KR102531947B1 - Catalyst for methane synthesis and preparation method thereof - Google Patents

Abstract

An object of the present invention is to provide a catalyst for methane synthesis capable of preventing activity degradation caused by the deposition of coke on a Ni-based active component under methanation reaction conditions in the presence of carbon dioxide and hydrogen. The catalyst for methane synthesis of the present invention includes a Ni-based active component and a hygroscopic material.

Description

Catalyst for methane synthesis and its manufacturing method {CATALYST FOR METHANE SYNTHESIS AND PREPARATION METHOD THEREOF}

The present invention relates to a catalyst for methane synthesis and a method for preparing the same.

The reaction of synthesizing methane by reacting carbon dioxide and hydrogen is called methanation reaction. As raw materials used in the methanation reaction, carbon dioxide generated in a wide range of industries, such as the petrochemical industry, oil refining industry, and steel industry, and hydrogen generated through electrolysis of water supplied with electricity from renewable energy can be used. The process of this methanation reaction is a P2G (Power to Gas) technology, which is a process capable of synthesizing gaseous material, that is, methane, from electricity.

The reaction formula of the methanation reaction using carbon dioxide and hydrogen as raw materials is as follows.

CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O, ΔH = -164 kJ/mol Equation (1)

As can be seen from the above formula (1), in order to synthesize methane from carbon dioxide, 4 molecules of hydrogen per carbon dioxide are required in the stoichiometric ratio.

Since this methanation reaction is an exothermic reaction, the equilibrium conversion rate of carbon dioxide rapidly decreases when the temperature rises as the methanation reaction progresses. At high temperatures, the reverse water-gas shift reaction (RWGS), an endothermic reaction, dominates (see equation (2)), increasing the equilibrium conversion of the methanation reaction again.

CO ₂ + H ₂ → 2H ₂ O Equation (2)

On the other hand, when the hydrogen/carbon dioxide ratio (H ₂ /CO ₂ ) is low in the presence of carbon dioxide and hydrogen, a side reaction in which coke (C) is produced may occur (see Equation (3)). In addition, methane produced by the methanation reaction is decomposed to produce coke (see equation (4)) or coke can be produced from carbon monoxide produced by the RWGS reaction (see equation (5)).

CO ₂ + 2H ₂ → C + 2H ₂ O Equation (3)

CH ₄ ↔ C + H ₂ Equation (4)

2CO ↔ C + CO ₂ Equation (5)

Since such coke is deposited on the active component of the catalyst and causes a decrease in activity, a method for efficiently removing coke is required.

Korean Patent Registration No. 10-0024128

An object of the present invention is to provide a catalyst for methane synthesis capable of preventing activity degradation caused by the deposition of coke on Ni-based active components under methanation reaction conditions in the presence of carbon dioxide and hydrogen.

According to one aspect of the present invention, as a catalyst for methanation reaction using carbon dioxide and hydrogen, a catalyst for methane synthesis including a Ni-based active component and a hygroscopic material is provided.

According to another aspect of the present invention, preparing a catalyst for methane synthesis comprising the steps of forming a Ni-based active component by adding a basic compound to a Ni ion-containing metal precursor solution, and mixing the Ni-based active component with a hygroscopic material A method is provided.

According to the present invention, in the methanation reaction using hydrogen and carbon dioxide, by using a catalyst in which a Ni-based active component and a hygroscopic material are mixed, coke is prevented from being deposited on the Ni-based active component to prevent deterioration of the activity of the Ni-based active component can do.

In addition, when the catalyst is used, the carbon dioxide conversion rate and methane selectivity can be increased even under methanation reaction conditions having a low hydrogen/carbon dioxide ratio.

1 is a graph showing the carbon dioxide conversion rate according to temperature in Examples according to the present invention and Comparative Examples.
2 is a graph showing methane selectivity according to temperature in Examples according to the present invention and Comparative Examples.
Figure 3 is a graph showing the weight change according to the temperature in Examples and Comparative Examples according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

The present invention provides a catalyst for methane synthesis comprising a Ni-based active component and a hygroscopic material so that less carbon deposition (coking) can occur under methanation reaction conditions with a low hydrogen/carbon dioxide ratio.

