Patent Application
20240316536
The present application claims priority to Korean Patent Application No. 10-2023-0038550, filed Mar. 24, 2023, the entire contents of which is incorporated herein for all purposes by this reference.
The present disclosure relates to the decomposition of perfluorocompounds (PFCs) and, more specifically, to a catalyst for decomposing perfluorocompounds and a method of preparing the same.
PFCs (CF4, C4F8, CHF3, CxHyFz) generated in a semiconductor process act as serious greenhouse gases when released into the atmosphere.
A hydrolysis method using a catalyst has been used to treat PFCs contained in waste gases discharged from a semiconductor process. The hydrolysis method is known as a process in which the PFC decomposition reaction proceeds at a high temperature in a range of 700° C. to 900° C. using an alumina catalyst and water vapor. However, in this high-temperature decomposition reaction, the properties of a carrier of the alumina catalyst are converted and the specific surface area of the carrier is reduced, leading to a decrease in active points and finally to a decrease in durability.
CF4+2H2O→CO2+4HF(ΔG°=−150 kJ/mol)
Therefore, there is a need to improve the durability of a catalyst for decomposing PFCs. In addition, there is a demand in the industry for a catalyst for decomposing PFCs to have an improved conversion rate and improved durability, compared to conventional catalysts for decomposing PFCs. Furthermore, a catalyst for decomposing PFCs with improved activity and durability, and at the same time with optimized shape, size, and strength is needed considering formulation in a PFC decomposition system.
A solution to the problem of the present disclosure is to provide a catalyst for decomposing PFCs with high reaction activity and durability by combining aluminum oxide with zinc (Zn) as an active component for performance improvement and tungsten (W) as an auxiliary component to prepare a W—Zn—Al catalyst.
Without limitation, the precursor of zinc (Zn) applied in the catalyst for decomposing PFCs may be any one selected from zinc nitrate (Zn(NO3)2), zincsulfatehydrate (ZnSO4H2O), and zincacetate ((CH3CO2)2Zn). The precursors of tungsten (W) may be any one selected from ammonium metatungstate ((NH4)6H2W12O4O·3H2O), ammonium paratungstate ((NH4)10H2W12O42·4H2O), sodium tungstate (Na2WO4 2H2O), tungsten oxide (WO3), and tungsten chloride (WCl6), or mixtures thereof. Aluminum oxide may be any one selected from gamma alumina (γ-Al2O3), aluminum trihydroxide, boehmite, and pseudo-boehmite.
In addition, the W—Zn—Al catalyst is provided as a catalyst for decomposing PFCs with a weight ratio of Al, Zn, and W at 100:30 to 100:1 to 11.
Another solution to the problem is to provide a catalyst for decomposing PFCs, the catalyst being prepared using an impregnation method, a co-precipitation method, or a physical mixing method as a method of preparing the catalyst.
Yet another solution to the problem is to provide a method for preparing a molded body of a catalyst for decomposing PFCs. The method includes mixing aluminum oxide with zinc (Zn) as an active component for performance improvement and tungsten (W) as an auxiliary component and molding the mixture into one or more of the following shapes: particles, spheres, pellets, and rings.
Yet another solution to the problem is to provide a method for decomposing PFCs, and the method includes introducing water vapor from the outside into the reactor to perform a hydrolysis reaction in a catalyst reactor filled with a molded body of a catalyst for decomposing PFCs.
A catalyst for decomposing PFCs according to the present disclosure has an effect of having durability against fluorine generated by decomposition of PFCs, as well as a synergistic effect of improving reaction activity.
Another effect is that the catalyst for decomposing PFCs of the present disclosure decomposes perfluorocompounds at a lower temperature than conventional catalysts for decomposing PFCs, making it easier to reduce operating costs and ensure the durability of a system during continuous operation, as well as making it possible to miniaturize the system due to the high reaction activity of the catalyst.
Perfluorocompounds may include carbon-containing PFCs, nitrogen-containing PFCs, and sulfur-containing PFCs which all contain two or more fluorine (F). Carbon-containing PFCs may include cyclic aliphatic and aromatic perfluorocarbons, as well as saturated and unsaturated aliphatic components such as CF4, CHF3, CH2F2, C2F4, C2F6, C3F6, C3F8, C4F8, and C4F10. Nitrogen-containing PFCs may typically include NF3, and sulfur-containing PFCs may include SF4 and SF6. Furthermore, PFCs may even include compounds that can be decomposed by a catalyst to form gaseous products such as HF.
