GB2166661A

GB2166661A - Methanation catalysts

Info

Publication number: GB2166661A
Application number: GB08428562A
Authority: GB
Inventors: Reginald George Sinclair Banks; James William Alexande Buckley; James Alexander Oliver; Alan Williams
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1984-11-12
Filing date: 1984-11-12
Publication date: 1986-05-14
Also published as: GB2166661B; GB8428562D0

Abstract

Catalysts, suitable for methanating synthesis gas e.g. those obtained by the ash slagging gasification of coal, are prepared by a process which includes the steps of (a) admixing an aqueous solution of water soluble salts of at least one divalent Group VIII metal and at least one trivalent metal in which is suspended at least one kandite mineral, the weight ratio of Group VIII and trivalent metals (calculated as oxides in the calcined precursor form) being not less than 3:1, and an aqueous solution of an alkaline compound which when reacted with said water soluble salts produces a water insoluble compound of said metals, thereby to precipitate a water insoluble complex of said metals in admixture with said kandite, (b) calcining said complex and (c) reducing the thus formed calcined precursor.

Description

SPECIFICATION Methanation Catalysts This invention relates to catalysts, particularly to the production of methanation catalysts and to processes for the methanation of synthesis gases in the production of substitute natural gas (SNG).

Gases produced by the gasification of coal, for example by the British Gas/Lurgi Ash Slagging Process contain major amounts of carbon oxides and hydrogen which can be catalytically reacted to form methane.

Although a number of catalysts are known for methanation purposes they are not satisfactory for operation at high temperatures and pressures. Known catalysts become deactivated by sintering which leads to loss of both surface area and mechanical strength and current research has been directed towards finding a catalyst which has improved sinter resistance.

In our UK patent application No.83 13123 there is described a catalyst precursor (i.e. unreduced catalyst) which is a Feitnecht compound of a divalent metal e.g. nickel and a trivalent metal e.g. aluminium intermixed with a clay mineral which in one instance is Kaolin.

The Feitnecht compound is prepared by coprecipitation of insoluble compounds of the metals from a mixed solution of their salts e.g. nitrates. An alkali such as sodium or potassium carbonate is used as the precipitating agent and the clay is contained in the precipitant solution. On combination of the mixed salt solution and the alkali-clay suspension a modified Feitnecht compound in which the clay becomes interstratified within the Feitnecht lattice.

We have found unexpectedly that the following properties can be realised viz: (i) high initial strength and good retention thereof (ii) good retention of surface area (iii) high activity and good dispersion of the catalytic metal which is itself pressed in small crystallite size in catalysts if, in the preparation stage, the clay is incorporated into the mixed salt solution as opposed to the precipitant solution.

Accordingly, the present invention provides a process for the production of a catalyst precursor which includes the steps of admixing: I: an aqueous solution of water soluble salts of at least one divalent Group VIII metal and at least one trivalent metal in which is suspended at least one Kandite mineral, and II: an aqueous solution of an alkaline compound which when reacted with said water soluble salts produces a water insoluble compound of said metals, thereby to precipitate a water insoluble complex of said metals in admixture with said Kandite mineral, and containing said complex, the weight ratio of said Group VIII metal to trivalent metal (calculated as oxides in the claimed product) being not less than 3:1.

The Kandite mineral is preferably Kaolin (china clay) and is incorporated into the salt solution to give a concentration in the final catalyst precursor of not more than 50% by weight, preferably of the order of 30% by weight.

In forming the coprecipitated complex it is preferred to blend the dry Kandite into the mixed salt solution to form a smooth suspension and thereafter to add the precipitant to the suspension.

The precipitant is an alkaline compound which will react with both metal salts to produce an insoluble compound or salt. Typically the precipitant is an aqueous solution of potassium or sodium carbonate or bicarbonate; the resulting precipitate being a complex of the carbonates of the two metals.

The precipitation is preferably carried out after both the suspension and the precipitant have been heated to, for example, about 90"C, before the precipitant is added to the suspension.

The mixed salt solution may be prepared by forming separate aqueous solutions of the respective salts and then mixing the solution followed by blending in of the clay.

The catalyst precursors of the invention are preferably nickel-alumina catalysts, nickel being the Group VIII metal and aluminium being the trivalent metal. Catalyst precursors having the preferred metal composition are disclosed in UK Patent Specification No. 1525017. However, the invention encompasses within its scopes mixtures of Group VIII and/or trivalent metals provided that the overall weight ratio of Group VIII metals to trivalent metals is at least 3:1. Thus, for example, the trivalent metal might be a mixture of aluminium and chromium in the proportions disclosed in UK Patent Specification No. 1550749.

