Note: Descriptions are shown in the official language in which they were submitted.
~- 11364~3
NOVEL CARBONACEOI~S MATERIAL
AND PROCESS FOR PRODUCING
A HIG~ BTU GAS FROM T~IS
MATERIAL
Hydrogen reacts rapidly with the carbonaceous material to produce
a methane rich gas containing at least 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
with hydrogen. The carbon depleted material may be replenished
with carbon by exposure to carhon 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 promoted carbonaceous material may be
reacted with hydrogen without deactivating the material for
carbon deposition or methanation.
.
~~ACKGROUND OF THE INVENT ION
,,
Vario~s carbonaceous material are well known and
have been used as pigments, sources of coke, chemical absorbers',
7~ etc. One type of carbonaceous material'forms through the di~pro-
~'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--
,. ~.,
~,i," ,~
'
.
31-006C
. ~.
i~36~13
the reactions which result in the deposition of carbon from carbon
monoxide, such as the following:
- 2 CO- ) C ~ C2
CO + ~2 ~ C + H2O
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. Gènerally, 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
process based on this reaction was not feasible. Society's
demand for methane has, howe~er, increased and almost outstripped
the supply. It has been propo3ed that methane may~be produced t
from coal, and consequently, extensive research is be~ng 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 buFning coal ln a mixture of oxygen and steam. ~xygen is
used rather than air because the mixture of carbon monoxide and
: ::
hydrogen used for methane synthesis should not cont~ain substantial
- 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
-2-
; ~B
,............................................ .
31-006C
113~4i3
monoxide-hydrogen feed stream, in order to have a final pr~duct
gas of high Btu content. It is relatively expensive to remove the
carbon dioxide gas from the carbon monoxide-hydrogen feed stream
because such removal involves a gas separation step.
THE INVENTION :-
Carbonaceous Material
We have dis~overed 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 passi~g
hydrogen over the unpromoted material. The carbonaceous
material comprises a multiphase, intimate association of a carbon-
;~ rich major phase and one or more ferrous group metai-rich minor
lS phases that are dispersed in, and at least partially bonded to,
the carbon. The ferrous group metal components catalyze
the reactions of carb`on formation from carbon monoxide and of
methane forma*ion 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 peraent based on the total weight of the
material. Preferably, the ferrous qroup 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 l 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 catalyze 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
1136413
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. This reactivity with
hydrogen is a distinguishing characteristic of our materials, and
is substantially highe~- than that of other forms of carbon.
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
Lo which methane is formed. Consequently, at atmospheric
;..
pressure, the hydrogen should contain less than about 1
water by volume.
$he ferrous group metals appear to be transported
into the partly-crystallized carbon network, and become dispersed
1~5 randomly in this network. At least 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
~Z invention is formed by passi~g carbon m~noxide over a ierrous
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
-~ -4-
,. ,
~ 3
., ~ , '
31-006C
il36413
surface of the disproportionation initiator. Carbon monoxide
is maintained in contact with the disproportionation initiator
until substantial amounts of unpromoted carbonaceous material
deposit on the-ini~iator.
The ferr~us qroup metal-based ~arbon monoxide dispropor-
tionation initiators are selected fxom 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 alloy~, such as iron/
nickel alloys, and ores of iron, cobalt and nickel. We shall
refer to such ferrous group metal-based carbon monoxide
disproportionation initiators as the "bulk metal" in order
to distinguish them from the metal dispersed in and at least partly
~15 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
~20 forms those initiators taXe, are: ferric Qxide powder, hematite
type iron ore composed mostly of Fe203, 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.
2S Various ferrous metal ores may be used to initiate the formatlon
of the carbonaceous material. For example, we have used Mesabi
Range iron ore with good results. The use of such ore and the
llke is desirable because it is readlly 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
.
, .
,;. -, ~ ;
, ~ :
1136413 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
carbonace~us 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 square meters per gram
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 flbers. Typically, the fibers have a di-
ameter in the range of about 0.02 micron to about Z.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
; 25 materïal 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.
