Flash heating of coal

The results of exposing 10 to kO u diameter particles of a high volatile bituminous coal from Spring Canyon Mine, Utah, to a light pulse from a high energy capacitor discharge lamp are described in this work. It has been found that this energy input has in all cases caused the coal to be broken into two physically and chemically distinct substances. One is a black-colored material, termed "B", which is highly aromatic, very stable thermally, difficult to oxidize, and composed o of small colloidal-sized spheres probably polymeric and 350 A in diameter. B makes up approximately 6l$ of the weight of the coal. The other distinct material appears yellow when in dilute solution or in thin films on glass. It has been termed "Y". Y is highly saturated, unstable thermally, easily oxidized, of average molecular weight 750, of the consistency of thick tar, similar chemically in many ways to B, 85$ soluble in benzene, essentially 100$ soluble in acetone, by weight about 75$ of the ASTM volatile matter in the coal, composed of a mixture of related compounds and making up about 39$ of the weight of the coal. At higher intensity flashes (3000-volt capacitor charge) considerable amounts of Y are gasified (26$). These gases are mostly hydrogen, carbon monoxide, and acetylene.

Michael Joseph Mcintosh A thesis submitted to the facility of the University of Utah in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Fuels Engineering University of Utah June FLASH HEATING OF COAL by McIntosh A. faculty 1965 . :~,,~ :' ~:r t;"~ T ~\" ··.' ·1 J" .. ... . , , .' :... ~ ., i' This Thesis for the Doctor of Philosophy Degree Michael Joseph Mcintosh has been approved April Chairman;, Supervisory Committee ReaderJ7#upervisory- Committee •2 Reader, Supervisory Committee Head, Maj^r Department Dean, Graduate School 574848 by McIntosh 1965 Reader, Supervisory Committee 574R48 ACKNOWLEDGMENT The author gratefully acknowledges the assistance received from Dr. George Richard Hill, Head of the Fuels Engineering Department, University of Utah. Appreciation is also expressed to Dr. Norman W. Ryan of the Department and Dr., A„ Metallurgical Engineering Department, University of Utah, for much valuable advice. Particular appreciation is expressed to Mr. L. Dougan whose fellowship has enabled the author to undertake this research. The advice of Earl Pound in electrical circuit design has been invaluable; likewise Mr. John Keller and Mr, Jih-Tien Cheng of the Chemical Engineering Department, University of Utah, have given much advice concerning heat flux gage measurements. Thanks are expressed to Miss Diana Marlowe and Mrs. Ann Underwood for typing of the manuscript. iii Chemical Engineering Departm.ent an.d Dr. Ferron A. Olson of the Metallurgica.l .Utah} fOr J. Mr. invaluable,; Mr. Mrs ~ pf TABLE OF CONTENTS Page ACKNOWLEDGMENT iii LIST OF TABLES v LIST OF FIGURES vi ABSTRACT., vii INTRODUCTION. . 1 LITERATURE SURVEY . 3 Flash Photolysis and Flash Heating . . . . 3 The Physical Nature of Coal 8 The Chemical Nature of Coal. 12 MATERIALS AND EXPERIMENTAL METHODS. 19 RESULTS AND DISCUSSION 33 Appearance of Product - Qualitative Results 33 Volatile Matter and Coking Test 35 Infrared Spectra . . . . . . . 37 Formation of B $6 Formation of Y 60 Material Balances. 65 Ultimate and Structural Analysis . . . . . j6 Irradiation of Coal in the Presence of Various Gases . . . . 78 Heat Flux and Temperature Measurements . , 8l Thermodynamics of the Flash Heating of Coal 10^ SUMMARY 110 Chemical Model of Coal 110 Physical Model of Coal Ill LIST OF REFERENCES. 115 iv • TABLES. . . . . ABSTRACT ••. • aod • The Physical Nature of Coal •••. The Cherriical Nature of Coal. . • • MATERIALS AND EXPERIMENTAL METHODS. • RESULTS AND DISCUSSION ••••••• Appearance of Product - Qualitative Results. Volatile Matter and Coking Test. • • ..• • Infrared Spectra • • • • • Formation of B • • Formation of Y . 9 • 0 •• • • • • • • • • • • • Material Balances. •• •••• •• • • Ul timate and Structural Analysis • • • • . . • • • Irradiation of Coal in the Presence of Various Gases • Heat Flux and Temperature Measurements • , . Thermodynamics of the Flash Heating of Coal. SUMMARY • • • • • • • • • , . . . . ~ -- . . . 1 8 12 19 33 33 35 37 56 60 65 76 78 81 104 110 110 111 115 LIST OF TABLES Table Page 1 Band Positions in the Infrared Spectra of Coals and Their Assignments. . . . . . . . . . 17 2 ASTM Volatile Matter Test Data on B and Coal 36 3 Material Balances . . . . . . . . 69 k Material Balance Including Gases. « 7^- 5 Mass Spectrometer Analysis of Product Gases from 3000-Volt Flash. . . . . . . . . . . . . . . . 76 6 Elemental Composition of Coal and Reaction Products . . . 77 7 Structural Parameters of Coal and Y . 77 8 Data Obtained from Mass Spectrometer Analysis of Gaseous Products Formed from Flash Heating of Coal in Various Atmospheres. 79 9 Relative Infrared Spectrometer Absorption in One Meter Cell of Gaseous Products Formed from Flash Heating of Coal in Various Atmospheres 1 Their Assignments. . .•.• 2 ASTM Volatile Matter Test Data on B and Coal. . 3 Material Balances • . • • 4 Material Balance Including Gases •• 5 Mass Spectrometer AnalYHis of Product Gases from 3000-Volt 17 36 69 74 Fl.ash j) 0 • " ,. 0 • • 0 ~ Q • • • • • 76 6 Elemental Composition of Coal and Reaction Products • 77 7 Structural Parameters Y . • . . • 8 Dat,a Obtained from Mass Spectrometer Analysis of Gaseous Prod.ucts Formed frum Flash Heating of Coal in Various 9 Atmospheres. . .. . . . . . . . . . • In:frared Product.s Goa::L. • . . • . • . • . . . • v 77 79 80 Figure Page 1 Sink and float scheme for fractionating coal 21 2 Circuit diagram for photoflash unit. . . 2k 3 Flash heating apparatus k Sink and float scheme for fractionating reaction product. 30 5 Infrared spectra of coals kS 6 Infrared, spectra of B flashed at high and low voltages ^9 7 Comparison of B and the product from flashing B (Bf) . 50 8 Infrared spectra of coke 51 9 Comparison of Y spectra from Spring Canyon coal. . . . 52 10 Infrared spectra of Y obtained from BCR No. 1031 and No* 1007 coals . 53 1 1 Infrared spectra of Y obtained by flashing coal, B, and the reaction product from B (B') 5^ 12 Infrared comparison of benzene 1st Y, coal extract using cold benzene, benzene-soluble low temperature tar, and clear oil 55 13 Electron microscope pictures of B 58 Ik Blowup of a small area from Fig. 13c 59 Gasification of coal as a function of flashtube input voltage and energy 66 16 Density distribution of B 68 17 Diagram showing how pressure increments due to coal gasification vary along reaction tube length . . . . 75 18 Heat flux gage circuit 83 19 Cutaway view of flashtube showing position of heat flux gage. . 85 vi LIST OF FIGURES 1 • . 2 unit .. 3 •....... 4 5 6 7 8 9 10 11 ., (' J..C 14 product ... lnl"rared spectra of coals. Infy-s,r8d speC'.tra of B flashed at high and low voltages C01!'iJf1r:l3,Jr of B and the product from flashing B (B t) • :rrre-Y'sr'sd spectra of coke . • . . . . . . . C\:;wpA.:d son of Y spectra from Spring Canyon coal. . In:frs.red spectra of Y obtained from BCR No. 1031 ana. N,:, 0 1007 coals . . . . . . . . . . . Im:ca.red spectra of Y obtained by flashing coal, B, aGd, the reaction product from B (B') • • • • . • :rn~'rared c:omparison uS~',ng benzenep and, . . . . B. . 15 fUnction 16 17 18 19 voltage and energy Densi ty' dtstribution of B. Diagram shOWing how pressure increments due to coal gasifi.cation vary along reaction tube length • • Heat flux gage circuit ••.•.. Cutaway view of flashtube shOWing position of heat fl.m~ gage. .. .. to • • • • • • • • • • • • • • • • 24 26 30 48 49 50 51 52 53 66 68 75 83 Figure Page 20 Bare gage flashed at 3000 volts 21 Spectral range of FT 52*4- flashtube . 22 Effect of coal on temperature rise . , 93 23 Coal-covered gage flashed at 25OO volts. . . . . . . . 2k Coal-covered gage flashed at 3000 volts 25 Assumed packing geometry of coal particles in gage layer. 102 -tH ^ 24 •. 524 • Qn . . fl~shed 2500 volts. partic~es layer. , . . . . . . . . . . . 89 91 96 99 102 ABSTRACT The results of exposing 10 to kO u diameter particles of a high volatile bituminous coal from Spring Canyon Mine, Utah, to a light pulse from a high energy capacitor discharge lamp are described in this work. It has been found that this energy input has in all cases caused the coal to be broken into two physically and chemically distinct substances. One is a black-colored material, termed "B", which is highly aromatic, very stable thermally, difficult to oxidize, and composed o of small colloidal-sized spheres probably polymeric and 350 A in diameter. B makes up approximately 6l$ of the weight of the coal. The other distinct material appears yellow when in dilute solution or in thin films on glass. It has been termed "Y". Y is highly saturated, unstable thermally, easily oxidized, of average molecular weight 750, of the consistency of thick tar, similar chemically in many ways to B, 85$ soluble in benzene, essentially 100$ soluble in acetone, by weight about 75$ of the ASTM volatile matter in the coal, composed of a mix­ture of related compounds and making up about 39$ of the weight of the coal. At higher intensity flashes (3000-volt capacitor charge) con­siderable amounts of Y are gasified (26$). These gases are mostly hydrogen, carbon monoxide, and acetylene. viii 40 !-l uB", of small colloid&l-sized spheres probably polymeric and 350 A in diameter. B makes up approximately 61% of the weight of the coal. The other distinct material appears yellow when in dilute solution or in thin f:tlms on glass. It has been termed "y". Y is highly saturated, unstable ttermally, easi.ly OXidized, of average molecular weight 750, of the consistency of thick tar, similar chemically in many ways to B, 85% soluble in benzene, essentially 100% soluble in acetone, by weight about 75% of the ASTM volatile matter in the coal, composed of a mix-ture of relatea. compounds and making up about 39% of the weight of the coal. At higher intensi.ty flashes (3000-volt capacitor charge) con­siderable amounts of Yare gasified (26%). These gases are mostly hydrogen, carbon monoxide, and acetylene. Infrared spectra were obtained for B, Y, and coal. The coal and B spectra are very similar but differing considerably in relative aromatic to aliphatic hydrogen contents. Oxygen-containing functional groups are present in both B and Y apparently in a similar manner, hydroxy1 and carbonyl oxygen being prevalent in both B and Y. Two bituminous coals from West Virginia of lower volatile con­tent were also subjected to flash heating and the infrared spectra of their B and Y obtained along with the coal spectrum. The coal and B spectra were identical with the Utah coal. The Y spectra were similar in most ways but somewhat different especially in having a higher aromatic hydrogen content. The temperature rise and thermodynamics of flash heated coal were studied using thin film resistance thermometry. The resistance-time function of a platinum film covered with a coal layer and subjected to flash heating gave the temperature rise of the coal layer. This was obtained photographically from an. oscilloscope trace. The heat flux through the coal could also be obtained by con­sidering the resistance thermometer as a semi.-infinite body and using unsteady state heat transfer theory. Flashing an exposed platinum film also gave output data for the flashtube. The temperature rise of the coal is no more than 300°C compared with a theoretical rise of about 7000°C calculated from the heat capa­city of coal. The coal thus acts as an energy sink dissipating large quantities of energy. An attempt to account for these energy quantities has been made. It is assumed from the above-mentioned facts that B and Y form from physical breakup with a minimum of chemical rearrangement. ix containing B Y hydroxyl Band "lvi th speci;;rum. most: aromat.ic of' obtaineo. an con­sid. ering semi-unstead.y flashtlibe. 70000mad.e. assumed. INTRODUCTION The work reported herein is based upon the rapid heating of small coal particles due to light absorption from a flash discharge lamp. During the past twenty years photographers have used these lamps for illumination. In the last ten years chemists have used them to pro­duce large quantities of free radicals via photochemical reactions. 1 2 This has been termed "Flash Photolysis." 9 In 195^> L. S. Nelson and J. L. Lundberg discovered that these same flash lamps could produce extremely rapid heating of small, dark 3 particles, apparently in the absence of any known photochemical effect. The heating effect is due to the relatively large radiant absorptivity of the dark colored sample plus the large surface area-to-mass ratio of very finely divided material. Much energy absorbed, with little mass in which it may be dispersed, thus produces high temperatures. This method has been termed "Flash Heating." Coal, being black, easily pulverized and the subject of much com­mercial and theoretical interest is thus a natural subject for this type of pyrolysis. In this paper the results of an investigation of the flash heating-induced reactions of a high volatile bituminous coal from Spring Canyon Mine, Utah, is reported. A mechanism of reaction is proposed along with a new model for the physical and chemical structure of coal. Several other coals were given a cursory examination. This has been termed "Flash PhotolYSis.,,1,2 In 1956, L. S. Nelson and J. L. Lundberg discovered that these same flash lamps could produce extremely rapid heating of small, dark particles, apparently in the absence of any known photochemical effect. 3 The heating effect is due to the relatively large radiant absorp~ivity of the dark colored sample plus the large surface area-to-mass ratio of very finely divided material. Much energy absorbed, with little mass in which it may be dispersed, thus produces high temperatures. Th:l.s method has been termed "Flash Heating." Coal, being black, easily pulverized and the subject of much com­mercial and theoretical interest is thus a natural subject for this type of pyrolysis. In this paper the results of an investigation of the flash heating­induced reactions of a high volatile bituminous coal from Spring Canyon Mine, Utah, is reported. A mechanism of reaction is proposed along with a new model for the physioal and chemical structure of coal. Several other coals were given a cursory examination. - 2 - It is believed that this method will provide a new approach to coal, research and some speculations are advanced with the hope that they will stimulate an interest in other investigators to exploit the possibilities of this method. coal LITERATURE SURVEY Flash Photolysis and Flash Heating The development of the high intensity flash discharge lamp was pioneered "by Harold E. Edgerton of the Massachusetts Institute of Technology. Edgerton and co-workers developed lamps of input energies up to hOO joules per flash.^ The technology of the flash lamp was now established and it remained for G. Porter and R. G. W. Norrish working at the University of Cambridge to apply this to the production of photochemical reaction intermediates.^ These intermediates were studied by absorption spectroscopy. Photochemical systems required much higher energies than the lamps of Edgerton; therefore, Norrish and Porter developed lamps capable of dissipating 10,000 joules per flash, corresponding to about x 10 ^ einsteins of ultraviolet light. This method received much attention and now is a classical method in photochemistry. A complete review was published in 1 9 5 7 - 6 In 1956, L. S. Nelson of the Bell Telephone Laboratories was working in the field of flash photolysis using a spiral flash lamp similar to the General Electric FT524. (Porter used a straight flash lamp initially.) At the same laboratories J. L, Lundberg was studying the effects of sunlight aging on polyethylene. The techniques were com­bined to see what results could be gained with very short exposure times. A single discharge produced a drastic change in the polymer. Apparently by 400 flB.