JP2005305414A - Detoxifying method for chlorine gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which simplifies the control of pH and enables the efficient removal of chlorine gas while preventing the precipitation of hydrogencarbonates and carbonates. <P>SOLUTION: The detoxifying method for chlorine gas that selectively absorbs/removes the chlorine gas from an exhaust gas containing the chlorine gas and carbon dioxide gas comprises a step for continuously supplying the exhaust gas to a first absorption column, a step for supplying an aqueous water of sodium hydroxide of 1.0 to 1.2 times the theoretical amount required to absorb the chlorine gas to the first absorption column, and a step for supplying the aqueous water of sodium hydroxide of 0.001 to 0.2 times the theoretical amount to a second absorption column connected to the first absorption column. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for removing chlorine gas, and more particularly to a method for removing chlorine gas contained in exhaust gas discharged in a process for obtaining chlorine gas from hydrogen chloride and oxygen.

  In the following Patent Document 1, chlorine gas is obtained by using a multi-stage countercurrent absorption facility with alkali metal hydroxide and / or alkaline earth metal hydroxide and operating at a liquid side pH of about 7.5. And a method for removing only chlorine from a mixed gas containing carbon dioxide.

  However, since the vicinity of pH 7.5 is near the dissociation constant of hypochlorous acid, when the pH is lower than 7.5, hypochlorous acid tends to be decomposed in the form of a free acid. When it is larger than 7.5, hydrogen carbonate is likely to be precipitated and there is a high possibility of causing a clogging problem.

  Patent Document 2 below discloses alkali metal sulfite and / or alkaline earth metal sulfite, and 0 to 2 moles of alkali metal hydroxide and / or alkaline earth hydroxide with respect to the sulfite. While supplying an aqueous solution or suspension containing water and adjusting the pH of the cleaning liquid to 1.9 to 6.3, the mixed liquid containing chlorine gas and carbon dioxide gas is washed with this cleaning liquid, and the chlorine in the mixed gas The method of removing only is described.

However, in the method disclosed in Patent Document 2, a large amount of expensive sulfite is used, or when the pH is lower than 1.9, sulfite gas is released, and the sulfite gas is toxic and difficult to treat. Therefore, it is necessary to control the pH to be 1.9 or more, which is a problem from an economic and environmental standpoint.
JP 50-125974 A Japanese Patent No. 2567023

  The present invention has been made in order to solve the above-described problems of the prior art, and its purpose is to prevent the precipitation of hydrogen carbonate and carbonate, and to manage pH easily and efficiently. It is to provide a method capable of removing gas.

  According to one aspect of the present invention, there is provided a chlorine detoxification method for selectively absorbing and removing chlorine gas from an exhaust gas containing chlorine gas and carbon dioxide gas, wherein the exhaust gas is continuously supplied to a first absorption tower. Connecting to the first absorption tower an aqueous solution of sodium hydroxide 1.0 to 1.2 times the theoretical amount required to absorb chlorine gas, And a step of supplying 0.002 to 0.2 times the theoretical amount of an aqueous solution of sodium hydroxide to the second absorption tower.

  Preferably, the theoretical amount is calculated by continuously measuring the chlorine gas concentration and flow rate in the exhaust gas.

  Preferably, the method further includes a step of supplying a gas containing carbon dioxide gas and unreacted chlorine gas from the first absorption tower to the second absorption tower.

  Preferably, the method further includes a step of supplying a part of the circulating liquid of the second absorption tower to the first absorption tower.

  Preferably, the sodium hypochlorite solution discharged from the first absorption tower and the second absorption tower is heated at a temperature within a range of 30 to 90 ° C. within a pH range of 7.0 to 8.0. And further pyrolyzing the sodium hypochlorite.

  Preferably, the method further includes a step of adding sodium sulfite to the liquid after the thermal decomposition.

  Preferably, the step of measuring the concentration of chlorine gas sent from the first absorption tower to the second absorption tower with a first chlorine gas monitor connected to the top of the first absorption tower; and the second absorption And a step of measuring the concentration of chlorine gas discharged from the second absorption tower to the outside by a second chlorine gas monitor connected to the top of the tower.

  Preferably, the exhaust gas is supplied through an exhaust gas supply path connected to the first absorption tower, and a chlorine gas concentration in the exhaust gas supply path is measured by a chlorine monitor connected to the exhaust gas supply path. .

  Preferably, a control device is connected to the chlorine monitor and a first alkaline aqueous solution supply device connected to the first absorption tower, and the calculation result of the chlorine gas concentration measured by the chlorine monitor and the exhaust gas flow rate are controlled. The amount of the aqueous solution of sodium hydroxide that is 1.0 to 1.2 times the theoretical amount required to absorb the chlorine gas concentration is calculated by the control device. The amount of sodium hydroxide aqueous solution supplied from the mono-alkaline aqueous solution supply device is controlled.

