Bubble Pressure Measurement and Modeling for n-Alkane + Aromatic Hydrocarbon Binary Mixtures by Qingchen Liu A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in CHEMICAL ENGINEERING Department of Chemical and Materials Engineering University of Alberta © Qingchen Liu, 2017 Abstract Commonly-used cubic equations of state (EOS) over predict the bubble point pressures (BPPs) for binary long-chain n-alkane + aromatic mixtures and frequently predict the incorrect phase diagram type. In this work, BPPs for 15 representative n-alkane + aromatic hydrocarbon binary mixtures were measured. The experimental results were compared with computed values obtained using the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) EOS. For these cubic EOS, potential causes of the incorrect prediction of BPPs were studied. Binary interaction parameters (kij) for the PR and SRK EOS were regressed from experimental vapor-liquid equilibrium (VLE) data. It was found that negative kij values are required for cubic EOS in order to get accurate BPP predictions, contrary to the commonly-used positive or zero kij values for hydrocarbon mixtures. Regressed kijs trend towards larger negative values with increased size asymmetry of binary mixtures. Fitted kij values significantly improve the performance of PR and SRK EOS in predicting BPPs for highly asymmetric n-alkane + aromatic hydrocarbon binary mixtures. Experimental data were also used to validate other common thermodynamic models, including PC-SAFT, NRTL, UNIFAC and COSMO-SAC. These models were found to provide good BPP estimates for alkane + aromatic hydrocarbon mixtures without modification. Key words: bubble point pressure, binary interaction parameter, equation of state, thermodynamic models, prediction ii Acknowledgement I am grateful to my supervisor, Dr. John M. Shaw, whose patient guidance and constant support have made it possible for me to work on this interesting topic and complete this work. I would like to thank him for his efforts in making my studying experience in Edmonton a most memorable and rewarding one. His rigorous working attitude, great sense of humor, thought- provoking anecdotes, keen dedication to mentoring students, and energetic way of living have inspired me profoundly. I have been blessed to have a supervisor like him. I would like to express my gratitude to everyone in the Petroleum Thermodynamic Research Group who made my journey here such a wonderful experience. Specifically, I would like to thank my colleague Sourabh Ahitan for his thoughtful insights and generous advice in equipment, phase behavior modeling and my thesis. I would like to thank Mildred Becerra for her help in laboratory work, procurement of experimental materials and my thesis writing. It is a great pleasure to have their valuable assistance. I would like to gratefully acknowledge the sponsors of the NSERC Industrial Research Chair in Petroleum Thermodynamics: Natural Sciences and Engineering Research Council of Canada (NSERC), Alberta Innovates – Energy and Environmental Solutions, BP Canada Energy Corporation, ConocoPhillips Canada Resource Corporation, Nexen Energy ULC, Shell Canada, Total E & P Canada, Virtual Materials Group Incorporated. I am hugely indebted to my parents who keep supporting me emotionally and friends without whom I would not have made it through the MSc program. This thesis is dedicated to you. iii Table of Contents Abstract .......................................................................................................................................... ii Acknowledgement ........................................................................................................................ iv List of Tables ............................................................................................................................... vii List of Figures ............................................................................................................................. viii Nomenclature ............................................................................................................................... xi Chapter 1. Introduction ............................................................................................................... 1 1.1 Bubble pressure—Practical importance ................................................................................ 1 1.2 Thermodynamic models—The need for reliable data ........................................................... 3 1.3 Mixtures of interest ............................................................................................................... 5 1.4 Objectives .............................................................................................................................. 6 1.5 References ............................................................................................................................. 8 Chapter 2. Literature Review .................................................................................................... 10 2.1 EOS models used for hydrocarbon mixtures....................................................................... 10 2.1.1 Cubic EOS .................................................................................................................... 10 2.1.2 Binary interaction parameter for cubic EOS and its dependency on temperature and chain length............................................................................................................................ 12 2.1.3 Shortcomings for cubic EOS ........................................................................................ 18 2.1.4 Advanced EOS based on statistical theory ................................................................... 19 2.2 Available data in literature .................................................................................................. 21 2.3 Experimental techniques ..................................................................................................... 22 2.4 Summary of literature review .............................................................................................. 25 2.5 References ........................................................................................................................... 26 Chapter 3. Experimental ............................................................................................................ 33 3.1 Materials .............................................................................................................................. 33 3.2 Equipment ........................................................................................................................... 33 3.3 Mixture preparation ............................................................................................................. 35 3.4 Mixture measurement .......................................................................................................... 35 3.5 Uncertainty analysis and validation .................................................................................... 36 3.6 References ........................................................................................................................... 43 iv Chapter 4. Results and Discussion ............................................................................................ 44 4.1 Experimental data ................................................................................................................ 44 4.2 Computed bubble pressures (kij=0) ..................................................................................... 51 4.3 Regressed composition and temperature independent kij values for the PR and SRK EOS 75 4.4 Uncertainty of regressed kij values ...................................................................................... 94 4.4.1 Uncertainties in regressed kij values introduced by BPP measurement uncertainty .... 94 4.4.2 Impact of input parameter variability ........................................................................... 99 4.5 Impact of mixing rule selection on computed outcomes for cubic EOS ........................... 104 4.6 Performance of other EOS for predicting BPPs for aromatic + long chain alkane binaries at low pressure............................................................................................................................. 109 4.7 References ......................................................................................................................... 114 Chapter 5. Conclusions and Future Work ............................................................................. 115 5.1 Conclusions ....................................................................................................................... 115 5.2 Future work ....................................................................................................................... 116 Bibliography .............................................................................................................................. 117 v List of Tables Table 1.1 Selected binaries with n-alkanes and aromatics ............................................................. 7 Table 2.1 Cubic EOS9 a is cross energy term of cubic EOS. b is co-volume parameter.R is gas constant. Tr is reduced temperature. m is characteristic constant calculated from ω. .................. 11 Table 3.1 Materials information ..................................................................................................