Thermogravimetric Analysis–Fourier Transform Infrared Spectroscopy Study on the Effect of Extraction Pretreatment on the Pyrolysis Properties of Eucalyptus Wood Waste

Eucalyptus wood is one of the important hardwood resources with attractive properties of rapid growth and good quality, which are widely used for the manufacture of wood-based boards, furniture, pulp and paper, and so on. In order to explore the potential of sawdust waste from the eucalyptus wood furniture factory as a bioenergy feedstock, its pyrolysis properties after different solvent extractions were examined using thermogravimetric analysis coupled with Fourier transform infrared spectrometry. The mass ratio of extractives in eucalyptus wood sawdust by benzene–alcohol, hot water, and sodium hydroxide solution was 4.25, 9.68, and 16.11%, respectively. After extraction, the thermal decomposition process of eucalyptus wood was promoted with a higher weight loss rate, lower activation energy, and lower residue content compared to the raw sample without pretreatment, and the promotion level was positively correlated to the strength of extracting solvent. CO2, CO, CH4, H2O, acids, aldehydes, aromatics, ethers, and alcohols were identified as the important intermediates in pyrolysis vapors, which can be tuned by different extraction pretreatments. In terms of typical gas products, benzene–alcohol enhanced the release of carbon dioxide, and hot water enhanced the water generation from dehydration reactions and slightly increased the production of carbon monoxide, while sodium hydroxide promoted the formation of methane at the early stage under 280 °C and later stage over 460 °C during the pyrolysis of eucalyptus wood. It is believed that the extraction pretreatment can not only obtain the bioactive extractive products but also benefit the pyrolysis process by lowering the energy barrier and tuning the composition of pyrolysis products.