Abstract

In this research, by using derivation of Langmuir isotherm model and sharing point of this model with Volmer, Kiselev and Fowler-Guggenheim models, a new simple approach to derivation of isotherm models named Adsorption Effective Surface (AES) was introduced. Using AES method, one can explain such behavior of theoretical models as in predicting maximum adsorption capacity (q_m). In this method, adsorption and desorption follow first order kinetics and all non-idealities appears in term S_eff(θ). Three new isotherm models, two models with monolayer adsorption mechanism based on Langmuir equation and one model with monolayer-multilayer adsorption mechanism based on Langmuir and Elovich equations are derived using AES method. The adsorption equilibrium isotherms of five benzoic compounds from aqueous solutions onto two granular activated carbons (GAC) with average granulometries of 1.5 and 2.5 mm were studied. Benzene (B), Toluene (T), Phenol (P), Chlorobenzene (CB) and Nitrobenzene (NB) were chosen for adsorption test and effect of adding groups such as methyl, hydroxide, chlorine and nitroxide on benzene ring in its adsorption were discussed. Uptake of Benzoic compounds increase in the following order P<B<T<NB<CB, which correlates in general with increase in polarisability and decrease in solubility. Activated carbon adsorbent with lower particle size (1.5 mm) has more adsorption capacities about 10% in average. The proposed equations named AES, Logarithmic and Hybrid model were used to model the experimental data, and results were compared with corresponding equations. Regression results showed that in all cases, the new models had better fittings with experimental data than corresponding models.

Key words: Isotherm model, adsorption effective surface, benzoic compounds, activated carbon.