$h. 4 intermediates.5 3 10-3 1957. 6 FT524.7 L. com-bined - 3 - h specks of dust trapped in the polyethylene absorbed a large amount of polymer. Scrupulous exclusion of impurities from the polymers will prevent this 9 effect.^ The lamps used were activated with 5>l8^ joules and yielded 9.6 x 10 1y 9 2 ° Q quanta/cm in the 2000-^900 A region. The polymer degradation products observed were mainly hydrogen and small fragments of the hydrocarbon skeletons of the polymers. Methane was most prevalent. That a finely divided solid is heated to very high temperatures in a very short time is indicated by the fact that Ag, C, Cr, Ni, Zn, Mo, and W can be evaporated in glass tubes. They condense in smooth 11 mirrors on the tube walls. Just how hot the materials become is still a problem. Nelson and Lundberg present an equation, based on a heat balance, 1 1 for the temperature rise of a single carbon particle upon radiation: T T ) = - o sph pCr + kAt (T2 ^ ) ( j 3 r N o o' where (T - TQ) ^ is the temperature rise of a spherical particle of radius r, emissivity a, density p, and heat capacity C, irradiated with a radiant flux F of duration At where the particle is embedded in a transparent matrix of thermal conductivity k and a is the Stephan- Boltzmann radiation constant. Nelson concludes, "If the matrix is a gas at low pressure, the lower thermal conductivity causes the temperature to approach 5000°C at radii below 10 -k cm." 11 8 - 4 - radiant energy, became very hot, and decomposed the surrounding pOlymer.effect.9 5,184 101 quanta/cm2 in the 2000-4900 A° region. 9 10 a. tiue andW TIley mirrors on the tube walls. Just how hot the materials become is still a problem.> Nelson and Lundberg present an equation, based on a heat balance, for the temperature rise of a single carbon particle upon radiation:11 (T - T) = OF o sph pCr + .k.6t + ao.6t (~ + ~)(T + T ) 3 roo where (T - To) sph is the temperature rise of a spherical particle of radius r, emissivity 0, denSity p, and heat capacity C, irradiated with a radiant flux F of duration 6t where the particle is embedded in a transparent matrix of thermal conductivity k and 0 is the Stephan- Boltzmann radiation constant. Nelson concludes, tllf the matrix is a gas at low pressure, the lower thermal conductivity causes the temperature to approach 5000°C -4 tI 11 at radii below 10 cm. Coal does hot reach temperatures even approaching this order of magnitude, as will he seen in the body of this paper. Nelson1"1' summarizes the differences between flash heating and flash photolysis as follows: 1 . Only slight dependence of absorption on wavelength for flash heating whereas in flash photolysis often the reacting molecules absorb only in the blue or ultraviolet range. Thus more of the lamp output is converted into chemical excitation. 2. A threshold flash intensity below which pyrolytic excitation cannot occur is present in flash heating but not flash photolysis. In flash photolysis often the parent molecules have spectral absorption in the same range as the species under study. Free radicals produced by flash heating do not exhibit this hindrance to absorption spectroscopy. k. The flash heating technique creates a hot, very reactive surface. Such a heterogeneous energy transfer medium will complicate many reactions, just as with homogeneous sensitizers. Flash heating has been used to prepare short-lived atomic and molecular species for kinetic absorption spectroscopy just as is done with flash u . 12,ll+,15 photolysis. 7 13 Nelson has used a graphite cylinder or radiometer in which a thermocouple has been inserted in order to obtain total flashtube out­put and maximum irradiance of the FT 52k flashlamp. The total sensible energy input to the cylinder was measured via the thermocouple and the - 5 - not temPeratures be Nelsonll photolYSiS 1. reayting photolYSis. 3. photolYSiS qave 4. homogeneou9 U$ed prep~e photolys2. s. 12 ' 14, Nelson13 has used a graphite cylinder or radiometer in which a thermocouple has been inserted in order to obtain total flashtube out-put and maximum irradiance of the FT 524 flashlamp. The total sensible energy input to the cylinder was measured via the thermocouple and the - 6 - variation with, time was obtained by correlating the area under an oscil­loscope trace of a photocell with the total energy input. The vertical deflection at any time is thus the instantaneous irradiance. 71 Lincoln has made essentially the same measurements using a 72 Lincoln has developed a technique whereby mass spectra of the gaseous products from flash heating of polymers and metals can be ob­tained directly from the flashtube. The samples vaporize directly into the ion source of a time of flight mass spectrometer. A review covering work done on flash heating up to April, 1962, l6 has been published. The flash heating of coal has received some attention to this date. Working with Nelson at the Bell Telephone Laboratories, Hawk, Schlesinger, and Hiteshue irradiated six samples of high volatile C bituminous coal suspended at 20-micron size on the walls of pyrex 17 tubes^ the tubes being centered in the coils of the discharge lamp. Irradiations of 2592 and 5lQh joules input were carried out for three cases: (l) evacuated tube, (2) Hg at 1 atmosphere in tubes, and (3) solid iodine added to the coal. The atmosphere of the tube was then withdrawn and analyzed by mass spectrometry. The solid products were not analyzed. The gases present in largest amounts were H^, CO, H^O, and CH^. The lower intensity flashes gave relatively more H^, H^O, COg, and HCN and less CO and CH^. The hydrogen test gave similar products to the vacuum test. Acetylenes were also present and were taken to indicate that high temperatures were reached and that effective quenching occurred. The effect of iodine was uncertain. with oscil-loscope Lincoln71 has made essentially the same measurements using a blackened platinum radiometer. Lincoln72 has developed a technique whereby mass spectra of the gaseous products from flash heating of polymers and metals can be ob-tained directly from the flashtube. The samples vaporize directly into the ion source of a time of flight mass spectrometer. A review covering work done on flash heating up to April, 1962, has been publishedol6 The flash heating of coal has received some attention to this date. Working with Nelson at the Bell Telephone Laboratories, Hawk, Schlesinger, and Hiteshue irradiated six samples of high volatile C bituminous coal suspended at 20-micron size on the walls of pyrex ~. tubes) 17 the tubes being centered in the coils of the discharge lamp. Irradia.tions of 2592 and 5184 joules input were carried out for three ~ cases: (1) evacuated tube, (2) H2 at 1 atmosphere in tubes, and (3) solid iodine added to the coal. The atmosphere of the tube was then withdrawn and analyzed by mass spectrometry. The solid products were not analyzed. The gases present in largest amounts were H2, CO, H2O, and CH4 · The lower intensity flashes gave relatively more H2, ~OJ CO2, and HCN and less CO and CH4. The hydrogen test gave similar products to the vacuum test. Acetylenes were also present and were taken to indicate that high temperatures were reached and that effective quenching occurred. The effect of iodine was uncertain. Working at the PMC Corporation, Princeton, New Jersey, E. Rau and L. Seglin irradiated coals of total carbon contents 70.6, 78.^, 80.6, 18 and 85.I per cent. The particle size was less than 10 microns and the energy and flash duration were variables. Gas compositions were obtained as functions of input and rank of coal. As the energy of the flash was increased, E"2 and CO increased, acetylene remained constant, and the saturated hydrocarbons and CO^ decreased. This was taken to mean increased cracking at higher energies. The lower rank coals showed less H 2 and CH^. Atmospheres of N2, H^, and HgO were investigated. The only significant effect seen was the increase of CH^ and decrease of acetylene with H2 atmospheres. Material balances to show the percentage gasified were inconclusive. The photographs of certain areas of the reaction vessel before and after flashing showed a very small number of places where the shape of the particles appears the same. From this the conclusion was reached that complete decomposition of the coal does not occur. This conclusion seems somewhat oversimplified since decomposition products of the coal could conceivably retain approximately the original shape of the coal particle. It also seems significant that over 80$ of the material was changed. The suggestion is made that coal tar was not formed. The basis for this is not clear. G. R. Hill, M. Mcintosh, and L. Charlott, working at the University of Utah, flashed coal in a spectrum of thirteen different gaseous atmos­pheres and analyzed the resulting gases with mass spectrometry and infra- 19 red spectroscopy. Since this report was a part of the work peresented here, it will be discussed in the Results and Discussion section. - 7 - FMC 70,6, 78.4, 80.6, and 85.1 per cent. The particle size was less than 10 microns and the energy and flash duration were variables. Gas compositions were obtained as functions of input and rank of coal. As the energy of the flash was increased, ~ and CO increased, acetylene remained constant, and the saturated hydrocarbons and CO2 decreased. This was taken to mean increased cracking at higher energies. The lower rank coals showed less H2 and CH4• Atmospheres of N2, H2, and H20 were investigated. The only significant effect seen was the increase of CH4 and decrease of acetylene with E2 atmospheres. Material balances to show the percentage gasified were inconclusive. The photographs of certain areas of the reaction vessel before and after flashing showed a very small number of places where the shape of the particles appears the same. From this the conclusion was reached that complete decomposition of the coal does not Occur. This conclusion seems somewhat oversimplified since decomposition products of the coal could conceivably retain approximately the original shape of the coal particle. It also seems significant that over 80% of the material was changed. The suggestion is made that coal tar was not formed. The basis for this is not clear. G. R. Hill, M. McIntosh, and L. Charlott, working at the University of Utah, flashed coal in a spectrum of thirteen different gaseous atmos-pheres and analyzed the resulting gases with mass spectrometry and infra­red spectroscopy.19 Since this report was a part of the work peresenteq here, it will be discussed in the Results and Discussion section. - 8 - Ac Go Sharkey, I. L. Schultz, and R. A. Friedel have irradiated 20 coal samples by flash heating and lasers. The flash heating experiment produces gases richer in acetylene, CO, and H^, and poorer in CH^ and higher hydrocarbons than from high temperature carbonization,, according to these authors. Laser irradiation gave higher acetylene, ethylene, and higher hydrocarbon bases than from flash heating and carbonization at 900°C. The laser was thought to be of a higher temperature but it gave less Fg and more unsaturated gases. As can be observed above, all investigations on the flash heating of coal published to date have dealt with analysis of the gaseous products. From the results reported in this paper it is hoped to show that the solid products are more interesting and instructive in regard to mechanism of reaction and the basic structure of coal. The Physical Nature of Coal In this section the submicroscopic structure of coal will be considered without emphasis on the types of atoms and their linkages. A review of the chemical nature of coal will be given later. Colloidal Properties of Peat 21 Francis has put the chief colloidal characteristics of peat into two categories: 1. The power of absorbing water into the ultra-microscopic structure, accompanied by swelling. 2. Acidity and base-adsorption, A considerable proportion of the ulmin present in peat is composed of weak and insoluble acids. A. G. r. coal samples by flash heating and lasers.The flash heating experiment produces gases richer in acetylene, CO, and H2) and poorer in CH4 and higher hydrocarbons than from high temperature carbonization, according to these authors. Laser irradiation gave higher acetylene, ethylene, and higher hydrocarbon 'bases than from flash heating and carbonization at 900°C. The laser,ras thought to be of a higher temperature but it gave less F2 and more unsatlrrated gases. As c:an be observed above, all investigations on the flash heating of coal published to date have dealt with analysis of' the gaseous producTs" From "Che results reported in this paper it is hoped to show that the so .. ;,id p.'~oducts are more interesting and instructive in regard to mech'3Lism of 2:"eact;ion and the basic structure of coal. The Physical Nature of Coal In this section the submicroscopic structure of coal will be considered 'without emphasis on the types of atoms and their linkages. A review of the chemical nature of coal will be given later. . Francls has put the chief colloidal characteristics of peat into two categories: 1. The power of absorbing water into the ultra-microscopic structure, accompanied by swelling. 2. Acidity and base-adsorption. A considerable proportion of the ulmin present in peat is composed of weak and insoluble acids. Such material in the colloidal state causes the acidic properties. 22 Mack and Hulett believed peat to be a hydrosol becoming a hydrogel 23 in low rank coals. Gauger noted that lignite has a sponge-like 2k structure with ultra-microscopic capillaries of various radii. Stach considered peat formation as the conversion of plant material to humic 25 acid gels which age to form ulmins. Lavine called attention to the colloidal characteristics of lignites and sub-bituminous coals which exhibit the following properties: 1 . Hysteresis on wetting and drying 2. Response to electric current 3. Adsorption properties h. Peptization by treatment with alkaline solutions. Peat, which dries out before coalification, apparently does not 26 become a normal coal, thus showing the importance of the gel stage in coalification. Since the genesis of coal includes a colloidal stage, we will not be surprised to find colloidal properties in coal. Colloidal Properties of Coal Coal has the properties of a very porous solid. It will adsorb gases, swell in vapors and liquids and develop heat on wetting. Gases will penetrate into the coal substance to a greater or lesser degree depending on the molecular size of the gas. The helium o molecule can penetrate into pores smaller than 3 A. It has a slight 27 measured by immersion in helium have been reported by Franklin. These values range from 1.301 to 1.6^5- The water density is different - 9 - Mack and Hulett believed peat to be a hydrosol becoming a hydrogel in low rank coals. Gauger23 noted that lignite has a sponge-like structure with ultra-microscopic capillaries of various radii. Stach 24 acid gels which age to form ulmins. Lavine25 called attention to the colloidal characteristics of lignites and sub-bituminous coals which exhibit the following properties: 1. Hysteresis on wetting and drying 2. Response to electric current 3. Adsorption properties 4. Peptization by treatment with alkaline solutions. Peat, which dries out before coalification, apparently does not become a normal COal,26 thus showing the importance of the gel stage in coalification. Since the genesis of coal includes a colloidal stage, we will not be surprised to find colloidal properties in coal. Colloidal Properties of COaJ Coal has the properties of a very porous solid. It will adsorb gases, swell in vapors and liquids and develop heat on wetting. Gases will penetrate into the coal substance to a greater or lesser degree depending on the molecular size of the gas. The helium o molecule can penetrate into pores smaller than 3 A. It has a slight heat of adsorption. The densities of anthracite and bituminous coals measured by immersion in helium have been reported by Franklin.1.645. because of its polar interaction with coal. The porosity is normally calculated from density measurements in helium and mercury, assuming mercury does not penetrate at all into the pore system. Van Krevelen reports a pore volume of 0.052 cm /gm for a coal of 93-1% carbon. At very high pressures mercury can be forced into part of the coal pores, coming to an upper limit of penetration at high pressures. 