Hybrid adaptive neuro-fuzzy inference systems for forecasting benzene, toluene & m-xylene removal from aqueous solutions by HZSM-5 nano-zeolite synthesized from coal fly ash

Abstract

In this research study, a mesoporous HZSM-5 nano-zeolite (SiO2/Al2O3=40) was hydrothermally synthesized from a type of coal fly ash containing high amounts of muscovite plates. The physicochemical properties of coal fly ash and HZSM-5 were examined by various characterization techniques. The synthesized HZSM-5 was applied in simultaneous removal of benzene (B), toluene (T) and m-xylene (X) from aqueous solutions. The effect of adsorption parameters such as solution pH, adsorbent dosage, contact time, initial concentration and temperature on the removal efficiencies of benzene, toluene and m-xylene were evaluated in batch-scale experiments. The maximum adsorption capacity (qmax) of synthesized HZSM-5 was achieved at optimum conditions; pH=7 and t=90 min qmax;B=9.03<T=9.16<X=9.37 mg/g. The kinetic and isotherm studies revealed that the adsorption data were well fitted with pseudo-first order kinetic and Freundlich isotherm models and the equilibrium adsorption was attained within 90 min. Thermodynamic assessments at three different temperatures of 25, 45 and 65 °C displayed that the uptakes of benzene, toluene and m-xylene onto HZSM-5 were exothermic, feasible and spontaneous at ambient temperature. Furthermore, three hybrid intelligence models comprising adaptive neuro-fuzzy inference system integrated with grid partition, subtractive clustering and fuzzy c-means were employed to estimate the removal efficiencies of benzene, toluene and m-xylene. Statistical analysis clearly proved the acceptable performance of all developed hybrid models. The highest accuracy was obtained by ANFIS-FCM models R2 >0.98 with minimum number of fuzzy rules (nR−FCM=10) which is indicative of the superiority of this method over others. The overall results suggested that the synthesized mesoporous HZSM-5 nano-zeolite could be an efficient and cost-effective adsorbent to eliminate the contamination of benzene, toluene and m-xylene from aqueous solutions.