One Stone for Three Birds: Synergistic Preparation of Nitrogen-Enriched Biochar, High-Quality Bio-Oil, and Syngas via Pyrolysis of Waste Chinese Medicine Residues

Abstract This study addresses the resource waste and environmental pollution resulting from the conventional disposal of waste Chinese medicine residues (WCMRs) and examines the feasibility of high-value resource recovery using pyrolysis technology. Products obtained through oxygen-constrained pyrolysis of underground (UM) and above-ground (GM) biomass were compared systematically, and a catalyst, CaO, was added to enhance the production of syngas. Several characterization methods and batch adsorption experiments were used to comprehensively assess the performance and composition of the three-phase products. The results revealed that biochar produced at 700 °C (UMB-700 °C) had a high specific surface area of 184.78 m2·g–1 and an ammonium nitrogen theoretical maximum adsorption capacity of 38.93 mg·g–1, and that the predominant adsorption pathway was physical adsorption, which indicates its potential as a slow nitrogen fertilizer carrier. The bio-oils of both kinds of WCMRs contained high-value products, including levoglucosan, phenols, and fatty acids, with UM-based bio-oil having a higher suitability for use as a biodiesel precursor, and GM-based bio-oil having fine chemical extraction advantages. The catalysis process of CaO greatly enhanced the level of light gas constituents in the UM-derived syngas, enhancing the quality of the gas produced. This study demonstrates the regulatory impacts of various components of WCMRs on the characteristics of pyrolysis products, which offers a “one-stone, three-birds” green technology pathway to the high-value use of WCMRs and potential agricultural applications.