Methanation process using stabilized catalyst support comprising transition alumina

Abstract

In a broad form the present disclosure relates to a stabilized catalyst support comprising in oxide form; aluminum, zirconium, and one or more lanthanoid elements taken from the lanthanoid group of the periodic system characterized in that at least a part of the aluminum is present as transition alumina such as χ, κ, γ, δ, η, ρ and θ-alumina, characterized in the concentration of zirconium being at least 1.5 wt %, 5 wt % or 10 wt %, the concentration of lanthanoid being at least 0.5 wt %, 1.0 wt %, 2 wt % or 4 wt % and the combined concentration of zirconium and lanthanoid being at least 4 wt %, 7 wt % or 10 wt %, with the associated benefit of a support comprising transition alumina being a high surface area due to the small crystallites typical for transition alumina, and the benefit of the combined presence of oxides of zirconium and lanthanoid in the stated amounts being that at these levels these oxides stabilize the structure of the transition alumina.

Claims

1. A process for producing a gas rich in methane by reacting a synthesis gas comprising carbon oxide and hydrogen in the presence of a catalyst comprising a catalyst support comprising in oxide form: aluminum, zirconium, and one or more lanthanoid elements of the lanthanoid group of the periodic system, wherein at least a part of the aluminum is present as transition alumina selected from the group consisting of χ, κ, γ, δ, η, ρ and θ-alumina, and wherein the concentration of zirconium is at least 1.5 wt %, the concentration of lanthanoid is at least 0.5 wt %, and the combined concentration of zirconium and lanthanoid is at least 4 wt %.

2. The process according to claim 1 wherein the temperature of the synthesis gas prior to contacting the catalytically active material is from 200° C. to 800° C.

3. The process according to claim 1 wherein the temperature increase of the gas comprising methane after contacting the catalytically active material is at least 50° C.

4. The process according to claim 1, wherein the synthesis gas prior to contacting the catalytically active material has a molar ratio M=(H.sub.2—CO.sub.2)/(CO+CO2) between 1 and 20.

5. The process according to claim 1, wherein the fraction of transition alumina in the support being χ, κ, γ, δ, η, ρ and θ-alumina is at least 0.1.

6. The process according to claim 1, wherein the one or more lanthanoid elements are selected from the group consisting of lanthanum, cerium, praseodymium, samarium, gadolinium, neodymium, europium, dysprosium and ytterbium.

7. The process according to claim 1, wherein the elemental concentration of the one or more lanthanoid elements present as oxide is at least 0.5 wt % and below 10 wt %.

8. The process according to claim 1, wherein the elemental concentration of zirconium is at least 1.5 wt % and below 50 wt %.

9. The process according to claim 1, wherein the catalyst support further comprises magnesium in an oxide form, in which the elemental concentration of magnesium is 1-30 wt %.

10. The process according to claim 1, wherein the catalyst comprises nickel in a concentration of 5-80 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an XRD diagram illustrating the crystal structure of Catalyst A before and after aging.

(2) FIG. 2 is a graph showing the relative amount of alumina present as alpha alumina in the support (y-axis) vs. wt % ZrO.sub.2 (x-axis).

DETAILED DESCRIPTION OF THE INVENTION

(3) According to the present disclosure, a methanation catalyst with improved stability is provided according to which, the Al.sub.2O.sub.3 carrier is stabilized against phase transformation by introducing of both a refractory oxide such as ZrO.sub.2 and an element from the lanthanoid group of the periodic system such as La into the carrier. Without being bound by theory the effect of ZrO.sub.2 is assumed to be two-fold, both to hinder phase transformation towards α-Al.sub.2O.sub.3 and to increase the mechanical strength of the shaped bodies. Also without being bound by theory, the lanthanoid is assumed to work as a promoter to minimize the phase transformation of high surface area Al.sub.2O.sub.3 and to improve the catalytic activity.

(4) The manufacturing methodology for the catalysts of the present 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.

(5) 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 inventions. The mixing steps are usually followed by drying steps, optionally preceded by filtration as in the case of (co)precipitation.

