Oppervlakchemiese evaluering van die ontsoedeling van uitgeputte geaktiveerde koolstof met superkritieke koolstofdioksied

Abstract

The purpose of the study developed from the shortcomings of previous investigations in which no satisfactory explanations could be found why exhausted activated carbon which had been thermally reactivated before cannot be regenerated by sc-C02; the iodine number does not improve after regeneration by sc-CO2 despite the removal of material from the surface of exhausted activated carbon as depicted by a mass loss; sc-C02 is incapable of regenerating exhausted carbon to the same extent as thermal reactivation. The strategy to accomplish this purpose was to find answers to the crucial questions by virtue of titrimetric methods (iodine and caramel number), spectrographic techniques (scanning electron microscopy) and adsorption methods (BET analysis and mercury porosimetry). Samples of activated carbon exhausted during the refining of sugar were investigated to establish to what extent these samples could be regenerated by sc-CO2. The titrimetric results showed that both the iodine and caramel number indeed improved as a result of sc-C02 regeneration provided that the samples had not been exposed to thermal reactivation before. Thermal reactivation burns substances onto the pore surface, and these blocked pores cannot be decontaminated by sc-C02. The surface chemistry quantities proved that sc-C02 is incapable of creating new pores, and thus the iodine number does not improve in cases where sc-C02 removes material from previously reactivated carbon. It could be shown by virtue of a few thermodynamic quantities and activation parameters that the mechanism of sc-CO2 regeneration is based upon physical desorption, which totally differs from the mechanism of thermal reactivation by which new pores are created.