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

Abstract

Toluene is the primary material in chemical process industries and is often usedas a raw material in the production of many chemicals and as a solvent in manyengineering processes. In this study, the material of char, which is used as anadsorbent, was produced from almond shells. The adsorption process of gasphase toluene onto char was investigated using a laboratory-scale fixed-bedreactor under atmospheric pressure. The structure of the char was characterizedby BET and FTIR. The influences of adsorption parameters such as nitrogen (N2)flow rate as the gas-phase toluene carrier, char amount, gas-phase tolueneconcentration at the inlet and the adsorption temperature on both theadsorption capacity and adsorption efficiency were examined. It was found thatthe adsorption of the gas-phase toluene onto char could be well represented bythe pseudo-second-order kinetic model. Equilibrium isotherm data wereanalyzed by the Langmuir and Freundlich isotherm models and the resultsindicated that the adsorption process was described well by the Langmuirisotherm model. The maximum monolayer adsorption capacity (qmax) of the charwas determined as 15.42 mg g-1 for 303 K. Thermodynamic parameters such as?G° = -7.93 kJ mol-1, ?H°= -17.18 kJ mol-1, ?S°= -0.013 kJ mol-1 K-1 showed that theadsorption process was spontaneous, exothermic and physical. The resultsshowed that the material of char produced from almond shells could be used asa biosorbent to remove the material of gas-phase toluene from various industrialand natural sources through the adsorption method.