EQUILIBRIUM PHASE

Author: PÁMIES COROMINAS JOSEP.
Year: 2003.
University: ROVIRA I VIRGILI [www.urv.cat].
Place of defense: INGENIERÍA QUÍMICA.
Place of preparation: ESCOLA TÈCNICA SUPERIOR D'ENGINYERIA QUÍMICA.

Summary: In this work we have developed molecular modeling techniques, specifically the statistical theory of fluids asociantes (in English, SAFT) and molecular simulation (Monte Carlo and molecular dynamics), and have been applied in the field of modern molecular thermodynamics. The techniques mentioned have been used to study the behavior and properties of fluids in equilibrium thermodynamic systems, mainly líquido balances, but also liquid-liquid coexistence and critical behavior. They are also the subject of this thesis work of the properties of interfaces flat from an approach to SAFT together with the theory of the density gradient. The systems covered include real pure n-alkanes, 1-alcanos, n-perfluoroalcanos, hydrogen, oxygen, xenon, carbon dioxide and some of their blends. The properties termofísicas affect many aspects of the design and operation of chemical plants. On the one hand, data from property and predictive models are the raw material for the design of chemical processes. On the other hand, process simulation has become the main tool for the development, design, scaling and optimization of chemical processes. The properties termofísicas and, in particular, the equilibrium phases are consequently entries key to the development of these models process. The properties termofísicas can be obtained experimentally and by theoretical models, either from the point of view phenomenological or molecular. However, today the experimental measures are undertaken only for systems or thermodynamic conditions under which existing models fail or are not sufficiently accurate. Phenomenological models are physically reasonable way to represent experimental data, but because of its limited predictive power usually do not work outside the range of adjusting their parameters. A molecular perspective, on the other hand, allows derive fundamental relationship between the forces and underlying intermoleculares resulting macroscopic behavior of fluids. An important advantage of using a molecular model is that the parameters have physical sense and are independent of the thermodynamic conditions. In addition, the joint use theories of molecular simulations and provides a way to determine separately the effect of inter-forces and the effect of approximations of the theories in the macroscopic behavior. As explained in the title of this thesis, this work is included in the field of molecular modeling. The work focuses on the development of accurate and reliable tools of molecular model for the prediction of thermodynamic behavior of complex fluids. The statistical theories fluid asociantes, the theory of the density gradient, and molecular simulations, both Monte Carlo and molecular dynamics have been used to study the behavior of the bulk properties (breast fluid) and interfaciales of flulidos string in thermodynamic equilibrium. The systems covered include real pure n-alkanes, 1-alcanoles, n-perfluoroalcanos, hydrogen, oxygen, xenon, carbon dioxide and some of their blends. A version of the equation of state SAFT, the so-called equation soft-SAFT based on the potential for interaction between soft (soft) molecules, the potential Lennard-Jones, has been used in the study of phase equilibrium and behavior critic fluid-type chain. It has proposed a set of molecular parameters optimized for the 8 s first e64 he members of the series of n-alkanes, 1-alcanoles and n-perfluoroalcanos, which correlate linearly with the number of carbons in the chain. Using these parameters form transferable permits accurate prediction of phase diagram of long strings and mixtures without the need to optimize parameters mixture in many cases. It shows that the equation gives very good results in predictions of phase equilibria and critical behavior of asymmetrical n-alkanes and mixtures thereof. It also proves that the equation soft-SAFT is able to quantitatively predict the properties critical relatively large chain lengths, showing a shift towards field behavior when it reaches half the regime of infinite length of string. In addition, assuming that the volume and energy dispersive per molecule maintain proportionality regarding the molecular weight chains for very long, it has been found that the equation predicts a value for the critical compressibility factor equal to 1 / 5 for chains infinite length. The solubility of hydrogen in long strings of n-alkanes is another of the successful applications of the equation of state soft-SAFT. It shows that you model soft-SAFT provides very accurate and reliable results for these systems very skewed. The extension of the equation systems with cross partnership allows the description of the parameters with physical sense, showing trends and reasonable by comparing the parameter values with other models whenever possible. The study of binary mixtures of carbon dioxide concludes that for a correct description of these systems, the effect of cuadrupolo carbon dioxide should be included in the model SAFT. The equation soft-SAFT has been coupled to the theory of gradient density Cahn and Hilliard for calculating properties of interfaces flat n-alkanes, 1-alcanoles and some of their blends. It shows that the properties interfacilaes of pure compounds and mixtures subcritical can be predicted correctly with this theoretical approach. However, a crossover treatment would improve the description of mixtures in which appears a critical point. Although most of the work has focused on the development of a reliable and accurate tool based on SAFT for predicting thermodynamic behavior of complex fluids, molecular simulations have also been used for the calculation of bulk properties and interfaciales of flulidos simple. In particular, it has expanded molecular dynamics code for calculating properties interfaciales. It also presents the influence of radio cutting potential molecular interactions on the properties coexisting. This thesis especially want to emphasize that the keys of a proper use of the tools of molecular modeling is the selection of specific models suitable representative of the structure and interactions of the relevant real system, and the use of parameters that would have to trends show physical (within a series chemistry) and be transferable (within the same range as other chemical compounds) whenever possible.

