(446f) Measuring the Torrefaction Products of Xylan and D-Xylose

Xylan torrefaction plays a crucial role in the pre-treatment of biomass, so this work examines its reactions by measuring the differences between torrefaction products of xylan vs. its monomer, D-xylose at 250° and 300°C. Xylan is a major component of hemicelluloses and one of the least thermally stable polymers in lignocellulosic biomass. While xylan pyrolysis at higher temperatures has received attention [1], its torrefaction kinetics and its differences with the torrefaction kinetics of D-xylose are largely unstudied.

A sample of 0.1 – 0.3 mg of xylan (Sigma Aldrich) or d-xylose (Acros Organics) is dried at 105°C for 15 mins before being flash-torrefied (Pyroprobe Model 5000, CDS) at the selected temperature 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. The products are divided into three categories: common products, products identified only in D-xylose torrefaction, and products identified only in xylan torrefaction. The % peak areas of common products are used to analyze the effects of temperature on the product distribution.

In both raw materials and at both torrefaction temperatures, the % total peak area of water is the largest among all the products. It is above 30% in each case, while the peak areas for the other products are less than 10 %. Interestingly, water % peak area significantly decreases at higher temperature (from 64% to 32 % in d-xylose torrefaction), possibly due to formation of additional products formation at higher temperatures. Water production due to water elimination reactions may play an important role in D-xylose and xylan torrefaction.

D-Xylose torrefaction yields higher % peak areas at 300°C than at 250°C for the most common products (CO₂, glycoladehyde, furfural, furanmethanol, acetol, acetic acid and formic acid), while for xylan, % peak area of CO₂ and formic acid decreased at 300°C. Furfural had the second largest peak area % among the other products of xylan and the highest % peak area for D-xylose (6.56% at 300°C). Another significant result is that methanol, ethanol, propanoic acid, and butyrolactone are identified as torrefaction products only from xylan. On the other hand, furancarboxaldehyde and 4-cylcopentene-1,3-dione are identified in only in D-xylose 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.