COMPOSITION AND APPARATUS FOR PURIFYING NITROGEN-OXIDE-CONTAINING GASES

Abstract

A composition and a device for purification of nitrogen-oxide-containing gas is provided. It can purify harmful nitrogen-oxide-containing gases, such as nitric oxide or nitrogen dioxide. The composition includes an alkaline substance and at least one organic acid, the organic acids having an enediol group, enediamine group, or amine group of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, or phenanthrene compounds.

Claims

1. A composition for purification of nitrogen-oxide-containing gases, comprising: an alkaline substance; and at least one organic acid, the organic acids having an enediol group ##STR00010## enediamine group ##STR00011## or amine group ##STR00012## of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, parallel or phenanthrene compounds.

2. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the alkaline substance has a concentration of 0.01-3.0M.

3. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the organic acid has a concentration of 0.01-3.0M.

4. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the alkaline substance comprises sodium hydroxide, potassium hydroxide, calcium hydroxide, or a combination thereof.

5. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the organic acid has an ortho-diaminobenzoic group.

6. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 5, wherein the organic acid is 3,4-diaminobenzoic acid.

7. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the organic acid is ascorbic acid, gallic acid, ketonic acid, 1,2-dihydroxy-3-one cyclopentene, or hydroxymalonaldehyde.

8. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the organic acid is uric acid, or 5-aminouracil.

9. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the composition has a pH of 5-14.

10. The composition for purification of nitrogen-oxide-containing gases as claimed in claim 1, wherein the composition has an oxidation-reduction potential of 600 to 40 mV.

11. A device for purification of nitrogen-oxide-containing gases, comprising: a conversion module for converting nitric oxide to nitrogen dioxide; and a purification tank connected to the conversion module to serve as a reservoir for the composition as claimed in claim 1.

12. The device for purification of nitrogen-oxide-containing gases as claimed in claim 11, wherein the conversion module is equipped with a palladium (Pd)-based oxide, a platinum (Pt)-type oxide, a rhodium-based oxide, a lanthanum (La)-based oxide, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0010] FIG. 1 is a configuration view of a device according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0011] Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout.

[0012] One embodiment of the disclosure provides a composition for purifying nitrogen-oxide-containing gases, which includes an alkaline substance which adjusts the pH, and at least one organic acid that serves as a reductant to reduce the nitrogen-oxide-containing substances. Therefore, the harmful nitrogen-oxide-containing gases, for example NO or NO.sub.2, can be purified with excellent purifying results.

[0013] According to the present disclosure, the organic acids have an enediol group

##STR00001##

enediamine group

##STR00002##

or amine group

##STR00003##

of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, parallel or phenanthrene compounds.

[0014] According to the present disclosure, the alkaline substances are sodium hydroxide, potassium hydroxide, or calcium hydroxide etc. which are used to adjust a composition to have a pH of 5-14.

[0015] In one embodiment of the disclosure, the alkaline substances are sodium hydroxide, potassium hydroxide, or calcium hydroxide etc, and the organic acids have enediol group

##STR00004##

of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, or phenanthrene compounds.

[0016] Another embodiment of the disclosure includes alkaline substances that are sodium hydroxide, potassium hydroxide, or calcium hydroxide etc, and the organic acids have enediamine group

##STR00005##

of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, or phenanthrene compounds, for example having an ortho-diaminobenzoic group.

[0017] In an alternative embodiment of the disclosure, the alkaline substances are sodium hydroxide, potassium hydroxide, or calcium hydroxide etc, and the organic acids have amine group

##STR00006##

of cyclopentane compounds, cyclohexane compounds, cycloheptane compounds, or phenanthrene compounds.

[0018] According to the present disclosure, the organic acids are croconic acid, gallic acid, ascorbic acid, 3,4-Diaminobenzoic acid, ubiquinone, anthocyanidin, catechin, -carotene, lycopene, or 2,6-di-tert-butyl-p-cresol (BHT) etc.

[0019] In one embodiment, the alkali substance which is used to adjust the composition solution has a concentration of 0.01-3.0M.

[0020] According to the present disclosure, the organic acid has a concentration of 0.01-3.0M.

[0021] In one embodiment of the disclosure, the solution of the composition for purifying nitrogen-oxide-containing gases has an oxidation-reduction potential (ORP) of 600-40 mv, for example.

