs at the ~llver eurfnce-fluld lnter-
face. Many of the ~ubstance~ commonly employed a~
catalyst ~upports not only have the u~ual external
sur~ace, whlch provldes a varying surface area, de-
pendlng on the shape of the support bodi~s and thepacklng of the bodles, but are al~o of a porous na-
ture and, therefore, have a large lnternal ~urface
~hich ~ontrlbutes to the overall surface ~rea of the
supported catalyst. Such ~upport materlal6 pro~ide a
greater capacity for sorbing not only the catalyst
--10--
~77%
material during catalyst preparation (when the ~up-
port i8 impregnated with a ~olution containlng the
catalyst component~) in ~oluble form) but al~o a
greater capac~ty for the flow of the flu~d reactants
within the cataly~t during the reactlon or which the
catalyst is intended. The ~upport al~o improve~
performance by lower~ng the pressure drop through the
reactor and by facilitating heat and mass tran~fer.
Among the large variety of ~ub~tances employed
in the past a~ ~upports for catalytic materials,
alumina ha~ exhibited ~uperiority in many respects as
a cataly~t ~upport material. In addition to the low
cost of the materlal, alumina has good ther~al sta-
billty and some forms have a relatively large ~urface
area.
Alumlna, ln lt~ varlous`forms, partlcularly
alpha-alumina, ha~ been preferred as a support mater-
ial for silver-containing cataly~ts in the prepara-
tion of alkene oxides. Numerous varlatlon~ of ~ur-
face area, pore dimen~ions, pore volume and particle
~lze have been sugge~ted a6 providing the ideal
physical propérty or combination of properties for
improving e~iciency, activity or u~eful llfe of ~he
catalyst.
Holler ~U. S~ ~atent 3,908,002) dl~clo~es an Dl-
pha-alumlna, useful as a c~taly~t support for reac-
tlons conducted at temperatures below 800 degrees C,
such as oxidation reactions of hydrocarbon~ to oxyhy-
drocarbons. The support, having a ~urface area re-
ported to be at lea~t about 40 m2/g, 1~ produced by
thermally decompo~ing a porou~ alumlnum ion chain-
bridged, polymeric carboxylate. Indlcatlng that a
lnrge ~urface area ~n a carrier may be detrimental to
its ef~icient operation and catalyst activity, Belon
(U. S. Patent 3,172,866~ describes a method of pro-
1501
~r
~282~
ducing a macroporous catalyst carrler which may be
u6ed ~n the catalytlc production of ethylene oxlde
hav~ng pore diameters of between O.l and 8.0 mlcrons
and a ~pecific surfa~e area between a few equare
meters and one square de~imeter per gram. The eup-
port i~ prepared by heating a mixture of actlve and
calcined aluminum oxide~ and a small amount of boron
oxide at temperature~ of between about l,C00 and
1,800 degree~ C. Waterman (U. S. Patent 2,901,441)
describes a process for preparing highly active and
selective cataly~ts for the oxidatlon of olefins to
olefIn oxldes on a support havlng an average porosity
of at lea~t 35 percent. The method involve~ washing
an alpha-alumina or ~lllcon carbide support havlng an
average poro~ity of between 3~ and 65 percent with an
aqueous ~olution of lactic acid, washlng wlth water
untll neutrbl, and then lmpregnating the ~upport wlth
an aqueou~ solution of silver lactate. The lmpreg-
nated ~upport 1~ thereafter heat-treated to deposlt
elemental silver. A silver-supported catalyst for
the vapor pha~e oxldatlon of ethylene to ethylene
oxide, exhiblting lmproved productlon of ethylene
oxide snd catalyst longevlty, i8 described by Brown
et al ~U. S. !Patent 3,725,307). The catalyst 1~
2~ disclo~ed as being ormed from support partlcles
havlng an average pore diameter of at lea~t lO ml-
cron~ up to, preferably, 70 mlcrQns and a ~urface
area of lefls than about l m2/g. The ~electivltlea
reported do not range ~bove about 73 percent. The
support 1~ preferably compo~ed of slllca-alumlna.
silver-~upported catalyst whlch lncludes a ~upport of
ulpha-alumlna, sillcon carblde, fused aluminum oxlde,
or mixture~ of lumlna and sillca was a~serted by
DeMaio (U. S. Patent 3,664,970) to elimlnate the need
or halogenated lnhibitors in the oxidation o~ ethy-
15017
~ '
~.zaz7~
lene to ethylene oxldeO The ~upport i~ compo~ed ofparticles having a minimum apparent porosity of about
30 percent ~nd whereln at lea~t 90 percent of the
pores have diametee~ in the range o 1 to 30 micron~,
the average of the diameters being ln the range of 4
to 10 mlcron~. Wattimena (U. S. Pa~ent 3,563,914)
dieclo~es sllver cataly~ts using aluminum o~lde BUp-
port~ having pore volumes between 0.1~ and 0.30 cc/g
and BUrface area~ below about 10 m2/g.
Hayden et al (U. K. Patent Application
2,014,133t disclose a sllver catalyct employing a
support having a specific ~urface area in the range
of 0.05 to 10 m2/g, an apparent poro~ity of at least
20 percent, and mean pore diameter~ of 0.1 to 20
mlcron~, the pore size di~tributlon being bimodal, in
which the smaller pore~ preferably account for at
least 70 percent of the total pore volume. Alpha-
alumina supports are described by Rashkin (U. ~.
Patent Application 2,122,913A) having a ~relatlvely
low ~urface area~ of less than 30 m2/g. Mitsuhata et
al ~Japane~e Published Patent Application 56-089~43)
and Mit~uhata et al ~U. S. Patent 4,368,144) de~cribe
supported sllver catalysts ln which the ~upport i8
formed from alpha-alumina having a specific eurface
area of 0.5 to 5 m~/g. Watanabe et ~1 ~Japane~e
Published Patent Appllcatlon 56-105750) employ a
simllar catalyst ~upport havlng a surface area of 1
to 5 m2/g. Hayden et al ~U. S. Patent 4,007,135)
de~crl~e sllver-contalning catalysts ln whlch the
j 30 porous heat-re~isting ~upport ha6 a ~pecific surface
~rea ~n the range o~ 0.04 to 10 m2/g, an nppaeent
poro~ity of at lea~t 20 percent, and a median pore
dlameter of 0.3 to 15 microns. Mit~uha~a et al
(U. S. Patent 4,24a,740) describe the use of hlgh
~lpha-alumlna content ~upport6 havlng a ~peclflc
-13-
surface area of not more than 10 ~2/g, an ~pparent
poro~ity of 40 to 60 percent by volume, and a pore
volume of 0.1 to 0.5 cc/g. Armstrong et al (U. S.
Pa~ent ~,342,667) disclose a supported sllver ~at~-
lyst, useful ln the oxldation o ethylene to ethyleneoxlde, ln which the ~upport has a surf~ce area of
0.02 to 2 m2/g, an aver~ge pore dlameter of 0.5 to 50
microns and an average pore volume of 0.2 to 0.5
cc/g.
There has also been some lnterest in the purity
of supports employed, both as to compositlon and
phase. E~amples o~ hlgh purity alumina include U. S.
Patent 2,901,441 whlch uses alpha-alumlna having a
purity of about 99.5 percent as a support for cat~-
ly~ts used to o~ldlze olefln~ to olefin oxldes. Anethylene oxldatlon catalyst i8 disclosed ~n German
Patent Publlcation DE 2,933,950 which attains a long
catalyst life wlthout a 1088 in actlvlty or sele~-
tlvity by u~ing an alpha-alumina ~upport havlng less
~han 0.001 welght percent of alkall-soluble ~llicon
compound~. The cataly~t iB prepared by boiling com-
mercial quallty alpha-alumina with 1 welght percent
sodium hydroxide solution and washing to a pH v~lue
of B. If desired, the ellicon compound conc~ntration
may be reduced below 1 p~rt p~r milllon ~ppm) by
washing further wlth 1 weight percent ~F. U. ~.
Patent Appllcation 2,122,913A de~cribes eupported
sllver cataly~ts in which the support ls composed of
sllica, ~lumina or mixture~ thereof, one example of
whlch 1B ~n alumlna having a purlty of 99.3 percent
by ~elght. The silver-supported cataly~t de~crlbed
in Japanese Publi~hed Patent ~pplication 56-OB9843
~mploys an alpha-alumina carrler h~ving a ~odlum
content of le~s than 0.07 welght percent. Japanese
Published Patent Applic~tlon 56-105750 dessribes the
~n2 ,
' u~e of an alpha-alumlna ~upport in con~unction wieh a
j ~ilve~ cataly~t or producing ethylene oxide, which
! ~upport hafi a Rodium content le58 than 0.07 welght
¦ percent. A ~ilver cataly~t lncludlng an alpha-
j S alumina carrier having a sodium content of not more
than 0.07 percent 1~ de3cribed by Mitsuhata et al (U.
S. Patent 4,368,144). The ~upport al~o ha~ ~ ~urface
area withln the range of O.S to 5 m2/g, an appDrent
porosity of 25 to 60 percent, a specific pore volume
of 0.2 to 0.5 cc/g, and a partlcle dlameter ~ithin
the range oE 3 to 20 mm. An alpha-alumlna support
havlng a purity of 98~ weight percent, for use wlth
~ilver in the catalytic oxidatlon of ethylene, iB
descrlbed by Warner et al in U. S. Patent
4,455,392. ~he patent additionally disclose~ that
the carrier iB generally a conventlonal microporou~
~upport with surface areas of le~ than 10 m2/g, pore
volume~ ranging from about 0.15 to 0.8 cc/g, and pore
j dlameters of about 0.1 to 100 microns.
In addition to compositional purity, both pha~e
purity Dnd morphology of the support have been areas
in which 1mprovements in efflciency, selectlvlty or
~tabillty of the catalyst have been sought. Example~
lnclude U. S. Patent 2,901,441 ln which alumlnum
oxide ie sub~tantially completely converted to the
alpha form of alumlna by heatlng aluminum oxlde to a
temperature of ~bout 1,~00 to 2,050 degree3 C. WeiB~
(U. S. Patent 2,209,908) and Carter ~V. S. Patent
2,294,3~3) de~crlbe the u~e o~ ~Tabular Corundum~ a5
¦ 30 a cataly3t support for metalllc oxide~, ~uch as those
oxlde~ of metal~ selected from the flfth and sixth
group of the periodic system, for example, vanadlum,
molybdenum, uranlum, etcetera, ln the o%idatlon of
varlous orgAnic materlal~ to maleic acid and maleic
anhydride and silver for the catalytic oxldatlon of
-lS-
ethyle~e to ethylene o~ide, respecelvely. ~el~
indicate~ that Tabular Corundum, ~h$ch i8 almost
entirely aluminum o~ide and ha~ the alpha-corundum
crystalline form of ~luminum oxlde, may be formed by
mlxing aluminum oxlde with one or more of several
compounds, ~uch a8 sodlum oxlde and chromic oxl~e,
and heating the mixture to a temperature in the range
of about ~00 to about 1,800 degrees C. Tabular Co-
rundum i~ further descrlbed a~ havlng lmpurlties
present in only ~mall quantitle~, the material also
includes ~readily bonded surfaces and consi~ting
es~entially cf interlocked corundum crystal~ ln tabu-
lar form, having the contalned lmpurlties dls-
semlnated ln mlnute globules throughout the crystal-
line alumlna~. ~rengle et al ~U. S. Patent2,709,173) also employ Tabular Corundum a~ ~ support
in one of their examples.
