六氟丙烷热分解性能及机理研究

Thermal Decomposition Properties and Mechanism of Hexafluoropropane

在管式反应器中对六氟丙烷进行热分解,用气相色谱-质谱仪、气相色谱仪和化学滴定法对热分解气体进行分析。结果发现：六氟丙烷在600~800℃热分解时主要发生脱氟化氢（HF）反应,随着反应温度和停留时间的增加,六氟丙烷分解程度提高。根据均裂的化学键类型提出六氟丙烷热分解的5个初级反应路径,通过密度泛函理论DFT-（U）B3LYP/6-31G＊计算六氟丙烷各化学键离解能,发现H转移反应所需活化能最低,C—C键断裂反应次之,分别为282.74和381.88 kJ/mol,表明六氟丙烷热分解过程中最易发生H转移反应脱去HF。在高温热分解气体中还检测到微量CF4、CHF3、CF2CHF等多种产物,分析是由H转移反应产物与C—C键断裂产生的自由基相互结合或者分解再结合形成。

The thermal decomposition properties of hexafluoropropane are studied in a tubular reactor.The decomposed gas is characterized by gas chromatography-mass spectrometry（GC-MS）,gas chromatography（GC） and titration.The results show that the hydrogen fluoride eliminated from hexafluoropropane is the main reaction between 600~800 ℃.As the reaction temperature and residence time increase,the thermal decomposition degrees of the hexafluoropropane become high.Five primary reaction pathways are proposed based on the chemical bond types of the homolytic cleavage.Using the DFT-（U）B3LYP/6-31G＊ method,the bond dissociation energies（BDE） for all kinds of bonds are calculated.It is found that the activation energy of the H-transfer reaction and the C—C bond fission reaction,which are 282.74 and 381.88 kJ/mol respectively,are smaller than the BDEs of other bonds.The result illustrates that the hydrogen fluoride elimination is the most feasible reaction.Minor products including CF4,CHF3,CF2CHF are detected at high temperature.These products originate from the combination directly or after further decomposition between products of H-transfer reaction and radicals of C—C bond fission reaction.