Note: Descriptions are shown in the official language in which they were submitted.
1:1079~i7
.
.
This in~rention re].ates to a process for methanation
an~ more paIticularly, to the catalytic metllarlatior. of
2` gases such as synthesis gas.
A col~ercially important reaction is the con~ersion
of synthesis gas (CO ~ H2 ~ C02) o~tained
by the steam reforming o~ hydrocarbons e g naphtha dis-
tillates or by the gasification of coal, Ths gas is con-
verted into "pipeline quality" methane for use as sub-
.`stitute na~ural gas (sometimes referred to as SN~) using
.~ two main reactions, namely,
~ ~ 3H2 + co = a~ + H20 (A), and
4H2 + C2 = CH4 ~ 2H2 (B)
1 ~he CO/H2 ratio may be ad~usted if required by the
. water gas shift reaction:
. ' CO ~ H20 ~ C02 ~ H2
. ~or a value in the region of 3-1 which lS general7y the
ratio required for the methanation reaction.
. According to one aspect of the present in~ention a
process for the methanation of synthesis gas comprises
. reacting together CO, CO~ and H2 in contact with a catalyst
- comprlsing a temperature stable metallio monolith, having
a plurality of channels bearing on at least a part of
. their surfaces or formed ofi a catalytic material for
~r ~ 2 - .
~''' ' `'-' '' . ~
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. ~
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ccltaly,iln~ tl~c ~ cliol~ ga~se~ ~lnring passage through the
chanllels. ~rhe l eactiol~ .is carried out for a sufficient time
and under such condition~s that a significant proportion of the
carbon containinc3 gases are converted to methane.
Preferably the metallic monolith is made from or the
channels bear on at least a part of their surfaces one or more
of the metals Ru, Rh, Pd, Ir, Pt, Ni, Re or alloys containing
one or more of these metals. Ru and alloys containing
ruthenium are particularly preferred. Alternatively the
metallic monolith is made from a base metal alloy capable of
withstanding rigorous process conditions. Examples of such a
base metal alloy include:
Alloy Approximate Composition ~ by weight
Fe Cr Al Co Ni
. _ _ _ .. ... _ _ . . . . . . . _
Fecralloy Bal* 15.5 4 - -
Kanthal DSC Bal 23 6 2
Armco Bal 18 3 - 1/2
Incoloy 800 Bal 21 1/2 - 32 1/2
Brightray S 1 20 - - 78
Inconel 600 8 15.5 - - 72
Esshete 800 46 20 - - 32
Stainless 304 Bal18 - - 9
(* including 0.25~ yttrium)
+ trademarks
It will be appreciated from the above list that Brightray
S and Iconel 600 have a large nickel content, and are
.~
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thus the most: suita~)lc for ~roducing a catalytically
active monolitll without the further deposition of catalytie
metal. In the case of "Fecralloy" and "Kanthal" alloys which
do not contain N1, the catalytic metals Ru, Rh, Pd, Ir, Pt,
Re and or Ni, may be deposited or coated upon the alloy
prior to or during fabrication of the monolith by one of the
methods hereinafter described.
In addition to those listed above, suitable base
metal alloys are nickel and chromium alloys having an
aggregate Ni + Cr content greater than 20~ by weight and
alloys of iron including at least one of the elements
Cr (3-40 wt%), Al (1 10wt%) Co (trace - 5 wt%),
Ni (trace -72 wt%) and carbon (trace -0.5 wt%). Such
substrates are described in German DOS 2,450,664.
Other examples of base metal alloys capable of with-
standing the rigorous conditions required are the iron-
aluminium-chromium alloys which may also contain yttrium.
These contain 0.5-12 wt% Al, 0.1-3.0 wt%Y,0-20 wt% Cr and
balance Fe. These are described in United States Patent
No. 3,027,252.
Base metal alloys which contain one or more of the
above mentioned catalytic metals may also be used as the
catalytic metallic monolith. Alloys described in German
DOS 2,530,245 contain at least 40 wt% Ni or at least 40
wt% Co, a trace to 30 wt% Cr and a trace to 15 wt% of one
379~7
or morc o~ tlle ~ ti.llu~ roup met;als (inc].udirl~ Ru),
The allo~s Illay also contain from a trace to t.he
percellt~ge specified of any one or more of the fo].lowillg
optional elements:- -
. ~ b~ wei~ht,
Co 25
Ti 6
. Al
c. 20
:1 Mo ~ 20
~f 2
. - 2
:. Si 1.5
. V . 2.0
;~ Nb 5
~ . B 0.15.
-~ . C ~ . - 0-05
Ta- . 10
. 3
Fe ` ~20
~ ;
; ; . . Rh and rare earth metal
-~ on oxides. . 3.
