United States Patent [19]
Tolman et at
[11]
[45]
4,372,755
Feb. 8, 1983
[54] PRODUCfION OF A FUEL GAS WITH A
STABILIZED METAL CARBIDE CATALYST
[75] Inventors: Radon Tolman, Evergreen; Frank M.
Stephens, Jr., Lakewood, both of
Colo.
[73] Assignee: Enrecon, Inc., Golden, Colo.
[21] Appl. No.: 202,319
[22] Filed: Oct. 30, 1980
Related U.S. Application Data
[63] Continuation-in-part of Ser. No. 928,506, Jul. 27, 1978,
abandoned.
4,II8,204 10/1978 Eakman et al. 48/197 R
4,134,907 111979 Stephens 48/197 R
4,184,852 111980 Russ 48/197 R
OTHER PUBLICATIONS
Burton et aI., Levy, Properties of Carbides, Nitrides,
Borides, Advanced Materials in Catalysis, pp. 101-127,
1977.
EPRI, "Thermodynamically Stable Forms of Elements
in the Hygas Gasifier".
Bulletin of Alloy Phase Diagrams, vol. 2, No.1, 1981, p.
25.
Kirk-Othmer, Encyclopedia of Chern. Tech., vol. 18,
2nd Ed., 1969, pp. 125-128.
27 Claims, 2 Drawing Figures
Primary Examiner-Peter F. Kratz
Attorney, Agent, or Firm--:Sheridan, Ross & McIntosh
A fuel gas containing methane is produced from a carbonaceous
material in a single reaction zone by reacting
the carbonaceous material in the presence of a stabilized
metal carbide catalyst and water vapor and/or carbon
dioxide at a temperature of from about 500· C. to about
900· C. The water vapor and/or carbon dioxide is maintained
in an amount of from about 10 to about 30 percent
by volume.
[51] Int. Cl.3 C10J 3/54
[52] U.S. Cl 48/197 R; 48/202;
48/209; 48/210
[58] Field of Search 48/197 R, 202, 206,
48/209, 210; 252/373; 585/733
[56] References Cited
U.S. PATENT DOCUMENTS
1,495,776 5/1924 Burdick 48/210
2,113.774 4/1938 Schmalfeldt 48/202
2,527,130 8/1950 Hemminger.
2,589,925 5/1952 Cain et al. .
2,694,623 1111954 Welty et al. 48/197 R
3,031,287 4/1962 Benson et al. 48/197
3,847,567 1111974 Kalina et al. 48/202
[57] ABSTRACf
6
7
HEAT
RECOVERY
BOILER
6
5
REHEATER
2/
/
REACTOR
20
CARBONACEOUS
FEED
(7) CO + 3Hz --CH4 +HzO· ( co ~I )
(6) CO+HzO......Hz+COz
HEAT
>--
~
?-
00
~
""C a("D
:::1
~
-\0
00
VJ
CIl ::r
(D
.(.D...
o......
N
c..en
~
'"w
-J
N
'"-J
Ul
Ul
(n xM+2CO-MxC+COz
(2) xM+C-+MxC
CATALYST 1l (c(]~l)
(3) MxC+Hz-+CH4+xM
( co<l )
( ca ~I )
HzO, CO, Hz
(CH4 , COz)
t
INLET
GAS
PRODUCT
GASf
( H2 , CO)
HZO, CO2 , CH4
(co<l)
CH4 rH2
(8) ex H
y
t
CARBONACEOUS
MATERIAL
Fig- J
(5) C+Hz0--'CO+ Hz
(4) C+COz-+ 2CO
c..en
I ~/I
10c PRODUCT n:GAS
12~
6J
No
"""'l
N
"Tj
(I) r::r
00
......
\0
00
VJ
~
~
(1)
=:s
!'""'t'"
C/)
i:l'"
(I)
.(.I.)..
..
N---,6"L..
120~
13.) ~WATER
16
6
7
HEAT Pr8 9
RECOVERY GAS
BOILER CLEANER
8(
r--
H
5
REHEATER
1./3
V 22
1/'19
sa
I
REACTOR
20",--
CARBONACEOUS
FEED
~
'"W
~
N
'"-J
Ul
Ul
L-r14
15
SEPARATOR
AIR
(17
18
REFORMER I*J
2/ - ~ ~ COMB~STOR
ASH
Fig_ 2
2
PRIOR ART STATEMENT
4,372,755
1
BACKGROUND ART
PRODUCTION OF A FUEL GAS WITH A
STABILIZED METAL CARBIDE CATALYST The use of iron carbides as catalysts in gasification
processes has also been taught. Stephens in U.S. Pat.
5 No.4, 134,907 teaches a means for enhancing the fuel
value of a gas by heating it to a temperature of
600·-1200· F. (315·-650· C.) at a pressure of 1-10 atmospheres
to promote the production of carbon from carbon
monoxide and hydrogen in the presence of iron.
10 The iron and carbon react to form Fe3C which in turn
reacts with hydrogen to form methane and reform iron.
Russ in U.S. Pat. No. 4,184,852 teaches the use of
metal carbide complexes to form methane; however, his
process consumes the metal carbide complexes in the
15 methane reactor. Moreover, he forms binary or ternary
metal carbides at a temperature of about 2200· F. and a
low pressure of about 2 atmospheres and then forms the
The prior art discloses numerous methods of obtain- methane in another reactor maintained at a maximum
ing hydrocarbon gases from carbonaceous materials, temperature of 350· F.
such as those proposed in U.S. Pat. No. 3,775,072, 20 Benson, et al in U.S. Pat. No. 3,031,287 form a carbuwherein
the organic material is reacted under pressure rized iron in a reduction stage of their process which is
with steam; U.S. Pat. No. 2,759,677 which provides for then utilized in an oxidation or,methanation stage to aid
use of steam generated in the process for reaction with in the production of a gas mixture comprised of hydrowaste
materials; U.S. Pat. No. 3,776,150 which uses a gen, carbon monoxide and methane. Benson, et aI, prefluidized
bed for methanation reactions; U.S. Pat. No. 25 fer the methanation to be conducted at a temperature of
3,817,724 wherein oxygen-free recycle gases are intro- 1000·-1200· F.
duced into the combustion zone; and U.S. Pat. No. U.S. Pat. No. 2,527,130 to Hemminger discloses the
3,817,725 wherein methanated gases are recycled to a addition of small amounts of silicon to iron type catacombustion
zone for purposes of transferring sensible lysts used in the production of liquid hydrocarbons in
heat and increasing methane content in the product. 30 order to reduce the tendency of the catalyst to carbon-
Many hydrogenation, gasification and methanation ize. The temperature of the Hemminger process for the
processes utilize metals as catalysts. For example, U.S. production of synthetic liquids is about 650· F., and it is
Pat. Nos. 3,759,677 and 3,817,725 disclose alkali carbon- conducted in a manner to avoid the formation ofmethates
as preferred gasification catalysts. U.S. Pat. No. ane and to enhance the formation of butane and higher
3,817,725 further uses Group VIII metals, such as 35 hydrocarbons.
nickel, either as oxides or sulfides, as catalysts in a met- U.S. Pat. No. 2,589,925 teaches a hydrocarbon synhanation
zone having a temperature of 500·-1000· F. thesis process conducted at a temperature of 550·-750·
Catalysts consisting of single metals, including oxides, F. which utilizes an iron catalyst preconditioned with
sulfides or carbonates or mixtures of these, selected carbon monoxide to form mainly Fe2C in order to prefrom
Groups IB, VIB and VIII, in addition to an alkali- 40 .vent non-carbiqecarbon formation on the catalyst. This
type promoter from Group lA, IIA and VII rare earths, reference further discloses maintaining a sufficiently high hydrogen partial pressure in order to impair the
are used in a two stage gasification and methanation formation of non-carbide carbon: on the catalyst.
