The kinetic study of juice industry residues drying process based on TGA-DTG experimental data

Abstract

Sustainable development and mitigation of the climate changes are one of the main challenges of the circular economy, while the use of food industry residues could make an important contribution in tackling these challenges. In order to improve energy efficiency aspects of the industry residue treatment, generally, the drying process as the first step of the entire processing chain should be further analyzed. Regarding this, a comprehensive kinetic study was performed to provide the detailed mechanism of moisture removal from base raw material. Industrial residues from apple juice production were used for isothermal thermogravimetric analysis in the air atmosphere at different temperatures. Based on experimental data, different kinetic models were applied to determine kinetic parameters and dominant conversion functions. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the drying process is complex one. The mechanism of drying process and corresponding kinetic parameters were determined by multivariate nonlinear regression program (model-based analysis) and checked by modulated isothermal prediction (for quasi-isothermal conditions) and the isothermal prediction (for different isothermal conditions) tests. It was pointed out that temperature-dependent reaction step controlling overall mechanism represents releasing of CO2 which can suppress autocatalytic action of the ethylene, influencing the flavor and texture changes of the apple tissue. Obtained results can be used for prediction of the life-time of studied material, corresponding to selected temperatures and different conversion levels.