RU2455065C1 - Method of producing catalyst for synthesis of higher hydrocarbons from co and h2 and catalyst obtained using said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to petrochemistry, gas chemistry and catalytic chemistry. The method of producing a catalyst for synthesis of higher hydrocarbons from CO and H₂ involves preparation of an exothermic mixture of powder of starting components containing aluminium and at least cobalt oxide or cobalt oxide and at least one oxide selected from a group comprising nickel oxide, iron oxide, vanadium oxide, putting the mixture into a heat-resistant mould whose inner surface is coated with a functional protective coating of corundum, putting the mould with the mixture into a centrifuge, igniting the mixture and conducting synthesis in combustion mode with centrifugal acceleration of 40-80 g in an air atmosphere, separating the end molten alloy from synthesis by-products, grinding the alloy, separating the fraction of granules with size from 0.5-1.5 mm, subsequent leaching of the obtained product with aqueous solution of an alkali metal hydroxide and washing the catalyst, wherein content of cobalt oxide in the exothermic mixture is equal to 25-43 wt %. The exothermic mixture of starting components can contain not less than 5 wt % zirconium. The catalyst is a polymetallic material based on cobalt aluminides or cobalt and nickel aluminides or cobalt and iron aluminides or cobalt and vanadium aluminides or cobalt and zirconium aluminides with a highly grained, nanostructured active surface and specific surface area of 11.2-25.5 m²/g.

EFFECT: simple synthesis method, high efficiency of synthesis, high catalytic activity of the catalyst with a nanostructured active surface for synthesis of higher hydrocarbons from CO and H₂, low cost, high output (selectivity) of the end product (C₅₊).

3 cl, 2 tbl, 2 dwg, 5 ex

Description

The invention relates to the field of petrochemistry, gas chemistry and catalytic chemistry, in particular to catalysts based on polymetallic materials containing cobalt, and methods for their preparation, which can be used to produce synthetic hydrocarbons C _5-25 from carbon monoxide CO and hydrogen H ₂ (synthesis Fischer-Tropsch).

The resulting products serve as components of motor fuels (gasoline and diesel fuel), and are also intended for further processing of hydrocarbons in petrochemical processes, in particular linear alcohols and α-olefins.

Many inventions are known for the implementation of the Fischer-Tropsch reaction using cobalt-based catalysts. Common features of methods for their preparation are impregnation with a soluble salt of cobalt carrier, which includes aluminum oxide, γ-alumina, aluminum monohydrate, aluminum trihydrate, aluminosilicate, magnesium silicate, silicon dioxide, silicate, silicalite, γ-zeolite, mordenite, titanium, thorium, zirconium, niobium, hydrocalcite, kieselguhr, attapulgite clay, zinc oxide, other clays, other zeolites and their combinations: RU 2292238 C2, 01.27.2007; Gibbsit - RU 2279912 C1, 07.20.2006; Zeolite RU 2297879 C1, 04/27/2007, Hallumin RU 2256502, 07/20/2005.

A common disadvantage of the above methods for producing catalysts is the complexity and energy intensity of the cooking process.

A common disadvantage of the catalysts thus obtained is the low thermal conductivity of the carriers, which complicates the heat removal from the exothermic reaction zone and leads to the occurrence of local overheating of the catalysts.

A known catalyst for the synthesis of aliphatic hydrocarbons C ₅ -C ₂₅ from CO and H ₂ containing cobalt on a support, which is used as a powder of aluminum metal, the catalyst has the following composition, wt.%: Co 10-50, Al - the rest ( RU 2256501 C1, B01J 23/75, B01J 23/89, C07C 1/04, 07.20.2005). The patent also describes a method of producing a catalyst, which includes two stages: in the first stage, a certain amount of cobalt nitrate is dissolved with distilled water, aluminum powder is added to the resulting solution with stirring, it is kept for 15 minutes and dried in a water bath with constant stirring for 1 hour, then the resulting powder mixed with quartz (particle diameter of quartz - 3-4 mm) in a volume ratio of 1: 1 and calcined in a stream of air at 450 ° C for 1 h, the sample is cooled to room temperature and separated from quartz. In the second stage, a certain amount of cobalt nitrate Co (NO ₃ ) ₂ × 6H ₂ O is dissolved in 15 ml of distilled water and added to a calcined sample with stirring. Stand for 15 minutes and dried in a water bath for 1 hour and get a catalyst composition, wt.%: With 10-50, Al - the rest.