[0022] Referring to FIG. 1, according to another embodiment of the disclosure, a device for purification of nitrogen-oxide-containing gases is provided. The device 1 includes a conversion module 2 and a purification tank 3, wherein the conversion module is for converting nitric oxide to nitrogen dioxide, and starts as needed. The purification tank serves as a reservoir for the aforementioned composition to purify the harmful or pollution-causing nitrogen-oxide-containing gases. In addition, the device 1 further comprises a connecting element 4, and the purified gas passes through the connecting element 4 into the purification tank.

[0023] In one embodiment of the disclosure, the conversion module 2 may contain a palladium (Pd)-based oxide, a platinum (Pt)-based oxide, a rhodium (Rh)-based oxide, a lanthanum (La)-based oxide, or a combination thereof.

[0024] Experimental method and purifying ratio of calculation for purifying nitrogen-oxide-containing gases

[0025] Production of nitrogen-oxide-containing gases (simulating the exhaust gases in the environment)

[0026] Nitrogen (N.sub.2), oxygen (O.sub.2), and nitrogen dioxide (NO.sub.2) were mixed at a constant rate by means of a mass flow controller (MFC) and then passed into an oxidizing catalytic reactor at a constant temperature to produce nitrogen-oxide-containing gases, and converting most of the nitric oxide gas into nitrogen dioxide gas to simulate the composition of yellow smoke in industrial exhaust gases. The composition of the nitric oxide and nitrogen dioxide gas (where the nitrogen oxides contained nitric oxide and nitrogen dioxide) was analyzed and recorded by a gas analyzer (Horiba MEXA-584L).

[0027] The aforementioned simulation gas was passed through a gas-purifying washing bottle containing the composition used for purifying nitrogen-oxide-containing gas disclosed in the present disclosure, and the gas composition after purification and washing was analyzed with a nitrogen-oxide-containing gas detector (Horiba MEXA-584L).

[0028] Purifying ratio formula for purifying nitrogen-oxide-containing gases

[00001]$.Math.\mathrm{formula}.Math..Math.I$$\mathrm{Purifying}.Math..Math.\mathrm{ratio}.Math..Math.\left(\%\right)=\frac{\begin{array}{c}\mathrm{Amount}.Math..Math.\mathrm{of}.Math..Math.\mathrm{nitrogen}.Math.\text{-}.Math.\mathrm{oxide}.Math..Math.\mathrm{containing}.Math..Math.\mathrm{gas}.Math..Math.\mathrm{before}.Math..Math.\mathrm{purifying}-\\ \mathrm{Amount}.Math..Math.\mathrm{of}.Math..Math.\mathrm{nitrogen}.Math.\text{-}.Math.\mathrm{oxide}.Math..Math.\mathrm{containing}.Math..Math.\mathrm{gas}.Math..Math.\mathrm{after}.Math..Math.\mathrm{purifying}\end{array}}{\mathrm{Amount}.Math..Math.\mathrm{of}.Math..Math.\mathrm{nitrogen}.Math.\text{-}.Math.\mathrm{oxide}.Math..Math.\mathrm{containing}.Math..Math.\mathrm{gas}.Math..Math.\mathrm{before}.Math..Math.\mathrm{purifying}}100.Math.\%$

EXAMPLES

[0029] Converting Nitric Oxide to Nitrogen Dioxide

[0030] Preparation of Oxidizing Catalyst

[0031] The honeycomb-shaped cordierite carrier was coated with 10 g mixed powder of 50 wt % lanthanum oxide-50 wt % cerium oxide mixture and was sintered in a high-temperature furnace at 400-1000 C. The mixed powder was fixed in a cordierite carrier to complete the oxidizing catalyst production. The oxidizing catalyst was formed.

[0032] Gas Conversion Experiment (Nitric Oxide Convert to Nitrogen Dioxide)

Example 1

[0033] The oxidizing catalyst was placed in a tubular furnace and a fixed ratio of nitrogen, oxygen and nitric oxide was introduced at 300 C. The nitric oxide, either before or after the oxidizing catalyst was passed through, was converted into nitrogen dioxide. The amount of nitrogen-oxide-containing gas before and after the conversion was measured with a gas analyzer (Horiba MEXA-584L) until the gas concentration was stabilized to complete the reaction. The amount of nitrogen oxides before and after the conversion were measured with a gas analyzer (Horiba MEXA-584L) until the gas concentrations were stabilized. Then the reaction was completed.

