RU2215579C1 - Method of preparing nickel-based metal fiber catalyst - Google Patents

Abstract

FIELD: all-purpose catalysts. SUBSTANCE: catalysts designed for chemical, food, and varnish-and-paint industries, which can be employed both in liquid-phase and gas-phase catalytic processes, is prepared by melting alloy and immersing therein rotating cooled disc for extraction of melt in the form of edges of solidified metal fibers, said alloy is preliminarily supplemented by aluminum in amounts 0.5 to 20 wt % and said fibers thus obtained are subjected to leaching to a depth of 0.01 to 0.1 equivalent diameters fiber. EFFECT: increased specific activity of catalyst. 1 tbl, 5 ex

Description

 The invention relates to catalytic chemistry, in particular to a method for producing a metal-fiber catalyst based on nickel. The catalyst resulting from the use of the present invention can be used in the chemical, food and paint industries, both in liquid-phase and gas-phase catalytic processes.

A known method of producing a catalyst based on Nickel, the so-called catalyst "Raney Nickel" (see J. Anderson. The structure of metal catalysts. M: Mir, 1978, S. 238-240, 456-457). A known catalyst is obtained in the form of a porous powder or a skeletal granular structure. A known method for producing a nickel-based catalyst includes the following operations: nickel is introduced into the aluminum melt and slowly cooled; the cooled alloy is ground into powder by grinding or sprayed and then treated with an alkali solution. After leaching of aluminum, the specific surface area of the catalyst is 50-130 m ² / g. The disadvantages of the known catalyst are:
- its high pyrophoricity;
- heterogeneity in particle size;
- the need to use it in the catalytic process in a dispersed state, which requires the introduction of costly and energy-intensive filtering operations to filter the final products from the catalyst powder into the technological scheme;
- the spent catalyst cannot be regenerated and is characterized by significant difficulties in its disposal.

The closest in technical essence to the proposed solution is a method for producing a nickel-based metal-fiber catalyst, which includes melting the alloy, immersing a rotating cooled disk into it and obtaining metal fiber by extraction of a thin metal layer hardened at the disk edges (high-speed solidification of the melt - VZR) (see VA Vasiliev et al. High-speed solidification of the melt. Theory, technology and materials. M.: SP INTERMET ENGINEERING, 1998, p. 369-371). Modes of the production process: disk rotation speed of 1000 rpm, melt overheating above a melting point of 250 K. The process is carried out in an argon atmosphere. In the known method receive particles of an alloy of a needle and scaly shape. With these parameters of the process of formation of metal particles, their thickness is 100-180 microns. The disadvantages of the nickel-based metal-fiber catalyst obtained in this way are the low specific surface area of 0.1-1 m ² / g and the narrow scope of the catalyst.

 The objective of the invention is to increase the specific surface of the metal fiber of the catalyst and, as a consequence, increase the specific activity of the entire catalyst.

The essence of the invention is to obtain a metal-based catalyst based on nickel by melting the alloy and immersing a rotating cooled disk into it to extract the edges of the hardened metal fibers, in which according to the invention aluminum is preliminarily introduced into the alloy in an amount of 0.5-20 wt.%, And the resulting the fibers are leached to a depth of (0.01-0.1) d _eq , where d _eq is the equivalent fiber diameter.

 Introduction to aluminum alloy allows you to remove it as a result of alkaline treatment from the surface of the fibers. Alkaline surface treatment of the fibers gives an increase in the specific surface of the metal-fiber catalyst and, as a result, an increase in its specific activity. The resulting rapidly crystallized fibers can be directly used as metal-fiber catalysts in liquid-phase and gas-phase catalytic processes. In addition, catalysts of this type can be used to obtain catalyst blocks in reactors with a regular spatial structure.

 Thus, the use of this method makes it possible to obtain rapidly crystallized material that can be directly used as a catalyst with high activity due to the special conditions of the formation of the structure of materials during high-speed solidification of the melt and subsequent leaching, as well as the shape of the catalyst in the form of fibers makes it possible to obtain catalyst blocks for reactors with a regular spatial structure, which makes it possible to eliminate a number of disadvantages inherent in the catalysts obtained by traditional methods.

