Thermal analysis of physical and chemical changes occuring during regeneration of activated carbon

High-temperature thermal process is a commercial way of regeneration of spent granular activated carbon. The paper presents results of thermal analysis conducted in order to examine high-temperature regeneration of spent activated carbon, produced from coconut shells, previously used in drinking water treatment. Results of performed thermogravimetric analysis, derivative thermogravimetric analysis, and differential thermal analysis, enabled a number of hypotheses to be made about different phases of activated carbon regeneration, values of characteristic parameters during particular process phases, as well as catalytic impact of inorganic materials on development of regeneration process. Samples of activated carbon were heated up to 1000 degrees C in thermogravimetric analyser while maintaining adequate oxidizing or reducing conditions. Based on diagrams of thermal analysis for samples of spent activated carbon, temperature intervals of the first intense mass change phase (180-215 degrees C), maximum of exothermic processes (400-450 degrees C), beginning of the second intense mass change phase (635-700 degrees C), and maximum endothermic processes (800-815 degrees C) were determined. Analysing and comparing the diagrams of thermal analysis for new, previously regenerated and spent activated carbon, hypothesis about physical and chemical transformations of organic and inorganic adsorbate in spent activated carbon are given. Transformation of an organic adsorbate in the pores of activated carbon, results in loss of mass and an exothermic reaction with oxygen in the vapour phase. The reactions of inorganic adsorbate also result the loss of mass of activated carbon during its heating and endothermic reactions of their degradation at high temperatures