PL220538B1 - Process for the preparation of nickelized methanation catalysts - Google Patents

Description

Description of the invention

The subject of the invention is a method of obtaining nickel methanation catalysts, most often used in ammonia plants. They make it possible to remove carbon monoxide and carbon dioxide from synthesis gas to the level of approx. 2 ppm. Oxygen compounds are strong catalyst poisons for the synthesis of ammonia.

Methanation reactions:

CO + 3H CH4 + H2O Δ H298 = -206.2 kJ mol ^-1

CO2 + 4H2 CH4 + 2H2O Δ H298 = -165.0 kJ mol ^-1 catalyzes a number of metals. Only nickel and ruthenium have found practical application. Nickel catalysts are the most commonly used.

The catalysts differ significantly: strength properties, activity, thermal stability, resistance to temperature shocks and ease of reduction.

The activity of the catalyst is determined by the size of the nickel surface and the grain size and porosity, since the reactions run in the area of strong internal diffusion influences.

The process for nickel catalysts is carried out in the temperature range of 180-450 ° C and under a pressure of up to 4 MPa. Catalysts operated at temperatures not exceeding 300-320 ° C can work for over 10 years.

In the methanation process, nickel catalysts differing in shape (pellets, spheres, extrudates and Raschig rings), substitute grain size (5-8 mm), bulk density ₃ (0.7-1.4 g / cm ³ ), nickel content (20-40% as nickel oxide), type of carrier (oxides of aluminum, silicon, magnesium, calcium, rare earth metals - silicates and others).

A number of additives are used to increase the activity of methanation catalysts. The most common promoters are noble metals and rare earth metal oxides. A review of the scientific literature on the promotion of nickel catalysts of cerem and lanthanum methanation can be found in: L. Znak, Catalysis Today, 2005, 101, 65.

As the active component of the catalyst is metal nickel, the catalyst needs to be activated by reduction with hydrogen. The reduction is carried out in an industrial reactor or at the catalyst manufacturer.

Catalysts are produced in various ways. The following operations are used: impregnation, precipitation, precipitation on a carrier, sol-gel and others. The variety of methods for the preparation of nickel catalysts is illustrated by the descriptions presented in the following patents:

The patent US 168257 describes the preparation of a nickel catalyst with various promoters such as: manganese, iron, cobalt, platinum, rhodium, palladium, silver, gold, osmium, iridium, and mixtures of these metals. They can be prepared on a carrier, the most common of which are: Al ₂ O ₃ , SiO ₂ , TiO ₂ and rare earth metal oxides. These catalysts were obtained by the methods of co-precipitation, impregnation and the sol-gel method, which turned out to be the best.

The patent US 4,215,998 describes the preparation of catalysts for the methane-steam conversion process (reverse reaction to the methanation reaction) containing 60-90% nickel oxide, 5-30% alumina, 2-15% cerium oxide and / or lanthanum. The catalysts are obtained by the precipitation method in three stages:

• in the first stage, the alkaline substance solution is added to the aluminum salt solution, • in the second stage, the alkaline solution is added to the lanthanum and / or cerium salt solution in the presence of the precipitated substance in the first stage, • in the third stage, the alkaline substance solution is added to the salt solution nickel and / or cobalt in the presence of the mixture precipitated in the second step.

The University materials of Swati Jain Education Group, 33 Harvard Street, Sampat farm, Bicholi Mardana, Indore, India present a nickel-aluminum methanation catalyst with the addition of cerium or lanthanum and preparation methods:

• a method of wet impregnation, which consisted in adding aluminum oxide to an aqueous solution of nickel nitrate and cerium or lanthanum. The resulting precipitate was filtered, dried in a desiccator for 6 hours and calcined. Instead of nickel nitrate, nickel acetate was also used, • the method of two-stage co-precipitation, with the use of nickel and aluminum nitrates and sodium hydroxide in the first stage and the addition of a promoter (cerium or lanthanum) in the form of a salt solution in the second stage. The precipitate formed in this way was seasoned, filtered and dried.