  Preferably, the control device is further connected to a second alkaline aqueous solution supply device connected to the second absorption tower, and based on the result of the chlorine gas concentration and the exhaust gas flow rate transmitted to the control device, the chlorine The amount of the aqueous solution of sodium hydroxide 0.001 to 0.2 times the theoretical amount necessary to absorb the gas concentration is calculated in the control device, and based on the calculation result, the second alkaline aqueous solution supply device The supply amount of the aqueous solution of sodium hydroxide is controlled.

  Preferably, the concentration of the aqueous sodium hydroxide solution supplied to the first absorption tower is in the range of 7 to 13% by mass, and the aqueous sodium hydroxide solution supplied to the second absorption tower. The concentration of is in the range of 1 to 5 mass%.

  Preferably, the exhaust gas is discharged in a chlorine production method including the following steps 1 to 4. 1. Reaction step: a step of oxidizing a gas containing hydrogen chloride with oxygen in the presence of a catalyst containing ruthenium and / or a ruthenium compound to obtain a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen; . Absorption step: A gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction step is brought into contact with water and / or hydrochloric acid and / or cooled to be chlorinated. 2. recovering a solution containing hydrogen and water as main components to obtain a gas containing chlorine and unreacted oxygen as main components; 3. drying step: a step of obtaining a dried gas by removing moisture in the gas obtained in the absorption step; Purification step: A step of obtaining chlorine by separating the dried gas obtained in the drying step into a liquid or gas mainly composed of chlorine and an exhaust gas containing carbon dioxide gas and chlorine gas mainly composed of unreacted oxygen. .

  Preferably, when the content of carbon dioxide gas in the exhaust gas is less than 1%, it is treated in an alkali abatement tower that maintains a pH of 10 or more before being supplied to the first absorption tower.

  According to the chlorine detoxification method of the present invention, there is no precipitation of bicarbonate or carbonate, and chlorine gas can be efficiently detoxified.

  The present invention is a chlorine detoxification method for selectively absorbing and removing chlorine gas from exhaust gas containing chlorine gas and carbon dioxide gas, the step of continuously supplying the exhaust gas to a first absorption tower, Supplying the first absorption tower with an aqueous solution of sodium hydroxide 1.0 to 1.2 times the theoretical amount necessary to absorb water; and a second absorption tower connected to the first absorption tower. And a step of supplying an aqueous solution of 0.001 to 0.2 times the theoretical amount of sodium hydroxide.

Accordingly, it is possible to efficiently absorb and decompose chlorine gas without reducing or generating precipitation of bicarbonate such as Na ₂ CO ₃ or carbonate. This can be understood as follows. In the present invention, the exhaust gas contains chlorine gas and carbon dioxide gas. For example, when sodium hydroxide (NaOH) is used as an alkali metal hydroxide, such exhaust gas is reacted with an aqueous sodium hydroxide solution. Then, chlorine (Cl ₂ ) reacts with sodium hydroxide to produce sodium hypochlorite (NaClO) and sodium chloride (NaCl).

_{Cl 2 + 2NaOH → NaClO + NaCl} + H 2 O
At the same time, at pH 7.0 and above, carbon dioxide (CO ₂ ) reacts with sodium hydroxide (NaOH), but at pH 7.0 to 10.33, sodium carbonate (Na ₂ CO ₃ ) is not produced and hydrogen carbonate. Only sodium (NaHCO ₃ ) is produced.

CO ₂ + NaOH → NaHCO ₃
Furthermore, at a pH of 7 to 7.5, the amount of sodium hydrogen carbonate (NaHCO ₃ ) produced is small, and this slightly produced sodium hydrogen carbonate (NaHCO ₃ ) reacts with chlorine (Cl ₂ ) to produce dioxide. Since sodium hypochlorite (NaClO) is produced while producing carbon (CO ₂ ), sodium hydrogen carbonate (NaHCO ₃ ) and sodium carbonate (NaCO ₃ ) are substantially not produced.

2NaHCO ₃ + Cl ₂ → NaClO + NaCl + 2CO ₂ + H ₂ O
Therefore, in the present invention, the first absorption tower and the second absorption tower to which exhaust gas containing chlorine gas and carbon dioxide gas is supplied in order to promote absorption of chlorine gas while suppressing the generation of hydrogen carbonate and carbonate. The first absorption tower is supplied with an alkaline aqueous solution 1.0 to 1.2 times the theoretical amount necessary to absorb chlorine gas, and the second absorption tower It is characterized by supplying an alkaline aqueous solution having a theoretical amount of 0.001 to 0.2 times.

  In the present invention, the theoretical amount refers to the molar concentration of sodium hydroxide that can absorb chlorine gas having the molar concentration relative to the molar concentration of chlorine gas contained in the exhaust gas.

  Here, when the sodium hydroxide supplied to the first absorption tower is less than 1.0 times the theoretical amount, chlorine may not be sufficiently absorbed. If it exceeds 1.2 times, carbonate or hydrogen carbonate This is a problem because it tends to form salt. Preferably, they are 1.0 times or more and 1.1 times or less.

