Energy & Fuels 1987,1, 525-529 some additional phenomena, such as mass-transfer limitations, had affected those data. The two-step reaction model is admittedly a simplified representation of the actual mechanism, which includes a myriad of species and reactions. Nevertheless, the observed agreement between experimental yields and yields predicted from the model demonstrate the utility of the model in describing the decomposition of the parent kerogen to bitumen products. Examination of some of the data suggests the justification of a still more complicated model involving an additional "lumped" intermediate. However, insufficient data are available to determine, with confidence, the parameters required for the additional sequential step.
Conclusions Over 95% of the Green River kerogen is converted to soluble bitumen by parallel, competing reactions-one that is rate controlling above 350 "C and another that is rate controlling below 350 "C. Approximately 75% of the parent kerogen in the Sunbury oil shale can be removed by thermal solution in tetralin. The Sunbury kerogen decomposition is best described by a two-step series decomposition model. The implication of the thermal decomposition being described by a series of reactions for the Sunbury oil shale and by parallel reactions for the Green River oil shale is consistent with the known reactivity of the molecular structures of the two oil shales. Aromatic eastern US. oil shales, such as Sunbury oil shale, have a coal-like structure with large fractions of condensed aromatic, polycyclic, and heterocyclic rings.18 These cyclic portions of the kerogen molecule are known to form chars upon pyrolysis and form the residues upon thermal solution.1° A sequential-reaction model represents the increasingly sluggish steps that occur as the tetralin solvent attacks the more and more unreactive structures that remain in the (18)Miknis, F. P.;Smith, J. W.Oil Shale Symp. h o c . 1982, 15th, 50-62.
525
shale matrix after the reactive bonds are cleaved to form soluble molecular fragments. The final residue at 430 "C, comprising approximately 20% of the kerogen for the Sunbury oil shale samples, is over 60% aromatic and contains the most unreactive portions of the kerogen. In the Green River oil shale, virtually all of the kerogen (over 95%) is reactive with tetralin at 400 "C. Almost no organic structures are so unreactive that they cannot be removed from the shale matrix as soluble fragments. Thus a sequential reaction model should not be needed to describe the bitumen formation. In fact, for a given temperature region, the bitumen formation is described by a single step.
Glossary Arrhenius pre-exponential factor min-' Activation energy, cal/mol, kcal/mol fraction or organic material, dimensionless f K kerogen reaction rate constant, min-' k mass of organic material, g m n reaction order, dimensionless series approximation of exponential integral P(Z) gas constant, cal/(mol K) R T temperature K, "C t time, min Y yield, dimensionless yield at stoichiometric conversion Y* heating rate (dT/dt), "C/min P weight fraction, dimensionless 4 stoichiometric constant, dimensionless Y A E
Subscripts carbonaceous residue unreacted Sunbury kerogen KO first intermediate Sunbury kerogen K1 predicted P raw oil shale r spent or partially spent oil shale S T total unreacted species 0 1 first reaction step, first intermediate second reaction step, second intermediate 2
C
Isolation and Identification of Carboxylic Acid Salts as Major Components of Green River Oil Shale J. F. McKay* and M. S. Blanche Western Research Institute, Laramie, Wyoming 82071 Received June 15, 1987. Revised Manuscript Received September 8, 1987 Carboxylic acid salts were isolated from Green River shale by treating the shale in an autoclave with methanol and water at 400 "C (for 5 min to 1 h). Approximately 22 w t % of the organic matter in the shale was isolated in the form of carboxylic acid salts when the shale was treated for about 18 min. The carboxylic acid salts were characterized by spectroscopic techniques such as mass, infrared, and atomic absorption spectrometry and were shown to be a complex mixture of n-alkanecarboxylic acids, branched and cyclic aliphatic carboxylic acids, heteroatom-containing carboxylic acids, and dicarboxylic acids. The authors suggest that carboxylic acid salts are indigenous to the shale and can be isolated rapidly by solvent extraction at elevated temperatures. With treatment times of about 45 min or more the salts are converted to free carboxylic acids.