process of U.S. Pat. No.' 3,904,386. U.S. Pat. No. The prior art teaches the use of Group VIII metals,
3,594,305 teaches the use of a two component catalyst 45 including iron carbides, an methanation catalysts or
system for the hydrogasification of coal at a tempera- reactants at temperatures that are generally less than
ture of 750·-800· F., wherein the first catalyst is se- 1200· F. (650· C.) in order to produce methane in re1alected
from Group VIII and is preferably an alloy such tively high amounts. Generally, as temperature inas
cobalt/molybdenum, nickel/tungsten or nickel/- creases, the production of methane decreases. Moremolybdenum
and the second catalyst is a noble metal. 50 ovei', many of the methanation catalysts of the prior art
U.S. Pat. No. 3,505,204 obtains hydrocarbons from will act as methane reforming catalysts at temperatures
carbonaceous materials in a single reactor having aofgrtea er than about 1300· F. (705· C.), e.g., U.S. Pat.
temperature of 800·-1200· F. by using a twocomponent No. 3,847,567, and/or will lose catalytic activity, e.g.,
catalyst comprising an alkali metal or alkaline earth due to oxidation, at temperatures ofabout 1200· F. (650·
metal in conjunction with a Group VIII metal. U.S. Pat. 55 C.) and higher. The prior art does not combine in one
No. 3,847,567 utilizes a Group VIII or an alkali metal as reactor the gasification of a carbonaceous material with
a methane reduction catalyst in a gas reformer of a coal the methanation of the gas produced by the gasification
hydrogasification process. U.S. Pat. No. 2,629,728 dis- of the carbonaceous material, because the temperatures
closes the use of an iron nitrite catalyst to hydrogenate for gasification are not generally conducive to methanacarbon
oxides. Additionally, iron and iron oxide are 60 tion. In order to obtain adequate rates of gasification of
taught as catalysts in a methanation zone having a tem- carbonaceous material, a minimum temperature of
perature of 800·_1200· F. for the production of gaseous about 500· C., with over 800· C. being preferred, is
fuels by synthesis in U.S. Pat. No. 2,543,759. U.S. Pat. usually used. Moreover, many of the prior art catalysts
No. 1,495,776 teaches a catalytic process for converting are active site catalysts, e.g., nickel, cobalt, vanadium
carbonaceous material into gases. Lime is the preferred 65 and molybdenum, which are prone to sulfur poisoning.
catalyst; however, other reagents such as calcium, alu- The stabilized metal carbide catalysts of the present
mina, magnesia, silica, iron, nickel or copper and mix- invention maintain their catalytic activity at temperatures
thereof may be used. tures exceeding 650· C. and, therefore, can be used in a
CROSS REFERENCE TO RELATED
APPLICAnONS
This application is a continuation-in-part application
of Ser. No. 928,506, filed July 27, 1978 now abandoned.
TECHNICAL FIELD
The present invention relates to a process for producing
a fuel gas by reacting in a single reaction zone a
carbonaceous material with water vapor in the presence
of a stabilized metal carbide catalyst.
4,372,755
This combination provides most of the heat required to
gasify the organic feed material and increases. overall
thermal efficiency of the process. Overall thermal efficiency
can be further increased by using the sensible
heat in the off-gas to produce steam by direct contact
with water being fed into the system and by further
heating this steam and an inlet gas stream to a temperature
above the temperature of the gasification/methanation
reaction zone.
The gasification/methanation reaction zone is composed
of a reactor bed containing a catalytic bed material
of the stabilized metal carbide particles, sized to
prevent the agglomeration and caking of the organic
feed. A fluidized bed is preferred as it provides isothermal
operation, high surface area for catalysis and permits
control of particle residence time.
Hydrogen for hydrogasification of the carbonaceous
feed material can be produced by heating a recycle gas
stream, using the sensible heat in the reactor off-gas and
hot gases from char combustion, to a temperature over
800° C., thereby shifting the composition of the recycled
gas to higher levels of hydrogen and carbon monoxide
by reforming the methane with water vapor. The
sensible heat in the recycled gas also helps provide the
heat required to raise the carbonaceous feed material to
gasification temperature. Thus, the ratio of hydrogen,
carbon monoxide, methane, water vapor and carbon
dioxide must be properly maintained within the gasification/
methanation reactor to maintain the catalytic
activity of the stabilized metal catalyst and to maintain
a desirable production level of methane.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the primary
reactions involved in a combined gasification/methanation
process utilizing a stabilized metal carbide catalyst.
FIG. 2 is a flow diagram for a process which combines
gasification of a carbonaceous material and methanation
of its gas in the presence of a stabilized metal
carbide catalyst.
4
equilibrium of the Boudouard reaction toward the production
of carbon monoxide. Therefore, carbon deposition
and carbide formation can be controlled by the
addition of water vapor and/or carbon dioxide to the
fluidized bed reactor. Thus, water vapor and/or carbon
dioxide is continuously added to the fluid bed in an
amount of from about 10 to about 30 volume percent of
the gas contained in the reaction zone. The steam carbon
and Boudouard reactions are endothermic, and
they can influence the carbon deposition and carbide
formation as a function of temperature. Moreover, since
the presence of either two much water vapor and/or
carbon dioxide can cause excessive oxidation of the
stabilized metal catalyst resulting in a loss of its methanation
activity, the resistance to oxidation of the stabilized
metal carbide catalyst is also controlled by temperature
and/or the amount of water vapor or carbon dioxide
present.
The methanation reaction and the side reactions pro-
20 ducing carbon dioxide are highly exothermic, whereas
the reactions producing carbon monoxide and hydrogen
from the organic feed materials and steam are endothermic.
Combining these reactions in a single system
provides a very nearly thermoneutral overall reaction
approaching the following:
DISCLOSURE OF THE INVENTION
The present invention provides a process for production
of a fuel gas from organic materials, such as coal
and solid municipal waste. The produced fuel gas con- 25
tains greater than 8 mole percent methane, and greater
than 30 mole percent under preferred conditions, in
addition to carbon monoxide, carbon dioxide and hydrogen.
The carbonaceous material is reacted in a
chemically active fluid bed in the presence of hydrogen, 30
carbon monoxide, steam and a stabilized metal carbide
catalyst. The stabilized metal carbide may be added to
the reactor directly or it may be formed in the reactor
by the deposition of carbon on the stabilized metal to
form surface carbides. The stabilized metal carbide 35
catalyst remains catalytically active at gasification temperatures
which exceed about 6500 C. (12000 F.),
thereby allowing the gasification and methanation processes
to be conducted in a single reaction zone.
The term "stabilized" as used herein in reference to a 40
metal carbide catalyst refers to the ability of the catalyst
to maintain its catalytic activity, including its physical
integrity, under gasification conditions and it primarily
refers to an oxidation resistant metal carbide catalyst.
The term is not intended to imply total chemical stabil- 45
ity or inertness, because the stabilized metal carbide
catalyst must have the ability to act as a bulk chemical
catalyst, actively partaking in the formation of methane.
The stabilized metal carbide catalyst must be sufficiently
chemically active to enable it to accept carbon, 50
e.g., to enable the stabilized metal to be carbided, and
sufficiently chemically active to transfer carbon to hydrogen
to form methane. In accepting carbon from
carbon monoxide, the stabilized metal also accepts oxygen
which is subsequently transferred to carbon monox- 55
ide resulting in the formation of carbon dioxide. Thus,
the stabilized metal catalyst is continuously carbided
and decarbided.
