EP2776164A1

EP2776164A1 - Process for producing methanation catalyst and process for methanation of synthesis gas

Info

Publication number: EP2776164A1
Application number: EP12847684.3A
Authority: EP
Inventors: Claudia Querner; Andrian Milanov; Stephan Schunk; Andreas Strasser; Guido WASSERSCHAFF; Thomas ROUSSIÈRE
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2011-11-08
Filing date: 2012-11-07
Publication date: 2014-09-17
Also published as: CN104039452B; RU2014123057A; CN104039452A; KR20140097308A; CA2854914A1; JP2015502247A; ZA201404092B; WO2013068931A1; JP6125518B2; EP2776164A4

Abstract

The present invention relates to a process for producing a catalyst for carrying out methanation reactions. The production of the catalyst is based on contacting of a hydrotaicite-comprising starting material with a fusible metal salt. The compounds brought into contact with one another are intimately mixed, thermally treated so that the metal salt fraction melts and subsequently subjected to a low-temperature calcination step and a high-temperature calcination step. The metal salt melt comprises at least one metal selected from the group consisting of K, La, Fe, Co, Ni, Cu and Ce, preferably Ni. The metal salt melt more preferably comprises/contains nickel nitrate hexahydrate. The hydrotaicite-comprising starting material is preferably hydrotaicite or a hydrotalcite-like compound as starting material, and the hydrotaicite-comprising starting material preferably comprises magnesium and aluminum as metal species. The catalyst of the invention is preferably used for carrying out methanation reactions at elevated pressures (from 10 to 50 bar) and elevated temperatures.

Description

PROCESS FOR PRODUCING METHANATION CATALYST AND PROCESS FOR METHATION OF S YNTHESIS GAS

The invention relates to a process for the preparation of a methanation catalyst and to a process for the methanation of CO and / or CO 2 -containing gas streams, preferably at high temperatures. To prepare the catalyst, hydrotalcite-containing starting material is brought into contact with a meltable metal salt, preferably containing nickel nitrate, intimately mixed and subjected a.) To a thermal treatment step and b.) To a calcination step.

The use of methane for the production of synthetic natural gas has been of great economic and technical interest for half a century. The synthetic natural gas that can be produced by methanation is often referred to as Substituted Natural Gas or SNG.

To illustrate the state of the art in the field of methanation, a brief overview of the development of methanation processes and methanation catalysts is given below. Already for many decades, catalysts based on nickel-containing active components have been used for methanation. In a large number of these catalysts, the nickel is present together with an oxide support of aluminum oxide. The preparation of the catalysts is often carried out by precipitation of the active components in the presence of an aluminum-containing carrier component or by the co-precipitation of active component and carrier component. The products obtained in the precipitation are first dried and then calcined. In order to obtain the catalyst in a suitable particle size, a shaping process is often interposed between the drying and the calcining. For example, US Pat. No. 3,912,775 describes the preparation of a precipitate with the composition NieAl.sub.2 (OH) .sub.16 CO.sub.3.times.H.sub.2O.sub.2, which is obtained by the precipitation of nickel nitrate and aluminum nitrate from aqueous solution using sodium carbonate solution. The precipitation may also be carried out in the presence of a carrier component. Further, it is disclosed that the precipitate is dried at a temperature in the range of 80 to 180 ° C and calcined at a temperature in the range of 300 to 550 ° C. Characteristic for the production process is that the temperature increase between the drying process and the calcining process takes place by applying a temperature gradient by means of a controlled heating rate. To produce the methane-containing product gas, naphtha and water vapor are used as starting materials which, at a temperature in the range of 270 ° C. and 460 ° C. and a pressure in the range from 15.8 to 29.6 bar, come into contact with the active composition to be brought. The efficiency of nickel-containing catalysts for the methanation can be increased in accordance with US Pat. No. 3,865,753 by additionally adding magnesium species to the aluminum-containing synthesis system. By synthesis and subsequent post-treatment, a nickel-containing magnesium aluminate is obtained as the active composition, which has a high activity and stability with respect to the methanation. With regard to the precipitate, it is required that the divalent metals (magnesium and nickel) and the trivalent aluminum be at least in a 1: 1 molar ratio, with a preferred molar ratio between M 2 ⁺ and M ^{3 +} in a range of 2.5 : 1 to 3: 1. The increased activity of the catalyst is also explained by the fact that - after drying, calcination and reduction - a magnesium spinel forms during the reaction.

US 3,988,262 discloses an improved catalyst obtained by depositing the nickel-containing component on the aluminum-containing support in the presence of zirconia. The catalyst according to the invention has a nickel oxide content of 15 to 40 wt .-%, wherein at least a large part of the nickel oxide is reduced to nickel before the start of the methanation.

According to DE 26 24 396, the thermal stability of the methanation catalysts can be further increased in that the catalyst has a certain proportion of molybdenum oxide. In this case, a molybdenum content which has 0.25 to 8% by weight of molybdenum or molybdenum oxide has proved to be advantageous.

EP 2 308 594 A2 discloses a nickel-containing catalyst for the production of synthesis gas from methane, water and carbon dioxide with a ratio in the range of 1, 0/1, 0-2.0 / 0.3-0.6. The improved stability of the catalyst is achieved by adding Ce and / or Zr. In the experimental examples, a synthesis using magnesium aluminum hydrotalcite as a starting material is also disclosed. An impregnation process is disclosed in which hydrotalcite as carrier is impregnated with an aqueous nickel nitrate solution, the water subsequently being removed in a vacuum evaporator at 70 ° C. The process for the production of a synthesis gas disclosed in EP 2 308 594 A2 is characterized in that the educt stream used has a minimum content of 1 mol of water per mol of methane and the process is carried out at a pressure in the range from 0.5 to 20 atm. EP 2 308 594 A2 discloses an example in which the catalytic studies for the production of synthesis gas were carried out at 10 atm.

EP 031 472 A2 discloses and claims a methane production catalyst prepared with thermally decomposable salts of nickel, cobalt and magnesium which are fixed on a carrier. The support is converted by thermal treatment in the metal oxides.

DE 29 52 683 discloses a methanation catalyst containing Co and Ni species as active components. As support materials are aluminum oxides or mixed oxides of alumina and silica or silica, wherein the catalytic properties of the catalyst is improved by the addition of magnesium-containing salts to the synthesis mixture. In connection with the thermal treatment of the catalyst precursor material, the formation of a spinel-containing phase is reported. The catalysts are used for methanation reactions, which are carried out at temperatures below 500 ° C and where the pressure is in the range of atmospheric pressure.

One of the objects on which the invention is based is to provide an improved process and an improved catalyst for the methanation of CO and / or CO 2 -containing synthesis gas. In particular, a catalyst material should be provided here whose thermal and mechanical resistance is superior to the materials known from the prior art. Methane formation by the reaction of carbon monoxide and / or carbon dioxide with hydrogen is a highly exothermic process. In the presence of a suitable catalyst, the reaction usually proceeds to equilibration. Catalytic methane formation is carried out under adiabatic process conditions. The increase in temperature within the reactor associated with the adiabatic process is determined, among other things, by the composition of the gas, the temperature of the gas supplied and the working pressure. Typically, the temperature rise in carrying out the methanation is in a range of 200 to 500 ° C.

The temperature of the gas supplied to the reactor is chosen so that the effectiveness of the catalyst can be used with a high degree of conversion. For this purpose, the supplied gas must already be preheated to a suitable inlet temperature. When carrying out the methanation process, it should be noted that methane formation within the catalyst bed is limited to a narrow reaction zone. The local area of the reaction zone depends on the operating time of the methanation process. At the beginning of the methanation process, methane formation first extends to the area of the catalyst bed which is close to the educt gas feed. With increasing operating time and progressive deactivation of the catalyst within the reaction zone, this then shifts in the gas flow direction from the inlet region to the outlet region of the catalyst bed.

