Note: Descriptions are shown in the official language in which they were submitted.
l`Si
NOVEL CARBONACEOUS MATERIAL AND PROCESS FOR
PRODUCING A HIGH BTU GAS FROM THIS MATERIAL
_
This application is a division of Canadian Serial No.
306,997r filed July 7, 1978.
5 Hydrogen reacts rapidly with the carbonaceous material to produce
a methane rich gas containing at ~east 20~ by volume methane,
thereby providing an economical method for producing a methane
rich gas. The carbonaceous material may be substantially depleted
of carbon without diminishing its high specific rate of reactivity
10 with hydrogen. The carbon depleted material may be replenished
with carbon by exposure to carbon monoxide. This carbon deposition-
methanation cycle may be repeated continuously, thus providing
the basis for a commercial process to make methane from producer-
type gas. In the course of cycling the material between carbon
15 rich and carbon lean states, the carbonaceous material undergoes
a transformation into a hydrogen promoted material which has a
higher deposition rate and methanation rate than the unpromoted
material used at start up. Almost all the carbon in both the
unpromoted and hydrogen pro ted carbonaceous material may be
20 reacted with hydrogen without deactivating the material for
carbon d~position or methanation.
BACXGROUND O~ THE INVENTIO~
-
Various carbonaceous material are well known and
have been used as pigments, sources of coke, chemical absorbers,
etc. One type of carbonaceous material forms through the dispro-
portionation or carbon deposition reactions of carbon monoxide in
the presence of a ferrous group metal-based catalyst material.
As used herein, the word "disproportionation" means any of
-- 1 --
` 31-006C
the r.eactions which result in the deposition of carbon from carbon
monoxide, such as the following:
2 CO ) C + C2
CO + ~2 ~ C + ~2
In many chemical processes the formation of such carbonaceous
materials through the carbon monoxide disproportionation reaction
is an undesirable side reaction and may even deactivate the
catalyst used in such processes due to carbon deposition
on the catalyst. Generally, the carbonaceous material so
formed has had little commercial value. It has been known that
carbonaceous materials will react with hydrogen to form methane,
the main ingredient of natural gas. But the known carbonaceous
materials have had such a slow rate of reaction that a commercial
1~ process based on this reaction was not feasible. Society's
demand for methane has, however, increased and almost outstripped
the supply. It has been proposed tha~ methane may be produced
from coal, and consequently, extensive research is being conducted
to find ways to economically convert coal into methane. For
example, prior art workers have synthesized methane from carbon
monoxide and hydrogen. Carbon monoxide and hydrogen are produced
by burning coal in a mixture of oxygen and steam. Oxygen is
used rather than air because the mixture of carbon monoxide and
hydrogen used for methane synthesis should not contain substantial
2~ amounts of nitrogen, because nitrogen cannot be readily separated
from the synthesis gas or the methane product. One disadvantage
of this process is that large and costly oxygen producing plants
are used. Moreover, the carbon dioxide produced in the pre-
methanation steps of the process is removed from the carbon
31-006C
monoxi,~e-hydrogen feed stream, in order to have a final product
gas of high Btu content. It is relatively expensive to rem~ve the
carbon dioxide gas rom the carbon monoxide-hydrogen feed stream
because such removal involves a gas separation step.
s
THE INVENTION
Carbonaceous Material
We have dis o~ered novel carbonaceous materials which
are highly reactive, particularly with hydrogen, to form methane.
The carbonaceous materials may be in two forms, one being
unpromoted carbonaceous material and the other being hydrogenated
promoted carbonaceous material. The latter is formed by passing
hydrogen over the unpromoted material. ~he carbonaceous
material comprises a multiphase, intimate association of a carbon-
rich major phase and one or more ferrous group metal-rich minor
phases that aré dispersed in, and at least partlally bonded to,
the carbon. The ferrous group metal components catalyze
the reactions of carbon formation from carbon monoxide and of
methane formation from the hydrogenation of the carbonaceous
material. To attain this catalytic activity, it appears that
the ferrous group metal component should be present in an amount
of at least 0.5 weight percent based on the total weight of the
material. Preferably, the ferrous group metal component should
comprise at least 1 weight percent of the total weight of the
material~ In the unpromoted carbonaceous material the ferrous
group metal component preferably comprises between 1 weight
percent and 3.5 weight percent; based on the total weight of the
material. When the ferrous group metal is present in this amount,
it has the capability to cataly2e the reaction between the carbon
present in the composition and hydrogen to form methane at a
methanation rate of at least 0.1 mole of methane formed per
hour per mole of carbon present when the carbon is contacted
;
~ -3-
31-006C
~ ~t~
with hydrogen at a temperature of 550C, one atmosphere pressure,
and ia minLmum hydrogen feed ra~e of 2 moles of hydrogen per
hour per mole of carbon present. This reactivity with
hydrogen is a distinguishing characteristic of our materials, and
is substantially higher than that of other forms of càrbon.
Moreover, our materials maintain their high rate of reactivity
even after being substantially depleted of or enriched in
carbon. Water has an effect on the reactivity of our
material, and under some conditions may impede the rate at
which methane is formed. Consequently, at atmospheric
pressure, the hydrogen should contain less than about 1%
water by volume.
The ferrous group metals appear to be transported
into the partly-crystallized carbon network, and become dispersed
randomly in this network. At lea5t some of the dispersed metal
is bonded to the carbon. Some metal may occupy spaces between
the planes of the carbon. Whatever the structure may be,
our carbonaceous materials appear to be unique.
The unpromoted form of carbonaceous material of our
invention is formed by passing carbon monoxide over a ferrous
group metal-based carbon monoxide disproportionation initiator.
The carbonaceous material forms on the surface of the dispro-
portionation initiator when the initiator is exposed to a
carbon monoxide-containing gas at a temperature of between
300C and about 700C, preferably 400C to 600C. The
pressure may vary between about 1 and about 100 atmospheres,
but the preferred range is from 1 to 25 atmospheres. Preferably
the carbon monoxide-containing gas includes some hydrogen.
Initially ferrous group metal carbides form, but as the reaction
proceeds the carbonaceous material begins to accumulate on the
31-006C
surface of the disproportionatio~ initiator. Carbon monoxide
is maintained in contact with the disproportionation initiator
until substantial amounts of unpromoted carbonaceous material
deposit on the initiator.
The ferrous qroup metal-based car~on monoxide dispropor-
tionation initiators are selected from the group consisting of
iron, cobalt and nickel, and mixtures thereof, oxides of iron,
cobalt and nickel, such as cobalt oxide, nickel oxide, ferrous
oxide, ferric oxide, and mixtures thereof, alloys of iron,
cobalt and nickel, and mixtures of such alloys, such as iron/
nickel alloys, and ores of iron, cobalt and nickel. We shall
refer to such ferrous gro~p metal-based carbon monoxide
disproportionation initiators as the "bulk metal" in order
to distinguish them from the metal dispersed in and at least partly
bonded to the carbon forming the minor phase in the
carbonaceous material of our invention. Only the dispersed and
bonded metal forms part of our new, catalytic compositions of
matter.
Examples of the ferrous metal-based initiators, and the
forms those initiators take, are: ferric oxide powder, hematite
type iron ore composed mostly of Fe2O3, electrolytic iron chips,
carbon steel spheres, steel wool, nickel oxide, cobalt oxide,
high purity nickel chips, high purity cobalt chips, iron-nickel
alloy buttons, iron-cobalt alloy buttons, and stainless steel.
Various ferrous metal ores may be used to initiate the formation
of the carbonaceous material. ~or example, we have used Mesabi
Range iron ore with good results. The use of such ore and the
like is desirable because it is readily available and inexpensive.
Alternatively, the bulk metal may be on a support of, for example,
silica, alumina or the like without adversely affecting the
formation of the carbonaceous material. One of the advantages
X~ 5
~ 4j 31-006C
of both the unpromoted and hydrogen promoted carbonaceous material,
however, is that it is not necessary to use a support to
increase its surface area because the carbonaceous material has a
high surface area-itself. For example, the surface area of the
; carbonaceous material may range from 50 square meters per
gram to as high as 500 square meters per gram, with the
normal range being from about 150 s~uare meters per g~am
to about 300 square meters per gram.
