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The objective of this research is to study the solid-fluid phase equilibria of binary and ternary mixtures using molecular simulation. Solid-fluid phase equilibria plays an important role in many chemical processes, especially crystallization. This research provides insight into the underlying phenomena that govern these processes. We first calculate complete phase diagrams, that is showing the solid, liquid, and vapor phases, for 29 binary mixtures of Lennard-Jones molecules characterized by different sets of interaction parameters using the Gibbs Duhem integration technique. The impact of including the possibility of a solid phase on the global phase behavior of such mixtures is investigated by comparing the complete phase behavior calculated by simulation to the global phase diagram calculated from a fluid-phase-only equation of state. Complete phase diagrams from each region of the global phase diagram are presented and compared with the fluid-phase-only phase behavior for the same mixture. It is found that for mixtures in which the components have greatly dissimilar critical temperatures, the presence of the solid phase significantly alters the fluid phase equilibria. In those cases, the phase behavior classification based on experimental observations should differ from that predicted by an equation of state approach. The Gibbs Duhem integration technique is then extended to calculate ternary phase diagrams at constant temperature and pressure. We calculate solid-fluid phase equilibria for ternary mixtures of Lennard-Jones molecules. The simulation parameters were selected to roughly model a mixture of two diastereomeric molecules in a solvent, where the two 'diastereomer' molecules are of similar melting point and diameter and the solvent has a considerably lower melting point and a slightly smaller diameter. The cross-species well-depth and diameter between the two diastereomers are varied to determine their impact on the phase equilibria. We find that increa.
The objective of this thesis is to study the phase equilibria ofbinary mixtures using molecular simulation. Vapor-liquid, vapor-solid, liquid-liquid, and liquid-solid coexistence lines arecalculated for binary mixtures of Lennard-Jones spheres using MonteCarlo simulation and the Gibbs-Duhem integration technique. Completephase diagrams, i.e., showing all types equilibrium betweenvapor, liquid, and solid phases are constructed. The calculations presented in this thesismark the first time that molecular simulation hasbeen used to obtain phase diagrams describing all types of equilibriabetween vapor, liquid, and solid phases. We present complete phase diagrams for binary Lennard-Jones mixtureswith diameter ratios ranging from 0.85 to 0.95 and attractivewell-depth ratios ranging from 0.45 to 1.6, at reduced pressuresranging from 0.002 to 0.1. The Lorentz-Berthelot combining rules areused to calculate the cross-species interaction parameters. Wesystematically explore how the complete phase diagrams change as afunction of the diameter ratio, well-depth ratio, binaryinteraction parameter, and system pressure. We first calculate complete phase diagrams for several binary mixtures at a single pressure and find that for well-depth ratios of unity (equal attractions among species) there is no interference between the vapor-liquid and solid-liquid coexistence regions. As the well-depth ratio increases or decreases from unity, the vapor-liquid and solid-liquid phase envelopes widen and interfere with each other, leading to the appearance of a solid-vapor coexistence region. For diameter ratios of 0.95, the solid-liquid lines have a shape characteristic of a solid solution (with or without a minimum melting temperature); as the diameter ratio decreases the solid-liquid lines fall to lower temperatures until they eventually drop below the solid-solid coexistence region, resulting in either a eutectic or peritectic three-phase line. We then vary the binary interaction parameter in th.
Keywords: Phase equilibria, Molecular simulation, Lennard-Jones.
Keywords: phase equilibria, molecular simulation.
Molecular simulation is an emerging technology for determining the properties of many systems that are of interest to the oil and gas industry, and more generally to the chemical industry. Based on a universally accepted theoretical background, molecular simulation accounts for the precise structure of molecules in evaluating their interactions. Taking advantage of the availability of powerful computers at moderate cost, molecular simulation is now providing reliable predictions in many cases where classical methods (such as equations of state or group contribution methods) have limited prediction capabilities. This is particularly useful for designing processes involving toxic components, extreme pressure conditions, or adsorption selectivity in microporous adsorbents. Molecular simulation moreover provides a detailed understanding of system behaviour. As illustrated by their award from the American Institute of Chemical Engineers for the best overall performance at the Fluid Simulation Challenge 2004, the authors are recognized experts in Monte Carlo simulation techniques, which they use to address equilibrium properties. This book presents these techniques in sufficient detail for readers to understand how simulation works, and describes many applications for industrially relevant problems. The book is primarily dedicated to chemical engineers who are not yet conversant with molecular simulation techniques. In addition, specialists in molecular simulation will be interested in the large scope of applications presented (including fluid properties, fluid phase equilibria, adsorption in zeolites, etc.).Contents: 1. Introduction. 2. Basics of Molecular Simulation. 3. Fluid Phase Equilibria and Fluid Properties. 4. Adsorption. 5. Conclusion and Perspectives. Appendix