The input temperature and the process parameters should be chosen so that the formation of Ni (CO) _{4 is} prevented. For example, in the methanation of CO-containing educt gas by means of nickel-containing catalysts, an inlet temperature of greater than 250 ° C is required. The methanation of C02-containing educt gas can also be carried out at lower inlet temperatures, for example at a temperature of 200 ° C. or even below 200 ° C. The implementation of the methanization with educt gas, which has a lower inlet temperature, is also possible in conjunction with nickel-free catalysts. Due to the mode of operation mentioned herein, that part of the catalyst bed that is near the reactor exit is exposed to a higher thermal load than that part of the catalyst bed that is near the reactor inlet. Here, the higher thermal stress of the catalyst material, which is located in the catalyst bed in the vicinity of the reactor outlet before it is used for methanation. To limit the thermal load of the catalyst, the temperature of the

Gas stream that emerges downstream of the reactor. In the corresponding manner, in carrying out the methanation process, the operating parameters are set in such a way that the temperature of the product mixture at the reactor outlet does not exceed an upper temperature limit. This can be achieved, for example, by diluting the educt stream with a certain proportion of product stream (recycle). Due to the dilution, the CO or CO 2 content in the educt current is reduced and the temperature increase caused by the exotherm is limited. It should be noted that all temperature data, which are referred to in the context of the present disclosure in relation to the methanation process according to the invention, always refer to the temperature of the reaction chamber-side obtained gas mixture, unless otherwise specified. The objects mentioned here, as well as other objects which are not mentioned here, are achieved by providing a process for the preparation of a catalyst for the methanation of CO and / or CO 2 -containing synthesis gases. The method relates to the impregnation of a starting material with a meltable metal salt, the production method comprising the following steps:

(i) contacting refractory metal salt and finely divided hydrotalcite-containing starting material,

(ii) thorough mixing of the refractory metal salt and the hydrotalcite-containing starting material,

(iii) thermal treatment of the refractory metal salt and hydrotalcite-containing starting material and tempering of the mixture under conditions such that the metal salt is in the form of molten metal salt, preferably at a temperature in the range of 30 to 250 ° C, more preferably at temperature in the range of 50 to 140 ° C,

(iv) Cryogenic calcination of the mixture at a temperature <500 ° C, preferably at a temperature in the range of 250 to 500 ° C, wherein the time for the low temperature calcination is preferably in the range of 0.1 to 24 hours , preferably less than 2 hours, in the case of continuous process control, the preferred calcination time is <1 hour.

(v) impression or shaping,

(vi) high-temperature calcination of the mixture at a temperature> 500 ° C, preferably at a temperature in the range of 500 to 1000 ° C, wherein the time for the high-temperature calcination is preferably in the range of 0.1 to 24 hours, be - preferably less than 2 hours, in the case of a continuous process, the preferred calcination time is <1 hour.

In a preferred embodiment, the method is characterized in that the calcining according to the process steps (iv) and (vi) is carried out using a defined heating rate and / or cooling rate, wherein the heating and / or cooling rate preferably in the range of 0.01 to 10 ° C per minute, more preferred is a range of 0.1 to 5 ° C per minute. In a preferred embodiment of the method, the molding step (v) is followed by a screening step.

It is further preferred that the metal salt fraction used in (i) contains a nickel salt, preferably nickel nitrate hexahydrate.

The hydrotalcite-containing starting material preferably has defined proportions of magnesium and aluminum, preferably at least 10 mol% of magnesium and at least 10 mol% of aluminum.

The subject of the invention also relates to a catalyst for the methanation of CO and / or CO 2 -containing synthesis gas, this catalyst being obtainable by the following steps.

(ii) intimate mixing of the metal salt and the hydrotalcite-containing starting material,

(iii) thermal treatment of the refractory metal salt and the hydrotalcite-containing starting material and tempering of the mixture under conditions such that the metal salt is in the form of a melt, preferably at a temperature in the range of 30 to 250 ° C, more preferably at a temperature within Range from 50 to 140

° C

(iv) cryogenic calcination of the mixture at a temperature <500 ° C, preferably at a temperature in the range of 250 to 500 ° C, the time for the cryogenic calcination preferably being in the range of 0.1 to 24 hours, preferably smaller 2 hours, in the case of a continuous process, the preferred calcination time is <1 hour.

(v) impression or shaping,

(vi) high-temperature calcination of the mixture obtained from the above steps at temperature> 500 ° C, preferably at temperature in the range of 500 to 1000 ° C, wherein time for the high-temperature calcination preferably in the range of 0.1 to

24 hours, preferably less than 2 hours, in the case of a continuous process, the preferred calcination time is <1 hour. Characteristic of the catalyst according to the invention is that the nickel is very highly dispersed on the carrier oxide and that the carrier oxide consists of or contains very small particles of MgA C. This results in catalysts with an improved property profile, which manifests itself both in improved sintering stability at high temperatures and improved coking behavior.

The production method according to the invention has advantages over those production methods which are based on precipitation methods. The process according to the invention does not give rise to any significant amounts of process water or the process according to the invention can also be carried out in a manner in which no process water is produced at all. At the same time as avoiding the formation of process water, precipitation reagents can also be saved. The problems associated with precipitation reagents, which is the result of contamination, can be prevented. With regard to the synthesis of the catalysts according to the invention, it should also be emphasized that an extremely energy-efficient and environmentally friendly process is provided due to the largely anhydrous production process.

Based on the total pore volume of the hydrotalcite-containing carrier used, preferably hydrotalcite, the amount of water used is preferably 100 100%, more preferably -i 90%, more preferably 70 70%, more preferably ≦ 50%, still more preferably ≦ 40% , more preferably <30%, and more preferably <20% of the total pore volume of the carrier. In a further preferred embodiment of the invention, the catalyst can be prepared without the addition of water, since the water necessary for the synthesis in this case is supplied solely by the water of hydration of the salt.

In addition, by means of the method according to the invention, high metal loading or deposition of metal-containing phase on the carrier oxide or deposition on a material which is a precursor for the carrier oxide can be achieved.

The type of mixing and the resulting compound of hydrotalcite-containing starting materials with the molten metal salt according to the method of the invention is extremely effective in terms of the application and incorporation of active components into the framework structure.

Without wishing to be bound by theory to any limitation of the present invention, based on structural studies of the formation mechanism, the following explanation for the formation of the catalyst according to the invention seems plausible: The treatment according to the invention of the hydrotalcite-containing starting material with the nickel containing nitrate melt at a temperature of less than or equal to 500 ° C leads to a nanostructuring of the material. From the layered preform th carbonate-containing precursor material magnesium is dissolved out. Together with the nickel, the hydrotalcite forms a nanocrystalline mixed crystal phase Ni _x Mg (i _-X ) 0 with a periclase-bunsenite structure. In addition, a Mg spinel phase and aluminum oxide phases form, which are partly amorphous and which only transform into crystalline spinel at higher calcining temperatures, in which the particles are nanocrystalline.

Catalysts are obtained which have nickel crystallites at temperatures up to 1000 ° C. which are less than 100 nm, preferably less than or equal to 70 nm and particularly preferably less than or equal to 40 nm, and which have high resistance to sintering and coking processes , The present nanostructuring of the material is particularly advantageous in terms of its catalytic properties. In particular, the material of the invention over the prior art has proven to be an advantageous catalyst, which is particularly suitable for the methanation of CO and / or CO 2 -containing synthesis gases.

