U.S. patent application number 10/579799 was filed with the patent office on 2007-09-20 for method for conversion of hydrocarbons.
This patent application is currently assigned to STATOIL ASA. Invention is credited to Knut-Ivar Aaser, Tore Arnesen, Emil Edwin, Johan Amold Johansen, Erling Rytter.
Application Number | 20070215520 10/579799 |
Document ID | / |
Family ID | 34639861 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070215520 |
Kind Code |
A1 |
Edwin; Emil ; et
al. |
September 20, 2007 |
Method for Conversion of Hydrocarbons
Abstract
The invention provides a method for the conversion into carbon
of gaseous hydrocarbons extracted from a natural hydrocarbon
reservoir, which method comprises contacting said gaseous
hydrocarbon at an elevated temperature in a reactor with a catalyst
capable of converting said hydrocarbon to carbon and hydrogen;
burning hydrogen produced by the conversion of the hydrocarbon,
optionally after separating hydrogen produced from unconverted
hydrocarbon, burning said hydrogen to generate energy; and using
the energy generated to heat said reactor or the gaseous
hydrocarbon flow thereto, or to heat or power a heat or power
consuming apparatus.
Inventors: |
Edwin; Emil; (Stavanger,
NO) ; Arnesen; Tore; (Stavanger, NO) ; Aaser;
Knut-Ivar; (Stavanger, NO) ; Rytter; Erling;
(Stavanger, NO) ; Johansen; Johan Amold;
(Stavanger, NO) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
US
|
Assignee: |
STATOIL ASA
Stavange
NO
N-4035
|
Family ID: |
34639861 |
Appl. No.: |
10/579799 |
Filed: |
November 21, 2003 |
PCT Filed: |
November 21, 2003 |
PCT NO: |
PCT/GB03/05086 |
371 Date: |
January 12, 2007 |
Current U.S.
Class: |
208/46 ; 196/46;
423/461 |
Current CPC
Class: |
B82Y 30/00 20130101;
D01F 9/1272 20130101; C01B 2203/0405 20130101; C01B 3/505 20130101;
C01B 2203/1047 20130101; Y02E 60/32 20130101; C01B 3/26 20130101;
C01B 2203/0475 20130101; D01F 9/127 20130101; C01B 2203/0277
20130101; D01F 9/133 20130101; C01B 2203/048 20130101; C01B
2203/1241 20130101; C01B 2203/047 20130101; D01F 9/1271
20130101 |
Class at
Publication: |
208/046 ;
196/046; 423/461 |
International
Class: |
C10G 31/00 20060101
C10G031/00 |
Claims
1. A method for the conversion into carbon of gaseous hydrocarbons
extracted from a natural hydrocarbon reservoir, which method
comprises contacting said gaseous hydrocarbon at an elevated
temperature in a reactor with a catalyst capable of converting said
hydrocarbon to carbon and hydrogen; separating hydrogen produced
from unconverted hydrocarbon; burning said hydrogen to generate
energy; and using the energy generated to heat said reactor or the
gaseous hydrocarbon flow thereto, or to heat or power a heat or
power consuming apparatus.
2. A method as claimed in claim 1 wherein the energy generated is
used to heat said reactor or the gaseous hydrocarbon flow
thereto.
3. A method as claimed in claim 1 wherein the energy generated is
used to power an electricity generator.
4. A method as claimed in claim 1 wherein said catalyst is
particulate.
5. A method as claimed in claim 1 wherein said catalyst is a Raney
metal.
6. A method as claimed in claim 1 wherein said catalyst comprises
an element selected from Ni, Co and Fe.
7. A method as claimed in claim 1 wherein said catalyst is
particulate with a mode particle size of 1 to 300 .mu.m.
8. A method as claimed in claim 1 wherein hydrogen is burned in an
internal combustion engine.
9. A method as claimed in claim 1 wherein the hydrogen is separated
from the unconverted hydrocarbon using a hydrogen-permeable
membrane.
10. An apparatus for the conversion of hydrocarbon gas to carbon,
said apparatus comprising a reactor vessel (2) having a gas inlet
port (18) and a gas outlet port (19); a separator (4) for removing
hydrogen from a hydrocarbon and hydrogen containing gas; a gas
conduit (3) from said gas outlet port to said separator; a
combustor (9) arranged to burn hydrogen from said separator to
generate energy; and an energy transferrer (11) arranged to
transfer energy from said combustor to said reactor vessel or to a
further heat or power consuming apparatus (20).
