RU2295385C1 - Heat-conducting composite catalyst and process of steam conversion of carbon monoxide - Google Patents

Abstract

FIELD: disproportionation process catalysts.

SUBSTANCE: invention relates to generation of hydrogen through steam conversion of carbon monoxide and development of catalyst for indicated process. Invention provides carbon monoxide conversion catalyst showing high catalytic activity and heat-conductivity and a process of steam conversion of carbon monoxide using indicated catalyst. Catalyst is characterized by heat-conductivity at least 1 W(mK)-1, which enables performing process with low temperature gradient in direction transversal to gas stream direction.

EFFECT: increased catalytic activity and heat-conductivity.

7 cl, 4 dwg, 3 tbl, 10 ex

Description

The invention relates to the field of hydrogen production by steam conversion of carbon monoxide and the development of catalysts for this process.

The reaction of steam reforming WITH can be represented by the equation

СО + Н ₂ О СО ₂ + Н ₂ (ΔН ° _298К = -41.1 kJ / mol)

The steam carbon conversion process is widely used in large industrial hydrogen plants. The process is carried out in two stages in which the conversion of CO proceeds sequentially at high temperatures of 320-450 ° C on iron-chromium catalysts and at low temperatures 180-250 ° C on Cu / Zn / Al (Cr) oxide catalysts. Steam conversion is carried out in axial (shelf) or radial type adiabatic reactors with fixed catalyst beds. The designs of such reactors are well known. Axial reactors are simpler in design than radial ones. However, the latter have a number of technological and operational advantages [Process gas cleaning. Ed. T.A.Semenova and I.L. Leites. M., Chemistry, 1977, 488 pp.]. In radial reactors with a uniform distribution of gas in the catalyst bed, the hydraulic resistance does not exceed 0.01 MPa and practically does not change during operation. In axial reactors, the hydraulic resistance increases from 0.02-0.04 MPa to 0.2-0.4 MPa during operation, which may lead to the need for early discharge of the catalyst.

The two-stage process has a rather cumbersome hardware design due to the separation into stages and large volumes of used catalysts. To improve the overall dimensions, the process of steam conversion of CO can be carried out by organizing the optimal temperature profile in the catalyst bed operating in a wide temperature range. It is advisable to carry out the reaction at high temperatures, at the same time, low concentrations of CO (less than 1-1.5 vol.%) At the outlet can be achieved at temperatures no more than 270-300 ° C. Therefore, the temperature in the catalyst bed should vary from about 400 to 200 ° C. Such a change can be achieved by organizing several isothermal catalyst beds or an optimal temperature profile in one catalyst bed by continuous heat removal. In [D.Myers, T. Krause, J.-M.Bae and C. Pereira. Extending Abstracts. 2000 Fuel Cell Seminar, p.280-283, 2000] considered these options for organizing heat removal.

The implementation of the steam reforming reaction in a catalyst bed with an optimal temperature profile in a tubular reactor using a traditional catalyst, stably operating in the range up to 350 ° C, is described in the patent [US 5990040, B 01 J 023/00, C 01 B 031/00, 28.07 .1997]. To efficiently remove reaction heat, tube reactors with tube diameters of 50-60 mm or less are usually used for very heat-intensive processes. Conventional catalysts used in CO steam reforming reactors are oxides or metals on oxide supports and have a low ability to conduct heat. The heat transfer from the catalyst pellet to the wall of the reactor is through the reaction gas. The small coefficient of heat transfer from a solid to a gas and from gas to a solid determines the heating of the catalyst layer. The effective coefficient of thermal conductivity of the catalyst layer in the direction transverse to the gas stream does not exceed 0.5-1 W (mK) ^-1 , therefore, the temperature difference in the radial direction in the catalyst layer of the CO vapor conversion for tubes with a diameter of 50-60 mm reaches 20-30 ° C [Beskov S.D. Technochemical calculations. Moscow Higher School 1968; Boreskov G.K. Heterogeneous catalysis. Moscow "Science" 1988].

In the present invention, the problem of intensive heat removal in the catalyst bed in the radial direction is proposed to be solved: (1) by creating a catalyst with high thermal conductivity of the catalyst body and (2) efficiently organizing the catalyst layer, for example, by using a catalyst body with transverse dimensions comparable in size to the dimensions reactor, and / or providing direct contact with the wall of the reactor through which heat is removed.