28 Since this value is less than the total value calculated from helium, we must conclude that coal contains both a macro-pore system and a micro-pore system. The surface area of coal can be obtained by heat of wetting and gas absorption methods. There is some discrepancy between these two methods, especially for low rank coals (probably due to polar groups present in low ranks)j however, general values would be about 86 m /gm 2 2 for a coal of 93*6$ carbon and between 55 m /gm and 196 m /gm for a coal of.83$ carbon. The value of 55 m /gm is obtained from absorption 2 - 2Q and i.96 m /gm from heat of wetting. During carbonization, Franklin^0 showed that up to 500°C porosity increases while accessibility decreases. True density rises with carbonization temperature. Solvent Extraction of Coal - Kreulen's Model, Dryden's Model Wheeler,^ using pyridine solvent, extracted a resin-like material to which he ascribed the coking properties of coal. The residue would 32 33 no longer coke. Fisher and Bone, using benzene, obtained similar results except they were able to separate the extracted material into two fractions, one having the coking properties. - 10 - cm3/gm 93.7% 28 cOming Since this value is less than the total value calculated from helium}28 'we must conclude that coal contains both a macro-pore system and a micro'-pore system, The surface area of coal can be obtained by heat of wetting and gas absorption methods. There is some discrepancy between these two methods! especially for low rank coals (probably due to polar groups present in loVl rar.:.ks); however, general values would be about 86 m 2 /gm 2 2 for a coal of 93.6% carbon and between 55 m /gm and 196 m /gm for a coal of 83% carbon. 2 The value of 55 m /gm is obtained from absorption .,1' ,96 m2 //g m f-'rom h eat 0 f we tt·l ng. 29 Fr~klin30 porOSity Wheeler, 31 no longer coke. Fisher32 and Bone, 33 using benzene} obtained similar results except they were able to separate the extracted material into two fractions} one having the coking properties. - 11 - The residue has significance in the coking reaction since Broche and Schinitz shewed that the residue from a non-coking coal could not be made to coke by the addition of an extract from a coking coal. That solutions of coal extract show colloidal features is well O r 0*7 established. ' 9 ^ There is, however, evidence that broad distrj.- butions of sizes are present. The smallest sizes have a molecular weight of 300* The subfractions with molecular weights greater than 38 600 showed resemblance to the parent coal. Ethyleneidamine extracts o show the presence of roughly spherical particles of 200 to 700 A diameter.~><^9^ 37 Kreulen has proposed a model of coal structure that would account for the colloidal extracts plus the action of various solvents on coal. According to him, solid coal is made up of micelle nuclei encased in protective olephilic layers and embedded in an oily medium. The micelles and dispersing medium are fundamentally different. Of this model, van Krevelen has said; This simple picture may go far to explain the properties of coal. For example, it accounts for the surface tension effects of extraction liquids, the influence of temperature and rank on the yields of extract and also provides an explanation for peptization and flocculation phenomena.^8 Van Krevelen then goes on to explain that this model seems to be over­simplified because it is based somewhat on surface tension effects of solvent and these are proportional to electron donating capacity which he considers (along with Dryden)^ to be the real explanation of solvolysis. It is generally known that extracts of coal are very similar in structure to the parent coal. Also there is evidence that the coal Schinitz34 showed established. 35,36,37 There is, however, evidence that broad distri­butions of sizes are present. 38 The smallest sizes have a molecular weight of 300. The subfractions with molecular weights greater than 38 600 showed resemblance to the parent coal. Ethyleneidamine extracts o show the presence of roughly spherical particles of 200 to 700 A diameter. 39, 40 Kreulen37 has proposed a model of coal structure that would account for the colloidal extracts plus the action of various solvents on coal. According to him, solid coal is made up of micelle nuclei encased in protective olephilic layers and embedded in an oily medium. The micelles and dispersing medium are fundamentally different. Of this model, van Krevelen has said~ This simple picture may go far to explain the properties of coal. For examplej it accounts for the surface tension effects of extraction liquids, the influence of temperature and rank on the yields of extract and also provides an explanation for peptization and flocculation phenomena. 28 Van Krevelen then goes on to explain that this model seems to be over-simplified because it is based somewhat on surface tension effects of solvent and these are proportional to electron donating capacity which he considers (along with Dryden)4l to be the real explanation of solvolysis. It is generally known that extracts of coal are very similar in 42 structure to the parent coal. Also there is evidence that the coal - 12 - k^> particles in solution have a wide size distribution, ^ as suggested above. In explanation of these facts, Dryden has suggested a model kk similar to Kreulen's. A matrix of larger and more strongly linked micelles is associated with smaller, less strongly bonded micelles. The difference is not sharp between the two; possibly they form a continuous series. This model explains many observations made in the kk field of solvent extraction. The difference is that there is no mention of the oily medium of Kreulen in the Dryden model. It might be mentioned here that the pore structure of coal would be trouble­some to the Kreulen model but not so to Dryden's model since the large and small micelles would certainly give a large and small system of pores as is observed. The physical model of coal suggested in this paper is a compromise between these two, but closer to the Kreylen model in that an oily medium is proposed. The Dryden model does not account for two physically distinct substances as is indicated from flash heating experiments. The Chemical Nature of Coal The chemical nature of coal is here taken to mean the kind and distribution of atoms occurring in coal along with information concerning bonding linkages. The amount of material published within this area is very large so that a review such as this must of necessity cover only the most important work considered to be applicable to the present problem. particles in solution have a wide size distribution,43 as suggested similar to Kreulen's.44 A matrix of larger and more strongly linked micelles is associated with smaller, less strongly bonded m.icelles. The difference is not sharp between the tWOj possibly they form a continuous series. This model explains many observations made in the field of solvent extraction. 44 The difference is that there is no mention o~ the oily medium of Kreulen in the Dryden model. It might be mentioned here that the pore structure of coal would be trouble-some to tb.e Kreulen model but not so to Dryden's model since the large and small micelles would certainly give a large and small system of pores as is observed. The physical model of coal suggested in this paper is a. compromise between these two, but closer to the Kreylen model in that an oily medium is proposed. The Dryden model does not account for two physically distinct substances as is indicated from flash heating experiments. The Chemical Nature of Coal The chemical nature of coal is here taken to mean the kind and distribution of atoms occurring in coal along with information concerning bonding linkages. The amount of material published within this area is very large so that a review such as this must of necessity cover only the most important work considered to be applicable to the present problem. - 13 - Total Analysis and the Additivity Principle The elements in coal are carbon, hydrogen, oxygen, and nitrogen with minor amounts of sulphur (organic and inorganic) and ash (inorganic), Over the coalification range approximately the following changes in weight per cent occur. Peat to Anthracite Carbon 57$ 97$ Hydrogen 5$ 0.6$ Oxygen 37$ 1.8$ Nitrogen 1$ 0.6$ Such properties as molar volume and molar heat of combustion can be considered to be a summation of the contributions from each of the individual atomic components plus contributions due to certain structural factors. Thus, we can write after Traubes Molar volume = V,M, = i 2 ni. • Vi. - Km + M (l) wherei n^ - number of atoms of the i ^ kind per molecule V^ = = $^ = Van Krevelen^'^ assumes: (l) this equation applies to coal, (2) is solely determined by the number of rings (R) per molecule, (3) average values can be used for the atomic contributions, and (k) fl> is negli­gible in a macromolecular substance. He divides the equation by (c), the number of carbon atoms per molecule and obtains: - 13 - wi th inorganic). 57'10 97'10 5% 0.6% 37% 1.8% 1% 0.6% properti.es 'atomie: ;?ontr:J.butions factors, '\ole wTite Traube: 45 where~ n. = number of atoms of the ith kind per molecule 1 Vi volume of atoms per gram atom ~ = molar volume contraction caused by structural factors ~M = molar free space due to end groups 46 28 Krevelen' 1) ~ R) 4) ~M (C), Ik M - f - 9.9 + 3-1 § + 3 . 7 § + 1 . 5 § + Ik § - (9.1 - 3-6 §) S (2) where Mc is the molecular weight per gram atom carbon, d is density, and the other symbols have the same significance as c). R/C can now equation has been shown to give very good results on known compounds. This same principle was applied by van Krevelen and Chermin using model substances, including pitch fractions, to prepare a graph from which it is possible to obtain (f ), the fraction of aromatic a carbon (aromaticity). As was mentioned above, molar heat of combustion can be considered k8 as an additive property. Shuyer and van Krevelen, obtaining data from known hydrocarbons, derived the semi-empirical equation: = 82.VC 287 3.25 68 .'f (3) a ria where f^a Is the fraction of aromatic hydrogen. Thus, -f • or -fjj may be calculated from heat of combustion data if the other is known, f can also be calculated from R by the formula: f a = (1 - §) [1 - 2 (10 65 as shown by Dryden. Structural Analysis Coal is a complicated mixture of high molecular weight substances and as such an exact structural formula would have little exact meaning It difficulty, - 14 - Mc H 0 N S H R ~ = 9·9 + 3·1 C + 3·7 C + 1·5 C + 14 C - (9.1 - 3.6 C) C (2) M c (C). Ric be derived from data on elementary composition and density. This equation has been shown to give very good results on known compounds.28 This same principle was applied by van Krevelen and Chermin47 using model substances, including pitch fractions, to prepare a graph from '''hich it is possible to obtain (fa)' the fraction of aro~tic carbon (aromatici ty). As was mentioned above, molar heat of combustion can be considered as an additive property. Shuyer and van Krevelen, 48 obtaining data from known hydrocarbons, derived the semi-empirical equation: Q 82.4 C + 287 H - 3.25 f C + 68fH . a a H (3) where f Ha is the fraction of aromatic hydrogen. Thus,fa or fH a may be calculated from heat of combustion data if the other is known. f a can I also be calculated from l' by the formula: = (1 - li) + [1 _ 2 (R-l)] a C C 4) as shown by Dryden. sub~tances struct~al . 28 unless it covered several pages. Realizing this diff~culty, van Krevelen has devised several structural parameters which describe the mean - 15 - structure of coal. Three of these will be considered in this paper: 1. _ number of aromatic carbon atoms a ~ C Hydrogen aromaticity = f„ = a _ number of aromatic hydrogen atoms H ~ total number of hydrogen atoms = R^ The other important parameter is the size of the aromatic clusters which exist in all coals. It will not be calculated in this paper because it requires a very refined technique of X-ray diffraction which was not I4.9 attempted. This method is discussed by Diamond. Methods for calculating aromaticity and rings per carbon atom have been given above and the remaining parameter, hydrogen aromaticity, can be calculated by infrared spectroscopy. sections,^ ^ 52 and pressed KBr disks. Of these, the pressed KBr disk technique was used in the research reported in this paper because of its ease and also because KBr has no absorption bands below 15 u. The infrared spectra of coals are all somewhat similar and are all compatible with a highly aromatic material. This high degree of aromaticity is also reflected in the low hydrogen-to-carbon ratios found in coals. p~per: 2. 3. Aromaticity = C a nBIDher fa = C- = total number of carbon atoms R Hydrogen aromaticity f Ra ~ = total number of hydrogen atoms R Rings per average structural unit per carbon atom C attempted. This method is discussed by Diamond. 49 Methods for calculating aromaticity and rings per carbon atom have been given above and the remaining parameter, hydrogen aromaticity, can be calculated by infrared spectroscopy. Infrared Spectroscopy There are several methods used to support a coal sample so that the infrared spectrum can be observed: thin sections) 50 mulls, 51, and pressed KBr disks. Of these, the pressed KBr disk technique was used in the research reported in this paper because of its ease and also because KBr has no absorption bands below 15 ~. The infrared spectra of coals are all somewhat similar and are all compatible with a highly aromatic material. This high degree of aromaticity is also reflected in the low hydrogen-to-carbon ratios found in coals. A very excellent review of the present knowledge of infrared kk spectra of coal has been given by Tschamler and de Ruiter. A table from this is reproduced as Table 1 . An important area, especially in this paper, is the 3000 cm area. This is the carbon hydrogen stretching region. Peaks below 3000 cm ^ denote aliphatic hydrogen and peaks above 3000 cm ^ denote aromatic hydrogen. 5k , Brown has calculated Da / Ds for various vitrains where the optical density, D, equals log IQ/l- I is the intensity of the incident radiation and I is the intensity of radiation transmitted by the sample in accordance with Beer's Law. From the infrared spectrum of coal, D & is taken at 3030 cm 1 which is the C-H stretching band for aromatic hydrogen and D s is taken at 2920 which is one of the important C-H stretching bands of aliphatic, alicyclic, and hydroaromatic hydrogen. From Beer's Law, D / D is related to H-/H by the extinction coefficient a s as ratio Es /E . That is: 7 a VHs (VEa) (W (5) Since Ea / Es is not known for coal, Brown used several reference compounds with to condensed rings and with attached aliphatic chains or alicyclic rings. Since D / D could be measured and H /H was known, a s as he could then calculate E /E . The value was found to vary from 0.3 to a s 1 . 