对二甲苯氧化反应器非均匀混合模型

Three-region Model for p-Xylene Oxidation Reactor

对二甲苯氧化是一个复杂的气-液-固三相反应过程。今根据实验测取的对二甲苯氧化反应动力学关系与数据,建立了工业氧化反应器的非均匀混合模型,用以考察气、液相的混合状况及其对反应的影响。模型采用三区串联加区间返混的结构,区间返混参数由工业反应器实测轴向温度分布拟合确定。计算表明,釡内液相混合接近全混流,而气相氧浓度存在明显的轴向梯度;溶剂蒸发与液相混合相互竞争造成反应器内有一定的温度梯度;氧浓度梯度和温度梯度共同作用使得CO2、CO量增多,燃烧副反应加剧,这其中氧浓度梯度起主要作用。

p-Xylene liquid phase oxidation involves a series of gas-liquid-solid exothermic reactions. Dramatic solvent evaporation in the gas inlet region and imperfect mixing result in a non-uniform distribution of temperature and concentration in the reactor. To investigate the extent of non-uniformity and its effect on the reactions, a three-region model was developed. The reactor was divided into three connected regions in the axial direction with the back mixing between them. The calculating methods for getting the coefficient of reaction kinetics and mass transfer were obtained from the previous works and were used here to check a specific industrial reactor. The back mixing coefficients between the regions of the model were obtained from the fitting of the temperature profile measured from the industrial reactor. The computation results show that the liquid phase in the reactor is well stirred and nearly uniform throughout, and gas phase concentration of oxygen exists a remarkable axial gradient. Both temperature and oxygen gradient makes more consumption of solvent by burning than that in CSTR (continuous stirred tank reactor), and the effect of the oxygen gradient on burning is more remarkable than that of the temperature gradient.