Evaluation of the structure and fuel properties of lignocelluloses through carbon dioxide torrefaction

Two typical lignocelluloses, pine and poplar, were torrefied in a tubular reactor under carbon dioxide medium at temperatures ranging from 220 to 340 degrees C. The effect of torrefaction temperature on the structure and properties of the chars obtained was investigated to evaluate their fuel applications. As the temperature raised from 220 to 340 degrees C, the mass yield decreased from 96.7% to 48.7% for pine, and from 97.1% to 43.8% for poplar. The higher heating value of the torrefied pine increased to 25.6 MJ/kg for the sample torrefied at 340 degrees C. An increase in reaction temperature resulted in a decrease in the contents of cellulose and hemicelluloses but notable increase of the content of lignin, especially for the sample subjected to the strongest torrefaction. The variation of C, H, and O contents of the samples after torrefaction suggested that a high temperature promoted the dehydration and deacetylation reactions. Thermal analysis indicated that the combustion activity of the sample was improved to a level of lignite after torrefaction. The hydrophobicity of lignocelluloses was notably increased with increased torrefaction severity, suggesting the prepared samples are good feedstocks for further processing. (C) 2016 Elsevier Ltd. All rights reserved.