11. An apparatus as claimed in claim 9 further comprising an
electricity generator (20) powered by energy from said
combustor.
12. A process for the preparation of fibrous carbon which comprises
contacting a metallic catalyst with a carbon-containing gas at
elevated temperature, characterized in that said catalyst is sponge
iron.
Description
[0001] This invention relates to a process for the conversion of
hydrocarbons to an environmentally friendly product, particularly
carbon, more particularly carbon comprising carbon nanofibres
(CNF), otherwise known as filamentous carbon or carbon fibrils.
[0002] The CO.sub.2-emissions to the atmosphere caused by the
combustion of hydrocarbons such as natural gas have in recent years
become quite a hot environmental topic. Thus great resources have
been applied to the development of methods and devices for energy
conversion of hydrocarbons such as natural gas, whereby the
CO.sub.2-emissions to the atmosphere may be avoided or at least
reduced significantly.
[0003] In hydrocarbon extraction from underground reservoirs, it is
frequently the case that liquid hydrocarbons are the desired
product and gaseous hydrocarbons, in particular C.sub.1-3
hydrocarbons and particularly methane, are extracted in undesirably
large quantities. One solution has been to return the gases to the
underground reservoir, however this is expensive. Another solution
has been simply to burn off unwanted gases: however this generates
carbon dioxide, which is undesirable from the environmental point
of view.
[0004] Energy conversion of hydrocarbons normally includes
combustion producing water and CO.sub.2. The CO.sub.2-emission may
be reduced by separating the emission into a fraction rich in
CO.sub.2, which is deposited e.g. through injection into an oil
field, and a fraction poor in CO.sub.2, which is discharged to the
atmosphere. The required equipment is cumbersome and expensive, and
is normally only suitable for large plants.
[0005] It has long been known that the interaction of hydrocarbon
gas and metal surfaces can give rise to dehydrogenation and the
growth of carbon "whiskers" on the metal surface. More recently it
has been found that such carbon whiskers, which are carbon fibres
having a diameter of about 3 to 100 nm and a length of about 0.1 to
1000 .mu.m, have interesting and potentially useful properties, eg
the ability to act as reservoirs for hydrogen storage (see for
example Chambers et al. in J. Phys. Chem. B 102: 4253-4256 (1998)
and Fan et al. in Carbon 37: 1649-1652 (1999)).
[0006] Such hydrocarbon conversion to hydrogen and carbon however
is endothermic and has not been proposed as a means of disposal of
hydrocarbons or a means of energy generation.
[0007] We have now realized that using such a dehydrogenation
reaction hydrocarbon gas may be converted to a commercially
valuable and readily transportable product, namely carbon, without
any significant production of CO.sub.2 emissions.
[0008] Thus viewed from one aspect the invention provides a method
for the conversion into carbon of gaseous hydrocarbons extracted
from a natural hydrocarbon reservoir, which method comprises
contacting said gaseous hydrocarbon at an elevated temperature in a
reactor with a catalyst capable of converting said hydrocarbon to
carbon and hydrogen; separating hydrogen produced from unconverted
hydrocarbon; burning said hydrogen to generate energy; and using
the energy generated to heat said reactor or a gaseous hydrocarbon
flow thereto, or to heat or power a heat or power consuming
apparatus.
[0009] Viewed from a further aspect this invention provides an
apparatus for the conversion of hydrocarbon gas to carbon, said
apparatus comprising a reactor vessel having a gas inlet port and a
gas outlet port;
[0010] a separator for removing hydrogen from a hydrocarbon and
hydrogen containing gas;
[0011] a gas conduit from said gas outlet port to said
separator;
[0012] a combustor arranged to burn hydrogen from said separator to
generate energy; and
[0013] an energy transferrer arranged to transfer energy from said
combustor to said reactor vessel (e.g. by heating the reactor
vessel directly or by heating a gas flow to said inlet port) or to
a further heat or power consuming apparatus.
[0014] The further heat or power consuming apparatus may be any
apparatus requiring such input, e.g. an electricity generator or an
air or water heating apparatus for example a central heating
system.
[0015] While hydrogen is separated from unconverted hydrocarbon
gas, such that the product of its burning is essentially carbon
dioxide free, separation can be only partial resulting in decreased
rather than totally eliminated CO.sub.2 emission.
[0016] The separated hydrogen typically contains no more than 30
mole % hydrocarbon, especially no more than 10 mole %, particularly
no more than 5 mole %, more particularly no more than 1 mole %.
