Kinetic study of coal extraction by tetralin with ultrasonic irradiation

This investigation was concerned with the kinetics of coal extraction by 1,2,3,4-tetrahydronaphthalene (tetralin) under the influence of ultrasonic waves. The coal used in this study was obtained from the working face of the Utah Spring Canyon Mine. The extraction of coal has been carried out at five different temperatures: 24° G, 29°C, 34*C, 44°C, and 54°C. At each of these temperatures the yield of extract increases rapidly in the early stages of extraction, levels off later to approach an asymptotic value. Analysis of the data from this study showed that a modified firstorder rate equation best describes the kinetics of the extraction process. In this study on the solvent extraction of coal, the enthalpy of activation (6.0 kcal/mole) was found to remain constant throughout the extraction process. However, an increase in free energy of activation ) that was observed is accounted for by a decrease in entropy of activation. The values of free energy of activation were found to be 24»5 kcal/mole during the early stages of the extraction process and 25.1 kcal/mole near the end of the extraction process. An experiment was conducted to see if tetralin undergoes decomposition when subjected to ultrasonic irradiation for 20 hours. The results show that no significant decomposition of tetralin occurs during the first 15 hours under ultrasonic irradiation and less than one percent of the tetralin was found to be decomposed at the end of 20 hours.

Ching University June, 1 9 67 A KINETIC STUDY OF COAL EXTRACTION BY TETRALIN WITH ULTRASONIC IRRADIATION by Virginia Cheng Chen Cbing A thesis submitted to the faculty of the University of Utah in partial fulfillment of the requirements for the degree of Master of Science Department of Fuels Engineering Uni versi ty of Utah 1967 This Thesis for the Master of Science Degree by has been approved June9 1 9 6 7 Cnairmanf---^pervisory Committee Reader, Supervisory Committee c Head, Major Department LTJffl LIBW Virginia Cheng Chen Ching Junep 1967 ~--7f~~~ Reader, Supervisory Committee Dean, Graduate School ACKNOWLEDGMENT The author wishes to express her appreciation to those who assisted in the research and in the preparation of the manuscript for this thesis, especially Professors L. L. Anderson, W. H. Wiser and G. R. Hill: to Professor Anderson, thesis adviser, for his counsel and guidance, and for his many suggestions on the experimental work; to Professor Wiser for his very valuable suggestions and discussions; to Professor Hill for his incessant encouragement throughout this work* Appreciation is expressed to Dr. J. Keller for his assistance in the improvement of English structure. iii work. The author is also grateful to her husband for his keen interest in this research and his suggestions, to Mrs. Carolyn Hansen for her careful typing of the thesis, and to Mr. Surjit Singh for his help in preparing the figures. This research was sponsored by the Office of Coal Research. TABLE OF CONTENTS Page • vi • 1 4 . •••••• 4 • • • • 4 • • • • • • « • • • • • • • • • • • • • • • • • 5 Particle Size of Coal 5 and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Structure of Solvent . . . . . . . . . 7 Rank of Coal 7 Solvents of the Benzene Type . . . . . . . . . . . . . . 7 Solvents of the Pyridine Type 8 Extraction Products . . . . . . . . . . . . . . . . . . . . 8 The Effect of Ultrasonic Irradiation on Extraction of Coal . . 9 Mechanism and Models Proposed for Coal Extraction . . . . . . . 19 EXPERIMENTAL PROCEDURES AND RESULTS 23 Coal Preparation . . . . . . . . . . . . . . . . . 23 Sample Preparation . . . . . . . . . . . . . Solvent Preparation . . . . . . . . . . . . . . . 24 Extraction Apparatus . . . . . . . . . . . . . 24 Determination of Optimum Coal to Solvent Ratio . . . . . . . 26 Experimental Procedure . . . . . . . . . . . . . . . . . . . 26 Preliminary Experiments 29 iv ACKNOWLEDGMENT • • • • • • • • • • • • •• • • • • • • • • • • • LIST OF FIGURES • • • • • • • • • • • • • • • • • • • • • • • • • LIST OF TABLES • • • • • • • • • • • • • • • • • • • • • • • • • • ABSTRACT ••• • • • • • • • • • • • • • • • • • • • • • • • • • INTRODUCTION • • • • • • • • • • • • • • • • • • • • • • • • • • • LITERATURE REVIEW • • • • • • • • • • • • • • • • • • • • • • • • Effect of Experimental Variables on Yield of Extract for Conventional Extraction Processes • • • • • • • • • • • • • • • Extraction Time ••••••• Temperature ••••••••• • • • • Moisture Atmospheric Oxygen Pretreatment of the Coal • • • Nature of the Solvent •••• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •••• • • • •• • • • • • • • • • • • • • • • • • • • • iii viii x 4. 5 6 6 6 Physical Properties of the Solvent ••••••• g • • • 6 Chemical Structure of Solvent • • • • • • • • • • • • • • 7 Rank of Coal • • • • • • • • • • • • • • • • • • • • • • • • 7 Solvents o~ the Benzene Type •••••••••••••• 7 Pyridine Type • • • • • • • • • • • • • • 8 Extraction Products • • • • • • • • • • • • • • • • • • • • The Effect of Ultrasonic Irradiation on Extraction of Coal • • 9 Mechanism and Models Proposed for Coal Extraction •• • • • • • 19 EXPERIMENTAL PROCEDURES AND RESULTS • • • • • • • • • • • • • • • 23 Coal Preparation • • • • • • • • • • • • • • • • • • • • •• Sample Preparation • • • • • • • • • • • • • • • • • • • •• 24 Solvent Preparation •••••••• • • • • • • • • • • •• 24 Extraction Apparatus • • • • • • • • • • • • • • • • • • •• 24 Determination of Optimum Coal to Solvent Ratio • • • • • •• 26 Experimental Procedure • • • • • • • • • • • • • • • • • •• 26 Preliminary Experiments • g • • • • • • • • • • • • • • •• 29 Decomposition of Tetralin • • • • • • • • • • • 29 • • • • • • • • • • • • • • • • » 30 • • • • • • • • • • • • 30 . . . . . . 31 . . . . . . . . . • 31 31 Ultrasonic 32 » . 33 34 34 Extraction • • » • • • • • • • • • • • • • • • • • • 41 an Ultrasonic 57 59 Infrared Spectra 6l CONCLUSIONS 68 BIBLIOGRAPHY 70 NOMENCLATURE 74 RESEARCH PROPOSAL * • 76 APPENDIX • • . 80 VITA • • 101 TABLE OF CONTENTS (continued) • • • • • ••• II •• Blank Tests on Benzene ••••••••••••••••• Blank Tests on Trichloroethylene ••••••••• 8 • 0 Blank Tests on Benzene and Trichloroethylene •••• II • Blank Tests on Tetralin • • • • • • • • • • • • • • • II II Precipitation Tests on Extract • II •• II •••••••• II • Coal Extraction by Tetralin without Ultrasonio Irradiation • Coal Extraction by Tetralin with Ultrasonic Irradiation •• DISCUSSION OF RESULTS • • • • • • • • • • • • • • • • • • • • • • Page :t9 30 30 31 31 31 32 33 34 Analysis of Experimental Data • • • • • • • • • II • • • II • •• 34 Proposed Mechanism for Extraotion of Coal with Ultrasonic Irradiation • • • • • • • • • • • • • • • • • • • • • • • • •• 41 Comparison of Experimental Results with and without Ultrasonio Irradiation • • • • • • • • • • • • • • • • • • •• 57 Rate and Yield • • • • • • • • • • • • • • Infrared Spectra • • • • • • • • • • • • • • • • • • • • • It • • • • • • • • • CONCLUSIONS • • • • • • • • • • • • • • • • • • • • • • • • s • • BIBLIOGRAPHY • •• • •••• • • • • • • • • • • • • • • • • • • • NOMENCLATURE • • • • • • • • • • • • ••••• • • • • • • • • • • RESEARCH PROPOSAL • • • • • • • • • • • • • • • • • ••••• 10 e APPENDIX. • • • • • • • • • • • • • • It • • • • • • • • • 8 GO. VITA II • • • • • • • ••• • • • • • • • • • • • • • . . . . ." • • v 59 61 68 70 74 76 80 101 LIST OF FIGURES 1 . Effect of Attenuation in Transformer Oil on Yield of Extract • 14 2 . Effect of Input Power on Yield of Extract 15 3 . Infra-red Spectra of the Extract of Aldwarke 5 0 1 Goal • • • 17 4» Photograph of Experimental Apparatus Used for Coal • • • • 25 5» Percent of Extraction Versus Coal/Solvent Ratio at 50°C and 5 Hours •••••• 28 6 . Yield Ultrasonic Irradiation • • • 7 . Time-Yield Curves for Extraction of Coal on Tetralin with Ultrasonic Irradiation • • • • 36 8„ Plot of - Versus -%•-r for Extraction of Coal with Wc (AW/Wc) 24* C 9 . A Plot of fo/^fr Versus Square Root of Fraction Extracted, (1-x) xs, for Extraction of Coal with Tetralin at a Temperature of 2 4 ° C ' 40 1 0 . A Plot of Rate of Extraction of Coal as a Function of Driving Force to the First Power. Temp. 2 4°C Solvent, Tetralin . • . 43 1 1 . A Plot of Versus t for 24°C * a-x 1 2 . ln(of Coal with Tetralin at Five Different Temperatures: 24, 2 9 , 3 4 , 44, 54°C . . 46 1 3 . Arrhenius Plot for Evaluation of the Activation Energy • • 50 1 4 • Entropy for Coal Extraction with and without Ultrasonic Irradiation * 51 1 5 . A Plot of In | Versus i for Variation of Activation Entropies with Fraction Extracted 53 vi Figures Page 1. Extract • • • • • • • . ~ . . . . . . . . • • • • • • • • • 2. Effect of Input Power on Yield of Extract • • • • • • • • • 14 15 3. Infra-red Spectra of the Extract of Aldwarke ,501 Coal • •• 17 4. Photograph of Experimental Apparatus Used for Coal •••• 25 5. Percent of Extraction Versus Coal/Solvent Ratio at 50·C and 5 Hours • • • • • • • • • • • • • • • • • • • • • • •• 28 6. Time-Yield Curves for Extraction of Coal on Tetralin with ••••••• • • • • • • • • •• 35 7. ••• • • • • • • • • • • • • • •• 8.. ~ t ... w/wc) Tetralin at a Temperature of 24°C • • • • • • • • • • • • • ~ 1'1-iY 10. 1 x~, '24°C • • • • • • • • • • • • • • • • • • • • • • • • • • 24°C. •• • • • • • • • • • • • • • • • • • • • • • • • 38 40 11. -1- 24·• • • • • • • • • • • • •• 44 a-x 12. Plot of In(k) Versus Fraction Extracted, x, for Extraction of Coal with Tetralin at Five Different Temperatures: 24, 29, 34, 44, 54°C •••••••••.•••••••••••• 46 13. • • 14. Eyring's Plot for Evaluation of the Activation Enthalpy and • • • • • • .. • • • • • • • • • • • • • • • •• 15. 1n ~ ~ ••••••••• • • • • LIST OF FIGURES (continued) Figures Page 1 6 • A Sketch of Reaction Coordinate Versus Activation Free Energy for Extraction of Coal • 1 7 . Time-Yield Curves for Extraction of Coal by Tetralin with and without Ultrasonic Irradiation • • • • • 18 • Infrared Spectrum of Tetralin, Benzene, and • • • • • 1 9 . Infrared Spectrum of the Extracts from Coal Extraction by Tetralin (a) without the Aid of Ultrasonic Irradiation, (b) with the Aid of Ultrasonic Irradiation . . . . . . . 64 20. Infrared Spectrum of the Concentrated Extracts from Coal Extraction by Tetralin (a) without the Aid of Ultrasonic Irradiation, (b) with the Aid of Ultrasonic Irradiation • 65 vii 16. • • • e e • • • • • • • • • 55 17. ••• • • • • • • 58 18. Trichloroethylene Solvent Mixture • • • • • • • • • • • • 63 19. ••••• •• • • • • • • • • • • • • • • • • • • • • • • 1 . Extraction of Coal for Different Coal/Solvent (C/s) R&tlO . . a e . o e e ' e o o e . a e o . . . . . * , * * , * 27 2 . from on » o . © © © © o o . » e < » » » © . o o . 32 3 . Variation of Versus Square Root of Fraction x£, • o • • 41 4 . a-x with Tetralin at 24°C, (a= 0 o l 0 2 , x=Fraction of Coal Extracted) e o e e o o e o o o o e < > o . « « « o « o « . » * 42 5 . Final Results for Solvent Extraction of Coal with Tetralin . 49 6 . Variation of Entropy of Activation with Fraction Extracted • 52 7 . Helds of Extract After 2 0 Hours in the Presence and Absence of Ultrasonic Energy . . • o o • « 59 8 . 81 9 . 82 1 0 . at 54°C«, Using a Conventional Extraction Process • . 0 • • • • 83 1 1 a . 2 4 ° C the Aid . o o . e o . o . . 84 lib. Variation of Rate Constant, k , with Fraction Extracted, at 24°C„ a= O o l 0 2 by the Method of Finite Differences . . . 86 1 2 a . 2 9 °C the <> <> • , » • • » • • 87 1 2 b . k , at 2 9 ° C a= O o l 0 5 by the Method of Finite Differences . . . 89 1 3 a . the « • • • » < > . > . » • • • » • • 90 1 3 b . Rate k , x, at 34°C. a=0ol06 by the Method of Finite Differences . . . 92 viii LIST OF TABLES Table 1. (S) Ratio ••• Ci 0 0 Q Q' Q 0 0 0 • " • 0 • • • • • • • Summary of Data Obtained fram Precipitation Tests on Extracts with Tetralin ~ •• 0 ••• 0 0 • Q •••• 4(x~) I-x Extracted, xi, for Extraction of Coal with Tetralin Variation of l with Time (Minutes) for Extraction a-x with Tetralin at 24°C, (8=00102, ~Fraction of Coal Extracted) • 0 • • • • • • Q • • • • 0 • • • • • • 0 Page • • • • • 0 • • 32 • • • • 41 of Coal • • • • 5. Final Results for Solvent Extraction of Coal with Tetralin. 49 6. Variation of Entropy of Activation with Fraction Extracted • 52 7. Yields of Extract After 20 Hours in the Presence and Absence of Ultrasonic Energy • 0 0 0 0 • 0 • • • .. . • • • • 59 8. Experimental Data for Extraction of Coal with Tetralin at 24°C. Using a Conventional Extraction Process • • • • • •• 81 9. Experimental Data for Extraction of Coal with Tetralin at 34°C. Using a Conventional Extraction Process • • • • Q •• 82 10. Experimental Data for Extraction of Coal with Tetralin at 54°C. Using a Conventional Extraction Process •• 0 • • •• 83 lla. Experimental Data for Extraction of Coal at 24°C with the of Ultrasonic Irradiation • 0 0 • • 0 0 0 & • • • • •• 84 lIb. k, x, at 24°C. &=0.102 by the Method of Finite Differences ••• 86 12&. Experimental Data for Extraction of Coal at 29°C with the Aid of Ultrasonic Irradiation Q G • • • • • • • • • • • •• 87 l2b. Variation of Rate Constant, k, with Fraction Extracted, x, at 29°C. a=O.105 by the Method of Finite Differences ••• 89 l3a. Experimental Data for Extraction of Coal at 34°C with the Aid of Ultrasonic Irradiation Q.... 0 • • • 0 • • • •• 90 Db. Variation of ~te Constant, k, with Fraction Extracted, at 34°C. a=Ool06 by the Method of Finite Differences ••• 92 LIST OF TABLES (continued) Table Page 1 4 a . Experimental Data for Extraction of Coal at 44°C with the Aid of Ultrasonic Irradiation 93 1 4 b . Variation of Rate Constant, k, with Fraction Extracted, x, at 4 4°C a= 0 . 1 1 1 by the Method of Finite Differences . . . 1 5 a . Experimental Data for Extraction of Coal at 54°C with the Aid of Ultrasonic Irradiation 96 1 5 b . Variation of Rate Constant, k, with Fraction Extracted, x, at 54'C. a= 0 . 1 1 4 by the Method of Finite Differences . . . 98 1 6 . Determination of k by Using the Integrated Form of Proposed Model . 