Patent Application
20090155154
1. Field of the Invention
The invention relates to a decomposition method for waste gas and decomposition apparatus thereof, and more particularly to a decomposition method for sulfur-fluorine-containing compound and decomposition apparatus thereof.
2. Description of the Related Art
Currently, perfluorochemicals (PFCs) such as CF4, C2F6, C3F8, c-C4F8, CHF3, NF3, and SF6 are utilized in the photoelectricity or semiconductor manufacturing industries, for example, thin-film process, etching process and implantation process. Specifically, SF6 is utilized to clean up equipments for dry-etching and chemical vapor deposition (CVD).
Techniques approved by Intergovernmental Panel on Climate Change (IPPC), with destruction and removal efficiency (DRE) to waste gas of 90%, comprise fueled combustion, plasma and catalytic.
For fueled combustion, CH4 and combustion air are required to generate energy for decomposition of S—F bond by combustion and then produce SO2F2, SO2, SO3, CO, CO2 and HF. Typically, a wet scrubbing tower is placed at a rear end of fueled combustion equipment to remove caustic gases and particles. Advantages of furled combustion are fuel CH4 is required, and byproducts, CO and C2H4 are produced.
For plasma, the equipment is placed between turbo pumps and dry pumps. PFCs are bombed by electrons to break C—F bond and transform into HF, CO and CO2 by washing. Plasma technique for PFCs is only utilized in etching process and its market share is relatively small. Possible reason is that various, high risk gases such as HCN or COF2 are produced after bombing. Even wet scrubbing towers are unable to effectively remove the all derivatives produced after bombing. Moreover, plasma equipment is located close to vacuum equipment resulting in reactor pollution.
Catalytic is generally utilized in treatment of waste air produced by etching process in the photoelectricity manufacturing industry or semiconductor manufacturing industry. For catalytic equipment, a wet scrubbing tower is placed at the front end of the catalyst bed to remove particles or caustic gases and provide sufficient hydrogen atoms for decomposition of PFCs. Another wet scrubbing tower is placed at the rear end of the catalyst bed for washing HF produced after decomposition of PFCs.
A method for decomposing sulfur-fluorine-containing compound and method thereof is described in EP patent No. 1205234, owned by HITACHI. A gas comprising sulfur-fluorine-containing compound, such as C2F6, CF4, CHF3, SF6 or NF3, is led into a reactor and oxygen and water are then led to the reactor to contact with sulfur-fluorine-containing compound for decomposition. The method, however, requires a reaction temperature in the reactor of up to 650° C.
With expansion of the photoelectricity manufacturing industry and semiconductor manufacturing industry, and reduction in PFCs, requirement of catalytic apparatus for treating waste air has increased. Thus, a decomposition method having effective decomposition of PFCs and reductive transfer ratio of pernicious byproducts is required.
Accordingly, the invention provides a method for decomposing a gas comprising sulfur-fluorine-containing compound in low temperature which is oxygen-free and has a two steps catalyst process for decomposition. The method comprises: contacting a sulfur-fluorine-containing compound with a first catalyst; decomposing the sulfur-fluorine-containing compound to produce a first decomposition; and contacting the first decomposition with a second catalyst to decompose and produce a second decomposition capable of water-solubility. By using the method, sulfur-fluorine-containing compound can be decomposed into the compound capable of high water-solubility, such as SO3 and HF, at low temperature of about 500° C. to 800° C., preferably 580° C. Moreover, sulfur-fluorine-containing compound can be decomposed without oxygen. Because of the resulting compounds water-solubility, they can be removed by washing. For the method, destruction and removal efficiency (DRE) to sulfur-fluorine-containing compound is greater than 99.9% and transfer ratio of the compound incapable of water-solubility can be less than 0.1 mol %.
Also, the invention provides an apparatus for decomposing sulfur-fluorine-containing compound. The apparatus comprises: a first reactor having a first inlet for providing a sulfur-fluorine-containing compound for contacting with a first catalyst therein to decompose and produce a first decomposition and a first outlet for leading the first decomposition out of the first reactor; and a second reactor having a second inlet for providing the first decomposition for contacting with a second catalyst therein to decompose and produce a second decomposition and a second outlet for leading the second decomposition out of the second reactor. In the apparatus, the first outlet connects to the second inlet to lead the first decomposition into the second reactor.
Sulfur-fluorine-containing compound can be decomposed into the compound capable of high water-solubility, such as HF or SO3, at low temperature of 500° C. to 800° C., preferably 580° C., and under an oxygen-free environment, by the apparatus. Because the resulting compound is capable of water-solubility, compounds can be removed by washing. Moreover, transfer ratio of compound incapable of water-solubility can be less than 0.1 mol % and DRE to sulfur-fluorine-containing compound is more than 99.9%.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more completely understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
a-4c are IR analysis charts of the residual sulfur-fluorine-containing compound.