The invention will now be illustrated by the following Examples. Examples 1-9 & 14 are not examples of the invention but are included for comparison purposes.

A range of catalyst precursors were prepared with varying nickel to alumina ratios, varying Kaolin contents and alternative ways of incorporation of the clay.

In each preparation the amounts of nickel nitrate Ni(NO3)3. 6H2O and aluminium nitrate Al(N03)2 H2O as shown in Table 1 were separateiy dissolved in 1.9 litres of water and adding the two aqueous solutions were admixed to form the mixed salt solution (A). Similarly to 1.9 litres of water were added the amounts of potassium carbonate (K2CO3) shown in Table 1, to form solution (B).

To either solution (A) or (B) was blended the amount of Kaolin shown in Table 1.

In Examples 1-12, both the suspension and precipitant were heated to 90"C and the carbonate added to the suspension over a period of 30 minutes with continuous vigorous stirring of the thus formed mixture.

The temperature of the mixture during the addition was maintained at 900C. After completion of the precipitation, the resultant slurry was filtered. The filter cake was washed free of the water soluble potassium compounds by repeated re-slurrying of the precipitate with de-ionized water at 60"C and re-filtering. The potassium free cake was dried by heating in a stream of air at 125 C, followed by calaimation in air for 2 hours at 450"C. The calcined precursor was crushed (to pass an 850 sieve), blended with 2% graphite and pelleted to produce 3.2x3.2 mm pellets.

The catalysts of Examples 13 and 14 were made by a similar method except that the slurry was boiled after precipitation.

Each catalystwasfirstreduced in a stream of hydrogen at5000C/24.5 barsforl6 hours and then subjected to a Sinter Test. In the Sinter Test, the catalyst was subjected to a flow of a mixture of steam and hydrogen under the following conditions: Examples Nos. 1-12 13 & 14 Time 270 hours 610 hours Temperature 550"C 600 C Pressure 24.5 bars 45 bar Steam/H2 ratio 9:1 (molar) 9:1 (molar) Steam flowrate 102 ml hr-' 102 ml hr-l Hydrogen flowrate 14.16 litres hr1 14.16 litres hr~ after which the samples were passivated in carbon dioxide at room temperature.

The passivated catalysts were then tested for the physical properties reported in Table 2.

It will be seen that from the results in Table 2 that good crushing strength commensurate with a low activity temperature is obtained from only those catalysts of Examples 10--13 i.e. those in which the Ni:AI ratio is at least 3:1 and the kaolin was present in the mixed salt solution (A).

The catalysts prepared in accordance with the present invention may be used for the methanation of synthesis gases containing hydrogen and carbon oxides, e.g. those obtained from the steam-oxygen-ash slagging gasification of coal.

Accordingly the present invention also provides a process for the methanation of a gaseous mixture of steam, hydrogen and oxides of carbon which comprises passing said mixture at a temperature of from 250"C to 550"C over a catalyst consisting of a divalent Group VIII metal, a trivalent metal and a Kandite mineral which catalyst has been prepared by a process including the steps of (a) admixing an aqueous solution of water soluble salts of at least one divalent Group VIII metal and at least one trivalent metal in which is suspended at least one Kandite mineral, the weight ratio of Group VIII and trivalent metals (calculated as oxides in the calcined precursor form) being not less than 3: :1, and an aqueous solution of an alkaline compound which when reacted with said water soluble salts produces a water-insoluble compound of said metals, thereby to precipitate a water insoluble complex of said metals in admixture with said Kandite, (b) calcining said complex and (c) reducing the thus formed calcined precursor.

The catalysts prepared in accordance with the present invention are useful for catalysing methanation reaction as described in for example UK Patent Specification No. 1544245 and GB-A-21 16581.

TABLE 1

Component A B Ni(N03)26H2O Al(NO3)29H2O Ni:AI Kaolin K2CO3 Kaolin Ex. No. 9. 9 (w/w) 9. g. 9. Kaolin 1 830 2450 1:2 0 2100 - 0 2 740 2210 1:2 50 1890 - 10 3 580 1710 1:2 150 1460 - 30 4 410 1230 1:2 250 1050 - 50 5 1240 1840 1::1 0 1930 - 0 6 1110 1660 1:1 50 1730 - 10 7 870 1290 1:1 150 1350 - 30 8 620 920 1:1 250 960 - 50 9 1860 920 3:1 0 1670 - 0 10 1670 830 3:1 50 1500 - 10 11 1300 640 3:1 150 1170 - 30 12 930 460 3:1 250 840 - 50 13 930 460 3:1 250 840 - 50 14 930 460 3::1 0 840 250 50 TABLE 2

Property Crushing strength' Surface area2 Ni Crystal lite3 Activity4 A kg B% % size (A) "C Ex. No.

