WO2018141646A1

WO2018141646A1 - Nickel methanation catalysts doped with iron and manganese

Info

Publication number: WO2018141646A1
Application number: PCT/EP2018/051993
Authority: WO
Inventors: Klaus Koehler; Oliver THOMYS; Kai-Olaf Hinrichsen; Franz KOSCHANY; Thomas Burger
Original assignee: Clariant Produkte (Deutschland) Gmbh; Wacker Chemie Ag; Technische Universität München
Priority date: 2017-01-31
Filing date: 2018-01-26
Publication date: 2018-08-09

Abstract

The invention relates to a catalyst for the methanation of carbon monoxide and/or carbon dioxide, comprising aluminium oxide, an Ni-active mass and Fe and Mn, characterised in that the molar Ni/Fe-ratio in the catalyst is 5.0 to 10.0, preferably 5.3 to 7.0 and particularly preferably 5.4 to 5.7. The catalyst preferably has a molar Ni/Mn-ratio of 5.0 to 32.0, preferably 9.0 to 10.0. The catalyst is characterised by improved activity combined with improved stability. The invention also relates to a method for producing a catalyst according to the invention, comprising the following steps: a) coprecipitation from a solution containing AI, Ni, Mn and Fe in the dissolved form, in order to obtain a precipitate; b) isolation of the precipitate from step a), c) drying of the isolated precipitate from step b); and d) calcination of the dried precipitate from step c).

Description

Iron and manganese-doped nickel methanation catalysts

The energy supply through the so-called renewable energy photovoltaic and wind energy suffers from the problem of weather and daytime dependent fluctuations in electricity production. To ensure security of supply, a way has to be found to intercept weather and time-dependent fluctuations in electricity production. One potential method of chemically storing the energy is the power-to-gas process, which uses excess electricity to split water into hydrogen and oxygen by electrolysis. Hydrogen in which the energy is stored after the electrolysis of water can itself be stored only with great effort or transported to the consumer. After the power-to-gas process, the hydrogen is therefore converted in a further step with carbon dioxide, which acts in the atmosphere as a greenhouse gas harmful to the climate, in the methanation reaction to methane and water. Methane can be easily stored in existing infrastructures, which have capacities for storage in the range of several months, can be transported almost lossless over longer distances and can be reconverted in times of energy demand. The methanation reaction, which is associated with high energy release and usually catalyzes, forms the heart of the process. The high exothermicity of the reaction (-165 kJ / mol) gives rise to two direct problems. On the one hand, the thermodynamic equilibrium limits the maximum achievable methane yield at high temperatures. On the other hand, a high level of purity is necessary for the feeding of methane into the natural gas network. As a result, there is a demand for high catalyst activity and selectivity so that higher yields of methane can be achieved at industrially applied reaction pressures at low temperatures.

The high exothermicity of the methanation reaction may cause hot spot formation in the reactor under adiabatic reactor operation. This leads to the development of high temperatures locally, which can damage the catalyst. There is therefore a strong interest in developing catalyst systems that are as stable as possible in order to minimize costs for catalyst replacement / downtime and material costs. Furthermore, there is a need for highly active and selective catalysts for the methanation reaction of C0 ₂ . For the methanation reaction mainly nickel-based catalysts are used, but there are also approaches with other active metals, such as Ru thenium or rhodium. In addition to aluminum oxide, the oxides of silicon, titanium and zirconium are also used as carriers. Such systems are described, for example, in the publications CN 104043454 A, CN 103480375 A, CN 102091629 A, CN 104888783 A and WO 20081 10331 A1.

Additionally one finds catalysts, which contain not only an active metal, but are promotiert. It is known from the literature that a promotion with iron or manganese can have a positive influence on the catalyst performance. A doping of nickel-based methanation catalysts with manganese is described, for example, in CN 103464163 A, CN 103752315 A, CN 102600860 A, CN 102553610 A, CN 102527405 A, CN 102513124 A, CN 102463120 A and CN 1024631 19 A and by Zhao et al. , Journal of Natural Gas Chemistry (2012), 21 (2), 170-177. A doping of nickel-based methanation catalysts with iron is described, for example, in CN 104399482 A, CN 104399466 A, CN 104209127 A, CN 102872874 A, CN 101703933 A, CN 101537357 A and WO 2007025691 A1 and by Pandey et al., Journal of Industrial and Engineering Chemistry (2016), 33, 99-107 and Gao et al., RSC Advances (2015), 5 (29), 22759-22776.

