Note: Descriptions are shown in the official language in which they were submitted.
llfA,'5 7ff~
L~ L` f ` .l ~lt;.~ o ~ :L' O C f ~ ., .[ ( ) f" t, lf l f ` ' ~ t~llJ~
i~C.i~ iiOII o.L` hydrogcn u:lp~-l;d~-contain:in~ wast- frascs
i~ cont~cii.nf, s~.i.d wastl^ ga.;es wi.~h a scoichiometr c
excess o 1' OXygf n Wi tn recpect to the containf_d hydrogen
sulphide in the presence of a catalyst. It also relates
to a eatalyst comp.)si.tion which can suitabl.y be applifd
in such a process.
Viewed i.n the light of increasingly stringent re-
quirements with respect to air pollution abateme.nt,
various procedures have been developed to remove
hydrogen sulphide (H2S) from proeess off-gases, and
even reeover, if possible, H2S or reaetion products of
H2S contained therein. For example, the well-known
Claus process produees an effluent normally eontaining
up to 2% or even 3% by weight sulphur eompounds, a
substantial proportion thereof being H2S.
To remove this eoneentration of sulphur eompounds,
seleetive absorption by eontaeting the Claus off-gases
with a suitable absorption solvent, after a hydrogen-
ation treatment of the off-gases, has been practised.
In this proeedure, the bulk of the desorbed H2S after
regeneration of the absorption solvent, is returned to
the Claus unit, and the final off-gas or tail gas,
eontaining nitrogen, C02 and quite minor amounts of
H2S is incinerated. During incineration, H2S is con-
ver~ced to sulphur dioxide (S02), a material which
~1~S731
as rig;~d ;lS those apr)l-ic(l to ll2~. IIowcver, ;ncirIcratic)n
is costly because of the necQssary heat input. Again,
al.houg'l some work has been done with regard to
catalytic conversion of H2S in the off-gas or tail
gas to S02, concomi-tant formation of sulphur trioxide
(S03) has been a problem.
A process is known for the purification of gases
contaminated with hydrogen sulphide by oxidizing said
hydrogen sulphide in the presence of catalysts which
contain as the main constituents metals, such as
niekel, iron, cobalt, manganese, zine and eopper, or
their eompounds, either alone or together with metals
or metalloids of Groups 4, 5 and 6 of the Periodie
System of Elements and in addition thereto, small
quantities of an aetivating material, such as lead or
bismuth or their compounds, or alkali metal or
alkaline earth metal compounds. The amount of the
aetivating material employed is up to about 10%, based
on the weight of the total amount of metals present.
Said known eatalysts have a disadvantage in that their
aetivity deereases rapidly~ requiring a temperature
raise of about 5C every three days. Moreover, about
10~ of the hydrogen sulphide present is eonvertc-d to
S03~ whieh is a highly objectionable compound from an
air pollution-abatement point of view.
~1~25731
Accoriingly, there still exists a need for an economical method
for the purificatioll of i-12S-containing streams, particularly off-gas streams
of the type mentioncd, which method would provide substantial conversion of
the H~S values in the off-gas, and concomitantly provide low SO3 emissions.
The method should be economical in that the necessary heat input should be
as low as possible as evidenced by relatively low process temperatures.
~breover, the catalysts to be applied should show an activity which remains
constant over a long period.
The present invention has as its object to satisfy that need.
The present invention accordingly relates to a process for the
catalytic incineration of hydrogen sulphide-containing waste gases by con-
tacting said waste gases with a stoichiometric excess of oxygen with respect
to the contained hydrogen sulphide in the presence of a catalyst in which
process the hydrogen sulphide-containing waste gases are contacted with
oxygen at a temperature in the range of from 150 to 450C in the presence
of a catalyst comprising as the catalytically active components bismuth in
an amount of from 0.6 to 10% by weight and copper in an amount of from 0.5
to 5% by weight, based on the total weight of the catalyst.
~1~57;~1
Z -i slZ~ r~ ~ ~)( rl ~:c,~ cl tilat ~ o r a
catalyst contain;n~r both bismuth (Bi) anc1 copper (Cu),
in spt?cifit-d proportions and amounts, givr-s resultc not
att?illablt? by use of comparable arnounts of Cu or Bi
alone. The une~pected aspect of the process of the
invent:ion resides in the ability to utiliz? temper-
atures of reaction not attainable, on a weight basis,
with catalysts of Cu or Bi alone. Additionally, any
combustibles, e.g., H2, C0, CH4, present in the
streams to be treated appear unaffected or substantially
unaffected by the catalyst of the invention. The S02
r^ormed may be vented or recovered in a manner known
to those skilled in the art.
