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Effect of Catalytic Hydropretreatment of Petroleum Vacuum Resid on Coprocessing with Coal Paul E. Hajdu,† John W. Tierney, and Irving Wender* Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 Received September 15, 1995X
The coprocessing of coal with petroleum vacuum resids can be used to produce distillable oils. Improved coprocessing performance by using hydrotreated resids as host oils in coprocessing with coal was studied. Four host oils were prepared from petroleum vacuum resids (538 °C+/ 1000 °F+) by catalytic hydrogenation and hydrocracking. The untreated and pretreated resids were then thermally coprocessed with an Illinois No. 6 and with a Wyodak coal. Using solubility in tetrahydrofuran (THF) and pentane, products were separated into asphaltenes, pentane-soluble oils (PSO), coke, and gas. Phenolic compounds, derived mainly from coal, were present in the PSO products and their concentration, measured by IR spectroscopy, was used to estimate the fraction of coal liquids in the PSO products. The yield of PSO was strongly affected by the concentration of coal in the feed; depending on the pretreatment used, the yields of PSO from a 33% coal/resid mixture varied from 48 to 78 wt %. The yield of PSO from Illinois No. 6 coal and untreated resid, as well as resids hydrogenated at temperatures where cracking was low, was greater than that predicted from runs made when the resids and coal were processed separately for coal-feed concentrations up to about 33 wt %. Coal conversion during thermal coprocessing with petroleum vacuum resid can be significantly increased if the resid is first hydrogenated at conditions where cracking is suppressed. However, pretreatment of the resids, by methods used in this study, resulted in only minor improvements in PSO yields.
Introduction The world’s supply of petroleum crude is becoming heavier and the amount of vacuum tower bottoms (resids) produced in refining has been steadily increasing. Coprocessing of coal with petroleum resid has been examined as a possible way of obtaining valuable distillates from these readily available hydrocarbon sources.1-4 Petroleum resids and coals differ in several ways; coal is more aromatic, contains more inorganic material, is richer in oxygen, and has smaller clusters of organic material. Resids, on the other hand, are more aliphatic and less aromatic, richer in hydrogen, have very little oxygen, somewhat smaller amounts of nitrogen, significantly more sulfur, and small amounts of vanadium, nickel, and iron, some of which are held in porphyrin structures. In general, petroleum is a poor coal liquefaction solvent; coal conversion in petroleum resids in the absence of a catalyst is usually less than that achieved using a coal-derived recycle solvent in conventional coal liquefaction processes.5,6 Recycle solvents derived from * Author to whom correspondence should be addressed. † Present address: The Geon Co., 1 Geon Center, Avon Lake, OH 44012. X Abstract published in Advance ACS Abstracts, February 15, 1996. (1) Shinn, J. H.; Dahlberg, A. J.; Keuhler, C. W; Rosenthal, J. W. Proc. Ninth Annu. EPRI Contractors Conf. Coal Liquefaction, CA 1984. (2) Greene, M.; Gupta, A.; Moon, W. Proc. DOE Direct Liquefaction Contractors’ Rev. Meet. PA 1986. (3) Duddy, J.; Panvelker, S.; Popper, G. Proc. Fifteenth Annual EPRI Conf. Fuel Sci. CA 1991. (4) Kelly, J. F.; Fouda, S. A.; Rahimi, P. M.; Ikura, M. Proc. CANMET Coal Conversion Contractors’ Rev. Meet. Alberta 1984. (5) Cugini, A. V.; Lett, R. G.; Wender, I. Energy Fuels 1989, 3, 120126.
