(687g) Sustainable Co-Production of Poly(3-hydroxybutyrate) and Bio-Oil from Forest Harvest Residues: An Integrated Biorefinery Approach

The second-generation biorefinery approach for biofuels and value-added bioproducts (e.g., bioplastics) production has seen limited commercial success despite considerable interest and effort, mostly because of high production costs and partial utilization of biomass. To address these challenges, this project uses an innovative hybrid process to co-produce bioplastics (poly(3-hydroxybutyrate); PHB) and biofuel (bio-oil) from forest harvest residue biomass (FRB). FRB generated from harvesting operations, including treetops, branches, and low-grade wood material, is one of the low-cost and abundantly available feedstocks for second-generation biorefinery. The sugars obtained from the hydrolysis of structural carbohydrates were fermented to PHB and the lignin-rich residues were processed through hydrothermal liquefaction (HTL) to produce energy-dense bio-oil. To reduce the biomass recalcitrance, FRB was pretreated using a chemical-free two-step hydrothermal pretreatment process (hot water pretreatment followed by disk refining). The pretreatment experiments were performed using a central composite design for three variables: temperature, time, and solid loading. Hydrothermally pretreated biomass was disk milled and hydrolyzed using commercial cellulase and hemicellulase enzymes, and resulted in significantly higher cellulose conversion compared to raw biomass. The hydrolysate obtained from biomass pretreated at two optimized conditions was evaluated as the carbon source for PHB synthesis by Recombinant Escherichia coli LSBJ, and the PHB yields were found comparable to those from pure sugars. From the HTL of lignin-rich fractions, it was observed that higher bio-oil yield is obtained using alcoholic solvents (ethanol and methanol) in the liquefaction reaction, however, liquefaction using water produced a comparable bio-oil yield (~40.0 wt.%) with high selectivity of 2,6-dimethoxy phenol compared to Kraft lignin. Thus, a complete utilization of biomass enhances the potential economic viability of bioplastic and bio-oil coproduction in a second-generation biorefinery approach.