B
~i36413
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-
aceous material of our invention, we conducted a series oftests 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 pèrcent by weight of dispersed iron
component as determined by both spectroscopic analysis and -``
. .1
ashing techniques. The balance of the material contained
principally carbon with trace~amounts of hydrQgen~ 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 contactin~
a carbonaceous material made up of carbon and a ferrous group
'' 25 metal component which 1s dispersed throughout the carbon and
intimately associated with and at leàst 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
l .
~ 30 the carbonaceous materlal to form a methane-rich gas.
~ , ' ` ~ `''
,
~l
, . .
113~i413
The inverltion contemplates a fiber which includes partially
graphitized carbon and a nodule comprising a metal alloy con-
taining as one ingredient of the metal alloy a ferrous group metal,
the nodule being at least partially bonded to the car~on.
The invention also contemplates a method of increasing
the reactivity of a carbonaceous material formed by disproportion-
ation of carbon monoxide and having a`first level 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.
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 in-
ventive apparatus, shown with Fig. 3;
Fig. 6 ls another schematic presen~atlon of the in-
ventive apparatus;
,
Pig. 7 is another schematic presentation of the in-
ventive apparatus;
Flg. 8 is another schematic presentation of the in-
ventive apparatus;
Fig. 9 is a photomicrograph of another carbonaceous
material.
~ '
--8--
'~ .
31-006C
11364i3
We have examined carbonaceous fibers formed on
an iron plate using a scanning electron microscope. Fig-
ure 2 is a micrograph showing fibers of our material as
seen through a scanning electron microscope under rela- ?
tively low magnificiation. Figure l is a micrograph show-
ing, 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 3000A long and about 1000A wide. This analysis
was made according to the analytical procedures~described
by J. R. Ogren in ~Electron Microprobe," Chapter~6, in
Systematic Materials Analysis," Volume l, 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 l.S~ by weight iron. ~ -
,, . ~ .
,~ ~
.,
~; _9_
. '' ' ~ . .
,,~ ~ ' . .
~~ 31-006C
113Çi413
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 1 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
; 20 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 o~ 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 (Pe3C), and a simple physical
- ;
~ ~ -10-
il36413 31-006C
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
S at the rates approaching the rate attained using our car-
bonaceous material. This is shown in the following
Table I.
~ . ' '
:'
'
:
''
',; .
.
31-006C
~ 1~364i3
TABLE 1
Methanation
Carbonaceous C/Fe Rate
Material Separated Atom(Moles CH4/Hr/
Starting MaterialFrom Iron Initiator RatioMole Carbon)
1. Carbon deposited from C0/H2 No 27.3* 0.10
gas stream at 550C and 1 atm
onto high purity iron Eoil.
2. Carbonaceous material from Yes 176 0.]0
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 C0/H2 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
CO/H2 BaS stream,
5. Mesabi range iron ore pre- No 7* 0.24
reduced in H2 and then used to
catalyze carbon deposition
from C0/H2 gas stream at
.
500C and 1 atm.
6. Same as sample 5 except ex- No 7* 0.20
posed to ambienc air for 96 hrs
at 25~C 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-
,Y_ :
~ ., _.
,,.
11364i3 31-006C
Figure 9 shows a scanning electron micrograph
of another of our casbonaceous 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
material was found to contain 98.42% C, 0.48% 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 ~
nickel in approximately equal amounts. X-ray analysis -
; of a representative sample of the fibers indicated the
presence of iron-nickel alloy. It appears likely that
the nodule C shown in the circle in Figure 9 aatually
5 ` consists of an iron-nickel alloy. Whether or not the
nodule C shown in Figure 9 is a true solid soIution alloy
of iron and nickel, our analysis clearly shows that very
small crysta11ites 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 ~ibers.
," :
~t.',
~ ~ * Unnormalized data which does not add up exactly to 100%.
:~
' .
