Chuh-Yung Chen

CONVERTING METHANE BY USING AN RF PLASMA REACTOR

A radio-frequency (RF) plasma system was used to convert methane gas. The reactants and final products were analyzed by using an FTIR (Fourier transform infrared spectrometer). The effects of plasma operational parameters, including feeding concentration (C) of CH4, operational pressure (P) in the RF plasma reactor, total gas flow rate (Q) and input power wattage (W) for CH4decomposition were evaluated. The results showed that the CH4decomposition fraction increases with increasing power input, decreasing operational pressure in the RF plasma reactor, decreasing CH4feeding concentration, and decreasing total gas flow rate. In addition, mathematical models based on the obtained experimental data were developed and tested by means of sensitivity analysis.

Decomposition of SF6 in an RF Plasma Environment

Abstract Sulfur hexafluoride (SF6)-contained gas is a common pollutant emitted during the etching process used in the semiconductor industry. This study demonstrated the application of radio-frequency (RF) plasma in the decomposition of SF6. The decomposition fraction of SF6 [ηSF6 (Cin–Cout)/Cin x 100%] and the mole fraction profile of the products were investigated as functions of input power and feed O2/SF6 ratio in an SiO2 reactor. The species detected in both SF6/Ar and SF6/O2/Ar RF plasmas were SiF4, SO2, F2, SO2F2, SOF2, SOF4, S2F10, S2OF10, S2O2F10, and SF4. The results revealed that at 40 W, ηSF6 exceeded 99%, and the reaction products were almost all converted into stable compounds such as SiF4, SO2, and F2 with or without the addition of oxygen. Sulfur oxyfluorides such as SO2F2, SOF2, SOF4, S2OF10, and S2O2F10 were produced only below 40 W. The results of this work can be used to design a plasma/chemical system for online use in a series of a manufacturing process to treat SF6-containing exhaust gases.

Phosgene formation from the decomposition of 1,1-C2H2Cl2 contained gas in an RF plasma reactor

Abstract In this study, a radio-frequency (RF) plasma system was used to decompose the 1,1-dichloroethylene (DCE) contained gas. The reactants and final products were analyzed by using an FTIR (Fourier Transform Infrared Spectroscopy). The effect of plasma operational-parameters for DCE decomposition was evaluated. In addition, the possible reaction pathways for DCE decomposition and phosgene (COCl2) formation were built up and discussed. Both DCE decomposition efficiency and the fraction of total carbon mass converted into CO2 and CO were decreased by the increasing DCE feeding concentration. The DCE decomposition efficiency at varied equivalence ratios, o (stoichiometric O2/actual O2), was controlled by both oxidation and energy transfer efficiency. At lower equivalence ratios having an excess of oxygen, a larger amount of COCl2 was formed due to a higher oxygen-feeding concentration. Higher input power wattage can increase both the DCE decomposition efficiency and the fraction of total-carbon mass converted into CO2 and CO, resulting in the reduction of the COCl2 effluent concentration. However, more soot was found in the plasma reactor when the input power wattage was higher than 60 W. Because high concentrations of C2Cl4, CHCl3 and CCl4 were detected and because copper inner-electrode might act as catalyst, the most possible pathways for the COCl2 formation were C2Cl4 + OH, C2Cl3 + O2, CHCl3 + O, CHCl 2 + O, CCl3 + O and CO + Cl2.

Decomposition of carbon dioxide in the RF plasma environment

Application of radio-frequency (RF) plasma as an alternative technology for the decomposition of carbon dioxide with methane gas is demonstrated. The results of this study revealed that in CO2/CH4/Ar plasma, the best decomposition fraction of carbon dioxide was 60·0%, which occurs around 316°C in the condition designed for 5% feeding concentration of CO2, 5% feeding concentration of CH4, 20 torr operation pressure, 100 sccm total gas flow rate and 90 watts input power wattage. The CH, CH2 and CH3 radicals obtained from the destruction of CH4 could result effectively in high decomposition of CO2 in the plasma reactor. The optimal mathematical models based on the experimental data obtained were also developed and tested by means of sensitivity analysis, which shows that the input power wattage (W) was the most sensitive parameter for the CO2 decomposition.

