Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the s~nthesis of methane, ethane
and other hydrocarbons and alcohols from hydrogen and the oxides
of car~on through the use of a new catalyst and novel processes
based thereon. These catalytic processes can also be used for
the removal of carbon oxides from process streams whera their
presence is undesirable. Furthermore~ the oxides of carbon can be
hydrogenated to produce even higher hydrocarbons and various alcohols.
Prior art methods for the production of meth~ne and
ethane have employea carbon monoxido and hydrogen over
nickel catalysts of ~arious types. The cost of nickel
catalysts is quite high, because of both raw material costs
and difficulties experienced in the manufacturing process,
the latter requiring that the nickel be supported on some
type of inert base. Furthermore, the attrition of nickel
catalysts is high because the reaction requires relatively
high temperatures, which in turn causes a sintering tyoe of
breakdown that rapldly decreases the activity of the catalyst
with time.
Nickel catalysts are also sensitive to poisoning by a
number of the impurities usually found in hydrogen and
carbon oxide reactants. Hydrogen sulfide has been found to
poison nickel catalysts, even in very small concentrations,
by forming nickel sulfide. The ~hermodynamics of the system
is such that sulphur poisoning can be reversed by raising
the temperature or increasing the hydrogen to hydrogen
sulfide ratio in the feed or both. However, the use of
higher operating temperatures witn nickel catalysts are
restricted by sintering problems. Also, the purity of the
feed gas has inherent limitations dictated by the costs of
purification.
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As p~eviously indicated, one o~ the present raw ~aterials
for methane production is carbon monoxide. This gas is most
often produced by gasification of coal at relatively high
temperatures of 500 C. or better. Carbon monoxide is also
produced from hydrogan and carbon dioxide by conventional
water-gas shift reactions which require even higher temperatures
above 500 C. lhe reaction of carbon monoxide with hydrogen
in the presence of nickel catalysts also requires similarly
elevated temperatures in the range of 300 to 500 C. to
produce significant reaction rates. These ranges of ter,peratures
cause relatively rapid deterioration of the nickel catalysts.
In addition, very little ethane can be produced with nic~el
catalysts since the ethane ~eaction is favored only at lower
temperatures. Furthermore, practically no alcohol formation
is observed over nic~el catalysts. In general, the formation
of alcohols is thought to follow a mechanis~ different from
that prevailing i~ the synthesis o~ hydrocarbons. Heretofore,
a di~ferent catalyst, namely zinc oxide, was required for
the synthesis of methanol.
A further problem restrictir,g the use of prior art
catalysts is carbonyl formation. The carbonyls of metals
like nickel, ruthenium and iron are extr~ely toxic compounds.
They also have very low boiling temperatures such that they
would be present in their vapor states at the usual te~peratures
for synthasis of methane, ethane and the higher carbon
compounds. Carbonyl formation thus causes depletion of thè
catalyst as well as posing severe health and safety problems.
Such problems with prior art catalysts can be avoided only
by carefully controlling the operating temperature, pressure,
the carbon oxide to hydrogen ratio, and other operating
parameters and conditions.
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Even at the elevated temperatures indicated, the
~eaction rates with nickel and other known catalysts are
relatively slow and require a high residence time in the
reactor vessel, which in turn produces a relatively slo~
production rate for the final product desired. At the
present time, the production rate by known processes using
carbon monoxide is marginally economical from the standpoint
of the valua of the final product which must compete wi~h
natural gas of comparable value. Since known reactions of
carbon dioxide with hydrogen over prior catalysts require
even higher temperatures and proceed at slower reaction
rates as compared to corresponding reactions with carbon
monoxide, the use of carbon dioxide as a feed material for
methane production has not proven economically feasible to
date. Furthermore, reactions with carbon dioxide have
heretofore failed to produce any significant quantities of
ethane or higher hydrocarbons which are more valuable as
fuel because of higher heat values.
The foregoing disadvantages encountered with the
carbon monoxide-hydrogen reaction over nickel catalysts are
avoided through the use of the present invention. The
present invention for the first time allows the use of
carbon dioxide for the production of methane on a commercial~
basis. ~he mixture Oc carbon dioxide and hydrogen is passed
over a novel catalyst formed of a hydrided binary alloy of
iron and ti~anium. The catalysts described also greatly
enhance the reactions for synthesis of methane, ~thane and
higher hydrocarbons and alcohols from carbon monoxide and
hydrogen. As might be expected, reaction rates are faster
with a carbon monoxide feed as compared to those attainable
with the carbon dioxide feed, and this reaction also gives
greater yields of ethane, alcohols and the more complex
carbon compounds relative to the methane yield.