The deposition of carbon on the stabilized metal carbide
and/or the stabilized metal within the reactor is 60
dependent upon the interaction of the contact of the
stabilized metal catalyst with the carbonaceous feed
material, the Boudouard reaction (C02+~2CO) and
the steam carbon reaction (C+H20+ZCO+H2). Carbon
monoxide, e.g., produced by the steam carbon reac- 65
tion, reacts readily with steam to produce carbon dioxide
via the water gas shift reaction (CO+ H20+ZC02+
H2)' The carbon dioxide aids in maintaining the
3
combined gasification and methanation reactor for the
production of a synthetic gas having a relatively high
methane content from carbonaceous material. Although
generally the temperatures required for gasification will
reduce methane production, the gasification of the car- 5
bonaceous material, e.g., coal, will cause the formation
of some methane by the volatilization of higher hydrocarbons
than methane. These volatilized higher hydrocarbons
react with hydrogen to form methane. Moreover,
the stabilized metal carbide catalysts are active 10
methanation catalysts at much lower carbon levels than
those of conventional metal carbides such as cementite,
Fe3C, and they are not poisoned by the presence of
gaseous sulfur compounds.
Additionally, the process of the present invention can 15
utilize untreated water and/or effluents, unsuitable for
use in a boiler, to generate steam by means of heat from
product gas being cleaned by the water. Process char
can be used to heat the steam and recycle gases to create
a heat-efficient, thermoneutral reaction.
4,372,755
5 6
With respect to a particular stabilized metal catalyst,
PREFERRED MODE FOR CARRYING OUT THE the particular alloy component should be comprised of
INVENTION metals which exhibit a relative difference in free energy
The process of the present invention entails the use of of formation of the carbides of each metal such that one
a stabilized metal carbide as a catalyst in the production 5 metal forms a sufficiently stronger carbide to act as a
of fuel gas by synthesis. Depending upon the carbona- stabilizing component thereby enhancing the chemical
ceous feedstock, a wide variety of fuel gases can be activity of the other metal carbide. It is preferred that
produced including a medium Btu (British thermal unit) there be a difference in free energy of formation befuel
gas having a Btu value of greater than about 300 tween at least two of the metal components of the alloy
Btu per cubic foot for gas turbine fuel, synthetic natural 10 of at least about 5,000 British thermal units per pound
gas and synthesis gas for methanol or gasoline produc- atom of carbon. Additionally, the effects of combining
tion. The process can be operated at a thermal effi- two or more metals to form the alloy or stabilized metal
ciency of greater than 80 percent while producing a fuel component of the catalyst results in the alloy having a
gas which can have a Btu value of over 400 Btu per lower capability for carburization and oxidation than
cubic foot offuel gas. The carbonaceous material can be 15 each of the metals separately, Moreover, the alloy apany
of a number of carbon containing materials which pears to exhibit metastable oxidation states thereby
are combustible, for example, peat and lignite, sub- allowing for its absorption and desorption of both carbI"
tummous, bI u'tm'mous and anthracI'te coaIs and soII'd bidEe andloxfygen. b'I' d I b'd . I 'I d
mUnI"ClpaI and'mdustrl'alwaset. , xam'1'p.es 0 sta 'dI Ize meta car Ihe ca'ta ysts mcbu'd e
Although the exact mechanism of action of the stabi- 20 Iron Sl lCld~ carbl ~, manganese c romlUm car ! e,
II,zed metaI carbI'de cataIyst'IS not known, I't I's thoUght ferrochromlUm carbIde and m.an. ganese cobalt .carbIde.
, , . '" One group of preferred stabIlIzed metal carbIde catathat'
the stabIlIzed metal ca,rbIde c.atalyst IS actmd"g pn- Iysts I"S Iron S'I1I'CI'de carbI'de cataIysts contam,.mg from
manly as a, bulk cat"alyst whIch acts as an mterm. e late m about 4 t0 about 50 wel'ght percent 0 f Sl'I'ICI'de or Sl'II'con
.th'e chem..Ical reactlOn(s)'behmg catalydzefd hand IS p're(sen)t 25 and from about 0.5 t b t 3 0 'ht t f car 0 a ou . welg percen 0 -
mItS on~l~al concentratI~n at teen 0 t e reactIOn. s , bon by weight of the catalyst. With respect to iron
The stab~lIze~ metal carbIde ,catalyst may also be ~ctmg silicide carbides, it is preferred that the catalyst contain
as an ,actIve Slt~ catalyst, whIch does not partake .m the less than about 32 weight percent of silicon, because
chemIcal reactlOn(s) bemg, cataly~ed but wh.erem the within this range the catalyst is magnetic allowing for
surface of the catalyst pro":l?es a sIte for re~ctlOn of the 30 its more convenient separation from elutriated char and
reactants, Beca~se th~ stabIlI~ed .metal,carbl?e, cat,alysts ash for subsequent reuse. Moreover, as long as the iron
of the present mventlOn mamtam theIr a~tlvlty m the silicide carbide catalyst contains a sufficient amount of
pr~sen~e of s~lfur, they are not susce~tIble, to sulfur silicon to maintain its stability, then generally the more
pOISOnIng and It appears th~t th~~ ac~ pnman~y. as buI,k iron present in· the catalyst, the greater its catalytic
~ataly~ts, Therefo!e: for slmplIclt~, m descnbmg t~IS 35 activity. It is more preferred that an iron silicide carbide
mventlOn, ,the actIvlt~ of t,he stabIlIzed metal carbIde catalyst contain from about 10 to about 20 percent by
catalyst ",:Ill be descnbed m terms of a bulk catalyst, weight of silicon. At silicon levels less than about 4
alt~ough, It ~ust ,be remembered that they may also be percent, the catalyst looses its stability at temperatures
actmg as a~t,lve sIte catalys~s, , , greater than about 6500 C. At silicon levels greater than
The stabIlIzed metal carbIde catalyst IS compnsed of 40 about 50 percent, the silicon impedes the surface carbutwo
components, carbon and an alloy of at least two rization of the iron silicide preventing the formation of
different metals, each of which is capable of forming a the iron silicide carbide catalyst. If an iron silicide carmetal
carbide. More specifically, the catalyst is defined bide catalyst has a carbon level less than about 0.5 peras
a composition of these components which has a free cent by weight, the catalyst is not sufficiently active.
energy of formation of from about - 30,000 to about 45 Since the maximum carbide content of an iron silicide is
10,000 British thermal units per pound atom of carbon about 3 percent, any carbon present on the catalyst
at a temperature offrom about 500° to about 900° C. and which is above about 3 percent will be in the form of
a pressure from about 100 to about 8,300 kilopasca1s elemental carbon, not as a surface carbide. Silvery pig
(about 15 to about 1200 p.s.i.a.) and preferably a temper- iron, which generally contains from about 0.5 to about
ature from about 750° C. to about 900° C. and prefera- 50 1.5 percent carbon, from about 12 to about 20 percent
bly a pressure from about 1,000 to about 4,000 kilopas- silicon and from about 82 to about 84 percent iron by
ca1s (about 150 to about 600 p.s.i,a.). weight, is an example ofa preferred iron silicide carbide
Each of the metals which comprise the alloy compo- catalyst.
nent must have the ability to form a metal carbide at the The catalyst is employed in a fluidized bed reactor
process conditions ofthe gasification/methanation reac-.55 which has a single reaction zone for the production of
tion zone. Examples of suitable metals include, iron, fuel gas. The stabilized metal carbide catalyst employed
silicon, manganese, cobalt, chromium, nickel, alumi- in the reaction zone is sufficiently physically stable and
num, vanadium, tungsten, molybdenum, calcium, bo- dense to remain in the bed during the gasification of
ron, sodium and magnesium. It is preferred that one or many tons of feed material, requiring only makeup as a
both metals be selected from the group consisting of 60 result of elutriation and sulfidation. The amount of catasilicon
and those metals which form intermediate car- Iyst required in a particular system is dependent upon
bides (carbides which are intermediate in character the temperature of the fluidized bed, time of contact
between ionic and interstitial carbides), I.e., iron, cobalt, with the carbonaceous material and the reactivity of the
chromium, manganese and nickel. The intermediate carbonaceous material. There should be a sufficient
carbides tend to be more chemically active than intersti- 65 amount of the stabilized metal carbide catalyst in the
tial carbides and tend to exhibit a greater physical stabil- reaction zone to prevent caking and agglomeration of
ity and chemical stability, e,g., with respect to oxida- the carbonaceous materials and provide adequate surtion,
than ionic carbides. face area for catalysis. Therefore, it is preferred that the
4,372,755
7
catalyst be present in a greater amountthan the amount
of fresh, unreacted (as opposed to char) carbonaceous
material. For example, a suitable mixture in the reactor
may comprise about four parts by weight of the stabilized
metal carbide catalyst to about one part by weight 5
of fresh carbonaceous material.
