Product Distribution from the Fast Pyrolysis of Hemicellulose

Abstract

Hemicellulose is one of the major constituents of biomass. Surprisingly, only very limited information regarding its product distribution under fast pyrolysis conditions is available in the literature. In the present study, a combination of several analytical techniques, including micro-pyrolyzer-GC-MS/FID, gas analysis, and capillary electrophoresis, were used to study the primary pyrolysis product distribution of hemicelluloses extracted and purified from switchgrass. A total of 16 products were identified and quantified, which accounted for 85% of the overall mass balance. The pyrolysis behavior of hemicellulose was found to be considerably different than cellulose and was explained on the basis of a proposed mechanism for glycosidic bond cleavage. Further, the effect of minerals and temperature was investigated. The study provides insight into the fast pyrolysis behavior of hemicellulose and provides a basis for developing models that can predict bio-oil composition resulting from overall biomass fast pyrolysis.

Quantitative Insights into the Fast Pyrolysis of Extracted Cellulose, Hemicelluloses, and Lignin

“…If compared to previous work on the fast pyrolysis of extracted hemicelluloses,6 considerable deviations in the composition of condensates were observed. This is attributed mainly to the different botanical origin of the feedstock from which the hemicelluloses were extracted.…”

“…This is attributed mainly to the different botanical origin of the feedstock from which the hemicelluloses were extracted. Indeed, hemicelluloses derived from Zea Mays leaves contained less xylose, 31.1–31.6 wt % on average (Table S1), than that from switchgrass (66.2 wt %) 6. We may also expect that the type of isolation and/or purification methods also influenced this product distribution.…”

“…For several decades, researchers have tried to elucidate the main degradation pathways for biomass fast pyrolysis modelling 6, 7, 8, 9, 10, 11. As a result, the overall degradation scheme of biomass fast pyrolysis is seen as an interplay between physical and chemical events, which are often impossible to separate 12.…”

“…Indeed, the chemical aspect of biomass fast pyrolysis can be described as a combination of parallel and successive reactions of a nonionic and ionic nature 13. If radical mechanisms are invoked and are predominant in coal pyrolysis,14 recent experimental evidence6, 7, 15 and theoretical calculations16, 17 for biomass fast pyrolysis suggest the predominance of nonionic reactions during the primary pyrolysis stage. This ongoing discussion on the importance and predominance of the ionic and/or nonionic character of fast pyrolysis reactions13 has provided important clues that have not yet been used to rationalize the degradation modes.…”

Biomass torrefaction: Modeling of volatile and solid product evolution kinetics

“…Kinetically limited, fast pyroylsis of pure (ash free) hemicellulose derived from switchgrass) at 500 ○ C results in similar products including carbon dioxide (18.8 %wt), water (15.1% wt), formic acid (8.4%wt), and char (11%wt), hydroxyacetone (3% wt) and other dehydration products including dianhydro xyloses(8%wt) (Patwardhan et al, 2011). Lower temperatures (300 ○ C) and the addition of minerals (alkali and alkaline salts) were found to increase char yield significantly.…”