Crop Management Impacts Biofuel Quality: Influence of Switchgrass Harvest Time on Yield, Nitrogen and Ash of Fast Pyrolysis Products.

Although upgrading bio-oil from fast pyrolysis of biomass is an attractive pathway for biofuel production, nitrogen (N) and mineral matter carried over from the feedstock to the bio-oil represents a serious contaminant in the process. Reducing the N and ash content of biomass feedstocks would improve process reliability and reduce production costs of pyrolytic biofuels. This study investigated: (1) How does switchgrass harvest date influence the yield, N concentration ([N]), and ash concentration of biomass and fast pyrolysis products? and (2) Is there a predictive relationship between [N] of switchgrass biomass and [N] of fast pyrolysis products? Switchgrass from five harvest dates and varying [N] from central Iowa were pyrolyzed using a free-fall reactor. Harvestable biomass peaked in August (8.6 Mg ha), dropping significantly by November (6.7 Mg ha, P = 0.0027). Production of bio-oil per unit area mirrored that of harvested biomass at each harvest date; however, bio-oil yield per unit dry biomass increased from 46.6 % to 56.7 % during the season ( P = 0.0018). Allowing switchgrass to senesce lowered biomass [N] dramatically, by as much as 68 % from June to November ( P < 0.0001). Concurrently, bio-oil [N] declined from 0.51 % in June to 0.17 % by November ( P < 0.0001). Significant reductions in ash concentration were also observed in biomass and char. Finally, we show for the first time that the [N] of switchgrass biomass is a strong predictor of the [N] of bio-oil, char, and non-condensable gas with R values of 0.89, 0.94, and 0.88, respectively. [ABSTRACT FROM AUTHOR]