Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~7~
CATALYST AND PROCESS FOR OXIDIZING
-
HYDROGEN SULFIDE
The present Inventton relates to a process for
oxldlzlng H2S, and particularly to a process for cataly-
ttcally oxldtzlng H2S to sulfur, SO2, or both in the pre-
sence of a substantlal proportlon of water vapor.
Current atr pollutlon regulattons am very
restrlctlve concerntng the amount of H2S that may be dls-
lo charged to the atmosphere. In some lnstances, gas streams
may not be dlscharged to the atmosphere If they contaln
more than aboutlprppmv of H2S. Thus, many processes have
been developed to remove H2S from gas streams prlor to thelr
d1scharge to the atmosphere.
One method known tn the art for removlng H2S In-
volves catalytlc oxldatlon, that Is, a gas stream contalnlng
i~S 15 blended wlth atr or free oxygen, and the resultlng
mlxture is then passed through a bed of catalyst parttcles
under approprtate condtt1Ons such that the H2S ls converted
to elemental sulfur vapor or S02~ or both, as deslred. One
catalyst useful for the gas phase conversion of H2S to sul-
fur or S02 Is dlsclosed In U.S. Patent No. 4,092,404; tt
o~mprlses one or more vanadtum oxides or sulfldes su~ported
on a refractory oxide such as alumlna or sTllca-alumlna.
Another such catalyst Is disc!osed ln U.S. Patent No.
4,012,486, wheretn a catalyst havlng acttve components con-
slstlng of blsmuth ts used to catalytlcally tnclnerate H2S
to SO2.
When compared, the blsmuth catalyst of U.S.
Patent No. 4, 012,486 wtll generally be found to be less
active than the vanadla catalyst of U.S. Patent No. 4,092,
404 for oxldlzing H2S to SO2. On the other hand, a blsmuth
catalyst Is much more stable than a vanadla catalyst at
operatlng temperatures below about 600 F. when H2S must
be removed from a gas stream, such as an off-gas derlved
from a geothermal power plant, whlch contains water vapor
at a water vapor partlal pressure about 1.0 psla, usually
at least 4.0 psla. In general, vanadTa catalysts have
satlsfactory stablllty in the presence of water vapor at
partlal pressures below about 1.0 psla or at operating temr
1~'7~QZ~
peratures above about 600 F. 9 but under the comblned con-
ditlons of temperature below 60Q F. and water vapor par~
tlal pressures above about 1.0 psia9 and partTcularly at
1.5 psla or above, vanadia catalysts deactivate rapldlyO
It ts believed that the reason for this d~9activatlon ts
due to a complexserltes of chemtcal reactions Involvtng the
converston of the vanadium oxide or sulftde active catalytic
components to less active forms of vanadtumj such as vanadyl
sulfate (VOSO4).
As stated above9 vanadia catalysts are hlghly
acttve for the oxidation of H2S and, as disclosed tn U.S.
Patent No. 4,243,647 corresponding to Canadian Patent 1,102,094,
such catalysts have proven most useful for oxidtztng H2S to
sutfur by reaction with either oxygen or SO2. In the pre-
sence of less than about 1.0 psia water vapor, vanadiacatalysts have proven to be remarkably stable, provtdtng
hlgh conversions of H2S to sulfur for a tlme pertod of more
than I year wtth Itttle If any deactivation betng nottced.
Desplte the remarkable propertles of vanadia catalysts,
however, It ts an object of the present inventlon not only
to improve the stablllty of vanadlum-containing catalysts In
the presence of water vapor but to substanttally tmprove
their activity for convertlng H2S to sulfur. More specift-
cally wtth respect to water vapor, tt ts an obJect of the
tnventton to provTde a process for catalytically oxtdtztng
H2S In the presence of water vapor at a parttal pressure of
more than about 1.0 psia, partlcularly above about 1.5 psla,
and more parttcularly sttll, above about 2.0 psta. It ts
yet another object of the tnventton to achieve the foregolng
30 wtthout oxldtzlng such components as H2, C09 NH3, and CH4
that mlght be present during the oxidation of the H2S.
Other obJects and advantages wlll become apparent from the
followlng descrtptton of the Inventlon.
It has now been found that catalysts comprtslng
blsmuth and vanadtum components are hlghly acttve and stable
for the gasphase oxidatton of hydrogen sulftde, espectally
tn the pr0sence of water vapor. Such catalysts combtne the
htgh acttvlty of vanadta catalysts wtth the stablltty of
blsmuth catalysts. In addltlon, It has been found fhat the
~.
1~7~
catalyst of the invention is usually substantially more stable in the presence
of water vapor than catalysts comprising bismuth or vanadium alone, especially
at operating temperatures below about 600F.
According to the present invention therefore, there is provided
a process for oxidizing H2S in the gas phase comprising contacting H2S in the
presence of a catalyst comprising vanadium and bismuth under oxidizing con-
ditions at a temperature less than 900F such that said H2S is at least
substantially converted to sulfur or S02 or a mixture thereof.
In another aspect, the invention provides a catalyst composition
comprising supported vanadium and bismuth components catalytically active
for oxidizing H2S in the gas phase, said catalyst comprising about 8 to about
20 weight percent bismuth components, calculated as Bi203, and at least about
S weight percent vanadium components, calculated as V205.
The catalyst of the invention is particularly useful when H2S
must be oxidized in the gas phase in the presence of water vapor at a partial
pressure of more than about 1.0 psia. Because H2S produces an equivalent
volume of water vapor for each volume of H2S converted to sulfur or S02, it
will be understood that the invention is useful in a process wherein the
water vapor partial pressure in the feed gas is less than about 1.0 psia
initially but, during contact with the catalyst, increases about 1.0 psia.
An advantage in the invention resides in the highly selective nature
of the catalyst. Components selected from the group consisting of H2, C0,
NH3, and those saturated hydrocarbon gases containing no more than 6 carbon
atoms (i.e., light hydrocarbons) are not oxidized in the process of the
invention. Additionally, the oxidation of H2S, if performed at a temperature
less than about 900F, produces essentially no S03.
In addition to the foregoing, and perhaps most remarkable of all,
vanadium-bismuth catalysts have been found to provide higher activity than
llt~O'~
comparable vanadia catalysts for the conversion of H2S to sulfur. This dis-
covery came as a distinct surprise, for vanadia catalysts are themselves
highly active for the conversion of H2S to sulfur. But comparable vanadium-
bismuth catalysts prove not only to be more active than vanadia catalysts but
substantially more so. For example, as will be shown hereinafter in Example
VI, where prior art vanadia catalysts consisting essentially of about 10 wt.%
vanadium pentoxide on silica-alumina are known to be active for lighting off
the reaction between H2S and oxygen to produce sulfur at a temperature of
about 375 F., vanadium-bismuth catalysts having the same support but com-
prising 8.7 wt.% vanadium components and 12.9 wt.% bismuth components prove
active for lighting off the conversion of H2S to sulfur at temperatures
below 300 F~
All referénces herein to catalysts containing
-3a-
Q~8
--4--
vanadium and bismuth or to catalysts cont~-ntng vanadium
and bTsmuth components Include wTthTn thetr meanlng cata-
lysts actlve for oxldizTng H2S contatnlng (I) elemental
vanadlum and elemental bTsmuth) (2) eleme~tal vanadlum and
one or more blsmuth compounds, (3) elemental bTsmuth and ona
or more vanadTum compounds, (4) one or more vanadlum com-
pounds a~d'one or more blsmuth compounds, (5) one or more
compounds of blsmuth and vanadlum (e.g., a blsmuth vanadate),
or (6) a comblnatlon of any of the foregolng.
