WO2008041781A1 - Method for removal of chlorine gas - Google Patents

Abstract

Disclosed is a method for removing a chlorine gas contained in an exhaust gas. The method comprises the step of reacting the chlorine gas with sodium hydroxide in an amount of 1.0 to 1.2 times the theoretical amount required for neutralizing the chlorine gas and a sulfite salt and/or a bisulfite salt in an amount of 1.0 to 1.2 times the theoretical amount required for neutralizing the chlorine gas to remove the chlorine gas.

Description

 Chlorine gas removal method Technical Field

 The present invention relates to a chlorine gas detoxification method, and more particularly, to a chlorine gas detoxification method using an alkaline solution, and to a chlorine gas detoxification method in which chlorate is not generated.

 Rice field

 book

 Background art

 In general, exhaust gas containing chlorine gas is treated by neutralizing it with an alkaline solution such as an aqueous sodium hydroxide solution. When chlorine gas is neutralized with aqueous sodium hydroxide solution, sodium hypochlorite is produced, and sodium chlorate is also produced. Although there are no regulations on the emission of chlorates such as sodium chlorate (hereinafter referred to as chlorate) in Japan, there are known adverse effects on aquatic plants. It is desirable to discharge Japanese wastewater.

 Here, as a method of decomposing sodium hypochlorite in the neutralized wastewater generated by neutralizing the exhaust gas containing chlorine gas with an aqueous sodium hydroxide solution, for example, using a catalyst There are known a method, a method by thermal decomposition, a method of degrading by lowering pH, and a method of reducing using sulfite.

 For example, in Japanese Patent Application Laid-Open No. 2000-305-0 14 (Patent Document 1), chlorine gas is selectively used from an exhaust gas containing chlorine gas and carbon dioxide gas using an aqueous sodium hydroxide solution. Describes the method of detoxifying chlorine to be absorbed and removed. The generated hypochlorite aqueous solution can be decomposed by thermal decomposition and, if necessary, sulfite to decompose hypochlorite. It is disclosed.

However, depending on the treatment method using sulfite, it is possible to decompose a part of the chlorate produced together with hypochlorite by neutralization treatment with chlorine gas solution. Concentrate enough It cannot be reduced by. In addition, when the generated hypochlorite aqueous solution is pyrolyzed, hypochlorite is decomposed and chlorate is by-produced. In addition, if the aqueous hypochlorite solution is allowed to stand, there is a problem that hypochlorite is spontaneously oxidized to produce chlorate and the chlorate concentration increases.

 In this way, when chlorine gas is neutralized with an alkaline solution, chlorate is produced together with hypochlorite, and this chlorate may be sufficient depending on the conventionally known methods for decomposing hypochlorite. Not decomposed. Therefore, the present inventor has developed a method for performing decomposition of hypochlorite without generating chloride, or a method for reducing both the produced hypochlorite and chloride to a sufficient extent. I tried to develop. Disclosure of the invention

 The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a method for detoxifying exhaust gas containing chlorine gas using an alkaline solution without generating chlorate. It is.

 The chlorine gas detoxification method of the present invention is a method for detoxifying chlorine gas contained in exhaust gas, which is 1.0 to the theoretical amount necessary for neutralizing the chlorine gas to the chlorine gas. By reacting with sodium hydroxide twice and 1.0 to 1.2 times the theoretical amount of sulfite and / or bisulfite necessary for reducing the chlorine gas, the chlorine The method includes a step of removing gas.

 The chlorine gas detoxification method of the present invention includes the step (A) of supplying the following aqueous solution (al) and the following aqueous solution (a 2) while supplying the exhaust gas to the first absorption tower. It is characterized by.

Aqueous solution (a l): An aqueous solution of sodium hydroxide 1.0 to 1.2 times the theoretical amount necessary to neutralize the chlorine gas.

Aqueous solution (a 2): An aqueous solution of sulfite and Z or bisulfite that is 1.0 to 1.2 times the theoretical amount necessary to reduce the chlorine gas.

Here, the second absorption tower connected to the first absorption tower is supplied with the exhaust gas after the step (A), and the following aqueous solution (bl) and the following aqueous solution (b 2 ) Is preferably included.

Aqueous solution (b l): An aqueous solution of sodium hydroxide in an amount of 0 · 001 to 0.2 times the theoretical amount necessary to neutralize the chlorine gas.

Aqueous solution (b 2): An aqueous solution of sulfite and / or bisulfite that is 0.001 to 0.2 times the theoretical amount necessary to reduce the chlorine gas.

 The exhaust gas may contain chlorine gas and carbon dioxide gas. In this case, according to the present invention, chlorine gas can be selectively removed.

 The action of the chlorine gas, sodium hydroxide, sulfite and / or sulfite hydrate is preferably performed in the range of 10 to 40 ° C.

 According to the chlorine detoxification method of the present invention, chlorine gas can be efficiently detoxified with little generation of chlorate. Brief Description of Drawings

 FIG. 1 is a schematic view showing an example of a chlorine gas removal system preferably used in the chlorine removal method of the present invention.

 FIG. 2 is a schematic view showing another example of a chlorine gas removal system preferably used in the chlorine removal method of the present invention.

 Fig. 3 is a schematic diagram showing an example of a system used in a process for producing chlorine gas from oxygen gas and hydrogen chloride gas.

 Explanation of symbols

1 0 1 1st absorption tower, 1 02 2nd absorption tower, 1 03 1st receiver, 1 0 4, 4 0 5 packing, 1 06, 1 07 exchanger, 1 08 Chlorine gas monitor and flow meter 1 1 0 9 Control device 1 1 0 1st aqueous solution supply device 1 1 1 2nd aqueous solution supply device 1 1 6 Pretreatment tower 1 1 7 Reaction tower 1 1 8 Absorption tower 1 1 9 Drying tower, 1 2 0 Washing tower, 12 1 Chlorine purification tower, 1 22 Hydrochloric acid absorption tower, 1 2 3 Activated carbon tower, 2 0 1, 202, 203, 203 a, 204, 20 5, 206, 2 0 7, 208 , 2 09, 2 1 0, 22 1, 22 2, 223, 224, 22 5, 22 6, 22 7, 228, 229, 230, 23 1, 232, 233, 234, 2 3 5, 23 6, 2 3 7, 238, 239, 240 lines, PI, P 2 pump. BEST MODE FOR CARRYING OUT THE INVENTION

 The chlorine gas detoxification method of the present invention is a method for detoxifying chlorine gas contained in an exhaust gas, wherein the chlorine gas has a theoretical amount of 1.0 to 1.0 to a neutral amount necessary for neutralizing the chlorine gas. 1. 2 times sodium hydroxide and 1.0 to 1.2 times the theoretical amount necessary to reduce the chlorine gas, sulfite and / or bisulfite are allowed to act to The method includes a step of removing gas.

