JPS6135892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for deodorizing exhaust gas or waste fluid containing odorous substances. In recent years, exhaust gases and liquids containing odorous substances generated from human waste, sewage treatment plants, food, pulp and paper factories, poultry farms, garbage treatment plants, oil refineries, petrochemical plants, foundries, various chemical plants, etc. have become an environmental problem. From this point of view, it is not permissible to release it as is. Conventionally, direct combustion methods, activated carbon adsorption methods, and chemical absorption methods have been proposed as means for treating this type of odorous substances. However, the direct combustion method has high processing efficiency;
Although it has the advantage of having a large variety of substances to be treated, it requires high equipment and operating costs, so it is not economically advantageous, especially when processing a large amount. In addition, the activated carbon adsorption method is limited in the types of odorous substances that can be treated, and its absorption capacity is relatively small, which, like the above-mentioned method, is not advantageous from an economic point of view, especially when treating large quantities. As an absorption method using chemicals, a reaction absorption method is known, in which odorous substances in exhaust gas or liquid are brought into contact with a chemical solution that reacts with them to make them odorless, but it is still not necessarily an efficient and inexpensive treatment method. difficult,
There is also the possibility that secondary pollution may be caused by the liquid after treatment. As a result of various research and examinations in order to eliminate the drawbacks of these conventional methods and find a method that can efficiently deodorize, the present inventor has determined that exhaust gas or waste fluid containing oxidizable odorous substances can be treated with effective bromine and aqueous soluble The odorous substances in the exhaust gas or waste liquid are decomposed by contacting with an aqueous liquid containing a chlorinated substance, and the aqueous liquid after the contact is electrolyzed, and the aqueous liquid is transformed by the action of the hypochlorous acid thus generated. A method of activating and regenerating an effective bromine-containing aqueous liquid and recycling it has already been proposed in Japanese Patent Application No. 7751/1983. However, according to the inventor's subsequent studies, when the waste gas to be treated contains carbon dioxide gas or the waste liquid to be treated contains a relatively large amount of carbon dioxide, the effect becomes more effective as the content increases. It was found that the current efficiency of hypochlorous acid, which is generated by electrolyzing chlorine substances contained in a bromine-containing aqueous liquid to activate and regenerate the liquid, was significantly reduced. As a result of various studies aimed at improving these points, the present inventors added hydrochloric acid to the electrolyte solution prior to the electrolysis to reduce carbonate groups in the solution, thereby achieving the above objective. I have discovered what can be achieved. Thus, the present invention is capable of removing oxidizable odorous substances and exhaust gas or waste liquid containing carbon dioxide gas or carbon dioxide radicals by contacting them with an aqueous liquid containing effective bromine and water-soluble chlorine substances. Decomposes odor substances,
While controlling the amount of dissolved carbonate radicals by adding hydrochloric acid to at least a portion of the resulting aqueous solution after contact, the aqueous solution after contact is electrolyzed, and by the action of the hypochlorous acid thus generated. It is an object of the present invention to provide a method for activating and regenerating the aqueous liquid as an effective bromine-containing aqueous liquid and recycling it. The odorous substances contained in the exhaust gas or waste liquid that can be treated in the present invention include a wide range of oxidizable odorous substances that can be oxidized in an acidic solution of potassium permanganate and are designated as malodorous substances. Typical examples include sulfur compounds such as hydrogen sulfide, methyl mercaptan, and methyl sulfide; nitrogen compounds such as ammonia, methylamine, and trimethylamine;
Butylene, butadiene, isoprene, styrene,
Examples include hydrocarbons such as toluene and phenol, and aldehydes such as formaldehyde and acrolein. Among these, in the present invention, hydrogen sulfide, mercaptans, methyl sulfide, ammonia,
Effective in deodorizing amines. Although the content of these oxidizable and odorous substances in the exhaust gas or waste liquid is not particularly limited, the treatment method of the present invention is extremely efficient, so that the content of particularly harmful and odorous components can be reduced to several ppm. This method is advantageous when applied to dilute exhaust gas that is difficult to process because the cost of normal treatment equipment is high. Examples of such exhaust gas include exhaust gas and liquid from human waste treatment plants, sewage treatment, food paper and pulp factories, poultry farms, garbage treatment plants, oil refineries, petrochemical factories, and foundries such as shell molding factories. usually also contain relatively large amounts of carbon dioxide gas or carbonate radicals. The effective bromine used in the present invention means a substance that generates elemental bromine in an aqueous liquid, and includes, for example, molecular bromine, oxygen acid of bromine chloride, or a salt thereof. Among these, alkali metal salts of hypobromous acid, particularly sodium salts, are most preferred in terms of performance and handling, as well as in terms of activation and regeneration of the liquid, which will be described later. The aqueous medium containing effective bromine is preferably water, but in some cases it may also be the aqueous waste liquid itself to be treated, and seawater can also be used.