99 1 7 . Variation of Contribution Activation Entropies, AS£, with Fraction Extracted, x 102 ix 14&. •••• • • • • • • i • • •• 14b. 44°C. O.111 ••• 95 15a. • • • • • • • • • • • • • •• 15b. 54°O.114by ••• 16. ko • • • • • • • • • • • • • • • • • • • • • • • 17. .6.st:, •• • • • • • • • • • • • • • • • •• 102 ABSTRACT This investigation was concerned with the kinetics of coal extrac­tion by 1,2,3,4-tetrahydronaphthalene (tetralin) under the influence of ultrasonic waves. The coal used in this study was obtained from the working face of Utah at five different temperatures: 24° G, 29°C, 34*C, 44°C, and 54°C. At activation mole) ) that was observed is accounted for by a decrease in entropy of 24»5 mole mole An decomposi­tion extrac-tion tetrahydronaphthalene waves .. the utah Spring Canyon Mine. The extraction of coal has been carried out C, 29°C, 34°C, C, and 54°C. each of these temperatures the yield of extract increases rapidly in the early stages of extraction, levels off later to approach an asymptotic value. Analysis of the data from this study showed that a modified first-order rate equation best describes the kinetics of the extraction process. In this study on the solvent extraction of coal, the enthalpy of acti vation (6.0 kcal/mole) was found to remain constant throughout the extraction process. However, an increase in free energy of activation ~pf) that was observed is accounted for by a decrease in entropy of activation. The values of free energy of activation were found to be 24.5 kcal/mole during the early stages of the extraction process and 25.1 kcal/mole near the end of the extraction process. experiment was conducted to see if tetralin undergoes decomposi-tion when subjected to ultrasonic irradiation for 20 hours. The results show that no significant decomposition of tetralin occurs during the first 15 hours under ultrasonic irradiation and less than one percent of the tetralin was found to be decomposed at the end of 20 hours. x INTRODUCTION Solvent extraction of coal has been extensively studied by various investigators, but many aspects of the action of organic solvents on coal are still unexplained. Through these studies, however, researchers have been able to separate one or more of the individual chemical substances from coal or at least they have been able to separate main organic con­stituents from coal. Also, through these studies the physical and near room temperature. It is well known that the low temperature extrac­tion of coal offers the mildest and most appropriate method for studying the behavior of coal towards dissolution. Solvent extraction at low temperatures provides a means of separating organic compounds from coal without substantially changing their composition. In this investigation 1,2,3,4-tetrahydronaphthalene (tetralin) was used as a solvent to extract organic materials from coal under ultrasonic irradiation,, Ultrasonic irradiation was employed to accelerate the rate of the extrac­tion process, Idttlewood (l) has studied the extraction of coals with pyridine using ultrasonic irradiation. He found that by placing the extraction vessel at a nodal point in a high-intensity ultrasonic beam the rate of extraction of the vitrain component of bituminous coals with pyridine was greatly accelerated. He also found that the amount of extract was dependent upon: (a) the distance of the extraction vessel chemical properties of coal, the constitution of coal, and the action of solvents on coal are better understood. In the work for this thesis, a kinetic study was made of the solvent extraction process for removing organic substances from coal with the aid of ultrasonic irradiation. The extraction of coal was carried out at or substantially- tetrahydronaphthalene irradiationo process. Littlewood 1) 2 from the quartz disk which produced the ultrasonic vibrations; (b) the thickness of the extraction-vessel diaphragm; (c) the input power to the generator; and (d) the rank of the coal. He concluded that at the intensities employed in his work the effects of ultrasonic irradiation were essentially of a physical nature; that is, the ultrasonic irradia­tion degraded materials to smaller sizes so that they were more readily dispersed. Littlewood, also, concluded that the effects of ultrasonic degradation are twofold: the first effect was the temporary breaking of the loose gel network of the van der Waals bonds between adjacent mole­cules; and the second effect was the actual breaking of the chemical bonds to give smaller molecules than those originally present. From a subsequent study on solvent extraction with ultrasonic 3) operates with an input power of 125 watts. An X-cut quartz-crystal transducer, driven by the generator, gives vibrations of Kilocycle/sec which are transmitted from a copper membrane to the water bath holding the extraction vessel. -270 drying C ultrasonievibrations; e) were essentially of a physical nature; that is, the ultrasonic irradia­tion degraded materials to smaller sizes so that they were more readily dispersed. Littlewood, also, concluded that the effects of ultrasonic effeet and irradiation of Alberta coals, Berkowitz (2) estimated that between 15 and 40 percent of the sonic energy available at the extraction vessel can be used. Kirby, and Sarjant (3) support this view by similar conclusions from their solvent-extraction studies on a series of bituminous coals. The ultrasonic generator employed in the research for this thesis 40 sec. For this study on solvent extraction of coal, only one kind of coal, a sample from the Utah Spring Canyon Mine, was used. The particle size of the coal used was Z'/O +330 mesh. The following experimental proce­dures were followed throughout the study: (a) the coal sample was kept at the same moisture content by at 105°C under vacuum in an oven for three hours before performing an experiment, (b) the extraction ratio was kept constant. In this way the effect of other variables which might affect the extraction process are minimized so that the extraction of coal depends primarily on the temperature and the extrac­tion time. In the experimental part of this study data were obtained on the variation of the rate of extraction with the extraction time. The fraction of coal extracted up to a given time was evaluated by subtrac­ting the weight of coal residue which is left in the thimble after extraction, followed by fractionation with benzene and trichloroethylene with a Soxhlet apparatus, from the weight of the original coal. Not many views concerning the kinetics of the low-temperature proposed* vessel (a 25-ml. Pyrex flask) was always placed at the same position in the ultrasonic field during extraction, and (c) the coal to solvent 3 extraction of coal with the aid of ultrasonic energy can be found in the literature. Therefore, in this work some effort was expended to obtain a better understanding of the mechanism and kinetics of the sol­vent extraction process. As a consequence of this work, a new model for the mechanism of coal extraction is proposed. LITERATURE REVIEW While there is a great amount of published literature on coal extraction in the absence of an ultrasonic field, very few articles can be found on coal extraction which describes the effect of ultrasonic energy on extract!on* Since it is generally believed (l) that the basic process of extraction is the same in the presence or absence of ultra­sonic energy, the conventional extraction process will be discussed first in this literature surveyo Later the specific effect of ultra­sonic energy on extraction will be examinedo One of the first extensive studies on solvent extraction of coal was published by Massily (5) in 1860o He used boiling chloroform, ether, alcohol and carbon di sulphide as solventso A review of the early literature up to and including the year 1950 is available in the classical monograph by Dryden (6)« The application of ultrasonic energy to solvent extraction of coal was introduced by Littlewood (l)<, A more current review of this subject is found in the book, "The Chemistry of Coal Utilization" edited by Lowry (7)<* Effect of Experimental Variables on Held of Extract for Conventional Extraction Proccesses Extraction time process; the extraction of organic material from bituminous coal proceeds at a very high rate© The curve showing the relation between the yield of extract and time deflects after a period of a few hours and becomes substantially a straight line, which makes a very small angle with the horizontal axis (8)e Deppeler and Borchers (9) studied the extraction extraction" 1) energyjl litera.ture 18600 disulpbide 0 applioation 1) 0 bookjl 7) 0 Yield ~ In the initial stage of the extraction bitURdnous rateo linejl 8)0 5 of finely ground, high-volatile coal with tetralin under pressure and mechanically efficient. The effect of temperature is most marked for benzene type solvents. Dryden (ll) concluded that ethylenediamine extracts half as much material from low-rank bituminous coals at room temperature as it extracts at its boiling point (ll6°C)«> Kiebler (12) has stated that data for solvent extraction of coal with three types of solvents (benzene, pyridine, aniline) can be corre­lated x » a •+- B where x is the yield of extract, is the internal pressure of solvent, & functions param­eter $ C, coal for the less effective extraction solvents (8). Helds tend to increase . found that a parabolic curve fitted their results for up to seven hours extraction time. It is generally observed that the initial extraction is very rapid in comparison with the rate after a few hours (6). This is most noticeable during the extraction of lower rank coals with pyridine. Temperature It has been shown (10) that the yield of extract obtained from a particular coal with a specific solvent depends only on the temperature at which the extraction is conducted and does not appear to be affected by the method of extraction employed as long as it is solvents" 11) 116°c). Kieb1er by the following equation: x == a + BPi Pi and the parameters a and 13 are ftmctions of temperature. The param-eter 13 increases approximately linearly with temperature, and a does likewise up to a temperature of 220 to 250°C, but the rate of increase with temperature above this value becomes much more rapid. Particle -size -of c-oal The dependence of the yield of extract on . the particle size for the effective extraction solvents differs from that Yields 6 when the particle size of coal to be treated is reduced ( 1 3 , 6 ) . The greatest yields of extract are obtained on coals that are milled to a particle size of about one micron. Moisture and atmospheric oxygen solvent and oxygen in the extraction apparatus both tend to decrease the yield ( 1 3 ) . The efficiency of extraction of coals by alcoholic potash and by ethylenediamine is reduced by the presence of water ( 1 4 ) « However, the presence of moisture does not appear to be critically important with the majority of solvents that are immiscible with water. Pretreatment of the coal Illingworth ( 1 5 ) in 1 9 2 2 observed that preheating of a low rank coal to 2 1 0 * C increased the subsequent rate of extraction with pyridine at its boiling point, but did not affect the ultimate yield. Walther and Steinbrecher l 6 ) obtained maximum yields of extract with pyridine after preheating the coal to 2 5 0 * C . Oxidation of coal matter by pretreatment with air at atmospheric or slightly higher temperatures, up to about 1 0 0 ° C , also, influences the yield from the extraction process. The results from some studies reported are somewhat contradictory on this subject. Nature of the solvent Physical properties of the solvent The solubility of a solid in a liquid with which it forms an ideal solution, one which obeys Raoults law, can be predicted in terms of the melting point and the heat of fusion of the solid ( 1 7 ) » Losikow ( 1 8 ) and Dryden (ll) pointed out that one of the functions of solvents is to swell the coal. Agde and Hubertus ( 1 9 ) attempted to determine if the amount of solvent absorbed by coal was related to the function M^/e , where u is the dipole moment 13, 6). 6 ox;ygen The presence of moisture in the 13). (14). ~ 15) 1922 2l0·C ( 16) 250·C. lOO·C, PhYsical 17). 18) 11) 19) dete~ne ~2/f. ~ 7 and e the dielectric constant of the solvent« Their results were too few to enable them to arrive at a conclusion about this, but solvents with y of about 2 , 5 x KT-^e.s.u. and e of 13 to 2 0 were found to be most effective. Among those tested was acetone. Pertierra ( 2 0 ) agrees that the relation between yield and internal pressure of the solvent at a given temperature is approximately linear. Chemical of Wlthrow ( 2 1 ) groupso 6 ) high power, 2 2 ) pyridine 2 3 ) , 400*linkage true)o containing ( 2 4 ) « Rank of coal of type ( 2 5 ) , Killer, Graf, and Gruber ( 2 6 ) , and Dyakova and Davtyan ( 2 7 ) extracted coal with trichloroethylene, tetralin, and naphthalene, respectively. All of these authors report an increase in yield of extract with E the dielectric constant of the solvent. Their results were too few to enable them to arrive at a conclusion about this, but solvents with lJ of about 2 .. 5 x 10-lee.sou" and E of 13 to 20 were found to be most effective.. Among those tested was acetone. Pertierra (20) agrees that the relation between yield and internal pressure of the solvent at a given temperature is approximately linear. Chem1.cal structure !2! solvent Pew and Wi throw (21) have 7 suggested that the solvent power is related to the presence of hydroxyl groups.. Dryden ( 6) showed that primary aliphatic amines, with or without aromatic substituent, share with pyridine and certain other heterocyclic bases an abnormally solvent power.. Crussard ( 22) and Dryden (ll) treated solvent extraction by benzene or p,yridine as proceeding by two mechanisms. Orchin and Storch ( Z3), extracting coal at about 400°C, found that a solvent with a two-ring system containing a hydroxyl group attached to an aromatic ring was a very effective solvent. Substitution of a radical for the hydrogen in bond-linkage groups, such as OH, NH, NH2 increased the solvent power (with aliphatic amines at lower temper­atures, the reverse is true).. There is evidence that for coals contain­ing less than 90 percent carbon the unshared electron pair in the solvent interacts, thus releasing heat, with some oxygen-containing group in the coal which is exposed to solvent action (24)0 Rank £!