As a result, chlorine gas can be efficiently removed with little generation of chlorate. This can be understood as follows. In the present invention, the exhaust gas contains chlorine gas. For example, when sodium hydroxide (NaOH) is used as the alkali metal hydroxide, the exhaust gas reacts with an aqueous sodium hydroxide solution. Chlorine (Cl ₂ ) reacts with sodium hydroxide (the following formula (1)) to produce sodium hypochlorite (N a C 1 O) and sodium chloride (N a C 1).

C 1 _z + 2 N a OH → Na C 1 O + Na C 1 + H ₂ 0 (1) When contacting exhaust gas with sodium hydroxide aqueous solution, not only sodium hydroxide but also sulfite, for example When sodium sulfite (Na ₂ S0 ₃ ) coexists as sodium hydrogen chlorite (Na ₂ C0), it becomes possible to decompose sodium hypochlorite (N a C 10) by the reaction of the following formula (2).

N a C 1 O + N a ₂ S 0 ₃ → N a C l + N a ₂ S 0 ₄ (2) The sodium hypochlorite (N a CIO) once generated by the reaction of the above formula (2) is It is decomposed into Na C l and N a ₂ S_〇 ₄ before changed to chlorate (Na C 10 ₃₎ by natural oxidation or the like. Alternatively, for example, sodium sulfite (Na ₂ S0 ₃ ) coexists as a sulfite, so that the reaction shown by the following formula (3) does not produce sodium hypochlorite (Na CIO), and chlorine is decomposed. It may be removed.

_{C 1 2 + Na 2 S0 3} + 2 N a OH → 2 N a C 1 + N a 2 S 0 4 + H 2 O (3)

Thus, when detoxifying chlorine gas, it is possible to use alkaline metal hydroxide such as sodium hydroxide. By coexisting sulfite with the compound, hypochlorite is not produced at all or can be decomposed before it is converted to chlorate. As a result, it is possible to decompose and remove chlorine gas with little generation of chlorate.

Here, when the exhaust gas contains carbon dioxide (carbon dioxide, C0 ₂ ) together with chlorine gas, sodium hydroxide reacts with carbon dioxide at pH 7.0 or higher, but pH 7.0 ~: 10 in 33, sodium carbonate (Na ₂ C_〇 ₃₎ does not generate, carbonated water containing sodium (NaHC_〇 ₃₎ only generates (the following formula (4)).

C_〇 ₂ + Na_〇_H → N AHC_〇 ₃ (4)

Furthermore, the pH 7 ~ 8, the generation amount of sodium bicarbonate (NaHC_〇 ₃₎ is slight, moreover, the slightly generated sodium bicarbonate (N AHC_〇 ₃₎ is reacted with chlorine (C l ₂₎ because it produces carbon dioxide (C0 ₂₎ sodium hypochlorite while generating a (NaC IO) Te, substantially, sodium bicarbonate (N a HC_〇 ₂₎ and sodium carbonate (N a CO _s) does not generate (Formula (5) below).

2 N aHC0 ₃ + C 1 ₂ → NaC IO + NaC 1 + 2 CO _z + H ₂ 0 (5)

Here, sodium hypochlorite produced by the reaction of sodium bicarbonate with (N AHC_〇 ₃₎ and chlorine _{(C l 2) (N a'C} IO) is sulfite (and / or nitrous hydrogen sulfate) By coexisting, it is decomposed by the reaction of the above formula (2). Alternatively, through a reaction similar to the above formula (3), sodium hypochlorite (NaC10) is not substantially formed, and sodium hydrogencarbonate (NaHC0 ₃ ) and chlorine (Cl ₂ ) Reacts. Therefore, even if the exhaust gas contains carbon dioxide, the chlorine gas is removed with little generation of chlorate, and the chlorine gas is selectively removed. Furthermore, it is possible to minimize the generation of sodium bicarbonate (NaHC_〇 ₂₎ and carbon sodium (Na ₂ C0 _3).

In the chlorine gas detoxification method of the present invention, the amount of the Al force acting on the chlorine gas is 1.0 to 1.2 times the theoretical amount necessary to neutralize the chlorine gas. If it is less than 1.0 times the theoretical amount, chlorine may not be sufficiently absorbed, and if it exceeds 1.2 times, carbonates and bicarbonates are likely to be formed. Preferably The amount of alkali that acts on the chlorine gas is not less than 1.0 times and not more than 1.1 times the theoretical amount necessary to neutralize the chlorine gas.

 Here, “theoretical amount necessary for neutralizing chlorine gas” means the stoichiometric amount necessary for neutralizing the total amount of chlorine gas contained in the exhaust gas. For example, the theoretical amount required to neutralize chlorine gas l m o 1 is 2 m o l when sodium hydroxide is used as the alkali. Therefore, in this case, 1.0 to 1.2 times the theoretical amount necessary to neutralize chlorine gas means 2.0 to 2.4 mol. “Alkaline” action of chlorine on chlorine gas specifically means that chlorine gas and alkali are brought into contact with each other and at least a part thereof is reacted.

 As the alkali, for example, an alkali metal hydroxide, an alkaline earth metal hydroxide, or the like can be preferably used. Conventionally known alkali metal hydroxides and alkaline earth metal hydroxides can be used. The alkali metal hydroxide and alkaline earth hydroxide may be used alone or in combination. In other words, a plurality of materials belonging to the alkali metal hydroxide may be used, a plurality of materials belonging to the alkaline earth metal hydroxide may be used in combination, or these may be combined with each other. Good. Among these, in the present invention, it is particularly preferable to use sodium hydroxide. When a plurality of alkalis are used in combination, the amount is set so that the total amount of alkali used is within the above range.

