Modeling bicomponent adsorption of aromatic compounds onto nonpolar polymeric resin MN200

A large number of organic contaminants are commonly found in industrial and municipal wastewaters. Aromatic compounds, such as phenol, aniline and their derivatives, are contaminants of high priority and usually coexist in waste streams from industries of, for example, aromatic amine compounds and ammonolysis of phenols. Thus, for proper unit design to remove contaminant mixtures by adsorption, multi-component adsorption models are necessary. The present work was aimed at examining the applicability of Ideal Adsorbed Solution Theory (IAST), a prevailing thermodynamic model, and its derivative i.e. Segregated IAST (SIAST) and Real Adsorbed Solution Theory (RAST) to multi-solute adsorption from the aqueous phase, specifically, bi-solute adsorption of phenols, anilines and nitrobenzene onto a hyper-crosslinked polystyrene resin, MN200. Based on the experimental bi-solute adsorption isotherms, we have successfully developed methods for modeling with RAST incorporated with Wilson equation, Nonrandom two-liquid (NRTL) model, and an empirical four-parameter equation developed in this work. It turns out that our proposed four-parameter equation can fit the activity coefficients, gammai, better than the other two equations and thus enhanced the accuracy of RAST in predicting bi-solute adsorption equilibrium. Besides successfully developing methods for properly designing binary-solute batch experiments and accurately modeling with RAST, two empirical linear relationships have been developed for the adsorption of a number of infinite dilute solutes in the presence of a major contaminant (either 4-methylphenol or nitrobenzene). Results show that polyparameter linear free energy relationships have a great potential in predicting adsorbed phase activity coefficients of solutes when the adsorbed amounts are dominated by the major contaminant and the adsorbed mixture resembles infinite dilute solution. Activity coefficients under such conditions were represented by gamma infinityi and were successfully extrapolated to gammai at non-infinite conditions by gamma i models i.e. Wilson equation. To the best of our knowledge, this is the first systematic study predicting adsorbed phase activity coefficients for bi-solute adsorption. In addition, our tri- and tetra-solute adsorption data showed that the predominating solute, NB in this case, solely contributed to the competitive effect while the dilute solutes tend not to interact with each other. This indicates that for each solute, the competitive effects can be independently considered and a multi-component system with n components but only one component dominating can be treated as (n-1) bi-solute systems separately. This will significantly simplify the calculation for modeling multi-component adsorption while it is also close to many real systems where there is one major contaminant or a large amount of NOM in present. Our findings have proved a major step forward to accurately modeling multi-solute adsorption for proper unit design of adsorption processes.