(490p) Mass and Energy Balance of Biomass Hydrothermal Pretreatment

Hydrothermal pretreatment is a process for treating lignocellulosic biomass to prepare for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 ˚C and 275 ˚C, and at pressures above the liquid vapor pressure for times less then 30 min. In this study, mass and energy balances of the hydrothermal pretreatment process are performed with loblolly pine used as a representative biomass feedstock. Temperature is the only process variable that has a significant affect on the product distribution and the pre-treated solid qualities. Pretreatment in the range of 200-260 °C can achieve an energy density increase of 11-47% with a mass yield of 41-87% of the pre-treated solid. A careful energy balance shows that the reaction is either slightly endothermic or heat neutral.

Fiber analysis shows that hemicellulose can be mainly extracted as a water-soluble fraction at 200-230 ˚C, while the cellulose fraction was hydrolyzed at higher temperatures (230-275 ˚C) or recovered as solid residue from this treatment. Detailed analysis of the pre-treated solid indicates the dramatic compositional change of the solid residue during the hydrothermal pretreatment (e.g. lower oxygen content, higher carbon content, higher fixed carbon and lower volatiles). A comprehensive process model is also developed for biomass hydrothermal pretreatment using the ASPEN PLUS simulator.