[0017] This separated hydrogen, at least in part, is preferably
burned to provide heat to the reactor. This may be direct or
indirect or both, e.g. with the vapour from the combustion being
used in a heat exchange and/or to drive an electrical power
generator the output of which may be used to heat the reactor or
the gas input therefor. The hydrogen typically will be burned in an
internal combustion engine, however conversion to water using a
catalytic converter is considered to be encompassed by the term
burning.
[0018] The gaseous hydrocarbon used in the method of the invention
is preferably taken direct from a hydrocarbon well, optionally
after transfer down a pipeline, but preferably at the well head.
Alternatively however it may be packaged, e.g. in canisters, before
use.
[0019] The catalyst used in the method of the invention will
typically be a metal as described by De Jong et al in Catal. Rev.
Sci. Eng. 42: 481-510 (2000) or Rodriguez et al in J. Mater. Res.
8: 3233-3250 (1993), the contents of which are incorporated by
reference. Thus the metal catalyst used according to the invention
preferably is selected from group 5 to 10 metals, eg nickel, iron,
cobalt, vanadium, molybdenum, chromium and ruthenium and alloys
thereof, eg Fe/Ni, Cu/Ni etc alloys. Lanthanides may also be used.
In general the requirement seems to be that the metal is able to
form carbides which are unstable at the temperatures used in the
carbon production process. Precious metals, such as Pt, Au and Ag
may also be deposited on such metals or alloys. Especially
preferably the transition metal of the catalyst is nickel, iron or
cobalt or a mixture of two or three thereof, eg Ni/Fe. Particularly
preferably the transition metal content of the catalyst metal is at
least 50% wt nickel, eg 70% Ni/30% Fe or 100% Ni.
[0020] The catalyst may also include a promotor, e.g. a structural
promotor such as aluminium.
[0021] More preferably the catalyst used is a porous metal catalyst
comprising a transition metal or an alloy thereof, e.g. as
described in PCT/GB03/002221, a copy of which is filed herewith and
the contents of which are hereby incorporated by reference.
[0022] By porous is meant metals with a high surface area,
typically Raney metals which are produced by leaching one metal out
of a metal alloy. The person skilled in the art will readily
understand that the term porous is not applicable in this context
to grids or meshes formed from solid, i.e. non porous, metals. For
particulate porous metal catalysts, surface area (e.g. determined
by gas adsorption) will typically be at least 20 m.sup.2/g, more
preferably at least 40 m.sup.2/g, especially at least 50 m.sup.2/g
e.g. up to 200 m.sup.2/g, for example 50-100 m.sup.2/g. The mode
particle size, before carbon formation begins, will typically be in
the range 1 to 300 .mu.m, preferably 5 to 100 .mu.m, especially 10
to 80 .mu.m, more especially 20 to 40 .mu.m. Porous moreover refers
to the metal catalyst rather than any catalyst support, i.e. a
solid metal catalyst deposited on a porous support, e.g. silica or
alumina, is not a porous metal catalyst.
[0023] Especially preferably the metal catalyst is produced by
total or partial removal of one metallic element from an alloy, eg
removal of aluminium from an aluminium-transition metal alloy. Such
aluminium-transition metal alloys or intermetals from which
aluminium has been removed are available commercially (eg under the
trade name Amperkat.RTM. from H.C. Starck GmbH & Co AG, Goslar,
Germany) or may be prepared from the aluminium alloys by leaching
with acid, eg nitric acid. Examples of Amperkat.RTM. catalysts
available from H.C. Starck include Amperkat SK-NiFe 6816, SK-Ni
3704, SK-Ni 5544, and SK-Ni 5546 which contain respectively 4-7% wt
Al: 62-67% wt Ni: 26-30% wt Fe, 4-7% wt Al: 93-96% wt Ni: <1% wt
Fe, 5-9% wt Al: 90-95% wt Ni: <0.6% wt Fe, and 5-9% wt Al:
90-95% wt Ni: <0.6% wt Fe. These Amperkat catalysts have a grain
size of about 80 .mu.m (i.e. 80-90% below 80 .mu.m), a solid
concentration of about 20-50% and an apparent density (by watery
catalyst slurry) of about 1300 to 1800 kg/m.sup.3. The use of SK-Ni
5546 is preferred.
[0024] The catalyst is preferably particulate, conveniently having
a particle size as described above, or of from 10 nm to 100 .mu.m,
preferably 50 nm to 1000 nm, especially 80 to 200 nm.
