Gas-Phase Oxidative Dehydrogenation of Ethane via NO/O2 Mixtures

A kinetic and thermodynamic tubular reactor model for the oxidative dehydrogenation of ethane using homogeneous NO/O2 mixtures is developed to investigate the factors controlling the ethylene selectivity. Two primary mechanisms for ethane oxidative dehydrogenation are identified from the model: the reaction between NO and NO2 to form OH radicals drives ethane dehydrogenation at large NO volume fractions (≥5%), and H2O2 homolysis drives the reaction at low NO volume fractions (2H6 conversion; a near three-fold increase in conversion was achieved with a final 53% ethane conversion and a 90% ethylene selectivity. CO, CO2, H2O, He, and N2 were explored to control the selectivity and reaction kinetics but had little impact. Under optimal conditions, most initial NO radicals were converted into NO2; replacement of NO with NO2 was investigated. NO2/O2 mixtures achieved a maximum of 38% ethane conversion at a 90% ethylene selectivity with a 5% NO2 conversion.本研究构建了一套用于均相一氧化氮（NO）/氧气（O2）混合体系下乙烷氧化脱氢反应的动力学与热力学管式反应器模型，以探究调控乙烯选择性的关键影响因素。通过该模型，本研究识别出乙烷氧化脱氢的两类主要反应机制：当NO体积分数≥5%时，NO与二氧化氮（NO2）反应生成羟基自由基（OH radicals），该过程主导高NO体积分数下的乙烷脱氢反应；而当NO体积分数较低时，过氧化氢（H2O2）均裂过程主导反应进行。体系乙烷转化率提升近三倍，最终可实现53%的乙烷转化率与90%的乙烯选择性。研究考察了一氧化碳（CO）、二氧化碳（CO2）、水（H2O）、氦气（He）与氮气（N2）对反应选择性及反应动力学的调控作用，但发现其影响甚微。在最优反应条件下，初始投入的绝大多数NO转化为了NO2；本研究同时探究了以NO2替代NO的反应体系：NO2/O2混合体系可在90%的乙烯选择性下实现最高38%的乙烷转化率，且此时NO2转化率为5%。