Catalytic incineration of hydrogen sulfide from gas streams

A process for the conversion of H.sub.2 S to SO.sub.2 in a feed gas containing H.sub.2 S is effected by oxidation with air or oxygen at temperatures between 300.degree. and 900.degree. F. The oxidation is conducted in the presence of an extremely stable oxidation catalyst comprising an oxide and/or sulfide of vanadium supported on a non-alkaline porous refractory oxide. The preferred catalyst comprises between 5 and 15 wt.% V.sub.2 O.sub.5 on hydrogen mordenite or alumina. Hydrogen, carbon monoxide, light hydrocarbons, and ammonia present in the feed gas are not oxidized. The invention is especially contemplated for use in treating waste gases from geothermal steam power plants.

BACKGROUND AND SUMMARY OF THE INVENTION 
Current air pollution regulations in most industrialized parts of the world 
are very restrictive concerning the amounts of H.sub.2 S industry can 
discharge into the atmosphere. Los Angeles, for example, requires that no 
more than 10 ppmv be so discharged. The discharge requirements of 
SO.sub.2, however, are not nearly so restrictive. Los Angeles waste gas 
streams containing up to 500 ppmv SO.sub.2 can be safely discharged while 
Canada and Germany allow up to 2000 and 4000 ppmv, respectively. As a 
result, there is provided by law a strong incentive for industries engaged 
in such diverse activities as petroleum refining, meat packing, soap 
production, sewage treatment, electrical generation, and chemical 
production to convert the H.sub.2 S in their waste gas streams to SO.sub.2 
prior to atmospheric discharge. The manner in which this is presently 
accomplished is through the use of a stack gas incinerator, i.e., by 
blending sufficient natural gas or other fuel with the waste gas stream to 
provide a combustible mixture, and then burning the resultant mixture in 
the temperature range of 1350.degree.-1550.degree. F. at the point of 
discharge. 
With the advent of the energy crisis another incentive has been provided to 
industry--namely, that of saving expensive fuel. Ideally, therefore, it 
would be most desirable to oxidize the H.sub.2 S to SO.sub.2 
catalytically, without adding fuel. The development of a catalytic 
incinerator, however, has been hampered by the fact that waste gas streams 
containing H.sub.2 S usually also contain in uncombustible amounts such 
highly oxidizable components as CO, H.sub.2, and light hydrocarbons, 
which, if oxidized in a catalytic incinerator would release large 
quantities of heat and hence increase the operating temperature of the 
catalytic incinerator to undesirable levels. Consequently, most catalytic 
incinerators need cooling facilities which may necessitate as much energy 
input, and more maintenance requirements, than burning in a stack gas 
incinerator. 
From the preceding discussion, it is apparent that for a catalytic 
incinerator to be most effective it must be selective for the oxidation of 
H.sub.2 S to SO.sub.2. A major objective of the invention, therefore, is 
to provide a novel process for selectively incinerating H.sub.2 S in the 
presence of other normally oxidizable components. Another objective is to 
provide novel catalysts for effecting the selective incineration of 
H.sub.2 S to SO.sub.2. Another objective is to utilize the catalytic 
incineration process of the invention for treating vent gases emanating 
from geothermal power plants. 
The present invention is a revised version of a known catalytic 
incineration process largely abandoned by the art. In United Kingdom Pat. 
No. 733,004, published Jan. 23, 1953, it is taught that a catalyst 
composed of 5-10 weight-percent V.sub.2 O.sub.5 on alumina is effective in 
reducing H.sub.2 S concentrations in Claus tail gas streams by converting 
the same to SO.sub.2. However, no mention is made therein that said 
catalyst is selective for the incineration of H.sub.2 S to SO.sub.2 in the 
presence of H.sub.2, CO, light hydrocarbons, or ammonia. 
By the process of the present invention it has been found that catalysts 
composed of 5-15 weight-percent V.sub.2 O.sub.5 on alumina, hydrogen 
mordenite, or any other non-alkaline, porous refractory oxide are very 
selective for the oxidation of H.sub.2 S to SO.sub.2 in the presence of 
H.sub.2, CO, light hydrocarbons, or ammonia. Even more surprisingly, it 
has been found that these normally oxidizable components of H.sub.2, CO, 
light hydrocarbons, and ammonia remain unoxidized even when excess air is 
utilized to perform the H.sub.2 S to SO.sub.2 conversion. Furthermore, 
conversions of H.sub.2 S to SO.sub.2 are essentially 90 to 100 percent 
complete and space velocities varying in the wide range of 1,000 to 
100,000 GHSV can be utilized. Operating temperatures can vary from a 
minimum of 300.degree. to a maximum of about 900.degree. F. Also, no 
detectable amount of SO.sub.3 is formed when hydrogen is a component of 
the feed gas or when temperatures below about 500.degree. F. are utilized 
when hydrogen is not a component of the feed gas. 
All gas space velocity data herein are reported in terms of volumes of gas 
(calculated at one atmosphere and 60.degree. F.) passing through one 
volume of catalyst per hour.

DETAILED DESCRIPTION OF THE INVENTION 
This invention is particularly concerned with the selective oxidation of 
H.sub.2 S to SO.sub.2 in a feed gas comprising H.sub.2 S and any of the 
relatively inert inorganic gases such as nitrogen, carbon dioxide, water 
vapor, argon, helium, neon, etc., and/or any of the normally oxidizable 
components such as H.sub.2, CO, light hydrocarbons, and ammonia. As used 
herein, the term "light hydrocarbons" refers to those saturated 
hydrocarbons containing no more than six carbon atoms. Many other gases 
may be present in the feed gas but, as those skilled in the art will 
readily understand, the remaining gaseous components (except for sulfur 
vapor as will be shown hereinafter) should be chemically inert under the 
conversion conditions specified herein, and should not adversely affect or 
poison the catalyst. The process is particularly contemplated for the 
catalytic oxidation of H.sub.2 S present in waste gas streams which 
discharge from petroleum refineries, sewage plants, meat packing plants, 
geothermal power plants, soap factories, and chemical manufacturing 
plants. Additionally, the process is useful in situations wherein it is 
desired to reduce the H.sub.2 S content of sour natural gases, sour 
refinery gases, etc. 
In general, the process of the invention is suitable for treating feed 
gases containing 10 ppmv-10 mole % H.sub.2 S, usually 10 ppmv-5 mole % 
H.sub.2 S, and at least about 100 ppmv of one or more components selected 
from the class consisting of hydrogen, carbon monoxide, ammonia, and light 
hydrocarbons. The process is most advantageously utilized for treating 
"sour" gases containing at least about 50, usually about 100 ppmv - 5 mole 
% of H.sub.2 S, and at least about 100, usually at least about 500 ppmv, 
of at least one oxidizable component selected from the class consisting of 
hydrogen, carbon monoxide, ammonia, and light hydrocarbons. Other 
components found in the feed gases usually consist of one or more of: 
CO.sub.2, N.sub.2, H.sub.2 O, O.sub.2, SO.sub.2, and COS. 
The basic process can be more readily understood by reference to the 
accompanying FIG. 1. A feed gas directed through lines 1, 2, 4, and 5 is 
blended with an oxygen-containing gas, preferably air, from line 6 so that 
the resultant mixture in conduit 7 preferably contains more than the 
stoichiometric amount of oxygen necessary to convert the H.sub.2 S therein 
to SO.sub.2. This mixture in conduit 7 is passed to a suitable preheater 8 
to heat the gases to at least about 300.degree. F., preferably to some 
temperature between about 300.degree. and 900.degree. F. The heated 
mixture is then fed through lines 9 and 10 to the catalytic incinerator 11 
at a space velocity of at least 100 v/v/hr, usually between 1,000 and 
100,000 v/v/hr, and preferably between about 2,000 and 20,000 v/v/hr when 
a temperature in the 600.degree.-900.degree. F. range is used and between 
about 1000 and 5000 v/v/hr when a temperature in the 
300.degree.-800.degree. F. range is used. The gases contact a catalyst in 
incinerator 11, which catalyst comprises one or more vanadium oxides 
and/or sulfides supported on a non-alkaline, porous refractory oxide. This 
catalyst, described in fuller detail hereinafter, is highly active for the 
conversion of H.sub.2 S to SO.sub.2, and, depending upon the space 
velocity and temperature utilized, can effect H.sub.2 S conversions at 
least about 80%, usually between about 90 and 100%, complete. Furthermore, 
the catalyst is so selective for the oxidation of H.sub.2 S that such 
highly oxidizable components as H.sub.2, CO, ammonia, and light 
hydrocarbons, any or all of which might be present, remain almost 
completely unoxidized, thus greatly reducing the overall amount of heat 
generated. 