In the present invention, the Ni-based active component contains Ni, and may further contain Al, Mg or Fe. When the Ni-based active component further contains Al, Al may be a component for dispersing Ni. In this case, the Ni-based active component may include 5 to 40 wt% of Ni and 10 to 95 wt% of Al based on the total weight of the Ni-based active component. If the content of Ni is less than 5% by weight, the number of active sites is small, so the efficiency of methane production compared to the amount of Ni-based active ingredient added may be reduced. On the other hand, when the content of Ni exceeds 40% by weight, the Al content is relatively low, so the Ni particles may not be dispersed and the particle size may increase. An excessively large particle size is undesirable because the activity of the Ni-based active component is reduced. Conversely, when the Al content is less than 10% by weight, the particles of the Ni-based active component become very large and the activity of the Ni-based active component may decrease, and when the Al content exceeds 95% by weight, the Ni content is relatively low, resulting in methane Production efficiency may be reduced.

Meanwhile, when the Ni-based active ingredient contains Ni, Mg, and Fe, Ni, Mg, and Fe may be contained in a weight ratio of 40:10:5, respectively.

The Ni-based active ingredient can be obtained, for example, by co-precipitation. Specifically, the Ni-based active component can be obtained by precipitating by introducing a precipitant into a metal precursor solution containing Ni ions, and the anion of the metal precursor is not particularly limited, but NO ₃ ^- , CH ₃ COO ^- , SO ₄ ^2- , Cl ⁻ , CO ₃ ^{2− ,} and the like. The metal precursor solution may further contain Al ions, Mg ions or Fe ions together with Ni ions. The concentration of the metal precursor solution may be 0.1 to 1.5M, preferably 1.2M. If the concentration of the metal precursor solution is less than 0.1 M, the volume of the solution becomes too large, and thus the productivity of the Ni-based active component decreases. On the other hand, even if an excessive amount of the metal compound is added, it may be difficult to prepare a metal precursor solution having a concentration of more than 1.5M due to limited solubility.

Meanwhile, the precipitant may be an aqueous solution of a basic compound such as NaOH, Na ₂ CO ₃ , NaHCO ₃ , NH ₄ OH, etc., and the concentration of the aqueous solution may be 0.1 to 16.0M. If the concentration of the aqueous solution of the basic compound is less than 0.1 M, the volume of the solution becomes excessively large and the productivity of the Ni-based active component decreases. On the other hand, even if an excessive amount of basic compound is added, it may be difficult to prepare an aqueous basic compound solution having a concentration exceeding 16.0 M due to limited solubility.

The temperature of the metal precursor solution may be room temperature (20 °C) to 70 °C, for example, 50 °C. After sufficiently dissolving metal ions by stirring the metal precursor solution in the above temperature range, a basic compound may be added to precipitate the metal. The basic compound may be added until the pH of the metal precursor solution becomes 7 to 9, preferably 7 to 8. If the pH is less than 7, the metal ions in the solution are not sufficiently precipitated, and if the pH exceeds 9, the metal ions are rapidly precipitated and the size of the metal particles may increase and the catalytic activity may decrease.

When the precipitation is completed, the temperature is raised to room temperature (20 ° C) to 100 ° C, preferably 50 ° C to 95 ° C, more preferably 60 ° C to 90 ° C, and then stirred to mature the precipitate. At this time, it is preferable to increase the aging time as the aging temperature decreases. For example, when the aging temperature is 90° C., the aging time may be 2 hours.

Thereafter, the precipitate-containing solution may be cooled, and distilled water may be additionally added to filter and wash the solution. In this process, unnecessary ions may be removed. The filtered precipitate is dried at room temperature (20° C.) to 150° C., preferably 90 to 120° C., and then calcined to obtain an active ingredient in the form of a metal oxide.

In the present invention, the hygroscopic material is a material capable of containing and releasing moisture generated during the methanation reaction, and can activate the reverse reaction of equation (3) by providing moisture to the Ni-based active component on which coke is deposited. As the reverse reaction of Formula (3) progresses, methane can be stably synthesized by suppressing the deactivation of the Ni-based active component and additionally supplying hydrogen.

Examples of the hygroscopic material include, but are not limited to, CHA-type zeolite, LTA-type zeolite, USY-type zeolite, silica gel, and the like, and any material capable of containing and releasing moisture may be used without limitation.