Known from the prior art are nickel-alumina catalysts which may be promoted with several elements, including CN 102259003 A and in particular CN 103706366 A, CN 104028270 A and CN 101745401 A. CN 103706366 A describes a catalyst comprising 15 to 55% an active component, 1 to 6% of a 1. catalytic promoter, 3 to 15% of a second catalytic promoter and, moreover, a catalytic support, wherein the active component is nickel oxide, the catalytic support is Al ₂ O ₃ , the 1. the catalytic promoter is one selected from lanthanum oxide, cerium oxide or samarium oxide, the second catalytic promoter is at least one of magnesium oxide, manganese oxide, iron oxide and zirconium oxide. The production method comprises the steps of dissolving a reducing agent in water to obtain a reducing solution, mixing in nickel nitrate, aluminum nitrate, the 1. Metal salt and the 2nd metal salt in water to obtain a raw material solution, and adding the reducing mixture to the raw material solution with uniform stirring to obtain a 1. To obtain solution, adding an alkali solution to the 1st Solution with vigorous stirring to obtain a 2nd solution, transfer to a sealed reactor, and conduct a reaction at 100 to 200 ° C for 10 to 15 hours, cooling Room temperature, filtering and washing to a pH of 6 to 7, drying at 80 to 120 ° C for 4 to 30 hours and calcining at 300 to 550 ° C for 2 to 12 hours to obtain a catalyst in which the reducing agent is one selected from formaldehyde, hydrazine hydrate, sodium hypophosphite and ascorbic acid, wherein the 1. The metal salt is one selected from lanthanum nitrate, cerium nitrate and samarium nitrate, the second metal salt is at least one selected from magnesium nitrate, manganese nitrate, iron nitrate and zirconium nitrate, the alkali solution is an aqueous solution of sodium carbonate, sodium hydroxide, potassium carbonate, ammonium carbonate, urea or NH ₃ ^* H ₂ 0 is. The catalyst may be mixed with a binder (calcium aluminate), a lubricant (graphite) and water and then pressed in particulate form. The catalyst is suitable for methanating coal gas at high temperature and high pressure to produce synthetic natural gas.

CN 104028270 A discloses a methanation catalyst comprising 5 to 60 wt .-% of a catalytically active NiO component, based on the total weight of the catalyst and otherwise Al ₂ 0 ₃ , which also 1 to 25 wt .-%, based on the total weight of Catalyst, may participate in participating component M, wherein the co-acting component M is selected from one or more oxides of the metals Ce, Ca, Co, La, Sm, Zr, Ba, Mn, Fe, Mo, Ti and Cu. The document also provides a method of preparing the methanation catalyst which comprises admixing the precursor of the catalytically active component, precursor of the co-acting component M, and a catalyst support according to the proportion in the methanation catalyst composition of an organic fuel and thoroughly mixing and drying to form a gel-like product, carrying out a combustion reaction, cleaning and drying to obtain the final product.

CN 101745401 discloses a supported sulfur-resistant methanation catalyst characterized by comprising a main metal M as the active component, a second metal M1 as an excipient and S as a support material, wherein the weight ratio between M1, M and S is between 0.01 to 39 : 1 to 30: 0.01 to 90, M is one or more of Mo, W and / or V, the second metal M1 is one or more of Fe, Co, Ni, Cr, Mn, La, Y or / and Ce and the support S is Zr0 ₂ , Al ₂ 0 ₃ , MgO or Ti0 ₂ . The supported sulfur-resistant methanation catalyst is prepared by a sol-gel method. It is an object of the invention to provide a methanation catalyst for the methanation of carbon monoxide and / or carbon dioxide, which has a high selectivity compared to the catalysts of the prior art improved activity and stability.