[0034] Preparation of the Composition for Purifying Nitrogen-Oxide-Containing Gases

Example 2

[0035] An aqueous solution of 0.2 M ascorbic acid (C.sub.6H.sub.8O.sub.6) and 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 5.6 and the oxidation-reduction potential (ORP) was 107 mV with pH meter (Clean Instruments, PH200) and ORP analyzer (Clean Instruments, PH200) individually. Next, the nitrogen-oxide-containing gases passed through the cleaning agent and were analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 81%, and the purification rate of nitrogen dioxide was 99%, calculated using formula I.

Example 3

[0036] An aqueous solution of 0.2 M ascorbic acid (C.sub.6H.sub.8O.sub.6) and 0.4 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 12.2 and the oxidation-reduction potential (ORP) was 516 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 87%, and the purification rate of nitrogen dioxide was 99%, calculated using formula I.

Example 4

[0037] An aqueous solution of 0.01 M ascorbic acid (C.sub.6H.sub.8O.sub.6) and 0.04 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 12.3 and the oxidation-reduction potential (ORP) was 400 mV with pH meter and ORP analyzer. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 100%, calculated using formula I.

Example 5

[0038] An aqueous solution of 3 M ascorbic acid (C.sub.6H.sub.8O.sub.6) and 3 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 5.9 and the oxidation-reduction potential (ORP) was 509 mV. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 100%, calculated using formula I.

Example 6

[0039] An aqueous solution of 0.2 M gallic acid (C.sub.7H.sub.6O.sub.5) and 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 8.8 and the oxidation-reduction potential (ORP) was 156 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 84%, and the purification rate of nitrogen dioxide was 98%, calculated using formula I.

Example 7

[0040] An aqueous solution of 0.2 M gallic acid (C.sub.7H.sub.6O.sub.5) and 0.4 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 10.7 and the oxidation-reduction potential (ORP) was 215 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 86%, and the purification rate of nitrogen dioxide was 99%, calculated using formula I.

Example 8

[0041] An aqueous solution of 0.015 M croconic acid (C.sub.5H.sub.2O.sub.5) and 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.1 and the oxidation-reduction potential (ORP) was 160 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 88%, calculated using formula I.

Example 9

[0042] An aqueous solution of 0.015 M croconic acid (C.sub.5H.sub.2O.sub.5) and 0.4 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.4 and the oxidation-reduction potential (ORP) was 220 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 91%, calculated using formula I.

Example 10

[0043] An aqueous solution of 0.2 M 5-aminouracil and 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 11.0 and the oxidation-reduction potential (ORP) was 161 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 96%, calculated using formula I.

Example 11

[0044] An aqueous solution of 0.2 M 5-aminouracil and 0.4 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.2 and the oxidation-reduction potential (ORP) was 325 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 100%, calculated using formula I.

Example 12

[0045] An aqueous solution of 0.2 M 3,4-diaminobenzoic acid and 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 6.6 and the oxidation-reduction potential (ORP) was 35 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 98%, calculated using formula

[0046] I.

Example 13

[0047] An aqueous solution of 0.2 M 3,4-diaminobenzoic acid and 0.4 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.5 and the oxidation-reduction potential (ORP) was 231 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 99%, calculated using formula I.

COMPARATIVE EXAMPLE

Comparative Example 1

[0048] An aqueous solution of 0.2 M ascorbic acid (C.sub.6H.sub.8O.sub.6) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 2.3 and the oxidation-reduction potential (ORP) was 139 mV with pH meter and ORP analyzer individually. Next, the nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 9%, and the purification rate of nitrogen dioxide was 80%, calculated using formula I.

Comparative Example 2

[0049] An aqueous solution of 0.5 M gallic acid (C.sub.7H.sub.6O.sub.5) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 2.9 and the oxidation-reduction potential (ORP) was 210 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The nitrogen-oxide-containing gases purifying rate was calculated to be 20%, and the purification rate of nitrogen dioxide was 51%, calculated using formula I.

Comparative Example 3

[0050] An aqueous solution of 0.2 M 3,4-diaminobenzoic acid was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 3.5 and the oxidation-reduction potential (ORP) was 178 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 74%, calculated using formula I.

