PRODUCT REVIEW
Upgrading Coal Liquids to Gas Turbine Fuels. I . Analytical Characterization of Coal Liquids Robert B. Callen, Joseph G. Bendoraitis, Charles A. Simpson, and Sterling E. Voltz* Mobil Research and Dsvelopmenf Corporation. Paolsboro, New Jersey
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Robert B. Callen is a supervising chemist responsible for Separations Research within the Composition and Structure Research Group. He holds a B.S. degree in Chemistry from Boston College and a Ph.D. degree in Chemistry from Notre Dame. Dr. Callen is a member of ACS, ASMS, and Sigma Xi. His primary research interests have been centered on the development of gas and liquid chromatographic techniques for the analysis of hydrocarbon process streams.
Joseph G . Bendoraitis is a
research associate in the Composition and Structure Research Group. His current interests lie in the deuelopment of procedures for the analysis of petroleum and coal-derived materials using mass spectrometry, nuclear resonance, and gas chromatography. He holds a B.S. degree in Chemistry from Wilkes College, an M.S. degree i n Chemistry from Lehigh Uniuersity, and a Ph.D. i n Chemistry from Temple Uniuersity. Dr. Bendoraitis is a member of ACS, ASMS, ASTM, and Sigma Xi. He has numerous publications in the areas of petroleum analysis, petroleum geochemistry, and radiolysis of hydrocarbons.
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Ind Eng. Chem., Prod. Res Dev., Vol. 15, No. 4, 1976
Charles A. Simpson is a senior research chemist in the Composition and Structure Research Group. He received his Ph.D. degree in Analytical and Physical Chemistry from the University of Delaware in 1958. His primary research activities are the identificationand analysis of complex mixtures, including petroleum residua and related substances. Dr. Simpson is a member of ACS.
Sterling E. Voltz is a research associate in the Process Research and Development Section. He is currently working on processes for synthetic fuels. His past industrial experience includes positions at General Electric. Sun Oil. and Houdi'Y Process. Dr. Voltz obtained a Ph.D. in Physical Chemistry from Temple University and he also did graduate work at the University of Pennsylvania. He has numerous patents and publications in catalysis, surface chemistry, kinetics, petroleum and petrochemical processing, synthetic fuels, and automotive emission control. He is a member of ACS, Catalysis Society and Sigma Xi.
The physical properties and chemical compositions of three coal liquids (SRC, H-Coal, and Synthoil) were determined. Coal liquids contain less hydrogen (6-8 wt % vs. about 11 wt % ) than petroleum fuels or residua, whereas their concentrations of nitrogen and oxygen are considerably higher. The aromaticities of coal liquids are much greater (60-75 vs. 20-35 atom YO aromatic carbon) than petroleum residu,a; they also have very high concentrations of asphaltenes. The detailed molecular compositions were analyzed by gradient elution chromatography. Improvement in certain physical and chemical properties will be required to upgrade coal liquids for use as gas turbine fuels.
Introduction Several processes have been developed for the liquefaction of coal. Large scale pilot plants have been operated, and demonstration plants are being constructed. If progress in coal liquefaction technology continues to advance, it is anticipated that coal liquids will become commercially available during the 1980’s. They will probably be utilized initially as boiler fuels for stationary power plants. Further processing will undoubtedly be required to enable them to be used as gas turbine fuels. Both their physical properties and chemical composition need to be upgraded. High-temperature gas turbines operate commercially on both gaseous and liquid fuels (Foster et al., 1972,1974). The latter include petroleum distillate and residual fuels. Petroleum distillate fuels are free of ash and can normally be used without any further treatment. However, both the physical properties and certain chemical constituents of residual fuels can cause serious problems. Those physical properties related to fluidity (Le., viscosity, pour point) and cleanliness (i.e., ash, filterable dirt, water, sediment) are particularly important. Trace metals such as sodium, potassium, vanadium, calcium, and lead are highly corrosive to turbine blades and contribute to the formation of deposits. Both sulfur and nitrogen in the fuel must be limited to meet environmental emission standards. Also, sulfur oxides react with sodium and potassium to form sulfates, which are highly corrosive. Fuel treatments are utilized to remove and/or reduce the effects of contaminants (Foster et al., 1972, 1974; Krulls, 1973; Doering and Vincent, 1972). Oil desalting removes watersoluble compounds from the fuel such as sodium, potassium, and calcium salts. Since vanadium is generally present in residual fuels as oil-soluble compounds, it is not removed by desalting procedures. Fuel additives are also commonly used. for example, certain magnesium compounds significantly reduce corrosion by vanadium. Due to the physical properties of residual fuels, preheating may be required (Foster et al., 1972, 1974; Krulls, 1973). The fuel temperature is