Author: SANZ GARCÍA EDUARDO SANTIAGO.
Year: 2005.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS QUÍMICAS.
Place of preparation: FACULTAD DE CIENCIAS QUÍMICAS.

Summary: This thesis has studied the equilibrium phase of some models of realistic potential. One of the objectives when facing the study of equilibrium phase through simulation is to check the validity of the model potential. In addition, the phase diagram of a model is the basis for other studies that require knowledge of the same-for example, studies on nucleation and crystallization -. A step beyond calculation of the phase diagram is the analysis of the amendment thereto with the characteristics of the model potential. This allows conclusions to be drawn from interest on the physical characteristics of the models, as well as improving the same. In the thesis, as its title indicates, we have worked with the thermodynamic equilibrium of solids in the coexistencias calculated always has been present a solid phase. The other could well be another solid or a liquid or a dissolution. Therefore, much of the work done has been devoted to calculating the chemical potential of the three types of phases mentioned: * The balance sólido-sólido has appeared many times in the thesis. In the chapter "The phase diagram of water," the most extensive and exhaustive, we have calculated the phase diagram of two models of water used widely in the community simuladora: SPC / E (single point charge / extended) and the TIP4P (transferable intermolecular potential 4 points). We believe that this has been the most important scientific contribution of the thesis. The phase diagram of these models, which have a rich variety of structures ice, the balance sólido-sólido has played a key role. * In the same chapter has sought balance solid. In the phase diagram of TIP4P. For example, there are six distinct phases of the ice coexisting with liquid water. In the chapter "Haluros alkaline type NaCl" we have also studied the solid-liquid equilibrium, this time for different alkali halides crystallizing NaCl type structure. * The balance sólido-disolución has appeared in the chapter "Solubility of ionic solids in water," where we have calculated the maximum solubility salts KF and NaCl in water. It listed the ten most important conclusions drawn in the thesis: 1 - The TIP4P describes how qualitatively correct diagram of experimental stages, while the SPC / E did not. Both models reproduce well the properties of liquid water at ambient conditions and calculate the phase diagram has served to discern which of the two potential is higher. 2-A model not polarizable without tetrahedral provision of cargo and purely ionic hydrogen liaison, has been able to qualitatively predict a diagram of the experimental phases that have been considered possible structures twelve-between stable and metaestables - . 3 - The difference between TIP4P and SPC / E responsible for the success of failure of the first and second is the location of the negative charge. This should be placed along the bisector of the molecule and moved toward the position of hidrógenos. The models of water that do not have this feature (SPC / E, SPC, TIP3P and TIP5P), submitted to ice II and not to Ih as solid phase stable at atmospheric pressure. 4-We have observed behavior reentrante in coexistence hielo-agua for all ice except high pressure (VII and VIII). We believe that extrapolation of experimental lines toward coexistence areas metaestabilidad take wing same observation. This would lead to the melting ice III or V by isothermal understanding, as with the Ih. 5 - The calculation of the melting point of alkali halides has uncovered misconduct genetic potential Tosi-Fumi. Predicen correctly melting temperature of NaCl, KCl, Kbr, NaBr and RbBr, away from the experiment a little more in RbCl and RbF and fail completely in the KF, LiCl and especially NaF. The salts with small ions are not well described with such potential. 6-Unable to parametri 8 czar m 75c odelo of an alkali halide with a functional type Lennard-Jones more loads so that either simultaneously predict the density and temperature fusion. 7-We have proposed a new methodology for calculating the potential chemical solutes. Plays well with results obtained another method computationally more expensive and more difficult concept. 8 - The model used for dissolutions (Tosi-Fumi interaction ion-ion, Smith-Dang, agua-ion, SPC / E agua - agua) describes the qualitative trend of the maximum solubility of solutions of NaCL and KF, but quantitatively the value is quite experimental, especially in the case of KF. 9 - The bad prediction of chemical potential in the solid model Tosi-Fumi of KF is a cause of discrepancy with the experimental solubility, but does not rule out that the interaction agua-ion also have something to do. In the case of NaCl the main cause lies in the interactions agua-ion. 10-dependence potential chemical salts in solution with the ratio of number pairs ionic / number of water molecules is approximately linear.

