Energy & Fuels 1989, 3, 533-535
terunit linkages connecting them, in this case the degree of aromatic substitution. Acknowledgment. We gratefully acknowledge the support of this work by the Office of Basic Energy Sci-
N
533
ences, Division of Chemical Sciences, US.Department of Energy, under Contract No. W-31-109-ENG-38. The ele m e n d microanalyses were performed by Steve Newnam of the Analytical Chemistry Laboratory at Argonne National Laboratory.
. *
Communtcattons Aliphatic Structural Elements of a Pocahontas No. 3 Coal
Sir: During the past few years, we have used ruthenium tetraoxide oxidation reactions to convert coal macromolecules to a wide array of aliphatic carboxylic and benzenecarboxylic acids'" to gather qualitative and quantitative information about their aliphatic and aromatic structural elements. We recently obtained some very novel new information about the aliphatic carbon atom distribution in Pocahontas No. 3 coal with this oxidation method. A premium sample of Pocahontas No. 3 coal was obtained from the Argonne National Laboratory. This lowvolatile material contains 4.77% ash, and its elemental composition is C100H62,9N1.15~o.1,03.26. Each sample was prepared for oxidation by extraction using aqueous hydrochloric acid, aqueous sodium hydroxide, benzenemethanol, and chloroform as described previously.6 The oxidation was carried out by using coal (1g), ruthenium(111) trichloride trihydrate (27 mg), and sodium periodate (21.4 g) in a mixture of carbon tetrachloride (20 mL), acetonitrile (20 mL), and water (30 mL). The black organic phase became yellow-brown after 2 h. The reaction was continued for 24 h at room temperature before the products were collected and analyzed. Duplicate analyses by the method that we have previously used3 indicated that the oxidation reaction produced 25.7 f 0.7 mol of carbon dioxide/100 mol of C in the coal. The abundances of the volatile carboxylic acids were determined in one set of experiments by using isotope dilution procedure^,^^^ and the less volatile acids were methylated prior to analysis in another set of experiments by gas chromatography-mass spectroscopy as described previously3 (Figure 1). In the first series of duplicate experiments, we observed that the ruthenium tetraoxide oxidation of this coal produced 7.28 f 0.04 mol of ethanoic acid/100 mol of C. This yield is far greater than the yields obtained in the oxidation of the other coals: lignite (Rockdale, TX), 1.1; subbituminous coal (Rawhide, WY), 1.2; bituminous coal (Pittsburgh No. 8), 3.4.2 The Pocohontas No. 3 coal also gives about 0.25 mol of propanoic acid/100 mol of C and about 0.05 mol of butanoic acid/100 mol of C. The yields of these three and four carbon atom materials are similar to the yields of these acids obtained with the other coals.2 Thus, the methyl group concentration in Pocahontas No. 3 coal is unusually high. We have previously inferred that eth-
14
-
7
.
20
30
40
Time (min.)
Figure 1. GC/MS chromatography of the oxidation products of Pocahontas No. 3 coal: (1)1,2-benzenedicarboxylic acid; (2) 3-methylbenzene-1,2-dicarboxylicacid; (3) 4-methylbenzene1,2-dicarboxylicacid; (4)dimethylbenzenedicarboxylic acid; (5) dimethylbenzenedicarboxylic acid; (6) dimethylbenzenedicarboxylic acid; (7) 1,2,3-benzenetricarboxylicacid; (8) 1,2,4benzenetricarboxylic acid; (9) methylbenzenetricarboxylic acid; (10) methylbenzenetricarboxylic acid; (11)dimethylbenzenetricarboxylic acid; (12) trimethylbenzenetricarboxylic acid; (13) 1,2,4,5-benzenetetracarboxylicacid; (14) 1,2,3,4-benzenetetracarboxylic acid; (15) 1,2,3,5-benzenetetracarboxylicacid; (16) methylbenzenetetracaboxylic acid + 2,3,2'-biphenyltricarboxylic acid; (17) methylbenzenetetracarboxylic acid; (18) biphenyltetracarboxylic acid; (19) 2,6,2',6'-biphenyltetracarboxylic acid; (20) benzenepentacarboxylic acid.
