US 4,552,635 AGranted

Electrodialytic methods for removal of sulfur oxides from waste gases

AssigneeAllied Corporation

InventorsTheodore J. Jenczewski, William H. Skinner, Jr.

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Abstract

Methods for removal of sulfur oxides, e.g., SO.sub.2 and SO.sub.3, from sulfuric acid tail gases by alkaline solution scrubbing, acidification of the alkaline scrubbing solution containing absorbed sulfur valves, liberation of concentrated SO.sub.2 from the acidified solution and regeneration of the alkaline scrubbing solution by means of two- or three-compartment electrodialytic water splitters are disclosed. A completely closed loop method suitable for continuous removal of sulfur oxides from sulfuric acid tail gas, recovery of concentrated SO.sub.2 for use in sulfuric acid plants, regeneration of alkaline scrubbing process solution and improvement in the water balance in sulfuric acid plant by use of two- and three-compartment electrodialytic water splitters is also disclosed.

Claims23

Dependent claims

A method for removing and recovering SO.sub.2 and SO.sub.3 from gases, and regenerating the process liquors, which comprises the steps of:

(a) contacting, in a first reaction zone, gases containing SO.sub.2 and SO.sub.3 with a reaction liquid comprising aqueous hydroxide to produce an aqueous salt solution containing aqueous soluble sulfites, bisulfites and sulfates, and a gas comprising water vapor and depleted in SO.sub.2 and SO.sub.3 ;
(b) contacting, in a second reaction zone, said aqueous salt solution with a reaction liquid comprising sulfuric acid and water to form an aqueous solution comprising sulfurous acid and aqueous soluble sulfates;
(c) separating the sulfurous acid from said aqueous solution by liberating SO.sub.2 as a gas therefrom;
(d) providing an electrodialytic water splitter comprising at least one unit cell, each unit cell comprising an acid and a base compartment;
(e) feeding the liquid comprising aqueous soluble sulfates to the base compartment of the electrodialytic water splitter;
(f) feeding a liquid comprising dilute aqueous sulfuric acid and substantially free of soluble sulfate salts to the acid compartment of the electrodialytic water splitter;
(g) passing current through said electrodialytic water splitter to produce a liquid enriched in sulfuric acid in the acid compartment, and a liquid comprising aqueous hydroxide in the base compartment.

4 more elements

A method for removing and for recovering SO.sub.2 and SO.sub.3 from gases, and regenerating process liquors which comprises the steps of:

(a) contacting, in a first reaction zone, gases containing SO.sub.2 and SO.sub.3 with a reaction liquid comprising aqueous hydroxide to produce an aqueous salt solution containing soluble sulfites, bisulfites, and sulfates, and a gas comprising water vapor and depleted in SO.sub.2 and SO.sub.3 ;
(b) contacting, in a second reaction zone, said aqueous salt solution with a reaction liquid comprising sulfuric acid and water to form an aqueous acid solution comprising sulfurous acid and aqueous soluble sulfates;
(c) separating the sulfurous acid from the aqueous acid solution be liberating SO.sub.2 as a gas therefrom;
(d) providing an electrodialytic water splitter comprising at least one unit cell, each unit cell comprising an acid, base and salt compartment;
(e) feeding at least a portion of said aqueous soluble sulfate to the salt compartment of the three-compartment electrodialytic water splitter;
(f) feeding a liquid comprising water to the base compartment of said electrodialytic water splitter;
(g) feeding a liquid comprising dilute aqueous sulfuric acid and substantially free of soluble sulfate salts to the acid compartment of said electrodialytic water splitter;
(h) passing current through said electrodialytic water splitter to produce a liquid enriched in sulfuric acid in the acid compartment, a liquid comprising aqueous hydrogen ions and soluble sulfate in the salt compartment and a liquid comprising aqueous soluble hydroxide in the base compartment;
(i) forwarding at least a portion of the liquid enriched in sulfuric acid to the second reaction zone;
and
(j) forwarding the liquid comprising aqueous soluble hydroxide to the first reaction zone.

8 more elements

Dependencies are inferred from the claim text.