Adsorption kinetics, equilibrium and thermodynamics of gas-phase toluene onto char produced from almond shells

Toluene is the primary material in chemical process industries and is often used as a raw material in the production of many chemicals and as a solvent in many engineering processes. In this study, the material of char, which is used as an adsorbent, was produced from almond shells. The adsorption process of gas-phase toluene onto char was investigated using a laboratory-scale fixed-bed reactor under atmospheric pressure. The structure of the char was characterized by BET and FTIR. The influences of adsorption parameters such as nitrogen (N2) flow rate as the gas-phase toluene carrier, char amount, gas-phase toluene concentration at the inlet and the adsorption temperature on both the adsorption capacity and adsorption efficiency were examined. It was found that the adsorption of the gas-phase toluene onto char could be well represented by the pseudo-second-order kinetic model. Equilibrium isotherm data were analyzed by the Langmuir and Freundlich isotherm models and the results indicated that the adsorption process was described well by the Langmuir isotherm model. The maximum monolayer adsorption capacity (qmax) of the char was determined as 15.42 mg g^-1 for 303 K. Thermodynamic parameters such as ΔG° = -7.93 kJ mol^-1, ΔH°= -17.18 kJ mol^-1, ΔS°= -0.013 kJ mol^-1 K^-1 showed that the adsorption process was spontaneous, exothermic and physical. The results showed that the material of char produced from almond shells could be used as a biosorbent to remove the material of gas-phase toluene from various industrial and natural sources through the adsorption method.