KR20030062901A - Method for abatement of hazardous gases and hybrid system therefor - Google Patents

Abstract

PURPOSE: A hybrid system for purification of hazardous gas is provided, which can treat a large volume of lean emission gas of VOCs or PFC of semi-conductor process containing more than 95% of air by passing through membrane consuming low energy and enhancing treating efficiency. CONSTITUTION: The system includes the steps of separating non-harmful gas and harmful gas of PFC or VOCs, which are contained in carrier gas, by passing the carrier gas containing harmful gas through separation membrane(101); mixing the separated harmful gas with additive gas obtaining mixed gas; and treating the mixed gas with plasma generated by plasma generator(103) or treating the harmful gas directly with plasma.

Description

Hybrid hazardous gas disposal system and method {Method for abatement of hazardous gases and hybrid system therefor}

The present invention relates to a hybrid noxious gas disposal system and method capable of treating a large amount of carrier gas (or exhaust gas) containing a small amount of noxious gas of the present invention.

Air pollution is an important environmental concern. Despite various air pollution prevention laws, widespread and persistent air pollution causes deterioration of human health and the environment. Even in Korea, about 5-10% of people live in polluted atmosphere, which can harm public health. Furthermore, the destruction of the ozone layer that absorbs ultraviolet rays may cause skin cancer or the like by excessive exposure to ultraviolet rays, which may damage human health. This air pollution is mainly caused by the emission of harmful gases.

Emissions of volatile organic compounds (VOCs), such as benzene, toluene, ethane, ethanol, etc., contribute to the threat of human health to the destruction of the environment due to air pollution and cancer. For example, benzene and toluene are known as cancer-causing substances, and other VOCs that can react with sulfur, carbon and oxygen may form smog in the presence of heat and sunlight. On the other hand, perfuorinated compounds (PFCs) such as CF ₄ , CHF ₃ , C ₂ F ₆ , C ₂ HF ₅ , C ₂ H ₂ F ₄ , NF ₃ , SF _6, etc. It is known to cause contamination.

Various methods have been proposed for treating harmful gases causing the above problems. Examples include catayst-assistant decomposition, thermal decomposition or plasma-assistant decomposition, or mixing with other gases to solidify and treat the same.

Hazardous Gas Disposal System adopting this method usually has to deal with air that does not need to be disposed of when carrier gas containing less than 5% of harmful gas is used. It is inefficient and furthermore makes it difficult to deal with harmful gases that have to be treated.

In the method proposed in the present invention, a carrier gas containing a small amount of harmful gas (typically less than 5% of the harmful gas) is separated and treated only by using a membrane separation method to reduce the energy required for the disposal of the harmful gas and consequently It is a way to treat very large emissions. The membrane separation method used in this method is to separate air and harmful gas through the separation membrane, to release air without treatment, and to collect only harmful gas.

An object of the present invention is to discharge a non-hazardous gas into the atmosphere by using a separation membrane of a carrier gas (or exhaust gas) containing a harmful gas, and the mixed gas obtained after mixing the separated noxious gas directly or with an additive gas, the plasma generator It is to provide a method for removing by treatment with a plasma generated in the.

Another object of the present invention is to provide a hybrid noxious gas disposal system used in the method.

1 is a schematic flowchart of a hybrid system for treating noxious gas of the present invention.

Figure 2 shows a preferred example of the membrane portion that can be used for the treatment of VOC.

3 shows a preferred example of a separator that can be used for the treatment of PFC.

4 illustrates a preferred example of an atmospheric plasma generator used in the hybrid system.

5 shows another preferred example of an atmospheric plasma generator used in the hybrid system.

6 is a configuration diagram of an intermediate plate used in the atmospheric plasma generator of FIGS. 5 and 6.

The present invention relates to a hybrid noxious gas disposal system and method capable of treating a large amount of carrier gas containing a small amount of noxious gas.

In the method of the present invention, a carrier gas (or exhaust gas) containing harmful gas is passed through a separation membrane to separate a non-hazardous gas that does not need treatment contained in the carrier gas from a harmful gas that requires treatment, and to separate the separated harmful gas. Treating the mixed gas obtained either directly or after mixing with the additive gas using a plasma generated in a plasma generator, preferably an atmospheric pressure plasma generator.