Introduction Knowledge of chemical composition is important for assessing the commercial potential of shale resources as well as for the design of new or more efficient oil recovery 0887-0624/87/2501-0525$01.50/0
processes. It is especially useful for predicting product distributions from recovery processes and predicting potential environmental problems associated with recovery processes. The magnitude of the domestic shale resource 0 1987 American Chemical Society
526 Energy & Fuels, Vol. 1, No. 6, 1987
emphasizes the importance of obtaining detailed and accurate chemical information on the resource. In general, the chemical composition of bitumen, the organic material easily extracted from western U S . shale by common organic solvents, is well-known. The major compound types have been identified.' To a lesser extent compositional information has also been obtained on the organic material insoluble in common organic solvents, the so-called kerogen. The focus of this paper is on a single compound type, carboxylic acid salts, found in Green River oil shale. These salts are thought to represent a major fraction of the organic material or kerogen in the shale. Organic acids have been isolated by solvent extraction techniques2+ and have been characterized in Examples of the kinds of acids found in Green River shale are n-alkanecarboxylic acids, branched aliphatic carboxylic acids, terpenoid acids, and dicarboxylic acids. Until recently all of the carboxylic acids isolated have represented about 2 or 3 w t % of the total organic matter in Green River shale. Robinson and Cummins' and Chong8 and others reported that from 21 to 26 wt % of the total organic matter in Green River shale could be isolated as carboxylic acids when the shale was treated with carbon monoxide and water at temperatures between 300 and 400 "C. Detailed GC-MS characterization work by Chong et al.8 led to the conclusion that the same types of carboxylic acids were present in the carbon monoxide-water product as were found in the solvent-soluble portions of the raw shale. These important findings not only identified a major organic component of Green River oil shale but also provided clues to the nature of the organic matter in the shale and suggested new methods for recovering the organic matter from the shale.g Several workers have suggested4J0 that carboxylic acid salts may exist in Green River shale and account, in part, for the insolubility of the organic matter in common organic solvents. In 1980, Vandegrift5isolated small amounts of carboxylic acid salts (less than 1%) from Green River shale using benzenemethanol extraction and an HC1-HF treatment. Carboxylic acids identified were monocarboxylic acids, dicarboxylic acids, methylketo carboxylic acids, alicyclic and unsaturated acids, and branched aliphatic acids. He concluded that only a small fraction of the acidic material is present as free acids and suggested that most of the acids are bound to or coprecipitated with carbonate minerals as acids or acid salts. In 1984 Chong and McKay showed that carboxylic acid salts could be isolated in higher yields (about 3.6 wt %) when Green River shale was extracted with methanol. Pronounced even-odd predominance of n-alkanecarboxylic acid salts indicated that the shale had not been subjected to severe thermal degradation and the structural similarity between the derived acids of the salts (1)Chong, S.-L.; Cummins, J. J.; Robinson, W. E. Isr. J. Technol. 1979,17, 36-50. (2) Fester, J. I.; Robinson, W. E. Adu. Chem. Ser. 1966, No. 55, 22.
(3) Lawlor, D. L.; Robinson, W. E. Prepr.-Am. Chem. Soc., Diu. Pet. Chem. 1965, 1, 5. (4) Burlingame, A. L.; Simoneit, B. R. Nature (London) 1968, 218, 2524. (5) Vandegrift, G. F.; Winans, R. E.; Scott, R. G.; Horwitz, E. P. Fuel 1980, 59, 627. (6) Chong, S.-L.; McKay, J. F. Fuel 1984, 63, 303-309. (7) Robinson, W. E.; Cummins, J. J. ERDA TPR 75/1, 1975, 1-14. (8) Chong, S.-L.; Cummins, J. J.; Robinson, W. E. Prepr. Pop.-Am. Chem. SOC.,Diu. Fuel Chem. 1976, 21(6), 265-277. (9) McKay, J. F.; Chong, S.-L.; Gardner, G. W. Abstracts of Papers, 182nd National Meeting of the American Chemical Society, New York; American Chemical Society: Washington, DC, 1981; GEOC 25. (10) Jones, D. G.; Dickert, J. J., Jr. Chem. Eng. Prog., Symp. Ser. 1965, 65, 25.
McKay and Blanche and the acids in benzene-extracted organic material suggested that there was an equilibrium relationship between the salts and free carboxylic acids during or after deposition of Green River oil shale. This paper reports the isolation and characterization of carboxylic acid salts that represent about 22 wt % of the total organic matter in Green River shale. The salts are thought to be indigenous to the shale. Acid salts, rather than free carboxylic acids, were isolated in short reaction time experiments by using a methanol-water treatment a t 400 "C followed by a benzene-methanol extraction. For characterization the carboxylic acid salts were converted to free carboxylic acids, and the carboxylic acids were then derivatized to form esters. The esters were characterized by a variety of spectroscopic and chemical analyses. The apparent role of carboxylic acid salts in the recovery of organic material from Green River oil shale is also discussed.