In a preferred embodiment of the invention, the catalyst support comprises a magnesium spinel in intimate contact with a mixed oxide phase of nickel and magnesium. Characteristic of this catalyst or catalyst precursor according to the invention is that both the nickel-containing and the spinel-containing phase have very small crystallite sizes. In the case of the spinel-containing phase, the average crystallite size is <100 nm, preferably the average crystallite size is <70 nm, more preferably the average crystallite size is <40 nm.

In a further preferred embodiment of the invention, the phase composition of the catalyst according to the invention is characterized in that the intensity of the diffraction reflection at 43.15 ° ± 0.15 ° 2Θ (2 theta) (d = 2.09 ± 0.01 Å) is smaller or is equal to the intensity of the diffraction reflection at 44.83 ± 0.20 ° 2Θ (d = 2.02 ± 0.01 Å), more preferably the intensity of the diffraction reflection is at 43.15 ° ± 0.15 ° 20 (2 theta ) (d = 2.09 ± 0.01 Å) smaller than the intensity of the reflection at 44.83 ± 0.20 ° 2Θ (d = 2.02 ± 0.01 Å), and even more preferably that Intensity ratio of the two diffraction reflections l (43.15 °) / l (44.83 °) in a range of 0.3 to 1, 0, preferably from 0.5 to 0.99, more preferably from 0.6 to 0, 97, and more preferably from 0.7 to 0.92. An exemplary representation of a typical diffractogram (5-80 ° 2Θ) of a catalyst according to the invention is shown in FIG. It is not excluded that the catalyst material according to the invention or the catalyst precursor material also contains small amounts of Ni spinel phase and possibly also NiO. However, if a Ni spinel phase is present in the precursor material of the present invention, then it is believed that it will convert at the high pressures and high temperatures of the catalyst use of the present invention.

By means of the process according to the invention, all active metals can be applied to hydrotalcite or to hydrotalcite-containing starting material which is in the temperature range of 30 ° C to 250 ° C as a metal salt melt and in which the resulting catalysts have a catalytic activity as a methanation catalyst. In a preferred embodiment, promoters may be added to the metal salt melt and / or, in addition to the hydrotalcite-containing starting material, further carrier oxides, pore-forming agents or binders may be added to the synthesis system.

For the preparation of the catalyst according to the invention, preference is given to using metal salts which do not decompose during the melting process or in which the decomposition is kinetically strongly inhibited. Examples of such metal salts include nitrates, nitrites, halides, chlorates, bromates, iodates, sulfates, sulfites. Particularly preferred are nitrates, nitrites or molten salts containing nitrates and nitrites. The addition of certain additives to the melts - such as urea, ethylene glycol - is included.

As a cationic species, the meltable metal salts may include, for example, Na, K, Ca, Mg, Sr, Ba, Al, La, Y, Mo, W, Nb, Zr, Ti, Fe, Co, Ni, Cu, a platinum metal, and / or Ce contain. Suitable anionic species are, in particular, nitrogen-containing anions, such as nitrates and nitrites. In principle, however, it is also possible to use other anions such as halogens, sulfates and sulfites and other inorganic and organic anions known to the person skilled in the art. Preferably, the metal salts contain at least one nickel-containing or cobalt-containing component, preferably nickel nitrate or cobalt nitrate hydrate such as hexahydrate. Particularly preferred is nickel nitrate hexahydrate.

The term hydrotalcite-containing starting material in the sense of the present disclosure means that the material used contains as essential constituent at least one hydrotalcite-like compound and may optionally contain oxidic aggregate and / or minor constituents. The proportion of hydrotalcite-like compound and the oxidic aggregate is greater than 50 wt .-%, preferably greater than 70 wt .-% and especially preferably greater than 90 wt .-%. In addition to hydrotalcite-like compounds and oxidic additives, the hydrotalcite-containing starting material may also have minor constituents, for example consisting of metal salts, which serve, for example, to adjust the metal concentration of trivalent to divalent metal salt. Such secondary constituents of metal salts are less than or equal to 10% by weight, preferably less than or equal to 5% by weight. Hydrotalcite-like compounds are composed of polycations

Mixed hydroxides between divalent and trivalent metals, which have a layer structure. Hydrotalcite-like compounds are also referred to in the literature as Anionic Clays, Layered Double Hydroxides (= LDHs), Feitknecht compounds or bilayer structures. As divalent metals, for example, metals from the group of Mg, Zn, Cu, Ni, Co, Mn, Ca and / or Fe and as trivalent metals, for example, metals from the group AI, Fe, Co, Mn, La, Ce and / or Cr be used. In a preferred embodiment, the hydrotalcite-like compound is hydrotalcite. Preferably, the hydrotalcites used for the process according to the invention comprise magnesium as bivalent metal and aluminum as trivalent metal. Preferably, the metals of the hydrotalcites used consist predominantly of magnesium and aluminum.

The oxidic aggregate may also be mixtures, these preferably containing aluminum-containing compounds. Examples of such aluminum-containing oxidic additives include gibbsite, boehmite or pseudoboehmite. Typical contents of such aluminas, hydroxides or oxide hydrates may be between 30 and 95 percent by weight calculated on the basis of alumina. This corresponds to a molar proportion of aluminum based on total metal of 26 to 84 mol%. Particularly preferred are ranges of 50 to 80 weight percent calculated based on alumina. This corresponds to a molar proportion of aluminum based on total metal of 44 to 70 mol%. Most preferred is a range of from 60 to 75 weight percent based on alumina. This corresponds to a molar proportion of aluminum based on total metal of 53 to 66 mol%.

It is also characteristic that the hydrotalcite-like compounds and the oxidic aggregate have a very thorough mixing. The same applies to minor constituents, if they should be contained in the hydrotalcite-containing starting material.

Such mixing can be carried out, for example, by a physical mixing of hydrotalcite-like and aluminum hydroxide-containing powders. For example, be carried out by powder mixing in suitable technical equipment such as mixers. Such mixing methods are known to the person skilled in the art. Another possibility is to mix the hydrotalcite-like and the aluminum hydroxide-containing powders in suitable dispersants. For example, water, alcohols, such as methanol, ethanol, propanol, butanol, ethylene glycol and / or butanediol, and ketones, such as acetone or methyl ethyl ketone, can be used as the dispersing agent. It is also possible that the dispersants are present as mixtures and contain surface-active agents such as surfactants. Examples of such surfactants include polyethylene glycols, mersolates, carboxylates, long chain ammonium compounds such as CTAB. Another possibility of intimate mixing is the direct synthesis of a mixture of hydrotalcite-like and aluminum hydroxide-containing mixtures by precipitation reactions. Such methods can be carried out, inter alia, as described in DE 195 03 522 A1 on the basis of the hydrolysis of water-sensitive precursors, which allows a large number of possible compositions. Other alternative processes for the preparation of mixtures of hydrotalcite-containing and aluminum hydroxide-containing mixtures can also be carried out on the basis of precipitation reactions from aqueous media. Carbonate-containing precipitants may be used here, for example, or carbon dioxide-containing gas generators may be used. be applied under pressure to suitable precursor solutions of metal salts or hydroxides.

Examples of hydrotalcite-containing starting materials used in the invention are products of the company Sasol, which are commercially available under the trade name Pural MG (Pural MG 5 to Pural MG 70 are commercially available, wherein Pural MG 70 is a Mg-Al hydrotalcite without aluminum hydroxide admixture ) to be expelled. The intimate mixing of magnesium and aluminum-containing hydrotalcites with other carbonates, hydroxides or hydroxycarbonates is also included within the scope of the invention.