As used herein, the term “hazardous gas” refers to harmful gases that cause destruction of humans and the atmosphere, in particular the ozone layer and the greenhouse effect, and examples thereof include VOC and PFC.

As used herein, the term "addition gas" refers to a gas added when a harmful gas is treated using plasma. For example, to treat VOCs, high concentrations of VOCs pose a risk of explosion, requiring the addition of a gas that can be diluted to an appropriate concentration (about 2-5%). Therefore, in the case of VOC, the non-explosive dilution gas is added as the additive gas, and examples thereof include nitrogen and the like. In case of treating PFC, hydrogen (H ₂ ); Ammonia (NH ₃ ); Saturated hydrocarbons including methane (CH ₄ ), ethane (C ₂ H ₆ ) and propane (C ₃ H ₈ ); Hydrogen compounds such as unsaturated hydrocarbons containing ethene (C ₂ H ₄ ) and propene (C ₃ H ₆ ) are added to react with fluorine, a decomposition product of PFC, to treat PFC.

The present invention also relates to a hybrid noxious gas disposal system for use in the above method, wherein said waste system comprises a separator unit, an additive gas supply and a plasma generator. Include. 1 shows a schematic diagram of a hybrid hazardous gas disposal system of the present invention.

The carrier gas containing noxious gas such as PFC or VOC passes through the separation membrane portion 101 of the waste system 100. There, the carrier gas is separated into air components (oxygen, nitrogen, etc.) and harmful gases which are non-hazardous gases. Air components are released to the atmosphere and noxious gases are concentrated. The separated and concentrated noxious gas is mixed with the additive gas supplied by the additive gas source 102 and supplied to the plasma generator 103, where it is treated by the plasma. The separation membrane unit 101 is not particularly limited as long as it can at least separate the harmful substances and air components, and usually includes a compressor, a filter, a mass flow controller, and a separation membrane module. A condenser may be further included to condense the water vapor if it is necessary to remove moisture in the carrier gas in advance.

Hereinafter, the present invention will be described in more detail based on the treatment examples of VOC and PFC, which are representative examples of harmful gases.

2 illustrates a preferred example of a separator that can be used for the treatment of the VOC, wherein the separator 200 includes a compressor 201, a condenser 202, a filter 203, a mass flow controller (MFC) ( 204 and membrane module 205. The carrier gas containing the VOCs discharged from various processes including the chemical process is compressed through the air compressor 201 and the moisture contained in the carrier gas containing the VOC is removed while passing through the condenser 202. The compressed and condensed carrier gas passes through the filter 203 to remove suspended matter such as dust, which may exist in the carrier gas, and enters the membrane module 205 through the inlet 206 under the control of the mass flow controller 204. do. The carrier gas introduced into the membrane module 205 is separated into air and VOC which are non-hazardous gases, and the VOC is concentrated there.

The separator 207 that can be used for the separator module 205 is not particularly limited as long as it is a conventional separator that can be used for separation of the VOC. A common characteristic of large-volume molecules, such as VOCs, is that they have a high critical temperature and these compounds have high solubility in polymeric materials. Furthermore, such a compound has a permeability coefficient mainly determined by solubility in the polymer material rather than the diameter of the molecule, and therefore, a polymer membrane having a very flexible structure is preferable in order to exhibit high permeability relative to air. Examples thereof include silicone rubber, and preferably PDMS (Polydimethylsiloxane), which is commercially available in the United States and Europe.

The carrier gas passing through the membrane module 205 is separated into VOC and air and is discharged to the atmospheric pressure plasma generator and the atmosphere through the VOC outlet 208 and the air outlet 209, respectively. Reference numerals 210 and 211 are pressure gauges and pressure regulating valves, which are used for measuring and controlling pressure. The use of the condenser in the membrane portion 200 for the VOC can be excluded when the moisture content is negligibly low, the use of MFC can also be adjusted in consideration of the appropriate conditions.

