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THE SYSTEM ACETONE—N-PENTANE the Ohio State Unive This dissertation has been microfilmed exactly as received bo—15,075 CHERRY, Jr., Robert Homer, 1931- AZEOTROPIC BEHAVIOR IN THE CRITICAL REGION: THE SYSTEM ACETONE—n-PENTANE The Ohio State University, Ph.D., 1966 Engineering, chemical University Microfilms, Inc., Ann Arbor, Michigan AZEOTROPIG BEHAVIOR IN THE CRITICAL REGION: THE SYSTEM ACETONE— n-PENTANE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By ROBERT HOMER CHERRY, JR., B.S., M.S.E, The Ohio State University 1966 Approved by; Adviser Department of Chemical Engineering ACKNOWLEDGMENTS The author takes this opportunity to express his sincere thanks to Professor Webster B. Kay for his guidance, patience, and understanding. To the Department of Chemical Engineering, and to Professor Joseph H. Koffolt, in particular, are due thanks for providing the Linde Postgraduate Fellowship in Chemical Engineering (1958-59 and 1960-61); and the DuPont Postgraduate Teaching Assistantship (1959-80). The National Science Foundation is thanked for grants covering the period of this research, and for the National Science Foundation Summer Teaching Fellowship, i960. ii CONTENTS Page ABSTRACT ..................................... 1 INTRODUCTION . ................................... 3 RELATED LITERATURE ................................. 7 EQUIPMENT AND PROCEDURE ........................... 10 RESULTS 17 Phase Behavior . ........................... 17 Volumetric Behavior ........................... 17 PRECISION AND ACCURACY............................. 26 Temperature................................... 26 Volume ..... ............................. 27 P r e s s u r e ..................................... 28 Composition................................... 29 DISCUSSION OP THE R E S U L T S ............ 32 Phase B e h a v i o r ............................... 32 Reproducibility of Dew and Bubble Points . 32 Dew Line for Sample 2 5 .................. 32 Correlation of Critical Properties .... 3^ The Azeotropic Locus ..................... 37 Volumetric Behavior ........................... ^0 DEVELOPMENT OF AN ENERGY PARAMETER................ ^9 CONCLUSIONS ....................................... 6l RECOMMENDATIONS................................... * '64 iii CONTENTS— (Continued) Page APPENDIX........................................... 65 I PREPARATION OF PURE COMPONENTS........... 66 Source and Preparation.................. 66 Degassing Procedure .................... 66 II VOLUME CALIBRATION............ .......... 69 III CALCULATION OF SAMPLE COMPOSITION ........ 77 IV DETAILS OF EXPERIMENTAL P R O C E D U R E ........ 83 Determination of a Border Curve ..... 85 Dew P o i n t .......................... 85 Bubble Point ...................... 86 Critical P o i n t .................... 87 Determination of an Isotherm............ 88 V CALCULATION OF TEMPERATURE, VOLUME AND PRESSURE ........................ 90 Temperature............................. 91 V o l u m e .............................. 91 Pressure................................. 9^ Dead-weight G a g e .................. 9^ Bourdon Gauge ...................... 95 Mercury Legs .......... ...... 95 Capillarity .............. ..... 96 Mercury Vapor Pressure ............ 97 Absolute Pressure .................. 98 Sample Calculation ...................... 98 iv CONTENTS— (Cont inued) Page VI EFFECT OF MERCURY ON THE OBSERVED PRESSURE. 104- VII EXPERIMENTAL DA T A ......................... 109 BIBLIOGRAPHY ....................................... l4l ' AUTOBIOGRAPHY ..................................... 1^5 v FIGURES Figure Page 1 Experimental T u b e ..................... 11 2 Apparatus............................. 12 3 Vacuum Loading Train ......... ...... 1^ k Pressure-Temperature Border Curves .... 19 5 Density-Temperature Border Curves ......... 20 6 Critical Temperature-Composition Locus . 21 7 Critical Pressure-Composition Locus .... 22 8 Critical Volume-Composition Locus ......... 23 9 Isotherms for Sample 22(80.03mole^ n - p e n t a n e ) .......................... .... 2^ 10 Isotherms in the Low-density Region, Sample 22 (80.03 mole$ n-pentane) ........ 25 11 Azeotropic Locus on the P-x P l a n e ..... 36 12 Azeotropic Locus on the log P-log x Plane . 39 - 13 Azeotropic Locus: Dependence of P and x upon T . .................. ^1 1^ Z - Tr Isochors for Sample 2 2 ......... 51 15 Energy Derivative as a Function of Reduced, Density . .............. 55 16 A£(x) as a Function of Reduced Energy . 57 17 Energy Parameter as a Function of Composition at Constant Reduced Density . 60 18 Calibration of Glass Capillary Tube .... 72 19 Schematic Diagram of Mercury Heads .... 92 20 Estimated Correction for the Effect of Mercury on the Sample Pressure .......... 