0887-0624/96/2510-0493$12.00/0
coal contain aromatic compounds which facilitate transfer of hydrogen from the gas phase and catalyst surface to coal and petroleum. These include hydroaromatics, which can function as hydrogen donors, and polynuclear aromatic compounds, which are able to shuttle hydrogen during coal liquefaction. Both types of compounds are effective for bringing about high levels of coal dissolution. One approach for improving coal-resid coprocessing is to modify the resid prior to coprocessing with coal. Takeshita and Mochida7 obtained a coal conversion of 88% in a petroleum pitch that had first been hydrotreated at high pressure over a Ni/Mo/Al2O3 catalyst. Sato and co-workers8 obtained a coal conversion of 96% and a distillable oil yield of 72% from a Japanese subbituminous Taiheiyo coal using a tar sand bitumen prehydrotreated with a Ni/Mo/Al2O3 (Nippon Ketjen, KF-840) catalyst with sulfur. Curtis and co-workers9-11 showed that high levels of coal conversion can be obtained in a host oil that contained a mixture of both petroleum resid and hydrogen donor compounds, which included hydroaromatics and cyclic olefins. In this study, pretreatments using catalytic hydrocracking and hydrogenation reactions were made to improve the vacuum resid as a coprocessing vehicle. Objectives were to (1) convert aromatic structures in the (6) Miller, T. J.; Panvelker, S. V.; Wender, I.; Tierney, J. W. Fuel Process. Technol. 1989, 23, 23-38. (7) Takeshita, K.; Mochida, I. Japanese Patent 80-45703, 1980. (8) Sato, Y.; Yamamoto, Y.; Kamo, T.; Inaba, A.; Miki, K.; Saito, I. Energy Fuels 1991, 5, 90-102. (9) Curtis, C. W.; Tsai, K.-J.; Guin, J. A. Fuel Process. Technol. 1987, 16, 71-87. (10) Bedell, M. W.; Curtis, C. W.; Hool, J. L. Fuel Process. Technol. 1994, 37, 1-18. (11) Owens, R. M.; Curtis, C. W. Energy Fuels 1994, 8, 823-829.
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Table 1. Properties of Petroleum Resids (538 °C+/1000 °F+) Citgo sp gr (15 °C) C, wt % H, wt % S, wt % N, wt % O, wt % atomic H/C V, ppm Ni, ppm Fe, ppm pentane insolubles, wt % available hydrogen, H atoms/100 C atoms fa, afraction of total C a
85.4 10.1 3.4 0.8 0.3 1.4 555 110 12 29 9.9 0.33
fa ) fraction of aromatic carbon, determined by the Brown and Ladner method (1960).
1H
Table 2. Properties of Coals from Argonne Premium Sample Bank Amoco 1.03 84.3 10.2 4.6 0.5 0.4 1.4 251 57 13 20 0.32
NMR using
petroleum to hydroaromatics capable of donating hydrogen, (2) crack the resid to lower molecular weight material that might serve as a better solvent, (3) reduce the coking propensity of the resid by hydrogenation of polynuclear aromatic compounds, and (4) remove metals and heteroatoms that might poison a catalyst during subsequent upgrading. In this paper, the term host oil refers to any petroleumderived liquid that is coprocessed with coal. This may include untreated vacuum resid or the liquid product from resid pretreatments. The four pretreated resids are identified as host oils A, B, C, and D, corresponding to the pretreatment used. The acronym PSO is used to designate the fraction of starting resid, pretreated resid, or products generated from coprocessing that are soluble in pentane. Coal conversion is defined as the percentage of coal converted to gases and THF solubles. Experimental Section Materials. Two petroleum vacuum tower resids (538 °C+), one from the Amoco Oil Co. and the other from the Citgo Oil Co., were used in this work. Properties of the resids are listed in Table 1. The Amoco resid was derived from a wide mixture of crude oils from many countries; the Citgo resid was from Venezuela. Experiments were first conducted with the Amoco resid to explore reaction conditions required to hydrogenate and hydrocrack a petroleum vacuum resid and to evaluate the sensitivity of reaction parameters such as time, temperature, and pressure on product yields. Based on these experiments, four pretreatment procedures were selected. The Citgo resid was chosen as the primary oil to test because it came from a single country, Venezuela. Properties of the two resids are similar except for the metal contents, which were much higher for the Citgo resid, perhaps making it a more difficult material to process. Two coals were used, an Illinois No. 6 bituminous coal and a Wyodak subbituminous coal; the Illinois coal was used in most of the study. Both coals were premium samples from the Argonne National Laboratory Coal Sample Bank. The coals had been ground to -100 mesh and stored in sealed glass vials. Properties of the coals are listed in Table 2. Two different finely dispersed catalyst systems were used: Mo/Fe2O3/SO4 and Mo naphthenate. The sulfated iron oxide, synthesized in our laboratory, contained 1 wt % Mo and approximately 3 wt % SO4 and has been previously described and successfully tested in coal liquefaction and coprocessing reactions.12-14 Mo naphthenate, which contained 6 wt % Mo, was obtained from ICN Biomedical Inc. It is known that the (12) Pradhan, V. R.; Hu, J.; Tierney, J. W.; Wender, I. Energy Fuels 1993, 7, 446-454.