The particle size of the catalyst is such as to prevent
caking and agglomeration of materials in the fluidized
bed. Generally, the particle size of the catalyst should
be compatible with the space velocity required for its 10
fluidization in the reaction zone.
The catalyst may be added directly to the reactor or
it may be formed in the reactor. It can be formed in the
reactor by the addition of the metal alloy component to
the reactor and the deposition of carbon in amounts 15
which are sufficient to form a stabilized metal carbide
having a free energy of formation of from about
- 30,000 to about 10,000 British thermal units per
pound atom of carbon at the gasification/methanation
conditions of the process. The carbon should be in a 20
reactive form, for example, carbon produced from a
gaseous reaction.
The gasification of a carbonaceous material and/or
the methanation of a gas inyolves a number of dynamic
and interrelated chemical reactions. Heretofore, the 25
prior art has separated gasification and methanation
reactions in order to utilize different conditions to affect
the separate chemical reactions involved in gasifying a
carbonaceous material and those reactions involved in
forming methane. Although the process of the present 30
invention can be used to gasify carbonaceous material
or to increase the methane value of a gas containing
hydrogen and carbon monoxide, the essence of the
invention lies in balancing the equilibriums and/or kinetics
ofthe chemical reactions to allow for the gasifica- 35
tion and methanation of a carbonaceous material to
occur within the same reactor while maintaining the
catalytic activity of a stabilized metal carbide catalyst.
The primary reactions involved in a combined reaction
zone are those relating to the gasification of carbon, the 40
water gas shift reaction, the carbiding and decarbiding
of the catalyst acting as a bulk catalyst, the oxidation
and reduction of the catalyst acting as a buik catalyst,
and the formation of methane. A schematic representation
of these reactions is presented in FIG. 1. Since the 45
optimization of some of the reactions is detrimental to
others in the reaction zone, it is necessary to control the
kinetics and equilibriums of the chemical'reactions involved
in order to maximize methane production while
still obtaining adequate gasification of the carbonaceous 50
material. The control is a function of the ratio of gases
present, temperature, pressure and catalyst used. The
kinetics and equilibriums of the chemical reactions are
preferably controlled primarily by temperature and the
addition of water vapor and/or carbon dioxide. The 55
chemical interactions can be explained with reference
to FIG. 1. (The numbers used to depict the reactions are
for reference purposes only and are not indicative ofthe
order of occurrence. Additionally, "M", as used in the
figure, refers to the metal alloy component of the cata- 60
lyst).
In FIG. 1, an inlet gas comprising primarily water,
hydrogen and carbon monoxide with lesser amounts of
methane and carbon dioxide is injected into a reaction
zone containing a source of carbon, e.g., a carbonaceous 65
material, and a stabilized metal carbide catalyst, MxC.
The carbon activity (ca) of the gases contained within
the reaction zone will vary from a value less than one to
8
approximately one depending upon the location in the
reaction zone. The carbon activity of a gas is an equilibrium
value which denotes the ability of the gas to form
elemental carbon. A value of one represents equilibrium,
at a value greater than one the gas will tend to
form elemental carbon and at a value of less than one
the gas will tend to consume elemental carbon. The
inlet gas will have a carbon activity of less than one
enabling its water and carbon dioxide components to
readily react with the carbon from the carbonaceous
material, including char, causing the gasification of the
carbon by the formation of carbon monoxide and hydrogen,
reactions (4) and (5). Since the stabilized metal
carbide catalyst is not readily oxidized at reaction conditions,
the inlet gas will preferentially oxidize the carbonaceous
material as long as the concentrations' of
water and/or carbon dioxide are not excessive, e.g.,
greater than about 30 volume percent of the gas in the
reaction zone. The presence of hydrogen in the inlet gas
and from reaction (5) allows for the decarburization of
the stabilized metal carbide catalyst, reaction (3),
thereby forming the desired methane. The stabilized
metal alloy is carbided in accordance with reactions (1)
and (2). To a lesser extent, methane is also formed by
the reaction of carbon or a source of carbon, e.g., carbon
monoxide, with hydrogen, reaction (7). The production
of any significant quantity of methane from
reaction (7) occurs to the extent that the stabilized metal
carbide catalyst is acting as an active site catalyst. The
carbon monoxide reacts with water vapor to form hydrogen
and carbon dioxide, reaction (6). The heat given
off in the formation of carbon dioxide and methane
provides most of the heat necessary for gasifying the
carbonaceous material.
The presence of water, in the form of steam, aids the
gasification of elemental carbon. Since the kinetics of
the reactor are controlled, mainly by temperature, any
inlet gas, e.g., recycle gas or feed gas, added to the
process will be at least the temperature of the gasifier,
about 500· to about 900· C., and preferably of a sufficient
temperature to maintain the reactor at the preferred
temperature for a particular process. At these
temperatures, a portion .of the carbonaceous material
readily volatilizes in the form of higher hydrocarbons
which react w,ith hydrogen to form methane, reaction
(8). The product gas comprising carbon dioxide, methane
and water is continuously removed from the process.
Thus, FIG. 1 represents the favored primary reactions
of the process. However, since all of the reactions
portrayed are reversible, their equilibriums are shifted
toward the forward reactions by the addition of carbonaceous
material, water vapor, hydrogen and carbon
monoxide. Carbon dioxide can be used in place of or in
conjunction with water vapor. Water vapor is preferred
to carbon dioxide because it is more easily produced
within the process, for example, through a recycle gas
stream, and it supplies a source of hydrogen. The source
of water vapor is not critical and it can be from the
carbonaceous material and/or the inlet gas, e.g., a recycle
gas or feed gas. Although the addition of water
vapor (or carbon dioxide) to the reactor is not narrowly
critical, it cannot be so great to cause excessive or rapid
oxidation ofthe stabilized metal carbide catalyst. Therefore,
water vapor and/or carbon dioxide is maintained
in the reactor in an amount from about 10 to about 30
volume percent of the gas used in the reactor. At water
vapor and/or carbon dioxide levels ofless than about 10
4,372,755
9 10
volume percent excess carbon deposition will occur The pressure of the process can vary over a wide
which can cause plugging of the off-gas system. Water range offrom about 100 kilopascals (15 p.s.i.a.) to about
vapor and/or carbon dioxide levels greater than about 8,300 kilopascals. However, a pressure of 1,000 kilopas-
30 volume percent will tend to cause excessive oxida- cals (150 p.s.i.a.) to about 4,000 kilopascals (600 p.s.i.a.)
tion of the catalyst. However, within this recited range, 5 is preferred.
generally as the temperature of the reactor is increased, The stabilized metal carbide catalyst is useful in any
the more water vapor and carbon dioxide which can be process for synthesizing hydrocarbon gases from carbopresent.
naceous sources. It is especially useful in those pro-
The additional source of hydrogen and carbon mon- cesses wherein heat is taken from the produced gas and
oxide supplied to the reactor may be a recycle gas 10 is used to heat water to produce steam and to reheat a
stream from a portion of the product gas. In such an portion of the produced gas which is recycled in the
application, it is preferred that the recycled product gas process and wherein the char produced in the process is
be reformed, by the addition of heat, water and a re- combusted and the heat produced therefrom is used to
forming catalyst, to higher levels of carbon monoxide further heat the recycle gas in order to reform the methand
hydrogen which is recycled into the reaction zone. 15 ane contained therein to carbon monoxide and hydro-
The reforming catalyst is a steam hydrocarbon reform- gen. Preferred processes utilize fluidized bed reactors.