. Preferably, the metallic monolith used in th~. catalyst
of the present invention is made from metallic sheets which
are deformed in such a way that when compared with plain non-
deformed sheets of the same overall dimensions present a
very much increased exposed surface area. Typically the
:jl - , . .. .
~ 5 -
~ ~ , - . . .. . . .
' ~ ~
:, . ' .:
. .
~, . .
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incrensed sllrf~ce area is achieved by corrugating, or
otherwise shaping , folding in a forner and winding u~
a flat foil and a corrugated or otherwise shaped foil
together into a tube of a spiral cross section.
In a prefvrred embodiment of the present invention,
' the metallic sheets which may be collstructed from the
~ catalytic metal or employed as a monolith ~or supporting
! the catalyst,are first crimped, corrugated, folded,
indented and/or perforated or otherwise shaped in such
~' a way that the exposed surface area per~unit volum~-is ~rer~i mu-~
~-~ increàsed. Such a sur~ace area is normally much greater
: than that presented by ceramic honeycombs or by partic-
ulate catalyst supports for the same given volume. An
. example of a metallic monolith made in accordance with
this invent on comprises a ~oll of corrugated sheet
- made ~rom a h~at resisting alloy interleaved ~ith a~
- - - non-corrugated sheet o~ such alloy Alternatively two
orrugated sheets may be used with the corrugations in
~; each sheet parallel with each other or at an angle to
~ each other. Again the corrugation in different sheets
-~- - may be of different pitch, depth and cross-sectional
- shape.
~¦ As catalysts, such metallic mono]iths e2hibit a
; low ~ressure drop and have quite considerable surface
.~j . .
i to volume ratios A 0.003" thick Kanthal D sheet can
be ~abricated as a monolith possessing a surface area
.
., .
-- 6 --
!
. . .. . .. ...... .. .. . . ..
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11~7967
oi 1]00 s~ ft/ft~ wllcreas a 0.00~" thick l~antllal D sheet
can bc fa~ricated as a monolith possessing a surface
area of 2000 sq ft/ft3.
f` Suitable foil thicknesses fall within the range
0 0015 ana 0.0045 inch. Preferably, however, the foil
has a thickness of 0.002 inch and when corrugated an~
assembled to form a monolith as described has approxim-
. _ . .
ately 400 cells per square inch when considered in
cross section. A preferred range of cell sizes is 200-
800 cells per square inch. Suitable surface to volume
ratios are 1200 sq ft. per cubic foot with 400 cells
per square inch and 2000 sq. ft. per cubic foot with
~00 cell~ per s~uare inch.
A fabricated monolith is preierably provided with
a firmly adherent coating (sometimes referred to as a
"wash coating") which is porous and absorbent and pre-
sents a high surface area and which acts as the carrier
for the second catalytically active layer containing
one or more o~ the catalytic metals as herein defined.
The coating may be a reiractory metal oxide or it may be a
high surface area alumino silicate such as a zeolite.
The coating may also be a mixture o~ oxide and zeolite.
Suitable refractory metal oxides comprising the
said first coating are one or more oi the oxides of B,
Al, Si, Be, Mg, Caj Sr, Ba, Sc, Y, Ti, Zr, Hi, Th,
the lanthanides and the actinides. The refractory
metal oxide layers may include members of the gamma
f
.j
.. ~ .~_ _ _ . _, . , _, . .. _,_ _, . . . . _ .. ~ . .. . . _ .... ~ ... . .... _ ,.. _ .. . ~ ... : .. _ _.. ,.. ... . ... _ ..
. .. .. . . ., . _ .. ~ ., .. .... . .. .. , _ .
, ' .
'..
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or nctivntcd nlulllina family. Such metal oxide layers
can be prepnre~d, for cxample~ by precipitating a
hydrous aluluina gel and, therea~ter, drying and
~ calcining to expel hydrated ~ater and provide acti~e
i ga~ma alumina. A pre~erred active refractory metal
oxide is obtained by drying and calcining (at tempera-
3 tures of 300 to 800C) a precursor mixture of hydrous
~ 1
alumina phases predominating in crystalline ~rihydrate, that
is, containing in excess of 50 per cent by weight of
-~ the total alumina hydrate composition (preferably from65 to 95 per cent by weight) of one or more o~ the
trihydrate forms of gibbsite, bayerite and norstrand-
.
