Pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor

Abstract

Investigation on the biomass components pyrolysis behaviors in a lab-scale reactor is a necessary step before its industrialization due to the poor transportability of the findings obtained from the micro-scale pyrolyzer which often neglects the heat and mass transfer effect. In present study, the pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor was investigated. The residue evolution and bio-oil composition of xylan, xylose, arabinose and glucose show the close relationship of pyrolysis characteristics between xylan and its components. It is noteworthy that the xylan and those mono-sugar units melted during pyrolysis, and many bubbles formed. Investigation of the effect of temperature, material thickness and carrier gas flow rate on the products distribution and bio-oil composition indicates that high temperature promotes the xylan conversion and increases the yield of bio-oil, however, if the temperature is too high (>500°C), violent decomposition of xylan occurs and leads to the formation of low molecular weight compounds (such as hydroxyl acetaldehyde, acetic acid and 1-hydroxyl-2-propaone etc.). And interestingly, the bio-oil yield increases monotonically with the material thickness, and thick material layer can increase the content of furfural in bio-oil. Carrier gas flow rate has a little influence on the xylan char yield, and relative high carrier gas flow rate (>2.55L/min) could decrease the secondary decomposition of primary didehydrated pentose but reduce the bio-oil yield.