0 . He chose 0.5 as a working average value for coal. This value was later shown to give good agreement with values for H /H , determined a s 55 by nuclear magnetic resonance. ^ It will be used for calculations in this paper. - 16 - spectra of coal has been given by Tschamler and de Ruiter. 44 A table from this is reproduced as Table 1. -1 An important area, especially in this paper, is the 3000 cm area. This is the carbon hydrogen stretching region. Peaks below 3000 cm-l -1 denote aliphatic hydrogen and peaks above 3000 cm denote aromatic hydrogen. Brown54 has calculated Da /D s for various vitrains where the optical density, D, equals log I /1. I is the intensity of the incident o 0 radiation 8,nd I is the intensity of radiation transmitted by the sample in accordance with Beer's Law. From the infrared spectrum of coal, Da -1 is taken at 3030 cm which is the C-H stretching band for aromatic /n H /a s a s E E. s H /H = (E /E )(D /D ) ass a a s 3 5 he could then calculate Da /n s Ha Hs Ea /Es . The value was found to vary from 0.3 to 1.0. He chose 0.5 as a working average value for coal. This value H a s by nuclear magnetic resonance. 55 It will be used for calculations in this paper. TABLE 1 BAND POSITIONS IN THE INFRARED SPECTRA OF COALS AND THEIR ASSIGNMENTS Band Position Assignment Band Position •' -^ 1 - 1 Assignment -1 cm H - 1 cm 3300 -OH str. 1300 7.7 C-0 str. (phenol) -NH str. to to OH def. Ca r -0-C ar str. C-0 str. (alcohol) C -0-C _ str. ar al C -0-C _ str. 3 .3 aromatic CH str al al 2978 CH^ str. 3.42 CH3, CH^ 900 1 1 . 1 1700 3-5 5.9 al. CH str. C=0 str. to to 1^.3 aromatic 6.25 ar. C=C str. C=0 HO- 1 1 . 6 ar, HCC rk. (single and cond. rings) 6.65 ar. C=C str. 750 1 3 .3 1^50 6.9 CH^ assym. def. 1 1 . 5 subst. benzene ring w/lH CHg scissor 1 2 .3 subst. benzene ring v/2 ar. C=C str. 1 3 .3 neigh. H's 0-subst. 7.25 CH- sym. def. 1 1 . 2 H atoms in meso posit. 1 2 .2 1 3 .2 (anthracene) angular cond. ring system 0-subst. benzene rings mono subst. benzene rings cond. ring systems em ~ 3030 2925 2860 1600 1500 1450 1380 3 ·3 3.36 3·5·9 - 17 - OR NH CR str. CR 3 CR3'C~ CR O O ...• HO-ar. CH3 CH2 C::CH 3 em ~ 1000 700 860 873 816 751 893 820 758 7·7 10.0 11.1 14.3 11.6 13·3 11.5 12·3 13·3 O OR r- O-O Car-O-Cal Cal-O-Cal str. ar. condo IH w/HI s O-subst. benzene ring condo O-subst. condo 18 Brown has obtained infrared spectra for the extract and residue for various solvent extractions of coal. He finds that all extracts and residues contain similar structures. He finds further that less highly condensed materials are extracted with the poorer solvents. These are also extracted at lower temperatures. The Chemical Constitution of Coal One of the great workers in coal science, D. W. van Krevelen, is quoted directly on this subject. The structural picture as we know it today may be briefly des­cribed as follows. Coal possesses a composition which in some aspects Is similar to that of substances like pitch and bitumen, being made up as it is of a large number of chemical units, similar in type but very different in molecular fine structure and molecular weight.. All these units, however, have one feature in common, namely a more or less lamellar shape. The mean values of ring condensation index (a number proportional to R/c) and aromaticity and the dimensions of the condensed aromatic nuclei of the lamellae, as well as the number and character of the functional atom groups in the molecule periphery, can be derived from the results of structural analysis. When coalification starts, the aromatic clusters are still relatively small and probably connected by non-aromatic bridges. This explains why the first few terms of the coalification series possess a pronounced polymeric character and a more or less open structure. From a chemical point of view, coalification must be considered as a process in which the degree of condensation and aromaticity of the starting material increase continuously; the bridge structures become less stable as the interaction forces between the aromatic nuclei grow stronger. On continued coalifi-cation, the polymeric structure, in which not only covalent bridges but also interaction between the polar groups play an important part, is modified into what has become known as the "liquid" structure, which is typical of coking coal (broad mole­cular weight distribution). ° - IS - Brown56 o~ is simil~ weight" Ric) bridge structures become less stable as the interaction forces between the aromatic nuclei grow stronger. On continued coalifi­cation, the polymeric structure, in which not only covalent bridges but also interaction between the polar groups play an important part, is modified into what has become known as the "liquid" structure, which isS typical of coking coal (broad mole­cular weight distribution).2 MATERIALS AND EXPERIMENTAL METHODS Sample Preparation The high volatile bituminous coal -which was the primary subject of investigation herein was hand picked from a working face of the Spring Canyon Mine, Utah. The ultimate and proximate analyses are as follows: Ultimate Proximate Carbon 72.88 Water Hydrogen 5.58 Ash 8.37 Nitrogen 1.51 Volatile matter ^5-71 Oxygen 10.82 Fixed carbon V5.92 Sulfur 0.65 Chlorine 0.19 Heating value - 1 3 , 2 3 7 Btu/lb, dry basis In the body of this paper when the word "coal" is used, it will always mean the coal described above. The other coals used were obtained from Bituminous Coal Research Inc., with sample numbers 1007 and 1031. The data available are as follows: - 19 - which 8.37 matter 45· 71 Oxygen 10.82 Fixed carbon 45.92 Sulfur 0.65 Chlorine 0.19 Heating value - 13,237 Btu/lb, dry basis In the body of this paper when the word "coal" is used, it will always mean the coal described above. The other coals used were obtained from Bituminous Coal Research Inc., with sample numbers 1007 and 1031. The data available are as follows: BCR No. 10O*f07 - Pocahontas No. 3 bed, McDowell County, West Virginia Proximate Water Dry basis Ash 5.6k Volatile matter 17-6 Fixed carbon 76.76 Sulfur 0.66 « * r e ^ e c ' t a n c e RQ " 1-65 BCR No. 1031 P~ ~ Tiller bed, Russel County, Virginia Proximate Water Dry basis 6.02 29.k 6^.58 O.65 3s ~ 1 ^ 6l0 8.5. reflectance (R Q #) - 1.07. abo\Pv e consistePed reaction produiAicts. lumpf^P~size c o a l w a s ground in a ball mill for a period of 2k theni31 ^00-Particle diame^ter °f 0*037 v&s i#n & ^ s - 20 - BeE 100'@'07 5·64 17.6 0.66 Coal r ~reflectance (Ro %) - 1.65 103l ~ - Till er Ash 6.02 Volatile matter 29.4 Fixed carbon 64.58 Sulfur 0.65 Heating value ~ - 14,610 Btu/lb, dry basis. Free swelling index - 8.5. Coal reflect~ce R o %) - 1.07· The abo~ve two coals were given only a very cursory examination which consiste~ed mainly of obtaining the infrared spectra of their prodUiructS. The lumpf~ - size coal was ground in a ball mill for a period of 24 hours and then?n sieved wet through a 400-mesh screen corresponding to a particle diame~ter of 0.037 mm. This suspension of fine coal in water Was filtered i~a Buchner funnel and the resulting wet cake was removed and stored in ~ a wet condition. Coal is not- a uniform homogeneous material but a rock mineral composed of various fractions differing in physical and chemical properties. These fractions are called macerals. Two methods have been used to isolate individual macerals for study: hand picking under a microscope and density fractionation by sink and float techniques. A sink and float method vas used in this work. The advan­tages are ease and rapidity of separation. The disadvantages are incomplete separation. For example, only about 90$ of the 1 . 2 5 to 1 . 3 5 density fraction is vitrinite. Dormans has discussed this method. In this research the separation medium used was a zinc chlpride-water solution. Various densities were made by using more or less ZnClg. A hydrometer was used to measure solution density. The wet cake from the sieving operation was well dispersed in the ZnClg solution by a mechanical mixer and the resulting dispersion centrifuged and then allowed to settle. The coal sample preparation was as follows: Original Coal Sample ZnCl2 Solution density 1 . 35 discard floats on 1.25 Fraction rich in exinite ZnClp solution density 1 . 35 sinks 1. 25 floats on 1 . 35 sample sinks in I.25 used Fraction rich in vitrinite sinks in 1 . 35 discard Fig. 1 , Sink and float scheme for fractionating coal. - 21 - not min~r~ pick~ng was advan-tages example} 90% 1.25 1.35 methOd. 57 chlqride-water ZnC12 • ZnC12 ZnC12 I <--Fraction 1. 1.25 ~ densi ty 1. I sinki in 1.25 1.35 t 1. - 22 - The coal fraction retained was vitrinite (density between 1.25 and 1.35)» This fraction was selected for study because it is the most homogeneous maceral and has been studied more than the others. The vitrinite fraction was obtained as outlined in Fig. 1. Each centri-fuging operation was repeated three times and the unwanted fraction discarded three times in order to obtain a vitrinite of a very exact density range. The reason for such an exactly known sample density is so the reaction products can be separated from the unreacted coal by the same sink and float technique. The wanted coal fraction was separated by filtration from the zinc chloride solution and washed on the filter with kOOO ml of distilled water containing several drops of concentrated HC1. The acid is to dissolve any zinc hydroxide that may have formed. The coal was found to contain a very small amount of zinc chloride even after washing.; however, there is no reason to suppose that this small quantity of salt will have any effect on the results reported in this paper. After washing', the coal was dried in a vacuum oven at 80°C for a period of four hours. It was stored in a stoppered bottle. Equipment The main piece of equipment used was the photoflash unit. It was assembled entirely in this laboratory and consists of a power supply, high capacity condenser bank, photoflash tube, and a supporting structure for these parts. Power supply.--Two power supplies were used. The first one required a relatively long time to bring the capacitor charge up to 1.35). centri­fuging ;'Tas 1.8 so t.he reaction products can be separated from the unreacted coal by the same sink and float technique. The wanted coal fraction was separated by filtration from the zinc chloride solution and washed on the filter ,\lith 4000 ml of distilled water containing several drops of concentrated HCl. The acid is to dissolve any zinc hydroxide that may have formed. The coal was found to contain a very small amount of zinc chlori.de even after washing; however~ there is no reason to suppose that this small quantity of salt will have any effect on the resul +'5 r eport:ed tn this paper. M'ter washi.ng, Povler Two , useful values (about nine minutes to reach 3000 volts). The second supply was built from heavier, higher rated components in order to apply a greater charging current to the capacitors (3000 volts reached in 15 seconds). A complete circuit diagram for the larger source is given in Fig. 2. Condenser bank.--The condenser bank used in this unit consisted of three 125 microfarad capacitors purchased from National Capacitor Company and rated at 4000 volts direct current maximum charge. The energy content of a capacitor bank is given by the formula: 1 2 E « ± c\r where E is the energy in joules, C is the capacitance in microfarads, and V is the charge voltage in kilovolts. It is seen that the input energy to the flash lamp can be regulated by adjustments of capacitance or voltage. If extremely accurate input energies are required, it is best to vary capacitance because energy varies as the square of voltage and the reading of a meter as the voltage rises could possibly give a one or two per cent reading error in the energy. A variable capacitance at constant voltage will give no human error. A capacitor bank of perhaps 30 microfarad increments would be ideal for this purpose. Photoflash tube.-'The photoflash tube used was a General Electric FT 524. It consisted of a quartz tube wound into a helix with an electrode sealed into each end. The tube was filled with xenon gas and had a trigger electrode on the external wall. The electrodes were connected across the capacitor bank as is shown in Fig. 2 . The bank was charged to various voltages depending on the energy required. The ~ 23 - The consiste4 12 E=~~ where E is the energy in joules, C is the capacitance in microfarads, and V is the charge voltage in kilovolts. It is seen that the input energy to the flash lamp can be regulated by adjustments of capacitance or voltage. If extremely accurate input energies are required, it is best to vary capacitance because energy varies as the square of voltage and the reading of a meter as the voltage rises could possibly give a one or two per cent reading error in the energy. A variable capacitance at constant voltage will give no human error. A capacitor bank of perhaps 30 microfarad increments would be ideal for this purpose. Photoflash tube.--The photoflash tube used was a General Electric FT 524. It consisted of a quartz tube wound into a helix with an electrode sealed into each end. The tube was filled witp xenon gas and had a trigger electrode on the external wall. The electrodes were connected across the capacitor bank as is shown in Fig. 2. The bank was charged to various voltages depending on the energy required. The 866 A 5 A Power ruse switch 41- 115 V 115 Motor-driven time delay -o^o Standby switch RO 100 K 100 w 2 . Circuit diagram for photoflash unit. fA use s·witch D~ :: 115 V V lamp 866 3000 V 50 ma o,;r 0 5A Variac -::: 0-100 ma . Choke 100 K 100 100 W • ____ -J ~----------------r-----.-----.--__.L_~ ____ ~--~ Trigger circuit 125 Fig. 2. 2mi' 4 Kv f\) .j::"" - flashtube was triggered by applying a high voltage pulse (supplied herein by a Ford ignition coil setup and a 6-volt battery) to the trigger electrode which ionized the gas, making it conductive. The capacitor bank discharged its energy into the flashtube causing a brilliant flash of light. Figure 3(b) shows the lamp with reaction vessel inside its coils. The spectral energy distribution of a flashtube is continuous, except for a few superimposed higher intensity lines. The range is from, about 1,800 A to about 18,000 A, (See FIGO 2 1 . ) If a glass reaction vessel is used, the energy reaching the sample is cut off at o about 3000 A. A quartz reaction vessel would* of course, pass this energy,, The flash time or duration of flash is a function of the electrical circuitO The variables existing in this case were voltage and inductance in the discharge path. Operation at 3?000 volts gave an energy input of 1,687 joul.es 0 Since the manufacturer did not recommend operation at this value without inductance, and since external arcing occurred occasionally without inductance, an inductance coil of unknown value was introduced into the circuit. This prevented external arcing and lengthened the tube life but increased flash duration. For a circuit without inductance operating at about 1850 joules we would have a flash duration (defined as the duration above one-third peak power) 7 of about 375 microseconds." In our system the inductance had the effect of spreading this duration out to 2000 microseconds. The output of the lamp is considerably less than the input, Published data show that the FT ^2k emits 15 optical joules/cm - 25 - volt fel'i o Q from 1} 800 Fig" 21.) ve.sselis ust'~d; o about 3000 A. A quart.::;: rea.ction vessel would~ of course) pass this energy" The fl.a.:-:;h ti.me or durat:Lon of flash is a function of the electrical circui t" The vari.ab~.es existing in this case were voltage and inductance in the discharge path. Operation at 3)000 volts gave an energy input of 1,687 joul.es, Since the manufacturer did not recommend operation a.t this value wi t.hout inductance} and since external arcing occurred occasionally without inductance, a.n inductance coil of unknown value was introduced into the circuit. This prevented external arcing and lengthened the tube life but increased flash duration. For a circuit without inductance operating at about 1850 joules we would have a flash duration (defined as the duration above one-third peak power) of about 375 microseconds. 