Pyrolysis of switchgrass (Panicum virgatum) harvested at several stages of maturity

Authors

A. A. Boateng, USDA-ARSFollow
K. B. Hicks, USDA-ARS
Kenneth P. Vogel, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2006

Citation

Boateng, A.A., K.P. Hicks, K.P. Vogel. 2006. Pyrolysis of switchgrass (Panicum virgatum) harvested at several stages of maturity. J. Anal. Appl. Pyrolysis 75:55-64.

Comments

U.S. government work

Abstract

The pyrolysis of switchgrass (Panicum virgatum) of the cultivar, ‘‘Cave-in-Rock’’ harvested at three stages of physiological maturity was studied in a PY–GC/MS system at the 600–1050 °C temperature range. Under these conditions, the decomposition was complete within 20 s yielding char, and two sets of pyrolysis gas, condensable and non-condensable. The former consisted of acetaldehyde (CH₃CHO), acetic acid (CH₃COOH) and higher molecular weight compounds possibly from the hydroxyl group and from the methoxy groups of the cell wall components. The non-condensable gases were mainly CO, CO₂ and C₁–C₃ hydrocarbons. For these, there was a 900 °C temperature boundary where dramatic change occurred in their evolution rates. Below this temperature, CO₂ decreased but CO and the C₁–C₃ hydrocarbons increased almost linearly with temperature. Above this temperature boundary, the hydrocarbons leveled off but there was a rapid rise in CO and CO₂ evolution at a constant CO/CO₂ ratio. These suggest the appearance of secondary or tertiary pyrolysis reactions involving rearrangement and release of CO and hydrocarbons prior to this temperature boundary and the release of CO and CO₂ from the tightly bond oxygen functionalities including C–C bonds thereafter. At <750 >°C, there were modest increases in condensable gas yield and decrease in non-condensable gas due to differences in plant maturity at harvest. However, the effect of switchgrass physiological maturity on gas yield was statistically insignificant at high temperatures. The energy content of the non-condensable gas measured was about 68% of the gross energy content of the biomass for the early harvest crop and 80% for the mature crop. The activation energy for the decomposition, estimated assuming first order reaction kinetics, showed a linear increasewith plant physiological maturity. The results demonstrate that physiological maturity at harvest of switchgrass biomass can result in different concentrations of pyrolysis products at different temperatures. These results also demonstrate the need for additional research with a broader array of herbaceous biomass materials to develop a better understanding of the synergies of crop cultivation, harvesting and processing of dedicated herbaceous biomass energy crops during their thermochemical conversion.