Energy & Fuels 1990,4, 333-335
insert has an input line for oxygen addition and a platinum heater. An oxygen flow of 10 cm3/min and a temperature of about 800 "C in the platinum heater were employed. Results are presented for a Zap lignite in Figure 18. Figure 18a presents the weight loss, which is almost identical with that in Figure 12a. Parts b, c, and d of Figure 18 present the yields of H20, COP,and SO2,which are the primary oxidation products of the volatile species. We could not see significant amounts of NO in the combustion products. The other volatile species (tar, CHI, C2H4, CO, NH,, and COS) have also been oxidized and are thus absent from the spectra. To analyze the results, the H20, C02, and SO2 observed in pyrolysis (Figure 12) have been subtracted from the curves in Figure 18b-d and the results presented in Figure 18e-g. The H20,C02, and SO2difference curves now have peaks that match the tar evolution peak in Figure 12c. These data determine the C, H, and S composition of the tar. In addition, the H20 evolution profile has a wide peak at elevated temperatures believed to result from the oxidation of hydrogen. The COPhas a high-temperature peak from the oxidation of CO. The SO2has peaks at 449 and 565 "C related to the release of H2S. The peak a t 565 OC is close to that for a sample of pure pyrite run in the TG-FTIR. Thus, the postoxidation section adds significant new information to the analysis. Summary and Conclusions
A single TG-FTIR analysis provides an extensive characterization of coal with regard to the decomposition kinetics, char reactivity, functional group compositions, and conversion behavior. The paper presents the following: 1. The TG-FTIR apparatus for pyrolysis, oxidation of pyrolysis products, and oxidation of the sample is described.
333
2. Pyrolysis results are presented for the eight Argonne coals, several demineralized coals, and two oxidized samples of Pittsburgh Seam coal. 3. There are certain evolution peaks that match in shape and temperature for more than one species, suggesting common chemistry responsible for the evolution of these species. 4. Several peaks in the C02 evolution have been identified with mineral decomposition. 5. Increases in tar yield are observed for the demineralized coals (especially low-rank coals) while decreases in tar yield are observed for the oxidized samples. 6. A kinetic analysis was applied to species evolution data collected at several different heating rates. There is a systematic variation in rate with rank. The rate for tar evolution from Pittsburgh Seam coal is in good agreement with that of Burnham et al.17 using a similar set of data. 7. Analyses of the amounts of evolved products also show a systematic variation with rank consistent with the coal's elemental and functional group compositions. 8. Postoxidation of the volatile products has been successful in providing elemental composition information on the volatile products as well as showing the evolution of H2, which is not infrared active, and H,S (in the postoxidized SO2 profile), which is a weak infrared absorber. 9. Oxidation of the char yields the ash amount as well as two measures of the char's reactivity, the oxygen absorbed by the char, and the temperature a t which significant oxidation of the char occurs. Acknowledgment. This work was supported by the
U.S.Department of Energy, Morgantown Energy Technology Center, under Contract No. DE-AC21-86MC23075 and the National Science Foundation, Grant No. ISI8703520. We acknowledge the contributions of Z. Z. Yu and S. Charpenay on the modeling of the TG-FTIR data. We also thank Jean Whelan of Woods Hole Oceanographic Institute for supplying the siderite sample.
Communications Decrease of Extraction Yields after Acetylation or Methylation of Bituminous Coals
Sir: Acetylation and alkylation of a coal are known to
increase the extraction yield with solvent^.'-^^'^* Liotta, Rose, and Hippo' reported that 0-methylation of a coal increased the extraction yield with THF, benzene, and chloroform. They considered that the breaking of hydrogen bonds by 0-alkylation increased extraction yields. Mallya and Stock2and Miyake and Stock3suggested that the increase of extraction yields for high-rank coals after alkylation is attributed to the disruption of noncovalent bonding interactions such as the stacking of aromatic (1) Liotta, R.; Rose, K.; Hippo, E. J . Org. Chem. 1981, 46, 277-283.
(2) Mallya, N.; Stock, L. M. Fuel 1986, 65, 736-738.
(3) Miyake, M.; Stock, L. M. Energy Fuels 1988,2, 815-818.