An acid gas referred to herein is a gas that becomes acidic when in contact with water, and non-limiting examples thereof include halogen, hydrogen halide, nitrogen oxides (NOx), sulfur oxides (SOx), acetic acid, sublimated mercury, hydrogen sulfide, and carbon dioxide. The acid gas not only causes corrosion but can also reduce the activity of the catalyst.
A hydrolysis reaction that occurs between PFCs and moisture is an endothermic reaction. Accordingly, the hydrolysis reaction can induce a spontaneous reaction, which means the higher the temperature, the easier it is to decompose PFCs. Thus, PFC decomposition progresses faster. However, the thermal stability of the catalyst decreases due to high temperature. In other words, the operating conditions at a temperature in a range of 700° C. to 900° C. are high-temperature conditions for the catalyst to maintain activity for a long time without physical or chemical changes, so securing the durability of the catalyst is the biggest problem. In particular, there is a need to develop a catalyst that continues to be durable in a reaction atmosphere at a temperature in a range of 700° C. to 900° C. where both HF and water vapor generated as by-products exist.
The present disclosure provides a catalyst for decomposing PFCs that has excellent decomposition activity and durability for PFCs used in a semiconductor manufacturing process and can maintain catalytic activity for a long time. The present disclosure relates to a catalyst for decomposing PFCs that has an excellent performance in decomposing perfluorocompounds even at low temperatures, making it easy to reduce operating costs and ensure system durability during continuous operation.
Various embodiments are presented to achieve the objectives of the present disclosure.
A first embodiment of the present disclosure relates to a catalyst for decomposing PFCs. In the catalyst, zinc as an active component for performance improvement and tungsten (W) as an auxiliary component are added to an alumina precursor selected from at least one of gamma alumina, aluminum trihydroxide, boehmite, and pseudo-boehmite. The catalyst has a weight ratio of Al, Zn, and W at 100:30 to 100:1 to 11.
A second embodiment of the present disclosure presents a method in which an aqueous solution of a zinc precursor and tungsten (W) precursor dissolved in distilled water is mixed with at least one alumina precursor selected from gamma alumina, aluminum trihydroxide, boehmite, and pseudo-boehmite, followed by drying and mixing to prepare a Zn—W—Al catalyst.
The Zn—W—Al catalyst has a weight ratio of Al, Zn, and W at 100:30 to 100:1 to 11.
A third embodiment of the present disclosure provides a method for treating perfluorocompounds, including decomposing PFCs in a perfluorocompound-containing gas using the catalyst for decomposing PFCs of the first embodiment.
A fourth embodiment of the present disclosure relates to a semiconductor manufacturing process including decomposing a perfluorinated compound in a perfluorocompound-containing gas using the catalyst for decomposing PFCs of the first embodiment.
The precursors of zinc (Zn) in the catalyst for decomposing PFCs may be any one selected from zincnitrate (Zn(NO3)2), zincsulfatehydrate (ZnSO4H2O), and zincacetate (CH3CO2)2Zn). The precursors of tungsten (W) may be any one selected from ammonium metatungstate ((NH4)6H2W12O40·3H2O), ammonium paratungstate ((NH4)10H2W12O42·4H2O), sodium tungstate (Na2WO4·2H2O), tungsten oxide (WO3), and tungsten chloride (WCl6), or mixtures thereof. Alumina may be any one selected from alpha alumina, gamma alumina (γ-Al2O3), aluminum trihydroxide, boehmite, and pseudo-boehmite.
One example of a catalyst for decomposing PFCs is to prepare a catalyst for decomposition by combining alumina, zinc, and tungsten to the weight ratio of Al, Zn, and W at 100:30 to 100:1 to 11 after impregnating gamma alumina with zinc and tungsten precursors sequentially or simultaneously. The method for preparing the catalyst for decomposing PFCs is any one selected from an impregnation method, a co-precipitation method, and a physical mixing method.
In the catalyst for decomposing PFCs, γ-alumina is preferred as a support or carrier working with an active component for performance improvement and auxiliary component. In addition, when the transition of γ-alumina to the c phase can be suppressed, there is a synergistic effect of maintaining a high PFC decomposition ability of the catalyst for a long time.
When zinc (Zn) is added as an active metal for performance improvement, desirable results can be given in terms of improvement in conversion rate during the PFC catalytic decomposition reaction. Additionally, durability is greatly improved when tungsten (W) is impregnated as a co-catalyst or auxiliary component.