  Further, when sodium hydroxide supplied to the second absorption tower is less than 0.001 times the theoretical amount, chlorine may not be sufficiently absorbed, and when it exceeds 0.2 times, carbonate or bicarbonate This is a problem because it is easy to generate. Preferably, it is 0.001 times or more and 0.1 times or less.

  Moreover, in this invention, when supplying with the quantity with respect to the above theoretical amounts, it is preferable that the density | concentration of the aqueous solution of sodium hydroxide supplied to a 1st absorption tower exists in the range of 7-13 mass%. . If it is less than 7% by mass, the amount of the aqueous solution increases, which is disadvantageous in terms of volumetric efficiency. If it exceeds 13% by mass, carbonates and hydrogen carbonates are likely to precipitate, which is a problem. Preferably, it is 9 mass% or more and 11 mass% or less.

  Moreover, it is preferable that the density | concentration of the aqueous solution of sodium hydroxide supplied to said 2nd absorption tower exists in the range of 1-5 mass%. If the amount is less than 1% by mass, the amount of liquid is increased, which is disadvantageous in terms of volumetric efficiency. Preferably, they are 1 mass% or more and 3 mass% or less.

  In the present invention, the flow rate of the sodium hydroxide solution supplied to the first absorption tower can be determined from the chlorine concentration and gas flow rate in the exhaust gas.

  In the present invention, a known alkali metal hydroxide can be used, and is not particularly limited. For example, sodium hydroxide can be used. In particular, sodium hydroxide is preferred in the present invention.

  Moreover, a well-known thing can be used for alkaline-earth metal hydroxide, It does not specifically limit.

  The alkali metal hydroxide and alkaline earth hydroxide may be used alone or in combination. That is, 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. .

  However, in the present invention, the theoretical amount of alkali metal hydroxide and alkaline earth metal hydroxide should be set with respect to the total amount of hydroxide used.

  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 that can be used in the present invention.

  In FIG. 1, the chlorine gas abatement system includes a first absorption tower 101 and a second absorption tower 102 connected to the first absorption tower 101, and receives a product discharged from the first absorption tower. A first receiver 103 is connected to the first absorption tower.

  The first absorption tower 101 and the second absorption tower 102 are filled with packings 104 and 105, respectively, whereby the gas-liquid contact efficiency can be increased and chlorine can be quickly removed.

  As the fillers 104 and 105, for example, known materials such as Raschig rings and pole rings can be used, and examples of the material include fluorine resin, vinyl chloride resin, ceramics, and inorganic glass. .

  Exhaust gas discharged by a predetermined chlorine generation process described later is input to the first absorption tower 101 through the path 202. The exhaust gas contains oxygen gas as a main component and contains chlorine gas and carbon dioxide gas. In addition, sodium hydroxide adjusted to 1.0 to 1.2 times the theoretical amount of chlorine gas contained in the exhaust gas is introduced into the first absorption tower 101 through the passage 201. In addition, when the carbon dioxide content in the exhaust gas is less than 1%, it is preferably treated in an alkali abatement tower that maintains a pH of 10 or more (not shown) before being supplied to the first absorption tower 101.

  Thus, in the first absorption tower 101, as described above, the reaction between chlorine gas and carbon dioxide gas and sodium hydroxide occurs. Hypochlorite and bicarbonate produced by the reaction are discharged to the first receiver 103 through the passage 203. Hypochlorite and bicarbonate in the first receiver 103 are sucked by the pump P1 and controlled by the exchanger 106 and sent again through the path 203 into the first absorption tower, or It is used for the next process through the path 210.

  Moreover, the pH in the 1st receiver 103 is maintained in the range of about 7-7.5. Thereby, sodium carbonate does not precipitate and does not adversely affect the cycle of the chlorine gas abatement process. The temperature in the first receiver is preferably maintained at about 30 ° C. or higher. This is because hypochlorous acid promotes thermal decomposition.

  In the first absorption tower 101, unreacted and / or regenerated carbon dioxide gas and unreacted oxygen gas are input to the second absorption tower 102 through the path 204. At this time, a small amount of chlorine gas may be contained in the gas supplied to the second absorption tower through the passage 204.

  In the present invention, the reason why the unreacted gas group is introduced into the second absorption tower in the first absorption tower in this way is that a small amount of chlorine gas may be contained in the unreacted gas group. Therefore, in order to completely absorb and remove the chlorine gas, a second absorption tower is provided, and the unreacted chlorine gas is completely absorbed and removed in the second absorption tower.

  In this way, 0.001 to 0.2 times as much alkaline aqueous solution as the theoretical amount of chlorine gas is supplied to the second absorption tower 102 through the path 206 with respect to the unreacted gas introduced into the second absorption tower. To do. Thereby, the chlorine gas that has not been absorbed and removed in the first absorption tower 101 can be completely absorbed and removed.

