Potential demonstrations of hot spots presence by adsorption-desorption of toluene vapor onto granular activated carbon under microwave radiation

Differences of adsorption-desorption process between microwave irradiation and conductive heating were studied to prove potential possibility of hot spots presence. Breakthrough curves of toluene vapor were recorded at different initial conditions. The results show that the time required to reach equilibrium (t(e)) is shortened by 6-15% and adsorption capacity (N-(exp)) is reduced by 6-13% at various constant conditions under microwave heating. Yoon-Nelson and Bed Depth Service Time models were applied to analyze adsorption process. Values of k(y) calculated by Yoon-Nelson model under microwave radiation are larger by 2-36%, while values of No determined by BDST model are smaller by 7-12%. Langmuir, Freundlich and Sips models were used to fit equilibrium data and describe adsorption isotherms. Values of q(m) and q(s) obtained from Langmuir and Sips models under microwave heating are smaller than that under conductive heating. Moreover, heat of adsorption calculated from Clausius-Clapeyron equation under microwave radiation are also lower. It is found that the desorption rate under microwave radiation is faster and SBET and V-T obtained after desorption process are larger. Differences of adsorption desorption process between microwave and conductive heating can be explained by the presence of the hot spots induced by microwave radiation that the temperature of some microstructures of surface regions is much higher than the overall temperature. (C) 2017 Elsevier B.V. All rights reserved.