Energy & Fuels 1989,3, 585-589 walls and cell fillings in such vitrinites.21 Using transmission electron microscopy, Taylor observed very thin sheets (0.1 pm thick) of "exinite-like" material contained in ~ i t r i n i t e . ~The J ~ 'exinite-like" material was described to have the appearance of collapsed cell walls. Reactivity differences within a piece of originally featureless vitrinite have been reported when the piece was treated with selected organic reagents a t elevated temperatures and pressure^.^^,^^ These observations also support the presence of chemically distinct submicroscopic materials within vitrinite. Thus, our observations, which imply that at least two distinct species of vitrinite-like particles are present in at least one of the coal samples, are not unexpected. However, the origin of these two vitrinite materials cannot be defined at this time. The fact that an organic alkylammonium hydroxide or an inorganic hydroxide can both lead to chemical maceral comminution, coupled with the fact that comminution by the tetrahydrofuran solvent alone does not occur, is strong evidence for the importance of hydrogen bonds in holding the maceral particles together. However, swelling also would be (21) Stach, E. In Stach's Textbook of Coal Petrology, 3rd ed.; Gebruder Borntraeger: Berlin, 1982. (22) Shibaoka, M. Fuel 1981,60, 240-6. (23) Shibaoka, M.; Liu, S.; Taylor, G. H. Fuel 1985, 64, 237-241. (24) Even though the coal samples are treated with acid to neutralize the base, the photographic evidence show no indication of re-formation of particulate species. "his is expected, since the chance of strong particle hydrogen bonds re-forming would require intimate contact of surfaces. It is highly unlikely that the original particle surfaces will ever again be sufficientlyjuxtaposed to allow reconstructionof the original particles.
585
expected to play a role in the comminution, but from our results, it appears to be a secondary role. A much broader study would be necessary to fully understand the interaction and roles between hydrogen bonds and solvent swelling.24 The potential of a base-catalyzed maceral comminution scheme is indeed attractive. If the goal is the enrichment of maceral groups, extensive grinding, which is very energy intensive, is not necessary if selective separation at the intermaceral boundaries can be achieved. The liberation of relatively large macerals with intact morphological features has many benefits. Most types of maceral separation processes will have increased throughputs and yields, because the larger particles will be more rapidly separated and a smaller amount of fines must be handled. The identification of the macerals becomes easier, because the morphology is not necessarily destroyed as with the fine grinding traditionally employed in maceral separation. Furthermore, as the present work suggests, previously undetected macerals or submacerals that are intimately associated may also be liberated, thereby allowing the separation of materials that have not yet been defined or cannot be defined by standard petrographic techniques.
Acknowledgment. We acknowledge the assistance of C. A. A. Bloomquist in density gradient centrifugations and for reviewing this manuscript and J. V. Muntean for recording the solid 13C NMR spectra. Registry No. THF,109-99-9; tetrabutylammonium hydroxide, 2052-49-5.
Effects of Pressure upon the Isothermal Plastic Behavior of High-Volatile Bituminous Kentucky Coals William G . Lloyd* and John W. Reasoner Department of Chemistry and Center for Coal Science, Western Kentucky University, Bowling Green, Kentucky 42101
James C . Hower and Linda P. Yates Kentucky Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506 Received October 24, 1988. Revised Manuscript Received July 7,1989 The plastic character of six high-volatile bituminous coals has been examined by using a Gieseler plastometer under 0.1-2.8 MPa (15-400 psia) of helium, measuring in an isothermal manner and a t uniform torque. For all coals studied, the maximum fluidities increase with increasing pressure, attaining values ranging from 9-fold to 620-fold greater than the corresponding maximum fluidities at atmospheric pressure. Fluidities increase most sharply over the first megapascal of superatmospheric pressure and then flatten out smoothly with further increases of pressure, approaching asymptotic values. Melting slopes very similarly with pressure; coking slopes are nearly independent of pressure in this range. These observations are consistent with the view that, for these coals, the predominant pyrolysate fraction is a liquid with significant vapor pressure in the vicinity of 400 'T.
Introduction The maximum fluidities of plastic coals are sharply increased by superatmospheric pressures, whether measured at the traditional 3 K/min temperature ramp1"' or under (1) Kaiho, M.; Toda, Y. Fuel 1979,58, 397-398.