(6) 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 O.sub.2 containing gases, 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. As known to the person skilled in the art, transition alumina as such is unstable at temperatures above 1050° C., but if alumina is modified by a stabilizer such as lanthania, zirconia or nickel oxide firing at higher temperatures is not a problem. Firing must also be made at elevated temperatures (600-1200° C.) to ensure that at least one of the stabilizing zirconium and lanthanoid oxides are structurally integrated in the transition alumina, and thereby providing a stabilized crystal structure.

(7) 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 said component(s) in dissolved state. Impregnation steps are followed by thermal treatment e.g. calcination and finally reduction. Optionally, the impregnation steps are preceded by calcination at 600-1200° C. Impregnation may be made with one or more component solutions of appropriate purity or a mixture of components of limited purity dependent on the desired catalyst quality, cost and other practical issues.

(8) The assessment of catalyst stability involved an aging procedure in combination with an evaluation of the aged catalyst.

(9) The accelerated lab aging procedure involved exposing the fresh catalyst to high temperatures and high steam partial pressures in the laboratory. Relevant catalysts were used as whole pellets and subjected to a gas consisting of steam and hydrogen in high levels 30 barg, 670° C. for 2 weeks. These conditions are not often found in normal operation, but it allows the investigation of the long term sintering stability in a relatively short time in the laboratory. The relevant catalysts are then analyzed for various properties after the aging procedure. A similar procedure was also carried out for inactive catalyst supports, to evaluate physical and structural parameters of the catalyst supports.

(10) The evaluation of the activity of the aged catalyst was made by determining the intrinsic methanation activity of the fresh and aged catalysts under the same operating condition: the relevant catalyst was crushed to 0.1-0.3 mm fraction and diluted with an appropriate inert also crushed to the same fraction such that the catalyst weight fraction in the mixture was approximately 4%. The reason to mix the catalyst with inert was to limit the conversion inside the catalyst bed and obtain the most representative intrinsic activity measurements. One gram of the catalyst and inert mixture was loaded in a fixed bed reactor and exposed to approximately 10 L/h of a gas containing 10% CO and 90% H.sub.2. The exit gas was analyzed for composition using a standard gas chromatograph.

(11) The temperature inside the reactor was monitored both inside the catalyst bed and on the reactor wall. The catalyst activity may thus be calculated from the CH.sub.4 produced and the CO and H.sub.2 consumed. The intrinsic activity was measured several times at the same temperature, and was measured from 275 to 325° C. Under these conditions, it was confirmed that there was insignificant temperature increase through the catalyst bed, as well as insignificant mass and heat transfer limitations such that the effectiveness of the catalyst particles was close to 1. This means that the measured catalyst activity was the true intrinsic methanation activity.

(12) A simpler assessment of the stability of the catalyst was the determination of the relative amount of alumina which was present as α-alumina by XRD. For the present examples the fresh catalyst had a relative amount of α-alumina of 0, and this increases with sintering; in some cases to 1, corresponding to full conversion of transition alumina to α-alumina.

(13) The determination of the distribution between crystal structures by XRD is based on analysis by Rietveld refinement of XRD diagrams such as shown in FIG. 1. FIG. 1 illustrates the crystal structure of Catalyst A before (solid line) and after (dashed line) aging. As it is well known to the person skilled in the art the XRD for large crystal α-alumina is characterized by sharp peaks, whereas transition alumina having small crystallites, like γ-Al.sub.2O.sub.3 in this case, are characterized by broad soft “bumps”. Catalyst A does not comprise zirconia or lanthania, so only alumina peaks are visible.

EXAMPLE 1

(14) Eight catalysts containing Ni on a high surface area γ-Al.sub.2O.sub.3 support were prepared using the following method.

(15) Catalyst A according to the prior art was prepared as follows:

(16) Commercial high surface area transition alumina extrudates (primary gamma alumina), were used as a catalyst carrier. The extrudates were impregnated with an aqueous Ni(NO.sub.3).sub.2 solution, calcined under air at 450° C. and reduced under a flow of H.sub.2 at 600° C.

(17) Catalyst A consisted of 31 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support.

(18) Catalyst B according to the prior art was prepared from Catalyst A, by impregnation of the calcined NiO containing extrudates with an aqueous La(NO.sub.3).sub.3 solution. The final catalyst was then obtained after further calcination and reduction as mentioned above.

(19) Catalyst B consisted of 30 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, and stabilized by 2.5 wt % La as La.sub.2O.sub.3. The amount of La relative to the support was 3.6 wt %.