PL 220 538 B1

In the above-mentioned patents, similar methods of preparation of methanation catalysts are used. Significant differences concern the chemical composition, the method and conditions of precipitation and the method of introducing promoters into the active phase. The drawbacks of the above inventions are: large optimal amounts of promoters, unused possibilities to increase the activity of catalysts as a result of the addition of promoters, the need to use complicated and expensive sol-gel technologies to obtain catalysts with the highest activity.

Extensive research has been carried out on methods for the preparation of cerium or lanthanum promoted nickel catalysts for the methanation process.

It was established that:

• The promoting effect of the addition of cerium and / or lanthanum and the optimal amounts of promoters significantly depend on the method of obtaining the catalysts.

• No synergistic influence of cerium and lanthanum oxides on the catalyst activity was found.

• Catalysts formed into small extrudates or spheres with an equivalent diameter of about 2 mm, containing 15-25% nickel oxide, have very high activity.

• Good strength properties and high porosity of the small extrudates are achieved by using active aluminum hydroxide as a commercial carrier.

• Good strength properties and high porosity of small spheres are obtained by using a mixture of aluminum oxide and aluminum cement (in the amount of 10-30%) as a carrier, and the forming is carried out continuously by the plate method.

Surprisingly, it turned out that the catalysts in which the entire amount of promoters were introduced into the nickel-aluminum mass of the hydrotalcite structure had the best properties.

The above findings are the basis of the original methods of preparing the catalysts of the invention.

The essence of obtaining nickel methanation catalysts consists in the fact that the starting material is a catalyst precursor containing, expressed as oxides: more than 75 wt. % nickel, 10-20 wt. % aluminum, 1-5 wt.%. cerium and / or lanthanum, preferably 1.5-3.5% and not more than 0.5% of alkali metals, preferably not more than 0.1%, with a hydrotalcite structure of at least 70%, preferably more than 90%, which is calcined or calcined, reduced and passivated. Then it is mixed with active aluminum hydroxide and the resulting mixture containing 50-88% aluminum hydroxide is formed into extrudates and dried or mixed with aluminum oxide and aluminum cement, and the resulting mixture containing 10-80% aluminum oxide and 10-30% aluminum cement is molded into balls by the disc granulation method, it is seasoned in an atmosphere of water vapor and dried.

The catalyst precursor is obtained in the precipitation process, which is carried out at a constant pH = 7.0-7.5, at a temperature of 70-85 ° C, and the raw materials are mixtures of nitrates: nickel, cerium and / or lanthanum and aluminum and a mixture of sodium carbonate and sodium hydroxide. The catalyst precursor, after washing from sodium ions, is dried and calcined at 350-450 ° C, and reduction with hydrogen is carried out at 350-500 ° C.

The catalyst is formed into extrudates with an equivalent diameter of 1.5-2.5 mm or into balls with dimensions of 1.5-3 mm.

The catalysts so obtained preferably contain 15-25% nickel and have very good strength properties, high activity and thermal stability at temperatures up to 500 ° C, are easy to reduce and are resistant to temperature shocks.

The subject of the invention is explained in more detail in the following examples. The activity of the formed catalysts was measured in the diffusion region by the non-gradient method (measurement of the reaction rate at constant temperature and gas composition) within the industrial process parameters.

P r z k ł a d 1

The catalyst precursor with the composition of: 83.5% nickel oxide, 15% alumina and 1.5% cerium oxide was obtained in the precipitation process conducted at a constant pH = 7.2 and temperature of 80 ° C, and a mixture of nitrates: nickel was used as raw materials , aluminum and cerium; and a basic mixture of sodium carbonate and sodium hydroxide. The precursor, which contained greater than 90% of the hydrotalcite form after washing from sodium ion to 0.1%, was dried, recalcined at 400 ° C and mixed with aluminum hydroxide. The resulting mixture containing 80% aluminum hydroxide was formed into extrudates with an equivalent diameter of about 2 mm, and dried to obtain a finished product with the composition: 25% NiO, 74.6% Al2O3 and 0.4% Ce ₂ Os.

PL 220 538 B1

P r z k ł a d 2

The obtained catalyst precursor of Example 1 was dried, calcined at 400 ° C, reduced with hydrogen at 400 ° C, and then mixed with alumina and aluminum cement. The resulting mixture containing 60% alumina and 20% alumina cement was formed into balls 1.5-3 mm in size using the disc granulation method, seasoned in a water vapor atmosphere and dried to obtain a finished product with the composition: 24% NiO, 47.1% Al ₂ O ₃ , 32.1% CaO and 0.4% Ce ₂ O ₃ .

