(639i) Analyzing the Torrefaction Products of Galactomannan and its Monosaccharide Constituents

Galactomannans are hemicellulose copolymers often found in lignocellulosic biomass and play a role in biomass torrefaction, so measuring their torrefaction products and kinetics is of interest. They are thermally more stable than other hemicellulose polymers such as xylans. While galactomannan’s pyrolysis at higher temperature (600°C) has been considered [1], its torrefaction kinetics and its differences versus the torrefaction kinetics of constituent monosaccharides (D-galactose and D-mannose) are not well understood. In the present study, an effort has been put to understand the differences.

For torrefaction experiments, a 0.1 – 0.3 mg sample of galactomannan (Alfa Aesar) or D-galactose (Acros Organics) or D-mannose (Acros Organics) is dried at 105°C for 15 mins before being flash-torrefied (Pyroprobe Model 5000, CDS) at 300°C and held for 30 s. Product analysis is by two-dimensional gas chromatography followed by time-of-flight mass spectrometry (Pegasus 4D, LECO). Products are considered to be identified if they have greater than 80% similarity with the library spectra and their S/N ratio is greater than 100.

Somewhat surprisingly, no 5-hydroxymethylfurfural (5-HMF) or no anhydrosugars were detected from the torrefaction of galactomannan. Both of them are reported to be major pyrolysis products at 600°C [1]. Other major products include water, carbon dioxide, glycoladehyde, acetaldehyde, acetol, glycidol, furanmethanol, furfural, 2-(5H)-furanone, 1,2-cyclopentadione, 2-hydroxy-gamma-butyrolactone, dihydro-4-hydroxy-2-(5H)-furanone.

By comparison from D-mannose and D-galactose torrefaction, strong peaks for furfural, 5-hydroxymethylfurfural, anhydropyranose and anhydrofuranose sugars are detected along with lighter compounds (molecular weight <=74). 3-Hydroxy-2,3-dihydromaltol is also identified as a product, which is not found in galactomannan torrefaction.

[1] X. Zhou, W. Li, R. Mabon, L.J. Broadbelt, L. J., “A critical review on hemicellulose pyrolysis,” Energy Tech., 2016, 4, 1 –29.