 The alkali is preferably used as an aqueous solution. When sodium hydroxide is used as the alkali, the concentration of the aqueous sodium hydroxide solution is preferably in the range of 7 to 20% by mass. If the amount is less than 7% by mass, the amount of the aqueous solution increases, which is disadvantageous in terms of volumetric efficiency. If the amount exceeds 20% by mass, carbonates and hydrogen carbonates are likely to precipitate, which is a problem. Preferably, the concentration of the aqueous sodium hydroxide solution is 9% by mass or more and 13% by mass or less.

In addition, the amount of sulfite and / or bisulfite that acts on chlorine gas is 1.0 to 1.2 times the theoretical amount necessary to reduce the chlorine gas. If it is less than 1.0 times, the production of chlorate may not be sufficiently suppressed, and if it exceeds 1.2 times, the production of chlorate will be sufficiently suppressed. This is because, however, a large amount of expensive sulfite is used, and the concentration of sulfite in the wastewater increases, resulting in an increase in chemical oxygen demand (COD). 'Preferably, the amount of sulfite and / or bisulfite that acts on chlorine gas is not less than 1.0 times and not more than 1.1 times the theoretical amount necessary to reduce the chlorine gas.

 Here, “theoretical amount necessary for reducing chlorine gas” means the stoichiometric amount necessary for reducing the total amount of chlorine gas contained in the exhaust gas. For example, the theoretical amount necessary to reduce chlorine gas l m o 1 is l m o l when using sulfite. Therefore, in this case, 1.0 to 1.2 times the theoretical amount necessary to reduce chlorine gas means 1.0 to 1.2 mol. The term “acting” sulfite and / or hydrogen sulfite with chlorine gas specifically means contacting chlorine gas with sulfite and / or bisulfite to react at least partly. . 'As the sulfite, for example, sodium sulfite, potassium sulfite and the like can be preferably used. As the bisulfite, for example, sodium bisulfite, potassium bisulfite and the like can be preferably used. These may be used alone or in combination. Among these, in the present invention, it is particularly preferable to use sodium sulfite and / or sodium hydrogen sulfite. When using a combination of multiple types as sulfites and bisulfites, the total amount of sulfites and bisulfites used should be within the above range.

The sulfite and / or hydrogen sulfite is preferably used as an aqueous solution. For example, when sodium sulfite is used, the concentration of the sodium sulfite aqueous solution is preferably in the range of 2 to 20% by mass. If it is less than 2% by mass, the amount of the aqueous solution is large, which is disadvantageous in terms of volumetric efficiency. If it exceeds 20% by mass, Na ₂ S 0 _{4 and the} like are likely to precipitate, which is a problem. . Preferably, the concentration of the sodium sulfite aqueous solution is 3% by mass or more and 15% by mass or less.

When the alkaline aqueous solution and the aqueous solution of sulfite and Z or bisulfite are allowed to act on chlorine gas, the alkaline aqueous solution and the aqueous solution of sulfite and / or bisulfite may be allowed to act respectively. Well, al force And an aqueous solution containing sulfite and z or bisulfite may be allowed to act.

 Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an example of a chlorine gas abatement system preferably used in the present invention. In the following description, the case where sodium hydroxide, sulfite, and / or sodium sulfite is used as the alkali will be described as an example.

 In FIG. 1, the chlorine gas abatement system includes a first absorption tower 1 0 1 and a second absorption tower 1 0 2 connected to the first absorption tower 1 0 1. A first receiver 10 3 for receiving the product discharged from the tower 1 0 1 is connected to the first absorption tower 1 0 1. In the first absorption tower 101, exhaust gas is preferably continuously supplied, and sodium hydroxide in an amount of 1.0 to 1.2 times the theoretical amount necessary for neutralizing the chlorine gas is used. And a step of removing chlorine gas by supplying 1.0 to 1.2 times the theoretical amount of sodium sulfite required for reducing the chlorine gas (step (A)). It is.

 The insides of the first absorption tower 1 0 1 and the second absorption tower 1 0 2 are filled with packing materials 1 0 4 and 1 0 5, respectively, thereby improving the gas-liquid contact efficiency and chlorine. Can be removed quickly. As the fillers 10 4 and 10 5, known materials such as Raschig rings and pole rings can be used, for example, and the materials include, for example, fluorine resin, vinyl chloride resin, ceramics, inorganic glass, and the like. Can be mentioned.

For example, exhaust gas discharged by a predetermined chlorine generation process, which will be described later, is input to the first absorption tower 10 1 through a path 2 0 2. The exhaust gas contains chlorine gas and carbon dioxide gas. The exhaust gas may not contain carbon dioxide gas. In addition, the first absorption tower 101 has sodium hydroxide adjusted to 1.0 to 1.2 times the theoretical amount necessary to neutralize chlorine gas contained in the exhaust gas, In addition, sodium sulfite adjusted to 1.0 to 1.2 times the theoretical amount necessary for reducing chlorine gas is introduced through the passageway 201. Note that the sodium hydroxide aqueous solution and the sodium sulfite aqueous solution may be supplied as separate aqueous solutions from the route 210, and the aqueous solution containing sodium hydroxide and sodium sulfite as the aqueous solution. It may be performed from 2 0 1. Further, either a sodium hydroxide aqueous solution or a sodium sulfite aqueous solution may be supplied from a route (not shown) different from the route 201. In this way, in the first absorption tower 101, the reaction of chlorine gas and carbon dioxide as described above with sodium hydroxide and sodium sulfite occurs. Sodium chloride and sodium sulfate produced by the reaction are discharged to the first receiver 10 3 through the path 20 3. Sodium chloride and sodium sulfate in the first receiver 10 3 are sucked by the pump P 1 and controlled by the exchanger 1 0 6 and again through the path 2 0 3 a to the first absorption tower 1 0 1 To be sent in or discharged through path 2 10.

The pH of the treatment solution in the first receptor 10 3 is maintained in the range of about 7-8. As a result, sodium carbonate and sodium bicarbonate do not precipitate, and the cycle of the chlorine gas abatement process is not adversely affected. Further, p H can be prevented occurrence of S_〇 ₂ gas by be excessive too be low.

