Hydrothermal Carbonization (HTC) and Pelletization of Two Arid Land Plants Bagasse for Energy Densification

In this study, bagasse from two arid land plants, grindelia and rabbitbrush, were hydrothermally carbonized (HTC) along with their raw biomass at 200–260 °C for 5 min. Prior to HTC, biocrude was extracted from grindelia (Grindelia squarrosa), whereas rubber was extracted from rabbitbrush (Ericameria nauseosa). Solid hydrochars and HTC process liquids of extracted feedstocks were characterized by ultimate, proximate, fiber, FTIR, higher heating value (HHV), and GC–MS analyses and the results were compared with their corresponding unextracted conditions. Hydrochars were pelletized in a single-press pelletizer and mass and energy densities of the pellets were measured. From the proximate, ultimate, FTIR, and fiber analyses, the bagasse show similar properties of the raw biomass, although the HHV was slightly increased with crude extraction from grindelia and decreased with rubber extraction from rabbitbrush. With the increase of HTC temperature, solid mass yield was decreased up to 44% for grindelia bagasse and 57% for rabbitbrush bagasse. HHV increases for all the feedstocks up to about 26 MJ kg^–1, regardless of biomass type, when treated at 260 °C. HTC process liquid becomes acidic in the presence of short-chain organic acids with HTC temperature