For the carbonaceous material to have the desired
reactivity, it appears that it must be formed in-situ. That
is, simply mixing the bulk metal with carbon does not result
in our carbonaceous material. Typically, the carbonaceous
material grows from the surface of the bulk metal as fibers,
possibly hollow fibers. Typically, the fibers have a di-
ameter in the range of about 0.02 micron to about 2.0 micron
and a length to diameter ratio greater than about 10. We
have analyzed these fibers and found that most contain minute
particles of a metal component (minor phases), such as alpha-
iron, iron carbide or iron/nickel alloys. Apparently, the
ferrous metal component is transported into the carbonaceous
fibers. This transported ferrous metal component is no
longer physically associated with the bulk ferrous metal and
is an essential part of the highly reactive carbonaceous
material. When we methanate our iron-based carbonaceous
material to convert over 95% of its free carbon to methane,
mix the resulting carbon-lean material with particulate
carbon, and then expose this mixture to hydrogen at the pres-
sure and temperature ranges we normally use for methanation,
no methane forms.
l ~t~
It should be understood that it is difficult to
distinguish the active ferrous metal component in the carbon-
aceous material from the bulk ferrous metal when small particles
of bulk ferrous metal are used. In characterizing the carbon-
S aceous material of our invention, we conducted a series oftes's using plates of iron, nickel, cobalt and an iron-nickel
alloy as the initiator of the carbon monoxide disproportionation
reaction and deposited the carbonaceous material on these
plates. The carbonaceous material formed as a billowy mound
of fibers on the plate, permitting the plate to be simply
physically separated from the carbonaceous material. This
allowed us to analyze the carbonaceous material separately
from the bulk metal. Starting with an iron plate, the (as
separated) carbonaceous material formed in-situ contained
from about 1 to about 3.5 percent by weight of dispersed iron
component as determined by both spectroscopic analysis and
ashing techniques. The balance of the material contained
principally carbon with trace amounts of hydrogen. The carbon
was partially graphitized. Partially graphitized carbon has
been discussed in detail by R. E. Franklin in his paper published
in "Acta Cryst", vol. 4, pp. 253, (1951).
In one broad aspect, the invention contemplates a
process for producing a high Btu gas which comprises contacting
a carbonaceous material made up of carbon and a ferrous group
metal component which is dispersed throughout the carbon and
intimately associated with and at least partly bonded to the
carbon, the carbonaceous material having a high reactivity
with hydrogen to form methane, with a hydrogen containing
gas, under conditions that cause the hydrogen to react with
the carbonaceous material to form a methane-rich gas.
The invention contemp]ates a fiber which includes
partially graphitized carbon and a nodule comprising a metal
alloy containing as one ingredient of the metal alloy a
ferrous group metal, the nodule being at least partially
bonded to the carbon.
The invention also contemplates a method of increasing
the reactivity of a carbonaceous material formed by dis-
- proportionation of carbon monoxide and having a first ~cvcl
of reactivity, and it includes the steps of reacting the
material with hydrogen to produce methane, thereby
depleting a portion of the carbon content of the material,
and reacting the carbon depleted material with carbon
monoxide to replenish the carbon content through dis-
proportionation of the carbon monoxide to increase the
reactivity from the first level to a higher level.
In another aspect, the invention contemplates a
method of preparing a carbonaceous material which comprises
contacting a carbon monoxide containing gas with an initiator
including a ferrous group metal under conditions to form on
the initiator a carbonaceous material. The carbonaceous
material includes nodules containing the ferrous group
metal. A hydrogen containing gas is contacted with the
carbonaceous material formed in the carbon monoxide containing
step under conditions to remove at least 15% by weight of
the carbon contained in the carbonaceous material formed
in that step.
In another aspect, the invention comprehends a process
where carbonaceous particles derived from the disproportion-
ation of carbon monoxide are mixed with fluids by the method
of separating the particles from the fluid by subjecting
the particles to a magnetic field and also a method for
removing sulfur compounds from a gas stream by contacting
the gas stream with a carbonaceous material formed by the
-- 8 --
.21~i
d:isproportionation of carbon n)onoxide in the presence
o1E an initiator including a ferrous group metal.
The invention further comprehends a process for
producing electricity and a carbonaceous material from a
low Btu gas including carbon monoxide, which process
comprises contacting the low Btu gas with an initiator
including a ferrous group metal to disproportionate a part
~ of the carbon monoxide in the low Btu gas to Eorm a carbon-
aceous material that reacts rapidly with hydrogen to
produce methane, the disproportionation reaction being
exothermic, thereby elevating the temperature of the un-
reacted portion of the low Btu gas. The unreacted portion
of the low Btu gas is separated from the cal-bonaceous mat~rial
formed in the initiator contacting step and burns this
unreacted portion to provide an essentially fully combusted
gas. The essentially fully combusted gas derived from
separating the carbonaceous material step is then passed
through a turbine to generate electricity.
One aspect of the invention is a product fiber
which includes partially graphitized carbon and a nodule
comprising a metal alloy containing as one ingredient of
the metal alloy a ferrous group metal, the nodule being at
least partially bonded to the carbon.
A further product is an enhanced carbonaceous material
produced by disproportionating carbon monoxide on an
initiator including a ferrous group metal to form a carbon-
aceous material. A part of the first carbonaceous material
is reacted with hydrogen to produce methane, thereby
reducing the carbon content of the first carbonaceous
material. Additional carbon monoxide is disproportionated
in the presence of the first carbonaceous material to thereby
produce a second, carbon enriched carbonaceous material,
- 8a -
2~6~
and the sccond car~onaceous ma~erial is reacted with
hydrogen to produce methane and remove a part of the carbon
therein, thereby producing the enhanced carbonaceous
material.
A variation of the latter product is a carbonaceous
material comprising carbon, hydrogen, and at least 0.5 weight
percent of a ferrous group metal component dispersed through-
out the carbon. The carbonaceous material has been subjected
to at least two cycles of carbon deposition and methanation,
carbon deposition being accomplished by disproportionation
of carbon monoxide to form the carbonaceous material and
methanation being accomplished by contacting the carbonac-
eous material after carbon deposition with hydrogen to
produce methane, not all of the carbon in the carbonaceous
material being removed therefrom during methanation.
A further variation is a carbonaceous material
comprising carbon, hydrogen, and at least 0.5 weight per-
cent of a ferrous group metal component dispersed
throughout the carbon. The carbonaceous material has been
subjected to at least two cycles of carbon deposition and
methanation so that the carbonaceous material exhibits a
greater carbon deposition rate and a greater methanation
rate than a carbonaceous material having about the same
concentration of carbon and ferrous group metal component
and not having been subjected to carbon deposition and
methanation.
A still further product variation is a carbonaceous
material including carbon and at least 0.5 weight percent
of a ferrous group metal component dispersed in and at
least partiaily bonded to the carbon in the material. The
material is subject to a series of carbon deposition and
- 8 b -
methanation cyclic treatments to enhance its rate of carbon
deposition and rate of methanation.
Yet another inventive product is a carbonaceous
material for providing a source of carbon having a high
reacti~ity level to react with hydrogen. The material has
a composition of partially graphitized carbon in the range
of from about 65% by weight to 99.5% by weight and a
ferrous group metal component in the range of from about
0.5~ by weight to about 35% by weight. A minimum reactivity
level is measured by the formation of methane at the rate
of at least 0.3 mole of methane formed per hour per mole of
carbon at a reaction temperature of 550C, one atmosphere
pressure, and a minimum hydrogen feed rate of 2 moles of
hydrogen per hour per mole of carbon.
The invention also contemplates a method of catalyzing
chemical reactions by carrying out such reactions in the
presence of a catalyst comprising a fibrous, carbonaceous
matrix containing chemically incorporated ferrous group metal-
rich nodules. The nodules extend across substantially the
entire diameter of the fibers, and the fibers are otherwise
substantially free of ferrous group metal. The nodules are
intimately associated with and at least partially bonded to
the carbon in the matrix.