As those skilled in the art will realize, the proportion of H.sub.2 S 
converted to SO.sub.2 in incinerator 11 is dependent upon the temperature 
maintained therein and the space velocity utilized, with the conversion 
increasing with increasing temperature and/or decreasing space velocity. 
For a 90% conversion of H.sub.2 S to SO.sub.2, it will usually be found 
that any temperature between 600.degree. and 900.degree. F. and a space 
velocity up to about 10,000 v/v/hr will suffice. Similar conversions are 
obtainable at temperatures between 300.degree. and 500.degree. F. when the 
space velocity is maintained below about 2500 v/v/hr and at temperatures 
between 500.degree. and 600.degree. F. when the space velocity is 
maintained below about 5,000 v/v/hr. For at least an 80% conversion of 
H.sub.2 S to SO.sub.2, a temperature in the 600.degree.-900.degree. F. 
range is suitable, with increasingly higher temperatures in this range 
being necessary for increasingly higher space velocities above 10,000 
v/v/hr. An 80% or better conversion is obtainable at temperatures between 
300.degree. and 600.degree. F. with a space velocity less than 10,000 
v/v/hr, again with increasingly higher temperatures being necessary for 
increasingly higher space velocities approaching 10,000 v/v/hr. 
A unique feature of the invention is that, when the feed gas contains 
H.sub.2, CO, NH.sub.3, light hydrocarbons, or combinations thereof, 
essentially none of these normally oxidizable components is oxidized in 
incinerator 11, even when temperatures between 600.degree.-900.degree. are 
used. This is considered surprising inasmuch as, based on thermodynamic 
equilibria calculations, these components should be oxidized prior to 
H.sub.2 S at temperatures in the 300.degree.-900.degree. F. range. 
Evidently, however, the rates of reaction for the oxidation of H.sub.2, 
CO, NH.sub.3, and light hydrocarbons at temperatures less than 900.degree. 
F. and in the presence of a vanadium oxide and/or sulfide catalyst as 
described are slower than that for H.sub.2 S. 
Another unique feature of the invention lies in the fact that, although a 
vanadia catalyst is used to convert the H.sub.2 S in the feed gas to 
SO.sub.2, at temperatures below 900.degree. F. the use of excess air fed 
via line 6 does not result in the production of SO.sub.3, provided the 
feed gas contains H.sub.2 in proportions of at least about 100 ppmv, and 
preferably in a proportion of at least about 1.0 mol %. This result is 
considered surprising because vanadia catalysts are used commercially to 
convert SO.sub.2 to SO.sub.3 in the sulfuric acid industry. When treating 
feed gases containing essentially no H.sub.2, either the operating 
temperature of incinerator 11 should be maintained below about 500.degree. 
F., or only about 0.8 to 1.05 times the stoichiometric amount of air 
should be fed via line 6, or H.sub.2 should be blended in with the air fed 
via line 6, or some combination of these operating procedures should be 
done to prevent the formation of more than about 10 ppmv of SO.sub.3. 
The reaction in the catalytic incinerator 11 is highly exothermic: 
EQU 2H.sub.2 S+30.sub.2 .fwdarw.2SO.sub.2 +2H.sub.2 O (I) 
(.DELTA.h.sub.400.degree. f. =-220,275 btu/lb-mole H.sub.2 S oxidized) 
and the temperature in said incinerator will rise depending on the quantity 
of H.sub.2 S present in, and the heat capacity of, the entering feed 
gas-oxidant mixture. For feed gas streams containing only small quantities 
of H.sub.2 S the temperature rise will be relatively insignificant, thus 
permitting simple adiabatic operation, with the exit gas temperature being 
held at between about 350.degree. and about 900.degree. F. without means 
for cooling. For feed gas streams containing larger quantities of H.sub.2 
S, however, the generation of heat via Reaction (I) can become a problem. 
In one embodiment, therefore, the gases in the reactor are cooled 
externally by indirect heat exchange so that the conversion of H.sub.2 S 
to SO.sub.2 takes place more or less isothermally; in this embodiment, the 
feed gas-oxidant mixture can be preheated to any desired isothermally-held 
incinerator temperature between about 300.degree. and 900.degree. F., 
preferably between about 500.degree. and 850.degree. F. 
In commercial practice, however, it is a substantial impossibility to 
maintain true isothermal conditions. Hence, if the temperature, H.sub.2 S 
content, and heat capacity of the influent gases are such that adiabatic 
operation would result in temperatures exceeding about 900.degree. F., one 
or more internal temperature control measures may be adopted. In a 
preferred embodiment, the influent gases are diluted with sufficient 
additional oxidant gas that, when the total mixture is preheated to 
between about 300.degree. and about 750.degree. F., an exit gas 
temperature between about 500.degree. and about 900.degree. F., preferably 
between about 600.degree. and 850.degree. F., is maintained. This dilution 
can be accomplished simply by adding more oxidant gas via line 6. 
Alternatively, a combined dilution-quenching technique may be utilized by 
admitting cool air at one or more downstream points in the incinerator via 
supply line 6a. If desired, a portion of the purified gas to be discharged 
to the atmosphere via line 12 can be recycled to line 10 via blower 13 and 
line 14 to provide all or a portion of the desired dilution. This latter 
alternative has the additional advantages of at least partially heating 
the fresh influent gases, thus reducing the load on preheater 8, and of 
allowing for further conversion of any H.sub.2 S remaining in the recycled 
gases. 
Although it is within the scope of the invention to blend at least 80% of 
the amount of oxygen necessary for the conversion of H.sub.2 S to SO.sub.2 
with the feed gas, it is highly preferable in carrying out the oxidation 
that at least stoichiometric oxygen for Reaction (I) be used. If less than 
the stoichiometric amount is utilized, then the formation of sulfur by the 
Claus reaction: 
EQU 2H.sub.2 S+SO.sub.2 .revreaction.3S+2H.sub.2 O (II) 
becomes a distinct possibility because incineration of H.sub.2 S to 
SO.sub.2 is incomplete. The discharge of gaseous elemental sulfur may then 
violate other air pollution laws. Also, if the sulfur vapor were to exceed 
its dewpoint, it would condense on the catalyst and incinerator surfaces. 
This would then result in deactivation of the catalyst and, possibly, 
plugging of the incinerator. Lastly, some H.sub.2 S would remain unreacted 
and the purpose of the incinerator might be defeated. Thus, although the 
use of less than stoichiometric oxygen may be found feasible or 
utilitarian in some instances, it is recommended that oxygen, preferably 
in the form of air, should be used in any excess amount above that 
required for Reaction (I), usually up to about 5.0 times stoichiometric. 
Preferably between about 1.1 and 5.0 times the stoichiometric amount is so 
used. 
One very desirable feature of the invention is that Reaction (I) has an 
extremely favorable equilibrium constant (i.e., K.sub.p 400.degree. 
F.=4.98.times.10.sup.52) for the production of SO.sub.2. As a result, the 
process is most useful for treating feed gases containing substantial 
amounts of water vapor. 
There are several situations in which it is foreseen that control of the 
effluent gas SO.sub.2 concentration and/or temperature is, if not 
necessary, at least desirable. For example, if the H.sub.2 S concentration 
of the feed gas-oxidant mixture is excessive, the product SO.sub.2 
concentration may itself violate air pollution laws. Also, in the absence 
of means for external cooling, the processing of gases containing high 
concentrations of H.sub.2 S would, because of the exothermic nature of 
Reaction (I), result in effluent gas temperatures in excess of the desired 
maximum operating temperature. At temperatures above about 500.degree. F. 
when no H.sub.2 is present or at temperatures above about 900.degree. F. 
when H.sub.2 is present, some SO.sub.2 produced in incinerator 11 may be 
converted to SO.sub.3, which, in addition to being a more noxious air 
pollutant than either H.sub.2 S or SO.sub.2, might also attack the 
catalyst support. Also, if hydrogen is present, operating at above 
900.degree. F. may bring about a combination of hydrogen with oxygen to 
form water and/or a combination of hydrogen with SO.sub.2 to form the 
original starting material, H.sub.2 S: 
EQU so.sub.2 +3h.sub.2 .fwdarw.h.sub.2 s+2h.sub.2 o (iii) 
fortunately, none of these problems arises when the process is operated to 
control both the temperature and the SO.sub.2 concentration in the 
effluent gas, as will now be explained. 
