Abstract
A versatile pore network model is used to study deactivation by coking in a single catalyst particle. This approach allows to gain detailed insights into the progression of deactivation from active site, to pore, and to particle—providing valuable information for catalyst design. The model is applied to investigate deactivation by coking during propane dehydrogenation in a Pt‐Sn/Al2O3 catalyst particle. We find that the deactivation process can be separated into two stages when there exist severe diffusion limitation and pore blockage, and the toxicity of coke formed in the later stage is much stronger than of coke formed in the early stage. The reaction temperature and composition change the coking rate and apparent reaction rate, informed by the kinetics, but, remarkably, they do not change the capacity for a catalyst particle to accommodate coke. Conversely, the pore network structure significantly affects the capacity to contain coke. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. AIChE J, 65: 140–150, 2019
Highlights
Propylene is a key feedstock in the petrochemical industry, which is widely used in the production of many important chemicals.[1,2] Propylene is traditionally produced as a byproduct from steam cracking and fluid catalytic cracking, but these processes cannot satisfy the ever-growing demand for propylene in recent years.[3]
The parameters used in the simulation are: Ccm = 4 × 10−3 g/m2, T = 838 K, PC3H8,b = 0.8 bar, PC3H6,b = 0.1 bar, PH2,b = 0.1 bar, Z = 4, ra = 5 nm, σ = 0.5, R = 2 mm. [Color figure can be viewed at wileyonlinelibrary.com]
The parameters used in the simulation are: Ccm = 4 × 10−3 g/ m2, T = 838 K, PC3H8,b = 0.8 bar, PC3H6,b = 0.1 bar, PH2,b = 0.1 bar, Z = 4, ra = 5 nm, σ = 0.5, R = 2 mm. [Color figure can be viewed at wileyonlinelibrary.com]
Summary
Propylene is a key feedstock in the petrochemical industry, which is widely used in the production of many important chemicals (e.g., polypropylene, acrylonitrile, propylene oxide, and cumene).[1,2] Propylene is traditionally produced as a byproduct from steam cracking and fluid catalytic cracking, but these processes cannot satisfy the ever-growing demand for propylene in recent years.[3]. A pore network model is first proposed to describe the coupled diffusion, reaction, coking, and deactivation processes in a catalyst particle for propane dehydrogenation. With this pore network model, we obtain and analyze representative distributions of coke in the catalyst particle, concentration profiles of reactant and products, and the relation between coke content and apparent reaction rate. The solution of the pore network model yields concentration profiles of reactant, products, and coke in the pore network, as well as distributions of reaction rates for propane dehydrogenation and coke formation With these results, the dimensionless coke content in the catalyst particle (Wc) can be calculated by[32]: PN. Rapp can correlate with Wc, which gives the relationship between deactivation and coking
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