moisture, wt % ash, wt % volatile matter, wt % rank C, wt % (maf) H, wt % (maf) N, wt % (maf) S, wt % (maf) Cl, wt % (maf) O, wt % (maf) atomic H/C faa
Illinois No. 6
Wyodak
8.0 14.3 35.8 hvB 77.7 5.0 1.4 2.4 0.06 13.5 0.77 0.71
28.1 6.3 32.2 subbit 75.0 5.3 1.1 0.5 0.03 18.0 0.85 0.62
a f ) fraction of aromatic carbon, determined by 1H NMR using a the Brown and Ladner method (1960).
iron compound used in this study is transformed to fine particle pyrrhotites (Fe1-xS) at reaction conditions in the presence of sulfur, which was supplied in our experiments by either adding H2S gas or elemental sulfur in excess to the reactants. It is generally accepted that pyrrhotites, along with H2S, function as hydrogenation catalysts. Under similar conditions, the Mo compounds are transformed to MoS2 particles. An alternative method of hydrogenating a resid using a homogeneous catalyst was also studied. Dicobalt octacarbonyl, Co2(CO)8, in the presence of a 1:1 mixture of H2/CO was found by Friedman et al.15 to catalyze the conversion of polynuclear aromatic compounds to hydroaromatics at relatively low temperatures, below 250 °C, but is unreactive with single-ring aromatic compounds such as benzene and toluene. Project SEACOKE,16 carried out by ARCO, also tested transition metal carbonyls using coal model compounds as well as coal-derived liquids. Petroleum Resid Pretreatment Reactions and Product Workup. The petroleum vacuum resids were reacted in a well-stirred stainless-steel 300 mL autoclave batch reactor. The system consists of high-pressure gas cylinders for supplying H2, CO, or a mixture of 3% H2S in H2. The reactor was fitted with a magnetic stirrer for providing adequate mixing (1200 rpm+) and heated by an electric furnace. Liquid and gas temperatures and reaction pressures were measured continuously and displayed and stored on a PC. During a typical pretreatment run, the reactor was charged with catalyst and 50-100 g of resid. The resids are semisolid at room temperature and it was necessary to heat them to about 100 °C to make them fluid enough to pour into the reactor. For pretreatments made with the Co2(CO)8 catalyst, it was not possible to heat the resid because the carbonyl catalyst is sensitive to heating in air and would lose CO upon contacting the hot oil. In these runs, the resid and catalyst were dissolved in toluene at room temperature and this homogeneous solution was poured into the reactor. The reactor was then sealed, pressure-tested with He, and charged with 1000 psig (cold) of H2, or a mixture of H2/H2S, or of H2/ CO (1:1), depending on the pretreatment. Preliminary work with the Amoco resid showed that hydrogen pressure had little, if any, influence on PSO yields within the 1500-3000 psig pressure range, a result consistent with the findings by Heck et al.17,18 However, these authors found that hydrogen suppressed both coke yield and secondary conversion of primary products. (13) Pradhan, V. R.; Herrick, D. E.; Tierney, J. W.; Wender, I. Energy Fuels 1991, 5, 712-720. (14) Pradhan, V. R.; Holder, G. D.; Wender, I.; Tierney, J. W. Ind. Eng. Chem. Res. 1992, 31, 2051-2056. (15) Friedman, S.; Metlin, S.; Svedi, A.; Wender, I. J. Org. Chem. 1959, 24, 1287. (16) ARCO Chemical Co. “Catalytic Hydrogenation of Coal-Derived Liquids”, Project SEACOKE, Phase II, Final Rep., Contract No. 1401-0001-472, Off. Coal Res., U.S. Dept. of Interior: Washington, DC, 1966.
