The catalyst for the oxidation of ammonia

 

(57) Abstract:

1 Proposed a catalyst for the oxidation of ammonia on the basis of mixed oxides with perovskite structure and the General formula ABO3, where A is the calcium cations, or a mixture of calcium and lanthanum, and B - cations of manganese, iron, Nickel, cobalt or mixtures thereof, regular patterns, additionally containing oxides of aluminum, chromium, zirconium, silicon, silicates or mixtures thereof. The catalyst is thermally stable, resistant to thermal shocks. Due to the high activity and regular structure increases process safety (there is virtually no leakage of ammonia). 2 C.p. f-crystals, 1 table.

The invention relates to catalysts based perovskites for the ammonia oxidation process.

The main industrial catalyst for the oxidation of ammonia is currently platinum and its alloys with palladium and rhodium. In conditions of acute shortage of platinum group metals and their high cost, it is important to reducing investments and losses of platinum. Developed several formulations of oxide catalysts in which the active component is an oxide of iron III, cobalt oxide, chromium oxide. So the authors of [I] offer the catalyst produced meth is yellow binder and additive on the basis of oxynitride or oxychloride followed step by annealing the catalyst mass to a temperature of 850oC.

Known oxide catalyst, a mixture of oxides of aluminum, iron, calcium and chromium, followed by pelletizing and annealing at 875 900oC [2]

Known oxide catalyst produced in the form of tablets, consisting of iron oxide and aluminum oxide [3] the preparation Method of the catalyst is a mixture of iron oxide and aluminum hydroxide in an acidic medium and subsequent termomaslyanym catalyst mass at 600 700oC, grinding, pelletizing and sintering of the finished tablets. In the pilot test shows that it works on the second stage of the oxidation of ammonia [4]

The disadvantages of such catalysts should include significant gas-dynamic resistance of the catalyst layer, the phase change composition during operation, the presence of ammonia in the gas stream.

As a prototype of the selected catalyst with perovskite structure for selective oxidation of ammonia to nitric oxide with the release of not less than 90% [5], the Authors [5] have experienced powders of the perovskite series La1-xSrxMeO3where Me=Co, Mn, a x= 0.25 to 0.75 and LaMeO3where Me=Co, Mn, Ni, Cr, Fe in the oxidation of ammonia (sample was 0.05 0.1 g) at temperatures from 500 to 1050 K basin with a developed surface were obtained by precipitation from dilute solutions ototoxicity salts, taken in appropriate ratios, tetraethylammonium. However, for use in industry, the catalyst must be formed into pellets. And received by the co-deposition of the powders are not formed not only in the form of honeycomb structures, but in plain pellets.

The problem to which the invention is directed, is to develop a modular catalyst honeycomb structure for the oxidation of ammonia with high activity, resistance to thermal shock, do not contain noble metals and improve process safety by reducing the hydraulic resistance of the catalyst layer and the stabilization of the gas flow.

This technical result is achieved that, as catalysts for the oxidation of ammonia using complex oxide systems with surface structure of the perovskite and the General formula ABO3, where A is the calcium cations, or a mixture of calcium and lanthanum, and B cations of manganese, iron, Nickel, cobalt or mixtures thereof, as structural components, providing the strength and stability of the catalyst to thermal shocks, use connections that give the annealing oxides of zirconium, chromium, aluminum, silicon, ILM, the proposed block catalyst honeycomb structure for the ammonia oxidation process contains a perovskite of the General formula ABO3where a Ca cation or a mixture of calcium and lanthanum, and B cations of manganese, iron, Nickel, cobalt or mixtures thereof, and optionally oxides of aluminum and/or silicon oxides, zirconium, chromium in the following ratio of components, wt.

The perovskite 50 95

The A1 oxides and/or Si, Zr, Cr 5 50

in perovskites Ca1-xLaxMeO3and CaMe11-xMe2xO3(Me, Mn, Fe, Co, Ni) x 0,9 0,1.

Distinctive features of the catalyst according to the invention is the use of perovskites CaMeO3and CaxLa1-xMeO3where Me is Mn, Co, Ni, Fe, and x 0,9-0,1 as an active ingredient together with strukturoobraznyh "oven" and oxides of zirconium, chromium, aluminum, silicon, silicates, and the catalyst is a blocks cell structure.

The method of preparation of the bulk catalyst based perovskites consists of the following stages:

1) Preparation of the active component of the catalyst of oxides with perovskite structure. The perovskite series Ca-La-Me1-Me2-O3prepare by the method of mechanochemical si, will overhaul mechanochemical activation and then the powder calcined at 600 - 800oC 2 4 h Specific surface area of the obtained perovskite is 10 -20 m2/,

Mixing and forming. In the mixer powder mix of the active ingredient powder of perovskite bonding with Al, Cr, Si or Zr-containing agent in an acidic environment. To improve the stability of the catalyst to thermal shocks at the stage of mixing the paste composition may be optionally entered reinforcing aluminosilicate fiber. As Al-containing bonding agent used xinitrc aluminum or pseudoboehmite, Cr-containing chromic acid, Si-containing kaolin, Zr-containing xinitrc zirconium. To improve the rheological characteristics of the paste in the composition to add a surfactant ethylene glycol, polyethylene oxide, carboxymethylcellulose, polyvinly alcohol, glycerin and others. From the obtained paste is formed by extrusion blocks cell structure.