ing catalyst and any such catalyst active at these condi- A general process ofthis type is shown in FIG. 2. In the
tions may be used. Examples of such catalysts include process of FIG. 2, carbonaceous feed material is intro-
Group VIII metals, for example, nickel, nickel oxide duced into reactor 1 wherein it is reacted in a single
and chromium oxide. The gasification of the carbona- 20 reaction zone consisting of a fluidized bed comprised of
ceous material results in the formation of char which unreacted carbonaceous feed material and a catalytic
can be removed and combusted in a separate combus- bed material comprised of a stabilized metal carbide and
tor. The heat from the combustor can be used in the a process recycle gas stream 3 which is reheated by the
reformation of the product gas which can then be recy- combustor gases prior to entry into reactor 1. The offcled
to the reactor. 25 gas produced in reactor 1 is then conducted to separator
Temperature and pressure are also used to favorably 4 wherein the particulate matter is removed. The particbalance
the equilibriums and the kinetics of the reac- ulate free off-gas is then conducted to reheater 5
tions. The temperature must be sufficient to cause the wherein the temperature of the off-gas is reduced from
gasification of the carbonaceous material but not so a temperature from about 500° C._900° C. to a temperahigh
so as to substantially reduce methane equilibrium. 30 ture of about 400° C.-750° C. by indirectly heating
Therefore, the temperature is a function of the reactiv- recycle gas stream 6 having a temperature from about
ity of the particular carbonaceous feed material and the 90° C.-325° C. to a temperature of about 400° C.-825°
desired methane content of the produced fuel gas. Thus, C. The reactor off-gas is then conducted from reheater
the temperature of the reactor will be from about 500° 5 to a heat recovery boiler 7 where it is further cooled
C. to about 900° C. The more reactive the carbonaceous 35 to a temperature of about 200° C.-550° C. by the indimaterial
is, generally, the lower the temperature of the rect heating ofwater vapor stream 8.
process and the more methane the fuel gas will contain. The reactor off-gas then passes from heat recovery
Hence, the process temperature required for peat will boiler 7 to gas Cleaner 9 wherein any tar or water conbe
lower than that required for a lignite coal which is tained with the gas are separated from the product gas
lower than that required for bituminous coal which is 40 10. The tar and water are removed from gas cleaner 9
lower than that required for anthracite coal. For exam- via conduit 11. The tars and water 11 are cooled in heat
pIe, if the carbonaceous feed is a peat, the temperature exchanger 12 from a temperature of from about 200°
of the process could be about 500° C., its gasification C.-550° C. to a temperature of about 100°-300° C. by
temperature, whereas, the temperature of the process the indirect heating of water stream 13. The cooled tar
for a bituminous coal would be from about 760° C. to 45 and water stream 14 undergoes separation in separator
about 870° c., its gasification temperature. Peat, there- 15. The water from separator 15, which is directed
fore, has a greater potential for producing greater through heat exchanger 12a where its temperature is
amounts of methane compared to a bituminous coal. A further reduced to about 70°-90° C. by indirect heating
preferred temperature of a particular process is the with water stream 16, can be recycled to gas cleaner 9
threshold temperature at which the carbide form of the 50 for reuse.
stabilized metal carbide catalyst is more stable than its The non-water materials from separator 15, e.g., tars,
oxidized form. Threshold temperature is defined as the and the particulate matter 19 from separator 4 are added
temperature range at which the carbide activity of the to combustor 2 wherein they are combusted in the prescatalyst,
i.e., the activity of the carbide form of the ence of air (or another source ofoxygen) 17 at a tempercatalyst
relative to the oxidized form ofthe catalyst, just 55 ature of from about 950° C. to about 1650° C. The comexceeds
a value of one. The carbide activity of the cata- bustor gases 22 and ash 21 are removed from the comlyst
is an equilibrium value, wherein a value of one bustor.
represents equilibrium and a value greater than one The water for reactor 1 is supplied through recycle
represents a greater tendency of the catalyst to be in a gas stream 3. Water 16 is introduced into the process
carbided form as opposed to an oxidized form. Within 60 and is subsequently heated in exchangers 12 and 120 and
the process conditions heretofore described, e.g., tem- then introduced into heat recovery boiler 7 as water
perature, pressure, and amount of water vapor, the stream 8. The water stream 8 is further heated in heat
threshold temperature of a particular process is primar- recovery boiler 7 to a temperature of from about 200° to
ily dependent upon the particular stabilized metal car- about 350° C. after which it is combined as saturated
bide catalyst. For example, when silvery pig iron is the 65 steam with recyCle gas stream 6 and introduced into
stabilized metal carbide catalyst, the threshold tempera- reheater 5 where they are heated to a temperature of
ture will be from about 775° C. (1425° F.) to about 845° about 400°-825° C. The combined recycle gas stream 3
C. (1550° F.). is introduced into reformer 18 where it is reformed to
"Composition of the catalyst at the beginning of the test, about 3% of carbon was
present at the end of the test (a portion of the 3% carbon may have been in elemental
form).
Gas-catalyst
Catalyst % CH4in Contact Time, Rate %
Composition OfT-gas min. ClLVmin.
24 Fe 68 Cr 6.2C 24 7.4 3.24
% Gas-catalyst Rate %
Catalyst Composition Steam CH4in Contact Time ClLV
wt,% Vol,% OfT-gas min. min.
76.6 Mn 21.2 Cr 4.4C 0.99 40 6.04 6.62
67.5 Mn 22.2 Co 2.6C 0.74 33 3.8 8.81
Si02 (sand) 10.0 10 10.1 0.99
"Fe304 FeSi03 0.74 15 26.5 0.54
·Obtained from an excess oxidation of an iron silicide carbide catalyst.
EXAMPLE 2
A gas comprising 3 parts hydrogen and 1 part carbon
monoxide was used to fluidize a 2 inch continuous fluid
bed reactor containing the gas and different catalysts.
Steam was also present in the gas in the amount indicated
in Table 2. Because a carbonaceous material was
not being gasified, it was not necessary that water vapor
and/or carbon dioxide be present in the reactor in an
amount of from about 10 to about 30 volume percent.
The bed was maintained at a pressure of 100 psig (690
kilopascals) and a temperature of 700° C. The composition
of the catalyst used in each run is given in Table 2
as is the volume percent of methane in the produced
off-gas, the actual contact time between the gas and
catalyst and the rate of methanation.
TABLE 2
12
TABLE I-continued
4,372,755
11
higher levels of carbon monoxide and hydrogen. It is
preferred that the recycle gas stream be reformed by
increasing its temperature to about 850° C.-lloo° C. at
a pressure offrom about 1,725-2,750kilopascals in the
presence of a steam hydrocarbon reforming catalyst. 5
The reformation of the recycled gas stream with water
vapor need not be performed in the combustor 2. However,
the combustor supplies a ready source of heat.
Reformed recycle gas stream 20 is introduced into reac- 10
tor 1 to provide carbon monoxide, hydrogen and water
to reactor 1.
Since a process for the combined gasification and
methanation of a carbonaceous feed material in the
presence of a metal stabilized carbide catalyst is prefera- 15
bly conducted in a manner which is heat efficient, there
are a wide variety of changes which could be made in
the flow diagram of FIG. 2. For example, a portion of
the recycled product gas stream might be used to preheat
the carbonaceous feed material prior to its injec- 20
tion into reactor 1. The water added to the system, i.e.,
water 16, could be heated e~ternally from the process or
converted to steam by direct contact of the water
stream 16 with a portion of the hot reactor off-gas or
product gas. Since air being added to a combustor is 25
generally preheated, air 17 might be preheated externally
from the process or by heat produced in the process,
e.g., heat of the stack gases. Depending upon the
nature of the carbonaceous feed material, product gas 30
10 may be subjected to an acid removal step. If an acid
removal step is included, it would be preferable that the
recycled gas stream 6 be taken from the acid cleaned
product gas.