Hydrotalcites or hydrotalcite-like compounds of particular purity are preferably used for the process according to the invention. The process for preparing these hydrotalcite-like compounds which are particularly preferably used in the process according to the invention is described by J.P. van Berge et al. disclosed in DE 195 03 522 A1.

According to DE 195 03 522 A1, the hydrotalcites or hydrotalcite-like compounds are formed by the hydrolysis of metal alcoholates with water and subsequent drying of the precipitated hydrolysis products. The metal alkoxides are formed by reacting mono-, di- and / or trivalent alcohols with one or more divalent metals and / or one or more trivalent metals. The water used for the hydrolysis preferably contains water-soluble anions selected from the group consisting of hydroxide anions, organic anions, in particular alcoholates, alkyl ether sulfates, aryl ether sulfates and / or glycol ether sulfates and / or inorganic anions, in particular carbonate, bicarbonate, chloride, nitrate, sulfate and / or polyoxometalanions. The counterion used is preferably ammonium.

As hydrotalcite-containing materials, which are particularly suitable as starting materials for the preparation of the catalyst and which have been prepared by hydrolysis of metal alcoholates, are materials which are sold by the company Sasol under the trade name Pural MG5, Pural

MG20, Pural MG30, Pural MG50 and Pural MG70 can be sourced. It is the indication of the manufacturer, whereby the numerical value in the product name refers to the percentage weight content of MgO. In order to obtain a total weight of 100%, the proportion by weight of MgO must be supplemented with the content of Al2O3. It should be noted that the information given here is given based on the oxides, the samples also containing hydroxide groups and water. It is possible that the samples may also contain other anions, such as carbonate anions. It is also possible to obtain materials which have other MgO-to-A Os ratios. In particular with those products or materials with low magnesium contents, it is possible that they contain not only magnesium-aluminum-containing hydrotalcite but also fractions of finely dispersed aluminum hydroxide or hydrated oxide. A particularly preferred hydrotalcite-containing starting material Pural MG30, for example, consists of a mixture of hydrotalcite (ie, a component having a composition of Mg6Al2 (OH) i8 ^* 4H ₂ 0 or Mg6Al2 (OH) i6C03 ^* 4H ₂ 0) and boehmite, wherein the mixture has an overall AOS / MgO ratio close to seventy to thirty percent by weight. These numerals in the trade name of the product used herein refer to the calcined material and means that in this particularly preferred example the starting material has a boehmite content of about 55% by weight.

Instead of the hydrotalcite, which is particularly preferred according to the preparation process according to the invention as a constituent of the hydrotalcite-containing starting material, it is also possible to use other metal hydroxides or hydroxycarbonates as starting materials. Particularly preferred are those which can be prepared by the same synthesis method as hydrotalcites and hydrotalcite-like compounds. It is also essential to the invention that the hydrotalcite-containing starting material has a preferred Al / Mg ratio. In describing the composition of the hydrotalcite-containing starting material, considering the oxides contained therein (in calcined form), the preferred alumina / magnesia ratio (ie, the A Os / MgO ratio) is in a range of 0.5 to 20 by weight Base, with an alumina / magnesia ratio of 1 to 10 on a weight basis being more preferred.

The preferred Al / Mg ratio is in a range of 1.5 to 2.5 on a molar basis, with an Al / Mg ratio of 1.7 to 2.3 on a molar basis being more preferred. By high temperature calcination at temperatures greater than 500 ° C, the preferred hydrotalcite-containing starting material should preferably be convertible in significant proportions, more preferably almost completely, to a material having spinel or spinel-related structures or phase mixtures of such structures.

An important aspect of the invention also relates to the very thorough mixing of the hydrotalcite-containing starting material with the refractory metal salt, which provides close contact between the nickel species and the carrier precursor component and leads to an unexpectedly good stabilization of the nickel species. After calcination, as mentioned above, this leads to a mixed oxide phase of Ni _x Mg (i _-X ) 0 with x = 0.3-0.7, preferably 0.4-0.6. (The molar mass range for x = 0.3 - 0.7 corresponds to a NiO content of about 44 - 81 wt .-% and for x = 0.4 - 0.6, the NiO content is about 55 - 73.5 wt .-%.) Furthermore, a certain proportion of Ni spinel could be detected after calcination by XRD analysis.

The XRD results indicate that in the mixed oxide phase Ni _x Mg (i _-X ) 0, _magnesium species are depleted. The Mg species are incorporated in Ni spinel as a substitute for Ni species. A possible explanatory approach, which is not intended to limit the invention, would be that even at high temperatures some of the aluminum will be present further than alumina hydrate. Under reductive conditions at high temperatures, a precipitate tion of the metallic nickel from the mixed oxide phase Ni _x Mg (i _-X ) 0 take place, in which case the liberated magnesium reacts with the Aluminiumoxihydrat to magnesium-aluminum spinel. With regard to the molar ratio of metal species in the hydrotalcite-containing starting material MHT and metal species in the molten salt Ms, it can be said that the molar ratio of metals MHT / MS is always greater than 1. Preferably, the molar ratio MHT / MS is in a range of 15 to 1.5 and more preferably in a range of 10 to 3. The use of a preferred ratio is important to the conditions for good mixing of the components and a homogeneous coating to ensure the hydrotalcite and thus ensure the nano-structuring, in particular the high dispersion and fineness of the nickel or the mixed oxide of Ni and Mg and the fineness of the Mg spinel, the material according to the invention. In a preferred embodiment, the powdered hydrotalcite-containing material is heated prior to contacting with the refractory metal salt and, when brought into contact with the metal salt, has a temperature in the range of 30 to 250 ° C, preferably the temperature is in the range of 50 ° C to 140 ° C. The temperature required to melt the metal salt depends on the properties of the particular metal salt or metal salt mixture used. The metal salts which are particularly suitable for the process according to the invention have a melting point in the range from 30 to 250.degree. In one preferred embodiment of the process according to the invention, the hydrotalcite-containing starting material is brought into contact with the metal salt melt. In order to prevent the solidification of the metal salt melt during the contacting and the mixing with the hydrotalcite, it is advantageous to preheat the metal salts to a temperature which is at least 10 ° C., preferably 20 ° C., above the temperature of the melting point of the salts or salt mixture used lies.

When selecting the process parameters when contacting the powder with the melt, it should be noted that the water of crystallization of the hydrotalcite and the metal salt melt is subject to evaporation. The evaporation depends on the temperature, the gas exchange, the gas atmosphere and the time of the process. Complete evaporation of the water of crystallization may be undesirable, since thereafter decomposition of the salt or hydrotalcite may occur before the mixture is homogenized. The solidification of an area in the melt which has not yet been intimately mixed with the hydrotalcite-containing material impairs the homogeneity of the distribution of the metal species on the solid hydrotalcate-containing starting material. The time for the contacting should be as short as possible, ie preferably less than or equal to 30 minutes. Preferably, the gas atmosphere should contain a certain amount of water in order to suppress the decomposition of metal salt or the hydrotalcite-containing starting material during the mixing. The content of water vapor may here be, for example, in a range of 0 to 10 vol .-%.

It is advantageous to heat the hydrotalcite-containing starting material to a temperature which corresponds approximately to the temperature of the molten salt before it is brought into contact with the molten salt, in order to prevent uncontrolled solidification of the molten salt.

I. Contacting and mixing hydrotalcite with metal salt

First, it should be noted that the process step of contacting the hydrotalcate-containing starting material with the metal salt is not subject to any limitation. In the following, however, several embodiments of the contacting are listed, which are advantageous.