[0025] We also propose to improve the economy of carbon production,
by using a porous iron catalyst, i.e. sponge iron (direct reduced
iron). Sponge iron has the major advantage that it is inexpensive,
thus offering a cheap alternative to the previously used transition
metal catalysts. Moreover, it is free from elements that are
usually present in ferrous scrap such as copper, zinc, tin,
chromium and molybdenum etc. It has low sulphur and phosphorous
contents.
[0026] By sponge iron is meant the metallic product formed when
iron ore is reduced by carbon at a temperature below the melting
point of iron (i.e. below 1538.degree. C.). It is porous in nature
and commonly used in steel-making.
[0027] While preferably used in a method for converting
hydrocarbons according to the invention, use of sponge iron is
novel and therefore provides a further aspect of the invention.
[0028] Thus viewed from a further aspect the present invention
provides a process for the preparation of fibrous carbon which
comprises contacting a metallic catalyst with a carbon-containing
gas at elevated temperature, characterized in that said catalyst is
sponge iron.
[0029] The gas used in the process of the invention may be any
hydrocarbon-containing gas, eg C.sub.1-3 hydrocarbons (such as for
example methane, ethane, propane, ethene, ethyne, etc), napthenes
or aromatics from a natural subsurface hydrocarbon reservoir (e.g.
oil well). Preferably the gas is or comprises methane. Especially
preferably the gas used is a hydrocarbon-containing gas separated
from the oil removed from an oil well, optionally after treatment
to remove hydrocarbons having four or more carbon atoms per
molecule, water, nitrogen and carbon dioxide, and preferably
treated to remove catalyst poisons, e.g. sulphur compounds and
possibly halogens. Conventional means for poison removal may be
used. The methane content of such "natural" gas will generally lie
in the range 80 to 95% mole.
[0030] In one especially preferred embodiment the gas comprises
methane and carbon monoxide as this lowers the energy supply needed
since the carbon production reaction is less endothermic with
carbon monoxide than with methane alone. In particular it is
especially preferred that the feed gas comprise methane and carbon
monoxide in a mole ratio of 1:99 to 99:1, more particularly 10:90
to 90:10. Thus it is preferred that the gas comprises methane and
carbon monoxide in a mole ratio of from 1:99 to 99:1 preferably
with the gas being introduced into the reactor vessel in at least
two streams, at least one stream being substantially carbon
monoxide free and being at a higher temperature than another carbon
monoxide-containing stream, e.g. using a first, carbon monoxide
containing, stream at a temperature of 300.degree. C. or less and a
second, methane-containing, stream at a temperature of 600.degree.
C. or more, or using a single gas stream at a temperature of
300.degree. C. or less, e.g. 200-290.degree. C.
[0031] It is also especially preferred that the gas fed into the
reactor should, for at least part of the reaction period, contain a
small proportion of hydrogen, e.g. 1 to 20% mole, more preferably 2
to 10% mole. This has the effect of reducing the carbon activity of
the catalyst metal (i.e. the rate of carbon uptake by the metal)
and serves to prolong carbon production, increase total yield and
reduce the weight percentage of the carbon product which is in the
form of amorphous carbon. Hydrogen can be added to the gas feed to
the reactor or off-gas from the reactor may be, in part, recycled
into the reactor to provide the desired hydrogen content. Depending
on reactor design however, the hydrogen generated by carbon
production may be sufficient to provide an appropriate hydrogen
content in the carbon/catalyst bed.
[0032] The use of hydrogen as a component of the feed gas is, as
mentioned above, preferred. However the need for hydrogen input may
be reduced or avoided if the reactor is constructed to provide
internal recirculation of the gases leaving the catalyst bed.
[0033] In the method of the invention, carbon production is
preferably effected so as to yield carbon in an amount of at least
1 g carbon per gram metal catalyst, more preferably at least 10
g/g, still more preferably at least 50 g/g, especially at least 100
g/g, more especially at least 150 g/g, eg 100 to 400 g/g, typically
150 to 250 g/g.
[0034] The process of the invention will typically be effected by
flowing the hydrocarbon-containing gas past the catalyst.
[0035] The hydrogen produced is at least in part separated out of
the gas flow from the reactor so that it may be burned to provide a
heat source for the reaction. Moreover it is preferred that the gas
flow to the catalyst should contain hydrogen, eg 1 to 20% mole, for
example 5 to 15% mole, preferably 8 to 11%, and to this end it is
preferred that a part of the gas flow from the reactor be drawn off
and mixed with the hydrocarbon-containing gas flow to the catalyst.