increased sufficiently above the pour point to provide free flow and reduce the viscosity. Coal liquids are more analogous to petroleum residual fuels than other petroleum products. Their chemical compositions and certain physical properties are sufficiently different, however, that additional problems can be anticipated in the use of coal liquids as gas turbine fuels. The carbon/hydrogen ratios of most coal liquids are considerably higher than those for petroleum crudes and fuels. Moreover, the concentrations of heteroatoms such as nitrogen and oxygen are much higher. The sulfur contents of coal liquids and petroleum residua can vary considerably. The physical properties of coal liquids are also quite variable; they depend on the type of coal and liquefaction process employed. Petroleum residua have higher concentrations of nickel and vanadium than coal liquids; the latter, however, often contain more iron. Both theoretical and experimental studies have been conducted on the upgrading of coal liquids based on petroleum refining technology. For example, Eisen (1975) prepared several hundred gallons of gas turbine engine fuel from a synthetic crude oil derived from a Western Kentucky coal. The hydrogenation of the coal liquid was conducted a t 3000
psig hydrogen pressure with a nickel-molybdenum catalyst. Rapid catalyst deactivation was attributed to the high nitrogen and oxygen content of the coal liquid. Efforts are also underway to develop improved gas turbine materials and technology (Ahner, 1974; Gas Turbine Technology, 1975). The results are expected to contribute to a reduction in the fuel quality requirements for the use of petroleum residual fuels and coal liquids in gas turbines. A study was initiated in 1975 on the potential use of coal liquids as gas turbine fuels. The objectives of this study were to identify process and quality problems which exist in using coal liquids as gas turbine fuels and compatibility problems of blends of coal liquids with conventional petroleum fuels. Samples of SRC (Solvent Refined Coal), H-Coal, and Synthoil were investigated. The areas of work have encompassed analytical characterization, compatibility studies, turbine fuel specifications, and exploratory process studies. The results of the analytical characterization of the three coal liquids are described in this paper. The physical properties, elemental composition, and molecular composition were determined. Analytical methods which had been previously developed for petroleum residua were modified and used to characterize the molecular composition. Also, comparisons are made between some physical and chemical properties of the coal liquids and gas turbine fuel specifications. The compatibility of coal liquids in petroleum fuels and the exploratory process studies will be described in future publications. Experimental Section
A. Materials. Three coal liquids were used in this study. Samples of SRC (Solvent Refined Coal) and H-Coal were furnished by the Electric Power Research Institute. The sources of these two materials were, respectively, the SRC pilot plant operated by Southern Services, Inc. in Wilsonville, Ala. and the H-Coal pilot plant, Hydrocarbon Research, Inc., Trenton, N.J. A sample of Synthoil was obtained directly from the Energy Research Center, Energy Research and Development Administration, Pittsburgh, Pa. Some further information on the coal liquids is listed in Table I. The SRC samples included SRC product, process recycle solvent, and light organic liquid product. Two drums of SRC product and 10 gal each of the other two liquids were obtained. Only 2 gal each of H-Coal and Synthoil were available for this study. The SRC and H-Coal were prepared from Illinois No. 6 (Burning Star Mine), whereas the Synthoil was made from West Virginia Coal (Pittsburgh Seam from Ireland Mine). The petroleum fuels for this study were obtained from commercial refinery sources. B. Analytical Methods. The physical properties and elemental compositions of the coal liquids were measured using the ASTM tests listed in Table I1 and the techniques given in Table 111. Most of these analyses involve well-known procedures and they will not be described further. The analytical techniques used to determine molecular composition included gradient elution chromatography (GEC), infrared spectroscopy, low and high resolution mass spectrometry, carbon-13 nuclear magnetic resonance ( 13C Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 4, 1976
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Table I. Identification and Source of Coal Liquids
Coal liquefaction product Source Run no. Sample no. Quantity, gal
SRC
H-Coal
Svnthoil
SRC Recycle Light organic product solvent liquid SRC Pilot Plant in Wilsonville, Alabama
Filtered liquid
Centrifuged product oil
-
-
HRI Pilot Plant in Trenton, ERDA Pilot Plant in Pittsburgh, N.J. Pa. PDU 130-69 % T/D catalytic unit LS 720 2 2 (1 x 2)" (2 x 1)O Illinois No. 6 W. Virginia (Pittsburgh (Burning Star Mine) Seam from Ireland Mine) 58088 57992
Pilot Plant Sample No. 125 4787 4785 4786 110 10 10 (2 x 55)O (2 x 5)" (2 x 5)" Coal Source Illinois No. 6 (Burning Star Mine) Mobil sample no. 75D-42 57949 57951 75D-43 57959 57952 a (Number of containers X gallons in each one). Combined sample.