In a preferred embodiment of the invention, simultaneous control of 
temperature and SO.sub.2 concentration in the exit gas is effected by 
diluting the feed gas with air via line 6, recycle gases via line 14, 
externally derived gases (not referenced in FIG. 1), or any combination 
thereof, so that the resultant mixture entering the incinerator via line 
10 contains some predetermined maximum H.sub.2 S concentration. 
(Alternatively, all or a portion of the oxygen can be added via line 6a 
instead of line 6 to achieve the same ultimate objectives of control of 
exit gas temperature and SO.sub.2 concentration). Since the catalyst is 
selective for the oxidation of H.sub.2 S, any adiabatic temperature rise 
in the incinerator is due almost exclusively to the exothermic nature of 
Reaction (I). Thus, assuming the heat capacity of the gases within the 
incinerator remains relatively constant during the oxidation of the 
H.sub.2 S, the temperature rise therein is directly proportional to the 
concentration of H.sub.2 S in the feed gas-oxidant mixture: 
EQU .sup.T exit-.sup.T inlet=CM 
(where M is the H.sub.2 S concentration in mole % and C is the 
proportionating constant, hereinafter termed the temperature rise 
coefficient, in .degree.F./mole%). Therefore, in the preferred embodiment, 
the feed gas-oxidant mixture is heated to some temperature between about 
300.degree. and 750.degree. F. such that a predetermined maximum 
concentration of H.sub.2 S in said mixture will produce a predetermined 
maximum exit gas temperature in the range of about 500.degree.-900.degree. 
F. When operated in this manner, the process normally results in 
incineration of at least about 95%, and usually between about 98 and 100%, 
of the available H.sub.2 S to SO.sub.2. The following hypothetical Example 
is illustrative of the points discussed above. (All Examples herein are 
illustrative only and are not intended to be limiting). 
EXAMPLE I 
A Canadian industry must discharge a hydrogenated Claus tail gas 
(hydrogenated to convert all sulfur compounds to H.sub.2 S as described, 
e.g., in Canadian Pat. No. 918384). The gas contains 3 mole % H.sub.2 S 
and a substantial amount of hydrogen. To avoid the production of SO.sub.3, 
or H.sub.2 S (by Reaction (III)), it is specified that the exit gas 
temperature of the incinerator be no more than 750.degree. F. It is also 
necessary to maintain the exit gas SO.sub.2 concentration at 2000 ppmv, 
the maximum permissible discharge limit. Thus, air must be added to the 
feed gas stream such that the ratio of feed gas to air in the resultant 
mixture is 1:14. Assuming the temperature rise coefficient of this mixture 
is 205.degree. F./mole % H.sub.2 S oxidized to SO.sub.2, and assuming 100% 
conversion of H.sub.2 S to SO.sub.2, the preheater need only heat the 
mixture to 709.degree. F. (750 -T=205.times.0.2; T=709). The preheated 
mixture of feed gas and air enters the incinerator and contacts a catalyst 
comprising 10 weight % V.sub.2 O.sub.5 on hydrogen mordenite, which 
catalyst is effective for the exothermic oxidation of H.sub.2 S to 
SO.sub.2. Once the exit gas achieves a temperature of 750.degree. F., a 
portion of it may be recycled back to be blended with the feed gas, and 
the air feed suitably reduced, so that the H.sub.2 S concentration of the 
gases entering the incinerator is still maintained at 0.2 mole %. However, 
for best results, the reduction in air feed must not be so extensive that 
only stoichiometric or less oxygen (for Reaction (I)) is blended into the 
feed gas stream. 
In many cases, especially in the case of feed gases containing more than 
about 400 ppmv of H.sub.2 S, it may be desirable prior to incineration to 
oxidize a portion of the H.sub.2 S to elemental sulfur. In FIG. 1 this is 
accomplished by adjusting valves 3 and 16 so that all or a portion of the 
feed gas is directed through line 15, valve 16 and lines 17 and 18 to 
preheater 19. Prior to entering said preheater, however, an oxygen 
containing gas, preferably air, is blended with the feed gas via line 20. 
The amount of air so introduced is any amount less than the stoichiometric 
amount necessary for the oxidation of H.sub.2 S in the feed gas to 
SO.sub.2 via Reaction (I); however, in the preferred operation, air is 
supplied via line 20 in substantially the exact stoichiometric amount 
necessary for the oxidation of said H.sub.2 S to sulfur via: 
EQU 2H.sub.2 S+O.sub.2 .fwdarw.2S+2H.sub.2 O (IV) 
since Reaction (IV) is known to proceed, at least in part, by Reaction (I) 
followed by Reaction (II), and since the latter is equilibrium-limited by 
water vapor, sulfur production is enhanced if the feed gas is 
substantially dehydrated. Hence, an optional condenser 21, or other 
dehydrating means, is provided to remove water via line 22. The amount of 
water so removed depends upon the operating characteristics of the 
condenser 21 and the amount of feed gas processed through valve 23 versus 
the amount allowed to pass through valve 16. Preferably, however, all of 
the feed gas is fed via valve 23 to condenser 21 to remove sufficient 
water so that the feed gas entering line 17 contains less than about 15%, 
preferably less than about 10% by volume, of water vapor. 
The mixture of feed gas and air is fed to preheater 19 wherein it is heated 
to a temperature of at least about 250.degree. F. but no more than about 
325.degree. F., and then fed via line 24 to oxidation reactor 25 at a 
space velocity between about 250 and 2000 v/v/hr, but preferably between 
about 800 and 1000 v/v/hr. The gases contact a catalyst in the oxidation 
reactor 25 at a temperature in the range of about 250.degree.-450.degree. 
F., but preferably in the range of about 300.degree.-400.degree. F. The 
preferred catalyst is one which comprises reduced vanadium pentoxide 
(V.sub.2 O.sub.5), between about 5 and 15% by weight, on alumina; however, 
any of the catalysts hereinafter described in more detail for use in 
catalytic incinerator 11 can be used in oxidation reactor 25. When 
utilized in oxidation reactor 25 under the preferred conditions 
hereinbefore specified, these catalysts are capable of effecting an air 
oxidation of H.sub.2 S to sulfur of at least 50%, and preferably at least 
90%, complete, and of effecting the same without also oxidizing 
significant amounts of H.sub.2, CO, NH.sub.3, and light hydrocarbons, any 
or all of which may be present in the feed gas. In addition, they also 
retain these desired properties of high activity and selectivity for 
extended periods of time; their estimated life when processing suitable 
feed gases under the conditions hereinbefore specified is considered to be 
at least about one year. 
The gases leaving the oxidation reactor 25 are passed via line 26 to sulfur 
condenser 27 which lowers the temperature of said gases to preferably 
between about 250.degree. and 270.degree. F. As the sulfur condenses, it 
is removed via line 28. The remaining noncondensable off-gases are then 
sent via lines 29 and 30 to be blended in line 5 with that portion of the 
feed gas, if any, which by-passes reactor 25 via line 4. This mixture of 
gases is then incinerated as previously described. 
If desired, a portion of the gases leaving the sulfur condenser 27 via line 
29 can be recycled by blower 31 through line 32, manifold line 33, and 
lines 34 and/or 34a directly into the oxidation reactor 25. These recycle 
gases can also be conducted through line 35 into line 18 to admix with the 
gases entering the preheater 19. The purpose in recycling these gases is 
primarily to prevent sulfur deposition on the catalyst by so diluting the 
H.sub.2 S in the gases entering, or already in the oxidation reactor 25, 
that, even if it were all oxidized to sulfur, the sulfur dewpoint of said 
gases would still be maintained below the operating temperature of 
oxidation reactor 25. Secondarily, Reaction (IV) being highly exothermic, 
these recycle gases can maintain the oxidation temperature rise in 
oxidation reactor 25 within the narrow 250.degree.-450.degree. F. range 
recited hereinbefore by: (1) injecting (250.degree.-270.degree. F.) quench 
gases directly into oxidation reactor 25 via lines 34 and/or 34a, and/or 
(2) by diluting via line 35 the H.sub.2 S concentration in the feed gases 
prior to entering the preheater 19 in a manner and for results similar to 
those hereinbefore set forth in Example I. With respect to this second 
temperature control method, the only demonstrable difference between it 
and that described for incinerator 11 is that for any mixture of gases 
entering oxidation reactor 25, the temperature rise coefficient is 
dependent upon the heat of reaction of Reaction (IV), rather than that of 
Reaction (I). 