Additionally, the inventive process also contemplates
a method for producing a methane containing product gas from
a fossil fuel which comprises burning the fuel in air under
controlled conditions to form a producer gas including
carbon monoxide, hydrogen, carbon dioxide, and nitrogen, and
contacting the producer gas with an initiator including a
ferrous group metal under conditions which form on the
initiator a carbonaceous material comprising carbon and a
ferrous group metal component ~Ihich is dispersed throughout
- 8 c -
f~
t~ ?~j
the carbon and intimately associated with and at least
partially bonded to the carbon, wherein the carbonaceous
material has a reactivity with hydrogen to form methane at
a rate of at least 0.1 mole of methane formed per hour per
S mole of carbon present in the carbonaceous material when
the carbonaceous material is contacted with hydrogen at a
temperature of 550C, one atmosphere pressure and a minimum
hydrogen feed rate of 2 moles of hydrogen per hour per
mole of carbon present. The carbonaceous material is reacted
with a gas containing hydrogen to form a methane containing
product gas, thereby at least partially depleting the carbon
in the carbonaceous material, and the carbon depleted carbonac-
eous material is contacted with producer gas under conditions
which form additional amounts of the carbonaceous material
which is thereafter contacted with a gas containing hydrogen
to form a methane containing product gas.
The invention additionally contemplates a method of
making a composition which catalyzes the reaction between
hydrogen and carbon monoxide to form hydrocarbons with the
composition including a predetermined amount of a ferrous
group metal component and carbon, which includes the steps
of selecting a metallic substance which includes a ferrous
group metal, the substance being inactive, or of low
activity, as a catalyst for the reaction between hydrogen
and carbon monoxide. A carbon monoxide containing gas is
contacted with the substance under conditions where the
carbon monoxide disproportionates to form a fibrous carbon-
aceous material including carbon and a ferrous group metal
component transported from the substance with the component
being dispersed throughout the fibrous carbon matrix as
noduIes which extend across substantially the entire diameter
of said fibers, said fibers being otherwise substantially free
of ferrous group metal, and said nodules being intimately
.. .
~g~ - 8 d -
.~ ~
~ ~t;~Zlf~
associated with and at least partially bonded to the carbon,
and the carbonaceous material is contacted with hydrogen under
conditions where the hydrogen reacts rapidly with the carbon
in the material to form methane with the contacting being
continued until the carbonaceous material is enriched with the
ferrous group metal component an amount equal to the predeter-
mined amount.
In a further embodiment, the invention contemplates a
method of catalyzing chemical reactions by carrying out such
reactions in the presence of a catalyst comprising a fibrous,
carbonaceous matrix containing chemically incorporated ferrous
group metal-rich noduIes with the nodules extending across
substantially the entire diameter of the fibers. The fibers
are otherwise substantially free of ferrous group metal, and
the nodules are intimately associated with and at least parti-
ally bonded to the carbon in the matrix. The catalyst comprises
a predetermined amount of the ferrous group metal-rich nodules
formed by removing some carbon from the matrix.by reaction with
hydrogen, or adding some carbon ts the matrix by reaction with
carbon monoxide, or a combination of the two.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a photomicrograph showing fiber detail;
Fig. 2 is a photomicrograph of the fibers in lesser
detail than Fig. l;
Fig. 3 is a graph showing the methanation rate;
Fig. 4 is a schematic presentation of the inventive
apparatus;
Fig. 5 is a further schematic presentation of the
inventive apparatus, shown with Fig. 3;
Fig. 6 is another sehematic presentation of the
inventive apparatus;
- 8 e -
~,
3,1~
Fig. 7 is another schematic presentation of the
inventive apparatus;
Fig. 8 is another s~hematic presentation of the
inventive apparatus;
Fig. 9 is a photomicrograph of another carbonaceous
material.
We have examined carbonaceous fibers formed on
an iron plate using a scanning electron microscope. Figure
2 is a micrograph showing fibers of our material as seen
through a scanning electron microscope under relatively low
magnification. Figure 1 is a micrograph showing, in
greater detail, some of the fibers under relatively high
magnification using the scanning electron microscope. The
fibers shown in Figures 1 and 2 are unpromoted, i.e., not
hydrogenated. In one representative sample fiber, identified
as A, an area of high iron concentration was positively
identified. Fiber areas with an electron microprobe analyzer,
and the nodule B was positively identified as containing iron.
This nodule was about 3000~ long and about lo00A wide. This
analysis was made according to the analytical procedures
described by J. R. Ogren in "Electron ~icroprobe," Chapter 6,
in "Systematic Materials Analysis," Volume 1, Academic Press,
Inc., New York 1975. Assuming the fiber is solid and it
exhibits a density intermediate between that of amorphous
and fully graphitized carbon, the detectability limit of the
microprobe analysis is about 1.5% by weight iron.
,, ~ g_
~_a~
31-006C
21~
X-ray analysis of the samples of unpromoted car-
bonaceous material (deposited on bulk iron plates) showed
iron to be present as a form of iron carbide and, pos-
sibly, as alpha-iron as well. The Debye-Scherrer method
was used to obtain powder diffraction patterns on a
General Electric Model XRD-5 X-ray spectrometer. Using
the same method to analyze hydrogenated promoted material
revealed that the X-ray detectable iron in the hydrogenated
material was present only as alpha-iron.
As the micrograph in Figure l shows, the iron
component is bonded to the carbon. We have attempted to
break this bond and separate the iron component from the
carbon by simple physical means such as sifting through
sieves and pulling the iron from the carbon with magnets.
These methods, however, did not achieve separation. Since
the iron component in the carbonaceous material cannot be
separated from the carbon by simple physical means, this
indicates to us that at least a part of the iron is inti-
mately associated with the carbon and at least part of the
iron is bonded to the carbon, possibly at the atomic or
molecular levels. Or, perhaps the iron is in solid solu-
tion in the carbon. If this is so, the interfaces of the
iron-carbon solid solution and crystals of the iron compo-
nent may be active sites which cause the rapid reaction
rate. Whatever bond is formed between the iron and carbon,
we have found that iron by itself, activated charcoal by
itself, commercial cementite (Fe3C), and a simple physical
--10--
~ ., .
31-006C
Zlfj
mixture of iron and activated charcoal do not have the
properties of the carbonaceous material of our invention.
None of these compounds or mixtures, when contacted with
hydrogen at elevated temperatures, will form methane
at the rates approaching the rate attained using our car-
bonaceous material. This is shown in the following
Table I.
X
31-006G
TABLE 1
Methanation
Carbonaceous C/Fe Rate
Material Separated Atom (Moles CH4~Hr/
Starting Material From Iron`Initiator Ratio Mole Carbon)
1. Carbon deposited from C0/H2 No 27.3* 0.10
gas stream at 550C and 1 atm
onto high purity iron foil.
2. Carbonaceous material from Yes 176 0.10
sample 1 separated from foil
and rehydrogenated.
3. Carbonaceous material deposited Yes 220 0.28
on 1/8 inch carbon steel spheres
at 500C from COIH2 gas
stream at 1 atm pressure.
4. Carbonaceous material** Yes 12.6 0.49
initially prepared by several cycles
of carbon deposition and hydro-
genation at 550C and pressure
from 100-250 psi over 3/16 inch
carbon steel spheres. Sample
separated from spheres and
carbon deposited from 1 atm
C0/H2 gas stream.
5. Mesabi range iron ore pre- No 7* 0.24
retuced in H2 and then used to
catalyze carbon deposition
from C0/H2 gas stream at
500C and 1 atm.
6. ~a~e a~ sample 5 except ex- No 7* 0.20
posed to ambient air for 96 hrs
at 25C before hydrogenation,
7. Commercial cementite Fe3C. - 0.33 <0.05
(no CH4 detected)
8. Norit-A activated charcoal. - >1000 <0.0004
9. Char from coal gasification. - >1000 <0.0004
10. Norit-A charcoal mixed with - 4-7* <0-0004
electrolytic iron powder 50:50
wt. basis.
11. Spectoscopic graphite powder. - >10,000 ~10-7
*Includes bulk iron.