0887-0624/89/2503-0585$01.50/0
isothermal conditions.s*6 Similarly, studies with a highpressure microdilatometer show that elevated pressures (2) Lancet, M. S.; Sim, F.A. R e p r . Pap.-Am. Chem. SOC.,Diu.Fuel Chem. 1981,26(3), 167-171. (3) Lancet, M. S.;Sim, F. A.; Curran, G. P. R e p r . Pap.-Am. Chem. SOC.,Diu.Fuel Chem. 1982, 27(1), 1-24.
0 1989 American Chemical Society
Lloyd et al.
586 Energy & Fuels, Vol. 3, No. 5, 1989
coal no. coal bed county (KY) % moisture' % ash % volatile matter heating valuen MJ/kg Btu/lb elemental anal." % carbon % hydrogen % nitrogen % sulfur pyritic organic % vitrinite % liptinite % fusiniteb % micrinite % macrinite vitrinite max reflectance, % ASTM Gieseler plastometry softening T,OC max fluid T, "C solidifcn T, "C maximum fluidity, ddpm free swelling index
Table I. Characteristics of Coals Used" 6102 7846 7799 7912 Mason No. 11/12 KY No. 6 KY No. 11 Bell Muhlenberg Union Union 4.5 4.3 3.2 3.6 15.7 12.3 8.7 8.3 40.1 33.6 37.0 37.8
7913 KY No. 9 Ohio 3.0 10.2 39.5
7957 Amos Butler 6.4 1.7 37.1
29.7 12 800
30.2 13000
32.0 13 800
30.7 13200
30.5 13 100
34.1 14 700
71.2 4.66 1.83 1.84 0.94 0.87 85.0 4.3 6.1 4.6
71.5 5.04 1.62 2.61 1.89 0.71 89.4 2.2 6.7
0.0
0.87
0.6 0.60
76.1 5.06 1.62 2.88 1.17 1.64 88.4 4.4 5.4 1.4 0.4 0.69
73.6 4.94 1.46 3.52 1.24 2.25 88.8 4.8 4.2 2.0 0.2 0.56
72.3 4.92 1.60 3.61 1.35 2.23 85.6 3.0 8.7 2.6 0.1 0.57
82.2 5.42 1.81 0.82 0.11 0.69 88.1 7.4 1.9 2.5 0.1 0.61
382 429 466 19900 8
392 427 442 7.2 3.5
376 422-435 467 >25000 6
387 425 448 64.4 3.5
388 427 454 352 3
405 439 456 37.9 2.5
1.1
" Moisture is as determined; other chemical analyses are on a dry, ash-included basis. Includes semifusinite. Averages of quadruplicate determinations. extend the plastic range7-9 and in c e r t a i n cases increase the absolute swelling maxima9 of mid rank coals. Microdilatometric evidence shows that h e a t i n g rate (25-65 K / m i n ) has a major impact upon p l a ~ t i c i t y . ' ? ~ Gieseler plastometry at elevated pressures shows3 that an increase in heating ramp above the standardlo 3 K/min has a considerable impact upon plastic properties, similar to that found"J2 in atmospheric-pressure studies. This temperature-ramp variable can be removed by measuring plasticity under isothermal conditions. Isothermal plast o m e t r y also simplifies analysis, for example in affording well-defined melting13J4 and coking15J6 slopes, in permitt i n g a good estimation of maximum fluidities beyond the experimental range of the Gieseler p l a s t ~ m e t e r ? ~ Jand ~J~ in e s t i m a t i n g empirical activation e n e r g i e ~ . ~ * ~FurJ~J~ (4) Read, R. B.; Reucroft, P. J.; Lloyd, W. G.; Francis, H. E. Fuel 1986, 64,627-630. ( 5 ) Read, R. B.; Reucroft, P. J.; Lloyd, W. G. Fuel Process. Technol. 1986,11, 133-151. (6) Lloyd, W. G.; Reasoner, J. W.; Hower, J. C.; Yates, L. P.; Clark, C. P.; Davis, E.; Fitzpatrick, A.; Irefii, A.; Jiminez, A.; Jones, T. M.; Reagles, C. L.; Sturgeon, L. P.; Whitt, J. M.; Wild, G. D. 'Predictors of Plasticity in Bituminous Coals"; final report to the U.S.Department of Energy on Grant DE-FG22-81PC40793,19&i,pp 18-30. (7) Jenkins, R. G.; Khan, M. R. "Plastic and Coking Behavior of Coals at Elevated Pressure"; final report to the Electric Power Research Inst. on Grant EPRI-AP-2337, 1982; parts 2.4 and 5.1.1. (8) Khan, M. R.; Jenkins, R. G. Fuel 1984,63,109-115. (9) Khan, M. R.; Jenkins, R. G. Fuel 1986,64,189-192. (10) Plastic Properties of Coal by the Constant-Torque Gieseler Plastometer; ASTM D-2639; ASTM Philadelphia,PA, 1987. (11)Van Krevelen, D. W.; Huntjens, F. J.; Dormans, H. N. M. Fuel 1966,35,462-475. (12) Loison, R.; Peytavy, A.; Boyer, A. F.; Grillot, R. The Plastic Properties of Coal. In The Chemistry of Coal Utilization; Lowry, H. H., Ed.; John Wiley & Sons: New York 1963; SupplementalVolume. (13) Lloyd, W. G.; Francis, H. E.; Yewell, M. R.; Kushida, R. 0.; Sankur, V. D. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1980,25(2), 128-137. (14) Lloyd, W. G.; Reasoner, J. W.; Hower, J. C.; Yates, L. P. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1984,29(1), 191-197. (15) Fitzgerald, D. Fuel 1966,35, 178-183. (16) Fitzgerald, D. Trans. Faraday SOC.1966,52,362-369.