~ Solvents 2! the benzene ~ Peters and Cremer (25), Muller, 26), Zl) 8 decreasing rank of coal. Fisher. Peters, and Cramer noted a conspicuous exception to this observed trend (28). They found that results reported by Bakes (29), an increase in yield with an increase in rank of coal, was reversed when a coal of a still higher rank, a Welsh dry steam coal, was extracted. Dyakova and Davtyan (27) found that for coals with a carbon content greater than about 88 to percent, or less than 25 percent volatile material, the amount of extract obtainable decreased rapidly with an increase in carbon content. For coals with a carbon content lower than this limit, no definite trend in amount of extract yield with rank has been observed0 Solvents of the pyridine type Using pyridine as an extrac­tive solvent, Baker found an increase in yield with decrease in rank of the coal (30)* The samples used by Baker ranged from anthracite to Durham coal. Dryden (6), using ethylenediamLne, found it to give a more rapid increase in rate of extraction of 85 to 87 percent carbon coal than other solvents. Bone and Sarjant (31) found that pyridine-type solvents gave the opposite effect with two coals in the medium volatile range. A coking coal yielding more extract than a lignite was found by Malanowicz (32). Cockram and Wheller (33) found in the case of American Pittsburg seam coals an overall decrease in yield with an increasing carbon content of up to 86.5#* followed by a more rapid decrease in yield for coals with higher carbon content. Extraction products There is general agreement that the swell­ing and agglutinating properties of coal are attributed to materials found in the extract, particularly in the y-chloroform soluble fraction 8 decreasing rank of coal. Fisher, Peters, and Cremer noted a conspicuous dry DaTtyan Zl) oontent 89 this limit, no definite trend in amount of extract yield with rank has been observed. Solvents ~ ~ pyridine .!:m. Using pyridine as an extrac-tive solvent, Baker found an increase in yield with decrease in rank of the coal (30). The samples used by Baker ranged from anthracite to Durham coal. Dryden using ethylenediamtne, found it to give a more rapid increase in rate of extraction of 85 to percent carbon coal than other solvents.. Bone and Sarjant (31) found that pyridine­type solvents gave the opposite effect with two coals in the medium range.. l1gni te found by Malanowicz (32). Cockram and Wheller (33) found in the case of American Pittsburg seam coals an overall decrease in yield with an increasing carbon content of up to 86.5%, followed by a more rapid decrease in yield for coals with higher carbon content. Extraotion products There is general agreement that the swell-ing and agglutinating properties of coal are attributed to materials found. in the extract, particularly in the y -chloroform soluble fraction 9 of pyridine extract, and that the residue by itself is almost or entirely inert in this respect„ Bakes (29) states that the 3 -fraction of some coals undoubtedly cokes (residue of Y-fraction) on heating and he con­cludes that this fraction may be important in promoting swelling. In compounds consisting largely of hydrocarbons of large molecular weight, basic acidic found, $ y ) between 560 and 617, depending on the concentration, for the molecular weights of compounds in the extract, Asbury (35) found that the extract solution obtained with aniline at 225 °C and phenol at 250 to 300°C con­tains numerous particles smaller than micron size in Brownian motion, Tetralin extracts prepared at 250 to 400°C contained only relatively large motionless aggregates. Biggs (36) concludes from data on extrac­tion of coal by benzene under pressure that the fundamental coal unit has a molecular weight of the order of 300, and that the larger units are held together by relatively weak linkages, Dryden (ll) reports that ethylenediamine extract prepared at atmospheric pressure contains o particles a few hundred Angstroms in diameter. on Extraction of Coal According to Weissler (37), a sound wave of high intensity (10 watts/sq,cm, at a frequency of 1 Megacycle/sec) travelling through small 10~5 However, the water molecules are accelerated to values about 250,000 9 respect" a y -con-eludes swelling" traces of ba.sic and a.cidic bodies were found. Kuznetzov (34), who determined cryoscopically the average molecular weight of a pyridine extract ( s and y) in an unspecified solvent, obtained values of extract.. 225°C C con-tains motion. C extrac-tion linkages. 11) particles a few hundred Angstroms in diameter. The Effect of Ultrasonic Irradiation sq.cm. sec.) water imparts to the molecules an amplitude as as lO~cm. 10 gravity. velocity is about 40 em0/seco, and the pressure at a given point in the water varies over a range of about atmospheres. Obstacles in the path of the wave experience a repulsive force along the direction of propaga­tion because of the "radiation pressure" of about 1 go/sqocmo - cavitation© violent collapse of small bubbles or cavities in the liquid as a result of pressure changes (l) o According to Freundllch and Gillings (38)* there appears to be an optimum ultrasonic intensity that coincides with maximum formation of cavitation voidso For intensities above this value, further increases in power will cause a decrease in yieldo This can be best explained on the basis of the scattering of energy by the numerous bubbles in the extraction vessel, and the removal of dissolved gases so that the residual amount is insufficient to maintain extraction at its maximum ratee The other explanation is that this enormously intense ultrasonic wave possibly causes the destruction of the solvent structure, separation of the extracted materials from the solvent, etc0 l) twofoldo any cavitations inter-molecular moleo present• These chemical bonds have bond strengths in the range of 50 to times that for acceleration due to gravityo The maximum instantaneous cme/secoB 5 atmospherese sqocmo One effect of the great changes in pressure (between ± 5 atm.) is the development of cavita.tion" Cavitation leads to the formation and 1)" According to Freundlich and Gillings 38) j) voids" yield" by vesselj rate.. etco Littlewood (1) concludes that the effects of ultrasonic degradation are twofold0 The first effect is believed to be the temporary breaking of the loose-gel network of van der Waals bonds between adjacent mole­cules, and this does not take place to appreciable extent in the absence of cavitatione The inter~molecular van der Waals forces are of the order of 1 to 10 Kcalo/molee The second effect is the actual break­ing of chemical bonds to give smaller molecules than those originally present 0 11 100 Kcalo/mole. In support of these views, Lockwood et. alo, (39) and Stacey 40) preferential cleavage of components of higher molecular weights before fragmentation of lower molecular weight components commences. review 41) the utilization efficiency of the sonic energy varies between 15 and 40 Kc./see. the major portion of the energy was merely reflected from the surfaces of the coal particles and that unless the greater portion of the absorbed molecular bonds© Lakey, 42) intensity 880 Kc./mesh 300 + 3 3 0 ) They concluded that under identical conditions: (a) the percentage extraction of a variety of coals 9»l£, 12a6%, 19% for 802, 701, 401 N.B.C. coals, respectively) bears a close relationship to their chemical compositions; (b) the extraction of coals with polar solvents can be accelerated by the application of a ultrasonic field of low-intensity sqocm*,) extract is dependent upon the temperature of extraction; (d) the rate of extraction is highest with smallest particle size; and (e) the penetra­tion of the ultrasonic vibrations appears to be limited to the external surface of the coal particles. KCalo/mole.. stacey (40) state that the trend in ultrasonic degradation is towards a This revi.ew of the literature revealed that Berkowitz (41) was the first to report the use of an ultrasonic field to a coal-solvent system. He noted from the results of a subsequent study of Alberta coals that percent at a frequency of 0.25 Ic./sec. Consequently, he stated that the major portion of the energy was merely reflected from the surfaces of the coal particles and that unless the greater portion of the absorbed energy was regarded as being concentrated at specific bonds, such as weak van der Waals inter-molecular bonds, it was quite inadequate to break such bondso Kirkby, Lakey" and Sarjant (42) used a low-intensity ultrasonic generator at a frequency of sao Kco/sec. in their extractions of a series of bituminous coals (mesh size: -300 +330) using pyridine. (901%, 1206%, NeB.C~ low.(0.1 watts/sq .. cmo) insufficient to induce cavitation in the carrier liquid or to bring about chemical degradation; (c) the total amount of particles .. 12 Rybicka 4 3 ) monomethylformamide monomethylcyclohexanone/dimethyl-formamide. They maximum favorably ethylenediamine • With ultrasonic 50 they the extractable material from a coal in 1 5 minutes at room temperature compared with 3 1 percent in 60 hours at 1G0°C using a Soxhlet apparatus. Van Vucht, ete ale, ( 4 4 ) in an attempt to prepare dispersions of coal particles which have sizes smaller than l/20 of the wave length of the irradiation used in a mulling agent suitable for examination by infrared spectroscopy, by They frequency 1 0 Kco/seco 3 0 0 mg« than half a micron in one hour. With anthracites, however, cavitation caused no disintegration whatsoever© by LoomLs p maximum energy solid-liquid beam, diaphragm vibrates oscillations. littlewood l) 7 2 extracto 1 littlewoodfs work), Brown and Ry-bicka ( 43) used ultrasonic irradiation in the extraction of coals with solvent mixtures, such as equi-molecular proportions of acetophenone/monomethy-lformamide and monomethylcy-elohexanone/dimeth;yl­formamide~ They- found that the maximum. yields of extract compared favorably- with those obtained with ethylenediamine. Wi th an ultrasoni c output equivalent to 50 watts they- were able to extract 44 percent of the extractable material from a coal in 15 minutes at room temperature compared with 31 percent in 60 hours at 100°C using a Soxhlet apparatus. Van Vucht, eto al~, (44) in an attempt to prepare dispersions of coal particles which have sizes smaller than 1/20 of the wave length of the irradiation used in a mulling agent suitable for examination by­infrared spectroscopy-, subjected a suspension of coal in n-heptane to the cavitating action of an ultrasonic field generated by- magneto­striction of a nickel tubeo They- found that at a frequency- of 10 seeo 300 mgo of coal could be reduced to a particle size of less houro whatsoevero According to the literature stated by- Loomis and Richards (45)9 the maximu.m amount of sonic energy- is transmitted to a solid~llquid. system if the extraction vessel is placed at a nodal point in the sonic be~ and if the dif.phra.gm of the extraction vessel vibratea with a frequency equal to that of the quartz disk producing the oseillationso It was found by Littlewood (1) using a 72 mesh size coal to position the extraction vessel accurately in the transformer oil above the quartz disk in order to obtain a maximum yield of e.xtracto The graph of Fig. 1 (based on Littlewoodts work)g shows how the distance of separation between the extraction vessel and transducer affects the yield of coalo Fig* 1, (a) that the maxima c) is a maximum when the thickness of the extraction vessel in the trans­ducer corresponds to an integral number of half-wavelengths. The effect of input power on the yield of extract is shown for several British coals N,B,C<> no,) Fig, 2, Fig, (l). levels. Fig, (a) For coals with carbon content in the range of about 84 to percent, the input power required to obtain a maximum yield of extract remains constant at about 200 watts, but for lower-rank coals (containing 82 to 83 percent carbon) maximum yield is obtained at lower input power. For a higher-rank coal with 92 percent carbon the maximum yield is obtained for an input power of 40 watts and for coals with carbon contents above 92 percent the maximum yield of extract is obtained at a much lower value of input power, (b) Extrapolation of the curves to the ordinate of zero watts illustrates the effect of rank on the degree of extraction© Coals of lower rank usually give higher yields, (c) In the case of the code 206 coal containing 92 percent carbon, the yield of extract decreases as 13 extract from coalQ It can be seen from the graph of Figo l,(a) that the maximum yield of extract coincides with the positions of the nodal points, (b) that these decrease with increasing distance from the quartz disc, and (0) that the sound energy which passes through a barrier half~wavelengthso (classified with N.BoCo Code noo) by the curves of Figo 20 The data used for preparing the graph of Figs 2 are those reported by Littlewood (1)0 As the input power to the quartz transducer was increased over the range of about 15 to 225 watts, the yield of extract for a four-hour irradia­tion period increased to a maximum somewhere in this range and then decreased as power was increased to higher levelso The main features of the curves shown in Figo 2 are as follows: 89 lower=powers powero extractiono yields. carbong 9 1 2 3 4 5 Distance of extraction vessel from transducer, mm. lo on yield of extract«, ~ • ~ ~ ~ 0 ~ ~ ~ 0 M~ ~ ~ ~ ~ ~ ~ 0 M ~ ~ ~ ~--------~----------~----------~--------~----------~----~ 6 Figo la Effect of attenuation in transformer oil extract~ N c B e C c 6 50 250 Input power, wattso • Figo 2 o Effect of input power on yield of extracts ~30 0 C\1 't:"j '-" 0 +> t.l ell M >< ED II) ~ ~ (I) 0 ~10 ~ 6 t \ 150 power9 SYffibol ~ 0 • ~ ... )( CJ 20 ext.racto N.,B.,Co Code Noo~ !Q. 101 206 92 301 above 92 501 602 84-89 701 82-~83 802 1 6 input power is increased to a constant value which more or less coincides with the value obtained by extrapolation of the curve to the ordinate of zero watts* The results shown in Fig» 2 are best explained by assuming that three important processes, solution, dispersion and agglomeration, are occurring simultaneouslye Agglomeration and subsequent separation do in fact take place during extraction in an ultrasonic field, but the effect is often marked by the dispersive action of cavitation* The results of Figo indicate that ultrasonic irradiation during the extraction process does not produce any chemical effects0 The two spectra are shown in Fig. on extracts from coalo One extract was obtained using l) S3A 0 . 2 1 0 0 comparable. that the effects of a high-intensity ultrasonic field on extraction naturee inten­sities irradi­ation, pyridine. 