The hydrogen produced may also be separated out from the gas flow
inside the reactor. One option is to separate the hydrogen from the
catalyst bed by use of membranes (for example ceramic membranes)
followed by a subsequent separation and discharge of the carbon
product.
[0036] The process of the invention is performed at elevated
temperature, typically 350 to 1200.degree. C., preferably 400 to
700.degree. C., more preferably 500 to 680.degree. C., especially
525 to 630.degree. C., eg about 600.degree. C. Particularly
preferably the temperature is below 900.degree. C., more especially
below 850.degree. C., particularly below 800.degree. C., especially
below 750.degree. C., e.g. below 700.degree. C., and above
550.degree. C., especially above 600.degree. C., particularly above
630.degree. C. Operating temperatures of between 630 and
680.degree. C. have been found to give rise to especially good
carbon production rates and yields.
[0037] The gas flow to the catalyst is preferably at elevated
pressure, eg 2 to 15 bar, especially 3 to 6 bar. The use of
pressures above 15 bar is not preferred when methane is the source
gas for the carbon, due to undue methane adsorption.
[0038] Quite surprisingly, catalyst activity and yield may be
maintained if reaction temperature is increased by also increasing
gas pressure and vice versa. However use of prolonged reaction time
(or residence time in the reactor for a continuous production
process) tends to increase the percentage of amorphous carbon in
the carbon product. By reaction or residence time is meant the time
that the catalyst/carbon spends in the reactor under reaction
conditions. The reaction time (or residence time as appropriate) is
preferably up to 30 hours, more preferably up to 10 hours,
especially up to 3 hours.
[0039] The catalyst may be presented as a reaction region with gas
flow from bottom to top. However, alternatively, the gas is passed
through a catalyst bed in a generally horizontal direction, To this
end the reactor may be a substantially horizontal tube, optionally
having a cross section which increases in the gas flow direction.
Since the catalyst bed will expand as carbon generation proceeds,
since carbon coating on catalyst particles causes the particulate
to adhere to the reactor walls, and since compression of the
catalyst bed reduces carbon growth rate, the lower wall of the
reactor may be provided with a downward slope in at least one
portion following the initial location of the catalyst bed. Such a
horizontal reactor design has the benefit that the carbon product
compacts naturally during production without any significant
adverse effect on carbon yield. Typically the carbon may compact in
this way to a density of about 0.4 to 0.9 g/cm.sup.3, more
typically 0.5 to 0.7 g/cm.sup.3. Without compaction the density is
usually 0.4 to 0.5 g/cm.sup.3. Alternatively the catalyst/carbon
bed may be mechanically agitated, for example to improve gas and
heat distribution and/or to facilitate flow of the carbon product
towards an outlet.
[0040] The method of the invention may be performed continuously or
batchwise. In the former case the reactor in which the method is
carried out may be provided with means for introducing fresh
catalyst at the upstream end of the catalyst bed and for removing
carbon from the downstream end of the catalyst bed, eg isolatable
settling tanks. In the production of carbon products, particularly
for bulk applications, a reactor design similar to the reactor
designs used in the polyolefin-industry could be used. These
reactors are designed to achieve a favourable mass transport and
enhance the reactivity of the reacting gas molecules at the
catalytically active metal surfaces.
[0041] The reactor used in the method of the invention will
conveniently have a volume of 10 to 100 m.sup.3, preferably 50 to
70 m.sup.3 allowing a total product content in the thousands of
kilograms. The reactor volume will typically be at least 10 L per
kg/hour of carbon production. For continuous operation, methane
feed rates of 500 to 2000 kg/hour, eg 1000 to 1500 kg/hour, and
carbon removal rates of 200 to 2000 kg/hour, eg 750 to 1250 kg/hour
may thus typically be achieved. The energy supply necessary to
operate such a reactor will typically be in the hundreds of kW, eg
100 to 1000 kW, more typically 500 to 750 kW. Alternatively
expressed, the energy demand will typically be in the range 1 to 5
kW/kgC.hour.sup.-1, e.g. 2-3.5 kW/kgC.hour.sup.-1. On the small
scale, energy supply into the reactor may be achieved by external
heating of the reactor or by inclusion within the reactor of
heating means or heat exchange elements connected to a heat source.