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The reaction rate obtainable at a given temperature
with this new process is greater by a factor of at least 2
than that experienced with prior art catalysts and reaction
Furthermore, there is no attrition of the type causing
deterioration of nickel catalysts. To the contrary, the
activity of the Fe-Ti _atalyst increases with aging in the
hydrogen atmosphere which cracks the catalyst particles both
microscopically tsurface crac~s) and macroscopically (into
smalle~ particles), with attendant ir.creases in active
surface area. There is also much less poisoning or deactiva-
tion of the catalyst through smothering of the adsorbing sites
with the reactants themselves. By controlling process conditions,~
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activation of this new catalyst can continue simultaneously with
the production reaction.
~'~ The unit cost of the new catalyst is also substantially
less than that of prior art catalysts, the cost of the raw
materials as well as the cost of actually producing the
catalyst being less. In this regard, the Fe-Ti catalyst is
used in its unsupported form, resulting in substantial cost
savings in making up the catalyst bedu
It is also possible with the new catalyst to attain
significant reac~ion rates at substantially lower temperatures
than those previously employèd in the prior art for methane
and ethane synthesis. These lower temperatures are particularly~
favorable for the formation of ethane and lesser amounts of
higher hydrocarbons and alcohols which are more valuable as
a fuel than methane because of their higher heat values.
It also follows that greater reaction rates at a given
temperature are obtainable by a relatively small increase in I -
pressure. Operating temperatures as low as 150 C. at
pressures as low as 30 atmospheres are believed to be possible
in commercial processes based on the new catalyst.
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With regard to the cost of raw materials, carbon divxide
is significantly cheaper than carbon monoxide and is much
safer to use. With reference specifically to coal gasific~tion
as the source of feed materials, lower temperatures ~avor
the ~ormation Orc carbon dioxide over the formation of carbon
monoxide, resulting in a substantial enerqy saving in providing I
those raw materials for subsecluent methane and ethane synthesis.
With regard to safety~ it is well known that carbon monoxide
is an extremely hazardous material while there is no such
disadvantage in employing carbon dioxide as the carbon oxide
component of the feed material. Of course, the overall
economics of the specific production processes and equipment
employed will dictate whether to use carbon monoxide, carbon
dioxide, or a mixture of both, in the feed stream.
It is therefore an object of this invention to provide
a novel process for the manufacture of methane, ethane and other
hydrocarbon and alcohols from carbon dioxide and hydrogen using
less expensive raw materials and a less expensive catalyst than
heretofore employed at lower temperatures and pressures than
previously possible.
Yet another object of the present invention is to
provide a process for making methane, ethane and other hydro-
carbons and alcohols at substantially increased production rates
from raw materials produced by gasification or coking of coal.
Still another object of the present invention is to
employ in the production of methane, ethane and other hydrocarbons
and alcohols a long-lived catalyst capable of being continuously
activated during the production process.
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A further object of the present invention is to produce
a catalyst resistant to any loss of activity at -the reaction
temperatures required for the production of methane, ethane and
other hydrocarbons and alcohols from carbon oxides and hydrogen
and resistant to poisoning by contaminants found in commercial
grades of carbon oxides and hydrogen, which does not contain any
constituents for the formation of a carbonyl compound from the
carbon oxides present.
Another object of the present invention is to provide a ¦
catalytic process for the removal of carbon oxides from
gaSeOUS process streams where their presence is undesirable.
A .urther object of the present invention is to economically
increase the heating value o the gas initially obtained
from coal gasification by converting the carbon dioxide,
carbon monoxide, and hydrogen components of that gas to
methane, ethane and higher hydrocarbons bv catalytic synthesis.
Another object of the invention is to provide a co~ercially
feasible process for the production of a gasoline fuel
substitute by converting hydrogen and the oxides of carbon
into a methane-ethane mixture also containing alcohols and
other liquid hydrocarbons.
The exact nature of the invention as well as other
objects and alvantages thereof will be readily apparent from
the following specific descripticn of the preferred embodiment
of the invention.
