| The impact of narrow pore size distribution (PSD) of activated carbon fibers (ACFs) on the oligomerization of phenolic compounds was conducted in this study. Four types of microporous ACFs with increasing degrees of activation, namely ACC-10 (8.0 A), ACC-15 (12.8 A), ACC-20 (17.4 A) and ACC-25 (19.7 A), and one granular activated carbon (GAC) F400 (4-800 A) were used as adsorbents. Seven commonly encountered phenolic pollutants were used as adsorbates - phenol, 2-methylphenol, 2-ethylphenol, 2-chlorophenol, 2-nitrophenol, 4-chlorophenol, and 4-nitrophenol. Single, binary and ternary adsorption of phenolic compounds were conducted under anoxic (absence of molecular oxygen) and oxic (presence of molecular oxygen) conditions.; Single solute adsorption of phenolic compounds was found to be well described by Myers equation (Ce,i = qe,iHi x exp(Kiqe,ipi)). For each adsorbate except nitrophenols, higher adsorptive capacities were achieved under oxic than anoxic conditions. The extent of oligomerization which was represented by the difference between the oxic and anoxic adsorptive capacity, were changing in the order of F400 > ACC-25 > ACC-20 > ACC-15 > ACC-10. This is in the same order as the decrease of the adsorbent pore diameter. At the same time, F400 showed least adsorption under anoxic conditions among all the adsorbents. The narrow PSD of ACFs was effective in hampering oligomerization in the single solute adsorption. Higher extraction efficiencies were achieved for ACFs than F400. The lower the extent of oligomerization, the higher regeneration efficiency was achieved. On each adsorbent, the extents of adsorbates oligomerization were related to the adsorbates critical oxidation potential (COP), molecular size, and adsorbent pore diameter. Low COP, small molecular size, large pore diameter always favored oligomerization.; Binary adsorption for different phenolic compounds was conducted on ACC-10, ACC-15 and F400. No difference between anoxic and oxic binary adsorption isotherms were found on ACC-10. The Ideal Adsorbed Solution Theory (IAST), using the Myers equation for correlating the single-solute anoxic isotherms, successfully predicted the anoxic and oxic binary adsorption on ACC-10. For binary adsorption on ACC-15 and F400, the oxic adsorption was higher than anoxic ones and IAST well predicted the anoxic isotherms, but under predicted the oxic ones due to occurrence of oligomerization of the adsorbates on the adsorbent surface. The deviation of the experimental adsorption isotherms from predictions for F400 was larger than that of ACC-15. (Abstract shortened by UMI.)... |