1 1 10 15 158 256 2 6.5 52 45 130 230 3 6.7 62 47 117 242 4 8.6 105 56 120 276 5 1 10 23 159 232 6 8.3 37 47 137 218 7 8.8 73 54 115 230 8 11.6 96 52 106 260 9 1 10 39 138 215 10 4.6 36 51 136 207 11 11.9 67 67 123 218 12 15.6 98 60 124 251 13 20.9 81 45 233 * 14 15.1 61 50 213 * Notes: Crushing strength; the mean force (kg), applied along the diameter of the pellets needed to crush them. The results are given for both as the measured strength (A) and as a proportion (%) (B) of the strength before the sinter test.

2 Total surface area measured by nitrogen adsorption at the boiling point of liquid nitrogen, using the method of Brunauer, Emmett and Teller (J. American Chemical Society, 1938,60,309). The results are expressed as a proportion (%) of the original surface area.

3 Nickel crystallite size as measured by X-ray diffraction line broadening.

4Activity as measured by the temperature at which the catalyst initiates the reaction of carbon monoxide and hydrogen in a stoichiometric mixture (3 H2:CO), the lower the temperature the more active the catalyst.

* Activity not tested.

1. A process for production of catalyst precursors including the steps of incorporating a Kandite mineral into a water insoluble complex formed by coprecipitation of at least one divalent Group VIII metal compound and at least one trivalent metal compound from a mixed solution of water soluble salts thereof with an alkaline precipitant followed by calcining of the complex, characterised in that said Kandite mineral is incorporated into the mixed salt solution prior to precipitation and that the weight ratio of Group VIII metal to trivalent metal is not less than 3:1 (calculated as oxides in the calcined precursor).

2. A process as claimed in claim 1 characterised in that the Kandite is kaolin.

3. A process as claimed in either claim 1 or claim 2 characterised in that the kandite is present in an amount of less than 50% by weight.

4. A process as claimed in claim 3 characterised in that the amount of kandite is about 30% by weight.

5. A catalyst precursor as claimed in any one of the preceding claims in which the Group VIII metal is nickel and the trivalent metal is aluminium.

6. A process for the production of catalyst precursors according to Claim 1 and substantially as hereinbefore described.

7. Catalyst precursors wherever produced by the process claimed in any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. TABLE 2 Property Crushing strength' Surface area2 Ni Crystal lite3 Activity4 A kg B% % size (A) "C Ex. No. 1 1 10 15 158 256 2 6.5 52 45 130 230 3 6.7 62 47 117 242 4 8.6 105 56 120 276 5 1 10 23 159 232 6 8.3 37 47 137 218 7 8.8 73 54 115 230 8 11.6 96 52 106 260 9 1 10 39 138 215 10 4.6 36 51 136 207 11 11.9 67 67 123 218 12 15.6 98 60 124 251 13 20.9 81 45 233 * 14 15.1 61 50 213 * Notes: Crushing strength; the mean force (kg), applied along the diameter of the pellets needed to crush them. The results are given for both as the measured strength (A) and as a proportion (%) (B) of the strength before the sinter test. 2 Total surface area measured by nitrogen adsorption at the boiling point of liquid nitrogen, using the method of Brunauer, Emmett and Teller (J. American Chemical Society, 1938,60,309). The results are expressed as a proportion (%) of the original surface area. 3 Nickel crystallite size as measured by X-ray diffraction line broadening. 4Activity as measured by the temperature at which the catalyst initiates the reaction of carbon monoxide and hydrogen in a stoichiometric mixture (3 H2:CO), the lower the temperature the more active the catalyst. * Activity not tested. CLAIMS

2. A process as claimed in claim 1 characterised in that the Kandite is kaolin.

8. A catalyst composition comprising a reduced form of a precursor according to claim 8.

9. A process for the production of methane-containing gases wherein a mixture of steam, hydrogen and oxides of carbon are passed over a methanation catalyst at a temperature of from 250"C to 550"C, characterised in that the catalyst has been prepared by a process including the steps of (a) admixing an aqueous solution of water soluble salts of at least one divalent Group VIII metal and at least one trivalent metal in which is suspended at least one kandite mineral, the weight ratio of Group VIII and trivalent metals (calculated as oxides in the calcined precursor form) being not less than 3: :1, and an aqueous solution of an alkaline compound which when reacted with said water soluble salts produces a water insoluble compound of said metals, thereby to precipitate a water insoluble complex of said metals in admixture with said kandite, (b) calcining said complex and (c) reducing the thus formed calcined precursor.