Actlve catalysts for use In the Inventlon com-
prlse vanadlum and blsmuth as the essentlal actlve compo-
nents. The essentTal actTve components may be present as
the elements V and BT, or as a mTxture of lndlvldual vanadlum
and blsmuth compounds (for example9 BT2S3 admTxed wlth V2S53,
or as a compound of both blsmuth and vanadlum, such as
Bt~V03)~ or BiVO~. AlternatTvely, the catalyst may contaln
any combinatlon of elements and compounds of vanadlum and
btsmuth as the essential active components. Preferred cata-
lysts contaln at least one vanadlum oxlde or sulfide (e.g.,
V2O5, V203, V2S5, and V2S3) and at least one blsmuth oxlde
or sulfide (e.g., B10, BT2O3, B12O5~ Bi2S3, and ~i204).
The most hlghly preferred catalyst contalns at least some
blsmuth vanadate (I.e., as the orthovanadate, 81VO4 or
Bi203V205, metavanadate, Bl(VO3)3, or pyrovanadate
B14(V27)3)
The typlcal catalyst contalns vanadlum and bls-
muth components tn an IntTmate mlxture, and although the
catalyst may conslst essentlally of such a mTxture~ It Is
hlghly preferred that the vanadlum and blsmuth components be
composited, as by Impregnatlon or comulllng, wTth a carrler
mai-erlal. The carrler (or support) materlal usually comprl-
ses a porous refractory oxlde, Includ~lng, fo~,example, such
preferred refractory oxldes as alumlfl~-~llle~, zlrconla,
tltania, magnasla, sllica-alumlna, slllca-zlrconla, slllca-
tltanla, slllca-magnesla, slllca-zirconta-tTtanTa, and com-
blnatlons thereof. Sultable refractory oxldes Include acldlc
metal phosphates and arsenates, such as alumlnum phosphate,
boron phosphate, alumlnum arsenate, chromium phosphate, etc.
Othersuit~le supports Include the hydrophoblc, crystalllne
~'7~Z8
--5--
slilcas, such as the sillcalites taught In U.S. Patent No.
4,061,724. (As used herein, a refractory oxide 1s hydro-
phobtc tf tt Is capable of absorblng no more than about 0.5
cc/gm of water.) Also suitable are the amorphous and crys-
talltne alumtnoslllcate zeolltes, whether naturally-occur-
rlng or synthetlcally made. The most useful crystalllne
alumtnostltcate zeo1ttes are ton-exchanged so as to remove
essenttally all lon-exchangeable alkalt or alkalIne earth
components. Of partlcular usefulness are the crystalllne
alumlno-slllcate zeolltes whlch are hydrophoblc and essen-
tlally free of alkall and alkallne earth components.
Illustratlve of such zeolltes are the ZSM-5 zeollte dlsclosed
In U.S. Patent No. 3~702~886S the ZSM-II zeolIte dlsclosed
In U.S. Patent No. 3,709,979, and the several hydrophoblc
15 zeolItes dlsclosed In U.S. Patent No. 4,019,880. Such
zeolItes are characterized by hlgh ratlos of sillca-to-
alumlna.
The most htghly preferred refractory oxlde
carrler Ts slltca-alumtna when the alumtna is present tn a
proportton of at least 10 weight percent, preferably be-
tween about 20 and 30 wetght percent. Catalysts prepared
from such supports are usually more active for oxtdlztng
H2S than are catalysts prepared from most other refractory
oxldes. In addltion, such supports are hlghly reslstant
25 to sulfatlon, that ts, in the presence of SO3 and/or S02
plus 2' such supports are reslstant to the formatton of
alumtnum sulfate and the consequent loss of surface area,
crushlng strength, and acttvlty. In general, tt can be
expected that catalysts prepared from sllica-alumlna sup-
ports contalning at least 10 weight percent alumlna will ex-
perlence llttle If any deactlvatlon due to sulfatlon under
the condltlons of the process herelnafter descrlbed.
There are several methods known In the art by
whlch the vanadlum and btsmuth components may be composlted
wlth a refractory oxlde support. One such method Involves
ImpregnatTon, that is, a sultable support, such as pellets
or extrudates of 75~ StO2-25% A12O3 sllica-alumlna, Is con-
tacted wtth a solutlon of ammontum vanadate (or other
soluble vanadium compound)~ drled at an elevated temperature
.1~'7~0;~8
~6~
(usually about 230 F.), and then contacted wlth a solutlon
of a blsmuth salt, such as an acldlc solutlon of a bismuth
nltrate or chlorlde. The composite may also be prepared
by any of a varlety of comulllng techniques. A typical pro-
cedure tnvolves mulllng slllca-alumina wlth soltd ammonium
metavanadate, solid bismuth nltrate, and sufflclent water
to create a past sultable for extruslon through a dle.
i~ore preferably, elther or both of the vanadlum and blsmuth
salts may be added to the mulllng mlxture In solutlon form.
In a preferred embodlment, a mlxture of slllca-alumlna, a
solutlon of blsmuth nitrate In dllute nitrtc acld, and an
aqueous solutlon of ammonlum metavanadate are comulled.
Alternatlvely, a sllTca-alumina or other refractory oxlde
Is comulled, for example, wlth an ammonlum metavanadate
solutlon, then drled or calclned at an elevated temperature,
and then comulled with an aqueous solutlon of a blsmuth
salt, such as a solutlon of bismuth nitrate~in dllute
nltric acid. Comulllng may also be accomplished by mixing
sllica-alumlna wlth one or more bismuth vanadates In the
presence of water. Alternatively stlll9 the composlte may
be prepared by a comblnatlon of Impregnatlon and comulllng
techniques9 as by impregnatlng sillca-alumina wlth ammontum
vanadate, calclnlng, and then comulllng wlth an acidlc solu-
tlon of blsmuth nltrate or chlorlde.