-13-
~.,
~` -
31-006~
li3~413
One way of thinking about our material is that
the active errous group metal component is a catalyst
that is dispersed throughout a carbon matrix. This fer-
rous group metal component catalyzes the reaction of the
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-
containing 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 speci~ic
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-
- 113~413 31-006C
rapidly. If the carbon rich material had contained,
initially, 95 weight percent carbon and ~ 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 cycles, and have obtained our
unique, hydrogen-promoted material each time.
::. 10
1~ Our new carbonaceous materials also retain their
properties after extended periods of storage, whether stored
I 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 aceivity, we avoid ex~posing them to air
during storage. After we store our iron-based carbonaceous
-: ~
~ material for 24 hours at room temperature, we observe no
i ~ 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:
~1
','',i,~ ~ ' '
, -
.,,~ , ............................ .
. , .
, . . ..
~,
-15-
.,
` -
113~413
General ~ Preferred %
by weight by weight
Partially Graphiti~ed Carbon 65-99.5% 75~99%
Dispersed FerrousGroup
Metal Component 0.5-35% 1-25%
Weiyht 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
percent of carbon.
Hydrogen Promoted Material
We have found that at least some of our carbonaceous
materials, when subsequently hydrogenated, have an enhanced
; 15 carbon deposition rate and methanation rate. Specifically,
~ where the ferrous group 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 caxbon monoxide per
hour per gram of dispersed iron using a feed gas that contains
80~ by volume carbon monoxide and 20% by volume hydrogen.; 25 The methanation rate was measured at 550C, one atmosphere
pressure, and a minimum hydrogen feed rate of 2 moleæ of
j'
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
-16-
1~3~413 31-006C
'
material formed initially is subjected to hydrogenation to
produce methane, then our hydrogen promoted material begins
to form. 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 l~ water by volume.
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-~5
i Hydrogen .1-3.0
~ i
The hydrogen in our new materials is strongly associated.
When we heat our iron-based carbonaceous material
f 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
- 17 -
31-006C
1~3~;4i3
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,
both hydrogenated promoted and unpromoted, after it has been
separated from the bulk metal.
Examples of Carbonaceous Material
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
Carbon was deposited on one-eighth inch mild
` steel balls (5 grams) by decomposition 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 balis, and 0.27
grams of the separated 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 o~ 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-hydroaen 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 -
31-006C
113~413
TABLE II
CAR13ON DEPC)SITIO2~ T~A~lATION RAT~:
CYCLE NO.(Grams/Hr/Gram of Dis- ~Moles/Hr/Mole of
persed Iron)_ Carbon)
l-C~ 8 8
l-H~* 0 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 hydrogenation
The hydrogen promoted material had a carbon deposition
rate well in excess of lQ grams of carbon deposited per hour
; p-r gram of disperse~d iron present Aft-r this material was
subjected to several cycles of~carbon d-position and methanation, ~ -~
it- methanatlon~rate increas-d substantially to in excess of
~ 1 mole of methane ~ormed per hour per mole of car~on present
`~ Example 2
~ Six hundred grams of Mqsabi Range Iron Ore ~hematite
`~ 25 type iron ore containing S5 3~ Fe, 8 1~ silica, o.a~ .
alumina) ~f ~particIe size 60 to 150 mesh and bul~ 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 ~ ft The ore was
redueed by a hydrogen~gas stream contacting the iron
ore at a space velocity of 2300 volumes of gas per
volume of iron ore per hour The reduced ore was æub-
i jected to a series of carbon deposition/methanation cycles
Carbon deposition was perfQrmed using nitroqen~car~on
;, 30 monoxide/hydrogen gas mixtures of different compositions,
i and the methanation was performed usinq 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 cycles are shown
on the following Tabl- III
.
~ , - 19 _
31-006C
li36413
TABLE III
CARBON ~EPOSITlON
Cycle Gas Composition (X) Av.Pres- Av. Time Atomic
:;~ N2 H2 CO Tempsure Res- Minutes C:Fe -
. 5 C atm idence After
~: abs Time Carbu-
Seconds retion :
:.~
: A46.6 8.1 45,3 4566.1 1.9 65 1.29
~ B42.5 6.9 50.6 4403.4 1.7 75 0.88
:~ 10 C44.2 6.9 48.9 435: 3.5 1.6 90 0.80
D44.2 7.4 48.4 4164.7 1.8 110 1.12
METHANATION
Cyc~le ~Temp. : ~Preseure ~Av.: Ga8~ Time~ CH4 ~: Atomic ;.