**Hydrogen promoted material.
-12-
31-006C
.;*21~
Figure 9 shows a scanning electron micrograph
of another of our carbonaceous materials.prepared by
carbon monoxide disproportionation over a bulk metal
alloy plate consisting essentially of about 50% nickel
and about 50% iron. After separating the fibrous car-
bonaceous material from the alloy plate, the carbonaceous
materlal was found to contain 98.42~ C, 0.4&% Fe, 0.73% Ni
and 0.94% H.* The area marked by a circle in the micro-
graph was analyzed with an electron microprobe and was
found to contain high concentrations of both iron and
nic~el in approximately equal amounts. X-ray analysis
of a representative sample of the fibers indicated the
presence of iron-nickel alloy. It a~pears likely that
the nodule C shown in the circle in Figure 9 actually
consists of an iron-nickel alloy. Whether or not the
nodule C shown in Figure 9 is a true solid solution alloy
of iron and nickel, our analysis clearly shows that very
small crystallites or nodules containing both iron and
nickel were transported from the bulk metal alloy plate
to the carbon fibers and became intimately associated with,
and probably bonded to the fibers.
* Unnormalized data which does not add up exactly to 100~.
~7
~ . ~
31-006C
2~
One way of thinking about our material is t~at
the active ferrous group metal component is a catalyst
that is dispersed throughout a carbon matrix. This fer-
rous group metal component catalyzes the reaction of the
S carbon in the matrix with other reactants. Carbon is
depleted as the reaction proceeds, but the material may
be replenished with carbon by exposure to a carbon monoxide-
containi~g gas. When exposed at elevated temperatures
to carbon monoxide, the active component catalyzes the
disproportionation of carbon monoxide.
We have discovered that even though carbon is
depleted from the material by reaction with hydrogen, the
material retains its high specific methanation rate. Sur-
prisingly, we have been able to remove almost all the carbon
from the carbonaceous material and still maintain a rela-
tively high specific rate of methanation. This property
of the material is illustrated by Figure 3 where the specific
methanation rate of the carbonaceous material is plotted
against the percent of the carbon removed by hydrogenation
of the material. (The rates shown in Figure 3 were determined
at 570-600C, and 1 atmosphere pressure.) The carbon
rich material (i.e., the material containing about 96%
carbon) had an initial reactivity of about 0.30 moles CH4/
hr/mole of carbon. This reactivity ~radually increased to
about 0.63 moles CH4/hr/mole of carbon when about 88~
of the carbon was removed. When about 90% of the carbon
was removed, or when the material contained about 25 weight
percent of the iron component, its reactivity decreased
-14-
`~'.'.~
. i . ,~.
31-006C
~ 1t.~
rapidly. If the carbon rich material had contained,
initially, 95 weight percent carbon and 5 weight percent
iron, the final material, after removal of about 90% carbon,
would contain about 35 weight percent of iron.
The new carbonaceous material retains its important
and valuable properties after many cycles of carbon enrichment~
carbon depletion. Using iron as the ferrous group metal component,
we have completed 55 such cyeles, and have obtained our
unique, hydrogen-promoted material each time.
Our new carbonaceous materials also retain their
properties after extended periods of storage, whether stored
in the carbon-enriched or in the carbon-depleted states.
However, because exposure of these materials to oxygen may
oxidize the ferrous metal group components, and thus impair
lS their catalytic activity, we avoid exposing them to air
durins storage. After we store our iron-based carbonaceous
material for 24 hours at room temperature, we observe no
deterioration in its rate of methanation.
Based on the above experiments we have found that
the carbonaceous material of our invention may vary in
composition approximately as follows:
"''~
31-~06C
21tj
General % Preferred %
by weight by weight
i?artially Graphitized Carbon 65-99.5% 75-99%
~ispersed FerrousGroup
Metal Component 0.5-35% 1-25%
Weight percentages were determined after the carbonaceous
material was separated from the bulk ferrous group metal.
For iron-based materials, we prefer the unpromoted carbonaceous
material to contain from about 1% to about 3.5~ weight percent
of ferrous metal component and from about 99 to 96.5 weight
L0 percent of carbon.
Hydrogen Promoted Material
We ha~e found that at least some of our carbonaceous
materials, when subse~uently hydrogenated, have an enhanced
carbon deposition rate and methanation rate. Specifically,
where the ferrousgroup metal component is iron, the hydrogen
promoted carbonaceous material has a carbon deposition
rate exceeding 10 grams of carbon deposited per hour per gram
of dispersed iron present, and a methanation rate exceeding
0-3 moles of methane formed per hour per mole of carbon present.
The carbon deposition rate was measured at 500C, one atmosphere
pressure, and a feed rate of 10 moles of carbon monoxide per
hour per gram of dispersed iron using a feed gas that contains
80% by volume carbon monoxide and 20% by ~olume hydrogen.
25 The ~ethanation rate was measured at 550C, one atmosphere
pressure, and a minimum hydrogen feed rate of 2 moles of
hydrogen per hour per mole of carbon present.
Although the feed stream used to make the
carbonaceous material may contain hydrogen, the hydrogen promoted
material is not produced as long as conditions prevail where
carbon is deposited on the bulk metal. When the carbonaceous
31-006C
material formed initially is subjeGted to hydr~genation to
procluce methane, then our hydrogen promoted material begins
to i.orm. We have observed the formation of this material
when about 15~ by weight of the carbon was removed by hydroge-
nation of the carbonaceous material initially prepared.
Moreover, the hydrogen used normally should contain not more than
about 1% water by Yolume.
We have separated the hydrogen promoted material
from the bulk metal and found that this material has the same
general physical appearance as the material initially
prepared, but the X~ray identification indicates that, where
the ferrous group metal component is iron, the iron is alpha-
iron rather than carbidic iron. The hydrogenated material,
when subjected to several cycles of carbon deposition and
methanation, has an even greater reactivity than prior to
such cyclic treatment. Moreover, as it undergoes such cyclic
treatment, its composition may vary approximately as follows:
% by weight
Partially Graphitized 65-99.5
Carbon
Ferrous Metal Component .5-35
Hydrogen .1-3.0
The hydrogen in our new materials is strongly associated.
When we hea~ our iron-based carbonaceous material
in a nitrogen gas stream from a temperature of about 200C
to a temperature of about 950C, and analyze the carrier
stream for desorbed gases, principally hydrogen and carbon
monoxide, we find that the quantity of hydrogen present in
our carbonaceous material is more than fifty thousand times
the quantity we can dissolve in alpha-iron. Moreover, more
.. ~ .
~ 31-006C
than two-thirds of the hydrogen released during such runs
comes off at temperatures above 700C.
Again, it is emphasized that when we speak of weight
percentages, we are speaking of our carbonaceous material,
5 both hydrogenated promoted and unpromoted, after it has been
separated from the bulk metal.
Exa les of Carbonaceous Material
mp
The following Examples show how some of
the carbonaceous materials of our invention were prepared.
10 Example 4 shows the methanation rates for several different
ferrous group metal catalysts of our invention. Example 5
shows the unexpectedly good thermal stability of our catalytic
materials.
Example 1
lS Carbon was deposited on one-eighth inch mild
steel balls (5 grams) by decom~osition of carbon-
monoxide at 550C from a carbon monoxide and hydrogen
gas mixture in a tube furnace. The flow rate of the
carbon monoxide was 100 cubic centimeters per minute
and the flow rate of the hydrogen was 20 cubic centi-
meters per minute. After about 4 hours, 2.7 grams of
the carbonaceous material containing 3.7% by weight
of iron was separated from the steel balls, and 0.27
grams of the separa~ed carbonaceous material was also
exposed to the same carbon monoxide and hydrogen
gas mixture at 500C and 1 atmosphere pressure. It
was found that the carbon deposition rate was 8.8 grams
of carbon per hour per gram of dispersed iron in the
carbonaceous material present. This carbonaceous
material, had a methanation rate of 0.52 moles of
methane formed per hour per mole of carbon. Carbon
was again deposited on the hydrogenated material using
the same carbon monoxide-hydrooen gas mixture and
contacting the material at 500C at one atmosphere.
The carbon deposition rate was 39.4 grams of carbon
per hour per gram of dispersed iron. Cycling as
above between the carbon monoxide disproportionation
reaction to deposit carbon and thereafter hydrogenating
the resulting carbonaceous material to remove most
of the carbon was continued for several cycles. The
result of all the cycles is summarized in Table II
below.
