Cannabis Sativa L. Hemp Hurd Biochar: Influence of Pyrolysis Conditions on Carbonization and Residual Volatile...

Cannabis sativa L. (hemp) is increasingly recognized not only as an agricultural commodity for textile fibers and cannabidiol (CBD) products but also as a platform for domestic innovation in biobased materials. Hemp hurd (HH), the woody inner core of the hemp stalk, is a fibrous, carbon-rich (∼50 wt %) lignocellulosic biomass with potential for conversion into value-added biochar. Herein, HH-derived biochar was investigated with emphasis on how pyrolysis conditions influence yield, carbonization, structure, and residual volatile organic compounds (VOCs). The effects of temperature (250-650 °C), residence time (15-60 min), particle size (1.0-12.7 mm), and sample mass (5.0-20.0 g) were evaluated. HH biochar structure was characterized by Raman spectroscopy, while residual VOCs associated with a representative high-loading condition were analyzed using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS). Within the resolution of the data set, reduced particle size and temperatures ≥550 °C were associated with enhanced carbonization and greater structural ordering, while increased biomass loading at fixed reactor volume led to elevated apparent biochar yields consistent with partial retention of condensable species. Biochar produced at ≥550 °C exhibited low H/C ratios (∼0.20) and aromatic carbon structures indicative of extensive carbonization. These results guide rational optimization and scale-up of HH-derived biochar production.