;C* ~ ~Atm ~ Res~MInutes in Pr ~u t Gases(%) C ~ ;
~ S conds ~ Attaine- nat1on
J5''~ A~540-673 6,8 4.9174 ; :53.5 0.08
B~500-700 11.6 ~9.1 ~~120~ 63.0 0.04
ZO~ :: C500-672 1~1.;6 ~ 1,0~~:: 140~ 62.0 0.01
:D500-635 13.6 ~ 15.0 ~ 165 70.0 0.15
.: ;
j."
.
~ *Reaction was highly exothermic and the temperature was held under control`' only by adjustment of hydrogen flow.
':`''
: - 20 -
. ~
` - ~
113~413
31-006C
Example 3
A 2.88 gram sample of iron-nickel alloy containing
about S0 percent by weight of each of these 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
S 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.
:;
,, .
., ~
,-'''''~' .
~':
.,
,~
t
::
- 21 -
.
~ `
113~413
31-006C
TABLE IV
CYCLE t CARBON DEPOSITION RATE METHANATION RATE
(Grams/Hr/Gram Dispersed (Moles/Hr/Mole of Carbon)
Iron)
-: ;
l-H** 0.10
l-C* 3S~2
2-H 0.12
:~ 2-C 38.8
3-H 0.20 ~ ~
~' -
3-C 45.3
* Denotes Carbon Deposition
:
~ ~* Denotes Hydrogenation
,, ,
'~ , ' '
.~ ' ' . ~.
.,
- 22 -
. . .
: :
;
413
31-006C
Example 4
Following the process of our invention, we
prepared samples of free-carbon containing carbonaceous
materials from the disproportionation of carbon monoxide
over p~ates or buttons of iron, nickel, cobalt, and an
iron-nickel alloy containing about 50% iron and about
50% nickel. In ea~h sample, the fibrous carbonaceous
material formed was separated from the bulk metal and
exposed, at 550C and 1 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/NOLE CARBON
IRON 0.10
NICKEL 0.19
COBALT 0 34
IRON/NICXEL ALLOY 0.10 ;
- 23 -
1~3~13 31-006C
Example 5
Ten grams of carbon steel spheres measuring one-
eighth inch in diameter were placed in an alumina boat
which 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 an 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 concentration
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 C~ /hr/mole of carbon. The gas stream
flowing over the carbo~aceous sample was then changed from
hydrogen to pure nitrogen t40 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 continued until an additional 0.2
grams of car~on 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)
thermal exposure to flowing nitrogen followed ~y 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 expo~ure
,'
- 24 -
il3v4~3 31-006C
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 suah 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, Fe304 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 -
1~3~413 31-006C
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 com~rising 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 sa~ple 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
Fe3C. After 4 hours, however, the sample had about a 75~
weight gain and the deposited carbon was partially graphitized.
The 15 minute, 3~ minute, and 60 minute samples did not have
the required methanation rate. In contrast to these samples,
the fourth sample (the 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 Maki~g High Btu Gas
We have also invented a process for producing a
high Btu gas from coàl 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 nitrogen, carbon dioxide or other inert
gases from the feed stream. According to our process the
- 26 -
,
,
- ' . ` . , :
31-Q06C
113~413
carbon monoxide and hydrogen are extracted from the feed
stream by forming our novel carbonaceous material on the bulk
ferrous metal. A hydrogen-containing gas is then contacted
with the carbonaceous material at a temperature, pressure,
and space velocity that produces a methane containing
product gas including at least 20% by volume methane. Because
the carbonaceous material is so highly reactive with hydrogen,
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 hv~rooen
to produce a gas containing as high as 75% by volume or ~reater
methane. 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 a~d about 100 atmospheres, preferably 1-25 atmospheres.