As a result, the use of catalysts obtained by the proposed method, instead of catalysts obtained by traditional technologies, allows to increase the efficiency and durability of the catalytic reactor, namely:
- significantly increase the compactness of the reaction zone of the catalytic reactor;
- exclude the use of filters for trapping fine catalyst particles;
- provide the required gas permeability of the catalyst;
- eliminate the effect of diffusion inhibition;
- eliminate sintering of the catalyst;
- make full use of the catalytic mass.

MODES FOR CARRYING OUT THE INVENTION
Obtaining nickel-based metal fibers.

Metallic fibers were obtained by the method of extraction of a hanging drop of melt (EEC), which is a variant of the VZR method. Nickel-based alloys containing aluminum were melted to form a hanging drop of melt, which was in contact with the outer edge of the crystallizer disk, and the hardened material was pulled out of the melt in the form of fiber. In this example, the upper flow of the melt to the disk was performed. In the EECR method, the temperature of the hanging melt drop corresponds to the melting temperature of the material used. The fiber was obtained in vacuum with a residual pressure in the chamber of 5-10 ^-3 Pa. In this case, a copper crystallizer disk was used to extract the fiber from the melt. As a result, thin homogeneous fibers having a cross-sectional shape close to an ellipse were obtained. In this case, the catalytic fibers obtained in these modes of implementation of the EECR method consist of a microcrystalline metastable phase.

 The leaching operation of aluminum from metal fibers.

 The process of leaching aluminum from the surface layer of metal fibers was carried out dosed with a 3-4% aqueous KOH solution to the specified leaching depths, for which, in each case, we selected our own regimes (alkali concentration and leaching time).

 Determination of the catalytic activity of samples of metal-fiber catalysts in liquid-phase catalytic reactions.

The determination of the catalytic activity of metal-fiber catalyst samples in liquid-phase catalytic reactions was carried out using hydrogenation of nitrobenzene and dinitrotoluenes at atmospheric pressure and a temperature of 60 ^o C. The experiments were carried out in a standard glass laboratory reactor. The test results are shown in the table.

 As a result of the experiments, it was found that a metal-based catalyst based on nickel with specified characteristics is obtained only when the aluminum content is within the specified limits, namely 0.5-20 wt.%.

 If the aluminum content is less than the specified limits, then the increase in the specific surface area of the fibers necessary to increase the specific activity of the catalyst will not be achieved; if the aluminum content exceeds the specified limits, then the mechanical characteristics of the metal-fiber catalyst will not be maintained at the required level.

As a result of the experiments, it was found that a nickel-based metal fiber catalyst with specified characteristics is obtained only at a leaching depth of (0.01-0.1) d _equiv , where d _equiv is the equivalent fiber diameter.

 If the depth of leaching of aluminum from the surface of the fibers is less than the declared limits, then the increase in the specific surface of the catalyst necessary to increase the specific activity of the catalyst will not be achieved; if the depth of leaching of aluminum from the surface of the fibers is higher than the declared limits, then the mechanical characteristics of the metal-fiber catalyst will not be maintained at the required level.

 Therefore, for the optimal combination of the catalytic and mechanical properties of the metal-fiber catalyst, it is necessary that the aluminum content and the leaching depth correspond to the specified limits.

 This allows us to conclude that the indicated limits of the aluminum content and the leaching depth are among the essential features of this invention, and if they go beyond these limits, then the necessary characteristics will not be achieved, i.e. the technical result in the invention will not be obtained.

 When conducting patent research, no solutions were found that are identical to the claimed method for producing a metal-fiber catalyst, therefore, the proposed solution meets the criterion of "novelty." We believe that the invention does not follow explicitly from known solutions, and therefore, the present invention meets the criterion of "inventive step". We believe that the information set forth in the application materials is sufficient for the practical implementation of the invention.

 The proposed method provides for the production of a metal-fiber catalyst with high specific activity.

Claims (1)

A method of producing a nickel-based metal-fiber catalyst, comprising melting the alloy and immersing a rotating cooled disk into it for extracting it with the edges of the hardened metal fibers, characterized in that aluminum is preliminarily introduced into the alloy in an amount of 0.5-20 wt. %, and the resulting fiber is leached to a depth of 0.01-0.1 d _eq , where d _eq is the equivalent fiber diameter.

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