  That is, the present invention, as described above, in the first absorption tower and the second absorption tower, the hydroxylation of 1.0 to 1.2 times and 0.001 to 0.2 times the theoretical amount of chlorine gas, respectively. By supplying sodium in two stages, chlorine gas can be completely absorbed and removed without producing precipitation of sodium carbonate or the like.

  In the apparatus of FIG. 1, unreacted oxygen gas and unreacted and / or regenerated carbon dioxide gas are released from a path 208 provided at the top of the second absorption tower 102. In addition, unreacted sodium hydroxide, sodium bicarbonate and a small amount of hypochlorite are discharged from the bottom of the second absorption tower 102 through the passage 209, and these sodium hydroxide, sodium bicarbonate and Chlorite is sucked by the pump P2 and sent to either the path 205 or the path 207 by the exchanger 107.

  When it is sent through the path 207, it is again put into the first absorption tower 101 through the path 203. Hypochlorite supplied to the first absorption tower 101 through the path 203 is discharged from the bottom of the first absorption tower 101 to the first receiver 103 through the path 203.

  In addition, in the sodium hydroxide, sodium hydrogen carbonate and hypochlorite supplied to the second absorption tower 102 through the path 205, the sodium hydroxide and sodium hydrogen carbonate are again chlorine gas in the second absorption tower 102. The hypochlorite is discharged from the bottom as it is, and the above cycle is repeated.

  In the present invention, an apparatus used for the process after being sent through the path 210 in FIG. 1 is shown in FIG. In FIG. 2, the path 210 is connected to the pyrolysis tank 112, and hypochlorite and bicarbonate sent from the path 210 are input to the pyrolysis tank 112.

  The pyrolysis tank 112 is also charged with hypochlorite discharged from an exhaust gas detoxification tower (not shown) in a chlorine generation process described later. The third receiver 113 holds the aqueous hypochlorite solution, and is sucked from the third receiver 113 by the pump P5 and is introduced into the pyrolysis layer 112 through the passage 212. . Here, the hypochlorite aqueous solution held in the third receptor 113 usually has a pH in the range of about 13 to 14 and a concentration of about 10%.

In the pyrolysis tank 112, the hypochlorite aqueous solution charged through the passage 210 and the passage 212 is maintained within a pH range of 7.0 to 8.0 and heated to 30 ° C. or higher. By heating to the temperature, hypochlorite is thermally decomposed to produce chloride and oxygen (O ₂ ). The produced oxygen is led out of the system by a purge valve (not shown).

  Here, if the temperature is lower than 30 ° C., it takes a long time to thermally decompose hypochlorite, which is not practical, and a large amount of undecomposed hypochlorite remains. This is not preferable because the amount of the sulfur-based reducing agent tends to increase. A higher heating temperature is preferable because hypochlorite can be thermally decomposed in a shorter time, but from the viewpoint of durability of the material used for the thermal decomposition tank 112, it is usually about 60 ° C. or lower. Moreover, it is preferable to adjust the pH in the thermal decomposition layer 112 in the range of 7-8 in order to accelerate | stimulate decomposition | disassembly of sodium hypochlorite. In order to adjust the pH, an inorganic acid such as hydrochloric acid may be supplied through the path 213b.

  The pyrolysis tank 112 may be made of an inexpensive resin material such as glass fiber reinforced plastic, and the surface in contact with the hypochlorite aqueous solution. It is preferable to be comprised with the fluororesin material, and the inner surface may be comprised with the titanium-type material and the fluororesin material over the whole surface. Thereby, the pyrolysis tank 112 can heat the hypochlorite aqueous solution to 60 ° C. or higher without being eroded by hypochlorite or the like. Examples of the titanium-based material include titanium alloy in addition to titanium metal.

  In the pyrolysis tank 112, it may be thermally decomposed by heating until the effective chlorine concentration in the pyrolyzed liquid after pyrolysis becomes 0. However, since it requires a lot of time and energy, it is usually undecomposed. Hypochlorite until the hypochlorite remains in the pyrolysis solution, specifically, 1/5 or less, preferably 1/10 or less of the effective chlorine concentration of the hypochlorite aqueous solution before heating. What is necessary is just to thermally decompose the salt.

  The heating time in the pyrolysis tank 112 is usually preferably 1 hour or more and 50 hours or less, more preferably 1 hour or more and 20 hours or less. Further, the hypochlorite aqueous solution is usually heated and pyrolyzed in a batch system, but may be heated and pyrolyzed in a continuous system. Note that undecomposed hypochlorite remaining in the thermal decomposition solution is reductively decomposed in the reductive decomposition tank 114 using a sulfur-based reducing agent.