~fter a composlte Is prepared by one of the
foregolng Impregnatlon and/or comulllng methods or thelr
equlvalents, the composite Is calclned, usually at a tem-
perature between about 700 and about 1600 F., preferably
900-1200 F. Calclnatlon produces a catalyst contalnlng
vanadlum and blsmuth largely In the form of the oxldes there-
of9 but usually the 700-1600 F. calclnatlon also produces
sufflclent blsmuth vanadate9 usually In the form of monocllnTc
blsmuth orthovanadate (BiV04), to be detected by X-ray
dlffractlon analysls. Blsmuth orthovanadate and other bls~.
muth vanadates are usually produced even when Impregnatlon
or comulllng is accomplIshed wlthout the delIberate addltlon
of a blsmuth vanadate. For example, when slllca-alumlna Is
comulled (as in Example I herelnafter) wlth ammonlum meta-
vanadate, then further comulled wlth an acidic solution of
.1~'71~
--7--
blsmuth nttrate, extruded cut Into particulate ~orm, and
then calclned at 900-1000 F.9 the flnal product contalns
sufflcient blsmuth orthovanadate to be detected by X-ray
dTffractlon analysls.
Although the inventton ts not to be so limlted,
lt ts believed that catalysts containTng blsmuth vanadate
are more active and more stable than catalysts contalnlng
no blsmuth vanadate. Such is especially belleved to be the
case wtth respect to bismuth orthovanadate (BIV04). It Is
also belleved that the reason the catalyst usually demon-
strates hlgher stabillty tn the presence of water vapor
than Is the case for catalysts containing only vanadlum
components or only btsmuth components is due to the presence
of blsmuth vanadate. Hence, catalysts contalntng a btsmuth
vanadate, and partlcularly blsmuth orthovanadate, are pre-
ferred In the lnventton.
Finished catalysts heretn should contaln at
least 5.0 weight percent of vanadium and 5.0 wetght percent
of bismuth, calculated as V205 and Bt203~ respectl V8Iy.
~thas been found that catalysts contalntng less than 5.0
welght percent of elther metalp whtle more actlve or stable
than catalysts contatnlng elther vanadtum components or
blsmuth components alone, are somewhat less acttve and less
stable than catalysts containtng at least 5.0 wetght per-
cent of each component. Preferably, the catalyst contatns
between 5 and 15 wetght percent of each components, but It
may, tf deslred, contatn up to 40 wetght percent of each
component. A hlghly preferred catalyst conta7ns between
about 7 and 15 welght percent vanadium as V205 and between
}O about 8 and 20 welght percent bismuth as 8t203, w7th the
most hlghly preferred catalyst contatntng at least 8.0
wetght percent vanadlum components as V205 and at least
10 wetght percent blsmuth components as 8t203. (All calcu-
lattons heretn wlth respect to the proporttons of actlve
metal components on the catalyst are reported as the wetght
percent of vanadtum and blsmuth as V205 and Bt203, respec-
ttvely. Thus, a catalyst particle wetghtng 5 grams and
contatnlng elemental vanadfum, elemental b1smuth 9 btsmuth
sulflde ~Bt2S3), vanadtum sulflde ~V2S5)p and btsmuth ortho-
78C~
--8--
vanadate (BTV04)9 each in a wetght of 0.1 gramC9 contalns
vanadium components In a proportlon o-f 5.52 welght percent
as V205 and bismuth components in a proportlon of 5.48
welght percent as B7203.)
The followlng two Examples demonstrate pre-
ferred procedures for preparlng catalysts useful In the
tnventlon.
EXAMPLE I
Four hundred twenty-one grams of 75% StO2-
25~ A1203 s11ica-alum1na, commerctalIy sold by the Davison
Chem1cal Dtvlston of W. R. Grace ~ Co. as htgh alumlna
cracklng catalyst~ were placed In a steel muller~ to whlch
was added 44.2 grams of ammonium metavanadate SNH4V03) and
6 grams of powdered methylated cellulose. The mlxture was
mulled for 45 mlnutes. A solutlon was then prepared by dls-
solving 88.8 grams of blsmuth nitrate (Bi(N03)35H20) In a
liquld conslst1ng of 200 cc. water and 32 cc. concentrated
nitr1c ac1d. The solutlon was added to the prevlously-mul-
led mlxture, and mull1ng was continued for 15 m1nutes. Anextrudable paste was then formed by mulllng w1th 71 cc. of
water for 15 m1nutes. The resulting paste was then extru-
ded through a 1/8 1nch d1ameter dte and cut 1nto partTcles
having lengths between about 1/8 and 1/2 1nch. The extru-
dates were then allowed to dry overnTght at 230 F. Theextrudates were then calcined in the presence of alr at
932 F. for 2 hours. The resulting catalyst contalned 9.1
we1ght percent vanadium components (as V~05) and 11.2
we1ght percent bismuth components as B1203. The catalyst
contalned an X-ray detectable proportlon of blsmuth ortho-
vanadate.
EXAMPLE 11
Sufficient ammonium metavanadate (NH4V03) was
mulled w1th the hlgh alumina slllca-alum}na descrlbed tn the
precedlng Example so that, after extrusion and cuttlng 1nto
1/8 inch diameter by 1/16-1/2 Inch cyllndrical extrudates
and calcTnatlon at a temperature of about 932~ F. for 2
hours tn alr, the resulting product contained 10 welght per-
11'7~,8
g
cent vanadlum components as V205. One hundred grams of suchproduct were then contacted with a solutlon prepared by dls-
solvlng 35 srams of bTsmuth n~trate (Bi(N03)3 5H20) ln a
mixture of 100 ccO water and 15 cc. concentrated nltrlc
acld to whlch was added sufficient water to provide a solu-
tlon of 120 cc. volume. The solutlon was allowed to contact
the extrudate material for two hours to Insure full Impreg~
natlon. The extrudate material was then filtered, dried
overnlght at 230 F., and calcTned at 932 F. for two hours
In the presence of alr. The resultlng catalyst contained
an X-ray detectable proportlon of btsmuth orthovanadate and
further contalned 8.63 weight percent vanadlum components as
V205 and 11.6 weight percent bTsmuth components as BT203.
Catalysts prepared by the foregolng methods or
their obvlous equTvalents have been found to be hlghly ac-
tive for the gas phase oxTdatlon of H2S to eTther SO29
sulfur, or some percentage combinatlon of both, as desired.
In addTtlon, such catalysts are highly selectTve throughout
the temperature range of 250-900 F.9 oxidTzTng H2S with-
out formlng essentTally any S03 and without oxldlzlng anyH2, 00, NH3~ or llght hydrocarbons whlch may also be present
wlth the H2S. Of partlcular lmportance Ts the fact that tha
catalyst Is remarkably stable Tn the presence of water -
vapor. The ITfe of the catalyst for oxTdlzlng H2S at tem-
peratures below about 600 F. ln the presence of watervapor at a partlal pressure of more than about 1.0 psla Is
at least 90 days, usually at least one year. The catalyst
Is especlally useful for oxldlzlng H2S Tn the presence of
water vapor at a partlal pressure of at least 1.5 psla, pre-
ferably at least 4.0 psla, and partlcularly at water vaporpartlal pressures up to about 10.0 psTa. Useful results
have been obtatned, for example, In convertTng H2S to
elemental sulfur by reactTon wlth oxygen at a temperature
of about 380 F. Tn the presence of water vapor at a partTal
pressure of about 9.0 psTa.