In the present invention, the catalyst for methane synthesis may include 0.1 to 20% by weight, preferably 1 to 20% by weight, more preferably 5 to 10% by weight of a hygroscopic material based on the total weight of the catalyst, and the balance Ni-based active component there is. If the content of the hygroscopic substance is less than 0.1% by weight, the water containing and releasing effect may be lowered, so that the performance of preventing coke deposition may be reduced, and if it exceeds 20% by weight, the active ingredient content is relatively small, so methane production may be reduced.

Meanwhile, in the methanation reaction using hydrogen and carbon dioxide, the stoichiometric ratio of hydrogen/carbon dioxide is 4, but the use of the catalyst for methane synthesis according to the present invention shows high carbon dioxide conversion and methane selectivity even when the hydrogen/carbon dioxide ratio is 4 or less. This is because, in the process in which the hygroscopic material contains and then releases moisture, a reverse reaction of the reaction of Formula (3) occurs, suppressing deactivation of the catalyst, and additionally supplying hydrogen. In the present invention, the lower limit of the hydrogen / carbon dioxide ratio may be 3, and when the lower limit is less than 3, the amount of hydrogen is too small compared to carbon dioxide, so the methanation reaction does not occur well, and the reaction of formula (3) is more likely to occur do. Therefore, there is a risk that coke is deposited on the Ni-based active component and its activity is lowered.

As in the present invention, coke can be prevented from being deposited on the Ni-based active component by using a catalyst containing a hygroscopic material in the methanation reaction. In addition, since additional hydrogen can be supplied as the coke reacts with water, the carbon dioxide conversion rate and methane selectivity can be increased even under reaction conditions with a low hydrogen/carbon dioxide ratio.

Example

Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for understanding of the present invention, but do not limit the present invention.

1. Example 1

(1) Manufacture of Ni-based active ingredient

A metal precursor solution (1.2 M) was prepared to contain Ni ions, Mg ions, and Fe ions in a weight ratio of 40:10:5, respectively. The metal precursor solution was stirred at 50° C. to sufficiently dissolve the metal ions.

Ammonia water (NH ₄ OH) having a concentration of 15.7 M (30% by weight) was added to the metal precursor solution to precipitate metal ions. When the pH of the metal precursor solution reached about 7-8, the addition of ammonia water was stopped, and the temperature was raised to 90° C. to mature the initial precipitate, followed by stirring for 2 hours. After aging, the precipitate-containing solution was cooled, and filtered and washed by additionally supplying distilled water to remove unnecessary ions. The filtered precipitate was dried in an oven at 120° C., and then calcined in a furnace at 600° C. for 5 hours to convert to a metal oxide form.

(2) Preparation of catalyst for methane synthesis

A pellet type catalyst for methane synthesis was prepared by mixing 90 wt% of the calcined metal oxide and 10 wt% of CHA-type zeolite. 20 mL of the catalyst having a diameter of 1-3 mm was injected into a reactor and reduced at 600° C. for 5 hours to prepare a catalyst for methane synthesis including 40Ni10Mg5Fe and CHA-type zeolite.

2. Comparative Example 1

A calcined metal oxide was prepared in the same manner as in Example. 20 mL of the metal oxide was injected into a reactor and reduced at 600° C. for 5 hours to prepare a Ni-based active component in the form of 40Ni10Mg5Fe.

3. Measurement of carbon dioxide conversion rate and methane selectivity according to temperature

The catalyst for methane synthesis (40Ni10Mg5Fe + CHA-type zeolite) prepared in Example was introduced into a reactor in which H ₂ and CO ₂ were present at a ratio of 3.8, and carbon dioxide conversion and methane selectivity according to temperature were measured.

Meanwhile, the Ni-based active component (40Ni10Mg5Fe) of Comparative Example was introduced into a reactor in which H ₂ and CO ₂ were present at a ratio of 4.0, and carbon dioxide conversion and methane selectivity according to temperature were measured.

Carbon dioxide conversion and methane selectivity were analyzed through gas chromatography (GC), and the measured values are shown in Table 1, FIGS. 1 and 2 below.

