Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3~
REDVCTION OF CARBON MONOXIDE
IN SUBSTOICHIOMETRIC COMBUSTION
This invention relates to the substoichiometric
combustion of combustible gases o~ low heat content in the
presence of a catalyst which causes a substantial reduction
in the carbon monoxide content of the combusted gas stream.
The invention is particularly directed to the recovery
of liquid carbonaceous fuel components from subterranean
formations by an in situ combustion process in which the
low heating value waste gas stream resulting from the
subterranean combustion is itself combusted above ground.
This combusted waste gas stream is preferably utilized to
power a turblne-compxessor unit which compresses the air '-
for injection into the formation for the in situ combustion.
The low heàt content gas stream can also be a factory waste r
gas stream resulting from incomplete combustion, solvent
evaporation and the like, or it can be a low heating value
producer gas stream containing hydrogen and carbon monoxide
as its major combustibles.
~ ~ .
Various carbonaceous materials occur in underground
deposits in substantial quantities but are resistive to
recovery for aboveground use. This includes viscous oils
the oil remaining in petroleum deposits after primary or
secondary production of the oil bearing formation, shale
oil occurring in solid bituminous deposits, tar sands,
~coal seams~too deep or too thin to mine, and the like.
It has been proposed that these fuel materials be recovered
by an in situ combustion process and some limited
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attempts have been rnade to accomplish this. The in situ
recovery of underground fuel values invo~ves the injection
of air into the carbonaceous deposit to burn a minor
portion of the deposit in order to produce a further
portion of the deposit for use above ground as a liquid
and/or gas. Such recovery procedures generally result in
a yas stream of low heating value, particularly in those
operations which produce a liquid hydrocarbon as the
desired product. As used herein, the expressions
heating value and heat content both refer to the energy
obtainable by burning the combustible components in the
stream of waste gas.
The obvious way to handle a waste gas stream of
low heat content is to discard it directly into the atmos-
phere. But in recent years a greater recognition andconcern about atmospheric pollution has led to legal
standards in many areas controlling the direct emission
to the atmosphere of waste gases eontaining significant
amounts of hydrocarbon and carbon monoxide. Furthermore,
there is a growing recognition and concern regarding the
social as well as economic loss in wasting energy.
Although these waste gas streams resulting from in situ
combustion may have a low heating value on a unit volume
analysis, they do contain a very large heating value overall
because of the enormous vol~aes of gas involved. It has
therefore become most desirable and ~ven necessary tha~
the heat content of these waste gas streams be utilized
and that the atmosphere be spared contamination.
The combustible components in a waste gas stream
from an in situ combustion process can be burned using a
suitable oxidation catalyst. This hot gas can then be used
to drive the turbine-compressor unit which injects the ~ `
re~uired large volumes of air at high pressure into the
underground carbonaceous deposit undergoing in situ combus-
tion. In order to obtain the full heating value of this
waste gas as well as to avoid the emission of undesirable
components into the atmosphere, these waste gas streams
can be burned to substantially stoichiometric completion
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in the presence of an oxidation catalyst. But these
stoichiometrically combusted waste gas streams generally
vary in temperature over relatively short periods of time
due to inherent variations in the heating value of these
5 waste gas streams. In an effort to protect the gas
turbine against damage resulting from these temperature
fluctuations and to operate at the turbine's design
temperature, the combustion process invo7ves auxiliary
temperature control such as is accomplished by the injec-
10 tion of supplemental fuel into the waste gas during
heating value minimums and the injection of cooling air
into the combusted waste gas during heating value peaks
to provide a constant gas temperature.
We have determined that a waste gas stream of
lS low heat content which varies with time can be
effectively combusted at a substantially constant combustion
temperature for use in a gas turbine. This is accomplished
by combusting the gas with a constant amount of air which
is substantially less than the amount of air required for
20 stoichiometric combustion. Furthermore, if the heat
content of the waste gas is relatively constant but so r
high that its stoichiometric cornbustion results in a gas
temperature too high for use in a gas turbine, its combus-
tion temperature can be effectively restricted to the
25 design limits o~ the gas turbine by operating at substan-
tial substoichiometric conditions with a constant quantity
of combustion air. We have further discovered that this
substoichiometric cornbustion can be carried out using
a particular catalyst for the production of reduced and
-30 acceptable carbon monoxide levels.
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Thus according to the present invention there is
provided:
the in situ combustion process for recovering
liquid hydrocarbons from subterranean formations which
comprises injecting a stream of combustion air into at
least one injection well leading to a combustion ~one in
said subterranean formation, producing liquid hydrocarbons
and combustion gas from at least one production well,
separating the liquid hydrocarbons from the stream of
combustion gas whereby a separated stream of flue gas is
obtained having a heating value between about 500 kJ/m3
and about 7,500 kJ/m3 and containing at least one
aliphatic hydrocarbon having from one to about seven carbon
atoms, passiny said gas stream admixed with air for
combustion in contact with at least one supported platinum
oxidation catalyst having incorporated therewith at least
one metal oxide cocatalyst selected from Groups IIA and
VIIB, Group VIII up through atomic No. 45, the lanthanides,
chromium, zinc, silver, tin and antimony in at least one
combustion zone at a temperature high enough to initiate
and maintain combustion of said gas stream, the total amount
of combustion air being sufficient to pro~ide an air
equivalance ratio of less than 1.0, expanding the gas stream
in a gas turbine following said catalyzed combustion; and
driving an air compressor with said gas turbine to compress
and inject said stream of combustion air into the said
subterranean combustion zone.