As reactor size increases however it will become more necessary to
heat the feed gas that is supplied into the reactor, e.g. to
temperatures of 300 to 1200.degree. C., more preferably 300 to
1000.degree. C., especially 500 to 900.degree. C., more especially
800 to 850.degree. C. To minimize catalyst deactivation, heated
feed gas is preferably fed into an agitated catalyst/carbon bed at
a plurality of points or over the entire undersurface of a
gas-fluidized bed. Where the feed gas includes carbon monoxide and
methane, the carbon monoxide is preferably introduced at a lower
temperature (e.g. <300.degree. C.), for example through a
separate feed line, e.g. to avoid dusting of ferrous metal feed
lines.
[0042] Since, as mentioned above, compression of the catalyst bed
slows carbon formation, the reactor in which the method of the
invention is carried out is preferably provided with means for
agitating the catalyst bed. Where the catalyst bed is a horizontal
fluidized bed such agitation may be effected by the gas flow
through the bed. However, where gas flow is substantially
horizontal, the reactor is preferably provided with moving or
static mixers downstream of the start of the catalyst bed. Where
the method is to be performed batchwise, the carbon generation
process may be slowed down or halted towards the end of each batch
by compression of the catalyst/carbon bed, either actively or
passively by allowing the catalyst/carbon bed to compress itself
against the end of the reaction zone in the reactor.
[0043] In general, carbon produced by the method of the invention
will be subjected to compaction following production and/or to
mechanical agitation (e.g. milling) following production. The
carbon product is in the form of fibrous particles (e.g.
"furballs")--milling can release the fibres if a fibrous product is
desired while compaction can be used to increase the density and
mechanical strength of the product.
[0044] Gas removed from the reactor is preferably passed through a
separator in which hydrogen is removed by metallic hydride
formation. Pellets of a metallic hydride in a column absorb the
produced hydrogen at a low temperature, and the absorbed hydrogen
can then be recovered by raising the temperature in the column.
Alternatively, the hydrogen can be removed by passage of the gas
through a hydrogen-permeable membrane, eg a palladium membrane,
which is not permeable to the carbon-containing components of the
gas. Pressure Swing Adsorption (PSA) is also an alternative
separation principle that may be employed. Another separation
method which may be used involves the use of polymer membranes.
Such polymer membranes are commercially available for separation of
hydrogen and other gas components. The resulting gas with a reduced
hydrogen contact may then be recycled into the reactor.
[0045] The hydrogen may be absorbed using other metals if desired,
e.g. Mg, Mg/Ni, Ca/Ni, La/Ni, Fe/Ti, Ti/Cr, etc.
[0046] In a particularly preferred aspect, the catalyst is
subjected to an initiation or pretreatment. This serves to increase
carbon production rate and carbon yield and may be achieved with
any carbon production catalyst, i.e. not just porous metal
catalysts, by a limited period of exposure to a feed gas with
reduced or no hydrogen content at a lower temperature than the
reaction temperature in the main carbon production stage. Such
pretreatment is preferably under process conditions under which the
carbon activity of the catalyst is greater than in the main carbon
production stage. This process thus comprises in a first stage
contacting a catalyst for carbon production with a first
hydrocarbon-containing gas at a first temperature for a first time
period and subsequently contacting said catalyst with a second
hydrocarbon-containing gas at a second temperature for a second
time period, characterized in that said first gas has a lower
hydrogen (H.sub.2) mole percentage than said second gas, said first
temperature is lower than said second temperature, and said first
period is shorter than said second period. If a higher graphitic
contact of the carbon product is desired, the first temperature may
be reduced and/or the second temperature may be increased.
[0047] In this aspect of the invention, the catalyst is preferably
a transition or lanthanide metal or an alloy thereof, especially a
transition metal and more especially a porous metal, in particular
a nickel containing metal, especially a Raney metal. The
temperature, pressure and gas composition, in the second period are
preferably as described above for carbon production. The
temperature in the first period is preferably in the range 400 to
600.degree. C., especially 450 to 550.degree. C., more especially
460 to 500.degree. C. The hydrogen mole percentage in the first
period is preferably 0 to 2% mole, especially 0 to 1% mole, more
especially 0 to 0.25% mole, particularly 0 to 0.05% mole. The
pressure in the first period is preferably 5 to 10 bar, especially
6 to 9 bar. The duration of the first period is preferably 1 to 60
minutes, more especially 2 to 40 minutes, particularly 5 to 15
minutes.
[0048] This pretreatment or initiation of the catalyst causes the
catalyst to become a catalyst/carbon agglomerate comprising
particles of a carbon-containing metal having carbon on the
surfaces thereof.