thermore, for certain applications, such as screw extruder feeding s y s t e m s for s u p e r a t m o s p h e r i c coal reactor^,'^-'^ analysis under isothermal conditions m a y provide useful design information. The objective of t h i s work is to determine the nature of the pressure effect upon Gieseler plasticity under isothermal conditions. We here report the effects of varying helium pressures upon the isothermal plastic behavior of six high-volatile b i t u m i n o u s (hvb) K e n t u c k y coals.
Experimental Section The Gieseler plastometer used for this work is a special adaptation of the research model manufactured by Standard Instrumentation, Charleston, WV. The drive, torque clutch, shaft, and crucible are mounted on the head of a steel pressure vessel, and the solder-pot furnace is mounted at the bottom of the veasel. This unit is substantially identical with the pressure plastometer built for Conoco and described by Lancet and Sim2 and is the same instrument used by Read et a L 3 s 4 The crucible and rabble-arm stirrer geometry are identical with those of a standard Gieseler plastometer; the stirrer is driven by a 300 rpm constant speed motor, and the highest measuable fluidity is 30 0o0 dial divisions/min (ddpm), as with the standard instrument.1° Coals were selected to be representative of a larger group of 40 coals studied at atmospheric pressure.s T h e present coals, freshly sampled from active mines, were rough-crushed to -25 mm (-1 in). Splits, reduced to -0.425 mm ( 4 0 mesh) for Gieseler analysis and to -0.25 mm (-60 mesh) for chemical analysis, were stored under nitrogen in a freezer prior to use. Characteristics of the six coals are given in Table I. Under isothermal conditions the maximum fluidities of plastic coals are sharply dependent upon temperature? For each of these coals an isothermal temperature was selected to provide a max(17) Ryason, P. R.; England, C. Fuel 1978,57, 241-244. (18) England, C. Proc. Intersoc. Energy __ Convers. Ena. - Conf. . 1982, 17th, 2, 864-868. (19) Schatz, W. J.; Carpenter, E. G.; Daksla, C. S.; England, C.; Feinstein, S. P.: Kushida. R. 0.: Lewis. D. W.: Llovd. W. G.: Sankur. V. D. Coal hmpDeuelop&nt-Phose IFeasibility Report; S L 503Cb235; Jet Propulsion Laboratory, California Institute of Technology: Pasadena, CA, 1978.