The catalyst of the present invention is comprised of I
a binary or bi-metallic alloy of iron and titanium with
compositions in the range from 2 moles o iron per mole of !
titanium to 1 mole of iron to 3 moles of titanium. It has
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been found that ~hen hydrided these alloy compositions form
extremely active catalysts for the production of methane ~nd
ethane, along with smaller amounts of corresponding alcohols
and higher hydrocarbons, from hydrogen and the gaseous
oxides of carbon principally carbon dioxide and carbon
monoxide. The specific alloys used are available from the
International Nickel Company. These alloys are described in
a boo~ entit'ed Constitution of Binary Alloys, First
~pplement as authored by R. P. ~lliott and published hy
~5cGraw-Hill, New York, N.Y., 1965, and also in the paper of
Reilly, et al. referenced fully below. They are formed from
the relatively pure metals by a melting process at temperatures
in the range of 15~0~ to 190~ C. The alloy compositions
found active as catalysts here always contain as one of the
alloy phases the bimetallic compound havin~ a titanium to
iron ratio of 1Ø The catalysts are preferably made from
commercial grade titanium and electrolytic iron. The alloy
composition with a titanium to iLon mole ratio of 1 to 2 is
also an intermetallic compound. Alloys with a titanium to
iron ratio of greater than l consist of t~o phases, three
such alloys being those with a titanil~ to iron ratio of
1.1, 2 and 3. These latter are more active. The preferred
bi-metallic alloy use2 as a catalyst in this invention is
i that having a composition of 1.1 moles of titanium to 1 mole I
of iron. As indicated in the Reilly et al. article, between
the equiatomic ratio o~ 1.0 and a mole ratio of titanium to
iron of 1.085, free titanium will be present in the alloy
but may exist either as a dissolved component in the bimetallic
phase or as a separate titanium phase. Free titanium will
always be present as a distinct phase at titanium to iron
ratios greater than 1.085. Upon exposure to hydrogen, the free
titanium is converted to its stable dihydride form.
It is to be understood that all alloy compositions
containing the 1 to 1 binary compound of these two metals
are catalytically active for methane and ethane formation.
Compositions with mole ratios of titanium to iron in the
range of 0.5 to 3.0 have been actually tested and are
preferred. Compositions richer in titanium do not appear to
be co~mercially available due to difficulties experienced in
their manufacture. The catalysts are active at all temperatures
at and above room temperature (20 C.) and at all pressures
at and above atmospheric, the higher the temperature and the
pressure, the greater the rate of reaction. The activity of
the catalysts were found to be in the following order from
highest activity to least activity: titanium to iron ratio
of 1.1, titanium to iron ratio of 2.0, titanium to iron
ratio of 3.0, titanium to iron ratio of 1.0, and titaniu~ to
iron ratio of 0.5. Therefore the preferred catalyst for
this reaction is hat of highest activity, namely, the
titanium to iron ratio of 1.1. It follows that the catalyst
with a titanium to iron ratio of 2 is the second most active.
It is ~elieved that both the hydride form of the alloy (Iron
Titanium Hydride) and the Fe-Ti alloy itself are catalytically
active in the reactions concerned.
Prior to using the binary alloy as a catalyst, it is
activated with hydrogen, first to remove oxides and other
impurities and then to produce iron titaniu~ hydrides. When
the alloy is received from the manufacturer, it is relatively
large in size (larger than 16 mesh) and i~ coated with an
oxide layer. In this form, the bi-metallic alloy will not
form the hydrides which are believed to be one of the active
forms of the catalyst. Activation of the catalyst also
removes other surface impurities such as carbon and nitrogen
compounds.
Activation of the catalyst is accomplished by treating
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it with hydrogen at temperaturcs in the xange of 200D to
400 C and a pressure of approximately 200 psia. The catalyst
is further activated by successively outgassing.and treating
it.with pressurized hydrogen so that it is alternately
hydrided and dehydrided. This second ste~ of the activation
process causes multiple crac~s in the surface of each particle
and breaXs up the catzlyst particles into smaller particles,
thereby grsatly increasing the reactive surface area o' the
bed. This process preferrably is continued until the average
particle size is approximately 200 mesh. l`he hydriding
cycle is generally carried out at room temperat~lre and 1,000
psia and the dehydriding cycle at approximately 200 C. with
outqassing. Outgassing may be accomplished at atmospheric
pressure with helium purging or by drawing a.slight vacuum
of one or two inches of water.