This object is achieved by a catalyst for the methanation of carbon monoxide and / or carbon dioxide, comprising aluminum oxide and a Ni active composition, and Fe and Mn, characterized in that the molar Ni / Fe ratio in the catalyst is 5.0 to 10.0, preferably 5.3 to 7.0 and more preferably 5.4 to 5.7.

The stability of the catalyst in the sense of the application means the property of the catalyst to deactivate as little as possible under reaction conditions and to maintain the high selectivity / activity as far as possible. The alumina need not be stoichiometric Al 2 O 3, but may be a non-stoichiometric alumina.

It is preferred that the molar Ni / Mn ratio in the catalyst is 5.0 to 32.0, preferably 9.0 to 11.0, more preferably 10 to 10.6, or else 27 to 34, preferably 28 to 32 is.

Particularly preferred are catalysts having a Ni / Mn and Ni / Fe ratio (each in this order) 9.3 to 9.8 and 6.6 to 7.1; 29 to 30 and 6.6 to 7.1; 9.5 to 10.1 and 5.1 to 5.9; and 26 to 27 and 4.9 to 5.9.

Most preferred are the catalysts having the following Ni / Mn and Ni / Fe ratios (each in that order): 9.4 and 6.8; 29.5 and 6.9; 9.8 and 5.6; as well as 26.5 and 5.4. The promoters Fe and Mn may be contained completely or partially in the Ni active material. The catalyst may contain further promoters in addition to Mn and Fe, but it may also contain exclusively the promoters Mn and Fe. The oxidation states of Al, Ni and the promoters can vary depending on the treatment of the catalyst. Al, Ni and the promoters are typically present as metal cations (eg Al ³⁺ , Ni ²⁺ , Mn ²⁺ , Mn ³⁺ , Mn ⁴⁺ , Fe ²⁺ , Fe ³⁺ ). After calcination, eg in air, high oxidation states or the maximum oxidation states can be achieved. If the catalyst is heated at Reduced temperatures above room temperature, for example under reaction conditions with hydrogen, AI, Ni and the promoters can assume lower oxidation states or partially or completely in the oxidation state 0 occur. The charge balance to the metal cations is carried out by oxygen anions (0 ^{2 ~} ).

The catalyst of the present invention may contain other components in addition to alumina (i.e., Al xx of x <1.5) Ni, Fe, and Mn (as well as the oxygen anions necessary for charge balance), but may be composed solely of alumina Ni, Fe, and Mn. Preferably, the catalyst does not contain any of the elements selected from Ta, In, Cu, Ce, Cr, Bi, P, Sb, Sn, B, Si, Ti, Zr, Co, Rh, Ru, Ag, Ir, Pd and Pt. Preferably, the catalyst does not contain a noble metal.

The atomic Al / Ni ratio may be between 0.5 and 1.5, preferably between 0.8 and 1.2, more preferably the Al / Ni ratio is approximately 1.

The catalysts according to the invention can advantageously have crystallites in the Ni active composition with a diameter of less than 20 nm, preferably less than 10 nm. The Ni active composition may also consist wholly or substantially of crystallites having a diameter of less than 20 nm, preferably less than 10 nm. The Ni active material is preferably in a metallic state.

The C0 ₂ absorption capacity of the catalysts at 35 ° C may be greater than 200 μηιοΙ / g and is preferably in the range between 200 to 400 μηιοΙ / g, more preferably, between 250 to 300 μπιοΙ / g.

The BET surface area of the catalyst according to the invention is preferably greater than 100 m ² / g, preferably greater than 200 m ² / g, in particular in the range between 200 and 400 m ² / g and in particular in the range between 200 and 300 m ² / g.

The specific metal surface area (Swiet) of the catalyst according to the invention may be greater than 5 m ² / g, preferably greater than 10 m ² / g, or between 5 and 25 m ² / g, preferably between 10 and 20 m ² / g, or in the range between 6 and 9 m ² / g.