The cholce as to whether or not the H2S Tn 3
glven gas stream Is to be converted to elemental sulfur or
S2 wlll most likely depend upon local aTr pollution regu-
latlons. Typlcally, the maxlmum concentratlon of H2S allow-
7~8
-10--
able for discharge to the atmosphare is about 10 ppmv
whlie S02 may be discharged in a maximum concentration
varylng between about 500 ppmv and 2.0 vol.%. Hence, In-
clneratlon, I.e., conversion of H2S to SO2~ wlll usually
be dlrected to gas streams containing between about 10
ppmv and 2.0 vol.% H25, whlle the typical gas stream
treated for converslon to elemental sulfur wlll contaln at
least about 500 ppmv H2S9 usually 500 ppmv to 10.0 vol.~
H2S, preferably 50 ppmv to 5.0 vol.% H25, and most prefer-
ably 500 ppmv to 2.0 vol.% H2S.
Normally, the gas streams treated In the processof the Tnventlon contain, In addltton to H2S, any of such
components as N2, CO29 C09 H2, SO29 29 Ar~ NH39 ~2' and
light hydrocarbons. Typical gas streams for treatment here-
tn tnclude such H2S- contalnlng gas streams as sour natural
gases, off-gases derlved ~rom geothermal steam, and htgh
temperature, gasified coal or gasifted residual oil. The
gas stream may also contaln such sulfur contalning compo-
nents as COS, CS2, and llght mercaptans (t.e., saturated
mercaptans contatnlng no more than six carbon atmos). If
such sulfur-contalnlng components are present, it Ts pre-
ferred that the gas stream be pretreated by the process
dlsclosed In U.S. Patent No. 3,752,877, herein Incorpor-
ated by reference. According to thls process, CS29 C0S, and
llght mercaptans, along with SO2 tf present, are slmultan-
eously converted at elevated temperatures (usually 300 to
900 F.) to H2S by reaction with H2 and/or water vapor tn
the presence of a catalyst comprtslng one ore more active
catalytlc components of Co, Mo, Fe, W, Ni, with combinatlons
of Co wlth Mo or Nl wlth Mo being most preferred. The pre-
treated gas stream will then contain H2S as essenttally the
only gaseous sulfur component and may be treated by a pro~
cess descrlbed herein so that the H25 may be converted to
SO2 and/or elemental sulfur as deslred.
A gas stream especially sulted to the fore-
golng pretreatment method is a Claus tail gas. Other gas
streams whlch are preferably pretreated prlor to contact
with the catalyst of the tnvention are those contatnlng
oleflnsor aromatics. 01efins deactivate the catalyst herein
~ 8()21~
by formlng gums that deposit on the catalyst surfacas, and
arcmatics such as benzene, when present in significant pro-
portions5 e.g., 100 ppmv; deactivate the catalyst when the
operating temperature is below about 350 F. Both types
of deactivation, however, are only tsmporary9 the olefin
deactlvation being overcome by high temperature oxidatlon
of the gum-containing catalyst and the aromatics deactiva-
t1On by raislng the operating temperature above 350 F.
Alternatively and more preferably7 gas streams contalning
aromatlc or olefln components are pretreated so as to remove
these deleterlous components prior to contact wtth the
catalyst of the inventlon. One such pretreatment method,
partTcularly suitable for gas streams containing oleflns,
is catalytic hydrogenatton under the condittons and wtth the
catalyst heretnbefore specifTed for gas streams containing
S02, CS2, COS, and Itght mercaptans.
Gas streams to be treated by inctneratlon should
etther contain suffictent oxygen or be blended with sufft-
ctent oxygen or atr so as to provtde at least the stoichto-
metrtc proportion requtred for:
tl) 2H2S + 32 ~ 2SO2 + 2H20.riore preferably9 oxygen ts present tn a proportton tn excess
of stolchiometrtc, usually tn a proportton between about 1.1
and 2.5 ttmes the stotchiometrtc proportton. Other condl-
ttons usually employed tn tnctnerating H2S in an adtabattcor tsothermal reactor tnclude (a) operattng pressures between
about 5 and 500 psta, wtth pressures of 15-75 psta betng pre-
ferred, (b) tnlet operattng temperatures tn the range of
250-900 F., wtth temperatures below about 600 F. and es-
peclally below about 450 F. betng preferred, and (c)space veloctties between 100 and 509000 v/v/hr, wtth 500-
5000 v/v/hr being preferred. Operating condttions are ap-
propriately adjusted so that at least 90% of the H2S ts in-
clnerated to SO2. Preferably, the operattng condtttons are
adjusted so that essentially all the H2S ts tnctnerated.
Condttlons known to produce essentially full converston of
H2S to S02 tnclude: 450 F., 50 psta, 2000 v/v/hr tgas
volume calculated at 60 F.), 2.2 tlmes the stotchtometrlc
proportion of atr, and 2700 ppmv H2S In the feed gas. The
- ~B
~ . -
B~
-12-
followtng ~xample 111 demonstrates the suitabTlity of these
conditions.
EXAMPLE 111
A feed gas stream-having a composition shown Tn
Table I was blended at a rate of 460 scc~mtn tgas volume
measured at 60 F.) with water vapor fed at a rate of 40 scc/
mtn and alr fed at the rate of 19.8 scc/min. The resultant
gas mixture,.havTng a water vapor content of 7.7 vol.% and
an oxygen content of about 0.80 vol.~ (2.23 tTmes stoichlo-
metric) was then passed for 15 days at a pressure of 50 psig,
a constant temperature of 450 F. 9 and a space velocTty o~
about 2000 v/v/hr through an Tsothermal catalytlc reactor
contalning 15 cc. of catalyst partTcles comprising 11.6
T5 weTght percent bTsmuth components (as Bi203) and 8~6 we7ght
percent vanadlum components (as V205). The cataIyst was
prepared as descrTbed in Example 11, and the water partlal
pressure wTthtn the reactor was about 5 0 psia. The pro-
duct gas was analyzed on the 15th day by approprTate mass
spectrometrTcal techniques, and the results are reports on
an anhydrous basls in Table 1. As shown, the H2S was com-
pletely converted to SO29 and no H2 or methane was oxldized.
The S03 content of the effluent gas was determined to be
from 3 to 5.0 ppmO
TABLE I
Feed Composj~lon Product Composttlon
Hydrogen 873 ppmv 838 ppmv
Methane 1.68 vol.~ 1.60 vol.%
Nitrogen O ppmv 2.77 ~ol.