4 1 ) 4 6 ) 0 ( 4 7 ) ; i©e. 16 leas wattso Fig. simultaneously 0 cavitationo 3 effects o Figo 3 ooalo ultrasonic irradiation and the other was obtained by simply allowing the coal to stand in contact with pyridine for the requisite length of time. The spectra were recorded by Littlewood (1) with a Grubb Parsons model S3A double beam spectrometer in which the samples were examined as 0~percent extract in potassium bromide diskso Since the reference beam was in each instance set to give 100 percent transmission without the sample, the spectra are directly comparableo This again lends weight to the conclu­sion that the effects of a high-intensity ultrasonic field on extraction are essentially of a physical natureo It is concluded that at the inten~ sities used, physical degradation is the sole effect of ultrasonic irradi~ ation, leading to sizes of material that are readily dispersed in pyridineo This analysis is probably also true for the observations reported by Berkowitz ( 41) and Ayre ( 46)0 Their explanation is based on thixotropic properties, and is possibly in error because many thixotropic systems exhibit the opposite property of rheopexy (47); ioee the solidification time is decreased (and not increased as they suggested) if the sol is 3 5 7 11 13 15 17 Fig. 3 o Infra-red spectra of the extract of Aldwarke 5 0 1 coalo 11~--~--------'---------~-------'r--------'--------~---------r--------' with irradiation b without irradiation 51----~~~--~~~--+_------+_------~------~------._----~ b 2~ __ ~ ________ ~ ________ ~ ________ ~ ______ ~ ________ ~ ________ ~ ______ ~ 3 5 7 9 II 15 17 Wave length in microns 30 501 18 subjected to a more or less uniform mechanical vibration. Berkowitz (41) stated that an ultrasonic field was used to increase the efficiency of the extraction process at room temperature. Mertins (48) observed that a temperature rise of 80*C for extrac­tion of coal with pyridine In the presence of an ultrasonic field, gave a threefold increase in yield over that for a conventional extraction process when ultrasonic intensity of about 0«1 watt/sq*cm* was applied to the system. However, he stated that an upper limit of yield was eventually reached which was quite Independent of any farther increase in temperature* Mertins also noted that the extracts obtained at U0O°C did not precipitate any of extracted material on cooling which indicates that his solutions were unsaturated* This suggests that for a given coal there is a maximum solubility of the extract in pyridine and that this maximum solubility cannot be exceeded by altering the conditions of the extraction process* Mertins also found that: (a) the extraction of different coals by pyridine was affected to varying degrees by an ultrasonic field of the same intensity, and (b) the acceleration of the extraction process by the same increase in intensity of the field varied with different coals* Neither atmospheric oxidation of the coal, nor concentration of the solution significantly affected the amount of extract obtained for a given set of experimental conditions* He found that the presence of imparities such as benzene or water in the pyridine greatly reduced the amount of extract obtained* A very weak field of 0*1 watt/sq. cm. gave an initial rapid rate of extraction which fell off with time until no more extract could be obtained at that temperature* Extraction at & stated that an ultrasom.c field was used to increase the efficiency of the extraction process at roam temperature. Hertins obsel"Ted 80°in preSeJ1ce field. gaTe abOllt 0.1 Sq.CDl. to the s)"8tem. However, he stated that an u.pper lill1t of yield was eventually reached which was ~te independent of further increase in temperature. Mertins also noted that the extract. obtained at 100°C did not precipitate anT of extracted material on cooling which indicates that hi. solutions were 'Unsatvated. This nggests that for a g1. ven coal there is a I118Jd.mum solubility of the extract in wridine and that this max1Jmm solubil1 t1' cannot be exceeded b7 altering the conditions of the extraction process. fOWld difterent by attected by ultrasomc ot intensity. ot coals. signifieantl1 exper.lmsntal conditions. impurities p,yridine greatl1 ot obtained. field. 0.1 em. imtial extract. obt.ained t.hat temperature. ,':: " higher temperatures with a weak field resulted in an increase in the mq-H mnm amount of extracto Mertins concluded that the ultrasonic field does not disperse material which is otherwise insolubleo The effect of particle size of coal on the amount of extract was also investigated and it was found that the effect of the field on the rate of extraction increases with a decrease in particle size* Mechanism and Models Proposed for Coal Extraction The kinetic mechanism of the solvent extraction of coal proposed by (8) datae that the reaction proceeds with a zero-order forward reaction which was immediately followed by a first-order backward reaction,. He believed the backward reaction to be the precipitation of the dissolved coal particles back to the crystal form0 The differential equation that describes the mechanism is; ^ = k f - k b x 1) Eqc (l) yields§ ln(l - V ) = -k^t (2) kf at equilibrium and by substitution ln(l - f - S = ~k,t (4) Teq where k^ is the rate constant for the forward reaction, k^ is the rate constant for the backward reaction, and x is the fraction of coal extracted. 19 maximum Merlins sizee Oele has been widely used in correlating kinetic dataQ He assumed order reactiono formo is: (1) integration of Eqo (1) yieldsg kf = ~Xeq (.3) kf reaction~ ~ 20 each temperature can be found; and from = __f at equilibrium, k„ for the corresponding temperature can be calculated. Another mechanism of solvent extraction of coal has been suggested by Hill, Hariri, Reed, and Anderson (49)© They describe their model as follows© A coal particle is considered to be permeated by the solvent through its macro and micro pores, and the other materials lodged in the coal are then accessible to the action of the solvent, tetralin. There is experimental evidence (50, 51) supporting this mechanism. The ultra-fine structure of the pores has vacancies of the order of a few Angstroms in diameter. Also, larger capillaries and fissures are present. Because a different kinetic mechanisms for coal extraction are possible. According to the mechanism suggested by Hill eteal, (49) the dis­solving out of the organic material from the coal is the diffusion of the solution of organic materials in tetralin out of the pores into the main body of the solvent surrounding the coal particleo This is consid­ered as first order process with respect to both the coal and the solvent. The hydrogen transfer reaction will be considered as a second order process since the transfer reaction from the tetralin to the coal will not be a prominent process at the temperature of the experiment, A kinetic expression describing a concurrent reaction of the first and second order must be used. The kinetic expression describing this process is: dx dt :)(bT - x) (5) By plotting (1 - ~) versus time on a semi-log graph paper, ~ for Xeq x = kf kf kb calculatede 49)" deseri be thei r follows. poresg mechanism.. ultra- II fine Alsog present.. different kinds of microstructure are found in coal particle, several etoal. dis= solving consid-ered solvent 0 experiment& usedG 21 where a^is the initial concentration of the coal and bp is that of tetralin, k ? is the first-order reaction rate constant, and k2 is the constant© definition0 Integration and simplification of Eq. (5) gives 2 o 3 0 3 log (JIjjO = ^ t(kf - k 2at kab^) (6) From an Arrhenius plot of their data, kf 1 0 1 2 ° 8 e"50cO/RTp sec-^-9 and k2 ^ o r ^he extraction of the interspersed materials in the coal is 1C>5 e " 2 6 ^ , secl1 EL11 and Lyon (52) have proposed the following model for coalo The high-volatile coal consists of large alkylated, polynuclear, oxygenated, aromatic and heterocyclic nuclei0 The porous structure of the coal matrix is held together by three-dimensional tetrahedral bonds with some oxygen and sulfur. It is believed that the first material that is transferred from the coal into solution is that trapped in coal pores which may be weakly bonded to the main coal structure. It requires the least amount of activation energy to dissolve the coal present in this form. The remain­ing micelles of coal are strongly bonded. A higher activation energy is required to break these bonds. As the extraction process continues, the activation energy for extraction of coal increases. Accordingly, Hariri (4) proposed the following reaction mechanism for the thermal dissolution of coal based on his study0 .... a i is b.r tha.t , first~order second-order reaction rate constanto The other symbols have their usual definition 0 Eq .. a 20303 (--1) ~ + k' k...&i + k2b...) ~=x btl 1(,-- _0,J; (6) data9 k' = 101208 e-5000/RTg sec~l, for the extra.ction 9 x 105 e-26/ RT$ sec;l Hill alkylateds nucleio tetrahedr&l structure 0 forme remain-ing bondedo increases.. studyo 22 i 0 coal -- Ro + Lo + G„ o 2 Q R0 _ Rl + Ll 3o R l - k 2 >. R 2 + L 2 + G 2 »• V 2 - ^ V i + V i + G„-i where kQ is greater than k-j, k^ is greater than k2 oooo, and greater than l^o In the first, unimelecular reaction RQ is the solid coal, L Q is the liquid, and GQ is the gas© When this reaction is well advanced the first reaction becomes the main route for the extraction of R^ (with the rate constant k^), and so on<> His experimental data did not fit the simple, first-order reaction. « - dt because the rate constant kf was found to be a linear function of x© The rate equation that described his data dt k' (1 - sx)(l - x) (7) 0 where s is a constant that is equal to the reciprocal of the maximum x^) obtainable* Eqe (7) = 0 , x = 0, obtains! L1J Z-J Ls.x = s - l)klt (8) u 10 k 0 :7 Ro 1'0 Go 2., Ro k -~-7 Rl L1 + G1 3" Rl k;Z :7 R2 L2 G2 no ko k1i kl oooOD ~-l is ~o first. unimolecular Ro Lo liquidjl Go gaso ~ k1)D ono simplejl order reactiono ~ = k'(l ~ x) dt because the rate constant k' was found to be a linear function of xo The rate equation that described his data was: dx = k' (1 ~ ax)(l ~ x) dt 0 possible fraction of extract (xm) obtainable~ When Eqo is integrated with the initial condition t = 9 X = 09 one obtains~ In 1 ~ x = (s = 1) k' t 1 - ax 0 EXPERIMENTAL PROCEDURES AND RESULTS The experimental results obtained from extraction studies on coal employed.* coal© study* Coal preparation from Mine© analysis on this coal made by the Commercial Testing and Engineering Company is listed in the following tabulation: Ultimate analysis Proximate anal ysis Element W t o | W t o # 7 2 , 8 8 0 0 0 0 e 5 * 5 8 Ash 8 , 3 7 1 . 5 1 Volatile Matter 4 5 . 7 1 1 0 , 8 2 Fixed Carbon 4 5 * 9 2 Sulfur O065 0 o l 9 Heating v a l u e - - 1 3 , 3 3 7 BTU/lb, calculated on dry basis. The sample of coal was ground and sized to - 2 7 0 + 3 3 0 mesh. This ground coal was then kept in a stock sample bottle and stored in a desiccator. Tbe are somewhat dependent on the experimental procedures employedo Several different experimental methods have been used by different investigators for extraction of ooalo The experimental procedure described in this section was found to be best for this study" Q2!! The coal sample selected for this study was taken from. a working face of the Utah Spring Canyon Mineo The chemical analzsis PrOximate analYsis Wto% Component Wto% Carbon 72,,88 Water 0000_ Hydrogen 5058 8 .. 37 Nitrogen 1051 45071 Oxygen 10,,82 45092 0065 Chlorine 0019 value-~=-13,237 lb, calculated'on basisc to-ZlO +330 24 5©97 sample0 Sample beakero G hour© 2 5 mlo balance, Samples runs way) 0 Grade 1,2,3,4-tetrahydronaphthalene tetralin), Coleman Corporation solvent. 25-frequency Kc/sec, 1 2 5 transducer. Fig, is a photograph of the experimental apparatus showing the Sonogen ultra­sonic generatoro The transducer converts the output of the generator into mechanical vibrations which are referred to as ultrasonic waveso The frequency of these vibrations is above the audible range© The trans­ducer was attached to the bottom of a tank, which contains water, and into which the mechanical (ultrasonic) energy is transmitted. The average power of mechanical vibrations per unit area is 0 , 5 9 watt/cm^, •*This than and is probably due to the use of a different apparatus and period of coal, Ash determinations on the sample of ground coal were made, and an average value of 5097 percent* was observed which was used to correct for the available coal in the coal sampleo SamPle preparation About one gram of ground coal was removed from the stock bottle and put into a beaker., The sample was then dried in a vacuum oven at 105°0 for a period of three hours, removed from the oven, and then placed in a desiccator for one houro The sample of coal was then placed in 25 mlo Pyrex-glass flask and the weight of the coal determined by weighing on an analytical balancee (Samples of coal for all extraction rune were prepared in the same way} 0 Solvent preparation The solvent used for coal extraction was Practical-Grade 1,2,3,4~tetrahydronaphthalene (tetralin)g manufactured by Matheson Ooleman and Bell Oorporationo No purifying or preparative procedure was applied to the solvent o Extraction apparatus An ultrasonic generator, Sonogen Model AP-25-B, generating a radio freqaency of 40 Kc.,/seco with an average input power of 125 watts was used to drive the quartz transducero Figo 4 ultra.= sonic rangeo trans~ ducer tankg transmittedo 0059 cm2a *This value is lower the one given in the original analysis time for heating the co~l., 25 (b) Sanogen Ultrasonic Generator0 (c) Reservoir0 Fig0 4<> Photograph of experimental .apparatus used for coal extraction studies„ ..... ' .. Sonogen Generatoro Cooling Water Reservoiro ~pparatu8 studiesu 25 26 A copper stand with a height of 4»45 centimeters was specially designed to hold the extraction flask in the bottom of the tank at the nodal point of the sonic wave* A constant-head cooling water reservoir was constructed to provide cooling water for maintaining a constant tempera­ture in the water bath during the extraction perid. The water flow was regulated by a small clamp on the hose leading from the reservoir to the cooling coil of the water bath. Determination of optimum coal to solvent ratio In order to determine the best ratio of coal to solvent to be used in extraction studies, experiments were performed with different ratios of coal (in grams) to solvent (in cubic centimeters) under the influence of an ultra­sonic field. For these preliminary tests the extraction time was five hours and the bath temperature was 20°C. The experimental procedure outlined below was employed in the preliminary work. The experimental results are tabulated in Table 1 . As a result of the preliminary study, a ratio of solvent to coal of 5 0 to was chosen as the ratio to be used throughout this extraction study. A plot of fraction of coal extracted, x, versus coal to solvent ratio (grams of coal/milliters of solvent) is shown in Fig. 5« The fraction coal extracted, x, is the weight of coal extracted, AW, divided by the initial weight of coal, Wc, on an ash free basis. Experimental procedure To a flask containing about 1 0 cubic centimeters of tetralin, 0 . 2 gm of coal was added and the covered flask was placed on the copper support in the water bath of the transducer. (The term "transducer" is used to describe the complete system composed of the water bath and quartz-crystal transducer.) The regulated cooling 26 • 4.45 wave. pend. cooling coil of the water bath. Determinat!on ~ optimum~!2 In performed. time Table-l. 50 1 irllllters 5. &, divided by the initial weight of coal, Wc' on an ash free basis. 