Process for removing SOx and NOx compounds from gas streams

Claim 2

A process for removing NO X compounds from a feed gas stream and producing a purified product gas stream of reduced NO X content, which process comprises: (1) contacting a feed gas stream containing one or more nitrogen compounds selected from the group consisting of NO and NO 2 with an absorbent composition comprising a ferrous chelate-containing aqueous liquid having dissolved therein formic acid and an alkanolamine containing a tertiary amine functional group under conditions such that at least some of said NO X compounds are absorbed into said absorbent, thereby producing a purified product gas stream of reduced NO X content; (2) withdrawing from step (1) a liquid stream of spent absorbent containing absorbed NO X compounds in dissolved form; (3) regenerating said spent absorbent to a form active for absorbing NO X compounds by adding formic acid or oxalic acid to said spent absorbent and heating the resulting admixture to a temperature sufficient to lower the concentration of said dissolved NO X compounds; (4) separating the products of step (3) at least into a product gas stream containing nitrogen and a regenerated liquid absorbent; (5) recycling at least some of said regenerated liquid absorbent obtained in step (4) to step (1); and (6) discharging a purified product gas stream of reduced NO X content from step (1) and discharging said product gas stream containing nitrogen from step (4).

Claim 3

A process for removing NO from a feed gas stream and producing a purified product gas stream of reduced NO content, which process comprises: (1) contacting in an absorption zone a feed gas stream containing NO with an absorbent composition comprising an aqueous liquid solution having dissolved therein a ferrous chelate and the reaction product of formic acid and an alkanolamine containing a tertiary amine functional group under conditions such that at least some of said NO is absorbed into said absorbent, thereby producing a purified product gas stream of reduced NO content; (2) withdrawing from step (1) a liquid stream of spent absorbent containing absorbed NO in dissolved form; (3) regenerating said spent absorbent back to a form active for absorbing NO by admixing formic acid with said spend absorbent and heating the resulting admixture to a temperature sufficient to lower the concentration of dissolved NO; (4) separating the products of step (3) into a product gas stream containing nitrogen and a regenerated liquid absorbent; (5) recycling at least some of said regenerated liquid absorbent obtained in step (4) to step (1); and (6) discharging said purified product gas stream of reduced NO content from step (1) and discharging said product gas stream containing nitrogen from step (4).

Claim 4

A process for removing NO from a feed gas stream and producing a purified product gas stream of reduced NO content, which process comprises: (1) contacting in an absorption zone a feed gas stream containing NO with an absorbent composition comprising an aqueous liquid solution having dissolved therein a ferrous chelate and the reaction product of formic acid and an alkanolamine containing a tertiary amine functional group under conditions such that at least some of said NO is absorbed into said absorbent, thereby producing a purified product gas stream of reduced NO content; (2) withdrawing from step (1) a liquid stream of spent absorbent containing absorbed NO in dissolved form; (3) regenerating said spent absorbent back to a form active for absorbing NO by admixing formic acid with said spend absorbent and heating the resulting admixture to a temperature sufficient to lower the concentration of dissolved NO; (4) separating the products of step (3) into a product gas stream containing nitrogen and a regenerated liquid absorbent; (5) recycling at least some of said regenerated liquid absorbent obtained in step (4) to step (1); and (6) discharging said purified product gas stream of reduced NO content from step (1) and discharging said product gas stream containing nitrogen from step (4).

Claim 5

A process as defined in claim 1 or 2 wherein said feed gas stream contains oxygen but is relatively free of SO x compounds.

Claim 6

A process as defined in claim 1 or 2 wherein said regeneration in step (3) is accomplished at a temperature above 150° while said spent absorbent is withdrawn in step (2) at a temperature below about 140° F.

Claim 7

A process for removing SO X and NO X compounds from a feed gas stream and producing a purified product gas stream of reduced SO X and NO X content, which process comprises: (1) contacting a feed gas stream containing one or more sulfur compounds selected from the group consisting of SO 2 and SO 3 and one or more nitrogen compounds selected from the group consisting of NO and NO 2 with an absorbent composition comprising an aqueous liquid solution having dissolved therein a ferrous chelate and the reaction product of formic acid and an alkanolamine containing a tertiary amine functional group under conditions such that at least some of said SO X and NO X compounds are absorbed into said absorbent, thereby producing a purified product gas stream of reduced SO X and NO X content; (2) withdrawing from step (1) a liquid stream of spent absorbent containing absorbed SO X and NO X compounds in dissolved form; (3) regenerating said spent absorbent back to a form active for absorbing SO X and NO X compounds by admixing with said spent absorbent formic acid or oxalic acid and heating the resulting admixture to a temperature sufficient to lower the concentration of dissolved SO X and NO X compounds; (4) separating the products of step (3) at least into a product gas stream containing nitrogen and a regenerated liquid absorbent; (5) recycling at least some of said regenerated liquid absorbent obtained in step (4) to step (1); and (6) discharging said purified product gas stream of reduced SO X and NO X content from step (1) and recovering said product gas stream containing nitrogen from step (4).