Although the invention is apparently applicable
to any H2S-containing stream of low to moderate H2S
concentration, the invention is ideally suited to the
treatment of H2S-containing off-gases fronZ various
processes from which no further or little recovery of
other materials is made. The invention is eminently
suited, as indicated, to the treatment of the effluent
from a Claus plant. The Claus process is normally
itself a "clean-up" process, wherein elemental sulphur
is prepared by partial oxidation of H2S, using an
oxygen-containing gas (including pure oxygen) to form
S02, followed by the reaction of S02 produced with the
remaining part of the H2S, in the presence of a catalyst.
11~5731
i'`l~` `~)I~C `.: iS fI~ IIen'C~.y used clt rei irleri . ~ind al; o
ior t;~-1e ioric-ul) oi`ll2S recovered from various gas
Stl'eamS, such as natural gas. Since the yield of
elem-ental sulpl1ur, relative to the hydrogen sulphide
introduced, is not quantitative, a minor amount of
unreacted H2S, COS, CS2, and S02 remains in the
Claus off-gases. To some extent, the amount of
elemental sulp}1ur recovered depends on the number
of catalyst beds employed in the Claus process. In
lQ principle, about ~% of the total sulphur available
can be recovered when three catalyst beds are used.
The invention is eminently suited to the removal of
H2S from Claus plant effluents.
Additionally, as indicated, Claus plant effluents
or Claus off-gases may previously have been processed
by a Claus tail gas treating process. Such a process
may comprise the steps of reducing S02, COS, CS2, and
S03 contained in the gas under suitable conditions to
H2S in the presence of a catalyst, absorbing the H2S,
followed by desorption of the H2S and recycle of the
desorbed H2S to the Claus plant. Where this procedure
is practised, the invention provides for the oxidation
of the quite miinor or reduced ~mounts of H2S, and the
like, remaining -in the final off-gas by contacting said
off-gas with oxygen under the conditions indicated.
~125731
'ih~ talyst e~ loycd :in tl,c pro~es. jf th~ :in-
v lltiOIl ~ )c a sol;cl mattrial containing copper
alld bismutrl as the catalytically active components.
The particular form ~.Aiherein the catalytically acti-~e
components are present in the catalyst, i.e., whether
as compounds or the elements or compounds combined in
a carrier material, does not appear to be critical.
Where a carrier is employed, the only apparent re-
quirement concerning the sources of the copper and
bismuth is that the copper and bismuth be in a form
adapted to solution, either as an ordinary solution
(both aqueous and organic solvents) or as a solution
of a liquid or complex of copper or bismuth. Certain
salts and the oxide and hydroxide of copper and
bismuth may change cduring the preparation of the
catalyst, during heating in a reactor prior to use in
the process of -this invention, or may be converted to
another form under the described reaction conditions,
but such materials still function as effective catalysts
in the defined process. For example, the nitrates,
nitrites, carbonates, hydroxides, citrates and
acetates may be converted to the corresponding oxide
and then to the sulphide under the reaction conditions
defined herein. Such salts as the phosphate, sulphate,
halides, and the li~e, which are stable or partially
stable at the defined reaction temperature, are
1~573~
similarly effective under the conditions of the described reaction, as well
as such compounds which are converted to another stable form in the reactor.
Copper nitrate and bismuth nitrate are, however, preferred materials, since
they are inexpensive and are readily soluble in water and can easily be
deposited on carriers. The catalysts of this invention are solid at room
temperature or are essentially solid under the conditions of reaction
(although some volatilization may occur).
To achieve meaningful lowering of the reaction temperature with
concomitant COS conversion the presence of minimum amounts of Cu and Bi is
essential. In general, concentrations of at least 0.5% Cu and 0.6% Bi
(all by weight) are required in the reaction zone, with concentrations of at
least 0.8% Bi being preferred. Dramatic improvement over the Cu and Bi alone
occurs when the concentration of Cu is at least about 1.0% and the con-
centration of Bi is at least about 2.0% (all by weight). Where a carrier is
employed, for example, the Cu will normally be present in an amount of up to
about 5% by weight, based on the total weight of the catalyst material.