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moieties. Botto et a1.I reported that in alkylation of bituminous coals by the method of Liotta5 C-alkylation on acidic methylene or methine hydrogens also occurred. The similar possibility of C-acetylation for asphaltene and preasphaltene was reported by Baltisberger et a1.6 The increase of extraction yield with pyridine after Cmethylation of an 0-methylated coal was reported by Chambers, Hagaman, and Woody.7 Nair, Kumari, and (4) Botto, R. E.; Choi, C.; Muntean, J. V.; Stock, L. M. Energy Fuels 1987, I , 270-273. (5) Liotta, R. Fuel 1979, 58, 724-728. (6)Baltisbereer. R. J.: Patel. K. M.; Woolsey, N. F.; Stenberg, V. I. Fuel 1982, 61, g48-852. (7) Chambers, R. R.; Hagaman, E. W.; Woody, M. C. Polynuclear Aromatic Hydrocarbons; Ebert, L., Ed.; Advances in Chemistry 217: American Chemical Society: Washington, DC, 1987; Chapter 15, pp 255-268.
0 1990 American Chemical Society
334 Energy & Fuels, Vol. 4, No. 3, 1990 Table I. Extraction Yields of the Raw Coals and of Acetylated and Methylated Coals with CS,-Pyridine Mixed Solvent (1:l by Volume)
coal Zao Zhuang Shin-Yubari Pittston Ping Ding Shan Miike
%C (daf) 86.9 86.7 86.6 85.4 83.4
extraction yield, wt %, daf acetylated methylated raw coal coal" coalb 33.4 41.4 (41.1)c 40.4 (30.3)d 35.0 38.7 43.3 17.1 22.3 28.2 18.7 28.2 29.3 29.9 43.6 (32.61e 37.9 (37.4)d
"Acetic anhydride in pyridine, reflux. bMethyl iodide and tetrabutylammonium hydroxide in T H F , room temperature. e Blank experiment of acetylation; reflux with pyridine. dStirring in T H F and tetrabutylammonium hydroxide, room temperature.
Table 11. Extraction Yields of the Raw Coals and of Acetylated and Methylated Coals with CS2-NMP Mixed Solvent (1:l by Volume)
coal Zao Zhuang Shin-Yubari Pittston Ping Ding Shan Miike
extraction yield, wt %, daf acetylated raw coal coal" methylated coalb 63.0 47.9 (47.8)c 57.1 (63.4Id (54.0)O 56.8 40.9 (50.2)' 54.0 (57.0)d 35.5 28.6 37.6 43.0 33.1 39.8 31.1 45.6 (32.3)c 40.3 (33.51d (43.21e
OAcetic anhydride in pyridine, reflux. bMethyl iodide and tetrabutylammonium hydroxide in T H F , room temperature. e Blank experiment of acetylation; reflux with pyridine. Blank experiment of methylation; stirring in THF, room temperature. e Stirring in THF and tetrabutylammonium hydroxide, room temperature.
PardhasaradhP reported that reductive acetylation of a coal increased the extraction yield with pyridine, possibly due to a decrease in noncovalent polar interactions. CS2-N-methyl-2-pyrrolidinone (NMP) mixed solvent was found to give very high extraction yields for many bituminous coals at room temperature.+" It is important to estimate the quantity of extractable substances originally present in a coal for not only the elucidation of coal structure but also coal liquefaction and other coal utilization processes.12 Thus, we have examined whether more enhanced yields with the mixed solvent are obtained by the treatments mentioned above, or not. We find that the extraction yields with the mixed solvent unexpectedly decrease after acetylation and methylation for some coals and report here. Five bituminous coals giving high extraction yields with CS2-NMP mixed solvent were used. A 5.0-g sample of a coal (particle size C250 pm) was acetylated with 5 mL of acetic anhydride in 60 mL of pyridine under reflux for 20 h. Methylation was conducted according to the procedure by L i ~ t t ai.e., ; ~ 5.0 g of a coal in 60 mL of tetrahydrofuran (THF) was stirred at room temperature, with slow addition of 10 mL of 40% aqueous solution of tetrabutylammonium hydroxide, and after 2 h, 5 mL of methyl iodide was added. As blank experiments, a coal was refluxed with pyridine for 20 h without acetic anhydride, or a coal was stirred in THF for 20 h at room temperature. All the treated sam!8) Nair, C. K. S.; Kumari, B. K.; Pardhasaradhi, M. Fuel 1989, 68, 127-128. (9) Iino, M.; Kumagai, J.; Ito, 0. J . Fuel SOC.J p n . 1985,64, 210-212. (10) Iino, M.; Takanohashi, T.; Ohsuga, H.; Toda, K. Fuel 1988, 67, 1639-1647. ... -. .. . ~
(11) Iino, M.; Takanohashi, T.; Obara, H.; Tsueta, H.; Sanokawa, Y. Fuel 1989, 68, 1588-1593. (12) Wei, X.-Y.; Shen, J:L.; Takanohashi, T.; Iino, M. Energy Fuels 1989,3, 575-579.
