# US 5,348,715 A · Processes to remove acid forming gases from exhaust gases > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,348,715 A - Document ID: US5348715A - Status: Granted - Kind: A - Application number: 07/853,904 - Filed: 1992-03-19 - Granted: 1994-09-20 - Earliest claimed: 1988-10-24 - Assignees: The Regents of the University of California - Inventors: Shih-Ger Chang - Web page: https://patentgrep.com/patent/US5348715A ## CPC - B01D 53/60: Simultaneously removing sulfur oxides and nitrogen oxides - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) ## Abstract The present invention relates to a process for reducing the concentration of NO in a gas, which process comprises: (A) contacting a gas sample containing NO with a gaseous oxidizing agent to oxidize the NO to NO.sub.2 ; (B) contacting the gas sample of step (A) comprising NO.sub.2 with an aqueous reagent of bisulfite/sulfite and a compound selected from urea, sulfamic acid, hydrazinium ion, hydrazoic acid, nitroaniline, sulfanilamide, sulfanilic acid, mercaptopropanoic acid, mercaptosuccinic acid, cysteine or combinations thereof at between about 0.degree. and 100.degree. C. at a pH of between about 1 and 7 for between about 0.01 and 60 sec; and (C) optionally contacting the reaction product of step (A) with conventional chemical reagents to reduce the concentrations of the organic products of the reaction in step (B) to environ-mentally acceptable levels. Urea or sulfamic acid are preferred, especially sulfamic acid, and step (C) is not necessary or performed. ## Claims ### Claim 1 An improved process for reducing the concentration of NO in a gas, which process comprises: (A) contacting a gas containing NO and SO.sub.2 with a gaseous oxidizing agent to oxidize the NO to NO.sub.2 ; and (B) contacting the oxidized gas of step (A) comprising NO.sub.2 with an aqueous reagent of bisulfite in admixture with sulfite formed by the reaction of SO.sub.2 and water and a compound selected from urea, sulfamic acid, hydrazinium ion, hydrazoic acid, nitroaniline, sulfanilamide, sulfanilic acid, mercaptopropanoic acid, mercaptosuccinic acid, cysteine or combinations thereof to reduce the formation of any compounds comprising both nitrogen and sulfur at between about 0.degree. and 100.degree. C. at a pH of between about 1 and 7 for between about 0.01 and 60 sec to reduce the concentration of NO in the gas. ### Claim 2 (depends on 1) The process of claim 1 wherein a compound in step (B) is selected from urea, sulfamic acid, or combinations thereof. ### Claim 3 (depends on 1) The process of claim 1 wherein a compound in step (B) comprises sulfamic acid, and the reduction product of HNO.sub.2 in step (B) comprises nitrogen. ### Claim 4 (depends on 1) The process of claim 1 wherein in step (A) the gaseous oxidizing agent is selected from O.sub.3, ClO.sub.2, the gaseous reaction product of P.sub.4 and O.sub.2, or combinations thereof. ### Claim 5 (depends on 4) The process of claim 4 wherein in step (B) the compound is selected from urea, sulfamic acid or combinations thereof, and the temperature is between about 10.degree. and 90.degree. C. ### Claim 6 (depends on 4) The process of claim 4 wherein in step (B) the compound is selected from hydrazinium ion, hydrazoic acid, nitroaniline, sulfanilamide, sulfanilic acid, mercaptopropanoic acid, mercaptosuccinic acid, cysteine or combinations thereof, and the temperature is between about 10.degree. and 90.degree. C. ### Claim 7 (depends on 1) The process of claim 1 wherein in step (B), the compound is sulfamic acid, the temperature is between 10.degree. and 90.degree. C., the pH is adjusted to between about 2 and 5, and the time is between about 0.1 and 30 sec. ### Claim 8 (depends on 7) The process of claim 7 wherein the temperature is between about 20.degree. and 80.degree. C. ### Claim 9 (depends on 7) The process of claim 7 wherein the gaseous oxidizing agent is selected from ozone, ClO.sub.2, or the gaseous oxidizing species produced by the reaction of P.sub.4 and O.sub.2. ### Claim 10 (depends on 1) The process of claim 1 wherein in step (B) the bisulfite is present in between about 0.001 and 0.5 Molar and the compound is sulfamic acid present in between about 0.1 and 5M. ### Claim 11 An improved process for reducing the concentration of one or more nitrogen-oxygen-containing compounds in a gas, which process comprises: (a) contacting a gas containing NO and SO.sub.2 with a gaseous oxidizing agent selected from O.sub.3, ClO.sub.2, the product of the reaction of P.sub.4 and O.sub.2, or combinations thereof to produce NO.sub.2 in the gas phase, (b) contacting the oxidized gas of step (a) with an aqueous reagent which first converts NO.sub.2 to