U. S. Patent~ 4,039,481 and 4,136,063 to Rimura
et al di~clo~e a catalyst carrler and a ~ethod for
maklng ~ame, the catalyst being the type used ln
catalytic converters ln automoblle exhaust system~.
Specifically,'the catalysts have ~ sur~ace layer
containing alpha-phase alumina and ~n lnner portlon
consl~tlng e~entially of alumlna of a phase other
than that of the alpha pha~e. The por~s in the ~1-
pha-alumina surface layer are larger than tho~e in
the lnner p~rtion of the catalyst body. A method of
preparlng the phase gradient support partlcles is
descrlbed whlch provlde~ for treating the surface of
the alumlna to a depth of about 400 mlcrons ~lth a
tran~ltion element, particularly lron, and thereafter
flring the carrler particles.
Weber et al (U. 5. Patent 4,379,134) descrlbe
high purlty alpha-alumina bodies, at least 85 percent
of the pore volume of ~he hodie~ having pores with a
I -16-
~2
! diameter of from 10,000 to 200,000 Ang~tro~. The
¦ high purity alpha-alumina bodies are prepared by
! peptlzing boehmlte ln an acldic aqueous, fluorlde
~nion-containlng mixture. An extrudable ml~ture 1
formed thereby whlch 1~ extruded and ~haped lnto
formed bodie~ which are thereafter drled at 100 to
3Q0 degrees C, calclned at a temperature of from ~00
to 700 degree~ C to convert the alumlna to the gamma
pha~e, and 3ub~equently calclned further at a temper-
ature of from 1,200 to 1,700 degrees C to convert thegamma pha~e to alpha-alumlna phase.
A method of produclng granulated porous corundum
havlng a homogeneou6 porous structure wlth a total
pore volume of 0.3 to 1.0 cm3/g and ~ predomln~nt
pore slze of 5,000 to 30,000 A 1~ de~crlbed by Bores-
kov et al (U. S. ~atent 3,950,507). The method of
preparlng the alpha-alumlna lnclude~ treating active
alumlna or alumlnum hydroxlde havlng a porous struc-
- ture to a flrst heat treatment in whlch the tempera-
i 20 ture 1~ increased from 20 to 700 degrees C, a ~econd
he~t treatment in the range of from 700 to 1,000
degrees C, ana a thlrd treatment ln the cange of from
1,000 to 1,400 degree~ C. Each of the heat treat-
ments i8 for a period of nt lea~t one-half hour, the
flrst heat treatment belng conducted ln ~n atmo~phere
~ of hydrogen 1uorlde ln whlch the alumlna absorbs the
! hydrogen fluorlde and the second heat treatment de-
sorbs the hydrogen fluorlde. The patent al~o de-
scrlbe~ a slmllar procedure employlng statlonary
i 30 thermal condltions ln whlch the granuleR of alumlna
or alumlnum hydro~lde are lmpregnated wlth other
fluorlne-contalning sub6tances prlor to the flr~t
thermal treatment. The recommended starting mater-
lals u~ed to form alpha-alumlna lnclude granulated
~5 pseudo-boehmlte, boehmlte or bayerite as the granu-
-
-17-
~1;2E~2772
lated aluminum hydroxide and granulated alpha-, ota-,
or theta-alumlna aB the active alu~lna.
Although alpha-alumina ha~ been con~idered by
~o~t to be the preferred alumlna BUppOrt materlal,
Smlth et al (U. S. Patent 2,422,172) have ~ugge~ed
th~t beta-alumlna~ are more de~lrable than the alpha
pha~e as A support material for ~ataly~t~, partlcu-
larly tho~e used ln catalytic converslon proces~es
such as dehydrogenatlon and hydroformlng.
In eeeklng the ldeal support materlal, there has
been 80me departure from the commonly employed sub-
stance3. For example, some u~e has been made of
alkall metal and alkallne earth metal ¢arbonates,
both a~ ~he ~ole ~upport materlal ~nd in comblnatlon
wlth other materiale as the carrler for proce~se~
such as dlrec~ oxidatlon of alkenes to epoxldes.
A number of ~upported sllver-containlng c~ta-
ly~t~ have been employed for epoxldatlon of alkene~
ln which the carrler lnclude~, ~ometl~e~ labelled a~
a promoter, a carbonate of a metal, generally an
alkall metal or alkallne earth metal. Some examples
of the use of;one or more alkall and/or alkallne
earth carbonate~ may be ~ound ln U. S. P~tents
2,424,084, 2,424,086, 2,615,900, 2,713,586,
25 3,121,~99, 3,258,433, 3,~63,913, 3,563,gl4,
3,5B5,217, 4,007,135, 4,033,903, 4,039,561,
4,066,575, ~,094,889, 4,123,385, 4,125,480,
4,168,247, 4,186,106, 4,226,7B2, 4,229,321,
4,324,699, ~uropean Patent Publlcatlons 0,003,642 ~nd
30 0,011,356, Japane~e Patent~ 41-11847 and 57-107242,
U. g. Patents 590,479, 1,571,123 and 2,014,133A, and
Murray, ~A ~tudy Of The Oxldatlon Of ~thylene To
Et~ylene Oxlde On A Silver Cataly~t~, Au~trallan
Journal of æclentlflc Research, Volume 3A, P~ges 433-
35 449 (1950). In addltlon, U. 5. Patent 3,332,~87 to
15017
.
-
~772
Endler employs zlnc and/or cadmlum carbonate~, Gelb-
~teln, (DS 2,352,608) di3clo~e~ the use of th~ latter
carbonate and European Patent Publicatlon 0,003,64~
~entions the use of ~olybdenum carbonate. ~oreskov
et al (U. S. Patent 4,130,570) describe a method of
produclng ethylene oxide u~lng a catalyst whlch ln-
clude~ sllver, cadmium carbonate and/or cad~ium oxlde
and fu~ed alumlna. Oprescu et al (French Publlshed
Patent Applicatlon 2,005,9781 descrlbe a 011ver-based
catalyst for u~e in the preparation of ethylene oxlde
whlch i8 a coprec~pltate of sllver and other carbon-
ates.
SeverAl patents have descrlbed the use of fluo-
rlne-contalnlng ~ubstances to treat support mater-
lal~, ln some cases to provide a composltlonally pure~upport, and in other ca~e~ as a fluxing agent to
improve the pha~e purity of the support. Thus, U. ~.
- Publlshed Patent Speciflcatlon 590,479 and U. S.
Patent 2,424,086 lndicate that a more actlve catalyst
1~ formed lf the support materlal has undergone a
prellminary treatment wlth a dilute ~olution o hy-
drofluorlc acld prlor to lmpregnatlon wlth sllver.
V. S~ Patent 4,379,134 teaches the preparatlon o~
hlgh purlty alpha-alumina bodle~ by peptlzing boah-
mlte alumlna ln an aqueous acldlc mlxture containlngfluorlde anlon~ and water. German Patent 2,933,950
teaches the reductlon of ~lllcon content by treatment
wlth ~F. U. S. Patent 3,950,507 teache~ the prepara-
tlon of granulated porous corundum by n multlple step
heat treatment ln which initlal steps may be carrled
out ln an atmosphere of hydrogen fluorlde. ~osoda et
al (U. S. Patent 3,144,4161 sugge~t tbat ~ small
amount of a halogen compound, sulfur co~pound, nltro-
gen compound, or phosphorous compound may be ~dded
elther to the reaction ga~ or the catalyst to lmprove
--19--
32772
the selectlvity of the catalyst.
The n~tute of the ~ilver ltself h~s al80 been
examlned and msdified ln attempts to lmprove the
efficlency and stabillty of the catalyst. Cavltt
tU. S. Patent 4,229,321) teaches that a supporeed
silver catalyst of lmproved aelectlvlty and nctlvlty
~ay be psepared by mechanlcally removlng t~e outer
~urface or skin of the cataly~t ~fter the impresnated
catalyst has been heated to evaporate volatlle mater-
~al and reductlon of the sllver salt to ~llver metal,thereby actlvating the cataly~t.
Since the early work on the dlrect catalytlc
oxldatlon o ethylene to ethylene oxide, workers ln
~he fleld have ~uggested that the addltion of certain
compound~ to the gaseou~ feed~tream or dlrect lncor-
poratlon of metals or compounds in the cataly~t could
enhance or promote the production of ethylene ox-
ide. Such metal~ or compounds have been known vari-
ou~ly a~ ~anti-cataly~ts~, ~promoters~ and ~lnhl-
bitor~. These substances, which are not themselve~consldered catalysts, have been proposed by prior
workers to contrlbute to the efficiency of the pro-
ces~ by lnhibiting the form~tlon of carbon dloxlde or
promotlng the productlon of othylene oxlde. The
sclentlfic llterature 1~ rcplete ~lth e%ample~ of the
use of alkall metals ~nd alkallne earth metal~ and
thelr catlon~ to promote the efflclency of sllver
cataly~ts u~ed in epoxldatlon reactlons. For ~%a~-
ple, eodlum, potasslum and calclum ~ere ~lsclosed ae
belng sultable promoters ln ~. S. P~tent 2,177,361.
Numerou3 examples may be found ln llterature of pref-
erence for one or ~everal metal~ or cations and e~-
clu~ion of one or more metal~ or catlons a~ pro~oter~
in silver catalysts.
-20-
.~ .
Among those anlon~ 2s~0ciated ~ith the catlon
promoter~ used ln preparlng sllv~r-contalnlng c~ta-
ly5t~ employed ln direct epoxldatlon reactlon~ that
ha~e been suggested as belng ~ultable include cAr-
~ 5 boxylates, for example, formate, acetate, malonate,
I oxalate, l~ctate, tartrate, nnd/or cltrate, and ~nor-
ganic salt~, ~uch as carbonates, bicarbonates, phos-
phate~, nltrate~, and/or nltrltes, chlorides, lo-
dides, bromate~, and 13Opropoxldes. ~owever, al-
though many examples may be found ln the literature
lndlcatlng that such compound~ are sultable, numerous
patent~, such a~ U. S. Patents 3,962,136~ 4,012,425S
4,066,5~5~ 4,207,210; nnd 4,4~1,0~1, suggest that no
unu~ual effectlvenes~, partlcularly wlth regard to
catalytic actlvlty, 18 observed wlth any partlcular
anlon of an alkall metal promotec. U. S. Patent~
4,007,135; 4,094,889; 4,125,480; 4,226,782~
4,235,757; 4,324,699; 4,342,667; 4,356,312;
j 4,36B,144; and ~,455,392 dlsclose that potas~lum
1 20 nltrate may be added to the catalyst as a su~table
promoting materlal. Pota~lum nltrate may al~o be
formed in sltu when a carr$er materlal 1~ tre~ted
wlth certaln amlnes ln the pce~ence o~ potn~lum lon~
a8, for lnetance, when 011ver i~ lntroduced to a
carrler materlal ~n a ~llver-impregnatlng ~olutlon
contalnlng an amlne and pota~sium ion~, followed by
roa~tlng.
