Process for catalytically reducing nitrogen oxides in industrial stack gases

Abstract

Abstract <PICT:0829581/III/1> Noxious gases containing nitrogen oxide fumes are made innocuous by producing a gas free from nitrogen oxides and hydrogen cyanide by adding a reducing gas and passing the resulting mixture first over a noble metal catalyst then over a heterogeneous gas phase reduction catalyst, the catalysis being conducted at 100 DEG C. to 1000 DEG C., preferably 500-1000 DEG C. Reducing gases may be natural gas, methane, ethane, propane, butane, or mixtures thereof alone or with hydrogen, oil or coke oven hydrocarbon gas, or hydrogen alone. 40% H2 may be used with an alkane, and the presence of H2 renders preheating of the catalyst layer unnecessary. The gases treated may be those containing NO, N2O and/or NO2, from the HNO3 oxidation of cyclic alkanones or cyclic alkanols or from the oxidation of NH3 to HNO3. A mixture of natural gas and air enters catalyst converter 1 through inlet manifold 7 and is ignited by spark plug 9. The resulting gas flame is passed through catalyst bed 2, which is divided into at least two layers with, or without a gas permeable partition 2a, until the desired temperature is attained. The air feed is discontinued, the gas containing nitrogen oxides after passing through preheater 10, or not, enters converter 1 at 6 and natural gas, with or without H2, enters through distributer 4. Steam or nitrogen enters through inlet manifold 7 and gas, wherein the nitrogen oxides have been converted to N2, and containing CO2 and H2O is withdrawn from outlet 8 through heat exchanger 10 to stack. The temperature is controlled by the extent of preheating, by the amount of steam, or nitrogen used, and by water jacket 3, in response to indications of thermocouple in well 11. The first catalyst is a thin layer of gold, ruthenium, iridium, platinum, rhodium or palladium, or mixtures thereof, as gauzes, or mats, or supported on alumina, infusorial earth or kieselguhr. The second catalyst is nickel on alumina or nickel aluminate, copper chromite, copper impregnated alumina, or oxides of metals, such as titanium, calcium, cerium, zirconium, aluminium, thorium, tin, tungsten, molybdenum, niobium, chromium, manganese, zinc, copper, cobalt, nickel and iron, particularly mixed oxides of copper and chromium and of nickel and chromium. The nickel on alumina is prepared by precipitating basic nickel carbonate with ammonium carbonate or bicarbonate on alumina hydrate, dried and calcined to convert nickel salt to oxide and dehydrate the alumina, the nickel oxide is reduced to nickel, and the mixture of nickel and alumina is mixed with a volatilizable lubricant, e.g. high melting wax, pelleted, heated to 500 DEG C. in O2, and finally heated to 1050 DEG C.

Inventors

• 👤 Childers Eugene
• 👤 Ellis Charles William
• 👤 Ryan Donald James

Bibliographic Details