In carrying out a hydrocarbon recovery operation
by in situ combustion such as in a tertiary recovery process
in a partially depleted oil field, combustion air is pumped
at a substantial pressure through an in~ection well into the
combustion ~one. By a combination of heating and cracking
the oil is liquefied and caused to flow to one or more
production wells. The hot, substantially oxygen-free gas
stream, after passage through the combustion zone is cooled
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down to the reservoir temperature by the time it arrives at
the production well. As it is produced, it contains
significant quantities of ~ntrained liquid hydrocarbons as
well as gaseous hydrocarbons and minor amounts of carbon
monoxide, hydrogen and hydrogen sul~ideO The liquid
hydrocarbons are removed from the gas stream in an above-
ground separator. The combustible component o the waste
gas stream leaving the separator is principally methane
but it also contains minor amounts of other hydrocarbons
having up to about five carbon atoms and in some instances
up to about seven carbon atoms, as well as the carbon
monoxide, hydrogen and hydrogen sulfide. The remainder
is principally nitrogen and carbon dioxide.
The combustible components in this waste gas ;
stream can be mixed with a stoichiometric excess of air
and burned in the presence of a suitable oxidation catalyst
such as platinum if it is at its ignition, or light of~,
temperature, ~hich varies with the gas composition and the
nature o~ the oxidation catalyst. If the catalyst is
provided in a suitable physical form to provide adequate
contact of the large volume of gas with the catalyst,
substantially complete combustion of the hydrocarbon to
carbon dioxide and water is accomplished. Thiscombusted
gas stream~ at an elevated pressure, can be directed to
the turbine~compressor unit for compressing the combustion
air which is injected into the underground combustion zone.
But, unfortunately the waste gas stream generally
varies in heating value over a perioa of time, even from
hour to hour, as a result of inherent variations in the
underground formation and the combustion process. As a
result, the temperature of the combusted waste yas stream
will vary in temperature with complete comhustion. Since
gas turbines are designed for constant temperature
operation, adjustments must be made to control the tempera-
ture of the combusted gas stream so that it can be utilizedin a gas turbine.
We have discovered that an in situ combus~ion
process can be successfully carried out in a subterranean
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hydrocarbon deposit by an integrated operation in which
th~ heat en~rgy i~ the combusted waste gas directly powers
a turbine driven air compressor even though the heating
value of the waste gas stream varies with time. Even
though the waste gas stream varies in heating value, we
obtain a constant combustion temperature by using a con-
stant substoichiometric amount of air for the combustion
which is also suficient to provide the desired turbine
operating temperature. As a result of this substoichiomet
ric combustion, the combusted waste gas stream will still
have a variable but generally minimal heating value. The
heating value in t`he compresssor exhaust gas, if significant,
can be recovered by a further catalytic combustion and
utilized to produce steam or heated water as may be needed
on the recovery site. Or the turbine exhaust can be
directly vented to the atmosphere. We have further dis-
covered that the carbon monoxide content of the turbine
exhaust can be restricted to acceptable amounts, notwith
standing the substoichiometric combustion, if the waste
gas is combusted in the presence o~ a multicomponent
oxidation catalyst as described herein.
The substoichiometric combustion of the low
heating value waste gas stream is carried out by our process
using an air e~uivalence ratio, or A.E.R., of less than
1.0, generally of at least about 0.20 up to about 0.90 tthe
denominator of this ratio being 1.0 is not expressed), and
more generally an air equivalence ratio of at least about
0.4 and a maximum of about 0.80. As used herein, air
equivalence ratio is the ratio of the amount of air actually
used in the partiaI combustion process to the amount of air
required at the same conditions of pressure and temperature
for stoichiometric combustion of all combustible components
in the gas stream
In~our study of the platinum-catalyzed, sub-
stoichiometric combustion o a dilute hydrocarbon streamwe made several interesting observations. First, it was
found that the only combustibles present in this partially
combusted gas stream are carbon monoxide, hydrogen and
.
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6' ~;1
unreacted hydrocarbon. Second, we observed that in this
p~rtial combustion the amount of carbon monoxide reached a
maximum at an air equivalence ratio of about 0.6. In fact,
we found that the amount of carbon monoxide substantially
exceeded the amount of carbon dioxide in the combusted gas
at an A.E.R. of 0.6, such that the ratio of carbon dioxide
to carbon monoxide was less than 1.0 at an A.E.R. between
about 0.4 and about 0.7.
As would be expected in the platinum-catalyzed
reaction, the molar ratio of carbon dioxide to carbon
m~noxide rapidly increased as the A.E.R. approached 1Ø
But ~urprisingly, we discovered that the molar ratio of
carbon dioxide to carbon monoxide also rapidly increased
as the A.E.R. was reduced to values less than about 0.4.
This is surprising because it is not consistent with the
conventional teaching that carbon monoxide is the result
of incomplete combustion of a hydrocarbon. I~ this con-
ventional teaching were applied to this particular com-
bustion system, the ratio of carbon monoxide to carbon
dioxide would be expected to increase as the air equivalence
ratio decreased, and that it would be expected to be
particularly large at small air equivalence ratios. We
conclude from our combustion studies that the carbon mon-
oxide in this platinum-catalyzed, substoichiometric
combustion of a dilute hydrocarbon is primarily the result
of secondary reactions including the steam reforming and
water gas shift reaction~.