 The action of chlorine gas, sodium hydroxide and sodium sulfite is preferably carried out in the range of 10 to 40 ° C. Below 10 ° C, chlorine gas, sodium hydroxide and sodium sulfite may not react sufficiently. If it is higher than 40 ° C, the reaction may become too violent. The temperature can be confirmed, for example, by confirming the temperature of the treatment solution in the first receiver 10.

Subsequently, the exhaust gas containing unreacted and regenerated or regenerated carbon dioxide gas through the step (A) in the first absorption tower 101 is introduced into the second absorption tower 10 2 through the path 204. Step (B) is performed. Here, the step (B) is based on the premise that chlorine gas is contained in the exhaust gas supplied to the second absorption tower 10 2 through the channel 20 4. Therefore, the step (B) is provided as necessary, and if the entire amount of chlorine gas can be removed by the first absorption tower 101, the step (B) is not performed. May be. In the present invention, there is chlorine gas that could not be completely removed by the first absorption tower 101, and in order to completely absorb and remove this, as shown in FIG. 1, the second absorption tower It is preferable to provide 100 and completely absorb and remove unreacted chlorine gas in the second absorption tower 102. Hereinafter, process (B) Will be described.

The second absorption tower 10 2 is supplied with the exhaust gas that has undergone the step (A) and has a theoretical amount of 0.001 to 0.2 that is necessary for neutralizing chlorine gas. Double alkali and 0.01 to 0.2 times the theoretical amount of sulfite and / or bisulfite required to reduce the chlorine gas is fed through path 2 06 (step ( B))). If the amount of alkali is less than 0.001 times the theoretical amount necessary to neutralize chlorine gas, chlorine may not be sufficiently absorbed. This is because hydrogen carbonate is easily generated. Preferably, the amount of the Al force acting on the chlorine gas in the second absorption tower 102 is not less than 0.001 times the theoretical amount necessary to neutralize the chlorine gas. Is less than double. In addition, if the amount of sulfite and hydrogen or bisulphite is less than 0.01 times the theoretical amount necessary to reduce chlorine gas, the formation of kurate is sufficiently suppressed. If it exceeds 0.2 times, it is possible to sufficiently suppress the production of chlorate, but a large amount of expensive sulfite will be used, and the concentration of sulfite in the wastewater will increase. This is because the problem arises that the chemical oxygen demand (COD) increases due to the increase. Preferably, the amount of sulfite and / or hydrogen sulfite that acts on chlorine gas is not less than 0.001 times and not more than 0.1 times the theoretical amount necessary to reduce the chlorine gas. The chlorine gas here means the total chlorine gas contained in the exhaust gas supplied to the first absorption tower 101 in the step (A). As a result, chlorine gas that has not been absorbed and removed in the first absorption tower 101 can be completely absorbed and removed. The action of chlorine gas, sodium hydroxide and sodium sulfite in the second absorption tower 102 is in the range of 10 to 40 ° C, as in the case of the first absorption tower 101. The ρ 行 な わ of the treatment solution obtained as a result of this action is preferably maintained within the range of about 7 to 8.5. As the alkali supplied into the second absorption tower 102, the above-mentioned alkalis can be used, but it is preferable to use the same ones used in the step (A). The alkali is preferably used as an aqueous solution. When sodium hydroxide is used as the alkali, the concentration of the aqueous sodium hydroxide solution is preferably in the range of 1 to 10% by mass. If it is less than 1% by mass, 1 A large amount of liquid is disadvantageous in terms of volumetric efficiency, and if it exceeds 10% by mass, it is a problem because carbonates and bicarbonates are likely to precipitate. Preferably, the concentration of the aqueous sodium hydroxide solution is 1% by mass or more and 5% by mass or less.

As the sulfite and Z or hydrogen sulfite supplied into the second absorption tower 102, those described above can be used, but the same as those used in step (A) can be used. preferable. The sulfite and / or hydrogen sulfite is preferably used as an aqueous solution. For example, when sodium sulfite is used, the concentration of the sodium sulfite aqueous solution is preferably in the range of 2 to 20% by mass. If the amount is less than 2% by mass, the amount of the aqueous solution is large, which is disadvantageous in terms of volumetric efficiency. If the amount exceeds 20% by mass, Na ₂ S 0 _{4 and the} like are likely to precipitate, which is a problem. . Preferably, the concentration of the sodium sulfite aqueous solution is 3% by mass or more and 15% by mass or less.

 The supply of the sodium hydroxide aqueous solution and the sodium sulfite aqueous solution in the second absorption tower 102 may be carried out as separate aqueous solutions from the passage 206, respectively, and the aqueous solution containing sodium hydroxide and sodium sulfite. May be performed from road 2 0 6 as follows. Further, either a sodium hydroxide aqueous solution or a sodium sulfite aqueous solution may be supplied from a route (not shown) different from the route 206.

 Through the process (B) as described above, other unreacted and / or regenerated carbon dioxide contained in the exhaust gas from the channel 2 08 provided at the top of the second absorption tower 10 2. Gas is released. Also, from the bottom of the second absorption tower 102, unreacted sodium hydroxide, sodium chloride, and sodium sulfate (which may also include sodium hydrogen carbonate, etc.) are discharged through the path 210, Sodium hydroxide, sodium chloride and sodium sulfate are sucked by the pump P 2 and sent to either the path 2 0 5 or the path 2 0 7 by the exchanger 1 07.

When it is sent through the path 2 0 7, it is again put into the first absorption tower 1 0 1 through the path 2 0 3 a. The sodium chloride and sodium sulfate fed into the first absorption tower 1 0 1 through the path 2 0 3 a are passed from the bottom of the first absorption tower 1 0 1 through the path 2 0 3 to the first It is discharged to the receiver 1 0 3. In addition, sodium hydroxide, sodium chloride and sodium sulfate supplied to the second absorption tower 10 2 through the path 2 0 5 2, sodium hydroxide (and sodium hydrogen carbonate) again contributes to the reaction with chlorine gas in the second absorption tower 10 2, and sodium chloride and sodium sulfate are discharged from the bottom as they are, and the above cycle is repeated. repeat.

