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Molecular Simulation Of Highly Asymmetric Model Fluids And The Real Fluids Confined In Nano-Materials

Posted on:2003-10-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:D P CaoFull Text:PDF
GTID:1101360125970238Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
This thesis contains two relatively independent parts, i.e. molecular simulation of highly asymmetric model fluids and the real fluids confined in porous nano-materials.As is well known, colloid chemistry is an important branch of physical chemistry, and is the basis of biochemistry, materials and environment sciences. Moreover, the highly asymmetric model fluid often acts as a reference of colloid systems. Therefore, in part one, the highly asymmetric hard sphere and square well model fluids were simulated.Porous nano-materials and confined fluids constitute complicated systems in chemical engineering field. The fantastic phase behavior of the confined fluid is an important factor to cause the application of porous nano-materials in chemical engineering and other fields. Accordingly, in part two, complicated systems composed of three modeled materials (i.e. one-dimension MCM-41, two-dimension activated carbon, quasi-two dimension layered pillared nano-materials) and fluids confined, were investigated using the combine method 'experiment data-molecular simulation -theory analysis'. The investigation provides guidance and points of reference for the development of new absorbents and new adsorption materials. The main contents and findings are summarized as follows.The linked cell algorithm was firstly introduced into traditional Monte Carlo (MC) method to simulate the highly asymmetric hard' sphere (HS) mixtures. Compared with the traditional MC, the, linked cell algorithm saves a lot of CPU time, and greatly improves the simulation efficiency. Then, a series of simulation data of highly asymmetric HS mixtures in colloid limit, was obtained using the linked cell algorithm. The existing equations of states (EOSs) were checked using the data simulated. Improvement of the existing EOSs was also analyzed and discussed.By taking into account the high density and low density boundary conditions for a coordination number model, a new coordination number model (CNM) for square well (SW) pure fluids, which fulfills the two boundary conditions, is proposed. Using results from the close-packed theory for asymmetric solid particle systems, the CNM for SW pure fluid was generalized to asymmetric SW mixtures. Based on the van der Waals theory, equations of siates (EOSs) for pure and mixture SW fluids were derivedfrom the CNM Models. In order to test the EOSs derived, high asymmetric SW mixtures with various interaction energies and size ratios as well as mole fractions of large molecule, were simulated. The coordination number, internal energy and compressibility factor were obtained. Compared with LS and GWL models, the new CNM and EOS are in better agreement with MC data, especially for the highly asymmetrical SW mixtures in colloid limit.Adsorption isotherm of nitrogen in MCM-41 at temperature 7=77 K was measured, by using the ASAP2010 volumetric adsorption analyzer produced by Micromeritics Instrument Corp. The BET specific surface, the BJH adsorption cumulative pore volume and average pore diameter were solved. Grant canonical Monte Carlo (GCMC) simulation was also carried out to investigate the adsorption of nitrogen in MCM-41 at T=77 K. A set of parameters representing MCM-41 were determined by fitting the experiment and simulation isotherms, which is a basis and bridge for predicting the adsorption of other adsorbates in MCM-41. Then, the GCMC and density functional theory (DFT) were used to predict the adsorption of supercritical methane and CCU in MCM-41. The results from GCMC and DFT are in good agreement, which indicates that both the two methods are powerful tools for describing confined fluids.Based on the experiment data of methane at ambient temperature, the pore size distribution (PSD) of an activated carbon adsorbent was solved by combining GCMC and statistical integral equation (SIE) methods. The combined method can effectively represent geometric heterogeneity of activated carbons. By considering the PSD of the activated carbon, adsorption recovery of CCU in the activated carbon at ambient temper...
Keywords/Search Tags:Highly asymmetric hard sphere fluid, square well fluid, Monte Carlo simulation, grand canonical ensemble, MCM-41, activated carbon, pillared layered nano-materials.
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