In practicing the sulfur recovery-incineration process shown in FIG. 1, it 
should be noted that some sulfur vapor may well be present in the feed gas 
entering the incinerator 11. Because the catalyst employed therein 
oxidizes sulfur vapor (as well as H.sub.2 S) to SO.sub.2, it is necessary 
in the preferred method of operation to blend at least sufficient oxygen 
via line 6 or 6a for the oxidation of both the sulfur vapor and H.sub.2 S. 
Normally, however, the sulfur vapor concentration in such gases is 
relatively small, or even insignificant, and thus will play essentially no 
role in the commercial operation of the process. 
Both the incineration and oxidation operations described above are 
preferably carried out at about atmospheric pressure, but pressures 
ranging between about 5-500 psia are contemplated. 
The most critical aspect of the invention resides in the nature of the 
catalyst utilized in the incinerator. In general, catalysts comprising one 
or more vanadium oxides and/or sulfides supported on a non-alkaline porous 
refractory oxide are operative. Suitable non-alkaline supports, as defined 
herein, include such refractory oxides as silica, alumina, silica-alumina, 
silica-magnesia, zirconia, silica-zirconia, titania, silica-titania, 
silica-zirconia, titania, or combinations of the aforementioned materials. 
Acidic metal phosphates and arsenates such as aluminum phosphate, boron 
phosphate, chromium phosphate, rare earth phosphates, aluminum arsenate, 
etc., may also be used, as also may certain amorphous and crystalline 
aluminosilicate zeolites, including such naturally occurring zeolites as 
mordenite, erionite, stilbite, faujasite and the like (in their 
"non-alkaline" forms -- as hereinafter defined). Synthetic hydrogen "Y" 
zeolites having a silica-to-alumina (SiO.sub.2 /Al.sub.2 O.sub.3) ratio 
between about 4:1 and 6:1, and synthetic forms of the natural zeolites 
noted above can also be used with success. Preferred crystalline 
aluminosilicate zeolites, whether natural or synthetic, consist of silica 
and alumina in a ratio between about 4:1 and 100:1. Especially preferred, 
however, are those natural and synthetic crystalline aluminosilicate 
zeolites having a silica-to-alumina ratio between about 6:1 and 100:1, 
mordenite and erionite, particularly in the hydrogen or decationized 
forms, being found to be most suitable. 
The "non-alkaline supports" employed herein may be characterized as 
materials which contain no more than about 4 weight percent, preferably 
less than about 2 weight percent, of alkali metal or alkaline earth metal 
compounds, calculated as oxides, which compounds are sufficiently basic to 
form salts with anionic oxides of the active metal component, e.g., 
vanadates. Such salt formation is believed to be at least one 
alkali-induced transformation leading to rapid deactivation of the 
catalyst. Sodium zeolites are exemplary of such undesirable basic 
compounds. 
Alumina is a preferred support, particularly in the presence of large 
quantities of water vapor. However, it has also been discovered, as will 
be shown hereinafter in Examples IV and X, that in the presence of 
excessive amounts of SO.sub.2 and O.sub.2, alumina based catalysts appear 
to be susceptible to sulfation, and consequent gradual deactivation. 
Evidently, SO.sub.2 and O.sub.2 react on the catalyst surface to sulfate 
the catalyst, either directly or indirectly via the intermediate formation 
of SO.sub.3. (This discovery probably best explains the lack of 
commercialization of the process described in United Kingdom Pat. No. 
733,004 which teaches the use of catalysts comprising V.sub.2 O.sub.5 on 
alumina for H.sub.2 S incineration of Claus tail gases). Hence, although 
alumina based catalysts are operable in the wide range of conditions 
specified hereinbefore, their lives are probably somewhat limited when 
they are used to process feed gas-oxidant mixtures containing more than 
about 1 to 1.5 mole % H.sub.2 S. It is therefore recommended that when 
alumina based catalysts--or other sulfatable supported catalysts 
comprising silica-magnesia, zirconia, silica-zirconia, titania, 
silica-titania, silica-zirconia-titania, etc.,--are to be used for 
processing feed gas-oxidant mixtures containing more than about 1 mole % 
H.sub.2 S, that conditions be chosen for operation which reduce the 
likelihood of catalyst sulfation. Among these include lower operating 
temperatures, the use of externally derived diluent gases, and the use of 
oxygen or air in amounts at or just slightly above the stoichiometric (for 
Reaction (I)) amount required to convert all of the H.sub.2 S to SO.sub.2. 
The remaining catalyst supports hereinbefore mentioned have been found to 
be stable in the presence of SO.sub.3 or SO.sub.2 plus O.sub.2 and their 
use in environments containing such reactants is normally preferred, 
depending upon other environmental factors. Silica, for example, does not 
sulfate but because of its wellknown susceptibility to decomposition and 
volatilization in the presence of water vapor, it should not be used in 
environments wherein the water dew point can exceed about 120.degree. F. 
Likewise, amorphous aluminosilicates (unless steam stabilized so as to 
maintain a surface area above about 200 m.sup.2 /gm in the presence of 
steam) should not be used if the water dew point can exceed about 
150.degree. F. On the other hand, crystalline aluminosilicates having a 
silica-to-alumina mole-ratio between about 4:1 and 100:1, and particularly 
those having a silica-to-alumina ratio between about 6:1 and 40:1, are 
largely immune to attack by water vapor, SO.sub.3 or SO.sub.2 plus 
O.sub.2. Thus, hydrogen "Y" zeolite, hydrogen mordenite and hydrogen 
erionite are excellent examples of catalyst supports which will render 
long and useful service over a wide range of operating conditions. 
Hydrogen mordenite is especially preferred because of its substantial 
immunity to SO.sub.3 or SO.sub.2 plus O.sub.2 attack. Even when prepared 
in the wide silica-to-alumina ratios from about 10:1 to about 100:1, 
hydrogen mordenite is extremely SO.sub.3 -resistant. In ratios higher than 
about 40:1, however, the hydrogen mordenite tends to become unstable 
hydrothermally; consequently, the preferred catalyst support in the 
presence of SO.sub.3 (or SO.sub.2 plus O.sub.2) and/or water vapor is one 
composed of hydrogen mordenite with a silica-to-alumina ratio between 
about 10:1 and about 40:1. 
The foregoing supports are compounded as by impregnation, with from about 
0.2 to 30 weight percent, preferably 2 to 20 weight percent, of a vanadium 
promoter. Specifically, any oxide and/or sulfide of vanadium will perform 
satisfactorily. The preferred active metal component, however, is vanadium 
pentoxide (V.sub.2 O.sub.5) in proportions between about 1 and 30% by 
weight. Especially preferred, however, is a catalyst comprising between 2 
and 20 weight percent V.sub.2 O.sub.5, more preferably between about 5 and 
15 weight percent V.sub.2 O.sub.5. 
After being pelleted or extruded, the catalyst is subsequently dried and 
calcined at 800.degree.-1200.degree. F. for about 1-12 hours. If reduction 
is necessary (i.e., because the catalyst is to be utilized in oxidation 
reactor 25), it can be accomplished by passing a mixture of gases 
consisting of 10 mole % H.sub.2 S and 90 mole % H.sub.2 at a temperature 
of about 400.degree. F. and at a space velocity between about 400 and 600 
v/v/hour over the catalyst for about two hours. If a reduced catalyst is 
used in incinerator 11, it can effect the intended air oxidation of 
H.sub.2 S to SO.sub.2 ; however, the operating conditions in said 
incinerator 11 are such that the active metal promoter will eventually 
become oxidized and/or sulfided. 
One catalyst of the invention is prepared as follows: 
10% V.sub.2 O.sub.5 on alumina: 
200 gm of Al.sub.2 O.sub.3 (as hydrated spray-dried alumina) was soaked in 
a hot solution of 28.5 gm of NH.sub.4 VO.sub.3 in 500 ml water. The paste 
so formed was dried at 90.degree.-100.degree. F., remoistened and extruded 
through a 1/8 inch die, dried at 212.degree. F. and calcined at 
932.degree. F. for 3 hours. 