Preferably, the amount of Cu will not exceed about 3% by weight and the
amount of Bi, preferably, does not exceed 5% by weight. It is preferred,
however, that the amount of bismuth
--8--
112573~
p~.ent in th~` c;.t,alyst; :iS a]W~ly.. 'UlCIl t,h'lt, t,l-l''`
ce t;;',l~''it COIIlpI'i '>~`S cl major amc~urlt of bismllth and a
IllillOr ;lr.lOUnt of copper.
If solid compouncls of Cu and Bi are employed, or
if heavy concentrations of Cu and Bi on a carrier are
employed, the catalytically active materials will
normally be diluted with inert rnaterials so that
activity may be regulated. Proper dilution to the
concentrations specified is within the skill of the
art, and need not be detailed herein.
Excellent results have been obtained by packing
the reactor with the defined catalyst particles as
the method of introducing the catalytic surface. The
size of the catalyst particles may vary widely, but
generally the maximum particle size will at least
pass through a Tyler standard screen which has an
opening of 2 inches, and the largest particles of
catalyst will pass through a Tyler screen with one
inch openings. Very small particle size carriers may
be utilized, the only practical objection being that
extremely small particles cause excessive pressure
drops across the reactor. In order to avoid high
pressure drops across the reactor, at least 50% by
weight of the catalyst should be retained by a 4 to 5
rnesh Tyler standard screen. However, if a fluid bed
reactor is utilized, catalyst particles may be quite
5731
small, such as from about 10 to 300 microns. Those skilled in
the art can readily determine appropriate particle slze depending
on reactor configuration and size, and gas velocity to be applied.
If a carrier is used, the catalytically active compon-
ents may be deposited on the carrier by methods known in the art,
such as by preparing in aqueous solution or dispersion of the des-
cribed catalyst, and mixing the carrier particles with the solu-
tion or dispersion until the active ingredients are deposited in
or on the carrier. The coated particles may then be dried, for
example, in an oven at about 110C. Various other methods of
catalyst preparation known to those skilled in the art may be
used. Very useful carriers (and dilutants) are fused aluminas
(Alundum*), silica, silicon carbide (Carborundum*), pumice, kiesel-
guhr, asbestos, zeolites, and the like. The fused aluminas or
other alumina carriers and silica are particularly preferred.
The carriers may be of any shape, including irregular shapes.
Another method for introducing the required surface is
to utilize as a reactor a small diameter tube wherein the tube
wall is catalytic or is coated with catalytic material. If the
tube wall is the only source of catalyst, the tube wall will
generally be of an internal diameter of no greater than one inch,
* Trademarks
--10--
57~1
SUCIl as le~, than 3/4 inch in diaineter, or prefer~bly
will be no greater than about 1/2 inch in diameter.
Othel methods may be utilized to introduce the
catalytic surface. For example, the techniqlle of a
fluidized bed may be used.
The concentration of H2S in the streams treated
may vary widely. Thus, the concentrations may range
from trace quantities to quite significant amounts,
and it will be recognized by those skilled in the
art that H2S concentrations are not generally a
limiting factor of the invention. For example, con-
centrations of H2S in the gases treated may range
from 0.005% to 5.0%, or even 10.0% (molar basis).
Concentrations of COS and CS2 present in Claus
effluents are normally also minor~ and will range
for example from about 0.01% to about 0.5% (molar
basisj.
Reaction conditions ernployed may vary con-
siderably. While the temperatures at which the re-
action is carried out are not critical, it is an
advantage of the invention that lower or more moder-
ate temperatures may be employed. Temperatures of
150C to 450C are quite satisfactory, while temper-
atures of 250C to 420C are preferred.
Similarly, the pressures employed are not
critical, and a wide range of pressures may be used.
~1~5731
tll~ t~t~ ss~lre i~l t~ ,y~t~i.l Or th~
invelltiOIl normally will be at or in excess of~ at-
mospllei~ic pressure, altllo-lgh in some embodimen~,s, a
partial vacuum may be used. Preferably, pressures
will range from atmospheric to higher pressures, such
as 5 or even 10 atmospheres. Steam may be present in
the system, and in some instances, is preferred.