It can also be used as an aqueous liquid containing effective bromine. The effective bromine content in the aqueous liquid is strictly determined by the amount of odorous substances in the exhaust gas or liquid to be treated, but is generally 10 mg/or more, preferably
Approximately 100 mg/approx. When the effective bromine-containing aqueous liquid is brought into contact with the exhaust gas or liquid to be treated, it is preferable that the pH of the liquid be alkaline than acidic because the treatment efficiency will be higher.
A pH of 10 or higher is preferable. In the present invention, a water-soluble chlorine substance is allowed to coexist in the treatment solution in addition to effective bromine. This can be achieved by coexisting a water-soluble chlorine substance in the treatment liquid and by electrolyzing the treatment liquid after contact with exhaust gas or wastewater. For example, if salt is coexisting as a water-soluble chlorine substance, This is because sodium chlorate is generated, and this can activate and regenerate modified products of available bromine, such as sodium bromide and hydrobromic acid, as available bromine. However, if a large amount of carbonate radicals is present in the treated liquid after contact with exhaust gas or waste liquid, if this is electrolyzed as is, a large amount of ClO ₃ ^- , which does not have the activation and regeneration effect to effective bromine, will be generated. . In the present invention, in order to prevent such a phenomenon as much as possible, the amount of dissolved carbonate radicals is controlled by adding hydrochloric acid to at least a portion of the treatment solution containing carbonate radicals. The amount of hydrochloric acid to be added is strictly determined by the amount of carbonate radicals contained in the treatment solution and the allowable amount of carbonate radicals to be dissolved, but it is generally added so that the pH of the treatment solution is about 6 to 1. It is appropriate to do so. If the pH is higher than 6, the efficiency of decarboxylation is poor, and if the pH is lower than 1, the amount of hydrochloric acid consumed will simply increase, and no further effect can be expected, so both are preferable. do not have. When the pH is between 4 and 1, a sufficient decarboxylation effect can be expected and it is practical, so it is particularly preferable. As the water-soluble chlorine substance to be subjected to electrolysis in the present invention, for example, in addition to common salt, chlorine, chlorides of alkali metals or alkaline earth metals, oxyacidates of chlorine, etc. can be used. As the water-soluble chlorine substance, the substances mentioned above can be directly added and used, but as mentioned above, since the treatment liquid is recycled, hydrochloric acid is added for the purpose of reducing carbonate groups to lower the pH. After electrolysis, when it comes into contact with the waste gas or liquid to be treated, alkali such as caustic soda is added to raise the pH of the absorption liquid to a desired level, as described above, to generate chlorine substances such as common salt. It is more realistic to use this. It is desirable that the concentration of the water-soluble chlorine substance in the treatment solution is approximately equimolar to the available bromine contained therein. Known means can be used for electrolysis of the above treatment solution,
It is usually performed without a septum. For the anode of the electrolytic cell, for example, platinum group metal or its oxide coated on a titanium or tantalum base material is used, and for the cathode, mild steel or rust-free steel is used. Electrolysis conditions are strictly determined by the type and composition of the electrolyte, but usually the cell voltage is 3~