3) Heat treatment. The catalysts are dried at finite temperature 120oC, and then calcined in air at 900 950oC 2 4 h

The invention is illustrated by the following examples of the preparation of the catalysts and the results of their tests in R is Torah 850 950oC. Under activity S-I understand the degree of conversion of ammonia to nitrogen oxides after the catalytic system, including: (I Pt mesh and oxide catalyst; S-2 after one platinum mesh. Varied testing temperature T C and the linear velocity of the gas stream V in m/s, the Concentration of ammonia in the air was about 10. Residual ammonia (the so-called leakage of ammonia) were determined by using the apparatus of kildala [4]

Example 1. A mixture of oxides of lanthanum, calcium and manganese atomic ratio 0,9 0,1 1 is subjected to mechanochemical activation, calcined at 700oC. To the obtained powder of Caa 0.1Lafor 0.9MnO3add pseudoboehmite, a solution of acetic acid, aluminosilicate fiber, ethylene glycol. The total moisture content of the paste 26% Molded blocks cellular structures, dried, and calcined. The composition of the catalyst: perovskite (Caa 0.1Lafor 0.9MnO3) 90% Al2O38% SiO22% of the Catalyst can withstand at least 25 cycles of rapid heating to 700oC and cooling to room temperature without cracking.

Example 2. A mixture of oxides of calcium and manganese atomic ratio of 1 to 1 is subjected to mechanochemical activation, calcined at 800oC. To the resulting powder CaMnO3add kaolin, localvault. The composition of the catalyst: CaMnO360% Al2O330% SiO210% of the Catalyst can withstand without rastreskivanija at least 25 cycles.

Example 3. A mixture of carbonates of calcium, lanthanum and iron oxide with an atomic ratio of 0,5 0,5 1 is subjected to mechanisatie, calcined at 800oC. To the obtained powder of Ca0,5La0,5FeO3add a solution of oxynitride zirconium, carboxylmethylcellulose. The total moisture content of the paste 28% Molded blocks cellular structures, dried and calcined. The composition of the catalyst: Ca0,5La0,5FeO395% ZrO25% of the Catalyst is resistant to thermal shocks.

Example 4. A mixture of hydroxides of calcium and iron with an atomic ratio of cations 1 1 is subjected to mechanochemical activation, then calcined at 600oC, 4 o'clock To the obtained powder of Ca2Fe2O5add pseudoboehmite, nitric acid, silica-alumina fiber, water until the total moisture content of 28% is Formed into blocks of honeycomb structure, dried and calcined. The composition of the catalyst: Ca2Fe2O570% of Al2O325% SiO25% of the Catalyst is resistant to thermal shocks.

Example 5. A mixture of oxides of calcium, lanthanum and cobalt atomic ratio of cations 0,2 0,8 1 is subjected to mechanical aktivacija humidity 25% is Formed into blocks of honeycomb structure, dried, calcined. The composition of the catalyst Caof 0.2La0,8CoO370% of Al2O320% Cr2O310% of the Catalyst is resistant to thermal shocks.

Example 6. The mixture of calcium carbonate, manganese oxide and iron oxide is subjected to activation with an atomic ratio of cations 1 0,4 0,6, then calcined at 700oC. To the resulting powder add pseudoboehmite, nitric acid, water, kaolin up to a total moisture 24% Molded blocks cellular structures, dried and calcined. The composition of the catalyst CaMnfor 0.4Fefor 0.6O370% of Al2O325% SiO25% of the Catalyst is resistant to thermal shocks.

Example 7. A mixture of oxides of calcium and cobalt is subjected to mechanochemical activation, then calcined at 600oC. To the resulting powder in a mixer add chromic acid and glycerol formed before the formation of the paste. Molded blocks, dried and calcined. The composition of the catalyst CaCoO390% Cr2O310% of the Catalyst is resistant to thermal shocks.

Example 8. A mixture of carbonates of calcium, lanthanum and Nickel is subjected to mechanochemical activation, and then calcined at 800oC. To the resulting powder add pseudoboehmite, a solution of acetic acid, aluminosilicate fiber. Pasta with vlazhnoe350% Al2O345% SiO25% of the Catalyst is resistant to thermal shocks.

Check the stability of the catalysts for continuous operation in industrial conditions within three months showed that the catalyst retains a high level of activity and strength. In addition, calculations show that the use of oxide catalyst for the oxidation of ammonia regular structure as a second stage catalytic system will reduce investment and loss of platinum 30% and 20% respectively. The proposed catalysts due to the regular structure improves the dynamics of the process, it becomes more resistant, no leakage of ammonia, which increases process safety. Catalysts resistant to sudden temperature changes.

1. The catalyst for the oxidation of ammonia on the basis of oxides with perovskite structure, characterized in that it contains a perovskite of the General formula ABO3where a calcium cation or a mixture of calcium and lanthanum, and B cations of manganese, iron, Nickel, cobalt or mixtures thereof, and optionally oxides of aluminum and/or silicon, zirconium, chromium in the following ratio, wt.

The perovskite 50 95

Oxides of aluminum and/or silicon, the CID is the torus in p. 1, characterized in that it contains a perovskite Ca1-xLaxMeO3where Me manganese, iron, cobalt, Nickel, x 0,9 0,1.

3. The catalyst p. 1, characterized in that it contains a perovskite CaMe11-xMe2xO3where Me1Me2manganese, Nickel, cobalt, iron, x 0,9 0,1.

 

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4 dwg, 1 tbl, 2 ex

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