Influence of lignocellulose thermal pretreatment on the composition of condensable products obtained from char devolatilization by means of thermogravimetric analysis-thermal desorption/gas chromatography-mass spectrometry

- Quantification of condensable volatiles produced from char devolatilization.
- Volatiles yields from 21 to <0.5 wt.% depending on pretreatment temperature.
- Correlation between constituents degradation and char devolatilization products.
- Volatiles from char pretreated at T > 300 °C are mostly aromatic compounds.

Four lignocellulosic biomass types, i.e. pine, bamboo, corn cob and corn stover were converted at varying temperatures (250-400 °C) and hold times (30 or 60 min). Chars produced were devolatilized in a thermogravimetric analyser (TGA) and evolved condensable volatile products were captured and quantified by thermal desorption/gas chromatography-mass spectrometry. Based on the mass loss rate curves (dTG), char devolatilization products distribution was consistent with the extent of biomass modification by thermal pretreatment. It was evident that pretreatment at 250 and 275 °C led to significant conversion of hemicelluloses, the latter resulting in a 2-3 factor decrease in acids yield from char devolatilization. Except for pine (with more crystalline structure), significant cellulose conversion was achieved at 300 °C resulting in a decreased levoglucosan yield and at least a 10 factor reduction in furans production from char devolatilization compared to raw biomass. Most of the oxygenated groups were converted during pretreatment at a temperature of 350 °C while the char became a more condensed aromatic structure. Therefore the condensable organic products were obtained in low yields (<1 wt%) and were characterized by a majority of aromatic hydrocarbons and the absence of most of the oxygenated compounds, except for the phenolic products.