7 In our system the inductance had the effect of spreading this duration out to 2000 microseconds. The output of the lamp is considerably less than the input. Published data show that the FT 524 emits 15 optical jOUles/cm2 Fig. 3« Flashheating apparatus: (a) Complete apparatus, (b) Flashtube and reaction vessel. - 26 - (a) (b) 3. - 27 - energy 3200 joules.1 3 2 helix is 62 cm '. Supporting structure.-The supporting structure was a heavy iron frame covered with wire screen to protect the operator and bystanders from electrical shock. Clamps and supporting aluminum rods were fixed inside the cage in order to provide support for the sample tubes. The complete apparatus is shown in Fig. 3(a). Reaction tubes .---Three types of reaction vessels were used in this research? ail made of pyrex glass. For reactions in which the ratio of vessel volume to surface area of inner tube walls was to he minimum, a small diameter tube was used. The dimensions were 1.235 cm 0«Lo and 1.02 cm I.D. and 10.l6 cm long. This type of vessel was also used for experiments giving extent of reaction, as determined by quali­tative observations, as a function of energy input to the flashtube. When a large surface area was required (corresponding to larger amounts of coal exposed per flash) a tube of 2.5 cm. O.D. and 2.l8 I.D. was used. When experiments were done with small amounts of coal and only smaller amounts of product were required, the length of the tube used was 5»7 c m> necking down to a 1.235 O.D. tube of 7-6 cm. It became evident during these investigations that the extremely small quantities of reaction products obtained using the above-described reaction vessels were not sufficient. In order to obtain more product within a reasonable amount of time, it was decided to use a tube of O.D. 2.5 cm, I.D. 2 . 1 8 cm, and length 1.22 meters. It was exposed in steps, flash by flash, over the whole length. All the coal was not I with an input ent;;rgy of 3200 jOules.13 The internal surface of the helix is 62 cm . Supporting structure.--The supporting structure was a heavy iron frame covered with wire screen to protect the operator and bystanders from electrical shock. Clamps and supporting aluminum rods were fixed inside the cage in order to provide support for the sample tubes. 'The complete apparatus is shown in Fig. 3(a). ReactIon tutes,_--·Three types of reaction vessels were used in ~:I:-d,s rese':!rC'h,; al: made of pyrex glass. For reactions in which the ra"Gio of vedse::;', volume tc. 3u:vfa.ce area of inner tube walls was to be IKLn::Lm.UfilJ a 3mall. OoI~ 0 arJ,6. 1.02 em diameter tube 'was ~.I: ~ j) • and 10.16 em used. long. The dimensions were 1. 235 em This type of' vessel was also useCL 1\n ex:pe:"imern;s giving ext.ent of reaction., as determined by quali­tative observe.ti(JUs J as a :fmw'c.ion of energy input to the flashtube. "hThen a. large surface area \-T&S required (corresponding to larger amounts of cosJ, eXpiJ8ed per flash) a tu'be of 2 _ 5 elL O.D. and 2.18 LD. wa3 used.. '\{.ben expei:'irr!,ents 1,/e;'e done with small amounts of coal and only smaller amounts of product were required, the length of the tube used was 5.7 em, necking down to a 1.235 O.D. tube of 7v6 cm. It became evident during these investigations that the extremely small quantities of reaction products obtained using the above-described reaction vessels were not sufficient. In order to obta.in more product within a. reasonable amount of time, it was decided to use a tube of O.D. 2.5 cm, loD. 2.18 em, and ler-gth 1.22 meters. It was exposed in steps,. flash by flash; over the whole length. All the eoal was not - 28 - reacted by this method and an estimate of how much remains unreacted is given later. This, as will be seen, amounts to Ijfo of the total sample remaining unreacted. In all the above-described tubes the coal particles were sus­pended on the inner walls of the tube. If the tube was washed with laboratory glassware detergent, rinsed with water, and then air dried, it was found that the glass surface retained the small coal particles evenly. Except for the cases where a gaseous atmosphere was used, the reaction vessel was evacuated to a pressure of mm and sealed with a piece of tygon tubing slipped onto the glass and clamped tightly shut. This arrangement held the vacuum well. The reaction vessel was exposed to the flash by placing it within the coils of the flash tube helix. Preparation of Reacted Coal for Analysis After the reaction vessel had been exposed to flashing it was either examined visually, the gases withdrawn for infrared spectrometry and mass spectrometry gas analysis, or the solid reaction products removed and analyzed. The long tubes of length 1.22 meters were used primarily for the preparation of solid reaction products and also for the material balances. Usually from k to of these long tubes had to be used in order to obtain sufficient quantities of product. The solid product was abstracted from the reaction vessel by washing it out with an organic liquid, usually acetone or benzene. The slurry obtained from This., 13% evenly 0 3 t'lbing TbL'S arra.ngement co:i:~.s Prepara-c:ioI"l prepara.tion balances 0 4 36 liquid) washing was filtered and the filter cake washed in turn with sufficient quantities of benzene and acetone to abstract all materials soluble in these solvents. For the experiments wherein the non-soluble material was fractionated according to density, the cake was washed with water. The effluents, benzene and acetone, were placed in turn in a solvent evaporation system consisting of a 500-ml round-bottom flask rotated by an electric motor, immersed in a mineral oil bath of 120°F and attached to a vacuum pump. The solvent was evaporated away by this method leaving the acetone or benzene soluble reaction products. Water-soluble material was not observed. For the density fractionations, the wet filter cake was not allowed to dry out because when dried it is not easy to wet completely with water again. The wet cake was dispersed in a zinc chloride-water solution of density 1.20. It was fractionated according to density by the scheme shown in Fig. k. The density fractions were washed with kOOO ml of very dilute HC1 and 1000 ml of distilled water, dried in a vacuum oven, placed in a desiccator for one hour, and weighed. Preparation of Samples for Infrared Spectroscopy The acetone- and benzene-soluble material was dissolved in a small amount of the solvent and the solution was placed on a NaCl disk. When the solvent evaporated, a layer of sample was left and this was run in the infrared spectrometer. NaCl does not have absorption in the ^000 cm- 1 to 700 cm- 1 range. The material from the density fractionations was a fine-grained powder. The pressed KBr disk method, as is explained in the Literature - 29 - 1200F purr~" 4. 4000 ml of very dilute Rel and 1000 ml of distilled water, dried in a ovenJ soluble a 4000 cm-l cm-l Filter Cake ReaIc tion Product "B* ZnCl2 Solution density 1.20 d > 1.20 product 1.20 d 1.25 product 1 . 2 5 d 1.30 product 1.30 d 1 . product 1 , 3 5 d 1.40 product 1 . 4 0 < d < 1.1+5 product 1.1+5 d 1.50 product 1.50 < d < I.55 product 1 . 5 5 d 1.60 1.20 sinks floats sinks sinks floats floats sinks floats sinks floats sinks floats sinks on 1 in 1 1 in 1 on 1 1 on 1 1 on 1 in 1 on 1 in 1 on 1 1 on 1 in 1 -25 ,20 • 30 ,25' •35. 30 1+0. 35 .1+0 50 •^5 55 50 ,60 ,50 sinks in 1.20 I ZnCl^ solution density 1.25 I.25 J ZnCi,., solution I density 1.30 sinks in 1.30 ZnCl2 sLo lution dens:. Lty I.35 1 . 35 ZnCl.2 solution density 1.1+0 sinks iTn 1.40 ZNCL2 solution density 1.45 sinks in 1.45 I ZNCL2 s°lu"ki°n density I.50 I.50 1 ZnClg solution density 1 . 55 1-55 ZnClg solution density 1.60 sinks in 1.60 product d 1.60 " Fig. 4. Sink and float scheme for fractionating reaction produc product > 1.20 < < 1.25 < < 1. 30 prodD.ct < < 1..35 1.35 < d. < produ("i~ 1. 40 d 1. 45 1. 45 < < 1. 50 1.50 1.55 1. 55 < < 1. 60 - 30 - Reaction B" I ZnC12 densi ty 1.20 I floats on 1.20 I ZnC1 2 floats on 1.25 ______________________ ~~~1 1.20 sinks in 1.25 flOE',ts on 1. 30 31nk5 in 1.25 I ZnCL, deRsiGY 1. 30 1.'30 floats on 1.35 __________________ _ in 1.30 sinks in 1.35 I floats on 1.40 __________________ __ sinks in 1.35 in ! ZnC12 dens i ty 1. 45 floats on 1.45 ___________________________ ~ 1.40 ZnC12 solution dens i ty 1. floats on 1.50 ______________________ ~~_7 1.45 sinks in 1.50 1 ZnC12 densi ty 1. floats on 1.55 ______________________ ~~~ in 1.50 sinks in 1.55 I ZnC12 1.60 floats on 1.60 ________________________ ~~1 1.50 1060 product, ________________________________________________ ~1 > product. Survey section, was used for obtaining infrared spectra of these materials. A Beckman 5020 die was used to press the disks. The instru­ment used to obtain all the spectra used in this work was a Beckman 421 grating double beam spectrophotometer. Preparation of Samples for Electron Microscopy A small amount from each of the fractions of the density fractio­nated material was dispersed in distilled water. A copper grid with a colloidon film was prepared by placing three drops of a one per cent colloidon solution on a water surface and the small grids dropped on the surface of the film.. The grids and film were scooped up on a glass slide. A drop of the water containing the dispersed sample was placed on the grid and allowed to evaporate. The particles were supported within the grid work by the colloidon film. The grid was placed in the electron microscope and the particles viewed. If the material from the fractionation (which will later be given the designation "B") is flashed at high voltages, it produces a very thin film on the inner wall of the reaction vessel. This film can be floated off onto water where it is scooped up on a small copper grid and placed in the electron microscope. Preparation of Samples for Heat of Combustion The samples from the density fractionation and the coal sample were pressed into a pellet before combusting in a Parr plain jacket calorimeter. The benzene- and acetone-soluble material was not compressed. - 31 - 'col1oidon film. - 32 - Preparation of Samples for Osmometry The benzene-soluble material was taken from the evaporating flask and weighed. It was then dissolved in a known quantity of benzene; this was diluted in order to prepare samples of one-half and one-quarter the original concentrations. The concentrations were deter­mined in a Mechrolab Model 301 osmometer. The average molecular weight could then be calculated. - ~ - one~half one­quarter concentr~tions moleGular RESULTS AND DISCUSSION Appearance of Product - Qualitative Results When fine coal particles were suspended on the inner walls of a pyrex tube and the tube evacuated and sealed, then flashed at 3000 volts, the appearance of the tube was completely changed. Previous to flashing, it appeared transparent and a dusky grey color due to the suspended coal* Upon flashing, it became opaque and black due to a coating of material on the tube walls. This appeared to occur instantaneously. Streamers and strings of gossamer-appearing material filled the inside of the tube. Visually it appears amazing that so much material could come from such a small amount of coal. When the vails of the tube were examined with a ikx hand lens a variable particle size was observed ranging from coarse particles the size of the original coal down to particles at and presumably below the limit of resolution of the lens. Using much less coal so that upon reaction the tube does not become opaque, the tube was flashed and immediately withdrawn and held near a strong lamp. It was observed that not much of the gossamer material had formed, but it was in the process of forming. Convection currents could be seen carrying material around and around within the tube. Gossamer structures were forming by what appeared to be mechanical •buildup of the fine, light particles. When the tube was opened much lof the material within was so light and fluffy that it floated right pout of the tube when there were small disturbances in the air. - 33 - flashingJ coal 0 instantaneously 0 insi.de tube 0 ama.zing material. C!ould wa1ls l4x t.he lenso goSsamer fOrming buildup of out - 3^ - If Spring Canyon coal is flashed similarly at a lover voltage (about 1500 volts) in a good vacuum so that not much oxygen is present, the result will be a coating of yellow material covering the inner walls of the tube. There is so much of this present that it appears at first glance as if all the coal has been changed into this yellow material. If the tube walls are examined carefully with a ikx hand lens, specks of black material can be noticed scattered among the homogeneous, even coating of yellow material. If the experiment is repeated several times using a slightly higher voltage, each time the yellow coating becomes darker and darker and finally at a value of about 1900 volts grades into the opaque black color described above. Thus we have two physically distinct substances--a black material and a yellow material formed from the same coal. Since the obvious difference initially was their color and since they will be referred to a great deal in the following pages, they will be given the con<- densed notation B and Y. B will mean black material and Y will mean yellow material. When Spring Canyon coal is flashed at low voltage in a good vacuum or in a non-oxidizing atmosphere, Y will apparently form to a considerable extent with not much formation of B. If the tube is withdrawn from the flashtube immediately after flashing, a yellow gas or suspension of fine particles of Y can be observed. This yellow cloud will flow to the bottom of the tube if the tube is held vertically. 34 lower l4x voltage) e~ch bla~k tvo con­densed After several seconds this gas-like material condenses in an even coating on the tube walls. This cloud of Y does not stay in suspension as long as the B, and it doesn't collect in gossamer strands as B does. Convection currents are not observed and the suspended Y appears much more homogeneous and dense than the suspended B. If the low voltage experiment is repeated with one atmosphere of oxygen alone present in the tube, no trace of Y is found. If a hydrogei atmosphere is used, the usual quantity of Y is seen. The dense yellow cloud when observed will always be confined to the lower part of the tube, presumably because of its density compared to hydrogen. The Y formed In a. hydrogen atmosphere gives an identical infrared spectrum to that formed in a vacuum. B will form in oxygen or any other atmosphere. Volatile Matter and Coking Test If the B obtained from low voltage and high voltage flashing experiments as described above is tested for volatile matter using the standard ASTM procedure (7 minutes in an air-tight capsule at 950°C), It is found that the low voltage B has more volatile material than the high voltage B. These relationships are shown in Table 2 along with the volatile matter test data on the original coal. Two other observations of significance were made from this test. The visual appearance of the volatile material emanating from the furnace was much more yellow for the coal and the low voltage B than for the high voltage B. The coal coked into relatively hard lumps of coke; the low voltage B coked into lumps of coke which could be crushed - 35 - hydrogm tube) in a hydrogen atmosphere gives an identical infrared spectrum Volat:Lle descri.bed it 2 - 36 - ASTM VOLATILE MATTER TEST DATA ON B AND COAL High Voltage Low Voltage I 1 B B SpringC oCaaln yon Initial weight gra 0.64S gm 1A59 gm Weight volatilized 0 . 