Thermogravimetry : a method to evaluate the regenerability of activated carbon

Abstract

A method was developed to evaluate solid phase adsorbate distribution and implied regenerability of activated carbon used in water reclamation. The method is based on thermal analysis principles and consists of heating the activated carbon in a nitrogen atmosphere to 850 °C. From the wide range of thermoanalytical techniques currently in use, thermogravimetry and evolved gas analysis were selected as the most appropriate techniques. The physical properties measured with these techniques were mass loss and moisture content. The different adsorbate fractions which influence regenerability, were characterised with respect to temperature intervals, based on first derivative minima. A specific advantage of adsorbate characterisation is the possibility of quantifying the highly volatile adsorbate fraction (desorbing at temperatures below 230 °C). This quantification was done by distinguishing between moisture and total mass loss in this temperature range. In this study the emphasis lay in the development of a test method for the evaluation of spent activated carbons from a regenerability point of view and also on the practical evaluation of this test method. The activated carbons studied were evaluated for the influence liquid phase oxidative pre-treatment has on regenerability. The overall tendency was that, of the pretreatments used, preozonation had a more favourable influence on regenerability than preoxygenation and prechlorination. The test method was also used to study carbons used to reclaim secondary treated wastewater for paper production. With the developed test method, it was possible to advise the user on the reusability and regenerability of the carbons in question. This practical application of the developed test method helped to prove that substantial cost savings can be obtained by proper regeneration of spent activated carbons.