Temperature-Dependent Chemical Profiles of Pyroligneous Liquor Fractions from a Kiln-Furnace System

Pyroligneous liquor (PL) is a by-product of charcoal production with potential applications in agriculture, forestry, and industry. This study evaluated the influence of carbonization temperature on the yield, chemical composition, and physicochemical properties of PL obtained from Eucalyptus spp. in a sustainable kiln-furnace system. PL fractions were collected at four temperature intervals: T1 (60–170 °C), T2 (171–270 °C), T3 (271–350 °C), and T4 (351–400 °C). The recovery of condensable gases did not affect the quality of the charcoal and minimized pollutant emissions. Gas chromatography–mass spectrometry (GC-MS) identified 78 organic compounds, mainly carboxylic acids, phenolic compounds, alcohols, carbohydrates, and aromatics. The highest PL yield was obtained in T3 (271–350 °C), accounting for 27% of the recovered liquor and showing high phenolic content, including syringol and catechol. In contrast, T1 (60–170 °C) showed the lowest yield and was dominated by carboxylic acids, particularly acetic acid. Carbonization temperature affected both PL composition and physicochemical properties, resulting in higher electrical conductivity and vegetable tar content at higher temperatures. Hierarchical cluster analysis revealed distinct compound groups according to their concentration patterns across the evaluated temperature intervals. These results reinforce the notion that the evolution of pyrolysis vapors is not a continuous or homogeneous process, but rather occurs through discrete and chemically distinct stages driven by the sequential decomposition of hemicellulose, cellulose, and lignin—a behavior that directly justifies the temperature-based fractionation approach adopted. It was found that temperature-controlled fractionation effectively yields pyrolysis liquid (PL) fractions with distinct chemical profiles, facilitating the selective recovery of value-added compounds for forest biomass biorefineries and specific end-use applications, in addition to offering environmental benefits.