  By heating the hypochlorite aqueous solution as described above, a thermal decomposition liquid in which hypochlorite is thermally decomposed is obtained. The thermal decomposition liquid is sucked by the pump P3, passes through the path 211, passes through a cooler (not shown), and is guided to the reductive decomposition tank 114 via the path 215. Here, when the pyrolyzed liquid after thermal decomposition is not sufficiently cooled, undecomposed hypochlorite remains, so that the pump P3, the path 211, the path 215, etc. It is preferable from the viewpoint of durability that the surface in contact with the substrate is made of a titanium-based material, a fluororesin, or the like.

  A sulfur-based reducing agent is introduced into the reductive decomposition tank 114 through the passage 214, and the cooled thermal decomposition liquid and the sulfur-based reducing agent are mixed. By mixing the pyrolysis solution with the sulfur-based reducing agent, undecomposed hypochlorite contained in the pyrolysis solution is reduced and decomposed. The pyrolysis liquid is usually reduced and decomposed in a batch system, but may be reduced and decomposed in a continuous system. As the sulfur-based reducing agent, sodium sulfite can be used.

  In this way, hypochlorite contained in the hypochlorite aqueous solution is decomposed. However, since the hypochlorite aqueous solution is usually alkaline, the pyrolysis solution is also usually alkaline. Therefore, it is preferable to neutralize. In order to neutralize, for example, the thermal decomposition solution can be neutralized by adding an acid sent through the passage 213 to the thermal decomposition solution via the passage 215 in the reductive decomposition tank 114.

  As the acid, for example, an inorganic acid such as hydrochloric acid, sulfuric acid, and nitric acid is preferably used, and hydrochloric acid is preferable from the viewpoint that hydrochloric acid can be obtained by a chlorine generation process described later and hydrochloric acid can be reused. The amount of the acid used is preferably adjusted as appropriate according to the pH of the thermal decomposition solution.

  In this way, the hypochlorite discharged from the first absorption tower 101 is decomposed. That is, in the pyrolysis layer 112, the hypochlorite aqueous solution is heated to 30 ° C. or more to pyrolyze hypochlorite contained in the aqueous solution, and the pyrolysis solution after pyrolysis is performed as necessary. After cooling, the mixture is mixed with a sulfur-based reducing agent, and the undecomposed hypochlorite contained in the thermal decomposition solution is reduced and decomposed in the reduction decomposition layer 114, whereby the hypochlorite contained in the hypochlorite aqueous solution. The chlorate can be decomposed, and the reductive decomposition solution after reductive decomposition does not contain hypochlorite.

  Next, the reductive decomposition liquid is sucked by the pump P4 and is introduced into the second receiver 115 through the path 217 and the path 216. In addition, the acid generated in the chlorine generation process, which will be described later, is input to the second receiver 115 via the path 218, whereby the reductive decomposition solution can be neutralized.

  Next, the liquid after the reaction in the second receiver 115 is sucked by the pump P6 and drained through the path 219.

  Next, the control method of the sodium hydroxide aqueous solution supplied into the first absorption tower and the second absorption tower will be described with reference to FIG. In addition, the structure of the number which is not demonstrated in FIG. 3 is the same as the thing of FIG.

  In FIG. 3, a chlorine gas monitor and a flow meter 108 are connected to the path 202 to continuously measure the concentration and flow rate of chlorine gas in the exhaust gas passing through the path 202. A control device 109 is connected to the chlorine gas monitor / flow meter 108 and receives signals from the chlorine gas monitor / flow meter 108. Here, continuously measuring means that the measurement is performed intermittently or at intervals of 10 minutes or less.

  Further, a first alkaline aqueous solution supply device 110 and a second alkaline aqueous solution supply device 111 are connected to the control device 109, and the first alkaline aqueous solution supply device 110 holds sodium hydroxide via a path 201. The second alkaline aqueous solution supply device 111 holds sodium hydroxide and supplies it into the second absorption tower 102 via the path 206.

  Next, control using these devices will be described. First, a signal related to the concentration of chlorine gas in the exhaust gas passing through the path 202 measured by the chlorine gas monitor and the flow meter 108 is transmitted to the control device 109. The control device 109 that has received the signal calculates the theoretical amount of alkali metal salt and / or alkaline earth metal salt necessary to absorb chlorine gas by a program incorporated in the device, and calculates the calculation. An amount of 1.0 to 1.2 times and an amount of 0.001 to 0.2 times the value are calculated.

  Next, the control device 109 controls the first alkaline aqueous solution supply device 110 and the second alkaline aqueous solution supply device 111 according to the calculation result, and based on the calculation result, the first absorption tower 101 and the second absorption tower 102. The amount of the alkaline aqueous solution supplied to is adjusted.

  The control of the control device 109 includes the concentration and flow rate of the alkaline aqueous solution supplied from the first alkaline aqueous solution supply device 110 into the first absorption tower 101. Similarly, the control includes the concentration and flow rate of the alkaline aqueous solution supplied from the second alkaline aqueous solution supply apparatus 111 into the second absorption tower 102.

