Energy & Fuels 1991,5, 771-773
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they release hydrogen which is a source for partial hydrogenation of aromatics.21t22 However, reaction in 15% formic acid at 315 "C completely converted 1-phenoxynaphthalene to phenol (100 mol %) and 1-naphthol (98.6 mol 9%) over 3 days with only traces of naphthalene (0.8 mol %) and 1-tetralone (0.6 mol 9%)formed. Comparison of conversions in formic acid (36.6%) and water (4.5%) after 2 h clearly shows that acid-catalyzed hydrolysis, rather than any reduction properties of formic acid, is important. With 15% sodium formate at 315 "C over 3 days, however, 1-phenoxynaphthalene underwent 24.6% conversion to phenol (24.6 mol %), 1-naphthol (13.0 mol %), 1,2-dihydronaphthalene (5.8 mol %), and naphthalene (5.8 mol %). Thus,reaction in sodium formate was slower than reaction either in acid or water, but reduction was of greater importance, This result is reinforced by similar studies in 15% phosphoric acid where 1-phenoxynaphthalene gives 91.6% conversion in only 30 min with only traces (1.2 mol 9%)of reduction products formed, and in basic calcium carbonate where cleavage and reduction reactions are completely inhibited. Mechanistically (Scheme 11),hot water can act as an acid to protonate 1-phenoxynaphthalene. The protonated intermediate reacts with water to give phenol and 1naphthol. The tautomeric forms of 1-naphthol may undergo reduction to furnish 1,2-dihydro- and 3,4-dihydronaphthol. The former can either lose water to form naphthalene or undergo further reduction to form 1,2dihydronaphthalene. The latter would tautomerize to tetralone. Formic acid and sodium formate are most likely the hydride ion sources for the reduction pathway as shown. (18)Rou, D. S.; N uyen, Q. C. Fluid Phase Equilib. 1983, IO, 319. (19) Rou,D. 9.; I+ cMillsn, ! D. F.; Hum, G. P.; Miin, T. C. DOE/ PC 70811-9, Janua 1987. (20) HorvAth, I. Sirkin, M., rubmittad for publication. (21) Stainberg, V. I.; Wang, J.; Baltisberger, R. J.; Van Buren, R.; W o o b y , N. F. J. Org. Chem. 1978,43, 2991. (22) Baltbbeger, R. J.; Stainbag, V. I.; Wang, J.; Woolsey, N. F. Prep. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1979,24,74.
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The larger ring system, 9-phenoxyphenanthrene,is much more reactive than 1-phenoxynaphthaleneand is cleaved in water at 315 "C in 3 h (97% conversion) to form primarily 9-hydroxyphenanthrene and phenol. A small amount of phenanthrene (4.5 mol %) is also formed. Addition of 15% formic acid resulta in complete conversion to yield phenol (100 mol %), 9-hydroxyphenanthrene (87 mol %), and some additional phenanthrene (13 mol %), most likely by a reductive dehydroxylation pathway. In the presence of sodium formate, the acid-catalyzed cleavage was retarded, yielding phenol and phenanthrene as the only products after 3 days in 47.8% yield. Mechanistically, reduction of the 9-hydroxyphenanthrene product probably proceeds in a manner similar to that as described for 1-naphthol (produced from 1-phenoxynaphthalene). Aquathermolysis of 9-hydroxyphenanthrene at 315 OC for 3 days resulted in the formation of only small amounts of phenanthrene (2.2%). In the presence of reducing systems such as 15% formic acid or 15% sodium formate, however, reductive dehydroxylation was increased to give phenanthrene (63.4 and 98.5%, respectively). Phenanthrene itself was unreactive in water, but in 15% formic acid or 15% sodium formate over 3 days, small amounts of 9,lO-dihydrophenanthrene(0.5% and 1.070, respectively) were observed. This is analogous to previous work on coal related aromatic model compounds carried out in water and carbon monoxide.21i22 Thus, the present results on cleavage of diary1 ethers reinforce our previous conclusion that the presence of water during a coal pretreatment or conversion step will facilitate depolymerization of the macromolecuar structure to give an increased proportion of liquids by cleaving important thermally stable covalent cross-links in the coal structure. Registry No. 1-Phenoxynaphthalene, 3402-76-4; phenol, 108-95-2; 1-naphthol,90-153;%phenoxyphenanthrene,52978957; 9-hydroxyphenanthrene,484-17-3; water, 7732-18-5. Michael Siskin* Corporate Research Science Laboratory Exxon Research and Engineering Company Route 22 East, Clinton Township Annandale, New Jersey 08801 -0998 Alan R.Katritzky,* Marudai Balasubramanian Department of Chemistry University of Florida Gainesville, Florida 32611 -2046 Received April 17, 1991 Revised Manuscript Received June 7, 1991
XANES Evidence for Selective Organic Sulfur Removal from Illinois No.6 Coal Sir: We have continued our investigation of new methods for the desulfurization of the organic compounds in coal and have used XANES spectroscopic analysis to distinguish between two different classes of organically bound sulfur forms and to follow qualitatively the chemistry of organic sulfur removal in a sample of Illinois No. 6 coal from the Argonne Premium Coal Sample Program (APCSP 3).l (1) Vorres, K.S . Energy Fuela 1990, 4, 420.
