A discussion of realistic feedstocks: can we use the entire poplar tree for biofuels and biochemicals production?

The economic success of a potential biorefinery is directly related to the use of low cost biomass. Due to high cost, it is unlikely that a wood-based biorefinery would use only whitewood chips from mature trees during bioconversion. Using a more heterogeneous raw material is less costly, but the efficacy of the bioconversion process using whole trees (including leaves, bark, branches and whitewood chips) has not been investigated. This research studied influence of using whole 2-year-old hybrid poplar trees on the overall sugar production via steam pretreatment and enzymatic saccharification. A whole poplar tree mixture was obtained from Jefferson, OR; it comprised 37% leaves, 9% bark, 12% branches, and 42% whitewood chips (dry weight basis). From this, three different biomass samples were studied: (1) the whole poplar mixture, (2) whole poplar mixture without leaves, and (3) leaves from whole poplar mixture. All were impregnated with 3% SO₂and steam pretreated at 195¢ªC for 5 minutes and the sugar recovery before and after enzymatic hydrolysis was calculated. Preliminary results show that converting the whole poplar mixture may be challenging, with lower sugar yields than literature values for mature whitewood chips.  However, the removal of leaves increased the overall sugar recovery. Unsurprisingly, the substrate derived from pure leaves performed poorly. These results show that removal of leaves from 2-year-old poplar trees prior to harvest may increase the overall sugar yield. In an associated techno-economic analysis, we examine the economics of a biorefinery using 2-year-old hybrid poplar mixture as a feedstock.