anoic acid is derived primarily from the oxidation of arylmethanes.2 Additional work was directed toward the identification of the benzenecarboxylic acids that were formed in the reaction. They were converted to their methyl esters for convenient analysis. The observations, Figure 1, revealed that a significant amount of 1,2-benzenedicarboxylicacid was produced with traces of 1,3- and 1,4-benzenedicarboxylic acids. This observation established the predominance of the well-recognized 1,Bfusion pattern in this coal. It was also evident that methyl- and dimethyl-
0887-0624/89/2503-0533$01.50/00 1989 American Chemical Society
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534 Energy & Fuels, Vol. 3, No. 4, 1989
benzenedicarboxylic acids were produced in the oxidation. Comparison of the mass spectra of the reaction products with the spectra of authentic samples established that 3-methyl-and 4-methylbenzene-l,2-dicarboxylic acids were present but that the corresponding homophthalic acids were absent. The yields of these acids, which are shown with the structures of their methyl esters, were measured by isotope dilution techniques. COOCHri
0 . 0 7 9 mo1/100 mol of C
0.029 mo1/100 mol of C
$ 0 0 ~ ~ 3
Table I. Aliphatic Dicarboxylic Acids Obtained by Oxidation of Pocahontas No. 3 Coal yield, mo1/100 compound mol of C 0.17 butanedioic acid 0.10 2-methyl-1,4-butanedioic acid 0.08 pentanedioic acid 2,2-dimethyl-1,4-butanedioic acid 0.02 0.09 P-methyl-l,5-pentanedioic acid 0.12 hexanedioic acid 2,2-dimethyl-1,5-pentanedioic acid 0.03 0.03 2,3-dimethyl-1,5-pentanedioic acid heptanedioic acid 0.10
accord with the results for the benzenecarboxylicacids and suggest that the abundance of the methyl hydroaromatic compounds parallel the abundances of the methyl aromatic compounds.
PCoocH3
HOOCCH(CH3)CH2CH2C00H derived from @)coal
CH3
0.050 mo1/100 mol of C
The Pocahontas coal produced the methyl derivatives in greater abundance than any other coal that has been in~estigated.~*'-~ Further investigation of the reaction products led to the detection of a variety of other mono- and dimethylbenzenetricarboxylic acids as shown in Figure 1. These substances are formed in much greater abundance from this coal than from the other, principally lower ranking coals that we have studied. The GC-MS data indicate that 0.22 mol of methyl groups/100 mol of C appear among the identified benzenecarboxylic acids. Obviously, additional methyl groups are present among the other unidentified oxidation products. The methylated benzenedicarboxylic acids and benzenetricarboxylic acids can be produced from methylnaphthalene fragments and from more complex, methylated polycyclic and heterocyclic structural elements. The occurrence of these higher molecular weight aromatic compounds in this coal was confirmed by the facile detection of biphenylpolycarboxylic acids which appear in readily detectable quantities in the oxidation products. Benzenepentacarboxylicacid is also formed in appreciable yield. These acids are produced from polycyclic aromatic hydrocarbons with four or more rings.
CH3
HOOCCH(CH3)CH2CH2CH2COOHderived from p
o
a
1
CH3
In summary, the oxidation work has established that this Pocahontas No. 3 coal contains 7.8 mol of methyl groups per 100 mol of C. At least 7.6 mol/100 mol C of these carbon atoms are present as pendant methyl groups on aromatic structural elements, 0.3 mol of other pendant alkyl groups/100 mol of C also occur. H3CC02Hderived from H,C-aryl-coal fragment The study has also definitely established the identities of 2.3 methylene, 0.3 methine, and 0.1 quaternary aliphatic carbon fragments/100 mol of C. The methylated and unmethylated tri- and tetramethylene fragments probably result from the oxidation of hydroaromatic structures. Thus, 10.5 aliphatic carbon atoms/100 mol of C in the coal have been identified. Solid-state NMR spectroscopy implies that this pristine sample contains 13 aliphatic carbon atoms, 7 of which occur in methyl or quaternary carbon atoms.l0J1 Infrared spectroscopy also suggests that methyl groups are abundant in this coal.12 Adoption of the NMR measurement implies that more than 80% of the aliphatic carbon atoms have been located in the oxidation experiments. Knowledge of the aliphatic carbon atom distribution at this confidence level has not, insofar as we are aware, been realized previously. The results provide strong encouragement to elaborate the aromatic structures. Investigations directed to this goal are under way.
