Study On Adsorption And Desorption Behaviors Of PAHs On Granular Activated Carbon

PAHs (Polycyclic Aromatic Hydrocarbons) are a class of persistent organic pollutants. By impacting of human production and living (such as waste incineration, fossil fuel combustion, etc.), PAHs in the global environment is widespread. There is a growing concern about its existence, as a result of its complex composition, bio-accumulation, semi-volatile and very strong effect,and now it has becaming a hot topic research in the energy and environmental field.In order to grasp the PAHs emission characteristics in waste incineration flue gas, get the efficient and practical adsorption technology, and provide theoretical guidance for the industrial application of fixed bed, in this paper, the modified granular activated carbon as adsorbent was used to research the behaviors of PAHs'on the carbon with the static and dynamic adsorption respectively by fixed bed experimental. Thermal gravimetric analyzer was used to study the PAHs'thermal desorption process on activated carbon. Using the numerical fitting process to determine the mechanism of the reaction model, and finish the systematic study of the PAHs'adsorption and desorption behaviors on the activated carbon.In the fixed bed device, the adsorption process was studied, and the reaction mechanism was verified by adsorption isotherm model and adsorption breakthrough curve model. The results showed that naphthalene, acenaphthene, phenanthrene, the three typical medium and low-ring PAHs, adsorption on activated carbon using Langmuir model fits better. PAHs on activated carbon followed by decreasing trends generally; in dynamic adsorption, the axial diffusion model based on linear driving force equation can fit the dynamic adsorption process, the breakthrough time point in curves with the continuous advance by the adsorbed times increase.With the thermal analysis devices, the thermogravity curves that activated carbon have been adsorbed naphthalene, acenaphthene, phenanthrene, fluoranthene, under the condition of thermal desorption, were investigated. The results showed that:with the increase in the number of benzene rings, the PAHs on activated carbon desorption time and temperature of the peak point where continued backward. Obtained by thermal analysis kinetics parameters,it was indicated that the activated carbon of the four PAHs had the same reaction mechanism of desorption, consistent with random nucleation and subsequent growth mechanism functions model. And the desorption activation energy and pre-exponential factor showed a growth trend with the number of benzene rings. Through the multi-heating rate method, single and multi-heating rate combination method, it was showed that the results of the two methods for solving were consistent, However, the multi-heating rate method was more accuracy but less simplicity of calculation than the combining method.The physical adsorption instrument and environmental scanning electron microscope were also used to study the activated carbon's morphology before and after modification of adsorbent and adsorption-desorption conditions. The results showed that the modified activated carbon using acid and alkaline can significantly increase pore size distribution and help to increase the adsorption capacity of activated carbon.SEM images showed,623K with the first time regenerated made the greatest pore structure of activated carbon with naphthalene desorption, but the desorption of acenaphthene in this temperature get the efficient residual on the carbon, thus affected the efficiency of re-adsorption,and by the oxygen-containing functional groups with 723K impacted, absorbent pore structure were destructed, and then the adsorption efficiency continue to getting lower.