Engineering Pore Network Structure of Binders for Improved Catalytic Performance of Zeolite Pellets Using a Multiscale Model

Abstract

Binders are needed for the pelletization of zeolite catalysts, and the pore network structure of binders can significantly affect the catalytic performance of zeolite catalyst pellets. In this work, a multiscale model directly coupling model equations at crystal, pellet, and reactor levels is proposed to engineer the pore network structure of binders. Benzene alkylation with ethylene catalyzed by ZSM-5 zeolite pellets in a fixed-bed reactor is taken as the model reaction system. The results show that strong diffusion limitations exist in crystals (micropores) and binders (macro-/mesopores). Shrinking the crystal size or adding intracrystalline pores in crystals can reduce the diffusion limitation in micropores but also can enhance the diffusion limitations in macro-/mesopores. An optimal volume fraction of binders can balance diffusion in binders and reaction in crystals and thus results in a maximum conversion of ethylene. The zeolite pellet with a higher binder porosity and a larger binder pore diameter is more favorable, and the influence of binder porosity is stronger than that of the binder pore diameter. In addition, crystallizing the binder into the zeolite phase can largely enhance the catalytic performance of zeolite catalyst pellets, especially when the volume fraction and porosity of the binder are high. This work gives a multiscale model and some useful guidance for developing zeolite catalyst pellets used in industry.

Preparation of the Al13 Sol via Electrodialysis as an Effective Binder of FCC Catalysts

“…), and other species with higher degrees of polymerization. 5,6 As a rule of thumb, the effective alumina species with higher porosity and larger pore diameter are more favorable in accelerating the diffusion of hydrocarbon molecules, 7 which is hard to be realized by assembling and calcining the sol precursor with a range of diameters from 0.75 to 2 nm. In particular, the sol is rich in monomers with lower hydroxyl density, poor activity, and bonding properties.…”

“…Industrial alumina sol is generally produced through the reaction between Al and hydrochloric acid at a certain temperature and pressure. Final products containing multiple aluminum species include monomers (Al 3+ ,Al­(OH) 2 + , and Al­(OH) 2+ ), dimer (Al 2 (OH) 2 4+ ), and other species with higher degrees of polymerization. , As a rule of thumb, the effective alumina species with higher porosity and larger pore diameter are more favorable in accelerating the diffusion of hydrocarbon molecules, which is hard to be realized by assembling and calcining the sol precursor with a range of diameters from 0.75 to 2 nm. In particular, the sol is rich in monomers with lower hydroxyl density, poor activity, and bonding properties.…”

Effects of Surface, Interface, and Defect on Zeolite Catalysis Probed by a 3D Anisotropic Model

“…D i,self and D ij can be calculated using the method reported in the literature. 37,47 θ i can be calculated using the multisite Langmuir isotherm…”

“…The elements in the matrix B can be calculated by where q i ,sat is the saturation loading of component i , θ i is the coverage of component i , D i ,self is the self-diffusion coefficient of component i , and D ij is the binary diffusivity of component i in a mixture of i and j . D i ,self and D ij can be calculated using the method reported in the literature. , θ i can be calculated using the multisite Langmuir isotherm Herein, b i , j is the Langmuir adsorption parameter of component i at the adsorption site j , and p i is the partial pressure of component i . The elements in the matrix Γ can be obtained from eq The relation between p i and q i follows the IAST. , Besides, for a three-dimensional zeolite, the diffusion coefficients in the x , y , and z directions (i.e., D ix , D iy , and D iz ) can be calculated by the diffusion coefficient ( D i ) and random walk model when the diffusivity ratio in the x and y directions of component i ( D iy / D ix ) is given For a three-dimensional isotropic zeolite, the diffusion coefficients in the x , y , and z directions (i.e., D ix , D iy , and D iz ) are all equal to the diffusion coefficient ( D i ).…”