Communications ples were extracted with CS,-NMP or CS2-pyridine (Py) mixed solvent, the latter which usually gives a lower extraction yield than CS2-NMP mixed solvent,l0under ultrasonic irradiation a t room temperature. Table I and Table I1 show the results of extraction of the raw, acetylated, and methylated coals with CS2-Py and CS,-NMP mixed solvent, respectively. When CS2-Py mixed solvent was used (Table I), the yields of the treated coals increased compared to untreated coals, in agreement with the previous works mentioned above. However, for CS2-NMP mixed solvent (Table 11), the extraction yields unexpectedly decreased after both treatments for Zao Zhuang, Shin-Yubari, and Ping Ding Shan coals, and after acetylation for Pittston coal. Table I1 also shows that the higher the extraction yield for a raw coal, the larger the degree of decrease after the treatment. The blank experiment of acetylation, i.e., only the refluxing with pyridine (Tables I and 11), shows that, for Miike coal, which gives a relatively low extraction yield for the raw coal, the effect of acetylation itself was confirmed, since the yields of blank experiment for its coal do not change, compared to that of the raw coal. Also, the yields of blank experiment of acetylation for Zao Zhuang and Shin-Yubari coals decrease with the CS2-NMP mixed solvent and increase with the CS2-Py mixed solvent, as we have preliminarily reported.1°J3 The increase in the extraction yield may be explained as follows. The refluxing with pyridine at about 110 "C can release some extractable substances from inside of the coal network, which cannot be extracted at room temperature by extraction with CS2-Py mixed solvent, due to the insufficient penetration into the insi'de of the coal network. These extractable substances may not return to inside of the network after pyridine has been removed. Therefore, the extraction yield with CS2-Py mixed solvent after the refluxing with pyridine increases, compared to that of an untreated coal. On the other hand, the reasons for the decrease in the extraction yields are not clear at present, although several explanations are possible. Nishioka and Larsen14 also reported that immersing a coal in pyridine at room temperature or warming it in chlorobenzene or toluene decreased pyridine extractabilities. The detailed study on influences of solvent treatment will be reported in the future. In the blank experiment of methylation, no change of extraction yields with CS2-NMP mixed solvent for three coals used, compared to that of the raw coals, is seen in Table 11, indicating that the stirring in THF is not responsible for the change of extraction yields by methylation. Also, when a coal was treated (stirring) with THF and 40% aqueous solution of tetrabutylammonium hydroxide for 20 h (no methyl iodide), the extraction yields with both mixed solvents changed greatly, i.e., a decrease for Zao Zhuang and Shin-Yubari coals, and an increase for Miike coal (Tables I and 11). Mallya and Stock2also noted the changes in pyridine extractability after THF and tetrabutylammonium hydroxide treatment of coals. The difficulty in removing retained tetrabutylammonium hydroxide,15J6the evidence of base reagent incorporation in the coal," and the possibility of some competing side reaction in the presence of the base1J8were suggested. Thus, (13) Seki, H.; Ita, 0.;Iino, M. Energy Fuels, submitted for publication. (14) Nishioka, M.; Larsen, J. W. Energy Fuels 1990, 4, 100-106. (15) Hagaman, E. W.; Chambers, R. R.; Woody, M. C. Anal. Chem. 1986,58, 387-394. (16) Ettinger, M.; Nardin, R.; Mahasay, S. R.; Stock, L.M. J . Org. Chem. 1986,51, 2840-2842. (17) Hagaman, E. W.; Chambers, R. R.; Woody, M. C. Energy Fuels 1987, 1, 352-360. (18) Choi, C. Y.; Dyrkacz, G. R.; Stock, L. M. Energy Fuels 1987, 1 , 280-286.
Energy & Fuels 1990,4,335-336 the extraction yield with the mixed solvents after methylation may be affected by the action of tetrabutylammonium hydroxide, besides the increasing effect of methylation itself. The results obtained above suggest that other factors such as influences of the solvents and reagents used and reaction conditions should be considered in the evaluation of the effect of acetylation or alkylation on solvent extraction and other processes. Registry No. CS2,75-15-0; tetrabutylammonium hydroxide, 2052-49-5;N-methyl-2-pyrrolidone,872-50-4.
