Energy & Fuels 1989, 3, 55-59 possibility is that the CO yield is affected by the water gas shift reaction, which can couple it to other reactions generating Hz, C02,and H20. However, it is unlikely that the water gas shift reaction is dominant. While the C02 evolution profiles vary with coal, corresponding changes in H2 and CO are not present. In any event, it is evident that a multiple parallel reaction model based on an initial precursor with a Gaussian distribution of activation energies is inadequate for explaining CO evolution. A final issue is that a parallel reaction model by itself cannot account for secondary polymerization and cracking reactions that affect product yield and composition. These must be treated by more complex models with sequential and competing reactions, which may include thermodynamic limits to the product distribution. Conclusions Pyrolysis temperatures and reaction kinetics from Rock-Eva1 pyrolysis are consistent with independent measurements in a pyrolysis-TQMS apparatus. As coal rank increases, the temperature at which product evolution reaches a maximum increases and the profile width decreases, for both total hydrocarbons and most individual species. A first-order reaction with Gaussian-distributed activation energies is usually inadequate to fit the profile width well, and a discrete activation energy distribution works much better. Our results are generally consistent with comparable literature results, although exceptions were noted. In particular, we agree with the pyrolysis temperatures in the most recent work from Advanced Fuel Research,36which are 20-30 "C higher (implying slower kinetics) than those from their earlier A multiple reaction model is capable of describing many aspects of coal reactivity. One can not make convincing theoretical arguments that use of an activation energy distribution should result in global kinetic parameters that extrapolate well over hundreds of degrees, but the empirical evidence is that this works quite well. While some might argue that it is just the result of an effective curve-fitting exercise, this successful extrapolation does
55
seem to be reflecting some of the more fundamental aspects of coal pyrolysis chemistry. Much of our data are consistent with a model that associates the changes in global and functional group kinetic parameters with a parallel reaction model that has been partially reacted naturally. The increase in total hydrocarbon T,, and the decrease in activation distribution width are predicted reasonably well. Similarly, the multiple parallel reaction model predicts that functional group parameters, if they also require activation energy distributions, should not be independent of rank. Many of the observed changes in evolution characteristics of individual compounds are consistent with a multiple parallel reaction model. However, certain aspects of coal pyrolysis are in conflict with a multiple parallel reaction model. For example, total hydrocarbon yield per organic carbon increases from lignite to hvb coal by more than can be attributed to simple elimination of COz and H 2 0 diluents from the coal structure. While the changes with rank in methane and hydrogen profiles are consistent with such a model for hvb and higher ranks, changes during the lignite to hvb transformation are not. From lignite to hvb, the hydrogen profile changes at temperatures in the 600-700 OC range, which implies that laboratory char-forming reactions for low-rank coals are different from their geological counterparts. This suggests that there are competing pathways in the reaction network that are not satisfactorily treated by the multiple parallel reaction model. Acknowledgment. We thank K. Vorres and P. Solomon for supplying samples and information for this work. We also appreciate the help of K. Foster and A. Alcaraz with the TQMS experiments and R. Braun with some of the kinetic analysis. This work was performed under the auspices of the US.Department of Energy by the Lawrence Livermore Laboratory under Contract No. W7405-Eng-48. Registry No. COz, 124-389; CO, 630-080; hydrogen, 1333-74-0; methane, 74-82-8; ethene, 74-85-1; ethane, 74-84-0; propane, 7498-6; butane, 106-97-8; water, 7732-18-5; acetic acid, 64-19-7; benzene, 71-43-2; toluene, 108-88-3; phenol, 108-95-2.