0887-0624I91 l2505-0771%02.60/0 0 1991 American Chemical Societv
Communications
772 Energy & Fuels, Vol. 5, No. 5, 1991
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Figum 1. XANES spectra (top)and the third derivative (bottom) of the pyrite-free Illinois No. 6 coal (APCSP 3).
The Illinois No. 6 coal was freed of pyrite by treatment with lithium aluminum hydride as described in a previous report.2 The product contained 1.8% S (mf), 8.5% ash, and only 0.09% iron. There were no reflections for pyrite in the powder diffraction X-ray spectrum. The dry product was then treated with a single electron transfer (SET) desulfurization reagent as described previously.2 The reaction with potassium naphthalenide(-1) in tetrahydrofuran reduced the sulfur content to 1.1% (mf) and 8.4% ash. In a separate experiment, the pyrite-free material was treated with a 1:l mixture of n-butyllithium and potassium tert-butoxide (Lochmann’s BASE) in heptane at 98 O C for 6 h.S Hydrolysis of the reaction product with dilute aqueous acid gave a coal with 1.2% S (IT$and 5.2% ash.3 The sulfur species in the pyrite-free starting material and the products of the reactions with the SET and BASE reagents were analyzed by X-ray absorption near edge structure (XANES) spectroscopy at the National Synchrotron Light Source at Brookhaven National Laboratory. Previous work has established that useful information about the forms of organically bound sulfur in coals can be obtained by XANES spectros~opy.~* The XANES spectrum of the pyrite-free coal is shown in Figure 1. The XANES spectrum and the third derivative of this sample showed no evidence for the presence of pyritic sulfur, and reconstruction of the third derivative by a previously described methods indicated that about 65% of the organically bound sulfur compounds have aromatic character and about 35% sulfidic character. These values are comparable to the starting coal? indicating that the LAH treatment does not alter the organically bound sulfur forms. The third derivatives of the absorption spectra of the pyrite-free sample and the two different reaction products are displayed in Figure 2. The third derivative of the XANES spectrum exhibits two key features near 2469.6 and 2470.5 eV. According to the information that is currently available, the feature (2) Chatterjee, K.; Wolny, R.; Stock,L. M.Energy Fuels 1990,4,402.
(3) Chatterjee, K.; Stock,L. M. Energy Fuels, in prese. (4) George, G. N.; Gorbaty, M. L. J. Am. Chem. Soc. 1989,111,3182. (5) George, G.N.; Gorbaty, M. L.; Kelemen, S. R. Fuel 1990,69,945. (6)George, G. N.; Gorbaty, M. L.; Kelemen, S. R. Energy Fuels 1991, 5,93.
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Figure 2. (A, top) Third-derivative XANES spectra of the pyrite-free Illinois No. 6 coal (upper) and the SET treated coal (lower). Numbers on the left-hand side of the traces are % sulfur (mf).(B,bottom) Third-derivative XANES spectra of the pyrite-free Illinois No. 6 coal (upper) and the BASE treated coal (lower). Numbers on the left-hand side of the traces are % sulfur (mf).