-
-
*
Table 11. ASTM Tests Used for Coal Liquids Test no. D86 D93 D95 D97 D129 D189 D287 D445 D482 D664 D1298 D1552 D1796 D2382 D2887
Title Distillation of Petroleum Products Flash Point by Pensky-Martens Closed Tester Water in Petroleum Products and Bituminous Materials by Distillation Pour Point Sulfur in Petroleum Products by Bomb Method Conradson Carbon Residue of Petroleum Products API Gravity of Crude Petroleum and Petroleum Products (Hydrometer Method) Kinematic Viscosity of Transparent and Opaque Liquids (Calculation of Dynamic Viscosity) Ash from Petroleum Products Neutralization Number by Potentiometric Titration Density, Specific Gravity, or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method Sulfur in Petroleum Products (High Temperature Method) Water and Sediment in Crude Oils and Fuel Oils by Centrifuge Heat of Combustion of Hydrocarbon Fuels by Fuel Calorimeter (High Precision Method) Boiling Range Distribution of Petroleum Fractions by Gas Chromatography
Table 111. Chemical Analyses Used for Coal Liquids Analysis Water C, H 0 S N Basic Nitrogen Trace Ca, Na, K Trace Ti Trace Al, Pb, Fe Trace Ni, V Qual. Trace Metals Molecular Weight
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Method Karl Fischer titration Pregl-type microcombustion Direct pyrolysis X-ray fluorescence Micro-Dumas Nonaqueous acidimetry Flame emission photometry of ashed sample Spectrophotometric measurement of ashed sample Emission spectrographic measurement of ashed sample Atom absorption measurement of ashed sample Emission spectrographic examination of ash Vapor pressure lowering (osmometry) in benzene or THF, depending on solubility
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 4, 1976
\
Sample C o l u m n 28-29 m m 0. D.
M a i n Colump 28-29 mm 0.0. 129 cm Long
V a r i a n Techtron
Solvent Striooer
Analytical Balance t o Weigh A m o u n t of Sample i n Cut
Figure 1. Schematic of GEC Method.
NMR), and laser Raman spectroscopy. Some additional comments on three of these techniques are given below. 1. Gradient Elution Chromatography (GEC). The gradient elution scheme is essentially a scaled-up procedure originally described by Middleton (1967) that has been extended to handle highly refractive materials such as coal liquids and vacuum residua. This extended, preparative procedure provides a more detailed classification of asphaltene-like substances than was formerly possible and yields sufficient quantities of well-defined fractions for further detailed analysis. The preparative scale GEC is shown schematically in Figure 1and is described below. About 25 g of sample is dissolved in a relatively volatile solvent such as methylene chloride (MeC12) or tetrahydrofuran (THF). This solution is adsorbed on alumina in an amount sufficient to fill the sample column. The solvent is evaporated, and the dry sample-on-alumina mixture is packed into the sample column. The main column is packed with Alcoa F-20 alumina which has been activated to a 5.5 wt % moisture level. The particular sequence of solvents employed for this analysis along with the required solvent volumes is presented
Figure 2. A typical GEC chromatogram.
Table IV. Solvents for Gradient Elution Chromatography Eluentsa
Volume, cm3
Table V. Physical Description of GEC Fractions GEC fraction
Description
1. Saturates
500 Pentane, used to fill mixer 220 1. Pentane 500 2. 3% MeC12 in hexane 500 3. 6% MeClz in hexane 500 4. 9% MeClz + 2% THF in hexane 500 5. 12% MeC12 4% THF in hexane 500 6. 15%MeC12 6% THF in hexane 500 7 . 18%MeC12 8%THF 2.5% MeOH in hexane 500 8. 21% MeC12 10%THF 5% MeOH in hexane 500 9. 25% MeClz 12% THF + 10% MeOH in hexane 500 10. 27%MeC12 15%THF 15%MeOH in hexane 500 11. 45% MeC12 40% THF 15%MeOH (no hexane) 500 12. THF only 500 13. 15%MeOH in THF 2000 14. 15%MeOH + 4% HzO in THF 0 Expressed as volume %. THF = tetrahydrofuran.