[0049] Before this pretreatment, the catalyst may if desired be
treated with hydrogen at elevated temperature, e.g. to reduce any
surface oxide.
[0050] The carbon produced in the process of the invention may be
processed after removal from the reactor, eg to remove catalyst
material, to separate carbon fibres from amorphous material, to mix
in additives, or by compaction. Catalyst removal typically may
involve acid or base treatment; carbon fibre separation may for
example involve dispersion in a liquid and sedimentation (eg
centrifugation), possibly in combination with other steps such as
magnetic separation; additive treatment may for example involve
deposition of a further catalytically active material on the
carbon, whereby the carbon will then act as a catalyst carrier, or
absorption of hydrogen into the carbon; and compaction may be used
to produce shaped carbon items, eg pellets, rods, etc.
[0051] Processing of the carbon product to reduce the catalyst
content therein may also be achieved by heating, e.g. to a
temperature above 1000.degree. C., preferably above 2000.degree.
C., for example 2200 to 3000.degree. C. The total ash content is
also significantly reduced by this treatment.
[0052] Catalyst removal from the carbon product may also be
effected by exposure to a flow of carbon monoxide, preferably at
elevated temperature and pressure, e.g. at least 50.degree. C. and
at least 20 bar, preferably 50 to 200.degree. C. and 30 to 60 bar.
The CO stream may be recycled after deposition of any entrained
metal carbonyls at an increased temperature, e.g. 230.degree. to
400.degree. C.
[0053] As a result of such temperature and/or carbon monoxide
treatment an especially low metal content carbon may be produced,
e.g. a metal content of less than 0.2% wt, especially less than
0.1% wt, particularly less than 0.05% wt, more particularly less
than 0.01% wt, e.g. as low as 0.001% wt.
[0054] Publications referred to herein are hereby incorporated by
reference.
[0055] The method and apparatus of the invention will now be
described further with reference to the Example and the
accompanying drawing in which:
[0056] FIG. 1 is a schematic drawing of one embodiment of the
apparatus of the invention.
[0057] FIG. 1 schematically shows the construction of an apparatus
according to the invention. Hydrocarbon-containing gas, preferably
methane-containing gas enters reactor vessel 2 through a gas inlet
line 14 and gas inlet port 18. Off-gas from the reactor vessel
leaves through gas outlet port 19 and gas outlet line 3. The off
gas is fed to separator 4 which, in the form shown comprises two
chambers separated by a palladium membrane 5. Hydrogen is separated
from the off gas and is fed via supply line 7 to combustor 9 where
it is burned, e.g. using air, oxygen or oxygen enriched air or an
oxygen/inert gas mixture. The hydrogen supply line 7 may be
provided with a heat exchanger 16 to transfer energy to the
hydrocarbon gas supply or the air supply.
[0058] In the embodiment shown, air supply for the combustor is
brought via air supply line 6 into the separator via a heat
exchanger 12.
[0059] Exhaust gas from the combustor is vented via exhaust line 10
which, in the embodiment shown is provided with heat exchangers 11
and 12 to heat the hydrocarbon and air supply lines.
[0060] Electrical energy generated by the combustor is used to heat
the reactor vessel and/or the hydrocarbon supply or to power
electricity generator 20.
[0061] The hydrogen-poor gas from separator 4 is removed via exit
line 8 with none, some or all being vented through line 13 or fed
through line 13 to a burner, not shown. The remaining portion is
mixed with the source hydrocarbon gas (e.g. methane or natural gas)
in mixer 15 before being fed, via heat exchanger 11 to supply line
14. The source gas is preferably supplied via inlet line 1 at a
pressure of about 200 bar. Mixer 15 may take the form of an ejector
pump 15 that is driven by the source hydrocarbon gas being
depressurised from a pressure of about 200 bar to 1-5 bar.
[0062] The reactor 2 may be a fluidized bed reactor constructed
with a minimal pressure drop. It is also possible for the reactor
to be constructed in a manner so as to allow continuous replacement
of deactivated catalyst and removal of carbon while adding new
catalyst. The reactor should be compact, as heat loss is
proportional to the surface area.
[0063] The combustor 9 may for example be any type of internal
combustion engine run on an air/hydrogen mixture, e.g. a piston
engine, a Wankel engine or a turbine.
[0064] The exhaust gas from the combustor will typically have a
temperature of 500-1400.degree. C., e.g. around 900.degree. C.