Furthermore, the invention relates to a process for the preparation of a methanation catalyst, comprising the steps:

a) co-precipitation from a solution containing Al, Ni, Mn and Fe in dissolved form to obtain a precipitate, b) isolating the precipitate from step a),

c) drying the isolated precipitate from step b) and

d) calcining the dried precipitate from step c). It is preferred here that the solution from step a) is an aqueous solution and Al, Ni, Mn and Fe are present dissolved in the aqueous solution as ionic compounds.

Al is preferably dissolved as aluminum nitrate, aluminum trichloride or aluminum sulfate. Mn is preferably present in the oxidation state II or IV and is dissolved as manganese nitrate, manganese acetate, manganese dichloride, manganese sulfate or in the oxidation state VII as a permanganate ion. Ni is preferably dissolved as nickel nitrate, nickel dichloride, nickel sulfate, nickel acetate or nickel carbonate. Fe is preferably in the oxidation state II or III and is dissolved as iron nitrate, iron or trichloride, iron acetate, iron sulfate or iron hydroxide.

Preferably, Al, Ni, Mn and Fe are in dissolved form as ionic compounds in the aqueous solution and have the same anion, which may be, for example, nitrate. The coprecipitation is carried out by adding the solution containing Al, Ni, Mn and Fe to a basic solution or by adding a basic solution to the solution which contains Al, Ni, Mn and Fe. Alternatively, the solution containing Al, Ni, Mn and Fe and the basic solution are simultaneously added to a vessel which may already contain a solvent such as water and is mixed therein. The basic solution has a pH greater than 7, preferably in the range from 8 to 10, and preferably contains an alkali hydroxide and / or an alkali carbonate. For example, the basic solution is an aqueous solution of sodium hydroxide and sodium carbonate. The coprecipitation is preferably carried out under temperature control, so that the temperature of the solution is approximately room temperature or, for example, 30 ° C.

After precipitation by coprecipitation, preferably the precipitate in the solution is aged for at least 30 minutes, preferably for more than 1 hour, more preferably for longer than 12 hours. The aging preferably takes place in that the precipitate is left in the solution (mother liquor) with stirring at approximately room temperature. The precipitate obtained by the coprecipitation is isolated, for example by filtering. The filtering can be done in a suitable manner, for example by a filter press. The isolated precipitate is preferably washed, for example with distilled water, until a neutral pH is reached.

In the following, the isolated precipitate can be dried, for example at elevated temperature in air. Preferably, the drying takes place at a temperature between 70 ° C and 90 ° C for a period longer than 4 hours, preferably longer than 12 hours.

The isolated precipitate is calcined, this can be done in air at a temperature between 300 ° C to 600 ° C, preferably at 400 ° C to 500 ° C and in a period of 3 hours to 10 hours, preferably 5 to 7 hours.

The catalyst according to the invention is intended to be used in particular in the methanation of carbon monoxide and / or carbon dioxide. The methanation of carbon dioxide can be represented by the following reaction equation:

4H ₂ + C0 ₂ -> CH ₄ + 2H ₂ 0

The methanation of carbon monoxide can be represented by the following reaction equation:

3H ₂ + CO -> CH ₄ + H ₂ O

In the method for carrying out the methanation, the reaction gas containing carbon dioxide and / or carbon monoxide or a mixture of both is contacted with the catalyst at a temperature higher than 200 ° C.

FIG. 1: activity / stability diagram of the samples described. methods

Elemental analysis

The determination of the composition of the calcined catalysts was carried out by means of inductively coupled plasma optical emission spectroscopy (ICP-OES). 50 mg of catalyst were dissolved in 50 ml of 1 molar phosphoric acid (VWR, pA) at 60 ° C. To dissolve any brownstone formed, 50 mg Na ₂ S0 ₃ (Sigma Aldrich, pA) was added to the solution. After cooling, the solutions were diluted 1/10 and filtered by 0.1 μηι filters (Pall). The calibration solutions were prepared at 1, 10 and 50 mg I ^-1 (Merck). Determination of metal concentrations was performed using an Agilent 700 ICP-OES. Determination of the specific surface

