Nitrogen oxides formed in combustion engines are recycled such that the nitrogen oxides can be utilized for producing liquid or solid chemicals. The nitrogen oxides are recycled by a method including an adsorber material adsorbing nitrogen oxides from an exhaust-gas stream of the combustion engine, removing the adsorber material laden with nitrogen oxides, desorbing the adsorbed nitrogen oxides from the adsorber material, and converting the nitrogen oxides desorbed from the adsorber material into liquid or solid nitrogen-containing compounds.

Nitrogen oxides formed in combustion engines are recycled such that the nitrogen oxides can be utilized for producing liquid or solid chemicals. The nitrogen oxides are recycled by a method including an adsorber material adsorbing nitrogen oxides from an exhaust-gas stream of the combustion engine, removing the adsorber material laden with nitrogen oxides, desorbing the adsorbed nitrogen oxides from the adsorber material, and converting the nitrogen oxides desorbed from the adsorber material into liquid or solid nitrogen-containing compounds.

An apparatus is provided for treatment of process gas formed during nitric acid production by catalytic oxidation of NH.sub.3. The apparatus includes a reactor, a first catalyst bed for N.sub.2O decomposition, an absorption tower to react the NO.sub.x formed with an absorption medium downstream of the first catalyst bed, a device for adding NH.sub.3 added to tailgas entering the second catalyst bed, and a second catalyst bed for NO.sub.x reduction and further decrease in N.sub.2O in the tailgas exiting the absorption tower. The second catalyst bed contains at least one iron-loaded zeolite catalyst. N.sub.2O removal in the first catalyst bed is limited such that the process gas exiting the first catalyst bed exhibits a N.sub.2O content of >100 ppmv and a molar N.sub.2O/NO.sub.x ratio of >0.25. Treated gas exiting the second catalyst bed has a NO.sub.x concentration of <40 ppmv and a N.sub.2O concentration of <200 ppmv.

An apparatus is provided for treatment of process gas formed during nitric acid production by catalytic oxidation of NH.sub.3. The apparatus includes a reactor, a first catalyst bed for N.sub.2O decomposition, an absorption tower to react the NO.sub.x formed with an absorption medium downstream of the first catalyst bed, a device for adding NH.sub.3 added to tailgas entering the second catalyst bed, and a second catalyst bed for NO.sub.x reduction and further decrease in N.sub.2O in the tailgas exiting the absorption tower. The second catalyst bed contains at least one iron-loaded zeolite catalyst. N.sub.2O removal in the first catalyst bed is limited such that the process gas exiting the first catalyst bed exhibits a N.sub.2O content of >100 ppmv and a molar N.sub.2O/NO.sub.x ratio of >0.25. Treated gas exiting the second catalyst bed has a NO.sub.x concentration of <40 ppmv and a N.sub.2O concentration of <200 ppmv.

An ammonia burner comprising an ammonia section for ammonia oxidation and a combined heat exchange section for heating a process stream, wherein said ammonia section and heat exchange section are coaxially arranged in a pressure vessel of the burner and the hot nitrogen oxides-containing effluent gas from the ammonia section is directed to a shell side of the heat exchange section so that said effluent gas transfers heat to the process stream.

An ammonia burner comprising an ammonia section for ammonia oxidation and a combined heat exchange section for heating a process stream, wherein said ammonia section and heat exchange section are coaxially arranged in a pressure vessel of the burner and the hot nitrogen oxides-containing effluent gas from the ammonia section is directed to a shell side of the heat exchange section so that said effluent gas transfers heat to the process stream.

Digestion of impure alumina with sulfuric acid dissolves all constituents except silica. Resulting sulfates, produced from contaminants in the impure alumina, remain in solution at approximately 90 C. Hot filtration separates silica. Solution flow over metallic iron reduces ferric sulfate to ferrous sulfate. Controlled ammonia addition promotes hydrolysis and precipitation of hydrated titania from titanyl sulfate that is removed by filtration. Addition of ammonium sulfate forms ferrous ammonium sulfate and ammonium aluminum sulfate solutions. Alum is preferentially separated by crystallization. Addition of ammonium bicarbonate to ammonium alum solution precipitates ammonium aluminum carbonate which may be heated to produce alumina, ammonia, and carbon dioxide. The remaining iron rich liquor also contains magnesium sulfate. Addition of oxalic acid generates insoluble ferrous oxalate which is thermally decomposed to ferrous oxide. Carbon monoxide reduces the ferrous oxide to metallic iron. Further oxalic acid addition precipitates magnesium oxalate which is thermally decomposed to magnesium oxide.

There is provided a method for the synthesis of nitrogen oxides (NOx) comprising the steps of providing a gas mixture comprising oxygen and nitrogen; and heating the gas mixture to a temperature of at least 2300 K at a pressure of 10-100 bar in a thermal reactor forming a gas mixture comprising NOx. There is also provided a method for the production of HNO3.

There is provided a method for the synthesis of nitrogen oxides (NOx) comprising the steps of providing a gas mixture comprising oxygen and nitrogen; and heating the gas mixture to a temperature of at least 2300 K at a pressure of 10-100 bar in a thermal reactor forming a gas mixture comprising NOx. There is also provided a method for the production of HNO3.

The present invention solves the existing problem of using very expensive oxidation reagents, such as H.sub.2O.sub.2 and ozone, in removal of NO.sub.x and SO.sub.x from flue gases, by performing simultaneous oxidation of NO.sub.x and SO.sub.x with atmospheric oxygen in a combined system for catalytic oxidation and wet-scrubbing of both NO.sub.x and SO.sub.x from a flue gas and manufacturing fertilisers. Two major configurations of the oxidation system are disclosed in the present invention. The first configuration operates on oxygen-enriched air to increase efficiency of the oxidation reaction and requires an additional oxygen concentrator unit. The second configuration operates on atmospheric air at ambient conditions and requires an additional catalyst activation unit. In the second configuration, the efficient oxidation process is carried out at low temperatures of about 30-90 C. in the presence of recovered and re-activated catalyst. This temperature is a result of the exothermic character of the reaction, and therefore, no heating is required in the process.