Isothermal Plastic Behavior of Coals
Energy & Fuels, Vol. 3, No. 5, 1989 587
I
C
C
D
---> 35 Figure 1. Isothermal plastometry of coal 7799 under helium at 419 "C: open squares, 0.10 MPa; solid squares, 2.76 MPa. m
t i a In rirutg
imum fluidity between 100 and 2000 ddpm at atmospheric pressure. Gieseler fluidities are well-known to be difficult to reproduce. In addition to the avoidance of prior adventitious oxidation, we have paid special attention to consistent laboratory procedure in these areas: (1)The standard torque setting of 101.6g cm (1.41 oz in.) usually does not change from day to day. We measured it daily with a torque wrench,making fiie adjustments as needed. (2)The process of tamping the pulverized coal into the Gieseler crucible is critical. We followed the tamping procedure specified in ASTM D-2639," using a 10-kg weight with 12 tamping strokes. (3)Introduction of the crucible to the solder-pot furnace causes an immediate temperature drop of about 40 K. During the recovery period the head is secured and the apparatus flushed twice with helium before pressurization. When the furnace temperature recovers to within 2.0 K of the set temperature-approximately 3 min after introducing the crucible to the furnace-the run commences. A total of 273 pressurized runs were made with these coals. The instrument output provides temperature and fluidity measurements at 60-sintervals. The melting and coking slopes and intercepts are calculated from In (fluidity)va time. For slope calculations the lower limit is 1 ddpm or 0.1% of the observed maximum fluidity,whichever is larger; the upper limit is half the maximum observed fluidity. Maximum fluidity is determined analytically by the intersection of the melting and coking slopes. This analytical measure of maximum fluidity is in our experiences,l8J4a better measure than observed maximum fluidity, especially for highly plastic coals. This also permits us to make all measurements at the standard torque setting. The ASTM requirementlo for repeatability (same instrument and same operator) of maximum Gieseler fluidity is equivalent to a relative standard deviation (sd) of 14.1%. Few laboratories consistently achieve this standard. A careful Japanese study of several coals yielded an averagerelative sd of 20% .n In this study our repeatability is 0.33-0.72 In unit, for an average relative sd of 50-55%. We have therefore measured each coal at a number of intermediate pressures, with triplicate determinations at each pressure.
Results Figure 1 shows typical data for Gieseler plastometer runs with a hvAb coal under helium a t atmospheric pressure and at 2.76 MPa (400psia). The logarithmic scale tends to mask substantial differences in maximum fluidity. The observed maxima differ by a factor of 40 (416and 17000 ddpm); analytical maxima differ by a factor of 56 (1070 and 60500 ddpm). The increase in fluidity with pressure is associated with the steeper melting slope and expansion of the interval between softening and resolidification times. The two coking slopes are nearly identical. Our expectations concerning the nature of this pressure dependency reflect our views about what is occurring at
Figure 2. Expected effects of pressure upon In (maximum fluidity): horizontal, pressure; vertical, In (maximum fluidity); A-A, null effect (high molecular weight pyrolysate); B-B, asymptotic dependence (volatile liquid pyrolysate); C-C, linear dependence (dissolution of pressurant gas); D-D, parabolic dependence (compressionof vapor and gas bubbles).
the molecular level when coal is brought to the plastic state. If the dominating feature is a simple melting of high molecular weight fusible material (the classic bitumenma') or a surface softening of micellar structures to provide we would predict no first-order effect at moderate pressures (curve A-A in Figure 2). If the liquid phase of the coal melt is composed mainly of medium-size molecules%% that possess significant vapor pressures at 400 OC,then the coal melt is continuously losing this material by evaporation. An increase in pressure retards this fluid loss. This physical effect is augmented by the chemical effect of retaining more H-donor molecules and hence stabilizing more pyrolysis fragments. The consequenceof an initial pressure increase, therefore, is an increase in fluid fraction of the coal melt and hence% greater fluidity. The incremental changes resulting from further increases in pressure, however, become progressively less, so for this case we would expect an asymptotic curve (B-B in Figure 2). If the controlling feature of increasing pressure is the consequent increase in the equilibrium solubility of the pressurant gas in the coal melt,' then to a first approximation (Henry's Law) the gas solute concentration is proportional to gas pressure. In (maximum fluidity) is essentially a linear function of fluid fraction,26 so In (maximum fluidity) may be expected to increase linearly with pressure (curve C-C). For a gassy coal, we expect pressure to exert two opposing physical effecta. The coal melt in this case includes a substantial amount of gas microbubbles and is continuously losing these gases. An increase in external pressure retards the rate of gas loss and hence increases the fluid fraction of the coal melt, which increases the maximum fluidity. At the same time, increasing pressure results in PV compression of the gas phase in the coal melt; total fluid fraction is diminished, and maximum fluidity is reduced. As pressure is first increased, the first factor is (20) Jones, D. T.;Wheeler, R. V. J. Chem. SOC.1916,107,1318-1324. (21) Fischer, F.; Gluud, W. Ber. Dtsch. Chem. Ces. 1916, 49, 1460-1468. (22) Berkowitz, N. Fuel 1949,28,97-102. (23) Broche, H.; Schmitz, H. Brenmt.-Chem. 1932,13, 81-85. (24) Neavel, R. C. Proc. Coal Agglom. Conuers.Symp. 1975,119-133. (26) Neavel, R. C. Coal Sci. 1982,1,1-19. (26) Lloyd, W. G.; Yates, L. P. Fuel 1987,66, 831-834. (27) Fukuyama, T.; Miyazu, T.; Kimota, S. J . Fuel SOC.Jpn. 1972,51, 623-626.