Under favorable circumstances this catalyst is known to be able 
successfully to incinerate H.sub.2 S with no measurable loss of activity 
after 30 days operation. Its useful life is considered to be about a year. 
An incineration of H.sub.2 S to SO.sub.2 between about 90 and 100% 
complete can be expected from this catalyst when utilized under the 
conditions shown in the following four Examples. (It should be noted that 
all feed and product compositions shown in these four Examples are 
reported on a dry mole-percent basis and that the water dew point of each 
of the feed gases, unless otherwise specified, was 55.degree. F.). 
EXAMPLES II AND III 
A waste gas having the dry composition shown in Table I was blended with 
excess air such that 1.5 times the stoichiometric amount of oxygen 
necessary for Reaction (I) was available as a reactant, and the resultant 
mixture was passed at a pressure slightly above atmospheric and at a space 
velocity of 1752 GHSV over a catalyst comprising 10% V.sub.2 O.sub.5 on 
Al.sub.2 O.sub.3, prepared substantially as above described. The 
incinerator temperature was maintained isothermally at 400.degree. F. No 
recycle or other diluent gases were used. A product gas of the indicated 
dry composition was obtained. Another waste gas having the dry composition 
shown in Table II was treated similarly except that an isothermally-held 
incinerator temperature of 350.degree. F. was used. A product gas having 
the dry composition shown in Table II was obtained. As shown in both 
Examples, essentially complete conversion of the H.sub.2 S to SO.sub.2 was 
effected and essentially no oxidation of H.sub.2, CO or CH.sub.4 occurred. 
TABLE I 
______________________________________ 
Mole % in Mole % in 
Gas Component Feed Product 
______________________________________ 
Hydrogen 5.3372 5.3371 
Carbon Monoxide 0.7407 0.8086 
Methane 0.0357 0.0352 
Nitrogen 87.6917 87.6628 
Oxygen 0.0126 0.0374 
Hydrogen Sulfide 0.0196 0.0006 
Argon 0.0389 0.0430 
Carbon Dioxide 6.0594 6.0332 
Methyl Mercaptan 0.0003 0.0004 
Carbonyl Sulfide 0.0055 0.0066 
Sulfur Dioxide 0.0186 0.0352 
Carbon Disulfide 0.0 0.0001 
Total Sulfur Compounds.sup.1 
0.0440 0.0430 
Overall H.sub.2 S Conversion = 96.94% 
______________________________________ 
.sup.1 Expressed as moles of SO.sub.2 or monatomic sulfur compounds. 
TABLE II 
______________________________________ 
Mole % In Mole % In 
Gas Component Feed Product 
______________________________________ 
Hydrogen 5.4118 5.4964 
Carbon Monoxide 0.8629 0.8661 
Methane 0.0360 0.0362 
Nitrogen 87.3931 87.3036 
Oxygen 0.0103 0.0583 
Hydrogen Sulfide 0.0066 0.0000 
Argon 0.0416 0.0439 
Carbon Dioxide 6.2357 6.1853 
Methyl Mercaptan 0.0003 0.0004 
Carbonyl Sulfide 0.0001 0.0011 
Sulfur Dioxide 0.0018 0.0088 
Carbon Disulfide 0.0001 0.0000 
Total Sulfur Compounds.sup.1 
0.0090 0.0103 
Overall H.sub.2 S Conversion = 100% 
______________________________________ 
EXAMPLE IV 
In seven different experimental runs, a feed gas-air mixture (water vapor 
dew point=68.degree. F.) having the average dry composition shown in Table 
III was passed over the 10% V.sub.2 O.sub.5 on Al.sub.2 O.sub.3 catalyst 
hereinbefore described. Each run was conducted at a different isothermally 
held temperature but in all other respects the runs were identical. No 
recycle or other diluent gases were used. Other pertinent data concerning 
the runs were as follows: Pressure=3-15 in. H.sub.2 O (above atmospheric); 
GHSV=4189; Excess Air Available=1.5 times stoichiometric (for Reaction 
(I)). The results were as follows: 
TABLE III 
__________________________________________________________________________ 
Run No. 1 2 3 4 5 6 7 
Temperature, .degree. F. 
402 503 604 700 803 854 902 
Component Feed 
__________________________________________________________________________ 
H.sub.2 mol % 
16.67 16.73 17.10 16.90 16.32 16.07 16.13 13.44 
CH.sub.4 mol % 
12.13 12.22 12.23 12.36 12.47 12.41 12.49 13.04 
N.sub.2 mol % 
11.71 11.63 11.80 11.95 11.32 11.46 12.14 12.39 
O.sub.2 mol % 
2.82 2.21 0.86 0.75 0.48 0.44 0.23 0.00 
Ar mol % 0.13 0.14 0.13 0.14 0.14 0.14 0.14 0.15 
CO.sub.2 mol % 
55.28 56.17 55.83 55.79 56.87 57.01 56.69 59.33 
H.sub.2 S ppmv 
12234 4579 227 23 50 33 22 6328 
CH.sub.3 SH ppmv 
13.6 15 0 0 0 13 0 15 
COS ppmv 18.3 9 9 12 24 29 21 683 
SO.sub.2 ppmv.sup.2 
152 3441 12518 13092 12926 13244 13455 5819 
CS.sub.2 ppmv 
5.6 4 8 5 3 7 5 8 
Total S 
Compounds, ppmv.sup.1,2 
12430 8051 12771 13137 13001 13333 13408 12861 
% H.sub.2 S Conversion 
62.6 98.14 99.812 
99.591 
99.730 
99.820 48.3 
__________________________________________________________________________ 
.sup.1 Expressed as ppmv SO.sub.2 or ppmv monotomic sulfur compounds. 
.sup.2 The slight increase of total sulfur compounds is due to analytical 
errors in determining SO.sub.2 ; SO.sub.2 values should be somewhat lower 
 
It is seen from the foregoing that a conversion of H.sub.2 S to SO.sub.2 at 
least 98% complete is effected whenever the exit gas temperature of the 
incinerator is maintained between about 500.degree. and 850.degree. F. 
Also, a conversion between 99 and 100% complete is consistently obtained 
when the exit gas temperature is maintained between 600.degree. and 
850.degree. F. The high content of H.sub.2 S in the product gas from Run 7 
apparently means either that, when the oxygen becomes depleted, hydrogen 
begins to combine with SO.sub.2 to reform H.sub.2 S (Reaction III), or 
that at about 900.degree. F. hydrogen begins to react with O.sub.2 to form 
water, thus depleting the O.sub.2 available for oxidizing H.sub.2 S. In 
any event it is apparent that temperatures in excess of 900.degree. F., at 
least with the instant catalyst, result in some oxidation of H.sub.2 to 
water and some reaction of CO.sub.2 with H.sub.2 S to form COS. Lastly, it 
is concluded that essentially no SO.sub.3 forms at temperatures below 
about 900.degree. F. because any available hydrogen would reduce the 
SO.sub.3 to SO.sub.2 and water; since no loss in hydrogen is found below 
900.degree. F. in Table III, no demonstrable evidence of SO.sub.3 
production is found. This result is considered surprising inasmuch as 
vanadia catalyts used in the sulfuric acid industry are known to be very 
active for oxidizing SO.sub.2 to SO.sub.3 even at temperatures as low as 
750.degree. F. 
EXAMPLE V 
In a run to demonstrate the effectiveness of the combined sulfur 
recovery-incineration process shown in FIG. 1 and described in more detail 
hereinbefore, a waste gas was utilized having the following dry feed 
composition in mole %: 
______________________________________ 
H.sub.2 5.5380 Ar 0.0412 
CO 0.7965 C0.sub.2 6.2010 
CH.sub.4 0.0367 CH.sub.3 SH 0.0004 
N.sub.2 87.3190 COS 0.0011 
O.sub.2 0.0093 SO.sub.2 0.0164 
H.sub.2 S 0.0403 CS.sub.2 0.0 
Total Sulfur Compounds.sup.1 
0.0582 
______________________________________ 
.sup.1 Expressed as moles of SO.sub.2 or monatomic sulfur compounds 
This feed gas was blended with air such that a stoichiometric amount of 
oxygen (for Reaction (IV)) was available as a reactant. The resultant 
mixture was fed at 325.degree. F. and 876 GHSV to an oxidation reactor 
containing a catalyst of the same composition as those used in Examples II 
through IV herein except that it was reduced with a reducing gas mixture 
of 90% H.sub.2 -10% H.sub.2 S passed over said catalyst at a temperature 
of about 400.degree. F. and at a space velocity of 500 v/v/hour for about 
2 hours. The gases within the oxidation reactor were maintained at about 
325.degree. F. by external cooling means. The gases leaving the oxidation 
reactor were passed through a sulfur condenser which cooled the gases to 
260.degree. F. and removed sulfur. No recycle gases were used for 
temperature control or for dilution of sulfur vapors. The off gas from the 
sulfur condenser had the dry composition shown in the first column of 
Table II and was further treated as described in Example III. The results 
obtained were those shown in the second column of Table II. 