Experimental Section Apparatus. Short reaction time experiments were conducted in a 1-L 20 cb3 stainless-steel autoclave (Tem-Pres Division/Leco Corp.). The autoclave was fitted with a feed hopper than permitted shale at ambient temperature to be dropped into supercritical fluid. Rapid cooling was achieved upon termination of an experiment by pneumatically opening the furnace doors and initiating a water-circulating system that surrounded the reactor. Cooldown from 400 to 40 "C was achieved in 12 min. oil was recovered by extracting treated shale in a Soxhlet apparatus. Pressure of the autoclave was monitored with an American Instrument Co. pressure gauge in direct line with the reactants. Reagents. All reagents were distilled-in-glass, high-purity solvents obtained from commercial supply houses. Oil Shale Samples. Green River shale, mined at Anvil Points, Colorado, was used in the short reaction time experiments. The Fischer assay of the shale used in seven experiments was 51 gal/ton, and two additional experiments used 91 gal/ton shale. The 3/4-in.cubes of shale, sawed from blocks of raw shale, weighed approximately 17 g. Although the sample cubes cut from one piece of shale were similar, it is generally understood that they cannot be considered truly homogeneous, and some inconsistencies in analyses can be expected. In a typical experiment, 3/4-in.cubes of Green River shale were placed in the autoclave feed hopper, and methanol (120 mL) and water (120 mL) were placed in the 1-L reactor vessel. The system was sealed and purged with argon for 5 min, leaving 500 psi argon in the system. The autoclave was heated to 400 "C over a period of 1.25 h to generate supercritical fluid in the autoclave. During the heat up period, argon was fed to the feed hopper from an external tank to maintain a positive pressure of argon in the feed hopper. Final operating pressures were on the order of 4500 psi (32 MPa). To begin supercritical treatment of the shale, a pneumatic ball valve was opened to drop the shale into the heated fluid in the autoclave. The valve was then closed. The temperature of the autoclave dropped to about 365 "C and then climbed to 400 "C in about 5.5 min. Depending upon the experiment, the blocks of shale were exposed to supercritical fluid for an additional period of from 1s (immediate cooldown) to 34 min. cooldown from 400 to 40 "C was accomplished in 12 min by pneumatically opening the furnace doors and passing water through the cooling jacket of the autoclave. The contents of the autoclave were recovered by washing the autoclave with both water and methylene chloride. The combined liquids were filtered and placed in a separatory funnel to separate aqueous and non-aqueous phases. Once separated, the aqueous layer was extracted three times with methylene chloride to remove additional organic materials. Water was removed from the aqueous layer by using rotary evaporation a t 90 "C. The solid product was then weighed. The remaining spent shale was placed in a Soxhlet extraction unit with 60% benzene and 40% methanol and refluxed for 24 h. The extraction solution was placed in a separatory funnel and washed with water to remove additional aqueous phase material. The water was then removed from the aqueous phase as described previously. The solids materials from
Energy & Fuels, Vol. 1, No. 6, 1987 527
Carboxylic Acid Salts in Oil Shale the aqueous extractions were combined and redissolved into distilled water. After removal of water the combined water-soluble extracts, representing the carboxylic acid salts, were weighed. Organic materials in the methylene chloride and benzenemethanol fractions were recovered by removing the solvent with a rotary evaporator. The organic materials were then weighed. The totalorganic material recovered in each experiment was then calculated by summing the amounts of materials recovered from aqueous, methylene chloride, and benzene-methanol phases. Conversion of Carboxylic Acid Salts to Free Acids and Esters. A portion of the solid carboxylic acid d t s was redissolved in distilled water and acidified with 1 N hydrochloric acid to produce free carboxylic acids. A portion of the free carboxylic acids was esterified by using boron trifluoride-methanol. Calculation of Yields of Liquid Organic Material. All recovery data reported in this paper are based on gravimetric amounts of liquid organic material recovered from the shale. Weight percents (yields) of recovered liquid organic material were calculated in the following manner. First, the weight percent of organic material in the shale was calculated by using
wt % organic material in the shale = wt % organic carbon in shale/wt % carbon in shale organic matter X 100 The weight percent of organic carbon in the shale was determined experimentally as the difference between total carbon and mineral carbon. The weight percent of carbon in the shale organic matter was determined from an elemental analysis of the liquid organic material recovered from the shale. The weight percent of total recovered liquid organic material was then calculated by using wt % recovery of total organic material = wt of recovered liquid organic material/(wt of shale X w t fraction of organic material in the shale) X 100
