CFD modeling of coupled flow-reaction behavior in a microwave-assisted circulating vibrated fluidized bed for polymer surface fluorination

Abstract

Abstract Fluorinated polymers are strategic materials with high added value; however, their industrial production is constrained by conventional screw-rod and batch autoclave reactors that suffer from extreme temperatures (>300 °C), severe equipment corrosion, and limited product quality. To address these limitations, this study proposes a circulating vibrated fluidized bed microwave fluorination (CVFB-MF) reactor that integrates mechanical vibration, microwave volumetric heating, and fluorine gas recycling into a single continuous unit. A coupled computational fluid dynamics (CFD) model was developed by integrating the Euler–Euler two-fluid approach with surface reaction kinetics via user-defined functions (UDFs). The kinetic theory of granular flow (KTGF) and the Gidaspow drag model were employed to close the solid-phase governing equations and characterize interphase momentum exchange, respectively. The model was rigorously validated against experimental pressure drop, bed expansion ratio, and radial solid volume fraction data, with relative deviations within ±15 %. Parametric investigations reveal that mechanical vibration effectively suppresses bubble coalescence and enhances particle mixing, while microwave heating ensures rapid and uniform temperature elevation across the bed. The Damköhler number analysis indicates a transition from mass-transfer-controlled behavior in the lower dense-phase region to reaction-controlled behavior in the upper dilute-phase region along the bed height, and an optimal operating window was identified through multi-parameter response surface analysis (conversion ∼88 % at f = 50–60 Hz and U p = 1.0–1.3 m s−1). The established coupled model provides a scalable theoretical framework for the design, optimization, and scale-up of next-generation fluorination reactors.