(20) Catalyst C according to the prior art was prepared from an aqueous suspension containing Al (as böhmite), Zr (as hydroxide) and Ni (as basic carbonate). The suspension was dried and the powder was pressed into tablets after addition of graphite. The tablets were calcined in air at 925-1000° C. and reduced with H.sub.2 up to 840° C.

(21) Catalyst C consisted of 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized by 21 wt % Zr as ZrO.sub.2. The amount of Zr relative to the support was 27 wt %.

(22) Catalyst D according to the present disclosure was prepared from Catalyst C by impregnation of the calcined tablets with an aqueous La(NO.sub.3).sub.3 solution. The final catalyst was then obtained after calcination at 450° C. and reduction up to 840° C., as mentioned above.

(23) Catalyst D consisted of 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized by 2.1 wt % La as La.sub.2O.sub.3 and 21 wt % Zr as ZrO.sub.2. The amount of La and Zr relative to the support was 2.7 wt % and 27 wt % respectively.

(24) Catalyst E according to the present disclosure was prepared from Catalyst C by impregnation with an aqueous Pr(NO.sub.3).sub.3 solution. The final catalyst was then obtained as mentioned above for Catalyst D.

(25) Catalyst E comprises 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized 2 wt % by Pr as Pr.sub.6O.sub.11 and 21 wt % Zr as ZrO.sub.2. The amount of Pr and Zr relative to the support was 2.6 wt % and 27 wt % respectively.

(26) Catalyst F according to the present disclosure was prepared from Catalyst C by impregnation with an aqueous Ce(NO.sub.3).sub.3 solution. The final catalyst was then obtained as mentioned above for Catalyst D.

(27) Catalyst F comprises 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized by 1.6 wt % Ce as CeO.sub.2 and 21 wt % Zr as ZrO.sub.2. The amount of Ce and Zr relative to the support was 2.1 wt % and 27 wt % respectively.

(28) Catalyst G according to the present disclosure was prepared from Catalyst C according to the procedure of Catalyst D. Catalyst G consisted of 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized by 1.1 wt % La as La.sub.2O.sub.3 and 21 wt % Zr as ZrO.sub.2. The amount of La and Zr relative to the support was 1.4 wt % and 27 wt % respectively.

(29) Catalyst H according to the present disclosure was prepared from Catalyst C according to the procedure of Catalyst D. Catalyst H consisted of 23 wt % Ni on a high surface area transition Al.sub.2O.sub.3 support, stabilized by 0.5 wt % La as La.sub.2O.sub.3 and 21 wt % Zr as ZrO.sub.2. The amount of La and Zr relative to the support was 0.7 wt % and 28 wt % respectively.

(30) The properties of the catalysts after the accelerated lab aging procedure are shown in Table 1. It can be seen that the procedure induces a large degree of both Ni and carrier sintering, in that the aged catalyst has a large Ni crystallite size, hence a significant reduction in the intrinsic methanation activity, and that the high surface area transition Al.sub.2O.sub.3 carrier has been transformed into α-Al.sub.2O.sub.3, leading to the loss of surface area.

(31) It is also seen that both La.sub.2O.sub.3 and ZrO.sub.2 stabilize the transition Al.sub.2O.sub.3, and that the stabilization in the two catalysts with ZrO.sub.2 in combination with either La.sub.2O.sub.3 or Pr.sub.6O.sub.11 is even higher that what would be expected from the stabilization by one of these. To the extent that experimental data was available it was confirmed that this increased stability of transition Al.sub.2O.sub.3 was reflected as increased intrinsic methanation activity.