HNO.sub.2, said aqueous reagent comprising bisulfite in admixture with sulfite formed by the reaction of SO.sub.2 and water, and a compound selected from urea, sulfamic acid or combinations thereof to reduce the formation of any compounds comprising both nitrogen and sulfur, at between about 5.degree. and 95.degree. C. at a pH of between about 1 and 7 for between about 0.01 and 60 sec in an amount sufficient to substantially convert the nitrogen atom present in the HNO.sub.2 to nitrogen; and (c) producing a gas having a reduced concentration of NO. ### Claim 12 (depends on 11) The process of claim 11 wherein the compound is sulfamic acid. ### Claim 13 (depends on 12) The process of claim 12 wherein SO.sub.2 is present and the pH is adjusted to between 1 and 7 by the addition of CaCO.sub.3, Ca(OH).sub.2, NaHCO.sub.3, NA.sub.2 CO.sub.3, Na.sub.2 SO.sub.3, flyash, or combinations thereof. ### Claim 14 (depends on 11) The process of claim 11 wherein the pH is adjusted to between about 3 and 4. ### Claim 15 (depends on 11) The process of claim 11 wherein the temperature of the reaction in steps (a) and (b) is between about 20.degree. to 80.degree. C. ### Claim 16 (depends on 11) The process of claim 11 wherein steps (a) and (b) are performed in a simultaneous manner. ### Claim 17 (depends on 11) The process of claim 11 wherein step (b), bisulfite is present in between about 0.001 and 0.5M, sulfamic acid is present in between about 0.1 and 5M, the temperature is between about 20 .degree. and 80.degree. C., and the pH is adjusted to between about 1 and 5 using CaCO.sub.3, Ca(OH).sub.2, NaHCO.sub.3, NaHCO.sub.3, Na.sub.2 CO.sub.3, Na.sub.2 SO.sub.3, flyash, or combinations thereof. ### Claim 18 (depends on 11) The process of claim 11 wherein the gas of step (a) is an exhaust gas comprising initially from between about 15 to 3000 parts per million of NO.sub.x where x is 1 to 2. ### Claim 19 (depends on 18) The process of claim 18 wherein SO.sub.2 is also present in step (a) in form between about 100 and 5,000 ppm. ### Claim 20 An improved process for reducing the concentration of NO in a gas, which process comprises: (A) contacting a gas containing NO and SO.sub.2 with a gaseous oxidizing agent to oxidize the NO to NO.sub.2 ; (B) contacting the oxidized gas of step (A) comprising NO.sub.2 with an aqueous reagent of bisulfite in admixture with sulfite formed from the reaction of SO.sub.2 and water, and a compound selected for urea, sulfamic acid, hydrazinium ion, hydrazoic acid, nitroaniline, sulfanilamide, sulfanilic acid, mercaptopropanoic acid, mercaptosuccinic acid, cysteine or combinations thereof to reduce the formation of any compounds comprising both nitrogen and sulfur, at between about 0 .degree. and 100.degree. C. at a pH of between about 1 and 7 for between about 0.01 and 60 sec; (B') producing a gas having a reduced concentration of NO.sub.2 ; and (C) contacting the reaction product of step (B) with means to reduce the concentrations of the organic products of the reaction of step (B). ### Claim 21 (depends on 20) The process of claim 20 wherein the compound is selected from urea, sulfamic acid, or combinations thereof. ### Claim 22 (depends on 20) The process of claim 20 wherein the reagent comprises sulfamic acid, and the reaction product of step (B) comprises nitrogen. ### Claim 23 (depends on 20) The process of claim 20 wherein in step (A) the gaseous oxidizing agent is selected from O.sub.3, CIO.sub.2, the product of the reaction of P.sub.4 and O.sub.2 , or combinations thereof. ### Claim 24 (depends on 23) The process of claim 23 wherein in step (B) the compound is selected from urea, sulfamic acid or combinations thereof. ### Claim 25 (depends on 23) The process of claim 23 wherein in step (B) the compound is selected from hydrazinium ion, hydrazoic acid, nitroaniline, sulfanilamide, sulfanilic acid, mercaptopropanoic acid, mercaptosuccinic acid, cysteine or combinations thereof. ### Claim 26 (depends on 20) The process of claim 20 wherein in step (B), the compound is sulfamic acid, the temperature is between 10 .degree. and 90.degree. C. the pH is adjusted to between about 2 and 5, and the time is between about 0.1 and 30 sec. ### Claim 27 (depends on 26) The process of claim 26 wherein the temperature is between about 20.degree. and 80.degree. C. ### Claim 28 (depends on 26) The process of claim 26 wherein the gaseous oxidizing agent is selected from ozone, CIO.sub.2, or the gaseous oxidizing species produced by the reaction of P.sub.4 and O.sub.2. ### Claim 29 (depends on 20) The process of claim 20 wherein in step (B) the bisulfite is present in between about 0.001 and 0.5 Molar and the compound is sulfamic acid present in between about 0.1 and 5M.