- 18 -
i ;ii
~ t ~Xl~j 3l-006c
TABLE II
CARBON DEPOSITIO~ RATE M~T~A~ATION RAT~
CYCLE NO (Grams/~r/Gram of Dis- ~Moles/Hr/Mole of
persed Iron) Carbon)
l-C* 8.8
l-H~* a . 52
2-C 39.4
2-H 0 53
3-C 47.8
3-H 1.12
4-C 41.5
4-H 1.33
* Denotes carbon deposition
*~ Denotes hydrogen~tion
The hydrogen promoted material had a carbon deyosition
rate well in excess of 10 grams of carbon deposited per hour
per gram of dispersed iron present. After this material was
2~
subjected to several cycles of carbon deposition and ~ethanation,
its methanation rate increased substantially to in excess of
1 mole of methane formed per hour pe.r mole of carbon present.
Example 2
Six hundred grams of Mesabi Range Iron Ore (hematite
type iron ore containing 55.3% Fe, 8.1% silica, 0.8~
alumina) ~f particle size 60 to 150 mesh and bulk density
1.91 g/cm was ~laced in a stainless steel ~ressure resis-
tant verticle tube reactor having an inner-diameter of
1 5 inches and a height of about 8 ft. The ore was
reduced by a hydrogen gas stream contacting the iron
ore at a space velocity of 2330 volumes of gas per
volume of iron ore per hour. The reduced ore ~as sub-
jected to a series of carbon deposition/methanation cycles~
Carbon deposition was performed using nitrogen/carbon
monoxide/hydrogen gas mixtures of different compositions,
and the methanation was performed using pure hydrogen.
The volumes of gases entering into the reactor and
exiting after cooling the reactor to room temperature were
measured with flow indicators and wet test meter, and the
composition of gases was determined by gas chromatography.
The conditions and results of several cycle~ are shown
on ~he following Table III.
. ~ ;~. . .
31-006C
TA8LE III
CARBON DEPOSITION
Cycle Gas Composition (%) Av. Pres- Av. Time Atomic
N2 H2 CO Temp sure Res- Minutes C:Fe
C atm idence After
abs Time Carbu-
Seconds retion
A 46.6 8.145.3 456 6.1 1.9 65 1.29
B 42.5 6.950.6 440 3.4 1.7 75 0.88
C 44.2 6.948.9 435 3.5 1.6 90 0.80
D 44.2 7.448.4 416 4.7 1.8 110 1.12
METHANATION
Cycle Temp.Pressure Av. Gas Time CH4 Atomic
C* Atm. Res- Minutes in Product Gases(%) Ratio
Abs. idence Maximum AfFer
Seconds Attained Metha-
nation
A 540-6736.8 4.9 17453.5 0.08
B 500-70011.6 9.1 12063.0 0.04
C 500-67211.6 11.0 14062.0 0.01
D 500-63513.6 15.0 16570.0 0.15
*Reaction was highly exothermic and the temperature was held under control
only by adjustment of hydrogen flow.
- 20 -
3 .?~ 31-006C
Example 3
A 2.88 gram sample of iron-nickel alloy containing
about 50 percent by weight of each of th~se two metals was
oxidized at 982C for 10 minutes in a muffle furnace. The
oxidized alloy was then carburized at 500C using a mixture
of gases comprising 85 percent by volume carbon monoxide
and 15 percent by volume hydrogen flowing at the rate of 200
milliliters per minute for 9.33 hours. After separating
the carbonaceous material from the bulk alloy, we found that
the elemental analysis of the resulting carbonaceous material
was: Carbon:98.06%; iron:0.54%; nic~el:0.53~ and hydrogen:
0.16%. The separated carbonaceous material was then subjected
to a series of three methanation/carburization cycles. The
conditions and results of these cycles are set forth in the
following TableIV. The data in Table IV establish that both
the carbon deposition rates and the methanation rates improved
with cycling of the material between carbon deposition and
methanation.
~i
i~ 31-006
TABLE IV
CYCLE ~ CARBON DEPOSITION RATE METHANATION RATE
~Grams/Hr/Gram Dispersed (Moles/Hr/~ole of Carbon)
Iron)
0.10
l-H**
l-C* 35.2
0.12
2-H
2-C 38.8
0.20
3-H
3-C 45.3
* Denotes Carbon Deposition
** Denotes Hydrogenation
-- 22 -
31-006C
Example 4
Following the process of our invention, we
prepared samples of free-carbon containing carbonaceous
mal:erials from the disproportionation of carbon monoxide
over plates or buttons of iron, nic~el, cobalt, and an
iron-nickel alloy containing about 50% iron and about
50% nickel. In ea~h sample, the fibrous carbonaceous
S material formed was separated from the bulk metal and
exposed, at 550C and l atmosphere pressure, to a stream
of dry hydrogen flowing at a rate of about 2 moles of
hydrogen per hour per mole of the carbon present. The
specific rates of methane formation for each of the
samples is shown in Table V below.
TABLE V
SPECIFIC RATE OF METHANE
CO DISPROPORTIONATIONFORMATION FOR FIBERS
INITIATOR SEPARATED FROM BULK METAL
IN MOLES/HOUR/MOLE CARBON
-
IRON 0.10
NICKEL 0.19
COBALT 0.34
IRON/NICXEL ALLOY 0.10
- 23 -
31-006C
l ~ti;~14j
Example 5
Ten grams of carbon steel spheres measuring one-
ei~hth inch in diameter were placed in an alumina boat
whllch was then suspended in the center of a ceramic reactor
tube. A mixture of 100 ml/min of carbon monoxide and
20 ml/min of hydrogen was passed over the spheres at
510C and atmospheric pressure for five hours. A total
of 1.94 grams of carbon was deposited. The deposited
carbonaceous material was carefully separated from the
carbon steel spheres, and found to contain 2.08% iron. Of
the separated material, 0.992 gram was placed in a~ alumina
boat and returned to the reactor. A mixture of 100 ml/min
of carbon monoxide and 20 ml/min of hydrogen was passed
over the 0.992 gram sample at 408C for 2 hours. An esti-
mated additional 0.2 grams of carbon was deposited as
determined by measuring the carbon dioxide con~entration
of the effluent gas stream. Next, a gas stream of pure hydrogen
(110 ml/min) was passed over this modified sample at a temper-
ature of 560C. Methane began to form and the hydrogenation
was continued until approximately 0.2 grams of carbon were
gasified, as determined by measuring the methane concentration
and flow rate of the effluent gases. The average methanation
rate was 0.20 moles CH /hr/mole of carbon. The gas stream
flowing over the carbo~aceous sample was then changed from
hydrogen to pure nitrogen (40 cc/min) and the carbonaceous
material was slowly heated to 865C. The sample was held at
865C for about one hour, and then cooled in flowing nitrogen
lS to 560C. At 560C, the gas stream was again changed to
pure hydrogen, flowing at a rate of 110 cc/min to effect
methanation. Methanation con~inued until an additional 0.2
gra~ms of carbon were gasified. The average methanation rate
after the high temperature thermal exposure was 0.26 moles
CH /hr/gram-atom carbon. The cycle of high temperature (865C)
th~rmal exposure to flowing nitrogen followed by hydrogenation
at 560C was repeated. The average methanation rate was again
determined and found to be 0.26 moles CH /hr/gram atom of
carbon. Apparently, this short term exposure of our carbona-
ceous material to high temperature does not impair its reac-
tivity with hydrogen. Nor did the high temperature exposure
- 24 -
~r,
f~
31-006C
~ ~ti~
impair its catalytic activity in the direct conversion of
carbon monoxide and hydrogen to methane. After the same
thermal cycles, the remaining carbonaceous material was
exposed to a mixture of 110 cc/min of hydrogen and 30 cc/min
of carbon monoxide at 450C. Methane found in the effluent
gas formed at an average rate of 0.24 moles/hr/mole catalyst.
When iron oxides such as iron ore are used at start
up as the disproportionation initiator, they are first reduced
by the carbon monoxide-hydrogen feed gas and then the carbona-
ceous material begins to collect on the bulk iron. Consequently,
the length of time the carbon monoxide containing gas contacts
the bulk iron is important. If, for example, Fe3O4 is
used and the carbon monoxide containing gas is at 600C
and one atmosphere, initially the iron oxide is at least
partially reduced to iron. This is indicated by a loss
- 25 -
31-006C
llt~
of weight of iron oxide due to the loss of oxygen. For example,
after the iron oxide was contacted with pure carbon monoxide
gas for 15 minutes, the sample had a weight loss of about 22%
(oxygen comprising about 27.6% by weight of the iron catalyst) and
little carbon was deposited on the bulk iron. What carbon
was deposited was in the form of Fe3C. After 30 minutes of
contact the sample had a 15% weight loss and the carbon
deposited on it was in the carbide form, primarily Fe3C.