P r z k ł a d 3

The catalyst precursor composed of: 83% nickel oxide, 15% alumina and 2% lanthanum oxide was obtained in the precipitation process conducted at a constant pH = 7.2 and temperature of 80 ° C, and a mixture of nitrates: nickel, aluminum and lanthanum was used as raw materials. and a basic mixture of sodium carbonate and sodium hydroxide. The precursor, which contained greater than 90% of the hydrotalcite form after washing from sodium ion to a level of 0.1%, was dried and calcined at 400 ° C and mixed with aluminum hydroxide. The resulting mixture containing 75% aluminum hydroxide was formed into extrudates with an equivalent diameter of about 2 mm, and dried to obtain a finished product with the composition: 23% NiO, 76.2% Al2O3 and 0.8% La2O3.

P r z k ł a d 4

The obtained catalyst precursor of Example 3 was dried, calcined at 400 ° C, reduced with hydrogen at 400 ° C, and then mixed with alumina and aluminum cement. The resulting mixture containing 65% alumina and 15% alumina cement was formed into balls 1.5-3 mm in size by the disc granulation method, seasoned in a water vapor atmosphere and dried to obtain a finished product with the composition: 20% NiO, 46.8% Al ₂ O ₃ , 32.4% CaO and 0.8% La ₂ O ₃ .

P r z k ł a d 5

A catalyst precursor composed of 83% nickel oxide, 15% alumina, 1% lanthanum oxide and 1% cerium oxide was prepared according to Example 3, dried, calcined at 400 ° C and mixed with aluminum hydroxide. The resulting mixture containing 75% aluminum hydroxide was formed into extrudates with an equivalent diameter of 2 mm, and dried to obtain a finished product with the composition: 22% NiO, 77% Al2O3, 0.5% La2O3 and 0.5% Ce2O3.

The catalysts obtained in this way with the addition of promoters were subjected to the activity evaluation in a stirred tank reactor and it was found that they had 2 times higher activity at the temperature of 200 ° C than the catalysts obtained in the same way but without the addition of promoters.

Claims (6)

Patent claims A method for obtaining nickel methanation catalysts in the process of continuous precipitation, calcination, reduction and passivation, characterized in that the starting material is a catalyst precursor containing, expressed as oxides: more than 75 wt. % nickel, 10-20 wt. % of aluminum, 1-5%, preferably 1.5-3.5% by weight. cerium and / or lanthanum and not more than 0.5%, preferably 0.1% by weight. alkali metals, with a hydrotalcite structure, at least 70%, preferably more than 90%, which is calcined or calcined, reduced and passivated and then mixed with active aluminum hydroxide, and the resulting mixture containing 50-88% aluminum hydroxide is formed into extrudates and dried or mixed with alumina and alumina cement, and the resulting mixture containing 10-80% alumina and 10-30% alumina cement is formed into balls by the disc granulation method, seasoned in a water vapor atmosphere and dried. 2. The method of obtaining nickel catalysts according to claim The method of claim 1, characterized in that the catalyst precursor is obtained by a precipitation process which is carried out at a constant pH X 7.0-7.5, at a temperature of 70-85 ° C, and the raw materials are mixtures of nitrates: nickel, cerium and / or lanthanum and aluminum, and a mixture of sodium carbonate and sodium hydroxide. 3. Catalyst preparation method according to claim 1 The process of claim 1, wherein the catalyst precursor, after washing from sodium ions, is dried and calcined at 350-450 ° C, and reduction with hydrogen is carried out at 350-500 ° C. 4. Catalyst preparation method according to claim 1 The process of claim 1, wherein the catalyst is formed into extrudates with an equivalent diameter of 1.5-2.5 mm. 5. The catalyst preparation method according to claim 1 The process of claim 1, wherein the catalyst is formed into spheres 1.5-3 mm in size. 6. The method of obtaining a catalyst according to claim The process of claim 1, characterized in that the finished catalyst preferably contains 15-25% nickel.