Process for removing nitrogen oxide from a waste gas

Claim 1

A process for removing nitrogen monoxide from a waste gas containing relatively low concentrations of said nitrogen oxide comprising the successive steps of (a) contacting the nitrogen oxide containing waste gas with a molar excess of nitric acid vapors in an oxidation column at a temperature of about 50° to about 150° C in the presence of a porous adsorbing agent selected from the group consisting of silica gel, alumina, colloidal earth and molecular sieves, thereby oxidizing the nitrogen oxide to nitrogen dioxide, (b) contacting the thus treated waste gas with a countercurrent of water to remove the excess nitric acid therefrom while the nitrogen dioxide remains in the waste gas, (c) contacting the nitrogen dioxide-containing waste gas with an aqueous alkaline solution to absorb and remove the nitrogen dioxide contained therein, and (d) discharging the thus treated waste gas substantially freed of nitrogen dioxide into the atmosphere.