Even after 60 minutes of contacting the iron oxide with
carbon monoxide the sample still showed a weight loss of about
10%, and substantially all of the carbon deposited on the
iron oxide was in the carbide form, again primarily as
Pe3C. After 4 hours, however, the sample had about a 75%
weight gain and the deposited carbon was partially graphitized.
The 15 minute, 30 minute, and 60 minute samples did not have
the required methanation rate. In contrast to these samples,
the fourth sample Ithe four hour sample) did form methane
at at least 0.1 mole of methane per hour per mole of carbon
when contacted with hydrogen at 550C, one atmosphere, and
a minimum hydrogen feed rate of 2 moles of hydrogen per hour
per mole of carbon present.
Process for Making High Btu Gas
We have also invented a process for producing a
high Btu gas from coal or other carbonaceous fuels through
the vehicle of our novel carbonaceous material. In our
process methane can be made without the need to use pure
oxygen or to remove nitroqen, carbon dioxide or other inert
gases from the feed stream. According to our pxocess the
- 26 -
31-Q06C
carbon monoxide and hydrogen are extracted from the feed
stream by forming our novel carbonaceous material on the bulk
ferrous metal. ~ hydrogen-containing gas is then contacted
with the carbonaceous material at a temperature, pressure,
and space velocity that produces a methane containi~g
product gas including at least 20% by volume methane. Because
the carbonaceous material is so highly reactive with hydrogPn,
the residence time of the hydrogen in contact with the carbona-
ceous material may be very short. We have found that the
carbonaceous material requires little residence time with hvdrogen
to produce a gas containing as high as 75% by volume or ~reater
met~ane. For example, the residence time may vary from 1
second to 50 seconds to produce such a methane rich gas.
The preferred hydrogen residence time is from 5 seconds to 30
seconds. The desirable minimum temperature at which methanation
is conducted is 350C. The preferred range is from about
400 to about 700C. The pressure may range between about
1 and about 100 atmospheres, preferably 1-25 atmospheres.
In the process of our invention almost any carbon
monoxide containing gas can be used to produce a high Btu
methane containing gas. Specific gases which may be used in
our process are those gases produced by gasifying coal using
air or a mixture of air and steam to produce a low Btu
producer gas of from about 70-150 Btu's per cubic feet. For
example, coal may be burned in-situ (i.e., without removing
the coal from its natural site) to produce a gas having about
100 Btu per cubic foot. As used here, a producer gas
- 27 -
`~ !
~ ~ .
~ l~t~ 31-006C
is one which contains carbon monoxide, hydrogen, nitrogen, and
carbon dioxide. Preferably, the coal is burned in a mixture
of air and steam to ~rovide a producer gas rich in carbon
noxide and hydrogen. For example, producer gaSeS normally
will contain on a dry basis from about 15% to about 30%
carbon monoxide, from about 5% to about 30% hydrogen, from
about 40~ to about 60% nitrogen, and from about 2% to
about 10% carbon dioxide. All of these carbon monoxide-
containing gases may be converted to a methane-rich gas
similar to natural gas and having a heat content of from
500 to as much as 1000 Btu per cubic feet.
In general, such producer gases will also
contain water and small amounts of other gases such as methane,
hydrogen sulfide, carbonyl sulfide, e~c. For operation at
atmospheric pressure, the water content should be reduced
below about 6% by volume; the sulfur content, below about
10 parts per million. If the carbon monoxide feed gas contains
hydrogen, the molar ratio of carbon monoxide to hydrogen should
be greater than about 1:2, preferably greater than 1:1. The
preferred molar ratio of carbon monoxide to hydrogen is between
about 1:1 to about 100:1. When the feed gas contains carbon
dioxide, preferably the molar ratio of carbon monoxide to
carbon dioxide is bigh. In general the carbon monoxide to
carbon dioxide molar ratio should be 1:1 or greater, preferably
greater than 2:1 - 3:1. ~owever, carbon deposition proceeds
at acceptable rates even when the ratio of carbon dioxide
to carbon monoxide is as high as 3.
We have found that the initial feed gas containing
carbon monoxide should not contain appreciable amounts of
- 28 -
31-006C
21~
sulfur. Specifically, the carbon monoxide feed gas should not
contain more than about 20, preferably not more than 10,
parts per million of sulfur calculated as hydrogen sulfide.
When required, sulfur removal may be accomplished by well
known methods, for example, amine systems, or by contacting
the feed gas with an aqueous solution of an alkali metal or
alkaline earth metal carbonate such as hot potassium carbonate.
In addition to conventional methods of remo~ing hydrogen
sulfide from feed gases, we have also found that hydrogen
sulfide can be removed by passing the feed gas over the
carbonaceous material or a mixture of the carbonaceous material
and the bulk ferrous group metal. When this is done, the ferrous
metal reacts with the sulfur to form metal sulfides within
the material. This reaction deactivates the carbonaceous
material. Therefore if this method is used to remove the
sulfur from the feed gas, the sulfur containing carbonaceous
material cannot be used to produce methane.
cince our invention is able to use gases containing
nitrogen in relatively large amounts (e.g. nitrogen may be
present in amounts as great as 70~ by volume or greater),
it is not necessary to form the carbon monoxide containing
gas in a nitrogen free oxygen atmosphere. That is, air may
be used to burn coal rather than pure oxygen. What makes our
process economically attractive is that the combustible portion
o the feed stream, principally the carbon monoxide, is
extracted or separated at low cost from the inert or non-
combustible portion of the feed stream through the formation
of the solid carbonaceous material as an intermediate. A
- 29 -
~'
31-006C
l~t~
methane rich gas is subsequently produced by simply contacting
the carbonaceous material with hydrogen. This solid car-
bonaceous material need not be immediately reacted with
hy~drogen, since it retains its reactivity for a considerable
period of time. For ex~mple, we have stored one sample for
five days and reacted the sample with hydrogen and formed
methane at the same high rates as freshly prepared carbonaceous
material. This enables energy to be stored until needed.
One feature of our invention is that partially
depleted producer gas may be used to produce our carbonaceous
material which is subsequently converted to methane. In
this instance, coal is burned in air under controlled
conditions to form the producer gas which is con~acted with
oxides of iron to reduce the oxides principally to
iron, iron carbides, and iron oxides of lower oxygen content,
and ~o provide the partially depleted producer gas. For
example, the partially depleted pro~ucer gas may contain about
half as much ca.bon monoxide and about half as much hydrogen
as the producer gas initially contacting the oxides of iron.
The partially depleted producer gas is used to make the
carbonaceous material by contacting it with the bulk ferrous
metal group disproportionation initiator under conditions
which form the carbonaceous material. Hydrogen may be produced
by contacting the reduced oxides of iron with steam. This
2i hydrogen is then contacted with the carbonaceous material to
produce methane.
According to one embodiment of our invention
carbonaceous material (ordinarily mixed with the bulk ferrous
metal) is cycled between two reaction zones, one in which the
carbonaceous material is contacted with the partially depleted
producer gas and one in which the material is contacted with
the hydrogen rich gas to make methane. Thus, the material
- 30 -
~ 31-006C
undergoes a transition betw~en a carbon rich state and a carbon
lean state. The material being fed to the zone producing
methane is rich in carbon. Some of the carbon is stripped
(at least 15 weight percent) from this material during the
formation of methane to produce the carbon lean material which
is transferred to the other zone where it is again enriched
with carbon by contact with the producer gas. The carbon lean
material ~i.e., hydrogen promoted carbonaceous material)
will, in the first cycle, contain between about 5 to 35 weight
percent dispersed ferrousmetal, about 95 to 65 weight percent
carbon,and about 0.1 to 3 weight percent hydrogen. The
carbonaceous material may, however, remain in one zone and
the gas streams flowing through such zones are alternated
between producer gas and hydrogen rich gas streams.
Another feature of our invention is that the
carbonaceous material entrained in the process fluids may be
separated from these fluids by means of a magnetic field.
The ferrous group metal component of the carbonaceous material
retains its ferromagnetic properties, thus renderinq the
material magnetic.
