In Situ Fe-Doped Hierarchically Porous Carbon Derived from Astragalus and Licorice Residues: Pore Engineering and Thermal Conductivity Enhancement for Methanol Adsorption Refrigeration

Approximately 40–70 million tons of traditional Chinese medicine (TCM) residues are produced annually in China, which poses severe environmental challenges. Meanwhile, adsorption refrigeration driven by low-grade heat is limited by the lack of high-performance, low-cost adsorbents. Herein, in situ Fe-doped hierarchically porous carbon (denoted as ZYC-ZFe) was fabricated using residues of Astragalus membranaceus (55 wt%) and Glycyrrhiza uralensis (45 wt%). The resultant material exhibited a Brunauer–Emmett–Teller specific surface area (SBET) of 1244.69 m2/g, a total pore volume (VT) of 1.123 cm3/g, a thermal conductivity of 4.517 W/(m·K), and a maximum Langmuir methanol adsorption capacity of 713.06 mg/g. A desorption efficiency of 97.6% was realized within 30 min at 90 °C, and only 3.2% reduction in adsorption capacity was observed after 100 consecutive adsorption–desorption cycles. In scaled-up CFD simulations using adsorbent beds of different sizes, the adsorption refrigeration bed packed with ZYC-ZFe shortened the core temperature rise time. Within a 30 min working cycle, ZYC-ZFe delivered a specific cooling power of 1534.6 kJ/(kg·h) and a coefficient of performance (COP) of 0.52 at 90 °C. This study offers a feasible technical strategy for the high-value reutilization of TCM residues and facilitates the practical application of adsorption refrigeration driven by low-grade waste heat.