The following description is of the embodiments for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
Preparation of a First Catalyst
Then, Al2O3 serving as the first carrier was immersed in an immersion solution consisting of a first metal slat aqueous solution. In one embodiment, the slat in the first metal slat aqueous solution may be oxalate, nitride or sulfate, preferably nitride. The metal in the first metal salt aqueous solution may be tungsten (W), nickel (Ni), zinc (Zn) or cerium (Ce), preferably Zn. It is appreciated that the amount of Al2O3 relates to that of the metal in the immersion (concentration). In one embodiment where zinc nitride (Zn(NO3)2) solution served as the immersion solution, the molar ratio of Zn to the sum of Zn and Al was about 5 mol % to 20 mol %, preferably 10 mol %.
In an exemplary embodiment, 15 g of Al2O3 was immersed in 0.1 L of 10 mol % zinc nitride solution at room temperature (25° C.), under low pressure (<1 atm), for 3 hrs to 12 hrs to absorb active component such as Zn on the first carrier such as Al2O3. Thus, the first catalyst, such as a monometallic catalyst, was prepared. In the case, the monometallic catalyst was Zn-catalyst. It is understood that the monometallic catalyst may be W-catalyst, Ni-catalyst or Ce-catalyst while the first metal slat aqueous solution comprising W, Ni or Ce, is used.
Referring to
Next, the first catalyst was calcined at a temperature of about 650° C. to 800° C. for 4.5 hrs to 5.5 hrs. Preferably, the first catalyst was calcined at about 800° C. for 5 hrs to enhance hardness and obtain appropriate active thereof.
Preparation of a Second Catalyst
Referring to
In an exemplary embodiment, 15 g of Al2O3 was immersed in 0.1 L of the immersion solution, consisting of 5 mol % copper nitride and 5 mol % cerium nitride, at room temperature (25° C.), under low pressure (<1 atm) for 3 hrs to 12 hrs to absorb active components such as Cu and Ce on the second carrier such as Al2O3. Thus, the second catalyst, such as a bimetallic catalyst, was obtained. In the case, the bimetallic catalyst was Cu—Ce-catalyst. It is understood that Cu or Ce in bimetallic catalyst may be replace of Mn or Zn thereof while the second metal slat aqueous solution comprising Mn or Zn, is used.
Referring to
Next, the second catalyst was calcined at a temperature of about 650° C. to 800° C. for 4.5 hrs to 5.5 hrs. Preferably, the second catalyst was calcined at a temperature about 800° C. for 5 hrs to enhance hardness and obtain appropriate active thereof.
Note that aluminum oxide does not only serve as the carrier for the first catalyst and the second catalyst, but also a catalyst itself to increase decomposition efficiency of the sulfur-fluorine-containing compound.
Method for Decomposing Sulfur-Fluorine-Containing Compound
Before sulfur-fluorine-containing compound is provided, an inert gas such as nitrogen (N2) or helium (He) is provided through an inert gas supply 4 to detect gas leakage. Moreover, the inert gas may also be utilized to dilute and maintain concentration of the sulfur-fluorine-containing compound.
After gas leakage has been detected, the inert gas supply 4 is closed and the sulfur-fluorine-containing supply 2 is opened to provide a gas consisting of 10000 ppm SF6 for the apparatus 1. The SF6 gas is led to the apparatus 1 via a valve 5 connected to the inert gas supply 4 to the sulfur-fluorine-containing supply 2 to control gas into the apparatus 1.
After passing the valve 5, the SF6 gas is led to wetting equipment 8 via a third inlet 84 to add moisture into the SF6 gas. Moreover, before wetting, the SF6 gas flow is controlled through a flow controller 6.
The wetting equipment 8 comprises an injector 81, a vaporizer 82 and an injective hole 83, in which the injector 81 connects to and leads external water to the vaporizer 82 via the injective hole 83. Water is vaporized through the vaporizer 82 at a temperature of about 150° C. and then is added into the SF6 gas with vapor. Because water is in vapor state, the relatively huge amount of moisture is mixed with the SF6 gas. Note that the led water flow relates to concentration of the SF6 gas, for example, volume ratio of vapor to the SF6 gas is of about 30 to 120.
While SF6 gas passes through the third inlet 84 into the wetting equipment 8, the SF6 gas is wet and then passes through a third outlet 85 to obtain the SF6 gas with moisture.