 Next, a method of controlling the sodium hydroxide aqueous solution and the sodium sulfite aqueous solution supplied into the first absorption tower 101 and the second absorption tower 102 will be described with reference to FIG. FIG. 2 is a schematic view showing another example of a chlorine gas removal system preferably used in the chlorine removal method of the present invention. Note that the configuration of numbers not described in FIG. 2 is the same as that of FIG.

 In FIG. 2, a chlorine gas monitor and a flow meter 10 8 are connected to the path 2 0 2, and the concentration and flow rate of chlorine gas in the exhaust gas passing through the path 2 0 2 are continuously measured. The chlorine gas monitor and flow meter 10 8 is connected with a control device 10 9 and receives signals from the chlorine gas monitor and flow meter 10 8. Here, continuous measurement means that measurement is performed intermittently or at intervals of 10 minutes or less.

 Further, a first aqueous solution supply device 110 and a second aqueous solution supply device 11 1 1 are connected to the control device 109, and the first aqueous solution supply device 110 is a sodium hydroxide solution. And an aqueous solution containing sodium sulfite, which is supplied into the first absorption tower 1 0 1 via the path 2 0 1, and the second aqueous solution supply device 1 1 1 includes sodium hydroxide and 1 An aqueous solution containing sodium sulfite is held, and this is supplied into the second absorption tower 10 2 via the path 2 0 6. Note that another aqueous solution supply device (not shown) is connected to the control device 109, and separates the sodium hydroxide aqueous solution and the sodium sulfite aqueous solution into the first absorption tower 10 0 1 and the second absorption tower 1 0 separately. 2 may be supplied. In this case, the sodium hydroxide aqueous solution and the sodium sulfite aqueous solution supplied into the first absorption tower 101 and the second absorption tower 102 are respectively connected to the same passage 2 0 1 and passage 2 0 6. It may be supplied via a different route, or a different route not shown in the figure may be used in combination.

Next, control using these devices will be described. First, a signal related to the concentration and flow rate of chlorine gas in the exhaust gas passing through the path 2 0 2 measured by the chlorine gas monitor and the flow meter 1 0 8 is transmitted to the control device 1 0 9. Receive the signal The control device 10 9 is required to reduce the theoretical amount of sodium hydroxide and the chlorine gas required to neutralize chlorine gas by the program incorporated in the control device 10 9. The theoretical amount of sodium sulfite is calculated, and the amount of 1.0 to 1.2 times and the amount of 0.0 0 1 to 0.2 times the calculated value is calculated.

 Next, the control device 1 09 controls the first aqueous solution supply device 1 1 0 and the second aqueous solution supply device 1 1 1 according to the calculation result, and based on the calculation result, the first absorption tower The amount of the aqueous solution containing sodium hydroxide and sodium sulfite supplied to 101 and the second absorption tower 102 (or the amount of each of the aqueous sodium hydroxide solution and the aqueous sodium sulfite solution) is adjusted.

 For the control of the control device 1 0 9, an aqueous solution containing sodium hydroxide and sodium sulfite supplied from the first aqueous solution supply device 1 1 0 into the first absorption tower 1 0 1 (or an aqueous sodium hydroxide solution) Concentration and flow rate of sodium sulfite aqueous solution). Similarly, the control includes an aqueous solution (or sodium hydroxide aqueous solution) containing sodium hydroxide and sodium sulfite supplied from the second aqueous solution supply device 1 1 1 into the second absorption tower 10 2. And sodium sulfite aqueous solution, respectively).

 In this way, management by the control device 109 can reduce human management. Moreover, since the chlorine gas concentration in the exhaust gas is not constant, it is difficult to fine-tune the aqueous solution containing sodium hydroxide and sodium sulfite (or sodium hydroxide aqueous solution and sodium sulfite aqueous solution, respectively) to be supplied. By using 1 0 9 to control, fine adjustment is possible, chlorine absorption and removal can be more reliably performed, precipitation of carbonates and the like can be prevented, and generation of chlorate can be more reliably suppressed. Can do.

In FIG. 2, a path 2 0 4 connected to the first absorption tower 10 1 and a path 2 0 8 connected to the second absorption tower 1 0 2 are respectively connected to a first chlorine gas module (not shown). It is preferred that a tanabata and a second chlorine gas monitor are connected. The gas module can also be installed at the top of the first absorption tower 101 and the second absorption tower 102, respectively. As a result, the chlorine gas concentration in the gas supplied from the first absorption tower 1001 to the second absorption tower 1002 can be measured. 4 When there is an excessive supply of chlorine gas to the absorption tower 102, it is possible to easily deal with abnormal situations in the system. In addition, an aqueous solution containing sodium hydroxide and sodium sulfite supplied to the second absorption tower 102 by connecting the monitor and the control device 109 (or an aqueous solution of sodium hydroxide and an aqueous solution of sodium sulfite, respectively) ) Can be controlled.

 Similarly, by installing a second chlorine gas monitor, it is possible to measure the chlorine gas concentration in the gas released from the second absorption tower 10 2 to the outside. Excessive chlorine release to the outside can be prevented by stopping the system operation when there is an excessive supply of chlorine gas. Also, an aqueous solution containing sodium hydroxide and sodium sulfite to be supplied to the second absorption tower 102 by connecting the monitor and the control device 109 (or an aqueous solution of sodium hydroxide and an aqueous solution of sodium sulfite, respectively) ) Can be controlled to extinguish chlorine gas released to the outside.

 Next, in FIG. 1 and FIG. 2, the chlorine gas-containing exhaust gas supplied from the passage 220 will be described. The exhaust gas containing chlorine gas used in the chlorine gas detoxification method of the present invention is not particularly limited as long as it is a gas containing chlorine gas or a gas containing chlorine gas and carbon dioxide gas. The chlorine gas detoxification method of the invention is a chlorine production method in which, for example, a gas containing hydrogen chloride is oxidized using a gas containing oxygen, comprising the following (1) reaction step, (2) absorption step, ( It can also be suitably used for exhaust gas discharged by a chlorine production method comprising: 3) a drying step; and (4) a purification step.