30 Oxygen O ppmv 0.43 vol.~O
Argon 3 ppmv 365 ppmv
Carbon Dloxide97.96 volO% 94.85 vol.%
Hydrogen Sulflde2717 ppmv O ppmv
Methyl Mercaptan2 ppmv O ppmv
35 Carbonyt Sulfide 4 ppmv O ppmv
Sulfur Dloxide 36 ppmv 2212 ppmv
Carbon DisulfideO ppmv O ppmv
Total Sulfur Clom-
pounds as S2 2759 ppmv 2212 ppmv
11~7~8
-13~
1. Note: The reason a lower concentrafion of total sulfur
compounds was found In the product gas than In the feed
was due to dllution by the blend of air oxldant and also
by the fact that on the 15th day of operatlon the H2S
concentration In the feed was somewhat lower than snown
In Table 1.
EXA~PLE IY
_
STx differently prepared catalysts were tested
under the condltions of Example 111 to determine how actlve
and stable they were for inclneratlng H2S In the presence of
50 psla water vapor pressureO The six catalysts were pre-
pared as follows:
10 weight percent V2_~ on silica-alumlna
A mtxture of ammonium vanadate and the hlgh alu-
mlna crack1ng catalyst described in Example I were
mulled In the presence of sufficlent water to create
a paste suitable for extruslon. The paste was ex-
truded through a 1/8 inch dle, cut Into pieces
about 1/16-1/2 Tnch in length, drted at 230 F.,
and calclned ln air at 932 F. for two hours. The
catalyst consisted of 10 weight percent vanadium
components (calculated as V205) and sillca-alum1na
(75% slllca-25~ alumina).
36.6 weight percent V2_5 on slltca-alumtna
One hundred and elght grams of ammonium meta-
vanadate, 291 grams of the high alumina sllica-
alumlna described tn Example 1~ and 7.74 grams
of methylated cellulose were mulled In the pre-
sence of sufflc1ent water to produce an extrud-
able paste. The paste was then extruded and
cut into 1/8 Inch d1ameter by 1/16-1 t2 i nch long
cyllndrlcal pleces. The extrudates were drled
overnight at 230 F. and calclned at 932 F. for
two hours In the presence of air. The catalyst
~o-produced contained 36.6 welght percent vana-
dlum components (calculated as V205) on sllica-
alumlna ( 75~ S t 02-25~ A 1203)
10.2 wei ht ercent Bi O on alumlna
9 P 2-3
Z~
~14-
Thls catalyst was prepared according to a
method slmilar to that taught in Example l of
U.S. Patent No. 4,012,486. The procedure utTI-
lzed was as fol IGWS: 17 gm BTC13 was dissolved
in 40 cc. water to which was added 40 cc. con-
centrated hydrochloric acld. The solution was
then dlluted wlth 100 cc. water. The solutlon
so produced was allowed to contact 100 grams
of gamma alumina 1/16 Inch diameter extrudates
for two hoursO The excess llquid was then
decanted off, and the impregnated extrudates
were washed wlth a solution consistlng of 30%
concentrated NH40H and 70% water until the
extrudates were chlorlde free. The extrudates
were then washed wlth 500 cc. water and cal-
clned for 2 hours at 932 F. The catalyst con-
talned 10,;2~ bismuth components (calculated
at Bi203) supported on gamma alumlna.
4.5 weight percent B1203-9.4 weight percent
-2-5 on sllica alumlna
Thls catalyst was prepared by first pre-
paring the 10 weight percent V205 on silica-
alumlna catalyst.as descrlbed above. One
hundred grams of thls catalyst was contacted
with a solution prepared by first dlssolvlng
11.6 gm bismuth nltrate In 100 cc. water to
whlch was added 5 cc. concentrated nitric
acid, and then further addlng sufflcent water
to make the solutlon up to 120 cc. The con-
tactlng tlme was 2 hours, after whlch the ex-
cess llquld was decanted off. The Impreg-
nated extrudates were then drled at 230 F.
overnight and calclned for 2 hours at 932 F.
In the presence of air. The finished catalyst
contained 4.5 weight percent blsmuth compo-
nents (calculated as Bi203) and 9.4 welght per-
cent vanadlum components (calculated as (V205~.
By X-ray dlffractlon analysis, it was determlned
.11'~0~
-15-
that the flnished catalyst contained blsmuth
orthovanadateO
7 _ weight percent B12_3-9.0 welght percent
- 2_ 5 on silica alumina
Thls cata1yst was prepared accordlng to
the method shown above for the 405 welght per
cent Bi 23-9 4 welght percent V205 catalyst
except that the impregnating solutton was pre-
pared as fol 10~5: 23D2 gm bismuth nltrate
were dlssolved In 100 cc. of water plus 10 cc.
nitrtc acid. The solutlon was then sufflciently
dlluted with water to provide a total volume of
120 cc. The finished catalyst contained 7.95
IS weight percent of bismuth components (as
B1203) and 9.0 weight percent vanadium compo-
nents ~as V205)O The catalyst was found by
X-ray diffractlon analysls to contaln bismuth
orthovanadate.
11.6 w ght percent B12_~-8.63 weight percent
-2-5 on sillca-alum~na
This catalyst was prepared according to
the method shown in Example 11.
Each of the foregoing catalysts was uttllzed to
inc7nerate H2S to S02 under the conditlons recited In
Example 111. The only condition was was varied for the In-
divldual catalysts was operating temperature. After oper-
atlng wtth the varlous catalysts for sever31 days duration
at temperatures varying between about 450 and 510 F.
the stability of each catalyst was determined by comparlng
the concentration of unreacted H2S in a sample of the pro-
duct gas at a speclfTed operating temperature early In the
run versus the concentratlon of unreacted H2S in a sample
of the product gas produced at the same specified tempera-
ture later in the run. The data so obtained are tabulated
In Table 11 and the s1abilities of the varlous catalysts
In terms of the increase of unreacted H2S in the product
1~7~0~3
-16-
gas per day9 are also tabulated In Table ll. As shown
the catalysts which proved most stable were those consTsttng
of bismuth components or bismuth and vanadium components
as the essential active catalytic components. Catalysts
contatning only vanadium components as the essential active
catalytic components deactivated at unacceptably hlgh
rates. The most stable catalysts were those containing
blsmuth and vanadlum components In proportions of at least
about 8.0 weight percent and 7~0 weight percent9 respec-
tlvely. Such catalysts proved remarkably more stable thanthe 10~ or 36.6% V205 catalyst and roughly twlce as stable
as the 102% Bi203 catalyst.
Also sTgnlficant is the fact that the two cata-
lysts contalnlng at least about 800 weight percent blsmuth
components and at least about 7.0 weight percent vanadlum
components malntained an H2S concentration in the product
below about 3.5 ppmv tn comparison to about 6 ppmv for the
vanadlum-blsmuth catalyst contalning only 4.5 weight per-
cent bTsmuth. Many envlronmental regulations permit no
more than about lO ppmv of H2S to be discharged to the at-
mosphere and It can be seen that the two vanadium-blsmuth
catalysts contalning at least about 8.0 weight percent bls-
muth components provide actlvtty and stabilTty that will
insure agalnst reaching such high levels of H2S in the pro-
duct gas whereas the 4.5 welght percent bismuth-9.4 weight
percent vanadTum catalyst is less suitable for this purpose.