A number of compound~ have been proposed in the
llterature as nddltlves to the feedstream or re-
1 30 actants to l~prove the efflciency of the dlrect,
~llver-catalyzed oxldation of alkenes to ~lkene ox-
Ides. For example, Law and Chltwood (U. S. Patent
2,194,602) dlsclose the use of a ~repre~sAnt~, l.e.,
antl-cataly~t, such a~ ethylene dlchlorlde, chlorlne,
sulfur chlorlde, sulur trloxlde, nltrogen dloxlde,
-21-
~28~72
or other halogen contalnlng or acld-formlng ~ter
. Numerous additional anti-catalyst6 are pre-
~ented by the same paten~ee~ ln U. 8. ~at~nt
2,279,469. The antl-catalysts, broadly ll~te~ ln
S categorle~ euch aB halogen~ and compounds contalnlng
halogen, hydrocarbons, compounds cont~lnlng c~rbon,
hydrogen and oxygen, compounds contalnlng sulfur, an~
compound~ contalnlng nltrogen are repre~ented ~nd, ln
addltlon to those compound3 already mentloned ~bove,
adaitlonal representat~ve compounds ~nclude, as nl-
trogen-contalning compounds, nitrlc oxlde, ~m~onla,
amlnes such aB ethylenedlamlne, diphenyla~lne ~nd
analine, nitro compound~ such as o-nltroanisole and
o-nltrotoluene as organic oxygen-cont~lnlng organlc
compounds, alcohols ~uch as methyl, ethyl ~nd l~o-
propyl alcohols, ether~ ~uch a~ l~opropyl and dibutyl
ethers~ ~8 well a~ glycol ethers, ketone~ ~uch BB
methyl ethyl ketone and acetone, a~ hydrocarbon~ ~uch
a~ benzene, ~nd N-he~anes sulfur compounde ~uch as
sulfur dloxlde, hydrogen ~ulfide and dlethyl~ulflde~
chlorine-cont~lnlng compounds ~uch as carbon tetr~-
chlorlde, chlorobenzene and dlchlor~ethyl et~r.
~erl (U. S. Patent 2,270,780) ll~t~ a number of com-
pounds a8 antl-detonatlng or ~ntl-knock m~terlal~ to
control the o%ldatlon o~ ethyl~ne an~ propylene to
their o~lde~. nlsclo~ure~ of other feedstream addl-
tlves u~ed :In the productlon of alkene o%ldes, partl-
cularly halogen compound~, may be found ln U. ~.
Patent~ 2,279,470l 2,799,687~ 3,144,416s ~,007,135
4,206,12~ and 4,368,144. In addltlon, EPO Patent
0,003,642 and U. ~. Patent Appllcatlon 2,014,133A
dlsclo~e processe~ for the productlon o ol~fln o~-
ldes employlng ~lver-contalnlng cataly~t~ ln ~hlch a
chlorine-contalnlng reactlon modlfler and ~ nltrlte
or nltrlte-formlng substance are de~crlbed. Rumanl~n
15017
1`
-22-
~.28Z77~
Patent 530l2, publiRhed Dece~ber 2, 1971, ~isclo~es
dlrect, ~llver-caealyzed direct epoxldatlon procedure
~hlch employs oxldes of nltrogen ln the Eeed~t~eam.
U. ~. Patent 524,007 lnclude~ ethylene dlchlorlde or
nitrogen dlo~lde in the feedstream of a sll~er-caea-
lyzed epoxlaation procedure.
Although much of the art dl~cu~ed above h~
resulted ln lmprovements ln the efflclency, activity
or ~tabllity of the catalytic ~yatem, many of the
lmprovements have indlvidually been rather ~llght.
In some of the catalytlc system~, gain~ in one of
these performance parameter~ have been frequently
ofset by 106~es ln anotherS th~t i8, enhancement of
one lndex of performance has been accompanled by a
deleterlous effect on another of the lndlces. For
example, lf a reaction ~y~tem 18 de~igned whlch has a
very short useful llfe, the system may be commer-
cially impractical even though the efflclency and
initlal actlvlty of the catalyst are out~tanding.
Accordingly, a ey~tem that provlde~ ~n lncrease ln
the efficlency of the overall catalytlc reactlon
~y~tem, whlle only mlnlmally decreaslng the actlviey
and u~eful Llfe of the cataly3t, would be partlcular-
ly beneflclal aq would a sy~tem ln whlch the u~eful
llfe ls lmproved at llttle expen~e to th~ e~flclency
or actlvlty.
Di~closure Of The Inventlon:
The pre~ent inventlon 1~ dlrected ~o catalytlc
processe~ for the epoxldation o~ alkone ln the pre~-
ence of an oxygen-cont~lnlng gas and to the catnlyst
u~ed therefor. The process compri~e~ contactlng an
~lkene wlth an oxygen-contalnlng ga~ under epoxida-
tlon condltlon~ ln ~he pre6ence of at least one 9~-
15017
,
-23-
eou~ efficlency-enhanclng member of a redox-half
reactlon palr and a ~olid catalyst. The catalyst
comprlse~ a catalyeically effectlve amount of ~llver
on a solld porous ~upport and an efflciency-enhanclng
S amount of at lea~t one eficlency-enhanclng salt of a
member of a redox-half reactlon palr. The support
employed for the catalyst compri~e~ at least one
carbonate salt of barium, ~trontium, calclum, mag-
ne~lum, or mixture~ theceof. The porous ~upport may
be either one whlch consi~ts essentially of a carbon-
ate ~alt or one in which the carbonate ~lt 1~ as-
~ociated wlth an inert sub~tructure, ~uch a5 alumlna.
The pre~ent invention i~ al50 directed to a
cataly~t for u~e in epoxidatlon of alkene wlth an
lS oxygen-contalning ga~ wh~ch comprise~ a catalytlcally
effectlve amount of silver on a solld ~upport and at
least one efficlency-enhancing ~alt of a member of a
redox-half re~ction palr. The comblnatlon of B por-
ou~ ~upport comprising a carbonate salt and the pees-
ence of a ~alt of a member of a redox-half reaction
pair produce~ a cataly~t of enhanced performance
which 18 both highly actlve and capable of ~alntaln-
ing ~uch activlty for extended perlod~ of tlme. In
additlon to these lndlce~ of performance, a catalytic
~ygtem employing such a catalyst, partlculnrly when
used ln the pre~ence of a ga~eou~ member of a redo~-
half reactlon pair, also re~ults ln enhancement of
efficlency. Thus, efflclencles on the order of about
~4 percent for the epoxldatlon of ethylene ~re the
norm under Standard Test Condlt~on~ and of about 88-
92 percent or greater are not uncommon. In a~dltlon,
the catalyst~ of the present lnventlon are c-pable of
maintalnlng hlgh actlvlty well as long term ~ta-
bility.
-24-
Detailed ~escription Of The Inventlon-
The pre~ent lnventlon ~s dlrected to a proce~s
for the vapor pha~e oxidation of alkenes to alkene
oxldes, l.e., an epox~datlon proces~, in the presence
of an oxygen-contalnlng ga~ and to ehe ~llver cata-
lyQt~ employed therein.
The proce~s and catalyst o~ the pre~ent lnven-
tlon are useful ln the epoxldatlon of the alkene~
ethylene and propylene, the epoxide~ of whlch are ln
great demand for uBe a8 intermedlates ln produclng
such materials as polymer~, surfactants, ~ynthetlc
flbers and antlfreeze. However, the present lnven-
tlon 1B not llmlted to the~e compounds but may be
used to o~ldlze cycllc and acycllc alkenes whlch are
~n the gaseous state or have ~lgnlflcant vapor pres-
sures under epoxidatlon conditions. Typically these
compound~ are characterlzed as having on the order of
12 carbon atoms or le~ whlch are gaseou~ under epox-
ldation condltlons. In addltlon to ethylene andpropylene, e~amples of other alkenes whlch may be
used ln the present lnventlon lnclude such compound~
a~ butene, dodecene, cyclohexene, 4-vlnylcyclohexene,
Gtyrene and norbornene.
~E~
The aupport materlal used ln the present lnven-
tlon ~ay be ~elected from one of several carbonate-
contalnlng carrler materlals. In each embo~lment ofcarrler, thc carbonate employed le an ~norganlc car-
bonate, preferably havlng a cation whlch ls an alka-
llne earth metal lon, partlcularly calclum, stron-
tlu~, magnesium or barium wlth calcium belng mo~t
preferred. The carrlers of the pre~ent lnvention may
-25-
~28;~772.
e%ist ln varlou~ forms~ In one e~bodi~ent, the car
rier 1~ one ln which the curbonate 1B the predo~lnant
or, preferably, ~ubstantially ~he exclusive co~ponent
of the ~upport. In other embodl~ents of the lnven-
tlon, the lnorganic support materlal 1~ used ln con-
~unction with a ~olid substrate, l.e., a ~ub~uppcrt
or ~ub~tructure composed of a more conventlonal ~up-
port materlal, such as alumina and preerably alpha-
~lumina. Thl~ latter type of ~upport may employ the
carbonate materlal coated on lndlvidual, relatlvely
small partlcle~ of substructure or subsupport or on 2
larger unlt such a~ a three-dlmen~lonal framework
havlng a honeycomb-type of 6tructure.
When used wlth a subsupport, the percentage of
cnrbonate materlal present in the ~upport materlal
1~, by welght, frequently about 0.5 to about 15,
ba~ed on the weight of the total support. Most often
the carbonate 13 present ln an amount of about 2 to
about ll percent, by welght.
A granular or cry~talline form of the carbonate
~upport materlal i~ preferred ln the pre~ent lnven-
tlon, partlcularly when used a~ the excluslve or
predomlnant component of the eupport~ Commerclally
avallable c~lrbonate materlal~ suitable for use ln the
pre~ent lnventlon may be obtalned ~B powders ~hlch
can be convl~rted to the preCerred granulJr ~orm by
formlng a paste and ~preadlng lt thlnly on a flat
~urf~ce, ~u~h as a large tray. After ~preadlng the
materl~l on the surEace to a ~ultable depth, uaually
appro%lmately one-quarter lnch, the carbonate ~ater-
lal ~ay be dried and calclned at a tempera~ure of
from about 2~ to about 75 degree~ C below th~ ~eltlng
or ~ecomposltlon temperature of the ~aterlal. In one
embodl~ent t~e pa~te of the carbonate ml~ture IB
drled and calclned by placlng lt lnto a ~urnace at
-26-
~2
about 120 degree~ C and heatlng to about 500 degree~
C over a flfteen m~nute perlod and holdlng ~t at th~t
~emperature for an additlonal flfteen minutes. The
caacined carbonate 18 then broken into ~maller pleces
~nd 4creened to partlcles of the appropriate ~lze, on
the order of one-eighth to three-elghths Inch, pref-
erably ~bout one-quarter lnch in dlameter. As de-
scclbed ln greater detall below, the carbonate BUp-
port may then be lmpregnated, or coated, wlth a ~olu-
tlon containlng a ~ilver compound and thereafterreduced to elemental silver.
