异形催化剂上乙烯催化氧化失活动力学反应工程计算

doi:10.11949/0438-1157.20230168

摘要/Abstract

摘要：

以乙烯催化氧化制环氧乙烷体系为研究对象，采用有限元算法对异形催化剂失活动力学方程与反应-传质-传热方程组同时求解，模型收敛性和计算结果准确性均很好。催化剂颗粒经过16个月反应后，主副反应活性系数均下降明显，且副反应失活速率大于主反应。随着催化剂失活，第一类失活内扩散效率因子随时间增加而上升，第二类失活内扩散效率因子随时间增加先下降然后小幅度上升。通过定量计算表明催化剂内扩散阻力的存在能“延缓”由于失活导致的表观反应速率下降。对于存在强内扩散限制的此反应体系，表观失活速率只有不存在内扩散影响的失活速率的50.8%。内扩散对失活动力学方程实验测量有很大影响，必须区分本征失活动力学和宏观失活动力学。当催化剂活性降低到一定程度，可以提高反应温度以保证反应在高速率区间进行。应用此模型能指导反应器设计和失活状态下反应器的操作参数优化。

关键词: 失活动力学, 失活内扩散效率因子, 非稳态过程, 异形催化剂, 有限元算法

Abstract:

For the reaction of ethylene catalytic oxidation to ethylene oxide, the finite element method (FEM) is employed to solve the deactivation kinetics and reaction-mass transfer-heat transfer model simultaneously. The convergence of the model and accuracy of calculation results are very well. After the catalyst particles reacted for 16 months, the activity coefficients of the main and side reactions decreased significantly, and the deactivation rate of the side reactions was greater than that of the main reactions. With the deactivation of catalysts, the first kind deactivation internal effectiveness factor increases with time, and the second kind deactivation internal effectiveness factor decreases at first and then increases slightly. It is shown by quantitative calculation that the internal diffusion resistance can “delay” the reduction of apparent reaction rate caused by catalyst deactivation. For ethylene catalytic oxidation system with severe internal diffusion limitations, the apparent deactivation rate is only 50.8% of intrinsic deactivation value. The parameter values of the deactivation kinetic equations by experiments are strongly influenced by internal diffusion, and a distinction must be made between intrinsic and macroscopic deactivation kinetics. When the activity factors are reduced to a certain value, the reaction temperature can be increased to ensure the reaction at a high range. This model can be applied to guide reactor design and optimize the operation parameters with deactivation process.

Key words: deactivation kinetics, deactivation internal effectiveness factor, transient process, irregular-shaped catalysts, finite element method

中图分类号:

TQ 021.4

周继鹏, 何文军, 李涛. 异形催化剂上乙烯催化氧化失活动力学反应工程计算[J]. 化工学报, 2023, 74(6): 2416-2426.

Jipeng ZHOU, Wenjun HE, Tao LI. Reaction engineering calculation of deactivation kinetics for ethylene catalytic oxidation over irregular-shaped catalysts[J]. CIESC Journal, 2023, 74(6): 2416-2426.

图/表 18

图1 固定床反应器失活曲线随时间移动示意图

Fig.1 Deactivation curve moving over time in fixed bed reactor

图2 含失活过程的反应模型变量耦合关系

Fig.2 Variable relationship with deactivation process

图3 催化剂几何结构及1/16网格图

Fig.3 Geometry and grid map of catalyst

图4 主反应活性系数a1计算值和实验值

Fig.4 Calculated and experimental values of main reaction activity factor

图5 16个月后主反应活性系数a1分布

Fig.5 Distribution of catalyst main reaction activity factor after 16 months

图6 16个月后副反应活性系数a2分布

Fig.6 Distribution of catalyst side reaction activity factor after 16 months

图7 z=0平面主反应活性系数随时间变化

Fig.7 Distribution of catalyst main reaction activity factor after 2, 4, 8 and 12 months

图8 不同温度下16个月后主反应活性系数

Fig.8 Main activity factor under different temperature condition after 16 months

图9 16个月后催化剂内ET浓度分布

Fig.9 ET concentration distribution after 16 months

图10 16个月后温度分布

Fig.10 Temperature distribution after 16 months

图11 16个月后生成EO反应速率分布

Fig.11 Reaction rate distribution of EO after 16 months

图12 16个月后截线B上归一化反应速率

Fig.12 Normalized reaction rate distribution in line B after 16 months

图13 16个月后反应选择性

Fig.13 Reaction selectivity after 16 months

图14 第一类失活内扩散效率因子

Fig.14 The first kind internal effectiveness factor of deactivation

图15 第二类失活内扩散效率因子

Fig.15 The second kind internal effectiveness factor of deactivation

图16 操作条件（温度）对主反应活性系数的影响

Fig.16 Influence of temperature on catalyst main reaction activity factor

图17 操作条件（温度）对第二类失活内扩散效率因子的影响

Fig.17 Influence of temperature on the second kind internal effectiveness factor of deactivation

图18 操作条件（温度）对反应速率的影响

Fig.18 Influence of temperature on reaction rate

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