Catalytic Hydropretreatment of Petroleum Vacuum Resid An electric furnace brought the reactants to the set point temperature at a rate of about 7.5 °C/min. At the end of the reaction time, measured from the time reaction temperature was reached, the reactor was quenched with water and cooled to room temperature; the gases were vented and collected for analysis. The first step in the product workup procedure was atmospheric distillation to remove any low boiling point (bp < 193 o C) products directly from the reactor. During distillation, the reactor head was fitted with a water-cooled condenser and the reactor contents were stirred and slowly heated. Following distillation, the reactor was opened and the contents contacted with THF. The THF-washed material was sonicated for 30 min and solids were filtered out and vacuum dried at 90 °C overnight. THF and toluene, if used, were removed from the liquid product by distillation. Because the boiling points of THF and toluene are well below that of the higher boiling products, good separation with minimal product losses was possible by distillation. The THF-soluble liquid, which contained PSOs and asphaltenes, was used as the host oil in coprocessing runs. Asphaltenes are soluble in THF but insoluble in pentane. The lower boiling oil fraction removed by distillation was recombined with the THF-soluble fraction before use as a host oil. Products containing Co2(CO)8 were refluxed for 3 h to destroy the carbonyl. To facilitate removal of cobalt, silica-alumina powder was added to the product mixture prior to filtering. Coal-Resid Coprocessing Reaction and Product Workup. Coprocessing experiments were performed in a horizontal, stainless-steel microreactor fitted with a thermocouple to measure liquid temperature and a pressure transducer to measure reactor pressure. The microreactor system has been previously described.12 In a typical run, the reactants were weighed (5-10 g) and placed into the reactor body, which has a total volume of about 30 mL. The reactor was then sealed, pressure tested, and charged with reactant gas, which in most runs was H2. Reactants were brought to the set-point temperature, usually within 15 min, by immersing the reactor into a preheated fluidized sand bath. The reactor was shaken horizontally (3 times/s) to ensure adequate mixing. At the end of the desired reaction time, the reactor was removed from the sand bath and quenched with water. Gases were vented at room temperature and collected for analysis. PSO products were recovered by washing the reactor with pentane, and asphaltenes were recovered by washing with THF. The material that was insoluble in both pentane and THF consisted of unconverted organic material and coalderived mineral matter. Pentane was removed from the filtered oil by rotovapor at atmospheric pressure instead of under vacuum to minimize losses of low boiling components during the product recovery step. However, under these mild separation conditions, a small amount of pentane did remain dissolved in the oil; the amount was later measured by simulated distillation. THF was removed from the asphaltenes by rotovapor followed by vacuum drying at 90 °C overnight. Reactant and Product Characterization Techniques. Product gases containing H2, H2S, CO2, and C1-C5 compounds were analyzed using an HP 5880A GC. PSO samples were analyzed with an HP 5890 series II GC/HP 5970 mass selective detector. A boiling point curve for PSO samples was estimated by simulated distillation using the ASTM D2887 procedure with an HP 5890 series II GC.19 PSO and asphaltene samples were analyzed for their hydrogen type and aromatic content by 1H NMR using a Bruker 3000 MSL spectrometer; samples were prepared in deuterated chloroform with tetramethylsi(17) Heck, R. H.; DiGuiseppi, F. T. Proc. 205th National Meet. American Chemical Society, CO 1993. (18) Heck, R. H.; Rankel, L. A.; DiGuiseppi, F. T. Fuel Process. Technol. 1992, 30, 69-81. (19) ASTM Designation: D 2887-89, Annual Book of ASTM Standards; ASTM: Philadelphia, PA, 1995.