Alternatlvely, as descrlbed below, the powdered
carbonate materlal may be comblned wlth ~n approprl-
ate sllver-contalnlng solution, ~uch ~8 that u~ed
conventlonally to lmpregnate solld ~upportq to form a
slurry or pa~te. Thl~ materlal may then be spre~d on
a su~table surface and drled and roasted at ~n appro-
prlate temperature, such as ~bout 500 degree~ C, on
belt roaster. Thls result~ ln a carbonate support
wlth ~llver belng supported thereon ln lts elemental
state~ The cataly~t may then be lmpregnated ~ith
~olutlon of a salt of a member oE a redox-h~lf
reactlon palr and thereafter drled. As an alterna-
tlve, the 8alt of a member o~ a redox-hal reactlon
palr m~y be ~alssolved ln the ~ame ~llver-cont~inlng
impregnatlon ~olution used to form the aoating paste
or ~lurry with the carbonate materlal.
The partlculate carbonate partlcles, ~hether or
not prepared from a sllver-contalnlng pa~te, oan be
30 formed lnto shaped composite~ suItable for u~e ln
alkylene oxlde manuf~cture. The composltes may be
for~ed by any sultable technlque. For ln~tance, lt
1~ po3sIble to form the composltes by compre~slng the
partlcle3 lnto a mold havlng a de~lred conf lgurn-
tlon. Sul~able pre~ures may be at le~st 1,000 pslg,
-27-
~7Z ,
say ~bout 3,000 to ~bout 20,0Q0 p~lg. The ~l~e of
the partlcle~ may be ~elected to be ~pproprlate or
the formatlon of the compo~lte and are often In the
ra~ge of about 0.301 to about 5 milllmeter~ ln ~a~or
dlmenslon.
When coated cataly~t~, l.e., tho~e catalysts ln
which the carbonate materlal iB coated on a ~ub~truc-
ture, are employed, a ~lurry of the carbonate ~ater-
lal, ln either powder or granular form, 1B mlxed wlth
the partlcle~ of support ma~erlal or the honeycomb
structure and thereafter drled in nn oven. A~ wlth
the predomlnant or exclu~lve carbonate ~upport mater-
lalA de~crlbed above, the coated cataly~t~ may also
be prepared by u~lng n ~olutlon of ~ ~llver compound
or the silver compound and a ~alt of a member of a
redox-half reactlon palr to form the ~lurry, followed
by suitable drying and roa~tlng.
The surface areas of the carbonate ~upport ma-
terials generally r~nge from about 0.6 to about 14
m2/g, preferably from about 1.5 to about 10 m2/g.
The ~urface area is measured by the conventlonal B.
E. T. method u~lng nltrogen or krypton descrlbed by
Brunauer, Emmet and Teller in J. Am. Chem. Soc. 60,
309-16 ~1938).
The carrler matetlals of the pre~ent lnventlon
may generally be deecrlbed ~ porous or microporous.
As lndlcated above, when the carbonate ~upport
materlals are used ln con~unctlon wlth a con~entlonal
carrler a~ a substructure, the preferred support
materlal 1~ alpha-alumlna. It 1B ~1BO preferr~d that
the alpha-alumina be of high purlty, partlcularly
oontalnlng a low sodlum content, and ~lffo be formed
from ~afer or platelet-type partlcles, at lea~t 80~e
of which form an ~nterpenetratlng crystalllne ~atrl%,
as de~cribed ln commonly ~ssigned, copendlng appllca-
-28-
tions to Notermann et al, entitled "Improved
Catalytic System For Epoxidation Of Aklenes Employing
Low Sodium Catalyst Support", having Canadian
Application No. 515,864, filed August 13, 1986 and to
Naumann et al, entitled "Improved Catalytic System
For Epoxidation of Alkenes", having Canadian
Application No. 515,816, filed August 13, 1986.
The carbonate supported particles of the
present invention are generally used as individual
particles of irregular shape and size. This is true
both for the predominant or exclusive carbonate
supports as well as the carbonate-coated supports.
However, in some instances the supports, particularly
the carbonate-coated supports, may have a particular
shape and size and this is especially true of the
subsupports used with the carbonates. Typically the
subsupports are formed into aggregates or "pills" of
a size and configuration to be usable in co~nercially
operated ethylene oxide tubular reactors. These
pills may be formed by conventional extrusion and
firing techniques, l~he pills generally range in size
from about 2 mm to about 15 mm, preferably about 3 mm
to about 12 mm. The size is chosen to be consistent
with the type of reactor employed. In general, in
fixed bed reactor appllications, sizes rangin~ from
about 3 mm to about 10 mm have been found to be most
suitable in the typical tubular reactors used in
commerce, The shapes of the carrier aggregates
useful for purposes of the present invention can vary
widely. Common shapes include spheres and cylinders,
especially hollow cylinders. Other shapes include
amphora (such as defined in U.S. Patents 3,848,033,
3,966,639 and 4,170,569), amorphous, Raschig rings,
saddles, cross-partitioned hollow cylinders (e.g.,
having at least
,,,l,../ji,
. ,
-29-
~282~72
one partitlon extending between walls), cyllnder~
having ga~ ~hannels from ~lde wall to ~1ae wall,
cylinders hsvlng two or more gas channel~, an~ rlbbed
or flnned ~tructure~. ~hlle the cyllnder~ are often
clrcul~r, other cro~-sec~lon3, such a~ oval, hexa-
qonal, quadrllateral, trilateral, etcetera, may be
usef ul .
Catalvst3:
A~ lndlc~ted above, the catalyst~ of the present
inventlon may lnclude, a~ a ~upport material, ~t
lea~t one carbonate o~ or an alkallne earth metal
catlon, preEerably Mg, Ca, ~ or Sr, mo~t pre~erably
5 C6. The support may be pre~ent clther ~8 pre-
dominantly or exclu~lvely the carbonate, de~lgnated
hereln as ~carbonate-~upport~. The corre~pondlng
cataly~t which lncludes ~uch ~upport 1B de~ignated
~carbonate-~upported catalyst~. When the carbonate
1~ coated on or ln the pre~ence of a ~ub~trate or
sub~upport, the support 1~ de~ignated ~carbonate-
coated support~ and when the 3upport 18 u~ed ln a
complete catalyst, the de~lgnatlon for the c~taly~t
i8 a ~carbonate-coated cataly~t~. A~ u~ed hereln,
2S the term ~coated~ 1~ not intended to lmply that one
~ubstance neces~arlly form~ a layer on or en~elop~ a
~econd substance but merely refers to the procedure
lnvolved in the preparatlon of such materlal.
The carbonate- and carbonate-coated 6upport~ may
be prepared as lndicated above or, when a carbonate
~upport 1~ u~ed, obtained commerclally. The carbon-
ate-supported cataly~t of the present lnvent~on may
be prepared by any known method of lntrodu~lng ~ilver
- and/or a salt, such as a sale of a redo~-half
reactlon palr, ln solu~le form, to a ~upport. A
I -30-
1~2~72
preferred method of introduclng sllver to the carbon-
ate ~upport 1~ by an lmpregnatlon proce~s ln whlch a
solu~ion of a soluble 3alt or complex of ~llver ln an
amount suficlent to depo~lt the de~ired welght of
,! 5 ~llver upon the carrier 1~ dlssolved ln ~ sultable
solvent or ~complexing/solubllizlng~ ~gent. The
solutlon may be used to impregnate the support or
carrler by immer~ing the carrier ln the ~llver-
, contaln~ng lmpregnatlng ~olutlon and formlng ~ pa~ty
3 10 mlxture or slurry. The slurry 1~ then ~pread on
flat lnert surface, fiuch aB h tr~y, to a sultable
depth of about one-slxteenth to about one-quarter
lnch, preferably a thickness of about one-elghth
inch. Th~ carbonate/~llver compound mixture 1~ then
15 dried and roa~ted by placlng the mi~ture ln a furnace
nt about 100 to ~bout 120 degree~ C ~nd heatlng the
mixture to about 400 to about 600 degrees C over ~
I flfteen minute period, thereafter holdlng the ml~ture
¦ at a temperature wlthin thi~ range for an ~dditlonal
¦ 20 fifteen mlnute~ and removlng the calclned materlal
from the fucnace. Thi~ procedure accomplishes drying
of the carbonate/sll~er m~xture, remove~ volatile
components ~nd reduce~ the silver present to lt~
element~l form.
The ~alt Oe a redox-hal~ re~ctlon palr may be
¦ lntroduced to the cataly~t D~ ~n lmpregnbtion ~olu-
I tlon ln A separate impregnatlon step. Ag~ln, thl~
may be done by any known m~nner of lmpregnatlng Q
porous materlal. Convenlently, thls may be carrled
¦ 30 out by placlng the cataly~t materlal ln a contalner,
I evacuatlng the contalner and thereafter lntroduclng
I the solutlon of a salt of a member of a redo~-half
eeaction p~lr. Alternativ01y, the support may be
~prayed or ~prlnkled wl~h the lmpregnatlng ~olu-
35 tlon. The exces~ ~olutlon may then be allowed to
-31-
~2~ .
drain off or the ~olvent may be removed by ~vapor~-
tion under reduced pres~ure at a sul~able te~pera-
ture. The catalyst may then be drled at 120 degrees
C ln an oven for two hours. Such a procedure 1~
known a8 a a~equentlal~ or ~con~ecutlve~ method of
preparatlon. The carbonate-supported catalyst may
~180 be prepared by a ~slmultaneous~ or ~colnclden-
tal~ ~ethod of preparatlon. Wlth thls method, the
salt of a member of a redox-half reactlon palr 18
lncluded ln the sllver compound-containlng solution
used to lmpregnate the carbonate ~upport.
The carbonate-coated catalysts are prepared by
coatlng a sultable sub~tructure or 6ubsupport mater-
lal, preferably alumlna, ~nd most preferably alpha-
alumlna~ wlth a carbonate-containlng slu~ry, Thls
may contaln only the carbonate, ln ~hlch case the
carbonate-coated support i8 further treated as indl-
cated above to produce a sllver or a sllver/salt of
redox-half reactlon pair carbonate-coated catalyst.
