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Modelling of the intra-granular mass transfer within catalytic reactors

Abstract : The chemical activity of catalysts has long been the core of R&D studies, leading to an increased influence of internal diffusion limitations. It is therefore important to model and quantify these mass transfer limitations in order to optimize catalyst design and increase performance.In the framework of our project, 2D or 3D pore networks, constituted by interconnected cylindrical pores, are randomly generated by a Monte Carlo approach to reproduce the porosity, specific surface area and pore volume of gamma-alumina supports. A highly efficient tool, capable of generating 2D networks of 18000×18000 and 600×600×600 nodes in 3D, containing up to 2 billion pores. Only 4s are required to generate 2D networks of size 200x200.Mass transfer is simulated by the 1D Fick’s diffusion model within each pore of the network. 200×200 networks, containing up to 80,000 pores, can be simulated. The confrontation of the calculated tortuosities as a function of porosity, to theoretical correlations shows a good agreement. However, when comparing with experimental values from fixed-bed tracer experiments obtained for different gamma-alumina pellets, actual aluminas exhibit higher tortuosities, probably due to the organisation of the porous structure in two levels.Hence, by modifying the developed model to generate two-level networks, we have been able to reproduce both textural and diffusion properties of one alumina. Taking a 2D periodic network of size 100×100 and concerning the textural properties, relative errors less than 10% were obtained. In addition, a good agreement was found for the tortuosity values, 2.34 against the experimental value of 2.40
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Sonia Carreira Ferreira. Modelling of the intra-granular mass transfer within catalytic reactors. Catalysis. Université de Lyon, 2018. English. ⟨NNT : 2018LYSE1002⟩. ⟨tel-01785391⟩

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