Non-isothermal pyrolysis of grape marc

Abstract

The non-isothermal decomposition behavior of grape marc (GM) residues from wine industry was investigated by using different thermal analysis techniques, including: (1) thermogravimetric analysis/differential thermogravimetry (TGA-DTG) to study the thermal decomposition kinetics; (2) thermogravimetry (TG-DTG) coupled with Fourier transform infrared spectroscopy (FTIR) to investigate the nature of the gas-phase products released during the pyrolytic breakdown; and (3) simultaneous thermogravimetry/differential scanning calorimetry (TGA–DSC) analysis to obtain information on the heat flows associated with the thermal decomposition of grape marc. Thermogravimetric measurements at five different heating rates (i.e., 2.5, 5, 10, 20, 40 K min−1) were performed for the kinetic computations, which were carried out by adopting a “model-free” approach based on the application of isoconversional methods. In more details, two different integral methods, i.e., the linear Ozawa–Flynn–Wall (OFW) method and the nonlinear Vyazovkin incremental method, were comparatively used in order to obtain a set of kinetic parameters useful for the conceptual design of thermochemical processes involving grape marc. The reliability of the obtained parameters was confirmed by the successful application of the same data to reproduce experimental TG curves not included in the kinetic computations. The effect of the heating rate on the nature of the gas-phase products arising from grape marc decomposition as well as on the heat flows associated with the pyrolytic process was also investigated. Finally, the study was complemented with an extensive investigation on chemical and physical properties of grape marc residues (i.e., ultimate analysis, proximate analysis, calorific values determination, FTIR analysis and cellulose, hemicellulose and lignin content determination), which provides useful input data for modeling grape march conversion processes.