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Figure 1. Available hydrogen content of the THF-solubles from catalytic and thermal pretreatments of the Amoco resid. It is temperature dependent and decreases significantly at temperatures greater than 400 °C. lane for internal reference. Catalytic dehydrogenation20 was used to estimate the “available” hydrogen in untreated and pretreated resids. Available hydrogen is defined as the amount of hydrogen gas evolved from a sample that is catalytically dehydrogenated at atmospheric pressure in boiling phenanthridine (bp ) 349 °C) for 285 min over a reduced Pd/CaCO3 catalyst. Metal contents (V and Ni) of selected samples were measured by The Pittsburgh Applied Research Corp. using the ICP technique. Elemental compositions (C, H, S, and N) of selected samples were determined by Galbraith Laboratories Inc. using microanalyses and by CONSOL Inc. using macroanalyses. The phenolic oxygen concentrations of PSO samples were measured by CONSOL Inc. using FTIR.21
Results and Discussion Resid Pretreatment Experiments. A critical property of a host oil is its ability to supply hydrogen during coprocessing. One way of assessing the available (donatable) hydrogen content of a sample is to measure the amount of hydrogen gas released when it is catalytically dehydrogenated. For example, the compound 9,10dihydroanthracene loses the two hydroaromatic hydrogen atoms per molecule to form anthracene. Using this technique, we found that the available hydrogen content of the resids was sensitive to pretreatment temperatures, as shown in Figure 1. At a reaction temperature of 440 °C, using Mo naphthenate as the catalyst, there was a decrease in the available hydrogen content of the Amoco resid, yet when the same resid was pretreated at 400 °C using either Mo/Fe2O3/SO4 or Mo naphthenate, the available hydrogen content was almost twice that of the untreated resid. Below 400 °C, cracking rates were low and hydrogen was likely available on the catalyst surface to convert aromatic structures to hydroaromatics and other hydrogen donors in the resid, resulting in an increase in available hydrogen. At 440 (20) Hu, J.; Whitcomb, J. H.; Tierney, J. W.; Wender, I. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1992, 1258-1264. (21) Robbins, G. A.; Winschel, R. A.; Burke, F. P. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1986, 155-163.
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Table 3. Reaction Conditions and Product Yields for Pretreatments of Citgo Resida A
B
C
D
catalyst concentration
MN 1000 ppm
MN 1000 ppm
Co2(CO)8 6.2 wt %
gas used temperature, °C pressure (cold), psig time, h gas yield, wt % liquid (THF sol) yield, wt % coke yield, wt %
H2 440 1000 2 25 72 3
H2 375 1000 5 1 97 2
Mo/Fe2O3/SO4, 200 ppm Mo, 13000 ppm Fe H2 375 1000 5 3 95 2
CO/H2 (1:1) 135 2000 2 0 100 0
a MN ) Mo naphthenate (6 wt % Mo). Note: elemental sulfur was added in pretreatments A, B, and C in excess of amount needed to sulfide the Mo and Fe.
