The Pennsylvania State University The Graduate School Department of Energy and Geo-Environmental Engineering AN EMPIRICAL APPROACH FOR PREDICTING VISCOSITIES OF HYDROCARBON SYSTEMS: DEFINED COMPOUNDS, DIRECT COAL LIQUID OILS AND LIGHT CRUDE OILS A Thesis in Energy and Mineral Engineering by Vijayaragavan Krishnamoorthy 2010 Vijayaragavan Krishnamoorthy Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science August 2010 The thesis of Vijayaragavan Krishnamoorthy was reviewed and approved* by the following: Sharon F. Miller Research Associate at EMS Energy Institute Thesis Advisor Harold H. Schobert Professor of Fuel Science Caroline E. Burgess Clifford Senior Research Associate at EMS Energy Institute Bruce G. Miller Senior Research Associate at EMS Energy Institute R. Larry Grayson Professor of Energy and Mineral Engineering Graduate Program Officer of Energy and Mineral Engineering * Signatures are on file in the Graduate School ABSTRACT A single parameter empirical method, based on the Effective Carbon Number (ECN) concept proposed by Allan and Teja (1991), was modified and extended to predict the viscosities of defined compounds (pure hydrocarbons and their mixtures) and undefined hydrocarbon liquids (petroleum fractions, crude oil, coal liquids, and coal liquid fractions) over a wide range of temperatures, pressures up to 700 bars, and compositions. Two correlations, n-alkane correlation and aromatic correlation, were developed to calculate the ECN for the liquid under investigation. The n-alkane correlation was obtained by correlating viscosity data of normal alkanes to their carbon number, while the aromatic correlation was obtained by correlating viscosity data of selected coal liquid model compounds with their carbon number. The aromatic correlation was used in calculating ECN only in certain cases. Andrade‘s equation [Reid et al (1987)] was used in obtaining the viscosity-temperature relationship. Viscosity-pressure relationships for ECN <12 and ECN ≥12 were obtained from high pressure n-alkane and synthetic crude oil data. Thus, viscosities over a wide range of temperatures and pressures up to 700 bars can be calculated with a single reference viscosity datum. The model thus obtained was tested with viscosity data of 13 pure aromatics, 11 olefins, 28 alicylics, 7 defined hydrocarbon liquid mixtures at low pressures, 8 pure liquid hydrocarbons and mixtures at high pressures, and 53 undefined liquid hydrocarbon mixtures. The overall Average Absolute Error (AAE), which is defined as the average of the percent absolute difference between predicted and experimental viscosity data points, in predicting the viscosities of various categories of liquids was as follows: 6.28% for aromatics, 3.44% for olefins, 4.09% for alicyclics, 2.90% for defined hydrocarbon mixture at low pressure, 3.90% for pure hydrocarbons iii and mixtures at high pressures, 9.99% for coal liquids and 4.69% for crude oil and petroleum fractions. The developed method compared favorably with the Generalized Corresponding State Principle (GCSP); a widely recognized model in predicting the viscosities of coal liquids. Moreover, the developed method was found to compare favorably with the method of Kabadi and Palakkal and the method of Sharma and Goel, for limited coal liquid data points. The distinguishing characteristics of the developed method over the method of Allan and Teja (1991) are their applicability to high pressure data and the prediction of viscosities for heavy coal liquid distillates. Overall, the model has been shown to be a powerful technique in predicting viscosities of defined and undefined compounds (light and middle distillates of coal liquid oils, and light crude oils and fractions) over a wide range of temperatures (253.15-673.15 K) and pressures (1.01-700 bars). However, the developed method should be used with caution when predicting viscosities of heavy distillates at low temperatures (<340 K) and light and middle distillates at very high temperatures (>673.15 K). iv TABLE OF CONTENTS Page LIST OF FIGURES ............................................................................................................. vii LIST OF TABLES ............................................................................................................... viii NOMENCLATURE ............................................................................................................. x ACKNOWLEDGEMENTS ................................................................................................ xii Chapter 1. Introduction .......................................................................................................... 01 Chapter 2. Literature Review ................................................................................................. 03 2.1. Semitheoretical Methods ................................................................................. 04 2.1.1. Corresponding States Principle .................................................................... 05 2.1.1.1. Ely and Hanley Method (1981)................................................................ 06 2.1.1.2. Generalized Corresponding States Principle (GCSP) .............................. 09 2.1.1.3. Pedersen Method (1984) .......................................................................... 13 2.1.2. Conclusions of the Semitheoretical Methods .............................................. 15 2.2. Empirical Methods ........................................................................................... 15 2.2.1. Method of Amin and Maddox (1980) .......................................................... 16 2.2.2. Methods of Twu (1985, 1986) ..................................................................... 17 2.2.3. Method of Sharma and Goel (1997) ............................................................ 19 2.2.4. Method of Kabadi and Palakkal (1996) ....................................................... 20 2.2.5. Method of Allan and Teja (1991) ................................................................ 20 2.2.6. Conclusions of the Empirical Methods ........................................................ 22 2.3. Conclusions of the Literature Review.............................................................. 23 Chapter 3. Experimental Methods ......................................................................................... 24 3.1. Coal, Coal Preparation and Solvent Selection ................................................. 24 3.2. Liquefaction Procedure .................................................................................... 25 v 3.3. Boiling Point and Specific Gravity Measurements .......................................... 29 3.4. Viscosity Measurements .................................................................................. 30 Chapter 4. Model Development and Results ......................................................................... 32 4.1. Development of the Viscosity Model .............................................................. 32 4.1.1. Viscosity-Temperature Relationship ........................................................... 32 4.1.2. Viscosity-Pressure Relationship .................................................................. 36 4.1.3. Procedure for Calculating Viscosity using the Developed Method ............. 38 4.1.4. Effectiveness of the Model .......................................................................... 41 4.2. Results .............................................................................................................. 41 4.2.1. Evaluation of the Model to Predict Viscosities of Hydrocarbon Systems ... 43 4.2.1.1. Evaluation of the Model with Defined Compounds ................................ 44 4.2.1.2. Evaluation of the Model with Undefined Compounds (DCLOs) ............ 49 4.2.1.3. Evaluation of the Model with Undefined Compounds (Light Crudes and Fractions)........................................................................................... 53 4.2.3. Summary of the Results ............................................................................... 56 Chapter 5. Comparison with the GCSP Model ...................................................................... 57 Chapter 6. Conclusions and Recommendations ..................................................................... 61 Bibliography .......................................................................................................................... 63 Appendix A. Liquefaction Conversion Data, GC-MS Operating Conditions and Compositional Information of Surrogate Coal Liquid Oils ............................. 68 Appendix B. Physical Properties and Viscosity Data of Surrogate Coal Liquid Oils ........... 70 Appendix C. Repeatability Study .......................................................................................... 72 Appendix D. Sample Calculations ......................................................................................... 74 Appendix E. Results of Various Hydrocarbon Systems ........................................................ 76 vi LIST OF FIGURES Page Figure 2.1 Various liquid viscosity models [adapted from Mehrotra et al (1996)] .............. 04 Figure 3.1 Picture of a microreactor used in this work ......................................................... 26 Figure 3.2 Block diagram of the experimental procedure followed in this work ................. 28 Figure 3.3 Picture of a Bohlin Gemini HR Nano rheometer