Methods of Analyses. Elemental analyses for C, H, N, 0, and S were performed by a commercial laboratory. C, H, and S were determined by a combustion method, N by a modified Dumas method, and 0 by difference. Vapor pressure osmometry (VPO) molecular weight determinations were made at a commercial laboratory by using pyridine solvent at 60 "C. The molecular weights were recorded at three different dilutions, and the number-average molecular weight was determined by extrapolation to infinite dilution. Solid-state infrared spectra of carboxylic acid salts were recorded by using KBr pellets having a 1OO:l KBr:sample ratio, by weight. The infrared spectra of free carboxylic acids and esters were recorded in methylene chloride. Infrared spectra were recorded on a Nicolet MX-1 Fourier Transform Infrared Spectrometer having a resolution of 1 wavenumber. Field ionization mass spectra were recorded a t SRI International, Menlo Park, CA, on a single-focusing, 25.4-cm radius, 60" magnetic sector ionization mass spectrometer. Atomic Absorption Spectrometry. The salt was first digested in a mixture of sulfuric, nitric, and perchloric acids to remove interferences from the organic matrix. The digested sample was diluted and aspirated into a Varian AA-1275 atomic absorption unit for quantification of each element. Sodium was measured by flame emission, and the other elements were measured by absorption. Inductively Coupled Argon Plasma (ICAP) Analysis. Samples were prepared for ICAP analysis by dissolving the sample in a 10% nitric acid solution and subsequently filtering the solution. Analysis was performed on a Gerald Ash Adamcomp 1100 instrument utilizing induced coupled plasma emission spectrosCOPY. Gas Chromatography/Mass Spectrometry Analysis. M w analyses were obtained on a Hewlett-Packard 5985C quadrapole instrument having a DB5 silica base phenolic column (J&W Scientific Inc.). The column inlet temperature was 250 "C, and the column was programmed from 30 "C to 320 "C at a rate of 8" min-'. Results and Discussion Experiments a t 400 "C using 3/4-in. shale cubes in the
Legend 0
Total Organic Carbon (Toto1 Oil)
A Carboxylic Acid Salts
A
Heat-Up and Treatment Time, min
Figure 1. Weight percent of total organic material recovered from Green River shale vs. time. Table I. Elemental Analysis and Molecular Weight Data for Carboxylic Acid from 5- and 18-min Experiments at 400 "C
anal., % sample C H N S 0 from 5-min expt 74.4 10.0 1.8 0.8 13.0 from 18-min extp 77.7 10.4 1.9 1.3 8.7
M" VPO, field 60 "C ionization pyridine MS 683 486
862 857
1-L autoclave showed that up to 22 w t % of the organic matter in the shale can be recovered in the form of carboxylic acid salts within a treatment time of about 18 min. The amounts of salts recovered in short reaction time experiments are shown in Figure 1. At a treatment time of 6 min a t 400 "C, only about 8% of the organic material in the shale is recovered, but about two-thirds of it is carboxylic acid salt. At a treatment time of 12.5 min, the yield of total organic material was 20%, and almost all of the material was carboxylic acid salt. Salt yields reached their maximum a t a treatment time of 18.5 min, maintained a plateau, and then decreased. The maximum carboxylic acid salt yield is the same as the maximum amount of free carboxylic acids recovered from the liquid product of 1-h supercritical extraction Apparently all of the carboxylic acid salts in the shale can be recovered in 15-to l&min treatment times. It appears that, at treatment times of about 35 min or longer, the salts are converted through protonation reactions to free carboxylic acids and are recovered as such. Possible changes in pH as a function of time have not been measured. Carboxylic acid salts recovered in these experiments were characterized by inductively coupled argon plasma (ICAP) and atomic absorption spectroscopy. The cations associated with these salts may or may not be the cations associated with the organic material in the virgin shale. ICAP analysis of the acid salts indicated that sodium was the most prominent cation, in a ratio of 20:l over potassium, the next most abundant cation. Other cations found, in order of decreasing amounts, were calcium, boron, arsenic, magnesium, and iron. Atomic absorption analysis of the same salt sample showed iron to be the most prominent cation followed by sodium, calcium, potassium, and magnesium. The reason for the differences in results by the two methods is not known. Earlier work6indicated that sodium was the most prominent cation in salts extracted from Green River shale. ~~
~
(11)McKay, J. F.; Chong, S.-L.Lip. Fuels Technol. 1983,1,289-324.