Temperature (℃) CO ₂ Conversion (%) CH ₄ selectivity (%) 40Ni10Mg5Fe 40Ni10Mg5Fe+CHA 40Ni10Mg5Fe 40Ni10Mg5Fe+CHA 450 86.5 95.2 88.9 95.7 500 86.9 94.2 85.5 93.4 600 87.5 94.9 74.9 91.5 700 88.4 95.3 55.2 82.1

In the case of the comparative example (40Ni10Mg5Fe), the carbon dioxide conversion rate slightly increased as the temperature increased, showing 86.5% at 450 °C and 88.4% at 700 °C. However, the methane selectivity rapidly decreased as the temperature increased, showing methane selectivities of 88.9% at 450 °C and 55.2% at 700 °C. This is due to the characteristics of the methane synthesis reaction, which is an exothermic reaction. In the case of the example in which 40Ni10Mg5Fe was mixed with the hygroscopic material CHA-type zeolite, the carbon dioxide conversion rate and methane selectivity were higher than those of the comparative example. Specifically, the carbon dioxide conversion rate was increased by about 7% compared to the comparative example, and this is because the CHA-type zeolite absorbed moisture generated during the methanation reaction, shifting the equilibrium of the reaction to the direction of methane production. On the other hand, the methane selectivity increased by about 7% at 450 ° C. and by about 27% at 700 ° C. compared to the comparative example.

4. Measurement of mass change with temperature

In order to confirm the degree of coke production according to the addition of the hygroscopic material, after the completion of the methanation reaction, the catalyst for methane synthesis (40Ni10Mg5Fe + CHA-type zeolite) of Example and the Ni-based active component (40Ni10Mg5Fe) of Comparative Example were taken and subjected to thermogravimetric analysis (TGA) was carried out and the results are shown in Figure 3.

When the temperature was raised to 500 ° C. in an oxygen atmosphere, the weight increased by about 9-10% as Ni was converted to NiO in both Examples and Comparative Examples. Above 500 °C, coke deposited in 40Ni10Mg5Fe reacts with oxygen and is removed. In the case of the comparative example, the weight of 40Ni10Mg5Fe decreased by about 3% in the range of 500 ° C to 600 ° C, and the weight decreased by about 1% in the range of 600 to 900 ° C. On the other hand, in the case of the examples, the weight of the catalyst for methane synthesis was reduced to less than 1% at 500 ° C to 900 ° C. This result means that the amount of coke deposited in 40Ni10Mg5Fe of the comparative example is large.

From these results, it can be seen that when a catalyst containing a hygroscopic material was used in the methanation reaction, water released from the hygroscopic material reacted with coke, and coke deposition was suppressed.

Claims (5)

A catalyst for methane synthesis using carbon dioxide and hydrogen at a stoichiometric ratio of less than 4 molecules of hydrogen per molecule of carbon dioxide,
0.1 to 20% by weight of a hygroscopic material that is a CHA type zeolite and the balance active component, wherein the active component includes Ni, Mg and Fe in a weight ratio of 40:10:5,
A catalyst for methane synthesis, 1-3 mm in diameter, having CH ₄ selectivity at a temperature of 450° C. or higher. According to claim 1,
The catalyst for methane synthesis comprises 5 to 10% by weight of a hygroscopic material that is a CHA-type zeolite and the remainder of the active component. Injecting a basic compound into a metal precursor solution containing Ni, Mg, and Fe ions to form an active component containing Ni, Mg, and Fe ions in a weight ratio of 40:10:5, and
Mixing the active ingredient and a hygroscopic material, which is a CHA type zeolite, to include 0.1 to 20% by weight of the hygroscopic material and the balance active ingredient,
A method for preparing a catalyst for methane synthesis, wherein methane is synthesized by using carbon dioxide and hydrogen at a stoichiometric ratio of less than 4 molecules of hydrogen per molecule of carbon dioxide. According to claim 3,
The basic compound is added so that the pH of the metal precursor solution is 7 to 9, method for preparing a catalyst for methane synthesis. According to claim 3,
The method for preparing a catalyst for methane synthesis, wherein the catalyst for methane synthesis comprises 5 to 10% by weight of a hygroscopic material that is a CHA-type zeolite and the remainder of the active component.

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