(729d) Recovery of Energy-Dense Hydrochar and Sugars from Sweet Sorghum Bagasse

Sweet sorghum, a C4 crop in the grass family has potential to produce ethanol biofuel due to its high carbohydrate content and high biomass productivity. It consists of 8% seed head, 19% leaf matter, 36% bagasse, and 37% juice and can be cultivated on marginal lands, has low input requirements, and is adapted to nearly all temperate climates. Sweet sorghum accumulates fermentable sugars in the stem which is extracted in a conventional roller press and fermented into ethanol using yeast and engineered microbes. A large amount of biomass residue (or bagasse) is left behind the extraction unit operation and its utilization will be critical to sustainability of ethanol production from sweet sorghum. Hydrothermal carbonization (HTC) is an effective technology for converting waste biomass and crop residues into a uniform, energy-dense solid fuel that has improved storage/handling characteristics. This study evaluates the HTC of sweet sorghum bagasse into an energy-dense hydrochar for subsequent energy use as fuel or further conversion by combustion/pyrolysis and a sugar rich water soluble product. HTC treatment of three varieties of sweet sorghum bagasse, namely, Theis, M81-E, and Dale, was performed in pressurized batch reactors at 175-275oC and 30 min residence time. HTC products were separated into hydrochar, water soluble phase, and gases, which were analyzed by standard laboratory methods. HTC resulted in 45-65% hydrochar that had 15-20% higher energy than the raw bagasse. The water soluble products showed about ~10,000 ug/mL sugars that consisted of glucose, sucrose, and fructose. Pelletization of hydrochar generated robust pellets that showed superior qualities than pellets from woody biomass feedstocks.