2 5 3 O.65O gm Per cent volatilized matter 3 9 .2 41+.5 ( 0 . 1 8 fln (0.6l m B ) „ O.il^ram. material 1 gm B gm ceal removed per gram of coal that does not correspond to Y for the case of B from a 3000-volt flash. We will see in a later section that there is 0.6l gm B/gm coal. Another observation that could be made at this point is the fact that the coal when observed by reflected light, as when the powdered material is viewed through the walls of a glass container, appears to have a yellowish cast. This effect is also observed for the low voltage B but not as much. The high voltage B appears black when viewed in this manner. This effect was also noticed for the BCR No. 1 0 07 and No. 1031 coals, the No. 1031 appearing more yellowish than the Np. 1007. The No. 1031 has 29.4$ volatile matter and the No. 1007 has 17*6$ volatile matter. more easily than the coke from the coal; the high voltage B did not coke at all except for one or two small very loosely consolidated lumps. TABLE 2 Spring Canyon 0.424 gm 0.645 gm 0.079 gm 0.253 gm 18.6 39·2 The figures indicate that there is (0.18 gm removed) (0.61 8m B) 1 = 0 .1J,.--,gram. material Coal 1.459 0.650 44·corres~ond Case vol t there. 0.61 o'f 1097 No. 29.4% 17.6% - 37 - Infrared Spectra Figures 5 through 12 give the infrared spectra of coal, B, Y, and various other spectra. These will he discussed. Except where noted, all the spectra are of Spring Canyon coal or its reaction products. Two important general observations can at once be drawn from these spectra. First, the spectra of Y are very different from those of B and second, the spectra are nearly identical to the coal spectra. Below, when the word "peak" is used it will really mean inverse peak since the absorption band occurs as a minimum in the curve. Figure shows the spectra of the three coals used in this work. The KBr pressed disk method was used to obtain these spectra. Because of the micro amounts of coal that have to be used it was not feasible to match concentrations; therefore, only relative depths of two dif­ferent peaks can be compared for the various curves and the vertical axis has no significance. Even though the volatile content varies from k-Ofo to 18$, no obvious differences between the spectra can be distinguished. Information concerning band assignments has been taken mainly 62 63 from Bellamy and Nakanishi. Table 1 gives a brief summary of the assignments of various bands made by a number of authors. In more detail we can make the following observations. The OH stretching region extends in a broad band from about 365O cm ^ to somewhere below 3100 cm "L. This broadness is a strong indication of the total band being a combination of several bands. These are quite possibly the following: Free OH (no hydrogen bonding) from 365O to 3590 cm ^; be products. Two important general observations can at once be drawn from these spectra. First, the spectra of Yare very different from those of Band secondj the spectra are nearly identical to the coal spectra. Below; peaktl Figur'e 5 amoants dif-ferent 46% to 18%} no Bellamy62 63 OR -1 3650 -1 OR 3650 cm-l ; 38 inter- and intramolecular single bridge hydrogen bonded OH from 3^00 to 3200 cm 1 and chelated intramolecular hydrogen bonded OH extending below 3200 cm 1 . These OH groups in coal are mostly phenolic as kk evidenced by the marked decrease of intensity upon acetylation. The broadness of the band suggests, then, that coal is a complicated mixture of high molecular weight compounds containing hydrogen bonded phenolic functional groups. Absorption near the 3000 cm 1 region is due entirely to C-H stretching vibrations. The aromatic C-H stretching vibration produces bands near 303O cm 1 , They are generally three in number for single ring compounds and are weaker than the saturated C-H stretching band absorbing below 3000 cm 1 . For multiple ring compounds a more complex pattern is produced. We note from the figure that three prominent peaks are seen along with small shoulders on either side. Aliphatic C-H stretching vibrations can be differentiated into CH^, CH^, and CH absorptions. The CH^ absorption appears as two strong - 1 -1 -1 bands at 2962 cm and 2872 cm + 10 cm . The CH2 absorption gives rise to two bands at 2926 cm"1 and 2853 cm"1 + 10 cm"1. The CH group gives a weak band at 2890 cm 1 . From Figure 6 we may suspect that CH^ CH^ hidden by the large CH^ absorption. Review section. The values obtained are as follows: - ~ - 3400 cm-l and chelated intramolecular hydrogen bonded OH extending -1 • These OH groups in coal are mostly phenolic as 44 evidenced by the marked decrease of intensity upon acetylation. The broadness of the band suggests, then, that coal is a complicated mixture of high molecular weight compounds containing hydrogen bonded phenolic functional groups. -1 Absorption near the 3000 cm region is due entirely to C-H stretching vibrations. The aromatic C-H stretching vibration produces -1 bands near 3030 em . They are generally three in number for single ring compounds and are weaker than the saturated C-H stretching band -1 absorbing below 3000 em For multiple ring compounds a more complex pattern is produced. We note from the figure that three prominent peaks are seen along with small shoulders on either side. Aliphati~ C-H stretching vibrations can be differentiated into CH 3 ' CH2, and CH absorptions. The CH 3 absorption appears as two strong bands at 2962 cm-l and 2872 cm-l ± 10 cm-l . The CH2 absorption gives rise to two bands at 2926 cm-l and 2853 cm-l + 10 cm-l The CH group gives a weak band at 2890 cm-l . From Figure 6 we may suspect that the CH 3 group is absent in the coals studied or is in slight amount relative to the CH2 group. The CH group is not apparent but may be hidden by the large CH2 absorption. These C-H stretching band intensities can be used to obtain hydrogen aromaticity values as has been explained in the Literature Review section. The values obtained are as follows: 39 - 1031 1007 Spring Canyon Coal 1 . 1 32 1 . 51 1,5k Thus the lower the volatile content, the higher is the concentration of aromatic hydrogen. It is not possible from the infrared spectra to make an estimate of much reliability concerning the presence, absence, or amounts of alkenes, allenes, or alkynes in the coals. Most of the characteristic absorptions are in places where aromaties or alkenes absorb strongly. Probably acetylenic materials are not present because of the absence - 1 of the C=C stretching absorptions near 2200 cm • The allenic C=C=C stretching absorption (1950 and 1060 cm is not obvious and the 1680 - 1620 cm"1, 1310 - 1295 cm"1, and 970 - 960 cm"1 alkene bands do not show strongly. These facts, along with the fact that the whole spectrum can be explained well by considering only aromaties and alkanes, suggest that these structures essentially make up the whole coal molecule other than oxygen containing functional groups. It might be further supposed, since CH^ groups are assumed in slight amounts relative to CH^ groups and there is evidence for very few long 6k chains in coal, that saturated CHg groups comprise closed cyclic systems for the most part. If we assume no alkenes or allenes, the three small peaks between - 1 -1 2000 cm and 1750 cm can be assigned to overtone and combination tone bands of aromaties. Unfortunately, the carbonyl stretching absorption - 1 obscures the 1700 cm area, but 1700 cm - 1 we can use this area pl uisf wteh ea s10s0u0m et oon e65 Omo rcem -s1 maalndl p1e2a2k5 atto 950 cm - Ha IH s = 1..132 BCR No. Ha IH s = 1..BCR No. Ha IH s .- 1..54 hydrogen, " ' allenes:. aromatics of the C=C stretching absorptions near 2200 em-l . The allenic ~C=C stretching absorption (1.950 and 1060 cm-l ) is not obvious and the 1680 - 1620 cm-\ 1310 - 1295 cm -\ and 970 - 960 cm-l alkene bands do not show strongly 0 'These facts, along with the fact that the whole spectrum can be explained well by considering only aromatics and al.kanesp suggest that these structures essentially make up the whole coal molecule ot.her than oxygen containing functional gr'oups. It might be further supposedJ since CH 3 groups are assumed in slight amounts relative to CE2 groups and there is evidence for very few long chains in coall 64 that saturated CB2 groups comprise closed cyclic systems for the most part. allenes) 2000 cm-l and 1750 cm-l can be assigned to overtone and combination aromatics. Unfortunately} obscures the 1700 em-l area, but if we assume one more small peak at 'em-I plus the 1000 to 650 em -1 and 1225 to em-1 - 40 - region to estimate the aromatic substitution pattern. The arrangement of absorption peaks between 2000 and 1750 cm 1 fits only the mono and 1, 2. substitution pattern. The mono substitution pattern is consistent with C-H out of plane deformation peaks from 770 to 730 cm 1 and 710 to 690 cm 1 . The 1 , 2, 3 pattern is consistent with 780 to 76O cm 1 and 7^5 "to 705 cm 1 peaks. The arrangement of peaks in the 1225 to 950 cm 1 region, which are the C-H in plane deformation absorptions, is closest to being consistent with the mono, meta, or 1, 2, 3 patterns. Since we have out of plane deformation at 7^5 cm 1 and 695 cm \ the mono substitution pattern appears the most likely from the infrared spectra. The 1 , 2 / pattern seems most likely from the present knowledge gained from X-ray investigations.^1 The 1 , 2, pattern could correspond to condensed ring structures. The necessary peak shift is, of course, easily possible. If the mono pattern is the major one, there must be many condensed rings also present in order to be consistent with the large carbon-to-hydrogen ratios. In this case, the 700 and 750 cm 1 peaks would be strong as observed since most of the aromatic hydrogen would exist in this form. The pattern of three prominent aromatic C-H stretching peaks near 3000 cm 1 also suggests that mono linkages may be present. The band at 1715 is exactly in the position of a non-hydrogen bonded ketone C=0 stretching absorption. The 1600 cm peak has received much attention. Aromatic C=C 53 stretching absorbs here. However, it has been shown that quionone oxygen, hydrogen bonded with a neighboring phenolic hydroxyl gives absorption at 1600 cm The apparent double peak observed is ascribed o~ cm-l ~its only the mono and 2, 3 -1 H o~ and -1 em • The 1, 2, 3 pattern is consistent with 780 to 760 cm-l and 745 705 cm-l peaks. The arrangement o~ peaks in the -1 region, which are the C-in plane deformation absorptions" l.S patterns, o~ 745 em -1 -1 ) infrared. 1, 2, 3 ~rom ~rom investigations. 61 . 1, 3 shi~t is) hydrogen -1 700 750 em peaks would be strong as observed since ~orm. o~ H 3000 cm-~ also o~ O cm-l stretching absorbs here. However, it has been shown53 that quionone oxygen, hydrogen bonded with a neighboring phenolic hydroxyl gives -1 absorption at 1600 cm . The apparent double peak observed is ascribed - 41 - herein to this effect. The sharper assumed C=C peak is seen to extend below the broad hydrogen bonded phenolic peak. These observations raise another question concerning the coal structure. Are the aliphatic carbonyls free from hydrogen bonding as indicated by the 1715 cm 1 peak? If so, hydrogen bonding exists for both hydroxyl and carbonyl oxygen only on the aromatic part of the coal molecule. The sharp peak at 1940 cm 1 is simply another skeletal aromatic C=C in plane stretching vibration. The sharp peak at 1.445 cm 1 is caused by C-H bending in both CR"2 and CH^ groups. An indication that the earlier assumption of small methyl concenr tration Is justified Is seen from the small size of the 1370 cm 1 symmetric deformation peak which is normally strong for appreciable methyl concentration. In order to be consistent with the hypothesis advanced above, that saturated cyclic structures are present, we should observe some characteristic absorptions arising from saturated ring deformations. The peaks at 1020 cm 1 and 900 cm 1 appear to fill this need and since the absorption of saturated ring deformations are quite non-specific, |these could be due to anything from cyclopropane to cyclohexane. The only peak left to discuss is the 550 cm 1 peak in a range l^ery infrequently studied. This peak may be due to skeletal vibrations or perhaps a methyl group frequency or both. -1 peak? If so, hydrogen bonding exists for cm-l is simply another skeletal aromatic -1 1445 is caused by C-H bending in both CH2 CH 3 concen~ is is cm-l -1 -1 1020 and 900 cm appear to fill this need and since absorption of saturated ring deformations are quite non-specific, could be due to anything from cyclopropane to cyclohexane. cm- l peak in a range k2 B Spectra Figure 6 shows spectra of B obtained from flashing Spring Canyon coal at 1500 volts and at 3000 volts. No differences are seen between these spectra and the coal spectra of Fig. 5. All that has been said for coal could then apply to B, except for the H /H values. a s Figure 7 shows the spectrum of B compared to the spectra of materials obtained by the high voltage flashing of B which has had all the Y removed by benzene and acetone washings. Part of the product material forms the gossamer strands spoken of above and part of it forms a uniform'film on the tube walls. Only micro amounts of a material resembling Y are formed. Its spectrum is discussed later. Again the spectra appear the same for the film, the gossamer material, and the starting material. The only differences are the H /H values which a s are as follows: B from Spring Canyon Coal H /H =1. 70 a s Gossamer reaction product • Ha/Hg = 1.68 Film reaction product - H H - I.76 a s Coke Spectra Figure 8 shows spectra of coke from Spring Canyon coal, B formed from flashing Spring Canyon coal at 1500 volts and 3000 volts. The higher voltage B did not consolidate into a coke as has been discussed. The KBr pellet used to obtain curve B became cloudy due to moisture absorption during the run and so curve B is not a perfect spectra. .'It does, however, show all the peaks even though they are a little obscured. The spectra show in general that coking at 950°C does not change the absorption pattern. - 42 - H a s Figure 7 shows the spectrum of B compared to the spectra of materials obtained by the high voltage flashing of B which has Aad all the Y removed by benzene and acetone washings. Part of the product material forms the gossamer strands spoken of above and part of it forms a "W1iform film on the tube walls. Only micro amoimtsof a material resembling Yare formed. Its spectrum is discussed later. Again the spectra appear the same for the film, the gossamer material, and the starting material. The only differences are the H /H values which a s are as follows: B from Spring Canyon Coal Ha /H s :;:;; 1. 