Molecular Simulation And Experimental Study On Adsorptive Separation Of Aromatic Isomers With Simulated Moving Bed

Simulated moving bed technology possesses a promising application in the field of adsorptive separation for aromatic isomers, and the core of this process lies in adsorbents and desorbents with high performance. With studies on preparation and characterization of adsorbent, dynamic adsorption experiments, and molecular simulation, adsorptive separation performances of three aromatic isomers including xylene, dichlorobenzene and cresol on FAU zeolites with simulated moving bed were investigated systematically.The KY adsorbent was prepared through the modification of NaY zeolite by means of ion-exchange. The zeolites samples were analyzed with flame photometer and X-ray diffraction (XRD), and quantitative determination of ion exchange degree was achieved using the linear relationships between intensity percentage and area percentage of the peak at 2θ=20.3°in full scale of the spectra and potassium ion exchange degree.The adsorptive separation performances of xylene, dichlorobenzene and cresol were evaluated by pulse test on a fixed bed column with KY and NaY zeolites as adsorbents, and with p-diethylbenzene, o-dichlorobenzene and the mixture of 3-pentone and n-butanol as desorbents respectively. The results showed that, the selectivities of p-xylene and o-dichlorobenzene over their own other isomers were increased, while there was no separation observed as for cresols. The mixture of 3-pentone and n-butanol was considered as a more suitable desorbent since it eliminated the tailing of concentration profiles obtained from the tests with o-xylene as desobent.On the study of molecular simulation, frameworks of X and Y zeolites were built with different spacegroups, the locations of cations including alkali metals, alkali-earth metals, transition metals and their mixtures were predicted with energy minimization method, and the charges distribution of zeolites and adsorbates were calculated with the methods of QEq and equalization of orbital electronegativityrespectively. On the basis of confirmation for reliability and accuracy of zeolites models established, adsorptive conformations and energies of the three kinds of aromatic isomers on FAU zeolites with various cations in them were calculated via the method of combination of MM and MD simulation, the results were in good agreement with those got from pulse tests and references. The separation performances of cresols on siliceous MFI and FER were also investigated in the meantime. With the analysis of mechanisms of adsorption and desorption in detail, the possibilities of separation for p-dichlorobenzene using simulated moving bed with adsorbents of Cu(II) exchanged X zeolite was suggested, and the shape-selective effect of siliceous FER zeolite on the adsorptive separation of m-cresol was anticipated.The works in this thesis indicated that molecular simulation could be used efficiently on the development and screening of adsorbents and desorbents for adsorptive separation of aromatic isomers with simulated moving bed.