| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 89 === Application of radio-frequency (RF) plasma for the decomposition of Methyl tert-Butyl Ether (MTBE) is demonstrated. For these three plasma systems （MTBE/Ar, MTBE/O2/Ar and MTBE/H2/Ar）, experiments were conducted to elucidate the effects of operational parameters on MTBE decomposition fraction (ηMTBE) and product formation fractions. The operational parameters including input power wattage, O2/MTBE ratio, H2/MTBE ratio, operational pressure, total gas flow rate and MTBE feeding concentration were investigated. Furthermore, the possible reaction pathways of decomposing MTBE in an RF plasma system were built-up and discussed. The results showed that a ηMTBE be increased as increasing a input power wattage or a O2/MTBE ratio, respectly, but a ηMTBE be decreased with increasing a H2/MTBE ratio, an operational pressure, a total gas flow rate and a MTBE feeding concentration, respectly. For the effect on ηMTBE, the input power wattage is the most dominant operational parameter, while the operational pressure or total gas flow rate acts little effect on ηMTBE. In addition, there are more significant reactive radicals（O · and OH ·）in MTBE/O2/Ar system than that in MTBE/Ar or in MTBE/H2/Ar system. Therefore, the ηMTBE in MTBE/O2/Ar system is the highest.
In addition, there are a great amount of highly excited Ar* and electrons in MTBE/Ar system. Hence, the reactions are favorable for the decomposition of higher molecular weight hydrocarbon（more than four carbons） to lower molecular weight hydrocarbon (one or two carbons), such as CH4, C2H2, C2H4 and CO. In MTBE/O2/Ar system, existing more amount of highly reactive O and OH radicals reacted with iso-C4H10, iso-C4H8, C2H4, C2H2 and CH4 and converted them into oxygen contained species, such as CH3OH, CH2O, CO and CO2. Furthermore, as input power wattage increases, CH3OH and CH2O would be decomposed as CO and CO2. However, in MTBE/H2/Ar system, adding hydrogen makes Ar concentration be decreased relatively. Due that the hydrogen is with high electron affinity, it would absorb electrons and make the number of excited Ar* and electrons decrease in the plasma system. This not only decreased the ηMTBE but also decreased the formation of lower molecular weight hydrocarbon decrease. In the MTBE/H2/Ar plasma system, the main products are iso-C4H8, iso-C4H10, CH3OH and CH2O. The optimum condition for the decomposition of Methyl tert-Butyl Ether (MTBE) by using RF plasma system was suggested as follows: O2/MTBE ratio was 7.5, input power wattage was 50 watts, operational pressure was controlled at 20 Torr, total flow gas rate was 100 sccm, and MTBE feeding concentration was 5%; at this condition the ηMTBE is up to 98.69%; and the amounts of both soot and PAHs formation were the lowest; This condition will also provide the most economical use of energy.
A comprehensive experimental and numerical study has been performed on the detailed MTBE/O2/Ar plasma decomposition kinetics and the sensitivity analysis. The reaction mechanism used in this study consisted of 45 species and 152 elementary reactions. Based on both the numerical results and sensitivity coefficients, the main reactions of MTBE decomposition were the collisions between electrons and oxygen to form O radical. Second, the O radical reacted with MTBE to form t-C4H9OCH2 · and t-C4H8OCH3 ·, then a number of consecutive reactions occurred.
|
|---|
