Experimental Study And Molecular Simulation Of Adsorption Of Gaseous Polycyclic Aromatic Hydrocarbons On Mesoporous Materials

On the basis of the demands for high-efficiency adsorption and low-consumption regeneration in purifying gaseous polycyclic aromatic hydrocarbons(PAHs)with adsorption methods,this thesis adopts mesoporous adsorbents,studying the key problems of PAH adsorption thermodynamics and kinetics,regeneration properties and adsorption mechanisms at micro-level.A series of experimental and molecular simulation investigation is conducted.A quasi-equilibrium adsorption experiment for gaseous PAHs is established.The adsorption equilibra and kinetics of three types of PAHs(naphthalene,phenanthrene and pyrene)on three typical mesoporous adsorbents(mesosilicas MCM-41,SBA-15,and mesocarbon CMK-3)are studied with corresponding adsorption isotherms and breakthrough curves at various concentrations.Freundlich and Langmuir isotherm models are able to describe the adsorption equilibra for larger and smaller PAHs,respectively,and the constant-pattern breakthrough model agrees with the experiment data well.The results show that internal diffusion is the rate-determining step for PAHs adsorption,based on which the mesoporous materials have greater adsorption kinetics compared to traditional adsorbents.The coexisting micropores increase the PAHs adsorption capacities and the crosslinking micro-mesoporous structure facilitates the adsorption mass transfer,while the disordered micropore structure could increase the internal diffusion resistance for the larger adsorbates(phenanthrene and pyrene).The thermogravimetric analysis technique has been improved for PAH desorption on mesoporous materials.Based upon the temperature programmed desorption(TPD)experiments,desorption peak temperatures and kinetic triplets for each sorbent-sorbate pair are obtained.The nucleation and growth model is found to be the main kinetic model for PAH desorption,except for the special cases on phenanthrene/SBA-15 and pyrene/CMK-3 due to the two-dimensional diffusion and the π-π interaction,respectively.For MCM-41,PAH desorption behaves consistently in one-dimensional mesopores.For SBA-15,desorption mass transfer is improved by the crosslinking micro-mesoporous structure.For CMK-3,the network of carbon rods abundant in micropores intensifies adsorption but limits desorption diffusion.A reasonable micropore distribution is critical to the selection of high-performance PAH adsorbents.A multi-scale molecular simulation is developed,with rationally constructed mesoporous models of MCM-41 and SBA-15.The grand canonical Monte Carlo and molecular dynamic methods are applied in modelling PAHs adsorption effects and status,combining the experimental results to menifest the key roles of the crosslinking micro-mesoporous structure in improving the adsorption capacity,stablizing the adsorption heat and balancing the adsorbate distribution.With increasing molecular size,the extent of the tiled adsorption configuration,the degree of order and the stability of PAH adsorbates on the mesosilica surface increase.The first-principles calculations are further conducted to explore the adsorption configuration,interaction energy,and adsorption bondings.It is demonstrated that based on phyical adsorption,PAH adsorption is dominated by dispersion force which is able to significantly promote adsorption on the hydrophobic surface.The PAH aromatic delocalizing π electrons contribute to electrostatic attractions,while the hydrogen bonds function as lateral confinement for PAH adsorbates.The research findings in this thesis can provide theoretical and technical references for the adsorptive purification of PAHs using mesoporous materials,which is meaningful to both academic and engineering applications.