Lloyd et al.
588 Energy & Fuels, Vol. 3, No. 5, 1989 Table 11. Pressure Dependency of In (maximum fluidity) coal no. 6102 7846 7799 7912 7913 7957
T,O C 389 420 419 424 418 438
av error
sd' 0.6 0.6 0.5 0.6 0.5 0.6
sdb 1.6 1.5 0.8 0.8 0.9 1.1
0.54
1.1
In (maximum fluidity) at 0.1 MF'a at 2.8 MPa 7.25 9.48 9.82 4.54 11.2 7.13 6.07 12.58 11.2 7.15 5.62 11.2
sde 0.54 0.60 0.34 0.50 0.33 0.72 0.51
conformity to modelsd linear parae asympf 0.52 0.55 0.47 0.63 0.52 0.38 0.49 0.34 0.27 0.96 0.48 0.35 1.04 0.59 0.17 0.76 0.39 0.23 0.73
0.48
0.31
'Average of standard deviation of temperature within a run. Standard deviation of temperature averages, run to run. Average of sd of In (maximum fluidity) from pooled triplicate runs. dStandard error of estimate for experimental data vs best fit of model. eParabolic model: In (max fluidity) = a + bP - cP.'Asymptotic model (power or exponential fit). #Maximum pressure attained is 2.41 MPa. Table 111. Pressure Dependencies of Melting and Coking Slopes coal no. 6102 7846 7799 7912 7913 7957
T,O C 389 420 419 424 418 438
at 0.1 MPa 0.34 0.56 0.93 0.73 0.98 0.69
melting slope, min-' at 2.8 MPa sd' 0.074 0.52 2.04 0.24 1.81 0.15 0.38 2.8gd 2.04 0.23 2.26 0.29
seb 0.058 0.14 0.091 0.21 0.079 0.13
at 0.1 MPa -0.07 -0.50 -0.37 -0.84 -0.50 -0.88
cokine sloDe. min-l at 2.8 MPa sda -0.07 0.009 -0.76 0.095 -0.40 0.042 -0.98d 0.102 -0.44 0.048 -1.16 0.12
sec 0.009 0.055 0.031 0.079 0.088 0.036
Average of standard deviation of slope from pooled triplicate runs. Standard error of estimate, fitting experimental data to asymptotic model. e Standard error of estimate, fitting experimental data to linear model. Slope measured at 2.41 MPa.
P
P 0.0 281)
. ..
Figure 3. Effect of helium pressure upon the maximum fluidity of coal 7799 at 419 "C: Horizontal,helium pressure (psia); vertical,
B
m
4m
Figure 4. Effect of helium pressure upon the melting slope of coal 7799 at 419 OC: horizontal, helium pressure (psia); vertical,
In (maximum fluidity) (maximum fluidity in ddpm).
melting slope (mi&).
likely to dominate, but at high pressures PV compression will become more important. For this case, therefore, the observed maximum fluidity is expected to pass through a maximum (curve D-D). Results of a series of determinations with coal 7799 at 15-400 psia (0.101-2.76 MPa) are shown in Figure 3. The asymptotic model clearly provides the best fit for these data. Table I1 summarizes the data for all six coals. In all cases the exRerimental curves conform best to the asymptotic model. For each of these coals the standard error of asymptotic fit of averaged triplicate determinations is less than the repeatability error. Over this range of helium pressures the maximum fluidities increase by factars ranging from 9 to 620. This variation probably arises chiefly from the selection of isqthermal temperatures for each coal. The greatest increases in maximum fluidity (coals 7846,7912, and 7957) occur when the isothermal measurement is made at a temperature close to the ASTM maximum fluid temperature" of the coal. The smallest increase (coal 6102) is found when the selected isothermal temperature is 40 K below the ASTM maximum fluid temperature.