335
C l i 1 , ,
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Toshimasa Takanohashi, Masashi Iino*
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Chemical Research Institute of Non-Aqueous Solutions, Tohoku. University Katahira, Aoba-ku, Sendai 980, J a p a n
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Received September 5, 1989 Revised Manuscript Received March 5, 1990
Paraffinic Materials in Coals Sir: Linear hydrocarbons are present in coal extracts and are frequently obtained in thermal reactions.' Alkanes can originate in several ways. First, they may be present in the coal and be isolable via conventional extraction. Second, they may be present as alkanes but be unextractable as a consequence of deep occlusion. Third, they may be covalently anchored and produced during reactions in which chemical bonds are cleaved. Their origins are closely associated with the mobile phase of coal concept.'-3 Unfortunately, major confusion can result when the strategy used for the detection of an unbonded alkane approaches the severity required for thermal degradation of a bonded derivative. This problem is compounded when nonquantitative analytical methods are used. To examine this issue in a new way, we carried out experiments in which the thermal reactions that decompose the macromolecular molecule are performed in a deuterium-rich environment. The approach is based on the fact that paraffinic hydrocarbons undergo exchange with tetralin-d12or tetrahydroquinoline-2,2,3,4,4-d, slowly under conditions (420 "C for 1 h) that decompose the coal. In this situation, hydrocarbons that were entrapped within the macromolecular network are obtained essentially free of deuterium whereas the hydrocarbons that were formed as a consequence of thermal bond cleavage are labeled. Three relatively familiar coals were examined: Illinois No. 6 (APCSP 5 ) , another hvb coal with about 10% sporinite from the Upper Kittanning seam of West Virginia (PSOC 732), and a Millmerran coal that had been investigated by Nelson and c o - w ~ r k e r s . ~ ~ ~ Preliminary experiments established the degree of exchange of pentadecane, heptadecane, and eicosane. In a typical experiment, eicosane (3 mg) was dissolved in tet(1) Given, P. H. Coal Sci. 1984, 3, 179. (2) Given, P. H. Fuel 1986,65, 155.
( 3 ) Derbyshire, F.; Marzec, A.; Schulten, H.-R.; Wilson, M. A.; Davis, A.; Tokely, P.; Delpuech, J.-J.;Jurkiewicz, A.; Bronniman, C. E.; Wind, R. A.; Maciol, G.E.; Narayan, R.;Bartle, K.; Snape, C. Fuel 1989, 68, 1091. (4) The compositions of the coals have been presented in refs 5,6, and
9. (5) Nelson, P. F. Fuel 1987, 66, 1264-1268.
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0 1 2 3 4 5 6 7 8
Figure 1. Deuterium distribution of the alkanes that were obtained in the deuteriodegradation of extracted PSOC 732 coal.
ralin-d12(100 vL) and tetrahydroquinoline-d5 (100 FL) and heated in a glass vessel at 420 OC for 2 h. The mass spectrum revealed that the P:(P l):(P + 2) ratio for eicosane changed from 100:22.3:2.4 to 100:31.0:4.5 during the reaction. Thus, about 8% of the original eicosane was converted to eicosane-d. Linear alkanes with up to 30 carbon atoms were present in the products of an Illinois No. 6 coal after treatment for 1 h at 420 "C in tetrahydroquinoline and tetralin. Next, the coal was thoroughly extracted with pyridine. The alkane fraction as previously reported by the Argonne group6 constituted about 1% of the coal. The residues were reacted at 420 "C for 1h in the donor solvent. There were less than 0.05% alkanes in the soluble products. The dissolution experiment was repeated in tetrahydroquinoline-d, and tetralin-d,,. The linear hydrocarbons with 16-30 carbon atoms did not contain deuterium in excess of the amounts anticipated for exchange. Thus, the very small quantities of alkanes that were obtained after donor solvent dissolution of the residue were physically entrapped within the solid and were not covalently anchored. Similar experiments were performed with the Lower Kittanning cod. Donor solvent dissolution of the extracted coal provided approximately 0.015% alkanes. The isotope distribution in the products is shown in Figure 1. The linear alkanes with 16-18 carbon atoms contain only modest amounts of deuterium. These substances, which constitute 0.01% of the coal, apparently are liberated via physical destruction of the matrix. The remainder of the alkanes, which have as many six deuterium atoms per molecule, constitute about 0.005% of the coal and have been formed through the cleavage of covalent bonds. The results are distinctive because two classes of alkanes are obtained in the thermal reactions.
+
( 6 ) Xia,
Y. J.; Neill, P. H.; Winans, R. E. Prepr. Pap.-Am. Chem.
SOC.,Diu. Fuel Chem. 1987, 32 ( 4 ) , 340.
0 1990 American Chemical Society