7V and a current density of 10-30A/ ^dm2 can be adopted. There is no particular restriction on the means for contacting the exhaust gas or liquid containing the odorous substance and carbon dioxide gas or carbonate radical with the treatment liquid containing effective bromine. For example, perforated plate towers, packed towers, tray towers, spray towers, ventilate scrubbers, bubble towers, etc. can be used as appropriate, and if the object to be treated is exhaust gas, the gas-liquid contact can be carried out countercurrently or cocurrently. do not have. An embodiment of the means for carrying out the method of the present invention will be outlined below, taking exhaust gas containing odorous substances and carbon dioxide as an example. Exhaust gas containing odorous substances and carbon dioxide gas is introduced from the lower part of the perforated plate column and a suitable reaction column, while an aqueous liquid containing available bromine and water-soluble chlorine substances is introduced from the upper part of the column, countercurrently with the exhaust gas. be contacted. Most of the absorption liquid that has reached the bottom of the column is circulated back to the top of the column, but a portion of the absorption liquid is extracted from the system, and the majority of it is sent to an electrolytic cell that electrolyzes water-soluble chlorine substances. It is activated and regenerated as an aqueous liquid containing effective bromine using hypochlorous acid (salt) produced by electrolysis. On the other hand, hydrochloric acid is added to a portion of the absorption liquid extracted from the system to adjust the pH to 6 to 1 to remove dissolved carbonate radicals. The rate of carbonate radical removal here is determined by the amount of hypochlorous acid (salt) produced in the above-mentioned electrolysis. The decarboxylated liquid is returned to the previous reaction tower, and an alkali for pH adjustment is added to the liquid or the reaction tower, if desired. In this way, the amount of carbonate radicals dissolved in the aqueous liquid containing available bromine and water-soluble chlorine substances can be maintained at a desired value. In addition, the absorption liquid extracted from the reaction tower to the outside of the system is
It is also possible to add hydrochloric acid to the entire amount and electrolyze some or all of it after removing dissolved carbonate radicals, or the entire amount of the absorption liquid that has reached the bottom of the column can be extracted out of the system and then It is also possible to carry out treatment, but in these cases, when it is necessary to increase the pH when bringing it into contact with the exhaust gas or liquid to be treated, the amount of alkali added for this purpose increases, so it is costly. is not very advantageous. Next, the present invention will be specifically explained using examples. Example 1 Methyl mercaptan 0.25ppm, dimethyl sulfide 0.15ppm, methyl sulfide 0.03ppm, hydrogen sulfide
Exhaust gas containing 0.6 ppm and 300 ppm of carbon dioxide is collected in a column with a diameter of 20 mm.
It was fed from the bottom of the tower at a rate of 300 Nm ³ /hour into a perforated plate tower with cmφ and three absorption stages. The absorption liquid was supplied from the upper part of the column from the circulation tank through a pump at a rate of 0.9 m ³ /hour. The absorption liquid is 10% by weight NaCl and 2g/NaBr,
It contained 10g/carbonate radical, and the pH of the solution was adjusted to 11 with caustic soda. In order to regenerate the NaBr reduced by absorption into sodium hypobromite, a portion of the absorbed liquid was fed into the electrolytic cell via a pump at a rate of 1 m ³ /hour. The electrolytic cell uses a platinum-plated titanium anode and an iron cathode, and the electrode area is 2 dm ² . Then, membraneless electrolysis was performed at a voltage of 3.6 V and a current density of 12 A/dm ² , and as a result, the concentration of sodium hypobromite in the absorption liquid was maintained at 500 mg/dm. On the other hand, in order to keep the concentration of carbonate groups in the absorption liquid constant,
A portion of the absorption liquid was withdrawn from the circulation tank at a rate of 0.7/hour, hydrochloric acid was added thereto to maintain the pH at 3, decarboxylation was performed, and then this was returned to the circulation tank. Thus, the concentrations of odorous components in the flue gas at the outlet of the tower in a steady state treated in the perforated plate tower are 0.002 ppm of methyl mercaptan and 0.002 ppm of dimethyl sulfide.