FIG. 3 shows a preferred example of a separator that can be used for the treatment of the PFC, wherein the separator 300 includes a compressor 301, a filter 302, a mass flow controller 303, and a separator module 304. Include. In the case of PFC, the use of a condenser is unnecessary because there is almost no moisture content, but it can be added if necessary. The carrier gas containing the PFC discharged from the semiconductor process, specifically the ashing step and the washing step, etc., is compressed by the compressor 301, and the suspended solids such as dust that may exist in the carrier gas through the filter 302 are removed. , Under the control of mass flow controller 303, enters membrane module 304 through inlet 305, where the PFC is separated from air and concentrated. The separator 306 that can be used in the separator module 304 is not particularly limited as long as it is a conventional separator capable of separating the PFC from the air. Preferably, the separator can be separated from the air using the diameter of the molecule. It is a separator. Examples may include polysulfone (hereinafter referred to as "PS") or ozonated polysulfone. According to an embodiment of the present invention, in the case of polysulfone, in the case of CF ₄ which is one of the PFCs, the selectivity of passing 1 / 52.35 when one molecule of nitrogen passes, and the permeation selectivity of 1 / 37.25 for C ₂ F ₆ Indicated. In the case of ozone treated polysulfone, the permeation selectivity was further improved, showing 1 / 62.1 and 1 / 54.08, respectively. Thus, ozone treated polysulfone provided more improved results. Fluoroelastromer-based polymers are solubilized membranes, which have relatively low solubility for CF ₄ and C ₂ F ₆ , and do not provide satisfactory results.

Table 1 and Table 2 below summarize the gas permeability using the PS separator and ozone-treated PS separator, respectively. As can be seen in Tables 1 and 2, the PS separator can be a suitable membrane material for the purpose of concentrating the PFC mixed in the trace amount in the air, it can be seen that this effect can be further improved through ozone treatment.

Permeability of Gas and Permeation Selectivity to Nitrogen in PS Membranes Gas P (permeability) × 10 ¹¹ (barrier) Transmission selectivity (P _N2 / P) N ₂ 1.194435 O ₂ 7.686455 0.15 He 76.86455 0.015 H ₂ 85.28217 0.014 CH ₄ 1.36977 0.87 CF ₄ 0.02281 52.35 C ₂ F ₆ 0.03206 37.25

Permeability of Gas and Permeation Selectivity to Nitrogen in PS Membrane Gas P (permeability) × 10 ¹² (barrier) Transmission selectivity (P _N2 / P) N ₂ 4.884595 O ₂ 38.92441 0.125 He 62.00544 0.079 H ₂ 61.82027 0.078 CH ₄ 0.2701584 18.1 CF ₄ 0.078673 62.1 C ₂ F ₆ 0.090321 54.08

The carrier gas passing through the membrane module 304 is separated into a PFC and a non-hazardous gas, for example, air (oxygen, nitrogen, etc.), and then, through the PFC outlet 307 and the air outlet 308, to the atmospheric plasma generator and the atmosphere. Each is discharged. Reference numerals 309 and 310 are pressure gauges and pressure regulating valves, which are used to measure and control pressure.

The VOC or PFC separated and concentrated by the separator is mixed with the additive gas used for their treatment and then introduced into an atmospheric plasma generator where it is treated by plasma. Examples of the additive gas are as described above.

The plasma generator used for the treatment of VOC or PFC is not particularly limited as long as it is a general plasma generator used for the treatment of VOC and / or PFC. Specifically, it is not particularly limited as long as it is a general plasma generator including two electrodes insulated by one or more insulators, a plasma generating space, and a high voltage power supply. Atmospheric pressure plasma can be generated by Pulsed Corona Discharge and Dielectric Barrier Discharge [1], which generate plasma without using a separate pump or expensive vacuum chamber at atmospheric pressure. By converting the harmful gas into a harmless gas, it can provide a simple treatment and a reduction in the processing cost. Therefore, an atmospheric pressure plasma generator based on the above discharge principle is more preferable.

