DK201400705A1

DK201400705A1 - A catalyst for prereforming and/or steam reforming

Info

Publication number: DK201400705A1
Application number: DKPA201400705A
Authority: DK
Inventors: Herman Theodoor Teunissen
Original assignee: Haldor Topsoe As
Priority date: 2014-12-03
Filing date: 2014-12-03
Publication date: 2016-04-18

Abstract

The invention relates to a catalyst for prereforming and/or steam reforming, comprising an active material supported on a ceramic material, where the active material is Ni and the ceramic material comprises oxides of Mg, Al as well as of one or more lanthanide elements, wherein the atomic ratio between Mg and Al is between 1:0.05 and 1:0.25, the atomic ratio between Mg and Ni is between 1:0.10 and 1:0.45 and the atomic ratio between Mg and the one or more lanthanide elements is between 1:0.005 and 1:0.05. The invention also relates to a precursor for a catalyst according to the invention, the use of a catalyst according to the invention and a prereforming and/or steam reforming process, wherein a hydrocarbon fuel is passed over a catalyst of the invention in the presence of steam.

Description

Title: A catalyst for prereforming and/or steam reforming

The present invention relates to a catalyst for prereforming and/or steam reforming, the catalyst comprising an active material supported on a ceramic material, where the active material is Ni and the ceramic material comprises oxides of Mg, A1 as well as of one or more lanthanide elements. The catalyst of the invention is suitable for prereforming and/or steam reforming of a hydrocarbon feedstock. The invention also relates to a precursor for a catalyst of the invention, the use of a catalyst according to the invention and a prereforming and/or steam reforming process.

Prereforming of a hydrocarbon feedstock in the preparation of synthesis gas is well known in the art. Prereforming is generally employed with hydrocarbon feed containing higher hydrocarbons or for increasing the capacity of existing reformer plants. Process gas of the hydrocarbon feedstock and steam is thereby introduced in a prereformer at temperatures of about 450°C to 550°C. Within the prereformer a plurality of reactions may take place: - Sulfur removal - Steam reforming of higher hydrocarbons, also denoted "HHC" or C2+ hydrocarbons. Examples of such C2+ hydrocarbons, viz. C2-, C3- or C4-hydrocarbons, are for example ethane, propane, butane.

(1) CnH(2n+2) + n H20 (n + (2n+2)/2) H2 + n CO

- Methanation of CO

(2) CO + 3 H2 CH4 + H20 - Water-gas shift: (3) CO + H20 ^ H2 + C02.

Steam reforming of a hydrocarbon feedstock in the preparation of synthesis gas is also well-known. Steam reforming of methane corresponds to the case of eguation (1) where n=l: (la) CH4 + H20 CO + 3H2.

The steam reforming of methane typically reguires temperatures of about 600°C to 1000°C.

Important parameters for prereforming and steam reforming catalysts are thermal stability and mechanical strength, as well as activity and durability.

The problem solved by the invention is to provide a catalyst for prereforming and/or steam reforming, having increased durability. In particular, the problem solved is to provide a catalyst for prereforming and/or steam reforming with improved resistance to carbon formation and/or improved resistance to sintering.

One aspect of the invention relates to a catalyst for prereforming and/or steam reforming, comprising an active material supported on a ceramic material, where the active material is Ni and the ceramic material comprises oxides of Mg, A1 as well as of one or more lanthanide elements. The atomic ratio between Mg and A1 is between 1:0.05 and 1:0.25, the atomic ratio between Mg and Ni is between 1:0.10 and 1:0.45 and the atomic ratio between Mg and the one or more lanthanide elements is between 1:0.005 and 1:0.05. The above ratios are valid for both fresh and aged catalysts. Ni, Mg and A1 are typically present in crystalline phase as Ni, MgO and MgAl2C>4, respectively r whilst the one or more lanthanide elements is/are predominantly present as a non-crystalline phase. Furthermore, small quantities of oxidized nickel are also present. The term "support" refers to the structural support or carrier of the catalyst, which has a wide range of important characteristics known to the person skilled in the art, including the provision of a high surface area for the active material, i.e. nickel, dispersed on the catalyst support.