For example, the hydrotalcite-containing starting material can first be combined with the powdered metal salt at a temperature below the melting point of the salt and mixed before it is melted. The combination of substances takes place initially in the cold. The combination and mixing can be done in several steps or in a single step.

In another preferred embodiment of the process according to the invention, the pulverulent hydrotalcite-containing starting material is initially introduced into a receiver and the metal salt melt is added while the solid is agitated. The melt can be added in portions to the hydrotalcite in several steps or in a single step.

Again in another embodiment, which is also preferred, the hydrotalcite-containing starting material is first coated with the metal salt before it is then melted. In this case, for example, the hydrotalcite-containing starting material can first be suspended in water and combined with a metal salt-containing solution. The mixture of the hydrotalcite-containing starting material and the metal salt-containing solution forms a suspension which can be dried, for example by spray-drying.

In order to ensure intimate mixing of the meltable metal salt and the hydrotalcite-containing starting material, the components brought into contact with each other must be mixed and homogenized by means of mechanical mixing elements. As a mixer, for example, powder mixer, tumbler, kneader, etc. can be used. The person skilled in the art should be familiar with the appropriate technical means for mixing. Preferably, for the mixing step, the time duration is> 2 minutes, more preferred is a time duration> 10 minutes, and even more preferred is a time duration> 30 minutes. Preferably, the mixing according to step (ii) and the thermal treatment according to step (iii) are carried out simultaneously. During the mixing process, it is preferable that the material to be mixed is heated to prevent solidification or solidification of the molten salt.

II. Further process steps for the preparation of the catalyst

(A) The homogenized mixture of metal salt and hydrotalcite (or the hydrotalcite-containing starting material) is subjected to a cryogenic calcination. The low-temperature calcination is carried out by a thermal treatment of the homogenized

Mixture in a temperature range between 100 ° C to 500 ° C for a period in the range between 0.1 h and 24 h. The heating of the material is preferably carried out using a controlled heating rate. Preferably, the heating rate is less than 20 ° C / min, preferably less than 10 ° C / min, and more preferably less than 5 ° C / min.

The material obtained after the low-temperature calcination may be present as a finely divided powder or as a coarse-grained bulk material. To use the material as a bulk material catalyst, a shaping process may be necessary. As a shaping step, for example, division, grinding, tableting or extrusion can be performed.

(b) Preferably, the material calcined at low temperature is subjected to a molding process to obtain a molded material. This shaping process may include one or more of the following steps:

b.i) compacting, b.ii) crushing, b.iii) sieving and / or b ') tableting.

In a further variant of the method, the shaping process consists of an extrusion process. The melt-impregnated catalyst mass is processed, for example, with additives with an extruder to the desired moldings. When using a shaping process by means of extrusion, it is conceivable that the process step of the low-temperature calcination step (iv) does not have to take place. The process can be carried out in a manner in which the calcination takes place only after the extrusion in the form of a high-temperature calcination step. Generally precalcination is performed prior to extrusion.

(c) The molded material is always subjected to a high-temperature calcination process. The target temperature in the high-temperature calcination is in the range of greater than or equal to 500 ° C, preferably in the range of 500 to 1000 ° C. The duration of the high-temperature calcination, ie the temperature of the sample at the target temperature, is in the range of 0.1 to 24 h. (d) High temperature calcination may be carried out in the presence of an oxygen-containing atmosphere, preferably air. The heating of the sample to the target temperature is preferably carried out using a controlled heating rate, preferably the heating rate is less than 20 minutes and more preferably less than 10 ° C / min.

In the preparation of the catalyst according to the invention, it may be preferred that at least individual substeps of the preparation process are carried out in a continuous manner. It is particularly preferred, for example, to carry out the low-temperature calcination in a continuously operated rotary kiln.

In a further process step, the calcined catalyst may be exposed to a reductive gas atmosphere while heating, in order to reduce at least part of the metal species, preferably of the nickel. This thermal treatment is preferably carried out under a reductive gas atmosphere in the same reactor in which the catalytic process is carried out.

In an embodiment which is particularly preferred, the invention relates to a catalyst for catalyzing heterogeneous reactions, preferably the reaction of methane, carbon dioxide and water to synthesis gas comprising at least the three phases nickel-magnesium mixed oxide, magnesium spinel and aluminum oxide hydroxide and characterized in that the nickel-magnesium mixed oxide has an average crystallite size of <100 nm, preferably <70 nm, more preferably <40 nm, and the magnesium spinel phase has an average crystallite size of <100 nm, preferably <70 nm preferably <40 nm, the proportions of nickel in the range of 7 to 28 mol%, of magnesium in the range of 8 to 26 mol%, of aluminum in the range of 50 to 70 mol% and the BET surface area in the range of 10 - 200 m ² / g.

Particular preference is also given to an embodiment of the catalyst according to the invention which has a nickel content in the range from 6 to 30 mol% and a magnesium content in the range from 8 to 38 mol%, preferably in the range from 23 to 35 mol%. The aluminum content is preferably in the range of 50-70 mol%.

It should be emphasized that particularly powerful catalysts and thus particularly preferred embodiments of the invention are obtained when the physico-chemical properties of the catalysts have specific values.

In a preferred embodiment, the catalyst according to the invention is characterized in that its physicochemical properties selected from the group of phase composition according to XRD, BET surface area, average pore diameter and / or ramming weight have preferred values. The phase composition of a particularly preferred catalyst is characterized in that the intensity of the diffraction reflection at 43.15 ° ± 0.15 ° 29 (2 theta) (d = 2.09 ± 0.01 Å) is less than or equal to the intensity of the diffraction reflection 44.83 ± 0.20 ° 2Θ (d = 2.02 ± 0.01 Å), more preferably the intensity of the diffraction reflection is at 43.15 ° ± 0.15 ° 29 (2 theta) (d = 2, 09 ± 0.01 Å) is smaller than the intensity of the reflex at 44.83 ± 0.20 ° 29 (d = 2.02 ± 0.01 Å), and even more preferably, the intensity ratio of the two diffraction peaks is l (43, 15 °) / l (44.83 °) from 0.3 to 1.0, preferably from 0.5 to 0.99, more preferably from 0.6 to 0.97, and most preferably from 0.7 to 0 , 92nd A diffractogram (5-80 ° 29) of a catalyst according to the invention with molar ratios of Ni / Mg / Al in the ratio of 14/29/57 is shown by way of example in FIG.

A particularly preferred embodiment of the catalyst has a BET surface area whose value is in the range from 10 to 200 m ² / g, preferably from 15 to 150 m ² / g, more preferably from 20 to 100 m ² / g, even more preferably from 30 to 80 m ² / g, more preferably from 30 to 78 m ² / g and especially preferably from 30 to 76 m ² / g. The BET specific surface area was determined according to DIN 66131.

In addition, a preferred embodiment of the catalyst also has a characteristic ramming weight which is preferably <1500 g / L, more preferably <1350 g / L, and still more preferably <1 100 g / L. The determination of the characteristic ramming weight was carried out by means of a ramming volume STAV 2003 from JEL. For the measurement, a 0.5-1.0 mm split fraction of the catalyst was used.

III. Method of methanation

Another and essential aspect of the invention relates to a process for methanation, preferably high-temperature methanization, which is characterized by the features set forth in claims 7 to 14 features. The preparation of the catalyst according to the invention is carried out according to one of claims 1 to 4 or the methanation catalyst according to the invention can be prepared according to claims 5 to 6.

The methanation process according to the invention can be carried out over a temperature range from 300.degree. C. to 900.degree. It is preferred to carry out the methanation method according to the invention in a temperature range above 500 ° C, more preferably, the implementation of the method in a temperature range of 500 ° C to 800 ° C, even more preferred is a temperature range of 600 ° C 750 ° C.

