(27d) Willow Biomass As a Feedstock for Biorefinery: Evaluation of Bark Effect on Hot Water Extraction Output, and Lifecycle Assessment of Cellulosic Ethanol Production

The use of cellulosic biofuels is projected to increase in order to offset greenhouse gas emissions from the combustion of non-renewable fuels. Shrub willows are being developed as a short rotation woody crop (SRWC), and have a high net energy ratio (energy produced/ fossil fuel energy consumed), low greenhouse gas footprint and high carbohydrate production potential. Willow biomass can be combined with woody biomass from forests but willow often has higher bark levels that creates challenges because it increases the ash content and lowers the melting point.

This study evaluated how the amount of bark (0%, 33%, 66% and 100%) on three willow cultivars impact the output of hot water extraction in term of mass removal and extract composition, as well as its influence on the heating value and ash. Additionally, a cradle-to-grave life cycle assessment (LCA) was performed to assess the greenhouse gas emissions associated with the production of bioethanol from the hot water extract of willow biomass.

The hot water extraction process reduced ash content up to 50% for sugar maple and willow, but there was variation among the varieties of willow. After hot water extraction the heating value of biomass increased about 5% with removal of mostly hemicelluloses that have relatively low heating value. The hot water extraction provided a fermentable sugar stream for biofuels and bioproducts production, and improved the characteristics of the hot water processed willow biomass that can be used to produce high quality pellet. The lifecycle assessment revealed the greenhouse gas saving associated with ethanol production from willow biomass via fermentation of sugars extracted by the hot water extraction process. The most sensitive parameters to greenhouse gas emissions included fermentation yield, mass removal by hot water extraction, and amount of belowground carbon sequestration, in addition to transportation distance.