Another analysis of the reaction products designed to resolve the aliphatic esters provided the information presented in Table I. I Only the principal aliphatic products that could be determined quantitatively are listed in Table I. Perhaps the most interesting feature of these results centers on the high yields of the 2-methyl carboxylic acids. For example, the 2-methylbutanedioic acid/butanedioic acid ratio is 0.62 and the 2-methylpentanedioic acid/pentanedioic acid is 1.12. These ratios are remarkably large compared to the results obtained with other coals. The detection of these 2-methyl derivatives in significant quantities is fully in
Registry No. Ruthenium oxide, 11113-84-1; ethanoic acid, 64-19-7; propanoic acid, 79-09-4; butanoic acid, 107-92-6; butanedioic acid, 110-15-6; 2-methyl-1,4-butanedioic acid, 498-21-5; pentanedioic acid, 110-94-1; 2,2-dimethyl-1,4-butanedioic acid, 597-43-3; 2-methyl-l,5-pentanedioic acid, 617-62-9; hexanedioic acid, 124-04-9; 2,2-dimethyl-1,5-pentanedioic acid, 681-57-2; 2,3-dimethyl-l,5-pentanedioic acid, 17179-91-8;heptanedioic acid, 111-16-0; 1,2-benzenedicarboxylic acid, 88-99-3; 3-methyl-
(7) Mallya, N.; Zingaro, R. A. Fuel 1984,63, 423. (8)Olson, E.S.; Diehl, J. W. Prepr. Pup.-Am. Chem. SOC.,Diu.Fuel Chem. 1984,29,217. (9) Ilsley, W . H.; Zingaro, R. A.; Zoeller, J. H., Jr. Fuel 1986,65, 1216.
(10)Solum, M. S.;Pugmire, R. J.; Grant, D. M. Energy Fuels 1989, 3, 187. (11) Muntean, J. V. Private communication. (12)Dyrkacz, G. Private communication.
Acknowledgment. Work was performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, United States Department of Energy, under Contract No. W-31-109-ENG-38.
Energy & Fuels 1989,3,535-536
benzene-1,2-dicarboxylicacid, 37102-74-2; 4-methylbenzene-1,2dicarboxylic acid, 4316-23-8; dimethylbenzenedicarboxylic acid, 70174-65-1; 1,2,3-benzenetricarboxylicacid, 569-51-7; 1,2,4benzenetricarboxylic acid, 528-44-9; methylbenzenetricarboxylic acid, 67595-78-2;dimethylbenzenetricarboxylicacid, 70174-69-5; trimethylbenzenetricarboxylicacid, 76720-50-8; 1,2,4,5-benzenetetracarboxylic acid, 89-05-4; 1,2,3,4-benzenetetracarboxylicacid, 476-73-3; 1,2,3,5-benzenetetracarboxylicacid, 479-47-0; methylbenzenetetracarboxylic acid, 67595-79-3; 2,3,2'-biphenyltricarboxylic acid, 4371-39-5;biphenyltetracarboxylic acid, 6906695-1; 2,6,2',6'-biphenyltetracarboxylic acid, 4371-27-1; benzenepentacarboxylic acid, 1585-40-6.
535 MV
Ar
I
I
(y!....I
II
M~
I ~~
I
D
l
I I
Furnace
Timer
Figure 1. Schematic diagram of the reaction apparatus: V1, stop valve; MV, mass flow control valve; SV, three-way solenoid valve; a and b, quartz reactor tubes (5.5 mm i.d.).