Followins the activation steps, a gaseous feed stream
comprised of carbon oxides and hydrogen is continually
passed over the catalyst bed in the production reaction that
yives a high yield of methane and ethane in the product, .
20 with methane being the greater component by a ratio of at
least lb to 1. Although significant yields of the product
are obtainable at room temperature (20 C.) and atmo~pheric
pressure, commercial yields require higher temperatures and
p~essures in the range of 100 to 200 C. and 30 to 200
atmospheres of pressure. Greater temperatures and pressures
will yield even greater reaction rates which are limited
only by restrictions on equipment parameters and adverse
side reactions such as smothering the catalyst with deposited
carbon from either the breakdown of carbon dioxide or the
cracking of methar.e or ethane. At temperatures at or above
200 C. and pressures at or above 100 atmospheres yields
- approaching 100~ of theoretical are attainable.
Catalytic activitv a~pears to be the optimum when the partial
pressure of the hydrogen used in hydriding is equal to or greater than
the e~uilibri~m dissociation pressure of iron titani~m
hydride. It is therefore believed, as previously inàicated,
that the most active state of the catalyst is the hydride
form of the alloy, without any intention of being bound ~y
this hypothesis. The partial pressure of the hydrogen to be
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used at a given temperature to achieve the optimum reaction
rate can therefore be determined from the equilibriu~ dîssociation
pressure of iron titanium hydride at that temperature, the
latter relationship being set forth in the literature. For ¦ -
determination of this pressure, particular reference is made
to the article entitled "Formation and Properties of Iron
Titanium Hydride" by J. J. ~eilly and R. ~. Wiswall, Jr., of
Broo~haven National ~aboratory as published in norg~nic
Chemistry, Volume 13, No. 1, 19~4, at pages 218 through 222.
The preferred processes for both activacins the catalyst
and subsequently producing methane and ethane through the
use thereof with a carbon dioxide feed are set out below.
The catalyst as pur~hased is charged to a conventional
reactor vessel such as pxesently used in producing methane
from carbon monoxide and hydrogen. The reactor is heated to
400 C. and purged with helium for approximately six to
eight hours. While maintaining the vessel at 400 C., the
reactor is pressurized with hydrogen to 200 psia and maintained ¦
in that condition for approximately ~hree to four hours.
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~his step is sufficient to remo~e the oxide films ana other
adsorbed impurities from the surface of the catalyst 50 as
to enhance diffusion of hydrogen into the alloy, as well as
later adsorption of the reactant gases during the produc~ion
reaction. The initial treatment of the catalyst with
hydrogen is preferably carried out with the hydrogen confined
to the xea_tor vessel in a static condition, instead of
utilizing any type of flow regime.
The reactor is then allowed to cool to room temperature
(20 to 25 C.) and throughout the cooling process is continuously
purged with helium to outgas the hydrogen. Upon reaching
roo~ temperature, the reactor is pressurized with hydrogen
to 1,000 psia (a pressure above the equilibrium pressure of
the hydride) while being maintained at room temperature
(hydriding). ~fter sr;h pressurization has been maintained
for approximately one-hal an hour, the reactor is pu~ged
with helium and again while the purge is in progress is
heated to 400 C. and then cooled (dehydriding). These
hydriding and dehydriding cycles are repeated until the
desired particle size is attained, which usually requires
three to four cycles. The catalyst bed is then ready for
the production reaction.
Following the last activation cycle, the reactor is
heated to 2C0~ C. and pressuri~ed with hydrogen to 100
atmospheres. The feed composition of carbon dioxide and
hydrogen is then introduced into the xeactor and the product
drawn off on a continuous basis at a flGw rate determined by
a space velocity (ratio of feed rate to total weight of
catalyst) not to exceed 1,000 cubic meters (at standard
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temperature and pressure) per hour per ton of catalyst. A
; variety of feed compositions may be employed but should not
exceed a molar ratio of carbon dioxide to hydrogen of 1 to
10 if continuous activation of the catalyst is desired.
Feed compositions with greater amounts of carbon dioxide may
tend to smo~her the catalyst, thereby interfering with the
diffusion characteristics of the hydrogon within the alloy. This
is therefore the preferred ratio for the production of
methane and ethane.