Alternatlvely, a carbonate/sllver compound slurry or
a carbonate/sllver compound/salt of a member of a
redox-half reactlon palr slurry ln a sequentl~l or
colncldental procedure. Thu~, ln a 8equentlal pro-
cedure, partlcles or pills of a ~ultable aubsupport
materlal, ~uch a~ ~lph~-~lumlna, are coated with a
61urry of ~ carbonate m~terlal and a ~oluble ~alt or
complex of allver di~solved ~n a comple~lng/solu-
billzing agent. The partlcles or plll8 are there-
after dralned and calclned ln an oven at a tempera-
ture of about 250 to about 600 degrees C for aboutthree mlnutes to ~bout four hours, the ~uratlon o~
heatlng belng lnversely proportlonal to the tempera-
ture employed. The catalyst i~ then lmpregnated ln
the manner descrlbed ~bove wl~h a solutlon of ~t
least one salt of a member of a redox-half reactlon
-32~
~2~Zm
pair and then drl~a. The carbonate-coated supports
may al~o be formed by a colncldental procedure ln
whlch a carbonate/~ilver compound/~alt of a ~ember of
redox-half react~on pair ~lurry 1~ u~ed to coat
S partlcle~ or pills of a sultable ~ub~upport. After
drainlng, the cataly~t l~ dried at a temperature and
for a durat~on indicated above for those carbonate-
j coated cataly~ts prepared by the sequentlal proce
I dure. The partlcular silver salt or compound used to
form the ~llver-containlng impregnatlng ~olutlon ln a
solvent or a complexing/solublllzing agent l~ not
particularly critical and any ~ilver salt or compound
generally known to the art which iB both soluble ln
and does not react wlth the solvent or comple~lng/-
solubillzlng agent to form an unwanted product m~y beemployed. Thus, the ~llver may be introduced to the
solvent or complexing/solubilizing agent a~ an oxlde
or a salt, such as nitrate or carboxylate, for exam-
ple, ~n ~cetate, propionate, butyrate, oxalate,
~ malonate, malate, maleate, lactate, cltrate, phth~-
late, generally the sllver salt~ of hlgher fatty
acids, and the like.
The chemical practitioner may choo~e frcm a
large number of ~ultable eolvents or complexlng/~olu-
billzing agents to form the ~llver-cont~inlng lmpreg-
n~ting solutlon. Be~ide~ adequ~tely dis~olving the
silver or converting lt to a solubl¢ form, a sultable
solvent or comple%ing/solubllizing agent ~hould be
capable of being readlly removed in sub~equent steps,
elther by ~ washlng, volatilizing or oxl~atlon proce-
dure, or the llke. The complexlng/solublllz1ng
agent, preferably, should also permit solutlon to
psovide sllver ln the finlshed catalyst to the extent
of about 2 to about 60 percent silver or hlgher,
based on the total weight of the cataly~t. It 18
-33-
9:;282~7;~
al~o generally preferred that the solvent~ or co~-
plexlngJ~olublllzing agen~ be readlly ~l~clble wlth
water ~lnce aqueou~ ~olutions may be ~onvenlently em-
ployed~ Among the materiale found ~ultable a~ ~ol-
vent~ or comple~lng/~olubllizing agents for the pre-
paratlon the ellver-contAinlng ~olution~ are alco-
hols, lncluding glycol~, such a~ ethylene glycol
tV. S. Patent~ 2,B2S,701 to Endler et al and
3,~63,914 to Wattlmena), ammonla (U. S. Patent
2,463,228 to We~t et al), amines and aqueous ml~ture~
of a~lne~ (V. S. Patents 2,459,896 to Schwartz,
3,563,914 to Wattimena, 3,702,25g to Nlel~en, and
4,097,414 to Cavltt, and carboxyllc ac~d~, such a~
lactlc acid (U. S. Patents 2,4~7,435 to Arles ~nd
3,501,417 to DeMalo)~
Typlcally, a silver-containlng ~olutlon 18 pre-
pared by dlssolvlng ~llver ln a ~ultable ~olvent or
comple~lng/solublllzlng agent as, for e~ample, a
mlxture of ~ater, ethylenedlamlne, oxallc acld, ~
ver o~lde, and monoethanolamlne. ~he solutlon 18
then mlxed wlth support partlcle~ and dralnea.
Thereafter the particles are sultably drled.
As lndicated above, after impregnatlon, the
silver-lmpregnated carr~er partlcles are treated to
convert the ~ er salt or complex to ~llv~r metal
and thereby effect depo~ition o~ sllver on the sur-
fnce of the support. A~ used hereln, the term ~sur-
face~, as applled to the support, lncludes not only
the externnl ~urface~ of the carrler but al~o the
lnternal ~urfaces, that 1~, the surface~ deflnlng the
pore~ or lnternal portlon of the ~upport partlcle~.
Thl~ may be done by trea~lng the lmpregnated partl-
cles wlth a reduclng agent, ~uch aQ oxallc acld or
alkanolamine and/or by roastlng, at an elevated tem-
3~ perature to decompose the sllver compound and reduce
-34-
the sll~er to lt~ free metalllc state.
The concentratlon of sllver ln the flnlshed
cataly~t ~ay vaey from about 2 percent to 60 percen~,
by weight, based on the total welght of ~he catalyst,
S more preferably the sllver concenttation ranges from
about 8 percent to about 50 percent, by weight. When
a ~hlgh ~ilver~ content cataly~t i8 preferred, the
sll~er range~ from about 30 ~o about 60 percent, by
welght~ The preferred concentratlon for ~l~w ~llver~
content catalyst range~ from about 2 to about 20
welght percent. Lower ~llver concentratlons sre
preferred from a capltal expen~e standpolnt. ~ow-
ever, the optlmum sllver concentratlon for a partlcu-
lar cAtalyst should al90 take lnto conslderatlon
increased productlvlty resultlng from performance
chal~Cter 18tlc~, such a~ ~atalyst actlvlty, 5y8tem
efficiency and the rate of cat~lyst aging. In many
lnstances higher concentratlons of sllver are prefer-
red slnce t~ey demonstrate levels of enhanced per-
formance, partlcularly catalyst stability, whlchcompen~ate~ ~or the greater capltal expendlture.
EfficlencY-Enhanclnq Compound:
A preferred aspect of the present inventlon
lncludes an efflciency-enhancing amount of at least
one efficlency-enhancing salt of a member o a redo~-
half reactlon palr. The term ~redox-half rea~tlon~
18 deflned hereln to mean half-reactlons llke those
found ln equatlon~ pre3ented ln table~ of etandard
reauctlon or o~ldatlon potentlals, aleo known AB
~tandard or eingle electrode potentlals, of t~e type
found in, for lnstance, ~Nandboo~ of Che~l~try~
A. L~nge, ~dltor, McGr~lw-Hlll Book Comp~ny, Inc.,
pages 1213-1218 (1961) or ~CRC Nandbook of Chemlstry
-35-
~2~!32772
~nd Physlc~, 65th 2dltlon, CRC Pre~, Inc~, Boc~
~aton, Florlda, page~ D15S-162 (198~). The te~m
~redox-half reaction pair~ refer~ to the palrs of
atoms, ~olecule~ or lons or mixtures thereof wh~ah
are depicted a~ undergoing oxldatlon or reductlon ln
such half-reactlon equa~lons. A member of a redox-
half re~ction palr 18, therefore, one of the atoms,
moleculeq or ions that appears ln a partlcular redox-
half reactlon equatlon. Such term~ a~ redox-balf
reactlon pairs or like terms ~re used hereln to ln-
clude tho~e member6 of the clas~ of ~ub~tance whlch
provlde the deslred performance enhancement, rather
than a mechanl~m of the chemlstry occurrlng. Prefer-
ably, such compounds, uhen as~oclatea ~lth the cata-
lyst ~8 salts of members of a half-reactlon pnlr, are
salts ln which the anions are oxyanions, preferably
an oxyanion of a polyvalent atoms that 18, the ~tom
of the anlon to whlch oxygen ~8 bonded i~ capable of
existing, when bonded to a dl~lmllar ato~, in dlf-
ferent v~lence states. Pota~slum 18 the preferredcatlon and the preferred anlons are nltrate, nltrlte
and other anlons capable of undergolng dlsplacement
or other che~lcal reactlon and forming nltrate Anlon~
under epoxldatlon or catalyst prepar~tlon condl-
tlon~. Preferrod salt~ lnclude ~NO3 nnd ~NO2, ~lth~NO3 belng mo~t preferred.
Introduction Of Efficlency-
~nhanclng Salt To The Carrler:
3~
The ef~lclency-enhanclng salt of a member of a
redox-half reactlon p~ir may be lntroduced to the
cataly~t ln any known manner. Thus, lmpregnat~on ~nd
~eposltion of sllver and an efficlency-enhanclng ~alt
oP a member of a redox-half reactlon palr ~ay be
15017
X
-36-
effected coincldentally or sequentlally, a~ descrlbed
above under the heading ~Catalyst~ hen more than
one 8alt of a member of a redox-half re~ction pair 18
I employed, ~hey may be depo~ited together or sequentl-
~lly. It is preferred, however, to introduce the
~alt~ to the support in a ~ingle solutlon, rather
than use ~equential treatment~ u~ing more th~n one
~olution and a drylng step between impregnation
steps, since the latter technigue may result in
le~chlng o~ the fir3t introduced salt by the ~olution
contalning the secona salt. Typical, and in m~ny
ca~es preferred, of such method~ include concurrent,
or coincidentnl, impregnation in whlch the solution
which 18 used to impregnate the support wlth ~ilver
also ~ontains at least one dl~olved efflclency-
¦ enhancing Ralt member of a redox-half reaction
¦ pair. This procedure permits introductlon of both
the ~ilver compound and the efflciency-enhancing ~alt
~imultaneou~ly to the support in a eingle ~tep and
~olutlon.
The otheF commonly employed method i8 the se-
quential impregnation of the ~upport in wh~ch initlal
introdu~tlon of the silver-contalning solution or
ef1clency-enhancing ~alt ~olution ~d~pendlnq upon
the sequen~e employed) iB followed by drylng o~ the
~ilver-contaln~ng support ~and heating ~nd/or chemi-
cai reduction of the ~ilver if thi~ iB the flrst
added eub~tance). This ~upport iB then impregn~ted
with a solutlon of the second 3ubstance, that 18, the
~ficiency-enh~ncing salt ~lf the ~llver wa~ the
first ~dd~d subst~nce).
In order to perform the former procedure, l.e.,
coincldental lmpregnation, the efflciency-enhancing
~alt must be eoluble ln the same solvent or complc~-
lng/~olubillzing llquid u~ed with the sllver-lmpreg-
-37-
~8Z~
natlng ~olutlon. ~ith the sequentlal procedure ln
which ~he ~ilver 1~ added first, any solvent capable
of di~solvlng the ~alt which wlll neither react ~lth
the ~llver nor leach lt from the Bupport 18 BU~t-
able. Aqueou~ solutlons are generally prefer~ed, butorganlc llquld~, ~uch ~ alcohol~, ~ay al~o be e~-
ployed. Sultable procedures for effectlng introduc-
tlon of the efflclency-enhancing salt to the solld
~upport may be found ln many of the patents ll~ted
10 ~,bove.