In the steam reforming reaction, hydrocarbons
such as methane and water are in equilihrium with carbon
monoxide and hydrogen. In the water gas shift reaction
carbon monoxide and water are in equilibrium with carbon
; dioxide and hydrogen. Thus, a study of these equilibrium
reactions suggests several mechanisms for the unexpected
product mixture of the oxides of carbon including the
sub~tantial production of carbon monoxide and a corresponding
minimum in the carbon dioxide to carbon monoxide ratio at
a~ air equivalence ratio of about 0.6.
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When methane is the primary combustible component
in the waste gas stream, it will be substantially the only
hydrocarbon in the gas exhausted to the atmosphere which
is fortuitous since methane, in limited arnounts, is not
considered to be a pollutant in the atmosphere. It can be
shown that a mixture of diluted, gaseous, paraffinic
hydrocarbons will react at different rates when burned in a
dèficiency Qf air. The higher paraffinic hydrocarbons
burn readily, while the lower the number of carbon atoms
in the molecular structure the more resistant to combustion
is the hydrocarbon. As a demonstration of this variable
combustibility, a nitrogen-diluted two weight percent mixture
of one to five carbon paraffinic hydrocarbons was burned in
a com~ustion furnace with fifty percent of the stoichiometric
15 amount of air for complete combustion. The gas, heat d to ~;~
449 C. and passed in contact with a supported platinum
oxidation catalyst, reached a maximum temperature of 777 C.
In this combustion experiment 100 percent o~ the n-pentane
was converted, 54.5 percent of the n-butanel 44.1 percent
of the propane, 31.8 percent of the ethane and 11 percent
of the methane. This demonstrates that partial combustion
of a dilute gaseous hydrocarbon mixture inc~uding methane -
will substantially increase the proportion of methana in ~;
the product gas.
The temperature of the waste gas stream will only
be moderately higher than ambient temperature due to the
cooling effect of the formation following the under-
ground combustion. Therefore, it is necessary to preheat
the waste gas stream for catalytic combustion, preferably
after the air for combustîon has been injected into the
waste gas stream. This preheating must be at least as
high as the ignition, or light of, temperature of the gas.
The preferred means for preheating the waste gas stream is
by heat exchange with the hot combusted gas stream leaving
the combustion zone. In general, two combustion chambers
in series are preferred in order to avoid an excessive
temperature rise in a single combustion chamber. In this
two-stage combustion process, the waste gas stream is
~esirably preheated after the first combustion stag~.
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The temperature of the combusted gas stream is dependent on
a numbe.r of factors .including the heatlng value oE the
waste gas stream, the temperature of the waste gas stream
prior to preheating, the amount of air that is used for
combustion, the inherent heat losses in the system, and
the like.
With regard to the many conditions and variables
which may be involved .in any specific in s.itu comhustion
operation, the waste gas streams which are combusted to :~
temperatures that are useful in gas turb.ines have a heat
content of at least about 1/500 kJ/m3 (kilo Joule per
cubic meter), preferably a.bout 2~000 kJ/m3r however, ~:
heating values as low as 500 to 1,000 kJ/m3 can be utilized
with the injection of supplemental fuel~ All heat contents
are based on the gas at one atmosphere pressure and
; 15.5 C. The maximum heating value of the waste gas stream
obtained by the in situ combustion procedure will be about
; 7,500, more generally a maximum of about 5,500 and most
likely a maximum heating value of about 4,000 kJ/m3,
although some other sources of waste gas streams having a
heating value of between about 200 and about 20,000 kJ/m3
may be utilized.
As pointed out, the substoichiometric combustion
is carried out in the presence of a suitable oxidation
catalyst, which is also capable of reducing the carbon
monoxide content of the gas stream resulting rom the
partial combustion. ~ supported platinum catalyst is
; used as one of the catalyst components because platinum i9
both a highly active oxidation catalyst and is also
relatively ~ulfur tolerant. I~ a platinum oxidation
catalyst is used as the only active component in the
catalyst, the gas stream resulting from the substoichio-
metric combustion will contain a relatively high amount of
carbon monoxide, which may be unacceptable in localities
35 which have laws regulating atmospheric polluti.on. ~ -
In order to reduce the carbon monoxide content
of the combusted gas stream for environmental or other
reasons, a platinum and cocatalyst combination is usedO
Thus, we have determined that the carbon monoxide level
_g
in the ~ubstoichiometric combustion of low heating value
gas ~treams can be sub~tantially reduced in compaxison
with a monocomp~nent hydrogen catalys by the use of a
suitable cocataly3t. We have determined that cocatalysts
selected from Group~ IIA and VIIB, Group VIII up through
atomic No. 45, the lanthanides, chromiuml zinc, silver,
tin, and antimony are useful when associa~ed with a
platinum oxidation catalyst for reducing the carbon
monoxide content of the partially combus~ed low heating ¦.
10 value ga stream. The metal~ in thes~ namad group~ which .
are particularly u~eful as a cocatalyst wi~h platinum are
magnesium, calcium, manganese, iron, cobalt, nickel,
xuthenium, rhodium, cerium and mixed lanthanides containing
cerium. .