Examples include US Pat. No. 5,387,775, US Pat. No. 6,146,599, US Pat. No. 6,245,299, and the like. Specifically, US Pat. No. 5,387,775 discloses a plasma generator using an insulator discharge comprising one metal electrode, another electrically conductive liquid electrode, one or more insulators positioned between the electrodes and a high voltage power source. U.S. Patent No. 6,146,599 discloses a plasma generator in which a pretreatment discharge cell employing corona discharge and a main treatment discharge cell employing insulator discharge are arranged in series. In addition, US Patent No. 6,245, 299 discloses a plasma generator using a method of connecting a plurality of insulator discharge cells in series to sequentially apply and remove harmful gases to the plurality of insulated discharge cells.

4 and 5 illustrate another example of the atmospheric pressure plasma generator, and the principle of generating the atmospheric pressure plasma and the method of treating the noxious gas will be described in detail. However, FIGS. 4 and 5 are provided to explain the present invention in more detail, and the scope of the present invention is not limited thereto, and as described above, a conventional plasma generator may be used in the disposal system of the present invention. It must be understood.

As shown in FIG. 4, the atmospheric pressure plasma generator 400 as an example of a plasma generator that can be used in the present invention includes a mixing chamber 401, a gas disperser 406, an insulator discharge cell 408, and a high voltage power source ( 413). The mixing chamber 401 used in the atmospheric pressure plasma generator 400 includes an inlet 402 for concentrating harmful gas, an inlet 403 for addition gas required for the treatment of noxious gas, and an outlet 404 for discharging the mixed gas. And a first mixing of the additive gas and the noxious gas is made. The inflow amount of the additive gas may be appropriately adjusted by the gas flow controller (MFC) 405 according to the amount of harmful gas introduced therein. If necessary, the mixing chamber 401 can be arranged in a number corresponding to a plurality of insulator discharge cells 408 arranged in parallel, an example of which is shown in FIG. Sign was used).

In the mixing chamber 401, the noxious gas and the additive gas having the first mixing are sent to the gas disperser 406 through the outlet 404 under the control of the valve 415, where more uniform mixing and uniformity of the mixed gas is performed. The formation of the distribution takes place.

The gas disperser 406 is formed in a small cube shape with a flat plate 407 interposed therebetween. In the intermediate plate 407, a plurality of holes 407a are uniformly present throughout the plate (see FIG. 6), and the total cross-sectional area of the holes is preferably larger than the cross-sectional area of the pipe to prevent the gas from entering. . Some of the small amount of solid emissions present in the form of impurities in the noxious gas and the additive gas collide with the middle plate 407 of the gas disperser 406 and move to the bottom of the gas disperser 406, which is a collector. H) may be installed below the gas disperser 406 to remove it during operation or after completion of the operation. The noxious gas and the additive gas passing through the gas disperser 406 flow into the plurality of insulator discharge cells 408 arranged in parallel. The amount flowing into each of the insulator discharge cells 408 is preferably uniform, but does not exclude a case in which the amount flowing into the insulator discharge cells 408 is different.

Each insulator discharge cell 408 has two electrodes 410 insulated by one or more insulators 409 (these can facilitate the release of heat generated by the plasma discharge by the heat sink 412) and plasma generation It is composed of a space 411, the plurality of insulator discharge cells 408 may be connected to a plurality of high frequency power source 413 independently of each other, but it is preferable to be connected in parallel to one high frequency power source for simplicity of structure. . In the latter case, each insulator discharge cell may be provided with a high voltage switch 414 to replace and repair a failed insulator discharge cell 408 even during operation of another insulator discharge cell. The number of insulator discharge cells 408 can be appropriately selected in consideration of the processing capacity. The mixed gas of the noxious gas and the additive gas reacts with the plasma while passing through the plasma generating space 411 formed inside the insulator discharge cell 408. In general, the geometrical shape of the plasma reactor is a planar discharge using two plate electrodes and a cylindrical discharge using two cylindrical electrodes are used a lot, Figure 4 illustrates a planar discharge using two plate electrodes for convenience, but the present invention It will be apparent to those skilled in the art that a cylindrical discharge using two cylindrical electrodes can be employed.