70 Gossamer reaction product Ha /H s = 1.68 Ha /H s :: 1. forme~ It - 43 - Y Spectra Figure 9 is a comparison of different solution fractions of Y obtained by flashing Spring Canyon coal at 3000 volts and washing the solid products with acetone and benzene in different orders. If the reaction vessel is washed out with cold benzene and the slurry obtained is filtered with more benzene, the benzene-soluble materials obtained give the infrared spectrum AO Curve B is obtained in the same way using acetoneO After all the benzene-soluble material in the first case has been washed from the solids on the filter paper, the solids are washed with acetone. This acetone-soluble material gives curve C. Curve D is obtained by a second washing with benzene of the solids obtained from using acetone as the initial solvent. The solution was evaporated on a NaCl disk leaving a coating of YO The disks were used to obtain the spectra. All the acetone was assumed gone because of the absence of peaks at 900, IO85, 1400, 3^00, and 36OO cm 1 in most of the Y spectra. Chemical reaction of solute and solvent cannot be ruled out, but it seems unlikely at room temperature. It can be noted regarding especially the 0-H stretching and the aromatic C-H stretching regions of the Y spectra that whereas the acetone 1st and 2nd curves are quite similar, the benzene 1st and 2nd curves are quite different. Apparently the acetone will dissolve most of the aromatic material leaving little for the benzene. Both the 0-H and aromatic C-H peaks are essentially absent from curve D. This is an indication that the assumption of all hydroxyl groups being phenolic, made previously, is valid, for Y at least. That benzene will dissolve some aromatic material is evidenced by the absorption in the aromatic differ'ent A. acetone" ''with "by Y. 1085, 3400, 36 0 0 em -1 in most of the Y spectra. Chemical reaction of solute O-R R O-R R evi,denced - hk C-H stretching region in curve A« All the aromaties will not dissolve in benzene as is seen from curve CO An important difference between the Y spectra and the coal and B spectra is the great difference in aliphatic hydrogen content. The aromatic C-H stretching is simply a shoulder on the very deep aliphatic C-H stretching peaks. The structure of the aliphatic peak also indicates that some CH^ groups are present in Y whereas they were only slightly detectable in coal or B, The hydrogen aromaticity values for these curves are as follows; Y benzene 1st H /H 0.106 a! s Y benzene 2nd H H = 0.077 a s Y acetone 1 S T H /H = 0.186 -- a! s Y acetone 2nd H /H = 0.099 a s The aromatic overtone and combination tone peaks between 2Q00 cm 1 and 165O cm 1 are absent due to the small aromatic hydrogen concentrations, The peak near 1700 cm is the carbonyl oxygen characteristic absorption. It occurs at 1690 cm M and is small for both curves A and D. It occurs at 1715 cm 1 and is strong for curves B and C. The shift from 1715 to 1695 cm 1 could possibly be due to attachment of the carbonyl carbon to an aromatic ring. The benzene-soluble material shows only a weak l695 cm 1 peak while the acetone-soluble material shows the 1715 cm 1 peak with a small 1695 cm 1 shoulder. Curve D has a considerably diminished 1600 cm 1 peak which taken along with its slight 3030 cm 1 peak suggests that the 1600 cm 1 peak is at least in large part due to aromaties for these materials. The aliphatic C-H 44 - A. aromatics C. CH 3 coal. B. hyCl.2'"ogen follows~ 'Ha Hs = Y benzene 2nd Ha /Hs = 0.077 y acetone 1st Ha /Hs = 0.186 Y acetone 2nd Ha /Hs = 0.099 anc~ 2000 -1 1650 em-l are absen1:; due to the small aromatic hydrogen concentrations. - 1 The peak near 1700 cm is the carbonyl oxygen characteristic absorption. -1 It occurs at 1690 cm and is small for both curves A and D. -1 It occurs at 1715 em and is strong for curves B and C. The -1 shift from 1715 to 1695 em could possibly be due to attachment of the carbonyl carbon to an aromatic ring. The benzene-soluble material shows only a weak 1695 cm-l peak while the acetone-soluble material shows the 1715 cm-l peak with a small 1695 cm-l shoulder. Curve D -1 has a considerably diminished 1600 em peak which taken along with its slight 3030 em-l peak suggests that the 1600 cm-l peak is at least in large part due to aromatics for these materials. The aliphatic C-H - 1*5 - bending peak at lV?0 cm 1 is understandably strong in all curves. The last recognizable peak in the A and D curves is the 1370 cm 1 CH^ symmetric deformation peak which is stronger in the benzene extracts than the acetone. This CH^ peak is also more intense in the Y spectra than in the coal or B spectra. The complicated system of absorption between 1300 and i+000 cm ^ is explained most reasonably as absorption due to the ketone type of molecule, possibly from some motion of the carbonyl group coupled with the rest of the molecule. Aliphatic ketones usually give bands in the 1 3 2 5 to 1215 cm 1 region and aromatic ketones in the range 1225 to 1075 cm \ These bands are quite non­specific. Since the bands extend down to 1050 cm 1 for curves B and C and since curve B also shows aromatic C-H out of plane bending absorption at 730 and 800 cm we conclude that these ketones are connected to both aliphatic and aromatic structures albeit the small H /H values that a s must exist. The acetone 1st curve (B) shows more cm 1 shift. Since this shift is small and many other cm 1 absorption bands. dif­ferent substances. Figure 10 shows Y obtained from BCR No. 1031 and No. 1007 coals. Acetone was the first solvent used in both cases. In general, these spectra show the same relationships as have been pointed out for the Spring Canyon Y. The main differences are the larger relative depth 45 1450 cm-l is understandably strong in all curves. The -1 em CH 3 CH3 1300 4000 cm-l 1325 -1 region and aromatic -1 1075 non-specific. -1 em for curves Band eurve 730 800 cm-l , connected to both aliphatic and aromatic structures albeit the small Ha Hs B) peaks in the aromatic range than the acetone 2nd curve. The above reasoning is directly in contrast to the explanation proposed above -1 of the 1700 em shift. Since this shift is small and many other reasons could be proposed for it, we accept as most likely the ketone explanation for the 1300 to 1000 cm-l absorption bands. The differences in the curves show that Y is a mixture of dif-ferent 46 of the aromatic C-R\ stretching absorption to the. aliphatic and the presence of an additional large peak at 1 1 1 5 cm 1 . This peak Is likely-due to the ketone system but because of the non-specific nature of these absorptions an estimate of its specific cause will not be attempted here. It doesn't appear to be caused by aromatic linked ketones because of its presence in curve A. Another possible explanation could be de­formations of closed aliphatic rings. For the benzene-dissolved materials the absence of peaks at 3030 cm- 1, 1600 cm"1, 150Q cm"1, and the 700 cm"1 to 900 cm"1 region is more obvious than before and clearly indicates the lack of aromatic material available for benzene to dissolve after the acetone^wash has been completed. Figure 11 compares Y obtained by flashing Spring Canyon coal at 3000 volts, flashing B from Spring Canyon coal at 3000 volts (termed ^ f and Y»), and flashing B' at 3000 volts (B" and Y"). The materials ere obtained by washing out the reaction vessel with acetone. Curve B s, from Y" and C is from Y' compared to Y as curve A. Curve C appears similar to curve A except for the high frequency range where relatively sharp peaks appear at 3500 cm and 3^30 cm . This may indicate less antermolecularly hydrogen bonded polymeric phenolic groups and more inter and intramolecular single bridge hydrogen bonding. The 3^30 cuT1 peak may be due to 0-H stretching or to N-H stretching since the nitrogen content of Y' is larger than that of Y. The Y" spectrum shows the same high frequency absorption as Y'. Y" shows no aromatic hydrogen and no carbonyl oxygen. The main absorption appears to be at 1615 cm"1 which could indicate C=C stretching. These materials may represent a more tightly held substance on the Y-B intervace. The spectra appear - h6 - o£ H. aliphatic anq the o£ 1115 -1 This peak is likely due k~tone system but because o£ the non-speci£ic nature of ~ o£ speci£ic beca~e o£ curVe d~~ £ormations o£ benzene-d~ssolved o£ em-I, cm-l, 1500 cm -1, cm-l . -1 cm t.han ind;l.cates the the acetone "vol ts.~ Spr:Lng term~d Y') .. and flashing B' at 3000 volts (Bit and y"). The materials B and C is from Y' compared to Y as curve A. Curve C appears £or sha~rp 3500 -1 34 3 0 -1 • intermolecularly 3430 cm..,.l O-H y" y" no 1615 cm -1 could indicate C=C stretching. These materials m~ represent a more tightly held substance on the Y-B intervace. The spectra appear - kl - different from both the Y and B spectra but more similar to the Y than the B spectra. Figure 12 compares Y from initial benzene solution (curve A) with a benzene-soluble material obtained by treating the reacted coal with cold benzene just as the B and Y mixture from the reaction tube is treated (curve B), the benzene-soluble portions of a low temperature 400-800°C) coal tar (curve C), and a clear colored oil which appeared to separate from the Y after the solvent was evaporated off in a 100°C solvent evaporation flask (curve D'). The spectra are complicated and an assignment of the various individual bands will not be attempted. In general, the following observations and conclusions can be made: 1 . The structures of all four of the materials are quite different. 2. The low temperature tar and the benzene-soluble coal extract spectra contain sharper, more distinct aromatic C-H stretching peaks than the Y spectrum, possibly indicating less highly substituted rings. The out-of-plane deformation peaks of curves B and C also indicate this. 3. The low temperature tar contains relatively more aromatic hydrogen than the Y. - 47 - (4oo-8000 c) solvent evaporation flask (curve D). The spectra are complicated and an assignment of the various individual bands will not be attempted. In general, the following observations and conclusions can be made: 1. soluble H Band FREQUENCY {CM'1 Fig. 5- Infrared spectra of coals, curve B - BSE No. 103l7 c^e C - S A " ***** ^ • "_ ~.~- "- 'II" $ .k. • , v.v i ~I y,11 , i I I I I I ! -/ I I +- r- j- I , -+ - 1- ~+-- ~ 1 f -- I I I I i'\ I f"'\. ~ NJ l- _~l I i V -f ~ It f--1~ ·V I 1- --+- -~ I ! 02 , ! --r . ~- -J-~ ~~= ~I I i I---- <U~ --1 - -- J-- - I "': I II ! , : i?! V ;:::: I I I J, .1/- I In \ i/ I 0.6 J I iJi ! -~ / h, ~-~-t I t-·-----+--.--1! -- -'T i -1I --- ---t- 0.4 I I I f--- fn- --~ '--V -+ It ! i rk t-, ---4-~- r---" V .. - - 1 I /1 i\ \ fi j I I I I I 61~· . - t-'"" '/ -", I , I. I I - --+-t I \ !, I f -i- i : i ~ O.S ----r i I [) [ , I i I I 1.0 \ j : \ ! ! 1/ --- I I' ,I . I I I I i J i :'.1' 1.5 , 1 I I I L __ L ULli ~ .J I , I -- iII i 3500 3000 ~ 2000 1500 1000 FREQUENCY (CM1 ) Fig. 5· lni'rared spectra ot: coals, curve A - Spring Canyon COal, curve B - BCR No. 1031, curve C - BCR No. 1007. \ fl~ i I ~, J 1;1 Y I j Yr J.-I\ ~t t! 1- Vt II: ' +-~- ,II \ I \,1 1 ..li.j JL I .1 I I ! PERKI' I 5 00 Fig. Infrared spectra of B flashed at high and low voltages; curve A-B from 3000-volt flash, curve B-B from 1500-volt flash. -- - 100 I ~ / r ,/ rv 1\ /"" r-. II /11 \ /' \ HI ,/ / ~I ~ 80 /'\ 80 I -~-Ll - - - 11 r ../ p ~ ( \ I ~ ..J \ V" f \ Ir ~v h V - r---.. - -- ~-----I - -~ ~-- -- _.- . -- - ~ ~ - ~v --< p ~ r .......... - ~ [- - -- -- c---- -- \ 60 V 60 ---r~ If r:-- 'I V i "" --- -_. .. II l • 1 /" ~ ru I V \ ..-.. L ,/ '" ./ U \~ J L I~ ~ / / 1\ 1\ II l, ,J , "- If - - \ \,., / I I 40 40 \ I / \.. J -- 20 20 -T~ - --- -~ -- 0 I 3500 3000 2000 : 1800 1600 1400 1200 1000 800 FREQUENCY (CM:if FREQUENCY (CM-1 ) 6. volt l500-voltflash. - f \ I \ \ / 1\ I ~ U 600 Fig. Comparison of B and the product from flashing B (B 1); curve A-B spectrum. Curve B - spectrum of B1 forming goassamer strands, curve C - spectrum of B1 forming wall film. , , I I II I ( Ij 80 80 ..... 1- ~I-- ,- - I-- r-- (\ 1\( / r-. .L'- t-- 1 lC ~ II II t- ~ ,....., 1\ Ir II I'-.. J.J I 1'- J 60'- III 1'- r-- v t-" \ \ I-- c- If 20 20 l/ --l-f- E r ( "n k- I ( t'-- J...-': II I, II 1'- LL 0 I'1Vl II [/ IU 1\ ,f" Ir J 11'1 II U I \..l{ , r-- 0 V 80 , If ..& " "'"' t-: Ifl'l "= .L 160'" '-'111 V ..-f-r- -r ,- - ~ n I { I- It\h ,/ II 1i1 f-- I-- f-- - -I-- '" \ t- \, 1\ '0 ~ 1 I-III I--r 1-1-- 20 -f-- I I I-- I 20 i I i 3500 3000 20 00 FREQUENCY (CM') 1500 1000 7. Band (' ); B' strands) B' . .L jJ I -t--- l , '\ l I 01 -.1 60 1-U I Ir\AO I' I' II II J 20 \ i j I 0 f1 /\ \ II \. I-e-- -t- r-- t--- AO e-- 20 5( o \J1 o Fig. 8. Infrared spectra of coke. Curve A - spectrum of high voltage B subjected to coking test, curve B - spectrum of coke from low voltage B, curve C - spectrum of coke from coal. - , , -=- , -- - -f- { - ...... A /"' In \ /' \ /11 - r-- r-+ /'If ~ \ ~ ,..-'-' .r If I /." III, I ~ \ " I ")~ ~ '-r '\ '" 80\ I \ i .....- I ,/" -- \ J I \I \1/ \ J Y ::-~ I\, -/ - V'\ I I / /-- L--- 60 v--. 60 Ie \ :--- i V /l \ III r II \ I I.., V I II "- fJ IV f-- Vi \ ........ r-- ( \ / I-- - / r- f-- - "\ ( 7 l/ .0 40 1/ '--f-- \ '--- I 20 ....,.. '--- ,.,.... ..,.-. ~ ~7 (-t~ - ~ ......., - 20 '-- / - - t I / \.( l ( - '-- - - '---"}' - I If J L H-L--- l---j ~ i 1 - f-- 1---1 f-- /-- 1-----, f- 0 0 '- ./ THE PERKIN - ElMER CORP., NORWALK, CONN. 3500 3000 2000 1500 1000 FREQUENCY (CM-') 10\01 C 500 Fig. 9* Comparison of Y spectra from Spring Canyon Coal. Curve A - material dissolved with benzene first, curve B - material dissolved with acetone first, curve C - material soluble in acetone after benzene was used, curve D - material soluble in benzene after acetone was used. ;;;~ i.e.$ _ , ffi.U _H1f. .L~ I ; i I -t- ........ i 1 ........ ,~ -f--r 1\ b I 1 f J- II- - - t- j --~ I 02 i -l- r-.,'I - I-- 1 1 - j I i"- e---- I 1/1 I u ! r--... B I I Y N li., i 1/ D.' I! V - J I f' " I U i l"- ). h- WI! I ~ i vV i IIIJ I i-I---- 0 .• ,. ,] " r 1.0 I ,I, i , I ! I I ~ 1 ,..., I 30m 3500 j U- A--- _~_IAj- E[- I I 1 : hi i J-- /i I-I I j-_. r-·-r-·_· :1 ! I ! I vIIr Ir! - ! j;;1-- i_~ -r I I f+- ->] =1= ! 1--1- ¥ i VI L- I ---t- - I I I I i I I i : ,, I I 1 ! [ ! I I _L._ -- ! FREQ 2000 UENCY (CMI) 1\ U ~ '\ t-h I V I Pli -i- I I ~ I. 1I.l j--~ \ 1\1 N II J\ I \ I : U ! ! I v- I h I ........ 1-" t I If' I VVIi r ' I~ VIv -- r--r- J- 't 2 U t- -- I J I V-I----i'- ir : 'v1 L l'l D .• J .1' J.I I I Iii f If \ JJ-'l -.J U I" v, VI VO 1/\ V~ }, \ i -.ill IV 11 i 1/ ' . j ilo.V lL I I I 1.0 W,I, r \j ~ I 1500 1000 9. -yri th .laS I I \. rf-' ..-j--. I "-v- I IV ! I I v- ~ l.; 1 ! i ! ~ I I PERKI Vl I\) 3500 3000 2000 1500 1000 500 F i g . I n f r a r e d s p e c t r a o b t a i n e d c o a l s . s o l v e n t ; a c e t o n e f i r s t s o l v e n t ; s o l v e n t; c u r v e a c e t o n e f i r s t s o l v e n t. , , '00 , F::::: / A VI -- Ir" I"\, I, 7 B'" .-- I \ \.. / "- / II II If -I "- 80 ;r- 80 1\ J "- v \ II / 1\ fJ r- 1\ I"';: , Uj.-- 11/ '-v-- /' F 1.7 p 1\ n 1\ D " ~ 1\ :..--' "- 1\ /' r--- ~ lr\ .60 '~60 f-... _f-- / If\. I \ - I { "'"\ If"I 11\ 1II \ In 17 I 1L.h. AO 1\ II r I h o I II \ II rJ 11\ iJ " h I IJ ! / II nl II 1\ rT\ II \ } \ v 1\ Vt- 20 v II I ~ It \ -= D 20 k II / \ ( I h II -III \J II II I 0 1\ 0 IN IV 0 THE PERKIN - ELMER CORP., NORWALK, CONN . 1 FREQUENCY (CM') Fig. 10. Infrared spectra of Y obtained from BCR No. 1031 and No. 1007 coals. Curve A-Y from 1007, benzene 2nd solvent; curve B-Y from 1031 acetone first solvent; curve C-Y from 1031 benzene 2nd solvent; curve D-Y from 1007 acetone first solvent. . 1 V1 UJ 0 2 \ 5 s \ \ N 4 1 1 \ f v\ r J 0 6 / \ w 1, \ i ^ 0 8 \ 1i1.5 oo 3000 2000 CM"1) 1500 1000 500 F i g . 