The problem cannot be solved by the use of metal plates, foam metals or composite materials with good thermotechnical properties as catalysts and for which it is easy to arrange direct contact with the walls of the reactor due to the fact that they are obtained by sintering of oxide and metal components at high temperatures, have a low specific surface and do not exhibit high catalytic activity [US 6517805, C 01 B 3/02, 02.10.1998; US 6432871, B 01 J 023/70, 10/18/1999]. An increase in the catalytic activity of these materials can be achieved by applying a catalytically active component to their surface. However, in this case, there is a problem of the strength of fixing the active substance. If the fastening is not strong enough, it is possible to shed and carry off the catalyst during operation.

Closest to the present invention is a patent [EP 1232790, B 01 J 23/722, 1.08.2002], which provides catalysts for endo-and exothermic reactions in which the thermal conductivity and activity of the catalyst body are achieved using metal plates on the surface of which it is synthesized active component.

The invention solves the problem of intensive heat removal in the catalyst bed in the radial direction.

To solve this problem, it is proposed to use a composite with a high activity and thermal conductivity of at least 1 W (m K) ^-1 in the reaction of steam reforming of CO. The body of the catalyst is a composition of a catalytically active component of an oxide nature and metal particles with a mass ratio of at least 0.25.

In the catalyst body, the catalytically active component of an oxide nature is a copper and zinc based catalyst promoted by elements of groups III, IV, VI, preferably Zr.

In the catalyst body, the catalytically active component of an oxide nature is an iron and chromium based catalyst promoted by elements of groups I, II, VII, preferably Cu.

In a composite, metal particles are particles of metallic copper of a dendritic texture.

The catalyst is used in the form of bodies, the maximum overall dimension of which is not less than 0.8 of the minimum overall dimension of the reactor.

The inventive heat-conducting catalyst consists of particles of a catalytically active component of an oxide nature and heat-conducting metal particles, which serve simultaneously as a reinforcing component. Such a composite can be obtained by the sequence of operations used in powder metallurgy and including: 1) preparation of a mixture of powders of a catalytically active component of an oxide nature, a metal and a pore-forming component, 2) compaction of the mixture and 3) sintering at elevated temperatures, which do not lead to catalytic properties active component.

By a catalytically active component of an oxide nature is meant a set of phases including an oxide phase containing active metal cations, for example, Cu ²⁺ cations or iron cations. The catalytically active component can be prepared by precipitation [RU 2118910, B 01 J 23/84, 09/20/1998; US 5990040, B 01 J 023/00, C 01 B 031/00, 07/28/1997] followed by calcination of the obtained hydroxo compound, or by any other known method. It is necessary that the oxide catalyst exhibits stable activity in the CO steam reforming reaction in the medium temperature (300-450 ° C) region or in the low temperature (180-250 ° C) region, preferably in the entire temperature range 450-180 ° C.

As a heat-conducting metal particles in the composition of the composite, particles of metallic copper of a dendritic structure with characteristic sizes of less than 50-100 μm can be used. The ratios of the amounts of heat-conducting substance, disintegrant and oxide catalyst are determined by the requirements of heat conductivity, strength and developed surface of the heat-conducting catalyst body.

The desired shape of the heat-conducting catalyst body can be carried out using any of the known tabletting methods, preferably at a compaction pressure of more than 1500 kgf / cm ² . The minimum volume of the working layer is achieved by optimal placement of tablets with dimensions comparable to the transverse dimensions of the reactor tube, and the optimal surface-to-volume ratio.

The heat treatment of the heat-conducting catalyst body is carried out in an inert gas stream at temperatures above the Tammann temperature (about 0.5 of the absolute melting temperature).

The catalysts prepared in this way satisfy the requirements of high thermal conductivity and strength, and also show high activity in the reaction of steam conversion of carbon monoxide.

The invention is illustrated by the following examples, tables and drawings.

Figure 1 (a) Data of electron scanning microscopy about the characteristic topology of the heat-conducting catalyst body.

(b) Data on the uniform distribution of the catalytically active component (dark gray areas) and the heat-conducting component (light gray areas) in the optical micrograph.

Figure 2 Laboratory reactor of rectangular cross-section as an option for the optimal organization of the catalyst layer using heat-conducting catalyst plates.

Figure 3 Comparison of changes in temperature in the radial direction during the reaction of steam reforming of CO on the body of a heat-conducting catalyst with a diameter of 50 mm (circles, •) and on the catalyst in the form of tablets of a conventional industrial form in a tubular reactor with a diameter of 50 mm (triangles, ▲).