The catalyst according to the known invention allows:

- increase the activity and selectivity in the synthesis of C ₅ -C ₂₅ hydrocarbons from CO and H ₂ : at atmospheric pressure and low temperatures, the CO conversion is 50-75%, the yield of C ₅ -C ₂₅ hydrocarbons is 85-120 g / m ³ , and the selectivity of their formation is 70-91%;

- by improving the heat removal from the reaction zone to increase the stability of the catalyst.

A disadvantage of the known catalyst is the low degree of conversion of CO.

The disadvantage of this method of obtaining the specified catalyst is the length of time and the complexity of the process of applying cobalt.

The objective of the invention is to provide a high-performance method for producing a catalyst with a highly branched nanostructured active surface for producing higher hydrocarbons from CO and H ₂ (Fischer-Tropsch synthesis), with high catalytic activity due to the balanced chemical composition of the catalyst components.

The technical result of the invention is to simplify the production method, increase its productivity, increase the catalytic activity of a catalyst with a nanostructured active surface for the synthesis of higher hydrocarbons from CO and H ₂ , reduce the cost, increase the yield (selectivity) of the target product (C ₅₊ ), increase chemical uniformity and structural composition.

The technical result in terms of the method is achieved by the fact that the method of producing a catalyst for the synthesis of higher hydrocarbons from CO and H ₂ includes the preparation of an exothermic mixture of powders of the starting components containing aluminum and at least cobalt oxide or cobalt oxide and at least one oxide from the group comprising nickel oxide, iron oxide, vanadium oxide, placing the mixture in a refractory form coated with a functional protective layer of corundum from the inner surface, placing the form with the mixture in a centrifuge, ignited mixing the mixture and carrying out synthesis in the combustion mode at centrifugal acceleration of 40-80 g, in an atmosphere of air, separating the target cast alloy from the by-products of synthesis, grinding the alloy, isolating the granule fraction from 0.5 to 1.5 mm in size, then leaching the resulting the product with an aqueous solution of alkali metal hydroxide and washing the catalyst, while the content of cobalt oxide in the composition of the exothermic mixture is 25-43 wt.%. Additionally, at least 5 wt.% Zirconium is introduced into the exothermic mixture.

The technical result in terms of the substance is achieved in that the catalyst is a polymetallic material based on cobalt aluminides, or cobalt and nickel aluminides, or cobalt and iron aluminides, or cobalt and vanadium aluminides, or cobalt and zirconium aluminides with a highly branched, nanostructured active surface and specific a surface of 11.2-25.5 m ² / g.

The essence of the method of producing the catalyst consists in the use of thermal energy released during exothermic reactions in the combustion wave after initiating a mixture of the starting reagents under centrifugal acceleration of 40-80 g. As a result of the implementation of high temperatures directly in the combustion wave, the synthesis process is short-term and takes several tens of seconds. The synthesis is carried out in an atmosphere of air in centrifugal units. A functional protective layer based on aluminum oxide deposited on the inner surface of the mold eliminates the contact of the melt of the target product with the mold material and reduces the cooling rate of the melt, acting as a heat-insulating layer. In general, the presence of a functional layer leads to an increase in the “life” time of the melt, which contributes to a more complete phase separation at overloads of 40–80 g, allows us to simplify the design of the centrifuge and carry out the synthesis on large masses of the initial mixtures. The layer thickness depends on the ratio of the initial components, the magnitude of gravity and the volume of the form.

