Hot water and dilute acid pretreatment of high and low specific gravity Populus deltoides clones

Populus sp. are hardwood feedstocks that grow in forest management areas that are logged for softwoods; however, they are also being considered as an energy-destined feedstock. The objective of this work was to determine the effect of xylose yield from dilute acid and hot water pretreatments performed in unstirred batch stainless steel reactors at temperatures ranging from 140 to 200°C. Populus deltoides clones S13C20 and S7C15 used in this study originated from Eastern Texas and were cultivated for 14 years in Pine Tree, AR. P. deltoides clones S13C20 and S7C15 had specific gravities of 0.48 and 0.40, respectively. Bark and wood were examined separately. As expected, hot water pretreatments, in the tested temperature range, resulted in very little direct xylose recovery. However, the 140°C dilute acid pretreatment of the lower specific gravity clone, S7C15, wood yielded the highest average xylose recovery of 56%. This condition also yielded the highest concentration of furfural, 9 mg/g sample, which can be inhibitory to the fermentation step. The highest xylose recovery from bark samples, 31%, was obtained with clone S7C15, using the 160°C dilute acid pretreatment for 60 min.