McKay and Blanche
528 Energy &Fuels, Vol. 1, No. 6,1987
a
(KBr pellet)
200
Acidified salts (in CH,CI,)
400
600
800
1200
1000
1400
1600
1800
2000
Mars, m / r
Figure 3. Field ionization mass spectrum of esters from 5-min recovery experiment.
Methyl esters derived from salts (in CH,CI,)
C
1725 200
400
600
800
1000
1200
1400
1600
1800
2000
Mass. m/z
-
Figure 4. Field ionization mass spectrum of esters from 18-min recovery experiment.
4 3600
3400
3200
I
1800
1700
1600
I
IS00
Wavenumberr (cm-' )
Figure 2. Infrared spectra of carboxylic acid salts, free acids, and ester derivatives.
Free acids were characterized by elemental analysis, molecular weight determination by VPO (Table I), field ionization mass spectrometry, and infrared spectrometry. The acids have a high oxygen content and a number-average molecular mass between about 500 and 900 Da, depending on the sample and method of determination. Calculations based on elemental oxygen content and molecular weight data suggest that many molecules contain more than one carboxylic acid functional group. Further analyses are required to determine the extent to which carboxylic acid functional groups account for the elemental oxygen found in these fractions. The infrared spectrum of the carboxylic acid salts (Figure 2a) shows carboxylate absorption a t 1565 cm-', the spectrum of the free acids (Figure 2b) shows carbonyl absorption a t 1710 cm-', and the spectrum of the methyl esters derived from the acid salts (Figure 2c) shows carbonyl absorption at 1725 cm-l. All of these absorption bands are similar to those found in corresponding model compounds. The absorption bands are broader than those of model compounds due to the complexity of the mixture. Figures 3 and 4 show field ionization mass spectra of methyl esters derived from carboxylic acid salts. Figure 3 shows the spectrum of esters derived from carboxylic acid salts recovered in the 5-min experiment, and Figure 4 shows the corresponding spectrum of material recovered in the 18-min experiment. A total of 94 wt % of the sample from the 5-min experiment and 90 wt % of the sample from the 18-minute experiment evaporated into the mass spectrometer. Thus a representative sample was analyzed in both cases. The field ionization spectra indicate that the carboxylic acid salts have a molecular mass
range of from 100 to almost 2000 Da. Number-average molecular masses calculated from mass spectrometry data were about 850 Da for both samples. Gas chromatography/mass spectrometry analysis of the ester derivatives of the carboxylic acid salts from the 18min experiment indicated that the samples contain normal carboxylic acids and/or branched acids. Isoprenoid carboxylic acids, aromatic carboxylic acids, and dicarboxylic acids were also found. The above data lead to the conclusion that the chemical nature of the carboxylic acid salts influences the recovery of these materials from Green River shale. Assuming that carboxylic acid salts are present in raw shale, it would appear that recovery by distillation would be prevented by the inherent nonvolatility of the ionic compounds. Thus even relatively low molecular weight compounds are not recovered by distillation. Under more drastic distillation conditions, where pyrolysis reactions occur, the acid salts are probably decomposed to form hydrocarbons and carbon dioxide. Therefore, carboxylic acid salts or free acids are not found in significant quantities in retorted shale oil. Second, the carboxylic acid salts may be bound to the mineral matrix by ionic bonds. If such bonding does occur, the carboxylic acid salts would be expected to be insoluble in common organic extraction solvents such as cyclohexane, benzene, or methylene chloride. Both of these factors would inhibit the recovery of about one-fourth of the organic matter in Green River shale under typical retorting or solvent extraction conditions. Conclusion Published experimental results demonstrate that approximately 25 wt % of the organic matter in Green River shale can be isolated as free carboxylic acids when the shale is treated for 1h or more with solvents and water under various supercritical and subcritical conditions. The experiments described in this paper show that 22 wt % of
Energy & Fuels 1987,1, 529-534 the organic matter in Green River shale can be isolated as carboxylic acid salts when treatment times are limited to about 18 min. Conclusions are as follows: (1) 22 w t % of the organic matter in Green River shale exists in the form of carboxylic acid salts, and (2) the s a l h are possibly converted at longer treatment times to free carboxylic acids through a proton exchange in the aqueous media. The authors also suggest that the chemical nature of the car-
529
boxylic acid salts influences the recovery of these materials from Green River shale.