Our process also permits production of substantial
quantities of energy from the depleted producer gas or other
gas used as a source of carbon monoxide. Thus, after the
producer gas has been utilized to manufacture our new carbonaceous
material, and to maXe hydrogen by the steam-iron process, the
depleted gases are preferably then burned in air to oxidize
any remaining combustibles and the resulting gases are
expanded through a gas turbine to reco~er their energy as
electricity.
- 31 -
`,~1
~ it~ 31-006C
Detailed Descri tion of the Preferred Processes
p
The best mode which we presently conte~plate for
practicing our invention is shown schematically in Figure 8.
In Figure 8, desulphurized producer gas from source 100 is
S the feed stream. This gas may include, say, 50 percent nitrogen,
25 percent carbon monoxide, 18 percent hydrogen, 6 percent
carbon dioxide and 1 percent methane, on a dry basis. Its
sulphur content must be less than about 20 parts per million.
The producer gas passes via line 101 to fluidized
10 bed carbon deposition reactor 102, which contains carbon-
lean solids of a ferrous metal such as iron. Carbon deposition
occurs in reactor 102 by disproportionation of the carbon
monoxide in the producer gas at a temperature of about 650C
and at a pressure in the range 150-250 pounds per square inch.
The carbonaceous material of our invention formed
in reactor 102 passes through line 103 to methanator 104.
There, at a temperature in the range of about 525C to about
700C, the carbon in the carbonaceous material reacts with
dry hydrogen entering methanator 104 through line 106 to form
methane and hydrogen. Because methanation is highly exothermic,
and because lower temperatures favor the formation of methane
in higher concentrations, methanation is effected in stages,
with the solids and gases cooled between the stages. Depending
on the desired product composition, one or more interstage coolers
may be required. Here, cooling is effected with water entering
methanator 104 through line 107 and exiting as steam through
line 108.
- 32 -
31-006C
21~
The methane/hydrogen gas mixture lea~es m2thanator
104 in line 109, passes through cooler 110, and emerges in line
llL, ready for further processing.
The partially depleted producer gas from carbon
deposition reactor 102 passes therefrom through line 112 to
heat exchanger 113. There, the temperature of the gas is
raised from, say, 670C to about 920C, and the residual
methane in the mixture converts to a mixture of water, carbon
monoxide and carbon dioxide. The partially depleted producer
gas leaving heat exchanger 113 has a lower ratio of carbon
monoxide to carbon dioxide, and contains principally nitrogen,
carbon monoxide, hydrogen, water and carbon dioxide. Though
lower, the CO/CO2 ratio is sufficiently high to permit its
use for reducing iron oxides.
The partially depleted producer gas leaves heat
exchanger 113 and passes through line 114 to iron oxide reducer
115. There, the mixture reduces ferric oxide to ferrous oxide,
and oxidizes carbon monoxide to carbon dioxide and hydrogen
to water. The reduced iron oxides pass from reducer 115
via line 116 ~o hydrogen producing reactor 117. Steam
enters reactor 117 through line 118 and reacts with the ferrous
oxide to produce ferric oxide and hydrogen. The ferric oxide
passes to reducer 115 through line 119. The wet hydrogen
produced passes from reactor 117 via line 120, is cooled in
heat exchanger 121, and then passes through line 123 to
condenser 122. In condenser 122, the water content of the
hydrogen stream is reduced to less than about 1~ by weight.
Dry hydrogen emerges fxom condenser 122 in line 124, and
passes to methanator 104 through line 106.
X - 33 -
~ti~Z~ 31-006C
The partially aepleted producer gas entering reducer
115 passes therefrom in line 125 as a nearly depleted gas.
However, the gas still contains useful residual energy.
That energy is preferably utilized by burning the gas in
furnace 126 with air from source 127. Pressurizer 128 raises
the inlet air pressure in furnace 126 to the range of about
150-250 psi. The heat produced in furnace 126 is partially
consumed in heat exchanger 113 to raise the temperàture of
partially depleted producer gas from reactor 102. The `
remaining heat in the gases from furnace 126 passes from
heat exchanger 113 via line 129 to turbine 130, where the
gases are expanded to produce electrical power at 131. The
depleted gas exits turbine 130, is cooled in heat exchanger
133, and passes to the atmosphere via line 134.
This embodiment of our process has several out-
standing advantages. First, a very high percentage of the
cold gas heating value of the producer gases is utilized
effectively in conversion to high value products, synthetic
natural gas and electricity. Secondly, expensive oxygen is
not required in this process. Third, the heat released in
-the methanation step and the remaining sensible
heat in the depleted producer gas are available for use at
high temperatures. This leads to high efficiencies in the
utillziation and conversion of this heat to electric power,
minimizing waste.
Anot~er embodiment of our process is shown schematically
in Figure 4. Desulfurized producer gas from source 1 is the
feed stream. This gas, which may comprise, for example, of
50% N2, 25% CO, 18~ H2, 6% CO2, and 1~ CH4 on a dry basis,
- 34 -
31-006C
may he derived from conventional gasification of coal with
stea~ and air, ~in-situ" gasi~ication of coal, etc. The
raw producer gas is desulfurized to below about 10 ppm of
H2S .
~esulfurized producer gas and, for example, oxidized iron
solids such as a mixture of Fe2O3, Fe3O4, and FeO are contacted in
a fast fluidized bed or entrained solid lift pipe type reactor
2 at temperatures from about 5~0D-850C and a~ pressures of
1-100 atm, preferably about 1-20 atm. Choice of temperature
and pressure are dependent on the overall heat balance and the
desired methane concentration~of the product gas. Solid-gas
contact is maintained for a sufficient time to cause partial
reduction by the H2 and CO in the producer gas of the iron
oxides to reduced iron compounds such as FeO, Fe and Fe3C.
The H2 and CO content of the producer gas feed is partially
but not fully consumed in the reduction of the iron oxides.
~We believe that the H2 will be more fully utilized than the
CO in this step of our process.
The entrained, reduced iron solids and partially
reacted producer gas are next fed to a cyclone or similar
device 3, where the reduced iron solids are separated from
the partially reacted producer gas. The separated, reduced,
iron solids are fed through line 4 to the bottom of a second
~ lift pipe reactor 5 where they are contacted with steam from
source 6 at temperatures of about 500-800C and pressures
of 1-100 atm. A hydrogen rich gas is obtained from the
reaction of the steam with the reduced iron solids. In
addition to hydrogen and unreacted steam this gas will also
contain some methane, carbon monoxide, and carbon dioxide.
'~.
31-006C
The hydrogen rich gas and entrainea oxidized iron
solids frQm the hydrogen production reactor S exit through
line 7 and are next fed to a cyclone or similar device 8,
which separates the solids from the gases. The oxidized iron
solids are returned via line 9 to the first lift pipe reactor
2 to complete the solid circulation loop between reactors
2 and 5.
After separation of the solids, the partially reacted
producer gas, which now may contain, for example, 15% CO,
6% ~2~ 16% CO2, 1~ CH4, and 62S N2 on a dry basis, is cooled
in heat exchanger 10 generating process steam. This coolad
gas is fed via line 11 to the bottom of the lift pipe carbon
deposition reactor 12, where it contacts and entrains carbon
lean solids. The gas and solids are maintained in contac~
with each other for a sufficient length of time at temperatures
of 300-600C and pressures of 1-100 atm to cause carbon to
deposit on the carbon lean solids and enrich their carbon
content. Carbon deposition occurs by disproportionation of
the carbon monoxide content of the partially reacted producer
gas to a lesser extent by reaction of CO and H2 or by the
reduction of CO by other reducing agents present.
The entrained carbon rich solids leaving the
carbon deposition reactor 12 are separated from the now
depleted producer gas in a cyclone or similar device 13 and
fed to the bottom of a lift pipe methanation reactor 14,
where they are entrained by the hydrogen rich gas stream
coming from the hydrogen production reactor 5 via heat
exchange 8a and cooler 8b. The entrained carbon rich solids
- 36 -
31-006C
*~
reac~ with h~drogen in the first stage 15 of the methanation
predominately by the direct reaction of carbon and hydrogen.
