US4186176A
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Method of simultaneously removing sulfur dioxide and nitrogen oxides from exhaust gases
Assignee: Asahi Kasei Corp
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Filing: 1978-07-21
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Granted: 1980-01-29
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Expires: 1998-07-21
Abstract
Abstract A method of simultaneously removing sulfur dioxide and nitrogen oxides from an exhaust gas which comprises the steps of: contacting the exhaust gas with an aqueous absorbing solution containing an iron chelate complex and an alkali metal sulfite to form alkali metal sulfur oxides comprising an alkali metal dithionate in the aqueous absorbing solution; separating the alkali metal sulfur oxides formed and accumulated from part or the whole of the aqueous absorbing solution by crystallization; and subjecting the alkali metal sulfur oxides separated together with a carbonaceous material to decomposition-reduction reaction at a temperature of at least about 700° C. to form an alkali metal sulfide and a gas comprising sulfur dioxide and carbon dioxide.
Inventors
- 👤 Taketsugu Kitamura
- 👤 Hitoshi Takagi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 21:54
CPC Classifications
B; B01; B01D; B01D53/00; B01D53/34; B01D53/46; B01D53/60; Y; Y02; Y02A; Y02A50/00; Y02A50/20
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
112 words
A method of simultaneously removing sulfur dioxide and nitrogen oxides from an exhaust gas which comprises: contacting the exhaust gas with an aqueous absorbing solution containing an iron chelate complex and an alkali metal sulfite to form alkali metal sulfur oxides comprising an alkali metal dithionate in the aqueous absorbing solution; separating the alkali metal sulfur oxides formed and accumulated from part or the whole of the aqueous absorbing solution by crystallization; and subjecting the alkali metal sulfur oxides separated together with a carbonaceous material to decomposition-reduction reaction at a temperature of at least about 700° C. to form an alkali metal sulfide and a gas comprising sulfur dioxide and carbon dioxide.
Claim 2
Independent Claim
112 words
A method of simultaneously removing sulfur dioxide and nitrogen oxides from an exhaust gas which comprises: contacting the exhaust gas with an aqueous absorbing solution containing an iron chelate complex and an alkali metal sulfite to form alkali metal sulfur oxides comprising an alkali metal dithionate in the aqueous absorbing solution; separating the alkali metal sulfur oxides formed and accumulated from part or the whole of the aqueous absorbing solution by crystallization; and subjecting the alkali metal sulfur oxides separated together with a carbonaceous material to decomposition-reduction reaction at a temperature of at least about 700° C. to form an alkali metal sulfide and a gas comprising sulfur dioxide and carbon dioxide.
Claim 3
Dependent Claim
35 words
The method as claimed in claim 1, wherein the mother liquor separated from the alkali metal sulfur oxides comprising the alkali metal dithionate is reused as the aqueous absorbing solution for further exhaust gas treatment.
Claim 4
Dependent Claim
13 words
The method as claimed in claim 1, wherein the carbonaceous material is coal.
Claim 5
Dependent Claim
25 words
The method as claimed in claim 1, wherein the decomposition-reduction reaction is carried out at a temperature of about 850° C. to about 1,000° C.
Claim 6
Dependent Claim
25 words
The method as claimed in claim 1, wherein the iron chelate complex is a complex of ferric ion and/or ferrous ion with an aminopolycarboxylic acid.
Claim 7
Dependent Claim
14 words
The method as claimed in claim 5, wherein the aminopolycarboxylic acid is ethylenediaminetetraacetic acid.
Claim 8
Dependent Claim
15 words
The method as claimed in claim 1, wherein the alkali metal sulfite is sodium sulfite.
Claim 9
Dependent Claim
39 words
The method as claimed in claim 1, wherein the method further comprises: converting the alkali metal sulfide to an aqueous solution thereof; and reacting the aqueous solution with carbon dioxide to form an alkali metal carbonate and hydrogen sulfide.
Claim 10
Dependent Claim
65 words
The method as claimed in claim 8, wherein the reaction between the aqueous solution of the alkali metal sulfide and carbon dioxide is carried out in a two-step process comprising conducting the reaction in a pH of about 9 to about 12 to form an alkali metal carbonate and conducting the reaction in a pH of about 7 to about 9 to form hydrogen sulfide.
Claim 11
Dependent Claim
66 words
The method as claimed in claim 8, wherein the carbon dioxide free from sulfur dioxide obtained by treating a mixed gas of sulfur dioxide and carbon dioxide having been produced in the decomposition-reduction reaction of the alkali metal sulfur oxides together with a carbonaceous material is employed as the carbon dioxide in the reaction between the aqueous solution of the alkali metal sulfide and carbon dioxide.
Claim 12
Dependent Claim
43 words
The method as claimed in claim 10, wherein the aqueous absorbing solution and at the same time the carbon dioxide generated from the carbonate radical in the aqueous absorbing solution are employed to treat the mixed gas of sulfur dioxide and carbon dioxide.