108 vi TABLES Table Page 1 Critical Properties for the System Acetone— n-Pentane ........................... 18 2 Critical Properties of Purified Acetone S a m p l e ............................. 31 3 Duplicate Measurements of Dew and Bubble P o i n t s ....................................... 33 4 Correlation of the Critical Properties . 35 5 Azeotropic Locus for the Acetone— n- Pentane S y s t e m ............................... 38 6 Least-Squares Constants for the Isotherms: Sample 21 (51*41 Mole Percent n-Pentane) . 43 7 Least-Squares Constants for the Isotherms: Sample 22 (80.03 Mole Percent n-Pentane) . 44 8 Least-Squares Constants for the Isotherms: Sample 23 (64.90 Mole Percent n-Pentane) . 45 9 Least-Squares Constants for the Isotherms: Sample 24 (59*87 Mole Percent n-Pentane) . 46 10 Least-Squares Constants for the Isotherms: Sample 25 (71*88 Mole Percent n-Pentane) . 47 11 Least-Squares Constants for the Isotherms: Sample 26 (54.30 Mole Percent n-Pentane) . 48 12 Calculated Values of the Energy Derivative . 54 13 Calculated Values of the Function . 56 14 Calculated Values of the Integral Energy P a r a m e t e r ................................... 58 15 Values of Volume Calibration Constants . 76 16 Calculated Values of the Loading Parameters. 81 17 Composition of the Six Mixtures of Acetone— n-Pentane ........................... 82 vii ABSTRACT The pressure-volume isotherms and phase behavior were determined for the binary system acetone— n-pentane at six compositions from 51*^1 to 80.03 mole$ n-pentane over a pressure range from 75-1000 psia, and a temperature range from 130-230°C. The critical pressures and temperatures were correlated with composition by a quadratic in which an interaction parameter was assigned as the arithmetic mean of the values for the six mixtures. The critical volume locus appeared to be composed of two curves which intersect near the composition of the critical azeotrope. The system acetone— n-pentane forms a positive azeotrope in the critical region. The azeotropic locus was established by applying the Gibbs-Konawalow criteria to the P - x isotherms. The azeotropic locus does not inter­ sect the critical locus at its point of minimum temperature. An energy derivative based on the thermodynamic equation of state was evaluated along the border curve for all six mixtures and for pure n-pentane. Values of this energy derivative at the critical point were nearly constant for the mixtures' and for pure n-pentane; the maximum deviation from the mean of the seven values was about 1 percent. An integral energy parameter calculated from the energy derivative showed a weak maximum with respect to composition at constant reduced density. This weak maximum appeared to follow the trend in the azeotropic locus. However, the existence of a unique configuration at the azeotropic composition remains in doubt. Direct measurement of the isochors (rather than isotherms) within a volume accuracy of one part in ten thousand will probably be required to settle this question. CHAPTER I INTRODUCTION One of the most common examples of non-ideality in liquid solutions is the formation of a constant boiling mixture. Such a mixture is known as an azeotrope and is characterized by the fact that the composition of the liquid and vapor in equilibrium are identical. So far as is known, Dalton (1) in 1802 was the first to report the existence of constant boiling mixtures. However, the extent to which azeotropes form was not realized until 1918 when Lecat (2) published his first monograph of azeotropic data in which some 6000 - 7000 binary azeotropic systems were reported. Since that time, through the efforts of Lecat (3)» Sweitoslawski (^) (5) (6), and others, thousands of additional azeotropic systems have been examined. Horsley’s latest compilation (7) lists some 17,000. Almost without exception these experimental studies were concerned with the examination of the systems in the region at atmospheric pressure. Around 1950 Kay and his students (8) (9) (10) at Ohio State University started a systematic study of azeotropic systems covering a pressure range from atmospheric to the critical pressure. As a result of these studies it was found that systems which form azeotropes in the critical region exhibit much greater diversity in their phase behavior than systems that do not form azeotropes. This diversity manifests itself in the form of the P-T critical locus curve of the system. In nonazeotrope-forming systems the critical locus may vary from a straight line to a convex curve with a maximum pressure point, whereas in systems that form positive azeotropes the critical locus curve may possess a minimum temperature point and maximum and minimum pressure points. This work showed that
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