Efeitos estruturais e moleculares da carbonização hidrotérmica no comportamento pirolítico de Corymbia Torelliana Via Py/Gcms

Abstract

This work aimed to evaluate the effects of hydrothermal carbonization (HTC) pretreatment on the pyrolysis of Corymbia torelliana wood waste, using the technique of fast pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). The biomass was subjected to HTC at temperatures of 180∘C, 220∘C, and 240∘C, with a residence time of 60 minutes, under autogenous pressure and a biomass-to-water ratio of 1:4. The raw biomass and the produced hydrochars were characterized using proximate, ultimate, GCV, FTIR, XRD, ICP-OES, and TGA analyses. The gravimetric hydrochar yield reduced with increasing temperature: 70.49% (180∘C), 60.31% (220∘C), and 41.94% (240∘C). The gross calorific value (GCV) increased from 19.34 MJ/kg in the biomass to 28.53 MJ/kg in the hydrochar treated at 240∘C. The fixed carbon content increased from 14.09% to 50.48%, while volatile matter reduced from 84.48% to 48.91%. The ultimate analysis indicated an increase in carbon content from 47.14% to 64.59%, a reduction in oxygen from 45.38% to 28.98%, and a decrease in the atomic ratios H/C (1.39 to 0.92) and O/C (0.72 to 0.34), suggesting increased aromaticity and thermal stability. Thermogravimetric analysis (TGA) revealed that the hydrochars possess greater thermal stability, with less mass loss in the temperature ranges up to 500∘C and a higher residue content above 400∘C. X-ray diffraction (XRD) analysis indicated an increase in relative crystallinity index (CRI) from 51.36% (biomass) to 66.45% (HTC-240∘C). FTIR analysis confirmed the degradation of −OH, C–O, and C–H groups, along with the enrichment of the aromatic structure. The evaluation of volatile products by Py-GC/MS, performed at temperatures of 450∘C, 550∘C, and 650∘C, demonstrated that the raw biomass generated higher proportions of oxygenated compounds, such as acids and phenols. In contrast, the hydrochars, especially those treated at 240∘C, showed an increased formation of anhydro-sugars (e.g., D-Allose) and valuable phenolic compounds, with a reduction in undesirable oxygenated compounds. It is concluded that HTC is an efficient strategy to enhance the physicochemical properties of biomass, making it more suitable for thermochemical processes, such as pyrolysis, with the generation of energetic and chemical products of higher quality and added value. The HTC temperature of 240∘C demonstrated the best results regarding favorable characteristics for applications such as bio-oil.