Thermal transformations of pine wood components under pyrolysis/gas chromatography/mass spectrometry conditions

The analysis of thermal transformations of the main components of sound pine wood was performed through the application of Py/GC/MS. A gradient of sub-pyrolysis temperatures (200, 250, 300 and 350 °C) and a double-shot pyrolysis at 450 and 500 °C after a pre-pyrolysis step at 250 °C were performed. Then, a flash pyrolysis at 500 °C was also applied. The pyrograms obtained after applying a gradient of sub-pyrolysis temperatures showed the no detection of carbohydrate and lignin-derived compounds at 200 °C as well as a high relative abundance of trans-coniferaldehyde at 250 and 300 °C. An increase in the total released carbohydrates and the most selected methoxyphenols (guaicol, methylguaiacol, ethylguaiacol, vinylguaicol, and acetovanillone) was observed with the increase of sub-pyrolysis temperature up to 350 °C. The pyrograms corresponding to the double-shot pyrolysis showed a series of carbohydrate-derived compounds which were not detected at sub-pyrolysis temperatures. Moreover, at these conditions an increase in the total lignin peaks was observed except in the case of using 250 °C. In the pyrograms obtained after flash pyrolysis at 500 °C an increase in the total carbohydrates was detected compared with that obtained when the pyrolysis was applied after a pre-pyrolysis step. This result corroborates the higher release of carbohydrate-derived compounds at pre-pyrolysis conditions. Although at 250 °C the main biomarkers of lignin can be detected, higher temperatures are required to get a more complete information on lignin constituents of pine wood.