Thermogravimetric Studies on Condensed Wood Residues in Polyhydric Alcohols Liquefaction

To further clarify reasons for formation of condensed residues during the last stage of wood liquefaction in the medium of polyhydric alcohols and sulfuric acid catalyst, the weight loss behaviors and thermal reaction kinetics of condensed residues were studied by thermogravimetric analysis (TGA). Simultaneously, chemical methods were used to analyze the contents of lignin, cellulose, and holocellulose in the condensed residues. For all the unliquefied wood residues, the contents of cellulose decreased, and the residual ratios after TGA pyrolysis and the contents of lignin increased as a function of liquefaction time. Moreover, the highest weight loss rate went gradually to the higher temperature region after the liquefaction time and heating rate were extended. The values for apparent activation energy were lower at 150 minutes and 180 minutes and higher at 25 minutes. Liquefaction time had a smaller effect on the pyrolysis mechanism, as revealed by TGA. In conclusion, the thermal stabilities of condensed residues were higher than those of decomposed residues and wood. The condensation reaction occurred mainly during wood liquefaction, and condensed residues resulted possibly from mutual reaction among small molecules from decomposed lignin.