JP2003024735A - Method for removing noxious gas component in air - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for continuously and efficiently removing a noxious gas component such as sulfur oxide, hydrogen sulfide, nitrogen oxide, or the like from the atmosphere and to especially adapt this method as an air cleaner for a clean room for manufacturing a semiconductor to well keep an air environment exerting effect on the capacity or yield of a semiconductor. SOLUTION: In the method for removing the noxious gas component in air, an inorganic salt solution is passed through an ion moving device, in which one or more ion exchange membranes are arranged between an anode and a cathode, while applying a current thereto to prepare a gas treatment liquid. Air to be treated is brought into contact with the gas treatment liquid to absorb a noxious gas component in air by the gas treatment liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing harmful gas components such as sulfur oxides, hydrogen sulfide and nitrogen oxides contained in a gas, and an apparatus therefor.

[0002]

2. Description of the Related Art In recent years, semiconductors have become more and more integrated,
Cleanliness of semiconductor manufacturing raw materials, manufacturing equipment and manufacturing environment is required more than ever. In particular, the air environment in a clean room greatly affects the performance and yield of semiconductors, so it is important to manage it at an appropriate level.

In order to control the air environment in the clean room, chemical filters capable of removing chemical substances in the gas are often installed in the air circulation line and the outside air intake line. In this case, the chemical filter installed in the outside air intake line is
Hazardous gas components such as hydrogen sulfide and nitrogen oxides must be continuously and efficiently removed, and a long filter life has been desired.

Conventionally, in this application, a filter composed of activated carbon or activated carbon fiber impregnated with acid or alkali, ion exchange resin or ion exchange fiber is often used. However, these filters have a short service life, and it is necessary to perform a regeneration process at an early stage or replace them with new ones, which has been a factor of cost increase. In particular, the filter installed in the outside air intake line was severely contaminated by particles and organic substances in the outside air, and it was practically impossible to recycle it.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the conventional methods as described above, and removes sulfur oxides from the atmosphere.
It is an object of the present invention to provide a method for continuously and efficiently removing harmful gas components such as hydrogen sulfide and nitrogen oxides. The method of the present invention makes it possible to favorably maintain an air environment that affects the performance and yield of semiconductors by applying this method as an air cleaning device for a clean room for semiconductor manufacturing.

[0006]

In order to solve the above-mentioned problems, the present invention provides an ion transfer device in which one or more ion exchange membranes are arranged between a positive electrode and a negative electrode while applying a current. A gas treatment liquid is prepared by passing an aqueous solution of an inorganic salt, and a gas to be treated is brought into contact with the gas treatment liquid to absorb harmful gas components in the gas into the gas treatment liquid. The present invention relates to a method for removing harmful gas components. Hereinafter, the present invention will be described in detail.

When a liquid is introduced into a chamber sandwiched between a positive electrode and a negative electrode and an electric current is applied between both electrodes, the cations in the liquid move to the cathode side and the anions move to the anode side. here,
When an ion exchange membrane is placed inside the chamber, a desired preparation liquid can be formed due to the ion selectivity of the membrane. For example,
The chamber was placed a cation-exchange membrane between the electrodes is divided into an anode chamber and a cathode chamber, Na ₂ S in the both chambers as an inorganic salt aqueous solution
When an electric current is applied between both electrodes while flowing an O ₄ aqueous solution,
Sodium ions move from the anode chamber side to the cathode chamber side through the cation exchange membrane. As a result, the ion concentration fluctuates, and the cathode chamber becomes alkaline (NaOH) and the anode chamber becomes acidic (H ₂ SO ₄ ). Further, when the same operation is performed by disposing an anion exchange membrane between the electrodes, sulfate ions move from the cathode chamber side to the anode chamber side through the anion exchange membrane,
As a result, the cathode chamber becomes alkaline (NaOH) and the anode chamber becomes acidic (H ₂ SO ₄ ).

