Extractives in Douglas-fir forestry residue and considerations for biofuel production

Forestry residues are a plentiful, low environmental impact feedstock for biofuels and bioproducts. Douglas-fir is the most prevalent tree species in the timberlands of western North America, with approximately 5 million tons of sustainably harvestable forestry residues available each year. These forestry residues are an important potential biomass feedstock containing holocellulose, lignin, protein, ash, and phytochemicals commonly identified as “extractives”. The phytochemical extractive category make up 5–25 % of the dry weight for different tissues of Douglas-fir, but are rarely represented with molecular detail in feedstock models of residues for biofuel or other bioproduct. These extractives contain both primary and secondary metabolites and represent potential revenue sources as side products from processing, but also includes species that are astringent, toxic, endocrine disruptors and/or reactive in similar chemical processes. Within the “extractives” category are phytochemicals such as proanthocyanidins, phlobaphenes, waxes, flavonoids, terpenoids, phytosterols, lignans and many more. This review first identifies phytochemical molecules found in different Douglas-fir tissues, then quantities these by category and individual molecular species, to the extent allowed by the literature. We combine the literature into a quantitative, molecularly detailed, mass conserving model for a particular Douglas-fir forestry residue (“slash”). This model is used in a sulfite/bisulfite biofuel process simulation for understanding the molecular partitioning of extractives in different process streams. Model results are used to explore some implications for extractive species in the production of sugars and waste products from Douglas-fir forestry residue feedstock.