(32) TABLE-US-00001 TABLE 1 Properties of fresh and lab-aged catalysts. The relative α-Al.sub.2O.sub.3 represents the weight fraction of α-Al.sub.2O.sub.3 relative to the total amount of Al.sub.2O.sub.3 in the carrier, as measured by XRD. Relative Relative intrinsic Ni Relative surface metha- crystallite α-Al.sub.2O.sub.3 area nation Catalyst size (Å).sup.1 (wt/wt) BET activity Catalyst A Fresh  80 0 1 1 Ni/Al.sub.2O.sub.3 Aged 728 1 0.05 0.04 Catalyst B Fresh 0 Ni/Al.sub.2O.sub.3/La.sub.2O.sub.3 Aged 333 0.36 Catalyst C Fresh 180 0 0.20 0.27 Ni/Al.sub.2O.sub.3/ZrO.sub.2 Aged 324 0.53 0.09 0.08 Catalyst D Fresh 120 0 0.26 1 Ni/Al.sub.2O.sub.3/La.sub.2O.sub.3/ZrO.sub.2 Aged .sup. 240.sup.2 0.04.sup.3 0.16 0.30 Catalyst E Fresh 0 Ni/Al.sub.2O.sub.3/Pr.sub.6O.sub.11/ZrO.sub.2 Aged .sup. 225.sup.2 0.09.sup.3 0.31 Catalyst F Fresh 0 Ni/Al.sub.2O.sub.3/CeO.sub.2/ZrO.sub.2 Aged 240 0.06.sup.3 0.28 Catalyst G Fresh 0 Ni/Al.sub.2O.sub.3/La.sub.2O.sub.3/ZrO.sub.2 Aged 226 0.20 0.21 Catalyst H Fresh 0 Ni/Al.sub.2O.sub.3/La.sub.2O.sub.3/ZrO.sub.2 Aged 233 0.27 0.14 .sup.1Measured using XRD .sup.2Corrected value .sup.3Corresponding to <0.1.

EXAMPLE 2

(33) Further 12 high surface area catalyst supports were prepared using the following method. As it will be appreciated by the person skilled in the art, stability of the support will not be negatively affected by the presence of active constituents such as nickel.

(34) Support I

(35) A mixture of 36 g HNO.sub.3 (65 wt %) and 605 g water is added to 1000 g Böhmite and mixed thoroughly at 65° C. using a mixer such as a z-mixer. Then, the mixture is extruded and the extrudates are calcined at 500° C. The calcined extrudates are crushed, mixed with water and magnesium stearate, and tabletized. Finally, the tablets are calcined at 1150° C. for 2 h. Support I consisted of pure Al.sub.2O.sub.3.

(36) Support J

(37) Support J was prepared according to the procedure of support I using 36 g HNO.sub.3 (65 wt %), 617 g water, 974 g Böhmite and 26 g Zirconium hydroxide. Support J consisted of 97.5 wt % Al.sub.2O.sub.3 stabilized by 1.9 wt % Zr as ZrO.sub.2.

(38) Support K

(39) Support K was prepared according to the procedure of support I using 36 g HNO.sub.3 (65 wt %), 651 g water, 949 g Böhmite and 51 g Zirconium hydroxide. Support K consisted of 95.0 wt % Al.sub.2O.sub.3 stabilized by 3.7 wt % Zr as ZrO.sub.2.

(40) Support L

(41) Support L was prepared according to the procedure of support I using 36 g HNO.sub.3 (65 wt %), 649 g water, 889 g Böhmite and 111 g Zirconium hydroxide. Support L consisted of 89.2 wt % Al.sub.2O.sub.3 stabilized by 8.0 wt % Zr as ZrO.sub.2.

(42) Support M

(43) Support M was prepared according to the procedure of support I using 36 g HNO.sub.3 (65 wt %), 643 g water, 753 g Böhmite and 247 g Zirconium hydroxide. Support M consisted of 75.9 wt % Al.sub.2O.sub.3 stabilized by 17.9 wt % Zr as ZrO.sub.2.

(44) Support N

(45) Support N was prepared according to the procedure of support I using 29 g HNO.sub.3 (65 wt %), 417 g water, 544 g Böhmite and 339 g Zirconium hydroxide. Support N consisted of 62.3 wt % Al.sub.2O.sub.3 stabilized by 27.9 wt % Zr as ZrO.sub.2.

(46) Support O

(47) The uncalcined tablets, obtained as Support I were impregnated with an aqueous La(NO.sub.3).sub.3 solution to obtain a La content of 4 wt %. Finally, the tablets are calcined at 1150° C. for 2 h. Support O consisted of 95.3 wt % Al.sub.2O.sub.3, stabilized by 4 wt % La as La.sub.2O.sub.3.