Of spectal note is the h1gh stabllity of he 11.6 weight
percent blsmuth-863 weight percent vanadium catalyst.
Because of the hlgh stability and hlgh activity of this
catalyst9 it and other catalysts containlng at least 10
weight percent blsmuth components9 calculated as B1203
and at least 8.0 welght percent vanadium components9 calcu-
lated as V205~ are most hlghly preferred tn the inventlon.
EXAMPLE V
To compare the initlal activities of the cata-
lysts of the Invention with those of the prior art data
comparlng the product H2S obtained at various temperatures
In the runs of Example IV prior to any signiflcant cata-
--17--
C sd
V ~ . '.
~~ ~ ~ U~
c~l o a~
.. . . . .
~t ~C`J O ' OO o '1:5
E3
Cl t~ ~ ,_
. IJ
.J~ I ~ a~ _~ ~ o ~ ~_
c~ r~
O ~d
V
00 ~ O O O ~ O C~
C v o u~ n ~
U~ ~ ~ ~ O
~ ~ ~ h
C~
OE~
i~i
P~
P~
U~U C`~ ~ ~ U~ o
. . , . . . C~
- ~ ~1 ~ ~D ~ ~ JJ
~1 ~ o.~ ~ .
.
~:1
V
.,.
u~ ~
~`w ~ vs
u~ ~ ~ ~a ~ :~:
O
Q.
u~ ll
u~ o~ oc~J
o~
~o o ~o ~c
o~co .~l
c' ll v
I ~f'~
~ o ~ o o
o c`~ o c`~
~ ~ c~ ~
~ o~ ~~ ~ ~
:~
~ ~ ~ ~ c:
~a o
c~ ~ ~
:1~'7~
, ~
Iyst deactlvation were tabulated ln lable 111. Also tabu-
Iated In Table 111 were data obtalned from an experiment
run under the same conditions of Example 111 but uslng a
catalyst consisting of 13.Q weight percent Bi203 and
sllica-alumlna (75% SiO2-25% A1203)~ whtch catalyst was
prepared by impregnating slllca-alumlna extrudates wlth a
bJsmuth nltrate solutlon followed by calcination at 932 F.
for two hours in the presence of air.
As shown In Table 111, the vanadia and vanadlum-
blsmuth catalystsh~d comparable acttvlties under the condi-
tlons of the experlmentT leavlng almost no unreacted H2S at
temperatures In the 420-450 F. range. On the other hand,
the 10.2~ and 13.0% bismuth catalysts were only usefui at
temperatures above about 500 F. At temperatures in the
15 490-500 F.range9 the two bismuth catalysts both showed
evidence of loss of actlvlty, with unreacted H2S belng as
hlgh as 50 ppmv. Thus~ the vanadla and vanadlum-blsmuth
containlng catalysts exhlblted substantlally better acti-
vtty forthe conversion of H2S to SO2 than the catalysts
containlng only bismuth components as the essentlal actlve
catalytlc components.
TABLF 111
Càtalyst Temperature~ F.ppmv H~S
10% V20 445 4.4
2 5 490 3.4
500 1.5
36.6% V205 400 25
410 17
420 4.8
440 1.5
10.2% Bt O 500 S0
2 3 510 11.8-13.4
520 3.3-8.6
530 3.6
13.0% Bl 0 490 i7.1
2 3 500 1-0
510 0.9
354-5g B123-9.4% V2O5 440-450 F. 1.7-6.0
795% Bl2o3-g.o% V205 450-460 F. 1.1-3.5
11.6~ Bi2O3-8.63~ V205 450-470 Fo 0.3-4.5
1~7~QZ~
_1~9_
The catalysts of the invention may also be util-
ized to oxidize H2S to elemental sulfur as well as for In-
cineration to 52 To produce elemental sulfur~ conditlons
are usually chosen for adiabatic or isotherrnal reactors
from the following ranges: 250 to 900 F., 100 to lO,OOû
v/v/hr9 and 5 to 75 psia, preferably from the following
ranges: 275 to 475 Fo~ 200 to 2500 v/v/hr, and 15 to 30
psla,andmost preferably: 275 to 425 F., 500 to 1500
v/v/hr, and 15 to 20 pslaO In addition, the inlet tempera-
ture is preferably ma7ntained below about 400 F., most
preferably below 350 F. 9 with at least some H25 being con-
verted to elemental sulfur below such temperatures. An
oxidant gas is also necessary, so oxygen, usually supplTed
Inthe form of air9 is blended with the feed gas stream so
as to produce sulfur vapor according to the following
reactlon:
(II) 2~ S + 2 ~~~~ 2S + 2H20
~lost preferably,the amount of atr or oxygen so blended with
the feed gas is such that oxygen is present in a proportion
near or at the stolchiometric proportion for Reactlon (Il),
usually between about 0 9 and lol times the stoichiometric
proportion. As is well-known, the highest possible conver-
sions of H2S to sulfur are accomplished when oxygen is
avallable in its stoichio~etric proportion. Also contrlbu-
ting to high sulfur ylelds are low water vapor partial
pressured and temperatures below about 475 F. 9 particularly
below about 450 F., with sulfur yields increasing wTth de-
creasTng temperature and decreasing water vapor partial
pressure.
It 7s~ of course9 well-known that S02 may be
used In place of oxygen for the conversion of H2S to sulfur9
the sulfur being formed by the following reaction: -
(111) 2H2S + S02 = 3S + 2H20
Thus, If S02 ts present in the feed gas stream in any H2S
to S02 ratio greater than 2.0, oxygen need only be added in
an amount sufficient to react with the H2S not converted by
ReactTon (111). In other words, if the ratio of H2S to S02
Is greater than 2:~ then the stoichiometric proportlon of
oxygen Is that proportion sufficient to provide a molar or
~, 3
1~'7~2~3
-20-
volumetric ratlo of H~S to (S0 + 2~ equal to 2Ø
For feed gases inherently containlng H2S and
S2 in an H2S to S02 ratio less than 2.0, the highest
posslble conversions to sulfur are obtalned by firstly
prstreating the feed so as to convert the S02 to H2S7 as
by the method shown hereinbefore Tn U.S~ Patent No.
~?g2,877and then blending the pretreated gas with suffi-
cient oxygen or alr to provide an H2S to 2 ratlo equal to
2Ø For feed gases contalntng H2S to S02 In a ratio equal
to 20, no pretreatment or add1tion of oxygen Is necessary;
the catalyst may be used for the direct conversion of H2S
to sulfur vla React1On (111).