In this way, an acidic liquid and an alkaline liquid are obtained by passing the inorganic salt aqueous solution through the ion transfer device. By sending the liquid obtained here as a gas treatment liquid to a gas-liquid contact device and bringing it into gas-liquid contact with the gas to be treated, a desired gas component can be absorbed in the gas treatment liquid and removed. For example, when the gas to be treated contains an acidic gas such as sulfur oxide, hydrogen sulfide, or nitrogen oxide, the alkaline liquid generated by the ion transfer device is used as the gas treatment liquid, and the gas is used in the gas-liquid contact device. The acid gas can be absorbed in the gas treatment liquid by bringing the treatment liquid into contact with the gas. When the gas to be treated contains an alkaline gas such as ammonia or amines, the acidic liquid generated by the ion transfer device is used as the gas treatment liquid, and the gas treatment liquid and the gas are mixed in the gas-liquid contact device. The alkaline gas can be absorbed in the gas treatment liquid by contacting with. Furthermore, by adjusting the type of the inorganic salt aqueous solution supplied to the ion transfer device, the applied voltage, etc., a redox gas such as hydrogen gas or chlorine gas is generated, and by contacting this with the atmosphere, It is also possible to change a gas having a small polarity, which is difficult to dissolve in water, into a form which easily dissolves in water.

As the ion transfer device which can be used in the present invention, for example, the structure shown in FIG. 1 can be adopted. The ion transfer device shown in FIG. 1 has an anion exchange membrane arranged between a positive electrode and a negative electrode,
When, for example, an aqueous solution of sodium sulfate is passed through while flowing an electric current through this, an acidic liquid is obtained from the anode chamber and an alkaline liquid is obtained from the cathode chamber due to the movement of ions as described above.

Further, an example of the construction of a device for removing harmful gas from gas according to the present invention using such an ion moving device is shown in FIG.
Shown in. In the device shown in FIG. 2, an ion transfer device 10 as shown in FIG. 1 and a gas-liquid contact device 13 are connected. The alkaline liquid obtained from the cathode chamber 11 of the ion transfer device 10 is supplied as a gas treatment liquid to the gas-liquid contact device 13 and is sprayed from above. In the gas-liquid contact device 13, a filler 14 for increasing the gas-liquid contact efficiency is arranged, and the gas to be treated (atmosphere) is supplied from the lower side, and the inside of the gas-liquid contact device is directed upward. Flowing. Then, in the portion filled with the filler 14, the alkaline liquid from above and the gas to be treated from below sufficiently come into gas-liquid contact, and the acidic gas contained in the gas to be treated is in the alkaline liquid. Is absorbed by.

In a preferred embodiment of the present invention, the gas treatment liquid which has absorbed harmful gas components in the gas-liquid contactor is
It can be recovered from the bottom portion 15 of the gas-liquid contact device and returned to the ion transfer device 10. In the embodiment shown in FIG.
The alkaline liquid (gas treatment liquid) that has absorbed the acidic gas component is recovered from the bottom portion 15 of the gas-liquid contact device and returned to the cathode chamber 11 of the ion transfer device 10. In the ion transfer device 10, the acidic gas components absorbed in the alkaline liquid (gas treatment liquid), such as carbon dioxide gas, sulfur oxides, hydrogen sulfide, etc., pass through the anion exchange membrane of the ion cathode chamber 10 and pass through the anode chamber side. It moves to (12) and is discharged out of the system through the discharge pipe 16. As a result, the alkaline solution is regenerated.

Further, if the acidic liquid obtained from the anode chamber 12 of the ion transfer device 10 is sent to the gas-liquid contact device 13, the alkaline harmful gas component in the gas to be treated can be absorbed and removed similarly.

In the present invention, the concentrations of the alkaline liquid and the acidic liquid generated by the ion transfer device are appropriately determined according to the air volume of the gas to be treated, the concentration of harmful gas components contained in the gas to be removed, and the like. The concentration can be adjusted to the determined concentration by adjusting the concentration of the alkaline liquid and / or the acidic liquid at the initial stage of operation. Also, for changes in salt concentration due to evaporation of liquid during operation, etc.,
The predetermined concentration can be maintained by discharging the circulating liquid or adding a replenisher.