 (1) Reaction process: In the presence of a catalyst containing ruthenium and Z or a ruthenium compound, a gas containing hydrogen chloride is oxidized with oxygen to obtain a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen. Process.

 (2) Absorption process: by contacting the gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction process with water and / or hydrochloric acid water and cooling or cooling A step of recovering a solution mainly composed of hydrogen chloride and water to obtain a gas mainly composed of chlorine and unreacted oxygen.

(3) Drying process: By removing the moisture in the gas obtained in the absorption process. Obtaining the necessary gas.

 (4) Purification step: The step of obtaining chlorine by separating the dried gas obtained in the drying step into a liquid or gas mainly containing chlorine and a gas mainly containing unreacted oxygen. At least a part of the gas mainly composed of unreacted oxygen in the purification process becomes the exhaust gas in the present invention.

 Each of the above steps will be specifically described with reference to FIG. FIG. 3 is a schematic diagram showing an example of a system used in a process for producing chlorine gas from oxygen gas and hydrogen chloride gas.

 In FIG. 3, the raw material hydrogen chloride gas is fed into the pretreatment tower 1 1 6 through path 2 2 2. As the raw material hydrogen chloride gas, a hydrogen chloride-containing gas generated by a process known in the art such as hydrogen chloride generated in a pyrolysis reaction of a chlorine compound can be used. In this case, carbon monoxide, phosgene, hydrogen sulfide, sulfur dioxide, carbon tetrachloride, black benzene, dichlorobenzene, and the like are included as impurities. In the pretreatment tower 1 1 6, the impurities are removed. is there . The raw hydrogen chloride gas preferably contains about 50% by volume or more of hydrogen chloride gas.

 The raw material hydrogen chloride gas from which impurities have been removed in the pretreatment tower 1 1 6 is introduced into the reaction tower 1 1 7 through the path 2 2 3 together with the oxygen gas introduced through the path 2 2 1. As the oxygen gas, oxygen or air can be used, but preferably the oxygen concentration is 80% by volume or more.

In the reaction tower 1 1 7, the reaction shown in the reaction step is performed. That is, in the presence of a catalyst containing ruthenium and / or a ruthenium compound, a gas containing hydrogen chloride treated in the pretreatment tower 1 16 is oxidized with a gas containing oxygen, and chlorine, water, unreacted hydrogen chloride and unreacted A gas mainly composed of reactive oxygen is obtained. When hydrogen chloride is oxidized with oxygen, it is reacted in a fixed bed reactor using a catalyst containing ruthenium and a ruthenium or ruthenium compound. As a result, it is possible to produce chlorine at a temperature that is balanced and advantageous, without causing troubles such as piping clogging due to volatilization or scattering of the catalyst component, without requiring a treatment process for the volatilized or scattered catalyst component. Recovering unreacted hydrogen chloride and water, separating chlorine and unreacted oxygen, and reacting unreacted oxygen Therefore, it is possible to simplify the process of supplying the product and to keep the equipment cost and operation cost low.

 As catalysts containing ruthenium and z or ruthenium compounds, known catalysts

(Japanese Patent Laid-Open No. 9-6 7 103, Japanese Patent Laid-Open No. 10-1 82 1 04, Japanese Patent Laid-Open No. 10-1 94705, Japanese Patent Laid-Open No. 10-338 502, Japanese Patent Laid-Open No. 11-11 80 70 1 gazette) can be used. Of these, catalysts containing ruthenium oxide are preferred. Further, the content of ruthenium oxide in the catalyst is preferably 0.1 to 20% by mass. If the amount of ruthenium oxide is too small, the catalytic activity may be low and the conversion rate of hydrogen chloride may be low. If the amount of ruthenium oxide is excessive, the catalyst price may increase. For example, Japanese Patent Application Laid-Open No. 10-338502 discloses a supported ruthenium oxide having a ruthenium oxide content of 0.1 to 20% by mass and a ruthenium oxide central diameter of 1.0 to 10.0 nanometers. Catalysts or ruthenium oxide composite oxide type catalysts are described.

 Gas mainly composed of chlorine, water, unreacted hydrogen chloride, and unreacted oxygen generated by the catalytic reaction performed in the above reaction tower 1 1 7 is input to the absorption tower 1 18 through the path 224. Is done. Here, the absorption process mentioned above is performed. That is, by bringing the gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction step into contact with water and Z or hydrochloric acid supplied from line 2 36, and / or By cooling, a solution containing hydrogen chloride and water as main components is recovered, and a gas containing chlorine and unreacted oxygen as main components is obtained. The obtained gas will be supplied to the drying tower 1 1 9 through the path 2225. Further, a solution containing hydrogen chloride and water as main components is introduced into the hydrochloric acid absorption tower 122 through a path 237.

 In the absorption step, the contact temperature is preferably 0 to 100 ° C. and the pressure is 0.05 to lMPa. The concentration of hydrochloric acid to be contacted is preferably 25% by mass or less. In order to prevent the precipitation of chlorine hydrate, it is preferable to employ the method described in JP-A No. 2003-261306.

Next, the drying step described above is performed in the drying tower 1 1 9. That is, moisture in the gas obtained in the absorption process is removed. The moisture in the gas after the drying step is 0.5 mgZ 1 or less, preferably 0.1 mg / 1 or less. A compound that removes moisture in the gas and Examples thereof include sulfuric acid, calcium chloride, magnesium perchlorate, and zeolite. Among them, sulfuric acid is preferable.

 The concentration of sulfuric acid is preferably 90% by mass or more. If the sulfuric acid concentration is less than 90% by mass, the moisture in the gas may not be removed sufficiently. The contact temperature is preferably 0 to 80 ° C and the pressure is preferably 0.05 to IMPa. In addition, the waste liquid of sulfuric acid used in the drying process will be disposed through Route 2 39. When sulfuric acid is used as the desiccant, it is preferable to remove the sulfuric acid mist immediately after the drying process. For example, purine query miner is disclosed in Japanese Patent Application Laid-Open No. 2 0 0 3-1 8 1 2 3 5 The method described in the gazette can be used.

