Chemical Composition of Bio-oils Produced by Fast Pyrolysis of Two Energy Crops

TLDR

The chemical composition of bio‑oil is important because it may give insights into its quality, stability, or suitability for downstream upgrading. The authors performed fast pyrolysis of switchgrass forage and alfalfa stems at 500 °C in a 2.5 kg h⁻¹ fluidized‑bed reactor and analyzed the resulting bio‑oils by wet‑chemical assays, GC‑MS, and HPLC, then compared the compositions to those of the feedstocks. The analysis identified 62 compounds, 27 of which were quantified, revealing that alfalfa‑stem bio‑oils contain higher nitrogen, water, and aromatics but lower levoglucosan and hydroxyacetaldehyde compared to switchgrass bio‑oil, and that the two alfalfa stages have similar compositions while differing markedly from switchgrass.

Abstract

Bio-oils from the fast pyrolysis of switchgrass forage and two sets of alfalfa stems (from two stages of development—bud and full flower stages) have been analyzed by wet-chemical methods, GC-MS, and HPLC. The chemical composition of bio-oil is important because it may give insights into its quality, stability, or suitability for downstream upgrading. Pyrolysis experiments were conducted at 500 °C under a nitrogen atmosphere in 2.5 kg/h fluidized bed reactor. A total of 62 chemical species were positively identified in the liquids. Of the identified compounds, 27 have been quantified. The chemical compositions of the bio-oils are compared with what is known about the compositions of these feedstocks. While the compositions of the bio-oil from the two alfalfa stems were similar, there were numerous differences in the compositions of the alfalfa and switchgrass bio-oils. Noted are the higher levels of nitrogen, water, and aromatic hydrocarbons in bio-oils produced from alfalfa stems than from switchgrass and woody feedstocks that have been previously characterized. Also noted is a much lower concentration of levoglucosan and hydroxyacetaldehyde concentrations among bio-oils from alfalfa stems compared with bio-oil from switchgrass or woody biomass.