After wetting, the SF6 gas is then led to a first reactor 10 where a first catalyst 12 is disposed to contact with the SF6 gas via a first inlet 13, decompose the SF6 gas and produce a first decomposition such as SO2F2, HF and SO3. Moreover, a heater 11 such as heating coil surrounds the first reactor 10 for heating and a thermocouple 9 is utilized to detect and control temperature of the first reactor 10. Preferably, the first catalyst 12 is a monometallic catalyst such as a Zn-catalyst. W-, Ni- or Ce-catalyst, however, may also be possible.
The first reactor 10 is heated by the heater 11 up to a reaction temperature of about 500° C. to 800° C., preferably 580° C., for 10 mins. While the reaction temperature is stable, the SF6 gas is led from the first inlet 13 to the first reactor 10 to contact with the first catalyst 12 for producing the first decomposition. The first decomposition is then led out of the first reactor 10 via a first outlet 14. Note that the first catalyst 12 is piled up and disposed in the first reactor 10.
The first decomposition is led from the first outlet 14 to a second reactor 20 via a second inlet 23. A second catalyst 22 is disposed in the second reactor 20 and is in contact with the first decomposition to decompose the first decomposition and produce a second decomposition which comprises SO3 and HF. Moreover, the second reactor 20 comprises a heater 21 such as heating coil surrounding the second reactor 20 for heating and a thermocouple 9 for detecting and controlling reaction temperature of the second reactor 20. Preferably, the second catalyst 22 is a bimetallic catalyst, for example a Cu—Ce-catalyst. Mn or Zn may also be in place of Cu or Ce.
Note that the first decomposition may be directly in contact with the second catalyst 22 in the first reactor 10 to decompose and obtain the second decomposition rather than being led out of the first reactor 10. The second decomposition is then led to a chamber 30 via the first outlet 14 and the resulting compounds, namely sulfur- or fluorine-containing compound decomposed in the second decomposition, are removed by washing. That is, sulfur-fluorine-containing compound may be decomposed in a single reactor such as the first reactor where the first catalyst 12 and the second catalyst 22 are disposed and is separately in contact with sulfur-fluorine-containing compound to produce the second decomposition. Then, the second decomposition comprising SO3 and HF is removed by washing.
Moreover, before the first decomposition is led from the second outlet 23 to the second reactor 20, the first decomposition is optionally led to a wetting equipment (not shown) to add moisture to the first decomposition. Through the wetting step, the first decomposition is not only wet, but compounds capable of water-solubility such as HF and SO3 are also removed from the first decomposition. Furthermore, ratio of compound incapable of water-solubility in the first decomposition, such as SO2F2, is increased to increase decomposition efficiency of the sulfur-fluorine-containing compound.
The second reactor 20 is heated up by the heater 21 to a reaction temperature of about 500° C. to 800° C., preferably 580° C., for 10 mins. While the reaction temperature is stable, the first decomposition is led to the second reactor 20 via the second inlet 23 to contact with the second catalyst 22, and decompose and produce the second decomposition which is then led out of the second reactor 20 via the second outlet 24. The second catalyst 22 is piled up and disposed in the second reactor 20 with decomposition efficiency to the first decomposition of 99.9%.
The second decomposition is then led to the camber 30, such as a water trough, a froth trough, or a laundering room, via the second outlet 24. Because the resulting compounds in the second decomposition are capable of water-solubility, such as HF and SO3, they can be removed by washing.
a and 4b are IR analysis charts of residual SF6 and SO2F2 after treatment of the decomposition apparatus according to the invention, in which abscissa axis is time and ordinate axis is residual concentration of SF6 and SO2F2. In
A gas containing 12161 ppm of SF6 was provided through the sulfur-fluorine-containing compound supply 2 and ratios of the SF6 gas flow to volumes of the first catalyst 12 and the second catalyst 22 were about 100 h−1 (gas hour space velocity; GHSV). The SF6 gas was wet by the wetting equipment 8, in which water was vaporized to be added into the SF6 gas and ratio of vapor volume to the SF6 flow was about 30. The wet SF6 gas was led from the first inlet 13 to the first reactor 10 and was then decomposed into the first decomposition by the first catalyst 12. The first decomposition was led out of the first reactor 10 to the second reactor 20 via the second inlet 23 and was in contact with the second catalyst 22 to decompose and produce the second decomposition comprising the resulting compound such as SO3, HF and SO2F2. Reaction temperatures in the first reactor 10 and the second reactor 20 were both at a temperature of about 680° C. After decomposition, DRE to the SF6 gas was about 99.9% and transfer ratio of the residual SO2F2 to SF6 was lower than 0.1 mol %. That is, sulfur-fluorine-containing compound was almost completely decomposed into the resulting compounds capable of water-solubility, such as SO3 or HF. Thus, the second decomposition was removed by water.