After synthesis, the product is an ingot, which consists of two layers: the lower is an intermetallic alloy based on Co, Ni, Fe, V and Zr aluminides and the upper is a cast oxide material based on Al ₂ O ₃ (corundum), the layers are separated from each other and use as directed. Cast oxide material based on Al ₂ O _{3 is} used to make a suspension for coating the inner surface of the used molds from graphite material.

The intermetallic alloy based on the aluminides Co, Ni, Fe, V, and Zr is subjected to grinding and classification using standard equipment, the time takes from 20 to 30 minutes, after which the separated granule fractions with sizes from 0.5 to 1.5 mm are leached with an aqueous solution of hydroxide alkali metal for 20-40 minutes in stainless steel tanks, followed by washing the catalyst to a neutral wash water reaction.

The catalyst obtained by the described method is a polymetallic material in the form of granules with a particle size of 0.5-1.5 mm with a complex two-level structure of polymetallic alloys based on cobalt aluminides, or cobalt and nickel aluminides, or cobalt and iron aluminides, or aluminides cobalt and vanadium, or cobalt and zirconium aluminides with a highly branched, nanostructured active surface and a specific powder surface of 11.2-25.5 m ² / g.

Catalyst granules are used to produce higher hydrocarbons from CO and H ₂ (Fischer-Tropsch synthesis) a promising process that allows to diversify the petrochemical raw material base by processing coal, gas, shale and other carbon-containing raw materials into synthesis gas with its subsequent conversion to higher hydrocarbons.

The essence of the method is illustrated by examples.

Example 1

An exothermic reaction mixture of the starting components is prepared in the following ratio, wt.%: CoO = 43.0; Al = 47.0.

Previously, a suspension is prepared on the inner surface of the graphite form, prepared from a crushed cast oxide phase based on corundum (a by-product of the method) and an organic binder (alcohol polyvinyl butyral). The laminated form is dried at a temperature of 150 ° C for at least 1.5 hours. Then the finished mixture is poured into a mold and placed in a centrifugal installation. The centrifuge rotor is rotated and creates an overload of 40 g, after which the reaction mixture is ignited by an electric spiral. After completion of the combustion process, the synthesis product is cooled and removed from the reaction form. The synthesis product consists of two layers: the lower is an intermetallic alloy based on cobalt aluminides and the upper (by-product of synthesis) is a cast oxide material Al ₂ O ₃ (corundum) with minor impurities of unreduced starting metal oxides. Layers are easily separated from each other. The intermetallic alloy is subjected to grinding and classification on standard equipment for 60 minutes, after which the separated granule fractions with a size of 0.5 to 1.5 mm are leached with an aqueous alkali metal hydroxide solution for 20 minutes, followed by washing the catalyst to a neutral wash water reaction.

The catalyst is a polymetallic material, including cobalt and lower cobalt aluminides, its composition in terms of elements, wt.%: Co - 89.2; Al - 11.8. The specific surface area of the granules is 23.2 m ² / g.

Other examples of the method are presented in table 1.

The composition and properties of the target material by examples are presented in table 2.

As can be seen from the data presented, the proposed method allows to obtain a polymetallic catalyst in the form of granules with sizes of 0.5-1.5 mm, with a specific surface area of 11.2-25.5 m ² / g, containing Co and Al; Co, Ni and Al; Co, Fe and Al; Co, V and Al; Co, Zr and Al, depending on the composition of the initial exothermic mixture with a content of not more than 0.6 wt.% Impurities. The yield of the target catalyst, from the calculated values, is 95-97% (depending on the conditions of gravity and the ratio of components).

X-ray phase analysis of the synthesized polymetallic catalyst revealed the presence of five main intermetallic phases: CoAl ₃ , NiAl ₃ , Ni ₂ Al ₃ , Co ₄ Al ₃ , Fe ₄ Al ₁₃ .