Coal Swelling Using Binary Mixtures Containing THQ Kazuyoshi Amemiya, Masaya Kodama, Kunio Esumi,* Kenjiro Meguro, and Hidemasa Honda Department of Applied Chemistry and Institute of Colloid and Interface Science, Science University of Tokyo, Kagurazaka, Shinjuku-ku, Tokyo 162, J a p a n Received M a y 23, 1988. Revised Manuscript Received November 1, 1988 The solvent swelling and liquefaction of three coals (Yallourn, Taiheiyo, and Miike coals) were carried out by using binary mixtures containing tetrahydroquinoline (THQ). In THQ-methanol and THQ-ethanol systems, the swelling ratios of Yallourn and Taiheiyo coals were enhanced remarkably by increasing the amount of alcohol in the binary mixture. The maximum amount of THQ absorbed occurred at the maximum swelling ratio for both systems. Changes in the swelling ratio of Miike coal were small. The conversions of Yallourn and Taiheiyo coals that had been previously swelled were slightly increased. Introduction Recently, Hellgeth and Taylor' reported that the liquefactionproduct yield in the conversion of subbitumi(1) Hellgeth,
J. W.;Taylor, L. T. Fuel
1984, 63,961-967.
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nous coals decreased markedly when the surface water was m-"d by drying in a vacuum at room temperature prior to the liquefaction. It seems that the water contained in the coal which can interact through hydrogen bonding significantly affects coal conversion. Hydrogen bonding between basic nitrogen heterocyclic compounds, such as 0 1989 American Chemical Society
Amemiya et al.
56 Energy & Fuels, Vol. 3, No. 1, 1989 Table I. Ultimate and Proximate Analysis of Coals ~~
ultimate anal.,' wt 70
Yallourn Taiheiyo Miike
C 61.5 74.8 85.2
H 4.6 6.0
6.5
proximate anal.,b wt M A' VM' 66.7 12.7 1.5 8.4 49.3 6.6 7.8 43.2 1.2
%
FC' 31.8 42.3 49.0
I
I
l6I
dried
undr'ed
n
nr
n
l
On a dry, ash-free basis. Key: M, moisture; A, ash; VM, volatile matter; FC,fixed carbon. e On a dry basis.
tetrahydroquinoline (THQ) and water? plays an important role in incorporating the solvent into the coal structure. Similarly, alcohols are expected to provide effects similar to water because of their ability to hydrogen bond and enhance the solubility of basic nitrogen heterocyclic compounds. Furthermore, if an appreciable amount of hydrogen donor solvent is incorporated into the coal structure through a swelling process, the liquefaction product yield is enhanced under mild conditions. In this study, the swelling behavior of three coals with different coal ranks using binary solvents containing THQ was investigated by measuring the swelling ratio and absorption amount of each component in the coal. Further, the liquefaction of the coals that had been swelled in the binary solvents was examined.
0
S +
-
$ S1
S
Figure 1. Swelling ratios of Taiheiyo coal by various solvents. undried 0 dried
Experimental Section Materials. The three different coals (Yallourn, Taiheiyo, and Miike coals) were supplied by the Government Industrial Research Institute of Kyushu. An analysis of the coals by the Fuel Society of Japan is shown in Table I. The coals were used with and without drying, where the drying was performed under a condition of 107 "C for 1day in a vacuum. The 1,2,3,4-tetrahydrcquinolinewas obtained from Tokyo Kasei Kogyo Co., Ltd. The other solvents used were as follows: methanol, benzene, tetralin (Kokusan Chemical Works Co., Ltd.); ethanol (Imazu Yakuhin Kogyo Co., Ltd.); methylcyclohexane (Tokyo Kasei Kogyo Co., Ltd.). THQ, methanol, and ethanol were dehydrated by molecular sieves 3A. The other solvents were used without further purification. Approximately 320-420 mg of coal was charged in a 7-mm-0.d. Pyrex tube and then centrifuged at 3000 rpm for 5 min in order to pack the coal particles. The height of the coal measured was defined as hl. A 2-3-fold excess of the swelling liquid (1-2 mL) was added and the contents of the tube were vigorously stirred to ensure complete mixing. Then the tube was left to swell at 25 "C. The coal was again centrifuged and the height was measured. Swelling and centrifugation were repeated until an equilibrium height of coal, h2,was reached. The volumetric ratio3 on a dry basis, Sve, was defined as