The ~alt of a member of a redox-half reactlon
palr 18 added ln an amount ~ufficlent to enhance the
efflclency of the epoxldatlon reactlon. The preclse
amount ~111 vary dependlng upon ~uch varlables ~8 the
gaseous efflclency-enhancing member of a redox-half
reactlon palr used and concentratlon thereof employed
ln the epoxldatlon procedure, the concentratlon of
other components in the gas pha~e, the amount of
sllver contained in the catalyst, the ~urface srea of
the ~upport, the proce~s condltlons, e.g., space
veloclty and temperature, ~nd morphology of 8Up-
port. Generally, however, a sultable range of con-
centration of the added efflc1ency-enhanclng ~Dlt,
calculated a8 cation, 1B about 0.01 to about 5 por-
2~ cent, preferably ~bout 0.02 to about 3 percent, byweight, based on the total welght of the cataly~t.
Most pre~erably the Balt 18 added in an amount of
about 0.03 to about 2 welght percent.
It has been noted that when conventlonal ana-
ly~e~ have been conducted wlth catalyste prepared by
co-lmpregnatlon wlth sllver and efflclency-enhanclng
~alt, not all the anlon as~oclated wlth the catlon
has been accounted for. For example, cataly~ts pre-
pared by co-lmpregnatlon ~lth a pota~slum n~trate
3~ ~olutlon have been analyzed by conventlonal tech-
-38-
niques and abo~t 3 ~oles of the nitrate anlon h~ve
been observed for every 4 moles of the pota3sium
catlon. This 18 believed to be due to lim~ta~lons ln
the conven~lonal analytlcal technlqueQ and doe~ not
S nece~arily mean that the unaccounted ~or anlons are
not nitrate. For thl~ reason, the amount of the
efflclency-enhancing ~alt ln the cataly3t la given,
in some lnstances, in terms of the welght percentage
of the catlon of the efflclency-enhanclng salt (based
~n the welght of the entlre cataly~t), wlth the un-
derstandlng that the anlon associated wlth the cation
~8 al~o pre~ent in the cataly~t in an amount roughly
proportional (on a molar basis) to the catlon.
Epoxldatlon Procedure:
AB in conventional proce~es of thls type, an
alkene and an oxygen-contalnlng ga~ are brought to-
~ether ln a reactor in the presence of a ~ultable
epoxidation cataly~t under epoxldation condltlons.
Typlcal epoxldatlon conditions lnclude temperatures
withln the reactlon zone of the reactor on the order
of about 180 to 300 degrees C and pres~ure~ ~rom
about 1 to about 30 atmospheres.
The gaseou~ eEflclency-enhanclng member of ~
redox-half reactlon palr may generally be supplied to
the reaction zone wlthln the reactor by lntroducing
the component to the feeastreAm contalning alkene and
oxygen. Under commerclal epoxldatlon ~onditlons,
such a8 those u~ed ln the pre~ent lnventlon, the
feedstream al~o contalns a gas ph~se halogen com-
pound, ~uch a~ an alkyl hallde, a hydrocArbon, and,
~hen the effluent stream from the reactor 1~ re-
cycled, unreacted alkene. When recycle of the e~flu-
ent stream 1~ used, carbon dloxlde may al~o be pres-
-39-
ent. The presence and amount of carbon dlo%lde de-
pend~ on, ~mong other thlng~, whether ~ ~crubblng
devlce i~ used ln the process and, if ~o, to the
extent lt ~emalns carbon dlo%lde.
The term~ ~gaseou~ member of a redo~-half
reaction palr~, ~gaseous efflclency-enhanclng member
of a redox~half reactlon palr~, or llke term~
referred to here~n have a meaning ~lmll~r to that for
the ~salt of a member of a redox-half reactlon palr~
or.like teem~, deflned above. ThAt 1B~ the~e e~rms
refer to members of half-reactions, repre~ented ln
standa~d or slngle electrode potentlal tables ln
~tandard reference texts or h~ndbooks whlch ~re ln a
ga~eous ~tate and are ~ubstances ~hlch, ln the
reactlon equatlone repre~ented ln the text~, are
elther o%idlzed or reduced. The preferred gaseous
efficlency-enhancing materlals are compounds
contain~ng an element capable of exl~tlng ln more
than two valence ~tates, preferably nltrogen, ~n~
another element which 1B~ preerably, o~ygen.
~xamples of pteferred ga~eous e~ficiency-enhanclng
members of a redo~-half reactlon palr lnclude at
lea~t one o~!NO, NO2, N2O4~ N2O3 or any gaBeou3
substance capable of forming one of the
aforementloned gases, particularly N0 and ~2~ ~nder
epoxld~tion con~itions, and ml~tures Oe one o~ the
foregolng, pa~tlcularly NO, with one or more o CO,
~H3, SO3 and SO2. NO 1B mo~t pre~erred as thc ga~-
eou~ efflclency-enhanclng member of a redox-half
reactlon palr.
Although ln ~ome ca~es lt i8 preferre~ to employ
members of the same half-reactlon palr ln the reac-
tion æy~tem, l.e., both the ef~iciency-enhanclng salt
member a~sociated with the catalyst and the gaseous
member ln the eed~tream, as, for example, ~i~h a
15017
.~
, .
- ~o -
preferred comblnatlon of pota~slum nitrate and nltrlc
oxlde, thl~ 1B not nece~ary ln all ca~e~ to achleve
sati~factory re~ult~. Other preferred combinatlons,
~uch ~8 ~N03/N203, RN03/N02, RN03/N204, ~N02/~,
~NO2tNO2, and KNO3/a mixture of SO2 ~nd NO, may al~o
be employed ln the same ~y~tem. In some in~tanc~s,
the ~alt and gaseous members may be found in differ-
ent half-reactions which repre~ent the flr~t and l~st
reactlons ln a series of half-reaction equatlon~ of
an overall reactlon.
The gaseou~ efficlency-enhanclng member of a
redox-half react~on pair i~ also present ln an amount
~ufficlent to enhance the performance, such as the
actlvlty of the catalyst, and, particularly, the
efficiency of the epoxldat~on reaction. ~he preclse
amount i6 determined, in part, by the particular
efficiency-enhancing salt of a member of 8 redox-half
reaction pair u~ed and the concentratlon ~hereof, the
partlcular alkene undergolng oxidatlon, and by other
factor~ noted above which influence the amount of
efficiency-enhancing salt of a member of a redo~-half
reaction pair. Typlcally, a suitable concentration
of the ga~eou~ member oE a redo~-half reactlon pair
for epoxldatLon of most alkenes, lncludlng propylene,
i~ ~bout 0.1 to ~bout 2,000 ppm, by volume, ~hen N2
i~ ù~ed ~B bi~lla~t. When ~ preferred ga~eous member
of ~ redox-half reactlon pair, such a8 NO, ls used in
the epo~ldatlon of propylene, the preferred
concentrat~on i9 about 5 to about 2,000 ppm, by
volume, wlth an N2 balla~t. ~owever, when ethylene
1~ being oxidized, a ~uitable concentratlon 18 ln the
range of from about 0.1 to ~bout 100 ppm, by volume,
of the gaseous feed~trcam components. Prefer~bly,
when ethylene 1~ being oxldlzed, the gaseous
e~ficlency-enhancing member of
~282~
a redox-half reactlon palr i8 pre~ent ~n an amount of
about l to about 80 ppm when about 3 percent, by
volume, C02 19 pre3ent. When nitric ox~de i~
employed as the gaseous efflciency-enhancing member
of a redox-half reaction pair ln ~n ethylene
epo~ldatlon ~ystem, it 1B pre~ent ln an amount of
about O.l to about 60 ppm, preferably about l to
about 40 pp~, when C02 1~ pre~ent.
The ~oxygen-cont~lnlng gas~ employed ln the
reactlon may be deflned as lncluding pure molecular
oxygen, atomlc oxygen, any tr~n~lent radical ~pe~les
derlved from atomlc or molecular oxygen capable of
exl~tence under epoxldatlon condltlons, mlxture~ of
another ga~eou~ sub~tance with at lea~t one o~ the
oregoing, and ~ubstance~ capable of formlng one of
the foregolng under epoxldatlon condltlon~. Such
oxygen-containlng ga~ 1~ typlcally lntroduced to the
reactor elther a~ air, commerclally pure oxygen or
other aubstance whic~ under epoxldatlon condltlon~
both exl~t~ ln a gaseou~ state and form~ molecular
oxygen.
The ga~eous component~ whlch are supplied to the
reactlon zone~ or that reglon of the reactor where
reactant~ and catalyst are brought togethee under
epo%ldatlon condltlons, are gener~lly comblned beore
belng lntroduced to the reactor. The reactor~ ln
whlch the process and catalyst of the present lnven-
tlon are employed may be o~ any type known to the
art. A brlef descrlpt~on of ~everal of the r~actor
parame~ers whlch may be used ln the present Inventlon
are pre~ented below.
In additlon to an alkene, oxygen, and the ga~-
eous cfflclency-enhanclng member of a redo~-half
reactlon palr, the feed~tream also contaln~ ~ per-
formance-enhanclng halogen-containlng sompound, pref-
42-
~Z8Z~;2
erably an organlc hallde, $ncludlng both saturated
and unsa~urated halldes, such A~ e~hylene dichlorlde,
ethyl chlorlde, vlnyl chlorlde, methyl chloride ~nd
methylene chlorlde. Preferably, in commerclal pro-
ductlon, ethylene dichlorlde i~ employed as ~he halo-
~ gen-contalnlng compound~ l'he amount of hallde em-
¦ ployed wlll vary depending upon a varlety of factors,
j includlng the part~eular alkene belng o~idlzed and
¦ the concentration thereof, the particular efficiency-
enhanclng salt and gaseous members of redox-half
reaction pairs and the concentration~ thereof, ~9
well as other factors noted above as influenclng the
amount of efflciency-enhanclng salt and gaseou~ com-
pound. However, a sultable range of concentratlon
for the halogen-contalnlng compound in the oxidatlon
of mo~t alkenes, lncluding propylene, 18 typlcally
abou~ 0.1 to about 2,000 ppm, by volume, of the gas-
eous makeup feedstream. When ethylene 18 oxldlzed,
the range of concentratlon for the halogen-contalnlng
compound 18, however, about 0.1 to about 60 ppm, by
volume. In addltlon, a hydrocarbon, ~uch a8 ethane,
may be included ln the feedstream. ~he feedstream
may also contaln ~ ballast or diluent, such a~ nltro-
gen, or other inert ga8, particularly w~en alr 10
2~ used as the oxygen-containing ga5. Vaeylng amounts
of carbon dloxlde and water vapor may also be pres-
ent, dependlng upon whether means bave been provlded
to remove such substances from the effluent ~tr~am
prlor to comblnatlon of at lea~t a portlon of the
effluent stream with the lnlet stream. Other than
the gaseou~ efflclency-enhanclng member o ~ redox-
half reactlon palr, the components are typ$cally
pre~ent ln amounts shown ln the followlng tQbles for
propylene ~nd ethylene.
-43-
~2 827~7~
" Volume ~ercent (or ppm)
ComPonent for PropYlen~
prapylene about 2 to about 50
oxygen about 2 to about 10
alkyl hallde about 5 to about 2~000 ppm
10 hydrocarbon 0 to about 5
carbon dloxlde up to about 15
nltrogen or remalnder.