0.007ppm, methyl sulfide 0.006ppm, hydrogen sulfide
It was 0.01ppm. For comparison, in this example, when decarboxylation with hydrochloric acid was omitted, the carbonate radicals in the absorbent gradually increased and the current efficiency of sodium hypochlorite by electrolysis decreased.
The current efficiency after about 300 hours was less than 1/5 of the initial value. Therefore, even if electrolysis is performed at a voltage of 5V and a current density of 35A/ ^dm2 , the concentration of sodium hypobromite in the absorption liquid will be
It did not reach 500 mg/, and the carbonate concentration was 30 g/. At this time, the concentration of odorous components in the exhaust gas at the tower outlet was 0.01 ppm of methyl mercaptan, 0.04 ppm of dimethyl sulfide, 0.025 ppm of methyl sulfide, and 0.02 ppm of hydrogen sulfide.
It was 0.05ppm. Examples 2 to 4 Exhaust gas containing odorous components and carbon dioxide gas as shown in the following table was similarly supplied to the perforated plate column as in Example 1. In addition, the absorption liquid is passed through the pump from the circulation tank.
It was supplied from the top of the column at a rate of 0.9 m ³ /h. The composition of the absorption liquid is as shown in the table, and the pH of the liquid was adjusted to 11 with caustic soda. In order to regenerate NaBr reduced by absorption into sodium hypobromite, a portion of the absorbed liquid was sent to the same electrolytic cell as in Example 1 at a rate of 1 m ³ /hour and electrolyzed under the conditions shown in the table. , the concentration of NaBrO was kept at 500 mg/. On the other hand, in order to keep the concentration of carbonate groups in the absorption liquid constant,
A portion of the absorption liquid is extracted from the circulation tank in the proportion shown in the table, and hydrochloric acid is added to it to adjust the pH of each liquid.
After decarboxylation, the mixture was returned to the circulation tank. The concentrations of odorous components in the exhaust gas at the outlet of the tower in a steady state treated in the perforated plate tower are as shown in the table. 【table】

Claims (1)

[Scope of Claims] 1. Odorous substances in the exhaust gas or waste liquid are removed by contacting exhaust gas or waste liquid containing oxidizable odorous substances and carbonic acid radicals with an aqueous liquid containing effective bromine and water-soluble chlorine substances. Hydrochloric acid is added to at least a portion of the aqueous solution after contact to control the amount of dissolved carbonate radicals, while the aqueous solution after contact is electrolyzed, thus generating hypochlorous acid. The aqueous liquid is activated and regenerated as an effective bromine-containing aqueous liquid by the action of
A method for deodorizing exhaust gas or liquid, characterized by recycling. 2 At least a portion of the aqueous liquid after contact with this
The method according to claim 1, wherein hydrochloric acid is added to adjust the pH to 6-1. 3. The contact between the oxidizable odorous substance and the exhaust gas or liquid containing carbon dioxide gas or carbonic acid radicals and the aqueous liquid containing effective bromine and water-soluble chlorine substances is carried out at a pH of 10 or higher. Method. 4. The method according to claim 1, wherein the oxidizable odorous substance is a sulfur compound, a nitrogen compound, a hydrocarbon, or an aldehyde. 5. The method of claim 1, wherein the aqueous liquid containing available bromine is an aqueous solution of bromine, bromine chloride, or an oxyacid salt of bromine. 6. The method of claim 1, wherein the water-soluble chlorine substance is chlorine, chloride, or chlorine oxyacid. 7. The method according to claim 1, wherein the electrolysis is diaphragmless electrolysis. 8 Electrolysis is performed at a cell voltage of 3 to 7 V and a current density of 10 to 30
8. The method of claim 1 or 7 carried out at Å/dm ² .