Table 4. Properties of Citgo Untreated and Pretreated Resids
bpa < 565 °C, wt % bpb > 565 °C, wt % C, wt % H, wt % S, wt % N, wt % O, wt % atomic H/C atomic C/S atomic C/N V, ppm Ni, ppm available hydrogen, H atoms/100 C atomsc wt % H2 added
Citgo resid
A
B
C
D
85.4 10.1 3.4 0.8 0.3 1.4 67 124 555 110 9.9
62.6 37.4 85.1 10.6 2.2 0.9 1.2 1.5 103 110 393 67 12.4
29.7 70.3 85.9 10.4 2.7 0.9 0.1 1.4 85 111
17.9 82.1 84.8 10 2.9 0.8 1.5 1.4 78 124
16.8
33.3 66.7 85.6 10.8 2.9 0.8 0 1.5 79 125 472 95 14
1.4
0.5
0.5
0.5
17.5
a
Bp < 565 °C consists of pentane-soluble oil having a simulated distillation bp < 565 °C. b Bp > 565 °C consists of pentaneinsoluble asphaltenes and pentane-soluble oil having simulated distillation bp > 565 °C. c Value based on catalytic dehydrogenation.
°C, cracking rates were significant and there was less hydrogen available for hydrogenating aromatic structures in the resid. Under hydrogen-poor conditions, it is possible that hydrogen was transferred from hydroaromatic structures present in the resid to cap free radicals. The end result was a liquid product that was slightly richer in hydrogen, but although the hydrogen content increased by about 1%, the available (donatable) hydrogen was less than that of the starting resid. Since experiments with the Amoco resid had indicated that severe hydrotreating was undesirable, a slate of four pretreatments (one severe and three mild) was selected and used for the Citgo resid. Conditions for these treatments are summarized in Table 3. In the first pretreatment, referred to as A, the resid was reacted with Mo naphthenate at 440 °C for 2 h with the objective of reducing molecular weight and removing sulfur and metals. In pretreatments B, C, and D the temperature was below 400 °C, where cracking is suppressed. The objective of these runs was to increase the available hydrogen content of the pretreated resid. In pretreatment B, the Citgo resid was reacted at 375 °C under hydrogen gas, 1000 psig (cold), for 5 h using Mo naphthenate (1000 ppm Mo). In C, the Citgo resid was treated using a finely dispersed Mo/Fe2O3/SO4 catalyst (2 wt %); other conditions were the same as used in B. In pretreatment D, the Citgo resid was dissolved in toluene and hydrogenated using dicobalt octacarbonyl at 135 °C for 2 h under 2600 psig of 1:1 synthesis gas. The objective of this last treatment was to selectively hydrogenate polynuclear aromatic struc-
tures in the vacuum resid to generate hydroaromatic structures.15 Table 4 lists properties of the untreated Citgo resid and the four pretreated resids. Host oil A contained a larger fraction of material that had a boiling point C > untreated Citgo resid > B > A. The differences among the PSO yields for host oil D, C, and untreated Citgo resid are small; only small improvements in PSO yields were realized as a result of pretreatments of the Citgo resid at a coal-feed concentration of 33%.
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Figure 4. Effect of concentration of coal in the feed on the yield of pentane solubles, asphaltenes, and coke generated by coprocessing Illinois No. 6 coal and host oil A; yields are expressed as wt % of feed. Conditions: 425 °C, 1000 psig (cold) of H2, 30 min reaction time.
Figure 5. Effect of concentration of coal in the feed on the yield of pentane solubles and asphaltenes generated by coprocessing Illinois No. 6 coal and host oil B; yields are expressed as wt % of feed. Conditions: 425 °C, 1000 psig (cold) of H2, 30 min reaction time.
Properties of the PSOs and asphaltenes from the various coprocessing runs are listed in Table 6 for a coalfeed concentration of 33 wt %. In general, the PSO had atomic H/C ratios above 1.6, a low concentration of nitrogen (about 0.3%) and contained significant amounts of oxygen (higher than 1.4%) and sulfur (above 1.5%). Essentially all the oxygen is derived from the coal. Over 55 wt % of the PSO generated from the coprocessing run with host oil A had a simulated distillation boiling range below 343 °C. PSO products from the other coprocessing runs contained over 25 wt % of material that boiled above 565 °C; over 65 wt % of the PSO boiled above 343 °C, indicating that less than 30% of the
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Figure 6. Effect of concentration of coal in the feed on the yield of pentane solubles and asphaltenes generated by coprocessing Illinois No. 6 coal and host oil C; yields are expressed as wt % of feed. Conditions: 425 °C, 1000 psig (cold) of H2, 30 min reaction time.
