Chlorophenol reactions on fly ash .2. Equilibrium surface coverage and global kinetics

The adsorption properties of chlorophenols, mostly 2,3,4,6-tetrachlorophenol, on MSWI fly ash were measured as a function of temperature and gas-phase chlorophenol concentration. Chlorophenols were found to be highly adsorptive on fly ash while satisfying a Freundlich adsorption isotherm with theta(s) = cP(g)(0.50+/-0.05), where theta(s) is the fractional surface coverage, c is a function of temperature, and P-g is the gas-phase chlorophenol concentration. Adsorption studies at low temperatures suggested that the fly ash used had about 6 x 10(18) adsorption sites per gram, The catalytic mechanism for chlorophenol conversion to polychlorinated dibenzo-p-dioxins (PCDD) on fly ash was consistent with a Langmuir-Hinshelwood model. The global rate of PCDD formation from chlorophenols on fly ash was best represented by r(PCDD) = kP(g)(1.0), where k is a complicated function of temperature incorporating the reaction rate constant and the temperature-dependent Freundlich isotherm constant.