Rice University logoGeorge R. Brown School of Engineering
Chemical and Biomolecular Engineering

Thermophysical Properties and Solution Thermodynamics of Hydrocarbon Systems at High Temperatures and Pressures, August 1, 2017, 10:00 AM - 12:00 PM

Thesis Defense

Graduate and Postdoctoral Studies

Fei Wang
Doctoral Candidate

Abercrombie Engineering Laboratory

Hydrocarbon liquids and solutions are widely used in industry to produce different chemical products. Thermophysical properties and phase behavior are important for enhancing production, improving operational efficiency and also increasing environmental sustainability. Various experimental methods have been proposed to evaluate different properties and models have been proposed to describe their behavior at diverse conditions. Easier, faster and more accurate approaches for property evaluations and solubility behavior predictions are in need, especially for complex hydrocarbon systems under extreme conditions, to which current methods may not be successfully applied. The solubility parameter is an inherent property of a certain material and also a key input parameter in most solution models. Accurately solubility parameter evaluations at high temperatures and pressures are not feasible by the conventional experimental method, to measure the heat of vaporization. Correlations have been proposed by previous researchers to relate solubility parameter to other properties and to describe its changing trends with temperature and pressure. However, those correlations are not applicable at elevated conditions. The pressure effect on solubility parameter is usually ignored in previous research. A novel approach to calculate solubility parameters using volumetric properties is proposed in this work. The temperature and pressure dependence of solubility parameter is derived based on exact thermodynamic relations. The proposed equations are applied to various hydrocarbon systems with great accuracy. For most non-polar hydrocarbon systems, the regular solution theory can be applied to describing their solution behavior successfully. The solubility parameters of those mixtures can be calculated using a simple mixing rule. However, for mixtures consisting of components in different shapes and sizes, their behavior shows modest non-ideality that the regular solution theory provides satisfactory predictions. By introducing a binary parameter, the solubility parameter of the mixture and activity coefficient of the component can be better predicted in this work. Easier and faster method to volumetric properties using optical property, refractive index, measurements is proposed in this work. The correlations between thermal expansivity and isothermal compressibility are developed based on Lorenz-Lorentz equation and a saturation density correlation. The new approach allows volumetric property evaluations using only refractive index measurements for pure hydrocarbons, their mixtures, and crude oils, which significantly reduces the complexity of experiments. A particular system involving asphaltenes, heaviest fraction in crude oil, is discussed in this thesis. Density, refractive index of crude oils and asphaltenes in aromatic solvents measured. The use of the refractive index to predict the asphaltene thermodynamic behavior of certain oil sample is demonstrated as well. The work presented in this thesis aims to stimulate new approaches to correlate various thermophysical properties of nonpolar hydrocarbons in order to accurately and easily obtain those properties and to better predict behavior of non-ideal hydrocarbon mixtures.