Diffusion Properties of C9 Petroleum Resin in Porous γ-Al₂O₃: A Molecular Dynamics Study

C9 petroleum resin hydrogenation is a classic macromolecular heterogeneous catalyzed reaction that can markedly improve the material's thermal stability and compatibility. The diffusion of these macromolecules within the catalyst pores significantly influences the mass transfer there and the overall hydrogenation process. However, due to experimental limitations, the diffusivity of reactants in the pores remains challenging to determine, which affects the accurate design and operation of the catalytic reaction process. A more realistic model of γ-Al₂O₃ was developed by incorporating atomic charge considerations, and a more precise interaction between the guest molecule and γ-Al₂O₃ was described using the INTERFACE force field. The model was characterized by calculating the accessible surface area, total pore volume, hydroxyl group density, wide-angle X-ray diffraction patterns, and benzene adsorption. The calculated results were validated and compared with the corresponding laboratory data. Molecular dynamics simulations were further employed to evaluate the diffusion behavior of C9 petroleum resin within the generated γ-Al₂O₃. The effects of temperature, the kinetic diameter of C9 petroleum resin, pore size, and pore window size of γ-Al₂O₃ on diffusion performance were examined. It was found that an increase in temperature can accelerate molecular diffusion, with larger molecules being more sensitive to temperature variations. A linear relationship between the diffusion coefficient and the kinetic diameter of C9 petroleum resin was observed for a given γ-Al₂O₃ pore structure. Additionally, the diffusion coefficient exhibited a parabolic dependence on pore size at a constant kinetic diameter, while the pore window size had a crucial influence on the diffusion of C9 petroleum resin. These results provide optimized operating conditions and valuable guidance for the preparation of feasible porous γ-Al₂O₃ catalysts for C9 petroleum resin hydrogenation.