 The gas from which moisture has been removed by the drying process is then supplied to the chlorine purification tower 1 2 1 through path 2 26. Here, before being supplied to the chlorine purification tower 1 2 1, it may be passed through a compressor if necessary. With this compressor, the gas after moisture removal is compressed to facilitate liquefaction of chlorine.

 Next, the above-described purification process is performed in the chlorine purification tower 1 2 1. That is, chlorine is obtained by separating the gas obtained in the drying step into a liquid or gas containing chlorine as a main component and a gas containing unreacted oxygen as a main component. As a method for separating the liquid or gas mainly containing chlorine and the gas mainly containing unreacted oxygen, a method of compressing and / or cooling, and / or a known method (Japanese Patent Laid-Open No. Hei 3). No. 2 6 2 5 1 4 and No. 1 1 1 5 0 0 9 5 4).

 For example, by compressing and / or cooling the gas obtained in the drying step, a liquid containing chlorine as a main component is separated from a gas containing unreacted oxygen as a main component. The liquefaction of chlorine is carried out to the extent that chlorine specified by pressure and temperature can exist in the liquid state. The lower the temperature is within this range, the lower the compression pressure, so the compression power can be reduced. However, industrially, due to problems with equipment, the compression pressure and cooling temperature must be within the optimal economic conditions within this range. It is decided in consideration. In normal operation, the compression pressure for liquefaction of chlorine is 0.5 to 5 MPa and the cooling temperature is -70 to 40 ° C.

The obtained liquid containing chlorine as a main component is collected through the route 2 28 and can be used as it is, or after partially or fully vaporized, and used as a raw material for vinyl chloride, phosgene and the like. When part or all of the product is vaporized, By exchanging heat with the gas obtained in the process, a part of the heat necessary for vaporization is obtained, and at the same time, the cooling load by the external refrigerant necessary for liquefaction of chlorine in the gas obtained in the drying process is reduced. It is possible. Similarly, it can be used for cooling the reflux liquid of the chlorine purification tower 1 2 1.

 In the above purification process, most of the gas mainly composed of unreacted oxygen is circulated to the reaction process through path 2 30 or treated as exhaust gas through path 2 29. It will be. Here, the gas mainly composed of unreacted oxygen may contain a chlorine gas. In the present invention, chlorine gas in such exhaust gas is one of the targets for detoxification.

 As described above, a part or all of the gas containing unreacted oxygen as a main component passes through the passage 230 and is supplied to the above-described circulation process. That is, a part or all of the gas containing unreacted oxygen as a main component is supplied as oxygen used in the reaction step. When sulfuric acid mist is contained in the gas supplied to the reaction step, it is preferable to remove the sulfuric acid mist. That is, in the washing tower 1 20 to which water is supplied through the path 2 40, the sulfuric acid mist is removed, the gas is washed, and the washed oxygen gas is passed through the path 2 3 2 to the reaction tower. 1 1 Supply to 7. Examples of other methods for removing sulfuric acid mist include a known method (Japanese Patent Laid-Open No. 2000-136086 25). In addition, the sulfuric acid mist dissolved in water is supplied from the washing tower 1 2 20 through the path 2 3 1 to the absorption tower 1 1 8 and can be used in the absorption step in the same manner as hydrochloric acid.

 In the above purification process, the exhaust gas mainly composed of unreacted oxygen discharged through the path 2 29 is further introduced into the first absorption tower 10 1 through the path 2 0 It will be used for the method of removing the chlorine gas.

In the absorption process, the solution mainly composed of hydrogen chloride and water discharged from the path 2 37 is heated with chlorine contained in the solution and bubbling of inert gas such as soot or nitrogen. Then, it is put into the hydrochloric acid absorption tower 1 2 2. The hydrochloric acid concentration is adjusted in the hydrochloric acid absorption tower 1 2 2. The treated chlorine is sent to an exhaust gas detoxification tower (not shown). Further, the solution after the treatment is further introduced into the activated carbon tower 1 2 3 through the path 2 3 4, and after removing organic impurities and the like in the solution, the solution is sent out through the path 2 3 5 and sent out. Hydrochloric acid is adjusted to ρ の in the electrolytic cell, boiler feed It can be used as a raw material for water neutralization, condensation rearrangement reaction of aniline and formalin, hydrochloric acid water electrolysis, food additives, and the like. Further, the solution discharged from the passage 237 can be used as a reaction raw material by recovering hydrogen chloride by the method described in JP-A-2 001-139305. Example

 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

 <Example 1>

Chlorine gas, oxygen gas, and carbon dioxide gas (volume ratio 2: 1: 1) from a gas introduction tube into a 500m1 bottom discharge glass flask equipped with a mechanical stirrer, thermometer, gas introduction tube and liquid introduction tube ) Are introduced so that the respective flow rates are 28 Om 1 Zm in, 140 ml / min, and 140 ml 1 Zm in, and at the same time, a 10% by mass sodium hydroxide aqueous solution and A 13 mass% sodium sulfite aqueous solution was introduced so that the flow rates would be 25. Ommol / min and 12.5 mmol / min, respectively. While discharging the solution in the flask (hereinafter referred to as “treatment solution”) from the bottom drainage part, maintaining the liquid level so that the amount of solution in the flask is constant, the volume (V) of the treatment solution in the flask is reduced. The average residence time (= V / v ₀ ) shown by dividing by the liquid flow rate (v ₀ ) to be supplied was about 30 minutes. The temperature inside the flask was maintained at about 30 ° C. In addition, the pH of the treatment solution was maintained in the range of 7-8. The concentration of sodium chlorate (chlorate) in the discharged treatment solution 3 hours after passing through was measured by ion chromatography and found to be 30 mass ppm or less. In addition, when measured by the iodometric titration method, sodium hypochlorite was not detected. The concentration of sodium chloride was 6.21% by mass.

