Ethane Monte Carlo simulation

A7 Ethane/methane selectivity calculated from grand canonical Monte Carlo simulations of mixtures in slit IS at a temperature of 296 K. The selectivity is defined as the ratio of the mole fractions in the pore to the ratio of mole fractions in the bulk. H is the slit width defined in terms of the methane collision diameter (Tch,- (Figure awn from Crackncll R F, D Nicholson and N Quirke 1994. A Grand Canonical Monte Carlo Study ofLennard-s Mixtures in Slit Pores 2 Mixtures of Two-Centre Ethane with Methane. Molecular Simulation 13 161-175.)... 

An important step in understanding the local structure around a nonpolar solute in water was made by Jorgensen et al. Using Monte Carlo simulations based on an intermolecular potential, which contained Lennard-Jones and Coulomb contributions, they determined the number of water molecules in the first hydration layer (located between the first maximum and the first minimum of the radial distribution function) around a nonpolar solute in water. This number (20.3 for methane, 23 for ethane, etc.) was surprisingly large compared with the coordination numbers in cold water and ice (4.4 and 4, respectively). These results provided evidence that major changes occur in the water structure around a nonpolar solute and that the perturbed structure is similar to that of the water—methane clathrates, ... 

Fig. 5-44. Composite cell map in which the Monte Carlo simulations have been applied to methane, ethane and propane anomalies in the Overthrust Belt, Wyoming-Utah, highlighting the regions where all three of these gases are above their respective medians.

In this paper, we present an exact calculation of the statistical mechanics of a lattice model of hydrocarbon adsorption in the quasi one-dimensional pores of zeolites, based on a matrix method that utilises the Constant Pressure partition. The model is tested on benzene adsorption, where it reproduces experimentally observed steps in isotherms. The model has been extended also to linear alkanes where it reproduces very accurately experimental adsorption isotherms as well as Monte-Carlo simulation results of ethane. 

Finn and Monson [139] first tested the predictability of IAS theory for binary systems using the isothermal isobaric Monte Carlo simulation on a single surface. However, this system does not represent real adsorption systems. Tan and Gubbins [140,141] conducted detailed studies on the binary equilibria of the methane-ethane system in slit-shaped micropores using the nonlocal density function theory (NLDFT). The selectivity of ethane to methane was studied in terms of pore width, temperature, pressure, and molar fractions. 

Skipper NT, Sposito G, Chang FC (1995b) Monte Carlo simulation of interlayer molecular stmcture in swelling clay minerals 2. Monolayer hydrates. Clays Clay Miner 43 294-303 Smit B (1995) Simnlating the adsorption isotherms of methane, ethane, and propane in the zeohte silicalite. 

We describe proeedures, based on the slit pore model and Monte Carlo simulation, for predicting the adsorption of pure gases in active carbons given only a single carbon dioxide probe adsorption isotherm. Predictions are made at ambient temperature up to quite high pressure for methane, ethene, ethane, propene and propane. The key development in our work concerns our method for calibrating gas - surface interactions, i.e. we calibrate these interactions to a reference active carbon rather than a low surface area carbon as in most other work of this type. Our predictions highlight limitations in our surface model and experiments. 

The isosteric heats of adsorption of methane in BPL activated carbon and ethane in MCM-41 were obtained by Monte Carlo simulation. The simulated absolute isosteric heats were converted into their experimental excess counterparts using a thermodynamie equation, which was derived by the thermodynamic analysis of the Clausius-Clqieyron equation for the isosteric heats. The difference between absolute and excess adsorption is small at low pressure in small pores but becomes bigger as the pressure increases, and is substantial in pores with a pore size bigger than 20 A even at low pressures. Excellent fits were obtained between experimental and simulated isosteric heats of adsorption of methane in BPL activated carbon and ethane in an MCM-41 sample. A pore size distribution model was used to relate simulation results for pores of different sizes to the experimental adsorbent. It is found that the isosteric heat is a more sensitive measure of the structure of activated carbon adsorbents than an adsorption isotherm. 

In this work, the adsorption of ethane at 264 K and nitrogen at 77 K was studied on a sequence of samples. These date were then analysed by DFT and a more accurate method for microporosity based on Monte Carlo simulations. A method based in the population balance approach was developed to follow the development of the PSD in the microporosity range. The process of PSD development has been proven to be a much more complicated process than growth of the pores. 

Molecular mechanics (MM), molecular dynamics (MD), and Monte-Carlo (MC) methods were employed to simulate the adsorption of methane, ethane, propane and isobutane on silicalite and HZSM-5. The silicalite was simulated using the same cluster-model adopted in the diffusion calculations. The H-ZMS-5 structure was constructed according to the procedure suggested by Vetrivel et al. [32], which consists in replacing one atom at the channel intersection by and protonating the oxygen atom bridging the Ta and Tg sites in order to preserve the lattice neutrality. 

In this paper, we present a model for activated carbon that takes into account the characteristics of the adsorbent that affect the adsorption of both polar and non-polar species. The structure of the carbon is represented by a PSD, obtained from the analysis of pure-ethane adsorption, and chemical heterogeneity is included by placing regularly distributed carbonyl sites on the surface of the pores. The single-pore isotherms for water and ethane are calculated by grand canonical Monte Carlo (GCMC) simulation. 

Up to now, numerous studies have been conducted on their synthesis [9,10], treatment [5,13] and physical properties [4], However only limited number of studies has been carried out on die adsorption of gas in CNTs, including experimental works [8,11] and molecular simulations [3,7,14-lS]. Adsorption behavior depends strongly on the microporous structure of the particular adsorbent. In this work the effect of pore size on the adsorption behavior is of interest. The adsorption equilibria of methane, ethane and their mixture into SWNTs were studied by using a Grand Canonical Monte Carlo (GCMC) method. We reported equilibrium isotherms of methane and ethane, and the selectivity from their equimolar mixture. 

Cracknell R F, D Nicholson and N Quirke 1994 A Grand Canomcal Monte Carlo Study of Lennard-Jones Mixtures in SUt Pores 2 Mixtures of Two-Centre Ethane with Methane Molecular Simulation 13-161-175. 

GCMC simulations, in which the temperature, the volume of the simulation cell and the chemical potential of the adsorbate are kept constant, were carried out for the adsorption isotherms of methane and ethane in slit-sh ed pores (representing pores in BPL carbon) and of ethane in cylindrical pores (representing pores in MCM-41). The absolute configurational energy of the adsorbates was obtained by a Canonical Monte Carlo (CMC) simulation, in which the number of molecules in the pore, the temperature and the volume of the simulation cell are kept constant. Details of the GCMC and CMC simulations can be found in refe. [8,9]. 

Again, utilization of this type of unnatural Monte Carlo move turns out to be limited to small molecules. For example, Goodbody et al. have used this Monte Carlo trick to determine the adsorption isotherms of methane in a zeolite. In such a simulation one can observe that out of the 1000 attempts to move a methane molecule to a random position in the zeolite-999 attempts will be rejected because the methane molecule overlaps with a zeolite atom. If we were to perform a similar move with an ethane molecule, we would need 1000 x 1000 attempts to have one that was successful. Clearly, this random insertion scheme will break down for any but the smallest alkanes. 

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