+ + + + + + +
+ + + +
in Table IV. The mixing chamber, placed between the solvent reservoir and the column, provides a gradual and continuous increase in the eluting power of the solvent mixture entering the sample column. Separation is provided by the competition between the solvent power of the liquid phase and adsorption sites on the alumina. Thus, saturated hydrocarbons, which are only weakly bound to alumina, are the first to be eluted; asphaltenes, which interact strongly with alumina and have low solubility in the earlier eluents, are the last to be eluted. The column effluent is passed through a variable UV-VIS wavelength spectrophotometer (Varian Techtron Model 635), which records absorbance as a function of time. The spectrophotometer signal provides the principal criteria for fraction selection and a typical GEC chromatogram is shown in Figure 2. This gradient elution procedure separated the coal liquids into 13 fractions. The fraction names along with a brief physical description of the fractions are presented in Table V. The chemical composition of these cuts is described in detail below. T o obtain a weight percent analysis, the solvent is evaporated from each fraction under a stream of nitrogen on a series
Colorless oil or white wax, melting slightly above room temperature. Very soluble in paraffinic solvents. 2. MNA-DNA oil Very light yellow heavy oil, sometimes with waxy solids, easily melted. Very soluble in aromatic solvents. 3. PNA oil Bright yellow-orangeoil. Usually a tacky orange-red semisolid, 4. PNA soft resin slow to turn fluid at elevated temperature, but pours readily at 200 OF. 5. Hardresin Red-brown powders which turn tacky 6. Polar resin slightly above 100 OF. Extremely viscous liquids at 240 OF. 7. Eluted asphaltenes Dark brown powder. Behavior intermediate between resins and polar asphaltenes. Very soluble in methylene chloride. 8-12. Polar asphaltenes Black powder, very friable. Very high softening point. Poorly soluble in methylene chloride, very soluble in THF. 13. Noneluted Among others, can be strongly acidic components (carboxylic acids), inorganic solids (carbon, catalysts fines, etc.).
of hot plates a t different temperatures. The cut (residue) is then cooled to room temperature under vacuum for the final weighing. 2. Mass Spectrometry. Selected GEC fractions from SRC, H-Coal, and Synthoil were analyzed for hydrocarbon group types in accordance with standardized methods employed for the mass spectrometrc analysis of petroleum fractions. These methods are based on a revised version of the computational matrices originally published by Hood and O'Neal (1958) for analysis of saturated hydrocarbons, and the method of Robinson and Cook (1969) for analysis of aromatic fractions. Mass spectra were obtained using a Hitachi Model RMU-6L spectrometer equipped with a sample inlet system operating a t 325 "C. The first four fractions obtained by GEC were amenable to analysis by the above procedures, but the more polar fracInd. Eng. Chem., Prod. Res. Dev., Vol. 15,No. 4, 1976
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Table VI. Simulated Distillation of Coal Liauids
Vol. % off
SRC light organic liquid 5-7951
SRC recycle solvent 5-7950
181 OF
326 O F 362 398 405 408 434 454 492 526 566 595 657 877
IbP 3 10 15 20 30 40 50 60 70
235 284 307 325 335 348 365 375 397 407 415 561
80
90 FbP
SRC 75D-42 dried
H-Coal 5-8088
-
650 O
482 O 526 569 593 620 667 705 759 866 >963 >963 >963 >963
F
-
950 >950 >950 >950 >950 >950 >950 >950 >950 >950
El Palito no. 6 fuel oil
Synthoil 5-7992 341 O F 410 473 507 534 591 654
F
347 OF -
594 -
715 779 832 893 >990 >990 >990 >990 >990
715 800 >890 >890 >890 >890
Table VII. Some Important Physical Properties of Coal Liquids
ProDertv
SRC light organic liquid 5-7951
Heating value, Btu/lb 17226 1.441 Kinematic viscosity, cSt, 100 OF Kinematic viscosity, cSt, 210 OF 0.647 Specific gravity, 60 OF 0.9182 Pour point, OF 115 320 17.3 200 a
