Synergistic effect and kinetics of co-pyrolysis of lignocellulosic residues from the winemaking industry: A waste-to-biofuel conversion example toward a low-carbon economy

The wine industry generates substantial lignocellulosic waste with potential for biofuel production via co-pyrolysis. This study investigates the co-pyrolysis behavior of winemaking residues, including grape stalks (GS), grape pomace from red winemaking (GPW), and grape pomace from grappa production (GPG), in binary and ternary combinations, with the aim of optimizing energy recovery. The biomasses underwent characterization, including compositional, proximate, ultimate, bulk density, and higher heating value analyses. The pyrolysis of the individual residues and their mixtures was conducted in a thermogravimetric analyzer at 5, 10, 20, and 30 °C min⁻¹. The activation energy (E_a) and the pre-exponential factor (A) were estimated using the Kissinger-Akahira-Sunose isoconversional and the Kissinger methods, respectively. Synergistic effects were assessed by comparing theoretical values of solid residue mass (W) and E_a, with experimental values. The average E_a ranged between 190.25 and 233.13 kJ mol⁻¹, with A between 4.76 × 10¹⁶ and 4.26 × 10²⁰ min⁻¹. The ternary mixture exhibited a positive synergistic effect by reducing E_a, lowering the energy barrier for thermal decomposition, and enhancing the reaction's feasibility. In contrast, binary mixtures exhibited a negative synergy, with higher E_a values than individual residues. Notably, the GS + GPG mixture exhibited a positive synergy in terms of W, T_max, and decomposition rates. These findings show that co-processing winemaking residues can have both beneficial and adverse effects, depending on the combination. The results highlight the untapped potential of this agro-industrial waste as valuable biofuel feedstocks and offer a simplified, practical approach for industrial use, with sustainable organic residue management aligned with circular economy principles.