Figure 2. Swelling ratios of Yallourn coal by various solvents. bomb (inner diameter 9.6 mm, length 200 mm, and thickness 0.9 mm).S After 1 day of standing to promote swelling, the tubing-bomb reactor was immersed horizontally into the preheated sand bath and shaken, with a 50-mm stroke, 130 times/min. Coal liquefaction was carried out a t 400 "C for 10 min under autogenous pressure. The reaction was then quenched by plunging the reactor into some finely crushed ice (about 90 s to heat and cool the coal). The products in the reactor were washed out with a small amount of benzene and were refluxed in 30 mL of benzene for 30 min. The insoluble matter was separated by centrifuging a t 5000 rpm for 15 min and washing several times with benzene before drying. The coal conversion was calculated as follows:
(A - a) x 104 conversion = A(100 - Q ) (d70, daf) where V, is the volume of the solvent absorbed by a unit volume of dry coal, V". The amounts of THQ and alcohol absorbed into the coals were determined as follows: about 1.5 g of coal was put into a sedimentation tube and then 5 mL of the THQ-alcohol vehicle was added to it. After swelling, the supernatants were analyzed by using a Shimadzu GC-7A Series GC. In this analysis, methylcyclohexane was used as an internal standard. The absorption amounts were reproducible to about &5%. A detailed calculation was conducted as described by Larsen et a1.4 Coal (1.5 g), THQ (3.0 g), and some amount of an alcohol were charged into a stainless-steel (SUS-304) reactor, called a tubing (2) Fujii, Y.; Akezuma, M.; Esumi, K.; Meguro, K.; Honda, H. Fuel 1986,65, 1616-1617. ( 3 ) Green, T. K.; Kovac, J.; Larsen, J. W. Fuel 1984, 63, 935-938. (4) Green, T. K.; Larsen, J. W. Fuel 1984,63, 1538-1543.
where A is the percentage of ash in the dry residue and Q is the percentage of ash in the dry feed coal. The experimental error for the conversion was =3%.
Results and Discussion The volumetric swelling ratios for Taiheiyo coal were measured in several solvents. The results are shown in Figure 1. In these data, the swelling ratios were higher for undried Taiheiyo coal than for dried Taiheiyo coal, indicating that the water contained in the coal plays an important role in swelling. The swelling ratio by THQ was higher than that by tetralin, a well-known good solvent for (5) Kawai, T.; Esumi, K.; Meguro, K.; Honda, H. Fuel 1984, 63, 1615-1618.
Coal Swelling Using Binary Mixtures
Energy & Fuels, Vol. 3, No. 1, 1989 57
THQ-MeOH: undried ( A ) THQ-EtOH u n d r i e d ( 0 )
14
THQ-Me0H:undrled ( A ) dried (A) THO-EtOH: u n d n e d ( 0 ) dried ( 0 )
l.Z 20
0
60
40
80
100
Weight percent of alcohol in mixture
20
0
Figure 3. Swelling ratios of undried Miike coal as function of
40
60
80
I00
Weight percent of alcohol in mixture
weight percent of alcohol in THQ-alcohol mixtures.
Figure 5. Swelling ratios of undried and dried Taiheiyo coal as a function of weight percent of alcohol in THQ-alcohol mixtures.
I
Taiheiyo coal
1. 8
1.6
.-0
B
THO-E t OH ( 0 , O )
0
12
24
-.-m 2VI 48
I
Swelling time / h
THO-MeOH: undried(A) dried( A ) THQ-EtOH: undried(0) dried(.)
1.2
Figure 4. Swelling ratios of undried Taiheiyo and Yallourn coals by THQ-alcohol mixtures (THQ:alcohol = 9:l by weight) as a function of swelling time.
liquefaction.6 Alcohols such as methanol and ethanol showed a high swelling ratio for undried Taiheiyo coal. Furthermore, the mixtures of THQ and alcohols provided high swelling ratios for both undried and dried Taiheiyo coals. On the other hand, the behavior of the swelling ratio for Yallourn coal was significantly different from that of Taiheiyo coal (Figure 2). In the alcohol and THQ-alcohol systems, the swelling ratios were higher for dried Yallourn coal than for undried Yallourn coal. In particular, the THQ-alcohol system remarkably increased the swelling ratios. However, the swelling ratio of Miike coal is nearly constant in the alcohol and THQ-alcohol systems (Figure 3). The swelling ratios for Taiheiyo and Yallourn coals are affected differently by drying the coals. The role of water in coal solvent swelling is not fully understood at the present time. Further, in order to study the swelling behavior of coals with binary solvents containing THQ in more detail, the swelling ratios of the coals were measured as a function of swelling time. Figure 4 indicates that a substantial amount of swelling occurs rapidly. It is apparent that the swelling ratios of undried Taiheiyo coal increase with an increase in the swelling time and reach a constant after 24 h, while those of undried Yallourn coal gradually in(6)Hausigk,V. D.; Koelling, G.; Ziegler, F. Brennst.-Chem. 1969,50, 8-11.
