BioEnergy Research

, Volume 6, Issue 1, pp 103–113 | Cite as

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

  • Danielle M. Wilson
  • Dustin L. Dalluge
  • Marjorie Rover
  • Emily A. Heaton
  • Robert C. Brown


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−1), dropping significantly by November (6.7 Mg ha−1, 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 2 values of 0.89, 0.94, and 0.88, respectively.


Biomass crop Thermochemical conversion Biofuel contaminants Bioenergy Bio-oil Panicum virgatum L. 



This work was supported by ConocoPhillips Company and the Iowa State University Department of Agronomy. We thank Nicholas Boersma, Nick Ohde, George Patrick, Dave Sundberg, Ryan Smith, Alex Maeder, and Ashley Greve who helped with the project; Preston Gable and Ben Franzen for assisting in the operation of the free-fall reactor; Patrick Johnston for analysis of samples on the TGA; and John Hoyt for analysis of the samples on the CHN analyzer. We thank Nicholas Boersma, Nick Ohde, Scott McQueen, Mark Hughes, and Matt Liebman for the comments on early drafts of this manuscript, and Karl Pazdernik for statistical consulting.


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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Danielle M. Wilson
    • 1
  • Dustin L. Dalluge
    • 2
  • Marjorie Rover
    • 3
  • Emily A. Heaton
    • 1
  • Robert C. Brown
    • 2
    • 3
  1. 1.Department of AgronomyIowa State UniversityAmesUSA
  2. 2.Department of Mechanical EngineeringIowa State UniversityAmesUSA
  3. 3.Center for Sustainable Environmental TechnologiesAmesUSA

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