The flow rates of the H2S-containing gas and the
oxygen are largely a matter of choice. However, as
will be recognized by those skilled in the art, lower
space velocities improve conversion levels. Generally,
gaseous flow rates of from about 1,000 GHSV to about
50,000 GHSV may be used, with rates of from 2,000 GHSV
to about 25,000 GHSV being preferred. Good results have
been obtained with space velocities of 2,000 to 10,000
GHSV. Contact times, accordingly, are widely variable,
and may range from 0.07 seconds to about 4.0 seconds,
with contact times of from about 0.14 seconds to about
2.0 seconds being preferred.
The amount of oxygen supplied to the reaction zone
is important, in that a stoichiometric excess, prefer-
ably a large excess, of oxygen is desired in order to
react all the H2S and any COS and CS2 present. In
general, at least twice, and normaIy up to five times
the stoichiometric arnount of oxygen required for the
reaction may be supplied. Preferably, an excess of
1~573~
about .'0 to a~out 2~0,' of` the stoichio111et-ric a1-nourlt o,
oxy~en, based upon all total combustibles, will be
supplied. Amounts as high as lOO or even 20Q times the
stoichiometric amount of oxygen may be supplied, if
desired. The oxygen may be supplied as relatively
pure oxygen, as air, or mixtures of air and oxygen,
as well as from other gaseous streams containing
significant quantities of oxygen and other com-
ponents which do not interfere significantly with
the reaction contemplated.
EXA~iPLE I
In order to demonstrate the invention, the following
experiments were conducted. In each run, a synthetic tail
gas containing H2S and other sulphur compounds is passed
into a reactor containing the catalyst. Oxygen, as air,
is introduced from a separate line. Temperature is
measured by suitable means, and conversion results are
obtained by analysis of the effluent stream from the
reactor.
Employing this general procedure, samplings were
ta~en employing a catalyst containing Bi and Cu
deposited on alumina (Kaiser A-201 spherical gamma-
alumina, l~ x 6 mesh) in amounts of 3% and 1%
respectively, each by weight, based on the total weight
of the catalyst. Copper and bismuth were deposited as
a basic solution of the nitrates. The catalyst was then
~573~
dl~ie(l .ln(i c;~ ;nt~d ~t 4dlC for ono to t~o hc,urs b~rore~
use. Con(lition, or operation are shown more speci-
fically -in Table I. Significant H2S-removal is ob-
tained, and the results for two di.fferent space
velocities are shown in Table II.
TABLE I
Composition, %v
H2S o.8
S2 0.4
S1 0.15
COS 0 o4
CS2 0.04
C2 5.00
C0 0.50
H2 1.00
H20 3-
Air variable
N2 remainder
_perating conditions
Pressure : 1 atmosphere
Temperature : 290-425C
Space velocity: 2500 to 5000 vol./vol./h
(basis reactor outlet)
Air rate : 20-2c30% excess 2 ~)
~) Based upon all total combustibles, including hydro,,en.
573~
TABl.E II
Catalyst 1% Cu - 3% Bi/A1203
Space velocity,
; vol./vol./h 2500 5000
Temperature, C 370 370
Excess 2' ~ 150 150
Wet chemical analysis
Product gas (dry basis)
H2S~ ppmv 0.1 0.7
S2~ %v 2.23 1.95
S03, ppm~ 6 14
EXAMPLE II
Employing a procedure similar to Example I, a
catalyst containing only 3% by weight (based on the
weight of the active material and carrier) bismuth on
alumina and a catalyst containing only 1% by weight
(based on the weight of the active material and
carrier) copper on alumina were prepared and tested.
Results are shown in Table III and compared with those
for a catalyst in accordance with the invention.
-16-
-16-
1~5'7;~1
'l'.~l3rE -[IL
Co~ilparison of cata]yst compositions
Catalyst 3%i/Al203 1% Cu/A1203 1% Cu-3,~ Bi/Al20
Space velocity,
vol./vol./h -2500
Temperature, C 315
Exeess 2' % 150
Wet chemical analysis
Product gas (dry
basis)
H2S,ppmv 2.1 0.1 0.14
S02, %v 2.18 2.04 2.10
S03, ppmv 22 71 8
The data in Table III demonstrate clearly the
superiority of the Cu - Bi catalyst with respect to the
reduced S03-concentration in the product gas. The com-
bination eatalyst in accordance with the invention also
shows a very high conversion for carbonyl sulphide and
earbon disulphide. At the reaetion eonditions specified
the carbonyl sulphide conversion is better than 50% and
the earbon disulphide eonversion is better than 90%.