The specific surface area of the catalysts (SBET) was determined by N ₂ -BET analysis on a NOVA 4000e (Quantachrome). For this purpose, 100 mg of catalyst were degassed for 3 hours at 120 ° C and then absorbed adsorption and Desorptionsiso- therme in the p / p ₀ range of 0.007 to 1. To determine the BET surface area, the data points in the p / p ₀ range of 0.007 to 0.28 were used.

chemisorption

Chemisorption experiments were performed on an Autosorb 1C (Quantachrome). Before the measurement, 100 mg of catalyst were activated at 500 ° C in 10% H ₂ in N ₂ for 6 hours. The heating ramp was 2 Kmin ^-1 . The determination of the metal surface (SMET) was carried out according to DIN 66136-2 (Ver., 2007-01) and was carried out by means of H ₂ chemisorption at 35 ° C. For this purpose, 20 adsorption points were recorded equidistant from 40 mmHg to 800 mmHg. The equilibration time for the adsorption was 2 min, the thermal equilibrium 10 min. To determine the metal surface, a metal atom / H stoichiometry of 1 was used. For the C0 ₂ chemisorption measurements to determine the C0 ₂ uptake capacities (U (C0 ₂ )), the equilibration time for the adsorption was set to 10 min with otherwise unchanged parameters. Before the absorption of the chemisorption data, a possible kinetic inhibition of C0 ₂ chemisorption under these conditions was excluded experimentally. Metal surfaces and CO ₂ uptake capacities were extrapolated to a pressure of 0 mmHg according to the extrapolation method. synthesis

The catalysts were prepared by coprecipitation and the atomic ratio of nickel and aluminum was adjusted to 1. To study the effect of iron on catalyst behavior, iron (III) nitrate was added to the salt solution of nickel and aluminum nitrate during catalyst synthesis. To investigate the simultaneous effect of iron and manganese on the catalyst behavior, manganese nitrate and iron (III) nitrate were added to the salt solution of nickel and aluminum nitrate during the catalyst synthesis. The purity of all the chemicals used was pa Water was purified by a Millipore filter system and the degree of purity was verified by means of conductivity measurements. The synthesis was carried out in a double-walled, 3 l stirred tank. The double jacket, which was filled with water, controlled the temperature of the synthesis batch to 30 ° C via a thermostat, and two flow breakers provided for improved mixing. For stirring, a KPG stirrer with 150 revolutions min ^-1 was used. For the synthesis, 1H ₂ 0 was placed in the stirred tank and adjusted to pH = 9 ± 0.1. The dosage of the mixture of dissolved nitrates was 2.5 ml min ^-1 . At the same time, the controlled addition of the precipitating reagent was used to maintain the pH. As starting materials molar solutions of the respective nitrates were used (Ni (N0 ₃₎ ₂ ^* 6H ₂ 0, AI (N0 ₃₎ ₃ ^* 9H ₂ 0, Fe (N0 ₃₎ ₃ ^* 9H ₂ 0 and Mn (N0 ₃₎ ₂ ^* 4H ₂ 0). These were mixed as shown in Table 2 to a total volume of 120 ml min ^-1 before dropping into the reactor. The precipitation reagent was a mixture of 0.5M NaOH and 0.5 M Na ₂ C0 ₃ solutions of equal volume, for the metering of which a titrator was used. With constant stirring, the suspension was aged overnight in the mother liquor, the precipitate was then filtered off and washed with H ₂ 0 until the filtrate had a neutral pH. After drying at 80 ° C in a drying oven overnight, the dried precipitate (precursor) was heated at a heating rate of 5 K min ^-1 to 450 ° C and calcined for 6 hours under synthetic air.

Activity and stability measurement

In order to be able to compare different catalysts in terms of their activity in terms of C0 ₂ methanation, a test program was developed which provides information on their activity and stability. For this purpose, 25 mg of catalyst in the sieve fraction 150-200 μηι were diluted with nine times the amount of SiC and incorporated into the reactor. The measurement steps carried out successively in the order of reduction, shrinkage, S-curve 1, aging and S-curve 2 are listed in detail in Table 1. Table 1: Parameters of the measurement steps for determining the activity and stability profile

As a measure of the activity was representative temperature T ₇ 5, i determined, which is necessary in order to achieve a CC conversion of 75% during the measuring step S-curve 1. For this purpose, the temperature in the specified range was gradually increased by 25 ° C. Therefore, the lower T ₇ 5, i, the higher the activity of the catalyst.

