| High purity chars derived from phenol-formaldehyde resin were synthesized, and their behaviour in low temperature was studied. It was found that their properties successfully model those of naturally occurring carbonaceous materials in many respects. The chemical structure of phenolic resin chars was found to involve highly condensed aromatic rings, and a conceptual model of such a structure was formulated.Oxygen chemisorption, as a tool for active surface area determination, was critically evaluated, especially in its application to "young" chars, i.e. those that have been pyrolysed under relatively mild conditions. It was concluded that this technique is inadequate for quantitative ASA measurements, primarily due to strong dependence of oxygen uptake upon arbitrarily selected temperature and oxygen partial pressure. On the other hand, oxygen chemisorption may be successfully used in studying surface reactions between carbon and oxygen containing agents. It was also confirmed after other workers that oxygen uptake during chemisorption correlates favourably with oxidation reaction rates, much better than total surface area.Thermal annealing of phenolic resin chars was also studied. It was determined that this process is associated with a dramatic decrease in the number of active sites. Changes in activation energy, as well as in the CO... |
