Hybrid Process for Conversion of Pyrolysis Oil into Lipid

Lignocellulosic feedstocks are the most abundant renewable resources in the world. To use these materials as a carbon source for advanced biofuel production, a hybrid biorefinery process, which combines fast pyrolysis to produce bio-oils enriched in levoglucosan, and the follow-up fermentation for lipid microbial production, has been developed. In this project, we have studied several strategies to maximize the production of levoglucosan in the fast pyrolysis step. The sugars are easily separated from the lignin derived molecules by water extraction. The high lipid producing oleaginous strains including bacterium Rhodococcus jostii RHA1 and yeast Yarrowia lipolytica Po1f were metabolically engineered to produce lipid from levoglucosan. The lipid and the lignin derived molecules produced can then be further processed for the production of “drop-in” fuels. The metabolic pathway of levoglucosan was introduced into these two strains by heterologous expression of the gene encoding levoglucosan kinase (LGK) involved in the anhydrosugar utilization, respectively. The expression level of the target gene, lgk in the recombinants was optimized to improve the growth performance and substrate utilization. The recombinants were able to utilize levoglucosan effectively, while accumulating lipids to more than 40% of cell dry weight (CDW) under nitrogen-limiting conditions. We further investigated the lipid yield from the generated pyrolysis oils mainly consisting of anhydrosugars, carboxylic acid and mono and oligo-phenols by the developed strains. This hybrid thermochemical and biochemical process offers a new option for the conversion of biomass into lipid-derived “drop-in” fuels and chemicals.