Claim 13
Dependent Claim
23 words
The method as claimed in claim 10, wherein an aqueous alkaline solution having absorbed sulfur dioxide is reused as the aqueous absorbing solution.
Claim 14
Dependent Claim
35 words
The method as claimed in claim 8, wherein the mother liquor from which the alkali metal carbonate and the alkali metal hydrogencarbonate have been removed is employed in preparing the aqueous alkali metal sulfide solution.
Claim 15
Dependent Claim
24 words
The method as claimed in claim 8, wherein the alkali metal carbonate and the alkali metal hydrogencarbonate separated is reused as the absorbing solution.
Claim 16
Dependent Claim
35 words
The method as claimed in claim 8, wherein the mother liquor separated from the alkali metal sulfur oxides comprising the alkali metal dithionate is reused as the aqueous absorbing solution for further exhaust gas treatment.
Claim 17
Independent Claim
284 words
A method of simultaneously removing sulfur dioxide and nitrogen oxides from an exhaust gas which comprises the steps of: (a) contacting the exhaust gas with an aqueous absorbing solution containing an iron chelate complex and an alkali metal sulfite to form alkali metal sulfur oxides comprising an alkali metal dithionate in the aqueous absorbing solution; (b) separating the alkali metal sulfur oxides formed and accumulated from part or the whole of the aqueous absorbing solution by crystallization; (c) reusing the mother liquor obtained in step (b) as the aqueous absorbing solution for further exhaust gas treatment; (d) subjecting the alkali metal sulfur oxides separated together with a carbonaceous material to decomposition-reduction reaction at a temperature of at least 700° C. to form an alkali metal sulfide and a gas containing sulfur dioxide and carbon dioxide; (e) contacting part or the whole of the gas containing sulfur dioxide and carbon dioxide with part of the aqueous absorbing solution or an aqueous alkali solution to form a gas containing carbon dioxide free from sulfur dioxide; (f) adding water and/or the mother liquor obtained in the following step (h) of separating an alkali metal carbonate and an alkali metal hydrogencarbonate to the alkali metal sulfide formed in step (d) to quench and to form an aqueous solution of the alkali metal sulfide; (g) contacting the aqueous solution of the alkali metal sulfide with the gas containing carbon dioxide free from sulfur dioxide formed in step (e) to form hydrogen sulfide and an aqueous slurry containing the alkali metal carbonate and the alkali metal hydrogencarbonate; and (h) separating the alkali metal carbonate and the alkali metal hydrogencarbonate from the aqueous slurry for reuse in the exhaust gas treatment.
Claim 18
Independent Claim
284 words
A method of simultaneously removing sulfur dioxide and nitrogen oxides from an exhaust gas which comprises the steps of: (a) contacting the exhaust gas with an aqueous absorbing solution containing an iron chelate complex and an alkali metal sulfite to form alkali metal sulfur oxides comprising an alkali metal dithionate in the aqueous absorbing solution; (b) separating the alkali metal sulfur oxides formed and accumulated from part or the whole of the aqueous absorbing solution by crystallization; (c) reusing the mother liquor obtained in step (b) as the aqueous absorbing solution for further exhaust gas treatment; (d) subjecting the alkali metal sulfur oxides separated together with a carbonaceous material to decomposition-reduction reaction at a temperature of at least 700° C. to form an alkali metal sulfide and a gas containing sulfur dioxide and carbon dioxide; (e) contacting part or the whole of the gas containing sulfur dioxide and carbon dioxide with part of the aqueous absorbing solution or an aqueous alkali solution to form a gas containing carbon dioxide free from sulfur dioxide; (f) adding water and/or the mother liquor obtained in the following step (h) of separating an alkali metal carbonate and an alkali metal hydrogencarbonate to the alkali metal sulfide formed in step (d) to quench and to form an aqueous solution of the alkali metal sulfide; (g) contacting the aqueous solution of the alkali metal sulfide with the gas containing carbon dioxide free from sulfur dioxide formed in step (e) to form hydrogen sulfide and an aqueous slurry containing the alkali metal carbonate and the alkali metal hydrogencarbonate; and (h) separating the alkali metal carbonate and the alkali metal hydrogencarbonate from the aqueous slurry for reuse in the exhaust gas treatment.
Claim 19
Dependent Claim
35 words
The method as claimed in claim 16, wherein elemental sulfur is prepared from part of the gas containing sulfur dioxide and carbon dioxide formed in step (d) and the hydrogen sulfide formed in step (g).
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-01-28 | 1983-07-30 | 1984-01-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-01-28 | 1987-07-30 | 1988-01-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-01-28 | 1991-07-30 | 1992-01-29 | $7700.00 | Window Closed / Lapsed |