Method of removing nitrogen monoxide from a nitrogen monoxide-containing gas

Claim 1

A method of removing nitrogen monoxide from a nitrogen monoxide-containing gas by reducing the nitrogen monoxide, which comprises contacting a nitrogen monoxide-containing gas with an aqueous solution containing a sulfite and a ferrous ion complex formed from a ferrous ion and an organic compound selected from the group consisting of a. thioglycolic acid, mercaptosuccinic acid, dimercaptosuccinic acid, mercaptoethyliminodiacetic acid, cysteine and o-mercaptobenzoic acid, b. ethylenediamine, triethylenediamine, N,N'-di(2-hydroxyethyl)ethylenediamine, 1,2-diaminopropane, diethylenetriamine, trimethylenetetraamine, triethylenetetraamine, 2,2',2"-triaminotriethylamine and 2,2',2"-trihydroxytriethylamine, c. aspartic acid, iminodiacetic acid, iminodipropionic acid, phenyliminodiacetic acid, hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, aminoethyliminodiacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediamine-N,N'-diacetic acid, ethylenediamine-N,N',N'-triacetic acid, ethylenediamine-tetraacetic acid, ethylenediamine-tetrapropionic acid, 1,2-propylenediamine-tetraacetic acid, trans-cyclohexane-1,2-diamine-tetraacetic acid, 1,2-diaminopropane-N,N,N',N'-tetraacetic acid, diethylenetriamine-N,N,N',N",N"-pentaacetic acid, trimethylenetetraaminehexaacetic acid, triethylenetetraaminehexaacetic acid and triethylenetetraamine-hexapropionic acid, and d. lithium, potassium, sodium, magnesium, calcium or ammonium salts of any of (a) to (c), the ferrous ion concentration in the aqueous solution being at least 0.01 gram ion per liter of water, 0.01 to 100 moles of the organic compound being present per gram ion of ferrous ion, the concentration of sulfite plus any sulfide in the aqueous solution being 0.01 to 3.0 mole per liter of water, and the pH value of the aqueous solution being maintained at 2.0 to 13.0.

Claim 2

A method of removing nitrogen monoxide from a nitrogen monoxide-containing gas by reducing the nitrogen monoxide, which comprises contacting a nitrogen monoxide-containing gas with an aqueous solution containing a sulfite and a ferrous ion complex formed from a ferrous ion and an organic compound selected from the group consisting of a. thioglycolic acid, mercaptosuccinic acid, dimercaptosuccinic acid, mercaptoethyliminodiacetic acid, cysteine and o-mercaptobenzoic acid, b. ethylenediamine, triethylenediamine, N,N'-di(2-hydroxyethyl)ethylenediamine, 1,2-diaminopropane, diethylenetriamine, trimethylenetetraamine, triethylenetetraamine, 2,2',2"-triaminotriethylamine and 2,2',2"-trihydroxytriethylamine, c. aspartic acid, iminodiacetic acid, iminodipropionic acid, phenyliminodiacetic acid, hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, aminoethyliminodiacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediamine-N,N'-diacetic acid, ethylenediamine-N,N',N'-triacetic acid, ethylenediamine-tetraacetic acid, ethylenediamine-tetrapropionic acid, 1,2-propylenediamine-tetraacetic acid, trans-cyclohexane-1,2-diamine-tetraacetic acid, 1,2-diaminopropane-N,N,N',N'-tetraacetic acid, diethylenetriamine-N,N,N',N",N"-pentaacetic acid, trimethylenetetraaminehexaacetic acid, triethylenetetraaminehexaacetic acid and triethylenetetraamine-hexapropionic acid, and d. lithium, potassium, sodium, magnesium, calcium or ammonium salts of any of (a) to (c), the ferrous ion concentration in the aqueous solution being at least 0.01 gram ion per liter of water, 0.01 to 100 moles of the organic compound being present per gram ion of ferrous ion, the concentration of sulfite plus any sulfide in the aqueous solution being 0.01 to 3.0 mole per liter of water, and the pH value of the aqueous solution being maintained at 2.0 to 13.0.