Further, in the present invention, an ion transfer device having a configuration as shown in FIG. 3 can be used. The apparatus shown in FIG. 3 is one in which an anion exchange membrane and a cation exchange membrane are arranged adjacent to a positive electrode and a negative electrode, respectively, between both electrodes, and is a so-called electric desalination apparatus (electrodialysis apparatus).
It has the same form as. When an inorganic salt, such as an aqueous solution of sodium sulfate, is passed through each chamber of the ion transfer device having such a structure while applying a current between both electrodes, anions such as sulfate ions are discharged from the central deionization chamber to the anion exchange membrane. Cations, such as sodium ions, pass through the cation exchange membrane from the central deionization chamber to the cathode chamber, and as a result, the ion concentration in each chamber fluctuates. Thus, an acidic liquid is obtained from the anode chamber and an alkaline liquid is obtained from the cathode chamber. By using the ion transfer device having such a configuration, for example, a gas treatment device having a configuration as shown in FIG. 4 can be formed. In the gas treatment device shown in FIG. 4, the alkaline liquid obtained from the cathode chamber 21 of the ion transfer device 20 is supplied to the gas-liquid contact device 23 as a gas treatment liquid to bring it into gas-liquid contact with the gas to be treated (atmosphere). Due to
The acidic gas contained in the gas to be treated is absorbed in the alkaline liquid. The gas treatment liquid that has absorbed the acidic gas is returned to the demineralization chamber at the center of the ion transfer device 20, and the absorbed acidic gas component moves to the anode chamber in the ion transfer device to regenerate the alkaline liquid. To be done. On the other hand, the acidic liquid obtained from the anode chamber 22 of the ion transfer device 20 is supplied to the gas-liquid contact device 24 as a gas treatment liquid, and is brought into gas-liquid contact with the gas to be treated (atmosphere), so that the gas is treated. The contained alkaline gas is absorbed in the acidic liquid.
The gas treatment liquid which has absorbed the alkaline gas is returned to the demineralization chamber in the center of the ion transfer device 20, and the absorbed alkaline gas component moves to the cathode chamber in the ion transfer device to regenerate the acidic liquid. To be done. The regenerated alkaline liquid and acidic liquid can be sent as they are to the gas-liquid contactor. As described above, according to the gas treatment device of the present invention, it is possible to circulate and use the gas treatment liquid to continuously remove harmful gas components having different properties in parallel.

In the ion transfer device according to the present invention,
An ion exchanger can be filled in the chamber between the ion exchange membrane and the electrode to improve the moving speed of ions in the chamber. For example, as shown in FIG. 5, it is possible to arrange an anion exchange membrane between the electrodes and fill the anion chamber with the anion exchanger and the cathode chamber with the cation exchanger. Further, as shown in FIG. 6, a cation exchange membrane can be arranged between the electrodes to fill the cation exchanger in the anode chamber and the anion exchanger in the cathode chamber. As a form of the ion exchanger that can be used for this purpose, an ion exchange resin, an ion exchange fiber, an ion exchange net, or the like can be used. Since harmful gas components in the atmosphere are generally at a relatively low concentration, their concentration after being absorbed in the gas treatment liquid is also low. In order to efficiently move the components contained at such a low concentration in the ion transfer device, it is preferable to fill the chamber with an ion exchanger to improve the ion transfer efficiency. In addition,
The ion exchanger may be filled in both electrode chambers as shown in FIGS. 5 and 6, or may be filled in only one of the electrode chambers.

It is conceivable that a trace amount of harmful gas components may still remain in the gas after the harmful gas components have been adsorbed and removed by the gas-liquid contact device according to the present invention. A chemical filter known in the art can be arranged as a subsequent stage of the gas-liquid contactor. That is, another aspect of the present invention provides a method for removing a harmful gas component in a gas, which is characterized in that the gas to be treated from which the harmful gas component is removed by the above-described method is further brought into contact with a chemical filter. .

In the present invention, a chemical filter and / or
Alternatively, a radiation graft polymerization method known in the art can be used as a method for producing the ion exchanger packed in the ion transfer device. In the radiation graft polymerization method, the ion-exchange group can be introduced into the polymer base material of various shapes even to the inside thereof, so that the ion-exchange capacity can be increased. Further, since the ion exchanger prepared by the radiation graft polymerization method does not have a crosslinked structure, it is possible to increase the moving speed of the adsorbed ions.

