Design Optimisation and Numerical Simulation of Cellulose Nanocrystal Agitated Reactor

Abstract

: Cellulose nanocrystals (CNCs) are highly promising renewable nanomaterials, yet their pilot-scale production is constrained by poor solid–liquid mixing and severe particle adhesion in conventional stirred reactors. This study presents a systematic design optimization of a baffle-free spherical stirred reactor for CNC preparation via the periodate-chlorite oxidation method, using computational fluid dynamics (CFD) simulations with the Eulerian– Eulerian multiphase model and the standard k - ε turbulence model. The flow fields of cylindrical and spherical reactors are compared at rotational speeds from 400 to 700 rpm and, more importantly, under equivalent impeller tip-speed conditions to isolate the effect of vessel geometry from the effect of impeller speed. The spherical geometry significantly improves mixing performance, exhibiting higher upward axial velocity (0.738 vs. 0.619 m/s under equivalent tip-speed conditions) and turbulent kinetic energy (1.31 vs. 0.572 m 2 /s 2 under equivalent tip-speed conditions) at matched impeller tip speed. However, because the two reactors also differ in impeller diameter and d/D ratio, these improvements reflect the combined effects of vessel geometry and impeller configuration rather than vessel geometry alone. The spherical geometry also notably reduces bottom particle accumulation. Parametric optimization of impeller diameter (0.4D–0.45D), installation height (0.25D–0.35D), and rotational speed (500–700 rpm) reveals that d = 0.45D, c = 0.25D, and n = 650 rpm yield optimal solid–liquid uniformity. Nevertheless, residual particle deposition persists even under optimal conditions, indicating that supplementary sliding or cleaning mechanisms are necessary-corroborating the mechanical design proposed herein. This work provides quantitative design criteria and a transferable CFD-driven methodology applicable to other high-viscosity solid–liquid suspension systems, demonstrating how numerical simulation bridges the gap between laboratory innovation and industrial scale-up. The findings support the development of energy-efficient, scalable CNC production processes, contributing to the sustainable manufacturing of lightweight and high-performance structural materials.