Impact of harvest time and cultivar on conversion of switchgrass to bio-oils via fast pyrolysis

Authors: Serapiglia, Michelle; Mullen, Charles; Boateng, Akwasi; Dien, Bruce; Casler, Michael

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2017
Publication Date: 5/9/2017
Citation: Serapiglia, M., Mullen, C.A., Boateng, A.A., Dien, B.S., Casler, M.D. 2017. Impact of harvest time and cultivar on conversion of switchgrass to bio-oils via fast pyrolysis. BioEnergy Research. 10:388-399.

Interpretive Summary: Switchgrass is a promising bioenergy crop within the United States for biofuels production. Previously we reported that the time the switchgrass is harvested can have a significant effect on the biomass yield potential, biomass quality and composition, and conversion to ethanol. This report expands upon the study by considering the impacts harvest time has on thermochemical conversion through fast pyrolysis and production of bio-oil. Delaying harvest time of the switchgrass crop led to improved efficiency of fast pyrolysis and bio-oil quality. The changes in pyrolysis product yield were related to biomass compositional changes and relationships between biomass composition, mineral content in the biomass, and pyrolysis products were identified. Findings show that the loss of mineral content in the biomass as harvest time is delayed combined with an increase in cellulose and lignin content in the biomass have a significant positive influence on conversion through fast pyrolysis. These results are critical in improving harvest management strategies and conversion efficiency for switchgrass bioenergy crops.

Technical Abstract: The study of the effects of harvest time on switchgrass (Panicum virgatum L.) biomass and bioenergy production reported herein is the final part complementing two prior studies reporting on the harvest of six switchgrass cultivars grown at three northern United States locations over three years, harvested at upland peak crop (anthesis), post-frost, and post-winter. Previously we reported that delaying harvest of switchgrass until after frost and until after winter resulted in decreased yields of switchgrass, but it reduced the amount of ash and nutrients in the biomass. This report expands upon the study by considering the impacts harvest time and the other experimental factors have on thermochemical conversion through fast pyrolysis and associated products. A subset (50) of the population was analyzed for fast pyrolysis and catalytic pyrolysis (HZSM-5) product yield using a pyrolysis-GCMS system. The subset was used to build calibrations that were successful in predicting pyrolysis product yield using near-infrared reflectance spectroscopy (NIRS) and partial least square predictive models were applied to the entire sample set. Pyrolysis product yield was significantly affected by field trial location, year of harvest, cultivar, and harvest time. Delaying harvest time of the switchgrass crop led to greater production of deoxygenated aromatics improving the efficiency of the catalytic fast pyrolysis and bio-oil quality. The changes in pyrolysis product yield were related to biomass compositional changes and key relationships between cell wall polymers, potassium content in the biomass, and pyrolysis products were identified. Findings show that the loss of mineral content in the biomass as harvest time is delayed combined with the increase in cellulose and lignin content in the biomass have significant positive influence on conversion through fast pyrolysis.