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH3SCH3, DMS) and methanethiol (CH3SH) in a cold plasma reactor. The DMS and CH3SH were successfully destroyed at room temperature. DMS decomposed less than CH3SH at the same conditions. In oxygen-free condition, CS2 and hydrocarbons were the major products, while SO2 and COx were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS2 than that of CH3SH/Ar plasma. In the CH3SH/O2/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO2 and CO2 than those in the DMS/O2/Ar plasma; and remained only a trace of total hydrocarbons, CH2O, CH3OH, CS2, and OCS. The major differences between the reaction mechanisms of DMS and CH3SH were also proposed and discussed.

Decomposition of methyl chloride by using an RF plasma reactor

Abstract Application of radio-frequency (RF) plasma as an alternative technology for the decomposition of methyl chloride (CH 3 Cl) with oxygen is demonstrated. The results of this study revealed that, in the CH 3 Cl/O 2 /Ar plasma, the decomposition fraction of CH 3 Cl was over 99.99%, which occurred at the condition designed for 3% of CH 3 Cl feeding concentration, 1.0 of equivalence ratio ( φ ), 20 Torr of operation pressure, 100 sccm of total gas flow rate and 100 W of input power wattage. Higher input power wattage can increase both the CH 3 Cl decomposition efficiency and the fraction of total-carbon input converted into [CO 2 +CO], resulting in the reduction of the harmful products (COCl 2 ) effluent concentration. However, more soot was found in the plasma reactor when the input power wattage was higher than 70 W. The species detected in the effluent gas stream included CO, CO 2 , H 2 O, HCl, CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 2 H 3 Cl, C 2 H 5 Cl and COCl 2 . The optimal mathematical models based on obtained experimental data were also developed and tested by means of the sensitivity analysis, which showed that the input power wattage (W) was the most sensitive parameter for both CH 3 Cl decomposition and temperature elevation in the RF plasma reactor.

CH2Cl2 decomposition by using a radio-frequency plasma system

In this study, a radio-frequency plasma system was used to decompose a dichloromethane (CH 2 Cl 2 ) containing gas. Analyses of the reactants and final products were conducted by using Fourier Transform Infrared Spectroscopy. Then, the effects of plasma operation-parameters, including the gas flow rate, the feeding CH 2 Cl 2 concentration, the equivalence ratio Φ (=stoichiometric O 2 needed/actual O 2 used) and the input power wattage, for CH 2 Cl 2 decomposition and for the fraction of total carbon input converted into CO 2 and CO were investigated. Mole fraction profiles for each experimental condition were determined for the reactants (CH 2 Cl 2 and O 2 ) and for CO, CO 2 , H 2 O, HCl, CHCl 3 , CCl 4 , COCl 2 , C 2 HCl 3 and C 2 Cl 4 . In addition, the possible reaction pathways were built up and discussed.

Reaction Mechanisms in Both a CCl2F2/O2/Ar and a CCl2F2/H2/Ar RF Plasma Environment

Decomposition of dichlorodifluoromethane (CCl2F2 or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl2F2decomposition fractions ηCCl2F2 and mole fractionsof detected products in the effluent gas stream of CCl2F2/O2/Ar andCCl2F2/H2/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O2/CCl2F2 or H2/CCl2F2 ratio,operational pressure, and CCl2F2 feeding concentration wereinvestigated. The main carbonaceous product in the CCl2F2/O2/Arplasma system was CO2, while that in the CCl2F2/H2/Ar plasma systemwas CH4 and C2H2. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl2F2 molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO2,CH4, and C2H2 formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl3F, CClF3, CF4, andCCl4. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl2F2.

Decomposition of ethoxyethane in the cold plasma environment

A radio frequency (RF) plasma system was used to decompose the ethoxyethane (EOE) contained gas. The reactants and final products were analyzed by using an FTIR (Fourier Transform Infrared) spectrometer. The effects of plasma operational parameters, including input power wattage (W), equivalence ratios (Φ), feeding concentration (C) of EOE and total gas flow rate (Q) for EOE decomposition were evaluated. In addition, the possible reaction pathways for EOE decomposition and the formation of final products were built up and are discussed in this paper. The mole fraction profiles of C2H5OC2H5, CH3CHO, CH4, C2H6, C2H4, C2H2, CO2 and CO were detected and are also presented in this paper. At lower input power wattages, the creation of glow discharge is strongly dependent on the plasma production index (PPI). When input power wattages are smaller than 30u2009W, the minimum values of PPI to create glow discharge ranged between 18.2 and 19.0. The results of this study revealed that, in the RF plasma reactor, the decomposition fraction of EOE could reach 100% under most operational conditions. n n n n© 2000 Society of Chemical Industry