射流冷却下过氧化二叔丁基瞬时热解反应的研究

High-Temperature Flash Pyrolysis of Di-tert-butyl Peroxidee in a Jet-cooled Expansion

采用射流冷却和高温瞬时热解技术研究了过氧化二叔丁基（ＤＴＢＰ）热解产物的质量分布和飞行时间谱。ＤＴＢＰ解离率与热解温度的关系表明，１３００Ｋ时ＤＴＢＰ全部解离。以Ａｒ为载气时，ＤＴＢＰ热解产物ＣＨ＿３ＣＯＣＨ＿３的飞行时间谱上出现双峰，而以Ｈｅ或Ｎ＿２为载气时只出现单峰，表明在射流冷却下可能有部分ＣＨ＿３ＣＯＣＨ＿３分子与Ａｒ生成了范德华分子ＣＨ＿３ＣＯＣＨ＿３·Ａｒｎ·此外，还讨论了射流冷却下ＤＴＢＰ瞬时热解的机理。

The mass distribution and time-of-flight(TOF)spectra for the pyrolytic fragments of di-tert-butyl peroxide (DTBP) seeded in He or Ar carrier gas have been achieved by using time-resolved mass spectrometric and high ternperature flash pyrolysis techniques,The dependence of DTBP conversion yield on the heated SiC tube temperature(Ts) shows that the precursor molecule in the carrier gas starts to decompose obviously at 900 K,and reaches complete decomposition at 1 300 K. Two major fragments CH3COCH3 and CH3·radical are observed.In a pulsed free jet expansion of 4%mole fraction of DTBP/Ar gas mixture,the TOF spectra of pyrolytic fragments measured at Ts=1000 K show that there are two peaks for CH3COCH ion(m/e=58)and its fragment ions,CH3CO+ and CH (m/e=43 and 15).When He or N2is used as a carrier gas,however,only one peak is observed in its TOF spectra. This result implies that a fraction of jet-cooled CH3COCH3(m/e=58) molecules combine with Ar and form the van der Waals molecules CH3COCH3.Arn. Formation of CH3COCH3·Arn is also suggested via the TOF experiments in which acetone is used as a precursor seeded in Ar carrier gas. The proposed mechanism of DTBP flash pyrolysis mainly involves the initial split of the O-O bond of DTBP to generate(CH3)3CO·radical,followed by the decomposition of this radical into CH3COCH3 and CH3·radical,and the recombination or secondary bi-molecular reactions of product radicals are suppressed in the flash pyrolysis of DTBP with a very shot contact time.