RU2401699C1 - Method of forming active layer of tubular catalyst - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to pulse method of forming active crust layer of straight-through tubular catalyst of heterogeneous chemical reactions. Proposed method comprises pulsed application of material on specifically prepared surface of carrier wall. Note here that dispersion and fixation of the mix of nanostructured cluster particles and those with grain size varying from 0.1 to 100 mcm are performed by electric blasting at current density of 10⁶-10⁷ A/cm² of conductors accommodated inside the tube, conductors featuring diametres of up to 10 mcm and larger and being made from metals, alloys and chemical compounds.

EFFECT: ease of low costs of production.

7 dwg

Description

The invention relates to pulsed methods of forming an active scab layer of a straight-through tubular catalyst of heterogeneous chemical reactions by sequentially depositing nanodispersed clusters of catalytically active metals, their alloys and chemical compounds, usually oxides, nitrides, carbides, etc. onto a prepared wall of a support

Direct-flow tubular catalysts for heterogeneous chemical reactions are used under conditions of sharply changing and high speed (millisecond range) of contacting of reacting components of a chemical process. In recent years, they have been widely used in systems for the comprehensive purification and neutralization of exhaust gases from internal combustion engines, exhaust gases from chemical and other industries, and in oil and gas reforming production processes. Tubular catalysts are in demand in the production of hydrogen and synthesis gas, in the pyrolysis of ethane and natural gas to produce ethylene, and in fuel cells for powering mobile radio electronics. The use of the invention in research works and in the mass production of gas-sensitive layers of sensor detectors of the concentration of gases and gas impurities in air, etc.

At present, the fact of the preferred use of ultrafine nanostructured particles of active materials in catalytic chemistry can be considered established. Almost all of the catalysts used consist of clusters whose sizes range from units to hundreds of nanometers. The fundamental difference between nanoclusters and bulk materials is that in them the fraction of surface atoms is comparable with the number of atoms in the volume, and the radius of curvature of the surface is comparable to the lattice constant. Although the mechanism of catalysis on dispersed particles is still not fully understood, it is already universally recognized that it is these features that provide them with high catalytic activity compared to their analogues based on bulk (solid) materials. It is believed that their active centers are mainly located on the outer surface.

For a number of important practical applications, shapeless (needle-shaped), with a large number of sharp angles, nanoclusters consisting of metals Cu, Pt, Pd, Ni, Fe, Co, etc., their alloys and chemical compounds, usually oxides, are even more active. , nitrides, carbides, etc. All other things being equal, this increases the specific catalytic activity, reduces the required contact time of the reactants with the catalyst, reduces the size of the reactors, and reduces the cost of production.

Known methods for the manufacture of tubular catalysts using highly dispersed active materials include condensation processes that are thermally vaporized or by magnetrons, laser radiation or electron beam. Chemical reduction from salt solutions is used, followed by lengthy crystallization, fixing and activation processes. Technologies are also used for applying polydisperse cluster structures to carriers in various ways, usually by immersion and further processing.

The disadvantages of such methods are well known. The large duration and complexity of technological operations, including the application of suspensions, drying, evaporation, heat treatment and recovery (> 900 ° C, 10-20 hours). The resulting catalytic reactors are not durable, not stable in time, contain active substance poisoning active centers in the active material, which got into it during the manufacturing process and reduce its catalytic activity. A significant part of the used precious and rare-earth metals is used inefficiently and wastefully, increasing the cost of already expensive devices.

The objective of the invention is a method of manufacturing a tubular catalyst, which provides an economical working layer with increased activity, which allows to form a crust structure with a nanorelief in which the active centers are on the outer surface, thereby improving the operational characteristics of catalytic reactors by improving the quality of the resulting layer.

Known methods using pulsed methods of applying catalytically active layers by loading the active mixture with a detonation wave of an external explosive charge (USSR Author's Certificate No. 1273156, class B01J 37/34, Russian Patent No. 2036721, class B01J 37/34, Russian Patent Federations No. 2188708, class B01J 37/34, 35/00) were recognized not only in the Russian Federation, but also abroad. However, these technologies for their implementation require the organization of highly hazardous blasting operations, the use of complex technological equipment, including an explosive chamber, high consumption of explosives and catalytic mass. In the resulting wall layer, with a thickness of two to five millimeters, containing from two or more percent of noble and rare earth metals, a surface layer with a thickness of several microns is involved in the heterogeneous reaction. The rest, more than 80%, the mass of the used catalytically active material does not take part in the reaction and, therefore, is spent unproductively, thereby increasing the cost of production.

The solution to the problem posed by the invention is to eliminate the above disadvantages.

A significant technical result can be achieved by using an electric explosion coaxially placed inside a tubular reactor wire of a catalytically active metal or alloy. Moreover, depending on the problem solved by the reactor, all kinds of tubes from various types of ceramics, silica fabric, metals, foil and lattices from them, various composites, oxides, carbon materials, etc. can be used as carriers.

=10⁵-10⁶ см/сек, температурой ~10⁴ К и размерами от 0,1 до 100 мкм.The energy of the heating current pulse with a density of 10 ⁶ -10 ⁷ A / cm ^{2 is} chosen in the region of 0.2-0.7 of the sublimation energy of the metal of the exploding conductor, and the wire is used with a diameter of 10 microns or more, depending on the electrical capabilities of the pulse power source and required layer thickness. In this case, the products of the explosion of the wire are highly dispersed cluster particles, scattering, as a rule, in a plane perpendicular to the axis of the conductor with an initial radial velocity

= 10 ⁵ -10 ⁶ cm / s, temperature ~ 10 ⁴ K and sizes from 0.1 to 100 microns.