Author: GINER PARACHE BEATRIZ.
Year: 2006.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The work has been the characterization termofisica mixing liquid formed by a cyclic ether, 1,3-dioxolano, 1,4 - Dioxane, tetrahydrofuran or tetrahidropirano and each of the isomers of clorobutano, 1-clorobutano, 2-clorobutano, 1 - cloro-2-metilpropano and 2-cloro-2-metilpropano based on the experimental determination of the thermodynamic and transport properties, the volume of excess, compressibility isentropic excess deviation of the index of refraction, diversion of surface tension, diversion the absolute viscosity, vapor liquid equilibrium Insulated and isobárico, according to Gibbs and excess surface concentration of excess mixtures mentioned and its variation with temperature and pressure in some of the properties. The experimental results have been subjected to analysis and has been offered an interpretation of the potential effects occurred during the mixing process, with particular emphasis on the molecular characteristics of the components that are pure mixtures. The most important conclusions of you experimental results were: 1) The molecular characteristics of the pure substances which are mixtures largely determine the behavior of the properties of mixture. 2) The behavior of properties such as diversion of surface tension, viscosity or diversion of excess surface concentration, depends mainly on ether present in the mixture, while for the volume of excess property, misuse of refractive index and compressibility isentropic excess, behavior depends primarily isomer of clorobutano present in the mixture. 3) Analysis of the results indicates that the energy phenomena that operate during the mixing process are on the one hand, the weakening of the interactions in the pure components forming mixtures and on the other, the establishment of new interactions between them . 4) Various structural effects, such as the packaging of the mixture with respect to the structure of the pure components, are crucial to interpret the phenomena occurring during the mixing process. The structure branched isomer 2-cloro-2-metilpropano largely determines the behavior of mixtures containing it. 5) The strength of the union éter-éter is higher in diéteres 1,3-dioxolano and 1,4 - Dioxane in the monoéteres tetrahydrofuran and tetrahidropirano, and the sequence continues as shown in earlier studies: 1,3-dioxolano> 1.4-dioxano> tetrahidropirano> tetrahydrofuran. 6) The strength of the interaction Cl-O between cyclic ethers studied in this work and isomers of clorobutano continues, apparently, the following sequence: cyclic ether + 1-clorobutano or 1-cloro-2-metilpropano> ether cyclical + 2 - clorobutano> ether cyclical +2- cloro-2-metilpropano. Subsequently, the model has been applied SAFT, more specifically, the version SAFT-VR, mixtures studied in order to obtain an estimate of the thermodynamic properties of the same. We have modeled the pure components of mixtures using the model SAFT-VR, obtaining the best parameters that characterize and has obtained the equilibrium vapor liquid mixtures studied using the equation of state SAFT-VR. There has been analyzed and validated the results, which have been considered satisfactory. There has been a second calculation of equilibrium vapor liquid mixtures under study by the model SAFT-VR with the incorporation of an additional parameter to improve the energy estimate. It has made use of only one additional parameter applies to all blends formed by the monoéteres cyclical one hand and the diéteres cyclical by another and all the conditions of measurement. In most cases, the estimate has improved with regard to the calculation without additional parameter. Furthermore, the results have been associated 8 with 4b5 molecular features of real substance. It has been shown that the model SAFT-VR is valid to describe the behavior of both the pure substances and mixtures studied. Moreover, the great versatility and applicability of the theory has been demonstrated. The results obtained in this study can be extrapolated to other mixtures involved in the compounds similar to those studied here and in other conditions of measurement, which gives the model SAFT and, in particular, to version SAFT-VR, very useful and applicability.