Figure 1 shows that the melting slope of coal 7799 increases markedly with increasing pressure. Determinations at intermediate helium pressures show this increase in slope to follow an asymptotic curve (Figure 4) not unlike that found for ln(maximum fluidity). The overall changes in melting slope for all six coals are shown in Table 111. All coals show a clear pressure dependency, best fit by an asymptotic model. For each coal the fit of the experimental data to the asymptotic model has a smaller standard error than the run-to-run repeatability error. As with maximum fluidities, the greatest increases in melting slopes are found with coals 7846, 7912, and 7957; the smallest increase is found with coal 6102. From Figure 1 it might be inferred that coking slope is independent of pressure. A plot of coking slope vs helium pressure for coal 7799 (Figure 5) indicates a small positive slope. The best linear slope is 1.2 X lo4 min-l MPa-' (1.4 X IO-4 min-' psi-*), three times greater than the standard deviation of slope. From the t-test (15 degrees of freedom), the probability of a nonzero value for this slope is >99%. Similar analyses show a 99+ % probability of significance for three of the other five coals (coals 7912,7846, and 7957).
Energy & Fuels 1989,3,589-594
589
to our expectations if the dominant processes in the transformation of coal into the plastic state are chiefly producing liquids with significant vapor pressures at 400 OC. This is also in accord with the results of a pyrolysis/GC study of 40 hvb coals,w which found a high-boii pyrolysate fraction to be an excellent predictor of maximum fluidity. For the purposes of superatmospheric reactor design, these data indicate that effective maximum fluidity at 2.8 MPa is typically increased by 2 orders of magnitude over that measured a t atmospheric pressure. At still higher pressures some coals show promise of achieving appreciably higher maximum fluidities. At constant temperature, the time span of fluidity also increases with increasing pressure. Selection of the isothermal temperature has a substantial impact upon both maximum fluidity and fluidity span. Maximum fluidity is optimized at higher temperatures while fluidity span is greatest at lower temperatures. These values can be predicted when the empirical activation energies have been determined.6J4
I
Figure 5. Effect of helium pressure upon the coking slope of coal 7799 at 419 OC: horizontal, helium pressure (psia); vertical, negative slope (min-l). I t is inferred that coking slopes exhibit a small but real pressure dependency. Precision of the data does not justify attempts to fit nonlinear models here.
Discussion
In the range of pressures studied, the maximum fluidities of these hvb coals show substantial increases with increasing helium pressure. Under isothermal conditions, maximum fluidity increases rapidly over the first megapascal of superatmosphericpressure and then progressively flattens out with further pressure increases. This conform
Acknowledgment. This work was supported by the US. Department of Energy under Grant DE-FG2281PC40793. Eileen Davis, Anita Fitzpatrick, and Garry Wild assisted in acquiring the plastometry data. We are grateful to our universities for providing additional support. (28) Reasoner, J. W.; Hower, J. C.; Yates, L. P.; Lloyd, W. G. Fuel 1986,64, 1269-1273.
Accessibility, Reactive Site Distribution, and Swelling Properties of Argonne Premium Coal Samples Studied by a Spin Probe EPR Method Janina Goslart and Lowell D. Kispert* Chemistry Department, The University of Alabama, Tuscaloosa, Alabama 35487 Received March 14, 1989. Revised Manuscript Received July 10, 1989 Five Argonne premium coal samples (APCS No. 3, No. 4, No. 5,No.6, and No. 8) varying in rank from low volatile (Pocahontas, No. 5) to lignite (Beulah-Zap, No. 8) were studied by using an EPR spin probe method. The relative number distribution of acidic functionalities deduced by the EPR spin probe method is linearly related to the ratio of phenolic to alkyl OH groups determined by DRIFT measurements. The predicted increase in elongated voids in Pittsburgh No. 8 (APCS No. 4) upon swelling with pyridine was confirmed and studies as a function of rank correlate well with the destruction of the hydrogen-bond network as a major reason for the change in pore shape. The accessibility of pore volume studied by using spin probes with differing shapes shows a dependence on carbon content similar to that obtained from other measurements.
Introduction During the past few years, Argonne premium coal samples (APCS) have been studied and characterized by different methods in many laboratories. Although the properties deduced depend in a complex way on the rank, composition, and geographic distribution of coal, com~~
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parisons and correlations among data obtained from the various techniques have been made. Studies of surface area, pore volume, and pore size distribution have been carried out to obtain information about surface properties of c0als.l Structural group analyses of APCS have been made by FTIR spectroscopy.2 Studies have also been (1) Bartholomew, C. H.; White, W. E.; Thornock, D.; Wells, W. F.; Hecker, W. C.; Smoot, L. D.; Williams, F. L. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1988,33,24-31.
0 1989 American Chemical Society