In the present invention, when a chemical filter or an ion exchanger is produced by using a radiation graft polymerization method, the base material is a fiber material, for example, a polymer material fiber or a woven or non-woven fabric which is an aggregate thereof. Can be used particularly preferably. The fibrous polymer has a large surface area, can increase the removal rate of a trace amount of ions, is light in weight, and is easy to be molded. Specific examples of these shapes include long fibers and processed products thereof, short fibers and processed products thereof, and cut short bodies thereof. The long fibers include, for example, continuous filaments, and the short fibers include, for example, staple fibers. Processed products of long fibers and short fibers include various woven and non-woven fabrics produced from these fibers. Further, the woven / nonwoven material can be suitably used as a substrate for radiation graft polymerization, is lightweight and can be easily processed into a filter shape, and is suitable for use in the method of the present invention.

In the radiation graft polymerization method that can be preferably used for the purpose of the present invention, the radiation that can be used includes α rays, β rays, γ rays, electron beams, and ultraviolet rays. Γ-rays and electron beams are suitable for use in the present invention. The radiation graft polymerization method includes a pre-irradiation graft polymerization method in which a graft base material is pre-irradiated with radiation and then brought into contact with a polymerizable monomer (graft monomer) to cause a reaction, and radiation in the coexistence of the base material and the monomer. There is a simultaneous irradiation graft polymerization method of irradiating
Either method can be used in the present invention. Further, by the method of contacting the monomer and the base material, a liquid phase graft polymerization method in which the base material is immersed in the monomer solution for polymerization, a gas phase graft polymerization method in which the base material is brought into contact with vapor of the monomer for polymerization, Examples of the method include an impregnated gas phase graft polymerization method in which a substrate is immersed in a monomer solution and then taken out from the monomer solution to carry out a reaction in a gas phase. Any method can be used in the present invention.

A woven / nonwoven fabric, which is a fiber or an aggregate of fibers, easily holds a monomer solution, and is therefore suitable for use in an impregnated gas phase graft polymerization method. In the present invention, as the ion exchange group that can be introduced into the substrate in the production of the chemical filter or the ion exchanger, for example,
Examples thereof include a sulfonic acid group, a phosphoric acid group, a carboxyl group, a quaternary ammonium group, and a lower or lower tertiary amino group.

In the present invention, in order to produce a chemical filter or an ion exchanger by using a radiation graft polymerization method, the above polymerizable monomer having an ion exchange group (monomer) is grafted onto the main chain of the substrate. Polymerization method and a grafted polymer side chain after graft-polymerizing a polymerizable monomer having an ion-exchange group but having a group convertible to an ion-exchange group onto the main chain of a substrate. And a method of converting the above group into an ion exchange group.

As the polymerizable monomer having an ion exchange group which can be used for this purpose, for example, those having a sulfonic acid group include sodium styrenesulfonate,
Sodium vinyl sulfonate, sodium methallyl sulfonate, etc .; Acrylic acid, methacrylic acid, etc. having a carboxyl group; Vinyl benzyl trimethyl ammonium chloride (VBTAC), dimethylaminoethyl methacrylate (DMAEMA) having an anion exchange group , Diethylaminoethyl methacrylate (DEAEMA), dimethylaminopropyl acrylamide (DMAPAA), and the like;

As the polymerizable monomer which does not have an ion exchange group itself but has a group which can be converted into an ion exchange group, glycidyl methacrylate, styrene, acrylonitrile, acrolein, chloromethylstyrene and the like can be used. Can be mentioned. For example, a sulfonic acid group can be introduced onto a side chain of a graft polymer by graft-polymerizing styrene on a substrate and then reacting with sulfuric acid or chlorosulfonic acid to sulfonate. Also,
For example, a quaternary ammonium group can be introduced onto a side chain of a graft polymer by graft-polymerizing chloromethylstyrene on a substrate and then immersing the substrate in a trimethylamine aqueous solution for quaternary ammonium conversion.

[0024]

The present invention will be described in more detail with reference to the following examples. The following examples show particularly preferred specific examples of the present invention, but the present invention is not limited thereto.

