Simulation of moisture removal in microwave regeneration of carbon adsorbents: Comparing conventional heating and multiple microwave frequencies with economic implications

Microwave (MW) regeneration offers a promising alternative to energy-intensive, long-cycle thermal regeneration technologies due to its rapid molecular-level heating. However, the role of residual moisture in adsorbents is often neglected in MW regeneration efficiency. Since water is a polar dielectric material, it significantly affects the efficiency of adsorbent regeneration. While 2450 MHz MW frequency has been effective at the laboratory scale, the industrially prevalent 915 MHz frequency has received less attention. This study investigates moisture issues on carbon during MW regeneration through a comparative analysis of moisture removal using 2450 MHz, 915 MHz, and conventional heating (CH) methods. By integrating experimental and simulation approaches, the heat and mass transfer processes of gas, liquid, and solid phases under different heating methods were discussed. The impacts of heating methods and process parameters on drying rate were analyzed, using ketoprofen removal efficiency to evaluate the adsorption performance of the dried material. An economic cost analysis was conducted to inform a proposed strategy for moisture removal during MW regeneration. The results indicate that MW heating offers higher energy utilization than CH. Although 2450 MHz MW heating achieves the highest efficiency, it suffers from poor uniformity, leading to localized excessive temperatures and increased carbon loss. In contrast, MW at 915 MHz provides a more uniform temperature distribution and lower energy consumption. Enhancing vacuum degree improves the drying rate. Therefore, employing MW at 915 MHz under low vacuum conditions can reduce water removal costs in the MW regeneration. This study provides a theoretical foundation for the industrial application of MW regeneration.