Zeolites configurational-bias Monte Carlo

The configurational-bias Monte Carlo method (CB-MC) (112) was developed to overcome these sorts of problems. Instead of a random insertion into the zeolite host, the guest molecule is grown atom by atom within the host in a way that avoids unfavorable overlap with the zeolite atoms. 

The configuration-bias Monte Carlo (CB-MC) technique (112) has also been extensively applied to characterize the sorption of alkanes, principally in silicalite (111, 156, 168-171) but also in other zeolites (172-174). Smit and Siepmann (111, 168) presented a thorough study of the energetics, location, and conformations of alkanes from n-butane to n-dodecane in silicalite at room temperature. A loading of infinite dilution was simulated, based on a united-atom model of the alkanes and a zeolite simulation box of 16 unit cells. Potential parameters were very similar to those used in the MD study of June et al. (85). As expected, the static properties (heat of adsorption, Henry s law coefficient) determined from the CB-MC simulations are therefore in close agreement with the values of June et al. The... 

Pressure Swing Adsorption (PSA) unit is a dynamic separation process. In order to create a precise model of the process and thus an accurate design, it is necessary to have a good knowledge of the mixture s adsorption behaviour. Consequently, the dilAision rates in the adsorbent particles and the mixture isotherms are extremely vital data. This article intends to present a new approach to study the adsorption behaviour of isomer mixtures on zeolites. In a combined simulation and experimental project we set out to assess the sorption properties of a series of zeolites. The simulations are based on the configurational-bias Monte Carlo technique. The sorption data are measured in a volumetric set-up coupled with an online Near Infra-Red (NIR) spectroscopy, to monitor the bulk composition. Single component isotherms of butane and iso-butane were measured to validate the equipment, and transient volumetric up-take experiments were also performed to access the adsorption kinetics. 

S. P. Bates, W. J. M. van Well, R. A. van Santen, B. Smit, Energetics of n-alkanes in zeolites A configurational-bias monte carlo investigation into pore size dependence, /. Am. Chem. Soc. 118 (1996) 6753. 

Af/ads is the heat of adsorption from the gas phase, which takes into account the dispersion interaction of hexene with the oxygen atoms in the wall of the zeolite pores. This energy depends both on the size of the reactant (hexene in this case) and the size o .the pores in the zeolite (Figure 8a and 8b) and is estimated with the configurational-bias Monte Carlo method (CB-MC). - The CB-MC method differs from conventional Monte Carlo (see Monte Carlo Simulations for Polymers) in so far as.ti guest species is grown atom by atom inside the host rather than inserted as a complete molecule. ... 

For symmetric generation probabilities like in equation 6.16 the factors Pg (o —> n) and Pg (u —> o) cancel. However, one can construct trial moves for which Pg (o —> n) Pg (n —> o). A well-known example of such a trial move is Configurational-Bias Monte Carlo (CBMC, see chapter 2). This can, for example, be used to change the orientation of the tail of a long branched molecule like 2-methylpentane, as such a reorientation will not be observed on the time-scales of MD in a narrow channel of a zeolite. It is important to note that one is able to construct many variations of the shooting trial move, for example, one can use rotation moves or choose the time t with a bias. However, one has to ascertain that the new configuration at time t does not differ too much from the old configuration at t because otherwise the new path will not start in A or end in B. 

S. Jakobtorweihen, N. Hansen and F. J. Keel. Combining reactive and configurational-bias Monte Carlo Confinement influence on the propene metathesis reaction system in various zeolites. J. Ghem. Phys. 125, 2006, 224709. 

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