RU2349380C1 - Catalyst and method of obtaining synthetic gas from carbon dioxide conversion of methane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention pertains to chemical industry, particularly to catalysts used for converting natural gas, and can be used in petrochemical and oil-refining industry for making catalysts and in gas synthesis process. Description is given of a catalyst, containing a nickel aluminide matrix, inside of which nickel and molybdenum are dispersed, with the following ratio of components, in wt %: Ni₃Al - 80-90, Ni - 5-10, Mo -2-10. The catalyst is obtained through self-propagating high-temperature synthesis and is used in the process of carbon dioxide conversion of methane.

EFFECT: high catalytic activity and stability of the catalyst.

2 cl, 4 tbl, 3 ex

Description

The invention relates to the chemical industry, in particular to catalysts used for the conversion of natural gas, namely, catalysts for reactions affecting CH bonds of hydrocarbons and contributing to the breaking of these bonds with the formation of compounds containing multiple bonds (CO) and hydrogen, a mixture of which is called synthesis gas, and carbon dioxide conversion methods, and can be used in the petrochemical, oil refining and other industries for the production of catalysts and the organization of the production process syngas. Subsequently, the resulting synthesis gas can be widely used in large-capacity chemical processes, such as the synthesis of dimethyl ether (DME), methyl methacrylate, alcohols, aldehydes, etc. The resulting dimethyl ether can be used as an environmentally friendly fuel for diesel engines without significant changes in their designs. .

Traditionally, synthesis gas is produced by the methods of steam, carbon dioxide, steam-air or steam-oxygen conversion of hydrocarbon feedstocks. The composition of the resulting synthesis gas depends on temperature, the pressure of the process, the catalyst used, the ratio of the pairs of the starting components, space velocity, the composition of the starting mixture of components. As a rule, the feedstock hydrocarbon (natural gas) is purified from sulfur compounds.

The disadvantages of traditional methods for the production of synthesis gas by the catalytic conversion of hydrocarbon feedstocks are the use of an insufficiently active and stable catalyst having relatively large geometric dimensions, a large aerodynamic resistance of the granular layer, restrictions on the supply of heat to the reaction zone, the need for oxygen in mine reactors, limitations on the possibility of creating low power production.

The authors of MCJ Bradford and MA Vannice propose to use, for example, nickel catalysts using various ceramic-based supports as catalysts for the carbon dioxide conversion process, but often they undergo significant carbonization (MCJ Bradford and MA Vannice. CO ₂ reforming of methane. Catal. Rev. Rev. . - Sci. Eng., 1999, v.41, pp. 1-42).

In works (Claridge JB, York APE, Brungs AJ ea Journal of catalysis, 1998, v. 180, No. 1, p. 85-100; WO 02076885, J. Sehested, CJH Jacobsen, S. Rokni, and JR Rostrup-Nielsen Activity and Stability of Molybdenum Carbide as a catalyst for CO ₂ Reforming, Journal of Catalysis, 2001, v.201, p.206-212) shows the fundamental possibility of using Mo and W carbides as catalysts for UKM. However, despite the relatively high activity in all three methane conversion reactions, a significant drawback is the implementation of the process only at high pressures — at ordinary pressures, carbides are deactivated due to oxidation to MO ₂ oxides.

It is known that oxides can be catalysts for carbon dioxide methane conversion (RF patent 96100764, 1998; Krylov OV, Mamedov A.Kh. Heterogeneous-catalytic reactions of carbon dioxide. Advances in Chemistry, 1995, v.64, No. 9, p.935 -959). Also known are those that consist of an oxide support (Al ₂ O ₃ , SiO ₂ , ZrO ₂ , BaO, CaO, etc.) and coatings from metals (Pt, Pd, Ru, Rh, Ni, etc.). Despite the fact that they have sufficient activity, they all undergo coking. Over time, this leads to the deactivation of the catalysts, which requires their regeneration and leads to an increase in production costs. A disadvantage of the known catalysts and carriers is the fact that at high temperatures in the conditions of the redox environment, they are oxidized, which significantly reduces the contact strength between the particles.