A gas containing 11719 ppm of SF6 was provided through the sulfur-fluorine-containing compound supply 2, in which the GHSVs were the same as example 1. The SF6 gas was wet by the wetting equipment 8 and ratio of the added vapor volume to the SF6 flow was about 50. The wet SF6 gas was led from first inlet 13 to the first reactor 10 to decompose and produce the first decomposition. The first decomposition was then led out of the first reactor 10 to the second reactor 20 via the second inlet 23 and was in contact with the second catalyst 22 to decompose and produce the second decomposition. Reaction temperatures of the first reactor 10 and the second reactor 20 were at a temperature of about 580° C. DRE to the SF6 gas in example 2 was about 99.9% and transfer ratio of the residual SO2F2 to SF6 was less than 0.1 mol %. Accordingly, the SF6 gas was completely decomposed into the resulting compound capable of water-solubility through the decomposition apparatus 1. The resulting compound such as SO3 and HF in the second decomposition was removed by water.
A gas containing 1073 ppm of SF6 was provided through the sulfur-fluorine-containing compound supply 2, in which the GHSVs were 1216 h−1. The SF6 gas was then wet and ratio of the added vapor to the SF6 gas flow was 120. The wet SF6 gas was led from the first inlet 13 to the first reactor 10 and was decomposed by the first catalyst to produce the first decomposition. Then, the first decomposition was led out of the first reactor 10 to the second reactor 20 via the second inlet 23 and was in contact with the second catalyst 22 to decompose and produce the second decomposition which comprised SO3, HF and SO2F2. Reaction temperatures in the first reactor 10 and the second reactor 20 were at a temperature of about 780° C. DRE to the SF6 gas was about 99.9% and transfer ratio of the residual SO2F2 to SF6 was less than 1.6 mol %. That is, the SF6 gas was completely decomposed into compounds capable of water-solubility through the decomposition apparatus according to the invention. Thus, the sulfur- or fluorine-containing compound in the second decomposition was removed by water.
A gas containing 1007 ppm of SF6 was provided through the sulfur-fluorine-containing compound supply 2, in which both GHSVs were 2160 h−1. The SF6 gas was wet by the wetting equipment 8 in vapor and ratio of the added vapor volume to the SF6 gas flow was about 75. The wet SF6 gas was led from the first inlet 13 to the first reactor 10 and was decomposed to produce the first decomposition. The first decomposition was then led out of the first reactor 10 to the second reactor 20 via the second inlet 23 and was in contact with the second catalyst 22 to decompose and produce the second decomposition which comprised SO3, HF and SO2F2. Reaction temperatures in the first reactor 10 and the second reactor 20 were at a temperature of about 780° C. Moreover, DRE to the SF6 gas in the example 4 was about 97.6% and transfer ratio of the residual SO2F2 to the SF6 gas was less than 3.5 mol %. That is, sulfur-fluorine-containing compound was almost completely decomposed into the resulting compounds capable of water-solubility by using the decomposition apparatus according to the invention. Thus, the resulting compounds in the second decomposition were removed by washing.
A gas containing 237 ppm of SF6 was provided through the sulfur-fluorine-containing compound supply 2, in which the GHSVs were 916 h−1. The SF6 gas was wet by the wetting equipment 8, ratio of the added vapor volume to the SF6 gas flow was about 75. The wet SF6 gas was led to the first reactor 10 via the first inlet 13 and decomposed to produce the first decomposition. The first decomposition was then led out of the first reactor 10 to the second reactor 20 via the second inlet 23 and was in contact with the second catalyst 22 to decompose and produce the second decomposition comprising SO3, HF and SO2F2. DRE to the SF6 gas was about 99.9% and transfer ratio of the residual SO2F2 to SF6 was less than 7.1 mol %. That is, sulfur-fluorine-containing compound was almost completely decomposed into the resulting compound capable of water-solubility through the decomposition apparatus according to the invention. Accordingly, the resulting compound in the second decomposition was removed by washing.
Although the residual SO2F2 existed after decomposition by using the decomposition apparatus according to the invention, the resulting concentration of residual SO2F2 was less than low detection limitation (LDL) and transfer ratio, meaning SF6 transferred into SO2F2, were almost less than 0.1 mol %. Thus, the overall SF6 was almost completely decomposed into the compound capable of water-solubility, such as HF or SO3. Accordingly, the decomposition apparatus for sulfur-fluorine-containing compound according to the invention had high decomposition efficiency and the resulting decomposition was almost completely dissolved in water, to be removed by washing.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