Table 1. Preparation parameters and thermal conductivity values of catalyst bodies of various shapes.

Table 2. The degree of use of catalyst grains in a heat-conducting catalyst body and in a traditional tablet in a flow-circulation reactor of ideal mixing at various reaction temperatures.

Table 3. The results of catalytic tests of heat-conducting catalyst plates in a rectangular laboratory reactor at a reaction gas mixture speeds of 20 l / h and 250 l / h.

Example 1A

The heat transfer catalyst 1A is prepared as follows:

1) 38 wt.% Powder of the joint oxide of copper-zinc-aluminum-chromium obtained in accordance with the patent [RU 2118910, B 01 J 23/84, 09/20/1998], 52 wt.% Powder of a heat-conducting substance and 10 wt.% powder disintegrant with a particle size of less than 70 microns is thoroughly mixed,

2) the resulting mixture of powders is compacted at a pressure of 2490 kgf / cm ² , then crushed and sifted out a fraction of particles with a size in the range of 100-200 μm,

3) the resulting fraction is tabletted at a pressure of P = 2490 kgf / cm ² in the form of a ring with an external diameter of 18 mm, an internal diameter of 7 mm, and a height of 2.5 mm,

4) heat treatment is carried out in an inert gas stream at a temperature of T = 380 ° C.

The characteristic topology of the heat-conducting catalyst body according to electron scanning microscopy is presented in Figure 1 (a). In the optical micrograph (see Figure 1 (b)), the distribution of the catalytically active component (dark gray areas) and the heat-conducting component (light gray areas) is clearly visible.

Examples 2A-6A.

Heat-conducting catalysts are prepared analogously to example 1A, but at different tabletting pressures and heat treatment temperatures. The parameters for the preparation of heat-conducting catalysts 1A-6A are presented in Table 1.

Example 7A

The heat-conducting catalyst is prepared analogously to example 1A, but the powder of the joint iron-chromium-copper oxide obtained in accordance with the patent [BG 32877, B 01 J 23/86, 11/15/1982], at a tableting pressure P = 1720 kgf / cm ² and using heat treatment temperature T = 380 ° C.

Example 8

The heat-conducting catalyst body Z1 is prepared analogously to example 1, but when tabletting it is shaped like a square plate with dimensions 25 × 25 × 2.5 mm, the pressure of tabletting is P = 1720 kgf / cm ² .

Example 9

The heat-conducting catalyst body is prepared analogously to example 8, but the temperature of the heat treatment is T = 410 ° C.

Example 10 (comparative).

The catalyst is prepared according to patent RU 2118910 in the form of tablets in the form of a cylinder with a diameter of 5 mm and a height of 5 mm, typical for use in traditional industrial reactors.

Coefficients of thermal conductivity of the body in the form of a ring with dimensions: outer diameter D = 18 mm, inner diameter d = 7 mm, ring height h = 10 mm; it is determined when the heat flux through the sample is changed in a laboratory unit specially created for these purposes at the ITF SB RAS. To test the installation, the thermal conductivity of a sample made of stainless steel (12X18H10T) was measured. From the measurements it was shown that the thermal conductivity of the test sample differs from the reference data by no more than 5%. The error in determining the thermal conductivity of the samples presented in the patent is about 7%. The experimental values of thermal conductivity are presented in Table 1 in comparison with the thermal conductivity of a tablet of the industry-standard form of copper-zinc-aluminum catalyst promoted with chromium prepared according to patent RU 2118910.

Catalytic tests of heat-conducting catalysts are carried out in a flow-through ideal mixing reactor with the composition of the reaction mixture СО 16 vol.%, CO ₂ 9 vol.%, Н ₂ 75 vol.% At a pressure of 0.1 MPa in the temperature range 270-350 ° С. The results of the catalytic tests are presented in Table 2 as the degree of use of the grain of the catalytically active component, that is, as the ratio of the experimental value of the reaction constant on a heat-conducting catalyst (or tablet of a traditional form) to the experimental reaction rate constant in the kinetic region on particles of a catalytically active component with a size of 0.25- 0.5 mm. This value characterizes the activity of a real catalyst and allows you to quantitatively compare the activity of the catalysts proposed by the present invention and described in the examples with known catalysts in the form of cylindrical tablets of 5 mm × 5 mm

The results of catalytic tests of heat-conducting catalysts according to examples 8 and 9 in a laboratory reactor of rectangular cross section (Figure 2) at a reaction gas mixture speeds of 20 l / h and 250 l / h are presented in Table 3.