The oxidation catalyst that is used in our suh- :
6toichiometric combustion process i5 desirably carri2d on
an inert support. Since the catalytic combustion
inherently involve~ a relatively large volume of the s re~m
of low heat~ng value gas, the support is preferably of a
desi~n to permit good svlid-gas aontact at relatively low
pressure drop. A suitable ~upport can be formed as a
monolitA with hexagonal cells in a honeycomb design. Other :
cellular relatively open-celled designs are also suitable. :
The support for the catalysts to be used in th~
proces~ of this invention can be ~ny of the refractory oxide
~upports well known in the art,. such a~ those prepare~ from
alumina, ~iliGa, magnesia, thoria, titania, zirconia,
~ilica-aluminas~ silica-zirconias, magnesia-alumi~as, and
the like. Other suitabl~ ~upports include the naturally
oc~urring clays, such as diatomacaous earth. Additional
desirable supports for use herein are the more recently
developed corrugated ceramic materials made, for example,
from alumina, silica, magnesia, and the like. ~n example
of such material i8 described in U. ~. Patent No. 3,255,027
and is sold by E. I. duPont de Nemours & Company as Torvex~*.
More recently, metallic monoliths have been fabricated as
catalyst supports and these may be used to mount the
catalytic material. An example of the~e supp~rt~ i5
* Trade Mark
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Fecralloy*manufactured by Matthey Bis~op, Inc. under UO S.
PatentEI NOB . 3, Z98, 826 and 3, 920, 5B3 .
If desired, the catalyst and cocatalyst, lf u~ed,
can be mounted ~irectly onto the ~urface o~ ~he monolith.
S Or the monolith can first be coated with refractory oxlde,
such as defined above, prior to the deposition of these
materials. The addit~on of the refractory oxide coating
allow~ the catalyst to be ~Dre securely bound to the
monolith and al~o aids in ~ t8 di~persion on the ~upport.
The~e coated monoliths pos~ess the advantage of being easily
formed in one piece with a configuration suitable to permit
the pa~age of the combu~tion gaQe~ with little pre~ure
d~op. The surfac~ area of the monolith generally i~ les~
~han one square meter per gram. Howev~r, the coating
. generally ~a~ a surface area of between about ten ~nd abau~
. 300 m2~g. Since the coating ~8 generally about ten percent
of the ~oated support, the ~urface rlea of the coated ~upport
will therefore ~enerally be between about one and about
30 m2~g.
In preparing the platinum and cocataly~t co~bina-
tion it is preferred that the cocatalyst be placed on the
upport be~ore the platinum. Bowever, the rever~e nrder of
emplacement i~ also ~uitable or the platinum and cocatalyst
can be added i~ a single step. In the preferred procedure
a suita~le salt o~ the cocatalyst metal is dissolved in a
~ol~ent, pre~erably water. The support is impregnate~ with
the ~olution o~ th~ cocataly~t metalO In a preferred ...
emb~diment the impregnated ~upport i8 next gas~ed w~th a
uitable gas, generally ammonia or hydrogen sulfide, ~o
cause the cataly~t metal to precipitate uniformly on the
~upport as th~ hydroxide or ~ulfide a~ the case may be.
It i~ then dried ~nd calcined in air at about 425 to 650 C.,
prefera~ly at about 540 C. Hydrogen may be u~ed to reduce
the cooatalyst compound to the metal if desired.
Platinum i~ impregnated onto the support, aither
alone or in association wi~h a cocatalyst as an aqueou~
~olution o a water-~oluble compound ~uch as chloropl~tinic
acid, ammonium chloroplatinate, platinum tetramine dinitrate,
- * Trade Mark
B
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and the like. The catalyst is then gassed with hydrogen
sulfide in a preferred embodiment to cause precipitation
of the platinum as the sulfide to ensure uniform distri-
bution of the platinum on the support. It is again dried
5 and then calcined in air at about 425 to 650 C./
preferably at about 540 C. The same general procedure
can be used for the incorporation of a di~erent oxidation
catalyst on the support. In general r it i~ not certain
whether calcination converts the catalyst metal ~ulfides
and hydrated sulfides to another compound or how much is
converted to the oxide~ sulfite or sulfate, or to the
metal itself. Nevertheless, for convenience, the noble
metals such as platinum are reported as the metal and the
other catalyst metals are reported as ~he oxide.
The catalyst can also be added to the coated
monolith as a slurry of ~inely ground powdersO In the
case of th~ noble metals such as platinum, powdered metal
is preferred but the platinum could also he added as the
powdered oxide. The other catalyst metals would preferably
be added as the powdered oxide or sulfide. The powdered
metals could be added together or in succession with
calcining as described above. In a urther alternative
the coating material such as powdered alumina is
impregnated with a solution of the metal compound and
calcined. The monolith is then coated with a slurry of
this powder and calcined. In this latter technique all
of the catalys~ components can be added to the monolith
in one step.
The supported catalyst is prepared so that it
30 contains between about 0.005 and about 20 weight percent of
the catalyst metal reported as the oxide, and preferably
between about 0.1 and about 15 weight percent of the metal
oxide. The platinum or other noble metal is used in an
amount to form a finished supported catalyst containing
between about 0~005 and about ten weight percent of the
metal, and preferably about between 0.01 and about seven
weight percent of the metal. When the platinum and
cocatalyst combination is used for lowered car~on monoxide
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content in the product ga~ Btream, the relative amount of
the cocatalyst and the pla~inum has an effect on the
comSustion, including an efect in the amount o~ carbo~
monoxide in the combu~ted ga~. The cataly6t will broadly
contain a mol ratio of cocataly~t as the oxide to platinum
a~ the metal of between about 0.01:1 and a~out 200:1
preferably between about 07 1 1 and about 100:1~ and mo~
preferably between about O~S:l and abou~ 50:1.