In one embodiment, the atomic ratio between Mg and A1 is between 1:0.10 and 1:0.20. In one embodiment, the atomic ratio between Mg and Ni is between 1:0.20 and 1:0.35. In one embodiment, the atomic ratio between Mg and the one or more lanthanide elements is between 1:0.010 and 1:0.030. It has been found that these atomic ratios provide a catalyst with a good resistance to carbon formation as well as a good resistance to sintering.

In one embodiment, the one or more lanthanide elements is Lanthanum.

In one embodiment, the catalyst is promoted with K in a concentration between 10 and 2000 ppm. Potassium suppresses the carbon formation on the catalyst. In one embodiment, the K concentration is between 50 and 1000 ppm.

In one embodiment, the ceramic support further comprises mixed oxides of Mg, Al, Ni and Mg. A non-exhaustive list of such mixed oxides comprises: (NixMg(i-x)) A1204, (NixMg (i_x)) 0 (0<x<l) and LaAlCb. A small amount of non-reduced Ni can be anticipated due to incomplete reduction.

In one embodiment, the catalyst is formed as pellets or is of tablet form. The catalyst in pellet or tablet form may be shaped with a plurality of holes, also denoted multihole shape catalyst. The catalyst size may range from about 4 mm to about 35 mm in diameter. The length of the catalyst may range from about 3 mm to 40 mm. The ideal size for a given application depends on a number of factors, including the catalyst shape and nickel loading, the operating temperature, pressure, and feed composition, and the allowable pressure drop. A catalyst with a multi-hole shape with a diameter in the range from 5 mm to 25 mm and a height to diameter ratio of 0.5 to 1.2 will be suitable for a prereforming catalyst. One example of such a catalyst is a multi-hole catalyst having a diameter of 11 mm, a height of 6 mm and seven holes with a hole diameter of 2 mm. The person skilled in the art is able to select a suitable catalyst with a suitable shape for prereforming purposes.

Another aspect of the invention relates to a precursor for a catalyst according to the invention, wherein the precursor comprises (NixMg(i_x)) AI2O4 having a crystallite size (D440 ) of less than 600Å, such as less than 300Å, such as less than 200Å.

In one embodiment, the precursor for a catalyst according to the invention comprises (NixMg(i_x)) 0 having a crystallite size (D220 ) of less than 600Å, such as less than 300Å, such as less than 200Å.

A further aspect of the invention relates to the use of a catalyst according to the invention for catalysis of one of the following reactions: methanation, prereforming, steam and/or oxygen reforming.

Yet another aspect of the invention relates to a prereforming and/or steam reforming process comprising the steps of: i. providing the catalyst according the invention; ii. passing a hydrocarbon fuel over said catalyst in the presence of steam.

The manufacturing of the catalyst according to the invention is based on creating intimate contact between the components involved, either on nanometer scale or on micrometer scale. Thus, the catalysts of the present invention can be produced by any method known in the art which renders an effective mixture of the individual components. This may involve precipitation of a single constituent or co-precipitation of multiple constituents, which methods are described in more detail in Synthesis of Solid Catalysts, edited by Krijn de Jong, 2009 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim. Alternatively, the preparation might involve mixing of constituent (s) followed by extrusion or high energy milling in the dry or wet phase. High energy milling may be carried out using a range of methods, of which some are disclosed in section 2.4 of

Mechanochemistry in Nanoscience and Minerals Engineering by Peter Balaz, Springer 2008.

Suitable precursors comprise water soluble salts of the constituents, in the case of (co)precipitation.

Furthermore, oxides, hydroxides, carbonates, basic carbonates and mixtures thereof are suitable materials for mixing, extrusion and high energy milling. These examples should be understood as illustrations rather than limitations of the present invention. The mixing steps are usually followed by drying steps, optionally preceded by filtration as in the case of (co)precipitation.

After drying, the mixtures are transformed into so-called green bodies by a shaping method such as tabletizing. Alternatively, the green bodies comprise the extrudates, which are obtained prior to the drying step. The green bodies may be fired under air, other O2 containing gasses, nitrogen or other inert gasses at temperatures of 600-1200°C after which the active Ni catalyst is obtained by a reduction treatment using dihydrogen at elevated temperatures of 500-1000°C.

In one aspect of the present disclosure, the green body consists of some of said components and the addition of the remaining components may be carried out by an impregnation step comprising at least one aqueous solution containing the component(s) in a dissolved state.

