Hidrodesoxigenação catalítica do bio-óleo do resíduo de sisal (Agave sisalana) empregando platina suportada em H-ZSM-5 com diferentes porosidades

Abstract

The growing global energy demand and the environmental issues caused by the consumption of fossil fuels and their derivatives have driven the development of alternative technologies and research with greater ecological and sustainable potential. In this context, bio-oil has emerged as one of the most promising routes for supplying clean energy, particularly when derived from the fast pyrolysis of biomass. Among the available biomasses, sisal (Agave sisalana) stands out due to its high stored energy content, residual origin, and chemical versatility, with a broad and complex composition. However, raw bio-oil is unsuitable for direct use as fuel, diesel additive, or lubricant, as it contains oxygenated and nitrogenated compounds, necessitating careful upgrading processes. Catalytic hydrodeoxygenation (HDO) plays a significant and promising role in refining this lignocellulosic matrix, enabling the production of upgraded by-products and eco-friendly biofuels. ZSM-5 is one of the zeolites that excels in promoting HDO reactions, converting oxygenated bio-oil species into olefins and light aromatic hydrocarbons. In this study, various ZSM-5-based catalysts were produced, incorporating platinum and featuring different pore structures, for application in the hydrotreatment of bio-oil obtained from sisal residue. ZSM-5 was synthesized from commercial reagents, using silica extracted from coal fly ash as the silicon source. To enhance the accessibility to the active sites of the zeolite, the effect of hydrothermal desilication on increasing the pore diameter was investigated. The ashes, silica, support materials, and catalysts were characterized by multiple analytical techniques, confirming their morphology and physicochemical properties. The bio-oil produced by fast pyrolysis of sisal residue was processed in a continuous-flow reactor, and the reaction products were identified by gas chromatography coupled with mass spectrometry (GC-MS) and FTIR spectroscopy. Silica extraction achieved a 35 wt% yield with 97% purity. The HZ05Pt catalyst exhibited superior performance, increasing hydrocarbon yield to 68.8%, with selectivity toward the C9–C12 (15.89%) and C13–C20 (30.86%) fractions, while reducing oxygen content to 14.26 wt% (O/C = 0.15). In contrast, excessive desilication (HZ20Pt) resulted in reduced catalytic activity and increased oxygen retention (25.03 wt%), indicating structural degradation. Nitrogen-containing compounds remained dispersed and unconverted, suggesting limited hydrodenitrogenation. The results highlight the synergistic effect of moderate hierarchization and platinum incorporation in producing stable, energy-dense biofuels. Furthermore, the use of coal fly ash as a silica source reinforces the sustainability and circular economy potential of the process.