EXAMPLE 1 35
A gas representative of one produced by a carbonaceous
material and having a composition of 6.3 percent
carbon dioxide, 33.4 percent carbon monoxide, 4.8 percent
methane and 55.5 percent hydrogen was used to 40
fluidize a 2 inch continuous fluid bed reactor containing
the gas and different catalysts. (All percentages of gases
given in the examples are volume percent). Steam was
also present in the gas in an amount of about 0.3 volume
percent or less by volume of fluidizing gas to control 45
the deposition of carbon. Because a carbonaceous material
was not being gasified, it was not necessary that
water vapor and/or carbon dioxide be present in the
reactor in an amount of from about 10 to about 30 vol- 50
ume percent. The bed was maintained at a pressure of
100 psig (690 kilopascals) and a temperature of 700° C.
The composition of the catalyst used in each run is
given in Table 1 as is the volume percent of methane in
the produced off-gas, the actual contact time between 55
the gas and catalyst and the rate of methanation. The
volume percent of methane is based on the equilibrium
gas composition normalized to 100 percent by volume
on a dry basis.
TABLE 1
EXAMPLE 3
A gas comprising 32.2 percent hydrogen, 3.5 percent
carbon monoxide, 10.3 percent carbon dioxide and 54.0
percent methane was used to fluidize a two inch continuous
fluid bed reactor containing the gas and iron carbide
as cementite, Fe3C. Steam was also present in the
gas in an amount of about 10 volume percent or less by
volume of the fluidizing gas. The fluidized bed was
maintained at a pressure of 100 psig (690 kilopascals)
and a temperature of 700° C. After the reactor reached
stabilized conditions, the off-gas comprised 7.5 percent
nitrogen (nitrogen was used to initially purge the reactor),
46.0 percent hydrogen, 33.5 percent methane, 6.9
percent carbon monoxide and 0.8 percent carbon dioxide.
A Mossbauer analysis ofthe composition ofthe iron
carbide was taken prior to initiating the reactor (Starter
Bed) and after the completion of the reactor run (Final
Bed) and the compositions are given below in Table 3.
Catalyst
Composition
% CH4in
OfT-gas
Gas-catalyst
Contact Time,
min.
Rate %
ClLVmin.
60
Compound
Fe3C
Fe304
Fe203
FeO
Fe
TABLE 3
Starter
Bed (wt %)
72.1
3.5
3.5
o
10.5
Final
Bed (wt %)
91.8
2.1
ooo
46.8 Fe 46.0 Si 2.OC
"46.8 Fe 46.0 Si 2.OC
69.1 Fe 27.0 Si 2.9C
"82.3 Fe 15.1 Si O..,C
89.3 Fe 6.1 Si 1.6C
31
35
35
32
35
18.1
12.0
15.4
6.0
4.6
1.73
2.92
2.27
5.27
7.61
65
EXAMPLE 4
A gas comprising 34.8 percent hydrogen, 19.2 percent
carbon monoxide, 32.0 percent carbon dioxide and
25
14
ing a free energy of formation of from - 30,000 to
10,000 British thermal units per pound atom of carbon
at the reaction conditions, said metal alloy comprising
at least two metals selected from the group consisting of
5 iron, silicon, manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium,
boron, sodium and magnesium wherein one of said two
metals forms a sufficiently stronger carbide to act as a
stabilizing component thereby enhancing the chemical
IO activity of the other metal carbide and a gas of which
from about 10 to about 30 volume percent is selected
from the group consisting of water vapor, carbon dioxide
and mixtures thereof at a temperature and pressure
sufficient to cause the gasification of the carbonaceous
15 material and cause the formation of a sufficient amount
of methane to produce a fuel gas wherein the temperature
is from about 500· C. to about 900· C. and the
pressure is from about 100 kilopascals to about 8300
20 kilopascals.
2. The process of claim 1 wherein the relative difference
of at least two of the metals in their free energy of
formation of their respective carbides is at least 5,000
British thermal units per pound atom of carbon.
3. The process of claim 1 wherein the temperature of
the reaction zone is within the threshold temperature
range of the stabilized metal carbide catalyst.
4. The process of claim 1 wherein the stabilized metal
carbide catalyst is selected from the group consisting of
iron silicide carbide, manganese chromium carbide,
ferrochromium carbide and manganese cobalt carbide.
5. The process of claim 4 wherein the stabilized metal
carbide catalyst is an iron silicide carbide.
6. The process of claim 5 wherein the stabilized metal
carbide catalyst comprises from about 4 to about 50
weight percent silicon, from about 0.5 to about 3 weight
percent carbon and the remainder of the catalyst comprises
primarily iron.
7. The process of claim 6 wherein the stabilized metal
carbide catalyst comprises from about 10 to about 20
weight percent silicon, from about 0.5 to about 3 weight
percent carbon and from about 77 to about 90.5 weight
percent iron.
8. A process for the production of a fuel gas from a
solid carbonaceous material comprising:
(a) reacting the solid carbonaceous material in a single
fluidized reactor in the presence of a stabilized
metal carbide catalyst comprising carbon and a
metal alloy and having a free energy of formation
offrom - 30,000 to 10,000 British thermal units per
pound atom of carbon at the reaction conditions,
said metal alloy comprising at least two metals
selected from the group consisting of silicon, manganese,
cobalt, chromium, nickel, aluminum, vanadium,
tungsten, molybdenum, calcium, boron, sodium
and magnesium, wherein one of said two
metals forms a sufficiently stronger carbide to act
as a stabilizing component thereby enhancing the
chemical activity of the other metal carbide and
wherein said metal alloy has a lower capacity for
carburization and oxidation than each of the individual
metals of the alloy and a fluidizing gas
wherein from about 10 to about 30 volume percent
of the fluidizing gas is selected from the group
consisting of water vapor, carbon dioxide and mixtures
thereof at a temperature of from about 500·
C. to about 900· C. and a pressure of from about
4,372,755
42.4
26.1
o
25.5
o
Final
Bed (wI %)
91.8
2.1
ooo
Slarter
Bed (WI %)
TABLE 4
EXAMPLE 5
Fe3C
Fe304
Fez03
FeO
Fe
Compound
Fuel gases were produced from Illinois No.6 coal, a
bituminous coal containing about 3.45 percent by
weight sulfur, by fluidizing the coal with a gas comprising
about 7-7.5 percent carbon dioxide, about 34.8 per- 30
cent carbon monoxide, about 4.2 percent methane and
about 53.9 percent hydrogen and gasifying the coal,
constituting about 5 weight percent of the fluidizing
gas, at a temperature of about 700· C. and a pressure of
about 100 p.s.i.g. in the presence of an iron silicide car- 35
bon catalyst. Steam was maintained in the reactor in an
amount of from about 6 to about 10 percent by volume
of the fluidizing gas. In sample 1, the iron silicide carbon
catalyst was produced in the reaction vessel by the
carbiding of an iron silicide comprising about 50 weight 40
percent iron and about 50 weight percent silicon. In
sample 2, the iron silicide carbide catalyst comprised, at
the beginning of the reaction process, about 82 weight
percent iron, about 16 weight percent silicon and about
0.6 weight percent carbon. The actual contact time 45
between the gas and catalyst in sample 1 was about 6
minutes and the equilibrium composition of the fuel gas
produced was about 1.1 percent nitrogen, about 55.5
percent hydrogen, about 21.5 percent methane, about
15 percent carbon monoxide and about 7.4 percent car- 50
bon dioxide. The rate of methanation in sample 1 was
about 3.62 percent methane per minute.