15 other ballast
gas, e.g., ~ethane
Volume Percent (or pp~
omPonent for EthYlene Oxldatlon
ethylene at least about 2,
often about 5 to ~bout 50
oxygen about 2 to about a
alkyl hallde about 0.1 to about 60 ppm
hydrocarbon 0 to about 5
30 carbon dlo~lde up to about 7
nltrogen or remalnder.
other ballast
ga3, e.g., methane
~.Z8~
~ hen hlgher alkene~, such a~ those preYlouuly
Aiscussed, are epoxldl~ed, condielon~ and concentrn-
elons typlcally u~ed for the epox~dation of propylene
~ay be employed.
Standard Alkene Oxide Proce~ Te~t Condltlona:
The ~uccessful commerclal productlon of alkene
oxlde~, partlcularly ethylene oxldeF by the ~llver-
catalyzed oxldatlon of alkene, particularly ethylene,depends upon a varlety of factors. Many of the~e
factors lnfluence, elther dlrectly or lndirectly, the
e~flclency of the cataly~lc sy~tem, the actlvl~y or
the aglng rate l.e., stablllty, of the cat~ly~t. The
manner in whlch cataly~t~ and catalytlc ~ystems are
evaluated ln the laboratory strongly lnfluence~ the
value~ obtalned for the~e parameter~. Technlque~ and
experlments deslgned to asses~ ~uch catalyst~ and
catalytic ~ystem~ commonly employ mlcroreactors
(i.e., tlny tubular reactor3 for testlng crushed
catalyst partlcles) or back-mlxed autocl~ve~ of the
Berty type (i.e., larger reactors whlch te~t full-
~ized catalyst pellets and generally employ full ga~
recycle) as ~le~crlbed in Flgure 2 of the article by
2S J. M. ~erty, ~Reactor For Vapor Pha~e-Cat~lytlc
Studles~, Chomlcal Englneerlng Proqre~, 70, Number
5, pages 78-84 (1974), and partlcularly Flgure 2.
Microreactor~ are capable o~ yieldlng, ln moat te~t
~ltuatlon3, the hlghe~t efflciency number~, typlcally
approxlmately the same a~ or ~omewhat greater than
tho~e obt~lnable ln commercl~l tubular reactor oper~-
tlon~ employlng the ~ame catalyst~ ln non-cruahed
condition. ~ack-mlxed autoclave~ commonly provide
lower efficiency values because, al~hough condltlons
c~n be varled, generally the entire cataly~t 1~ cx-
15017
.
. ~ ,.
-45-
'12~ 772
posed to the outlet gas ~hi~h ha~ the lowe3t concen-
tratlon of re~ctant~ ~nd the hlghest concentratlon o
product~. Values obtained u~ing one type of reactor
are,seldom ldentlcal to those obtalned in ~noth~r
reactor sy~tem. A~ a result, clalms of ~uperlor
results or the deslrablllty of one catalyst over
another are preferably based on tests conducted unaer
controlled and comparable conditlons.
~5
. -46-
lZ~Z~
Although the conditlon~ ~et forth ~pra may be
e~ployed both for reactor~ employed in commercial
production a~ well a~ those employed ln a laboratory,
~8 a ba~i~ of comparl~on, the cataly~t~ and oatalytlc
syatem~ for epoxldation of ethylene employed ln the
examples ~et forth below have been te~ted under ~om-
parable conditlona known a~ Standard Alkene Oxide
Proce~s Test Conditlons, or Standard Test Condltlons
(referred to hereinafter as STC). The STC employed
for testing and characterlzlng the catalyst~ ~nd the
catslytlc sy~tem~ of the present lnventlon lnYolve
the use of a standard back-mixed boteom-agitated
~Magnedrlve~ autocl~ve, or ~erty autoclave, a~ de-
. scrlbed above.
In dlscu~slng the enhancement of effloiency
provlded by the pre~ent lnvention, lt may be notedthat, when an effiolency-enhanclng amount o~ a salt
of a member redox-half reaction pair 1B employed, an
efflclency for the epoxldatlon of ethylene of at
least about 84 percent 16 obtalned under Standard
Test Condltlons. ~Standard Te~t Condltlons~ for
ethylene may be deflned aB compri~lng ehe followlng:
by volume, 30 percent C2H4, 8 percent 2~ 5 ppm ethyl
chlorlde, 5 ppm, by welght, NO, no added C2~6 or CO2,
N2, ballast, 240 degree8 C, 275 p~lg, gae hourly
~pace veloci~.y ~GHSV) ~ 8,000 hr 1.
Although the pre~ent lnventlon can be used wlth
any slze and type of alkene oxlde reactor, Includlng
both flxed bed and fluldlzed bed reactors known to
3~ the ~rt, lt is contemplated that the pre~ent lnven-
tlon wlll flnd ~08t wldespread applicatlon ln ~tan-
~ard fl%ed bed, multl-tubular reactor~. The8e gener-
~lly lnclude wall-oooled aB well a~ adlabatlo or non-
wall-oooled reactors. Tube lengths may typlcally
range from about 5 to about 60 feet but wlll fse-
15017
X
~8Z~
quently b~ in the range of from about 1~ to ~bout 40~eet~ The tube~ may have internal dlameter~ from
~bout 0.5 to about 2 lnche~ and are expectea to be
typically from about 0.8 to about 1.5 lnches. G~SV
5 generally range from about 16~000 to about 1,000
br~l. ~yp~cally GHSV value~ range from about 2,000
to about 8,000 hours 1 at pres~ure~ from about 1 to
about 30 atmo~phere~, commonly about 10 to about 25
atmospheres.
While the lnventlon 1~ susceptlble to varlous
modiflcatlons and alternatlve forms, certaln spe~lfic
embodl~ent~ thereof are descrlbed ln the examples ~et
forth below. It should be understood, however, that
these examples are not lntended to llmit the lnven-
15 tlon to the partlcular forms dlsclosed but, on the
contrary, the lnventlon 18 to cover all ~odlfl~a-
tlons, equlvalent~ and alternatlve3 falllng ~lthln
the ~plrlt and scope of the lnventlon.
20 Ex~mple 1 - Preparatlon Of A CaCO3-Supported
CatalYst BY A Sequentlal Procedure:
Calclum carbonate ln granular form ~a~ prep~red
by comblnlng ioo. o 9 of powdered cnlclum car~onate
~Baker Analyzed Reagent) and 250.0 9 ~lstllled water
to form a thlck pa~te which wa~ ~pread to a thlcknes~
of approxlmate one-quarter lnch on a stalnless eteel
tray and calclned at a temperature of sbout 800 de-
grees C for slxteen hour~. The c~lclned product ~a8
30 then fractured lnto fragment~ whlch were Dcreenea to
obtaln plece~ approxlmately one-guarter lnch ln ~la-
~eter. The partlcle~ were lmpregnated wlth an ague-
ou~ sllver ~mlne ~olution by allowlng the~ to ~tand
ln ~ solutlon contalnlng 41.2 9 ~thylenedla~lne, 40.8
35 g dlstllled water, 41.2 9 oxallc ~cld, 72.2 9 sllver
-48-
lZ82772
oxlde, and 14.4 9 monoethanola~lne. The ~lurry or
paste formed from the nllver-aontainlng ~olutlon and
c~lclum carbonate were spread on a ~t~lnle~ ~teel
trpy to a th~ckne~s of approxlmately l/~ Inch. ~he
S m~xture was c~lcined by placlng lt lnto ~ furnace at
l20 degrees C and heating to a temperature of 500
degrees C over a ~lfteen minute period. The ml~eure
waQ thereafter held at a temperature of 500 degrees C
for a fleteen mlnute perlod and then removed from the
furnace~ Upon cooling, the calclum carbonate ~up-
ported sllver catalyst was impregnated wlth ~N03 by
immerslng 50.7 9 of the cAtalyst ln ~ 40lutlon for~e~
by dls~olving 2.03 9 KN03 ln lO0 mI of dl~tllled
~atee. The cataly~t partlcles were drled ~t 120
degrees C ln ~n oven for two hours. The catalyst
contalned 40 percent Ag and 0.6 percent ~, a~ deter-
~lned by ~nalysis.
After autoclave testlng for twelve days, the
above catalyst was lmpregnated a second tlme to ln-
crease the RN03 concentration. The catalyst pleces~47.7 g) were, lmmersed ln a ~olutlon prepared from
7.6 g RN03 d~olved ln lO0 ml water. The resulting
materlal was'drled at 120 degrees C for a p~rlod of
two hourY. The re~ultlng catalyst h~d a Ag concen~
tratlon of 39 percent and a X aoncentr~tlon of 1.7
percent, by welght, based on the total welght of
catalyst a~ determlned by analysls.
3S
-4g-
~282m
~xample 2 - Preparation Of A Calclum
CnrbDnate-Coated, Potassium Nitrate-Impregn~ted
Silver Cataly~t By A Coincidental Procedure:
About 23.5 9 of low den~lty ~30 pore3/lnch),
irregularly-shaped catalyst support partlcles o
alpha-alumina formed from a honeycomb structure
available from ~lgh Tech Ceramic~, Alfred, ~ew Yosk,
having average dlameter~ of 5/8 lnch, were coated by
thoroughly mlxlng the partlcles wlth a slurry formed
from calclum carbonate ln ~n aqueous sllver a~ine/po-
tassium n~trate solutlon for ~ perlod of flve mlnute~
~nd then drainlng. The sllver amine ~olutlon ~as
prepared by ml%lng 41.1 9 ethylenediamlne, 40.B g
dlstllled ~ater, 41.2 g oxalic acld, 71.2 g ~ilver
oxlde, 14.4 g monoethanolamine, and 6.2 g potassium
nltrate. After adding an ~dditional 15 ~1 dl~tilled
water, 51.4 9 of Mallinckrodt ~pre wriptlon grade~
calclum carbonate was added with thorough mlxlng.
2~ The lrre~ularly-shaped catalyst support partlcles
were then added to the sllver amlne/calclum carbonate
slurry and t~oroughly mlxed. The exce~s slurry or
llquld was dralned ~nd the coated partlcles ~ere
calcined in an oven at 300 degree8 C for ~ perlod of
- 25 three hours. The cataly~t ¢ontalnod 29 percent Ag,
0.7 percent R and 11 percent CaCO3, by ~elght, based
on the tot~l welght of the catalyst.
~o-
~12~nz
~xample~ 3-5 - Productlon Of Ethylene
Oxide With Pota~lum Nitrate-Containing,
Calcium Carbonate-SuPPorted CatalY~t~:
-
The epoxidation re*ctlons descrlbed ln the e~amD
ples ~et forth below were conducted employlng cata-
ly~tP of the type prepared in Example 1. The epoxi-
datlon ~tud~e~ for whlch data are pre~ented below
were conducted ln A contlnuously Rtlrred tank reac-
tor, al~o known as a back-mixed autoclave, of the
type describea above. The procedure involved charg-
lng approximately 80 ml of catalyst to the auto-
clave. The volume of catalyst was measured ln a one
lnch ;.D. graduated cyllnder after tapplng the cylln-
der several t~mes to thoroughly pack the catalyst.The back-mlxed autoclave was heated to about reaction
temperature under a nltrogen atmosphere wlth the f~n
of the autoclave operating at about 1,500 rpm. The
nitrogen flow wa~ then dl~contlnued and the feed-
stream was lntroduced to the reactor.