- ite by X-ray diffraction. We prefer to proviae-the
- ~etalli~ substrate with a first firmly adherent oxide
layer in an essentially two stage process. In the
~irst stage the metallic substrate is thermally oxid-
ised to produce a thin first oxide layer which acts
~ as a key. We pre~er to carry out thermal oxidation
-~- by maintaining the formed metallic substrate at from
1000 - 1200C in air or moist cracked ammonia vapour
:~ .
for 1 hour. The higher temperature is required for
.
very oxidation resistant alloys such as the Kanthal
l .,
~i- - range and the moist hydrogen atmosphere is preferred
~or alloys having a high Ni content.
The adherent oxygen containing or oxlde film may
~ li . . ..
be produced by any one o~ several kno~n methods includ-
g chemical techniques. The film must be of sufficient
-
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thickncss to gi~c ndeqllate ~bsorbti.ve capacity for
retainin~ the catn:lyticcllly acti.ve alloy comprising for
exaulple OtlC or morc! of the platinum group metals as
previousl~ described. The film is preferably from
0.0004 to ~.002 inches thick.
l~lere aluminium is present in the alloy forming the
extended metal substrate, the oxide film may be produced
by treating tlle aluminium containing surface with a solut-
ion of an alkaline carbonate, for example, a sodium car-
bonate chromate solution. .The film may ~e produced by
the anodic oxidati.on o~ the metal surface whereby the
.
metal is made the anode in an electrolytic ~olution. In
.
anodising alwnïnium containing surfaces, a 15% sulphuric
.. ~ . - .
~-' acid solution is commonly employed as the electrolyte
j but other acid eaectrolytes such as chromic acid, oxalic
aci~, phosphoric acid and sometimes boric acid may be
used. 'rhe o~ide film is -deliber~-tely applie~ and
~ . does not include the relatively thin natural oxide films
.~ which sometimes occur on metal surfaces which have been
exposed to the atmosphere
Another method of forming an alumina l.ayer on those
. - alloys which do not contain sufficient aluminium to form
their own alumina layer upon o~idation is the use o~
Calorising (Registered Trade Mark). This involves the
vapour deposition of an aluminium coating followed by
. . . anodising or heating in an o~ygen-containing gas. Alter-
native coatings such as chromate, phosphate, silica or
i . silicate or zirconia may all be deposited by known methods.
. ' , ' .
:~ ' ~ 9 -~
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There arc many dilfererlt techni~ues for the prepar-
ation of a higll surf.lce area catalytically active refract-
.
ory metal oxide wash coat containing one or more o~ the
refractory metal oxides ~hich confer beneficial properties
as regard ageing a2ld inertness to deposited catalytic metals
.
' at high te~perature undèr reducing conditions. -
{ The preferred adherent oxide coating deposited upon
the extended metal substrate is alwnina.
One method ~or the d~position of hydrous alumina is
.
proposed in United States Patent No 2,406,420. .~ny con-
~enient aluminium compound such as alkali metal aluminates
and aluminium salts may be used as the starting material.
Either acidic or basic precipitants are used, depending
upon the character of the starti~g material. Suitable
acidic precipitants are ammonium chloride, ammonium
sulphate, ammonium nitrate, hydrochloric acid, nitric acid,
. .
etc. Suitable basic precipitants are ammonium hydroxide,
sodium hydroxide, hexa-methylene tetramine, etc.
~i . -
~nother method is to precipitate the hydrous alumina
.i~ . . ,
~rom an alkali metal hydroxide directly on to the e~tended
metal substrates forming part of the present invention. I.
the aluminate solution is maintained at a temperature of
60 - 85C a film or coating of alpha alumina trihydrate
,
(Gibbsite) i9 deposited. Subsequent heating at 250 - 180C
converts the trihydrate to the monohydrate and subsequent
heating at 540C converts the monohydrate to gamma alumina
- without loss of the very high surface area coating ~hich is
~- produced by this ~ethod. The high surface area results
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~75~67
frolu thc fo~ ation oi' hexagolla] crystal a6gregates of
apprO~illlate si7.e 8x8x20 micrcll~. Micropores of size 402
diameter are present in the hexagonal crystal aggregates
but appear to play no part in the catalytic activity of
the structure.
We prefer a washcoat loading which is within the
range of 5 - 30% by weight of the metallic mono]ith sub-
strate. A suitable loading of A1203 on Kanthal D having
400 cells per square inch is 10% by weight. The surface
area of the alumina is 50 - 500 square metres per gram
of alumina. The aluminate method of deposition of alumina
described above, gives a surface area of from 120 - 160
square meters per gram of alu~ina. - -
An alternative preferred method for the depositionof an adherent alumina washcoat on the metallic substrate
is to prepare a siurry of a pre-activated Gibbsite (Alumina
,trihydrate) and an alumina monohydrate having a solid
liquid ratio of ~etween 25 and 50/0 and a pH less than 7
and using this to impregnate the shaped substrate by
complete immersion. The exact strength of the slurry used
which may be determined by trial and error) should be
sufficient to produca an alumina washcoat of the required
thickness. The substrate is then allowed to dry in l~arm
air and finally fired for 2 hours at 450C to form an adher-
ent coating of chi - and gamma-al~ina having a thickness
up to O.G02 in. thick on the metallic substrate. Crystal
aggregates of diameter 3 - 7 microns are produced having
micropores of appro~imately the same size, i.e. 40 R in
diame ter .
