محاسبه و بررسي نفوذ گاز دي سولفيد كربن در زئوليت ITQ-7 به روش شبيه سازي ديناميك مولكولي

چكيده انگليسي :

Calculation and investigation of self diffusivity of carbon disulfide gas in ITQ 7 zeolite via molecular dynamics simulation Mohammad Mohsen Loghavi e mail mohsen loghavi@gmail com December 8 2009 Department of Chemistry Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiBijan Najafi najafi@cc iut ac irSaman Alavi samanalavi@gmail comAbstract In this thesis molecular dynamics simulation has been used to study of the diffusion of carbon disulfidemolecules in an almost new zeolite with ISV code and Si64O128 chemical formula Zeolites are an importantclass of molecular sieves in which separations are obtained by selecting the pore size such that in mixturesmolecules that are too large are being blocked The basic building blocks of zeolites are corner sharing TO4units where the T atoms usually refer to Si Al or in some cases also P These tetrahedrals can form differenttypes of units such as 6 rings 8 rings or 12 rings From a scientific point of view zeolites are challenging As most of the activity occurs inside the material it is very difficult to carry out experiments that provide usinformation at the molecular level ITQ 7 structure type ISV has a three dimensional system of large poresdefined by windows containing 12 member rings of about 6 in diameter CS2 is very toxic and is harmfulby inhalation of the vapor skin absorption of the liquid or ingestion Molecular dynamics is a method for the simulation of thermodynamic behavior of materials in three phases solid liquid and gas via forces velocities and positions of particles Among these factors force is the mostimportant factor In classical molecular dynamics simulation force is obtained from the classical potential each atom in the zeolite is assumed to interact with each site on the adsorbed molecules through both aLennard Jones potential and electrostatic interactions All interatomic interactions between the atoms in thesimulation box and the nearest image sites were calculated within a cutoff distance of Rcutoff 13 for allsimulated systems The electrostatic interactions were evaluated using the Ewald method with a precision of1 10 6 Simulations were performed at loadings of 2 4 6 8 10 12 14 and 16 molecules per unit cell and at200 K 298 K 400 K 500 K 600 K and 700 K temperatures The main purpose of this simulation is the study of properties such as the mean square displacement diffusion coefficient radial distribution function adsorption energy and activation energy In all thesimulations via DL POLY2 software pressure and time step of each system were fixed at 1 bar and 0 001ps respectively First the simulations for each loading were performed in canonical ensemble at six differenttemperatures during 300 ps 300 000 steps to reach the equilibration of the systems Then each of theequilibrium systems was simulated in micro canonical ensemble during 500 ps 500 000 steps to get thedynamic properties as named above The slope of the curves of mean square displacement vs time increaseswith temperature at all loadings The calculated diffusion coefficient at fixed loading increases withtemperature and decreases as the loading increases at a given temperature The predicted activation energiesvia Arrhenius equation at all loadings were nearly the same which implies that the diffusion coefficients areless dependent on the loading and more dependent on temperature Radial distribution functions of differentatomic sites were obtained at various temperatures and loadings and the highest peak shifts were observed incarbon carbon RDFs Adsorption energies per a carbon disulfide molecule in the ITQ 7 zeolite werecalculated as a function of the number of molecules in the unit cell which increase with increasing loadingand decrease with temperature Key Words ITQ 7 zeolite Molecular dynamics Simulation diffusion coefficient Carbon disulfide

لغوي، محمد محسن

محاسبه و بررسي نفوذ گاز دي سولفيد كربن در زئوليت ITQ-7 به روش شبيه سازي ديناميك مولكولي

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