Figure 3 presents a comparison of changes in temperature in the radial direction during the reaction of steam reforming of CO on the body of a heat-conducting catalyst with a diameter of 50 mm (circles, •) and on the same catalyst in the form of tablets of a conventional industrial form in a tubular reactor with a diameter of 50 mm (triangles, ▲ )

The presented examples indicate that the heat-conducting catalysts claimed by the present invention are not inferior to the known catalysts with low thermal conductivity in the degree of use of the grain of the catalytically active component, but provide a much smaller temperature gradient of the catalyst layer in the radial direction of the reactor.

A variant of the proposed effective organization of the catalyst layer is provided by the comparable transverse dimensions of the heat-conducting catalyst body and the reactor itself (Figure 2). At the same time, it is preferable, but not necessary, to ensure direct contact of the heat-conducting catalyst body with the wall of the reactor. From the outer wall of the reactor, the heat of reaction can be removed using known methods of heat exchange with the refrigerant.

Table 1.
Preparation parameters and thermal conductivity values of catalyst bodies of various shapes. Sample P, kgf / cm ² T, ° C Thermal conductivity, W / m · K Example 1A 2940 380 2.8 Example 2A 2200 380 2.8 Example FOR 1720 380 2.8 Example 4A 2940 440 3.2 Example 5A 2200 440 3.2 Example 6A 1720 440 3.2 Example 7A 1720 380 2.6 Example 8 1720 380 2.8 Example 9 1720 410 3.0 Example 10 (comparative) cylinder d = 5 mm, h = 5 mm 0.3

Table 2.
The degree of use of catalyst grains in a heat-conducting catalyst body and in a traditional tablet in a flow-circulation reactor of ideal mixing at various reaction temperatures. Sample The degree of use of the catalyst grain in the form of a traditional tablet and a heat-conducting catalyst body at reaction temperatures: 270 ° C 300 ° C 330 ° C 350 ° C Example 10 (comparative) 0.41 0.37 0.36 0.34 Example 1A 0.50 0.44 0.35 0.27 Example 2A 0.47 0.44 0.35 0.29 Example 3A 0.53 0.46 0.36 0.39 Example 4A 0.31 0.28 0.23 0.20 Example 5A 0.39 0.38 0.28 0.24 Example 6A 0.51 0.40 0.33 0.33 Example 7A 0.47 0.45 0.38 Example 8 0.55 0.46 0.37 0.37 Example 9 0.60 0.48 0.40 0.40

Table 3.
The results of catalytic tests of heat-conducting catalyst plates in a rectangular laboratory reactor at a reaction gas mixture speeds of 20 l / h and 250 l / h. Sample The degree of use of the grain of the catalyst of the heat-conducting catalyst body at various speeds of the reaction gas mixture and reaction temperatures: 20 l / hour 250 l / h 270 ° C 300 ° C 330 ° C 350 ° C 270 ° C 300 ° C 330 ° C 350 ° C Example 8 0.48 0.40 0.34 0.33 0.50 0.43 0.35 0.35 Example 9 0.55 0.42 0.36 0.36 0.57 0.46 0.38 0.38

Claims (5)

1. The catalyst for the vapor conversion of carbon monoxide, which is a composition of a catalytically active component of an oxide nature and a metal component, characterized in that as a metal component it contains particles of metallic copper with a size of less than 100 microns with a mass ratio of catalytically active component to metallic copper particles of not less than 0.25 and the catalyst is a composite having a thermal conductivity of at least 1 W / (m · K). 2. The catalyst according to claim 1, characterized in that in the composite the catalytically active component of an oxide nature is a catalyst based on copper and zinc, promoted by elements of groups III, IV, VI, preferably Zr. 3. The catalyst according to claim 1, characterized in that in the composite the catalytically active component of an oxide nature is a catalyst based on iron and chromium, promoted by elements of groups I, II, VII, preferably Cu. 4. The method of steam conversion of carbon monoxide, characterized in that it is carried out using a catalyst according to any one of claims 1 to 3. 5. The method according to claim 4, characterized in that the catalyst is used in the form of plates, the area of which is not less than 0.65 from the cross-sectional area of the reactor.

Images