As a measure of the activity after the aging, the temperature T ₇ 5.2 was determined representative, which is necessary to achieve a CC conversion of 75% during the measuring step S-curve. 2 For this purpose, the temperature in the specified range was gradually increased by 25 ° C. The lower T _{7 is} 5.2, therefore, the higher the activity of the catalyst after aging.

Calculating the difference of T ₇₅ , i and T ₇₅ , 2 from the two conversion temperature characteristics, one obtains a measure of the stability of the catalyst. Again, the lower the difference, the more stable the catalyst. For better comparability, all specific activities and stabilities were normalized to those of the un-promoted nickel-alumina (Ni) catalyst. The normalized activity and stability results from:

Standardized activity

T _{75 2} (Ni / AlO _x )

Normalized stability = ^{T? S} (dot cat.)

l (dot cat)

Both effects, increase in activity by promotion with manganese and increase in stability by doping with iron can be combined, albeit not linearly, as shown in FIG. 1, in order to purposefully synthesize both activity- and stability-improved catalysts. Examples

Table 2: Molar metal salt solutions used in co-precipitation

Table 3: Composition of calcined catalysts

Table 4: Characterization data of the catalysts

a normalized to the mass of the calcined catalyst

Table 5: Results of the catalytic test reaction

Claims

Claims:

A catalyst for the methanation of carbon monoxide and / or carbon dioxide, comprising aluminum oxide, a Ni active composition and Fe and Mn, characterized in that the molar Ni / Fe ratio in the catalyst is 5.0 to 10.0, preferably 5.3 to 7, 0 and more preferably 5.4 to 5.7.

Catalyst according to claim 1, characterized in that the molar Ni / Mn ratio in the catalyst is 5.0 to 32.0, preferably 9.0 to 10.0.

Catalyst according to one of the preceding claims, characterized in that the Ni active composition crystallites having a diameter of less than 20 nm, preferably less than 10 nm.

Catalyst according to one of the preceding claims, characterized by a C0 ₂ uptake capacity at 35 ° C of greater than 200 μηιοΙ, preferably 200 to 400 μηιοΙ per gram of catalyst.

Use of a catalyst according to one of the preceding claims, for the methanation of carbon monoxide and / or carbon dioxide with gaseous hydrogen.

A process for preparing a catalyst according to claim 1, comprising the steps of: a) co-precipitating from a solution containing Al, Ni, Mn and Fe in dissolved form to obtain a precipitate,

b) isolating the precipitate from step a),

c) drying the isolated precipitate from step b) and

d) calcining the dried precipitate from step c).

A method according to claim 6, characterized in that the solution from step a) is an aqueous solution.

A method according to claim 6 or 7, characterized in that the precipitate is aged in the solution for at least 30 minutes.

A method according to claim 6 to 8, characterized in that the isolated precipitate from step b) is washed. A method according to claim 6 to 9, characterized in that Ni, Al, Mn and Fe are present in dissolved form as ionic compounds in the solution and these ionic compounds have the same anion.

A method according to claim 10, characterized in that the anion is a nitrate, sulfate, a halide, chloride, or acetate.

Method according to one of claims 6 to 1 1, characterized in that Mn is present in the solution of step a) in the oxidation state II.

Method according to one of claims 6 to 12, characterized in that Fe is present in the solution of step a) in the oxidation state II or III.

A method according to claim 6, characterized in that the calcination of the dried precipitate takes place at a temperature of 300 to 600 ° C in air.

A process for the methanation of carbon dioxide and / or carbon monoxide in which a gas containing carbon dioxide and / or carbon monoxide is brought into contact with a catalyst according to claim 1.

The process of claim 15, wherein the gas is contacted with the catalyst at a temperature above 200 ° C.