Descri~tion of Pre~erred Embodiments
_ _
The reac~or u~ed i~ the following experiments, ~t
atmospheric pre~sure was a one-inch I.D. forged ~te~l unit,
which wa~ heavi}y insulated to give adiabatic reaction
condition~. The reactor used in the combustion under
pressure was made from Incoloy 80~ alloy (32 percent Ni,
46 perc~nt F~ and 20.5 percent Cr) but wa~ otherwise the
same. The cataly~t cvn~i~ted of three 2.5 centimeter
monoliths wrapped in a thin shee~ of a refractory material
(Fi~erfraX,* available from Carborundum Cs~). The catalyst
composition~, a~ specified, are onl~ approximate becau e
they are ba~ed on the composition of the impregnating
solution and the amount absorbed and are not ba~ed on a
complete ch~mical analysis of the finished catalyst. Well
insulated preheaters were used to heat the ga~ stream
before it was introduced into the reactor. The temperatures
25 were measured directly be:Eore and after the cataly~t bed
to provide the inlet and outlet temperatures. An
appropria~e flow of preheated ni~ro~en and air wa~ passed
over the ca~aly~t until the desired feed temperature wa~
obtained.
. Preheated hydrocarbon wa~ then introduced a~ a
- qa~ hourly space velocity of 42, 000 per hour on an air-free
basi~ and conbustion was allowed to proceeti until steady
~tate conditions were reached. The feed ga~ ~tream
contais~ed 94 . 5 mol percent nitrogen, 3 . 75 mol percent
methane, 0.98 mol percent ethane, 0.77 mol pexcent propane
and 400 ppm. hydrogen sulfide~ ~xcepk where otherw~e
notedP The heating value of thi~ feed stream is abou
2,800 kJ~m3. The experiment~ were conducted at atmo~pheric
* Trade Marks
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pressure or at a slightly elevated pressure, except where
otherwise noted. The analyses were made after steady
state conditions were reached on a water-free basis. The
conversion is the overall conversion o all hydrocarbon
constituents. No measurable free oxygen occurred in the
product gas stream.
Example 1
The preparation of a catalyst containing antimony
as the cocatalyst is now described. A Torvex monolith was
used as the support. The Torve~ support, a product of
E. I. duPont de Nemours ~ Company was a mullite ceramic in
the shape of a honeycomb having a coating of alumina of about
25 m2/g. surface area. The support was cut into one inch
diameter by one inch deep pieces and freed from dust. This ~;
support material was impregnated with a solution containing
15.96 g A of antimony trichloride in 44.04 g. of a 1:3 solu-
tion of HCl and water by soaking for 15 minutes. These
pieces of support were drained of excess solution and
treated with gaseous ammonia for 30 minutes to precipitate
the antimony as the hydroxide~ The support material was
then dried at 12Q C. and calcined at 540 C.
Th~ pieces were next soaked or 15 minutes in an
aqueous solution of chloroplatinic acid containing 23 mg. of
platinum per ml~ After removing excess solution from the
support material, it was gassed with hydrogen sulfide for 30
minutes to precipitate the platinum as platinum sulfide.
The catalyst was then dried at 120 C. and calcined at 540C.
O~her catalysts were prepared in an identical
manner except that where necessary the cocatalyst was pre-
cipitated with hydrogen sulfide instead of with ammonia such asa catalyst prepared by impregnating the support with an
aqueous solution of nickel nitrate.
Example 2
A catalyst was made as described in Example l
containing about 0.3 percent platinum but the cocatalyst was
omitted or comparison purposes. The operating data,
including the inlet and outlet gas temperatures, and results
for a number of combustion runs over a series of air
equivalence ratios are set out in Table lo
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Table I
Te~perature, ~C . CO CO~
Run Al~R Inlet utletMol ~MoI % Conv. %
Ia 0.2371 506 0.14 1.28 19.3
2 0.3343 572 0.45 1.6~ 23.3
3 0.4343 62~ 1.17 1.~9 42.1
4~ ~.5343 669 ~.94 1.66 57.3
0.6343 713 2.42 1.7g 71.4
6a 0.7343 769 2.11 2.43 81.5
7 o.~343 869 0.75 4.03 - ;~
a Averag~ of 2 run~ on different days.
A ~tudy of Table I discloses that over a wide ~`~
range of air equivalence ratios the amount o~ carbon
dioxide remains relatively aonstant betw~en an A.E,R. o~
about 0.3 to about 0.6 while the amount of carbon monoxide
rapidly increases in this range to an unexpected peak at an
A.E.R. of about 0~6~ Over this range o~ increasing oxygen,
the conversion and o~erall amount o carbon oxide~ increase,
:.,
as would be expected. It is ~urther noted that the largest
carbon~dioxide to carbon monoxide ratio surprisingly occurs
at minimum ox~gen, such as illustrated at an h.E.R. o~ 0.2,
since the production o carbon dioxide unexpectedly decreases
much~more~than the production o carbon monoxlde as the
amount~of oxyqen decreases in the low ra~ge of air equi~alence `~
25~ ~atios.~
That the maximum carbon dioxide to carbon monoxide ~;
ratio occurs at minimum oxygen strongly sugyest3 to us that
the principal source o carbon monoxide in the system i~ not ;;~
from incomplete combustion, that is, the direct but partial
oxidation of the hydrocarbon to carbon monoxide and water.