In vlew of the foregoing, It should be apparent
that when elemental sulfur Is deslred, S02 may be utlllzed
as an alternatlve oxldant to oxygenO That is, for any gas
stream contaTning H2S, elemental sulfur may be produced
hereln by blendlng elther S02 or oxygen oxtdant wlth the
gas stream such that a ratlo of H2S to oxidant of 2.0 Ts
provlded. However> oxygen is inherentiy superlor to S02,
not only because of Its ready availabllity in the form of
air but also due to the hlgher converslons to sulfur obtain-
able therewlth. A comparison of Reactions (Il) and (111)
reveals that, for the same amount of H2S converted to sul-
fur, 50% more sulfur is formed by Reaction (111) wTth S02
oxidant than by Reaction (Il) with 2 oxidant. The formation
of 50~ more sulfur by Reactlon (111) necessltates higher
operatng temperatures for Reactlon (111) than for Reactlon
~Il) If the sulfur vapor dew polnt is not to be exceeded.
But at operatlng temperatures below 1000 F., the conver-
slon of H2S to sulfur decreases wlth Increaslng tempera-
ture. Thus, because H2S can be converted to sulfur by
Reactlon (Il) at a lower temperature than Reactlon (111)
without exceeding the dew polnt, an inherent advantage -
I.e., a hlgher conversion - Is obtained when oxygen Is
used as oxTdant than when S02 is utillzed.
Whether oxygen or S02 Is uttlTzed as oxldant, it
wlll be found that the catalyst of the invention is highly
useful for converting H2S to elemental sulfur. The percen-
tage converslon in any given situatTon~ of course~ will
11'78Q~'13
-21-
depend upon such factors as operating temperature operat
ing pressure, water vapor partial pressure, and choice of
oxidant But the vanadium-bismuth cataiysts disclosed
hereinbefore usually provide a conversion of H2S to ele-
mental sulfur within 10/o~ often wlthin 5~.9 of theoretical.And because of their high activity for converttng H2S to
sulfur, the vanadium-bismuth catalyst of the tnvention pro-
vTdes high conversions of H2S to sulfur under lower opet~a-
ting temperature and/or higher space velocity conditlons
iO than are required for comparable prior art catalysts, such
as the vanadia catalyst disclosed in U.SO Patent No
4,243,647.
The following Example demonstrates the high
actlvity of vanadium-bismuth catalysts for oxidizing H2S
to elemental sulfurO
EXAMPLE Vl
A catalyst was prepared containing 8~7 weight
percent vanadium components, âS V2O5, and 12.9 weight per-
cent bismuth components, as ~i2039 and the balance being asupport consisting of silica-alumina having a 25~ by weight
alumina content. The catalyst was in particulate form~
had a surface area of 239 m2/gm, and 3 compact bulk density
of 0.67 g/cc. (This catalyst was prepared in a manner very
similar to that described in Example 11.)
The foregoing catalyst (950 gm~ was charged to
an isothermal reactor and utilTzed to treat a feed gas
containing (on an anhydrous basis) about 99% C02 and H2S in
a concentratlon varyins between about 750 ppmv and 1200
ppmv. Alr was blended with the feed gas such that stoichio-
metric oxygen was available within a 10~ tolerance to oxi-
dlze the H2S tn the feed gas to sulfur. Elemental sulfur
produced in the reactor was removed therefrom in the vapor
form and recovered by condensation. The experiment was
conducted over a ttme period of more than 5 months, and the
data shown ln Table IV were derived from analyses of
samples of the feed and product gases when the operattng
conditions were those shown tn Table IV.
~: ~ It is noted wtth respect to the foresotng exper-
Q~3
-22~
iment that the catalyst throughout the run evinced no
deactlvation9 except when the operating temperature fell
below the sulfur vapor dew potnt temperature and sulfur
deposlted on the catalyst. Such deactlvations, however,
were only temporary, elevated temperatures restoring the
catalyst to full activityO
As shown by the data In Table IV 7 the vanad1um-
blsmuth catalyst of the InventTon is active for llghting
offth~ converslon o~ H2S to sulfur at temperatures below
300 F. Thts result Is considered surprising for a number
of roasons9 not the least of whTch ts that a comparable
prlor art catalyst -- and one known to b0 highly actTve for
the converslon of H2S to elemental sulfur, i.e., a 10%
V205 on 75~ SiO2-25~ A1203 catalyst -- Is active for light-
i5 ing off the oxldation of H2S to sulfur In the presence ofwater vapor at partlal pressures less thgan ~about 0.7 psia
only at temperatures at or above about ~ F. Thus, the
catalyst of the invent10n proves to be substantlally more
actTve than comparable vanadia catalysts for the converslon
of H2S to elemental sulfur, and such Is yet more surprlslng
when the fact the foregolng experiments were conducted
wlth water vapor at partlal pressures between about 2.5
and 50 psiats taken into consideration. As those sk711ed
in the art are aware, IncreasTng the amount of water vapor
tends to increase the light-off temperature for a catalyst
by Increaslng the amount of water vapor absorbed on the
catalytic surfaces, thereby reduclng the amount of absorbed
H2S and 2 tor S02). Yet desplte the adverse condltlon of
3.0 psla water vapor, the catalyst of the Invention still
exhibited activity for llghting off the reactlon of H2S
wlth oxygen at about 285 F. whereas a comparable vanadla
catalyst ~nder the more favorable condttion of less than 0.7
psla ~Jater vapor Is useful only at temperatures at or above
about 375 F.
Another surprislng aspect of the in~entlon as
shown by the data in Table IV Is the hlgh stabtltty of the
vanadtum-btsmuth catalyst tn the presence of water vapor.
As shown by the data tn Table 11, vanadia catalysts deactt-
vate raptdiy tn the presence of water vapor at temperatures
QZ~3
-23-
c~ o ~ o r~
C~l . o ~ ~ ~ o~ . ,~
C~l ~ ~
o U~ o o ~ ~ ~ ~ o
,1~ ~ ~ O ~ o r~
C~ ~ ,~
oU~ o o C~ o o
O ~ ~ ~ `D . u~
. ~ ,, ,, ~ ,~
C~ ~ ,~
u) o o ~ o ~ r~ o'
O O cr~
r~ ~ ~ 0 ,1 ln 1~ .
.
`D u~ o o O ~ O ~ O
o _~ 0 ~ ~ n
~
_, ,~
C'~ o U~ ~ o
~D ~
~ ~ ,
b
o u~ ~~ o
OCr~
~ _l ~
o ~ o U~ C`J ~~ ~ o~
u~ 0.
_l oo
e~ ~ o ~ o ~ V~ oo o
o ~ U~ ~ ~ U~
C~ ~ ~ 0
o ~ o co 0 r~ o
o o o~ U~ ~ oo . U~
oo ~ ~ o ~ '
,~
0 ~d
o
to
~ E ~
~u) a~ P. ~.
D~a) E
o
. o ~~ o a~ ~
Z ~ l V L~
a~ J- V
F: Va~ O' O ~I V~
V~ , ~ Oo ~ P~
-2a-
below about 600 F.~ but the data in Table IV show that
vanadium-blsmuth catalysts resist such deactivatton even
when uti1i7ed tn the presence of 2.5 to 5.0 psia water
vapor for a time period of greater than 5 months.