Particularly noteworthy here is the high thermal stability of the catalyst material in carrying out the methanation process according to the invention in comparison to carrying out the process with a catalyst material which is known from the prior art. Due to the high thermal stability of the catalyst according to the invention Its deactivation is relatively low even under high temperature load. By means of the method according to the invention, the service life of the catalyst can be significantly extended, which leads to an improvement in the economy of the process. In addition to the improved thermal stability of the catalyst, the catalyst of the invention also has a higher mechanical hardness over comparable prior art catalysts. Due to the increased mechanical stability of the inventive method can be made at high process pressures. The process pressures can be in a range of 10 to 50 bar, usually between 20 and 30 bar, for example 25 bar.

The coking tendency is low in connection with the process according to the invention, which is conducive to obtaining the high activity.

A preferred embodiment of the process according to the invention relates to the methanation of synthesis gas which has a h / CO ratio in the range from 2.5 to 4, more preferably in the range from 3 to 3.5. In a particularly preferred embodiment of the process according to the invention, the synthesis gas is provided, for example, from a coal gasification (for example Lurgi process). Usually, this synthesis gas originating from the coal gasification is first purified before the methanization. For example, the sulfur-containing components and much of the CO2 are removed prior to performing the methanation.

The Lurgi process is characterized by the fact that a relatively high proportion of methane is already present in the synthesis gas. After purification, the dry synthesis gas contains the following main components in the following typical concentrations in volume fractions: -35 vol% CH ₄ , ~ 45 vol% H2 and -15 vol% CO, secondary components may be: in particular CO2, but also nitrogen or higher hydrocarbons , for example ethane. In terms of process technology, the reaction starting temperature is limited by reducing the CO content in the synthesis gas by recycling part of the product stream in order to limit the exothermicity of the overall reaction.

The catalyst is thus treated according to Lurgi process with a synthesis gas of the following composition: CH ₄ content in the range of 36 to 42 vol .-%, H ₂ content in the range of 35 to 45 vol .-%, CO content in the range of 9 to 12 vol.%, H 2 O content in the range of 8 to 12 vol.% and CO 2 in the range of 0 to 3 vol.%.

Due to the high temperature stability of the catalyst according to the invention can be dispensed in a further embodiment, the recycle stream and directly the purified synthesis gas from the coal gasification, which was previously subjected to the usual purification steps used. The synthesis gas may also contain other components - such as nitrogen, argon - that do not participate themselves in the methanation reaction. The sulfur content of the synthesis gas should be as low as possible to avoid poisoning of the nickel centers by sulfidation.

By means of the method according to the invention, it is possible to achieve a high methane yield per nickel atom, which is located on the catalyst support or contained therein. It can be assumed that this is related to the specific structure of the catalyst material and the good accessibility of the active sites.

The inventive method is operated in a driving manner, the GHSV in the range of 500 to 50,000 r ^1, preferably in a range from 1,000 to 15,000 r ^1, and particularly preferably is in a range of 1000 to 5000 hr. ¹

The use of the catalyst according to the invention in the form of shaped bodies is also advantageous, in particular, with regard to carrying out the methanation reaction, since it is possible by means of the shaped body to achieve a lower pressure drop within the reactor than by means of a bulk material catalyst. A particular suitability of the catalyst material in connection with the use in methanation reactions is also based on the high mechanical stability of the material.

With regard to shaped bodies, they have a nearly identical shape and have a certain minimum extension in each direction of the three spatial axes, the extent in each direction of a spatial axis being greater than 2 mm.

Examples

production method

By way of example M1, the process according to the invention for the preparation of the catalyst is illustrated in more detail. First, 41 1, 4 g of powdered nickel nitrate hexahydrate, which had been triturated by means of mortar and pestle to a finely divided powder, and 600 g of hydrotalcite (namely Pural MG30 from Sasol) was intimately mixed to prepare a premix of metal salt and hydrotalcite and introduced into the rotary tube of a rotary kiln. The masterbatch was heated to 80 ° C in the rotary kiln and held there for 1 hour at 80 ° C with the rotary tube and the premix therein moved at two revolutions per minute and an air flow of 150 L / h was passed through the rotary tube , The amount by weight of the premix obtained after cooling was 886 g.

Subsequently, 400 g of the sample obtained in the premix was subjected to cryogenic calcination. For this purpose, the sample was placed in a quartz glass flask, this mounted in a rotary kiln and heated therein at a heating rate of 5 ° C / min to a target temperature of 425 ° C and heated at 425 ° C for one hour. During the thermal treatment of the sample, the quartz flask was moved at a rotation frequency of 12 revolutions per minute while simultaneously passing air through the piston at a flow rate of 1 L / min.

The sample obtained in the low-temperature calcination was mixed with graphite powder and pressed by means of a stamp press into tablets. The graphite powder serves as a lubricant, and instead of the graphite, it would also be possible to use stearic acid or magnesium stearate. The tablets produced by means of the press used here had a diameter of 4.75 mm and a thickness of about 4-5 mm. The lateral compressive strength of the tablets was 60-70 N.

The tablets were comminuted with a screen mill and forced through a sieve to obtain a split fraction of <1.6 mm. The precompacted material was again tableted, yielding tablets with a diameter of 4.75 mm and a thickness of 3-4 mm. The tablets had a lateral compressive strength of 130-150 N.

The thus-obtained sample material was calcined in a muffle furnace while passing air at 850 ° C for one hour and then cooled to room temperature. The sample material positioned in the muffle furnace was heated from room temperature to 850 ° C using a heating rate of 5 ° C / min. The air which was passed through the furnace during the heating phase, the calcination and the cooling phase had a flow rate of 6 L / min. The calcined sample material was subjected to chemical and physical characterization. In the elemental analysis, the following composition was found: 21 wt .-% NiO, 53 wt .-% Al ₂ 0 ₃ and 23 wt .-% MgO, wherein the information refers to the oxides. In the XRD analysis, magnesium spinel (MgA 0 ₄ ) or MgNiO 2 were detected as phases. Using the Scherrer equation, the mean crystallite size of the phases was determined using the reflections. The result was that the spinel particles had a crystallite size of 9.0 nm and the mixed oxide particles had a crystallite size of 16.5 nm.

The sample material was characterized by nitrogen sorption and Hg porosimetry. The sample material had a BET surface area of 67 m ² / g. The sample material had a Hg

Pore volume of 0.31 mL / g and a pore surface of 83 m ² / g, the sample material had a monomodal pore structure. On average, the pores of the sample material had a pore diameter of about 15 nm. A further catalyst M2 was prepared analogously to M1, this was calcined at a temperature of 950 ° C. In the elemental analysis, the following composition was found: 21 wt .-% NiO, 53 wt .-% Al ₂ 0 ₃ and 23 wt .-% MgO, the information on refers to the oxides. In the XRD analysis, magnesium spinel (MgA C) or MgNiO 2 were detected as phases (see FIG. 1). Using the Scherrer equation, the mean crystallite size of the phases was determined using the reflections. The result was that the spinel particles had a crystallite size of 14 nm and the mixed oxide particles had a crystallite size of 13 nm.

The sample material was characterized by nitrogen sorption and Hg porosimetry. The sample material had a BET surface area of 58 m2 / g. The sample material had a Hg pore volume of 0.41 mL / g and a pore surface area of 48 m ² / g, with the sample material having a monomodal pore structure. On average, the pores of the sample material had a pore diameter of about 34 nm.

