3-07: Wood pellets; does densification effect their suitability as a biomass-to-ethanol feedstock?

Wood pellets are one of the world’s most tradable sources of bioenenrgy and their compressed format, increased density, uniform shape and moisture content make them a favorable biomass source for handling and storage systems when compared to wood chips or straw bales. Although several studies have looked at the thermo-chemical conversion of biomass pellets, the suitability of these feedstocks for biochemical based biomass-to-ethanol processes has not yet been investigated. In the work that will be described, we have assessed whether softwood pellets act similarly to corresponding wood chips with regard to their amenability to pretreatment and subsequent enzymatic hydrolysis. When softwood chips and pellets were both steam pretreated and hydrolyzed under comparable conditions the pellets appeared to behave in a similar fashion to wood chips in terms of overall product recovery after steam pretreatment and sugar yield after enzymatic hydrolysis. Steam treatment had been previously shown to be effective for pelletization of softwood derived saw dust.  This improved the pellet’s density, hydrophobicity, and storage stability. We will describe how steam pretreatment improves both the quality/properties of pellets while enhancing the subsequent processing of softwoods (with or without bark) in a typical biomass-to-ethanol process.