(48) Support P

(49) The uncalcined tablets, obtained as Support J were converted to Support P according to the procedure of support O. Support P consisted of 93.0 wt % Al.sub.2O.sub.3 stabilized by 1.8 wt % Zr as ZrO.sub.2 and 4 wt % La as La.sub.2O.sub.3.

(50) Support Q

(51) The uncalcined tablets, obtained as Support K were converted to Support Q according to the procedure of support O. Support Q consisted of 90.6 wt % Al.sub.2O.sub.3 stabilized by 3.5 wt % Zr as ZrO.sub.2 and 4 wt % La as La.sub.2O.sub.3.

(52) Support R

(53) The uncalcined tablets, obtained as Support L were converted to Support P according to the procedure of support O. Support R consisted of 85.1 wt % Al.sub.2O.sub.3 stabilized by 7.6 wt % Zr as ZrO.sub.2 and 4 wt % La as La.sub.2O.sub.3.

(54) Support S

(55) The uncalcined tablets, obtained as Support M were converted to Support S according to the procedure of support O.

(56) Support S consisted of 72.3 wt % Al.sub.2O.sub.3 stabilized by 17.0 wt % Zr as ZrO.sub.2 and 4 wt % La as La.sub.2O.sub.3.

(57) Support T

(58) The uncalcined tablets, obtained as Support N were converted to Support T according to the procedure of support O.

(59) Support I consisted of 59.4 wt % Al.sub.2O.sub.3 stabilized by 26.6 wt % Zr as ZrO.sub.2 and 4 wt % La as La.sub.2O.sub.3.

(60) TABLE-US-00002 TABLE 2 Composition and properties of fresh and lab-aged supports. The relative α-Al.sub.2O.sub.3 represents the weight fraction of α-Al.sub.2O.sub.3 relative to the total amount of Al.sub.2O.sub.3 in the carrier, as measured by XRD. Relative α-Al.sub.2O.sub.3 (wt/wt) Support Zr wt % La wt % fresh aged I 0 0 0.96 0.96 J 1.9 0 0.95 0.98 K 3.7 0 0.95 0.96 L 8.0 0 0.92 0.98 M 17.9 0 0.95 0.94 N 27.9 0 0.61 0.96 O 0 4 0.05.sup.1 0.36 P 1.8 4 0.04.sup.1 0.20 Q 3.5 4 0.04.sup.1 0.09.sup.1 R 7.6 4 0.04.sup.1 0.08.sup.1 S 17.0 4 0.06.sup.1 0.09.sup.1 T 26.6 4 0.07.sup.1 0.06.sup.1 .sup.1<0.1 alpha alumina.

(61) For proper evaluation of the stability of a support to be used in methanation and reforming catalysts the proper test is the accelerated lab aging procedure described above. The relative amount of alumina which is present as alpha alumina in the support after the aging test is listed in Table 2. In FIG. 2 the relative amount of alumina which is present as alpha alumina in the support after the aging test is shown on the y-axis, as a function of composition. Open symbols correspond to supports I, J, K, L, M, N i.e. supports without presence of lanthanoides, and closed symbols correspond to supports O, P, Q, R, S, T i.e. with a presence of 4 wt % lanthanum as La.sub.2O.sub.3. The x-axis corresponds to the wt % ZrO.sub.2.

(62) The data of the calcined samples prior to aging testing show that for partial stabilization (61% conversion of transition alumina to alpha alumina) 27 wt % Zr is required in the absence of La, but this is not sufficient for stabilization during the accelerated long term aging test.

(63) For an aged support stabilized with La.sub.2O.sub.3 but no ZrO.sub.2 about 36% of the alumina is present as alpha alumina, but the stabilization synergy of La.sub.2O.sub.3 and ZrO.sub.2 is already evident in the presence of 1.9 wt % Zr, where a significant stabilization is seen as only 20% of the alumina in the aged support is present as alpha alumina. For 3.7-27 wt % Zr the amount of alpha alumina is substantially constant at around 5-10 wt % indicating substantial stabilization of the transition alumina.

(64) The graph therefore shows a strong synergy in the stabilization of transition alumina from the combined presence of oxides of zirconium and lanthanoides. The synergetic stabilization is very strong at combined elemental concentrations in the support of zirconium and lanthanoides from 4 wt %, and close to complete from 7 wt % or 10% wt/wt.