Currently, one of the main directions in solving the problem of searching for UKM catalysts is the development of improved nickel systems that would contribute to kinetic inhibition of carbon formation on their surface under conditions thermodynamically favorable for carbon deposition. As a result of combination with suitable carriers such as La ₂ O ₃ , MgO, TiO ₂ and CeO ₂ ; using effective promoters, including La ₂ O ₃ , LiO _2, and even iron oxide, as well as new methods of preparation, such as solid phase crystallization method, sol-gel method, citrate method (Krylov O.V. Heterogeneous catalysis. M. : Academic Book, 2004, 679 pp .; Hu YH, Ruckenstein E. Catalytic Conversion of Methane to Synthesis Gas by Partial Oxidation and CO ₂ Reforming. Adv. Catal., 2004, v. 48, p. 297-345; Tomishige K. Syngas production from methane reforming with CO ₂ / H ₂ O over NiO-MgO solid solution catalyst in fluidized bed reactors. Catal. Today., 2004, v. 89, p. 405-418; Hao Z., Zhu HY, Lu GQ Zr-Laponit pillared clay-based nickel catalysts for methane reforming with carbon dioxide. Appl. Catal., 2003, v.242, p.275-286).

At present, there is no industrial technology for the production of synthesis gas by the method of carbon dioxide conversion of methane. Available developments are most often based on nickel catalysts used in the steam reforming process, they do not have sufficient selectivity and are quickly deactivated due to the formation of carbon, which covers active metal centers during catalysis, and accumulate in the pores of the catalyst, causing destructive changes and ultimately - decontamination.

The process of carbon dioxide conversion of methane is carried out at high temperatures, so the surface area of the catalysts will inevitably decrease. One of the most important requirements for such catalysts is resistance to temperature extremes and thermal shock. It is desirable that they have increased thermal conductivity to reduce the likelihood of local overheating. Some transition metal intermetallic compounds, such as nickel, which are widely used to produce skeletal Raney nickel, possess these properties.

There is practically no data in the literature on the use of intermetallic catalysts for the process of carbon dioxide methane conversion.

The closest to the achieved result and technical essence is the catalyst obtained by self-propagating high-temperature synthesis (SHS) and consisting of an Ni ₃ Al intermetallic matrix in which free nickel is dispersed (L.A. Arkatova, T.S.Kharlamova, L.V. Galaktionova et al. Carbon dioxide conversion of methane on nickel aluminides. Journal of Physical Chemistry, 2006, vol. 80, No. 8, pp. 1403-1406). Among the studied intermetallic compounds of the Ni-Al system, the highest catalytic activity comparable with the industrial catalyst for steam conversion was manifested by precisely this composition of Ni ₃ Al, which ensured 82.2% conversion of CO ₂ and 79.6% of CH ₄ at 1223 K. The yield of synthesis gas was СО - 43.1 mol.%, H ₂ - 37.8%. The known catalyst is obtained by the high-performance and economical SHS method from a pressed mixture of nickel and aluminum powders in the form of beads, which are then crushed and sieved to obtain the desired fraction.

However, after catalytic studies on the known catalyst, carbon deposition is observed, accompanied by the formation of nickel carbide and graphite-like carbon, which leads to the fact that the activity of the catalyst decreases (the catalyst is deactivated).

The present invention is to develop an effective catalyst that is resistant to temperature extremes and thermal shock, having increased thermal conductivity to reduce the likelihood of local overheating, eliminating carbon deposition in the process of carbon dioxide methane conversion and increasing the productivity of the process.

The problem is solved by using as a catalyst for carbon dioxide conversion of methane a material obtained by self-propagating high-temperature synthesis and containing a nickel aluminide matrix inside which nickel and molybdenum are dispersed, and consisting of 80-90 wt.% Ni ₃ Al, 5-10 wt.% Ni and 2 -10 wt.% Mo.

The problem is also solved by the method of producing synthesis gas by carbon dioxide conversion of methane using the inventive catalyst.

