Prospecting pecan nutshell pyrolysis as a source of bioenergy and bio-based chemicals using multicomponent kinetic modeling, thermodynamic parameters estimation, and Py-GC/MS analysis

This work reports the first detailed investigation of the physicochemical properties of the pecan nutshell waste (PNS) and its suitability for pyrolytic conversion into bioenergy and bio-based chemicals based on the kinetic triplet, thermodynamic parameters, and Py-GC/MS analysis. The pyrolysis behavior of PNS was assessed using a thermogravimetric analyzer at five heating rate programs under an oxygen-free atmosphere. The Asym2Sig deconvolution function showed that pyrolysis of PNS might be successfully modeled as three parallel devolatilization events (R2 > 99%), which are categorized as the devolatilization of hemicellulose (DE-HC), devolatilization of cellulose (DE-CL), and devolatilization of lignin (DE-LG). The activation energy was obtained for each devolatilization event by concurrent use of four isoconversional methods (Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink), with average values in the range of 100.3–109.0 kJ mol−1 for DE-HC, 124.3–135.3 kJ mol−1 for DE-CL, and 357.1–398.9 kJ mol−1 for DE-LG. Calculations using the compensation effect method indicated pre-exponential factor values of 5.50 × 108 min−1 for DE-HC, 1.32 × 109 min−1 for DE-CL, and 4.86 × 1018 min−1 for DE-LG. It is inferred that the DE-CL corresponds to a geometrical contraction reaction model while the DE-HC and DE-LG follow order-based reaction models. Finally, the summative kinetic interpretation was successfully obtained based on multiple kinetic triplets, providing a useful mathematical tool able to describe the pyrolysis behavior of PNS. From the thermodynamic viewpoint, PNS has significant potential for application as raw material for bioenergy production. Also, the condensable fraction of the volatile products derived from pecan nutshell pyrolysis is a potential source of valuable bio-based chemicals.