[0065] When using a palladium membrane, the air is pre-heated
through heat exchange with exhaust gas from the combustor, e.g. in
heat exchanger 12, before being sent into the separator 4, to a
temperature typically of at least 400.degree. C. in order to avoid
a steep temperature gradient across the membrane. The mixture of
air and hydrogen should then be cooled with cold air or possibly
incoming natural gas in line 1, in a heat exchanger or intercooler
16, before the mixture is led into the combustor 9.
[0066] Even though an internal combustion engine is a relatively
inefficient energy converter, the total energy production from the
present apparatus is large, because heat from the exhaust gas is
used to heat the gas supply, and consequently to drive the
endothermic reaction in the reactor vessel 2.
[0067] The above illustrated solution for transferring heat from
the hot exhaust gas from the internal combustion engine to the
reactor can be implemented in other ways than that described above.
As an example, some of the heat from the exhaust gas may be used
for direct heating of the catalyst bed in the reactor vessel 2,
e.g. by the exhaust gas or some of it being passed through channels
through the catalyst bed, and some of the heat may be used for
heating the incoming gas prior to this entering the reactor vessel
2. Direct heating of the catalyst bed in the reactor vessel 2 is
desirable in order to achieve a high conversion by means of a high
temperature throughout the catalyst bed, including at the outlet
end.
EXAMPLE
[0068] The following simulation exemplifies a device or energy
converter according to the present invention as described above and
shown in FIG. 1: TABLE-US-00001 TABLE 1 Mass balance for the
reactor Methane consumption 0.32 kmol/h H.sub.2 production through
membrane 5 0.6 kmol/h Recycling, line 8 0.7 kmol/h Purge stream,
line 13 0.02 kmol/h Air in, line 6 (0.3 kmol/h O.sub.2 + 1.2 kmol/h
N.sub.2) 1.5 kmol/h Exhaust, line 10 (0.6 kmol/h H.sub.2O + 1.2
kmol/h N.sub.2) 1.8 kmol/h
[0069] TABLE-US-00002 TABLE 2 Energy balance for the energy
converter Energy production Engine 25.8 kW Exhaust, 910-500.degree.
C., heat exchanger 11 7.3 kW Endothermic energy for reactor 2 at
30% methane -7.3 kW conversion Exhaust, 500-120.degree. C., heat
exchanger 12 6.1 kW Air, 20-500.degree. C., heat exchanger 12 -6.1
kW Air + H.sub.2, 500-20.degree. C., intercooler 16 8.4 kW
CH.sub.4, 20-500.degree. C., heat exchanger 11 -1.9 kW Air-air
cooling in intercooler 16 -6.5 kW Carbon fibres 7.2 kW Total energy
production 33.0 kW
[0070] The carbon fibres produced in this model amount to 3.6 kg of
carbon per hour. In the model, these carbon fibres are considered a
product, hence entering into the model with an energy yield of 7.2
kW.
[0071] Moreover, the model is based on an ideal situation, among
other things without heat loss. It is also possible to combust the
purge gas from line 13 in the combustor 9, or it may be combusted
for direct heating of the reactor vessel or the gas supply thereto,
which would at least partly compensate for the heat loss
experienced in practice.
[0072] The above described apparatus may be constructed as a
compact and relatively small unit that may be used for
CO.sub.2-free energy conversion in sparsely populated areas, e.g.
in the form of small, possibly mobile generator plants for electric
power. Such units may be used in ships, mobile and fixed offshore
installations, land vehicles and also other isolated locations.
Instead of releasing CO.sub.2, carbon may be removed in a
relatively easy to handle form, as carbon whiskers.
[0073] In order for the device to have an acceptable noise level
and energy efficiency, the heat exchangers 11, 12 should preferably
be combined with mufflers in order to minimize the pressure drop on
the exhaust side of the combustor.
[0074] Carbon whiskers may have many different applications. As
mentioned above, they may be used for transport of hydrogen, as
relatively large amounts of hydrogen may be adsorbed on these
carbon whiskers. As an example, it has been reported that more than
23 litres may be stored per gram of carbon. After the hydrogen has
been removed again, the carbon may be regenerated and re-used for
storage of hydrogen.
[0075] In addition, carbon whiskers in the form of microfibres have
a potential use in composite materials, plastics, etc. for
reinforcement of these. Moreover, they may be used as catalyst
supports, as well as for adsorption of various gases.
[0076] In addition to the above described unit, various alterations
and modifications may be envisaged.
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