Figure 8. Resids pretreated at milder temperatures, when coprocessed with Illinois No. 6 coal, gave slightly higher pentane-soluble oil yields than the untreated Citgo resid or the resid that was pretreated at 440 °C; yields are expressed as wt % of feed. Conditions: 425 °C, 1000 psig (cold) of H2, 30 min reaction time, host oil:coal ) 2:1.
Figure 7. Effect of concentration of coal in the feed on the yield of pentane solubles and asphaltenes generated by coprocessing Illinois No. 6 coal and host oil D; yields are expressed as wt % of feed. Conditions: 425 °C, 1000 psig (cold) of H2, 30 min reaction time.
starting host oil and coal were converted to PSO that had a boiling point below 343 °C. The fraction of distillate products that boiled in the gasoline and diesel range was small at all coal loadings studied. The asphaltenes had about the same concentration of S and O as the corresponding PSO but were richer in N and contained almost all the metals. The asphaltenes had a high aromatic carbon content (over 60%), according to 1H NMR, and had an average atomic H/C ratio of less than 1. Determination of Coal Liquids in the PentaneSoluble Products. To better understand the roles of coal and host oil in coprocessing, it is desirable to know
the distribution of coal-derived and petroleum-derived components in the oil products. However, these are commingled and cannot easily be separated from one another. Steer et al.22 have developed a method, used by others,23,24 for the quantitative determination, by 13C/ 12C ratios, of the amount of coal incorporated into an oil generated by coprocessing. However, this method is complicated and requires that a sample first be converted to CO2, which is then separated from H2O and noncondensible gases before being analyzed by mass spectroscopy. Further complications arise from the fact that coal and petroleum are not isotopically homogeneous and that selective isotopic fractionation may cause certain products to become enriched in either 12C or 13C during coprocessing. In the present study, we estimated the fraction of coal liquids in the PSO by measuring phenolic oxygen concentration. Since Illinois coal contains much more oxygen than that of the Citgo resid (Tables 1 and 2) and about half the oxygen in coal is phenolic oxygen,25 it was assumed that the phenolic compounds in the PSO products were from coal. Robbins et al.21 measured the phenolic OH concentration of distillate and resid process samples during an extended test of the Lummus and HRI two-stage direct coal liquefaction processes. The phenolic concentration of these materials was determined from the height of the peak corresponding to the phenolic OH stretch in the infrared spectrum, around 3300 cm-1. The (22) Steer, J. G.; Ohuchi, T.; Muehlenbachs, K. Fuel Process. Technol. 1987, 15, 429-438. (23) Ettinger, M. D.; Stock, L. M. Energy Fuels 1994, 8, 960971. (24) Winschel, R. A.; Lancet, M. S; Burke, F. P. Stable Carbon Isotope Analysis of Coprocessing Materials, Final Technical Report, DOE/PC 88800-43, April 1991. (25) Whitehurst, D. D.; Mitchell, T. O.; Farcasiu, M. Coal Liquefaction: The Chemistry and Technology of Thermal Processes; Academic Press: New York, 1980; p 17.
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Table 6. Properties of Pentane-Soluble Oils and Asphaltene Products Obtained by Coprocessing Illinois No. 6 Coal with Untreated Citgo Resid and Four Pretreated Resids (Conditions: 425 °C, 1000 psig (cold) of H2, Host Oil:Coal ) 2:1, 30 min Reaction Time) Citgo resid + Illinois No. 6 properties
PSO