at 2469.6 eV is attributed to sulfidic sulfur compounds and includes aromatic and aliphatic thiols, aliphatic sulfides, and aryl alkyl sulfidesS6 The feature near 2470.5 eV is dominated by sulfur bound to sp2-hybridizedcarbon atoms such as thiophene and ita derivatives including benzothiophene, dibenzothiophene, and other sulfur-containing heterocycles, and diary1 sulfides.6 Comparison of the third derivatives of the spectra of the reaction produds with that of the starting coal reveals that, depending on the chemistry used, features are selectively diminished. The SET reagent removes sulfur compounds that contribute to the feature near 2470.5 eV whereas BASE removes the forms which give rise to the feature at 2469.6 eV. The results are exactly in accord with the chemical expectation that the SET reagent should be especially effective for the removal of heterocyclic sulfur compounds whereas BASE should selectively react with the sulfidic sulfur compounds. To test this interpretation
Energy & Fuels, Vol. 5, No. 5, 1991 773
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yet unidentified, form of sulfur not present in the starting coal, centered at about 2469.0 eV. The new feature is at too low an energy (too electron rich) to correspond with those obtained from pure thiols or elemental sulfur. We speculate that this feature could arise from an inorganic sulfide byproduct that resists solubilization in dilute aqueous acid. In accordance with this, further work revealed that there was no elemental sulfur in the reaction products' and that vigorous acid hydrolysis reduced the total sulfur content from 1.1to 0.2% S.* In future work, XANES spectra of a number of inorganic sulfides will be obtained in order to define the origin of the 2469.0-eV feature and to provide the data necessary for approximate quantification of the sulfur forms. Unfortunately, the hydrolytic reactions were not performed in the absence of dioxygen and some oxidation products were detectable in the XANES spectra. In spite of this deficiency, the results provide an unambiguous demonstration that the third-derivative reconstruction procedure can provide highly informative data about the organically bound sulfur forms in coal and about the chemistry used to remove them. The new results for the Argonne premium sample of Illinois No. 6 coal support the previous finding that about 35% of the total sulfur in this coal is sulfidic in nature. The results also support the suggestions of Attar, Calkins, and Hippo and their associates that certain bituminous coals contain appreciable quantities of sulfidic sulfur compounds."" This new information has important consequences for the design of targeted desulfurization reagents. Acknowledgment. The work at Argonne National Laboratory was supported by the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy. The XANES spectra were recorded on line X-lOc at the National Synchrotron Light Source (Brookhaven National Laboratory), which is funded by the Division of Material Sciences, U S . Department of Energy, under the Contract DE-AC02-76CH-00016. Registry No. Potassium naphthalemide, 4216-48-2;butyllithium, 109-72-8; potassium tert-butoxide, 865-47-4.
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Figure 3. (A, top) From top to bottom: third-derivative XANES spectra of the pyrite-free Illinois No. 6 coal, the SET-treated coal, and the product obtained on BASE treatment on the SET treated coal. Numbers on the left-hand side of the traces are % sulfur (mD. (B, bottom) From top to bottom: third-derivative XANES spectra of the pyrite-free Illinois No. 6 coal, the BASE-treated coal, and the product obtained on SET treatment on the BASE treated coal. Numbers on the left-hand side of the traces are % sulfur (mf).
in another way, we treated the SET reaction product with BASE and the product of BASE reaction with the SET reagent. The sulfur contents decreased significantly after the second reaction; the values are 0.8% in the former case and 0.7% in the latter case. The XANES results, Figure 3, show that the preliminary interpretation was correct, BASE removing sulfidic sulfur from the product that had first been treated with SET reagent, and the SET reagent removing thiophenic sulfur from the product that had fmt been treated with BASE. The third derivatives of the XANES spectra indicate that both the SET and BASE reagents create another, as
(7) Dr.D. H. Buchanan of Eastern Illinois University determined the elemental sulfur content by extraction with hot perchloroethylene. Details of this method are given by: Buchnnan, D. H.; Warfel, L. C. Prepr. Pap-Am. Chem. SOC.,Diu.Fuel Chem. 1990,35(2), 516. (8) McBeth, R. Unpublished resulta. (9) Attar, A.; Dupuis, F. In Coal Structure; Gorbaty, M . L., Ouchi, K., Eds.;Advances in Chemistry Series 192; American Chemical Society: Washington, DC, 1981; Chapter 16. (10)Calkins, W. H. Energy Fuels 1987,1, 59. (11) Palmer, S. R.; Kruge, M. A.; Hippo, E. J.; Crelling, J. C. Proceedings: Fourteenth Annual EPRI Conference on Fuel Science; Electric Power Research Institute: Palo Alto, CA, 1990.
Kuntal Chatterjee, Leon M. Stock* Chemistry Division Argonne National Laboratory 9700 South Cass Avenue Argonne, Illinois 60439 Martin L. Gorbaty,* Graham N. George Simon R. Kelemen
Exxon Research & Engineering Company Annandale, New Jersey 08801 -0998 Received April 17, 1991 Revised Manuscript Received June 10, 1991
