Thermo-Acoustic Catalytic Effect on Oxidizing Woody Torrefaction

Oxidative Conversion of Chars Generated from the Fixed-Bed Pyrolysis of Wood Torrefied at Different Temperatures and Holding Times

Fixed-bed pyrolysis of torrefied spruce wood, for a heating temperature of 800 K, results in char yields between about 27–57 wt% (versus 23 wt% for untreated wood), depending on both pre-treatment temperatures (533–583 K) and holding times (8–25 min). In this study char oxidation behavior and kinetics are investigated by means of thermogravimetric analysis. The differential thermogravimetric curves always showed a low-temperature zone of slow rates (oxidative devolatilization), followed by a high-rate zone with a well-defined peak (oxidation). As the torrefaction severity increases, the temperature range of the oxidative devolatilization enlarges. Moreover, the oxidation rates become slower (both burning and burnout temperatures tend to increase). As already found for untreated wood chars, the two stages are well described by a linear and a power-law rate reaction, respectively. Volatiles released from the devolatilizations are approximately around 20 wt%, but torrefaction causes lower activation energies (66–92 kJ/mol versus 117 kJ/mol). The oxidation activation energies also decreas (170–168 kJ/mol versus 193 kJ/mol), accompanied by small variations in the reaction order.

Towards a sustainable waste-to-energy pathway to pequi biomass residues: Biochar, syngas, and biodiesel analysis

The waste-to-energy (WTE) valorization pathway of Caryocar brasiliense (pequi) seeds was investigated via pyrolysis, gasification, and transesterification to understand its potential as biochar, syngas, and biodiesel. First, the pyrolysis (300-700 °C) was conducted in N₂ atmosphere for pequi seeds (PS) and pequi seeds without its extractives (PSWE), characterizing its biochar properties. The PSWE was then gasified at 1000 °C under O₂/N₂, O₂/CO₂/N₂ and O₂/H₂O/N₂ atmospheres to evaluate the characteristics of the producer gas. The PS extractives were then transesterified and characterized for biodiesel production. Finally, a multiple-criteria decision analysis assessed the PS products' potential within the thermochemical routes. The results evidenced better biochar (up to 22.29% HHV enhancement, higher mass and energy yield, up to 75.9 and 85.5% reduction of O/C and H/C, respectively, and enriched N content) via PSWE pyrolysis than PS considering biofuel application and optimistic perceptions for soil amendment. This indicates that the preceding extraction of vegetal fat from PS strengthens the WTE by including further processing of extracted oil. The produced syngas under O₂/H₂O/N₂ gasification atmosphere showed better applicability as a biofuel (16.37 MJ·kg^-1 lower heating value, 107.33% cold gas efficiency, and 113.55% carbon conversion efficiency) with up to 24% higher success rate. The transesterification of the extractives revealed its potential (98% conversion rate) for use as feedstock for in situ power generation, or blended for biodiesel production. The results provide insights into the circular economy in agro-extractivist communities that may support Brazil's small and medium agro-food industries with their energy demands.