The harmful gas mixed with the additive gas passes through the plasma generating space 411 and collides with the electrons in the accelerated plasma between the two electrodes 410 to break molecular bonds and generate radicals having high reactivity. The resulting radicals tend to react chemically with other molecules. If, for example, CF ₄ is treated with hydrogen as an additive gas, the hydrogen radicals generated from hydrogen combine with the fluorine radicals generated from CF ₄ to form hydrogen fluoride. If unsaturated hydrocarbons are used as the reaction gas, polymers are formed by a chain reaction with hydrogen radicals and fluorine radicals. In this reaction, since hydrogen radicals and fluorine radicals are formed, hydrogen fluoride can be generated, but the amount of hydrogen fluoride generated is smaller than when using hydrogen molecules. The resulting polymer is extracted in the form of a powder or a film depending on the input power to the plasma. The same principle can be applied to VOC, in which case molecules such as benzene are converted into harmless hydrogen and the like.

In the hybrid type harmful gas disposal system and method according to the present invention, when considering that 95% or more of the carrier gas discharged by the semiconductor process is air and the remainder is harmful gas, harmless air is separated by using a membrane separation method. Emissions and disposal of hazardous gases alone can significantly improve the disposal rate by using a large amount of environmentally polluting gases with less energy. Therefore, the hazardous gas disposal system of the present invention may be widely used for the disposal of PFC, VOC, etc. from the semiconductor process.

The specific cost savings are described with the VOC as an example.

In order to remove the 90% of the transportation gas 1 m ³ containing 100 ppm of VOC is approximately three won takes the current standard of 500 ppm VOC electricity rate is on the order of about six circles. The concentration has increased fivefold, but the cost has only doubled, resulting in a 60% reduction in electricity costs compared to before the condensation. In practical situations, the concentration will be increased by 5,000 times, so electricity costs can be reduced by more than 90%. Another cost saving is to carry only a small amount of harmful gas in the transport gas, thus reducing the transport cost. Chemical complexes built in Yeocheon or Ulsan transport VOCs from explosion-proof (explosion-proof) areas to non-explosion-proof areas. Since the radius of explosion-proof area is more than 5km, transporting only harmful gas to non-explosion area will reduce the transportation cost. In practice, a carrier gas containing about 1,000 ppm of VOC generates more than 1,000 m ³ per minute, and only one m ³ of harmful gas can be transported out of 5 km.

references

[1] U.Kogelschatz et al., J. Phys. IV France, 7, C4-47 (1997)

Claims (10)

The carrier gas containing the harmful gas is passed through a separation membrane to separate the non-hazardous gas that does not need treatment from the harmful gas and the noxious gas to be treated, and the mixed harmful gas is directly or mixed with the additive gas. And processing the gas using the plasma generated by the plasma generator. The method of claim 1, wherein the harmful gas is PFC or VOC. a) membrane section for separating and concentrating harmful gases from a carrier gas containing harmful gases, b) an additive gas source for supplying the additive gas necessary for the treatment of the noxious gas, and c) A hybrid noxious gas disposal system comprising a plasma generator for generating a plasma for treating a mixture of separately concentrated noxious gases and additive gases. The hybrid noxious gas disposal system according to claim 3, wherein the noxious gas is PFC. The hybrid noxious gas disposal system according to claim 3, wherein the noxious gas is VOC. The hybrid noxious gas disposal system according to claim 3, wherein the noxious gas is PFC, and the membrane unit includes a compressor, a filter, a mass flow controller, and a membrane module. The hybrid noxious gas disposal system according to claim 6, wherein the separator used in the separator module is a PS separator or an ozone-treated PS separator. The hybrid noxious gas disposal system according to claim 3, wherein the noxious gas is VOC, and the membrane part includes a compressor, a condenser, a filter, a mass flow controller, and a membrane module. 4. The hybrid hazardous gas disposal system according to claim 3, wherein the plasma generator comprises two electrodes insulated by an insulator, a plasma generating space, and a high voltage power supply. 4. The plasma generator of claim 3, wherein the plasma generator is a mixing chamber for mixing noxious and additive gases, a gas disperser for forming a uniform distribution and uniform distribution of noxious gases and additive gases, an insulator discharge cell connected in parallel, and a high voltage. Hybrid type hazardous gas disposal system, characterized in that the atmospheric pressure plasma generator including a power source.