Phase Equilibria of Heavy Oil Systems in Hydroprocesses: Experiments and Modeling

The objective of this thesis was to examine the phase equilibria of heavy oils. The main interest of the research was on hydrogen solubility in heavy oil systems. First, a novel apparatus and procedure were developed for phase equilibria measurements. Second, hydrogen solubility in heavy oil systems was measured at elevated temperatures and pressures. Finally, hydrogen solubility in heavy oils was predicted with the PC-SAFT equation of state and the heavy oil characterization method developed in this thesis. The work was conducted successfully. A continuous flow apparatus was first developed for vapor-liquid equilibria experiments and later the apparatus was modified for hydrogen solubility measurements. The apparatus and measurement methods were validated by measuring vapor pressures for pure components, bubble point pressures for an ethanol+water system and hydrogen solubility in toluene and in n-hexadecane and comparing the measurement results with literature values. The results proved that vapor-liquid and gas-liquid equilibria could be measured accurately with the continuous flow apparatus. The modified continuous flow apparatus was utilized for measuring hydrogen solubility in hydrocracked vacuum gas oil and mixtures of modified vacuum residue with toluene at elevated temperatures (498-596 K) and pressures (2-11 MPa). The experiments demonstrated that hydrogen solubility in heavy oil systems increased as the partial pressure of hydrogen were increased. In addition, the amount of toluene in the system was found to have a notable impact on hydrogen solubility. In the modeling part of this study, the target was to model hydrogen solubility in heavy oil systems with PC-SAFT. Due to the lack of a suitable heavy oil characterization method for PC-SAFT, such a method was developed in this thesis. In the method, binary interaction parameters for diphenylmethane+toluene and diphenylmethane+n-heptane pairs were utilized. These parameters were regressed against the experimental data measured in this work. The method was validated by predicting the densities and saturation pressures for selected heavy oil systems and comparing the predictions with experimental data. The method was found to model the properties of studied systems accurately. Finally, hydrogen solubility in heavy oil systems was modeled with PC-SAFT combined with the heavy oil characterization method that was developed and for comparison with the Peng-Robinson equation of state, Shaw's correlation and the Riazi and Roomi method. The study demonstrated that PC-SAFT and Shaw's correlation predicted hydrogen solubility in the studied systems superiorly and these models were the most accurate of the examined models.