GC/MS characterization of liquids generated from low-temperature pyrolysis of wood

Conventional pyrolysis of beech wood has been carried out for heating temperatures in the range 600-900 K, reproducing conditions of interest in countercurrent fixed-bed gasification. The yields of liquids (water and tars) increase with the heating temperature from about 40 to 55% of dry wood mass, confirming results previously obtained with a laboratory-scale gasifier. Apart from qualitative identification of similar to90 species, GC/MS techniques have been applied to quantify 40-43% of tars (40 species, with major contributions from acetic acid, hydroxypropanone, hydroxyacetaldehyde, levoglucosan, formic acid, syringol, and 2-furaldehyde). Decomposition of holocellulose leads to the formation of furan derivatives and carbohydrates, with a temperature-dominated selectivity toward hydroxyacetaldehyde against levoglucosan. Syringols and guaiacols, originating from primary degradation of lignin, present a maximum for heating temperatures of about 750-800 K whereas, owing to secondary degradation, phenols continuously increase. A comparison is also provided with fast pyrolysis liquids obtained from four commercial plants.