Each of the following three Examples describes a preferred catalyst useful 
in the incineration and oxidation steps. 
EXAMPLE VI 
600 gm Zeolon, a commerical synthetic sodium mordenite manufactured by the 
Norton Company, was slurried in 5000 ml 1.0 N HCl at room temperature for 
60 minutes. It was then filtered and the treatment was repeated on the 
filter cake. The filter cake from the second treatment was slurried in hot 
1.0 N HCl (73.degree. C.) for one hour, then filtered, and finally washed 
on the filter with four 1000 ml washes of hot water. After the filter cake 
was dried, the Na.sub.2 O content was 0.57% by weight (about 93% exchanged 
to the hydrogen form). The hot treatment was repeated twice more for 45 
minutes each, after which time the Na.sub.2 O level was 0.21% by weight 
(97.5% exchanged). The amount of aluminum extracted was relatively small, 
so the product had a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of 11.5 compared to 
the original ratio of 10. 
An amount of the dried hydrogen mordenite, corresponding to 225 gm of 
anhydrous powder, was mulled together with 424 gm of a silica hydrogen 
(containing about 6% SiO.sub.2 or 25 gm of anhydrous silica) and 36.1 gm 
of NH.sub.4 VO.sub.3 (or 27.8 gm of V.sub.2 O.sub.5). The mixture was 
dried during mulling with a flow of hot air until it was of extrudable 
consistency. It was then extruded through a 1/8-inch die, dried, and 
calcined at 932.degree. F. for 3 hours. The product containing 10% by 
weight of V.sub.2 O.sub.5 had excellent physical properties and had a deep 
golden color. 
EXAMPLE VII 
A silica hydrogel was prepared in a manner similar to that used for the 
preparation of the hydrogel binder of Example VI. Two solutions (A) and 
(B) were prepared as follows: 
(A) 70 ml of concentrated (96%) H.sub.2 SO.sub.4 was diluted to 2500 ml 
with deionized water and cooled to 10.degree. C.; 
(b) 655 ml of 41 Be commercial sodium silicate (sp. gr. 1.394, 28.65 wt. % 
SiO.sub.2 and 8.90 wt. % Na.sub.2 O) was diluted to 2500 ml with deionized 
water and cooled to 10.degree. C. When equal volumes of (A) and (B) were 
mixed, the pH was too low for rapid gelation, so 3.0 gm NaOH was dissolved 
in solution (B). 
Solution (B) was poured rapidly into Solution (A); with stirring and after 
41/2 minutes the mixture set to a vibrant hydrogel. After syneresis 
overnight, the hydrogel was cut into 1/2- to 1-inch pieces and placed on a 
large Buchner funnel. It was washed free of sodium by soaking in 0.3 N 
HNO.sub.3 for half an hour, followed by draining and repeating of this 
sequence four times. The product so formed was then washed with water in 
the same way for a total of five times. 
The hydrogel was partially dried and then mulled with enough NH.sub.4 
VO.sub.3 to give 10% by weight of V.sub.2 O.sub.5 and 90% by weight of 
SiO.sub.2 in the final calcined product. The moisture content of the 
mulled mixture was adjusted until an extrudable product was formed. It was 
then extruded, dried, and calcined as in Example VI. 
EXAMPLE VIII 
An aluminum phosphate hydrogel was prepared substantially as described in 
Example IV of U.S. Pat. No. 3,147,227. A slight excess of Al.sub.2 O.sub.3 
(5-10%) remained in the preparation in order to preserve a high surface 
area. This hydrogel was combined with 10% V.sub.2 O.sub.5 as in Example 
VII and finished in the same way. 
The following Example demonstrates the ability of the catalyst of Example 
VI to oxidize H.sub.2 S to SO.sub.2. 
EXAMPLE IX 
In seven different experimental runs, a feed gas-air mixture (water vapor 
dew point=68.degree. F.) having the average dry composition shown in Table 
IV was passed over the catalyst prepared as described in Example VI. Each 
run was conducted at a different isothermally held temperature but in all 
other respects the runs were identical. No recycle or other diluent gases 
were used. Other pertinent data concerning the runs were as follows: 
Pressure=3.5-5.3 in. H.sub.2 O (above atmospheric); GHSV-4189; Excess Air 
Available=1.5 times stoichiometric (for Reaction (I)). 
The results obtained are summarized in columns 1 through 7 of Table IV. It 
was observed that results with this catalyst with respect to percent 
H.sub.2 S oxidized were similar to those produced by the alumina based 
catalyst of Example IV. Additionally, this catalyst appeared to perform 
better at high temperatures inasmuch as less COS was formed, less H.sub.2 
was oxidized and the oxidation of H.sub.2 S to SO.sub.2 was almost 
complete. (However, as will be explained more fully in Example XI, these 
results are probably not related as much to the performance of the 
catalyst as they are to the fact that oxygen was present in the product 
gas in this Example and none was available in run 7 of Example IV). Also, 
this example shows that the presence of NH.sub.3 in the feed gas had no 
noticeable effect upon the performance of the catalyst. 
TABLE IV 
__________________________________________________________________________ 
Run No. 1 2 3 4 5 6 7 
Temperature of Run, .degree.F. 
502 601 701 802 853 883 903 
Component Feed 
__________________________________________________________________________ 
H.sub.2, mol % 
16.48 16.94 16.61 15.59 16.34 15.78 15.62 15.82 
CH.sub.4, mol % 
12.03 12.19 12.39 12.58 12.34 12.50 12.77 12.56 
N.sub.2, mol % 
11.46 11.73 11.73 12.05 11.81 11.67 12.06 11.65 
O.sub.2, mol % 
2.79 0.99 0.55 0.09 0.41 0.41 0.35 0.14 
Ar, mol % 0.13 0.14 0.14 0.14 0.14 0.14 0.14 0.13 
CO.sub.2, mol % 
55.88 56.84 57.29 58.32 57.72 58.11 57.77 58.33 
H.sub.2 S, ppmv 
12059 316 27 108 26 23 16 26 
CH.sub.3 SH, ppmv 
13 0 0 0 0 4 0 15 
COS, ppmv 15 14 17 30 34 49 27 27 
SO.sub.2, ppmv.sup.2 
193 11306 12874 12271 12307 13826 12907 13594 
CS.sub.2, ppmv 
6 30 4 7 7 8 6 6 
NH.sub.3, ppmv 
500 -- -- -- -- -- -- -- 
Total S 
compounds, ppmv.sup.1,2 
12292 11696 12926 12423 12381 13918 12962 13674 
% H.sub.2 S Conversion 
-- 97.3796 
99.7761 
99.1044 
99.7844 
99.8093 
99.8673 
99.7844 
__________________________________________________________________________ 
.sup.1 Expressed as ppmv SO.sub.2 or ppmv monatomic sulfur compounds. 
.sup.2 The slight increase of total sulfur compounds is due to analytical 
errors in determining SO.sub.2 ; SO.sub.2 values should be somewhat lower 
 
The following Example shows how resistant the mordenite based catalysts are 
to sulfation. 
EXAMPLE X 
A 10% V.sub.2 O.sub.5 of alumina catalyst prepared in the manner set forth 
hereinbefore and a catalyst prepared as described in Example VI were each 
used to incinerate H.sub.2 S in a feed gas-air mixture (water vapor dew 
point=68.degree. F.) having the nominal feed compositions shown in Tables 
III and IV, respectively. After the alumina based catalyst had been 
continuously used for 8 days and the mordenite based catalyst for 18 days 
under identical operating conditions of: pressure 3.5-15 in. H.sub.2 O 
(above atmospheric); GHSV-4189; excess Air available=1.5 times 
stoichiometric (for Reaction (I)); operating temperature range 
--300.degree.-950.degree. F.; the catalysts were analyzed for sulfur 
content by means of an induction furnace analytical technique (ASTM D-1552 
modified for determination of sulfur in inorganic solids). The alumina 
based catalyst was found to contain 2.21% sulfur while the mordenite based 
catalyst contained only 0.54% sulfur. Since no sulfur could be leached 
from either catalyst by a carbon disulfide extraction, it was concluded 
that the sulfur was present in the catalysts as sulfate. Thus, although 
the mordenite based catalyst was used to incinerate H.sub.2 S for 10 more 
days of sustained operation than the alumina based catalyst, it was found 
to be sulfated less than 25% as much. 