Higher carbon dioxide to hydrogen ratios favor higher
ratios of ethane in the final product, as well as ~he production~
of methanol and ethanol, particularly at lower reaction
temperatures (less than 200~ C.). ~nere these products are
desired in the exit stream, alternating cycles of greater
hydrogen content (hydrogen ratios of 10 to 1 and above) can
be employed to reactivate the catalyst.
Higher space velocities and corresponding feed rates
are also possible, but may give lower yields. Nevertheless,
faster throughput and lower yields ~.ay be more economical
depending on the parameters of downstream separation and
recycle equipment. A further restriction on the process is
the same as that found in conventional methane production
techniques, namely, an upper temperature limit is defined
for a given pressure where exceeding that limit would result
in carbon deposition on the catalyst, either from cracking
of the methane or dissociation of the carbon dioxide feed.
Carbon deposition is an irreversible phenomenon and should
be carefully avoided in all instances. ~ full discussion of
those upper limits is found in an article enti~led ~Catalytic
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; ~lethanation" by G. A. Mills and F. ~7O Steffgen in Catal~fsLs
~eviewsl Vol. 8 at pages 155 to 210, 1974.
The relativ~ proportion of ethzne to methane from the
foregoing embodiment would be in the range of one part
ethane for approximately 20 parts of methane. The relative
proportion of ethane in the product mixture can be substantially
increased by lowering the temperature to 100 C. This
would give a ratio of ethane to methane of approximately one
to 10. It is also to be understood that greater yield
ratios of ethane to methane and faster reaction rates are
attainable under most process conditions by substituting
oarbon monoxide for carbon dioxide or using a mixture o~
both of said carbon oxides in the feed stream. Carbon
dioxide was employed in the preferred emboaiment above for
the reason that commercial produc~ion rates using this gas
as the predominant carbon oxide component in the feed have
not been heretofore attainable.
Significant amounts of the corresponding alcohols can
also be produced by increasing the molar ratio of carbon
oxides to hydrogen in the feed to greater than 1 to 10 and
by employing lower process temperatures of arourd 200 C or
less. Although lower temperatures would proauce a less
efficient reaction, the value of the product gas may be
correspondingly increased by the increased percentage of
alcohols and higher hydrocarbons present.
The product stream leaving the catalyst bea will contain
the carbon oxide and hydrogen reactants and the products
methane and ethane, with an ethane to methane ratio of
usuall~ less than 0.1 wherc the dioxide is the principal
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component in the feed. Greater ratios of ethane to methane
and the presence of methanol, ethanol and liquid hydrocarbons
may be enhanced by the feed composition and process conditions
selected as discussed a~ove. Each of these products can be
separated from the exit stream in conventional fashion if
desired and the reactants recycled to the reactor vessel.
If the product is going to be used as a uel, such as a
substitute for natural gas, both the hydrogen and the alcohols
can be left in the product stream. ~hether to leave any or
all of these in a fuel stream will of course be determined
by the economics of separation and the use to be made of the
pxoducts. It may be desirable to separate the carbon oxides
only and this could be done by conventional adsorption
techniques, such as contacting the exit stream with an
alkaline solution. If separation of the exit stream into
all of its constituents is desired, conventional liquefaction
techniques followed by fractionation can be employed for
that purpose.
~lthough but ~ sin~le embodi~ent of the present invention
has been described, other embodiments and variations will
occur to those s~illed in the art.
For example, it is possible to combine the titanium and
iron intermetallic compounds with known catalytically
active metals for this reaction such as ruthenium and nickel,
~ither in the form of mixtures or multi-component ~e.g.
ternary, quarternary or higher) alloys, or to support those
compounds on an inert carrier material or other substrate.
It is also possible, of course, to use various feat~res
of the specific embodiment described, such as the catalyst
at other temperatures and pressures, and such uses are within
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the contemplation of the present invention. Further~ore,
ma-y changes of the process steps are possiblc and arb
intended to be within the scope of this disclosure. It is
therefore to be understood that the foregoing specification
merely illustrates and describes a preferred embodiment of
the invention and that other embodiments are contemplated
within the scope of the appended claims. For example,
activation of the catalyst can be achicved, although at a
slower rate, by exposure to the hydrogen in the feed stream
itself.
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