All ethylene epoxldation reactions, except where
lndicated otherwise, were examlned under Standard
Te~t Cond~tions comprl~lng, by volume, 30 percent
C2H4, ~ percent 2~ 5 ppm ethyl chlorlde, 5 ppm nl-
trlc oxlde, no ~dded C2H6 or C02, N2 balla~t, 240
degrees C, 27S pslg, at a 10w rate of 22.6 8CFH, ~nd
GHSV ~ 8,000 hour 1.
--51--
~8~
T~ e I
epo~ld~lon Ot ~thyl-n~ In An
Autool-vo ~ y~n~ C C ~-Su~eort~ C~t-ly-t~
~-opl- Perc-ntL9n An-ly~ed Perc~ntagff ~-~lnu~ P~rc~nt D-y-
Ag ~lcentag~ C- ~YIcerl~ IS~tlcl~ncy Ob~ved
1~ IK/A9~ ~Ag/C-Co3) eo
0 ~A91ng
R~te,
eO/d~ y )
_
39 1.7 25 ~0.62) 1.0 ~3 47
~0.041~ ~.6
_3~
2~ 0.6 3n ~1).29~ 1.2 09 12
~0.02~ 15.2
lo-2)
0.5 35 ~0.11) 0.9 ~9 3
(0.050) ~7
10 1
-52-
~2~3Z77~
Example~ 6-19 - Production Of Ethylene Oxlde
With Pota~31um Nitra~e Containing Cal¢ium
CarbonateLAlumlna-Coated_Silver CatalystR
The epoxidation examples ~et forth below were
conducted using cataly5t8 prepared in the manner
de~cribed in Example 2, other hlkaline e~rth carbon-
ates belng substituted for CaCO3 ln Example~ 1~ to
l9~ A back-mlxed autoclave of the type discu~sed
above was used for the epoxldatlon ~tudie~ for whlch
dat~ are presented below. The procedure lnvolved
charging approximately 80 ml of c~taly~t to the auto-
clave. The volume of cataly~t wa8 mea ured ln a one
inch I~D. graduated cyllnder nfter tapping the cylln-
der several tlme~ to thoroughly pack the c~talyst.The back-mixed autoclave was he~ted to ~bout reactlon
temperature ln a nltrogen flow of 11~3 SCF~ wieh the
fan operatlng ~t about 1,500 rpm. The nltrogen flow
wa~ then discontlnued and the feedstream ~as lntro-
duced to the reactor.
An ~aging rate~, defined as the 810pe of a plotof activity or outlet ethylene oxide (EO) (i.e.,
-d(~EO)/dt, at constant temperature) v~. time, ha~
al~o been provlded in T~ble 2.
~%~7æ
TA~tlC 2
~hrl4n- ~polld~tlon ~n A~ Autocl~v- ~Itb Pot~-~lu~ Nltr~t--
C~n~htnlng Al~-lln- e-r~h C-~bonet~
5 On Alph -Alu~ln- C~t-lVJt~
b~pl~alln~ Perc-nt~q~ P~rcent~g- P-~ent-g~ u~ P~tc~nt
e-rt~ Ag K l~/A9~ lln~ P-rc-nt ~ttlcl-ncy
Cerbon~- E~rth EO
(Ag/ ~Aglnq
Al~ R~t-,
eerth ~ EO/d-y)
C-rbon~t~
_
C-COl 29 ~ 7 11 1 1 88
0~6~~1,03~ ~1 3
1o~2~
~ '~ 20 1.2 1.2 1.0 ~9
lo.n~o~ ~6 67~
O ~ 13 0 3 e l.o 90
~0.023~~0 ~5~ 11 3
lo-2~
~ 6 0 05 0 ~ 0 S ~6
~0 008~ ~3 00~ ~1.
lo 1~
10 ~' 24 1 ~2 2 2 I.S 91
10 076~ ~.36~ ~6 S
10 ~
1~ " 2~ 0 46 2 2 I S ~n
(0 0191 ~-,16~
15017
--54--
~827 72
I1J~ P~ IIn- ~-rc1 nt-g~ Ps~c~ntn~ cont-ge tl~ ua ~-~c-nt
~rth Ag 11 l~t~Ay~ All~llno ~ nt ~ttloloncy
C-tbon-t- ~rth 1~0
~Ag~ IA41n9
A l ll - l l n~ tc
e~ t~ ~ ~O~d~y~
C- r bon~l t- ~
1~ ''' 1~ 1.~ 1.5 1.~ ~0
0 ~o.n76~~2.12~ ~9.6 1~
10-~)
11 1~.~1 1.~ 0.9 1.5 91
~0.076~~1.16~ 19.
10 ~
1~ ~I Cl 1~ 1 2.7 0.75 ~15
lo-n76~12.07~
lo-3~
16 1.~ 3 ~ 1.7 ~1
0.00~~2.~ 7.6
10'~
1~ 20 0. ~ ~.0 1.~ ~1
- 10.02~ 12.~7~ ~9.5 -
lo-~)
17 D~CO~ 17 I.~ 5.6 1.2 90
0. 02~ 12. 1 1~ 16. 1
10'~
1~ 20 0.~ 6.~ 1.5 90
~0.02~ ~2.1~ ~9.0
10'~
25 1~ ~IgC01 17 0.~ 1.0 1.00 ~7
1(~.1~2~ IS.0~ 1-.5 ~1
10-~
15017
` i,~"
. . .
-55-
12~3Z~
~xamples 20-21 - Preparation Of Pres~ed
Alkaline Rarth Carbonate-Supported Catalyst~
Bv A Sequential Procedure:
Example 20:
~ calcium carbonate catalyst was prepared by
combining 30.0 9 CaC03 with 81.8 9 of a Bilver-
lmpregnatlng ~olution prepared by comblnlng 101.7 9
ethylenediamine, 100 9 distilled water, 103.B g
oxalic acid, 181.6 9 ~llver oxide, and 38.3 9 ~ono-
ethanolamlne and dllutlng the ~olutlon to 500 ml with
dl~tllled water. The slurey formed by combinatlon of
the calclum carbonate and ~llver-lmpregnating ~olu-
tlon was placed in A porcelain dish and roasted ln amuffle furnace at 300 degrees C for a perlod of about
16 hours. ~he dried catalyst w~ subsequently
oooled, removed from the porcelain dl~h and ground to
a powder ~lth a mortar and pestle. ~he powdered
material was placed ln a steel die havlng a dlameter
of 1 lnch and force of 10,000 pounds ~a~ ~pplled wlth
a hydraullc E~res~ to fcrm the materlal lnto a 1 lnch
dlameter w~fe!r havlng a thicknes~ of about 1/16 tc
1/8 lnch. 5everal wafer~ orme~ ln thls m~nner were
then cru~hed and claa~l1~d to pa~s a 14/30 meeh
screen.
The cataly~t was lmpregnated wi~h RN03 by lm-
mer~lng 5 9 of the cataly~t ln a ~olutlon formed by
dissolving 0.20 g ~N03 ln 90 drop~ of dl~tllled
water. ~he lmpregnated materlal was then drled ln an
oven ~t 110 degrees C foe a perlod of about 1 to
about 2 hour~. The re~ultlng catalyst had a Ag con-
centratlon of 40 percent and a RN03 concentraeion of
4 percent, by weight, ba~ed on ~he total welght of
the catalyst.
- -56-
~:8Z77';2
Example 21:
A ~N03-lmpregnated SrC03-supported cat~lyst wa~
prepared ~n the same manner aB in Example 20. The
~ame amount~ of SreO3 and Ag solutlon were used to
prepare the ~ilver-containlng cataly~t, 5 9 of whl~h
waq lmpregnated wlth a solution containlng 0.05 9
~03 dlssolved in 55 drop~ of water. The resultlng
catalyst had a Ag concentratlon of 40 percent and a
K~03 concentr~tlon of l percent, by welght, ba~ed on
the total weight of the catalyst.
Examples 22-23 - Productlon Of Ptopylene
Oxlde With Pot~sium Nltrate-Containing,
Alkallne Earth Carbonate-SuPPorted Catalyst~:
The examples of epo~ldatlon set forth below ~ere
conducted uslng catalyst~ pcepared ln the manner
described in Example 20 and 21. A tubular rea~tor or
mlcroreactor of the type dlscu~sed above wa~ ueed for
the epoxldation ~tudle~ for whlch data are presented
below. For ejch oE the te~t~, a me~ured ~mount of
~atalyst was placed ln the tube of c etalnless ~teel
tubular microreactor, the tube havlng ~ length of
10~2 centlmeters, an outslde dlameter of 9.52 mllll-
meters, and an lnslde dlameter of 7.75 mllll~eters.
Prlor to lnitlatlng reactlon, ~he reactor was heated
to the preferred temperature, wlth the cataly~t ln
place, ln a 10~1ng nltrogen atmosphere.
128Z77æ
E~ample 22:
A mlxture of ga~ con~alning, by volume, 9.67
percent propylene, 9.15 percent oxygen, 200 ppm ethyl
chlorlde, 200 ppm nltrlc oxlde, 1.43 percent methane,
and nltrogen a~ a balla~t ga~ W~8 lntroduced lnto a
heated tubular reactor at 245 degrees C. The tube of
the tubular reactor contained 1 gram (0.9 ml) of
14/30 mesh cataly~t at a flow rate of 1,330 hr 1 at
sl~ghtly greater than atmospheric pre~sure. The
catalyst had a composltlon, by welght, of 4 percent
KNO3 and 40 percent Ag on pressed calclum ca~bon-
ate. After 155 hours, the outlet propylene oxlde
concentratlon lactlvltY) was 1.6 percent ~lth a æe-
lectlvlty of 47 percent.
ExamPle 23:
A ml~ture o~ gas contalnlng, by volume, 9.21
percent propylene, 9.06 percent oxygen, 200 ppm ethylchlorlde, 200 ppm nltric oxlde, 2.21 percent methGne,
and nltrogen ga~ a~ a ball~st wa~ lntroduced to a
heated tubuLar reactor malntained at a temperature of
245 degrees C. The tube of the tubular re~ctor con-
talned 1 gr~m ~ ml) of 14/30 m~h cat~ly~t ~t Aflow ra~e of 1,500 hr~l at slightly grester than
atmospheric pressure. The cataly~t employed in the
mlcroreactor h~d a compo~ltion of, by weight, 1 per-
cent KNO3 and 40 percent Ag on pre~sed strontlum
carbon~te. After 35 hours, the outlet propylone
oxl~e concentr~tlon (actlvlty) was 0.62 percent and
the selectlvlty was S3 percent.
15017
'~`.