The following Example illustrates the use of a silica based catalyst in the 
invention. 
EXAMPLE XI 
In four experimental runs utilizing a first feed gas-air mixture, and in 
three other runs utilizing a second feed gas-air mixture (all having a 
water vapor dew point--68.degree. F.), the respective gas mixtures were 
passed over the catalyst of Example VII (SiO.sub.2 gel base). The feed 
gases had the dry compositions designated first feed and second feed in 
Table V. Each run was conducted at a different isothermally held 
temperature but in all other respects the runs were identical. No recycle 
or other diluent gases were used. Other pertinent data concerning the runs 
were as follows: Pressure--5.4-8.0 in. H.sub.2 O (above atmospheric); 
GHSV--4189; Excess Air Available=1.5 times the stoichiometric amount (for 
Reaction (I)) in first feed and 2.0 times the stoichiometric amount (for 
Reaction (I)) in second feed. 
The results obtained are summarized in columns 1 through 7 of Table V. It 
was observed that results with this catalyst with respect to percent 
H.sub.2 S oxidized were similar to those obtained with the alumina based 
catalyst of Example IV and the mordenite based catalyst of Example IX. In 
addition, two other facts were apparent: 
(1) In comparing columns 4 and 7 of Table V it appears obvious that if 
oxygen is available in the product gas at temperatures above about 
900.degree. F., no H.sub.2 S is produced via Reaction (III) nor is any 
appreciable amount of COS formed. It appears likely that when less than 
about 2 times the amount of excess air required for Reaction (I) is 
present at temperatures in excess of 900.degree. F., the oxidation of 
H.sub.2 with O.sub.2 takes place to some extent in competition with 
Reaction (I). Once the oxygen is depleted, conditions evidently become 
favorable for Reaction (III). 
(2) Since 2.0 times the stoichiometric air was used to produce the results 
of column 7, it was surprising that no significant loss of hydrogen was 
detected. Also, no SO.sub.3 was produced even under temperature and 
oxidizing conditions most likely to lead to such a result. This conclusion 
was confirmed by the fact that when the product gases obtained from the 
experiment described herein were bubbled through a water bath no "SO.sub.3 
plume" was seen emanating therefrom. Similarly, no "SO.sub.3 plume" was 
found when the product gases obtained in the experiments of Examples IV 
and IX were bubbled through water baths. Hence, the process of the 
invention produces essentially no SO.sub.3, even when sufficient oxygen is 
available to oxidize at least some of the produced SO.sub.2 to SO.sub.3. 
TABLE V 
__________________________________________________________________________ 
Run No. 1 2 3 4 5 6 7 
Temperature of Run. .degree. F. 
503 703 883 953 703 883 953 
1st 2nd 
Component Feed Feed 
__________________________________________________________________________ 
H.sub.2, mol % 
15.59 
16.08 
15.04 
14.94 
11.44 
14.20 
14.42 
12.98 
11.55 
CH.sub.4, mol % 
12.09 
12.02 
12.44 
12.46 
13.28 
10.61 
10.82 
11.18 
N.sub.2, mol % 
11.65 
11.95 
11.81 
12.10 
12.54 
18.81 
19.33 
19.76 
20.33 
O.sub.2, mol % 
2.85 
1.04 
0.47 
0.12 
0.00 
4.74 
2.86 
2.43 
1.34 
Ar, mol % 0.13 
0.13 
0.14 
0.60 
0.15 
0.22 
0.22 
0.23 
0.24 
CO.sub.2, mol % 
56.39 
57.41 
58.72 
58.30 
61.36 
50.34 
51.19 
52.50 
54.14 
H.sub.2 S, ppmv 
12714 
431 23 20 9187 
10558 
22 21 23 
CH.sub.3 SH, ppmv 
9 2 0 0 8 4 0 0 0 
COS, ppmv 12 13 33 61 1437 
17 16 35 31 
SO.sub.2, ppmv.sup.2 
173 13252 
13770 
14641 
1693 
238 11524 
11720 
12144 
CS.sub.2, ppmv 
4 9 6 5 28 5 7 14 6 
NH.sub.3, ppmv 
500 -- -- -- -- 500 -- -- -- 
Total S 
compounds, ppmv.sup.1,2 
12916 
13716 
13838 
14732 
12381 
10827 
11576 
11804 
12210 
% H.sub.2 S Conversion 
-- 96.61 
99.82 
99.84 
27.74 
-- 99.79 
99.80 
99.78 
__________________________________________________________________________ 
.sup.1 Expressed as ppmv SO.sub.2 or ppmv monatomic sulfur compounds. 
.sup.2 The slight increase of total sulfur compounds is due to analytical 
errors in determining SO.sub.2 ; SO.sub.2 values should be somewhat lower 
 
EXAMPLE XII 
In another experimental run an H.sub.2 S-containing feed gas stream at a 
water vapor dew point of about 75.degree. F. was blended at 266.6 scc/min 
(dry basis as measured at 60.degree. F.) with (a) sufficient air, fed at 
the rate of 7.0 scc/min, to provide about 9.26 times the stoichiometric 
amount of oxygen necessary to convert the H.sub.2 S to SO.sub.2 and (b) an 
NH.sub.3 -containing gas produced by vaporizing an aqueous ammonia 
solution containing 8.78 g NH.sub.3 /l and having a pH of 10.9 at the rate 
of 6.1 ml/hr. The feed gas had a dry composition as shown in Table VI. The 
mixed blend of feed gas, air, and vaporized ammonia solution was passed at 
a pressure slightly above atmospheric into an incinerator containing a 
catalyst prepared as described in Example VI. The temperature of the 
incinerator was maintained isothermally at 700.degree. F. and the gases 
were passed therethrough at a space velocity of 4000 GHSV. The gaseous 
effluent obtained from the incinerator was cooled so as to condense water 
at 70.degree. F., thereby leaving a product gas of composition shown in 
Table VI. 
The experiment was continued over a 24-hour period. A total of 147 ml of 
aqueous ammonia solution was vaporized and blended with the feed gas 
stream while 148 ml of condensate was collected. The condensate had a pH 
of 7.3 and contained 8.78 g/l of ammonia, 12.1 g/l of dissolved SO.sub.2, 
and essentially no H.sub.2 S, thereby indicating that essentially all the 
H.sub.2 S had been converted to SO.sub.2 and that essentially all the 
ammonia that entered the incinerator had passed through the catalyst bed 
without being oxidized. Hence, the process of the invention is not only 
selective for oxidizing H.sub.2 S to SO.sub.2 in the presence of H.sub.2, 
CO, and light hydrocarbons, but also in the presence of ammonia. 
TABLE VI 
______________________________________ 
Component.sup.1 
Feed Gas.sup.2 
Product Gas 
______________________________________ 
H.sub.2, mol % 4.11 3.98 
CO.sub.2, mol % 
1.00 0.95 
N.sub.2, mol % 94.78 94.83 
O.sub.2, mol % 0.00 0.16 
CH.sub.4, ppmv 192 193 
H.sub.2 S, ppmv 
397 0 
Ar, ppmv 354 603 
CH.sub.3 SH, ppmv 
1 1 
COS, ppmv 5 10 
SO.sub.2, ppmv 99 10 
NH.sub.3, ppmv N.D..sup.3 42 
______________________________________ 
.sup.1 All values in Table VI were obtained by mass spectrometrical 
analysis except those for NH.sub.3, which were obtained by calculation. 
.sup.2 The composition data of the feed gas indicates the concentration o 
constituents therein prior to having the NH.sub.3 -containing gas blended 
therewith. 
.sup.3 Not determined. The ammonia concentration in the feed gas was 
believed to be less than 200 ppmv. An ammonia balance based on 200 ppmv i 
the feed gas would show that the total loss of ammonia through the 
incinerator was about 3.7%. 
The following Example compares the hydrolytic stability of a mordenite 
based catalyst and a silica based catalyst. 