  In this way, control by the person can be reduced by controlling the supply of the sodium hydroxide solution. In addition, since the chlorine gas concentration in the exhaust gas is not constant, it is difficult to finely adjust the alkaline aqueous solution to be supplied. However, fine adjustment is possible by controlling using the control device, and chlorine absorption and removal can be performed more reliably. This makes it possible to prevent precipitation of carbonates and the like.

  In FIG. 3, a first chlorine gas monitor and a second chlorine gas monitor (not shown) are connected to the path 204 connected to the first absorption tower 101 and the path 208 connected to the second absorption tower 102, respectively. Is preferred. The gas monitor can also be installed at the top of the first absorption tower 101 and the second absorption tower 102, respectively.

  Thereby, the chlorine gas concentration of the gas supplied from the first absorption tower 101 to the second absorption tower 102 can be measured, and the supply of excess chlorine gas to the second absorption tower 102 can be performed by the measurement. In some cases, it is possible to easily deal with abnormal situations in the system. In addition, the supply amount of the alkaline aqueous solution supplied to the second absorption tower 102 can be controlled by connecting the monitor and the control device 109.

  Similarly, by installing the second chlorine gas monitor, it is possible to measure the chlorine gas concentration of the gas released from the first absorption tower 102 to the outside. Excessive supply of chlorine to the outside can be prevented by stopping the operation of the system when there is supply. In addition, the monitor and the control device 109 can be connected to control the supply amount of the alkaline aqueous solution supplied to the second absorption tower 102, and the chlorine gas released to the outside can be extinguished.

  Next, the generation process of the chlorine gas-containing exhaust gas supplied from the path 202 will be described with reference to FIGS. That is, it is a chlorine production method in which a gas containing hydrogen chloride is oxidized using a gas containing oxygen, and is discharged by a chlorine production method having the following steps.

  Reaction step: A step of oxidizing a gas containing hydrogen chloride with oxygen in the presence of a catalyst containing ruthenium and / or a ruthenium compound to obtain a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen. Absorption process: A gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction process is brought into contact with water and / or hydrochloric acid and / or cooled to be chlorinated. A step of collecting a solution containing hydrogen and water as main components to obtain a gas containing chlorine and unreacted oxygen as main components. Drying step: A step of obtaining a dried gas by removing moisture in the gas obtained in the absorption step. Purification step: A step of obtaining chlorine by separating the dried 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. In this process, the present invention treats a part of the gas containing unreacted oxygen as a main component.

  Each of the above steps will be specifically described with reference to FIG. FIG. 4 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. 4, the raw material hydrogen chloride gas is introduced into the pretreatment tower 116 through a path 222. 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. At this time, carbon monoxide, phosgene, hydrogen sulfide, sulfur dioxide, carbon tetrachloride, chlorobenzene, dichlorobenzene, and the like are included as impurities. The pretreatment tower 116 removes the impurities. In addition, it is preferable that about 50 volume% or more of hydrogen chloride gas is contained in the raw material hydrogen chloride gas.

  The raw material hydrogen chloride gas from which impurities have been removed in the pretreatment tower 116 is supplied to the reaction tower 117 through the path 223 together with the oxygen gas input through the path 221. As the oxygen gas, oxygen or air can be used, but an oxygen concentration of 80% by volume or more is preferable.

  In the reaction tower 117, 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 116 is oxidized with a gas containing oxygen, and chlorine, water, unreacted hydrogen chloride and unreacted oxygen are oxidized. Is obtained as a main component.

  In oxidizing hydrogen chloride with oxygen, a catalyst containing ruthenium and / or a ruthenium compound is used and reacted in a fixed bed reactor. Because of this, it is possible to produce chlorine at a temperature that is advantageous in an equilibrium manner, without causing troubles such as clogging of piping due to volatilization or scattering of the catalyst component, and without requiring a treatment process of the volatilized or scattered catalyst component. The step of recovering unreacted hydrogen chloride and water, the step of separating chlorine and unreacted oxygen, and the step of supplying unreacted oxygen to the reaction can be simplified, so that the equipment cost and operating cost can be kept low.

  As catalysts containing ruthenium and / or ruthenium compounds, known catalysts (Japanese Patent Laid-Open Nos. 9-67103, 10-182104, 10-194705, 10-338502, 10-338502, 11-180701). Of these, a catalyst containing ruthenium oxide is preferable. Furthermore, 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. On the other hand, if the amount of ruthenium oxide is excessive, the catalyst price may be high. For example, JP-A-10-338502 discloses a supported ruthenium oxide catalyst 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. A ruthenium oxide composite oxide type catalyst is described.

  A gas mainly composed of chlorine, water, unreacted hydrogen chloride, and unreacted oxygen generated by the catalytic reaction performed in the reaction tower 117 is input to the absorption tower 118 through the path 224. Here, the absorption process described above is performed.

