CA1107967A

CA1107967A - Catalytic methanation of synthesis gas

Info

Publication number: CA1107967A
Application number: CA299,708A
Authority: CA
Inventors: David T. Thompson; Michael Wyatt
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 1977-03-28
Filing date: 1978-03-23
Publication date: 1981-09-01
Also published as: FR2385665B1; GB1603101A; FR2385665A1; JPS53130605A; DE2813329A1

Abstract

ABSTRACT

In the catalytic methanation of synthesis gas, the catalyst is a temperature stable metallic monolith made of or coated with a catalytic material, which preferably comprises one or more of the metals Ru, Rh, Pd, Ir, Pt, Ni and Re or an alloy containing one or more of these metals, and formed with a plurality of channels in which CO, CO2 and H2 are reacted together in contact with the catalytic material to convert a significant proportion of the carbon-containing gases into methane.

Description

1:1079~i7 .

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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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-``" 11¢~7~67 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 .~

'7~67 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 - , . .. .
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, '7.~67 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 .

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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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7~i7 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.

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~7~67 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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, ' ~g7~67 ~ 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 . ;, :

(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.
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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.

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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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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 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 /.

- 4~0 75 55 ` 66 ~:

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE

PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the methanation of synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide wherein the gas is contacted with a catalyst to form methane, the improvement comprising using, as the catalyst, a fabricated temperature stable metallic monolith made of a chromium alloy and having a plurality of channels bearing on at least a part of their surface, a catalytic material for catalyzing the reaction gases during passage through the channels, said catalytic material comprising ruthenium and the fabricated monolith being provided with a wash coating which acts as the adherent carrier for a layer of said catalytic material and which comprises a refractory metal oxide or zeolite or a mixture of oxide and zeolite.

2. A process according to claim 1, wherein said base metal alloy is a nickel and chromium alloy.

3. A process according to claim 1, wherein the alloy also contains at least one of the following elements: Co, Ti, Al, W, Mo, Hf, Mn, Si, V, Nb, B, C, Ta, Zr, Fe, Rh and rare earth metal on oxides.

4. A process according to claims 1, 2 or 3 wherein the metallic monolith is made of the catalytic material.

5. A process according to claims 1, 2 or 3 wherein the metallic monolith is made of a base metal alloy and at least one of the metals Ru, Rh, Pd, Ir, Pt, Re and Ni is deposited or coated thereon prior to or during fabrication of the monolith.

6. A process according to claims 1, 2 or 3 wherein the base metal alloy is an alloy of iron which also includes at least one of the elements Cr, Al, Co and C and at least one of the metals Ru, Rh, Pd, Ir, Pt, Re and Ni is deposited or coated thereon prior to or during fabrication.

7. A process according to claims 1, 2 or 3 wherein the base metal alloy is an iron-aluminium-chromium alloy and at least one of the metals Ru, Rh, Pd, Ir, Pt, Re and Ni is deposited or coated thereon prior to or during fabrication.

8. A process according to claims 1, 2 or 3 wherein said alloy is an alloy of iron which also includes at least one of the elements Cr, Al, Co and C together with yttrium, and at least one of the metals Ru, Rh, Pd, Ir, Pt, Re and Ni is deposited or coated thereon prior to or during fabrication.

9. In a process for the methanation of synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide wherein the gas is contacted with a catalyst to form methane, the improvement comprising using, as the catalyst, a fabricated temperature stable metallic monolith of metallic sheets deformed to present a greater exposed surface than that presented by undeformed sheets of the same dimension made of a chromium alloy and having a plurality of channels bearing on at least a part of their surface, a catalytic material for catalyzing the reaction gases during passage through the channels, said catalytic material comprising ruthenium and the fabricated monolith being provided with a wash coating which acts as the adherent carrier for a layer of said catalytic material and which comprises a refractory metal oxide or zeolite or a mixture of oxide and zeolite.

10. A process according to claim 9 wherein said metallic monolith deformation is effected by crimping, corrugating, folding, indenting and/or perforating.

11. A process according to claim 10 wherein said metallic monolith is a deformed sheet wound together with another deformed sheet or an undeformed sheet into a tube or roll.

12. A process according to claim 11 wherein said roll comprises a corrugated sheet interleaved with a non-corrugated sheet.

13. A process according to claim 11, wherein said roll comprises two interleaved corrugated sheets.

14. A process according to claim 13, wherein the corrugations in one sheet extend parallel with or at an angle to the corrugations in the other sheet.

15. A process according to claim 11, wherein the corrugations in one sheet are of different pitch, depth or cross-sectional shape to the corrugations in the other sheet.

16. A process according to claim 13 wherein the corrugations in one sheet are of different pitch, depth or cross-sectional shape to the corrugations in the other sheet.

17. A process according to any one of claims 9, 10 or 11 wherein the thickness of each sheet is from 0.0015" to 0.0045".

18. A process according to claim 9, 10 or 11 wherein the thickness of each sheet is 0.002".

19. A process according to claim 9, 10 or 11 wherein each sheet has from 200 to 800 cells per square inch.

20. A process according to claim 9, 10 or 11 wherein each sheet has 400 cells per square inch.

21. A process according to claim 9, 10 or 11 wherein each sheet has 800 cells per square inch.

22. A process according to claim 9, 10 or 11 wherein the surface to volume ratio of the monolith is 1200 sq.ft/ft3.

23. A process according to claim 9, 10 or 11 wherein the surface to volume ratio of the monolith is 2000 sq.ft/ft3.

24. A process according to claims 1, 2 or 3 wherein said refractory metal oxide is an oxide of s, Al, Si, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, Th, the lanthanides or the actinides.

25. A process according to claims 1, 2 or 3 wherein said refractory metal oxide is alumina.

26. A process according to claims 1, 2 or 3 wherein said washcoat also contains one or more of the oxides titania, zirconia, hafnia, and thoria, other rare earth oxides, alkaline earth oxides or alkali metal oxides.

27. A process according to any one of claims 1, 2 or 3 wherein said coating is keyed to the metallic substrate by a thin oxide layer produced by thermal oxidation of the substrate.

28. A process according to any one of claims 1, 2 or 3 wherein the washcoat loading is within the range of 5-30% by weight of the metallic monolith substrate.

29. A process according to any one of claims 1, 2 or 3 wherein said catalytic material is applied to said wash coating by immersing the latter in a solution of a water soluble inorganic salt of at least one of the metals Ni, Re, Rh, Ru, Pd, Ir and Pt.