The actual contact time between the gas and the
catalyst of sample 2 was about 7.44 minutes and the
equilibrium gas composition of the fuel gas produced 55
was about 1.5 percent nitrogen, about 31 percent hydrogen,
about 44 percent methane, about 17.5 percent carbon
monoxide and about 5.5 percent carbon dioxide.
The rate of methanation for sample 2 was about 5.94
percent methane per minute. 60
What is claimed is:
1. A process for the production of a fuel gas from a
solid carbonaceous material comprising reacting in a
single reaction zone the solid carbonaceous material in
the presence of a stabilized metal carbide catalyst capa- 65
ble of substantially maintaining its physical integrity and
chemical activity under gasification conditions, said
catalyst comprising carbon and a metal alloy and hav-
13
14.0 percent methane was used to fluidize a two inch
continuous fluid bed reactor containing the gas and iron
carbide as cementite, Fe3C. Steam was also present in
the gas in an amount of about 20 volume percent of the
fluidizing gas. Additionally, carbon dioxide was added
intermittently throughout the reaction in order to maintain
the volume percent of water and carbon dioxide at
a level of about 35 percent by volume of the fluidizing
gas. The bed was maintained at a pressure of 100 psig
(690 kilopascals) and a temperature of 700· C. The reactor
off-gas obtained a maximum of 33.9 percent methane
and then the methane content decreased, apparently as
a result of the decomposition of the catalyst which is
shown by the Mossbauer analyses of the composition of
the iron carbide in Table 4.
4,372,755
16
15. A process for the production of a fuel gas from a
solid carbonaceous material comprising reacting in a
single reaction zone the solid carbonaceous material in
the presence of a stabilized metal carbide catalyst comprising
a carbon and a metal alloy and having a free
energy of formation of from -30,000 to 10,000 British
thermal units per pound atom of carbon at the reaction
conditions, said metal alloy comprising at least two
metals selected from the group consisting of iron, sili-
10 con, manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium, boron, sodium
and magnesium, wherein one of said two metals
forms a sufficiently stronger carbide to act as a stabilizing
component thereby enhancing the chemical activity
15 of the other metal carbide, said catalyst having characteristics
of a bulk chemical catalyst and capable of substantially
maintaining its physical integrity and chemical
activity under gasification conditions and a gas mixture
comprising hydrogen, carbon monoxide and from
about 10 to about 30 volume percent of gas selected
from the group consisting of water vapor, carbon dioxide
and mixtures thereof at a temperature and pressure
sufficient to cause the gasification of the carbonaceous
material and cause the formation of a sufficient amount
of methane to produce a fuel gas having a Btu value
greater than about 300 Btu per cubic foot of fuel gas,
wherein a portion of the hydrogen and carbon monoxide
is obtained by recycling a portion of the methane
and the recycled gas is reformed to hydrogen and carbon
monoxide by the addition of heat and water
wherein the temperature is from about 500· C. to about
900· C. and the pressure is from about 100 kilopascals to
about 8300 kilopascals.
16. The process of claim 14 wherein the stabilized
metal carbide catalyst is selected from the group consisting
of iron silicide carbide, manganese, chromium
carbide, ferrochromium carbide and manganese cobalt
carbide.
17. The process of claim 16 wherein the stabilized
metal carbide catalyst is an iron silicide carbide comprising
from about 4 to about 50 weight percent silicon,
from about 0.5 to about 3 weight percent carbon and the
remainder of the catalyst comprises primarily iron and
wherein the temperature of the process is the threshold
temperature range of the stabilized metal carbide catalyst.
18. The process ofclaim 17 wherein the Btu value of
the fuel gas produced is greater than 400.
19. A process for the production of a fuel gas from a
solid carbonaceous material comprising:
(a) reacting the solid carbonaceous material in a single
reactor in the presence of a stabilized metal
carbide catalyst capable of maintaining its physical
integrity and chemical activity under gasification
conditions, said catalyst comprising carbon and a
metal alloy and having a free energy of formation
of from - 30,000 to 10,000 British thermal units per
pound atom of carbon at the reaction conditions,
said metal alloy comprising at least two metals
selected from the group consisting of iron, silicon,
manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium, boron,
sodium and magnesium, wherein one of said two
metals forms a sufficiently stronger carbide to act
as a stabilizing component thereby enhancing the
chemical activity of the other metal carbide, and a
gas mixture comprising hydrogen, carbon monoxide
and from about 10 to about 30 volume percent
15
100 kilopascals to about 8,300 kilopascals to produce
a fuel gas containing methane;
(b) removing char produced in step (a) to a combustor
and combusting it;
(c) removing a portion of the fuel gas produced in 5
step (a) for recycle back to the reactor;
(d) removing a portion of the heat contained in the
fuel gas produced in step (a) to heat water to produce
water vapor and to heat a portion of the recycle
gas;
(e) using the heat produced from the combustion of
the char to further heat the water vapor and to
further heat the recycle gas; and
(t) introducing the water vapor and the heated recycle
gas into the reactor.
9. The process of claim 8 wherein the water vapor
and recycle gas stream are combined and then heated
with the heat produced from the combustion of the
char.
10. The process of claim 8 wherein the temperature of 20
the reactor is the threshold temperature range of the
stabilized metal carbide catalyst.
11. The process of claim 10 wherein the stabilized
metal carbide catalyst comprises (rom about 10 to about
20 weight percent silicon, from about 0.5 to about 3 25
weight percent carbon and from about 77 to about 90.5
weight percent iron, and wherein the threshold temperature
of this stabilized metal carbide catalyst is from
about 775· C. to about 845" C.
12. The process of claim 10 wherein the stabilized 30
metal carbide catalyst is selected from the group consisting
of iron silicide carbide, manganese chromium
carbide, ferrochromium carbide and manganese cobalt
carbide.
13. The process of claim 10 wherein the stabilized 35
metal carbide catalyst is an iron silicide carbide comprising
from about 4 to about 50 weight percent silicon,
from about 0.5 to about 3 weight percent carbon and the
remainder of the catalyst comprises primarily iron.
14. A process fot the production of a fuel gas from a 40
solid carbonaceous material comprising reacting in a
single reaction zone the solid carbonaceous material in
the presence of a stabilized metal carbide catalyst having
a free energy of formation of from - 30,000 to
10,000 British thermal units per pound atom of carbon 45
at the reaction conditions, said metal alloy comprising
at least two metals selectedfrom the group consisting of
iron, silicon, manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium,
boron, sodium and magnesium, wherein one of said two 50
metals forms a sufficiently stronger carbide to act as a
stabilizing component thereby enhancing the chemical
activity of the other metal carbide, said catalyst having
characteristics of a bulk chemical catalyst and capable
of substantially maintaining its physical integrity and 55
chemical activity under gasification conditions, and a
gas of which from about 10 to about 30 volume percent
is selected from the group consisting of water vapor,
carbon dioxide and mixtures thereof under reaction
conditions to cause the formation of carbon monoxide, 60
carbon dioxide, hydrogen and methane wherein the
heat produced by the formation of carbon dioxide and
methane is directly used to supply heat needed for the
formation of hydrogen and carbon monoxide and
wherein a sufficient amount of methane is formed to 65
produce fuel gas wherein the temperature is from about
500· C. to about 900· C. and the pressure is from about
100 kilopascals to about 8300 kilopascals.
4,372,755
10
17
of a gas selected from the group consisting of water
vapor, carbon dioxide and mixtures thereof at a
temperature of from about 500· C. to about 900· C.
and a pressure of from about 100 kilopascals to
about 8,300 kilopascals to produce a fuel gas con- 5
taining methane; .
