环己烷液相非催化/催化氧化反应动力学特性比较

Comparison of kinetic behavior of non-catalytic/catalytic liquid-phase oxidation of cyclohexane

分别以不同氧浓度气体及纯氧作为氧源,利用鼓泡塔反应器在1.1MPa、不同温度、不同气体流量条件下比较了环己烷液相非催化氧化和催化氧化反应特性。通过比较分析,讨论了环己烷液相氧化的链式反应机理。理论分析和实验数据表明,环己烷液相催化氧化反应诱导期短,其表观速率与环己烷浓度和氧气浓度都为一级;而非催化氧化反应诱导期长,是由烃直接氧化引发过程控制,只有当过氧化氢积累到一定浓度以后,过氧化物分解产生自由基速率变得显著,反应才表现出自催化反应特征。而在催化剂存在的情况下,环己基过氧化氢分解非常迅速,环己基过氧化氢浓度在整个反应过程中稳定在一个很低的水平,反应由氧化生成酮的链传递反应过程控制。

The kinetic behavior of the liquid-phase oxidation of cyclohexane was investigated in a bubble column under 1.1 MPa at various temperatures,in which gases with O2 concentrations ranging from 5% to 99% were used as oxidants.By comparing the non-catalytic and catalytic oxidation of cyclohexane,the free radical mechanism of the oxidation was discussed in detail.Both the mechanism analysis and experimental data showed that the catalyzed liquid-phase oxidation of cyclohexane was a reaction of first-order with respect to both cyclohexane and oxygen.For the non-catalytic oxidation,an induction period was obvious.During the non-catalytic oxidation of cyclohexane by oxygen,the chain initiating reaction was the rate determining step.Beyond the induction period,the reaction was accelerated and exhibited auto-catalytic behavior due to the release of radicals through the decomposition of cyclohexyl hydroperoxide when its concentration accumulated to a certain degree.On the other hand,in catalytic oxidation the cyclohexyl hydroperoxide decomposed rather quickly,and then accelerated the reaction.And during the reaction,the concentration of cyclohexyl hydroperoxide kept very low and the chain propagation became the rate limiting step.