2rocedure 10 0.2 gm was placed on the copper support in the water bath of the transducer. (The term "transducer" is used to describe the complete system composed of the water bath and qQartz-crystal transducer.) The regulated cooling 27 water kept the transducer water at a constant temperature throughout the extraction process© (The ultrasonic generator was turned on at least forty minutes before samples were put into the transducer.) After the desired extraction time, the vessel was removed from the water bath. The contents of the flask were transferred to a weighed thimble and washed in a Soxhlet apparatus using benzene followed by trichloroethylene as washing agents. The extract from the coal was freed from the residue by extracting all the material (solution of extract and residue) for about 25 hours with benzene and about 50 hours with trichloroethylene. Extrac­tion was normally continued until the liquid descending to the boiler was colorless© The thimble was taken out of apparatus and dried in an oven tb 110°C hours© 1© for different coal/solvent (C/S) ratio© (Temperature: 20°C, Extraction Time: 5 hours) P „ C/S ratio ^ O o (grams/ml) extracted, x. Ool 2 0©05 0.0878 0©033 0.0911 0©025 0.0923 ©0©0909 0.0167 processo Saxhlet Extrac-tion colorless,. dri ed at 105 to 110·C for 24 hours,. Run Noo 1 .2 3 4 5 6 Table 10 Extraction of coal (ciS) ratio~ 20·cis Fraction of coal (extracted, x. 001 0.0715 0005 0 .. 0878 00033 Oo09ll 00025 0 .. 0923 00 02 000909 000167 0.0915 28 O . l O r Pig, coal/solvent ratio at 20 °G and 5 hours 0.1 ,U 0.09 v 0 0 0.0 8 0.0 7 - 0.0 6 0.0 5 o 0.02 0.04 0.06 0 .. 08 0 .. 1 cis coal (grams) / solvent (ml) Fig. 5. Percent of extraction versus ·C hours. 29 desiccator for 1 5 minutes for cooling <> The weighing bottle containing the coal residue and dry thimble was then weighed0 The weight of coal residue was obtained by subtracting the weight of the empty thimble from the total weight of the coal residue, and thimble^, The amount of extract was found by subtracting the weight of the coal residue from the weight of the original coalo With these data, the fraction of coal extracted could then be determined0 By varying the extraction time for different samples of coal, the rate of dissolution of extractable material in the coal was calculated for use in determining the kinetics of the extrac­tion processo For analysing data, the fraction extracted, x, determined from four extraction experiments at the same conditions were used0 Preliminary coal, decom­position solvent^ b) benzene, trichloroethylene^ tetralin0 meters put ml Pyrex-glass flask0 containing the tetralin was placed in the transducer and subjected to ultrasonic irradiationo The system was maintained at 25°C for a period of five hours and then a liquid sample was taken© Next the temperature was raised to 34°C and kept at this level for another five hours0 Another liquid sample was taken after this periodo The same procedure was repeated for temperature of C and Co The samples were then cent! The dried thimble was placed in a weighing bottle and held in a 15 coolingo weighedo w~s residueg thimble... dataB determinedo By coalp dissolu.tion analyzing datap extractedg Xg usedo Prelimin~ experiments Before starting study on the extraction process for oo&1p the following tests were performedo (a) Experiments were conducted to determine the amount and resulting products of deco~ position of the pure solvent,.9 tetralin, 9 in the ultrasonic fieldo (b) Blank extraction tests were run on benzenep trichloroethylene, benzene and trichloroet,hylen~ and tetralino DeComposition of tetralin Approximately fifty cubic centi-meters of tetralin were in a 50 Pyrex=glass flask" The flask G Uqaid takeno G hourso 44°G 54°Go 30 chromatography*. 44* C, 25 °C 0 . 0 6 1 . 9 4 decahydron-aphthalene). on 1 0 0 . 2 covered flask was kept undisturbed for one hour at room temperature. The solution and coal residue were then transferred to a weighed thimble. The extract was separated from the residue by washing in the Soxhlet extraction apparatus, using benzene as a washing agent. After the ex­tract was completely separated from the residue (or when the overflowing liquid appeared to be colorless), the thimble was taken out and dried in an oven at 1 0 5 to 110°C for hours. The completely dry thimble was in dry 1 . 0 2 on procedure was the same as that used for benzene. The amount of coal 0 . 3 7 chromatograph 7 2 0 , Dual-Column, analyzed by gas chromatograph1*". For temperatures below 44 ·C, the solvent which had been under ultrasonic irradiation for fifteen hours showed a trace of decomposition. After a period of twenty hours at temperatures in range of 25°C to 54°C, there was a small but insignifi­cant amount of decomposition of the tetralin (less than one percent). Chromatographic analysis of the original solvent showed that the solvent contained 98 percent tetralin, 0.06 percent naphthalene and 1.94 percent other impurities, which included a small amount of decalin (decahydron­aphthalene). Blank tests ~ benzene To a flask containing about 10 cubic centimeters of benzene, 0.2 gram of coal was added and the 105 25 then placed in a weighed weighing bottle and placed a desiccator to cool. The bottle with the cool residue and thimble was then weighed. The result showed that 1.02 percent of coal was extracted by washing with benzene in the Soxhlet extraction unit. Blank tests ~ trichloroethylene For this solvent, the extracted was found to be 0.37 percent. *The gas chromatogra.ph used was Model 720, Dtial-Column, Programmed Temperature. Gas Chromatograph made by F & M Scientific Corp. Blank :feeft& on. benzene and trichloroethylene test, the same procedure was used as that for blank tests on benzene © The extract was separated from the residue by washing in the Soxhlet extraction apparatus using benzene followed by trichloroethylene as the washing agentSo The result showed that 1©18 percent of coal was extracted © Blank tests on tetralin Using the same procedure as that for blank tests on benzene, 10 ml of tetralin were used as solvent© The flasks containing the tetralin and coal were allowed to sit for one hour, five hours, and twenty hours, and then the contents of the flasks were washed with benzene followed with trichloroethylene in a Soxhlet apparatus for twenty and fifty hours respectively© The extractions were found to be 3°08, 3*26, and 3<»46 percent of the coal after one, five, and twenty hours, respectively© These values are very close to the results reported by Hariri ( 4 )0 Precipitation tests on extract Experiments were performed to detect whether precipitation of the extract from the solvent, tetralin, occurs when the extraction process is continued for a longer time* The coal sample was dried in a vacuum oven at 100°C for three hoursa 0©2 gm 2 5 ml fixed 1© mixed 54°C and irradiated for five hours© One of the flasks was removed after five hours© The coal residue was freed from the solution in a Soxhlet apparatus and then dried in the oven until no trace of solvent was found © The dried coal residue in the thimble was put into a weighing 31 t~eilts ,gnbenz!m.$ ~ trlchloroeth.zleru! For this .. agentso 1018 wag .. IDa.rIk Q!l U sing aa m1 solvento hourg respectivelyo 30089 3 .. 3046 respectivelyo ver,y Harlrl. 4) 0 ~ time~ hourse Four 002 samples were placed in 25 extraction flasks and tetralin was added to give a fi~ed solvent to coal ratio of 50 to 10 Flasks of mi~ed samples were placed in the transducer at the bath temperature of C hours.. hourse 0 3 2 bottle and weighed on an electric balance. The fraction extracted was found to be 1 1 * 2 4 percent of the original coal. When the first flask was removed, the temperature of the water bath was lowered to 4 4 ° C, determined, held at a temperature of 3 4 ° C for 1 5 hours of reaction time and for samples held at 24°C for 2 0 hours. The results are summarized in Table 2 . These data show that precipitation of the extract does not occur for longer extraction times in tetralin. Table 2 , Summary of data obtained from precipitation tests on extracts with tetralin. No, Wi (gm) Wf (gm) 5w x 1C)3 % (gm) (gm) X (» Time (min,) Temp, ( • c ) 1 0 , 2 8 4 0 0 , 2 5 4 0 3 0 , 0 2 0 , 2 6 7 2 1 1 , 2 4 3 0 0 5 4 2 0 , 3 2 0 7 0 , 2 8 6 9 3 3 082 0 , 3 0 1 8 1 1 , 2 ! 6 0 0 44 3 0 , 3 3 7 1 0 , 3 0 1 6 3 5 . 4 6 0 , 3 1 6 8 1 1 , 3 2 9 0 0 3 4 4 0 o 2 5 4 2 0 , 2 2 7 1 2 7 * 0 8 0 , 2 3 9 4 1 1 , 3 1 1 2 0 0 Coal extraction by tetralin without ultrasonic irradiation The experimental procedure described on page 26 was used for making conven­tional extractions on coal. The coal-tetralin mixture was only stirred during the extraction period. These experiments containing 0 , 2 gm, of coal and 1 0 ml, of tetralin were carried out at three temperatures; balance" 11024 44°Go The experiment was continued for another five hours and the yield for another sample was determinedo The yield was also determined for samples 34°G 15 G 20 hourso tetralin" 20 tetralino Sample (~) l~ x 103 W x Temp" Noo (gm) "(gm) (~) (%) min.) (oG) 1 002840 002540 30.02 002672 lL24 300 54 2 0,,3207 002869 33082 003018 ll"Zl 600 44 3 0.3371 003016 35.46 003168 11032 900 34 4 002542 002271 ' 27.08 002394 11,,31 1200 24 Bz conven-tional coaL period" 0,,2 gmo 10 mlo 33 2 4 , 3 4 and 54°C, and samples were analyzed after five extraction periods, 2 , 5, 1 0 , 15, and 2 0 hours. The experimental data obtained at the three temperatures are tabulated in Tables 8, and 1 0 . The results from this study are compared with results obtained on extraction of coal in the presence of an ultrasonic field in a later section. Coal extraction by tetralin with ultrasonic irradiation Coal was extracted by tetralin in the presence of an ultrasonic field using the experimental procedure described on page 2 6 . Extraction experiments were performed at five different temperatures; 2 4 , 3 4 , 4 4 , and 54°C, and the data from these tests corresponding to these temperatures are given in Tables 1 1 , 1 2 , 1 3 , 1 4 * and 1 5 , respectively,. Extraction times were varied over the range of a few minutes to 20 hours© The data obtained from this experimental work are analyzed and the results are discussed in the next section© 33 24, 34 2, 10, 20 hourso 9, 10e Bl 26. 24, 29, 34, 44, 11, 12, 13, 14, 15, respectivelyo hoUTso sectiono DISCUSSION OF RESULTS Analysis of Experimental Data Oele's ( 8 ) mathematical expression for the kinetics of coal extrac­tion (refer to page 1 9 ) is simple and convenient to use, but it fails to describe the experimental data obtained in this study© Oele's equation for kinetics of the reaction process considers a forward extraction reaction of the zero order opposed by a first-order reaction for reprecipitation of material extracted from the coal© Experimental data that fit his proposed model, when plotted in the form of ln(l - x/xeq) versus time, are defined by a straight line© The data from this study, plotted in the form suggested by Oele's model, do not fit the equation Oele© unsaturated© 4 ) * © extraction time versus yield in Figure for temperatures of 29 and C and in Figure for temperatures of 2 4 , 3 4 , and 44°C© Da.ta 8) 19) studyo order reprecipi tation coalo In(X/Xeq) lineo eqnation obtained by Oelso Furthermore, the data obtained indicates that for the entire extraction period, the extraction solution remains unsaturated. No precipitation or recrystallization of coal was observed during the experiments of this study or in the study made by Hariri ( 4). It appears that the decrease in rate of extraction with time that was observed in this work can be attributed to the progressive decrease in the amount of coal that is able to dissolve in the solvent, and does not appear to be related to an increase in the backward reaction postulated by Oele (precipitation of extract from the solution)o Experimental data obtained in this study on the extraction of coal by tetralin with ultrasonic irradiation are plotted in the form of 6 2ft 54°C 7 24, 34, 44 °Co 35 P l g o 60 by Time-yield curves for extraction of coal tetralin with ultrasonic irradiation0 I 0 -{ ~ I-- -- Q) e-- «:.) «:.) 0 0 M<> 1..1;'t\ Rl ~ '"3 ! 0 0 CI) f-- )--c --j---- f--' ~ r-' '\ [ R \ 0, \ ~ ~ ~ N r-I 0 " .... ....... 1 ..n.J..-.{u - ~ t:1 ~ to -..0 -:t C"IR 0 0 0 0 0 0 0 0 0 0 0 0 0 0 x=~ Fraction Extracted We Figo 60 Time~yield b,Y ultrasonio irradiation" I , 35 8 ~ g '" 0 g 8 t- 8 -..0 '"III' Q) go -e~I=l 0 S 0 0 ~ @ oo r-I o '-' ~ - U - 0 Q- • 0 O0 • o o by tetralin with ultrasonic irradiation0 --{ -<l ~ C,,) 0 0 :•l ~•. ~• o <I 0 , -[ -<1 rO ~ c" \ [ <I ~ ~ \ ~ ~, ~ ~ <> o ~- ~ ~ ~ ttl '-D 4- 000 o 0 " 000 IS. X == ~ Fraation Extracted We , , .. ' o'" o o Fig .. 7 fJ Time-yield ourves for extraotion of coal irradiationo 36 8 ~ 8 '" a g ~ '"«l' ~ i ..1..1... §~ 8 C"\ ~ ~ o 37 Another model for coal extraction can be described as follows: In the extraction of coal by solvent, the process can be considered to proceed by two different mechanisms. One takes place at the coal-tetralin interface where the extraction reaction is the kinetically controlled step, and the other is the flow of extract and tetralin inside the pores where diffusion processes become the rate controlling step. The model considered here has a close analogy to the oxidation of metals in which the phase-boundary reaction and diffusion reaction have been concluded in the theoretical model as two separate parallel reactions 5 3 ) • Therefore, the overall process of coal extraction can be represented by the following equations: 1 , 1 AW = t (Qs wc Where: ka is phase-boundary extraction rate constant, kjj is diffusion extraction rate constant, t is time, £M is weight of coal extracted, Wc is weight of original coal (ash free). Fig, 8 is a plot of AW/fa versus t^W/fa for extraction of coal at a c c temperature of 24°C, It is seen from this plot that the experimental data are not consistent with the model described by Equation (9)» It appears that the parameters, k& and k^, may possibly be a function of £ w / w c . The author then employed the method of finite differences to evaluate A x / A t for the experimental data at the five temperatures. The diffUsion ( 53). t = EW Wc Where: ka is phase-boundary extraction rate constant, kd is diffusion extraction rate constant, t is time, l:M is weight of coal extracted, Wc is weight of original coal (ash free). Fig. 8 is a plot of l::M/Wc versus t/ISW/Wc for extraction of coal at a temperature of 24°e. It is seen from this plot that the experimental data are not consistent with the model described by Equation (9). It appears that the parameters, ka and ~, may possibly be a function of l::JJI/Wc • The author then employed the method of finite differences to evaluate ~~t for the experimental data at the five temperatures. The 36 ZWO~------~--------~--------~------~----9~--' 2~r-------4-------~------~--------__ ~6~ __ ~ AW t Fig .. 