If this~ reaction were the principal source of the carbon
monoxide~ then the minimum car~bon ~ioxi~de to car~on monoxide
ratio would be expected to occur at minimum oxygen.
Instead the surprising occ~rrence of maximum carbon monoxide
and minimum carbon dioxide ratio in the mid A.E.R. range,
~strongly ~uggests that another me`chanism is the primary
.:
:. .
~ 15-
source of the carbon monoxide, such as the steam reforming
reaction and the water gas shift reaction.
Example 3
A catalyst was made as described in Example 1
containing tin calculated as about 1.0 percent tin oxide,
SnO2, and about 0.3 percent platinum. The operating data
and results over a series of air equivalence ratios are set
out in Table II~
Table II
Te~perature~C. CO CO~
Run AER Inlet Outlet Mol % Mol % Conv. %
__ __ _ _ _
8 0.2 896 ~76 0.06 1.35 19.9
9 0 3 342 632 0.14 1.8g 27.8
0.4 342 702 0.37 2.19 37.5
15 11 0.5 342 768 0.63 2.49 44.~
12 0.6 342 826 0.79 2.79 56.2
a 0.7 342 882 1.08 3.12 70.5
14 0.8 342 974 0.86 3.86 91.3
a Average of 2 runs ~n different days.
Exam~
A series of catalysts were prepared by the two-
stage procedure used in Example 1 and tested to illustrate
the effect of the cocatalyst co~bination in carbon monoxide
reduction. Many of these catalysts were tested at different
air equivalence ratios and it was found that the maximum
carbon monoxide occurred at an A.E~R. of about 0.7 when a
cocatalyst was used with platinum. This contrasts with
maximum carbon monoxide occurring at an A.E.R. of 0.6 when no
cocatalyst is used with platinum.
Table III summari2es a series of experiments by
setting forth the results of various catalytic combinations
at an A.E.R~ of 0.7 for the two-component catalysts, and an
A~E.R. of 0.6 for the platinum-only catalysts. All runs were
carried out at an inlet temperature of 342C. The
catalysts contained approximately 0.3 weight percent platinum,
except where specially noted.
: .: . - : , . .,., -.~, . . .. . .. .. . .
-lG~
Tabl~ III
Out- CO C~2
Ru~ Cocatalyst let~C, Mol% Mol% Conv.%
15a _ 696 2.85 1.59 76.3
- 713 2.42 1.79 71.4
b 0.7%Fe203 870 1.15 3~00 70.5
17b 0.5~SnO2875 1.12 3.18 72.4
18 1%~oO 885 0.85 3.09 72.0
19 1%CaO 894 0.83 2.96 67.6
2ob 3%SnO2 880 0.68 3.32 69.2
21 l~NiO goo 0.48 3.34 68.2
22 1%Sb203 918 0.46 3.40 65.8
ia 0~5% platinum~-
b Average of 2 runs on different days.
Example 5
Data for a further series of bimetallic catalysts
that were unsuccessfully tested at an air equivalence ratio :`
of 0.7 are set out in ~able IV. All of the catalysts
contained approximately 0.3 weight percent platinum except :~
where indicated otherwise.
Table IV
Run Cocataly~t Pt Inlet_Temp.c, Conv.
23a CuO 0.3% 41n
. 24a 1%Bi2030.3~ 410
25a 1%V205 0~3% 389
?6a 0.3%CuO+
0.3%Cr203 0~3% 3g9
27b 0.3%CuO~
o.3%cr2o3 none 343
28b l~PbO 0.3% 342
a Unstable combustion, steady state combustion
never reached.
b ~0 combustion.
The data in this table show that some metals
that are known to be effective oxidation catalysts are not
effective ai~ cocatalysts with platinum in the present
substoichiometric process. For exampl~, copper oxide,
vanadium oxide, lead oxide and copper chromite are
~3~G
--17--
recognized as oxidation ca-talysts. In contrast, tin oxide
which is shown in Table III to be an effective suppressor of
carbon monoxide with a pla*inum oxidation catalyst in
substoichiometric combustion, is not itself effective as an
oxidation catalyst.
Example 6
In this experiment a different low heating value
gas stream containing higher hydrocarbons and carbon monoxide
was used. It contained 5.5 volume percent of a hydrocarbon~
carbon monoxide mixture which compri~sed 67.89 mol percen~
methane, 7.76 percent ethane, 5.83 percent propane, 7.73
percent n-butane, 5.04 p0rcent n-pentane, 0.96 percent
n-hexane and 4.79 mol percent carbon monoxide. The remainder
was nitrogen a~d 400 ppm. hydrogen sulfide. The catalyst,
containing about 0~5 percent platinum on an alumina-coated
Torvex support, was the same as the catalyst used in Run 15.
The operating data over a series of air equivalence ratios
are set out in Table V.
Table V
Temperature,C. CO CO2
Run AER Inlet Outlet Mol% Mol% Conv.%
29 0.2343 49~ 0~10 1.56 18.3
0.3343 564 0.68 1.86 25.9
31 0.4343 621 1.76 1.64 36.9
32 0.5343 668 3.20 1.23 59.2
33a 0.6343 715 3.64 1. 51 81. 3
34 0.7~ 343 766 3.11 2. 42 85 . 7 `:~
~.~3~3 846 1.77 3.46 ~100
Average of 2 runs on different days.