EXAMPLE XIII 
A 10% V.sub.2 O.sub.5 -mordenite based catalyst prepared as described in 
Example VI, and a 10% V.sub.2 O.sub.5 on silica catalyst prepared as 
described in Example VIII were steamed at 850.degree. F. for 112 hours. 
Saturated steam was used. The physical characteristics of the catalysts 
after this severe hydrothermal treatment are shown in Table VI. 
TABLE VI 
______________________________________ 
Vanadia-Mordenite 
Vanadia-Silica 
Physical After After 
Characteristics 
Fresh Steam Fresh Steam 
______________________________________ 
Crushing Strengths, 
pounds per 1/8" 
7.0 6.3 2.7 2.3 
Surface Area, m.sup.2 /gm 
467 349 554 296 
______________________________________ 
In a specific embodiment of the invention, the H.sub.2 S in the vent gases 
emanating from geothermal power plants is incinerated. As shown in FIG. 2, 
these power plants send geothermal steam containing usually between about 
(by weight) 100-500 ppm H.sub.2 S, 100-800 ppm CH.sub.4 and 25-300 ppm 
H.sub.2, through lines 40 and 50 to a turbine 60. The exhausted steam is 
passed via conduit 70 to a contact condenser 80 wherein it is condensed by 
intimate intermingling with 40.degree.-150.degree. F. cooling water from 
lines 90 and 100. The resulting mixture is then routed through lines 110 
and 120 to a cooling tower 130, in which the heat absorbed by the cooling 
water is released to a cross or countercurrently flowing air stream. Off 
gases (i.e., air plus gases stripped from the cooling water in the cooling 
tower) are then emitted to the atmosphere via line 140. 
Only some of the H.sub.2 S in the exhausted steam is soluble in the cooling 
water; thus, a portion of H.sub.2 S is emitted from the cooling tower via 
line 140 and the remainder is withdrawn from the condenser with the other 
noncondensable gases. Normally, the H.sub.2 S from the condenser is 
discharged to the atmosphere with the other noncondensable gases by means 
of a jet ejector. By the process of this invention, however, these gases 
are sent by jet ejector 160 through lines 150, 1, 2, 4, and 5 to effect 
ultimate incineration of the H.sub.2 S contained in said gases by one of 
the embodiments hereinbefore described with reference to FIG. 1. 
Alternatively, prior to incineration, all or a portion of the 
noncondensable gases can be routed by jet ejector 160 to line 15 to be 
treated by one of the embodiments hereinbefore described with reference to 
FIG. 1, in which the oxidation reactor 25 converts to elemental sulfur at 
least 50%, and preferably 90%, of the H.sub.2 S contained in said 
noncondensable gases. In either case, the purified off gases can then be 
discharged from the incinerator 11 to the atmosphere via line 12. However, 
they are preferably conducted via conduit 170 to a conventional SO.sub.2 
scrubber 180 wherein SO.sub.2 is dissolved in an aqueous solvent and the 
remaining purified gases are discharged to the atmosphere through line 
200. 
A preferred aqueous medium for absorbing SO.sub.2 in SO.sub.2 scrubber 180 
is a portion of the cooling water from cooling tower 130, which portion 
may be diverted to scrubber 180 via line 240. If desired, caustic or lime 
can be added via line 190 to increase the absorbtion of SO.sub.2 in 
scrubber 180. However, since SO.sub.2 is partially soluble in aqueous 
solutions having a pH as low as 3.5, the cooling water, which desirably is 
maintained in the pH range of about 5.5-7.5, is preferably used without 
adding alkaline chemicals. 
Normally, the waste water from the SO.sub.2 scrubber 180 is discharged to 
waste via line 210 and 220. In the preferred mode of operation, however, 
at least a portion of this waste water is directed via lines 210, 230, and 
120 to cooling tower 130 to maintain the cooling water in the desired pH 
range of 5.5-7.5. It will be understood that geothermal steam normally 
contains some ammonia, which would build up in the cooling water, raising 
its pH to above 7.5, thereby creating potential scaling problems, 
especially if ground waters are used as partial make-up to the cooling 
water system. Thus, this embodiment of the invention relieves the 
geothermal power plant of reliance on chemicals for cooling water pH 
control. Additionally, if the waste water containing dissolved SO.sub.2 
aids in dropping the pH of the cooling water into the lower part of the 
5.5-7.5 pH range, e.g., 5.5-6.0, H.sub.2 S absorption by the cooling water 
in the contact condenser will be reduced. Therefore, more H.sub.2 S would 
be withdrawn as a non-condensable gas via line 150, and less would be 
discharged from the cooling tower. Finally at least a portion of the 
H.sub.2 S that is absorbed by the cooling water would form elemental 
sulfur via the aqueous Claus Reaction (II), thus further reducing H.sub.2 
S discharges from the cooling tower. 
As hereinbefore set forth, externally derived gases can be utilized for 
temperature control purposes in incinerator 11. FIG. 2 shows the use of 
geothermal steam as one such externally derived gas being added as a 
diluent via lines 260 and 280. Although the catalysts of the invention, 
especially one comprising V.sub.2 O.sub.5 on alumina, are physically 
stable even in the presence of saturated steam, it is anticipated that 
saturated or wet-saturated steam might decrease the activity of the 
catalyst for incinerating H.sub.2 S. This may be caused either by 
condensation of water in the catalyst pores or by the displacement of 
adsorbed H.sub.2 S from the catalyst's active sites. In either event, to 
prevent catalyst deactivation, the steam is preferably flashed through 
reducing valve 270, or other suitable device, to insure contact of only 
dry steam with the catalyst. 
As a final note to the embodiment illustrated in FIG. 2, it is conceived 
that such embodiment is also applicable to geothermal power plants 
utilizing surface condensers, rather than contact condensers as in FIG. 2. 
In fact, those that employ surface condensers, or can otherwise be 
modified to have their cooling water systems made independent of their 
steam cycle, permit recovery of essentially all the H.sub.2 S as a 
noncondensable gas. Thus, all the H.sub.2 S emitted by the power plant 
could be treated by one of the incineration, or sulfur 
recovery-incineration, embodiments hereinbefore described, and none would 
be discharged by the cooling tower. 
The following Example is illustrative of the performance of the process 
when utilized to treat noncondensable gases emanating from geothermal 
power plant condensers. 
EXAMPLE XIII 
A geothermal power plant must treat the vent gases (water dew 
point=72.degree. F.) emitted from its contact condenser. A typical dry gas 
composition of these vent gases is as follows (in mole %): H.sub.2 
--17.79; CH.sub.4 --13.12; N.sub.2 --6.26; O.sub.2 --2.21; CO.sub.2 
--59.23; H.sub.2 S--1.34 and NH.sub.3 --0.05. Except for the lack of trace 
amounts of Ar, CH.sub.3 SH, COS, SO.sub.2 and CS.sub.2 and the presence of 
more water vapor, this composition is very similar to the feed gas of 
Example IX. It can therefore be expected that when these vent gases are 
incinerated under the conditions specified in that Example, and at the 
temperatures indicated in Table IV, substantially the same results shown 
in columns 1 through 7 of Table IV would be obtained. 
In another embodiment of the invention, the raw geothermal steam can be 
processed prior to entering the geothermal power plant turbine by any of 
the incineration embodiments hereinbefore set forth and shown 
schematically in FIG. 1. Another application in which H.sub.2 S in 
geothermal steam can be incinerated without firstly separating it from the 
steam is in the purification of gaseous effluents from "wild" geothermal 
wells. A "wild" geothermal well is a term used in the art in reference to 
those geothermal wells which must be continuously bled to minimize the 
internal pressure. Such bleeding usually discharges to the atmosphere 
steam containing H.sub.2 S, CH.sub.4 and H.sub.2 in concentration ranges 
hereinbefore described. For this embodiment the use of hydrogen mordenite 
or alumina as catalyst supports is preferred because of their resistance 
to deactivation in the presence of water vapor. 
The term "non-condensable gases" as employed herein refers to those gases 
derived from geothermal steam which remain uncondensed at 150.degree. F. 
or less and at atmospheric pressure or less. 
It will be apparent to those skilled in the art from the foregoing that 
numerous modifications of the invention are contemplated. Accordingly, any 
and all such embodiments are to be construed as coming within the scope of 
the invention as defined in the appended claims or substantial equivalents 
thereto.