0
20
40
60
80
100
Weight percent of alcohol in mixture
Figure 6. Swelling ratios of undried and dried Yallourn coal as a function of weight percent of alcohol in THQ-alcohol mixtures. crease and become constant in a short swelling time, i.e., 12 h. The difference in the swelling time required to reach a constant swelling ratio may be explained as follows: since the porosity of Yallourn coal is greater than that of Taiheiyo coals,’ the THQ-alcohol solvents can penetrate more easily for Yallourn coal than Taiheiyo coal and the equilibrium swelling time becomes shorter for Yallourn coal. Figures 5 and 6 show the swelling ratios of Taiheiyo and Yallourn coals as a function of the weight percent alcohol in THQ-alcohol mixtures. As can be seen, over the whole range the swelling ratios of undried Taiheiyo coal are higher than those of dried Taiheiyo coal, whereas the swelling ratios of dried Yallourn coal are higher than those of the undried coal. The amounts of THQ and alcohols absorbed by coals from the THQ-alcohol mixtures are shown in Figures 7 and 8. An enormous effect on the swelling of the coals was observed upon the addition of alcohol. As the additive amount of alcohol increased, the absorbed amount of al(7) Berkowitz, N.; Schein, H.G. Fuel 1952, 31, 19-32. (8) Derbyshire, F. J.; Odoerfer, G. A.; Whitehurst, D. D. Fuel 1984,63, 56-60.
Amemiya et al.
58 Energy & Fuels, Vol. 3, No. I, 1989
1
I
THQ(O!-MeOH(A)
Table 11. Comparison of Measured and Calculated Swelling Ratios for Undried Coals Using THQ-Alcohol Mixtures MeOH EtOH wt % of alcohol SJmeasd) SJcalcd) SJmeasd) SJcalcd) Taiheiyo Coal 10 20 30 40 60
1.47 1.53 1.57 1.62 1.57
1.43 1.59 1.55 1.58 1.55
10 20 30 40 60
1.50 1.57 1.63 1.60 1.49
1.58 1.57 1.45
1.55 1.55 1.51 1.47 1.42
1.44 1.65 1.69 1.65 1.64
1.36 1.46 1.57 1.54 1.51
Yallourn Coal 20
0
60
LO
Weight percent of alcohol in mixture
Figure 7. Absorbed amounts of THQ and alcohol into undried Taiheiyo coal as a function of weight percent of alcohol in THQ-alcohol mixtures.
c
9oc
h!
w Taiheiyo coal
THO-MeOHW
I
//
A.
80
1.41 1.47 1.53 1.47 1.43
THQ- Et OH(0)
Yallourn coal c u 0
80 THCI-MeOH(A)
70
THQ-EtOH(0) ,
0 0
20
40
60
Weight percent of alcohol in mixture
Figure 8. Absorbed amounts of THQ and alcohol into undried Yallourn coal as a function of weight percent of alcohol in THQ-alcohol mixtures.