  That is, the gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction step is brought into contact with water and / or hydrochloric acid supplied from the path 236 and / or cooled. As a result, 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 is supplied to the drying tower 119 through the path 225. 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 1 MPa. The concentration of hydrochloric acid to be contacted is preferably 25% by mass or less. In order to prevent precipitation of chlorine hydrate, it is preferable to employ the method described in JP-A-2003-261306.

  Next, the drying process described above is performed in the drying tower 119. 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 mg / l or less, preferably 0.1 mg / l or less. Examples of the compound that removes moisture in the gas 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 lower than 90% by mass, moisture in the gas may not be sufficiently removed. The contact temperature is preferably 0 to 80 ° C. and the pressure is 0.05 to 1 MPa. In addition, the waste liquid of sulfuric acid used in the drying process is discarded through the path 239. When sulfuric acid is used as the desiccant, it is preferable to remove the sulfuric acid mist immediately after the drying step. For example, a blink eliminator or a method described in Japanese Patent Application Laid-Open No. 2003-181235 can be used.

  The gas from which moisture has been removed by the drying process is then supplied to the chlorine purification tower 121 through the path 226. Here, before being supplied to the chlorine refining tower 121, a compressor may be provided as necessary. With the 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 121. That is, chlorine is obtained by separating the gas obtained in the drying step into a liquid or gas mainly containing chlorine and a gas mainly containing unreacted oxygen. As a method of 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. 3-262514, No. 11-500954).

  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 a liquid state. The lower the temperature, the lower the compression pressure, so the compression power can be reduced. However, from the industrial viewpoint, the compression pressure and cooling temperature take into account the optimal economic conditions within this range. Can be decided. 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 passage 228, and can be used as a raw material for vinyl chloride, phosgene or the like as it is or after partially or completely vaporizing. When using after vaporizing part or all of it, by exchanging heat with the gas obtained in the drying process, part of the heat necessary for vaporization is obtained and at the same time chlorine in the gas obtained in the drying process. It is possible to reduce the cooling load due to the external refrigerant necessary for liquefaction. Similarly, it can be used for cooling the reflux liquid of the chlorine distillation column 117.

  In the purification step, most of the gas mainly composed of unreacted oxygen is circulated to the reaction step through the passage 230 or processed as exhaust gas through the passage 229. Here, the gas mainly composed of unreacted oxygen may contain chlorine gas. In the present invention, the chlorine gas in the exhaust gas is one of the targets for detoxification.

  As described above, part or all of the gas mainly composed of unreacted oxygen is supplied to the above-described circulation process through the passage 230. That is, part or all of the gas containing unreacted oxygen as a main component is supplied as oxygen used in the reaction process. 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 120 to which water is supplied through the passage 240, the sulfuric acid mist is removed, the gas is washed, and the washed oxygen gas is supplied to the reaction tower 117 through the passage 232. . Examples of other methods for removing sulfuric acid mist include a known method (Japanese Patent Laid-Open No. 2002-136825). Further, the sulfuric acid mist dissolved in water is supplied from the washing tower 120 through the path 231 to the absorption tower 118, and can be used in the absorption step in the same manner as hydrochloric acid.

  In the purification step, the exhaust gas mainly composed of unreacted oxygen discharged through the passage 229 is further introduced into the first absorption tower 101 through the passage 202, and the chlorine gas detoxification method of the present invention. Will be served.

  In the absorption process, after the solution containing hydrogen chloride and water discharged from the path 237 as main components, the chlorine contained in the solution is removed by heating and / or bubbling of an inert gas such as nitrogen. The hydrochloric acid absorption tower 122 is charged. In the hydrochloric acid absorption tower 122, the hydrochloric acid concentration is adjusted. The chlorine subjected to the treatment is sent to an exhaust gas abatement tower (not shown). Further, the solution after the treatment is further introduced into the activated carbon tower 123 through a path 234, and after organic impurities and the like in the solution are removed, the solution is sent out through the path 235. PH adjustment, neutralization of boiler feed water, condensation rearrangement reaction of aniline and formalin, raw materials for 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-2001-139305.

  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.

It is a schematic diagram which shows an example of the system used for the chlorine elimination method of this invention. It is a schematic diagram which shows an example of the system used for the chlorine elimination method of this invention. It is a schematic diagram which shows another example of the system used for the chlorine elimination method of this invention. It is a schematic diagram which shows the discharge process of the waste gas supplied to the chlorine elimination method of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 1st absorption tower, 102 2nd absorption tower, 103 1st receiver, 104,105,106,107 exchanger, 108 Chlorine gas monitor and flow meter, 109 control apparatus, 110 1st alkaline aqueous solution supply apparatus, 111 2nd Alkaline aqueous solution supply device, 112 thermal decomposition tank, 113 third acceptor, 114 reductive decomposition tank, 115 second acceptor, 116 pretreatment tower, 117 reaction tower, 118 absorption tower, 119 drying tower, 120 washing tower, 121 chlorine Purification tower, 122 Hydrochloric acid absorption tower, 123 Activated carbon tower, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 213b, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 2 29,230,231,232,233,234,235,236,237,238,239,240 passages, P1, P2, P3, P4 pumps.

