Optimizing pyrolysis of herbal tea and Salvia miltiorrhiza residues for sustainable energy and product recovery

Abstract

• Both N 2 and CO 2 atmospheres enriched the pyrolytic products of herbal tea and Salvia miltiorrhiza residues. • Pyrolytic stages, kinetics and thermodynamics of herbal tea and Salvia miltiorrhiza residues were characterized. • Slow and rapid pyrolytic volatiles of herbal tea and Salvia miltiorrhiza residues were identified. • CO 2 promotes the oxidation pathway and promotes the formation of oxygen-containing compounds such as esters and alcohols. With the global shift to renewable energy and a circular economy, the pyrolysis of traditional Chinese medicine residues offers a promising alternative for resource recovery. This study characterized the pyrolysis behaviors and products of herbal tea residues (HBR) and Salvia miltiorrhiza residues (SMR) in the N 2 and CO 2 atmospheres. A three-stage pyrolysis process was identified for both fuels, with the primary reaction occurring between 180–620 °C for HBR and 170–600 °C for SMR. Kinetic analysis demonstrated that CO 2 reduced the activation energy of pseudo-components in HBR but increased it for SMR. Under N 2 , slow pyrolysis produced eicosane (C 20 H 42 ) as the main product for HBR (32.90 %) and dodecanoic acid (C 12 H 24 O 2 ) for SMR (26.61 %). In CO 2 , 1-nonadecene (C 19 H 38 ) was the primary product for HBR (45.22 %), and 1-tetradecanol (C 14 H 30 O) for SMR (42.17 %). Fast pyrolysis in N 2 predominantly produced acetic acid (C 2 H 4 O 2 ) for both HBR (16.40 %) and SMR (18.70 %). These findings offer new insights into the valorization of both fuels as a sustainable energy source and provide a basis for further exploring their scalability and economic feasibility.