I
L. M. Stock,* Shih-Hsien Wang Chemistry Division, Argonne N a t i o n a l Laboratory Argonne, Illinois 60439 Received February 28, 1989 Revised Manuscript Received April 26, 1989
-a
I
0 U c
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0
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> c
2
5
Cyclic Feed C02 Gasification of Iron-Loaded Coal Char. Approach To Activate Iron Catalyst in Coal Gasification
3
V
2
Sir: Many studies have been reported on the iron-catalyzed gasification of carbon and coal with steam and COz.' In the iron-catalyzed gasification of char in C02, significant loss of catalytic activity during gasification was reported.liZ Metallic iron on the char surface was oxidized to Fe304or Fel,O during gasification, depending on the concentration of carbon dioxidea2Differences in the catalytic activities of iron species in C02gasification have been reported by Ohtsuka et al.3 We reported pulsed C02gasification of iron-loaded Yallourn coal char and obtained evidence for the following redox cycle between Fe,O, and Fe,O,+' using W02as probe.4
-
+ C02 Fe,O,+l + C
Fe,O,
Fe,O,+l Fe,O,
+ CO + CO
4
0
(1)
(2)
This led to the development of a cyclic feed gasification process in which a gasification agent and an inert gas were alternately fed to the iron-loaded char bed. Cyclic operation of the catalytic conversion was recently reviewed by Silve~ton.~Certain catalytic processes offer higher activity per unit catalyst load by changing composition of reactants periodically. This communication deals with the first example of cyclic feed gasification of iron-loaded coal char and has demonstrated activation of the iron catalyst by periodic operation. Iron nitrate (Fe(N03)3.7H20)was loaded into Yallourn Australian brown coal (67.5% C and 4.5% H daf; 1.1%ash dry) by the usual impregnation method (0.3 mmol of Fe/g of dry coal). Char was prepared by heating the catalystloaded coal at 800 OC for 30 min under an argon atmosphere at a heating rate of 20 "C/min. A schematic diagram of the experimental apparatus is illustrated in Figure 1. Fifty milligrams of catalyst-loaded char was charged into both reactors a and b, and the char was heated to 800 (1) Hiittinger, K. J.; Adler, J * Hermann, G. In Carbon and Coal Gasification; Figueiredo,J. L., Mokjn, J. A., as. NATO ; AS1 Series, Series
E Martinus Nijhoff Dordrecht, The Netherlands, 1986. (2)Furimsky, E.; Sears, P. L.; Suzuki, T. Energy Fuels 1988, 2, 634-639 and references therein. (3)Ohtsuka, Y.; Tamai, Y.; Tomita, A. Energy Fuels 1987,1,32-35. (4)Suzuki, T.; Inoue, K.; Watanabe, Y. Energy Fuekr 1988,2,673-679. ( 5 ) Silveston, P.L. Sadhana (India) 1987,10,217-246.
0887-06241 89 / 2503-0535$01.50 / 0
0
40
20 Time
60
min
Figure 2. Cumulative CO yield against reaction time. Conditions: 50 mg of char X 2 (0.6 mmol of Fe/g of char), at 800 "C; C02and Ar flow rate, 10 and 15 mL/min. Key: (0)50 mg of char and steady feed gasification; (0) cycle time 30 s; ( 0 )cycle time 60 s; (a) cycle time 90 s; (- - -) hypothetical nonregeneration case.
"C at a heating rate of 20 OC/min under an argon stream. When the temperature reached 800 "C, C02 was introduced by opening stop valve V1 through a three-way solenoid valve SV, which was operated by a timer. The solenoid valve periodically switched over (cycle time tJ the COz feed either into reactor a or reactor b. Argon was continuously fed into both reactors a and b. Combined effluent gas from reactors a and b was collected in gas burets at certain intervals. C02was periodically fed to the iron-loaded char (CFG). During gasification with C02,the iron species would be oxidized to a higher oxidation state. When COz was switched to Ar, C02 was swept out, reduction of the higher oxidation state iron oxide would follow as shown in eq 2, and catalyst regeneration was accomplished. For comparison using only one reactor tube of the same apparatus, gasification of the same char was carried out under a steady flow of a mixture of C02and Ar of the same concentration used for CFG (SG). The cumulative CO production against reaction time is shown in Figure 2. In the SG mode, 50 mg of the char (half of the CFG) was employed, and on the other hand, in the CFG process, the contact time of COPwith the char loaded to the respective reactor tube is half of the total reaction time. Therefore, it is difficult to evaluate the validity of the CFG process over the SG mode. For simplicity, a hypothetical cumulative CO production curve is drawn by plotting the double amounts of CO formed at reaction time ti against twice the reaction time ti, illustrated in Figure 2 as a dotted line. The dotted line corresponds to the CO production behavior at a cycle time of 30 min in CFG with total reaction time of 60 min or indicates a hypothetical CO formation curve by the CFG method without catalyst regeneration (nonregeneration Q 1989 American Chemical Societv