~ In the process of our invention almost any carbon
; 20 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 gase~ produced by gasifying c~al using
air or a mixture of air and steam to produce a low Btu
producer gas of from about 7Q-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 -
~ - `
1~3~413 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 provide a producer gas rich in carbon
noxide and hydrogen. For example, producer gases normally
S 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 ~rom 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, etc. 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 high. In general the carbon monoxide to
- carbon dioxide molar ratio should be 1:1 or greater, preferably
greater than ~ 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 -
., .
` 113~413 31-006C
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 remoYal 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 removing 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 mater al. This reaction deactivates the carbonaceous
material- Therefore if this method is used ~o remove the
sulfur from the feed gas, the sulfur containing carbonaceous
~ material cannot be used to produce methane.
; Since our invention is able to use gases containingnitrogen in reIatively large amounts (e.g. nitrogen may be
: i~
present in amounts as great as 70% by volume or greater),
it is not necessary to form the car~on monoxide aontaining
gas in a nitroqen free oxygen atmosphere. That is, air may
` be used to burn coal rather than pure oxygen. What makes our
I process economically attractive is that the com~ustible portion
of 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
113~413 31-006C
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
hydrogen, since it retains its reactivity for a considerable
period of time. For example, 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 contacted with
oxides of iron to reduce the oxides principally to
iron, iron carbides, and iron oxides of lower oxygen content,
and to provide the partially depleted producer gas. For
example, the partial}y depleted producer gas may contai~l about
half as much carbon 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 ~he reduced oxides of iron with steam~ This
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 reaation 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 -
il3~413 31-006C
undergoes a transition between 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 S 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.
lS Another feature of our invention is that the
carbonaceous material entrained in the process fluids may be
separated from these fIuids by means of a magnetic field.
The ferrous group metal component of the carbonaceous material
- retains its ferromagnetic properties, thus renderinq the
-<~ 20 material magnetlc.
Our prQ~ess also permits production o~ substantial
: ,:
quantitles 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 tQ manufacture our new carbonaceousmaterial, and to make 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 recover their energy as
electricity.
'
- 31 -
113~413
31-006C
Detailed Description of the Preferred Processes
T~e best mode which we presently contemplate 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 peraent 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
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 iD the range 150-250 pounds per square inch. ~ -
The carbonaceous mat-rLal of our invention formed
in reactor 102 pas~es through line 103 to ~ethanator 104.
There, at a tempe~ature 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
methan~ and hydrogen. Because methanation 1~ hlghly 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 i~terstage coolers
-l~ 25 may be required. Here, cooling is effected with water entering
., .
methanator 10~ through line 107 and exiting as steam through
line 108.
~' :
,
- 32 -
:' .
1~3~413 31-006C
The methane/hydrogen gas mixture leaves methanator
104 in line 109, passes through cooler 110, and emerges in line
111, 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 C0/C02 ratio is sufficiently high to permit its
use for reducing iron oxides.
The partially deple;ted 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 wat-r. The reduced iron oxides pass from reducer 115
via line 116 to hydrogen producing reactor 117. Steam
enters reactor 117 through llne 118 and reacts with the ferrous
oxide to produce ferric oxide and hydrogen. The ferric oxide
;::
,
passes to reduc~er 115 through line 119. The wet hydrogen
produced passes from reactor 117 via line 120, is cooled in
heat exchanger 121, and then passeæ through line 123 to
condenser 122. In condenser 122, the water content of tbe
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.
- 33 -
;
,.,:,~ . '
~136413 31-006C
The partially depleted 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 temperature 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 ~tep and the rema~ning sensible
heat in the depleted producer gas are a~ailable for use at
high temperatures. This leads to high efficiencies in the
~; utiliziation and conversion of this heat to electric power,
minimizing waste.
Another embodiment of our process is shown schematically
,."
,~,',5i, in Figure 4. Desulfurized producer gas,from source 1 is the
~6 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
~3~413
may ~e derived from conventional gasification of coal with
steam and air, "in-situ" gasification of coal, etc. The
raw producer gas is desulfurized to below about 10 ppm of
H2S ~
Desulfurized 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 550--850C and at 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.