20
I
C
/
40
Weight percent of alcohol in mixture
Figure 9. Coal conversion of undried Taiheiyo and Y d o u m coals swelled in THQ-alcohol mixtures.
coals. As the coal conversion in both THQ-ethanol and THQ-methanol increases with increasing amounts of alcohol in the binary vehicles and then decreases, the concoho1 decreased, reached a minimum value, and increased, version curves shown in Figure 9 illustrate trends similar while the absorbed amount of THQ increased, reached a to those in the swelling curves. In particular, the conmaximum value, and then decreased. These trends are version of Taiheiyo coal in the THQ-ethanol and THQobserved for both undried Taiheiyo and Yallourn coals in methanol mixtures was enhanced. Further, it should be the THQ-ethanol and THQ-methanol systems. It is pointed out that the conversions of both coals increase in noteworthy that the maximum swelling ratio coincides with spite of decreasing amounts of THQ added. As expected the maximum absorbed amount of THQ for both undried from the swelling experiments, the conversion of Miike coal Taiheiyo and Yallourn coals. This indicates that an apdid not increase at all. Since the swelling measurements preciable swelling of the coals in the THQ-alcohol mixtures and coal liquefactions were conducted at different temoccurs by incorporating THQ. The swelling ratios calcuperatures, they can not be directly compared. These data, lated for the THQ-methanol and THQ-ethanol systems however, support the view that there is a mutual relaby using the absorption data are in good agreement with tionship between coal liquefaction and swelling. It is the measured swelling ratios for Taiheiyo coal, while for postulated that hydrogen bonding among THQ, alcohol, Yallourn coal the calculated values are a somewhat lower and the coal structure form complexes and that the rethan the measured ratios (Table 11). In a previous paper,* sulting swelling of the coal facilitates the liquefaction rewe found that the amount of ethanol absorbed by undried action by increasing the permeation of THQ in the coal Taiheiyo coal from THQ-ethanol mixtures was negligibly structure. Indeed, Spencerg mentioned that hydrogen small. However, in that case, the detection system was bonding between basic nitrogen heterocycles and water inadequate. plays a role in incorporating the solvent into the coal The swelling results obtained above indicate that, at the structure. In THQ-alcohol mixtures that are miscible in optimum solvent composition, THQ, which is a hydrogen donor vehicle and has a high activity for l i q ~ e f a c t i o n , ~ ~ ~each other, THQ is incorporated into coal and it is possible to form hydrogen bonding between THQ and coal sites swells coal effectively and penetrates into the coal structhat have been hydrogen bonded to water. This situation ture. Thus, the coal swelled with a hydrogen donor vehicle would ensure that THQ is available at the right sites when should provide higher coal conversion. Figure 9 shows coal conversion in THQ-ethanol and THQ-methanol for undried swollen Taiheiyo and Yallourn (9) Spencer, D. EPRI J. 1982, 31-34.
Energy & Fuels 1989,3, 59-64
the liquefaction reaction begins. In conclusion, this study shows that the THQ-methanol and THQ-ethanol systems make Tallourn and Taiheiyo coal swell significantly whereupon a considerable amount of THQ is incorporated into the coals. By liquefaction of
59
the coals thus swelled, a higher liquefaction yield is obtained under mild conditions. Registry No. 1,2,3,4-Tetrahydroquinoline, 635-46-1; methanol, 67-56-1; benzene, 71-43-2; tetralin, 119-64-2; ethanol, 64-17-5; methylcyclohexane, 108-87-2.
Promotion of Coal Liquefaction by Iodomethane. 2. Reaction of Coal Model Compounds with Iodomethane at Coal Liquefaction Temperatures Moetaz I. Attalla,* Michael A. Wilson, Robinson A. Quezada, and Anthony M. Vassallo CSIRO Division of Coal Technology, P.O. Box 136, North Ryde, N S W 2113, Australia Received M a y 5, 1988. Revised Manuscript Received September 29, 1988
The reactions of iodomethane with a number of simple organic substances representative of structural groups in coal have been studied in an attempt to explain the success of iodomethane in promoting coal liquefaction. Iodomethane promotes dehydrogenation of hydroaromatic rings under nitrogen, hydrogenation of aromatic rings, hydrogenolysis of phenols and phenol ethers, and the conversion of pyridine heterocycles to naphthalene and its derivatives under hydrogen. In the presence of molecular hydrogen, hydrogen iodide is as effective as iodomethane. This suggests that iodine is the important reactive moiety and probably functions in hydrogenation and hydrogenolysis by catalyzing the formation of hydrogen radicals from hydrogen gas.