80 Plot of w;; versus (f::.WlW e ) for extraction of coal with tetralin at a temperature of 24°C .. ~ ~r --'1~~------~-----)--~------~------~f~----~ ~ J ~ l400~-------r--------r--------+----~~+-------~ We ~~-------+--------~--------~-------+--------~ 600~ ______ ~ ________ ~ ______ ~ ________________ ~ 00 0 0.,2 Ou4 006 0.8 38 39 assumed order© g - k U (10) The parameter, Ax/At, was plotted against (l-x)© From this graph, it was found that the data plotted as a definite curve© This implies that the parameter, in Equation ( 1 0 ) is a function, @(x), of the fraction x© Furthermore, Fig© 9 this graph are given in Table 3)p it is found that (4S)/(l-x) or Q (x) is a function of x i , and the kinetic equation for this extraction process can be written in the following forms - kj(l- dx4)(l - (11) equation, d maximum possible yield of extract, xm)^o x) In ll) study© 1 , extraction© work, (a-x) evalua­ting data© a extract, x^ curves versus time (see Figs© 6 and ? ) o 39 kinetics of the extraction process were as~d to be represented by a reaction of the first ordara dx , dt = k( 1 - x) (10) parameter» 6x/6t, was plotted against (l-x) 0 From this graph, it a. curveo k, (10) a. E1(x)g extracted, xo Furthermoreg from Figo (the data used in preparing .3)9 (~)/(or 9 xig wrl tten form: dx dt = e (X)( 1 - x) = k~(l~ dxt)(l ~ x) (11) In this equationg g turns out to be the reciprocal of square root of the extracti l/(xm)io The concentration term (l-x) in Equation (11) needs to be carefully considered with respect to the experimental data obtained from this study.. The integer, k in the concentration term implies that one hundred percent of the coal is available for extractiono For the data obtained in this workg a concentration term a~was used for evalua-ting the experimental datao The value for ~ for extraction at a given temperature is equivalent to the maximum possible yield of extra.ct, XmD for a given set of conditions; and is evaluated from CUr7es of yield Figso 7)0 1166xx1l0"O -3~------------------~------------------~ ~ H la ~ ~ ~ ~ ro S ~ ID ~ ~ Fig. 90 14~----------_4~----_+------------------~ U l0r-____________ _ I 2 1 Square root of fraction extracted, x~ A plot of (x/~) I-x versus square root of fraction extracted, x!, for extraction of coal with tetralin at a temperature of 24°C o Table Variation of (gj*- )/(1-x) versus square root of fraction extracted, x i , for extraction of coal with tetralin at 24°C. ^/(l-x) X xi 0.138 0.036 0.048 0.012 0.011 0.011 0.070 0.01 0.01 0.280 0.01 0.286 0.01 0.01 From the preliminary analysis of the experimental data, the term, param­eter to analyze the original experimental data. It is first assumed that the extraction process observed is repre­sented by a first-order reaction: I ? = k'(a x ) 3. VariaticTl. (f l-x!, ~(l-x) .6.t x x' 0.015 0.019 0.013 0.191 0.012 0.219 0.057 0.239 O.Oll 0.064 0.253 0.265 0.075 0.273 0.079 0.082 0.085 0.291 0.087 0.295 Proposed Mechanism for Extraction of Coal with Ultrasonic Irradiation 41 concentration te~ (a-x), was chosen as a variable concentration par~ eter order dx , -dt = k(a - x) (12) 42 X a-x 1 a-x 0 0 0 . 1 0 2 .8 1 5 0 . 0 1 9 1 2 . 0 6 3 0 0 . 0 36 0 . 0 66 1 5 . 2 4 45 0 . 0 48 0 . 0 54 18.54 60 0 . 0 57 0 . 0 45 75 0 . 0 64 0 . 0 38 2 6 . 49 0 . 0 70 3 1 . 2 5 1 0 5 0 . 0 75 0 . 0 27 3 6 . 6 3 1 2 0 0 . 0 79 0.023 4 2 . 7 4 1 3 5 0 . 0 20 4 9 . 50 a of x) A t line. In the work reported in this paper, however, the plot is a curve (see Pig. 1 0 ) . The first-order assumption is therefore rejected, and a second-order reaction mechanism was assumed. (-i-) a-x out to be a curve instead of the straight line predicted by the inte­grated form of Equation ( 1 3 ) (see Fig. 1 1 ) . The data used for Fig. 1 1 are listed in Table 4* 4* i a-x for extraction of coal with tetralin at 24°C, (a = 0 . 1 0 2 , x = fraction of coal extracted). According to this equation, & plot of~ vs (a-x) should give a straight ~t line. In the work reported in this paper, however, the plot is a curve (see Fig. 10). The first-order assumption is therefore rejected, and a second-order reaction mechanism was assumed. dx _ 2 dt - kia-x) This was also rejected because a plot of (..1....) versus time also turns a-x out to be a curve instead of the straight line predicted by the inte­grated form of Equation (13) (see Fig. 11). The data used for Fig. 11 are listed in Table 4. Table 4. Variation of 1 with time (minutes) a-x for extraction of coal with tetralin at 24·C, (a = 0.102, x = fraction of coal extracted). t(min.) x 0 0 0.102 15 0.019 0.083 30 0.036 0.066 45 0.048 0.054 60 0.057 0.045 75 0.064 0.038 90 0.070 0.032 105 0.075 0.027 120 0.079 1.35 0.082 0.020 ..1.... 9 .. 8 12.06 15.24 18054 22.25 26.49 31.25 36.63 42.74 49.50 43 12x10-4 Ax At 10x10 -2 Pig. 10. A Temp. 24°C. Solvent, tetralin. 1~-4r--------+--------~--------r-------~~------, 8r-------~--------_+--------_HL-------4_------~ 4r--------r------~r--------+--------+-------~ o 4 6 8 lOxlO-(S}-X) Fig. plot of rate of extraction of coal as a function of driving force to the first power. " ~ o I.t'\ '"\ Figo 11. ~ \ '-~ --. MI~ 1\ o ('f"\ . ~ A plot of a1:x versus t for 24°C. '" 44 , .... o 45 When the experimental data for all five temperatures were plotted in the form of ln(^)/(a-x)f versus x as shown by Fig. 12, the data were well represented by straight parallel lines. Since the term (££)/( a-x) Zjt resembles a rate constant, the parameter, k, is used to describe it. Values for k as a function x are not hard to find from the data given in Pig. 12 (54). -b'x k' - k0e RT (14) where kQ is the initial rate constant, and b* is a constant. The data of Fig. 12 shows this relationship is valid for about 90 percent of the extraction period. The differential expression which describes the extraction rate for the data obtained in this study is -b'x f ~k0(eR T)(a-x) (15) According to the Eyring's absolute reaction rate theory, the initial rate constant is given by kc -if 1 £ 8 Xp(- go) " RT Hence Equation (15) can be written as: 4 & - * f f « P < - * & (16) Where: x is weight of coal extracted/weight of original coal (ash free), a is the maximum change in weight of original coal (ash free), ^ is transmission coefficient, assumed to be approximately 1, k is Boltzmann constant, h is Planck's constant, torm ln~)/(a-x), a8 by ~)/(a-x) resembles a rate constant, the parameter, k, is used to describe it. Values for k as a function x ,are not hard to find trom the data given in Fig. 12 (54). -b'x k' = k o e ~ where ko is the initial rate constant, and b' is a constant. The data of Fig. 12 shows this relationship is valid for about 90 percent of the extraction period. The differential expression whioh describes the extraction rate for the data obtained in this study is (15) According to the Eyring's absolute reaotion rate theory, the initial rate constant is given by ko = c}{ -hk'l' exp( - a *Q) RT Henoe Equation (15) can be written as: , * a~tt = rf !hI exp( - ~R.T - .ReT.! A) (a-x) Where: x is weight of coal extracted/weight of original coal (ash free), (16) a is the ma.ximum change in weight of original coal (ash free), ~ is transmission coefficient, assumed to be approximately 1, k is Boltzmarm constant, h is Planck's constant, 46 l(r -3.2~--------~------------~~----------~~------~ Fig. 12. Plot of In(k) versus traction extracted, x, for extraction of coal with tetralin at five different temperatures: 24, 29, 34, 44,54°Co -3.6r---~~---~---------------~~ _______________ +-_________ ~ -3.9r---~~---+--~---------p~-----------~--~~~ -4.·21-'--'~-----t-"-~:--------I"~------+-------300.....---j \l '. 54°C o 44°C o 34°C o 29°C b,. 124°C -4.8~ ________ ~ ____________ ~ ____________ ~ ______ __ 4 7 10 (x)102 Fraction Extracted AFQ R The above expression upon integration does not give a linear relationship between the logarithm of x and time (t). It predicts a more complex reaction mechanism than a simple first order reaction for the extraction of coal. It appears that the complexity of the coal reacting with the solvent (tetralin) varies with time during the extrac­tion process, and such change in composition corresponds to a different free energy of activation (AF )• Because AF is composed of terms for activation enthalpy activation entropy, a factor, f(x), a concentra­tion term, can be added that might be attributed to either of these components as expressed by the following equation: AF =AFQ f(x) =AH* bx - TAS0 = AF* bx (17) or the equation: AF AF0 + x) A H Q T(ASQ A F Q + (18) (l6) ^ = (a-x) JLI e X p ( ~ A H o +A>O _ ^ (1 9) dt h RT R RT If br=b then Equation (17) is valid and the contribution is to the enthalpy term; but if bts=bT, the contribution is to the entropy term. A reliable way to determine the temperature dependence of b' is to plot ln(k) versus x for different temperatures (Fig. 12). It was found that the slopes of the lines do not vary with temperature, therefore 47 :f Mo is the initial free energy of activation, T is absolute temperature, R is gas constant, t is time. extrac-tfiroene penroecrgeys so, fa nadc tisvuachti ocnha n(.g6Fe* i)n . cBomecpaoussiet i&o nt ciosrr ecsopmopnodsse dt oo fa tedrimffse rfeonr t and x), concentra-tion t t * t b,.F b,.Fo + x) b,.Ho + ~o b,.F 0 + (17) f * f * b,.F =b,.Fo + f(x) = b.Ho - T~o - bx) = b,.Fo + bTx (18) By substitution, Equation (16) becomes: * f dx = a-x) II exp(-b.Ho +b.So - b'x) (19) R b'=b'=In(_'" -- coefficient for x has to be in the form: b,==bT, and it is included in the entropy term, A s t From Fig. 1 2 , § was found to be 7 . 2 cal/mole-deg by averaging the slopes of the five straight lines. The value of b calculated was 1 4 . 4 0 . 2 cal/mole-deg. With this value of b, the contribution to entropy would range from a value of zero e.u. when x=0 to 1 . 6 6 e.u. when X^XJJJ, the maximum yield for the given test conditions. According to Hill's 5 7 ) interpretation, the decrease of activation entropy (A£> ) with extraction yield is probably a result of the decrease in number of surface sites. Since a change of 4*6 entropy units in the apparent activation entropy corresponds to a change in surface sites availability by roughly a factor of ten, the decrease of 1 . 6 6 entropy units in this experiment is, therefore, corresponding to a decrease of about one quarter of the original available surface sites where the extraction is taking place. The changes of activation entropy as a function of extrac­tion yield for the five experimental temperatures are shown as Table 17. The final data on rate constants for the extractions of coal are given in Table 5 . By employing Arrhenius* and Eyring's equations, the activa­tion energy is obtained by plotting ln(kQ) against the reciprocal of test absolute temperature. The kjs were found for different temperatures by determining the intercepts with the y-axis for the lines shown in Fig. 1 2 for data plotted in the form ln(k) versus the fraction of coal extracted, x. From Figure 1 3 one can find the activation energy for the process, Ef t = 6 . 7 kcal/mole. By plotting ln(k0/'S) versus l/T, the activation enthalpy and the initial activation entropy were found from Fig. 1 4 to be 6 kcal/mole and - 5 4 * 5 e.u. respectively. b'=6S~ 12, ~ 7.2 mole-14.4 ± 0.2 caJ./~ - 1.66 ~, ( 57) (~gF) probably- 4.6 1.66 ~arter fUnction extrac-tion yield for the five experimental temperatures are shown as Table 17. - The final data on rate constants for the extractions of coal are given in Table 5. By employing Arrhenius' and Eyring's equations, the activa­tion energy is obtained by plotting In(ko) against the reciprocal of test absolute temperature. The kbs were found for different temperatures by determining the intercepts with the y-axis for the lines shown in Fig. 12 In(13 Ea=6.7 kcal/mole. By- plotting In(kolT) versus lIT, the activation enthalpy and the initial activation entropy were found from Fig. 14 to be kcal/mole and 54.5 e.u. respectively. Table 5* Final results for solvent extraction of coal with tetralin. T°K (l/r)K)3 kQ f (ko/WflO* kQ I (k^Dj-lO5 Mk0)T lnCk^^ ln(kQ)f ln(kc/T)f 297 302 0.02148 7 . 1 1 2 6 3.S393 3.725 10.9148 11. 1 9 24 -3.366 9.1259 327 3.058 0.0482 14.7401 0.04763 -3.0448 8.8355 - 3 . 0 33 8.824 E a kcal/g-mole AHQ = kcal/g-mole = in Table 5. Final results for solvent extraction of coal with tetralin. 297 3.367 0.0172 5.7912 0.01694 5.7037 -4.0788 -9.7735 -4.0635 -9.7583 3.311 0.0208 6.8874 0.02l48 7.1126 -3.8393 -9.5527 -3.874 -9.5855 307 3.257 0.0246 8.0130 0.02402 7.824 -3.72.5 -9.4574 -3.705 -9.4329 317 3.155 0.0346 10.,9148 0.03548 II 0 1924 -3.3394 -9.0995 -9.12.59 3Z7 000482. 0004763 14.5657 -8.8355 -3.0:33 -80824 Ea = 6.7 kca1/g-mo1e l ~Ho = 6.0 kca1/g-mo1e f = method of finite differences I = Integrated form of equation (see Table 16 Appendix) 1n ko 50 -2.9r------,--------------~--------------------------~ -3.0 ~-- -- ---~-----.. -------. Ea = 6. T':~.eM~, A = 1336 ndn-l -3.1 -3.2 -3.3 -3.4 -3.5 -3.6 -3.7 -3.8 -309 I------'''r----+----------.- --+---~--.-------- - - -----" -- o Method of .finite differences • Integrated form of differential equation ----------+._--_._-------1---> ...... -_._----_ ... ,._._- -4.l~--~--------~-----------~--------~ 3.05 3.10 3.20 3.30 3.40xlO-3 (lIT) Fig. 13. Arrhenius plot for evaluation of the activation energy. Fig* 1 4 o Eyringfs plot for evaluation of the activation enthalpy and entropy for coal extraction with and without ultrasonic irradiation I -9 oll---___ .~ I I ; Wi th ultrasoni c irradiation: o Method of finite differences • Integrated form of differential Equation .6.Ht = 6 .. 0 kcalo 6.st :; -54.5 eu. Wi thout ultrasonic irradiation: () Evaluation from the curves 51 -9 .. 2t----+-----~_. in Fig .. 17 6Hi = 1.65 kcal .. --- --- ----------------1 -9Q4~----~~----~~~---+------~------~----------------4 -9.6~--~-r----------_+-----------~~-----------~ -907~----~------------~------------~----~------__I -9.8~ ____ ~ ____________ ~ ____________ ~ ________ ~ __ ~ 3,,05 3,,10 Fig. lA~ Eyring's irradiationo Table 60 Variation of entropy of activation with fraction extracted0 T°K ( | } x l o 3 (x=0) I n kQ x=Oo05 In k -|xK) o 3 6 6 0 I n k /T I n k -|x=Oc731S I n k /T 2 9 7 3 o 3 6 ? ~ 4 c 0 6 3 5 - 9 o ? 5 8 3 - 4 . 4 2 95 - 1 0 0 1 2 42 - 4 . 7 9 5 4 ~ ! 0 o 4 9 Q 2 302 3 o 3 1 1 - 3 c 8 7 4 - 9 o 5 8 5 5 - 4 . 2 3 9 9 - 9 o 9 5 14 - 4 o 6 0 5 9 - 1 0 . 3 1 7 4 3 0 7 3c257 - 3 . 7 0 $ - 9 . 4 3 2 9 - 4 c 0 7 1 0 - 9 o 7 9 88 = 4 . 