Slow pyrolysis processing of industrial hemp by-products

While the primary product obtained from cultivating fiber hemp is fiber, there is a growing need for development of new applications with high commercial potential and value from other parts of the hemp plant. Suitability of slow pyrolysis as a processing method for hemp (Cannabis sativa L.) residue was studied together with the yields of distillates, charcoal, and gases at different stages of the process. The slow pyrolysis process, reaction product yields and compositions of decorticated bark, woody core, roots, and leaves were studied separately. Hemp hurd, that is, the woody core of the plant, commercially available as animal bedding was used as a reference material. The slow pyrolysis was performed as a multistage batch process with drying, torrefaction, pyrolysis and cooling stages in a protective CO2 atmosphere. Nominal temperatures of the main stages were 135°C, 275°C, and 350°C, respectively. The distillates were collected with condensers at temperatures of 130°C, 70°C, 5°C, and 0°C. The yields of distillates from green and dry materials obtained from the torrefaction and pyrolysis stages differed from each other being 74%–87% and 39%–41% of dry mass, respectively. The charcoal yield of raw material dry mass was 38%–48%. This study shows that slow pyrolysis is a suitable method for processing hemp residues into charcoal and distillates, which have shown potential in high-value applications.