Example 1 An ion transfer device having a 10 cm × 20 cm electrode plate and having a shape as shown in FIG. 1 in which an ion exchange membrane can be mounted was prepared. This ion transfer device was connected to a gas-liquid contact device as shown in FIG. An acrylic column having a diameter of 50 mm was used as a gas-liquid contact device, and glass fibers were filled inside the column to form a gas-liquid contact layer. The distance between the ion exchange membrane and the electrode plate was 3 mm. A cation exchange membrane (manufactured by Asahi Glass, trade name CMV) was attached to this device. While applying a voltage of 20 V between both electrodes, Na ₂ is added to the positive electrode side chamber.
A 0.5% SO ₄ aqueous solution and pure water were supplied to the negative electrode side chamber at a flow rate of 500 mL / min. -Vapor-liquid contact device (acrylic column) for alkaline liquid obtained from the electrode side chamber
Was dripped from above. The effluent from the bottom of the column was returned to the chamber on the negative electrode side of the ion transfer device. The liquid on the + electrode side (Na ₂ SO ₄ aqueous solution) was circulated as it is as shown in FIG. When the pH of the alkaline liquid circulating between the negative electrode chamber of the ion transfer device and the gas-liquid contact device was measured, it was 1
It was 1.2.

Atmosphere adjusted to have a hydrogen sulfide concentration of 1.3 ppm was introduced into the lower part of the gas-liquid contactor column at a flow rate of 300 mL / min to pass the gas-liquid contact layer from the lower part to the upper part, and the upper part of the column. Discharged from. Generation of hydrogen sulfide was performed by a permeator.

The hydrogen sulfide concentration at the gas discharge port at the upper part of the column was measured by a gas detector tube and found to be 0.1 ppm or less. Example 2 Anion exchange membrane (manufactured by Asahi Glass Co., Ltd., trade name AMV) was attached to the ion transfer device of Example 1, and pure water was placed in the + electrode side chamber, −.
500% each of Na ₂ SO ₄ 0.5% aqueous solution was placed in the electrode chamber
Supplying at a flow rate of mL / min, the acidic liquid obtained from the + electrode side chamber is circulated between the gas-liquid contact column and the − electrode side liquid as it is, and ammonia is supplied to the gas-liquid contact column. An operation test was conducted in the same manner as in Example 1 except that the atmosphere adjusted to 2 ppm was introduced. The concentration of ammonia at the gas outlet of the gas-liquid contact column was 0.06ppm, and the removal rate was 97%.
It showed high removal efficiency.

Example 3 Preparation of Strongly Acidic Cation Exchange Nonwoven Fabric A basis weight of 55 g / m ² composed of a polyethylene (sheath) / polypropylene (core) composite fiber having a fiber diameter of 17 μm, and a thickness of 0.35.
150 mm of electron beam in a nitrogen atmosphere on a thermally fused non-woven fabric of mm
y irradiated. This irradiated non-woven fabric was impregnated with glycidyl methacrylate so as to be 140% of the substrate. After putting this non-woven fabric in a vacuum container and reducing the pressure with a vacuum pump,
The reaction was carried out at 50 ° C for 3 hours. The non-woven fabric taken out was dry. Add this to the dimethylformamide solution,
The homopolymer was removed by treatment at 3 ° C. for 3 hours.

This nonwoven fabric was immersed in a solution of sodium sulfite / isopropyl alcohol / water = 15/10/75 and reacted at 80 ° C. for 9 hours to be sulfonated. After the non-woven fabric taken out was thoroughly washed, the neutral salt decomposition capacity was measured, and a strongly acidic cation exchange non-woven fabric of 2.59 meq / g was obtained.

Gas Treatment Test Using the strongly acidic cation exchange nonwoven fabric obtained above as a chemical filter, the gas at the gas outlet of the gas-liquid contact column of Example 2 was passed through this chemical filter. The concentration of ammonia in the gas passed through the chemical filter is 1
It was below ppb and was almost completely removed. After 24 hours, the concentration of ammonia in the gas after the treatment was maintained at 1 ppb or less.

Comparative Example 1 Preparation of Strongly Basic Anion Exchange Nonwoven Fabric The non-woven fabric substrate used in Example 3 was irradiated with electron beams in the same manner as in Example 3, and then chloromethylstyrene purified by activated alumina (made by Seimi Chemical, CMS-AM) was impregnated to 120% of the base non-woven fabric, the non-woven fabric was placed in a vacuum container, the pressure was reduced by a vacuum pump, and the reaction was carried out at 50 ° C. for 3 hours. The non-woven fabric taken out was dry.
This was placed in a toluene solution and treated at 70 ° C. for 3 hours to remove the homopolymer. Due to the change in weight of the nonwoven fabric, the graft ratio was calculated to be 116%. The difference between the impregnation rate of 120% and the actual graft rate of 116% was that the monomer adhered to the vacuum vessel, evaporated and evacuated, and was mostly used for graft polymerization.

