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A numerical approach is developed to simulate the formation of pseudomorphs with presence of chemical fluids at the mesoscopic scale. This approach consists of the lattice Boltzmann method (LBM) for transport of chemical species in the pore space, a chemical reaction model including basic kinetics of the coupled dissolution and precipitation reactions, and a mesoscopic model for nucleation and crystal growth. Our study confirms the mechanism of the solution chemistry-driven interface-coupled dissolution-precipitation for the formation of pseudomorphs and identifies several sources for the generation of porosity in the pseudomorphs. We demonstrate that epitaxial precipitation is not necessary and random crystal growth may be more favorable for pseudomorphs. We show that the difference of precipitation barrier on the surface of the primary and secondary minerals should not be too large. Otherwise only the rim of the primary phase is roughly preserved. [ABSTRACT FROM AUTHOR]

For applications of reactive transport in porous media, optimal porous structures should possess both high surface area for reactive sites loading and low mass transport resistance. Hierarchical porous media with a combination of pores at different scales are designed for this purpose. Using the lattice Boltzmann method, pore-scale numerical studies are conducted to investigate diffusion-reaction processes in 2D hierarchical porous media generated by self-developed reconstruction scheme. Complex interactions between porous structures and reactive transport are revealed under different conditions. Simulation results show that adding macropores can greatly enhance the mass transport, but at the same time reduce the reactive surface, leading to complex change trend of the total reaction rate. Effects of gradient distribution of macropores within the porous medium are also investigated. It is found that a front-loose, back-tight (FLBT) hierarchical structure is desirable for enhancing mass transport, increasing total reaction rate, and improving catalyst utilization. On the whole, from the viewpoint of reducing cost and improving material performance, hierarchical porous structures, especially gradient structures with the size of macropores gradually decreasing along the transport direction, are desirable for catalyst application. [ABSTRACT FROM AUTHOR]