Comparative Example 4

[0051] Purified water was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 7.6 and the oxidation-reduction potential (ORP) was 283 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 16%, calculated using formula I.

Comparative Example 5

[0052] An aqueous solution of 0.2 M sodium hydroxide (NaOH) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.7 and the oxidation-reduction potential (ORP) was 183 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 27%, calculated using formula I.

Comparative Example 6

[0053] An aqueous solution of 0.2 M sodium thiosulfate (Na.sub.2S.sub.2O.sub.3) was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 6.8 and the oxidation-reduction potential (ORP) was 34 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 44%, calculated using formula I.

Comparative Example 7

[0054] An aqueous solution of 0.2 M sodium thiosulfate (Na.sub.2S.sub.2O.sub.3) and 0.2 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.1 and the oxidation-reduction potential (ORP) was 137 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 51%, calculated using formula I.

Comparative Example 8

[0055] An aqueous solution of 0.2 M citric acid was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 1.9 and the oxidation-reduction potential (ORP) was 333 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 21%, calculated using formula I.

Comparative Example 9

[0056] An aqueous solution of 0.2 M citric acid and 0.4 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 4.8 and the oxidation-reduction potential (ORP) was 260 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 21%, calculated using formula I.

Comparative Example 10

[0057] An aqueous solution of 0.2 M citric acid and 1.0 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.3 and the oxidation-reduction potential (ORP) was 118 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 44%, calculated using formula I.

Comparative Example 11

[0058] An aqueous solution of 0.2 M glycerol was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 5.8 and the oxidation-reduction potential (ORP) was 272 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 17%, calculated using formula I.

Comparative Example 12

[0059] An aqueous solution of 0.2 M glycerol and 0.4 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 13.4 and the oxidation-reduction potential (ORP) was 184 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 26%, calculated using formula I.

Comparative Example 13

[0060] An aqueous solution of 0.2 M tartaric acid was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 1.7 and the oxidation-reduction potential (ORP) was 365 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 25%, calculated using formula I.

Comparative Example 14

[0061] An aqueous solution of 0.2 M tartaric acid and 0.4 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 5.28 and the oxidation-reduction potential (ORP) was 202 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 8%, calculated using formula I.

Comparative Example 15

[0062] An aqueous solution of 0.2 M tartaric acid and 0.5 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 12.82 and the oxidation-reduction potential (ORP) was 110 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 27%, calculated using formula I

Comparative Example 16

[0063] An aqueous solution of 0.2 M oxalic acid was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 1 and the oxidation-reduction potential (ORP) was 352 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 13%, calculated using formula I.

Comparative Example 17

[0064] An aqueous solution of 0.2 M oxalic acid and 0.4 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 5.7 and the oxidation-reduction potential (ORP) was 175 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 7%, calculated using formula I.

Comparative Example 18

[0065] An aqueous solution of 0.2 M oxalic acid and 0.5 M sodium hydroxide was prepared as a cleaning agent for purifying nitrogen-oxide-containing gases. The pH of the aqueous solution was 12.81 and the oxidation-reduction potential (ORP) was 86 mV with pH meter and ORP analyzer individually. The nitrogen-oxide-containing gases were passed through the cleaning agent and analyzed with a gas detector. The purification rate of nitrogen dioxide was 24%, calculated using formula I

[0066] In order to illustrate the present disclosure, the aforementioned examples and comparative examples are summarized in Table 1 and Table 2.

[0067] As shown in Table 1, according to the results of the examples, the organic acids in the composition for purifying nitrogen-oxide-containing gases, which have enediol group

##STR00007##

enediamine group

##STR00008##

or amine group

##STR00009##

had a great effect in the purification of nitrogen-oxide-containing gases, especially when purifying nitrogen dioxide. If the cleaning agent doesn't contain any alkali substances, it is formed of organic acids such as an organic acid with enediol group, and the purification rate is 80%, which is superior to that of using the organic acid shown in Table 2 as the cleaning agent.

[0068] As shown in Table 1, adjusting the pH of the organic acid cleaning agent to 5-14 can greatly enhance the nitrogen dioxide purification rate, even up to 100%.

