III International Conference

PP-III-77DISTINCTION OF DIFFUSION IN CALIBRATED AND CHAOTIC PORES.COMPUTER SIMULATION AND EXPERIMENTMel’gunov M., Kovalev M., Patrushev Yu., Sidelnikov V., Parmon V., Anikeenko A. 1 ,Medvedev N. 1Boreskov Institute of Catalysis, SB RAS, Novosibirsk, Russia1 Institute of Chemical Kinetics and Combustion, SB RAS, Novosibirsk, RussiaE-mail: max@catalysis.ruDiffusion of molecules through ordered calibrated mesopores of MCM-41 type materialsappears to be accompanied with narrower distribution of molecule retention time comparingto disordered porous space of traditionally prepared materials. This phenomenon wasexamined both with computer modeling and chromatographic studies of adsorption-diffusionof gas mixtures. Simulation of Knudsen diffusion in pores of different geometry wasperformed, and average value of retention time and its dispersion were calculated. Obtaineddiffusion characteristics are used for interpretation of the experimental data.Computer and analytical modeling of molecular diffusion through porous spaces waselaborated during the last century. As a result, powerful methods for simulation of variousmass-transfer processes were developed. Since the named task is mathematically verydifficult, analytical approaches are restricted to the models of pores of simple forms, e.g.cylinders. To deal with pores of complex forms computer simulation is necessary. In reality amolecule can leave a pore after only a few contacts with the surface, or can be “lost” in thelabyrinth of pores for ambiguous time. It means that the distribution of molecules retentiontime in various systems of pores can be very different. This has a significant meaning formass-transfer processes, such as adsorption and catalysis. In the latter case the number ofmolecule (reagent or product) contacts with a catalyst surface is one of the key factors forselectivity. Since the former case appears to be easier to consider we have startedinvestigation of this field from chromatographic separations as an example of adsorptionmass-transfer process.Diffusion of molecules in calibrated (cylindrical) and disordered (inside random packingof spheres) pores has been performed using molecular dynamic computer simulation in theframe of Knudsen approximation. Ensemble of cylindrical pores is a model of MCM-41 typematerials, and a disordered packing of spheres represents porous space for silica gel.Adsorption interaction was modeled by accounting time of adsorption as = exp( ΔH RT )τ ,where τ 0 =10 -13 s is the characteristic time for molecular vibration, and Δ H is the adsorptionτ 0614