The resulting catalyst is highly active, thermostable, resistant to local overheating and thermal shock, operates at an average contact time of 0.1-1 s in a one-step reaction of carbon dioxide methane conversion at 600-1000 ° С at atmospheric pressure.

The catalyst is a chemical compound of several metals and is an intermetallic compound consisting of coarse particles or particle aggregates.

The amount of nickel and aluminum required to obtain Ni ₃ Al is selected according to the phase diagram. The amount of introduced modifying additive - molybdenum no more than 10 wt.% Is determined by its influence on the microstructure of the active phase. The introduction of more than 10 wt.% Mo leads to the coarsening of the structure of the active phase.

The catalytic system was obtained by the method of self-propagating high-temperature synthesis (SHS), carried out in the regimes of layer-by-layer combustion or thermal explosion, based on the use of internal chemical energy of the starting reagents and devoid of a number of drawbacks of traditional methods for producing intermetallic compounds. It has a number of undoubted advantages - low energy costs, simplicity and one-step synthesis cycle, expressness, high productivity, low-cost equipment, high purity of the product.

The method of producing the catalyst proposed in this invention includes drying the powders of the respective metals, dry mixing the components, molding the mass into the desired form by double-sided pressing, initiating combustion in a thin layer and directly burning, crushing and fractionation.

The invention provides a process for the catalytic conversion of light hydrocarbons, preferably methane, which makes it possible to obtain mixtures of H ₂ and CO with molar ratios of the components 0.5-1.5, preferably 1. Natural gas can be used as a feedstock.

The conversion is preferably carried out in one step using Mo-modified nickel aluminide intermetallide in the temperature range of 600-1000 ° C, preferably 950 ° C, at atmospheric pressure. When using methane, the desired volumetric ratio of CO ₂ : CH ₄ is 0.5-1.0, preferably 1. The reaction mixture containing methane (natural gas) and carbon dioxide is heated before entering the reactor. During the start-up and operation of the catalyst, the gas temperature at the inlet to the reactor and the temperature of the catalytic unit are controlled. The efficiency of the catalyst is characterized by the degree of conversion of methane and carbon dioxide, as well as the amount of synthesis gas obtained, expressed in volume percent. The composition of the initial reaction mixture and reaction products are analyzed chromatographically.

The invention is illustrated by the following examples.

Example 1. To obtain a catalyst Ni ₃ Al + 2% Mo, powders of nickel metals (grade PNE-1) weighing 86 g, aluminum (ASD-4) weighing 12 g, molybdenum (osch) weighing 2 g, are preliminarily dried for 5 hours at a temperature of 150 ° C in an argon atmosphere. The powders are mixed and a cylindrical preform is prepared by double-sided pressing on a table press with a collapsible mold and a floating piston. The porosity is 30-40%. SHS of pressed samples is carried out in a 3-liter constant pressure bomb. Combustion is carried out in an argon atmosphere, the pressure of which is 0.1 MPa. A thermal impulse is brought to the end part of the pressed billet using a tungsten spiral, igniting the billet. At the same time, a chemical reaction is excited in the surface layer, which spontaneously propagates in the form of a combustion wave running along the axis of the workpiece, leaving a cooling product. The sample obtained in the form of a staff is then crushed and sieved. The resulting material is a system consisting of Ni ₃ Al, Ni and molybdenum dispersed in it (according to XRD).

For catalytic studies, fractions with a particle size in the range of 400-600 μm and 600-1000 μm, which in the amount of 1 cm ³ are placed in a tubular quartz reactor with an inner diameter of 5 mm, are selected. Methane and carbon dioxide are passed through the catalyst in the temperature range 600–950 ° C and a contact time of 0.6 s. The methane conversion process is carried out in a fixed catalyst bed at a pressure of 1 atm. Gas chromatographic analysis of the gas is carried out starting from 600 ° C, and continues to 950 ° C. The volumetric rate of the feed gas mixture is adjusted while maintaining 100 ml / min. The starting components methane and carbon dioxide are supplied based on the molar ratio of CO ₂ : CH ₄ = 1: 1. Based on on-line chromatographic analysis, the conversions of methane and carbon dioxide and the yields of the desired products are calculated. The conversions of methane and carbon dioxide, as well as the yields of the target products carbon monoxide and hydrogen for each composition are shown in tables 1-3. Data on the stability of the catalyst are presented in table 4.