Example 7
Runs 36-42 were carried out under pressure using
an inlet pressure to the reactor o~ 620 kPa. The catalyst
again contained about 0.5 percent platinum on an alumina-
coated Torvex support. The operating data over a series of
air equivalence ratios and gas hourly space velocities
(10 3hr. 1) are set out in Table VI.
, , .: , : ~ . :
3~7;~
-18-
~f T~ble VI :
Temfperature,C. CO C02
GHSV AERInletOutlet Mol% Mol%Conv.%
0.~ 3g3 60~f 1.12 ~.06 38.6
42 0.4 199 619 0.52 2.41 36.3
0.4 260 694 0.86 2.09 37.9
lOO 0.4 ~60 721 0.81 2.03 36.6
15a 0.42 260 580 0.54 2.23 40.8
100 0.5 ~60 t73 1.61 2.00 49.9
25b 0.61 343 644 1.01 2.03 66.5
a Gas contained 5.27 percent hydrocarbon and
2,700 kJ/m3.
b Gas contained 3.7 percent hydrocarbon and
1,910 kJ/m3. ~;
Example 8
Runs 43-51 were also carried out: at a pressure of
620 kPa. in the comhustion reactor but using a different
catalyst containing about 0.3 percent platinum and about
one percent cobal oxidf~. The operating data over a series ~-
of air equivalence ratios and ga~ hourly space veloci~ies
(10~3hr.~l) are set out in Table VII,
Table VII , :~
Tempersture,C. CO C0
GHSV AER Inlet Outle~ Mol% Mol% Conv.%
~ :25 42a 0 4 260~ 668 0.20 2.89 35.2 :
`~: : ;;looa 0,4 ~ 260 710 0.20 2.43 33.0
: 42b 0.4 260 669 0.21 2.52 33.3 ~ .
0.4 ~:~ 260~ 727 0.38 2.44 33.1
140C 0.4 : 260: 700 ~.32 2.28 32.4 `~
3~ 80 0.6 260 833 0.~8 3.03 53.9 `~
42d 0.7 274 786 0.60 3.67 65.4
42 0.7 343 874 0.89 3.46 67.5
: ~0 0.8 260 g60 1.06 3.74 72.1 ~`
a At 420 kPa- ';
b Average of 2 runs on differen~ days.
c Gas contained 5.37% hydrocarbon and 2,740 kJ/m3.
d Gas contained 5,0no ppm~- H2S
, . :
~3~
-19--
Example 9
Several of the bimetallic catalysts, which
resulted in the greatest reduction in the production of
carbon monoxide, as set forth in Table III were tested to
determine the minimum temperature to which a feed gas
stream must be heated to maintain continuous combustion.
This temperature is designated the light off temperature
(L.O.T.). The various light of~ temperatures and the carbon
monoxide produced under the specific conditlons of these
runs are set out in Table VIII a~ter relatively steady state
operation was apparently reached~
Table VIII
Run Pt~% Other Metal L.O.T.~C. C~,Mol %
52 0.3 - 269 1.50
15 53 0.3 1%CoO 280 0.72
54 0.3 l~Sb~03 293 0-39
0.3 1%SnO2 310 0.86
56 0.3 170NiO 324 0.78
57 0.3 1%CaO 343 0.83
Since the light off temperature is an indicator of the
relative oxidation activity of a catalyst, the lower the
light off temperature the more active the catalyst, this
data indicate that the cocatalyst does not promote the
oxidation activity of the platinum.
The data in the above examples suggests that the
cocatalyst in the bimetallic catalyst does not affect the
oxidation reaction per se, but rather that it functions
in some other manner to cause a reduction in carbon monoxide
such as, for example, by directing the steam reorming
reaction and the water yas shi~t reaction to reduced carbon
monoxide levels. When two combustion ~ones are utilized,
the bimetallic catalyst can be used in both combustion
zones for reduced carbon monoxide levels. Or, if preferred,
for reduced carbon monoxide levels, the bimetallic catalyst
can be used in the first combustion zone and a monometallic
oxidation catalyst, such as platinum, can be used in the
second combustion zone.
~iL33~ ~
-20-
The information obt~ined ~rom these experiments is
utilized in an integrated tertiary oil recovery operation
by in situ combus-tion according to the following example.
Example 10
An in situ fire flood is initiated in an oil zone
in an underyround petroleum reservoir at an overall depth
of about 1,830 meters. Oil production from the formation had
been exhausted following secondary recovery by water injection.
The fire is initiated in the formation and s eady state
conditions are reached in about 10 weeks. At this time about
2.6 X 105 cubic meters per day of air at a temperature of
about 93 C. and a pressure of about 19.3 MPa are pumped
into the injection well by a multistage compressor, which
is driven by a gas turbine. The combusted gas and entrained
hydrocarbon liquids are produced in adjacent production wells.
The entrained liquids are removed in a separator resulting
in about 2.1 X 105 cubic meters per day of liquid-free,
waste flue gas of low heat content. The temperature of this
1ue gas is abouk 35 C. and its gauge pressure is about 1.04
MPa~ Its average analysis over a l9-day period is about 2.2
percent methane, about 0.5 percent ethane, about 0.4 percent
propane, about 0.3 percent butane, about 0.25 percent
pentanes, about 0.2 percent hexanes and higher, about 500 ppm.
sulfur, about 15 percent carbon dioxide, about one percent
argon and the remainder nitrogen. Its average heat content
for this l9-day period is about 2,920 kJ/m3 with a maximum
value of about 3,400 and a minimum value of about 2,300
during this period.