Comparative example

As comparative example VM1, the catalytic properties of a catalyst which had been produced by means of the precipitation process were tested. To prepare this catalyst, 175.7 g of hydrotalcite (Pural MG30 from Sasol with a loss on ignition of 34.2% by weight) were initially introduced into a container containing 6 L of deionized water, which had been preheated to 48.degree. In a separate container, a solution of nickel nitrate salt and aluminum nitrate salt was prepared by dissolving 612.8 g of nickel nitrate hexahydrate and 313.1 g of aluminum nitrate nonahydrate in 509.2 g of deionized water and heating the solution to 48 ° C. The precipitating reagent used was an aqueous soda solution which had a soda content of 20% by weight and which was also preheated to 48 ° C.

To precipitate the metal species, the solution of the metal nitrate salts and the soda solution were simultaneously dropped into the aqueous hydrotalcite dispersion container. The template with the aqueous hydrotalcite dispersion was heated to 48 ° C and the dispersion with a stirrer durmischt. During the addition of the salt solution and the precipitating reagent into the aqueous receiver, the pH of the aqueous dispersion was controlled and the addition of the soda solution was controlled to maintain the pH in the receiver at 8.0. After the complete transfer of the metal salt solution into the original container, a total of 3.5 L soda solution had been used as the precipitation reagent.

After completion of the precipitation, the suspension obtained by the precipitation process was stirred for a further 15 minutes and then the precipitate was filtered off with suction by means of a suction filter. The filter cake was washed with deionized water, at the same time the nitrate content of the filtrate was determined. The temperature of the water used for washing was 20 ° C. The washing process was stopped as soon as nitrate ions could no longer be detected in the filtrate (the nitrate content was thus below the detection limit of 10 ppm). To wash the filter cake, an amount of water of 350 L was needed. The washed filter cake was then dried at 120 ° C for a period of 16 h in a drying oven. The dried solid was heated for 5 h at 700 ° C in a muffle furnace. The muffle furnace and the solid contained therein were heated to 700 ° C at a controlled heating rate, and during heating, an air stream was passed through the muffle furnace at a flow rate of 20 L / min. The solid obtained in this calcination was mixed with 3% by weight of graphite powder and the mixture was compressed to tablets with a stamping press. The tablets obtained had a diameter of 4.75 mm and a thickness of about 2 mm. The tablets were comminuted with a sifting mill and forced through a sieve with a mesh size of 1 mm to obtain a split fraction with particles smaller than 1 mm.

The fracture fraction obtained after precompacting was mixed with 10% by weight of Puralox (Bohmite from Sasol) and 3% by weight of graphite, intimately mixed and subjected to tableting. The resulting tablets had a diameter of 4.75 mm and a thickness of about 3 to 4 mm. The lateral compressive strength of the tablets was 100 N.

By chemical analysis, the composition of the tablets or the calcined samples was determined, which has a Ni content of 29.8 wt .-%, an Al content of 21, 1 wt .-%, an Mg content of 4.7 Wt .-% and a carbon content of 3.1 wt .-% had. At a temperature of 900 ° C, the samples showed an ignition loss of 7.3% by weight. With regard to the oxides, the following composition was determined for the calcined precipitate: 41% by weight NiO, 43% by weight Al ₂ O ₃ , 8.4% by weight MgO and 3.3% by weight C.

The XRD analysis of the calcined sample identified nickel oxide (NiO) and nickel spinel (Ni-AI2O4). The nickel oxide particles had an average crystallite size of 5.0 nm, which was determined from an analysis of the respective reflections using the Scherrer equation.

The sample material had a BET surface area of 165 m ² / g. The sorption test was carried out with nitrogen. In an analysis of the sample material with Hg porosimetry, a pore volume of 0.33 mL / g was determined. The sample material showed a bimodal pore structure: the majority of the pores had a mean pore diameter of 6 nm and the small part of the pores a mean pore diameter of 30 nm. On average, a pore diameter of 11 nm was determined. A calculation of the surface area of the sample material based on the Hg analysis revealed a surface area of 123 m ² / g.

catalyst testing

The catalysts Example M1, Example M2 and Comparative Example VM1 were sequentially exposed to the process conditions of CO methanation in a pilot reactor to produce synthetic natural gas to further characterize the performance characteristics of the catalysts in terms of CO methanation. The experimental reactor was equipped with a equipped with 50 ml_ of the respective catalyst sample before the individual tests (ie example M1, example M2 or comparative example VM1). When filled, the catalyst samples were in the form of tablets. The catalyst built into the tube reactor and the test stand Comparative Example VM1 was first subjected to activation. For this purpose, the catalyst VM1 was heated in the presence of a stream of nitrogen to 280 ° C and then exposed for 16 h a reductive atmosphere by the nitrogen stream 5 vol .-% Hb were admixed. The catalysts according to the invention, Example M1 and Example M2, were not activated but were incorporated and started directly in the oxidic form. It should be mentioned as an advantage that a start-up of the method according to the invention is also possible without activation of the catalysts.

Following activation under the reducing atmosphere in the case of VM1 or directly after incorporation in the case of M1 or M2, the methanation reaction was started, with the catalyst exposed to a feed gas stream preheated to 280 ° C. The feed gas stream had a flow rate of 1202 NL / h and comprised the six components hydrogen, CO, CO2, CH4, N2 and H2O, which were composed of the respective individual volume flows in the following ratio: 468 NL / h hydrogen, 132 NL / h CO , 12 NL / h C0 ₂ , 456 NL / h CH ₄ , 24 NL / h N ₂ and 1 10 NL / h H ₂ 0. The experimental parameters chosen here and the plant configuration led to the fact that during the execution of the methanation a Reaction temperature in the reactor, which was in the range of 600 to 620 ° C. The reactant gas stream and the product gas stream were each characterized in the water-free state by GC analysis. The characterization of the educt gas stream was carried out before the addition of the water and the characterization of the product gas stream after condensation of the water. Tables 1 and 2.A give a summary of measured data representing the gas compositions of the reactant and product streams. The respective values form the average values which were determined over the individual values during the entire test duration.

The catalyst of the invention (Example M1) showed a CO conversion of 93% and the comparative example (VM1) showed a CO conversion of 88%. Thus, the CO conversion of Example M1 was 5% higher than that achieved with Comparative Example VM1. In addition, the catalyst according to the invention (Example M1) was able to provide the high conversion over a period of more than 1200 h, whereas the catalyst from Comparative Example VM1 already showed a significant loss of activity after approximately 300 h, which led to the discontinuation of the experiment. It is also noteworthy that, in addition to the higher activity and long-term load-bearing capacity, the catalyst from Example M1 also had a significantly higher mechanical resistance than the catalyst from Comparison Example VM1. The catalysts of Example M1, Example M2 and Comparative Example VM1 were removed from the reaction tube after the completion of the methanation test and subjected to characterization. The samples were the expansion catalyst Example M1, the expansion catalyst Example M2 and the expansion catalyst Comparative Example VM1.

The catalyst of the invention (Example M2) showed a higher CO conversion of 95%. Thus, the CO conversion achieved on the catalyst of Example M2 was 2% higher than that achieved with the catalyst of Example M1. In addition, the catalyst according to the invention (Example M2) was able to deliver the high conversion over a period of more than 480 h, whereas the catalyst from Comparative Example VM1 already showed a significant loss of activity after approximately 300 h, which led to the discontinuation of the experiment. The catalyst from Example M2 also had a higher mechanical resistance than the catalyst from Example M1 with a lateral compressive strength of 168 N.

Table 1 shows the composition of the educt gas before it was contacted with the catalyst and the product gas obtained after contacting with the inventive catalyst Example M1. The data for the individual components refer to% by volume. The duration of the catalyzed experiment was 1200 h.