; 15 The ~2 and CO content of the producer gas eed 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
devloe 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 thcy 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 tfie
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.
- 35 -
i~3~413 31-006C
The hydrogen rich gas and entrained oxidized iron
solids from the hydrogen production reactor 5 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 l~ne 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~ C0,
6~ H2, 16~ C02, 1% CH4, and 62% N2 on a dry basis, is cooled
in heat exchanger 10 generating process steam. This cooled
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 contact
with each other for a sufficient length of time at temperatures
` of 3Q0-600C and pressures of 1-100 atm to cause carbon to
deposit on the carbon lean solid-c 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 C0 and ~2 or by the
reduction of C0 by other reducing agents present.
The`entrained carbon rich solids leaving the
carbon deposition reactor 12 are separated from ~he now
depleted produccr gas in a cyclone or similar device 13 and
~` 25 fed to the bottom of a lift pipe methanation reactor 14j
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 -
J U ~
113~>4i3
react with hydrogen in the first stage 15 of the methanation
predominately by the direct reaction of carbon and hydrogen.
Tllis is an ex~thermic reaction and the solids and/or gases
must be cooled between stages 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 reactors may vary from about 1
; 10 to about 100 atm, but preferably will be from about 1 to about
20 atm. Again, depending on the desired product, one or
several staqes of 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
Ieaving the methanation reactor 14 are primarily separated
` in cyclone 18. The carbon lean solids are then recycled
via 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
.
- 37 -
il~413 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 H2 and CO, is burned by the addition
of excess air to yield a high temperature combustion gas
product, containing N2, CO2, and H2O. This hot gas is
expanded through a gas turbine 24 to produce by-product shaft
work 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 ~igure 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 required in conventional
technology, and (b) that the producer gas in this process is
more fully utilized in conversion to a CH4/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 ~nitially compressed
to about 3 to 4 atmogpheres 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 i8 maintained at a temperature of about ~50-500C and a
pressure of about 3 to 4 atmospheres. In reactor 2 about
~.
- 38 -
31-006C
113~413
70% 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 may 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 carbonaceGus 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. ~he
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 resultinq lron
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 5.
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
- 39 -
31-006C
113G413
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 reduced iron to form hydrogen gas. 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
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
~, 25 material.
In Figure 7 there is shown another embodiment of
our invention 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 usea, the pores of which allow passage of gas
therethrough but are too small to permit passage of our solid ;
.,
- 40 -
~ 31-006C
113~i413
carbonaceous material or the bulk iron carrying the
carbonaceous material. The preferred form of bulk
disproportionation initiators are iron spheres.
The iron spheres are initially located within a
; 5 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 carbon deposition reactor 4 having a cavity
5 inside. At the top of cavity 5 is gas inlet 6 for passage
into cavity 5 of a partially depleted producer 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 spherei carrying the carbonaceous material pass into methana-
tion reactor lO which is defined by outside gas porous wall
ll, and inside gas poxous wall 12. Coaxially surrounding the
outside porous wall 11 is impervious wall 13 which, with
wall ll, defines an annular chamber 14. Hydrogen gas flows
through gas inlet 16 and into cavity 15 where the hydrogen
passes through the openings of inside porous wall 12 and
into contact with the carbonaceous material in methanation
reactor lO to form a methane rich gas. This methane rich
gas then passes out of reactor 10 through the openings in
outside gas porous wall ll, 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
- 41 -
~13e~13
31-006C
19. The cavity 18 and reactor 19 are separated by inside
gas porous wall 20.
The partially carbon depleted carbonaceous solid
material fro~ methanation reactor lO passes out of
~: 5 reactor lO 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 :
agai~ 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 wal} 24 and gas outlet 26. Carbon depleted
iron-carbonaceous -olids are then transferred to solids hopper
l via lift return 27 to be used again in the process.
- ~:
, ~ ' .
'h'
- 42 -
,.
.
