Evaluation on activation energy of deposited clay based on thermo-gravimetric analysis (TGA) and four kinetics models

Abstract

In order to evaluate and compare the accurate activation energy variations of two kinds of deposited clays (i.e. non-organic clay and organic clay), thermo-gravimetric analysis (TGA) was firstly conducted to study the reaction characteristics of the two clay samples. Two periods of weight losses were observed according to each TGA curve for both clay samples. The first period happened due to water evaporation, while the second period was mainly caused by the composition reactions of clay minerals, especially influenced by the de-hydroxylation of kaolinite. An obvious phenomenon is that the organic clay with a high soil organic matter (SOM) has a higher activity energy. Then, four common kinetics models [i.e. the Coats-Redfern method, the Doyle integral method, the maximum rate method, and the distributed activation energy model (DAEM)] were used to calculate and compare the activation energy values. And the Doyle integral method and the DAEM method are considered as two recommended models to analyze the activation energy performance during thermal treatment. Some interesting conclusions can be summarized as: (1) The multi-period reactions of deposited clays during the heating process are common, especially for organic clay. It would be beneficial knowing its biomass resource feasibility concerning the second weight loss; (2) The high SOM has a significant influence on the potential energy unitization of deposited clays, while the variations of activity energy for deposited clays are influenced by the mineral compositions and microstructure features; (3) It is possible to evaluate the accurate activity energy of deposited clays combined with TGA tests and two recommended models (i.e. the Doyle integral method and DAEM method).