During the leaching of the intermetallic alloy, aluminum is removed from the composition of higher intermetallic compounds with a decrease in its content from 47 to 10-12 wt.% In the target catalyst.

Figure 1 presents the data of scanning electron microscopy of the microstructure of the surface of the granules of the cobalt-based catalyst at various magnifications (composition Co 89.2 wt.% And Al - the rest), which indicate a strongly eroded nature of the particle topography (a, b). In the photographs with a larger magnification, it is seen that nano formations are formed on the surface of the obtained catalysts, which are complex two-level structures. The main element of the structure (first level) is correctly formed hexagons with a smooth surface of Fig. 1 (c, d), described with a diameter of about 1 μm and a thickness of 70-100 nm. The lateral surfaces of the hexagons have a second-level structure of Fig. 1 (e, f), consisting of ordered (arranged in rows) hexagons 10-15 nm in size. Structures of this kind were first discovered on the surface of polymetallic catalysts. Apparently, they determine the high activity and selectivity of the obtained catalysts in the Fischer-Tropsch process.

The catalyst compositions shown in Table 2 were used for the synthesis of hydrocarbons from CO and H ₂ (1: 2 vol. Ratio). The experiments were carried out in a steel tubular reactor at a pressure of 2.0 MPa. The catalyst was preactivated in the reactor in a stream of hydrogen at 400 ° C. Syngas with 5 vol% argon added as an internal standard was passed through the reactor at a space velocity of 3750 h ^-1 .

Figure 2 presents the temperature dependence of the degree of conversion of CO (a) and selectivity for target hydrocarbons C ₅₊ (b). It can be seen that the selectivity of most catalysts at a level of> 80% is maintained with a CO conversion of up to 40%. Such results are obtained at sufficiently low temperatures (≤220 ° C), which indicates a high activity and selectivity of the proposed catalysts. The synthesized hydrocarbons consisted mainly of linear paraffins (the ratio of linear to isoparaffins is 6.7) and were characterized by a chain growth index of α = 0.92, which indicates a high content of diesel fraction and solid paraffins. These data indicate the possibility of efficient use of the obtained catalysts to produce higher hydrocarbons.

Thus, the combination of features claimed in the formula makes it possible to obtain an intermetallic alloy based on aluminides Co Ni, Fe, V, and Zr, which after chemical treatment (leaching) is a polymetallic material used as a catalyst for the production of higher hydrocarbons from CO and N ₂ .

The proposed method for producing catalytic material does not require large expenditures of electricity, has high productivity, is environmentally friendly, and the resulting catalyst has a high level of catalytic activity in the production of higher hydrocarbons.

Claims (3)

1. A method of producing a catalyst for the synthesis of higher hydrocarbons from CO and H ₂ , comprising preparing an exothermic mixture of powders of the starting components containing aluminum and at least cobalt oxide or cobalt oxide and at least one oxide from the group comprising nickel oxide , iron oxide, vanadium oxide, placing the mixture in a refractory form coated with a functional protective layer of corundum from the inner surface, placing the form with the mixture in a centrifuge, igniting the mixture and carrying out synthesis in the combustion mode by accelerating 40-80 g in an atmosphere of air, separating the target cast alloy from by-products of synthesis, grinding the alloy, isolating a fraction of granules with a size of 0.5 to 1.5 mm, then leaching the resulting product with an aqueous alkali metal hydroxide solution and washing the catalyst, while the content of cobalt oxide in the composition of the exothermic mixture is 25-43 wt.%. 2. The method according to claim 1, characterized in that at least 5 wt.% Zirconium is additionally introduced into the exothermic mixture. 3. The catalyst obtained by the method of claims 1 and 2, which is a polymetallic material based on cobalt aluminides, or cobalt and nickel aluminides, or cobalt and iron aluminides, or cobalt and vanadium aluminides, or cobalt and zirconium aluminides with a highly branched, nanostructured active surface and specific surface area 11.2-25.5 m ² / g.

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