Adsorption and decolorization of hydrogenated coal tar on resin-based activated carbon spheres

Resin-based activated carbon spheres (ACSs) were prepared by a combined suspension polymerization, carbonization and activation method. The ACSs were then oxidized with nitric acid (NACSs) to modify the surface properties to increase the decolorization of hydrogenated coal tar. The morphology, pore structure, elemental composition and pyrolysis kinetics of the polymer sample were characterized by SEM, N₂ adsorption, FTIR, XPS and TGA. Results showed that this oxidation modification of the ACSs has little influence on their surface morphology and pore structure while the numbers of surface oxygen functional groups were remarkably increased. P-benzoquinone (DBD) and N,N-di-sec-butyl-1,4-phenylenediamine (PBQ) were selected as model color compounds for decolorization tests with ACSs and NACSs. The effects of adsorption time, temperature and amount of adsorbent on the decolorization performance were investigated. Under the same adsorption conditions, the amounts of decolorization of DBD and PBQ were 94.5% and 96.6%, respectively for NACSs while those for ACSs were much lower, indicating the outstanding adsorption performance of NACSs. Hydrogen bonds formed between surface functional groups and colored compounds may play a key role in improving the adsorption performance. Moreover, the decolorization of NACSs was still more than 90% after NACSs were recycled 6 times. The decolorization effect of NACSs for real hydrogenated coal tar was also significant and its color faded after adsorption by NACSs, confirming their feasibility for practical use.