1 1 . I n f r a r e d s p e c t r a of Y o b t a i n e d by f l a s h i n g c o a l , B, and t h e r e a c t i o n B ' ) « M a t e r i a l s d i s s o l v e d i n acetone f i r s t . c o a l , B~Y f l a s h i n g curve f l a s h i n g -I---l - [\ .... \ \ -~ v.v I v.v ~ f"- v-I-- I-- ~ \ '" I'-- V I--'"" I'-~ I I 1/1\ hI 0.2 II II u 1\ / \ "'\ '2\ r\ , ' 1/ I-- 1-- f--- I I 1.1 lL II = ~ " 1:::1. ---- ~ v-~ V I-t- V t- .\ IrY I-----I----- " I r V b::::> v.- \.. II . 0.' V I L _c-+-- l \ r ~ 0.6 ./ """"-- I r \ Irl\ 0.6 l1\. !:::: r-- I li , \ I ~ - 0.8 I II \ ) \ 0.8 \ v • nfII.. ' .0 1.0 ,I, \ 1/\ 1.5 00 - 00 I 3500 FREQUENCY (CM') Fig. 11. Inf'rared spectra obtained flashing coal, and the reaction product from B ( B'). Materials were dissolved in acetone first. Curve A-Y from coal, curve B-Y from flashing B' (Y"), curve C-Y from flashing B. V t--i' !-J ---l-f---. v J...- I '- 1/\ J 1'--. II \ / -I r./ V PEAK'" . Fig* I n f r a r e d 1 s t A; e x t r a ct u s i n g cold B; b e n z e n e - s o l u b l e , t e m p e r a t u r e t a r Cj c l e a r o i l t h a t s e p a r a t e d h e a t i n g t o 1 1 r-r--K f-'- F--- ....... r--.., V I' -- " I ..r- '\ ....., V'-" "-v-eo "" 1::1. vr 80 \ / r1 1'-1-- \ II B lr ~ r.... \ ~ -, ....... 1/\ bO ~ II ..-- \ I 1\ r.. / , \ '\ / \ / \ \ '\ 1\ II \ .., ./ 1\ J ~ r-->-- If ) \.. " II "'- I \ n .., '\n j\ In I /11 /1 \ V-A \ / \ In '\. '~l 1/\ ./ V i\ \ \ Ii\ I' \ I I 1\ n IJ T I \ "- ;,- -... III I v ,,' 10 "- I'-.. j .., I ~ , \I 1 ]; 117 n I \ t - - 20 (1 \ I t I \ I I r.I 0 0 \ \. THE PERKIN - ELMER CO I 3500 3000 00 1500 1000 Fig . 12. Infrared comparison of benzene 1st Y - curve Aj coal extract using cold. benzene - curve Bj benzene-soluble, low temperature coal tar - curve C; clear oil that separated from Y upon heating to 100°C - curve D. 1 v-r h v .f\ ~ II / P., NQRWAl V1 V1 - 56 - Formation of B appearing reaction we gossamer and material the tube coal. formed apparently have a high surface energy for they quickly come together to form these dendrix.es or gossamer strands. The variable voltage experiment, which shows that the above effect does not occur until a certain energy of flash is reached, indicates that it takes a considerable energy input to separate these smaller particles. The fact that Y comes out before shows that at least part of the Y comes out at lower energies. B was separated from Y and fractionated according to density (Fig. k.). Each density fraction was viewed in the electron microscope in order to determine how the particle size and physical buildup of the particle varied, if at all, with density. It was found that no trends with density could be observed. However, interesting fine structures of individual particles were observed. These are seen in Figs. 1 3 and iK. Fig. 13a shows the appearance and size of the majority We have discussed the appearance of the reacted coal. When a transparent-appearing glass tube with just a small amount of powdered coal becomes opaque after reactionl-re must assume a change in particle size. The extreme difference in appearance between a reacted and unreacted tube suggests that many small particles were formed from each coal particle; these particles then coat the walls of the tube. The formation of gossa.rner strands and. the fact that the infrared spectra of the ma.terial coating treV0.be walls and the gossamer strands are identical and similar to the coal spectra suggest that chemically not much is happening to the coaL The small particles that are being fonned -t,hese dendri -r,UJ:' volt8ge exper5,m'2n~~d whi"ch ocellI' a. c erl-:,ai.n 4.). Of allJ observed, 13 14. l3a - 57 - 13b micro­scope build­up of 13a form on the tube walls, as has been discussed. In one experiment B was flashed at 3500 volts and the film showed interference colors. Most of the film showed a yellow color, but some blue, red, and another yellow were observed at the neck of the tube. The thickness of the film, based on optical interference, is given by the formula: where p. refractive index, X wavelength of yellow light, and b order 60 ° of reflection. For yellow light, X is A. The refractive index for coal is about 1.75* If we assume first order reflection, we have o t = 316 A. This same film when obtained whole by floating it off the glass with water and viewed by the electron micrscope showed a very interesting grain structure. This is shown in Figures 13c and lk. Figure 13c shows the complete film and Fig. iK shows a blow-up of a small area from Fig. 13c. We see that the particles are spherical 0 and on the average about 350 A in diameter. From the optical estimate we then assume the film to be only one particle thick. This correlates well with the sizes reported from solvent extraction as has been dis­cussed in the Literature Review section. The infrared spectra of this t of the material observed. Fig. l3b shows an unusual type of particle. This type of particle was observed infrequently when scanning the micro-scope field. These particles appear to be dendrites and their presence suggests very strongly that the larger particles formed from the build-up of smaller particles. The fine structure on the right side of Fig. 13a suggests this also. If coal or B is flashed at high voltages, a film of material will 3500 vults colOrS. of t = (2b - 1) A 4il ~ = A = = 0 A 2209 1.75. t = 316 A. This same film when obtained whole by floating it off the glass with water and viewed by the electron micrscope showed a very interesting grain structure. This is shown in Figures l3c and 14. Figure 13c shows the complete film and Fig. 14 shows a blow-up of a small area from Fig. l3c. We see that the particles are spherical o and on the average about 350 A in diameter. From the optical estimate we then assume the film to be only one particle thick. This correlates 'well with the sizes reported from solvent extraction as has been dis-cussed in the Literature Review section. The infrared spectra of this Fig. 1-3• Electron microscope pictures of B: (a) and (b) particles from inside reaction vessel, (c) film formed on reaction vessel vail when B was flashed at volts. - 58 - (a) Scale: I ' , , , I ~ 51J.----- 13. - waIl 3500 Fig. Ik, Blowup of a small area from Fig. 13c. material is the same as other B spectra and similar to the coal spectrum. o If we assume coal to "be made of spherical particles of diameter 35° A, these will give a pore diameter of about 1^0 A, As has been discussed in the Literature Review section, coal has a large and small system of pores. At increased pressures mercury can be forced into the larger system, coming to a constant value of penetration at high pressures. This amount of penetration can be correlated with a pore diameter o somewhere below 200 A. This method and the calculations involved are 28 discussed by van Krevelen. - 59 - Scale I .. "!',,,iI 0 o 1000 A 14. 13c. spectr~ o If we assume coal to be made of spherical particles of diameter 350 A, o these will give a pore diameter of about 140 A. As has been discussed in the Literature Review section, coal has a large and small system of pores. At increased pressures mercury can be forced into the larger system, coming to a constant value of penetration at high pressures. This amount of penetration can be correlated with a pore diameter o somewhere below 200 A. This method and the calculations involved are 28 discussed by van Krevelen. The density fractions of B were also ashed in order to determine if a variation in ash content occurred. It was found that all the density fractions contained about the same quantity of ash and no trends were found. Elemental composition, heats of combustion, and particle size distribution were also measured for each of the density fractions. No trends with density for these properties were observed. From the above observations we conclude that coal is composed of colloidal sized spherical particles of B which upon flash heating become separated from each other and immediately begin to coalesce into a wall film and large (gossamer strands) and small (Fig. 13b) dendritic structures. Formation of Y In view of the facts reported above, Y must not form from some homogeneous coal, substance but must form from some initial yellow material that is at least similar in color while it exists in the original coal. Moreover, Y is distinct physically and chemically from a black colored material termed B that makes up around 60f> of the coal substance. Y makes up the balance of the weight of the coal. There is good evidence that B consists of roughly spherical particles o o of diameter 300 A to 350 A in the original coal structure. In contrast to the above postulates it might be postulated that the Y is formed not from a heterogeneous mixture of Y and B but from a single material that makes up a homogeneous coal substance. - 60 - 'that all the ash and no trends were size No flash heating become to into a l3b) dendritic Fc,Ti1l.a.tion repo:rted above) coal original and chemically from around 6~ of the the weight of the coal. particles of diameter 300 A to 350 A in the original coal structure. In contrast to the above postulates it might be postulated that the Y is formed not from a heterogeneous mixture of Y and B but from a single material that makes up a homogeneous coal substance. 6l It might further he postulated that Y is a pyrolysis product differing from B due to higher temperatures in some portion of the homogeneous coal substance. Another postulate might be that B and Y form from the same starting material (coal) but are created through different but com­peting reactions. However, if the original coal were completely homogeneous, it would be difficult to explain the fact that the bituminous coals used in this work when finely ground show a very real and distinct yellowish cast or tinge of color which they lose after being flash heated. Moreover, along with this yellow cast these coals lose their ability to coke after flash heating. This loss of the coking property is pro­portional to the yellow cast remaining with the coal (coals flashed at very low energies retain some yellowish color; coals flashed at very high energies are completely black), as has been discussed previouslyn If Y were a pyrolysis product formed from homogeneous coal due to higher temperatures, say at the surface of a particle, then the core of the particle which would remain as coal should retain the color and coking properties of the original. The black residue should also continue to form Y upon further flashing. This does not occur. If B and Y form from the same starting materials via competing reactions, we should notice: (l) a variation in yield of both products when input energies are varied, (2) considerable variation of infrared spectra between the starting material and both products, (3) no similarity - 61 - be explai.n yellOiv remai.ning previously" reactions; 1) Similarity in physical structure between the starting material and both products, and (k) for a reaction in which high energy inputs are involved and for a high carbonaceous fuel like coal we would expect such a reaction to yield carbon as one of the products. In fact, however, for all voltages above about 1800 volts the same yield of B is observed within the limits of material balance accuracy (see Table 3)» Below 1800 volts the B retains some yellow color and some coking property, thus indicating that it still contains some Y« The infrared spectra of coal and B are strikingly similar. The main difference is the ratio of peak heights of aromatic and non-aromatic hydrogen* This fits the heterogeneous coal postulate if the Y can be supposed as similar in structure to B except containing a more saturated carbon skeleton. This has been indicated by structural parameters, 66 infrared spectra, and some recent literature. A discussion follows. It has been shown that when B is flashed at high voltages (see Figures 13 and 1*0, it- does not decompose chemically but forms in part an extremely thin film on the reaction tube walls. This film has been o shown to be composed of spherical B particles of diameter 300 to 350 A. It has been shown further that coal extracts contain these spherical 39 ^0 particles, ' and that the macro pore system of coal corresponds in 28 size to openings between particles of this size (see also Formation of B section herein). Carbon gives an intense background on infrared spectra. As can be seen from Figures 5 through 12, carbon has never been observed from the flash heating of coal. - 62 - 4) however; 3). Bel~~ and. Y. rat.i.o he:Lghts hydrogen~ Th:i.s simi .. lar i.ndicated l.. n f rared spec t raj and some recent 1l" terat.u re. 66 A dl'. SCUSS.l .on f 0 11o ws. It has been shown that when B is flashed at high voltages (see Figures 13 and 14)) it does not decompose chemically but forms in part an extremely thin film on the reaction tube walls. This film has been o shown to be composed of spherical B particles of diameter 300 to 350 A. It has been shown further that coal extracts contain these spherical particles, 39,40 and that the macro pore system of coal corresponds in size to openings between particles of this size28 (see also Formation of B section herein). Carbon gives an intense background on infrared spectra. As can be seen from Figures 5 through 12, carbon has never been observed from the flash heating of coal. - 63 - From these and other evidences which will be summarized in a later section, it is seen that a heterogeneous coal substance is the simplest postulate explaining fully the results of the flash heating reaction. These observations are consistent with the model of Kreulen (see Chapter 10, reference 28). The manner in which the Y is attached to or mixed with the spherical B particles is a more difficult consideration. Some possi­bilities ares 1. The B particles are simply imbedded in a matrix of Y. This postulate, which is similar to Kreulen fs, would not provide for a macro pore system. 2. The B particles are coated with Y which may be chemisorbed, physically adsorbed, or just sticking to the B particle. 3. Another very speculative postulate would be a spherical coal particle made up of a polymeric three-dimensional carbon skeleton, the inner part of which hi'gh'ly aromafekc and relatively low in oxygen-containing functional groups. As the outer surface of this particle is approached, the carbon-carbon bonds become more saturated and more oxygen-containing functional groups are present, giving a yellow color to the outer layers. The flash heating would break relatively non-resonance, stabilized, saturated carbon-carbon bonds creating Y and leaving the spherical, stable B particle. When B was flashed again only micro amounts of Y somewhat different in chemical structure would be formed. The successive 28). are~ I 5, dimensional inn~r PBft whic):l :1'1;1: h;tgliily aroma~*¢ containing As oxygen­containing When B was flashed again only micro amounts of Y somewhat different in chemical structure would be formed. The successive - 6k - flashings of B do in fact give this situation. The Y formed from flashing B is different in chemical structure (Fig. 1 1 ) but not obviously closer to the B structure. If the same coal is heated to 500°C in a furnace in the absence of air, it will evolve a yellow material which can be condensed on the walls of the reaction tube. This material is usually called low-temperature tar. The benzene-soluble part of this was extracted and a molecular weight determination was made. The average molecular weight was about kOO, The average molecular weight of the benzene-soluble portion of the Y was about 750* The chemical structure of this material is different from Y as seen in Fig. 1 2 . The tar appears to contain more aromatic hydrogen (although still quite aliphatic) and from the many more peaks observed probably is a more complicated mixture of d