In a specTfic embodlment of the invention par-
ticularly useful for treating feed gas streams contalning
between about 5 and 40 volume percent H2S9 especially when
the feed gas stream contains water vapor at relatively
hlgh partlal pressures, e.g.9 above about 2.0 psia and, more
usually, above about 400 psia9 the feed gas stream is blen-
ded with atr, preferably In a stoichlometric amount9 and
the resultlng blended gases are passed through an adiabatlc
reactor contalning a particuiate vanadlum-blsmuth catalyst
under condittons described hereTnbefore such that a substan-
tlal proportlon of the H2S is converted to elemental sul~urvapor. The product gas contalning elemental sulfur is
passed to a sulfur condenser or other suitable means for
separating sulfur from the product gas9 leaving a purlfled
product gas containing residual H2S. A portion of the pur-
Ified product gas Is then recycled and blended wlth the ~eedgas such that the blend of feed gas9 alr, and recycle gas
entering the reactor contains H2S tn a predetermined range,
such as 3 to 6 volume percent, or below a predetermined
maxlmum, typically and preferably9 5 volume percent. The
rema7nTng portion of the purifled product gas is treated
by any of three methods. The three methods (whlch are
applicable to any embodiment of the inventton In whtch the
H2S content of a gas stream recovered after treatment with
the vanadium-blsmuth catalyst is too high for discharge to
the atmosphere) are:
(I) If the H2S to S02 volumetric ratio in the
purtfted product gas stream is about ~.09 the gas stream
may be contacted with any porous refractory oxlde-contaln~ng
catalyst~ such as alumina, under conditions of elevated
35 temperature9 e.g., 400 to 900 Fo~ such that a substan-
tlal proportion of the H2S is converted by Reaction (111)
to elemental sulfur9 whlch is then recovered, as by conden-
sation. In this embodiment of the Inventlon9 It Is most
preferred that a vanadium-bismuth catalyst as descrlbed
-25-
heretnbefore be utilized to carry out the conversion to
sulfur such catalysts having far greater actlvity than
typlcal alumlna catalysts and therefore belng useful for
provldlng the same conversion of H2S to sulfur as alumina,
but under the more difficult conditions of lower operatlng
temperature and~or htgher space velocity.
(2) If the H2S to S02 volumetrlc ratio i5 sub-
stantially above 2.0, or if one desires to allow for fluc-
tuatlons in the H2S to S02 ratlo in the purlfied product
1~ gas stream, the purlfied product gas stream Is blended wlth
sufficient air to provide a volumetric ratio of H2S/
(S2 ~ 2) of about 2.09 and the resultlng mlxed gases are
then contacted with a vanadlum~bismuth catalyst under condl-
tlons herelnbefore disclosed for conversion to elemental
sulfur. Alternatively but less preferably, a vanadia
catalyst consisting essentially of a vanadium oxide or sul-
fide on a porous refractory oxide support may be subst1tu-
ted for the vanadTum~bismuth catalyst, provided the water
vapor of the mixed gases In contact therewlth Is at a par-
tlal pressure below about 1.0 psia or the operattng tem-
perature Is above about 600 F. Use of the vanadia catalyst
provides less act7vity for the converslon of H2S to sulfur
than Is the case with vanad7um-bismuth catalysts, but the
lower actlvlty may be suitable In certaln Instances, as
when cost of the catalyst is of speclal Importance.
(3) If the H2S content of eTther the purified
product gas stream or the gas streams recovered after sulfur
condensatTon from methods (I) and (2) above is too high for
dlscharge to the atmosphere, but such gas streams could be
dlscharged to the atmosphere If the H2S were converted to
S2 (due to less strtngent air pollutTon standards for S02
than for H2S), such gas streams are subjected to Inclnera-
tlon to convert the H2S therein to S02. The inctneration
may be accompllshed thermally at temperatures above about
1000 F. Tn the presence of excess oxygen, but it is pre-
ferred that the incineratlon be accomplished catalytically
by contact with the vanadium-bismuth catalyst of the Inven~
tlon as described heretnbefore under the range of conditions
for converslon to S02 also described hereinbefore. Use of
1~ 0~
the vanadium-bismwth catalyst provides a dtstinct advantage
over thermal Tncineration in that the gas stream to be
treated does not require as much preheating, the vanadlum-
bismuth catalyst being active for the conversion of H2S
to S02 at temperatures substantially beiow 500 Fo
Although the inventlon has besn descrlbed In
conjunctlon with speciflc exarnp~es and embodiments thereof,
1t ls evident that many alterations, modTficatlons, and
var7atlons wlll be apparent to those skilled In the art In
llght of the foregolng description. For example9 It should
be self-evident that the catalyttc process of the inventlon
may easllybe modifted to oxidlze H2S to any deslred percen-
tage comblnatlon of suifur and S02 by simply controlllng
the proportion of oxygen between the amount requlred for
Reaction ~1) and that required for Reactlon (Il). Accor-
dlngly, Tt Is Intended in the invention to embrace these
and all such alternatives, modiflcatlons9 and varlattons
as may fall wlthTn the scope of the appended cla7ms.
i~7~Z8
SUPPLEMENTARY DISCLOSURE
When gas streams containing relatively large proportions
of water vapor are to be treated with a catalyst prepared from
alumina, silica-alumina, or other porous support materials, it is
preferred that the catalyst have pore size characteristics
preventing capillary condensation of water in a substantial number
of the pores. In general, porous catalysts typically utilized
in the invention have mean pore diameters greater than about 50
angstroms, and such catalysts, as well as many catalysts of mean
pore diameter below 50 angstroms, are useful in environments
wherein the water vapor partial pressure is less than about 75%
of the saturation pressure. However, when the water vapor partial
pressure increases above about 75% of the saturation pressure,
capillary condensation of liquid water in the pores of the catalyst
may interfere to an undesirable extent with the diffusion of H2S
and oxidant reactants to the catalytic active sites within the
pores. These detrimental effects of capillary condensa~ion may
be reduced by either lowering the water vapor partial pressure,
increasing the operating temperature, or increasing the size of
the pores, and in many instances, it is most convenient to prepare
the catalyst with a porous support suited to the water environment
than to raise the operating temperature or remove water in a
contact condenser or other separation means. To this end, it has
been determined by calculation that pores having diameters of 200
angstroms or greater will not encounter significant capillary
condensation if the water vapor is present at a partial pressure
no greater than about 95~ of the saturation pressure. Similarly,
pores of 80 angstroms diameter or greater will not encounter a
- 27 -
0~
significant amount of capillary condensation at water vapor
partial pressures up to about 88% of the saturation pressure.
Accordingly, a substantial number of the pores in a catalyst
having a mean pore diameter of 200 angstoms or more will remain
free of liquid water at water vapor partial pressures up to at
least 95% of saturation while a mean pore diameter of 80 angstroms
or more yields a similar result up to 88% of the saturation
pressure.
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