(b) removing char produced in step (a) to a combustor
and combusting it;
(c) removing a portion of the fuel gas produced in
step (a) for recycle back to the reactor;
(d) removing a portion of the heat contained in the
fuel gas produced in step (a) to heat a water stream
and to heat a portion of the recycle gas;
(e) combining the heated water stream and the heated
recycle gas; 15
(f) using the heat produced from the combustion of
the char to further heat the combined water and
recycle gas stream to form water vapor and to
reform a portion of the methane contained in the
recycle gas to increase its level of hydrogen and 20
carbon monoxide; and
(g) introducing the combined stream of step (f) into
the reactor.
20. A process for the production of a fuel gas from a
solid carbonaceous material comprising reacting in a 25
single reaction zone the solid carbonaceous material in
the presence of a stabilized metal carbide catalyst comprising
carbon and a metal alloy and having a free energy
of formation of from - 30,000 to 10,000 British
thermal units per pound atom of carbon at the reaction 30
conditions, said metal alloy comprising at least two
metals selected from the group consisting of iron, silicon,
manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium, ·boron, sodium
and magnesium, wherein one of said two metals 35
.forms a sufficiently stronger carbide to act as a stabilizing
component thereby enhancing the chemical activity
of the other metal carbide, said catalyst having characteristics
of a bulk chemical catalyst and capable of substantially
maintaining its physical integrity and chemi- 40
cal activity under gasification conditions and a gas mixture
comprising hydrogen, carbon monoxide and from
about 10 to about 30 volume percent of a gas selected
from the group consisting of water vapor, carbon dioxide
and mixtures thereof at a temperature of from about 45
500· C. to about 900· C. and a pressure of from about
10<? kilopascals to about 8,300 kilopascals under conditions
which maintain the ratio of the reactant gases and
product gases in order to cause the gasification of the
carbonaceous material and the formation of a sufficient 50
amount of methane to produce a fuel gas having a Btu
value of from about 400 to about 450 Btu per cubic foot
of fuel gas while maintaining the activity of the stabilized
metal carbide catalyst.
21. The process of claim 19 or claim 20 wherein the 55
temperature of the reactor is the threshold temperature
range of the stabilized metal carbide catalyst.
22. The process of claim 21 wherein the stabilized
metal carbide catalyst is selected from the group consisting
of iron silicide carbide, manganese, chromium 60
carbide, ferrochromium carbide and manganese cobalt
carbide.
23. The process of claim 22 wherein the stabilized
metal carbide catalyst is an iron silicide carbide catalyst
comprising from about 4 to about 50 weight percent 65
silicon, from about 0.5 to about 3 weight percent carbon
and the remainder of the catalyst comprises primarily
iron.
18
24. A process for the production of a fuel gas from a
solid carbonaceous material comprising:
(a) reacting the solid carbonaceous material in a single
reactor in. the presence of a stabilized metal
carbide catalyst capable of maintaining its physical
integrity and chemical activity· under gasification
conditions, with a gas comprising hydrogen and,
carbon monoxide and from about 10 to about 30
volume percent of the gas is selected from the
group consisting of water vapor, carbon dioxide
and mixtures thereof at a temperature of from
about 500· C. to about 900· C. and a pressure of
from about 100 kilopascals to about 8,300 kilopascals,
wherein the stabilized metal carbide catalyst
comprises carbon and a metal alloy and has a free
energy of formation of from - 30,000 to 10,000
British thermal units per pound atom of carbon at
the reactor conditions, said metal alloy comprising
at least two metals selected from the group consisting
of iron, silicon, manganese, cobalt, chromium,
nickel, aluminum, vanadium, tungsten, molybdenum,
calcium, boron, sodium and magnesium
wherein one of said two metals forms a sufficiently
stronger carbide to act as a stabilizing component
thereby enhancing the chemical activity of the
other metal carbide, and wherein the reactant gases
and product gases are maintained at ratios which
allow for the gasification of the carbonaceous material
and the formation of a sufficient amount of
methane to produce a fuel gas having a Btu value
of at least about 400 Btu per cubic foot of fuel gas;
(b) removing char produced in step (a) to a combustor
and combusting it;
(c) removing a portion of the fuel gas produced in
step (a) for recycle back to the reactor;
(d) removing a portion of the heat contained in the
fuel gas produced in step (a)to heat a water stream
and to heat a portion of the recycle gas;
(e) reforming the recycle gas stream of step (c) to
obtain higher levels of hydrogen and carbon monoxide;
(f) using the heat produced from the combustion of
the char to further heat the water vapor and to
further heat the recycle gas to aid in reforming the
methane contained in the recycle gas to hydrogen
and carbon monoxide; and
(g) introducing the water vapor and the reformed
recycle gas into the reactor.
25. The process of claim 24 wherein the temperature
of the reactor is the threshold temperature range of the
stabilized metal carbide catalyst and the stabilized metal
carbide catalyst is selected from the group consisting of
iron silicide carbide, manganese chromium carbide,
ferrochromium carbide and manganese cobalt carbide.
26. A process for the production of a fuel gas from a
solid carbonaceous material comprising reacting in a
single fluidized reaction zone the solid carbonaceous
material in the presence of a stabilized metal carbide
catalyst comprising carbon and a metal alloy and having
a free energy of formation of from -30,000 to
10,000 British thermal units per pound atom of carbon
at the reaction conditions, said metal alloy comprising
at least two metals selected from the group consisting of
iron, silicon, manganese, cobalt, chromium, nickel, aluminum,
vanadium, tungsten, molybdenum, calcium,
boron, sodium and magnesium, wherein one of said two
metals forms a sufficiently stronger carbide thereby
enhancing the chemical activity of the other metal car4,372,755
15
19
bide and a lower capacity for carburization and oxidation
than each of the individual metals of the alloy and
a fluidizing gas wherein from about 10 to about 30 volume
percent of the fluidizing gas is selected from the
group consisting of water vapor, carbon dioxide and 5
mixtures thereof at a temperature and pressure sufficient
to carbide the stabilized metal alloy, to cause the gasification
of the carbonaceous material and cause the formation
of a sufficient amount of methane to produce a
fuel gas having a Btu value greater than about 300 Btu 10
per cubic foot of fuel gas wherein the temperature is
from about 500· C. to about 900· C. and the pressure is
from about 100 kilopascals to about 8300 kilopascals.
27. A process for the production of a fuel gas from a
solid carbonaceous material comprising:
(a) reacting the solid carbonaceous material in a single
reactor in the presence of a stabilized metal
carbide catalyst comprising at least two metals
selected from the group consisting of iron, silicon,
manganese, cobalt, chromium, nickel, aluminum, 20
vanadium, tungsten, molybdenum, calcium, boron,
sodium and magnesium, wherein one of said two
metals forms a sufficiently stronger carbide to act
as a stabilizing agent thereby enhancing the chemical
activity of the other metal carbide and having a 25
lower capacity for carburization and oxidation
than each of the individual metals of the alloy and
20
a gas wherein from about 10 to about 30 volume
percent of the gas is selected from the group consisting
of water vapor, carbon dioxide and mixtures
thereof at a temperature of from about 500· C. to
about 900· C. and a pressure of from about 100
kilopascals to about 8,300 kilopascals to cause the
carbiding of the stabilized metal alloy, to cause the
gasification of the carbonaceous material and the
formation of a sufficient amount of methane in
order to obtain a fuel gas having a fuel value of at
least 300 Btu per cubic foot of fuel gas, said metal
carbide catalyst being formed at said conditions by
the carbidizing of said metal alloy;
(b) removing char produced in step (a) to a combustor
and combusting it;
(c) removing a portion of the gas produced in step (a)
to a combustor and combusting it;
(d) removing a portion of the heat contained in the
gas produced in step (a) to heat water to produce
water vapor and to heat a portion of the recycle
gas;
(e) using the heat produced from the combustion of
the char to further heat the water vapor and to
further heat the recycle gas; and
(f) introducing the water vapor and the reformed
recycle gas into the reactor.
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