This graft nonwoven fabric is dipped in a 10% aqueous solution of trimethylamine and reacted at 50 ° C. for 3 hours,
It was converted to quaternary ammonium. After sufficiently washing the taken out nonwoven fabric, the neutral salt decomposition capacity was measured to be 2.21.
A strongly basic anion exchange nonwoven fabric of meq / g was obtained.

Gas Treatment Test Using the strongly basic anion exchange nonwoven fabric obtained above as a chemical filter, the atmosphere prepared to have a hydrogen sulfide concentration of 1.3 ppm was passed through at a flow rate of 1 L / min. The hydrogen sulfide concentration in the air at the outlet of the filter gradually increased and reached 0.7 ppm 2 hours after passing the gas.

It can be seen that the method for removing hydrogen sulfide of the present invention is more stable than the chemical filter alone. Comparative Example 2 The strong acid cation exchange nonwoven fabric manufactured in Example 3 was used as a chemical filter without using an ion transfer device.
Ammonia having a concentration of 2 ppm was directly passed through the chemical filter. The ammonia concentration on the outlet side started to rise gradually from the 3rd hour of passing the gas and became about the same as the inlet concentration at the 5th hour, and it had to be replaced.

[0035]

According to the present invention, the harmful gas in the gas can be continuously removed by circulating the gas treatment liquid by the combination of the ion transfer device and the gas-liquid contact device. Furthermore, when this is combined with a chemical filter, harmful gas in the gas can be removed more completely, and the service life of the chemical filter is significantly improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a specific example of an ion transfer device according to the present invention.

FIG. 2 is a conceptual diagram showing a specific example of a gas treatment device according to the present invention.

FIG. 3 is a conceptual diagram showing a configuration example of an ion transfer device according to another aspect of the present invention.

FIG. 4 is a conceptual diagram showing a configuration example of a gas treatment device according to another aspect of the present invention.

FIG. 5 is a conceptual diagram showing a configuration example of an ion transfer device according to another aspect of the present invention.

FIG. 6 is a conceptual diagram showing a configuration example of an ion transfer device according to another aspect of the present invention.

Continued front page    F-term (reference) 4D006 GA17 HA48 HA93 KA33 KA72                       KB19 KD30 MA03 MA13 MA14                       MB07 PB12 PB25 PB26                 4D020 AA04 AA05 AA06 BA01 BA12                       BA23 BB03 BC03 CB01 CC02                       CC12

Claims (6)

[Claims] 1. A gas treatment liquid is prepared by passing an aqueous solution of an inorganic salt while applying a current to an ion transfer device in which one or more ion exchange membranes are arranged between a positive electrode and a negative electrode. A method for removing a harmful gas component in a gas, which comprises bringing a gas to be treated into contact with the treatment liquid so that the harmful gas component in the gas is absorbed in the gas treatment liquid. 2. The method according to claim 1, further comprising the step of returning the gas treatment liquid having absorbed the harmful gas component to the ion transfer device, and removing the harmful gas component to regenerate the gas treatment liquid in the ion transfer device. . 3. A method for removing a harmful gas component in a gas, which comprises contacting the gas from which the harmful gas component is removed by the method according to claim 1 or 2 with a chemical filter. 4. An ion transfer device having one or more ion exchange membranes arranged between a positive electrode and a negative electrode; a supply pipe for supplying an inorganic salt aqueous solution to the ion transfer device; and a liquid discharged from the ion transfer device. A device for removing harmful gas components from a gas, comprising a gas-liquid contact device for contacting a processing gas. 5. The harmful gas component removal from the gas according to claim 4, further comprising a recirculation pipe for returning the liquid, which has come into contact with the gas to be processed and has absorbed the harmful gas component in the gas to be processed, to the ion transfer device. apparatus. 6. The harmful gas component removing device according to claim 4, further comprising a chemical filter for further treating the gas discharged from the gas-liquid contact device.