Input gas output gas

CH ₄ 37.1 53.0

H ₂ 41, 0 22.8

CO 9,7 0,7

co ₂ 1, 1 3.0

H ₂ 0 9.1.1 18.2

N ₂ 2,0 2,3

Table 2.A shows the reactant and product gas composition of the methanation test of the comparative catalyst (Comparative Example VM1) over a test period of 300 h. After this time, a decline in turnover was observed, i. H and CO content in the product stream increased and the CH content decreased. The details of the individual components are given in% by volume.

Table 2.B shows the composition of the educt gas before it was contacted with the catalyst and the product gas obtained after contacting with the inventive catalyst Example M2. The data for the individual components refer to% by volume. The duration of the catalysis experiment was 480 h.

Input gas output gas

CH ₄ 37.9 55.1

H ₂ 41, 7 21, 2

CO 9,9 0,5

co ₂ 1, 1 2,4

H ₂ 0 8.5 18.2

N ₂ 1, 9 2.6

Table 3 shows a summary of the parameters determined by XRD, nitrogen sorption, and Hg porosimetry analysis of expanded catalyst Example 1 (after 1200 h of testing) and maturing catalyst VM1 (after 300 h of testing). The Scherrer equation was used to estimate the crystallite size.

Physical characterization

The XRD analyzes were performed on a Bruker / AXS D8 Advance Series 2 using CuK alpha source (0.154nm wavelength at 40kV and 40mA). The measurements were made over the measuring range: 5-80 ° (2Theta), 0.02 ° steps with 4.8 seconds / step. The structural analysis software TOPAS (Bruker AXS) was used to determine the mean crystallite sizes of the individual phases. Figure 4 shows a plot of the powder diffractogram plotted on catalyst sample Example M2 after high temperature calcination.

Claims

claims

Process for the preparation of a methanation catalyst by impregnating a starting material with a refractory metal salt, the production process comprising the following steps:

(i) bringing into contact refractory metal salt and finely divided hydrotalcite-containing starting material,

(ii) thorough mixing of the meltable metal salt and the hydrotalcite-containing starting material,

(iii) thermal treatment of the refractory metal salt and the hydrotalcite-containing starting material and storage of the mixture under conditions such that the metal salt is in the form of molten metal salt, preferably at a temperature in the range of 30 to 250 ° C, more preferably at a temperature in the range of 50 to 140 ° C,

(iv) cryogenic calcination of the mixture at a temperature of <500 ° C, preferably at a temperature in the range of 250 to 500 ° C, wherein the time for the cryogenic calcination is preferably in the range of 0.1 to 24 hours, preferably less than 2 Hours, in the case of a continuous process, the preferred calcination time is <1 hour.

(v) impression or shaping,

(vi) high-temperature calcination of the mixture at a temperature> 500 ° C, preferably at a temperature in the range of 500 to 1000 ° C, wherein time for the high-temperature calcination is preferably in the range of 0.1 to 24 hours, preferably less than 2 hours In the case of a continuous process, the preferred calcination time is <1 hour.

A method according to claim 1, characterized in that the calcination in steps (iv) and (vi) is carried out using a temperature program in which the heating and / or cooling rate is in the range of 0.01 to 10 ° C per minute and a range of 0.1 to 5 ° C is preferred, and further preferred that the performance of process step (ii) occurs simultaneously with the performance of step (iii).

Method according to one of the preceding claims, characterized in that the thermal treatment of step (iii) and the low-temperature calcination of the mixture according to step (iv) takes place in a cohesive process step.

Method according to one of the preceding claims, characterized in that the meltable metal salt contains a nickel salt and / or cobalt salt, preferably in the form of a hexahydrate, more preferably the meltable metal salt is nickel nitrate hexahydrate; and where it is preferred that the fusible metal salt is present in the performance of step (i) in the form of the molten metal salt.

Catalyst for carrying out methanation reactions obtainable by

(iii) thermal treatment of fusible metal salt and hydrotalcite-containing starting material and storage of the mixture under conditions such that metal salt is in the form of melt, preferably at a temperature in the range of 30 to 250 ° C, more preferably at temperature in the range of 50 up to 140 ° C,

(iv) cryogenic calcination of the mixture at a temperature <500 ° C, preferably at a temperature in the range of 250 to 500 ° C, wherein the time for the cryogenic calcination is preferably in the range of 0.1 to 24 hours, preferably smaller 2 hours, in the case of a continuous process, the preferred calcination time is <1 hour.

(v) impression or shaping,

(vi) high-temperature calcination of the mixture obtained from the above steps at temperature> 500 ° C, preferably at temperature in the range of 500 to 1000 ° C, wherein time for high temperature calcination is preferably in the range of 0.1 to 24 hours, preferably less than 2 hours, in the case of a continuous process, the preferred calcination time is <1 hour.

Catalyst for carrying out methanization reactions according to claim 5, characterized in that the calcination in steps (iv) and (vi) takes place in the presence of an oxygen-containing atmosphere, preferably air, and preferably the rate of calcination less than or equal to 20 ° C / min, preferably less than or equal to 10 ° C / min.

Process for carrying out methanation reactions, characterized in that a catalyst according to claims 5 to 6 or a catalyst prepared by the process according to claims 1 to 4 is used and the methanation process in a temperature range from 300 ° C to 900 ° C. , preferably from 500 ° C to 800 ° C, more preferably from 600 ° C to 750 ° C is carried out and the process pressure in the range of 10 to 50 bar, preferably from 20 to 30 bar.

Process for methanation, preferably high-temperature methanization, comprising the following steps, a.1) treatment of a catalyst precursor material in a reducing gas atmosphere, preferably in the methanation reactor prior to carrying out the methanation,

a.2) heating a CO and / or CO 2 -containing synthesis gas before contacting with the methanation catalyst,

a.3) contacting the CO- and / or CO 2 -containing synthesis gas with a methanation catalyst according to claims 5 to 7 or a methanation catalyst prepared by the process according to claims 1 to 4.

Method of methanation according to claim 8, characterized in that the temperature of the methanation catalyst in contacting with the synthesis gas is in a range of 300 ° C to 900 ° C, preferably the temperature of the methanation catalyst is in a range of 500 ° C to 800 ° C, more preferably in the range of 600 ° C to 750 ° C.

Method for methanation according to claim 8 or claim 9, characterized in that the synthesis gas used has a h / CO ratio which is in the range of 2.5 to 4, preferably the h / CO ratio is in a range from 3 to 3.5.

A methanation process according to any one of claims 8 to 10, characterized in that the synthesis gas used has a ChU content greater than or equal to 10% by volume, preferably the ChU content is in a range from 20 to 50 vol. %, more preferably, the ChU content is in a range of 35 to 45 vol%.

12. Method for methanation according to one of the preceding claims 8 to 1 1, which is characterized in that the synthesis gas used has a water vapor content of 2 to 16 vol .-%, preferably from 6 to 14 vol .-% and more preferably from 8 to 12 vol .-% has.

Process for the methanation according to one of the preceding claims 8 to 12, characterized in that the synthesis gas used has at least the following components and parts by volume: ChU content in the range of 36 to 42 vol .-%, H ₂ content in the range of 35 to 45 vol.%, CO content in the range of 9 to 12 vol.%, H O content in the range of 8 to 12 vol.% And CO 2 content in the range of 0 to 3 vol.% ,

14. A method for methanation according to any one of the preceding claims 8 to 13, which is characterized in that a product stream having a CO content <2 vol .-%, preferably with a CO content <1 vol .-% is obtained and / or preferably at least part of the product stream obtained is fed again into the educt fluid stream and contacted once more with the catalyst.