 <Comparative Example 1>

Exfoliation treatment was carried out in the same manner as in Example 1 except that no sodium sulfite aqueous solution was introduced. The concentration of sodium chlorate (chlorate) in the obtained treatment solution was measured by ion chromatography and found to be 3.19% by mass. Ma The concentration of sodium hypochlorite was 6.49% by mass as measured by the iodometric titration method. The concentration of sodium chloride was 6.57% by mass. Next, we tried to reduce sodium chlorate and sodium hypochlorite by reacting the treatment solution with 1.3 times the theoretical amount of sodium sulfite solution required to reduce chlorine gas. . As a result, sodium hypochlorite was 0% by mass, but sodium chlorate (chlorate) was only reduced to 0.7% by mass. Example 2>

 The effect of the present invention was confirmed using an apparatus similar to the apparatus shown in FIG. To make the explanation easier to understand, refer to FIG. In the first absorption tower 10 1 (made of glass, packed 6 mm magnetic Raschig ring) with a diameter of 30 mm and a height of 300 mm, a mixed gas consisting of chlorine gas, carbon dioxide gas and air is supplied at a flow rate of 130 m 1 / min (5.8 mm o 1 / min), 260 ml l Zm in, 60 ml l Zm in, so as to continuously feed from the path 202 and simultaneously from the path 201 to 11 mass% sodium hydroxide aqueous solution and 13 A mass% aqueous sodium sulfite solution was continuously fed so that the respective flow rates were 12.76 mmol Zmin and 6.38 mmol 1 Zmin. These amounts are equivalent to 1.1 times the theoretical amount necessary to neutralize chlorine gas and 1.1 times the theoretical amount necessary to reduce chlorine gas, respectively. The cooling water was allowed to flow through the jacket at the bottom of the first absorption tower 101 so that the temperature of the treatment solution in the first absorption tower 101 was about 30 ° C.

 On the other hand, in the second absorption tower 102 (made of glass, packing 6 mm magnetic Raschig ring) with a diameter of 30 mm and a height of 300 mm connected to the first absorption tower 101, 3% by mass of hydroxide from the path 206 An aqueous sodium solution and an aqueous 5% by mass aqueous sodium sulfite solution were continuously fed so that the respective flow rates were 1. S Smmol Zmir 0. 64 mmo 1 / min. These amounts are equivalent to 0.1 times the theoretical amount necessary to neutralize chlorine gas and 0.1 times the theoretical amount necessary to reduce chlorine gas, respectively. Similarly, cooling water was passed through the jacket at the bottom of the second absorption tower 102 so that the temperature of the treatment solution in the second absorption tower 102 was about 30 ° C.

The mixed gas and the aqueous sodium hydroxide solution and sulfurous acid in the first absorption tower 101 2 The treatment solution produced by the reaction with the aqueous sodium acid solution was circulated back to the first absorption tower 100 1 using the pump P 1. Similarly, the treatment solution generated by the reaction with the aqueous sodium hydroxide solution and the sodium sulfite aqueous solution in the second absorption tower 102 is used as the first absorption tower 101 or the second absorption water using the pump P2. It was returned to Tower 1 0 2 and circulated. In this way, the reaction was carried out in the first absorption tower 101 and the second absorption tower 102, and the treatment solution was continuously circulated.

In addition, while supplying mixed gas, sodium hydroxide and sodium sulfite, a part of the processing solution in the apparatus is discharged from the path 210, so that the amount of solution in the apparatus becomes constant, The average residence time (= V / v ₀ ) shown by dividing the volume (V) of the treatment solution by the liquid flow rate (V) to be supplied was about 30 minutes. The concentration of sodium chlorate (chlorate) in the discharged treatment solution 3 hours after passing through the solution was measured by ion chromatography and found to be 30 mass] ppm or less. In addition, sodium hypochlorite was not detected when measured by the iodometric titration method. The pH of the treatment solution was 7.3.

 <Comparative Example 2>

 Detoxification treatment was performed in the same manner as in Example 2 except that the sodium sulfite aqueous solution was not supplied into the first absorption tower 101 and the second absorption tower 102. The concentration of sodium chlorate (chlorate) in the processing solution obtained was measured by ion chromatography and found to be 2.5% by mass. The concentration of sodium hypochlorite was 5.0% by mass as measured by an iodometric titration method. The pH of the treatment solution was 7.3.

 As described above, according to the chlorine gas detoxification method of the present invention, chlorine gas can be efficiently removed with almost no chlorate being generated. Thus, reducing chlorate to the pm order is usually not possible with the method of using hyposulfite and the like after forming hypochlorite.

It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. Industrial applicability

 According to the chlorine detoxification method of the present invention, chlorine gas can be efficiently detoxified while almost all chlorate is generated.

Claims

The scope of the claims A method for removing chlorine gas contained in exhaust gas,  To the chlorine gas, 1.0 to 1.2 times the theoretical amount necessary to neutralize the chlorine gas, and 1.0 to the theoretical amount necessary to reduce the chlorine gas 1. A chlorine gas detoxification method characterized by including a step of removing the chlorine gas by reacting with double sulfite and / or bisulfite. 2.  2. The method according to claim 1, further comprising a step (A) of supplying the exhaust gas to the first absorption tower and supplying the following aqueous solution (al) and the following aqueous solution (a 2). How to remove chlorine gas. Aqueous solution (a l): 1.0 to 1 of the theoretical amount necessary to neutralize the chlorine gas. Double aqueous solution of sodium hydroxide. Aqueous solution (a 2): 1.0 to 1.2 times the theoretical amount required to reduce the chlorine gas, and an aqueous solution of sulfite and Z or bisulfite. 3.  Step (B) of supplying the following aqueous solution (bl) and the following aqueous solution (b 2) to the second absorption tower connected to the first absorption tower while supplying the exhaust gas after the step (A) The method for removing chlorine gas according to claim 2, comprising: Aqueous solution (b l): An aqueous solution of sodium hydroxide in an amount of 0.001 to 0.2 times the theoretical amount necessary to neutralize the chlorine gas. Aqueous solution (b2): Aqueous solution of sulfite and hydrogen or bisulfite, 0.001 to 0.2 times the theoretical amount necessary to reduce the chlorine gas. Four 4. The chlorine gas detoxifying method according to claim 1, wherein the exhaust gas contains chlorine gas and carbon dioxide gas, and the chlorine gas is selectively removed. Five .  The action of the chlorine gas, sodium hydroxide and sulfite and / or sulfite hydrate is carried out in the range of 10 to 40 ° C. A method for removing chlorine gas according to any one of the above.