Reaction Mechanisms of Acrylonitrile Decomposition in an RF Plasma System

• Main Authors: Ying-Da Lee, 李盈達
• Other Authors: Wen-Jhy Lee
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/16055088027193651441

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 91 === Application of radio-frequency (RF) plasma for the decomposition of Acrylonitrile (ACN) is demonstrated. For these three plasma systems ( ACN/Ar, ACN/O2/Ar and ACN/H2/Ar ), experiments were conducted to elucidate the effects of operational parameters on ACN decomposition fraction (ηACN) and products formation fraction. The operational parameters including input power wattage, O2/ACN ratio, H2/ACN ratio, and ACN feeding concentration were investigated. Furthermore, the possible reaction pathways of decomposing ACN in an RF plasma system were built-up and discussed. The results showed that a ηACN be increased as increase a input power wattage or a O2/ACN ratio, respectly, but a ηACN be decreased with increasing a H2/ACN ratio and a ACN feeding concentration, respectly. For the effect on ηACN, the H2/ACN ratio is the most dominant operational parameter. In addition, there are more significant reactive radicals( O‧and OH‧) in ACN/O2/Ar system than that in ACN/Ar or in ACN/H2/Ar system. Therefore, the ηACN in ACN/O2/Ar system is the highest. In addition, there are a great amount of highly excited Ar* and electrons in ACN/Ar system. Hence, the reactions are favorable for the decomposition of the ACN ( three carbons ) to lower molecular weight hydrocarbon ( one or two carbons ) , such as CH4 and C2H2. In ACN /O2/Ar system, existing more amount of highly reactive O and OH radicals reacted with ACN itself, C2H2 and CH4 and converted into oxygen contained species, such as HCHO, CH3CHO, CH3OH, CO and CO2. Furthermore, as input power wattage increases, CH3OH and HCHO would be decomposed as CO and CO2. However, in ACN/H2/Ar system, adding hydrogen make Ar concentration decrease 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 ηACN but also decreased the formation of lower molecular weight hydrocarbon decrease. In ACN/H2/Ar plasma system, increase the inlet H2/ACN ratio will promote the formation of hydrocarbons (i.e. C2H2 and C2H6) in the effluent. The optimum condition for the decomposition of Acrylonitrile (ACN) by using RF plasma system was suggested as follows: O2/ACN ratio was 2.5, input power wattage was 30 watts, operational pressure was controlled at 10 Torr, total flow gas rate was 100 sccm, and ACN feeding concentration was 5 %; at this condition the ηACN is up to 99.86 %; and the amounts of both soot and PAHs formation were the lowest; This condition will also provide the most economical use of energy. In ACN/O2/Ar environment, the sensitivity analysis indicated that the signficance of sensitivity for the ACN decomposition fraction, the CO formation fraction, the CO2 formation fraction, and the CH3OH formation fraction were：CACN > W > RO2/ACN；RO2/ACN > W > CACN；W > CACN > RO2/ACN；W > RO2/ACN > CACN, respectively. In ACN/H2/Ar environment, the sensitivity analysis indicated that the signficance of sensitivity for the ACN decomposition fraction, the C2H2 formation fraction, and the C2H6 formation fraction were：RH2/ACN > W > CACN；RH2/ACN > CACN > W；W > RH2/ACN > CACN, respectively.