This flue gas is combusted in two stages. The
catalyst in the first stage i8 a bimetallic oxidation
catalyst comprising about one percent cobalt oxide and about
0.3 percent platinum impregnated on an alumina-coated
Torvex monolithic ceramic support. The catalyst in the
second~stage is a monometallic platinum oxidation catalyst `
35 comprising about 0.3 percent platinum on the same support ;~
as used in the first stage. Over this l9-day period under
study the flue gas is combusted by the injection of a
constant amount of air, approximately egually divided
-21-
between the input to each combustion stage, to provide an
average air equivalence ratio of a~out 0.64. As a result the
combustion is substoichiometric over the entire l9-day
period. The flue gas-air mixture is heated above i~5
ignition ~emperature by heat exchange with the combusted
gas from the Eirst stage before it is introduced into the
first combustor. The combusted flue gas is mixed with the
second portion of combustion air after the heat exchanger and
prior to entering the second combustor. ~he gas stream
leaving the second combustor has a temperature of about
843 C. This hot gas stream is used to drive the gas
turbine which is desiyn~d for an operating temperature of
788 C. Therefore, a sufficient quantity of the 93 C.
compressed air is bled from the compressed air line and `
in~ected into the combusted flue gas prior to the turbine
inlet to drop its temperature to about 788 C. The
combusted flue gas is introduced into the turbine at a gauge
pressure of about 620 kPa and exits at near atmospheric
pressure. Since the first combustor used the bimetallic
catalyst, the turbine exhaust contains less than one
percent carbon monoxide permitting it to be vented directly
to the atmosphere.
The pressure of the air injected into sub-
terranean deposits of carbonaceous materials will vary over
a wide range, such as about 3.5 MPa to about 35.0 MPa
or even wider. Th~ actual pressure used depends on many
factors including the depth and down-hole pressure in the
formation, the permeability of the formation, the distance
between the injection and producing holes, and the like.
In any particular recovery operation utilizing in situ
combustion the injection pressure limits are a minimum
pressure sufficient to obtain adequate flow of gas through
the formation and a maximum pressure less than the amount
which would crack the ormation and permit the air to
bypass the combustion zone. There will generally be a
substantial diminution of the gas pressure between the
injection and production wells, the amount depending on
the many variables inherent in the characteristics of
:, ,: ~ . : . .
~; :, . . i :: ,:......... , . . : . i: . , ,,
- -:: : ,; . :: . . . :: :.: :,. :: -; . :
3~
-22-
the formation as well as the variables in the operating
procedures. In order to effectively carry out an integrated
operation in which the flue gas under pressure is combusted
and used to drive a gas turbine, as described herein, it is
desirable that the recovered flue gas possess a pressure
of at least about 500 kPa.
The air compressor can be operated at a
temperature as low as about 650 C or eve~ lower, but
since efficiency exhibits a significan~ drop at the lower
temperatures, it is preferred to operate at a temperature
at which significant efficiency is obtained, and particularly
a temperature of at least about 760 C. The maximum
temperature is determined by the temperature resistance
of the materials from which the turbine is constructed and
can be about 1,100 C~ or even higher particularly if the
compressor is designed with provision for auxiliary
cooling but it is prefexred that the maximum operating
temperature be about 1,000 C~ Generally, a large capacity
turbine of the type which would be used in the utilization
of waste gases from subterranean in situ combustiQn processes
is designed for optimum operation within a specific
restricted temperature range.
In the two stage combustion procedure, it is
desirable if at least about one-third of the total air
which is to be used in the substoichiometric combustion
be added in one combustor, and it is generally preferred
that about one-half of this combustlon air be added in
each combustor. This variation in the amount o
combustion air added to each combustor permits the tem-
perakure of the waste gas stream, entering the firststage reactor ollowing heat exchange with the combusted
gas from the first stage,to be varied~ This air that is
used for combustion of the waste gas,as well as the air
that may be used for cooling the combusted waste gas down
to the desired turbine operating temperature, needs to
have a pressure only moderately higher than the pressure
of the gas streams into which it is injected. For this
reason, it is preferred that this air be obtained from
, :: :.:: , , .:.: :: . :: :, .: . , .,,: ,
, .- : .,: ,: ::.: . ;.:.: , . :: ,. . . ..
~;33 7~
-23-
a separate low pressure compressor or from a low pre~sure
stage in the multis-tage compressor rather than using the
high pressure air that is obtained for injection into the
in situ combustion zone.
As indicated, the temperature of the gas stream
following the combustion zone cools down as it flows
through the formation so that it is at ~bout the reservoir
temperature by the time it is producedO ~s a result, water
vapor in the gas will condense out into the formation
prior to the production wellsO Additionally, it is believed
that sulfur dioxide which may be produced in the under-
ground combustion will remain in the reservoir with the
water.
As *he final stages of the in situ combustion
near, the combustion zone approaches a production well and
shows its presence by causing a significant temperature
elevation. Since some of the down-hole gases are used to
replace the hydrocarbons which are displaced in the
direction of the production wells, and since some of the
gases leak off into other formations, the amount of flue
gas will be less than the amount theoretically obtainable
from the quantity of injected air.
It is to be undexstood that the abova disclosure
is by way of specific example and that numerous modifications
and variations are available to those of ordinary skill
in the art without departing from the true spirit and
scope~of the invention.