An exemplary catalyst of the present invention was prepared by suspending MgO in a solution comprising the nitrate salts of Ni and La (Ni(N03)2 and La(N03)3) and precipitation with basic solution comprising KAIO2 and KOH. The precipitate was filtered, washed with water and dried. The powder was shaped to green bodies. The green bodies were calcined in air at a temperature of between 800°C and 1200°C, e.g. at about 950°C. Optionally, the calcined bodies were washed with water in order to reduce the K content to reach the target concentration of K in the catalyst. Alternatively the calcined bodies were impregnated with aqueous KNO3 in order to arrive at a target concentration of K in the catalyst. The catalyst was reduced in H2 at a temperature of between 700°C and 900°C, e.g. 840°C.

It has turned out that an exemplary catalyst of the invention prepared as described above had relatively small nickel particle sizes. It is well known that a catalyst having smaller nickel particle sizes is less prone to carbon formation than a catalyst having larger nickel particle sizes. This is inter alia described in "Concepts in Syngas Manufacture" by Jens Rostrup-Nielsen and Lars J. Christiansen, Imperial College Press, 2010, where figure 5.16, page 251, depicts the thermodynamic potential for carbon formation at temperatures between 400°C and 700°C as a function of the ratio H2O/CH4, for various nickel particle sizes. Thus, since the catalyst of the invention has smaller nickel particle sizes than comparable catalysts, it is less prone to carbon formation. Moreover, it has been shown experimentally that the La-promoted Ni-catalyst of the invention has an improved activity and reduced Ni-sintering compared to an unpromoted Ni-catalyst.

The exemplary catalyst precursor consisted of 7 wt% (NixMg(i-x)) A1204, having a D440 crystallite size of about 70Å, and 93 wt% (NixMg(i_x)) 0 with a D220 crystallite size of about 180Å. The exemplary catalyst precursor included La where the atomic ratio between Mg and La was between 1:0.005 and 1:0.05. It has turned out that a catalyst of the invention comprising both La and K is especially durable and resistant to carbon formation. It is expected that this is due to advantageous structural properties of the catalysts, probably due to the presence of La and/or the relatively small nickel crystallite sizes.

Claims

1. A catalyst for prereforming and/or steam reforming, comprising an active material supported on a ceramic material, where the active material is Ni and the ceramic material comprises oxides of Mg, A1 as well as of one or more lanthanide elements, wherein the atomic ratio between Mg and A1 is between 1:0.05 and 1:0.25, the atomic ratio between Mg and Ni is between 1:0.10 and 1:0.45 and the atomic ratio between Mg and the one or more lanthanide elements is between 1:0.005 and 1:0.05.

2. A catalyst according to claim 1, wherein the atomic ratio between Mg and A1 is between 1:0.10 and 1:0.20.

3. A catalyst according to claim 1 or 2, wherein the atomic ratio between Mg and Ni is between 1:0.20 and 1:0.35.

4. A catalyst according to any of the claims 1 to 3, wherein the atomic ratio between Mg and the one or more lanthanide elements is between 1:0.010 and 1:0.030.

5. A catalyst according to any of the claims 1 to 4, where the one or more lanthanide elements is Lanthanum.

6. A catalyst according to any of the claims 1 to 5, wherein the catalyst is promoted with K in a concentration between 10 and 2000 ppm.

7. A catalyst according to claim 6, wherein the K concentration is between 50 and 1000 ppm.

8. A catalyst according to any of the claims 1 to 7, wherein the ceramic support further comprises mixed oxides of Mg, Al, Ni and La.

9. A catalyst according to any of the claims 1 to 8, wherein the catalyst is formed as pellet or tablet form.

10. A precursor for a catalyst according to any of the claims 1 to 9, wherein the precursor comprises (NixMg(i-x)) A1204, (0<x<1) having a crystallite size (D440 ) of less than 600Å, such as less than 300Å, such as less than 2 0 0Å.

11. A precursor for a catalyst according to any of the claims 1 to 9, wherein the precursor comprises (NixMg(i-x)) 0 (0<x<l) having a crystallite size (D220 ) of less than 600Å, such as less than 300Å, such as less than 200Å.

12. Use of a catalyst according to claims 1 to 9 for one of the following reactions: methanation, prereforming, steam and/or oxygen reforming.

13. A prereforming and/or steam reforming process comprising the steps of: i. providing the catalyst according to any one of the claims 1 to 9; ii. passing a hydrocarbon fuel over said catalyst in the presence of steam.