Modeling of Activated Carbon and Coal Gasification Char Adsorbents in Single-Solute and Bisolute Systems
Thacker, William Eric
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Permalink
https://hdl.handle.net/2142/66902
Description
Title
Modeling of Activated Carbon and Coal Gasification Char Adsorbents in Single-Solute and Bisolute Systems
Author(s)
Thacker, William Eric
Issue Date
1981
Department of Study
Civil Engineering
Discipline
Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Sanitary and Municipal
Language
eng
Abstract
A mathematical model of fixed-bed adsorption was able to predict the bed response to a sustained step change in influent concentration. The model was employed to compare the performance of different adsorbants in the removal of organics from water and to analyze factors that affect desorption. Model equations, which considered that film transfer and surface diffusion controlled the adsorption rate, were solved with the technique of orthogonal collocation. Three species, 3,5-dimethylphenol (DMP), 3,5-dichlorophenol (DCP) and rhodamine 6G (R6G), were the single solutes studied, and the two phenols were also examined as a mixture. Four activated carbons and a coal gasification char were the adsorbents studied. Several single-solute and bisolute column experiments were conducted to provide data for model verification; the model predicted not only adsorption, but also desorption that resulted from a step change in influent concentration and from competition. The pretreatment of one of the carbons with free chlorine reduced the capacity, surface diffusivity and film transfer coefficient for the DMP. The model was used to compare the adsorbents in the removal of DMP, R6G and the bisolute mixture, and equilibrium capacity was found to have a greater influence than kinetics on fixed-bed performance. The char performed poorly relative to the carbons because of low capacity. From single-solute model predictions of desorption due to a reduction in influent concentration, it was determined that lower initial effluent concentrations resulted when the mass transfer coefficients, capacity, isotherm slope and bed length were decreased and the flow rate and adsorbent particle size were increased. Simulations of bisolute adsorption demonstrated that mass transfer resistance reduced the chromatograhic overshoot of the weakly adsorbed species. Finally, it was observed that, under conditions approximating a drinking water plant, the time during which the effluent concentration of a desorbed species was higher than the influent concentration was significant (on the order of weeks) whether a reduced influent concentration or competition was responsible for the desorption.
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