Example 2. To obtain a catalyst Ni ₃ Al + 5% Mo, powders of nickel metals (grade PNE-1) weighing 84 g, aluminum (ASD-4) weighing 11 g, molybdenum weighing 5 g are taken. Next, operations similar to example 1 are carried out. The catalytic data are shown in table 2.

Example 3. To obtain a catalyst Ni ₃ Al + 10% Mo, powders of nickel metals (grade PNE-1) weighing 81 g, aluminum (ASD-4) weighing 9 g, molybdenum (osch) weighing 10 g are taken. Next, the procedure described in example 1. The catalytic data are shown in table 3.

Table 4 shows data on the stability of the catalyst Ni ₃ Al + 5% Mo. The stability of the claimed catalyst is higher than that of the prototype composition of Ni ₃ Al, subjected to coking after 16 hours. Catalysts with molybdenum, as can be seen from tables 1-3, also exhibit increased catalytic activity compared to the catalyst Ni ₃ Al.

In the systems under study, synthesis gas of the composition H ₂ : CO is formed, approaching 1: 1. With an increase in the modifier concentration in the system, the H ₂ : CO ratio gradually increases from 0.94 for Ni ₃ Al + 2% Mo, 1 for Ni ₃ Al + 5% Mo, and 1.1 for Ni ₃ Al + 10% Mo.

Thus, the proposed catalyst in the process of methane conversion exhibits high catalytic activity and stability.

Table 1
Catalytic data of the process of carbon dioxide conversion of methane for the catalyst Ni ₃ Al + 2% Mo Catalyst T, K Conversion% Yield, (mol.)% CO ₂ CH ₄ With H ₂ Ni ₃ Al + 2% Mo 873 0 0 0 0 973 0 0 0 0 1073 49 25 22 fifteen 1123 71 42 31 25 1173 87 59 39 34 1223 94 74 44 41 table 2
Catalytic data of the process of carbon dioxide conversion of methane for the catalyst Ni ₃ Al + 5% Mo Catalyst T, K Conversion% Yield, (mol.)% CO ₂ CH ₄ With H ₂ Ni ₃ Al + 5% Mo 873 0 2 0 0 973 0 5 one 0 1073 44 eighteen 19 12 1123 83 fifty 38 29th 1173 97 77 41 46 1223 99 89 44 46

Table 3 Catalytic data of the process of carbon dioxide conversion of methane for the catalyst Ni ₃ Al + 10% Mo Conversion% Yield, (mol.)% Catalyst T, K CO ₂ CH ₄ With H ₂ 873 0 0 0 0 973 one 0 0 0 1073 38 eighteen 17 eleven Ni ₃ Al + 10% Mo 1123 56 thirty 26 17 1173 79 49 35 29th 1223 95 80 41 46 Table 4
The stability data of the catalyst Ni ₃ Al + 5% Mo Catalyst Working hours Conversion% Yield, (mol.)% CO ₂ CH ₄ With H ₂ Ni ₃ Al + 5% Mo one 99 89 44 46 four 99 89 44 46 8 98 88 44 45 12 98 88 43 45 24 97 87 43 44 36 96 86 42 43

Claims (2)

1. The catalyst for producing synthesis gas by carbon dioxide conversion of methane, characterized in that it is obtained by self-propagating high-temperature synthesis and contains a matrix of Nickel aluminide, inside which are dispersed Nickel and molybdenum, in the following ratio, wt.%:
Ni ₃ Al 80-90 Ni 5-10 Mo 2-10. 2. The method of producing synthesis gas by carbon dioxide conversion of methane using a catalyst containing a matrix of Nickel aluminide, inside which is dispersed Nickel, characterized in that the process is carried out in the presence of a catalyst according to claim 1.