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.