Claims (13)

  A chlorine detoxification method that selectively absorbs and removes chlorine gas from exhaust gas containing chlorine gas and carbon dioxide gas, the step of continuously supplying the exhaust gas to a first absorption tower, and absorbing chlorine gas Supplying an aqueous solution of sodium hydroxide 1.0 to 1.2 times the theoretical amount necessary for the first absorption tower; and the second absorption tower connected to the first absorption tower; A step of supplying an aqueous solution of sodium hydroxide 0.001 to 0.2 times the amount of chlorine gas.   The method of claim 1, wherein the theoretical amount is calculated by continuously measuring a chlorine gas concentration and a flow rate in the exhaust gas.   The chlorine gas removal method according to claim 1, further comprising a step of supplying a gas containing carbon dioxide gas and unreacted chlorine gas from the first absorption tower to the second absorption tower.   The chlorine gas detoxification method according to any one of claims 1 to 3, further comprising a step of supplying a part of the circulating liquid of the second absorption tower to the first absorption tower.   By heating the sodium hypochlorite solution discharged from the first absorption tower and the second absorption tower at a temperature within a range of 30 to 90 ° C. within a pH range of 7.0 to 8.0, The method for detoxifying chlorine gas according to any one of claims 1 to 4, further comprising a step of thermally decomposing sodium chlorite.   The chlorine gas detoxification method according to claim 5, further comprising a step of adding sodium sulfite to the pyrolyzed liquid.   Measuring the concentration of chlorine gas sent from the first absorption tower to the second absorption tower by a first chlorine gas monitor connected to the top of the first absorption tower; and the tower of the second absorption tower And a step of measuring the concentration of chlorine gas discharged from the second absorption tower to the outside by a second chlorine gas monitor connected to the top. Harmful way.   The exhaust gas is supplied through an exhaust gas supply path connected to the first absorption tower, and a chlorine gas concentration in the exhaust gas supply path is measured by a chlorine monitor connected to the exhaust gas supply path. The method for removing chlorine gas according to any one of claims 1 to 7.   The control device is connected to the chlorine monitor and the first alkaline aqueous solution supply device connected to the first absorption tower, and the calculation result of the chlorine gas concentration measured by the chlorine monitor and the exhaust gas flow rate are transmitted to the control device. The control device calculates an amount of aqueous sodium hydroxide solution that is 1.0 to 1.2 times the theoretical amount required to absorb the chlorine gas concentration, and the first alkaline aqueous solution is calculated based on the calculation result. The chlorine gas detoxification method according to any one of claims 1 to 8, wherein an aqueous solution supply amount of sodium hydroxide from the supply device is controlled.   The control device is further connected to a second alkaline aqueous solution supply device connected to the second absorption tower and absorbs the chlorine gas concentration based on the result of the chlorine gas concentration and the exhaust gas flow rate transmitted to the control device. The amount of the aqueous solution of sodium hydroxide 0.001 to 0.2 times the theoretical amount necessary for the calculation is calculated in the control device, and based on the calculation result, the aqueous solution of sodium hydroxide from the second alkaline aqueous solution supply device The method for removing chlorine gas according to claim 9, wherein the supply amount is controlled.   The concentration of the aqueous sodium hydroxide solution supplied to the first absorption tower is in the range of 7 to 13% by mass, and the concentration of the aqueous sodium hydroxide solution supplied to the second absorption tower is The chlorine gas detoxifying method according to claim 1, wherein the chlorine gas detoxifying method is in the range of 1 to 5 mass%. The said exhaust gas is discharged | emitted in the manufacturing method of chlorine including the following steps 1-4, The chlorine gas elimination method in any one of Claims 1-11 characterized by the above-mentioned.
1. Reaction step: oxidizing a gas containing hydrogen chloride with oxygen in the presence of a catalyst containing ruthenium and / or a ruthenium compound to obtain a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen;
2. Absorption step: A gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction step is brought into contact with water and / or hydrochloric acid and / or cooled to be chlorinated. Recovering a solution mainly composed of hydrogen and water to obtain a gas mainly composed of chlorine and unreacted oxygen;
3. Drying step: a step of obtaining a dried gas by removing moisture in the gas obtained in the absorption step;
4). Purification step: A step of obtaining chlorine by separating the dried gas obtained in the drying step into a liquid or gas mainly composed of chlorine and an exhaust gas containing carbon dioxide gas and chlorine gas mainly composed of unreacted oxygen. .   When the carbon dioxide content in the exhaust gas is less than 1%, it is treated in an alkali detoxification tower that maintains a pH of 10 or more before being supplied to the first absorption tower. The chlorine gas elimination method according to any one of -12.

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