Hydrothermal Processes for Extraction and Conversion of Biomass to Produce Biofuels and Value-Added Products

An integrated biorefinery approach based on subcritical hydrothermal processes was developed to maximize utilization of biomass components by producing multiple products. Biomass from various sources like agricultural waste (lignocellulose), food waste (spent yeast), and dedicated cultivation (micro-algae) was used in this research. Corn stover (agricultural waste) was hydrothermally pretreated to remove lignin and xylan while preserving most of the glucan. The pretreated corn stover was utilized to produce levulinic acid (thermochemically) and fermentable sugars (biochemically). The solid residue generated during levulinic acid production was utilized to produce biocarbon electrode material. The results generated from the experiments were used for designing a pilot facility to process one ton of corn stover per day. A continuous-flow hydrothermal treatment ‘flash hydrolysis’ was deployed for yeast protein recovery. The liquid hydrolysate with the solubilized amino acids and peptides was tested as nutrient for cultivation of E. coli in a continuous bioreactor and the yields were compared with the commercial yeast extract. Finally, the kinetic parameters for yeast solubilization like reaction order, activation energy, and pre-exponential factor were determined. High-protein micro-algae (Scenedesmus sp.) slurry was parallelly fractionated using flash (continuous mode) and acid (batch mode) hydrolysis. Most of the proteins and carbohydrates in micro-algae were recovered in liquid hydrolysate whereas the lipids in solid residue were extracted using organic solvent. The flash and acid hydrolysis derived post extraction solid residue was thermally activated to produce highly porous biocarbon nanosheets. Overall, the developed processes provide multiple value-added products generated from renewable sources for a greater financial and environmental sustainability. Also, strategies to improve and down select the developed technologies were discussed