Having met with the wall of the carrier, the nanocluster gives it kinetic and thermal energy, deforming its surface at the point of contact, melting, penetrating and welding to it, forming a microcrater with shapeless (including needle) sharp-angled edges from the material of the wire. The maximum possible adhesion of the catalytically active material to the carrier wall and the formation and activation of the optimal crust of the catalyst working surface are realized.

This gives, firstly, a 2-3-fold increase in specific catalytic activity per gram of expendable material due to its nanodispersion. Secondly, by increasing the adhesion strength it allows you to create crusty, within a few microns, mechanically and thermostable active layers.

All together makes it possible, with the same efficiency, to reduce the contact time of the reactants to milliseconds, reduce the size of the reactors and significantly reduce the consumption of precious and rare-earth metals, and therefore the cost of the reactors and their maintenance.

The method allows you to quickly create and study more complex, more effective, cheap and promising compositions of materials for catalysts for heterogeneous chemical reactions.

Verification of the proposed method was carried out on the installation with the parameters:

Inductance of the discharge circuit 1.6 μG;

Capacitor bank capacity 1.5 uF;

The voltage of the VZU varied in the range from 10 to 30 kV.

=10⁵ см/сек, в плоскости, перпендикулярной оси проволочки. Схема процесса приведена на Фиг.4. В качестве мишени была использована стеклянная трубочка, позволявшая визуально оценивать получающиеся слои. Трубочка была изготовлена из обыкновенного химического стекла и имела следующие размеры: длина-2,5 см; внешний диаметр D=0,5-1,0 см; внутренний диаметр d=0,3-0, 5 см.The electrical circuit is shown in figure 1. The principle of operation of the electrical circuit of the installation is to form and supply a pulse for a wire explosion. The high-voltage charger VZU charges a capacitive energy storage device (capacitor bank C ³ -C ⁸ to a predetermined potential. At the same time, the control capacitance C ^{2 of the} arrester is charged with the same potential. When KN1 closes and triggered triggered arrester UR1 is activated, the capacitive energy is supplied to the electrodes AK of the device САР1, between which a wire is installed coaxially with the tube, etc. (See also Fig. 2, 3). If the conditions are met for the current pulse to reach the required density and energy, the wire explodes, turning into nanostructured cluster particles with a temperature of the order of ~ 10 ⁴ K and flying radially with speed

= 10 ⁵ cm / sec, in a plane perpendicular to the axis of the wire. The process diagram is shown in Fig.4. A glass tube was used as a target, which made it possible to visually evaluate the resulting layers. The tube was made of ordinary chemical glass and had the following dimensions: length-2.5 cm; outer diameter D = 0.5-1.0 cm; inner diameter d = 0.3-0.5 cm.

The catalytically active layers obtained as a result of the experiment were studied by transmission electron microscopy, as well as by a scanning microscope with field emission. The layer was strengthened with carbon and separated from the wall surface. We studied the structure, phase composition, shape and distribution of the geometric dimensions of the nanoclusters, the latter is shown in Fig.5, 6.

For comparison, the graph shows graph paper. The image scale is 1 mm = 100 nm = 0.1 μm. The sizes of nanoclusters, according to the densitometry of the image, lie in the range from 0.1 to 100 microns.

Figure 7 shows a photograph of a catalytic tube with copper deposited on the inner surface using an electric explosion.

The research results suggest that the new method makes it possible to technologically simple and quick to create and study more effective, cheap and, therefore, promising compositions of materials for heterogeneous chemical processes and apply them to the working surfaces of tubular catalytic reactors. Conduct targeted selection of catalysts for chemical processes and chemical processes for catalysts.

The increase in activity reduces the contact time of the reactants with the catalyst, and this in turn leads to a decrease in the size of the catalytic reactors.

The reduction in size allows the use of thin-walled pipes for carriers, and this allows you to work in conditions of abruptly changing temperature conditions (for example, internal combustion engines).

The list of drawings and other materials.

Figure 1 A simplified circuit diagram of a switching power supply, where A, K are electrodes, Tr is a catalyst carrier tube, Pr is a wire of a catalytically active metal or alloy.

Figure 2 A diagram of the mutual arrangement of the wire, before its electric explosive dispersion, relative to the tubular carrier, where 1 is the tubular carrier, g is the inner radius of the tube, 2 is the wire, L is the length of the tube.

Figure 3 Schematic physical diagram of the technological process, where 1 is a tubular carrier of a catalytically active layer, 2 is a longitudinal section of a tubular carrier with catalytically active nanodispersed electroexplosion particles embedded on the inner surface.

Figure 4 Photo of the active layer of the catalyst Cu + Ni on the surface of chemically pure glass, obtained by transmission electron microscopy X9000.1 mm ~ 0.1 μm ~ 100 nm.

Figure 5 Photo of a tubular catalyst on the inner surface of a glass tube with an active layer of Cu + CuO, pipe length 120 mm, outer radius ~ 12 mm, inner radius ~ 7 mm.

Claims (1)

A method of forming a crusty wall active layer of straight-line tubular catalysts for heterogeneous chemical reactions, including the pulsed deposition of material on a prepared surface of a carrier wall in a specific way, characterized in that the process of dispersing and fixing a mixture of nanostructured cluster particles and particles from 0.1 to 100 microns in size is carried out by the method consecutive electric blasting at a current density of 10 ⁶ -10 ⁷ A / cm ² coaxially placed inside the pipe conductors with a diameter of 10 microns and more of metals, alloys and their chemical compounds.

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