Acknowledgment. The authors express thanks and appreciation to the US. Department of Energy for fundihg of this work under Cooperative Agreement No. De-FC2183FE60177. Registry No. CH,OH, 67-56-1.
Explosive Comminution of Bituminous Coal Using Steam? Thong Hang, Mahendra P. Mathur,* Nand K. Narain, Dennis N. Smith, and John A. Ruether Pittsburgh Energy Technology Center, United States Department of Energy, Pittsburgh, Pennsylvania 15236 Received June 11, 1987. Revised Manuscript Received August 17, 1987
The explosive comminution of Illinois No. 6 coal (Burning Star mine) was performed with steam in a batch reactor. Parametric studies were conducted to investigate the effects of key variables, such as temperature (347-506 "C),pressure (2400-5000 psig), coal slurry concentration (14%-75%), and heating rate, on both the particle size reduction and the desulfurization. Data on particle size reduction and SEM (scanning electron microscopy) micrographs provided evidence that the thermoplastic properties (softening, swelling, etc.) probably played a major role in explosive comminution. Coal was comminuted most effectively a t temperatures in the plastic range. Volume mean particle size was typically reduced from 90 pm to the range of 15-40 pm by treatment; using lump coal feed resulted in an even finer product. Sulfur removal as H2S fell in the range 6%-15%, but it could not be determined if any organic sulfur was removed.
Introduction Explosive comminution provides an alternative method to the traditional crushing and grinding techniques for achieving size reduction. As far back as 1870, the method was used on processes that cooked fibrous materials under pressure and disintegrated the resulting pulp by allowing it to discharge at inte~alsinto a low-pressure region.' The method was later developed to be used as a unit operation in the process industries to pulverize a number of materials, such as wood pulp, cereals: glass, and fused quartz? The applicability of explosive shattering to various ores was studied extensively by U S . Bureau of Mines invest i g a t o r ~ . Pulverization ~ as a means of preparing coal for use in gasification or combustion could be brought about by rapid release of high-pressure (1500 psi) steam used to saturate the coal.5 Yellott and Singh demonstrated the feasibility of such a technique in a continuous process.6 It is estimated that two-thirds of the sulfur dioxide generated in the United States comes from power plants burning fossil fuels.' Reduction of sulfur content in coal prior to combustion is potentially important in controlling noxious emissions. This can be done by coal-washing techniques, which in general include a size-reduction step. The finer the coal is comminuted, the greater the extent of mineral matter separation theoretically possible. Thus, t Reference in this report to any specific commercial product, process, or service is to facilitate understanding and does not necessarily imply its endorsement or favoring by the US.Department of Energy.
0887-0624/87/2501-0529$01.50/0
there is currently an interest in investigating methods for producing very finely divided coal. Within the last decade, increased interest has been shown in explosive comminution as a coal preparation technique. Both mineral matter and sulfur content of coal can be reduced by use of explosive comminution. For example, workers a t Consolidated Natural Gas are developing a process to produce superfine clean coal by pressuring and heating a coal/water slurry to supercritical conditions and rapidly expanding it through an orifice to atmospheric ~ o n d i t i o n s . ~Ash ~~ then could be separated from the hydrocarbonaceous particles by using separators such as hydrocyclones. The principle of explosive comminution rests on the fact that porous materials, when exposed to compressed fluids under high pressure, undergo enormous interhal stresses upon a sudden release of the restraining pressure. Stresses exceeding the tensile strength of the materials result in explosive shattering.1° Since the mineral matter in coal (1) Blackman, H. U.S. Patent 369836,1887. (2)Meigs, D. Chem. Metall. Eng. 1941,48,122-125. (3)Poulter, T.J. Phys. Rev. 1932,40,877-880. (4)Dean, R.S.;Gross, J. U.S. Bur. Min. Rep. Znuest. 1932,-US. Bur. Mines No. 3118;1933, No. 3201. (5) Godwin, F. W. "Coal Pulverization by Internal Explosion"; Report from the Armour Research Foundation to the Peabody Coal Co., August, 1939. ~. .. (6) Yellott, J. I.; Singh, A. D. Power Plant Eng. 1945,49,82-86.
(7)Ember, L. R. Chem. Eng. News 1981,59(37),20-31. (8)Massey, L.G.; Brabets, R. I.; Abel, W. A. U S . Patent 4313737,
1982.
(9)Massey, L.G.; George, D. A.;Brabets, R. I.; Abel, W. A. U.S. Patent 4 421 722,1983.
0 1987 American Chemical Society