. . .
,~
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~ f~lr~)el^ nletl~od of de~osi~ion of an adherent alumina
washcoat on ~he metall;c su~strate entails the use of a slurry
of alpha alumina monohydrate. After firing at 450C, gamma
alumina is formed having a surface area between 180 and 300
square metres per gram. Gamma alumina is added to alpha alumina
monohydrate at the slurrying stage before firing in order to
form a thixotropic mixture. Crystallite or crystal aggregates
of 20 - 100A are formed. Micropore diameters remain the same
at 40A.
Suitable proprietary alumina trihydrates (Gibbsite)
are "FRF 80" supplied by British Aluminium Chemicals Ltd.
and "C 333" supp]ied by Conoco. Suitable alumina mono-
hydrates (Boehmite) are "Sol-Gel Alumina"+ supplied by the
United Kingdom Atomic Enerty Authority. "~ispal M" supplied
by Conoco and "Condea F" supplied by the Condea Group.
Gibbsite is added to "Sol-Gel Alumina" (which is micro-
crystalline Boehmite) at the slurrying stage in order to form
a thixotropic mixture.
Optionally, one or more of the oxides titania, zirconia,
hafnia and thoria may be present in the alumina for the purpose
of producing additional stabilisation of the intermediate
oxide (washcoat) layer. Other rare earth oxides, alkaline
earth oxides and alkali metal oxides may also be used.
Impregnation or deposition of one or more of the
catalytic metals, upon the first refractory metal oxide
containing adherent layer may be accomplished by known methods
of deposition of catalytically active metals on
+ trademarks
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7967
(o~lt~ ol oll~ c,~ il a ~ rll sllrlace ~ a
rcrrnct,(.)r~ let,~ o.~i~le L~ tlle adlleren~ oxygcn contailling
~ilm, the ~up~)Ort ma~rlle immersecl in a sollltion of water
sol~lb]e inorgnnjc ~alt or salts or one or more of tJhe metals
Ni, Re~ ~u, R~l~ Pd, Ir and/or Pt.
EX~IPL~ 1.
Using a commercial niclcel catalyst (Harshaw Ni - 0104
T, 1~ pellets) and a ~eedstock consisting of 3.1 parts
hydrogen, 1 part carbon monoxide and 1 part water in nitrogen
the following results were obtained at a tota~ space velocity
of 65,ooo hr 1.
I ~empeOraturePressure Carbon Monoxide Selectivity to
¦ ( C) (psig) conversion (%) methane (~
~1 35 ~75 75 63
; 400 , 75 80 61
EXAMPLE 2.
.~
Using identical conditions to Example 1 but employing a
j ' monolithic catalyst of equal volume manufactured from Kanthal
.~ .
D (0,002 inch thick, cell density of 400 cells/square inch)
with an alumina washcoat and a ruthenium loading of 135 gm/cu. ft.
, which is equi~-alent in terms of total weight of metal per unit
volume to 0.5 wt. % Ru on pellets, the results given in the table
below were obtained. The catalyst was prepared by dipping the
~3 washcoated monolith in ruthenium trichloride solution,and drying.
- .
Tempe~ature Pressure Carbon monoxide Selectivitv to
( ~) (psig) conversion (C/o) methane (%~
35 75 77 74 '
' l~OO 75 74 64 ' ' ,
,, - 13 -
, . . .
. . ~ . . .
- . .
. . ~ - .
':" ' ' ' ~ '
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1SL~7~67
F`~ II'T,I~ ;.
.
Ilsing a f~lrt~lel- ~aIrl~le of nickel cata~yst OlO~T a9 in
E`xn~ le l bllt a to-tal space veloci-ty of 135,000 hr l
the fo]lo~ing results werc obtained.
TempeI~atlIr~ Pressure Carbon Monoxide . Sele¢tivity
(C~ (psig) conversion (%) to methane ,~0
, 35 75 62 61
~ 400 75 55 57
1 EXAMPLE 4
J Using tha conditions o~ Example 3 but a monol-thic ruthenium
~¦ catalyst as in Example 2, the follo~ing results were obtained.
j Temperature Pressure Carbon monoxide Selectivity
(C) (psig? conversion to methane /.
35 75 67 74
- 4~0 75 55 ` 66
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