This is an exothermic reaction and the solids and/or gases
must be cooled between stag~s if high concentrations of methane
are desired. Entrained solids and gases are cooled in an
interstage cooler 16, and then further reacted in a second
reactor stage 17 to produce additional methane. Depending
on the desired ratio of CH4/H2 in the product gas, operating
pressures in the methanation reac~ors may vary from about 1
to about 100 atm, but preferably will be from about 1 to about
20 atm. Again, depending on the desired product, one or
several stages o~ intercooling may be employed. Operating
temperatures in the initial stages of the methanation reactor
may go up as high as 700-750C, but lower temperatures must
be held in the final methanation stages if a high CH4/H2
ratio is desired.
The product gas and entrained carbon-lean solids
leaving the methanation reactor 14 are primarily separated
in cyclone 18. The carbon lean solids are then recycled
~ia line 19 to the carbon deposition reactor 12. The
raw product gas still containing some entrained dust is further
cleaned in a dust separation unit 20, which may be a magnetic
separation device since most of the dust will be ferromagnetic.
Sand filters, bag-house, or other type of dust cleaning
operations may, however, be used. The dust free product gas
is cooled in heat exchanger 21, producing process steam and
further cooled and dried in cooler 22 to produce the final
product gas.
The hot depleted producer gas leaving cyclone 13
is fed to a dust separator 23 which removes entrained dust not
separated by the cyclone 13. The dust separator may be a
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~ 31-006C
magnetic separatiOn device since the solids are ferromagnetic,
or it may be a more conventional system such as a sand filter
or bag-house. The hot, dust free, depleted producer gas,
still containing some ~2 and CO, is burned by the addition
of excess air to yield a hiqh temperature combustion gas
product, containing N2, CO2, and H~O. This hot gas is
expanded through a gas turbine 24 to produce by-product shaf~
wor~ and/or electric power. Finally the spent producer gas
may be further cooled to produce additional process steam.
Two of the major advantages of the process depicted
in Figure 4 are ~a) that separation of undesirable N2 and
C2 from CH4/H2 product gas occurs through the relatively
easy separation of solids and gases rather than the much
more difficult separation of N2 from 2 as re~uired in conventional
lS technology, and (~) that the producer gas in this process is
more fully utilized in conversion to a C~4/H2 product
than in a conventional steam-iron process since the producer
gas is first partially used to reduce iron oxides (steam-
iron Prcess) and then more fully utilized to deposit
reactant carbon.
A third way of practicing our invention is shown
in Figure 5. Here, producer gas is initially compressed
to about 3 to 4 atmospheres in compressor 1 and fed into a
carbon deposition/ferrous metal oxide, e.g., iron oxide
reduction reactor 2 where it initially contacts iron oxides
and reduces these oxides and simultaneously deposits
carbonaceous material on the reduced oxides. The reactor
2 is maintained at a temperature of about 350-500C and a
pre~sure of about 3 to 4 atmospheres. In reactor 2 about
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~i -'I
31-006C
71D% of the carbon monoxide and hydrogen in the producer gas
reacts with the iron oxides to form reduced iron compounds
and the carbonaceous material of this invention. The depleted
producer gas, at a temperature of about 350-500C, is mixed
with air and burned in combustion zone 3. This gas ~ay be
then passed directly to a compressor or an electric generator
for expansion without passing through a waste heat boiler.
However, the gas is preferably passed through a magnetic
separator to remove any entrained dust.
The carbonaceous material, including the bulk
iron, is circulated through fluidized stand pipes to a fluid
bed methanation reactor 5 where it is contacted with hydrogen
gas at temperatures of about 480C-535C and a pressure of
about 3 to 4 atmospheres to form a methane rich gas. The
methane rich gas is cooled in waste heat boilers 6 to produce
process ste~m. The carbon depleted material from methanation
reactor 3 is circulated via fluidized stand-pipes to the
fluid bed hydrogen generation reactor 4 and contacted with
steam at about 535C-650C and a pressure of from 3 to 4
atmospheres to produce wet hydrogen. The resulting iron
oxides are recirculated back to the carbon deposition reactor
2. The wet hydrogen is cooled in cooler 7 to condense the
water vapor and the dry hydrogen circulated to the methanation
reactor ~.
Sulfur compounds such as H2S, COS, CS2, and SO2, if
present in the producer gas, may be removed by contacting
the gas with a portion of the carbonaceous material formed
in carbon deposition reactor 2. Alternatively, the portion
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X
- 31-~06C
3 ~t;~
of the carbonaceous material which has been hydrogenated
may be removed from the methanation reactor 5 and contacted
with the producer gas to remove the sulfur compounds.
In Figure 6, there is shown another altnerative
embodiment wherein the solids remain in the individual reactors,
either as fixed beds or fluid beds, and the gas feed streams
to the reactors are periodically switched between producer
gas and steam-water. The reactors may be operated in one of
the two modes,the first mode shown by the solid lines and the
second mode shown by the broken lines. In the first mode,
producer gas is fed into reduction reactor 6 where it contacts
iron oxides. The partially depleted producer gas is then
passed through a process steam boiler into reactor 2 where it
contacts bulk iron to form the carbonaceous material.
Simultaneously, steam is fed into hydrogen generator reactor 4
where it contacts redùced iron to form hydrogen ~as. The
hydrogen gas is then passed into methanation reactor 3 where
it contacts previously formed carbonaceous material to form methane.
At selected intervals, the gas feeds to reactors 2, 3, 4, and
2~ 6 are switched. As shown by the dotted line, hydrogen which
is formed in reactor 6 passes into reactor 2 causing the
formation of methane from the reaction of hydrogen with the
carbonaceous material. The depleted producer gas passes
from reactor 4 and into reactor 3 to form the carbonaceous
material.
In Figure 7 there is shown another embodiment of
our inven~ion in which partially depleted producer gas is used
to produce a methane rich gas in a single reactor shown in
cross section. In this apparatus porous walled reaction
cylinders are used, the pores of which allow passage of gas
therethrough but are too small to permit passage of our solid
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31-006C
carbonaceous material or the bulk iron carrying the
car]bonaceous material. The preferred form of bulk
disproportionation initiators are iron spheres.
The iron spheres are initially located within a
hopper 1 having an outlet 2 at the bottom through which the
spheres are conveyed by gravity into passage way 3 and then
into porous walled ca,rbon deposition reactor 4 having a cavity
5 inside. At the top of ca~ity 5 is gas inlet 6 for passage
into cavity 5 of a partially depleted producex gas. The
partially depleted producer gas passes through inside porous
walls 7 and into reactor 4 where the gas contacts the iron
catalyst for a sufficient length of time, and at a pressure
and temperature to form our carbonaceous material on the
spheres. Thereafter, the fully depleted producer gas passes
through the openings or pores of outside porous wall 8.
At the bottom of reactor 4 is outlet 9 through which
the spheres carrying the carbonaceous material pass into methana-
tion reactor 10 which is defined by outside gas porous wall
11, and ir.side gas porous wall 12. Coaxially surrounding the
outside porous wall 11 is impervious wall 13 which, with
wall 11, defines an annular chamber 14. Hydrogen gas flows
through gas inlet 16 and into cavity 1~ where the hydrogen
passes through the openings of inside porous wall 12 and
into contact with the carbonaceous material in methanation
reactor 10 to form a methane rich gas. This methane rich
gas then pa~ses out of reactor 10 through the openings in
outside gas porous wall 11, into cavity 14, then through
gas outlet 16, into gas transfer pipe 17 which transfers it
to cavity 18 located within a second methanation reactor
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.i, ,~,
l ~ 21
31-006C
19. The cavity 18 and reactor 19 are separated by inside
gas porous wall 20.
The partially carbon depleted carbonaceous solid.
material from methanation reactor 10 passes out of
reactor 10 via solids outlet 21 and is cooled with water in
solids cooler 22 by passing water into cooler 22 through
water inlet 23 to produce steam which passes out of the
cooler through steam outlet 24. The cooled solids then
pass into the second methanation reactor 19 where they are
again contacted with the methane-hydrogen gas passing
through porous wall 20 to further react with the carbonaceous
material to form methane. The enriched methane containing
gas passes out of second methanation reactor 19 through
outside porous wall 24 and gas outlet 26. Carbon depleted
lS iron-carbonaceous solids are then transferred to solids hopper
1 via lift return 27 to be used again in the process.
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. ~,