Claim 8

A process for removing SO X and NO X compounds from a feed gas stream and producing a purified product gas stream of reduced SO X and NO X content, which process comprises: (1) contacting a feed gas stream containing one or more sulfur compounds selected from the group consisting of SO 2 and SO 3 and one or more nitrogen compounds selected from the group consisting of NO and NO 2 with an absorbent composition comprising an aqueous liquid solution having dissolved therein a ferrous chelate and the reaction product of formic acid and an alkanolamine containing a tertiary amine functional group under conditions such that at least some of said SO X and NO X compounds are absorbed into said absorbent, thereby producing a purified product gas stream of reduced SO X and NO X content; (2) withdrawing from step (1) a liquid stream of spent absorbent containing absorbed SO X and NO X compounds in dissolved form; (3) regenerating said spent absorbent back to a form active for absorbing SO X and NO X compounds by admixing with said spent absorbent formic acid or oxalic acid and heating the resulting admixture to a temperature sufficient to lower the concentration of dissolved SO X and NO X compounds; (4) separating the products of step (3) at least into a product gas stream containing nitrogen and a regenerated liquid absorbent; (5) recycling at least some of said regenerated liquid absorbent obtained in step (4) to step (1); and (6) discharging said purified product gas stream of reduced SO X and NO X content from step (1) and recovering said product gas stream containing nitrogen from step (4).

Claim 9

A process as defined in claim 3, 4, or 5 wherein said ferrous chelate is selected from the group consisting of iron (II) EDTA and iron (II) HEDTA.

Claim 10

A process as defined in claim 1, 2, or 5 wherein said alkanolamine is selected from the group consisting of methyldiethanolamine, triethanolamine, and triisopropanolamine.

Claim 11

A process as defined in claim 5 wherein said regeneration in step (3) is accomplished at a temperature above about 300° F., producing hydrogen sulfide which is recovered with said product gas in step (6).

Claim 12

A process as defined in claim 1, 2 or 5 wherein SO 2 is present in said feed gas stream, and temperatures above about 300° F. are employed during the regeneration of step (3), producing hydrogen sulfide, which is recovered as a component of said product gas stream in step (6).

Claim 13

A process for converting NO to elemental nitrogen comprising contacting a gas stream containing NO but essentially free of oxygen with a heated, aqueous liquid having dissolved therein formic acid, an alkanolamine containing a tertiary amine functional group, and ferrous chelate precursors, said formic acid being present in a sufficient amount such that a substantial proportion of the NO is removed from said gas stream and converted to elemental nitrogen.

Claim 14

A process for converting NO to elemental nitrogen comprising contacting a gas stream containing NO but essentially free of oxygen with a heated, aqueous liquid having dissolved therein formic acid, an alkanolamine containing a tertiary amine functional group, and ferrous chelate precursors, said formic acid being present in a sufficient amount such that a substantial proportion of the NO is removed from said gas stream and converted to elemental nitrogen.

Claim 15

A process as defined in claim 10 wherein said at least some portion of said aqueous liquid is at a temperature above 125° F.

Claim 16

A process for converting NO 2 to elemental nitrogen comprising contacting NO 2 in an essentially oxygen-free environment with a heated, aqueous liquid having dissolved therein formic acid and an alkanolamine containing a tertiary amine functional group, said formic acid being present in a sufficient amount such that a substantial proportion of the NO 2 is converted to elemental nitrogen.

Claim 17

A process for converting NO 2 to elemental nitrogen comprising contacting NO 2 in an essentially oxygen-free environment with a heated, aqueous liquid having dissolved therein formic acid and an alkanolamine containing a tertiary amine functional group, said formic acid being present in a sufficient amount such that a substantial proportion of the NO 2 is converted to elemental nitrogen.

Claim 18

A process for treating a feed aqueous solution containing a dissolved ferrous chelate having associated therewith a nitrogen oxide component, said solution also having dissolved therein formic acid and an alkanolamine containing a tertiary amine functional group, which process comprises: (1) heating said aqueous solution under conditions such that a substantial proportion of said nitrogen oxide component is converted to nitrogen, thereby freeing said ferrous chelate of its associated nitrogen oxide component, and (2) separating a gas containing said nitrogen from a product aqueous solution containing an increased concentration of ferrous chelate having no nitrogen components associated therewith.

Claim 19

A process for treating a feed aqueous solution containing a dissolved ferrous chelate having associated therewith a nitrogen oxide component, said solution also having dissolved therein formic acid and an alkanolamine containing a tertiary amine functional group, which process comprises: (1) heating said aqueous solution under conditions such that a substantial proportion of said nitrogen oxide component is converted to nitrogen, thereby freeing said ferrous chelate of its associated nitrogen oxide component, and (2) separating a gas containing said nitrogen from a product aqueous solution containing an increased concentration of ferrous chelate having no nitrogen components associated therewith.

Claim 20

A process as defined in claim 13 wherein said feed aqueous solution also contains dissolved SO 2 .

Claim 21

A process as defined in claim 13 or 14 wherein said feed aqueous solution also contains dissolved nitrate or nitrite ions, a substantial proportion of which are converted to elemental nitrogen in step (1).