Introduction When coal is reacted with molecular hydrogen under mild liquefaction conditions (6.9 MPa cold charge and 400 OC) in the presence of tetralin and conventional coal liquefaction catalysts, a brittle solid called solvent-refined coal is formed.' However, when coal is reacted with molecular hydrogen at the same pressure and temperature but in the presence of iodomethane, high yields of volatile liquid products are obtained? The reasons for the success of iodomethane in coal liquefaction have not yet been established. Consequently we have examined the reactions of suitable model compounds (representing some of the functional and structural groups in coal) with iodomethane and molecular hydrogen. The compounds studied include pyridine, a series of bicyclic aromatics, hydroaromatics, ethers, and benzylic compounds known to be pyrolysis or hydrogenation product^.^*^ In order to elucidate the mechanism of the reaction, some reactions were also carried out in the presence of hydrogen iodide. I3C-labeled iodomethane was used to investigate the mechanism by which nitrogen is removed from pyridine. Reactions were also carried out in the presence of an inert gas, namely nitrogen, since these conditions may occur in parts of the coal not reached by molecular hydrogen. Experimental Section Iodomethane (reagent grade) was used directly as received from Fluka. The other compounds were all of reagent grade and were obtained from various commercial sources. All were found by gas chromatography to be of suitable purity (>97%) and thus were used without further purification. (1) Jones, D. G.; Rottendorf, H.; Wilson, M. A.; Collii, P. J. Fuel 1980. 59, 19-26. (2) Vassallo, A. M.; Wilson, M. A.; Attalla, M. Energy Fuels 1988,2, 539-547. (3) Collin, P. J.; Gilbert, T. D.; Philp, R. P.; Wilson, M. A. Fuel 1983, 62,450-458.
In a typical reaction procedure, iodomethane and model compound were placed in a glass-lined 1-Lrocking Parr autoclave. The autoclave was pressurized with hydrogen or nitrogen to 6.9 MPa and then heated to 400 "C a t a rate of 4 "C/min. After 1 h a t reaction temperature, the autoclave was allowed to cool to room temperature (5 "C/min) and vented. The reaction products were analyzed on a Packard 437A gas chromatograph fitted with a SGE 12 m X 0.2 mm vitreous microcapillary column packed with methylsilicone (BP 1). The oven temperature was programmed from 20 to 250 "C at 10 "C/min. Specific identification of products was made by coinjection of standards or by a Finnigan 4023 gas chromatograph-mass spectrometer (GC/MS) by comparison with library spectra. An SE-30capillary column (50 m X 0.2mm) was used on the GC/MS. The temperature controller was programmed from 15 to 100 "C at 10 "C/min and then from 100 to 290 "C at 4 "C/min. An electron-impact ionizing voltage of 70 eV was used with a filament emission current of 0.25 mA and an ion source temperature of 200 "C. Data were processed with an INCOS 2300 data processing system. 13C NMR spectra were obtained on a JEOL FX9OQ NMR spectrometer using chromium acetylacetonate as relaxation reagent, a 45" pulse, inverse gated decoupling, and 4 s pulse delays. Details of the NMR analytical method can be found e l s e ~ h e r e . ~The ~ GASPE technique5 was also used to aid assignment. In some experiments aqueous hydrogen iodide was substituted for iodomethane. Details of reaction conditions and products are shown in Table I.
Results and Discussion Reactions. Table I shows that iodomethane accelerates the decomposition of tetralin to naphthalene in both hydrogen (experiments 1and 2) and nitrogen (experiments 3 and 4) atmospheres. Thus under coal liquefaction conditions hydroaromatic rings might be expected to be converted to aromatic rings by iodomethane. It is clear that (4) Wilson, M. A.; Pugmire, R. J.; Vassallo, A. M.; Grant, D. M.; Collin, P. J.; Zilm, K. W. Ind. Eng. Chem. Prod. Res. Deu. 1982,21, 477-483. (5) Cookson, D. J.; Smith, B. E. Org. Magn. Reson. 1981,16, 111-116. (6) Wilson, M. A.; Vassallo, A. M.; Collin, P. J.; Bath, B. D. Fuel Process. Technol. 1984, 8, 213-229.
0887-0624/89/2503-0059$01.50/00 1989 American Chemical Society
