Mass Transfer Mechanism in the Adsorption of Orange Phenols by Macroporous Resin Pretreated by High-Intensity Ultrasound

This study aimed to investigate the effect of high-intensity ultrasound pretreatment on the mass transfer characteristics in the adsorption of orange phenols by macroporous resin. To reveal the mass transfer mechanism, the adsorption process was modeled numerically using the pore volume and surface diffusion model (PVSDM). After ultrasound pre-treatment at 302.2 W/L for 30 min, the particle size of the resin was decreased by 85.8%, and the surface area was increased by 24.5 times without any significant change in chemical properties. After ultrasonic treatment for 30 min, the adsorption equilibrium time was dramatically reduced from 90 to 2 min without any significant change in the equilibrium adsorption capacity. Meanwhile, ultrasound pre-treatment augmented the diffusion capability (D_S) of the phenols within the solid skeleton of the resin, and increased the mass transfer flux (N_AS) of the phenols along the skeletal surface and the surface diffusion contribution percentage (SDCP). However, when the resin was disrupted ultrasonically to a certain particle size, both N_AS and SDCP dropped, while the mass transfer flux (N_AP) with the diffusion of liquid within the pores of the resin rose. These findings confirmed that the mass transfer mechanism in phenol adsorption by macroporous resin changed as the resin particle size decreased to a threshold value. Therefore, ultrasound pretreatment enhanced the resin adsorption of phenols mainly through decreasing the particle size, rather than increasing the surface roughness of resin. Overall, the mass transfer distance is a critical parameter influencing the adsorption efficiency of the resin. The decrease in mass transfer distance can alter the mechanism of mass transfer during resin adsorption. These findings provide a theoretical foundation for the efficient and precise separation and purification of plant phenols.