4 3 6 9 - 1 0 c 1 6 4 8 3 1 7 3 . 1 55 - 3 . 3 6 6 - 9 < > 1 2 59 - 3 e 7 3 2 0 9 0 4 9 1 9 - 4 * 0 9 7 9 - 9 c 8 5 79 3 2 7 3 c 0 5 8 - 3 . 0 3 3 - 8 o 8 2 4 1 - 3 . 3 9 9 0 - 9 . 1 9 00 - 3 0 7 6 4 9 - 90 5 5 59 extractedo ------~--~=~~.~--------------------~~------------------------~----------~ 297 30367 :302 3.,311 307 30257 317 3e155 327 30058 ., k ...n 0 ~400635 ~·30874 =.30705 ~30366 =30033 L"l =90758,3 =;"04295 -905855 -4 .. 2399 ~9043c} -4c0710 -901259 =301'320 -808241- ~3,,3990 b ~p:=o03660 In kiT ~·lOo:!.242 - 909514 - 907988 - 904919 - 901900 Ink ~4,,7954 -406059 -404369 ~4,,0979 ~307649 b ~~o7319 L" In kiT ~lOo4902 -10,,3174 -1001648 = 90 8579 = 905559 5533 -8.8 0 For x = 0.0 -9.0 l:l For x = 0.05 0 For x = 0.1 -9.2 -9.4 ~------~-+----------~----------r----------; -9.6 -9.8 -10.0 -10.2 3.15 3.25 3035 1 Fig. 15. k T A plot of In T versus ~ for variation of activation entropies with fraction extracted. 54 Data showing the variation of entropy of activation with fraction extracted are listed in Table 6 and are plotted in Fig. 15. The solution of the differential equation for the extraction process kQe "TT (a-x) (20) integrated between the following boundary conditions; t=0 for x=0, and t=t for x=x, is kGt -e R Ma-x)-|(a-x)+^(a-x)2-Ig3(a-x)3 + . . . . J a _ . g £ + S > * | + . , W) This can be simplified to: * + ¥ + ( - 2 a x + x*) - ^ 3 + kQt = -e R 4R^ 18RJ 3 a x ^ - 3 ^ ) . . . . . . . . . . o (22) The fifth and subsequent terms can be neglected as calculations show that they are less than 1 percent of the first term. From this kinetic study on solvent extraction of coal, the following model for extraction is proposed. In most reactions, the free energy of activation (AF^) remains constant throughout the entire reaction period. However in the case of coal extraction by tetralin, an increase in reaction Accord­ing to the absolute reaction rate theory, the data show that the increase in free energy of activation corresponds to a decrease in entropy of activation as the extraction process proceeds. This result is illus­trated by Fig. 16 in which activation free energy is plotted against the reaction coordinate. In interpreting the graph, the following physical model for coal is assumed. The coal structure is composed of a central nucleus of 54 Fig .. adxt = koe - 1b[x" ( x) (20) O ~, Rab [ b b 2 kot = In(a-x) - Ii (a-x) + 4R2 (a-x) 2 -la~RJ (a-x)3 ba b 2 • 2 ~a3 J + .... -In(a) + R - W-+ l8R3 + .. , .. u........ (21) In ~ + bx + b 2 2 (-2ax + x2) - ~ (-3a"x + a R 4R l8R .... ... o ................ j ~~) free energy of activation with the time of reaotion is observed. Accord-ing illus-trated Reaction Coordinate Pig. 1 6 . A sketch of reaction coordinate versus activation free energy for extraction of coal. 1 coacervates in which the micelles form an ordered assembly and are surrounded by flocculates in a disordered mass. The micelles of the disordered mass become immobilized to different degrees. The stable ones form new aggregates which pack together uniformly. This model is basically supported by information given by Bangham et. al. (55). 1 6 Fig. 16. ale (55). With this model in mind, it can be assumed that the valley on the left hand in Fig. 16 represents various energy levels of coal in an unreacted state. Level 1 is the free energy level of coal that is 55 56 extracted initially* As extraction goes on, it is harder for the energy barrier* Level is the lowest free energy level of coal that can be extracted at a given temperature* An increase in temperature is one of the factors, which will further drop this lowest free-energy level* AF° represents the standard free energy change for extraction of coal* According to the foregoing physical model one readily sees that the first extract leaving the parent coal complex relieves the hindering van der Waal's bonds which bond the disordered flocculates* As more substances are extracted, more stably-packed coal constituents are left behind* This produces an activation entropy decrease along with the extrac­tion the compounds remaining are less inclined to leave; in other words, the in v described as follows: Co -> E-l °1 -** + E 2 c 2 k2 c 3 + E3 c 3 k3 C4 E4 •> Cn+1 + ^+1 initially. soluble material in the coal to surmount the activation-energy barrier because the lower-lying energy levels correspond to a higher energy barrier. 2 temperature. ane which will further drop this lowest free-energy level • .6Fo coal. band flocculates. packed behind. process. Obviously with the more ordered coal matrix left behind, extraction becomes more difficult. To overcome this increasing tendency for the compounds to remain the coal structure, ~ a corresponding increase in activation free energy must be overcome. In terms of a mathematical expression, the whole process can be ko) Cl + El ~) C2 + E2 k2 ) C,3 +~ k3 ) C4 + E4 ~ ) Cn+l + ~+l where C Q is the initial coal, . . . « « < > « » o C n represent the steadily deactivated residual coal, E-^ <>©©....«En represent the compounds extrac­ted by tetralin, ICQ is the initial rate constant, and k ^ • • • • • • • • k n represent the subsequent rate constants as the extraction proceeds. It is expected that k Q > k-^> K2 « > * o . o . . « > k n because of decrease in entropy resulting in an increase in the required activation free energy. Comparison of Experimental Results on the coal extraction process, a series of conventional extraction experiments were also carried out. In these experiments three tempera­tures, 34, and 54°C, and five extraction periods, 2, 10, 15, and 20 hours, were used. The experiment was conducted by simply placing the coal-tetralin mixture in a constant temperature bath for the desired time of extraction. During this period, the mixture was continuously stirred. The experimental data from these runs are in Tables 8, 9, and 10 in the Appendix and plotted in Fig. 17 together with the results for extraction of coal with ultrasonic energy. Comparison of experimen­tal results with and without an ultrasonic effect will be discussed in two parts, the first part is the comparison of rate and yield of the extracts and the other is the comparison of infrared spectra. 57 Co Cl •• oooooooCn re~resent El ooo~ •• QoEn ko kl .o •••••• ~ ko > kl > k2 0"" " ... Q" > ~ With and Without an Ultrasonic Irradiation In order to understand the absolute effect of ultrasonic irradiation · 24, 5, tetralin ~ o ori +o' 0.12~--------~------~--~--------~----------~----------~--------~ 0.09 Figo 17. Time-yield curves for ext~action of coal by tetralin with and without ultrasonic irradiation. ~.. 0805 ~k+--------4------------'-----------.----------~r-----------~--------~ <~I]; 3:0 II >< 0 .. 02 fHI-1f.1-----------l------ 0.00 L-________ ~------__ ~L---------~--------~----------~--------~ o 200 400 600 800 1000 1200 t (minutes) 5 9 Rate and yield Table 7 shows a comparison of yields after 2 0 hours of extraction with and without ultrasonic irradiation* Table 7 . Tields of extract after 2 0 hours in the presence and absence of ultrasonic energy. Extraction Temp. (°C) Yield (wt.#) Without ultra- With sonic effect sonic ultra-effect 2 4 3o70 10.21 3 4 3.97 10.61 5 4 4.10 lloAl The following observations can be made from an examination of the results of coal extraction in the' presence and absence of ultrasonic field: ( 1 ) A transient region was found to exist in both processes. The rate of extraction within this region, however, was found to be widely different. The difference can be seen from the (see Pig. 1 7 ) o On the average the rate of yield under ultra­sonic irradiation is 0.06#/min. as compared to 0o03#/min. without ultrasonic energy, a factor of two. ( 2 ) A significant difference in the maximum Jield of extract was also observed. On the average, the maximum yield of extract with the aid of ultrasonic irradiation is 10o7% as compared to 59 ~ 20 irradiations 7. Yields 20 TEexmtrpa. cCtioocn) Cwt .. %) ultra-sonic effect 24 3,,70 10.21 34 3 .. 97 10061 54 4 .. 10 lloU the/presence and absence of ultrasonic 1) , ." different slopes during the first two hours of extraction Fig. 17)0 0 .. 06%/min .. Oo03%/two .. 2) held observed.. 10 0 7% 3»92# of the original coal without ultrasonic effect, a factor of 2.7» The increased amount of extract obtained with ultra­sonic irradiation is presumably the result of the breaking of more bonds in the coal matrix. It appears that affects of ultrasonic vibration on the coal extrac­tion process are: (a) to increase the collision frequencies between the solvent and coal particles, resulting in an increase in the rate of extraction. In a sense this is equivalent to an increase of temperature of the extraction which raises the kinetic energy of both solvent and extractable molecules in the coal particle, and (b) to break bonds which, otherwise, stay intact in the coal structure. It is unlikely that the intensity of ultrasonic field used in this work (0.59 watt/cm^) will break strong chemical bonds. However, the moderately bonded com-pounds (held with van der Waal bonds) are strong enough to resist dissolution by the conventional extraction process but seem to be affected by the ultrasonic energy. It is this action of the ultrasonic irradiation that increases the total yield of extract« The extraction experiments on coal by tetralin without the aid of ultrasonic field were only carried out at three temperatures, i,e., 24°G, 34°C and 54°C The initial enthalpy of activation, AHj~, for this process was evaluated to be about I 0 6 5 kcal/mole from an Eyring's plot of ln(ko/T) versus l/T (see Fig, o The initial rate constant, kQ, was evaluated from the average rate of extraction over the period of zero to fifteen minutes. The reason for choosing the zero to fifteen minutes extraction period was that in the case of extraction with the aid of ultrasonic field, the average kQ calculated over the first 60 3.92% 207~ ultra-sonic matrix" extrac-tion solvent and coal particles, resulting in an increase in the rate of extraction. In a sense this is equivalent to an increase of temperature of the extraction which raises the kinetic energy of both solvent and extractable molecules in the coal particle, and (b) to break bonds which, otherwise, stay intact in the coal strncturec It is unlikely cm2) will break strong chemical bonds. However, the moderately bonded com-pounds (held with van der Waal bonds) are strong enough to resist dissolution by the conventional extraction process but seem to be affected by the ultrasonic energyo It is this action of the ultrasonic irradiation that increases the total yield of extract" i~e., C, Co 6Hf, 1065 mole In(T) liT Figo 14)0 ko' ko 6 1 15-minute period was found to be very close to the value obtained by Pig. 1 2 ) 0 The lo65^keal/mole field. Apparently, without an ultrasonic effect the material available for extraction by tetralin is limited to those very weakly bonded substances. Since the bonding energy for the materials extracted is small, the temperature has little effect on the rate of extraction0 Therefore, one obtains a low activation enthalpy. These weakly bonded substances are not abundant in the coal, consequently the maximum amount of extrac­tion is only a few percent« charac­terize differences• 7$ also the benzene and trichloroethylene used are not pure reagents, how­ever, the maximum concentration of extracted materials in the solvent mixture is only about 0o01#o As a result, no new peaks corresponding to the extracted substances could be foundo There is, of course, one alternative; that is, to concentrate the extracts before they are ana­lyzed by a gas chromatography However by doing so, the concentration of impurities are also relatively increased and little significant gain can be obtained by this procedure0 materials» l5-extrapolating the data to zero extraction time (see Fig. 12)0 The activation enthalpy of lo65~kcal/in this case is much lower than the value obtained for coal extraction with the ultrasonic fieldo 61 extractiono enthalpya co819 percent0 Infrared spectra Some effort has been spent trying to charac-terize the extraction products by use of gas chromatography. The analysis showed little significant differences& A reason for these results setback is because the tetralin used contains about 2% impurity, 0001%0 resultg foundo iSa chromatograph~ procedureo In this case, there is, however, a sensitive method which can be employed to help understand at least qualitatively the characteristic of extracted materials~ The employed method is infrared spectroscopy. 62 method0 (a) the mixture of tetralin, benzene and trichloroethylene in a ratio extracts; the ratio is 1 s 10 : 10 by volume; (b) the extracts from the extraction without the aid of ultrasonic field at 54°C for 10 hours; (c) the extracts from the extraction with the aid of ultrasonic field at 54*C for 10 hours; (d) the concentrated extracts from samples in (b); and (e) the concentrated extracts from samples in (c)o The further concentration of extracts was done by use of a micro-distillation unite This unit is operating in vacuum© The distillation temperature was 60°Co The concentrated samples were collected when three quarters of solution had evaporatedo The spectra of these five materials are shown in Figso 18, 19, and 200 Comparing Fig0 19(a) and FigG 19(b), we find that the spectra of with simLlarity0 is,v cnT^- cmT^ 2851 cnf"^- csT^-o effect« extracts, Comparing the spectra of concentrated and original extracts, we see that only the two absorption regions already mentioned above change 62 Five types of materials have been analyzed by this methodQ They are tetralins corresponding to the actual content of these three solvents in the ~ 0 54·C distillation unit. This unit is operating in vacuumo The distillation temperature was 60°Co The concentrated samples were collected when three quarters of Figso 200 Figo Figo b)9 extracts without and wi th ultrasonic effect show a striking similar! ty" There is,' however, a slight difference in absorption intensity which occurs in two absorption regions, wave numbers from 1435 cm~l to 1450 cm-l and wave numbers from .2851 cm~l to 2890 cm-lo For these two absorption regions the extracts with the aid of ultrasonic field exhibit a slightly higher absorption intensity than those without the aid of ultrasonic effecto Since there is no difference in the position of peaks between the spectra of these two extracts~ the extracts from both extraction processes presumably contain the same materials but in dif­ferent quantitieso Fig c 18 o Infrared spectrum of tetralin, benzene, and trichloroethylene solvent "mixture© (MICRONS) 2.5 4 5 6 7 8 9 10 12 15 20 3040 3500 3000 2500 2000 1500 1000 500 250 (CM"1) W '-. 