The catalyst for decomposing PFCs prepared is dried at a temperature in a range of 150° C. or higher and can be fired in an air atmosphere at a temperature in a range of 600° C. to 900° C. The final shape of the catalyst may be a granular shape such as a sphere, pellet, or ring, or may be molded into a honeycomb.
The catalyst for decomposing PFCs exhibits excellent decomposition effect and durability in decomposing and removing perfluorocompounds containing halogen acid gases. Therefore, the catalyst can be used in processes containing halogen acid gases, especially to decompose perfluorocompounds used in the semiconductor manufacturing industry.
The temperature during the PFC catalytic decomposition reaction is in a range of 600° C. to 800° C., preferably 650° C. to 750° C.
To perform a hydrolysis reaction in the catalytic reactor, water may be introduced into the reactor from the outside. Water may be supplied through a separately provided source outside the reactor, and may be supplied in the form of water vapor before flowing into the reactor. Preferably, pure water is used as the water supplied into the reactor, and the supply amount can be adjusted considering the hydrolysis reaction rate.
Hereinafter, the catalyst will be prepared in detail and the effects of the prepared catalyst will be described.
A solution of 63 g of zincnitrate in distilled water was mixed with 83 g of aluminum oxide, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A solution of 107 g of zincnitrate in distilled water was mixed with 71 g of aluminum oxide, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A solution of 162 g of zincnitrate in distilled water was mixed with 56 g of aluminum oxide, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A solution of 5.5 g of ammoniummetatungstate dissolved in distilled water was mixed with 95 g of the catalyst prepared in Example 2, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A Co—Zn—Al catalyst was prepared in the same manner as in Example 4, except that 20 g of cobaltnitrate was dissolved in distilled water instead of ammoniummetatungstate.
A Ni—Zn—Al catalyst was prepared in the same manner as in Example 4, except that 20 g of nickelnitrate was dissolved in distilled water instead of ammoniummetatungstate.
A Zr—Zn—Al catalyst was prepared in the same manner as in Example 4, except that 17 g of zirconiumacetate was dissolved in distilled water instead of ammoniummetatungstate.
A Mo—Zn—Al catalyst was prepared in the same manner as in Example 4, except that 6 g of ammoniummolybdate was dissolved in distilled water instead of ammoniummetatungstate.
A solution of 1.1 g of ammoniummetatungstate dissolved in distilled water was mixed with 99 g of the catalyst prepared in Example 2, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A solution of 3.3 g of ammoniummetatungstate dissolved in distilled water was mixed with 97 g of the catalyst prepared in Example 2, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
A solution of 102 g of zincnitrate and 3.3 g of ammoniummetatungstate dissolved in distilled water was mixed with 69 g of aluminum oxide, dried at a temperature of 150° C. for 3 hours, and fired at a temperature of 750° C. for 10 hours.
To compare the removal efficiency of perfluorocompounds (CF4) by the catalysts prepared in the Examples and Comparative Examples, the performance was evaluated under the following experimental conditions.
18 ml of each of the catalysts prepared in Examples and Comparative Examples were taken and filled in a 1-inch Inconel reaction tube. The reaction temperature was adjusted to 700° C. using an external heater. 2000 ppm of tetrafluoromethane (CF4) was decomposed by each of the catalyst samples at a space velocity of 17,000 h−1 and in an atmosphere of 6% oxygen (O2), and 10% water (H2O). The tetrafluoromethane removal efficiency was calculated using Equation 1 below, and the reactant was analyzed using FT-IR.
CF4 removal efficiency(%)═(CF4 concentration at reactor inlet−CF4 concentration at reactor outlet)/CF4 concentration at reactor inlet*100 <Equation 1>
Accelerated evaluation (in an aged state of the catalysts) was evaluated under the same experimental conditions after treating the prepared catalysts in a hydrofluoric acid (HF) solution for 3 hours followed by drying and re-firing.
The evaluation results are summarized in Tables 2 and 3.
Hereinafter, the design process and evaluation results for selecting the active components for performance improvement and auxiliary components according to the present disclosure will be described with reference to the tables and drawings below.
Referring to the described examples and experiment examples, the aluminum oxide catalyst for decomposing PFCs and a method of preparing the same according to the examples of the present disclosure can improve decomposition efficiency and durability for PFCs, and although the present disclosure has been described with reference to preferred examples, it will be understood that those skilled in the art can make various modifications and changes to the present disclosure without departing from the spirit and scope of the present disclosure disclosed in the claims below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0038550 | Mar 2023 | KR | national |
