While numerous studies have explored scale-up strategies for mixing and coating processes such as powder blending, wet granulation, tablet coating, and spray drying, none have addressed the challenges of impregnation in inherently porous particles. Unlike surface treatments, dry impregnation involves liquid uptake into the internal pore structure of the particles—up to 98–99% of the pore volume—using only the precise amount of liquid needed. Once saturation is achieved, the bed remains dry on the outside, making this process fundamentally different from other liquid–solid interactions studied in the literature.
In this work, we present a systematic study of dry impregnation in rotating drums using Discrete Element Method (DEM) simulations to explore the roles of Froude number (Fr), flow rate number (CQ), and Thiele modulus (ϕ). While Fr and CQ are essential for capturing bulk motion and liquid delivery, they are not sufficient to predict impregnation uniformity. Our simulations reveal that successful impregnation occurs within a slanted elliptical region in the Fr–CQ space, where the relative standard deviation (RSD) of liquid content remains below 0.1. The slant of this region highlights the interplay between speed and flow: lower Fr requires higher CQ to achieve uniformity, while at higher Fr, lower CQ suffices due to enhanced mixing.
Despite these trends, variability in RSD within the safe Fr–CQ region indicates that internal mass transfer phenomena—captured by the Thiele modulus—also play a critical role. A 3D RSD surface plot confirms that adsorption–diffusion dynamics captured by the Thiele modulus must be considered to fully optimize the process. Our findings show that particle size, speed, cohesion (Bond number), and internal diffusivity influence the wetting mechanism. At high speeds, large particles impregnate rapidly through percolation aided by collisions and void space, while small cohesive particles wet from the surface inward due to capillary forces and passive zone effects. At low speeds, small particles exhibit vertical percolation similar to a static bed, with gravity-driven wetting of the inner core followed by diffusion.
Ultimately, impregnation uniformity—both across the bed and within individual particles—is governed by a complex interplay of six key parameters: Fr, CQ, Bo, Pe, Thiele modulus (ϕ), and the mass transfer coefficient (h). Incorporating all six into a unified framework allows for predictive design and optimization of industrial-scale impregnation processes, offering new insight into liquid distribution and solute uptake in porous media.