Kinetics models for trichloroethylene transformation by zero-valent iron

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Five models that account for experimental observations of kinetics and surface properties during trichloroethylene (TCE) transformation by iron were compared in terms of accuracy in fitting sixteen TCE concentration versus time profiles obtained from the literature. The models were based on Henri-Michaelis-Menten/Langmuir-Hinshelwood-Hougen-Watson (HMM/LHHW) kinetics and considered sorption to inactive sites, sorption and reaction at multiple binding energy sites, and catalyst deactivation in increasing order of complexity. The internal and overall effectiveness factors for all datasets were one, indicating that TCE transformation kinetics were not mass transfer limited during the initial stages of the reaction. At low TCE loading, model results suggest that the overall transformation is reaction limited. At high TCE loading however, the overall transformation appears to be sorption limited due to competitive self-inhibition of TCE on the iron surface. Model results suggest that the addition of an exponential decay term that describes catalytic deactivation best described reaction kinetics under widely different experimental conditions. Model results also suggest that TCE adsorbs to two adjacent sites, and that concentrations of active and inactive sites and TCE loading (TCE concentration per active site) are the dominant factors that control TCE transformation kinetics. The results also suggest that in experiments initiated in the zero-order region, the order of the reaction may change to first-order and then back to zero-order as the reaction progresses due to a decrease in active site concentration as the catalytic surface is deactivated. Comparisons of fitted and reported model parameters suggest that specific surface area of iron from BET isotherms may not provide a true representation of the actual number of sites on the iron surface. © 2002 Elsevier Science B.V. All rights reserved.

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Applied Catalysis B: Environmental