[0069] Referring to comparative example 1 and examples 2 to 4, comparative example 2 and examples 6 to 7, and comparative example 3 and examples 12 to 13, The nitrogen dioxide purifying rate is greatly reduced when the alkaline substance is not added to the composition for purifying nitrogen-oxide-containing gases.

[0070] As shown in Table 1 and example 2 to example 13, the composition for purifying nitrogen-oxide-containing gases in the present disclosure has an oxidation-reduction potential of 600 to 40 mV.

TABLE-US-00001 TABLE 1 concentration of NO.sub.2 (ppm) organic composition for purifying before after purification ORP acid group nitrogen-oxide-containing gases purifying purifying rate of NO.sub.2 pH (mV) comparative enediol 0.2M Ascorbic acid 196 40 80% 2.3 139 example 1 example 2 0.2M Ascorbic acid + 0.2M NaOH 196 2 99% 5.6 107 example 3 0.2M Ascorbic acid + 0.4M NaOH 196 1 99% 12.2 516 example 4 0.01M Ascorbic acid + 0.04M NaOH 103 0 100% 12.3 400 example 5 3M Ascorbic acid + 3M NaOH 116 0 100% 5.9 509 comparative 0.2M Gallic Acid 196 135 51% 2.9 210 example 2 example 6 0.2M Gallic Acid + 0.2M NaOH 196 3 98% 8.8 156 example 7 0.2M Gallic Acid + 0.4M NaOH 196 1 99% 10.7 215 example 8 0.015M Croconic acid + 0.2M NaOH 144 17 88% 13.1 160 example 9 0.015M Croconic acid + 0.4M NaOH 144 13 91% 13.4 220 example 10 amine 0.2M 5-Aminouracil + 0.2M NaOH 144 6 96% 11 161 example 11 0.2M 5-Aminouracil + 0.4M NaOH 144 0 100% 13.2 325 comparative enediamine 0.2M 3,4-Diaminobenzoic acid 144 37 74% 3.5 178 example 3 example 12 0.2M 3,4-Diaminobenzoic acid + 0.2M NaOH 144 3 98% 6.6 35 example 13 0.2M 3,4-Diaminobenzoic acid + 0.4M NaOH 144 2 99% 13.5 231

[0071] As shown in Table 2 and comparative example 1-15, The organic acid functional groups of the cleaning agent are also important factors, even if the cleaning agent has a pH of 5-14, or has an oxidation-reduction potential of 600 to 40 mV.

TABLE-US-00002 TABLE 2 concentration of NO.sub.2 (ppm) functional composition for purifying before after purification ORP group nitrogen-oxide-containing gases purifying purifying rate of NO.sub.2 pH (mV) comparative OH.sup. pure water 196 164 16% 7.6 283 example 4 comparative 0.2M NaOH 196 144 27% 13.7 183 example 5 comparative S.sub.2O.sub.3.sup.2 0.2M Na.sub.2S.sub.2O.sub.3 196 109 44% 6.8 34 example 6 comparative 0.2M Na.sub.2S.sub.2O.sub.3 + 0.2M NaOH 196 95 51% 13.1 137 example 7 comparative OH 0.2M Citric Acid 196 155 21% 1.9 333 example 8 comparative 0.2M Citric Acid + 0.4M NaOH 196 155 21% 4.8 260 example 9 comparative 0.2M Citric Acid + 1.0M NaOH 196 109 44% 13.3 118 example 10 comparative OH 0.2M Glycerol 144 119 17% 5.8 272 example 11 comparative 0.2M Glycerol + 0.4M NaOH 144 107 26% 13.4 184 example 12 comparative OH 0.2M Tartaric acid 144 108 25% 1.7 365 example 13 comparative 0.2M Tartaric acid + 0.4M NaOH 144 132 8% 5.28 202 example 14 comparative 0.2M Tartaic acid + 0.5M NaOH 112 82 27% 12.82 110 example 15 comparative COOH 0.2M Oxalic acid 144 126 13% 1 352 example 16 comparative 0.2M Oxalic acid + 0.4M NaOH 144 134 7% 5.7 175 example 17 comparative 0.2M Oxalic acid + 0.5M NaOH 114 87 24% 12.81 86 example 18

[0072] Accordingly, the composition for purifying nitrogen-oxide-containing gases disclosed in the present disclosure has an extremely large purifying effect as indicated by the examples and comparative examples.

[0073] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed methods and materials. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents.