316
Energy & Fuels 1988,2, 316-320
amounts of oxygen in the saturate and aromatic fractions. They proposed that oxidation of bitumen at low temperatures involves conversion of original resins to asphaltenes with simultaneous conversion of oils to resins. These authors suggested that in these processes oxygen is for the most part a catalyst for condensation reactions, being initially incorporated as labile functional groups that promote these reactions and subsequently eliminated as water. Our chemical kinetic model is consistent with this interpretation, indicating a weak dependence of the rate of depositional processes on oxygen pressure and a stronger effect of pressure of oxygen on the rate of combustion processes. The increase in saturates and decrease in
polyaromatic and polar fractions that we observed in the produced oil relative to the original bitumen, in combination with the increasing aromaticity (decreasing molar H/C ratio) of cokes produced with increase in temperature, also support this interpretation. Acknowledgment. We are grateful to D. D. McIntyre for performing chromatographic separations and for many helpful discussions. We also thank Y .-M. Xu for preparation of the calorimetric sample, and Z.-L. Zhang and J. F. Smith for much good advice. We thank the Alberta Oil Sands Technology and Research Authority for support of this and related research.
Structural Compositions of Tars from Hydropyrolysis of Coal. Effect of Reaction Severity Jana M. Jacobson and Murray R. Gray* Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6
Allan K. Chambers Coal and Hydrocarbon Processing Department, Alberta Research Council, Devon, Alberta, Canada
Jacek Thiel Department of Chemistry, Adam Mickiewicz University, Poznan, Poland Received November 16, 1987. Revised Manuscript Received January 11, 1988
The tars from five hydropyrolysis testa of Highvale (subbituminous, Alberta) coal were studied to determine the effects of reaction severity on concentrations of structural groups. The yields of gases and vapors (carbon oxides light hydrocarbons + benzene, toluene, and xylene) were used as an internal measure of reaction severity for tars produced from an entrained flow reactor operated at 6 0 0 0 "C,7 MPa hydrogen pressure, and 0.5-5 s residence times. The structural groups in the tars were estimated by combining data from 'H NMR, '% NMR, and infrared spectroscopy, nitrogen titration, and elemental analysis. The samples processed at higher severity showed overall concentration increases in aromatic groups and decreases in aromatic side chains, naphthenic rings, and oxygen-containing structures relative to low-severity tars.
+
Introduction Hydropyrolysis of coal provides potentially valuable liquid products, along with a char that may have combustion characteristics compatible with electric power generation. In this process, pulverized coal is rapidly heated in the presence of gaseous hydrogen and converted to char, liquids and volatiles. The char in some instances is up to three times more reactive on combustion than the parent coal,' which may allow for substitution of char for coal in some utility boilers. The use of a hydrogen atmosphere boosts the yield of liquid hydrocarbon products,2 which have potential for separation into marketable products or refining into fuel or feedstocks. Prior work on the liquids from hydropyrolysis centered on determining the yields of benzene, toluene, and xylenes (BTX); phenol, cresol, and xylenol (PCX); and tar,which may include liquids extracted from the c0al.~9~Studies
* Author to whom correspondence should be addressed.
wing a variety of experimental systems and ranks of coal have demonstrated yields of up to 16 kg of BTX/100 kg of daf coal at 700-850 0C.134-7 The yield depended on the reaction temperature and pressure, coal composition, and reactor configuration. An important intermediate in this process is the tar,which predominates at lower temperatures and is converted to BTX under more severe conditions. Clearly the chemical composition of the tar must be known in order to understand the sequential pyrolysis and hydrogenation reactions that give rise to a desirable BTX (1) Chambers, A. K.; Knill, K. J.; Mendiuk, J.; Ungarian, D. Prepr. 35th Can. Chem. Eng. Conf. 198K,260-265. (2) Gavalaa, G. R. Coal Pyrolysis; Elsevier: Amsterdam, 1982. (3)Furfari, S.Hydropyrolysis of Coal; Report ICTIS/TR20; IEA Coal
Research London, 1982. (4)Dobner, S.;Graff, R. A.; Squires, A. M. Fuel 1976,55,113-116. (5) GFaff, R. A.; Dobner, S.; Squires, A. M. Fuel 1976,55,109-112. (6) Fmn,M. J.: Fynes, G.; Ladner, W. R.; New", J. 0. H.Fuel 1980, 59,397-404. (7) Stangeby, P. C.; Sears, P. L. Fuel 1981,60, 131-135.
0887-062418812502-0316$01.50/0 0 1988 American Chemical Society
Energy & Fuels, Vol. 2, No. 3, 1988 317
Structural Compositions of Tars Table I. Composition oP Highvale Coal (Prom Chambers et al.') Proximate (wt %) moisture 5.0 ash (dry) 12.0 volatiles (daf) 40.2 fixed carbon (daf) 59.8 Ultimate (wt % daf)
C H N S 0 (by diff)
74 4.6 1.0 0.2 20.2
product. Wu and Harrisons used gas chromatography/ mass spectrometry to analyze the volatile tar components from low-pressure hydropyrolysis of lignite in a fixed-bed apparatus, including BTX and PCX. The use of a hydrogen atmosphere reduced the yield of alkanes and alkenes and increased the yield of aromatic species. No significant changes in total product composition were noted in the range 500-800 "C. Snape et alsoused NMR to analyze tars from hydropyrolysis of Linby coal (bituminous) in a fixed-bed reactor at 500 and 600 "C. An increase in temperature gave a tar with more aromatic carbon, less alkyl chains, and less hydroaromatic groups. This work suggested several possible mechanisms for the conversion of the tar but considered only two levels of conversion. Cypres and Furfari'O used gas chromatography to analyze approximately 55% of the tar components from hydropyrolysis of bituminous coal in a fiied-bed reactor at low heating rates. Identified phenolic compounds reached a maximumat approximately 650 "C, while the yield of BTX and naphthalenes increased monotonically with temperature in the range 485-850 OC. The purpose of this study was to analyze the effect of process severity on the characteristics of tars from the hydropyrolysis of a subbituminous coal (Highvale coal, Alberta, Canada). This coal is strip-minable from the Paskapoo formation, and is of Upper Cretaceous-Lower Tertiary age. The effects of reaction temperature and time were studied in relationship to the distribution of structurd groups. The concentrations of the principle structural groups were determined by combining data from lH NMR, 13C NMR, and IR spectroscopy, elemental analysis, and nitrogen titration.
Experimental Section Materials and Analytical Methods. The tars were obtained from hydropyrolysisof Highvale coal in a single-passentrainedflow reactor. A mixture of 1kg/h pulverized coal (to -100 mesh) and 2 kgf h preheated hydrogen was passed through an entrained down-flow reactor to form char, tar and water, and gases. The BTX components were eluted with the gas products. The composition of Highvale coal is given in Table I. The water was separated from the tar by azeotropic distillation with toluene. The dry toluene/tar solution was fiitered to remove toluene insolubles and rotary evaporated to remove toluene. The distilled water product contained l e a than 0.06% phenols as determined by gas chromatography. Hydrocarbon gas (CI-C4), carbon oxide, and BTX concentrations in the effluent gas were determined by gas chromatography. The BTX content of the tar product was negligible. Experimental details are given by Chambers et al.' Each sample of tar was subjected to 'H NMR, 13C NMR and E t spectroscopy,nitrogen titration, and analysis for C, H, N, 0, and S. The 'H and 13CNMR spectra were obtained on a Bruker Model WH-200 instrument. The 13C NMR data were recorded (8) Wu, D. M. P.; Harrison, D. P. Fuel 1986,65,747-751. (9) Snape, C. E.; Ladner, W. R.; Bartle, K. D. Fuel 1985, 64, 1394-1400;
(10) Cypres, R.;
Furfari, 5.Fuel 1981,150, 768-778.
Table 11. Proton NMR Band Assignments for Coal Liquids band 1 2 3 4
5 6 7
range, ppm 0-1.0 1.0-1.4 1.4-1.95 1.95-2.9 2.9-4.2 6.3-8.3} 8.7-9.5 8.3-8.7
typical chemical structures y+ methyl
8-methyl, paraffiiic methylene naphthenic methylene a-methyl, methylene and methyne, aromatic amide, sulfide, sulfoxide, ether, and indole methylene bridge aromatic H aromatic hydroxyl H on aromatic nitrogen, 4,5-phenanthrene hydrogen
Table 111. Carbon-13 NMR Band Assignments for Coal Liauids range, band mm twical chemical structures 1 0-23 methyl carbon (a, 8, y) 2 23-37 chain, naphthenic, and a-methylene, methylene bridge, aromatic sulfoxide 3 37-60 a-methyne 4 100-129 aromatic C bonded to H 5 129-143 aromatic C bonded to C 6 143-160 aromatic C bonded to 0, N, S 7 160-250 aromatic ketone, carboxylic acid, and amide by using the Fourier transform pulsed technique with NOE suppression, a spulse width of 28 ps (at 30°), an acquisition time of 0.54 s, a spectral width of 15 kHz, and broad-band decoupling. The samples were prepared as 20-40% solutions in CDC13with tetramethylsilane as an internal standard and chromium tris(acetylacetonate)as the relaxation reagent. Quantitative infrared spectra analysis followed the methods of McKay et al." and Bunger,12while nitrogen titration analysis followed the method of Buell.13 Elemental analyses were performed by the University of Alberta Microanalytical Laboratory. S t r u c t u r a l Analysis. Structural analysis, as put forth by Petrakis et al.14and Khorasheh et al.,16 is the solution of the set of linear equations
X A i j q = bi (i = 1, ..., m)
1''
subject to the constraint nj 2 0, where A;, are stoichiometric coefficients for each structural group xk The bj values are data from elemental analysis and 'H NMR spectroscopy, as well as data from IR spectroscopy and nitrogen titration for specific functional groups. The data on hydrocarbon structures from NMR are less precise than those from 'H NMR, due to overlapping bands and lees precise quantitation. These data were used to construct an objective function, F, which is minimized subject to (1):
..., +
where bk (k = m + 1, m 7) is the fraction of carbon in each band of the 13CNMR spectrum. The minimum value of F from (2), subject to (l),gives the best estimate of the concentrations of the structural groups, xi. The 'H NMR and NMR spectra were each divided into seven bands for analysis of the coal tars; see Tables 11 and 111, respectively. Additional bands would be required in the 'H NMR (11)McKay, J. F.; Cogswell, T. E.; Weber, J. H.; Latham, D. R. Fuel 1975,54,50-61. (12) Bunger, J. W. In Shale Oil, Tar Sanda, and Related Fuel Sources; Yen, T. F., Ed.; Symposium Series 151; American Chemical Society: Washington, DC, 1976; pp 121-136. (13) Buell, B. E. Anul. Chem. 1967,39, 756-761. (14) Petrakia, L.; Allen, D. T.; Gavalas, G. R.; Gates, B. C. Anul. Chem. 1983,55,1557-1564. (15) Khorasheh, F.; Gray, M. R.; Dalla Lana, 1. G. Fuel 1987, 66, 505-511.
Jacobson et a1.
318 Energy & Fuels, Vol. 2, No. 3, 1988 2-
"1 60
-
40-
3
Legend O
9
0 Phenanthrene
8
0 Char
e
Legend
0
0
1.5-
1% L... W!?!. ,.,*.#.
-
.-P e
\*
R
..........
8 Total Aromatics
1
\*
e1x
0 Tar Aromatics
8
/*A'
1-
e
8
sP e
0
/f
0.5-
5
10
