Calculation of Vapour-Liquid Equilibria of Lennard-Jones Binary Systems by the Gibbs Ensemble Monte Carlo Simulation

Abstract

The Gibbs ensemble Monte Carlo simulation has been used to calculate vapour-liquid equilibria of a Lennard-Jones (LJ) binary mixture. The mixture studied is the LB-2-1 model which has been used in our previous calculations on PVT relation and density-dependent local composition. The P-x-y relation has been established at two different temperatures and used to determine vapour-liquid coexistence region in the PVTx space.     

Application of Gibbs Ensemble and NPT Monte Carlo Simulation to the Development of Improved Processes for H2S-rich Gases

The design of improved processes for producing hydrogen sulphide (H₂S)-rich natural gases faces a general scarcity of experimental data, because of the high toxicity and corrosive character of H₂S. We present here a prospective application of Monte Carlo simulation to predict desired fluid properties.

A first step was the selection of intermolecular potentials for water, H₂S, carbon dioxide (CO₂) and methane on the basis of pure component properties (vapour pressures, vapourisation enthalpies, liquid densities, supercritical densities at high pressure). A second step involved the prediction of phase diagrams of binary and ternary mixtures of the methane–H₂S–water system, using two-phase and three-phase Gibbs ensemble simulations. In a third step the density and excess enthalpy of the CO₂–H₂S system were computed for a large range of pressure, temperature and compositions.

Comparison with available experimental data showed that all investigated properties could be consistently predicted without needing parameter calibration on binary data. The results also provided a qualitative understanding of water solubility in H₂S-rich fluids based on molecular self-association.     

Monte Carlo Simulation of Polyampholyte Chains

Abstract

Polyampholyte copolymers containing both positive and negative monomers regularly dispersed along the chain were studied. The Monte Carlo method was used to simulate chains with charged monomers interacting by screened Coulomb potential. The neutral polyampholyte chains collapse due to the attractive electrostatic interactions. The nonneutral chains are in extended conformations due to the repulsive polyelectrolyte effects that dominate the attractive polyampholyte interactions. The results are in good agreement with experiment.     

Theoretical Calculation of the Liquid—Vapor Coexistence Curve of Water,Chloroform and Methanol with the Cavity-Biased Monte Carlo Method in the Gibbs Ensemble

Abstract

The Gibbs ensemble computer simulation method of Panagiotopoulos is combined by the cavity-biased sampling technique used previously in the grand-canonical ensemble. The combined technique is applied to the determination of the liquid—vapor coexistence curve of the Lennard—Jones fluid as a test case, two water models (SPC and TIP4P) as well as methanol and chloroform, both described with the OPLS model. The application of the virial-based sampling technique, used earlier in the isobaric ensemble is also discussed.