2.!5 100 .... ~ z 1&,1 80 ~. -If 1&,160 ~ !C ~40 j I ~20 i 3 c 180 Infrared' 'spectrwn of tetralin$ benzene$ Ird.xtur.e~ ./ WAVELENGTH (MICRONS) 4 !5 .. 0 4000 !SOO o ~--------~~---------3~OO~0---------2-!5~OO----------2-0~OO-----------~~0----------~~O-O---------~!5~0-0--~250 FREQUENCY C~I) . , .~ . . , - .. , ~. ~. ~ ~ ,~ , .... 4000 3500 3000 4 5 T 20 3040 2500 2000 FREQUENCY (CM"') 1500 1000 500 250 2.3 100 4000 Figo.19. 3500 3000 - 5 T 8 9 10 12 15 20 3040 2500 2000 BOO 1000 500 FREQUENCY (CM"') extracts coal, extraction by (a)^fithout the aid of ultrasonic irradiation, (b) with the aid of ultrasonic irra&iationd f 250 2.5 100 -i lj80 It: -I! ... 60 uz !Ie ~40 2 , CI) ... 120 t- O 4000 • 3' 3500 3000 '.': . .,.-",- 3500 3000 WAVELENGTH (MICRONS) '4 5 2500 2000 FREQUENCY (C~') ,,-. WAVELENGTH (MICRONS) , '4 5' . ...:.. ."Ii. .• 1!500 ', .... '..,; ~ .... ' 1000 -, : ... 2500 2000 ~ 1000 . FREQUENCY (CM-') , . \ .. ~" 80 60 40 80 60 (b) of ultrasonic irradiationg (b) Wl.th the &:id of"ultrUQnic. irra&iatlon,,' ' t, " , ,'. , ' Infrared spectrum of the extract~ from. coal, extrac,t i" on bY,'tetralin ,(a>r""'- t"houtthe aid . .~. : ',' ~ .. .,,: . <. '-' .. ", . ~" , '. . ':'~~!:- ~~~", -'. --,,- ~ .. ~,~~~:~.~~.'~.~.,~<> ~".~.J;,~,>_~~~~, .. ·.-<.f,,~<~~· ~ WAVELENGTH (MICRONS) 4 .5 T 2500 2000 FREQUENCY (CM"») 1500 1000 500 250 4 T 4000 Fig. 20 20 30 40 100 2500 2000 CM"1) by ( a) without the aid of ultrasonic irradiation, (b) with the- aid of ultrasonic 3 5 ~ ~~ ·~------------~--------------~r-~--~--T------T~--T-~r-~-T--4r~r--'---r~IOO -!z 1&1 80 ~ .... 80 i t: 40 i en .i.. ~ I ,./ ( &) 4~~OO~-------3~5~0~0~------~3000~~------~2~560~0------~2;0~OO~--~---'moo~'-----~~~~O'-------~X>--~ FREQUENCY (CM-I) WAVELENGTH (MICRONS) 80 60 40 20, 1020 .·5l "- --------------3- -----~-------------4- ------------5 ~r-------_;~----~----~--i__T_T----~~r_~-!O-~ 4I0O O ( . \ .. " ........ ' " ',' ' ..... ( b) 4O0C00- ------3-5-00- '~ ~----3-0-00~ ~----'- 2-eQ-O- -~~---2~00~0~ ~-----1-5~00~ ------1_00.0 ~~------~o_~ 20 .. FREQUENCY (CM-I) Infrared spectrum of the concentrated extracts 'from coal extraction tetralin Without irradiation" ultf~,sonic ~_~_..l..!_..Lo' 60 same© *hieh is obviously due to the effect of being concentratedo Since no significant new peaks are produced because of the change of concentra­tion, the concentrated and original extracts are considered to be essentially the same© There is, however, one rather weak new peak, at 3510 cnf1 appeared in the spectrum of concentrated extracts without the aid of ultrasonic wave, (Fig© 20 a ), but not in the spectrum of the Fig© a ) 3 tan process0 insignificant0 places0 mixture cm"1, cm"1, cnT1, cm"1, cm"12890 cm"1© extracts© © -CH2-0 C--CH^, G-CH3 H© frequency correlation, functional Ch*2, CE3 compounds© matrix, this result suggests that in the solvent extraction of coal at moderate temperatures only the side chains of coal matrix are affected© 66 their absorption intensitieso Other peaks remain nearly the same~ Of course, there are some relative change of intensity for some peaks, _hl9h is obviously due to the effect of being concentratedo Since no significant new peaks are produced because of the change of concentra­tion, the concentrated and original extracts are considered to be essentially the same o There is, howeverp one rather weak new peak, at 3510 cm-l appeared in the spectrum of concentrated extracts without the aid of ultrasonic wavejl (Figo 20 a LJ but not in the spectrum of the original extracts, (Figo 19 a):, There is no way to explain whether this is due to .an increase in concentration or due to the contamination during the distillation processo Since the peak is rather weak it is considered insignificanto A comparison of the spectra of solvent mixture and the spectra of extracts show changes at a number of placeso Stronger absorption inten­sity is recorded for the extracts than the solvent mixt,ure at wave numbers, 1352 em-I, 1435 cm=\ 1450 cm=l, 2851 em-I, 2874 cm-l , and cm-lo There is no new peak found in the extractso Apparently the extracted compounds have at least the same chemical groups as the sol­vents 0 The first three frequencies are the bending and scissoring vibrations of C-H and =CH~o The other three frequencies are stretching vibrations of C=H in chemical groups like =CH~9 C=CH) and tertiary C-Ho According to the structure-frequency correlationp the fUnctional groups CH, CH2, and CH) in these absorption bands are from aliphatic compoundse Since aliphatic compounds are mostly found as side chains in the coal affectedo i For extraction process with ultrasonic irradiation more side chains are extracted as compared with the process without ultrasonic irradiation0 irradiationo 67 An experimental method has been developed for the solvent extrac­tion of coal under the influence of ultrasonic irradiation. The rate of extraction of bituminous coals with tetralin is accelerated because the ultrasonic field hastens the dispersal of the coal micelles without inducing decomposition of the large extractable molecules. This investigation shows that the extraction process is essentially-complete after 10 hours of extraction, although the largest portion of the possible extract yield for a given test condition is obtained in two and a half hours. For coal extraction at or near room temperature, a modified first-order series reaction was found to represent the experimental data. The data show that the coal structure is held together by bonds of 24*5 mole 25*1 mole. all extracted. proc­ess 54<>5 e.u. tetralin tetralin 112.8 u.) e.u.), a total of -116.2 e0u. The method used for the calculation of entropy is that described by Glasstone, et. al., (56). Although CONCLUSIONS extrac-tion bit~nous ooals , essentially complete ooal various strengths. The dissolution of the weakly-bonded compounds in the coal requires an activation free energy of about 240' kcal/mole to 25.1 kcal/mole. The extraction process ends when the weakly bonded materials have been extractedo The activation entropy for the initial phase of the extraction proc-ess was calculated to be -5405 eou.. This value is considerably lower than the value calculated by assuming tetrali.n as a gas molecule absorbed on a solid site of coal to form an activated complex. In the formation of the activated complex the tetrali.n molecule loses three translational degree of freedom (-112.8 e.ue) and one rotational degree of freedom (-3.4 11602 eouo etc alo, (56). tetralin is a liquid and the value of each translational and rotational calculated for this process is still of the right order of magnitude and The rate of extraction is very fast initially and then decreases C were found to min""** min""1 C, were found to min"1 min""1 irradiation. G ultrasonic effect are 0.025^/min. and 3«71# as compared with 0.06/$/min. 10.2$ 0.029#/4.1# 0.091^/11.4#* ... 69 tetral1n degree of freedom is less than that for a gas, the activation entropy calculated for this process is still of the right order of magnitude and is quite reasonable. The rate of extraction is very fast initially and then decreases with time. The rate constants for extraction at 24° C were found to be 0.0172 min-l in the initial phase of the extraction process and 0.0082 min-l near the end of extraction, and at 54° C, were found to be 0.0482 min-l for the former and 0.0211 min-l for the latter. Extraction experiments were also performed without the aid of ultrasonic irradiation. The rate and yield of extracts were both found to be much smaller compared with those under the aid of ultrasonic irradiationo At 24°C the average rate and the maximum yield without 0.025%/3.71% 0.064$/and 1002% with the aid of ultrasonic effect. At 54° for the former are O.029%/min. and 4.1% and for the latter are O.09l%/min. and 11.4%. BIBLIOGRAPHY 1. Littlewood, K., ,!The Application of Ultrasonic Irradiation to Solid-liquid Systems with Particular Reference to the Extraction of Coals with Pyridine," Fuel Soc. J. Univ. Sheffield 27-39, (i960). 2. Berkowitz, N., "Dispersibility of Coal in Supersonic Field," Nature, 163. ( 1 9 4 9 ). 3 . Kirkby, W. A. and Sarjant, R. J., "Constitution of coal and the Formation of Coke," Nature, Lond. 170. 5 9 7 , (1952). 4 . Hariri, H., "Kinetic Studies of Thermal Dissolution of High Volatile Bituminous Coal," Unpublished Ph.D. Thesis, Dept. of Fuels Engineer­ing, Univ. of Utah, ( 1 9 6 4 ) . 5 . De Marsilly, C , "Solvent Extraction of Coal," Ann. Chem© et Phys., 66, (1862). From Kreulen, D « J. Wo, "Elements of Coal Chemistry," Rotterdam, (1948). 6. Dryden, I. G. C , "Action of Solvent on Coal at Lower Tempo," Nature, 1 6 6 , 606, (1950). 7 . Dryden, I. G. 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NOMENCLATURE Definition a The maximum change in weight of original coal (ash free). •i gocc*"-'-. b Constante b' Constant equivalent to b or bT. brp Initial concentration of tetralin, g cc-L. co Initial coal. h The steadily deactivated residual coals. d ( x ^ ^ ) "^ mole"*"^ E^ ...... Compounds extracted by tetralin. Initial free energy of activation, Kcal mole*"1. AF Free energy of activation, Kcal mole"1. AF° Standard activation free energy. GQ •«• • .^jj-l Cases, g. h AH A ^ A H 0 . 6 2 x l 0 ~ 2 7 e r g sec. Enthalpy of activation, Kcal mole"1. coal. Kcal mole- 1. k 1.3803xl0~1^erg deg^^molecule-1. k' First order reaction rate constant. * 2 Second order reaction rate constant. *a Phase boundary extraction rate constant. *b The rate constant for the backward reaction. Symbols C1·······Cn E1••••• .. ·En :j: .6.Fo -.6.l free) 0 Initial concentration of the coal, gocc-1• Constant. bT. CC-1e Ini tial coal .. Constant equivalent to (xmax)-i .. Activation energy, Kcal mo1e-1 o tetralino mo1e-1& mo1e-1• energy .. Gases, go Planck's constant, 6 .. 62x10-27erg sec .. activationi mo1e-1• Initial enthalpy of activation of the conventional extrac­tion of coal., Initial enthalpy of activation, Kca1 mo1e-1• Boltzmann constant, le3803x10-16erg deg-~01ecu1e-1o constant .. constante kd Diffusion extraction rate constant. The rate constant for the forward reaction. Initial rate constant. Initial rate constant of second order reaction. ICQ • • • e •kn-l Rate constants. V - liquid, g. pi Internal pressure of solvent. R Gas constant, 1,987 cal mole~ldeg~-'-» Rc.... Solid coal, g. AS* mole^^deg""^". A S ; mole^deg" . s (^max^"^"0 t Time, minutes. T °K, W Initial weight of coal on ash free basis, g. Pinal weight of coal, g. «L Initial weight of coal, g. AW Weight of coal extracted, g. *c extracted. xeq Fraction of coal extracted at equilibrium. xm The maximum fraction of coal extracted. Temperature dependent constant. e Temperature dependent constant e Dielectric constant. u Dipole moment, esu cm. H Transmission coefficient, assumed to be approximately 1. 75 kd kf ko constanto kb ko.e ••• kn_l Pi solvento 10987 mole-~eg-l~ Ro ••••• Rn-l ~Sf Entropy of activation, cal mole-ldeg-l • ~st Initial entropy of activation, cal mole-ldeg-l • Constant equivalent to (xmax)-l., minutesQ Absolute temperature, oK. Wc Wf Final go Wi go ~W c,oal g .. X= ~W Fraction of coal extracted., We Xeq xm extracted& a constanto B £ constant e ~ cm~ }j 10 RESEARCH PROPOSAL 1. Experiments could be performed with variation of input power disce power. simple0 understood. instead of increasing, because of the adverse effect of the enormously intense ultrasonic wave, such as destruction of the solvent structure, separation of the extracted materials from the solvent, etc© This ceiling input power corresponding to each operating temperature is a very important information. Different compounds may also be expected at different rates. Gas chromatography and infrared spectroscopy can be employed to identify the different extracted compounds«, From a study of different compounds extracted at different input power, a better under­standing of the structure of coal and how the structure is attacked by ultrasonic energy may be possible. 2. Pretreatments of coal before it is subjected to extraction by solvent often prove very helpful. The most common method of pretreat­ment is to heat the coal to certain temperature in the absence of air* In the conventional extraction process, it has been found that for a fixed rank of coal there exists an optimum heating temperature at which the extraction yield exhibits a maximum, for example 300°C for Durham coal and 310°C for South Wales coking coal (l)o le to the quartz disco Extraction rate and yield are expected to vary with input power~ The rate probably increases linearly with input power, but the maximum yield may not be so simpleo It is suggested that a study of the rate and yield of extraction of coal can be made by using different input power for several temperatures so that the effect of input power on extraction can be better understoodo For each temperature there may be a corresponding ceiling input power beyond which the yield decreases structureg solventg etcG informationo ratese compoundso under~ standing possibleo helpful~ cammon pretreat= ment airo maximums 1) ~ 77 The main purpose of heat treatment is to disturb slightly the structure of coal so that the treated solids will be more vulnerable to the attack of solvent. Since the ultrasonic wave has been found to have greatly assisted the extraction yield as well as rate, it is recommended that a study be made in which the efficiency of extraction with the aid of ultrasonic field will be compared with the efficiency of extraction where pretreatment by heat alone is done. Also in this program one treatment. 3<> may and yield of coal extraction is size of coal particles© In the presence of ultrasonic wave, there is one more complication of energy interfer­ence at the coal particle-solvent interface* When the energy carried by the ultrasonic wave is transferred to the interfaces between the coal and solvent, part of the energy will be reflected and scattered by the interface. If considerable amount of energy is concentrated at specific bonds, subsequent bond breaking is expected© Since scattering and reflection are a function of geometry, an optimum size of coal particles may exist which will provide the maximum rate and yield of extraction by the more bonds being concentrated with the ultrasonic energy. A study of coal extraction with coal particle size as a varying parameter will reveal more information about choosing a set of appropriate operating parameters. 4« From the study of solvent extraction of low-rank coals, it has been recognized that the polar characteristic of solvent plays a should include the study of in what mode the presence of ultrasonic wave will further affect the extraction process of coal preceded by a heat treatment .. :3.. One of the mo