Assessment of the pyrolysis kinetics and mechanism of vegetable-tanned leathers

Abstract

The pyrolysis kinetics and mechanism of leathers that were tanned with mimosa extract and tannic acid were investigated in this paper. The Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods were applied to calculate the activation energy and thermodynamic parameters, including the preexponential factor, Gibbs free energy, enthalpy, and entropy. The Criado method was further employed to determine the kinetic model of the pyrolysis process. Thermogravimetric analysis in combination with Fourier-transform infrared spectroscopy (TG-FTIR) analyses revealed that the evolved gaseous products from vegetable-tanned leather (VTL) pyrolysis were carbon dioxide, water, ammonia, isocyanic acid, and pyrrole. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) results showed that the main components of VTL pyrolysis were nitrogen-containing compounds (such as nitriles and diketopiperazines), aromatic hydrocarbons or hydrocarbons, and phenols. The results also indicated that the kinetics, mechanism, and pyrolysis products of the vegetable-tanned leathers depended on the type of tanning agent that was used. Nitro-ketone compounds accounted for more than 65% of the pyrolysis products of leather that was tanned with mimosa extract. In the case of tannic acid-tanned leather pyrolysis, phenols accounted for the highest percentage of the pyrolysis products. This research provides further insight into the mechanism and product characteristics of VTL pyrolysis, which provides a theoretical basis and evidence for converting solid leather wastes into value-added products.